research communications
9.36]heptadecane
of 7,8,15,16,17-pentathiadispiro[5.2.5aInstitut für Pharmazie, Universität Greifswald, Friedrich-Ludwig-Jahn-Strasse 17, 17489 Greifswald, Germany, and bInstitut für Biochemie, Universität Greifswald, Felix-Hausdorff-Strasse 4, 17489 Greifswald, Germany
*Correspondence e-mail: link@uni-greifswald.de, carola.schulzke@uni-greifswald.de
The title compound, C12H20S5, crystallizes in the monoclinic P21/c with four molecules in the In the crystal, the comprises the entire molecule with the three cyclic moieties arranged in a line. The molecules in the pack in a parallel fashion, with their longitudinal axes arranged along a uniform direction. The packing is stabilized by the one-dimensional propagation of non-classical hydrogen-bonding contacts between the central sulfur atom of the S3 fragment and the C—H of a cyclohexyl group from a glide-related molecule [C⋯S = 3.787 (2) Å].
CCDC reference: 1916548
1. Chemical context
Cyclic ), as well as a plethora of H2S-mediated effects relying on H2S formation (Szabo & Papapetropoulos, 2017). The benefits imparted by these compounds have led to the evolution of synthetic pathways in many natural products, as well as organoleptic detection mechanisms in organisms confronted by them, including the senses of smell and taste in humans. Thus, volatile organic are among the most odorous compounds in natural products, including meat (Zhao et al., 2019), plants (Liang et al., 2017), and algae (Block et al., 2017). In fungi, 1,2,4-trithiolane, 1,2,4,6-tetrathiepane, and 1,2,3,4,5,6-hexathiepane have been found to contribute to the unique aroma of shiitake (Lentnius edodes), but it is 1,2,3,5,6-pentathiepane (lenthionine) that combines the most potent biological (antibacterial, antifungal, and anti-coagulative) and sensory activity (Davison & Sperry, 2017). Structural characterizations of this type of compounds are rather rare. The very few reports available in the literature include the crystal structures of pentathiepanes featuring two vicinal carbon atoms (Sugihara et al., 1999). The conformational study of the title compound, 7,8,15,16,17-pentathiadispiro[5.2.59.36]heptadecane (C12H20S5), is supposed to aid in the elucidation of the mechanism of action by which naturally occurring and synthetic pentathiepanes exert potent activity (Behnisch-Cornwell et al., 2019) and to advance the application of lenthionine derivatives for medical and material purposes (Tanagi et al., 2019).
comprise a of pharmacologically interesting organosulfur compounds that – depending on constitution and conformation – have been shown to exert specific antibacterial, antifungal, allelopathic and cytotoxic activity (Davison & Sperry, 20172. Structural commentary
The title compound 7,8,15,16,17-pentathiadispiro[5.2.59.36]heptadecane, C12H20S5, crystallizes in the monoclinic P21/c. The molecule constitutes the while Z =4. The title compound consists of three rings in a corner-sharing juxtaposed arrangement (Fig. 1). The two outer cyclohexyl rings are both in a typical, rather unremarkable, chair conformation. They are connected to the central ring via spiro carbon atoms, which are tethered to each other by one S2 and one S3 moiety, thereby forming the central seven-membered ring. Crystal structures of such heterocyclic rings bearing five sulfur atoms in groups of two and three plus two carbon atoms are extremely rare, with only one example being available to date (Mloston et al., 2002; refcode: MOSYOI in the CSD, version 5.40, March 2019; Groom et al., 2016). In MOSYOI, the cyclohexyl substituents of this structure are replaced by 2,2,4,4-tetramethylcyclobutan-1-one moieties. The arrangement of the seven atoms of the central ring appears to be quite inflexible, at least in the solid state, as emphasized by an overlay of the two structures (Fig. 2), which shows distances of the overlayed atoms all well below 0.1 Å and an r.m.s. deviation of 0.0846 Å. Considering that the four-membered and heavily substituted rings in MOSYOI (Mloston et al., 2002) are