Shigenobu Okuda

Rhizoxin binding to tubulin at the maytansine-binding site

The binding of rhizoxin, a potent inhibitor of mitosis and in vitro microtubule assembly, to porcine brain tubulin was studied. Tubulin possesses one binding site for rhizoxin per molecule with a dissociation constant (Kd) of 1.7.10(-7) M. Ansamitocin P-3, a homologue of maytansine, was a competitive inhibitor of rhizoxin binding, with an inhibition constant of 1.3.10(-7) M. Vinblastine also inhibited rhizoxin binding, but was not fully competitive, and the inhibition constant was 2.9.10(-6) M. In contrast, both rhizoxin and ansamitocin P-3 were potent inhibitors of vinblastine binding. Rhizoxin inhibited tau-promoted tubulin assembly, but it, differing from vinblastine, did not induce tubulin aggregation into spirals, even at a concentration as high as 2.10(-5) M. In addition, rhizoxin strongly inhibited vinblastine-induced tau-dependent tubulin aggregation. Rhizoxin binding to tubulin was completely independent from colchicine binding. These effects resemble those of maytansine. The results suggested that rhizoxin binds to the maytansine-binding site and that the binding sites of rhizoxin and vinblastine are not the same.

3,4-dihydroxy-2-hydroxymethylpyrrolidine from Arachniodes standishii

Abstract 3,4-Dihydroxy-2-hydroxymethylpyrrolidine, which has not been encountered naturally before, was isolated from the Pteridophyte Arachniodes standishii . Its configuration was determined as 2,3- cis and 3,4- trans from NMR spectra.

Isolations of phytotoxic substances produced by pyricularia oryzae cavara

Aus obigen Spezies werden als weitere phytotoxische Verbindungen die beiden Tetralone (I) und (II) neben dem substituierten Salicylaldehyd (III) und zwei Isomeren des hydrierten Benzofurans (IV) isoliert.

Cerulenin resistance in a cerulenin-producing fungus. Isolation of cerulenin insensitive fatty acid synthetase.

Abstract Cerulenin, an antifungal antibiotic isolated from a culture filtrate of Cephalosporium caerulens , is a potent inhibitor of fatty acid synthetase systems. This antibiotic specifically blocks the activity of β-ketoacyl thioester synthetase (condensing enzyme). The mechanism of the resistance of C. caerulens to cerulenin was investigated. The rate of growth in medium containing up to 100 gmg/ml cerulenin was as rapid as that in cerulenin-free medium. At a cerulenin concentration of 300 μg/ml, the rate of growth was still more than half that of the control. The addition of cerulenin (200 μg/ml) to a culture of growing cells has almost no effect on the incorporation of [ 14 C ]acetate into cellular lipids. Fatty acid synthetase was purified from C. caerulens to homogeneity. Properties of this fatty acid synthetase were almost the same as those of yeast fatty acid synthetase except for the sensitivity to cerulenin. C. caerulens synthetase is much less sensitive to cerulenin than fatty acid synthetases from other sources. These findings suggested that the insensitivity of C. caerulens fatty acid synthetase plays an important role in the cerulenin resistance of this fungus.

Enantioselective hydrolysis of dialkyl 3-monosubstituted glutarates with pig liver esterase: Structure-optical purity relationships

Abstract Dialkyl 3-monosubstituted glutarates are subjected to hydrolysis with pig liver esterase to afford the corresponding chiral half-esters. Synthetically useful half-esters of higher optical purity are obtained from the prochiral substrates of more hydrophobic nature.

A versatile method for preparation of O-alkylperoxycarbonic acids: epoxidation with alkyloxycarbonylimidazoles and hydrogen peroxide

Abstract A variety of O-alkylperoxycarbonic acids ( 2 ) were conveniently prepared in situ by utilizing alkyloxycarbonylimidazoles ( 1 ) as their precursors. Epoxidation of alkenes with such peroxy-acids was studied and their reactivities were compared with those of peroxycarboxylic acids.

A study on the transition state in the photooxygenations by aromatic amine N-oxides

Abstract Oxygen—atom transfer process in the photolysis of aromatic amine N-oxides was suggested to involve the primary oxygen—atom elimination from N-oxides to give “oxene” follwed by its reactions with the oxygen-acceptors.

Stereochemical studies of hydrogen incorporation from nucleotides with fatty acid synthetase from Brevibacterium ammoniagenes.

The biosynthesis of fatty acids from malonyl-CoA and acetyl-CoA was investigated with an enzyme preparation which was purified 100-fold from Brevibacterium ammoniagenes. Fatty acids synthesized in the presence of D2O and stereospecifically deuterated NADPH and NADH were isolated and analyzed by mass chromatography to examine the localization of deuterium in the molecule. The following results were obtained: 1) HB hydrogen of NADPH was used for beta-ketoacyl reductase. 2) HB hydrogen of NADH was used for enoyl reductase. 3) Hydrogen atoms from water were found on the even-numbered methylene carbon atoms (2-hydrogen atoms per carbon atom) and some were also found on the odd-numbered methylene carbon. 4) Hydrogen atoms from NADPH were found on odd-numbered methylene carbon atoms (1-hydrogen per carbon). 5) Hydrogen atoms from NADH were also found on the odd-numbered methylene carbon atoms, but the number of incorporated hydrogen atoms was less than expected. The exchange of HB hydrogen of NADH with water catalyzed by enoyl reductase was suspected. 6) The exchange of methylene hydrogen atoms of malonyl-CoA with proton of water was suggested by 13C NMR analysis.

Studies on morphine alkaloids—VIII : Some reactions of 14β-bromocodeine and related compounds☆

Abstract Solvolysis of 14β-bromocodeine (V) was examined in detail and some considerations on the mechanism of this reaction are described.

Stereochemistry of 2-aminopimelic acid and related amino acids in three species of asplenium

Abstract We previously reported two free D -amino acids, D-2-aminopimelic acid ( D -APA) and trans -3,4-dehydro- D -2-aminopimelic acid (D-Δ-APA), from Asplenium unilaterale . In the present work we isolated 4-hydroxy-2-aminopimelic acid (OH-APA) from the same plant and determined it to be the α- L -form. We also investigated the configurations of these amino acids isolated from A. prolongatum and A. wilfordii which are morphologically distinct from A. unilaterale . In A. prolongatum , APA was the D - and OH-APA was the L -isomer. In contrast, APA from A. wilfordii was partially racemized and the degree of racemization was significantly different in plant material collected in July and November, L:D = 3:2 and 3:7, respectively. In A. wilfordii OH-APA was almost pure L - and Δ-APA was mostly the D -isomer.