(S)-2-((S)-2-{(2R,4S,5S)-5-[(S)-2-((S)-2-Benzyloxycarbonylamino-propanoylamino)-propanoylamino]-4-hydroxy-6-phenyl-2-propyl-hexanoylamino}-3-methyl-butanoylamino)-3-methyl-butyric acid methyl ester AIDS-050854 AIDS050854 Hydroxyethylene isostere