Development of Photocatalytic Organic Synthesis Processes of Next Generation

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L-Pipecolinic acid, a kind of optically active cyclic imino acid, is a basic skeleton of piperidine alkaloids and useful intermediate for the organic synthesis of various drugs. However, at present, there have not been industrial synthesis procedures. This project aims to develop a novel method to obtain optically active L-pipecolinic acid from L-lysine, which is a cheap starting material produced via an industrial fermentation process. First, screening of photocatalyst was achieved and found that a commercially available titanium (IV) dioxide (titania) as well as newly developed laboratory-made titanias (via HyCOM,TD,and THyCA procedures) showed markedly high photocatalytic activity to produce L-pipecolinic acid readily and selectively. The role of platinum particles loaded on, with various methods, titania has been also clarified ; sufficient loading of dispersed platinum particles is requisite for the best photocatalyst. Such properties of platinum-loaded titanias were alSo investigated with the photocatalytic transfer hydrogenation of Schiff bases. During this screening, it was also clarified that amorphous, but not titanium (IV) hydroxide nortitania hydrate, is completely inactive toward photocatalytic reactions maybe due to the higher possibility of recombination of photoexcited electron and positive hole. Second, the mechanism of the photocatalytic N-cyclization of L-lysine was investigated by usig platunm-looded titanias. It is observed that the positive holes oxidize amino group in L-lysine intoimine which is then hydrolyzed to carbonyl compounds and intramolecularly condensed with remaining amino group into cyclic schiff base intermediate. This is reduced by photoexcited electrons to give final product, L-pipecolinic acid.