DOI: 10.1002/cmdc.200800176 Synthesis and Evaluation of 1,1’- Hydrocarbylenebis(indazol-3-ols) as Potential Antimalarial Drugs Miriam Martins Alho, [a] Rory N. García-Sµnchez, [b] Juan JosØ Nogal-Ruiz, [b] JosØ Antonio Escario, [b] Alicia Gómez-Barrio, [b] Antonio R. Martínez-Fernµndez,* [b] and Vicente J. Arµn* [c] This paper is dedicated to our dear colleagues Drs. Vicente Gómez Parra and Salvador Vega Noverola (IQM, CSIC, Madrid) for their out- standing contribution to Medicinal Chemistry, on the occasion of their retirement. Introduction In recent years, we have developed different methods of the synthesis of indazoles, [1–4] indoles, [5] cinnolines [6] and quinoxa- lines. [7] Some of these compounds have shown interesting properties as cytostatic drugs [2–4] and/or antiparasitic agents against Trypanosoma cruzi [4, 8] and Trichomonas vaginalis. [4, 9] In silico investigations followed by the synthesis and screen- ing of the predicted active compounds as inhibitors of biomin- eralization (or more appropriately, biocrystallization) of ferripro- toporphyrin IX (heme) to hemozoin, [10] led to the discovery of indazole 5, and its potential as an antimalarial drug. [11] 1,1’-(o- Xylylene)bis(indazol-3-ol) (5) had previously been obtained in low yield (24 %) as a by-product in the preparation of the cyto- static agent 4 starting from 5-nitroindazolol (1) and a,a’-dibro- mo-o-xylene (2) (Scheme 1). [2] Malaria, mainly caused by the protozoan Plasmodium falcipa- rum, is one of the most deadly diseases in the world, affecting 400–500 million people and causing 1–2 million deaths each year. Plasmodium ingest and digest large amounts of hemo- ACHTUNGTRENNUNGglobin within their digestive vacuole at the intraerythrocytic stage, in order to obtain the amino acids needed to synthesize their own proteins. After cleavage of the peptidic chain, the re- maining ferriprotoporphyrin IX is toxic and it is converted through a Plasmodium specific biocrystallization process into the inert pigment called hemozoin (b-hematin). Chloroquine, a known antimalarial agent hypothesized to act by inhibiting the detoxification of heme, [12, 13] has been the mainstay of antima- larial treatments for decades but, the emergence of resistant parasites in the early 1960 s has seriously limited its efficacy. It is generally assumed that this same mechanism, i.e., the pre- vention of hemozoin formation leading to enhanced heme toxicity, also mediates the antimalarial activities of some chlor- oquine analogues, antifungal imidazoles, xanthones, porphyr- [a] Dr. M. Martins Alho CIHIDECAR (CONICET), Departamento de Química Orgµnica Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires 1428 Buenos Aires (Argentina) [b] R. N. García-Sµnchez, Dr. J. J. Nogal-Ruiz, Dr. J. A. Escario, Dr. A. Gómez-Barrio, Dr. A. R. Martínez-Fernµndez Departamento de Parasitología, Facultad de Farmacia Universidad Complutense, 28040 Madrid (Spain) Fax: (+ 34) 91-394-1815 E-mail : arm@farm.ucm.es [c] Dr. V. J. Arµn Instituto de Química MØdica (IQM), CSIC c/Juan de la Cierva 3, 28006 Madrid (Spain) Fax: (+ 34) 91-564-4853 E-mail : vjaran@iqm.csic.es Bis(indazol-3-ol) derivatives (5, 30–38) were prepared by alkyla- tion of 3-alkoxyindazoles with a,w-dibromides, followed by re- moval of the O-protecting groups. These compounds were subse- quently evaluated as inhibitors of biocrystallization of ferriproto- porphyrin IX (heme) to hemozoin, a Plasmodium detoxification specific process. Most bis(5-nitroindazol-3-ols) were good inhibi- tors, however, a denitro analogue (38), the intermediate bis(3-al- koxyindazoles) (15–29) as well as bis(indazolin-3-ones) (39–42) were not active, showing the importance of the NO 2 and OH groups in the inhibition process. Scheme 1. Reported synthesis of compound 5. Reagents and conditions : a) K 2 CO 3 , acetone, reflux, 5 h. 78  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemMedChem 2009, 4, 78 – 87 MED