INTRODUCTION:

Damage-causing free radicals are often deactivated by antioxidants at the molecular and cellular level. Oxidation processes generate free radicals, which set off a series of events that result in cell death and a host of degenerative illnesses. Reactive oxygen species have been shown to play a role in the spread of progressive illnesses. Antioxidant activity is the capacity of substances to stop or reduce cellular damage brought on by reactive oxygen species (ROS) and free radicals¹.

Free radicals are unstable chemicals that can contribute to oxidative stress, which damages cells and is a contributing factor in a number of diseases, such as cancer, heart disease, and neurological problems. Compounds known as antioxidants work to counteract free radicals and shield the organism from oxidative stress². Many foods include them, but especially fruits, vegetables, nuts, seeds, and whole grains. Vitamins C, E, flavonoids, and selenium are examples of common antioxidants. These are essential substances that support the fight against oxidative stress in living things, which can result in a number of illnesses, such as cancer and heart problems³. Natural antioxidants found in plants include flavonoids, carotenoids, phenolic chemicals, and vitamins. These phytochemicals are essential for defending cells from the harm that free radicals can do. Research into the antioxidant activity of plants not only highlights their health benefits but also underscores their potential as therapeutic agents in modern medicine. This exploration of plant-based antioxidants opens avenues for developing natural remedies and enhancing dietary strategies for disease prevention. The study of antioxidant activity is essential for understanding how these compounds can contribute to health and prevent diseases. To assess how well various substances scavenge free radicals, researchers frequently measure antioxidant activity using a variety of assays, including the DPPH (2, 2-diphenyl-1-picrylhydrazyl) assay, FRAP (Ferric Reducing Antioxidant Power) assay, and ORAC (Oxygen Radical Absorbance Capacity) assay. The aim of the current review is to indicate the current progress in the novel drugs, phytocompounds and plants proved for antioxidant activity.

Plants proved for antioxidant activity:

Turmeric (Curcuma longa):

Turmeric, particularly its active compound curcumin, is known for its strong antioxidant properties. Curcumin is the major active constituent followed by demethoxycurcumin and bisdemethoxycurcumin. Pharmacological importance can be attributed to polyphenols namely, curcuminoids (1-5%)⁴. Free radicals can result in oxidative stress and cell damage; antioxidants aid in their neutralization. Because it can scavenge free radicals and increase the activity of the body's own antioxidant enzymes, curcumin is thought to have antioxidant properties. Curcumin may offer protection against oxidative stress-related diseases such as cancer, heart disease, and neurological conditions, according to research. Turmeric is a useful ingredient in endorsing health and also for preventing illness since the anti-inflammatory properties also enhance its antioxidant activity⁵. Integrating turmeric into the diet can be beneficial, though the bioavailability of curcumin is relatively low. Combining it with black pepper (which contains piperine) can significantly enhance its absorption. Curcumin, the active compound in turmeric, exhibits significant antioxidant activity, contributing to its anti-inflammatory and health-promoting effects.

Spinach (Spinacia oleracea):

Spinach is abundant in vitamins E, C and as carotenoids, all contributing to its antioxidant activity⁶. Spinach is rich in various antioxidants, as well as phytochemicals corresponding flavonoids and carotenoids⁷. Through their ability to neutralize free radicals and lessen cellular damage, these substances aid in the fight against oxidative stress.

Key antioxidants in spinach include:

1. Vitamin C: An effective antioxidant that promotes immunological function and guards against oxidative stress.

2. Beta-carotene: A precursor to vitamin A, which has antioxidant properties and supports eye health⁸.

3. Two carotenoids that are very good for eye health and may lower the risk of age-related macular degeneration are lutein and zeaxanthin⁹.

4. Quercetin: A flavonoid with anti-inflammatory and antioxidant effects¹⁰.

Aloe Vera (Aloe barbadensis):

Aloe Vera contains antioxidants such as polyphenols, flavonoids, ascorbic acid, beta-carotene, and alpha-tocopheralkaloids, Aloe Vera leaf gel shows antioxidant capacity¹¹. Because of the abundance of vitamins it contains, aloe vera is well-known for its antioxidant qualities, minerals, besides bioactive compounds.

Key components that contribute to its antioxidant activity include:

1. Vitamins: Aloe Vera contains vitamins A, C, and E, which are well-known antioxidants that help neutralize free radicals.

