2-{[((2R,4S)-2-{(1R)-2-(Ethylamino)-2-oxo-1-[(phenylacetyl)amino]ethyl}-5,5-dimethyl-1,3-thiazolidin-4-yl)carbonyl]oxy}ethyl (2R,4S)-2-{(1R)-2-(ethylamino)-1-[methyl(phenylacetyl)amino]-2-oxoethyl}-5,5-dimethyl-1,3-thiazolidine-4-carboxylate AIDS-033409 AIDS033409 Penicillin C2-sym dimer