Multiple Regioselective Functionalizations of Quinolines via Magnesiations

Synthesis and Antifungal Activity of Stereoisomers of Mefloquine Analogs

Cryptococcal neoformans and Candida albicans are among the most prevalent causes of life-threatening fungal infections globally. The high mortality associated with these infections despite current antifungal therapy highlights the need for new drugs. In our previous work, we demonstrated that an analogue of the clinically used antimalarial mefloquine, (8-chloro-2-(4-chlorophenyl)quinolin-4-yl)(piperidin-2-yl)methanol (4377), has both antifungal activity and the ability to penetrate the central nervous system. Herein we describe the synthesis and antifungal assay of all four stereoisomers of 4377. All four stereoisomers retain potent antifungal activity with the erythro enantiomers having MIC values of 1 and 4 μg/mL against C. neoformans and C. albicans, respectively, and threo enantiomers, MIC values of 2 and 8 μg/mL, respectively. These results indicate that the stereochemistry of the piperidine methanol group is not critical for the antifungal properties of 4377 and gives guidance to future medicinal chemistry optimization efforts.

Synthesis of 7-Chloroquinoline Derivatives Using Mixed Lithium-Magnesium Reagents

We have prepared a library of functionalized quinolines through the magnesiation of 7-chloroquinolines under mild conditions, employing both batch and continuous flow conditions. The preparation involved the generation of mixed lithium-magnesium intermediates, which were reacted with different electrophiles. Mixed lithium-zinc reagents allowed the synthesis of halogenated and arylated derivatives. Some of the synthesized 4-carbinol quinolines have shown interesting antiproliferative properties, their hydroxyl group being a suitable amino group bioisostere. We also report a two-step approach for optically active derivatives.

TIPS-Ethynylated Naphthodiquinoline and Naphthodiacridine: Novel Diazabisacenes

The synthesis of two diazabisacenes is reported. A bisboronated naphthalene was Suzuki‐coupled to substituted ethyl nicotinates, then cyclized by intramolecular Friedel‐Crafts acylation. The resulting diketones were alkynylated and reduced to give the title compounds, bis(TIPS‐ethynyl)‐substituted naphtha[1,8‐gh:5,4‐g′h′]diquinoline and naphtho[1,8‐bc:5,4‐b′c′]diacridine. Nitrogen incorporation stabilizes the bisacenes with respect to oxidation compared to their consanguine nonaza analogs.

Regioselective Bromine/Magnesium Exchange for the Selective Functionalization of Polyhalogenated Arenes and Heterocycles

Using the bimetallic combination sBu2 Mg⋅2 LiOR (R=2-ethylhexyl) in toluene enables efficient and regioselective Br/Mg exchanges with various dibromo-arenes and -heteroarenes under mild reaction conditions and provides bromo-substituted magnesium reagents. Assessing the role of Lewis donor additives in these reactions revealed that N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDTA) finely tunes the regioselectivity of the Br/Mg exchange on dibromo-pyridines and quinolines. Combining spectroscopic with X-ray crystallographic studies, light has been shed on the mixed Li/Mg constitution of the organometallic intermediates accomplishing these transformations. These systems reacted effectively with a broad range of electrophiles, including allyl bromides, ketones, aldehydes, and Weinreb amides in good yields.

Preparation, crystal structures, properties, and time-dependent density functional theory of two cobalt complexes with 3-hydroxy-2-methyl-quinoline-4-carboxylate

One organic compound [HMCA]2 (1) and two novel cobalt complexes [Co(MCA)(bipy)(H2O)]·(H2O) (2), [Co2(MCA)2(Phen)3]·3(H2O) (3) are synthesized by a solvothermal approach and are structurally determined by single-crystal X-ray diffraction. Compound 1 exhibits a two-dimensional structure by hydrogen bond and π. . .π stacking interaction. The complexes exhibit a three-dimensional and one-dimensional metal-organic framework. Solid-state photoluminescence spectrums reveal that they show blue emission bands at 449 nm, and theoretical calculation results of time-dependent density functional theory show that all belong to ligand-to-ligand charge transfer. Solid-state diffuse reflectance spectrums reveal the presence of a narrow optical band gap of 1.72 and 1.60 eV in the complexes 2 and 3, respectively.

