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

Conformational Analysis Explores the Role of Electrostatic Nonclassical CF···HC Hydrogen Bonding Interactions in Selectively Halogenated Cyclohexanes

The conformational equilibria of selectively halogenated cyclohexanes are explored both experimentally (VT-NMR) for 1,1,4,-trifluorocyclohexane 7 and by computational analysis (M06-2X/aug-cc-pVTZ level), with the latter approach extending to a wider range of more highly fluorinated cyclohexanes. Perhaps unexpectedly, 7ax is preferred over the 7eq conformation by ΔG = 1.06 kcal mol-1, contradicting the accepted norm for substituents on cyclohexanes. The axial preference is stronger again in 1,1,3,3,4,5,5,-heptafluorocyclohexane 9 (ΔG = 2.73 kcal mol-1) as the CF2 groups further polarize the isolated CH2 hydrogens. Theoretical decomposition of electrostatic and hyperconjugative effects by natural bond orbital analysis indicated that nonclassical hydrogen bonding (NCHB) between the C-4 fluorine and the diaxial hydrogens at C-2 and C-6 in cyclohexane 7 and 9 largely accounts for the observed bias. The study extended to changing fluorine (F) for chlorine (Cl) and bromine (Br) at the pseudoanomeric position in the cyclohexanes. Although these halogens do not become involved in NCHBs, they polarize the geminal -CHX- hydrogen at the pseudoanomeric position to a greater extent than fluorine, and consequent electrostatic interactions influence conformer stabilities.

Preparation of 18F-Labeled Tracers Targeting Fibroblast Activation Protein via Sulfur [18F]Fluoride Exchange Reaction

Early detection and treatment of cancers can significantly increase patient prognosis and enhance the quality of life of affected patients. The emerging significance of the tumor microenvironment (TME) as a new frontier for cancer diagnosis and therapy may be exploited by radiolabeled tracers for diagnostic imaging techniques such as positron emission tomography (PET). Cancer-associated fibroblasts (CAFs) within the TME are identified by biomarkers such as fibroblast activation protein alpha (FAPα), which are expressed on their surfaces. Targeting FAPα using small-molecule 18F-labeled inhibitors (FAPIs) has recently garnered significant attention for non-invasive tumor visualization using PET. Herein, two potent aryl-fluorosulfate-based FAPIs, 12 and 13, were synthetically prepared, and their inhibition potency was determined using a fluorimetric FAP assay to be IC50 9.63 and 4.17 nM, respectively. Radiofluorination was performed via the sulfur [18F]fluoride exchange ([18F]SuFEx) reaction to furnish [18F]12 and [18F]13 in high activity yields (AY) of 39-56% and molar activities (Am) between 20-55 GBq/µmol. In vitro experiments focused on the stability of the radiolabeled FAPIs after incubation with human serum, liver microsomes and liver cytosol. Preliminary PET studies of the radioligands were performed in healthy mice to investigate the in vivo biodistribution and 18F defluorination rate. Fast pharmacokinetics for the FAP-targeting tracers were retained and considerable bone uptake, caused by either 18F defluorination or radioligand accumulation, was observed. In summary, our findings demonstrate the efficiency of [18F]SuFEx as a radiolabeling method as well as its advantages and limitations with respect to PET tracer development.

N-(2-Tetrafluoro(trifluoromethyl)-λ6-sulfanyl(CF3SF4)-ethyl) Amines: The Influence of the CF3SF4 Group on Lipophilicity and pKa

A practical synthetic path for the preparation of trans-CF3SF4-substituted amines has been described. Primary and secondary amines bearing a variety of different functional groups including amino acids, cyclic amines, and nucleosides were prepared. The desired amines were synthesized under mild conditions. The influence of the CF3SF4-group on the pKa and log D of a standard amine was established. The unusual conformation of the trans-CF3SF4-substituted tosylate has been verified via its crystal structure.

