Abstract:
The present invention relates to novel 2-fluoro-pyrrolo[2,1-c][1,4]benzodiazepine dimers useful as antitumour agents and to a process for the preparation thereof.

Description:
FIELD OF THE INVENTION 
     The present invention relates to novel 2-fluoro-pyrrolo[2,1-c][1,4]benzodiazepine dimers useful as potential antitumour agents. The present invention also relates to a process for the preparation of novel 2-fluoro-pyrrolo[2,1-c][1,4]benzodiazepine dimes useful as potential antitumour agents. The present invention particularly relates to a process for the preparation of new bis-2-fluoro-pyrrolo[2,1-c][1,4]benzodiazepines useful as anticancer agents. More particularly, it provides a process for the preparation of 1,1′-{[(bisalkane-1,N-diyl)]dioxy}bis[(11aS)-2-fluoro-7-metoxy-1,2,3,11a-terahydro-5H-pyrrolo [2,1-c][1,4]benzodiazepin-5-one, with aliphatic chain length variations for the compounds and also describes the anticancer (antitumour) activity. The structural formula of novel bis-2-fluoro-pyrrolo[2,1-c][1,4]benzodiazepine is as follows, wherein n=3, 4, 5, 6, 7, 8, 9, 10. 
     
       
                 
         
             
             
         
      
     
     BACKGROUND OF THE INVENTION 
     Pyrrolo[2,1-c][1,4]benzodiazepine antitumour antibiotics are commonly known as anthramycin class of compounds. In the last few years, a growing interest has been shown in the development of new pyrrolo[2,1-c][1,4]benzodiazepines (PBDs). These PBDs are a family of sequence selective DNA-binding antitumour antibiotics that bind exclusively to the exocyclic N2-guanine in the minor groove of DNA via an acid-labile aminal bond to the electophilic imine at the N10-C11 position. (Kunimoto, S.; Masuda, T.; Kanbayashi, N.; Hamada, M.; Naganawa, H.; Miyamoto, M.; Takeuchi, T.; Unezawa, H.  J. Antibiot.,  1980, 33, 665.; Kohn, K. W.; Speous, C. L.  J. Mol. Biol.,  1970, 51, 551.; Hurley, L. H. Gairpla, C.; Zmijewski, M.  Biochem. Biophys. Acta.,  1977, 475, 521.; Kaplan, D. J.; Hurley, L. H.  Biochemistry,  1981, 20, 7572.) All biologically active PBDs possess the (S) configuration at the chiral C11a position which provides the molecule with a right-handed twist, which allows them to follow the curvature of the minor groove of B-form double-stranded DNA spanning three base pairs. Recently, PBD dimers have been developed that comprise two C2-exo-methylene-substituted DC-81 subunits tethered through their C-8 position via an inert propanedioxy linker. (Gregson, S. J.; Howard, P. W.; Hartely, J. A.; Brooks N. A.; Adams, L. J.; Jenkins, Kelland, L. R.; Thurston, D. E.  J. Med. Chem.,  2001, 44, 737.). A recent development has been the linking of two PBD units through their C-8 positions to give bisfunctional alkylating agents capable of cross-linking DNA (Thurston, D. E.; Bose, D. S.; Thomson, A. S.; Howard, P. W.; Leoni, A.; Croker, S. J.; Jenkins, T. C.; Neidle, S.; Hurley, L. H.  J. Org. Chem.,  1996, 61, 8141–8147). Recently, noncross-linking mixed imine-amide PBD dimers have been synthesized that have significant DNA binding ability and potent anti-tumour activitiy (Kamal A.; Laxman, N.; Ramesh, G.; Ramulu, P.; Srinivas, U.S. Pat. No. 636,233; Kamal, A.; Ramesh, G.; Laxman, N.; Ramulu, P.; Srinivas, O.; Neelima, K.; Kondapi, A. K.; Srinu, V. B.; Nagarajaram, H. M.  J. Med. Chem.  2002, 45, 4679.). 
     PBDs are of considerable current interest due to their ability to recognize and subsequently form covalent bonds to specific base sequences of double-stranded DNA. Naturally occurring pyrrolo[2,1-c][1,4]benzodiazepines belong to a group of antitumour antibiotics derived from  Streptomyces  species with family members including anthramycin, tomaymycin, sibiromycin, chicamycin, neothramycins A and B, and DC-81. 
     
