B12: reminiscences and afterthoughts.

This paper describes some of the chemistry of synthetic corrinoids and corphinoids carried out at the ETH (Swiss Federal Institute of Technology) after the completion of the non-enzymic synthesis of vitamin B12 and attempts to delineate the interplay between mechanistic hypotheses, model studies and the experimental research in B12 biosynthesis which had spurred this work. The afterthoughts deal with why and how the work on corrinoids eventually led to an experimental involvement in the problem of a chemical aetiology of the structure of natural nucleic acids.