Abstract:
The present invention relates to alkyl derivatives of nitazoxanide and tizoxanide and isomers thereof. More specifically, the present invention is directed to compounds possessing anti-parasitic, antibacterial, antiviral and antifungal activities, and to methods of treatment and/or prevention of parasitic, bacterial, viral and/or fungal diseases in humans and animals using said compounds and pharmaceutical compositions thereof.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a non-provisional of provisional application No. 60/617,412 filed Oct. 8, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to alkyl derivatives of nitazoxanide and tizoxanide and isomers thereof. More specifically, the present invention is directed to compounds possessing anti-parasitic, antibacterial, antiviral and antifungal activities, and to methods of treatment and/or prevention of parasitic, bacterial, viral and/or fungal diseases in humans and animals using said compounds and pharmaceutical compositions thereof.  
         [0004]     2. Discussion of the Related Art  
         [0005]     It is known that tizoxanide (2-hydroxy-N-(5-nitro-2-thiazolyl) benzamide, Compound A, U.S. Pat. No. 5,578,621) and nitazoxanide (2-acetyloxy-N-(5-nitro-2-thiazolyl)benzamide, Compound B, U.S. Pat. No. 3,950,351) possess potent activity against parasites, bacteria, viruses and fungi, as described, for example, in U.S. Pat. Nos. 4,315,018; 5,578,621; and 5,856,348.  
         [0006]     Tizoxanide (Compound A) and nitazoxanide (Compound B) are compounds according to formula (I) in which:  
                         
 
 Compound A (tizoxanide): wherein R 1 =—OH and R 2 -R 5 =—H; and 
 
 Compound B (nitazoxanide): wherein R 1 =—OCOCH 3  and R 2 -R 5 =—H. 
 
         [0007]     There is a need in the art for benzamide compounds that possess improved potency and/or improved target specificity compared to the compounds of the prior art. For example, for the treatment of parasitic or viral diseases, benzamide derivatives lacking antibacterial activity would be beneficial in order to avoid disruption of the gut flora when administered orally.  
         [0008]     There is therefore a need in the art for benzamide compounds that possess superior activity against parasitic, bacterial, viral and fungal diseases suitable for treatment of humans and animals, and which do not suffer from the above-mentioned drawbacks of the compounds of the prior art. All this and more will be apparent to one of ordinary skill upon reading the following description, non-limiting examples, and claims.  
       SUMMARY OF THE INVENTION  
       [0009]     The present inventors have surprisingly discovered that certain alkyl derivatives of tizoxanide and nitazoxanide, and isomers of such derivatives, possess improved anti-parasitic, antibacterial, antiviral and antifungal activities.  
         [0010]     Thus, in a first embodiment, the present invention is directed to compounds according to formula (I):  
                         
 
 in which the R 1  substituent is —OH or —OCOCH 3 , one of the R 2 -R 5  substituents is alkyl and the remaining positions are —H, and salts, solvates or hydrates thereof. 
 
         [0011]     In a second embodiment, the invention is directed to a method of treating or preventing a parasitic, bacterial, viral or fungal disease in a human or animal subject by administering an effective amount of the compound of formula (I) according to the first embodiment.  
         [0012]     In a third embodiment, the invention is directed to pharmaceutical compositions comprising at least one compound according to formula (I) and a pharmaceutically acceptable carrier.  
         [0013]     While the compounds of the first embodiment possess R 1  substituents that are —OH or —OCOCH 3 , (as in Compound A (tizoxanide) and Compound B (nitazoxanide), respectively), the present invention is not so limited.  
         [0014]     Thus, in a fourth embodiment, the invention is directed to compounds according to formula (I) comprising an —OH or —OCOCH 3  substituent at any one position among R 1 -R 5 , and in which one of the remaining R 1 -R 5  substituents is alkyl and the remainder are —H, including salts, solvates and hydrates thereof.  
         [0015]     In a fifth embodiment, the invention is directed to a method of treating or preventing a parasitic, bacterial, viral or fungal disease in a human or animal subject by administering to the subject an effective amount of the compound of according to the fourth embodiment.  
         [0016]     In a sixth embodiment, the invention is directed to pharmaceutical compositions comprising a compound according to the fourth embodiment and a pharmaceutically acceptable carrier. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     The present invention is directed to compounds according to formula (I), their methods of use, and pharmaceutical compositions thereof:  
                         
 
 in which: one of R 1 -R 5  is —OH or —OCOCH 3 , and is preferably —OH; one of R 1 -R 5  is alkyl, preferably C 1 -C 4  alkyl, most preferably —CH 3 ; and 
 
 substituents R 1 -R 5  that are not alkyl, —OH or —OCOCH 3  are —H. 
 
         [0018]     The compounds of the present invention include organic and inorganic salts, solvates and hydrates of the compounds according to formula (I).  
         [0019]     The term “alkyl” includes both branched alkyl and linear alkyl.  
         [0020]     The compounds of the present invention possess improved activity against certain parasitic, bacterial, viral and fungal diseases, including but not limited to pathogens against which tizoxanide and/or zitaxoanide exhibit activity, as described, for example, in U.S. Pat. Nos. 4,315,018; 5,578,621; and 5,856,348.  
         [0021]     Suitable formulations and dosages will be readily understood by one of ordinary skill from the formulations and dosages of prior art benzamide compounds as set forth in U.S. Pat. No. 6,117,894 (acid-stabilized compounds) and U.S. Pat. No. 5,968,961 (particle size).  
         [0022]     Certain U.S. patents have been referred to herein, which are hereby incorporated for their cited teachings, and in their respective entireties, by reference.  
         [0023]     The invention is now illustrated by the following, non-limiting, examples:  
       EXAMPLE 1  
     Compound D (2-acetyloxy-3-methyl-N-(5-nitro-2-thiazolyl) benzamide)  
       [0024]     Compound D is a compound according to formula (I) in which R 1 =—OCOCH 3 , R 2 =—CH 3  and R 3 , R 4  and R 5 =—H.  
         [0025]     Compound D is synthesized from 3-methyl salicylic acid and 2-amino-5-nitro thiazole as shown in the following scheme:  
                         
