The benzophenones: Isolation, structural elucidation and biological activities

Guttiferones: An insight into occurrence, biosynthesis, and their broad spectrum of pharmacological activities

Guttiferones belong to the polyisoprenylated benzophenone, a class of compounds, a very restricted group of natural plant products, especially in the Clusiaceae family. They are commonly found in bark, stem, leaves, and fruits of plants of the genus Garcinia and Symphonia. Guttiferones have the following classifications according to their chemical structure: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, and T. All of them have received growing attention due to its multiple biological activities. This review provides a first comprehensive approach to plant sources, phytochemical profile, specific pharmacological effects, and mechanisms of guttiferones already described. Studies indicate a broad spectrum of pharmacological activities, such as: anti-inflammatory, immunomodulatory, antioxidant, antitumor, antiparasitic, antiviral, and antimicrobial. Despite the low toxicity of these compounds in healthy cells, there is a lack of studies in the literature related to toxicity in general. Given their beneficial effects, guttiferones are expected to be great potential drug candidates for treating cancer and infectious and transmissible diseases. However, further studies are needed to elucidate their toxicity, specific molecular mechanisms and targets, and to perform more in-depth pharmacokinetic studies. This review highlights chemical properties, biological characteristics, and mechanisms of action so far, offering a broad view of the subject and perspectives for the future of guttiferones in therapeutics.

Assessment of human exposure to benzophenone-type UV filters: A review

To avoid the harmful effects of UV radiation, benzophenone-type UV filters (BPs) are widely used in personal care products and other synthetic products. Biomonitoring studies have shown the presence of BPs in various human biological samples, raising health concerns. However, there is a paucity of data on the global human exposure to this group of contaminants. In this study, we compiled data on the body burden of BPs along with the possible exposure routes and biotransformation pathways. BPs can easily penetrate the skin barrier and thus, they can be absorbed through the skin. In the human body, BPs can undergo Phase I (mainly demethylation and hydroxylation) and Phase II (mainly glucuronidation and sulfation) biotransformations. From a total of 158 studies, most of the studies are related to urine (concentration up to 92.7 mg L^-1), followed by those reported in blood (up to 0.9 mg L^-1) and milk (up to 0.8 mg L^-1). Among BPs, benzophenone-1 and benzophenone-3 are the most commonly detected congeners. The body burden of BPs is associated with various factors, including the country of residence, lifestyle, income, education level, and ethnicity. The presence of BPs in maternal urine (up to 1.1 mg L^-1), placenta (up to 9.8 ng g^-1), and amniotic fluid (up to 15.7 μg L^-1) suggests potential risks of prenatal exposure. In addition, transplacental transfer of BPs is possible, as demonstrated by their presence in maternal serum and cord serum. The possible association of BPs exposure and health effects was discussed. Future human biomonitoring studies and studies on the potential health effects are warranted. Overall, this review provides a summary of the global human exposure to BPs and can serve as supporting evidence to guide usage in order to protect humans from being exposed to BPs.

Biological Activity Evaluation and In Silico Studies of Polyprenylated Benzophenones from Garcinia celebica

This study aimed to isolate polyprenylated benzophenones from the rootbark of Garcinia celebica and assess their activities in vitro and in silico. The antioxidant activity was evaluated by the DPPH, ABTS, and FRAP methods. The cytotoxicity was evaluated against HeLa, MCF-7, A549, and B16 cancer cell lines. The antiplasmodial activity was performed against the chloroquine-sensitive Plasmodium falciparum strain 3D7. Molecular docking was analyzed on alpha-estrogen receptor (3ERT) and P. falciparum lactate dehydrogenase enzyme (1CET). The prediction of ADMET for the compounds was also studied. For the first time, (-)-cycloxanthochymol, isoxanthochymol, and xanthochymol were isolated from the root bark of Garcinia celebica. The antioxidant and cytotoxicity evaluation showed that all benzophenones exhibited antioxidant activity compared to gallic acid and quercetin as positive controls and also exhibited strong activity against HeLa, MCF-7, A549, and B16 cell lines compared to cisplatin as the positive control. The antiplasmodial evaluation showed that isoxanthochymol exhibited activity against the chloroquine-sensitive P. falciparum strain 3D7. In addition, the in silico molecular docking study supported in vitro activities. The ADMET analysis also indicated the isolated benzophenones are potential oral drug candidates.

