Cytotoxicity and DNA binding properties of the plant alkaloid burasaine

Supramolecular and suprabiomolecular photochemistry: a perspective overview

In this perspective review article, we have attempted to bring out the important current trends of research in the areas of supramolecular and suprabiomolecular photochemistry. Since the spans of the subject areas are very vast, it is impossible to cover all the aspects within the limited space of this review article. Nevertheless, efforts have been made to assimilate the basic understanding of how supramolecular interactions can significantly change the photophysical and other related physiochemical properties of chromophoric dyes and drugs, which have enormous academic and practical implications. We have discussed with reference to relevant chemical systems where supramolecularly assisted modulations in the properties of chromophoric dyes and drugs can be used or have already been used in different areas like sensing, dye/drug stabilization, drug delivery, functional materials, and aqueous dye laser systems. In supramolecular assemblies, along with their conventional photophysical properties, the acid-base properties of prototropic dyes, as well as the excited state prototautomerization and related proton transfer behavior of proton donor/acceptor dye molecules, are also largely modulated due to supramolecular interactions, which are often reflected very explicitly through changes in their absorption and fluorescence characteristics, providing us many useful insights into these chemical systems and bringing out intriguing applications of such changes in different applied areas. Another interesting research area in supramolecular photochemistry is the excitation energy transfer from the donor to acceptor moieties in self-assembled systems which have immense importance in light harvesting applications, mimicking natural photosynthetic systems. In this review article, we have discussed varieties of these aspects, highlighting their academic and applied implications. We have tried to emphasize the progress made so far and thus to bring out future research perspectives in the subject areas concerned, which are anticipated to find many useful applications in areas like sensors, catalysis, electronic devices, pharmaceuticals, drug formulations, nanomedicine, light harvesting, and smart materials.

DNA Related Enzymes as Molecular Targets for Antiviral and Antitumoral Chemotherapy. A Natural Overview of the Current Perspectives

BACKGROUND

The discovery of new chemotherapeutic agents still remains a continuous goal to achieve. DNA polymerases and topoisomerases act in nucleic acids metabolism modulating different processes like replication, mitosis, damage repair, DNA topology and transcription. It has been widely documented that Polymerases serve as molecular targets for antiviral and antitumoral chemotherapy. Furthermore, telomerase is a ribonucleoprotein with exacerbated activity in most of the tumor cell lines, becoming as an emergent target in Cancer treatment.

METHODS

We undertook an exhaustive search of bibliographic databases for peer-reviewed research literature related to the last decade. The characteristics of screened bibliography describe structure activity relationships and show the principal moieties involved. This work tries to summarize the investigation about natural and semi-synthetic products with natural origin with the faculty to inhibit key enzymes that play a crucial role in DNA metabolism.

RESULTS

Eighty-five data references were included in this review, showing natural products widely distributed throughout the plant kingdom and their bioactive properties such as tumor growing inhibitory effects, and anti-AIDS activity.

CONCLUSION

The findings of this review confirm the importance to find new drugs and biologically active natural products, and their potential medicinally useful benefits.

WITHDRAWN: Structural and biophysical insight into dual site binding of the protoberberine alkaloid palmatine to parallel G-quadruplex DNA using NMR, fluorescence and circular dichroism spectroscopy

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.biochi.2018.02.002. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Lanthanide-Based Polymers with Charged Ligand Backbones: Triple-Stranded Chain Structures and their DNA Cleavage Studies

Four rare-earth metal complexes, [Ln(Ccbp)3(H2O)3]n (Ln = La (1), Ce (2), Pr (3) and Nd (4)) are synthesised from the ligand H2CcbpBr (H2CcbpBr = 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide) and the respective lanthanide metal ions. Complexes 1–4 are isostructural in that every three Ccbp– ligands juxtapose two Ln3+ ions in a monodentate coordination mode to form triple-stranded one-dimensional chain structures. Each central Ln3+ atom further associates with three H2O molecules, furnishing a monocapped square-antiprism geometry. Agarose gel electrophoresis studies indicate that 1–4 are capable of cleaving DNA in the presence of H2O2, most probably via an oxidative cleavage mechanism. Complexes 1 and 2 exhibited catalytic efficiencies (kmax/KM) of 37.69 and 34.11 h–1 mM–1, and are approx. 15- and 20-fold more effective than those of complexes 3 (kmax/KM = 1.75 h–1 mM–1) and 4 (kmax/KM = 2.21 h–1 mM–1).

