A chemical synthesis of S-adenosylhomocysteine from homocysteine and the vitamin B12 coenzyme

The Photolysis of Methylcobalamin*

“…is trapped to yield methionine or S-methylcysteine, respectively (Johnson et al, 1963b). These observations suggest that the photolytic cleavage of coenzyme B12 and the alkylcobalamins involves the homolytic fission of the carbon-cobalt bond with the production of vitamin B!2r and a 5'-deoxyadenosyl or alkyl radical.…”

The Chemistry of the Vitamin B12 Group.

“…The methyl coenzyme analog has become of especial interest (155) since in an enzymic system it methylates homocysteine. An in vitro demonstration of this methyl transfer has also been made (196); the methyl coenzyme analog when photolyzed under reducing conditions (NaBH4) methylates homocysteine to give methionine in 58% yield as the dinitrophenyl derivative. Similarly the vitamin B12 coenzyme gives S-adenosylhomocysteine, an observation which may be significant in the problem of the generation of active methionine (252).…”

A Model for the Cobalamin-Dependent Methionine Synthase

“…As mentioned above, Johnson and coworkers suggested a homolytic cleavage of the intermediate methylcobalt complex for the Me transfer to homocysteine [31]. Therefore, we photolyzed a mixture 4a/5a with an excess of pyridine and hexanethiol 8 with a 150-W sun lamp at room temperature or under reflux.…”