Natural product
A natural product is a natural compound or substance produced by a living organism—that is, found in nature.<ref name="url_Natural_product_Webster">Webster's Revised Unabridged Dictionary (1913). "Natural product". Free Online Dictionary and C. & G. Merriam Co. A chemical substance produced by a living organism; – a term used commonly in reference to chemical substances found in nature that have distinctive pharmacological effects. Such a substance is considered a natural product even if it can be prepared by total synthesis.
</ref><ref name="pmid17576412">"All natural". Nature Chemical Biology. 3 (7): 351. July 2007. doi:10.1038/nchembio0707-351. PMID 17576412. The simplest definition for a natural product is a small molecule that is produced by a biological source.
</ref> In the broadest sense, natural products include any substance produced by life.<ref name = "Samuelson_1999">Samuelson G (1999). Drugs of Natural Origin: A Textbook of Pharmacognosy. Taylor & Francis Ltd. ISBN 978-91-86274-81-8.</ref><ref name="urlNatural Products Research—Information for Researchers | NCCAM">National Center for Complementary and Integrative Health (13 July 2013). "Natural Products Research—Information for Researchers | NCCIH". U.S. Department of Health & Human Services. Natural products include a large and diverse group of substances from a variety of sources. They are produced by marine organisms, bacteria, fungi, and plants. The term encompasses complex extracts from these producers, but also the isolated compounds derived from those extracts. It also includes vitamins, minerals and probiotics.
</ref> Natural products can also be prepared by chemical synthesis (both semisynthesis and total synthesis) and have played a central role in the development of the field of organic chemistry by providing challenging synthetic targets. The term natural product has also been extended for commercial purposes to refer to cosmetics, dietary supplements, and foods produced from natural sources without added artificial ingredients.<ref name="url_NPF_about_us">"About Us". Natural Products Foundation. Retrieved 7 December 2013. Natural products are represented by a wide array of consumer goods that continue to grow in popularity each year. These products include natural and organic foods, dietary supplements, pet foods, health and beauty products, "green" cleaning supplies and more. Generally, natural products are considered those formulated without artificial ingredients and that are minimally processed.
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Within the field of organic chemistry, the definition of natural products is usually restricted to organic compounds isolated from natural sources that are produced by the pathways of secondary metabolism.<ref name = "Hanson_2003">Hanson JR (2003). Natural Products: the Secondary Metabolite. Cambridge: Royal Society of Chemistry. ISBN 0-85404-490-6. Natural products are organic compounds that are formed by living systems.
</ref> Within the field of medicinal chemistry, the definition is often further restricted to secondary metabolites.<ref>"Natural Products". Stedman's Medical Dictionary. Lippincott Williams & Wilkins. Archived from the original on 3 August 2016. Retrieved 7 December 2013. Natural products: naturally occurring compounds that are end products of secondary metabolism; often, they are unique compounds for particular organisms or classes of organisms.
</ref><ref>Williams DA, Lemke TL (2002). "Chapter 1: Natural Products". Foye's Principles of Medicinal Chemistry (5th ed.). Philadelphia: Lippincott Williams Wilkins. p. 25. ISBN 0-683-30737-1. Natural product: A single chemical compound that occurs naturally. This term is typically used to refer to an organic compound of limited distribution in nature (often called secondary metabolites).
</ref> Secondary metabolites (or specialized metabolites) are not essential for survival, but nevertheless provide organisms that produce them an evolutionary advantage.<ref name="pmid1612430">Maplestone RA, Stone MJ, Williams DH (June 1992). "The evolutionary role of secondary metabolites—a review". Gene. 115 (1–2): 151–7. doi:10.1016/0378-1119(92)90553-2. PMID 1612430.</ref> Many secondary metabolites are cytotoxic and have been selected and optimized through evolution for use as "chemical warfare" agents against prey, predators, and competing organisms.<ref name="pmid18762775">Hunter P (September 2008). "Harnessing Nature's wisdom. Turning to Nature for inspiration and avoiding her follies". EMBO Reports. 9 (9): 838–40. doi:10.1038/embor.2008.160. PMC 2529361. PMID 18762775.</ref> Secondary or specialized metabolites are often unique to species, which is contrasted to primary metabolites which have broad use across kingdoms. Secondary metabolites are marked by chemical complexity which is why they are of such interest to chemists.
Natural sources may lead to basic research on potential bioactive components for commercial development as lead compounds in drug discovery.<ref name="Li_2009">Li JW, Vederas JC (July 2009). "Drug discovery and natural products: end of an era or an endless frontier?". Science. 325 (5937): 161–5. Bibcode:2009Sci...325..161L. doi:10.1126/science.1168243. PMID 19589993. S2CID 207777087.</ref> Although natural products have inspired numerous drugs, drug development from natural sources has received declining attention in the 21st century by pharmaceutical companies, partly due to unreliable access and supply, intellectual property, cost, and profit concerns, seasonal or environmental variability of composition, and loss of sources due to rising extinction rates.<ref name=Li_2009/>
Classes
The broadest definition of natural product is anything that is produced by life,<ref name = "Samuelson_1999"/><ref name = "Bhat_2005">Bhat SV, Nagasampagi BA, Sivakumar M (2005). Chemistry of Natural Products. Berlin; New York: Springer. ISBN 81-7319-481-5.</ref> and includes the likes of biotic materials (e.g. wood, silk), bio-based materials (e.g. bioplastics, cornstarch), bodily fluids (e.g. milk, plant exudates), and other natural materials (e.g. soil, coal).
Natural products may be classified according to their biological function, biosynthetic pathway, or source. Depending on the sources, the number of known natural product molecules ranges between 300,000<ref>Rutz A, Sorokina M, Galgonek J, Mietchen D, Willighagen E, Gaudry A, et al. (May 2022). "The LOTUS initiative for open knowledge management in natural products research". eLife. 11: e70780. doi:10.7554/eLife.70780. PMC 9135406. PMID 35616633.</ref><ref name="pmid25300487">Banerjee P, Erehman J, Gohlke BO, Wilhelm T, Preissner R, Dunkel M (January 2015). "Super Natural II--a database of natural products". Nucleic Acids Research. 43 (Database issue): D935–D939. doi:10.1093/nar/gku886. PMC 4384003. PMID 25300487.</ref> and 400,000.<ref>Sorokina M, Steinbeck C (April 2020). "Review on natural products databases: where to find data in 2020". Journal of Cheminformatics. 12 (1): 20. doi:10.1186/s13321-020-00424-9. PMC 7118820. PMID 33431011.</ref>
Function
Following Albrecht Kossel's original proposal in 1891,<ref name = "Kossel_1891">Kossel A (1891). "Ueber die chemische Zusammensetzung der Zelle" [The chemical composition of the cell]. Archiv für Physiologie (in Deutsch): 181–186.</ref> natural products are often divided into two major classes, the primary and secondary metabolites.<ref name = "Kliebenstein_2004">Kliebenstein DJ (2004). "Secondary metabolites and plant/environment interactions: a view through Arabidopsis thaliana tinged glasses". Plant, Cell and Environment. 27 (6): 675–684. doi:10.1111/j.1365-3040.2004.01180.x. In 1891, following Stahls work on plant biochemistry, Kossel suggested a distinction between basic and secondary metabolism (Stahl 1888).
</ref><ref name = "Karlovsky_2008">Karlovsky P (2008). "Secondary Metabolites in Soil Ecology". Soil Biology. Soil Biology. Vol. 14. pp. 1–19. doi:10.1007/978-3-540-74543-3_1. ISBN 978-3-540-74542-6. The current, generally accepted concept in line with Kossel's view is that primary metabolites are chemical components of living organisms that are vital for their normal functioning, while secondary metabolites are compounds which are dispensable.
