Mefloquine derivatives : synthesis, mechanisms of action, antimicrobial activities.

Alexandra Dassonville-Klimpt, Alexia Jonet, Marine Pillon, Catherine Mullié and Pascal Sonnet.

UMR-CNRS 6219, Laboratoire des glucides, UFR de Pharmacie, Université de Picardie Jules Verne, 1 rue des Louvels, 80037 Amiens, France.

Malaria is a serious public health problem. More than 100 tropical and sub-tropical countries are endemic for malaria. Pregnant women and children are the most sensitive to this disease and more than 750 000 people die of malaria each year. Among the five species of Plasmodium, P. falciparum is the parasite responsible for the most serious form of the disease and it has developed varying degrees of resistance to many classes of antimalarial drugs; consequently the development of new drugs to treat malaria is in full rise. Mefloquine was proposed, for a long time, as the drug of choice for chloroquine-resistant malaria. Emergence of resistance to mefloquine and its associated severe side effects have limited the use of this drug. Nowadays, there is no effective alternative, especially, in the zone of multi-drug resistance. Since a few years, the mechanisms of resistance to antimalarial drugs, the mechanism of action of the mefloquine and the origin of the side effects begin to be understood. On these bases, several approaches are considered to enhance the design of the mefloquine including its synthesis as a pure enantiomer or even the modulation of the mefloquine core as a pure enantiomer.

Keywords: malaria, mefloquine, mechanisms of action, resistance, quinolinemethanol.

1. Introduction

According to the World Health Organization (WHO), more than 100 tropical and sub-tropical countries are endemic for malaria and as many as 3.3 billion people are exposed to malarial infection [1]. Each year, more than 250 million people suffer from acute malaria, and over 750.000 people die of malaria. Most of the deaths are among young children under the age of five. Malaria also representes a significant threath to travelers and military personnel deployed for long periods of time in countries where malaria is endemic [2]. Human malaria is caused by protozoa belonging to five species of the genus Plasmodium. The parasites are transmitted to humans through bites of female Anopheles mosquitoes. Plasmodium falciparum, which is dominant in Africa, is the most pathogenic one and responsible for most of the fatalities. P. falciparum has developed varying degrees of resistance to many classes of antimalarial drugs; consequently the development of new highly efficacious drugs to treat malaria remains a public health priority. Surprisingly whereas the development of chloroquine analogues has been extensively reported without much success, fewer research is carried out on mefloquine analogues [3]. Since mefloquine was proposed as the drug of choice for chloroquine-resistant malaria, the synthesis of new analogues keeps all its interest to overcome the emergence of resistance toward mefloquine. Throughout this review, we will give an overview of the development of mefloquine derivatives. The mechanism of action, resistance, synthesis and structure-activity relashionships as well as other activities of antimalarial amino-4-quinolinemethanol will be described.

2. Mefloquine

The first treatment of malaria dates back to the early 18th century and made use of the bark of Cinchona trees. In 1820, Pelletier and Caventou isolated quinine (Fig. 1), a 4-quinolinemethanol, as the active compound of this crude bark. Thus, quinine was the first pure chemical compound used to treat malaria, it represents the first generation of quinolinemethanol [4]. During World War I, quinine was used for prophylaxis and routine treatment by Allied and German armies. Unfortunately, natural production became insufficient and its total synthesis was too complex for commercial production. In addition, important side effects such as fever, confusion, respiratory arrests and arrhythmias were frequently associated with quinine treatment [4]. These data led British and German scientists to develop synthetic alternatives. Shortly after World War II, chloroquine (CQ), a 4-aminoquinoline, and pyrimethamine largely replaced quinine. CQ is the most used because it is effective, inexpensive and involves little side effects when used at the prescribed doses. In the early 1960s, in an effort to eradicate malaria, CQ was used extensively. Afterwards, the first case of CQ resistance appeared and today, CQ -resistance strains of P. falciparum are common in all endemic areas throughout the world. CQ resistance was responsible of heavy losses during the Vietnam War. Consequently, a massive screening program, undertaken by the Walter Reed Army Institute of Research (WRAIR), started in USA and a score of years later some of 300,000 compounds had been screened [5]. Among these compounds, more than 300 4-quinolinemethanols were included among which approximately one hundred 2-phenyl-4-quinolinemethanol-type compounds [6]. The most promising drug to emerge was SN 10275 (Fig. 1), a 6,8-dichloro-2-phenyl-α-(2-piperidyl)-4-quinolinemethanol. It was tested in man but provided a long-lasting phototoxic reaction [7]. After pharmacomodulation

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of the 2-phenylquinolinemethanol core to reduce phototoxicity, WR030090 (Fig.1) was discovered. Its high activity with less phototoxic effects led to its use by the U.S. Army for the treatment of recrudescent malaria infections during the 1970s [8]. Unfortunately, this compound was only partially effective as a prophylactic agent and required a dosing regimen similar to that of quinine. These problems were due to its unfavorable pharmacokinetic characteristics and subsequently it was abandoned. SN 10275 and WR030090, in which a 2-phenyl substituent is introduced, represent the second generation of quinolinemethanol. During this same period, a third generation of quinolinemethanol was discovered and is represented by WR 142490 (Fig. 1), subsequently named mefloquine (MQ). In this structure, the 2-phenyl moiety of the previous generation is replaced by a trifluoromethyl group. Due to its more potent activity with no appreciable phototoxicity, this quinine derivative was thus developed and marketed, under the name Lariam®, by Hoffman La Roche and the U.S. Army [9]. For a long time, MQ was the drug of choice for U.S. military deployments because its longer half-life allows weekly administration and thereby makes compliance less problematic. But, MQ use was rapidly associated with neuropsychiatric side effects and, for some years now, the spread of resistance to MQ has limited its use. In addition, MQ is relatively expensive compared to other antimalarial drugs, which limits its accessibility to developing countries. Yet, MQ is particularly efficient against chloroquine-resistant strains of malaria parasites. In addition to its longer half-life as compared to others antimalarial drugs, MQ is safe in the second half of pregnancy [10].

N

MeO

OH N

N

NHN

Cl

NH

N

CF3

CF3

OH

HOH

N

Cl

Cl

Cl

N

Cl

NH

OH

H

N

Cl

Cl

Quinine Chloroquine WR 142490, Mefloquine(MQ)WR030090SN 10275

Fig. 1 Structures of some quinoline-based antimalarial drugs.

2.1 Mefloquine structure and synthesis of differents stereoisomers.

MQ is a α-2-piperidinyl-2,8-bis(trifluoromethyl)-4-quinolinemethanol and possesses two asymmetric carbon atoms. It exists under two racemic forms, erythro and threo, each one composed of a pair of enantiomers (Fig. 2). In 1974, Caroll and Blackwell prepared all four optical isomers and assigned the both relative and absolute configuration of the erythro and threo racemates by NMR and circular dichroism studies [11]. One the one hand, the (+)- and (-)-erythro have the (11R, 12S) and (11S, 12R) configurations, respectively. On the other hand, the (+)- and (-)-threo have the (11R,12R) and (11S,12S) configurations, respectively.

NH

N

CF3

CF3

OH

HNH

N

CF3

CF3

OH

HNH

N

CF3

CF3

OH

HNH

N

CF3

CF3

OH

H

erythro enantiomer of mefloquine

(+)-(11R, 12R) (-)-(11S, 12S) (+)-(11R, 12S) (-)-(11S, 12R)

threo enantiomer of mefloquine Fig. 2 Optical isomers of mefloquine

In clinical practice, MQ is commonly used as a racemic mixture of erythro enantiomers; (+)-(11R,12S)-α-2-piperidinyl-2,8-bis(trifluoromethyl)-4-quinolinemethanol and (-)-(11S,12R)-α-2-piperidinyl-2,8-bis(trifluoromethyl)-4-quinolinemethanol. Two studies have shown an equal activity for the four optical isomers of mefloquine against P. berghei in mice [11] and against P. yoelii [12]. Basco et al. [13] reported a best activity for the erythro racemate against P. falciparum in vitro as compared with pure enantiomer; (+)-erythro and (-)-erythro. But, the use of MQ as an enantiopur isomer could be more beneficial. Indeed, in another study, Karle et al. showed that (+)-enantiomers of MQ were more potent than (-)-enantiomers by a factor of 1.69 for erythro mefloquine and 1.95 for threo mefloquine (IC50 values against Sierra Leone and Indochina P. falciparum strains) [14]. Moreover, neurological side effects associated with MQ use seems to be due to the (-)-enantiomer of the mefloquine [15]. Consequently, due to the different properties and activities of the different MQ enantiomers, several syntheses have been realized in order to obtain enantiopur MQ. The first synthesis of racemic MQ was published in 1971 by Ohnmacht et al. [16]. As shown in Fig. 3, this synthesis begins with the condensation of p-trifluoromethylaniline with ethyl 4,4,4-trifluoroacetate in the presence of polyphosphoric acid to provide a 4-quinolone which was converted to 4-bromoquinoline 3 using POBr3. A carboxylation reaction led to cinchonic acid 4 with 86% yield. Addition of 2-pyridyl lithium salt to this acid provided a pyridylketone 5 which, is reduced with H2/Pt, gave MQ. This stereospecific reduction led only to the erythro enantiomers.

