Expeditious synthesis of tri- and tetrahydroxyazepanes from D-(-)-quinic acid as potent glycosidase inhibitors

(Chemical Equation Presented) Several new stereoisomers of 3,4,6-trihydroxyazepanes and 7-hydroxymethyl-3,4,5-trihydroxyazepanes as well as known 3,4,5-trihydroxyazepanes were synthesized as potent glycosidase inhibitors from D-(-)-quinic acid in an efficient manner. The key step employs dihydroxylation of protected chiral 1,4,5-cyclohex-2-enetriols under RuCl3/NaIO₄/phosphate buffer (pH 7) condition, followed by reductive amino cyclization. We found the choice of an appropriate protecting group to Cl-OH of chiral 1,4,5-cyclohex-2-enetriols would increase the yields of cyclization. The preliminary biological data indicate some of these azepanes possess potent inhibition against α-mannosidase and α-fucosidase.