Synthesis of chiral and bioactive fluoroorganic compounds

Chemistry of 3-hydroxy-2-aryl acrylate: syntheses, mechanisms, and applications

3-Hydroxy-2-aryl acrylate is important scaffold which is widely used for the synthesis of pharmacologically active compounds. This review summarises the synthetic methods of the 3-hydroxy-2-aryl acrylate including mechanisms and applications.

Applications of alkyl orthoesters as valuable substrates in organic transformations, focusing on reaction media

In this review we focus on applications of alkyl orthoesters as valuable and efficient substrates to perform various classes of two-component and multi-component organic reactions. The article has classified them according to two aspects, which are: (i) a focus on the reaction medium (solvent-free conditions, aqueous media, and organic solvents); and (ii) an examination of product structures. Reaction accomplishment under solvent-free conditions is an eco-friendly process with the absence of volatile toxic solvents, which puts it in line with green chemistry goals. Water is an interesting choice in organic transformations due to its inexpensiveness and safety. The authors hope their assessment will help chemists to attain new approaches for utilizing alkyl orthoesters in various organic synthetic methods. The review covers the corresponding literature up to the beginning of 2020.

In this review we focus on applications of alkyl orthoesters as valuable and efficient substrates to perform various classes of two-component and multi-component organic reactions.

Experimental and computational studies on the formation and biological properties of the simplest polyfluoroalkyl phosphonates

The simplest polyfluoroalkyl phosphonates exhibit high cell-line specific cytotoxicity.

Electrophilic Triflyl-arylation and Triflyl-pyridylation by Unsymmetrical Aryl/Pyridyl-λ3-iodonium Salts: Synthesis of Aryl and Pyridyl Triflones

Unsymmetrical diaryl-λ³-iodonium salts containing aryl triflone (Ar-SO₂CF₃) were designed and synthesized. X-ray crystal structure analysis of the salt indicated a T-shaped geometry at the iodine atom. The salts were found to be powerful electrophilic reagents for triflyl-arylation of C-, N-, and O-centered nucleophiles under mild conditions. Electrophilic transfer of pyridine triflone (Py-SO₂CF₃) to nucleophiles was also realized by the use of corresponding triflylpyridyl-aryl-λ³-iodonium salts. Selection of auxiliaries (dummy ligands) of unsymmetrical diaryl-λ³-iodonium salts is crucial for this transformation.

Synthesis and Antiviral Evaluation of Fluorinated Dipyridodiazepinones and Dipyridodiazepines (Nevirapine Derivatives)

The synthesis of trifluoromethyldipyridodiazepinones, which are analogues of nevirapine, one of the non-nucleoside inhibitors of the HIV-1 RT enzyme, is described. The condensation of 3-amino-2-chloro-4-tri-fluoromethyl pyridine with 2-chloronicotinoyl chloride followed by a cyclization with cyclopropylamine provided the corresponding trifluoromethylated dipyridodiazepinone. Similarly, the dipyridodiazepine analogues were synthesized by condensation of 3-amino-2-chloro-4-trifluoromethylpyridine with the O-mesyl derivative of 2-chloro-3-pyridincarbinol followed by reaction with cyclopropylamine. The inhibitory effect of these compounds on the HIV-1-induced cytopathic effect in MT4 cells has been evaluated.

Studies toward the oxidative and reductive activation of C-S bonds in 2'-S-aryl-2'-thiouridine derivatives

Studies directed toward the oxidative and reductive desulfurization of readily available 2'-S-aryl-2'-thiouridine derivatives were investigated with the prospect to functionalize the C2'-position of nucleosides. The oxidative desulfurization-difluorination strategy was successful on 2-(arylthio)alkanoate surrogates, while extension of the combination of oxidants and fluoride sources was not an efficient fluorination protocol when applied to 2'-S-aryl-2'-thiouridine derivatives, resulting mainly in C5-halogenation of the pyrimidine ring and C2'-monofluorination without desulfurization. Cyclic voltammetry of 2'-arylsulfonyl-2'-deoxyuridines and their 2'-fluorinated analogues showed that cleavage of the arylsulfone moiety could occur, although at relatively high cathodic potentials. While reductive-desulfonylation of 2'-arylsulfonyl-2'-deoxyuridines with organic electron donors (OEDs) gave predominantly base-induced furan type products, chemical (OED) and electrochemical reductive-desulfonylation of the α-fluorosulfone derivatives yielded the 2'-deoxy-2'-fluorouridine and 2',3'-didehydro-2',3'-dideoxy-2'-fluorouridine derivatives. These results provided good evidence of the generation of a C2'-anion through carbon-sulfur bond cleavage, opening new horizons for the reductive-functionalization approaches in nucleosides.

