Troger's base molecular scaffolds in dicarboxylic acid recognition

Synthetic strategies and diversification of dibenzo[1,5]diazocines

Dibenzo[1,5]diazocine scaffolds are present in a wide range of organic building blocks, for example in pharmaceuticals, materials and structural chemistry. However, the development of these structural frameworks has not received significant attention owing to limited synthetic protocols and strategies. Herein, a summary of the attractive synthetic approaches for the construction of dibenzo[1,5]diazocines, epiminodibenzo[1,5]diazocines and epoxydibenzo[1,5]diazocines developed over the past two decades is presented. The spectroscopic, synthetic mechanisms for the formation of the heterocyclic rings and remarkable structural features, including in the solid-state, are discussed.

Identification of a novel small-molecule inhibitor of miR-29b attenuates muscle atrophy

Muscle atrophy is debilitating and can be induced by several stressors. Unfortunately, there are no effective pharmacological treatment until now. MicroRNA (miR)-29b is an important target that we identified to be commonly involved in multiple types of muscle atrophy. Although sequence-specific inhibition of miR-29b has been developed, in this study, we report a novel small-molecule miR-29b inhibitor that targets miR-29b hairpin precursor (pre-miR-29b) (Targapremir-29b-066 [TGP-29b-066]) considering both its three-dimensional structure and the thermodynamics of interaction between pre-miR-29b and the small molecule. This novel small-molecule inhibitor has been demonstrated to attenuate muscle atrophy induced by angiotensin II (Ang II), dexamethasone (Dex), and tumor necrosis factor α (TNF-α) in C2C12 myotubes, as evidenced by increase in the diameter of myotube and decrease in the expression of Atrogin-1 and MuRF-1. Moreover, it can also attenuate Ang II-induced muscle atrophy in mice, as evidenced by a similar increase in the diameter of myotube, reduced Atrogin-1 and MuRF-1 expression, AKT-FOXO3A-mTOR signaling activation, and decreased apoptosis and autophagy. In summary, we experimentally identified and demonstrated a novel small-molecule inhibitor of miR-29b that could act as a potential therapeutic agent for muscle atrophy.

Tröger's Base Chemistry in Solution and in Zr(IV)-Based Metal-Organic Frameworks

Tröger's base (TB) and its derivatives have been studied extensively due to their unique concave shape stemming from the endomethylene strap. However, the strap-clipped TB chemistry has been largely overlooked in metal-organic framework (MOF) solids, leading to a gap in our knowledge within this field. In this work, we report the in situ strap elimination of a carboxylate-carrying TB in the presence of formic acid, both in solution and in Zr(IV)-based MOFs. In the solution system, the methanodiazocine nucleus can be exclusively transformed into an N,N'-diformyl-decorated phenhomazine derivative, regardless of the solvent used (DMF, DMA, or DEF), as unambiguously uncovered by single crystal X-ray crystallography. In contrast, while in the MOF synthetic system, the degree of derivatization reaction can be effectively controlled to give either the secondary diamine or formyl-decorated diamine, depending on the solvent used (DMF or DEF), resulting in the formation of two Zr-MOFs with 8-connected bcu (NU-1900) and 12-connected fcu (NU-407) topologies, respectively. The derivatization mechanism is proposed to be topology-guided and dependent on the local acid concentration during the MOF formation processes. Moreover, we discovered a novel post-synthetically water-induced in situ linker formylation process in NU-1900 through sequential formic acid elimination, migration, and condensation processes, affording an isostructural framework with the same linker as in NU-407, which further corroborates our proposed mechanism. Additionally, the highly defective NU-1900 with abundant accessible Zr sites was demonstrated to be an outstanding catalyst for the detoxification of a nerve agent simulant with a half-life of less than 1 min.

A nitrogen-based chiral catenane for enantioenriching photocatalytic aerobic oxidation

Tröger's base's chirality merges catenanes’ photosensitizing characteristics to introduce the first nitrogen-based chiral hetero[2]catenane that proceeds enantioenriching photocatalytic aerobic oxidations.

Fluorescent 4-amino-1,8-naphthalimide Tröger's bases (TBNaps) possessing (orthogonal) 'α-amino acids', esters and di-peptides and their solvent dependent photophysical properties

The synthesis of fifteen luminescent bis-naphthalimide based Tröger's bases (TBNaps) derived from 4-amino-1,8-naphthalimide (4-Amino-Nap) precursors is described; these scaffolds possess α-amino acids, esters or di-peptides conjugated at the imide site and show minor fluorescence in aqueous solution while being highly emissive in organic solvents. The investigation shows that these TBNaps possessing ICT excited state properties are capable of generating either positive or negative solvatochromic effects in response to changes in polarity and/or the hydrogen bonding capabilities of the medium.

