Abstract:
The present invention provides a compounds of general formula (8), (11) and (14), useful as potential antitumour agents against human cancer cell lines. The present invention further provides a process for the preparation of pyrrolo [2,1-c][1,4]benzodiazepine hybrids of general formula (8), (11) and (14).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to novel benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine hybrids as potential antitumour agents. The present invention also relates to a process for the preparation of novel benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine hybrids. Particularly, the present invention relates to benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine hybrids of general formula A. 
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         [0002]    More particularly, the present invention relates to benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine hybrids of general formula 8, 11 and 14 
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         [0003]    The present invention further relates to a process for the preparation of 7-Methoxy-8-{n-[2-(2-furyl)-1H-benzimidazol-1-yl]alkyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one/7-Methoxy-8-{n-[2-(2-thienyl)-1H-benzimidazol-1-yl]alkyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrr-olo[2,1-c][1,4]benzo diazepin-5-one/7-Methoxy-8-{n-[2-(1-Methyl-2-pyrrolyl)-1H-benzimidazol-1-yl]alkyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one/7-Methoxy-8-{n-[2-(2-pyridyl)-1H-benzimidazol-1-yl]alkyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one/Ethyl-2-[4-(benzyloxy)phenyl]-[(n-(11aS)-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one-8-yl)oxyalkyl]-2-benzi-midazol-6-carboxylate/7-Methoxy-8-{n-[2-[(4-(benzyloxy)phenyl)-6-morpholino]benzimidazol-1-yl]alkyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one/Ethyl-1-[(n-(11aS)-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one-8-yl)oxyalkyl]-2-(1-methyl-3-indolyl)benzimidazol-6-carboxylate with aliphatic chain length variations. 
       BACKGROUND OF THE INVENTION 
       [0004]    Pyrrolo[2,1-c][1,4]benzodiazepines (PBDs), a group of potent naturally occurring antitumour antibiotics from various  Streptomyces  species, are of considerable interest because of their ability to recognize and subsequently form covalent bonds to specific base sequence of double strand DNA (Dervan, P. B.  Science  1989, 232, 464; Hurley, L. H.  J. Med. Chem.  1989, 32, 2027; Thurston, D. E.; Thompson, A. S.  Chem. Br.  1990, 26, 767). Well-known members of this group include anthramycin, DC-81, sibiromycin, tomamycin, chicamycin and neothramycin of A and B (Hurley, L. H.  J. Antibiot.  1977, 30, 349; Schimizu, K.; Kawamoto, I.; Tomita, F.; Morimoto, M.; Fujimoto, K.  J. Antibiot.  1982, 35, 992; Lown, J. W.; Joshua, A. V.  Biochem. Pharmacol.  1979, 28, 2017; Thurston, D. E.; Bose, D. S.  Chem. Rev.  1994, 94, 433; Molina, P.; Diaz, I.; Tarraga, A.  Tetrahedron  1995, 51, 5617; Kamal, A.; Rao, N. V.  Chem. Commun.  1996, 385; Kamal, A.; Reddy, B. S. P.; Reddy, B. S, N.  Tetrahedron Lett.  1996, 37, 6803). The cytotoxicity and antitumour activity of these agents are attributed to their property of sequence selective covalent binding to the N2 of guanine in the minor groove of duplex DNA via an acid-labile aminal bond to the electrophilic 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. and Speous, C. L.  J. Mol. Biol.,  1970, 51, 551; Hurley, L. H.; Gairpla, C. and Zmijewski, M.  Biochem. Biophys. Acta.,  1977, 475, 521; Kaplan, D. J. and Hurley, L. H.  Biochemistry,  1981, 20, 7572). The molecules have 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. 
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         [0005]    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, and Hurley, L. H.  J. Org. Chem.  1996, 61, 8141). 
         [0006]    Recently, PBD dimers have been developed that comprise of 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, T. C.; Kelland, L. R. and Thurston, D. E.  J. Med. Chem.  2001, 44, 737). A non-cross-linking mixed imine-amide PBD dimers have been synthesized that have significant DNA binding ability and potent antitumour activity (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). However, the clinical efficacy for these antibiotics is hindered by several limitations, such as poor water solubility, cardiotoxicity, development of drug resistance and metabolic inactivation. Due to the excellent activity of these molecules, there is need to develop novel derivatives which are devoid of above limitations. 
         [0007]    Benzimidazoles are small synthetic molecules that contain a benzene ring fused to a imidazole ring. These simple molecules have shown remarkable antitumour properties, whose mode of action is thought to result from their inhibition of microtubule formations (Nare, B.; Liu, Z.; Prichard, R. K. and George, E.  Biochem Pharmacol.  1994, 48, 2215). Substituted benzimidazoles have proven as drug leads, which have exhibited pharmacological interest (Al-Mahaimeed, H.  Int. Med. Res.  1997, 25, 175). In addition 2-substituted benzimidazoles cover a broad range of biological activities, including antitumour (Pedini, M.; Bistocchi, G. A.; Meo, G. D.; Lepri, E.; Bastianini, L.  II Farmaco  1999, 54, 327; Hida, F.; Robert, J.; Duc, L. C.  Farmaco  1994, 49, 489). A series of 2-aryl benzimidazole-4-carboxamides have been synthesized and evaluated for in vitro and in vivo antitumour activity and DNA binding affinity (Denny, W. A.; Rewcastle, G. W. and Baguly, B. C.  J. Med. Chem.  1990, 33, 814). Moreover, the architecture of benzimidazole moiety as a new platform for the DNA-minor groove recognition elements for (Marques, M. A.; Doss, R. M.; Foister, S.; Dervan, P. B.  J. Am. Chem. Soc.  2004, 126, 10339), selective base pair recognition can be achieved by introduction of heteroatoms and substituents in this ring system (Viger, A.; Dervan, P. B. Bioorg.  Med. Chem.  2006, 14, 8539; Foister, S.; Marques, M. A.; Doss, R. M.; Dervan, P. B.  Bioorg. Med. Chem.  2003, 11, 4333). This ring system can also be considered as a new tool for the target specific transcription factor at the binding sites relevant to biological systems. Recently, Dervan and coworkers reported the down-regulation of the angiogenetic vascular endothelial growth factor (VEGF) by a DNA-binding fluorescein-polyamide conjugate in cell culture (Olenyuk, B. Z.; Zhang, G.; Klco, J. M.; Nickols, N. G.; Kaelin, W. G.; Jr.; Dervan, P. B. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 16768). Based on the potent anticancer activity of pyrrolo[2,1-c][1,4]benzodiazepines and benzimidazole ring system the new PBD hybrids have been designed and synthesized by linking benzimidazole moieties at C8-position of pyrrolo[2,1-c][1,4]benzodiaze-pine with varying alkane spacers. 
       OBJECTIVES OF THE INVENTION 
       [0008]    The main objective of the present invention is to provide novel benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine hybrids useful as antitumour agents. 
         [0009]    Yet another object of the present invention is to provide a process for the preparation of novel benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine hybrids. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly the present invention provides novel pyrrolo[2,1-c][1,4]benzodiazepine hybrids of general formula A, 
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         [0011]    In an embodiment of the present invention the novel pyrrolo[2,1-c][1,4]benzodiazepine hybrids of general formula A according to claim  1  is represented by the group of the following compounds
   a) 7-Methoxy-8-{3-[2-(2-furyl)-1H-benzimidazol-1-yl]propyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (8a);   b) 7-Methoxy-8-{4-[2-(2-furyl)-1H-benzimidazol-1-yl]butyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (8b);   c) 7-Methoxy-8-{5-[2-(2-furyl)-1H-benzimidazol-1-yl]pentyl}oxy-(11aS)-1,2,3,11 a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (8c);   d) 7-Methoxy-8-{3-[2-(2-thienyl)-1H-benzimidazol-1-yl]propyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (8d);   e) 7-Methoxy-8-{-4,2-(2-thienyl)-1H-benzimidazol-1-yl]butyl]oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (8e);   f) 7-Methoxy-8-{5-[2-(2-thienyl)-1H-benzimidazol-1-yl]pentyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (8f),;   g) 7-Methoxy-8-{3-[2-(1-Methyl-2-pyrrolyl)-1H-benzimidazol-1,4]propyl}-oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (8g).   h) 7-Methoxy-8-{3-[2-(2-pyridyl)-1H-benzimidazol-1-yl]propyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (11a);   i) 7-Methoxy-8-{5-[2-(2-pyridyl)-1H-benzimidazol-1-yl]pentyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one (11b);   j) 7-Methoxy-8-{5-[2-[(4-(benzyloxy)phenyl)-6-morpholino]benzimidazol-1-yl]pentyl}oxy-(11aS)-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one(11c).   k) Ethyl-2-[4-(benzyloxy)phenyl]-[(5-(11aS)-7-methoxy-1,2,3,11a-tetrahy-dro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one-8-yl)oxypentyl]-2-benzimidazol-6-carboxylate (11d);   l) Methyl-1-[(4-(11aS)-7-methoxy-1,2,3,11a-tetrahydro-5H-pyrrolo[2,1-c][1,4]benzodiazepin-5-one-8-yl)oxybutyl]-2-(1-methyl-3-indolyl)benzimidazol-6-carboxylate (14).   
 
