Rearranged Abietane Diterpenoids from Clerodendrum Mandarinorum

Five new abietane derivatives which have a commonly rearranged abietane skeleton contained a 17(15-->16),18(4-->3)-diabeo-abietane framework, mandarones D-H, were isolated from the stem of Clerodendrum nmantarinorum Diels (Verbenaceae). The structures were characterized as (16S)-12,16-epoxy-11-hydroxy-17(15-->16), 18(4-->3)-diabeo-abieta-3,5,8,11,13-pentaene-7-one (mandarone D, 1), 12,16-epoxy-11,14-dihydroxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11, 13,15-hexaene-7-one (mandarone E, 2), 12,16-epoxy-6,11,14-trihydroxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11,13,15-hexaene-7-one (mandarone F, 3),12,16-epoxy-11,14-dihydroxy-6-methoxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11,13,15-hexaene-2,7-dione (mandarone G, 4) and 12,16-epoxy-11,14-dihydroxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11,13,15-hexaene-1,7-dione (mandarone H, 5) respectively, mainly based on the spectral analysis and by comparison with those of closely related compounds.