Tuberculostearic acid synthesis

Wallace, P.A., D.E. Minnikin, K. McCrudden, and A. Pizzarello, Synthesis of (R,5)-10-Methyloctadecanoic Acid (Tuberculostearic Acid) and Key Chiral 2-Methyl Branched Intermediates, Chem. Phys. Lipids 71 145-162 (1994). 

Additional C-atoms (see the formula of ergosterol, Fig. 120) in the side chains of certain sterols derive from the methyl group of L-methionine. When there are additional ethyl side chains, e.g., in stigmasterol and jff-sitosterol (Fig. 120), two subsequent methylations take place. One hydrogen atom of the methyl group of L-methionine is lost during the methylation (Fig. 123). The mechanism in this respect resembles that of the synthesis of tuberculostearic acid from oleic acid (D 3.2.1). 

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