Table I.

Affinities of adenosine derivatives at rat brain A₁, A_2a, and A₃ receptors, arranged in order of decreasing affinity at rat A₃ receptors.^a

Compound	R1	R2	R3	Ki (μM)
				Ki(A1)	Ki(A2a)	Ki(A3)
1b	CH3NHCO	Cl	3-I-Bz	0.82	0.47	0.00033
2c	CH3NHCO	H	3-I-Bz	0.054	0.056	0.0011
3d	CH3NHCO	H	3-I-4-NH2-Bz	0.018	0.197	0.0013
4	CH3NHCO	CH3S	3-I-Bz	2.140	3.210	0.0023
5	CH3NHCO	CH3NH	3-I-Bz	4.89	4.12	0.00312
6e	EtNHCO	H	Bz	0.087	0.095	0.0068l
7	HOCH2	H	3-I-Bz	0.02	0.0175	0.0095
8f	CH3NHCO	H	H	0.0836	0.0668	0.072l
9g	EtNHCO	H	H	0.0063	0.0103	0.113l
10h	HOCH2	H	4-NH2-(CH2)2	0.014	0.172	0.116
11i	HOCH2	Cl	cyclopentyl	0.0006	0.95	0.237l
12j	HOCH2	H	cyclopentyl	0.00059	0.462	0.24l
13k	EtNHCO	NH(CH2)2-φ-p-(CH2)2-COOH	H	2.6	0.015	0.584l
14	HOCH2	Cl	H	0.0093	0.063	1.89l

^aK_i ± SEM determined in radioligand binding assays expressed in μM (n = 3–6), using the following radioligands: A₁, [³H]PIA in rat cortical membranes; A_2a, [³H]CGS 21680 binding in rat striatal membranes; A₃, [¹²⁵I]AB-MECA binding, unless noted, in membranes of CHO cells stably transfected with the rat A₃-cDNA. A percent value indicates the percent displacement of radioligand at the concentration (M) given in parentheses.

^bCl-IB-MECA;

^cIB-MECA;

^dI-AB-MECA;

^eBz-NECA;

^fMECA;

^gNECA;

^hAPNEA;

ⁱCCPA;

^jCPA;

^kCGS 21680.

^lA₃ affinity determined versus [¹²⁵I]APNEA binding.