Table 2. Exploration of the 5-Position of the Pyrazine Ring.

example	R	X	CCR4 pIC50a
1	5-chloro-2-thienyl	Br	7.2 ± 0.2
2	2-thienyl	Br	6.2 ± 0.2
3	3-thienyl	Br	5.9 ± 0.1
4	4,5-dichloro-2-thienyl	Br	6.0 ± 0.1
5	3-bromo-5-chloro-2-thienyl	Br	7.4 ± 0.2
6	3-phenyl-2-thienyl	Br	6.0 ± 0.1
7	phenyl	Br	6.1 ± 0.1
8	2-chlorophenyl	Br	6.8 ± 0.2
9	3-chlorophenyl	Br	7.0 ± 0.2
10	4-chlorophenyl	Br	6.9 ± 0.2
11	2,6-dichlorophenyl	Br	6.2 ± 0.2
12	2,5-dichlorophenyl	Br	5.5 ± 0.1
13	2,4-dichlorophenyl	Br	6.9 ± 0.2
14	3,5-dichlorophenyl	Br	5.3 ± 0.1
15	3,4-dichlorophenyl	Br	6.7 ± 0.2
16	2,3-dichlorophenyl	Br	8.0 ± 0.2
17	2,3-dichlorophenyl	Cl	7.9 ± 0.2
18	3,4-dichloro-2-thienyl	Cl	8.1 ± 0.2
19	2-chloro-3-fluorophenyl	Cl	7.8 ± 0.2
20	3-chloro-2-fluorophenyl	Cl	7.1 ± 0.2
21	3-chloro-2-methylphenyl	Cl	7.7 ± 0.2
22	2-chloro-3-(trifluoromethyl)phenyl	Cl	7.2 ± 0.1
23	3-chloro-2-cyanophenyl	Cl	7.2 ± 0.2
24	3-chloro-2-methylthiophenyl	Cl	7.1 ± 0.2
25	2,3-dichloro-4-pyridyl	Cl	5.0 ± 0.1
26	butyl	Cl	5.5 ± 0.2

^aPotency is given as pIC₅₀ values with n = ≥ 2 replicates.