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

Synthesis, antimicrobial properties and in silico evaluation of coumarin derivatives mediated by 1,4-dibromobutane

In this study, monobrominated coumarins (5-6) and bis-coumarins (7-9) were synthesized from 3-carboxylic coumarin and 7-hydroxy-4-methyl coumarin using 1,4-dibromobutane as a binding agent, according to the synthesis procedures described in the literature. Amongst these coumarins, three are new compounds: monobrominated coumarin 5 and bis-coumarins 7 and 9. The structures of the synthesized coumarins were confirmed by FTIR, NMR and HRMS-ESI. In vitro antimicrobial evaluation of these coumarins against strains of twelve bacteria and four fungi revealed their bactericidal and fungicidal properties, with increased antibacterial activity for monocoumarins and improved antifungal activity for bis-coumarins. It was also found that the antibacterial activity was enhanced by the etheric bond, Br atom and alkyl chain and reduced by the ester bonds at position 3 of the pyrone ring or an additional coumarin unit, while the antifungal activity was reinforced by ester bonds and deactivated by the Br atom. For the first time, the in silico investigations of such coumarins were carried out and it was observed that they are less toxic, suitable for oral administration with good permeability through cell membrane, are able to circulate freely in the bloodstream and cross Blood-Brain-Barriers. Moreover, their molecular docking in DNA indicated stable coumarin-DNA complexes with good scores. The results of molecular dynamics simulations performed for 200 ns revealed the rigidity and stability of bis-coumarins (7-9) in the DNA binding pocket and predict that they are potent binders.Communicated by Ramaswamy H. Sarma.

Mono- and Difluorinated Saturated Heterocyclic Amines for Drug Discovery: Systematic Study of Their Physicochemical Properties

A comprehensive study of physicochemical properties (pKa , LogP, and intrinsic microsomal clearance) within the series of mono- and difluorinated azetidine, pyrrolidine, and piperidine derivatives was performed. While the number of fluorine atoms and their distance to the protonation center were the major factors defining the compound's basicity, both pKa and LogP values were affected considerably by the conformational preferences of the corresponding derivatives. For example, features of "Janus face" (facially polarized) cyclic compounds (i. e., unusually high hydrophilicity) were identified for cis-3,5-difluoropiperidine, preferring a diaxial conformation. Intrinsic microsomal clearance measurements demonstrated high metabolic stability of the compounds studied (with a single exception of the 3,3-difluoroazetidine derivative). According to pKa - LogP plots, the title compounds provide a valuable extension of the fluorine-containing (e. g., fluoroalkyl-substituted) saturated heterocyclic amine series as building blocks for rational optimization studies in early drug discovery.

Lipophilicity Modulations by Fluorination Correlate with Membrane Partitioning

Bioactive compounds generally need to cross membranes to arrive at their site of action. The octanol-water partition coefficient (lipophilicity, logPOW ) has proven to be an excellent proxy for membrane permeability. In modern drug discovery, logPOW and bioactivity are optimized simultaneously, for which fluorination is one of the relevant strategies. The question arises as to which extent the often subtle logP modifications resulting from different aliphatic fluorine-motif introductions also lead to concomitant membrane permeability changes, given the difference in molecular environment between octanol and (anisotropic) membranes. It was found that for a given compound class, there is excellent correlation between logPOW values with the corresponding membrane molar partitioning coefficients (logKp ); a study enabled by novel solid-state 19 F NMR MAS methodology using lipid vesicles. Our results show that the factors that cause modulation of octanol-water partition coefficients similarly affect membrane permeability.

