(S)-2-{(S)-2-[(2R,4S,5S)-2-Benzyl-5-((S)-2-benzyloxycarbonylamino-propanoylamino)-4-hydroxy-6-phenyl-hexanoylamino]-3-methyl-butanoylamino}-3-methyl-butyric acid methyl ester AIDS-050379 AIDS050379 Hydroxyethylene isostere