Molecular docking evaluation of xanthone derivatives as ACE2 inhibitors

A comprehensive molecular docking study was conducted on xanthone derivatives to evaluate their binding energy toward ACE2, a critical receptor involved in SARS-CoV-2 viral entry. This analysis included the prototype inhibitor MLN-4067, natural xanthone derivatives, and their tautomers, totaling 237 compounds docked against the ACE2 (PDB ID: 1R4L) receptor. The docking scores for the ACE2-ligand complexes ranged from -9.26 to -1.26 kcal/mol. These negative values indicate favorable and spontaneous binding of the xanthone derivatives to the ACE2 inhibitory site, suggesting their potential as effective ACE2 inhibitors. The binding free energies (in kcal/mol) provide insight into each compound’s relative binding energy, with more negative scores indicating stronger binding [44]. Interestingly, when compared to the prototype inhibitor MLN-4067 (binding energy of -6.9 kcal/mol), five xanthone derivatives, XAN71, XAN72, XAN7, XAN70, and XAN68, demonstrated superior binding affinities, making them top candidates for ACE2 inhibition. To further confirm the effectiveness of the applied method, we perform prime MM-PBSA calculation via Glide [45].

Fig. 3

Molecular docking scores (A) Prime/MMGBSA binding energy (ΔGbind) (B) and molecular redocking scores (C) of the five lead compounds and the prototype inhibitor with ACE2

Table 1 Glide docking, prime MM/GBSA, and DFT optimization

As illustrated in Fig. 3; Table 1, the results from Glide docking reveal that XAN71 (-9.26 kcal/mol) and XAN72 (-8.93 kcal/mol) demonstrated the highest binding affinities compared to the reference inhibitor MLN-4760 (-6.91 kcal/mol). These values indicate that both xanthone derivatives exhibit strong interaction potential within the ACE2 active site, surpassing the prototype ligand’s ability to occupy and stabilize within the binding pocket. To further validate the binding stability, Prime MM/GBSA calculations were performed(L). This method integrates solvation effects and interaction energies, offering a more comprehensive evaluation of binding affinities. The results showed significantly lower (more favorable) binding energies for XAN71 (-109.94 kcal/mol) and XAN72 (-63.56 kcal/mol), underscoring their superior interaction stability compared to MLN-4760 (-29.07 kcal/mol). Interestingly, XAN71 exhibited the strongest binding energy among all tested compounds, highlighting its potential as a leading candidate for ACE2 inhibition. Following DFT optimization of the ligand geometries, redocking was conducted to refine and reassess the interaction energies. Post-DFT optimization, XAN71, and XAN72 retained their superior binding scores (-9.28 kcal/mol and − 8.95 kcal/mol, respectively). While XAN68 and the reference MLN-4067 also improved their scores, XAN7 exhibited an exception with the lowest score of 6.70 kcal/mol. The enhanced scores can be attributed to the optimized geometry, which likely improved spatial alignment and interactions with key residues within the binding pocket. The improved energy values demonstrate that DFT optimization enhances molecular conformations, resulting in better accommodation within the receptor’s active site and stronger binding interactions.

Interaction analysis

The activity of enzymes is closely associated with a specific region within their structure known as the active site, typically shaped as a cavity or groove. Ligands or inhibitors interact with the active site of the target enzyme by forming connections with surface residues located within this cavity, particularly with specific residues that characterize the active site. In the case of the ACE2 protein, the binding cavity is characterized by key residues, including TYR510, LYS363, ASP368, PRO346, ARG273, THR371 and HIS345. The prototype inhibitor MLN-4067 interacts with these residues within the ACE2 binding site, stabilizing its binding through van der Waals forces, hydrogen bonds, hydrophobic, and other key interactions that influence its inhibitory activity [25, 39]. Ligands interacting with this receptor are expected to develop a variety of interactions with some of these amino acids.

