Bun-ichiro Nakajima

Synthesis of linear, cyclic and polypeptides having the sequence -Asp-βAla-Gly-Ser-βAla-Gly-His-βAla-Gly- as catalysts in hydrolytic reactions

Abstract Boc-Asp-βAla-Gly-Ser-βAla-Gly-His-βAla-Gly-OEt, Boc-Asp-βAla-Gly-Ser-βAla-Gly-Ser-βAla-Gly-His-βAla-Gly-OH, cyclo(Asp-βAla-Gly-Ser-βAla-Gly-His-βAla-Gly) and poly(Asp-βAla-Gly-Ser-βAla-Gly-His-βAla-Gly) were synthesized as catalysts in hydrolytic reactions. Asp and Ser residues were protected with a benzyl group, but the His residue was not protected during the synthesis. The protected linear-nonapeptides were prepared by synthesis and subsequent fragment condensation of three kinds of tripeptide which have the sequences-Asp(OBzl)-βAla-Gly-,-Ser(Bzl)-βAla-Gly- and -His-βAla-Gly-, respectively. The protected cyclic-nonapeptide was obtained by cyclization of H-Asp(OBzl)-βAla-Gly-Ser(Bzl)-βAla-Gly-His-βAla-Gly-OH with DCC-HOBr and the subsequent purification by silica gel column chromatography. The protected poly-nonapeptide was prepared by polymerization of H-Asp(OBzl)-βAla-Gly-Ser(Bzl)-βAla-Gly-His-βAla-Gly-OH with DPPA. Deprotection was performed with catalytic hydrogenation for the protected linear- and cyclic-nonapeptides, and with methanesulphonic acid for the protected polynonapeptide, respectively, to give final products. Catalytic actions of the linear-, cyclic- and polypeptides for hydrolysis of p -nitrophenyl acetate are also reported briefly.

Silk fibroin model, poly(l-alanylglycyl-l-alanylglycyl-l-alanylglycyl-l-seryglycine)

Abstract l -Alanylglycyl- l -alanylglycyl- l -alanylglycyl- l -serylglycine and its pentachlorophenyl ester methanesulphonate have been synthesized as monomers for the preparation of silk fibroin model polypeptide. The former octapeptide was polymerized with diphenylphosphorylazide (DPPA) and triethylamine in DMSO or in HMPA—pyridine, and the latter octapeptide pentachlorophenylester was polymerized by adding triethylamine in DMSO to give poly( l -alanylglycyl- l -alanylglycyl- l -alanylglycyl- l -serylglycine). This sequential polypeptide gave a similar i.r. pattern to the crystalline part of Bombyx mori silk fibroin, which indicated antiparallel β-conformation. Dialysis of the solution of this polymer in 60%, aqueous LiBr against water gave mainly the polymer of α-form. O.r.d. measurements suggest that this polypeptide exists as a random structure in dichloroacetic acid on in 60% aqueous LiBr.

Catalytic activity of linear-, cyclic- and polypeptides having a sequence of -Asp-β-Ala-Gly-ser-β-Ala-Gly-His-β-Ala-Gly in the hydrolysis of p-nitrophenyl acetate

Abstract Catalytic activities of Boc-Asp-β-Ala-Gly-Ser-β-Ala-Gly-His-β-Ala-Gly-OEt(Boc-9-Oet), Boc-Asp-β-Ala-Gly-Ser-β-Ala-Gly-His-β-Ala-Gly-OH(Boc-9-OH), cyclo(Asp-β-Ala-Gly-Ser-β-Ala-Gly-His-β-Ala-Gly) (Cyclic 9) and poly(Asp-β-Ala-Gly-Ser-β-Ala-Gly-His-β-Ala-Gly) (Poly 9) in the Hydrolysis of p-nitrophenyl acetate were investigated in detail and compared with each other and with poly(His-β-Ala-Gly) (Poly 3) which has no Ser and Asp residues. Generally, Poly 3 was less active than the others, which contain Ser and Asp residues together with the His residue. The reaction rate-substrate concentration for Boc-9-OEt, Boc-9-OH. Cyclic 9 and Poly 3 gave straight lines, while that for Poly 9 showed slightly the tendency of saturation at high substrate concentration. The reaction rates were all proportional to the concentration of the peptides. All peptides gave similar, sigmoid-type pH-kcat profiles. The pK values obtained from these pH-kcat profiles agreed fairly well with those of histidine residues obtained from 13C n.m.r. chemical shifts, which suggests that the predominant participating functional group in the catalytic reaction is the imidazole group in the histidine residue. The pK values of the His residue in peptides with the -Asp-β-Ala-Gly-Ser-β-Ala-Gly-His-β-Ala-Gly- sequence were shifted to higher pH region compared with Poly 3, suggesting that the effect of the carboxyl group in the Asp residue and the extents of pK-shift for linear peptides were larger than for Cyclic 9 or Poly 9. The catalytic reaction rates by Boc-9-OEt or Cyclic 9 increased steadily with increase in temperature, while the reaction rate-temperature profiles for Poly 9 and Poly 3 gave the optimum temperatures at around 40–50°C.