Triterpenoid saponins from the fruits of Caryocar glabrum

Twenty-one new triterpenoid saponins, named caryocarosides (1-21), glycosides of 2 beta-hydroxyoleanolic acid, hederagenin, bayogenin, and gypsogenic acid, have been isolated from the fruits of Caryocar glabrum along with nine known triterpenoid saponins (22-30) that are described for the first time from a plant in the Caryocaraceae. Their structures were established by 1D and 2D NMR techniques (C-13, COSY, TOCSY, HSQC, HMBC, and ROESY experiments), ESIMS, and acid hydrolysis. The isolated compounds could be classified into two series: glucosides (1-8, 22, 27, and 30) derived from the 3-O-monoglucoside and glucuronides (9-21, 23-26, 28, and 29) derived from the 3-O-monoglucuronide. In 22 of the saponins (1-8, 12-22, and 24-26), a galactose moiety was linked to C-3 of a glucuronic acid or a glucose moiety. The galactose was substituted in position 3 by a second galactose unit (6, 7, 20, and 21) or by a xylose unit (8). Seven saponins (4, 5, 16-19, and 26) were found to be bidesmosides with one glucose unit linked to C-28 of the aglycon. The hemolytic activity of the major saponins (2, 3, 5, 12-15, 17, 24, and 28) was measured on sheep erythrocytes in order to establish structure-activity relationships based on the type of sugar attached to the aglycon and on the structure of this aglycon.