Abstract: In order to prepare new potential therapeutic agents,chelation between antimony and various complexones was studied.It was reported by Schwarzenbach et al that the calcium chelate of cyclohexane-1,2-diaminetetraacetic acid (Ⅱ) was more stable than the corresponding chelate of ethylenediaminetetraacetic acid (Ia).Since the introduction of substituents on the carbon chain of Ia might render the chelates more stable and thus reduce the toxicity of the metallic compounds,it would be advisable to prepare antimonial chelates from Ⅱ as well as from propylenediaminetetraacetic acid (Ⅲ). The antimonial chelate was readily formed on the treatment of the trisodium salt of Ⅲ with antimony trichloride,or on the treatment of Ⅲ with antimonial catechol or freshly precipitated antimonous acid,and the last method was the most convenient one.Ethylene- diaminetetraacetic or propylenediaminetetraacetic acid and potassium antimonyltartrate were dissolved together in water,and hydrochloric acid was then introduced to decompose the latter compound.The newly formed antimonous acid was taken up by ethylenediaminete- traacetic acid or propylenediaminetetraacetic acid present in the solution,and the chelate was readily formed.Several water-soluble salts were prepared on neutralization of the chelate with various alkalis.The corresponding chelating compound of cyclohexane-1,2- diaminetetraacetic acid was similarly prepared. Both N-(β-hydroxyethyl)-ethylenediaminetriacetic acid and N-benzylethylenediamine- triacetic acid gave the corresponding antimonial chelates on treatment with antimonous acid, but such chelates are less stable than those prepared from Ⅱ or Ⅲ.Attempts to prepare some water-soluble salts were not successful,because the chelates were decomposed on addi- tion of one mole of alkali.Lengthening of the carbon chain between the two nitrogen atoms of ethylenediaminetetraacetic acid weakens its chelating power,and antimonial com- plexes could not be obtained under similar conditions from tetramethylenediaminetetraacetic acid (Ib),3-thiapentane-1,5-diaminetetraacetic acid (Ⅵ) and p-phenylenediaminetetra- acetic acid (Ⅶ). Either ammoniatriacetic acid (Ⅷ) or β-hydroxyethylaminediacetic acid (Ⅹ),on treatment with antimonous acid or butyl antimonite,gave the corresponding antimonial chelates.In such complex salts an antimonial atom combined with two moles of chelating agents.These chelates are less stable than those from Ⅱ or Ⅲ.β-Carboxyethylamine- diacetic acid (Ⅸ),a higher homologue of Ⅷ,however,failed to chelate with antimony under similar conditions.Antimonial chelates could not be afforded by a series of alkyl o aralkyl aminediacetic acid (XIa—h) as well. Many of the complexones employed in the present work are known compounds.The preparation of propylenediaminetetraacetic acid was only briefly noted in a patent.We tried to synthesize it by the carboxymethylation of propylenediamine according to Smith’s general procedure,but Ⅲ was obtained only in a yield of 27%.A modified method for carboxymethylation was then applied and sodium cyanide and formalin were in- troduced in several small portions into an aqueous solution of propylenediamine and sodium hydroxide.Propylenediaminetetraacetic acid was afforded in 58.5% on acidification of the reaction mixture.N-(β-hydroxyethyl)-ethylenediaminetriacetic acid,the preparation of which has not been recorded in literature,was similarly prepared.Since the antimonial chelate is only sparingly soluble in water,the complexon was more easily isolated from the reaction mixture in the form of the antimonial compound. Preliminary pharmacological tests revealed that the antimonial chelates of Ⅲ,Ⅷ and Ⅹ were as active as tartar emetic against Schistosomiasis japonica in white mice.