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A new hemicryptophane host with a ditopic molecular cavity combining a cyclotriveratrylene (CTV) unit with a tris‐urea moiety was synthesized. The complexation of halides, tetramethylammonium (TMA+) cation, and ion pairs was investigated. A positive cooperativity was observed, since halides display a higher binding constant when a TMA+ cation is already present inside the cage. When TMA+ was complexed alone, a decrease of temperature from 298 K to 230 K was required to switch from a fast to a slow exchange regime on the NMR time scale. Nevertheless, the prior complexation of a halide guest in the lower part of the host resulted in significant decrease of the exchange rate of the subsequent complexation of the TMA+ cation. Under these conditions, the 1H NMR signals characteristic of a slow exchange regime were observed at 298 K. Addition of an excess of salts, increases the ionic strength of the solution, restoring the fast exchange dynamics. This result provides insight on how the exchange rate of a cation guest can be modulated by the complexation of a co‐guest anion. [ABSTRACT FROM AUTHOR]

The persistent organic pollutant chlordecone massively contaminates water resources of the French West Indies. Hemicryptophanes are cages capable of complexing chlordecone in organic solvents. Here we demonstrate that a hemicryptophane cage is not only able to recognize this pollutant in chloroform but is also efficient for the removal of chlordecone from water. This evidences that, beyond our previously reported proof of concept, this receptor could be apply as a direct and efficient depolluting agent, making it a promising system for applied supramolecular chemistry. A simple pH switch (basic washing) enables the release of chlordecone from the host, under its deprotonated form, allowing the empty supramolecular cage to be recycled and reused. This method for recycling the receptor, is to the best of our knowledge unprecedented. [ABSTRACT FROM AUTHOR]

The recognition of carbohydrate plays a key role in numerous biological processes. Thus, artificial receptors have been synthesized to mimic these biological systems. To date, most of the receptors reported for carbohydrate complexation present highly symmetrical cavities, probably because their syntheses require less synthetic efforts and are easier to achieve and control. However, carbohydrates display complex, asymmetrical structures suggesting that hosts with low symmetry might be more adapted to recognize these guests. Here, we described the strategies that have been used to complex carbohydrates with macrocycles and cages presenting low symmetry and the potential of this approach. Self‐assembled cages are first described, then covalent macrocycles and cages are presented and for each example the binding properties of low‐symmetry systems are compared to those of their higher‐symmetry counterparts. [ABSTRACT FROM AUTHOR]

Chlordecone (CLD), a Persistent Organic Pollutant, is still present in water and food chain of the French West Indies (FWI), leading to dramatical public health problems. One of the major issues is the lack of an easy, non‐expensive, sensitive and robust method for the detection of chlordecone to ensure chlordecone‐free water and foods for the residents of the FWI. This study reports on the development of a fluorescent molecular cage that allows a simple and convenient detection of chlordecone in water at environmental concentration. The specific structural features of chlordecone prompted the choice of hemicryptophanes as receptor. First, the size, shape of the cavity, as well as the recognition units, were optimized to identify the most efficient non fluorescent host for CLD complexation. Then, this selected compound was equipped with fluorophores at different positions in order to find the most efficient system for CLD detection by fluorescence. Among the two most promising fluorescent cages, the newly synthesized hemicryptophane with biphenyl moieties allowed the development of a fast, easy, reproducible and cheap procedure to detect CLD in water. Based on its sensitivity and scalability, with modulation of hemicryptophane, concentration, CLD concentrations were estimated over five orders of magnitude (10−2–103 μg/L) including the environmental levels of contamination and the permissible limit for drinking water in the FWI. [ABSTRACT FROM AUTHOR]

The design of molecular cages with low symmetry could allow for more specific tuning of their properties and better mimic the unsymmetrical and complex environment of protein pockets. However, the added value of lowering symmetry of molecular receptors has been rarely demonstrated. Herein, C3‐ and C1‐symmetrical cages, presenting the same recognition sites, have been synthesized and investigated as hosts for carbohydrate recognition. Structurally related derivatives of glucose, galactose and mannose were found to have greater affinity to the receptor with the lowest symmetry than to their C3‐symmetrical analogue. According to the host cavity modelling, the C1 symmetry receptor exhibits a wider opening than its C3‐symmetrical counterpart, providing easier access and thus promoting guest proximity to binding sites. Moreover, our results show the high stereo‐ and substrate selectivity of the C1 symmetry cage with respect to its C3 counterpart in the recognition of sugars. [ABSTRACT FROM AUTHOR]

