Many natural products that contain basic nitrogen atoms—for example alkaloids like morphine and quinine—have the potential to treat a broad range of human diseases. However, the presence of a nitrogen atom in a target molecule can complicate its chemical synthesis because of the basicity of nitrogen atoms and their susceptibility to oxidation. Obtaining such compounds by chemical synthesis can be further complicated by the presence of multiple nitrogen atoms, but it can be done by the selective introduction and removal of functional groups that mitigate basicity. Here we use such a strategy to complete the chemical syntheses of citrinalin B and cyclopiamine B. The chemical connections that have been realized as a result of these syntheses, in addition to the isolation of both 17-hydroxycitrinalin B and citrinalin C (which contains a bicyclo[2.2.2]diazaoctane structural unit) through carbon-13 feeding studies, support the existence of a common bicyclo[2.2.2]diazaoctane-containing biogenetic precursor to these compounds, as has been proposed previously.

Covering: 2005 to 2007. Previous review: Nat. Prod. Rep., 2005, 22, 516. Organic guanidine compounds are reviewed, with emphasis on natural products isolation, identification, synthesis and biological activities. The literature survey includes purely synthetic guanidine derivatives, guanidine alkaloids and non-ribosomal peptides from bacteria and cyanobacteria, as well as related compounds isolated from marine and terrestrial invertebrates and higher plants.

Covering: 2010 and 2011. Previous review: Nat. Prod. Rep., 2010, 27, 1871 The chemistry and biology of organic natural guanidines are reviewed, including the isolation, structure determination, synthesis, biosynthesis and biological activities of alkaloids, non-ribosomal peptides, guanidine-bearing terpenes, polyketides and shikimic acid derivatives from natural sources.

Covering: 2002 to 2004. Previous review: Nat. Prod. Rep., 2002, 19, 617–649 The literature on guanidine-bearing natural products is reviewed, with emphasis on occurrence, isolation, structure determination, biosynthesis, synthesis and biological activities, with 365 references. The literature survey includes macrocycles and peptides from bacteria and cyanobacteria, as well as alkaloids and peptides isolated from marine and terrestrial invertebrates and higher plants.

Covering: 2008 and 2009. Previous review: Nat. Prod. Rep., 2008, 25, 919 Organic guanidine compounds are reviewed, with emphasis on natural product isolation, identification, synthesis, biosynthesis and biological activities. The literature survey includes purely synthetic guanidine derivatives, guanidine alkaloids and non-ribosomal peptides from bacteria and cyanobacteria, as well as related compounds isolated from marine and terrestrial invertebrates and higher plants.

Covering: 2012 to 2014. Previous review: Nat. Prod. Rep., 2012, 29, 1382 The present review discusses the isolation, structure determination, synthesis, biosynthesis and biological activities of secondary metabolites bearing a guanidine group. Topics include non-ribosomal peptides, alkaloids, guanidine-bearing terpenes, polyketides and shikimic acid derivatives from natural sources. A critical analysis of some yet underdeveloped aspects of guanidine metabolites is also presented.