much more strained than the cyclohexane rings in the title compound, the conserved conformation of the central ring points towards the observed arrangement being thermodynamically rather favorable. In the context of investigating these compounds as pharmaceutical leads, such highly conserved structural motives are quite beneficial. The mean planes of the two cyclohexane rings, calculated from the positions of the six carbon atoms (Mercury software; Macrae et al., 2006), enclose an angle of 21.96 (9)°, i.e. the two rings are not coplanar. The angles between the plane calculated from the positions of all seven atoms of the central ring and both cyclohexane-derived planes are 82.90 (5)° (C1 → C6) and 76.79 (5)° (C7 → C12), which are both close to perpendicular. This is similar in MOSYOI, with the four-membered rings being nearly perpendicular to the central seven-membered ring. The sulfur–sulfur bond distances range from 2.026 (1) to 2.035 (1) Å, which is a little bit shorter than the sum of the covalent radii of 2.06 Å (Pyykkö & Atsumi, 2009). The shortest S—S distance is between the two sulfur atoms of the S2 moiety, while the S3 moiety is slightly unsymmetrical [2.028 (1) and 2.035 (1) Å]. The shorter S—S bond in the S3 moiety is the one that points towards a non-classical hydrogen-bonding contact (vide infra), implying that this interaction might influence the relative distances in the S3 fragment. The angles involving central S atoms range from 105.16 (5)° (around S1) to 106.89 (5)° (around S3) while the S—C—S angles are slightly wider with 111.58 (7)° (around C1) and 114.31 (7)° (around C7), i.e. they are more and less acute, respectively, than the ideal tetrahedral angle.
3. Supramolecular features
In the crystal packing all molecules are oriented along parallel lines, although turned/flipped alternately by roughly 180° around the molecules' approximate longitudinal axes through the three rings which rest on crystallographic glides in the ac planes. The crystallographic direction of these vectors approximates [40]. The crystal packing is stabilized by non-classical hydrogen-bonding contacts between the central sulfur atom (S2) of the S3 fragment as acceptor and a C—H of one cyclohexyl moiety (C6—H6B) as donor, pointing roughly into opposite directions and protruding along the c-axis direction (C6—H6B⋯S2i and S2⋯H6Bii—C6ii; symmetry codes: (i) x, − y, + z, (ii): x, − y, − + z) (Fig. 3 and Table 1).
4. Synthesis and crystallization
The title compound was synthesized based on a modified literature procedure (Magnusson, 1959). A 20% aqueous solution of ammonium polysulfide (63.9 ml, 187 mmol) was cooled to 273 K and added dropwise over 10 min to stirred cyclohexanone (25.8 ml, 250 mmol) cooled to the same temperature, leading to a uniform mixture of yellow color. Deviating from the reported procedure, addition of colloidal sulfur (4.0 g, 125 mmol), albeit quickly dissolving, leads to liquid–liquid and a change of color from yellow to green. After stirring for 24 h at 295 K, 100 ml of 10% aqueous acetic acid was added to the reaction mix, which then was extracted in 3 × 50 ml of diethyl ether. The organic fractions were combined and washed with aqueous, saturated NaHCO3 (1×100 ml) and water (1×100 ml), before being dried over Na2SO4. The solvent was reduced to 5 ml in vacuo and adsorbed onto isolute® HM-N, prior to purification by flash (silica 60, 20-45 µm particle diameter, 5 cm column diameter, 50 cm column length, 15 ml min−1 ethyl acetate (0–25%) in n-hexane, detection by thin layer and fluorescence quenching at 254 nm). Recrystallization from 0.1 ml mg−1 methanol yielded colorless block-like crystals, the identity of which was confirmed by melting point determination (356.5 K). As a result of the lipophilic nature of the analyte, the purity and stability of the colorless product was accessible to (stationary phase: Torus DIOL column, mobile phase: scCO2 (A) and methanol containing 20 mM ammonium formate (B), isocratic mode (5% B), oven temperature: 313 K). Yield: 5.0 g (14%).
