Product name: Protocatechualdehyde
Synonym name:
Catalogue No.: BP1154
Cas No.: 139-85-5
Formula: C₇H₆O₃
Mol Weight: 138.122
Botanical Source: heartwood of Cassia garrettiana
Physical Description: Powder
Type of Compound: Phenols

Purity: 95%~99%
Analysis Method: HPLC-DAD or/and HPLC-ELSD
Identification Method: Mass, NMR
Packing: Brown vial or HDPE plastic bottle

Storage: Store in a well closed container, protected from air and light. Put into refrigerate or freeze for long term storage.
Whenever possible, you should prepare and use solutions on the same day. However, if you need to make up stock solutions in advance, we recommend that you store the solution as aliquots in tightly sealed vials at -20℃. Generally, these will be useable for up to two weeks.

The product could be supplied from milligrams to grams, up to kilograms
Inquire for bulk scale.

Descriptions:
3,4-Dihydroxybenzaldehyde, isolated from the outer skin of green ,has been shown to inhibit the growth of Gloeosporium musarum, a fungus which causes ripe fruit rot in the banana.[1]
3,4-Dihydroxybenzaldehyde can inhibit oxidative DNA damage and apoptosis via its antioxidant activity.[2]
3,4-Dihydroxybenzaldehyde inhibits the phosphotransferase activity of CKII with IC(50) of about 783 microM, it may function by inhibiting oncogenic disease, at least in part, through the inhibition of CKII activity.3]
3,4-Dihydroxybenzaldehyde inhibits the H2O2-induced apoptosis of granulosa cells, promotes estradiol secretion in granulosa cells and enhanced the mRNA expression levels of steroidogenic factor 1, a promoter of key steroidogenic enzymes. [4]
3,4-Dihydroxybenzaldehyde has tyronase inhibitory effect.[5]

References:
[1] Mulvena D, Webb E C, Zerner B. Phytochemistry, 1969, 8(2):393-5.
[2] Jeong J, Hong S H. Phytomed Intl J Phytother Phytopharm, 2009, 16(1):85-94.
[3] Lee B H, Yoon S H, Kim Y S, et al. Nat Prod Res, 2008, 22(22):1441-50.
[4] Kono R, Nomura S, Okuno Y, et al. Acta Histochem Cytoc, 2014, 47(3):103-12.
[5] Shin Dong-Soo, Paik, Do-Hyeon, Yoon Do-Young, et al. The Korea Jounnal of Herbology, 2006, 21(2):1-7.
[6] Xia C Y, Chen L M, Hu W X. Synthetic chemistry, 2004, 12 (5): 484-6.

HPLC of Protocatechualdehyde

Storage conditions：Short-term storage at 2~8℃, long-term storage at -20 ~ -80℃

Introduction/Overview

Natural products, as an important treasure trove for drug discovery, play an irreplaceable role in the history of human disease prevention and treatment. Among them, polyphenolic compounds have attracted much attention due to their extensive biological activity and low toxicity. Protocatechhualdehyde (PCA), also known as 3,4-dihydroxybenzaldehyde, is a simple polyphenolic compound isolated from traditional Chinese medicine plants such as Salvia miltiorrhiza Bunge. Its CAS number is 139-85-5 and its molecular formula is C7H6O3. Despite its relatively simple structure, protocatechuic aldehyde exhibits remarkable and diverse biological activities, including antioxidant, anti-inflammatory, antibacterial, cardiovascular protective, and neuroprotective effects, making it highly applicable in multiple medical fields, especially in the prevention and treatment of cardiovascular and cerebrovascular diseases. This article aims to systematically review the chemical properties, plant sources, pharmacological activities, molecular mechanisms of action, pharmacological evaluation, and clinical application prospects of protocatechuic aldehyde, in order to provide comprehensive scientific references for the in-depth research and development of this natural product.

