3.1. Abietane
The abietane diterpenoids are the main components of conifers
oleoresins, which play crucial roles in plant to resist pests and
pathogens. Abietane diterpenoids isolated in recent years can be divided
into five sub-classes, namely, classical abietanes, rearranged
abietanes,[78] aromatic
abietanes,[79] abietane
lactones,[80] and abietane dimers.
In previous studies, more than 90 diterpenoids belonging to abietane
have been reported from the genusIsodon .[81] During ongoing investigation onIsodon rugosiformis , rugosiformisin A, a skeleton-rearranged
abietane-type diterpenoid with potent NO inhibitory activity, has been
obtained (58 ).[82] The stereochemistry of58 has been determined using single-crystal X-ray diffraction
analysis.
Officinalins A (59 ) and B
(60 ),[83] which are a pair of unique
C23 terpenoid epimers possessing an unprecedented
tetracyclic 6/7/5/5 carbon skeleton with a
tetracycline[9.6.0.03,8.012,16]heptadecane
core, have been isolated from the leaves of Salvia officinalis .
Another rearranged abietane diterpenoid, salviyunnanone A
(61 ),[84] has been isolated fromSalvia yunnanensis . 61 possesses an unprecedented
7/5/6/3 fused ring system comprising an unusual 9,11-epoxy moiety.
Recently, a series of highly oxidized abietane diterpenoids with potent
inhibitory activity against cancer cells were identified fromEuphorbia fischeriana .[85]
A unique abietane diterpenoid dimer, fischdiabietane A
(62 ),[86] possessing
2-oxaspiro[4.5]decane-1-one and 2-oxabicyclo[3.2.2]nonane
framework, has been isolated from Euphorbia fischeriana . The
absolute configuration of 62 has been determined by
single-crystal X-ray diffraction analysis. 62 has induced
apoptosis in T47D cells through the activation of caspase-3 and the
degradation of poly (ADP-ribose) polymerase.