Method of isolating 5'-guanylic acid

摘要

51-Guanylic acid is isolated from a solution containing it by adjusting the pH of the solution to a value within the range 1 to 5 inclusive and recovering it in the form of a mono-alkali metal salt or a mixture of a mono-alkali metal salt and the free acid or a mixture of mono- and di-alkali metal salts. The 5-guanylic acid solution may be obtained by chemical synthesis, microbiological fermentation, enzymatic degradation of ribonudeic acid with 51-phosphaiesterose or by extraction from natural sources. Guanosine may be phosphorylated with an organo-phosphorylating agent such as tetra-p - nitro - phenyl pyrophosphate, bis - p - nitrophenyl phosphochlorilate, diphenyl phosphochloridate, dibenyl, phosphochloridate, 2-cyanoethyl phosphate, tetra-chloro-pyrophosphate or phosphorous oxychloride, after the 21,31-positions of guanosine have been protected with an isopropylidene group, acyl group or a benzylidene group. Then the protective group present in the phosphorylating agent is removed by a known method. Subsequently the protective group at the 21,31-positions of guanosine is removed by a known method. Then from the resulting solution 51-guanylic acid is precipitated in the form of free acid or monoalkali metal salt by standing the solution adjusted to pH 1.0-5.0 in a cool place after removing, if necessary, the phosphorylating agent remaining and compounds derived from the protective group of the agent. The precipitate is collected, washed with organic solvent, dissolved in water, neutralized with an alkali metal hydroxide and cooled to give the dialkalimetal salt of 51-guanylic acid. In a typical example, 21,31-O-isopropylidene guanosine is phosphorylated with bis - p - introphenylphosphate and di-p-tolylcarbodiimide, the protective group of the phosphorylating agent is removed with potassium hydroxide, the p-nitro-phenyl group and isopropylidene groups are removed by heating with concentrated hydrochloric acid at pH 2.5. The mono-potassium salt of 51-guanylic acid is recovered as a precipitate by cooling the solution and is then dissolved in water, the resulting solution neutralised with potassium hydroxide and the dipotassium salt of 51-guanylic acid isolated. Similar examples are given for isolating the disodium salt.