Discovery Potent of Bagasse ( CMC-L-Phe ) As Bioactive Material Based on DFT Calculations

This present work deals with evaluating the safety application of synthesizing nanoCMC-L-Phe bioactive compound, as drug discovery application, using DFT theories. In this respect, the stereochemistry studies as well as geometrical optimization of ligand at density functional theory (DFT), using DFT\B3LYP with 631G* level of theory calculation of frontier molecular orbitals (FMOs) were carried out. These calculations were performed for studying the stability and reactivity of ligand, heat formation, dipole moment, polarizability, thermodynamic parameters, calculated global, local chemical reactivity to give better understanding; as well as structure-property relationships (SPR) based on electronic structure of the CMC-Phe. The global and local chemical reactivity were examined for synthesized biopolymer, which showed the Lform more reactive against surrounding biological media than D-form. The ADMET profile was calculated in silico, the pharmacokinetic parameters of the ligand showed the promising futures for drug application. The docking study was suggested that, the CMC-L-Phe have a good binding affinity, and interacted with FAK active site to form stable complex, this is evident the ligand is suitable FAK inhibitor.


INTRODUCTION
Cellulose acetate (CA) and carboxymethyl cellulose (CMC) regard the most chemistry market cellulose derivatives.Where, they have wide range of applications, e.g., RO-membranes for water desalination, metal absorbents, stabilizing agents and paper additive [1][2][3][4][5].Moreover, CMC has been applied in tissue engineering of cartilage [6][7][8], for treating dry eye after phacoemulsification [9], as filler in tablet with active ingredients [10], as well as additive to increase the drug bioavailability and releasing [11], Mixtures of amino acid and CMC, have been used to obtain zero-order releases of drugs, with water as the releasing medium [12], or simulated gastric media [9].The literature reported different methods to evaluate the bioactive compound, e.g., via biological, using antimicrobial plate diffusion method [13][14][15], as well as anti-tumor test, using the microculture tetrazolium Assay (MTT) [16,17] Where, cell viability was assessed and cytotoxic index IC50 was calculated.Moreover, computational programs, e.g., the TarFishDock, TargetHunter, Similarity Ensemble Approach ChemMapper and HitPick methods are reported, to give us the information's about the molecular structure [18][19][20][21][22][23][24].The Discrete Fourier Transform (DFT) regards the most benefit discrete transform, used in many practical applications, moreover to efficiently solve partial differential equations, and convolutions or multiplying large integers [25].On the other hand, pharmacokinetic information is required to optimize the pharmacodynamic response [26], and consequently indicates the bioavailability of drug (percentage of the administered drug which arrives in the central compartment).

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Despite most of literatures deal with approaches to cancer treatment are based on chitin and chitosan derivatives [27][28][29][30], however till now additional innovative approaches are required to design the low cost drugs for treating the anticancer, together with reducing the toxicity and improving the rapeutic indices.In our previous work, we succeeded in synthesizing CMC-based biological active agent, in nano-size structure, from modifying the carboxymethyl cellulose (market) with L-phenylalanine (L-Phe) [29].Bagasse is promising cellulosic material available in Egypt and other many countries, as non-wood source, therefore, in continuation and supporting the safety application of this novel nano compound in pharmaceutical purpose, in this present work the performance of bagasse-CMC-L-Phe compound, as bioactive, is assessed beside its ability to demonstrate and predict safety drug discovery applications and rationalizing drug side effects.For this purpose, we study some quantum theories, and highlight on structure geometry, moreover we shed light on the geometries-electronic properties as well as quantum structure-property relationship.

MATERIALS AND METHODS
Conjugate compound: Carboxymethyl cellulose (CMC) and L-phenylalanine (L-Phe) were used as materials for the synthesis bioactive conjugate compound.CMC was prepared from α-cellulose extracted bagasse; according to method described in Ref 28.Its purity and DS are 99% and 0.92, respectively.While, the L-Phe was purchased from Oxford, India, with specifications (purity 99.5 %; other amino acid content, 0.01 %).The synthesis approach was carried out under recommended conditions reported at our previous work [29].In this method CMC and L-Phe were reacted (in ratio 1.5) by condensation reaction at temperature 250 o C for 1.5 hr.
Morphological Characterization of the synthesized bagasse-CMC-L-phe in nano form was carried out by using transmission electron microscopy, of type QUANTA FEG250, Japan (System running at 200 keV).While, the evidence of modification of CMC was performed by Infrared spectra, using Jasco FT/IR, Nicolet, and Model 670.The samples were mixed with KBr and pressed as tablet.The bands were recorded in the region from 4000 to 400 cm -1 with Deuterated Triglycine Sulfate (DTGS).

