Synthesis and antimicrobial screening of novel 9-{2-[(1<Emphasis Type="Italic">H</Emphasis>-1,2,3-triazol-4-yl)methoxy]phenyl}-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1<Emphasis Type="Italic">H</Emphasis>-xanthene-1,8(2<Emphasis Type="Italic">H</Emphasis>)-dione derivatives

A series of novel 9-{2-[(1H-1,2,3-triazol-4-yl)methoxy]phenyl}-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione derivatives were synthesized by a click chemistry approach. The structures of all the newly synthesized compounds were characterized by IR, MASS, ¹H and ¹³C NMR spectral data. The final analogues showed good to excellent antibacterial and antifungal activities in an agar well diffusion assay. Compounds 6i and 6f were the most active against all the test bacterial and fungal strains.     

Biocatalytic Self-Assembly Cascades

The properties of supramolecular materials are dictated by both kinetic and thermodynamic aspects, providing opportunities to dynamically regulate morphology and function. Herein, we demonstrate time-dependent regulation of supramolecular self-assembly by connected, kinetically competing enzymatic reactions. Starting from Fmoc-tyrosine phosphate and phenylalanine amide in the presence of an amidase and phosphatase, four distinct self-assembling molecules may be formed which each give rise to distinct morphologies (spheres, fibers, tubes/tapes and sheets). By varying the sequence or ratio in which the enzymes are added to mixtures of precursors, these structures can be (transiently) accessed and interconverted. The approach provides insights into dynamic self-assembly using competing pathways that may aid the design of soft nanostructures with tunable dynamic properties and life times.     

Palladium-catalyzed synthesis of indole fused coumarins via cross-dehydrogenative coupling

The present method describes a palladium-catalyzed cross-dehydrogenative coupling reaction of coumarin and aniline for the synthesis of indole fused coumarin derivatives. The one-pot method is operationally simple and molecular oxygen is used as sole oxidant. The target compounds are obtained in good yields from commercially available precursors.     

Protecting group directed cyclization: asymmetric synthesis of both cis- and trans-dihydrexidine from a common precursor

Protection group of amino- and tethered o-arene functionality of 1,4-aryl-2-amino-1-butanol derived from l-serine dictates the cyclization mode under acidic conditions leading to reverse diastereoselectivity. N-Boc and acetal protected amino alcohol undergo cascade cyclization providing exclusively cis-dihydrexidine via reduction, where formation of C-ring (isoquinoline unit) prior to Friedel–Crafts cyclization control the cis-stereochemistry of the B-ring. N-Cbz and O-benzyl protection direct first F–C cyclization yielding the trans-1-aryl-2-aminotetralin and subsequent deprotection-cyclization forming the C-ring afforded dihydrexidine.     

Molecular transition-metal phosphonates

Molecular transition-metal phosphonates are of relatively recent origin and can be assembled by several synthetic strategies. The nuclearity and the structure of the metal aggregates can be modulated by several factors including the stoichiometry of the reactants, nature of the metal precursor and the type of phosphonic acid used. This perspective summarizes some of the recent work carried out on copper(II)-, zinc(II)- and cadmium(II) phosphonates with particular emphasis on their synthesis and structure.     

One-pot regio- and stereoselective synthesis of α'-methoxy-γ-pyrones: biological evaluation as mitochondrial respiratory complex inhibitors

The one-pot construction of functionalized α'-methoxy-γ-pyrones is detailed. Starting from α,α'-dimethoxy-γ-pyrone, molecular diversity is attained by a regio- and stereoselective desymmetrization using allyllithium followed by vinylogous aldol reaction. Mechanistic considerations including density functional theory calculations and insightful experiments have been gathered to shed light on this complex multistep process. To illustrate the versatility of this methodology, some of the molecules prepared were evaluated for their ability to inhibit NADH-oxidase and NADH-ubiquinone oxidoreductase. In the process, a potent new inihibitor of NADH-oxidase activity (IC(50) 44 nM) was identified.     

A selective fluoride encapsulated neutral tripodal receptor capsule: solvatochromism and solvatomorphism

The dinitrophenyl functionalized tris-(amide) receptor behaves as a selective chemosensor for fluoride by encapsulation within the tripodal pseudocavity in polar aprotic solvents exhibiting solvatochromism and solvatomorphism.     

Switchable Optical Probes for Simultaneous Targeting of Multiple Anions

Traditional optical probes primarily work on the concept of one‐to‐one recognition strategy. Therefore, simultaneous detection of multiple anions is difficult using this kind of sensory systems. Similarly, designing of multi‐responsive array‐based materials is synthetically challenging as well as difficult to optimize. Thus, researchers across the globe became interested in developing single molecular probes, capable of detecting multiple anions (or anionic biomolecules) by simultaneously activating optically distinguishable output channels. Here, the modes of interaction largely depend on the structural features of the binding sites (cleft size, number of available coordination sites etc.), characteristics of the anions (ionic radius, hydration enthalpy, basicity, coordination number, pk_a of corresponding acids etc.) and the microenvironment around the probe molecules (micropolarity, viscosity, dielectric constant etc.) in the host matrix. In this review, we are mostly focusing on the structure‐activity relationships of such multiple anions sensing optical probes and their stimuli‐responsive properties.     

Hydrogen-Bonded Complexes of Fluorophenylacetylenes: To Fluoresce or Not?

The hydrogen-bonded complexes of fluorophenylacetylenesexhibit unusual and interesting fluorescence turn ON/OFF behaviour following excitation to ¹ππ* (S₁) state. The fluorescence switching behaviour can be realized by (i) “change in the intermolecular structure, (ii) change in the position of fluorine substitution and (iii) change in the hydrogen bonding partner or a combination thereof. Experiments indicate that the ≡C−H⋅⋅⋅X (X=O, N) hydrogen bonding with the acetylenic group plays a pivotal role in this switching behaviour. Intriguingly, weaker ≡C−H⋅⋅⋅X hydrogen bonding leads to fluorescence OFF state, which is turned ON by stronger hydrogen bonding. The observed fluorescence this switching behaviour is rationalized on the basis of a phenomenological model which suggests a coupling between the initially excited S₁ state and a dark S_n state in the Franck-Condon region with limited window controlled by the ≡C−H⋅⋅⋅X hydrogen bonding as a crucial parameter. Such fluorescence switching behaviour in hydrogen-bonded complexes is unprecedented and these intriguing results hopefully will stimulate theoreticians to test ′state of the art′ theories to explain these observations in a consistent manner.