2. Phenolic Compounds: These include flavonoids and other polyphenols that provide significant antioxidant effects, helping to reduce oxidative stress ¹².

3. Anthraquinones: These substances work as anti-inflammatory agents and have antioxidant qualities.

4. Studies show that aloe vera can help skin health, shield cells from oxidative stress, and possibly lower the risk of a number of oxidative stress-related disorders.

Neem (Azadirachta indica):

Crude extract of neem leaves had moderate antioxidant activity against the DPPH radical. The extract contained secondary metabolites like phenols, tannins, flavonoids, and flavanols. The abundant phytochemical content of neem (Azadirachta indica) is responsible for its well-known antioxidant qualities¹³.

Key components contributing to its antioxidant activity include:

1. Flavonoids: Quercetin and kaempferol, two flavonoids found in neem, can suppress oxidative stress and free radicals¹⁴.

2. Triterpenoids: Strong antioxidants such as nimbidin and azadirachtin are among the compounds that give neem its anti-inflammatory effects¹⁵.

3. Phenolic substances are important for scavenging free radicals and shielding cells from oxidative damage¹⁶.

Mentha piperita: Mint:

Mint has a potent antioxidant effect because it includes a lot of flavonoids (such as luteolone, quartzetin, rosmarinic, chlorogenic, and vanillic acid) and phenolic acids (such as caffeine, rosmarinic, and chlorogenic acid)¹⁷.

Key components contributing to its antioxidant activity include:

1. Flavonoids: Mint contains flavonoids like hesperidin and rosmarinic acid, that help to scavenge free radicals and as to diminish oxidative stress¹⁸.

2. Phenolic Compounds: These compounds, including caffeic acid and other polyphenols, contribute significantly to mint's ability to combat oxidative damage¹⁹.

3. Vitamins: Mint is a source of vitamins A and C both of which have antioxidant effects and support overall health.

According to research, mint's antioxidant properties may strengthen the immune system, lower the risk of chronic illnesses, and guard against cellular damage.

Lemon (Citrus limon):

Lemons have many antioxidants, including flavonoids, limonoids, kaempferol, quercetin, and ascorbic acid. It is well renowned for having strong antioxidant qualities, mostly because of how much vitamin C and other healthy substances it contains²⁰.

Key components contributing to its antioxidant activity include:

1. Vitamin C: A powerful antioxidant that helps neutralize free radicals, supporting immune function and skin health²¹.

2. Flavonoids: Lemons contain various flavonoids, such as hesperidin and eriocitrin, which have been shown to enhance antioxidant activity and protect against oxidative stress²².

3. Citric Acid: While primarily known for its role in metabolism, citric acid also contributes to antioxidant effects by enhancing the bioavailability of other antioxidants.

4. Essential Oils: Lemon essential oil contains compounds like limonene, which exhibit antioxidant in addition anti-inflammatory belongings²³. A combination of those antioxidants in lemons helps protect against cellular damage and may reduce the risk of chronic diseases, including heart disease and certain cancers. Incorporating lemon into the diet can enhance overall health and well-being.

Coriander (Coriandrum sativum):

It is also known as cilantro, that possesses distinguished antioxidant possessions attributed to its annoying content of various bioactive composites.

Crucial components contributing to its antioxidant activity include:

1. Flavonoids: Coriander is rich in flavonoids such as quercetin and kaempferol, that help to neutralize all free radicals then diminish oxidative stress²⁴.

2. Phenolic Compounds: These compounds, including caffeic acid and rosmarinic acid, contribute significantly to coriander's antioxidant effects, aiding in the protection against cellular damage²⁵.

3. Vitamins: The vitamins A and C found in coriander are crucial for antioxidant defense²⁶.

4. Essential Oils: Coriander's essential oils, particularly linalool, had been revealed to have antioxidant besides anti-inflammatory possessions²⁷.

Research indicates that the antioxidant activity of coriander may help protect against various diseases linked to oxidative stress, comprising disease of heart besides certain cancers²⁸.

Rosmarinus officinalis: Rosemary

It is well known for having potent antioxidant qualities, which are mostly brought about by the abundance of different phytochemicals it contains.

Key components contributing to its antioxidant activity:

1. One of rosemary's most researched antioxidants, carnosic acid, is known to scavenge free radicals and shield cells from oxidative damage ²⁹.

