IDENTIFICATION OF COUPLING CONDITIONS PROCEEDING WITH LOW C-TERMINAL EPIMERIZATION DURING THE ASSEMBLY OF FULLY PROTECTED BACKBONE-SUBSTITUTED PEPTIDE SEGMENTS

The coupling of Fmoc-Asp(OBu(t))-L-Phe-OH 1 and H-Lys(Boc)-PepsynKA 2 was used as a model to assess C-terminal epimerization in solid-phase segment condensation. A wide range of coupling reagents and reaction c onditions were examined and an optimal combination of good coupling ra te along with low phenylalanine epimerization was achieved by using 1- hydroxybenzotriazole-catalysed diisopropylcarbodiimide reaction in dic hloromethane. Application of these conditions in the coupling of backb one protected HIV-1(Bru) tat protein related segments(13-mer + resin-b ound 16-mer) gave quantitative reaction within 6 h, and a maximum of < 3% epimerization of C-terminal lysine.