New Insights on Acanthus ebracteatus Vahl: UPLC-ESI-QTOF-MS Profile,Antioxidant, Antimicrobial and Anticancer Activities

This study investigated the antioxidant, antimicrobial, anticancer, and phytochemical profiling of extracts from the leaves and stem/root of Acanthus ebracteatus (AE). The total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical-scavenging activity, 2, 2′-azino-Bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical-scavenging activity, metal chelating activities (MCA), ferric reducing antioxidant power (FRAP) and oxygen radical antioxidant capacity (ORAC) were used for antioxidant assessment. The ethanolic extracts of the leaves (AEL-nor) and stem/root (AEWP-nor) without chlorophyll removal and those with chlorophyll removal, using sedimentation process (AEL-sed and AEWP-sed), were prepared. Generally, AEL-sed showed the highest antioxidant activity (FRAP: 1113.2 µmol TE/g; ORAC: 11.52 µmol TE/g; MCA: 47.83 µmol EDTA/g; ABTS 67.73 µmol TE/g; DPPH 498.8 µmol TE/g; TPC: 140.50 mg/GAE g and TFC: 110.40 mg/CE g) compared with other extracts. Likewise, AEL-sed also showed the highest bacteriostatic (MIC) and bactericidal (MBC) effects, as well as the highest anticancer and antiproliferative activity against oral squamous carcinoma (CLS-354/WT) cells. UPLC-ESI-QTOF/MS analysis of AEL-sed and AEWP-sed tentatively identified several bioactive compounds in the extracts, including flavonoids, phenols, iridoids, and nucleosides. Our results provide a potentially valuable application for A. ebracteatus, especially in further exploration of the plant in oxidative stress-related disorders, as well as the application of the plant as potential nutraceuticals and cosmeceuticals.     

Chiral ruthenium Lewis acid catalyzed intramolecular Diels-Alder reactions

Single point binding ruthenium Lewis acid catalysts [Ru(acetone)(S,S)-BIPHOP-F)Cp][SbF(6)] ((S,S)-1b) and [Ru(acetone)(S,S)-BIPHOP-F)(indenyl)][SbF(6)] ((S,S)-1c) efficiently catalyze intramolecular Diels-Alder (IMDA) reactions under mild conditions to afford the endo cycloaddition products as the major product in excellent yields with high diastereo- and enantioselectivities.     

Intramolecular Diels-Alder reactions using chiral ruthenium Lewis acids and application in the total synthesis of ent-ledol

One-point binding chiral ruthenium Lewis acids incorporating the C(2)-symmetric electron-poor bidentate phosphinite ligand BIPHOP-F and a Cp or an indenyl 'roof' can efficiently catalyze asymmetric intramolecular Diels-Alder reactions of trienes to form bicyclic adducts with good to excellent asymmetric induction. This reaction forms the key step in a total synthesis of ent-ledol in 96% ee. The synthesis also helps to clarify the stereochemical assignment of ledol and inconsistencies in the measured optical rotation.     

Ruthenium Lewis Acid‐Catalyzed Asymmetric Diels–Alder Reactions: Reverse‐Face Selectivity for α,β‐Unsaturated Aldehydes and Ketones

Acrolein, methacrolein, methyl vinyl ketone, ethyl vinyl ketone, 3‐methyl‐3‐en‐2‐one, and divinyl ketone were coordinated to a cationic cyclopentadienyl ruthenium(II) Lewis acid incorporating the electron‐poor bidentate BIPHOP–F ligand. Analysis by NOESY and ROESY NMR techniques allowed the determination of conformations of enals and enones present in solution in CD₂Cl₂. The results were compared to solid‐state structures and to the facial selectivities of catalytic asymmetric Diels–Alder reactions with cyclopentadiene. X‐Ray structures of four Ru‐enal and Ru‐enone complexes show the α,β‐unsaturated C=O compounds to adopt an anti‐s‐trans conformation. In solution, enals assume both anti‐s‐trans and anti‐s‐cis conformations. An additional conformation, syn‐s‐trans, is present in enone complexes. Enantioface selectivity in the cycloaddition reactions differs for enals and enones. Reaction products indicate enals to react exclusively in the anti‐s‐trans conformation, whereas with enones, the major product results from the syn‐s‐trans conformation. The alkene in s‐cis conformations, while present in solution, is shielded and cannot undergo cycloaddition. A syn‐s‐trans conformation is found in the solid state of the bulky 6,6‐dimethyl cyclohexanone‐Ru(II) complex. The X‐ray structure of divinyl ketone is unique in that the Ru(II) center binds the enone via a η² bond to one of the alkene moieties. In solution, coordination to Ru–C=O oxygen is adopted. A comparison of facial preference is also made to the corresponding indenyl Lewis acids.     

Morita-Baylis-Hillman reaction of masked 5-alkylidene-2-cyclopentenones: general entry to 5-alkylidene-2-(hydroxyalkyl)- 2-cyclopentenones

The reaction of masked 5-alkylidene-2-cyclopentenones with aldehydes catalyzed by tributylphosphine in the presence of phenol provided the corresponding Morita-Baylis-Hillman adducts, which were subjected to flash vacuum pyrolysis to afford 5-alkylidene-2-(hydroxyalkyl)-2-cyclopentenones.