Yutaka Koike

An efficient enantioselective preparation of 2-substituted-3-hydroxypropionic acids via chemo-enzymatic reaction

Abstract The key intermediates, 2-substituted-3-hydroxypropionic acids 1 , of the potent renin inhibitors were synthesized enantioselectively starting from 2-substituted-l,3-propanediols via chemo-enzymatic reaction.

Preparation and characterization of quenched KNbO3-Nb2O5 glass

KNbO3-Nb2O5 glasses were prepared with molar ratio of K/(K + Nb) from 0.16 to 0.5 by using a twin-roller quenching apparatus. Most KNbO3-Nb2O5 glasses crystallized to stable phases such as KNbO3, K2Nb4O11, K3Nb7O19, KNb3O8 and K2Nb8O21 via metastable phases after heat treatment and K4Nb6O17 glass directly crystallized to K4Nb6O17 crystal. KNbO3 glass consisted of the corner-shared NbO6 octahedra, while the amounts of the edge-shared NbO6 octahedra in the KNbO3-Nb2O5 glass structure increased with decreasing K+ ion content. The band gap energies and the ionic conductivity of the KNbO3-Nb2O5 glasses increased with increasing K+ ion content, but the density and the activation energy of the ionic conduction decreased. The glasses possessed high dielectric constants appfoaching those of ferroelectric crystals at high temperature around the crystallization temperature. The dielectric constants of the glasses, however decreased greatly with decreasing temperature and with increasing frequency.

Structure of gymnopilin, a bitter principle of an hallucinogenic mushroom, gymnopilus spectabilis

Abstract Structure of gymnopilin ( 1 ), a bitter principle of an hallucinogenic mushroom Gymnopilus spectabilis , was elucidated by chemical degradation and spectroscopic methods.

Corrosion and strength degradation of Si3N4 and sialons in K2CO3 and K2SO4 melts

Si3N4-based ceramics, such as hot isostatically pressed Si3N4, hot-pressed Si3N4, hot-pressed sialons containing 0, 30, 60 and 100% a phase, were corroded by K2SO4 and K2CO3 melts at 1150 to 1300 and 925 to 1150° C, respectively. The surface chemical reaction-controlled shrinking core model adequately described the relationship between the weight loss of the specimen and time for the corrosion reactions in both K2SO4 and K2CO3 melts, and the apparent activation energies were 380 to 608 and 157 to 344 kJ mol−1, respectively. The corrosion rate in K2CO3 melt decreased with increasing content of aluminium and yttrium ions in the specimens, but no systematic relation was observed for the reaction in K2SO4 melts. The fracture strength of the specimens corroded by K2SO4 and K2CO3 melts degraded to 2/3 to 2/5 of the original values up to a 2% weight loss, and then was almost constant up to 30% weight loss.

Isolation and structure of gymnoprenols, a novel type of polyisoprenepolyols from Gymopilus spectabilis

Abstract Gymnoprenols, a novel type polyisoprenepolyols, have been isolated from the fruiting body of an hallucinogenic mushroom, Gymnopilus spectabilis . The structure of these polyols which occur as a mixture of isoprene homologues have been elucidated by chemical degradations and spectroscopic analyses.

A stereospecific synthesis of a renin inhibitor(BW-175) which incorporates a sulfonemethylene isostere and a dihydroxyethylene isostere

Abstract (2 S , 3 R , 4 S )-4-[L-N-[(2 S )-3-ethylsulfonyl-2-(1-naphthylmethyl) propionyl]norleucyl]amino-5-cyclohexyl-1-morpholino-2,3-pentanediol(BW-175) was synthesized stereospecifically.

Absolute stereochemistry of the triol moiety of gymnoprenols

Abstract Absolute configuration of the triol portion in gymnoprenols, the polyisoprenepolyols obtained from mushroom Gymnopilus spectabilis , has been established as 2S and 3R by a stereocontrolled synthesis of the enantiomer of a chemical degradation product of gymnoprenol.

Revision of the absolute configuration of triol moiety of gymnoprenols

Abstract The absolute configurations of triol moiety of gymnoprenol-A, -B and gymnopilin have been revised as 2R,3S, on the basis of the synthesis of (2S,3R)-lactone diacetate (1a) from (R)-(-)-linalool.

Stereospecific Synthesis of a Dihydroxyethylene Isostere of Cyclohexylalanine Amide, (2S,3R,4S)-4-Amino-5-Cyclohexyl-1-Morpholino-2,3-Pentanediol(ACMP) from a Protected Sugar

ABSTRACT A transition-state analogue of a renin inhibitor at the scissile site, a dihydroxyethylene isostere of cyclohexylalanine amide, (2S,3R,4S)-4-amino-5-cyclohexyl-1-morpholino-2,3-pentanediol(ACMP), was synthesized from 1,2:5,6-di-O-isopropylidene-α-D-allofuranose stereospecifically.