Chem. Pharm. Bull. 53(12) 1555—1558 (2005)

has long been used as a Chinese folk medicine in the treatment of edema and scrofula. The constituents of L. stenocephala have been previously investigated and shown to contain benzofuran derivatives. Here, we report the isolation and structural elucidation of three new dimeric benzofuran derivatives, ligulacephalins A (1), B (2) and C (3), together with three known compounds from the roots of L. stenocephala. The known compounds were identified as 5,6dimethoxy-2-isopropenylbenzofuran (4), euparin (5) and (R)-( )-hydroxytremetone (6), respectively, by comparison of their spectroscopic data with those previously described in the literature. Ligulacephalin A (1) was obtained as an amorphous powder. The molecular formula was determined to be C26H28O6 by high-resolution (HR)-electron ionization (EI)-MS, indicating thirteen degrees of unsaturation. The UV absorption maxima at 206, 249sh, 255 and 295 nm indicated the presence of a benzofuran ring. The presence of 13 carbons and 14 hydrogens shown in the NMR spectra, and an intense ion peak at m/z 218 (M /2, 100%) in the EI-MS, suggested the symmetrical nature of 1. The Hand C-NMR data (vide Experimental) indicated that 1 possessed one methyl group, one methylene group, two methoxyl groups, one quaternary carbon and a benzofuran skeleton. Interpretation of the Hdetected heteronuclear multiple-bond coherence (HMBC) and nuclear Overhauser effect correlation spectroscopy (NOESY) data led to the half-unit of the molecule (Fig. 1). Based on the molecular formula, C-10 must form a cyclobutane ring with C-10 or C-12 . The coupling pattern and the constants for the methylene protons [d 1.94 (2H, AA XX type, H-12a , H-12 b), 2.78 (2H, AA XX type, H-12b , H12 a); Coupling constants, JAX 11.3 Hz, JAX 9.5 Hz, JAA 9.0 Hz, JXX 3.8 Hz] suggested a head-to-head dimeric structure. Thus the gross structure of ligulacephalin A was determined to be as shown in 1. The relative stereochemistry was determined as follows. In the long-range H–H shift correlation spectroscopy (H–H COSY) spectrum, a Wtype coupling was observed between H3-11 and H-12 a , indicating their anticoplanar orientation (Fig. 2). The NOESY December 2005 Chem. Pharm. Bull. 53(12) 1555—1558 (2005) 1555