Tetrandrine Derivatives as Promising Antibacterial Agents

This work reports on the antibacterial activity of two tetrandrine derivatives, with acridine (MAcT) and anthracene (MAnT) units, against Gram-positive and Gram-negative bacteria of clinical importance by the broth microdilution method as well as their antioxidant activity against ABTS•+ and DPPH•+ radicals. Unlike natural tetrandrine, its derivatives inhibited bacterial growth, showing selectivity against Staphylococcus aureus with notable activity of MAnT (MIC = 0.035 μg/mL); this compound also has good activity against the ABTS•+ radical (IC50 = 4.59 μg/mL). Cell membrane integrity studies and reactive oxygen species (ROS) detection by fluorescent stains helped to understand possible mechanisms related to antibacterial activity, while electrophoretic mobility assays showed that the derivatives can bind to bacterial DNA plasmid. The results indicate that MAnT can induce a general state of oxidative stress in S. aureus and Escherichia coli, while MAcT induces an oxidative response in S. aureus. Complementary electrochemical studies were included.

DNA-Binding Properties of Bis-N-substituted Tetrandrine Derivatives

A series of bis-N-substituted tetrandrine derivatives carrying different aromatic substituents attached to both nitrogen atoms of the natural alkaloid were studied with double-stranded model DNAs (dsDNAs) to examine the binding properties and mechanism. Variable-temperature molecular recognition studies using UV-vis and fluorescence techniques revealed the thermodynamic parameters, ΔH, ΔS, and ΔG, showing that the tetrandrine derivatives exhibit high affinity toward dsDNA (K ≈ 10⁵-10⁷ M^-1), particularly the bis(methyl)anthraquinone (BAqT) and bis(ethyl)indole compounds (BInT). Viscometry experiments, ethidium displacement assays, and molecular modeling studies enabled elucidation of the possible binding mode, indicating that the compounds exhibit a synergic interaction mode involving intercalation of one of the N-aryl substituents and interaction of the molecular skeleton in the major groove of the dsDNA. Cytotoxicity tests of the derivatives with tumor and nontumor cell lines demonstrated low cytotoxicity of these compounds, with the exception of the bis(methyl)pyrene (BPyrT) derivative, which is significantly more cytotoxic than the remaining derivatives, with IC₅₀ values against the LS-180, A-549, and ARPE-19 cell lines that are similar to natural tetrandrine. Finally, complementary electrochemical characterization studies unveiled good electrochemical stability of the compounds.

Mimicking Biological Recognition: Lessons in Binding Hydrophilic Guests in Water

Selective molecular recognition of hydrophilic guests in water plays a fundamental role in a vast number of biological processes, but synthetic mimicry of biomolecular recognition in water still proves challenging both in terms of achieving comparable affinities and selectivities. This Review highlights strategies that have been developed in the field of supramolecular chemistry to selectively and non-covalently bind three classes of biologically relevant molecules: nucleotides, carbohydrates, and amino acids. As several groups have systematically modified receptors for a specific guest, an evolutionary perspective is also provided in some cases. Trends in the most effective binding forces for each class are described, providing insight into selectivity and potential directions for future work.

A Chiral Bis-Naphthylated Tetrandrine Dibromide: Synthesis, Self-Assembly into an Organic Framework Based On Nanosized Spherical Cages, and Inclusion Studies

Crystalline framework materials have gained interest because of their many potential applications. A novel chiral tetrandrine salt (DNT) has been synthesized and characterized by conventional analytical techniques and single-crystal X-ray diffraction analysis, and its self-assembly behavior studied. In the solid state, 48 molecules of the compound self-assemble into an organic framework based on nanospherical aggregates formed exclusively through weak noncovalent interactions. Additionally, it was demonstrated by UV-vis spectroscopy and TGA that assembled DNT can include the Nile Red dye, giving a fluorescent material. To the best of our knowledge, these spherical assemblies are the largest among the purely synthetic organic self-assembled molecular crystals reported to date.

Design, synthesis and bioactivity investigation of tetrandrine derivatives as potential anti-cancer agents

Twenty-four 14-sulfonamide-tetrandrine derivatives as potential anti-cancer agents were synthesized. The synthetic derivatives were investigated for their cytotoxic activity against human cancer cell lines MDA-MB-231, PC3, WM9, HEL and K562. Initially, the IC50 values (50% inhibitory concentrations) of all of the compounds were determined. These derivatives exhibited potent, but distinct, inhibitory effects on the above-mentioned cell lines. Among them, compound 23, which was modified with a 2-naphthalenesulfonyl group at the 14-amino position, showed impressive inhibition of all five cancer cell lines, and especially of MDA-MB-231 cells with an IC50 value of 1.18 ± 0.14 μM. Further mechanism exploration showed that 23 induced potent apoptotic cell death on MDA-MB-231 cancer cells in a concentration-dependent manner. The results revealed that 23 might be a potential anti-cancer drug candidate.

