(E)-(S)-4-[2-(3-{[1-(5-Methyl-isoxazol-3-yl)-methanoyl]-amino}-2-oxo-2H-pyridin-1-yl)-butanoylamino]-5-(2-oxo-pyrrolidin-3-yl)-pent-2-enoic acid cyclobutyl ester AIDS-177699 AIDS177699