| Abstract: | 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 . |
