SYNTHESIS OF PROTECTED SECRETIN_16–27 ON A MERRIFIELD RESIN

The partially protected dodecapeptide to secretin, H ‐ Ser(Bzl) ‐ Ala ‐ Arg(Tos) ‐ Leu ‐ Gln ‐ Arg(Tos) ‐ Leu ‐ Leu ‐ Gln ‐ Gly ‐ Leu ‐ Val ‐ NH₂ (protected secretin_16–27) was prepared using a standard Merrifield resin and solid phase synthesis methods. For comparative purposes the unprotected peptide also was prepared on a benzhydrylamine resin. Contrary to previous reports, the valine C‐terminal peptide can be cleaved from the resin and the amide obtained in high yield. A variety of conditions were examined to accomplish the cleavage of the peptide from the resin in its carboxamide terminal form. The best conditions found were transesterification followed by ammonolysis in a mixed solvent system. A thin‐layer chromatography system which clearly separates the methyl ester and carboxamide terminal secretin_16–27 was developed.