Microwave Assisted Synthesis and Evaluation of Pyrrole Derivative

Heterocyclic compounds represent an important class of organic molecules due to their broad applications in medicinal chemistry and pharmaceutical sciences. Among nitrogen-containing heterocycles, pyrrole has gained considerable attention because of its unique structural characteristics and diverse biological activities. Pyrrole (C₄H₅N) is a five-membered aromatic heterocyclic compound containing one nitrogen atom, where the lone pair of electrons contributes to aromatic stabilization according to Hückel’s rule [1]. The electron-rich nature of pyrrole makes it highly reactive toward electrophilic substitution reactions, especially at C-2 and C-5 positions.

Pyrrole derivatives occur naturally in several biologically important molecules such as heme, chlorophyll, vitamin B12, and cytochromes, indicating their significance in essential physiological functions [2]. Owing to these properties, pyrrole has become an important pharmacophore in medicinal chemistry.

Pyrrole derivatives possess a wide spectrum of biological activities including antimicrobial, anti-inflammatory, antioxidant, antiviral, anticancer, anticonvulsant, and antihypertensive effects [3]. The biological activity of pyrrole compounds mainly depends upon the nature and position of substituents attached to the pyrrole ring. Structural modifications at various positions influence pharmacokinetic properties, receptor binding affinity, and biological selectivity [4].

Several clinically important drugs contain pyrrole or pyrrole-related scaffolds such as Atorvastatin, Sunitinib, Ketorolac, and Tolmetin, demonstrating the pharmaceutical significance of this nucleus [5]. Among various synthetic methods available for pyrrole synthesis, the Paal–Knorr synthesis is one of the most commonly used methods involving cyclization of 1,4-dicarbonyl compounds with primary amines or ammonia [6].

Recently, the development of environmentally friendly synthetic approaches has attracted significant interest in medicinal chemistry research. Microwave-Assisted Organic Synthesis (MAOS) has emerged as an efficient green chemistry technique due to its ability to reduce reaction time, improve yield, minimize solvent use, and decrease energy consumption [7]. Microwave-assisted synthesis of pyrrole derivatives has shown considerable advantages over conventional heating methods by providing rapid and efficient synthesis under eco-friendly conditions.

Molecular docking has also become an important computational approach in drug discovery for predicting ligand–receptor interactions and evaluating binding affinity. It provides useful information regarding molecular interactions and helps in identifying compounds with potential biological activity [8].

Therefore, pyrrole derivatives synthesized using microwave-assisted approaches represent promising candidates for the development of novel biologically active compounds with improved pharmacological potential.

MATERIALS AND METHODS

Pyrrole derivatives were synthesized by microwave-assisted Paal–Knorr synthesis using corresponding amines and diketones. Synthesized compounds were purified and analyzed by TLC and spectroscopic techniques.

Synthesized Compounds

N-(3,4-dimethoxybenzyl)-2,5-dimethylpyrrole

Analytical Results

The synthesized compounds showed acceptable melting point, Rf value and percentage yield (75–76%). Spectral studies confirmed successful synthesis.

Table no.1:-Analytical description of N-(3,4-dimethoxybenzyl)-2,5-dimethylpyrrole

Parameter	Property
Chemical name	N-(3,4-dimethoxybenzyl)-2,5-dimethylpyrrole
Molecular formula	C₁₅H₁₉NO₂
Structure
Molecular weight	245.32 g/mol
Physical state	Solid
Appearance	Off-white to pale yellow crystalline powder*
Odor	Characteristic
Solubility	Soluble in methanol, ethanol, chloroform, DMSO; sparingly soluble in water*
Nature	Aromatic heterocyclic compound
Melting point	110-115oc
Rf value (TLC)	0.48
Microwave irradiation synthesis % yield	75%