         [0024]    In yet another embodiment the structural formula of the represented compounds of novel pyrrolo[2,1-c][1,4]benzodiazepine hybrids are 
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         [0025]    In yet another embodiment the novel pyrrolo[2,1-c][1,4]benzodiazepine hybrids exhibits of formula A an in vitro anticancer/antitumour activity against sixty human cancer cell lines derived from nine cancer types selected from the group consisting of leukemia, non-small-cell lung, colon, CNS, melanoma, ovarian, prostate, and breast cancer. 
         [0026]    The present invention further provides a pharmaceutical composition comprising novel pyrrolo[2,1-c][1,4]benzodiazepine hybrids, its derivatives, analogues, salts or mixture thereof optionally with pharmaceutically acceptable carriers, adjuvants and additives. 
         [0027]    In yet another embodiment the novel pyrrolo[2,1-c][1,4]benzodiazepine hybrids used in pharmaceutical composition is represented by a general formula A, 
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         [0028]    The present invention further provides a process for the preparation of benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazine hybrids of general formula A 
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         [0029]    and the said process comprising the steps of:
       a) reacting (2S)—N-[4-(n-bromoalkyl)-oxy-5-methoxy-2-nitrobenzoyl]pyrrolidine-2-carboxaldehyde diethylthioacetal of formula 2a-c with benzimidazole derivatives of formula 3a-c, 4a-c or 5, isolating (2S)—N-{4-(n-[2-(2-furyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-nitrobenzoyl]pyrrolidine-2-carboxaldehyde diethyl thio acetal/(2S)—N-{4-(n-[2-(2-thienyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-nitro benzoyl]pyrrolidine-2-carboxaldehyde diethyl thioacetal/(2S)—N-{4-(n-[2-(1-methyl-2-pyrrolyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-nitrobenzoyl}pyrrolidine-2-carboxaldehyde diethyl thioacetal of formula 6a-g and (2S)—N-{4-(n-[2-(2-pyridyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-nitrobenoyl}pyrrolidine-2-carboxaldehyde diethyl thioacetal/(2S)—N-{4-(n-[2-[(4-(benzyloxy)phenyl)-6-morpholino]benzimidazol-1-yl]alkyl) oxy-5-methoxy-2-nitrobenzoyl}pyrrolidine-2-carboxaldehyde diethyl thioacetal/Ethyl-2-[4-(benzyloxy)phenyl]-{[n-[4-(2S)—N-pyrrolidine-2-carboxaldehydediethylth ioacetal]alkyl]-2-methoxy-5-nitrophenoxy}benzimidazol-6-carboxylate of formula 0.9a-d and methyl-1-{[4-[4-(2S)—N-pyrrolidine-2-carboxaldehyde diethylthioacetal]butyl]-2-methoxy-5-nitrophenoxy}-2-(1-methyl-3-indolyl)benzimidazol-6-carboxylate of formula 12, respectively:   b) reducing the above nitro compounds of formula 6a-g, 9a-d and 12 with SnCl 2 .2H 2 O, in presence of organic solvent selected from methanol and ethanol up to a reflux temperature, isolating the (2S)—N-{4-(n-[2-(2-furyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-aminobenzoyl}pyrrolidine-2-carboxaldehyde diethyl thio acetal/(2S)—N-{4-(n-[2-(2-thienyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-amino benzoyl}pyrrolidine-2-carboxaldehyde diethyl thioacetal/(2S)—N-{4-(n-[2-(1-methyl-2-pyrrolyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-aminobenzoyl}pyrrolidine-2-carboxaldehyde diethyl thioacetal of formula 7a-g, (2S)—N-{4-(n-[2-(2-pyridyl)benzimidazol-1-yl]alkyl)oxy-5-methoxy-2-aminobenoyl}pyrrolidine-2-carboxaldehyde diethyl thioacetal/(2S)—N-(4-(n-[2-[(4-(benzyloxy)phenyl)-6-morpholino]benzimidazol-1-yl]alkyl)-oxy-5-methoxy-2-aminobenzoyl}pyrrolidine-2-carboxaldehyde diethyl thioacetal/Ethyl-2-[4-(benzyloxy)phenyl]-{[n-[4-(2S)—N-pyrrolidine-2-carboxaldehyde diethyl thioacetal]alkyl]-2-methoxy-5-amino phenoxy}benzimidazol-6-carboxylate of formula 10a-d and methyl-1-{[4-[4-(2S)—N-pyrrolidine-2-carboxaldehyde diethylthioacetal]butyl]-2-methoxy-5-aminophenoxy}-2-(1-methyl-3-indolyl)benzimidazol-6-carboxylate of formula 13, respectively.   c) reacting the above amino compounds of formula 7a-g, 10a-d and 13 with mercurous chloride and calcium carbonate by known method to obtain the desired novel pyrrolo[2,1-c][1,4]benzodiazepine hybrids of formula 8a-g, 11a-d and 14.       
 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    The precursors 2-(2-furyl)benzimidazole/2-(2-thienyl)benzimidazole/2-(1-methyl-2-pyrrolyl)benzimidazole of formula 3a-g (Brthini, Y.; Lown, J, W.  Synthetic Commun.  1990, 20, 955; Hua, J. Y.; Bur, D.; Hasler, W.; Schmitt, V. R.; Dorn, A.; Bailly, C.; Waring, M. J.; Hochstrassera, R.; Leupina, W.  Bioorg. Med. Chem.  2001, 9, 2905) and (2S)—N-[4-(hydroxy-5-methoxy-2-nitrobenzoyl]pyrrolidine-2-carboxaldehyde diethylthioacetal of formula 2 (Thurston, D. E.; Murthy, V. S.; Langley, D. R.; Jones, G. B.  Synthesis.  1990, 81) have been prepared by literature methods. The other benzimidazole precursors 2-(2-pyridyl)benzimidazole/4-{2-[4-(Benzyloxy)phenyl]benzimidazol-6-yl}morpholine/Ethyl-2-[4-(benzyloxy)phenyl]benzimidazol-6-carboxilate of formula 4a-c have been prepared condensation followed by oxidation of substituted 2,3-diaminobenzene with benzylated protected benzaldehydes in presence of sodium metabisulphate (Kamal, A.; Ramulu, P.; Srinivas, O.; Ramesh, G.; Kumar, P, P.  Bioorg. Med. Chem. Lett.  2004, 12, 4337). methyl-2-(1-methyl-3-indolyl)benzimidazol-6-carboxylate of formula 5 has been prepared by methyl 3,4-diaminobenzoate with corresponding 1-methyl-1H-3-indolecarbaldehyde 
         [0034]    These new analogues of pyrrolo[2,1-c][1,4]benzodiazepine hybrids linked at C-8 position have shown promising DNA binding activity and efficient anticancer activity in various cell lines. The molecules synthesized are of immense biological significance with potential sequence selective DNA-binding property. This present invention is illustrated in schemes 1-3 which comprise:
       1) The ether linkage at C-8 position of DC-81 intermediates with benzimidazole moieties.   2) Refluxing the reaction mixtures for 48 h.   3) Synthesis of C-8 linked PBD antitumour antibiotic hybrid imines.   4) Purification by column chromatography using different solvents like ethyl acetate, hexane, chloroform and methanol.       
 
