research communications
Structural characterization of the azoxy derivative of an antitubercular 8-nitro-1,3-benzothiazin-4-one1
aMartin-Luther-Universität Halle-Wittenberg, Institut für Pharmazie, Wolfgang-Langenbeck-Str. 4, 06120 Halle (Saale), Germany, and bMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
*Correspondence e-mail: ruediger.seidel@pharmazie.uni-halle.de
(Z)-1,2-Bis[4-oxo-2-(piperidin-1-yl)-6-(trifluoromethyl)-4H-benzo[e][1,3]thiazin-8-yl]diazene oxide, C28H24F6N6O3S2, was obtained and its structure determined while attempting to crystallize and structurally characterize 8-nitro-2-(piperidin-1-yl)-6-(trifluoromethyl)-4H-benzo[e][1,3]thiazin-4-one, a simplified analogue of the antituberculosis clinical drug candidate BTZ043. X-ray crystallography revealed the structure of the azoxy compound to be comprised of two benzothiazinone moieties linked by a Z-configured azoxy group in an almost coplanar arrangement. In the crystal, the molecules are densely packed, revealing a herringbone pattern.
Keywords: benzothiazinones; azoxy compound; antituberculosis drugs; reaction mechanism; crystal structure.
CCDC reference: 2219153
1. Chemical context
8-Nitro-1,3-benzothiazin-4-ones (BTZs) are a class of covalently binding inhibitors of decaprenylphosphoryl-β-D-ribose-2′-epimerase (DprE1), an enzyme crucial for cell-wall synthesis in Mycobacterium tuberculosis, the primary pathogen causing tuberculosis (Chikhale et al., 2018). BTZ043 (Fig. 1; Makarov et al., 2009) is one of the most advanced candidates and has recently completed a Phase Ib/IIa clinical study (ClinicalTrials.gov Identifier: NCT04044001). Compound 1 (Fig. 1) represents a simplified analogue of BTZ043, lacking the spiroketal moiety (Richter et al., 2018). The generally accepted mechanism of action of BTZs is a reduction of the nitro group to a nitroso group by FADH2, followed by a semimercaptal formation with Cys387 (Trefzer et al., 2010, 2012; Neres et al., 2012; Richter et al., 2018). Tiwari et al. (2013) suggested an alternative mechanism in which the reduction to the nitroso form is initiated by nucleophilic addition of thiolate to C-7 of the BTZ system. Subsequent formation of the azoxy form was postulated, but no proof of the structure is available. Liu et al. (2019) reported detection of the BTZ043 azoxy form by LC/MS in a reaction mixture. To the best of our knowledge, an azoxy derivative of an antitubercular BTZ has not been structurally characterized thus far.
The azoxy derivative of 1 was obtained unintentionally during an attempt to grow crystals of 1 for X-ray crystallography by leaving a dimethylformamide (DMF) solution of 1 at ambient conditions and allowing the solvent to evaporate slowly. Fig. 2 shows a possible reaction pathway to the azoxy derivative. Compound 1 is reduced to the nitroso congener 2 and then to the hydroxylamine 3, which reacts with excess of 2 in a condensation reaction to yield the azoxy compound 4. Although it remains unclear how the reduction of the nitro group in 1 was induced in the absence of an intended reducing agent, this pathway has some plausibility (Chen et al., 2017; Cole et al., 2017). Possibly DMF acted as a reducing agent here (Heravi et al., 2018). Moreover, DMF usually contains small amounts of water, which causes partial hydrolysis (Meglitskii & Kvasha, 1972). Thus, trace amounts of dimethylamine often contained in DMF may have initiated reduction of 1 by nucleophilic addition to C-7 of the BTZ system. A related reaction of BTZs with nucleophilic attack by thiolates on C-7 was postulated by Tiwari et al. (2013).
The identification and structural characterization of 4 could be relevant for drug stability assessment of BTZs. To the best of our knowledge, targeted synthesis of an azoxy derivative of an antitubercular BTZ and antimycobacterial testing has not been reported so far. In this context, it is interesting to note that a variety of azoxy compounds occur naturally and have various biological effects, including potent growth inhibition of M. tuberculosis in vitro exerted by the compound elaiomycin (Dembitsky et al., 2017; Wibowo & Ding, 2020).
2. Structural commentary
Fig. 3 shows the molecular structure of 4 in the crystal. The two benzothiazinone moieties and the Z-configured azoxy linkage exhibit a nearly planar structure. The dihedral angles between the mean plane of the azoxy group (i.e. N1′, N1 and O2) and the mean planes of the attached benzene rings are 6.7 (1)° for the ring C4A–C8A and 5.4 (1)° for the ring C4A′–C8A′. The tilt angle between the mean planes of the two benzene rings is 4.15 (6)°. The planar conformation is assumed to be the ground state, possibly stabilized by intramolecular C—S⋯O and C—S⋯N chalcogen bonds (Scilabra et al., 2019). Additional stabilization, however, does not appear to be necessary, considering that (Z)-azoxybenzene (diphenyldiazene oxide) is planar in the gas phase, as revealed by electron diffraction and ab initio calculations (Tsuji et al., 2000) but not in the crystal (vide infra). The piperidine rings attached to C-2 of the BTZ system both adopt a low-energy chair conformation with slight distortions from the ideal tetrahedral angle (Table 1). The azoxy oxygen atom O2 has a significant effect on an otherwise symmetrical hypothetical azo-BTZ structure, with the N1′—C8′ distance at 1.394 (1) Å being notably shorter than the N1—C8 distance of 1.459 (1) Å and a clear geometry change at the C-8 position. The difference between the two parts of the molecule is highlighted in Fig. 4, which shows a superposition of the benzene rings of the BTZ moieties of two identical molecules.
|
3. Supramolecular features
In the ), which was calculated with PLATON (Spek, 2020). A view of the along the [101] direction reveals a herringbone pattern (Fig. 5). The separation between the planes of stacked molecules is ca 3.31 Å, similar to the interplanar distance in graphite (3.35 Å; Delhaes, 2001). As can be seen in the the trifluoromethyl groups of adjacent molecules are in close proximity to one another, but no intermolecular F⋯F contacts shorter than the sum of the corresponding van der Waals radii (Bondi, 1964) are encountered.
