Phytosterol biosynthesis

The y-ketotriazole did not inhibit C-14a-demethylation in fungi or ent-kaurene oxidase, the cytochrome P450 monooxygenase target site of 

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Lee MH et al (2004) Enhanced triterpene and phytosterol biosynthesis in Panax ginseng overexpressing squalene synthase gene. Plant CeU Physiol 45 976... 

NT325 Reid, W. W. Accumulation of squalens-2,3-oxide during inhibition of phytosterol biosynthesis in Nicotiana tabacum. Phytochemistry 1968 7(3) NT338... 

Similar types of alkylation have been applied in syntheses of other steroidal side-chains, including that of 22-trans-26,27-dinorergosta-5,22-dien-3j8-ol (387), a novel marine sterol. In addition, the Wittig reaction has been used to prepare various possible polyene intermediates in phytosterol biosynthesis. The aldehydes (389) and (390) were prepared (Scheme 26) from stigmasterol acetate (388b) by modification of a known procedure. These aldehydes were then alkylated with a variety of ylides derived from phosphonium salts, leading to a series of polyenes (391) and (392). ... 

Goad, L. J., Inhibition of phytosterol biosynthesis and the consequences for plant growth, in Ecological Chemistry Biochemistry of Plant Terpenoids (J. B. Harbome and F. A. Tomas-Barber, eds.). Phytochemistry Society of Europe Vol. 31, 209-229, Clarendon, Oxford, 1991b. 

Szafranek, B.M. S3mak, E.E. Cuticular waxes from potato (Solanum tuberosum). Ph3ftochemistry 2006, 67, 80-90. Nes, W.D. Nichols, S. D. Phytosterol biosynthesis pathway in Mortierella alpina. Phytochemistry 2006, 67,... 

In common with the e /-kaurene synthetase inhibitors, KOls may also affect phytosterol biosynthesis. Indeed, most of these compounds arose from fungicide screening programmes where the principal requirement is for inhibition of lano-sterol or 24-methylenedihydrolanosterol 14a-demethylase [28]. The equivalent enzyme in phytosterol biosynthesis, obtusifoliol 14a-demethylase, has been extracted from maize embryos and shown to be a cytochrome P-450 monooxygenase [40], which is inhibited more strongly by certain triazole fungicides than by related growth retardants [44]. 

This class of natural compounds is interesting primarily with respect to phytosteroid biosynthesis. It was found that weakly polar representatives of this class, especially cycloartenol, play the role of a precursor or intermediate in the biogenesis of plant sterols. Cyclization of squalene-2,3-oxide in plants occurs with the formation of an additional 9,19-three-membered ring, which is a signature of phytosterol biosynthesis. 

We have recently demonstrated the existence in a microsomal prepai ation from maize seedlings of an enzyme catalyzing the NADPH dependent reduction of the A -bond of A -sterol precursors to produce the final A -sterols, i.e. A -SR, thus providing the first direct evidence for the participation of A -sterols in A -phytosterols biosynthesis [1] (Figure 1). 

R.J. Kemp, A.S.A. Hamman, L.J. Goad and T.W. Goodwin, Studies on phytosterol biosynthesis observations on the esterifled sterols of higher plants. Phytochemistry 7 447 (1986)... 

Consequences for the so-called segregation model ofisoprenoid biosynthesis The presence of such alternative pathways as outlined above could provide a further explanation for the observations obtained with the HMGR inhibitor mevinolin, viz. its great efficiency in blocking cytoplasmic sterol biosynthesis, but its low efficiency to affect ubiquinone biosynthesis, and its practically complete inefficiency to block the accumulation of isoprenoids and prenyl lipids of the chloroplast (summarized and discussed earlier 14, 17]. It could also explain the puzzling observation that, in contrast to phytosterols, prenyl-subsituted coumarins were not labeled from [2- ]acetate or [2- C]MVA in elicitor-treated cultures oiAmnd majus, suggesting that the DMAPP needed for the (plastid ) umbelliferone dimethylallyl transferases (EC 2.5.1.3) is formed from IPP synthesized de novo within the plastid, rather than from IPP imported into the plastid from the cytosol [86]. Elicitor-induced inhibition of phytosterol biosynthesis should occur by specific inhibition of one of the enz)ones on the c) osolic pathway from MVA to DMAPP. 

Fulton DC, Kroon PA, Matem U, Threlfall DR, Whitehead IM. Inhibition of phytosterol biosynthesis in elicitor-treated cultures of Ammi majus. Phytochemistry, 1993 34 139-145. 

FIGURE 18.5 Phytosterol biosynthesis pathway reconstructed based on the Dunaliella tertiolecta transcriptome. 

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