Chemical Glycosylations for the Synthesis of Building Units of Post‐Translational Modifications

In chemical glycosylation reactions, a glycosyl donor couples with a glycosyl acceptor through glycosidic linkage. Most of the products end up with a mixture due to the formation of a stereogenic center at the anomeric carbon. Activation with a suitable Lewis acid and introduction of the non‐participating protecting group on donor and acceptor results in a selective product. Herein, we used a suitably protected donor and acceptor which produced an orthogonally protected building block with α‐selectivity. We used also a donor for the synthesis of modified phosphoribosylated amino acid. The formation of glycoside products can be used to synthesize complex biologically important organic molecules.     

Sonication‐Assisted Fabrication and Post‐Synthetic Modifications of Graphene‐Like Materials

Chemistry of and with graphene constitutes a rapidly evolving field that holds much promise for the generation of advanced materials with salient, and often unique, properties and potential applications in different fields. However, reliable, mild, and scalable methods to produce this layered carbonaceous material represent an important bottleneck and are critical for progress in this research area to continue. In this context, the use of ultrasound has become a routine and indispensable step in numerous synthetic protocols, even though most researchers usually overlook the science behind it. This minireview provides some fundamentals on the interaction of sound waves with matter and equally illustrates how sonication assists further synthetic decorations under benign conditions.     

How Post‐Translational Modifications Influence Amyloid Formation: A Systematic Study of Phosphorylation and Glycosylation in Model Peptides

A reciprocal relationship between phosphorylation and O‐glycosylation has been reported for many cellular processes and human diseases. The accumulated evidence points to the significant role these post‐translational modifications play in aggregation and fibril formation. Simplified peptide model systems provide a means for investigating the molecular changes associated with protein aggregation. In this study, by using an amyloid‐forming model peptide, we show that phosphorylation and glycosylation can affect folding and aggregation kinetics differently. Incorporation of phosphoserines, regardless of their quantity and position, turned out to be most efficient in preventing amyloid formation, whereas O‐glycosylation has a more subtle effect. The introduction of a single β‐galactose does not change the folding behavior of the model peptide, but does alter the aggregation kinetics in a site‐specific manner. The presence of multiple galactose residues has an effect similar to that of phosphorylation.     

First Successful Post‐Synthetic Self‐Assembly of Polyaniline with Poly(N‐vinylpyrrolidone) into Aqueous Nanocolloids

Summary: Polyaniline (PANI) is successfully self‐assembled with poly(N‐vinylpyrrolidone) (PVP) into aqueous nanocolloids. The typical morphology of the colloids is studied by atomic force microscopy (AFM), which reveals spherical nanoparticles with a diameter of 80–150 nm. A possible mechanism for such a post‐synthetic self‐assembly process is proposed.

AFM micrograph of PANI aqueous nanocolloids stabilized by PVP via a novel post‐synthetic self‐assembly method.     

Nickel‐Catalyzed Carbofluoroalkylation of 1,3‐Enynes to Access Structurally Diverse Fluoroalkylated Allenes

A nickel‐catalyzed 1,4‐carbofluoroalkylation of 1,3‐enynes to access structurally diverse fluoroalkylated allenes has been established. This method has demonstrated high catalytic reactivity, mild reaction conditions, broad substrate scope, and excellent functional‐group tolerance. The key to success is the use of a nickel catalyst to generate different fluoroalkyl radicals from readily available and structurally diverse fluoroalkyl halides to access 1,4‐difunctionalization of 1,3‐enynes by a radical relay. This strategy provides facile synthesis of structurally diverse multisubstituted allenes, and offers a solution for batch production of various fluorinated bioactive molecules for drug discovery by further transformations.     

Topotactic Conversion of β‐Helix‐Layered Silicate into AST‐Type Zeolite through Successive Interlayer Modifications

AST‐type zeolite with a plate morphology can be synthesized by topotactic conversion of a layered silicate (β‐helix‐layered silicate; HLS) by using N,N‐dimethylpropionamide (DPA) to control the layer stacking of silicate layers and the subsequent interlayer condensation. Treatment of HLS twice with 1) hydrochloric acid/ethanol and 2) dimethylsulfoxide (DMSO) are needed to remove interlayer hydrated Na ions and tetramethylammonium (TMA) ions in intralayer cup‐like cavities (intracavity TMA ions), both of which are introduced during the preparation of HLS. The utilization of an amide molecule is effective for the control of the stacking sequence of silicate layers. This method could be applicable to various layered silicates that cannot be topotactically converted into three‐dimensional networks by simple interlayer condensation by judicious choice of amide molecules.     

Synthetic Channel Specifically Inserts into the Lipid Bilayer of Gram‐Positive Bacteria but not that of Mammalian Erythrocytes

A series of tubular molecules with different lengths have been synthesized by attaching Trp‐incorporated peptides to the pillar[5]arene backbone. The tubular molecules are able to insert into the lipid bilayer to form unimolecular transmembrane channels. One of the channels has been revealed to specifically insert into the bilayer of the Gram‐positive bacteria. In contrast, this channel cannot insert into the membranes of the mammalian rat erythrocytes even at the high concentration of 100 μm . It was further demonstrated that, as a result of this high membrane selectivity, the channel exhibits efficient antimicrobial activity for the Gram‐positive bacteria and very low hemolytic toxicity for mammalian erythrocytes.     

