Application of a catalytic palladium biaryl synthesis reaction, via C–H functionalization, to the total synthesis of Amaryllidaceae alkaloids

Divergent Total Syntheses of Lycorine Alkaloids via a Sequential C-H Functionalization Strategy

A Pd-catalyzed one-pot sequential C-H functionalization strategy was utilized to prepare four lycorine alkaloids and one pseudo-lycorine alkaloid from the common intermediate 4. By switching the followed oxidative conditions of air, DMSO/H2O/I2, and DMSO/O2, based on the Pd(PPh3)4/K2CO3/toluene catalytic system, three key intermediates 12a, 12b, and 12c with different substitution patterns could be obtained in a well-controlled manner. As a result, four natural products γ-lycorane, hippadine, anhydrolycorinone, and anhydrolycorine as well as a pseudo-lycorine alkaloid Δ(4a,10b)-6-oxodihydrolycorine were successfully synthesized within 10 steps through this divergent route.

5-Fluoro/(trifluoromethoxy)-2-indolinone derivatives with anti-interleukin-1 activity

The pro-inflammatory cytokine interleukin-1 (IL-1) drives the pathogenesis of several inflammatory diseases. Recent studies have revealed that 2-indolinones can modulate cytokine responses. Therefore, we screened several 2-indolinone derivatives in preliminary studies to develop agents with anti-IL-1 activity. First, the putative efficacies and binding interactions of 2-indolinones were evaluated by docking studies. Second, previously synthesized 5-fluoro/(trifluoromethoxy)-1H-indole-2,3-dione 3-(4-phenylthiosemicarbazones) (compounds 47-69) which had the highest inhibitory effect in the screening were evaluated for inhibitory effects on the IL-1 receptor (IL-1R). Compounds 52 (IC50  = 0.09 µM) and 65 (IC50  = 0.07 µM) were selected as lead compounds for the subsequent synthesis of new derivatives. The novel 5-fluoro/(trifluoromethoxy)-1H-indole-2,3-dione 3-(4-phenylthiosemicarbazones) (compounds 70-116) were designed, synthesized, and in vitro studies were completed. The compounds 76, 78, 81, 91, 100, 105, and 107 tested showed nontoxic inhibitory effects on IL-1R-dependent responses in the range of 0.01-0.06 µM and stronger than the lead compounds 52 and 65. In vitro and in silico findings showed that compounds 78 (IC50  = 0.01 µM) and 81 (IC50  = 0.02 µM) had the strongest IL-1R inhibitory effects and the most favorable drug-like properties. Molecular modeling studies of the compounds 78 and 81 were carried out to determine the possible binding interactions at the active site of the IL-1R.

Visible-Light-Induced Cascade Difunctionalization of Indoles Enabled by the Synergy of Photoredox and Photoexcited Ketones: Direct Access to Alkylated Pyrrolophenanthridones

Herein, we describe a methodology to construct polycyclic pyrrolophenanthridones with an (amino)alkyl side chain that involves visible-light-induced decarboxylative radical addition for the intermolecular dearomatization of indoles and subsequent photoinduced C(sp²)-X bond activation via photoexcited ketones for an intramolecular cyclization cascade. Carboxylic acids serve both as a radical source toward indole dearomatization and as reductants to initiate an electron transfer with photoexcited N-acylindole derivatives in the reaction toward pyrrolophenantridone skeletons, which occurs under mild reaction conditions with good functional group tolerance.

New 1H-indole-2,3-dione 3-thiosemicarbazones with 3-sulfamoylphenyl moiety as selective carbonic anhydrase inhibitors

1-Methyl/ethyl/benzyl-5-(un)substituted 1H-indole-2,3-diones (2, 3, and 4) were synthesized by reaction of 5-(un)substituted 1H-indole-2,3-diones (1) with methyl iodide, ethyl chloride, and benzyl bromide. (3-Sulfamoylphenyl)isothiocyanate (6) was obtained by the treatment of 3-aminobenzenesulfonamide (5) with thiophosgene. Compound 6 was reacted with hydrazine to yield 4-(3-sulfamoylphenyl)thiosemicarbazide (7). Novel 1-(un)substituted/methyl/ethyl/benzyl-5-(un)substituted 1H-indole-2,3-dione 3-[4-(3-sulfamoylphenyl)thiosemicarbazone] derivatives (8-11) were prepared by condensation of 7 and 1-4. The structures of the synthesized compounds were confirmed by elemental analysis and spectral data. Inhibition of the widely distributed cytosolic off-targets human carbonic anhydrases (hCAs) I and II, and two tumor-associated membrane-bound isoforms (hCAs IX and XII), by 8-11 was investigated. The hCA II inhibitory effects of all tested compounds were in the subnanomolar to low nanomolar levels (K_i  = 0.32-83.3 nM), and generally high selectivity for hCA II isoenzyme over hCA I, IX, and XII isoenzymes was observed. The strongest inhibitors of hCA II, 1-benzyl-5-(trifluoromethoxy)-substituted 11c (K_i  = 0.32 nM) and 1-ethyl-5-chloro-substituted 10e (K_i  = 0.35 nM), were docked within the enzyme active site. Molecular modeling studies with the most effective hCA IX and XII inhibitors were also carried out.

