ABT-538, aza-Val deriv. AIDS-043431 AIDS043431 {(1S,2S)-1-Benzyl-2-hydroxy-3-[N'-{(R)-2-[3-(2-isopropyl-thiazol-4-ylmethyl)-3-methyl-ureido]-3-methyl-butanoyl}-N-(tetrahydro-furan-3-ylmethyl)-hydrazino]-propyl}-carbamic acid thiazol-5-ylmethyl ester