Erythromycin methyl group from methionine

The O-methyl group of L-cladinose (2) is also derived from L-methionine. The O-methylation step does not, however, take place at the level of the nucleotide-sugar, but it occurs when the substrate is erythromycin C, which contains L-mycarose and D-desosamine as glycosidic components9 (see Scheme la). The O-methylation of the L-mycarose moiety of erythromycin C by a partially purified enzyme from Streptomyces erythreus was described by Alpine and Corcoran.10,11 The reaction catalyzed is shown in Scheme la. 

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