Acid, nicotinic acid, carboxylic acids, lactic acid, p-amino benzoic acid and erotic acid. Preferred acyl substituents are compounds which are normally present in the body, either as a food component or as intermediate metabolites. The term "pharmaceutically acceptable salts" as used herein denotes the addition salts of these derivatives and pharmaceutically acceptable acids or bases, which include, but are not limited to, salts of sulfuric, hydrochloric or phosphoric acids, or, in the case of rotate salts with sodium hydroxide or calcium, and cationic salts with amino acids such as lysine. The term "amino acid" as used herein includes, but is not limited to glycine, L-forms of alanine, valise, leonine, isoleucine, phenylalanine, tyrosine, proline, hydroxyproline, serine, threonine, cysteine, cysteine, methionine,..


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