Study On The Synthesis Of Cilastatin

Cilastatin is an important inhibitor of dehydropeptidase-I, which can enhance the antibacterial activity of Imipenem and has widely clinic applications. In our country, there has not been the industrial procedure for Cilastatin, and it is necessary to research the synthesis route with high efficiency and low pollution. This thesis is mainly about the total synthesis of Cilastatin. On the base of design and study for the synthesis of S-(+)-2,2-dimethylcycloproprane carboxamide and 7-chloro-2-oxoheptanoic acid, which are the key intermediates of Cilastatin, the total synthesis procedure of Cilastatin was optimized.Using 2-methylbutenoic acid as starting material, 2,2-dimethylcyclopropane carboxylic acid was synthesized via esterification, cyclopropanantion and hydrolysis, with 48% yield. This route had advantages such as avoiding cyanide, short reaction time and lower cost. Especially, using ultrasonic-acetyl chloride catalyst system, cyclopropanation of alkenes with withdrawing-electron group and low active dibromomethane could proceed smoothly. This catalyst system was applied in the cyclopropanation of other alkenes, and the results indicated that the catalyst system excelled mono-catalyst.The chiral resolution of 2,2-dimethylcyclopropane carboxylic acid and the synthesis of S-(+)-2,2-dimethylcycloproprane carboxamide were improved. Firstly,2,2-dimethylcyclopropane carboxylic acid was resolved by L-carnitine hydrochloride with21.4% yield, [α]_D²⁰ + 139.5° (c=0.85, CHCl₃). The product S- (+)-2,2-dimethylcyclopropranecarboxylic acid was converted to S-(+)-2,2-dimethylcycloproprane carboxamide with 76% yield. Then, L-carnitine oxalate was used in the improved chiral resolution of 2,2-dimethylcyclopropane carboxylic acid. In the improved procedure, S-(+)-2,2-dimethylcycloproprane carboxamide was obtained with 19.5% yield via four steps: converted to acid chloride, formed oxalate, fractional crystallization and hydrolysis. Themelting point of product was 135.5¹37.5℃, [α]_D²⁰ +95.5° (c=1.0, CHCl₃). Comparing two chiral resolutions, the steps of ion exchange and oxalate formation was omitted by using L-carnitine oxalate as the resolution reagent. At last, R-(-)-2,2-dimethylcyclopropranecarboxylic acid was converted to acid chloride and racemized with the yield was 86%, which is important for the utilization of enantiomer.The solubilities of S-(+)-2,2-dimethylcycloproprane carboxamide in toluene, dichloromethane, trichloromethane, ethyl acetate, ethanol and water were measured experimentally using a synthetic method with a laser monitoring observation technique. The solubility data were correlated with a semi-empirical correlation, and the calculated values were in good agreement with those of the experimental. The re-crystallization process of S-(+)-2,2-dimethylcycloproprane carboxamide was optimized according to the solubility data. The result indicated that the carboxamide produced through different process needed different crystallization solvents. To the carboxamide obtained from the ammonolysis of chiral oxalate, 70% ethanol-water solution was good re-crystallization solvent, and could get 80% yield. But ethyl acetate obtained good result to the carboxamide produced from S-(+)-2,2-dimethylcycloproprane carboxylic acid via ammonolysis, 78% yield.The synthesis of 7-chloro-2-oxoheptanonic acid was improved. Using dichloroacetic acid, 1,3-propanedithiol and l-bromo-5-chloro-pentane as starting materials, 7-chloro-2-oxoheptanoic acid was produced via five steps with 31% yield: esterification, cyclization, alkylation* oxidation and transesterification. In the alkylation, l-bromo-5-chloro-pentane was used instead of 1,5-dibromopentane, which increased the conversion rate of l,3-dithiane-2-carboxylate and deceased the byproduct of di-alkylation. Then, the oxidation mechanism of 2-(5-chloropentane)-l,3-dithiane-2-carboxylate by NBS was induced. The HOBr produced by NBS and H2O is considered the main oxidant, and the bromine produced by NBS and HBr is subsidiary oxidant.In addition, the new synthesis techniques of 7-chloro-2-oxoheptanoic acid using Grignard method was studied. The ethyl 7-chloro-2-oxoheptanoate was synthesized from the addition of mono-Grignard reagent of l-bromo-5-chloro-pentane to diethyl oxalate, then, the transesterification was carried out between the ester and formic acid to give 7-chloro-2-oxoheptanoic acid. The total yield was 43%. After that, the techniques conditions were optimized. Using the addition of NaHSO3 to ketones, the enol form of a -keto esters could be transformed to the keto form.Finally, Cilastatin was synthesized via two steps. First step was the reaction of S-(+)-2,2-dimethylcycloproprane carboxamide and 7-chloro-2-oxoheptanoic acid, which gave (+)-(Z)-7-chloro-2-(2,2-dimethylcyclopropanecarboxamido)-2-heptenoic acid. In this reaction, dimethylbenzene was used as solvent to increase the ratio of Z- product and E-product. Consequently, the yield was improved to 35% (literature value 28%). Second step produced the aim product Cilastatin from the reaction of heptenoic acid and L-cysteine hydrochloride anhydrous, which needed following process: preparation of the sodium L-cysteine, thiolation, ion exchange and column chromatography. The yield was 61%,[aj° +17.9° (c=0.51, CH3OH). The product was characterized by *H NMR and 13C NMR.Especially, L-cysteine hydrochloride anhydrous was used instead of L-cystine used in the literature, so the reaction could carry out under mild condition.