Mass spectrometric study of oligourea macrocycles and their anion binding behavior

Two series, one of tris‐urea macrocycles and another of hexakis‐urea macrocycles, are examined by (tandem) Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometry with respect to their fragmentation patterns and anion binding properties. All macrocycles are based on two different building blocks, one of which is a very rigid xanthene unit and the other one is a more flexible diphenyl ether. The composition and the sequence of these units thus determine their flexibility. During the fragmentation of deprotonated oligourea macrocycles in the gas phase, one urea N? CO bond is cleaved followed by a scrambling reaction within the macrocycle structure. Consequently, fragments are observed that deviate from those that would be expected from the sequence of the subunits. Interesting anion binding properties involve the simultaneous recognition of two chloride anions by one of the hexakis‐urea macrocycles, whose flexibility allows this host to form a double‐helical structure. Flexibility also determines which of the hexameric receptors bears a high sulfate affinity. The interaction energy between some of the macrocycles and sulfate is high enough to even stabilize the intrinsically unstable sulfate dianion. Copyright © 2009 John Wiley & Sons, Ltd.     

Glycoclusters presenting lactose on calix[4]arene cores display trypanocidal activity

A new series of water-soluble tetravalent glycoclusters incorporating β-lactosyl residues attached to a central calix[4]arene core was synthesised using azide-alkyne Cu(I)-catalysed cycloaddition (‘click chemistry’). Carbohydrate moieties were attached either to the upper or lower rim of rigid cone-shaped or partial cone macrocycles via 14-21 atom spacer arms. The glycoclusters with a C₄-symmetrical arrangement of β-lactosyl residues showed trypanocidal activity, with one of them showing comparable activity to established anti-trypanosomal drug benznidazole in in vitro anti-parasite assays.     

Tunable organic particles: An efficient approach from solvent-dependent Schiff base macrocycles

The synthesis of cyclopolymers upon controlling the degree of macrocyclic polymerization, followed by the discovery of new properties has attracted increasing attention in supramolecular chemistry. Herein, a Schiff-base condensation method performed at room temperature was used to control the formation of [1 + 1] and [2 + 2] macrocycles. In pure MeOH, the isomer [1 + 1] macrocycles were synthesized and organic particles such as dendritic, rods, and solid microspheres were directly precipitated from the reaction solution. The [1 + 1] macrocycles can be efficiently converted into their corresponding [2 + 2] macrocycles accompanied by the tunable morphology of the organic particles when n-hexane was added to the MeOH solution. Further studies showed that these organic particles have potential application toward the selective removal of Cd²⁺ ions with different adsorption ability in MeOH solution.     

Synthesis and properties of a graphene-like macrocycle based on tetraphenylethene

In this work, tetraphenylethene macrocycles are selectively synthesized in one step from McMurry coupling reaction of 1,1-bis(4-phenylcarbonyl)-2,2-diphenylethene in 45% overall yield. A more planar cyclized compound can be obtained by oxidization of tetraphenylethene macrocycles with iron (III) chloride in nitromethane. Their unusual optical properties and electrical properties are explored. The measured mobilities are 0.7022 and 0.0055 cm² V⁻¹ s⁻¹, respectively. The decomposition temperatures are also measured by thermal gravimetric analysis as, respectively 342 °C and 455 °C, indicating good thermal stabilities. The understanding of the structure and properties will benefit to the chemical synthesis of graphene.     

Size-Induced Highly Selective Synthesis of Organometallic Rectangular Macrocycles and Heterometallic Cage Based on Half-Sandwich Rhodium Building Block

The controlled synthesis of organometallic supramolecular macrocycles cages remains interesting and challenging work in the field of supramolecular chemistry. Here, two tetranuclear rectangular macrocycles and an octuclear cage were designed and synthesized utilizing a rigid and functionalized pillar linker, 2,6-bis(pyridin-4-yl)-1,7-dihydrobenzo [1,2-d:4,5-d′]diimidazole (BBI4PY) based on three half-sandwich rhodium building blocks bearing different sizes. X-ray crystallography in combination with ¹H NMR spectroscopy elucidated that the two building blocks with shorter spacers only result in rectangular macrocycles. However, the building block of bulkier size to avoid the π-π stacking interactions between two ligands BBI4PY led to the formation of an octuclear cage complex. The latter cage contains two types of metal ions, namely Rh³⁺ and Cu²⁺, showing significant characteristics of heterogeneous metal-assembling compounds. In addition, the cage accommodates two free isopropyl ether solvent molecules, thus displaying host–guest behavior.     

