Stereochemical and structural aspects of the variations in the C-terminal residue of L-aspartyl-L-phenylalanine methyl ester have been investigated. Novel configurational analogues such as L-aspartyl-D-alanine benzyl ester and L-aspartyl-D-alpha-aminobutyric acid benzyl ester were found to be sweet. In addition, chiral and achiral alpha, alpha-dialkylglycine and alpha-aminocycloalkanecarboxylic acids were incorporated into the dipeptides. The L-aspartic acid based dipeptide derivatives of alpha-aminoisobutyric acid methyl ester, alpha-aminocyclopropanecarboxylic acid methyl ester, alpha-aminocyclobutanecarboxylic acid methyl ester, and alpha-aminocyclopentanecarboxylic acid methyl ester are sweet. Dipeptides with alpha-aminocyclohexanecarboxylic acid methyl ester and alpha-aminocycloheptanecarboxylic acid methyl ester are bitter, whereas the analogues with alpha-aminocyclooctanecarboxylic acid methyl ester, alpha, alpha-diethylglycine methyl ester, and alpha-aminoisobutyric acid benzyl ester are tasteless. Aspects on chirality and effective volume of the C-terminal residue are discussed and correlated with taste.
Zusammenfassung: Wegen der starken Oxidationsanfälligkeit des Methionin-Restes-15 im Human-Little-Gastrin-I wurden dessen Norleucin-15-, Methoxinin-15-und Leucin-15-Analoga synthetisiert (letzteres nach einer verbesserten Route); für die erforderlichen Vergleichsuntersuchungen wurde auch das [Methionin-15]-Heptadecapeptidamid des natürlichen Hormons erstellt. Der Aufbau der allseits geschützten Heptadecapeptidamide erfolgte unter Optimierung der Fragmentkondensationen. Acidolytische Schutzgruppenabspaltung und anschließende Verteilungschromatographie der erhaltenen Rohprodukte an Sephadex G-25 (fine) führte in guter Ausbeute und hoher Reinheit zu den gewünschten Endprodukten.
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