Pre‐targeted Imaging of Protease Activity through In Situ Assembly of Nanoparticles

The pre‐targeted imaging of enzyme activity has not been reported, likely owing to the lack of a mechanism to retain the injected substrate in the first step for subsequent labeling. Herein, we report the use of two bioorthogonal reactions—the condensation reaction of aromatic nitriles and aminothiols and the inverse‐electron demand Diels–Alder reaction between tetrazine and trans‐cyclooctene (TCO)—to develop a novel strategy for pre‐targeted imaging of the activity of proteases. The substrate probe ( TCO‐C‐SNAT4 ) can be selectively activated by an enzyme target (e.g. caspase‐3/7), which triggers macrocyclization and subsequent in situ self‐assembly into nanoaggregates retained at the target site. The tetrazine‐imaging tag conjugate labels TCO in the nanoaggregates to generate selective signal retention for imaging in vitro, in cells, and in mice. Owing to the decoupling of enzyme activation and imaging tag immobilization, TCO‐C‐SNAT4 can be repeatedly injected to generate and accumulate more TCO‐nanoaggregates for click labeling.     

Silver‐Mediated N‐Trifluoromethylation of Amides and Peptides

We report herein the direct N‐trifluoromethylation of N‐H amides. Promoted by AgOTf and 2‐fluoropyridine, the reaction of a variety of amides with Selectfluor, TMSCF₃ and CsF proceeds smoothly at room temperature leading to the corresponding N‐trifluoromethylated products in satisfactory yields. The protocol is also applicable to amino acid derivatives, resulting in efficient and chemoselective N‐trifluoromethylation of di‐ and tri‐peptides with retention of configuration. A mechanism involving reductive elimination of Ag(III) intermediates to form N—CF₃ bonds is proposed.     

Covalent Grafting of Carbon Nanotubes with a Biomimetic Heme Model Compound To Enhance Oxygen Reduction Reactions

The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble‐metal Pt‐based ORR electrocatalysts by nonprecious‐metal catalysts is crucial for the large‐scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well‐defined, bio‐inspired ORR catalyst that consists of a biomimetic model compound—an axial imidazole‐coordinated porphyrin—covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio‐inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state‐of‐the‐art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel‐cell technology.     

Ir‐Catalyzed Asymmetric Hydrogenation of α‐Alkylidene β‐Lactams and Cyclobutanones

Chiral β‐lactams and cyclobutanones are present in numerous natural and pharmaceutical products. The stereoselective construction of chiral four‐membered cyclic compounds is an ongoing challenge for the chemical community. Herein, we report a highly stereocontrolled construction of four‐membered ring (mini‐sized) β‐lactams and cyclobutanones via an Ir/ In‐BiphPHOX ‐catalyzed asymmetric hydrogenation, providing the corresponding optically active four‐membered ring carbonyl products bearing an α‐chiral carbon center with excellent yields (up to 99%) and enantioselectivities (up to 98%) under mild reaction conditions (1.0—2.5 bar H₂ for 1.0—10 h). The reaction presents wide substrate scope. Diverse transformations of the catalyzed products were also conducted to show the potential utility of this protocol.     

Regulating the Rate of Molecular Self‐Assembly for Targeting Cancer Cells

Besides tight and specific ligand–receptor interactions, the rate regulation of the formation of molecular assemblies is one of fundamental features of cells. But the latter receives little exploration for developing anticancer therapeutics. Here we show that a simple molecular design of the substrates of phosphatases—tailoring the number of phosphates on peptidic substrates—is able to regulate the rate of molecular self‐assembly of the enzyme reaction product. Such a rate regulation allows selective inhibition of osteosarcoma cells over hepatocytes, which promises to target cancer cells in a specific organ. Moreover, our result reveals that the direct measurement of the rate of the self‐assembly in a cell‐based assay provides precise assessment of the cell targeting capability of self‐assembly. This work, as the first report establishing rate regulation of a multiple‐step process to inhibit cells selectively, illustrates a fundamentally new approach for controlling the fate of cells.     

Palladium‐Catalyzed Formal [4+2] Cycloaddition of Benzoic and Acrylic Acids with 1,3‐Dienes via C—H Bond Activation: Efficient Access to 3,4‐Dihydroisocoumarin and 5,6‐Dihydrocoumalins

We report a palladium‐catalyzed formal intermolecular [4+2] cycloaddition of benzoic and acrylic acids with 1,3‐dienes including the stock chemicals 1,3‐butadiene and isoprene leading to synthetically useful 3,4‐dihydroisocoumarins and 5,6‐dihydrocoumalins. Stepwise C—H bond cleavage and annulation are likely involved in the reaction pathway. The synthetic potential of the methodology was demonstrated by two short derivatizations and total synthesis of natural product Clausamine B.     

