Design And Synthesis of Sulfoxamide Modified Pantoprazole Analogue for Enhanced PPI Activity

1.1 Background on Peptic Ulcers and Gastroesophageal Reflux Disease (GERD)

Acid-related disorders represent a significant category of gastrointestinal pathologies that affect a vast proportion of the global population, contributing substantially to morbidity and healthcare costs [Engevik et al., 2020]. These problems mostly happen when there is an imbalance between hostile substances like gastric acid (hydrochloric acid) and pepsin and the body's defences that keep the mucosa healthy, like bicarbonate secretion, mucus production, and good blood flow [Laine et al., 2016]. When the physiological regulation of gastric acid secretion is disrupted, or when mucosal defenses are overwhelmed, it leads to a spectrum of conditions ranging from mild dyspepsia to severe ulcerative diseases.

Gastro-oesophageal Reflux Disease (GERD) is likely the most common of these disorders. It is characterised as a chronic condition in which the retrograde movement of gastroduodenal contents into the oesophagus results in distressing symptoms and possible mucosal damage [Vakil et al., 2006]. The pathogenesis of GERD is multifaceted, primarily influenced by the transitory relaxation of the Lower Esophageal Sphincter (LES), compromised esophageal clearance, and delayed stomach emptying. The chronic exposure of the esophageal epithelium to acidic refluxate can lead to erosive esophagitis and, in severe cases, Barrett’s esophagus, which is a precursor lesion for esophageal adenocarcinoma [Maregalia et al., 2012]. The condition is clinically characterized by persistent heartburn and acid regurgitation, significantly impairing the patient's quality of life.

Peptic Ulcer Disease (PUD) persists as a significant clinical problem, marked by the development of discrete lesions in the mucosal lining of the stomach (gastric ulcer) or the proximal duodenum (duodenal ulcer), penetrating the muscularis mucosae [Lanas & Chan, 2017]. The discovery of Helicobacter pylori (H. pylori), a gram-negative bacterium that colonises the stomach antrum and damages mucosal protective barriers, has transformed the understanding of the aetiology of PUD. In addition to infectious reasons, the prevalent utilisation of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) serves as a significant secondary factor. NSAIDs block cyclooxygenase (COX) enzymes, which lowers the production of cytoprotective prostaglandins and makes the mucosa more likely to be damaged by acid [Malfertheiner et al., 2009].

Gastric acid hypersecretion is a defining characteristic of Zollinger-Ellison Syndrome (ZES), in addition to these other illnesses. Zollinger-Ellison syndrome (ZES) is a serious disorder caused by a gastrin-secreting neuroendocrine tumour (gastrinoma) that is usually found in the pancreas or duodenum. The tumor releases excessive amounts of gastrin, stimulating the parietal cells to secrete massive volumes of hydrochloric acid, leading to intractable peptic ulcers and diarrhea [Jensen et al., 2021].

Despite the distinct etiologies of GERD, PUD, and ZES, they share a common therapeutic target: the reduction of gastric acidity. This shared pathophysiology underscores the critical importance of pharmacological agents capable of effectively suppressing acid secretion, specifically Proton Pump Inhibitors (PPIs), which target the final pathway of acid production—the H+/K+ ATPase enzyme [Shin & Kim, 2013].

1. 2. Proton Pump Inhibitors (PPIs) and the H+/K+ ATPase Enzyme

The gastric H+/K+ ATPase enzyme, sometimes called the "proton pump," is what makes gastric acid secretion happen. This enzyme is a member of the P-type ATPase family and is only found in the apical secretory membranes of stomach parietal cells [Shin et al., 2009]. This enzyme's job in the body is to use the energy from breaking down ATP to speed up the electroneutral exchange of cytoplasmic hydrogen ions (H+) for extracellular potassium ions (K+). This active transport mechanism is capable of generating a massive concentration gradient of over a million-fold, lowering the pH in the secretory canaliculus to less than 1.0 [Sachs et al., 2006].

Because the H+/K+ ATPase represents the terminal step in acid production—functioning downstream of the histamine (H2), gastrin (CCK2), and acetylcholine (M3) receptors—it constitutes the most effective pharmacological target for suppressing acid secretion. Inhibiting this single enzyme effectively blocks acid secretion regardless of the stimulating pathway.

