2-Oxo-2H-chromen-7-yl 3-methyl­butano­ate

Abou, A.; Bazié, H.; Akonan, L.; Djandé, A.; Francotte, P.

doi:10.1107/S2414314625001610

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 10| Part 2| February 2025| x250161

https://doi.org/10.1107/S2414314625001610

Open

access

2-Oxo-2H-chromen-7-yl 3-methylbutanoate

Akoun Abou,^a ^* Hypolite Bazié,^b Ludovic Akonan,^c Abdoulaye Djandé ^b ^* and Pierre Francotte ^d

^aJoint Research and Innovation Unit for Engineering Sciences and Techniques, (UMRI STI), Research Team: Instrumentation, Image and Spectroscopy, Félix Houphouet-Boigny National Polytechnic Institute, BP 1093 Yamoussoukro, Côte d'Ivoire, ^bLaboratory of Molecular Chemistry and Materials (LC2M), Research Team: Organic Chemistry and Phytochemistry, University Joseph KI-ZERBO, 03 BP 7021 Ouagadougou 03, Burkina Faso, ^cLaboratory of Fundamental and Applied Physics, Nangui Abrogoua University, Abidjan, Côte d'Ivoire, and ^dCenter for Interdisciplinary Research on Medicinal Chemistry, University of Liège, Avenue Hippocrate 15 (B36), B-4000, Liège, Belgium
^*Correspondence e-mail: abouakoun@gmail.com, djandeabdou@yahoo.fr

Edited by S. Bernès, Benemérita Universidad Autónoma de Puebla, México (Received 13 January 2025; accepted 21 February 2025; online 28 February 2025)

The title compound, C₁₄H₁₄O₄, was synthesized by O-acylation of umbelliferone with isovaleryl chloride in the presence of diethyl ether as a solvent and pyridine as a base. The side chain moiety i.e. the acetate fragment linking to the methylethyl group is almost orthogonal to the almost planar (r.m.s deviation = 0.020 Å) coumarin ring system, making an angle of 76.26 (7)°. In the crystal, the molecules form centrosymmetric dimers through pairwise C—H⋯O hydrogen bonds, generating R₂²(8) and R₂²(18) loops that lie within the crystallographic ac plane and propagate along the [001] direction.

Keywords: crystal structure; coumarin derivative; umbelliferone; hydrogen bonds.

CCDC reference: 2426608

Structure description

Molecules containing the coumarin moiety have attracted the attention of researchers since examples of these compounds have been shown to have extensive biological properties, including anti-HIV (Yu et al., 2003 , 2007 ), anti-coagulant (Abernethy et al., 1969 ), anti-oxidant (Vukovic et al., 2010 ), anti-tumour (Basanagouda et al., 2009 ), anti-bacterial (Vukovic et al., 2010) and anti-inflammatory (Emmanuel-Giota et al., 2001 ) activity. They are also used in the perfumery and agrochemical industries as activators and stabilizers (Bauer et al., 1988 ; Boisde & Meuly, 1993 ).

IIn this work, we describe the synthesis and structure of the title compound, C₁₄H₁₄O₄, Fig. 1. An analysis of the bond lengths in this structure shows a slightly uneven distribution around the pyrone ring, as indicated by the lengths of the C2=C3 [1.345 (3) Å] and C1—C2 [1.453 (3) Å] bonds, which are shorter and longer, respectively, than what would be expected for a C_ar—C_ar bond. This suggests that the electron density is less concentrated in the C2=C3 bond of the pyran-2-one ring, resulting in the formation of a double bond, as observed in other coumarin ester derivatives (Abou et al., 2020 ; Koulabiga et al., 2024 ; Yao et al., 2024 ). Furthermore, the structure highlights an almost planar coumarin ring system (puckering τ parameter = 0.7; Spek, 2009 ). Likewise, the crystal structure reveals the generation of dimeric units via C—H⋯O interactions. These dimers are linked by further C—H⋯O contacts into chains along the [001] direction (Table 1, Fig. 2).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3⋯O4ⁱ	0.98 (3)	2.46 (3)	3.296 (2)	142.6 (19)
C6—H5⋯O1ⁱⁱ	0.96 (3)	2.51 (3)	3.444 (2)	167 (2)
C11—H11A⋯O2ⁱⁱ	1.03 (3)	2.60 (3)	3.245 (2)	120.5 (18)
Symmetry codes: (i) $[-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (ii) .