Enzymatic Synthesis of a DNA Triblock Copolymer that is Composed of Natural and Unnatural Nucleotides

DNA molecules have come under the spotlight as potential templates for the fabrication of nanoscale products, such as molecular‐scale electronic or photonic devices. Herein, we report an enhanced approach for the synthesis of oligoblock copolymer‐type DNA by using the Klenow fragment exonuclease minus of E. coli DNA polymerase I (KF^?) in a multi‐step reaction with natural and unnatural nucleotides. First, we confirmed the applicability of unnatural nucleotides with 7‐deaza‐nucleosides—which was expected because they were non‐metalized nucleotides—on the unique polymerization process known as the “strand‐slippage model”. Because the length of the DNA sequence could be controlled by tuning the reaction time, analogous to a living polymerization reaction on this process, stepwise polymerization provided DNA block copolymers with natural and unnatural bases. AFM images showed that this DNA block copolymer could be metalized sequence‐selectively. This approach could expand the utility of DNA as a template.     

Synthetic,Chemically Defined Polymer‐Coated Microcarriers for the Expansion of Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSC), also called marrow stromal cells, are adult cells that have attracted interest for their potential uses in therapeutic applications. There is a pressing need for scalable culture systems due to the large number of cells needed for clinical treatments. Here, a tailorable thin polymer coating—poly(poly(ethylene glycol) methyl ether methacrylate‐ran‐vinyl dimethyl azlactone‐ran‐glycidyl methacrylate) [P(PEGMEMA‐r‐VDM‐r‐GMA); PVG]—to the surface of commercially available polystyrene and glass microcarriers to create chemically defined surfaces for large‐scale cell expansion is applied. These chemically defined microcarriers create a reproducible surface that does not rely on the adsorption of xenogenic serum proteins to mediate cell adhesion. Specifically, this coating method anchors PVG copolymer through ring opening nucleophilic attack by amine residues on poly‐l ‐lysine that is pre‐adsorbed to the surface of microcarriers. Importantly, this anchoring reaction preserves the monomer VDM reactivity for subsequent functionalization with an integrin‐specific Arg‐Gly‐Asp peptide to enable cell adhesion and expansion via a one‐step reaction in aqueous media. MSCs cultured on PVG‐coated microcarriers achieve sixfold expansion—similar to the expansion achieved on PS microcarriers—and retain their ability to differentiate after harvesting.     

Gold‐Catalyzed Cycloisomerization and Diels–Alder Reaction of 1,4,9‐Dienyne Esters to 3 a,6‐Methanoisoindole Esters with Pro‐Inflammatory Cytokine Antagonist Activity

A synthetic method to prepare 3a,6‐methanoisoindole esters efficiently by gold(I)‐catalyzed tandem 1,2‐acyloxy migration/Nazarov cyclization followed by Diels–Alder reaction of 1,4,9‐dienyne esters is described. We also report the ability of one example to inhibit binding of tumor necrosis factor‐α (TNF‐α) to the tumor necrosis factor receptor 1 (TNFR1) site and TNF‐α‐induced nuclear factor κ‐light‐chain‐enhancer of activated B cells (NF‐κB) activation in cell at a half‐maximal inhibitory concentration (IC₅₀) value of 6.6 μM . Along with this is a study showing the isoindolyl derivative to exhibit low toxicity toward human hepatocellular liver carcinoma (HepG2) cells and its possible mode of activity based on molecular modeling analysis.     

Laser Microbeams and Optical Tweezers in Ageing Research

We show how a technique developed within the framework of physics and physical chemistry—in a true interdisciplinary approach—can answer questions in life sciences that are not solvable by using other techniques. Herein, we focus on blood‐pressure regulation and DNA repair in ageing studies. Laser microbeams and optical tweezers are now established tools in many fields of science, particularly in the life sciences. A short glimpse is given on the wide field of non‐age‐research applications in life sciences. Then, optical tweezers are used to show that exerting a vertical pressure on cells representing the inner lining of blood vessels results in bursts of NO liberation concomitant with large changes in cell morphology. Repeated treatment of such human umbilical vein endothelial cells (HUVEC) results in stiffening, a hallmark of manifest high blood pressure, a disease primarily of the elderly. As a second application in ageing research, a laser microbeam is used to induce, with high spatial and temporal resolution, DNA damages in the nuclei of U2OS human osteosarcoma cells. A pairwise study of the recruitment kinetics of different DNA repair proteins reveals that DNA repair starts with non‐homologous end joining (NHEJ), a repair pathway, and may only after several minutes switch to the error‐free homologous recombination repair (HRR) pathway. Since DNA damages—when incorrectly repaired—accumulate with time, laser microbeams are becoming well‐used tools in ageing research.     

