Studies on Peptides. XCV. Alternative Synthesis of Porcine Vasoactive Intestinal Polypeptide (VIP)

Two alternative deprotecting procedures were employed for the synthesis of porcine vasoactive intestinal polypeptide (VIP). Besides HF, TFA-thioanisole was found to cleave all the protecting groups employed, Z, Bzl and Mts, suppressing a newly found side reaction, i.e., acid-catalyzed succinimide formation from Asp residues with the free carboxyl group. A small amount of the N-terminal His residue linked to Ser-Asp was found to be released on standing at pH 6.