JOURNAL OF RAMAN SPECTROSCOPY J. Raman Spectrosc. 2008; 39: 95–107 Published online 1 October 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jrs.1822 Antioxidant phenolic esters with potential anticancer activity: A Raman spectroscopy study R. Calheiros, 1 N. F. L. Machado, 1 S. M. Fiuza, 1 A. Gaspar, 1 J. Garrido, 1,2 N. Milhazes, 1,3 F. Borges 1,4 and M. P. M. Marques 1,5* 1 Unidade I &D ‘Qu´ ımica-F´ ısica Molecular’, Faculdade de Ci ˆ encias e Tecnologia, Universidade de Coimbra, 3000 Coimbra, Portugal 2 Departamento de Engenharia Qu´ ımica, Instituto Superior de Engenharia do Porto, 4200-072 Porto, Portugal 3 Instituto Superior de Ci ˆ encias da Sa ´ ude, Norte, 4585-116 Gandra, PRD, Portugal 4 Departamento de Qu´ ımica Org ˆ anica, Faculdade de Farm ´ acia, Universidade do Porto, 4050-047 Porto, Portugal 5 Departamento de Bioqu´ ımica, Faculdade de Ci ˆ encias e Tecnologia, Universidade de Coimbra, Ap. 3126, 3001-401 Coimbra, Portugal Received 12 June 2007; Accepted 26 July 2007 A Raman study of hydroxycinnamic and hydroxybenzoic esters (caffeates, ferulates and gallates) displaying antioxidant and anticancer properties was undertaken, with particular emphasis on the analysis of the effect of the ring substituents and the nature of the ester alkyl chain on their spectroscopic features. A complete assignment of the spectra was carried out for all the compounds investigated, in the light of the corresponding calculated wavenumbers (at the density functional theory level). Distinct vibrational patterns were observed for each type of ester, thereby allowing their ready characterisation and identification by Raman spectroscopy. Evidence of the occurrence of intermolecular hydrogen bonds, leading to the formation of dimers in the condensed phase, was also obtained. Copyright  2007 John Wiley & Sons, Ltd. Supplementary electronic material for this paper is available in Wiley InterScience at http://www.interscience.wiley.com/ jpages//suppmat/ KEYWORDS: Raman spectroscopy; phenolic esters; caffeates; ferulates; gallates; anticancer INTRODUCTION Hydroxycinnamic and hydroxybenzoic esters, present in most fruits and vegetables, 1–4 display a huge variety of biological functions 5–11 such as antioxidant capacity, anti- inflammatory action and carcinogenesis modulation. 12 – 16 However, despite its undisputable importance for human health, the mechanisms underlying the absorption and metabolism of this type of compounds after food con- sumption are still scarcely known. 17 The evaluation of the antioxidant and antiproliferative activity of this type of phe- nolic derivatives, either of natural or synthetic origin, as well as the identification of their specific molecular targets, is nowadays an important area of research in the field of medic- inal chemistry. In fact, numerous studies have been carried out in order to obtain new lead compounds for the design of cancer preventive or therapeutic agents. 10,18 Neverthe- less, even though there is a wealth of data on the relevance of phenolic compounds as growth-inhibiting compounds, L Correspondence to: M. P. M. Marques, Departamento de Bioqu´ ımica, Faculdade de Ciˆ encias e Tecnologia, Universidade de Coimbra, Apartado 3126, 3001-401 Coimbra, Portugal. E-mail: pmc@ci.uc.pt the correlation between anti-tumour activity and chemical structure is far from clear. Caffeic acid (trans-3-(3,4-dihydroxyphenyl)-2-propenoic acid, CA) and its ester derivatives have been synthesised recently and screened for their antioxidant and anticancer activities. 9,10,19 – 24 Methyl caffeate (MC), propyl caffeate (PC) and octyl caffeate (OC) were found to display significant antiproliferative and cytotoxic effects towards human cervix adenocarcinoma (HeLa), coupled to a low toxicity against non-neoplastic cells, 23 which is in accordance with reported data for other hydroxycinnamic synthetic analogues. 25 Fer- ulic acid (trans-3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid, FA) is the most abundant hydroxycinnamic acid in the plant world and has been described to be an effective antiox- idant, essential for preserving the physiological integrity of cells. 26 – 28 Gallic acid (3,4,5-trihydroxybenzoic acid, GA) and its ester derivatives, in turn, are hydroxybenzoic compounds used as antioxidant additives in both food and pharma- ceutical industry – E-310 (propyl gallate) and E-311 (octyl gallate). The antioxidant and antiproliferative properties of these phenolic derivatives have been proposed to be ruled by specific structure–activity relationships (SARs). The Copyright  2007 John Wiley & Sons, Ltd.