Studies on DNA binding behaviour of biologically active transition metal complexes of new tetradentate N2O2 donor Schiff bases: inhibitory activity against bacteria

A series of Cu(II), Ni(II) and Zn(II) complexes of the type ML have been synthesized with Schiff bases derived from o-acetoacetotoluidide, 2-hydroxybenzaldehyde and o-phenylenediamine/1,4-diaminobutane. The complexes are insoluble in common organic solvents but soluble in DMF and DMSO. The measured molar conductance values in DMSO indicate that the complexes are non-electrolytic in nature. All the six metal complexes have been fully characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments and spectroscopic data. The analytical data helped to elucidate the structure of the metal complexes. The Schiff bases are found to act as tetradentate ligands using N(2)O(2) donor set of atoms leading to a square-planar geometry for the complexes around all the metal ions. The binding properties of metal complexes with DNA were investigated by absorption spectra, viscosity measurements and cyclic voltammetry. Detailed analysis reveals that the metal complexes intercalate into the DNA base stack as intercalators. All the metal complexes cleave the pUC19 DNA in presence of H(2)O(2.) The Schiff bases and their complexes have been screened for their antibacterial activity against five bacterial strains (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, Klebsiella pneumoniae) by disk diffusion method. All the metal complexes have potent biocidal activity than the free ligands.

Study on the interaction of amino phosphine ester derivatives with DNA by spectroscopy, modeling and calorimetry

The binding properties of amino phosphate ester derivatives, compound 1 and 2 with calf thymus DNA (CT-DNA) were investigated by UV spectra, fluorescence spectra, molecular modeling and isothermal titration calorimetry (ITC). The intrinsic binding constants K(b) of compound 1 and 2 with CT-DNA were determined by fluorescence spectroscopy and ITC, respectively. The results indicated that the two compounds bind to CT-DNA with different binding affinity, which is in the order of compound 1>compound 2. At the same time, fluorescence spectra suggested that the mechanism of the binding of the two compounds to CT-DNA is a static enhancing type. According to the ethidium bromide displacement experiments, UV spectra, molecular modeling and ITC studies, it can be concluded that compound 1 and 2 are intercalators that can slide into the G-C rich region of CT-DNA. Furthermore, ITC data showed that compound/DNA binding is enthalpy controlled.

Polymorphic nucleic Acid binding of bioactive isoquinoline alkaloids and their role in cancer

Bioactive alkaloids occupy an important position in applied chemistry and play an indispensable role in medicinal chemistry. Amongst them, isoquinoline alkaloids like berberine, palmatine and coralyne of protoberberine group, sanguinarine of the benzophenanthridine group, and their derivatives represent an important class of molecules for their broad range of clinical and pharmacological utility. In view of their extensive occurrence in various plant species and significantly low toxicities, prospective development and use of these alkaloids as effective anticancer agents are matters of great current interest. This review has focused on the interaction of these alkaloids with polymorphic nucleic acid structures (B-form, A-form, Z-form, H^L-form, triple helical form, quadruplex form) and their topoisomerase inhibitory activity reported by several research groups using various biophysical techniques like spectrophotometry, spectrofluorimetry, thermal melting, circular dichroism, NMR spectroscopy, electrospray ionization mass spectroscopy, viscosity, isothermal titration calorimetry, differential scanning calorimetry, molecular modeling studies, and so forth, to elucidate their mode and mechanism of action for structure-activity relationships. The DNA binding of the planar sanguinarine and coralyne are found to be stronger and thermodynamically more favoured compared to the buckled structure of berberine and palmatine and correlate well with the intercalative mechanism of sanguinarine and coralyne and the partial intercalation by berberine and palmatine. Nucleic acid binding properties are also interpreted in relation to their anticancer activity.