1H NMR (400MHz, CDCl3) δ 1.45 ppm (q, 4H), 1.6 ppm (m, 8H), 1.9 ppm (t, 8H). 13C{1H} NMR (101MHz, CDCl3) δ 25.4 ppm, 37.8 ppm. IR (FT–IR): (υ cm−1) = 2926 (s), 1439 (s). Elemental analysis calculated for C12H20S5: C 44.40; H 6.21; S 49.39. Found: C 44.72; H 6.03; S 49.25.
5. Refinement
Crystal data, data collection and structure . All C-bound hydrogen atoms constitute methylene protons, which were attached in calculated positions (C—H = 0.99 Å) and treated as riding with Uiso(H) = 1.2Ueq(C).
details are summarized in Table 2Supporting information
CCDC reference: 1916548
https://doi.org/10.1107/S2056989019007138/fy2136sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019007138/fy2136Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989019007138/fy2136Isup3.cml
Data collection: X-AREA (Stoe & Cie, 2010); cell
X-AREA (Stoe & Cie, 2010); data reduction: X-AREA (Stoe & Cie, 2010); program(s) used to solve structure: SHELXT2018 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2006); software used to prepare material for publication: CIFTAB (Sheldrick, 2015).C12H20S5 | F(000) = 688 |
Mr = 324.58 | Dx = 1.464 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 9.4174 (19) Å | Cell parameters from 16821 reflections |
b = 9.970 (2) Å | θ = 6.3–58.9° |
c = 15.877 (3) Å | µ = 0.76 mm−1 |
β = 98.94 (3)° | T = 170 K |
V = 1472.6 (5) Å3 | Block, colourless |
Z = 4 | 0.39 × 0.36 × 0.28 mm |
Stoe IPDS2T diffractometer | 3534 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.039 |
Detector resolution: 6.67 pixels mm-1 | θmax = 29.4°, θmin = 3.1° |
ω scans | h = −13→12 |
16257 measured reflections | k = −13→13 |
4048 independent reflections | l = −21→21 |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.028 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.071 | H-atom parameters constrained |
S = 1.07 | w = 1/[σ2(Fo2) + (0.035P)2 + 0.4842P] where P = (Fo2 + 2Fc2)/3 |
4048 reflections | (Δ/σ)max = 0.001 |
154 parameters | Δρmax = 0.35 e Å−3 |
0 restraints | Δρmin = −0.39 e Å−3 |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.31425 (3) | 0.61591 (3) | 0.37879 (2) | 0.02374 (8) | |
S2 | 0.38015 (3) | 0.68085 (4) | 0.26964 (2) | 0.02454 (8) | |
S3 | 0.57525 (3) | 0.59559 (3) | 0.26792 (2) | 0.02661 (8) | |
S4 | 0.65189 (4) | 0.83978 (3) | 0.38610 (2) | 0.02869 (9) | |
S5 | 0.58752 (3) | 0.72925 (4) | 0.48039 (2) | 0.02763 (8) | |
C1 | 0.38995 (13) | 0.73599 (13) | 0.46088 (8) | 0.0209 (2) | |
C2 | 0.33611 (14) | 0.87799 (13) | 0.44215 (9) | 0.0248 (3) | |
H2A | 0.357462 | 0.905539 | 0.385535 | 0.030* | |
