2-Pentenoic acid, 5-[(3S)-2-oxo-3-pyrrolidinyl]-4-[[[(3S)-1,2,3,5-tetrahydro-6-[[(5-methyl-3-isoxazolyl)carbonyl]amino]-5-oxo-3-indolizinyl]carbonyl]amino]-, ethyl ester, (2E,4S)- AIDS-121704 AIDS121704