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N

CF3

CF3

NO

CF3

NH2

O

CF3O

EtO

N

Br

CF3

CF3N

CF3

CF3

CO2H

N Li

NH

N

CF3

CF3

OH

H NH

N

CF3

CF3

OH

H

+

i) PPA, 75%ii) POBr3, 95%

i) BuLi ii) CO2

H2, PtO2

Ohnmacht at al., 1970 racemic mixture

(+)-(11R, 12S) (-)-(11S, 12R)

+

86% 61% 53%

1 2 3 4 5

Fig. 3 First synthesis of (±)-erythro-MQ

Since this first synthesis, new synthetic routes have been explored, in particular to improve the process of preparation of the pyridylketone 5 previously reported by Ohnmacht in 1971 [17]. Figure 4 shows the first asymmetric synthesis of (11R,12S)-mefloquine which was reported in 1993 by Roche’s group using an enantioselective Rhodium-catalyzed hydrogenation of 2-pyridyl-2,8-bis(trifluoromethyl)-quinolineketone 5 [18]. The corresponding (R)-alcohol (R)-6 was obtained using an unsymmetrical ligand containing one dicyclohexylphosphino and one diphenylphosphino moiety, which afforded 91% ee. Later, Schmid’s group tried to improve this enantioselective hydrogenation using several others Rh catalyst but the best result was obtained with the ligand previously reported by Roche [19]. In the two cases, the second hydrogenation leads to a mixture of (11R, 12S)-α-2-piperidinylquinolinemethanol and (11R, 12R)-α-2-piperidinylquinolinemethanol with quantitative yield in a ratio of 5.7:1, respectively.

N

OHNHH

CF3

CF3N

CF3

CF3

NO

N

CF3

CF3

NOH

PR1R1

PR2R2Roche et al., 1993Schmid et al., 1996

(R)-6 (R,S)-MQ/(R,R)-MQ 5.7:1

Rh catalyst :

Rh catalyst(R)-ligand

91% ee (Roche)92% ee(Schimd)

R1 =

R2 =

Rh[(R)-P^P]Cl (Schimd)

(P^P)-Ligand:H2, Pt

Rh[(R)-P^P]F4B (Roche)

5

86% 100%

Fig. 4 Asymmetric hydrogenation of α-2-pyridyl-2,8-bis(trifluoromethyl)-quinolineketone 5 More recently, Xie et al.[ 20] reported a new and enantioselective synthesis of the (11R,12S)-MQ hydrochloride using a proline-catalyzed asymmetric direct aldol reaction and a Beckmann rearrangement as key steps as shown in Fig. 5. Formylation of 4-bromoquinoline 3 was conducted in presence of n-BuLi/DMF to give aldehyde 7 in 71% yield. The key aldol reaction is carried out by reaction of this aldehyde with cyclopentanone in presence of 30% of proline as catalyst. After chromatography purification, the syn-aldol 8 and the anti-aldol 9 were obtained with 69% yield with a ratio of 6.8:1. Then syn-aldol 8 reacted with NH2OH.HCl to give oxime 10 which was put in presence of TsCl in a Beckmann rearrangement. Finally, reduction with BH3.DMS followed by addition of condensated HCl affords to give (11R,12S)-MQ hydrochloride in a 70% yield. The experimental analysis confirmed the absolute configuration of (+)-MQ as (11R,12S) as previously reported by Caroll and Blackwell [11].

N

Br

CF3

CF3N

CF3

CF3

CHO

N

OH

CF3

CF3

O

N

OH

CF3

CF3

O

N

OH

CF3

CF3

H NOH

N

OHNHH

CF3

CF3

O

N

OHNHH

CF3

CF3

+

Zhi-Xiang et al., 2008

n-BuLi/DMFcyclopentanone

L-proline

NH2OH.HCl95%

TsCl then AcOH1. BH3.DMS2. HCl

71% 69%

72% 70%

.HCl

3 7 8 9

10 11

8/9 6.8:1

(11R, 12S)-MQ

Fig. 5 Asymmetric synthesis of (11R, 12S)-mefloquine

2.2 Mechanisms of action of Mefloquine and derivatives

The life cycle of malaria parasites is complex and consists in several distinct phases. Briefly, there are two basic cycles; an asexual cycle in humans and a sexual cycle in the female Anopheles mosquito. The asexual cycle can be further divided into a pre-erythrocytic stage (in liver) and an erythrocytic stage. The clinical symptoms of malaria, such as intense fever, exclusively occur during this erythrocytic phase. Indeed, just after the bite of an infected mosquito, the parasite establishes an asymptomatic infection of liver cells (lasting 7 to 15 days for P. falciparum). Incubation thus begins and will at least last one week. Plasmodia parasites are then released in the blood stream develop and multiply

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inside host erythrocytes. During this intra-erythrocytic stage, the parasite ingests the cytosol of the infected cell by a mechanism of endocytosis into its food vacuole. This cytosol contains more than 95% of hemoglobin which is an essential source of amino acids for the parasite. Hemoglobin digestion within the parasite food vacuole by aspartic proteases leads to the release of a proteic moiety (globin), potential source of aminoacids, and a free heme moiety, ferriprotoporphyrin IX. The latter moiety is toxic for the parasite. Indeed, it can generate reactive oxygen species which may induce membrane and DNA damages [21]. To overcome the free heme toxicity, the malaria parasite possesses efficient heme detoxification systems. The most important mechanism of detoxification takes place in the parasite food vacuole. The acid conditions (pH = 5.2) of this digestive vacuole promote the conversion of heme into insoluble and non-toxic crystals termed hemozoin or malaria pigment [22]. The remaining free heme passes through the food vacuole membrane and reaches the cytosol of the parasite. Within the cytosol three additional systems of detoxification exist. Thus, free heme can either be neutralized; (i) by interaction with glutathione (GSH), (ii) by binding with others proteins such as glutathione S-transferase or P. falciparum glutathione reductase [23]or by (iii) reaction with H2O2, which is generated by spontaneous oxidation of the released heme in the cytosol [24]. Like 4-aminoquinolines, arylaminoalcohols as MQ primarily acts on the intra-erythrocytic asexual stages but its mechanism of action is not completely understood. It is known that 4-aminoquinolines inhibit both the hemozoin formation and the oxidative and glutathione-dependent degradation of heme [25]. Heme interaction is the major mode of action of 4-aminoquinolines. The resulting quinoline-heme complexes formed are toxic for the parasite, just like free heme is. Studies showed that MQ and quinine inhibit the accumulation of hemozoin in infected cells [26]. However, MQ interacts relatively weakly with free heme (Kd = 3 10-7 M to 1.6 10-5 M) as compared to CQ (Kd ≈ 3.5 10-9 M) [ 27]. Indeed, due to its lower basicity (pKa1 = 2/pKa2 = 8.6 vs pKa1 = 8.1/pKa2 = 10.2 for CQ), MQ accumulates less inside the acidic food vacuole and the concentration required to inhibit heme polymerization is not achieved. Other mechanisms of action could explain the antimalarial activity of MQ. In 1982, Chevli et al. [28] showed that MQ binds with phospholipids with a good affinity. Since the malaria parasites are enriched in phosphatidylinositol, these authors suggested that the possible interaction between MQ and phosphatidylinositol could be the second mode of action of MQ. In 1996, Desneves et al.29 identified two high-affinity MQ-binding proteins with apparent molecular masses of 22–23 kDa and 36 kDa in P. falciparum-infected erythrocytes. The identities of these polypeptides have not been established yet, but they may be involved in MQ uptake or action. In 1999, Famin et al. [30] and more recently our group [31] showed in vitro activity of MQ on GSH-mediated hemin degradation. However, when a red blood cell leaky white ghost was used as model membrane (membrane being a target for the toxic activity of free heme): the amount of heme dissolved in ghost membranes as well as partition coefficients were lower for MQ and quinine as compared to CQ [30]. These authors are also showed that both MQ and quinine no affect GSH-mediated degradation of membrane-associated hemin. Maertins et al. [32] described that MQ affects volume-regulated anion channels (VRAC). This transmembrane pathway would be used by the parasite to bring substrates necessary to its growth and to allow the efflux of toxic compounds. This suggests that VRAC may also be a target of action for MQ. In 2002, Famin and Ginsburg reported a reduction of hemoglobin levels in MQ–treated P. falciparum FCR3 parasites [33]. They suggest that MQ could act by blockage of endocytosis. Indeed, two years later, Hoppe et al. [34] showed that MQ inhibits endocytosis in the P. falciparum D10 strain.

