New triterpene and new flavone glucoside from Rhynchospora corymbosa (Cyperaceae) with their antimicrobial, tyrosinase and butyrylcholinesterase inhibitory activities

The CH sub(2)Cl sub(2)-MeOH (1:1) extract of the whole plant of Rhynchospora corymbosa (L.) Britton, led to the isolation of two new secondary metabolites 1, 2 (1 and 2a) together with nine known compounds 3-11. The flavone named tricin (11) was partially modified by esterification reaction to three semi-synthetic derivatives 11a-11c). Their structures were elucidated on the basis of spectroscopic analysis. The antimicrobial, tyrosinase and butyrylcholinesterase inhibitory activities revealed that, extract and compounds 1, 2a, 6, 11, 11a-c exhibited variable MICs (1-512 mu g/mL) and significant antimicrobial activity, depending on the microbial species; Antifungal activity of 11 and 11c was more important than that of nystatine used as reference antifungal drugs. The inhibitory activity of 4 (IC sub(50) = 43.28 mu g/mL) was higher than that of the kojic acid (IC sub(50) = 49.62 mu g/mL) which is known tyrosinase inhibitor. The extract, compounds 1, 7-10, and 11a-c exhibited significant (p < 0.05) differences in the concentrations of 50% BuChE inhibition (IC sub(50)). These results suggest that the, R. corymbosa could be exploited as a potential source of natural antimicrobial, and antibutyrylcholinesterase agents as well as tyrosinase inhibitors.