       
                 
         
             
             
         
      
     
     However, the clinical efficacy for these antibiotics is hindered by several limitations, such as poor water solubility and cardiotoxicity and development of drug resistance and metabolic inactivation. 
     OBJECT OF THE INVENTION 
     The main object of the invention is to provide new bis-2-fluoro pyrrolo[2,1-c][1,4]benzodiazepines useful as antitumour agents. 
     Another object of the invention is to provide a process for the preparation of novel fluoro pyrrolo[2,1-c][1,4]benzodiazepines useful as antitumour agents. 
     SUMMARY OF THE INVENTION 
     According the present invention provides fluoro pyrrolo[2,1-c][1,4]benzodiazepine dimers of formula IX where n is 3 to 10. 
     
       
                 
         
             
             
         
      
     
     In one embodiment of the invention, the compound of formula IX is 1,1′-{[(propane-1,3-diyl)dioxy]bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetra-hydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one]}. 
     In another embodiment of the invention, the compound of formula IX is 1,1′-{[(butane-1,4-diyl)dioxy]bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetra-hydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one]}. 
     In another embodiment of the invention, the compound of formula IX is 1,1′-{[(pentane-1,5-diyl)dioxy]bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetra-hydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one]}. 
     The present invention also provides a process for the preparation of bis 2-fluoro pyrrolo[2,1-c][1,4]benzodiazepines of formula IX. 
                                
where n is 3 to 10, which comprises:
     (a) reacting methyl (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-hydroxypyrrolidine-2-carboxylate dissolved in an organic solvent;   (b) cooling the solution and adding a solution of diethylaminosulfurtrifluoride (DAST) in an organic solvent drop wise;   (c) isolating the methyl (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2carboxylate with DIBAL-H formed in the presence of an organic solvent and cooling;   (d) isolating methyl (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde formed;   (e) protecting methyl (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde with EtSH in presence of an organic solvent;   (f) isolating (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde diethylthioacetal;   (g) reacting the (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde diethylthioacetal with a debenzylating agent to obtain (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde-diethylthioacetal of formula VI,   
     
       
                 
         
             
             
         
      
         
         (h) reacting (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoro-2-carboxaldehyde diethylthioacetal of formula VI with a dibromoalkane in an aprotic water miscible organic solvent and in the presence of a mild inorganic base up to refluxing temperature and isolating 1,1′-{[(alkane-1,N-diyl)dioxy}bis[(2-nitro-5-methoxy-1,4-phenylene)carbonyl]bis[4-fluoropyrrolidin-2-carboxaldehyde diethylthioacetal] of formula VII where n is 3–10 
       
    
     
       
                 
         
             
             
         
      
         
         (i) reducing the compound of formula VII with SnCl 2 .2H 2 O in presence of organic solvent up to a reflux temperature and isolating 1,1′-{[(alkane-1,N-diyl)dioxy}bis[(2-amino-5-methoxy-1,4-phenylene)carbonyl]]bis[4-fluoro-pyrrolidin-2-carboxaldehyde diethylthioacetal]] of formula VIII where n is 3–10 
       
    
     
       
                 
         
             
             
         
      
         
         (j) reacting the compound of formula VIII with a deprotecting agent to obtain bis 2-fluoro pyrrolo[2,1-c][1,4]benzodiazepines of formula IX wherein n is as stated above. 
       
    
     In one embodiment of the invention, the organic solvent used in steps (a), (b) and (c) comprises CH 2 Cl 2 . 
     In another embodiment of the invention, in step (a) the solution is cooled to a temperate of −78° C. 
     In another embodiment of the invention, the drop wise addition in step (b) is carried out for a period of 40 min. 
     In another embodiment of the invention, step (c) is carried out after 15 hours of step (b). 
     In yet another embodiment of the invention, the cooling in step (c) is done to a temperature of −78° C. and for a period of 45 minutes. 
     In another embodiment of the invention, step (e) is carried out in presence of an organic solvent and at room temperature. 
     In yet another embodiment of the invention, the (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoro-2-carboxaldehyde diethylthioacetal of formula VI is reacted with a dibromoalkane in an aprotic water miscible organic solvent selected from the group consisting of acetone, acetonitrile and DMF and in the presence of a mild inorganic base selected from the group consisting of K 2 CO 3 , CsCO 3  and BaCO 3 . 
     In another embodiment of the invention, step (h) is carried out for a period of about 48 hours. 
     In another embodiment of the invention, the reduction in step (i) is carried out in the presence of an organic solvent comprising methanol. 
     In yet another embodiment of the invention, the deprotecting agent comprises a combination of HgCl 2  and HgO in CH 3 CN/H 2 O. 
     The present invention also provides a process for the preparation of bis 2-fluoro pyrrolo[2,1-c][1,4]benzodiazepines of formula IX 
                                
where n is 3 to 10, which comprises:
     (a) (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde-diethylthioacetal of formula VI,   
     
