Regioselective synthesis and estrogenicity of (±)-8-alkyl-5,7-dihydroxy-4-(4-hydroxyphenyl)-3,4-dihydrocoumarins

Supramolecule-Controlled Enantioselectivity for Electrochemical Asymmetric Hydrogenation of Coumarins with a Chiral Macrocyclic Compound

The supramolecular strategy was subjected to the asymmetric hydrogenation of 4-methylumbelliferone by electrochemical reduction in the presence of a chiral macrocyclic multifarane[3,3], which offered a l-7-hydroxy-4-methylchroman-2-one product with a chemical yield of 65% and enantioselectivity up to >99% ee. The high stability of the developed chiral supramolecular electrode guaranteed the recyclability and repeatability in the electrolysis, and therefore, the application was extended to more coumarin derivatives to provide satisfactory chemical yields and enantioselectivities.

MPAI-Ligand Accelerated Pd-Catalyzed C(sp3)-H Arylation of Free Aliphatic Acids

Here, we report the development of a class of bifunctional monoprotected amino-imidazoline (MPAI) ligands and their applications in Pd-catalyzed C(sp³)-H arylation of free aliphatic acids. The newly developed MPAI ligand allows the use of 1.0 equiv of aliphatic acids containing an alpha hydrogen for the first time.

Human estrogen receptor α antagonists, part 2: Synthesis driven by rational design, in vitro antiproliferative, and in vivo anticancer evaluation of innovative coumarin-related antiestrogens as breast cancer suppressants

New twelve in silico designed coumarin-based ERα antagonists, namely 3DQ-1a to 3DQ-1е, were synthesized and confirmed as selective ERα antagonists, showing potencies ranging from single-digit nanomolar to picomolar. The hits were confirmed as selective estrogen receptor modulators and validated as antiproliferative agents using MCF-7 breast cancer cell lines exerting from picomolar to low nanomolar potency, at the same time showing no agonistic activity within endometrial cell lines. Their mechanism of action was inspected and revealed to be through the inhibition of the Raf-1/MAPK/ERK signal transduction pathway, preventing hormone-mediated gene expression on either genomic direct or genomic indirect level, and stopping the MCF-7 cells proliferation at G₀/G₁ phase. In vivo experiments, by means of the per os administration to female Wistar rats with pre-induced breast cancer, distinguished six derivatives, 3DQ-4a, 3DQ-2a, 3DQ-1a, 3DQ-1b, 3DQ-2b, and 3DQ-3b, showing remarkable potency as tumor suppressors endowed with optimal pharmacokinetic profiles and no significant histopathological profiles. The presented data indicate the new compounds as potential candidates to be submitted in clinical trials for breast cancer therapy.

Reaction of imidazo[1,2-a]pyridines with coumarin-3-carboxylic acids: a domino Michael addition/decarboxylation/oxidation/annulation

A palladium-catalyzed decarboxylative domino reaction of imidazo[1,2-a]pyridines and coumarin-3-carboxylic acids has been developed, which provides access to dibenzoisochromenoimidazo[1,2-a]pyridin-6-ones possessing six fused rings.

Rhodium-Catalyzed Asymmetric Hydrogenation of 3-Benzoylaminocoumarins for the Synthesis of Chiral 3-Amino Dihydrocoumarins

An asymmetric hydrogenation of 3-benzoylaminocoumarins was achieved for the first time using our BridgePhos-Rh catalytic system, providing chiral 3-amino dihydrocoumarins in high yields (up to 98 %) and with excellent enantioselectivities (up to 99.7 % ee). The relationship between the enantioselectivities of the hydrogenations and the dihedral angles and the resulting π-π stacking effects of the BridgePhos-Rh complexes, which were determined by X-ray diffraction analysis, are discussed. The corresponding hydrogenated products allow for many transformations, providing several chiral skeletons with important physiological and pharmacological activities.

Synthesis of Functionalized Dihydrocoumarins by NHC-Catalyzed [3 + 3] Annulation of Enals with 2-Substituted Naphthoquinones

The [3 + 3] annulation of α,β-unsaturated aldehydes with 2-substituted 1,4-naphthoquinones allowing the facile synthesis of functionalized dihydrocoumarins catalyzed by N-heterocyclic carbene (NHC) is reported. The initially formed NHC-homoenolates underwent an efficient Michael-isomerization-lactonization cascade to furnish the products. Preliminary studies on mechanism shed light on the homoenolate pathway over the intermediacy of the α,β-unsaturated acylazolium intermediates. Moreover, using chiral NHCs, the desired products were formed in up to 49% yield and 99:1 er.

