The corrinoids from the obligate anaerobe Clostridium cochlearium were extracted as a mixture of Co-cyano derivatives. From 50 g of frozen cells, approximately 2 mg (1.5 µmol) of B₁₂ derivatives was obtained as a crystalline sample. Analysis of the corrinoid sample of C. cochlearium by a combination of high-pressure liquid chromatography and UV-Vis absorbance spectroscopy revealed the presence of three cyano corrinoids in a ratio of about 3:1:1. The spectroscopic data acquired for the sample indicated the main components to be pseudovitamin B₁₂ (Co-cyano-7"-adeninylcobamide) (60%) and factor A (Co-cyano-7"-[2-methyl]adeninylcobamide) (20%). Authentic pseudovitamin B₁₂ was prepared by guided biosynthesis from cobinamide and adenine. Both pseudovitamin B₁₂ and its homologue, factor A, were subjected to complete spectroscopic analysis by UV-Vis, circular dichroism, mass spectrometry, and by one- and two-dimensional ¹H, ¹³C-, and ¹⁵N nuclear magnetic resonance (NMR) spectroscopy. The third component was indicated by the mass spectra to be an isomer of factor A and is likely (according to NMR) to be 7"-[N⁶-methyl]-adeninylcobamide, a previously unknown corrinoid. C. cochlearium thus biosynthesizes as its native "complete" B₁₂ cofactors the 7"-adeninylcobamides and two homologous corrinoids, in which the nucleotide base is a methylated adenine.