research communications Acta Cryst. (2016). E72, 1587–1589 http://dx.doi.org/10.1107/S2056989016016273 1587 Received 31 August 2016 Accepted 13 October 2016 Edited by W. T. A. Harrison, University of Aberdeen, Scotland Keywords: crystal structure; olivetolic acid; Cetrelia sanguinea. CCDC reference: 1509626 Supporting information: this article has supporting information at journals.iucr.org/e Crystal structure of olivetolic acid: a natural product from Cetrelia sanguinea (Schaer.) Friardi Ismed, a Aulia Farhan, a Amri Bakhtiar, a Erizal Zaini, a Yuda Prasetya Nugraha, b Okky Dwichandra Putra b and Hidehiro Uekusa b * a The Laboratory of Natural Resource of Sumatra (LBS) and Faculty of Pharmacy, Andalas University, 26163 Padang, Indonesia, and b Department of Chemistry and Materials Science, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro-ku, Tokyo 152-8551, Japan. *Correspondence e-mail: uekusa@cms.titech.ac.jp The title compound, C 12 H 16 O 4 (systematic name: 2,4-dihydroxy-6-pentylbenzoic acid) is a natural product isolated from C. sanguinea (Schaer.) and is reported to have various pharmacological activities. The molecule is approximately planar (r.m.s. deviation for the non-H atoms = 0.096 A ˚ ) and features an intramolecular O—HO hydrogen bond. In the crystal, each olivetolic acid molecule is connected to three neighbours via O—HO hydrogen bonds, generating (10 1) sheets. This crystal is essentially isostructural with a related resorcinolic acid with a longer alkyl chain. 1. Chemical context Monoaromatic compounds from lichens have attracted a great interest in the pharmaceutical field due to their potential pharmacological activities such as antibacterial, antifungal, cytotoxic, and photoprotective activities (Gianini et al.,2008: Stocker-Wo ¨ rgo ¨ tter, 2008; Ismed et al., 2012). The title compound, C 12 H 16 O 4 , is a derivative of alkyl resorcinolic acid which is commonly found in certain species of lichens (Gomes et al., 2006). 2. Structural commentary The title compound (Fig. 1) crystallizes with monoclinic metric symmetry and adopts a roughly planar conformation (r.m.s. deviation = 0.093 A ˚ ). All bond distances, angles and dihedral angles appear to be usual except the bond angle of C6—C5— C12 [124.61 (13)  ] compared to the mean value and their standard deviation of selected 24 similar structures reported in Cambridge Structural Database (CSD, Version 5.37, Update 2 Feb 2016; Groom et al., 2016). In this case, the deviating bond angle may be a result of the strong intramolecular O2— H2O3 interaction. ISSN 2056-9890