Roles of Fluorine in Drug Design and Drug Action

Controllable Synthesis of Cyclopenta[b]indolines via Photocatalytic Fluoroalkylative Radical Cyclization Cascade of Ynamides

A de novo method for direct construction of cyclopenta[b]indolines via a photocatalytic fluoroalkylative radical cyclization cascade of ynamides has been established, which proceeds via a sequence of radical addition, 1,5-HAT, 5-endo-trig cyclization, intramolecular arylation, and oxidative deprotonation. This protocol allows for the controllable assembly of a tricyclic architecture with three contiguous stereocenters, showcasing its high efficiency, compatibility, and regio- and diastereoselectivity for accessing pharmacologically significant fluoroalkylated cyclopenta[b]indolines. It represents one of the very few examples of tetrafunctionalization of alkynes.

The Role of Small Molecules Containing Fluorine Atoms in Medicine and Imaging Applications

The fluorine atom possesses many intrinsic properties that can be beneficial when incorporated into small molecules. These properties include the atom's size, electronegativity, and ability to block metabolic oxidation sites. Substituents that feature fluorine and fluorine-containing groups are currently prevalent in drugs that lower cholesterol, relieve asthma, and treat anxiety disorders, as well as improve the chemical properties of various medications and imaging agents. The dye scaffolds (fluorescein/rhodamine, coumarin, BODIPY, carbocyanine, and squaraine dyes) reported will address the incorporation of the fluorine atom in the scaffold and the contribution it provides to its application as an imaging agent. It is also important to recognize radiolabeled fluorine atoms used for PET imaging in the early detection of diseases. This review will discuss the many benefits of incorporating fluorine atoms into small molecules and give examples of fluorinated molecules used in the pharmaceutical industry and imaging techniques.

Insights into the mechanism of [3+2] cycloaddition reactions between N-benzyl fluoro nitrone and maleimides, its selectivity and solvent effects

We present a theoretical study of the [3+2] cycloaddition (32CA) reactions of N-benzyl fluoro nitrone with a series of maleimides producing isoxazolidines. We use the Molecular Electron Density Theory at the MPWB1K/6-311G(d) level. We focus on the reaction mechanism, selectivity, solvent, and temperature effects. In addition, we perform topological analyses at the minimal and transition states to identify the intermolecular interactions. Electron Localization Function approach classifies the N-benzyl fluoro nitrone as zwitterionic (zw-) three-atom components (TACs), associated with a high energy barrier. The low polar character of the reaction is evaluated using the Conceptual Density Functional Theory analysis of the reactants, confirmed by the low global electron density transfer computed at the transition states. Computations show that these 32CA reactions follow a one-step mechanism under kinetic control, with highly asynchronous bond formation and no new covalent bond is formed at the TS. Besides, the potential energy surfaces along the reaction pathways in gas phase and in solvent are mapped. The corresponding Gibbs free energy profiles reveal that the exo-cycloadducts are kinetically and thermodynamically more favored than endo-cycloadducts, in agreement with the exo-selectivity observed experimentally. In particular, we found that solvent and temperature did not affect this selectivity and mainly influence the activation energies and the exothermic character of these 32CA reactions.

Chiral phosphoric acid-catalyzed transfer hydrogenation of 3,3-difluoro-3H-indoles

A convenient and efficient method for the synthesis of optically active difluoro-substituted indoline derivatives starting from the corresponding 3H-indoles by chiral phosphoric acid-catalyzed transfer hydrogenation was developed. Using Hantzsch ester as the hydrogen source under mild reaction conditions, the target products can be obtained with excellent yield and enantioselectivity.

