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. Author manuscript; available in PMC: 2011 Feb 18.

Published in final edited form as: J Org Chem. 2009 Dec 18;74(24):9245–9264. doi: 10.1021/jo901767e

Table 3.

Comparative Biological Activities of the Four Isomers of Ac-Nle-c-[Asp-His-DPhe-Arg-βMeTrp-Lys]-Nle at the MC1Rs in Frogs and Humans

peptide	frog skin MC1R		hMC1R binding
peptide	EC₅₀ (nM)	relative potency	IC₅₀ (nM)	relative potency
MT-II	0.10	1.0	0.50	1.0
[(2S,3S)-β-MeTrp⁹]-MT-II	0.44	0.23	0.50	1.0
[(2R,3S)-β-MeTrp⁹]-MT-II	0.06	1.6	3.0	0.17
[(2S,3R)-β-MeTrp⁹]-MT-II	29	0.0035	15	0.030
[(2R,3R)-β-MeTrp⁹]-MT-II	0.30	0.30	2.0	0.25