Integrase Inhibitor Prodrugs: Approaches to Enhancing the Anti-HIV Activity of β-Diketo Acids

HIV integrase, encoded at the 3'-end of the HIV pol gene, is essential for HIV replication. This enzyme catalyzes the incorporation of HIV DNA into human DNA, which represents the point of "no-return" in HIV infection. Integrase is a significant target in anti-HIV drug discovery. This review article focuses largely on the design of integrase inhibitors that are β-diketo acids constructed on pyridinone scaffolds. Methodologies for synthesis of these compounds are discussed. Integrase inhibition data for the strand transfer (ST) step are compared with in vitro anti-HIV data. The review also examines the issue of the lack of correlation between the ST enzymology data and anti-HIV assay results. Because this disconnect appeared to be a problem associated with permeability, prodrugs of these inhibitors were designed and synthesized. Prodrugs dramatically improved the anti-HIV activity data. For example, for compound, 96, the anti-HIV activity (EC50) improved from 500 nM for this diketo acid to 9 nM for its prodrug 116. In addition, there was excellent correlation between the IC50 and IC90 ST enzymology data for 96 (6 nM and 97 nM, respectively) and the EC50 and EC90 anti-HIV data for its prodrug 116 (9 nM and 94 nM, respectively). Finally, it was confirmed that the prodrug 116 was rapidly hydrolyzed in cells to the active compound 96.

Visible light-mediated atom transfer radical addition via oxidative and reductive quenching of photocatalysts

Herein, the development of visible light-mediated atom transfer radical addition (ATRA) of haloalkanes onto alkenes and alkynes using the reductive and oxidative quenching of [Ir{dF(CF(3))ppy}(2)(dtbbpy)]PF(6) and [Ru(bpy)(3)]Cl(2) is presented. Initial investigations indicated that the oxidative quenching of photocatalysts could effectively be utilized for ATRA, and since that report, the protocol has been expanded by broadening the scope of the reaction in terms of the photocatalysts, substrates, and solvents. In addition, further modifications of the reaction conditions allowed for the efficient ATRA of perfluoroalkyl iodides onto alkenes and alkynes utilizing the reductive quenching cycle of [Ru(bpy)(3)]Cl(2) with sodium ascorbate as the sacrificial electron donor. These results signify the complementary nature of the oxidative and reductive quenching pathways of photocatalysts and the ability to predictably direct reaction outcome through modification of the reaction conditions.

Asymmetric catalytic Mannich-type reaction of hydrazones with difluoroenoxysilanes using imidazoline-anchored phosphine ligand-zinc(II) complexes

Asymmetric Mannich-type reaction of hydrazones with difluoroenoxysilanes using chiral zinc(II)-imidazoline-phosphine complexes as catalysts have been established, giving the corresponding adducts in good to excellent enantioselectivity and chemical yields under mild conditions.

Fluorine: a new element in protein design

Fluorocarbons are quintessentially man-made molecules, fluorine being all but absent from biology. Perfluorinated molecules exhibit novel physicochemical properties that include extreme chemical inertness, thermal stability, and an unusual propensity for phase segregation. The question we and others have sought to answer is to what extent can these properties be engineered into proteins? Here, we review recent studies in which proteins have been designed that incorporate highly fluorinated analogs of hydrophobic amino acids with the aim of creating proteins with novel chemical and biological properties. Fluorination seems to be a general and effective strategy to enhance the stability of proteins, both soluble and membrane bound, against chemical and thermal denaturation, although retaining structure and biological activity. Most studies have focused on small proteins that can be produced by peptide synthesis as synthesis of large proteins containing specifically fluorinated residues remains challenging. However, the development of various biosynthetic methods for introducing noncanonical amino acids into proteins promises to expand the utility of fluorinated amino acids in protein design.

The conformers of 3-fluoroalanine. A theoretical study

Quantum chemical calculations (DFT, SCS-MP2) show that the relative energies of the four principal alanine conformations are only marginally altered by the introduction of a single fluorine substituent into the methyl group. The fluorine gauche effect and attractive interactions of fluorine to the O-H or N-H moieties (formation of hydrogen bridges) do stabilize particular conformers of 3-fluoroalanine. This is true for the neutral molecule both in the gas phase and in aqueous solution (CPCM-model), but also for the zwitterionic forms and the conformers of the related carboxylate ions and also for the respective ammonium ions in aqueous solution. In water (CPCM calculations), the zwitterion is almost equal in energy to the most stable conformer of the neutral 3-fluoroalanine. Compared to alanine the atomic charges of the amino group and the carboxyl function of 3-fluoroalanine are not significantly influenced by the fluorine at C3, which relates to the fact that both experimental pK(a) values are almost equal for alanine and 3-fluoroalanine.