2. Rosmarinic acid is a potent antioxidant with anti-inflammatory qualities that lowers oxidative stress and may boostimmunity³⁰.

3. Flavonoids: Rosemary's total antioxidant activity is attributed to a number of flavonoids, including luteolin and apigenin.

According to research, rosemary's antioxidant properties may help prevent a number of illnesses associated with oxidative stress, such as different cancers and neurological diseases³¹.

Phytoconstituents proved for antioxidant activity:

Phytocompounds of Bacopa monnieri:

While traditionally a natural remedy, various synthetic derivatives of compounds in Bacopa have shown antioxidant properties. Because it contains a lot of bioactive chemicals, including bacosides, it has significant antioxidant action.

Here are some key points regarding its antioxidant properties:

1. Scavenging Free Radicals: Bacosides and other phytochemicals in Bacopa monnieri are effective at neutralizing free radicals, which helps reduce oxidative stress in cells.

2. Prevention of Oxidative Damage: Research has indicated that Bacopa monnieri can prevent oxidative damage to cellular constituents like proteins, lipids, and DNA, which may reduce the likelihood of developing chronic illnesses ³³.

3. Strengthening Antioxidant Enzymes: The extract may increase the actions of endogenous antioxidant enzymes, including catalase and superoxide dismutase (SOD), strengthening the body's defenses against harm.

4. Neuroprotective Effects: Through combating oxidative stress, Bacopa monnieri may help protect neurons and support cognitive health, making it beneficial in the context of neurodegenerative diseases.

5. Anti-inflammatory Possessions: The extract's ability to reduce inflammation also complements its antioxidant effects, as inflammation can contribute to oxidative damage.

Overall, Bacopa monnieri extract is recognized for its potential to enhance antioxidant defences, support cognitive function, and promote overall health.

Curcumin Analogues:

The key ingredient in turmeric, curcumin, is being researched extensively for its potential as an antioxidant, but various Analogues of curcumin have also been developed to enhance its effectiveness.

Here are some notable aspects of curcumin Analogues concerning antioxidant activity:

1. Increased Potency: Many curcumin Analogues have been synthesized to improve the potency of antioxidant activity compared to curcumin itself. Their capacity to scavenge free radicals and prevent oxidative stress is frequently improved by these changes³⁴.

2. Improved Bioavailability: Curcumin has low bioavailability, but some Analogues are designed to be more easily absorbed in the body, thus increasing their effectiveness in exerting antioxidant effects.

3. Diverse Mechanisms: Curcumin Analogues may act through various mechanisms, such as up regulating the expression of antioxidant enzymes (e.g., Nrf2 pathway activation) and enhancing the body's overall antioxidant capacity.

4. Comparative Studies: Research has shown that certain curcumin Analogues, such as bisdemethoxycurcumin and other modified forms, exhibit stronger antioxidant properties than curcumin itself, making them potential candidates for therapeutic applications³⁵.

5. Potential in Disease Prevention: Due to their antioxidant activity, curcumin Analogues are being explored for their potential in preventing or treating various diseases associated with oxidative stress, including cancer, neurodegenerative disorders, and cardiovascular diseases.

Overall, curcumin Analogues represent a promising area of research in enhancing antioxidant activity and developing more effective therapeutic agents.

Quercetin derivatives:

Synthetic modifications of quercetin enhance its antioxidant capacity and bioavailability. The antioxidant qualities of quercetin, a flavonoid present in many fruits and vegetables, are widely recognized. Research on quercetin derivatives has revealed enhanced antioxidant activity and other beneficial effects.

Here are some key points regarding quercetin derivatives and their antioxidant activity:

1. Enhanced Potency: Many derivatives of quercetin, such as quercetin glycosides and quercetin aglycone, have been synthesized to improve their antioxidant potency. These modifications can increase their ability to scavenge free radicals more effectively than quercetin itself.

Bioavailability Improvements: Some derivatives are designed to enhance solubility and bioavailability, allowing for better absorption in the body. For example, quercetin-3-O-glucoside has shown improved stability and absorption³⁶.

Mechanisms of Action: Quercetin derivatives can act through manifold mechanisms:

2. Reactive oxygen species synthesis (ROS).

a. Up regulating antioxidant enzymes like superoxide dismutase (SOD) and catalase.

b. Modulating signalling pathways related to oxidative stress.

