Esterase-catalysed regioselective 6-deacylation of hexopyranose per-acetates, acid-catalysed rearrangement to the 4-deprotected products and conversions of these into hexose 4- and 6-sulfates

The esterase from Rhodosporidium toruloides has been used to catalyse the hydrolysis of a series of per-acetylated alpha-D-hexopyranoses and alpha-D-hexopyranosides. Per-acetylated glucose 4, mannose 6, N-acetylgalactosamine 8, galactose 10, methyl alpha-D-glucoside 12, methyl alpha-D-mannoside 14 and methyl alpha-D-galactoside 16 have been selectively cleaved at the C-6 position by the esterase to give the 6-OH derivatives 5, 7, 9, 11, 13, 15 and 17. Acid-catalysed rearrangement of acetates 5, 7, 13, 15, 11, 17 and 9 with 4-->6 acetyl migration gives the corresponding 4-deprotected derivatives 22-28, respectively. Hydrolyses of beta-D-glucose pentaacetate 20 and alpha-D-lactose octaacetate 21 have been attempted, but no hydrolyses have been observed. 1,2,3,6-Tetraacylated alpha-D-hexopyranoses 3 and 22, derivatives of N-acetylglucosamine and glucose respectively and 2,3,6-triacetylated alpha-D-hexopyranosides 24 and 25, derivatives of glucose and mannose, respectively, have been hydrolysed by the esterase to the corresponding 4,6-dihydroxy acetates 29, 18, 30 and 31. Acylation of methyl alpha-D-glucopyranoside 32 catalysed by the esterase provides the C-6 monoacetate 33 and the C-3 monoacetate 34 in 4 and 5% yield, respectively. The sodium salts of N-acetylglucosamine, glucose, N-acetylgalactosamine, galactose and mannose 6-sulfates 38-42, respectively, are prepared in two steps from the 6-deacetylated hexopyranoses 2, 5, 9, 11 and 7, respectively. The sodium salts of N-acetylglucosamine, glucose and mannose 4-sulfates 43-45, respectively, are prepared in two steps from the 4-deacetylated precursors 3, 22 and 26 which are obtained via acid catalysed 4-->6 acyl migration of compounds 2, 5 and 7.