Synthesis and biological activity of fluorinated intermediates of the methionine salvage pathway

Visible-Light-Driven Organophotocatalyzed Multicomponent Approach for Tandem C(sp3)-H Activation and Alkylation Followed by Trifluoromethylthiolation

A visible-light-driven organophotocatalyzed multicomponent approach has been developed for tandem direct C(sp³)-H activation and alkylation followed by trifluoromethylthiolation in a one-pot operation. We report a completely metal-free, tandem, three-component approach for the difunctionalization of activated alkenes via the photoinduced radical pathway. This protocol allows the formation of two new C(sp³)-C(sp³) and C(sp³)-SCF₃ bonds using a bench-stable, easy-to-handle trifluoromethylthiolating reagent under mild reaction conditions. The generosity of this reaction is shown with a library of C(sp³)-H donors and alkenes derivatives. The reaction conditions can tolerate a wide variety of functional groups. Gram-scale synthesis using environmentally benign and straightforward conditions highlights the synthetic advancement of the methodology. Further functionalization of the final product is also successfully demonstrated.

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.

Chemoselective Perfluoromethylation of Thio- and Selenoamides

A chemo- and regioselective perfluoromethylation using thioamides/selenoamides (prepared one step from corresponding lactams) as starting materials has been discovered. The reaction demonstrated complementary chemoselectivity to the C-H trifluoromethylation of (hetero)arenes as well as remarkable functional group compatibility especially toward radical sensitive olefin-, alkyne-, and arylhalide-bearing substrates. The examples of perfluorothio-/selenolated drug molecules indicated application potential of this strategy in drug modification and drug-analogue preparation.

Synthesis of α-Trifluoromethylthio-α,β-Unsaturated Carbonyl Compounds by DABCO-Mediated Electrophilic Trifluoromethylthiolation with N-SCF3-Dibenzenesulfonimide

A DABCO-mediated electrophilic α-trifluoromethylthiolation of α,β-unsaturated carbonyl compounds comprising no β-substituents has been achieved using N-trifluoromethylthio-dibenzenesulfonimide as the SCF₃ source. The direct trifluoromethylthiolation provides the corresponding α-trifluoromethylthio-α,β-unsaturated carbonyl products in good yields (up to 88%). Furthermore, the vinyl group in the α-trifluoromethylthio-α,β-unsaturated carbonyl product was successfully transformed into diverse functional groups in good to excellent yields (70-95%) by reactions such as epoxidation, aziridination, hydrocyanation, and hydrogenation.

Construction of unique SCF3-containing building blocks via allylic alkylation of Morita-Baylis-Hillman adducts

Lewis base-catalyzed allylic alkylation of Morita-Baylis-Hillman adducts with α-SCF3 ketones has been demonstrated. The developed strategy provides efficient access to a series of highly functionalized scaffolds featuring trifluoromethanesufinyl motif on a stereogenic carbon.

Visible-Light-Induced, Copper-Catalyzed Three-Component Coupling of Alkyl Halides, Olefins, and Trifluoromethylthiolate to Generate Trifluoromethyl Thioethers

Photoinduced, copper-catalyzed coupling reactions are emerging as a powerful method for generating Csp³-Y (Y = C or heteroatom) bonds from alkyl electrophiles and nucleophiles. Corresponding three-component couplings of alkyl electrophiles, olefins, and nucleophiles have the potential to generate an additional Csp³-Y bond and to efficiently add functional groups to both carbons of an olefin, which serves as a readily available linchpin. In this report, we establish that a variety of electrophiles and a trifluoromethylthiolate nucleophile can add across an array of olefins (including styrenes and electron-poor olefins) in the presence of CuI/binap and blue-LED irradiation, thereby generating trifluoromethyl thioethers in good yield. The process tolerates a wide range of functional groups, and an initial survey of other nucleophiles (i.e., bromide, cyanide, and azide) suggests that this three-component coupling strategy is versatile. Mechanistic studies are consistent with a photoexcited Cu(I)/binap/SCF₃ complex serving as a reductant to generate an alkyl radical from the electrophile, which likely reacts in turn with the olefin and a Cu(II)/SCF₃ complex to afford the coupling product.

Synthesis of o-Methyl Trifluoromethyl Sulfide Substituted Benzophenones via 1,2-Difunctionalization of Aryne by Insertion into the C-C Bond

An efficient process for the preparation of valuable o-methyl trifluoromethyl sulfide substituted benzophenones has been developed. The transition-metal-free method features insertion of aryne into a C-C σ-bond under mild reaction conditions for the first time to achieve ortho-difunctionalized arenes containing a pharmaceutically important trifluoromethylthio functional group. A wide substrate scope has been demonstrated for the developed protocol.

Visible-Light-Promoted Activation of Unactivated C(sp3)-H Bonds and Their Selective Trifluoromethylthiolation

Selective functionalization of ubiquitous C(sp³)-H bonds using visible light is a highly challenging yet desirable goal in organic synthesis. The development of such processes relies on both rational design and serendipitous discoveries from innovative tools such as screening technologies. Applying a mechanism-based screening strategy, we herein report photoredox-mediated hydrogen atom transfer catalysis for the selective activation of otherwise unactivated C(sp³)-H bonds, followed by their trifluoromethylthiolation, which has high potential as a late-stage functionalization tool. The generality of this method is exhibited through incorporation of the trifluoromethylthio group in a large number of C(sp³)-H bonds with high selectivity without the need for an excess of valuable substrate.

