Iron-Catalyzed Intermolecular Oxyamination of Terminal Alkenes Promoted by HFIP Using Hydroxylamine Derivatives.

An atom-economical intermolecular iron-catalyzed oxyamination of alkenes is described herein. The insertion of oxygenated and nitrogenated moieties from the hydroxylamine substrate was observed with full regio- and chemo-selectivity for terminal alkenes in good yields. HFIP as a solvent appeared to have a synergistic effect with the iron catalyst to promote the formation of the oxyaminated products. Preliminary mechanistic studies suggest a pathway going through an aziridination reaction followed by an in situ ring opening.

Access to Functionalized Imidazolidin-2-one Derivatives by Iron-Catalyzed Oxyamination of Alkenes.

Functionalized imidazolidin-2-one were prepared by using an iron-catalyzed alkene oxyamination reaction. Hydroxylamine derivatives were used in this atom-economical process, and the addition of an external oxidant was not required. The conditions developed were shown to be efficient for mono-, di-, and trisubstituted double bonds, and a large scope of diamino alcohol precursors were delivered in good yields with good diastereoselectivities. The mechanistic pathway was studied and appears to involve both a fused aziridine and a carbocationic species.

Synthesis of γ-lactams and γ-lactones via intramolecular Pd-catalyzed allylic alkylations.

CONSPECTUS: Lactones and lactams are a well-known class of natural products and can be used as building blocks in organic synthesis. In addition, they can be found in many natural sources and synthetic drugs and have a broad range of biological or odorant properties. Chemists can create these useful compounds through palladium catalysis, which is a highly efficient tool for organic synthesis and is conveniently functional group tolerant. In this Account, we describe our work over the past 15 years in intramolecular Pd-catalyzed allylations where we have tethered the nucleophile and the electrophile by either an amide or an ester moiety, to produce γ-lactams and γ-lactones. We discuss in detail how the nature of the heteroatom tether influences the regioselectivity of the reaction. For example, a ketone [-C(O)CH2-] tether leads to mixtures of 5-exo and 7-endo cyclization products, while ester or amide [-C(O)X-] tethers afford sole 5-exo products. However, in the case of X = O, we were required to overcome two issues in the synthesis of γ-lactones. First of all, the tethering ester function can compete with the allylic leaving group in the oxidative addition to the Pd(0) center. Second, in this case, the proportion of the conformers that have a suitable geometry for cyclization is very low. When we insert a juxtaposed silyl group on the allyl fragment, the molecule can undergo oxidative addition and functionalization of the lactone via Hiyama cross-coupling. We also performed DFT calculations on these systems, which allowed us to better understand the behavior of [-C(O)X-] and [-C(O)CH2-] tethers. Computations also let us rationalize the different reactivities that we observed as a function of the geometry (Z or E) of the starting substrates. In addition, we were able to synthesize natural products or analogs (α-kainic acid, isoretronecanol, and picropodophyllin). We could turn these allylation reactions into asymmetric transformations and incorporate them into domino sequences. Thus, an allylation/Mizoroki-Heck sequence allowed us to straightforwardly access an aza-analog of picropodophyllin, as well as reach the lysergic acid backbone. Finally, we found that through carbopalladation of allenes, we could efficiently synthesize the key η(3)-allylpalladium intermediates that were then ready for allylation reactions.

Microwave-assisted preparation of 4-amino-3-cyano-5-methoxycarbonyl-N-arylpyrazoles as building blocks for the diversity-oriented synthesis of pyrazole-based polycyclic scaffolds.

The synthesis of 4-amino-3-cyano-N-arylpyrazoles A based on a Thorpe-Ziegler cyclization as the key step has been achieved using microwave activation. Via a new diversity-oriented synthetic pathway, these highly functionalized building blocks allowed the access to various heteroaromatic scaffolds such as pyrazolo-pyridines B, pyrazolo-pyrimidines C and pyrazolo-oxadiazoles D. Interestingly, these platforms contain three to four reactive sites that could be used for post-functionalization in order to further increase the molecular diversity.

Molecular modeling study of the induced-fit effect on kinase inhibition: the case of fibroblast growth factor receptor 3 (FGFR3).

Tyrosine kinases are a wide family of targets with strong pharmacological relevance. These proteins undergo large-scale conformational motions able to inactivate them. By the end of one of these structural processes, a new cavity is opened allowing the access to a specific type of inhibitors, called type II. The kinase domain of fibroblast growth factor receptor 3 (FGFR3) falls into this family of kinases. We describe here, for the first time, its inactivation process through target molecular dynamics. The transient cavity, at the crossroad between the DFGout and Cα helix out inactivation is herein explored. Molecular docking calculations of known ligands demonstrated that type II inhibitors are able to interact with this metastable transient conformation of FGFR3 kinase. Besides, supplemental computations were conducted and clearly show that type II inhibitors drive the kinase inactivation process through specific stabilization with the DFG triad. This induced-fit effect of type II ligands toward FGFR3 might be extrapolated to other kinase systems and provides meaningful structural information for future drug developments.

