Combining Designer Cells and Click Chemistry for a One‐Pot Four‐Step Preparation of Enantiopure β‐Hydroxytriazoles

The multistep catalytic process using designer cells, either added as freshly prepared suspensions or as stable lyophilized powder, and click reaction can be performed in one pot. The sequence of four reactions allows the production of both enantiomers of β‐hydroxytriazoles with high enantiomeric excess.     

Copper‐in‐Charcoal‐Catalyzed,Tandem One‐Pot Diazo Transfer‐Click Reactions

Copper‐in‐charcoal (Cu/C) is an effective heterogeneous catalyst for tandem diazo transfer/click reactions. In the presence of Cu/C, various azides can be generated in situ from the corresponding amines, and subsequently undergo [3+2] cycloaddition with terminal alkynes to afford triazoles in good yields. The catalyst is also easily recycled.     

One‐Step Derivatization of Reducing Oligosaccharides for Rapid and Live‐Cell‐Compatible Chelation‐Assisted CuAAC Conjugation

We report a new reagent for the functionalization of unprotected oligosaccharides with a picolyl azide group at the anomeric position for chelation‐assisted copper‐catalyzed alkyne–azide cycloaddition (CuAAC) glycoconjugation. We show that oligosaccharides functionalized with this moiety react with an apparent second‐order rate constant of 193 m ^?1 s^?1 and can be used to functionalize biomolecules bearing alkyne moieties introduced through metabolic labeling, including in live cells.     

One‐Pot Three‐Component Click Reaction of Cyclic Sulfates and Cyclic Sulfamidates

A one‐pot, three‐component methodology involving tandem azidation and click copper(I)‐catalyzed azide‐alkyne cycloaddition (CuAAC) of cyclic sulfates or cyclic sulfamidates in the presence of sodium azides and alkynes is reported. The developed protocol takes also advantage of the concomitant use of microwave (MW) irradiation and heterogeneous catalysis. The protocol allows the fast and efficient preparation of (alkyl sulfate)‐ and (alkyl sulfamidate)‐1H‐1,2,3‐triazoles in a simple manner.     

An Odorless,One‐Pot Synthesis of Thioesters from Organic Halides,Thiourea and Benzoyl Chlorides in Water

Thioesterification can be realized via an odorless, one‐pot reaction through the in situ generation of S‐alkylisothiouronium salts from organic halides and thiourea in aqueous Triton X‐100 (TX100) micelles. The protocol is free of foul‐smell thiols and organic solvents, and operates under mild conditions, thereby offering considerable potential for applications in organic synthesis.     

Clickable 4‐Oxo‐β‐lactam‐Based Selective Probing for Human Neutrophil Elastase Related Proteomes

Human neutrophil elastase (HNE) is a serine protease associated with several inflammatory processes such as chronic obstructive pulmonary disease (COPD). The precise involvement of HNE in COPD and other inflammatory disease mechanisms has yet to be clarified. Herein we report a copper‐catalyzed alkyne–azide 1,3‐dipolar cycloaddition (CuAAC, or ′click′ chemistry) approach based on the 4‐oxo‐β‐lactam warhead that yielded potent HNE inhibitors containing a triazole moiety. The resulting structure–activity relationships set the basis to develop fluorescent and biotinylated activity‐based probes as tools for molecular functional analysis. Attaching the tags to the 4‐oxo‐β‐lactam scaffold did not affect HNE inhibitory activity, as revealed by the IC₅₀ values in the nanomolar range (56–118 nm ) displayed by the probes. The nitrobenzoxadiazole (NBD)‐based probe presented the best binding properties (ligand efficiency (LE)=0.31) combined with an excellent lipophilic ligand efficiency (LLE=4.7). Moreover, the probes showed adequate fluorescence properties, internalization in human neutrophils, and suitable detection of HNE in the presence of a large excess of cell lysate proteins. This allows the development of activity‐based probes with promising applications in target validation and identification, as well as diagnostic tools.     

Asymmetric One‐Pot Synthesis of 1,4‐Dihydroquinolines via an Organocatalytic Aza‐Michael/Michael Cascade Strategy

A synthetic method for the construction of fully substituted enantioenriched 1,4‐dihydroquinolines using an organocatalytic aza‐Michael/Michael cascade reaction has been developed. The asymmetric reaction of 2‐(tosylamino)phenyl α,β‐unsaturated ketones with alkynyl aldehydes, promoted by diphenylprolinol O‐TMS ether as an organocatalyst, generated chiral 1,4‐dihydroquinolines in good to high yields with excellent enantioselectivities (up to 97 % ee).

