|Budget Amount *help
¥3,600,000 (Direct Cost : ¥3,600,000)
Fiscal Year 1999 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1998 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1997 : ¥2,600,000 (Direct Cost : ¥2,600,000)
1. Course of the formation of a quinonoid species absorbing in the 500-nm region, which should serve as a model for the key intermediate in reaction catalyzed by pyridoxal phosphate enzymes, was studied in the reaction of pyridoxal, ethyl L-alaninate and Al(III) in methanol by means of UV-visible spectroscopy, chromatography with a multi-UV detector, optical rotation and ^1H-NMR. The species was chromatographically separated in the form of the Al(III) chelate and its quantitative transformation to the aldimine chelate was observed. The formation of the species in the transamination reaction of pyridoxamine, ethyl pyruvate and A1(III) was also studied.
2. Quinonoide species absorbing in the 500-nm region, which should serve as a model for the key intermediate in reaction catalyzed by pyridoxal phosphate enzymes, was observed in the reaction of pyridoxalmine (PM) with pyrroloquinoline quinine (PQQ), 1,7-phenathroline-5,6-quinone and 4,7-phenathroline-5,6-quinone in alkaline methanol at 25℃. Crystalline product was prepared from PM and PQQ. This may be the first example of meta-stable quinonoid species in pyridoxal catalysis which are not in the form of metal chelate.
3. By the formation of the hexacoordinated mixed chelate, the Cu(II)-quinonoid-ligand should retard the protonation of the quinonoid to convert to the aldimine, as clearly observed in the reaction of α,α',α"-terpyridine. Although the reasons for these phenomena are not fully understood at this stage, the decrease of the carbanion property of the quinonoid by effective chelation to polyvalent metal ions may hinder protonation. The stability of the quinonoid chelate may be enhanced by the formation of mixed chelates with the strongly chelating tridentate planar ligand. The results indicated that the stability of the chelate was determined not only by the interaction of the metal and the quinonoid, but also by the interaction of the metal with the other ligands.