Dimeric pyrrole-imidazole alkaloids: sources, structures, bioactivities and biosynthesis

[Display omitted] •Dimeric pyrrole-imidazole alkaloids (PIAs) are important marine natural products.•The sources and structure of dimeric PIAs are summarized.•The promising biological activities and cellular targets are discussed.•Dimeric PIAs have interesting biosynthetic pathway. Pyrrole-imidazole alkaloids (PIAs) constitute a highly diverse and densely functionalized subclass of marine natural products. Among them, the uncommon dimeric PIAs with ornate molecular architectures, attractive biological properties and interesting biosynthetic origin have spurred a considerable interest of chemists and biologists. The present review comprehensively summarized 84 dimeric PIAs discovered during the period from 1981 to September 2022, covering their source organisms, chemical structures, biological activities as well as biosynthesis. For a better understanding, these structurally intricate PIA dimers are firstly classified and presented according to their carbon skeleton features as well as biosynthesis pathways. Furthermore, relevant summaries focusing on the source organisms and the associated bioactivities of these compounds belonging to different chemical classes are also provided, which will help elucidate the fascinating chemistry and biology of these unusual PIA dimers.