Abstract:
This application relates to monomers of the general formula (I) for the preparation of PNA (peptide nucleic acid) oligomers and provides method for the synthesis of both predefined sequence PNA oligomers and random sequence PNA oligomers:  
                         
wherein E is sulfur or oxygen; J is nitrogen or C—R′; 
 
R1, R′ is independently H, halogen, alkyl, nitro, nitrile, alkoxy, halogenated alkyl, halogenated alkoxy or a functional group having one of following general formulae:  
                         
 
wherein A 1 , A 2 , A 3 , A 4 , A 5 , is independently selected from H, halogen such as F, Cl, Br or I, CF 3 , alkyl, preferably C 1 -C 4  alkyl, nitro, nitrile, alkoxy, preferably C 1 -C 4  alkoxy, halogenated (such as F, Cl, Br and I) alkyl, preferably halogenated C 1 -C 4  alkyl, halogenated (such as F, Cl, Br and I) alkoxy, preferably halogenated C 1 -C 4  alkoxy, phenyl, and halogenated (such as F, Cl, Br and I phenyl; 
R2 is H or protected or unprotected side chain of natural or unnatural α-amino acid; and B is a natural or unnatural nucleobase, wherein when said nucleobase has an exocyclic amino function, said function is protected by protecting group which is labile to acids but stable to weak to medium bases in the presence of thiol.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to monomers suitable for the preparation of PNA oligomers. The present invention also relates to precursors to the monomers and methods of making the PNA monomers from the precursors. Further, the invention relates to methods of making PNA oligomers using the PNA monomers.  
         [0003]     2. General Background and State of the Art  
         [0004]     In the last two decades, attempts to optimize the properties of oligonucleotide by modification of the phosphate group, the ribose ring, or the nucleobase have resulted in a lot of discoveries of new oligonucleotide derivatives for the application in the fields of DNA diagnostics, therapeutics in the form of antisense and antigene, and the basic research of molecular biology and biotechnology (U. Englisch and D. H. Gauss, Angew. Chem. Int. Ed. Engl. 1991, 30, 613-629; A. D. Mesmaeker et al. Curr. Opinion Struct. Biol. 1995, 5, 343-355; P. E. Nielsen, Curr. Opin. Biotech., 2001, 12, 16-20.). The most remarkable discovery is peptide nucleic acid which was reported by the Danish group of Nielsen, Egholm, Buchardt, and Berg (P. E. Nielsen et al., Science, 1991, 254, 1497-1500). PNA is DNA analogue in which an N-(2-aminoethyl)glycine polyamide replaces the phosphate-ribose ring backbone, and methylene-carbonyl linker connects natural as well as unnatural nucleo-bases to central amine of N-(2-aminoethyl)glycine. Despite radical change to the natural structure, PNA is capable of sequence specific binding to DNA as well as RNA obeying the Watson-Crick base pairing rule. PNAs bind with higher affinity to complementary nucleic acids than their natural counterparts, partly due to the lack of negative charge on backbone, a consequently reduced charge-charge repulsion, and favorable geometrical factors (S. K. Kim et al., J. Am. Chem. Soc., 1993, 115, 6477-6481; B. Hyrup et al., J. Am. Chem. Soc., 1994, 116, 7964-7970; M. Egholm et al., Nature, 1993, 365, 566-568; K. L. Dueholm et al., New J. Chem., 1997, 21, 19-31; P. Wittung et al., J. Am. Chem. Soc., 1996, 118, 7049-7054; M. Leijon et al., Biochemistry, 1994, 9820-9825.). Also it was demonstrated that the thermal stability of the resulting PNA/DNA duplex is independent of the salt concentration in the hybridization solution (H. Orum et al., BioTechniques, 1995, 19, 472-480; S. Tomac et al., J. Am. Chem. Soc., 1996, 118, 5544-5552.). And PNAs can bind in either parallel or antiparallel fashion, with antiparallel mode being preferred (E. Uhlman et al., Angew. Chem. Int. Ed. Engl., 1996, 35, 2632-2635.).  
         [0005]     A mismatch in a PNA/DNA duplex is much more destabilizing than a mismatch in a DNA/DNA duplex. A single base mismatch results in 15° C. and 11° C. lowering of the Tm of PNA/DNA and DNA/DNA, respectively. Homopyrimidine PNA oligomers and PNA oligomers with a high pyrimidine/purine ratio can bind to complementary DNA forming unusually stable PNA2/DNA triple helices (P. E. Nielsen et al., Science, 1991, 254, 1497-1500; L. Betts et al., Science, 1995, 270, 1838-1841; H. Knudsen et al., Nucleic Acids Res., 1996, 24, 494-500.). Although PNAs have amide bonds and nucleobases, PNAs show great resistance to both nuclease and protease. In contrast to DNA, which depurinates on treatment with strong acids and hydrolyses in alkali hydroxides, PNAs are completely acid stable and sufficiently stable to weak bases.  
         [0006]     Generally, PNA oligomers are synthesized using the well established solid phase peptide synthesis protocol. New strategies for monomers have been developed independently by several groups to optimize PNA oligomer synthesis. The preparation of PNA monomers can be divided into the synthesis of a suitably protected N-(2-aminoethyl)glycine and a suitably protected nucleobase acetic acid derivatives, which is followed by coupling both.  
