8α,9α-Epoxy-7-oxoroyleanon,ein Diterpen-Epoxychinon aus einer abessinischen Plectranthus-Art (Labiatae)

8α,9α-Epoxy-7-oxoroleyanone, a Diterpenoid Epoxyquinone from an Abyssinian Plectranthus Species (Labiatae) Reexamination of the title plant, in additon to the previously identified abietanoid hydroxy-1,4-benzoquinones 1a, 1b, 1c, 1e, 1f, 1g , and 1h , yielded the known 7α-acetoxyroleanone ( = 7-O-acetylhorminone; 1d ) and the novel 8α, 9α-epoxy-7-oxoroyleanone ( 2a ). Spectroscopic methods, partial synthesis by epoxidation of 7-oxoroyleanone ( 1h ), and chiroptical correlation establish the structure 2a . Royleanone 2a is the first diterpenoid epoxyquinone isolated so far. Moreover, a detailed ¹³C-NMR analysis of the royleanones 1b, 1c, 1e, 1g , and 1h lead to the complete assignment of their spectra.