Visible-Light Catalytic Photooxygenation of Monoterpene Indole Alkaloids: Access to Spirooxindole-1,3-oxazines

Recent research on the physicochemical properties and biological activities of quinones and their practical applications: a comprehensive review

Quinones represent a class of crude organic compounds ubiquitously distributed in nature. Their distinctive quinone-type structure confers upon them unique properties and applications. Quinones demonstrate significant biological activities, including antioxidant, antimicrobial, and antitumor properties. Additionally, they demonstrate noteworthy physicochemical characteristics, including excellent dyeing properties and stability. Given their diverse qualities, quinones hold significant promise for applications in industrial manufacturing, healthcare, and food production, thus garnering considerable attention in recent years. While there is a growing body of research on quinones, the existing literature falls short of providing a comprehensive review encompassing recent advancements in this field along with established knowledge. This paper offers a comprehensive review of research progress for quinones, encompassing structural classification, source synthesis, extraction methods, properties, functions, and specific applications. It serves as a reference and theoretical foundation for the further development and utilization of quinones.

Copper-Catalyzed Tunable Oxygenative Rearrangement of Tetrahydrocarbazoles

Herein, we report a general copper-catalyzed method for the tunable oxygenative rearrangement of tetrahydrocarbazoles to cyclopentyl-bearing spiroindolin-2-ones and spiroindolin-3-ones. The method demonstrates excellent chemoselectivity, regioselectivity, and product control simply by using the H2O and O2 as oxygen source, respectively. This open-flask method is safe and simple to operate, and no other chemical oxidants are required. Besides, inspired from the unique pathway of 1, 2-migration rearrangement, a highly controllable hydroxylation of indoles for the construction of C3a-hydroxyl iminium indolines was also developed. Mechanistic experiments suggest that a single-electron transfer-induced oxidation process is responsible for the tunable selectivity control.

Switchable Skeletal Rearrangement of Hexahydro-4H-indol-4-ones: Divergent Synthesis of Dihydroxy-4H-cyclopenta[b]pyridin-4-ones and 8-Alkenyl Oxepane-2,6-diones

An unprecedented base-controlled selective skeletal rearrangement reaction of hexahydro-4H-indol-4-ones has been developed. In this protocol, highly functionalized dihydroxy-4H-cyclopenta[b]pyridin-4-ones and 8-alkenyl oxepane-2,6-diones were prepared with a broad substrate scope and high chemoselectivity in moderate to excellent yields selectively by modulating LiOH and Et3N. In addition, the newly formed 8-alkenyl oxepane-2,6-dione scaffolds could be easily further derivatized to 5-(pyrrol-2-yl)dihydrofuran-2(3H)-ones through a rare intramolecular rearrangement reaction.

Spirooxindol‐1,3‐oxazine alkaloids: highly potent and selective antitumor agents evolved from iterative structure optimization

Spirooxindole‐1,3‐oxazines are a small and structurally unique class of spirooxindole alkaloids. To date, only four of these compounds have been isolated from natural sources, and their biological properties remained unknown thus far. Dioxyreserpine is a synthetic spirooxindole‐1,3‐oxazine, that can readily be prepared from the Rauvolfia alkaloid (–)‐reserpine by catalytic photooxygenation. While dioxyreserpine itself was now identified as a moderately effective antitumoral agent, structurally modified analogs of it emerged as a new class of highly potent and selective growth inhibitors of various human cancers, including pancreatic cancers. Systematic structural optimization ultimately led to an inhibitor displaying low‐micromolar IC₅₀‐values against six cancer cell lines as well as selective apoptosis induction in vitro.

Diaminoanthraquinone Enhances Alkaloid Ionization in MALDI-MS

The alkaloids epinastine, 3-methylxanthine and camptothecin were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The ionization efficiencies of epinastine and 3-methylxanthine were improved upon the addition of 1,5-diaminoanthraquinone (DAAQ). DAAQ did not show ultraviolet absorbance peaks at wavelengths around 337 nm and 355 nm that are used in conventional MALDI-MS instruments. In addition, the DAAQ ion peak was very weak relative to those of the analytes due to the low absorbance efficiency. These properties of DAAQ are advantageous for the DAAQ-MALDI-MS analysis of alkaloids.

Visible-Light Cascade Photooxygenation of Tetrahydrocarbazoles and Cyclohepta[b]indoles: Access to C,N-Diacyliminium Ions

Tetrahydrocarbazoles and perhydrocyclohepta[b]indoles undergo a catalytic cascade singlet oxygenation in alkaline medium, which leads to chiral tricyclic perhydropyrido- and perhydroazepino[1,2-a]indoles in a single operation. These photooxygenation products are new synthetic equivalents of uncommon C,N-diacyliminium ions and can be functionalized with the aid of phosphoric acid organocatalysis.

Visible light-mediated chemistry of indoles and related heterocycles

The impact of visible light-promoted chemistry on the functionalization of indoles and related heterocycles is reviewed.