Table 2. Structure and IC₅₀ values of substituted quinolines for inhibition of chymotryptic activity of the 20S proteasome. All IC₅₀ values are averages of two independent experiments (each performed in triplicate).

	R1	R2	R3	R4	R5	IC50
BTZ	—	—	—	—	—	0.0062 (±0.0003)
7	CH3		CH3	H	CH3	14.4 (±0.5)
8	CH2CH3		CH3	H	CH3	19.9 (±0.7)
9	H		CH3	H	CH3	13.8 (±1.3)
10	CH2CH3		CH3	H	CH3	>25.0
11	CH3		CH3	H	CH3	8.2 (±1.2)
12			CH3	H	CH3	>25.0
13	CH3		H	H	H	>25.0
14	H		Cl	H	Cl	>25.0
15	H		Br	H	Br	>25.0
16	CH3		H	Br	H	9.9 (±0.6)
17	CH3		H	Cl	H	>25.0
18	CH3		H	F	H	>25.0
19	CH3		H	CH3	H	8.5 (±0.1)
20	CH3		H	(CH2)3CH3	H	7.6 (±1.3)
21	H		H	N(CH3)2	H	6.3 (±0.3)
22	CH3		H	N(CH3)2	H	6.1 (±0.2)
23	CH2CH3		H	N(CH3)2	H	5.6 (±0.4)
24	CH3		H		H	9.1 (±0.5)
25	CH3		H		H	5.4 (±0.1)
26	CH3		H	OCH3	H	>25.0
27	CH3		OCH3	OCH3	OCH3	15.6 (±0.7)
28	H		H	N(CH3)2	H	5.5 (±0.8)
29	CH3		H	N(CH3)2	H	6.7 (±0.2)
30	CH3		H	CH(CH3)2	H	7.8 (±0.1)
31	H	C(CH3)3	H	N(CH3)2	H	>25.0
32	(CH2)3CH3	H	H	N(CH3)2	H	>25.0
33	CH2CH3	CH2CH3	H	N(CH3)2	H	18.7 (±1.0)
34	CH3		H	N(CH3)2	H	10.0 (±0.6)
35			H	N(CH3)2	H	>25
36	CH3		H	(CH2)3CH3	H	21.6 (±1.1)
37	CH3		H	CH(CH3)2	H	>25.0
38	CH3		H	Br	H	>25.0