Ir-Catalyzed Ortho-Selective C-H Borylation of Difluoromethyl Arenes

The difluoromethyl group (CF2H) has received great attention due to its distinct properties in recent years. Herein, we report a new strategy for postmodification of difluoromethyl compounds. Ortho-selective C-H borylation of difluoromethyl arenes is achieved by a cyclometalated mesoionic carbene-Ir complex. The regioselectivity is controlled by a hydrogen bond between CF2H and the boryl group via the outer-sphere direction.

Obtaining Pure 1H NMR Spectra of Individual Pyranose and Furanose Anomers of Reducing Deoxyfluorinated Sugars

Due to tautomeric equilibria, NMR spectra of reducing sugars can be complex with many overlapping resonances. This hampers coupling constant determination, which is required for conformational analysis and configurational assignment of substituents. Given that mixtures of interconverting species are physically inseparable, easy-to-use techniques that enable facile full 1H NMR characterization of sugars are of interest. Here, we show that individual spectra of both pyranoside and furanoside forms of reducing fluorosugars can be obtained using 1D FESTA. We discuss the unique opportunities offered by FESTA over standard sel-TOCSY and show how it allows a more complete characterization. We illustrate the power of FESTA by presenting the first full NMR characterization of many fluorosugars, including of the important fluorosugar 2-deoxy-2-fluoroglucose. We discuss in detail all practical considerations for setting up FESTA experiments for fluorosugars, which can be extended to any mixture of fluorine-containing species interconverting slowly on the NMR frequency-time scale.

The wide presence of fluorinated compounds in common chemical products and the environment: a review

The C-F bonds, due to their many unique features, have been incorporated into numerous compounds in countless products and applications. These fluorinated compounds eventually are disposed of and released into the environment through different pathways. In this review, we analyzed the occurrence of these fluorinated compounds in seven types of products (i.e., refrigerants/propellants, aqueous film-forming foam, cosmetics, food packaging, agrochemicals, pharmaceuticals, coating materials) and discussed their fate in the environment. This is followed by describing the quantity of fluorinated compounds from each source based on available data. Total on- and off-site disposal or other releases of 536 fluorinated compounds in 2021 were analyzed using the data sourced from the U.S. EPA Toxics Release Inventory (TRI). Among the chemicals examined, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were the primary contributors in terms of total mass. Upon examining the seven sources of fluorinated compounds, it became evident that additional contributors are also responsible for the presence of organofluorine compounds in the environment. Although various toxic degradation products of fluorinated compounds could form in the environment, trifluoroacetic acid (TFA) was specifically highlighted in this review given the fact that it is a common dead-end degradation product of > 1 million chemicals. This paper ended with a discussion of several questions raised from this study. The path forward was elaborated as well for the purpose of protecting the environment and human health.

Aryl (β,β',β″-Trifluoro)-tert-butyl: A Candidate Motif for the Discovery of Bioactives

The (β,β',β″-trifluoro)-tert-butyl (TFTB) group has received very little attention in the literature. This work presents a direct synthesis of this group and explores its properties. The TFTB group arises when the methyl groups of a tert-butyl moiety are exchanged for fluoromethyl groups. Sequential fluoromethylations result in a decrease of Log P (increasing hydrophilicity), ultimately by 1.7 Log P units in the TFTB group relative to that of tert-butyl benzene itself. A focus is placed on synthetic transformations, conformational analysis, and metabolism of the TFTB group in the context of presenting a favorable profile as a motif for the discovery of bioactives.

Drug Discovery Based on Fluorine-Containing Glycomimetics

Glycomimetics, which are synthetic molecules designed to mimic the structures and functions of natural carbohydrates, have been developed to overcome the limitations associated with natural carbohydrates. The fluorination of carbohydrates has emerged as a promising solution to dramatically enhance the metabolic stability, bioavailability, and protein-binding affinity of natural carbohydrates. In this review, the fluorination methods used to prepare the fluorinated carbohydrates, the effects of fluorination on the physical, chemical, and biological characteristics of natural sugars, and the biological activities of fluorinated sugars are presented.

