Chemical synthesis and application of aryldihydronaphthalene derivatives

Aryldihydronaphthalenes (ADHNs) and their derivatives are widely found in many types of natural products, bioactive compounds, and functional materials, and are also important synthetic intermediates in organic chemistry, attracting widespread attention from both organic and pharmaceutical chemists. In the past two decades, the chemical synthesis and biological activity of ADHNs and their derivatives have become two hot spots. This review summarizes the synthetic protocols of ADHN derivatives, introduces some representative examples of the reaction mechanism, and focuses on the research progress of ADHNs in natural product chemistry and chemical biology since 2000.

New oxacycles on the block: benzodioxepinones via a Passerini reaction

Oxacycles and benzoxepanes are privileged motifs present in a variety of natural products and functional molecules. However, their synthetic access is limited. Here, we demonstrate a rapid synthesis of unprecedented benzoxepanes from readily available starting materials in one step via a Passerini multicomponent reaction. The reaction proceeds smoothly under mild reaction conditions. We have obtained a single-crystal X-ray structure, revealing a butterfly conformation, combined with useful structural features. In addition, we have performed both a full interaction map on the X-ray structure and a profile analysis of a virtual library based on the proposed scaffold with a special focus on certain physicochemical parameters to demonstrate their potential usage in drug discovery.

Assessment of the dual role of Lyonia ovalifolia (Wall.) Drude in inhibiting AGEs and enhancing GLUT4 translocation through LC-ESI-QTOF-MS/MS determination and in silico studies

Introduction: Diabetes mellitus (DM) is a metabolic disorder that results in glucose accumulation in the blood, accompanied by the production of advanced glycation end products (AGEs) through glycation of cellular proteins. These AGEs interfere with insulin signaling and prevent GLUT4 membrane translocation, thereby promoting the accumulation of more glucose in the blood and causing post-diabetic complications.

Methods: In this study, we examine the anti-diabetic potential of Lyonia ovalifolia (Wall.) Drude, a well-known ethnomedicinal plant of the Indian Himalayas. Considering its various medicinal properties, we analyzed its ethanolic extract and various solvent fractions for in vitro antiglycation activity and antidiabetic potential, i.e., stimulation of GLUT4 translocation.

Result and Discussions: The results showed that the extract and fractions exhibited increased antiglycation activity and an increased level of GLUT4 translocation. Analysis of a further 12 bioactive compounds of ethanolic extract, identified through LC-ESI-QTOF-MS/MS, revealed the presence of three new compounds: leucothol B, rhodoterpenoids A, and leucothol A. Moreover, we performed molecular docking of identified compounds against key proteins of diabetes mellitus: the sirtuin family of NAD (+)-dependent protein deacetylases 6 (SIRT6), aldose reductase (AR), and tyrosine kinase (TK). The results showed that flavonoid luteolin showed the best binding affinity ((−12.3 kcal/mol), followed by eriodictyol, astilbin, and syringaresinol. An ADMET study showed that luteolin, eriodictyol, astilbin, and syringaresinol may be promising drug candidates belonging to the flavonoid class of compounds, with no harmful effects and complying with all the drug-likeness guidelines. Furthermore, molecular dynamics (MD) simulations on a 50 ns timescale revealed that AR protein was most stable with luteolin throughout the simulation period. Therefore, this study reveals for the first time that L. ovalifolia plays an important role in insulin homeostasis, as shown in in vitro and in silico studies.

Propargyl Chalcones' Radical Annulation/Sulfonation Reaction: Efficient Synthesis of Benzo[b]oxepin-5(2H)-one and Chromane Derivatives

A novel and facile methodology for the synthesis of sulfonated benzo[b]oxepinone and chromane derivatives was reported by the reaction of propargyl chalcones with arylsulfonyl chloride via radical cascade annulation/sulfonation under laboratory conditions. Readily available propargyl chalcones, commercialized arylsulfonyl chloride, and simple reaction conditions make this six(seven)-membered oxygen-containing heterocycles' synthetic strategy more attractive and with significant application values.

