Highly potent growth hormone secretagogues

During an effort to search for more potent growth hormone secretagogues, we discovered a class of compounds of which the best compound 8 was 7-fold more active in vitro than the best compound in the series we revealed before [Tata, J. R.; Lu, Z.; Jacks, T. M.; Schleim, K. D.; Cheng, K.; Wei, L.; Chan, W.-S.; Butler, B.; Tsou, N.; Leung, K.; Chiu, S.-H. L.; Hickey, G. J.; Smith, R. G.; Patchett, A. A. Bioorg. Med. Chem. Lett.1997, 7, 2319.]. Animal studies show that compound 8 can stimulate growth hormone release at the oral dose as low as 0.06 mpk. Chemistry and biological studies are discussed.