Structure–Taste Relationships of Aspartyl Tetrapeptide Esters

A series of fourteen analogues of l-α-Asp–Gly–Gly–Gly–OMe has been synthesized in relation to structural features of sweet peptides. The rule in the structure-taste relationships of tripeptides barely applies to the aspartyl tetrapeptide esters. In order for the aspartyl tetrapeptide esters to be sweet, the second amino acid must have a d-configuration and a small, compact alkyl side chain. However, the sweetness was accompanied by a bitter or astringent taste. Moreover, some of the tetrapeptides were not sweet but bitter, though they satisfied the requirements for sweet peptides. With increasing length of a peptide, it becomes difficult to fit the deep receptor pocket.