Isoentenyl diphosphate (IPP), the triterpenapoid precursor, is synthesized though two independent pathways: the cytosolic mevalonate (MVA) pathway and the plastidal 2-C-methyl-D-erythnitrol 4-(dihydrogen phosphate) (MEP) pathway) [10]. Both IPP and dimethylallyl diphosphate (DMAPP) are catalytically converted by geranyl pyrophosphate synthase (GPS) into geranyl pyrophosphate (GPP). Then, IPP and GPP can further form farnesyl pyrophosphate via a reaction catalyzed by methylene pyrophosphate synthase (FPS). Next, under the action of squalene synthase (SQS), two molecules of farnesyl pyrophosphate combine at the head and tail to form squalene, which is then converted into 2,3-oxidosqualene in a reaction catalyzed by squalene cyclooxygenase (SE). In triterpenapoid synthesis, the first important step is the cyclization of the common acyclic precursor 2,3-oxidosqualene by oxidosqualene cyclase (OSC) to form various triterpene scaffolds [11]. The chair-chair-chair (C-C-C) conformation produces the dammarenyl intermediate cation, while the chair-boat-chair (C-B-C) conformation forms the protostane intermediate cation, a precursor of sterol, parkeol, and isobarorinol (Figure S1) [12; 13; 14]. Finally, triterpeneoid skeletons are modified by cytochrome P450 monooxygenase (CYP450), UDP-glycostransferase (UGT), and glucosidases, forming different types of active triterpenapoids. Members of the _OSC_ supergene family play crucial roles in the production of triterpene precursors and sterols. Generally, OSCs can be preliminarily identified by specific structures, specifically, highly conserved sequences such as the DCTAE and QW sequences. The conserved DCTAE sequence is involved in substrate binding and plays an important role in substrate connection and initial cyclization. The QW motif (QXXXXXW), a negatively charged aromatic amino acid region, stabilizes the cationic intermediate during the cyclization of 2,3-oxidosqualene. These repetitive sequences may be related to the structure and function of stable proteins. One of the conserved sequences in OSCs, MWCYCR, is even more highly conserved in \(\beta\)-amyrin synthase (\(\beta\)-AS). The Trp within this domain is highly likely to play an important role in the formation of triterpene skeletons [15]. The MWCYCR sequence not only contains amino acid residues responsible for the determination of product specificity between lupped and \(\beta\)-amyrin but also a Trp residue responsible for the formation of pentacyclic triterpenes. The Trp of \(\beta\)-AS regulates the formation of \(\beta\)-amyrin by stabilizing oleanyl cations, while the lack of a Leu residue may terminate the reaction at the lupaned cationic stage. When the conserved Tyr residue found in all OSCs that produce pentacyclic triterpenes is mutated into a His residue, the reaction products are tetracyclic carbon skeletons instead of pentacyclic triterpenes, inferring the significance of the X site. The X site of this motif harbors His residues, resulting in the generation of tetracyclic products, while Tyr residues result in the generation of pentacyclic products [15]. The roles of certain OSCs in triterpene synthesis have been functionally analyzed in several species, such as _Arabidopsis thaliana_, _Glycine max_, _Gentiana straminea_ Maxim, _Panax ginseng_, and _Glycyrrhiza uralensis_[16; 17]. Since triterpenes are the main active compounds in bitter gourd (_Momordia charantia_ Linn. ), recent studies have focused on OSCs in this species. Bitter gourd, also known as bitter melon, kugua, balsam pear, or karela, is an edible and medicinal vine from the Cucurbitaceae family that is cultivated worldwide. It is valued as an edible vegetable and for its multiple medicinal properties [18; 19]. The triterpenoids in bitter gourd not only have the potential to prevent and manage diabetes but also have antineoplastic effects. For instance, mashinic acid with high antioxidant activity [20; 21] can protect against alcohol-induced liver oxidative stress and inflammatory injury by inhibiting the P38 MAPK pathway [22].