(S)-2-((S)-2-{(2R,4S,5S)-2-Benzyl-5-[(S)-2-((S)-2-benzyloxycarbonylamino-propanoylamino)-propanoylamino]-4-hydroxy-6-phenyl-hexanoylamino}-3-methyl-butanoylamino)-3-methyl-butyric acid methyl ester AIDS-050856 AIDS050856 Hydroxyethylene isostere