Halogen bonding-driven formation of supramolecular macrocycles and double helix

Halogen bonding has been used to hold two hydrogen bonded aromatic amide foldamers to form supramolecular macrocycles.     

Novel chiral macrocycles containing two electronically interacting arylene chromophores

Novel chiral macrocycles consisting of two rigid oligoarylene rods and two chiral spiroindane clips have been synthesized by condensation of spiroindane diols and CF3-activated alpha-omega-difluorooligoaryls. Since a broad variety of planar aromatic macrocycles is known, our non-planar, chiral rings represent a new class of macrocyclic compounds. The first two examples, which contain quaterphenylene and diphenylbithiophene rods, are presented in this communication; for one of them a crystal structure is given. The chiroptical properties of the macrocycles can be interpreted as an interplay of the "intra-rod" helicity of individual oligoarylene rods and the "inter-rod" helicity between both chromophores of the macrocycle. The macrocycles can act as chiral dopands of commercially available, and novel, polymeric nematic liquid crystals (emissive polyfluorenes). The "intra-rod" helicity of individual oligoarylene rods is the main feature in determining the resulting helical twisting power (HTP). The cholestric induction in mesogenic, emissive polyfluorenes is of special interest for a realization of electronic devices that have a circularly polarized electroluminescence. The results are also important for an understanding of larger ensembles of chiral rodlike molecules, especially their pi-pi interactions.     

Can a Proton be Encapsulated in Tetraamido/Diamino Quaternized Macrocycles in Aqueous Solution and Electric Field?

The proton‐binding behavior of solvated tetraamido/diamino quaternized macrocyclic compounds with rigid phenyl and flexible phenyl bridges in the absence or presence of an external electric field is investigated by molecular dynamics simulation. The proton can be held through H‐bonding interactions with the two carbonyl oxygen atoms in macrocycles containing rigid (phenyl) and flexible (propyl) bridges. The solute–solvent H‐bonding interactions cause the macrocyclic backbones to twist to different extents, depending on the different bridges. The macrocycle with the rigid phenyl linkages folds into a cuplike shape due to π–π interaction, while the propyl analogue still maintains the ellipsoidal ringlike shape with just a slight distortion. The potential energy required for proton transfer is larger in the phenyl‐containing macrocycle than in the compound with propyl units. When an external electric field with a strength of 2.5 V nm^?1 is exerted along the carbonyl oxygen atoms, a difference in proton encircling is exhibited for macrocycles with rigid and flexible bridges. In contrast to encapsulation of a proton in the propyl analogue, the intermolecular solute–solvent H‐bonding and intramolecular π–π stacking between the two rigid phenyl spacers leads to loss of the proton from the highly distorted cuplike macrocycle with phenyl bridges. The competition between intra‐ and intermolecular interactions governs the behavior of proton encircling in macrocycles.     

Rigid, cross-conjugated macrocycles: a cyclic alternative to 4,4'-bipyridines in supramolecular chemistry

[structure: see text]. The synthesis of two fully conjugated, rigid macrocyclic analogues to 4,4'-bipyridine is described. The use of these macrocycles in self-assembly processes is demonstrated by axial coordination to metalloporphyrins, and one system (R = Me) has been characterized by single-crystal X-ray crystallography.     

CyClick Chemistry for the Synthesis of Cyclic Peptides

Here, we report a novel “CyClick” strategy for the macrocyclization of peptides that works in an exclusively intramolecular fashion thereby precluding the formation of dimers and oligomers via intermolecular reactions. The CyClick chemistry is highly chemoselective for the N‐terminus of the peptide with a C‐terminal aldehyde. In this protocol, the peptide conformation internally directs activation of the backbone amide bond and thereby facilitates formation of a stable 4‐imidazolidinone‐fused cyclic peptide with high diastereoselectivity (>99 %). This method is tolerant to a variety of peptide aldehydes and has been applied for the synthesis of 12‐ to 23‐membered rings with varying amino acid compositions in one pot under mild reaction conditions. The reaction generated peptide macrocycles featuring a 4‐imidazolidinone in their scaffolds, which acts as an endocyclic control element that promotes intramolecular hydrogen bonding and leads to macrocycles with conformationally rigid turn structures.     

