. Author manuscript; available in PMC: 2008 Aug 25.

Published in final edited form as: J Med Chem. 2006 Apr 20;49(8):2496–2511. doi: 10.1021/jm0512037

Table 1.

Relative Binding Affinity (RBA)^a of Cyclofenil Derivatives for the Estrogen Receptors α and β.


#	structure	RBA (E₂ = 100)^a		β/α^b	#	Structure	RBA (E₂ = 100)^a		β/α^b
#	structure	ERα	ERβ	β/α^b	#	Structure	ERα	ERβ	β/α^b
2		5.61	20.5	3.7	27		4.88	2.82	0.58
3		17.8	137	7.7	28		3.77	1.45	0.38
4		124	285	2.3	21a		6.77	3.02	0.45
5		110	354	3.2	21b		10.7	1.72	0.16
29a		66.5	274	4.1	37b		122	129	1.1
29b		62.7	75.6	1.2	37c		160	91.4	0.57
20		27.0	61.8	2.3	35a		24.8	39.6	1.6
26a		18.1	41.5	2.3	35b		33.9	57.6	1.7
26b		15.9	18.9	1.2	35c		47.2	46.1	0.98
18		0.327	0.307	0.94	30a		23.7	36.5	1.5
24a		0.846	0.841	0.99	32		58.5	10.3	0.18
24b		2.61	0.372	0.14	30b		19.5	0.234	0.012

Relative Binding Affinity (RBA) values are determined by a competitive radiometric binding assay with [³H]estradiol and full length human ERα and ERβ, using methods described in the Experimental Section. The RBA of estradiol (E₂) is defined as 100, and the measured RBA values represent the mean of two or more independent determinations (CV <0.3).

The binding affinity of the tracer estradiol to the ERs is K_d(ERα) = 0.2 nM and K_d(ERβ) = 0.5 nM. Thus, on an absolute scale of binding affinities, the β/α ratios would be reduced by a factor of 2.5.