2.3 Mefloquine resistance

The first case of resistance to arylaminoalcohols was observed back in 1910 with quinine. Resistance to MQ appeared in 1982 in Thailand where MQ was used intensively [35 ].Then, pockets of clinical resistance to MQ were reported in Southeastern Asia [36]. In order to overcome the spread of the MQ resistance, drug combinations such as MQ/artesunate [37] or MQ/artemether [38] were introduced. Thus, most of the parasites are removed by the most active drug (artemisinin derivatives) which is eliminated in hours and the residual population is eradicated by MQ which has a long half-life. This combination MQ-artemisinin or artesunate is actually the most effective treatment for P. falciparum malaria in the area of increasing MQ- and multidrug- resistance. But artemisinin resistances have recently been described [39]. The molecular mechanisms of resistance depend on the chemical class of a drug and its mechanisms of action. Generally, resistance arises from mutations in genes encoding the drug target and/or influx/efflux pumps which regulate the concentration of the drug at the target location. Resistance to CQ is mainly determined by mutations in Plasmodium falciparum Chloroquine Resistance Transporter (PfCRT) [40] while resistance to quinine is due to the mutation of either P-glycoprotein homologue 1 (Pgh-1) or PfCRT or both [41]. Resistance to MQ and structurally related arylaminoalcohols in P. falciparum results from amplifications in Plasmodium falciparum MultiDrug Resistance Pfmdr-1, which encodes an energy demanding p-glycoprotein pump (Pgh-1). This protein, mainly located on the food vacuole membrane [42], could extrude antimalarial drugs from the food vacuole as proposed by Rohrbach et al. in 2006 [43]. Riffkin et al. [44] suggested that quinolinemethanols compounds are good substrates for P-glycoprotein transporters. The precise mechanism by which pfmdr1 mediates MQ resistance is still poorly understood. Several studies showed that MQ selection of MQ-resistance in vitro leads to amplification and overexpression of the pfmdr1 gene [45]. And, as reported by Ruetz et al. [46], an increasing of resistance to the quinoline compounds correlated with

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a transport of the drugs out of the cell. Consequently, as previously suggested by Foley and Tilley [25], an overexpression of Pgh-1 could result in an enhancing transport of MQ. However clinical resistance to MQ may also occur in the absence of pfmdr1 amplification in some cases [38]. Indeed, some strains such as D6 strain, derived from Sierra Leone P. falciparum isolate, exhibit a natural resistance to MQ. Some molecules, such as reversal agents or chemosensitizers, are able to interact with efflux pumps in order to restore the activity of antimalarial drugs. In 1987, verapamil, a calcium channel-blocker, was the first antimalarial reversal agent discovered [47]. Verapamil reverses CQ-resistance but possesses no effect on MQ-resistance. Reversal of MQ-resistance was observed with penfluridol, an antipsychotic agent [48]. Recently, others reversal agents of MQ-resistance have been reported such as cyproheptidine, NP-30 and icajine [49].

2.4 Side effects of Mefloquine

MQ use is associated with undesirable side effects on the central nervous system (CNS) such as nausea, vertigo, and more serious ones such as disturbed sleep, heightened anxiety, hallucinations, depression and acute psychosis [50].

Indeed, several experiments showed that MQ accumulates in the CNS and interacts with cellular targets within a pharmacological concentration range. The incidence of severe neuropsychiatric symptoms were reported to be 1 out of 10,000 with prophylactic use and 1 out of 200-1200 patients with therapeutic use. Efforts were made to explain the neuropsychiatric disturbances associated with MQ use. Several mechanisms are proposed including interactions with the cholinergic system, interactions with the human P-glycoprotein, blockage of the human adenosine A2A receptor, inhibition of ATP-sensitive potassium(K)-channels or even perturbations of the endoplasmic reticulum (ER). The effects of MQ on the cholinergic system were demonstrated in 1994 by Speich and Haller [51]. They reported that physostigmine, an anticholinesterase agent, could reverse the neuropsychiatric side effects due to MQ. In 1997, Baudry et al.[ 52] demonstrated that MQ crosses the blood-brain barrier in the rat but not its quinoline carboxylic acid derivative metabolite. A stereoselective cerebral transport of MQ has been established, in rat [53], in mice [54] and in human [55], in each specie the cerebral concentration of (-)-MQ being higher than that of (+)-MQ. These data suggest that the brain penetration of (-)-MQ is greater than its corresponding enantiomer. In contrast, there is a species-dependent stereoselective pharmacokinetic in the plasma. In rat, plasma concentrations of (+)-MQ were higher than those of its enantiomer, opposite to those observed in mice and in human [53-55]. Pharmacokinetics differences between the two enantiomers were already reported by these authors [56]. Baudry et al. [52] proposed four mechanisms which could explain the stereoselective (-)-MQ brain distribution; (i) active passage through the blood-brain barrier; (ii) passive passage through the blood-brain barrier with higher availability of (-)-MQ in the plasma compartment; (ii) possible metabolism in the brain; and (iv) stereospecific efflux. In 2004, Barraud et al. [54] demonstrated, for the first time, in vivo (in mice), that an enantioselective cerebral efflux transport is implied. MQ and most particularly (+)-MQ would be able to interact with human P-glycoprotein (P-gp) pumps. P-gp is a membrane-bound ATP-dependent drug efflux pump which plays important detoxification roles, particularly at the blood-brain barrier. Its activity results in the decrease of the intracellular concentration of toxic agents and xenobotics such as MQ. Experiments showed that (+)-MQ was excreted back to the central nervous system more rapidly than its enantiomer. All these data suggest that (+)-MQ would be more adequate to reduce toxicity. One of the target of (-)-MQ is the adenosine receptor A2. Indeed, Gillespie et al. [57] reported a stereoselective antagonism effect of MQ on central nervous adenosine receptors. The (-)-enantiomer of MQ binds to the adenosine receptor, particularly subtypes A2, while (+)-enantiomer is without significant activity at this binding site. Adenosine receptor antagonists such as theophylline, a bronchodilatator drug which is a mixed antagonist of adenosine A1 and A2A receptor, or caffeine may be involved in seizure disorders [58]. The inhibition of ATP-sensitive K-channels, which are present in neurons of the CNS may also be an explanation for the neurotoxicity of MQ as mentioned by Gribble et al. [59]. In 2003, Dow et al. [60] indicated that neurotoxicity of MQ could be mediated through a perturbation of ER function via a disruption of calcium homeostasis. Indeed, prolonged disruptions in Ca2+ homeostasis can result in damage of neuronal function and cell death [61]. Neuronal death in specific brain regions could explain symptoms as vertigo, anxiety and disturbances in emotion. As previously mentioned by Dow in 2004 [62], several approaches could be considered to decrease the MQ neurotoxicity; (i) administration of neuroprotective drugs (physostigmine); (ii) reformulation of MQ as a pure enantiomer ((+)-erythro-MQ); (iii) modulation of MQ core and; (iv) modulation of MQ core as a pure enantiomer.

3. Mefloquine derivatives

The structure-activity relationships of chloroquine and related quinoline antimalarial compounds were reviewed extensively [4,5,63]. Structure-activity studies of MQ indicated that the presence and the orientation of the hydroxyl and amine groups are essential to antimalarial activity [64]. Consequently, the synthesis of MQ analogues has been developed.

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3.1  Quinolinemethanol derivatives

In 1971, Cheng [65] then Chien and Cheng [66] showed, using molecular models and mass spectral data, that the active conformation of antimalarial compounds (analogues of MQ) is such that it allows hydrogen bonding between the amine of the piperidine and the hydroxyl function. These data are in accord with other results found in a series of phenanthrenemethanols [67]. The presence of a substituent such as phenyl group into the 2-position of the quinoline ring (in place of trifluoromethyl group) can induce, or greatly augmente, the antimalarial activity but increases the phototoxic effects of the quinoline [68]. Sweeney et al. [69] reported that the aromatic ring system could be interchangeable with a phenanthrene or a pyridine ring. Since some years, the interest to synthesis of MQ derivatives have increased and complementary structure-activity relashionships have been established. In order to reduce MQ neurotoxicity, Dow et al. [62] synthesized C2, C6 and C8 quinoline substituted MQ analogues. Some of them showed curative antimalarial activities in vivo (P. falciparum strains W2, D6 and multi-drug resistant TM91C235) with a higher therapeutic index than MQ against TM91C235 (Fig. 6). Among the most active compounds, the compound WR007930 is neutrotoxic in the same concentration range as MQ, as shown in Table 1. Shortly after, the same authors reported the antimalarial activity and pharmacological properties of a library of 21 2-phenyl substituted dialkylaminoquinolinemethanols related to WR030090 cited above (Fig.1) [70].