       
                 
         
             
             
         
      
         
         (b) reacting (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoro-2-carboxaldehyde diethylthioacetal of formula VI with a dibromoalkane in an aprotic water miscible organic solvent and in the presence of a mild inorganic base up to refluxing temperature and isolating 1,1′-{[(alkane-1,N-diyl)dioxy}bis[(2-nitro-5-methoxy-1,4-phenylene) carbonyl]bis[4-fluoropyrrolidin-2-carboxaldehyde diethylthioacetal] of formula VII where n is 3–10 
       
    
     
       
                 
         
             
             
         
      
         
         (c) reducing the compound of formula VII with SnCl 2 .2H 2 O in presence of organic solvent up to a reflux temperature and isolating 1,1′-{[(alkane-1,N-diyl)dioxy}bis[(2-amino-5-methoxy-1,4-phenylene)carbonyl]]bis[4-fluoro-pyrrolidin-2-carboxaldehyde diethylthioacetal)]] of formula VIII where n is 3–10 
       
    
     
       
                 
         
             
             
         
      
         
         (d) reacting the compound of formula VIII with a deprotecting agent to obtain bis 2-fluoro pyrrolo[2,1-c][1,4]benzodiazepines of formula IX wherein n is as stated above. 
       
    
     In yet another embodiment of the invention, the (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoro-2-carboxaldehyde diethylthioacetal of formula VI is reacted with a dibromoalkane in an aprotic water miscible organic solvent selected from the group consisting of acetone, acetonitrile ad DMF and in the presence of a mild inorganic base selected from the group consisting of K 2 CO 3 , CsCO 3  and BaCO 3 . 
     In another embodiment of the invention, step (b) is carried out for a period of about 48 hours. 
     In another embodiment of the invention, the reduction in step (c) is carried out in the presence of an organic solvent comprising methanol. 
     In yet another embodiment of the invention, the deprotecting agent comprises a combination of HgCl 2  and HgO in CH 3 CN/H 2 O. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present process provides a process for the preparation of bis 2-fluoro pyrrolo[2,1-c][1,4benzodiazepines of formula IX as given above where n is 3 to 10 which comprises reacting (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoro-2-carboxaldehyde diethylthioacetal of formula VI with a dibromoalkane in an aprotic water miscible organic solvents. The solvent is preferably chosen from acetone, acetonitrile, and DMF. The reaction is also carried out in the presence of a mild inorganic bases such as K 2 CO 3 , CsCO 3  and BaCO 3  and up to refluxing temperature for a period of 48 hours. The 1,1′-{[(alkane-1,N-diyl)dioxy}bis[(2-nitro-5-methoxy-1,4-phenylene) carbonyl]bis[4-fluoropyrrolidin-2-carboxaldehyde diethylthioacetal] of formula VII formed where n is 3–10 is then isolated by conventional methods and reduced with SnCl 2 .2H 2 O in presence of organic solvent up to a reflux temperature. The 1,1′-{[(alkane-1,N-diyl)dioxy}bis[(2-amino-5-methoxy-1,4-phenylene)carbonyl]]bis[4-fluoro-pyrrolidin-2-carboxaldehyde diethylthioacetal]] of formula VIII formed where n is 3–10 is then isolated by known methods. The compound of formula VIII is then reacted with a known deprotecting agent in a conventional manner to obtain the novel bis 2-fluoro pyrrolo[2,1-c][1,4]benzodiazepines of formula IX wherein n are as stated above. 
     In the alternate, the process comprises first reacting methyl (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-hydroxypyrrolidine-2-carboxylate dissolved in an organic solvent such as CH 2 Cl 2  and cooling the solution to −78° C. To this cooled solution, a solution of diethylaminosulfurtrifluoride (DAST) in an organic solvent such as CH 2 Cl 2  is added drop wise over a period of 40 min. After 15 hours methyl (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxylate of formula II with DIBAL-H formula III is isolated and then cooled in the presence of organic solvent such as CH 2 Cl 2  −78° C. for a period of 45 min. The methyl (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde formed is isolated by conventional methods and protected with EtSH in the presence of organic solvent at room temperature. The (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde diethylthioacetal obtained is then isolated by known methods and reacted with any conventional debenzylating agent to give (2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]-4-fluoropyrrolidine-2-carboxaldehyde-diethylthioacetal of formula VI. The compound of formula VI is then converted to the compound of formula IX in the manner indicated above. 
     The precursor, methyl (2S)-N-(4-benzyloxy-5-methoxy-2-nitrobenzoyl)-4-hydroxypyrrolidine-2-carboxylate (intermediates of DC-81) was prepared by literature methods (Thurston, D. E.; Murthy, V. S.; Langley, D. R.; Jones, G. B.  Synthesis,  1990, 81.) 
     Some representative compounds of formula IX of present invention are given below:
     1) 1,1′-{[(propane-1,3-diyl)dioxy]bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetra-hydro-5H-pyrrolo[2,1-C][1,4]benzodiazepin-5-one]}   2) 1,1′-{[(butane-1,4-diyl)dioxy]bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetra-hydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one]}   3) 1,1′-{[(pentane-1,5-diyl)dioxy]bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetra-hydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one]}   