Species-specific lipophilicities of fluorinated diketones in complex equilibria systems and their potential as multifaceted reversible covalent warheads

Combined molecular, physicochemical and chemical properties of electrophilic warheads can be applied to create covalent drugs with diverse facets. Here we study these properties in fluorinated diketones (FDKs) and their multicomponent equilibrium systems in the presence of protic nucleophiles, revealing the potential of the CF2(CO)2 group to act as a multifaceted warhead for reversible covalent drugs. The equilibria compositions of various FDKs in water/octanol contain up to nine species. A simultaneous direct species-specific 19F-NMR-based log P determination of these complex equilibria systems was achieved and revealed in some cases lipophilic to hydrophilic shifts, indicating possible adaptation to different environments. This was also demonstrated in 19F-MAS-NMR-based water-membrane partitioning measurements. An interpretation of the results is suggested by the aid of a DFT study and 19F-DOSY-NMR spectroscopy. In dilute solutions, a model FDK reacted with protected cysteine to form two hemi-thioketal regioisomers, indicating possible flexible regio-reactivity of CF2(CO)2 warheads toward cysteine residues.

Exploring multivalent carbohydrate-protein interactions by NMR

Nuclear Magnetic Resonance (NMR) has been widely employed to assess diverse features of glycan-protein molecular recognition events. Different types of qualitative and quantitative information at different degrees of resolution and complexity can be extracted from the proper application of the available NMR-techniques. In fact, affinity, structural, kinetic, conformational, and dynamic characteristics of the binding process are available. Nevertheless, except in particular cases, the affinity of lectin-sugar interactions is weak, mostly at the low mM range. This feature is overcome in biological processes by using multivalency, thus augmenting the strength of the binding. However, the application of NMR methods to monitor multivalent lectin-glycan interactions is intrinsically challenging. It is well known that when large macromolecular complexes are formed, the NMR signals disappear from the NMR spectrum, due to the existence of fast transverse relaxation, related to the large size and exchange features. Indeed, at the heart of the molecular recognition event, the associated free-bound chemical exchange process for both partners takes place in a particular timescale. Thus, these factors have to be considered and overcome. In this review article, we have distinguished, in a subjective manner, the existence of multivalent presentations in the glycan or in the lectin. From the glycan perspective, we have also considered whether multiple epitopes of a given ligand are presented in the same linear chain of a saccharide (i.e., poly-LacNAc oligosaccharides) or decorating different arms of a multiantennae scaffold, either natural (as in multiantennae N-glycans) or synthetic (of dendrimer or polymer nature). From the lectin perspective, the presence of an individual binding site at every monomer of a multimeric lectin may also have key consequences for the binding event at different levels of complexity.

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.

Fast Prediction of Lipophilicity of Organofluorine Molecules: Deep Learning-Derived Polarity Characters and Experimental Tests

Fast and accurate estimation of lipophilicity for organofluorine molecules is in great demand for accelerating drug and materials discovery. A lipophilicity data set of organofluorine molecules (OFL data set), containing 1907 samples, is constructed through density functional theory (DFT) calculations and experimental measurements. An efficient and interpretable model, called PoLogP, is developed to predict the n-octanol/water partition coefficient, log P_o/w, of organofluorine molecules on the basis of the descriptors of polarization, which is a combination of polarity descriptors, including the molecular polarity index and molecular polarizability (α), and hydrogen bond (HBs) index, consisting of the number of donors (N_HB^D) and acceptors (N_HB^A and N_HB-F^A). The present PoLogP with a combination of polarity descriptors is demonstrated to perform better than the dipole moment (μ) alone for the F-contained molecules. With the aid of a multilevel attention graph convolutional neural network model, the fast generation of polarity descriptors of organofluorine molecules could be achieved with the DFT accuracy based only on a topological molecular graph structure. The performance of PoLogP is further validated on synthesized organofluorine molecules and 2626 non-fluorinated molecules with satisfactory accuracy, highlighting the potential usage of PoLogP in high-throughput screening of the functional molecules with the desired solubility in various solvent media.