         [0007]     The first synthetic strategy reported for PNA oligomer synthesis was Merrifield solid phase synthesis using t-Boc/benzyloxycarbonyl protecting group strategy wherein the backbone amino group protected with the t-Boc and the exocyclic amino groups of the nucleobases are protected with the benzyloxycarbonyl (P. E. Nielsen et al., Science, 1991, 254, 1497-1500; M. Egholm et al., J. Am. Chem. Soc., 1992, 114, 9677-9678; M. Egholm et al., J. Am. Chem. Soc., 1992, 114, 1895-1897; M. Egholm et al., J. Chem. Soc. Chem. Commun., 1993, 800-801; K. L. Dueholm et al., J. Org. Chem., 1994, 59, 5767-5773; WO 92/20702). PNA monomers protected with t-Boc/benzyloxycarbonyl are now commercially available but are inconvenient to use because repeated treatment with TFA is required for t-Boc deprotection and the harsh HF or trifluoromethanesulfonic acid treatment required for cleavage from the resin and deprotection of benzyloxycarbonyl group from exocyclic amine of nucleobases. Thus, this strategy is not compatible with the synthesis of many types of modified PNA oligomers such as PNA-DNA chimera. Furthermore, the use of hazardous acids, such as HF or trifluoromethanesulfonic acid, is not commercially embraced in view of safety concerns for the operator and the corrosive effect on automation equipment and lines. In addition, the t-Boc/benzyloxycarbonyl protection strategy is differential strategy which is defined as a system of protecting groups wherein the protecting groups are removed by the same type of reagent or condition, but rely on the different relative rates of reaction to remove one group over the other. For example, in the t-Boc/benzyloxycarbonyl protecting strategy, both protecting groups are acid labile, but benzyloxycarbonyl group requires a stronger acid for efficient removal. When acid is used to completely remove the more acid labile t-Boc group, there is a potential that a percentage of benzyloxycarbonyl group will also be removed contemporaneously. Unfortunately, the t-Boc group must be removed from amino group of backbone during each synthetic cycle for the synthesis of oligomer. Thus TFA is strong enough to prematurely deprotect a percentage of the side chain benzyloxycarbonyl group, thereby introducing the possibility of oligomer branching and reducing the overall yield of desired product.  
         [0008]     In another effort to find a milder deprotecting method for PNA oligomer synthesis that would be compatible with DNA oligomer synthesis, several research groups have developed PNA monomers protected with Mmt/acyl wherein the backbone amino group protected with the Mmt and the exocyclic amino groups of the nucleobases are protected with an acyl group such as benzoyl, anisoyl, and t-butyl benzoyl for cytosine and adenine, or isobutyryl, acetyl for guanine (D. W. Will et al., Tetrahedron, 1995, 51, 12069-12082; P. J. Finn et al., Nucleic Acid Research, 1996, 24, 3357-3363; D. A. Stetsenko et al., Tetrahedron Lett. 1996, 3571-3574; G. Breipohl et al., Tetrahedron, 1997, 14671-14686.).  
         [0009]     Alternative PNA monomers protected with Fmoc/benzhydryloxycarbonyl are also commercially available wherein the backbone amino group protected with the Fmoc and the exocyclic amino groups of the nucleobases are protected with the benzhydryloxycarbonyl (J. M. Coull, et al., U.S. Pat. No. 6,133,444). But Fmoc/benzhydryloxycarbonyl strategy has several drawbacks such as side reaction during the Fmoc deprotection process and instability of monomer in solution. The most critical side reaction is the migration of the nucleobase acetyl group from the secondary amino function to the free N-terminal amino function of aminoethylglycine backbone under Fmoc deprotection condition (L. Christensen et al., J. Pept. Sci. 1995, 1,175-183). The N-acetyl transfer reactions in every cycles during oligomer synthesis result in accumulation of side products which are hard to separate due to similar polarity and same molecular weight. Also the Fmoc protecting group is very unstable in the presence of trace amine. Thus, the selection of the solvent for the PNA monomers should be cautious. Generally, N-methylpyrrolidone of high quality is recommended. This requires higher cost in the synthesis of PNA oligomer.  
         [0010]     The synthesis of PNA oligomers using Fmoc/benzyloxycarbonyl (S. A. Thomson et al., Tetrahedron, 1995, 6179-6194.) and Fmoc/Mmt (G. Breipohl et al., Bioorg. Med. Chem. Lett., 1996, 6, 665-670.) protected monomer has also been reported. However, all of these methods have serious drawbacks in terms of monomer solubility and preparation, harsh reaction condition, and side reactions either during monomer synthesis and/or PNA oligomer synthesis.  
         [0011]     In other efforts to find new monomers, cyclic monomers were reported by ISIS and Biocept. The first strategy developed by ISIS replaces protected backbone by morpholinone (U.S. Pat. No. 5,539,083), but the strategy has serious drawback in that the hydroxy functional group generated by coupling reaction should be converted to amine functional group in every elongation step during oligomer synthesis. Alternatively, the protected aminoethylglycine part is replaced by N-t-Boc-piperazinone (WO 00/02899). However, this strategy also has several drawbacks in terms of monomer reactivity in oligomerization and the same problems as seen in linear t-Boc strategy as described above.  
         [0012]     Despite recent advances, there remains a need for new monomer that increases yield, lowers synthetic cost, and is suitable for automatic and parallel synthesis.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention provides novel monomers for increased efficiency, high yield, and convenience during synthesis of PNA oligomers. Another object is to provide PNA monomers that can be conveniently applied to instrumentation such as automated synthesizer for synthesis of PNA oligomers. The novel monomers according to the present invention are compounds having general formula I:  
                         