N

OHNH

Cl

Cl

OH

N

NBu

Cl

Cl

Bu

WR069878

Dow et al. 2004 Dow et al. 2006

WR007930 (SN10275)

Fig. 6 Two mefloquine-derivatives (Dow et al. 2004-2006) The most promising compound in terms of activity and neurotoxicity was the compound WR069878 (Fig. 6). This non-piperidine analogue is even less neurotoxic than piperidine analogues previously described by Dow due to the opening of piperidine ring. Moreover, the cost of treatment with WR069878 is estimated much lower than that with MQ. Nevertheless, complementary studies concerning the phototoxicity, which is the main side effect of the second generation of quinolinemethanols, remain to be carried out. This compound also showed a weak metabolic stability.

Table 1 Antimalarial activity of WR007930 and WR069878

Compound Antimalarial activity (IC50 against P.

falciparum strain in nM) Neurotoxicity (IC50 in µM)

W2a D6b TM91C235c WR007930 3.2 7.8 18 28 WR069878 ND ND 3.4 200

MQ 9.9 33 39-82 20-25

a. chloroquine resistant and mefloquine sensitive.

b. chloroquine sensitive but naturally less susceptible to mefloquine.

c. resistant to mefloquine, chloroquine and pyrimethamine. Recently, Dow et al. [71] described several libraries of new racemic 2,8-trifluoromethylquinolinemethanol compounds with their antimalarial activities and physicochemical properties. The main modification of the quinoline scaffold concerns the 4-position which is substituted by a non-piperidine moiety in order to reduce neurotoxicity by a limited absorption through the blood-brain barrier. These analogues were prepared from a racemic epoxide 14 which can be synthesized by two routes shown in Fig. 7. The first one begins by the bromination of the 2,8-trifluoromethyl-4-quinolinol with phosphorus oxybromide to afford a 4-bromo-2,8-trifluoromethylquinoline. This compound was put in reaction with n-BuLi/DMF to give a quinoline-4-carboxaldehyde 7. Racemic epoxide 14 was then obtained using Corey’s dimethylsulfonium methylide. The first step of the second way consists equally to the formation of the 4-bromo-2,8-trifluoromethylquinoline. The second step is a Stille reaction catalyzed by Pd2(dba)3 which leads to a vinyl compound intermediate 13 with 62% yield. An oxidation with meta-chloro peroxybenzoic acid (m-CPBA) affords the racemic epoxide. The ring epoxide opening by different commercially available amines provided a library of 200 4-position MQ analogues.

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N

OH

CF3

CF3N

CF3

CF3

O

N

CF3

CF3

OHXR2

N

CF3

CF3

CHO

N

OH

CF3

CF3N

CF3

CF3

1. POBr3, 91%2. n-BuLi, DMF, NA

racemic epoxide 14

(CH3)2SOCH2

1. POBr3, 91%2. Bu3SnCHCH2

Pd2(dba)3, P(t-Bu)3, 62%m-CPBA

X = N, S, O, CR-H = alkyl, heterocyclealkyl group with additional heteroatoms

12 7 13 12

library of mefloquine non piperidine analogs

74%NA

NA = data no available

route 1route 2

Fig. 7 Synthesis of library of mefloquine non-piperidine analogues by Dow et al. 2010 The structure-activity relationships principally concern the nature of the amino side chain. The authors have established that: (i) a reduction of electron density around the nitrogen atom diminishes the antimalarial activity (for example a phenylamino group has a much lower activity than a benzylamino group); (ii) the presence of a second nitrogen atom on the side chain reduces the ability to cross the blood-brain barrier and therefore the corresponding neurotoxicity; (iii) access of the second amine must be restricted for good potency (for example methylamine was less active than propylamine); (iv) the presence of two carbon atoms between the two nitrogen atoms, like in WR308396, and/or a second amine cyclic promoted antimalarial activity (Fig. 8).

N

CF3

CF3

OHNH

N

CF3

CF3

OHNH

NH

NH

N CF3

OH

HR1

R2

R3

WR177000 WR308396

15 : R1=SF5, R2=H, R3 = H16 : R1=H, R2=SF5, R3=H17 : R1=H, R2=H, R3=SF5

pentafluorosulfanyl analogs of MQ 15-17

Other atoms (C; O, S) : no activity

reduction electrodensity decreased potency

chain length optimal

disubstitution no improved activity

generally decreased neurotoxicityimproved pharmacokinetics properties

access must be restricted

two carbons is optimaland/or cyclic amine as methyl pyrrolidine increased potency

Fig. 8 Two compounds WR177000, WR308396 and their SAR and racemic 6-, 7- and 8-pentafluorosulfanyl analogues of mefloquine 15-17 (Dow et al. 2010).

Among the most promising compounds, the activities and physicochemical properties of WR 177000 and WR 308336 were compared between. Both compounds were active in vivo after oral administration in the blood schizonticidal P. berghei-ICR mouse model and were more potent than MQ against different strains of P. falciparum as shown in table 2. WR 177000 is the most active compound against MQ-resistant strains of P. falciparum (C235 and C2A strains) and is metabolically stable. But, due to its lipophilicity, it has a greater propensity for accumulation into the CNS than MQ, as showed by the measure of permeability across MDR1-transfected MDCK cell monolayers in table 2. WR308396 which contains an additional H-donor (vs. WR177000) exhibited a lower permeability as compared to WR177000 but has an equivalent permeability compared to MQ. Thus, authors are currently investigating new libraries of compounds based on the rational lead optimization of diaminoquinolinemethanols such as WR308396. This second generation of diaminequinolinemethanols should have an equivalent potency to MQ with a reduced permeability across the blood-brain barrier. Since these compounds have been evaluated as a racemate mixture, the biological evaluation of the corresponding pure enantiomers or diastereoisomers is envisaged.

Table 2 Antimalarial activity and physicochemical properties of WR177000 and WR308396

Compound Physicochemical

properties Antimalarial activity (IC90 against P.

falciparum strain in ng/ml) Permeability

logD HBDsa W2b D6c C235d C2Ae Papp/

Recoveryf MQ 3.1 2 6.2 2.8 17 11 52 30 74 32 9.4

WR177000 2.8 2 1.7 6.7 8.9 12.3 25

WR308396 3.3 3 6.2 30 40 48 8.4

a HBDs = H-bond donors

b chloroquine resistant and mefloquine sensitive.

c chloroquine sensitive but naturally less susceptible to mefloquine.

d resistant to mefloquine, chloroquine and pyrimethamine.

e resistant to mefloquine, chloroquine and pyrimethamine (two pfmdr1 copy strain).

f apparent permeability in the typical direction across MDR1-transfected MDCK cell monolayers (units in 10-6 cm/s).

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Always in order to reengineer the quinolinemethanol scaffold to increase the antimalarial activity with reduced side effects, Wipf et al. [72] have replaced the -CF3 groups in MQ with –SF5 groups. Indeed, incorporation of two additional fluorine atoms should modify the physicochemical and pharmacological properties of the corresponding molecules with slight perturbations of the electron density of the heteroaromatic scaffold. The chemical route to access these derivatives was the same as the one used to synthesize MQ in 1991. All pentafluorosulfanyl analogues 15-17, shown in Fig. 8, were more potent than MQ and the racemic 8-pentafluorosulfanyl analog 17 showed the best balance activity/permeability through blood-brain barrier. Administrated in mice per os, compound 17 showed a higher activity than MQ with a longer half-life (68h vs 23h for MQ) [73]. Synthesis of enantiopure analogue of 8-pentofluorosulfanyl analog 17 is currently under way. Taking into account that MQ analogues side effects could be reduced by the formation of enantiopur compounds, Jonet et al. [74] recently reported an asymmetric synthesis of (R)- and (S)- 4-aminoquinolinemethanols (Fig 9). This library of compounds was obtained by regioselective SN2 epoxide opening with amines. This five steps convergent synthesis could easily be transposable in plant scale. To obtain (R)-compounds, the synthesis was begun by bromination of 4-2,8-bis(trifluoromethyl)quinolin-4-ol 12 which was followed by a Suzuki coupling. A Sharpless asymmetric dihydroxylation, in presence of AD-mix β, starting from the resulting 4-vinylquinoline 13 led to (R)-diol 18 which was then cyclized via Sharpless acetoxonium ion. The (R)-4-(oxiran-2-yl)-2,8-bis(trifluoromethyl)quinoline (R)-14 obtained was regiospecifically diversified, with various amines commercially available or quickly synthesized. Enantiopur (R)-4-aminoquinolinemethanols were thus obtained in 12-34 % overall yield and ees generally superior to 89%.

