TOTAL SYNTHESES OF GLUCOSIDASE INHIBITORS, CYCLOPHELLITOLS

A beta-D-glucosidase inhibitor, cyclophellitol [(1S,2R,3S,4R,5R,6R)-5-hydroxymethyl-7-oxabicyclo[4.1.0]heptane-2,3,4-triol, 1] and its epoxide diastereomer, 1,6-epicyclophellitol (2) have been synthesized by using an intramolecular [3 + 2]-cycloaddition of a nitrile oxide to an alkene as a key step. 2.3,4-Tri-O-benzyl-6,7-dideoxy-D-ido-hept-6-enose (E,Z)-oxime (6) was prepared from L-glucose in 11 steps. Intramolecular cycloaddition of 6 was realized by NaOCl via an intermediary nitrile oxide to afford the isoxazoline, (1S,2R,3S,4S,5R)-3,4,5-tribenzyloxy-2-hydroxy-8-oxa-7-azabicyclo[4.3.0]non-6-enc (7). Hydrogenolysis of 7 followed by a 5-step sequence gave cyclophellitol (1). Compound 2 was synthesized from methyl alpha-D-galactopyranoside by using a conceptually similar route. The glycosidase-inhibiting activities of 2 were examined.