From monomer to tetramer and beyond: the intriguing chemistry of Securinega alkaloids from Flueggea virosa

A biosynthesis directed search for alkaloid oligomers from Flueggea virosa returned fluevirosinine A (4) as the first tetramer of the Securinega structure family, flueggenines C (1) and D (2) as two new dimers, and fluevirosine D (3) as a new trimer. Absolute structures were assigned to them on the basis of spectroscopic methods especially 2D NMR and CD data, as well as biogenetic considerations. The plausible biosynthetic route of these interesting oligomeric alkaloids was discussed, and some potential new analogues were also predicted from the currently available structures.