Chiral phosphoric acid-catalyzed asymmetric transfer hydrogenation of 3-trifluoromethylthioquinolines

A chiral phosphoric acid-catalyzed asymmetric transfer hydrogenation of 3-trifluoromethylthioquinolines was developed, providing chiral 2,3-disubstituted 1,2,3,4-tetrahydroquinoline derivatives containing a stereogenic trifluoromethylthio group with up to 99% enantioselectivity.

2-Trifluoromethylthiolation of glycals

The direct 2-trifluoromethylthiolation of glycals has been realized for the first time, benefiting the carbohydrate-based drug discovery.

Biological chemistry of the carbon–sulfur bond

Carbon–sulfur biological chemistry encompasses a fascinating area of biochemistry and medicinal chemistry and includes the roles that methionine and S-adenosyl-l-methionine play in cells as well as the chemistry of intracellular thiols such as glutathione. This article, based on the 2014 Bernard Belleau Award lecture, provides an overview of some of the key investigations that were undertaken in this area from a bioorganic perspective. The research has ameliorated our fundamental knowledge of several of the enzymes utilizing these sulfur-containing molecules, has led to the development of several novel 19F biophysical probes, and has explored some of the medicinal chemistry associated with these processes.

Polyfluorinated groups in medicinal chemistry

Introduction of novel and diverse functional groups in drug discovery is always seen with hesitancy until good activity and low toxicity characteristics are proven. The introduction of fluorine in drug-like compounds is now a well-accepted strategy in medicinal chemistry. However, polyfluoroalkyl groups, with the exception of trifluoromethyl substituents, are not well explored yet. Our aim is to show to the readers how polyfluorinated groups can be beneficial to the properties of pharmaceutically active compounds by highlighting the structure–activity relationship (SAR) studies that led to the selection of polyfluorinated moieties as key structural features. Despite the fact that the use of higher polyfluoroalkyl/aryl moieties is still in its infancy, we believe that they will soon acquire the same importance of their lower parents.

Mechanism of inactivation of S-adenosyl-L-homocysteine hydrolase by 5'-deoxy-5'-S-allenylthioadenosine and 5'-deoxy-5'-S-propynylthioadenosine

5'-Deoxy-5'-S-allenylthioadenosine 1 and 5'-deoxy-5'-S-propnylthioadenosine 2, derived from adenosine, were prepared. 1 and 2 caused irreversible inactivation of AdoHcy hydrolase. ESI mass spectra analysis of the inactivated enzyme demonstrated that 1 and 2 were type II "mechanism-based" inhibitors.

The mechanism of inactivation of S-adenosylhomocysteine hydrolase by fluorinated analogs of 5'-methylthioadenosine

5'-Deoxy-5'-difluoromethylthioadenosine (DFMTA) 1a and 5'-deoxy-5'-trifluoromethyl-thioadenosine (TFMTA) 1b are inhibitors of beef liver S-adenosyl-L-homocysteine hydrolase. DFMTA and TFMTA are time-dependent and irreversible inhibitors of the enzyme. Both 1a and 1b are oxidized by E-NAD+ to produce E-NADH and fluoride anion is formed in the inactivation reaction (2.2 mol of fluoride/mole of enzyme subunit and 3.1 fluoride/mole of enzyme subunit from DFMTA and TFMTA respectively). Using [8-3H]-1a or [8-3H]-1b no trace of labelled adenosine was detected during the inactivation reaction but adenine was formed. The mechanism of inhibition of S-adenosyl-L-homocysteine hydrolase by these two fluorinated nucleosides is discussed.

Incorporation of trifluoromethionine into a phage lysozyme: implications and a new marker for use in protein 19F NMR

Much interest is currently focused on understanding the detailed contribution that particular amino acid residues make in protein structure and function. Although the use of site-directed mutagenesis has greatly contributed to this goal, the approach is limited to the standard repertoire of twenty amino acids. Fluorinated amino acids have been utilized successfully to probe protein structure and dynamics as well as point to the importance of specific residues to biological function. In our continuing investigations on the importance of the amino acid methionine in biological systems, the successful incorporation of L-S-(trifluoromethyl)homocysteine (L-trifluoromethionine; L-TFM) into bacteriophage lambda lysozyme (LaL), an enzyme containing three methionine residues, is reported. The L isomer of TFM was synthesized in an overall yield of 33% from N-acetyl-D,L-homocysteine thiolactone and trifluoromethyl iodide. An expression plasmid giving strong overproduction of LaL was prepared and transformed into an Escherichia coli strain auxotrophic for methionine permitting the expression of LaL in the presence of L-TFM. The analogue would not support growth of the auxotroph and was found to be inhibitory to cell growth. However, cells that were initially grown in a Met-rich media followed by protein induction under careful control of the respective concentrations of L-Met and L-TFM in the media, were able to overexpress TFM-labeled LaL (TFM-LaL) at both high (70%) and low (31%) levels of TFM incorporation. TFM-LaL at both levels of incorporation exhibited analogous activity to the wild type enzyme and were inhibited by chitooligosaccharides indicating that incorporation of the analogue did not hinder enzyme function. Interestingly, the 19F solution NMR spectra of the TFM-labeled enzymes consisted of four sharp resonances spanning a chemical shift range of 0.9 ppm, with three of the resonances showing very modest shielding changes on binding of chitopentaose. The 19F NMR analysis of TFM-LaL at both high and low levels of incorporation suggested that one of the methionine positions gives rise to two separate resonances. The intensities of these two resonances were influenced by the extent of incorporation which was interpreted as an indication that subtle conformational changes in protein structure are induced by incorporated TFM. The similarities and differences between Met and TFM were analyzed using ab initio molecular orbital calculations. The methodology presented offers promise as a new approach to the study of protein-ligand interactions as well as for future investigations into the functional importance of methionine in proteins.