Fig..no.1:- IR spectra of 3,4-dimethoxybenzylamine

Table .no.2:-IR spectra of 3,4-dimethoxybenzylamine interpretation

Peak (cm⁻¹)	Functional Group	Interpretation
3269	N–H stretching	Indicates presence of primary amine group
3091	Aromatic C–H stretching	Confirms aromatic ring
1559	N–H bending	Confirms amino group
1500	Aromatic C=C stretching	Indicates aromatic structure
1242	Ar–O–CH₃ stretching	Indicates methoxy group
1137	C–O stretching	Confirms ether linkage
1051	C–O stretching	Supports presence of methoxy group

Fig.no2:- UV spectrum of 3,4-dimethoxybenzylamine

Table.no.3:- UV spectrum of 3,4-dimethoxybenzylamine Interpretation

Wavelength (nm)	Assignment	Interpretation
205–210	π→π* transition	Indicates presence of aromatic ring system
225–240	Conjugated absorption band	Confirms conjugation within the molecule
290–310	n→π* transition	Indicates presence of heteroatom-containing groups

Fig.no.3:-Mass spectrum of 3,4-dimethoxybenzylamine

Table.no.4:-Mass spectrum of 3,4-dimethoxybenzylamine Interpretation

m/z Value	Fragment / Ion	Interpretation
183.05 [M+H]⁺	Molecular ion peak	Corresponds to protonated molecular ion of synthesized compound
182.05	Molecular mass (M)	Indicates molecular weight of compound

Fig.no.4:-Carbon 13 NMR spectrum of 3,4-dimethoxybenzylamine

Table.no.5:-Carbon 13 NMR spectrum of 3,4-dimethoxybenzylamine Interpretation

Chemical Shift (δ ppm)	Carbon Assignment	Interpretation
148–161	Methoxy substituted aromatic carbons	Indicates aromatic carbons attached to electronegative oxygen atoms
108–129	Aromatic carbons	Confirms presence of aromatic ring carbons
55.5	OCH₃ carbons	Indicates methoxy carbon atoms
~40	Benzylic CH₂ carbon	Indicates methylene carbon attached to aromatic system

Fig.no.5:-H1 NMR spectroscopy of 3,4-dimethoxybenzylamine

Table.no.6:-H1 NMR spectroscopy of 3,4-dimethoxybenzylamine Interpretation

Chemical Shift (δ ppm)	Proton Assignment	Interpretation
6.84–6.97	Aromatic protons	Indicates aromatic hydrogen atoms
3.45–3.64	CH₂–NH₂	Indicates methylene group attached to amino group
~3.8	OCH₃	Indicates methoxy groups
5.39–5.43	NH₂ protons	Confirms amino protons

Conclusion of the study:

Fig.no.6:- 3D binding pose of N-(3,4-dimethoxybenzyl)-2,5-dimethylpyrrole

Fig.no.7:- 2D interaction diagram of N-(3,4-dimethoxybenzyl)-2,5-dimethylpyrro

Table no.8:-Molecular Docking and MM-GBSA Results

Compound Code	Docking Score (kcal/mol)	MMGBSA Binding Energy (kcal/mol)	Human Oral Absorption (%)	Lipinski Rule
A.J.3	-4.72	-38.86	100	Passed

Interpretation

The molecular docking results indicated that the synthesized pyrrole derivative exhibited favorable interaction with the target receptor protein. Compound A.J.3 showed a docking score of −4.72 kcal/mol, indicating good receptor binding affinity and stronger interaction with the active site residues.

The MMGBSA binding energy value further supported the docking result. Compound A.J.3 displayed a ΔG bind value of −38.86 kcal/mol, suggesting higher binding stability with the receptor protein.

The ADME study predicted that compound A.J.3 possesses 100% human oral absorption and satisfied Lipinski's Rule of Five, indicating favorable drug-likeness properties and supporting its potential as a bioactive molecule for further investigation.

CONCLUSION

The present molecular docking and ADME study demonstrated that the synthesized pyrrole derivatives possess promising receptor binding characteristics and acceptable drug-likeness properties. Compound A.J.3 exhibited comparatively better binding affinity and stability among the tested compounds and may serve as a potential lead compound for further biological investigation.

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