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         [0000]    Representative compounds 8a-g, 11a-d and 14 of general structural formula 8, 11 and 14 
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                 Compound 
                 n 
                 X 
                 R 1   
                 R 2   
               
               
                   
                   
               
             
             
               
                   
                  8a 
                 3 
                 O 
                 — 
                 — 
               
               
                   
                  8b 
                 4 
                 O 
                 — 
                 — 
               
               
                   
                  8c 
                 5 
                 O 
                 — 
                 — 
               
               
                   
                  8d 
                 3 
                 S 
                 — 
                 — 
               
               
                   
                  8e 
                 4 
                 S 
                 — 
                 — 
               
               
                   
                  8f 
                 5 
                 S 
                 — 
                 — 
               
               
                   
                  8g 
                 3 
                 NMe 
                 — 
                 — 
               
               
                   
                 11a 
                 3 
                 N 
                 H 
                 H 
               
               
                   
                 11b 
                 5 
                 N 
                 H 
                 H 
               
               
                   
                 11c 
                 5 
                 C 
                 OBn 
                 Morpholine 
               
               
                   
                 11d 
                 5 
                 C 
                 OBn 
                 COOEt 
               
               
                   
                 14 
                 4 
                 — 
                 — 
                 — 
               
               
                   
                   
               
             
          
         
       
