meta-Substituted benzamide oligomers that complex mono-, di- and tricarboxylates: folding-induced selectivity and chirality

Structure-Activity Relationship of Synthetic Linear KTS-Peptides Containing Meta-Aminobenzoic Acid as Antagonists of α1β1 Integrin with Anti-Angiogenic and Melanoma Anti-Tumor Activities

To develop peptide drugs targeting integrin receptors, synthetic peptide ligands endowed with well-defined selective binding motifs are necessary. The snake venom KTS-containing disintegrins, which selectively block collagen α1β1 integrin, were used as lead compounds for the synthesis and structure-activity relationship of a series of linear peptides containing the KTS-pharmacophore and alternating natural amino acids and 3-aminobenzoic acid (MABA). To ensure a better stiffness and metabolic stability, one, two and three MABA residues, were introduced around the KTS pharmacophore motif. Molecular dynamics simulations determined that the solution conformation of MABA peptide 4 is more compact, underwent larger conformational changes until convergence, and spent most of the time in a single cluster. The peptides' binding affinity has been characterized by an enzyme linked immunosorbent assay in which the most potent peptide 4 inhibited with IC50 of 324 ± 8 µM and 550 ± 45 µM the binding of GST-α1-A domain to collagen IV fragment CB3, and the cell adhesion to collagen IV using α1-overexpressor cells, respectively. Docking studies and MM-GBSA calculations confirmed that peptide 4 binds a smaller region of the integrin near the collagen-binding site and penetrated deeper into the binding site near Trp1. Peptide 4 inhibited tube formation by endothelial cell migration in the Matrigel angiogenesis in vitro assay. Peptide 4 was acutely tolerated by mice, showed stability in human serum, decreased tumor volume and angiogenesis, and significantly increased the survival of mice injected with B16 melanoma cells. These findings propose that MABA-peptide 4 can further serve as an α1β1-integrin antagonist lead compound for further drug optimization in angiogenesis and cancer therapy.

Chiroptical Recognition of Carboxylates with Charge-Neutral Double-Stranded Zinc(II) Helicates

Chirality analysis of small molecules for the determination of their enantiopurity is nowadays ruled by streamlined chromatographic methods which utilize chiral stationary phases. Chiroptical probes which rely on host-guest interactions are so far overshadowed by the latter but have the benefit of depending only on common spectroscopic techniques such as CD spectroscopy to distinguish enantiomers and to quantify their ratio. Interest into this receptor-based approach is constantly rising because non-invasive high-throughput screenings with a minimal waste production can be performed. In this study we investigate the possibility to utilize metal-based containers in form of charge-neutral helicates able to recognize anions for this purpose. Key building block of the helicates are triazole units which show rotational freedom and give rise to either a meso-structure or a racemic mixture of the right- and left-handed complex. A chiroptical response of the probe is observed upon recognition of chiral mono- or dicarboxylates and chirality analysis of tartrate is conducted by CD spectroscopy.

The helical supramolecular assembly of oligopyridylamide foldamers in aqueous media can be guided by adenosine diphosphates

A metal-free and achiral tri-pyridylamide foldamer, DM 11, containing a critical naphthalimide side chain self-assembles in a left-handed helical manner in the presence of chiral adenosine phosphates, under physiological conditions. Surprisingly, a very high degree of helicity in the foldamer assemblies was observed with ADP compared to other nucleoside phosphates, including ATP.

Chiroptical Sensing of Amino Acid Derivatives by Host-Guest Complexation with Cyclo[6]aramide

A hydrogen-bonded (H-bonded) amide macrocycle was found to serve as an effective component in the host–guest assembly for a supramolecular chirality transfer process. Circular dichroism (CD) spectroscopy studies showed that the near-planar macrocycle could produce a CD response when combined with three of the twelve L-α-amino acid esters (all cryptochiral molecules) tested as possible guests. The host–guest complexation between the macrocycle and cationic guests was explored using NMR, revealing the presence of a strong affinity involving the multi-point recognition of guests. This was further corroborated by density functional theory (DFT) calculations. The present work proposes a new strategy for amplifying the CD signals of cryptochiral molecules by means of H-bonded macrocycle-based host–guest association, and is expected to be useful in designing supramolecular chiroptical sensing materials.

Helical Anion Foldamers in Solution

Using anions to induce molecular structure is a rapidly growing area of dynamic and switchable supramolecular chemistry. The emphasis of this review is on helical anion foldamers in solution, and many of the beautiful complexes described herein are accentuated by their crystal structures. Anion foldamers are defined as single- or multistrand complexes-often helical-that incorporate one or more anions. The review begins by discussing foldamer structure and nomenclature and follows with discourse on the anions which are employed. Recent advances in functional foldamers that bind a single anion are examined, including: induced chirality, stimuli-responsive dynamics, fluorescence changes, organocatalysis, anion transport, and halogen bonding. The review then inspects multianion foldamers, and this section is organized by the number of strands within the foldamer-from single- to triple-strand foldamers. Finally, the review is punctuated by recent hydrogen- and halogen-bonding triple-strand anion foldamers.

