Investigating the Influence of (Deoxy)fluorination on the Lipophilicity of Non-UV-Active Fluorinated Alkanols and Carbohydrates by a New log P Determination Method

Placing CF2 in the Center: Major Physicochemical Changes Upon a Minor Structural Alteration in Gem-Difunctional Compounds

Fluorine atoms play an important role in all branches of chemistry and accordingly, it is very important to study their unique and varied effects systematically, in particular, the structure-physicochemical properties relationship. The present study describes exceptional physicochemical effects resulting from a H/F exchange at the methylene bridge of gem-difunctional compounds. The Δlog P_(CF2-CH2) values, that is, the change in lipophilicity, observed for the CH₂ /CF₂ replacement in various α,α-phenoxy- and thiophenoxy-esters/amides, diketones, benzodioxoles and more, fall in the range of 0.6-1.4 units, which for most cases, is far above the values expected for such a replacement. Moreover, for compounds holding more than one such gem-difunctional moiety, the effect is nearly additive, so one can switch from a hydrophilic compound to a lipophilic one in a limited number of H/F exchanges. DFT studies of some of these systems revealed that polarity, conformational preference as well as charge distributions are strongly affected by such hydrogen to fluorine atom substitution. The pronounced effects described, are a result of the interplay between changes in polarity, H-bond basicity and molecular volume, which were obtained with a very low 'cost' in terms of molecular weight or steric effects and may have a great potential for implementation in various fields of chemical sciences.

Synthetic Approaches to Break the Chemical Shift Degeneracy of Glycans

NMR spectroscopy is the leading technique for determining glycans' three-dimensional structure and dynamic in solution as well as a fundamental tool to study protein-glycan interactions. To overcome the severe chemical shift degeneracy of these compounds, synthetic probes carrying NMR-active nuclei (e. g., ¹³ C or ¹⁹ F) or lanthanide tags have been proposed. These elegant strategies permitted to simplify the complex NMR analysis of unlabeled analogues, shining light on glycans' conformational aspects and interaction with proteins. Here, we highlight some key achievements in the synthesis of specifically labeled glycan probes and their contribution towards the fundamental understanding of glycans.

Relating Conformational Equilibria to Conformer-Specific Lipophilicities: New Opportunities in Drug Discovery

Efficient drug discovery is based on a concerted effort in optimizing bioactivity and compound properties such as lipophilicity, and is guided by efficiency metrics that reflect both aspects. While conformation–activity relationships and ligand conformational control are known strategies to improve bioactivity, the use of conformer‐specific lipophilicities (logp) is much less explored. Here we show how conformer‐specific logp values can be obtained from knowledge of the macroscopic logP value, and of the equilibrium constants between the individual species in water and in octanol. This is illustrated with fluorinated amide rotamers, with integration of rotamer ¹⁹F NMR signals as a facile, direct method to obtain logp values. The difference between logp and logP optimization is highlighted, giving rise to a novel avenue for lipophilicity control in drug discovery.

Selectively Deoxyfluorinated N-Acetyllactosamine Analogues as 19 F NMR Probes to Study Carbohydrate-Galectin Interactions

Galectins are widely expressed galactose-binding lectins implied, for example, in immune regulation, metastatic spreading, and pathogen recognition. N-Acetyllactosamine (Galβ1-4GlcNAc, LacNAc) and its oligomeric or glycosylated forms are natural ligands of galectins. To probe substrate specificity and binding mode of galectins, we synthesized a complete series of six mono-deoxyfluorinated analogues of LacNAc, in which each hydroxyl has been selectively replaced by fluorine while the anomeric position has been protected as methyl β-glycoside. Initial evaluation of their binding to human galectin-1 and -3 by ELISA and ¹⁹ F NMR T₂ -filter revealed that deoxyfluorination at C3, C4' and C6' completely abolished binding to galectin-1 but very weak binding to galectin-3 was still detectable. Moreover, deoxyfluorination of C2' caused an approximately 8-fold increase in the binding affinity towards galectin-1, whereas binding to galectin-3 was essentially not affected. Lipophilicity measurement revealed that deoxyfluorination at the Gal moiety affects log P very differently compared to deoxyfluorination at the GlcNAc moiety.

