Two new phthalide dimers from the rhizomes of Ligusticum chuanxiong.

Two pairs of diastereoisomers, namely (3'Z)-(3S,8S,3a'S,6'R)-4,5-dehydro-3.3a',8.6'-diligustilide (1) and (3'Z)-(3S,8R,3a'S,6'R)-4,5-dehydro-3.3a',8.6'-diligustilide (3), chuanxiongdiolide R3 (2), and chuanxiongdiolide R1 (4), were isolated from the 95% ethanolic aqueous extract of the rhizomes of Ligusticum chuanxiong. Among these Phthalide dimers, compounds 1 and 2 were new ones. The structures of the new isolates were elucidated based on spectroscopic data analyses, and their absolute configurations were determined by comparison of experimental and calculated electronic circular dichroism spectra.