A detailed examination of the binding interactions of the top four xanthone derivatives with ACE2 (Fig. 4) reveals a complex network of stabilizing interactions within the ACE2 active site. These interactions include conventional and unconventional hydrogen bonds, hydrophobic contacts, π-π stacking, and electrostatic interactions, all contributing to enhanced binding energy and stability. The lead compounds exhibit key pharmacophore features that facilitate specific interactions with ACE2. For instance, XAN71 and XAN72 possess hydroxyl and carbonyl groups that enable strong hydrogen bonding with polar residues, while their methoxy groups contribute to hydrophobic interactions with residues such as TYR127 and LEU144. Notably, XAN72 forms unconventional C-H bonds with THR371, and both compounds support π-π interactions through their aromatic rings. Hydrophobic moieties further enhance van der Waals interactions, improving ligand fit within the ACE2 binding site. Among these compounds, XAN71 demonstrates the highest stability due to its formation of 11 conventional and 2 unconventional hydrogen bonds with critical residues, including THR371, ARG518, GLU402, GLU375, PRO346, and HIS345. Importantly, while XAN71 and XAN72 show favorable interactions with ACE2, they do not share common amino acid interactions with the reference inhibitor MLN-4067. This lack of overlap may provide a beneficial specificity for these xanthone derivatives as potential inhibitors against SARS-CoV-2.

Fig. 4

2D representation of the interaction of top 4 ranked ligands plus the reference with ACE2

Similarly, XAN72 demonstrates strong stabilization through 7 conventional and 8 unconventional hydrogen bonds with residues such as ARG273, HIS345, and TYR515. Both ligands also establish electrostatic interactions, with XAN71 forming π-anion contacts with GLU145 and XAN72 establishing interactions with LYS363 and GLU145. These π-π stacking interactions, particularly with TYR510 and HIS345, stabilize ligand orientation, enhancing fit within the binding pocket. The top 4 xanthone derivatives, including XAN68 and XAN70, demonstrate an improved interaction profile over MLN-4067. Their strong networks of hydrogen bonds, along with hydrophobic interactions, π-π stacking, and van der Waals forces, contribute to a more stable and energetically favorable ligand-protein complex. These interactions highlight the enhanced binding potential of xanthone derivatives as ACE2 inhibitors, offering greater stability and efficacy than the prototype compound, MLN-4067.

However, despite the favorable outcomes from the initial docking and re-docking processes, further analysis was essential to prove the stability and reliability of the interactions between the top 4 xanthone derivatives and the ACE2 receptor. Docking scores, while valuable, provide a static snapshot of the binding energy and do not account for the dynamic nature of molecular interactions within a biological environment [46]. Therefore, the top candidate compounds were subjected to (MD) simulations to obtain a more comprehensive understanding of the stability and effectiveness of the ligand-protein interactions.

Molecular dynamic simulation

MD simulations enable observing the behavior of ligand-protein complexes over time, replicating the fluctuating conditions present in a biological environment [47, 48]. This step provides crucial information on binding stability and interaction dynamics. By running MD simulations, we can assess the stability of the ligand within the ACE2 binding pocket. This helps to understand if the ligand maintains a stable binding pose over time or if it dissociates, which is critical for determining the practical efficacy of the compound [49]. The simulation also allows tracking of specific ligand-protein interactions, including hydrogen bonds, van der Waals contacts, and hydrophobic interactions. These dynamic interactions reveal how consistently the ligand engages with key amino acids in the binding pocket site, offering insights into the robustness of the binding energy [50]. After the MD runs of 200 ns were completed, post-MD were calculated and analyzed accordingly.

Post MD analysis

The binding of an inhibitor to a specific biological target typically induces structural and conformational changes that can significantly influence the target’s biological function [51]. To investigate these structural modifications and their potential impact on the protein’s activity, we evaluated the Root Mean Square Deviation (RMSD), Radius of Gyration (RoG), and Root Mean Square Fluctuation (RMSF) of the alpha carbon (Cα) atoms for both the unbound protein and the inhibitor-bound complex. These parameters were monitored throughout a 200 ns molecular dynamics (MD) simulation to provide insights into the dynamic behavior over time. Additionally, we performed Molecular Mechanics/Poisson–Boltzmann Surface Area (MM/PBSA) calculations [52, 53] as part of the post-MD analysis to assess the binding affinities of the potential inhibitors. This approach allows for a comprehensive evaluation of the free energy changes associated with ligand binding, further elucidating how the observed structural alterations correlate with binding stability and affinity changes.