Haloazaphosphatranes are the halogenated parents of proazaphosphatranes, also known as Verkade's superbase. While the synthesis of iodo‐, bromo‐ and chloroazaphosphatranes was reported more than thirty years ago by J. G. Verkade, the first synthesis of fluoroazaphosphatranes was only described in 2018 by Stephan et al. Currently, no common and versatile procedure exists to access fluoroazaphosphatranes platform with different structural characteristics. In this report, a new and simple synthesis of this class of compounds was developed based on the nucleophilic attack of the fluoride anion on chloroazaphosphatrane derivatives with good to high isolated yields for the corresponding fluoroazaphosphatranes (70–92%). The scope of the reaction was widened to fluoroazaphosphatranes bearing various substituents and X‐ray molecular structures of two of them are reported. The stability of fluoroazaphosphatranes toward nucleophilic solvents like water has been investigated. As they revealed much more robust cations than their chloroazaphosphatrane parents, their chloride salts were tested as organocatalysts for the formation of cyclic carbonates from epoxides and CO2. Fluoroazaphosphatranes proved to be both efficient and stable catalytic systems for CO2 conversion with catalytic activities similar to those of azaphosphatranes, and no decomposition of the cation was observed at the end of reaction. [ABSTRACT FROM AUTHOR]

Proazaphosphatranes (also named Verkade's superbases) and their azaphosphatrane conjugated acids have been recently been shown to be confined in either covalent or self‐assembled molecular cages, or immobilized in nanopores of hybrid materials. The encapsulation of these phosphorus moieties turns out to strongly affect both their acid–base, catalytic, and recognition properties. The thermodynamics and kinetics of the proton transfer as well as the selectivity and catalytic activities of Verkade's superbases were strongly changed upon their confinement in a hemicryptophane cavity. Moreover, self‐assembled cages, including azaphosphatrane moieties, were found to display remarkable anion recognition properties in water. In this Minireview, these new aspects of the chemistry of aza‐ and proaza‐phosphatranes are presented, in order to highlight the great potential of such an approach [ABSTRACT FROM AUTHOR]

Verkade's superbases, entrapped in the cavity of enantiopure hemicryptophane cages, have been synthesized with enantiomeric excess (ee) superior to 98%. Their absolute configuration has been determined by using electronic circular dichroism (ECD) spectroscopy. These enantiopure encaged superbases turned out to be efficient chiral derivatizing agents for chiral azides, underlining that the chirality of the cycloveratrylene (CTV) macrocycle induces different magnetic and chemical environments around the phosphazide functions. [ABSTRACT FROM AUTHOR]

The five‐steps synthesis of a hemicryptophane cage combining a benzene‐1,3,5‐tricarboxamide unit and a cyclotriveratrylene (CTV) moiety is described. Chiral high‐performance liquid chromatography (HPLC) was used to resolve the racemic mixture. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental electronic circular dichroism (ECD) spectra with the calculated ones. X‐ray molecular structures reveal that the capped benzene‐1,3,5‐tricarboxamide unit adopts a structurally chiral conformation in solid state: the chirality of CTV moiety controls the Λ or Δ orientation of the three amides. [ABSTRACT FROM AUTHOR]

The synthesis of a hemicryptophane cage combining a CTV unit with a C3 symmetrical moiety bearing three urea functions is reported. This host was found to bind anions with higher binding constants than other previously reported hemicryptophanes. Due to its heteroditopic character this cage proved to be an efficient ion‐pair receptor. The best cooperativity effect was observed for the tetramethylammonium bromide (TMABr) salt, which was confirmed and rationalized by DFT calculations. A tris‐urea unit was combined with CTV moiety, leading to a heteroditopic hemicryptophane capable of binding ion pairs efficiently and selectively. [ABSTRACT FROM AUTHOR]

Covalent cages with a well‐defined cavity located close to a reactive center are of increasing interest because of their outstanding ability to mimic the catalytic properties of enzymatic systems. The size and shape of such synthetic nanosized reactors strongly affect the behavior of the trapped reaction partners, which can adopt specific conformations and orientations. In particular, the use of molecular cages with confined reactive functions strongly modifies the outcome of catalytic transformations that are carried out therein. This review article describes covalent molecular cages presenting an endohedral functionalization of their inner space and reports on their catalytic activities compared with those of model systems that lack cavity. The confinement of endohedral‐functionalized cavities affects their stability as catalysts and the rate and selectivity of reactions they mediate. [ABSTRACT FROM AUTHOR]

A frustrated Lewis pair (FLP) system was obtained by confinement of the Lewis base partner, a Verkade's superbase, in a molecular cavity. Whereas the model superbase lacking cavity displayed no catalytic activity in Morita–Baylis–Hillman (MBH) reactions, when associated to titanium (IV) chloride, the encaged superbase turns out to be an efficient catalyst under the same conditions. The crucial role of the endohedral functionalized cage on catalytic performance was further demonstrated by the fact that model superbases with bulky substituents were much less efficient to produce active catalysts, as well as by inhibition and substrate selection experiments. 31P NMR spectroscopy and mass spectrometry experiments evidenced that no interaction between the Lewis acidic and basic partners occurred when the superbase was capped by a cycloveratrylene (CTV) unit, thus creating a true FLP active system. Switching on the catalytic activity: A frustrated Lewis pair (FLP) system has been designed, where the Lewis base partner is encapsulated in a cage structure. Endohedral functionalization of a well‐defined cavity allows for the formation of a FLP, restoring the catalytic activity of the Verkade's superbase. [ABSTRACT FROM AUTHOR]

