Confluentic acid is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

belonging to the chemical class known as

depside A depside is a type of polyphenolic compound composed of two or more monocyclic aromatic units linked by an ester group. Depsides are most often found in lichens, but have also been isolated from higher plants, including species of the Ericaceae, ...

s. It serves as a

secondary metabolite Secondary metabolites, also called ''specialised metabolites'', ''secondary products'', or ''natural products'', are organic compounds produced by any lifeform, e.g. bacteria, archaea, fungi, animals, or plants, which are not directly involved ...

in certain lichens and plays a role in distinguishing closely related species within the genus '' Porpidia''. In 1899,

Friedrich Wilhelm Zopf Friedrich (or Friederich) Wilhelm Zopf (12 December 1846 – 24 June 1909) was a well-known German botanist and mycologist. He dedicated to his whole life with fungal biology, particularly in classification of fungi and dye production in fungi an ...

isolated a compound from '' Lecidea confluens'', which he initially named confluentin and noted for its

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 ...

of 147–148 °C. This substance demonstrated the ability to turn

litmus paper Litmus is a water-soluble mixture of different dyes extracted from lichens. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity. In an acidic medium, blue litmus pape ...

red and, when interacting with

alkali In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...

, decomposed into

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

and

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

-like compounds. Zopf subsequently revised the chemical formula and melting point of the compound. Siegfried Huneck renamed it confluentinic acid in 1962, characterising it as optically inactive, with distinct colour reactions and

solubility In chemistry, solubility is the ability of a chemical substance, substance, the solute, to form a solution (chemistry), solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form su ...

properties, and determined its

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 ...

as C₂₈H₃₆O₈. Researchers typically identify the presence of confluentic acid using methods such as

thin-layer chromatography Thin-layer chromatography (TLC) is a chromatography technique that separates components in non-volatile mixtures. It is performed on a TLC plate made up of a non-reactive solid coated with a thin layer of adsorbent material. This is called the sta ...

and

high-performance liquid chromatography High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures. The mixtures can origin ...

. Additionally, an alternative visual detection method involves examining the lichen's

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

apothecium An ascocarp, or ascoma (: ascomata), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascoc ...

(fruiting body) under a microscope on a slide treated with

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...

, which reveals oil droplets indicative of confluentic acid. Several

structural analog A structural analog, also known as a chemical analog or simply an analog, is a chemical compound, compound having a chemical structure, structure similar to that of another compound, but differing from it in respect to a certain component. It can ...

ues of confluentic acid have been isolated from a variety of lichen species.

History

In 1899,

reported isolating a substance from '' Lecidea confluens'', which he named confluentin, characterised by a

of . He also found that this substance turns

red, reacts with FeCl₃ to produce a red-brown colour, and decomposes into

, a volatile substance, and a

-like compound with a melting point of 52 °C upon interaction with

. Zopf initially proposed the formula C₃₇H₅₀O₁₀ for this compound before revising it to C₂₆H₃₆O₇, noting the updated melting point as . In his 1962 report of his chemical investigations into the substance, German chemist Siegfried Huneck proposed naming it 'confluentinic acid' due to the presence of the

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

functional group, aligning with the naming conventions of other

lichen product Lichen products, also known as lichen substances, are organic compounds produced by a lichen. Specifically, they are secondary metabolites. Lichen products are represented in several different chemical classes, including terpenoids, orcinol deri ...

s. Huneck described the substance as optically inactive and noted its poor

petroleum ether Petroleum ether is the petroleum fraction consisting of aliphatic hydrocarbons and boiling in the range 35–60 °C, and commonly used as a laboratory solvent. Despite the name, petroleum ether is not an ether; the term is used only figurativ ...

ethyl acetate Ethyl acetate commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This flammable, colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues, nail polish removers, ...

, and

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

, but found it readily soluble in

ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R� ...

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

, and

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

. He noted the following colour reactions: weak brownish with alcoholic FeCl₃ solution, blue, green, and finally violet with

and

chloroform Chloroform, or trichloromethane (often abbreviated as TCM), is an organochloride with the formula and a common solvent. It is a volatile, colorless, sweet-smelling, dense liquid produced on a large scale as a precursor to refrigerants and po ...

upon heating, orange to orange-red with tetrazotised

benzidine Benzidine (trivial name), also called 1,1'-biphenyl-4,4'-diamine (systematic name), is an organic compound with the chemical formula, formula (C6H4NH2)2. It is an aromatic amine. It is a component of a test for cyanide. Related derivatives are ...

