Inhibitory effect of synthetic C-C biflavones on various phospholipase A(2)s activity

Several prototypes of C-C biflavones (a-f) were synthesized and evaluated their inhibitory activity against phospholipase A(2)s (PLA(2)s) activity. The synthetic C-C biflavones (a-f) showed rather different inhibitory activity against various PLA(2)s. Most synthetic C-C biflavonoids exhibited potent and broad inhibitory activity against various sPLA(2)s and cPLA(2) tested regardless of their structural array. In particular, of natural and synthetic biflavonoids tested, the synthetic C-C biflavonoid (d) only showed inhibitory activity against sPLA(2) X. None of the natural and synthetic biflavonoids tested showed inhibitory activity against sPLA(2) IB. Further chemical modification of these basic structures will be carried out in order to investigate the synthetic C-C biflavones which possess more selective inhibitory activity against isozymes of PLA(2).     

Biflavonoids isolated from Selaginella tamariscina regulate the expression of matrix metalloproteinase in human skin fibroblasts

The methanol extract from Selaginella tamariscina significantly inhibited UV irradiation induced activity of matrix metalloproteinase-1 (MMP-1) in primary fibroblasts from human skin. Using the technique of bioassay-directed chromatographic separation, five biflavonoids were isolated from the ethyl acetate soluble fraction of S. tamariscina. Here, we investigated the effect of these five biflavonoids on the regulation of MMP-1 and -2 in UV irradiated cultured dermal fibroblasts from human neonatal foreskins. Among these biflavonoids, sumaflavone and amentoflavone showed significant MMP-1 inhibitory activity in primary human dermal fibroblasts after UV irradiation. The IC(50) values of sumaflavone, amentoflavone and retinoic acid, which was used as a positive control, were 0.78, 1.8, and 10microM, respectively.     

Naturally occurring biflavonoids with amyloid β aggregation inhibitory activity for development of anti-Alzheimer agents

Amyloid β (Aβ) aggregation plays an essential role in promoting the progression of Alzheimer’s disease (AD). Therefore, the inhibition of Aβ aggregation is a potential therapeutic approach for AD. Herein, twenty-seven biflavonoids with different inter-flavonyl linkages and methoxy substitution patterns were isolated from several plants, and their Aβ₄₀ aggregation inhibitory activity was evaluated by the thioflavin-T fluorescence assay. Amentoflavone (1) and its monomethoxy derivatives (2, 3, and 5) exhibited the most potent inhibitory activity, with IC₅₀ values of approximately 5 μM. It was clarified that increasing the number of methoxy substituents on the biflavonoid structures attenuated the inhibitory activity. Moreover, the linkage and the methoxy substitution pattern had a marked influence on the inhibitory activity. Our investigation strongly supports that biflavonoids can be considered a new type of anti-Alzheimer agents that may be successfully developed for AD patients.     

Screening for tyrosinase inhibitors among extracts of seashore plants and identification of potent inhibitors from Garcinia subelliptica

The tyrosinase inhibitory activity of methanol extracts of the leaves of 39 plant species growing on the seashore of Iriomote island (Okinawa, Japan) was investigated. The extracts of Hibiscus tiliaceus, Carex pumila, and Garcinia subelliptica showed potent activity among them. The inhibitors in the extract of Garcinia subelliptica were purified by assay-guided fractionation to give two biflavonoids. These were known compounds (2R,3S-5,7,4',5',7',3',4'-heptahydroxy flavanone[3-8'] flavone and 5,7,4',5',7',3',4'-heptahydroxy[3-8'] biflavanone), although their strong inhibitory activity toward tyrosinase is revealed for the first time in this work. One of these biflavonoids (2R,3S-5,7,4',5',7',3',4'-heptahydroxy flavanone[3-8'] flavone) showed much stronger activity (IC50 2.5 microM) than that of kojic acid (IC50 9.1 microM) when L-tyrosine was used as the substrate.     

Synthesis of phospholipase A2 inhibitory biflavonoids

A series of C-C biflavones was designed to investigate the relationship between structural array of different flavone-flavone subunit linkage and the inhibitory activity against phospholipase A2 (PLA2). Among six classes of C-C biflavones designed, four classes of C-C biflavones, which have flavone-flavone subunit linkages at A ring-A ring, A ring-B ring, B ring-B ring, and B ring-C ring, were synthesized. The synthetic biflavones exhibited somewhat different inhibitory activities against sPLA2-IIA. Among them, the biflavone a having a C-C 4'-4' linkage showed comparable inhibitory activity with that of the natural biflavonoid, ochnaflavone, and 7-fold stronger activity than that of amentoflavone. Further chemical modification is being carried out in order to obtain the chemically optimized biflavonoids.     

