Abstract : This work is dedicated to the biomimetic synthesis of complex polycyclic alkaloids namely the manzamine alkaloids and especially to manadomanzamine. The biogenetic hypotheses postulated for these alkaloids are reported in a first introductory chapter. A few examples of manzamine alkaloids biogenesis are described and compared. The second chapter is focused on the reactivity of reactive units (considered as simplified models of two key biosynthetic intermediates, namely glutaconaldehydes and aminopentadienals) resulting from the ring-opening of pyridinium salts, and their implication in natural products synthesis. Particularly detailed are the investigations conducted on 5-dimethylamino-2-methylpenta-2,4-dienal and the condensation of potassium glutaconaldehyde onto a pyridinium salt. The chemistry of these reactive units has been exploited to design several model studies towards the synthesis of pentacyclic indole nucleus of manadomanzamine A, isolated from an Indonesian sponge Acanthostrongylophora sp.. These biomimetic models, elaborated from a biosynthetic intermediate postulated in our biosynthesis hypothesis have culminated in the synthesis of the central pentacyclic indole nucleus. The last chapter reports the preparation of more or less oxidized analogs of pelletierine, the well known alkaloid isolated from Punica granatum. Compounds such as phenyloxazolopelletierine have been prepared and their reactivity investigated in view of the biomimetic synthesis of Lycopodium alkaloids.