Biotransformation of Benzoate to 2,4,6-Trihydroxybenzophenone by Engineered Escherichia coli

The synthesis of natural products by E. coli is a challenging alternative method of environmentally friendly minimization of hazardous waste. Here, we establish a recombinant E. coli capable of transforming sodium benzoate into 2,4,6-trihydroxybenzophenone (2,4,6-TriHB), the intermediate of benzophenones and xanthones derivatives, based on the coexpression of benzoate-CoA ligase from Rhodopseudomonas palustris (BadA) and benzophenone synthase from Garcinia mangostana (GmBPS). It was found that the engineered E. coli accepted benzoate as the leading substrate for the formation of benzoyl CoA by the function of BadA and subsequently condensed, with the endogenous malonyl CoA by the catalytic function of BPS, into 2,4,6-TriHB. This metabolite was excreted into the culture medium and was detected by the high-resolution LC-ESI-QTOF-MS/MS. The structure was elucidated by in silico tools: Sirius 4.5 combined with CSI FingerID web service. The results suggested the potential of the new artificial pathway in E. coli to successfully catalyze the transformation of sodium benzoate into 2,4,6-TriHB. This system will lead to further syntheses of other benzophenone derivatives via the addition of various genes to catalyze for functional groups.

In vitro protective effect of topical nanoemulgels containing Brazilian red propolis benzophenones against UV-induced skin damage

The overexposure of the skin to ultraviolet (UV) radiation may lead to oxidative stress, resulting in severe damage. The prevention of skin injuries through the topical application of natural compounds rich in antioxidants, such as propolis extracts, has shown promising results. In Brazil, the "red propolis" extract has stood out due to its complex constitution, based mainly on polyprenylated benzophenones (BZP). However, although the use of red propolis extracts has been shown to be encouraging, their addition in topical formulations is limited by the low solubility of BZP. For this reason, this study aimed to develop topical nanoemulgels containing Brazilian red propolis (BRP) extract to increase the potential of topical application, and the evaluation of skin protection against UVA/UVB radiation damage by means of protein carbonylation, protein thiol content and TBARS assays. The nanoemulgels were obtained by adding gelling polymer to nanoemulsions that were previously prepared by spontaneous emulsification. In this sense, a nanoemulgel containing BRP extract-loaded nanoemulsions (H-NE) and a nanoemulgel containing BRP extract-loaded nanoemulsions with DOTAP (H-NE/DT) were prepared. The physicochemical characterization of nanoemulgels showed monodisperse populations of 200-300 nm. The H-NE zeta potential was -38 mV, while that of H-NE/DT was +36 mV. BZP content in the formulations was around 0.86 mg g-1. These parameters remained stable for 90 days under cold storage. H/NE and H-NE/DT presented a non-Newtonian pseudoplastic rheological behavior. Permeation/retention studies, through porcine ear skin, showed the highest BZP retention (18.11 μg cm-2 after 8 h) for H-NE/DT, which also demonstrated, in an in vitro study, the highest ability to protect skin against oxidative damage after UVA/UVB radiation exposure. The results concerning the antioxidant activity revealed that formulations containing the BRP n-hexane extract were the most promising in combating oxidative stress, probable due to the presence of polyprenylated BZP. Altogether, the outcomes of this study suggest that nanoemulgels have suitable characteristics for topical application, and may be an alternative for the prevention of oxidative skin damage caused by UVA/UVB radiation.

