title: Chymotrypsin inhibitory conformation of dipeptides constructed by side chain-side chain hydrophobic interactions.
abstract: A complete series of configurational isomers (L-L, L-D, D-L and D-D) of a dipeptide Leu-Phe benzyl ester have been synthesized and assayed for chymotrypsin. In the conformational analysis by 400 MHz 1H NMR, the L-D and D-L isomers, but not the L-L and D-D isomers, showed fairly large upfield shifts (0.2-0.4 ppm) of Leu-beta CH2 and gamma CH proton signals, indicating the presence of shielding effects from the benzene ring. In addition to distinct signal splitting of Phe-beta CH2, the NOE enhancement observed between Leu-delta CH3 and Phe-phenyl groups revealed that these groups are in close proximity. These data indicated that L-D and D-L isomers form a hydrophobic core between side chains of adjacent Leu and Phe residues. When the dipeptides were examined for inhibition of chymotrypsin using Ac-Tyr-OEt as a substrate, the L-L isomer showed no inhibition, itself becoming a substrate. However, the other three isomers inhibited chymotrypsin in a competitive manner, and the D-L isomer was strongest with Ki of 2.2 x 10(-5) M. It was found that the D-L isomer was only slowly hydrolysed but the L(or D)-D isomer was not. H-D-Phe-L-Leu-OBzl with the inverse sequence of H-D-Leu-L-Phe-OBzl inhibited chymotrypsin more strongly (Ki = 6.3 x 10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sakamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Shimohigashi
authors.forename: I
authors.initials: I
authors.lastname: Maeda
authors.forename: T
authors.initials: T
authors.lastname: Nose
authors.forename: K
authors.initials: K
authors.lastname: Nakashima
authors.forename: I
authors.initials: I
authors.lastname: Nakamura
authors.forename: T
authors.initials: T
authors.lastname: Ogawa
authors.forename: K
authors.initials: K
authors.lastname: Kawano
authors.forename: M
authors.initials: M
authors.lastname: Ohno
mesh_terms: D002918:Chymotrypsin / Q000037:antagonists & inhibitors*; D004151:Dipeptides / Q000737:chemistry* / Q000494:pharmacology*; D007536:Isomerism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D004151:Dipeptides; D002918:Chymotrypsin