Conformational control of selectivity and stability in hybrid amide/urea macrocycles

The anion-binding properties of two similar hybrid amide/urea macrocycles containing either a 2,6-dicarboxamidophenyl or a 2,6-dicarboxamidopyridine group are compared. Significant differences in anion affinity and mode of interaction with anions are attributed to the presence of intramolecular hydrogen bonds in the pyridine system. In fact, remarkably, the phenyl macrocycle undergoes amide hydrolysis under neutral conditions in DMSO/water. The anion binding abilities of the receptors are compared to those of acyclic analogues of the macrocycles that show that the phenyl receptor behaves in a similar fashion to acyclic urea-containing receptors (i.e., showing little selectivity amongst oxo anions), whilst the pyridine-containing receptor shows a high affinity and selectivity for carboxylates.     

Synthesis of mono- and bibrachial naphthalene-based macrocycles with pyrene or ferrocene units for anion detection

Three bibrachial cyclobisintercaland-type macrocycles with a 2,6-naphthylene scaffold and pyrene, ferrocene, or primary amino groups in side chains were synthesized by a [2+2]-cyclocondensation of functionalized diethylenetriamine derivatives with naphthalene-2,6-dialdehyde, whereas their monobrachial counterparts were prepared by a [1+1]-cyclocondensation of polyamines with a corresponding dialdehyde building block. The pyrene-functionalized macrocycles are able to bind orthophthalate and terephthalate anions in aqueous medium, as monitored by the changes in their fluorescence (excimer or monomer) properties.     

Synthesizing Macrocycles under Thermodynamic Control – Dynamic Combinatorial Libraries and Templates

An effective way to synthesize macrocycles using a dynamic combinatorial library is demonstrated for the reaction of pyridine-2,6-dicarbaldehydes with several long diamines. According to the template ions present, a given library can be shifted towards several macrocycles as desired.     

Tuning the (Chir)Optical Properties and Squeezing out the Inherent Chirality in Polyphenylene-Locked Helical Carbon Nanorings

Distorting linear polyaromatic hydrocarbons (PAHs) out of planarity affects their physical properties and breaks their symmetry to induce inherent chirality. However, the chirality cannot be achieved in large distorted PAHs-based macrocycles due to a low racemization barrier for isomerization. Herein, we report the precise synthesis and tuning size-dependent (chir)optical properties of a new class of chiral PAHs-containing conjugated macrocycles (cyclo[n]paraphenylene-2,6-anthrylene, [n]CPPAn_2,6 ; n=6–8). Their inherent chiralities were squeezed out in small anthrylene-based macrocycles. Efficient resolutions for chiral enantiomers with (P)/(M)-helicity of small [6-7]CPPAn s were achieved by HPLC. Interestingly, these macrocycles showed enriched size-dependent physical, chiral, and (chir)optical properties. Theoretical calculations indicate that these macrocycles have high strain energy (E_strain=60.8 to 73.4 kcal/mol) and very small E_gap (∼3.0 eV). Notably, these enantiomers showed strong chiroptical properties and dissymmetry factors (|g_abs| and |g_lum|∼0.01 for an enantiomer of [6]CPPAn_2,6 ), which can give them potential applications in optically active materials.     

Surface modification of activated polymeric matrices by dendritic attachments

Aware of the growing interest in materials that exhibit specific physiochemical properties and potential applications, we focused our work on modifying commercial agarose with polyfunctional dendrons capable of molecular recognition through hydrogen bonding. 2,6‐Di(acylamino)pyridine moieties within the internal superstructure of dendritic macromolecules have been reported to be capable of forming H‐bonded complexes with imide groups, such as barbituric acid and its derivatives. We report the synthesis of new dendrons possessing multiple 2,6‐di(acylamino)pyridinyl sites, each capable of molecular recognition, and the development of new polymeric supports of an activated agarose matrix by surface modification. From comparative studies of the beads modified by different dendrons, we found improved results in those dendritic supports possessing 2,6‐di(acylamino)pyridinyl moieties, except when their juxtaposition between the groups promoted inner H bonds. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2779–2786, 2000     

One-pot synthesis of [1+1] and 62-membered [2+2] Schiff base macrocycles

New [1+1] and 62-membered [2+2] Schiff base macrocycles containing a 2,6-diamidopyridine subunit have been synthesized by condensation reaction of the precursors pyridine-2,6-dicarboxamide and 1,10-bis(20-formylphenyloxy)decane in the presence of phosphoric acid via a one-pot process. The cyclocondensed products were effectively isolated by gel column chromatography and characterized by ~1H NMR, FTIR, mass spectrometry and X-ray analysis. The two macrocycles have a twisted structure, and not an open ‘circular' conformation in the solid state.     

