Synthesis of 4-thio-L-rhamnofuranose

Article abstract of DOI:10.1016/0008-6215(91)89012-5

Sulfonylation of the HO-4 group of methyl 6-deoxy-2,3-O-isopropylidene-α-L-talopyranoside (1) afforded the mesyl (2), nosyl (3), and triflyl (4) derivatives. Attempted nucleophilic displacement of the sulfonyloxy group of 2, 3, and 4 by potassium thiocyanate was unsuccessful. Removal of the isopropylidene acetal from 3 and 4 gave the corresponding 4-nosylate (5) and 4-triflate (6) of methyl 6-deoxy-α-L-talopyranoside. On acetylation, 5 and 6 gave the 2,3-di-O-acetyl derivatives 7 and 8, respectively. Nucleophilic substitution of the sulfonate in 7 and 8 by potassium thiocyanate in N,N-dimethylformamide gave methyl 2,3-di-O-acetyl-4-deoxy-4-thiocyano-α-L-rhamnopyranoside (9) in 28 and 52% yields, respectively. Reduction of the thiocyano group of 9, followed by acetolysis, gave 1,2,3-tri-O-acetyl-4-S-acetyl-4-thio-α-L-rhamnopyranoside (12), which on deacetylation led to 4-thio-L-rhamnose (13). Acetylation of 13 afforded the α (14) and β (15) tetraacetates of 4-thio-L-rhamnofuranose. Sulfonylation of the HO-4 group of methyl 6-deoxy-2,3-O-isopropylidene-α-L-talopyranoside (1) afforded the mesyl (2), nosyl (3), and triflyl (4) derivatives. Attempted nucleophilic displacement of the sulfonyloxy group of 2,3, and 4 by potassium thiocyanate was unsuccessful. Removal of the isopropylidene acetal from 3 and 4 gave the corresponding 4-nosylate (5) and 4-triflate (6) of methyl 6-deoxy-α- L-talopyranoside. On acetylation, 5 and 6 gave the 2,3-di-O- acetyl derivatives 7 and 8, respectively. Nucleophilic substitution of the sulfonate in 7 and 8 by potassium thiocyanate in N,N-dimethyl- formamide gave methyl 2,3-di-O-acetyl-4- deoxy-4-thiocyano-α- L-rhamnopyranoside (9) in 28 and 52% yields, respectively. Reduction of the thiocyano group of 9, followed by acetolysis, gave 1,2,3-tri-O-acetyl-4- S-acetyl-4-thio-α- L-rhamnopyranoside (12), which on deacetylation led to 4-thio-L-rhamnose (13). Acetylation of 13 afforded the α (14) and β (15) tetraacetates of 4-thio-L-rhamnofuranose.