Catalytic Asymmetric C-7 Friedel-Crafts Alkylation/N-Hemiacetalization of 4-Aminoindoles

A unique catalytic asymmetric C-7 Friedel-Crafts alkylation/N-hemiacetalization cascade reaction of 4-aminoindoles with β,γ-unsaturated α-keto esters has been described. Using a chiral magnesium H₈-BINOL-derived bis(phosphate) complex as catalyst, the resulting functionalized 1,7-annulated indole scaffolds are obtained in high yields (up to 98%) and with good to excellent enantioselectivities (up to 99%) and diastereoselectivities (up to >20:1) under mild reaction conditions.

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

A metal-free route for the synthesis of biarenes has been developed. The approach is based on the photoextrusion of a phosphate moiety occurring upon irradiation of biaryl- and triaryl phosphates. The reaction involves an exciplex as the intermediate and it is especially suitable for the preparation of electron-rich biarenes.

Synthesis and anticancer properties of novel hydrazone derivatives incorporating pyridine and isatin moieties

Nine novel hydrazone derivatives (4a-i) incorporating pyridine and isatin moieties were synthesized through one-pot, four-component heterocyclic condensation reactions. The structures of all new compounds (2a-e, 3a, 3c-e, and 4a-e) were identified by ¹ H nuclear magnetic resonance (NMR), ¹³ C NMR, and Fourier-transform infrared spectroscopic techniques and elemental analysis. Cell viability assays for the tested hydrazone derivatives were performed and the log IC₅₀ values of the compounds were calculated after a 24-h treatment. All hydrazide derivatives tested showed a promising antitumor activity against A-2780 cells as compared with the standard drug docetaxel with a log IC₅₀ value of 0.2200 μM (p < .05). Seven of the examined compounds (4b-e, 4g-i) showed high cytotoxic activity against A-2780 cells as compared with the standard drug docetaxel. Whereas the log IC₅₀ of docetaxel was 0.2200 μM for A-2780 cells at 24 h, the IC₅₀ values of these compounds were -0.4987, -0.4044, -0.8138, -0.3868, -0.6954, -0.4751, and 0.1809 μM, respectively. Three of the compounds, 4b, 4d, and 4i, showed high cytotoxic activity against MCF-7 cells as compared with docetaxel (p < .05). Whereas the log IC₅₀ of docetaxel was 0.2400 μM for MCF-7 cells at 24 h, the log IC₅₀ values of compounds 4b, 4d, and 4i were -0.1293, -0.1700, and 0.2459 μM, respectively.

The Genus Nerine Herb. (Amaryllidaceae): Ethnobotany, Phytochemistry, and Biological Activity

Nerine Herbert, family Amaryllidaceae, is a genus of about 30 species that are native to South Africa, Botswana, Lesotho, Namibia, and Swatini (formerly known as Swaziland). Species of Nerine are autumn-flowering, perennial, bulbous plants, which inhabit areas with summer rainfall and cool, dry winters. Most Nerine species have been cultivated for their elegant flowers, presenting a source of innumerable horticultural hybrids. For many years, species of Nerine have been subjected to extensive phytochemical and pharmacological investigations, which resulted in either the isolation or identification of more than fifty Amaryllidaceae alkaloids belonging to different structural types. Amaryllidaceae alkaloids are frequently studied for their interesting biological properties, including antiviral, antibacterial, antitumor, antifungal, antimalarial, analgesic, cytotoxic, and cholinesterase inhibition activities. The present review aims to summarize comprehensively the research that has been reported on the phytochemistry and pharmacology of the genus Nerine.

Oxidative cross-coupling reaction of catechols with active methylene compounds in an aqueous medium using an AlPO4-supported Ru catalyst

A green oxidative coupling reaction of catechols with active methylene compounds was achieved using an AlPO₄-supported Ru catalyst, where O₂ and H₂O were used as the ideal oxidant and solvent, respectively.

Conjugated Thiophene-Fused Isatin Dyes through Intramolecular Direct Arylation

We report on the design, synthesis, and properties of innovative, planar, π-conjugated compounds in which a thiophene ring is fused with the skeleton of the naturally occurring dye isatin. The synthesis is achieved in high yields making use of an intramolecular direct arylation reaction as the key step, making the overall process potentially scalable. The synthetic sequence has been demonstrated also for an isatin bearing fluorine substituents on the aromatic ring. NMR and X-ray studies demonstrate the crosstalk occurring between the fused, coplanar, and conjugated moieties, making these novel dyes with a donor-acceptor character. Cyclic voltammetry and UV-vis studies confirm very interesting HOMO-LUMO levels and energy gaps for the new compounds.

