AbstractSelective ammonolysis of dicyano‐cobalt(III)cobyrinic acid heptamethyl ester (cobester,2) furnishes the four isomeric hexamethyl ester monoamides2b, 2d, 2e, 2fcarrying the amide function on one of the propionic acid side chains. The isomers were separated by liquid‐liquid chromatography and their structures determined by a comparison of their13C‐NMR spectra with the spectrum of2. Amide2fserved as the link between synthetic and authentic vitamin B12derived material in the total synthesis of vitami