Quantum chemical calculation was correlated with geometrical structure and total energy of fluoxetine and its five derivatives. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) have been calculated using ab initio (HF), density functional theory (B3LYP), semi-empirical (AM1, PM3) methods with different basis sets to design the fluoxetine drugs and its derivatives by a Gaussian 09 W program. Theoretical optimized geometric parameters and vibrational frequencies of fluoxetine have been compared with the corresponding five derivatives data. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies have been determined. The theoretical study includes the calculation of the thermodynamic properties of the drugs and its derivatives like zero-point energy, enthalpy, entropy, ionization energy, electron affinity to make a correlation between the gained results. The results of the four methods were not very clear, but an correlation between the dipole moment (potential character), static distribution (an active site character) and HOMO-LUMO energies (energy for electron transfer) shows that the patent 1.5 was important derivatives as a recommended drug relative to fluoxetine drug.

The complete computational study of the methyldopa drug and its derivatives prodrug 1-4(methyldopa-cellulose (Ce), methyldopa-carboxymethyl cellulose(CMC), methyldopa-maleic anhydride cellulose (MAC)and methyldopa-hydroxypropyl cellulose(HPC)) was performed by Density Function theory method with the Becker's three parameter hybrid functional (B3LYP) functional and 6-31G++ (d, p) basis set using Gaussian 09 program. The Density Function theory (DFT) DFT method is used to calculate the optimal molecular structure, vibrational spectra, highest occupied molecular orbital energies (HOMO), lowest unoccupied molecular orbital energies (LUMO), electronic properties (total energy, dipole moment, electronegativity, chemical hardness and softness), biological activity, and molecular surfaces. Using the reaction coordinate method to quantify the energy enthalpy and activation energy of O-R bond rupture. The result shows the derivatives that are hoped to have preference in their use as carriers are (methyldopa-Ce) and (methyldopa-MAC), which gave the drug acid as a product of the O-R bond breaking process in an irreversible reaction.

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