Computational Model
• The Quantum chemical computations were performed with the Becke3-Lee-Yang-parr (B3LYP) level, 6-311G*, basis as implement in Gaussian 09W program package [31] as implemented in MOE package [32].The optimization Geometry for molecular structure was carried out, for improving knowledge of chemical structure.
• The thermodynamic functions as, entropy, Zero-Point Vibrational Energies (ZPVE) at 298.15K and (1 atm) pressure, entropies (S 0 ) and enthalpy changes (∆H 0 ), for the compound were evaluated by the theoretical harmonic frequencies obtained from B3LYP/6-311G* method.The dipole moments and polarizability were calculated against to X, Y and Ztrace of the polarizability tensor, which is responsible to an external electric field at zero frequency; as following equations: • The following equation (BDE = H°•+ H°H -H°±) was used for estimating enthalpyof bond dissociation (BDE) values" where; H°•, H°H , H°±, the enthalpy of the radical generated by H releasing, H-atom, and the parent molecule, respectively.The adiabatic IP values were calculated according to the equation IP = I + -I ± , where I + (parent molecule), I ± (cation radical generated after electron transfer).
• Global chemical reactivity descriptors for molecules have been computed, as S; softness (measures stability of molecules and chemical reactivity with direct proportional) [33], η; hardness (reciprocal of softness), µ; chemical potential, χ; electronegativity (strength atom for attracting electrons to itself, ω; electrophilicity (measuring lowering energy due to maximal flowing electron between donor and acceptor) [34][35][36][37][38], μ−; electron donating chemical potentials, and μ+; electro accepting processes, ability powers for ω−; electro donating, and ω+; electro accepting.These expressions are in terms of the I; first ionization potential (the difference of the total electronic energy when an electron is removed (N − 1) from the neutral molecule with N electrons at a constant external electron potential), and the A; electron affinity (υ(r), which calculated under the same conditions when an electron is added (N + 1) [35], Electrophilicity index (ωi): ) Taking into account, the expression ω ± ; is net electrophilicity (ω ± =ω + + ω − ), it can be expressed as the measurement of the electron accepting power relative to its electron donating power [34], E is electronic energy, and υ(r) is external potential of an N-electron system.
• Energy back donation is equational expressed when a molecule received a specific quantity of charges ΔN+ , associated with the energy change ΔE+ as [35]: When a molecule back donates a specific quantity of charges ΔN − associated with the energy change ΔE − as: The Sum of ( 13) and ( 14) equations to give amount of charges received: ΔN − = − ΔN + .
The total energy change is minimum with respect to ΔN+ and implies that • The site selectivity of a chemical system cannot be studied by using the global descriptors of reactivity.Thus, appropriate local descriptors need to be defined.The HSAB principle has been used in a local sense in terms of DFT concepts [36], such as the Fukui function f(r), which described the reactivity of a specific atom in a molecule.It is necessary to condense the values of f(r) around each atomic site into a single value that characterizes the atomic contribution in a molecule.The atom k in a molecule, depending upon the type of electron transfer.Three kinds of condensed Fukui function of the atom k can be obtained.According to Ref.
36 the sites which have highest values of Fukui Function f(r) is more reactive center in chemical species.The Fukui function is defined as: where σ (electronic chemical potential), N (number of electrons), p (corresponds to the electron density) and γ( external potential exerted by the nucleus).The Fukui function is; a local reactivity descriptor that indicates the preferred regions, when modifying the number of electrons at chemical partials and changing the electron density.Therefore, it indicates the propensity of the electronic density to deform at a given position upon accepting or donating electrons [36][37][38][39].The second formula for f(r), (δσ/δγ)N is a quantity involving the electron density of the atoms or in its frontier valence regions.For an N-electron system, independent calculations have been made on (N-1), (N) and (N+1) electronic system with the same molecular geometry.Various population schemes yield qk(N- 1),qk(N) and qk(N+1) for all the atoms, then these values are substituted in the following equations and obtained the corresponding Fukui function values for  ± ,  − and  0 .In a finite-difference approximation, the values are calculated as: -The local softness contains the same information as the Fukui unction (i.e., the sensitivity of the chemical potential of a system to a local external potential), as well as additional information about the molecular softness.The local softness and electrophilicity (philicity) indices are calculated using Eqs.( 22) and ( 23), given respectively as: where "+" (nucleophilic),"-" (electrophilic) and "0" (radical).The intra-and inter-molecular reactivity descriptors can be elucidate by relative nucleophilicity   − /  ± and electrophilicity   ± /  − , this descriptors have been helpful tools for studding nucleophilic and electrophilic reactions [40][41][42].
-The changes of the electronic density when system is accepts electrons, ρ, are associated to the kth atom, ∆ρK Elec is expressed by The changes of the electronic density when system is donate electrons, ρ, are associated to the kth atom, ∆ρK Nuc is expressed by