Chemical structure and physicochemical properties

The chemical structure of protocatechuic aldehyde consists of a benzene ring, with a hydroxyl group (- OH) attached to the 3rd and 4th positions of the benzene ring, forming a catechol structure, and an aldehyde group (- CHO) attached to the 1st position. This structure gives it the chemical properties of both catechins and benzaldehyde. The structure of catechol is a powerful electron donor, endowing protocatechuic aldehyde with excellent antioxidant capacity. It can effectively scavenge free radicals such as superoxide anions and hydroxyl radicals, and may exert antioxidant effects by chelating metal ions. Aldehyde is a highly reactive electrophilic group, making it easy to undergo Schiff base reactions with the amino groups of proteins, which may be related to its partial biological activity and metabolic pathways.

From the perspective of pharmacological parameters, the molecular weight of protocatechuic aldehyde is 138.1220, which belongs to small molecule compounds. The calculated lipid water partition coefficient (LogP) is approximately 0.9682, indicating that it has moderate lipophilicity and is conducive to transmembrane transport. The topological polar surface area (TPSA) is 57.53 Å ², which is relatively small and indicates good membrane permeability. The water solubility data is 10.2780 mg/mL, indicating that it has a certain solubility in water, which is a favorable factor for its absorption and distribution in organisms. It is particularly important that the predictive model shows a high blood-brain barrier permeability, which provides an important material basis for its application in central nervous system related diseases such as neurodegenerative diseases and cerebral ischemia. In addition, the predicted risk of hERG inhibition is' no ', indicating a lower potential risk of arrhythmia; The Ames test value is 1.2, indicating a low risk of mutagenicity, and these preliminary data provide a positive signal for its safety.

Plant sources and extraction methods

Protocatechol is widely distributed in nature, but its most famous and primary plant source is Salvia miltiorroza, a plant in the family Lamiaceae and genus Salvia. Danshen, also known as "red root", is an essential medicine in traditional Chinese medicine that promotes blood circulation, removes blood stasis, and relieves pain. It is commonly used to treat cardiovascular and cerebrovascular diseases. The combination of protocatechuic aldehyde, danshensu, salvianolic acid, tanshinone, and other water-soluble active ingredients in Danshen is one of the important material foundations for its cardiovascular protective effects. In addition to Danshen, protocatechuic aldehyde is also present in various other plants, such as olive leaves, honeysuckle, and some edible fruits and vegetables, but the content is usually low.

The extraction of catecholaldehyde from plant materials mainly depends on its polarity and solubility. Traditional extraction methods include:
1. Solvent extraction method The most commonly used method. Usually, water, methanol, ethanol, or alcohol water mixed solvents with different ratios are used for reflux extraction or ultrasound assisted extraction. Due to the water-soluble nature of catechol, the aqueous extraction method is more economical and environmentally friendly, but the extract contains more impurities. The alcohol extraction method (such as 70% -95% ethanol) has higher efficiency and better selectivity.
2. Modern separation and purification technology After filtration and concentration, the crude extract needs to be further purified to obtain high-purity protocatechuic aldehyde. Common techniques include:
* Macroporous adsorption resin chromatography The adsorption of polar compounds by resin and elution with different concentrations of alcohol solutions can effectively enrich protocatechuic aldehydes.
* Silica gel column chromatography Traditional but effective separation methods commonly use gradient elution systems such as chloroform methanol or petroleum ether ethyl acetate.
* Preparation type high performance liquid chromatography (HPLC): is the final and critical step in obtaining high-purity monomeric compounds, with the advantages of high resolution and efficiency.
* High Speed Counter Current Chromatography (HSCCC)A liquid-liquid distribution chromatography technique that does not require a solid phase carrier and is suitable for the preparation and separation of polyphenolic compounds that are thermally unstable and prone to adsorption loss.

In recent years, green extraction technologies such as supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), and pressurized liquid extraction (PLE) have gradually been applied to the extraction of natural products to improve efficiency and reduce the use of organic solvents.

Pharmacological activity research

Numerous in vitro and in vivo studies have confirmed that protocatechuic aldehyde has a wide range of pharmacological activities, with its core functions revolving around antioxidant and anti-inflammatory effects, and extending to multiple systems.

