Catalytic Cleavage of Amide C-N Bond: Scandium, Manganese, and Zinc Catalysts for Esterification of Amides

Nonglycosidic C-O bond formation catalyzed by a bifunctional pseudoglycosyltransferase ValL

The C7N antibiotic validamycin A is an antifungal agent widely used as a crop protectant. It comprises a validoxylamine A unit linked to a glucose moiety, which is formed through a nonglycosidic C - N bond connecting a valienol moiety and a validamine moiety, a reaction catalyzed by the pseudoglycosyltransferase ValL. In this study, we analyzed the chemical composition of validamycins in Streptomyces hygroscopicus var. jinggangensis TL01. A series of novel oxygen-bridged analogues, namely, validenomycin, validomycin, and 1,1'-bis-valienol, were identified in the culture supernatants, and their chemical structures were elucidated using a combination of one- and two-dimensional nuclear magnetic resonance and mass spectrometry. Gene disruption and complementation experiments revealed that valL is essential for the biosynthesis of these new oxygen-bridged analogues of validamycins. Biochemical assays further demonstrated that ValL catalyzed the C-O bond formation between GDP-valienol and valienol-7-phosphate, producing 1,1'-bis-valienol-7-phosphate, which was subsequently dephosphorylated by ValO and glycosylated by ValG to yield validenomycin. Collectively, our findings revealed the unique ability of ValL to catalyze nonglycosidic C-O coupling, potentially enabling the generation of various chemical scaffolds for C7N family antibiotics.

Chemoselective Cleavage and Transamidation of Tertiary p-Methoxybenzyl Amides under Metal-Free Photoredox Catalysis

A metal-free and mild cleavage of tertiary p-methoxybenzyl amides (PMB tert-amide) under photoredox conditions is developed using Mes-Acr-Ph+BF4- and Selectfluor to activate the electron-rich benzylic C-H bond of the PMB moiety. The resulting acyl fluoride intermediate is versatile and facilitates a one-pot transamidation of the PMB tert-amide. The value of this protocol is highlighted by performing the chemoselective activation of the PMB tert-amide in bifunctional molecules containing more reactive functionalities than the amide.

Nanoproteases: Alternatives to Natural Protease for Biotechnological Applications

Some nanomaterials with intrinsic protease-like activity have the advantages of good stability, biosafety, low price, large-scale preparation and unique property of nanomaterials, which are promising alternatives for natural proteases in various applications. An especial term, "nanoprotease", has been coined to stress the intrinsic proteolytic property of these nanomaterials. As a new generation of artificial proteases, they have become a burgeoning field, attracting many researchers to design and synthesize high performance nanoproteases. In this review, we summarize recent progress on all types of nanoproteases with regard of their activity, mechanism and application and introduce a new and effective strategy for engineering high-performance nanoproteases. In addition, we discuss the challenges and opportunities of nanoprotease research in the future.

p-Methoxybenzyl-Radical-Promoted Chemoselective Protection of sec-Alkylamides

The hitherto difficult site-selective p-methoxybenzylation of secondary amides using p-methoxybenzylated alkylsilyl peroxides as a novel p-methoxybenzylation agent under copper catalysis is reported. The reaction proceeds under mild reaction conditions in a highly chemoselective manner. This approach was successfully applied to the site-selective p-methoxybenzylation of peptides.

Hydrolysis of amides to carboxylic acids catalyzed by Nb2O5

An efficient heterogeneous Nb₂O₅ catalytic system has been developed for industrially important and challenging amide hydrolysis reaction to carboxylic acid through cleavage of resonance stabilized amidic C–N bond.

Efficient cleavage of tertiary amide bonds via radical-polar crossover using a copper(ii) bromide/Selectfluor hybrid system

A novel approach for the efficient cleavage of the amide bonds in tertiary amides is reported. Based on the selective radical abstraction of a benzylic hydrogen atom by a CuBr2/Selectfluor hybrid system followed by a selective cleavage of an N-C bond, an acyl fluoride intermediate is formed. This intermediate may then be derivatized in a one-pot fashion. The reaction proceeds under mild conditions and exhibits a broad substrate scope with respect to the tertiary amide moiety as well as to nitrogen, oxygen, and carbon nucleophiles for the subsequent derivatization. Mechanistic studies suggest that the present reaction proceeds via a radical-polar crossover process that involves benzylic carbon radicals generated by the selective radical abstraction of a benzylic hydrogen atom by the CuBr2/Selectfluor hybrid system. Furthermore, a synthetic application of this method for the selective cleavage of peptides is described.

Esterification of Tertiary Amides: Remarkable Additive Effects of Potassium Alkoxides for Generating Hetero Manganese-Potassium Dinuclear Active Species

A catalyst system of mononuclear manganese precursor 3 combined with potassium alkoxide served as a superior catalyst compared with our previously reported manganese homodinuclear catalyst 2 a for esterification of not only tertiary aryl amides, but also tertiary aliphatic amides. On the basis of stoichiometric reactions of 3 and potassium alkoxide salt, kinetic studies, and density functional theory (DFT) calculations, we clarified a plausible reaction mechanism in which in situ generated manganese-potassium heterodinuclear species cooperatively activates the carbonyl moiety of the amide and the OH moiety of the alcohols. We also revealed details of the reaction mechanism of our previous manganese homodinuclear system 2 a, and we found that the activation free energy (ΔG≠ ) for the manganese-potassium heterodinuclear complex catalyzed esterification of amides is lower than that for the manganese homodinuclear system, which was consistent with the experimental results. We further applied our catalyst system to deprotect the acetyl moiety of primary and secondary amines.