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

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Abstract
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.