Yixi Xie

Antibacterial Activities of Flavonoids: Structure-Activity Relationship and Mechanism

Flavonoids are well known as antibacterial agents against a wide range of pathogenic microorganism. With increasing prevalence of untreatable infections induced by antibiotic resistance bacteria, flavonoids have attracted much interest because of the potential to be substitutes for antibiotics. In this review, the structure-relationship of flavonoids as antibacterial agents is summarized, and the recent advancements on the antibacterial mechanisms of flavonoids are also discussed. It is concluded that hydroxyls at special sites on the aromatic rings of flavonoids improve the activity. However, the methylation of the active hydroxyl groups generally decreases the activity. Besides, the lipopholicity of the ring A is vital for the activity of chalcones. The hydrophobic substituents such as prenyl groups, alkylamino chains, alkyl chains, and nitrogen or oxygen containing heterocyclic moieties usually enhance the activity for all the flavonoids. The proposed antibacterial mechanisms of flavonoids are as follows: inhibition of nucleic acid synthesis, inhibition of cytoplasmic membrane function, inhibition of energy metabolism, inhibition of the attachment and biofilm formation, inhibition of the porin on the cell membrane, alteration of the membrane permeability, and attenuation of the pathogenicity.

Systematic and efficient separation of 11 compounds from Rhizoma Chuanxiong via counter-current chromatography-solid phase extraction-counter-current chromatography hyphenation.

A counter-current chromatography (CCC)-solid phase extraction (SPE)-CCC system with high preparative capacity was used to realize rapid one-run systematic separation of natural products, in which two six-port valves and the SPE cartridge served as the interface. In the orthogonal separation system, equal column volumes of TEB-300A and TEB-300B were employed for the first dimension (1st-D) and second dimension (2nd-D), respectively. An optimized solid-phase column (25 mm × 10 mm i.d.) packed with Oasis HLB materials acted as the trapping SPE column. The analyte-focusing effect of the trapping column associated with the considerable preparative capacities of 1st-D and 2nd-D using totally different solvent systems significantly facilitated this one-run systematic separation of natural product. Therefore, this proposed approach was successfully applied to isolate chemical compounds from the crude extract of Rhizoma Chuanxiong. As a result, 11 compounds with widely different polarities were separated by running CCC for only one time. More importantly, this hyphenated strategy could serve as a rapid and efficient systematic pathway for the separation of natural products.

Separation of five flavonoids from tartary buckwheat (Fagopyrum tataricum (L.) Gaertn) grains via off-line two dimensional high-speed counter-current chromatography

An off-line two dimensional (2D) high-speed counter-current chromatography (HSCCC) strategy was successfully used for preparative separation of five flavonoids from tartary buckwheat (Fagopyrum tataricum (L.) Gaertn) grains with different solvent systems for the first time in this paper. n-Hexane-ethyl acetate-methanol-water 3:5:3:5 (v/v) was selected as the first dimension solvent system to purify quercetin (4) and kaempferol (5). The second dimension solvent system, ethyl acetate-n-butanol-water 7:3:10 (v/v), was used to isolate quercetin 3-O-rutinoside-3-O-β-glucopyranoside (1), rutin (2) and kaempferol 3-rutinoside (3). The purities of these compounds were all above 96.0% and their structures were identified through UV, MS and (1)H NMR. The results indicated that the off-line 2D HSCCC is an efficient technique to isolate flavonoids compounds from grains.

Fetal bovine serum influences the stability and bioactivity of resveratrol analogues: A polyphenol-protein interaction approach.

Fetal bovine serum (FBS) is a universal growth supplement of cell and tissue culture media. Herein, the influences of FBS on the stability and antioxidant activity of 21 resveratrol analogues were investigated using a polyphenol-protein interaction approach. The structure-stability relationships of resveratrol analogues in FBS showed a clear decrease in the stability of hydroxylated resveratrol analogues in the order: resorcinol-type>pyrogallol-type>catechol-type. The glycosylation and methoxylation of resveratrol analogues enhanced their stability. A linear relationship between the stability of resveratrol analogues in FBS and the affinity of resveratrol analogues-FBS interaction was found. The oxidation process is not the only factor governing the stability of resveratrol analogues in FBS. These results facilitated the insightful investigation of the role of polyphenol-protein interactions in serum, thereby providing some fundamental clues for future clinical research and pharmacological studies on natural small molecules.

Type 2 diabetes diminishes the benefits of dietary antioxidants: Evidence from the different free radical scavenging potential

The development of food fortified with polyphenols and polyphenol-rich foods represents a novel approach for preventing or managing type 2 diabetes. Herein, taking advantage of several radical scavenging, the impact of plasma proteins in diabetes on the benefits of dietary polyphenols was investigated. It illustrated that plasma proteins masked the dietary polyphenols, thus reducing their radical scavenging potential. The plasma proteins from type 2 diabetics bind and protect (i.e., mask) the polyphenol antioxidants less effectively than the non-glycosylated ones in healthy blood do. In the blood of diabetics the less-protected (non-masked) antioxidants react with free radicals before being delivered to the tissues that need them. We should pay more attention to in vivo benefits of dietary polyphenols for type 2 diabetics.

Improved enantioseparation via the twin-column based recycling high performance liquid chromatography

A long-neglected recycling high performance liquid chromatography (R-HPLC) strategy was adopted to improve the enantioseparation efficiency in this work. Taking intractable isoxazolidine mixtures as the example, two different R-HPLC methods including single-column and twin-column based strategy were applied to improve the enantioseparation efficiency. Under the optimized conditions, these two methods present distinct separation results: the conceptually simple and commonly used single-column based R-HPLC led to severe peak broadening and degraded separation efficiency; on the contrary, the enantioseparation was significantly improved by adopting the relatively complicated twin-column strategy. This observed difference might be mainly attributed to less peak spreading and sample mixing of the latter, as a result of avoiding redirecting the effluent back to LC pump.