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The thiol-dependent methylation of heptamethyl cob(II)yrinate 8r with methyl iodide and methyl tosylate was explored under a variety of conditions. The interaction of the heptamethyl cob(II)yrinate with a variety of thiols was monitored prior to the addition of the methylating agent, and the formation of the Co(I) complex was only apparent in the reaction with hexane thiol. Nevertheless, thiol-mediated methylation of the Co(II) complex 8r takes place with methyl iodide under most conditions. The Co-methylation with methyl tosylate showed a different reactivity, was inhibited by pyridine or N-methylimidazole, and was strongly dependent on the the acidity of the thiol used. Mechanistic aspects are discussed.

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Treatment of vitamin B 12a 1 (hydroxycobalamin hydrochloride, aquocobalamin) with NaBH 4 and ZnCl 2 leads to the selective cleavage of the nucleotide loop and gives dicyanocobinamide 2a in good yield. Methylcobinamide 4 was prepared from 2 via aquocyanocobinamide 3. The glutathione-mediated methylation of 3 in a pH 3.5 buffer solution proceeded with MeI, but not with MeOTs.