manno- and altro-Sucrose, and some amino-analogues

Preparatively useful procedures were developed for the conversion of sucrose into isomers with manno- and altro-configuration in the pyranoid moiety. The key compound was the 2-triflate-heptaacetate, generated from the readily accessible 3,4,6,1′,3′,4′,6′-hepta-O-acetylsucrose by standard triflation. SN2-Displacement on the triflate by acetate ion (→ manno-sucrose) or azide ion (→ manno-sucrosamine) proceeded in high yields, and on exposure to deacetylation conditions displacement was effected by the liberated 3-OH resulting in the manno-sucrose-2,3-epoxide; ring opening of the latter epoxide with water, ammonia, or azide proceeded in diaxial fashion to provide altro-sucrose, and its 3-amino and 3-azido derivatives, respectively. Sweetness evaluations proved manno-sucrose to be about 5 times less sweet than sucrose, whereas the altro-isomer was devoid of sweetness, correlating well with our refined AH-B-X structure-sweetness concept.