Sarains: A New Class of Alkaloids from the Marine Sponge Reniera Sarai

Reniera sarai, a marine sponge of the Ceractinomorpha subclass easily collectable in the Bay of Naples, is characterized by a series of cyclic nitrogenous compounds, which for many years have resisted all attempts of structural investigation. Complex separation steps have now led to three new compounds, named sarain-1, sarain-2 and sarain-3. Their structures have been partially determined mainly by a 500 MHz NMR study, utilizing the 1H-1H homonuclear and 1H-13c heteronuclear NMR Chemical shift correlation techniques. Sarains belong to a new class of pentacyclic alkaloids, containing in their skeletons a quinolizidine system linked to a tetrahydropyridine moiety. Two linear alkyl chains, placed between the two heterocyclic systems, supply the two remaining cycles. Recently a series of biologically active bis-quinolizidine and 1-oxa-quinolizidine alkaloids have been isolated from the sponges Petrosia seriata and Xestospongia exigua, respectively. A common biogenetic origin should connect these alkaloids to sarains. Sarains show phase transfer catalytic properties.