摘要:

The unreported title compound and its 2,6-di-O-benzyl derivative have been prepared from methyl β-D-galactopyranoside through a sequence involving the bisglycoside methyl 2,6-di-O-benzyl-5-O-methoxv-β-D-galactopyranoside8, the precursor of L-orabino-hexos-5-ulose, that was converted to the L-lyxoseries by inversion at C-3. The inversion was achieved in acceptable yields by selective triflation, followed by displacement with benzoate, and by an oxidation/reduction sequence. Whereas 2,5-di-O-benzyl-L-lyxo-hexos-5-ulose exists entirely as a mixture of the two anomeric 1,4-furanosic forms, the unprotected hexos-5-ulose involves at equilibrium in CD3CN/D2O at least eight tautomers, one of which is predominant.

ISSN:0732-8303    

DOI:10.1080/07328309808001891

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The rapid conversion of D-galactose, its 2-deoxy, 3-deoxy, 4-deoxy and 6-deoxy derivatives and L-arabinose to their UDP-derivatives (2-7) is described. The procedure involves thein situpreparation of the per-O-trimethylsilylated glycopyranosyl iodides and their direct reaction with UDP. All six sugar nucleotides were active as substrates for β(1→4)-galactosyltransferase and were used to enzymatically prepareN-acetyllactosamine (8) and five of its analogs (9-13).

ISSN:0732-8303    

DOI:10.1080/07328309808001892

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The regioselectivity of a pig liver esterase (PLE) catalyzed hydrolysis of methyl 2,3-di-O-acetyl-5-deoxy-α-D-arabinofuranoside (1) and methyl 2,3-di-O-acetyl-5-deoxy-β-D-arabinofuranoside (2) was established by GLC. Diacetate1gave exclusively methyl 3-O-acetyl-5-deoxy-α-D-arabinofuranoside while diacetate2produced both methyl 2-O-acetyl-5-deoxy-β-D-arabinofuranoside and methyl 3-O-acetyl-5-deoxy-β-D-arabinofuranoside which were resistant to subsequent hydrolysis. The Michaelis constants and maximal velocities were determined for1and2.The first-order rate constants were computed for1, 2, and all corresponding monoacetates. The results were evaluated on the basis of a Jones's active-site model for PLE and the additional criteria valid for acetyl esters of pentofuranosides were proposed.

ISSN:0732-8303    

DOI:10.1080/07328309808001893

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The syntheses of α-D-glucopyranose-(1→3)-D-mannopyranose, methyl α-D-glucopyranose-(1→3)-α-D-mannopyranoside and methyl α-D-glucopyranose-(1→3)-α-D-mannopyranose-(1→2)-α-D-mannopyranoside are reported. High stereoselectivity was observed during the coupling of glucose and mannose residues by the use of glucosyl trichloroacetimidate as donor.

ISSN:0732-8303    

DOI:10.1080/07328309808001894

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The synthesis of 5-O-[5-(pentanoic acid)]-phosphono-L-erythro-pent-2-ulose2was successfully achieved by coupling benzyl 5-hydroxypentanoate9band 1-O-benzyl-L-erythro-pent-2-ulose ethane- 1,2-diyl dithioacetal13with the enediol pyrophosphate18.Compound2was coupled to carrier proteins, porcine thyroglobuline and bovine serum albumin and the conjugates were treated with KCN to give conjugates of the hapten1, designed to raise catalytic antibodies.

ISSN:0732-8303    

DOI:10.1080/07328309808001895

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Three glycosidases, α-mannosidase fromJack beans, β-galactosidase fromAspergillus oryzaeand β-N-acetylhexosaminidase fromAspergillus oryzaewere evaluated for their ability to catalyze the glycosylation of non-saccharidic polyols. A series of monoglycosylated derivatives of tris(2-aminoethyl)cyanuric acid, pentaerythritol and bis(hydroxymethyl)benzene were obtained in pure form and characterized by NMR-spectroscopy.