Development of Isopropyl-Tailed Chalcones as a New Class of Selective MAO-B Inhibitors for the Treatment of Parkinson's Disorder

Thirteen isopropyl chalcones (CA1-CA13) were synthesized and evaluated for their inhibitory activity against monoamine oxidase (MAO). All compounds inhibited MAO-B more effectively than MAO-A. Compound CA4 most potently inhibited MAO-B with an IC₅₀ value of 0.032 μM, similar to that of CA3 (IC₅₀ = 0.035 μM) and with high selectivity index (SI) values for MAO-B over MAO-A (SI = 49.75 and 353.23, respectively). The -OH (CA4) or -F (CA3) group at the para position on the A ring provided higher MAO-B inhibition than that of the other substituents (-OH ≥ -F > -Cl > -Br > -OCH₂CH₃ > -CF₃). On the other hand, compound CA10 most potently inhibited MAO-A with an IC₅₀ value of 0.310 μM and effectively MAO-B (IC₅₀ = 0.074 μM). The Br-containing thiophene substituent (CA10) instead of the A ring showed the highest MAO-A inhibition. In a kinetic study, K _i values of compounds CA3 and CA4 for MAO-B were 0.076 ± 0.001 and 0.027 ± 0.002 μM, respectively, and that of CA10 for MAO-A was 0.016 ± 0.005 μM. A reversibility study showed that CA3 and CA4 were reversible inhibitors of MAO-B and CA10 was a reversible inhibitor of MAO-A. In docking and molecular dynamics, the hydroxyl group of CA4 and two hydrogen bonds contributed to the stability of the protein-ligand complex. These results suggest that CA3 and CA4 are potent reversible selective MAO-B inhibitors and can be used for the treatment of Parkinson's disease.

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.

Fluorine-Containing Prolines: Synthetic Strategies, Applications, and Opportunities

Fluorinated prolines play an important role in peptide studies, protein engineering, medicinal chemistry, drug discovery, and agrochemistry. Since the first synthesis of 4-fluoroprolines by Gottlieb and Witkop in 1965, their popularity started to grow exponentially. For example, during the past two decades, all isomeric trifluoromethyl-substituted prolines have been synthesized. In this Perspective, chemical properties and applications of fluorinated prolines are discussed. Synthetic approaches to all known fluorine-containing prolines are also discussed and analyzed. This analysis unexpectedly revealed an unsolved problem: in strict contrast to fluoro- and trifluoromethyl-substituted prolines, the corresponding analogues with fluoromethyl and difluoromethyl groups are mostly unknown. At the end of the paper, structures of several interesting, yet unknown, fluorinated prolines are disclosed─a good opportunity for chemists to make them.

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.

Synthesis and Physicochemical Properties of 2-SF5-(Aza)Indoles, a New Family of SF5 Heterocycles

Structural diversity in heterocyclic chemistry is key to unlocking new properties and modes of action. In this regard, heterocycles embedding emerging fluorinated substituents hold great promise. Herein is described a strategy to access 2-SF₅-(aza)indoles for the first time. The sequence relies on the radical addition of SF₅Cl to the alkynyl π-system of 2-ethynyl anilines followed by a cyclization reaction. A telescoped sequence is proposed, making this strategy very appealing and reproducible on a gram scale. Downstream functionalizations are also demonstrated, allowing an easy diversification of N- and C3-positions. Ames test, pK _a, log P, and differential scanning calorimetry measurements of several fluorinated 2-Rf-indoles are also disclosed. These studies highlight the strategic advantages that a C2-pentafluorosulfanylated motif impart to a privileged scaffold such as an indole.

Hydrogen Bond Acceptor Propensity of Different Fluorine Atom Types: An Analysis of Experimentally and Computationally Derived Parameters

The propensity of organic fluorine acting as a weak hydrogen bond acceptor (HBA) in intermolecular and intramolecular interactions has been the subject of many experimental and theoretical studies often reaching different conclusions. Over the last few years, new and stronger evidences have emerged for the direct involvement of fluorine in weak hydrogen bond (HB) formation. However, not all the fluorine atom types can act as weak HBA. In this work, the differential HBA propensity of various types of fluorine atoms was analyzed with a particular emphasis for the different types of alkyl fluorides. This was carried out by evaluating ab initio computed parameters, experimental ¹⁹ F NMR chemical shifts and small molecule crystallographic structures (extracted from the CSD database). According to this analysis, shielded (with reference to the ¹⁹ F NMR chemical shift) alkyl mono-fluorinated motifs display the highest HBA propensity in agreement with solution studies. Although much weaker than other well-characterized HB complexes, the fragile HBs formed by these fluorinated motifs have important implications for the chemical-physical and structural properties of the molecules, chemical reactions, and protein-ligand recognition.