Enantioselective Synthesis of α-Trifluoromethyl Amines via Biocatalytic N-H Bond Insertion with Acceptor-Acceptor Carbene Donors.

The biocatalytic toolbox has recently been expanded to include enzyme-catalyzed carbene transfer reactions not occurring in Nature. Herein, we report the development of a biocatalytic strategy for the synthesis of enantioenriched α-trifluoromethyl amines through an asymmetric N-H carbene insertion reaction catalyzed by engineered variants of cytochrome c552 from Hydrogenobacter thermophilus. Using a combination of protein and substrate engineering, this metalloprotein scaffold was redesigned to enable the synthesis of chiral α-trifluoromethyl amino esters with up to >99% yield and 95:5 er using benzyl 2-diazotrifluoropropanoate as the carbene donor. When the diazo reagent was varied, the enantioselectivity of the enzyme could be inverted to produce the opposite enantiomers of these products with up to 99.5:0.5 er. This methodology is applicable to a broad range of aryl amine substrates, and it can be leveraged to obtain chemoenzymatic access to enantioenriched ß-trifluoromethyl-ß-amino alcohols and halides. Computational analyses provide insights into the interplay of protein- and reagent-mediated control on the enantioselectivity of this reaction. This work introduces the first example of a biocatalytic N-H carbenoid insertion with an acceptor-acceptor carbene donor, and it offers a biocatalytic solution for the enantioselective synthesis of α-trifluoromethylated amines as valuable synthons for medicinal chemistry and the synthesis of bioactive molecules.

Characterization of an aromatic trifluoromethyl ketone as a new warhead for covalently reversible kinase inhibitor design.

An aromatic trifluoromethyl ketone moiety was characterized as a new warhead for covalently reversible kinase inhibitor design to target the non-catalytic cysteine residue. Potent and selective covalently reversible inhibitors of FGFR4 kinase were successfully designed and synthesized by utilizing this new warhead. The binding mode of a representative inhibitor was fully characterized by using multiple technologies including MALDI-TOF mass spectrometry, dialysis assay and X-ray crystallographic studies etc. This functional group was also successfully applied to discovery of a new JAK3 inhibitor, suggesting its potential application in designing other kinase inhibitors.

Fluorinated S-Adenosylmethionine as a Reagent for Enzyme-Catalyzed Fluoromethylation.

Strategic replacement of protons with fluorine atoms or functional groups with fluorine-containing fragments has proven a powerful strategy to optimize the activity of therapeutic compounds. For this reason, the synthetic chemistry of organofluorides has been the subject of intense development and innovation for many years. By comparison, the literature on fluorine biocatalysis still makes for a slim chapter. Herein we introduce S-adenosylmethionine (SAM) dependent methyltransferases as a new tool for the production of fluorinated compounds. We demonstrate the ability of halide methyltransferases to form fluorinated SAM (S-adenosyl-S-(fluoromethyl)-L-homocysteine) from S-adenosylhomocysteine and fluoromethyliodide. Fluorinated SAM (F-SAM) is too unstable for isolation, but is accepted as a substrate by C-, N- and O-specific methyltransferases for enzyme-catalyzed fluoromethylation of small molecules.

Waterproof-breathable films from multi-branched fluorinated cellulose esters.

Cellulose ester films were prepared by esterification of cellulose with a multibranched fluorinated carboxylic acid, "BRFA" (BRanched Fluorinated Acid), at different anhydroglucose unit:BRFA molar ratios (i.e., 1:0, 10:1, 5:1, and 1:1). Morphological and optical analyses showed that cellulose-BRFA materials at molar ratios 10:1 and 5:1 formed flat and transparent films, while the one at 1:1 M ratio formed rough and translucent films. Degrees of substitution (DS) of 0.06, 0.09, and 0.23 were calculated by NMR for the samples at molar ratios 10:1, 5:1, and 1:1, respectively. ATR-FTIR spectroscopy confirmed the esterification. DSC thermograms showed a single glass transition, typical of amorphous polymers, at -11 °C. The presence of BRFA groups shifted the mechanical behavior from rigid to ductile and soft with increasing DS. Wettability was similar to standard fluoropolymers such as PTFE and PVDF. Finally, breathability and water uptake were characterized and found comparable to materials typically used in textiles.

