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J Med Chem. 2016 Oct 13;59(19):8804-8811. Epub 2016 Sep 21.

Design and Synthesis of an Investigational Nonapeptide KISS1 Receptor (KISS1R) Agonist, Ac-d-Tyr-Hydroxyproline (Hyp)-Asn-Thr-Phe-azaGly-Leu-Arg(Me)-Trp-NH2 (TAK-448), with Highly Potent Testosterone-Suppressive Activity and Excellent Water Solubility.

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Pharmaceutical Research Division, Takeda Pharmaceutical Company Ltd , Fujisawa 251-8555, Japan.
CMC Center, Takeda Pharmaceutical Company Ltd , Osaka 532-8686, Japan.


Metastin/kisspeptin is an endogenous ligand of KISS1 Receptor (KISS1R). Metastin and KISS1R are suggested to play crucial roles in regulating the secretion of gonadotropin-releasing hormone (GnRH), and continuous administration of metastin derivatives attenuated the plasma testosterone levels in male rats. Our optimization studies of metastin derivatives led to the discovery of 1 (Ac-d-Tyr-d-Trp-Asn-Thr-Phe-azaGly-Leu-Arg(Me)-Trp-NH2, TAK-683), which suppressed plasma testosterone in rats at lower doses than those of leuprolide. Although 1 possessed extremely potent pharmacological activity, 20 mg/mL aqueous solution of 1 has a gel formation property. In order to improve this physicochemical property, we substituted d-Trp at position 47 with a variety of amino acids; we identified that substitution with cyclic amino acids, which could change peptide conformation, retained its potency. Especially, analogue 24 (TAK-448) with trans-4-hydroxyproline (Hyp) at position 47 showed not only superior pharmacological activity to 1 but also excellent water solubility. Furthermore, 20 mg/mL aqueous solution of 24 did not show gel formation up to 5 days.

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