Antibacterial constituents of Rumex nepalensis spreng and its emodin derivatives

The CH2Cl2−MeOH (1:1) extract of roots of Rumex nepalensis (Polygonaceae) displayed significant antibacterial activity against five bacterial strains with MICs (62.5–31.2 μg.mL−1). The EtOAc soluble fraction displayed a significant activity against the same strains with MICs (31.2–3.9 μg.mL−1). The purification of the EtOAc fraction yielded one new phenylisobenzofuranone derivative, berquaertiide (1), along with 19 known compounds (2–20). Their structures were elucidated based on the analysis of their NMR and MS data. All the isolated compounds were assessed for their antibacterial activity. Compound 2 was the most active against all the tested strains (15.7 to 1.9 μg.mL−1), while compounds 3–7 displayed good activities on at least one of the tested strains. In addition, seven analogues (21–27) of compound 2 were prepared and further assessed for their antibacterial activity. Compounds 26 and 27 were most active than 2 against Salmonella enterica and Klebsiella pneumoniae with MIC (125 and 15.6 μg.mL−1, respectively).