The Impact of Fluorination on the Design of Histone Deacetylase Inhibitors

In recent years, histone deacetylases (HDACs) have emerged as promising targets in the treatment of cancer. The approach is to inhibit HDACs with drugs known as HDAC inhibitors (HDACis). Such HDACis are broadly classified according to their chemical structure, e.g., hydroxamic acids, benzamides, thiols, short-chain fatty acids, and cyclic peptides. Fluorination plays an important role in the medicinal-chemical design of new active representatives. As a result of the introduction of fluorine into the chemical structure, parameters such as potency or selectivity towards isoforms of HDACs can be increased. However, the impact of fluorination cannot always be clearly deduced. Nevertheless, a change in lipophilicity and, hence, solubility, as well as permeability, can influence the potency. The selectivity towards certain HDACs isoforms can be explained by special interactions of fluorinated compounds with the structure of the slightly different enzymes. Another aspect is that for a more detailed investigation of newly synthesized fluorine-containing active compounds, fluorination is often used for the purpose of labeling. Aside from the isotope ¹⁹F, which can be detected by nuclear magnetic resonance spectroscopy, the positron emission tomography of ¹⁸F plays a major role. However, to our best knowledge, a survey of the general effects of fluorination on HDACis development is lacking in the literature to date. Therefore, the aim of this review is to highlight the introduction of fluorine in the course of chemical synthesis and the impact on biological activity, using selected examples of recently developed fluorinated HDACis.

Investigation of the Spatial Structure of Flufenamic Acid in Supercritical Carbon Dioxide Media via 2D NOESY

The search for new forms of already known drug compounds is an urgent problem of high relevance as more potent drugs with fewer side effects are needed. The trifluoromethyl group in flufenamic acid renders its chemical structure differently from other fenamates. This modification is responsible for a large number of conformational polymorphs. Therefore, flufenamic acid is a promising structural modification of well-known drug molecules. An effective approach in this field is micronization, employing "green" supercritical fluid technologies. This research raises some key questions to be answered on how to control polymorphic forms during the micronization of drug compounds. The results presented in this work demonstrate the ability of two-dimensional nuclear Overhauser effect spectroscopy to determine conformational preferences of small molecular weight drug compounds in solutions and fluids, which can be used to predict the polymorphic form during the micronization. Quantitative analysis was carried out to identify the conformational preferences of flufenamic acid molecules in dimethyl sulfoxide-d6 medium at 25 °C and 0.1 MPa, and in mixed solvent medium containing supercritical carbon dioxide at 45 °C and 9 MPa. The data presented allows predictions of the flufenamic acid conformational preferences of poorly soluble drug compounds to obtain new micronized forms.

Synthesis of Trifluoromethylated Monoterpene Amino Alcohols

For the first time, monoterpene trifluoromethylated β-hydroxy-benzyl-O-oximes were synthesized in 81–95% yields by nucleophilic addition of the Ruppert–Prakash reagent (TMSCF3) to the corresponding β-keto-benzyl-O-oximes based on (+)-nopinone, (−)-verbanone and (+)-camphoroquinone. Trifluoromethylation has been determined to entirely proceed chemo- and stereoselective at the C=O rather than C=N bond. Trifluoromethylated benzyl-O-oximes were reduced to the corresponding α-trifluoromethyl-β-amino alcohols in 82–88% yields. The structure and configuration of the compounds obtained have been established.

Synthesis of trifluoromethylated aza-BODIPYs as fluorescence-19F MRI dual imaging and photodynamic agents

Dual-imaging agents with highly sensitive fluorescence (FL) imaging and highly selective fluorine-19 magnetic resonance imaging (¹⁹F MRI) are valuable for biomedical research. At the same time, photosensitizers with a high reactive oxygen species (ROS) generating capability are crucial for photodynamic therapy (PDT) of cancer. Herein, a series of tetra-trifluoromethylated aza-boron dipyrromethenes (aza-BODIPYs) were conveniently synthesized from readily available building blocks and their physicochemical properties, including ultraviolet-visible (UV-Vis) absorption, FL emission, photothermal efficacy, ROS generating efficacy, and ¹⁹F MRI sensitivity, were systematically investigated. An aza-BODIPY with 12 symmetrical fluorines was identified as a potent FL-¹⁹F MRI dual-imaging traceable photodynamic agent. It was found that the selective introduction of trifluoromethyl (CF₃) groups into aza-BODIPYs may considerably improve their UV absorption, FL emission, photothermal efficacy, and ROS generating properties, which lays the foundation for the rational design of trifluoromethylated aza-BODIPYs in biomedical applications.

