A series of novel HIV-1 protease inhibitors based on the (hydroxyethylamino)-sulfonamide isostere incorporating substituted phenyls and benzheterocycle derivatives bearing rich hydrogen bonding acceptors as P2 ligands were synthesized. Prolonged chain linking the benzhereocycle to the carbonyl group resulted in partial loss of binding affinities. Introduction of a small alkyl substituent with appropriate size to the -CH2- of P1-P2 linkage as a side chain resulted in improved inhibitory potency, and in this study, isopropyl was the best side chain. Replacement of the isobutyl substituent at P1′group with phenyl substituent decreased the inhibitory potency. One of the most potent inhibitor, compound 23 showing high affinity to HIV-1 protease with an IC50 value of 5 nm, also exhibited good anti-SIV activity (EC50 = 0.8 μm) with low toxicity (TC50 > 100 μm). The flexible docking of inhibitor 23 to HIV-1 protease active site rationalized the interactions with protease.