Chemo-, regio- and stereoselective synthesis of monofluoroalkenes via a tandem fluorination-desulfonation sequence.

A widely applicable approach for the synthesis of Z-monofluoroalkenes from readily available alkyl triflones and NFSI has been reported. The reaction proceeded under mild conditions, affording mono-fluorinated alkenes in good to excellent yields with excellent chemo- regio- and stereoselectivity. The mechanism may involve electrophilic fluorination of triflones followed by the highly stereoselective concerted bimolecular elimination (E2) of CF3SO2H.

Synthesis and Biological Evaluation of CF3 Se-Substituted α-Amino Acid Derivatives.

Several CF3 Se-substituted α-amino acid derivatives, such as (R)-2-amino-3-((trifluoromethyl)selanyl)propanoates (5 a/6 a), (S)-2-amino-4-((trifluoromethyl)selanyl)butanoates (5 b/6 b), (2R,3R)-2-amino-3-((trifluoromethyl)selanyl)butanoates (5 c/6 c), (R)-2-((S)-2-amino-3-phenylpropanamido)-3-((trifluoromethyl)selanyl)propanoates (11 a/12 a), and (R)-2-(2-aminoacetamido)-3-((trifluoromethyl)selanyl)propanoates (11 b/12 b), were readily synthesized from natural amino acids and [Me4 N][SeCF3 ]. The primary in vitro cytotoxicity assays revealed that compounds 6 a, 11 a and 12 a were more effective cell growth inhibitors than the other tested CF3 Se-substituted derivatives towards MCF-7, HCT116, and SK-OV-3 cells, with their IC50 values being less than 10 µM for MCF-7 and HCT116 cells. This study indicated the potentials of CF3 Se moiety as a pharmaceutically relevant group in the design and synthesis of novel biologically active molecules.

The Effect of Vicinal Difluorination on the Conformation and Potency of Histone Deacetylase Inhibitors.

Histone deacetylase enzymes (HDACs) are potential targets for the treatment of cancer and other diseases, but it is challenging to design isoform-selective agents. In this work, we created new analogs of two established but non-selective HDAC inhibitors. We decorated the central linker chains of the molecules with specifically positioned fluorine atoms in order to control the molecular conformations. The fluorinated analogs were screened against a panel of 11 HDAC isoforms, and minor differences in isoform selectivity patterns were observed.

Copper-Catalyzed Enantioselective Difluoromethylation of Amino Acids via Difluorocarbene.

Difluoromethyl amino acids (DFAA) exhibit intriguing biological properties, making them highly desirable motifs in agrochemical and pharmaceutical science. However, stereochemical control of direct difluoromethyl transformation via the difluorocarbene species has not been demonstrated. Here we describe an efficient copper-catalyzed asymmetric difluoromethylation reaction that systematically delivers chiral DFAA as rationally designed mechanism-based inhibitors of PLP-dependent amino acid decarboxylases. The reaction employs difluoromonochloromethane, an abundant raw material, as the direct precursor of difluorocarbene species, enabling the unprecedentedly direct conversion of amino esters into corresponding valuable DFAA products in good yields with excellent enantioselectivities. This de novo synthesis creates opportunities to integrate an asymmetric catalytic platform for the preparation of diverse libraries of biologically important DFAA derivatives and will support efforts in both drug discovery and development.

Development of 18F-Labeled Radiotracers for PET Imaging of the Adenosine A2A Receptor: Synthesis, Radiolabeling and Preliminary Biological Evaluation.

