Synthesis of Ganbajunins D and E and the Proposed Structure of Thelephantin D

The syntheses of ganbajunins D and E and of the structure proposed for thelephantin D, as well as its regioisomer, were achieved in a divergent manner via a common monoester intermediate. The proposed structure of thelephantin D had NMR chemical shifts different from those of natural thelephantin D. This supported Takahashi's suggestion that the true structure of natural thelephantin D should be the same as that of terrestrin C, as was deduced from the similarities in their NMR spectra. The presence of isomerization equilibria between 2′,5′‐ and 2′,6′‐diacyloxy‐ p ‐terphenyl derivatives in solution, which are the cause of the inseparability of these derivatives, was also demonstrated by monitoring the dynamic transition from a 2′,6′‐diacyloxy‐ p ‐terphenyl‐rich mixture of the derivatives to an equilibrium mixture. The results of biological and chemical property tests – such as cytotoxicity against cancer cells, affinity towards Fe 2+ ion, and antioxidative activity – with the synthesized compounds are also described.