Isolation and characterization of phenolic compounds from antidiabetic plant, Costus speciosus

Abstract

The medicinal plant Costus speciosus (Koen) Sm. or crepe ginger, Thebu in Sinhala, belongs to the Family Costaceae and inherits a range of pharmacological activities, antidiabetic effect being reported as of great importance. The plant is also well known for its antioxidant, antibacterial, anthelmintic, anticancer, anxiolytic, anti-inflammatory, antipyretic, hepatoprotective and diuretic properties. Phenolic compounds are highly significant plant secondary metabolites that exert various health benefits in humans, including antioxidant effects, chemopreventive properties and anti-inflammatory activity. Therefore, the current study focused on isolating phenolic compounds in the leaf extracts of C. speciosus. Dried, powdered leaves were subjected to sequential extraction with hexane, ethyl acetate and methanol through ultrasound sonication. Ethyl acetate and methanol extracts were combined, re-dissolved in dichloromethane and partitioned with aqueous sodium bicarbonate followed by aqueous sodium hydroxide. Aqueous layers were re-extracted with ethyl acetate after neutralization, and the ethyl acetate extract was fractionated via silica gel column chromatography and size exclusion chromatography (Sephadex LH-20) and PTLC. Isolated compounds were characterized via ¹H NMR and ¹³C NMR spectroscopy. This approach furnished transcinnamaldehyde, p-coumaric acid, 4-hydroxybenzoic acid, vanillic acid, ferulic acid, indole-3- carboxaldehyde, kaempferol-3-O-β-D-glucopyranoside, sitosterol glucoside and (E)-1,3-bis(4- hydroxy-3-methoxyphenyl) prop-2-en-1-one. These compounds possess several bioactivities, including antioxidant, antibacterial and anti-inflammatory activities. Dissolving phenolic compounds into a basic aqueous layer and re-extraction with organic solvent after neutralization seems to be an efficient method to isolate phenolic compounds from plant extracts.