(OHEt)amide isostere AIDS-050402 AIDS050402 [(S)-1-((1S,2R)-1-Benzyl-3-{(R)-2-[(1-ethyl-propylcarbamoyl)-methyl]-3,3-dimethyl-butanoylamino}-2-hydroxy-propylcarbamoyl)-2-carbamoyl-ethyl]-carbamic acid benzyl ester