Table 3.

Adenosine receptor affinities and selectivities of 2-phenylimidazo[2,1-i]purin-5-one derivatives

Compd	R2	R4	R8	Ki (nM)±SEM or % displacement at concentration indicated (in brackets)
				A1 Affinity rat brain cortical membranes [3H]CCPA	A1 Affinity human brain cortical membranes [3H]CCPA	A2A Affinity rat brain striatal membranes [3H]MSX-2	A2A Affinity human brain caudate-putamen membranes [3H]CGS-21680	A3 Affinity human recombinant receptors [125I]AB-MECA
N1/N9-unsubstituted imidazopurinones
R-1 (PSB-11)	Phenyl	Methyl	(R)-Ethyl	44013a	1640±50	210013b	1280±430	2.313 3.5±0.39c
S-1	Phenyl	Methyl	(S)-Ethyl	11513a	305±25	330013b	440±80	9.813
2	Phenyl	Methyl	H	2230±200	n.d.d	14,100±4,460	n.d.	18,900±3200
S-3	Phenyl	Propyl	(S)-Ethyl	7.4±1.4	98±12	863±203	3400±2400	860±640
S-4	3,4-Dichlorophenyl	Propyl	(S)-Ethyl	46±1	n.d.	26%e (2.5 μM)	n.d.	116±17
S-5	2-chlorophenyl	Methyl	(S)-Ethyl	17±1	90±11	4170±350	2500±1200	420±340
S-6	3-Chlorophenyl	Methyl	(S)-Ethyl	30±2	n.d.	2530±240	n.d.	184±129
S-7	4-Chlorophenyl	Methyl	(S)-Ethyl	63±20	n.d.	2630±320	n.d.	12±1
R-8 (PSB-10)	2,3,5-Trichlorophenyl	Methyl	(R)-Ethyl	805±55	1700±200	6040±260	2700±500	0.433±0.045c 0.997±0.311f
N9-methylated derivatives
S-9	3,4-Dichlorophenyl	Propyl	(S)-Ethyl	2800±1,100g	36,000±16,500g	13,000±2,000g	6600±600g	2350±1150f,g
R-10	2,3,5-Trichlorophenyl	Methyl	(R)-Ethyl	12%±1e (10 μM)	35,500±18,500g	17%±1e (10 μM)	0%e (10 μM)	395±55f

^aDetermined versus [³H]CHA.

^bDetermined versus [³H]CGS21680.

^cDetermined versus [³H]NECA.

^dn.d. = not determined.

^ePercentage inhibition at concentration indicated.

^fDetermined versus [³H]PSB-11.

^gEstimated value; full curve could not be determined due to limited water solubility.