Tetracycline hydrochloric acid

Sample extraction/deproteinization is usually accomplished with mild acidic solvents to free the noncovalently bound tetracyclines from macromolecules. Mcllvaine buffer, pH 4.0 (286, 287), Mcllvaine/EDTA buffer, pH 4.0 (283, 287-293), succinate buffer, pH 4,0 (278-281,294-296), acidic acetonitrile (297-299), and acidic methanol (14, 199, 300) have all been used successfully. Moreover, trichloroacetic acid, pH 2.0 (301, 302), metaphosphoric acid (303), acetate buffer (126, 280), citrate buffer, pH 4.0 (304), citrate buffer/ethyl acetate, pH 4-5 (305), and hydrochloric acid/glycine buffer (306, 307) have all been employed with varying success to precipitate proteins from the sample homogenates. 

Miyazaki, S., M. Nakano, and T. Arita. 1975. A comparison of solubility characteristics of free bases and hydrochloride salts of tetracycline antibiotics in hydrochloric acid soluticSteem. Pharm. Bull. 23 1197-1204. 

Table 5.14. The increase in the solubility on the formation of the hydrochloride is readily attributable in the case of tetracycline to a lowering of the solution pH by the hydrochloride. The common ion effect can, however, produce an unexpected trend in the solubilities of bases in the presence of high concentrations of hydrochloric acid. Increase in Cl concentrations will cause the equilibrium between solid and solution forms...

In synthetic work towards tetracyclines the tricyclic dienone (99) was rearranged at 0 °C using boron trifluoride, to the anthraquinone (100 65%) apparently by a direct 1,5-shift. The quinamine (101) undergoes facile reorganization in hydrochloric acid to the biaryl (102) jn an aza-Claisen-like process. 

A microbiological assay is the method of choice (see p. 813) but spectro-photometric methods are also applicable. One spectrophotometric method is based on the formation of a yellow colour with an absorption maximum at 380 m//, when tetracycline is dissolved in 0-25N sodium hydroxide, another on the orange-brown colour (maximum absorption 490 m//) formed on mixing a dilute hydrochloric acid solution of the sample with ferric chloride solution. The former method which is described below is also applicable to oxytetracycline but not to chlortetracycline while the ferric chloride reaction, which is given in detail under oxytetracycline, applies to all three. 

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