Enantiomeric synthesis of polyhydroxylated indolizidine analogues related to castanospermine: 1-Deoxy-7-epicastanospermine and 1,7-dideoxy-7-fluorocastanospermine

Abstract

(6S,7S,8R,8aR)-6,7,8-Trihydroxyindolizidine (i) and its (7R)-deoxyfluoro analogue (2) was synthesised from 5,8-benzyloxycarbonylimino-5,6,7,8-tetradeoxy-1,2-O-isopropylidene- α-D-gluco-octose (3). The key step is an oxidation-reduction sequence. Introduction of a fluoro substituent at C-3 (6) was readily effected by displacement of the 3-trifluoromethanesulfonyl (triflate) group with tris-(dimethylamino)-sulfonium-difluorotrimethylsilicate (TASF).