Synthesis and solid-state organization of coil-ring-coil block copolymers

Shape-persistent macrocycles based on the phenyl-ethynyl-butadienyl backbone containing two extraannular hydroxyl groups were prepared by the oxidative coupling of the appropriate phenylethynyl oligomers. Carbodiimide-directed coupling with independently synthesized polystyrene carboxylic acid oligomers led to ABA coil-ring-coil block copolymers in which the central macrocycle serves as rigid and the polystyrene oligomers as flexible elements. Depending on the size of the coil blocks, these structures aggregate in cyclohexane into supramolecular hollow cylindrical brushes in which the rigid core is surrounded by the flexible matrix. However, in the solid state it is not possible to identify a morphology in which isolated channels based on aggregated macrocycles are embedded in a matrix of polystyrene. Detailed X-ray and electron diffraction studies on samples prepared from a solution in cyclohexane under equilibrium conditions show that the material adopts a lamellar morphology in the solid state in which columns of macrocycles are aggregated into layers which are separated by polystyrene.     

Synthesis and structures of pyrimidinophanes containing a nitrogen atom in the bridge

The reactions of 1,3-bis(5-bromopentyl)-5-methyl-or 1,3-bis(5-bromopentyl)-6-methyl-uracil with benzylamine afforded pyrimidinophanes containing the nitrogen atom in the polymethylene bridge. Single-crystal X-ray diffraction study and NMR and UV spectroscopic study in solution demonstrated that the phenyl and uracil fragments in the macrocycles are in spatial proximity. Unlike the known macrocycles containing the pyrimidine ring, the pyrimidinophanes under study are conformationally rigid. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 539–547, March, 2006.     

A new hexaaminomacrocycle for ditopic binding of bromide

A hexaaminomacrocycle L, containing four secondary and two tertiary amines has been synthesized and crystallized with hydrobromic acid. The structural analysis of the bromide complex suggests that the ligand in its tetraprotonated form, is involved in coordinating two bromides from both the sides via hydrogen bonding interactions with N?Br⁻ distance of 3.351 Å, forming a ditopic complex. The other two bromides are outside the cavity, and singly bonded to the macrocycle. The molecules are packed showing layer structures in which the internal bromides are locked between the layers of macrocycles. The bromide anions are coordinated alternatively by one and two hydrogen bonds with the protonated amines from the two adjacent macrocycles.     

Synthesis of rigid and C2-symmetric 18-crown-6 type macrocycles bearing diamide–diester groups: enantiomeric recognition for α-(1-naphthyl)ethylammonium perchlorate salts

A series of rigid and chiral C₂-symmetric 18-crown-6 type macrocycles (S,S)-4, (S,S)-5, (S,S)-6 and (R,R)-2 bearing diamide–ester groups were synthesized. The binding properties of these macrocycles were examined for α-(1-naphthyl)ethylammonium perchlorates salts by an ¹H NMR titration method. Taking into account the host employed, important differences were observed in the K_a values of (R)- and (S)-enantiomers of guests for macrocycles (S,S)-4 and (S,S)-6, K_S/K_R = 3.6, and K_S/K_R = 0.1 (K_R/K_S = 10.3) ΔΔG = 3.19 and ΔΔG = ?5.77 kJ mol^?1, respectively. The results indicated excellent enantioselectivity of macrocyclic (S,S)-6 towards the enantiomers of α-(1-naphthyl)ethylammonium perchlorate salts.     

Synthesis of phosphocyclic 2,2′,7,7′-tetrahydroxydinaphthylmethane derivatives

Two types of phosphocyclic derivatives were synthesized by phosphorylation of 2,2′,7,7′-tetrahydroxydinaphthylmethane with triamidophosphites: triphosphorus containing compounds with a phosphocine ring and two acyclic diamidophosphite fragments, and tetraphosphorus-containing macrocycles with a 24-membered ring and two eight-membered phosphorus rings. It was shown that interaction of triphosphorus compounds with resorcinarene gives tetraphosphorus macrocycles.     

