How a diversity-oriented approach has inspired a new hypothesis for the gabosine biosynthetic pathway. A new synthesis of (+)-gabosine C

A new synthesis of (+)-gabosine C has been accomplished as part of a general diversity-oriented approach that also delivered the previously unknown (−)-4-epi-gabosine C. The identification of the unexpected intermediate (+)-8, together with the isolation of ketones 9 and 10 in previous investigations, prompted us to formulate a new hypothesis for the biosynthesis of gabosines, based on a keto–enol equilibrium cascade pathway starting from 2-epi-5-epi-valiolone, along which the necessary precursors for all the different types of gabosines are generated.