A novel alkaloid, N-isobutyl-trans-2-trans-4-eicosadienamide, has been isolated from the fruits of Piper guineense and fully characterized. The structure of the compound has been confirmed by an unambiguous synthesis of the tetrahydro derivative. The known alkaloid, δαβ-dihydropiperine has also been isolated and the position of the double bond in this compound confirmed by the use of an NMR shift reagent. © 1977.