银杏叶单组分双黄酮分离制备及抗氧化活性研究

从银杏叶中分离制备高纯度双黄酮对照品,探讨其抗氧化活性强弱。以60%乙醇-水提取的银杏叶浸膏为原料,反溶剂沉淀得到含量80.40%的双黄酮粗品,再以甲醇-水为流动相,半制备色谱梯度洗脱。结果得到了4种符合中药化学对照品要求的高纯度双黄酮,在最佳制备条件下,4种双黄酮纯度:阿曼托黄素(98.45%)、白果素(98.66%)、银杏黄素异构体(98.87%)、金松双黄酮(99.29%),其产率(mg/kg)分别为:22.5、23.8、192.5、71.8,考察了它们的抗氧化活性,并采用60%乙腈和有机酸水溶液对银杏黄素异构体进行了完全分离。建立的制备方法快速简便,所得单组分双黄酮纯度、产量高。本工作为单组分银杏双黄酮新药的研究与开发提供重要的技术支持。     

Eight new biflavonoids with lavandulyl units from the roots of Sophora flavescens and their inhibitory effect on PTP1B

In the course of studying the components from the roots of Sophora flavescens, eight new unusual biflavonoids consisting of a flavanone fused with a dihydrochalcone skeleton were isolated. These new chemical structures were elucidated by means of UV, IR, HRESIMS, NMR and ECD spectroscopic data and a comparison of experimental ECD spectra with calculated ECD spectra. Some compounds were subjected to an antidiabetic bioassay on human recombinant PTP1B inhibition, and showed strong inhibitory activity.     

β-Secretase (BACE-1) inhibitory effect of biflavonoids

Here, we describe amentoflavone-type biflavonoids, which were isolated from natural sources and were found to inhibit β-secretase (BACE-1). The structure–activity relationship was studied, and compounds 1–8, 10, 17, and 18 showed BACE-1 inhibitory activity. Among these compounds, 2,3-dihydroamentoflavone 17 and 2,3-dihydro-6-methylginkgetin 18 exhibited potent inhibitory effects with IC₅₀ values of 0.75 and 0.35 μM, respectively.     

Biflavonoids from Torreya nucifera displaying SARS-CoV 3CL(pro) inhibition

As part of our search for botanical sources of SARS-CoV 3CL(pro) inhibitors, we selected Torreya nucifera, which is traditionally used as a medicinal plant in Asia. The ethanol extract of T. nucifera leaves exhibited good SARS-CoV 3CL(pro) inhibitory activity (62% at 100μg/mL). Following bioactivity-guided fractionation, eight diterpenoids (1-8) and four biflavonoids (9-12) were isolated and evaluated for SARS-CoV 3CL(pro) inhibition using fluorescence resonance energy transfer analysis. Of these compounds, the biflavone amentoflavone (9) (IC(50)=8.3μM) showed most potent 3CL(pro) inhibitory effect. Three additional authentic flavones (apigenin, luteolin and quercetin) were tested to establish the basic structure-activity relationship of biflavones. Apigenin, luteolin, and quercetin inhibited 3CL(pro) activity with IC(50) values of 280.8, 20.2, and 23.8μM, respectively. Values of binding energy obtained in a molecular docking study supported the results of enzymatic assays. More potent activity appeared to be associated with the presence of an apigenin moiety at position C-3' of flavones, as biflavone had an effect on 3CL(pro) inhibitory activity.     

