Photochemical Access to Fused 5-8-5 Carbotricycles

Dicyclopenta[a,d]cyclooctene (5-8-5) ring system is a privileged scaffold found in over 30 di- and sesterterpene natural products (e.g fusicoccin and ophiobolins). These natural products have gained attention due to their interesting biological properties. The limitation of exploring the potential of these small molecules is that modular routes to synthesize these 5-8-5 carbotricycles is underdeveloped. This is due to the fact that the majority of the synthetic strategies have been directed towards specific natural products, semi-synthesis, or long methodology routes. In addition, the method used to study biological structure-function properties has been via semi-synthesis, which limits the scope. Our group has developed a rapid and modular route to this 5-8-5 core, that can be performed on gram scale. We have shown that we can make this 5-8-5 scaffold via a photochemical cycloisomerization cascade reaction. This route provides a rapid entry to this particular 5-8-5 privileged scaffold, where functionality can easily be modified early on in the synthesis with simple starting materials. We have further expanded the utility of this 5-8-5 ring system by developing scalable routes to targeted peripheral functional groups. These functional groups can be useful for both as a functional handle and functional groups that are part of several different fusicoccin and ophiobolin natural products. This peripheral functionality is also important to be able to begin to study structure-function relations of fusicoccin and 14-3-3 PPIs.