Dolabellane diterpenoids from the liverworts Barbilophozia floerkei, B. lycopodioides, and B. attenuata: spectroscopic and X-ray studies of structure, stereochemistry, and conformation. X-Ray molecular structure of 3S,4S;7S,8S-diepoxy-10R,18-dihydroxydollabellane, 18-acetoxy-3S,4S;7S,8S-diepoxydolabellane, and 10R,18-diacetoxy-3S,4S-epoxydolabell-7E-ene

Abstract

The dolabellane diterpenoids 10R,18-diacetoxy-3S,4S;7S,8S-diepoxydolabellane (barbilycopodin)(1), 10R,18-diacetoxy-3S,4S-epoxydolabell-7E-ene (12), 18-acetoxy-3S,4S;7S,8S-diepoxydolabellane (4), and 18-hydroxydolabell-7E-en-3-one (14) have been isolated from the liverworts Barbilophozia floerkei, B. lycopodioides, and B. attenuata. The ¹H and ¹³C n.m.r. spectroscopic properties of the compounds and some of their transformation products are described. The structures, relative stereochemistries, and conformations of compounds (4), (12), and 3S,4S,7S,8S-diepoxy-10R,18-dihydroxydolabellane (2) were defined by X-ray crystallographic studies. The eleven-membered ring has essentially the same conformation in compounds (2), (4), and (12), a conformation which has been characterised as a low-energy form of cycloundeca-1,5-diene by molecular-mechanics calculations.