Two attractive chirons, aldehyde 6 and chloride 7, exhibiting functionalized ent-spongiane-type tricyclic skeletons (ABC ring system), have been constructed and their absolute configurations have been studied by NMR spectroscopy and confirmed by single-crystal X-ray diffraction. Both of these chirons are derived from commercially available andrographolide in good yield. Aldehyde 6 is obtained through a novel K2S2O8-catalyzed aquatic ring-closing reaction of allylic sodium sulfonate and intramolecular 1,7-hydrogen atom transfer process. Further mechanistic investigations demonstrate that the 1,7-hydrogen atom transfer is a free-radical process, whereby hydrogen migrates from C18 to C17, as evidenced by double-18- deuterium-labeled isotope experiments. Prospective applications of these two chiral sources are also discussed.
[1]E China Univ Sci & Technol, Shanghai Key Lab New Drug Design, Sch Pharm, Shanghai 200237, Peoples R China.
[2]Chinese Acad Sci, Shanghai Inst Organ Chem, Key Lab Synthet Chem Nat Subst, Shanghai 200032, Peoples R China.
[3]Shanghai Univ Tradit Chinese Med, Sch Pharm, Shanghai 201203, Peoples R China.
[4]Yangzhou Univ, Coll Chem & Chem Engn, Yangzhou 225002, Jiangsu, Peoples R China.
(8.0+极速模式)