Modulating the Efficacy of Carbonic Anhydrase Inhibitors through Fluorine Substitution

The insertion of fluorine atoms and/or fluoroalkyl groups can lead to many beneficial effects in biologically active molecules, such as enhanced metabolic stability, bioavailability, lipophilicity, and membrane permeability, as well as a strengthening of protein-ligand binding interactions. However, this "magic effect" of fluorine atom(s) insertion can often be meaningless. Taking advantage of the wide range of data coming from the quest for carbonic anhydrase (CA) fluorinated inhibitors, this Minireview attempts to give "general guidelines" on how to wisely insert fluorine atom(s) within an inhibitor moiety to precisely enhance or disrupt ligand-protein interactions, depending on the target location of the fluorine substitution in the ligand. Multiple approaches such as ITC, kinetic and inhibition studies, X-ray crystallography, and NMR spectroscopy are useful in dissecting single binding contributions to the overall observed effect. The exploitation of innovative directions made in the field of protein and ligand-based fluorine NMR screening is also discussed to avoid misconduct and finely tune the exploitation of selective fluorine atom insertion in the future.

From Carbohydrates to Complex Organofluorines: Synthesis, Conformation, and Lipophilicity of Multivicinal-Fluorine-Containing Hexitol Analogues

There is growing interest in the preparation of fluorine-containing organic molecules. Multivicinal-fluorine analogues are among the most intriguing and promising compounds, but their physical and biological investigations are held back by challenging syntheses. Herein, we report on the synthesis of a large set of novel polyfluorohexitols. The dominant solution-state conformation of all trifluorohexitols was determined, and the solid-state conformations of some analogues were compared. Finally, the lipophilicity of a large set of polyfluorinated hexopyranose and hexitol analogues was attributed by using a log P determination method based on ¹⁹ F NMR spectroscopy.

Forging C-SeCF3 Bonds with Trifluoromethyl Tolueneselenosulfonate under Visible-Light

This account highlights some of our recent work on photoinduced trifluoromethylselenolation reactions. This research program relies primarily on the design of a new key shelf-stable selenating reagent that can be involved in various radical processes In particular, we demonstrated that trifluoromethylselenolation of arenes, alkenes, alkynes as well as aliphatic organic building blocks can be readily achieved under visible-light irradiation. Mechanistic investigations based on ¹⁹ F NMR studies, EPR spectroscopy, cyclic voltammetry and luminescence studies allowed us to shed the light on the different proposed mechanisms in the designed methodologies. The applicative potential of these strategies was further demonstrated through the synthesis of bioactive analogue containing SeCF₃ motif.

Conformational Analysis of Acyclic α-Fluoro Sulfur Motifs

Bioactive small molecules containing α-fluoro sulfur motifs [RS(O)n CH2 F] are appearing with increasing frequency in the pharmaceutical and agrochemical sectors. Prominent examples include the anti-asthma drug Flovent® and the phenylpyrazole insecticide pyrafluprole. Given the popularity of these structural units in bioactive small molecule design, together with the varying oxidation states of sulfur, a conformational analysis of α-fluoro sulfides, sulfoxides, and sulfones, would be instructive in order to delineate the non-covalent interactions that manifest themselves in structure. A combined crystallographic and computational analysis demonstrates the importance of hyperconjugative donor-acceptor interactions in achieving acyclic conformational control. The conformational disparity in the syn- and anti-diastereoisomers of α-fluorosulfoxides is particularly noteworthy.