Turning the Other Cheek: Influence of the cis-Tetrafluorocyclohexyl Motif on Physicochemical and Metabolic Properties

The targeted introduction of substituents in order to tailor a molecule’s pharmacologic, physicochemical, and metabolic properties has long been of interest to medicinal chemists. The all-cis tetrafluorocyclohexyl motif—dubbed Janus face, due to its electrostatically polarized cyclohexyl ring—represents one such example where chemists might incorporate a metabolically stable, polar, lipocompatible motif. To better understand its potential utility, we have synthesized three series of matched molecular pairs (MMPs) where each MMP differs only in the cyclohexane unit, i.e., with a tetrafluorocyclohexyl or a standard cyclohexyl motif. With the introduction of the facially polarized all-cis tetrafluorocyclohexyl ring, the resulting compounds have significantly modified physicochemical properties (e.g., kinetic solubility, lipophilicity and permeability) and metabolic stabilities. These results further speak to the promise of this substituent as a tactic to improve the drug-like properties of molecules.

Octanol-Water Partition Coefficients of Fluorinated Drug Molecules with Continuum Solvation Models

In this work, we have examined the efficiency of continuum solvation models, used with density functional theory methods, in calculating octanol-water partition coefficients (logP) of 56 fluorine containing drug molecules. The solvation model based on density model computed logP values that are in good agreement with the benchmark values. The conductor-like polarizable continuum models computed results have issues in predicting correct trend, often with reversal of sign from benchmark. The choice of basis set does not show significant effect, and the selection of atomic radii affects geometry convergence during calculations.

Studying Lipophilicity Trends of Phosphorus Compounds by 31P-NMR Spectroscopy: A Powerful Tool for the Design of P-Containing Drugs

Systematically studying the lipophilicity of phosphorus compounds is of great importance for many chemical and biological fields and particularly for medicinal chemistry. Here, we report on the study of trends in the lipophilicity of a wide set of phosphorus compounds relevant to drug design including phosphates, thiophosphates, phosphonates, thiophosphonates, bis-phosphonates, and phosphine chalcogenides. This was enabled by the development of a straightforward log P determination method for phosphorus compounds based on ³¹P-NMR spectroscopy. The log P values measured ranged between -3.2 and 3.6, and the trends observed were interpreted using a DFT study of the dipole moments and by H-bond basicity (pK_HB) measurements of selected compounds. Clear signal separation in ³¹P-NMR spectroscopy grants the method high tolerability to impurities. Moreover, the wide range of chemical shifts for the phosphorus nucleus (250 to -250 ppm) enables a direct simultaneous log P determination of phosphorus compound mixtures in a single shake-flask experiment and ³¹P-NMR analysis.

The Synthesis and Glycoside Formation of Polyfluorinated Carbohydrates

Fluorinated carbohydrates have found many applications in the glycosciences. Typically, these contain fluorination at a single position. There are not many applications involving polyfluorinated carbohydrates, here defined as monosaccharides in which more than one carbon has at least one fluorine substituent directly attached to it, with the notable exception of their use as mechanism-based inhibitors. The increasing attention to carbohydrate physical properties, especially around lipophilicity, has resulted in a surge of interest for this class of compounds. This review covers the considerable body of work toward the synthesis of polyfluorinated hexoses, pentoses, ketosugars, and aminosugars including sialic acids and nucleosides. An overview of the current state of the art of their glycosidation is also provided.

