Chemical synthesis of urotensin II,a somatostatin-like peptide in the caudal neurosecretory system of fishes

In the goby, Gillichthys mirabilis, urotensin II (a bioactive neuropeptide present in the urophysis of teleost fish) has the dodecapeptide sequence, H₂N-AGTADC-FWKYCV-OH, which is homologous with mammalian somatostatin at positions 1, 2 and 7–9. The Merrifield solid phase synthesis of Gillichthys urotensin II (UII) was accomplished by stepwise assembly from the carboxy terminus using N^α-tert.-butyloxycarbonyl (Boc) amino acids containing benzyl-derived groups for protection of side-chain functionalities. Coupling of amino acids to the growing peptide was mediated by diisopropylcarbodiimide (DIC) in the presence of 1-hydroxybenzotriazole (HOBt). Residual α-amino groups remaining after coupling were blocked by acetylation with 1-acetylimidazole. Crude, synthetic UII was extracted from the HF-treated, protected peptide-resin product, reduced with dithiothreitol (DTT), reoxidized at high dilution with O₂, and separated into its components using a single, preparative, reverse-phase HPLC step. The pure, synthetic UII, obtained in 7.6% yield from oxidized crude UII, was indistinguishable from pure, native UII in specific bioactivity, amino acid sequence, and retention time in each of two different HPLC systems.