     The reaction scheme is given below: 
     
       
                 
         
             
             
         
      
     
     These new analogues of pyrrolo[2,1-c][1,4]benzodiazepine dimers substituted at C-2 position have shown promising anticancer activity in various cell lines. The molecules synthesized are of immense biological significance with potential sequence selective DNA-binding property. This resulted in design and synthesis of new congeners, which comprise:
     1. The fluoro substitution at C-2 position of DC-81 intermediates.   2. The ether linkage between two fluoro DC-81 monomers at C-8 position.   3. Refluxing the reaction mixture for 24–48 h.   4. Synthesis of fluoro PBD antitumour antibiotic dimer imines.   5. Purification by column chromatography using different solvents like ethylacetate, hexane, dichloromethane and methanol.   

     Representative compounds of Formula IX include 
     
       
                 
         
             
             
         
      
     
     The following examples are given by way of illustration and therefore should not be construed to the present limit of the scope of invention. 
     EXAMPLE 1  
     A solution of (2S)-N-(4-hydroxy-5-methoxy-2-nitrobenzoyl)-4-fluoro pyrrolidine 2-carboxaldehyde diethylthioacetal VI (418 mg, 1 mmol), 1,3-dibromopropane (101 mg, 0.5 mmol) and K 2 CO 3  (414 mg, 3 mmol) in dry acetone (40 ml) was refluxed for 48 h. After the completion of reaction as indicated by TLC, EtOAc-hexane (7:3), the reaction mixture was poured on to the water and then extracted with ethylacetate. Evaporation of the organic layer gave the crude product, which was further purified by column chromatography on silica gel eluting with EtOAc-hexane (1:1) to give the pure 1,1′-{[(Propane-1,3 diyl)dioxy]bis[2-nitro-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoro pyrrolidine-2-carboxaldehyde diethylthioacetal] VII. H 1  NMR (CDCl 3 , 200 MHz): δ 1.2–1.39 (m, 12H), 2.4–2.68 (m, 6H), 2.7–2.9 (m, 8H), 3.41–3.62 (m, 4H), 3.99 (s, 6H), 4.29–4.4 (m, 4H), 4.52 (d, j=3.9 Hz, 2H), 4.69–4.79 (m, 2H), 5.05 (t, 1H), 6.85 (s, 2H), 7.63 (s, 2H). FAB MASS: 877 (M+H) 
     1,1′-{[(propane-1,3diyl)dioxy]bis[2-nitro-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoro pyrrolidine-2-carboxaldehyde diethyl thioacetal] VII (876 mg, 1.0 mmol) was dissolved in methanol (10 mL) and to this was added SnCl 2 .2H 2 O (1.124 g, 5.0 mmol) and was refluxed for 1.5 h. The reaction mixture was then carefully adjusted to pH 8 with saturated NaHCO 3  solution and then extracted with ethyl acetate (3×20 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude 1,1′-{[(Propane-1,3 diyl)dioxy]bis[2-amino-5-methoxy-1,4-phenylene) carbonyl]}bis[4-fluoro pyrrolidine-2-carboxaldehyde diethyl thioacetal]. 
     A solution of the 1,1′-{[(propane-1,3 diyl)dioxy]bis[2-amino-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoro pyrrolidine-2-carboxaldehyde diethylthioacetal] VIII (846 mg, 1 mmol), HgCl 2  (794 mg, 2.93 mmol) and HgO (686 mg, 3.18 mmol) in CH 3 CN/H 2 O (3:1, 15 ml) was stirred at room temperature for 12 h until TLC (EtOAc), indicated complete loss of starting material. Then organic layer is evaporated in vacuum and the residue is diluted with EtOAc. To this, saturated NaHCO 3  solution was added slowly at room temperature and the mixture was filtered through celite and washed with ethylacetate. The filtrate was evaporated in vacuum to get crude 1,1′-{[(propane-1,3-diyl)]dioxy}bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4 benzodiazepin-5-one] of formula IXa, which was further purified by column chromatography on silica gel eluting first with ethyl acetate to remove traces of mercuric salts and further eluted with CHCl 3 -methanol (8.5:1.5). H 1  NMR (CDCl 3 , 200 MHz): δ 2.15–2.45 (m, 6H), 3.7–3.9 (m, 6H), 4.01(s, 6H), 4.22–4.3 (m, 4 H), 5.05 (t, 1H), 5.20 (t, 1H), 6.80 (s, 2H), 7.42 (s, 2H), 7.80 (d, 2H, J=4.2 Hz). FAB MASS: 569 (M+H) 
