Identification of a novel and potent inhibitor of phospholipase A(2) in a medicinal plant: crystal structure at 1.93Å and Surface Plasmon Resonance analysis of phospholipase A(2) complexed with berberine

Crystal of Russell Viper venom phospholipase A(2) complexed with an isoquinoline alkaloid, berberine from a herbaceous plant Cardiospermum halicacabum, was prepared and its structure was solved by X-ray crystallography. The crystal diffracted up to 1.93? and the structure solution clearly located the position of berberine in the active site of the enzyme. Two hydrogen bonds, one direct and the other water mediated, were formed between berberine and the enzyme. Gly 30 and His 48 made these two hydrogen bonds. Additionally, the hydrophobic surface of berberine made a number of hydrophobic contacts with side chains of neighboring amino acids. Surface Plasmon Resonance studies revealed strong binding affinity between berberine and phospholipase A(2). Enzyme inhibition studies proved that berberine is a competitive inhibitor of phospholipase A(2). It was inferred that the isoquinoline alkaloid, berberine, is a potent natural inhibitor of phospholipaseA(2).     

Synthesis and biological evaluation of a new series of berberine derivatives as dual inhibitors of acetylcholinesterase and butyrylcholinesterase

A series of novel berberine derivatives were designed, synthesized, and biologically evaluated as inhibitors of both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Among these derivatives, compound 48a, berberine linked with 3-methylpyridinium by a 2-carbon spacer, was found to be a potent inhibitor of AChE, with an IC₅₀ value of 0.048 μM and compound 40c, berberine linked with 2-thionaphthol by a 4-carbon spacer, acted as the most potent inhibitor for BuChE with an IC₅₀ value of 0.078 μM. Kinetic studies and molecular modeling simulations of the AChE-inhibitor complex indicated that a mixed-competitive binding mode existed for these berberine derivatives.     

Synthesis,biological evaluation,and molecular modeling of berberine derivatives as potent acetylcholinesterase inhibitors

By targeting the dual active sites of acetylcholinesterase (AChE), a new series of berberine derivatives was designed, synthesized, and evaluated as AChE inhibitors. Most of the derivatives inhibited AChE in the sub-micromolar range. Compound 8c, berberine linked with phenol by a 4-carbon spacer, showed the most potent inhibition of AChE. A kinetic study of AChE and BuChE indicated that a mix-competitive binding mode existed for these berberine derivatives. Molecular modeling studies confirmed that these hybrids target both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. This is the first report where AChE inhibitory activity has been associated with berberine as a lead molecule.     

Synthesis and DNA-binding affinities of protoberberine-based multivalent agents

Three novel berberine derivatives bearing two, three, and four primary amino groups at C(9), respectively, were synthesized and characterized on the basis of 1H- and 13C-NMR, MS, and HR-MS data. Their non-covalent binding with calf thymus (CT) DNA was investigated by means of spectrophotometric titration and ethidium bromide (EB) displacement experiments. The results indicated that these multivalent berberine derivatives exhibited up to 130-fold enhanced binding affinities relative to berberine, and thus, may be exploitable as potent DNA-binding agents.     

9-Substituted berberine derivatives as G-quadruplex stabilizing ligands in telomeric DNA

The interaction of berberine and its 9-substituted derivatives with human telomeric DNA d[G(3)(T(2)AG(3))(3)](telo21) has been investigated via CD spectroscopy, fluorescence spectroscopy, PCR-stop assay, competitive dialysis, and telomerase repeat amplification protocol (TRAP) assay. The results indicated that these semisynthesized compounds could induce and stabilize the formation of anti-parallel G-quadruplex of telomeric DNA in the presence or absence of metal cations. Compared with berberine, the 9-substituted derivatives exhibit stronger binding affinity with G-quadruplex and higher inhibitory activity for telomerase. Introduction of a side chain with proper length of methylene and terminal amino group to the 9-position of berberine would significantly strengthen the binding affinity with G-quadruplex, resulting in increasing inhibitory effects on the amplification of telo21 DNA and on the telomerase activity.     

Novel berberine-based derivatives with potent hypoglycemic activity

Four series of berberine derivatives were designed and synthesized. All the synthetic compounds were screened for in vitro glucose consumption activity in HepG2 cell lines. The results showed that most of the tested compounds exhibited potent hypoglycemic activity, and the most potent compound 20b exhibited its potency by 3.23-fold of berberine, 1.39-fold of metformin and 1.20-fold of rosiglitazone, respectively. Western blot assay indicated these novel berberine-based derivatives executed their glucose-decreasing activity via the activation of AMPK pathway.     

