The Biosynthesis of Artemisinin (Qinghaosu) and the Phytochemistry of Artemisia annua L. (Qinghao)

In the paper

“The largest group of such monocyclic monoterpenes in A. annua is the p-menthane series (Table 25), which incorporate a single six-membered ring.”

In the paper

“Studies with 14C-labeled LPP have shown that in A. annua this precursor is converted to cyclised monoterpenes such as 1,8-cineole (326) and α-pinene (347) with greater efficiency than the alternative precusors, NPP and GPP [109].”

What the sources say

• Not checked yetcites [109] Banthorpe, 1983, Metabolism of linaloyl, neryl and geranyl pyrophosphates in Artemisia annua, Phytochemistry source

In the paper

“Myrcene (254) is the most abundant regular acyclic monoterpene from A. annua, and can account for up to 5% of the essential oil [22,33,43].”

What the sources say

• Not checked yetcites [22] Liu, 1988, Preliminary analysis on chemical constituents of essential oil from inflorescence of of Artemisia annua L., Acta Botanica Sinica (Zhiwu Xuebao)
• Not checked yetcites [33] Libbey, 1989, Unusual essential oils grown on Oregon II, Artemisia annua L. J. Essent. Oil Res. source
• Not checked yetcites [43] Goel, 2007, Volatile metabolite composition of the essential oil from aerial parts of ornamanetal and artemisinin-rich cultivars of Artemisia annua, J. Essent. Oil Res. source

In the paper

“which is the major constituent of the essential oil in some varieties of A. annua [29,37,42,73], and can account for up to 50% of the total [22,25,33,43,45,53].”

What the sources say

• Not checked yetcites [22] Liu, 1988, Preliminary analysis on chemical constituents of essential oil from inflorescence of of Artemisia annua L., Acta Botanica Sinica (Zhiwu Xuebao)
• Not checked yetcites [25] Chalchat, 1991, A contribution to chemotaxonomy of Artemisia annua L., Asteraceae, Acta Pharm. Jugosl.
• Not checked yetcites [33] Libbey, 1989, Unusual essential oils grown on Oregon II, Artemisia annua L. J. Essent. Oil Res. source
• Not checked yetcites [43] Goel, 2007, Volatile metabolite composition of the essential oil from aerial parts of ornamanetal and artemisinin-rich cultivars of Artemisia annua, J. Essent. Oil Res. source
• Not checked yetcites [45] Jain, 2002, Essential oil composition of Artemisia annua L. "Asha" from the plains of Northern India, J. Essent. Oil Res. source
• Not checked yetcites [53] Charles, 1991, Characterization of the essential oil of Artemisia annua L., J. Essent. Oil Res. source

In the paper

“The vast majority of monocyclic monoterpenes from A. annua, however, are p-menthanes (Table 25), incorporating a six-membered ring, which is formed directly by cyclization of an LPP/NPP precursor.”

In the paper

“It is intriguing to note that there are exact structural homologies between six of the seven highly oxygenated 11,13-dehydro sesquiterpenes which have been isolated as metabolites of artemisinic acid (473) and a subset of the sixteen 11,13-dihydro metabolites which were obtained in the preceding study with dihydroartemisinic acid (480) (see Table 37).”

In the paper

“There is – as yet – no direct evidence from in vivo studies to suggest how further transformation of 481 to the 1,2,4-trioxane ring in artemisinin might occur in A. annua.”

In the paper

“Finally, it is worth reiterating that both in vivo and in vitro studies have shown that the tertiary allylic hydroperoxide 481 can be transformed into a wide variety of other compounds, in addition to artemisinin (495).”

In the paper

“These in vitro experiments have shown that 481 can indeed undergo sponataneous conversion to a transient enol as proposed in step ii) of Scheme 11 [204,238,243,302,303]”

What the sources say

• Not checked yetcites [204] Haynes, 1997, From Qinghao, marvelous herb of antiquity, to the antimalarial trioxane qinghaosu - and some remarkable new chemistry, Acc. Chem. Res. source
• Not checked yetcites [238] Acton, 1992, On the conversion of dihydroartemisininic acid into artemisinin, J. Org. Chem. source
• Not checked yetcites [243] Haynes, R.K., and Vonwiller, S.C. (1990). Catalyzed oxygenation of allylic hydroperoxides derived from qinghao (artemisinic) acid. Conversion of qinghao acid into dehydroqinghaosu (artemisitene) and qinghaosu (artemisinin). J. Chem. Soc., Chem. Commun., 451–453. source
• Not checked yetcites [302] Vonwiller, 1997, The formation of a peracetal and trioxane from an enol ether with Copper(II) triflate and oxygen: unexpected oxygenation of aldol intermediates, Tetrahedron Lett. source
• Not checked yetcites [303] Adam, W., Kliem, U., and Lucchini, V. (1988). Preparative UV-VIS laser photochemistry: Photocycloadditions of methylenelactones with benzophenone and p-benzoquinone: Oxygen trapping of Paterno-Buchi triplet 1,4-diradicals as model reactions for Qinghaosu-type 1,2,4-trioxanes. Liebigs Ann. Chem., 869–875. source

In the paper

“The evidence for steps ii)-iv) which are proposed in Scheme 12 comes solely from in vitro studies, conducted with the tertiary allylic hydroperoxide 481 [171,236,237,239,254], which can be obtained in good yield from photosensitized oxygenation of 480 [193,218].”

