Drug delivery to the malaria parasite using an arterolane-like scaffold

Abstract

Antimalarial agents artemisinin and arterolane act via initial reduction of a peroxide bond in a process likely mediated by ferrous iron sources in the parasite. Here, we report the synthesis and antiplasmodial activity of arterolane-like 1,2,4-trioxolanes specifically designed to release a tethered drug species within the malaria parasite. Compared with our earlier drug delivery scaffolds, these new arterolane-inspired systems are of significantly decreased molecular weight and possess superior metabolic stability. We describe an efficient, concise and scalable synthesis of the new systems, and demonstrate the use of the aminonucleoside antibiotic puromycin as a chemo/biomarker to validate successful drug release in live Plasmodium falciparum parasites. Together, the improved drug-like properties, more efficient synthesis, and proof of concept using puromycin, suggests these new molecules as improved vehicles for targeted drug delivery to the malaria parasite.

Keywords: Plasmodium falciparum; antimalarial agents; drug delivery; puromycin; targeted prodrugs; trioxolanes.

Figure 1

Structures of the antimalarial agent arterolane (1) and trioxolane conjugate 2, which confers parasite-selective delivery of a tethered DPAP1 inhibitor (ML4118S, or NH₂-R in 2).

Figure 2

Chromatograms showing generation of the retro-Michael intermediate 4 and subsequent release of 2,5-dichloroanilne (5) following reaction of 14 with FeBr₂ in DMEM/FBS media.

Figure 3

Quantification of puromycin incorporation in proteins of P. falciparum parasites treated with 19, 16, or 18. Negligible puromycin incorporation is observed for dioxolane conjugate 18, indicating that puromycin release from 16 is peroxide-dependent.

Scheme 1

Fe(II)-mediated reduction of trioxolane 3 leads to retro-Michael intermediate 4 which subsequently releases free drug 5 after β-elimination and decarboxylation.

Scheme 2

Reagents and conditions: (a) 2.4 equiv O-methyl 2-adamantaone oxime, CCl₄, O₃, 2.5 h, 0°C, 97%; (b) 3 equiv FeCl₃•6H₂O, acetone/CH₂Cl₂, 0°C-rt, 1.5 h, 96%; (c) NaBH₄, EtOH/THF, -78 to 0°C, 5 h, 67%.

Scheme 3

Reagents and Conditions: (a) R’NCO, pyridine, toluene, 50 °C, 42 h, 71% (for 11), 63% (R = for 12).

Scheme 4

Reagents and Conditions: (a) RNCO, pyridine, toluene, 50 °C, 18–72 h, 74% (for 13), 55–79% (for 14); (b) p-NO₂C₆H₄OC(O)Cl, i-Pr₂NEt, DMAP, CH₂Cl₂, 25 min, 0 °C-rt, 94% (for 15); (c) 19, i-Pr₂NEt, DMAP, DMF, rt, 44 h, 61% (for 16); 52% over two steps (for 18).