Polyamide-Polyamine Cryptand as Dicarboxylate Receptor: Dianion Binding Studies in the Solid State, in Solution, and in the Gas Phase

Polyamide-polyamine hybrid macrobicycle L is explored with respect to its ability to bind α,ω-dicarboxylate anions. Potentiometric studies of protonated L with the series of dianions from succinate (suc^2-) through glutarate (glu^2-), α-ketoglutarate (kglu^2-), adipate (adi^2-), pimelate (pim^2-), suberate (sub^2-), to azelate (aze^2-) have shown adipate preference with association constant value of K = 4900 M^-1 in a H₂O/DMSO (50:50 v/v) binary solvent mixture. The binding constant increases from glu^2- to adi^2- and then continuously decreases with the length of the anion chain. Further, potentiometric studies suggest that hydrogen bonding between the guest anions and the amide/ammonium protons of the receptor also contributes to the stability of the associations along with electrostatic interactions. Negative-mode electrospray ionization of aqueous solutions of host-guest complexes shows clear evidence for the selective formation of 1:1 complexes. Single-crystal X-ray structures of complexes of the receptor with glutaric acid, α-ketoglutaric acid, adipic acid, pimelic acid, suberic acid, and azelaic acid assist to understand the observed binding preferences. The solid-state structures reveal a size/shape complementarity between the host and the dicarboxylate anions, which is nicely reflected in the solution state binding studies.

Hünlich base derivatives as photo-responsive Λ-shaped hinges

The azo derivatives of the Hünlich base are introduced as a set of molecular switches with unique shapes and properties.

One-pot facile synthesis of 4-amino-1,8-naphthalimide derived Tröger's bases via a nucleophilic displacement approach

We report here a novel one-pot synthetic strategy for the synthesis of a family of N-alkyl-1,8-naphthalimide derived Tröger's bases (in overall yield of 65–96%) via a nucleophilic substitution reaction.

Experimental and theoretical investigations into the stability of cyclic aminals

Background: Cyclic aminals are core features of natural products, drug molecules and important synthetic intermediates. Despite their relevance, systematic investigations into their stability towards hydrolysis depending on the pH value are lacking. Results: A set of cyclic aminals was synthesized and their stability quantified by kinetic measurements. Steric and electronic effects were investigated by choosing appropriate groups. Both molecular mechanics (MM) and density functional theory (DFT) based studies were applied to support and explain the results obtained. Rapid decomposition is observed in acidic aqueous media for all cyclic aminals which occurs as a reversible reaction. Electronic effects do not seem relevant with regard to stability, but the magnitude of the conformational energy of the ring system and pKa values of the N-3 nitrogen atom. Conclusion: Cyclic aminals are stable compounds when not exposed to acidic media and their stability is mainly dependent on the conformational energy of the ring system. Therefore, for the preparation and work-up of these valuable synthetic intermediates and natural products, appropriate conditions have to be chosen and for application as drug molecules their sensitivity towards hydrolysis has to be taken into account.

Crystal structure of 1,1′-diformyl-4,4′-(6H,12H-5,11-methano-dibenzo[b,f][11,5]diazocine-2,8-diyl)dibenzene, C29H22N2O2

C29H22N2O2, triclinic, P1̅ (no. 2), a = 22.4995(6) Å, b = 9.9370(3) Å, c = 21.6466(6) Å, β = 115.941(1)°, V = 4352.1(2) Å3, Z = 4, R gt (F) = 0.0487, wR ref (F 2 ) = 0.1473, T = 296 K.

CuI-catalyzed amination of Tröger's base halides: a convenient method for synthesis of unsymmetrical Tröger's bases

A convenient and efficient Ullmann type copper catalyzed amination method has been developed for direct amination of halogen substituted Tröger's base analogues.

Design and synthesis of Tröger's base ditopic receptors: host-guest interactions, a combined theoretical and experimental study

Two flexible Tröger's base ditopic receptors C4TB and C5TB incorporating monoaza crown ether were designed and synthesized for bisammonium ion complexation. A comprehensive study of host-guest interactions was established by (1)H NMR spectroscopy and DFT calculations. Bisammonium chloride (A1) with a shorter alkyl chain spacer showed the highest affinity for the receptors. M06-2X/cc-pVTZ calculations including the solvent effects on host-guest complexes were employed to explain and rationalize the experimental trends. The short N-H···O or N-H···N hydrogen-bond distances observed in the range of 1.71-1.98 Å indicate the existence of a strong charge assisted hydrogen bonding between the host and the guest. The unusual behaviour (higher binding constant) of A5 in (1)H NMR titration is traced to the conformational folding of the guest.

