5-Isoxazoleacetic acid, 3-chloro-.alpha.-[[(3-chloro-4,5-dihydro-5-isoxazolyl)[[(9H-fluoren-9-ylmethoxy)carbonyl]amino]acetyl]amino]-4,5-dihydro- Fluorenylmethoxy carbonyl AT-125 dimer Fluoromethyl carbonyl AT-125 dimer NSC329080 U-58174