Stigmasterol, oleanolic acid, morolic acid, hederagenin, and 11α-hydroperoxy-hederagenin were isolated and characterized as the sapogenins present in the aerial parts of the medicinal plant Serjania triquetra (Sapindaceae). The structure of the novel triterpenoid derivative, 11α-hydroperoxy-diacetyl hederagenin, considered as a key biogenetic and chemical intermediate, was confirmed by relay synthesis from diacetyl hederagenin, via bromo-lactonization, dehydrobromination, and oxidation with H 2 O 2 . Biogenetic relationships are briefly described.