Gelserancines A–E, monoterpenoid indole alkaloids with unusual skeletons from Gelsemium elegans

Five monoterpenoid indole alkaloids (MIAs) with unusual skeletons, gelserancines A-E (1-5), along with their postulated biosynthetic intermediates (6-10) were isolated from the roots of Gelsemium elegans. Compound 1 features a new skeleton with an unusual trimethyl-dihydrofuranone unit. Compounds 2 and 3 are two novel gelsedine-iridoid adducts constructed through unusual C-19-C-11 ' and N-4-C-3 ' linkages forming an additional pyridine ring. Compounds 4 and 5 are a pair of photochemical E/Z tautomeric MIAs with a highly conjugated skeleton. Their structures and absolute configurations were elucidated by spectroscopic analysis, X-ray diffraction, and electronic circular dichroism (ECD) comparison. The plausible biosynthetic pathways of these alkaloids and their anti-inflammatory effects on zebrafish acute inflammatory models are also discussed.