1. 1. 1. The Benzimidazole Scaffold and Prodrug Activation

Proton Pump Inhibitors (PPIs), including Pantoprazole, Omeprazole, and Lansoprazole, share a common core structure: a 2-pyridylmethylsulfinylbenzimidazole scaffold. Chemically, these agents are weak bases with a pKa of approximately 4.0 (varying slightly among analogues). This physicochemical property is fundamental to their mechanism of action and tissue selectivity [Besancon et al., 1997].

Fig. 1.1: Representation of the chemical structure of 2-pyridylmethylsulfinylbenzimidazole.

PPIs are administered as inactive prodrugs. Being uncharged at neutral pH (7.4), they easily cross cell membranes and enter the parietal cell from the blood. However, once they diffuse into the highly acidic environment of the secretory canaliculus (pH < 1.0), they become protonated. This protonation traps the drug within the canaliculus (a phenomenon known as "ion trapping"), leading to a concentration accumulation of up to 1000-fold relative to the blood plasma [Roche, 2006].

1. 1. 2. Mechanism of Covalent Inhibition

The therapeutic efficacy of PPIs relies on an acid-catalyzed chemical rearrangement. Upon protonation at the benzimidazole nitrogen, the molecule undergoes an intramolecular rearrangement to form a reactive sulfenic acid, which rapidly dehydrates to form a cyclic sulfenamide intermediate.

This cyclic sulfenamide is an electrophile that reacts very quickly. It reacts only with the thiol (-SH) groups that are easy to reach on the extracellular domain of the H+/K+ ATPase alpha-subunit is cysteine residues. This reaction produces a stable, covalent disulphide link between the medication and the enzyme [Shin & Sachs, 2008].

The formation of this disulfide complex irreversibly inhibits the enzyme's catalytic activity. Consequently, acid secretion is halted and can only resume after the parietal cell synthesizes new H+/K+ ATPase molecules, a process that takes roughly 24 to 48 hours. This elucidates the reason for PPIs exhibiting an extended duration of action that endures well beyond the elimination of the medication from the plasma [Horn, 2000].

In the context of Pantoprazole, the binding is notably specific; it reacts with Cysteine-813 and Cysteine-822 deep within the membrane transport domain. This unique binding profile, particularly the interaction with Cys-822, is often cited as a reason for Pantoprazole's distinct stability and lower reversibility compared to other PPIs [Shin et al., 2011].

1. 3. Profile of Pantoprazole

Since it came out in the 1990s, pantoprazole has been a key part of treating acid-related gastrointestinal diseases. It is a second-generation proton pump inhibitor (PPI).

1. 1. 1. Structural Characteristics

Fig. 1.2: Representation of the chemical structure of Pantoprazole.

It is distinguished from other PPIs (like Omeprazole or Lansoprazole) by the presence of a difluoromethoxy group at the benzimidazole ring and a dimethoxy substitution on the pyridine ring. These substitutions exert significant electronic effects, influencing the molecule's pKa values (pKa1 ≈ 3.92 pyridinium N; pKa2 ≈ 8.19 benzimidazole N). This specific pKa profile makes Pantoprazole more stable at neutral pH compared to Omeprazole, preventing premature activation before it reaches the parietal cell [Kromer et al., 1998].

1. 1. 2. Current Clinical Use

Pantoprazole is used for the short-term management of erosive oesophagitis linked to GERD, the preservation of erosive oesophagitis healing, and the treatment of pathological hypersecretory disorders, including Zollinger-Ellison syndrome. It is also commonly used off-label to prevent stress ulcers in critically ill patients and to get rid of Helicobacter pylori as part of triple or quadruple therapy regimens [Stollman et al., 2010].

1. 1. 3. Limitations of Current Therapy

Despite its widespread use, Pantoprazole therapy is associated with specific pharmacokinetic and pharmacodynamic limitations that leave a gap for therapeutic improvement:

