Hexafluoroisopropyl alcohol mediated synthesis of 2,3-dihydro-4H-pyrido[1,2-a]pyrimidin-4-ones

Catalyst- and Additive-free, Regioselective 1,6-Hydroarylation of para-Quinone Methides with Anilines in HFIP

A simple and efficient method for the synthesis of diarylmethyl-functionalized anilines through the hexafluoroisopropanol (HFIP)-mediated regioselective 1,6-hydroarylation reaction of para-quinone methides (p-QMs) with anilines under catalyst- and additive-free conditions is reported. Various kinds of p-QMs and amines (e. g. primary, secondary and tertiary amines) are well tolerated in this transformation without the pre-protection of amino group, and the corresponding products could be generated with good to excellent yields and satisfactory regioselectivity under the optimized reaction conditions. In addition to adaptable amine compounds, indoles and their derivatives are also compatible with this reaction system. This transformation can be easily extended to a gram scale-synthesis level to synthesize the target product. Furthermore, it is worth noting that some complex small aniline molecules with biological activity can be selectively modified using this method. The possible reaction mechanism is proposed through the step-by-step control experiments and DFT calculations, showing that the key process for achieving the regioselective 1,6-hydroarylation of p-QMs is the hydrogen bonding effect of HFIP to substrates.

TFA-mediated stereoselective aza-Michael addition for the synthesis of 3β-arylamine derivatives of withaferin A and evaluation of their anticancer potential

A simple and efficient protocol for the aza-Michael addition of various aromatic anilines to ring A of withaferin A has been developed. Stereoselectivity, functional group tolerance, broad substrate scope, short reaction time and moderate to high yield are the merits of the protocol. One of the synthesized compounds 11 shows an IC 50 value of 3.8 μM against aggressive, highly metastatic triple-negative breast cancer cell line MDA-MB-231.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Reactions of 1-trifluoromethyl-prop-2-yne1-iminium salts with 2- and 3-aminopyridines

4-CF3-pyrido[1,2-a]pyrimidin-5-ium triflates could be prepared in fair to high yields from acetylenic iminium salts R-C≡C–C(CF3)=N+Me2·CF3SO3 − and 2-aminopyridinium triflate under thermal conditions. Their reactions with protic heteronucleophiles, leading to 4-CF3, 4-XR-substituted 1,4-dihydropyrido[1,2-a]pyrimidin-5-ium salts, have been studied and reversible addition as well as subsequent opening of the pyrimidine ring have been observed. The cyclocondensation of a 3-phenyl-propyniminium triflate and 3-aminoyridinium triflate required strong thermal activation and yielded a 4-CF3-and a 4-CF3,5-CH3-[1,7]naphthyridine. A 1-CF3-benzo[f][1,7]naphthyridine was obtained from the same propyniminium salt and 3-aminoquinolinium triflate.

Antimelanoma activities of chimeric thiazole-androstenone derivatives

The discovery of chimeric anti-melanoma agents is reported. These molecules are potent growth suppressors of melanoma cells in vitro with growth inhibition of 50% (GI₅₀) values as low as 1.32 µM. Compounds were more toxic to melanoma cells in vitro than commonly used anti-melanoma agent dacarbazine as measured by TUNEL assay. They induced both caspase-independent apoptosis evident by colocalization of TUNEL with endonuclease G (EndoG) and caspase-mediated apoptosis measured by colocalization of TUNEL with caspase-activated DNase (CAD). In addition, compounds 3 and 5 strongly induced oxidative injury to melanoma cells as measured by TUNEL colocalization with heme oxygenase-1 (HO1). Dacarbazine induced only caspase-independent apoptosis, which may explain why it is less cytotoxic to melanoma cells than compounds 3, 4 and 5.

Benign Synthesis of Fused-thiazoles with Enone-based Natural Products and Drugs for Lead Discovery

In an effort to synthesize a library of bioactive molecules, we present an efficient synthesis of fused-thiazole derivatives of natural products and approved drugs by using an environmentally usable solvent, acetic acid, and without any external reagent. Cholestenone, ethisterone, progesterone, and nootkatone-derived epoxyketones have been utilized to synthesize 50 novel compounds. The plausible mechanism of the reaction has been determined by theoretical calculation using M06-2X/6-31+G(d,p). These novel molecules have been tested against cancer cell lines and pathogenic bacterial strains. Several ethisterone-based fused-thiazole compounds are found to be potent growth inhibitors of cancer cell lines at submicromolar concentrations.

Unusual Overhauser Dynamic Nuclear Polarization Behavior of Fluorinated Alcohols at Room Temperature

The structure of fluorinated alcohols is a matter of considerable interest in view of wide-ranging biomolecular applications. The microheterogeneity of fluorinated alcohols in the liquid state, in particular, has been a matter of debate and discussion in recent years using experimental and theoretical methods, including neutron or X-ray diffraction, as well as density functional theory (DFT) and molecular dynamics (MD) simulations. Here, we show that ¹H and ¹⁹F Overhauser dynamic nuclear polarization (ODNP) buildup curves in solution state at room temperature show unusual behavior that could offer a novel approach to investigate the structural heterogeneity and dynamics of such homogeneous liquids with improved sensitivity. A detailed analysis of multiexponential ODNP buildup curves as a function of microwave irradiation time is shown to evidence microheterogeneity in such systems. Experimental ODNP buildup rates are interpreted using simple motional models that yield the motional correlation times of the relevant species in solution. It may be emphasized that this information is not available from standard approaches of high-resolution nuclear magnetic resonance (NMR) spectroscopy. While the present study focuses on fluorinated alcohols, it is to be anticipated that this approach would be valuable in the study of molecular assemblies in the solution state, including peptides, surfactant systems, etc.