1. Cardiovascular protective effect This is the most in-depth and promising field of research on protocatechuic aldehyde. Research has shown that protocatechuic aldehyde can:

   • Protect endothelial function of blood vessels By upregulating the expression of endothelial nitric oxide synthase (eNOS/NOS3), it promotes the production of nitric oxide (NO), thereby relaxing blood vessels, inhibiting platelet aggregation, and leukocyte adhesion.
   • Inhibit atherosclerosis Inhibit low-density lipoprotein (LDL) oxidation through strong antioxidant activity; Downregulate the expression of vascular cell adhesion molecule-1 (VCAM1) and intercellular adhesion molecule-1 (ICAM1), and reduce the adhesion and migration of monocytes to the vascular endothelium; Regulating lipid metabolism related targets.
   • Anti myocardial ischemia/reperfusion injury Relieve oxidative stress and inflammatory response in myocardial cells, inhibit cell apoptosis, and reduce the size of myocardial infarction.
   • Antithrombotic It may exert its effect by affecting platelet activation and aggregation related pathways.

2. Antioxidant and anti-aging effects The catechol structure of protocatechualdehyde is the chemical basis for its strong antioxidant capacity. It can directly eliminate various reactive oxygen species (ROS) and reactive nitrogen species (RNS), activate the endogenous antioxidant defense system of cells, such as the nuclear factor E2 related factor 2 (Nrf2) pathway, and upregulate the expression of antioxidant enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GPx). In anti-aging research, it has been shown to delay cellular replicative aging, protect mitochondrial function, and may act by affecting aging related signaling pathways such as SIRT1 and AMPK.

3. Anti inflammatory and immune regulatory effects Protocatechol can significantly inhibit the excessive production of inflammatory mediators (such as tumor necrosis factor - α, interleukin-6, nitric oxide) in macrophages induced by stimuli such as lipopolysaccharide (LPS). Its anti-inflammatory mechanism involves inhibiting the activation of key inflammatory signaling pathways such as nuclear factor kappa B (NF - κ B) and mitogen activated protein kinases (MAPKs).

4. Antibacterial and antiviral activity Research has shown that protocatechuic aldehyde has inhibitory effects on various Gram positive and Gram negative bacteria (such as Staphylococcus aureus and Escherichia coli), and its mechanism may be related to the destruction of bacterial cell membrane integrity and inhibition of biofilm formation. In addition, there are reports that it has certain inhibitory activity against certain viruses, such as influenza virus.

5. Neuroprotective effect Thanks to its excellent blood-brain barrier permeability, protocatechuic aldehyde has shown potential in neurodegenerative disease models. In the Alzheimer's disease model, it can reduce the neurotoxicity induced by β - amyloid protein; In the cerebral ischemia model, it can alleviate neuroinflammation and cell apoptosis, and protect neurological function.

6. Other activities: The study also suggests that protocatechuic aldehyde may have anti-tumor (by inducing apoptosis and inhibiting metastasis), anti diabetes (improving insulin resistance), liver protection and other activities, but the research in these fields remains to be in-depth.

Mechanism of action and molecular targets

The pleiotropic pharmacological effects of protocatechuic aldehyde stem from its regulation of multiple molecular targets and signaling pathways. Based on the provided target information and existing literature, its core mechanism of action can be summarized as follows:

1. Vascular protection and anti atherosclerosis related targets：

   • Adhesive molecules (VCAM1, ICAM1, SELP)Protocatechuic aldehyde can significantly inhibit the expression of these adhesion molecules on endothelial cells induced by inflammatory cytokines (such as TNF - α), thus blocking the adhesion of leukocytes to vascular endothelium, which is a key step in the initial stage of atherosclerosis.
   • Nitric oxide synthase 3 (NOS3)Upregulating the expression and activity of NOS3, increasing the bioavailability of NO with vasodilatory, anti-inflammatory, and anti proliferative effects, is the core mechanism for improving endothelial function.
   • Peroxisome proliferator activated receptor gamma (PPARG)PPAR γ is a nuclear receptor involved in regulating lipid metabolism, glucose homeostasis, and inflammation. Protocatechol may act as a regulator of PPAR γ, exerting anti-inflammatory and metabolic improving effects.
   • Protein kinase B (AKT1)AKT is the core kinase of the cell survival pathway (PI3K/Akt). Protocatechol can protect vascular endothelium by activating Akt signaling, inhibiting endothelial cell apoptosis, and promoting eNOS activation.