the molecules are densely packed, as revealed by a packing index of 73.0% (Kitaigorodskii, 19734. Database survey
A search of the Cambridge Structural Database (CSD; Groom et al., 2016) via the WebCSD interface (CCDC, 2017) in October of 2022 revealed no structure of an azoxy-BTZ, but four structures of 8-nitro-BTZs, viz. BTZ043 (CSD refcodes: HACQOY and HACQOV01; Richter et al., 2022a) and its 5-methyl derivative (MELLAU; Richter et al., 2022b), macozinone (PBTZ169; LOPXAS; Zhang & Aldrich, 2019) and 2-(4-Boc-piperazin-1-yl)-8-nitro-6-(trifluoromethyl)-BTZ (MESSOW; Richter et al., 2022c), with an average CBTZ—Nnitro bond length of 1.46 (1) Å. This can be compared with the C8—N1 bond length of 1.459 (1) and the C8′—N1′ bond length of 1.394 (1) Å in 4, which highlights the short C8′—N1′ bond length resulting from O2 being bonded to N1.
A et al., 2015) with a dihedral angle between the aromatic rings of ca 90°, illustrating that packing and steric effects are sufficient to disturb the ground-state conformation. The simplest azoxybenzene structure is that of (Z)-azoxybenzene (TIHTEK; Gonzáles Martínez & Bernès, 2007). The structure most related to that of 4, containing bicycles with fused six-membered rings, appears to be that of (Z)-1,2-bis[2-(2,2,2-trifluoroacetyl)naphthalen-1-yl]diazene oxide (XOZHUS; Belligund et al., 2019). In contrast to 4, in both TIHTEK and XOZHUS the aromatic rings are not coplanar and are significantly tilted out of the plane of the azoxy group. This can be reasonably attributed to effects of crystal packing in TIHTEK and steric effects of the substituents in ortho-position to the azoxy group in XOZHUS.
search for variously substituted acyclic azoxybenzene moieties yielded more than a hundred hits. Almost half of these have dihedral angles between the phenyl rings of less than 20°, although there are exceptions such as 1,3-dimethoxy-2-(phenylazoxy)benzene (VUNSII; Zhang5. Synthesis and crystallization
The synthesis of 1 is described elsewhere (Richter et al., 2018). DMF was of reagent-grade quality. Crystals of 4 suitable for single-crystal X-ray diffraction were obtained from a solution of 1 in DMF at room temperature, when the solvent was allowed to evaporate slowly over a period of several weeks.
6. Refinement
The SHELXL (Sheldrick, 2015b). The final structure was performed with Hirshfeld atom (HAR), using aspherical scattering factors with NoSpherA2 (Kleemiss et al., 2021; Midgley et al., 2021) partitioning in OLEX2 (Dolomanov et al., 2009) based on electron density from iterative single determinant SCF single-point DFT calculations using ORCA (Neese et al., 2020) with a B3LYP functional (Becke, 1993; Lee et al., 1988) and a def2-TZVPP basis set. Fig. 6 depicts the Fcalc(HAR)–Fcalc(IAM) deformation density map, showing the modelled deformation of the electron density as a result of bonding between independent spherical atoms. Crystal data, data collection and structure details are summarized in Table 2.
was initially refined to convergence by standard independent atom model (IAM) withSupporting information
CCDC reference: 2219153
https://doi.org/10.1107/S2056989022010842/tx2061sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989022010842/tx2061Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989022010842/tx2061Isup3.cdx
Supporting information file. DOI: https://doi.org/10.1107/S2056989022010842/tx2061Isup4.cml
Data collection: APEX4 (Bruker, 2017); cell
SAINT (Bruker, 2019); data reduction: SAINT (Bruker, 2019); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: olex2.refine (Bourhis et al., 2015); molecular graphics: Mercury (Macrae et al., 2020) and OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010).C28H24F6N6O3S2 | F(000) = 1378.110 |
Mr = 670.66 | Dx = 1.614 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 24.0754 (8) Å | Cell parameters from 9921 reflections |
