New sesquiterpenoids from the flowers of pentanema britannicum (L.) D.Gut.Larr

Five new sesquiterpenoids, (4S, 5S, 6S, 7S, 8 R)-5,6-dihydroxy-1-acetoxy-10(14)-en-britannilactone (1), (4S, 5 R, 6S, 7S, 8 R)-5,6-dihydroxy-1-acetoxy-10(14)-en-britannilactone (2), 6-O-propionyl­britannilactone (3), 1β-hydroxy-3α-acetoxyeudesma-11(13)-en-12,8β-olide (4) and 1β,5β-dihydroxyeudesma-11(13)-en-12,8β-olide (5), along with twelve known ones were isolated from the flowers of Pentanema britannicum (L.) D.Gut.Larr. Among them, compounds 1 and 2 were stereoisomers which belong to 1,10-seco-eudesmane sesquiterpenoid with rare double bond between C-10 and C-14. The structures of the isolated compounds were elucidated by various spectroscopic methods, including 1D and 2D NMR experiments.