Stepwise Docking Method
The 3D crystal structure of FAK was obtained from Protein Data Bank (PDB ID: 4K9Y) [43] and 4K9Y has a good resolution (2 Å) and attached co-crystallized inhibitors are used to identify the active site.The crystal structures of the (4K9Y1) as reference inhibitor molecule is used.Water and inhibitor molecule is removed, together with added hydrogen atoms.The parameters and charges are assigned with MMFF94x force field.Alpha-site spheres are generated using the site finder module of MOE.The optimized 3D structures of molecules were subjected to generate different poses of ligands using triangular matcher placement method, which generating poses by aligning ligand triplets of atoms on triplets of alpha spheres representing in the receptor site points, a random triplet of alpha sphere centers is used to determine the pose during each iteration.The pose generated is rescored using London dG scoring function.The poses generated are refined with MMFF94x force field; also, the solvation effects are treated.The Born solvation model (GB/VI) is used to calculate the final energy, and the finally assigned poses were assigned a score based on the free energy in kJ/mol.

RESULTS AND DISCUSSION
The synthesized bagasse-CMC-L-Phe, with nitrogen content 1.4%, is illustrated in Figure 1; while Figure 2 shows the stero-isomer forms and TEM.The TEM photograph (Figure 3.a) confirms the bagasse conjugate is synthesized in nano-particles (between 50 -100 nm).The insolubility behavior of this compound in water is strong evidence for the formation of this new compound, due to excellent solubility of the two reactants.It is clear that, conjugating the CMC with amino acid leads to blue shift the band of stretching vibration of OH groups from 3412 cm -1 to 3462 cm. - 1 Also the band related to C=O at 1616 cm -1 is shifted to 1652 cm -1 together with the appearance of noising bands at 1046 cm. - This confirms that the free unsubstituted hydroxyl groups of CMC (2ry alcohol) are condensed with COOH group included L-phenylalanine and consequently may be lead to liberate the hydrogen bonded of 2ry hydroxyl, during synthesis processes.

Molecular Modeling
In attempting to accomplish good understanding of the most stable stereoisomer polymer forms (Figure 4), the conformational analysis of the studied polymer CMC-L-Phe is performed using density function theory (Gaussian 09 package), as implemented in MOE2015.The geometrical optimization and computed molecular parameters are carried out using B3LYP with 6-311G* basis set.

Molecular Geometry
The synthesized polymer has a chiral C atom (*), thus, the two stereoisomer forms may be possible existence (Figure 2).Experimentally elucidation of the preferred stereoisomer for ligand structure is complicated.The total energy have been used to investigate the most stable form for a prepared polymer, and showed that, CMC-L-Phe form is more stable than CMC-D-Phe (Figure 4, Table 1).
• The CMC-L-Phe is stabilized by an arrangement of phenyl ring of amino acid perpendicular mode with pyranose ring; the distance of O-Na is lengthening in L form than D-Form due to free rotation of pyranose ring around axes.The bond between Carbonyl groups C17-O27 and C13-O24 are 1.18 and 1.17 °A for L and D forms, respectively.The lengthening distance between two carbonyl groups may be explained by adjacent electronegative oxygen atoms, which withdrawing electrons of C13 and releasing electron to O24, with  .thebond angles of C17-C19-O27 is larger than H31-O5-C3 (179° and 79 °), this is ascribed to inter-molecular interaction (Sup.Figure 3 and 4, in supplementary data).
• The computed vibrational frequencies (Sup.Figure 2 in supplementary data) and molecular parameters of the target compounds have been performed.The computed vibration values are agreement with slightly division comparable with our experimental results (Figure 1).The deviation values between the experimental and calculated, may be due to the performance theoretical calculations in the gaseous state for the single molecule without intra-molecular interactions, in contrary, the experimental values have been recorded in the presence of intermolecular interactions.