• Short Plasma Half-Life: Like most PPIs, Pantoprazole has a short plasma elimination half-life (t1/2) of approximately 1.0 to 1.9 hours [Wedemeyer, et al., 2014]. Although the biological effect lasts longer due to irreversible enzyme binding, the drug is cleared from the blood rapidly. This means that new proton pumps synthesized by the parietal cell during the night (when no drug is present in the plasma) remain active, leading to Nocturnal Acid Breakthrough (NAB), a phenomenon where intragastric pH drops below 4.0 for more than an hour at night in over 70% of patients [Peghini et al., 1998].
• Delayed Onset of Action: Pantoprazole is a prodrug that requires accumulation in the secretory canaliculi. Because it only inhibits active proton pumps, and not all pumps are active at any given moment, it typically takes 3 to 5 days of daily dosing to achieve steady-state inhibition (maximum antisecretory effect) [Shin et al., 2013]. This delay is suboptimal for patients requiring immediate symptom relief.
• CYP2C19 Metabolism Dependency: The liver breaks down pantoprazole a lot, mostly with the help of the cytochrome P450 isozyme CYP2C19 (demethylation) and to a lesser extent with CYP3A4. While it has a lower affinity for CYP2C19 than Omeprazole, its efficacy is still influenced by genetic polymorphisms. Patients who are "Rapid Metabolizers" (common in certain populations) may clear the drug too quickly, leading to therapeutic failure, while "Poor Metabolizers" risk higher systemic exposure [Chaudhry et al., 2010].
• Acid Instability: The sulfoxide core is inherently acid-labile. Without robust enteric coating, the drug degrades in the stomach lumen before absorption, losing efficacy.

1.4 Problem Statement

The clinical efficacy of current Proton Pump Inhibitors (PPIs) is fundamentally limited by their short plasma residence time and metabolic instability. While Pantoprazole offers improved pH stability over first-generation PPIs, it still suffers from rapid clearance and susceptibility to CYP2C19-mediated metabolism. This results in the "unmet medical need" of controlling nocturnal acid secretion and reducing inter-patient variability.

The core limitation lies in the sulfoxide (S=O) pharmacophore. While essential for the rearrangement to the active sulfenamide, the sulfoxide moiety is metabolically vulnerable to both oxidation (to sulfone) and reduction (to sulfide).

1.5 The Proposed Solution

This research proposes the bioisosteric replacement of the sulfoxide oxygen with a nitrogen species to form a Sulfoxamide (also known as Sulfoximine, S(O)=N-R) derivative.

Sulfoxamides are emerging as "chameleon" bioisosteres in medicinal chemistry. They retain the tetrahedral geometry and hydrogen-bonding capability of sulfoxides but exhibit significantly enhanced metabolic stability and chemical robustness [Frings et al., 2017].

By modifying Pantoprazole with a sulfoxamide core, this research aims to:

• Enhance Metabolic Stability: Resist CYP2C19 degradation, potentially extending the plasma half-life and reducing genetic variability.
• Sustain Acid Suppression: Provide a longer window of active drug presence to counter nocturnal acid breakthrough.
• Maintain Target Affinity: Preserve the ability to covalently bind to Cysteine-813/822 of the H+/K+ ATPase.

Therefore, the design and synthesis of a Sulfoxamide-modified Pantoprazole analogue represents a novel approach to developing a "next-generation" PPI with superior pharmacokinetic properties.

1.6 AIM AND OBJECTIVES

Aim: The aim of my present work is “Design and Synthesis of Sulfoxamide Modified Pantoprazole Analogue for Enhanced PPI Activity”, which was fulfilled by following objectives:

Objectives:

• To evaluate physicochemical parameters of Pantoprazole – Melting Point, solubility.
• To design and Synthesis of Sulfoxamide Modified Pantoprazole Analogue for Enhanced PPI activity using appropriate scheme.
• To characterize Sulfoxamide-modified Pantoprazole analogue – Melting Point, Solubility, % yield, UV, IR, NMR, MASS.

REVIEW OF LITERATURE

2. 1 Description of Pantoprazole

Many researchers have examined Pantoprazole due to its chemical nature as a substituted benzimidazole sulfoxide, characterized by a difluoromethoxy group (-OCHF₂) on the benzimidazole ring and dimethoxy groups (-OCH₃) on the pyridine moiety, which confer distinct physicochemical stability and targeted biological activity (Kromer et al., 1998). Its structure allows it to act as a selective prodrug by undergoing acid-catalyzed rearrangement to a reactive cyclic sulfenamide, and its ability to form stable covalent disulfide bonds allows it to irreversibly inhibit the H+/K+ ATPase enzyme, making it a cornerstone compound in studies on gastric acid suppression, biochemical pharmacology, and medicinal chemistry optimization (Shin & Sachs, 2008).

14.