The adenosine A2A receptor (A2AR) represents a potential therapeutic target for neurodegenerative diseases. Aiming at the development of a positron emission tomography (PET) radiotracer to monitor changes of receptor density and/or occupancy during the A2AR-tailored therapy, we designed a library of fluorinated analogs based on a recently published lead compound (PPY). Among those, the highly affine 4-fluorobenzyl derivate (PPY1; Ki(hA2AR) = 5.3 nM) and the 2-fluorobenzyl derivate (PPY2; Ki(hA2AR) = 2.1 nM) were chosen for 18F-labeling via an alcohol-enhanced copper-mediated procedure starting from the corresponding boronic acid pinacol ester precursors. Investigations of the metabolic stability of [18F]PPY1 and [18F]PPY2 in CD-1 mice by radio-HPLC analysis revealed parent fractions of more than 76% of total activity in the brain. Specific binding of [18F]PPY2 on mice brain slices was demonstrated by in vitro autoradiography. In vivo PET/magnetic resonance imaging (MRI) studies in CD-1 mice revealed a reasonable high initial brain uptake for both radiotracers, followed by a fast clearance.

Key Mechanistic Features of the Silver(I)-Mediated Deconstructive Fluorination of Cyclic Amines: Multistate Reactivity versus Single-Electron Transfer.

Density functional calculations have provided evidence that a Ag(I)-mediated deconstructive fluorination of N-benzoylated cyclic amines (LH) with Selectfluor [(F-TEDA)(BF4)2] begins with an association of the reactants to form a singlet state adduct {[(LH)-Ag]-[F-TEDA]2+}. The subsequent formation of an iminium ion intermediate, [L+-Ag]-HF-[TEDA]+, is, formally, a Ag(I)-mediated hydride abstraction event that occurs in two steps: (a) a formal oxidative addition (OA) of [F-TEDA]2+ to the Ag(I) center that is attended by an electron transfer (ET) from the substrate (LH) to the Ag center (i.e., OA + ET, this process can also be referred to as a F-atom coupled electron transfer), followed by (b) H-atom abstraction from LH by the Ag-coordinated F atom. The overall process involves lower-lying singlet and triplet electronic states of several intermediates. Therefore, we formally refer to this reaction as a two-state reactivity (TSR) event. The C-C bond cleavage/fluorination of the resulting hemiaminal intermediate via a ring-opening pathway has also been determined to be a TSR event. A competing deformylative fluorination initiated by hemiaminal to aldehyde equilibration involving formyl H-atom abstraction by a TEDA2+ radical dication, decarbonylation, and fluorination of the resulting alkyl radical by another equivalent of Selectfluor may also be operative in the latter step.

Design, synthesis and nematicidal activitives of trifluorobutene amide derivatives against Meloidogyne incognita.

Plant parasitic nematodes have always been a pressing problem in the field of plant protection. Well-established chemical nematicides, especially organophosphorus and carbamates are the most used products for nematode control worldwide. Due to long-term overuse, they have developed serious resistance and new innovative solutions are urgently required. In this study, thirty-one novel trifluorobutene amide derivatives were designed and synthesized, and their nematicidal activities were determined. Three different synthetic methods have been developed for the final amidation reaction enabling the successfully syntheses of the target compounds independently from the nucleophilicities of the substrate amino group. Most target compounds showed good nematicidal activity in our in vitro test. Among all the compounds, compounds A8 and A23 exhibited excellent nematicidal activity against Meloidogyne incognita, their LC50 values are 2.02 mg L-1 and 0.76 mg L-1, respectively. In particular, compound A23 has found to be almost as active as the commercial nematicide fluensulfone. Furthermore, most compounds gave full control (100% inhibition) of M. incognita at 40 mg L-1 in the in vivo tests in sandy soil, the best compounds were further investigated for in vivo activity in matrix soil. Among the compound tested, compound A8 showed excellent in vivo nematicidal activity. At a concentration of 5 mg L-1 still 56% inhibition was observed. The results of our study indicate that compound A8 possesses excellent in vitro and in vivo nematicidal activity, and can be considered as promising lead molecule for further modification.