     
         [0039]    The following examples are given by way of illustration of the working of the invention in actual practice and therefore should not be construed to limit the scope of present invention in any way. 
       Example 1 
       [0040]    To a solution of (2S)—N-[4-(3-bromopropyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2a (521 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-furyl)benzimidazole 3a (185 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 3% MeOH—CHCl 3  as eluent to afford pure compound of 6a (468 mg, 75%). 
         [0041]      1 H NMR (CDCl 3 ): δ 8.63 (d, J=5.2 Hz, 1H), 8.44 (d, J=7.55, Hz, 1H), 7.78-7.88 (m, 2H), 7.46-7.53 (m, 2H), 7.23-7.35 (m, 2H), 6.80 (s, 1H), 5.07-5.18 (m, 2H), 4.8 (d, J=3.0, 1H), 4.65-4.72 (m, 1H), 4.07-4.15 (m, 2H), 3.99 (s, 3H), 3.16-3.32 (m, 2H), 2.69-2.90 (m, 4H), 2.50-2.62 (m, 2H), 2.26-2.35 (m, 2H), 1.34-1.42 (m, 6H). 
         [0042]    ESIMS: m/z 625 (M + ). 
         [0043]    The compound 6a (625 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 7a (487 mg, 80%), which was used directly in the next step. 
         [0044]    A solution of 7a (609 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (90% CH 2 Cl 2 —MeOH) to give compound 8a (264 mg, 56%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0045]      1 H NMR (CDCl 3 ): δ 7.82 (d, J=7.8 Hz, 1H), 7.67 (s, 2H), 7.55 (s, 1H), 7.42-7.52 (m, 3H), 7.07-7.19 (m, 2H), 6.72 (s, 1H), 5.06-5.18 (m, 1H), 4.58-4.76 (m, 2H), 4.05-4.15 (m, 1H), 4.00 (s, 3H), 3.78-3.90 (m, 1H), 3.65-3.75 (m, 1H), 3.45-3.65 (m, 1H), 2.38-2.49 (m, 1H), 2.25-2.36 (m, 1H), 1.95-2.15 (m, 4H). 
         [0046]    ESIMS: m/z 471 (M + +1). 
       Example 2 
       [0047]    To a solution of (2S)—N-[4-(4-bromobutyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2b (535 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-furyl)benzimidazole 3a (185 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 3% MeOH—CHCl 3  as eluent to afford pure compound of 6b (498 mg, 78%). 
         [0048]      1 H NMR (CDCl 3 ): δ 7.71-7.75 (m, 1H), 7.58 (s, 1H), 7.54-7.57 (t, 1H), 7.34-7.39 (m, 1H), 7.21-7.26 (m, 3H), 6.77 (s, 1H), 6.58-6.59 (dd, J=1.8, J=3.3 Hz, 1H), 4.82 (d, J=3.7 Hz, 1H), 4.57-4.71 (m, 3H), 4.10 (t, J=5.4 Hz, 2H), 3.89 (s, 3H), 3.15-3.30 (m, 2H), 2.65-2.85 (m, 4H), 2.05-2.32 (m, 4H), 1.75-1.93 (m, 4H), 1.30-1.40 (m, 6H). 
         [0049]    ESIMS: m/z 640 (M + +1). 
         [0050]    The compound 6b (639 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 7b (486 mg, 78%), which was used directly in the next step. 
         [0051]    A solution of 7b (623 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (92% CH 2 Cl 2 -MeOH) to give compound 8b (291 mg, 60%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0052]      1 H NMR (CDCl 3 ): δ 7.77 (d, J=7.5 Hz, 1H), 7.62-7.69 (d, J=3.7 Hz, 1H), 7.57 (s, 1H), 7.44-7.55 (m, 2H), 7.10-7.33 (m, 4H), 6.50 (s, 1H), 5.00-5.52 (m, 1H), 4.76 (t, J=5.0 Hz), 4.65 (t, J=6.7 Hz, 2H), 4.10-4.19 (m, 2H), 3.92 (s, 3H), 3.45-3.87 (m, 2H), 2.30-2.39 (m, 2H), 1.85-2.20 (m, 6H) 
         [0053]    ESIMS: m/z 485 (M + ). 
       Example 3 
       [0054]    To a solution of (2S)—N-[4-(5-bromopentyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2c (549 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-furyl)benzimidazole 3a (185 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 3% MeOH—CHCl 3  as eluent to afford pure compound of 6c (470 mg, 72%). 
         [0055]      1 H NMR (CDCl 3 ): δ 7.71-7.75 (m, 1H), 7.58 (s, 1H), 7.54-7.57 (m, 1H), 7.34-7.39 (m, 1H), 7.21-7.26 (m, 3H), 6.77 (s, 1H), 6.58-6.59 (dd, J=1.8, J=3.3 Hz, 1H), 4.82 (d, J=3.7 Hz, 1H), 4.57-4.71 (m, 3H), 4.10 (t, J=5.4 Hz, 2H), 3.89 (s, 3H), 3.18-3.28 (m, 1H), 2.95-3.05 (m, 1H), 2.65-2.90 (m, 4H), 2.40-2.55 (m, 2H), 1.56-2.40 (m, 3H), 1.32-1.44 (m, 6H) 
         [0056]    ESIMS: m/z 654 (M + ). 
         [0057]    The compound 6c (653 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 7c (497 mg, 78%), which was used directly in the next step. 
         [0058]    A solution of 7c (666 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight. The reaction mixture was diluted with ethyl acetate (30 mL) filtered through a celite pad. The clear organic supernatant was extracted with saturated 5% NaHCO 3  (20 mL), brine (20 mL) and the combined organic phase was dried (Na 2 SO 4 ). The organic layer was evaporated under vacuum and purified by column chromatography using MeOH—CHCl 3  (4%) to give compound 8c (323 mg, 60%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0059]      1 H NMR (CDCl 3 ): δ 7.79 (d, J=7.5 Hz, 1H), 7.63-7.68 (d, J=3.7 Hz, 1H), 7.57 (s, 1H), 7.45-7.55 (m, 2H), 7.10-7.35 (m, 4H), 6.5 (s, 1H), 5.00-5.52 (m, 1H), 4.78 (t, J=5.0 Hz), 4.67 (t, J=6.7 Hz, 2H), 4.10-4.20 (m, 2H), 3.90 (s, 3H), 3.50-3.70 (m, 2H), 2.40-2.55 (m, 2H), 2.20-2.35 (m, 2H), 1.56-2.40 (m, 6H) 
         [0060]    ESIMS: m/z 499 (M + ). 
       Example 4 
       [0061]    To a solution of (2S)—N-[4-(3-bromopropyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2a (521 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-thienyl)benzimidazole 3b (201 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 3% MeOH—CHCl 3  as eluent to afford pure compound of 6d (448 mg, 75%). 
         [0062]      1 H NMR (CDCl 3 ): δ 7.72-7.80 (dd, J=2.9, J=7.3 Hz, 1H), 7.63 (d, J=2.9 Hz, 1H), 7.51 (s, 1H), 7.46 (d, J=4.4 Hz, 1H), 7.34-7.42 (dd, J=2.2, J=5.8 Hz, 1H), 7.18-7.30 (m, 2H), 7.07-7.14 (dd, J=3.6, J=5.1 Hz, 1H), 6.8 (s, 1H), 4.80-4.86 (d, J=3.6 Hz, 1H), 4.62-4.76 (m, 3H), 4.08 (t, J=4.4 Hz, 2H), 3.98 (s, 3H), 3.10-3.40 (m, 2H), 2.60-2.90 (m, 4H), 2.20-2.55 (m, 2H), 2.20-2.34 (m, 2H), 1.70-2.15 (m, 2H), 1.45-1.65 (m, 2H), 1.30-1.45 (m, 6H). 
         [0063]    ESIMS: m/z 641 (M + ). 
         [0064]    The compound 6d (641 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 7d (488 mg, 80%), which was used directly in the next step. 
         [0065]    A solution of 7d (611 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (96% CH 2 Cl 2 -MeOH) to give compound 8d (272 mg, 56%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0066]      1 H NMR (CDCl 3 ): δ 7.77-7.84 (m, 1H), 7.67 (d, J=4.5 Hz, 1H), 7.56 (s, 1H), 7.48 (d, J=4.53 Hz, 1H), 7.45 (d, J=2.26 Hz, 1H), 7.23-7.36 (m, 1H), 7.11-7.16 (m, 2H), 6.71 (s, 1H), 5.08-5.12 (m, 1H), 4.69 (t, J=7.45 Hz, 2H), 4.04-4.18 (m, 1H), 3.99 (s, 3H), 3.78-3.92 (m, 1H), 3.50-3.75 (m, 2H), 2.25-2.50 (m, 4H), 2.00-2.15 (m, 2H). 
         [0067]    ESIMS: m/z 487 (M + +1). 
       Example 5 
       [0068]    To a solution of (2S)—N14-(4-bromobutyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2b (535 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-thienyl)benzimidazole 3b (201 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 5% MeOH—CHCl 3  as eluent to afford pure compound of 6e (484 mg, 74%). 
         [0069]      1 H NMR (CDCl 3 ): δ 7.75-7.82 (dd, J=3.9, J=7.0 Hz, 1H), 7.61 (s, 1H), 7.56-7.61 (m, 1H), 7.51 (d, J=6.2 Hz, 1H), 7.35-7.43 (m, 1H), 7.24-7.32 (m, 2H), 7.10-7.17 (m, 1H), 6.8 (s, 1H), 4.85 (d, J=3.12 Hz, 1H), 4.62-4.80 (m, 1H), 4.58 (t, J=7.0 Hz, 2H), 4.06-4.20 (m, 2H), 3.91 (s, 3H), 3.20-3.35 (m, 1H), 2.95-3.05 (m, 1H), 2.60-2.90 (m, 4H), 1.60-2.40 (m, 8H), 1.25-1.45 (m, 6H). 
         [0070]    ESIMS: m/z 655 (M + ). 
         [0071]    The compound 6e (655 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 7e (512 mg, 82%), which was used directly in the next step. 
         [0072]    A solution of 7e (625 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (95% CH 2 Cl 2 -MeOH) to give compound 8e (300 mg, 60%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0073]      1 H NMR (CDCl 3 ): δ 7.75-7.85 (m, 1H), 7.69 (d, J=4.5 Hz, 1H), 7.54 (s, 1H), 7.50 (d, J=4.5, 1H), 7.40-7.47 (m, 1H), 7.26-7.34 (m, 3H), 7.07-7.16 (dd, J=3.7, J=5.2 Hz, 1H), 6.80 (s, 1H), 4.94-5.04 (m, 1H), 4.53 (t, J=7.5 Hz, 2H), 4.00-4.25 (m, 2H), 3.92 (s, 3H), 3.45-3.89 (m, 2H), 2.30-2.40 (m, 2H), 1.85-2.19 (m, 6H) 
         [0074]    ESIMS: m/z 501 (M + ). 
       Example 6 
       [0075]    To a solution of (2S)—N-[4-(5-bromopentyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2c (549 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-thienyl)benzimidazole 3b (201 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 3% MeOH—CHCl 3  as eluent to afford pure compound of 6f (501 mg, 75%). 
         [0076]      1 H NMR (CDCl 3 ): δ 7.74-7.81 (dd, J=1.7, J=6.0 Hz, 1H), 7.63-7.67 (m, 1H), 7.53 (s, 1H), 7.47 (d, J=4.3 Hz, 1H), 7.34-7.43 (m, 1H), 7.20-7.30 (m, 2H), 7.09-7.18 (m, 1H), 6.8 (s, 1H), 4.85 (d, J=4.3 Hz, 1H), 4.64-4.76 (m, 3H), 4.05-4.15 (t, J=4.3 Hz, 2H), 4.00 (s, 3H), 3.18-3.28 (m, 1H), 2.95-3.05 (m, 1H), 2.65-2.90 (m, 4H), 2.40-2.55 (m, 2H), 2.20-2.35 (m, 2H), 1.56-2.40 (m, 6H), 1.32-1.44 (m, 6H) 
         [0077]    ESIMS: m/z 669 (M + +1). 
         [0078]    The compound 6f (669 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 7f (530 mg, 83%), which was used directly in the next step. 
         [0079]    A solution of 7f (639 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (94% CH 2 Cl 2 -MeOH) to give compound 8f (298 mg, 58%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0080]      1 H NMR (CDCl 3 ): δ 7.72-7.80 (dd, J=1.7, J=6.0 Hz, 1H), 7.62-7.65 (m, 1H), 7.52 (s, 1H), 7.45 (d, J=4.3 Hz, 1H), 7.32-7.41 (m, 1H), 7.20-7.30 (m, 2H), 7.08-7.18 (m, 1H), 6.6 (s, 1H), 4.84 (d, J=4.3 Hz, 1H), 4.64-4.76 (m, 3H), 4.05-4.15 (t, J=4.3 Hz, 2H), 4.00 (s, 3H), 3.50-3.70 (m, 2H), 2.40-2.55 (m, 2H), 2.20-2.35 (m, 2H), 1.56-2.40 (m, 6H) 
         [0081]    ESIMS: m/z 516 (M + +1). 
       Example 7 
       [0082]    To a solution of (2S)—N-[4-(3-bromopropyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2a (521 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(1-methyl-2-pyrrolyl)benzimidazol 3c (197 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 3% MeOH—CHCl 3  as eluent to afford pure compound of 6g (445 mg, 70%). 
         [0083]      1 H NMR (CDCl 3 ): δ 7.77-7.81 (m, 1H), 7.63 (s, 1H), 7.37-7.42 (m, 1H), 7.26-7.31 (m, 1H), 6.83-6.85 (dd, J=1.70, J=2.55 Hz, 1H), 6.81 (s, 1H), 6.46-6.48 (dd, J=1.70, J=3.77 Hz, 1H), 6.23-6.26 (dd, J=3.77, J=2.5 Hz, 1H), 4.87 (d, J=3.77 Hz, 1H), 4.67-4.75 (m, 1H), 4.33 (t, J=7.44 Hz, 2H), 4.05 (t, J=6.54 Hz, 2H), 3.90 (s, 3H), 3.88 (s, 3H), 3.17-3.34 (m, 2H), 2.67-2.87 (m, 4H), 2.22-2.31 (m, 1H), 2.089-2.16 (m, 1H), 1.82-2.01 (m, 2H), 1.51-1.60 (m, 2H), 1.30-1.43 (m, 6H). 
         [0084]    ESIMS: m/z 639 (M + +1). 
         [0085]    The compound 6g (638 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 7g (486 mg, 80%), which was used directly in the next step. 
         [0086]    A solution of 7g (608 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (90% CH 2 Cl 2 -MeOH) to give compound 8g (278 mg, 56%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0087]      1 H NMR (CDCl 3 ): δ 7.70-7.85 (m, 1H), 7.64 (d, J=4.6 Hz, 1H), 7.47 (s, 1H), 7.10-7.42 (m, 3H), 6.78-6.83 (m, 1H), 6.75 (s, 1H), 6.38-6.44 (dd, J=1.5, J=3.9 Hz, 1H), 6.21 (t, J=3.1 Hz, 1H), 5.00-5.13 (m, 1H), 4.25 (t, J=7.0 Hz, 2H), 3.97 (t, J=6.25 Hz, 2H), 3.88 (s, 3H), 3.81 (s, 3H), 3.40-3.60 (m, 2H), 2.15-2.35 (m, 2H), 1.70-2.10 (m, 4H). 
         [0088]    ESIMS: m/z 484 (M + +1). 
       Example 8 
       [0089]    To a solution of (2S)—N-[4-(3-bromopropyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2a (521 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-pyridyl)benzimidazole 4a (195 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 3% MeOH—CHCl 3  as eluent to afford pure compound of 9a (464 mg, 73%). 