Figure 1
Molecular structure of the title compound with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are shown as spheres of arbitrary radius.

Figure 2
A view of the crystal packing showing the association of molecules into centrosymmetric dimers through C—H⋯O hydrogen bonds, forming R₂²(8) and R₂²(18) loops extending parallel to the ac crystallographic plane. H atoms not involved in hydrogen bonding have been omitted for clarity.

Synthesis and crystallization

To a solution of isovaleryl chloride (0.76 ml, 6.17 mmol, 1 equiv.) in dried diethyl ether (16 ml) was added dried pyridine (2.31 ml, 4.7 equiv.) and umbelliferone (1 g, 6.17 mmol, 1 equiv.) in small portions over 30 min, with vigorous stirring. The reaction mixture was left stirring at room temperature for 3 h. The resulting mixture was next poured into a separating funnel containing 40 ml of chloroform and washed with diluted hydrochloric acid solution until the pH was 2–3. The organic phase was extracted, washed with water to neutrality, dried with magnesium sulfate and the solvent removed in vacuo. The obtained crude product was filtered off with suction, washed with petroleum ether and recrystallized from the mixed solvents of chloroform–hexane (1:3), yielding a white powder of the title compound, 2-oxo-2H-chromen-7-yl-3-methylbutanoate (0.92 g, 60%). Colourless crystals suitable for single-crystal X-ray diffraction analysis were then obtained from an acetone solution, after the solvent was allowed to evaporate slowly at ambient conditions.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. Three reflections, ( $[\overline{3}]$ 46), ( $[\overline{2}]$ 04), ( $[\overline{1}]$ 04) with ΔF/σ(F) higher than 10, were found to have too low intensities, caused by a systematic error, probably by shielding by the beam-stop interference for reflections ( $[\overline{2}]$ 04), ( $[\overline{1}]$ 04) while for ( $[\overline{3}]$ 46) at higher 2θ angles, the less area irradiated would have an effect of decreasing diffraction intensity. The depth of penetration of the beam becomes commensurably deeper with higher angles. This effectively increases background as well as a sample displacement effect.. They were omitted from the refinement.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₄H₁₄O₄
M_r	246.25
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	15.370 (3), 5.4488 (10), 16.339 (3)
β (°)	117.426 (7)
V (Å³)	1214.5 (4)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.10
Crystal size (mm)	0.45 × 0.44 × 0.16

Data collection
Diffractometer	SuperNova, Dual, Cu at home/near, AtlasS2
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2022 $[Rigaku OD (2022). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ )
T_min, T_max	0.956, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	41227, 3741, 2799
R_int	0.068
(sin θ/λ)_max (Å⁻¹)	0.718

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.066, 0.203, 1.03
No. of reflections	41227
No. of parameters	219
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.50, −0.39
Computer programs: CrysAlis PRO (Rigaku OD, 2022 $[Rigaku OD (2022). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ ), SHELXT (Sheldrick, 2015a ), PLATON (Spek, 2020 ), SHELXL2018/3 (Sheldrick, 2015b ), publCIF (Westrip, 2010 ) and WinGX (Farrugia, 2012 ).

