Abstract:
A novel process for the preparation of 6-perdeoxy-6-per-halo Gamma cyclodextrin which is a useful intermediate in the synthesis of Sugammadex is disclosed in the invention. The process involves reacting Gamma cyclodextrin with phosphorous halide in the presence of organic solvent.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an industrially viable, cost effective process for manufacturing 6-perdeoxy-6-per-halo Gamma Cyclodextrin, a key intermediate in the synthesis of Sugammadex. 
     CROSS REFERENCE TO RELATED APPLICATION 
     This application is the complete specification and claims priority from the provisional specification No. 2459/CHE/2010 filed on 25 Aug. 2010 
     BACKGROUND OF THE INVENTION 
     Sugammadex is a modified γ-cyclodextrin, with a lipophilic core and a hydrophilic periphery. 
     
       
                 
         
             
             
         
      
     
     Sugammadex (designation Org 25969, trade name Bridion) is an agent for reversal of neuromuscular blockade by the agent rocuronium in general anaesthesia. It is the first selective relaxant binding agent (SRBA). This gamma cyclodextrin has been modified from its natural state by placing eight carboxyl thio ether groups at the sixth carbon positions. These extensions extend the cavity size allowing greater encapsulation of the rocuronium molecule. These negatively charged extensions electrostatically bind to the positively charged ammonium group as well as contribute to the aqueous nature of the cyclodextrin. Sugammadex&#39;s binding encapsulation of rocuronium is one of the strongest among cyclodextrins and their guest molecules. The rocuronium molecule (a modified steroid) bound within Sugammadex&#39;s lipophilic core, is rendered unavailable to bind to the acetylcholine receptor at the neuromuscular junction. Sugammadex sodium contains 8 recurring glucose units each with 5 asymmetric carbon atoms, in total 40 asymmetric carbon atoms for the whole molecule. 
     The Sugammadex was disclosed in U.S. Pat. No. 6,670,340 by Akzo Nobel. The process for preparing Sugammadex is there outlined as follows: (Scheme-I) 
     
       
                 
         
             
             
         
      
       
                 
         
             
             
         
       
     
     In above process step-1 involves the preparation of Vilsmeier Hack reagent by the reaction of DMF, triphenylphosphine and Iodine. Drawback associated with this step is formation of triphenylphosphine oxide as a byproduct. Removal of triphenylphosphine oxide is very difficult from the reaction; it requires repeated washing with DMF under argon atmosphere and leads to inconsistency in yield of final product. Due to this, process is lengthy and not feasible on commercial scale. 
     The present invention provides improved conditions for carrying out step-1 in the above scheme, whereby the product of step-1 is obtained in better purity and yield than has previously been possible. 
     SUMMARY OF THE INVENTION 
     The invention is a novel process for the preparation of 6-perdeoxy-6-per-halo Gamma cyclodextrin which is a useful intermediate in the synthesis of Sugammadex, the process comprising of reacting Gamma cyclodextrin with phosphorous halide in presence of organic solvent. The 6-perdeoxy-6-per-halo Gamma cyclodextrin synthesized by the novel process is used in the preparation of Sugammadex. 
     The object of the present invention is to provide a novel process for the synthesis of 6-perdeoxy-6-per-halo Gamma Cyclodextrin, a useful intermediate in the synthesis of Sugammadex. 
     Another object of the present invention is to provide a process for producing 6-per-deoxy-6-per-(2-carboxyethyl)thio-γ-cyclodextrin sodium salt (Sugammadex) by employing the 6-perdeoxy-6-per-halo Gamma Cyclodextrin synthesized by the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     In accordance with the present invention 6-perdeoxy-6-per-halo Gamma Cyclodextrin is obtained by the reaction of Gamma Cyclodextrin with phosphorous halide in an organic solvent. The process of the invention is depicted in following scheme-II 
     
       
                 
         
             
             
         
      
       
                 
         
             
             
         
       
     
     The Gamma Cyclodextrin which is the starting material for the present process is commercially available or can be synthesized by the teachings of the prior art. 
     Phosphorous halide is PX 5  or PX 3  where X is an F, Cl, Br and Iodine, preferable chlorine. 
     The organic solvent can be polar organic solvent consisting of C1-5 esters, acetonitrile, dimethylformamide, dimethylsulfoxide, preferably dimethylformamide and the reaction is effectively carried out in between 60-100° C., preferably at 65-70° C. 
     In one embodiment, the present invention 6-perdeoxy-6-per-chloro Gamma Cyclodextrin (Formula-II-a) is obtained by the reaction of Gamma Cyclodextrin (Formula-I) with phosphorous pentachloride and dimethylformamide (DMF). The process of the invention is depicted in following scheme-III 
     
       
                 
         
             
             
         
      
     
     In the present invention Vilsmerier-Hack reagent is generated by reaction of DMF and PCl 5 . 
     
