From the stem bark of Annonidium mannii annonidines A - E (3 - 7) have been isolated and their structures determined. 3 to 7 belong to a new structural type of prenylated bisindole alkaloids.2 The stem bark of the West African Annonidium mannii Engl. & Diels (Annonaceae) was extracted with petroleum ether; on concentration large quantities of polycarpal (1) precipitated and were removed. The better soluble constituents were subjected to column chromatography, and this yielded 47-(3-methyl-2-butenyl)-indole (2) and the hitherto unknown prenylated bisindole alkaloids 3 to 7. Since these compounds constitute a new group of bisindole alkaloids they were named annonidines.Structure determination is based on ¹H- (at 400 MHz) and ¹³C-NMR measurements and on UV- and MS-investigations of the original alkaloids and partly their hydrogenation derivatives. The spectra show, that in all compounds two indole systems are present and these are linked together by an isoprenoid C₅-unit. In annonidines A and B (3 and 4) both indoles are connected to C-1 of a 5 3-methyl-2-butene, whereas in annonidines C to E (5 to 7) the indoles are bound at C-1 and C-3 of a 3-methyl-1-butene. Another 3-methyl-2-butenyl unit is observed in 3 to 6 as a substituent of one of the indole nuclei. This C₅-substituent must be localized at C-7 of the indole; besides other arguments evidence comes from the ¹³C-NMR resonances of the methylene carbon atoms which appear at δ ≈ 31 ppm; in case of substitution at C-3 δ = 24 ppm and at C-6 δ = 35 ppm would be typical values. From analysis of the ¹³C-signals of the indole carbon atoms the other positions of substitution can be determined and this is particularly easy, if C-3 or C-7 are involved, since the resonances of these carbon atoms if unsubstituted appear typically at highest field (δ C-3 = 103 ppm; δ C-7 = 111 ppm³'⁵. Only annonidine D (6) contains an indole substituted at C-6 and this was deduced from the ¹H-NMR and a singlet at δ = 132.5 ppm in the ¹³C-NMR. The data mentioned above allow to establish structures 3 and 4 for annonidines A and B unambiguously; but for annonidines C and D (5 and 6) still exist the alternative formulae 5a and 6a. Therefore 5 and 6 were hydrogenated to give their tetrahydro derivatives 8 and 9, whose MS - fragmentation exhibit key fragments at m/r 228 and m/r 130 and thus exclude structures 5a and 6a.¹ The ¹H- and ¹³C-NMR of annonidine E (7) show close similarity with the spectra of 5 for all signals except for C-7 of the disubstituted indole nucleus and the C₅-unit attached to that carbon atom. However, the resonances of this substituent and all other data fit completely to an epoxylated prenyl group and therefore establish formula 7 for annonidine E.From a biogenetic point of view 3, 5 and 7 can be regarded as dimeric 7-prenylindoles (dimerization products of 2), whereas for the formation of 4 and 6 various pathways might be possible. Polycarpol (1) has exclusively been isolated from some plants of the Annonaceae family; 7-(3-methyl-2-butenyl)-indole (2) up-to-now has been only described from the liverworts Riccardia sinuata and R. incurvata.