Fluorinated Pyrazoles: From Synthesis to Applications.

Fluorinated pyrazoles play an important role in medicinal chemistry, drug discovery, agrochemistry, coordination chemistry, and organometallic chemistry. Since the early 1990s, their popularity has grown exponentially. Moreover, more than 50% of all contributions on the topic have been published in the last 5 years. In this review, analysis of novel synthetic approaches to fluorinated pyrazoles that appeared in recent years is performed. A particular emphasis is devoted to a detailed consideration of reaction mechanisms. In addition, the reasons that have led to the ever-increasing popularity of fluorinated pyrazoles in various areas of science are discussed. At the end of the review, several potentially interesting but yet mostly unknown classes of fluorinated pyrazoles are outlined.

Synthesis and evaluation of novel fluorinated hematoporphyrin ether derivatives for photodynamic therapy.

A photosensitizer with high phototoxicity, suitable amphipathy and low dark toxicity could play a pivotal role in photodynamic therapy (PDT). In this study, a facile and versatile approach was adopted to synthesize a series of novel fluorinated hematoporphyrin ether derivatives (I1-I5 and II1-II4), and the photodynamic activities of these compounds were studied. Compared to hematoporphyrin monomethyl ether (HMME), all PSs showed preferable photodynamic activity against A549 lung tumor cells. The longest visible absorption wavelength of these compounds was approximately 622 nm. Among them, II3 revealed the highest singlet oxygen yield (0.0957 min-1), the strongest phototoxicity (IC50 = 1.24 µM), the lowest dark toxicity in vitro, and exhibited excellent anti-tumor effects in vivo. So compound II3 could act as new drug candidate for photodynamic therapy.

Efficient chemoenzymatic synthesis of fluorinated sialyl Thomsen-Friedenreich antigens and investigation of their characteristics.

A set of fluorinated sialyl-T derivatives were efficiently synthesized using one-pot multi-enzyme (OPME) chemoenzymatic approach. The P. multocida α2-3-sialyltransferase (PmST1) involved in the synthesis showed extremely flexible donor and acceptor substrate specificities. These sialosides have been successfully investigated with stability towards Clostridium perfringens sialidase substrate specificity assay using 1H NMR spectroscopy. Hydrolysis studies monitored by 1H NMR clearly demonstrated that the fluorine substitution obviously reduced hydrolysis rate of Clostridium perfringens sialidase. To further investigate the fluorine influence, structure-dependent variation of sialoside-lectin binding was observed for MAL and different sialoside-immobilized surfaces. Subtle changes on the ligand of carbohydrate-binding protein were distinguished by SPR. These fluorinated sialyl-T derivatives obtained are valuable probes for further biological studies or antitumor drug design.

Rapid and Selective Labeling of Endogenous Transmembrane Proteins in Living Cells with a Difluorophenyl Ester Affinity-Based Probe.

The long-term stability of affinity-based protein labeling probes is crucial to obtain reproducible protein labeling results. However, highly stable probes generally suffer from low protein labeling efficiency and pose significant challenges when labeling low abundance native proteins in living cells. In this paper, we report that protein labeling probes based on an ortho-difluorophenyl ester reactive module exhibit long-term stability in DMSO stock solution and aqueous buffer, yet they can undergo rapid and selective labeling of native proteins. This novel electrophile can be customized with a wide range of different protein ligands and is particularly well-suited for the labeling and imaging of transmembrane proteins. With this probe design, the identity and relative levels of basal and hypoxia-induced transmembrane carbonic anhydrases were revealed by live cell imaging and in-gel fluorescence analysis. We believe that the extension of this difluorophenyl ester reactive module would allow for the specific labeling of various endogenous membrane proteins, facilitating in-depth studies of their distribution and functions in biological processes.