Synthesis and Antimicrobial Studies of 4-[3-(3-Fluorophenyl)-4-formyl-1H-pyrazol-1-yl]benzoic Acid and 4-[3-(4-Fluorophenyl)-4-formyl-1H-pyrazol-1-yl]benzoic Acid as Potent Growth Inhibitors of Drug-Resistant Bacteria

Microbial resistance to antibiotics is an urgent and worldwide concern. Several pyrazole-derived hydrazones were synthesized by using benign reaction conditions. Several of these molecules are potent growth inhibitors of drug-resistant strains of Staphylococcus aureus and Acinetobacter baumannii with minimum inhibitory concentration values as low as 0.39 μg/mL. Furthermore, these molecules are nontoxic to human cells at high concentrations. Some of these molecules were tested for their ability to disrupt the bacterial membrane by using the SYTO-9/propidium iodide (BacLight) assay.

Synthesis of Hydrazone Derivatives of 4-[4-Formyl-3-(2-oxochromen-3-yl)pyrazol-1-yl]benzoic acid as Potent Growth Inhibitors of Antibiotic-resistant Staphylococcus aureus and Acinetobacter baumannii

Microbial resistance to drugs is an unresolved global concern, which is present in every country. Developing new antibiotics is one of the guidelines of the Centers for Disease Control and Preventions (CDC) to combat bacterial resistance to drugs. Based on our lead molecules, we report the synthesis and antimicrobial studies of 27 new pyrazole derivatives. These new coumarin-pyrazole-hydrazone hybrids are readily synthesized from commercially available starting materials and reagents using benign reaction conditions. All the synthesized molecules were tested against 14 Gram-positive and Gram-negative bacterial strains. Several of these molecules have been found to be potent growth inhibitors of several strains of these tested bacteria with minimum inhibitory concentrations as low as 1.56 μg/mL. Furthermore, active molecules are non-toxic in in vitro and in vivo toxicity studies.

Hexafluoroisopropanol-Mediated Domino Reaction for the Synthesis of Thiazolo-androstenones: Potent Anticancer Agents

A cascade reaction of thioamides with 6β-bromoandrostenedione in hexafluoroisopropanol formed substituted thiazolo-androstenones. This is a simple and mild protocol to synthesize novel molecules by using readily available reagents and substrates. Feasibility of the reaction has been rationalized by density functional theory calculations. Moreover, these compounds are potent growth inhibitors of colon, central nervous system, melanoma, ovarian, and renal cancer cell lines with 50% growth inhibition values as low as 1.04 μM.

Benign Synthesis of Thiazolo-androstenone Derivatives as Potent Anticancer Agents

An unprecedented reaction of thiourea derivatives with 6β-bromoandrostenedione has been discovered for the formation of aminothiazolo-androstenones via a simple, safer, cascade protocol that enables the syntheses of novel molecules by using readily available reagents. The reaction mechanism of product formation has been rationalized by density functional theory calculations. This benign methodology accentuates a domino protocol deploying a renewable solvent, ethanol, while generating novel compounds that display potent growth inhibitory effects in in vitro studies for several cancer cell lines at submicromolar concentrations.

Hexafluoroisopropanol mediated benign synthesis of 2H-pyrido[1,2-a]pyrimidin-2-ones by using a domino protocol

Domino strategy has been used for the synthesis of 2H-pyrido[1,2-a]pyrimidin-2-ones. Four sequential reactions: aza-Michael addition, water elimination, intramolecular acyl substitution, and [1,3]-H shift were observed in this domino protocol. Hexafluoroisopropanol is used as a promotor and recyclable solvent in this cascade process. Availability of inexpensive 2-aminopyridines and wide variety of Michael acceptors such as commercially available acrylates and unactivated Baylis-Hillman adducts makes this methodology a huge reservoir of novel fused N-heterocycles as bioactive and potential therapeutic agents. The reaction mechanism has been proposed and rationalized by density functional theory calculation. Products are obtained up to 95% yield.

Modular synthesis of thiazoline and thiazole derivatives by using a cascade protocol

The first common synthetic protocol for thiazolines and thiazoles.

Thiazolines and thiazoles are an integral part of numerous natural products, a number of drugs, and many useful molecules such as ligands for metal catalysis. We report the first common synthetic protocol for the synthesis of thiazoles and thiazolines. Novel molecules are efficiently synthesized by using readily available and inexpensive substrates. The reaction conditions are mild and pure products are obtained without work-up and column purification.

Copper-catalyzed selective C–N bond formation with 2-amino, 2-hydroxy and 2-bromo-5-halopyridine

Copper catalyzed 1,2-diol promoted amination at electron-rich C-5 position of unprotected 2-amino/2-hydroxy-5-halopyridine and selective amination at C-5 in 2-bromo-5-iodopyridine provided excellent yields.