b = 6.3343 (2) Å | θ = 2.3–30.4° |
c = 19.6822 (8) Å | µ = 0.28 mm−1 |
β = 113.1511 (14)° | T = 100 K |
V = 2759.84 (17) Å3 | Prism, yellow |
Z = 4 | 0.06 × 0.05 × 0.03 mm |
Bruker AXS D8 Venture diffractometer | 8391 independent reflections |
Radiation source: IµS | 7021 reflections with I ≥ 2u(I) |
Incoatec Helios mirrors monochromator | Rint = 0.070 |
Detector resolution: 7.391 pixels mm-1 | θmax = 30.5°, θmin = 2.3° |
φ– and ω–scans | h = −39→40 |
Absorption correction: gaussian (SADABS; Krause et al., 2015) | k = −10→10 |
Tmin = 0.990, Tmax = 0.996 | l = −32→32 |
178787 measured reflections |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.030 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.080 | All H-atom parameters refined |
S = 1.06 | w = 1/[σ2(Fo2) + (0.0404P)2 + 0.5834P] where P = (Fo2 + 2Fc2)/3 |
8391 reflections | (Δ/σ)max = 0.001 |
502 parameters | Δρmax = 0.51 e Å−3 |
0 restraints | Δρmin = −0.41 e Å−3 |
0 constraints |
Experimental. Crystal mounted on a MiTeGen loop using Perfluoropolyether PFO-XR75 |
x | y | z | Uiso*/Ueq | ||
C2 | 0.28147 (4) | 1.62528 (16) | 0.35880 (6) | 0.01856 (18) | |
C4 | 0.18168 (5) | 1.66757 (16) | 0.27097 (6) | 0.01990 (19) | |
C4A | 0.18126 (4) | 1.46289 (16) | 0.23218 (5) | 0.01821 (18) | |
C5 | 0.12727 (5) | 1.41066 (17) | 0.17388 (6) | 0.02096 (19) | |
H5 | 0.0901 (6) | 1.516 (2) | 0.1592 (8) | 0.032 (3)* | |
C6 | 0.12223 (4) | 1.22486 (18) | 0.13493 (6) | 0.0215 (2) | |
C7 | 0.17143 (5) | 1.09111 (17) | 0.15219 (6) | 0.02065 (19) | |
H7 | 0.1706 (7) | 0.938 (2) | 0.1223 (8) | 0.034 (4)* | |
C8 | 0.22558 (4) | 1.14234 (16) | 0.20994 (5) | 0.01785 (18) | |
C8A | 0.23135 (4) | 1.32656 (15) | 0.25264 (5) | 0.01688 (17) | |
C9 | 0.06319 (5) | 1.1574 (2) | 0.07626 (6) | 0.0285 (2) | |
C10 | 0.38359 (5) | 1.58701 (17) | 0.45870 (6) | 0.0233 (2) | |
H10a | 0.3900 (6) | 1.455 (2) | 0.4242 (8) | 0.032 (3)* | |
H10b | 0.3783 (7) | 1.516 (3) | 0.5073 (9) | 0.046 (4)* | |
C11 | 0.43872 (5) | 1.72905 (19) | 0.48551 (7) | 0.0287 (2) | |
H11a | 0.4441 (7) | 1.795 (3) | 0.4356 (9) | 0.044 (4)* | |
H11b | 0.4809 (8) | 1.628 (3) | 0.5181 (10) | 0.054 (5)* | |
C12 | 0.43017 (5) | 1.91406 (19) | 0.52990 (7) | 0.0284 (2) | |
H12a | 0.4223 (7) | 1.856 (2) | 0.5775 (9) | 0.045 (4)* | |
H12b | 0.4717 (8) | 2.017 (3) | 0.5496 (9) | 0.050 (4)* | |
C13 | 0.37393 (5) | 2.03337 (17) | 0.48121 (6) | 0.0244 (2) | |
H13a | 0.3795 (7) | 2.092 (2) | 0.4309 (9) | 0.044 (4)* | |
H13b | 0.3658 (7) | 2.169 (2) | 0.5094 (8) | 0.042 (4)* | |
C14 | 0.31845 (5) | 1.89287 (17) | 0.45499 (7) | 0.0245 (2) | |
H14a | 0.3085 (7) | 1.838 (3) | 0.5017 (9) | 0.049 (4)* | |
H14b | 0.2788 (7) | 1.972 (2) | 0.4171 (8) | 0.042 (4)* | |
F3 | 0.07072 (4) | 1.02538 (16) | 0.02812 (5) | 0.0534 (3) | |
S1 | 0.297929 (11) | 1.37714 (4) | 0.329373 (14) | 0.01863 (6) | |
N1 | 0.27597 (4) | 0.99673 (14) | 0.22486 (5) | 0.01818 (16) | |
N2 | 0.32766 (4) | 1.70422 (14) | 0.41709 (5) | 0.02082 (17) | |
N3 | 0.23098 (4) | 1.73330 (14) | 0.33002 (5) | 0.02101 (17) | |
O1 | 0.13567 (3) | 1.77651 (13) | 0.24771 (5) | 0.02728 (17) | |
O2 | 0.32334 (3) | 1.03059 (13) | 0.28039 (4) | 0.02664 (17) | |
F1 | 0.02873 (3) | 1.05970 (15) | 0.10561 (5) | 0.0451 (2) | |
F2 | 0.03113 (3) | 1.32047 (13) | 0.03808 (4) | 0.03864 (18) | |
C2' | 0.20796 (5) | 0.37012 (16) | −0.00025 (6) | 0.02017 (19) | |
C4' | 0.29718 (5) | 0.18587 (16) | 0.07323 (6) | 0.02048 (19) | |
C4A' | 0.32046 (4) | 0.35975 (16) | 0.12869 (6) | 0.01907 (18) | |
C5' | 0.37853 (5) | 0.33989 (18) | 0.18380 (6) | 0.0223 (2) | |
H5' | 0.4033 (7) | 0.204 (2) | 0.1849 (8) | 0.044 (4)* | |
C6' | 0.40175 (5) | 0.49576 (18) | 0.23691 (6) | 0.0229 (2) | |
C7' | 0.36784 (5) | 0.67241 (18) | 0.23859 (6) | 0.0218 (2) | |
H7' | 0.3860 (6) | 0.787 (2) | 0.2804 (8) | 0.034 (3)* | |
C8' | 0.30904 (4) | 0.69248 (16) | 0.18499 (5) | 0.01844 (18) | |
