Anand Akhila

Biosynthesis of artemisinin in Artemisia annua

Abstract The isotope ratios ( 3 H: 14 C) in arteannuin B and artemisinin biosynthesized in Artemisia annua from [4 R - 3 H 1 ,2- 14 C]-, [5- 3 H 2 ,2- 14 C]- and [2- 3 H 2 ,2- 14 C](3 RS )- mevalonate have revealed that two specific 1,2-hydride shifts take place during the oxidation and lactonization of the germacrane skeleton to yield dihydrocostunolide. The gem -methyls of DMAPP retain their identity until the final steps of artemisinin biosynthesis. Arteannuin B is considered to be a late precursor of artemisinin and the following biosynthetic sequence is suggested: farnesylpyrophosphate → germacrane skeleton → dihydrocostunolide → cadinanolide → arteannuin B → artemisinin.

Biosynthesis of artemisinic acid in Artemisia annua

Abstract The isotopic and atomic 14 C/ 3 H ratios in artemisinic acid biosynthesized in Artemisia annua from [2- 14 C, 2- 3 H 2 ]-, [2- 14 C,4 R - 3 H 1 ]-, [2- 14 C,5- 3 H 1 ]MVA have revealed that two specific 1,2-hydrogen shifts take place during the formation of the cadinane skeleton of artemisinic acid and that the gem -methyls derived from DMAPP retain their identity during the formation of this compound.

Biosynthesis of andrographolide in Andrographis paniculata.

Andrographolide, a diterpene lactone, is isolated from Andrographis paniculata which is well known for its medicinal properties. The biosynthetic route to andrographolide was studied using [1-(13)C]acetate, [2-(13)C]acetate and [1,6-(13)C(2)]glucose. The peak enrichment of eight carbon atoms in the (13)C NMR spectra of andrographolide suggested that deoxyxylulose pathway (DXP) is the major biosynthetic pathway to this diterpene. The contribution of the mevalonic acid pathway (MVA) is indicated by the observed (13)C-labeling pattern, and because the labeling patterns indicate a simultaneous contribution of both methyl erythritol phosphate (MEP) and MVA pathways it can be deduced that cross-talk occurs between plastids and cytoplasm.

Biosynthesis of gossypol in Thespesia populnea

Abstract Flowering tips of Thespesia populnea were fed with various doubly-labelled precursors such as [2- 14 C, 5- 3 H 2 ],[2- 14 C ,2- 3 H 2 ], [2- 14 C, 4R- 3 H 1 ]MVA, [1- 14 C, 1- 3 H 2 ]geraniol, nerol and farnesol. Atomic and isotopic ratios in the gossypol, thus isolated, revealed that folding pattern of farnesyl pyrophosphate depends upon the precursor used. Degradation products obtained from gossypol (biosynthesized from above precursors) revealed a 1,3-hydrogen shift during the process of cyclization of FPP to cadinane skeleton and its oxidation to hemigossypol. A hypothetical mechanism of oxidative dimerization of hemigossypol to gossypol via free radical formation has also been discussed.

Biosynthesis of monoterpenes in Cymbopogon winterianus

Abstract The isotope ratios in geraniol, citronellol and citronellal biosynthesized in Cymbopogon winterianus from 3 H- and 14 C-labelled mevalonate indicate that geraniol is first converted into citronellol which in turn is converted into citronellal.

Biosynthesis of the clerodane furano-diterpene lactone skeleton in Tinospora cordifolia

Abstract The isotope ratios in cis -clerodane furanoditerpene lactones labelled from [4 R - 3 H 1 , 2- 14 C]MVA suggested two 1,2-hydrogen shifts and two 1,2-methyl shifts during the formation ofthe ring system of these diterpenes. Chemical degradation of clerodane diterpenoids radiolabelled from [2- 14 C]MVA revealed that the gem -methyls of geranylgeranyl pyrophosphate (GGPP) retained their identity during the cyclization.

Biosynthetic relationships of patchouli alcohol, seychellene and cycloseychellene in Pogostemon cablin

Abstract The 3 H/ 14 C isotope ratios in patchouli alcohol seychellene and cycloseychellene isolated from P. cablin that was fed with [4- 3 H 1 (4R) 14 C]MVA suggests that these three sesquiterpenes are biosynthesized from a common intermediate and they are not interconvertible within the plant system. The results reveal that a stereospecific 1,2-methyl shift takes place during the formation of seychellene and cycloseychellene in vivo .

Oxo acids and branched fatty acid esters from rhizomes of Costus speciosus

Five new compounds, isolated from the rhizomes of Costus speciosus have been characterized as tetradecyl 13-methylpentadecanoate, tetradecyl 11-methyltridecanoate, 14--oxotricosanoic acid, 14-oxoheptacosanoic acid and 15-oxo-octacosanoic acid by spectral and chemical studies. Triacontanol, 5α-stigmast-9(11)-en-3β-ol, triacontanoic acid, sitosterol and diosgenin have also been isolated and identified.

1,2-Hydrogen shifts during the biosynthesis of patchoulenes in Pogostemon cablin

Abstract The isotope ratio in α- and γ-patchoulenes in Pogostemon cablin , that has been fed with [2- 14 C, 4 R - 3 H 1 ]MVA, suggests that a proton loss is followed by a 1,2-alkyl shift and two 1,2-hydrogen shifts during the biosynthesis of these two sesquiterpene hydrocarbons. Whereas isotope ratios in β- and δ-patchoulene suggests that a proton loss is followed by one 1,2-hydrogen shift in β-patchoulene and two 1,2-hydrogen shifts in δ-patchoulene.

Biosynthesis and Translocation of Diosgenin in Costus speciosus

Summary Radio-actively labelled free and conjugated diosgenin was isolated from different parts such as stem, leaf, seeds, flowers, and rhizomes of Costus speciosus after feeding 14 C mevalonate, diosgenin, and diosgenin glycoside through different parts in separate sets of experiments. Percent distribution of radioactivity in various parts of the plant suggested: (a) diosgenin is biosynthesised in leaves and then translocated to all the parts of the plant. (b) glycosidation of diosgenin takes place in all the parts of the plant and diosgenin glycosides are stored in rhizomes, seeds, and flowers. (c) deglycosidation of saponin was observed only in the rhizomes indicating that some enzyme is present in the rhizome which is responsible for the hydrolysis.