2. Cardiovascular function regulation related targets：

   • Angiotensin converting enzyme (ACE)ACE is a key enzyme in the renin-angiotensin system, catalyzing the conversion of angiotensin I into the potent vasoconstrictor angiotensin II. Protocatechol may have ACE inhibitory activity, leading to hypotensive and cardioprotective effects.
   • β 2-adrenergic receptor (ADRB2)It may affect vascular function and cardiac rhythm by regulating this receptor.
   • Potassium voltage-gated channel subfamily H member 2 (KCNH2/hERG)Although drug prediction shows no hERG inhibition, as an important cardiac ion channel, it is a target that requires continuous attention for its cardiovascular safety.

3. Metabolic regulatory targets：

   • 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR)This is the rate limiting enzyme in the cholesterol synthesis pathway. Protocatechol may regulate blood lipids by affecting the activity or expression of HMGCR.

4. Core signaling pathway：

   • NF - κ B pathway Protocatechol inhibits the degradation of I κ B α and nuclear translocation of NF - κ B p65 subunit, widely suppressing the expression of downstream inflammatory factors and adhesion molecules, which is the main mechanism of its anti-inflammatory effect.
   • Nrf2/ARE pathway Protocatechol can promote the transfer of Nrf2 from cytoplasm to nucleus, activate antioxidant response elements (ARE), and drive the expression of a series of phase II detoxifying enzymes and antioxidant enzymes (such as HO-1, NQO1), which is the core mechanism of its antioxidant stress response.
   • MAPK pathway It can inhibit the excessive phosphorylation of p38, JNK, and ERK, thereby regulating cell proliferation, differentiation, inflammation, and apoptosis.

Evaluation of drug properties and pharmacokinetics

Although protocatechuic aldehyde exhibits excellent pharmacological activity, its success as a drug depends on its pharmacological properties, namely "pseudo pharmacological" and pharmacokinetic properties.

1. Absorption, distribution, metabolism, excretion (ADME)：

   • absorb As a small molecule, moderate LogP, and water-soluble compound, protocatechuic aldehyde is expected to have good passive diffusion absorption in the gastrointestinal tract. But the aldehyde and phenolic hydroxyl groups in its structure may make it easy to undergo binding reactions or be metabolized by microorganisms in the intestine.
   • distribution Its smaller molecular weight and moderate lipophilicity are beneficial for its distribution in the body. The predicted high blood-brain barrier permeability is its significant advantage, providing the possibility for the treatment of central nervous system diseases.
   • Metabolism Protocatechol is rapidly and widely metabolized in the body. The main metabolic pathways include: ① Aldehyde oxidation Under the action of aldehyde dehydrogenase, it is converted into protocatechuic acid, which is its main metabolite and also has biological activity; ② Methylation mediated by catechol-O-methyltransferase (COMT)Phenolic hydroxyl groups are methylated to produce methylated products; ③ Combined with glucuronic acid or sulfuric acid Forming a more water-soluble complex for easier excretion. Liver microsomal enzymes (such as CYP450) may also be involved in their metabolism.
   • excretion Metabolites are mainly excreted through the kidneys and urine.