Synthesis, spectroscopic, physicochemical and structural characterization of tetrandrine-based macrocycles functionalized with acridine and anthracene groups: DNA binding and anti-proliferative activity

In this work, we report on the synthesis of two new mono-alkylated tetrandrine derivatives with acridine and anthracene units, MAcT and MAnT. The compounds were fully characterized by physicochemical techniques and single-crystal X-ray diffraction analysis. In addition, both derivatives were studied as nucleotide receptors and double-stranded DNA binders in aqueous phosphate buffer at pH = 7.2 using UV-vis and fluorescence spectroscopy. According to the molecular recognition studies, MAcT and MAnT exhibit high affinity (K ∼ 10⁵ M^-1) and selectivity for ds-DNA, presumably in an intercalation mode. Finally, the anti-proliferative effects of the tetrandrine derivatives on different cancer cell lines were explored, revealing promising activities. Particularly, the mono-anthracene tetrandrine derivative MAnT showed an IC₅₀ of 2.74 μg/mL on the HeLa cervical cancer cell line, representing a value 3.3 times smaller than that obtained for unsubstituted tetrandrine. Examination of the cytotoxic effects on the HeLa cell line by inverted microscopy suggests that the cell death mechanism consists basically in apoptosis. The molecular modelling of three ds-DNA-MAcT complexes, suggested that the macrocycles may use an intercalation binding mode towards DNA. MAcT is predicted to bind into the major groove of the ds-DNA providing non-covalent interactions such as electrostatic, van der Waals and hydrophobic interactions that lead to selectivity. Overall experimental data supports the mode of action of MAnT and MAcT as cytotoxic compounds against cancer cell lines via a DNA interaction mechanism.

Host-Guest Chemistry of Alkaloids

Binding of alkaloids by different hosts (native and modified cyclodextrins, cucurbiturils, calixarenes, and metal complexes of porphyrin and Salphen-type ligands), as well as receptor properties of alkaloid based hosts are reviewed. With alkaloids as guests, the largest binding constants and most significant spectral changes, in particular strong fluorescence enhancements induced by complexation with isoquinoline alkaloids, are observed with cucurbituril hosts. Cyclodextrins are successfully employed for improvement of solubility and for chiral separation of alkaloids of different types. Receptor properties of native and modified cinchona and bisbenzylisoquinoline alkaloids have attracted considerable attention for development of chiral selectors for analysis and separation.

Functionalization of methyl orange using cationic peptide amphiphile: colorimetric discrimination between ATP and ADP at pH 2.0

A solvatochromic and non-fluorescent acid-base indicator, methyl orange (MO) was applied to colorimetric discrimination between adenosine triphosphate (ATP) and the corresponding diphosphate (ADP) at pH 2.0 in the presence of L-glutamic acid-derived cationic peptide amphiphile 1. This method is based on the fact that the amphiphile 1 can prevent MO from protonation even at pH 2.0. No similar colour change was observed when ADP was added instead of ATP under the same conditions. The effect of the molecular structure of several peptide amphiphiles and dyes was also investigated.

Colorimetric sensor for triphosphates and their application as a viable staining agent for prokaryotes and eukaryotes

The chromogenic complex 1 x Zn (where 1 is (E)-4-(4-dimethylamino-phenylazo)-N,N-bispyridin-2-ylmethyl-benzenesulfonamide) showed high affinity toward the phosphate ion in tetrabutylammonium phosphate in acetonitrile solution and could preferentially bind to adenosine triphosphate (ATP) in aqueous solution at physiological pH. This binding caused a visual change in color, whereas no such change was noticed with other related anions (adenosine monophosphate, adenosine diphosphate, pyrophosphate, and phosphate) of biological significance. Thus, 1 x Zn could be used as a staining agent for different biological cells through binding to the ATP, generated in situ by the mitochondria (in eukaryotes). For prokaryotes (bacteria) the cell membrane takes care of the cells' energy conversion, since they lack mitochondria. ATP is produced in their unique cell structure on the cell membrane, which is not found in any eukaryotes. These stained cells could be viewed with normal light microscopy. This reagent could even be used for distinguishing the gram-positive and the gram-negative bacteria (prokaryotes). This dye was found to be nonlipophilic in nature and nontoxic to living microbes (eukaryotes and prokaryotes). Further, stained cells were found to grow in their respective media, and this confirmed the maintenance of viability of the microbes even after staining, unlike with many other dyes available commercially.