Addressing the Structural Complexity of Fluorinated Glucose Analogues: Insight into Lipophilicities and Solvation Effects

In this work, we synthesized all mono-, di-, and trifluorinated glucopyranose analogues at positions C-2, C-3, C-4, and C-6. This systematic investigation allowed us to perform direct comparison of ¹⁹ F resonances of fluorinated glucose analogues and also to determine their lipophilicities. Compounds with a fluorine atom at C-6 are usually the most hydrophilic, whereas those with vicinal polyfluorinated motifs are the most lipophilic. Finally, the solvation energies of fluorinated glucose analogues were assessed for the first time by using density functional theory. This method allowed the log P prediction of fluoroglucose analogues, which was comparable to the C log P values obtained from various web-based programs.

Polar Organofluorine Substituents: Multivicinal Fluorines on Alkyl Chains and Alicyclic Rings

This Review outlines the progression, primarily of our own work, but with important contributions from other labs, on the synthesis and properties of multiple vicinally fluorinated alkyl chains and rings. Chain conformations of individual diastereoisomers with -CHF- at adjacent carbons are influenced by stereoelectronic factors associated with the polar C-F bond and the polarised geminal hydrogens. Generally, the chain will prefer a conformation which acts to minimise overall molecular polarity, and where the C-F bonds orient away from each other. However, when vicinal fluorine atoms are positioned on a ring then conformations are more constrained. The ring will adopt optimal conformations such as a chair in cyclohexane and then C-F bonds can be introduced with a stereochemistry that forces parallel (axial) orientations. In the case of cyclohexane, 1,3-diaxial arrangements of C-F bonds impart considerable polarity to the ring, resulting in an electronegative 'fluorine face' and an electropositive 'hydrogen face'. For all-syn 1,2,3,4,5,6-hexafluorocyclohexane, this arrangement generates an unusually polar aliphatic ring system. Most recently the concept has been extended to the preparation of all-syn 1,2,3-trifluorocyclopropanes, a rigid ring system with fluorine atoms on one face and hydrogens on the other. Lipophilicity Log P values of such compounds indicate that they are significantly more polar than their parent alicyclic hydrocarbons and give some positive indication for a future role of such substituents in medicinal chemistry. Expanding to such a role will require access to improved synthesis methods to these motifs and consequently access to a broader a range of building blocks, however some exciting new methods have emerged recently and these are briefly reviewed.

Stereoselective Synthesis of Fluorinated Galactopyranosides as Potential Molecular Probes for Galactophilic Proteins: Assessment of Monofluorogalactoside-LecA Interactions

The replacement of hydroxyl groups by fluorine atoms on hexopyranoside scaffolds may allow access to invaluable tools for studying various biochemical processes. As part of ongoing activities toward the preparation of fluorinated carbohydrates, a systematic investigation involving the synthesis and biological evaluation of a series of mono- and polyfluorinated galactopyranosides is described. Various monofluorogalactopyranosides, a trifluorinated, and a tetrafluorinated galactopyranoside have been prepared using a Chiron approach. Given the scarcity of these compounds in the literature, in addition to their synthesis, their biological profiles were evaluated. Firstly, the fluorinated compounds were investigated as antiproliferative agents using normal human and mouse cells in comparison with cancerous cells. Most of the fluorinated compounds showed no antiproliferative activity. Secondly, these carbohydrate probes were used as potential inhibitors of galactophilic lectins. The first transverse relaxation-optimized spectroscopy (TROSY) NMR experiments were performed on these interactions, examining chemical shift perturbations of the backbone resonances of LecA, a virulence factor from Pseudomonas aeruginosa. Moreover, taking advantage of the fluorine atom, the ¹⁹ F NMR resonances of the monofluorogalactopyranosides were directly monitored in the presence and absence of LecA to assess ligand binding. Lastly, these results were corroborated with the binding potencies of the monofluorinated galactopyranoside derivatives by isothermal titration calorimetry experiments. Analogues with fluorine atoms at C-3 and C-4 showed weaker affinities with LecA as compared to those with the fluorine atom at C-2 or C-6. This research has focused on the chemical synthesis of "drug-like" low-molecular-weight inhibitors that circumvent drawbacks typically associated with natural oligosaccharides.