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.
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Takeyama et al. (1980) studied this question.
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