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

Combination of Machine Learning and Empirical Computation for the Structural Validation of Trirosaline, a Natural Trimeric Monoterpene Indole Alkaloid from Catharanthus roseus

Chemical investigation of the emblematic Catharanthus roseus led to the discovery of trirosaline (1), the first example of a tris-ajmalicine-type monoterpene indole alkaloid and the first natural trimeric MIA ever reported from this deeply dug plant species. Its structure was primarily elucidated based on NMR and HRESIMS analyses, and the nature of its unique intermonomeric linkages was firmly confirmed based on a combination of empirical computation and ML-J-DP4 study. Its absolute configuration was mitigated by comparison of experimental and TDDFT-simulated electronic circular dichroism (ECD) spectra. A possible biosynthetic pathway for trirosaline (1) was postulated.

Short, Scalable Access to Pyrrovobasine

A concise gram-scale synthesis of pyrrovobasine (1) is reported. Key transformations include a three-step decagram-scale synthesis of the tetracyclic compound, Mn-mediated direct radical cyclization, and the introduction of a naturally rare pyrraline structure. The synthesis is designed to be applicable to gram-scale synthesis using inexpensive and readily available reagents.

From the Spectroscopic Reassessment of Authentic Alkaloid Samples to the Molecular Networking-Guided Discovery of Criophylline-Related Analogues from Callichilia inaequalis

The molecular network-guided exploration of the alkaloid extract of Callichilia inaequalis stems revealed a cluster attributed tentatively to dimeric monoterpene indole alkaloids of the rare criophylline subtype, initiating the dual study reported herein. A patrimonial-themed portion of this work was aimed at performing a spectroscopic reassessment of criophylline (1), a monoterpene bisindole alkaloid for which the nature of the inter-monomeric connectivity and configurational assignments have remained dubious. A targeted isolation of the entity annotated as criophylline (1) was undertaken to strengthen the available analytical evidence. An extensive set of spectroscopic data was acquired from the authentic sample of criophylline (1a) isolated earlier by Cavé and Bruneton. These spectroscopic studies proved the samples to be identical, and the complete structure of criophylline could be assigned, half a century after it was first isolated. The absolute configuration of andrangine (2) was also ascertained based on a TDDFT-ECD approach from the authentic sample. The forward-looking aspect of this investigation resulted in the characterization of two new criophylline derivatives from C. inaequalis stems, namely, 14'-hydroxycriophylline (3) and 14'-O-sulfocriophylline (4). Their structures, including absolute configurations, were elucidated by analysis of NMR and MS spectroscopic data and by ECD analysis. Notably, 14'-O-sulfocriophylline (4) is the first sulfated monoterpene indole alkaloid to have been reported. The antiplasmodial activity against the chloroquine-resistant strain of Plasmodium falciparum FcB1 was determined for criophylline and its two new analogues.

Implementation of a MS/MS database for isoquinoline alkaloids and other annonaceous metabolites

This data descriptor reports on the upload to a public repository (GNPS) of the IQAMDB, IsoQuinoline and Annonaceous Metabolites Data Base, comprising 320 tandem mass spectra. This project originated from our in-house collection of isoquinolines. The diversity of compounds included in this database was further extended through the contribution of two additional laboratories involved in isoquinoline alkaloids research: University of Angers and University of Manaus. The generated MS/MS data were processed and annotated on an individual basis to promote their straightforward reuse by natural product chemists interested in either the description of new isoquinoline alkaloids or the dereplication of isoquinoline-containing samples. The interest of the current repertoire for dereplication purposes has been validated based on the molecular networking of the well-investigated plant model Annona montana against the IQAMDB‐implemented GNPS.

Measurement(s)	electrospray ionization
Technology Type(s)	Ultra High-performance Liquid Chromatography • Tandem Mass Spectrometry