1,721,013 research outputs found
HIGH 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%
Enzymatic preparation and absolute configuration of (+)-2-(hydroxymethyl)cyclohexanone
No full textLipase mediated treatment of racemic 2-(hydroxymethyl)cyclohexanone, (+/-)-1, with vinyl acetate allows enantioselective acetylation to give the acetate (R)-(+)-4 and unreacted (S)-(+)-1 in satisfactory yield and enantiomeric purity. The absolute configuration of (S)-(+)-1 (and therefore that of (R)-(+)-4 as well) was determined by the analysis of the n-->pi* Cotton effect at 290 nm present in the CD spectrum of (S)-(+)-1 by means of the octant rule and CNDO/S calculations. Furthermore the optical rotatory power of optically pure (S)-(+)-1 and (R)-(+)-4 have been determined
Una semplice preparazione del D-Tagatosio e di alcuni suoi derivati a partire da alchil 3,4-O-isopropilidene-BETA-D-galattopiranosidi
No full textALKALINE AND ENZYMATIC-HYDROLYSIS OF ISOBUTYL 3,4-ANHYDRO-2,6-DIDEOXY-DL-HEXOPYRANOSIDES - PREPARATION OF ENANTIOMERIC BOIVINOPYRANOSIDES THROUGH A HIGHLY EFFICIENT KINETIC RESOLUTION
No full textRacemic isobutyl 3,4-anhydro-2,6-dideoxy-β-ribo-hexopyranoside and -lyxo-hexopyranoside have been prepared starting from the cycloadduct between 3-buten-2-one and isobutyl vinyl ether. Alkaline hydrolysis converted the lyxo isomer exclusively into isobutyl 2,6-dideoxy-β-DL-xylo-hexopyranoside (isobutyl β-DL-boivinopyranoside), the ribo isomer into a 57:43 mixture of the same glycoside, and its arabino diastereomer (isobutyl β-DL-olivopyranoside). Rabbit microsomal epoxide hydrolase similarly converted the racemic lyxo epoxide into the xylo diol in a regiospecific way and exhibited a high degree of enantioselectivity: when the enzymatic reaction was stopped at 50% conversion, isobutyl β-L-boivinopyranoside and isobutyl 3,4-anhydro-2,6-dideoxy-β-D-lyxohexopyranoside were obtained, both with an enantiomeric excess of at least 96%
NEW SYNTHETIC PATHWAYS TO 5-C-ALKOXYPYRANOSIDES AND TO HEXOS-5-ULOSE DERIVATIVES
No full textSeveral new 5-C-alkoxy-D-galactopyranosides, e.g., I, (R=PhCH2, Me) have been obtained by oxidn. of 4-deoxy-alfa-L-threo-hex-4-enopyranosides, e.g., II (easily available from beta-D-galactopyranosides), with 3-ClC6H4CO3H in alc. solvents. They have been converted into the so far unreported L-arabino-hexos-5-ulose and some of its derivs. through hydrolytic and hydrogenolytic steps. Tautomeric equil. for these keto aldoses have been investigated by NMR technique
Efficient differentiation of the hydroxyl groups of 3,4-O-isopropylidene-D-galactopyranosides by lipase catalyzed esterification and de-esterification
No full textThe Pseudomonas sp. (LPS) promoted acyl transfer from vinyl acetate to selected 3,4-O-isopropylidene-D-galactopyranosides takes place in a completely selective manner giving in high yield the corresponding 6-O-acetates. The acetylation rate is strongly dependent on the type and the orientation of the aglycon, varying from a maximum of reactivity for the 1-deoxy derivative, 1,5-anhydro-3,4-O-isopropylidene-D-galactitol (1d), to a minimum for beta configurated alkyl glycosides and showing a complete loss of reactivity for 3',4':2,3:5,6-tri-O-isopropylidenelactose dimethyl acetal (1e). The latter compound is, however, selectively 6'-O-esterified in good yield by lipase from Candida Antarctica and vinyl acetate. Also the course of the enzymatic hydrolysis of 2,6-di-O-acetyl-3,4-O-isopropylidene-D-galactopyranosides 2 is dependent on the type of the aglycon, both for the reaction rate and the selectivity. The 2-O-acetates 4 are selectively obtained in good yields with porcine pancreatic lipase (PPL) promoted hydrolysis in the case of beta- and alpha-methyl, and 1-deoxy derivatives (2a, 2b and 2d), while for beta-benzyl (2c) and lactose (2e) analogues satisfactory results are obtained with lipase from Mucor miehei (IM20)
Verso l'umanizzazione del latte vaccino: preparazione di derivati selettivamente protetti del lattosio.
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