Structural data

CCDC reference: 2426608

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314625001610/bh4093sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314625001610/bh4093Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314625001610/bh4093Isup3.cml

checkCIF report

Computing details top

2-Oxo-2H-chromen-7-yl 3-methylbutanoate top

Crystal data top

C₁₄H₁₄O₄	F(000) = 520
M_r = 246.25	D_x = 1.347 Mg m⁻³
Monoclinic, P2₁/c	Melting point = 341–343 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 15.370 (3) Å	Cell parameters from 3741 reflections
b = 5.4488 (10) Å	θ = 5.0–61.4°
c = 16.339 (3) Å	µ = 0.10 mm⁻¹
β = 117.426 (7)°	T = 296 K
V = 1214.5 (4) Å³	Prism, white
Z = 4	0.45 × 0.44 × 0.16 mm

Data collection top

SuperNova, Dual, Cu at home/near, AtlasS2 diffractometer	3741 independent reflections
Radiation source: micro-focus sealed X-ray tube	2799 reflections with I > 2σ(I)
Mirror monochromator	R_int = 0.068
Detector resolution: 5.3048 pixels mm^-1	θ_max = 30.7°, θ_min = 2.5°
ω scans	h = −22→21
Absorption correction: multi-scan (CrysAlisPro; Rigaku OD, 2022)	k = −7→7
T_min = 0.956, T_max = 1.000	l = −23→23
41227 measured reflections

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.066	Hydrogen site location: difference Fourier map
wR(F²) = 0.203	All H-atom parameters refined
S = 1.03	w = 1/[σ²(F_o²) + (0.1174P)² + 0.7176P] where P = (F_o² + 2F_c²)/3
41227 reflections	(Δ/σ)_max < 0.001
219 parameters	Δρ_max = 0.50 e Å⁻³
0 restraints	Δρ_min = −0.39 e Å⁻³