 
 in which: Ac 2 O is acetic anhydride, SOCl 2  is thionyl chloride, Et 3 N is triethylamine, and THF is tetrahydrofuran. Other synthesis methods, reagents and adaptations will readily occur to those of skill in the art, and the compounds of the present invention are not limited by their method of synthesis, which is provided for illustrative purposes only. Throughout this disclosure —OAc and —OCOCH 3  are equivalent. 
 
         [0026]     Compound D is effective against at least  H. Pylori, C. jejuni , Influenza A and B, Herpes VZV,  G. intestinalis, P. falciparum  and  T. vaginalis.    
       EXAMPLE 2  
     Compound C (2-hydroxy-3-methyl-N-(5-nitro-2-thiazolyl) benzamide)  
       [0027]     Compound C is a compound according to formula (I) in which R 1 =—OH, R 2 =—CH 3  and R 3 , R 4 , R 5 =—H.  
         [0028]     Compound C can be synthesized by de-acetylating Compound D, for example in the presence of a strong acid such as concentrated hydrochloric acid.  
         [0029]     Compound C possesses comparable or improved activity compared to nitazoxanide against  Helicobacter pylori  (IC 50 =2 μg/mL),  Campylobacter jejuni  (IC 50 =4 μg/mL), Influenza A (IC 50 =0.18 μg/mL), Influenza B (IC 50 =0.18 μg/mL), and Herpes Varicella A (IC 50 =0.9 μg/mL).  
       EXAMPLE 3  
     Compound H (2-acetyloxy-5-methyl-N-(5-nitro-2-thiazolyl) benzamide)  
       [0030]     Compound H is a compound according to formula (I) in which R 1 =—OCOCH 3 , R 4 =—CH 3  and R 2 , R 3 , R 5 =—H.  
         [0031]     Compound H can be synthesized from 5-methyl salicylic acid and 2-amino-5-nitro thiazole as shown in the following scheme:  
                         
 
         [0032]     Compound H is effective against at least  G. intestinalis  and  T. vaginalis.    
       EXAMPLE 4  
     Compound G (2-hydroxy-5-methyl-N-(5-nitro-2-thiazolyl) benzamide)  
       [0033]     Compound G is a compound according to formula (I) in which R 1 =—OH, R 4 =—CH 3  and R 2 , R 3 , R 5 =—H.  
         [0034]     Compound G can be synthesized by de-acetylating Compound H for example in the presence of a strong acid such as concentrated hydrochloric acid.  
         [0035]     Compound G is effective against at least  G. intestinalis  and  T. vaginalis.    
       EXAMPLE 5  
     Compound F (2-acetyloxy-4-methyl-N-(5-nitro-2-thiazolyl) benzamide)  
       [0036]     Compound F is a compound according to formula (I) in which R 1 =—OCOCH 3 , R 3 =—CH 3  and R 2 , R 4 , R 5 =—H.  
         [0037]     Compound F can be synthesized from 4-methyl salicylic acid and 2-amino-5-nitro thiazole as shown in the following scheme:  
                         
 
         [0038]     Compound F is effective against at least  G. intestinalis  and  T. vaginalis.    
       EXAMPLE 6  
     Compound E (2-hydroxy-4-methyl-N-(5-nitro-2-thiazolyl) benzamide)  
       [0039]     Compound E is a compound according to formula (I) in which R 1 =—OH, R 3 =—CH 3  and R 2 , R 4 , R 5 =—H.  
         [0040]     Compound E can be synthesized by de-acetylating Compound F for example in the presence of a strong acid such as concentrated hydrochloric acid.  
         [0041]     Compound E is effective against at least  G. intestinalis  and  T. vaginalis.    
       EXAMPLE 7  
     Comparative Testing  
       [0042]     Compounds C, D, E and G were tested in vitro against the protozoa,  Giardia intestinalis  and  Trichomonas vaginalis  with the results shown in TABLE I.  
                                           TABLE I                           IC 50  (μM)*                  Giardia intestinalis       Trichomonas         Compound   JKH-1     vaginalis  UCH-1                    C   0.31   6.148       D   0.56   8.04       E   0.195   0.287       G   0.20   0.751       Tizoxanide (Compound A)   Not done   1.521       Nitazoxanide   12.46   0.605       (Compound B)                 *Micromolar concentrations of drugs required to inhibit 50% of the growth of the organisms.             
 
         [0043]     Compounds C, D, E and G are significantly more potent than nitazoxanide against  Giardia  intestinalis.  
         [0044]     Compounds E and G exhibit improved activity, compared to tizoxanide, against Trichomonas vaginalis, with Compound E (methyl group at R 4 ) being the most effective. The methyl group at R 2 , R 3  or R 4  therefore improves the activity of nitazoxanide and tizoxanide. A comparison of the results for Compounds C and D shows that these compounds are most potent when R 1 =OH instead of —OCOCH 3 .