         [0090]      1 H NMR (CDCl 3 ): δ 8.65 (d, J=5.1 Hz, 1H), 8.45 (d, J=8.0 Hz, 1H), 7.75-7.88 (m, 2H), 7.47-7.52 (m, 1H), 7.46 (s, 1H), 7.20-7.36 (m, 3H), 6.78 (s, 1H), 4.86 (d, J=3.7 Hz, 1H), 4.54-4.70 (m, 3H), 4.00-4.14 (m, 2H), 3.98 (s, 3H), 3.18-3.28 (m, 1H), 2.94-3.04 (m, 1H), 2.64-2.90 (m, 4H), 2.40-2.55 (m, 2H), 1.55-2.40 (m, 4H), 1.30-1.44 (m, 6H) 
         [0091]    ESIMS: m/z 636 (M + ). 
         [0092]    The compound 9a (649 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 10a (485 mg, 80%), which was used directly in the next step. 
         [0093]    A solution of 10a (606 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (90% CH 2 Cl 2 -MeOH) to give compound 11a (250 mg, 52%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0094]      1 H NMR (CDCl 3 ): δ 8.68 (d, J=5.0 Hz, 1H), 8.48 (m, 1H), 7.65-7.69 (d, J=3.4 Hz, 1H), 7.75-7.88 (m, 2H), 7.49-7.52 (m, 1H), 7.47 (s, 1H), 7.22-7.36 (m, 3H), 6.79 (s, 1H), 5.04-5.19 (m, 1H), 4.52-4.76 (m, 2H), 4.04-4.14 (m, 1H), 4.02 (s, 3H), 3.77-3.90 (m, 1H), 3.67-3.75 (m, 1H), 3.46-3.65 (m, 1H), 2.39-2.50, (m, 1H), 2.26-2.36 (m, 1H), 1.94-2.15 (m, 4H). 
         [0095]    ESIMS: m/z 483 (M + +1). 
       Example 9 
       [0096]    To a solution of (2S)—N-[4-(5-bromopentyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2c (549 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 2-(2-pyridyl)benzimidazole 4a (195 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 2% MeOH—CHCl 3  as eluent to afford pure compound of 9b (498 mg, 75%). 
         [0097]      1 H NMR (CDCl 3 ): 8.62 (d, J=5.1 Hz, 1H), 8.44 (d, J=8.0 Hz, 1H), 7.75-7.87 (m, 2H), 7.47-7.51 (m, 1H), 7.45 (s, 1H), 7.20-7.35 (m, 3H), 6.77 (s, 1H), 4.82 (d, J=3.7 Hz, 1H), 4.57-4.71 (m, 3H), 4.02-4.15 (m, 2H), 3.97 (s, 3H), 3.10-3.30 (m, 1H), 2.90-3.08 (m, 1H), 2.65-2.85 (m, 4H), 2.45-2.62 (m, 2H), 1.60-2.40 (m, 6H), 1.44-1.50 (m, 2H), 1.30-1.42 (m, 6H) 
         [0098]    ESIMS: m/z 666 (M + ). 
         [0099]    The compound 9b (649 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 10b (519 mg, 82%), which was used in the directly next step. 
         [0100]    A solution of 10b (634 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (91% CH 2 Cl 2 -MeOH) to give compound 11b (285 mg, 56%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0101]      1 H NMR (CDCl 3 ): 8.69 (d, J=5.0 Hz, 1H), 8.43 (d, J=8.0 Hz, 1H), 7.74-7.86 (m, 2H), 7.46-7.50 (m, 1H), 7.45 (s, 1H), 7.20-7.37 (m, 3H), 6.78 (s, 1H), 5.02-5.52 (m, 1H), 4.76 (t, J=5.0 Hz), 4.66 (t, J=6.7 Hz, 2H), 4.10-4.20 (m, 2H), 3.92 (s, 3H), 3.52-3.70 (m, 2H), 2.42-2.55 (m, 2H), 2.22-2.35 (m, 2H), 1.56-2.40 (m, 6H) 
         [0102]    ESIMS: m/z 510 (M + ). 
       Example 10 
       [0103]    To a solution of (2S)—N-[4-(5-bromopentyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2c (52.1 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the 4-{2-[4-(Benzyloxy)phenyl]benzimidazol-6-yl}morpholine 4b (385 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 5% MeOH—CHCl 3  as eluent to afford pure compound of 9c (602 mg, 73%). 
         [0104]      1 H NMR (CDCl 3 ): δ 7.63 (d, J=9.0 Hz, 1H), 7.52-7.58 (m, 1H), 7.41-7.46 (m, 2H), 7.28-7.40 (m, 4H), 6.93 (d, J=9.0 Hz, 4H), 6.81 (s, 1H), 6.68 (s, 1H), 5.14 (s, 2H), 4.80 (d, J=3.7 Hz, 1H), 4.62-4.71 (m, 1H), 4.50-4.62 (m, 2H), 4.50-4.62 (m, 2H), 3.83-4.02 (m, 7H), 3.75-3.82 (m, 2H), 3.10-3.24 (m, 4H), 2.65-2.81 (m, 4H), 2.40-2.55 (m, 2H), 2.11-2.36 (m, 4H), 1.84-2.10 (m, 4H), 1.30-1.41 (m, 6H) 
         [0105]    ESIMS: m/z 855 (M + +1). 
         [0106]    The compound 9c (826 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 10c (557 mg, 70%), which was used in the directly next step. 
         [0107]    A solution of 10c (796 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (90% CH 2 Cl 2 -MeOH) to give compound 11c (278 mg, 56%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0108]      1 H NMR (CDCl 3 ): δ 7.77 (s, 1H), 7.60-7.69 (d, J=3.6 Hz, 1H), 7.55-7.60 (m, 1H), 7.42-7.48 (m, 2H), 7.30-7.40 (m, 4H), 6.95 (d, J=9.0 Hz, 4H), 6.81 (s, 1H), 6.68 (s, 1H), 5.00-5.50 (m, 3H), 4.84 (d, J=4.3 Hz, 1H), 4.64-4.76 (m, 3H), 3.83-4.04 (m, 7H), 3.50-3.70 (m, 2H), 3.10-3.24 (m, 4H), 2.40-2.55 (m, 2H), 2.20-2.35 (m, 2H), 1.56-2.40 (m, 6H). 
         [0109]    ESIMS: m/z 702 (M + +1). 
       Example 11 
       [0110]    To a solution of (2S)—N-[4-(5-bromopentyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2c (549 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the Ethyl-2-[4-(benzyloxy)phenyl]benzimidazol-6-carboxilate 4c (372 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 5% MeOH—CHCl 3  as eluent to afford pure compound of 9d (588 mg, 70%). 
         [0111]      1 H NMR (CDCl 3 ): δ 8.45 (s, 1H), 7.99-8.01 (dd, J=2.2, J=8.3 Hz, 1H), 7.60-7.68 (m, 3H), 7.55 (s, 1H), 7.29-7.44 (m, 5H), 7.07 (d, J=8.3 Hz, 2H), 6.57 (s, 1H), 5.13 (s, 2H), 4.82 (d, J=3.7 Hz, 1H), 4.62-4.70 (m, 1H), 4.36-4.46 (q, J=7.5 Hz, 2H), 4.25-4.35 (m, 2H), 3.85 (s, 3H), 3.84-3.29 (m, 2H), 2.65-2.85 (m, 4H), 2.17-2.32 (m, 0.2H), 1.85-2.11 (m, 6H), 1.44 (t, J=7.5 Hz, 3H), 1.29-1.39 (m, 6H) 
         [0112]    ESIMS: m/z 830 (M + +1). 
         [0113]    The compound 9d (841 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 10d (608 mg, 75%). 
         [0114]    A solution of 10d (811 mg, 1 mmol), HgCl 2  (613 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (90% CH 2 Cl 2 -MeOH) to give compound 11d (357 mg, 52%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0115]      1 H NMR (CDCl 3 ): δ 8.52 (s, 1H), 7.98-8.0 (m, 1H), 7.60-7.69 (m, 4H), 7.59 (s, 1H), 7.29-7.44 (m, 5H), 7.10 (d, J=8.3 Hz, 2H), 6.59 (s, 1H), 5.00-5.50 (m, 3H), 4.84 (d, J=4.3 Hz, 1H), 4.64-4.76 (m, 3H), 4.37-4.46 (q, J=7.5 Hz, 2H), 4.00-4.15 (m, 2H), 4.00 (s, 3H), 2.40-2.55 (m, 2H), 2.20-2.35 (m, 2H), 1.56-2.40 (m, 6H), 1.44 (t, J=7.5 Hz, 3H) 
