Diterpenoide Drüsenfarbstoffe: Coleon L, ein neues Diosphenol aus Coleus somaliensis S. M OORE ; Revision der Strukturen von Coleon H, I, I′ und K

Leaf‐gland Pigments: Coleon L, a New Diosphenolic Compound from Coleus somaliensis , S. M OORE ; Revision of the Structures of Coleon H, I, I′ and K From leaf‐glands of C. somaliensis a new, highly oxidized diosphenolic hydroquinone belonging to the abietane series was isolated in minute quantities. The new compound, coleon L ( 4c ; C 24 H 30 O 10 ), is very labile and transformed into its tautomer coleon K (5d) on standing in solution. 1 H‐NMR. spectra of coleon L showed clearly that the points of attachment of the two acetoxy groups are at C(3) and C(16) contrary to the positions expected from our previously published structure 3 for coleon K. Application of a recently elaborated conversion of trans ‐A/B‐6,7‐diketones of type 5 into the cis ‐isomers 6 allowed to assign unambiguously the β‐configuration to the hydroxyl group at C(3) using pyridin induced solvent shifts. This confirmed structure 4c and 5d for coleon L and K, respectively. Based on similar reasons, the configuration at C(3) of coleon H, I and I′ had to be revised, the structures of these coleons being 4b , 5b and 5c , respectively.