## 2 Triterpenoids
### 8,9-ene-triterpenoids  
This type of GT is the lanostane-type triterpenoid with a double bond between C-8 and C-9. In addition, C-3, C-7, C-11 and C-15 were generally substituted by the hydroxyl or carbonyl groups. The minority of compounds possessed hydroxyl or carbonyl groups at C-12. Different oxidation and reduction can happen in the side chain. Except the above structural features, compounds ganodermacal (**44**) and methyl ganoderate A acetonide (**45**) possessed an uncommon acetonide unit. Compound **44** was isolated from the basidiomycete _G. amboinense_, and was a natural product, but not an artefact, which resulted from the acetalization of native ganoderic acid C (**3**) and with acetone not being used during the isolation procedure [153]. However, compound **45** isolated from the fruiting bodies of _G. luculum_ was reported to be most likely not of natural origin due to the utilization of acetone during the isolation procedure [154]. Several studies on the bioactivity of triterpenoids showed that ganoderic acids had significant biological activities [107; 155; 156; 157; 158; 159] (Table 1). Ganoderic acid DM (**50**) displayed stronger 5\(\alpha\)-reductase inhibitory activity (IC\({}_{50}\) value of 10.6 \(\upmu\)M) than the positive control (\(\alpha\)-linolenic acid, 116 \(\upmu\)M). Meanwhile, compared to its methyl derivative, the inhibitory activities of 5\(\alpha\)-reductase at 20 \(\upmu\)M were 55% and 3% for **50** and its derivative, suggesting that the carbonyl group of the side chain for **50** is essential to elicit the inhibitory activity [155]. Liu et al. [156] evaluated the structure -activity relationship for inhibition of 5\(\alpha\)-reductase using ganoderic acid A (**1**), B (**2**), C (**3**), D (**19**), I (**5**) and DM (**50**). The results showed that the presence of the carbonyl group at C-3, and of the \(\alpha\),\(\beta\)-unsaturated carbonyl group at C-26, was characteristic of almost all inhibitors. Except for the aforementioned bioactivity, ganoderic acid DM (**50**) was also a selective potent osteoclast genesis inhibitor [157; 158]. Miyamoto et al. [159] found that ganoderic acid DM (**50**) can suppress the expression of c-Fos and the nuclear factor of activated T cells c1 (NFATc1). This suppression leads to the inhibition of the dendritic cell-specific transmembrane protein (DC-STAMP) expression and reduces osteoclast fusion. The study of Liu et al. [157; 158] also displayed that this compound can be used in therapeutics for prostate cancer by inhibiting the cancer cell proliferation and bone metastases by impeding the osteoclast differentiation. Meanwhile, Johnson et al. [160] indicated the possible mechanism by which ganoderic acid DM (**50**) induces cytotoxicity in both androgen-dependent and independent prostate cancer cells (Figure 3). Compound **50** can also induce DNA damage, G1 cell cycle arrest and apoptosis in human breast cancer cells [107]. Meanwhile, tubulin was identified as the target protein of ganoderic acid DM (**50**), which can explain and clarify the universal mechanism of its medicinal efficacy [161]. Ganoderic acid Df (**22**) is a ganoderma acid having a 23-oxo-24-en-26 oic acid side chain, different from ganoderic acid DM (**50**) which has a 24-en-26 oic acid side chain. Compound **22** exhibited potent human aldose reductase inhibitory activity with an IC\({}_{50}\) of 22.8 \(\upmu\)M in vitro, with the carboxyl group of this compound's side chain being essential for eliciting inhibitory activity because its methyl ester is much less active [162]. Similarly,Fatmawati et al. [163] analyzed the structure-activity relationships of ganoderma acids (ganoderic acids A, B, C, D, H, J, K, Df, ganoderenic acids A and D, as well as methyl ganoderate A, methyl ganoderenate A, and ganolucidic acid B) from _G. lucidum_ as aldose reductase inhibitors. The results revealed that the OH substituent at C-11 is a valuable feature and that the carboxyl group in the side chain is essential for the recognition of aldose reductase inhibitory activity.