Coumarins in the Rutaceae

Over the past 150 years, since Vogel in 1820 isolated the parent oxygen heterocycle, coumarin (1) from Coumarouna odorata = Dipteryx odorata (1), coumarins have been recognized as widely distributed plant products. The vast majority carry an oxygen substituent at C-7; consequently 7-hydroxycoumarin [umbelliferone, (2)], one of the most widely distributed coumarins, is often regarded as the parent, in a structural sense and also biogenetically, of a large number of the structurally more complex coumarins. A number of review articles on natural plant coumarins have appeared (154, 302, 344, 420, 525, 541, 548) since the last in this series (153), the most comprehensive, albeit dealing solely with coumarins of the Umbelliferae, being that of Nielsen in 1970 (419).

Naturally Occurring Plant Coumarins

The naturally occurring coumarins.

Two new coumarin compounds (1 and 2), phebalosin (3), its derived artifact murralongin (4), and murrangatin acetonide (5) were isolated from the leaves of Galipea panamensis. The structures of 1 and 2 were assigned as 7-{[(2R*)-3,3-dimethyloxiran-2-yl]methoxy}-8-[(2R*,3R*)-3-isopropenyloxiran-2-yl]-2H-chromen-2-one and 7-methoxy-8-(4-methyl-3-furyl)-2H-chromen-2-one, respectively, on the basis of their spectroscopic data (primarily NMR and MS). Compounds 1−3 were tested against axenic amastigote forms of Leishmania panamensis and displayed 50% effective concentrations (EC50) of 9.9, 10.5, and 14.1 μg/mL, respectively. These three compounds also displayed cytotoxicity (IC50) at concentrations of 9.7, 33.0, and 20.7 μg/mL, respectively, on human promonocytic U-937 cells.

Coumarins from Galipea panamensis and Their Activity against Leishmania panamensis

The structural determination of five new coumarins: murralonginol isovalerate (1b), isomurralonginol isovalerate (2b), murrangatin isovalerate (6b), minumicrolin isovalerate (7b), chloculol (4a), and a new indole alkaloid, paniculol (18), is described.The relative configurations hitherto reported for the α-glycol moieties in murrangatin (erythro) and minumicrolin (threo) have been revised to threo for compound (6a) and erythro for compound (7a), respectively on the basis of NOE experiments performed on the acetonides (6e) and (7e). Furthermore, the absolute configuration of (–)-murrangatin (6a) has been shown to be [R,R] by analysis of the CD spectrum of tetrahydromurrangatin dibenzoate (16b). The reaction of phebalosin (8) with hydrochloric acid has also been re-examined.

The chemical composition of Murraya paniculata. The structure of five new coumarins and one new alkaloid and the stereochemistry of murrangatin and related coumarins

The structure (II) has been assigned to the coumarin phebalosin, obtained from Phebalium tuberculosum and P. drummondii.

PR Jefferies

Papers

The chemistry of the Western Australian Rutaceae. V. The isolation of some coumarins and the structure of phebalosin