Fluorine in Pharmaceutical Industry: Fluorine-Containing Drugs Introduced to the Market in the Last Decade (2001–2011)

Assembly of Fluorinated Quaternary Stereogenic Centers through Catalytic Enantioselective Detrifluoroacetylative Aldol Reactions

A Cu-catalyzed asymmetric detrifluoroacetylative aldol addition reaction of 2-fluoro-1,3-diketones/hydrates to aldehydes in the presence of base and chiral bidentate ligand was developed. The reaction was carried out under convenient conditions and tolerated a wide range of substrates, resulting in fluorinated quaternary stereogenic α-fluoro-β-hydroxy ketone products with good chemical yields, diastereo- and enantioselectivities. This catalytic asymmetric detrifluoroacetylative aldol addition reaction provides a new approach for the preparation of biologically relevant products containing C-F quaternary stereogenic centers.

Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate

Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate is described. In the presence of a catalytic amount of CuOAc and 2,4,6-collidine in ethyl acetate, the reaction proceeded in good to high yields for various substrates under mild reaction conditions at room temperature.

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.

Electrophilic halogenation-reductive elimination chemistry of organopalladium and -platinum complexes

CONSPECTUS: Transition metal-catalyzed organic transformations often reveal competing reaction pathways. Determining the factors that control the selectivity of such reactions is of extreme importance for the design of reliable synthetic protocols. Herein, we present the account of our studies over the past decade aimed at understanding the selectivity of reductive elimination chemistry of organotransition metal complexes under electrophilic halogenation conditions. Much of our effort has focused on finding the conditions for selective formation of carbon (aryl)-halogen bonds in the presence of competing C-C reductive elimination alternatives. In most cases, the latter was the thermodynamically preferred pathway; however, we found that the reactions could be diverted toward the formation of aryl-iodine and aryl-bromine bonds under kinetic conditions. Of particular importance was to maintain the complex geometry that prohibits C-C elimination while allowing for the elimination of carbon-halogen bonds. This was achieved by employing sterically rigid diphosphine ligands which prevented isomerization within a series of Pt(IV) complexes. It was also important to understand that the neutral M(IV) products often observed or isolated in the oxidative addition reactions are not necessarily the intermediates in the reductive elimination chemistry as it generally takes place from unsaturated species formed en route to relatively stable M(IV) complexes. While aryl-halide reductive elimination for heavier halogens can be competitive with aryl-aryl coupling in diaryl M(IV) complexes, the latter reaction always prevails over aryl-fluoride bond formation. Even when one of the aryl groups is a part of a rigid cyclometalated ligand C-C coupling is still the dominant reaction pathway. However, when one of the aryl groups is replaced with a phenolate donor aryl-F bond formation becomes preferred over C-O bond elimination. During our studies, other interesting reactions have been discovered. For example, the fluorination of the C(sp(3))-H bond can be very selective and compete favorably with C-C coupling. Also, in electron-poor complexes, metal oxidation can have higher energy than oxidation of the coordinated iodo ligand resulting in I-F elimination instead of the formation of aryl-I bond. Overall, electrophilic fluorination can lead to often very selective elimination reactions giving new C-C, C-I, C-F, or I-F bonds, with this selectivity dependent on the metal center, supporting ligands, complex geometry, and electrophilic fluorine source. Together with the many reports on the halogenation of organometallic compounds that appeared in recent years, our results contribute to understanding the requirements for selective transformations under electrophilic conditions and design of new synthetic methods for making organohalogen compounds.

Recent advances in combinatorial biosynthesis for drug discovery

Because of extraordinary structural diversity and broad biological activities, natural products have played a significant role in drug discovery. These therapeutically important secondary metabolites are assembled and modified by dedicated biosynthetic pathways in their host living organisms. Traditionally, chemists have attempted to synthesize natural product analogs that are important sources of new drugs. However, the extraordinary structural complexity of natural products sometimes makes it challenging for traditional chemical synthesis, which usually involves multiple steps, harsh conditions, toxic organic solvents, and byproduct wastes. In contrast, combinatorial biosynthesis exploits substrate promiscuity and employs engineered enzymes and pathways to produce novel “unnatural” natural products, substantially expanding the structural diversity of natural products with potential pharmaceutical value. Thus, combinatorial biosynthesis provides an environmentally friendly way to produce natural product analogs. Efficient expression of the combinatorial biosynthetic pathway in genetically tractable heterologous hosts can increase the titer of the compound, eventually resulting in less expensive drugs. In this review, we will discuss three major strategies for combinatorial biosynthesis: 1) precursor-directed biosynthesis; 2) enzyme-level modification, which includes swapping of the entire domains, modules and subunits, site-specific mutagenesis, and directed evolution; 3) pathway-level recombination. Recent examples of combinatorial biosynthesis employing these strategies will also be highlighted in this review.

E- or Z-Selective synthesis of 4-fluorovinyl-1,2,3-triazoles with fluorinated second-generation Julia-Kocienski reagents

A highly modular approach to N-substituted 4-(1-fluorovinyl)triazoles is described. In situ desilylation and Cu-catalyzed ligation reaction of TMS-protected α-fluoropropargyl benzothiazole sulfone with aryl, alkyl, and metallocenyl azides furnished second-generation Julia-Kocienski reagents in good to excellent yields. Condensation reactions of these reagents with aldehydes can be tuned to yield E or Z-alkenes selectively. Under mild conditions with DBU as the base, reactions of aldehydes furnished E-alkenes as the major isomer. On the other hand, in condensation reactions with LHMDS as the base and in appropriate solvents, both aldehydes and ketones reacted to yield fluoroalkenes with Z-selectivity. Stereochemical assignment of E/Z olefins obtained in the reaction of a ketone with two Julia reagents was performed via X-ray crystallographic analysis and comparisons of NMR data. The method allows efficient and ready diversification of the N1-substituent and substituents at the double bond.