C8A' | 0.28619 (4) | 0.53676 (16) | 0.12859 (5) | 0.01775 (18) | |
C9' | 0.46319 (5) | 0.4618 (2) | 0.29701 (7) | 0.0313 (3) | |
C10' | 0.11963 (5) | 0.56488 (19) | −0.09017 (7) | 0.0272 (2) | |
H10c | 0.1317 (7) | 0.647 (3) | −0.1305 (9) | 0.051 (4)* | |
H10d | 0.1259 (7) | 0.666 (3) | −0.0433 (9) | 0.046 (4)* | |
C11' | 0.05376 (5) | 0.4965 (2) | −0.12664 (7) | 0.0288 (2) | |
H11c | 0.0264 (8) | 0.638 (3) | −0.1484 (10) | 0.055 (5)* | |
H11d | 0.0421 (8) | 0.432 (3) | −0.0822 (10) | 0.055 (5)* | |
C12' | 0.04379 (6) | 0.3354 (2) | −0.18782 (7) | 0.0306 (2) | |
H12c | −0.0026 (7) | 0.282 (3) | −0.2089 (9) | 0.051 (4)* | |
H12d | 0.0532 (7) | 0.410 (3) | −0.2314 (9) | 0.047 (4)* | |
C13' | 0.08662 (5) | 0.1495 (2) | −0.15767 (7) | 0.0285 (2) | |
H13c | 0.0763 (7) | 0.070 (2) | −0.1158 (8) | 0.040 (4)* | |
H13d | 0.0819 (7) | 0.034 (3) | −0.2003 (9) | 0.047 (4)* | |
C14' | 0.15169 (5) | 0.2246 (2) | −0.12305 (7) | 0.0326 (3) | |
H14c | 0.1830 (8) | 0.097 (3) | −0.0982 (10) | 0.058 (5)* | |
H14d | 0.1662 (7) | 0.307 (3) | −0.1646 (9) | 0.048 (4)* | |
N1' | 0.26622 (4) | 0.84787 (14) | 0.17848 (5) | 0.02021 (17) | |
N2' | 0.15965 (4) | 0.38055 (16) | −0.06438 (5) | 0.0264 (2) | |
N3' | 0.24492 (4) | 0.20906 (14) | 0.01250 (5) | 0.02222 (18) | |
O1' | 0.32738 (4) | 0.02386 (12) | 0.08251 (5) | 0.02674 (17) | |
F1' | 0.46238 (4) | 0.29899 (17) | 0.33958 (6) | 0.0656 (3) | |
F2' | 0.50496 (3) | 0.42022 (16) | 0.27055 (5) | 0.0510 (2) | |
F3' | 0.48340 (3) | 0.62741 (14) | 0.34161 (4) | 0.04065 (19) | |
S1' | 0.214168 (11) | 0.58337 (4) | 0.060830 (14) | 0.01939 (6) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C2 | 0.0182 (4) | 0.0166 (4) | 0.0206 (4) | −0.0010 (3) | 0.0073 (4) | −0.0014 (3) |
C4 | 0.0183 (4) | 0.0184 (5) | 0.0224 (5) | 0.0012 (3) | 0.0074 (4) | 0.0007 (4) |
C4A | 0.0168 (4) | 0.0189 (4) | 0.0185 (4) | 0.0009 (3) | 0.0065 (4) | 0.0003 (3) |
C5 | 0.0168 (4) | 0.0242 (5) | 0.0197 (5) | 0.0023 (4) | 0.0049 (4) | −0.0002 (4) |
C6 | 0.0164 (4) | 0.0258 (5) | 0.0193 (4) | 0.0010 (4) | 0.0037 (4) | −0.0027 (4) |
C7 | 0.0173 (4) | 0.0231 (5) | 0.0187 (4) | 0.0009 (4) | 0.0040 (4) | −0.0030 (4) |
C8 | 0.0161 (4) | 0.0194 (4) | 0.0167 (4) | −0.0004 (3) | 0.0049 (4) | −0.0013 (3) |
C8A | 0.0163 (4) | 0.0174 (4) | 0.0165 (4) | 0.0004 (3) | 0.0059 (3) | 0.0003 (3) |
C9 | 0.0189 (5) | 0.0349 (6) | 0.0236 (5) | 0.0025 (4) | −0.0002 (4) | −0.0064 (4) |
C10 | 0.0216 (5) | 0.0196 (5) | 0.0256 (5) | 0.0009 (4) | 0.0059 (4) | −0.0030 (4) |
C11 | 0.0210 (5) | 0.0289 (6) | 0.0319 (6) | 0.0006 (4) | 0.0058 (4) | −0.0100 (5) |
C12 | 0.0245 (5) | 0.0265 (5) | 0.0281 (6) | 0.0004 (4) | 0.0037 (4) | −0.0077 (4) |
C13 | 0.0270 (5) | 0.0184 (5) | 0.0255 (5) | −0.0004 (4) | 0.0080 (4) | −0.0038 (4) |
C14 | 0.0221 (5) | 0.0219 (5) | 0.0283 (5) | 0.0003 (4) | 0.0087 (4) | −0.0062 (4) |
F3 | 0.0275 (4) | 0.0711 (6) | 0.0430 (5) | 0.0112 (4) | −0.0060 (3) | −0.0325 (4) |
S1 | 0.01677 (11) | 0.01686 (11) | 0.01941 (11) | 0.00039 (8) | 0.00407 (9) | −0.00168 (8) |
N1 | 0.0181 (4) | 0.0188 (4) | 0.0167 (4) | 0.0000 (3) | 0.0059 (3) | −0.0013 (3) |
N2 | 0.0188 (4) | 0.0184 (4) | 0.0236 (4) | −0.0001 (3) | 0.0066 (3) | −0.0032 (3) |
N3 | 0.0191 (4) | 0.0189 (4) | 0.0236 (4) | 0.0009 (3) | 0.0070 (3) | −0.0022 (3) |
O1 | 0.0219 (4) | 0.0233 (4) | 0.0316 (4) | 0.0060 (3) | 0.0052 (3) | −0.0016 (3) |
O2 | 0.0203 (4) | 0.0250 (4) | 0.0275 (4) | 0.0034 (3) | 0.0017 (3) | −0.0062 (3) |
F1 | 0.0247 (4) | 0.0540 (5) | 0.0443 (5) | −0.0130 (3) | 0.0005 (3) | 0.0029 (4) |
F2 | 0.0277 (4) | 0.0455 (5) | 0.0299 (4) | 0.0071 (3) | −0.0024 (3) | 0.0017 (3) |
C2' | 0.0196 (4) | 0.0202 (5) | 0.0210 (5) | 0.0005 (4) | 0.0082 (4) | −0.0040 (4) |
C4' | 0.0222 (5) | 0.0180 (5) | 0.0236 (5) | 0.0022 (4) | 0.0116 (4) | 0.0004 (4) |
C4A' | 0.0185 (4) | 0.0197 (4) | 0.0198 (4) | 0.0027 (4) | 0.0084 (4) | 0.0014 (4) |
