(OHEt)amide isostere (R)-2-tert-Butyl-N4-(1-ethyl-propyl)-N1-((2R,3S)-2-hydroxy-3-{(S)-3-hydroxy-2-[(1-quinoxalin-2-yl-methanoyl)-amino]-butanoylamino}-4-phenyl-butyl)-succinamide AIDS-050409 AIDS050409