STUDIES ON VITAMIN-B12 AND RELATED COMPOUNDS .49. DIRECT SYNTHESIS OF ALKYLCOBALAMINS AND OF OMEGA-CARBOXYALKYLCOBALAMINES FROM VITAMIN-B12 AND ALIPHATIC CARBOXYLIC-ACIDS UNDER OXIDIZING-REDUCING CONDITIONS

Straight-chain aliphatic carboxylic acids CnH2n+1COOH (n =, e.g., 1-6) and certain dicarboxylic as well as branched carboxylic acids can be oxidized to organic radicals in the presence of vitamin B12r and converted into organocobalamins. Owing to the instability of secondary and tertiary alkylcobalamins and other steric effects, vitamin B12r acts as a selective scavenger of primary alkyl and ω-carboxyalkyl radicals. Accordingly, n-alkylcobalamins and ω-carboxyalkylcobalamins are isolated exclusively and often in quantitative yields. The alkyl and carboxyalkyl radicals are generated from the carboxylic acids by HO2∙, O2 -, or HO∙ radicals formed in reactions of limiting amounts of O2 preferably with V(III) salts, although V(IV), Mo(III), and certain other reducing metal ions can also be used. Oxygen can furthermore be replaced by H2O2, by Fenton reagent, or by electrochemically generated oxygen or oxygen radicals. The reducing metal ions, e.g., V(III), must be present in excess. They not only act as activators of oxygen, but also as reductants of vitamin B12, thus maintaining it in the reactive Co(II) state. The new method of synthesis of organocobalamins under “oxidizing-reducing” conditions may become useful for the preparation of otherwise difficultly accessible compounds. © 1979, American Chemical Society. All rights reserved.