Ericoside, a new antibacterial biflavonoid from Erica mannii (Ericaceae)

Two new flavone glycosides from the leaves of Ochna afzelii Oliv. (Ochnaceae)

Two new glycosylflavones, 6''-O-acetyl-8-C-β-D-galactopyranosylchrysoeriol (1) and 8-C-β-D-galactopyranosylchrysoeriol (2) were isolated from the methanol extract of the leaves of Ochna afzelii Oliv., along with four known compounds namely 8-C-β-D-galactopyranosylapigenin (3), ochnaflavone (4), sitosterol-3-O-β-D-glucopyranoside (5) and D-mannitol (6). Isolation was performed chromatographically and the structures of the purified compounds were elucidated by analyzing their spectroscopic and mass spectrometric data. The antibacterial activity of extract, fractions, and compounds 1 - 4 was evaluated using broth microdilution method against Gram-positive and Gram-negative bacteria while the antioxidant capacity was performed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the ferric reducing antioxidant power (FRAP) methods. The new flavones (1 and 2) displayed moderate antibacterial activities (MIC = 32 - 64 µg/mL) and weak antioxidant properties.

Proceedings of Chemistry, Pharmacology, Pharmacokinetics and Synthesis of Biflavonoids

Biflavonoids, composed of two monoflavonoid residues, occur naturally in angiosperms, bryophytes, ferns, and gymnosperms. More than 592 biflavonoids have been structurally elucidated, and they can be classified into two groups of C-C and C-linear fragments-C, based on whether the linker between the two residues contains an atom. As the linker can be established on two arbitrary rings from different residues, the C-C type contains various subtypes, as does the C-linear fragment-C type. Biflavonoids have a wide range of pharmacological activities, including anti-inflammatory, antioxidant, antibacterial, antiviral, antidiabetic, antitumor, and cytotoxic properties, and they can be applied in Alzheimer's disease and Parkinson's disease. This review mainly summarizes the distribution and chemistry of biflavonoids; additionally, their bioactivities, pharmacokinetics, and synthesis are discussed.

Prenylated Flavonoids and C-15 Isoprenoid Analogues with Antibacterial Properties from the Whole Plant of Imperata cylindrica (L.) Raeusch (Gramineae)

The local botanical Imperata cylindrica in Cameroon was investigated for its antibacterial potency. The methanol extract afforded a total of seven compounds, including five hitherto unreported compounds comprising three flavonoids (1–3) and two C-15 isoprenoid analogues (4 and 5) together with known derivatives (6 and 7). The novelty of the flavonoids was related to the presence of both methyl and prenyl groups. The potential origin of the methyl in the flavonoids is discussed, as well as the chemophenetic significance of our findings. Isolation was performed over repeated silica gel and Sephadex LH-20 column chromatography and the structures were elucidated by (NMR and MS). The crude methanol extract and isolated compounds showed considerable antibacterial potency against a panel of multi-drug resistant (MDR) bacterial strains. The best MIC values were obtained with compound (2) against S. aureus ATCC 25923 (32 µg/mL) and MRSA1 (16 µg/mL).

Natural biflavonoids as potential therapeutic agents against microbial diseases

Microbes broadly constitute several organisms like viruses, protozoa, bacteria, and fungi present in our biosphere. Fast-paced environmental changes have influenced contact of human populations with newly identified microbes resulting in diseases that can spread quickly. These microbes can cause infections like HIV, SARS-CoV2, malaria, nosocomial Escherichia coli, methicillin-resistant Staphylococcus aureus (MRSA), or Candida infection for which there are no available vaccines/drugs or are less efficient to prevent or treat these infections. In the pursuit to find potential safe agents for therapy of microbial infections, natural biflavonoids like amentoflavone, tetrahydroamentoflavone, ginkgetin, bilobetin, morelloflavone, agathisflavone, hinokiflavone, Garcinia biflavones 1 (GB1), Garcinia biflavones 2 (GB2), robustaflavone, strychnobiflavone, ochnaflavone, dulcisbiflavonoid C, tetramethoxy-6,6″-bigenkwanin and other derivatives isolated from several species of plants can provide effective starting points and become a source of future drugs. These biflavonoids show activity against influenza, severe acute respiratory syndrome (SARS), dengue, HIV-AIDS, coxsackieviral, hepatitis, HSV, Epstein-Barr virus (EBV), protozoal (Leishmaniasis, Malaria) infections, bacterial and fungal infections. Some of the biflavonoids can provide antiviral and protozoal activity by inhibition of neuraminidase, chymotrypsin-like protease, DV-NS5 RNA dependant RNA polymerase, reverse transcriptase (RT), fatty acid synthase, DNA polymerase, UL54 gene expression, Epstein-Barr virus early antigen activation, recombinant cysteine protease type 2.8 (r-CPB2.8), Plasmodium falciparum enoyl-acyl carrier protein (ACP) reductase or cause depolarization of parasitic mitochondrial membranes. They may also provide anti-inflammatory therapeutic activity against the infection-induced cytokine storm. Considering the varied bioactivity of these biflavonoids against these organisms, their structure-activity relationships are derived and wherever possible compared with monoflavones. Overall, this review aims to highlight these natural biflavonoids and briefly discuss their sources, reported mechanism of action, pharmacological uses, and comment on resistance mechanism, flavopiridol repurposing and the bioavailability aspects to provide a starting point for anti-microbial research in this area.