Structure

3.2 METHOD

3.2.1 Determination of Melting Point

Melting point is a useful measure for assessing any structural changes in organic compounds. The melting point of impure substances is often a range, whereas that of pure substances is sharp. Fill a capillary tube with a little, dry, finely powdered sample of Pantoprazole to get the melting point of a chemical. Carefully heat the tube in a melting point apparatus. Note the melting point of the sample; this will serve as an indicator of the beginning of the melting range. Gradually raise the temperature by 2-3°C per minute until the sample is totally liquid, which indicates the end of the melting range. Note both the initial and final temperatures, Pure substances usually melt within a narrow temperature range of 1-3°C, but the presence of impurities tends to broaden this ranges it. Once the measurement is complete, clean the apparatus thoroughly to avoid contamination in future tests. Reddy et al. [45]

3.2.2 Determination of Solubility

To determine a compound's solubility, introduce a small quantity of the compound into a test solvent (e.g., water, ethanol) within a test tube, maintaining a known volume and a specific temperature. In a study assessing the solubility profile of Pantoprazole, a 10 mg medication sample was dissolved in 10 ml of various solvents. Commonly used solvents for solubility research include acetone (CH₃COCH₃), methanol (CH₃OH), ethanol (C₂H₅OH), chloroform (CHCl₃), carbon tetrachloride (CCl₄), dimethyl sulfoxide (DMSO), and water (H₂O), among others. Ardita Veseli et al. [46]

3.2.3 Determination of Percentage Yield 

Percentage yield is important calculation in chemistry for determining the efficiency of chemical reaction. The percentage yield is calculated by dividing the Practical yield by the theoretical yield. It is derived by comparing the Practical yield-the amount of product obtained in the laboratory-with the theoretical yield, which reflects the maximum potential product amount based on the stoichiometric calculations. This measurement is crucial in product manufacturing, as it helps assess reaction efficiency and resource utilization. Shimaa Baraka et al. [47]

Equation (3.1) can be used to calculate the Percentage Yield as:

% Yield=Practical Yield ÷Theorectical Yield×100

 

3.3 SYNTHESIS METHODOLOGY

Step-by-step synthesis designed to produce the target Sulfoxamide Modified Pantoprazole Analogue. In which involves constructing the benzimidazole core, coupling it with the pyridine ring, and performing the late-stage functionalization to introduce the sulfoxamide group.

The synthesis of Sulfoxamide modified Pantoprazole analogue is the very crucial and important phase, which are followed by the three steps:

• Synthesis of the substituted 2-mercaptobenzimidazole core.
• Coupling with the pyridine moiety to form the sulfide intermediate (Pro-Pantoprazole).
•  Sulfoximination to convert the sulfoxide to the sulfoxamide.

Step 1: Synthesis of the substituted 2-mercaptobenzimidazole core

To synthesize 5-(difluoromethoxy)-2-mercaptobenzimidazole (5-(difluoromethoxy)-1H-benzo[d]imidazole-2-thiol), the essential scaffold that provides acid stability.

Reaction:

 

 

Fig. 3.1: Representation of the chemical structure of 5-(difluoromethoxy)-2-mercaptobenzimidazole.

 

 

Fig. 3.2: Representation of the chemical structure of 5-(difluoromethoxy)-2-(((3,4-dimethoxypyridin-2-yl) methyl) thio)-1H-benzo[d]imidazole

 

 

Fig. 3.3: Final synthetic scheme for the sulfoxamide modified Pantoprazole analogue.

Derivatives	Structure	IUPAC Name
3a		5-(difluoromethoxy)-2-mercaptobenzimidazole,
3b		5-(difluoromethoxy)-2-(((3,4-dimethoxypyridin-2-yl)methyl)thio)-1H-benzo[d]imidazole
3c		5-(difloromethoxy)-2[(3,4-dimethoxypyridin-2yl) methy)sulfonimidoyl]-1H-benzimidazole

 

 

 

 

Fig. 4.2 Mass Spectra of 3a.

 

 

Fig. 4.3 ¹H-NMR Spectra of 3a.

 

 

Fig. 4.4 FT-IR Spectra of 3b.

 

 

Fig. 4.5 Mass Spectra of 3b.

 

 

 

 

Fig. 4.7 FT-IR Spectra of 3c.

 

 

Fig. 4.8 Mass Spectra of 3c.

 

 

Fig. 4.9 ¹H-NMR Spectra of 3c.

DISCUSSION

In the above-mentioned experimental study, Pantoprazole was chosen for further analysis and sourced from Central Drug House.

Based on our findings, we believe Pantoprazole. is a safe, effective, and promising Proton pump inhibitor drug. However, Further investigation is important to ascertain the molecular pathways and the role of Pantoprazole in Peptic ulcer and a variety of gastrointestinal disorder, such as Gastritis.

