Ryuichi Isobe

A functional model of manganese catalase. Mass spectrometric and visible spectral evidence for {MnIV(O)}2 and MnIIMnIV(O) intermediates

A dinuclear manganese(II) complex [Mn2(L)(PhCO2)2(NCS)][L = 2,6-bis{N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenolate(1–)] decomposes H2O2 catalytically indimethylformamidesolution; two oxomanganese(IV) species {MnIV(O)}2 and MnIIMnIV(O) are detected for the first time as intermediates in the H2O2 disproportionation reaction based on mass spectrometric and visible spectral studies.

ISOLATION AND STRUCTURE OF THREE NEW CERAMIDES FROM THE STARFISH ACANTHASTER PLANCI

Three new phytosphingosine-type ceramides, AC-1-6, AC-1-10 and AC-1-11, were isolated from the ceramide molecular species AC-1, obtained from the less polar fraction of the CHCl3-MeOH extract of the starfish Acanthasterplanci. The structures of these ceramides were determined on the basis of chemical and spectroscopic evidence as (2S,2′R,3S,4R,9Z)-2-(2-hydroxyhexadecanoylamino)-9-docosene-1,3,4-triol (AC-1-6), (2S,2′R,3S,4R,)-2-(2-hydroxytricosanoylamino)hexadecane-1,3,4-triol (AC-1-10) and (2S,2′R,3S,4R,)-2(2-hydroxytetracosanoylamino)hexadecane-1,3,4-triol (AC-1-11). Positive ion FABMS/MS of each ceramide gave important information for their structure elucidation. Mass spectrometry of the dimethyl disulfide derivatives of ceramide was also useful for the determination of the double bond position in the long-chain base.

Negative ion fast atom bombardment mass spectrometry for native gangliosides using a neutral matrix

A hexamethylphosphoric triamide proved to be a useful solvent for negative ion fast atom bombardment mass spectrometry (FABMS) of underivatized gangliosides, using a conventional glycerol matrix. Analysis of the gangliosides using a hexamethylphosphoric triamide was more convenient and more efficient not only for molecular weight determination but also for elucidating the structure of the carbohydrate sequence. We also noted the significance of the high polarity of the solvent as well as the electron pair donicity of the matrix system for negative ion FABMS of underivatized gangliosides.

Isolation and Structure of a New Ganglioside Molecular Species

A ganglioside molecular species [LLG-3 (1)] has been obtained from the water-soluble lipid fraction of the CHCl3/MeOH extract of the starfish Linckialaevigata. On the basis of chemical and spectroscopic findings, the structure of 1 has been elucidated. Negative-ion FABMS provided important information concerning both the structure of the sugar moiety and the molecular mass of the ganglioside. On the other hand, positive-ion FABMS/MS of [M + Na]+ ions obtained in the positive-ion FABMS of the ceramide lactoside (4) derived from 1 indicated the structure of the fatty acid chain of the ceramide moiety. 1 represents a new ganglioside molecular species possessing a 211-linked tandem-type disialosyl moiety.

Isolation and Structure of Biologically Active Glycosphingolipids from the Sea CucumberCucumaria echinata

Five cerebrosides, CE-1-1, CE-1-2, CE-1-3, CE-3-1, and CE-3-2, and a ganglioside molecular species CG-1 have been obtained from the less polar and polar fractions, respectively, of the chloroform/methanol extract of the sea cucumber Cucumaria echinata. The structures of these glycosphingolipids have been determined on the basis of chemical and spectroscopic evidence. The cerebrosides show lethality toward brine shrimps. On the other hand, the ganglioside CG-1 exhibits neuritogenic activity toward the rat pheochromocytoma cell line, PC-12 cells.

ISOLATION AND STRUCTURE OF BIOLOGICALLY ACTIVE GANGLIOSIDES FROM THE SEA CUCUMBER HOLOTHURIA PERVICAX

Three ganglioside molecular species, HPG-8, HPG-3, and HPG-1, have been obtained from the polar fraction of the chloroform/methanol extract of the sea cucumber Holothuriapervicax. The structures of these gangliosides have been determined on the basis of chemical and spectroscopic evidence. They represent new ganglioside molecular species. HPG-8 is a sulfated monosialo-ganglioside, while HPG-3 and HPG-1 are disialo-gangliosides possessing 24-linked tandem-type disialosyl moieties. These three gangliosides qualitative neuritogenic activity toward the rat pheochromocytoma cell line, PC-12 cells.

Formation of a novel 20-hydroxylated metabolite of lipoxin A4 by human neutrophil microsomes.

Lipoxin A4 (LXA4) is a biologically active compound produced from arachidonic acid via interactions of lipoxygenases. Incubation of LXA4 either with human neutrophils or with the neutrophil microsomes leads to formation of a polar compound on a reverse‐phase high‐performance liquid chromatography. We have identified the metabolite as 20‐hydroxy‐LXA4, a novel metabolite of arachidonic acid, on the basis of ultraviolet spectrometry and gas chromatography‐mass spectrometry. The LXA4ω ‐hydroxylation requires both molecular oxygen and NADPH, and is inhibited by carbon monoxide, by antibodies raised against NADPH‐cytochrome P‐450 reductase, or competitively by leukotriene B4 (LTB4) and LTB5, substrates of LTB4 ω‐hydroxylase. These findings indicate that the formation of 20‐hydroxy‐LXA4 is catalyzed by a neutrophil cytochrome P‐450, the LTB4 ω‐hydroxylase.

Direct microanalysis by negative ion fast atom bombardment mass spectrometry

Abstract In negative ion fast atom bombardment (FAB) mass spectrometry, the use of a liquid matrix comprised of 15-crown-5—glycerol (1:10, v/v) enabled the molecular weight determination of small amounts of non-volatile acidic molecules. This ionization process could result in detection limits of less than one-fifth of those obtained using only glycerol as matrix. The function of the matrix as a proton acceptor is emphasized.

High-pressure Diels–Alder reaction of [60] fullerene with several tropones. Characterization of the 1 : 1-cycloadducts

The high-pressure Diels–Alder reaction of fullerite with tropone and several of its derivatives under 300 MPa gave 1 : 1-[4 + 2] cycloadducts of C60 in good yields. Their 1H and 13C NMR spectra were consistent with the structures depicted. These compounds quantitatively regenerate starting materials upon thermolysis.

Conformational effect on the fragmentations of peptide derivatives in field desorption mass spectrometry

Fragmentations of N-benzyloxycarbonyl-protected tri-peptide ethyl esters containing proline at the P2 site were compared with those of the corresponding peptide derivatives containing no proline in field desorption mass spectrometry. The fragment ion [M-107]+ due to a loss of the benzyloxy group from a molecular ion was observed in the field desorption mass spectra for the peptides containing no proline, while it was not found in the peptides containing proline at all. These results suggest that the conformational difference of the peptide derivatives attributable to the existence of proline has an effect upon fragmentations in the field desorption ionizing process.