Modular Assembly of Pyrrolo[3,4-c]isoquinolines through Rh-Catalyzed Cascade C-H Activation/Annulation of O-Methyl Aryloximes with Maleimides.

An efficient and practical strategy for the construction of pyrrolo[3,4-c]isoquinolines via Rh(III)-catalyzed cascade C-H activation and subsequential annulation process from easily available O-methyl aryloximes and maleimides has been disclosed. This facile protocol does not require any inert atmosphere protection with good efficiency in a low loading of catalyst and exhibits good functional group tolerance and broad substrate scope. Notably, the as-prepared products show potential photophysical properties.

A rhodium-catalyzed cascade C-H activation/annulation strategy for the expeditious assembly of pyrrolidinedione-fused 1,2-benzothiazines.

A cascade annulation strategy triggered by rhodium(III)-catalyzed C-H activation has been reported for the expeditious assembly of pyrrolidinedione-fused 1,2-benzothiazines from free NH-sulfoximines with maleimides under mild conditions. Without the need for inert atmosphere protection, a broad range of sulfoximines with maleimides were well tolerated, producing diverse fused-thiazine derivatives in moderate to good yields. Additionally, the late-stage transformation of the target product demonstrated the potential synthetic value of this protocol.

Synthesis of arene-functionalized fused heterocyclic scaffolds via a regioselective cascade 1,4-conjugate addition/5-exo-dig annulation strategy.

Facile access to furan fused heterocyclic scaffolds through a regioselective cascade reaction of propargylamines with 4-hydroxy-2H-pyran-2-ones and 4-hydroxy-6-methylpyridin-2(1H)-one has been achieved. This cascade reaction presumably involves the formation of ortho-alkynyl quinone methide (o-AQM), 1,4-conjugate addition, followed by regioselective 5-exo-dig annulation, and a 1,3-H shift process. Moreover, the reaction provides a new and efficient method for the synthesis of highly sterically congested 3-phenolic furo[3,2-c]pyran-4-ones and furo[3,2-c]pyridin-4(5H)-ones by the formation of a furan ring from readily available starting materials in good to high yields (50-82%) with broad functional group compatibility in a single step. Significantly, the strategy described here is easily scalable and several useful synthetic transformations of the prepared arene-functionalized 4H-furo[3,2-c]pyran-4-ones were also performed.

Cascade Annulation Strategy for Expeditious Assembly of Hydroxybenzo[c]chromen-6-ones and Their Photophysical Property Studies.

A 1,8-diazabicyclo[5.4.0]undec-7-ene-promoted cascade double-annulation of ortho-alkynyl quinone methide (in situ generated from modular propargylamine) for constructing of 2-aryl-4-hydroxybenzo[c]chromen-6-ones is developed. This synthetic strategy offers remarkable operational simplicity as it allows the use of benchtop-grade solvents without the need for predrying measures and inert atmosphere protection. Additionally, it demonstrates good functional group compatibility. The photophysical properties of these compounds were also examined, revealing bright fluorescence with high quantum yields.

Radical-Induced Cascade Annulation/Hydrocarbonylation for Construction of 2-Aryl-4H-chromen-4-ones.

A robust metal- and solvent-free cascade radical-induced C-N cleavage/intramolecular 6-endo-dig annulation/hydrocarbonylation for the synthesis of the valuable 2-aryl-4H-chromen-4-ones is described. This practical synthesis strategy utilizes propargylamines and air as the oxygen source and green carbonylation reagent, in which propargylamines are activated by the inexpensive and available dimethyl 2,2'-azobis(2-methylpropionate) (AIBME) and (PhSe)2 as the radical initiators. This simple and green protocol features wide substrate adaptability, good functional group tolerance, and amenability to scaling up and derivatizations.

Rapid screening of natural-origin tyrosinase regulators from Vernonia anthelmintica (L.) Willd. by offline two-dimensional liquid chromatography coupled with mass spectrometry.

Finding and developing safe and effective tyrosinase (TYR) regulators is of great significance for the prevention and treatment of melanin-related skin diseases in the medical and cosmetic industries. In the current research, an approach based on offline two-dimensional liquid chromatography coupled with mass spectrometry (offline 2D LC-MS) was established to screen TYR modulators from Vernonia anthelmintica (L.) Willd. (VA) extract. Firstly, the reliability of the proposed method was evaluated by using kojic acid (inhibitor), psoralen (activator) and ranitidine as positive and negative control, respectively. Some significant parameters including incubation time, TYR concentrations, and reaction temperature were investigated. Then, the developed new method was successfully applied to rapidly discover the active compounds from VA extract. Seven TYR ligands were successfully screened by comparing the chromatographic profiles of VA extract incubated with active and denatured TYR, respectively. To verify the activity of the screened compounds, in vitro bioassay was carried out and the result showed two of them, isorhamnetin and luteolin, had good TYR inhibitory activity with IC50 value of 0.86 and 1.00 mg/mL, respectively, while the other five compounds including eriodictyol, butochalcone, chlorogenic acid, isochlorogenic acid B, and isochlorogenic acid C showed strong activation against TYR. Furthermore, molecular docking displayed that these compounds could bind to the amino acid residues in TYR catalytic pocket. The results demonstrate that the established technique can be efficiently used for rapid screening of TYR-active compounds from plant extracts.