Methyl gallate

Deborah Bebout; Silvina Pagola

doi:10.1107/S1600536809001123

. 2009 Jan 14;65(Pt 2):o317–o318. doi: 10.1107/S1600536809001123

Methyl gallate

Deborah Bebout ^a,^*, Silvina Pagola ^b

PMCID: PMC2968310 PMID: 21581923

Abstract

The crystal structure of the title compound (systematic name: methyl 3,4,5-trihydroxybenzoate), C₈H₈O₅, is composed of essentially planar molecules [maximum departures from the mean carbon and oxygen skeleton plane of 0.0348 (10) Å]. The H atoms of the three hydroxyl groups, which function as hydrogen-bond donors and acceptors simultaneously, are oriented in the same direction around the aromatic ring. In addition to two intramolecular hydrogen bonds, each molecule is hydrogen bonded to six others, creating a three-dimensional hydrogen-bonded network.

Related literature

For natural extracts containing gallic acid methyl ester, see: Saxena et al. (1994 ▶); Schmidt et al. (2003 ▶); Hawas (2007 ▶). For studies concerning antioxidant activity, see: Aruoma et al. (1993 ▶); Schmidt et al. (2003 ▶); Hawas (2007 ▶). For studies concerning anticancer properties, see: Fiuza et al. (2004 ▶) and for antimicrobial properties, see: Saxena et al. (1994 ▶); Landete et al. (2007 ▶). For cocrystals containing gallic acid methyl ester, see: Sekine et al. (2003 ▶); Martin et al. (1986 ▶). Similar gallate ester conformations are found in Parkin et al. (2002 ▶); Okabe & Kyoyama (2002a ▶); Nomura et al. (2000 ▶); Mizuguchi et al. (2005 ▶). For structures with similar hydroxyl arrangements, see: Hitachi et al. (2005 ▶); Okabe et al. (2001 ▶); Okabe & Kyoyama (2002b ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶).

Experimental

Crystal data

C₈H₈O₅
M _r = 184.14
Monoclinic,
a = 7.6963 (2) Å
b = 9.9111 (2) Å
c = 10.5625 (2) Å
β = 95.9930 (10)°
V = 801.29 (3) Å³
Z = 4
Cu Kα radiation
μ = 1.12 mm⁻¹
T = 100 (2) K
0.31 × 0.23 × 0.21 mm

Data collection

Bruker SMART APEXII CCD diffractometer
Absorption correction: numerical (SADABS; Sheldrick, 2004 ▶) T _min = 0.723, T _max = 0.799
8192 measured reflections
1352 independent reflections
1311 reflections with I > 2σ(I)
R _int = 0.034

Refinement

R[F ² > 2σ(F ²)] = 0.033
wR(F ²) = 0.093
S = 0.69
1352 reflections
121 parameters
All H-atom parameters refined
Δρ_max = 0.23 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: APEX2 (Bruker , 2004 ▶); cell refinement: SAINT-Plus (Bruker, 2004 ▶); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: WinGX (Farrugia, 1999 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶) and Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809001123/rz2286sup1.cif

e-65-0o317-sup1.cif^{(13.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809001123/rz2286Isup2.hkl

e-65-0o317-Isup2.hkl^{(65.5KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3⋯O4	0.84	2.25	2.7075 (13)	115
O4—H4⋯O5	0.84	2.29	2.7247 (12)	112
O4—H4⋯O1ⁱ	0.84	2.15	2.9470 (13)	159
O3—H3⋯O1ⁱⁱ	0.84	1.99	2.7007 (12)	142
O5—H5⋯O3ⁱⁱⁱ	0.84	1.86	2.6859 (12)	166

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

We are indebted to the NSF (CHE-0443345) and The College of William and Mary for the purchase of X-ray equipment. This work was supported in part by the US National Science Foundation (CHE-0315934). Any opinions, findings and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. SP gratefully acknowledges the Physics Department of the College of William and Mary for funding and ICDD GIA 08–04.

supplementary crystallographic information

Comment

Gallic acid methyl ester (I) is a polyphenolic compound present in grape seeds and other natural substrates (Saxena et al., 1994; Schmidt et al., 2003; Hawas, 2007). Like other polyphenols, I shows antioxidant activity (Aruoma et al., 1993; Schmidt et al., 2003; Hawas, 2007). Formerly used as an astringent and in opthalmology, its anticancer (Fiuza et al., 2004) and antimicrobial properties (Saxena et al., 1994; Landete et al., 2007) have also been studied. The molecular structure of I is shown below.

The molecular geometry is as expected from chemical bond rules (Figure 1) and it shows an almost planar conformation, with maximum departures from the mean carbon and oxygen skeleton plane of 0.0343 (9) and 0.0348 (10) Å for O4 and C8, respectively. The relative positions of the carbonyl and the three hydroxyls were also observed in a cocrystal of I and 5-chloro-2-methyl-4-isothiazoline-3-one (Sekine et al., 2003). Four other compounds containing a gallic acid ester moiety have crystallized in an analogous conformation (Parkin et al., 2002; Okabe & Kyoyama, 2002a; Nomura et al., 2000; Mizuguchi et al., 2005). Three other planar conformations of gallic acid esters are found in the Cambridge Structural Database (Allen, 2002). I has one of these other conformations in a cocrystal with caffeine (Martin et al., 1986).

Crystallized I has intra- and intermolecular hydrogen bonding. The hydroxyl H atoms bound to O3 and O4 (donors) form intramolecular hydrogen bonds to O4 and O5 (acceptors), respectively. This is shown in Figure 1. Similar hydroxyl arrangements have been reported in other gallic acid derivatives, such as gallate ester solvates (Hitachi et al., 2005), a gallic acid monohydrate polymorph (Okabe et al., 2001) and 2,3,4-trihydroxybenzophenone monohydrate (Okabe & Kyoyama, 2002b).

Gallic acid methyl ester forms a three-dimensional H-bonded network lacking significant aromatic ring stacking interactions. There is one molecule of I in the asymmetric unit. The H-bonded network is shown in Figure 2. Using the carbonyl ester oxygen O1 (acceptor) and the hydroxyl O3 and O4 (donors), each molecule is linked to another four through two O1···H3—O3, and two O1···H4—O4 H-bonds. These H-bonds are likely relatively weak due to the spacial orientation of the H atoms with respect to the lone electron pairs of O1. In addition, there are two other O5—H5···O3 H-bonds. The three hydroxyl sites are used as hydrogen bond donors and acceptors simultaneously. In the ester group, only the carbonyl oxygen is used as an H-bond acceptor.

Experimental

Gallic acid methyl ester was commercially obtained from Sigma-Aldrich (98% purity) and used as received. The crystal structure determination was carried out from a crystal with rhombic prismatic habit selected from the powder.