No abstract

Anion-exchange resin Amberlite IRA-410 was found to be an effective and selective reagent for the nucleophilic displacement of primary tosyloxy (mesyloxy) groups in 3,5-disulfonates of xylofuranose derivatives I and III, as well as in 3,5,6-trisulfontes and 3,6-ditosyl derivatives of glucofuranose V, VII and IX. In all examined cases only the primary sulfonyloxy groups were replaced with chloride anions, whereupon the corresponding terminal chlorodeoxy derivatives were obtained in good yields.

The reactivity of the oxetane ring in 3,5-anhydro-1,2-O-cyclohexylidene- -D-xylofuranose (1) was exemplified by its regiospecific nucleophilic opening. The action of concentrated hydrobromic or hydroiodic acid on 1 resulted in the exclusive formation of the 5-deoxy-5-halo derivatives, while the action of acetyl chloride or acetyl bromide yielded the corresponding 3-O-acetyl-5-deoxy-5-halo derivatives in 70 - 90 % yield. Under strongly acidic reaction conditions, the protection of the cyclohexylidene acetal function remained intact.

The diastereoisomeric 1,2-O-cyc~ohexy~idene-~-~-xylofuranose 3,5-O-methylphosphonates have been synthesized as a mixture and separated by chromatography to give the pure (R,) and (S,) forms. The related thiono-and selenono-phosphonates have also been obtained. Their 13C, 'H, 31P, and 77Se NMR spectra are discussed and NOE experiments have been used to determine the chirality at phosphorus.

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-α-D-xylofuranose (II), obtained directly from the crude xylose syrup originated from corncobs. Partial acid hydrolysis of II gave 1,2-O-cyclohexylidene-α-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 VIII afforded I in an overall yield of 96% related to VI.