Synthesis and characterization of pyridine-based polyamido-polyester optically active macrocycles and enantiomeric recognition for D- and L-amino acid methyl ester hydrochloride

Five new chiral macrocycles, 3a-e, have been prepared by the acylation cyclization of chiral diamine dihydrobromide intermediates 2a-c with 2,6-pyridinedicarbonyl dichloride in highly diluted solution at room temperature. The chiral diesters 1a-c needed for the preparation of the macrocycles were obtained from condensation of corresponding N-(Z)-L-amino acids and 2,6-bishydroxymethyl pyridine in the presence of DCC and DMAP. The enantiomeric recognition of chiral macrocycles 3a-e for D- and L-amino acid methyl ester hydrochlorides has been characterized by fluorescence spectra, which indicate that some of them exhibited significant chiral recognition for the enantiomers of D- and L-amino acid methyl ester hydrochlorides. The stoichiometry and binding constants of 3a-L-Am(2) and 3c-L-Am(2) complexes have been determined. An X-ray analysis of the chiral macrocycle 3b show that the chiral ligand is rather rigid and strained.     

The syntheses of nitrogen‐oxygen donor macrocycles containing pyridine ring

Five new nitrogen‐oxygen mixed donor macrocycles have been prepared by condensation of 2,6‐bis [(2‐formylphenyl)oxymethyl]pyridine with different diamino compounds in hot methanol, followed by a one‐pot reduction of the intermediate bis‐Schiff base. All the macrocycles were identified by elemental analysis, and ir, uv, and nmr spectroscopy.     

New 2+2, 3+3 and 4+4 macrocycles derived from 1,2-diaminocyclohexane and 2,6-diformylpyridine

Two new Schiff base macrocycles - a 4+4 condensation product and a meso-type 2+2 condensation product - were obtained in a reaction of trans-1,2-diaminocyclohexane and 2,6-diformylpyridine. Reduction of these compounds led to the corresponding 4+4 and 2+2 macrocyclic amines. The macrocycles were characterised by NMR spectroscopy and electrospray mass spectrometry. The symmetry and stereochemistry of these macrocycles, as well as of new 3+3 and 4+4 diastereomers identified in solution, has been established. X-Ray structures of the 2+2 and 4+4 Schiff base macrocycles confirm the configurations determined on the basis of spectroscopic investigations. The crystal structures reveal that the centres of the square-shaped 4+4 macrocycles form channels as a result of columnar stacking.     

Synthesis of Novel C2—Symmetric Chiral Polyamide Macrocycles Containing Pyridyl Side—arm

Three novcl C2-symmetic macrocycles containing pyridyl units have been prepared by the cyclic condensation of chiral diamide intermediates with 2,6-pyridinedicarbonyl dichloride in highly diluted solution at room temperature.     

Thiocarbohydrazide as ``Diamine' to Construct Macrocyclic and Side-Off Compartmental Ligands

New dinuclear complexes of macrocycles/macroacycles/oximeshaving a reactive peripheral thioketo functional group were synthesized using2,6-diformyl-p-cresol as parent compound and thiocarbohydrazide/variousdiamines as side arms. Thioenolization and subsequent coordination to metal ionof the thio-keto sulfur is observed in asymmetric macrocycles and oxime complexes,while it is kept away from the coordination sphere in symmetric macrocycles. Magnetic susceptibility measurements over the range 7–300 K confirm that the copper(II) centersof the symmetric and asymmetric macrocycles are antiferromagnetically coupled, withvalues for the exchange coupling constant J through the phenolate oxygens of -610 to-580 cm^-1, respectively. The ligands and their complexes are found to be excellent fungistatic agents.     

Rigid optically-active D2 and D3 macrocycles

The synthesis and characterization of novel optically-active macrocycles, obtained by esterification reaction from a binaphthyl-containing diol and phthalic or terephthalic acids, and possessing overall D2 or D3 symmetry, is described.     

Efficient proton-templated synthesis of 18- to 38-membered tetraimino(amino)diphenol macrocyclic ligands: structural features and spectroscopic properties

A whole range of Robson-type tetraiminodiphenol macrocyclic ligands have been prepared as their perchlorate salts [H4L](ClO4)2 in high yield (ca. 90%) by a single-step [2 + 2] condensation reaction between 4-methyl(or tert-butyl)-2,6-diformyl(or diacyl)phenols and alpha,omega-diaminoalkanes (C2-C12) in the presence of acetic acid and NaClO4. The reduction of these 18- to 38-membered macrocyclic salts with NaBH4 have afforded corresponding tetraaminodiphenol macrocycles H2L'. The X-ray crystal structures of two of the tetraiminodiphenol macrocycles with the C2 and C4 lateral chains have been determined, and the optimized configurations for all of the macrocycles have been obtained by molecular mechanics calculations. The macrocycles have been characterized by elemental analysis and by IR, absorption, emission, and NMR spectroscopic study. The protonated tetraiminodiphenol macrocycles exhibit strong fluoroscence in methanol, acetonitrile, and nitromethane and undergo quenching when treated with triethylamine. The neutral macrocycles H2L, isolated by treating [H4L](ClO4)2 with excess of triethylamine, lack luminescence, as do the reduced tetraaminodiphenol macrocycles H2L'. The hydrolytic cleavage of [H4L](ClO4)2 has been studied.     