Simultaneous determination of eight bioactive alkaloids in Corydalis saxicola by high-performance liquid chromatography coupled with diode array detection

Corydalis saxicola Bunting (Papaveraceae), a traditional folk medicine, has been used to treat hepatic diseases for a long time. Owing to its signicant clinical effectiveness against hepatitis, cirrhosis and hepatoma, C. saxicola and its preparation are widely applied. In this study, eight alkaloids, namely isocorydine, scoulerine, dehydrocheilanthifoline, dehydrodiscretamine, dehydroisoapocavidine, dehydrocavidine, palmatine and berberine, which have been previously proven to possess potential antitumour activity, were selected as the chemical markers of C. saxicola. To evaluate the quality of C. saxicola, a simple, accurate and reliable HPLC-DAD method was developed for the simultaneous determination of the above eight compounds. Separation was achieved on a Gemini C(18) column (5 microm, 250 x 4.6 mm i.d., Phenomenex Inc., CA, USA) with a gradient solvent system of 20 mM aqueous ammonium acetate-acetonitrile, at a flow-rate of 1.0 mL/min and detected at 270 and 280 nm. All eight calibration curves showed good linearity (R(2) > 0.9992). The method was reproducible with intra- and inter-day variations of less than 5%. The recovery was in the range of 96.09-102.80%. This assay was successfully utilised to quantify the eight alkaloids in C. saxicola from different locations. The results demonstrated that this method is simple, reliable and suitable for the quality control of this medicinal herb.

Evaluation of the genotoxicity of piplartine, an alkamide of Piper tuberculatum, in yeast and mammalian V79 cells

The genus Piper belongs to the Piperaceae family, and includes species of commercial and medicinal importance. Chemical studies on Piper species resulted in the isolation of several biologically active molecules, including alkaloid amides, such as piplartine. This molecule, isolated from Piper tuberculatum, has significant cytotoxic activity against tumor cell lines, and presents antifungal, anti-platelet aggregation, anxiolytic, and antidepressant effects. In order to understand the biological properties of piplartine, this study investigated the genotoxicity and the induction of apoptosis by piplartine in V79 cells and its mutagenic and recombinogenic potential in Saccharomyces cerevisiae. Piplartine induced dose-dependent cytotoxicity in S. cerevisiae cultures in either stationary -- or exponential growth phase. In addition, piplartine was not mutagenic when cells were treated during exponential-growth phase and kept in buffer solution, but it increased the frequencies of point, frameshift, and forward mutations when cells were treated in medium during growth. Piplartine treatment induced DNA strand breaks in V79 cells, as detected by neutral and alkaline comet assay. In cell cycle analysis, piplartine induced G2/M cell cycle arrest, probably as a consequence of the DNA damage induced and repair. Moreover, piplartine treatment induced apoptosis in a dose-dependent manner, as observed by a decrease in mitochondrial membrane potential and an increase in internucleosomal DNA fragmentation. These data suggest that the DNA damage caused by piplartine induces G2/M cell cycle arrest, followed by apoptosis. Moreover, we suggest that cells surviving piplartine-induced DNA damage can accumulate mutations, since this alkaloid was mutagenic and recombinogenic in S. cerevisiae assays.

Molecular recognition of DNA by small molecules: AT base pair specific intercalative binding of cytotoxic plant alkaloid palmatine

The base dependent binding of the cytotoxic alkaloid palmatine to four synthetic polynucleotides, poly(dA).poly(dT), poly(dA-dT).poly(dA-dT), poly(dG).poly(dC) and poly(dG-dC).poly(dG-dC) was examined by competition dialysis, spectrophotometric, spectrofluorimetric, thermal melting, circular dichroic, viscometric and isothermal titration calorimetric (ITC) studies. Binding of the alkaloid to various polynucleotides was dependent upon sequences of base pairs. Binding data obtained from absorbance measurements according to neighbour exclusion model indicated that the intrinsic binding constants decreased in the order poly(dA).poly(dT)>poly(dA-dT).poly(dA-dT)>poly(dG-dC).poly(dG-dC)>poly(dG).poly(dC). This affinity was also revealed by the competition dialysis, increase of steady state fluorescence intensity, increase in fluorescence quantum yield, stabilization against thermal denaturation and perturbations in circular dichroic spectrum. Among the polynucleotides, poly(dA).poly(dT) showed positive cooperativity at binding values lower than r=0.05. Viscosity studies revealed that in the strong binding region, the increase of contour length of DNA depended strongly on the sequence of base pairs being higher for AT polymers and induction of unwinding-rewinding process of covalently closed superhelical DNA. Isothermal titration calorimetric data showed a single entropy driven binding event in the AT homo polymer while that with the hetero polymer involved two binding modes, an entropy driven strong binding followed by an enthalpy driven weak binding. These results unequivocally established that the alkaloid palmatine binds strongly to AT homo and hetero polymers by mechanism of intercalation.

