Corynanthean-Epicatechin Flavoalkaloids from Corynanthe pachyceras

Phytochemistry and biological activities of corynanthe alkaloids

Medicinal plants constitute a source for designing clinically useful drugs targeting diseases through various mechanisms. Plant secondary metabolites can be used as lead compounds of drugs. Corynanthe alkaloids are highly abundant natural bioactive substances of various core structures possessing important properties such as nerve excitation and antimalarial and analgesic effects. In this review, we summarize and review the state-of-the-art corynanthe-type alkaloid research focusing on phytochemistry, pharmacology, and structural chemistry. Approximately 120 articles reporting 231 alkaloids classified into simple corynanthe, yohimbine, oxindole corynanthe, mavacurane, sarpagine, akuammiline, strychnos, and ajmaline-type groups were compiled. Relevant biological properties discussed include antiviral, antibacterial, anti-inflammatory, antimalarial, muscle-relaxant, vasorelaxant, and analgesic activities and activities affecting the main nervous and cardiac systems, as well as NF-κB inhibitory and Na⁺-glucose cotransporter inhibitory properties. This review provides insights and a reference for future studies, thus paving the way for the discovery of drugs based on corynanthe alkaloids.

Implementation of an MS/MS Spectral Library for Monoterpene Indole Alkaloids

In less than 10 years, molecular networking (MN) strategy has revolutionized the art of Natural Products (NP) isolation to enter a rational workflow greatly increasing the probabilities of isolating new chemical entities. To pinpoint and streamline the isolation of new Monoterpene Indole Alkaloids (MIAs) in producing plants, we rendered publicly available the MIA database (MIADB), comprising MS² data for ca. 200 structurally diverse MIA, by uploading it to the Global Natural Products Social Molecular Networking (GNPS) platform. Here, we describe the key experimental aspects underlying data collection, data curation, and their subsequent upload to the GNPS libraries as a database. Practical tips are also provided at the end of this chapter to help optimizing the efficiency of the dereplication of MIA-containing plants against the MIADB-implemented GNPS library.

Pyrrovobasine, hybrid alkylated pyrraline monoterpene indole alkaloid pseudodimer discovered using a combination of mass spectral and NMR-based machine learning annotations

A new vobasine-tryptamine-based monoterpene indole alkaloid pseudodimer was isolated from the stem bark of Voacanga africana. As a minor constituent occurring in a thoroughly investigated plant, this molecule was targeted based on a molecular networking strategy and a rational MS²-guided phytochemical investigation led to its isolation. Its structure was formally established based on HRMS, 1D/2D NMR data, and the application of the tool Small Molecule Accurate Recognition Technology (SMART 2.0). Its absolute configuration was assigned by the exciton chirality method and TD-DFT ECD calculations. Besides featuring an unprecedented intermonomeric linkage in the small group of vobasine/tryptamine hybrids, pyrrovobasine also represents the first pyrraline-containing representative in the whole monoterpene indole alkaloids group. Biosynthetic hypotheses possibly underpinning these structural oddities are proposed here.

Voatriafricanines A and B, Trimeric Vobasine-Aspidosperma-Aspidosperma Alkaloids from Voacanga africana

Voatriafricanines A and B (1 and 2), the first examples of vobasine-aspidosperma-aspidosperma monoterpene trisindole alkaloids, were isolated from the stem barks of Voacanga africana, guided by a molecular networking strategy. Their structures, including absolute configurations, were elucidated by spectroscopic methods and ECD calculations. Compounds 1 and 2 possess intramolecular hydrogen bonding, sufficiently robust to transfer homonuclear and heteronuclear magnetizations. Compound 1 exhibited potent antimycobacterial activity with no discernible cytotoxic activity.

Targeted Isolation of Hemitheion from Mostuea brunonis, a Proposed Biosynthetic Intermediate of Theionbrunonines

Hemitheion (1), a new sulfur-containing vobasane-type indole alkaloid, was isolated, together with three known compounds, vobasine (2), gelsedine (3), and gelsemicine (4), from the alkaloid extract of the stems of Mostuea brunonis Didr. (Gelsemiaceae). Compound 1 could be straightforwardly isolated. Its structure was elucidated by a combination of spectroscopic methods. Besides corresponding to a formerly postulated biosynthetic intermediate toward theionbrunonines, hemitheion (1) stands among the few monomeric vobasanes lacking an oxygen at C-3. Hemitheion (1) showed moderate antiplasmodial activity in the micromolar range against the strain FcB1 of Plasmodium falciparum and no cytotoxic activity against the MRC-5 cell line at 20 μM.