13-Dihydrousnic acid

Estevez et al. (28J) isolated from cell-free extracts of Evernia prmastri the enzyme DL-usnic acid dehydrogenase which catalyzed the reduction of (-1-)- and (-)-usnic acid formula 495 was presumed to be that of the reduction product. Some time later Vicente and co-workers (708, 709) purified a second dehydrogenase which converted only the dextrorotatory enantiomer of usnic acid to 1-dihydrousnic acid (496) (see Scheme 154). The structure proposals for both dihydro derivatives were primarily based on the IR spectra and need to be confirmed by NMR, MS and/or X-ray analysis. Phenyl and isonicot-inoyl hydrazones of (—)-usnic acid (497, 498) have been reported, while reduction with sodium borohydride gave a mixture of 13a- and 13p-dihydrousnic acid (499) (555). 

Taguchi H, Shibata S (1970) The structure of isousnic acid with reference to isodihydrousnic acid derived from dihydrousnic acid. Chem Pharm BuU 18 374-378... 

Three-dimensional crystal structures of usnic acid and 2-desacylusnic acid were determined by X-ray diffraction 236, 259), but it was not until 1981 that Huneck etal. 178) established the absolute configurations of the usnic acids. X-Ray diffraction of the (— )-a-phenylethylimine of (H-)-usnic acid established the configuration 4a(R) for this isomer. By utilising the relationship of (-f-)-usnic acid and (+ )-isousnic acid to (— )-dihydrousnic acid (Scheme 63), (H-)-isousnic acid must also possess a 4a(R) configuration. 

Usnic Acid. X. The Pyrolysis of Tetrahydrodesoxyusnic and Dihydrousnic Acids. 

Usnic Acid. XIII. The Pyrolysis of the Oxidation Product of Dihydrousnic Acid. Chem. Pharm. Bull. (Japan) 26, 526 (1978). 

Diethylresorcinol. 2,4-Diethyl-l,3-benzenediol, 922 4,6-Diethylresorcinol. 4,6-Diethyl-l,3-benzenediol, 922 Dihydroeugenol acetate. 2-Methoxy-4-propylphenyl acetate, 927 Dihydrousnic acid. 2,6-Diacetyl-3,7,9-trihydroxy-8,9b-dimethyl-l-(4H,4aH,9bH)-dibenzo-furanone, 111... 

From dihydrousnic add [2552,2705] or from tetrahydrodeoxyusnic acid [2705] (from Lichens substances) by potassium permanganate oxidation in 10% aqueous potassium hydroxide at r.L, followed by distillation (5%) [2552]. 

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