Amplification of DNA-binding affinities of protoberberine alkaloids by appended polyamines

This communication describes a synthetic approach toward the amplification of the moderate DNA-binding affinities of protoberberine alkaloids. Specifically, three protoberberine derivatives bearing two to six primary amino groups at the 3- and 9-positions of protoberberine were synthesized and characterized by NMR ((1)H and (13)C) and HRMS. Studies on their affinities toward calf thymus (CT) DNA by ethidium bromide (EB) displacement and spectrophotometric titration experiments indicate that these polyamino protoberberines show more than 10(3)-fold enhanced DNA-binding affinities relative to palmatine and thus are exploitable as strong DNA-binders.

DNA-Binding Affinities and Sequence Specificities of Protoberberine Alkaloids and Their Demethylated Derivatives: A Comparative Study

Berberrubine (1a), jatrorubine (2a), and palmatrubine (3a) have been chemically prepared by partial demethylation of berberine (1), jatrorrhizine (2), and palmatine (3), respectively. Their interactions with calf thymus (CT) DNA, poly(dA-dT)poly(dA-dT), poly(dG-dC)poly(dG-dC), and eight AT-rich 12-mer double-stranded DNAs have been investigated by means of competitive ethidium bromide (EB) displacement experiments. The results showed that DNA-binding affinities of these protoberberine alkaloids have been significantly improved by partial demethylation, and that all of these alkaloids have the preferable binding affinities with AT-rich DNA. Especially, the sequence specificities of DNA-binding of demethylated derivatives 1a, 2a, and 3a had changed to a certain extent when compared with the parent alkaloids 1, 2, and 3, respectively. The binding mode of these alkaloids was further confirmed by UV spectroscopic titration experiments. All the compounds bind to double-stranded DNA most probably via an intercalating mode.

Quaternary protoberberine alkaloids

This contribution reviews some general aspects of the quaternary iminium protoberberine alkaloids. The alkaloids represent a very extensive group of secondary metabolites with diverse structures, distribution in nature, and biological effects. The quaternary protoberberine alkaloids (QPA), derived from the 5,6-dihydrodibenzo[a,g]quinolizinium system, belong to a large class of isoquinoline alkaloids. Following a general introduction, the plant sources of QPA, their biosynthesis, and procedures for their isolation are discussed. Analytical methods and spectral data are summarized with emphasis on NMR spectroscopy. The reactivity of QPA is characterized by the sensitivity of the iminium bond CN(+) to nucleophilic attack. The addition of various nucleophiles to the protoberberine skeleton is discussed. An extended discussion of the principal chemical reactivity is included since this governs interactions with biological targets. Quaternary protoberberine alkaloids and some related compounds exhibit considerable biological activities. Recently reported structural studies indicate that the QPA interact with nucleic acids predominantly as intercalators or minor groove binders. Currently, investigations in many laboratories worldwide are focused on the antibacterial and antimalarial activity, cytotoxicity, and potential genotoxicity of QPA.

Molecular aspects on the interaction of protoberberine, benzophenanthridine, and aristolochia group of alkaloids with nucleic acid structures and biological perspectives

Alkaloids occupy an important position in chemistry and pharmacology. Among the various alkaloids, berberine and coralyne of the protoberberine group, sanguinarine of the benzophenanthridine group, and aristololactam-beta-d-glucoside of the aristolochia group have potential to form molecular complexes with nucleic acid structures and have attracted recent attention for their prospective clinical and pharmacological utility. This review highlights (i) the physicochemical properties of these alkaloids under various environmental conditions, (ii) the structure and functional aspects of various forms of deoxyribonucleic acid (DNA) (B-form, Z-form, H(L)-form, protonated form, and triple helical form) and ribonucleic acid (RNA) (A-form, protonated form, and triple helical form), and (iii) the interaction of these alkaloids with various polymorphic DNA and RNA structures reported by several research groups employing various analytical techniques like absorbance, fluorescence, circular dichroism, and NMR spectroscopy; electrospray ionization mass spectrometry, thermal melting, viscosity, and DNase footprinting as well as molecular modeling and thermodynamic studies to provide detailed binding mechanism at the molecular level for structure-activity relationship. Nucleic acids binding properties of these alkaloids are interpreted in relation to their biological activity.

