Studies on Vitamin B12 and Related Compounds, 50 Synthesis of Substituted Alkylcobalamins from Vitamin B12r and Radicals Generated from Aldehydes, Alcohols and Ethers under 'Oxidizing-Reducing' Conditions. A New Synthesis of Coenzyme B12 [1]

Organic radicals generated by the oxidation of aldehydes, alcohols and ethers under reducing conditions are trapped by vitamin B12r to yield substituted organocobalamins. From higher n-alkyl aldehydes, acylcobalamins are formed. With acetaldehyde, a mixture of acetylcobalamin and of methylcobalamin is obtained due to the spontaneous decarbonylation of the CH3CO· radical. From saturated alcohols, w-hydroxyalkylcobalamins are produced, while w-alkoxyalkylcobalamins are formed in the corresponding reactions with radicals generated from ethers. Maximum yields of the organocobalamins are obtained if reducing conditions are maintained during the oxidation of the organic substrates. This is conveniently achieved by using V(III) salts as the reductants and the slow addition of oxidants (e.g. of O2, H2O2, Fenton reagent, or of electrochemically generated oxidizing equivalents). With 5′-deoxyadenosine, 5′-deoxyadenosylcobalamin is formed.