3. The potential of quercetin derivatives to prevent or treat a range of oxidative stress-related ailments, including cancer, neurological disorders, and cardiovascular diseases, has been investigated due to their antioxidant qualities.

4. Comparative Studies: Some studies have indicated that certain quercetin derivatives, like methylated forms (e.g., isoquercitrin), exhibit superior antioxidant effects compared to quercetin, highlighting the importance of structural modifications.

In summary, quercetin derivatives represent a promising area of research, with potential applications in health promotion and disease prevention due to their enhanced antioxidant activity³⁷.

Synthetic Compounds:

R- (+)-Borneol:

A synthetic derivative that exhibits significant antioxidant effects, particularly in protecting against oxidative stress. R- (+)-borneol is a bicyclic monoterpene with notable antioxidant properties. It is commonly found in essential oils from various plants, such as rosemary and mint.

Here are some key aspects of R- (+)-borneol in relation to antioxidant activity:

1. The ability of R- (+)-borneol to efficiently scavenge free radicals has been demonstrated to help reduce oxidative stress and shield cells from harm.

2. Mechanisms of action comprise modulating antioxidant enzyme activity, enhancing the body's natural defences.

3. Neuroprotective Effects: Studies suggest that R- (+)-borneol may offer neuroprotective benefits, potentially decreased risk of neurodegenerative illnesses and defense against oxidative damage to neural cells.

4. Anti-inflammatory Possessions: Besides antioxidant activity, R- (+)-borneol exhibits anti-inflammatory possessions, that can further contribute to its defensive role against oxidative stress-related conditions.

5. Applications: Given its antioxidant properties, R- (+)-borneol is being explored for various applications, including in cosmetics, pharmaceuticals, and food preservation, where reducing oxidative damage is beneficial.

Overall, R- (+)-borneol shows promise as a natural antioxidant with potential health benefits, particularly in combating oxidative stress and supporting overall health ³⁸.

N-Acetylcysteine:

It is a precursor to the cysteine amino acid and plays a significant role in antioxidant activity. It contributes to the synthesis of glutathione, one of the body's most important antioxidants. By increasing glutathione levels, NAC helps combat oxidative stress and neutralizes free radicals, which can damage cells and tissues³⁹.

Additionally, NAC exhibits direct antioxidant properties, scavenging reactive oxygen species (ROS) and reducing inflammation. Its potential therapeutic applications include mitigating oxidative stress-related circumstances like chronic obstructive pulmonary disease, liver diseases, and neurodegenerative disorders. Overall, NAC's ability to enhance the body's antioxidant defences makes it a valuable compound in both clinical and preventive health contexts⁴⁰.

Novel drugs for antioxidant activity:

Mitochondrial-targeted antioxidants:

Compounds like MitoQ and SkQ1 specifically target mitochondria, where a significant amount of oxidative stress occurs, improving cellular health. Mitochondrial-targeted antioxidants are designed to specifically target the mitochondria, the powerhouse of the cell, where the majority of reactive oxygen species (ROS) are generated ⁴¹. These antioxidants aim to reduce oxidative stress within mitochondria, which is implicated in various diseases and aging processes⁴².

Key Types of Mitochondrial-Targeted Antioxidants:

1. MitoQ (Mitoquinone): A derivative of coenzyme Q10 that accumulates in mitochondria and reduces oxidative stress by directly scavenging free radicals ⁴³.

2. SkQ1: A synthetic antioxidant that contains a cationic moiety allowing it to enter mitochondria, where it mitigates ROS and protects against mitochondrial dysfunction⁴⁴.

3. TPP+ (Triphenyl phosphonium): A positively charged molecule that can transport other antioxidants into the mitochondria, enhancing their protective effects.

4. MitoSOD: A mitochondrial-targeted superoxide dismutase mimetic that specifically targets superoxide radicals⁴⁵.

Benefits of Mitochondrial-Targeted Antioxidants:

· Reduced Oxidative Damage: They help prevent mitochondrial DNA damage and lipid peroxidation.

· Improved Cellular Function: By maintaining mitochondrial health, they support ATP production and overall cellular energy metabolism⁴⁶.

· Potential Therapeutic Applications: These antioxidants show promise in treating neurodegenerative diseases, cardiovascular diseases, and metabolic disorders.

