Naohiro Shirai

A New Quadruple Hydrogen-Bonding Module with a DDAA Array: Formation of a Stable Homodimer without Competition from Undesired Hydrogen-Bonded Dimers

A new DDAA hydrogen-bonding module (UImp-2), based on a ureidoimidazo[1,2-a]pyrimidine structure, forms a highly stable homodimer (K(dim) > 1.1 x 10(5) M(-1) in CDCl(3)) without competition from undesired hydrogen-bonded dimers.

Grayanotoxin-XVIII and grayanoside B, a new a-nor-b-homo-ent-kaurene and its glucoside from Leucothoe grayana

Abstract From Leucothoe grayana a new grayanoid (diterpene) and its glucoside have been isolated. The structures of these new natural compounds have been established by chemical and spectroscopic means and by correlation with a known compound.

Grayanoside A, a new diterpene glucoside from Leucothoe grayana

Abstract A new diterpenoid glucoside, grayanoside D, has been isolated from Leucothoe grayana . Its structure was elucidated by chemical and spectroscopic means and by correlation with grayanotoxin-XV to be 3- O -(β- D -glucopyranosyl)-(10S)-dihydrograyanotoxin-XV.

PH dependence of hydrolytic removal of silyl group from trialkylsilyl ethers

Abstract Rate constants for the acid and base-catalyzed hydrolysis of the trialkylsilyl ethers of alcohols were quantitatively correlated with Tafts σ* and Es values of the substituents on Si and O atoms of the ether linkage. The regression equations for kH, and kOH were satisfactorily computed.

Sommelet–Hauser or Stevens rearrangement of 1-methyl-2-(substituted-phenyl)piperazinium 1-methylides. Ring enlargement of piperazines to seven- or nine-membered cyclic amines

Fluoride ion-induced desilylation of 4-acetyl-1-methyl-2-(4-substituted phenyl)-1-trimethylsilyl-methylpiperazinium iodides 5 gave 5-acetyl-2-methyl-10-substituted 1,3,4,5,6,11a-hexahydro-2H-2,5-benzodiazonines 7 and/or 5-acetyl-2-methyl-10-substituted 2,3,4,5,6,7-hexahydro-1H-2,5-benzodiazonines 8(Sommelet–Hauser rearrangement products). However, a similar treatment of 1-methyl-3-oxo-2-phenyl-1-trimethylsilylmethylpiperazinium iodide 10 afforded 1-methyl-6-phenyl-2,3,6,7-tetrahydro-1H-diazepine-5-one 12(Stevens rearrangement product).

Abnormal products in the Bischler–Napieralski isoquinoline synthesis

Reaction of N-[2-(4-methoxyphenyl)ethyl]benzamides with phosphorus pentoxide (and phosphoryl chloride) gives 7-methoxy-1-phenyl-3,4-dihydroisoquinolines (a normal Bischler–Napieralski reaction product) and 6-methoxy-1-phenyl-3,4-dihydroisoquinolines (an abnormal reaction product). The reaction mechanism is discussed.

Relationship between structure, positive inotropic potency and lethal dose of grayanotoxins in guinea pig

Relationship between chemical structure, positive inotropic potency and lethal dose of grayanotoxins and the related compounds was studied using guinea pigs. The positive inotropic effect (PIE) was examined in their papillary muscle isolated from the heart.The potency of these compounds was expressed by pD2 values, and was determined by depicting the concentration-PIE curve for each compound. The study has clarified the contribution of functional groups in the molecule; the presence of 3β-hydroxyl, 6β-hydroxyl and 10β-methyl groups attached to the grayanane skeleton is established to be essential for the development of PIE. The inotropic potency of compounds carrying these essential groups is increased by a 10α-hydroxyl group and the acylation of the 14β-hydroxyl group. LD50 value of 10 compounds with a high cardiotonic potency (pD2>4) was determined by up and down method using male guinea pigs. The relation of LD50 to pD2 bore a significant correlation (r = 0.68, p<0.05). The most cardiotropic and toxic compound found in this study was asebotoxin III.

A stable intermediate in the Sommelet–Hauser rearrangement of 1-methyl-2-phenyl-piperidinium 1-methylides: the improved Sommelet–Hauser rearrangement

Reaction of 1-methyl-1-(trimethylsilyl)methyl-2-(substituted phenyl)piperidinium iodides (2) with caesium fluoride gave high yields of 2-methyl-1,3,4,5,6,11a-hexahydro-2H-2-benzazonines (4) which are regarded as unstable intermediates in the Sommelet-Hauser rearrangement of ammonium ylides (3) to 2-methyl-2,3,4,5,6,7-hexahydro-1H-2-benzazonine derivatives (5).

Synthesis and properties of n-trimethylgermylmethyl-n-nitrosourea, a germanium analogue of n-neopentyl-n-nitrosourea

Abstract The rate for hydrolysis, chemoselectivitly toward nucleophiles, and partition property of N-neopentyl-, N-trimethylsilylmethyl-, and N-trimethylgermylmethyl-N-nitrosoureas were compared. The latter two compounds are silicon and germanium analogues of the neopentyl derivative. The substitution effect of Ge in place of Si or C are discussed on the chemical and physicochemical properties.

Kinetic and molecular orbital analyses of dicarboxylic acylcarnitine methylesterification show that derivatization may affect the screening of newborns by tandem mass spectrometry

Newborns are routinely screened for organic acidemias by acylcarnitine analysis. We previously reported the partial catalytic methylesterification of dicarboxylic acylcarnitines by benzenesulfonic acid moiety in the solid extraction cartridge during extraction from serum. Since the diagnosis of organic acidemias by tandem mass spectrometry is affected by the higher molecular weight of these derivatized acylcarnitines, we investigated the methylesterification conditions. The kinetic constants for the methylesterification of carboxyl groups on the acyl and carnitine sides of carnitine were 2.5 and 0.24h(-1), respectively. The physical basis underlying this difference in methylesterification rates was clarified theoretically, illustrating that methylesterification during extraction proceeds easily and must be prevented.