Lingens B, Schild T A, Vogler B, Renz P
Institut für Biologische Chemie und Ernährungswissenschaft, Universität Hohenheim, Federal Republic of Germany.
Eur J Biochem. 1992 Aug 1;207(3):981-5. doi: 10.1111/j.1432-1033.1992.tb17133.x.
The 5,6-dimethylbenzimidazole moiety of vitamin B12 is formed from riboflavin in aerobic and some aerotolerant bacteria. Thereby C1' of riboflavin is transformed into C2 of the vitamin B12 base. In the present publication a study on this transformation with riboflavin 2H-labeled in the 1'R or 1'S position is described. This study was undertaken in order to find out if one of the two hydrogens at C1' is transferred to C2 of 5,6-dimethylbenzimidazole. The 2H-labeled riboflavin samples were synthesized starting from unlabeled or 1-2H-labeled ribose and 3,4-dimethylaniline yielding N-beta-D-ribopyranosyl-3,4-dimethylaniline. The unlabeled riboside was reduced to N-D-ribityl-3,4-dimethylaniline with sodium cyanoborotrideuteride, the 2H-labeled riboside with sodium cyanoborohydride. The ribityl derivatives were transformed into N-D-ribityl-2-phenylazo-4,5-dimethylaniline, and condensed with barbituric acid to riboflavin. The reduction of the ribosyl compound to the ribityl derivative is only partially stereospecific. Thus the riboflavin synthesized from unlabeled ribose had a 2H ratio of 3/1 (1'R/1'S), the riboflavin obtained from D-[1-2H1]ribose of 1/3 (1'R/1'S). The 2H content in these positions was determined from the 1H-NMR spectra. These spectra showed also that 1 mol 2H/mol riboflavin was present in position 1'. The deuterated riboflavin samples were incubated under aerobic conditions with broken cell preparations of Propionibacterium shermanii. The deuterium content of the 5,6-dimethylbenzimidazole isolated was determined by mass spectrometry and by 1H NMR. These measurements revealed that the hydrogen in the pro-S position at C1' of riboflavin is retained during 5,6-dimethylbenzimidazole formation, and is thus found at C2 of this base.
在需氧和一些耐氧细菌中，维生素B12的5,6-二甲基苯并咪唑部分由核黄素形成。由此，核黄素的C1'转化为维生素B12碱基的C2。在本出版物中，描述了一项对在1'R或1'S位置用2H标记的核黄素进行这种转化的研究。进行这项研究是为了弄清楚C1'处的两个氢原子之一是否转移到5,6-二甲基苯并咪唑的C2上。2H标记的核黄素样品从未标记的或1-2H标记的核糖和3,4-二甲基苯胺开始合成，得到N-β-D-核糖吡喃基-3,4-二甲基苯胺。未标记的核糖苷用氰基硼氘化钠还原为N-D-核糖醇基-3,4-二甲基苯胺，2H标记的核糖苷用氰基硼氢化钠还原。核糖醇衍生物转化为N-D-核糖醇基-2-苯基偶氮-4,5-二甲基苯胺，并与巴比妥酸缩合生成核黄素。核糖基化合物还原为核糖醇衍生物只是部分立体特异性的。因此，从未标记核糖合成的核黄素的2H比例为3/1（1'R/1'S），从D-[1-2H1]核糖获得的核黄素为1/3（1'R/1'S）。这些位置的2H含量由1H-NMR光谱测定。这些光谱还表明，在1'位置存在1摩尔2H/摩尔核黄素。将氘代核黄素样品在需氧条件下与谢氏丙酸杆菌的破碎细胞制剂一起孵育。通过质谱和1H NMR测定分离出的5,6-二甲基苯并咪唑的氘含量。这些测量结果表明，核黄素C1'处前手性S位置的氢在5,6-二甲基苯并咪唑形成过程中保留下来，因此在该碱基的C2处发现。