PCy3‐Catalyzed Ring Expansion of Aziridinofullerenes with CO2 and Aryl Isocyanates: Evidence for a Two Consecutive Nucleophilic Substitution Pathway on the Fullerene Cage

A PCy₃‐catalyzed ring‐expansion reaction of aziridine‐fused fullerenes (aziridinofullerenes) through the insertion of CO₂ and aryl isocyanates is disclosed. The reaction allows for CO₂ fixation by aziridinofullerenes, producing oxazolidinone‐fused fullerenes (oxazolidinofullerenes) in high yields, whereas treatment with aryl isocyanates led to a new fullerene family—imidazolidinone‐fused fullerenes (imidazolidinofullerenes)—in good to high yields. Furthermore, a mechanistically related unprecedented fullerenyl phosphonium salt was successfully isolated. Using the isolated salt, mechanistic studies were also investigated.     

RhodiumIII/SilverI Relay Catalyzed C—H Aminomethylation with Imine Equivalents and Lewis Acid Catalyzed [4+2] Cycloaddition of Indoles with Triarylhexahydrotriazine†

A Rh^III/Ag^I relay‐catalyzed C(sp²)—H coupling of indoles with triarylhexahydrotriazine (THT) is reported in this context. Upon merging Rh^III‐catalyzed C(sp²)—H bond activation and silver promoted THT dissociation, an efficient indole's C3 aminomethylation protocol is uncovered, providing C3 aminomethyl indoles in good yields and exhibiting potential applications for the synthesis of complicated bioactive compounds. We revealed the C3‐selectivity of this reaction through a detailed mechanistic investigation. Meanwhile, during the examination of the reaction conditions, we discovered another [4+2] cycloaddition pathway to afford tetrahydro‐indolo[3,2‐c]quinoline scaffold products via silver or Lewis acid catalysis.     

Electrochemical Oxidative Csp3—H/S—H Cross‐Coupling with Hydrogen Evolution for Synthesis of Tetrasubstituted Olefins

Tetrasubstituted olefins are significant scaffolds as they are prevalent in many biologically active compounds and versatile building blocks for organic synthesis. Herein, we report an electrochemical oxidative Csp³—H/S—H cross‐coupling reaction, in which various tetrasubstituted olefins were prepared under base‐free, transition metal‐free, and oxidants‐free reaction conditions.     

Synthesis of Novel Alkyl Amide Functionalized Trifluoromethyl Substituted Furo/thieno Pyridine Derivatives: Their Anticancer Activity and CoMFA and CoMSIA Studies

A series of novel alkyl amide functionalized trifluoromethyl substituted furo/thieno pyridine derivatives 4a–h , 5a–d , and 6a–h were prepared starting from 2‐oxo/thioxo‐6‐phenyl/thien‐2‐yl‐4‐(trifluoromethyl)‐1,2‐dihydropyridine‐3‐carbonitrile 1 on reaction with bromoethylacetate followed by reaction with different primary aliphatic amines, cyclic secondary amines, or l ‐amino acids under different set of conditions. All the synthesized compounds 4a–h , 5a–d , and 6a–h were screened for anticancer activity against four cancer cell lines such as HeLa—cervical cancer (CCL‐2), COLO205—colon cancer (CCL‐222), HepG2—liver cancer (HB‐8065), and MCF7—breast cancer (HTB‐22). Compounds 4g and 4h are found to have promising anticancer activity at micromolar concentration. CoMFA and CoMSIA methods were applied to derive 3D‐QSAR models for alkyl amide tagged furo/thieno pyridine derivatives as potential anticancer inhibitors. 3D‐QSAR models provided a strong basis for future rational design of more active and selective HeLa, COLO205, HepG2, and MCF‐7 cell line inhibitors.     

(9E)‐9‐Benzylidene‐3‐methyl‐2‐methylsulfanyl‐5‐phenyl‐5,6,7,8,9,10‐hexahydropyrimido[4,5‐b]quinolin‐4(3H)‐one: polarized molecules within hydrogen‐bonded bilayers

The molecules of the title compound, C₂₆H₂₅N₃OS, which was prepared by means of an acid‐catalysed cyclocondensation reaction between a 6‐aminopyrimidinone and 2,6‐dibenzylidenecyclohexanone, exhibit a polarized electronic structure, namely (9E)‐9‐benzylidene‐3‐methyl‐2‐methylsulfanyl‐5‐phenyl‐3,5,6,7,8,9‐hexahydropyrimido[4,5‐b]quinolin‐10‐ium‐4‐olate, involving charge separation in the vinylogous amide portion. Four hydrogen bonds, two each of the C—H...O and C—H...π(arene) types, link the molecules into bilayers comprising inversion‐related pairs of sheets, each containing a single type of R₄³(36) ring.     

