Nuclear magnetic resonance and mass spectrometry have been used to confirm that the nucleoside product formed when 5′-deoxyadenosylcobalamin is photolysed under anaerobic conditions is 8,5′-cyclic adenosine. The synthesis of 5′-deoxyadenosylcobalamin, which is tritiated at C8 of the adenosyl moiety, provides the confirmation that the photolysis mechanism involves a reaction between the 5′-methylene carbon radical and C8 of the adenine ring.
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The mass spectrum of the nucleoside product is shown in Fig. 2. The molecular ion is at m/e 249 which corresponds to the formula CloNs Hl103. The structure is substantiated as 8,5 '-cyclic adenosine by the fragmentation pattern (Scheme I). Peaks of m/e 249, 192, 177, 163,149, t35 and 108 are accounted for by this fragmentation scheme. These data confirm that the structure of the nucleoside photolysis product from 5'-deoxyadenosylcobalamin is 8,5'-cyclic adenosine, and support a mechanism of Y-carbon radical attack at C8. This research was supported by a grant from the U.S. Public Health Service AM