A Stereodynamic Redox-Interconversion Network of Vicinal Tertiary and Quaternary Carbon Stereocenters in Hydroquinone-Quinone Hybrid Dihydrobenzofurans

9-Trifluoromethylxanthenediols: Synthesis and Supramolecular Motifs

The synthesis of four derivatives and the single-crystal X-ray structures of six 9-trifluoromethylxanthenediols (TFXdiols) I-VI are analyzed in this work. These compounds were obtained through superacid-catalyzed condensation of dihydroxybenzenes with 1,1,1-trifluoroacetone or 2,2,2-trifluoroacetophenone. The title molecules have a convex molecular structure due to their three fused rings of the xanthene moiety. We have found that, similar to resorcinol, the configuration of the hydroxyl groups is of great relevance for the crystal packing favoring either interactions above and below their molecular plane or lateral interactions that create layers. Considering that reports of TFXdiols are very scarce, our findings contribute to a better understanding of the molecular conformation and intermolecular interactions in their crystal structures. A similar analysis was extended to a fortuitous cocrystal obtained between 9-trifluoromethyl-9-(4'-fluorophenyl)-xanthenediol and 1,4-dihydroxybenzene, showing that these structures might be used to obtain cocrystals in the future.

Modification of N-terminal α-amine of proteins via biomimetic ortho-quinone-mediated oxidation

Naturally abundant quinones are important molecules, which play essential roles in various biological processes due to their reduction potential. In contrast to their universality, the investigation of reactions between quinones and proteins remains sparse. Herein, we report the development of a convenient strategy to protein modification via a biomimetic quinone-mediated oxidation at the N-terminus. By exploiting unique reactivity of an ortho-quinone reagent, the α-amine of protein N-terminus is oxidized to generate aldo or keto handle for orthogonal conjugation. The applications have been demonstrated using a range of proteins, including myoglobin, ubiquitin and small ubiquitin-related modifier 2 (SUMO2). The effect of this method is further highlighted via the preparation of a series of 17 macrophage inflammatory protein 1β (MIP-1β) analogs, followed by preliminary anti-HIV activity and cell viability assays, respectively. This method offers an efficient and complementary approach to existing strategies for N-terminal modification of proteins.

Methods for selective modification of the N-terminus of proteins are of high interest, but mostly require specific amino acid residues. Here, the authors report a selective and fast method for N-terminal modification of proteins based on quinone-mediated oxidation of the alpha-amine to aldehyde or ketone, and apply it to diverse proteins.

Enamides and dienamides in phosphoric acid-catalysed enantioselective cycloadditions for the synthesis of chiral amines

This feature article describes how enamides and dienamides can participate in chiral phosphoric acid catalyzed enantioselective cycloadditions to prepare a wide range of cyclic amines.

Metal-Free C-H Borylation of N-Heteroarenes by Boron Trifluoride

Organoboron compounds are essential reagents in modern C-C coupling reactions. Their synthesis via catalytic C-H borylation by main group elements is emerging as a powerful tool alternative to transition metal based catalysis. Herein, a straightforward metal-free synthesis of aryldifluoroboranes from BF3 and heteroarenes is reported. The reaction is assisted by sterically hindered amines and catalytic amounts of thioureas. According to computational studies the reaction proceeds via frustrated Lewis pair (FLP) mechanism. The obtained aryldifluoroboranes are further stabilized against destructive protodeborylation by converting them to the corresponding air stable tetramethylammonium organotrifluoroborates.

Enantioselective Redox-Divergent Chiral Phosphoric Acid Catalyzed Quinone Diels-Alder Reactions

An efficient enantioselective construction of tetrahydronaphthalene-1,4-diones as well as dihydronaphthalene-1,4-diols by a chiral phosphoric acid catalyzed quinone Diels-Alder reaction with dienecarbamates is reported. The nature of the protecting group on the diene is key to the success of achieving high enantioselectivity. The divergent "redox" selectivity is controlled by using an adequate amount of quinones. Reversible redox switching without erosion of enantioselectivity was possible from individual redox isomers.