         [0116]    ESIMS: m/z 687 (M + +1). 
       Example 12 
       [0117]    To a solution of (2S)—N-[4-(4-bromobutyl)oxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxarbaldehyde diethyl thioacetal 2b (535 mg, 1 mmol) in dry DMF (10 mL) was added anhydrous K 2 CO 3  (552 mg, 4 mmol) and the Ethyl 2-(1-methyl-3-indolyl)benzimidazol-6-carboxylate 5 (319 mg, 1 mmol). The reaction mixture was stirred at room temperature for 48 h. TLC using ethyl acetate as a solvent system monitored the reaction. The potassium carbonate was removed by suction filtration and the solvent was removed under vacuum. The crude product was purified by column chromatography using 2% MeOH—CHCl 3  as eluent to afford pure compound of 12 (472 mg, 60%). 
         [0118]      1 H NMR (CDCl 3 ): δ 8.48 (s, 1H), 7.94-8.10 (m, 3H). 7.14-7.48 (m, 5H), 6.71 (s, 1H), 4.82 (d, J=3.5 Hz, 1H), 4.62-4.71 (m, 1H), 4.47-4.52 (m, 1H), 3.80 (s, 3H), 3.86 (t, J=5.2 Hz, 2H), 3.79 (s, 3H), 3.78 (s, 3H), 3.15-3.29 (m, 2H), 2.65-2.86. (m, 4H), 2.18-2.36 (m, 2H), 1.91-2.17 (m, 4H), 1.69-1.81 m, (m, 2H), 1.29-1.40 (m, 6H). 
         [0119]    ESIMS: m/z 761 (M + +1). 
         [0120]    The compound 12 (774 mg, 1 mmol) dissolved in methanol (20 mL) and added SnCl 2 .2H 2 O (1.125 g, 5 mmol) was refluxed for 5 h or until the TLC indicated that reaction was completed. The methanol was evaporated by vacuum and the aqueous layer was then carefully adjusted to pH 8 with 10% NaHCO 3  solution and then extracted with ethyl acetate and chloroform (2×30 ml and 2×30 mL). The combined organic phase was dried over Na 2 SO 4  and evaporated under vacuum to afford the crude amino diethyl thioacetal 13 (490 mg, 80%), which was used in the directly next step. 
         [0121]    A solution of 13 (758 mg, 1 mmol), HgCl 2  (788 mg, 2.26 mmol) and CaCO 3  (246 mg, 2.46 mmol) in acetonitrile-water (4:1) was stirred slowly at room temperature for overnight or until TLC indicates complete loss of starting material. The reaction mixture was diluted with ethyl acetate (30 ml) filtered through a celite. The clear redish organic supernatant was extracted with saturated 5% NaHCO 3  (20 ml), brine (20 ml) and the combined organic phase is dried (Na 2 SO 4 ). The organic layer was evaporated in vacuum and purified by column chromatography (90% CH 2 Cl 2 —MeOH) to give compound 14 (341 mg, 55%). This material was repeatedly evaporated from CHCl 3  in vacuum to generate the imine form. 
         [0122]      1 H NMR (CDCl 3 ): δ 8.49 (s, 1H), 7.99-8.12 (m, 3H), 7.60-7.69 (d, J=3.6 Hz, 1H), 7.14-7.48 (m, 5H), 6.71 (s, 1H), 5.00-5.50 (m, 1H), 4.76 (t, J=5.0 Hz, 2H), 4.65 (t, J=6.6 Hz, 2H), 4.36 (s, 3H), 3.92 (s, 3H), 3.81 (s, 3H), 3.45-3.87 (m, 2H), 2.30-2.39 (m, 2H), 1.85-2.20 (m, 6H) 
         [0123]    ESIMS: m/z 606 (M + +1). 
       Biological Activity: 
       [0124]    DNA binding affinity of novel benzimidazole linked PBD hybrids (8a-g, 11a-d and 14): 
         [0125]    Compounds have been subjected to thermal denaturation studies with duplex-form calf thymus DNA (CT-DNA) using an modification of a reported procedure (Newman, M. S.  Carcinog - compr. Surv.  1976, 1, 203; (b) Hecht, S. S.; Loy, M.; Hoffman,  Carcinog - compr. Surv.  1976, 1, 325). Working solutions in aqueous buffer (10 mM NaH 2 PO 4 /Na 2 HPO 4 , 1 mM Na 2 EDTA, pH 7.00+0.01) containing CT-DNA (100 μm in phosphate) and the PBD (20 μm) have been prepared by addition of concentrated PBD solutions in DMSO to obtain a fixed [PBD]/[DNA] molar ratio of 1:5. The DNA-PBD solutions have been incubated at 37° C. for 0 and 18 h prior to analysis. Samples have been, monitored at 260 nm using a Beckman DU-800 spectrophotometer fitted with high performance temperature controller, and heated at 1° C. mint&#39; in the 40-110° C. range. DNA helix→coil transition temperatures (T m ) have been obtained from the maxima in the d(A 260 )/d T derivative plots. Drug-induced alterations in DNA melting behavior are given by: ΔT m =T m (DNA+PBD)−T m (DNA alone), where the T m  value for the PBD-free CT-DNA is 69.1±0.01. The fixed [PBD]/[DNA] ratio used has not resulted in binding saturation of the host DNA duplex for any compound examined. 
         [0000]    The DNA binding activity for these novel C8-linked benzimidazole-PBD hybrids has been examined by thermal denaturation studies using calf thymus (CT) DNA. Melting studies show that these compounds stabilize the thermal helix→coil or melting stabilization (ΔT m ) for the CT-DNA duplex at pH 7.0, incubated at 37° C., where PBD/DNA molar ratio is 1:5. The data for the compounds 8a-g, 11a-d and 14 is included in Table 1 for comparison. 
         [0000]                                                    TABLE 1                   Thermal denaturation data for benzimidazole linked PBD hybrids with calf       thymus (CT) DNA                [PBD]:[DNA]   (ΔT m  ° C.) a  after incubation at 37° C. for            PBD hybrids   molar ratio b     0 h   18 h                8a   1:5   5.1   6.1        8b   1:5   0.1   1.0        8c   1:5   5.1   7.0        8d   1:5   3.9   5.1        8e   1:5   0.1   1.0        8f   1:5   6.1   6.1        8g   1:5   2.0   3.1       11a   1:5   3.0   4.2       11b   1:5   1.0   1.2       11c   1:5   2.9   3.2       11d   1:5   2.0   3.0       14   1:5   1.5   2.0       DC-81   1:5   0.3   0.7                 a  For CT-DNA alone at pH 7.00 ± 0.01, T m  = 69.1° C. ± 0.01 (mean value from 10 separate determinations), all ΔT m  values are ±0.1-0.2° C.         b For a 1:5 molar ratio of [PBD]/[DNA], where CT-DNA concentration = 100 μM and ligand concentration = 20 μM in aqueous sodium phosphate buffer [10 mM sodium phosphate + 1 mM EDTA, pH 7.00 ± 0.01].            
Anticancer activity: In vitro biological activity studies were carried out at the National Cancer Institute (USA).
 