Semi-synthesis as a tool for broadening the health applications of bioactive olive secoiridoids: a critical review

Covering: 2005 up to 2020Olive bioactive secoiridoids are recognized as natural antioxidants with multiple beneficial effects on human health. Nevertheless, the study of their biological activity has also disclosed some critical aspects associated with their application. Firstly, only a few of them can be extracted in large amounts from their natural matrix, namely olive leaves, drupes, oil and olive mill wastewater. Secondly, their application as preventive agents and drugs is limited by their low membrane permeability. Thirdly, the study of their biological fate after administration is complicated by the absence of pure analytical standards. Accordingly, efficient synthetic methods to obtain natural and non-natural bioactive phenol derivatives have been developed. Among them, semi-synthetic protocols represent efficient and economical alternatives to total synthesis, combining efficient extraction protocols with efficient catalytic conversions to achieve reasonable amounts of active molecules. The aim of this review is to summarize the semi-synthetic protocols published in the last fifteen years, covering 2005 up to 2020, which can produce natural olive bioactive phenols scarcely available by extractive procedures, and new biophenol derivatives with enhanced biological activity. Moreover, the semi-synthetic protocols to produce olive bioactive phenol derivatives as analytical standards are also discussed. A critical analysis of the advantages offered by semi-synthesis compared to classical extraction methods or total synthesis protocols is also performed.

3-Nitro-3,4-dihydrocoumarins: valuable precursors for the synthesis of enantiomerically enriched masked quaternary α-amino acid derivatives with a 3,4-dihydrocoumarin scaffold

A bifunctional squaramide catalyzed enantioselective formal [2 + 4] annulation reaction with 3-nitro-3,4-dihydrocoumarins and ortho-quinone methide has been developed. Novel chiral masked quaternary α-amino acid derivatives with a 3,4-dihydrocoumarin scaffold are obtained in a highly stereocontrolled manner. Representative transformation of the annulation product to a biologically important quaternary α-amino acid derivative is achieved without any appreciable loss in the diastereo- and enantioselectivity.

Organocatalytic Friedel-Crafts Alkylation/Lactonization Reaction of Naphthols with 3-Trifluoroethylidene Oxindoles: The Asymmetric Synthesis of Dihydrocoumarins

Naphthols and 3-trifluoroethylidene oxindoles were found to undergo an asymmetric Friedel-Crafts alkylation/lactonization reaction, catalyzed by only 2.5 mol % of a quinine-derived squaramide catalyst, to afford the corresponding α-aryl-β-trifluoromethyl dihydrocoumarin derivatives in high yields (up to 99 %) with excellent enantio- and diastereoselectivities (up to 98 % ee, >20:1 d.r.). Importantly, the lactonization proceeded by nucleophilic attack of the naphthol hydroxy group at the amide motif of the oxindoles under mild reaction conditions. This protocol represents a new strategy for the formation of dihydrocoumarins by an efficient intramolecular amide C-N bond-cleavage and esterification process.

Transition metal-free decarboxylative alkylation reactions

This review summarizes recent advances in the transition metal-free decarboxylative alkylation of carboxylic acids and their derivatives.

N-Heterocyclic carbene-catalyzed enantioselective annulations: a dual activation strategy for a formal [4+2] addition for dihydrocoumarins

A highly efficient asymmetric formal [4+2] annulation for the synthesis of dihydrocoumarins has been developed via an in situ activated NHC catalysis. Both electrophilic and nucleophilic species are generated in situ simultaneously whereby acyl imidazoles facilitated rapid formation of an NHC-enolate intermediate to afford the [4+2] dihydrocoumarin adducts.

A palladium-catalyzed enantioselective hydroesterification of alkenylphenols with phenyl formate. A facile approach to optically active dihydrocoumarins

An effective palladium-catalyzed enantioselective hydroesterification of alkenylphenols with phenyl formate as a CO source is described.

Tandem sp3 C-H functionlization/decarboxylation of 2-alkylazaarenes with coumarin-3-carboxylic acids

The catalyst-free sp(3) C-H functionalization of 2-alkylazaarenes has been achieved in the reaction with (thio)coumarin-3-carboxylic acids. Followed by a tandem decarboxylation, this method provides facile synthesis of biologically important azaarene-substituted 3,4-dihydro(thio)coumarins in a single step in high yields.

Catalyst-free tandem Michael addition/decarboxylation of (thio)coumarin-3-carboxylic acids with indoles: facile synthesis of indole-3-substituted 3,4-dihydro(thio)coumarins

The tandem Michael addition/decarboxylation of (thio)-coumarin-3-carboxylic acids with indoles gives biologically important indole-3-substituted dihydrocoumarins in good to excellent yields under catalyst-free conditions.

Synthesis and DPPH radical scavenging activity of novel compounds obtained from tyrosol and cinnamic acid derivatives

Novel compounds exhibiting DPPH radical scavenging activity were synthesised. The key step was the trifluoroacetic acid-mediated hydroarylation of cinnamic ester with tyrosol.

A palladium-catalyzed regioselective hydroesterification of alkenylphenols to lactones with phenyl formate as CO source

An effective Pd(OAc)2-PPh3 catalyzed hydroesterification of alkenylphenols with phenyl formate as CO surrogate is described. A variety of lactones are obtained in generally high yields with high regioselectivities. In one case, 76% ee is obtained with a chiral ligand.