Semburins and swertiols, novel 2,8-dioxabicyclo[3.3.1]nonanes and their precursory alcohols, from Swertia japonica Makino

The steam-volatile constituents of Swertia japonica Makino have been studied, and 71 components of the oil (comprising nearly 90% of the sample) have been identified. Structures of three novel 2,8-dioxabicyclo[3.3.1]nonanes (semburin, isosemburin, and neosemburin) and their precursory alcohols (swertiol, isoswertiol, and isoneoswertiol) have been established by spectroscopic analysis and chemical transformation data. The presence of 2-epi-isoneoswertiol, which was named neoswertiol, was detected by GC/MS. This is the first time that the 2,8-dioxabicyclo[3.3.1]nonane skeleton has been encountered in natural products.