Hypostictic acid

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Hypostictic acid
Hypostictic acid.svg
Names
IUPAC name
13,17-dihydroxy-5-methoxy-4,7,12-trimethyl-2,10,16-trioxatetracyclo[9.7.0.03,8.014,18]octadeca-1(11),3(8),4,6,12,14(18)-hexaene-9,15-dione
Other names
Hypostictinsäure
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/C19H16O8/c1-6-5-9(24-4)7(2)14-10(6)17(21)26-15-8(3)13(20)11-12(16(15)25-14)19(23)27-18(11)22/h5,19-20,23H,1-4H3
    Key: PGRWVCGZKIXMQW-UHFFFAOYSA-N
  • CC1=CC(=C(C2=C1C(=O)OC3=C(O2)C4=C(C(=C3C)O)C(=O)OC4O)C)OC
Properties
C19H16O8
Molar mass 372.3 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Hypostictic acid is a lichen secondary metabolite belonging to the depsidone class of aromatic compounds. It was first prepared in 1933 by catalytic hydrogenation of stictic acid isolated from the foliose lichen Lobaria pulmonaria , and as a natural product was later reported from an undescribed species of the crustose lichen genus Thelotrema collected in Venezuelan cloud forest. As a lichen metabolite it has been detected as a minor or trace component in several foliose and crustose lichen genera, including Pseudoparmelia , Xanthoparmelia , Nephroma , Aspicilia , Clandestinotrema , Porpidia and Rinodina . Hypostictic acid forms colourless crystals with a relatively high melting point and has been used as a model substrate in electrochemical studies that investigate the reduction behaviour of lichen depsidones.

History and synthesis

Before its discovery as a lichen metabolite, the compound now known as hypostictic acid was obtained only as a reduction product of stictic acid (Stictinsäure). In 1933 Yasuhiko Asahina and co-workers reduced stictic acid (Stictinsäure) from Lobaria pulmonaria with hydrogen in glacial acetic acid using palladium on carbon as catalyst, giving a C19H16O8 depsidone that crystallised as colourless needles decomposing at 263–264 °C. [1] They characterised this compound by elemental analysis, methoxy determinations and conversion into a dimethyl ether, and from the relationship of its methylated reduction products to those of salazinic acid concluded that stictic acid is a monomethyl ether of desoxysalazinic acid. [1] Later work showed that this reduction product is identical with naturally occurring hypostictic acid isolated from lichens. [2]

Occurrence

Hypostictic acid was first isolated from the foliose lichen species Lobaria pulmonaria. Lobaria pulmonaria (4037903744).jpg
Hypostictic acid was first isolated from the foliose lichen species Lobaria pulmonaria .

Hypostictic acid has been detected in several lichens, particularly in members of the family Parmeliaceae. As a natural product it was first isolated from a new species of the crustose lichen genus Thelotrema (family Graphidaceae) collected in cloud forest at about 2,300 m elevation in the San Eusebio region of Mérida State, Venezuela. [2] In the foliose lichen Xanthoparmelia quintaria , a South African endemic, thin-layer chromatography was used to show that hypostictic acid corresponds to Culberson's previously unnamed compound "PQ1" and co-occurs with hyposalazinic acid ("PQ2"). [2]

Hypostictic acid occurs as a minor chemical component in Pseudoparmelia sphaerospora , [3] Nephroma australae , [4] and has been reported from Xanthoparmelia species where it is usually present only in trace amounts. [5] It has also been recorded from crustose lichen species in the genera Aspicilia , [6] Clandestinotrema , [7] Porpidia , [8] and Rinodina . [9]

Chemical properties

Hypostictic acid is a lichen depsidone with the molecular formula C19H16O8 (relative molecular mass 372.32). It crystallises from acetone as colourless needles and has a melting point of about 263–264 °C, decomposing on heating. [1] [10] In infrared spectra it shows strong absorption bands around 1,695 and 1,750 cm−1, in the region expected for conjugated carbonyl groups, together with bands attributable to aromatic and phenolic functions. Proton NMR spectra in pyridine-d5 display three singlet methyl signals, a methoxy group and two aromatic protons, consistent with a heavily substituted aromatic framework. In the mass spectrum hypostictic acid gives a molecular ion peak at m/z 372 with a characteristic series of fragment ions. Acetylation with acetic anhydride in pyridine yields the diacetate, diacetylhypostictic acid, which forms crystals melting at about 244 °C and is used as a derivative for further analytical work. [10]