Synthesis and antifungal activity of a novel series of 13-(4-isopropylbenzyl)berberine derivatives

By replacing the methyl group of 13-(4-isopropylbenzyl)berberine 2 with various acyl, alkyl, and benzyl groups via the demethylated intermediate, 13-(4-isopropylbenzyl)berberrubine 4, a novel series of 9-O-alkyl-13-(4-isopropylbenzyl)berberine derivatives was synthesized and examined for antifungal activities against various human pathogenic fungi. The introduction of various alkyl groups led to enhanced antifungal activity but that of acyl groups resulted in decrease of the activity. Among them, 9-O-butyl-13-(4-isopropylbenzyl)berberine 6d exhibited the most potent antifungal activities against Cryptococcus neoformans, Candida species (MIC=0.25-1 μg/ml), and Aspergillus species (MIC=2-4 μg/ml). The compound was found to be relatively safe up to 900 mg/kg in oral administration to mice.     

Biotransformation of indole derivatives by mycelial cultures

Biotransformation of tryptophan to tryptamine and 3-methyl-indole by Psilocybe coprophila was performed. On the other hand, Aspergillus niger was able to transform tryptophan to 5-hydroxy-tryptophan. P. coprophila biotransformed 5-hydroxy-tryptophan to 5-hydroxytryptamine. These results prove once more that fungi are good tools to establish hydroxyindole derivatives.     

Synthesis and DNA-binding affinities of monomodified berberines

Four new monomodified berberines have been synthesized in moderate to good yields starting from berberine and fully characterized by HRMS and 1H NMR. Spectrometric titration and ethidium bromide displacement experiments indicate that these berberine derivatives, especially the one having primary amino group, strongly bind with calf-thymus DNA, presumably via an intercalation mechanism.     

Synthesis of 13-(substituted benzyl) berberine and berberrubine derivatives as antifungal agents

By introducing various aromatic groups in 13-C of berberine and berberrubine, a series of 13-(substituted benzyl) berberine and berberrubine derivatives were synthesized and examined for antifungal activities against various human pathogenic fungi. The synthesized compounds exhibited more potent antifungal activities than berberine and berberrubine. Among them, 13-(4-isopropyl benzyl) berberine (6e) exerted the most potent antifungal activities against Candida species (MIC=1-8 microg/ml) and a 4-fold stronger activity than 13-(4-isopropyl benzyl) berberrubine (7e) synthesized by pyrolysis of compound 6e.     

Synthesis and evaluation of 9-O-substituted berberine derivatives containing aza-aromatic terminal group as highly selective telomeric G-quadruplex stabilizing ligands

A series of new 9-O-substituted berberine derivatives (4a–j) as telomeric quadruplex ligands was synthesized and evaluated. The results from biophysical and biochemical assay indicated that introducing of positive charged aza-aromatic terminal group into the side chain of 9-position of berberine significantly improved the binding ability with G-quadruplex, and exhibited the inhibitory effect on the hybridization and on telomerase activity. These derivatives showed excellent selectivity for telomeric G-quadruplex DNA over duplex.     

Synthesis and antihyperglycemic evaluation of various protoberberine derivatives

Various berberine derivatives (2-17) were synthesized and their antihyperglycemic activities were evaluated in a model of beta-cell-membrane chromatography and a model of alloxan-induced diabetes mice. The results indicated that compounds 5 and 14 exhibited antihyperglycemic activity. Their structure-activity relationships were discussed.     

Synthesis and anticancer activity of a novel series of 9-O-substituted berberine derivatives: A lipophilic substitute role

To alter its hydrophobicity, a series of compounds bearing 9-O-alkyl- or 9-O-terpenyl- substituted berberine were synthesized and evaluated for anticancer activity against human cancer HepG2 and HT29 cell lines. We found that the lipophilic substitute of 9-O-alkyl- and 9-O-terpenyl berberine derivatives plays a role in inhibiting the human cancer cell growth and its activity could be maximized with the optimized substitute type and chain length. Most strikingly, nonetheless, of the six compounds prepared, sample 8, a farnesyl 9-O-substituted berberine, showed either comparable or better cytotoxic activity against human cancer HepG2 cell line than that of berberine. Compound 8 had also shown a 104-fold antiproliferation activity in compare with berberine against human hepatoma HepG2 cell lines after 48 incubation hours. Further, in Hoechst 33258 and annexin V-FITC/PI staining analyses it induced apoptosis in HepG2 cells at lower concentration than that of berberine for 24 h. Take all; farnesyl 9-O-substituted berberine could be a potential candidate for new anticancer drug development.     

Design,synthesis, and biological activity evaluation of a series of pleuromutilin derivatives with novel C14 side chains

In this work, according to the ‘me-too me-better’ design strategy, a peculiar side chain different from lefamulin at C14 position of pleuromutilin was introduced. A series of novel thioether pleuromutilin derivatives containing cyclohexane in the C14 chain was synthesized by ten-step synthesis reaction. All derivatives were characterized by Nuclear Magnetic Resonance (NMR) and High Resolution Mass Spectrometer (HRMS). Furthermore, majority of derivatives displayed moderate antibacterial activity in vitro. However, the compound 2C and 2J exhibited comparable or superior antibacterial activity to lefamulin. The summarized structure-activity relationship not only made the variety of pleuromutilin derivatives more diverse, but also provided new ideas for its design and development.     