The physiochemical characteristics of Sulfoxamide derivatives were assessed using standardized techniques. The melting points of the Sulfoxamide derivatives were determined using a capillary melting point apparatus in accordance with published research. Their solubility in various solvents was also evaluated, providing critical information for method development and dosage form selection.

In the current study, Sulfoxamide derivatives (3a-3c) were synthesized using methods described in the literature [33]. These derivatives were developed utilizing various secondary amines, and their physiochemical properties-including melting point, solubility, and yield percentage-were assessed. Additionally, the derivatives were characterized using FTIR, NMR, and MASS Spectroscopy to identify bonds and functional groups. The results confirmed the successful synthesis of Sulfoxamide derivatives.

Post Project beneficial for environment

Pantoprazole is one of several proton pump inhibitors (PPIs) used to treat acid-related gastrointestinal diseases (GERD, peptic ulcers, etc). However, the extensive global consumption, rapid metabolism, and subsequent excretion of these pharmaceuticals pose an emerging challenge in environmental science, particularly concerning the accumulation of active pharmaceutical ingredients (APIs) in wastewater and aquatic ecosystems. Developing novel sulfoxamide-modified analogues with enhanced metabolic stability can provide more potent, longer-lasting therapeutics, thereby reducing the overall dosage required by patients and decreasing the pharmaceutical footprint entering the environment. Develop a series of novel sulfoxamide-modified benzimidazole derivatives using environmentally friendly, highly selective catalytic synthetic pathways that minimize the use of harsh, toxic oxidants.

Need for doing this project

The fast metabolic clearance of present proton pump inhibitors is a key component of the pharmacological management of peptic ulcers and gastro-oesophageal reflux disease (GERD), although it often causes acid breakthrough throughout the night. Enhanced metabolic stability and bioisosteric properties found in this Sulfoxamide Modified Pantoprazole Analogue, allows it to resist rapid CYP2C19 degradation and provide sustained inhibition of the H⁺/K⁺ ATPase enzyme. Novel compounds, such as potassium-competitive acid blockers and extended-release PPI formulations, are being explored but require more advanced development to balance efficacy with long-term safety profiles. New synthetic analogues of established conventional drugs are often more effective due to improved chemical stability, prolonged half-life, specific target binding affinity, and pharmacokinetic consistency. These advantages allow this compound to better meet the demands of clinical treatments for conditions like severe GERD, Zollinger-Ellison syndrome, and other refractory acid-peptic diseases.

Outcomes of the Project

This project has several significant outcomes, spanning both scientific advancements and environmental benefits.

Scientific Outcomes

a. Novel Sulfoxamide-Modified Benzimidazole Compounds

• Development of a library of newly synthesized sulfoxamide-modified Pantoprazole analogues with confirmed H⁺/K⁺ ATPase inhibitory activity.
• Identification of lead compounds with optimized metabolic stability, extended half-life, and selectivity for proton pump inhibition.

b. Structure-Activity Relationship (SAR) Insights

• Comprehensive understanding of the chemical features, specifically the bioisosteric replacement of the sulfoxide center with a sulfoxamide group, that enhance H⁺/K⁺ ATPase inhibitory activity.
• Guidance for the rational design of future metabolically stable proton pump inhibitors in gastroenterological drug discovery.

Environmental Benefits

Development of environmentally compatible compounds that degrade naturally without accumulating in the food chain.

CONCLUSION

In this study, successful synthesis of the novel Sulfoxamide Modified Pantoprazole Analogue was achieved, driven by its well-documented primary antisecretory mechanism, irreversible H⁺/K⁺ ATPase inhibition, and the superior metabolic stability properties of sulfoximines. The synthesized compound undertook thorough physicochemical characterization, including assessments of solubility, melting point, and percentage yield. The findings indicate that the novel Sulfoxamide Modified Pantoprazole Analogue holds significant promise as a gastrointestinal therapeutic agent, demonstrating improved chemical stability and efficacy in preliminary evaluations.

More investigation is required to understand the exact molecular mechanisms behind the pharmacokinetic advantages of the Sulfoxamide Modified Pantoprazole Analogue, in light of these encouraging findings. This study concentrated on the synthesis of the novel Sulfoxamide Modified Pantoprazole Analogue, driven by literature reports of the powerful proton pump inhibitory and metabolically resistant characteristics of the sulfoxamide functional group. Its possible therapeutic uses in acid-related gastrointestinal disorders, such as peptic ulcers and Gastro-oesophageal Reflux Disease (GERD), as well as its involvement in important pathways for the secretion of stomach acid, should be the subject of future research.

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