Pyrrolizidine Alkaloids from Onosma leptantha

Three new pyrrolizidine alkaloids, leptanthine ( 2 ), its corresponding N ‐oxide 1 , and N ‐oxide of 3′‐ O ‐acetylechihumiline ( 3 ), were isolated from the aerial parts of Onosma leptantha , together with two known alkaloids of the same type, echihumiline ( 5 ) and echihumiline N ‐oxide ( 4 ). Their structures and configurations were determined by chemical and spectroscopic methods, especially 1D and 2D NMR analyses, including long‐range 1 H, 15 N correlations at natural abundance.