H2B | 0.388180 | 0.939484 | 0.485236 | 0.030* | |
C3 | 0.17466 (15) | 0.89094 (14) | 0.44305 (10) | 0.0285 (3) | |
H3A | 0.146241 | 0.986281 | 0.435293 | 0.034* | |
H3B | 0.121809 | 0.839446 | 0.394775 | 0.034* | |
C4 | 0.13306 (16) | 0.83957 (14) | 0.52607 (9) | 0.0295 (3) | |
H4A | 0.175028 | 0.899044 | 0.573399 | 0.035* | |
H4B | 0.027179 | 0.842519 | 0.522274 | 0.035* | |
C5 | 0.18500 (16) | 0.69697 (15) | 0.54533 (9) | 0.0298 (3) | |
H5A | 0.132692 | 0.635465 | 0.502332 | 0.036* | |
H5B | 0.163361 | 0.670101 | 0.602005 | 0.036* | |
C6 | 0.34657 (16) | 0.68404 (15) | 0.54448 (8) | 0.0280 (3) | |
H6A | 0.374816 | 0.588653 | 0.552229 | 0.034* | |
H6B | 0.399212 | 0.735309 | 0.592926 | 0.034* | |
C7 | 0.71249 (13) | 0.72138 (13) | 0.31199 (8) | 0.0219 (2) | |
C8 | 0.84149 (14) | 0.64097 (14) | 0.35539 (8) | 0.0252 (3) | |
H8A | 0.912118 | 0.703127 | 0.387439 | 0.030* | |
H8B | 0.809187 | 0.578098 | 0.396805 | 0.030* | |
C9 | 0.91472 (15) | 0.56165 (15) | 0.29197 (9) | 0.0289 (3) | |
H9A | 1.000340 | 0.515105 | 0.322612 | 0.035* | |
H9B | 0.847733 | 0.492960 | 0.263730 | 0.035* | |
C10 | 0.95977 (15) | 0.65513 (16) | 0.22523 (9) | 0.0291 (3) | |
H10A | 1.004584 | 0.602264 | 0.183578 | 0.035* | |
H10B | 1.032100 | 0.719631 | 0.253151 | 0.035* | |
C11 | 0.83096 (15) | 0.73143 (15) | 0.17883 (9) | 0.0280 (3) | |
H11A | 0.762969 | 0.667255 | 0.146541 | 0.034* | |
H11B | 0.863656 | 0.794214 | 0.137496 | 0.034* | |
C12 | 0.75366 (15) | 0.81008 (14) | 0.24074 (9) | 0.0264 (3) | |
H12A | 0.665632 | 0.851094 | 0.208864 | 0.032* | |
H12B | 0.816840 | 0.883488 | 0.266381 | 0.032* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.02576 (15) | 0.02375 (16) | 0.02281 (15) | −0.00552 (12) | 0.00722 (11) | −0.00510 (12) |
S2 | 0.02277 (15) | 0.03175 (17) | 0.01882 (15) | 0.00001 (12) | 0.00232 (11) | −0.00116 (12) |
S3 | 0.02379 (15) | 0.02383 (16) | 0.03371 (18) | −0.00428 (12) | 0.00918 (13) | −0.00932 (12) |
S4 | 0.02747 (16) | 0.02263 (16) | 0.03820 (19) | −0.00624 (13) | 0.01207 (14) | −0.01101 (13) |
S5 | 0.02292 (15) | 0.0385 (2) | 0.02067 (15) | 0.00173 (13) | 0.00072 (11) | −0.00585 (13) |
C1 | 0.0228 (5) | 0.0217 (6) | 0.0186 (5) | −0.0003 (5) | 0.0042 (4) | −0.0028 (4) |
C2 | 0.0276 (6) | 0.0192 (6) | 0.0296 (7) | −0.0005 (5) | 0.0106 (5) | −0.0007 (5) |
C3 | 0.0284 (6) | 0.0247 (7) | 0.0349 (7) | 0.0046 (5) | 0.0122 (5) | 0.0043 (5) |
C4 | 0.0309 (7) | 0.0280 (7) | 0.0327 (7) | 0.0002 (5) | 0.0146 (6) | −0.0021 (6) |
C5 | 0.0361 (7) | 0.0289 (7) | 0.0274 (7) | −0.0022 (6) | 0.0145 (5) | 0.0026 (5) |
C6 | 0.0350 (7) | 0.0306 (7) | 0.0195 (6) | 0.0034 (6) | 0.0075 (5) | 0.0033 (5) |