     EXAMPLE 2  
     A solution of (2S)-N-(4-hydroxy-5-metoxy-2-nitrobenzoyl)-4-fluoro pyrrolidine 2-carboxaldehyde diethylthioacetal VI (418 mg, 1 mmol), 1,4-dibromobutane (107 mg, 0.5 mmol) and K 2 CO 3  (414 mg, 3 mmol) in dry acetone (20 ml) was refluxed for 48 h. After the completion of reaction as indicated by TLC, EtOAc-hexane (7:3), the reaction mixture was poured on to the water and then extracted with ethyl acetate. Evaporation of the organic layer gave the crude product, which was purified by column chromatography on silica gel eluting with EtOAc-hexane (1:1) to give the pure 1,1′-{[Butane-1,4-diyl)dioxy]bis(2-nitro-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoro pyrroilidine-2-carboxaldehyde diethylthioacetal] VII. H 1  NMR (CDCl 3 , 200 MHz): δ 1.29–1.4 (m, 12H), 2.1–2.2 (m, 4H), 2.49–2.61 (m, 4H), 2.7–2.9 (m, 8H), 3.4–3.7 (m, 4H), 3.92 (s, 6H), 4.27 (t, 4 H), 4.58 (d, 2H), 4.70–4.85 (m, 2H), 5.08 (t, 1H), 5.29 (t, 1H), 6.82 (s, 2H), 7.65 (s, 2H). FAB MASS: 891 (M+H) 
     1,1′-{[Butane-1,4-diyl)dioxy]bis(2-nitro-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoro pyrrolidine-2-carboxaldehyde diethylthioacetal] of formula VII (890 mg, 1.0 mmol) was dissolved in methanol (10 ml) and added SnCl 2 .2H 2 O (1.124 g, 5.0 mmol) was refluxed for 1.5 h. The reaction mixture was then carefully adjusted to pH 8 with saturated NaHCO 3  solution and then extracted with ethyl acetate (3×20 ml). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude of pure 1,1′-{[Butane-1,4-diyl)dioxy]bis(2-amino-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoropyrrolidine-2-carboxaldehyde diethylthioacetal of formula VIII. 
     A solution of 1,1′-{[Butane-1,4-diyl)dioxy]bis(2-amino-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoropyrrolidine-2-carboxaldehyde diethylthioacetal of formula VIII (861 mg, 1 mmol), HgCl 2  (794 mg, 2.93 mmol) and HgO (687 mg, 3.18 mmol) in CH 3 CN/H 2 O (3:1, 15 ml) was stirred at room temperature for 12 h until TLC (EtOAc), indicted complete loss of starting material. Then organic layer was evaporated in vacuum and the residue is diluted with EtOAc. To this, saturated NaHCO 3  solution was added slowly at room temperature and the mixture is filtered through celite and washed with ethyl acetate. The filtrate was evaporated in vacuum to get crude 1,1′-{[(butane-1,4-diyl)]dioxy}bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one IXb, which was further purified by column chromatography on silica gel eluting first with ethylacetate to remove traces of mercuric salts and further eluted with CHCl 3 -methanol (9:1). H 1  NMR (CDCl 3 , 200 MHz): δ 1.94–2.09 (m, 4H), 2.1–2.5 (m, 4H), 3.5–3.82 (m, 6H), 3.98 (s, 6H), 4.1–4.37 (m, 4H), 5.29 (t, 1H), 5.5 (t, 1H), 6.80 (s, 2H), 7.45 (s, 2H), 7.80 (d, 2H, J=4.3 Hz). FAB MASS: 583 (M+H) 
     EXAMPLE 3  
     A solution of (2S)-N-(4-hydroxy-5-methoxy-2-nitrobenzoyl)-4-fluoro pyrrolidine 2-carboxaldehyde diethylthioacetal VI (418 mg, 1 mmol), 1,5-dibromopentane (114 mg, 0.5 mmol) and K 2 CO 3  (414 mg, 3 mmol) in dry acetone (20 ml) was refluxed for 48 h. After the completion of reaction as indicated by TLC, EtOAc-hexane (7:3), the reaction mixture was poured on to the water and then extracted with ethylacetate. Evaporation of the organic layer gave the crude product, which was further purified by column chromatography on silica gel eluting with EtOAc-hexane (1:1) to give the pure 1,1′-{[Pentane-1,5-diyl)dioxy]bis(2-nitro-5-methoxy-1,4-phenylene) carbonyl]}bis[4-fluoro pyrroilidine-2-carboxaldehyde diethyl thioacetal VII. H 1  NMR (CDCl 3 , 200 MHz): δ 1.2–1.42 (m, 12H), 1.65–2.1 (m, 6H), 2.4–2.61 (m, 4H), 2.7–2.91 (m, 8H), 3.29–3.67 (m, 4H), 3.99 (s, 6H), 4.09–4.25 (m, 4H), 4.52–4.68 (m, 2H), 4.82 (d, 2H), 5.10 (t, 1H), 5.32 (t, 1H), 6.89 (s, 2H), 7.69 (s, 2H). FAB MASS: 905 (M+H) 