Photophysical characterisation of Tröger's base molecular scaffolds: a combined theoretical and experimental study

The photophysics of Tröger's base in the ground and excited states was performed by comparing experimental and theoretical properties predicted using TD-DFT calculations.

Selective fluorescence sensing of salicylic acids using a simple pyrenesulfonamide receptor

The highest change in relative intensity of probe 3 among the probes 2–5 with 3,5-DNSA demonstrated the significance of sulfonamide N–H and imidazole C2–H with the highest association constant and complete quenching.

9-N-Alkylaminomethylanthracene probes for selective fluorescence sensing of pentafluorophenol

9-N-Alkylaminomethylanthracenes (1 and 2) were synthesised for halophenol sensing, and their selectivity and sensitivity towards pentafluorophenol (PFP) in ethanol were investigated.

Discovery of Tröger's base analogues as selective inhibitors against human breast cancer cell line: design, synthesis and cytotoxic evaluation

A library of structurally diverse Tröger's base analogues has been constructed via unusual amination of methylene bridge employing Vilsmeier-Haack conditions as well as by the incorporation of five and six membered heterocycles on the aromatic core of Tröger's base framework. The constructed structurally diverse frameworks were evaluated for their cytotoxic activities against a panel of three human cancer lines A549 (lung adenocarcinoma), MDAMB-231 (breast) and SK-N-SH (neuroblastoma). From the activity profile obtained, a redesign of Tröger's base analogues led to the construction of more potent molecular entities. The study led to development of a series of compounds with MDAMB-231 cell line specific cytotoxicity. Of the 30 compounds synthesized and evaluated, 7 compounds were found to possess cytotoxicity that is equivalent or better than standard drug doxorubicin against MDAMB-231 cell line while only one compound was found to be active against SK-N-SH cell line.

Steric inhibition of hydrogen bonding in molecular recognition of dicarboxylic acids: di-topic receptors containing a nitro group designed to behave like monotopic receptors

The ditopic macrocyclic receptors having NO₂ group show inhibition in hydrogen bonding molecular recognition towards the dicarboxylic acids to behave as monotopic receptors.

Tröger's base quasiracemates and crystal packing tendencies

A family of 7 Tröger's base (TB) compounds that vary in configuration (quasiracemates, racemates, and enantiomers) and chemical substitutions (Me, Cl, and Br) has been investigated.

Facile access to imidazole and imidazolium substituted dibenzo-diazocines

The C₂-symmetrical 2,8- and 4,10-diimidazo methano dibenzo diazocines were synthesized and converted into alkyl imidazolium salts.

Stabilization and structural alteration of the G-quadruplex DNA made from the human telomeric repeat mediated by Tröger's base based novel benzimidazole derivatives

Ligand-induced stabilization of the G-quadruplex DNA structure derived from the single-stranded 3'-overhang of the telomeric DNA is an attractive strategy for the inhibition of the telomerase activity. The agents that can induce/stabilize a DNA sequence into a G-quadruplex structure are therefore potential anticancer drugs. Herein we present the first report of the interactions of two novel bisbenzimidazoles (TBBz1 and TBBz2) based on Tröger's base skeleton with the G-quadruplex DNA (G4DNA). These Tröger's base molecules stabilize the G4DNA derived from a human telomeric sequence. Evidence of their strong interaction with the G4DNA has been obtained from CD spectroscopy, thermal denaturation, and UV-vis titration studies. These ligands also possess significantly higher affinity toward the G4DNA over the duplex DNA. The above results obtained are in excellent agreement with the biological activity, measured in vitro using a modified TRAP assay. Furthermore, the ligands are selectively more cytotoxic toward the cancerous cells than the corresponding noncancerous cells. Computational studies suggested that the adaptive scaffold might allow these ligands to occupy not only the G-quartet planes but also the grooves of the G4DNA.

Sensitivity of diamond-capped impedance transducer to Tröger's base derivative

Sensitivity of an intrinsic nanocrystalline diamond (NCD) layer to naphthalene Tröger's base derivative decorated with pyrrole groups (TBPyr) was characterized by impedance spectroscopy. The transducer was made of Au interdigitated electrodes (IDE) with 50 μm spacing on alumina substrate which were capped with the NCD layer. The NCD-capped transducer with H-termination was able to electrically distinguish TBPyr molecules (the change of surface resistance within 30-60 kΩ) adsorbed from methanol in concentrations of 0.04 mg/mL to 40 mg/mL. An exponential decay of the surface resistance with time was observed and attributed to the readsorption of air moisture after methanol evaporation. After surface oxidation the NCD cap layer did not show any leakage due to NCD grain boundaries. We analyzed electronic transport in the transducer and propose a model for the sensing mechanism based on surface ion replacement.