The antioxidant properties of the various extracts and flavonoids prepared from Oxytropis falcate Bunge were investigated by 1,1-diphenyl-2-picryldydrazyl (DPPH) radical-scavenging assay. In the chloroform, ethyl acetate and n-butanol extracts, the ethyl acetate extract exhibited the highest antioxidant activity (IC(50) = 2.05 mg mL(-1)). Furthermore, rhamnocitrin, kaempferol, rhamnetin, 2',4'-dihydroxychalcone and 2',4', beta-trihydroxy-dihydrochalcone were purified from chloroform and ethyl acetate extracts. The radical-scavenging activities of the five compounds were also measured and the results showed that kaempferol (IC(50) = 0.11 mg mL(-1)), rhamnetin (IC(50) = 0.14 mg mL(-1)) and rhamnocitrin (IC(50) = 0.15 mg mL(-1)) exhibited considerable antioxidant activities, but the antioxidant activities of the two dihydrochalcones were very weak. Although these flavonoids are known, this is the first report of antioxidant activity in this plant.
Preliminary studies with the four extracts of Oxytropis falcate Bunge exhibited that the chloroform and ethyl acetate extracts showed stronger antibacterial activities against the nine tested Gram-positive and Gram-negative bacteria. The HPLC-scanned and bioassay-guided fractionation led to the isolation and identification of the main flavonoid compounds, i.e. rhamnocitrin, kaempferol, rhamnetin, 2',4'-dihydroxychalcone and 2',4',beta-trihydroxy-dihydrochalcon. Except 2',4',beta-trihydroxy-dihydrochalcon, four other compounds had good antibacterial activities. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of the four compounds ranged between 125 and 515 microg mL(-1). Staphylococcus aureus was the most susceptible to these compounds, with MIC and MBC values from 125 to 130 microg mL(-1). This is the first report of antibacterial activity in O. falcate Bunge. In this study, evidence to evaluate the biological functions of O. falcate Bunge is provided, which promote the rational use of this herb.
The antioxidant activity of the essential oil from Oxytropis falcate Bunge was determined spectrophotometrically using the 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH) while the oil was analyzed by GC and GC/MS. The oil exhibited an IC 50 value at 0.17 mg/mL. Analysis revealed that 50 compounds were identified, consisting 89.0% of the total oil. Viridiflorol (11.5%), (E)-nerolidol (8.2%), ethyl hexadecanoate (6.5%), tricosane (5.6%) and spathulenol (5.4%) were the major components of the oil.
Antimicrobial drug resistance demands novel approaches for improving the efficacy of antibiotics, especially against Gram-negative bacteria. Here we report that conjugating a diglycine (GG) to a prodrug of antibiotics drastically accelerates intrabacterial hydrolysis of ester bond for regenerating the antibiotics against E. coli. Specifically, the attachment of GG to chloramphenicol succinate (CLsu) generates a novel conjugate (CLsuGG), which exhibits about an order of magnitude higher inhibitory efficacy than CLsu against E. coli. Further studies reveal that CLsuGG undergoes rapid hydrolysis catalyzed by intrabacterial esterases (e.g., BioH and YjfP) for generating chloramphenicol (CL) in E. coli. More importantly, the conjugate exhibits lower cytotoxicity to bone marrow stromal cells that CL does. The structural analogs of CLsuGG indicate that the conjugation of GG is an effective strategy for accelerating hydrolysis catalyzed by esterases and enhancing antibacterial efficacy of antibiotics. This work, for the first time, illustrates that dipeptide conjugation modulates intrabacterial hydrolysis for increasing antibiotic efficacy and reducing adverse drug effects.Infectious disease remains a major threat to public health.
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