New tris-alkoxycarbonyl arginine derivatives for peptide synthesis

α‐Alkoxycarbonyl protected ornithines were treated with N,N′‐[Z(2Cl)]2‐S‐methylisothiourea and N,N′‐[Z(2Br)]2‐S‐methylisothiourea, N,N′‐Z2‐S‐methylisothiourea and N,N′‐Boc2‐S‐methylisothiourea to form Nα, ω, ω′‐tris‐alkoxycarbonyl arginines. Two of them, Boc‐Arg‐{ω,ω′‐[Z(2Br)]2}‐OH and Boc‐Arg‐{ω,ω′‐[Z(2Cl)]2}‐OH, were used for the synthesis of dermorphin fragments containing two or three arginine residues. Examination of the products by HPLC and ESI‐MS revealed that the purity of the materials obtained with the use of the new derivatives was higher than that obtained in concurrent syntheses in which Boc‐Arg(Tos) was used. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd.