Some behaviors of diffractaic acid and barbatic acid

Abstract

1. Diffractaic acid is isolated from Usnea diffracta Vain. By using the column chromatography in chloroform and methanol (9 : 1) solvent system. 2. When diffractaic acid obtained from Usnea diffracta is developed in TLC by using acidic solvent, such as hexane, ether, formic acid (5 : 4 : O. 7), a small spot of barbatic acid can be observed with the large spot of diffractaic acid. 3. The NMR spectra of diffractaic acid and barbatic acid are measured in the solvent of acetone-d_6. Two signals of phenyl ring proton were broard. The integral ratio of 2-0-CH_3 proton and 4-0-CH_3 proton of diffractaic acid is 2.3 to 3.7. These facts lead us to deduce that the following rapid equilibrium between diffractaic acid and barbatic acid is present : R-Ome+H_20→R-OH+MeOH. 4. The -Ome of diffractaic acid is partially substituted by H_20 to form barbatic acid in the acidic condition, and the equilibrium between both acids can be established. Barbatic acid can be converted into 4-O-demethylbarbatic acid in some acidic conditions. The transfer of the chemical equilibrium is accelated in the presence of acidic catalists. The amount of the final products (barbatic acid or 4-0-demethylbarbatic acid) is changeable according to the acidic condition : 25% of the diffractaic acid is changed into barbatic acid under the presence of alminium chloride ; 50% under the presence of sulphuric acid. Furthermore, in the presence of hydrobromic acid, all diffractaic acid is converted into 4-0-demethylbarbatic acid (100%) probably through the intermediate substance, barbatic acid. 5. Even though without acidic catalysts, the equilibrium between diffractaic acid and barbatic acid is established, especially in acetone solvent. Thus, we consider that diffractaic acid itself plays as an acidic catalyst because diffractaic acid has a carboxylic acid. 6. Recently, most lichenologists used the acidic TLC solvent system, such as hexane, ether, formic acid (5 : 4 : O. 7), pastuka mixture, etc. Although acidic substances can be useful for the prevention to the tailing of some phenolic substances such as depsides or depsidones, they may accelate to form the demethyl substances of some O-methyl sub-stances. In such cases, dynamic behaviors to demethyl substances might be observed in some laboratory conditions, especially in solution.