Electrochemical studies in dry dimethylformamide (DMF) using a glassy carbon working electrode have examined hypostictic acid as a model lichen depsidone. In this medium the neutral molecule undergoes an irreversible one-electron reduction to a radical anion, followed by cleavage, disproportionation and a self-protonation step that give the reduced depsidone hypostictinolide. Prolonged controlled-potential electrolysis leads to further transformation of hypostictinolide into two additional derivatives, including a ring-opened depside and an aldehyde-bearing dibenzodioxepine, whose structures were assigned using high-resolution mass spectrometry together with one- and two-dimensional NMR spectroscopy. [11]

References

  1. 1 2 3 Asahina, Yasuhiko; Yanagita, Masaiti; Omaki, Tatuo (1933). "Untersuchungen über Flechtenstoffe, XXV. Mitteil.: Über Stictinsäure". Berichte der Deutschen Chemischen Gesellschaft (A and B Series) (in German). 66 (7): 943–947. doi:10.1002/cber.19330660706.
  2. 1 2 3 Keogh, Myles F. (1978). "New β-orcinol depsidones from Xanthoparmelia quintaria and a Thelotrema species". Phytochemistry. 17 (7): 1192–1193. Bibcode:1978PChem..17.1192K. doi:10.1016/S0031-9422(00)94315-2.
  3. ↑ White, Pollyanna; Oliveira, Rita; Oliveira, Aldeidia; Serafini, Mairim; Araújo, Adriano; Gelain, Daniel; Moreira, Jose; Almeida, Jackson; Quintans, Jullyana; Quintans-Junior, Lucindo; Santos, Marcio (2014). "Antioxidant activity and mechanisms of action of natural compounds isolated from lichens: a systematic review". Molecules. 19 (9): 14496–14527. doi: 10.3390/molecules190914496 . PMC   6271897 . PMID   25221871.
  4. ↑ Moroney, Simon E.; Ronaldson, Kathlyn J.; Wilkins, Alistair L.; Green, T.G. Allan; James, P.W. (1981). "Depsidone constituents from the quintaria group of Nephroma species". Phytochemistry. 20 (4): 787–789. Bibcode:1981PChem..20..787M. doi:10.1016/0031-9422(81)85175-8.
  5. ↑ Elix, J.A. (1981). "New species of Parmelia subgen. Xanthoparmelia (lichens) from Australia and New Zealand". Australian Journal of Botany. 29 (3): 349–376. Bibcode:1981AuJB...29..349E. doi:10.1071/BT9810349.
  6. ↑ Fryday, Alan M.; Wheeler, Timothy B.; Etayo, Javier (2021). "A new species of Aspicilia (Megasporaceae), with a new lichenicolous Sagediopsis (Adelococcaceae), from the Falkland Islands". The Lichenologist. 53 (4): 307–315. Bibcode:2021ThLic..53..307F. doi:10.1017/S0024282921000244.
  7. ↑ Medeiros, Ian D. (2018). "A new species of Clandestinotrema (Ascomycota: Ostropales: Graphidaceae) from montane cloud forest in the Venezuelan Andes". Plant and Fungal Systematics. 63 (1): 7–10. doi: 10.2478/pfs-2018-0002 .
  8. ↑ Zhao, Xiang-Xiang; Zhang, Lu-Lu; Miao, Cong-Cong; Zhao, Zun-Tian (2016). "A new species of Porpidia from China". The Lichenologist. 48 (3): 229–235. Bibcode:2016ThLic..48..229Z. doi:10.1017/S0024282916000128.
  9. ↑ Giralt, Mireia; Matzer, Mario (1994). "The corticolous species of the genus Rinodina with biatorine or lecideine apothecia in southern Europe and Macaronesia". The Lichenologist. 26 (4): 319–332. Bibcode:1994ThLic..26..319G. doi:10.1006/lich.1994.1026.
  10. 1 2 Huneck, Siegfried (1996). Identification of Lichen Substances. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 332–333. ISBN   978-3-642-85245-9. OCLC   851387266.
  11. ↑ Carvalho, Adriana E.; Barison, Andersson; Honda, Neli K.; Gilberto Ferreira, Antonio; Maia, Gilberto (2004). "Two new compounds from the electroreduction of hypostictic acid". Journal of Electroanalytical Chemistry. 572 (1): 1–14. doi:10.1016/j.jelechem.2004.05.019.
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