Cytotoxic Cardenolides from the Leaves of Acokanthera oblongifolia.

Three previously undescribed cardenolides, acovenosigenin A 3-O-α-L-acofriopyranoside (1: ), 14-anhydroacovenosigenin A 3-O-[β-D-glucopyranosyl-(1″→4')-O-α-L-acofriopyranoside] (2: ), and 14-anhydroacovenosigenin A 3-O-[β-D-glucopyranosyl-(1″→4')-O-α-L-acovenopyranoside] (3: ), together with the two already known ones, 14-anhydrodigitoxigenin 3-O-β-D-glucopyranoside (4: ) and acospectoside A (5: ), were isolated from the leaves of Acokanthera oblongifolia. The influence of cardenolides 1: - 3: and acovenoside A (found in the Acokanthera genus) on three cancer cell lines (HT29, HCT116, and AGS) was also investigated. The most promising results, in comparison with oxaliplatin, were obtained for compound 1: , which was found to be highly cytotoxic for all tested cell lines, HT29 (IC₅₀ = 63.49 nM), HCT116 (IC₅₀ = 67.35 nM), and AGS (IC₅₀ = 80.92 nM). Unfortunately, 1: also showed similar toxicity towards normal lymphocytes (IC₅₀ = 98.03 nM).