Synthesis, cytotoxicity, DNA binding and topoisomerase II inhibition of cassiarin A derivatives

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

Highly efficient and facile fabrication of monodispersed Au nanoparticles using pullulan and their application as anticancer drug carriers

This work presented a simple, rapid, green and efficient approach to the synthesis of gold nanoparticles using pullulan as a reducing/stabilizing/capping agent for drug delivery systems to increase the safety and efficacy of these systems. Monodispersed AuNPs@pullulan with prolonged stability were fully characterized by UV-VIS, FTIR, TEM, EDX, TGA and zeta potential analyses. A mechanism of AuNPs formation was proposed in which pullulan created reducing species for the reduction of Au³⁺ to AuNPs (Au⁰) that resulted in the formation of spherical AuNPs@pullulan with an average size of approximately 11±5nm, while the hydroxyl groups of pullulan were oxidized to carboxylate compounds. Novel cassiarin A chloride derivatives (3d and 3i) as candidate anticancer drugs were successfully loaded onto AuNPs@pullulan through electrostatic interactions. AuNPs@pullulan-3d (IC₅₀=6.0±0.1μM) and AuNPs@pullulan-3i (5.2±0.1μM) exhibited a 10.2-fold and 7.1-fold higher cytotoxicity against KATO-III cells than free compounds 3d (60.9±0.6μM), 3i (37.1±0.2μM) and cisplatin (64.5±0.9μM), respectively. AuNPs@pullulan exhibited high cellular uptake, biocompatibility and non-cytotoxicity to normal cells. Therefore, AuNPs@pullulan-3d or AuNPs@pullulan-3i have the potential to be developed for treatment of gastric cancer.

Synthesis of Natural Product-like Polyheterocycles via One-Pot Cascade Oximation, C-H Activation, and Alkyne Annulation

An efficient protocol for the direct transformation of chroman-4-ones to tricyclic fused pyridines with the skeleton of cassiarins, a family of alkaloids with antimalarial activity, was developed. Also, a general strategy for modular construction of polyheterocycles with diverse natural product-like skeletons was developed by using ketone-alkyne bifunctional substrates. These reactions involved a one-pot cascade oximation of ketones, rhodium-catalyzed C-H activation, and intermolecular/intramolecular alkyne annulations under mild conditions with high atom, step, and redox economy.