       
                 
         
             
             
         
      
     
     This reagent will react to gamma cyclodextrin to get halogenated product which is 6-perdeoxy-6-per-chloro Gamma Cyclodextrin. The reagent selectively reacts with per facial primary hydroxyl groups in presence of secondary hydroxyls. 
     In another embodiment, the preparation of 6-per-deoxy-6-per-(2-carboxyethyl)thio-γ-cyclodextrin sodium salt (Sugammadex) comprising: 
     a) Reacting gamma-cyclodextrin (Formula-I) with phosphorous pentachloride and dimethylformamide to obtain 6-perdeoxy-6-per-chloro Gamma cyclodextrin (Formula-IIa). 
     b) 6-perdeoxy-6-per-chloro Gamma cyclodextrin (Formula-IIa) is reacted with 3-mercapto propionic acid in presence of alkali metal hydrides and an organic solvent to give 6-per-deoxy-6-per-(2-carboxyethyl)thio-γ-cyclodextrin sodium salt. The process of the invention is depicted in following scheme-IV 
     
       
                 
         
             
             
         
      
       
                 
         
             
             
         
       
     
     The alkali metal hydrides are selected from the group consisting of sodium hydride, lithium hydride, potassium hydride preferably sodium hydride. 
     The advantage of the present process is there that there is no formation of by product such as triphenylphosphine oxide, as present in prior art process. So, purification is not required which leads to better purity and yields for the intermediate as well as for final product. 
     Another advantage of the present invention is the significant difference between molecular weight of 6-per deoxy-6-per-chloro-γ-cyclodextrin (Mol. wt. 1444) and the final product (Mol. wt. 2178). The use of 6-per deoxy-6-per-chloro-γ-cyclodextrin instead of 6-per deoxy-6-per-bromo-γ-cyclodextrin (Mol. wt. 1800) in the final stage of the process would extend the scope of selection of appropriate dialysis membranes with precise molecular weight cut off and there by facilitate efficient purification of Sugammadex. 
     The invention is further illustrated with following non-limiting examples: 
     Example: 1 
     Preparation of 6-perdeoxy-6-per-bromo Gamma Cyclodextrin 
     A portion of phosphorous pentachloride (256.5 g) was added in DMF (300 ml) at 0-5° C. Mixture was stirred at 20-25° C. for 1 hr. A solution of gamma-cyclodextrin (50 g) in DMF (400 ml) was added to above solution at 5-10° C. under nitrogen. Mixture was stirred at 65-70° C. 14 hrs. The reaction mixture was cooled to 20-25° C. and DMF was removed under vacuum. The viscous residue was diluted with water. 5M NaOH solution was added dropwise to the above solution at 5-10° C. until P H =8, the resulting slurry was stirred for one hour at 20-25° C. The slurry was filtered under vacuum and washed with water and dried. The crude product was diluted with water and resulting slurry was stirred at 20-25° C. for one hour. The slurry was filtered under vacuum and the solid dried at 55-60° C. under vacuum for 12 hrs. (Yield—94-98%, purity-98.5% by HPLC) 
     Example: 2 
     Preparation of Sugammadax 
     To a mixture of sodium hydride (24.4 g) in DMF (150 ml) at 0-5° C., a solution of 3-mercapto propionic acid (23.7 ml, 10 eq) in DMF (50 ml) was added slowly under argon maintaining the temperature below 10° C. The resulting mixture was stirred at 20-25° C. for 30 mins. Then 6-deoxy-6-chloro gamma cyclodextrin (40 g) in DMF (400 ml) was added slowly at 5-10° C. under argon and the resulting mixture was heated to 70-75° C. for 12 hrs. Reaction mixture was cooled to 20-25° C. and DMF removed partially under vacuum and the reaction mixture is diluted with ethanol (600 ml). The resulting precipitate was stirred at 20-25° C. for 1 hr and filtered under vacuum and the solid dried to afford the crude Sugammadex (wet) (100 g). The crude product was purified over silica gel and sephadex G-25 column using water as eluent. (Yield 60%)