Constituents of the Egyptian Centaurea scoparia; Part II. Guaianolides of the Aerial Parts.

Aerial parts of CENTAUREA SCOPARIA Sieb. afforded a new chlorinated guaianolide with an unusual isobutyl structural feature, diain ( 1), together with three known guaianolides, janerin ( 2), cynaropicrin ( 3), and deacylcynaropicrin ( 4). Structural assignments of the isolated compounds are based on spectroscopic methods including 1D- and 2D-NMR spectroscopy as well as mass spectroscopy. New and revised (1)H- and (13)C-NMR data are reported.