SOLID-PHASE ASSEMBLY OF BACKBONE AMIDE-PROTECTED PEPTIDE SEGMENTS - AN EFFICIENT AND RELIABLE STRATEGY FOR THE SYNTHESIS OF SMALL PROTEINS

In the preceding paper we showed that epimerization of the C-terminal residue of a fully protected peptide segment was minimized when activa tion (and subsequent coupling) was performed using 1-hydroxybenzotriaz ole-catalysed reaction with diisopropylcarbodiimide in dichloromethane (DCM). Good solubility of the segment in DCM was ensured by the incor poration of appropriately placed N-(2-acetoxy-4-methoxybenzyl) (AcHmb) backbone amide protection into the fully protected peptide. This low- epimerization protocol, combined with our previously described straigh tforward purification of AcHmb-substituted fully protected segments, p rovides an efficient, reliable and flexible strategy for the solid-pha se assembly of small proteins. We describe here the preparation of HIV -1(Bru) tat[1-72, Cys(ACm)(22,25,27,30,31,34,37)] protein through the sequential solid-phase assembly of five backbone-protected segments(11 -17 residues). Individual addition of each segment was very efficient, achieving > 95% acylation using a two-fold excess with reaction for 6 h. The target 72-mer was readily purified and isolated in 38.4% overa ll yield.