The pentacyclic ambiguines are an intriguing class of prenylated indole alkaloids with notable bioactivity including antibiotic and anti-fungal properties. Arguably more fascinating is their unique biosynthesis, which includes multiple oxidations believed to be catalyzed by the C-H functionalizing enzymes known as the Rieske-oxygenases. In addition, Liu and coworkers have identified the enzyme responsible for the novel C-H halogenation that takes place on the D-ring of the pentacyclic scaffold. While most ambiguines exist in both the chlorinated and reduced forms, one of these partners has not been isolated for ambiguines F, O, and P. We anticipate the total synthesis of these natural and non-natural compounds will shed light on the promiscuity of this C-H halogenation. While the pentacyclic ambiguine compounds have so far been synthetically inaccessible, we report the first synthesis of the pentacyclic core in addition to late-stage strategies for completing these natural products.

Late-stage strategies for the synthesis of ambiguine natural products

253rd National Meeting (2017)

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