(3S)-3-((2S)-2-{(2S)-2-[(tert-Butoxy)carbonylamino]-4-carboxybutanoylamino}-4-methylpentanoylamino)-5,5-difluoro-2-oxopentanoic acid .alpha.-Ketoacid-t-Boc-Glu-Leu-(difluoro)aminobutyric acid AIDS-110652 AIDS110652