     

Preparation of polyamide resin‐encapsulated melamine cyanurate/melamine phosphate composite flame retardants and the fire‐resistance to glass fiber‐reinforced polyamide 6

In this study, melamine cyanurate (MCA)/melamine phosphate (MP) composite flame retardants were synthesized in the solution of phosphoric acid/polyamide 6 (PA6). Phosphoric acid acted as the solvent of PA6, catalyst of melamine‐cyanurate self‐assembly reaction and reactant of melamine‐phosphoric acid reaction. With the consumption of the acid, the pH value of the system increased, and the solved PA6 precipitated on the surface of the flame retardant particles to form polymeric encapsulation. This technology realized the synthesis and surface modification of the flame retardants in one process. The catalyst and solvent, phosphoric acid, was finally converted into the product MP, and need no an additional removing process. The encapsulated MCA/MP (EMCMP) composite flame retardants were successfully applied in the fire‐resistance to glass fiber (GF)‐reinforced PA6. Because the encapsulated layer of EMCMP was also PA6, good interfacial compatibility and effective dispersion of EMCMP in PA6 resin can be obtained, and the corresponding flame retardant materials showed excellent flame retardancy and mechanical performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1773–1779, 2006     

Design and Synthesis of Pyrophosphate‐Targeting Vancomycin Derivatives for Combating Vancomycin‐Resistant Enterococci

As the last resort for intractable Gram‐positive bacterial infections, vancomycin is losing efficacy with the emergence of vancomycin‐resistant bacteria, especially vancomycin‐resistant Enterococci (VRE). To combat this threat, we rationally designed and synthesized 39 novel vancomycin derivatives by respective or combined modifications using metal‐chelating, lipophilic, and galactose‐attachment strategies for extensive structure–activity relationship (SAR) analysis. In a proposed mechanism, the conjugation of dipicolylamine on the seventh amino acid resorcinol position or C‐terminus endowed the vancomycin backbone with binding capacity for the pyrophosphate moiety in lipid II while maintaining the intrinsic binding affinity for the dipeptide terminus of the bacterial cell wall peptidoglycan precursor. The in vitro antibacterial activities were evaluated, and the optimal compounds indicated 16‐ to 1024‐fold higher activity against VRE than that of vancomycin. Compound 11 b (3′,5′‐bis(dipicolylaminomethyl)tyrosine [1,2,3]triazolylmethoxylethyoxyl ethylaminomethyl‐N‐decylvancomycin) was found to have particularly potent activity against VRE through synergistic effects brought about by combining two peripheral modifications.     

Utilizing Mor‐DalPhos/Palladium‐Catalyzed Monoarylation in the Multicomponent One‐Pot Synthesis of Indoles

The application of a Mor‐DalPhos/palladium catalyst system in the one‐pot, multicomponent assembly of substituted indoles from ortho‐chlorohaloarenes, alkyl ketones (including acetone), and primary amines is reported. The described protocols offer improved substrate scope in all three reaction components, under more mild conditions and without the need for an additional drying agent. Also reported are the first examples of such multicomponent reactions where all reactants are combined at the start of the reaction, without the need for inert atmosphere reaction conditions.

     

A Fluorescent Probe for Imaging Sirtuin Activity in Living Cells,Based on One‐Step Cleavage of the Dabcyl Quencher

Sirtuins (SIRTs) are a family of NAD⁺‐dependent histone deacetylases. In mammals, dysfunction of SIRTs is associated with age‐related metabolic diseases and cancers, so SIRT modulators are considered attractive therapeutic targets. However, current screening methodologies are problematic, and no tools for imaging endogenous SIRT activity in living cells have been available until now. In this work we present a series of simple and highly sensitive new SIRT activity probes. Fluorescence of these probes is activated by SIRT‐mediated hydrolytic release of a 4‐(4‐dimethylaminophenylazo)benzoyl (Dabcyl)‐based FRET quencher moiety from the ?‐amino group of lysine in a nonapeptide derived from histone H3K9 and bearing a C‐terminal fluorophore. The probe SFP3 detected activities of SIRT1, ‐2, ‐3, and ‐6, which exhibit deacylase activities towards long‐chain fatty acyl groups. We then truncated the molecular structure of SFP3 in order to improve both its stability to peptidases and its membrane permeability, and developed probe KST‐F, which showed specificity for SIRT1 over SIRT2 and SIRT3. We show that KST‐F can visualize endogenous SIRT1 activity in living cells.     