Reaction force analyses of nitro-aci tautomerizations of trinitromethane, the elusive trinitromethanol, picric acid and 2,4-dinitro-1H-imidazole

We have analyzed computationally, in terms of the reaction force, the nitro → aci tautomerizations of trinitromethane, trinitromethanol, picric acid and 2,4-dinitro-1H-imidazole. These processes involve intramolecular transfer of a hydrogen to an NO₂ oxygen, forming the aci tautomer (a nitronic acid). The reaction force naturally and unambiguously divides an activation barrier into two components: (1) the energy required for initial structural changes in the reactant(s), and (2) the energy associated with the first portion of the transition to product(s). In each of these tautomerizations, the first component is dominant. For trinitromethane, it is so large that the resulting total activation barrier makes C–NO₂ bond scission energetically preferable. On the other hand, trinitromethanol—which appears to be unknown—readily undergoes fragmentation in conjunction with hydrogen transfer. Picric acid has the interesting feature that the reaction is almost complete after the first portion of the activation process, marked by the minimum of the reaction force. In all four reactions, the properties of the systems at the force minimum, transition state and force maximum are consistent with the concept of a “transition” region in a chemical reaction versus simply a transition state.     

A Green BODIPY‐Based,Super‐Fluorogenic,Protein‐Specific Labelling Agent

We report the development of YC23, a novel green BODIPY‐based dimaleimide derivative that undergoes a fluorogenic addition reaction (FlARe) with a genetically encodable peptide tag (dC10α) that can be fused to a protein of interest (POI). We also demonstrate the application of this reaction for the fluorogenic labelling of a specific POI in bacterial lysate and in living mammalian cells.     

A Green BODIPY‐Based,Super‐Fluorogenic,Protein‐Specific Labelling Agent

We report the development of YC23, a novel green BODIPY‐based dimaleimide derivative that undergoes a fluorogenic addition reaction (FlARe) with a genetically encodable peptide tag (dC10α) that can be fused to a protein of interest (POI). We also demonstrate the application of this reaction for the fluorogenic labelling of a specific POI in bacterial lysate and in living mammalian cells.     

Syntheses and characterization of block copolymers of poly(aliphatic ester) with clickable polyphosphoester

We report a series of biocompatible and biodegradable block copolymers of poly(ε‐caprolactone) with “clickable” polyphosphoester (PPE). The block copolymers are synthesized through controlled ring‐opening polymerization of five‐membered cyclic phosphoester monomer, propargyl ethylene phosphate (PAEP), initiated with poly(ε‐caprolactone) macroinitiator. The polymerization followed first‐order kinetics with living polymerization characteristics, thus the molecular weight and composition of copolymers are tunable by adjusting the feed ratio of PAEP monomer to macroinitiator. Azide‐functionalized poly(ethylene glycol) has been grafted to the copolymer to demonstrate the reactive feasibility by Cu(I)‐catalyzed “click” chemistry of azides and alkynes, generating “brush‐coil” polymers. The mild conditions associated with the click reaction are shown to be compatible with poly(ε‐caprolactone) and PPE backbones, rendering the click reaction a generally useful method for grafting numerous types of functionality onto the block copolymers. The block copolymers also show good biocompatibility to cells, suggesting their suitability for a range of biomaterial applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A Chemical Probe for Dehydrobutyrine

Bacterial phosphothreonine lyases, or phospholyases, catalyze a unique post‐translational modification that introduces dehydrobutyrine (Dhb) or dehydroalanine (Dha) in place of phosphothreonine or phosphoserine residues, respectively. We report the use of a phospha‐Michael reaction to label proteins and peptides modified with Dha or Dhb. We demonstrate that a nucleophilic phosphine probe is able to modify Dhb‐containing proteins and peptides that were recalcitrant to reaction with thiol or amine nucleophiles under mild aqueous conditions. Furthermore, we used this reaction to detect multiple Dhb‐modified proteins in mammalian cell lysates, including histone H3, a previously unknown target of phospholyases. This method should prove useful for identifying new phospholyase targets, profiling the biomarkers of bacterial infection, and developing enzyme‐mediated strategies for bioorthogonal labeling in living cells.