AIDS-005331 AIDS005331 Cyclohexanehexamide, .delta.-[[[(1,1-dimethylethoxy)carbonyl]histidinyl]amino]-.gamma.-hydroxy-.alpha.-(1-methylethyl)-N-[2-methyl-1-[[(2-pyridinylmethyl)amino]carbonyl]butyl] U-81749E analog psi-[CHOHCH2] His-cHexAla Val-Ile isostere