Chemistry and Biological Activities of Isoprenylated Flavonoids from Medicinal Plants (Moraceous Plants and Glycyrrhiza Species)

Catalytic Asymmetric Diels-Alder Reaction of 2'-Hydroxychalcone as a Dienophile with a VANOL-Borate Ester Complex

Numerous flavonoid Diels-Alder-type natural products have been isolated and received great attention from the synthetic community. Herein, we reported a catalytic strategy for an asymmetric Diels-Alder reaction of 2'-hydroxychalcone with a range of diene substrates using a chiral ligand-boron Lewis acid complex. This method enables the convenient synthesis of a wide range of cyclohexene skeletons in excellent yields with moderate to good enantioselectivities, which is critical to prepare natural product congeners for further biological studies.

New dihydrobenzoxanthone derivatives with bacterial neuraminidase inhibitory activity isolated from Artocarpus elasticus

Artocarpus elasticus is a popular fruit tree in the tropical regions. Primary screenings of methanol extracts of the root bark confirmed its potent inhibition of bacterial neuraminidase (BNA), which plays an essential role in the pathogenesis of many microbial diseases. Assessments of the responsible phytochemicals were conducted by isolating eight compounds (1-8) and two of them (6 and 8) were identified as new compounds. Among the isolates, the dihydrobenzoxanthones attained the highest BNA inhibition with IC₅₀ values of 0.5 ∼ 3.9 µM. Further investigation of the inhibitory mechanism by Lineweaver-Burk plots revealed the phytochemicals to function as reversible noncompetitive inhibitors. Fluorescence quenching showed their binding affinities were highly correlated with their inhibitory potential dose-dependently. Molecular docking experiments suggested the dihydrobenzoxanthones (4 and 6) as noncompetitive inhibitors of BNA with unique interaction with Tyr435 of BNA in comparison with the mother flavonoid (7).

Isolation, structural elucidation and in vitro hepatoprotective activity of flavonoids from Glycyrrhiza uralensis

Two new flavonoid glycosides, 2',4'-dihydroxydihydrochalcone-4-O-β-D-glucopyranoside (1) and medicarpin-3-O-β-D-apiofuranosyl (1 → 2)-β-D-glucopyranoside (2), together with 34 known flavonoids were isolated from the 75% EtOH extract of the dried roots of Glycyrrhiza uralensis Fisch. Their structures were elucidated on the basis of spectroscopic analyses. The flavonoids were classified into ten sub-types, namely, dihydrochalcone (1), pterocarpans (2-4), flavones (5-6), flavanones (7-11), chalcones (12-15), retro-chalcones (16-18), isoflavans (19-21), isoflavones (22-28), 3-arylcoumarins (29-30), and coumestans (31-36). The isolated flavonoids were evaluated for in vitro hepatoprotective activity against D-galactosamine-induced toxicity in human hepatoma HepG2 cells.

Isoprenylated phenolic compounds with tyrosinase inhibition from Morus nigra

A new isoprenylated sanggenon-type flavanone, nigrasin K (1), together with three known analogs (2-4) and five known Diels-Alder adducts (5-9), were isolated from the twigs of Morus nigra. Their structures were elucidated by spectroscopic methods. Sanggenon M (2), chalcomoracin (5), sorocein H (6), kuwanon J (7), sanggenon C (8), and sanggenon O (9) showed significant inhibitory effects on mushroom tyrosinase.

Growth inhibitory effect of paratocarpin E, a prenylated chalcone isolated from Euphorbia humifusa Wild., by induction of autophagy and apoptosis in human breast cancer cells

Five flavones, including four flavonoids and one prenylated chalcone (paratocarpin E), were isolated from E. humifusa. and their chemical structures were established by spectroscopic analyses. We assessed the efficacy of these compounds against the growth of human breast cancer, leukemic, kidney cancer cell lines. Among them, paratocarpin E showed significant cytotoxicity against these cancer cell lines with an IC₅₀ of 19.6μM on the growth of MCF-7 cells. Paratocarpin E treatment of MCF-7 cells resulted in typical apoptotic features via increasing expression of activated caspase-8 and -9 and PARP cleavage. Moreover, paratocarpin E altered the expression of Bax and Bcl-2, leading to the release of cytochrome c from the mitochondria into the cytosol, suggesting that the mitochondria-mediated apoptosis was initiated. In addition, paratocarpin E increased the MDC-positive autophagic vacuoles, the ratio of LC3-II/LC3-I protein levels of Beclin-1, but decreased p62 expression, indicating the potent pro-autophagic effects of paratocarpin E in MCF-7 cells. Mechanistically, cell death induced by paratocarpin E is able to induce apoptosis of MCF-7 cells by activating p38 and JNK signaling pathway while inhibiting Erk pathway. Furthermore, paratocarpin E promotes the activation and nuclear translocation of NF-κB, which plays an important role in balancing paratocarpin E-mediated apoptosis and autophagy. The molecular docking study also revealed that paratocarpin E bound to Fas and NF-κB complex. These findings provide initial evidences that paratocarpin E can be used as a potential anti-cancer drug in future for breast cancer therapy.

