Table 1. Structure–activity relationship of C₄ substituted bis-tetrahydrofuran protease inhibitors.

Compound Ligand number		Ki (nM)	IC50 (nM)
13 (TMC-126)		0.014	1.4
14		0.0029	2.4
15		0.035	55
16		0.073	335
17		0.3	ND