Spiroalanpyrroids A and B, sesquiterpene alkaloids with a unique spiro-eudesmanolide–pyrrolizidine skeleton from <i>Inula helenium</i>

Abstract

Two sesquiterpene alkaloids with an unprecedented eudesmanolide–pyrrolizidine spiro[5.5] framework, together with two new sesquiterpene-amino acid adducts were isolated from the roots of <italic>Inula helenium</italic>.