Synthesis and X-ray crystal structures of three new nickel(II) complexes of benzoylhydrazones: Catalytic applications in the synthesis of 2-arylbenzoxazoles

Isosteric Replacement of Sulfur to Selenium in a Thiosemicarbazone: Promotion of Zn(II) Complex Dissociation and Transmetalation to Augment Anticancer Efficacy

We implemented isosteric replacement of sulfur to selenium in a novel thiosemicarbazone (PPTP4c4mT) to create a selenosemicarbazone (PPTP4c4mSe) that demonstrates potentiated anticancer efficacy and selectivity. Their design specifically incorporated cyclohexyl and styryl moieties to sterically inhibit the approach of their Fe(III) complexes to the oxy-myoglobin heme plane. Importantly, in contrast to the Fe(III) complexes of the clinically trialed thiosemicarbazones Triapine, COTI-2, and DpC, the Fe(III) complexes of PPTP4c4mT and PPTP4c4mSe did not induce detrimental oxy-myoglobin oxidation. Furthermore, PPTP4c4mSe demonstrated more potent antiproliferative activity than the homologous thiosemicarbazone, PPTP4c4mT, with their selectivity being superior or similar, respectively, to the clinically trialed thiosemicarbazone, COTI-2. An advantageous property of the selenosemicarbazone Zn(II) complexes relative to their thiosemicarbazone analogues was their greater transmetalation to Cu(II) complexes in lysosomes. This latter effect probably promoted their antiproliferative activity. Both ligands down-regulated multiple key receptors that display inter-receptor cooperation that leads to aggressive and resistant breast cancer.

Differential transmetallation of complexes of the anti-cancer thiosemicarbazone, Dp4e4mT: effects on anti-proliferative efficacy, redox activity, oxy-myoglobin and oxy-hemoglobin oxidation

The di-2-pyridylthiosemicarbazone (DpT) analogs demonstrate potent and selective anti-proliferative activity against human tumors. The current investigation reports the synthesis and chemical and biological characterization of the Fe(iii), Co(iii), Ni(ii), Cu(ii), Zn(ii), Ga(iii), and Pd(ii) complexes of the promising second generation DpT analog, di-2-pyridylketone-4-ethyl-4-methyl-3-thiosemicarbazone (Dp4e4mT). These studies demonstrate that the Dp4e4mT Co(iii), Ni(ii), and Pd(ii) complexes display distinct biological activity versus those with Cu(ii), Zn(ii), and Ga(iii) regarding anti-proliferative efficacy against cancer cells and a detrimental off-target effect involving oxidation of oxy-myoglobin (oxy-Mb) and oxy-hemoglobin (oxy-Hb). With regards to anti-proliferative activity, the Zn(ii) and Ga(iii) Dp4e4mT complexes demonstrate facile transmetallation with Cu(ii), resulting in efficacy against tumor cells that is strikingly similar to the Dp4e4mT Cu(ii) complex (IC50: 0.003-0.006 μM and 72 h). Relative to the Zn(ii) and Ga(iii) Dp4e4mT complexes, the Dp4e4mT Ni(ii) complex demonstrates kinetically slow transmetallation with Cu(ii) and intermediate anti-proliferative effects (IC50: 0.018-0.076 μM after 72 h). In contrast, the Co(iii) and Pd(ii) complexes demonstrate poor anti-proliferative activity (IC50: 0.262-1.570 μM after 72 h), probably due to a lack of transmetallation with Cu(ii). The poor efficacy of the Dp4e4mT Co(iii), Ni(ii), and Pd(ii) complexes to transmetallate with Fe(iii) markedly suppresses the oxidation of oxy-Mb and oxy-Hb. In contrast, the 2 : 1 Dp4e4mT: Cu(ii), Zn(ii), and Ga(iii) complexes demonstrate facile reactions with Fe(iii), leading to the redox active Dp4e4mT Fe(iii) complex and oxy-Mb and oxy-Hb oxidation. This study demonstrates the key role of differential transmetallation of Dp4e4mT complexes that has therapeutic ramifications for their use as anti-cancer agents.

Advances in the synthetic strategies of benzoxazoles using 2-aminophenol as a precursor: an up-to-date review

Benzoxazole is a resourceful and important member of the heteroarenes that connects synthetic organic chemistry to medicinal, pharmaceutical, and industrial areas. It is a bicyclic planar molecule and is the most favorable moiety for researchers because it has been extensively used as a starting material for different mechanistic approaches in drug discovery. The motif exhibits a high possibility of broad substrate scope and functionalization to offer several biological activities like anti-microbial, anti-fungal, anti-cancer, anti-oxidant, anti-inflammatory effects, and so on. There has been a large upsurge in the synthesis of benzoxazole via different pathways. The present article presents recent advances in synthetic strategies for benzoxazole derivatives since 2018. A variety of well-organized synthetic methodologies for benzoxazole using 2-aminophenol with aldehydes, ketones, acids, alcohols, isothiocyanates, ortho-esters, and alkynones under different reaction conditions and catalysts, viz. nanocatalysts, metal catalysts, and ionic liquid catalysts, with other miscellaneous techniques has been summarized.

F,O,S-Codoped Graphitic Carbon Nitride as an Efficient Photocatalyst for the Synthesis of Benzoxazoles and Benzimidazoles

Graphitic carbon nitride (g-C3N4) is a metal-free heterogeneous catalyst that has attracted attention because of its good chemical stability, cost-effectiveness, and environmental friendliness. In the work presented herein, F,O,S-codoped carbon nitride was synthesized by heating a mixture of melamine cyanurate and trifluoromethanesulfonic acid at 550 °C for 50 min. The obtained product was characterized by transmission electron microscopy, infrared spectroscopy, X-ray powder diffraction, CHNS elemental analysis, total combustion-ion chromatography, X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and UV-Vis spectroscopy. Results point to an F,O,S-codoped g-C3N4. The material was applied as a photocatalyst for the formation of benzoxazoles and benzimidazoles by condensation–aromatization of 2-aminophenol or 1,2-phenylenediamine with suitable aldehydes (viz. benzaldehyde, 4-chlorobenzaldehyde, 2-naphthaldehyde, 2-hydroxybenzaldehyde, and 2-methoxybenzaldehyde), obtaining yields of up to 90% in 15 min under visible light irradiation, with good selectivity and reusability. Thus, the reported findings suggest that this F,O,S-codoped g-C3N4 may hold promise as a metal-free photocatalyst for the rapid synthesis of 2-arylbenzoxazoles and 2-arylbenzimidazoles.

A green approach for the synthesis of 2-substituted benzoxazoles and benzothiazoles via coupling/cyclization reactions

We have developed the green method for the synthesis of benzoxazoles and benzothiazoles with moderate to good yields using imidazolium chlorozincate (II) ionic liquid supported into Fe3O4 nanoparticles (LAIL@MNP) under solvent-free sonication. The reaction was performed under mild conditions and only produced water as a sole byproduct. The reactions under solvent-free sonication showed advantages of faster reaction rate (30 min) and high yields of the products (up to 90%). Moreover, the LAIL@MNP material was easily separated from the reaction mixture and can be recycled for five consecutive runs with a slight decrease in its catalytic performance (from 82 to 73%).