Dormant versus evolving aminopalladated intermediates: toward a unified mechanistic scenario in Pd(II)-catalyzed aminations.

Pd(II)-catalyzed alkene aminopalladation and allylic C-H activation are two competing reaction sequences sharing the same reaction conditions. This study aimed at understanding the factors that bias one or the other path in the intramolecular oxidative cyclization of two types of N-tosyl amidoalkenes. The results obtained are in accord with the initial generation of a high-energy cyclic (5- or 6-membered) aminopalladated intermediate. However, this latter species can evolve only if the following specific conditions are met: the availability of distocyclic ß-H elimination pathway, the presence of a strong terminal oxidant, or the availability of a carbopalladation pathway. Conversely, the cyclic alkylpalladium complex is only a latent species in equilibrium with the initial substrate and cannot evolve. Such a reactivity hurdle leaves the way open for alternative reactivities such as allylic C-H activation of the olefinic substrate to generate a η(3)-allyl complex followed by its interception by the nitrogen nucleophile, [3,3]-sigmatropic rearrangement, or decomposition. This study proposes a unifying mechanistic picture that connects these competing mechanisms.

Systemic bis-phosphinic acid derivative restores chloride transport in Cystic Fibrosis mice.

Mutations in the Cystic Fibrosis Transmembrane Conductance Regulator gene (CFTR) are responsible for Cystic Fibrosis (CF). The most common CF-causing mutation is the deletion of the 508th amino-acid of CFTR (F508del), leading to dysregulation of the epithelial fluid transport in the airway's epithelium and the production of a thickened mucus favoring chronic bacterial colonization, sustained inflammation and ultimately respiratory failure. c407 is a bis-phosphinic acid derivative which corrects CFTR dysfunction in epithelial cells carrying the F508del mutation. This study aimed to investigate c407 in vivo activity in the F508del Cftrtm1Eur murine model of CF. Using nasal potential difference measurement, we showed that in vivo administration of c407 by topical, short-term intraperitoneal and long-term subcutaneous route significantly increased the CFTR dependent chloride (Cl-) conductance in F508del Cftrtm1Eur mice. This functional improvement was correlated with a relocalization of F508del-cftr to the apical membrane in nasal epithelial cells. Importantly, c407 long-term administration was well tolerated and in vitro ADME toxicologic studies did not evidence any obvious issue. Our data provide the first in vivo preclinical evidence of c407 efficacy and absence of toxicity after systemic administration for the treatment of Cystic Fibrosis.

γ- and δ-lactams through palladium-catalyzed intramolecular allylic alkylation: enantioselective synthesis, NMR Investigation, and DFT rationalization.

The Pd-catalyzed intramolecular allylic alkylation of unsaturated amides to give γ- and δ-lactams has been studied in the presence of chiral ligands. Ligand (R)-3,5-tBu-MeOBIPHEP (MeOBIPHEP = 6,6'-dimethoxybiphenyl-2,2-diyl)bis(diphenylphosphine)) afforded the best results and allowed the cyclization reactions to take place in up to 94:6 enantiomeric ratio. A model Pd-allyl complex has been prepared and studied through NMR spectroscopic analysis, which provided insight into the processes responsible for the observed enantiomeric ratios. DFT studies were used to characterize the diastereomeric reaction pathways. The calculated energy differences were in good agreement with the experimentally observed enantiomeric ratios.

Functionalized 2,3-dihydrofurans via palladium-catalyzed oxyarylation of α-allyl-ß-ketoesters.

The palladium-catalyzed reaction of (hetero)aryl bromides, chlorides, and nonaflates with α-allyl-ß-ketoesters provides ready efficient access to functionalized 2,3-dihydrofurans. The reaction tolerates several useful substituents including chloro, fluoro, ether, ketone, ester, cyano, and nitro groups.

Modulators of CFTR. Updates on clinical development and future directions.

Cystic fibrosis (CF) is the most frequent life-limiting autosomal recessive disorder in the Caucasian population. It is due to mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. Current symptomatic CF therapies, which treat the downstream consequences of CFTR mutations, have increased survival. Better knowledge of the CFTR protein has enabled pharmacologic therapy aiming to restore mutated CFTR expression and function. These CFTR "modulators" have revolutionised the CF therapeutic landscape, with the potential to transform prognosis for a considerable number of patients. This review provides a brief summary of their mechanism of action and presents a thorough review of the results obtained from clinical trials of CFTR modulators.

New insights into structure and function of bis-phosphinic acid derivatives and implications for CFTR modulation.