</ref> Primary metabolites have an intrinsic function that is essential to the survival of the organism that produces them. Secondary metabolites in contrast have an extrinsic function that mainly affects other organisms. Secondary metabolites are not essential to survival but do increase the competitiveness of the organism within its environment. Because of their ability to modulate biochemical and signal transduction pathways, some secondary metabolites have useful medicinal properties.<ref>Wink M (8 September 2015). "Modes of Action of Herbal Medicines and Plant Secondary Metabolites". Medicines. 2 (3): 251–286. doi:10.3390/medicines2030251. ISSN 2305-6320. PMC 5456217. PMID 28930211.</ref>
Natural products especially within the field of organic chemistry are often defined as primary and secondary metabolites. A more restrictive definition limiting natural products to secondary metabolites is commonly used within the fields of medicinal chemistry and pharmacognosy.<ref name = "Bhat_2005"/>
Primary metabolites
Primary metabolites as defined by Kossel are components of basic metabolic pathways that are required for life. They are associated with essential cellular functions such as nutrient assimilation, energy production, and growth/development. They have a wide species distribution that span many phyla and frequently more than one kingdom. Primary metabolites include the basic building blocks of life: carbohydrates, lipids, amino acids, and nucleic acids.<ref name = "Rogers_2011">Rogers K (2011). The Components of Life: From Nucleic Acids to Carbohydrates (1st ed.). New York, NY: Britannica Educational Publishing in association with Rosen Educational Services. ISBN 978-1-61530-324-3.</ref>
Primary metabolites that are involved with energy production include respiratory and photosynthetic enzymes. Enzymes in turn are composed of amino acids and often non-peptidic cofactors that are essential for enzyme function.<ref name = "Lehninger_2013">Cox DL, Nelson MM (2013). Lehninger Principles of Biochemistry (6th ed.). New York, N.Y.: W.H. Freeman. ISBN 978-1-4641-0962-1.</ref> The basic structure of cells and of organisms are also composed of primary metabolites. These include cell membranes (e.g. phospholipids), cell walls (e.g. peptidoglycan, chitin), and cytoskeletons (proteins).<ref>Boal D (2006). Mechanics of the Cell (4th printing ed.). Cambridge, UK: Cambridge University Press. ISBN 978-0-521-79681-1.</ref>
Primary metabolite enzymatic cofactors include members of the vitamin B family. Vitamin B1 as thiamine diphosphate is a coenzyme for pyruvate dehydrogenase, 2-oxoglutarate dehydrogenase, and transketolase which are all involved in carbohydrate metabolism. Vitamin B2 (riboflavin) is a constituent of FMN and FAD which are necessary for many redox reactions. Vitamin B3 (nicotinic acid or niacin), synthesized from tryptophan is a component of the coenzymes NAD+ and NADP+ which in turn are required for electron transport in the Krebs cycle, oxidative phosphorylation, as well as many other redox reactions. Vitamin B5 (pantothenic acid) is a constituent of coenzyme A, a basic component of carbohydrate and amino acid metabolism as well as the biosynthesis of fatty acids and polyketides. Vitamin B6 (pyridoxol, pyridoxal, and pyridoxamine) as pyridoxal 5′-phosphate is a cofactor for many enzymes especially transaminases involve in amino acid metabolism. Vitamin B12 (cobalamins) contain a corrin ring similar in structure to porphyrin and is an essential coenzyme for the catabolism of fatty acids as well for the biosynthesis of methionine.<ref name = "Dewick_2009"/>: Ch. 2
DNA and RNA, which store and transmit genetic information, are composed of nucleic acid primary metabolites.<ref name = "Lehninger_2013"/>
First messengers are signaling molecules that control metabolism or cellular differentiation. These signaling molecules include hormones and growth factors in turn are composed of peptides, biogenic amines, steroid hormones, auxins, gibberellins etc. These first messengers interact with cellular receptors which are composed of proteins. Cellular receptors in turn activate second messengers are used to relay the extracellular message to intracellular targets. These signaling molecules include the primary metabolites cyclic nucleotides, diacyl glycerol etc.<ref name = "Sitaramayya_1999">Sitaramayya A (1999). Introduction to Cellular Signal Transduction. Boston: Birkhäuser. ISBN 978-0-8176-3982-2.</ref>
Secondary metabolites
Secondary in contrast to primary metabolites are dispensable and not absolutely required for survival. Furthermore, secondary metabolites typically have a narrow species distribution.<ref>Herbert RB (1981). "Introduction". The Biosynthesis of Secondary Metabolites. Dordrecht: Springer Netherlands. pp. 1–2. ISBN 94-009-5833-1. Secondary metabolites are distinguished more precisely by the following criteria: they have a restricted distribution being found mostly in plants and microorganisms, and are often characteristic of individual genera, species, or strains; they are formed along specialized pathwasys from primary metabolites. Primary metabolites, by contrast, have a broad distribution in all living things and are intimately involved in essential life processes.
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Secondary metabolites have a broad range of functions. These include pheromones that act as social signaling molecules with other individuals of the same species, communication molecules that attract and activate symbiotic organisms, agents that solubilize and transport nutrients (siderophores etc.), and competitive weapons (repellants, venoms, toxins etc.) that are used against competitors, prey, and predators.<ref name="pmid11036689">Demain AL, Fang A (2000). "The natural functions of secondary metabolites". History of Modern Biotechnology I. Advances in Biochemical Engineering/Biotechnology. Vol. 69. pp. 1–39. doi:10.1007/3-540-44964-7_1. ISBN 978-3-540-67793-2. PMID 11036689.</ref> For many other secondary metabolites, the function is unknown. One hypothesis is that they confer a competitive advantage to the organism that produces them.<ref name="pmid2693613">Williams DH, Stone MJ, Hauck PR, Rahman SK (1989). "Why are secondary metabolites (natural products) biosynthesized?". Journal of Natural Products. 52 (6): 1189–208. doi:10.1021/np50066a001. PMID 2693613.</ref> An alternative view is that, in analogy to the immune system, these secondary metabolites have no specific function, but having the machinery in place to produce these diverse chemical structures is important and a few secondary metabolites are therefore produced and selected for.<ref name="Firn_2000">Firn RD, Jones CG (September 2000). "The evolution of secondary metabolism – a unifying model" (PDF). Molecular Microbiology. 37 (5): 989–94. doi:10.1046/j.1365-2958.2000.02098.x. PMID 10972818. S2CID 3827335.</ref>
General structural classes of secondary metabolites include alkaloids, phenylpropanoids, polyketides, and terpenoids.<ref name = "Hanson_2003"/>
Biosynthesis
The biosynthetic pathways leading to the major classes of natural products are described below.<ref name = "Bhat_2005"/><ref name = "Dewick_2009">Dewick PM (2009). Medicinal Natural Products: A Biosynthetic Approach (3rd ed.). Chichester: Wiley. ISBN 978-0-470-74167-2.</ref>: Ch. 2
- Photosynthesis or gluconeogenesis → monosaccharides → polysaccharides (cellulose, chitin, glycogen etc.)