New potently bioactive alkaloids from Crinum erubescens

Antimalarial bioassay-guided fractionation of the swamp lily Crinum erubescens led to the isolation of four compounds with potent antiplasmodial activity. Compounds 1 and 2 were determined from their spectroscopic data to be the known pesticidal compound cripowellin A and the known pesticidal and antiproliferative compound cripowellin B. 1D and 2D-NMR techniques were used to determine the identities of 3 and 4 as the new compounds cripowellin C and D. A fifth compound was identified as the known alkaloid hippadine, which was inactive against Plasmodium falciparum. The antiplasmodial IC₅₀ values of compounds 1-4 were determined to be 30±2, 180±20, 26±2, and 260±20nM, respectively, and their antiproliferative IC₅₀ values against the A2780 human ovarian cancer cell line were 11.1±0.4, 16.4±0.1, 25±2, and 28±1nM.

Chemical Composition of Bioactive Alkaloid Extracts from Some Narcissus Species and Varieties and their Biological Activity

Alkaloid extracts of eight Narcissus (Amaryllidaceae) species and varieties were studied with respect to their acetylcholinesterase (HuAChE) and butyrylcholinesterase (HuBuChE) inhibitory activity and alkaloid patterns. Thirty alkaloids were determined by GC/MS, and twenty-five of them identified from their mass spectra, retention times and retention indexes. Promising HuAChE inhibition activity was demonstrated by six Narcissus taxa and HuBuChE inhibition by N. jonquila cv. Double Campernelle and N. nanus cv. Elka with IC50 values of 24.1 ± 1.9 μg/mL and 25.1 ± 1.8 μg/mL, respectively. Two alkaloids were isolated in pure form using preparative TLC and identified as the galanthamine type alkaloid narwedine and the lycorine type alkaloid incartine. Both compounds were tested for their biological activity. They were considered inactive in HuAChE/HuBuChE assays, but showed promising prolyl oligopeptidase inhibition activities with IC50 values of 0.95 ± 0.12 mM and 0.91 ± 0.09 mM, respectively.

Alkaloids from Narcissus serotinus

Narcissus serotinus belongs to the Amaryllidaceae family, a group well known for an exclusive variety of alkaloids with interesting biological activities. This study was aimed at identifying the alkaloid constituents of N. serotinus collected in the Spanish region of Valencia, using a combination of chromatographic, spectroscopic, and spectrometric methods, including GC-MS and 2D NMR techniques. GC-MS analysis allowed for the direct identification of five known compounds. In addition, the isolation and structure elucidation of six new Amaryllidaceae alkaloids are described.

A novel approach to the pyridoacridine ring system: synthesis of the topoisomerase inhibitor 13-deazaascididemin

A novel approach to the pyridoacridine ring system of the ascididemin-type marine alkaloids is presented. This approach allows for the introduction of the ring A of the alkaloids by using a simple aromatic aldehyde building block. The viability of this approach is demonstrated with the synthesis of AK37, a bioactive deaza analogue of the alkaloid ascididemin. Starting from 3-cyano-4-methylquinoline, a sequence of regioselective homolytic benzoylation, annulation of a bromopyridine ring, and radical cyclization leads to the pentacyclic ring system.

Application of sequential Cu(I)/Pd(0)-catalysis to solution-phase parallel synthesis of combinatorial libraries of dihydroindeno[1,2-c]isoquinolines

Parallel solution-phase synthesis of combinatorial libraries of dihydroindenoisoquinolines employing a sequential Cu(I)/Pd(0)-catalyzed multicomponent coupling and annulation protocol was realized. The scope and limitations of the protocol with respect to the substitution pattern in the aryl ring of the indene core, as well as the N-substituent have been defined, revealing that the methodology is compatible with a wide-range of aliphatic linear, branched, and ester functionalized N-substituents. Unexpectedly, the formation of regioisomers featuring a 1,2,3-contiguous substitution pattern in the aromatic ring of the indene core was observed. Three distinct combinatorial libraries with a total of 111 of members were synthesized, and 80 highly substituted dihydroindenoisoquinolines structurally related to known medicinal agents including some consisting of mixtures of two regioisomers were made available for biological activity testing.

Two new amaryllidaceae alkaloids from the bulbs of Lycoris radiata

Two new Amaryllidaceae alkaloids, named lycoranines A (1) and B (2), were isolated from the bulbs of Lycoris radiata. Their structures were elucidated on the basis of extensive spectroscopic analysis. Compound 2 was a new-type alkaloid, which provided a new insight into the biosynthesis of alkaloids in Amaryllidaceae plants.