(S)-2-{(S)-2-[(2S,4S,5S)-5-((S)-2-Benzyloxycarbonylamino-propanoylamino)-4-hydroxy-2-isopropyl-6-phenyl-hexanoylamino]-3-methyl-butanoylamino}-3-methyl-butyric acid methyl ester AIDS-050378 AIDS050378 Hydroxyethylene isostere