Antimicrobial flavonoids as a potential substitute for overcoming antimicrobial resistance

BACKGROUND

Infectious diseases are the leading cause of death in 21^st century due to antimicrobial resistance and scarcity of new molecules to undertake rising infections. There could be a multiple reasons behind antimicrobial resistance whether it is increased drug metabolism or bacterial endotoxins. The demand of effective medication is increasing day by day to treat microbial infections and combat antimicrobial resistance. In recent years most of the synthetic antimicrobials developed resistance so natural products could provide better options to fulfill this demand. There has been increasing interest in the research on flavonoids because various flavonoids were found to be effective against pathogenic microorganisms.

OBJECTIVE

The objective of this article will be to explore antimicrobial activity of flavonoids with special focus on their possible mechanism of action.

METHODS

The article reviewed recent literature related to flavonoids with antimicrobial activity, which were isolated from various sources and the compounds showing fairly good activity against tested microbial species were discussed.

RESULTS

By throughout literature review it has been found that flavonoids show antimicrobial effect by inhibiting virulence factors, efflux pump, biofilm formation, membrane disruption, cell envelop synthesis, nucleic acid synthesis, and bacterial motility inhibition.

CONCLUSION

Most of the antimicrobial drugs available now a days are ineffective due to development of resistance to them. Flavonoids have the potential to overcome this emerging crisis as this class of natural products showed the antimicrobial activity by different mechanisms than those of conventional drugs, so flavonoid could be an effective treatment of pathogenic infections.

Natural disesquiterpenoids: an update

This review highlights the progress on the isolation, bioactivity, biogenesis and total synthesis of dimeric sesquiterpenoids since 2010.

Neo-clerodane diterpenoids from Conyza pyrrhopappa Sch.Bip. ex A.Rich

Two hitherto unknown neo-clerodane-type diterpenoids along with twelve known compounds have been isolated from Conyza pyrrhopappa Sch.Bip. ex A.Rich, a medicinal plant traditionally used across tropical Africa to relieve fever. The structures of isolates have been elucidated by a combination of spectroscopic techniques. The crude extract and the isolated compounds were evaluated in the Hela-S3 cell line and in a panel of microorganisms (bacteria and fungi) at concentrations up to 50 µg/mL. The new compounds were inactive while the pentamethylated flavonoids showed low to significant activity against the cancer cell line used. However, none of the samples showed any activity against the tested microorganisms at this concentration. The present manuscript is the first investigation of the cytotoxicity of phytochemicals and extract from C. pyrrhopappa.

Caffeate and piperidine-3-ol derivatives from the stem bark of Cassia sieberiana

A new caffeate derivative from the ethanol extract of the stem bark of Cassia sieberiana DC. is described herein along with the known secondary metabolites spectaline (2), iso-6-cassine (3), 3-O-methyl-chiro-inositol (4), monobehenin (5), octyl nonadecyloate (6), β-sitosterol (7), stigmasterol (8) and sitosterol 3-O-β-D-glucopyranoside (9). The chemical structures were elucidated by means of various spectroscopic and spectrometric techniques. Extract and isolated compounds were devoid of inhibitory action against the herein selected bacterial strains (MICs > 256 μg/mL) but showed capacities to reduce 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical (EC₅₀ < 3 μg/mL) considerably better than the "gold standard" trolox (EC₅₀ 6.47 ± 0.48 μg/mL).

A new polyketide from the bark of Hypericum roeperianum Schimp. (Hypericaceae)

The isolation and spectroscopic data of a hitherto undescribed polyketide (1) from Hypericum roeperianum Schimp. (Hypericaceae) together with six known compounds (2-7) is herein reported. The structure elucidation is based on extensive 1D- and 2D-NMR, infrared, UV and MS experiments. The structures of the known compounds were confirmed by comparison of their spectroscopic data with those of similar reported compounds in the literature. Some of the isolated compounds had a significant activity against a panel of multidrug-resistant bacterial strains.Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2019.1677655.

Challenges of traditional herbal teas: plant infusions and their mixtures with bioactive properties

Five traditional and medicinal plants have been individually characterized and analyzed in terms of bioactivities to determine how these characteristics are modified when preparing blends.

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

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.

Rothtalazepane, A New Azepane from the Wood of Rothmannia talbotii (Rubiaceae)

Rothmannia talbotii, a hitherto chemically unexplored medicinal plant, is used in the Western Region of Cameroon to relieve fever. In our ongoing search for bioactive compounds from Cameroonian medicinal plants, a previously undescribed compound rothtalazepane (1), along with six known compounds, aitchisonide B (2), D-mannitol (3), β-D-glucopyranosyl-(6→1’)-β-D-glucopyranoside (4), monopalmitin (5), stigmasterol (6), and sitosterol 3- O-β-D-glucopyranoside (7) were isolated and characterized from the crude ethanol extract of the wood of R. talbotii. Rothtalazepane (1) exhibits no significant activity against several microbial strains, thus its function likely lies not in antimicrobial defense and it is not the active principle against urinary infections described for Rothmannia.

A novel method for synthesis of α-spinasterol and its antibacterial activities in combination with ceftiofur

In this study, we designed a novel method of the synthesis of α-spinasterol from commercially available stigmasterol and explored the combinational effect of the α-spinasterol with ceftiofur in vitro against S. pullorum cvcc533, S. pneumoniae CAU0070, E. coli, and S. aureus. α-Spinasterol was obtained by a key reaction of Bamford-Stevens reaction with a desirable yield for five steps. The combination of α-spinasterol and ceftiofur showed stronger synergetic effect against the four pathogenic strains compared with that of stigmasterol and ceftiofur alone. In time-kill analyses, at concentrations above the MICs, ceftiofur in combination with α-spinasterol exhibited time-dependency and concentration-dependency comparing to time dependency with ceftiofur alone. We conclude that the combination usage of α-spinasterol and ceftiofur is an effective and promising strategy against the four pathogenic bacterial strains in vitro.