- Acetate pathway → fatty acids and polyketides
- Shikimate pathway → aromatic amino acids and phenylpropanoids
- Mevalonate pathway and methyletrythritol phosphate pathway → terpenoids and steroids
- Amino acids → alkaloids
Carbohydrates
Carbohydrates are an essential energy source for most life forms. In addition, polysaccharides formed from simpler carbohydrates are important structural components of many organisms such the cell walls of bacteria and plants.[citation needed]
Carbohydrate are the products of plant photosynthesis and animal gluconeogenesis. Photosynthesis produces initially 3-phosphoglyceraldehyde, a three-carbon atom containing sugar (a triose).<ref name = "Dewick_2009"/>: Ch. 8 This triose in turn may be converted into glucose (a six carbon atom containing sugar) or a variety of pentoses (five carbon atom containing sugars) through the Calvin cycle. In animals, the three carbon precursors lactate or glycerol can be converted into pyruvate which in turn can be converted into carbohydrates in the liver.[citation needed]
Fatty acids and polyketides
Through the process of glycolysis sugars are broken down into acetyl-CoA. In an ATP-dependent enzymatically catalyzed reaction, acetyl-CoA is carboxylated to form malonyl-CoA. Acetyl-CoA and malonyl-CoA undergo a Claisen condensation with lose of carbon dioxide to form acetoacetyl-CoA. Additional condensation reactions produce successively higher molecular weight poly-β-keto chains which are then converted into other polyketides.<ref name = "Dewick_2009"/>: Ch. 3 The polyketide class of natural products have diverse structures and functions and include prostaglandins and macrolide antibiotics.[citation needed]
One molecule of acetyl-CoA (the "starter unit") and several molecules malonyl-CoA (the "extender units") are condensed by fatty acid synthase to produce fatty acids.<ref name = "Dewick_2009"/>: Ch. 3 Fatty acid are essential components of lipid bilayers that form cell membranes as well as fat energy stores in animals.[citation needed]
Sources
Natural products may be extracted from the cells, tissues, and secretions of microorganisms, plants and animals.<ref name="GB2003">Strobel G, Daisy B (December 2003). "Bioprospecting for microbial endophytes and their natural products". Microbiology and Molecular Biology Reviews. 67 (4): 491–502. doi:10.1128/MMBR.67.4.491-502.2003. PMC 309047. PMID 14665674.</ref><ref name="pmid32529587"/> A crude (unfractionated) extract from any one of these sources will contain a range of structurally diverse and often novel chemical compounds. Chemical diversity in nature is based on biological diversity, so researchers collect samples from around the world to analyze and evaluate in drug discovery screens or bioassays. This effort to search for biologically active natural products is known as bioprospecting.<ref name="GB2003"/><ref name="pmid32529587"/>
Pharmacognosy provides the tools to detect, isolate and identify bioactive natural products that could be developed for medicinal use. When an "active principle" is isolated from a traditional medicine or other biological material, this is known as a "hit". Subsequent scientific and legal work is then performed to validate the hit (e.g. elucidation of mechanism of action, confirmation that there is no intellectual property conflict). This is followed by the hit to lead stage of drug discovery, where derivatives of the active compound are produced in an attempt to improve its potency and safety.<ref name="pmid22553861">Markossian S, Grossman A, Brimacombe K, Arkin M, Auld D, Austin CP, et al. (June 2020). Assay Guidance Manual. Bethesda: Eli Lilly & Company and the National Center for Advancing Translational Sciences. PMID 22553861.</ref><ref name="pmid26435527">Katsuno K, Burrows JN, Duncan K, Hooft van Huijsduijnen R, Kaneko T, Kita K, et al. (November 2015). "Hit and lead criteria in drug discovery for infectious diseases of the developing world". Nature Reviews. Drug Discovery. 14 (11): 751–758. doi:10.1038/nrd4683. PMID 26435527. S2CID 25863919.</ref> In this and related ways, modern medicines can be developed directly from natural sources.[citation needed]
Although traditional medicines and other biological material are considered an excellent source of novel compounds, the extraction and isolation of these compounds can be a slow, expensive and inefficient process. For large scale manufacture therefore, attempts may be made to produce the new compound by total synthesis or semisynthesis.<ref name="pmid24142193">Bauer A, Brönstrup M (January 2014). "Industrial natural product chemistry for drug discovery and development". Natural Product Reports. 31 (1): 35–60. doi:10.1039/c3np70058e. PMID 24142193.</ref> Because natural products are generally secondary metabolites with complex chemical structures, their total/semisynthesis is not always commercially viable. In these cases, efforts can be made to design simpler analogues with comparable potency and safety that are amenable to total/semisynthesis.<ref name="pmid25829247">Maier ME (May 2015). "Design and synthesis of analogues of natural products". Organic & Biomolecular Chemistry. 13 (19): 5302–43. doi:10.1039/c5ob00169b. PMID 25829247.</ref>
Prokaryotic
Bacteria
The serendipitous discovery and subsequent clinical success of penicillin prompted a large-scale search for other environmental microorganisms that might produce anti-infective natural products. Soil and water samples were collected from all over the world, leading to the discovery of streptomycin (derived from Streptomyces griseus), and the realization that bacteria, not just fungi, represent an important source of pharmacologically active natural products.<ref name="LJL2012">Zaffiri L, Gardner J, Toledo-Pereyra LH (April 2012). "History of antibiotics. From salvarsan to cephalosporins". Journal of Investigative Surgery. 25 (2): 67–77. doi:10.3109/08941939.2012.664099. PMID 22439833. S2CID 30538825.</ref> This, in turn, led to the development of an impressive arsenal of antibacterial and antifungal agents including amphotericin B, chloramphenicol, daptomycin and tetracycline (from Streptomyces spp.),<ref name="RIM2012">Procópio RE, Silva IR, Martins MK, Azevedo JL, Araújo JM (2012). "Antibiotics produced by Streptomyces". The Brazilian Journal of Infectious Diseases. 16 (5): 466–71. doi:10.1016/j.bjid.2012.08.014. PMID 22975171.</ref> the polymyxins (from Paenibacillus polymyxa),<ref name="SJ2015">Cochrane SA, Vederas JC (January 2016). "Lipopeptides from Bacillus and Paenibacillus spp.: A Gold Mine of Antibiotic Candidates". Medicinal Research Reviews. 36 (1): 4–31. doi:10.1002/med.21321. PMID 24866700. S2CID 46109250.</ref> and the rifamycins (from Amycolatopsis rifamycinica).<ref name="ARU2014">Saxena A, Kumari R, Mukherjee U, Singh P, Lal R (July 2014). "Draft Genome Sequence of the Rifamycin Producer Amycolatopsis rifamycinica DSM 46095". Genome Announcements. 2 (4): e00662–14. doi:10.1128/genomeA.00662-14. PMC 4082003. PMID 24994803.</ref> Antiparasitic and antiviral drugs have similarly been derived from bacterial metabolites.<ref>Saraiva, Raúl G.; Dimopoulos, George (2020). "Bacterial natural products in the fight against mosquito-transmitted tropical diseases". Natural Product Reports. 37 (3): 338–354. doi:10.1039/C9NP00042A. PMID 31544193. S2CID 202731385.</ref>