Capture‐Tag‐Release: A Strategy for Small Molecule Labeling of Native Enzymes

A strategy for labeling native enzymes in a manner that preserves their activity is reported: capture–tag–release (CTR). Key to this approach is the small molecule CTR probe that contains an enzyme inhibitor, benzophenone crosslinker, and aryl phosphine ester. After UV‐derived capture of the enzyme, addition of an azide‐containing tag triggers a Staudinger ligation that labels the enzyme. A further consequence of the Staudinger ligation is fragmentation of the CTR probe, thus releasing the inhibitor and restoring enzymatic activity. As a proof‐of‐principle, the CTR strategy was applied to the hydrolase β‐galactosidase. The enzyme was efficiently labeled with biotin, and the kinetic data for the biotinylated enzyme were comparable to those for unlabeled β‐galactosidase. The CTR probe exhibits excellent targeting specificity, as it selectively labeled β‐galactosidase in a complex protein mixture.     

Brook/Elimination/Aldol Reaction Sequence for the Direct One‐Pot Preparation of Difluorinated Aldols from (Trifluoromethyl)trimethylsilane and Acylsilanes

A methodology allowing the one‐pot preparation of difluorinated aldols directly from Ruppert–Prakash reagent, acyltrimethylsilanes and aldehydes is reported. The process, initiated by a catalytic amount of an ammonium salt, involves the addition of (trifluoromethyl)trimethylsilane to the acylsilane, followed by a Brook rearrangement and elimination of a fluoride anion that promotes the subsequent aldol reaction. An efficient racemic reaction catalyzed by tetrabutylammonium difluorotriphenylsilicate is described, as well as our first efforts towards an asymmetric version.

     

Catalytic Enantioselective Hydrophosphonylation of Aldehydes Using the Iron Complex of a Camphor‐Based Tridentate Schiff Base [FeCl(SBAIB‐d)]2

An iron(III)‐Schiff base‐catalyzed, highly enantioselective hydrophosphonylation of various aldehydes is described. Under the optimized reaction conditions, 5 mol% of the iron/camphor‐based tridentate Schiff base complex [FeCl(SBAIB‐d)]₂ produces high yields (up to 99%) of α‐hydroxy phosphonates in excellent enantioselectivities (up to 99%). The merits of this catalytic system are an easily synthesizable catalyst, inexpensive starting materials, practically simple aerobic reaction conditions, and low catalyst loading (5 mol%).

     

Copper‐Assisted Click Reactions for Activity‐Based Proteomics: Fine‐Tuned Ligands and Refined Conditions Extend the Scope of Application

Copper‐catalysed alkyne–azide 1,3‐dipolar cycloaddition (CuAAC) is the predominantly used bioconjugation method in the field of activity‐based protein profiling (ABPP). Several limitations, however, including conversion efficiency, protein denaturation and buffer compatibility, restrict the scope of established procedures. We introduce an ABPP customised click methodology based on refined CuAAC conditions together with new accelerating copper ligands. A screen of several triazole compounds revealed the cationic quaternary {3‐[4‐({bis[(1‐tert‐butyl‐1H‐1,2,3‐triazol‐4‐yl)methyl]amino}methyl)‐1H‐1,2,3‐triazol‐1‐yl]propyl}trimethylammonium trifluoroacetate (TABTA) to be a superior ligand. TABTA exhibited excellent in vitro conjugation kinetics and optimal ABPP labelling activity while almost exclusively preserving the native protein fold. The application of this CuAAC‐promoting system is amenable to existing protocols with minimal perturbations and is even compatible with previously unusable buffer systems such as Tris ? HCl.     

One‐Step Preparation of Pt on Pretreated Multiwalled Carbon Nanotubes for Methanol Electrooxidation

For the first time, intermittent microwave heating (IMH) is a one‐step technique applied to pretreat the multiwalled carbon nanotubes (MWCNTs) in H₂O₂ solution. The approach does not require washing and filtration of the sample, thus significantly reducing the loss of the material and treatment time. The IMH associated with H₂O₂ treatment, is optimised to fabricate efficient support for Pt electrocatalyst. Both as‐received and treated MWCNTs are used as Pt electrocatalyst supports, respectively. It demonstrates that the treated MWCNTs supported Pt has much better electrocatalytic performance than that of untreated MWCNTs supported Pt. The Pt on MWCNTs treated with an IMH irradiation mode in 10 s on and 20 s off for 5 times, shows the best performance for methanol oxidation. This work provides a novel approach to simply and economically fabricate an efficient MWCNT support at a large scale, for high performance Pt electrocatalysts.     

Synthesis of N,N′‐Disulfonylamidines from Sulfonamides and Alkynes by a Two‐Step,One‐Pot Reaction with Nonafluorobutanesulfonyl Azide

Nonafluorobutanesulfonyl azide is an advantageous alternative to triflyl azide for the efficient synthesis of sulfonyl azides from sulfonamides in terms of its higher reactivity, lower cost, and non‐hazardous nature. The reagent has proven its utility in a novel synthesis of N,N′‐disulfonylamidines from available sulfonamides by a copper‐catalyzed two‐step, one‐pot sequential process with added terminal alkynes.