Water-soluble Prodrugs of the Human Immunodeficiency Virus Protease Inhibitors Lopinavir and Ritonavir

We studied the synthesis, cleavage rates, and oral administration of prodrugs of the HIV protease inhibitors (PIs) lopinavir and ritonavir. Phosphate esters attached directly to the central hydroxyl groups of these PIs did not demonstrate enzyme-mediated cleavage in vitro and did not provide measurable plasma levels of the parent drugs in vivo. However, oxymethylphosphate (OMP) and oxyethylphosphate (OEP) prodrugs provided improved rates of cleavage, high levels of aqueous solubility, and high plasma levels of the parent drugs when dosed orally in rats and dogs. Dosing unformulated capsules containing the solid prodrugs led to plasma levels equivalent to those observed for dosing formulated solutions of the parent drugs. A direct synthetic process for the preparation of OMP and OEP prodrugs was developed, and the improved synthetic method may be applicable to the preparation of analogous soluble prodrugs of other drug classes with limited solubility.