Resveratrol Analogues:

Resveratrol is a polyphenolic compound known for its antioxidant properties, and its Analogues have been developed to enhance its efficacy and bioavailability⁴⁷. These Analogues exhibit various antioxidant activities and have potential therapeutic applications.

Key Features of Resveratrol Analogues:

1. Enhanced Stability and Bioavailability: Many Analogues are designed to be more stable and bioavailable than resveratrol itself, which is rapidly metabolized.

2. Structural Modifications: Changes to the chemical structure, such as modifications to the hydroxyl groups or the addition of different functional groups, can enhance antioxidant activity⁴⁸.

Notable Resveratrol Analogues and their Activities:

· Pterostilbene: A naturally occurring Analogue that has greater antioxidant activity and better bioavailability than resveratrol. It has the ability to efficiently scavenge free radicals and lessen oxidative stress.

· Dihydrostilbene: Analogue shows increased stability and has been considered for its capability to impede oxidative damage in various cell models.

· 4, 4’-Dihydroxy-trans-stillbene: This compound has demonstrated potent antioxidant effects, protecting cells from oxidative stress.

· Silybin-Resveratrol Conjugates: These combine resveratrol with silybin (from milk thistle), enhancing antioxidant properties and protective effects against oxidative damage in liver cells ⁴⁹.

Mechanisms of Action:

a. Free Radical Scavenging: Many Analogues can directly neutralize reactive oxygen species (ROS).

b. Enhancing Endogenous Antioxidants: Superoxide dismutase and catalase are two examples of antioxidant enzymes whose expression can be upregulated by certain substances.

c. Modulating Signalling Pathways: Resveratrol Analogues can influence pathways such as Nrf2, which regulates the antioxidant response⁵⁰.

Synthetic flavonoids:

Synthetic flavonoids are designed to mimic or enhance the properties of naturally occurring flavonoids. They often feature modifications in their chemical structure to improve their efficacy, stability, and bioavailability.

Key Characteristics of Synthetic Flavonoids:

1. Chemical Modifications: Alterations in hydroxyl groups, ring structures, and side chains can enhance antioxidant properties and cellular absorption.

2. Targeted Activity: Many synthetic flavonoids are designed to target specific oxidative stress pathways or cellular mechanisms⁵¹.

Examples of Synthetic Flavonoids:

· Quercetin Derivatives: Modified forms of quercetin often show increased antioxidant capacity and improved pharmacokinetics. For instance, quercetin glycosides may enhance solubility and bioavailability.

· Flavonolignans: These compounds combine flavonoid and lignin structures, exhibiting strong antioxidant properties. They can protect against oxidative damage in various biological models.⁵²

· Chalcone Derivatives: Chalcones are precursors to flavonoids and possess significant antioxidant activity. Synthetic chalcone derivatives can be optimized for better radical scavenging ability.

· Synthetic Flavonoid Conjugates: Combining flavonoids with other bioactive compounds can create synergistic effects, enhancing overall antioxidant activity.⁵³

Mechanisms of Antioxidant Activity:

a. Scavenging Free Radicals: Synthetic flavonoids can directly neutralize reactive oxygen species (ROS), reducing oxidative damage.⁵⁴

b. Modulating Antioxidant Enzyme Activity: Superoxide dismutase and glutathione peroxidase are examples of endogenous antioxidants whose expression they can upregulate.

c. Inhibiting Oxidative Stress Pathways: Some synthetic flavonoids can inhibit pathways that lead to increased ROS production, such as NF-kB signalling.⁵⁵

Applications:

Synthetic flavonoids have potential therapeutic applications in various fields, including:

Cardiovascular Health:

Lowering oxidative stress can help reduce heart disease risk.

· Neuroprotection: They may protect against neurodegenerative diseases by combating oxidative damage in neuronal cells. ⁵⁶

· Anti-inflammatory Effects: Many synthetic flavonoids exhibit anti-inflammatory properties, complementing their antioxidant activity.

L-theanine derivatives:

L-thiamine (vitamin B1) derivatives have gained attention for their potential antioxidant activities. These derivatives can enhance the ability of cells to fight oxidative stress.⁵⁷

Mechanism of Action: Metal ions can be chelated, free radicals can be scavenged, and other antioxidants can be renewed by L-thiamine and its components, such as vitamin C and E. This multifaceted action helps protect cells from oxidative damage.