N

OH

CF3

CF3

N

CF3

CF3

O

N

CF3

CF3

OHNHR

N

CF3

CF3

Br

N

CF3

CF3N

CF3

CF3

OHOHBF3K

POBr3-NHR = PhCH2-NH2;

n-alkylNH2, piperazinederivatives

AD-mix , K2OsO2(OH)4, t-BuOH/H2O

68%, 97%ee

1. MeC(OMe)3, APTS2.TBDMSCl3. K2CO3, MeOH

68%, 92%ee

PdCl2(dppf), Cs2CO3

97%

i-PrOH

35-98%89-99%ee

Jonet et al.

79%

12 3 13 18 (R)-14 enantiopurs aminoquinolinemethanols

Fig. 9 Enantioselective synthesis of a library of (R)-amino-2,8-bis(trifluoromethyl)quinolinemethanols Several compounds showed a promising antimalarial activity, in the range of nanomolar, against P. falciparum W2 and 3D7 strains. These compounds exhibited equally good antimicrobial activities. One of the enantiomers is two at fifty times more active than the others [75]. These results are supplementary proofs concerning the fact that the antimalarial activity is dependent on the stereoselectivity of the drugs. A more detailed structure-activity relashionships is currently being developed through the synthesis of additional analogues. The elucidation of the mechanism of action of the lead compounds is still under investigation.

3.2 Quinolinemethanol dual drugs

Since April 2001, [76] to overcome the resistance of malaria to conventional drugs, the use of artemisinin-based combination therapy (ACT) is the treatment of choice in the corresponding countries. Artemisinin derivatives are particularly effective in combination because of their very high killing rates, lack of adverse effects, and absence of significant resistance. In malaria drug combination therapy, the current trend is to co-formulate two or more agents into a single tablet, termed as multi-component drug (e.g., Coartem®, a lumefantrine-artemether association) as opposed to the traditional cocktail therapy, so as to improve patient compliance. However, based on the wide interest in hybrid molecules and the numerous encouraging efficacy and toxicity reports, the next generation of antimalarial drugs will undoubtedly be hybrid drugs. As aforementioned, MQ combined to artemisinin derivatives (artesunate, artemether…) constitutes one of the most effective combinations for the treatment of MQ- and multidrug-resistant P. falciparum. It combines the immediate effect of artemisinin derivatives with the prolonged effect of MQ. In 2005, Grellepois et al. [77] described two new dual molecules, shown in Fig. 10, in which a fluorinated artemisinin derivative is covalently linked to a MQ moiety; (i) by an easily cleavable ester bond (19), or (ii) by a non cleavable bond (20). The two chimeras were highly active against both CQ- and MQ-sensitive and resistant strains in the low nanomolar range. The divisible molecule 19 was slightly more efficient (IC50 = 2.4-6.6 nM) than the indivisible chimera (IC50 = 10.6-17.2 nM) in vitro. This difference was confirmed by preliminary in vivo experiments in mice. Moreover, the divisible chimera was as active the reference drug, artemether, in inhibiting the parasite growth. These results showed that the diester linker must be hydrolyzed in vivo to liberate the two pharmacophores and achieve maximum efficiency. Recently, Varotti et al. have studied a salt 21 derived from MQ.HCl and artesunate (Fig. 10) [78]. This salt exhibited better activity than artesunate and MQ against P. falciparum strains (W2 and 3D7). Its mechanism of action showed that two intracellular targets are involved: endoplasmic reticulum via disruption of Ca2+ homeostasis in the parasite and food vacuole by alteration of pH gradient. Other drugs could be combined covalently to MQ as for example chemosensitizers. This concept was previously studied with success with the association of CQ and imipramine [79].

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O

O

CF3

OO

OO

O

O

ONH

N CF3

H

CF3

O

O

CF3

OO

NOH

NCF3

CF3

H

O

O

OCOCH2CH2COO-

OO

OH

NCF3

CF3

N

H2+

hydrolysable bond

MQ

CF3-artemisinin derivative

divisible chimera 19 indivisible chimera 20

Grellepois et al. Varroti et al.

Mefloquine artesunate salt 21

Fig. 10 Mefloquine-hydrid drugs

4. Other antimicrobial properties of mefloquine and its derivatives

Racemic mixtures of MQ analogues were synthesized and evaluated for other antimicrobial properties such as the treatment of bacterial infections. Like for antimalarial drugs, there is a great urge to propose new drugs due to the multi-drug resistance of bacteria. During a screening carried out at the Walter Reed Amy institute of research, MQ and its derivatives were tested as antibacterial agents [80]. MQ exhibited bactericidal activity against several Gram-positive bacteria such as Staphylococcus aureus (Minimal Inhibitory Concentration (MIC) = 16 µg/ml) or Streptococcus pneumomiae (MIC = 0.4-0.8 µg/ml). However, MQ was not active against gram-negative strains. Some MQ derivatives that possess a piperidine attached to methanol in its 2-position were more active than MQ against staphylococci, enterococci and others Gram-positive bacteria except S. pneumoniae. Other substitutions led to compounds without activity [81]. MQ was tested against different strains of Streptococcus spp., Escherichia spp. and Neisseria gonorrhoeae and demonstrated even a high activity against S. pneumoniae (MIC = 0.06 µg/ml vs 4 µg/ml for sulphadoxine-pyrimethamine as reference). Previous studies showed that its target would be a bifunctionnal ATP synthase/ATPase [82]. In 2009, Vidal-Aroca et al. [83] reported MQ as an efflux-pump inhibitor of the Resistance-Nodulation-Division (RND) family in Pseudomonas aeruginosa. This efflux pump contributes to multi-drug resistance and, thus, MQ could be used in combination with drug whose activities are compromised by efflux to restore its activity. MQ was found to be relatively active against non-replicating persistent (NRP) tuberculosis strain (NRP-TB) [84]. Stereoselective activity was reported, indeed, in this study, the (±)-erythro-MQ (MIC ≈ 7 µM) were more active than the ()-threo-MQ (MIC ≈ 17 µM) against NRP Mycobacterium tuberculosis and the (+)-erythro isomer was less cytotoxic than the (-)-erythro isomer as in the case of antimalarial activity. Several libraries of MQ-derivatives were synthesized and tested against replicating (R-TB) and NRP tuberculosis strains and two hit compounds (Fig. 11) emerged of these structural modifications; (i) hydrazone 22 which has an improved anti-TB activity with both a lesser cytotoxicity and a lesser predicted CNS side effects than MQ [85] and (ii) isoxazole derivative 23, the isoxazole scaffold emerged following a screening against M. tuberculosis [86]. As expected by the authors, this last compound is the most active against R-TB (MIC = 0.9 µM vs 4 µM for 22 and 13 µM for MQ) with a less cytoxicity (IC50 128 µM) than both MQ (IC50 = 11 µM) and 22 (IC50 = 37 µM).

O N

N

O

CF3

CF3

O

ON NN

N CF3

CF3

Nhydrogenation of C=N bond decreased activity

-CF3 groups were favored6/7-position > 4-position

all ester substituents were favoredcarboxylic ester important to the binding

4,8-CF3 substituents

basic substitution increase potencyvarious aliphatic or unsaturatedchains tolerated

favored

hydrazone compound 22 isoxazole compound 23

Fig. 11 Antituberculosis MQ-derivatives

5. Conclusion

Since a few years, many efforts have being made in order to find alternatives compounds to current antimalarial drugs. MQ has several advantages; a good activity against chloroquine-resistant strains, a long half-life and a relatively safety in pregnancy. The newest data concerning its mechanism of action, the origin of its side effects and the structure-activity relashionships already established should permit a better design of the MQ core to propose news antimicrobial agents. For example, MQ derivatives as an enantiomeric pure compounds could reduce the side effects of MQ and an hybrid molecule with a MQ derivative moiety could limit the resistance spread.

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References

[1] WHO. World Malaria Report. WHO: Geneva, Switzerland, 2009. [2] Castelli F, Odolini S, Autino B, Foca E, Russo R. Malaria Prophylaxis: A comprehensive review. Pharmaceuticals. 2010;3:3212-

3239. [3] Bray PG, Ward SA, O’Neill PM. Quinolines and Artemisinin: Chemistry, Biology and History. Curr. Top. Microbiol. Immunol.

