Kazuhiko Saigo

Taurine as a constituent of mitochondrial tRNAs: new insights into the functions of taurine and human mitochondrial diseases

Taurine (2‐aminoethanesulphonic acid), a naturally occurring, sulfur‐containing amino acid, is found at high concentrations in mammalian plasma and tissues. Although taurine is involved in a variety of processes in humans, it has never been found as a component of a protein or a nucleic acid, and its precise biochemical functions are not fully understood. Here, we report the identification of two novel taurine‐containing modified uridines (5‐taurinomethyluridine and 5‐taurinomethyl‐2‐thiouridine) in human and bovine mitochondrial tRNAs. Our work further revealed that these nucleosides are synthesized by the direct incorporation of taurine supplied to the medium. This is the first reported evidence that taurine is a constituent of biological macromolecules, unveiling the prospect of obtaining new insights into the functions and subcellular localization of this abundant amino acid. Since modification of these taurine‐containing uridines has been found to be lacking in mutant mitochondrial tRNAs for Leu(UUR) and Lys from pathogenic cells of the mitochondrial encephalomyopathies MELAS and MERRF, respectively, our findings will considerably deepen our understanding of the molecular pathogenesis of mitochondrial encephalomyopathic diseases.

C60 fullerol formation catalysed by quaternary ammonium hydroxides

C60 Fullerol with 24–26 hydroxy groups was synthesized directly by the reaction of fullerene with aqueous NaOH in the presence of tetrabutylammonium hydroxide (TBAH), the most effective catalyst.

Phosphane Sulfide/Octacarbonyldicobalt‐Catalyzed Pauson – Khand Reaction Under an Atmospheric Pressure of Carbon Monoxide

Convenient access to cyclopentenones is provided by catalytic intra- and intermolecular Pauson - Khand reactions in the presence of octacarbonyldicobalt and tributylphosphane sulfide (see scheme). In contrast to other reactions of this type, they proceed under mild conditions (70 degrees C, 1 atm CO), and commercially available [Co(2)(CO)(8)] can be used without further purification.

Phosphine sulfides: Novel effective ligands for the palladium-catalyzed bisalkoxycarbonylation of olefins

Abstract Phosphine sulfides were found to be effective as a ligand in the palladium(II)-catalyzed bisalkoxycarbonylation of olefins. Aromatic olefins and vinylsilanes were converted into the corresponding succinates in high yields under mild conditions. Enantioselection was observed when chiral bisphosphine sulfides were used as ligands.

Design of resolving reagents: p-substituted mandelic acids as resolving reagents for 1-arylalkylamines

Abstract The resolution of 1-arylalkylamines 2–10 by mandelic acid 1 was studied. It was found that a substituent, which elongated the molecular length of the amines, diminished the resolution efficiency. On the basis of these results, (S)-p-methylmandelic acid (S)- 11 and (R)-p-methoxymandelic acid (R)- 12 were selected as new resolving reagents for the 1-arylalkylamines; these acids were found to have a higher resolving ability than (R)- 1 .

An efficient phosphorus-containing oxazoline ligand derived from cis-2-amino-3,3-dimethyl-1-indanol: application to the palladium-catalyzed asymmetric Heck reaction

Abstract Enantiopure 2-[2-(diphenylphosphino)phenyl]oxazoline, derived from a non-natural chiral aminoalcohol, cis -2-amino-3,3-dimethyl-1-indanol, was found to be an efficient ligand for the palladium-catalyzed asymmetric Heck reaction.

Rhodium(I)-Catalyzed Regioselective Ring- Expanding Rearrangement of Allenylcyclopropanes into Methylenecyclopentenes

A highly regioselective C-C bond cleavage of the cyclopropane rings occurs in substituted allenylcyclopropanes in the presence of cationic rhodium(I) complexes. Thus, ring expansion of readily accessible allenylcyclopropanes can be achieved to give 3-methylenecyclopentenes, which could have applications as multifunctional synthetic building blocks.

Diastereoselective ring-opening aldol-type reaction of 2,2-dialkoxycyclopropanecarboxylic esters with carbonyl compounds. 1. Synthesis of cis 3,4-substituted .gamma.-lactones

The Lewis acid-promoted reactions of 2,2-dialkoxycyclopropanecarboxylic esters 4a-c with aldehydes and unsymmetrical ketones to give γ-lactones were investigated. TiBr 4 is an excellent catalyst and gives cis 3,4-substituted γ-lactones in good yields with high diastereoselectivity. SnBr 4 promotes the reaction of 4a-c with aldehydes with high cis-selectivity, but does not promote the reaction of 4a with unsymmetrical ketones. ZrCl 4 is moderately trans-selective in the reaction of 4a with unsymmetrical ketones. Cis γ-lactones can be converted into their trans-isomers by treatment with NaOEt in EtOH

Novel chiral stationary phases for optical resolution by ligand-exchange high-performance liquid chromatography

Novel chiral stationary phases, (1R,2S)- and diastereomeric (1S,2S)-2-carboxymethylamino-1,2-diphenylethanol, were prepared from (1R,2S)- and (1S,2S)-2-amino-1,2-diphenylethanol, respectively, and were bound to silica gel pretreated with 3-glycidoxypropyltrimethoxysilane. The chiral stationary phases were found to be very effective for the optical resolution of amino acids, amino acid derivatives and hydroxy acids by ligand-exchange high-performance liquid chromatography.

An efficient phosphorous-containing oxazoline ligand derived from cis-2-amino-3,3-dimethyl-1-indanol: application to the rhodium-catalyzed enantioselective hydrosilylation of ketones

Abstract Enantiopure 2-[2-(diphenylphosphino)phenyl]oxazoline, derived from a non-natural amino alcohol, cis-2-amino-3,3-dimethyl-1-indanol, was found to be an efficient ligand for the rhodium-catalyzed enantioselective hydrosilylation of ketones.