Recent advances in the total synthesis of 2,7'-cyclolignans

The synthetic progress of bioactive 2,7'-cyclolignans is reviewed. After a short introduction to biosynthesis and chemoenzymatic synthesis, the chemical synthesis of various aryltetralin, dihydronaphthalene and 7'-arylnaphthalene-types of these lignans is demonstrated. Notably, newly developed methods, such as Pd-catalyzed C-H arylation, organocatalysis and photocatalysis under visible-light, are discussed during the construction of their skeleton. These efforts will stimulate further development of novel synthetic strategies for this kind of natural product with important biological activities.

A new cycloaddition profile for ortho-quinone methides: photoredox-catalyzed [6+4] cycloadditions for synthesis of benzo[b]cyclopenta[e]oxepines

Visible-light-induced [6+4] cycloaddition reactions of ortho-quinone methides have been developed. The reaction of ortho-quinone methides with pentafulvenes in the presence of a thioxanthylium photoredox catalyst afforded benzo[b]cyclopenta[e]oxepines. The present reaction represents a promising tool for the synthesis of natural products and bioactive compounds that contain a benzoxepine structure.

DDQ-Catalyzed Oxidative C(sp3)-H Functionalization of Aryltetralins and Subsequent Chemoselective Oxidative Demethylation to Access Dihydronaphthalenes and Dihydronaphthoquinones

A highly controlled DDQ-catalyzed oxidative C(sp³)-H functionalization of three contiguous carbon atoms in aryltetralins is reported for efficient access to diverse oxygenated dihydronaphthalene scaffolds. The first total synthesis of pachypostaudin B is realized. Further, a CAN-mediated chemoselective oxidative demethylation on the dihydronaphthalene scaffolds is demonstrated to arrive at the rarely observed dihydronaphthoquinone core in moderate to good yields. The present methodology enables quick access to a library of magnoshinin and merrilliaquinone analogs.

Scalable Total Synthesis of (+)- and (-)-Codonopiloneolignanin A via Ti(IV)/NHC Cooperative Control Highly Enantioselective Dimerization of Multisubstituted Cinnamaldehyde

The first gram-scale asymmetric total synthesis of (+)- and (-)-codonopiloneolignanin A has been achieved from multisubstituted cinnamaldehyde in four steps with 37% overall yield. The synthetically challenging tricyclic [5, 3, 0, 0^3,8] decane skeleton was efficiently constructed via a highly enantioselective dimerization of multisubstituted cinnamaldehyde, followed by a sequence of cascade reactions including Prins cyclization, cation mediated cyclization, and deprotection. Furthermore, the scope of NHC-catalyzed/Ti(IV)-mediated synergistic control multisubstituted cinnamaldehyde dimerization was investigated. Significantly, the bioactivity of codonopiloneolignanin A and its enantiomer, particularly scarce in nature, was tested and showed good anticancer activity.

Palladium-Catalyzed Cascade to Benzoxepins by Using Vinyl-Substituted Donor-Acceptor Cyclopropanes

A palladium-catalyzed intermolecular cascade (4+3) cyclocondensation of salicylaldehydes and vinylcyclopropanes is reported. A key feature of the reaction is the use of a phosphonate group as an acceptor moiety on the cyclopropane, exploiting its propensity to undergo olefination with aldehydes. Subsequent O-allylation enabled the formation of a range of substituted benzoxepinsWith a novel chiral ligand, the products were obtained in generally good yield and with reasonable enantioselectivity.

Bioactive megastigmane glucosides and monoterpenes from Lyonia ovalifolia

Three new megastigmane glucosides (1-3) and two new monoterpenes (4-5), together with 14 related known compounds (6-19) were isolated from the twigs and leaves of Lyonia ovalifolia. The structures of the new compounds were determined by extensive MS, NMR, CD experiments and chemical methods. Compounds 2, 6, and 18 displayed potent antiviral activity against Coxsackie B3, with IC₅₀ values between 6.4 and 14.6 µM. Additionally, compounds 6, 10, and 11 exhibited noteworthy anti-inflammatory activities, with inhibition rates ranging from 54.55% to 83.33% under the concentration of 10^-5 M.

Diverse lignans with anti-inflammatory activity from Urceola rosea

Seventeen structurally diverse lignans, comprising six new compounds, ecdysanols A (1), B (11), C - E (13-15), and F (17), were isolated from the caulis of Urceola rosea. The structures and absolute configurations of these new compounds were elucidated by means of extensive analysis of mass and NMR data, as well as chiroptical properties. A bioassay in vitro showed that all lignans possessed anti-inflammatory effects by inhibiting the production of TNF-α, NO and/or IL-6 in LPS-stimulated RAW264.7 cells. Ecdysanol F (17) showed the most strongly effect against NO and IL-6 levels.

