Road Map Toward Computer-Guided Total Synthesis of Natural Products. The Dysiherbol A Case Study: What if Serendipity Hadn't Intervened?

Revisiting the Structure of Cacospongionolide E: An Approach Based on Empirical Rules and NMR Calculations

In the field of natural product chemistry, the structures of several marine natural products have been erroneously determined. Here, we revisited the originally proposed structure of cacospongionolide E (1) using empirical rules in 13C NMR chemical shift analysis and density functional theory (DFT)-based NMR chemical shift calculations. Cacospongionolide E (1) is a marine natural product isolated from the Tyrrhenian sponge Fasciospongia cavernosa. Its originally proposed structure was established as sesterterpenoid of the trans-trans (TT) type, which adopts the trans-trans configuration of the 5-CH3/10-H-8-CH3/9-CH3 fragment. However, the present analysis based on empirical rules revealed that the reported 13C NMR chemical shifts of cacospongionolide E were more consistent with those of cis-trans (CT) type 2, which adopts the cis-trans configuration of the 5-CH3/10-H-8-CH3/9-CH3 fragment, than those of TT type 1. Furthermore, DFT-based 13C NMR chemical shift calculations, followed by the DP4 analysis, revealed that the reported 13C NMR chemical shifts of cacospongionolide E were more consistent with the calculated chemical shifts of CT type 2 than those of TT type 1. Thus, we propose the stereochemical revision of the structure of cacospongionolide E from the originally proposed structure 1 to our proposed structure 2. The study findings show that the proposed approach based on empirical rules and DFT-based NMR chemical shift calculations can identify the incorrect structures of marine natural products and provide the candidate for the correct structures.

Marine natural products

Covering: January to the end of December 2023This review covers the literature published in 2023 for marine natural products (MNPs), with 582 citations (541 for the period January to December 2023) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, the submerged parts of mangroves and other intertidal plants. The emphasis is on new compounds (1220 in 340 papers for 2023), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. An analysis of the progress in the study of prokaryote involvement in macro-invertebrate MNP production is discussed.

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.