Electrochemical nickel-induced fluoroalkylation: synthetic, structural and mechanistic study

Electrocatalytic generation of nickel catalysts in low oxidation states by reduction of nickel complexes with various ligands (2,2'-bipyridine, 2,2':6',2''-terpyridine, (S,S)-2,6-bis(4-phenyl-2-oxazolin-2-yl)-pyridine) in the presence of olefinic substrates and fluoroalkyl halides leads to new organic products derived from addition-dimerization processes. Due to the presence of two stereocenters in the dimerization products two diastereomers were characterized by a variety of analytical techniques including multi-dimensional NMR methods and X-ray single crystal diffraction. The formation of dimers was prevented by the inclusion of the hydrogen atom donor tributyltin hydride. The cyclic voltammetry study of selected nickel complexes along with fluoroalkyl halides demonstrated that Ni(I)L is the active form of the catalyst.

Discovery of a Potent HIV Integrase Inhibitor that Leads to a Prodrug with Significant anti-HIV Activity

Worldwide research efforts in drug discovery involving HIV integrase have produced only one compound, raltegravir, that has been approved for clinical use in HIV/AIDS. As resistance, toxicity and drug-drug interactions are recurring issues with all classes of anti-HIV drugs, the discovery of novel integrase inhibitors remains a significant scientific challenge. We have designed a lead HIV-1 strand transfer (ST) inhibitor (IC(50) 70 nM), strategically assembled on a pyridinone scaffold. A focused structure-activity investigation of this parent compound led to a significantly more potent ST inhibitor, 2 (IC(50) 6 ± 3 nM). Compound 2 exhibits good stability in pooled human liver microsomes. It also displays a notably favorable profile with respect to key human cytochrome P450 (CYP) isozymes and human UDP glucuronosyl transferases (UGTs). The prodrug of inhibitor 2, i.e., compound 10, was found to possess remarkable anti-HIV-1 activity in cell culture (EC(50) 9 ± 4 nM, CC(50) 135 ± 7 μM, therapeutic index = 15,000).

Efficient synthesis and biological properties of the 2′-trifluoromethyl analogues of acyclic nucleosides and acyclic nucleoside phosphonates

Efficient and optimized procedure for the preparation of several acyclic nucleosides and acyclic nucleoside phosphonates substituted at the C-2′ position of the aliphatic part by the trifluoromethyl group is described. Trifluoromethyloxirane was found to be an excellent reagent for the introduction of the 1,1,1-trifluoropropan-2-ol moiety. Surprisingly, the next reaction of these 1,1,1-trifluoropropan-2-ols with the reagent for the introduction of the methylphosphonic residue afforded the desired phosphonates in very high yields and finally a novel simple and scalable procedure for the isolation of free phosphonic acids, after the reaction of dialkyl phosphonates with bromotrimethylsilane, was developed. Prepared compounds were evaluated for their biological properties, but none of the prepared phosphonic acids or acyclic nucleosides exhibits any antiviral, antiproliferative or anti-toxin activities.

Beta-peptide bundles with fluorous cores

We reported recently that certain beta-peptides self-assemble spontaneously into cooperatively folded bundles whose kinetic and thermodynamic metrics mirror those of natural helix bundle proteins. The structures of four such beta-peptide bundles are known in atomic detail. These structures reveal a solvent-sequestered, hydrophobic core stabilized by a unique arrangement of leucine side chains and backbone methylene groups. Here we report that this hydrophobic core can be re-engineered to contain a fluorous subdomain while maintaining the characteristic beta-peptide bundle fold. Like alpha-helical bundles possessing fluorous cores, fluorous beta-peptide bundles are stabilized relative to hydrocarbon analogues and undergo cold denaturation. Beta-peptide bundles with fluorous cores represent the essential first step in the synthesis of orthogonal protein assemblies that can sequester selectively in an interstitial membrane environment.

A New Paradigm for Protein Design and Biological Self-Assembly

Very few molecules with biological origins contain the element fluorine. Nature's inability to incorporate fluorine into biomolecules is related to the low concentration of free fluoride in sea and surface water. However, judicious introduction of fluorine into proteins, nucleic acids, lipids and carbohydrates has allowed mechanistic scrutiny of enzyme catalysis, control of protein oligomerization in membranes, clustered display of ligands on surfaces of living cells, and in increasing the protease stability of protein and peptide therapeutics.

Fluorine--a new element in the design of membrane-active peptides

Antimicrobial peptides (also known as genetically encoded peptide antibiotics) are a diverse class of short cationic amphipathic polypeptides that exhibit a broad-spectrum of antimicrobial activities by selectively disrupting the bacterial cell membrane. In this review article, we present the use of fluorinated amino acids in the design of antimicrobial peptides and other membrane-active peptides.