Unremitting problems with chlorogenic acid Nomenclature: A review

Assuntos Gerais http://dx.doi.org/10.5935/0100-4042.20160063 Quim. Nova, Vol. 39, No. 4, 530-533, 2016 UNREMITTING PROBLEMS WITH CHLOROGENIC ACID NOMENCLATURE: A REVIEW Daniel Kremr, Tomáš Bajer, Petra Bajerová*, Silvie Surmová, and Karel Ventura University of Pardubice, Faculty of Chemical Technology, Department of Analytical Chemistry, Studentská 573, 532 10 Pardubice, Czech Republic Recebido em 08/12/2015; aceito em 12/01/2016; publicado na web em 12/04/2016 This paper summarizes a problematic nomenclature of isomers belonging to chlorogenic acid family since its first occurrence until present. During decades, there have been a high number of articles dealing with the family. Unfortunately, researchers who want to get knowledge about this topic may be strongly confused after reading a few articles. Due to gradual discoveries and isolations of the individual isomers from plenty of matrices and because of the changing system of terminology after these discoveries, discrepancies among articles are common. The cause of this confusion is that the main compound of the family, 5-caffeoylquinic acid (also wellknown as chlorogenic acid), was truly called as 3-caffeoylquinic acid before 1976, when new rules for nomenclature were published. Many researchers and also chemicals suppliers, however, keep using the “pre-IUPAC” nomenclature and wrongly call 3-caffeoylquinic acid as chlorogenic acid, the main substituent of the family. Despite there have been some works struggling with this issue, the problem is still appearing. Therefore, the present work was written. Keywords: chlorogenic acid; neochlorogenic acid; nomenclature; coffee. INTRODUCTION As is well known nowadays, chlorogenic acids (CGAs) are naturally occurring compounds found in all higher plants. It is a family of esters formed between quinic and certain trans-cinnamic acids.1,2 However, in spite of the “chloro” in the name, chlorogenic acids do not contain chlorine. This name comes from the Greek, which means light green. This is most likely because of the green color produced when the compounds are oxidized. CGAs are widely recognized to have many beneficial properties such as antioxidant activity, anticarcinogenic potential and may also slow the release of glucose into the bloodstream after a meal.3-5 Also, they have strong antiinflammatory, anti-bacterium and anti-obesity properties.6-8 Because of these many positive influences on human body, since the middle of the 19th century, when the first references about CGAs appeared, there have been a high amount of articles dealing with extraction and detection techniques of CGAs or studying their influence on human health. CGAs have been observed and isolated in many plant materials such as coffee9, apple10, tomato, papaya11, sweet potato12, prune13, pear14, cabbage15, yacon16, burdock17, cherry18, apricot19, orange20, etc. Coffee beans are undoubtedly the most common observed matrix because coffee is the main source of CGAs.21 In the final coffee beverage, content of CGAs is supposed to be responsible for cup quality.22 In potatoes, for instance, the compounds are considered to cause undesirable “after-cooking blackening or darkening”, in other words, they seem to be responsible for bluish-grey discoloration of potatoes exposed to air after boiling or steaming.23,24 The main purpose of this work is not to bring up some other new extraction or detection possibilities for obtaining CGAs from plant materials neither to reveal some new observed properties of these compounds. It is to point out the considerable differences in articles dealing with the chlorogenic acid esters. During last decade, there has been a big disorder in nomenclature of CGAs. Although there are books or articles also dealing with the nomenclature of chlorogenic acid isomers, some of them are confusing and the majority of them are inaccessible for many researchers. Despite this fact, the wrong *e-mail: nomenclature is still very common, thus the present paper focuses on a possibility of making this problem clear, thus helping further authors to overcome potential misunderstandings of the nomenclature. Unfortunately, it has to be announced sometimes that the direct source (mostly sources published before 1900) are not available and therefore secondary sources might be used here. History of CGAs isolation The problems with the nomenclature of CGAs are naturally closelylinked to their history. Therefore, the present work paid attention to this fact. The very first references of chlorogenic acid come from the mid-19th century. Since 1837, when Robiquet and Bourton25 observed physiologically active constituents in coffee and isolated acidic substances with green pigments that included ferulic chloride from green coffee beans, there have been a huge amount of articles dealing with CGAs. In 1846, Payen26 firstly used the term “chlorogenic acid” (CQA). However, Payen was perhaps affected by Rochleder,27 who described “caffeotanic acid” in coffee. In 1854, Ludwig and Kromeyer28 found the compound in sunflower seeds. More than half a century later, in 1908, CQA was first isolated by Gorter29, who found out that this compound is widely distributed in leaves and seeds of numerous plants. He isolated a crystalline complex, potassium caffeine chlorogenate, from which he prepared the pure compound. He also figured out that chlorogenic acid is decomposed by the action of alkalis with the formation of caffeic and quinic acids. Two years later in 1910, Charaux,30 who was one of the first workers to attempt the measurement of CQA content in plants, described a possibility of extraction process. He confirmed CQA to be broadly distributed in the vegetable kingdom and said that its quantity is approximately two times more than the amount of caffeic acid in plants. In 1920, Freudenberg31 described chlorogenic acid, the tannic compound of coffee, as depside of quinic acid and caffeic acid. In 1932, Fischer and Dangschat32 established the structure of 3-O-caffeoylquinic acid, which is 5-O-caffeoylquinic acid (5-CQA) in current nomenclature (for this terminology see nomenclature section), by its isolation from green coffee beans. Decades later, in 1950-1960’s, the other three “mono-caffeic isomers” of quinic acid were observed. Neochlorogenic acid was Vol. 39, No. 4 Unremitting problems with chlorogenic acid Nomenclature: A review described and isolated from Elberta and Halford peaches as a crystalline material by Corse in 1953.33 In 1955, Uritani and Miyano34 succeeded with the isolation of pseudochlorogenic acid (1-CQA) from sweet potatoes infected with black rot. The last possible mono isomer got the name cryptochlorogenic acid (4-CQA) and it was explored and isolated in 1964 by Waiss.35 These two acids are very easy to distinguish due to the fact their OH groups are placed directly across from the carbon carrying the COOH group or exactly at the carbon carrying the COOH group, respectively. Also, in 1950, Barn (...truncated)