Revisiting pesticide pollution: The case of fluorinated pesticides

Fluorinated pesticides acquired a significant market share in the agrochemical sector due to the surge of new fluoroorganic ingredients approved in the last two decades. This growing trend has not been accompanied by a comprehensive scientific and regulatory framework entailing all their potential negative impacts for the environment, especially when considering the hazardous properties that may result from the incorporation of fluorine into organic molecules. This review aims to address the safe/hazardous dichotomy associated with fluorinated pesticides by providing an updated outlook on their relevancy in the agrochemical sector and how it leads to their role as environmental pollutants. Specifically, the environmental fate and distribution of these pesticides in the ecosystems is discussed, while also analysing their potential to act as toxic substances for non-target organisms.

Fundamental curiosity of multivicinal inter-halide stereocenters

A stereoselective strategy allowed the striking impact of a single halogen on the physical properties of inter-halide alkane units to be unravelled.

Hexafluoroisobutylation of Enolates Through a Tandem Elimination/Allylic Shift/Hydrofluorination Reaction

The isobutyl side chain is a highly prevalent hydrophobic group in drugs, and it notably constitutes the side chain of leucine. Its replacement by a hexafluorinated version containing two CF3...

De Novo Synthesis of Orthogonally-Protected C2-Fluoro Digitoxoses and Cymaroses: Development and Application for the Synthesis of Fluorinated Digoxin

Inspired by Roush's pioneering work on rare sugars, we have developed a scalable, stereoselective, de novo synthesis of orthogonally protected C2-fluoro digitoxose and cymarose, utilizing Sharpless kinetic resolution and organocatalytic fluorination as key steps. The utility of this strategy is demonstrated by the synthesis of a fluorinated analogue of digoxin, which indicates the fluorine on the sugar ring may have a significant impact on biological activity.

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.

29th Annual GP2A Medicinal Chemistry Conference

The 29th Annual GP₂A (Group for the Promotion of Pharmaceutical chemistry in Academia) Conference was a virtual event this year due to the COVID-19 pandemic and spanned three days from Wednesday 25 to Friday 27 August 2021. The meeting brought together an international delegation of researchers with interests in medicinal chemistry and interfacing disciplines. Abstracts of keynote lectures given by the 10 invited speakers, along with those of the 8 young researcher talks and the 50 flash presentation posters, are included in this report. Like previous editions, the conference was a real success, with high-level scientific discussions on cutting-edge advances in the fields of pharmaceutical chemistry.

Fluorinated quorum sensing inhibitors: enhancement of potency through conformational control

The bacterial quorum sensing (QS) system is a target for non-lethal antibacterial agents that do not encourage the development of resistance. QS inhibitors commonly contain a polar "head" moiety and a lipidic "tail" moiety. In this work, we synthesised novel QS inhibitor candidates in which the lipidic "tail" is decorated with stereospecifically positioned fluorine atoms. The presence of fluorine is shown to bias the molecules into distinctive conformations that are pre-organised for binding to the QS receptor. This translates into significant increases in QS inhibitory potency.

Protecting-Group-Free Synthesis of GB1107: An Orally Active Galectin-3 Antagonist

Small-molecule galectin inhibitors are useful research tools that could also be used as potential drug candidates. In that context, GB1107, a monosaccharidic galectin inhibitor, was shown to be an orally active galectin-3 antagonist that inhibits lung adenocarcinoma growth. Herein, a protecting-group-free synthesis of GB1107, along with other analogues is described. Starting from inexpensive levoglucosan, a Payne rearrangement/azidation process was used as key step. Finally, the use of a log P determination method based on 19F NMR spectroscopy was explored to assess the lipophilicity of galectin inhibitors.

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.

An examination of the relationship between molecular dipole moment and blood-gas partition for common anaesthetic gases

The solubility of inhalational anaesthetics in the bloodstream is related to the minimum alveolar concentration (MAC), which is an indicator of anaesthetic gas potency. The blood-gas partition coefficient (Kbg) is a measure of how much anaesthetics bind to plasma proteins in the blood compared to air. Just like the octanol-water partition coefficient, the Kbg may be related to the molecular dipole moment (μ), which can be modulated by the molecular conformation. Our quantum-chemical calculations demonstrated that subtle stereoelectronic interactions, namely those responsible for the anomeric and gauche effects, control the conformational equilibrium of some widely used volatile fluorinated anaesthetics and, consequently, of their molecular dipole moments. Since a remarkable correlation between empirical Kbg and calculated μ was found for these anaesthetics, the average molecular dipole moments may be used to predict the anaesthetic gas potency and other properties, such as lipid solubility, of inhalational anaesthetic analogs.