2005;295:3-38. [4] Hofheinz W, Merkli B. Quinine and quinine analogues. In: Antimalarial Drugs II. In: Peters W, Richards WHG, eds. Berlin,

Springer; 1984:61-81. [5] Peters W. Chemotherapy and Drug Resistance in Malaria. Academic Press, London: 1987. [6] Wiselogle FY. A survey of antimalarial drugs. Edwards, Ann Arbor: 1946 [7] Pullman TN, Eichelberger L, Alving AS, Jones R Jr, Graige B Jr, Whorton CM. The use of SN-10,275 in the prophylaxis and the

treatment of sporozoite-induced vivax malaria (Chesson strain). J. Clin. Inves. XXVII:12-16. [8] (a) Canfield CJ, Hall AP, MacDonald BS, Neuman DA, Shaw JA.. Treatment of falciparum malaria from Vietnam with a

phenanthrene methanol (WR 33063) and a quinoline methanol (WR 30090). Antimicrob. Agents Chemother. 1973;3:224–227; (b) Clyde DF, McCarthy VC, Rebert CC, Miller. RM. Prophylactic activity of a phenanthrene methanol (WR 33063) and a quinoline methanol (WR 30090) in human malaria. Antimicrob. Agents Chemother. 1973;3:220–223; (c) Hall AP, Segal HE, Pearlman EJ, Phintuyothin P. Comparison of a 9-phenanthrene methanol (WR33063), a 4-quinoline methanol (WR30090), and quinine for falciparum malaria in Thailand. Trans. R. Soc. Trop. Med. Hyg. 1975;69:342–349; (d) Hall AP, Segal HE, Pearlman EJ, Phintuyothin P. Comparison of a 9-phenanthrene methanol (WR33063), a 4-quinoline methanol (WR30090), and quinine for falciparum malaria in Thailand. Trans. R. Soc. Trop. Med. Hyg. 1975;69:342–349.

[9] (a) Trenholme CM, Williams RL, Desjardins RE, Frischer H, Carson PE, Rieckmann KH, Canfield CJ. Mefloquine (WR 142,490) in the treatment of human malaria. Science 1975;190:792–794; (b) Palmer KJ, Holliday SM, Brogden RN. Mefloquine. A review of its antimalarial activity, pharmacokinetic properties and therapeutic efficacy. Drugs. 1993;45:430–475.

[10] Nosten F, Kuile E, Maelankiri L, Chongsuphajaisiddhi T, Nopdonrattakoon L, Tangkitchot S, Boudreau E, Bunnag D, White NJ. Mefloquine prophylaxis prevents malaria during pregnancy: a double-blind, placebo-controlled study. J. Infect. Dis. 1994;169:595-603.

[11] Caroll FI, Blackwell JT. Optical isomers of aryl-2-piperidylmethanol antimalarial agents. Preparation, optical purity, and absolute stereochemistry. J. Med. Chem. 1974;17:210-219.

[12] Peters W, Robinson BL, Mittelholzer ML, Crevoisier C, Sturchler D. The chemotherapy of rodent malaria. LII. Response of Plasmodium yoelii ssp. NS to mefloquine and its enantiomers. Ann. Trop. Med. Parasitol. 1995;89:465–468.

[13] Basco LK, Gillotin , Gimenez F, Farinotti R, Le Bras J. In vitro activity of the enantiomers of mefloquine, halofantrine and enpiroline against Plasmodium falciparum. Br. J. Clin. Pharmacol. 1992;33:517–520.

[14] Karle, J. M.; Olmeda, R.; Gerena, L.; Milhous, W. K. Plasmodium falciparum: role of absolute stereochemistry in the antimalarial activity of synthetic amino alcohol antimalarial agents. Exp. Pharmacol. 1993;76:345-351.

[15] Fletcher A, Shepherd R. Use of (+)-mefloquine for the treatment of malaria. 1998. WO98/39003 [16] Lutz RE, Patel AR, Ohnmacht CJ. Antimalarials. 7. Bis(trifluoromethyl)-α-(2-piperidyl)-4-quinolinemethanols. J. Med. Chem.

1971;14:926-928. [17] (a) Solange A. 4-Chinolinderivate und deren Herstellung. 1983;EP 0103259; (b) Adam S. An expedient and high yielding

synthesis of mefloquine, via fluoride ion catalyzed wittig rearrangement I. Tetrahedron. 1989;45;1409-1414; (c) Adam S. A straightforward and high yielding synthesis of mefloquine II. Tetrahedron. 1991;47:7609-7614; (d) Kumar MS, Nageshwar YVD, Meshram HM. A facile and alternative method for the synthesis of mefloquine. Synthetic comm. 1996;26;1913-1919.

[18] Braun A, Broger EA, Hofheinz W., Meili A. Asymmetric hydrogenation. 1993. EP 0553778 B1. [19] Schmid R, Broger EA, Cereghetti M, Crameri Y, Foricher J, Lalonde M, Müller RK, Scalone M, Schoettel G, Zutter U. New

developements in enantioselective hydrogenation. Pure & Appl. Chem. 1996;68:131-138. [20] Xie ZX, Zhang LZ, Ren XJ, Tang SY, Li Y. Asymmetric synthesis of (+)-(11R, 12S)-mefloquine hydrochloride. Chin. J. Chem.

2008;26:1272-1276. [21] Kumar S, Bandyopadhyay U. Free heme toxicity and its detoxification systems in human. Toxicol. Lett. 2005;157:175-188. [22] Kumar S, Guha M, Choubet V, Maity P, Bandyopadhyay U. Antimalarial drugs inhibiting hemozoin (β-hematin) formation: a

mechanistic update. Life sciences 2007;80:813-828. [23] Campanale N, Nickel C, Daubenberger CA, Wehlan DA, Gorman JJ, Klonis N, Becker K, Tilley L. Identification and

characterization of heme-interacting proteins in the malaria parasite, Plasmodium falciparum. J. Biol. Chem. 2003;278:27354-27361.

[24] Wright CW, Addac-Kyereme J, Breen AG, Brown JE, Cox MF, Croft SL, Gokcek Y, Kendrick H, Phillips RM, Pollet PL. Synthesis and evaluation of cryptolepine analogues for their potential as new antimalarial agents. J. Med. Chem. 2001;44:3187-3194.

[25] Foley M, Tilley L. Quinoline Antimalarials: Mechanisms of Action and Resistance and Prospects for New Agents. Pharmacol. Ther. 1998;79:55–87 and references cited.

[26] (a) Zhang J, Krugliak M, Ginsburg H. The fate of ferriprotorphyrin IX in malaria infected erythrocytes in conjonction with the mode of action of antimalarial drugs. Mol. Biochem. Parasitol. 1999;99:129-141; (b) Sullivan DJ, Matile H, Ridley RG, Goldberg DE. A common mechanism from blockade of heme polymerization by antimalarial quinolines. J. Biol. Chem. 1998;273:31103-31107.

[27] Chou AC, Chevli R, Fitch CD. Ferriprotoporphyrin IX fulfills the criteria for identification as the chloroquine receptor of malaria parasites. Biochemistry. 1980;19:1543– 1549.

32 ©FORMATEX 2011

Science against microbial pathogens: communicating current research and technological advances A. Méndez-Vilas (Ed.)______________________________________________________________________________

[28] Chevli R, Fitch CD. The antimalarial drug mefloquine binds to membrane phospholipids. Antimicrob. Agents Chemother.

1982;21: 581–586. [29] Desneves J, Thorn G, Berman A, Galatis D, La Greca N, Sinding J, Foley M, Deady LW, Cowman AF, Tilley L. Photoaffinity

labelling of mefloquine-binding proteins in human serum, uninfected erythrocytes and Plasmodium falciparum-infected erythrocytes. Mol. Biochem. Parasitol. 1996;82:181–194.

[30] Famin O, Krugliak M, Ginsburg H. Kinetics of inhibition of glutathione-mediated degradation of ferriprotoprophyrin IX by antimalarial drugs. Biochem. Pharmacol. 1999;58:59-68.

[31] Mullié C, Jonet A, Dassonville-Klimpt A, Gosmann G, Sonnet P. Inhibitory effect of ursolic acid derivatives on hydrogen peroxide-and glutathione-mediated degradation of hemin: a possible mechanism of action for antimalarial activity. Exp. Parasitol. 2010;125:202-207.

[32] Maertens C, Wie L, Droogmans G, Nilius B. Inhibition of volume-regulated and calcium activated chloride channels by antimalarial mefloquine. J. Pharm. Exp. Ther. 2000;295:29-36.

