Chymotrypsin inhibitory conformation induced by amino acid side chain–side chain intramolecular CH/π interaction
摘要:
Dipeptide amides H-D-Leu-Phe-NH-R have been found to assume a conformation induced by the CH/pi interaction and to inhibit chymotrypsin strongly. A series of benzyl amide derivatives H-D-Leu-Phe-NH-[CH2](n)-C6H5 (n = 0-4) have been assayed for chymotrypsin, They inhibit the enzyme in a competitive manner and the highest inhibition is achieved by the amide of n = 1 (K-1 3.6 x 10(-6) M), The activity enhancement is dependent upon the length of methylene chain, not upon the increase in molecular hydrophobicity, indicating the presence of an optimal distance between dipeptide backbone and C-terminal phenyl group for chymotrypsin inhibition, The C-terminal phenyl group has been found to interact with chymotrypsin stereospecifically, The R-isomer of H-D-Leu-Phe-NH-CH(CH3)-C6H5 is as active as the benzyl amide, while the S-isomer is about twenty-fold less active, When the fluorine atom is introduced at a para-position of the C-terminal phenyl group, the resulting dipeptide H-D-Leu-Phe-NH-CH2-C6H4F-p exhibits about six-times increased inhibitory activity (K-1 = 6.1 x 10(-7) M; this dipeptide is one of the most potent chymotrypsin inhibitors to date), H-1 NMR conformational analyses of these dipeptide amide derivatives show the CH/pi: interaction between D-Leu-isobutyl and Phe-phenyl as a key structural element for chymotrypsin inhibition, These structural examinations strongly suggest that in the inhibitory conformation the C-terminal phenyl group fits the chymotrypsin S-1 site, while the hydrophobic core constructed by D-Leu-Phe CH/pi interaction fits the chymotrypsin S-2 or S-1' site.
Structure−Activity Relationships on Phenylalanine-Containing Inhibitors of Histone Deacetylase: In Vitro Enzyme Inhibition, Induction of Differentiation, and Inhibition of Proliferation in Friend Leukemic Cells
摘要:
Inhibitors of histone deacetylases (HDACs) are a new class of anticancer agents that affect gene regulation. We had previously reported the first simple synthetic HDAC inhibitors with in vitro activity at submicromolar concentrations. Here, we present structure-activity data on modifications of a phenylalanine-containing lead compound including amino acid amides as well as variations of the amino acid part. The compounds were tested for inhibition of maize HD-2, rat liver HDAC, and for the induction of terminal cell differentiation and inhibition of proliferation in Friend leukemic cells. In the amide series, in vitro inhibition was potentiated up to 15-fold, but the potential to induce cell differentiation decreased. Interestingly, an HDAC class selectivity was indicated among some of these amides. In the amino acid methyl ester series, a biphenylalanine derivative was identified as a good enzyme inhibitor, which blocks proliferation in the submicromolar range and is also a potent inducer of terminal cell differentiation.
In this study, we report aminoacidamidation using hexylsilane and a catalytic amount of 1,2,4-triazole. The conventional protection/deprotection method for the α-amino group of aminoacids is not required. The corresponding α-amino amides were obtained in moderate to good yields with low to no racemization.