AIDS-028543 AIDS028543 Carbamic acid, [(1S,2S,4R)-5-[[(1S)-1-[[(aminoiminomethyl)amino]carbonyl]-2-methylpropyl]amino]-2-hydroxy-5-oxo-1,4-bis(phenylmethyl)pentyl]-, 1,1-dimethylethyl ester SB-205700 Val-Phe-Phe-HOCH2CH2 isostere analog