Protocetraric acid is a chemical compound with the molecular formula . It is a secondary metabolite produced by a variety of

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

s and is classified as a

depsidone Depsidones (+ " depside" + "one") are chemical compounds that are sometimes found as secondary metabolites in lichens. They are esters that are both depsides and cyclic ethers. An example is norstictic acid Norstictic acid is a depsidone produ ...

History

In 1845 Knop and Schnedermann isolated crystalline cetraric acid from the lichen '' Cetraria islandica''. O. Hesse proposed that cetraric acid does not exist in the lichen, but is rather the decomposition product of another acid that he called protocetraric acid, which is split up into fumaric and cetraric acids. In reviewing Hesse's work. O. Simon confirmed the statements of Knop and Schnedermann, finding cetraric acid in the plant in a free state. O. Simon did not find the protocetraric acid proposed by Hesse, but instead used that name for another acid he isolated. Protocetraric acid was first described in the 1930s. Rao and colleagues published the ultraviolet and infrared spectra of some lichen depsidones, including protocetraric acid, in 1967.

Properties

The

molecular formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as paren ...

of protocetraric acid is C₁₈H₁₄O₉; it has a

molecular mass The molecular mass () is the mass of a given molecule, often expressed in units of daltons (Da). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The derived quan ...

of 374.29

grams per mole In chemistry, the molar mass () (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical substance ( element or compound) is defined as the ratio between the mass () and the amount of substance ...

. In its purified crystalline form, it exists as short needles with a

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

range of . Its ultraviolet spectrum has three peaks of maximum absorption (λ_max) at 210, 238, and 312 nm. Its

infrared spectrum Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

has several peaks: 680, 745, 785, 814, 840, 990, 1020, 1080, 1115, 1150, 1190, 1270, 1380, 1440, 1562, 1642, 1738, 3000, and 3500 cm⁻¹. A number of

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

derivatives of protocetraric acid, such as succinprotocetraric acid and fumarprotocetraric acid, have also been identified in lichens. Preliminary research has been conducted into the potential pharmacology of protocetraric acid and related compounds. Protocetraric acid has broad spectrum antimicrobial properties against some pathogenic microbes such as ''

Salmonella typhi ''Salmonella enterica'' subsp. ''enterica'' is a subspecies of ''Salmonella enterica'', the rod-shaped, flagellated, aerobic, Gram-negative bacterium. Many of the pathogenic serovars of the ''S. enterica'' species are in this subspecies, includin ...

''. It also has weak activity against

SARS-CoV-2 Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. The virus previously had the Novel coronavirus, provisional nam ...

3C-like protease (K_i of 3.95 μM), as does the related depsidone salazinic acid, and therefore it is being studied as a scaffold for the potential discovery of more potent drugs for the treatment of

COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the coronavirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic. The symptoms of COVID‑19 can vary but often include fever ...

Biological activities

Laboratory experiments indicate that protocetraric acid has broad spectrum antimicrobial activity against some pathogenic microbes, including antibacterial activity against ''

'', and antifungal activity against ''

Trichophyton rubrum ''Trichophyton rubrum'' is a dermatophytic fungus in the phylum Ascomycota. It is an exclusively clonal, anthropophilic saprotroph that colonizes the upper layers of dead skin, and is the most common cause of athlete's foot, fungal infection of ...

''. It also has moderate antimycobacterial activity on the growth of ''

Mycobacterium tuberculosis ''Mycobacterium tuberculosis'' (M. tb), also known as Koch's bacillus, is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' ha ...

''.

Eponyms

Some authors have explicitly named protocetraric acid in the specific epithets of their published lichen species, thereby acknowledging the presence of this compound as an important

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

characteristic. These

eponym An eponym is a noun after which or for which someone or something is, or is believed to be, named. Adjectives derived from the word ''eponym'' include ''eponymous'' and ''eponymic''. Eponyms are commonly used for time periods, places, innovati ...

s are listed here, followed by their author citation and year of publication. *'' Usnea hossei'' var. ''protocetrarica'' *'' Hypotrachyna protocetrarica'' *'' Karoowia protocetrarica'' *'' Myriotrema protocetraricum'' *'' Ocellularia protocetrarica'' *'' Opegrapha protocetrarica'' *'' Oropogon protocetraricus'' *'' Xanthoparmelia protocetrarica'' Several derivatives of protocetraric acid were designed and synthesised using Diels-Alder reaction,

esterification In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

, and Friedel-Crafts alkylation of protocetraric acid with different reagents under

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...

. The products were tested for their

α-Glucosidase In biochemistry, glycoside hydrolases (also called glycosidases or glycosyl hydrolases) are a class of enzymes which catalyze the hydrolysis of glycosidic bonds in complex sugars. They are extremely common enzymes, with roles in nature includi ...

inhibitory using molecular docking analysis.

Related compounds

The related chemical 9'-(''O''-methyl)protocetraric acid was isolated from the lichen '' Cladonia convoluta''. Conhypoprotocetraric acid, identified from lichens '' Relicina'' cf. ''incongrua'' and '' Lecanora myriocarpoides'', was synthesized and characterized in 1995. *Confumarprotocetraric acid *Conhyopoprotocetraric acid *Conprotocetraric acid *Consuccinprotocetraric acid *Fumarprotocetraric acid *Hypoprotocetraric acid *Malonprotocetraric acid *4-0-Methylhypoprotocetraric acid * Succinprotocetraric acid

References

Cited literature

*{{cite book , authorlink=Siegfried Huneck , last=Huneck , first=Siegfried , title=Identification of Lichen Substances , publisher=Springer Berlin Heidelberg , publication-place=Berlin, Heidelberg , year=1996 , isbn=978-3-642-85245-9 , oclc=851387266 Lichen products Lactones Heterocyclic compounds with 3 rings Benzodioxepines Alpha hydroxy acids Aromatic aldehydes