Masakazu Nakazawa

Practical synthesis of α-aminoalkyl-α′-chloromethylketone derivatives. Part 1: Chloromethylation of N-protected 3-oxazolidin-5-ones

Abstract Reaction of N-protected 3-oxazolidin-5-ones with in situ-generated chloromethyllithium afforded N-protected 5-chloromethyl-5-hydroxy-3-oxazolidines without racemization. They were easily hydrolyzed to give α-aminoalkyl-α′-chloromethylketone derivatives, which are useful intermediates for several protease inhibitors.

Practical synthesis of α-aminoalkyl-α′-chloromethylketone derivatives. Part 2: Chloromethylation of N-imine-protected amino acid esters

Abstract Chloromethylation of N -imine-protected amino acid esters followed by acid hydrolysis gave α-aminoalkyl-α′-chloromethylketone as a HCl salt form in good yield without racemization. The amino group was conveniently protected with carbamate protecting reagents to give various useful intermediates for the protease inhibitors.

Dihalomethylation of N-protected phenylalanine esters

Abstract Dihalomethylation of several N-protected amino acid esters gave N-protected α-aminoalkyl-α′-dihalomethylketones, which are useful intermediates for the synthesis of erythro β-amino-α-hydroxycarboxylic acids, in good yield. The dihalomethylketones were successfully converted to N-protected α-aminoalkyl-α′-halomethylketones by selective catalytic hydrogenation.

Structure–CaSR–Activity Relation of Kokumi γ-Glutamyl Peptides

Modulation of the calcium sensing receptor (CaSR) is one of the physiological activities of γ-glutamyl peptides such as glutathione (γ-glutamylcysteinylglycine). γ-Glutamyl peptides also possess a flavoring effect, i.e., sensory activity of kokumi substances, which modifies the five basic tastes when added to food. These activities have been shown to be positively correlated, suggesting that kokumi γ-glutamyl peptides are perceived through CaSRs in humans. Our research is based on the hypothesis that the discovery of highly active CaSR agonist peptides will lead to the creation of practical kokumi peptides. Through continuous study of the structure-CaSR-activity relation of a large number of γ-glutamyl peptides, we have determined that the structural requirements for intense CaSR activity of γ-glutamyl peptides are as follows: existence of an N-terminal γ-L-glutamyl residue; existence of a moderately sized, aliphatic, neutral substituent at the second residue in an L-configuration; and existence of a C-terminal carboxylic acid, preferably with the existence of glycine as the third constituent. By the sensory analysis of γ-glutamyl peptides selected by screening using the CaSR activity assay, γ-glutamylvalylglycine was found to be a potent kokumi peptide. Furthermore, norvaline-containing γ-glutamyl peptides, i.e., γ-glutamylnorvalylglycine and γ-glutamylnorvaline, possessed excellent sensory activity of kokumi substances. A novel, practical industrial synthesis of regiospecific γ-glutamyl peptides is also required for their commercialization, which was achieved through the ring opening reaction of N-α-carbobenzoxy-L-glutamic anhydride and amino acids or peptides in the presence of N-hydroxysuccinimide.

Production of (R)-3-Amino-3-phenylpropionic Acid and (S)-3-Amino-3-phenylpropionic Acid from (R,S)-N-Acetyl-3-amino-3-phenylpropionic Acid Using Microorganisms Having Enantiomer-Specific Amidohydrolyzing Activity

(R)-3-Amino-3-phenylpropionic acid ((R)-β-Phe) and (S)-3-amino-3-phenylpropionic acid ((S)-β-Phe) are key compounds on account of their use as intermediates in synthesizing pharmaceuticals. Enantiomerically pure non-natural amino acids are generally prepared by enzymatic resolution of the racemic N-acetyl form, but despite the intense efforts this method could not be used for preparing enantiomerically pure β-Phe, because the effective enzyme had not been found. Therefore, screening for microorganisms capable of amidohydrolyzing (R,S)-N-acetyl-3-amino-3-phenylpropionic acid ((R,S)-N-Ac-β-Phe) in an enantiomer-specific manner was performed. A microorganism having (R)-enantiomer-specific amidohydrolyzing activity and another having both (R)-enantiomer- and (S)-enantiomer-specific amidohydrolyzing activities were obtained from soil samples. Using 16S rDNA analysis, the former organism was identified as Variovorax sp., and the latter as Burkholderia sp. Using these organisms, enantiomerically pure (R)-β-Phe (>99.5% ee) and (S)-β-Phe (>99.5% ee) with a high molar conversion yield (67%–96%) were obtained from the racemic substrate.

Design, synthesis, and taste evaluation of a high-intensity umami-imparting oxazole-based compound

Umami taste is imparted predominantly by monosodium glutamate (MSG) and 5′-ribonucleotides. Recently, several different classes of hydrophobic umami-imparting compounds, the structures of which are quite different from MSG, have been reported. To obtain a novel umami-imparting compound, N-cinnamoyl phenethylamine was chosen as the lead compound, and a rational structure-optimization study was conducted on the basis of the pharmacophore model of previously reported compounds. The extremely potent umami-imparting compound 2-[[[2-[(1E)-2-(1,3-benzodioxol-5-yl)ethenyl]-4-oxazolyle]methoxy]methyl]pyridine, which exhibits 27,000 times the umami taste of MSG, was found. Its terminal pyridine residue and linear structure are suggested to be responsible for its strong activity. The time taken to reach maximum taste intensity exhibited by it, as determined by the time-intensity method, is 22.0 s, whereas the maximum taste intensity of MSG occurs immediately. This distinct difference in the time-course taste profile may be due to the hydrophobicity and strong receptor affinity of the new compound. Intense umami-imparting molecule 11 was discovered by structural optimization of natural umami-imparting substance; rubenamine9 and rubescenamine 10.