Transfer Mechanism
Two serious mechanisms may be parallel occurred for bioactive molecules in chemical or biological system; one: the H-atom transfer mechanism (A + BOH → AH + BO•), and the other is the electron transfer mechanism (A + BOH → A + BOH + ).The activity of BOH molecule is related to radical stability (BO • ), which estimated by Hbond, conjugation, and resonance effects.The reactivity of an (BOH) is determined by calculating the bond dissociation enthalpy (BDE) for hydroxyl group.Thus, the generated cation radical from the electron transfer must be stable; hence, the antimicrobial potency can be exhibited by the adiabatic ionization potential (IP).Decreasing I, IP and BDE values are expected to enhancement antimicrobial activity.The CMC-L-Phe showed decreasing in I, IP and BDE values than CMC-D-Phe, this may be suggested the enhancement activity of L form than D-form derived from CMC (Table 1).

Frontier Orbital Analysis
The frontier molecular orbital's HOMO and LUMO are estimated the interaction pathway between the molecule and receptor.The EHOMO, is exhibited the ability electron donating of the molecule; while ELUMO is ability electron gaining of a molecule [43].The "simple Hückel Molecular Orbital theory (SHMO)" is used to study the frontier orbital gap; which exhibited the reactivity and stability of the molecule [43][44][45].The (HOMOs) and (LUMOs) are studied in the S0, which suggested the delocalization HOMOs around pyranose and phenyl rings; as well as LUMO is localized in carboxylate group for L-and D forms (Figure 5).The HOMO energy for CMC-L-Pheis is greater than CMC-D-Phe, and vise verse for LUMO energies (Table 1, Figure 5).The energy gap for CMC-L-Phe is smaller than for the CMC-D-Phe, which indicated favorable ability interaction with FAK receptor.

Thermodynamic Properties
The 2 nd law of thermodynamics parameters has been inducing helpful tools for estimation the activity direction of biomolecule.The total dipole moment (D), and related thermodynamic properties (mean polarizability(α), and anisotropy polarizability(β)), which showing the interacting power of the molecules with media, in case of L isomer are higher than D-isomer.Where, the polarizability of L isomer is -0.97Deby; while for D isomer is -3.264Deby.The anisotropic and polarizability of CMC-L-Phe are approximately ~ 2.5 and 4 times greater than CMC-D-Phe, respectively (Table 1).This leads to increase its ability of interaction with the surrounding environments.Thus, a The molecular volume (MV) has been the connection image between the tested polymer and the microbial surface [47].The observed higher volume (~418 A 2 ), with stronger binding energy (1623.32kcal/mol) for L-form it promotes the chance for stability binding interaction with receptor surface than D form, which showed volume (404.50A 2 ) with binding energy (1486.92kcal/mol) (Table 1).Generally, all calculated thermodynamic parameters for the CMC-L-Pheare are greater than CMC-D-Phe (Table 1).These parameters demonstrated that, the CMC-L-Phe is higher chance for biological application.
• The CMC-L-Phe has smaller hardness (4.17 ev) and larger value for softness (2.39 ev), which indicate the CMC-L-Phe is a reactive molecule toward FAK (Table 1).
• The negative value of μ− (-2.218, eV) for L-form is higher than (-1.92 eV) D-form, as well as the value for μ+ (-6.38 eV) is lower than (-6.58 eV) D form, In other hand, the electron donating power ω-(4.89eV) for Lisomer is greater one time than (4.65 eV) D form; while the electron accepting power ω+( 1.69) for CMC-L-Phe is smaller than ( 1.66 eV) CMC-D-Phe.This data suggested the higher ability of the CMC-L-Phe molecule for donating electron to environment.
• The calculated ΔNmax according to Ref. 47, is another quantum chemical parameter, which referred to a maximum number of electrons transferred in a chemical reaction (Table 1).The electrophilicity has been reflected the ability donating electrons to the media [48], the high electrophilicity compound is defined as a Lewis acid (electron-rich).The CMC-L-Phe is one time more electrophilicity properties than CMC-D-Phe, which explained by less electronegative atoms CMC-L-Phe interacted with negative charge located in microbial surface (Table 1).
• Energy back donation is the term determines the interaction between compounds and surface of FAK receptor.This term is combined with charge transfer and directly proportional with hardness.It is revealed that, the compound is energetically favored, if η more than zero and ΔE Back-donation less than zero [49].This observation reveals the greatest interaction efficiency of L-form than D-form (Table 1).