One-pot, three-component approach to diarylacetonitriles

Described herein is a novel one-pot, three-component reaction where aldehydes, electron-rich arenes, and TMSCN in the presence of BF₃-OEt₂ allowed direct access to a number of diarylacetonitriles under mild reaction conditions in good to excellent yields.

New iridoids from Lyonia ovalifolia and their anti-hyperglycemic effects in mice pancreatic islets

Phytochemical investigation on the aerial parts of Lyonia ovalifolia (Wall.) Drude led to the isolation of three new iridoids, lyonofolin A (1), lyonofolin B (2), and lyonofolin C (3), and a known iridoid, gelsemiol (4). Structures of compounds 1-4 were determined by extensive spectroscopic analyses, including EI-MS, HREI-MS, UV, IR, and 1D- and 2D-NMR (HMBC, HSQC, COSY, NOESY) spectroscopic methods. The effect of insulin secretion of compounds 1, 2, and 4 were evaluated in mice pancreatic islets cellular model. This insulin secretory assay demonstrated that compound 2 potentiates glucose-induced insulin secretion, and thus can serve as a new insulin secretagogue for the treatment of diabetes. The newly isolated compounds were further evaluated against normal 3 T3 cell lines for cytotoxicity, where they did not show any cytotoxicity.

Asymmetric total synthesis of (+)-ovafolinins A and B

(+)-Ovafolinins A and B are two homologous lignans containing unique polycyclic skeletons. Benefiting from a highly diastereoselective alkylation of (S)-Taniguchi lactone, a double Friedel-Crafts reaction, a global debenzylation and a Cu(OAc)₂-enabled benzylic oxidative cyclization, we present herein an efficient synthetic approach to (+)-ovafolinins A and B.

Rhodoterpenoids A‒C, Three New Rearranged Triterpenoids from Rhododendron latoucheae by HPLC‒MS‒SPE‒NMR

Rhodoterpenoids A‒C (1‒3), three new rearranged triterpenoids, together with one new biogenetically related compound, rhodoterpenoid D (4), were isolated and efficiently elucidated from Rhododendron latoucheae by high-performance liquid chromatography−mass spectrometry−solid-phase extraction−nuclear magnetic resonance (HPLC‒MS‒SPE‒NMR). Compounds 1 and 2 possess an unprecedented skeleton with a 5/7/6/6/6-fused pentacyclic ring system, while compound 3 contains a unique 6/7/6/6/6-fused pentacyclic carbon backbone. Their structures were determined by extensive spectroscopic methods and electronic circular dichroism (ECD) analyses. Plausible biogenetic pathways for 1‒4 were proposed. Compounds 1 and 4 showed potential activity against herpes simplex virus 1 (HSV-1) with IC₅₀ values of 8.62 and 6.87 μM, respectively.

Total Synthesis of Ovafolinins A and B: Unique Polycyclic Benzoxepin Lignans through a Cascade Cyclization

Ovafolinins A and B, isolated from Lyonia ovalifolia var. elliptica, are lignans that contain a unique bridged structure containing a penta- and tetracyclic benzoxepin and an aryl tetralin. We report the first total synthesis of these natural products in which an acyl-Claisen rearrangement was initially utilized to construct the lignan backbone with correct relative stereochemistry. Judicious use of a bulky protecting group placed reactive moieties in the correct orientation, thereby resulting in a cascade reaction to form the bridged benzoxepin/aryl tetralin from a linear precursor in a single step. Modification of this route allowed the enantioselective synthesis of (+)-ovafolinins A and B, which confirmed the absolute stereochemistry, and comparison of optical rotation suggests that these compounds are found as scalemic mixtures in nature.

Recent advances in research on lignans and neolignans

Covering: 2009 to 2015Lignans and neolignans are a large group of natural products derived from the oxidative coupling of two C6-C3 units. Owing to their biological activities ranging from antioxidant, antitumor, anti-inflammatory to antiviral properties, they have been used for a long time both in ethnic as well as in conventional medicine. This review describes 564 of the latest examples of naturally occurring lignans and neolignans, and their glycosides in some cases, which have been isolated between 2009 and 2015. It comprises the data reported in more than 200 peer-reviewed articles and covers their source, isolation, structure elucidation and bioactivities (where available), and highlights the biosynthesis and total synthesis of some important ones.