C7 | 0.0211 (5) | 0.0203 (6) | 0.0247 (6) | −0.0023 (5) | 0.0049 (4) | −0.0037 (5) |
C8 | 0.0245 (6) | 0.0279 (6) | 0.0233 (6) | 0.0015 (5) | 0.0040 (5) | 0.0019 (5) |
C9 | 0.0265 (6) | 0.0309 (7) | 0.0299 (7) | 0.0071 (5) | 0.0065 (5) | 0.0015 (5) |
C10 | 0.0236 (6) | 0.0381 (8) | 0.0268 (7) | −0.0002 (6) | 0.0073 (5) | −0.0016 (6) |
C11 | 0.0283 (6) | 0.0333 (7) | 0.0230 (6) | −0.0023 (6) | 0.0059 (5) | 0.0033 (5) |
C12 | 0.0276 (6) | 0.0216 (6) | 0.0304 (7) | −0.0009 (5) | 0.0059 (5) | 0.0032 (5) |
S1—C1 | 1.8306 (13) | C5—H5B | 0.9900 |
S1—S2 | 2.0353 (6) | C6—H6A | 0.9900 |
S2—S3 | 2.0284 (6) | C6—H6B | 0.9900 |
S3—C7 | 1.8579 (13) | C7—C8 | 1.5274 (18) |
S4—C7 | 1.8200 (13) | C7—C12 | 1.5325 (18) |
S4—S5 | 2.0261 (6) | C8—C9 | 1.5267 (19) |
S5—C1 | 1.8393 (13) | C8—H8A | 0.9900 |
C1—C2 | 1.5175 (18) | C8—H8B | 0.9900 |
C1—C6 | 1.5382 (18) | C9—C10 | 1.520 (2) |
C2—C3 | 1.5282 (19) | C9—H9A | 0.9900 |
C2—H2A | 0.9900 | C9—H9B | 0.9900 |
C2—H2B | 0.9900 | C10—C11 | 1.522 (2) |
C3—C4 | 1.5211 (19) | C10—H10A | 0.9900 |
C3—H3A | 0.9900 | C10—H10B | 0.9900 |
C3—H3B | 0.9900 | C11—C12 | 1.5277 (19) |
C4—C5 | 1.519 (2) | C11—H11A | 0.9900 |
C4—H4A | 0.9900 | C11—H11B | 0.9900 |
C4—H4B | 0.9900 | C12—H12A | 0.9900 |
C5—C6 | 1.529 (2) | C12—H12B | 0.9900 |
C5—H5A | 0.9900 | ||
C1—S1—S2 | 105.16 (5) | C1—C6—H6B | 109.2 |
S3—S2—S1 | 105.95 (3) | H6A—C6—H6B | 107.9 |
C7—S3—S2 | 106.89 (5) | C8—C7—C12 | 111.17 (10) |
C7—S4—S5 | 106.55 (5) | C8—C7—S4 | 110.87 (9) |
C1—S5—S4 | 105.47 (5) | C12—C7—S4 | 104.10 (9) |
C2—C1—C6 | 110.96 (10) | C8—C7—S3 | 105.87 (9) |
C2—C1—S1 | 112.92 (9) | C12—C7—S3 | 110.64 (9) |
C6—C1—S1 | 105.53 (9) | S4—C7—S3 | 114.31 (7) |
C2—C1—S5 | 111.44 (9) | C9—C8—C7 | 112.56 (11) |
C6—C1—S5 | 103.87 (9) | C9—C8—H8A | 109.1 |
S1—C1—S5 | 111.58 (7) | C7—C8—H8A | 109.1 |
C1—C2—C3 | 112.31 (11) | C9—C8—H8B | 109.1 |
C1—C2—H2A | 109.1 | C7—C8—H8B | 109.1 |
C3—C2—H2A | 109.1 | H8A—C8—H8B | 107.8 |
C1—C2—H2B | 109.1 | C10—C9—C8 | 110.22 (12) |
C3—C2—H2B | 109.1 | C10—C9—H9A | 109.6 |
H2A—C2—H2B | 107.9 | C8—C9—H9A | 109.6 |
C4—C3—C2 | 111.73 (12) | C10—C9—H9B | 109.6 |
C4—C3—H3A | 109.3 | C8—C9—H9B | 109.6 |
C2—C3—H3A | 109.3 | H9A—C9—H9B | 108.1 |
C4—C3—H3B | 109.3 | C9—C10—C11 | 110.86 (11) |
C2—C3—H3B | 109.3 | C9—C10—H10A | 109.5 |
H3A—C3—H3B | 107.9 | C11—C10—H10A | 109.5 |
C5—C4—C3 | 111.80 (11) | C9—C10—H10B | 109.5 |
C5—C4—H4A | 109.3 | C11—C10—H10B | 109.5 |
C3—C4—H4A | 109.3 | H10A—C10—H10B | 108.1 |
C5—C4—H4B | 109.3 | C10—C11—C12 | 111.65 (12) |
C3—C4—H4B | 109.3 | C10—C11—H11A | 109.3 |