Experimental lipophilicity scale for coded and noncoded amino acid residues

Among other features, the polarity of amino acid residues is the key parameter for understanding their role in proteins. The wide occurrence of protein modifications in nature and the advent of genetic code engineering techniques created a need for an experimental polarity value integrating both coded (canonical) and noncoded (noncanonical) residues on one universal scale. To address this issue, this work reports on a polarity scale based on the experimental lipophilicity of methyl esters of N-acetylamino acids. The derivatization of amino acids was performed in two steps under mild conditions that allowed conversion of a wide array of amino acids into analytical derivatives. The partitioning/distribution between octan-1-ol and water/buffer was measured using the intensity of the NMR signal as a characteristic for the concentration. The reference set of twenty coded amino acids generated log P values spanning 5.1 units: from tryptophan being the most hydrophobic to aspartate being the most hydrophilic. Furthermore, lipophilicity was measured for a set of analogues of phenylalanine, tyrosine, tryptophan, methionine, proline, and lysine that are typical in nature and/or laboratory practice. The polarity scale reported here will aid the rationalization of amino acid replacements in proteins, and will guide further efforts in experimental genetic code engineering.

Effects of Replacing Oxygenated Functionality with Fluorine on Lipophilicity

The replacement of oxygenated functionality (hydroxy and alkoxy) with a fluorine atom is a commonly used bioisosteric replacement in medicinal chemistry. In this paper, we use molecular matched-pair analysis to better understand the effects of this replacement on lipophilicity. It seems that the reduced log P of the oxygenated compound is normally dominant in determining the size of this difference. We observe that the presence of additional electron-donating groups on an aromatic ring generally increases the difference in lipophilicity between an oxygenated compound and its fluorinated analogue, while electron-withdrawing groups lead to smaller differences. Ortho-substituted compounds generally display a reduced difference in log P compared to para- and meta-substituted compounds, particularly if an ortho-substituent can form an intramolecular hydrogen bond. Hydrogen-bond acceptors remote to an aromatic ring containing fluorine/oxygen can also reduce the difference in log P between oxygen- and fluorine-substituted compounds.

Synthesis and Structural Characteristics of all Mono- and Difluorinated 4,6-Dideoxy-d-xylo-hexopyranoses

Protein-carbohydrate interactions are implicated in many biochemical/biological processes that are fundamental to life and to human health. Fluorinated carbohydrate analogues play an important role in the study of these interactions and find application as probes in chemical biology and as drugs/diagnostics in medicine. The availability and/or efficient synthesis of a wide variety of fluorinated carbohydrates is thus of great interest. Here, we report a detailed study on the synthesis of monosaccharides in which the hydroxy groups at their 4- and 6-positions are replaced by all possible mono- and difluorinated motifs. Minimization of protecting group use was a key aim. It was found that introducing electronegative substituents, either as protecting groups or as deoxygenation intermediates, was generally beneficial for increasing deoxyfluorination yields. A detailed structural study of this set of analogues demonstrated that dideoxygenation/fluorination at the 4,6-positions caused very little distortion both in the solid state and in aqueous solution. Unexpected trends in α/β anomeric ratios were identified. Increasing fluorine content always increased the α/β ratio, with very little difference between regio- or stereoisomers, except when 4,6-difluorinated.

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.