     1,1′-{[Pentane-1,5-diyl)dioxy]bis(2-nitro-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoro pyrroilidine-2-carboxaldehyde diethylthioacetal] of formula VII (905 mg, 1.0 mmol) was dissolved in methanol (10 ml) and to it was added SnCl 2 .2H 2 O (1.124 g, 5.0 mmol) and was refluxed for 1.5 h. The reaction mixture was then carefully adjusted to pH 8 with saturated NaHCO 3  solution and then extracted with ethyl acetate (3×20 ml). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude 1′-{[Pentane-1,5-diyl)dioxy]bis(2-amino-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoropyrrolidine-2-carboxaldehyde diethyl thioacetal of formula VIII. 
     A solution of 1,1′-{[Pentane-1,5-diyl)dioxy]bis(2-amino-5-methoxy-1,4-phenylene)carbonyl]}bis[4-fluoropyrrolidine-2-carboxaldehyde diethylthioacetal of formula VIII (875 mg, 1 mmol), HgCl 2  (794 mg, 2.93 mmol) and HgO (687 mg, 3.18 mmol) in CH 3 CN/H 2 O (3:1, 15 ml) was stirred at room temperature for 12 h until TLC (EtOAc) indicated complete loss of starting material. Then organic layer was evaporated in vacuum and the residue was diluted with EtOAc. To this, saturated NaHCO 3  solution was added slowly at room temperature and the mixture was filtered through celite and washed with ethylacetate. The filtrate was evaporated in vacuum to get crude 1,1′-{[(pentane-1,5-diyl)]dioxy}bis[(11aS)-2-fluoro-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one IXc, which was further purified by column chromatography on silica gel eluting first with ethylacetate to remove traces of mercuric salts and further eluted with CHCl 3 -methanol (9:1). H 1  NMR (CDCl 3 , 200 MHz): δ 1.58–1.81 (m, 4H), 1.90–2.01 (m, 2H), 2.38–2.50 (m, 4H), 3.08–3.2 (m, 4H), 4.01–4.20 (m, 4H), 4.92 (s, 6H), 5.21 (t, 1H), 5.5 (t, 1H), 6.81 (s, 2H), 7.49 (s, 2H), 7.83 (d, 2H, J=4.4 Hz). FAB MASS: 597 (M+H) 
     Biological Activity: In vitro biological activity studies were carried out at National Cancer Institute (USA). 
     Cytotoxicity: Compounds IXa and IXc were evaluated for in vitro against sixty human tumour cells derived from nine cancer types (leukemia, non-small-cell lung, colon, CNS, melanoma, ovarian, prostate, and breast cancer). For each compound, dose response curves against each cell line were measured at a minimum of five concentrations at 10 fold dilutions. A protocol of 48 h continuous drug exposure was used and a sulforhodamine B (SRB) protein assay was used to estimate cell viability or growth. The concentration causing 50% cell growth inhibition (GI50), total cell growth inhibition (TGI, 0% growth) and 50% cell death (LC50, −50% growth) compared with the control was calculated. The mean graph midpoint values of log 10 TGI and log 10  LC50 as well as log 10  GI50 for IXa and IXc are listed in Table 1. As demonstrated by mean graph pattern (Table 4), compound IXc exhibits an interesting profile of activity and selectivity for various cell lines. The mean graph mid point of log 10  TGI and log 10  LC50 showed similar pattern to the log 10  GI50 mean graph mid points. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 log 10  GI50 log 10  TGI and log 10  LC50 mean graphs midpoints (MG_MID) 
               