Colorimetric sensor for ATP in aqueous solution

A new chromogenic complex 1.Zn has been synthesized, and its interactions with different biologically important phosphates have been investigated in aqueous solution (pH approximately 7.2). A visual color change can be detected on binding of ATP to 1.Zn, whereas no such change is observed when other biologically related anions (AMP, ADP, PPi, or Phosphate) are used. Complex 1.Zn can also be used as a staining agent for yeast cells allowing detection under normal light microscopy.

Supramolecular Chemistry in Water

Supramolecular chemistry in water is a constantly growing research area because noncovalent interactions in aqueous media are important for obtaining a better understanding and control of the major processes in nature. This Review offers an overview of recent advances in the area of water-soluble synthetic receptors as well as self-assembly and molecular recognition in water, through consideration of the functionalities that are used to increase the water solubility, as well as the supramolecular interactions and approaches used for effective recognition of a guest and self-assembly in water. The special features and applications of supramolecular entities in aqueous media are also described.

Computational Study about Through-Bond and Through-Space Interactions in [2.2]Cyclophanes

An analysis of the electron density, obtained by B3PW91/6-31+G(d,p), B3LYP/6-31+G(d,p), and MP2/6-31+G(d,p) for [2,2]cyclophanes isomers, [2.2]paracyclophane, anti-[2.2]metacyclophane, syn-[2.2]metacyclophane, and [2.2]metaparacyclophane, was made through natural bond orbitals (NBO), natural steric analysis (NSA), and atoms in molecules (AIM) methods and through analysis of frontier molecular orbitals (MOs). NBO indicates that all compounds present through-bond interactions, but only the conformers of [2.2]metacyclophane present significant through-space interactions. The last interactions are observed in AIM analysis and by the plots of MOs. AIM indicates that these through-space interactions are closed-shell ones, and they stabilize the conformers. In contrast, all isomers present through-bond and through-space repulsive interactions. In addition, the atomic properties, computed over the atomic basins, showed that the position of the bridges and the relative displacement of the rings can affect the atomic charges, the first atomic moments, and the atomic volumes.

Optical sensing system for ATP using porphyrin-alkaloid conjugates

Tetrabrucin-porphyrin as a sensor for ATP was designed and tested; selectivity for ATP was proved in the presence of ADP and AMP.

A Computational Study of [2.2]Cyclophanes

A computational study of isomeric [2.2]cyclophanes, namely [2.2]paracyclophane 1, [2.2]metacyclophane 2, and [2.2]metaparacyclophane 3, has been carried out. For 1, geometry optimizations performed by various methods at different basis sets showed that MP2/6-31+G(d,p) and B3PW91/6-31+G(d,p) provide the best results in comparison to the X-ray data. Compound 1 has D(2) symmetry with distorted bridges. A conformational search was performed for [2.2]cyclophanes 2 and 3. Each cyclophane exists in two conformations which have different energies in the case of 3 but are degenerate in the case of 2. Relative energies and strain energies at the bridges follow the same order, indicating that the relief of bridge tension and repulsion between pi clouds are determining factors for the stability of [2.2]cyclophanes. Through a decomposition of strain energy, it can be concluded that both the rings or the bridges can absorb strain, but it depends on the conformer of butane that is considered in the calculation of SE(br). Changes in aromaticity of these compounds were evaluated by NICS and HOMA and were compared with benzene and xylenes dimers as models. Despite distortions from planarity and shortening and lengthening of the C-C bonds relative to the mean, the phenyl rings are aromatic. NICS suggests a concentration of electronic density between the rings as a result of bridging process. Computed MK, NPA, and GAPT charges were compared for the isomeric cyclophanes. The GIAO chemical shifts were calculated and indicate that 1 has a larger diamagnetic anisotropy than the other isomers.

Recognition of α-amino acid derivatives by N,N′-dibenzylated S,S-(+)-tetrandrine

Complexation of free and N-acetylated alpha-amino acid anions (Gly, Ala, Phe) and some structurally related guests by a dicationic cyclophane-type N,N'-dibenzylated chiral derivative of a bisisoquinoline macrocyclic alkaloid S,S-(+)-tetrandrine (DBT) has been studied by (1)H-NMR titrations in D(2)O. In contrast to other macrocyclic hosts like cyclodextrins and calixarenes, DBT shows highest affinity and large enantioselectivity (K(S)/K(R) >/=10) toward smaller N-acetylalanine and binds larger phenylalanine derivatives more weakly and non-selectively. With 1,2,3,4-tetrahydroisoquinoline-3-carboxylate, a rigid analog of phenylalanine, binding again becomes enantioselective with K(S)/K(R)= 3.8. The binding specificity of DBT is rationalized on the basis of molecular mechanics calculations.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.