Synthesis of 4-aza-5,6-dimethylbenzimidazole and biosynthetic preparation of 4- and 7-aza-5,6-dimethylbenzimidazolylcobamide.

We report on the preparation of 4-aza-5,6-dimethylbenzimidazolylcobamide and 5,6-dimethyl-7-azabenzimidazolylcobamide. These vitamin B12-analogs were required as reference compounds for comparison with a corrinoid previously isolated in small amounts for Eubacterium limosum grown in the presence of 4(5)-aminoimidazole. 4(7)-Aza-5,6-dimethylbenzimidazole was synthesized from N-1-benzyl-4-nitroimidazole which was reduced to N-1-benzyl-4-aminoimidazole and condensed with 1-dimethylamino-2-methylbutan-3-one to yield N-1-benzyl-4-aza-5,6-dimethylbenzimidazole. The benzyl group of this compound was split off by catalytic hydrogenation to form 4(7)-aza-5,6-dimethylbenzimidazole. 4(7)-Aza-5,6-dimethylbenzimidazole was transformed by a growing culture of Propionibacterium shermanii into 4-aza-5,6-dimethylbenzimidazolylcobamide and 5,6-dimethyl-7-azabenzimidazolylcobamide. Both vitamin B12-analogs were almost as active as Vitamin B12 in a growth test with the vitamin B12-dependent Escherichia coli-mutant DSM 4261.