C5' | 0.0195 (5) | 0.0241 (5) | 0.0236 (5) | 0.0053 (4) | 0.0088 (4) | 0.0024 (4) |
C6' | 0.0177 (4) | 0.0284 (5) | 0.0207 (5) | 0.0044 (4) | 0.0055 (4) | 0.0018 (4) |
C7' | 0.0178 (4) | 0.0256 (5) | 0.0196 (5) | 0.0021 (4) | 0.0047 (4) | −0.0016 (4) |
C8' | 0.0172 (4) | 0.0206 (5) | 0.0166 (4) | 0.0008 (3) | 0.0057 (4) | −0.0004 (3) |
C8A' | 0.0180 (4) | 0.0185 (4) | 0.0175 (4) | 0.0011 (3) | 0.0078 (4) | −0.0007 (3) |
C9' | 0.0208 (5) | 0.0376 (6) | 0.0294 (6) | 0.0072 (5) | 0.0033 (5) | 0.0008 (5) |
C10' | 0.0273 (5) | 0.0273 (5) | 0.0219 (5) | 0.0038 (4) | 0.0041 (4) | −0.0051 (4) |
C11' | 0.0249 (5) | 0.0316 (6) | 0.0262 (5) | 0.0075 (4) | 0.0063 (4) | −0.0017 (5) |
C12' | 0.0249 (5) | 0.0327 (6) | 0.0277 (6) | 0.0004 (5) | 0.0031 (5) | −0.0053 (5) |
C13' | 0.0244 (5) | 0.0290 (6) | 0.0288 (6) | −0.0002 (4) | 0.0069 (5) | −0.0085 (5) |
C14' | 0.0230 (5) | 0.0381 (7) | 0.0329 (6) | 0.0021 (5) | 0.0068 (5) | −0.0178 (5) |
N1' | 0.0214 (4) | 0.0211 (4) | 0.0177 (4) | 0.0020 (3) | 0.0073 (3) | −0.0030 (3) |
N2' | 0.0222 (4) | 0.0290 (5) | 0.0244 (5) | 0.0040 (4) | 0.0052 (4) | −0.0095 (4) |
N3' | 0.0223 (4) | 0.0197 (4) | 0.0248 (4) | 0.0013 (3) | 0.0093 (4) | −0.0043 (3) |
O1' | 0.0291 (4) | 0.0196 (4) | 0.0319 (4) | 0.0058 (3) | 0.0124 (3) | 0.0006 (3) |
F1' | 0.0411 (5) | 0.0661 (7) | 0.0601 (6) | 0.0001 (5) | −0.0119 (4) | 0.0341 (5) |
F2' | 0.0201 (3) | 0.0722 (6) | 0.0523 (5) | 0.0090 (4) | 0.0053 (3) | −0.0254 (5) |
F3' | 0.0266 (4) | 0.0545 (5) | 0.0303 (4) | 0.0095 (3) | −0.0002 (3) | −0.0110 (3) |
S1' | 0.01745 (11) | 0.02073 (12) | 0.01844 (11) | 0.00258 (9) | 0.00539 (9) | −0.00378 (9) |
C2—S1 | 1.7730 (10) | N1—N1' | 1.2685 (12) |
C2—N2 | 1.3416 (13) | C2'—N2' | 1.3402 (14) |
C2—N3 | 1.3135 (13) | C2'—N3' | 1.3115 (13) |
C4—C4A | 1.5026 (14) | C2'—S1' | 1.7750 (10) |
C4—N3 | 1.3595 (13) | C4'—C4A' | 1.4958 (15) |
C4—O1 | 1.2304 (12) | C4'—N3' | 1.3604 (14) |
C4A—C5 | 1.3938 (14) | C4'—O1' | 1.2291 (12) |
C4A—C8A | 1.4074 (13) | C4A'—C5' | 1.3981 (14) |
C5—H5 | 1.063 (14) | C4A'—C8A' | 1.3917 (13) |
C5—C6 | 1.3837 (15) | C5'—H5' | 1.041 (16) |
C6—C7 | 1.3855 (14) | C5'—C6' | 1.3858 (16) |
C6—C9 | 1.4987 (15) | C6'—C7' | 1.3931 (15) |
C7—H7 | 1.129 (15) | C6'—C9' | 1.5027 (15) |
C7—C8 | 1.3899 (14) | C7'—H7' | 1.053 (14) |
C8—C8A | 1.4127 (14) | C7'—C8' | 1.3994 (14) |
C8—N1 | 1.4589 (13) | C8'—C8A' | 1.4240 (14) |
C8A—S1 | 1.7461 (10) | C8'—N1' | 1.3943 (13) |
C9—F3 | 1.3284 (14) | C8A'—S1' | 1.7475 (10) |
C9—F1 | 1.3347 (15) | C9'—F1' | 1.3336 (16) |
C9—F2 | 1.3310 (14) | C9'—F2' | 1.3280 (15) |
C10—H10a | 1.124 (14) | C9'—F3' | 1.3313 (15) |
C10—H10b | 1.108 (16) | C10'—H10c | 1.082 (16) |
C10—C11 | 1.5162 (16) | C10'—H10d | 1.082 (16) |
C10—N2 | 1.4724 (13) | C10'—C11' | 1.5239 (17) |
C11—H11a | 1.120 (16) | C10'—N2' | 1.4712 (15) |
C11—H11b | 1.158 (18) | C11'—H11c | 1.094 (17) |
C11—C12 | 1.5234 (16) | C11'—H11d | 1.098 (17) |
C12—H12a | 1.089 (15) | C11'—C12' | 1.5240 (17) |
C12—H12b | 1.129 (17) | C12'—H12c | 1.082 (16) |
C12—C13 | 1.5173 (16) | C12'—H12d | 1.080 (16) |
C13—H13a | 1.114 (16) | C12'—C13' | 1.5231 (17) |
C13—H13b | 1.081 (15) | C13'—H13c | 1.076 (15) |
C13—C14 | 1.5168 (15) | C13'—H13d | 1.086 (16) |
C14—H14a | 1.095 (16) | C13'—C14' | 1.5182 (16) |
C14—H14b | 1.077 (16) | C14'—H14c | 1.080 (18) |
C14—N2 | 1.4709 (13) | C14'—H14d | 1.135 (16) |
N1—O2 | 1.2494 (11) | C14'—N2' | 1.4740 (14) |
N2—C2—S1 | 113.15 (7) | C4—N3—C2 | 123.92 (9) |
N3—C2—S1 | 127.50 (8) | N3'—C2'—N2' | 119.40 (9) |
N3—C2—N2 | 119.35 (9) | S1'—C2'—N2' | 114.27 (8) |
N3—C4—C4A | 121.86 (9) | S1'—C2'—N3' | 126.32 (8) |
O1—C4—C4A | 118.01 (9) | N3'—C4'—C4A' | 120.89 (9) |
O1—C4—N3 | 120.13 (10) | O1'—C4'—C4A' | 118.45 (10) |
C5—C4A—C4 | 116.16 (9) | O1'—C4'—N3' | 120.62 (10) |
C8A—C4A—C4 | 123.38 (9) | C5'—C4A'—C4' | 118.26 (9) |
C8A—C4A—C5 | 120.45 (9) | C8A'—C4A'—C4' | 122.71 (9) |