Binding energy calculation using the MM-PBSA methodTable 2 Binding energy components of the molecular complexes in Kcal/mol

The MM/PBSA method, as described by Hollingsworth SA [49], was used to estimate the binding energy (ΔGbind) between a ligand and a receptor [51]. Following 200 ns MD simulations, we assessed the binding energy of the prototype ligand MLN-4067 at the active sites of ACE2. Table 2 presents the binding energy components of ACE2 complexes with MLN-4067 and xanthone derivatives XAN68, XAN70, XAN71, and XAN72. These values provide insight into each compound’s binding energy and interaction stability [49]. The prototype inhibitor MLN-4067 shows a substantial ΔG_gas (-573.86 kcal/mol), driven by strong electrostatic interactions. However, its binding energy ΔG_bind is moderate (-61.33 kcal/mol) due to a high solvation penalty (+ 512.52 kcal/mol), which offsets much of its gas-phase affinity. Among the xanthone derivatives, XAN71 exhibits the strongest binding energy with ΔG_bind = -70.97 kcal/mol, attributed to favorable van der Waals and electrostatic interactions with values of -76.65 and  -72.71 kcal/mol, respectively, combined with a moderate solvation penalty (+ 78.39 kcal/mol). XAN72 follows closely with ΔG_bind = -69.85 kcal/mol, also driven by strong gas-phase interactions. In contrast, XAN68 and XAN70 show lower binding affinities (ΔG_bind = -44.46 kcal/mol and -36.95 kcal/mol, respectively), largely as a result of less favorable gas-phase interactions and relatively high solvation penalties. These findings align with our earlier docking scores, where XAN71 and XAN72 displayed higher affinities than XAN68 and XAN70. The MM/PBSA calculations further confirm that XAN71 and XAN72 exhibit the highest binding stability, with XAN71 showing the strongest overall binding energy, positioning it as a promising candidate for ACE2 inhibition. The combination of balanced van der Waals, electrostatic contributions, and moderate solvation penalties enhances their binding efficacy compared to the prototype inhibitor MLN-4067.

Protein and Ligand RMSD

The behavior of the protein backbone and ligands within the ACE2 receptor’s binding pocket was assessed using RMSD trajectory analysis. The structural organization of a protein is a key determinant of its biological function, and any significant structural alterations may positively or negatively impact its activity [54]. Protein RMSD provides insight into the structural stability of the unbound (apo) system compared to its complex forms with XAN71 and XAN72, revealing the degree of deviation in the protein’s Cα atoms. Low, stable RMSD values suggest maintained structural integrity, whereas higher or fluctuating RMSD values indicate decreased stability and potential conformational changes [55]. In Fig. 5A, the RMSD of the apo ACE2 protein shows an initial increase, reaching approximately 1.8 Å, before stabilizing around 20 ns. It maintains a relaxed conformation with fluctuations between 2.0 Å and 3.0 Å throughout the simulation. A slight deviation is observed between 170 ns and 180 ns, after which the system regains stability and remains consistent for the remainder of the 200 ns simulation. This reasonably stable behavior validates the molecular dynamics (MD) protocol used for our protein-ligand complex simulations. In Fig. 5B, both complexes with XAN71 and XAN72 demonstrate lower average RMSD values than the free protein, with XAN71 showing an average RMSD of 1.84 Å and XAN72 at 1.96 Å. These results indicate that both complexes are stable, with XAN72’s RMSD resembling the free proteins, suggesting comparable structural stability. Throughout the simulation, all systems displayed average RMSD values below 2 Å, indicating stable interactions between XAN71 and XAN72 with ACE2’s active site residues. For XAN71, the RMSD exhibited an initial increase up to approximately 20 ns, followed by minor fluctuations around 25 ns. The system reached convergence by 30 ns and maintained a relaxed and stable conformation for roughly 70% of the simulation. However, a slight rise in RMSD was observed near 170 ns, after which the system regained stability and remained steady for the remainder of the 200 ns simulation. Similarly, XAN72 exhibited an initial increase up to 10 ns, followed by minor fluctuations around 70 ns and a slight drop near 100 ns, maintaining stability for most of the simulation. The average RMSD for the prototype inhibitor MLN-4067 Fig. 5C. was recorded at 1.83 Å, showing a slight rise up to 10 ns before remaining stable throughout the simulation. While both XAN71 and XAN72 demonstrated superior stability compared to MLN-4067, their distinct binding interactions may offer unique advantages as potential inhibitors. The absence of common amino acid interactions between XAN71, XAN72, and MLN-4067 suggests that these xanthone derivatives could provide enhanced specificity in targeting ACE2 without competing directly with established inhibitors. Overall, the consistent RMSD values throughout most of the simulation suggest stable ligand-protein interactions for both xanthone derivatives, supporting their compatibility within the ACE2 binding pocket and highlighting their potential as effective therapeutic agents against SARS-CoV-2.