Comprehensive multivariate correlations between climatic effect, metabolite-profile, antioxidant capacity and antibacterial activity of Brazilian red propolis metabolites during seasonal study

The standardization of apiceutical products like as propolis extracts has been widely debated worldwide and variations in the propolis chemical composition are still very relevant topics for use-standardized of different propolis-type as medication by much of the world’s population. The present manuscript discuss important issues related to the climate effect and variations in propolis metabolite-profiling changes, antioxidant capacity and variations of the antibacterial activity of the Brazilian red propolis metabolites using comprehensive multivariate correlations. It was observed the increasing of guttiferones concentrations during the intense drought period and drastic decreasing in rainy period. The climate variation induced the high concentration of flavonoids in rainy period with pronounced dropped in some rainy months. The Pearson´s analysis demonstrated correlation between IC₅₀ from DPPH and guttiferones and flavonoids concentrations. The PCA-X and Hotelling T2 test showed outliers during the months with lowest concentrations of formononetin and isoliquiritigenin was observed in antibacterial tests. The PLS-DA, OPLS-DA and VIP analysis demonstrate guttiferone E, guttiferone B, liquiritigenin, naringenin are considered important substances responsible by anti-staphylococcal activity in red propolis composition during the rainy season and drought period, but a synergistic effect with other flavonoids and isoflavonoids are not ruled out.

The antioxidant activity and genotoxicity of isogarcinol

The antioxidant activity and genotoxicity of isogarcinol were assessed by several in vitro tests. Its IC₅₀ values for DPPH and ABTS were 36.3 ± 3.35 µM and 16.6 ± 3.98 µM, respectively, which were all lower than those of VC and BHT. Isogarcinol had no cyctotoxic or promotional activities at 1-10 µM in the CCK-8 assay, and negligible genotoxic effects at 50-500 µM on HepG2 cells by the single-cell gel electrophoresis assay. Pre-incubation of the cells with 0.5-1.5 µM isogarcinol, before exposure to H₂O₂, significantly increased cell viability in a concentration-dependent manner. Isogarcinol also reduced intercellular reactive oxygen species accumulation, lactate dehydrogenase release and malondialdehyde levels, and increased superoxide dismutase activity and glutathione levels. Western-blot analysis revealed that it up-regulated pro-caspase-3 and reduced cleaved caspase-3 during H₂O₂-induced oxidative stress. All the above results indicate that isogarcinol promises to be useful as a natural antioxidant.

Thalassiolin D: a new flavone O-glucoside Sulphate from the seagrass Thalassia hemprichii

Thalassiolin D, a new flavone O-glucoside sulphate along with three flavonoids, two steroids, p-hydroxybenzoic acid, 4,4'-dihydroxybenzophenone and nitrogen compound, octopamine were isolated from the seagrass Thalassia hemprichii, collected from the Saudi Red Sea coast. By extensive spectroscopic analysis including 1D and 2D NMR and MS data, the structure of the new compound was elucidated as diosmetin 7-O-β-glucosyl-2″-sulphate. The new compound displayed moderately in vitro antiviral HCV protease activity with IC₅₀ value 16 μM.

Novel long-chain compounds with both immunomodulatory and MenA inhibitory activities against Staphylococcus aureus and its biofilm

Menaquinone (MK) biosynthesis pathway is a potential target for evaluating antimicrobials in gram-positive bacteria. Here, 1,4-dihydroxy-2-naphthoate prenyltransferase (MenA) was targeted to reduce methicillin-resistant Staphylococcus aureus (MRSA) growth. MenA inhibiting, long chain-based compounds were designed, synthesized and evaluated against MRSA and menaquinone utilizing bacteria in aerobic conditions. The results showed that these bacteria were susceptible to most of the compounds. Menaquinone (MK-4) supplementation rescued MRSA growth, suggesting these compounds inhibit MK biosynthesis. 3a and 7c exhibited promising inhibitory activities with MICs ranging 1-8 μg/mL against MRSA strains. The compounds did not facilitate small colony variant formation. These compounds also inhibited the biofilm growth by MRSA at high concentration. Compounds 3a, 6b and 7c displayed a promising extracellular bactericidal activity against MRSA at concentrations equal to and four-fold less than their respective MICs. We also observed cytokines released from THP-1 macrophages treated with compounds 3a, 6b and 7c and found decreases in TNF-α and IL-6 release and increase in IL-1β. These data provide evidence that MenA inhibitors act as TNF-α and IL-6 inhibitors, raising the potential for development and application of these compounds as potential immunomodulatory agents.

