Acridone alkaloids. Part 9. Chemical constituents of Glycosmis citrifolia(Willd.) Lindl. Structures of novel linear pyranoacridones, furoacridones, and other new acridone alkaloids

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Abstract
Sixteen acridone alkaloids were isolated from Glycosmis citrifolia(Willd.) Lindl. (Rutaceae) collected in Taiwan. Seven of them are novel and are reported for the first time, and can be divided into four groups: the linear pyranoacridones glycofoline (1a) and pyranofoline (2a), the furoacridone furofoline-II (3b), the hexa-oxygenated acridone (4a), and the prenylated acridones glycocitrine-I (5a), -II (5c), and 3-O-methylglycocitrine-II (5d). The structures were elucidated from spectral data and chemical transformations. N.O.e. experiments on the methoxymethyl derivatives of phenolic acridones were successfully applied to the determination of the position of the hydroxy group on the acridone nucleus. The location of the prenyl group of (5c) was established by correlation with compound (8), employing cyclization of (5c) with benzeneselenenyl chloride. Formic acid-catalysed cyclization of (5c) induced undesirable rearrangement of the prenyl group to form the products (9) and (10).