Table 1. Comparison of the Probes’ Affinity to α₁-ARs.

	Kia(nM)			IC50 (nM)
compd	α1A	α1B	α1D	α1A	α1B	α1D
phentolamine	0.6	4.8	7.6	1.1	10.8	12.5
1a	2.1	NAc	NAc	3.9	<5b	<5b
1b	1.3	NAc	NAc	2.5	<5b	<5b
1c	0.3	0.1	0.4	0.6	1.2	2.2
1d	4.7	7.3	20.7	8.8	16.3	34.0
1e	29.9	29.9	27.5	52.4	52.4	45.2

^aK_i was calculated from IC₅₀ using the Cheng–Prusoff equation.

^bData was estimated from the unclassical binding-competitive curve.

^cNot available.