Naphthoquinone dimers and trimers from Euclea natalensis

The naphthoquinone dimers natalenone, 8′-hydroxydiospyrin and euclanone and the trimers galpinone and a compound with MW 562 were isolated from E. natalensis roots. Natalenone is a dehydrodimer of 7-methyl- juglone with the two moieties linked by two CC bonds to give a fused tetracyclic structure, one ring bearing a methylene bridge. Galpinone is a 7-methyljuglone linear trimer, the three units probably being linked C-8-C-6′and C-3′-C-3″. Euclanone is a new dimer of 7-methyljuglone and methylnaphthazarin, isomeric with 8′-hydroxydiospyrin.