Fig. 5

Protein RMSD (A) APO-Free Protein (B) Bound Systems and Ligand RMSD (C) APO-MLN-4067 (D) Bound Systems plots against ACE2

Ligand RMSD was analyzed using trajectory data to assess the behavior of ligands within the ACE2 binding pocket [47]. RMSD values provide insights into the stability of each ligand’s binding mode; high RMSD values indicate significant movement and less stable binding, while low RMSD values suggest consistent interactions with key residues in the binding pocket [56]. From Fig. 5C, the prototype inhibitor MLN-4067 displayed an average RMSD of 1.54 Å, with slight fluctuations observed up to 10 ns before relaxation for the remainder of the simulation. In contrast, XAN71 maintained a low and stable RMSD, averaging 1.20 Å between 2 ns and 120 ns, with only a slight increase observed before stabilizing for the remainder of the simulation. This consistency suggests strong and stable interactions with key residues in the active site, with no evidence of dissociation throughout the simulation. XAN72 demonstrated an even lower average RMSD of 0.85 Å, achieving equilibrium from the start and maintaining it throughout the 200 ns simulation. The low average RMSD values for XAN71 (1.20 Å) and XAN72 (0.85 Å) highlight their stability and consistent binding orientation within the ACE2 binding pocket. RMSD values below 1 Å indicate minimal positional drift [57], suggesting that both ligands establish stable, favorable interactions with key residues in the binding site. This stable behavior reinforces the suitability of XAN71 and XAN72 as potential ACE2 inhibitors, supporting robust ligand-protein interactions. When comparing these compounds to MLN-4067, XAN71 and XAN72 exhibit superior stability, as indicated by their lower RMSD values. The enhanced stability of XAN71 and XAN72 suggests that they may provide more effective inhibition of ACE2 than MLN-4067, potentially leading to better therapeutic outcomes. Collectively, these results validate the robustness of the XAN71-ACE2 and XAN72-ACE2 complexes, underscoring their promise as effective candidates in targeting SARS-CoV-2.

Protein RSMF and Protein RoG

The stability of protein-ligand complexes is significantly influenced by individual amino acid residues [58]. Analyzing the Root Mean Square Fluctuation (RMSF) trajectory provides valuable insights into the flexibility of various regions within a protein’s structure during molecular dynamics (MD) simulations, particularly in response to ligand binding. RMSF analysis highlights the role of amino acids in stabilizing the protein-ligand complex by identifying areas with varying levels of flexibility. Typically, high RMSF values indicate flexible or loop regions, whereas low RMSF values are associated with stable or rigid areas, often corresponding to secondary structural elements [59]. In this study, we calculated and plotted the RMSF values for the free ACE2 protein and its complexes with XAN71 and XAN72, as shown in Fig. 6E and F. The results reveal a notable reduction in ACE2 flexibility upon binding with XAN71 and XAN72, with both complexes exhibiting an average RMSF of 0.87 Å, compared to 0.89 Å for the prototype inhibitor MLN-4067 and 0.96 Å for the free protein. This decrease in RMSF indicates enhanced structural stability of ACE2 when bound to these ligands, suggesting that XAN71 and XAN72 effectively stabilize the ACE2 active site. The RMSF analysis also illustrates fluctuations across the protein’s residue indices, highlighting conformational changes that could impact its function. Notably, the free ACE2 protein exhibited greater fluctuations in several residues compared to the XAN71 and XAN72 complexes, particularly in regions outside the active site domain, such as between residues 350 and 400. This observation indicates that ACE2 becomes less flexible upon ligand binding. The lower RMSF values observed in the ligand-bound systems suggest enhanced structural compactness, which may influence ACE2’s functional integrity by potentially preventing viral entry into host cells [46, 60]. Additionally, regions in the apo (free) ACE2 structure displayed fluctuations exceeding 3.0 Å, especially around residues 0–10 and 320–325, indicating increased atomic movement in these domains. In contrast, the XAN71 and XAN72 complexes showed fewer fluctuations, reflecting less conformational variability in their ligand-bound states. Overall, the reduced RMSF values for the XAN71-ACE2 and XAN72-ACE2 complexes imply stabilized interactions, decreased conformational flexibility, and a more compact protein structure—all factors that support the inhibitory potential of XAN71 and XAN72 against ACE2, thereby limiting viral entry [57].

