Studies towards the Total Synthesis of Samaderine C and Related Analogues

The samaderines are quassinoids isolated from Samadera indica plants and have been shown to possess a range of biological activity. Samaderine C is a cogent antifeedent (55.3% feeding inhibition) and shows a good level of toxicity in pupal mortality screens (54.1%). The aims of this project were to investigate synthetic approaches to samaderine C and to synthesise analogues of samaderine C in order to evaluate structure-activity aspects. There were three main approaches considered for the synthesis of samaderine C. The first centred on a double 1,4-addition strategy to an enone starting material. Ultimately, model studies using organocuprate 1,4-additions highlighted shortcomings in this approach but we did develop a novel route to bicyclic enone 71 using desymmetrisation chemistry. The second approach utilised the Wieland-Miescher ketone 69 as a scaffold for the synthesis of the trans-allylic diol AB-ring structure of samaderine C. From dione 69, an enone 166 was synthesised and the plan was then for a diastereoselective reduction to give the trans-allylic diol motif. However, this approach was unsuccessful. Using enone 160 we were able to globally deprotect to access a dione 174 which is a general quassinoid AB-ring motif. The final approach to access a trans-allylic diol AB-ring motif used the methyl- Wieland-Miescher ketone 70. Using this starting material a trans-allylic diol AB-ring analogue was achieved using an α-hydroxylation reaction of enone 199 followed by reduction to give the trans-diol arrangement. To the best of our knowledge this represents the first synthesis of a quassinoidal trans-allylic diol AB-ring motif.