Disposable cartridge concept for the on-demand synthesis of turbo Grignards, Knochel-Hauser amides, and magnesium alkoxides

Magnesium organometallic reagents occupy a central position in organic synthesis. The freshness of these compounds is the key for achieving a high conversion and reproducible results. Common methods for the synthesis of Grignard reagents from metallic magnesium present safety issues and exhibit a batch-to-batch variability. Tubular reactors of solid reagents combined with solution-phase reagents enable the continuous-flow preparation of organomagnesium reagents. The use of stratified packed-bed columns of magnesium metal and lithium chloride for the synthesis of highly concentrated turbo Grignards is reported. A low-cost pod-style synthesizer prototype, which incorporates single-use prepacked perfluorinated cartridges and bags of reagents for the automated on-demand lab-scale synthesis of carbon, nitrogen, and oxygen turbo magnesium bases is presented. This concept will provide access to fresh organomagnesium reagents on a discovery scale and will do so independent from the operator’s experience in flow and/or organometallic chemistry.

Isolation and synthesis of cryptosanguinolentine (isocryptolepine), a naturally-occurring bioactive indoloquinoline alkaloid

Cryptosanguinolentine (isocryptolepine) is one of the minor naturally-occurring monomeric indoloquinoline alkaloids, isolated from the West African climbing shrub Cryptolepis sanguinolenta. The natural product displays such a simple and unique skeleton, which chemists became interested in well before it was found in Nature. Because of its structure and biological activity, the natural product has been targeted for synthesis on numerous occasions, employing a wide range of different strategies. Hence, discussed here are aspects related to the isolation of isocryptolepine, as well as the various approaches toward its total synthesis.

Preparation, photoluminescence, semiconductor properties, and theoretical calculations for a novel zinc zero-dimensional structure complex

The complex [Zn(CH3OH)4(MCA)2] (3-hydroxy-2-methylquinoline-4-carboxylic acid) has been synthesized through hydrothermal reactions and characterized by single-crystal X-ray diffraction. Its solid-state photoluminescence spectrum shows an emission in the blue region, which is assigned to ligand-to-metal charge transfer on the basis of time-dependent density functional theory calculations. Solid-state diffuse reflectance measurements show the existence of a narrow optical band gap of 1.73 eV.

Base-Controlled Regioselective Functionalization of Chloro-Substituted Quinolines

We prepared a number of di- and trifunctionalized quinolines by selective metalation of chloro-substituted quinolines with metal amides followed by reaction with different electrophiles. Metalation of the C-3 position of the quinolinic ring with lithium diisopropylamide at -70 °C is easy to achieve, whereas reaction with lithium-magnesium and lithium-zinc amides affords C-2 or C-8 functionalized derivatives in a regioselective fashion. These complementary methods could be rationalized by DFT calculations and are convenient strategies toward the synthesis of bioactive quinoline derivatives such as chloroquine analogues.

Selective remote C–H trifluoromethylation of aminoquinolines with CF3SO2Na under visible light irradiation in the absence of an external photocatalyst

A selective remote C–H trifluoromethylation of aminoquinolines with sodium trifluoromethanesulfinate (CF₃SO₂Na) under visible-light irradiation without an external photocatalyst was developed.

Selective functionalization of complex heterocycles via an automated strong base screening platform

An automated high throughput screening approach to optimizing strong base-mediated metalations.

Structural and Mechanistic Insights into s-Block Bimetallic Catalysis: Sodium Magnesiate-Catalyzed Guanylation of Amines

To advance the catalytic applications of s-block mixed-metal complexes, sodium magnesiate [NaMg(CH₂ SiMe₃ )₃ ] (1) is reported as an efficient precatalyst for the guanylation of a variety of anilines and secondary amines with carbodiimides. First examples of hydrophosphination of carbodiimides by using a Mg catalyst are also described. The catalytic ability of the mixed-metal system is much greater than that of its homometallic components [NaCH₂ SiMe₃ ] and [Mg(CH₂ SiMe₃ )₂ ]. Stoichiometric studies suggest that magnesiate amido and guanidinate complexes are intermediates in these catalytic routes. Reactivity and kinetic studies imply that these guanylation reactions occur via (tris)amide intermediates that react with carbodiiimides in insertion steps. The rate law for the guanylation of N,N'-diisopropylcarbodiimide with 4-tert-butylaniline catalyzed by 1 is first order with respect to [amine], [carbodiimide], and [catalyst], and the reaction shows a large kinetic isotopic effect, which is consistent with an amine-assisted rate-determining carbodiimide insertion transition state. Studies to assess the effect of sodium in these transformations denote a secondary role with little involvement in the catalytic cycle.