Osteoblast differentiation stimulating activity of biflavonoids from Cephalotaxus koreana

Six amentoflavone-type biflavonoids, bilobetin (1), ginkgetin (2), 4',7'-di-O-methyl-amentoflavone (3), 7-O-methyl-isoginkgetin (4), sciadopitysin (5), and 7,4',7',4'-O-methyl-amentoflavone (6), were isolated from the EtOAc fraction of Cephalotaxus koreana Nakai (Cephalotaxaceae) by bioactivity-guided fractionation technique using primary cultures of mouse osteoblasts as an in vitro assay system. Among the six biflavonoids isolated, bilobetin (1), sciadopitysin (5), and 7,4',7',4'-O-methyl-amentoflavone (6) significantly increased osteoblast differentiation as assessed by alkaline phosphatase activity, collagen synthesis, and mineralization. Considering structure-activity relationship, methoxyl groups at 4' and 4' in the B rings in amentoflavone-type biflavonoid might be important in osteoblast differentiation. Taken together, our present study suggests therapeutic potential of biflavonoids against bone diseases such as osteoporosis.     

Antilipoxygenase activity of compounds from Hypericum perforatum

The main biologically active constituents of Hypericum species are flavonoids (quercetin, isoquercitrin, hyperoside, rutin), biflavonoids and naphthodianthrones (hypericin, pseudohypericin). Lipoxygenase is the key enzyme in the biosynthesis of leukotriens, which have been postulated to play an important role in the pathophysiology of several inflammatory and allergic diseases. This work deals with the investigation of potential antilipoxygenase activity of different compounds and extracts isolated from Hypericum perforatum L. The highest inhibitory effect was exhibited by flavonoid derivative hyperoside (IC₅₀ 5.768 × 10⁻⁶ M). Acetone and ethanolic extracts caused also an inhibition of lipoxygenase. On the basis of inhibitory effect of compounds tested we assume that the most of them may be involved in the antiinflammatory principles of Hypericum perforatum L.     

Structurally unique biflavonoids from Selaginella chrysocaulos and Selaginella bryopteris

Chemical investigation of Selaginella chrysocaulos from Northeast India yielded three new (i.e., 1-3) and two known biflavonoids. From Selaginella bryopteris, collected in the southern part of India, one new (11) and eleven known biflavonoids of the amentoflavone- and hinokiflavone-type were isolated and identified. The structures of the compounds were elucidated by 1D- and 2D-NMR spectroscopy, and by mass spectrometry. The absolute configurations of chiral biflavonoids with flavanone subunits (from S. bryopteris) were determined with the aid of circular-dichroism (CD) spectroscopy. Several very rare or even unprecedented substructures in biflavonoids were found.     

Biflavonoids are superior to monoflavonoids in inhibiting amyloid-β toxicity and fibrillogenesis via accumulation of nontoxic oligomer-like structures

Polymerization of monomeric amyloid-β peptides (Aβ) into soluble oligomers and insoluble fibrils is one of the major pathways triggering the pathogenesis of Alzheimer's disease (AD). Using small molecules to prevent the polymerization of Aβ peptides can, therefore, be an effective therapeutic strategy for AD. In this study, we investigate the effects of mono- and biflavonoids in Aβ42-induced toxicity and fibrillogenesis and find that the biflavonoid taiwaniaflavone (TF) effectively and specifically inhibits Aβ toxicity and fibrillogenesis. Compared to TF, the monoflavonoid apigenin (AP) is less effective and less specific. Our data show that differential effects of the mono- and biflavonoids in Aβ fibrillogenesis correlate with their varying cytoprotective efficacies. We also find that other biflavonoids, namely, 2',8'-biapigenin, amentoflavone, and sumaflavone, can also effectively inhibit Aβ toxicity and fibrillogenesis, implying that the participation of two monoflavonoids in a single biflavonoid molecule enhances their activity. Biflavonoids, while strongly inhibiting Aβ fibrillogenesis, accumulate nontoxic Aβ oligomeric structures, suggesting that these are off-pathway oligomers. Moreover, TF abrogates the toxicity of preformed Aβ oligomers and fibrils, indicating that TF and other biflavonoids may also reduce the toxicity of toxic Aβ species. Altogether, our data clearly show that biflavonoids, possibly because of the possession of two Aβ binders separated by an appropriate size linker, are likely to be promising therapeutics for suppressing Aβ toxicity.     

Toxic Phenols in various Anacardiaceae species

The leaves and bark of fifteen species of Mexican Anacardiaceae were analyzed by paper and thin layer chromatography for the presence of toxic phenols such as catechols, resorcinols and biflavonoids. Based on the results of this and previous studies, toxic phenols are present in fifty-two species belonging to twenty-seven genera in Anacardiaceae. The majority of species contain toxic catechols, a few species contain toxic resorcinols and sixteen species contain biflavonoids. Genera from the basal group in Anacardiaceae, including Spondias and allied genera lack biflavonoids. Biflavonoids are present in the rest of the genera of Anacardiaceae.     