Special details top

Refinement. All non-H atoms were refined anisotropically. H atoms were located in difference Fourier maps and refined freely with an isotropic displacement parameter.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O3	0.30502 (9)	0.5548 (2)	0.49786 (9)	0.0262 (3)
O1	0.60720 (9)	0.1291 (2)	0.60615 (8)	0.0247 (3)
O2	0.74608 (10)	−0.0712 (3)	0.64517 (10)	0.0315 (3)
O4	0.25820 (10)	0.2488 (3)	0.56157 (10)	0.0362 (4)
C5	0.55518 (12)	0.3187 (3)	0.61799 (11)	0.0225 (3)
C4	0.60061 (12)	0.4940 (3)	0.68735 (11)	0.0230 (3)
C7	0.40292 (12)	0.5249 (3)	0.56429 (11)	0.0236 (3)
C6	0.45580 (13)	0.3301 (3)	0.55611 (11)	0.0240 (3)
C3	0.70488 (13)	0.4686 (3)	0.74636 (12)	0.0268 (4)
C11	0.13750 (13)	0.4489 (4)	0.42324 (12)	0.0276 (4)
C1	0.70685 (13)	0.1025 (3)	0.66096 (12)	0.0249 (3)
C12	0.10241 (13)	0.7130 (3)	0.42369 (12)	0.0262 (4)
C10	0.23739 (13)	0.3983 (3)	0.50137 (12)	0.0257 (3)
C9	0.54337 (13)	0.6854 (3)	0.69455 (12)	0.0260 (3)
C2	0.75496 (13)	0.2830 (4)	0.73351 (12)	0.0279 (4)
C8	0.44435 (13)	0.7026 (3)	0.63285 (12)	0.0258 (3)
C14	−0.00084 (16)	0.7484 (4)	0.34503 (14)	0.0361 (4)
C13	0.10591 (15)	0.7726 (4)	0.51641 (14)	0.0312 (4)
H5	0.4273 (19)	0.210 (5)	0.5086 (19)	0.040 (7)*
H3	0.7378 (17)	0.589 (5)	0.7957 (17)	0.036 (6)*
H9	0.5763 (18)	0.811 (5)	0.7445 (19)	0.041 (7)*
H8	0.4032 (18)	0.849 (5)	0.6331 (18)	0.037 (6)*
H2	0.8282 (17)	0.258 (4)	0.7702 (16)	0.027 (6)*
H11A	0.1421 (18)	0.418 (5)	0.3633 (18)	0.039 (7)*
H14A	−0.051 (2)	0.631 (6)	0.352 (2)	0.048 (7)*
H14B	−0.0221 (17)	0.929 (5)	0.3426 (17)	0.034 (6)*
H11B	0.0901 (18)	0.329 (5)	0.4256 (17)	0.035 (6)*
H12	0.1473 (16)	0.826 (4)	0.4176 (15)	0.026 (5)*
H13A	0.0868 (17)	0.946 (5)	0.5179 (17)	0.036 (6)*
H13B	0.1761 (18)	0.750 (4)	0.5683 (18)	0.033 (6)*
H13C	0.059 (2)	0.656 (6)	0.5256 (19)	0.052 (8)*
H14C	−0.005 (2)	0.709 (5)	0.282 (2)	0.051 (8)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O3	0.0272 (6)	0.0259 (6)	0.0257 (6)	0.0001 (5)	0.0122 (5)	0.0045 (5)
O1	0.0292 (6)	0.0230 (6)	0.0239 (6)	0.0005 (5)	0.0141 (5)	−0.0023 (5)
O2	0.0351 (7)	0.0299 (7)	0.0336 (7)	0.0045 (5)	0.0193 (6)	−0.0002 (5)
O4	0.0338 (7)	0.0409 (8)	0.0323 (7)	−0.0023 (6)	0.0138 (6)	0.0128 (6)
C5	0.0300 (8)	0.0205 (7)	0.0202 (7)	0.0000 (6)	0.0144 (6)	0.0010 (6)
C4	0.0293 (8)	0.0228 (7)	0.0196 (7)	−0.0012 (6)	0.0136 (6)	0.0009 (6)
C7	0.0266 (8)	0.0250 (8)	0.0211 (7)	−0.0005 (6)	0.0126 (6)	0.0031 (6)
C6	0.0291 (8)	0.0233 (8)	0.0205 (7)	−0.0021 (6)	0.0123 (6)	−0.0010 (6)
C3	0.0309 (8)	0.0291 (8)	0.0207 (7)	−0.0023 (7)	0.0121 (6)	−0.0005 (6)
C11	0.0277 (8)	0.0298 (9)	0.0241 (8)	0.0000 (7)	0.0108 (6)	−0.0022 (7)
C1	0.0301 (8)	0.0245 (8)	0.0234 (7)	0.0009 (6)	0.0152 (6)	0.0034 (6)
C12	0.0278 (8)	0.0281 (8)	0.0246 (8)	0.0000 (6)	0.0138 (6)	0.0015 (6)
C10	0.0289 (8)	0.0259 (8)	0.0242 (8)	−0.0002 (6)	0.0139 (6)	0.0008 (6)
C9	0.0336 (8)	0.0239 (8)	0.0228 (7)	−0.0022 (6)	0.0150 (7)	−0.0033 (6)
C2	0.0287 (8)	0.0318 (9)	0.0224 (8)	−0.0005 (7)	0.0112 (6)	0.0009 (7)
C8	0.0341 (9)	0.0226 (8)	0.0254 (8)	0.0011 (6)	0.0177 (7)	0.0000 (6)
C14	0.0345 (10)	0.0391 (11)	0.0289 (9)	0.0071 (8)	0.0097 (8)	0.0023 (8)
C13	0.0348 (9)	0.0335 (10)	0.0294 (9)	−0.0013 (7)	0.0184 (8)	−0.0033 (7)

