Synthesis of analogues of the carboxyl protease inhibitor pepstatin. Effects of structure on inhibition of pepsin and renin.

Analogues of the carboxyl protease inhibitor, pepstatin, were synthesized from optically pure forms of N-(tert-butoxycarbonyl)-4-amino-3-hydroxy-6-methylheptanoic acid (Boc-Sta), and the inhibition of pepsin and renin was determined. In addition, the new amino acid (3S,4S)-4-amino-3-hydroxy-5-phenylpentanoic acid [AHPPA] was synthesized and the stereochemistry of the 3 and 4 positions established. The tripeptides isovaleryl-L-valyl-(3S,4S)-4-amino-3-hydroxy-6-methylheptanoyl-L-alanine isoamylamide [Iva-Val-(3S,4S)-Sta-Ala-NHiC5H11] and Iva-Val-(3S,4S)-AHPPA-Ala-NHiC5H11 were found to be potent inhibitors of pepsin with Ki = 1 x 10(-9) and 0.9 x 10(-9) M, respectively. Changing the chirality of the (3S)-hydroxy group to 3R or shortening the peptide chain diminished binding to pepsin over 100-fold. Three structural requirements necessary for potent inhibition of pepsin are proposed.