Development of specific inhibitors for heparin-binding proteins based on the cobra cardiotoxin structure: an effective synthetic strategy for rationally modified heparin-like disaccharides and a trisaccharide Original Research Article

Recently, a new heparin disaccharide-binding site on the convex side of cobra cardiotoxin (CTX) was identified by NMR spectroscopy and molecular modeling. To further characterize this site two heparin-like disaccharides were synthesized for binding studies with CTX, and a trisaccharide was synthesized for testing the sequence of the disaccharide binding to CTX. Thus six differentially protected monosaccharide building blocks (three l-iduronic acids and three d-glucosamines) were prepared. These include a l-iduronic acid elongation building block namely methyl 2-O-acetyl-4-O-levulinoyl-3-O-pivaloyl-α-l-idopyranosyluronate trichloroacetimidate for which a single-crystal X-ray structure was determined to have Mr = 576.79, a = 9.3098(11) Å α = 90°, b = 10.3967(12) Å β = 90°, c = 28.026(3) Å γ = 90°, V = 2712.7(6) Å3, P212121, Z = 4, μ = 0.71073 Å, and R = 0.0378 for 7586 observed reflections. It shows that the molecular structure of the donor is in the 1C4 conformation with significant 1,3-diaxial interactions between O-1 and O-3 as well as O-2 and O-4. The disaccharides and trisaccharide vary in the degree and position of O- and N-sulfation. The pivaloyl group was used as permanent protecting group of hydroxyl. The levulinoyl group was used as the temporary protecting group to protect the hydroxyl for elongation.