Biotransformation of naphthalene and diaryl ethers by green microalgae

The role of green microalgae in thebiotransformation of naphthalene (a polycyclicaromatic hydrocarbon) and diaryl ethers wasinvestigated using axenic cultures ofChlorella vulgaris and two environmentalisolates, Scenedesmus SI1 andAnkistrodesmus SI2.Biotransformation experiments with dense cell culturesshowed that these three greenalgae transformed toxic xenobiotics to more polar metabolites.Chlorella vulgarismetabolized naphthalene to 1-naphthol (0.36–0.65%). Ankistrodesmus SI2 biotransformed dibenzofuran tosix metabolites (total over7%), three of which (possibly four) were identified as monohydroxylated dibenzofurans, the remaining two may be dihydroxylated derivatives. Scenedesmus SI1 biotransformeddibenzo-p-dioxin to three metabolites, one ofwhich was tentatively identified as2-hydroxydibenzo-p-dioxin (approximately 3.8%),the remainder may be dihydroxylated derivatives.This is the first time that the biotransformation of diaryl ethers by green microalgae has been investigated.     

Enhanced DNA binding of 9-ω-amino alkyl ether analogs from the plant alkaloid berberine

To understand the structure-activity relationship of isoquinoline alkaloids, absorption, fluorescence, circular dichroism, and thermodynamics were employed to study the interaction of five C-9-ω-amino alkyl ether analogs from the plant alkaloid berberine with double-stranded calf thymus DNA. The C-9 derivatization resulted in dramatic enhancements in the fluorescence emission of these compounds. The most remarkable changes in the spectral and binding properties were in the BC4 and BC5 derivatives. Interactions of these analogs, which have an additional recognition motif with DNA, were evaluated through different spectroscopic and calorimetric titration experiments. The analogs remarkably enhanced the DNA binding affinity and the same was directly dependent on the alkyl chain length. The analog with six alkyl chains enhanced the DNA binding affinity by about 33 times compared with berberine. The binding became more entropically driven with increasing chain length. These results may be of potential use in the design of berberine derivatives and understanding of the structure-activity relationship for improved therapeutic applications.     

Biotransformation of withaferin-a by a culture ofArthrobacter simplex

Arthrobacter simplex biotransformed withaferin-A under submerged conditions to 7 new derivatives while 4,27-di-O-acetylwithaferin-A was transformed to another 9 derivatives. The melting point of all these substances was determined, along with R_F values and colour reactions with 4-anisaldehyde reagent. Derivatives also differed in their biological effects on P388 cells. A marked inhibitory effect on the synthesis of nucleic acids and proteins in the leukemia cells P388 was found in 12 out of 16 new derivatives.     

Application of tandem biotransformation for biosynthesis of new pentacyclic triterpenoid derivatives with neuroprotective effect

Tandem whole-cell biotransformation was applied successfully to deliver novel pentacyclic triterpenoid derivatives for the first time. In this process, the starting substrate oleanolic acid (1) was biotransformed into a hydroxylated metabolite 1a by Rhizopus chinensis CICC 40335 and then was further glycosylated to 1b by Bacillus subtilis ATCC 6633. Moreover, metabolite 1a was furtherly oxidized by Streptomyces griseus ATCC 13273 and generated two new derivatives as 1c and 1d. To validate the feasibility, tandem biotransformation of 18β-glycyrrhetinic acid (2) by R. chinensis and B. subtilis was also conducted and offered a glycosylated derivative (2c). Finally, the neuroprotective effects of the derivatives were assessed on neural injury PC12 cell model induced by cobalt chloride.     

Synthesis, biological evaluation and molecular modeling of novel triazole-containing berberine derivatives as acetylcholinesterase and β-amyloid aggregation inhibitors

A series of novel triazole-containing berberine derivatives were synthesized via the azide-alkyne cycloaddition reaction. Their biological activity as inhibitors of both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were evaluated. Among them, compound 16d, which featured a diisopropylamino substitution at the 4-position of triazole ring, was found to be a potent inhibitor of AChE, with IC(50) value of 0.044 μM. Compound 18d, which beares a butyl at the 4-position of the triazole ring, showed the highest potency of β-amyloid aggregation inhibition (77.9% at 20 μM). Molecular modeling studies indicated that the triazole moiety of berberine derivatives displayed a face-to-face π-π stacking interaction in a 'sandwich' form with the Trp84 (4.09 ?) and Phe330 (4.33 ?) in catalytic sites of AChE.