Tannins and related compounds. LV Isolation and characterization of acutissimins A and B, novel tannins from Quercus and Castanea species

Two novel and closely related tannins, designated as acutissimins A (1) and B (2), have been isolated from various Fagaceous plants : Quercus acutissima, Q. miyagii, Q. stenophylla, Q. mongolica var. grosseserrata and Castanea crenata. Degradative and synthetic studies combined with 1H- and 13C-NMR spectrometry and various mass spectral measurements have permitted the assignments. of the structures, in which (+) -catechin (4) and the C-glycosylated ellagitannin, castalagin (3), are connected through a carbon-carbon linkage.