Hydrogen bonded arylamide-linked cholesteryl dimesogenic liquid crystals: a study of the length and side chain effects

Dimesogenic compounds 1a-c, 2a-i, and 3, that are composed of a hydrogen bonding-induced straight arylamide spacer and two appended cholesterol groups, have been designed and synthesized. The backbones of the rigid spacers of 1a-c, 2a-i, and 3 contain one, three, and five benzene units, which bear two, six, and ten alkoxyl (methoxyl, n-octoxyl, or n-dodecoxyl) groups, respectively. The thermal and optical properties of the compounds are investigated by using the differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (PXRD) analysis. It is revealed that 1a-c exhibit one or two liquid crystalline (LC) phases, 2a-i exhibit no, one or two LC phases, while 3 exhibits one LC phase in a wide temperature range. Generally, the more and longer alkoxyl chains facilitate the formation of the LC phases at low temperature. Notably, compound 2g, which bears two methoxyl and four dodecoxyl groups, displays a blue-red color change during both the heating and cooling cycle. The result illustrates that dimesogens with large rigid spacers can exhibit different LC phases when long aliphatic chains are appended to balance the strong stacking of the rigid backbones.     

Pre-organization-mediated macrocylization: efficient synthesis and structural investigations of BINOL-m-phenylenediamine-derived macrocycles

This letter describes a serendipitous discovery of an efficient synthetic route to BINOL-m-phenylenediamine-derived macrocycles. These macrocycles are quickly accessible in an one-pot procedure by the direct condensation of (R) and (S) BINOL bis-acids with suitably substituted m-phenylenediamine analogs. Structural investigations by single crystal X-ray crystallography and solution-state NMR studies provided convincing evidence of their intramolecular hydrogen bonding arrangement and rigid structural architecture. The striking feature of these macrocycles is their ready accessibility in optically pure form coupled with their ease of synthesis.     

A Tetrameric Cage with D2h Symmetry through Alkyne Metathesis

Shape‐persistent covalent organic polyhedrons (COPs) with ethynylene linkers are usually prepared through kinetically controlled cross‐coupling reactions. The high‐yielding synthesis of ethynylene‐linked rigid tetrameric cages via one‐step alkyne metathesis from readily accessible triyne precursors is presented. The tetrameric cage contains two macrocyclic panels and exhibits D_2h symmetry. The assembly of such a COP is a thermodynamically controlled process, which involves the initial formation of macrocycles as key intermediates followed by the connection of two macrocycles with ethynylene linkages. With a large internal cavity, the cage exhibits a high binding selectivity toward C₇₀ (K=3.9×10³ L mol^?1) over C₆₀ (no noticeable binding).     

Liquid crystalline paracyclophane derivatives

Various paracyclophane derivatives incorporating 4,4'-biphenyl, 2,5-diphenyl-1,3,4-thiadiazole, phenyl benzoate and 2,6-disubstituted naphthyl rigid cores were synthesized and their mesomorphic behaviour was studied using polarizing microscopy, DSC and X-ray diffraction. Most of these macrocyclic compounds possess liquid crystalline properties with unexpectedly high clearing temperatures compared to those of conventional calamitic mesogens. In this way, the coupling of two appropriate rigid units using flexible chains to form a macrocycle constitutes a new and powerful approach towards mesophase induction and stabilization. The types of mesophase formed by these macrocycles do not depend only on the nature of the bridging chains, but also strongly on the structure of the rigid aromatic system. The smectic A phase and the E phase are formed by polyetherbiphenylophanes. Poly-ethercyclophanes incorporating the 2,5-diphenylthiadiazole rigid core form nematic and smectic C phases. The nematic phase is the only mesophase when the rigid core is the phenyl benzoate unit. No mesomorphic properties could be detected for macrocycles which featured either the benzyl phenyl ether moiety or the 2,6-disubstituted naphthalene unit in their constitution.     

Cationic shape-persistent macrocycles: the unexpected formation of a nano-size supramolecular dimer

Shape-persistent macrocycles with a rigid pyridyl core and a flexible oligo-alkyl corona aggregate to some extent in nonpolar solvents to form large (tubular) aggregates. To increase the assembling tendency, the intraannular pyridyl groups of the macrocycles were alkylated. Unexpectedly, the quarternized macrocycles show no tendency at all to form tubular micellar-like structures but form well-defined dimers, as determined by X-ray and dynamic light scattering.