Mechanism of Pd-catalyzed acylation/alkenylation of aryl iodide: a DFT study

The detailed mechanism of the Pd(0)-catalyzed cross-coupling of aryl iodide, benzoic anhydride and ethyl acrylate was clarified by theoretical methods.

Discovery of bicyclic inhibitors against menaquinone biosynthesis

INTRODUCTION

Menaquinone is used for transporting electrons and is essential for the aerobic and anaerobic respiratory systems of all pathogens and prokaryotes. Many Gram-positive bacteria use only menaquinone in the electron transport system. Thus, menaquinone biosynthesis is a potential target for the development of inhibitors against bacteria including drug-resistant pathogens.

RESULTS

After modeling, synthesis and in vitro testing, we determined that 7-methoxy-2-naphthol-based inhibitors targeted the MenA enzyme of the menaquinone biosynthesis pathway. The developmental compounds 1 and 2 were active against Mycobacterium tuberculosis and methicillin-resistant Staphylococcus aureus with a minimal inhibitory concentration of 3-5 μg/ml.

CONCLUSION

Nontraditional bicyclic inhibitors, compounds 1 and 2 could serve as lead compounds for the development of an antimicrobial agent, with activities against M. tuberculosis and methicillin-resistant S. aureus.

Chemosystematic aspects of polyisoprenylated benzophenones from the genus Clusia

Benzophenone derivatives are special metabolites that arouse great scientific interest. The Clusiaceae family is known for producing large amounts of benzophenone derivatives with several isoprene residues on their structures, which are responsible for the observed complexity and structural variety in this class of substances, and also contribute to their biological activities. Clusia is an important genus belonging to Clusiaceae, with 55 different polyisoprenylated benzophenones identified so far. These substances were analyzed from biosynthetic and chemosystematic points of view, allowing the determination of characteristics regarding their production, accumulation and distribution within this genus. Polyisoprenylated benzophenones found in Clusiashowed a high prenylation degree, with 2 to 5 isoprene units and a greater occurrence in flowers and fruits. Section Cordylandra showed a very similar occurrence of 2,4,6-trihydroxybenzophenone derivatives and bicyclo[3.3.1]nonane-2,4,9-trione derivatives, the majority of them with 4 isoprene units. In section Anandrogyne there is a predominance of simple 2,4,6-trihydroxy-benzophenone derivatives, with 2 isoprene units, and in Chlamydoclusia predominates bicyclo[3.3.1]nonane-2,4,9-trione derivatives with 4 isoprene units. Although highly prenylated, these substances showed low oxidation indexes, which from an evolutionary perspective corroborates the fact that Clusiaceae is a family in transition, with some common aspects with both basal and derived botanical families.

In vitro growth inhibition by Hypericum extracts and isolated pure compounds of Paenibacillus larvae, a lethal disease affecting honeybees worldwide

The in vitro inhibitory potential of 50 extracts from various species of the flowering plant genus Hypericum was investigated using the Kirby-Bauer disk diffusion susceptibility test against Paenibacillus larvae, a spore-forming, Gram-positive bacterial pathogen that causes American foulbrood (AFB), a lethal disease affecting honeybee brood worldwide. Of the tested extracts, 14 were identified as highly active against P. larvae as compared to the activity of the positive control, indicating the presence of highly potent antibacterial compounds in the extracts. Examination of these extracts using TLC and HPLC/MS analyses revealed the presence of acylphloroglucinol and filicinic-acid derivatives. Six pure compounds isolated from these extracts, viz., hyperforin (1), uliginosin B (2), uliginosin A (3), 7-epiclusianone (4), albaspidin AA (5), and drummondin E (6), displayed strong antibacterial activity against the vegetative form of P. larvae (MIC ranging from 0.168-220 μM). Incubation of P. larvae spores with the lipophilic extract of Hypericum perforatum and its main acylphloroglucinol constituent 1 led to the observation of significantly fewer colony forming units as compared to the negative control, indicating that the acylphloroglucinol scaffold represents an interesting lead structure for the development of new AFB control agents.

First direct access to 2-hydroxybenzophenones via nickel-catalyzed cross-coupling of 2-hydroxybenzaldehydes with aryl iodides

The Nickel-catalyzed cross-coupling of 2-hydroxybenzaldehydes with aryl iodides proceeds in ethylene glycol to give the corresponding 2-hydroxybenzophenones.

