A Convenient Synthesis of 4-Thio-D-galactofuranose
The synthesis of 4-thio-D-galactofuranose (15) and derivatives, starting from methyl α-D-glucopyranoside (1), is described. Esterification of 1 with N-benzoylimidazole afforded regioselectively methyl 2,3,6-tri-O-benzoyl-α-D-glucopyranoside (2c). Further sulfonylation of HO-4 of 2c gave methyl 2,3,6...
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| Autores principales: | , , |
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| Formato: | JOUR |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_00223263_v54_n8_p1884_Varela |
| Aporte de: |
| Sumario: | The synthesis of 4-thio-D-galactofuranose (15) and derivatives, starting from methyl α-D-glucopyranoside (1), is described. Esterification of 1 with N-benzoylimidazole afforded regioselectively methyl 2,3,6-tri-O-benzoyl-α-D-glucopyranoside (2c). Further sulfonylation of HO-4 of 2c gave methyl 2,3,6-tri-0-benzoyl-4-0-(p-tolyl-sulfonyl)-α-D-glucopyranoside (2e) or methyl 2,3,6-tri-0-benzoyl-4-0-[(p-bromophenyl)sulfonyl]-α-D-glucopyranoside (2f). Nucleophilic substitution of the sulfonyloxy group by thiocyanate led to methyl 2,3,6-tri-0-benzoyl-4-deoxy-4-thiocyano-α-D-galactopyranoside (3). This reaction allowed the simultaneous introduction of a group precursor of thiol and the inversion of the configuration at C-4. Compound 3 was reduced to methyl 4-5-acetyl-2,3,6-tri-0-benzoyl-4-thio-α-D-galactopyranoside (4a) or methyl 2,3,6-tri-0-benzoyl-4-thio-α-D-galacto-pyranoside (4b). The latter was debenzoylated to give methyl 4-thio-α-D-galactopyranoside (5). This product was also obtained by alkaline methanolysis of 3. Ring contraction was achieved by acetolysis of 5, which produced l,2,3,5,6-penta-0-acetyl-4-thio-α-D-galactofuranose (10) and its β-anomer (11) as the main products. The product distribution in the acetolysis reaction of 4-thiopyranose derivatives would depend on the stability of the ionic intermediates involved. O-Deacetylation of 10 led to 4-thio-D-galactofuranose (15). © 1989, American Chemical Society. All rights reserved. |
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