Nanostructured electrochemical DNA biosensors for detection of the effect of berberine on DNA from cancer cells

Multi walled carbon nanotubes (MWNT) in dimethylformamide (DMF) or aqueous sodium dodecyl sulfate (SDS) solution, colloidal gold nanoparticles (GNP) in phosphate buffer solution (PBS), and a GNP-MWNT mixture in aqueous SDS solution have been investigated for chemical modification of a screen-printed carbon electrode used as the signal transducer of a dsDNA-based biosensor. Differential pulse voltammetry of the DNA redox marker Co[(phen)3]3+ and the guanine moiety anodic oxidation and cyclic voltammetry with K3[Fe(CN)6] as indicator revealed substantial enhancement of the response of the biosensor, particularly when MWNT in SDS solution was used. The biosensor was used in testing of berberine, an isoquinoline plant alkaloid with significant antimicrobial and anticancer activity. Berberine had a very strong, concentration-dependent, effect on the structural stability of DNA from the human cancer cells (U937 cells) whereas non-cancer cells were changed only when berberine concentrations were relatively high 75 and 50 microg mL(-1).

Spacer length and attaching position-dependent binding of synthesized protoberberine dimers to double-stranded DNA

Six jatrorrhizine homodimers and berberine-jatrorrhizine heterodimers have been synthesized in moderate to good yields from the reaction of jatrorrhizine with alpha,omega-dibromoalkanes and 9-O-(omega-bromoalkyl)berberines, respectively. Their binding activities toward calf thymus (CT) DNA and three double-stranded oligodeoxynucleotides, d(AAGAATTCTT)(2), d(TAAGAATTCTTA)(2), and d(TTAAGAATTCTTAA)(2), were investigated by means of spectrofluorimetric and spectrophotometric titrations. The results indicate that these dimers exhibit enhanced DNA-binding affinities due to the cooperative interaction of the two protoberberine subunits. A comparative study of the DNA-binding behaviors of berberine homodimers, jatrorrhizine homodimers, and berberine-jatrorrhizine heterodimers suggests that spacer length and attaching position are of great importance in modulating their DNA-binding affinities.

Effect of berberine on proliferation, biosynthesis of macromolecules, cell cycle and induction of intercalation with DNA, dsDNA damage and apoptosis in Ehrlich ascites carcinoma cells

Our primary aim was to study berberine, a potential anti-cancer drug, for its cytotoxic and antiproliferative activity in-vitro using Ehrlich ascites carcinoma (EAC) cells. Cytotoxicity was measured by the growth inhibition assay. We investigated the effect of berberine on the biosynthesis of macro-molecules (DNA, RNA, proteins), cell cycle effects and induction of dsDNA damage and apoptosis in berberine-treated EAC cells. Our results showed that berberine acts cytotoxically on EAC cells. The cytotoxicity was directly concentration and time dependent. The highest cytotoxic concentrations (100 and 50 microg mL(-1)) induced intercalation of berberine with DNA, formation of dsDNA breaks, inhibition of DNA synthesis and death of EAC cells. A concentration of 10 mug mL(-1) induced clear apoptotic cell death, which was followed by inhibition of protein synthesis.

Molecular aspects on the specific interaction of cytotoxic plant alkaloid palmatine to poly(A)

The interaction of the protoberberine alkaloid palmatine with single and double stranded structures of poly(A) was studied by various biophysical techniques. Comparative binding studies were also performed with double stranded DNA, t-RNA, poly(C).poly(G), poly(U) and poly(C). The results of competition dialysis, fluorescence, and absorption spectral studies converge to reveal the molecular aspects of the strong and specific binding of palmatine to single stranded poly(A). The binding affinity of palmatine to natural DNA, t-RNA and double stranded poly(A) was weaker while no binding was apparent with single stranded poly(U), poly(C) and double stranded poly(C).poly(G). The strong affinity of the alkaloid to single stranded poly(A) in comparison to the double stranded structure was also revealed from circular dichroic and viscometric studies. The effect of [Na+] ion concentration on the binding process revealed the significant role of electrostatic forces in the complexation. The presence of bound alkaloid also remarkably affected denaturation-renaturation of stacked helical poly(A). The energetics of the strong binding to poly(A) was studied from thermodynamic estimation from van Hoff' analysis of the temperature dependent binding constants and ultra sensitive isothermal titration calorimertry, both suggesting the binding to be exothermic and enthalpy driven. This study provides detailed insight into the binding specificity of the natural alkaloid to single stranded poly(A) over several other single and double stranded nucleic acid structures suggesting its potential as a lead compound for RNA based drug targeting.

