Salazinic acid is 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 produc ...

with a

lactone Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

ring. It is found in some lichens, and is especially prevalent in ''

Parmotrema ''Parmotrema'' is a genus of lichen belonging to the family Parmeliaceae. It is a large genus, containing an estimated 300 species, with a centre of diversity in subtropical regions of South America and the Pacific Islands. Members of the genus ...

'' and ''

Bulbothrix ''Bulbothrix'' is a genus of lichen-forming fungi in the family Parmeliaceae. This genus is synonymous with ''Bulbothricella'' V.Marcano, S.Mohali & A.Morales. ''Bulbothrix'' was circumscribed by lichenologist Mason E. Hale in 1974 with '' Bul ...

'', where its presence or absence is often used to help classify species in those genera.

History

In 1897,

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 ...

named the chemical he originally isolated from the African species '' Stereocaulon salazinum'' as salazinic acid. Later studies showed that the compound he named was actually

norstictic acid Norstictic acid is a depsidone produced as a secondary metabolite Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fun ...

. In 1933, Yasuhiko Asahina and J. Asano studied salazinic acid they had isolated from '' Parmelia cetrata'', and found a unique

ring system A ring system is a disc or ring, orbiting an astronomical object, that is composed of solid material such as dust and moonlets, and is a common component of satellite systems around giant planets. A ring system around a planet is also known as ...

with seven members containing two phenolic components. The fundamental structure was named

, that is, a seven-membered ring with an oxygen bridge binding two

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

rings. Japanese chemists demonstrated in the late 1960s that the isolated mycobiont of the lichen '' Ramalina crassa'' could produce salazinic acid when grown in laboratory culture. Subsequent studies tried to determine the influence of environmental factors on the production of salazinic acid in culture. For example, two studies in the late 1980s showed that only 4-''O''-demethylbarbatic acid (a precursor of salazinic acid) was produced by the isolated mycobiont of '' Ramalina siliquosa'' when grown in malt

yeast extract Yeast extracts consist of the cell contents of yeast without the cell walls; they are used as food additives or flavorings, or as nutrients for bacterial culture media. They are often used to create savory flavors and umami taste sensations, ...

medium supplemented with low amounts of sucrose. When extra sucrose was added to the growth medium, the production of salazinic acid was observed; the increased

osmolality Molality is a measure of the number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent. This contrasts with the definition of molarity which is based on a specified volume of solution. A commonly used unit for molali ...

enhances the reaction from 4-''O''-demethylbarbatic acid to salazinic acid.

Properties

Salazinic acid has a

molecular formula In chemistry, 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, ...

of C₁₈H₁₂O₁₀, and a

molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quanti ...

of 388.3 grams/

mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpida ...

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

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

range between that undergo a colour change to brown at about . Its

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

in water is about 27 milligrams per litre. The compound has been shown in ''

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...

'' studies to have

antimicrobial An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...

properties, but it did not have any substantive

antimycobacterial An antimycobacterial is a type of medication used to treat Mycobacteria infections. Types include: * Tuberculosis treatment Tuberculosis management describes the techniques and procedures utilized for treating tuberculosis (TB). The medical st ...

effects when tested against ''

Mycobacterium aurum ''Mycolicibacterium aurum'' is a species of the phylum Actinomycetota (Gram-positive bacteria with high guanine and cytosine content, one of the dominant phyla of all bacteria), belonging to the genus ''Mycolicibacterium''. The species is an ...

''. Recent (2021) research indicates that salazinic acid is a potent modulator of

Nrf2 Nuclear factor erythroid 2-related factor 2 (NRF2), also known as nuclear factor erythroid-derived 2-like 2, is a transcription factor that in humans is encoded by the ''NFE2L2'' gene. NRF2 is a basic leucine zipper (bZIP) protein that may reg ...

NF-κB Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is a protein complex that controls transcription of DNA, cytokine production and cell survival. NF-κB is found in almost all animal cell types and is involved in cellular ...

and

STAT3 Signal transducer and activator of transcription 3 (STAT3) is a transcription factor which in humans is encoded by the ''STAT3'' gene. It is a member of the STAT protein family. Function STAT3 is a member of the STAT protein family. In respons ...

signaling pathways in colorectal cancer cells. The complete ¹H and ¹³C NMR spectral assignments for salazinic acid were reported in 2000.

Occurrence

Salazinic acid is derived via the acetyl polymalonyl pathway, a

metabolic 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 reac ...

that uses acetyl-CoA and malonyl-CoA (derivatives of coenzyme A). The compound is common in the large lichen genus ''

'', and plays an important role in the

chemotaxonomy Merriam-Webster defines ''chemotaxonomy'' as the method of biological classification based on similarities and dissimilarity in the structure of certain compounds among the organisms being classified. Advocates argue that, as proteins are more cl ...

and systematics of that genus. A 2020 revision included 66 salazinic acid-containing species. The presence or absence of the compound is also important in the classification of genus ''

''. In nature, salazinic acid serves as an antioxidant as well as a photoprotectant, helping the lichen to survive in conditions of both

abiotic In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...

and

biotic stress Biotic stress is stress that occurs as a result of damage done to an organism by other living organisms, such as bacteria, viruses, fungi, parasites, beneficial and harmful insects, weeds, and cultivated or native plants. It is different from ...

. A study of three

foliose lichen Foliose lichen is one of the morphological classes of lichens, which are complex organisms that arise from the symbiotic relationship between fungi and a photosynthetic partner, typically algae. This partnership allows lichen to live in dive ...

species showed higher quantities of salazinic acid correlating with increases in altitude. An earlier study demonstrated other possible effects of environmental conditions on salazinic acid content. It was shown that the salazinic acid content of '' Ramalina siliquosa'' is higher where the annual mean temperature is higher, and the content of the lichens growing on the dark-coloured rock or on the southern rock face is higher than that of the lichens growing on the light-coloured rock or on the northern rock face.

Related compounds

The depsidones chalybaeizanic acid and quaesitic acid, isolated from the lichens '' Xanthoparmelia amphixanthoides'' and '' Hypotrachyna quaesita'', respectively, are

structurally A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

similar to salazinic acid. In consalazinic acid, the

aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

group of salazinic acid is replaced with a

benzyl alcohol Benzyl alcohol is an aromatic alcohol with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn" (not to be confused with "Bz" which is used for benzoyl), thus benzyl alcohol is denoted as BnOH. Benzyl alcohol is a colorless liquid w ...

functional group. 8'-''O''-Methylsalazinic acid was isolated from '' Parmotrema dilatatum''. Several new synthesised derivatives of salazinic acid were reported in 2021 using

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

, nucleophilic addition, Friedel-Crafts alkylation, and

esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

Eponyms

Several authors have explicitly named salazinic acid in the specific epithets of their published lichen species, thereby acknowledging the presence of this compound as an important taxonomic characteristic. These

eponym An eponym is a person, a place, or a thing after whom or which someone or something is, or is believed to be, named. The adjectives which are derived from the word eponym include ''eponymous'' and ''eponymic''. Usage of the word The term ''epon ...

s are listed here, followed by their

taxonomic authority In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...

and year of publication: * '' Acanthothecis salazinica'' * '' Bryoria salazinica'' * '' Graphina salazinica'' * '' Karoowia salazinica'' * '' Lepraria salazinica'' * '' Myelochroa salazinica'' * '' Ocellularia salazinica'' * '' Pertusaria salazinica'' * '' Phaeographina salazinica'' * '' Psiloparmelia salazinica'' * '' Diorygma salazinicum'' * '' Oropogon salazinicus''

References

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