Fluorine-decoupled carbon spectroscopy for the determination of configuration at fully substituted, trifluoromethyl- and perfluoroalkyl-bearing carbons: comparison with 19F-1H heteronuclear Overhauser effect spectroscopy

The synthesis of a series of α-trifluoromethylcyclohexanols and analogous trimethylsilyl ethers by addition of the Ruppert-Prakash reagent to substituted cyclohexanones is presented. A method for the assignment of configuration of such compounds, of related α-trifluoromethylcyclohexylamines and of quaternary trifluoromethyl-substituted carbons is described based on the determination of the (3)J(CH) coupling constant between the fluorine-decoupled (13)CF3 resonance and the vicinal hydrogens. This method is dubbed fluorine-decoupled carbon spectroscopy and abbreviated FDCS. The method is also applied to the configurational assignment of substances bearing mono-, di-, and perfluoroalkyl rather than trifluoromethyl groups. The configuration of all substances was verified by either (19)F-(1)H heteronuclear Overhauser spectroscopy (HOESY) or X-ray crystallography. The relative merits of FDCS and HOESY are compared and contrasted. (2)J(CH), (3)J(CH), and (4)J(CH) coupling constants to (19)F decoupled CF3 groups in alkenes and arenes have also been determined and should prove to be useful in the structural assignment of trifluoromethylated alkenes and arenes.

A highly regio- and stereoselective synthesis of α-fluorinated imides via fluorination of chiral enamides

A highly π-facial selective and regioselective fluorination of chiral enamides is described. The reaction involves an enantioselective fluorination exclusively at the electron-rich enamide olefin with N-F reagents such as Selectfluor and N-fluoro-benzenesulfonimide [NFSI] accompanied by trapping of the β-fluoro-iminium cationic intermediate with water. The resulting N,O-hemiacetal could be oxidized using Dess-Martin periodinane, leading to an asymmetric sequence for syntheses of chiral α-fluoro-imides and optically enriched α-fluoro-ketones.

New, non-quinone fluorogeldanamycin derivatives strongly inhibit Hsp90

Streptomyces hygroscopicus is a natural producer of geldanamycin. Mutasynthetic supplementation of an AHBA-blocked mutant with all possible monofluoro 3-aminobenzoic acids provided new fluorogeldanamycins. These showed strong antiproliferative activity and inhibitory effects on human heat shock protein Hsp90. Binding to Hsp90 in the low nanomolar range was determined from molecular modelling, AFM analysis and by calorimetric studies.

Straightforward synthesis of novel enantiopure α-trifluoromethylated azetidine 2-carboxylic acid and homoserines

The straightforward syntheses of enantiopure (2R)-2-trifluoromethyl-2-carboxyazetidine and (R)- and (S)-trifluoromethylhomoserines are reported. The key step is a Strecker-type reaction on a common chiral CF3-containing bicyclic oxazolidine intermediate obtained by a condensation reaction of (R)-phenylglycinol and ethyl-4,4,4-trifluoroacetoacetate (ETFAA).

Perfluoroalkylation reactions of (hetero)arenes

Methods for the perfluoroalkylation of (hetero)arenes can be classified as thermal and photochemical, which in turn can be conducted in the presence or absence of metals.

Asymmetric synthesis of α-(1-oxoisoindolin-3-yl)glycine: synthetic and mechanistic challenges

The NaOMe-catalyzed reactions between the chiral glycine Schiff base (S)-4 with 2-cyanobenzaldehyde 3 provide for a convenient preparation of the novel α-(1-oxoisoindolin-3-yl)glycine 1 of high pharmaceutical potential, which involve at least eight synthetic steps mechanistically.

Copper-catalyzed trifluoromethylation of organic zinc reagents with an electrophilic trifluoromethylating reagent

Trifluoromethylation of aryl and alkyl zinc reagents under mild conditions was described.

First efficient synthesis of SF5-substituted pyrrolidines using 1,3-dipolar cycloaddition of azomethine ylides with pentafluorosulfanyl-substituted acrylic esters and amides

Di-, tri- and tetrasubstituted pentafluorosulfanylated pyrrolidines have been efficiently synthetized via 1,3-dipolar cycloaddition of azomethine ylides.

Copper-mediated oxidative difluoromethylation of terminal alkynes with TMSCF2H

A copper-mediated oxidative coupling of terminal alkynes and TMSCF₂H has been described for the preparation of various difluoromethylated alkynes.

Gold trifluoromethyl complexes

This Perspective reviews the synthesis, structure, reactivity and applications of gold trifluoromethyl complexes. The recently reported reactions of gold(iii) trifluoromethyl complexes with potential application in synthesis are discussed.

Aryl-BIAN-ligated silver(i) trifluoromethoxide complex

The complex (Aryl-BIAN)AgOCF₃ has been synthesised and structurally characterised. The reactivity towards trifluoromethoxylation of benzyl bromides has also been examined.