Pyridine-borane complex-catalysed thioesterification: the direct conversion of carboxylic acids to thioesters.

Thioesters are a common class of biologically active fragments and synthetically useful building blocks. An attractive synthetic approach would be to use simple and bench-stable carboxylic acids as a coupling partner. Herein, we present a 4-bromo pyridine-borane complex as a catalyst for the direct coupling of carboxylic acids with thiols. A wide range of thioesters with good functional group compatibility could be prepared via this metal-free approach. The merit of this strategy is exemplified by the modification of carboxylic acid-containing drugs.

Cytotoxic alkaloids from the fruit pods of Macleaya microcarpa.

19 compounds, including seven previously undescribed alkaloids ((-)-macleayin K (1), (+)-macleayin K (2), macleayin M (3), macleayin N (4), macleayin L (5), macleayin O (6), oxohydrastinine A (7), one new natural product (8), and 11 known compounds, were isolated from the fruit pods of Macleaya microcarpa. Their structures were defined based on NMR, HRESIMS, and electronic circular dichroism (ECD) data. A network pharmacology approach combined with molecular docking and in vitro validation was performed to determine the bioactivity, key targets of the 19 compounds against breast cancer (BC) and cervical cancer (CC). EGFR and PIK3CA could become potential therapeutic targets based a network pharmacology. Moreover, molecular docking suggested that the 19 compounds combined well with EGFR and PIK3CA, respectively. Their cytotoxicity of selected compounds was tested against the MCF-7 and HeLa cells, and the preliminary structure-activity relationship is discussed. Compounds 1 (IC50: 6.00 µM) and 2 (IC50: 6.82 µM) exhibited strong inhibitory activity against the HeLa cells and are worthy of further study.

Reactivity of N-acyl hydrazone probes with the mammalian proteome.

Small molecule probes with distinct reactivities are useful tools for the identification and characterization of protein modifications and function. Herein, we show that hydrazone probes with an N-carbamate structural motif react differently from N-carbamates within the human proteome. Mass spectrometry analysis of probe-treated mammalian cell lysates identified several proteins that were covalently modified by the hydrazone probes, including the cytidine deaminase APOBEC3A. We used this enzyme as a model to explore the reactivity of the probes with amino acid residues using LC-MS/MS. Both reactive serine and cysteine residues outside of the enzyme active site were covalently modified. A 1-napthol leaving group provided the most extensive reactivity. These results confirm a unique chemotype for hydrazone probes which can be further optimized to target distinct targets of the human proteome.

Baicalensines A and B, Two Isoquinoline Alkaloids from the Roots of Thalictrum baicalense.

Baicalensines A (1) and B (2) were isolated from the roots of Thalictrum baicalense and structurally characterized using spectroscopic data, 13C NMR calculations, and the CASE algorithm. Compound 1, representing a new class of alkaloid dimers, contains berberine conjugated to a ring-opened isoquinoline. Compound 2 is the first reported natural benzylisoquinoline bearing a formyl group at C-3. Plausible biosynthetic pathways are proposed. Compound 1 exerted moderate cytotoxicity against the Caco-2 and HL-60 cell lines.

Organocatalysis using aldehydes: the development and improvement of catalytic hydroaminations, hydrations and hydrolyses.

Organocatalysis has emerged as a powerful approach to facilitate and accelerate various difficult reactions. This Feature article presents recent developments and improvements using aldehydes as catalysts in difficult Cope-type intermolecular hydroamination, hydration and hydrolysis reactions. Most reactions exploit temporary intramolecularity. In catalytic Cope-type hydroaminations of allylic amines, aldehydes act as tethering catalysts, and allow room temperature reactions and high enantio- or diastereoselectivities if chiral aldehydes or reagents are used. Mechanistic studies showed that simpler catalysts such as formaldehyde are more active due to an improved ability to form the temporary tether, which translated in an improved reaction scope. Gratifyingly, improved catalytic efficiency and broad reaction scope were also observed in the aldehyde-catalyzed hydration of α-amino nitriles. Since destabilized aldehydes often favor temporary intramolecularity, this led to a comparison of the catalytic activity of several carbohydrates, and to experiments relevant in the prebiotic "origin of life" chemistry context. Studies on catalytic hydrolysis reactions of organophosphorous reagents are also presented, in which o-phthalaldehyde performs electrophilic activation of phosphinic amides, and other substrates possessing the P([double bond, length as m-dash]O)NH motif. Overall, this Feature article shows that aldehydes can be efficient catalysts in a variety of reactions, and highlights the efficiency of destabilized aldehydes such as formaldehyde and simple carbohydrates in this context.

o-Phthalaldehyde catalyzed hydrolysis of organophosphinic amides and other P([double bond, length as m-dash]O)-NH containing compounds.

Over 50 years ago, Jencks and Gilchrist showed that formaldehyde catalyses the hydrolysis of phosphoramidate through electrophilic activation, induced by covalent attachment to its nitrogen atom. Given our interest in the use of aldehydes as catalysts, this work was revisited to identify a superior catalyst, o-phthalaldehyde, which facilitates hydrolyses of various organophosphorus compounds bearing P([double bond, length as m-dash]O)-NH subunits under mild conditions. Interestingly, chemoselective hydrolysis of the P([double bond, length as m-dash]O)-N bonds could be accomplished in the presence of P([double bond, length as m-dash]O)-OR bonds.

Iron-Catalyzed Decarboxylative (4+1) Cycloadditions: Exploiting the Reactivity of Ambident Iron-Stabilized Intermediates.

The first example of iron-catalyzed decarboxylative (4+1) cycloaddition reactions is described in this publication. By using this method, a wide range of functionalized indoline products were prepared from easily available vinyl benzoxazinanones and sulfur ylides in high yields and selectivities. A possible reaction pathway involving an allylic iron intermediate is discussed based on a series of control experiments and density-functional theory calculations.

Desulfonylation of tosyl amides through catalytic photoredox cleavage of N-S bond under visible-light irradiation.

All lit up: A novel and efficient desulfonylation method of tosyl amides has been developed by means of visible-light-promoted reductive cleavage of N-S bonds. This method has a broad substrate scope, good functional group tolerance, and excellent yields.

Synthesis of indoles through highly efficient cascade reactions of sulfur ylides and N-(ortho-chloromethyl)aryl amides.

Batting the ylides: A simple procedure carried out under mild conditions allows the direct and efficient synthesis of structurally diverse indoles. This approach involves a cascade reaction of sulfur ylides and N-(ortho-chloromethyl)aryl amides.