Total synthesis of guanacastepene K
Final Report Abstract
The initial project was aimed at the total synthesis of the terpenoid guanacastepene K. However, based on research conducted in the Sarpong group in advance to the beginning of my work, it seemed to be rather unlikely that the initial research proposal would have worked out. Due to this fact the topic was changed to an already DFG funded project aiming for the total synthesis of a family of natural products called sungeidines. Besides their challenging polycyclic structure, a bisosynthetic relationship to the biologically active dynemicins make the sungeidines attractive synthetic targets. The structure of the sungeidines can be divided into two fragments. An anthracene, which is annulated to a thiolactone and a briged tetracyclic moiety. Both fragments were addressed during this work. In terms of the anthracene portion, a previously inaccessible thiolactone was successfully synthesized. However, the completion of the anthracene moiety was not achieved. For the synthesis of the bridged fragment, two different approaches were investigated. Both of these were planned around a 1,3-dipolar cycloaddition as the key step. Using an intramolecular approach, the desired cycloaddition product could not be obtained due to steric constraints of the molecule. However, an intermolecular approach led to the desired intermediate in a stereoselective fashion. In addition to the work toward the sungeidines, an unexpected rearrangement of oxabenzonorbornadienes to 1-hydroxy-2-naphthoic acid esters, which are versatile synthetic intermediates, was investigated.