Antiviral Triterpenes from the Twigs and Leaves of Lyonia ovalifolia

Eleven new 9,10-seco-cycloartan triterpene glycosides (1-11), seven new lanostane triterpene glycosides (12-18), and two new ursane triterpenoids (19-20) were isolated from the twigs and leaves of Lyonia ovalifolia. The structures of these compounds were elucidated by extensive MS and NMR spectroscopic analysis. The absolute configuration of compound 1a (the aglycone of 1) was established by X-ray crystallography, and that of C-24 in compounds 2, 7, and 12 was established by Mo₂(OAc)₄-induced electronic circular dichroism experiments. All compounds were evaluated for their antiviral [herpes simplex virus-1 (HSV-1), influenza A/95-359 (A/95-359), and Coxsackie B3 (CVB3)] activity. Compounds 1, 1a, 2a, 12a, 13, and 16 exhibited potent activity against HSV-1, with IC₅₀ values from 2.1 to 14.3 μM, while compounds 1a, 2a, 12a, 13, and 12-2a exhibited potent activity against A/95-359, with IC₅₀ values from 2.1 to 11.1 μM. In turn, compounds 1, 1a, 2a, 12a, and 13 exhibited potent activity against CVB3, with IC₅₀ values from 2.1 to 11.1 μM.

Gold(iii)-catalyzed synthesis of aroylbenzo[b]oxepin-3-ones from ortho-O-propargyl-1-one substituted arylaldehydes

An efficient gold-catalyzed intramolecular cyclization of ortho-O-propargyl-1-one substituted arylaldehydes has been achieved for the generation of substituted aroylbenzo[b]oxepin-3-one derivatives in moderate to good yields. This synthetic transformation proceeds via gold-catalysed oxidation of the internal alkyne moiety followed by an intramolecular condensation leading to seven-membered oxacycles.

Antioxidant lignans and chromone glycosides from Eurya japonica

Four new 8,8',7,2'-lignans, (+)-ovafolinin B-9'-O-β-d-glucopyranoside (1), (-)-ovafolinin B-9'-O-β-d-glucopyranoside (2), (+)-ovafolinin E-9'-O-β-d-glucopyranoside (3), and (-)-ovafolinin E-9'-O-β-d-glucopyranoside (4), two neolignans, eusiderin N (5) and (7S,8R)-3,5,5'-trimethoxy-4',7-epoxy-8,3'-neolignan-9,9'-diol-4-O-β-d-xylopyranoside (6), and two new chromone glycosides, 5,7-dihydroxy-4H-chromen-4-one-3-O-β-d-glucopyranoside (7) and 5,7-dihydroxy-4H-chromen-4-one-3-O-β-d-xylopyranoside (8), together with 25 known compounds, were isolated from the stems of Eurya japonica. Structural elucidation of compounds 1-8 was established by spectroscopic methods, especially 2D NMR techniques, electronic circular dichroism data, and comparison with reported data. The isolates were evaluated for antioxidant and anti-NO production activities. Compounds 1, 2, 12-20, and 29 (ED50 23.40 μM for 1) demonstrated potent antioxidant activity compared to the positive control α-tocopherol (ED50 27.21 μM). On the other hand, compounds 1, 2, 7-9, 12-20, and 32 showed only weak anti-NO production activity when compared to the positive control quercetin.

Lyonin A, a new 9,10-Secograyanotoxin from Lyonia ovalifolia

Phytochemical studies on the branches and leaves of Lyonia ovalifolia yielded a new grayanane diterpenoid, lyonin A (1), together with two known compounds, secorhodomollolides A and D (2 and 3, resp.). The structure of 1 was elucidated by combination of 1D- and 2D-NMR, and MS analyses. Compound 1 turned out to be a new, highly O-acylated grayanane diterpenoid, of which ring B has undergone an oxidative cleavage between C(9) and C(10), yielding a system differing from the previously reported grayanane type with a 5/7/6/5 ring system. Results of the cAMP regulation activity assay showed that compounds 2 and 3 at 50 μM induced a significantly decreased cAMP level in N1E-115 neuroblastoma cells (p<0.001), indicating neuropharmacological potential.