Diterpenoide Drüsenfarbstoffe aus Labiaten: 6 neue p‐Chinomethane aus Plectranthus parviflorus W ILLD

Leaf‐gland Pigments: 6‐Novel p‐Quinomethanes of the Abietane Series from Plectranthus parviflorus WILLD The above mentioned plant accumulates in its red coloured leaf‐glands a complex mixture of strongly dehydrogenated abietanols. They were separated (with difficulties) to yield 6 novel compounds. Spectroscopic and chiroptic data show them to be esters of either 11, 19‐dihydroxy‐ or 2 α, 11‐dihydroxy‐abieta‐5, 7, 9 (11), 13‐tetraen‐12‐one 2a and 3a, respectively. Specifically, the 19‐O‐p‐hydroxybenzoate (2d) parvifloron C, the 19‐O‐vanilloate (2c) parvifloron B, the 19‐O‐p‐hydroxy‐benzoate (2d) parvifloron C, the 19‐O‐3′,4′‐dihydroxybenzoate (2e) parvifloron E, the 2 α‐O‐p‐hydroxybenzoate (3b) parvifloron D, and the 2 α‐O‐3′,4′‐dihydroxy‐benzoate (3c) parvifloron F. Reduction by LiAlH4 splits the ester function and reduces the p‐quinomethane to a colourless pyrocatechol derivative which, by air oxidation, regenerates the red p‐quinomethane system of 2a and 3a.