the present invention provides hiv protease inhibitors of formulas i , ia , ib , ib or ii , or pharmaceutically acceptable salts thereof , wherein r 2 may be , for example , 2 - pyridyl - ch 2 —, 3 - pyridyl - ch 2 —, 4 - pyridyl - ch 2 —, a sulfonyl group as described in the formulas herein including benzenesulfonyl or thiophenesulfonyl groups , r 2a — co )—, r 2a being selected from the group consisting of piperonyl , 2 - pyranzinyl or a picolylamine group as described herein , wherein r3 may be , for example , a phenyl group or diphenylmethyl group as described herein , and wherein cx may be , for example , cooh , conr 5 r 6 , ch 2 oh or ch 2 or 7 .