Design of serine protease inhibitors with conformation restricted by aminoacid side-chain-side-chain CH/pi interaction

A novel type of conformationally restricted peptides with the structure of H-D-Xaa-Phe-NH-CH2-C6H5 has been developed as inhibitors of serine proteina se chymotrypsin. The D-Xaa-alkyl and Phe-phenyl groups resulted in a format ion of the hydrophobic core due to the side-chain-side-chain CH/pi interact ion. Their spatial proximity was evidenced by 400 MHz H-1-nmr measurements, observing large upfield shifts of proton signals of D-Xaa-alkyl and nuclea r Overhauser effect (NOE) enhancements between the D-Xaa-alkyl and Phe-phen yl groups. This conformational restriction brought by CH/pi interaction pro duced an inhibitory structure, in which the C-terminal amide-benzyl group f its the chymotrypsin S-1 site and the hydrophobic core binds to the S-2 sit e. The inhibitory conformation was demonstrated crystallographically for th e complex between the dipeptide H-D-Leu-Phe-NH-CH2-C6H4(p-F) and gamma-chym otrypsin. Derailed structure-activity studies have substantiated the struct ure of dipeptides in the active center of the enzyme. (C) 1999 John Wiley & Sons, Inc.