Synthesis of multiply fluorinated N-acetyl-D-glucosamine and D-galactosamine analogs via the corresponding deoxyfluorinated glucosazide and galactosazide phenyl thioglycosides

Multiple fluorination of glycostructures has emerged as an attractive way of modulating their protein affinity, metabolic stability, and lipophilicity. Here we described the synthesis of a series of mono-, di- and trifluorinated N-acetyl-ᴅ-glucosamine and ᴅ-galactosamine analogs. The key intermediates are the corresponding multiply fluorinated glucosazide and galactosazide thioglycosides prepared from deoxyfluorinated 1,6-anhydro-2-azido-β-ᴅ-hexopyranose precursors by ring-opening reaction with phenyl trimethylsilyl sulfide. Nucleophilic deoxyfluorination at C4 and C6 by reaction with DAST, thioglycoside hydrolysis and azide/acetamide transformation completed the synthesis.

Modulation of the H-Bond Basicity of Functional Groups by α-Fluorine-Containing Functions and its Implications for Lipophilicity and Bioisosterism

Modulation of the H-bond basicity (pK_HB) of various functional groups (FGs) by attaching fluorine functions and its impact on lipophilicity and bioisosterism considerations are described. In general, H/F replacement at the α-position to H-bond acceptors leads to a decrease of the pK_HB value, resulting, in many cases, in a dramatic increase in the compounds' lipophilicity (log P_o/w). In the case of α-CF₂H, we found that these properties may also be affected by intramolecular H-bonds between CF₂H and the FG. A computational study of ketone and sulfone series revealed that α-fluorination can significantly affect overall polarity, charge distribution, and conformational preference. The unique case of α-di- and trifluoromethyl ketones, which exist in octanol/water phases as ketone, hemiketal, and gem-diol forms, in equilibrium, prevents direct log P_o/w determination by conventional methods, and therefore, the specific log P_o/w values of these species were determined directly, for the first time, using Linclau's ¹⁹F NMR-based method.

One-Step Synthesis of Carbon Nanoparticles Capable of Long-Term Tracking Lipid Droplet for Real-Time Monitoring of Lipid Catabolism and Pharmacodynamic Evaluation of Lipid-Lowering Drugs

Lipid droplets (LDs) are intracellular lipid-rich organelles, which not only serve as neutral lipid reservoirs but also involve in many physiological processes and are associated with a variety of metabolic diseases and cancers. Long-term tracking of the state and behavior of LDs is of great significance but challenging. The difficulty is largely due to the lack of low cytotoxicity, high photobleaching resistance, and long intracellular retention probes that are capable of long-term tracking LDs. Herein, we report the discovery of two amphiphilic LD-targeting carbon nanoparticles (CNPs, i.e., CPDs and CDs) prepared by one-step room-temperature and hydrothermal methods. Their high lipid-water partition coefficient (log P > 2.13) and strong positive solvatochromism property ensure the quality of LD imaging. Especially, CDs exhibit favorable biocompatibility (2 mg mL^-1, cell viability >90%), excellent photostability (after continuous laser irradiation on a confocal microscope for 2 h, relative FL intensity >85%), and superior intracellular retention ability, thereby enabling long-term tracking of LDs in hepatocytes for up to six passages. Based on the excellent long-term tracking ability, CDs are successfully applied to observe autophagy in a typical catabolic process and to evaluate the effect of a commonly used lipid-lowering drug atorvastatin on hepatocyte lipid uptake.

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.

Fluorinated carbohydrates as chemical probes for molecular recognition studies. Current status and perspectives

This review provides an extensive summary of the effects of carbohydrate fluorination with regard to changes in physical, chemical and biological properties with respect to regular saccharides. The specific structural, conformational, stability, reactivity and interaction features of fluorinated sugars are described, as well as their applications as probes and in chemical biology.

