412 VITAMIN Bi2 



the data do not contribute to the knowledge of the Hnkage of phosphate 

 to the ribose moiety. The descriptive formula X suggests a twofold attach- 

 ment of the benzimidazole glycoside residue to the cobalt-containing macro- 

 fragment of the vitamin B12 molecule, which is visualized as a planar struc- 

 ture similar in spacial arrangement to the porphyrins. The formulation 

 implies the existence of a stable coordinate link between the benzimidazole 

 glycoside residue and the planar cobalt complex of a character not pre- 

 viously recorded.^* It was inspired by the observation that the two bands 

 in the absorption spectrum of vitamin B12 at X = 2885 A. and 2785 A. 

 (Fig. 1) are characteristic of 5 , 6-dimethylbenzimidazole and also its ribo- 

 furanoside and ribofuranoside phosphate which were identified as acid 

 hydrolysis products of vitamin B12 (Fig. 2). An extensive research program 

 has been carried out on the chemistry of the benzimidazoles in support of 

 this formulation. 



It was observed that a number of synthetic 5 , 6-dimethylbenzimidazole 

 glycosides possess absorption spectra indistinguishable from each other 

 and from those of paper strip components a and ^ (a-ribazole phosphate 

 and a-ribazole, respectively). All these compounds show a well-defined 

 "notch" in their absorption spectra at X = 2850 A. in dilute acid and 

 X = 2880 A. in dilute alkali. ^^ The absorption spectrum of vitamin B12 

 shows only an inflection in this region which is unchanged in position over 

 the pH range 2 to 12.^^ If the absorption band of vitamin B12 in this region 

 is due to the presence of the 5 , 6-dimethylbenzimidazole grouping, then 

 some structural alteration must be postulated for this moiety which would 

 account for its change of absorption behavior. 



Two principal lines of evidence have been suggested to account for this 

 anomaly. The first of these is the observation that the absorption spectrum 

 of 5 , 6-dimethylbenzimidazole becomes much more like that of vitamin B12 

 when the benzimidazole enters into a coordination complex with a metal 

 ion. ^3 The second line of evidence is based on the observation that, when 



" G. Cooley, B. Ellis, V. Petrow, G. H. Beavea, E. R. Holiday, and E. A. Johnson, 

 /. Pharm. Pharmacol. 3, 271 (1951); M. T. Davies, P. Mamalis, V. Petrow, and 

 B. Sturgeon, /. Pharm Phamacol. 3, 420 (1951) 



