Langaside, a novel secoiridolactone glycoside derivative from Tachiadenus longiflorus Griseb. (Gentianaceae) formed by a [2+2] cycloaddition reaction

Langaside (1), a secoiridoid lactone glucoside possessing a novel skeleton formed by a [2 + 2] cycloaddition reaction between the secoiridolactone glucoside, 1,9-trans-9,5-cis-sweroside, and p-coumaric acid was isolated from the fruits and flowers of the Malagasy Tachiadenus longiflorus Griseb. (Gentianaceae), alongside another seven known compounds. The structure of langaside was established using HRESIMS, IR and NMR spectroscopy and comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Langaside was screened for its neuritogenic activity against SHSY-5Y cells and anticancer activity against the NCI59 human tumour cell panel but not found to be active.