Local reactivity and intermolecular interaction
• The global reactivity cannot be satisfying for explain intermolecular interaction, the local descriptors, using Fukui function, can be used for understanding reactivity site of bio molecule [50].The electrophilic, nucleophilic and radical attack have been calculated to help us understanding the intermolecular hydrogen bonding interaction.The site with higher" f(r)" Fukui parameter, is larger reactivity site in chemical species and vice versa.The values of electronic density distribution, electrophilicity and softness affect with both values of; the dual descriptor and Fukui function.The site with high positive values of ∆ρK Elec is most electrophilic region, and a nucleophilic attack may be took place.In contrary, increasing the negative value of ∆ρK Nuc in specific zone, indicating high nucleophilic in this site and attack may occur.The F +, F,F 0 Fukui functions and; F 2 dual descriptor, ω + ,ω -,ω ± electrophilicity and S + ,S -,S ± local softness, S -/ S + relative nucleophilicity and S + /S -electrophilicity are calculated using DFT theory (Sup.Table 1 and 2 in supplementary material).The C19 is the best sites for a nucleophilic attack with ∆ρK Elec =12.39 andS -/ S + =1.01, while the electrophile attack take place on O24 (CO of amino acid) with ∆ρK Nuc =0.76 and S + /S -=0.882, which provided that, O atom located in outside the plane of the aromatic ring, and due to localize lone pairs of electrons on the unsaturated system the basicity increased..
• The electrostatic potentials (ESP) mapped of CMC-L-Phe are identified the characteristic electronic and conformational likeness.The pink and blue regions, showed the negatively and positively sites of ESP, respectively.On comparison of the ESP of a ligand with complex, it indicates that, increasing positive charge regions located in the center of coordinating metal in comparison with ligand (Figure 6).The charge deformation upon the atoms exhibits the transformation of electrons during formation of donor and acceptor.The charged atoms with positive charges are; hydrogen, some carbon, the nitrogen, the O of N, and some carbon atoms have negative charges.The oxygen atom of carbonyl group is the most negative centers with isovalue (0.0005).On contrary, the maximum positive charge for ligand is located in Na with isovalue (0.0001138), due to attached with a carbonyl group (withdrawing nature).Electrostatic interactions between polymer and the receptor are derived from adsorption stability.The presence of electronegative atoms as NH, OH groups lead to polarity compound, which have a negative charge.The electrostatic attraction between the CMC-L-Phe molecule and the receptor atoms makes the adsorption possible.The hydrophobic nature of amino acid resides in active site receptor, led to lacking ionic character, and hence the overall effect the adsorption energy.

ADMET Factors Profiling
Oral bioavailability has a vital function in discovering the therapeutic bioactive molecules, which neglected in clinical trial, due to the ADMET (absorbance, distributing, metabolic, eliminating and toxicological) parameters.The calculation of ADMET was for bagasse CMC-APP, is also important, and performed as, i-(TPSA), which unreferred absorbed molecules if larger than 140 inactive bioavailability [51], ii-(% ABS) which was predicted by Zhao et al. [52], and iii-''Lipinski rule of five'' (Table 3).The data show that, the CLogP < 5 (factor lipophilicity [53], M.Wt< 500, H -acceptors = 4, H-donors = 1 and molar refractivity values ranged (~118).These evidence that, the The (ADME-T) algorithm [54,55] is used for predicting the drug-similarity (Table 3).It studying the transport ability of therapeutic agent compounds for transported through the intestinal epithelium.It may be have a strong interacting potency with plasma, through the blood-brain barrier, which necessary led to transport ability drug in the body.In general, No marked health effects in rodent toxicity profiles are observed among its compound CMC-L-Phe.From these data we can suggest that, the compound can be used as a good oral absorption.

