14‐Hydroxytaxodion als Hauptditerpen in Plectranthus grandidentatus GÜRKE; Isolierung von sieben neuen dimeren Diterpenen aus P. grandidentatus, P. myrianthus BRIQ. und Coleus carnosus HASSK.: Strukturen der Grandidone A, 7‐Epi‐A, B, 7‐Epi‐B, C, D und 7‐Epi‐D

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Abstract
Isolation of 14‐Hydroxytaxodione from Plectranthus grandidentatus GÜRKE and of Seven New Dimeric Diterpenoids from P. grandidentatus, P. myrianthus and Coleus carnosus Structures of Grandidone A, 7‐Epi‐A, B, C, D and 7‐Epi‐DFrom the leaf‐glands of the title plant the following abietane diterpenes have been isolated and their structures established by chemical, spectroscopical and X‐ray methods: 14‐hydroxytaxodione (5, 0,57%), new as a natural product, the already known coleons U (6, 0,17%) and V (7, 0,024%), and furthermore 7 novel dimeric compounds named grandidones (ca. 0,09%), Both grandidone A (1a) and 7‐epigrandidone A (1b) as well as grandidone B (2a) and 7‐epigrandidone B (2b) are C(7) acetals of 6, 7‐Dioxoroyleanone with catecholes such as coleon U (→ 1a, 1b) or coleon V (→ 2a, 2b). Based on the relative configuration at C(7) of 1a which was established by X‐ray analysis, the constitutions of 1b, 2a and 2b were assigned by HPLC. ‐ controlled interconversions. The unstable grandidone C (3) is a C(7)‐C(7′) linked bis‐6‐oxoroyleanone with C2‐symmetry. Grandidone D (4a) and 7‐epigrandidone D (4b) are spiro‐dihydrofurans formed from 3 via a hypothetical bis (14‐hydroxytaxodione) by intramolecular addition of HO‐C(14) or HO‐C(14′) to C(7′) to C(7′) or C(7). The relative configuration of 4a was established by X‐ray analysis of its diacetate 4c. The absolute configuration of all dimers was established by the partial syntheses from 14‐hydroxytaxodion (5) (entirely described in the following communication).