H5—C5—C4A | 119.2 (7) | C8A'—C4A'—C5' | 119.01 (10) |
C6—C5—C4A | 120.55 (10) | H5'—C5'—C4A' | 118.7 (8) |
C6—C5—H5 | 120.3 (7) | C6'—C5'—C4A' | 120.32 (10) |
C7—C6—C5 | 120.27 (9) | C6'—C5'—H5' | 120.9 (8) |
C9—C6—C5 | 121.30 (10) | C7'—C6'—C5' | 121.59 (10) |
C9—C6—C7 | 118.36 (10) | C9'—C6'—C5' | 118.16 (10) |
H7—C7—C6 | 124.0 (8) | C9'—C6'—C7' | 120.08 (10) |
C8—C7—C6 | 119.63 (10) | H7'—C7'—C6' | 120.2 (8) |
C8—C7—H7 | 116.4 (8) | C8'—C7'—C6' | 118.92 (10) |
C8A—C8—C7 | 121.38 (9) | C8'—C7'—H7' | 120.9 (8) |
N1—C8—C7 | 117.09 (9) | C8A'—C8'—C7' | 119.41 (9) |
N1—C8—C8A | 121.53 (8) | N1'—C8'—C7' | 128.73 (9) |
C8—C8A—C4A | 117.63 (9) | N1'—C8'—C8A' | 111.85 (8) |
S1—C8A—C4A | 121.80 (8) | C8'—C8A'—C4A' | 120.65 (9) |
S1—C8A—C8 | 120.55 (7) | S1'—C8A'—C4A' | 123.16 (8) |
F3—C9—C6 | 112.03 (9) | S1'—C8A'—C8' | 116.19 (7) |
F1—C9—C6 | 111.19 (10) | F1'—C9'—C6' | 110.62 (10) |
F1—C9—F3 | 107.41 (11) | F2'—C9'—C6' | 112.50 (10) |
F2—C9—C6 | 112.17 (10) | F2'—C9'—F1' | 107.08 (11) |
F2—C9—F3 | 107.29 (10) | F3'—C9'—C6' | 113.43 (10) |
F2—C9—F1 | 106.44 (10) | F3'—C9'—F1' | 106.67 (11) |
H10b—C10—H10a | 108.0 (11) | F3'—C9'—F2' | 106.14 (10) |
C11—C10—H10a | 109.9 (7) | H10d—C10'—H10c | 110.6 (12) |
C11—C10—H10b | 108.8 (8) | C11'—C10'—H10c | 108.7 (9) |
N2—C10—H10a | 110.6 (7) | C11'—C10'—H10d | 109.9 (8) |
N2—C10—H10b | 107.1 (8) | N2'—C10'—H10c | 108.0 (9) |
N2—C10—C11 | 112.23 (9) | N2'—C10'—H10d | 108.7 (8) |
H11a—C11—C10 | 107.7 (8) | N2'—C10'—C11' | 110.86 (10) |
H11b—C11—C10 | 108.8 (9) | H11c—C11'—C10' | 107.8 (9) |
H11b—C11—H11a | 108.3 (12) | H11d—C11'—C10' | 106.0 (9) |
C12—C11—C10 | 111.03 (10) | H11d—C11'—H11c | 108.3 (12) |
C12—C11—H11a | 107.6 (8) | C12'—C11'—C10' | 111.95 (10) |
C12—C11—H11b | 113.2 (9) | C12'—C11'—H11c | 110.9 (9) |
H12a—C12—C11 | 110.1 (8) | C12'—C11'—H11d | 111.6 (9) |
H12b—C12—C11 | 110.0 (9) | H12c—C12'—C11' | 109.3 (9) |
H12b—C12—H12a | 109.3 (12) | H12d—C12'—C11' | 108.4 (8) |
C13—C12—C11 | 108.02 (9) | H12d—C12'—H12c | 109.8 (12) |
C13—C12—H12a | 107.2 (8) | C13'—C12'—C11' | 109.74 (10) |
C13—C12—H12b | 112.2 (9) | C13'—C12'—H12c | 110.4 (9) |
H13a—C13—C12 | 109.9 (8) | C13'—C12'—H12d | 109.2 (8) |
H13b—C13—C12 | 111.6 (8) | H13c—C13'—C12' | 109.7 (8) |
H13b—C13—H13a | 107.4 (11) | H13d—C13'—C12' | 111.8 (9) |
C14—C13—C12 | 111.74 (9) | H13d—C13'—H13c | 106.8 (12) |
C14—C13—H13a | 106.9 (8) | C14'—C13'—C12' | 110.73 (11) |
C14—C13—H13b | 109.2 (8) | C14'—C13'—H13c | 108.1 (8) |
H14a—C14—C13 | 110.8 (9) | C14'—C13'—H13d | 109.5 (8) |
H14b—C14—C13 | 112.7 (8) | H14c—C14'—C13' | 112.5 (9) |
H14b—C14—H14a | 107.6 (12) | H14d—C14'—C13' | 112.1 (8) |
N2—C14—C13 | 111.16 (9) | H14d—C14'—H14c | 108.1 (12) |
N2—C14—H14a | 107.1 (9) | N2'—C14'—C13' | 110.78 (9) |
N2—C14—H14b | 107.2 (8) | N2'—C14'—H14c | 107.0 (9) |
C8A—S1—C2 | 101.43 (5) | N2'—C14'—H14d | 106.0 (8) |
O2—N1—C8 | 117.93 (8) | C8'—N1'—N1 | 122.53 (9) |
N1'—N1—C8 | 114.91 (8) | C10'—N2'—C2' | 124.91 (9) |
N1'—N1—O2 | 127.16 (9) | C14'—N2'—C2' | 120.14 (9) |
C10—N2—C2 | 123.85 (9) | C14'—N2'—C10' | 113.32 (9) |
C14—N2—C2 | 119.79 (9) | C4'—N3'—C2' | 125.14 (9) |
C14—N2—C10 | 114.52 (8) | C8A'—S1'—C2' | 100.51 (5) |
C2—N2—C10—C11 | 144.51 (11) | N1—N1'—C8'—C7' | −1.88 (12) |
C2—N2—C14—C13 | −143.83 (10) | N1—N1'—C8'—C8A' | 176.68 (10) |
C2—N3—C4—C4A | −0.99 (12) | C2'—N2'—C10'—C11' | −139.53 (12) |
C2—N3—C4—O1 | 179.08 (10) | C2'—N2'—C14'—C13' | 136.81 (12) |
C4—C4A—C5—C6 | −179.66 (9) | C2'—N3'—C4'—C4A' | −6.44 (12) |
C4—C4A—C8A—C8 | −177.90 (9) | C2'—N3'—C4'—O1' | 175.95 (11) |
C4—C4A—C8A—S1 | 3.77 (11) | C4'—C4A'—C5'—C6' | −179.23 (9) |
C4A—C5—C6—C7 | −1.77 (12) | C4'—C4A'—C8A'—C8' | 176.45 (9) |
C4A—C5—C6—C9 | 174.91 (10) | C4'—C4A'—C8A'—S1' | −3.91 (11) |
C4A—C8A—C8—C7 | −3.38 (11) | C4A'—C5'—C6'—C7' | 1.93 (12) |
C4A—C8A—C8—N1 | 177.15 (8) | C4A'—C5'—C6'—C9' | 177.12 (10) |
