Dimeric naphthylisoquinoline alkaloids: polyketide-derived axially chiral bioactive quateraryls

Covering: up to April 2019Dimeric naphthylisoquinoline (NIQ) alkaloids are an emerging group of structurally, biosynthetically, and pharmacologically intriguing natural products, as yet isolated from African and Asian lianas belonging to the genus Ancistrocladus Wall. (Ancistrocladaceae) exclusively. These metabolites and their monomers are the only known di- and tetrahydroisoquinoline alkaloids that do not originate from aromatic amino acids, but from polyketide precursors. Stereochemically, dimeric NIQs are characterized by the presence of several stereogenic centers and up to three consecutive chiral axes. The most recent highlight is the discovery of dimers that witness a new biosynthetic follow-up chemistry: by oxidative cyclization, leading to bridged, cage-like molecular architectures. Depending on their individual structures, the dimers show promising biological activities, including antiviral, antiprotozoal, and antitumor properties, most of them quite different from those of the monomers. This is the first review on these multi-facetted dimeric alkaloids, dealing with their isolation, their structural diversity, their biosynthetic origin, their pharmacological properties, and their total synthesis.