Molecular Docking
Focal adhesion kinase (FAK), is also defined as a protein tyrosine kinase 2 (PTK2), which play vital roles in controlling sign from the extracellular matrix (ECM) interceded with two receptors.These receptors are integrins and growing factor (GFR) [56].FAK is responsible for controlling several cellular transmission information, which regulate several vital processes.[57][58][59].The docking examination was performed for give better understanding mechanism of antimicrobial activity for CMC-L-Phe.Molecular docking is the powerful strategy for get a better insight into ligand-receptor interactions.All docking experiment is performed with MOE 2015.10 [31].In silico, the tested compounds are evaluated using X-ray crystal structures and FAK (ID: 4K9Y) [51], complexes with reference inhibitor.The active site of the enzyme is defined to include residues within a 10.0 Å radius for any inhibitor atoms.MOE scoring function of the most stable docking model for tested compounds is applied to evaluate the binding affinities between the inhibitors with (FAK) active site, (Table 3).The minimization in energy is preformed for complexes (inhibitor-active site) with an MMFF94 force field [41,] until the gradient convergence reached to 0.05 kcal/mol.The CMC-L-Phe docked successfully into the FAK active site, and compared with reference inhibitor.The compound CMC-L-Phe is exhibited highest binding score which reached to -18.04 Kcal/mol (Table 3).
The ligand is successfully interacted with the active sites of the FAK, which form two H-bonding interaction viz, Amino acids Glu.471 with good binding free energy (ΔG= -2.1 and -2.2) kcal/mol.. Also, the Cys.502 is bonded with ligand by two H-bond with higher binding energy than original ligand (ΔG= -3.8 and -3.2) kcal/mol, respectively.The residues ILe428 and Gly505 hold on the phenyl rings of the ligand through alkyl-π interactionsm, with good binding energy.Lys454 is involved in a ionic interaction with the ligand as simulated by MOE (Table 4).The ligand is stabilized with itself in binding pocket through, arranged of phenyl ring of amino acid with pyranose ring in coplanar position, which ligand stabilized with binding pocket through arranged L-phy with important active amino acids Lys and Cys in parallel mode (Figure 7).The results obtained clearly revealed that, the amino acid residues close to the reference molecule are mostly the same as observed in the tested compound (Figure 7).The higher observed binding interaction process, indicated the ligand acts potential inhibitor against FA, this may be explained, the presence of hydrophobic amino acid in the synthesized compounds.

CONCLUSIONS
The synthesized ligand derived from bagasse-based CMC with amino acid (L-Phe) was confirmed by different spectral analyses.The experimental results were supported with DFT quantum calculations.Full optimization geometry of the molecule, vibrational spectra, NBO, FMO, thermodynamic parameters, and ESP were calculated.The global and local reactivity: Fukui function index, local electrophilicity and softness were performed, which to be a helpful tool to predict a possible explanation for chemical reactivity of ligand.The BDE values for H gaining showed that the investigated molecule is stable biomolecule against degradation process, which prevent the autoxidation mechanism.Furthermore, the pharma kinetic characters proved the investigarted bioactive compound has low toxic effect and has promising oral bioavailability.The docking study is showed that, the ligand binds at the active site with strong hydrogen bond with catalytic amino, which obeyed with experimental data.

Figure 1 .
Figure 1.Synthesis of bioactive CMC-Phe polymer unit Figure 3.b shows the IR spectrum of bagasse -CMC-L-Phe in comparison with bagasse-CMC.

Figure 4 .
Figure 4. Ball and stick rendering for the most stable steroisomer CMC-L Phe with intramolecular hydrogen bond of the ligand, as calculated DFT molecular orbital with B3LYP/6-311G*

Figure 5 .
Figure 5. Plotting of the frontier molecular orbital for CMC-D/L-Phe

Figure 6 .
Figure 6.ESP mapping for the most stable stereoisomer form of the ligand as calculated DFT molecular orbital with B3LYP/6-311G*

Table 2 .
Minimal inhibitory concentration of the compound on the tested strains Bacteria and fungi

Table 3 .
Pharmacokinetic parameters for good oral bioavailability, ADME-Tox and Docking energy scores (kcal/mol) derived from the MOE of CMC-L-Phe .G.: free binding energy of the ligand from a given conformer, Int.: affinity binding energy of hydrogen bond interaction with receptor, H.B.: Hydrogen bonding energy between protein and ligand d

Table 4 .
Interaction between ligand and amino acid residues derived from MOE Docking Tools