Synthesis and biological activation of an ethylene glycol-linked amino acid conjugate of cyclic cidofovir

Abstract

Cidofovir (HPMPC) is a broad-spectrum anti-viral agent whose potential, particularly in biodefense scenarios, is limited by its low oral bioavailability. Two prodrugs (3 and 4) created by conjugating ethylene glycol-linked amino acids (L-Val, L-Phe) with the cyclic form of cidofovir (cHPMPC) via a P-O ester bond were synthesized and their pH-dependent stability (3 and 4), potential for in vivo reconversion to drug (3), and oral bioavailability (3) were evaluated. The prodrugs were stable in buffer between pH 3 and 5, but underwent rapid hydrolysis in liver (t(1/2) = 3.7 min), intestinal (t(1/2) = 12.5 min), and Caco-2 cell homogenates (t(1/2) = 20.2 min). In vivo (rat), prodrug 3 was >90% reconverted to cHPMPC. The prodrug was 4x more active than ganciclovir (IC50 value, 0.68 microM vs 3.0 microM) in a HCMV plaque reduction assay. However, its oral bioavailability in a rat model was similar to the parent drug. The contrast between the promising activation properties and unenhanced transport of the prodrug is briefly discussed.

Figure 1

Chemical structures of cidofovir (HPMPC) 1 and cyclic cidofovir (cHPMPC) 2.

Figure 2

Structure of the synthesized ethylene glycol-linked amino acid conjugates of cyclic cidofovir 3 and 4.

Scheme 1

Synthesis of ethylene glycol-linked amino acids 6 and 7. Reagents and conditions: (i) DMAP (0.15 eq), DCC (1.3 eq), CH₂Cl₂, rt, 18 h, 48–84%.

Scheme 2

Synthesis of 3 and 4: ethylene glycol-linked amino acid conjugates of cyclic cidofovir. Reagents and conditions: (i) PyBOP (2.5eq), DIEA, DMF, 40°C, 2.5–4h, 30–56%. (ii) TFA, CH₂Cl₂, rt 4h.