Methyl sterols

Volkman J. K., Barrett S. M., Dunstan G. A., and Jeffrey S. W. (1993) Geochemical significance of the occurrence of dinosterol and other 4-methyl sterols in a marine diatom. Org. Geochem. 20, 7-15. 

Vegetable Oil Desmethyl Sterols 4-Methyl Sterols 4,4-Dimethyl Sterols... 

It was originally postulated that the methyl groups at C-4 were removed as COj -a suggestion that has proved to be correct. These groups are hydroxylated by a mixed-function oxidase which is NAD(P)H and Oj dependent. First, the 4a-methyl is attacked, yielding the 4 -hydroxymethyl-4 -methyl sterol. This reaction is catalyzed by a methyl sterol oxidase which has been solubilized and partially purified in Gaylor s laboratory [108]. The same enzyme preparation will, with reduced pyridine nucleotide and dioxygen, oxidize the C-30 carbon to a carboxylic acid. The 4a-methyl-4/8-hydroxymethyl-5a-cholestan-3j8-ol is not a substrate for sterol biosynthesis while its epimer is [5]. The detailed mechanisms for the enzymatic removal of C-30 and C-31 are not fully understood. The initial reaction yields a 4a-hydroxy-methyl sterol by inference however, neither the isolation nor the enzymatic formation of a 4a-hydroxymethyl sterol has been demonstrated in animal tissues. This may well result from the fact that the hydroxylation reaction is the slow step in the demethylation process [5]. 

The biosynthesis of 4-methyl sterols from methyl ation of a 4-desmethylsterol precursor has not been suggested to occur in any other organism. 

We have recently discovered similar but not identical pathways in T. aceti and P. redivivus (Chitwood et al., unpublished). Cysts of Heterodera zeae did not contain 4-methyl sterols (27), but possibly other life stages of H. zeae or other parasitic nematodes may contain 4-methylsteroTs. 

Kritchevsky, D., Tepper, S. A., Czarnecki, S. K., and Kyle, D. J. (1999). Effects of 4-methyl-sterols from algae and of p sitosterol on cholesterol metabolism in rats. Nutr. Res. 19, 1649-1654. 

Homberg, E. and Bielefeld, B. Main components of 4-methyl-sterol and triterpene fraction of twelve vegetable fats and their influence on sterol analysis. Fat Science and Technology, 92(12), 478-480. 1990. 

Methyl sterols occur naturally in only minor amounts as they are precursors of the desmethyl sterols. In commercial soybean sterols, 98.1% are 4-desmethyl sterols, 1.3% are 4-methyl sterols and 0.6% are 4,4-dimethyl sterols (Sierksma et al, 1999). Compared with 4-desmethyl sterols, the number of different 4-methyl sterol compounds is small. 

Kritchevsky etal (1999) studied the effects of 4-methyl sterols from algae and of sitosterol on cholesterol metabolism in rats. He found that 4-methyl sterols (in an algal sterol blend containing 50% 4-methyl sterols and 40% desmethyl sterols) did not lower semm or liver lipid levels and confirmed the hypolipidemic properties of sitosterol. 

Prenyllipid biosynthesis under the influence of sethoxydim Most of the C-label was found in the sterol fraction, whereby the highest mol-specific radioactivity was detected in the 4-dimethyl and 4-methyl sterols, which are known as biosynthetic precursors of the desmethyl sterols (Table 6). High label was also found in the mitochondrial ubiquinone, which in maize leaves consists of the two homologues Q-9 and Q-10 (29). Much less radioactivity is found in the chloroplast prenyllipids (chlorophylls, carotenoids, prenyl-quinones) as is expected and known, since exogeneously applied mevalonic... 

Strain KMM 4500 of the species Stilbella aciculosa, harvested at a depth of 17 m in the Sea of Japan, owes its strong antibiotic activity to fusidic acid, a 4-methyl-sterol present in several species of Deuteromycetes, Ascomycetes and terrestrial Basidiomycetes, and discovered for the first time in a marine fungus (Kuznetsova et al, 2001). 

Some sterols with modified side chains or with atypical unsaturated systems, as well as 4-methyl sterols, have been fotmd in several genera, espedaHy Haliclona and Petrosia. 

Dow, W.C., Gebreyesus, T., Popov, S., Carlson, R.M.K., and Djerassi, C. (1983) Marine 4-methyl sterols synthesis C-24 epimers 4a,24-dimethyl-5a-cholestan-3 3-ol and 360MHz HNMR comparisons to the natural product from Plexaura homomaUa. Steroids, 42, 217-230. 

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