Fluorescent dyes with multiple quaternary ammonium centers for specific image discrimination and Gram-positive antibacterial activity.

Three quaternary ammonium compounds (QACs), TPQA, T2PQA, and T3PQA, were synthesized and employed in antimicrobial tests against E. coli and S. aureus. It was confirmed that they exhibit selective bacteriostasis against S. aureus. The antibacterial activities of the compounds were evaluated via determining their minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) against S. aureus using the 2,3,5-triphenyltetrazolium chloride (TTC) coloration method. Notably, T2PQA exhibited far better properties than TPQA and T3PQA, with the activity found to be dependent on the structure of the QA and the exposed hydrophobic groups. All three compounds showed promising potential for killing Gram-positive bacteria, efficiently guided by fluorescence imaging.

Cross-Module Enoylreduction in the Azalomycin†F Polyketide Synthase.

The colinearity of canonical modular polyketide synthases, which creates a direct link between multienzyme structure and the chemical structure of the biosynthetic end-product, has become a cornerstone of knowledge-based genome mining. Herein, we report genetic and enzymatic evidence for the remarkable role of an enoylreductase in the polyketide synthase for azalomycin F biosynthesis. This internal enoylreductase domain, previously identified as acting only in the second of two chain extension cycles on an initial iterative module, is shown to also catalyze enoylreduction in trans within the next module. The mechanism for this rare deviation from colinearity appears to involve direct cross-modular interaction of the reductase with the longer acyl chain, rather than back transfer of the substrate into the iterative module, suggesting an additional and surprising plasticity in natural PKS assembly-line catalysis.

N-Heterocyclic carbene-catalyzed stereoselective construction of olefinic carbon-sulfur bonds via cross-coupling reaction of gem-difluoroalkenes and thiols.

A novel organocatalytic olefinic carbon-sulfur bond forming reaction was developed. Under the catalysis of 10 mol% stable N-heterocyclic carbene, thiols undergo direct nucleophilic substitution reaction with gem-difluoroalkenes to produce α-fluorovinyl thioethers in high yields with excellent Z-selectivity. In this process, bases are not necessary.

Mitochondria-targeting NIR AIEgens with cationic amphiphilic character for imaging and efficient photodynamic therapy.

A new dual-cationic amphiphilic AIEgen TPhBT-PyP with NIR emission and efficient 1O2 generation was designed. The amphiphilicity of TPhBT-PyP was tuned with dual-positive charges of pyridinium and TPP groups, efficiently targeting mitochondria and distinguishing Gram-positive bacteria. TPhBT-PyP performed well in photodynamic therapy, inducing cancer cell apoptosis and killing S. aureus bacteria.

Rapid SERS Detection of Thiol-Containing Natural Products in Culturing Complex.

Thiol-containing natural products possess a wide range of bioactivities. The burst of synthetic biology technology facilitates the discovery of new thiol-containing active ingredients. Herein, we report a sensitive, quick, and robust surface-enhanced Raman scattering technology for specific and multiplex detection of thiol-containing compounds without purification requirements and also indicating the thiols with different chemical environments. Using this platform, we successfully demonstrated the simultaneous detection of thiol-containing compounds from as low as 1 µM of analytes spiked in complex culture matrices.

N-Heterocyclic carbene-catalyzed sulfa-Michael addition of enals.

An efficient N-heterocyclic carbene (NHC) catalyzed sulfa-Michael addition (SMA) between enals and thiols has been developed. Under the catalysis of 10 mol% stable free carbene IPr and with 20 mol% hexafluoroisopropanol (HFIP) as an additive, enals react with a variety of thiols to afford the SMA adducts in 54-98% yields. In this process, the free carbene preferentially interacts with thiols through hydrogen-bonding and no NHC-catalyzed extended Umpolung transformations were observed.