Chemical and toxicological studies on bracken fern, Pteridium aquilinum var. latiusculum. VI. Isolation of 5-O-caffeoylshikimic acid as an antithiamine factor.

5-O-Caffeoylshikimic acid (dactylifric acid) was isolated from bracken fern as a major constituent of its acutely toxic fraction, which causes depression of leucocytes and thrombocytes in calves. 5-O-Caffeoylshikimic acid exhibited an antithiamine effect in vitro, but had no hematuric effect in guinea pigs.