COLORED PEPTIDES - SYNTHESIS, PROPERTIES AND USE IN PREPARATION OF PEPTIDE SUB-LIBRARY KITS

Several methods were developed for the solid-phase synthesis (SPPS) of coloured peptides and peptide libraries. At first a bifunctional red compound, tyloxycarbonyl)aminopropyl)amino)phenylazo)benzoic acid (Boc -EPAB), was coupled with chloromethyl resin to obtain a new solid supp ort suitable for SPPS using Boc chemistry. Peptides synthesized on thi s coloured resin had the chromophore at their C-termini. N-terminally coloured peptides were synthesized on a traditional solid support, cou pled with chromophoric carboxylic acid before cleavage. A model pentap eptide, Phe-Ala-Val-Leu-Gly, and its ten derivatives were synthesized and their properties studied. It was found that the presence of chromo phores decreases the water solubility of peptides. However, insertion of solubilizing tags (penta-lysine sequences or polyoxyethyl chains) i nto the molecule of any coloured derivative resulted in enhancement of the solubility. The RP-HPLC hydrophobicity indexes (phi(o)) of the co loured peptides were also determined because rp, values are closely re lated to their water solubility. A coloured pentapeptide library was s ynthesized using the portioning-mixing method. Each component of this library contained the red azo dye (EPAB) and the penta-lysine tag. Bef ore the last coupling step the samples were not mixed. All of the 19 s ub-libraries obtained after cleavage were readily soluble in water, gi ving intense red solutions. The effect of chromophore (EPAB) and/or pe nta-lysine solubilizing tag on the biological activity was also studie d. Potencies of the bovine neurotensin 8-13 fragment and its different coloured and penta-lysine derivatives were compared in isolated longi tudinal muscle strips of guinea pig ileum. It was shown that the hexap eptide with penta-lysine tag had almost the same activity as the 8-13 fragment itself The activity of the EPAB-derivative was found to be ra ther low. However, the presence of the solubilizing tag in the coloure d hexapeptide compensated the negative effect of the chromophore. (C) 1998 European Peptide Society and John Wiley & Sons, Ltd.