Structural Conformational Study of Eugenol Derivatives Using Semiempirical Methods

We investigated the conformational structure of eugenol and eugenyl acetate under torsional angle effect by performing semiempirical calculations using AM1 and PM3 methods. From these calculations, we have evaluated the strain energy of conformational interconversion. To provide a better estimate of stable conformations, we have plotted the strain energy versus dihedral angle. So, we have determined five geometries of eugenol (three energy minima and two transition states) and three geometries of eugenyl acetate (two energy minima and one transition state). From the molecular orbital calculations, we deduce that the optimized trans form by AM1 method is more reactive than under PM3 method. We can conclude that both methods are efficient. The AM1 method allows us to determine the reactivity and PM3 method to verify the stability. 1. Introduction Eugenol (4-allyl-2-methoxyphenol) is a phenylpropene, an allyl chain-substituted guaiacol. It is the main phenolic compound extracted from certain essential oils especially from clove oil, nutmeg, cinnamon, basil, and bay leaf [1–14]. Eugenol is a phenol derivative used in many areas such as perfumes, flavorings agent, and dental materials. It is used as an antiseptic, analgesic, fungicide, bactericide, insecticide, anticarcinogenic, antiallergic, antioxidant, anti-inflammatory, and so forth [15–17]. As derivative, the eugenyl acetate was characterized and its structural properties have investigated by Dos Santos et al. [18, 19]. To our knowledge, a study of the conformational structure as a function of the dihedral angle was not reported. In the present paper, we investigated the conformational structure of eugenol and eugenyl acetate under torsional angle effect by performing semiempirical calculations using AM1 and PM3 methods. From these calculations, we have evaluated the strain energy of conformational interconversion to provide a better estimate of stable conformations. These results can be used to make future applications possible (Figure 1). Figure 1: Conformation structures of cis-eugenol and cis-eugenyl acetate. 2. Methodology Molecular modeling of the optimized eugenol and eugenyl acetate was carried out with the use of an efficient program for molecular mechanics (MM). Calculations are performed for all optimized geometries using AM1 and PM3 methods. The main molecular properties to characterize the geometry structures and the molecular orbital of the eugenyl acetate were calculated and compared. For each method, the geometry of the compound was optimized by using the Polak-Ribiere conjugate gradient