Table 3. Apparent IC₅₀ Values of Substituted 2-(Isoxazol-3-yl)-2-oxo-N′-phenyl-acetohydrazonoyl Cyanide Scaffolds with Modifications on the Linker for Competing with 8-NBD-cAMP in Binding to EPAC2.

Compd	Linker	R3	IC50 (μM)a
1		t-Bu	8.9
51		Me	NEb
52		t-Bu	NE
53		t-Bu	NE
54		t-Bu	NE
55		t-Bu	NE
56		t-Bu	NE
57		t-Bu	NE

^aThe values are the mean ± SE of at least three independent experiments.

^bNE: no effect, indicating that a specific IC₅₀ cannot be calculated from the data points collected.