, and gray-violet with ''p''-phenylenediamine; no colouration was observed with

barium hydroxide Barium hydroxide is a chemical compound with the chemical formula Ba(OH)2. The monohydrate (''x'' = 1), known as baryta or baryta-water, is one of the principal compounds of barium. This white granular monohydrate is the usual commercial form. ...

. Huneck used

elemental analysis Elemental analysis is a process where a sample of some material (e.g., soil, waste or drinking water, bodily fluids, minerals, chemical compounds) is analyzed for its elemental and sometimes isotopic composition. Elemental analysis can be qualita ...

and

molecular weight A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

determination by

titration Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of Quantitative research, quantitative Analytical chemistry, chemical analysis to determine the concentration of an identified analyte (a substance to be ...

to determine the molecular formula of confluentinic acid as C₂₈H₃₆O₈. The Zeisel determination for

methoxy In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula . On a benzene ring, the Hammett equation classifies a methoxy substituent at the ''para'' position a ...

l group analysis indicated two methoxyl groups per molecule. John Elix and Brian Ferguson's proposal for the

total synthesis Total synthesis, a specialized area within organic chemistry, focuses on constructing complex organic compounds, especially those found in nature, using laboratory methods. It often involves synthesizing natural products from basic, commercially ...

of confluentic acid in 1978 marked a significant advancement in understanding of this lichen substance, enabling scientists to better study and understand the compound's structure and biological activity without relying solely on natural extraction. The synthesis began with the direct

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...

of suitably substituted aromatic carboxylic acids and phenols, using

dicyclohexylcarbodiimide is an organic compound with the chemical formula (C6H11N)2C. It is a waxy white solid with a sweet odor. Its primary use is to couple amino acids during artificial peptide synthesis. The low melting point of this material allows it to be melte ...

. Key precursors involved were specially prepared

benzoic acid Benzoic acid () is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. The benzoyl group is often abbreviated "Bz" (not to be confused with "Bn," which ...

s, with protective measures for reactive groups. The process included steps like

bromination In chemistry, halogenation is a chemical reaction which introduces one or more halogens into a chemical compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs ...

alkylation Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting al ...

, and the strategic use of

protecting group A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In man ...

s for the phenol and

carboxyl In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl group (e.g. ...

functionalities. The synthesis culminated in the removal of protecting groups and

hydrogenolysis Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes lysis (breakdown) by hydrogen.Ralph Connor, Homer Adkins. Hydrogenolysis Of Oxygenated Organic Compounds. J. Am. Chem. Soc. ...

over palladised carbon to yield the desired depsides including confluentic acid. In 1993, G. Fegie and colleagues introduced a standardised high-performance liquid chromatographic method that enabled the separation and detection of hundreds of lichen products, confluentic acid included.

Properties

Confluentic acid is a member of the class of chemical compounds called

s. Its

IUPAC name In chemical nomenclature, a preferred IUPAC name (PIN) is a unique name, assigned to a chemical substance and preferred among all possible names generated by IUPAC nomenclature. The "preferred IUPAC nomenclature" provides a set of rules for choos ...

is 4- -hydroxy-4-methoxy-6-(2-oxoheptyl)benzoylxy-2-methoxy-6-pentylbenzoic acid. The

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

absorbance maxima (λ_max) has two peaks at 268 and 304 nm. In the

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 ...

, significant peaks indicative of the carboxylic acid

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

occur at 1700 cm⁻¹ (C=O stretching in

carbonyl group In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such as aldehydes ...

s) and within the broad range of 2600 to 3100 cm⁻¹ (O-H stretching). The broad band at 3100 is due to

hydrogen bonding In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

, while the peak at 3500 is the COOH stretching band. Confluentic acid's

is C₂₈H₃₆O₈; 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 500.57

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 form, it exists as crystalline needles with a

of .

Occurrence

The (fungal partner) of the lichen ''

Lecidea tessellata ''Lecidea tessellata'' is a species of saxicolous lichen, saxicolous (rock-dwelling), crustose lichen in the family Lecideaceae. It was species description, formally described as a species in 1819 by German botanist Heinrich Gustav Flörke, Hein ...

