I. INTRODUCTION
7-Ethyl-14-amino-camptothecin was reported as a promising candidate for tumor treatment based on its superiority to traditional camptothecin derivatives, including excellent efficacy, acceptable safety, significant brain penetration and poor substrate properties toward the major drug-resistant pumps (Duan et al., Reference Duan, Cai, Meng, Sun and Liu2011; Cheng et al., Reference Cheng, Qiu, Yang, Liu and Wen2015). The title compound, 7-ethyl-14-nitro-camptothecin (ENC, Figure 1), is an intermediate in the synthesis of 7-ethyl-14-amino-camptothecin from 7-ethylcamptothecin (Duan et al., Reference Duan, Cai, Meng, Sun and Liu2011). Therefore, it is very important to design the crystallization techniques of ENC as well as to be certain of its crystal structure.
Figure 1. Molecular diagram for 7-ethyl-14-nitro-camptothecin.
To date, detailed X-ray powder diffraction (XRD) data for ENC have not been reported.
II. EXPERIMENTAL
A. Sample preparation
ENC was obtained from Sichuan Sinovation Biotech Co., Ltd., China. It was re-crystallized in methanol–dichloromethane (1 : 1, v/v), then dried and ground into powder. The sample was characterized by melting point (306.9 °C), density (1.459 g cm−3), FT-IR (Supplementary Figure S1) and MS ([M + H]+ = 422.1, Supplementary Figure S2). Further, a purity of 98.5% was checked by HPLC (Supplementary Figure S3).
B. Diffraction data collection and reduction
XRD measurements were performed at room temperature using an X'Pert PRO diffractometer (PANalytical Co., Ltd., Netherlands) with a PIXcel one-dimensional detector and CuKα radiation (λ = 1.5406 Å, generator voltage and current were set at 40 kV and 40 mA). The diffraction data were collected over the angular range from 4° to 50° 2θ with a step size of 0.013 13° 2θ and a counting time of 29.07 ms per step (Figure 2).
Figure 2. XRD pattern of 7-ethyl-14-nitro-camptothecin using CuKα radiation.
Data evaluation was performed using the software package Material Studio 8.0 (Accelrys Co., Ltd., San Diego, California, USA) in the Analytical & Testing Center (Sichuan University, Chengdu, China). The XRD pattern was pre-treated by subtracting the background, smoothing, and stripping off the Kα 2 component. Automatic indexing results were obtained with DICVOL91 (Boultif and Louër, Reference Boultif and Louër1991). The following figures of merit were achieved: F 27 = 26.6 (0.0132, 77) (Smith and Snyder, Reference Smith and Snyder1979) and M 27 = 11.1 (de Wolff, Reference de Wolff1968). The indexing results were then refined using Pawley refinement (Pawley, Reference Pawley1981), which involves assigning the Miller indices (h, k, l) to each observed peak in the experimental XRD pattern.
III. RESULTS
The experimental powder diffraction pattern is depicted in Figure 2. Indexing results showed that ENC is triclinic, space group P-1 and unit-cell parameters: a = 10.987(5) Å, b = 10.941 (9) Å, c = 8.438 (2) Å, α = 71.321(6)°, β = 96.145(0) °, γ = 95.139(3)°, unit-cell volume V = 953.87 Å3, Z = 2, ρ cal = 1.467 g cm−3. The values of 2θ obs, d obs, I obs, h, k, l, 2θ cal, d cal, I cal, Δ2θ are listed in Table I. All measured lines were indexed and are consistent with the P-1 space group. No detectable impurities were observed.
Table I. Indexed XRD data for 7-ethyl-14-nitro-camptothecin, C22H19N3O6. The d-values were calculated using CuKα radiation (λ = 1.540 56 Å).
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0885715618000684.
