David D. N'Da

Artemisinin–quinoline hybrid-dimers: Synthesis and in vitro antiplasmodial activity

Novel artemisinin-quinoline hybrid-dimers were synthesized from dihydroartemisinin and different aminoquinolines at elevated temperatures (90-110°C). All compounds were obtained as the β-isomers and were tested against both chloroquine sensitive and resistant strains of Plasmodium falciparum. Hybrid-dimer 8 showed the highest antiplasmodial activity, inheriting the optimum chain length of three carbon atoms.

Prodrug strategies for enhancing the percutaneous absorption of drugs.

The transdermal application of drugs has attracted increasing interest over the last decade or so, due to the advantages it offers, compared to other delivery methods. The development of an efficient means of transdermal delivery can increase drug concentrations, while reducing their systemic distribution, thereby avoiding certain limitations of oral administration. The efficient barrier function of the skin, however, limits the use of most drugs as transdermal agents. This limitation has led to the development of various strategies to enhance drug-skin permeation, including the use of penetration enhancers. This method unfortunately has certain proven disadvantages, such as the increased absorption of unwanted components, besides the drug, which may induce skin damage and irritancy. The prodrug approach to increase the skin’s permeability to drugs represents a very promising alternative to penetration enhancers. The concept involves the chemical modification of a drug into a bioreversible entity that changes both its pharmaceutical and pharmacokinetic characteristics to enhance its delivery through the skin. In this review; we report on the in vitro attempts and successes over the last decade by using the prodrug strategy for the percutaneous delivery of pharmacological molecules.

Synthesis and in vitro biological evaluation of dihydroartemisinyl-chalcone esters.

A series of dihydroartemisinyl-chalcone esters were synthesized through esterification of chalcones with dihydroartemisinin (DHA). The hybrids were screened against chloroquine (CQ) sensitive (3D7) and CQ resistant (W2) strains of intraerythrocytic Plasmodium falciparum parasites, and were all found to be active, with IC50 values ranging between 1.5 and 11 nM against both strains, with SI values over 5800. The esters featuring oxygenated aryl rings (7, 10 and 11), were found to be equipotent to DHA, but were 2-3 times more active than artesunate against the 3D7 and W2 strains of the malaria parasites. They were also screened in vitro against a panel of three cancer cell lines consisting of TK-10, UACC-62 and MCF-7. Compound 7, bearing a furan ring, displayed the most potent overall antitumor activity against all three cancer cell lines. TGA revealed that the targeted hybrids were all thermally more stable than DHA, which may be beneficial to the high temperature storage conditions that prevail in malaria endemic countries. During this study, ester 7 was identified as the best candidate for further investigation as a potential drug in search for new, safe and effective antimalarial drugs.

Synthesis of methoxypoly(ethylene glycol) carbonate prodrugs of zidovudine and penetration through human skin in vitro

Objectives The aim of this study was to synthesise a series of novel methoxypoly (ethylene glycol) carbonate prodrugs of the antiretroviral drug zidovudine (azidothymidine, AZT) in an attempt to enhance the physicochemical properties for transdermal delivery, which may reduce the severe side‐effects and toxicity associated with high oral doses of AZT.

The Case for Development of 11-Aza-artemisinins for Malaria.

The current treatment regimens for uncomplicated malaria comprise an artemisinin in combination with another drug (ACT). However, the recent emergence of resistance to ACTs in South East Asia dramatically emphasizes the need for new artemisinins. The current artemisinins have been in use since the late 1970s and have relatively poor thermal, chemical and metabolic stabilities - all are metabolized or hydrolyzed in vivo to dihydroartemisinin (DHA) that itself undergoes facile decomposition in vivo. The current artemisinins possess neurotoxicity as demonstrated in animal models, an issue that mandates increased vigilance in view of trends to use of protracted treatment regimens involving sequential administration of different ACTs against the resistant disease. As artemisinins induce the most rapid reduction in parasitaemia of any drug, common sense dictates that any new artemisinin derivative, selected on the bases of more robust chemical and thermal stability, metabolic stability with respect to the generation of DHA in vivo, and relatively benign neurotoxicity should be used in any new ACT whose components are rationally chosen in order to counter resistant malaria and inhibit transmission. 11-Azaartemisinin and its N-substituted derivatives attract because of overall ease of preparation from artemisinin. Some derivatives also possess notable thermal stabilities and although metabolic pathways of the derivatives are as yet unknown, none can provide DHA. The azaartemisinins synthesized over the past 20 years are critically discussed on the basis of their synthetic accessibility and biological activities with the view to assessing suitability to serve as new artemisinin derivatives for treatment of malaria.