C407 is a compound that corrects the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein carrying the p.Phe508del (F508del) mutation. We investigated the corrector effect of c407 and its derivatives on F508del-CFTR protein. Molecular docking and dynamics simulations combined with site-directed mutagenesis suggested that c407 stabilizes the F508del-Nucleotide Binding Domain 1 (NBD1) during the co-translational folding process by occupying the position of the p.Phe1068 side chain located at the fourth intracellular loop (ICL4). After CFTR domains assembly, c407 occupies the position of the missing p.Phe508 side chain. C407 alone or in combination with the F508del-CFTR corrector VX-809, increased CFTR activity in cell lines but not in primary respiratory cells carrying the F508del mutation. A structure-based approach resulted in the synthesis of an extended c407 analog G1, designed to improve the interaction with ICL4. G1 significantly increased CFTR activity and response to VX-809 in primary nasal cells of F508del homozygous patients. Our data demonstrate that in-silico optimized c407 derivative G1 acts by a mechanism different from the reference VX-809 corrector and provide insights into its possible molecular mode of action. These results pave the way for novel strategies aiming to optimize the flawed ICL4-NBD1 interface.

Discovery, SAR study and ADME properties of methyl 4-amino-3-cyano-1-(2-benzyloxyphenyl)-1H-pyrazole-5-carboxylate as an HIV-1 replication inhibitor.

Inspired by the antiviral activity of known pyrazole-based HIV inhibitors, we screened our in-house library of pyrazole-based compounds to evaluate their in cellulo activity against HIV-1 replication. Two hits with very similar structures appeared from single and multiple-round infection assays to be non-toxic and active in a dose-dependent manner. Chemical expansion of their series allowed an in-depth and consistent structure-activity-relationship study (SAR) to be built. Further ADME evaluation led to the selection of 4-amino-3-cyano-1-(2-benzyloxyphenyl)-1H-pyrazole-5-carboxylate with an advantageous pharmacokinetic profile. Finally, examination of its mode of action revealed that this compound does not belong to the three main classes of anti-HIV drugs, a feature of prime interest in the context of viral resistance.

Phosphine-free palladium-catalyzed allene carbopalladation/allylic alkylation domino sequence: a new route to 4-(alpha-styryl) gamma-lactams.

Free to decide: Various 4-(alpha-styryl) gamma-lactams are synthesized in 61-88% yield by a phosphine-free palladium-catalyzed carbopalladation/allylic alkylation domino sequence (see scheme). The cyclization is totally regio- and diastereoselective in favor of the 3,4-trans-disubstituted gamma-lactam. The process is successfully applied to the synthesis of a new aza analogue of the naturally occurring lignan (+)-oxo-parabenzlactone.

Allylic alkylation and ring-closing metathesis in sequence: a successful cohabitation of Pd and Ru.

An allylic alkylation/ring-closing metathesis domino catalytic process, wherein a palladium and a ruthenium catalyst are concomitantly present in the reaction mixture from the outset of the reaction, is developed. Evidence for Grubbs' catalysts activity in allylic alkylation is also reported.

New picropodophyllin analogs via palladium-catalyzed allylic alkylation-Hiyama cross-coupling sequences.

Unsaturated malonyl esters underwent Pd-catalyzed intramolecular allylic alkylation to give 4-vinyl-substituted gamma-lactones. In contrast to the formerly studied cyclization of malonamides, this reaction could be achieved only with a substrate incorporating a suitably positioned silicon moiety, which directs the ionization toward the desired eta(3)-allylpalladium complex. The resulting 4-[dimethyl-(2-thienyl)silylvinyl]lactone could be subsequently engaged into Hiyama couplings with various iodoarenes, to give the corresponding 4-(alpha-styryl)-gamma-lactones. The use of a specifically substituted iodoarene generated an advanced tetracyclic lactone intermediate incorporating rings A-D of lignans belonging to the podophyllotoxin family. Subsequent electrophilic aromatic substitution with a variety of electron-rich arenes afforded the target picropodophyllin analogs.

Development of a One-Pot Four C-C Bond-Forming Sequence Based on Palladium/Ruthenium Tandem Catalysis.

A one-pot four C-C bond-forming sequence has been developed using two distinct transition metal complexes. The sequence entails a double Pd-catalyzed allylic alkylation followed by a Ru-catalyzed ring-closing metathesis and a Pd-catalyzed Heck coupling. The use of various active methylene nucleophiles was examined with yields up to 76% (93% per C-C bond).

Reductive Cleavage of Aromatic and Heteroaromatic Ester Functions via Copper-Catalyzed Proto-Decarbomethoxylation.

An unprecedented catalytic reductive cleavage of aromatic and heteroaromatic methyl ester functions was successfully achieved with a cheap, nontoxic, and air-stable Cu(OAc)2 catalyst. This reaction is fast, features good functional group tolerance, does not require inert atmosphere or anhydrous solvent, and can be scaled up to 1 g. Moreover, carboxylic acids and t-butyl esters also reacted smoothly under these conditions.

Enantioselective synthesis of aryl sulfoxides via palladium-catalyzed arylation of sulfenate anions.

Arylation of various sulfenate anions generated from beta-sulfinyl esters by retro-Michael reaction in the presence of palladium(0) and enantiopure ligands gave the corresponding aryl sulfoxides in enantio-enriched form. The Josiphos-type ligand (R)-(S)-PPF-t-Bu2 turned out to be the best ligand tested, allowing ee's up to 83% in a predictable sense.