Leoncaphthalide, a New Phthalide Derivative from the Roots of Leontopodium calocephalum
The genus Leontopodium (Asteraceae) comprises about 58 species in the world, and more than 36 species, including 18 endemic species, are distributed in Northeast and Northwest China [1] The aerial parts of several Leontopodium plants are used as traditional Chinese medicine for the remedy of abdominal aches, diarrhea, bronchitis, tonsillitis, dysentery, fever, etc. [2 5] Previous phytochemical investigations of this genus revealed that its characteristic secondary metabotites are sesquiterpenes, especially those with the bisabolane skeleton [6 10] In addition, other kinds of compounds such as benzofuran [8] coumarins [9] flavones [11] and lignans are also found [11, 12] Leontopodium calocephalum is mainly distributed in Northwest China. Apart from a Chinese patent report that the ethanol extract of this plant and its active ingredient leontopodic acid can be used for treating hepatitis [13] there is no other research concerning the chemical constituents of this plant up to now. In our investigation of the root of L. calocephalum, three compounds were isolated. Compound 1 was established as a new phthalide derivative by HR ESI MS, IR, and 1D and 2D NMR and named leoncaphthalide. Compounds 2 and 3 were identified as 7 O methylplatypterophthalide [14] and 2 methoxyhelikrausi chalcone [15] respectively. As far as we know, this is the first report on phthalide derivatives identified from Leontopodium species. Leoncaphthalide (1) was isolated as a colorless gum. Its HR ESI MS spectrum displayed a quasimolecular ion peak at m/z 231.0652 [M H] which suggested the molecular formula C13H10O4, indicating nine degree of unsaturation. Its IR spectrum showed the absorption bands of hydroxy group (3516 cm 1) aromatic ring (1627, 1558 and 1472 cm 1) and carbonyl moiety (1732 cm 1) The 1H NMR spectrum of 1 showed the presence of two aromatic or olefinic protons at 7.01 (1H, s) and 6.54 (1H, s) one terminal double bond proton at 5.80 (H, s) and 5.23 (H, s) one oxygened methylene at 5.44 (2H, s) one methyl at 2.11 (3H, s) and one hydroxy hydrogen at 7.92 (1H, br.s) The 13C NMR spectrum showed 13 carbon signals. Combined with the DEPT 135 experiment, these carbons were categorized into one carbonyl carbon 173.0) five aromatic quaternary carbons 160.0, 154.3, 139.2, 116.4, and 107.2) two olefinic quaternary carbons 158.6 and 131.9) two methine carbons 99.6 and 98.2) two methylene carbons 114.2 and 69.7) and one methyl carbon 19.1) (Table 1) These data, especially the 13C NMR signals of the carbonyl carbon at 173.0 (C) and methylene carbon at 69.7 (CH2) along with the IR frequency at 1732 cm 1, indicated the basic skeleton of compound 1 to be a phthalide [16] The 1H and 13C NMR data of compound 1 (Table 1) were similar to that of platypterphthalide [14] and compound 2 (Table 1) Compared with the data of platypterphthalide, there is only one more double bond in the structure of compound 1 than that of platypterphthalide.
Chemistry of Natural Compounds