What the sources say

• Not checked yetcites [171] Zhou, 1986, Total synthesis of arteannuin (Quinghaosu) and related compounds, Pure Appl. Chem. source
• Not checked yetcites [236] Ye, B., and Wu, Y.-L. (1990). An efficient synthesis of qinghaosu and deoxoqinghaosu from arteannuin acid. J. Chem. Soc., Chem. Commun., 726–727. source
• Not checked yetcites [237] Roth, 1991, A facile semisynthesis of the antimalarial drug qinghaosu, J. Chem. Educ. source
• Not checked yetcites [239] Nowak, 1998, Synthesis of (+)-artemisinin and (+)-deoxyartemisinin from arteannuin B and arteannuic aid, Tetrahedron source
• Not checked yetcites [254] Jung, 1986, Practical conversion of artemisinic acid into desoxyartemisinin, J. Org. Chem. source
• Not checked yetcites [193] Sy, 2002, The mechanism of the spontaneous autoxidation of dihydroartemisinic acid, Tetrahedron source
• Not checked yetcites [218] Sy, 2002, The role of the 12-carboxylic acid group in the spontaneous autoxidation of dihydroartemisinc acid, Tetrahedron source

In the paper

“furthermore, there was no evidence for conversion to any 11,13-dihydro metabolite, including artemisinin (495)”

What the sources say

• Not checked yetcites [155] Brown, 2007, In vivo transformations of artemisinic acid in Artemisia annua plants, Tetrahedron source

In the paper

“By contrast, artemisinic acid (473) seems to be obtained in maximum yield at the late vegetative stage”

In the paper

“It has also been observed that increased illumination or sunlight results in a higher yield of artemisinin [331,332,333].”

What the sources say

• Not checked yetcites [331] Chen, 1987, Studies of several physiological factors on artemisinin synthesis in Artemisia annua, Zhiwu Shenglixue Tongxun
• Not checked yetcites [332] Wang, 2008, Effects of irradiance on growth, photosynthetic characteristics and artemisinin content of Artemisia annua L., Photosynthetica source
• Not checked yetcites [333] Gupta, 2002, Morphogenetic variation for artemisinin and volatile oil in Artemisia annua, Ind. Crops Prod. source

In the paper

“This approach, pioneered by the synthetic biologist Jay Keasling at UC Berkeley (USA), has so far yielded microbially-produced artemisinic acid (473), which is then transformed to artemisinin (495) in a separate chemical process [see Section 3.3b for a discussion of the confusion surrounding the true biosynthetic status of artemisinic acid (473)].”

In the paper

“it has also been noted that the content of artemisinin can be up to ten-fold higher in flowers, as compared with leaves [19,329,330].”

What the sources say

• Not checked yetcites [19] Billa, 2008, GC-MS analysis of the volatile constituents of essential oil and aromatic waters of Artemisia annua L. at different developmental stages, Nat. Prod. Comm.
• Not checked yetcites [329] Jain, 1996, Isolation of high artemisinin-yielding clones of Artemisia annua, Phytochemistry source
• Not checked yetcites [330] Chen, 1986, Factors affecting the content of artemisinin in Artemisia annua, Zhongyao Tongbao

In the paper

“epi-Deoxyarteannuin B (478) was obtained as a minor metabolite of artemisinic acid (473), without any evidence for the accompanying formation of artemisinin (495), in the most recent study of the metabolism of artemisinic acid [155].”

What the sources say

• Not checked yetcites [155] Brown, 2007, In vivo transformations of artemisinic acid in Artemisia annua plants, Tetrahedron source

In the paper

“Correlations have been observed between peroxidase activity and artemisinin levels in hairy roots [354]”

What the sources say

• Not checked yetcites [354] Woerdenbag, 1992, High peroxidase activity in cell cultures of Artemisia annua with minute artemisinin contents, Nat. Prod. Lett. source

In the paper

“To date, investigators have concentrated on expressing the enzymes from phases 1 and 2 of the biosynthetic route to artemisinin in transgenic organisms (see Scheme 9 in Section 3). These have included: HMG-CoA reductase (HMGR) [370]; farnesyl diphosphate synthase (FPPS) [371, 372,373,374]; amorpha-4,11-diene synthase (ADS) [375,376,377]; and the P450 enzyme which oxidises amorpha-4,11-diene to art”

What the sources say

• Not checked yetcites [370] Kim, 2005, Cloning and expression of a farnesyl diphosphate synthase in Centella asiatica (L.) Urban, Mol. Cells source
• Not checked yetcites [371] Chen, 1999, Ri-mediated transformation of Artemisia annua with a recombinant farnesyl diphosphate synthase gene for artemisinin production, Plant Cell Tissue Org. Cult. source
• Not checked yetcites [372] Zhao, 2003, Cloning and enzymology analysis of farnesyl pyrophosphate synthase gene from a superior strain of Artemisia annua L., Chin. Sci. Bull.
• Not checked yetcites [373] Han, 2006, Effects of overexpression of the endogenous farnesyl diphosphate synthase on the artemisinin content in Artemisia annua L., J. Integr. Plant Biol. source
• Not checked yetcites [374] Huang, 2008, Cloning and expression of Artemisia annua L. amorpha-4,11-diene synthase gene, Guangzhou Zhongyiyao Daxue Xuebao
• Not checked yetcites [375] Kong, 2009, The improvement of amorpha-4,11-diene production by a yeast-conform variant, J. Appl. Microbiol. source
• Not checked yetcites [376] Chang, 2000, Amorpha-4,11-diene synthase of Artemisia annua: cDNA isolation and bacterial expression of a terpene synthase involved in artemisinin biosynthesis, Arch. Biochem. Biophys. source
• Not checked yetcites [377] Chang, 2007, Engineering Escherichia coli production of functionalized terpenoids using plant P450s, Nat. Chem. Biol. source

In the paper

“only one strain is so far reported as a potential source of artemisinin [358].”