Biflavonoids in the primitive monocots Isophysis tasmanica and Xerophyta plicata

In addition to the previously characterized amentoflavone and dihydroamentoflavone, two further biflavonoids have been identified from Isophysis tasmanica: hinokiflavone and podocarpusflavone A. This is the first time these two biflavonoids have been found in the monocotyledons. Amentoflavone has also been discovered in Xerophyta plicata; this constitutes the first record of biflavonoids in Velloziaceae.     

Synthesis and antifungal activities of natural and synthetic biflavonoids

The synthesis of some natural and synthetic biflavonoids was performed in good overall yields starting from readily available materials via high yielding aldol and Ullmann condensations. Some of these compounds, especially bichalcones, display an interesting activity against fungi, higher than that of the corresponding monomers.     

Biflavonoids from Brazilian pine Araucaria angustifolia as potentials protective agents against DNA damage and lipoperoxidation

A biflavonoid fraction (BFF) obtained from Araucaria angustifolia needles was effective to quench singlet oxygen (1O2), to protect plasmid DNA against single strand break (ssb) caused by 1O2 or Fenton reaction and to inhibit Fenton or UV radiation-induced lipoperoxidation in phosphatidylcholine liposomes. The activity of the biflavonoid fraction (BFF) was compared with quercetin, rutin (flavonoids), ginkgetin, amentoflavone (biflavonoids), alpha-tocopherol and Trolox. The BFF displayed a higher quenching rate constant compared to flavonoids and biflavonoids and protected against ssb induced by 1O2. Although the BFF was not as efficient as either flavonoids, alpha-tocopherol or Trolox in protection against ssb induced by Fenton-reaction or lipoperoxidation, these scavenging properties suggest that BFF is still an excellent candidate for successful employment as an antioxidant and photoprotector.     

Separation of bioactive biflavonoids from Rheedia gardneriana using chitosan modified with benzaldehyde

This paper shows the influence of benzenic groups on the chitosan surface for the separation of bioactive biflavonoids from Rheedia gardneriana leaves The yield of the biflavonoids using chitin modified with benzaldehyde (CH-Bz) as adsorbent in column chromatography was higher than that achieved with silica gel and chitosan. The presence of benzenic groups decreases the polarity of chitosan and consequently the interaction of hydrogen bonding between phenolic hydroxyl (OH) of biflavonoids and amine groups of the adsorbent. Therefore, the separation of these compounds appears to be the result of hydrophobicity and pi-pi interaction among electrons from the aromatic ring in sorbent and biflavonoid molecules.     

Antiplasmodial and Cytotoxic Activities of Extract and Compounds from Ozoroa obovata (Oliv.) R. & A. Fern. var. obovata

Ozoroa obovata (Oliv.) R. & A. Fern. var. obovata found in KwaZulu-Natal in South Africa was investigated for phytochemical constituents, and for antiplasmodial and cytotoxic effects. The plant leaves were collected from the University of KwaZulu-Natal (UKZN) arboretum on the Pietermaritzburg Campus, in March 2019. The inhibitory activity against 3D7 Plasmodium falciparum was determined using the parasite lactate dehydrogenase (pLDH) assay and cytotoxicity against HeLa cells was evaluated using the resazurin assay. The bioactive compounds were isolated by chromatographic purification and their structures were established with spectroscopic and spectrometric techniques. The plant leaf extract displayed significant antiplasmodial activity at 50 μg/mL and was also cytotoxic against HeLa cells. Chromatographic purification of the extract led to the isolation of two biflavonoids, four flavonoid glycosides, a steroid glycoside, and a megastigmene derivative. The compounds displayed antiplasmodial and antiproliferative activities at 50 μg/mL but the activity was substantially reduced at 10 μg/mL. The activities and compounds are being reported in O. obovata for the first time.     

Three biflavonoids from Daphne odora

Three new biflavonoids, daphnodorins G-I, were isolated from the roots of Daphne odora and their structures established from spectral and chemical means. These are two C-7/C-2″, C-8/C-3″ biflavonoids (upper half: apigenin, lower half: afzelechin), daphnodorins G and H and a spirobiflavonoid, daphnodorin I.