Structure--sweetness relationship of L-aspartyl dipeptide analogues. A receptor site topology

The relationship between structure and the sweet potency of L-aspartyl dipeptide analogues was investigated by physicochemical parameters and regression analysis. The dipeptide analogues reported were divided into the following four classes: L-aspartic acid amides, L-aspartylaminoethyl esters, L-aspartylaminopropionates, and L-aspartyl-aminoacetates. The analysis carried out for each class indicated that the electron-withdrawing effect of the substituents directed to the peptide bond and the steric dimensions of the molecules are important in eliciting the sweet taste. The values of coefficients of the electronic sigma terms in the correlations for L-aspartic acid amides, L-aspartylaminoethyl esters, and L-aspartylaminopropionates were approximately 0.7, indicating a common basic site on the receptor surface. The value for L-aspartylaminoacetates was approximately 1.5, and this value suggests, together with the factor of the participation of steric parameters, a closer or geometrically more proper fit to the receptor, explaining the generally higher potency of this class compared to the other three. The receptor model drawn based on these quantitative analyses appears to be consistent with other classes of sweeteners of apparently unrelated structures.