## 3 Results
### Fluoxetine Metabolites  
The pharmacokinetic and metabolic aspects of fluoxetine in the human body have been described in detail by [PERSON] and [PERSON] and by [PERSON] et al. [3; 5]. Fluoxetine is a lipophilic molecule that is almost completely absorbed after oral administration. Oral bioavailability is lower than 90% of the dose, due to hepatic first-pass extraction [53]. Fluoxetine highly accumulates in lungs, mainly due to lysosomal trapping, and it is characterized by a large volume of distribution (Vd), similar to that of TCAs [3]. Accumulation in the brain is lower than that of other SSRIs, with a brain to plasma ratio of 2.6:1 compared with 24:1 for fluvoxamine [54]. Fluoxetine is also characterized by a long half-life (t\({}_{1/2}\)), ranging from 24 h to 4 days, which implies that between 1-22 months may be required to reach steady-state conditions during therapy [3; 8]. Moreover, it has been observed that fluoxetine follows non-linear kinetics, since there is a disproportion between increase in blood concentration after dose escalation [3]. With a 20-60 mg/die dose, plasma levels range from 50 to 480 ng/mL [5]. R(\(-\))-fluoxetine and S(\(+\))-fluoxetine have different metabolic rates, since a four times greater clearance has been reported for the first, which means that the t\({}_{1/2}\) of the more active S(\(+\)) enantiomer is shorter [4]. Hepatic cytochrome P450 enzymes are responsible for the biotransformation in humans. Particularly, fluoxetine undergoes metabolic transformation mediated by CYP isoenzymes, and less than 10% is excreted unchanged or as fluoxetine N-glucuronide [55]. CYP2D6, and other isoforms such as CYP2C9 and CYP3A4, mediate N-demethylation to the active metabolite nonfluoxetine (**M1**). Concerning this metabolite, the pharmacological difference between enantiomers is even stronger: S(\(+\))-norfluoxetine is 20 times more potent in inhibiting serotonin uptake than the R(\(-\)) isomer [3]. Norfluoxetine has a longer t\({}_{1/2}\) (4-16 days), and it can also be converted to its glucuronide form [3; 5]. CYP2D6 also mediates the further degradation of R(\(-\))-fluoxetine, S(\(+\))-fluoxetine, and S(\(+\))-norfluoxetine, without influencing R(\(-\))-norfluoxetine concentration. Other studies report that CYP2C9 is more selective for the R(\(-\)) enantiomer, while the remaining isoforms catalyze N-demethylation on both isomers with similar rates [56]. The oxidative O-dealkylation reaction of fluoxetine can also lead to the formation of another metabolite, p-trifluoromethylphenol (**M2**). This reaction is mediated by CYP2C19 and CYP3A4 [5]. Several analytical methods have been developed through the years for the identification and quantification of fluoxetine and its metabolites in biological samples. HPLC-UV, mass spectrometry, and gas chromatography are some of the tools included in the methods currently available in the literature [5; 57; 58; 59]. The choice of applying one or more of such analytical techniques should also take into consideration the stereochemical aspects [6]. For the sake of completeness, we have investigated the scavenging activity of **M1** and **M2**. \(\Delta\)G\({}^{\circ}\)HAT are shown in Figure 4 and reported in Table S2. The results of norfluoxetine are very similar to those of **1**. Scavenging via HAT is thermodynamically most favored from C sites 7, 14-16. Particularly, in the gas phase, the largest (negative) \(\Delta\)G\({}^{\circ}\)HAT values are found for C 7 (\(-\)30.94 and \(-\)16.43 kcal mol\({}^{-1}\) for HO\({}^{\bullet}\) and CH\({}_{3}\)O\({}^{\bullet}\)), which become even more negative with increasing solvent polarity, i.e., \(-\)31.48 and \(-\)16.41 kcal mol\({}^{-1}\) in benzene and \(-\)32.61 and \(-\)17.53 kcal mol\({}^{-1}\) in water, respectively. In general, the reactivity of **M1** from these sites toward the hydroxyl and methoxyl radicals via HAT is enhanced when compared to that of **1**.