In-Vitro 5-Lipoxygenase Inhibiting Activity of Selected Malaysian Plants and Isolation of Constituents

5-Lipoxygenase (5-LO) is the key enzyme in biosynthesis of inflammatory mediators known as leukotrienes which are responsible for asthma, allergic inflammation and innate immunity. This paper reports the evaluation of 30 species of Malaysian plant extracts potential in inhibiting 5-LO activity. Five plant extracts exhibited >80% inhibition against 5-LO activity which include Phyllanthus watsonii, Euphorbia hirta, Anacardium occidentale, Acalypha wilkensiana and Piper betle. Nine plant extracts exhibited moderate value of inhibition (79-40%), while sixteen others exhibited <40% inhibition. From the screening work via inhibition of 5-LO activity, P. watsonii showed the highest inhibition with value of 97.3%, followed by E. hirta with 90.9% inhibition. Both plant extracts were further fractioned using organic solvent which include Dichloromethane (DCM), Ethyl Acetate (EA) and Butanol (BuOH) for evaluation of their inhibiting effects on 5-LO activity. For P. watsonii, DCM fraction exhibited the highest value with 75% inhibition, while for E. hirta, EA fraction exhibited the highest value of 72.5% inhibition. Both active fractions were further subjected to isolation and purification work in order to identify the major compounds. Subsequently, four major compounds managed to be isolated and purified which further identified as quercetin-3-O-rhamnoside (E1), myricetin-3-O-rhamnoside (E2), 26-nor-D: A-friedoolean-14-en-3β-ol (PW1) and glochidonol (PW2) using spectroscopic technique and their data comparison with literature.