C5—C6—C7—C8 | 1.37 (12) | C4A'—C8A'—C8'—C7' | 3.52 (11) |
C5—C6—C9—F3 | 156.95 (12) | C4A'—C8A'—C8'—N1' | −175.19 (10) |
C5—C6—C9—F1 | −82.85 (11) | C5'—C6'—C7'—C8' | −0.29 (12) |
C5—C6—C9—F2 | 36.21 (11) | C5'—C6'—C9'—F1' | −65.33 (12) |
C6—C7—C8—C8A | 1.25 (12) | C5'—C6'—C9'—F2' | 54.37 (11) |
C6—C7—C8—N1 | −179.25 (9) | C5'—C6'—C9'—F3' | 174.86 (11) |
C7—C8—C8A—S1 | 174.97 (8) | C6'—C7'—C8'—C8A' | −2.38 (12) |
C7—C8—N1—O2 | −174.00 (9) | C6'—C7'—C8'—N1' | 176.08 (9) |
C7—C8—N1—N1' | 6.35 (11) | C7'—C8'—C8A'—S1' | −176.14 (8) |
C8—N1—N1'—C8' | −178.86 (8) | C10'—C11'—C12'—C13' | 54.26 (12) |
C10—C11—C12—C13 | −57.50 (11) | C10'—N2'—C14'—C13' | −57.05 (11) |
C10—N2—C14—C13 | 51.03 (10) | C11'—C12'—C13'—C14' | −55.55 (12) |
C11—C12—C13—C14 | 58.50 (11) | C12'—C13'—C14'—N2' | 56.80 (11) |
C12—C13—C14—N2 | −55.30 (10) |
Footnotes
1Dedicated to Professor George M. Sheldrick on the occasion of his 80th birthday.
Acknowledgements
We would like to thank Dr Thomas Weyhermüller for providing measurement time at the X-ray diffraction facility of the Max-Planck-Institut für Chemische Energiekonversion (Mülheim an der Ruhr, Germany), and Heike Schucht and Elke Dreher for technical assistance. We acknowledge the financial support within the funding programme Open Access Publishing by the German Research Foundation (DFG).
References
Becke, A. D. (1993). J. Chem. Phys. 98, 5648–5652. CrossRef CAS Web of Science Google Scholar
Belligund, K., Mathew, T., Hunt, J. R., Nirmalchandar, A., Haiges, R., Dawlaty, J. & Prakash, G. K. S. (2019). J. Am. Chem. Soc. 141, 15921–15931. CSD CrossRef CAS PubMed Google Scholar
Bondi, A. (1964). J. Phys. Chem. 68, 441–451. CrossRef CAS Web of Science Google Scholar
Bourhis, L. J., Dolomanov, O. V., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2015). Acta Cryst. A71, 59–75. Web of Science CrossRef IUCr Journals Google Scholar
Bruker (2017). APEX4. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2019). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
CCDC (2017). CSD web interface – intuitive, cross-platform, web-based access to CSD data. Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, UK. Google Scholar
Chen, Y.-F., Chen, J., Lin, L.-J. & Chuang, G. J. (2017). J. Org. Chem. 82, 11626–11630. CSD CrossRef CAS PubMed Google Scholar
Chikhale, R. V., Barmade, M. A., Murumkar, P. R. & Yadav, M. R. (2018). J. Med. Chem. 61, 8563–8593. Web of Science CrossRef CAS PubMed Google Scholar
Cole, K. P., Johnson, M. D., Laurila, M. E. & Stout, J. R. (2017). React. Chem. Eng. 2, 288–294. CrossRef CAS Google Scholar
Delhaes, P. (2001). Graphite and Precursors. London: CRC Press. Google Scholar
Dembitsky, V. M., Gloriozova, T. A. & Poroikov, V. V. (2017). Nat. Prod. Bioprospect. 7, 151–169. CrossRef CAS PubMed Google Scholar
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
González Martínez, S. P. & Bernès, S. (2007). Acta Cryst. E63, o3639. CSD CrossRef IUCr Journals 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
Heravi, M. M., Ghavidel, M. & Mohammadkhani, L. (2018). RSC Adv. 8, 27832–27862. CrossRef CAS PubMed Google Scholar
Kitaigorodskii, A. I. (1973). Molecular crystals and molecules. London: Academic Press. Google Scholar
Kleemiss, F., Dolomanov, O. V., Bodensteiner, M., Peyerimhoff, N., Midgley, M., Bourhis, L. J., Genoni, A., Malaspina, L. A., Jayatilaka, D., Spencer, J. L., White, F., Grundkötter-Stock, B., Steinhauer, S., Lentz, D., Puschmann, H. & Grabowsky, S. (2021). Chem. Sci. 12, 1675–1692. Web of Science CSD CrossRef CAS Google Scholar
Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3–10. Web of Science CSD CrossRef ICSD CAS IUCr Journals Google Scholar
Lee, C., Yang, W. & Parr, R. G. (1988). Phys. Rev. B, 37, 785–789. CrossRef CAS Web of Science Google Scholar
Liu, R., Krchnak, V., Brown, S. N. & Miller, M. J. (2019). ACS Med. Chem. Lett. 10, 1462–1466. CrossRef CAS PubMed Google Scholar
