Pushing the Limits of Characterising a Weak Halogen Bond in Solution

Hypervalent Iodine (III)-Based Complexation for Chiroptical Supramolecular Glass, Deep Eutectic Solvent and Luminescent Switch

Hypervalent iodine(III) have widely been utilized for organic synthetic reagents. They are also recognized as positive charge-assisted, exceptionally robust biaxial halogen bond donors, while their potential in supramolecular materials is barely explored. This work reports a cyclic diaryliodonium ion as biaxial halogen bonding donor that displays remarkable binding affinity toward phenanthroline or acridine acceptors with chiral pendants. Biaxial halogen bonding enables chiroptical evolution in solution, allowing for rational control over supramolecular chirality. Leveraging their strong binding affinity, the halogen bonding complexes manifested amorphous properties and deep eutectic behavior in the solid state. Capitalizing on these attributes, this work achieves the successful preparation of supramolecular glasses and deep eutectic solvents. Additionally, halogen bonding appended light irradiation-triggered luminescence through a hydrogen atom transfer process, showing applications in anti-counterfeit and display.

Quantifying Intermolecular Interactions in Asymmetric Peptide Organocatalysis as a Key toward Understanding Selectivity

The kinetic resolution of trans-cyclohexane-1,2-diol with a lipophilic oligopeptide catalyst shows extraordinary selectivities. To improve our understanding of the factors governing selectivity, we quantified the Gibbs free energies of interactions of the peptide with both enantiomers of trans-cyclohexane-1,2-diol using nuclear magnetic resonance (NMR) spectroscopy. For this, we use advanced methods such as transverse relaxation (R2), diffusion measurements, saturation transfer difference (STD), and chemical shift (δ) analysis of peptide-diol mixtures upon varying their composition (NMR titrations). The methods employed give comparable and consistent results. The molecular recognition by the catalyst is approximately 3 kJ mol-1 in favor of the preferentially acetylated (R,R)-enantiomer in the temperature range studied. Interestingly, the difference of 3 kJ mol-1 is also confirmed by results from reaction monitoring of the acylation step under catalytic conditions, indicating that this finding is true regardless of whether the investigation is performed on the acetylated species or on the free catalyst. To arrive at these conclusions, the self-association of both the catalyst and the substrate in toluene was found to play an important role and thus needs to be taken into account in reaction screening.

Principles and Applications of CF2X Moieties as Unconventional Halogen Bond Donors in Medicinal Chemistry, Chemical Biology, and Drug Discovery

As an orthogonal principle to the established (hetero)aryl halides, we herein highlight the usefulness of CF2X (X = Cl, Br, or I) moieties. Using tool compounds bearing CF2X moieties, we study their chemical/metabolic stability and their logP/solubility, as well as the role of XB in their small molecular crystal structures. Employing QM techniques, we analyze the observed interactions, provide insights into the conformational flexibilities and preferences in the potential interaction space. For their application in molecular design, we characterize their XB donor capacities and its interaction strength dependent on geometric parameters. Implementation of CF2X acetamides into our HEFLibs and biophysical evaluation (STD-NMR/ITC), followed by X-ray analysis, reveals a highly interesting binding mode for fragment 23 in JNK3, featuring an XB of CF2Br toward the P-loop, as well as chalcogen bonds. We suggest that underexplored chemical space combined with unconventional binding modes provides excellent opportunities for patentable chemotypes for therapeutic intervention.

Ensemble determination by NMR data deconvolution

Nuclear magnetic resonance (NMR) is the spectroscopic technique of choice for determining molecular conformations in solution at atomic resolution. As solution NMR spectra are rich in structural and dynamic information, the way in which the data should be acquired and handled to deliver accurate ensembles is not trivial. This Review provides a guide to the NMR experiment selection and parametrization process, the generation of viable theoretical conformer pools and the deconvolution of time-averaged NMR data into a conformer ensemble that accurately represents a flexible molecule in solution. In addition to reviewing the key elements of solution ensemble determination of flexible mid-sized molecules, the feasibility and pitfalls of data deconvolution are discussed with a comparison of the performance of representative algorithms.

The unusual stability of H-bonded complexes in solvent caused by greater solvation energy of complex compared to those of isolated fragments

Here, the effect of solvent on the stability of non-covalent complexes, was studied. These complexes were from previously published S22, S66, and X40 datasets, which include hydrogen-, halogen- and dispersion-bonded complexes. It was shown that the charge transfer in the complex determines whether the complex is stabilized or destabilized in solvent.

Synthesis of Amino Acids Bearing Halodifluoromethyl Moieties and Their Application to p53-Derived Peptides Binding to Mdm2/Mdm4

Introduction

Therapeutic peptides are a significant class of drugs in the treatment of a wide range of diseases. To enhance their properties, such as stability or binding affinity, they are usually chemically modified. This includes, among other techniques, cyclization of the peptide chain by bridging, modifications to the backbone, and incorporation of unnatural amino acids. One approach previously established, is the use of halogenated aromatic amino acids. In principle, they are thereby enabled to form halogen bonds (XB). In this study, we focus on the -R-CF₂X moiety (R = O, NHCO; X = Cl, Br) as an uncommon halogen bond donor. These groups enable more spatial variability in protein-protein interactions. The chosen approach via Fmoc-protected building blocks allows for the incorporation of these modified amino acids in peptides using solid-phase peptide synthesis.

Results and Discussion

Using a competitive fluorescence polarization assay to monitor binding to Mdm4, we demonstrate that a p53-derived peptide with Lys24Nle(εNHCOCF₂X) exhibits an improved inhibition constant K_i compared to the unmodified peptide. Decreasing K_i values observed with the increasing XB capacity of the halogen atoms (F ≪ Cl < Br) indicates the formation of a halogen bond. By reducing the side chain length of Nle(εNHCOCF₂X) to Abu(γNHCOCF₂X) as control experiments and through quantum mechanical calculations, we suggest that the observed affinity enhancement is related to halogen bond-induced intramolecular stabilization of the α-helical binding mode of the peptide or a direct interaction with His54 in human Mdm4.