Fig. 6

Protein RMSF (E) APO-Free Protein (F) Bound Systems Protein RoG (G) APO-Free Protein (H) APO-MLN-4067 and Bound Systems plots against ACE2

The rigidity of protein-ligand complexes can be evaluated using the Radius of Gyration (RoG) parameter derived from molecular dynamics (MD) simulation trajectories. The RoG reflects the distribution of a protein’s mass relative to its center of mass, providing valuable insights into its overall compactness [61]. Lower RoG values typically indicate a more compact and stable structure, while higher RoG values may suggest unfolding or structural loosening [62]. Figure 6G and H display the RoG versus time plots for the systems analyzed. The average RoG values for the XAN71-bound (23.98 Å) and XAN72-bound (23.97 Å) complexes, as well as for the prototype inhibitor MLN-4067 (24.02 Å), were slightly lower than that of the unbound protein (24.11 Å), suggesting enhanced compactness upon ligand binding. In Fig. 6G, fluctuations in the RoG of the unbound protein are evident around 60 ns, 90 ns, 110 ns, and 135 ns, indicating periods of reduced compactness. Conversely, the XAN71 and XAN72 complexes exhibited an initial rise in RoG, stabilizing around 15 ns, with minor fluctuations around 40 ns before achieving stable compactness until the end of the simulation. Overall, these findings indicate that the compactness of the protein structure in the XAN71 and XAN72-bound systems remains stable and is not adversely affected by ligand binding. This stability further supports the structural integrity and rigidity of the complexes throughout the simulation period. The consistently lower RoG values for both ligand-bound systems compared to the free protein underscore their potential to maintain a more compact conformation, which is beneficial for effective inhibition of ACE2 and may enhance resistance to conformational changes that could facilitate viral entry.

Per-residue energy decomposition (PRED) analysis

A per-residue energy decomposition data (PRED) was generated as part of the MM/PBSA calculations to comprehend how individual residues contribute to ligand binding. This data highlights the essential residues that play a significant role in the binding energy of XAN71 and XAN72 to ACE2 protein. The eight residues with the highest energy contributions for each ligand complex are displayed in Fig. 7J and L, alongside their respective 3D interaction structures, highlighting hydrogen bonding regions.

Fig. 7

3D structure of the XAN71-ACE2 complex and XAN72-ACE2 complex (I, K) Per-Residue Energy Decomposition (PRED) of XAN71 and XAN72 with ACE2 (J, L)

For the XAN71-ACE2 complex (Fig. 7J), residues such as ASN131 and ARG255 showed significant contributions to the binding, with total energy values of -2.19 kcal/mol and -2.08 kcal/mol, respectively. These energies arise from van der Waals (vdW) and electrostatic interactions. Additionally, PHE256 and PRO328 exhibited notable vdW contributions, emphasizing their role in stabilizing hydrophobic interactions within the binding pocket. The overall binding free energy of XAN71 was primarily influenced by vdW forces, resulting in a highly favorable ΔGbind of -70.97 kcal/mol. In the case of the XAN72-ACE2 complex (Fig. 7L), ARG255 and GLU384 were identified as the most significant contributors, with total energy values of -3.78 kcal/mol and -5.83 kcal/mol, respectively. The substantial electrostatic contribution from GLU384 (-15.05 kcal/mol) highlights the critical role of ionic and polar interactions in the binding of XAN72.

Furthermore, residues HIE327 and PHE486 contributed significantly through both vdW and electrostatic interactions, reinforcing the structural stability of the complex. The overall binding free energy for XAN72 was measured at -69.85 kcal/mol, slightly lower than that of XAN71, indicating comparable binding affinities. The residue-level decomposition analysis illustrates the interplay between vdW and electrostatic forces in stabilizing these ligand-receptor complexes. Molecular dynamics (MD) simulations confirmed enhanced binding energies for both XAN71 and XAN72, validating the efficacy of the MM-PBSA method in quantifying interaction contributions. The predominance of van der Waals interactions suggests that the multi-ringed structure of these xanthone derivatives is particularly well-suited for engaging with the non-polar regions of the ACE2 active site, thereby enhancing ligand binding and stability.

