Large oligocyclic cavities for strong cation complexation

Transformation of a [4+6] Salicylbisimine Cage to Chemically Robust Amide Cages

In recent years, interest in shape-persistent organic cage compounds has steadily increased, not least because dynamic covalent bond formation enables such structures to be made in high to excellent yields. One often used type of dynamic bond formation is the generation of an imine bond from an aldehyde and an amine. Although the reversibility of the imine bond formation is advantageous for high yields, it is disadvantageous for the chemical stability of the compounds. Amide bonds are, in contrast to imine bonds much more robust. Shape-persistent amide cages have so far been made by irreversible amide bond formations in multiple steps, very often accompanied by low yields. Here, we present an approach to shape-persistent amide cages by exploiting a high-yielding reversible cage formation in the first step, and a Pinnick oxidation as a key step to access the amide cages in just three steps. These chemically robust amide cages can be further transformed by bromination or nitration to allow post-functionalization in high yields. The impact of the substituents on the gas sorption behavior was also investigated.

Nanopatterned superlattices in self-assembled C2 -symmetric oligodimethylsiloxane-based benzene-1,3,5-tricarboxamides

The synthesis of C3 - and C2 -symmetric benzene-1,3,5-tricarboxamides (BTAs) containing well-defined oligodimethylsiloxane (oDMS) and/or alkyl side chains has been carried out. The influence of the bulkiness of the oDMS chains in the aggregation behavior of dilute solutions of the oDMS-BTAs in methylcyclohexane was studied by temperature-dependent UV spectroscopy. The formation of hierarchically self-assembled aggregates was observed at different BTA concentrations, the tendency of aggregation increases by shortening or removing oDMS chains. Chiral BTAs were investigated with circular dichroism (CD) spectroscopy, showing a stronger tendency to aggregate than the achiral ones. Majority rules experiments show a linear behavior consistent with the existence of a high mismatch penalty energy. The most efficient oDMS-BTAs organogelators have the ability to form stable organogels at 5 mg mL(-1) (0.75 wt %) in hexane. Solid-state characterization techniques indicate the formation of an intermolecular threefold hydrogen bonding between adjacent molecules forming thermotropic liquid crystals, exhibiting a hexagonal columnar organization from room temperature to above 150 °C. A decrease of the clearing temperatures was observed when increasing the number and length of the oligodimethylsiloxane chains. In addition to the three-fold hydrogen bonding that leads to columnar liquid crystalline phase, segregation between the oDMS and aliphatic chains takes place in the BTA functionalized with two alkyl and one oDMS chain leading to a superlattice within the hexagonal structure with potential applications in lithography.

Benzene-1,3,5-tricarboxamide: a versatile ordering moiety for supramolecular chemistry

After their first synthesis in 1915 by Curtius, benzene-1,3,5-tricarboxamides (BTAs) have become increasingly important in a wide range of scientific disciplines. Their simple structure and wide accessibility in combination with a detailed understanding of their supramolecular self-assembly behaviour allow full utilization of this versatile, supramolecular building block in applications ranging from nanotechnology to polymer processing and biomedical applications. While the opportunities in the former cases are connected to the self-assembly of BTAs into one-dimensional, nanometer-sized rod like structures stabilised by threefold H-bonding, their multivalent nature drives applications in the biomedical field. This review summarises the different types of BTAs that appeared in the recent literature and the applications they have been evaluated in. Currently, the first commercial applications of BTAs are emerging. The adaptable nature of this multipurpose building block promises a bright future.

Synthesis and thermodynamic evaluation of mixed hexadentate linear iron chelators containing hydroxypyridinone and terephthalamide units

A series of new linear iron chelators containing hydroxypyridinone and terephthalamide (TAMmeg) moieties have been prepared. All are hexadentate ligands composed of a systematically varied combination of methyl-3,2-hydroxypyridinone and 2,3-dihydroxyterephthalamide binding units; most are based on a spermidine scaffold, but one incorporates the bifunctional 2,3-dihydroxyterephthalamide unit as an integral part of the backbone. Protonation and ferric iron complex formation constants have been determined from solution thermodynamic studies, giving log beta(110) values of 25.7, 30.7, 36.3, 43.8, and 45.0, respectively. The ferric complexes display reversible reduction potentials from -276 to -1032 mV (measured relative to the normal hydrogen electrode) in alkaline solution. The incremental replacement of hydroxypyridinone units by terephthalamide binding groups progressively reduces the ligand acidity, markedly increases the iron-chelate stability, and improves the selectivity for the ferric ion over the ferrous ion. While the majority of iron chelators forming very stable ferric complexes are based on a tripodal backbone such as TREN, the ferric 5-LIO(TAMmeg)(2)(TAM) complex, despite its nontripodal scaffold, is one of the most stable iron complexes yet reported. Moreover, the high affinity for the ferric ion of the discussed linear ligands strongly correlates with their ability to remove iron in vivo.

Terephthalamide-Containing Analogues of TREN-Me-3,2-HOPO

A series of terephthalamide-containing analogues based on TREN-Me-3,2-HOPO have been prepared. These analogues contain one, two, or three bidentate 2,3-dihydroxyterephthalamide (TAM) units in place of the 3,2-hydroxypyridinone (HOPO) units on the parent hexadentate ligand. One representative ligand in the series, TRENHOPOTAM2, and its gallium complex have been structurally characterized by X-ray diffraction. TRENHOPOTAM2 crystallizes in the monoclinic space group P2(1)/c with cell parameters a = 16.0340(17) A, b = 17.0609(18) A, c = 16.0695(17) A, beta = 113.837(2) degrees, and Z = 4. Ga[TRENHOPOTAM2] also crystallizes in the monoclinic space group P2(1)/c, with cell parameters a = 16.3379(14) A, b = 15.2722(13) A, c = 19.4397(17) A, beta = 91.656(2) degrees, and Z = 4. The conformation of the TRENHOPOTAM2 ligand structure suggests that the ligand is predisposed for metal ion binding. The aqueous protonation and ferric ion coordination chemistry of all ligands in the series were examined using potentiometric and spectrophotometric methods, giving log formation constants of 34.6(2) (beta110) and 38.8(2) (beta111) for the ferric TRENHOPO2TAM complexes, 41.0(3) (beta110) and 45.4(3) (beta111) for the ferric TRENHOPOTAM2 complexes, and 45.2(2) (beta110) and 50.9(2) (beta111) for the ferric TRENTAM3 complexes. These thermodynamic data confirm that adding terephthalamide units to a hydroxypyridinone-containing ligand tends to increase the stability of the resulting iron complex. The ferric TRENTAM3 complex is one of the most stable iron complexes yet reported.

Novel seco cyclopropa[c]pyrrolo[3,2-e]indole bisalkylators bearing a 3,3'-arylenebisacryloyl group as a linker

We synthesized the novel seco cyclopropa[c]pyrrolo[3,2-e]indole (CPI) bisalkylators and evaluated their antitumor activity. Among these derivatives, 11a (AT-760), in which the two seco 3-methoxycarbonyl-2-trifluoromethyl CPI (MCTFCPI) moieties are connected with a 3,3'-(1,4-phenylene)bisacryloyl group, was found to exhibit more potent cytotoxicity and antitumor activity against HeLaS3 human uterine cervix carcinoma cells and Colon 26 adenocarcinoma cells, respectively, than 8 (bizelesin, U-77,779). It also appeared that compound 11a exhibits improved in vivo efficacy in the human colon CX-1 model when compared to either compound 8 or mitomycin C (MMC). Efficacious doses for 11a were found to be 2-fold lower than those for 8.