1. Derivatives and Activities: Research has revealed that certain modifications of the thiamine structure can improve its stability and bioavailability, leading to enhanced antioxidant effects. For instance, lipid-soluble thiamine derivatives might be more effective in crossing cell membranes. ⁵⁸

2. Therapeutic Implications: These derivatives may have therapeutic potential in circumstances categorized by oxidative stress, and cardiovascular disorders. Studies suggest they could improve cellular resilience and reduce inflammation. ⁵⁹

3. Research Developments: Ongoing research is focused on synthesizing new thiamine derivatives and evaluating their efficacy in vitro and in vivo. Results indicate promising antioxidant properties, but more clinical studies are needed to establish their benefits.

4. Overall, L-thiamine derivatives represent a promising area of research in the development of antioxidants with potential health benefits. ⁶⁰

Nrf2 activators:

Nrf2 (nuclear factor erythroid 2-related factor 2) is a key regulator of the antioxidant response. Activators of Nrf2 enhance the expression of various antioxidant enzymes and protective proteins, contributing to cellular defence against oxidative stress. Here are some important points regarding Nrf2 activators and their antioxidant activity: ⁶¹.

Mechanism of Activation: Under normal conditions, Nrf2 is kept in the cytoplasm and degraded. When Nrf2 is exposed to oxidative stress or specific substances, it moves to the nucleus and attaches itself to DNA's antioxidant response elements (ARE), which stimulates the transcription of genes related to antioxidant defense.

Natural Activators: Many natural compounds have been identified as Nrf2 activators, including:

· Sulforaphane: Found in cruciferous vegetables, it is a potent activator of Nrf2.

· The main ingredient in turmeric, curcumin, has anti-inflammatory and antioxidant qualities.

· Resveratrol: A polyphenol found in grapes, which also exhibits cardio protective effects ⁶².

· Quercetin: A flavonoid with strong antioxidant properties.

1. Synthetic Activators: Researchers are also developing synthetic compounds that can activate Nrf2. These include:

2. Dimethyl fumarate: Used in multiple sclerosis treatment, it has been shown to activate Nrf2 and provide neuroprotection.

3. Tert-butylhydroquinone (tBHQ): Commonly used as a food preservative, it activates Nrf2 and exhibits antioxidant effects.

4. Health Implications: Nrf2 activators have potential therapeutic benefits in various conditions accompanying with oxidative stress, like neurodegenerative ailments, cardiovascular diseases, and cancer. They may help in reducing inflammation and improving metabolic health.

5. Research Directions: Ongoing studies aim to better understand the pathways involved in Nrf2 activation and its role in disease prevention. The goal is to identify more effective Nrf2 activators and explore their applications in clinical settings ⁶³.

Overall, Nrf2 activators represent a promising avenue for enhancing antioxidant defences and improving health outcomes associated with oxidative stress.

CONCLUSION:

Antioxidant activity for different plants varies widely due to the presence of diverse phytochemicals, including polyphenols, flavonoids, and vitamins. Generally, plants like berries, green tea, and certain herbs exhibit high antioxidant capacity, and lower the chance of developing chronic illnesses by shielding cells from oxidative stress. The effectiveness of these antioxidants is influenced by factors such as plant species, extraction methods, and environmental conditions. Overall, incorporating a variety of antioxidant-rich plants into the diet can enhance health and promote longevity. To completely comprehend these drugs' processes and synergistic effects, more research is required. In general, eating a range of plants high in antioxidants can improve health and lengthen life. To completely comprehend these drugs' processes and synergistic effects, more research is required.

CONFLICT OF INTEREST:

The authors declare no conflict of interest regarding this study.

ACKNOWLEDGEMENTS:

The management of Marri Laxman Reddy Institute of Pharmacy, Dundigal, Telangana, India, is appreciated by the authors for providing the resources needed to complete the review.

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Received on 22.12.2024 Revised on 31.03.2025

Accepted on 09.06.2025 Published on 10.02.2026

Available online from February 16, 2026

Research J. Pharmacy and Technology. 2026;19(2):946-954.

DOI: 10.52711/0974-360X.2026.00134

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Advances in Novel Drugs, Plants and Phytoconstituents proved for Antioxidant Activity - A Comprehensive Review