Reactions of phenyl chlorosulfate at OH-2 and OH-3 of aldohexopyranose derivatives. Competing substitution and displacement reactions

Side reactions with 2,2,2-trichloroethoxysulfates during the synthesis of glycans

Protected sulfate groups may be used as an alternative tool to provide sulfate esters at hydroxyl and amino groups, particularly on complex glycans. We examined 2,2,2-trichloroethoxysulfation at the mono-, di-, and trihydroxyl groups of saccharide moieties to show regioselective sulfation. We found some side reactions including inter- and intramolecular nucleophilic reactions with 2,2,2-trichloroethoxysulfates.

Divergent heparin oligosaccharide synthesis with preinstalled sulfate esters

Traditional chemical synthesis of heparin oligosaccharides first involves assembly of the full length oligosaccharide backbone followed by sulfation. Herein, we report an alternative strategy in which the O-sulfate was introduced onto glycosyl building blocks as a trichloroethyl ester prior to assembly of the full length oligosaccharide. This allowed divergent preparation of both sulfated and non-sulfated building blocks from common advanced intermediates. The O-sulfate esters were found to be stable during glycosylation as well as typical synthetic manipulations encountered during heparin oligosaccharide synthesis. Furthermore, the presence of sulfate esters in both glycosyl donors and acceptors did not adversely affect the glycosylation yields, which enabled us to assemble multiple heparin oligosaccharides with preinstalled 6-O-sulfates.

Preparation of 2-C- and 3-C-cyano-2-enopyranoside derivatives and their epoxidation

Methyl 4,6-O-benzylidene-2-C- and 3-C-cyano-2,3-dideoxy-D-erythro-hex-2-enopyranosides and -2-enitols were prepared and their epoxidation was performed.

Regioselectivity in the sulfation of some chemically-modified heparins, and observations on their cation-binding characteristics

Two modified forms of heparin, polymers A and B, have been prepared, one containing residues of nonsulfated alpha-L-idopyranosyluronic acid (3) and the other residues of alpha-L-galactopyranosyluronic acid (7), in place of the normal alpha-L-idopyranosyluronic acid 2-sulfate (1). In addition, both A and B contained 2-acetamido-2-deoxy-alpha-D-glucopyranosyl 6-sulfate residues (6) in place of the corresponding N-sulfated residues (2) of the original heparin. These polymers were subjected to sulfation under various conditions. Examination of the products by NMR spectroscopy showed that polymer A was sulfated initially at position-3 of residue 3, and that slower substitution occurred at position-3 of 6. By contrast, polymer B exhibited low regioselectivity, as sulfation occurred with about equal facility at positions-2 and -3 of 7, and -3 of 6. The sulfation products had no significant anti Xa activity. Based on the paramagnetic effects of Cu2+ and chemical shift displacements induced by Ca2+, NMR spectroscopy was used to compare cation-binding properties of A and B with those of heparin. In contrast to heparin, which forms a complex with Cu2+ detectable at a level of < 10(-3) mol per dimeric unit of the polymer, neither A nor B exhibited an interaction with the cation. However, polymer A was found to bind Ca2+, in this respect being distinct from the related modification, 1-->6, which contains a 2-sulfate group in 1, as well as from polymer B.

Sulfation of some chemically-modified heparins. Formation of a 3-sulfate analog of heparin

A modified form of heparin containing residues of nonsulfated alpha-L-idopyranosyluronic acid (7) in place of the normal 2-sulfate (1) was sulfated with sulfur trioxide-trimethylamine in dimethylformamide at 0 and 25 degrees. Examination of the reaction products by n.m.r. spectroscopy showed that sulfation occurred selectively at C-3 of residue 7, to give a new polymer that may be described as a 3-sulfate analog of heparin. A slower substitution reaction led subsequently to sulfation at C-3 of 2-deoxy-2-sulfamino-alpha-D-glucopyranosyl 6-sulfate residues (2), although this was accompanied by partial N-desulfation of 2. An analogous pattern of O-sulfation-N-desulfation was observed for the residues of 2 in two other modified heparins, one containing residues of 2,3-anhydro-alpha-L-gulopyranosyluronic acid and the other residues of alpha-L-galactopyranosyluronic acid, in place of residues of 1. The galacto diastereomer exhibited relatively low regioselectivity, as it was found to be sulfated at C-2 or C-2.3, or both. Selective resulfation of free amino groups gave the products that were examined for anticoagulant activity and susceptibility to enzymolysis by heparinase. Antithrombin-binding affinity measurements were also carried out. Although none of the materials had significant anti-Xa activity, nor were they affected by heparinase, their patterns of binding to antithrombinagarose were not dissimilar to that of heparin.