The effect of deoxyfluorination and O-acylation on the cytotoxicity of N-acetyl-D-gluco- and D-galactosamine hemiacetals

Fully acetylated deoxyfluorinated hexosamine analogues and non-fluorinated 3,4,6-tri-O-acylated N-acetyl-hexosamine hemiacetals have previously been shown to display moderate anti-proliferative activity. We prepared a set of deoxyfluorinated GlcNAc and GalNAc hemiacetals that comprised both features: O-acylation at the non-anomeric positions with an acetyl, propionyl and butanoyl group, and deoxyfluorination at selected positions. Determination of the in vitro cytotoxicity towards the MDA-MB-231 breast cancer and HEK-293 cell lines showed that deoxyfluorination enhanced cytotoxicity in most analogues. Increasing the ester alkyl chain length had a variable effect on the cytotoxicity of fluoro analogues, which contrasted with non-fluorinated hemiacetals where butanoyl derivatives had always higher cytotoxicity than acetates. Reaction with 2-phenylethanethiol indicated that the recently described S-glyco-modification is an unlikely cause of cytotoxicity.

Fluorinated Carbohydrates as Lectin Ligands: Simultaneous Screening of a Monosaccharide Library and Chemical Mapping by 19F NMR Spectroscopy

Molecular recognition of carbohydrates is a key step in essential biological processes. Carbohydrate receptors can distinguish monosaccharides even if they only differ in a single aspect of the orientation of the hydroxyl groups or harbor subtle chemical modifications. Hydroxyl-by-fluorine substitution has proven its merits for chemically mapping the importance of hydroxyl groups in carbohydrate-receptor interactions. 19F NMR spectroscopy could thus be adapted to allow contact mapping together with screening in compound mixtures. Using a library of fluorinated glucose (Glc), mannose (Man), and galactose (Gal) derived by systematically exchanging every hydroxyl group by a fluorine atom, we developed a strategy combining chemical mapping and 19F NMR T2 filtering-based screening. By testing this strategy on the proof-of-principle level with a library of 13 fluorinated monosaccharides to a set of three carbohydrate receptors of diverse origin, i.e. the human macrophage galactose-type lectin, a plant lectin, Pisum sativum agglutinin, and the bacterial Gal-/Glc-binding protein from Escherichia coli, it became possible to simultaneously define their monosaccharide selectivity and identify the essential hydroxyls for interaction.

Enantioselective Construction of Tertiary Fluoride Stereocenters by Organocatalytic Fluorocyclization

1,1-Disubstituted styrenes with internal oxygen and nitrogen nucleophiles undergo oxidative fluorocyclization reactions with in situ generated chiral iodine(III)-catalysts. The resulting fluorinated tetrahydrofurans and pyrrolidines contain a tertiary carbon–fluorine stereocenter. Application of a new 1-naphthyllactic acid-based iodine(III)-catalyst allows the control of tertiary carbon–fluorine stereocenters with up to 96% ee. Density functional theory calculations are performed to investigate the details of the mechanism and the factors governing the stereoselectivity of the reaction.

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.

Fluoroalkyl-Substituted Cyclopropane Derivatives: Synthesis and Physicochemical Properties

A series of all 12 cis- and trans-cyclopropanecarboxylic acids and cyclopropylamines bearing CH₂F, CHF₂, and CF₃ substituents were synthesized by different methods on a multigram scale. Dissociation constants (pK_a) and log P values were measured for the obtained compounds or their derivatives to evaluate the influence of the type and relative position of fluoroalkyl substituents on the acidity and lipophilicity of monofunctionalized cyclopropanes. An analysis of the selected products by X-ray crystallography was carried out to obtain a better insight into the observed differences in physicochemical properties.

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.

Lipophilicity trends upon fluorination of isopropyl, cyclopropyl and 3-oxetanyl groups

A systematic comparison of lipophilicity modulations upon fluorination of isopropyl, cyclopropyl and 3-oxetanyl substituents, at a single carbon atom, is provided using directly comparable, and easily accessible model compounds. In addition, comparison with relevant linear chain derivatives is provided, as well as lipophilicity changes occurring upon chain extension of acyclic precursors to give cyclopropyl containing compounds. For the compounds investigated, fluorination of the isopropyl substituent led to larger lipophilicity modulation compared to fluorination of the cyclopropyl substituent.