title: Comparative mechanisms of vitamin B6-catalyzed beta-decarboxylation and beta-dephosphonylation in model systems.
abstract: Reaction pathways and mechanisms of vitamin B6-catalyzed beta-decarboxylation and beta-dephosphonylation of aminocarboxylic and aminophosphonic acids in model systems are compared. It was found that both reactions require prior transamination of an aldimine intermediate to a ketimine. For ketimines having carboxylate or phosphonate groups substituted on the beta-carbon atoms of the keto acid residue, there is a hydrogen ion or metal ion-activated covalent bond pathway which involves a shift of electron pairs toward the coordinated ketimine nitrogen, leading to beta-gamma, C-C or C-P bond fission and release of carbon dioxide or metaphosphate, respectively. Comparison of these reactions indicates that beta-decarboxylation is 10(6) faster than the corresponding dephosphonylation reaction. Since only a few studies of vitamin B6-catalyzed dephosphonylation have been carried out, suggestions are made for further studies with substrates designed to elucidate the reaction mechanisms involved.
authors.affiliation: Department of Chemistry, Texas A & M University, College Station 77843-3255.
authors.forename: B
authors.initials: B
authors.lastname: Szpoganicz
authors.forename: A E
authors.initials: AE
authors.lastname: Martell
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D003653:Decarboxylation; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D063065:Organophosphonates / Q000378:metabolism*; D011736:Pyridoxine / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D063065:Organophosphonates; D011736:Pyridoxine