Highly Efficient and Enantiomer-Selective Hydrolysis of α-Amino Acid Active Ester Hydrochlorides by a Cyclic Hexapeptide Containing Histidines

Hydrolysis of various types of ester substrates with linear, cyclic and polymeric peptides containing His, Ser and Asp residues

“…Table 1 shows that the k , y values were smaller than the k z A values in all cases. These results indicate that an effect due to a large steric hindrance of the long alkyl chain in PNPL is more than the expected hydrophobic interaction between the substrate and the catalysts (1,11,15,22), which may accelerate the catal tic reactions. Table 1 also shows that the k& values for the reactions catalyzed by the cyclic and 01 values, while the k c T values for the linear peptides are almost the same as their k e y A values.…”

“…Overberger & Maki (32) reported the contribution of electrostatic force between catalyst and substrate for the ANTI hydrolysis with vinyl polymers containing imidazole and carboxyl groups. Tanihara & Imanishi (12,15) reported the importance of the electrostatic interaction along with the hydrophobic interaction for the solvolysis of various amino acid p-nitrophenyl esters with anionic linear and cyclic peptides. Reactions in the present investigation did not show the remarkable contribution of catalystsubstrate electrostatic interaction.…”

Solution Conformation of Cyclo(D-Leu-L-Glu-L-His)2 and Its Relation with Highly Efficient and Enantiomer-Selective Catalysis

“…1 The 270 MHz 1 H NMR spectrum of cyclo(o-Leu-L-Glu-L-His)z in (CD 3 )zSO was measured using a Bruker WH 270 spectrometer, the internal standard being (CH 3 ) 4 Si. The chemical shift, coupling constant, and isotope (H/D) exchange rate of the amide protons were measured at 23°C.…”

“…In a series of investigations, we succeeded in carrying out the very fast and enantiomerselective hydrolysis of the p-nitrophenyl ester hydrochlorides of leucine [Leu-0Ph(N02) • HCl] and valine [Val-0Ph(N0 2 ) · HCl] by a copper-ion complex of cyclo(n-Leu-L-Glu-L-His)2 consisting of hydrophobic (Leu), anionic (Glu) and nucleophilic (His) oc-amino acid residues. 1 In cyclic compounds, the freedom of internal rotation is severely restricted and therefore the number of available conformations is reduced. This situation is very convenient for investigating on the conformation/reactivity relationship.…”

“…1 In cyclic compounds, the freedom of internal rotation is severely restricted and therefore the number of available conformations is reduced. This situation is very convenient for investigating on the conformation/reactivity relationship.…”