What the sources say

• Not checked yetcites [358] Shen, 2006, Absolute configuration of new cytotoxic and other bioactive tricothecene macrolides, Chem. - Eur. J. source

In the paper

“Instead, the chemistry of undifferentiated callus and suspension cultures of A. annua seems to be dominated by sterols, such as stigmasterol (570) and sitosterol (568) (Section 2.7.2) [86,313]; as well as phenylpropanoids, such as scopoletin (184) (Section 2.3; Table 17), all of which are also found in significant quantities in the parent plants [86,313].”

What the sources say

• Not checked yetcites [86] Brown, 1994, Secondary metabolism in tissue culture of Artemisia annua, J. Nat. Prod. source
• Not checked yetcites [313] Covello, 2008, Making artemisinin, Phytochemistry source

In the paper

“the production of dihydroartemisinic acid (480) in yeast using the Dbr2 gene has now been described [298]”

What the sources say

• Not checked yetcites [298] Zhang, 2004, Molecular cloning of a classical plant peroxidase from Artemisia annua and its effect on the biosynthesis of artemisinin in vitro, Acta Bot. Sin.

In the paper

“Both Saccharomyces cerevisiae [379,380] and Escherichia coli [381,382,383] have been used as hosts when attempting to establish a viable recombinant microbial pathway for the biosynthesis of artemisinin.”

What the sources say

• Not checked yetcites [379] Lindahl, 2006, Production of the artemisinin precursor amorpha-4,11-diene by engineered Saccharomyces cerevisiae, Biotechnol. Lett. source
• Not checked yetcites [380] Newman, 2006, High-level production of amorpha-4,11-diene in a two phase partitioning bioreactor of metabolically engineered Escherichia coli, Biotechnol. Bioeng. source
• Not checked yetcites [381] Anthony, 2009, Optimization of the mevalonate-based isoprenoid biosynthetic pathway in Escherichia coli for production of the antimalarial drug precursor amorpha-4,11-diene, Metab. Eng. source
• Not checked yetcites [382] Picaud, 2007, Improved conditions for production of recombinant plant sesquiterpene synthases in Escherichia coli, Prot. Expr. Purif. source
• Not checked yetcites [383] Keasling, J.D. (2005, January March). Engineering microbes for anti-malarial production. Abstracts of Papers; In Proceedings of 229th ACS National Meeting, San Diego, CA, USA.

In the paper

“it has now been possible to demonstrate that dihydroartemisinic acid is a late-stage precursor to artemisinin and that the closely related secondary metabolite, artemisinic acid, is not”

In the paper

“and, furthermore, that the series of spontaneous rearrangement reactions which then convert this allylic hydroperoxide to the 1,2,4-trioxane ring of artemisinin are also non-enzymatic in nature.”

In the paper

“In the particular case of artemisinin, these in vivo results are also supported by in vitro studies, demonstrating explicitly that the biosynthesis of artemisinin proceeds via the tertiary allylic hydroperoxide, which is derived from oxidation of dihydroartemisinic acid.”

In the paper

“It is suggested that several of these peroxides result from the reaction of molecular oxygen with the tri-substituted double bond of an appropriate (and frequently abundant) mono- sesqui- or diterpene precursor.”

In the paper

“Saturated fatty acids have been obtained from A. annua as a continuous series between C12 [dodecanoic acid; (36)] and C20 [eicosanoic acid; (48)].”

In the paper

“As a result, the complete biosynthetic pathway to artemisinin could not be stated conclusively at the time.”

In the paper

“Most of the regular acyclic monoterpenes reported in Table 23 can be derived by further functional group modifications (dehydration, reduction or oxidation) of linalool (250) or its isomers, geraniol (244) and nerol (248).”

In the paper

“All possible saturated unbranched hydrocarbons between C16 [hexadecane; (5)] and C26 [hexacosane; (14)] have now been reported from GC-MS studies of A. annua (Table 1).”

In the paper

“These findings strongly support the hypothesis that many of the highly oxygenated sesquiterpenoids from this species arise by oxidation reactions involving allylic hydroperoxides, which seem to be such a defining feature of the chemistry of A. annua.”

In the paper

“(and some of the experiments also appeared to contradict one another)”

In the paper

“Quite remarkably, feeding experiments with labeled dihydroartemisinic acid and artemisinic acid have resulted in incorporation of label into roughly half of all the amorphane and cadinane sesquiterpenes which were already known from phytochemical studies of A. annua.”

In the paper

“The saturated fatty acids listed in Table 3 are likely to be the biogenetic parents of the saturated hydrocarbons, alcohols, aldehydes and ketones which appear in Table 1 and Table 2.”

In the paper

“The majority of these components are unique to this species and several have turned out to be relevant to the biosynthesis of artemisinin.”

In the paper

“However, A. annua is distinguished from the other members of the family both by the very large number of natural products which have been characterised to date (almost six hundred in total, including around fifty amorphane and cadinane sesquiterpenes), and by the highly oxygenated nature of many of the terpenoidal secondary metabolites.”

