title: 7-Azabenzimidazolylcobamide and 5,6-dimethyl-7-azabenzimidazolylcobamide, new vitamin B12-analogs synthesized from 4(5)-aminoimidazole by Eubacterium limosum.
abstract: In anaerobic bacteria, glycine, formate, and the amide-N of glutamine are building blocks for the biosynthesis of the imidazole moiety of the vitamin B12-base 5,6-dimethylbenzimidazole. These building blocks are also used for the biosynthesis of the imidazole moiety of purine bases. Therefore we tested 4(5)-aminoimidazole, the base moiety of the purine nucleotide precursor 5-aminoimidazole ribonucleotide, for its putative function as precursor of 5,6-dimethylbenzimidazole. The anaerobic vitamin B12-producer Eubacterium limosum, grown in the presence of [2-13C]4(5)-aminoimidazole, synthesized nonlabeled vitamin B12, but also [2-13C]7-azabenzimidazolylcobamide and [2-13C]5,6-dimethyl-7-azabenzimidazolylcobamide. [2-13C]limidazole was used by E. limosum to form [2-13C]imidazolylcobamide. Simultaneously nonlabeled vitamin B12 was synthesized. This shows that 4(5)-aminoimidazole and imidazole are not intermediates in the biosynthesis of 5,6-dimethylbenzimidazole. However, 4(5)-aminoimidazole has obviously a structure similar to the structure of an as yet unknown precursor of the vitamin B12-base, and is therefore transformed into the aza analogs. In order to prepare a reference compound 4(5)-azabenzimidazole was added to a culture of Propionibacterium shermanii and to a culture of E. limosum, P. shermanil transformed this base mainly to 4-azabenzimidazolylcobamide, as determined by 1H NMR-spectroscopy (NOE experiment). In contrast E. limosum produced mainly 7-azabenzimidazolylcobamide. The reason for this difference is discussed.
authors.affiliation: Institut für Biologische Chemie und Ernährungswissenschaft, Universität Hohenheim, Stuttgart, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Endres
authors.forename: A
authors.initials: A
authors.lastname: Würfel
authors.forename: B
authors.initials: B
authors.lastname: Vogler
authors.forename: P
authors.initials: P
authors.lastname: Renz
mesh_terms: D000693:Anaerobiosis; D002854:Chromatography, Paper; D003038:Cobamides / Q000096:biosynthesis* / Q000737:chemistry; D005051:Eubacterium / Q000254:growth & development / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008970:Molecular Weight; D011685:Purine Nucleotides / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: C098331:5,6-dimethyl-7-azabenzimidazolylcobamide; C098332:7-azabenzimidazolylcobamide; D003038:Cobamides; D007093:Imidazoles; D011685:Purine Nucleotides; C098330:4-aminoimidazole