A new natural product with in vivo anti-juvenile hormone (JH) activity, N-(2-methyl-3-oxodecanoyl)-2-pyrroline (2), has been isolated from Penicillium brevicompactum Dierckx. Its structure has been tentatively assigned based on spectral data and unambiguously confirmed by alternative syntheses. Compound 2 has been prepared by means of a sequence of reactions beginning with acylation of Meldrum's acid by octanoyl chloride. The subsequent steps have been aminolysis of the resultant intermediate with pyrrolidine, alkylation of the active position with iodomethane, introduction of a methoxy group in the pyrrolidine ring by anodic oxidation, and final elimination of methanol through adsorption on SiO2 and heating. The natural product 2 and its bicyclic isomer 2-heptyl-3-methyl-4-oxo-6,7,8,8a-tetrahydro-4H-pyrrolo[2,1-b]-1,3-oxazine (3) are also obtained. This reveals that 2 can be biogenetically related to the recently discovered brevioxime (1). Compound 2 and the synthetic precursors of 2 have shown important biological activities as insecticides (against Oncopeltus fasciatus Dallas) and fungicides. The natural product induces precocious metamorphosis in the target insect (70% precocious adults at 10 µg/nymph). In view of the above results, these products could be useful as lead molecules for the synthesis of analogues with enhanced biological activities.