A convergent liquid‐phase synthesis of salmon calcitonin

: Salmon calcitonin (sCT) was prepared in good yield and high purity by the condensation of Nα-Boc-cyclic decapeptide, Boc-C1SNLSTC7VLG-OH (1,7-disulfide), with protected docosapeptide (Psc)LSQE(OPse)LHK(Psc)LQTYPRTNTGSGTP-NH2·3TFA, followed by deprotection of Boc with trifluoroacetic acid and Psc/Pse with piperidine. The 2-(phenylsulfonyl)ethoxycarbonyl (Psc) and2-(phenylsulfonyl)ethyl (Pse) protecting groups were recently developed. The two peptides were built up by stepwise and fragment condensation using appropriate Nα-Boc-amino acids and subsequent deprotection in solution. The synthetic sCT exhibited hypocalcemic potency of more than 4000 IU/mg in rats.