Table 2.

Molecular structure of compounds 6–18

Compound	R1	R2	R3	PDE4D IC50 (nM)
6	−H			13
7	−H			9.4
8				2.3
9	−H			13.5
10	−H			2.7
11	−H			14
12	−H			0.4
13	−H			1.5
14	−H			17
15	−H			0.1
16	−H			240
17	−H			1.3
18	−H			0.5