Synthesis and Antimalarial Activity of 2-Phenyl-1 , 10-Phenanthroline Derivative Compounds

To develop new potential antimalarial drugs of 2-phenyl-1,10-phenanthroline 5 derivatives from 8-aminoquinoline as starting material were synthesized in good yields. The synthesis of 2-phenyl-1,10-phenanthroline 5 derivatives compounds with 8-aminoquinoline 4 as starting material through three steps has been carried out. The first step of reactions is aldol condensation of benzaldehyde 1 with acetaldehyde 2. The result of reactions is cinnamaldehyde 3 (92.14%) in the form of yellow solid. The second step of reactions was synthesized of 2-phenyl-1,10-phenanthroline 5 (brown solid, 54.63%) through cyclization of 8-aminoquinoline 4 with cinnamaldehyde 3 compound. The third step of reactions is methylation and ethylation of 2-phenyl-1,10-phenanthroline using dimethyl sulphate (DMS) and diethyl sulphate (DES) reagents that it was refluxed for 17 and 19 h, respectively. The results of reactions are (1)-N-methyl-9-phenyl-1,10-phenanthrolinium sulphate 6 and (1)-N-ethyl-9-phenyl-1,10-phenanthrolinium sulphate 7 in yield from 90.62% and 89.70%, respectively. The results of testing in vitro antiplasmodial activity at chloroquine-resistant Plasmodium falciparum FCR3 strain to 2-phenyl-1,10phenanthroline 5 derivatives obtained that (1)-N-ethyl-9-phenyl-1,10-phenanthrolinium sulphate 7 compound has higher antimalarial activity (IC 50 :0.13 ± 0.02 μM) than antimalarial activity of (1)-N-methyl-9-phenyl-1,10-phenanthrolinium sulphate 6 compound (IC 50 :0.25 ± 0.01 μM) and 2-phenyl-1,10-phenanthroline 5 compound (IC 50 :2.45 ± 0.09 μM). While, the results of testing in vitro antiplasmodial activity at chloroquine-resistant Plasmodium falciparum D10 strain to 2-phenyl-1,10phenanthroline 5 derivatives obtained that (1)-N-methyl-9-phenyl-1,10-phenanthrolinium sulphate 6 compound has higher antimalarial activity (IC 50 :0.10± 0.04 μM) than antimalarial activity of (1)-N-ethyl-9-phenyl-1,10-phenanthrolinium sulphate 7 (IC 50 :0.18 ± 0.01 μM) and 2-phenyl-1,10-phenanthroline 5 compound (IC 50 :0.55 ± 0.07 μM).


