Table 2.

K_i values for the binding affinity of chalcone derivatives (15–36) against rat (r) A₁ and A_2A ARs

#	Ring A			Ring B					Ki ± SEM (µM)a [specific binding (%)]b
	2	3	4	2′	3′	4′	5′	6′	rA1c vs [3H]DPCPXe	rA2Ad vs [3H]NECAf
	R1	R2	R3	R1′	R2′	R3′	R4′	R5′
Structural modification of ring A
15	H	H	H	H	H	H	H	H	(35)	(79)
16	OH	H	H	H	H	H	H	H	(65)	(129)
17	H	H	OH	H	H	H	H	H	(56)	(83)
18	H	H	OCH3	H	H	H	H	H	(141)	(106)
19	H	H	Br	H	H	H	H	H	(117)	(117)
Structural modification of ring B
20	H	H	H	H	OH	H	H	H	(32)	(40)
21	H	H	H	H	OCH3	H	H	H	(33)	(106)
22	H	H	H	H	H	OCH3	H	H	(45)	(78)
23	H	H	H	OCH3	H	OCH3	H	H	(30)	(50)
24	H	H	H	OCH3	H	OCH3	OCH3	H	5.3 ± 1	(28)
25	H	H	H	OCH3	H	OCH3	H	OCH3	(27)	(28)
26	H	H	H	Br	H	H	H	H	(24)	(50)
27	H	H	H	H	Br	H	H	H	(28)	(42)
28	H	H	H	H	H	Br	H	H	(110)	(91)
29	H	H	H	Cl	H	H	H	H	6.1 ± 1.1	(42)
30	H	H	H	H	Cl	H	H	H	(23)	(88)
31	H	H	H	H	Cl	Cl	H	H	(114)	(77)
32	H	H	H	H	H	F	H	H	(49)	(98)
33	H	H	H	H	H	CF3	H	H	(80)	(156)
34	H	H	H	H	CN	H	H	H	(52)	(155)
35	H	H	H	–	–	–	–	–	(55)	(75)
36	H	OCH3	H	–	–	–	–	–	(43)	(73)

^aAll K_i values were determined in triplicate and expressed as mean ± standard error of the mean (SEM) in µM

^bSpecific binding (%) of the radioligand at a maximum tested concentration of 100 µM were determined in duplicate and expressed as the mean in %

^cRat receptors were used (rA₁: rat whole brain membranes)

^dRat receptors were used (rA_2A: rat striatal membranes)

^e0.1 nM [³H]DPCPX

^f4 nM [³H]NECA