1,721,061 research outputs found
REGIOSELECTIVITY AND STEREOSELECTIVITY OF OXYRAN RING-OPENING REACTIONS OF 3,4-EPOXYTETRAHYDROPYRANE AND 2-METHYL DIASTEREOISOMER DERIVATIVES
No full textHIGH DIASTEREO-SELECTIVITY AND ENANTIOSELECTIVITY IN THE ENZYMATIC-HYDROLYSIS OF A RACEMIC ANHYDRODEOXYSUGAR - A TOTALLY SYNTHETIC APPROACH TO BOTH ENANTIOMERS OF BOIVINOSE
No full textThe microsomal epoxide hydrolase-promoted hydrolysis of racemic isobutyl 3,4-anhydro-2,6-dideoxy-β-lyxohexopyranoside, which is easily prepared from isobutyl vinyl ether and but-3-en-2-one, occurs with very high regio-and enantio-selectivity, with kinetic resolution leading to the L-and D-forms of isobutyl β-boivinoside, both with an enantiomeric excess of at least 96%
REGIOSELECTIVITY AND ENANTIOSELECTIVITY OF THE ENZYMATIC-HYDROLYSIS OF ISOBUTYL 3,4-ANHYDRO-2,6-DIDEOXY-BETA-DL-RIBO-HEXOPYRANOSIDE
No full textNew syntheses of D-tagatose and of 1,5-anhydro-D-tagatose from D-galactose derivatives.
No full text3,4-O-Isopropylidene-D-lyxo-hexopyranosid-2-ulose derivatives, obtained by oxidation of
3,4,6-protected D-galactopyranosides, can be alkylated in their anionic 2,6-pyranose forms to
produce bis-glycosides containing the 2,5-dioxabicyclo[2.2.2]octane ring system. The 1-benzyl-2-
methyl bis-glycoside 4b, when subjected to catalytic hydrogenolysis, produces the methyl
D-lyxo-hexopyranos-2-uloside 10, existing as an 8:2 mixture of 1,5-pyranose anomers 9. Computational
and NMR evidence is presented in favour of the hypothesis that the major anomer has the alfa
configuration. Reduction of 9/10 with NaBH 4 gives methyl 3,4-O-isopropylidene-beta-D-tagatopyranoside,
that can be hydrolyzed to D-tagatose. A simple synthesis of 1,5-anhydro-D-tagatose,
starting from 1,5-anhydro-D-galactitol, is also presented. All new compounds were fully characterized
by elemental analysis and by 1H and 13C NMR spectroscopy
A FACILE CONVERSION OF 3,4-O-ISOPROPYLIDENE-BETA-D-GALACTOPYRANOSIDES INTO 4-DEOXY-ALPHA-L-THREO-HEX-4-ENOPYRANOSIDE AND L-ARABINO-HEXOS-5-ULOSE DERIVATIVES
No full textTreatment of O-protected 3,4-0-isopropylidene-beta-galactopyranosides with
tert-BuOK in N,N-dimethylformamide or methyl sulfoxide produces 4-deoxy-a-Lthree-
hex-4-enopyranosides in good yields. The corresponding a-anomers and the
non-O-protected derivatives are resistant to this treatment. Reaction of methyl 4-
deoxy-2,6-di-O-methyl-alfa-L-threo-hex-4-enopyranoside with 3-chloroperbenzoic
acid in CH2Cl2 gave a crystalline adduct that was hydrolyzed to 2,6-di-O-methyl-LaraBino-
hexos-5-ulose
Derivati piranosidici insaturi quali intermedi per la sintesi glucidica: nuovi approcci a derivati L-arabino-esos-5-ulosici, all'L-tagatosio ed al corrispondente 2,3-glicale a partire dal D-galattosio.
No full textTHE STERIC COURSE OF THE REACTIONS OF 2,3-DIHALOTETRAHYDROPYRANS WITH GRIGNARD-REAGENTS
No full textThe steric course of some reactions of 2,3-dihalotetrahydropyrans with sodium methoxide and with methyl- and phenyl-magnesium bromides has been reinvestigated. Whereas the methanolysis of the cis- and trans-dichlorides occurs with practically complete inversion, it has been confirmed that their reactions, as well as those of the dibromides, with methyl-magnesium bromide are non-stereospecific, yielding mixtures of trans- and cis-3-halo-2-methyl-tetrahydropyrans in ratios that are independent of the configurations of the starting dihalides. It has been further established that Grignard reagents cause equilibration of cis- and trans-dihalide mixtures in a reaction that is much faster than the Grignard coupling step
CHEMICAL SYNTHESIS OF THE DESIALYLATED HUMAN CAD-ANTIGENIC DETERMINANT
No full textBenzyl 2-azido-2-deoxy-β-d-galactopyranoside was converted into benzyl 2-azido-4,6-O-benzyl-2-deoxy-β-d-galactopyranoside via benzylidenation, p-methoxybenzylation, acid hydrolysis, benzylation, and selective oxidation. Condensation of 1,2,3,4,6-penta-O-acetyl-β-d-galactopyranose with benzyl 2-azido-4,6-di-O-benzyl-2-deoxy- β-d-galactopyranoside in the presence of trimethylsilyl triflate gave crystalline benzyl 2-azido-4,6-di-O-benzyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-d-gal actopyranosyl)-β-d-galactopyranoside (76%), which was converted into benzyl 2-azido-4,6-di-O-benzyl-2-deoxy-3-O-(2,6-di-O-benzyl-β-d-galactopyr anosyl)-β-d-galactopyranoside and condensed with 3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-d-galactopyranosyl bromide in the presence of silver silicate on alumina and molecular sieve 4 Å to give 61% of benzyl O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-β-d-galactopyranosyl)- (1→4)-O-(2,6-di-O-benzyl-β-d-galactopyranosyl)-(1→3)-2- azido-4,6-di-O-benzyl-2-deoxy-β-d-galactopyranoside. Reduction with sodium borohydride followed by N-acetylation, O-deacetylation, and catalytic hydrogenolysis then gave O-(2-acetamido-2-deoxy-β-d-galactopyranosyl)-(1→4)-O-β-d- galactopyranosyl-(1→3)-2-acetamido-2-deoxy-d-galactopyranose, the desialylated human Cad-antigenic determinant. © 1986
UNUSUAL STERIC COURSE OF THE EPOXIDE HYDROLASE CATALYZED-HYDROLYSIS OF (+/-)3,4-EPOXYTETRAHYDROPYRAN - A CASE OF COMPLETE STEREO-CONVERGENCE
No full textThe steric course of the hydrolysis of racemic 3,4-epoxytetrahydropyran promoted by rabbit liver microsomal epoxide hydrolase has been investigated. Both enantiomers of the epoxide give (-)-(R,R)-trans-tetrahydropyran-3,4-diol at practically equal rates, the optical purity being at least 96% at any stage of conversion. These results can be justified by assuming that both enantiomers react in the 1,2-M conformation, nucleophilic attack by water taking place exclusively at position 3 of the 3S,4R enantiomer and at position 4 of the 3R,4S one, in contrast with the nonenzymic ring opening in which a high preference for attack at C(4) has been found
Una semplice preparazione del D-Tagatosio e di alcuni suoi derivati a partire da alchil 3,4-O-isopropilidene-BETA-D-galattopiranosidi
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