Geometric parameters (Å, º) top

O3—C10	1.366 (2)	C11—H11A	1.03 (3)
O3—C7	1.402 (2)	C11—H11B	0.99 (3)
O1—C5	1.373 (2)	C1—C2	1.453 (3)
O1—C1	1.380 (2)	C12—C14	1.526 (3)
O2—C1	1.212 (2)	C12—C13	1.526 (3)
O4—C10	1.201 (2)	C12—H12	0.96 (2)
C5—C6	1.392 (2)	C9—C8	1.388 (3)
C5—C4	1.398 (2)	C9—H9	1.00 (3)
C4—C9	1.404 (2)	C2—H2	1.01 (2)
C4—C3	1.447 (2)	C8—H8	1.02 (3)
C7—C6	1.380 (2)	C14—H14A	1.04 (3)
C7—C8	1.393 (2)	C14—H14B	1.03 (3)
C6—H5	0.96 (3)	C14—H14C	1.03 (3)
C3—C2	1.345 (3)	C13—H13A	0.99 (3)
C3—H3	0.98 (3)	C13—H13B	1.03 (2)
C11—C10	1.502 (2)	C13—H13C	1.03 (3)
C11—C12	1.538 (3)

C10—O3—C7	117.47 (13)	C13—C12—C11	110.59 (15)
C5—O1—C1	122.11 (13)	C14—C12—H12	110.5 (13)
O1—C5—C6	116.52 (14)	C13—C12—H12	105.5 (13)
O1—C5—C4	121.48 (15)	C11—C12—H12	109.0 (14)
C6—C5—C4	121.98 (15)	O4—C10—O3	122.46 (16)
C5—C4—C9	118.50 (16)	O4—C10—C11	127.06 (17)
C5—C4—C3	117.45 (15)	O3—C10—C11	110.44 (15)
C9—C4—C3	124.04 (16)	C8—C9—C4	120.59 (16)
C6—C7—C8	122.74 (16)	C8—C9—H9	121.2 (15)
C6—C7—O3	118.98 (15)	C4—C9—H9	118.2 (15)
C8—C7—O3	118.16 (15)	C3—C2—C1	121.56 (17)
C7—C6—C5	117.53 (15)	C3—C2—H2	124.7 (13)
C7—C6—H5	122.5 (15)	C1—C2—H2	113.7 (13)
C5—C6—H5	119.9 (15)	C9—C8—C7	118.63 (16)
C2—C3—C4	120.40 (16)	C9—C8—H8	121.7 (15)
C2—C3—H3	121.0 (14)	C7—C8—H8	119.5 (15)
C4—C3—H3	118.6 (14)	C12—C14—H14A	111.2 (16)
C10—C11—C12	113.02 (15)	C12—C14—H14B	109.9 (13)
C10—C11—H11A	106.7 (14)	H14A—C14—H14B	111 (2)
C12—C11—H11A	109.6 (15)	C12—C14—H14C	112.4 (16)
C10—C11—H11B	109.1 (14)	H14A—C14—H14C	106 (2)
C12—C11—H11B	110.5 (15)	H14B—C14—H14C	107 (2)
H11A—C11—H11B	108 (2)	C12—C13—H13A	110.6 (15)
O2—C1—O1	117.13 (16)	C12—C13—H13B	109.7 (14)
O2—C1—C2	125.87 (17)	H13A—C13—H13B	107.9 (19)
O1—C1—C2	116.99 (15)	C12—C13—H13C	108.1 (16)
C14—C12—C13	110.90 (16)	H13A—C13—H13C	110 (2)
C14—C12—C11	110.18 (15)	H13B—C13—H13C	110 (2)

