Microtropiosides A-F: ent-Labdane diterpenoid glucosides from the leaves of Microtropis japonica (Celastraceae)

From the leaves of Microtropis japonica, collected in the Okinawa islands, six ent-labdane glucosides, named microtropiosides A-F, were isolated. The structures of the compounds were elucidated by a combination of spectroscopic analyses, application of the β-d-glucopyranosylation-induced shift-trend rule in the 13C NMR spectroscopy and the modified Mosher's method.