All reagents were purchased and used as received.
DMF was of reagent grade and used as received. Reactions
and column chromatographies were monitored by
analytical TLC (length = 33 mm) with silica gel 60 F254
and 1:1 EtOAc/hexanes mixture as the eluent. Spots were
visualized by heating and 254 nm irradiation. CC was
performed using silica gel (230–400 mesh). The ratio of
the column height and width was 5:1. 1H NMR spectra
were recorded on Bruker (300, 400 or 500 MHz) spectrometers
in DMSO-d6, methanol-d4 (native ginkgolides
and bilobalide) and CDCl3 (ginkgolide derivatives).
Mass spectra were measured on JEOL JMS-HX110/
100A HF mass spectrometer under FAB conditions with
NBA as the matrix. In general, all ginkgolides and their
derivatives decomposed above 250 C.