It was concluded that the structure of agrimonolide (I), [α]_D⁵ +8.1°, would be formulated as (II), (III), or (IV), but (II) is a phthalide and its C=O vibration should be around 5.7μ, that of 6.05μ in (I) being too much to the longer wave-length region even with consideration of hydroxyl at 7-position. Infrared spectra (in Nujol) of natural dihydroisocoumarins showed this absorption at 6.04μ in hydrangenol (XIII) and 6.04μ in phyllodulcin (XIV), which are in good agreement with that of (I) and of monomethylagrimonolide (V) at 6.04μ (in Nujol), while that of bergenin (XII) at 5.88μ (Nujol) agrees with that of dimethylagrimonolide. This suggests that (I) is either (III) or (IV).
The two phenolic hydroxyls in agrimonol (XV), obtained by saponification of (I) followed by decarboxylation, were methylated with diazomethane and cautious oxidation of the methylated product afforded dimethylagrimonone and cautious oxidation of the methylated product afforded dimethylagrimonone (XVII) which was found to agree with 3, 5-dimethoxybenzyl p-methoxyphenethyl ketone (XIX), prepared by the route shown in Chart 2, by comparison of their 2, 4-dinitrophenylhydrazone, m.p. 104°. Consequently, (I) was proved to be d-3-(p-methoxyphenethyl)-6, 8-dihydroxy-3, 4-dihydroisocoumarin (III).