Synthesis, crystalline structure, conformational analysis, and azidolysis of methyl 2,3-anhydro-α-d-manno- and -allo-pyranoside p-bromobenzyl
作者:Xinfu Wu、Fanzuo Kong、Depei Lu、Genpei Li
DOI:10.1016/0008-6215(92)80086-g
日期:1992.11
Methyl 2,3-anhydro-4,6-di-O-p-bromobenzyl-alpha-D-allopyranoside (6) was synthesized from methyl 4,6-O-benzylidene-alpha-D-glucopyranoside (1) via the intermediate methyl 4,6-di-O-p-bromobenzyl-2,3-di-O-p-tolylsulfonyl-alpha-D-glucopyranoside. Treatment of 6 with sodium azide selectively afforded methyl 3-azido-4,6-di-O-p-bromobenzyl-3-deoxy-alpha-D-glucopyranoside in 70% yield. Methyl 2,3-anhydro-4,6-di-O-p-bromobenzyl-(17) and methyl 2,3-anhydro-4,6-di-O-benzyl-alpha-D-mannopyranoside (18) were obtained from 1 via the intermediates methyl 4,6-di-O-p-bromobenzyl- and methyl 4,6-di-O-benzyl-2-O-p-tolylsulfonyl-alpha-D-glucopyranoside. Azidolysis of 17 and 18 with sodium azide in the presence of tetraethylammonium chloride in N,N-dimethylformamide gave the respective 3-azidoaltropyransides, in yields of 80%, by exclusive 3-attack. The crystal structure of compound 6 is orthorhombic with a space group of P2(1)2(1)2(1), and the 2,3-anhydropyranose moiety is in an almost ideal degrees-H-5 half-chair conformation. The crystals of 17 are also orthorhombic, belonging to space group P2(1)2(1)2(1), but the conformation is a hybrid of the degrees-H-5 half-chair and the degrees-E sofa. Analysis by NMR spectroscopy suggests that in solution in CDCl3 the conformation of 17 remains the same as, and that of 6 undergoes a change from, the respective solid-state conformations.