Hydrophobically driven twist sense bias of hollow helical foldamers of aromatic hydrazide polymers in water

Aromatic hydrazide polymers bearingS-chiral tetraethylene glycol chains can fold into M hollow helices in water driven by the hydrophobicity.

Helical folding of an arylamide polymer in water and organic solvents of varying polarity

An arylamide polymer is driven by the solvophobicity and hydrogen bonding to form helical conformation in solvents of different polarity.

Donor–acceptor interaction-driven folding of linear naphthalene–glycol oligomers templated by a rigid bipyridinium rod

The construction of folded and helical supramolecular structures through the self-assembly of a series of flexible linear oligomers induced by a rigid rod-like template has been demonstrated.

Advances in anion supramolecular chemistry: from recognition to chemical applications

Since the start of this millennium, remarkable progress in the binding and sensing of anions has been taking place, driven in part by discoveries in the use of hydrogen bonding, as well as the previously under-exploited anion-π interactions and halogen bonding. However, anion supramolecular chemistry has developed substantially beyond anion recognition, and now encompasses a diverse range of disciplines. Dramatic advance has been made in the anion-templated synthesis of macrocycles and interlocked molecular architectures, while the study of transmembrane anion transporters has flourished from almost nothing into a rapidly maturing field of research. The supramolecular chemistry of anions has also found real practical use in a variety of applications such as catalysis, ion extraction, and the use of anions as stimuli for responsive chemical systems.

Aromatic amide and hydrazide foldamer-based responsive host-guest systems

CONSPECTUS: In host-guest chemistry, a larger host molecule selectively and noncovalently binds to a smaller guest molecule or ion. Early studies of host-guest chemistry focused on the recognition of spherical metal or ammonium ions by macrocyclic hosts, such as cyclic crown ethers. In these systems, preorganization enables their binding sites to cooperatively contact and attract a guest. Although some open-chain crown ether analogues possess similar, but generally lower, binding affinities, the design of acyclic molecular recognition hosts has remained challenging. One of the most successful examples was rigid molecular tweezers, acyclic covalently bonded preorganized host molecules with open cavities that bind tightly as they stiffen. Depending on the length of the atomic backbones, hydrogen bonding-driven aromatic amide foldamers can form open or closed cavities. Through rational design of the backbones and the introduction of added functional groups, researchers can regulate the shape and size of the cavity. The directionality of hydrogen bonding and the inherent rigidity of aromatic amide units allow researchers to predict both the shape and size of the cavity of an aromatic amide foldamer. Therefore, researchers can then design guest molecules with structure that matches the cavity shape, size, and binding sites of the foldamer host. In addition, because hydrogen bonds are dynamic, researchers can design structures that can adapt to outside stimuli to produce responsive supramolecular architectures. In this Account, we discuss how aromatic amide and hydrazide foldamers induced by hydrogen bonding can produce responsive host-guest systems, based on research by our group and others. First we highlight the helical chirality induced as binding occurs in solution, which includes the induction of helicity by chiral guests in oligomeric and polymeric foldamers, the formation of diastereomeric complexes between chiral foldamer hosts and guests, and the induction of helical chirality by chiral guests into inherently flexible backbones. In addition, molecular or ion-pair guests can produce supramolecular helical chirality in the organogel state. Such structures exhibit remarkable time-dependence and a "Sergeants and Soldiers" effect that are not observed for other two-component organogels that have been reported. We further illustrate that the reversible folding behavior of an aromatic amide foldamer segment can modulate the switching behavior of donor-acceptor interaction-based [2]rotaxanes. Finally we show that a folded oligomer can induce folding in one or two attached intrinsically flexible oligomers, an example of a solvent-responsive intramolecular host-guest system.

Host-guest chemistry of aromatic-amide-linked bis- and tris-calix[4]pyrroles with bis-carboxylates and citrate anion

A small library of polytopic receptors has been synthesized from meso-p- and meso-m-aminophenylcalix[4]pyrroles and p- or m-phthaloyl or trimesic chloride. Selected bis-carboxylates and the citrate anion, which either exhibit altered distribution profiles in cancerous tissues in comparison with healthy tissues or are metabolites of carcinogenic substances (for example, trans,trans-muconic acid from benzene exposure in humans) were tested as ligands. Varied affinities and binding modes were observed as a function of the number of calix[4]pyrroles and the topology of amide units present in each of the polytopic receptors. The structures of the 1:1 complexes derived by molecular modeling are in excellent agreement with the results of (1)H NMR complexation studies.