Table 1.

Binding affinity of a series of (N)-methanocarba adenosine derivatives at three subtypes of hARs and the functional efficacy at the hA₃AR.

Compd	Structure		Affinity (Ki, nM) or % inhibitiona			%Efficacyb
	R1 or R3	R2	hA1	hA2A	hA3	hA3
3c	Cl	3-Cl-Bn	260±60	2300±100	0.29±0.04	103±7
4c,d	Cl	3-I-Bn	136±22	784±97	1.5±0.2	100
5c	H	3-I-Bn	700±270	6200±100	2.4±0.5	100
6d	C≡CH	3-Cl-Bn	174±23	(48%)	1.30±0.38	ND
7d	C≡C(CH2)2CH3	3-Cl-Bn	1040±83	(80%)	0.82±0.20	ND
8c,d	Cl	CH3	2100±1700	(6%)	2.2±0.6	ND
9		CH3	(13%±6%)	(14%±7%)	0.85±0.22	89.3±7.7
10		CH3	(11%±4%)	(13%±4%)	1.01±0.36	86.8±9.2
11		CH3	(21%±4%)	(17%±2%)	0.97±0.38	97.7±9.1
12		CH3	(12%±2%)	(10%±5%)	0.97±0.24	95.8±6.7
13		CH3	(21%±11%)	(19%±3%)	0.53±0.09	80.3±5.8
14		CH3	(27%±7%)	(30%±5%)	0.58±0.04	84.2±6.2
15		CH3	(10%±2%)	1270±300	1.60±0.60	90.9±1.9
16		CH3	(14%±1%)	(30%±1%)	1.22±0.31	97.4±9.1
17		CH3	(13%±7%)	(26%±1%)	0.91±0.06	97.5±12.3
18		CH3	(10%±5%)	(19%±14%)	1.07±0.14	109±4.1
19		CH3	(6%±3%)	(6%±6%)	1.65±0.08	108±1.9
20		CH3	(8%±3%)	(47%±4%)	1.66±0.36	99.6±3.3
21		CH3	(13%±3%)	(38%±5%)	3.78±1.16	110±4.9
22		CH3	(23%±5%)	(7%±5%)	10.1±1.9	78.4±6.5
23		CH3	(15%±7%)	5300±600	2.57±0.78	87.4±9.9
24		CH3	(21%±6%)	(29%±8%)	3.10±1.26	110±2.9
25		CH3	(25%±1%)	(34%±8%)	1.67±0.18	94.6±4.4
26		CH3	(15%±5%)	(52%±1%)	3.48±1.36	108±3.5
27		3-Cl-Bn	(20%±3%)	(27%±3%)	1.34±0.30	101±5.9
28		3-Cl-Bn	(20%±6%)	(42%±2%)	2.16±0.34	102±1.4
29		3-Cl-Bn	(19%±2%)	(52%±12%)	1.92±0.57	103±1.5
30		3-Cl-Bn	(4%±4%)	1740±590	4.45±1.39	91.5±11.4
31		3-Cl-Bn	(6%±4%)	(41%±10%)	3.49±1.84	95.7±6.4
32		3-Cl-Bn	1520±300	(44%±4%)	2.27±0.70	76.6±13.1
33		3-Cl-Bn	(6%±5%)	(38%±5%)	6.75±2.78	86.7±5.4
34		3-Cl-Bn	(2%±2%)	(0%±0%)	3.06±1.35	89.0±4.5
35		3-Cl-Bn	(8%±2%)	3110±530	68.3±12.5	77.8±11.6
36		3-Cl-Bn	(11±5%)	(4±3%)	660±170	97.1±3.3

^aAll experiments were done on CHO or HEK293 (A_2A only) cells stably expressing one of three subtypes of the four hARs. The binding affinity for A₁, A_2A and A₃ARs was expressed as K_i values (n = 3–5) and was determined by using agonist radioligands ([³H]N⁶-R-phenylisopropyladenosine 52 (R-PIA), [³H]2-[p-(2-carboxyethyl)phenyl-ethylamino]-5′-N-ethylcarboxamidoadenosine 53 (CGS21680), or [¹²⁵I]N⁶-(4-amino-3-iodobenzyl)adenosine-5′-N-methyl-uronamide 54 (I-AB-MECA), respectively), unless noted.^29–31 A percent in parentheses refers to inhibition of radioligand binding at 10 μM (n = 3).

^bUnless noted, the efficacy at the hA₃AR was determined by inhibition of forskolin-stimulated cAMP production in AR-transfected CHO cells.^32–34 At a concentration of 10 μM, in comparison to the maximal effect of 5′-N-ethylcarboxamidoadenosine 48 (=100%) at 10 μM. Data are expressed as mean±standard error (n = 3).

^cValues from Lee et al.; Tchilibon et al.^15,16

^dValues from Melman et al.²¹

ND, not determined.