Poly(L‐histidyl‐L‐alanyl‐α‐L‐glutamic acid). I. Synthesis

Abstract

SynopsisPoly(L-histidyl-L-alanyl-a-L-glutamic acid) has been prepared in order to test the acid-base catalytic ability of a carboxyl-imidazole hydrogen-bonded system. Two different blocked histidyl-alanyl-glutamic acid monomers were used in the polymerization step. The imidazole ring was blocked with either a dinitrophenyl or a t-butyloxycarbonyl group. The y-carboxyl of glutamic acid was protected as the benzyl ester. Both the coupling reactions and the polymerization step were via the N-hydroxysuccinimide active ester method. Thiolysis removed the dinitrophenyl group, while hydrogen bromide removed the t -butyloxycarbonyl and the benzyl groups. The water-soluble unblocked polymers obtained were fractionated on Sephadex G-50 or Bio-Gel P30. Fractions within a range of average molecular weights of 2,000 to 25,000 were isolated. Enzymatic oxidation of the acid hydrolyzate of the polymers revealed that no detectable racemization had occurred.

Synthesis and β‐conformation of sequential polypeptides containing arginine, histidine, and leucine

“…The synthesis of poly(G1u-His-Lys-Tyr) using free histidine and dicyclohexylcarbodiimide was reported by Vajda.7 However, free histidine, when used together with p-nitrophenyl esters, introduced some undesirable side reactions, leading to insoluble polymers, as found by Trudelle in our laboratory (unpublished results). Poly(HisAla-Glu) was prepared by Goren et al 8 The imidazole ring was blocked with either dinitrophenyl (DNPIg or t-butyloxycarbonyl (Boc)lo groups. Thiolysis was used to remove the dinitrophenyl groups.…”

Poly(L‐lysyl‐L‐alanyl‐α‐L‐glutamic acid). II. Conformational studies

“…[0I208 -4000 fH 33,000 -4000 where fH is the fractional a-helix content and [8]208 is the ellipticity of a polypeptide solution at 208 nm. b) In the "2-wavelength method" the ellipticity a t 210 nm ([19]2~0) and 225 nm ([8lZz5) of a polypeptide may be described by the following equations: …”

“…c) The "3-wavelength method" is based on the same equations for [dl210 and [8]225 as for the "2-wavelength method" plus the following equation for [dlzig: …”

“…Circular dichorism (CD) studies on poly(His-Ala-Glu) (pH 2-9) demonstrated that the poly amino acid assumed a random conformation and could be made partially a-helical in the presence of high concentrations of trifluoroethanol. 8 The non-a-helical nature of poly (His-Ala-Glu) is probably due to electrostatic repulsive forces between the histidine side chains and between the glutamic acid side chains (ith and (i + 3rd) residue. Since the lysyl side chain is further away from the peptide backbone and has greater freedom of movement, it may be envisioned to have a less disruptive force on an a-helical conformation of poly(Lys-Ala-Glu).…”