Synthesis of 2,5- and 3,5-diphenylpyridine derivatives for DNA recognition and cytotoxicity

A New Concept of Enhancing the Anticancer Activity of Manganese Terpyridine Complex by Oxygen-Containing Substituent Modification

Eleven manganese 4'-substituted-2,2':6',2″-terpyridine complexes (1a-1c and 2a-2h) with three non-oxygen-containing substituents (L^1a-L^1c: phenyl, naphthalen-2-yl and naphthalen-1-yl, L^1a-L^1c) and eight oxygen-containing substituents (L^2a-L^2h: 4-hydroxyl-phenyl, 3-hydroxyl-phenyl, 2-hydroxyl-phenyl, 4-methoxyl-phenyl, 4-carboxyl-phenyl, 4-(methylsulfonyl)phenyl, 4-nitrophenyl and furan-2-yl) were prepared and characterized by IR, elemental analysis or single crystal X-ray diffraction. In vitro data demonstrate that all of these show higher antiproliferative activities than cisplatin against five human carcinoma cell lines: A549, Bel-7402, Eca-109, HeLa and MCF-7. Compound 2d presents the strongest antiproliferative effect against A549 and HeLa cells, with IC₅₀ values being 0.281 μM and 0.356 μM, respectively. The lowest IC₅₀ values against Bel-7402 (0.523 μM) Eca-109 (0.514 μM) and MCF-7 (0.356 μM) were obtained for compounds 2h, 2g and 2c, respectively. Compound 2g with a nitro group showed the best results on the whole, with relevantly low IC₅₀ values against all the tested tumor cells. The DNA interactions with these compounds were studied by circular dichroism spectroscopic and molecular modeling methods. Spectrophotometric results revealed that the compounds have strong affinities in binding with DNA as intercalators, and the binding induces DNA conformational transition. Molecular docking studies indicate that the binding is contributed by the π-π stacking and hydrogen bonds. The anticancer activities of the compounds are correlated with their DNA binding ability, and the modification of oxygen-containing substituents significantly enhanced the anticancer activity, which could provide a new rationale for the future design of terpyridine-based metal complexes with antitumor potential.

One-Pot Amberlyst 15-Controlled Cyclocondensation of Piperidines and Arylaldehydes: Synthesis of 3,5-Diarylmethylpyridines

Amberlyst 15-controlled one-pot easy-operational intermolecular cyclocondensation of substituted piperidines with arylaldehydes provides diversified 3,5-diarylmethylpyridines in high to excellent yields under refluxing toluene conditions. The uses of various acidic solid supports and reaction solvents are investigated for facile and efficient transformation. A plausible mechanism has been proposed.

In situ generation of N-unsubstituted imines from alkyl azides and their applications for imine transfer via copper catalysis

Although azides have been widely used in nitrene transfer reactions, in situ generation of N-H imines from azides for downstream transformations has rarely been explored. We report copper-mediated formation of N-unsubstituted aliphatic imines from easily available aliphatic azides using a customized phenanthroline-based ligand (L₁*). Through trapping in situ-generated N-H imines, multisubstituted pyridines or indoles were readily synthesized. ¹³C-labeled azide was used as part of an isotope labeling study, which suggests that the construction of pyridine derivatives involves a three-component dehydrogenative condensation. The construction of 2,3,5-triaryl pyridines using this method provided evidence supporting a proposed pathway involving both imine formation and abnormal Chichibabin pyridine synthesis. The generation of N-unsubstituted imine intermediates was also confirmed by formation of indole derivatives from alkyl azides.

Iron-Mediated One-Pot Synthesis of 3,5-Diarylpyridines from β-Nitrostyrenes

An operationally simple and mild one-pot protocol for the synthesis of a variety of 3,5-diarylpyridines from β-nitrostyrenes was achieved by using elemental iron. This reaction proceeds via reduction of the nitro group, resulting in in situ imine formation followed by trimolecular condensation with concomitant debenzylative aromatization. By employing this method, a series of symmetrical and unsymmetrical 3,5-diarylpyridines were synthesized with good to excellent yields. In addition, this method was also utilized for the synthesis of Sch-21418, an anti-inflammatory agent on gram scale.

Synthesis and pharmacological evaluation of indole-based sigma receptor ligands

A series of novel indole-based analogs were prepared and their affinities for sigma receptors were determined using in vitro radioligand binding assays. The results of this study identified several compounds with nanomolar sigma-2 affinity and significant selectivity over sigma-1 receptors. In particular, 2-(4-(3-(4-fluorophenyl)indol-1-yl)butyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (9f) was found to display high affinity at sigma-2 receptors with good selectivity (σ-1/σ-2 = 395). The pharmacological binding profile for this compound was established with other relevant non-sigma sites.

Synthesis of 2,6-diphenylpyrazine derivatives and their DNA binding and cytotoxic properties

A series of 2,6-diphenylpyrazine derivatives was synthesized from 2,6-dichloropyrazine and 4-methoxyphenylboronic acid using palladium(0) as catalyst in a Suzuki methodology. After deprotection of the hydroxyl, alkylation reactions with different halides afforded compounds 5-8 bearing hydrophilic chains. DNA binding and cytotoxic properties were investigated. Compound 11 bearing imidazoline terminal groups was found to be a potent AT-specific DNA minor groove binder but there was no relationship between DNA interaction and cytotoxicity. However, in all cases the incorporation of the pyrazine ring was found to promote the cytotoxicity of the molecules compared to the corresponding pyridine analogues, previously synthesized.