Plectranthone A, B, C und D. Diterpenoide Phenanthren‐1,4‐dione aus Blattdrüsen einer Plectranthuus sp. (Labiatae)

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Abstract
Plectranthons A, B, C, and D. Diterpenoid Phenanthrene‐1,4‐diones from Leaf‐glands a Plectranthus sp. (Labiatae)The following structures of four new 1,4‐phenanthraquionones, isolated in minute amounts from the coloured leaf‐glands of a Plectranthus sp. obtained from the borders of Lake Kiwu2, Rwanda, are proposed: plectranthon A (1; 3‐hydroxy‐5, 7,8‐trimethyl‐2‐(2‐propenyl)phenanthrene‐1, 4‐dione), plectranthon B (2; 2‐(2ξ‐acetoxypropyl)‐3‐hydroxy‐5,7,8‐trimethylphenanthrene‐1,4‐dione), plextranthon C (3; 3‐hydroxy‐ 7,8‐diemethyl‐2‐(2‐propenyl)phenanthrene‐1,4‐dione), and plectranthon D (4; 3‐hydroxy‐7,8,10‐trimethyl‐2‐(2‐propenyl)phenanthrene‐1,4‐dione). 2‐(2ξ‐Hydroxypropyl)‐3,6‐dihydroxy‐5,7,8‐trimethylphenanthrene‐1,4‐dione (11), a compound very similar to 1–4, was prepared by a Wagner‐Meerwein, rearrangement of coleon E (5). Biogenetically, the plectranthons are derived from abietanoic precursors. The compounds 1, 2 and 4 are the first natural C20‐phenanthrenes of diterpenoid origin.

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