A synthesis of 5' (R)-(2H1)- adenosine has been devised. It is proposed to utilize this form of chirally deuterated adenosine to elucidate the stereochemistry of the enzymatic reactions catalyzed by methionine S-adenosyltransferase, S-adenosylhomocysteinase, and B12s-adenosyltransferase. In addition, the chirally deuterated adenosine will be used to prepare 5'-(S)-(2H1)-coenzyme-B12. The deuterated coenzyme will be incubated with ethanolamine ammonia-lyase and diol dehydrase in the absence of substrate in an attempt to ascertain whether coenzyme-B12 activation proceeds via homolytic or heterolytic fission of the carbon-cobalt bond.