The structure of juruenolide, a constituent of Iryanthera juruensis and I. ulei is revised to (2S, 3R, 4S)-3-hydroxy-4-methyl-2-(19′-piperonyl-1′-n-nonadecyl)-butanolide. The compound is epimeric at C-3 of the γ-lactone unit with grandinolide [(2S, 3S, 4S)-3-hydroxy-4-methyl-2- (19′-phenyl-1′-n-nonadecyl)-butanolide] from I. grandis. An extract of I. juruensis contained additionally juruenolide-B [(4S)-4-methyl-2-(19′-piperonyl-1′-n-nonadec-7′-enyl)-but-2-enolide]. Analogous products with heptadecyl and pentadecyl side chains co-occur with the respective nonadecyl derivatives. © 1983.Instituto de Química Universidade de São Paulo, 05508 São PauloInstituto de Química Universidade Estadual Paulista, 14800 Araraquara, São PauloInstituto de Ciências Exatas Universidade Federal de Minas Gerais, 30000 Belo Horizonte, Minas GeraisInstituto de Ciências Exatas Universidade Federal Rural do Rio de Janeiro, 23460 Seropedica, Rio de JaneiroInstituto de Química Universidade Estadual Paulista, 14800 Araraquara, São Paulo