Although most of the drugs derived from bacteria are employed as anti-infectives, some have found use in other fields of medicine. Botulinum toxin (from Clostridium botulinum) and bleomycin (from Streptomyces verticillus) are two examples. Botulinum, the neurotoxin responsible for botulism, can be injected into specific muscles (such as those controlling the eyelid) to prevent muscle spasm.<ref name="MAD2013">Hallett M, Albanese A, Dressler D, Segal KR, Simpson DM, Truong D, Jankovic J (June 2013). "Evidence-based review and assessment of botulinum neurotoxin for the treatment of movement disorders". Toxicon. 67 (June): 94–114. doi:10.1016/j.toxicon.2012.12.004. PMID 23380701.</ref> Also, the glycopeptide bleomycin is used for the treatment of several cancers including Hodgkin's lymphoma, head and neck cancer, and testicular cancer.<ref>"Bleomycin". US National Library of Medicine. Retrieved 28 January 2015.</ref> Newer trends in the field include the metabolic profiling and isolation of natural products from novel bacterial species present in underexplored environments. Examples include symbionts or endophytes from tropical environments,<ref name="AKB2014">Alvin A, Miller KI, Neilan BA (2014). "Exploring the potential of endophytes from medicinal plants as sources of antimycobacterial compounds". Microbiological Research. 169 (7–8): 483–95. doi:10.1016/j.micres.2013.12.009. PMC 7126926. PMID 24582778.</ref> subterranean bacteria found deep underground via mining/drilling,<ref name="XSK2014">Wang X, Elshahawi SI, Shaaban KA, Fang L, Ponomareva LV, Zhang Y, et al. (January 2014). "Ruthmycin, a new tetracyclic polyketide from Streptomyces sp. RM-4-15". Organic Letters. 16 (2): 456–9. doi:10.1021/ol4033418. PMC 3964319. PMID 24341358.</ref><ref name="XKS2014">Wang X, Shaaban KA, Elshahawi SI, Ponomareva LV, Sunkara M, Copley GC, et al. (August 2014). "Mullinamides A and B, new cyclopeptides produced by the Ruth Mullins coal mine fire isolate Streptomyces sp. RM-27-46". The Journal of Antibiotics. 67 (8): 571–5. doi:10.1038/ja.2014.37. PMC 4146655. PMID 24713874.</ref> and marine bacteria.<ref name="DJD2012">Akey DL, Gehret JJ, Khare D, Smith JL (October 2012). "Insights from the sea: structural biology of marine polyketide synthases". Natural Product Reports. 29 (10): 1038–49. doi:10.1039/c2np20016c. PMC 3709256. PMID 22498975.</ref>
Archaea
Because many Archaea have adapted to life in extreme environments such as polar regions, hot springs, acidic springs, alkaline springs, salt lakes, and the high pressure of deep ocean water, they possess enzymes that are functional under quite unusual conditions. These enzymes are of potential use in the food, chemical, and pharmaceutical industries, where biotechnological processes frequently involve high temperatures, extremes of pH, high salt concentrations, and / or high pressure. Examples of enzymes identified to date include amylases, pullulanases, cyclodextrin glycosyltransferases, cellulases, xylanases, chitinases, proteases, alcohol dehydrogenase, and esterases.<ref name="CG2011">Bertoldo C, Antranikian G (2011). "Chapter 1: Biotechnology of Archaea" (PDF). Biotechnology Vol. IX. Paris: Encyclopedia of Life Support Systems (EOLSS).</ref> Archaea represent a source of novel chemical compounds also, for example isoprenyl glycerol ethers 1 and 2 from Thermococcus S557 and Methanocaldococcus jannaschii, respectively.<ref name="CTK2010">Thornburg CC, Zabriskie TM, McPhail KL (March 2010). "Deep-sea hydrothermal vents: potential hot spots for natural products discovery?". Journal of Natural Products. 73 (3): 489–99. doi:10.1021/np900662k. PMID 20099811.</ref>
Eukaryotic
Fungi
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Several anti-infective medications have been derived from fungi including penicillin and the cephalosporins (antibacterial drugs from Penicillium rubens and Cephalosporium acremonium, respectively)<ref name="pmid32973216"/><ref name="LJL2012" /> and griseofulvin (an antifungal drug from Penicillium griseofulvum).<ref name="AR20154">Beekman AM, Barrow RA (2014). "Fungal metabolites as pharmaceuticals". Aust J Chem. 67 (6): 827–843. doi:10.1071/ch13639.</ref> Other medicinally useful fungal metabolites include lovastatin (from Pleurotus ostreatus), which became a lead for a series of drugs that lower cholesterol levels, cyclosporin (from Tolypocladium inflatum), which is used to suppress the immune response after organ transplant operations, and ergometrine (from Claviceps spp.), which acts as a vasoconstrictor, and is used to prevent bleeding after childbirth.<ref name = "Dewick_2009"/>: Ch. 6 Asperlicin (from Aspergillus alliaceus) is another example. Asperlicin is a novel antagonist of cholecystokinin, a neurotransmitter thought to be involved in panic attacks, and could potentially be used to treat anxiety.[citation needed]
Plants
Plants are a major source of complex and highly structurally diverse chemical compounds (phytochemicals), this structural diversity attributed in part to the natural selection of organisms producing potent compounds to deter herbivory (feeding deterrents).<ref name="LE2015">Dang L, Van Damme EJ (September 2015). "Toxic proteins in plants". Phytochemistry. 117: 51–64. Bibcode:2015PChem.117...51D. doi:10.1016/j.phytochem.2015.05.020. PMC 7111729. PMID 26057229.</ref> Major classes of phytochemical include phenols, polyphenols, tannins, terpenes, and alkaloids.<ref name = "AMH2006">Crozier A, Clifford MN, Ashihara H (2006). "Chapters 1, 3 and 4". Plant Secondary Metabolites: Occurrence, Structure and Role in the Human Diet. Oxford, UK: Blackwell Publishing Ltd. pp. 1–24, 47–136. ISBN 978-1-4051-2509-3.</ref> Though the number of plants that have been extensively studied is relatively small, many pharmacologically active natural products have already been identified. Clinically useful examples include the anticancer agents paclitaxel and omacetaxine mepesuccinate (from Taxus brevifolia and Cephalotaxus harringtonii, respectively),<ref name="PCS2014">Kittakoop P, Mahidol C, Ruchirawat S (2014). "Alkaloids as important scaffolds in therapeutic drugs for the treatments of cancer, tuberculosis, and smoking cessation". Current Topics in Medicinal Chemistry. 14 (2): 239–52. doi:10.2174/1568026613666131216105049. PMID 24359196.</ref> the antimalarial agent artemisinin (from Artemisia annua),<ref name="S2014">Kano S (May 2014). "Artemisinin-based combination therapies and their introduction in Japan". Kansenshogaku Zasshi. The Journal of the Japanese Association for Infectious Diseases. 88 (3 Suppl 9–10): 18–25. PMID 24979951.</ref> and the acetylcholinesterase inhibitor galantamine (from Galanthus spp.), used to treat Alzheimer's disease.<ref name="PAA2013">Russo P, Frustaci A, Del Bufalo A, Fini M, Cesario A (2013). "Multitarget drugs of plants origin acting on Alzheimer's disease". Current Medicinal Chemistry. 20 (13): 1686–93. doi:10.2174/0929867311320130008. PMID 23410167.</ref> Other plant-derived drugs, used medicinally and/or recreationally include morphine, cocaine, quinine, tubocurarine, muscarine, and nicotine.<ref name = "Dewick_2009"/>: Ch. 6
Animals
Animals also represent a source of bioactive natural products. In particular, venomous animals such as snakes, spiders, scorpions, caterpillars, bees, wasps, centipedes, ants, toads, and frogs have attracted much attention. This is because venom constituents (peptides, enzymes, nucleotides, lipids, biogenic amines etc.) often have very specific interactions with a macromolecular target in the body (e.g. α-bungarotoxin from cobras).<ref name="chemical weaponry">Dossey AT (January 2010). "Insects and their chemical weaponry: new potential for drug discovery". Natural Product Reports. 27 (12): 1737–57. doi:10.1039/C005319H. PMID 20957283.</ref><ref name="pmid32535105"/> As with plant feeding deterrents, this biological activity is attributed to natural selection, organisms capable of killing or paralyzing their prey and/or defending themselves against predators being more likely to survive and reproduce.<ref name="pmid32535105">Herzig V, Cristofori-Armstrong B, Israel MR, Nixon SA, Vetter I, King GF (June 2020). "Animal toxins – Nature's evolutionary-refined toolkit for basic research and drug discovery". Biochemical Pharmacology. 181: 114096. doi:10.1016/j.bcp.2020.114096. PMC 7290223. PMID 32535105.</ref>
Because of these specific chemical-target interactions, venom constituents have proved important tools for studying receptors, ion channels, and enzymes. In some cases, they have also served as leads in the development of novel drugs. For example, teprotide, a peptide isolated from the venom of the Brazilian pit viper Bothrops jararaca, was a lead in the development of the antihypertensive agents cilazapril and captopril.<ref name="pmid32535105"/> Also, echistatin, a disintegrin from the venom of the saw-scaled viper Echis carinatus was a lead in the development of the antiplatelet drug tirofiban.<ref name="pmid31137917">Lazarovici P, Marcinkiewicz C, Lelkes PI (May 2019). "From snake venom's disintegrins and C-type lectins to anti-platelet drugs". Toxins. 11 (5): Article 303. doi:10.3390/toxins11050303. PMC 6563238. PMID 31137917.</ref>
