Diterpenes from the barks of Cinnamomum cassia and their immunomodulatory activity

Four new diterpenes, cinncassiols I (1), J (2), and D₆ (3), and 18-hydroxycinnzeylanol (4), together with 11 known related diterpenes (5-15) were isolated from the barks of Cinnamomum cassia. The structures of 1-4 were assigned by spectroscopic analyses and the absolute configurations of 1 and 2 were deduced by ECD calculations. Cinncassiol I (1) is a unique rearranged isoryanodane type diterpene with a cage-like 5/6/6/5/7-fused pentacyclic structure involving a 2,9-dioxatricyclo[4.3.1.0^3,8]decane core. Cinncassiols J (2) and D₆ (3) had a 5/6/5/6-isoryanodane skeleton, of which 2 is the first 6,11-de-epoxy isoryanodane type diterpene lacking an oxygen function at C-6. 18-Hydroxycinnzeylanol (4) is a ryanodane type diterpene. Cinncassiols I (1) and J (2) enhanced ConA-induced T cell proliferation in murine splenocytes.