Stereoselectivity in reactions of amino acids catalyzed by pyridoxal derivatives carrying rigidly-attached chirally-mounted basic groups--transamination, racemization, decarboxylation, retro-aldol reaction, and aldol condensation.

A tetrahydroquinoline ring was used to mount the critical functional groups of pyridoxal, and also two examples of rigidly held chirally mounted basic groups. They were able to selectively catalyze decarboxylation, aldol reaction, and retro-aldol reaction of amino acids rather than transamination, and with stereoselectivity. In the aldol reaction of glycine with acetaldehyde to synthesize threonine and allo-threonine, one of the catalysts reversed its stereoselectivity when the basic group was protonated. The observed stereoselectivities were all consistent with prediction.