In addition to the terrestrial animals and amphibians described above, many marine animals have been examined for pharmacologically active natural products, with corals, sponges, tunicates, sea snails, and bryozoans yielding chemicals with interesting analgesic, antiviral, and anticancer activities.<ref name="AKC2010">Mayer AM, Glaser KB, Cuevas C, Jacobs RS, Kem W, Little RD, et al. (June 2010). "The odyssey of marine pharmaceuticals: a current pipeline perspective". Trends in Pharmacological Sciences. 31 (6): 255–65. doi:10.1016/j.tips.2010.02.005. PMID 20363514.</ref> Two examples developed for clinical use include ω-conotoxin (from the marine snail Conus magus)<ref name="BL1998">Bowersox SS, Luther R (November 1998). "Pharmacotherapeutic potential of omega-conotoxin MVIIA (SNX-111), an N-type neuronal calcium channel blocker found in the venom of Conus magus". Toxicon. 36 (11): 1651–8. doi:10.1016/S0041-0101(98)00158-5. PMID 9792182.</ref><ref name="P2006">Prommer E (June 2006). "Ziconotide: a new option for refractory pain". Drugs of Today. 42 (6): 369–78. doi:10.1358/dot.2006.42.6.973534. PMID 16845440.</ref> and ecteinascidin 743 (from the tunicate Ecteinascidia turbinata).<ref name="R2000">Rinehart KL (January 2000). "Antitumor compounds from tunicates". Medicinal Research Reviews. 20 (1): 1–27. doi:10.1002/(SICI)1098-1128(200001)20:1<1::AID-MED1>3.0.CO;2-A. PMID 10608919. S2CID 25117225.</ref> The former, ω-conotoxin, is used to relieve severe and chronic pain,<ref name="P2006"/><ref name=" BL1998" /> while the latter, ecteinascidin 743 is used to treat metastatic soft tissue sarcoma.<ref name="BES2015">Petek BJ, Loggers ET, Pollack SM, Jones RL (February 2015). "Trabectedin in soft tissue sarcomas". Marine Drugs. 13 (2): 974–83. doi:10.3390/md13020974. PMC 4344612. PMID 25686274.</ref> Other natural products derived from marine animals and under investigation as possible therapies include the antitumour agents discodermolide (from the sponge Discodermia dissoluta),<ref name="RMP2008">Singh R, Sharma M, Joshi P, Rawat DS (August 2008). "Clinical status of anti-cancer agents derived from marine sources". Anti-Cancer Agents in Medicinal Chemistry. 8 (6): 603–17. doi:10.2174/187152008785133074. PMID 18690825.</ref> eleutherobin (from the coral Erythropodium caribaeorum), and the bryostatins (from the bryozoan Bugula neritina).<ref name="RMP2008" />
Medical uses
Natural products sometimes have pharmacological activity that can be of therapeutic benefit in treating diseases.<ref name=Brahmachari_2010>Brahmachari G (2010). Handbook of Pharmaceutical Natural Products. Weinheim: Wiley-VCH. ISBN 978-3-52732148-3.</ref><ref name="pmid18554253">Beghyn T, Deprez-Poulain R, Willand N, Folleas B, Deprez B (July 2008). "Natural compounds: leads or ideas? Bioinspired molecules for drug discovery". Chemical Biology & Drug Design. 72 (1): 3–15. doi:10.1111/j.1747-0285.2008.00673.x. PMID 18554253. S2CID 20973633.</ref><ref name="pmid15729362">Koehn FE, Carter GT (March 2005). "The evolving role of natural products in drug discovery". Nature Reviews. Drug Discovery. 4 (3): 206–20. doi:10.1038/nrd1657. PMID 15729362. S2CID 32749678.</ref> Moreover, synthetic analogs of natural products with improved potency and safety can be prepared and therefore natural products are often used as starting points for drug discovery. Natural product constituents have inspired numerous drug discovery efforts that eventually gained approval as new drugs<ref name="pmid17309302">Newman DJ, Cragg GM (March 2007). "Natural products as sources of new drugs over the last 25 years". Journal of Natural Products. 70 (3): 461–77. CiteSeerX 10.1.1.336.753. doi:10.1021/np068054v. PMID 17309302.</ref><ref name="Gransalke_2011">Gransalke K (February 2011). "Mother Nature's Drug Cabinet" (PDF). Lab Times. 11 (1): 16–19. Archived from the original (PDF) on 4 March 2016. Retrieved 8 December 2013. Drug Discovery – Is Mother Nature still the number one source for promising new drugs?
</ref>
Modern natural product-derived drugs
A large number of currently prescribed drugs have been either directly derived from or inspired by natural products.<ref name="CRC Press"/><ref name="pmid26281720">Atanasov AG, Waltenberger B, Pferschy-Wenzig EM, Linder T, Wawrosch C, Uhrin P, Temml V, Wang L, Schwaiger S, Heiss EH, Rollinger JM, Schuster D, Breuss JM, Bochkov V, Mihovilovic MD, Kopp B, Bauer R, Dirsch VM, Stuppner H (December 2015). "Discovery and resupply of pharmacologically active plant-derived natural products: A review". Biotechnology Advances. 33 (8): 1582–614. doi:10.1016/j.biotechadv.2015.08.001. PMC 4748402. PMID 26281720.</ref>
Some of the oldest natural product based drugs are analgesics. The bark of the willow tree has been known from antiquity to have pain relieving properties. This is due to presence of the natural product salicin which in turn may be hydrolyzed into salicylic acid. A synthetic derivative acetylsalicylic acid better known as aspirin is a widely used pain reliever. Its mechanism of action is inhibition of the cyclooxygenase (COX) enzyme.<ref name = "Schrör_2008">Schrör K (2008). "Chapter 1.1: History". Acetylsalicylic Acid. Weinheim: Wiley-VCH. pp. 5–24. ISBN 978-3-527-62600-7.</ref> Another notable example is opium is extracted from the latex from Papaver somniferous (a flowering poppy plant). The most potent narcotic component of opium is the alkaloid morphine which acts as an opioid receptor agonist.<ref name=Busse_2006>Busse GD, Triggle DJ (2006). "The history of opium and morphine". Morphine. New York: Chelsea House Publishers. pp. 8–23. ISBN 978-1-4381-0211-5.</ref> A more recent example is the N-type calcium channel blocker ziconotide analgesic which is based on a cyclic peptide cone snail toxin (ω-conotoxin MVIIA) from the species Conus magus.<ref name="pmid22407615">Lewis RJ, Dutertre S, Vetter I, Christie MJ (April 2012). "Conus venom peptide pharmacology". Pharmacological Reviews. 64 (2): 259–98. doi:10.1124/pr.111.005322. PMID 22407615. S2CID 6115292.</ref>
A significant number of anti-infectives are based on natural products.<ref name="pmid32529587">Cushnie TP, Cushnie B, Echeverría J, Fowsantear W, Thammawat S, Dodgson JL, Law S, Clow SM (June 2020). "Bioprospecting for antibacterial drugs: a multidisciplinary perspective on natural product source material, bioassay selection and avoidable pitfalls". Pharmaceutical Research. 37 (7): Article 125. doi:10.1007/s11095-020-02849-1. PMID 32529587. S2CID 219590658.</ref> The first antibiotic to be discovered, penicillin, was isolated from the mold Penicillium. Penicillin and related beta lactams work by inhibiting DD-transpeptidase enzyme that is required by bacteria to cross link peptidoglycan to form the cell wall.<ref>de la Bédoyère G (2005). The discovery of penicillin. London: Evans. ISBN 978-0-237-52739-6.</ref>
Several natural product drugs target tubulin, which is a component of the cytoskeleton. These include the tubulin polymerization inhibitor colchicine isolated from the Colchicum autumnale (autumn crocus flowering plant), which is used to treat gout.<ref name="pmid13198053">Hartung EF (September 1954). "History of the use of colchicum and related medicaments in gout; with suggestions for further research". Annals of the Rheumatic Diseases. 13 (3): 190–200. doi:10.1136/ard.13.3.190. PMC 1006735. PMID 13198053.</ref> Colchicine is biosynthesized from the amino acids phenylalanine and tryptophan. Paclitaxel, in contrast, is a tubulin polymerization stabilizer and is used as a chemotherapeutic drug. Paclitaxel is based on the terpenoid natural product taxol, which is isolated from Taxus brevifolia (the pacific yew tree).<ref name=Sneader_2005a>Sneader W (2005). "Paclitaxel (taxol)". Drug Discovery: A History (Rev. and updated ed.). Chichester: Wiley. pp. 112–113. ISBN 978-0-471-89979-2.</ref>
A class of drugs widely used to lower cholesterol are the HMG-CoA reductase inhibitors, for example atorvastatin. These were developed from mevastatin, a polyketide produced by the fungus Penicillium citrinum.<ref name=LI_2009>Li JL (2009). "Discovery of Lipitor". Triumph of the Heart: the Story of Statins. New York, NY: Oxford University Press. pp. 71–96. ISBN 978-0-19-804351-5.</ref> Finally, a number natural product drugs are used to treat hypertension and congestive heart failure. These include the angiotensin-converting enzyme inhibitor captopril. Captopril is based on the peptidic bradykinin potentiating factor isolated from venom of the Brazilian arrowhead viper (Bothrops jararaca).<ref name=Sneader_2005b>Sneader W (2005). "ACE Inhibitors". Drug Discovery: A History (Rev. and updated ed.). Chichester: Wiley. pp. 280–283. ISBN 978-0-471-89979-2.</ref>
Limiting and enabling factors
