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Synthesis of Enantiomerically‐Pure [ 13 C]Aristeromycylcobalamin and Its Reactivity in Dioldehydratase, Glyceroldehydratase, Ethanolamine Ammonia‐Lyase and Methylmalonyl‐CoA Mutase Reactions
Author(s) -
Weigl Ulrich,
Heimberger Martin,
Pierik Antonio J.,
Rétey János
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200390073
Subject(s) - adenosylcobalamin , chemistry , mutase , stereochemistry , cofactor , coenzyme a , hydroxocobalamin , lyase , corrin , enzyme , biochemistry , organic chemistry , cobalt , cyanocobalamin , reductase , vitamin b12
We describe a novel enantioselective synthesis of aristeromycin, the carbocyclic analogue of adenosine. The seven‐step synthesis is also suitable for the preparation of specifically‐labelled [6′‐ 13 C]aristeromycin. Both the unlabelled and 13 C‐labelled product was coupled to vitamin B 12 to form aristeromycylcobalamin. This carbocyclic analogue of coenzyme B 12 was examined for its coenzymic activity with several adenosylcobalamin‐dependent enzymes. For glyceroldehydratase and dioldehydratase, the reaction rate ( k cat ) was 38 and 44 % of that measured with adenosylcobalamin as coenzyme. In contrast, aristeromycylcobalamin showed no detectable activity with methylmalonyl‐CoA mutase and ethanolamine ammonia‐lyase. Instead, it was a weak inhibitor of the former and a strong inhibitor of the latter enzyme. The slower turnover rate with glyceroldehydratase raised the hope of detecting the 6′‐deoxyaristeromycyl radical intermediate. Comparison of the EPR spectra of the intermediates in the glyceroldehydratase reaction, which used adenosyl‐ and aristeromycylcobalamines, respectively, as coenzyme, revealed a significant shift and this suggests a different geometric position of these cofactors at the binding site during the cleavage of the carbon‐cobalt bond. However, we found no evidence for the existence of a 6′‐deoxyaristeromycyl radical during the reaction with [6′‐ 13 C]aristeromycylcobalamin. We conclude that the lifetime of this radical is still too short to be observed.