Pyrrolizidine alkaloids from Echium glomeratum (Boraginaceae)

Five pyrrolizidine alkaloids were isolated from Echium glomeratum Poir. (Boraginaceae). Three of these were (7 S, 8 R)-petranine ( 1), (7 S, 8 S)-petranine ( 2), and (7 R, 8 R)-petranine ( 3a) or (7 R, 8S)-petranine ( 3b), and two were known but to the species: 7-angeloylretronecine ( 4) and 9-angeloylretronecine ( 5). The methanolic extract of the whole plant of Echium glomeratum Poir. (Boraginaceae) has afforded five pyrrolizidine alkaloids, three that were (7 S, 8 R)-petranine ( 1), (7 S, 8 S)-petranine ( 2), and (7 R, 8 R)-petranine ( 3a) or (7 R, 8S)-petranine ( 3b), comprising a tricyclic pyrrolizidine alkaloids subclass; and two that were known but to the species: 7-angeloylretronecine ( 4) and 9-angeloylretronecine ( 5). All compounds were tested against a human tumor panel for cytotoxicity; no activity was observed (EC 50 values > 20 μg/ml).