Table 1.

Binding Affinities and in Vitro Activities for Peptide Derivatives at δ/μ Opioid Receptors

compd	hDORa, [3H]Deltorphinb		rMORa, [3H]DAMGOc		$K_{\mathrm{i}}^{\mu }/K_{\mathrm{i}}^{\delta }$	MVD (δ)	GPI (μ)	IC50 (GPI)/IC50 (MVD)
	log IC50d	Ki (nM)	log IC50d	Ki (nM)		IC50 (nM)e,f	IC50 (nM)e,f
1	−8.84 ± 0.11	0.72	−8.64 ± 0.07	1.1	1.53	33 ± 9.4	50 ± 6.5	1.5
2	−4.97 ± 0.16	240	−6.42 ± 0.08	172	0.72	1300 ± 221	9.2% at 1 μM	>0.75
3	−8.75 ± 0.11	450	−6.90 ± 0.08	57	0.13	1800 ± 266	1700 ± 306	0.9
4	−8.27 ± 0.14	480	−6.87 ± 0.11	62	0.13	710 ± 97	670 ± 139	0.9
Bphg		2.6		1.4	0.54	2.7 ± 1.5	8.8 ± 0.3	3.2

^aDisplacement of [³H]Deltorphin (μ-selective) and [³H]DAMGO (δ-selective) from rat brain membrane binding site.

^bK_d = 0.50 ± 0.3 nM.

^cK_d = 0.50 ± 0.1 nM.

^dThe log IC₅₀ ± standard error are expressed as logarithmic values determined from the nonlinear regression analysis of data collected from at least two independent experiments performed in duplicate. The K_i values are calculated using the Cheng and Prusoff equation to correct for the concentration of the radioligand used in the assay.

^eConcentration at 50% inhibition of muscle contraction in electrically stimulated isolated tissues (n = 4).

^f±SEM.

^gBiphalin (Bhp), refs 1b and 13.