Acrotrione: An Oxidized Xanthene from the Roots of Acronychia pubescens

Acrotrione B, a Prenylated and Highly Oxidized Xanthenoid with Antibacterial and Anti-proliferative Activities from the Roots of Acronychia pedunculata

A new prenylated xanthenoid with a highly oxidized core, acrotrione B (1: ), together with six previously reported acetophenones (2:  - 7: ), were isolated from the roots of Acronychia pedunculata. The structures of the isolated compounds were elucidated by thorough analysis of their 1D and 2D NMR spectroscopic data. The relative and absolute configurations of acrotrione B were determined by electronic circular dichroism (ECD) calculations. Acrotrione B is an unusual, oxidized xanthenoid with a cyclohexadienone core that has not been previously reported. It thus represents a new skeletal type within the xanthenoid class. Acrotrione B (1: ) exhibited anti-proliferative activity against Hela (IC₅₀ = 16.0 µM) and A549 (IC₅₀ = 16.3 µM) cell lines. 5'-Prenylacrovestone (4: ) and acrovestone (5: ) were even more potent with IC₅₀ values of 5.1 µM and 0.77 µM, respectively, against Hela cells and 11.8 µM and 1.13 µM, respectively, against A549 cells. Moreover, acrotrione B (1: ) displayed moderate antibacterial activities against Staphylococcus aureus, Bacillus cereus, and Bacillus subtilis, with MIC values in the range of 16 - 64 µg/mL. Finally, acropyrone (6: ) showed a significant suppression of lipopolysaccharide (LPS) induced NO production in murine macrophage J774.A1 cells (IC₅₀ = 8.9 µM).

Brønsted Acid Catalyzed Friedel-Crafts Alkylation of Naphthols with In Situ Generated Naphthol-Derived ortho-Quinone Methides: Synthesis of Chiral and Achiral Xanthene Derivatives

We disclose herein an enantioselective protocol for the Brønsted acid catalyzed addition of naphthols to in situ generated naphthol-derived ortho-quinone methides (o-QMs) followed by intramolecular cyclization, which delivers substituted chiral xanthene derivatives, in a one-pot reaction sequence under mild conditions. This process serves to convert naphthol-derived ortho-hydroxyl benzylic alcohols into reactive naphthol-derived o-QMs using a chiral phosphoric acid (CPA) catalyst. Moreover, it is helpful in controlling the enantioselectivity of the carbon-carbon bond-forming event via hydrogen-bonding followed by intramolecular cyclization. Additionally, for the first time, we observe a Brønsted acid catalyzed C(sp²)-C(sp³) bond cleavage of naphthol-derived ortho-hydroxyl benzylic alcohols for the synthesis of achiral xanthene (sigma plane containing) derivatives in good to excellent yields.

Acronyrones A-C, unusual prenylated acetophenones from Acronychia pedunculata

Two novel prenylated acetophenones with new carbon skeletons, acronyrones A and B (1 and 2), and a new analogue, acronyrone C (3), together with two known compounds (4 and 5) were isolated from the leaves of Acronychia pedunculata. Their structures with absolute configurations were identified by interpretation of spectroscopic data, single crystal X-ray diffraction, and electronic circular dichroism (ECD) calculations. Compounds 1 and 2 represent the first example of prenylated acetophenones possessed a C₇ (1) and a C₆ (2) side chain, forming a 4-isobutylchroman-2-one unit and a 3-(2-methylpropylidene)benzofuran-2(3H)-one moiety with the acetophenone core, respectively. In addition, compound 4 exhibited significant dose-dependent transcriptional activation effect against retinoid X receptor-α (RXRα), and could be regarded as a new type of non-classical RXR ligand.

Transition-metal-free intramolecular Friedel-Crafts reaction by alkene activation: A method for the synthesis of some novel xanthene derivatives

In this work, new derivatives (substituted 9-methyl-9-arylxanthenes) of xanthene compounds (5a-l) of possible biological significance were synthesized by developing a new synthesis method. In order to obtain xanthene derivatives, the original alkene compounds to be used as the starting materials were synthesized in four steps using appropriate reactions. A cyclization reaction by intramolecular Friedel-Crafts alkylation was carried out in order to synthesize the desired xanthene derivatives using the alkenes as starting compounds. The intramolecular Friedel-Crafts reaction was catalyzed by trifluoroacetic acid (TFA) and provided some novel substituted 9-methyl-9-arylxanthenes with good yields at room temperature within 6-24 hours. As a result, an alkene compound was used for activation with TFA in the synthesis of xanthene through intramolecular Friedel-Crafts alkylation for the first time.

New Acetophenones and Chromenes from the Leaves of Melicope barbigera A. Gray

The dichloromethane extract from leaves of Melicope barbigera (Rutaceae), endemic to the Hawaiian island of Kaua'i, yielded four new and three previously known acetophenones and 2H-chromenes, all found for the first time in M. barbigera. The structures of the new compounds obtained from the dichloromethane extract after purification by chromatographic methods were unambiguously elucidated by spectroscopic analyses including 1D/2D NMR spectroscopy and HRESIMS. The absolute configuration was determined by modified Mosher's method. Compounds 2, 4 and the mixture of 6 and 7 exhibited moderate cytotoxic activities against the human ovarian cancer cell line A2780 with IC₅₀ values of 30.0 and 75.7 µM for 2 and 4, respectively, in a nuclear shrinkage cytotoxicity assay.

Leptanoine D, a New Quinoline Alkaloid from the Australian Tree Pitaviaster haplophyllus (Rutaceae)

One new furoquinoline alkaloid, leptanoine D (1) and nine known alkaloids 2–10 were isolated from Pitaviaster haplophyllus. Leptanoine D (1) contains a typically unstable vinyl ether moiety and was structurally elucidated based on 2D NMR, (+)-HR-ESI-MS, and ECD data. The structures of the known furoquinoline alkaloids leptanoine A (11) and B (12) have also been revised. Compounds 1–10 were screened against three species of bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli), however they showed no activity at the highest dose tested (32µg mL−1). The compounds were also evaluated for anti-proliferative action against PC-3 and WPMY-1 cells, with 7–9 displaying weak activity at 100μM.

NaHSO4/SiO2 catalyzed generation of o-quinone/ o-thioquinone methides: synthesis of arylxanthenes/ arylthioxanthenes via oxa-6π-electrocyclization

ortho-Quinone methides, very reactive transient intermediates, are utilized successfully in synthesizing complex organic molecules of natural and biological significance. Among several synthetic protocols, the acid catalyzed generation of ortho-quinone methides from suitably substituted phenols is a promising method for further exploitation in organic synthesis. Such an interesting reactive species is conveniently employed in the synthesis of conformationally restricted triarylmethane derivatives such as 12/9-arylxanthenes/arylthioxanthenes starting from symmetrical/unsymmetrical 2-(hydroxydiarylmethyl)phenol/thiophenol, respectively, using SiO2-NaHSO4. Conformationally restricted 12/9-arylxanthenes/arylthioxanthenes were obtained in 52 to 96% yields using this protocol, which is believed to involve the formation of o-quinone methides followed by electrocyclic ring closure and isomerization at elevated temperature. Photophysical studies of selected examples in acidic media showed turn-on fluorescence by hydride ion transfer mediated π-conjugated xanthylium salt formation and suggested the application potential in bio-imaging and fluorescent sensors.