| Summary: | 碩士 === 國立彰化師範大學 === 化學系 === 101 === Denbinobin (1) and calanquinone A (3) were isolated from the stems of Dendrobium moniliforme (L.). The structures of denbinobin (1) and calanquinone A (3) were determined to be 1 and 2 by examination of IR, UV, NMR, and high-resolution mass spectra. Since 1 and 2 are the natural products proposed to possess a phenanthradiquinone core, we undertook the synthesis of the optically pure denbinobin dimmer (4) and phenanthradiquinones to confirm its overall structural assignment and to investigate its biological activity.
The synthesis of the optically pure denbinobin dimer is derived from denbinobin through radical oxidation, and then followed by the resolution of the racemic (±)-4. First, the preparation of alkynes 9 was obtained by Corey-Fuchs reaction from the commercially available 2,4,5-trimethoxy-benzaldehyde 12. In addition, the acetylene 16 was prepared via Sonogashira coupling reaction, and then reduction of 16 was manipulated under Pd-catalysis to get biaryl ethane 18. Further, 18 was treated by AgO with 6 N HNO3 to afford 1,4-benzoquinones 19, and followed by intra-molecular Lewis acid-mediated cyclization to provide 1,4-phenanthraquionone 20 and spirodiketone 21. Continually, 21 can be transformed by Lewis acid to give the desired 20, which was treated by selective demethylation with TMSI, and followed by oxidation to afford denbinobin (1). Finally, using radical oxidation of denbinobin with VOF3 provided (±)-denbinobin dimer 4. The resolution of the racemic (±)-4 was performed via alkylation with chiral center agent, and then followed by deprotection to get optically pure denbinobin dimer(+)-4 and (-)-4, respectively. In conclusion, the first synthesis of optically pure denbinobin dimer(+)-4 and (-)-4 has been achieved; the longest linear sequence 11 steps in overall yield 13.7%.
On the other hand, biaryl ethanes, 34, 39, and 52, were prepared by the previous strategy. With 34, 39, and 52 on hand, we have synthesized by our methods to obtain the corresponding phenanthradiquinones 5 and 6, respectively. In summary, we have developed the concise route to synthesize the phenanthradiquinones.
|
|---|