Redox-Neutral TEMPO Catalysis: Direct Radical (Hetero)Aryl C-H Di- and Trifluoromethoxylation.

Applications of TEMPO. catalysis for the development of redox-neutral transformations are rare. Reported here is the first TEMPO. -catalyzed, redox-neutral C-H di- and trifluoromethoxylation of (hetero)arenes. The reaction exhibits a broad substrate scope, has high functional-group tolerance, and can be employed for the late-stage functionalization of complex druglike molecules. Kinetic measurements, isolation and resubjection of catalytic intermediates, UV/Vis studies, and DFT calculations support the proposed oxidative TEMPO. /TEMPO+ redox catalytic cycle. Mechanistic studies also suggest that Li2 CO3 plays an important role in preventing catalyst deactivation. These findings will provide new insights into the design and development of novel reactions through redox-neutral TEMPO. catalysis.

Synthesis of Fluorinated 3,6-Dihydropyridines and 2-(Fluoromethyl)pyridines by Electrophilic Fluorination of 1,2-Dihydropyridines with Selectfluor®.

New fluorinated 3,6-dihydropyridines were obtained by the electrophilic fluorination of 1,2-dihydropyridines with Selectfluor®. These 3-fluoro-3,6-dihydropyridines were easily converted to corresponding pyridines by the elimination of hydrogen fluoride under mild conditions. A new approach to the synthesis of methyl 2-(fluoromethyl)-5-nitro-6-arylnicotinates by the fluorination of 3-fluoro-2-methyl-5-nitro-3,6-dihydropyridines or 1,2-dihydropyridines with Selectfluor® has been developed.

Metal-free [3+2] cycloaddition of glycosyl olefinic ester with in situ generated CF3CHN2: Access to CF3-substituted pyrazoline glycoconjugates.

An efficient [3 + 2] cycloaddition of glycosyl olefinic ester with in situ generated CF3CHN2 for the syntheses of CF3-substituted pyrazoline glycoconjugate has been developed. This mild, one-pot reaction condition avoiding the use of metallic catalyst and additive will be useful in the pharmaceutical industry. This reaction features are the broad substrate scope, good functional group tolerance with good to high yields.

Discovery of a Lead Brain-Penetrating Gonadotropin-Releasing Hormone Receptor Antagonist with Saturable Binding in Brain.

We report the synthesis, radiosynthesis and biological characterisation of two gonadotropin-releasing hormone receptor (GnRH-R) antagonists with nanomolar binding affinity. A small library of GnRH-R antagonists was synthesised in 20-67 % overall yield with the aim of identifying a high-affinity antagonist capable of crossing the blood-brain barrier. Binding affinity to rat GnRH-R was determined by autoradiography in competitive-binding studies against [125 I]buserelin, and inhibition constants were calculated by using the Cheng-Prusoff equation. The radioligands were obtained in 46-79 % radiochemical yield and >95 % purity and with a molar activity of 19-38 MBq/nmol by direct nucleophilic radiofluorination. Positron emission tomography imaging in rat under baseline conditions in comparison to pretreatment with a receptor-saturating dose of GnRH antagonist revealed saturable uptake (0.1 %ID/mL) into the brain.

The development of a structurally distinct series of BACE1 inhibitors via the (Z)-fluoro-olefin amide bioisosteric replacement.

The (Z)-fluoro-olefin amide bioisosteric replacement is an effective tool for addressing various shortcomings of the parent amide. In an effort to fine tune ADME properties of BACE1 preclinical candidate AM-6494, a series of structurally distinct (Z)-fluoro-olefin containing analogs was developed that culminated in compound 15. Herein, we detail design considerations, synthetic challenges, structure activity relationship (SAR) studies, and in vivo properties of an advanced compound in this novel series of BACE1 inhibitors.