## 2 Triterpenoids
### 8,9-ene-triterpenoids
#### 2.2.7 Rearranged Novel Triterpenoids  
Liu et al. [135] summarized the potential triterpenoids biosynthesis pathway in _G. lucidum_ and found that the pathway contained 14 steps catalyzed by different enzymes. The first 11 steps are the common steps for terpenoid skeleton biosynthesis, and the last three steps may be specific for different triterpenes in different species. It has been reported that this specific modification (cyclization, oxidation, hydroxylation and glycosylation) is carried out by cytochrome P450, glycosyltransferases and other enzymes [301; 302; 303; 304; 305; 306]. Therefore, the plentiful enzymes or enzyme systems of _Ganoderma_ produced diverse triterpenoids and different species may have unique novel structures. Ganorbiformin A (**454**) (Figure 19) is an unusually rearranged analogue and was isolated from the cultures of _G. orbiforme_ BBC 22324 [36]. The former researchers proposed a possible mechanism to account for the formation of **454** (Figure 20). This compound was the C-15 alcohol oxidation of **A** to the ketone **B**, whose methyl group (Me-30) on the \(\alpha\)-face migrated to the neighboring ketone carbon (C-15) under acid catalysis [36]. Ganosporelactones B (**455**) and A (**456**) (Figure 21) are two novel pentacyclic triterpenoids, which were isolated from the spores of _G. lucidum_[307]. They may be biogetically derived from the lanostane skeleton through the construction of the C-16 and C-23 bonds [307]. Figure 19: Chemical structure of ganorbiformin A (**454**) as a rearranged novel triterpenoid. Figure 18: Chemical structures of several C31 triterpenoids (**449–453**). Furanagonaderic acid (**457**) (Figure 22), a lanostane triterpenoid with a furan ring (21,23-epoxy) in the side chain, was isolated from the fruiting bodies of _G. applanatum_[188]. The further study on the chemical constituents of this macrofungus led to the isolation of 24\(\zeta\)-methyl-5\(\alpha\)-lanosta-25-one (**458**) (Figure 22) [308]. The analysis of its structure showed that it was a lanostane triterpenoid without any substituent, except for a keto group on the side chain, and the 2D NMR determined that Me-26 had shifted to C-24 [308]. Two polyoxygenated lanostane triterpenoids, austrolactone (**459**) and austridic acid (**460**) (Figure 23), were extracted from _G. australe_[276]. The austrolactone (**459**) was a C30 triterpenoid spirolactone, and was formed through the ketalation of the O-atoms (C-12 and COOH-26) and the carbonyl group (C-23). The austridic acid (**460**) was 3,4-_seco_-8,9-epoxy-23\(\rightarrow\)26 lactone and was similar to elfvingic acid H isolated from _Elfwingia applanata_ (Pers.) Pat. In the cytotoxicity assay, compounds **459** and **460** (IC\({}_{50}\) = 94 uM) specifically inhibited the viability and growth of the HL-60 cells through activation of the apoptotic cell-death pathway as demonstrated by morphological and biochemical analyses [276]. Figure 21: Chemical structures of ganosporelactones B (**455**) and A (**456**) as rearranged novel triterpenoids. Figure 22: Chemical structures of furanagonaderic acid (**457**) and 24\(\zeta\)-methyl-5\(\alpha\)-lanosta-25-one (**458**) as rearranged novel triterpenoids. A number of triterpenoid lactones (**461**-**471**) have been found from the rare species _G. colossum_. These types of triterpenoids have also been reported in plants including schisanlactones A and B (_Schisandra_ sp.) [309], kadsulactone A (_Kadsura heteroclita_) [310] and lanicalactones A-C (_K. lanicilimba_) [311]. Their structures were characterized by: (1) ring A: 3,4-_seco_ or 3,4-_seco_-3\(\rightarrow\)4 lactone (seven-membered lactone); (2) ring B: 9,19-cyclic-9,10-_seco_ (seven-membered ring) or six-membered ring; (3) side chain: 24-ene-22\(\rightarrow\)26 lactone (a,\(\beta\)-unsaturated-\(\delta\)-lactone) or 22-hydroxy-24-ene-26-acid.