I. INTRODUCTION
Antimicrobial peptides are natural antimicrobial materials involved in innate immunity mechanisms in vivo, and low-molecular weight peptide materials that retain antimicrobial activities against various, microorganisms including bacteria, fungi, and viruses and induce local biophylaxis and systemic immune response. The title compound as a tyrosine derivative has been reported to promote secretion of human antimicrobial peptides in vivo (Park et al., Reference Park, Bae, Jeong and Gwak2012). Therefore, it is usually used in cosmetics (Commo et al., Reference Commo, Sextius and Marat2014; Jeong et al., Reference Jeong, Kim, Shin, Kim, Lee, Jeon, Kim, Lee, Mauro, Uchida and Park2015). So far, the crystal structure of the title compound has not been reported.
II. EXPERIMENTAL
A. Sample preparation
The title compound (Figure 1) was purchased from Shanghai Superlan Chemical Technology Centre. The melting point and measured density of the title compound are 90–91 °C and 1.116 g cm−3, respectively. Crystallization of the title compound at room temperature was successful using methanol as solvent. Then, parts of crystals were dried and ground into powder and mounted on a flat zero background plate.
Figure 1. Molecular diagram of the title compound.
B. Diffraction data collection and reduction
The X-ray powder diffraction measurement was performed at 298 K using an X'Pert PRO diffractometer (PANalytical Co., Ltd., The Netherlands) with a PIXcel 1D detector and CuKα radiation (generator setting: 40 kV and 40 mA). The sample was mounted on a flat zero background plate. The diffraction data (Figure 2) 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 50 ms per step.
Figure 2. The raw XRD pattern of the title compound.
The software package Material Studio 8.0 (Accelrys Co., Ltd., San Diego, CA, USA) was used to process the data in the Analytical & Testing Center (Sichuan University, Chengdu, China). The X-ray powder diffraction pattern was pre-treated by subtracting the background, smoothing, and stripping off the Kα 2 component. Automatic indexing results were obtained by DICVOL91 method (Boultif and Louër, Reference Boultif and Louër1991). The following figures of merit were achieved: F 18 = 27.0 (0.0099, 67) (Smith and Snyder, Reference Smith and Snyder1979) and M 18 = 13.6 (de Wolff, Reference de Wolff1968). The indexing results were then refined using Pawley (R wp = 5.45%) (Pawley, Reference Pawley1981), which involves assigning the Miller indices (h, k, l) to each observed peak in the experimental powder XRD pattern (Table I).
Table I. X-ray powder diffraction data for (S)-methyl-2-hexanamido-3-(4-hydroxyphenyl)propanoate, C16H23NO4 at 298 K. The d-values were calculated using CuKα 1 radiation (λ = 1.540 56 Å).
C. Single-crystal X-ray diffraction
X-ray diffraction data for the title compound were collected on a New Gemini, Dual, Cu at zero, EosS2 diffractometer. The crystal was kept at 110 K during data collection. The structure was solved with Olex2 (Dolomanov et al., Reference Dolomanov, Bourhis, Gildea, Howard and Puschmann2009), using charge flipping and refined with the SHELXL (Sheldrick, Reference Sheldrick2008) refinement package using least-squares minimization (Azzam et al., Reference Azzam, Elgemeie, Elsayed and Jones2017; Park et al., Reference Park, Kim, Kwon and Kim2017).
III. RESULTS
Pawley refinement results confirmed that the title compound is orthorhombic with space group P212121 and unit-cell parameters: a = 17.795(4) Å, b = 15.101(1) Å, c = 12.746(3) Å, unit-cell volume V = 3425.51 Å3, Z = 8, ρ cal = 1.138 g cm−3. All measured lines (Table I) were indexed and are consistent with the P212121 space group.
The single-crystal experiment was carried out at the temperature of 110 K and the structure solution was obtained [a = 12.5998(3) Å, b = 17.6856(5) Å, c = 14.6711(5) Å, unit-cell volume V = 3269.25(16) Å3, Z = 8, ρ cal = 1.192 g cm−3, and space group P212121]. The detailed single-crystal data of title compound and the experimental data were listed in Table II. The figures were drawn with ORTEP-3 (Oak Ridge Thermal Ellipsoid Plot) and Mercury (Figure 3). The title compound as a simple antimicrobial peptide was synthesized by reacting l-tyrosine methyl ester and hexanoyl chloride. The hexanoyl group was rotated by 111.2(4)° (N1–C10–C9) with the methyl propionate. The methyl propionate was rotated by 96.4(6)° (C5–C6–C7–C10) with the plane of benzene ring. C13 in hexanoyl group was disordered. To some degree, the crystal structure was stabilized by some hydrogen bonds. Two strong H bond donors in the title compound were N1–H and O1–H, and two strong acceptors, namely, C9 = O3 and C11 = O4, competed for these H bond donors.
Figure 3. (Color online) (a) ORTEP drawing one of the two independent molecules in the asymmetric unit of the title compound with the labeling of non-H atoms. C13 in hexanoyl group was disordered. (b) Crystal packing of the title compound.
Table II. Crystal and experimental data of the title compound.
Because of the powder diffraction, data were measured at 298 K and the single-crystal diffraction data were measured at 110 K, the cell parameters, volume, and calculated density of single-crystal experiment have slight differences with powder diffraction results. The deviations of the two methods were between 0.6 and 4.5%.
SUPPLEMENTARY MATERIAL
The supplementary material for this article can be found at https://doi.org/10.1017/S088571561800074X.
