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The synthetic pentasaccharide (1) corresponding to the heparin sequence which binds to, and activates, antithrombin III (AT III) is a potent antithrombotic compound in several animal models of venous thrombosis. We describe here the preparation and the pharmacological properties of 34, an analogue of oligosaccharide 1 with the latter's N-sulfates being replaced by sulfate esters and hydroxyl groups being methylated. These structural modifications allow a simpler and more efficient synthesis of such anionic oligosaccharides. Affinity for human AT III, anti-factor Xa activity, ability to inhibit thrombin generation, antithrombotic activity in a rat model of venous thrombosis, and elimination half-life in the rat have been determined for 1 and 34. Surprisingly, introduction of O-sulfates in place of N-sulfates, and methylation of hydroxyl groups, contributes to reinforce the binding to AT III, resulting in an improved pharmacological profile.

Known allyl 4,6-O-benzylidene-alpha-D-glucopyranoside was first converted into methyl (prop-1-enyl 2,3-di-O-benzyl-4-O-chloroacetyl-alpha-D-glucopyranosid)-uronate. Acid hydrolysis, followed by treatment with (bromomethylene)dimethyl-ammonium bromide, gave methyl (2,3-di-O-benzyl-4-O-chloroacetyl-alpha-D-glucopyranosyl bromide)uronate. Condensation of this bromide with 3-O-acetyl-1,6-anhydro-2-azido-2-deoxy-4-O-(methyl 2,3-di-O-benzyl-4-O-chloroacetyl-beta-D-glucopyranosyluronate)-bet a-D-glucopyranose. Acetolysis, followed by treatment with titanium tetrabromide, then gave 3,6-di-O-acetyl-2-azido-2-deoxy-4-O-(methyl 2,3-di-O-benzyl-4-O-chloroacetyl-beta-D-glucopyranosyluronate)-alp ha-D-glucopyranosyl bromide. Condensation of this bromide with benzyl 6-O-acetyl-3-O-benzyl-2-benzyloxy- carbonylamino-2-deoxy-4-O-(methyl 2-O-acetyl-3-O-benzyl-alpha-L- idopyranosyluronate)-alpha-D-glucopyranoside provided benzyl O-(methyl 2,3-di-O-benzyl-4-O-chloroacetyl-beta-D-glucopyranosyluronate)-(1- ---4)-O-(3,6-di-O-acetyl- -2-azido-2-deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(methyl 2-O-acetyl-3-O-benzyl-alpha-L-idopyranosyluronate)-(1----4)-6-O-ac etyl-3-O- acetyl-3-O-benzyl-2-benzyloxycarbonylamino-2-deoxy-alpha-D-gluc opyranoside. O-Dechloroacetylation followed by condensation with 6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-alpha-D-glucopyranosyl bromide provided benzyl O-(6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-beta-D-glucopyranosyl)- (1----4)-O-(methyl 2,3-di-O-benzyl-beta-D-glucopyranosyluronate)-(1----4)- O-(3,6-di-O-acetyl-2-azido-2-deoxy-alpha-D-glucopyranosyl)-(1----4)-O-(m ethyl 2-O-acetyl-3-O-benzyl-alpha-L-idopyranosyluronate)-(1----4)-6-O-ac etyl-3-O- benzyl-2-benzyloxycarbonylamino-2-deoxy-alpha-D-glucopyranoside in 70% yield. O-Deacetylation followed by re-esterification, O-sulfation, saponification, catalytic hydrogenolysis, and N-sulfation gave the decasodium salt of O-(2-deoxy-2-sulfamido-6-O-sulfo-alpha-D- glucopyranosyl)-(1----4)-O-(beta-D-glucopyranosyluronic acid)-(1----4)-O-(2-deoxy-2-sulfamido-3,6-di-O-sulfo-alpha-D-gl ucopyranosyl)-(1----4)-O-(2-O-sulfo-alpha-L-idopyranosyluronic+ ++ acid)-(1----4)-2-deoxy-2-sulfamido-6-O-sulfo-D-glucopyranose. This synthetic pentasaccharide binds to antithrombin III with an association constant similar to that of high-affinity heparin and elicits a potent anti-factor Xa activity in plasma.

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