THE COENZYME B-12 ANALOGS-RIBOSYLCOBALAMINS - SYNTHESIS, CHARACTERIZATION, AND PHOTOLYSIS STUDIES

Two analogs of Coenzynze B-12, i.e., -methyl-5-deoxy-beta-D(-)ribofura nos-5-ylcobalamin (RibCbl) and ene-beta-D(-)-ribofuranos-5-yl-cobalami n(RibCbl), were synthesized. They were characterized by UV-vis and 2D (1)HNMR spectroscopies. Furthermore, aerobic and anaerobic photolysis of the two compounds have been studied. Kinetic data of anaerobic pho toinduced homolysis for two ribosylcobalamins(RibCbl, RibCbl) and 5'- deoxyadenosylcobalamin(AdoCbl) have been determined. The half-times un der the same experimental conditions are: RibCbl, t(1/2) = 488 min; R ibCl, t(1/2) = 122 min; and AdoCbl, t(1/2) = 3 min, respectively. Ther efore, both of ribosylcobalamins are less photosensitive than Coenzyme B-12. These results are discussed in terms of the in-cage chemical pr ocess as well as steric and electronic effects of the axial ligand on the Co-C bond homolysis. (C) 1997 Elsevier Science Inc.