The Shallenberger AH,B theory of sweetness' suggests that the fundamental unit of sweetness of a compound is an AH,B system, where A and B are each electronegative atoms in suitable geometric proximity. This unit can hydrogen bond with a complementary AH,B system in the receptor protein of the taste bud so that the resulting doubly hydrogen-bonded complex gives rise to the sweet stimulus. The Kier3 extension to the AH,B system is that a third hydrophobic (y) site is required to determine the intensity of the response. In sugars, the AH,B system can be a glycol group and the ideal sugar for taste studies is probably cy,a-trehalose. From the comparative taste of a series of deoxy derivatives of cw,a-trehalose and methyl cu-D-ghicopyranoside, it was found4 that there is a marked decrease in sweetness of the 3-deoxy derivatives, although a potential hydrophobic centre has been created. This accounts for our interest in the molecular and X-ray structure of 3,3'-dideoxy-a,a-arubio-trehalose
(1). 1 3~'-Dideoxya,a-ambinotrehalose The molecular structure of 3,3'-dideo~~,a-urubo-trehalose monohydrate, with the atomic numbering and molecular packing in the crystal, are shown Figs. 1 * Crystal Structure of Trehalose Derivatives. Part 2. For Part 1, see ref 1.