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

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Abstract
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 Nα‐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.