The use of Chalcones for malarial treatment

Focusing on design, experimental synthesis, model system, mechanization and results.

BYALEX PETER(A00014064)

INTRODUCTIONFor the past decades, efforts have been made to

alleviate mortality rate caused by diseases in third-world countries. Despite all these efforts, malaria is still one of the most deadly disease which claims millions of lives annually. This issue has been combated by the recent interest in the anti-malarial activity of chalcones. Chalcone is 1,3 diphenyl-2-propen-1-one. The anti-malarial property of chalcone was first discovered when Licochalcone A, a natural product extracted from Chinese liquorice roots, was reported to exhibit potent in vivo and in vitro anti-malarial activity. Chalcones act against anti-malarial cysteine protease, an enzyme used by the parasite for the degradation of host hemoglobin for its nutritional purposes.

SYNTHESISA series of alkoxylated and hydroxylated

chalcones can be synthesized and evaluated for in vitro(human being) anti-malarial activity. some can also be tested in vivo in plasmodium berghei infected mice. The alkoxylated chalcones were synthesized by a base- catalyzed Claisen Schmidt condensation of an aromatic aldehyde with the appropriate acetophenone. 2,4 Dimethoxy-4’-butoxychalcone was also synthesized as a standard compound for comparison of antimalarial activity against human(in vitro) and rodent(in vivo) parasites.

STRUCTURE 1The synthesis of alkoxylated chalcones

STRUCTURE 2

SYNTHESISFor the synthesis of hydroxylated chalcones,

protection of the phenolic groups on the acetophenone is necessary for improved product yields. The hydroxyl group on the acetophenone is protected with a 2H-3,4-dihydropyran, is reacted with aldehyde and is removed subsequently by acid hydrolysis to give the chalcone, which is purified by chromatography and crystallization. The Aromatic rings in the final chalcones are designated A(from the aldehyde) and B(from acetophenone) respectively.

TEST IN VITRO ANTIMALARIAL ACTIVITYIn vitro test, antimalarial activity was assessed

against a chloroquine-resistant human malarial parasite, p. falciparum. P. falciparum strains poW (IC50 of chloroquine=0.015) and Dd2(IC50=0.14) were maintained in continuous culture in human red blood cells (A+) diluted to 5% haemotocrit in RPMI. Antiplasmodial tests were performed on 96-well culture plates. All tests were performed in triplicate. The percentage of growth inhibition was calculated and the concentration at which growth was inhibited by 50% (IC50) was estimated by interpolation.

TEST IN VIVO ANTIMALARIAL ACTIVITYThe active chalcones identified from in vitro tests

(7 hydroxychalcones, IC50 < 20; methoxychalcones, IC50 < 10) were tested in mice infected with p. berghei ANKA, a chloroquine-susceptible strain of murine malaria. The mice were given the drugs for three consecutive days, and their survival times were monitored and compared with control mice receiving DMSO (untreated mice), chloroquine. The survivability of the mice were tested from the ratio of the average lifespan of the drug-treated animal to that of the untreated animals.

RESULTS AND CONCLUSIONIn the vitro tests, it was discovered that hydroxylated

chalcones were less active than their alkoxylated counterparts. There was also a good representation of active compounds from the trimethoxy, dimethoxy and methoxy series, but interestingly none from the ethoxy series. The IC50 also increased to 108.

In the vivo tests, 2,4 dimethoxy and 2,4 dihydroxy were the compounds which have T/Ccq > 1.5 which made them to be as good as chloroquine. The activity of 2,4 dimethoxy may have been anticipated due to its low IC50 value but the activity of 2,4 dihydroxy is surprising because it is not particularly active in the vitro tests.