Withanolides biosynthesis

The methyltransferase that catalyses the formation of 24-ethylidene sterols from 24-methylene precursors in bean rust uredospores (Uromyces phaseoli) can also alkylate lanosterol, 24-methylenecholesterol, zymosterol, and desmosterol to produce C29 sterols.[28- H]-24-Methylenecholesterol was efficiently (ca. 3% yield) incorporated into withaferin A (88) and withanolide D (89) by Withania somnif-era, whereas [28- H]-24-methylcholesterol did not act as a precursor in this system. However, since feeding experiments with [28- H]-24-methylcholesta-5,24-dien-3/8-ol gave ambiguous results it was not possible to rule out other 4-desmethyl sterols (with C28) as intermediates in withanolide biosynthesis. 

Keywords biosynthesis cardiac glycosides ecdysteroids metabolic pathways phylogeny pregnanes saponins secondary metabolites withanolides... 

Veleiro, A., Burton, G. and Gros, E. (1985) Biosynthesis of withanolides in Acnistus breviorus. Phytochemistry, 24, 2263-6. 

The structure of salpichrolide N (104) is particularly interesting regarding the biosynthesis of withanolides with an aromatic D ring. Whiting has proposed as a possible pathway to ring D aromatization, the oxidation of C-18 followed by a 1,2-shift of C-17 to form a new six-... 

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