Pharmacological effects and phenolic constituents of Rheum wittrockii

Medicinal plants are major sources of bioactive polyphenols. The plants of Rheum genus contain valuable phenolic compounds which exhibit various important pharmacological activities.

The current study was designed to investigate the polyphenols in Rheum wittrockii roots through bioassays and extraction/ isolate them via chromatophilic methods.

The roots biomass of R. wittrockii was extracted with methanol and fractionated into four sub-fractions, i.e. n-hexane, chloroform, ethyl acetate and n-butanol (FG1-FG4). Total Phenolic Content (TPC) assay was used to affirm the number of total phenolic contents equivalent to gallic acid. Antioxidant activities were measured via 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. α-amylase enzyme inhibition activities were performed using standard methods. Antibacterial activities were performed against Methicillin-Resistant Staphylococcus Aureus (MRSA) in dose dependent manner for all the fractions. The FG2 fraction was subjected to series of chromatographic separation using silica gel column to isolate the main phenolic compounds.

Chloroform fraction (FG2) showed TPC of 12.5 mg/g GAE, strong antioxidant activities i.e. 85±0.22% at dose of 100 mg/mL (IC₅₀= 6.25 mg/mL) against DPPH and also showed strong α-amylase inhibition activities with IC₅₀ values of 432 µg/mL, compared to IC₅₀ of standard acarbose (125 µg/mL). It was active antibacterial against MRSA at lower doses. The FG2 fraction was further subjected to various chromatographic separations to obtain three known phenolic compounds, protocatecutic acid (1), isovanilliic acid (2) and epipinoresinol (3) in appreciable quantities for the first time from this plant. The structures of all the three compounds were elucidated through FT-IR, NMR and Mass spectral studies.

The present investigation concluded that the roots of Rheum wittrockii is a good source of phenolics. Its chloroform fraction showed potent antioxidant, anti-diabetic and antibacterial effects probably due to its three compounds isolated for the first time. The compounds are valuable pharmaceuticals with promising biological actions.