Expanding the Scope of Group Transfer Radical Reaction: Toward the Synthesis of Fluorinated Nucleoside Analogues Incorporating Difluorophosphonylated Allylic Ether Moieties

Scope and limitations of the group transfer radical reaction of diisopropyl iododifluoromethylphosphonate onto carbohydrates and nucleosides are described. This key step allowed us to explore the synthesis of new fluorinated nucleoside analogues containing a difluorophosphonylated allylic ether moiety onto the 2'-position, in purine and pyrimidine series (B = A, C, G, T, U). Indeed, two unprecedented chemical approaches involving a late introduction of either the nucleobase or the fluorinated moiety are discussed.

Photocatalyzed Hydroaminodifluoroalkylation of Alkenes

The synthesis of undescribed β-aminodifluoroethylsulfinates and their uses in the hydroaminodifluoroalkylation of alkenes is reported. This reaction is performed in the presence of a photocatalyst (4CzIPN, Ru complexes) and enables the direct incorporation of a β-difluoroamine moiety into vinylic aryls, unactivated alkenes, and electron-rich, or -deficient alkenes. The mechanism was studied, and the formation of a gem-difluoromethyl radical was observed after the selective oxidation of the sulfinate function.

Convergent access to mono-fluoroalkene-based peptidomimetics

The convergent and selective preparation of (Z)-monofluoroalkene-based dipeptide isosteres from functionalized fluorosulfones as a cornerstone is described. In this approach, the N-terminal amino group is introduced by a conjugate addition reaction of phthalimide onto fluorinated vinylsulfones containing α-amino-acid side chains while the C-terminal motif is linked to the fluorovinylic peptide bond mimic via the Julia-Kocienski reaction between fluorosulfones and substituted aldehydes bearing α-amino-acid side chains.

Metal-Free Aminomethylation of Aromatic Sulfones Promoted by Eosin Y

A metal-free α-aminomethylation of heteroaryls promoted by eosin Y under green light irradiation is reported. A large variety of α-trimethylsilylamines as precursor of α-aminomethyl radical species were engaged to functionalize sulfonyl-heteroaryls following a Homolytic Aromatic Substitution (HAS) pathway. This method has provided a range of α-aminoheteroaryl compounds including a functionalized natural product. The mechanism of this late-stage functionalization of aryls was investigated and suggests the formation of a sulfonyl radical intermediate over a reductive quenching cycle.

Inhibition of d-alanylation of teichoic acids overcomes resistance of methicillin-resistant Staphylococcus aureus

Background

MRSA are high-priority multidrug-resistant pathogens. Although there are still some antibiotics active against MRSA, continuous efforts to discover new antibiotics and treatment strategies are needed because resistance to these new drugs has already been reported.

Objectives

Here we explore if d-alanylation of teichoic acids (TAs) mediated by the dlt operon gene products might be a druggable target to overcome β-lactam-resistance of MRSA.

Methods

MICs and bactericidal effects of several β-lactam antibiotics were monitored in a panel of clinical MRSA strains with genetic or chemically induced deficiency in d-alanylation of TAs. Efficiency of the chemical inhibitor to rescue MRSA-infected larvae of Galleria mellonella as well as its ability to prevent or eradicate biofilms of S. aureus were analysed.

Results

Genetic inactivation of the Dlt system or its chemical inhibition re-sensitizes MRSA to β-lactams. Among the 13 strains, the most pronounced effect was obtained using the inhibitor with imipenem, reducing the median MIC from 16 to 0.25 mg/L. This combination was also bactericidal in some strains and significantly protected G. mellonella larvae from lethal MRSA infections. Finally, inactivation of d-alanylation potentiated the effect of imipenem on inhibition and/or eradication of biofilm.

Conclusions

Our combined results show that highly efficient inhibitors of d-alanylation of TAs targeting enzymes of the Dlt system should be promising therapeutic adjuvants, especially in combination with carbapenems, for restoring the therapeutic efficacy of this class of antibiotics against MRSA.

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

The selective ring-opening reaction of fluoroalkylidene-oxetanes was directed by the presence of the fluorine atom, enabling a two-step access to tetrasubstituted fluoroalkenes with excellent geometry control. Despite its small van der Waals radii electronic, rather than steric influences of the fluorine atom governed the ring-opening reaction with bromide ions, even in the presence of bulky substituents.

Genetic and pharmacological inactivation of d-alanylation of teichoic acids sensitizes pathogenic enterococci to β-lactams

Background

Enterococci intrinsically resistant to cephalosporins represent a major cause of healthcare-associated infections, and the emergence of MDR makes therapeutic approaches particularly challenging.

