DIRECT PREPARATION OF 1,2/3,5-DI-O-CYCLOHEXYLIDENE-ALPHA-D-XYLOFURANOSE FROM CORNCOBS AND ITS CONVERSION TO 1-O-ACETYL-2,3,5-TRI-O-BENZOYL-D-RIBOFURANOSE

A novel synthesis of 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose (I) has been described starting from 1,2:3,5-di-O-cyclohexylidene-alpha-D-xylofuranose (II), obtained directly from the crude xylose syrup originated from corncobs. Partial acid hydrolysis of II gave 1,2-O-cyclohexylidene-alpha-D-xylofuranose (III). Selective benzoylation of primary C-5 hydroxyl group of III followed by tosylation of C-3 hydroxyl group afforded IV in an overall yield of 67%. Mild acid methanolysis of IV gave the corresponding methyl xylofuranosides V which were further benzoylated to afford 2,5-di-O-benzoyl derivatives VI in 65% yield. Solvolysis of VI in 95% DMF gave a mixture of 2,5- and 3,5-di-O-benzoylribofuranosides VII, which were subsequently converted into the corresponding tribenzoates VIII. An acetolysis of VII afforded I in an overall yield of 96% related to VI.