Table 2.

Structural modifications at positions X2 and X3.

Compound	X2	X3	IC50 (μM)†	inhibition‡
11			11
12			4.3
13			2.2
14		*	1.7
15			12.9
16			4.5
17			3.3
18			1.0
19			ND
20			>100
21			ND
22			ND
23			ND
24			ND
25				7%†
26				8%†

^*Racemic compound.

^†ND: not detectable.

^‡Inhibition at 50 μM compared with DMSO.