Strategies for the Synthesis of Scaffolds Found in Natural Products

Book excerpt: A major challenge to finding compounds that modulate protein function is the identification of chemical matter for screening. Although Nature provides excellent options for screening in the form of natural products, sufficient quantities can be difficult to obtain and characterize. Thus, chemical synthesis plays a lead role in providing molecules for screening, and chemists must ultimately decide what to synthesize based on the predicted value of the end products. We developed new synthetic strategies to access compounds for screening. In each case, natural products serve as an inspiration for the developed chemistry. First, a strategy was developed that provides access to scaffolds based on bioactive alkaloids and terpenoids. A key feature of this strategy is the use of transition metals to mediate the synthesis of multiple scaffolds from simple enynes and diynes. A t -butylsulfinamide group serves as a convenient tether to facilitate this chemistry. Principal component analysis (PCA) is used to analyze the relationship of our synthetic scaffolds to naturally occurring alkaloids and terpenoids. Then, a chemical reaction was studied that provides access to benzannulated medium rings inspired by natural products. In the developed reaction, three reagent classes (TsOH, Cu[BF 4 ] 2 , and Tf 2 0) were shown to polarize the carbonyl of a polycyclic cyclohexadienone and subsequently cause a cationic fragmentation reaction that generates an aromatic ring annulated to a medium ring. This process efficiently produces 7- to 11- membered rings while tolerating a variety of common functional groups. Work is presented on efforts to apply this reaction to the synthesis of two natural products, heliannuol A and puerol A.