Aerobic Benzylic C(sp3)-H Bond Oxygenations Catalyzed by NBS under Visible Light Irradiation

An efficient photocatalytic oxidation of benzylic C(sp3)-H bonds to ketones, esters, and amides has been developed using NBS as a metal-free photocatalyst and O2 as an oxidant. A variety of synthetically and biologically valuable compounds are assembled in moderate to excellent yields. The synthetic utility of this approach has been demonstrated by gram-scale experiments. A possible free radical mechanism was proposed to rationalize the reaction procedure.

Oxidative Cleavage of Csp3-Csp2 and Csp3-H Bonds with KOtBu: Highly Robust and Practical Synthesis of Diaryl/(het-Ar) Ketones

Herein, we report an efficient and practical approach for synthesizing diaryl(het) ketones from R-CO-CHR-Ar through a simultaneous oxidative cleavage of C-C and C-H bonds using KO^tBu. This method enables synthesizing a variety of unsymmetrical and symmetrical (hetero)aryl ketones in excellent yields, which are otherwise difficult to make. Besides, we synthesized natural products using this method.

Identification, Characterization, and Synthesis of Natural Parasitic Cysteine Protease Inhibitors: Pentacitidins Are More Potent Falcitidin Analogues

Protease inhibitors represent a promising therapeutic option for the treatment of parasitic diseases such as malaria and human African trypanosomiasis. Falcitidin was the first member of a new class of inhibitors of falcipain-2, a cysteine protease of the malaria parasite Plasmodium falciparum. Using a metabolomics dataset of 25 Chitinophaga strains for molecular networking enabled identification of over 30 natural analogues of falcitidin. Based on MS/MS spectra, they vary in their amino acid chain length, sequence, acyl residue, and C-terminal functionalization; therefore, they were grouped into the four falcitidin peptide families A-D. The isolation, characterization, and absolute structure elucidation of two falcitidin-related pentapeptide aldehyde analogues by extensive MS/MS spectrometry and NMR spectroscopy in combination with advanced Marfey's analysis was in agreement with the in silico analysis of the corresponding biosynthetic gene cluster. Total synthesis of chosen pentapeptide analogues followed by in vitro testing against a panel of proteases revealed selective parasitic cysteine protease inhibition and, additionally, low-micromolar inhibition of α-chymotrypsin. The pentapeptides investigated here showed superior inhibitory activity compared to falcitidin.