Flavonoids are one of the largest classes of small molecular secondary metabolites produced in different parts of the plant. They display a wide range of pharmacological and beneficial health effects for humans, which include, among others, antioxidative activity, free radical scavenging capacity, coronary heart disease prevention and antiatherosclerotic, hepatoprotective, anti-inflammatory, and anticancer activities. Hence, flavonoids are gaining high attention from the pharmaceutical and healthcare industries. Notably, plants synthesize flavonoids in response to microbial infection, and these compounds have been found to be a potent antimicrobial agent against a wide range of pathogenic microorganisms in vitro. Antimicrobial action of flavonoids results from their various biological activities, which may not seem very specific at first. There are, however, promising antibacterial flavonoids that are able not only to selectively target bacterial cells, but also to inhibit virulence factors, as well as other forms of microbial threats, e.g. biofilm formation. Moreover, some plant flavonoids manifest ability to reverse the antibiotic resistance and enhance action of the current antibiotic drugs. Hence, the development and application of flavonoid-based drugs could be a promising approach for antibiotic-resistant infections. This review aims to improve our understanding of the biological and molecular roles of plant flavonoids, focusing mostly on their antimicrobial activities.

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Comprehensive review of antimicrobial activities of plant flavonoids

Natural and synthetic chromenes, fused chromenes, and versatility of dihydrobenzo[h]chromenes in organic synthesis.

Natural Science Foundation of China[30000213, 30370160, 30670214]; National Basic Research Program of China (973 Program)[2009CB522300]; Chinese Academy of Sciences

Meliaceous limonoids: chemistry and biological activities.

Jin-Ming Gao,*,† Sheng-Xiang Yang,‡ and Jian-Chun Qin †Shaanxi Engineering Center of Bioresource Chemistry & Sustainable Utilization, Department of Chemistry and Chemical Engineering, College of Science, Northwest A&F University, 3 Taicheng Road, Yangling 712100, Shaanxi, China ‡College of Science, Zhejiang A&F University, Lin’an, Hangzhou 311300, Zhejiang, China College of Plant Sciences, Jilin University, Changchun, Jilin 130062, China

Azaphilones: Chemistry and Biology

Based on World Health Organization reports, resistance of bacteria to well-known antibiotics is a major global health challenge now and in the future. Different strategies have been proposed to tackle this problem including inhibition of multidrug resistance pumps and biofilm formation in bacteria and development of new antibiotics with novel mechanism of action. Flavonoids are a large class of natural compounds, have been extensively studied for their antibacterial activity, and more than 150 articles have been published on this topic since 2005. Over the past decade, some promising results were obtained with the antibacterial activity of flavonoids. In some cases, flavonoids (especially chalcones) showed up to sixfold stronger antibacterial activities than standard drugs in the market. Some synthetic derivatives of flavonoids also exhibited remarkable antibacterial activities with 20- to 80-fold more potent activity than the standard drug against multidrug-resistant Gram-negative and Gram-positive bacteria (including Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus). This review summarizes the ever changing information on antibacterial activity of flavonoids since 2005, with a special focus on the structure-activity relationship and mechanisms of actions of this broad class of natural compounds.

Antibacterial activity of flavonoids and their structure-activity relationship: An update review.

A dihydrobenzo[c]phenanthridine alkaloid, epizanthocadinanine A (1), together with 27 known compounds, including eight benzo[c]phenanthridines, i.e., oxynitidine (2), oxyavicine (3), oxychelerythrine (4), dihydrochelerythrine (5), 6-acetonyldihydrochelerythrine (6), norchelerythrine (7), decarine (8), and arnottianamide (9); two 2-quinolones, i.e., flindersine (10) and 4-methoxy-1-methyl-2-quinolone (11); two furoquinolines, i.e., skimmianine (12) and gamma-fagarine (13); three aporphines, i.e., liriodenine (14), N-acetyldehydroanonaine (15), and N-acetylanonaine (16); six lignans, i.e., sesamin (17), episesamin (18), piperitol-3,3-dimethylallyl ether (19), xanthoxylol-3,3-dimethylallyl ether (20), savinin (21), and 2,3-bis(3,4-methylenedioxybenzyl)but-2-en-4-olide (22); three terpenoids, i.e., alpha-cadinol (23), anticopalol (24), and spathulenol (25); one coumarin, i.e., aesculetin dimethyl ether (26); and two steroids, i.e., beta-sitosterol (27) and beta-sitostenone (28) were isolated from the stem bark of Zanthoxylum nitidum. Their structures were elucidated on the basis of extensive 1D- and 2D-NMR as well as MS analyses. Moreover, the recently reported structures 2'-4' of rhoifolines B and A, and '8-methoxynorchelerythrine', resp., isolated as new compounds from Z. rhoifolium and Z. nitidum, resp., could be assigned the revised structures 2-4 by reinvestigation of the spectroscopic data. In addition, the cytotoxicity of the isolates was evaluated on the MCF-7, NCI-H460, and SF-268 cell lines. Among these isolates, liriodenine (14) was the most active compound against the MCF-7, NCI-H460, and SF-268 cell lines with IC(50) values of 2.19, 2.38, and 3.19 microg/ml, resp.

Secondary metabolites and cytotoxic activities from the stem bark of Zanthoxylum nitidum.

A new phragmalin-type limonoid and anti-inflammatory constituents from the fruits of Swietenia macrophylla

Investigation of the roots of Beilschmiedia erythrophloia has led to the isolation of seven new endiandric acid analogues, erythrophloins A-F (1-6) and beilcyclone A (7), together with 11 known compounds. The structures of 1-7 were determined using spectroscopic techniques. Two constituents, erythrophloin C (3) and suberosol B (8), exhibited antitubercular activity against Mycobacterium tuberculosis H37Rv, showing MIC values of 50 and 28.9 microg/mL, respectively.

Endiandric Acid Analogues from the Roots of Beilschmiedia erythrophloia.

Four new flavanones, cryptoflavanones A-D (1-4, resp.), together with eight known compounds, were isolated from the leaves of Cryptocarya chinensis. The structures of these new compounds were determined by spectral analyses. Among the isolated compounds, pinocembrin (5) and cryptocaryone (6) exhibited antituberculosis activity against Mycobacterium tuberculosis H(37) Rv strain in vitro with MIC values of 3.5 and 25.0 μg/ml, respectively.

Ming Jen Cheng

Papers

Secondary metabolites and cytotoxic activities from the stem bark of Zanthoxylum nitidum.

A new phragmalin-type limonoid and anti-inflammatory constituents from the fruits of Swietenia macrophylla

Endiandric Acid Analogues from the Roots of Beilschmiedia erythrophloia.

New Flavanones from the Leaves of Cryptocarya chinensis and Their Antituberculosis Activity

Antioxidant activities of extracts and metabolites isolated from the fungus Antrodia cinnamomea.