Bright Luminescence by Combining Chiral [2.2]Paracyclophane with a Boron–Nitrogen-Doped Polyaromatic Hydrocarbon Building Block

Novel BN-doped compounds based on chiral, tetrasubstituted [2.2]paracyclophane and NBN-benzo[f,g]tetracene were synthesized by Sonogashira–Hagihara coupling. Conjugated ethynyl linkers allow electronic communication between the π-electron systems through-bond, whereas through-space interactions are provided by strong π–π overlap between the pairs of NBN-building blocks. Excellent optical and chiroptical properties in racemic and enantiopure conditions were measured, with molar absorption coefficients up to ϵ=2.04×10⁵ M⁻¹ cm⁻¹, fluorescence quantum yields up to Φ_PL=0.70, and intense, mirror-image electronic circular dichroism and circularly polarized luminescence signals of the magnitude of 10⁻³ for the absorption and luminescence dissymmetry factors. Computed g_lum,calcd. values match the experimental ones. Electroanalytical data show both oxidation and reduction of the ethynyl-linked tetra-NBN-substituted paracyclophane, with an overlap of two redox processes for oxidation leading to a diradical dication.     

Asymmetric Inverse-Electron-Demand Hetero-Diels–Alder Reaction for the Construction of Bicyclic Skeletons with Multiple Stereocenters by Using a Bifunctional Organocatalytic Strategy: An Efficient Approach to Chiral Macrolides

We have performed the first bifunctional organocatalytic highly enantioselective inverse-electron-demand hetero-Diels–Alder reaction of cyclic ketones with enones to afford densely functionalized bicyclic skeletons that contain three stereocenters (up 82 % yield, 10:1 d.r., and 97 % ee). Unlike the previous IEDDAR catalytic strategy, this method features a double HOMO_dienophile/ LUMO_diene-activated pathway. Moreover, this process provides a promising method for the construction of enantioenriched macrolides.     

Precursor Ion-Scan Mode-Based Screening Strategy for New Amorfrutin Derivatives from <Emphasis Type="Italic">Amorpha fruticosa</Emphasis> by UPLC–QqQ–MS and UPLC–Q-TOF–MS

This study presents a screening strategy for unknown compounds by coupling UPLC–QqQ–MS and UPLC–Q-TOF–MS analyses. Amorfrutins, potential PPARγ agonists in Amorpha fruticosa, were selected as the research target. First, MS/MS analysis of three amorfrutin references (AA, AB, and AC) by Q-TOF revealed the mass-spectrometric fragmentation patterns of amorfrutins, and m/z 225 was recognized as a characteristic and common fragment ion of amorfrutins. Then, unknown amorfrutins were screened in the fruits of A. fruticosa by UPLC–QqQ–MS operating in precursor ion-scan mode, and the product ion was set as m/z 225 for screening potential amorfrutins. According to the high-resolution MS–MS spectral data provided by UPLC–Q-TOF–MS, the molecular formula of potential amorfrutins and their respective characteristic fragments were calculated. Finally, three unknown amorfrutins, namely, amorfrutin D and two new amorfrutins, were identified. As far as we know, this is the first study to rapidly identify unknown compounds by combined application of QqQ–MS precursor ion scan and Q-TOF–MS formula calculation. This research strategy will also be effective for the discovery of other trace natural products and metabolites.     

A Silica Monolithic Column with Chemically Bonded l-Pipecolic Acid as Chiral Stationary Phase for Enantiomeric Separation of Dansyl Amino Acids by CEC–MS

A silica monolithic column chemically modified with l-pipecolic acid as chiral stationary phase has been developed for chiral separation of dansyl amino acids by capillary electrochromatography–mass spectrometry (CEC–MS). The monolithic column was prepared by a sol–gel process and subsequent chemical modification by l-pipecolic acid as chiral selector with 3-glycidoxypropyltrimethoxysilane as spacer. Interestingly, it was found that the l-pipecolic acid-modified monolithic column can hold copper(II) ions tightly after loading Cu(II) ions during column preparation and conditioning and allows CEC separation to be conducted based on chiral ligand exchange with MS detection by a mobile phase without copper ions. It has been demonstrated that the chiral monolithic column operates well for enantioseparation of several dansyl amino acids by CEC–MS.