92Planta medica 1988 5, and 6 were coumarins unsubstituted in the pyrone ring (5). The presence of a geranyl group in 1 was suggested by the 1H-NMR signals and mass spectral peaks at mlz 162 (M -C10H16) and 137 (C10H17), and this compound was identified as aurapten (1) by comparison of its physical data with the literature values (6). The presence of a 2,2-dimethylchromene ring in 4,5, and 6 was inferred from the singlet at ô = 1.47 ppm for six protons and two doublets (J = 10 Hz) centred at 5.72 and 6.4-6.9 ppm for two protons in the 1H-NMR spectrum of each compound. These compounds were identified as seselin (4), xanthyletin (5), and xanthoxyletin (6) by comparison with the reported data (7-9).The two compounds 2 (23 mg), m.p. 176-177 °C, C15H1604 and 3 (8 mg), m.p. 128-130 °C isolated from the TLC separation of the column fractions eluted with 30% CHC13-petrol and 80 % CHClpetrol, respectively, also showed JR and 'H-NMR spectral features characteristic of coumarins unsubstituted in the pyrone ring. The presence in 2 of a 3-hydroxy-3-methylbut-1-enyl side chain with the (E)-configuration of the double bond was deduced from its 1H-NMR spectrum: doublets (J = 17 Hz) at = 6.37 and 6.92 ppm (1H each), singlet at ô = 1.45 ppm for 6H, and the D20 exchangeable singlet at = 1.68 ppm. This compound was identified as suberenol (2) from its physical data (10). The compound 3 was identical to the hydrolysis (2 N HC1) product of aurapten (1), and together with the physical data the natural compound was identified as umbelliferone (3). which exhibited signals due to methylene = 3.30 ppm, d, J = 7.0 Hz) and vinyl ( = 5.50-6. 10 ppm, m, = CH and ô = 4.80-5.20 ppm, m, = CH2) groups. Convincing evidence for the structure of this compound was provided by mass spectrum [M at mlz 178 (100%) and fragments at 161 (2%), 151 (5%), and 135 (8%)] and the JR spectrum (3460, 1640,