In the paper

“These reactive hydroperoxides might then be responsible for the formation of a large number of the highly-oxygenated terpenes reported from A. annua.”

In the paper

“In addition, this species also contains an unusually large number of terpene allylic hydroperoxides and endoperoxides.”

In the paper

“The majority of these components are unique to this species and several have turned out to be relevant to the biosynthesis of artemisinin.”

In the paper

“The Chinese medicinal plant Artemisia annua L. (Qinghao) is the only known source of the sesquiterpene artemisinin (Qinghaosu), which is used in the treatment of malaria.”

• Also stated in: § 2. The Phytochemistry of Artemisia annua L. (Qinghao) · plain

  “The sesquiterpene, artemisinin, is however unique to A. annua – it has been searched for on several occasions in other species in the genus Artemisia, always without success [10,11].”

What the sources say

• Not checked yetcites [10] Klayman, 1984, Isolation of artemisinin (Qinghaosu) from Artemisia annua growing in the US, J. Nat. Prod. source
• Not checked yetcites [11] Balachandran, 1987, Chemical investigation of some Artemisia species: Search for artemisinin or other related sesquiterpene lactones with a peroxide bridge, Indian J. Pharm. Sci.

In the paper

“These flavones include: casticin (227), artemetin (228) [91], chrysosplenol D (225) and chrysoplenetin (226) [92]”

What the sources say

• Not checked yetcites [91] Elford, 1987, Potentiation of the antimalarial activity of qinghaosu by methoxylated flavones, Trans. R. Soc. Trop. Med. Hyg. source
• Not checked yetcites [92] Stermitz, 2002, Two flavanols from Artemisia annua which potentiate the activity of berberine and norfloxacin against a resistant strain of Staphylococcus aureus, Planta Med. source

In the paper

“Fortunately, studies which have been published in the last decade are now providing a clearer picture of the biosynthetic pathways in A. annua.”

In the paper

“Hexadecanoic acid (41; C16) and octadecanoic acid (45; C18) are the most dominant saturated lipids from A. annua (Table 3)”

In the paper

“while oleic acid (80) (C18) is the most abundant unsaturated fatty acid (Table 5).”

In the paper

“There is some evidence that the autoxidation of dihydroartemisinic acid to this tertiary allylic hydroperoxide is a non-enzymatic process within the plant, requiring only the presence of light”

In the paper

“A cDNA for (3R)-linalool synthase, which converts GPP to (3R)-linalool (250) by ionization of the pyrophosphate group, has been described recently from A. annua [110].”

What the sources say

• Not checked yetcites [110] Jia, 1999, (3R)-Linalool synthase from Artemisia annua L: cDNA isoation, characterization and wound induction, Arch. Biochem. Biophys. source

In the paper

“it has now been possible to demonstrate that dihydroartemisinic acid is a late-stage precursor to artemisinin and that the closely related secondary metabolite, artemisinic acid, is not”

In the paper

“This observation forms the basis of a proposal that the biogenesis of many of the highly oxygenated terpene metabolites from A. annua – including artemisinin itself – may proceed by spontaneous oxidation reactions of terpene precursors, which involve these highly reactive allyllic hydroperoxides as intermediates.”

In the paper

“The secondary and tertiary allylic hydroperoxides, α- and β-myrcene hydroperoxide (265 and 264), have been isolated from A. annua on more than one occasion [9,114]”

What the sources say

• Not checked yetcites [9] Brown, 2003, Terpenoids from the seeds of Artemisia annua, Phytochemistry source
• Not checked yetcites [114] Ruecker, 1987, α- and β-Myrcene hydroperoxide from Artemisia annua, J. Nat. Prod. source

In the paper

“1,8-Cineole (326) is the most abundant p-menthane monoterpene from A. annua [22,29,40,42,43,45,73]”

What the sources say

• Not checked yetcites [22] Liu, 1988, Preliminary analysis on chemical constituents of essential oil from inflorescence of of Artemisia annua L., Acta Botanica Sinica (Zhiwu Xuebao)
• Not checked yetcites [29] Genov, 1983, Gas-Chromatographic study of the essential oil of Artemisia annua L., Naunchi Trudove - Vissh Institut po Khranitelna i Vkusova Promishlenost, Plodiv
• Not checked yetcites [40] Dembitskii, A.D., Krotova, G.I., Kuchukhidze, N.M., and Yakobashvili, N.Z. (1983). Essential Oil of Artemisia annua L.. Maslozhirovaya Promyshlennost, 31–34.
• Not checked yetcites [42] Lari, 2002, The composition of essential oil from Artemisia annua L. growing wild in Iran, Falsnamah-i-Giyahan-i Daruyi
• Not checked yetcites [43] Goel, 2007, Volatile metabolite composition of the essential oil from aerial parts of ornamanetal and artemisinin-rich cultivars of Artemisia annua, J. Essent. Oil Res. source
• Not checked yetcites [45] Jain, 2002, Essential oil composition of Artemisia annua L. "Asha" from the plains of Northern India, J. Essent. Oil Res. source
• Not checked yetcites [73] Georgiev, 1978, On the distillation of annual wormwood (Artemisia annua Linnaeus), Rivista Italiana Essenze, Profumi, Piante Officinali, Arromatizanti, Syndets, Saponi, Cosmaetici, Aerosols

In the paper

“The formation of all three skeletons has been explained in terms of different cleavage reactions occurring at each of the three carbon-carbon bonds in the cyclopropyl ring of the common precursor, chysanthemyl pyrophosphate (Scheme 2) [126].”