INTRODUCTION
Malaria is the most important parasitic disease in the world.Its etiological agents are protozoa of the genus Plasmodium.Plasmodium falciparum is the most virulent among the four species infecting humans and is responsible for most of mortality.In 2008, among 3.3 billion people at risk, there were 243 million malaria cases, causing an estimated 863,000 deaths, mostly of children under five years.
From 109 countries endemic for malaria, 45 were within the World Health Organization (WHO 2009) Especially in African Region (Fernández et al. 2011;Fidock et al. 2004;Olumese 2005;Kayembe et al. 2010).Malaria remains one of the most important diseases of the developing world, killing 1-3 million people and causing disease in 300-500 million people annually (Fidock et al. 2004;Olumese 2005, Kayembe et al. 2010).Malaria endemic areas include Africa, South East Asia, India and South America; however, the disease is spreading to new areas, such as Central Asia, and Eastern Europe.
Local transmission of malaria in the United States, unheard of in the era between World War II and 1980, now accounts for an increasing number of cases (Molyneux et al. 1989).
Clinical cases in the US now average 1,300 per year (Wernsdorfer 1991).Worldwide, the majority of deaths occur in children; other high risk groups include pregnant women, refugees, migrant workers, and non immune travelers-over 20 million Western tourists at risk annually (fact sheets from Malaria Foundation International).Although four species of the genus Plasmodium cause human malaria, P. falciparum is the deadliest and will be the subject of this review.
The traditional remedies are no longer effective and the incidence of malarial by P. falciparum, the most dangerous species of parasite, continues to grow, while some traditional drugs such as chloroquine and its congeners are losing their activity due to the increasing multi drug resistance (Yapi et al. 2000;Yapi et al. 2006).Therefore, it is essential to find new drugs of anti malaria having a pharmacological activity higher than of currently available drugs of anti malaria.In this connection, quantitative structure-activity relationship (QSAR) analysis plays an important role to minimize trial and error in designing new antimalarial drugs.
The halofantrine as new anti malaria has good therapeutic effects (Basco et al. 1994).Halofantrine as more active against strains of P. falciparum that are resistant to chloroquine, pyrimethamine, and quine (Rang et al. 2003).
However, halofantrine is known to have some unwanted side effects, such as abdominal pain, nausea, vomiting, diarrhea, orthostatic, hypertension, prolongation of QTc intervals, pruritus, rash, and hepatotoxic (Karbwang et al. 1991;Bassi et al. 2006).The 1,10-phenanthroline derivatives are similar to halofantrine as antimalarial drug which its added at heterocyclic with two nitrogen atoms.(In 2000, Yapi reported) that the 1,10-phenanthroline ring system appeared as new class of potential antimalarial compound (Yapi et al. 2000).Now, part of our research was concerning the synthesis and biological activity of 1,10-phenanthroline derivatives.
In this program continuation of these studies, we report in this paper our results concerning the synthesis and the determination of the biological activity of compound type (1)-N-alkyl-and (1)-N-benzyl-1,10-phenanthrolinium (Widjayanti et al. 2006).Yapi et al. (2006) have synthesized diaza-analogs of phenanthrene by substituting the two nitrogen atoms in the phenanthrene skeleton.Antiplasmodial activity of series of diaza-analogs of phenanthrene derived from 3-amino-, 5-amino-, 6-amino-, 8-aminoquinoline and 5-isoquinoline showed that among the molecules evaluated the 1,10-phenanthroline skeleton was the most active compound in vitro on both chloroquine-resistant (FcB1) and chloroquine-sensitive (Nigerian) strain with an IC 50 of about 0.13 μM.Based on the skeleton, (Mustofa et al. 2003) have also synthesized thirteen derivatives of 1,10phenanthroline and evaluated the in vitro antiplasmodial activity (Yapi et al. 2000) and their Quantitative Structure Activity Relationship (QSAR) Mustofa et al. 2003.The resulting of the QSAR analysis found the best theoretical activity of six new compounds and its was synthesized and evaluated their in vitro antiplasmodial activity through experiment in laboratory.
This study were synthesized of 2-phenyl-1,10phenanthroline 5 derivatives from 8-aminoquinoline 4 as starting material were obtained two compounds of 2-phenyl-1,10-phenanthrolinium sulphate 6 and (1)-N-ethyl-9-phenyl-1,10-phenanthrolinium sulphate 7 which were synthesized through 3 stages reaction.The reactions condition and the results of synthesis of 2-phenyl-1,10-phenanthroline 5 derivative compounds were described in Figure 1.formed was filtered and washed with acetone to give brown solid compound (0.58 g; 90.62%) of (1)-N-methyl-6-nitro- Biological Activity.Parasites were cultured according to method described by Trager and Jensen (1976) with modification.FCBr3 was considered as a chloroquine resistant strain and D10 were considered as a chloroquine sensitive strain.Culture medium was replaced daily and the cultures were synchronized by 5% D-sorbitol lysis (Merk, Darmstadt, Germany).The method used for in vitro antimalarial activity testing was adapted from visual method.

Materials
The molecules were tested 3 times in triplicate in 96-well plates (TPP, Switzerland) with cultures at ring stage at 0.5-1.0%parasitemia (hematocrit 1%).For each test, the parasite cultures were incubated with the chemicals at decreasing concentrations for 24 and 72 h.The first dilution of the product (10 mg/mL) was perfomed with dimethylsulfoxide (DMSO, Merck), and the following with RPMI 1640.Parasites growth was estimated by coloring with giemsa (10%) for 30 second and calculated by β-caunter.
The parasite control in the presence without chemicals (mean of the corresponding wells was referred to as 100%).
Concentrations inhibiting 50% of the parasite (IC 50 ) were determined by SPPS 13.0 software.The IC 50 that indicated antiplasmodial activity of chemicals compound to determine by probit analysis method with percentage of concentration inhibition versus chemical doses.