Triterpenoids- A Comprehensive Overview of their Role in Plants and Applications

Triterpenoids and triterpenes are a diverse class of natural compounds found in various organisms, with plants being a rich source of these bioactive molecules. These compounds are derived from the isoprenoid pathway and play crucial roles in plant physiology, defense mechanisms, and have a wide range of applications in various industries. Many of them have significant pharmacological activities and have been used comprehensively as medicinal ingredients (Darshani et al., 2022). In this discussion, we will explore the structure, biosynthesis, functions, and applications of triterpenoids in plants.

Structure and Biosynthesis

Triterpenoids are a subgroup of terpenoids, which are organic compounds consisting of repeating units of isoprene. Triterpenoids specifically consist of six isoprene units, forming a 30-carbon skeleton. The most common triterpenoid precursor in plants is 2,3-oxidosqualene, which undergoes cyclization and modifications to yield diverse triterpenoid structures.

The biosynthesis of triterpenoids involves various enzymatic reactions, and the key enzymes include squalene synthase, oxidosqualene cyclases, and cytochrome P450 monooxygenases. These enzymes catalyze the cyclization and oxidation reactions necessary for the formation of different triterpenoid compounds.

The starting point is via mevalonic acid or 2-C-methyl-D-erythritol-4-phosphate (non-mevalonate) pathway to synthesize inositol pyrophosphate (IPP), the primary C-5 unit.

The structural diversity of triterpenoids arises from variations in these enzymatic reactions and modifications.

Role in Plants

Triterpenoids play multifaceted roles in plants, contributing to their growth, development, and defense mechanisms. Some of the key functions include:

1. Structural Components: Triterpenoids contribute to the structural integrity of plant cell membranes and wax layers. They are essential components of cuticular waxes, providing a protective barrier against environmental stresses, including water loss and pathogen attacks.
2. Defense Mechanisms: Triterpenoids serve as potent defense compounds against herbivores, pathogens, and pests. Some triterpenoids have antimicrobial properties, inhibiting the growth of bacteria and fungi. Additionally, they can act as feeding deterrents for herbivores, protecting plants from being consumed.
3. Signaling Molecules: Certain triterpenoids function as signaling molecules in plant communication. They are involved in the regulation of various physiological processes, including growth, development, and responses to environmental stimuli.
4. Secondary Metabolites: Triterpenoids are part of the secondary metabolites produced by plants. These compounds, although not directly involved in primary metabolic processes, play crucial roles in adaptation to the environment and interactions with other organisms.

Applications

The diverse chemical structures and biological activities of triterpenoids have led to their exploration and utilization in various applications, ranging from medicine to industry. Some notable applications include:

1. Pharmaceuticals: Triterpenoids have demonstrated a wide range of pharmacological activities, including anti-inflammatory, antioxidant, antiviral (Darshani et al., 2022) and anticancer properties. Compounds like oleanolic acid and ursolic acid, which belong to the triterpenoid group, have shown promising potential in the development of pharmaceutical drugs. Other applications include acting as hemolytic agents.
2. Cosmetics: Triterpenoids are utilized in the cosmetic industry for their skin-beneficial properties. They contribute to the formulation of skincare products due to their moisturizing, anti-aging, and anti-inflammatory effects.
3. Food and Beverages: Some triterpenoids present in plants are used as flavoring agents in the food and beverage industry. They contribute to the aroma and taste of certain fruits, vegetables, and herbs.
4. Biofuels: Triterpenoids derived from plant sources have gained attention as potential feedstocks for biofuel production. These compounds, when extracted from renewable plant resources, offer a sustainable alternative to traditional fossil fuels.
5. Pesticides: Certain triterpenoids exhibit insecticidal and fungicidal activities, making them attractive candidates for the development of eco-friendly pesticides. These natural compounds can be used as alternatives to synthetic chemical pesticides, contributing to sustainable agriculture practices.
6. Biological Activities: Triterpenoids have been studied for their diverse biological activities, including antiviral, antifungal, and anti-diabetic properties. Researchers continue to explore their potential applications in various therapeutic areas.

Conclusion

Triterpenoids, with their intricate structures and versatile functions in plants, have become subjects of extensive research and applications. From their fundamental roles in plant physiology to their diverse applications in pharmaceuticals, cosmetics, and other industries, triterpenoids showcase the intersection of biology and chemistry. As our understanding of these compounds deepens, the potential for discovering new applications and harnessing their benefits for human well-being and environmental sustainability continues to expand.

References

Darshani, P., Sen Sarma, S., Srivastava, A. K., Baishya, R., & Kumar, D. (2022). Anti-viral triterpenes: a review. Phytochemistry Reviews, 21(6), pp. 1761-1842