Synthetic Strategies to Construct the Spirocyclic Imine Pharmacophore of Cyclic Imine Marine Toxins

Cyclic imine (CI) marine toxins are a class of bioactive natural products originating from marine dinoflagellates during harmful algal blooms. The spirocyclic imine moiety of these marine toxins is the key pharmacophore responsible for the potent bioactivity profile of CI toxins, though the synthesis of these scaffolds remains a challenge. Nonetheless, many synthetic strategies to construct the spirocyclic imine pharmacophore have been developed over the years. This review aims to summarise all synthetic approaches to construct this interesting pharmacophore to date, with particular emphasis on the stereoselective construction of the requisite tertiary and quaternary stereocentres.