Objectives

Teichoic acids are cell wall glycopolymers present in Gram-positive bacteria. Teichoic acids can be modified by d-alanylation, which requires four proteins encoded by the dltABCD operon. Our objective was to evaluate the Dlt system as a druggable target to treat enterococcal infections.

Methods

The susceptibility of a d-alanylation-deficient strain of Enterococcus faecalis to β-lactam antibiotics individually and/or in combination was analysed. Moreover, a DltA inhibitor was synthesized to test pharmacological inhibition of d-alanylation in vivo and in host using the animal model Galleria mellonella with different clinical isolates of E. faecalis and Enterococcus faecium.

Results

Most cephalosporins used as mono treatment had no impact on survival of the parental strain, but were slightly lethal for the dltA mutant of E. faecalis. Addition of a very low concentration of amoxicillin significantly increased killing of the dltA mutant under these conditions. The most spectacular effect was obtained with a combination of cefotaxime (1 mg/L) and amoxicillin (0.03 mg/L). In the presence of the inhibitor, the WT strain was as susceptible to this combination treatment as the dltA mutant. This molecule associated with the antibiotics was also effective in killing other E. faecalis clinical isolates and successfully prevented death of Galleria infected with either E. faecalis or E. faecium.

Conclusions

The combined results support the potential usefulness of the Dlt system as a target to potentiate antibiotic combination therapies for the treatment of drug-resistant enterococci.

Radical Allylation: E-Selective Radical Conjugate Addition–Elimination Reaction from Morita–Baylis–Hillman Adducts

Triethylborane-mediated radical allylation was performed from Morita–Baylis–Hillman alcohols with no need of protecting group. The radical conjugated addition–elimination reaction is highly selective, and trisubstituted E-alkenes were obtained. This reaction opened a new route for the preparation of functionalized α,β-unsaturated ketones.

Synthesis of Fluoropyrrolidines and (Fluoroalkyl)pyrrolidines

Pyrrolidines and their derivatives are of great interest in medicinal chemistry and organic synthesis. Fluoropyrrolidines and (fluoroalkyl)pyrrolidines have been utilized in the preparation of medicinal drugs and also as organocatalysts. The synthesis of such compounds is achieved through the fluorination of pyrrolidine derivatives or by multistep synthesis from already containing fluoroalkyl precursors.

1 Introduction

1.1 General Interest of Fluorine-Containing Pyrrolidines

1.2 Fluoroalkylpyrrolidines and the Gauche Effect

2 Fluoropyrrolidines

2.1 3-Fluoropyrrolidines

2.2 3,3- and 3,4-Difluoropyrrolidines

2.3 3,3,4-Trifluoropyrrolidines

2.4 3,3,4,4-Tetrafluoropyrrolidines

3 (Difluoromethyl)- and (Trifluoromethyl)pyrrolidines

3.1 2-(Trifluoromethyl)pyrrolidines

3.2 3- and 4-(Trifluoromethyl)pyrrolidines

3.3 2-(Difluoromethyl)pyrrolidines

3.4 3- and 4-(Difluoromethyl)pyrrolidines

4 (Monofluoroalkyl)pyrrolidines

4.1 2-(Monofluoromethyl)pyrrolidines

4.2 2-(Monofluoroalkyl)pyrrolidines

4.3 2-(Monofluoroalkenyl)pyrrolidines

5 Conclusion

Synthesis of 5,5-difluoro-5-phosphono-pent-2-en-1-yl nucleosides as potential antiviral agents

A series of hitherto unknown acyclic 5,5-difluoro-5-phosphono-pent-2-en-1-yl-pyrimidines, -purines and -(1,2,4)-triazolo-3-carboxamide were successfully synthesized from (E)-1-bromo-5-diethoxyphosphoryl-5,5-difluoro-pent-2-ene in a stereoselective manner.

Synthesis of Fluorinated and Trifluoromethyl-Substituted Alkenes through the Modified Julia Olefination: An Update

The modified Julia olefination is now a powerful tool for the synthesis of a large range of functionalized alkenes. This short review covers the last five years and provides an overview of the synthesis of mono-, difluoro-, and trifluoromethyl-substituted alkenes via the modified Julia olefination focusing on the novel scope of this reaction.

1 Introduction

2 Monofluoroalkenes

2.1 Disubstituted α- and β-Monofluoroalkenes

2.2 Bis(trifluoromethyl)phenyl Sulfones

2.3 Conjugated Monofluoroalkenes

2.4 Intramolecular Julia Olefination

2.5 Smiles Rearrangement from Fluorinated Keto Sulfones

2.6 Fluoroallylamines

2.7 Fluorinated exo-Glycals

2.8 Monofluoroalkenes with an α-Stereocenter at the Allylic Position

3 1,1-Difluoroalkenes

4 Trifluoromethyl-Substituted Alkenes

5 Conclusion

Fluorinated hydroxypiperidines as selective β-glucosidase inhibitors

Synthesis and glucosidase inhibitory activity of piperidines revealed a reverse selectivity between F- and H-alkenes.

