Betulonaldehyde is a pentacyclic triterpenoid and derivative of the cholesterol biosynthesis inhibitor betulin that has been found in Betula. It is active against P. falciparum (IC50 = 3.36 µg/ml) and cytotoxic to NCI H187 lung cancer cells and non-cancerous Vero cells (IC50s = 19.23 and 17.09 µg/ml, respectively). Topical application of betulonaldehyde (1 mg/ear) reduces ear edema induced by phorbol 12-myristate 13-acetate (TPA; Item No. 10008014) in mice. It has also been used a precursor in the semisynthesis of C-2 and C-28 betulonic aldehyde derivatives.