Post‐Synthetic Reversible Incorporation of Organic Linkers into Porous Metal–Organic Frameworks through Single‐Crystal‐to‐Single‐Crystal Transformations and Modification of Gas‐Sorption Properties

The porous metal–organic framework (MOF) {[Zn₂(TCPBDA)(H₂O)₂]?30 DMF?6 H₂O}_n ( SNU‐30 ; DMF=N,N‐dimethylformamide) has been prepared by the solvothermal reaction of N,N,N′,N′‐tetrakis(4‐carboxyphenyl)biphenyl‐4,4′‐diamine (H₄TCPBDA) and Zn(NO₃)₂?6 H₂O in DMF/tBuOH. The post‐synthetic modification of SNU‐30 by the insertion of 3,6‐di(4‐pyridyl)‐1,2,4,5‐tetrazine (bpta) affords single‐crystalline {[Zn₂(TCPBDA)(bpta)]?23 DMF?4 H₂O}_n ( SNU‐31 SC ), in which channels are divided by the bpta linkers. Interestingly, unlike its pristine form, the bridging bpta ligand in the MOF is bent due to steric constraints. SNU‐31 can be also prepared through a one‐pot solvothermal synthesis from Zn^II, TCPBDA^4?, and bpta. The bpta linker can be liberated from this MOF by immersion in N,N‐diethylformamide (DEF) to afford the single‐crystalline SNU‐30 SC , which is structurally similar to SNU‐30 . This phenomenon of reversible insertion and removal of the bridging ligand while preserving the single crystallinity is unprecedented in MOFs. Desolvated solid SNU‐30′ adsorbs N₂, O₂, H₂, CO₂, and CH₄ gases, whereas desolvated SNU‐31′ exhibits selective adsorption of CO₂ over N₂, O₂, H₂, and CH₄, thus demonstrating that the gas adsorption properties of MOF can be modified by post‐synthetic insertion/removal of a bridging ligand.     

High‐Throughput Ligand Screening Enables the Enantioselective Conjugate Borylation of Cyclobutenones to Access Synthetically Versatile Tertiary Cyclobutylboronates

Cyclobutane rings are important in medicinal chemistry, yet few enantioselective methods exist to access this scaffold. In particular, cyclobutylboronates are receiving increasing attention in the literature due to the synthetic versatility of alkylboronic esters and the increasing role of boronic acids in drug discovery. Herein, a conjugate borylation of α‐alkyl,β‐aryl/alkyl cyclobutenones is reported leading to the first synthesis of enantioenriched tertiary cyclobutylboronates. Cyclobutanones with two stereogenic centers are obtained in good to high yield, with high enantioselectivity and diastereoselectivity. Vital to this advance are the development of a novel approach to α,β unsymmetrically disubstituted cyclobutenone substrates and the use of a high‐throughput chiral ligand screening platform. The synthetic utility of both the boronic ester and ketone functionalities is displayed, with remarkable chemoselectivity for either group being possible in this small ring scaffold.     

Biocatalytic Conversion of Cyclic Ketones Bearing α‐Quaternary Stereocenters into Lactones in an Enantioselective Radical Approach to Medium‐Sized Carbocycles

Cyclic ketones bearing α‐quaternary stereocenters underwent efficient kinetic resolution using cyclohexanone monooxygenase (CHMO) from Acinetobacter calcoaceticus. Lactones possessing tetrasubstituted stereocenters were obtained with high enantioselectivity (up to >99 % ee) and complete chemoselectivity. Preparative‐scale biotransformations were exploited in conjunction with a SmI₂‐mediated cyclization process to access complex, enantiomerically enriched cycloheptan‐ and cycloctan‐1,4‐diols. In a parallel approach to structurally distinct products, enantiomerically enriched ketones from the resolution with an α‐quaternary stereocenter were used in a SmI₂‐mediated cyclization process to give cyclobutanol products (up to >99 % ee).     

Metal‐Free Cross‐Coupling of Arylboronic Acids and Derivatives with DAST‐Type Reagents for Direct Access to Diverse Aromatic Sulfinamides and Sulfonamides

We have developed a simple and convenient method for the cross‐coupling of arylboronic acids and their derivatives with DAST‐type reagents under mild and metal‐free conditions to directly afford sulfinamides in moderate to good yields. Moreover, sulfonamides were obtained after a simple oxidation reaction. The reaction mechanism was investigated by ¹⁸O‐labeling experiments, and the synthetic utility was demonstrated by the sulfoxidation of natural products.     

Weak‐Acid Sites Catalyze the Hydrolysis of Crystalline Cellulose to Glucose in Water: Importance of Post‐Synthetic Functionalization of the Carbon Surface

The direct hydrolysis of crystalline cellulose to glucose in water without prior pretreatment enables the transformation of biomass into fuels and chemicals. To understand which features of a solid catalyst are most important for this transformation, the nanoporous carbon material MSC‐30 was post‐synthetically functionalized by oxidation. The most active catalyst depolymerized crystalline cellulose without prior pretreatment in water, providing glucose in an unprecedented 70 % yield. In comparison, virtually no reaction was observed with MSC‐30, even when the reaction was conducted in aqueous solution at pH 2. As no direct correlations between the activity of this solid–solid reaction and internal‐site characteristics, such as the β‐glu adsorption capacity and the rate of catalytic hydrolysis of adsorbed β‐glu strands, were observed, contacts of the external surface with the cellulose crystal are thought to be key for the overall efficiency.