ISSN:0732-8303    

DOI:10.1080/07328309808001896

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An efficient route for the synthesis of octamannan1, found in high mannose type sugar chains, is described. to construct octasaccharide1by as few synthetic steps as possible, we employed a chemoenzymatic strategy: the enzymatic synthesis of oligosaccharide blocks using glycosidases followed by chemical coupling to form a branched structure. By use of this methodology, many synthetic steps were eliminated and1was easily synthesized.

ISSN:0732-8303    

DOI:10.1080/07328309808001897

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The nickel(II) catalysed isomerisation reactions of D-fructose derivatives modified at positions 5 and/or 6 were investigated. 5,6-Dimodified open-chain D-fructose derivatives as well as an open-chain derivative of D-xylulose reacted to give complex mixtures containing no major product. 5-Modified ketohexoses invariantly were degraded to the corresponding methyl pentonates upon loss of C-1. 6-Modified D-fructofuranose furnished the desired rearrangement into a branched-chain derivative of D-ribose. In marked contrast to previous belief, from these results it appears that 5-OH plays an important role in the productive co-ordination of the D-fructose derivatives to the nickel-ethylenediamine complexes under consideration.

ISSN:0732-8303    

DOI:10.1080/07328309808001898

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The use of epoxides obtained by dimethyldioxirane epoxidation of 2,3-anhydro-1,3-dideoxy-4,5:7,8-di-O-isopropylidene-D-manno-oct-1-enitol as glycosyl donors is described. This method offers a simple and stereoselective access to precursors of Kdo glycosides. The stereochemical outcome of the reaction is rationalized by means of semiempirical calculations of the transition states leading to glycosides formation.

ISSN:0732-8303    

DOI:10.1080/07328309808001899

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Four derivatives of β-maltosyl-(1→4)-trehalose were prepared, each with two deoxy functions in one of the constitutive disaccharide building blocks. 2,3-Di-O-acetyl-4,6-dideoxy-4,6-diiodo-α-D-galactopyranosyl- (1→4) −1,2,3,6-tetra-O-acetyl-D-glucopyranose (3) was employed as a precursor for the 4‴,6‴-dideoxygenated tetrasaccharide9: coupling of3with 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3,6-tri-O-benzylidene-α-D-glucopyranoside (4) furnished the tetrasaccharide5which was deiodinated and deprotected to yield the target tetrasaccharide9.Secondly, the dideoxygenated maltose derivative 3-deoxy-4,6-O-isopropylidene-2-O-pivaloyl-β-D-glucopyranosyl- (1→4) −1,6-anhydro-3-deoxy-2-O-pivaloyl-β-D-glucopyranose (10) was ring-opened to the anomeric acetate11.A [2+2] block synthesis with4in TMS triflate mediated glycosylation gave a tetrasaccharide which was deprotected to the 3″,3‴-dideoxygenated analogue of β-maltosyl-(1→4)-trehalose. For the third tetrasaccharide, 2,3,2″,3′-tetra-O-benzyl-α,α-trehalose was iodinated at the primary positions and deiodinated in the presence of palladium-on-carbon, then this acceptor was selectively glycosylated with hepta-O-acetyl-maltosyl bromide (20). Removal of protective groups furnished the maltosyl trehalose tetrasaccharide deoxygenated at positions C-6 and C-6′. to prepare a 3,3′-dideoxygenated trehalose, the free hydroxyl groups of 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranosyl 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranoside (25) were reduced by Barton-McCombie deoxygenation. One of the benzylidene groups was opened reductively with sodium cyanoborohydride. The resulting free hydroxyl group at the 4′-position was glycosylated in a Koenigs-Knorr reaction with20to yield the 3,3′-dideoxygenated tetrasaccharide32, the fourth target oligosaccharide, after deprotection.

ISSN:0732-8303    

DOI:10.1080/07328309808001900

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor