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malaria is a vector borne disease , caused by the plasmodium parasite . according to who report ,
there were estimated 216 million episodes of malaria in 2010 , of which approximately 81% , or 174 million cases , were in the african region .
there were estimated 655,000 malaria deaths in 2010 , of which 91% were in africa .
in addition to acute disease episodes and deaths in africa , malaria also contributes significantly to anaemia in children and pregnant women , adverse birth outcomes such as spontaneous abortion , stillbirth , premature delivery , and low birth weight , and overall child mortality .   included in the who report was the fact that resistance to artemisinin
, a vital component of drugs used in the treatment of p. falciparum malaria , has been reported in a growing number of countries in southeast asia .
resistance to pyrethroids , the insecticides used in itns and most commonly used in irs , has been reported in 27 countries in africa and 41 countries worldwide .
the search for new antimalarial drugs requires identification of new biochemical targets for drug development and development of new chemical entities [ 2 , 3 ] .  
epidemiological studies have provided convincing evidence that natural dietary compounds , which humans consume as food , possess many biological activities .
one plant food that has been shown to be therapeutic against a number of diseases is pigeon pea , cajanus cajan l. ( fabaceae ) , an important grain legume crop in the tropics and subtropics .
the extracts of pigeon pea are commonly used to treat diabetes , fever , dysentery , hepatitis , and measles worldwide [ 5 , 6 ] .
cajanus cajan has been used traditionally as a laxative and was identified as an antimalarial remedy . in continuation of our study of the nigerian ethnomedicine for the discovery of new antimalarial drugs [ 7 , 8 ] , the present report is on the bioassay - guided fractionation and isolation of antiplasmodial compounds from cajanus cajan leaf extract .

 cajanus cajan leaves were collected from otu , oyo state of nigeria , in the month of january and authenticated at the herbarium of botany department , university of ibadan ( ui ) , and that of the forestry research institute of nigeria ( frin ) , ibadan , where a voucher specimen was deposited as fhi 106560 .
leaves of c. cajan were air dried at rt ( 2631c ) and pulverized with a hammer mill .
500  g of plant material was extracted in redistilled methanol ( 2.0  l ) by maceration at rt ( 30c ) for 72  h. after determination of yield of crude methanol extract , the sample was stored in the fridge ( 4c ) till needed for analysis .
2.0  g of dry weight of crude methanol extract was fractionated by suspension in meoh  :  h2o in a ratio of 70  :  30 to yield 0.35  g of hexane , 0.46  g of dichloromethane ( dcm ) , 0.41  g of etoac , and 0.73  g of aqueous methanol fractions , respectively .
the hexane and dcm fractions were combined based on the analysis and chromatographed on flash column using silica gel ( merck ) .
it was eluted with increasing polarity of hexane - dcm , and 50  ml portions were collected , respectively .
the fractions that eluted with hexane  :  dcm ( 50  :  50 to 20  :  80 ; 130  mg ) indicated the presence of predominantly 3 compounds on tlc analysis .
this was subjected to ptlc using chcl3  :  etoac ( 17  :  3 ) ( merck , 20  20  cm , 12 plates ) to give compounds 1 , 2 , and 3 with rf 0.45 , 0.55 , and 0.80 , respectively . the compounds were subjected to structural analysis using nmr and ms .
the asexual stages of plasmodium falciparum ( multidrug resistant strain k1 ) obtained from dr .
warhurst , london school of hygiene and tropical medicine , were cultured continuously according to the modified candle jar method .
the method of makler and hinrichs   was used in the estimation of parasite growth inhibition .
cultures were cryopreserved to contain at least 5% ring - form parasites and were maintained at 24% hematocrit ; this was used in preparing 2% hematocrit and washing with phosphate buffered solution ( pbs ) 3 times .
stock solutions of extracts were prepared by dissolving known quantities of dried extracts ( 500  g ) in 1  :  1 dimethyl sulphoxide ( 250  l ) and distilled water ( 250  l ) . serial dilutions ( 10 dilutions , 0.5500 
g / ml ) of the extracts / fractions were made in quadruplicates in 96-well microtitre plates .
the drug plate was placed in the chamber with a little sterile water in a petri dish .
this was placed in the laminar flow chamber ( envair , uk ) gassed with prefiltered mixture of 3% o2 , 4% co2 , and 93% n2 , and then swiftly sealed and incubated at 37c for 48 hours .
after incubation , acetylpyridine adenine dinucleotide ( apad ) regent was added to each well , followed by n - bromosuccinimide ( nbs ) and then incubated at 37c for 20  min .
optical density was measured in a plate reader at 550  nm and analysed with a wallac counter using an ms excel program .
ic50 values were estimated by plotting the % inhibition against the log drug concentration at 95% confidence limits using the linear and nonlinear regression analyses .
the crude methanol extract ( dry weight yield of 8.6  g ) had an ic50 of 53.5  g / ml , the hexane fraction had ic50 of 62.5 , and both dcm and aqueous meoh had ic50 of 31.3  g / ml , while ethyl acetate fraction had ic50 of 15.6  g / ml compared to chloroquine dipo4 with ic50 0.21  g / ml ( 0.66  m ) .
yields of compounds 13 were 5.0  mg ( 3.8% ) , 7.0  mg ( 5.3% ) , and 11.3  mg ( 8.7% ) with ic50 values of 2.0  g / ml ( 7.40  m ) , 5.4  g / ml , and 5.6  g / ml , respectively ( see table 1 for details ) .
compound 1 obtained from chromatographic analysis of the ethyl acetate fraction had an ic50 of 2.0  g / ml . the ei - ms of compound 1 had the [ m+ ] at m / z 270 , and c-13 nmr broad band indicated the presence of 16 carbon atoms and in agreement with c16h14o4 .
comparison of the spectroscopic data with those obtained from the literature identified the compound as 2,6-dihydroxy-4-methoxy chalcone ( cajachalcone ) ( figure 1 ) .
compound 2 with an ic50 > 5  g / ml also obtained from the ethyl acetate fraction , its ei - ms had a molar mass of 294 , the c-13 nmr , indicated 19c atoms and a formula of c19h17o3 , suggestive of a phenanthrone furandione derivative .
the data available were not sufficient to confirm the structure of compounds 2 and 3 .

 cajanus cajan l. , fabaceae , has been used locally as part of ethnotherapy for malaria infection in south western nigeria ; its utilization as an antimalarial agent cuts across the whole of sub - saharan africa as well as other tropical countries as reported by some authors [ 7 , 11 ] . from the result of this study ,
the crude methanol extract of this plant had an ic50 of 53.5  g / ml ; subsequently , bioassay - guided fractionation and chromatographic separations led to the isolation of the compound responsible for the displayed antimalarial activity 2,6-dihydroxy-4-methoxy chalcone ( cajachalcone ) ; the compound displayed significant antimalarial activity ic50 of 2.0  g / ml ( 7.4  m ) .
chloroquine diphosphate ( 10  g / ml ) was used as control and had ic50 value of 0.21  g / ml ( 0.66  m ) .
its structure was confirmed by comparison with h - nmr data reported for licochalcone a and 2,4-dimethoxy-4-butoxychalcone as shown in table 2 [ 12 , 13 ] . naturally occurring chalcones ( 1,3-diaryl-2-propen-1-one ) are the key intermediates for various plant metabolites .
they are biologically active compounds with known antibacterial [ 14 , 15 ] , antifilarial , antiviral [ 17 , 18 ] , antileishmanial , and cytotoxic [ 20 , 21 ] activities .
licochalcone a , an oxygenated chalcone ( figure 1 ) first isolated from roots of chinese licorice , showed antimalarial activity in both in vitro and in vivo systems . since then , investigators have been searching for new more - potent lead molecules based on chalcone scaffolds as potential antimalarial agents [ 23 , 24 ] .  
the simple structure and unambiguous synthesis of chalcones have attracted the attention of chemists to develop different analogs of this novel scaffold for various infectious diseases including malaria .
a series of alkoxylated , hydroxylated , prenylated , oxygenated , quinolylated chalcones from natural sources and syntheses have been evaluated for antiplasmodial activity with encouraging results [ 25 , 26 ] .
synthesized 4-methoxy ; 2,4-dimethoxy ; 2,5-dimethoxy ; 3,4-dimethoxy and 3,4,5-trimethoxy benzaldehyde series of chalcone derivatives . in the 4-methoxy series , with ic50 of 1.6  g / ml , the antimalarial activity compared favourably with licochalcone a ( ic50 of 1.43  g / ml ) against chloroquine - sensitive 3d7 strain . in 2,4-dimethoxy series , ic50 values of between 1.1 and 7.68 
the antimalarial activity of 2,4-dimethoxy chalcone ic50 2.1  g / ml ( a naturally occurring 4-methoxy derivative ) in our study was also compared favourably with the result of synthesized 4-methoxy series ( ic50 1.6  g / ml ) .
meanwhile , yadav and coworkers   concluded that the presence of methoxy groups at positions 2 and 4 in chalcone derivatives ( figure 1 ) appeared to be favorable for antimalarial activity as compared to other methoxy - substituted chalcones ; thus , we can infer that the isolated chalcone could be a template for the synthesis of 2,4-dimethoxy substituted derivatives , with methoxy substitution at position c-4 .  
it is believed that chalcone derivatives that possess antimalarial activity interact with parasite p. falciparum enzyme cysteine protease , one of the key enzymes involved in hemoglobin degradation within the acidic food vacuole of the intraerythrocytic parasite .
inhibition of this enzyme hampers digestion of hemoglobin within the food vacuole and proves fatal for the parasite .  
the world health organization 2011   has advised that the development of new tools is a necessary priority , particularly for vector control , diagnostic testing , treatment , and surveillance .
it is our belief that 2,4-dimethoxy chalcone isolated from cajanus cajan l could be a lead for antimalarial drug development .
chalcones and derivatives are small bioactive molecules that have been synthesized and so have a high potential as leads for discovery and development of antimalarial agents .
cajanus cajan l , a member of the family fabaceae , was identified from the nigerian antimalarial ethnobotany as possessing antimalarial properties . 
 the bioassay - guided fractionation of the crude methanol extract of c. cajan leaves was done in vitro using the multiresistant strain of plasmodium falciparum ( k1 ) in the parasite lactate dehydrogenase assay . 
 isolation of compound was achieved by a combination of chromatographic techniques , while the structure of the compound was elucidated by spectroscopy . 
 this led to the identification of a cajachalcone , 2,6-dihydroxy-4-methoxy chalcone , as the biologically active constituent from the ethyl acetate fraction . 
 cajachalcone had an ic50 value of 2.0  g / ml ( 7.4  m ) and could be a lead for anti - malarial drug discovery .