What the sources say

• Not checked yetcites [126] Allen, 1977, Terpene biosynthesis. Part 17. Biosynthesis of irregular monoterpenes in extracts from higher plants, Phytochemistry source

In the paper

“The most abundant member of this class of monoterpenoids is camphor (341) [25,29,37,45]”

What the sources say

• Not checked yetcites [25] Chalchat, 1991, A contribution to chemotaxonomy of Artemisia annua L., Asteraceae, Acta Pharm. Jugosl.
• Not checked yetcites [29] Genov, 1983, Gas-Chromatographic study of the essential oil of Artemisia annua L., Naunchi Trudove - Vissh Institut po Khranitelna i Vkusova Promishlenost, Plodiv
• Not checked yetcites [37] Holm, 1997, Variation in the essential oil composition of Artemisia annua L. of different origin cutivated in Finland, Flavour Frag. J. source
• Not checked yetcites [45] Jain, 2002, Essential oil composition of Artemisia annua L. "Asha" from the plains of Northern India, J. Essent. Oil Res. source

In the paper

“A cDNA clone encoding (E)-β-farnesene synthase, which catalyzes the formation of β-farnesene (382) from FPP (378), has recently been isolated from A. annua [133].”

What the sources say

• Not checked yetcites [133] Picaud, 2005, Expression, purification and characterization of recombinant (E)-β-farnesene synthase from Artemisia annua, Phytochemistry source

In the paper

“All are produced from farnesyl pyrophosphate (FPP; 378)”

In the paper

“Germacrene A synthase, the enzyme which catalyzes the cyclization of FPP (378) to germacrene A (390), has recently been isolated from the glandular trichomes of A. annua [137].”

What the sources say

• Not checked yetcites [137] Bertea, 2006, Isoprenoid biosynthesis in Artemisia annua: cloning and heterologous expression of a germacrene A synthase from a glandular trichome cDNA library, Arch. Biochem. Biophys. source

In the paper

“and could be induced in mature tissue in response to a fungal elicitor.”

What the sources say

• Not checked yetcites [139] Cai, 2002, A cDNA clone for β-caryophyllene synthase from Artermisia annua, Phytochemistry source

In the paper

“the most abundant eudesmane from A. annua is β-selinene (412) [40,42]”

What the sources say

• Not checked yetcites [40] Dembitskii, A.D., Krotova, G.I., Kuchukhidze, N.M., and Yakobashvili, N.Z. (1983). Essential Oil of Artemisia annua L.. Maslozhirovaya Promyshlennost, 31–34.
• Not checked yetcites [42] Lari, 2002, The composition of essential oil from Artemisia annua L. growing wild in Iran, Falsnamah-i-Giyahan-i Daruyi

In the paper

“The isolation of the eudesmane allylic hydroperoxide (414) from A. annua is significant, as its structure is suggestive of formation by spontaneous autoxidation of the hydrocarbon precursor selina-4,11-diene (422) [9].”

What the sources say

• Not checked yetcites [9] Brown, 2003, Terpenoids from the seeds of Artemisia annua, Phytochemistry source

In the paper

“Germacrene D (392) is the most abundant member of the germacrane class of sesquiterpenes [22,37,46]”

What the sources say

• Not checked yetcites [22] Liu, 1988, Preliminary analysis on chemical constituents of essential oil from inflorescence of of Artemisia annua L., Acta Botanica Sinica (Zhiwu Xuebao)
• Not checked yetcites [37] Holm, 1997, Variation in the essential oil composition of Artemisia annua L. of different origin cutivated in Finland, Flavour Frag. J. source
• Not checked yetcites [46] Yang, 2008, Investigation of essential oil from leaves of Artemisia annua L. in Guizhou, Shizen Guoyi Guoyao

In the paper

“The β-caryophyllene synthase gene was found to be expressed widely in most plant tissues during early development”

What the sources say

• Not checked yetcites [139] Cai, 2002, A cDNA clone for β-caryophyllene synthase from Artermisia annua, Phytochemistry source

In the paper

“A cDNA clone for β-caryophyllene synthase, the sesquiterpene cyclase which converts FPP (378) to β-caryophyllene (405) has now been isolated from A. annua [139].”

What the sources say

• Not checked yetcites [139] Cai, 2002, A cDNA clone for β-caryophyllene synthase from Artermisia annua, Phytochemistry source

In the paper

“α- and β-Bisabolene are the most abundant bisabolane sesquiterpenes from A. annua”

What the sources say

• Not checked yetcites [28] Mukhtar, 2007, GC-MS analysis of volatile oil of aerial parts of Artemisia annua L., J. Essent. Oil-Bearing Plants source
• Not checked yetcites [46] Yang, 2008, Investigation of essential oil from leaves of Artemisia annua L. in Guizhou, Shizen Guoyi Guoyao

In the paper

“the enzyme amorpha-4,11-diene synthase, which catalyses the formation of the bicyclic sesquiterpene amorpha-4,11-diene, (Section 2.6.3) also produces small amounts of acyclic sesquiterpenes such as trans-nerolidol (380) and (E)-1,3(15),6,10-farnesatetraene (382)”

What the sources say

• Not checked yetcites [134] Picaud, 2005, Expression, purification and characterization of recombinant amorpha-4,11-diene synthase from Artemisia annua L., Arch. Biochem. Biophys. source

In the paper

“Elemanes may thus be artifacts which are introduced during the extraction and isolation process, especially, perhaps, as a result of the high temperatures often associated with GC-MS analysis”

In the paper

“Several other bisabolanes, which have not yet been reported as natural products from A. annua, were also obtained from the cyclization of FPP which is catalysed by this enzyme [134]”

What the sources say

• Not checked yetcites [134] Picaud, 2005, Expression, purification and characterization of recombinant amorpha-4,11-diene synthase from Artemisia annua L., Arch. Biochem. Biophys. source

In the paper

“The six-membered ring in the bisabolane sesquiterpenes from A. annua (Table 30) is formed by cyclization of the C15 precursor, FPP (378), in much the same way that the p-menthane monoterpenes (Section 2.5.3) arise from the corresponding C10 precursor.”

