Ingadosides A-C, acacic acid-type saponins from Inga sapindoides with potent inhibitory activity against downy mildew

As part of a project aiming at the discovery of environmentally friendly alternatives to copper in organic agriculture, a 96% ethanolic extract from the leaves of Inga sapindoides showed potent inhibitory activity against grapevine downy mildew (Plasmopara viticola) in vitro (MIC₁₀₀ 25 μg/mL). Separation of the n-BuOH soluble fraction by silica gel column chromatography followed by a combination of RP₁₈ and HILIC HPLC resulted in the isolation of a series of bidesmosidic saponins characterized by the presence of a monoterpenoid unit attached to a triterpenoid aglycone, a p-methoxycinnamoyl residue, and rare sugar residues such as N-acetyl-d-glucosamine, d-quinovose, and d-fucose. The isolated compounds inhibited the formation or activity of P. viticola zoospores with MIC₁₀₀ values of 3 or 6 μg/mL, respectively. I. sapindoides, a tree which is often cultivated for shading coffee plantations in Central America, may represent a sustainable source of fungicidal products to be used in the replacement of copper.