'' has been shown to produce confluentic acid when cultured without its algal partner. Confluentic acid has also been reported from mycobiont cultures of '' Parmelina carporrhizans''. Confluentic acid is produced by almost all species of the genus '' Immersaria'', which is usually accompanied by 2'-''O''-methylmicrophyllinic acid. The absence of confluentic acid distinguishes ''

Inoderma nipponicum ''Inoderma'' is a genus of lichen-forming fungi in the family Arthoniaceae. It was resurrected for use in 2015 for a small group of species with the following features: elevated, white pruinose pycnidia, immersed to adnate white pruinose apotheci ...

'', from others in genus '' Inoderma'', which typically contain this chemical. The only character reliably distinguishing '' Porpidia contraponenda'' and the morphologically similar '' Porpidia cinereoatra'' is their secondary chemistry: the former contains 2'-''O''-methylmicrophyllinate and the latter has confluentic acid. A is a set of biosynthetically related compounds produced by a lichen. The confluentic acid chemosyndrome was identified in several lichens in the family

Lecideaceae The Lecideaceae are a family (biology), family of lichen-forming fungi in the order Lecideales. It contains about 30 genus, genera and roughly 250 species. A major distinguishing characteristic of the family is the form of the ascomata, fruit ...

; it contains confluentic acid as the major metabolite, and minor amounts of 2'-''O''-methylperlatolic acid, olivetonide monomethyl ether, and 2'-''O''-methylmicrophyllinic acid. Not just limited to lichen-forming fungi, confluentic acid has also been reported from the Brazilian plant '' Himatanthus sucuuba'', highlighting the compound's broader biological distribution. Christmas Lichen - Flickr - pellaea

A study on ''Cryptothecia rubrocincta'' reveals distinct biochemical compositions in various parts of its thallus, suggesting specialised roles for the compounds present. Specifically, confluentic acid was found exclusively in localised brown flecks within the red and pink zones of the thallus, alongside

calcium oxalate Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula or . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydr ...

monohydrate. This distribution is in contrast to other thallus areas, such as the white zone containing only calcium oxalate dihydrate and the dark red zone with chiodectonic acid,

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

, beta-carotene, and additional calcium oxalate dihydrate in the pink sub-zone. The presence of confluentic acid in specific areas without beta-carotene and chiodectonic acid—both known UV protectants—suggests that confluentic acid plays a different role in the lichen's survival strategy. While the exact function of confluentic acid in these localised brown flecks remains unclear, it is indicated that it is not required for radiation protection. The study also highlights a transition within the lichen from calcium oxalate dihydrate to the more stable monohydrate form, associated with the ageing process and possibly the metabolic activities involving confluentic acid.

Detection

Alan Fryday (1991) outlined a technique for the detection of confluentic acid in lichen samples. This method involves placing a

section Section, Sectioning, or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sig ...

of the lichen's

(fruiting body) on a microscope slide, which is then saturated with a 10% potassium hydroxide (KOH) solution. When examined under a

compound microscope Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive stru ...

at 40x magnification, a distinctive 'halo' of small oil droplets or bubbles emanating from the tissue section indicates the presence of confluentic acid. The oil droplets generated during this detection process consist of 4-''O''-methylolivetonide, a compound that is insoluble in potassium hydroxide solution. This substance forms as a result of confluentic acid undergoing

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

in the presence of potassium hydroxide. This test is particularly useful in distinguishing between morphologically similar yet chemically distinct species within the genus '' Porpidia'', aiding accurate identification and study.

Related compounds

The chemical diversity within lichens includes a variety of compounds related to confluentic acid, reflecting the complex biosynthetic capabilities of these symbiotic organisms and their significance in lichen taxonomy and ecology. In 1987, Chicita Culberson and colleagues reported the use of high-performance liquid chromatography to isolate and identify additional higher-carbon analogue substances in the "confluentic series", including hyperconfluentic acid, superconfluentic acid, and subconfluentic acid. These substances were isolated from the lichen '' Pseudobaeomyces pachycarpa''. The structure of subconfluentic acid (4- '-hydroxy-4'-methoxy-6'-(2"-oxopentyl)benzoyloxy2-methoxy-6-pentylbenzoic acid) was later established by synthesis. The compound 4-''O''-demethylsuperconfluentic acid, structurally similar to confluentic acid, was isolated from '' Stirtonia ramosa''. Another analogue, 2-''O''-methylconfluentic acid, was identified from ''

Lecidea fuscoatra ''Lecidea'' is a genus of crustose lichen, crustose lichens with a carbon-black ring or outer margin (exciple) around the fruiting body disc (apothecium), usually (or always) found growing on (Saxicolous lichen, saxicolous) or in (Endolithic lich ...