In the paper

“and its existence as an intermediate in Scheme 7 must therefore be inferred.”

In the paper

“(the remaining four metabolites are: annulide (457), isoannulide (490), deoxyarteannuin B (477) and artemisinic acid methyl ester (474), which were all isolated in trace amounts.”

What the sources say

• Not checked yetcites [155] Brown, 2007, In vivo transformations of artemisinic acid in Artemisia annua plants, Tetrahedron source

In the paper

“The amorphane/cadinane group of bicyclic sesquiterpenes is by far the largest class of sesquiterpenes found in A. annua.”

In the paper

“When labeled artemisinic acid (473), the 11,13-dehydro analogue of dihydroartemisinic acid (480), was fed to intact A. annua plants, slightly fewer labeled metabolites were isolated [155].”

What the sources say

• Not checked yetcites [155] Brown, 2007, In vivo transformations of artemisinic acid in Artemisia annua plants, Tetrahedron source

In the paper

“rather, each is the committed precursor to the two large families of highly oxygenated 11,13-dehydro and 11,13-dihydro sesquiterpene metabolites which are known from this species (see, for example, the nine pairs of compounds in Table 37).”

In the paper

“Clearly, the in vivo transformations of artemisinic acid (473) closely parallel those of its 11,13-dihydro analogue, dihydroartemisinic acid (480), as is shown by Scheme 5, Scheme 6 and Scheme 7.”

In the paper

“In addition, feeding experiments with both labeled precursors appear to show that artemisinic acid (473) and dihydroartemisinic acid (480) are NOT mutually interconvertible”

What the sources say

• Not checked yetcites [155] Brown, 2007, In vivo transformations of artemisinic acid in Artemisia annua plants, Tetrahedron source
• Not checked yetcites [185] Brown, 2004, In vivo transformations of dihydroartemisinic acid in Artemisia annua plants, Tetrahedron source

In the paper

“(However, note that in the case of artemisinic acid (473), no allylic hydroperoxide analogous to (481) in Scheme 6 was isolated in vivo as a natural product”

What the sources say

• Not checked yetcites [155] Brown, 2007, In vivo transformations of artemisinic acid in Artemisia annua plants, Tetrahedron source

In the paper

“The pattern of transformations of dihydroartemisinic acid (480) which was observed in vivo very closely paralleled the spontaneous autoxidation chemistry for dihydroartemisinic acid which had previously been demonstrated in vitro [193,218].”

What the sources say

• Not checked yetcites [193] Sy, 2002, The mechanism of the spontaneous autoxidation of dihydroartemisinic acid, Tetrahedron source
• Not checked yetcites [218] Sy, 2002, The role of the 12-carboxylic acid group in the spontaneous autoxidation of dihydroartemisinc acid, Tetrahedron source

In the paper

“It seems likely therefore that similar mechanisms are operative in the metabolism of both dihydroartemisinic acid (480) and artemisinic acid (473).”

In the paper

“Artemisinic acid (473) [105,147,148], arteannuin B (462) [105,147,149] and artemisinin (495) [105,147,150] are the most abundant representatives of this class of natural products”

What the sources say

• Not checked yetcites [105] Zheng, 1994, Cytotoxic terpenoids and flavonoids from Artemisia annua, Planta Med. source
• Not checked yetcites [147] Tu, 1982, Studies on the constituents of Artemisia annua: 2, Planta Med. source
• Not checked yetcites [148] Misra, 1993, Crystal structure of artemisinic acid: A possible biogenetic precursor of antimalarial artemisinin from Artemisia annua, J. Nat. Prod. source
• Not checked yetcites [149] Jeremic, D., Jokic, A., Behbud, A., and Stefanovic, M. (1973). New type of sesquiterpene lactone isolated from Artemisia annua. Arteannuin B. Tetrahedron Lett., 3039–42. source
• Not checked yetcites [150] Liu, 1979, Structure and reaction of arteannuin, Huaxue Xuebao

In the paper

“* The most significant products from this feeding study were dihydroarteannuin B (479), dihydro-epi-deoxyarteannuin B (485) and the dihydro seco-cadinane (493).”

What the sources say

• Not checked yetcites [185] Brown, 2004, In vivo transformations of dihydroartemisinic acid in Artemisia annua plants, Tetrahedron source

In the paper

“Deoxyartemisinin (499) is some 100-300 times less potent than artemisinin (495) as an antimalarial drug”

In the paper

“The aristolane sesquiterpenoid, β-gurjunene (1(10)-aristolene [73464-47-8]) (432) [34], is the only example of a 6,11-cycloeremophilane from this species.”

What the sources say

• Not checked yetcites [34] Ali, 2000, Volatile oil constituents of Artemisia annua leaves, J. Med. Aromat. Plant Sci.