               
                 of in vitro Cytotoxicity data for the compounds IXa and IXc against 
               
               
                 human tumour cell lines. 
               
             
          
           
               
                   
                 Compound 
                 Log 10  GI50 
                 Log 10  TGI 
                 Log 10 LC5O 
               
               
                   
                   
               
               
                   
                 IXa 
                 −5.21 
                 −4.75 
                 −4.31 
               
               
                   
                 IXc 
                 −7.14 
                 −6.27 
                 −4.87 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 In vitro one dose primary anticancer assay a  bisfluorinated PBDs of formula 
               
               
                 IXa, and IXc 
               
             
          
           
               
                   
                 Growth percentages 
               
             
          
           
               
                   
                   
                 (Lung) 
                 (Breast) 
                 (CNS) 
               
               
                   
                 PBD 
                 NCI-H460 
                 MCF7 
                 SF-268 
               
               
                   
                   
               
               
                   
                 IXa 
                 0 
                 0 
                 0 
               
               
                   
                 IXc 
                 0 
                 0 
                 0 
               
               
                   
                   
               
               
                   
                   a One dose of IXCa and IXc at 10 −4  molar concentration 
               
             
          
         
       
     
     The anticancer activity for two representative compounds has been given in Table 2. The comparison of the data of Table 3 reveals the importance of the alkane spacer. As the alkane spacer increased from 3–5 the cytotoxic activity has moderately enhanced. The 5 carbon spacer of compound IXc confers a suitable fit in the minor groove of double helix DNA and shows slightly higher activity in this series of compounds IXa and IXc. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Log GI50 (inhibitory concentration) Values for Compounds IXa, and IXc 
               
             
          
           
               
                   
                   
                 Compound 
                 Compound 
               
               
                   
                 cancer 
                 IXa 
                 IXc 
               
               
                   
                   
               
               
                   
                 leukemia 
                 5.668 
                 7.794 
               
               
                   
                 non-small-cell 
                 5.258 
                 7.318 
               
               
                   
                 lung 
               
               
                   
                 colon 
                 5.285 
                 7.064 
               
               
                   
                 CNS 
                 5.543 
                 7.625 
               
               
                   
                 melanoma 
                 5.490 
                 7.301 
               
               
                   
                 ovarian 
                 5.310 
                 6.620 
               
               
                   
                 renal 
                 5.315 
                 7.492 
               
               
                   
                 prostate 
                 5.180 
                 7.430 
               
               
                   
                 breast 
                 5.490 
                 7.234 
               
               
                   
                   
               
             
          
         
       
     
     Each cancer type represent the average of six to eight different cancer cell lines.