Density functional theory studies

Following the (MD) analysis, a DFT study assessed the chemical reactivity and electrostatic properties of XAN71 and XAN72. This investigation provides additional insights into their binding behavior and potential interactions with ACE2. Among the various reactivity descriptors, Molecular electrostatic potentials (MEPs) are frequently utilized to predict sites for electrophilic and nucleophilic attacks and enhance the understanding of biological recognition and hydrogen-bonding interactions. The MEP maps are color-coded from red to blue to represent different electrostatic potentials: deep red indicates electron-rich regions prone to electrophilic attack, while blue areas signify electron-deficient regions favoring nucleophilic attack. Green regions are near-neutral, and yellow areas denote regions with lower electron density.

Fig. 8

Molecular electrostatic potentials of the XAN71 and XAN72

Figure 8 presents the MEP maps for XAN71 and XAN72, which share similar regions of light blue on the xanthone ring, indicating electron-deficient sites. Slightly red regions are observed around the pyran rings, particularly near the 6-hydroxy groups, suggesting sites of potential electrophilicity. Notably, XAN71 has a deep blue area around the hydroxyl group at position 8 on the xanthone ring, indicating a site of nucleophilicity favorable for hydrogen bonding interactions. In contrast, XAN72 differs only in having a methoxy group at the same position, resulting in slightly altered electrostatic potential distribution. The MEP maps align with the hydrogen-bonding and hydrophobic interactions observed in the MD analysis, particularly around the hydroxyl, methoxy, and aromatic groups. These features enhance polar interactions and hydrogen bonding, reinforcing the stability of the XAN71 and XAN72 complexes with ACE2.

The HOMO-LUMO studies

The HOMO-LUMO energy gap (ΔE) offers valuable insights into the chemical reactivity and stability of XAN71 and XAN72, as shown in Table 3; Fig. 9. By examining the energies of the HOMO and LUMO, we can better understand the potential binding interactions of each compound with the ACE2 receptor. For XAN71, the LUMO energy is measured at -0.093 a.u. (or -2.532 eV), while XAN72 has a slightly lower LUMO energy of -0.090 a.u. (or -2.474 eV). The higher LUMO energy of XAN71 suggests that it may be marginally less reactive towards electron-rich regions than XAN72, as lower LUMO energies typically indicate easier access for electron-donating interactions.

Table 3 HOMO and LUMO Energies and their gap ΔEGapFig. 9

Frontier molecular orbitals LUMO (top) and HOMO (bottom)

As illustrated in Fig. 9, the LUMO and HOMO regions are highlighted in green and brown, respectively. The combination of these colors delineates the LUMO, while the same applies to the HOMO. Notably, the spatial arrangement of the green and brown orbitals for the LUMO differs from that of the HOMO, indicating potential interaction sites where electron density could facilitate bonding with electron donors. The HOMO energy for XAN71 is higher at -0.231 a.u. (or -6.299 eV), compared to -0.227 a.u. (or -6.203 eV) for XAN72. This slightly elevated HOMO energy for XAN71 suggests it may act as a stronger electron donor, potentially enhancing interactions with electron-deficient regions in the ACE2 binding site. In Fig. 9, the HOMO regions are depicted in green and brown, showcasing areas with increased electron density that may engage in interactions with electron-deficient sites within the receptor’s binding domain. Both compounds exhibit comparable HOMO-LUMO energy gaps, with XAN71 at 0.138 a.u. (or 3.767 eV) and XAN72 at 0.137 a.u. (or 3.729 eV).

The marginally smaller energy gap of XAN72 may indicate slightly higher reactivity than XAN71, potentially improving its adaptability in binding interactions. The energy gap illustrated in Fig. 9 reflects the relative stability and reactivity of the compounds; a smaller gap generally correlates with increased reactivity. The spatial distribution of HOMO and LUMO orbitals across each ligand emphasizes regions likely to interact with ACE2. For both XAN71 and XAN72, significant electron density is observed around the xanthone ring and functional groups such as hydroxyl and methoxy, which could facilitate hydrogen bonding or electrostatic interactions. This distribution aligns with the calculated reactivity, supporting stable binding interactions with ACE2 for both compounds while suggesting that XAN72 may have a slight advantage in reactivity due to its smaller energy gap. Conversely, the higher HOMO and LUMO energies of XAN71 may contribute to its overall stability, resulting in distinct binding characteristics that could enhance its effectiveness as an inhibitor. All these electronic properties suggest that these lead compounds are well-positioned to engage in favorable interactions with ACE2, potentially impeding viral entry into host cells.