In the paper

“This has lead to the proposal that the main metabolic route to all three of these metabolites and artemisinin (495) in A. annua involves the spontaneous autoxidation of dihydroartemisinic acid (480) and the subsequent chemical reactions of the derived tertiary allylic hydroperoxide (481), as is shown in Scheme 6.”

In the paper

“This group has been lost altogether, presumably as the result of ester hydrolysis, in the bis-nor-amorphane sesquiterpene, norannuic acid 501 [66,199].”

What the sources say

• Not checked yetcites [66] Ahmad, 1994, Terpenoids from Artemisia annua and constituents of its essential oil, Phytochemistry source
• Not checked yetcites [199] Misra, 1993, Bisnorcadinanes from Artemisia annua and definitive carbon-13 assignments of β-arteether, Phytochemistry source

In the paper

“A large number of other cadinane and amorphane sesquiterpenes, including: arteannuin B (462) [248,285]; epi-deoxyarteannuin B (478) [286]; dihydroarteannuin B (479) [249]; dihydro-epi-deoxyarteannuin B (485) [286]; the seco-cadinane (494) [217]; and artemisitene (497) [211,248,284] have also been suggested as late-stage intermediates at or around this point in the biosynthesis”

What the sources say

• Not checked yetcites [248] Nair, 1993, Bioconversion of arteannuin B to artemisinin, J. Nat. Prod. source
• Not checked yetcites [285] Wang, 1993, Studies on the biosynthesis of arteannuin. V. The role of 6-epi-deoxyarteannuin B in arteannuin biosynthesis, Chin. J. Chem. source
• Not checked yetcites [286] Towler, 2007, Evidence of artemisinin production from IPP stemming from both mevalonate and non-mevalonate pathways, Plant Cell Rep. source
• Not checked yetcites [249] Bharel, 1998, Enzymic synthesis of artemisinin from natural and synthetic precursors, J. Nat. Prod. source

In the paper

“natural phytene-1,2-diol (552) was therefore assigned as being a mixture of epimers at the 2-position on the basis of its NMR spectra and on the assumption that the configuration at the 7- and 11- positions of (552) remained fixed, as in phytol.”

In the paper

“A β-amyrin synthase, responsible for cyclization of squalene to the tritepene skeleton, has also been obtained from A. annua.”

In the paper

“Much of the interest in SQS stems from its position at a key point in terpenoid biosynthesis, in which FPP (378) branches either to triterpenes or sesquiterpenes.”

In the paper

“A cDNA clone encoding epi-cedrol synthase has been shown to catalyze the formation of the oxygenated sesquiterpene epi-cedrol from FPP (378) [258,259].”

What the sources say

• Not checked yetcites [258] Mercke, 1999, Cloning, expression and characterization of epi-cedrol synthase, a sesquiterpene cyclase from Artemisia annua L., Arch. Biochem. Biophys. source
• Not checked yetcites [259] Hua, 1999, The molecular cloning of 8-epicedrol synthase from Artemisia annua, Arch. Biochem. Biophys. source

In the paper

“The novel carbon skeleton of compound 500 is thought to be derived from the amorphane skeleton by migration of C-8 from C-7 to C-6 (i.e., compound 500 is an 8(7→6) abeo amorphane), which results in a contraction of the B ring from six atoms to five.”

In the paper

“indeed, it has recently been concluded that artemisinin biosynthesis occurs in the two outer apical cells of the glandular secretory trichomes [104]”

What the sources say

• Not checked yetcites [104] Olsson, 2009, Localization of enzymes of artemisinin biosynthesis to the apical cells of glandular secretory trichomes of Artemisia annua L., Phytochemistry source

In the paper

“which demonstrates that the peroxy linkage in artemisinin is indeed necessary for its biological activity.”

In the paper

“Trace amounts of the sesquiterpene hydrocarbons α-cedrene, β-cedrene, (E)-β-farnesene, α-acoradiene and (E)-β-bisabolene were also produced by the operation of this enzyme [258].”

What the sources say

• Not checked yetcites [258] Mercke, 1999, Cloning, expression and characterization of epi-cedrol synthase, a sesquiterpene cyclase from Artemisia annua L., Arch. Biochem. Biophys. source

In the paper

“Similarly, the formyl group in 1-oxo-2β-[3-butanone]-3α-methyl-6β-[2-propanol formyl ester]-cyclohexane (505) [218] is probably also derived from oxidative rearrangements, this time deriving from the 5-position of an appropriate bicyclic precursor”

What the sources say

• Not checked yetcites [218] Sy, 2002, The role of the 12-carboxylic acid group in the spontaneous autoxidation of dihydroartemisinc acid, Tetrahedron source

In the paper

“Structural revision was made on the basis of studies of the photo-oxygenation of commercially-available phytol, which produced both phytene-1,2-diol (552) (in racemic form), as well as its 2-hydroperoxy analogue (553) [260].”

What the sources say

• Not checked yetcites [260] Wong, H.-F., and Brown, G.D. (2002). Photo-oxygenation of phytol and the structure revision of phytene-1,2-diol from Artemisia annua to phytene-1-ol-2-hydroperoxide. J. Chem. Res., 30–33. source

In the paper

“The structure of the diterpene phytene-1-ol-2-hydroperoxide (553) [9,260] was wrongly assigned as phytene-1,2-diol (552), when it was first described as a natural product from A. annua [261].”

