Aromatic Oligoamide Research Articles

Shape‐Persistent Aromatic Amide Oligomers: New Tools for Supramolecular Chemistry

With an increasing number of folding and helical structures available, chemists have begun to pay greater attention to the functions of this family of structurally unique oligomers. Hydrogen-bonding-mediated aromatic oligoamide foldamers have the features of good structural predictability, synthetic facility, and structural modification, which make them very promising as scaffolds or platforms for supramolecular chemistry. Recent advances in the applications of this class of shape-persistent oligomers in the promoted synthesis of macrocycles, design of new nonring receptors, supramolecular self-assembly, molecular encapsulation, and reaction acceleration, are highlighted in this Focus Review.

Improving Foldamer Synthesis through Protecting Group Induced Unfolding of Aromatic Oligoamides

The hydrogen bond rigidified backbones of aromatic oligoamides are temporarily interrupted by replacing the amide hydrogens with the acid-labile 2,4-dimethoxybenzyl (DMB) group, which allows the efficient preparation of long folding oligomers that, upon removal of the DMB groups, fold into multiturn helices. [structure: see text]

Novel, Methanol Stable, Aromatic Oligoamide Foldamers

Several novel aromatic oligoamides were synthesized using well-established DCC coupling chemistry. The oligomers with n = 1-4 were found to fold into helical structures both in solution, as observed by 1H NMR, COSY, NOESY, UV-Vis and fluorescence spectroscopy, and in the solid state, as observed by X-ray crystallography. Both intramolecular hydrogen bonding and aromatic stacking interactions are believed to contribute to the secondary structure. Furthermore, comparison of the 1H NMR spectra in methanol and chloroform revealed greater stability of the helical structure in the former solvent. It was speculated that intermolecular hydrogen bonding between methanol and the helical structures was the root of this enhanced stability.

Phenanthroline Dicarboxamide-Based Helical Foldamers: Stable Helical Structures in Methanol

A series of new aromatic oligoamides 2-5 based on 1,10-phenanthroline diacid and o-phenylenediamine have been synthesized through a convergent segment coupling strategy. These oligomers can fold into well-defined helical structures in solution through intramolecular hydrogen bonds and aromatic stacking interactions, which has been established by 1H NMR, fluorescence, and UV/vis spectra. In particular, it was found that the oligomers were more favorable to fold into stable helical structures in methanol than in chloroform and dichloromethane. The helical foldamers formed in the solid state have been characterized by single-crystal X-ray diffraction analysis. The results showed that the high curvature of the strands led to one and a half turns for both 2 and 21, three turns for 4, and nearly four turns for 5.

Synthesis of Crescent Aromatic Oligoamides

[structures: see text] This article describes the synthetic procedures for the preparation of crescent (and helical) aromatic oligoamides developed in recent years in our laboratory. The large-scale preparation of a variety of monomers derived from various tetrasubstituted benzenes is presented. Three different strategies for constructing various oligomers consisting of meta- and meta/para-linked benzene residues are discussed. Factors affecting coupling efficiency and yields are analyzed. The developed synthetic methods have provided the basis for the preparation of longer oligomers and for the development of solid-phase synthesis.

Cyclic aromatic oligoamides as highly selective receptors for the guanidinium ion

A class of six-residue, shape-persistent aromatic oligoamide macrocycles bind the guanidinium ion with very high selectivity.

Helical Aromatic Oligoamides: Reliable, Readily Predictable Folding from the Combination of Rigidified Structural Motifs

Factors responsible for the folding of aromatic oligoamides with backbones rigidified by local three-center H-bonds were investigated. The stability of the three-center H-bonds was quantified by the half-lives of amide proton-deuterium exchange reactions, which show that the three-center H-bonds were largely intact at room temperature in the oligomer examined. This result is consistent with our current and previous 2D NMR studies. The overall helical conformation of nonamer 1 was found by variable-temperature NOESY studies to be dynamic. As temperature rose, the end-to-end NOEs rapidly disappeared, while the amide side chain NOEs were still readily detectable, corresponding to the "breath" and stretching of the helix by slightly twisting the local H-bonded rings. Based on the simple repetition of the same structural motif and local conformational preference, undecamer 2 was found to fold into well-defined helical conformation. The predictability of the folding of these backbone-rigidified aromatic oligoamides was demonstrated by a simple modeling method using structural parameters from oligomers with known crystal structures. The reliability and generality of the modeling methods were shown by the excellent agreement between the modeled structures corresponding to 1 and 2 and data from NOESY studies.

Strained aromatic oligoamide macrocycles as new molecular clips.

Can one join both ends of a helix? A helical aromatic oligoamide was macrocyclized into a saddle-shaped bifunctional clip molecule that self-assembles into discrete circular dodecamers in the solid state and shows great potential for binding aromatic acid guests in solution. The cyclization step requires that the helix is only partly denatured in the reaction medium.

