Usnic Acid and Related Compounds

Usnic acid is one of the biologically most active compounds which justifies a discussion of its three-dimensional structure. According to an X-ray analysis of (-)-usnic acid by Norrestam et al 566) the three hydroxyl hydrogens of the molecule are all involved in strong intramolecular hydrogen bonds and no intermolecular hydrogen bonds were found (see Fig. 4). In an X-ray analysis of +)-2-deacylusnic acid (a biodegradation product of usnic acid) Mac Donald et al. 519) observed the 0-0-distances shown in Fig. 5. Kutney and Sanchez 481) carried out an X-ray analysis of (-)-A -enaminousnic 

The absolute configuration of (-l-)-usnic acid has been determined by an X-ray analysis of the (—)-a-phenylethylamine derivative 492 (389). 

The absolute configuration at the C-9b-position of (-l-)-usnic add was fixed as R (559). Since the optical rotation of (-h)-8-methylcer-cosporamide, synthesized from (-t-)-usnic acid, is opposite in sign to that of naturally occurring (—)-cercosporamide, the latter should have the S-configuration at C-9b. The CD spectra of (-)-cercosporamide. 

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Huneck S, Schmidt J (1980) Lichen substances-126. Mass spectroscopy of natural products - 10. Comparative positive and negative ion mass spectroscopy of usnic acid and related compounds. Biomed Mass Spectrom 7 301-308... 

Kurokawa S, Elix JA, Watson PL, Sargent MV (1971) Parmelia notatay a new lichen species producing two new depsidones. J Jpn Bot 46 33-38 Kutney JP, Sanchez IH, Yee TH (1974) Mass spectral fragmentation studies in usnic acid and related compounds. Org Mass Spectrom 8 129-146 Laake Oy (1960) Institutional advertising of the La e Oy Pharmaceutical Manufacturers, Turku, Finland Lajide L (1984) Lichen depsides, depsidones and diphenyl ethers isolation, structure determination and synthesis. Thesis, Australian National Univ, Canberra Lam JKK, Sargent MV, Elix JA, Smith DO N (1972) Synthesis of valsarin and 5,7-dichloroemodin. J Chem Soc Perkin Trans 1 1466-1470... 

Kutney, J. P., I. H. Sanchez, and T. Yee Mass Spectral Fragmentation Studies in Usnic Acid and Related Compounds. Org. Mass Spectrom. 8, 129 (1974). 

Marshak, A., Schaefer, W. B., and Rajagopalan, S. (1949). Antibacterial activity of i/-usnic acid and related compounds on Mycobacterium tuberculosis. Proc. Soc. Exp. Biol. Med. 70, 565-568. 

Huneck S, Schmidt J (1980) Lichen Substances. 126. Mass Spectroscopy of Natural Products. 10. Comparative Positive and Negative Ion Mass Spectroscopy of Usnic Acid and Related Compounds. Biomed Mass Spectr 7 301... 

Usnic acid is found in oak moss and used in perfumes. Usnea barbata is a lichen species that occurs in oak moss. Cross-reactions between structurally related lichen compounds are unclear, but must be considered (Mitchell 1965 Hausen et al. 1993). Contact dermatitis in vaginal ovules and contact allergy in deodorant spray has been reported (Hein and Tarnick 1987 Rafanelli et al. 1995). The patch-test concentration is 0.1% pet. Allergic reactions are rare or uncommon. 

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