ALKYL TRANSFER FROM QUATERNARY AMMONIUM-SALTS TO COBALT(I) - MODEL FOR THE COBALAMIN-DEPENDENT METHIONINE SYNTHASE REACTION

The reaction of cobaloxime(I) with diverse quaternary ammonium salts leads, in general, to a group transfer from nitrogen to cobalt The behaviour of the salts in these transalkylations is consistent with an S(N)2 mechanism, involving Co(I) as a nucleophile. In a model study of the cobalamin-dependent methionine synthase reaction, 5-(CH3)-C-13-methyl labelled 5,5,6,7-tetramethyl-5,6,7,8-tetrahydropteridinium salt (23) -a model of the natural coenzyme 5-CH3H4-folate (I)- was allowed to react with cobaloxime(I) and cobalamin(I). In each case the formation of the methyl transfer product, namely, methylcobaloxime and methylcobalamin, respectively, was shown by C-13-NMR spectroscopy.