Pub No:
73
Title:
Model Studies for Coenzyme B12 Dependent Enzyme-Catalyzed Rearrangements. Kinetics and Mechanism of Decomposition of Formylmethylcobalamin and Its Acetals
Authors:
Silverman, R.B. and David Dolphin
Journal:
J. Am. Chem. Soc.
Year:
1976
Pages:
98, 4633-4639
Abstract:
Syntheses of formylmethylcobalamin (I) and the kinetics and mechanism of decomposition of the aldehyde and its acetals are reported. Two different pathways were observed for the acid-catalyzed decomposition of the cobalamin acetals: direct Co-C bond cleavage to B12b and a vinyl ether, and normal acetal hydrolysis to I, followed by a rate-determioning fission of the Co-C bond to B12b and acetaldehyde. The rate law of decomposition of I is d[I]/dt = -K[I][H O+ ]; the acid sensitivity and bimolecularity of the decomposition were rationalized as an initial protonation of the formyl carbonyl followed by a direct cleavage of the Co-C bond.

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