Macrae, C. F., Sovago, I., Cottrell, S. J., Galek, P. T. A., McCabe, P., Pidcock, E., Platings, M., Shields, G. P., Stevens, J. S., Towler, M. & Wood, P. A. (2020). J. Appl. Cryst. 53, 226–235. Web of Science CrossRef CAS IUCr Journals Google Scholar
Makarov, V., Manina, G., Mikusova, K., Möllmann, U., Ryabova, O., Saint-Joanis, B., Dhar, N., Pasca, M. R., Buroni, S., Lucarelli, A. P., Milano, A., De Rossi, E., Belanova, M., Bobovska, A., Dianiskova, P., Kordulakova, J., Sala, C., Fullam, E., Schneider, P., McKinney, J. D., Brodin, P., Christophe, T., Waddell, S., Butcher, P., Albrethsen, J., Rosenkrands, I., Brosch, R., Nandi, V., Bharath, S., Gaonkar, S., Shandil, R. K., Balasubramanian, V., Balganesh, T., Tyagi, S., Grosset, J., Riccardi, G. & Cole, S. T. (2009). Science, 324, 801–804. CrossRef PubMed CAS Google Scholar
Meglitskii, V. A. & Kvasha, N. M. (1972). Fibre Chem. 3, 327–329. CrossRef Google Scholar
Midgley, L., Bourhis, L. J., Dolomanov, O. V., Grabowsky, S., Kleemiss, F., Puschmann, H. & Peyerimhoff, N. (2021). J. Chem. Phys. 152, 224108. Google Scholar
Neese, F., Wennmohs, F., Becker, U. & Riplinger, C. (2020). J. Chem. Phys. 152, 224108. Web of Science CrossRef PubMed Google Scholar
Neres, J., Pojer, F., Molteni, E., Chiarelli, L. R., Dhar, N., Boy-Röttger, S., Buroni, S., Fullam, E., Degiacomi, G., Lucarelli, A. P., Read, R. J., Zanoni, G., Edmondson, D. E., De Rossi, E., Pasca, M. R., McKinney, J. D., Dyson, P. J., Riccardi, G., Mattevi, A., Cole, S. T. & Binda, C. (2012). Sci. Transl. Med. 4, 150r, a121. Google Scholar
Richter, A., Narula, G., Rudolph, I., Seidel, R. W., Wagner, C., Av-Gay, Y. & Imming, P. (2022c). ChemMedChem, 17, e202100733. PubMed Google Scholar
Richter, A., Patzer, M., Goddard, R., Lingnau, J. B., Imming, P. & Seidel, R. W. (2022a). J. Mol. Struct. 1248, 131419. CSD CrossRef Google Scholar
Richter, A., Rudolph, I., Möllmann, U., Voigt, K., Chung, C., Singh, O. M. P., Rees, M., Mendoza-Losana, A., Bates, R., Ballell, L., Batt, S., Veerapen, N., Fütterer, K., Besra, G., Imming, P. & Argyrou, A. (2018). Sci. Rep. 8, 13473. Web of Science CrossRef PubMed Google Scholar
Richter, A., Seidel, R. W., Graf, J., Goddard, R., Lehmann, C., Schlegel, T., Khater, N. & Imming, P. (2022b). ChemMedChem, 17, e202200021. PubMed Google Scholar
Scilabra, P., Terraneo, G. & Resnati, G. (2019). Acc. Chem. Res. 52, 1313–1324. Web of Science CrossRef CAS PubMed 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
Spek, A. L. (2020). Acta Cryst. E76, 1–11. Web of Science CrossRef IUCr Journals Google Scholar
Tiwari, R., Moraski, G. C., Krchňák, V., Miller, P. A., Colon-Martinez, M., Herrero, E., Oliver, A. G. & Miller, M. J. (2013). J. Am. Chem. Soc. 135, 3539–3549. Web of Science CSD CrossRef CAS PubMed Google Scholar
Trefzer, C., Rengifo-Gonzalez, M., Hinner, M. J., Schneider, P., Makarov, V., Cole, S. T. & Johnsson, K. (2010). J. Am. Chem. Soc. 132, 13663–13665. Web of Science CrossRef CAS PubMed Google Scholar
Trefzer, C., Škovierová, H., Buroni, S., Bobovská, A., Nenci, S., Molteni, E., Pojer, F., Pasca, M. R., Makarov, V., Cole, S. T., Riccardi, G., Mikušová, K. & Johnsson, K. (2012). J. Am. Chem. Soc. 134, 912–915. Web of Science CrossRef CAS PubMed Google Scholar
Tsuji, T., Takashima, H., Takeuchi, H., Egawa, T. & Konaka, S. (2000). J. Mol. Struct. 554, 203–210. Web of Science CrossRef CAS Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Wibowo, M. & Ding, L. (2020). J. Nat. Prod. 83, 3482–3491. CrossRef CAS PubMed Google Scholar
Zhang, G. & Aldrich, C. C. (2019). Acta Cryst. C75, 1031–1035. Web of Science CSD CrossRef IUCr Journals Google Scholar
Zhang, D., Cui, X., Yang, F., Zhang, Q., Zhu, Y. & Wu, Y. (2015). Org. Chem. Front. 2, 951–955. CSD CrossRef CAS 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.