2. Challenges and optimization of drug development：

   • chemical stability The structure of catechol is easily oxidized by air, especially under alkaline conditions, to form quinone substances. Aldehyde groups are also relatively active. This poses challenges for drug storage and formulation preparation.
   • Metabolism is too fast Rapid metabolism (especially first pass effects) may lead to low oral bioavailability and difficulty in maintaining blood drug concentrations.
   • Formulation strategy To overcome the above problems, strategies that can be adopted include: ① Structural modification Protecting phenolic hydroxyl or aldehyde groups (such as making prodrugs), or synthesizing derivatives with higher activity and better stability; ② New drug delivery system Develop drug delivery systems such as nanoparticles, liposomes, microspheres, etc. to improve stability, delay release, and enhance targeting (such as targeting cardiovascular or inflammatory sites); ③ combination therapy Combined with metabolic enzyme inhibitors (such as COMT inhibitors), or in combination with other active ingredients (such as other components in Danshen), may produce synergistic effects and improve pharmacokinetics.

Clinical application prospects and prospects

The diverse biological activities of protocatechuic aldehyde, especially its excellent cardiovascular protection, antioxidant and anti-inflammatory effects, have shown broad application prospects in the prevention and treatment of various diseases.

1. Main application directions：

   • Cardiovascular and cerebrovascular diseases As a potential drug or functional component to prevent and treat atherosclerosis, hypertension, myocardial ischemia, cerebral infarction and other diseases. Can be developed as oral preparations (tablets, capsules) or injections for acute phase treatment.
   • Neurodegenerative diseases Develop drugs or health supplements for the adjuvant treatment of Alzheimer's disease and Parkinson's disease by utilizing their ability to penetrate the blood-brain barrier and provide neuroprotection.
   • Metabolic diseases As a PPAR γ modulator, it may have practical value in the treatment of diabetes and its complications (such as diabetes angiopathy).
   • Anti aging and health products Its strong antioxidant capacity makes it an ideal candidate ingredient for anti-aging cosmetics, functional foods, and dietary supplements.
   • Anti inflammatory adjuvant therapy Can be used as an adjuvant therapy for chronic inflammation related diseases, such as rheumatoid arthritis and inflammatory bowel disease.

2. Future research prospects：

   • In depth mechanism research Using proteomics, metabolomics, chemical proteomics and other technologies, systematically reveal the network mechanism of multi-target action and discover new targets of action.
   • Pharmacokinetic optimization Focus on addressing the issues of low oral bioavailability and fast metabolism. Through rational drug design, a series of derivatives are synthesized, and their activity, stability, and pharmacokinetic properties are systematically evaluated to search for better candidate drugs.
   • Preclinical and clinical research At present, most research is still at the stage of cell and animal models. It is urgent to carry out systematic preclinical safety evaluation (long-term toxicity, reproductive toxicity, etc.), and promote standardized clinical trials based on this to verify its effectiveness and safety in humans.
   • Development of new formulations Develop new intelligent formulations that can improve efficacy and reduce side effects by combining nanotechnology and targeted delivery technology.
   • Research on the Integration of Traditional Chinese and Western Medicine In depth exploration of the role and synergistic mechanism of protocatechuic aldehyde in Danshen compound (such as Danshen Sanqi and Danshen Chuanxiong), providing scientific basis for the modernization and internationalization of traditional Chinese medicine.

Conclusion

As a natural polyphenolic compound derived from Danshen, protocatechuic aldehyde has attracted sustained attention from the pharmacological community due to its simple structure and wide range of activities. From a chemical structure perspective, its catechol and aldehyde groups are key pharmacophores that exert biological activity. In terms of pharmacological effects, it demonstrates core value in cardiovascular protection, antioxidant, anti-inflammatory and other fields by regulating multiple key targets and pathways such as NOS3, NF - κ B, Nrf2, PPARG, etc. Despite facing challenges such as rapid metabolism and stability in drug development, its excellent blood-brain barrier permeability and preliminary safety predictions have laid a positive foundation for its development. In the future, through in-depth mechanism exploration, rational structural modification, innovative formulation technology, and rigorous clinical verification, protocatechualdehyde is expected to be successfully transformed from a potential natural active molecule into an innovative drug or key functional ingredient for the prevention and treatment of important human diseases such as cardiovascular and cerebrovascular diseases and neurodegenerative diseases, fully reflecting the immortal value of natural products in modern drug development.