The aspartimide problem in Fmoc‐based SPPS. Part II

Abstract
The sequence dependence of base‐catalysed aspartimide formation during Fmoc‐based SPPS was systematically studied employing the peptide models H‐Val‐Lys‐Asp‐Xaa‐Tyr‐Ile‐OH. The extent of formation of aspartimide and related by‐products was determined by RP‐HPLC. Considerable amounts of by‐products were formed in the case of Xaa = Asp(OtBu), Arg(Pbf), Asn(Mtt), Cys(Acm) and unprotected Thr. Aspartimide formation could be diminished by incorporation of Asp(OMpe) or by employing milder methods for Fmoc cleavage, e.g. hexamethyleneimine/N‐methylpyrrolidine/HOBt/NMP/DMSO 4 : 50 : 4 : 71 : 71 (v/v/w/v/v). Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.