414 VITAMIN Bi2 



5. Miscellaneous Degradation Reactions 



The oxidation of vitamin B12 with hydrogen peroxide under mild alkaline 

 conditions'^ is reported to give a neutral and an acidic product. Both are 

 red crystalline compounds with absorption spectra identical to that of 

 vitamin B12, but with only a fraction of its microbiological activity. Dilute 

 alkali treatment of vitamin B12 in the absence of light gave an acidic red 

 crystalline product ; and potassium persulf ate gave a neutral red crystalline 

 product. Both had identical ultraviolet absorption spectra similar to that 

 of vitamin B]2, but they had very low microbiological activity. 



D. SYNTHESIS 



The structure of vitamin B12 is not yet fully elucidated, and no synthesis 

 of this vitamin has been accomplished. Synthesis of the various degradation 

 products of vitamin B12 has been accomplished. In one particular instance, 

 this has led to more extensive work. The synthesis of 5 , 6-dimethylben- 

 zimidazole was carried out at the time this compound was isolated.-^' ^° 

 Tests of its biological activity followed shortly." Both 5 , 6-dimethylben- 

 zimidazoie and the corresponding diamine, 1 ,2-dimethyl-4,5-diaminoben- 

 zene, were inactive for Lactobacillus lactis Dorner in the assay for vitamin 

 B12 activity, but both compounds possessed vitamin Bi2-like activity for 

 rats on a diet devoid of animal protein and containing 0.25 % of thyroid 

 powder." Daily quantities of 2 to 5 mg. of 5 , 6-dimethylbenzimidazole and 

 2 to 3 mg. of l,2-diamino-4,5-dimethylbenzene were comparable to 0.125 

 to 0.250 7 of vitamin B12. A series of other benzimidazole-type compounds 

 were synthesized and tested for vitamin Bi2-like activity. Only 5-methyl- 

 benzimidazole possessed significant growth activity; 2 , 5-dimethylbenzimi- 

 dazole appeared to act as a growth depressant. The following gave no sig- 

 nificant growth response on the test diet in rats: benzimidazole, 1-methyl-, 

 2-methyl-, 4-methyl-, and 4, 6-dimethylbenzimidazole. 



The synthesis of l-Q!-D-ribofuranosido-5, 6-dimethylbenzimidazole (a-ri- 

 bazole),^^ the hydrolysis product isolated from vitamin B12, has been 

 reviewed in the section of this chapter dealing with constitution. A program 

 of synthetic work on the glycosides of benzimidazole has been carried out 

 because of the interest in the possible biological activities of these com- 

 pounds.'*' '^' ^° The syntheses involved the glycosidation of an o-nitro- 

 aniline by boiling with the hexose or pentose sugars in ethanol in the 



"O. Schindler, Helv. Chim. Acta 34, 101 (1951). 



" G. Emerson, N. G. Brink, F. W. Holly, F. Koniuszy, D. Heyl, and K. Folkers, 



J. Am. Chem. Soc. 72, 3084 (1950). 

 "P. Mamalis, V. Petrow, and B. Sturgeon, J. Pharm. Pharmacol. 2, 491 (1950). 

 " P. Mamalis, V. Petrow, and B. Sturgeon, J. Pharm. Pharmacol. 2, 503 (1950). 

 6° P. Mamalis, V. Petrow, and B. Sturgeon, ./. Pharm. Pharmacol. 2, 512 (1950). 



I 



