HIGHER SUCROSE ANALOGS - HOMOLOGATION OF A GLUCOSE UNIT OF SUCROSE BY2 CARBON-ATOMS

The primary hydroxyl groups (at C-6 and C-6') in 2,3,4,3'4'-penta-O-be nzyl-1'-O-methoxymethyl sucrose (2) can be reactively differentiated w ith tert-butyldiphenylsilyl chloride. Reaction of 2 with TBDPSCl affor ded only one monosilylated product protected at C-6' (6). The regioiso meric monoprotected sucrose 8 was prepared by selective deprotection o f the double silylated derivative 7. Compound 6 was converted into -ca rbomethoxymethylidene-1'-O-methoxymethylsucrose 10 in three steps. Osm ylation of the double bond in 10 afforded stereoisomeric homologated s ucroses: 11a [6(S),7(R)] and 11b [6(R),7(S)] in the ratio 3:2. A large downfield shift of the H-1 (up to 0.5 ppm) was observed for 6'-silyla ted derivatives.