Synthesis of fluorophosphonylated acyclic nucleotide analogues via copper(I)-catalyzed Huisgen 1-3 dipolar cycloaddition

Preparation of several acyclonucleosides containing both a difluoromethylphosphonate group and a triazole moiety is described starting from a difluorophosphonosulfide. The key step of the synthesis involves a copper(I)-catalyzed Huisgen 1-3 dipolar cycloaddition between difluorophosphonylated azides and propargylated nucleobases derived from thymine and 2-amino-6-chloropurine.

Transition state chirality and role of the vicinal hydroxyl in the ribosomal peptidyl transferase reaction

The ribosomal peptidyl transferase is a biologically essential catalyst responsible for protein synthesis. The reaction is expected to proceed through a transition state approaching tetrahedral geometry with a specific chirality. To establish that stereospecificity, we synthesized two diastereomers of a transition state inhibitor with mimics for each of the four ligands around the reactive chiral center. Preferential binding of the inhibitor that mimics a transition state with S chirality establishes the spatial position of the nascent peptide and the oxyanion and places the amine near the critical A76 2'-OH group on the P-site tRNA. Another inhibitor series with 2'-NH 2 and 2'-SH substitutions at the critical 2'-OH group was used to test the neutrality of the 2'-OH group as predicted if the hydroxyl functions as a proton shuttle in the transition state. The lack of significant pH-dependent binding by these inhibitors argues that the 2'-OH group remains neutral in the transition state. Both of these observations are consistent with a proton shuttle mechanism for the peptidyl transferase reaction.

Modified Julia fluoroolefination: selective preparation of fluoroalkenoates

The modified Julia olefination reaction has been applied to develop a stereoselective synthesis of fluoroalkenoate derivatives from a fluorobenzothiazolyl sulfone and aldehydes or a ketone. The olefination reaction can be achieved by using a variety of bases. DBU and DBU in the presence of MgBr2 were found to be the most efficient systems to prepare either (Z)- or (E)-alkenoates in moderate to excellent stereoselectivity.

Regulated expression of functional external guide sequences in mammalian cells using a U6 RNA polymerase III promoter

A regulatable promoter has been stably integrated into a human embryonic kidney cell line. The promoter is a pol III mouse promoter and is under the control of ponasterone A, an ecdysone inducer. The promoter controls transcription of an external guide sequence (EGS) targeted against Rpp38, a protein subunit of human RNase P, or of lamin A/C, a gene product located in the nucleus. The amounts of protein of both gene products are severely reduced when the EGSs are made. Several other, but not all, of the protein subunits of RNase P are also inhibited in both mRNA and protein levels when Rpp38 mRNA is targeted.

Efficient synthesis of fluorothiosparfosic acid analogues with potential antitumoral activity

In this paper, we describe a short synthesis of N-(phosphonoacetyl)-L-aspartate (PALA) analogues. The mono- and difluorinated thioacetamide precursors were prepared in one step from methyl (diethoxyphosphono)di- and monofluoromethyldithioacetates 8 and 11 as starting materials. Antiproliferating properties on a L1210 strain and ATCase inhibition of these new compounds are disclosed. ThioPALA(FF) 5c showed a remarkable cytotoxic activity towards murine leukemia L1210, when used as tetraester.

Syntheses of α-Fluoro-α,β-unsaturated Thioamides and Thiazolines from a Fluorophosphonodithioacetate

A high-yielding synthesis of methyl fluoro(diethoxyphosphono)dithioacetate starting from its difluorinated analogue is reported. Fluorophosphonothioacetamides and -methylthiazolines, prepared from this new dithioester, have been successfully transformed into highly functionalized fluoroalkenes. Good stereoselectivity in favor of the E isomer was observed from the fluorophosphonomethylthiazolines. The potential of these new fluorinated olefinating reagents for the synthesis of modified peptides and glycosides is also disclosed.

Synthesis of thiazolines linked to a difluoromethylphosphonate diester via dithioester chemistry

[reaction: see text] A two-step, high-yielding synthesis of delta(2)-thiazolines containing a difluoromethylphosphonate diester moiety has been devised using a building block approach. Racemic or chiral beta-amino alcohols and diols were coupled with methyl difluoro(diethoxyphosphono)dithioacetate to give predominantly the corresponding beta-hydroxythioamides, which were then cyclized to provide a series of novel substituted delta(2)-thiazolines.