Preliminary communication In vitro antiplasmodial and cytotoxic activities of asymmetrical pyridinium derivatives Bel  en Rubio-Ruiz a, 1 , Víctor M. Castillo-Acosta b , Guiomar P  erez-Moreno b , Antonio Espinosa a , Dolores Gonz  alez-Pacanowska b , Luis M. Ruiz-P  erez b , Antonio Entrena a, * , Ana Conejo-García a, * a Departamento de Química Farmac eutica y Org anica, Facultad de Farmacia, Universidad de Granada, Campus de Cartuja s/n, 18071 Granada, Spain b Instituto de Parasitología y Biomedicina “L opez-Neyra”, Consejo Superior de Investigaciones Científicas, Parque Tecnol ogico de Ciencias de la Salud, Avenida del Conocimiento s/n, 18100 Armilla, Granada, Spain article info Article history: Received 29 May 2014 Received in revised form 23 July 2014 Accepted 29 July 2014 Available online 30 July 2014 Keywords: Pyridinium compounds Plasmodium falciparum Antimalarial activity Cytotoxicity abstract An in vitro investigation of the antiplasmodial and cytotoxic activities of a series of human choline kinase inhibitors against Plasmodium falciparum is reported. Structureeactivity relationship analyses have allowed us to determine the essential parameters for the antimalarial effect of these asymmetrical pyridinium derivatives. One of the compounds meets the World Health Organization's criteria for hit identification against P. falciparum exhibiting an IC 50 of 0.0016 mg/ml and a selectivity index of >3000. © 2014 Elsevier Masson SAS. All rights reserved. 1. Introduction Malaria is an important health problem, responsible for 219 million clinical cases and 660,000 deaths in 2010 [1]. A major obstacle to the eradication of this disease is the emerging resistance of the malaria-causing parasite Plasmodium falciparum to most marketed antimalarial drugs [2,3]. As such, new compounds acting through novel mechanisms of action are urgently needed. Choline kinase (CK) is the first enzyme in the Kennedy pathway for the biosynthesis of phosphatidylcholine, the most essential phospholipid in P. falciparum. The proliferation of this parasite within erythrocytes is concomitant with a massive increase of phosphatidylcholine biosynthesis. It has been demonstrated that the inhibition of PfCK disrupts the Kennedy pathway, which results in parasite death [4,5]. We have previously reported a series of asymmetrical pyr- idinium derivatives that target the choline phospholipid meta- bolism in cancer cells and tumors by inhibiting the human CK [6e8]. Their promising activities against human CK prompted us to evaluate these structures for their in vitro antimalarial effect. In this paper the antiplasmodial activities of these 33 mono- or bis- cationic compounds and also the cytotoxicity of the most active ones are reported. 2. Results and discussion Chemical structures for compounds 1 to 33 and their corre- sponding IC 50 values against P. falciparum are reported in Tables 1e3. The compounds were classified into three groups ac- cording to their structures: series A (1e 13), B (14e21) and C (22e33). Series A includes monocationic compounds bearing a 4- substituted pyridinium ring linked to the N-9 or N-3 atom of an adenine moiety through an aromatic linker. Among N-9 isomers (1e8), the 4-pyrrolidine derivatives display lower IC 50 values than the corresponding dimethylamine analogues, compound 7 being the only exception (Table 1). It is also noteworthy that the anti- malarial effect of these compounds is closely related to the linker size. In general, increasing the length of the alkyl chain of the linker Abbreviations: CK, choline kinase; SAR, structureeactivity relationship; SI, selectivity index. * Corresponding authors. E-mail addresses: aentrena@ugr.es (A. Entrena), aconejo@ugr.es (A. Conejo- García). 1 Present address: Edinburgh Cancer Research Centre, MRC IGMM, University of Edinburgh, Western General Hospital, Crewe Road, EH4 2XU Edinburgh, United Kingdom. Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech http://dx.doi.org/10.1016/j.ejmech.2014.07.105 0223-5234/© 2014 Elsevier Masson SAS. All rights reserved. European Journal of Medicinal Chemistry 85 (2014) 289e292