Amino acids and peptides. Part 31. Total synthesis of eglin c. Part 1. Synthesis of a triacontapeptide corresponding to the C-terminal sequence 41–70 of eglin c and related peptides and studies on the relationship between the structure and inhibitory activity against human leukocyte elastase, csthepsin G and α-chymotrypsin

Abstract

The peptides eglin c (41–70), eglin c (60–70), eglin c (50–70) and eglin c (45–70) have been synthesized by a conventional solution method in order to allow us to study the relationship between the structure and their inhibitory activity against human leukocyte elastase, cathepsin G and α-chymotrypsin. Six relatively small peptide fragments were coupled successively from the C-terminus by the azide method to minimize racemization and to avoid the need for protection of side-chain functional groups of the amino acid residues as much as possible during the peptide synthesis. The protected peptides were treated with 1 mol dm^–3 trimethylsilyl bromide in trifluoroacetic acid at 0 °C for 3 h in the presence of thioanisole and m-cresol, followed by purification by Sephadex G-25 column chromatography and preparative reversed phase HPLC to give the desired peptides, which exhibited a symmetrical, single peak on analytical HPLC. Eglin c (60–70) inhibited human leukocyte elastase (K_i 1.7 × 10^–3 mol dm^–3) but not cathepsin G or α-chymotrypsin. Eglin c (50–70) and eglin c (45–70) inhibited leukocyte elastase (K_i 2.0 × 10^–4 and 7.0 × 10^–5 mol dm^–3, respectively) and α-chymotrypsin (K₁ 3.4 × 10^–5 and 2.5 × 10^–5 mol dm^–3, respectively) but not cathepsin G. Eglin c (41–70) inhibited leukocyte elastase, cathepsin G and a-chymotrypsin with K₁-values of 1.2 × 10^–5, 2.1 × 10^–4 and 7.0 × 10^–6 mol dm^–3, respectively, while the K₁-values of acetyleglin c (1–70) for the above enzymes were 5.0 × 10^–9, 1.0 × 1^–9 and 2.3 × 10^–9 mol dm^–3, respectively.