Numerous challenges limit the use of natural products for drug discovery, resulting in 21st century preference by pharmaceutical companies to dedicate discovery efforts toward high-throughput screening of pure synthetic compounds with shorter timelines to refinement.<ref name=Li_2009/> Natural product sources are often unreliable to access and supply, have a high probability of duplication, inherently create intellectual property concerns about patent protection, vary in composition due to sourcing season or environment, and are susceptible to rising extinction rates.<ref name=Li_2009/>
The biological resource for drug discovery from natural products remains abundant, with small percentages of microorganisms, plant species, and insects assessed for bioactivity.<ref name=Li_2009/> In enormous numbers, bacteria and marine microorganisms remain unexamined.<ref>Gomez-Escribano JP, Alt S, Bibb MJ (April 2016). "Next Generation Sequencing of Actinobacteria for the Discovery of Novel Natural Products". Marine Drugs. 14 (4): 78. doi:10.3390/md14040078. PMC 4849082. PMID 27089350.</ref><ref name="pawar">Pawar SV, Ho JC, Yadav GD, Yadav VG (2017). "The Impending Renaissance in Discovery & Development of Natural Products". Current Topics in Medicinal Chemistry. 17 (2): 251–267. doi:10.2174/1568026616666160530154649. PMID 27237327.</ref> As of 2008, the field of metagenomics was proposed to examine genes and their function in soil microbes,<ref name=pawar/><ref name="blow">Blow N (May 2008). "Metagenomics: exploring unseen communities". Nature. 453 (7195): 687–90. Bibcode:2008Natur.453..687B. doi:10.1038/453687a. PMID 18509446. S2CID 29079319.</ref> but most pharmaceutical firms have not exploited this resource fully, choosing instead to develop "diversity-oriented synthesis" from libraries of known drugs or natural sources for lead compounds with higher potential for bioactivity.<ref name=Li_2009/>
Isolation and purification
All natural products begin as mixtures with other compounds from the natural source, often very complex mixtures, from which the product of interest must be isolated and purified. The isolation of a natural product refers, depending on context, either to the isolation of sufficient quantities of pure chemical matter for chemical structure elucidation, derivitzation/degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but historically, often more),[citation needed] or to the isolation of "analytical quantities" of the substance of interest, where the focus is on identification and quantitation of the substance (e.g. in biological tissue or fluid), and where the quantity isolated depends on the analytical method applied (but is generally always sub-microgram in scale).<ref name = MakinGower2010>Gower DB, Makin HL, eds. (2009). Steroid Analysis (2nd ed.). Dordrecht: Springer. ISBN 978-1-4020-9774-4.</ref>[page needed] The ease with which the active agent can be isolated and purified depends on the structure, stability, and quantity of the natural product. The methods of isolation applied toward achieving these two distinct scales of product are likewise distinct, but generally involve extraction, precipitation, adsorptions, chromatography, and sometimes crystallizations. In both cases, the isolated substance is purified to chemical homogeneity, i.e. specific combined separation and analytical methods such as LC-MS methods are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—with the goal being repeated detection of only a single species present in the putative pure sample. Early isolation is almost inevitably followed by structure determination, especially if an important pharmacologic activity is associated with the purified natural product.[citation needed]
Structure determination refers to methods applied to determine the chemical structure of an isolated, pure natural product, a process that involves an array of chemical and physical methods that have changed markedly over the history of natural products research; in earliest days, these focused on chemical transformation of unknown substances into known substances, and measurement of physical properties such as melting point and boiling point, and related methods for determining molecular weight.[citation needed] In the modern era, methods focus on mass spectrometry and nuclear magnetic resonance methods, often multidimensional, and, when feasible, small molecule crystallography.[citation needed] For instance, the chemical structure of penicillin was determined by Dorothy Crowfoot Hodgkin in 1945, work for which she later received a Nobel Prize in Chemistry (1964).<ref>Hodgkin DC. "Enhancing X-ray Vision". The Nobel Prize in Chemistry 1964 – Perspectives.</ref>
Synthesis
Many natural products have very complex structures. The perceived complexity of a natural product is a qualitative matter, consisting of consideration of its molecular mass, the particular arrangements of substructures (functional groups, rings etc.) with respect to one another, the number and density of those functional groups, the stability of those groups and of the molecule as a whole, the number and type of stereochemical elements, the physical properties of the molecule and its intermediates (which bear on the ease of its handling and purification), all of these viewed in the context of the novelty of the structure and whether preceding related synthetic efforts have been successful (see below for details).[citation needed]
Some natural products, especially those less complex, are easily and cost-effectively prepared via complete chemical synthesis from readily available, simpler chemical ingredients, a process referred to as total synthesis (especially when the process involves no steps mediated by biological agents). Not all natural products are amenable to total synthesis, cost-effective or otherwise. In particular, those most complex often are not. Many are accessible, but the required routes are simply too expensive to allow synthesis on any practical or industrial scale. However, to be available for further study, all natural products must yield to isolation and purification. This may suffice if isolation provides appropriate quantities of the natural product for the intended purpose (e.g. as a drug to alleviate disease). Drugs such as penicillin, morphine, and paclitaxel proved to be affordably acquired at needed commercial scales solely via isolation procedures (without any significant synthetic chemistry contributing).[citation needed] However, in other cases, needed agents are not available without synthetic chemistry manipulations.[citation needed]
Semisynthesis
The process of isolating a natural product from its source can be costly in terms of committed time and material expense, and it may challenge the availability of the relied upon natural resource (or have ecological consequences for the resource). For instance, it has been estimated that the bark of an entire yew tree (Taxus brevifolia) would have to be harvested to extract enough paclitaxel for just a single dose of therapy.<ref name="urlStory of Taxol">"The Story of Taxol" (PDF). The American Society of Pharmacognosy. Archived from the original (PDF) on 12 December 2013.</ref> Furthermore, the number of structural analogues obtainable for structure–activity analysis (SAR) simply via harvest (if more than one structural analogue is even present) is limited by the biology at work in the organism, and so outside of the experimentalist's control.[citation needed]
In such cases where the ultimate target is harder to come by, or limits SAR, it is sometimes possible to source a middle-to-late stage biosynthetic precursor or analogue from which the ultimate target can be prepared. This is termed semisynthesis or partial synthesis. With this approach, the related biosynthetic intermediate is harvested and then converted to the final product by conventional procedures of chemical synthesis.[citation needed]
This strategy can have two advantages. Firstly, the intermediate may be more easily extracted, and in higher yield, than the ultimate desired product. An example of this is paclitaxel, which can be manufactured by extracting 10-deacetylbaccatin III from T. brevifolia needles, then carrying out a four-step synthesis.[citation needed] Secondly, the route designed between semisynthetic starting material and ultimate product may permit analogues of the final product to be synthesized. The newer generation semisynthetic penicillins are an illustration of the benefit of this approach.[citation needed]
Total synthesis
