Studies on the synthesis of stable-isotope-labeled amino acids canying functional group and their conformational analysis

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Recently, the combination of stable isotope labeling and advanced multidimensional NMR spectroscopy has become more promising method for determining the overall and local structures of proteins in solution. In particular, the regio-and stereoselectively isotope-labeled amino acids are excellent probes for collecting precise structural information such as the side-chain conformations about specific residues. We have recently explored the methods for stereoselective deuteration of only one of the diastereotopic methyl groups and methylene protons of amino acid side-chains. However, investigation of amino acids carrying a functional group in the side chain, such as lysine, arginine, serine, cystein, aspartic acid, and so on, remains untouched despite their importance in protein function. In the present work, we investigated the regio-and stereoselective deuterium labeling of such amino acids. The representative results are as follows.1. Asymmetric synthesis of (2S,3S,4R,5R)-[2,3,4,5-D_4]o … More rnithine was examined. The chirally deuterated 3-aminopropanal was prepared by a catalytic deuteration of an unsaturated -γ-lactone derived from L-glutamic acid followed by several functional group interconversions. Condensation of the obtained deuterium-labeled 3-aminopropanal with a chiral glycine template afforded unsaturated ornithine. The dehydroornithine was then subjected to a catalytic deuteration followed by deprotection to give the L-[2,3,4,5-D_4]ornithine.2. Synthesis of L-[5,5,6,6-D_4]lysine starting from L-pyroglutamic acid was investigated. One carbon homologation of the side chain was carried out by cyanation of deuterated 5-iodonorvaline prepared from L-pyroglutamic acid. Catalytic deuteration of the obtained cyanide followed by the standard deprotection procedure afforded L-[5,5,6,6-D_4]lysine.3. Synthesis of a novel 3,4-didehydropyroglutamate derivative in which the carboxylic group is protected as an ABO ester was examined. Some reactions of the obtained unsaturated pyroglutamate template such as dihydroxylation, Michael addition, and some cycloadditions were found to take place in a stereospecific manner. Catalytic deuteration of the olefin followed by acidic hydrolysis gave (2S,3S,4R)-[3,4-D_2]glutamic acid. Less