Résumé : (13E,15E,18Z,20Z)-1-hydroxypentacosa-13,15,18,20-tetraen-11-yn-4-one 1- acetate, a new polyfunctionalized long chain derivative, was isolated from the venom of an as yet undetermined Crematogaster ant species from Brazil, and its structure established by a detailed high-field 1D and 2D NMR study.