Studies in the usnic acid series. VII. The biodegradation of (+)-usnic acid by a Pseudomonas species. Isolation, structure determination, and synthesis of (+)-6-desacetylusnic acid

Abstract

. Can. J. Chem. 55, 2336 (1977). Studies on the biodegradation of (+)-usnic acid (1) by a Pseudomonas species have revealed a novel aromatic deacylation process. The isolated metabolite, (+)-6-desacetylusnic acid (2) is crystalline and its structure is established by means of spectroscopic and chemical methods. The synthesis of 2 from usnic acid (1) is also reported and provides conclusive evidence for the structure of this metabolite.

Studies in the usnic acid series. IX. The biodegradation of (+)-usnic acid by Mucorglobosus

“…This compound proved identical as well to another of the metabolites characterized during our studies with the fungal isolate Mortierella isabellina (I). Moreover, during this work we were also able to show that chromium(I1) chloride reaction4 of (natural or synthetic) 9 afforded a 72% yield of (+)-2-desacetyl usnic acid (2), identical in all respects to the isolated metabolite.…”

“…To ensure proper aeration, the volume of the nutrient solution (2) should never exceed about two-fifths of the total volume of the flask.…”

“…The combined extracts were washed with water, dried over anhydrous sodium sulfate, and evaporated under reduced pressure to afford a yellow residue (68.3 mg). Purification by preparative layer chromatography (silica gel -oxalic acid plates, solvent A) produced (+)-2-desacetylusnic acid (2) Ozonolysis of (+)-2-desacetylusnic acid (2). Isolation of (*)-7-acetyl-3,5-dimethyl-4,6-dihydroxy-coumaran-2-one diacetate (3) A solution of (+)-2-desacetylusnic acid (2) (100 mg, 0.231 mrnol) in a 1 : I mixture of acetic anhydride -pyridine (6 rnL) was allowed to stand at room temperature overnight.…”

“…The organic fraction was then evaporated, washed with 2% sodium bicarbonate solution, water, dried over anhydrous sodium sulfate, and evaporated under reduced pressure to produce (+)-7-acetyl-3,5-dimethyl-4,6-dihydroxycouman-2-one diacetate (3) (32.1 mg, 0.100 mmol; 30%), colorless crystals from ethyl alcohol, mp 13 1 -132°C (lit. (4) Base cleavage of (+)-2-de.sace~llusnic acid (2). lsolatiorl of usrletic acid (4) (+)-2-Desacetylusnic acid (2) (48 mg, 0.1589 mrnol) in 75% potassium hydroxide (2 mL) was heated at 90-95OC (oil bath temperature) under nitrogen atmosphere for 25 min.…”

“…This organism is rather unique in the sense that it is capable of converting 1 quite efficiently via a novel and selective deacylation reaction predominantly to the metabolite (+)-2-desacetylusnic acid (2). In comparison, our preliminary studies of the biodegradation of 1 by the fungus Mortierella isabellina (1, 2) had yielded complex mixtures of metabolites.…”