(S)-2-((S)-2-{(2R,4S,5S)-5-[(S)-2-((S)-2-Benzyloxycarbonylaminopropanoylamino)propanoylamino]-4-hydroxy-2-methyl-6-phenylhexanoylamino}-3-methylbutanoylamino)-3-methylbutyric acid methyl ester AIDS-050853 AIDS050853 Hydroxyethylene isostere SKF 108390