Direct Synthesis of α-Fluoro-α-Triazol-1-yl Ketones from Sulfoxonium Ylides: A One-Pot Approach

The work reported herein showcases a new route to access α-fluoro-α-triazol-1-yl ketones from sulfoxonium ylides via α-azido-α-fluoro ketone intermediates. In a one-pot, two-step sequence, the ketosulfoxonium reactant initially undergoes insertion of F⁺ and N₃^-, followed by a subsequent CuAAC reaction with arylacetylenes to install a 1,4-triazolo moiety. The approach allows for modification to both the sulfoxonium ylide and arylacetylene reactants. Fifteen examples have been reported, with yields ranging between 22% and 75%.

Unexpected metal-free synthesis of trifluoromethyl arenes via tandem coupling of dicyanoalkenes and conjugated fluorinated sulfinyl imines

A novel strategy for the synthesis of policyclic trifluoromethyl arenes has been devised. It involves a DBU-promoted tandem cycloaromatization reaction of dicyanoalkenes and fluorinated conjugated sulfinyl imines. This unprecedented transformation is a metal-free and air-tolerant process that takes place from readily available starting materials under mild reaction conditions.

The Acidities of Nucleophilic Monofluoromethylation Reagents: An Anomalous α-Fluorine Effect

Fluorine incorporation into organic molecules is expected to lower the pK_a of neighboring functionality via its strong electron-withdrawing effect, and this strategy has been widely exploited in diverse disciplines. Herein, we report a striking anomalous α-fluorine substitution effect on the α-C_sp3 -H acidity. We have experimentally measured the pK_a values of a series of popular nucleophilic monofluoromethylating reagents α-fluoro(phenylsulfonyl)methane derivatives as well as their C-H analogues by Bordwell's overlapping indicator method in dimethyl sulfoxide solution. Contrary to expectations, we found that α-fluorine substituent does not generally enhance but rather weaken the α-C_sp3 -H acidity of most (phenylsulfonyl)methane derivatives. DFT computations reproduce and provide insight into the anomalous α-fluorine effect. A correlation was identified between the C-H pK_a of (phenylsulfonyl)methane derivatives and Mayr's nucleophilicity parameter (N) of the corresponding carbanions.

Quantitative Structure-Activity Relationship and Docking Studies on a series of H+/K+-ATPase inhibitors

Background:

The Gastric H+/K+-ATPase is also known as proton pump is the enzyme responsible for the acidification of gastric juice. H+/K+ GastroEsophageal Reflux Disease (GERD) and other acid related diseases mainly depend on the inhibition of the gastric H+/K+- ATPase which will finally result in acid secretion in stomach. GERD is one of the diseases that have significant effect on the quality of human life and are the major burden on health care systems is that leads to heart burn, acid regurgitation, chest pain, epigastric pain, and respiratory conditions such as chronic cough. Hence the study of the inhibitors of Gastric H+/K+-ATPase is desired.

Methods:

Research and online content related to imidazo [1, 2-a]pyrazine and heterocyclic ring analogues (I) that were synthesized and evaluated for their Gastric H+/K+-ATPase inhibitory activity is reviewed, and in order to design and develop still better and more effective H+/K+-ATPase inhibitors, we have made Quantitative Structure Activity Relationship (QSAR), docking and ADMET studies on these compounds.

Results:

The best MLR equation based on four descriptors along with statistical parameters is obtained using Statistica dataminer software. Using the model expressed by this study we predicted some new compounds of high H+/K+-ATPase inhibition potency. Each predicted compound has very high potency with which only a few compounds of existing series can match.

Conclusion:

The QSAR and molecular modelling studies suggested that still better compounds can be designed if the flexibility of the molecules can be increased for which attempts can be made to have more saturated atoms in the molecules. Such a compound predicted by us was found to have interactions with the enzyme H+/K+-ATPase almost in the same manner as the FDA approved compounds, lansoprazole, pantaprazole.