What the sources say

• Not checked yetcites [9] Brown, 2003, Terpenoids from the seeds of Artemisia annua, Phytochemistry source
• Not checked yetcites [260] Wong, H.-F., and Brown, G.D. (2002). Photo-oxygenation of phytol and the structure revision of phytene-1,2-diol from Artemisia annua to phytene-1-ol-2-hydroperoxide. J. Chem. Res., 30–33. source
• Not checked yetcites [261] Brown, 1994, Phytene-1,2-diol from Artemisia annua, Phytochemistry source

In the paper

“The observance of epimers is most easily explained if both the hydroperoxide (553) and alcohol (552) are products of the spontaneous autoxidation of phytol (550), occurring within the tissues of A. annua plants as is shown in Scheme 8.”

In the paper

“It was possible to produce the triterpene β-amyrin (559) in significant amounts when this enzyme was engineered into Saccharomyces cerevisiae (two other enzymes in the pathway: 3-hydroxy-3-methylglutaryl-CoA reductase and lanosterol synthase were also manipulated in these experiments) [269].”

What the sources say

• Not checked yetcites [269] Shukla, 1997, A new adenine derivative from Artemisia annua, J. Indian Chem. Soc.

In the paper

“Similarly, the unusual carbon skeleton of 503 might also have arisen from an amorphane precursor, in which the A ring has been contracted from six to five atoms, as a result of carbon-carbon bond migration of C-3 from C-4 to C-5 [9].”

What the sources say

• Not checked yetcites [9] Brown, 2003, Terpenoids from the seeds of Artemisia annua, Phytochemistry source

In the paper

“The SQS gene and cDNA have been successfully cloned and sequenced from A. annua on several occasions [263,264,265].”

What the sources say

• Not checked yetcites [263] Feng, 2004, Cloning and sequencing of Artemisia annua squalene synthase gene and its cDNA, Guangzhou Zhongyiyao Daxue Xuebao
• Not checked yetcites [264] Li, 2007, Escherichia coli expression, purification and functional identification of a squalene synthase from Artemisia annua L., Yingyong Yu Huanjung Shengwu Xuebao
• Not checked yetcites [265] Liu, 2003, Molecuar cloning, Escherichia coli expression and genomic organization of squalene synthase gene from Artemisia annua, Acta Bot. Sin.

In the paper

“Conversion of FPP (378) to sesquiterpenes, on the other hand, requires the operation of ionase and cyclase enzymes”

In the paper

“Kim and Kim have reported that artemisinic acid is not converted to dihydroartemisinic acid in A. annua [297]”

What the sources say

• Not checked yetcites [297] Zhang, 2008, The Molecular cloning of artemisinic aldehyde Δ11(13) reductase and its role in glandular trichome-dependent biosynthesis of artemisinin in Artemisia annua, J. Biol. Chem. source

In the paper

“The first step in phase 1 involves the conversion of IPP and DMAPP (both C5) to the C15 intermediate, farnesyl pyrophosphate (FPP; 378) by the enzyme farnesyl diphosphate synthase (FPPS).”

In the paper

“No enzymes have yet been described for any of these putative reactions in phase 3.”

In the paper

“Indeed, experiments with classical plant peroxidases, a class of enzyme with the potential for involvement in these kinds of reactions, have failed to increase the yield of artemisinin [299,300].”

What the sources say

• Not checked yetcites [299] Zhang, 2003, Effect of horseradish peroxidase on the biosynthesis of artemisinin in Artemisia annua in vitro, Yingyong Yu Huanjung Shengwu Xuebao
• Not checked yetcites [300] Lommen, 2006, Trichome dynamics and artemisinin accumulation during development and senescence of Artemisia annua leaves, Planta Med. source

In the paper

“However, the most recent evidence suggests that dihydroartemisinic acid (480), produced from the saturated “lower” branch in Scheme 11, is, in fact, the true precursor to artemisinin.”

In the paper

“The second phase in the biosynthesis of artemisinin (495) involves modification to the isopropylidene group (C-11, C-12 and C-13) in amorpha-4,11-diene (451), yielding putative biosynthetic intermediates such as dihydroartemisinic acid (480) and artemisinic acid (473).”

In the paper

“A cDNA encoding this enzyme, which catalyses the “head-to-tail” chain extension of a DMAPP starter by two molecules of IPP, has now been cloned from A. annua [290].”

What the sources say

• Not checked yetcites [290] Bouwmeester, 1999, Amorpha-4,11-diene synthase catalyses the first probable step in artemisinin biosynthesis, Phytochemistry source

In the paper

“Therefore, if dihydroartemisinic acid (480) is the true precursor to artemisinin (495) in phase 3 of the biosynthesis, then reduction of the exocyclic double bond in amorpha-4,11-diene (451) must be occurring before artemisinic acid (473) in Scheme 11.”

In the paper

“A trichome-specific cDNA for the cytochrome P450 enzyme, CYP71AV1, which catalyzes three successive oxidations at the 12-position of amorpha-4,11-diene (451) in the “upper” oxidative pathway in Scheme 11, has now been isolated (see also Section 4.4).”

In the paper

“and more recent biosynthetic studies, employing both labeled artemisinic acid [155] and dihydroartemisinic acid [185], have confirmed that there is no interconversion in either direction between dihydroartemisinic acid (473) and artemisinic acid (480)”

What the sources say

• Not checked yetcites [155] Brown, 2007, In vivo transformations of artemisinic acid in Artemisia annua plants, Tetrahedron source
• Not checked yetcites [185] Brown, 2004, In vivo transformations of dihydroartemisinic acid in Artemisia annua plants, Tetrahedron source