A class of hemicryptophane cages that adopt imploded conformations in solution and in the solid state has been described and studied by NMR spectroscopy and X-ray crystallography. It is reported that the degree of collapse of the molecular cavity can be controlled by changing the stereochemistry of the chiral elements of the hemicryptophanes, leading to a modulation of their physical and chemical properties. Upon the binding of an oxidovanadium unit, the collapsed molecular cavity can inflate to give an expanded conformation. Removal of the vanadium core by an ancillary complexing ligand restores the initial folded structure. Thus, coordination/de-coordination of the metal ion controls the dynamic motions of the cage, leading to a reversible nanomechanical process. This controlled motion between a collapsed and expanded cavity can be seen as that of a breathable molecular cage. [ABSTRACT FROM AUTHOR]

The synthesis of eight enantiopure molecular cages (four diastereomeric pairs of enantiomers) comprising a helically chiral cyclotriveratrylene (CTV) unit, three axially chiral binaphthol linkages, and three centrally asymmetric carbon atoms of a trialkanolamine core, is described. These new cages constitute a novel family of hemicryptophanes, which combine three classes of chirality. Their absolute configuration was successfully assigned by a chemical correlation method to overcome the signals overlap in the ECD spectra of the binaphtol and CTV units. Stereoselective recognition of glucose and mannose derivatives was investigated with these new chiral cages. Excellent enantio- and diastereoselectivity were reached, since in some cases, both exclusive enantio- and diastereo-discrimination have been observed. In addition, compared with the most relevant hemicryptophanes, these new cages also exhibit improved binding affinities. [ABSTRACT FROM AUTHOR]

The hydrogen-bonding activation of C=O bonds by azaphosphatranes was explored in a model reaction, i.e., the ring-opening polymerization of lactide. The polymerization process was controlled, and allowed the preparation of polylactides with narrow dispersity under mild conditions (20 °C, 24 h, 10 mol-% catalyst loading). Interestingly, the steric hindrance of azaphosphatranes, as globular rigid structures, prevents any undesired interaction with the tertiary amine cocatalysts, as shown by X-ray analysis and semi-empirical calculations. In contrast to their organocatalytic activity in the CO2/epoxide reaction, all of the phosphonium derivatives tested were found to be efficient catalysts in this ROP benchmark reaction. [ABSTRACT FROM AUTHOR]

A convenient and efficient gram-scale synthesis for enantiopure hemicryptophane-tren (tren=tris(2-aminoethyl)amine) derivatives has been developed. The four-step synthesis is based on the optical resolution of a key intermediate, cyclotriveratrylene, for which the energy barrier for racemization has been measured to ensure that no racemization occurs during the two last steps of the synthetic pathway. The assignments of the absolute configurations have been performed by electronic circular dichroism and the enantiopurity was determined by NMR spectroscopy in the presence of enantiopure camphor sulfonic acid. To highlight the interest of such compounds, the recognition of norephedrine neurotransmitter was investigated and showed a remarkable enantioselectivity towards the C3 symmetrical hosts. Finally, this highly modular synthetic pathway was used to provide eight enantiopure hemicryptophanes with different sizes, shapes, and functionalities. These results underline the high potential of this approach, which could lead to many applications in chiral recognition or asymmetric supramolecular catalysis. [ABSTRACT FROM AUTHOR]

In this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F- in DMSO or more competitive media (DMSO containing 10% water). In the presence of F-, the yellow and non-fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards F- was attributed to the formation of N-heterocyclic carbene deprotonated by F-, which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments. [ABSTRACT FROM AUTHOR]

The endohedral functionalization of a molecular cage by an azaphosphatrane unit has allowed for the creation of highly engineered catalytic cavities for efficient conversion of CO 2 into cyclic carbonates. Strong structure/activity/stability correlations have been demonstrated by careful adjustment of the size, shape, and electronic properties of the hemicryptophane host. [ABSTRACT FROM AUTHOR]

ABSTRACT Enantiopure hemicryptophanes efficiently discriminate chiral ammonium neurotransmitters. The ephedrine and norephedrine molecules associate with hemicryptophane hosts to form 1:1 and 1:2 host-guest complexes. Binding constants are determined by fitting the 1H (NMR) titration curves to give β1 and β2 values, which are used to characterize the diastereomeric and enantiomeric discriminating potentials of the hosts. Chirality 25:47-479, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The use of azaphosphatrane derivatives, which are the acidic counterparts of the well-known proazaphosphatrane superbases (also named Verkade's superbases), are found to function as phase-transfer catalysts. In four representative protocols of phase-transfer catalytic reactions-two alkylations of enolates, one generation of carbene, and one oxidation of an electrophilic alkene-azaphosphatranes act as catalysts in biphasic heterogeneous media. [ABSTRACT FROM AUTHOR]

ABSTRACT The hemicryptophane racemate (±)- M-1 P-1 was optically resolved by semipreparative HPLC on Chiralpak IC column. The absolute configuration of each isolated enantiomer was established from the analysis of their electronic circular dichroism spectra. Enantiodifferentiation of the chiral cationic cage (±)- M-1 P-1 was evidenced in solution using Δ-TRISPHAT as chiral solvating agent, and the diastereomeric associations were observed in 1H and 31P NMR spectra. Chirality 24:1077-1081, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]