''. Gowan (1989) suggested a close chemical and biosynthetic relationship between methyl 2'-''O''-methylmicrophyllinate and confluentic acid, noting that the

biosynthetic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical re ...

s leading to these compounds primarily differ in the length of the acetyl-polymalonyl segment. This means that the two compounds are synthesised through similar processes, differing mainly in the size of a specific chain within the molecule. Additionally, there is only a minor variation in their methylation patterns. Gowan further suggested that methyl 2'-''O''-methylmicrophyllinate likely originated from an ancestor that already produced confluentic acid.

Notes

References

{{Reflist, colwidth=30em, refs= {{cite journal , last1=Alors , first1=David , last2=Divakar , first2=Pradeep Kumar , last3=Calchera , first3=Anjuli , last4=Schmitt , first4=Imke , author-link5=Ana Crespo , last5=Crespo , first5=Ana , last6=Molina , first6=María Carmen , title=The temporal variation of secondary metabolites in the mycobiont culture and thallus of ''Parmelina carporrhizans'' and ''Parmelina quercina'' analyzed using high-performance liquid chromatography , journal=Separations , volume=10 , issue=7 , year=2023 , doi=10.3390/separations10070399 , doi-access=free , page=e399 {{cite journal , author-link1=Chicita F. Culberson , last1=Culberson , first1=Chicita F. , author-link2=William Louis Culberson , last2=Culberson , first2=William Louis , last3=Gowan , first3=Sharon , last4=Johnson , first4=Anita , title=New depsides from lichens: microchemical methodologies applied to the study of new natural products discovered in herbarium specimens , journal=American Journal of Botany , volume=74 , issue=3 , year=1987 , doi=10.1002/j.1537-2197.1987.tb08622.x , pages=403–414 {{cite journal , last1=Edwards , first1=Howell G.M. , last2=de Oliveira , first2=Luiz F.C. , author-link3=Mark Seaward , last3=Seaward , first3=Mark R.D. , title=FT-Raman spectroscopy of the Christmas wreath lichen, ''Cryptothecia rubrocincta'' (Ehrenb.:Fr.) Thor , journal=The Lichenologist , volume=37 , issue=2 , year=2005 , doi=10.1017/S0024282905014611 , pages=181–189 {{cite journal , author-link1=John Alan Elix , last1=Elix , first1=John , last2=Ferguson , first2=B.A. , title=Synthesis of the lichen depsides, olivetoric acid, confluentic acid and 4-''O''-methylolivetoric acid , journal=Australian Journal of Chemistry , volume=31 , issue=5 , year=1978 , doi=10.1071/CH9781041 , pages=1041–1051 {{cite journal , last1=Elix , first1=J.A. , last2=Wardlaw , first2=J.H. , last3=David , first3=F. , title=The structure of subconfluentic acid, a depside from the lichen ''Lecidella'' cf. ''cyanosarca'' , journal=Australian Journal of Chemistry , volume=49 , issue=1 , year=1996 , doi=10.1071/CH9960159 , pages=159–161 {{cite journal , last1=Endo , first1=Yuichi , last2=Hayashi , first2=Hiroko , last3=Sato , first3=Toshitsugu , last4=Maruno (M.Chin) , first4=Masao , last5=Ohta , first5=Tomihisa , last6=Nozoe , first6=Shigeo , title=Confluentic acid and 2'-''O''-methylperlatolic acid, monoamine oxidase B inhibitors in a Brazilian plant, ''Himatanthus sucuuba'' , journal=Chemical and Pharmaceutical Bulletin , volume=42 , issue=6 , year=1994 , doi=10.1248/cpb.42.1198 , pages=1198–1201 , url=https://www.jstage.jst.go.jp/article/cpb1958/42/6/42_6_1198/_pdf , doi-access=free, pmid=8069971 {{cite journal , last1=Feige , first1=G.B. , author-link2=Helge Thorsten Lumbsch , last2=Lumbsch , first2=H.T. , last3=Huneck , first3=S. , last4=Elix , first4=J.A. , title=Identification of lichen substances by a standardized high-performance liquid chromatographic method , journal=Journal of Chromatography A , volume=646 , issue=2 , year=1993 , doi=10.1016/0021-9673(93)83356-W , pages=417–427 {{cite journal , last1=Frisch , first1=Andreas , last2=Ohmura , first2=Yoshihito , last3=Ertz , first3=Damien , last4=Thor , first4=Göran , title=''Inoderma'' and related genera in Arthoniaceae with elevated white pruinose pycnidia or sporodochia , journal=The Lichenologist , volume=47 , issue=4 , year=2015 , doi=10.1017/S0024282915000201 , pages=233–256 {{cite journal , last=Gowan , first=Sharon P. , title=A character analysis of the secondary products of the Porpidiaceae (lichenized Ascomycotina) , journal=Systematic Botany , volume=14 , issue=1 , year=1989 , doi=10.2307/2419052 , pages=77–90, jstor=2419052 {{cite journal , last=Fryday , first=Alan , year=1991 , title=A microscopic test for confluentic acid , journal=British Lichen Society Bulletin , volume=70 , page=31 , url=https://britishlichensociety.org.uk/sites/default/files/bulletins/BLS%20Bulletin%2070%20Summer%201992.pdf {{cite journal , last=Fryday , first=Alan , year=1992 , title=The chemistry of the new confluentic acid test , journal=British Lichen Society Bulletin , volume=71 , page=41 , url=https://britishlichensociety.org.uk/sites/default/files/bulletins/BLS%20Bulletin%2071%20Winter%201992.pdf {{cite journal , last=Fryday , first=Alan M. , title=The genus ''Porpidia'' in northern and western Europe, with special emphasis on collections from the British Isles , journal=The Lichenologist , volume=37 , issue=1 , year=2005 , doi=10.1017/S0024282904014628 , pages=1–35 {{cite journal , last1=Hellwig , first1=Veronika , last2=Nopper , first2=Reilinde , last3=Mauler , first3=Frank , last4=Freitag , first4=Joachim , last5=Ji-Kai , first5=Liu , last6=Zhi-Hui , first6=Ding , last7=Stadler , first7=Marc , title=Activities of prenylphenol derivatives from fruitbodies of ''Albatrellus'' spp. on the human and rat vanilloid receptor 1 (VR1) and characterisation of the novel natural product, confluentin , journal=Archiv der Pharmazie , volume=336, issue=2 , year=2003 , doi=10.1002/ardp.200390008 , pages=119–126, pmid=12761765 {{cite journal , author-link=Siegfried Huneck , last=Huneck , first=Siegfried , title=Über Flechteninhaltsstoffe, I. Konstitution der Confluentinsäure , trans-title=About Lichen Constituents, I. Constitution of Confluentinic Acid , journal=Chemische Berichte , volume=95 , issue=2 , year=1962 , doi=10.1002/cber.19620950206 , pages=328–332 , language=de {{cite book , 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 , pages=244–245 {{cite journal , last1=Namada , first1=N. , last2=Tanahashi , first2=T. , last3=Goldsmith , first3=S. , last4=Nash III , first4=T.H. , year=1997 , title=Induction of secondary products in isolated mycobionts from North American Lichens , journal=Symbiosis , volume=23 , pages=219–224 {{cite book , authorlink1=Alan Orange , last1=Orange , first1=A. , author-link2=Peter Wilfred James , last2=James , first2=P.W. , last3=White , first3=F.J. , year=2001 , title=Microchemical Methods for the Identification of Lichens , publisher=British Lichen Society , isbn=978-0-9540418-0-9 , page=13 {{cite journal , last1=Xie , first1=Cong-Miao , last2=Wang , first2=Li-Song , last3=Zhao , first3=Zun-Tian , last4=Zhang , first4=Yan-Yun , last5=Wang , first5=Xin-Yu , last6=Zhang , first6=Lu-Lu , title=Revision of ''Immersaria'' and a new lecanorine genus in Lecideaceae (lichenised Ascomycota, Lecanoromycetes) , journal=MycoKeys , issue=87 , year=2022 , pmid=35210924 , pmc=8863769 , doi=10.3897/mycokeys.87.72614 , doi-access=free , pages=99–132 {{cite journal , author-link=Friedrich Wilhelm Zopf , last=Zopf , first=Wilhelm , title=Zur Kenntniss der Flechtenstoffe , trans-title=On the knowledge of lichen substances , journal=Justus Liebigs Annalen der Chemie , volume=306 , issue=3 , year=1899 , doi=10.1002/jlac.18993060304 , pages=282–321 , language=de Lichen products Organic acids Polyphenols Methoxy compounds Ketones