A new dibenz [b, d] oxocin derivative, named protosappanin C (3), C16H14O6, amorphous powder, [α] 23D -39.8° (MeOH), was isolated from Sappan Lignum (the dried heart-wood of Caesalpinia sappan L. (Leguminosae)). It yielded sappanin (4) on alkaline fusion, an oxime (5), a dimethyl acetal (6) on treatment with p-toluenesulfonic acid in methanol, and protosappanin B (2) on reduction with sodium borohydride. The circular dichroism spectra of 3 and 6 indicated that their biphenyl system preferentially takes S configuration, from which R configuration was assigned to C-7 of 3. On the basis of the above chemical and spectroscopic evidence, the chemical structure of 3 was established as (7R) -7, 8-dihydro-3, 7, 10, 11-tetrahydroxy-7 (6H) -dibenz [b, d] oxocincarbaldehyde. A possible route of biosynthesis of protosappanins from sappanchalcone is discussed.
The Pharmaceutical Society of Japan