Synthesis and chemical transformations of 2-cyclopropyl-2-diazoacetates

Synthesis and Pharmacological In Vitro Investigations of Novel Shikonin Derivatives with a Special Focus on Cyclopropane Bearing Derivatives

Melanoma is the deadliest form of skin cancer and accounts for about three quarters of all skin cancer deaths. Especially at an advanced stage, its treatment is challenging, and survival rates are very low. In previous studies, we showed that the constituents of the roots of Onosma paniculata as well as a synthetic derivative of the most active constituent showed promising results in metastatic melanoma cell lines. In the current study, we address the question whether we can generate further derivatives with optimized activity by synthesis. Therefore, we prepared 31, mainly novel shikonin derivatives and screened them in different melanoma cell lines (WM9, WM164, and MUG-Mel2 cells) using the XTT viability assay. We identified (R)-1-(1,4-dihydro-5,8-dihydroxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enyl 2-cyclopropyl-2-oxoacetate as a novel derivative with even higher activity. Furthermore, pharmacological investigations including the ApoToxGlo^TM Triplex assay, LDH assay, and cell cycle measurements revealed that this compound induced apoptosis and reduced cells in the G1 phase accompanied by an increase of cells in the G2/M phase. Moreover, it showed hardly any effects on the cell membrane integrity. However, it also exhibited cytotoxicity against non-tumorigenic cells. Nevertheless, in summary, we could show that shikonin derivatives might be promising drug leads in the treatment of melanoma.

Synthesis of 2,3-Dialkylated Tartaric Acid Esters via Visible Light Photoredox-Catalyzed Reductive Dimerization of α-Ketoesters

A mild transition-metal-free protocol to prepare 2,3-dialkylated tartaric acid esters has been developed by taking advantage of a visible light photoredox-catalyzed reductive dimerization of α-ketoesters with a combination of an organic dye photocatalyst and a Hantzsch-type 1,4-dihydropyridine hydrogen donor. A broad range of functional groups including cyclopropane, alkene, alkyne, 4-methoxybenzyl ether, acetal, silyl ether, carbamate, cyclic ether, cyclic thioether, bromoalkane, and N-alkoxyphthalimide are well-compatible. By employing the visible light photoredox-catalyzed reductive coupling and the subsequent optical resolution, both enantioenriched diastereomers of 2,3-dialkylated tartaric acid could be acquired conveniently.