Synthesis and antimalarial activity of ethylene glycol oligomeric ethers of artemisinin

Objectives  The aim of this study was to synthesize a series of ethylene glycol ether derivatives of the antimalarial drug artemisinin, determine their values for selected physicochemical properties and evaluate their antimalarial activity in vitro against Plasmodium falciparum strains.

1-Bromo-2-(10β-dihydro­artemisin­oxy)ethane

The title compound, C17H27BrO5, DEB, is a derivative of artemisinin which is used in malara therapy. The OR-group at C12 is cis to the CH3-group at C11 and axially oriented on ring D which has a chair conformation. The crystal packing is stabilized by several weak intermolecular C—H⋯O interactions, which combine to form a C—H—O bonded network parallel to (001).

In‐vitro transdermal penetration of cytarabine and its N4‐alkylamide derivatives

Objectives The aim of this study was to synthesise and determine the transdermal penetration of cytarabine alkylamide derivatives and assess the correlation of flux with physicochemical properties.

Synthesis and transdermal permeation of novel N4-methoxypoly(ethylene glycol) carbamates of cytarabine

Background: Cytarabine is a deoxycytidine analogue commonly used in the treatment of hematological malignant diseases. Its clinical utility, however, is severely limited by its short plasma half-life because of the catabolic action of nucleoside deaminases. Method: In this study, N4-carbamate derivatives of cytarabine (1) were synthesized and evaluated for transdermal penetration because this mode of administration may circumvent its limitations. The synthesis of these compounds was achieved in a two-step process. First, the methoxypoly(ethylene glycol) was activated by p-nitrophenyl chloroformate. Second, the activated intermediates were reacted with cytarabine in the presence of N-hydroxysuccinamide to give the N4-methoxypoly(ethylene glycol) carbamate derivatives. The transdermal flux values of the N4-carbamates of cytarabine were determined in vitro by Franz diffusion cell methodology. Aqueous solubility and log D (pH 7.4) values were determined and assessed for correlation with transdermal flux values. Results: The synthesized carbamates, particularly, (9)–(13), showed increased solubility in both aqueous and lipid media. Log D values decreased as the oxyethylene chain lengthened. Conclusion: Although none of the derivatives showed significantly higher transdermal penetration than cytarabine (1), it should be mentioned that the mean for cytarabine N4-methoxyethyleneoxycarbamate (8) was 10 times higher and the median was 2 times higher.

Activities of 11‐azaartemisinin and N‐sulfonyl derivatives against asexual and transmissible malaria parasites

Dihydroartemisinin (DHA), either used in its own right or as the active drug generated in vivo from the other artemisinins in current clinical use—artemether and artesunate—induces quiescence in ring‐stage parasites of Plasmodium falciparum (Pf). This induction of quiescence is linked to artemisinin resistance. Thus, we have turned to structurally disparate artemisinins that are incapable of providing DHA on metabolism. Accordingly, 11‐azaartemisinin 5 and selected N‐sulfonyl derivatives were screened against intraerythrocytic asexual stages of drug‐sensitive Pf NF54 and drug‐resistant K1 and W2 parasites. Most displayed appreciable activities against all three strains, with IC50 values <10.5 nm. The p‐trifluoromethylbenzenesulfonyl‐11‐azaartemisinin derivative 11 [(4′‐trifluoromethyl)benzenesulfonylazaartemisinin] was the most active, with IC50 values between 2 and 3 nm. The compounds were screened against Pf NF54 early and transmissible late intraerythrocytic‐stage gametocytes using luciferase and parasite lactate dehydrogenase (pLDH) assays. The 2′‐thienylsulfonyl derivative 16 (2′‐thiophenesulfonylazaartemisinin) was notably active against late‐stage (IV–V) gametocytes with an IC50 value of 8.7 nm. All compounds were relatively nontoxic to human fetal lung WI‐38 fibroblasts, showing selectivity indices of >2000 toward asexual parasites. Overall, the readily accessible 11‐azaartemisinin 5 and the sulfonyl derivatives 11 and 16 represent potential candidates for further development, in particular for transmission blocking of artemisinin‐resistant parasites.