I. INTRODUCTION
Letrozole (Figure 1), systematic name 4,4′-(H-1,2,4-triazol-1-ylmethylene)-dibenzonitrile, a non-steroidal aromatase inhibitor, which can inhibit the peripheral conversion of circulating androgens to estrogens and is approved for the treatment of advanced breast cancer in postmenopausal women. Letrozole is superior to tamoxifen and as well tolerated as tamoxifen (Cohen et al., Reference Cohen, Johnson, Li, Chen and Pazdur2002). Besides, letrozole can improve clinical outcome effectively and is superior to anastrozole in suppressing breast cancer tissue and plasma estrogen levels (Geisler et al., Reference Geisler, Helle, Ekse, Duong, Evans, Nordbø, Aas and Lønning2008).
Figure 1. Structural formula of letrozole.
The atomic structure based on single-crystal data of letrozole was reported by Xu et al. (Reference Xu, Ma, Wang, Chen, Yang and Wang2002) and Wang et al. (Reference Wang, Bei, Li, Yang and Wang2004), the average values of cell parameters were a = 7.030(0) Å, b = 16.170(3) Å, c = 13.360(3) Å, α = γ = 90°, β = 104.80(3)°, unit-cell volume V = 1468.3(5) Å3, Z = 4, and space-group P21/c. Presently, the detailed X-ray powder diffraction data for letrozole have not been reported in the literature.
II. EXPERIMENTAL
A. Sample preparation
The title compound letrozole was obtained from DaLian MeiLun Biology Technology Co., Ltd. (DaLian, China), recrystallized in methanol and dried. Then it was ground into powder (ρ = 1.31 g cm−3, T melt = 182–184 °C), sieved through a 200-mesh screen and then mounted on a flat zero background plate. It has also been characterized by UV (Figure S1) and elemental analysis. The elemental analysis showed the content of C, N, and H were 70.64, 24.57, and 3.38%, respectively.
B. Diffraction data collection and reduction
The diffraction pattern for the title compound was collected using an X'Pert PRO diffractometer (PANalytical) with an X'celerator detector and CuKα radiation (generator setting: 40 kV, 40 mA). The diffraction data were collected over the angular range from 5° to 50° 2θ with a step size of 0.013 13°2θ and a counting time of 60 ms step−1. Data evaluation was executed using the software package Material Studio 4.2 (Accelrys Co., Ltd., California, USA). All data were collected at room temperature and a controlled relative humidity of 60%.
Indexing was carried out by the X-Cell method, and then the indexing result was refined using the Pawley method (Pan et al., Reference Pan, Guo, Duan, Cheng and Li2012) resulting in final R wp of the structure was converged at 5.70%.
III. RESULTS
The experimental powder diffraction pattern is depicted in Figure 2. Indexing results show that letrozole is monoclinic with the space-group P21 /c and unit-cell parameters: a = 7.034(0) Å, b = 16.177(5) Å, c = 13.411(3) Å, α = γ = 90°, β = 105.71(9)°, unit-cell volume V = 1469.0(3) Å3, and Z = 4. The values of 2θ obs, d obs, I obs, h, k, l, 2θ cal, d cal, I cal, and Δ2θ are listed in Table I. All lines of powder and single-crystal data were indexed and are consistent with the P21 /c space group.
Figure 2. X-ray powder diffraction pattern of letrozole, using CuKα 1 radiation (λ = 1.540 56 Å).
Table I. Indexed X-ray powder diffraction data of letrozole. All measured lines were indexed and are consistent with the P21 /c space group. The d-values were calculated using CuKα 1 radiation (λ = 1.540 56 Å).
SUPPLEMENTARY MATERIAL
The supplementary material for this article can be found at http://www.journals.cambridge.org/PDJ
ACKNOWLEDGEMENTS
This work was supported by the Applied Basic Research Project of Sichuan Province (Grant no. 2014JY0042), the Testing Platform Construction of Technology Achievement Transform of Sichuan Province (Grant no. 13CGPT0049), and the National Development and Reform Commission and Education of China (Grant no. 2014BW011).
