Bio-guided isolation of antimicrobial compounds from Cnestis palala

Day khe (Cnestis palala (Lour.) Merr., Connaraceae) has been widely distributed in Hoa Binh province, Vietnam. The aqueous and ethanolic extracts of the stems of C. palala (10 mg/well) showed antibacterial effects on Staphylococcus aureus and Bacillus subtilis by agar diffusion method with diameter antibacterial zone values ranged from 8,3 ± 0,4 mm to 12,3 ± 0,4 mm. Maximum antibacterial activity was exhibited by ethanol 96 % extract against Staphylococcus aureus and Bacillus subtilis with MBC values of 5,2 and 41,5 mg/ml, respectively. This study aimed to isolate and evaluate the antimicrobial activity of some bioactive compounds from C. palala stem using bioguided fractionation. Their activities on S. aureus and S. epidermidis have been evaluated. Various chromatographical techniques were applied for isolation and purification. Antimicrobial activity was determined by multi-concentration dilution. Two bioactive compounds 3,4-dihydroxybenzoic acid (protocatechuic) (1) and 2,10-bis(3,4-dihydroxyphenyl)-3,5-dihydroxy-3,4,9,10-tetrahydro-2H,8H-pyrano[2,3-f]chromen-8-on (cinchonain) (2) were purified and determined structure. Their antimicrobial activities were confirmed using the microdilution method on S. aureus and S. epidermidis. The activity of compound 1 against S. aureus and S. epidermidis: MIC was 128 µg/ml and 16 µg/ml, respectively, and IC50 was 46,78 ± 1,36 µg/ml and 5,67 ± 1,36 µg/ml, respectively. The activity of compound 2 against S. aureus and S. epidermidis: MIC were 128 µg/ml và 16 µg/ml respectively, and IC50 was 43,23 ± 2,45 µg/ml and 6,34 ± 2,45 µg/ml, respectively. These results highlight the ethno-traditional use of Cnestis palala for infections and recommend further developing antimicrobial products.