Ultrasound assisted extraction and solvent partition for polyhydroxylated and polymethoxylated flavones and phenolic acids from orthosiphon aristatus

Abstract

The technique of ultrasound-assisted extraction was used to recover polyhydroxylated and polymethoxylated flavones, and phenolic acids from Orthosiphon aristatus. The compounds were then partitioned in different solvents such as hexane, chloroform, ethyl acetate, and acetone with increasing polarity. This workflow would reduce the complexity of chemical composition in crude extract to ease phytochemical profiling using a high throughput analytical tool of liquid chromatography with tandem mass spectrometry. Several newly reported flavone derivatives such as velutin, tricin, 3,7-dimethylquercetin, 4 ',7 '-dimethoxyluteolin, 4 ',7 '-dimethoxyluteolin-dimethyl ether, and 5-hydroxy-3,4 ',7-trimethoxyflavone, in addition to previously reported compounds were detected. The recovered flavone derivatives were mostly lipophilic in nature because they were partitioned in hexane and chloroform, particularly the dimer and trimer of sinensetin. Meanwhile, phenolic acids such as rosmarinic acid and salvianolic acid were detected in the ethyl acetate and acetone fractions, as well as in the remaining aqueous residue. These phenolic acids rich fractions were also found to have higher antioxidant capacity than crude extract. The combination of ultrasound-assisted extraction and solvent partition provided insights into the profile of polyhydroxylated and polymethoxylated flavones, and phenolic acids from the highly complex herbal plant of O. aristatus. The detection of the phytochemicals may explain the previously reported pharmacological properties of the herb.