Genome-Wide Identification and Characterization of Long Non-Coding RNAs from Mulberry (Morus notabilis) RNA-seq Data

Numerous sources of evidence suggest that most of the eukaryotic genome is transcribed into protein-coding mRNAs and also into a large number of non-coding RNAs (ncRNAs). Long ncRNAs (lncRNAs), a group consisting of ncRNAs longer than 200 nucleotides, have been found to play critical roles in transcriptional, post-transcriptional, and epigenetic gene regulation across all kingdoms of life. However, lncRNAs and their regulatory roles remain poorly characterized in plants, especially in woody plants. In this paper, we used a computational approach to identify novel lncRNAs from a published RNA-seq data set and analyzed their sequences and expression patterns. In total, 1133 novel lncRNAs were identified in mulberry, and 106 of these lncRNAs displayed a predominant tissue-specific expression in the five major tissues investigated. Additionally, functional predictions revealed that tissue-specific lncRNAs adjacent to protein-coding genes might play important regulatory roles in the development of floral organ and root in mulberry. The pipeline used in this study would be useful for the identification of lncRNAs obtained from other deep sequencing data. Furthermore, the predicted lncRNAs would be beneficial towards an understanding of the variations in gene expression in plants.

Diels-Alder adducts with PTP1B inhibition from Morus notabilis

Eight Diels-Alder adducts, morbilisins A-H (1-8), a known analogue, chalcomoracin (9), together with eleven known flavonoids and 2-arylbenzofurans, were isolated from the leaves of Morus notabilis. Their structures were elucidated by extensive spectroscopic analysis, including 1D, 2D NMR, MS, and ECD data. Compounds 1, 5, and 7-9 showed inhibition against PTP1B phosphatase activity in vitro.

2-Arylbenzofuran and tyrosinase inhibitory constituents of Morus notabilis

Phytochemical investigation of the stem of Morus notabilis led to the isolation and characterization of 10 compounds of 2-arylbenzofurans (1-10), including two new compounds, (2'R)-2',3'-dihydro-2'-(1-hydroxy-1-methylethyl)-2,6'-bibenzofuran-6,4'-diol (1) and 5,6-dimethoxy-2-(3-hydroxy-5-methoxyphenyl)benzofuran (2). Moracins O (6) and P (10) showed inhibitory effects on mushroom tyrosinase with IC₅₀ values being lower than that of kojic acid.

Isoprenylated flavonoids and adipogenesis-promoting constituents from Morus nigra

Ten new isoprenylated flavonoids, nigrasins A-J (1-10), and three known compounds were isolated from the twigs of Morus nigra. Compounds 8 and 9 promoted adipogenesis, characterized by increased lipid droplet and triglyceride content in 3T3L1 cells, and induced up-regulation of the expression of adipocyte-specific genes, aP2 and GLUT4.

Cytotoxic allyl retrochalcone from the roots of Glycyrrhiza inflata

Two known retrochalcones, licochalcone A (1) and licochalcone C (2), and one new retrochalcone, licochalcone E (4) were isolated by cytotoxicity-guided fractionation from the roots of Glycyrrhiza inflata along with an ordinary chalcone, isoliquiritigenin (3). The structure of the new retrochalcone was elucidated through a spectroscopic analysis.

Antimicrobial activity of 2-arylbenzofurans from Morus species against methicillin-resistant Staphylococcus aureus

Nine 2-arylbenzofurans isolated from Morus species were tested for their antimicrobial activities against methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), Micrococcus luteus, Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Among these compounds, chalcomoracin (a leaf phytoalexine of mulberry tree) exhibited considerable antibacterial activity against MRSAs (MICs 0.78 mug/ml).

Hypoglycemic effect of Egyptian Morus alba root bark extract: effect on diabetes and lipid peroxidation of streptozotocin-induced diabetic rats

The hypoglycemic activity of the flavonoids rich fraction of 70% alcohol extract of the Egyptian Morus alba root bark (MRBF-3) was evaluated after its oral administration to streptozotocin-induced diabetic rats. Diabetes was induced by injection of 60 mg kg(-1) i.p. The administration of MRBF-3 to streptozotocin (STZ)-diabetic rats for 10 days in a dose of 200 and 400 mg kg(-1)day(-1) was not significant. However, administration of MRBF-3 for 10 days (600 mg kg(-1)day(-1)) significantly reduced the amount of the glucose from control level (379+/-9 mg/dl) to a lower level (155+/-8 mg/dl) and significantly increased the insulin level from control (10.8+/-0.3 microU/ml) to a high level (15.6+/-0.3 microU/ml). The measurement of produced lipid peroxides (expressed as the amount of thiobarbituric acid (TBA) reactive substance, nmol TBARS/ml serum) indicated antiperoxidative activity of MRBF-3. The oral administration of MRBF-3 to STZ-diabetic rats significantly decreased the lipid peroxides from 6.3+/-0.8 to 5.1+/-0.7 nmol TBARS/ml serum. The phytochemical investigation of MRBF-3 resulted in the isolation of four hydrophobic flavonoids with one or two isoprenoid groups (log P=5-9): morusin, cyclomorusin, neocyclomorusin, and kuwanon E, a 2-arylbenzofuran, moracin M, and two triterpenes, betulinic acid and methyl ursolate. The data obtained from this study revealed that MRBF-3 may protect pancreatic beta cells from degeneration and diminish lipid peroxidation. However, this is the first biological screening of the Egyptian Morus alba root bark; further future merit studies including clinical study will be necessary in order to confirm the results obtained from this study.