Structural diversity and bioactivities of natural benzophenones

Natural benzophenones are a class of compounds with more than 300 members, mainly in the Clusiaceae family. We review key benzophenones, and provide an in-depth discussion of their great structural diversity and biological activity.

Cytotoxicity and modes of action of four naturally occuring benzophenones: 2,2',5,6'-tetrahydroxybenzophenone, guttiferone E, isogarcinol and isoxanthochymol

INTRODUCTION

The emergence of drug-resistant cancer cells drastically reduces the efficacy of many antineoplasic agents and, consequently, increases the frequency of therapeutic failure. Benzophenones are known to display many pharmacological properties including cytotoxic activities. The present study was aimed at investigating the cytotoxicity and the modes of action of four naturally occurring benzophenones 2,2',5,6'-tetrahydroxybenzophenone (1), isogarcinol (2), isoxanthochymol (3) and guttiferone E (4) on a panel of eleven cancer cell lines including various sensitive and drug-resistant phenotypes.

METHODS

The cytotoxicity of the compounds was determined using a resazurin reduction assay, whereas the caspase-Glo assay was used to detect the activation of caspases 3/7, caspase 8 and caspase 9 in cells treated with compounds 2-4. Flow cytometry was used for cell cycle analysis and detection of apoptotic cells, analysis of mitochondrial membrane potential (MMP) as well as measurement of reactive oxygen species (ROS).

RESULTS

The four tested benzophenones inhibited the proliferation of all tested cancer cell lines including sensitive and drug-resistant phenotypes. Collateral sensitivity of cancer cells to compounds 1-4 was generally better than to doxorubicin. Compound 2 showed the best activity with IC50 values below or around 1 μM against HCT116 colon carcinoma cells (p53+/+) (0.86 μM) and leukemia CCRF-CEM (1.38 μM) cell lines. Compounds 2-4 strongly induced apoptosis in CCRF-CEM cells via caspases 3/7, caspase 8 and caspase 9 activation and disruption of MMP.

CONCLUSIONS

The studied benzophenones are cytotoxic compounds that deserve more detailed exploration in the future, to develop novel anticancer drugs against sensitive and otherwise drug-resistant phenotypes.

Polyphenols with antiulcerogenic action from aqueous decoction of mango leaves (Mangifera indica L.)

This study was designed to determine the gastroprotective effect of a Mangifera indica leaf decoction (AD), on different experimental models in rodents. The administration of AD up to a dose of 5 g/kg (p.o.) did not produce any signs or symptoms of toxicity in the treated animals, while significantly decreasing the severity of gastric damage induced by several gastroprotective models. Oral pre-treatment with AD (250, 500 or 1000 mg/kg) in mice and rats with gastric lesions induced by HCl/ethanol, absolute ethanol, non-steroidal anti-inflammatory drug (NSAID) or stress-induced gastric lesions resulted in a significant decrease of said lesions. Phytochemical analyses of AD composition demonstrated the presence of bioactive phenolic compounds that represent 57.3% of total phenolic content in this extract. Two main phenolic compounds were isolated, specifically mangiferin (C-glucopyranoside of 1,3,6,7-tetrahydroxyxanthone) and C-glucosyl-benzophenone (3-C-β-D-glucopyranosyl-4’,2,4,6-tetrahydroxybenzophenone). These findings indicate the potential gastroprotective properties of aqueous decoction from M. indica leaves.

Oblongifolins A-D, polyprenylated benzoylphloroglucinol derivatives from Garcinia oblongifolia

Oblongifolins A-D (2-5), four new polyprenylated 3,4-dihydroxybenzoylphloroglucinol compounds, were isolated from the bark of Garcinia oblongifolia collected in Vietnam. The bark was also found to contain the known compounds camboginol and guttiferone B. Extraction of the leaves gave 2 and camboginol. Details of the structure elucidation of 2-5 and stereochemical comparisons with known natural derivatives of general formula 1a,b are presented. The biological activity of these compounds concerning interactions with tubulin was investigated.