In general, the total synthesis of natural products is a non-commercial research activity, aimed at deeper understanding of the synthesis of particular natural product frameworks, and the development of fundamental new synthetic methods. Even so, it is of tremendous commercial and societal importance. By providing challenging synthetic targets, for example, it has played a central role in the development of the field of organic chemistry.<ref name = "Heathcock_1996">Heathcock CH (1996). "As We Head into the 21st Century, Is there Still Value in Total Synthesis of Natural Products as a Research Endeavor?". Chemical Synthesis. NATO ASI Series. Vol. 320. pp. 223–243. doi:10.1007/978-94-009-0255-8_9. ISBN 978-94-010-6598-6.</ref><ref name="Nicolaou_2000">Nicolaou KC, Vourloumis D, Winssinger N, Baran PS (January 2000). "The Art and Science of Total Synthesis at the Dawn of the Twenty-First Century". Angewandte Chemie. 39 (1): 44–122. doi:10.1002/(SICI)1521-3773(20000103)39:1<44::AID-ANIE44>3.0.CO;2-L. PMID 10649349.</ref> Prior to the development of analytical chemistry methods in the twentieth century, the structures of natural products were affirmed by total synthesis (so-called "structure proof by synthesis").<ref name="DAL2013">Lightner DA (2013). Bilirubin: Jekyll and Hyde Pigment of Life: Pursuit of Its Structure Through Two World Wars to the New Millenium. Springer. p. 371. ISBN 978-3-7091-1637-1.</ref> Early efforts in natural products synthesis targeted complex substances such as cobalamin (vitamin B12), an essential cofactor in cellular metabolism.<ref name="Woodward_1973"/><ref name="Eschenmoser_1988"/>
Symmetry
Examination of dimerized and trimerized natural products has shown that an element of bilateral symmetry is often present. Bilateral symmetry refers to a molecule or system that contains a C2, Cs, or C2v point group identity. C2 symmetry tends to be much more abundant than other types of bilateral symmetry. This finding sheds light on how these compounds might be mechanistically created, as well as providing insight into the thermodynamic properties that make these compounds more favorable. Density functional theory (DFT), the Hartree–Fock method, and semiempirical calculations also show some favorability for dimerization in natural products due to evolution of more energy per bond than the equivalent trimer or tetramer. This is proposed to be due to steric hindrance at the core of the molecule, as most natural products dimerize and trimerize in a head-to-head fashion rather than head-to-tail.<ref name="pmid15270568">Voloshchuk T, Farina NS, Wauchope OR, Kiprowska M, Haberfield P, Greer A (July 2004). "Molecular bilateral symmetry of natural products: prediction of selectivity of dimeric molecules by density functional theory and semiempirical calculations". Journal of Natural Products. 67 (7): 1141–6. doi:10.1021/np049899e. PMID 15270568.</ref>
Research and teaching
Research and teaching activities related to natural products fall into a number of diverse academic areas, including organic chemistry, medicinal chemistry, pharmacognosy, ethnobotany, traditional medicine, and ethnopharmacology. Other biological areas include chemical biology, chemical ecology, chemogenomics,<ref>Bredel M, Jacoby E (April 2004). "Chemogenomics: an emerging strategy for rapid target and drug discovery" (PDF). Nature Reviews. Genetics. 5 (4): 262–75. CiteSeerX 10.1.1.411.9671. doi:10.1038/nrg1317. PMID 15131650. S2CID 11952369.</ref> systems biology, molecular modeling, chemometrics, and chemoinformatics.<ref>Galúcio JM, Monteiro EF, de Jesus DA, Costa CH, Siqueira RC, Santos GB, et al. (August 2019). "In silico identification of natural products with anticancer activity using a chemo-structural database of Brazilian biodiversity". Computational Biology and Chemistry. 83: 107102. doi:10.1016/j.compbiolchem.2019.107102. PMID 31487609. S2CID 201845232.</ref>
Chemistry
Natural products chemistry is a distinct area of chemical research which was important in the development and history of chemistry. Isolating and identifying natural products has been important to source substances for early preclinical drug discovery research, to understand traditional medicine and ethnopharmacology, and to find pharmacologically useful areas of chemical space.<ref>Harvey AL (October 2008). "Natural products in drug discovery". Drug Discovery Today. 13 (19–20): 894–901. doi:10.1016/j.drudis.2008.07.004. PMID 18691670.</ref> To achieve this, many technological advances have been made, such as the evolution of technology associated with chemical separations, and the development of modern methods in chemical structure determination such as NMR. Early attempts to understand the biosynthesis of natural products, saw chemists employ first radiolabelling and more recently stable isotope labeling combined with NMR experiments. In addition, natural products are prepared by organic synthesis, to provide confirmation of their structure, or to give access to larger quantities of natural products of interest. In this process, the structure of some natural products have been revised,<ref>Chhetri BK, Lavoie S, Sweeney-Jones AM, Kubanek J (June 2018). "Recent trends in the structural revision of natural products". Natural Product Reports. 35 (6): 514–531. doi:10.1039/C8NP00011E. PMC 6013367. PMID 29623331.</ref><ref>Heard DM, Tayler ER, Cox RJ, Simpson TJ, Willis CL (January 2020). "Structural and synthetic studies on maleic anhydride and related diacid natural products" (PDF). Tetrahedron. 76 (1): 130717. doi:10.1016/j.tet.2019.130717. hdl:1983/53998d06-9017-4cfb-822b-c6453348000a. S2CID 209714625.</ref><ref>Wu J, Lorenzo P, Zhong S, Ali M, Butts CP, Myers EL, Aggarwal VK (July 2017). "Synergy of synthesis, computation and NMR reveals correct baulamycin structures" (PDF). Nature. 547 (7664): 436–440. doi:10.1038/nature23265. hdl:1983/85161235-ea9f-4568-9f8a-19b42f4dff67. PMID 28748934. S2CID 205258282.</ref> and the challenge of synthesising natural products has led to the development of new synthetic methodology, synthetic strategy, and tactics.<ref>Corsello MA, Kim J, Garg NK (September 2017). "Indole diterpenoid natural products as the inspiration for new synthetic methods and strategies". Chemical Science. 8 (9): 5836–5844. doi:10.1039/C7SC01248A. PMC 5618777. PMID 28970940.</ref> In this regard, natural products play a central role in the training of new synthetic organic chemists, and are a principal motivation in the development of new variants of old chemical reactions (e.g., the Evans aldol reaction), as well as the discovery of completely new chemical reactions (e.g., the Woodward cis-hydroxylation, Sharpless epoxidation, and Suzuki–Miyaura cross-coupling reactions).<ref>Baran PS (April 2018). "Natural Product Total Synthesis: As Exciting as Ever and Here To Stay". Journal of the American Chemical Society. 140 (14): 4751–4755. doi:10.1021/jacs.8b02266. PMID 29635919.</ref>
History
Foundations of organic and natural product chemistry
The concept of natural products dates back to the early 19th century, when the foundations of organic chemistry were laid. Organic chemistry was regarded at that time as the chemistry of substances that plants and animals are composed of. It was a relatively complex form of chemistry and stood in stark contrast to inorganic chemistry, the principles of which had been established in 1789 by the Frenchman Antoine Lavoisier in his work Traité Élémentaire de Chimie.<ref name="ACS_ Lavoisier_Landmark">"Antoine Laurent Lavoisier The Chemical Revolution". International Historic Chemical Landmark. American Chemical Society.</ref>
Isolation
