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Eszopiclone (Lunesta™): An Analytical Profile Roxanne E. Franckowski, M.S.* and Robert A. Thompson, Ph.D. ABSTRACT: Eszopiclone (Lunesta™) is a nonbenzodiazepine hypnotic/sedative prescribed for treatment of insomnia. Analytical data (gas chromatography, mass spectrometry, infrared spectroscopy, ultra performance liquid chromatography, and proton and carbon-13 nuclear magnetic resonance spectroscopy) for eszopiclone are presented. KEYWORDS: Lunesta™, Eszopiclone, Hypnotic, Sedative, Forensic Chemistry Introduction The DEA Special Testing and Research Laboratory recently received a sample of eszopiclone (Figure 1) to add to its reference standards collection. Eszopiclone (the active “S” enantiomer of zopiclone) is a nonbenzodiazepine hypnotic/sedative prescribed for treatment of chronic (long-term) insomnia. It is currently marketed in tablet form as Lunesta™, in concentrations of 1, 2, or 3 milligrams per tablet (see Photo 1) (1). Although it has a reduced potential for abuse versus classic benzodiazepine hypnotic/sedatives, it is a Schedule IV controlled substance, and federal law restricts it to prescription use. Based upon its potential for abuse, and the limited literature available concerning its analysis, herein are provided GC, GC/MS, FTIR-ATR, UPLC, and 1H- and 13C-NMR data for eszopiclone.
Experimental and Discussion Eszopiclone Gas Chromatography (GC)
Approximately 8.95 milligrams and 8.63 milligrams of eszopiclone were added to 2 mL of methanol and 2 mL of chloroform, respectively, and vortexed until dissolved; eszopiclone took longer to dissolve in methanol than in chloroform. Utilizing the described experimental parameters, both solutions displayed a major chromatographic peak at 21.14 minutes. In addition, both solutions displayed the same chromatographic pattern with minor early eluting peaks - possibly due to eszopiclone breakdown. The chromatogram of the chloroform solution is illustrated in Figure 2. Gas Chromatography/Mass Spectrometry (GC/MS)
In methanol, one major peak at approximately 18 minutes was observed in the Total Ion Chromatogram (TIC) (Figure 3), with minor early eluting peaks as noted above. The fragmentation pattern shows a base peak at m/z 143 with other mass fragments at m/z 245, 99, 112, 217, 139, and 56 (Figure 4). The molecular ion was not detected. Fourier Transform Infrared Spectroscopy - Attenuated Total Reflectance (FTIR-ATR)
The eszopiclone standard was analyzed directly without preparation. Figure 5 (full spectrum) and Figure 6 (fingerprint region) illustrate the baseline-corrected spectra. The following is a list of assignments and corresponding wavenumbers (cm-1): Aromatic C-H stretch (3077), aliphatic C-H stretch (2941, 2837, 2789), ester carbonyl stretch (1730), amide carbonyl stretch (1713), CH2 bend (1462), CH3 bend (1417), tertiary aromatic amine (1370), aliphatic C-N (1290, 1238, 1140), C-O stretch (1086), and C-Cl stretch (848) (3). Ultra Performance Liquid Chromatography (UPLC)
A 100 mM phosphate buffer, pH 1.8, was added to 2.32 milligrams of eszopiclone until a 25.0 mL final volume was obtained. The solution was then sonicated for 15 minutes. Utilizing the above parameters, one peak at a retention time of 3.73 minutes was observed (Figure 7). Figure 8 illustrates the UV spectrum between the wavelengths 220 - 340 nm. The maximum UV absorbance is 301 nm. Nuclear Magnetic Resonance (NMR) Spectroscopy 1H- and 13C-NMR spectra (see Figures 9 and 10, respectively) were acquired on a Varian Mercury Plus 400 MHz instrument using a Nalorac 5 mm indirect detect pulse field gradient (PFG) probe at 25 °C. (1H parameters: Number of scans (nt) = 8, pulse width (pw) = 45 °, relaxation delay (d1) = 5 s, acquisition time (at) = 2.5 s; 13C parameters: nt = 4098, pw = 45 °, d1 = 1 s, at = 1.3 s, complete proton decoupling). Spectra were processed using ACD’s SpecManager software (Applied Chemistry Development Inc.©, Toronto, Canada). Eszopiclone was prepared in CDCl3 containing 0.05 % v/v tetramethylsilane (TMS; Aldrich Chemical Co., Milwaukee, WI) at 16.84 mg/mL. Chemical shifts (δ) are reported in parts per million (ppm) using TMS (0.0 ppm) as the reference standard. 1H data are reported as follows: Chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad), coupling constant, number of protons present. 1H-NMR (400 MHz, CDCl3) δ 8.90 (d, J = 2.5 Hz, 1H), 8.85 (d, J = 2.5 Hz, 1H), 8.52 (d, J = 8.9 Hz, 1H), 8.40 (d, J = 2.4 Hz, 1H), 8.02 (s, 1H), 7.80 (dod, J = 8.9, 2.5 Hz, 1H), 3.65 (br m, 1H), 3.54 (br m, 1H), 3.25 (br s, 2H), 2.42 (br m, 2H), 2.26 (s, 3H), 2.22 (br m, 1H), 2.05 (br m, 1H). 13C-NMR (100 MHz, CDCl3) * 165.4, 162.9, 155.6, 153.4, 148.4, 147.8, 146.8, 143.9, 138.1, 133.4, 128.3, 116.1, 79.1, 54.5, 52.3, 46.1, 44.1. Acknowledgements The authors wish to thank Senior Forensic Chemist Patrick A. Hays (this laboratory), for his time and NMR expertise, and Senior Forensic Chemist Dr. Edward S. Franzosa (this laboratory), for his time and help with imaging the tablets. References 1. Material Safety Data Sheet. Lunesta™ Tablets, Sepracor Inc., Marlborough, MA:2005, p. 1. 2. Material Safety Data Sheet. Lunesta™ Tablets, Sepracor Inc., Marlborough, MA:2005, p. 6. 3. Sepracor Inc., Marlborough, MA. Personal communication, May, 2006. - - - - - - - - - - [Figures 2 - 10 Follow.]
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