H4A—C4—H4B | 107.9 | C12—C11—H11A | 109.3 |
C4—C5—C6 | 111.52 (12) | C10—C11—H11B | 109.3 |
C4—C5—H5A | 109.3 | C12—C11—H11B | 109.3 |
C6—C5—H5A | 109.3 | H11A—C11—H11B | 108.0 |
C4—C5—H5B | 109.3 | C11—C12—C7 | 112.29 (11) |
C6—C5—H5B | 109.3 | C11—C12—H12A | 109.1 |
H5A—C5—H5B | 108.0 | C7—C12—H12A | 109.1 |
C5—C6—C1 | 112.17 (11) | C11—C12—H12B | 109.1 |
C5—C6—H6A | 109.2 | C7—C12—H12B | 109.1 |
C1—C6—H6A | 109.2 | H12A—C12—H12B | 107.9 |
C5—C6—H6B | 109.2 |
D—H···A | D—H | H···A | D···A | D—H···A |
C6—H6B···S2i | 0.99 | 2.96 | 3.787 (2) | 142 |
Symmetry code: (i) x, −y+3/2, z+1/2. |
Acknowledgements
The authors would like to thank Dr Anja Bodtke, Maria Hühr and Marlen Redies for NMR-spectroscopic and elemental analyses as well as Michael Eccius and Armin Rau (Thermo Fischer Scientific) for IR support.
References
Behnisch-Cornwell, S., Bandaru, S. S. M., Napierkowski, M., Wolff, L., Zubair, M., Urbainsky, C., Lillig, C., Schulzke, C. & Bednarski, P. J. (2019). J. Med. Chem. Submitted. Google Scholar
Block, E., Batista, V. S., Matsunami, H., Zhuang, H. & Ahmed, L. (2017). Nat. Prod. Rep. 34, 529–557. CrossRef CAS PubMed Google Scholar
Davison, E. K. & Sperry, J. (2017). J. Nat. Prod. 80, 3060–3079. CrossRef CAS PubMed Google Scholar
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CrossRef IUCr Journals Google Scholar
Liang, D., Bian, J., Deng, L. W. & Huang, D. (2017). J. Funct. Foods 35, 197–204. CrossRef CAS Google Scholar
Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453–457. Web of Science CrossRef CAS IUCr Journals Google Scholar
Magnusson, B. (1959). Acta Chem. Scand. 13, 1031–1032. CrossRef CAS Google Scholar
Mloston, G., Majchrzak, A., Senning, A. & Søtofte, I. (2002). J. Org. Chem. 67, 5690–5695. Web of Science CSD CrossRef PubMed CAS Google Scholar
Pyykkö, P. & Atsumi, M. (2009). Chem. Eur. J. 15, 186–197. Web of Science CrossRef PubMed Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Stoe & Cie (2010). X-AREA. Stoe & Cie GmbH, Darmstadt, Germany. Google Scholar
Sugihara, Y., Takeda, H. & Nakayama, J. (1999). Eur. J. Org. Chem. pp. 597–605. CrossRef Google Scholar
Szabo, C. & Papapetropoulos, A. (2017). Pharmacol. Rev. 69, 497–564. CrossRef CAS PubMed Google Scholar
Tanagi, H., Yamamoto, Y. & Horikoshi, H. (2019). Method for producing 1,2,3,5,6-pentathiepane. United States patent application publication, US 201970040035 A1. Google Scholar
Zhao, J., Wang, T., Xie, J., Xiao, Q., Du, W., Wang, Y., Cheng, J. & Wang, S. (2019). Food Chem. 274, 79–88. CrossRef CAS PubMed Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.