Lavoisier showed at the end of the 18th century that organic substances consisted of a limited number of elements: primarily carbon and hydrogen and supplemented by oxygen and nitrogen. He quickly focused on the isolation of these substances, often because they had an interesting pharmacological activity. Plants were the main source of such compounds, especially alkaloids and glycosides. It was long been known that opium, a sticky mixture of alkaloids (including codeine, morphine, noscapine, thebaine, and papaverine) from the opium poppy (Papaver somniferum), possessed a narcotic and at the same time mind-altering properties. By 1805, morphine had already been isolated by the German chemist Friedrich Sertürner and in the 1870s it was discovered that boiling morphine with acetic anhydride produced a substance with a strong pain suppressive effect: heroin.<ref name="Dias_2012">Dias DA, Urban S, Roessner U (2012). "A historical overview of natural products in drug discovery". Metabolites. 2 (4): 303–36. doi:10.3390/metabo2020303. PMC 3901206. PMID 24957513.</ref> In 1815, Eugène Chevreul isolated cholesterol, a crystalline substance, from animal tissue that belongs to the class of steroids,<ref>Chevreul ME (1823). "IX — De la cholestérine". Recherches chimiques sur les corps gras d'origine animale (in français). pp. 153–160.</ref> and in 1819 strychnine, an alkaloid was isolated.<ref>Pelletier PP, Caventou JB (1819). "Mémoire sur un nouvel alcali vegetal (la strychnine) trouvé dans la feve de Saint-Ignace, la noix vomique, etc" [Memoir on a new vegetable alkali (strychnine) found in the St. Ignatius bean, the nux-vomica, etc)]. Annales de Chimie et de Physique (in French). 10: 142–176.{{cite journal}}: CS1 maint: unrecognized language (link)</ref>
Synthesis
A second important step was the synthesis of organic compounds. Whereas the synthesis of inorganic substances had been known for a long time, the synthesis of organic substances was a difficult hurdle. In 1827 the Swedish chemist Jöns Jacob Berzelius held that an indispensable force of nature for the synthesis of organic compounds, called vital force or life force, was needed. This philosophical idea, vitalism, well into the 19th century had many supporters, even after the introduction of the atomic theory. The idea of vitalism especially fitted in with beliefs in medicine; the most traditional healing practices believed that disease was the result of some imbalance in the vital energies that distinguishes life from nonlife. A first attempt to break the vitalism idea in science was made in 1828, when the German chemist Friedrich Wöhler succeeded in synthesizing urea, a natural product found in urine, by heating ammonium cyanate, an inorganic substance:<ref>Wöhler F (1828). "Ueber künstliche Bildung des Harnstoffs" [About the artificial formation of urea]. Annalen der Physik und Chemie (in Deutsch). 88 (2): 253–256. Bibcode:1828AnP....88..253W. doi:10.1002/andp.18280880206.</ref>
- <math>\mathrm{NH_4OCN\ \xrightarrow {\ \ 60^{\circ}C \ \ }\ H_2NCONH_2}</math>
This reaction showed that there was no need for a life force in order to prepare organic substances. This idea, however, was initially met with a high degree of skepticism, and only 20 years later, with the synthesis of acetic acid from carbon by Adolph Wilhelm Hermann Kolbe, was the idea accepted. Organic chemistry has since developed into an independent area of research dedicated to the study of carbon-containing compounds, since that element in common was detected in a variety of nature-derived substances. An important factor in the characterization of organic materials was on the basis of their physical properties (such as melting point, boiling point, solubility, crystallinity, or color).[citation needed]
Structural theories
A third step was the structure elucidation of organic substances: although the elemental composition of pure organic substances (irrespective of whether they were of natural or synthetic origin) could be determined fairly accurately, the molecular structure was still a problem. The urge to do structural elucidation resulted from a dispute between Friedrich Wöhler and Justus von Liebig, who both studied a silver salt of the same composition but had different properties. Wöhler studied silver cyanate, a harmless substance, while von Liebig investigated silver fulminate, a salt with explosive properties.<ref name="Justus von Liebig and Friedrich Wöhler">"Justus von Liebig and Friedrich Wöhler". Science History Institute. June 2016. Archived from the original on 20 June 2018. Retrieved 21 March 2018.</ref> The elemental analysis shows that both salts contain equal quantities of silver, carbon, oxygen and nitrogen. According to the then prevailing ideas, both substances should possess the same properties, but this was not the case. This apparent contradiction was later solved by Berzelius's theory of isomers, whereby not only the number and type of elements are of importance to the properties and chemical reactivity, but also the position of atoms in within a compound. This was a direct cause for the development of structure theories, such as the radical theory of Jean-Baptiste Dumas and the substitution theory of Auguste Laurent.<ref>Liebig J (1838). "Ueber Laurent's Theorie der organischen Verbindungen" [About Laurent 's theory of organic compounds]. Annalen der Pharmacie (in Deutsch). 25 (1): 1–31. doi:10.1002/jlac.18380250102.</ref>[better source needed] However, it took until 1858 before by August Kekulé formulated a definite structure theory. He posited that carbon is tetravalent and can bind to itself to form carbon chains as they occur in natural products.<ref>Kekulé A (1858). "Ueber die Constitution und die Metamorphosen der chemischen Verbindungen und über die chemische Natur des Kohlenstoffs" [Concerning the constitution and the metamorphosis of the chemical compounds and the chemical nature of the carbon]. Annalen der Chemie und Pharmacie (in Deutsch). 106 (2): 129–159. doi:10.1002/jlac.18581060202.</ref>[better source needed]
Expanding the concept
The concept of natural product, which initially based on organic compounds that could be isolated from plants, was extended to include animal material in the middle of the 19th century by the German Justus von Liebig. Hermann Emil Fischer in 1884, turned his attention to the study of carbohydrates and purines, work for which he was awarded the Nobel Prize in 1902. He also succeeded to make synthetically in the laboratory in a variety of carbohydrates, including glucose and mannose. After the discovery of penicillin by Alexander Fleming in 1928, fungi and other micro-organisms were added to the arsenal of sources of natural products.<ref name="Dias_2012"/>
Milestones
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By the 1930s, several large classes of natural products were known. Important milestones included:[according to whom?]
- Terpenes, first systematically studied by Otto Wallach (Nobel Prize 1910) and later by Leopold Ružička (Nobel Prize 1939)
- Dyes based on porphins (including chlorophyll and heme), studied by Richard Willstätter (Nobel Prize 1915) and Hans Fischer (Nobel Prize 1930)
- Steroids, studied by Heinrich Otto Wieland (Nobel Prize 1927) and Adolf Windaus (Nobel Prize 1928)
- Carotenoids, studied by Paul Karrer (Nobel Prize 1937)
- Vitamins, studied among others by Paul Karrer, Adolf Windaus, Robert R. Williams, Norman Haworth (Nobel Prize 1937), Richard Kuhn (Nobel Prize 1938) and Albert Szent-Györgyi
- Hormones studied by Adolf Butenandt (Nobel Prize 1939) and Edward Calvin Kendall (Nobel Prize 1950)
- Alkaloids and anthocyanins, studied by, among others, Robert Robinson (Nobel Prize 1947)
See also
Journals
- Chemistry of Natural Compounds
- Journal of Natural Products
- Natural Product Reports
- Natural Product Research
References
Footnotes
Citations
Further reading
- Bhat SV, Nagasampagi BA, Sivakumar M (2005). Chemistry of Natural Products (2 ed.). Berlin: Springer. ISBN 3-540-40669-7.
- Hanson JR (2003). Natural Products: The Secondary Metabolites. Royal Society of Chemistry. ISBN 0-85404-490-6.
- Kaufman PB (1999). Natural Products from Plants. CRC Press. ISBN 0-8493-3134-X.
- Liang XT, Fang WS, eds. (2006). Medicinal Chemistry of Bioactive Natural Products. Wiley-Interscience. ISBN 0-471-73933-2.
- V. K. Ahluwalia; Lalita S. Kumar; Sanjiv Kumar (2022). Chemistry of natural products: amino acids, peptides, proteins and enzymes. Springer. ISBN 978-3-030-86697-6.
- Mayuri Napagoda, Lalith Jayasinghe, ed. (2022). Chemistry of natural products: phytochemistry and pharmacognosy of medicinal plants. De Gruyter. ISBN 978-3-11-059589-5.
External links
- Reusch W (2010). "Natural Products page". Virtual Textbook of Organic Chemistry. Ann Arbor, Mich.: Michigan State University, Department of Chemistry. Archived from the original on 3 February 2007.
- "NAPROC-13 Base de datos de Carbono 13 de Productos Naturales y Relacionados (Carbon-13 Database of Natural Products and Related Substances)". Spanish language tools to facilitate structural identification of natural products.
- Porter N, ed. (1913). "Natural product". Webster's Dictionary. Springfield, Massachusetts: C. & G. Merriam Co.
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