Assessing the reactivity of sodium alkyl-magnesiates towards quinoxaline: single electron transfer (SET) vs. nucleophilic alkylation processes

Structurally tracking the reaction of a sodium butylmagnesiate supported by a bulky silyl(bisamide) ligand towards quinoxaline, SET reactivity.

Synthesis of 8-heteroaryl nitroxoline analogues via one-pot sequential Pd-catalyzed coupling reactions

A series of 8-heteroaryl substituted quinolines were prepared, either by direct C–H arylation of five-membered heteroarenes, or Pd-catalyzed coupling of organoboron reagents with bromoquinolines.

Progress and developments in the turbo Grignard reagent i-PrMgCl·LiCl: a ten-year journey

The structural and kinetic perspectives of i-PrMgCl·LiCl help to rationalize the trends of its unique reactivity and selectivity.

Continuous flow magnesiation of functionalized heterocycles and acrylates with TMPMgCl⋅LiCl

A flow procedure for the metalation of functionalized heterocycles (pyridines, pyrimidines, thiophenes, and thiazoles) and various acrylates using the strong, non-nucleophilic base TMPMgCl⋅LiCl is reported. The flow conditions allow the magnesiations to be performed under more convenient conditions than the comparable batch reactions, which often require cryogenic temperatures and long reaction times. Moreover, the flow reactions are directly scalable without further optimization. Metalation under flow conditions also allows magnesiations that did not produce the desired products under batch conditions, such as the magnesiation of sensitive acrylic derivatives. The magnesiated species are subsequently quenched with various electrophiles, thereby introducing a broad range of functionalities.

Deproto-metallation using mixed lithium–zinc and lithium–copper bases and computed CH acidity of 2-substituted quinolines

The metallated quinolines were functionalized by iodolysis or aroylation.

Pre-inverse-crowns: synthetic, structural and reactivity studies of alkali metal magnesiates primed for inverse crown formation

The synthesis, structure and reactivity of donor-free sodium and potassium magnesiates are assessed culminating in the unique 1,4-dimetallation of naphthalene.

Development of quinoline-based disruptors of biofilm formation against Vibrio cholerae

Biofilm formation is a major cause of bacterial persistence in nosocomial infections, leading to extended treatment times and increased rates of morbidity and mortality. Despite this, there are currently no biofilm inhibitors approved for clinical use. The synthesis and biological evaluation of a library of amino alcohol quinolines as lead compounds for the disruption of biofilm formation in Vibrio cholerae is now reported. Application of selective metal-halogen exchange chemistry installed both stereocenters in one step, to afford a simpler scaffold than the initial lead molecule, with an EC50 < 10 μM.

Synthesis and photophysical properties of 2-aryl-6,8-bis(arylethenyl)-4-methoxyquinolines

Iodine-methanol mediated oxidative-aromatization of 2-aryl-6,8-dibromo-2,3-dihydroquinolin-4(1H)-ones afforded the corresponding 2-aryl-6,8-dibromo-4-methoxy-quinolines in high yield and purity. The isomeric 1-(2-amino-3,5-dibromophenyl)-3-aryl-2-propen-1-ones reacted with iodine in methanol afford in a single pot operation the corresponding 2-aryl-6,8-dibromo-4-methoxyquinoline (major) and 2-aryl-6,8-dibromoquinolin-4(1H)-one (minor) products that were separated in sequence by column chromatography on silica gel. Suzuki-Miyaura cross-coupling of the 6,8-dibromo-4-methoxyquinoline derivatives with excess arylvinylboronic acids afforded the corresponding 2-aryl-6,8-bis(2-arylethenyl)-4-methoxyquinolines. The absorption and fluorescence properties of these compounds were also determined.