Pfizer Handbook of Microbial Metabolites 



442 



tered as shown. When the aminopropanol group is in- 

 corporated by amide Unkage at the f-position, the name is 

 modified to cobinic acid ( all carboxyl groups as amides = 

 cobinamide), and when ribose is incorporated, the name 

 is modified to cobamic acid (cobamide). The name of 

 the heterocycle is then inserted at the beginning with the 

 suffix -yl. Thus, vitamin B12 is correctly named: a-(5,6- 

 dimethylbenzimidazolyl) cobamide cyanide. 



The two principal moieties are called the planar group 

 and the nucleotide, and these are essentially perpendicu- 

 lar in relative steric arrangement. 



A number of analogues of vitamin Bjo have been iso- 

 lated from natural sources. These sources include B12 

 fermentations, the rumen or the gut of various animals 

 and sewage sludge. The naturally occurring analogues 

 are listed below by trivial name, together with the charac- 

 teristic heterocycle of the nucleotide. 



TABLE I 

 Naturally Occurring Vifamin 612 Analogues 



*Not crysfoillne. t About 17 other cobamides were defected in this study. 



