Four New Sesquiterpenes from Petasites formosanus

Abstract
Four new eremophilane-type sesquiterpenes, petasones A (1) and B (2), S-petasitin (3), and petasinol (4), were isolated from the aerial parts of Petasites formosanus. Their structures were elucidated by spectroscopic and chemical methods as 3α-[(Z)-3-methylsulfinylacryloxy]eremophila-7(11),9-dien-8-one; 3α-[(E)-3-methylsulfinylacryloxy]eremophila-7(11),9-dien-8-one; 3α-[(Z)-3-methylthioacryloxy]-11-hydroxyeremophila-6,9-dien-8-one; and 3α-[(E)-3-methylsulfinylacryloxy]-8β-hydroxyeremophila-9,11-diene, respectively.