Structural functions of taste in the sugar series VII: taste properties of ketoses.

The preferable structural feature for sweetness is a lipophilic moiety, e.g., a five- or six-membered ring with a polar substituent containing an A-H/B system outside the ring. In ketoses, this unit is probably the 1,2-glycol. If a third feature (the lipophilic, gamma, site) is required for the attainment of optimum sweetness and if it is C-6 in ketoses, then this site can accommodate quite a large constituent, both above and below the plane of the ring. The removal of the hydroxyl group from the C-6 hydroxymethyl substituent to yield the 7-deoxy derivatives causes bitterness, thus implicating the primary hydroxymethyl group with bitterness.Therefore, the creation of lipophilic site(s) in the sugar ring causes the realignment of the sugar molecule on the taste receptor surface. The distrubance of the proposed A-H/B system, e.g., the removal of the C-2 hydroxyl group, causes the ring alpha-glycol unit (most likely the ring C-3 and C-4 hydroxyl groups) to function as the A-H/B system.