Structure-activity relation for synthetic phenoxazone drugs

In vitro interaction of nucleoside reverse transcriptase inhibitor, didanosine with calf-thymus DNA: Insights from spectroscopic studies

Many antivirals interact with DNA and alter their expression profile. Thus, it is necessary to understand the binding mode. Didanosine, a nucleoside reverse transcriptase inhibitor, is used to treat HIV infection in patients with or without acquired immunodeficiency syndrome. Understanding the mechanism of interaction of this nucleoside reverse transcriptase inhibitor with DNA can prove useful in the development of a rational drug designing system. In vitro studies (UV-vis, fluorescence, and viscometry techniques) under physiological conditions (Tris-HCl buffer solutions, pH 7.4) show that didanosine drug interacts with calf-thymus DNA (ct-DNA) via partial intercalative binding mode. UV-visible spectroscopy confirmed the formation didanosine-DNA complex with a binding strength of about 1.5 × 10⁵ M^-1 thus indicating their biological worth. Dye displace experiments and viscometry confirmed that didanosine partially intercalates toward DNA molecules. Negative value of Gibb's-free energy change revealed that the process is spontaneous. The thermodynamic parameters such as enthalpy change (ΔH) and entropy change (ΔS) showed that the acting forces between didanosine and ct-DNA mainly included hydrophobic interactions.

Application of spectral methods for studying DNA damage induced by gamma-radiation

Spectral methods can provide a variety of possibilities to determine several types of radiation-induced DNA damage, such as nucleobase destruction and local denaturation. DNA UV absorption and CD spectra measured at room temperature undergo noticeable alteration under the action of γ-radiation. We have applied the Spirin method of total nucleobases determination, and have measured the molar extinction coefficient of DNA and DNA CD spectra for solutions with different NaCl concentrations (3mM-3.2M) and containing MgCl₂, exposed to γ-radiation with the doses of 0-10³Gy. The melting temperatures of DNA in irradiated solutions at the doses of 0-50Gy were obtained with the help of spectrophotometric melting. It was found that the amount of destructed nucleobases and radiation-induced loss of DNA helicity significantly decreases with the rise of the ionic strength of the irradiated solution. Substitution of a portion of Na⁺ ions on Mg²⁺ while keeping the total ionic strength constant (μ=5mM) does not affect the considered radiation effects. The role of the structure and composition of the DNA secondary hydration layer in the radiation-induced damages is discussed.

Elloxazinones A and B, New Aminophenoxazinones from Streptomyces griseus Acta 2871†

Two new aminophenoxazinone compounds with antitumor activity, elloxazinone A and B, were isolated from the culture filtrate of Streptomyces griseus Acta 2871. Their chemical structures were determined by mass spectrometry, NMR spectroscopy and X-ray analysis. Elloxazinones A and B showed a moderate inhibition of the proliferation of human cells from gastric adenocarcinoma in vitro but a strong inhibition of hepatocellular carcinoma cells whereas elloxazinone B strongly inhibited the proliferation of human breast carcinoma cells.

Structural Basis for the Binding Affinity of a Homologous Series of Synthetic Phenoxazone Drugs with DNA: NMR and Molecular Mechanics Analysis

The molecular basis of the marked structure-activity relationship for a homologous series of DNA-binding phenoxazone drugs (ActII-ActIV) has been investigated by NMR spectroscopy and molecular mechanics. The spatial structures of the complexes between the drugs and a model deoxytetranucleotide, 5'-d(TpGpCpA), have been determined by molecular mechanics methods using homonuclear (1)H-(1)H 2D-NOESY and heteronuclear (1)H-(31)P (HMBC) NMR spectroscopic data. Observed intermolecular NOE contacts and equilibrium binding studies confirm that the binding affinity of the synthetic phenoxazone derivatives with d(TGCA) decreases with an increase in the number of CH(2) groups in the dimethylaminoalkyl side chains, i.e., ActII > ActIII > ActIV, in agreement with the observed biological activity of these compounds. Molecular mechanics calculations of the spatial structures of the intercalated complexes of ActII-ActIV with d(TGCA) indicate that the different binding constants of the phenoxazone derivatives with the DNA oligomer are due to the different degrees of intercalation of the chromophore and the different steric arrangements of aminoalkyl side chains in the minor groove of the tetramer duplex; this results in different distances between the negatively-charged phosphates of the DNA duplex and the terminal positively-charged N(CH(3))(2) groups of the side chains.

Silica-immobilized enzymes for multi-step synthesis in microfluidic devices

The combinatorial synthesis of 2-aminophenoxazin-3-one (APO) in a microfluidic device is reported. Individual microfluidic chips containing metallic zinc, silica-immobilized hydroxylaminobenzene mutase and silica-immobilized soybean peroxidase are connected in series to create a chemo-enzymatic system for synthesis. Zinc catalyzes the initial reduction of nitrobenzene to hydroxylaminobenzene which undergoes a biocatalytic conversion to 2-aminophenol, followed by enzymatic polymerization to APO. Silica-immobilization of enzymes allows the rapid stabilization and integration of the biocatalyst within a microfluidic device with minimal preparation. The system proved suitable for synthesis of a complex natural product (APO) from a simple substrate (nitrobenzene) under continuous flow conditions.