         [0126]    The compounds were evaluated for in vitro anticancer activity against sixty human tumour cells derived from nine cancer types (leukemia, non-small-cell lung, colon, CNS, melanoma, ovarian, prostate, and breast cancer) as shown in Table 3. For each compound, dose response curves for 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 8c, 8e, 11a, 11c and 14 are listed in Table 2. As demonstrated by mean graph pattern, compound 8c 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. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Log 10 GI50 log 10 TGI and log 10 LC50 mean graphs midpoints 
               
               
                 (MG_MID) of in vitro cytotoxicity data for the representative 
               
               
                 compounds against human tumour cell lines 
               
             
          
           
               
                   
                 Compound 
                 Log 10 GI50 
                 Log 10 TGI 
                 Log 10 LC50 
               
               
                   
                   
               
               
                   
                  8c 
                 −7.91 
                 −6.89 
                 −4.60 
               
               
                   
                  8e 
                 −5.81 
                 −5.18 
                 −4.51 
               
               
                   
                 11a 
                 −5.75 
                 −5.14 
                 −4.42 
               
               
                   
                 11c 
                 −5.83 
                 −5.00 
                 −4.24 
               
               
                   
                 14 
                 −6.19 
                 −5.65 
                 −4.92 
               
               
                   
                   
               
             
          
         
       
     
         [0000]                                                  TABLE 3                   Log 10  GI50 (concentration in mol/L) values for the representative       compounds 8a, 8e, 11a, 11c and 14                Cancer   8c   8e   11a   11c   14                       Leukemia   &lt;−8.00   −6.00   −5.51   −6.22   −6.88           Non-small-cell-   &lt;−7.92   −5.68   −5.80   −5.71   −6.08           lung           Colon   &lt;−7.92   −5.71   −5.72   −5.64   −6.04           CNS   &lt;−8.00   −5.80   −5.60   −5.57   −6.00           Melanoma   &lt;−7.92   −5.80   −5.66   −5.81   −6.27           Ovarian   &lt;−8.00   −5.70   −5.79   −5.66   −6.04           Renal   &lt;−7.92   −5.80   −5.85   −6.12   −6.10           Prostate   &lt;−7.64   −5.88   −5.87   −5.66   −6.62           Breast   &lt;−7.79   −6.04   −5.98   −5.81   −6.14                        
Each cancer type represents the average of six to nine different cancer cell lines.