Sinensetin, eupatorin, 3′-hydroxy-5,6,7,4′-tetramethoxyflavone and rosmarinic acid contents and antioxidative effect of Orthosiphon stamineus from Malaysia

An HPLC method was developed for the separation and determination of three methoxylated flavones:sinensetin (SEN), eupatorin (EUP) and 3-hydroxy-5,6,7,4'-tetramethoxyflavone (TMF) and rosmarinic acid (RA), a caffeic acid derivative in Orthosiphon stamineus (OS). All the compounds were separated using a reversed phase C 18, Lichrosorb column with the mobile phase of methanol-water-tetrahydrofuran (45:50:5 v/v). The HPLC method was applied for the quantification SEN, EUP, TMF and RA in OS from different places in Malaysia. The results showed significant variation in the amounts of these markers in methanolic extracts of leaf samples from different parts of Malaysia. A variation in antioxidant activities, ranging from 55.5% to 84.2% and variations in total phenolics, ranging from 6.7 to 10.1 mg caffeic acid/g dry weight of the methanol extracts, were observed. Antioxidative potency of the methanol extracts was comparable to that of pure quercetin and the synthetic antioxidant butylated hydroxylanisole (BHA). (C) 2004 Elsevier Ltd. All rights reserved.