Construction of the isocopalane skeleton: application of a desulfinylative 1,7-hydrogen atom transfer strategy.

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 K2 S2 O8 -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.

Synthesis of the scalarane sesterterpenoid 16-deacetoxy-12-epi-scalarafuranacetate.

The marine natural product 16-deacetoxy-12-epi-scalarafuranacetate, isolated from Spongua officinalis , was synthesized in 18 linear steps, starting from (-)-sclareol, with high stereoselectivity and an overall yield of 6.1%. The intermediate 16-deacetoxy-12-epi-scalarafuran could be easily transformed into a series of natural scalarane sesterterpenoids in a few steps.

Thiosemicarbazones active against Clostridium difficile.

A set of closely related furylidene thiosemicarbazones was prepared and screened against various clinically important Gram-positive bacteria. One compound containing an ethylene spacer and a 5-nitrofuryl group was found to have promising activity against Clostridium difficile.