Reversible pH-Controlled Catenation of a Benzobisimidazole-Based Tetranuclear Rectangle.

The development of methodologies to control on demand and reversibly supramolecular transformations from self-assembled metalla-structures requires the rational design of architectures able to answer to an applied stimulus. While solvent or concentration changes, light exposure or addition of a chemical have been largely explored to provide these transformations, the case of pH sensitive materials is less described. Herein, we report the first example of a pH-triggered dissociation of a coordination-driven self-assembled interlocked molecular link. It incorporates a pH sensitive benzobisimidazole-based ligand that can be selectively protonated on its bisimidazole moieties. This generates intermolecular electrostatic repulsions that reduces drastically the stability of the interlocked structure, leading to its dissociation without any sign of protonation of the pyridine moieties involved in the coordination bonds. Importantly, the dissociation process is reversible through addition of a base.

Multigram Synthesis of Advanced 6,6-Difluorospiro[3.3]heptane-derived Building Blocks.

A convenient methodology for constructing 6,6-difluorospiro[3.3]heptane scaffold - a conformationally restricted isostere of gem-difluorocycloalkanes - is developed. Alarge array of novel 2-mono- and 2,2-bifunctionalized difluorospiro[3.3]heptane building blocks was obtained through the convergent synthesis strategy using a common synthetic precursor - 1,1-bis(bromomethyl)-3,3-difluorocyclobutane. The target compounds and intermediates were prepared by short reaction sequences (6-10 steps) on multigram scale (up to 0.47 kg).

Metalla-Assembled Electron-Rich Tweezers: Redox-Controlled Guest Release Through Supramolecular Dimerization.

Developing methodologies for on-demand control of the release of a molecular guest requires the rational design of stimuli-responsive hosts with functional cavities. While a substantial number of responsive metallacages have already been described, the case of coordination-tweezers has been less explored. Herein, we report the first example of a redox-triggered guest release from a metalla-assembled tweezer. This tweezer incorporates two redox-active panels constructed from the electron-rich 9-(1,3-dithiol-2-ylidene)fluorene unit that are facing each other. It dimerizes spontaneously in solution and the resulting interpenetrated supramolecular structure can dissociate in the presence of an electron-poor planar unit, forming a 1:1 host-guest complex. This complex dissociates upon tweezer oxidation/dimerization, offering an original redox-triggered molecular delivery pathway.

Redox-Driven Transformation of a Discrete Molecular Cage into an Infinite 3D Coordination Polymer.

Two M12 L6 redox-active self-assembled cages constructed from an electron-rich ligand based on the extended tetrathiafulvalene framework (exTTF) and metal complexes with a linear geometry (PdII and AgI ) are depicted. Remarkably, based on a combination of specific structural and electronic features, the polycationic self-assembled AgI coordination cage undergoes a supramolecular transformation upon oxidation into a three-dimensional coordination polymer, that is characterized by X-ray crystallography. This redox-controlled change of the molecular organization results from the drastic conformational modifications accompanying oxidation of the exTTF moiety.

Synthesis of an Enantiomerically Pure Inherently Chiral Calix[4]Arene Phosphonic Acid and Its Evaluation as an Organocatalyst.

A facile method for the preparation of enantiomerically pure inherently chiral calix[4]arene phosphonic acid (cR,pR)-7 in four steps starting from the readily available and previously synthesized (cS)-enantiomer of calix[4]arene acetic acid 1 or its methyl ester 2 was developed. The first tests of this unique calixarene Brönsted acid with inherent chirality in organocatalysis of the aza-Diels-Alder reaction of imines with Danishefsky's diene and epoxide ring opening by benzoic acid were performed. The calixarene phosphonic acid (cR,pR)-7 shows good catalytic activities but with low enantioselectivities in these reactions.

Alkyl Triarylstannanecarbodithioates: Synthesis, Crystal Structures, and Efficiency in RAFT Polymerization.

Eight alkyl triarylstannanecarbodithioates were synthesized starting from the corresponding triarylstannyl chlorides. They were fully characterized by IR and 1 H, 13 C, and 119 Sn NMR spectroscopy and mass spectrometry. Their solid-state structures and geometric parameters were determined and compared to those of other classes of thiocarbonylthio compounds. These new organotin derivatives are efficient reversible chain-transfer agents for reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St) and n-butyl acrylate (BA), with controlled number-average molecular weights and narrow dispersities (Ð<1.3). In some cases, loss of control of the polymerization was evidenced and supported by the observation of side products by 119 Sn NMR spectroscopy. This phenomenon was attributed to the thermal instability of the Sn-RAFT terminal group.

Pyrrolidinone and pyrrolidine derivatives: Evaluation as inhibitors of InhA and Mycobacterium tuberculosis.

A series of GEQ analogues bearing pyrrolidinone or pyrrolidine cores were synthesized and evaluated against InhA, essential target for Mycobacterium tuberculosis (M.tb) survival. The compounds were also evaluated against M.tb H37Rv growth. Interestingly, some of the compounds, not efficient as InhA inhibitors, are active against M.tb with MICs up to 1.4 µM. In particular, compound 4b was screened with different M.tb mutated strains in order to identify the cellular target, but without success, suggesting a new possible mode of action.

Carbo-cyclohexadienes vs. carbo-benzenes: structure and conjugative properties.

