Synthesis and biological studies of steroidal pyran based derivatives

Chitosan catalyzed synthesis and mechanistic study of Steroidal 2H-Pyran ring formation

A simple and convenient method is reported for the preparation of steroidal 2H-pyran 2 by reacting 3β-acetoxy cholest-5-ene-7-one 1 with N-benzyl-2-cyanoacetamide in presence of chitosan, a green and heterogeneous catalyst. The product 2 was characterized by using NMR (¹H and ³C), IR, and mass spectroscopy. The mechanism of 2H-pyran ring formation is described by employing theoretical B3LYP/6-31G (d) density functional method. The reaction undergoes via formation of two intermediates A and B, and each intermediate undergoes through a transition state TS1 and TS2. The molecular properties like relative energy and FMO analysis were used to explain the mechanism of the reaction. The HOMOs and LUMOs were found in support of the present reaction mechanism. The stability of all the calculated structures which includes reactant (1a), intermediates (A and B), product (2a) as well as TS1 and TS2 transition states, was supported by calculating their energy minima and fundamental frequencies.

Metal ions modify DNA-protecting and mutagen-scavenging capacities of the AV-153 1,4-dihydropyridine

1,4-Dihydropyridines (1,4-DHP) possess important biochemical and pharmacological properties, including antioxidant and antimutagenic activities. AV-153-Na, an antimutagenic and DNA-repair enhancing compound was shown to interact with DNA by intercalation. Here we studied DNA binding of several AV-153 salts to evaluate the impact of AV-153 modifications on its DNA binding capacity, the ability to scavenge the peroxynitrite, to protect HeLa and B-cells cells against DNA damage. Affinity of the AV-153 salts to DNA measured by a fluorescence assay was dependent on the metal ion forming a salt in position 4 of the 1,4-DHP, and it decreased as follows: Mg > Na > Ca > Li > Rb > K. AV-153-K and AV-153-Rb could not react chemically with peroxynitrite as opposed to AV-153-Mg and AV-153-Ca, the latter increased the decomposition rate of peroxynitrite. AV-153-Na and AV-153-Ca effectively reduced DNA damage induced by peroxynitrite in HeLa cells, while AV-153-K and AV-153-Rb were less effective, AV-153-Li did not protect the DNA, and AV-153-Mg even caused DNA damage itself. The Na, K, Ca and Mg AV-153 salts were also shown to reduce the level of DNA damage in human B-cells from healthy donors. Thus, metal ions modify both DNA-binding and DNA-protecting effects of the AV-153 salts.

DNA binding, artificial nuclease activity and cytotoxic studies of newly synthesized steroidal pyrimidines

The new steroidal pyrimidine derivatives (4-6) were synthesized by the reaction of steroidal thiosemicarbazones with (2-methyl) diethyl malonate in absolute ethanol. After characterization by spectral and analytical data, the DNA interaction studies of compounds (4-6) were carried out by UV-vis, fluorescence spectroscopy, hydrodynamic measurements, molecular docking and gel electrophoresis. The compounds bind to DNA preferentially through electrostatic and hydrophobic interactions with K_b; 2.31×10³M^-1, 1.93×10³M^-1 and 2.05×10³M^-1, respectively indicating the higher binding affinity of compound 4 towards DNA. Gel electrophoresis demonstrated that compound 4 showed a strong interaction during the concentration dependent cleavage activity with pBR322 DNA. The molecular docking study suggested the intercalation of steroidal pyrimidine moiety in the minor groove of DNA. During in vitro cytotoxicity, compounds (4-6) revealed potential toxicity against the different human cancer cells (MTT assay). During DAPI staining, the nuclear fragmentations on cells occurred after treatment with compounds 4 and 5. Western blotting analysis clearly indicates that compound 4 causes apoptosis in MCF-7 cancer cells. The results revealed that compound 4 has better prospectus to act as a cancer chemotherapeutic candidate, which warrants further in vivo anticancer investigations.

Steroidal dihydrocarbothioic acid amido pyrazoles: synthesis, characterization, cytotoxicity and genotoxicity studies

A new series of steroidal dihydrocarbothioic acid amido pyrazole analogues were synthesized, and after characterization, evaluation for cytotoxicity, comet assay and western blotting was carried out. The synthesis of these analogues is convenient and involves two steps, i.e. aldol condensation as first step followed by nucleophilic addition of thiosemicarbazide across α, β-unsaturated carbonyl as a later step. Quantitative yields of more than 80 % are obtained in both the steps. After characterization by IR, (1)H NMR, (13)C NMR, MS and analytical data, all the compounds of both series were tested for cytotoxic activity against a panel of different human cancer cell lines by MTT assay, during which compound 3e, 3f, 4e, 4f and 4h are very potent especially against HepG2 and MCF-7 cancer cell lines. Cell cycle analysis depicted the cell death in S-phase while as annexin V-FITC/PI analysis showed that compounds effectively induce apoptosis. Apoptotic degradation of DNA of MCF-7 cells in the presence of different steroidal derivatives was analysed by agarose gel electrophoresis and visualized by ethidium bromide staining (comet assay). In western blotting analysis, the relative expressions of relevant apoptotic markers depicted an apoptosis by steroidal dihydropyrazole in MCF-7 cancer cells.

Fluorescence of N-acylated dansylamide with a long hydrophobic tail: sensitive response to premicellar aggregation of sodium deoxycholate

The present work describes the synthesis and photophysical studies of two fluorescent dansylamide derivatives, in which the amine group is acylated by a long hydrophobic chain (a part of a biologically relevant palmitic acid) and by a short hydrophobic tail (a part of acetic acid).

DNA-binding studies of AV-153, an antimutagenic and DNA repair-stimulating derivative of 1,4-dihydropiridine

The ability to intercalate between DNA strands determines the cytotoxic activity of numerous anticancer drugs. Strikingly, intercalating activity was also reported for some compounds considered to be antimutagenic. The aim of this study was to determine the mode of interaction of DNA with the antimutagenic and DNA repair-stimulating dihydropyridine (DHP) AV-153. DNA and AV-153 interactions were studied by means of UV/VIS spectroscopy, fluorimetry and infrared spectroscopy. Compound AV-153 is a 1,4 dihydropyridine with ethoxycarbonyl groups in positions 3 and 5. Computer modeling of AV-153 and DNA interactions suggested an ability of the compound to dock between DNA strands at a single strand break site in the vicinity of two pyrimidines, which was confirmed in the present study. AV-153 evidently interacted with DNA, as addition of DNA to AV-153 solutions resulted in pronounced hyperchromic and bathochromic effects on the spectra. Base modification in a plasmid by peroxynitrite only minimally changed binding affinity of the compound; however, induction of single-strand breaks using Fenton's reaction greatly increased binding affinity. The affinity did not change when the ionic strength of the solution was changed from 5 to 150 mM NaCl, although it increased somewhat at 300 mM. Neither was it influenced by temperature changes from 25 to 40°C, however, it decreased when the pH of the solution was changed from 7.4 to 4.7. AV-153 competed with EBr for intercalation sites in DNA: 116 mM of the compound caused a two-fold decrease in fluorescence intensity. FT-IR spectral data analyses indicated formation of complexes between DNA and AV-153. The second derivative spectra analyses indicated interaction of AV-153 with guanine, cytosine and thymine bases, but no interaction with adenine was detected.

CONCLUSIONS

The antimutagenic substance AV-153 appears to intercalate between the DNA strands at the site of a DNA nick in the vicinity of two pyrimidines.