Synthesis of nano-scale shape-persistent macrocycles via hydrogen bonding-promoted formation of amide and hydrazone bonds

This paper describes the synthesis of two series of rigid macrocycles from hydrogen bonding-induced folded aryl amide and hydrazone oligomers that bear two amines or one amine and one aldehyde. The diamines reacted with diacyl chloride to produce amide macrocycles, whereas the latter underwent self-coupling reactions to afford imine macrocycles. DFT calculations revealed that the new macrocycles possess rigid planar conformations and their cavity diameters were estimated to be 1.86 nm–2.75 nm.     

Hydrindacene‐Based Acetylenic Macrocycles with Horizontally and Vertically Ordered Functionality Arrays

The macrocyclization of 2,6‐diethynyl hydrindacenes ( 1 ) with functional groups at mutually perpendicular positions results in the formation of novel macrocycles which, as a result of the hindered rotation of the hydrindacene units, possess directionally persistent peripheral functionalities. The two hydrindacene units in the dimer macrocycle ( 2 ) have been shown to interact electronically through their respective butadiyne moieties, whereas the trimer macrocycle ( 3 ) demonstrates a moderate degree of geometrical flexibility as a result of the five‐membered hydrindacene rings. In addition, these trimer macrocycles contain a central cavity suitably sized for the inclusion of various solvent molecules. These new macrocycles can be further modified by introducing π‐conjugated side groups, such as styryl and thienyl groups, as well as by attaching a variety of peripheral ester groups.     

Novel podands and macrocycles with diacetal (tetraoxadecalin) cores: synthesis, structure, stereochemistry and cation inclusion

A series of functionalized 2,6-dialkyl-cis-1,3,5,7-tetraoxadecalin podands (3-10, alkyl = hydroxy-, mesyloxy-, halo-, azido- and aminomethyl and -ethyl) were prepared, characterized, and used as precursors for a new and interesting class of macrocycles and cryptands (12-21), with the aim to use these as host-guest inclusion systems. Extensive spectroscopic work was performed, structural endorsement was obtained from X-ray diffraction analyses and further insight into the structures was obtained from theoretical/computational studies. A number of macrocycles in the series exhibited good complexation with alkaline-earth metal ions.     

Solvent-mediated self-association of a Horning-crown macrocycle

A member of a new class of novel macrocycles possessing both polyether and phenolic functionalities, forms dimers in both the solid-state and in solution when exposed to chloroform, dichloromethane or toluene, but does not self-associate in the presence of dimethyl sulfoxide.     

Prospering the biphen[n]arenes family by tailoring reaction modules

Reported here is the comprehensive investigation on the formation of biphen[n]arenes by tailoring reaction modules. Five new macrocyclic arenes and four oligomers were synthesized by the condensation of monomers possessing different multimethoxyphenyl reaction modules and paraformaldehyde. We proved that the number and sites of methoxy on reaction modules greatly affected the reaction activity, shape, and connection mode of macrocycles. Moreover, the triangular and saddle-shaped configuration of macrocycles were revealed by single crystal structures. The results provided a typical and fundamental guidance in designing new macrocyclic arenes.     

The preparation and coordination chemistry of 2,2′:6′,2″-terpyridine macrocycles—VI. Planar hexadentate macrocycles incorporating 2,2′: 6′,2″-terpyridine

The template condensation of 6,6″-bis(-methylhydrazino)-2,2′: 6′,2″-terpyridines L² and L³ with 2,6-pyridinedialdehyde may give a number of different products depending upon the metal ion which is used. In the presence of nickel(II) the products are either the nickel(II) complexes of the 18-membered ring macrocycles L⁴ or L⁵ or the free macrocycles. The metal ion acts as a transient template and is removed in a chloride ion specific demetallation. The use of dimethyltin(IV) as a template results in the formation of complexes of the ring contracted macrocycles L⁶ or L⁷.     

Macrocycle breathing in [2]rotaxanes with tetralactam macrocycles

The structural dynamics of two pairs of [2]rotaxanes were compared using variable-temperature NMR. Each rotaxane had a surrounding tetralactam macrocycle with either 2,6-pyridine dicarboxamide or isophthalamide bridging units. Differences were observed in two types of rotational processes: spinning of the phenylene wall units in the surrounding macrocycle of squaraine rotaxanes and macrocycle pirouetting in xanthone rotaxanes. The rotaxanes with macrocycles containing 2,6-pyridine dicarboxamide bridges exhibited higher rotational barriers due to a cavity contraction effect, which disfavored macrocycle breathing.