Table 4.

Modifications at indole ring and linker regions of the scaffold. Potency and aqueous solubility^a

Entry		EP2 KB (nM)	Aqueous Solubilityb (μM)	Aqueous solubility of corresponding HCl salt in SGFc (μM)	Water solubility of corresponding HCl saltd (mM)
20o		9.7	150	>250	2.52
24a		13.0	5	ND	1.16
24b		28.3	20	ND	ND
24c		20	ND	>100	1.73
24d		25.1	ND	ND	2.38
24e		8.8	20	ND	ND
24f		66	45	ND	0.7
24g		254	70	ND	ND
24h		>1000	ND	ND	ND
24i		183	57	ND	ND

^aSchild K_B values are calculated similarly as indicated at Table 1 legend. K_B values are average of 2 measurements run in duplicate, except compound 20ofor which the values are average of 6 repeats

^bThe solubility of the compounds is measured in PBS buffer (pH 7.4) with 1% DMSO by nephelometry.⁴⁶

^cThe solubility of compounds measured in simulated gastric fluid at pH 2.0 by nephelometry. Compound 24dis a milky-white solution in DMSO and 24 h is an inactive compound. Therefore, their solubility is not determined by nephelometry, however, 24d.HClis highly water soluble.

^dWater solubility is determined by 24 h shake flask thermodynamic solubility method in neat water. Briefly, the compounds were dissolved in water at 2 mg/mL and shaken at 2200 rpm for 24 h. Then, the solutions were filtered through 0.2 μ syringe filters and analyzed the area under the curve (AUC) using HPLC, along with standard DMSO solution of each compound. ND = not determined.