Ideally Cs-/C2v-symmetric chromophores, constituted by two electro-active groups conjugated through the carbo-mer of the cyclohexa-1,3-diene core, are selectively prepared by the SnCl2-mediated reduction of tailored hexaoxy-[6]pericyclynes: in the latter substrates, one of the 1,4-dioxybut-2-yne edges is "chemically locked" by two CF3 substituents preventing complete reduction to the corresponding aromatic carbo-benzenic core, which is expected to be more "π-insulating" between the electro-active ends. The bis-trifluoromethylated carbo-cyclohexadiene products are also shown to be significantly stabilized with respect to their bis-phenylated analogues. Their structural (crystal X-ray diffraction analyses), spectroscopical (NMR and UV-vis spectra), physio-optical (dichromism in solution) and electrochemical (cyclic voltammograms) properties are compared on the basis of the electron-donating/electron-withdrawing nature of the substituents. These properties are also compared with those of their aromatic carbo-benzene and flexible carbo-n-butadiene counterparts.

RAFT Polymerization with Triphenylstannylcarbodithioates (Sn-RAFT).

A new range of tin-based reversible addition-fragmentation chain-transfer (RAFT) agents is described and evaluated for the polymerization of acrylamides, methyl acrylate and styrene. These organometallic compounds are highly reactive reversible transfer agents which allow an efficient control of the polymerization of substituted acrylamide monomers, whereas RAFT control for methyl acrylate and styrene polymerization is contaminated by side reactions at prolonged reaction times. 119Sn NMR is shown to be an informative instrument for the monitoring of Sn-RAFT-mediated polymerizations.

Synthesis of 3-heteryl substituted pyrrolidine-2,5-diones via catalytic Michael reaction and evaluation of their inhibitory activity against InhA and Mycobacterium tuberculosis.

In the present paper, we report the synthesis via catalytic Michael reaction and biological results of a series of 3-heteryl substituted pyrrolidine-2,5-dione derivatives as moderate inhibitors against Mycobacterium tuberculosis H37Rv growth. Some of them present also inhibition activities against InhA.

Design, chemical synthesis of 3-(9H-fluoren-9-yl)pyrrolidine-2,5-dione derivatives and biological activity against enoyl-ACP reductase (InhA) and Mycobacterium tuberculosis.

We report here the discovery, synthesis and screening results of a series of 3-(9H-fluoren-9-yl)pyrrolidine-2,5-dione derivatives as a novel class of potent inhibitors of Mycobacterium tuberculosis H37Rv strain as well as the enoyl acyl carrier protein reductase (ENR) InhA. Among them, several compounds displayed good activities against InhA which is one of the key enzymes involved in the type II fatty acid biosynthesis pathway of the mycobacteria cell wall. Furthermore, some exhibited promising activities against M. tuberculosis and multi-drug resistant M. tuberculosis strains.

Enhanced π-frustration in carbo-benzenic chromophores.

The synthesis, structure, and absorption spectra of highly π-frustrated carbo-benzenes with indolic enamine substituents more or less directly conjugated to the C18 macro-aromatic core are described, and their peculiar reactivity is analyzed.

2-(9H-Fluoren-9-yl)-4-(4-fluoro-anilino)-4-oxo-butanoic acid.

In the title compound, C23H18FNO3, the tricyclic 9-fluorenyl system is approximately planar (r.m.s. deviation = 0.0279 Å). The N-C(=O) bond length is comparatively short [1.359 (3) Å], which is typical for such conjugated systems. The N atom has a planar configuration [sum of bond angles= 359.8°] due to conjugation of its lone pair with the π-system of the carbonyl group. In the crystal, a three-dimensional network is formed through N-H⋯O and O-H⋯O hydrogen bonds between the amide and carb-oxy-lic acid groups and carbonyl O-atom acceptors.

Methyl N-(3-cyano-picolino-yl)-l-tryptophanate.

In the title compound, C19H16N4O3, the stereocenter has an l configuration; l-tryptophan methyl ester hydro-chloride being used as a starting material. The indole ring system and the pyridine ring are inclined to one another by 13.55 (14)°. In the crystal, adjacent mol-ecules are linked via N-H⋯O hydrogen bonds, forming chains propagating along the c-axis direction.

Highly π electron-rich macro-aromatics: bis(p-aminophenyl)-carbo-benzenes and their DBA acyclic references.

A series of stable quadrupolar bis(p-aminophenyl)-carbo-benzenes, featuring both donor-donor-donor π-frustration and central macro-aromaticity, is described and compared to the acyclic dibutatrienylacetylene (DBA) reference series.

rac-{[2-(Diphenyl-thio-phosphan-yl)ferrocen-yl]meth-yl}trimethyl-ammonium iodide chloro-form monosolvate.

The title compound, [Fe(C5H5)(C21H24NPS)]I·CHCl3, is built up from a (ferrocenylmeth-yl)trimethyl-ammonium cation, a iodine anion and a chloro-form solvent mol-ecule, all residing in general positions. The N atom of the ammonium group is displaced by 1.182 (2) Šfrom the plane of the substituted cyclo-penta-dienyl (Cp) ring towards the Fe atom, whereas the C atom attached to the same Cp ring is slightly below this plane by -0.128 (2) Å. These deviations might result from weak agostic interactions between the two H atoms of the CH2 group and the Fe atom.