[33] Famin O, Ginsburg H. Differential effects of 4-aminoquinoline-containing antimalarial drugs on hemoglobin digestion in Plasmodium falciparum-infected erythrocytes. Biochem Pharmacol. 2002;63:393-398.

[34] Hoppe HC, van Schalkwyk DA, Wiehart UIM, Meredith SA, Egan J, Weber BW. Antimalarial quinolines and artemisinin inhibit endocytosis in Plasmodium falciparum. Antimicrob. Agents Chemother. 2004;48:2370-2378.

[35] Boudreau EL, Webster HK, Pavanand K, Thosingha L. Type II mefloquine resistance in Thailand. Lancet 1982;ii':1335. [36] (a) Felix R, Gay F, Lyocoubi A, Bustos MDG, Diquet B, Danis M, Gentilini M. Resistance croisée à la mefloquine et a

l'halofantrine lors d'un paludisme a P. falciparum contracté en Sierre Leone. Bull. Soc. Pathol. Exot. 1990;83:43-45; (b) Karwacki JJ, Webster HK, Limsomwong N, Shanks GD. Two cases of mefloquine resistant malaria in Thailand. Trans. R. Soc. Trop. Med. 1989;83:152-153.

[37] Nosten F, Luxemburger C, ter kui le FO, Woodrow C, Eh JP, Chongsuphajaisiddhi T. Treatment of multidrug-resistant Plasmodium falciparum malaria with 3-days artesunate-mefloquine combination. J. Infect. Diseases. 1994;170:971-977.

[38] Price RN, Nosten F, Luxemburger C, Kham A, Brockman A, Chongsuphajaisiddhi T, White NJ. Artesunate versus artemether in combination with mefloquine for the treatment of multidrug-resistant falciparum malaria. Trans. R. Soc. Trop. Med. Hyg. 1995;89:523–527.

[39] (a) Noedl H, Se Y, Schaener K, Smith BL, Socheat D, Fukuda MM. Evidence of artemisinin-resistant malaria in Western Cambodia. N. Engl. J. Med. 2008;359:2619–2620;

(b) Dondorp AM, Norsten F, Yi P, Das D, Phyo AP, Tarning J, Lwin KM, Ariey F, Hanpithithakpong W, Lee SJ, Ringwald P, Silamut K, Imwong M, Chotivanich K, Lim P, Herdman T, An SS, Yeung S, Singhasivanon P, Day NPJ, Lindegardh N, Socheat D, White NJ. Artemisinin resistance in Plasmodium falciparum malaria. N. Engl. J. Med. 2009;361:455–467.

[40] Bray PG, Martin RE, Tilley L, Ward SA, Kirk K, Fidock DA. Defining the role of PfCRT in Plasmodium falciparum chloroquine resistance. Mol. Microbiol. 2005;56:323–333

[41] (a) Reed MB, Saliba KJ, Caruana SR, Kirk K, Cowman AF. Pgh1 modulates sensitivity and resistance to multiple antimalarials in Plasmodium falciparum. Nature. 2000;403;906–909; (b) Cooper RA, Ferdig MT, Su, XZ, Ursos LMB, Mu J, Nomura T, Fujioka H, Fidock DA, Roepe PD, Wellems TE. Alternative mutations at position 76 of the vacuolar transmembrane protein PfCRT are associated with chloroquine resistance and unique stereospecific quinine and quinidine responses in Plasmodium falciparum. Mol. Pharmacol. 2002;61:35–42

[42] Karcz SR, Galatis D, Cowman AF. Nucleotide binding properties of a P-glycoprotein homologue from Plasmodium falciparum. Mol. Biochem. Parasitol. 1993a;58:269–276.

[43] Rohrbach P, Sanchez CP, Hayton K, Friedrich O, Patel J, Sidhu AB, Ferdig MT, Fidock DA, Lanzer M. Genetic linkage of pfmdr1 with food vacuolar solute import in Plasmodium falciparum. EMBO J. 2006;25:3000–3011

[44] Riffkin C, Chung R, Wall D, Zalcberg JR, Cowman AF, Foley M, Tilley L. Modulation of the function of human MDR1 P-glycoprotein by the antimalarial drug mefloquine. Biochem. Pharmacol. 1996;52:1545–1552.

[45] (a) Wilson CM, Serrano AE, Wasley A, Bogenschutz MP, Shankar AH, Wirth DF. Amplification of a gene related to mammalian mdr genes in drug-resistant Plasmodium falciparum. Science. 1989;244:1184–1186; (b) Peel SA, Bright P, Yount B, Handy J, Baric RS. A strong association between mefloquine and halofantrine resistance and amplification, overexpression, and mutation in the P-glycoprotein gene homolog (pfmdr) of Plasmodium falciparum in vitro. Am. J. Trop. Med. Hyg. 1994;51:648–658; (c) Cowman AF, Galatis D, Thompson JK. Selection for mefloquine resistance in Plasmodium falciparum is linked to amplification of the pfmdr1 gene and cross-resistance to halofantrine and quinine. Proc. Natl. Acad. Sci. USA. 1994;91:1143–114.

[46] Ruetz, S., Delling, U., Brault, M., Schurr, E. and Gros, P. (1996) The pfmdr1 gene of Plasmodium falciparum confers cellular resistance to antimalarial drugs in yeast cells. Proc. Natl. Acad. Sci. USA 93: 9942–9947.

[47] Martin SK, Oduola AMJ, Milhous WK. Reversal of chloroquine resistance in Plasmodium falciparum by verapamil. Science 1987; 235:899–901.

[48] (a) Peters W, Robinson BL. The chemotherapy of rodent malaria. XLVI. Reversal of mefloquine resistance in rodent Plasmodium. Ann. Trop. Med. Parasitol. 1991;85:5–10; (b) Oduola AM, Omitowoju GO, Gerena L, Kyle DE, Milhous WK, Sowunm, A, Salako LA. Reversal of mefloquine resistance with penfluridol in isolates of Plasmodium falciparum from south-west Nigeria. Trans R. Soc. Trop. Med. Hyg. 1993;87:81–83.

[49] van Schalkwyk DA, Egan TJ. Quinoline-resistance reversing agents fort he malaria parasite Plasmodium falciparum. Drug Resist. Updates. 2006;9:211-226.

[50] (a) Weinke T, Trautmann M, Held T, Weber G, Eichenlaub D, Fleischer K, Kern W, Polhe HD. Neuropsychiatric side effects after the use of mefloquine. Am. J. Trop. Med. Hyg. 1991;45: 86-91; (b) van Riemsdijk MM, van der Klauw MM, van Heest JA, Reedeker FR, Ligthelm RJ, Herings RM, Stricker BH. Neuro-psychiatric effects of antimalarials. Eur. J. Clin. Pharmacol. 1997;52:1-6.

[51] Speich R, Haller A. Central anticholinergic syndrome with the antimalarial drug mefloquine. N. Engl. J. Med. 1994;331:57–58.

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[52] Baudry S, Pham YT, Baune B, Vidrequin S, Crevoisier CH, Gimenez F, Farinotti R. Stereoselective passage of mefloquine

through the blood-brain barrier in the rat. J. Pharm. Pharmacol. 1997;49:1086-1090. [53] Pham YT, Régina A, Farinotti R, Couraud PO, Wainer IW, Roux F, Gimenez F. Interactions of racemic mefoquine and its

enantiomers with P-glycoprotein in an immortalised rat brain capillary endothelial cell line, GPNT. Biochim. Biophys. Acta 2000;1524:212-219

[54] Barraud de Lagerie S, Comets E, Gautrand C, Fernandez C, Auchere D, Singlas E, Mentre F, Gimenez F. Cerebral uptake of mefloquine enantiomers with and without the P-gp inhibitor elacridar (GF1210918) in mice. Br. J. Pharmacol. 2004;141:1214–1222.

[55] Gimenez F, Pennie R, Koren G, Crevoisier Ch, Farinotti R. Stereoselective pharmacokinetics of mefloquine in healthy Caucasians after multiple doses. J. Pharm. Sci. 1994:6;824-827.

[56] Gimenez F, Farinotti R, Thuillier A, Wainer IW. Determination of the enantiomers of mefloquine in plasma and whole blood using a coupled achiral-chiral highperformance liquid chromatographic system. J. Chromatogr. 1990;529:339-346.

[57] Gillespie RJ, Adams DR, Bebbington D, Benwell K, Cliffe IA, Dawson CE, Dourish CT, Fletcher A, Gaur S, Giles PR, Jordan AM, Knight AR, Knutsen LJS, Lawrence A, Lerpiniere J, Misra A, Porter RHP, Pratt RM, Shepherd R, Upton R, Ward SE, Weiss SM, Williamson DS. Antagonists of the human adenosine A2A receptor. Part 1: Discovery and synthesis of thieno[3,2-d]pyrimidine-4-methanone derivatives. Bioorg. Med. Chem. Lett. 2008;18:2916-2919.