RNA specific molecules: cytotoxic plant alkaloid palmatine binds strongly to poly(A)

The cytotoxic plant alkaloid palmatine was found to bind strongly by partial intercalation to single stranded poly(A) structure with binding affinity (Ka) of (8.36+/-0.26) x 10(5) M(-1). The binding of palmatine was characterized to be exothermic and enthalpy driven with one palmatine for every two adenine residues. On the other hand, the binding to the double stranded poly(A) has been found to be significantly weak. This study identifies poly(A) as a potential bio-target for the alkaloid palmatine and its use as a lead compound in antitumor drug screening.

Synthesis, DNA-binding affinities, and binding mode of berberine dimers

Six novel berberine dimers (3a-f) were synthesized in 37-84% yield from the reaction of berberrubine (2) with dihaloalkanes of varying lengths from two to seven carbons. Their interactions with calf thymus (CT) DNA and three double helical oligodeoxynucleotides, d(AAGAATTCTT)2, d(AAGCATGCTT)2, and d(TAAGAATTCTTA)2, were investigated by means of fluorometric titration and ethidium bromide (EB) displacement experiments. Compared with the monomeric parent berberine (1), these dimers' DNA-binding affinities increased up to approximately 100-fold, suggesting a cooperative interaction of the two berberine subunits in the molecules. Furthermore, these dimers linked by different spacers show a prominent structure-activity relationship when bound with oligodeoxynucleotides. The relative binding affinities are in the order of 3b>3a>3c>3d>3e>3f with d(AAGAATTCTT)2 and d(TAAGAATTCTTA)2, and 3b>3c>3a>3d>3e>3f with d(AAGCATGCTT)2. Dimer 3b, linked with a propyl chain, exhibits the highest binding affinity. This suggests that a propyl chain may be the most suitable spacer to bridge the two berberine units for DNA binding. Spectrophotometric titration and competitive EB displacement of berberine (1) and dimer 3b indicate that both berberine and its dimers form intercalating complexes with duplex DNA. A larger redshift, a stronger hypochromic effect, and a much higher EB displacement ratio, observed in 3b, indicate that the dimer is in more intimate contact with DNA than berberine. In addition, no obvious binding of canadine (4), a hydrogenated product of berberine, with CT DNA was observed, suggesting critical roles of the quaternary ammonium cation and planar structure in the DNA-binding of berberine.

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.

Screening and analysis of bioactive compounds with biofingerprinting chromatogram analysis of traditional Chinese medicines targeting DNA by microdialysis/HPLC

Biofingerprinting chromatogram analysis, which is defined as the comparison of fingerprinting chromatograms of the extract of traditional Chinese medicines (TCMs) before and after the interaction with biological systems (DNA, protein, cell, etc.), was proposed for screening and analysis of the multiple bioactive compounds in TCMs. A method of microdialysis sampling combined with high performance liquid chromatography (HPLC) was applied to the study of DNA-binding property for the extracts of TCMs. Seven compounds were found to bind to calf thymus DNA (ct-DNA) from the TCMs of Coptis chinensis Franch (Coptis), but only three ones from Phellodendron amurense Rupr. (Phellodendron) and none from Sophoraflavescens Ait. (Sophora) to bind to ct-DNA, respectively. Three of them were identified as berberine, palmatine and jatrorrhizine and their association constants (K) to ct-DNA were determined by microdialysis/HPLC. Competitive binding behaviors of them to ct-DNA were also investigated.

Synthesis of linked berberine dimers and their remarkably enhanced DNA-binding affinities

This communication describes the facile synthesis of five novel berberine dimers and their strong affinities toward double-stranded DNA. These berberine dimers were synthesized in 37-84% yields from the reaction of berberrubine with dihaloalkanes of varying lengths, and fully characterized by HRMS and 1H NMR. Compared with the monomeric parent berberine, these dimers showed greatly enhanced binding affinities up to approximately 100-fold, with two double helical oligodeoxynucleotides, d(AAGAATTCTT)2 and d(TAAGAATTCTTA)2, which was investigated by means of fluorescence spectrometry.