in nature are capable of forming a wide variety of different salts with various inorganic and organic acids although such salts must be pharmaceutically acceptable for administration to animals it is often desirable in practice to initially isolate the compound of the present invention from the reaction mixture as a pharmaceutically unacceptable salt and then simply convert the latter back to the free base compound by treatment with an alkaline reagent and subsequently convert the latter free base to a pharmaceutically acceptable acid addition salt the acid addition salts of the base compounds of this invention are readily prepared by treating the base compound with a substantially equivalent amount of the chosen mineral or organic acid in an aqueous solvent medium or in a suitable organic solvent such as methanol or ethanol upon careful evaporation of the solvent the desired solid salt is readily obtained the desired acid salt can also be precipitated from a solution of the free base in an organic solvent by adding to the solution an appropriate mineral or organic acid those compounds of the present invention that are acidic in nature are capable of forming base salts with various pharmacologically acceptable cations examples of such salts.