L,2-Dimethyl-4,5-diaminobenzene

The addition of riboflavin to the system repeatedly caused a small but significant synthesis of cyanocobalamin. More efficient shunting of the synthesis toward cyanocobalamin took place when parts of the riboflavin molecule and related substances were added, e.g. l-amino-3,4-di-methyl-6-D-ribitylaminobenzene l,2-dimethyl-4,5-diaminobenzene and 5,6-dimethylbenzimidazole. These findings seem consistent with the view of Woolley (1951) that the metabolic paths of the two vitamins are closely interconnected. The activity of riboflavin itself in promoting the synthesis of cyanocobalamin need not of course imply that the vitamin is actually broken down to provide a precursor of cyanocobalamin nucleotide. It could equally well be that a common precursor of riboflavin and cyanocobalamin nucleotide is normally available in limiting amounts and is used preferentially in the synthesis of riboflavin. The provision of preformed riboflavin might then spare this precursor for the synthesis of cyanocobalamin. 

In relation to the concept that l,2-dimethyl-4,5-diaminobenzene is a metabolic precursor of riboflavin and cyanocobalamin, and the dichloro analog an antimetabolite, the signiflcance of all these findings is not readily apparent. Clearly, certain microorganism s can build several alternative nucleotides into the B12 molecule, and for them, dimethyl-diaminobenzene cannot be pictured as a specific metabolic precursor. Nor can its dichloro analog be regarded as an antimetabolite, at least in relation to the synthesis of vitamin B12 if, as it seems, it is readily utilized for the synthesis of a highly active form of the vitamin. 

The only substance which has yet been claimed to have any activity in replacing vitamin B12 for the Euglena is l,2-dimethyl-4,5-diaminobenzene which may be contained within the vitamin B12 molecule. Its action. 

---