10-Hydroxy-5-(1-methylethyl)-1-(2-pyridinyl)-3,6-dioxo-8,11-bis(phenylmethyl)-2-oxa-4,7,12-triazatridecan-13-oic acid, 5-thiazolylmethyl ester A-81525 AIDS-028479 AIDS028479 Ritonavir deriv.