the invention of formula i wherein r is hydrogen form pharmaceutically acceptable salts with both organic and inorganic acids and bases examples of suitable acids for salt formation are hydrochloric sulfuric phosphoric acetic citric oxalic malonic salicyclic malic fumaric succinic ascorbic maleic methansulfonic and the like the salts are prepared by contacting the free base form with an equivalent amount of the desired acid in the conventional manner the free base forms may be regenerated by treating the salt form with a base for example dilute aqueous base solutions may be utilized dilute aqueous sodium hydroxide potassium carbonate ammonia and sodium bicarbonate solutions are suitable for this purpose the free base forms differ from their respective salt forms somewhat in certain physical properties such as solubility in polar solvents but the salts are otherwise equivalent to their respective free base forms for purposes of the invention examples of suitable bases for salt formation are sodium hydroxide sodium carbonate sodium bicarbonate potassium hydroxide calcium hydroxide ammonia organic amines and the like the salts are prepared by contacting the free acid form with an equivalent amount of the desired base in the conventional manner the free acid forms may be regenerated by treating the salt form with an acid for example dilute aqueous acid solutions may be utilized dilute aqueous hydrochloric acid sulfuric acid or acetic acid are suitable for this purpose the free acid forms differ from their respective salt forms somewhat in certain physical properties such as solubility in polar solvents but the salts are otherwise equivalent to their respective free acid forms for purposes of the invention the compound of the invention wherein r is alkyl of from 1 to 6 carbon.