C1—O1—C5—C6	177.72 (14)	C5—O1—C1—C2	0.9 (2)
C1—O1—C5—C4	−0.8 (2)	C10—C11—C12—C14	−177.74 (16)
O1—C5—C4—C9	178.90 (14)	C10—C11—C12—C13	−54.8 (2)
C6—C5—C4—C9	0.5 (2)	C7—O3—C10—O4	4.3 (3)
O1—C5—C4—C3	0.1 (2)	C7—O3—C10—C11	−177.61 (14)
C6—C5—C4—C3	−178.32 (15)	C12—C11—C10—O4	119.0 (2)
C10—O3—C7—C6	74.6 (2)	C12—C11—C10—O3	−58.91 (19)
C10—O3—C7—C8	−109.20 (18)	C5—C4—C9—C8	−1.4 (3)
C8—C7—C6—C5	−2.0 (3)	C3—C4—C9—C8	177.38 (16)
O3—C7—C6—C5	174.03 (14)	C4—C3—C2—C1	−0.2 (3)
O1—C5—C6—C7	−177.36 (14)	O2—C1—C2—C3	−179.25 (18)
C4—C5—C6—C7	1.1 (2)	O1—C1—C2—C3	−0.4 (3)
C5—C4—C3—C2	0.4 (2)	C4—C9—C8—C7	0.6 (3)
C9—C4—C3—C2	−178.36 (17)	C6—C7—C8—C9	1.2 (3)
C5—O1—C1—O2	179.85 (15)	O3—C7—C8—C9	−174.88 (14)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···O4ⁱ	0.98 (3)	2.46 (3)	3.296 (2)	142.6 (19)
C6—H5···O1ⁱⁱ	0.96 (3)	2.51 (3)	3.444 (2)	167 (2)
C11—H11A···O2ⁱⁱ	1.03 (3)	2.60 (3)	3.245 (2)	120.5 (18)

Symmetry codes: (i) −x+1, y+1/2, −z+3/2; (ii) −x+1, −y, −z+1.

Acknowledgements

The authors thank the Institute Jean Barriol (Université de Lorraine, France) for the X-ray diffraction measurements and the AFRAMED project for the crystal structure determination..

References

Abernethy, J. L. (1969). J. Chem. Educ. 46, 561–568. CrossRef CAS Web of Science Google Scholar
Abou, A., Djandé, A., Ilagouma, A. T., Ouari, O. & Saba, A. (2020). Am. J. Org. Chem, 10, 1–16. CAS Google Scholar
Basanagouda, M., Kulkarni, M. V., Sharma, D., Gupta, V. K., Pranesha, P., Sandhyarani, P. & Rasal, V. P. (2009). J. Chem. Sci. 121, 485–495. CrossRef CAS Google Scholar
Bauer, K., Garbe, D. & Surburg, H. (1988). Flavors and fragrances. In Ullmann's Encyclopedia of Industrial Chemistry, Vol. A11, edited by W. Gerhartz, Y. S. Yamamoto, B. Elvers, J. F. Rounsaville & G. Schulz, 5th rev, pp. 208–209. New York: VCH Publishers Google Scholar
Boisde, P. M. & Meuly, W. C. (1993). Coumarin. In Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., Vol. 7, edited by J. I. Kroschwitz & M. Howe-Grant, M. pp. 647–658. New York: John Wiley. Google Scholar
Emmanuel–Giota, A. A., Fylaktakidou, K. C., Litinas, K. E., Nicolaides, D. N. & Hadjipavlou–Litina, D. J. (2001). J. Heterocycl. Chem. 38, 717–722. CAS Google Scholar
Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Web of Science CrossRef CAS IUCr Journals Google Scholar
Koulabiga, Z., Yao, K. H., Abou, A., Djandé, A., Giorgi, M. & Coussan, S. (2024). Am. J. Org. Chem. 12, 1–19. Google Scholar
Rigaku OD (2022). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England. 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. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2020). Acta Cryst. E76, 1–11. Web of Science CrossRef IUCr Journals Google Scholar
Vukovic, N., Sukdolak, S., Solujic, S. & Niciforovic, N. (2010). Arch. Pharm. Res. 33, 5–15. Web of Science CrossRef CAS PubMed Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Yao, H. K., Zakaria, K., Abou, A., Djandé, A., Giorgi, M. & Ouari, O. (2024). Am. J. Chem, 14, 13–26. Google Scholar
Yu, D., Morris–Natschke, S. L. & Lee, K.-H. (2007). Med. Res. Rev. 27, 108–132. Web of Science CrossRef PubMed CAS Google Scholar
Yu, D., Suzuki, M., Xie, L., Morris–Natschke, S. L. & Lee, K.-H. (2003). Med. Res. Rev. 23, 322–345. Web of Science CrossRef PubMed 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.