Diterpenoide Drüsenfarbstoffe aus Labiaten: Coleone U, V, W und 14‐<i>O</i>‐Formyl‐coleon‐V sowie 2 Royleanone aus <i>Plectranthus myrianthus</i> BRIQ.; <i>cis</i>‐ und <i>trans</i>‐A/B‐6, 7‐Dioxoroyleanon

Abstract

Leaf‐gland Pigments: Coleons U, V, W, 14‐ O ‐Formyl‐coleon‐V, and two Royleanones from Plectranthus myrianthus BRIQ. ; cis ‐ and trans ‐A/B‐6,7‐Dioxoroyleanones From leaf‐glands of the South‐African P. myrianthus (Labiatae) the following diterpenoids have been isolated and their structures established: coleon U, C 20 H 26 O 5 (6, 11, 12, 14‐tetrahydroxy‐abieta‐5, 8, 11, 13‐tetraene‐7‐one, 2a ); coleon V, C 20 H 26 O 5 (11, 12, 14‐trihydroxy‐abieta‐8, 11, 13‐triene‐6, 7‐dione, 4a ); coleon W, C 22 H 28 O 8 (16(or 17)‐acetoxy‐6, 11, 12, 14, 17 (or 16)‐pentahydroxy‐abieta‐5, 8, 11, 13‐tetraene‐7‐one, 6 ); 14‐ O ‐formyl‐coleon‐V, C 21 H 26 O 6 (14‐formyloxy‐11, 12‐dihydroxy‐abieta‐8, 11, 13‐triene‐6, 7‐dione, 4b ); 7α‐formyloxy‐6β‐hydroxyroyleanone, C 21 H 28 O 6 (7α‐formyloxy‐6β, 12‐dihydroxy‐abieta‐8, 12‐diene‐11, 14‐dione, 1a ); the already known 6β, 7α‐dihydroxyroyleanone ( 1c ) and a dimeric abietane derivative whose structure is not yet elucidated. This is the first record of a co‐occurrence of coleons and royleanones in the same plant. In the course of chemical investigations of 4a and 4b the highly oxidized trans ‐ and cis ‐A/B‐6,7‐dioxoroyleanones ( 5a and 5b ) were obtained.