[58] Chu CK. Caffeine and aminophylline induced seizures. Epilepsia 1981;22:85-94. [59] Gribble FM, Davis TME, Higham CE, Clark A, Ashcroft FM. The antimalarial agent mefloquine inhibits ATP-sensitive K-

channels. Br. J. Pharmacol. 2000;131:756-760. [60] Dow GS, Hudson TH, Vahey M, Koenig ML. The acute neurotoxicity of melfoquine may be mediated through a disruption of

calcium homeostasis and ER function in vitro. Malaria J. 2003;2:1-14. [61] a) Choi DW. Calcium-mediated neurotoxicity: relationship to specific channel types and role in ischemic damage. TINS

1988;11:465-469; (b) Hartley DM, Kurth MC, Bjerkness L, Weiss JH, Choi DW. Glutamate receptor-induced 45Ca2+ accumulation in cortical cell cultures correlates with subsequent neuronal degeneration. J Neurosci. 1993;13:1993-2000.

[62] Dow GS, Koenig ML, Wolf L, Gerena L, Lopez-Sanchez M, Hudson TH, Bhattacharjee AK. The antimalarial potential of 4-quinolinecarbinolamines may be limited due to neurotoxicity and cross-resistance in mefloquine-resistant Plasmodium falciparum. Antimicrob. Agents Chemother. 2004;48:2624-2632.

[63] (a) Coatney GR. Pitfalls in a discovery: the chronicle of chloroquine. Am. J. Trop. Med. Hyg. 1963;12:121–128; (b) Thompson PE, Werbel LM. Antimalarial Agents: Chemistry and Pharmacology. Destevens G, ed. Academic Press New York: 1972; (c) Ismail FM, Dascombe MJ, Carr P, North SE. An exploration of the structure-activity relationships of 4-aminoquinolines: novel antimalarials with activity in vivo. J. Pharm. Pharmacol. 1996:48:;841–850.

[64] Karle JM, Karle IL. Crystal structure and molecular structure of mefloquine methylsulfonate monohydrate: implications for malaria receptor. Antimicrob. Agents chemother. 1991;35:2239-2245.

[65] Cheng CC. Structure and antimalarial activity of aminoalcohols and 2-(p-chlorophenyl)-2(4-piperidyl)tetrahydrofuran. J. Pharm. Sci. 1971;60:1596-1598.

[66] (a) Chien PL, Cheng CC. Further side-chain modification of antimalarial phenanthrene amino alcohols. J. Med. Chem. 1973:16;1093-1096; (b) Chien PL, Cheng CC. Difference in antimalarial activity between certain amino alcohol diastereomers. J. Med. Chem. 1976:19:170-172.

[67] Loew GH, Sahakian R. titre J. Med. Chem. 1977;11:366. [68] Sweeney T. The present status of malaria chemotherapy: mefloquine, a novel antimalarial. Med. Res. Rev. 1981;1:181-301. [69] Sweeney, T. R. Drugs with quinine-like action In: Antimalarial Drugs II: Current Antimalarials and New Drug Developments,

Peters W, Richards WHG, eds. Berlin, Heidelberg ,Springer-Verlag: 1984:267-313. [70] Dow GS, Koenig ML, Wolf L, Gerena L, Lopez-Sanchez M, Hudson TH, Bhattacharjee AK. Utility of Alkylaminoquinolinyl

Methanols as New Antimalarial Drugs. Antimicrob. Agents Chemother. 2006;50:4132-4143. [71] (a) Milner E, McCalmont W, Bhonsle J, Caridha D, Cobar J, Gardner S, Gerena L, Goodine D, Lanteri C, Melendez V, Roncal

N, Sousa J, Wipf P, Dow GS. Anti-malarial activity of a non-piperidine library of next-generation quinoline methanols. Malaria J.2010;9:51-60; (b) Milner E, McCalmont W, Bhonsle J, Caridha D, Caroll D, Gardner S, Gerena, L, Gettayacamin M, Lanteri C, Luong T, Melendez V, Moon J, Roncal N, Sousa J, Tungtaeng A, Wipf P, Dow G. Structure–activity relationships amongst 4-position quinoline methanol antimalarials that inhibit the growth of drug sensitive and resistant strains of Plasmodium falciparum. Bioorg. Med. Chem. Lett. 2010;20:1347-1351.

[72] (a) Wipf P, Mo T, Geib SJ, Caridha D, Dow GS, Gerena L, Roncal N, Milner EE. Synthesis and biological evaluation of the first pentafluorosulfanyl analogues of mefloquine. Org. Biomol. Chem. 2009;7:4163–4165, (b) Mo T, Mi X, Milner EE, Dow GS, Wipf P. Synthesis of an 8-pentafluorosulfanyl analog of the antimalarial agent mefloquine. Tetrahedron Lett. 2010;51:5137–5140.

[73] Dow GS, Milner EE, Wipf P, Mo T. Derivatives of MQ and associated methods for making and using. 2010:WO 2010/144434A1.

[74] Jonet A, Dassonville-Klimpt A, Da Nascimento S, Leger JM, Guillon J, Sonnet P. First enantioselective synthesis of 4-aminoalcohol quinoline derivatives through a regioselective SN2 epoxide opening mechanism. Tetrahedron:Asymmetry 2011;28:138-148.

[75] Jonet, A.; Dassonville-Klimpt, A.; Mullié-Demailly, C., Taudon, N. ; Sonnet, P., Enantioselective synthesis method of 4-aminoalcoholquinoline derivatives and the use. 2011:EP11154229.

[76] WHO. Report of a WHO Technical Consultation. World Health Organization, Geneva, 2001. [77] Grellepois F, Grellier P, Bonnet-Delpon D, Bégu JP. Design, synthesis and antimalarial activity of trifluoromethylartemisinin–

mefloquine dual molecules. Chem. Bio. Chem. 2005;6:648 –652.

34 ©FORMATEX 2011

Science against microbial pathogens: communicating current research and technological advances A. Méndez-Vilas (Ed.)______________________________________________________________________________

[78] de Pilla Varotti F, Botelho ACC, Assunção AA, de Paula RC, Fagundes EMS, Valverde A, Mayer LMU, Mendonça JS¸ de

Souza MVN, Boechat N, Krettli AU. Synthesis, antimalarial activity, and intracellular targets of MEFAS, a new hybrid compound derived from mefloquine and artesunate. Antimicrob. Agents Chemother. 2008;52:3868–3874

[79] Peyton DH, Kelly JX, Burguess SJ, Liebman K, Gunsaru B, Hodson C. Development of reversed chloroquines as antimalarial drugs: efficacity in animal model. Amer. J. Trop. Med. Hyg. 2008:79 supp. Abstract.

[80] Kunin CM, Ellis WY. Antimicrobial activities of mefloquine and a series of related compounds. Antimicrob. Agents Chemother. 2000;44:848-852.

[81] Capan M, Mombo-Ngoma G, Makristathis A, Ramharter, M. Anti-bacterial activity of intermittent preventive treatment of malaria in pregnancy: comparative in vitro study of sulphadoxine-pyrimethamine, mefloquine, and azithromycin. Malaria J. 2010;9:303-308.

[82] Martin-Galiano AJ, Gorgojo B, Kunin CM, de la Campa AG. Mefloquine and new related compounds target the F0 complex of the F0F1 H+-ATPase of Streptococcus pneumonia. Antimicrob Agents Chemother. 2002;46:1680-1697.

[83] Vidal-Aroca F, Meng A, Minz T, Page MGP, Dreier J. Use of resazurin to detect mefloquine as an efflux-pump inhibitor in Pseudomonas aeruginosa and Escherichia coli. J. Microbiol. Methods. 2009;79:232–237.

[84] Jayaprakash S, Iso Y, Wan B, Franzblau SG, Kozikowski AP. Design, synthesis and SAR studies of mefloquine-based ligands as potential antituberculosis agents. Chem. Med. Chem. 2006;1:593-597.

[85] Mao J, Wang Y, Wan B, Kozikowski A, Franzblau SG. Design, synthesis and pharmacological evaluation of mefloquine-based ligands as potential antituberculosis agents. Chem. Med. Chem. 2007;2:1624-1630.

[86] Mao J, Yuan H, Wan Y, Wan B, Pak D, He R, Franzblau SG. Synthesis and antituberculosis activity of mefloquine-isoxazole carboxylic esters as prodrugs. Bioorg. Med. Chem. Lett. 2010;20:1263-1268.

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