Kunisuke Izawa

Photocatalytic racemization of amino acids in aqueous polycrystalline cadmium(II) sulfide dispersions

L-Lysine in an aqueous solution is partly racemized by photoirradiation (at wavelengths > 300 nm) in the presence of suspended cadmium(II) sulfide particles under a de-aerated atmosphere at room temperature. Loading of a small amount of platinum or its oxide inhibited the racemization, but enhanced N-cyclization of L-lysine into DL-pipecolinic acid. 2H and 1H NMR measurements of the racemate from photoirradiated reaction mixtures in deuterium oxide solutions revealed the substitution of the α-hydrogen of lysine with deuterium alongside the racemization. These facts suggest a mechanism for photocatalytic racemization that includes both reduction and oxidation by photoexcited electrons and positive holes, respectively. Similarly, the other amino acids, leucine and phenylalanine, undergo photocatalytic racemization under reaction conditions where the α-amino group is deprotonated, although glutamic acid gives no racemate during photocatalytic decomposition. Among the CdS photocatalysts used in this study, well grown cubic crystallites with a specific surface area of ca. 8 m2 g–1 showed the highest selectivity for the racemization of L-lysine.

Stereoselective synthesis of piperidine-2,6-dicarboxylic acids by photocatalytic reaction of aqueous cadmium(II) sulfide dispersion

Abstract Photoirradiation at wavelength > 300 nm onto a deaerated aqueous suspension of cadmium(II) sulfide (CdS) particles in an aqueous solution of a mixture of stereo isomers of 2,6-diamiopimelic acid (DAP) produced piperidine-2,6-dicarboxylic acid (PDC). Both yield and trans cis ratio of PDC markedly depended on the kind of CdS photocatalysts, its pre-treatment, and loading of fine platinum particles. A CdS photocatalyst prepared by heat-treatment at 1023 K in the presence of a small amount of air showed the highest yield and trans cis ratio.

Introduction of a benzoyl group onto riboside in aqueous solution: One-step synthesis of 6-chloropurine 2′,3′-di-O-benzoylriboside

Abstract A benzoyl group was introduced onto the 3′-hydroxyl group of 6-chloropurine riboside by treatment with benzoylating agents in the presence of an organic or inorganic base in aqueous solution, in which further reaction gave 6-chloropurine 2′,3′-di- O -benzoylriboside.

Synthesis of Fluorinated Nucleosides

Two practical synthetic approaches to the production of lodenosine [FddA, 9‐(2,3‐dideoxy‐2‐fluoro‐β‐D‐threo‐pentofuranosyl)adenine] via 6‐chloropurine riboside or 6‐chloropurine 3′‐deoxyriboside are described. The reaction sequence contains new fluorination methods and new applications of radical reduction. The reagents and reaction conditions of each step have been carefully selected to ensure robustness and safety.