Aromatic Oligoamide Foldamers.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Switching of chiral induction in helical aromatic oligoamides using solid state-solution state equilibrium.

The introduction of an R asymmetric center in an aromatic oligoamide that adopts stable helical conformations leads to a significant shift of the equilibrium between the right-handed and left-handed helices in solution: the R-P and R-M helices are diastereoisomers. However, these two species were found to cocrystallize in 1:1 proportions. Thus the chiral induction observed in solution is switched off in the solid state. This phenomenon represents an original and unexpected means to control handedness in helical oligomers.

Cover Picture: Aromatic Oligoamide Foldamers (Eur. J. Org. Chem. 1/2004)

AbstractThe cover picture shows a photograph of a helical origami, based on a modular ring designed by David Petty, surrounded by five examples of building blocks used in aromatic oligoamide foldamers. The background is an unfolded origami paper displaying the crease pattern that codes for a well‐defined folded shape. In the ancient Japanese art of paper folding, beautiful and complex yet predictable forms arise from a series a folding steps of a sheet of paper. Each step sets the relative orientation of the two sides of the fold. Similarly, the conformations of aromatic oligoamide foldamers are determined by interactions between consecutive units. In first approximation, the overall conformation is simply predicted as a linear combination of local conformational preferences. Details are discussed in the Microreview by I. Huc on p. 17 ff. We thank Professor Louis Cuccia for his inspiration and major contribution to this image.

Aromatic delta-peptides.

Oligoamides of 8-amino-2-carboxy-quinoline adopt a very stable helical conformation characterized in solution by 1H NMR and in the solid state by single-crystal X-ray diffraction. The helix comprises only 2.5 units per turn, which represents the highest curvature achieved by aromatic oligoamides until now. Monomers possessing alkoxy substituents in position 4 are easily available from 2-nitroaniline and dimethyl acetylenedicarboxylate.

Synthesis of aromatic and heteroaromatic oligoamides on methoxypoly(ethylene glycol) as solubilizing polymer support

A protecting-group-free procedure for the synthesis of short carbo- and heteroaromatic oligoamide chains on MeO-PEG as solubilizing support is introduced. Starting from nitrocarboxylic acids, oligoamides of carboxylic acids derived from N-methylpyrrole, N-methylimidazole and aniline are synthesized that contain up to five arene units. The polymer support facilitates work up procedures and markedly improves the otherwise poor solubility of the products. Each coupling step is monitored by 1H-NMR spectroscopy without cleavage of the product from the polymeric support.

Melt‐processable oligoamides having internal acetylene groups in the backbone, and thermally stable polyamides therefrom

AbstractAromatic oligoamides of DP = 5 and 11 that have all meta‐phenylene linkages were prepared by controlling the ratio of isophthaloyl chloride and diamines [m‐phenylenediamine and bis(3‐aminophenyl)acetylene], and then end‐capped with aniline or 2‐aminobiphenylene. Aromatic oligoamides having para‐phenylene linkages were also prepared similarly using terephthaloyl chloride as a monomer. The oligoamides that have all m‐phenylene linkages were soluble in organic solvents such as N‐methyl‐2‐pyrrolidone and N,N‐dimethylacetamide, though the oligoamides having p‐phenylene linkages were much less soluble. The oligoamides having acetylene units in the backbone showed exotherm due to crosslinking. The onset of the exotherm appeared at 310‐340°C for the oligoamides having all m‐phenylene linkages, and 330‐370°C for the oligoamides having p‐phenylene linkages. They were melt‐processed at 350 or 380°C for 1 h, giving tough and insoluble films from oligoamides having all m‐phenylene linkages and brittle films from oligoamides having p‐phenylene linkages. The films showed excellent thermal properties. For example, viscoelastic analyses showed little decrease of mechanical property up to 370°C, and Tg was not observed below the temperature. Thermogravimetric analyses also showed that thermal stability of the melt‐processed films were excellent. © 1992 John Wiley & Sons, Inc.

Oligomeric 1,4‐phenyleneterephthalamide. Synthesis by interfacial polycondensation and structural properties

AbstractThe synthesis of a fully aromatic oligoamide by low temperature interfacial polycondensation between terephthaloyl chloride and 1,4‐phenylenediamine is reported. The reaction product was characterized with respect to its physical properties and chemical structure by infrared, X‐rays, electron spectroscopy for chemical analysis (ESCA), and mass spectroscopic techniques. Elemental and thermal analysis, as well as viscosimetric and titrimetric methods were applied to evaluate the average molecular weight of the oligomer, whose chain length consists mainly of 3 to 4 monomeric units.