 
         [0014]     wherein  
         [0015]     E may be sulfur or oxygen,  
         [0016]     J may be nitrogen or C—R′ 
         [0017]     R1, R′ may be independently H, halogen such as F, Cl, Br or I, CF3, alkyl, preferably C1-C4 alkyl, or aryl having general formula:  
                         
 
         [0018]     A1, A2, A3, A4, A5, may be independently H, halogen such as F, Cl, Br or I, CF3, alkyl, preferably C1-C4 alkyl, nitro, nitrile, alkoxy, preferably C1-C4 alkoxy, halogenated (such as F, Cl, Br and I) alkyl, preferably halogenated C1-C4 alkyl, or halogenated (such as F, Cl, Br and I) alkoxy, preferably halogenated C1-C4 alkoxy, phenyl, or halogenated (such as F, Cl, Br and I) phenyl.  
         [0019]     In another embodiment, R1, R′ may be a general formula:  
                         
 
         [0020]     A1, A2, A3, A4, and A5 are as defined above.  
         [0021]     R2 may be H or protected or unprotected side chain of natural or unnatural α-amino acid, and B may be a natural or unnatural nucleobase, wherein when said nucleobase has an exocyclic amino function, said function is protected by protecting group which is labile to acids but stable to weak to medium bases in the presence of thiol. In another embodiment, B may be thymine (T), cytosine (C), adenine (A), or guanine (G).  
         [0022]     Further in particular, the protecting group for the exocyclic amino function of B has a general formula:  
                         
 
         [0023]     The group represented by R4 may have a general formula:  
                         
 
         [0024]     The residue represented by Y1-Y10 is independently selected from hydrogen, halogen, such as F, Cl, Br, alkyl, preferably methyl, ethyl, t-butyl, and alkoxy, such as methoxy, ethoxy, and t-butyloxy.  
         [0025]     In another embodiment, R4 may have a general formula:  
                         
 
         [0026]     The residue represented by Z1-Z5 is independently selected from hydrogen, halogen, such as F, Cl, Br, alkyl, preferably methyl, ethyl, t-butyl, and alkoxy, such as methoxy, ethoxy, and t-butyloxy, and methylenedioxy of adjacent two residues.  
         [0027]     The present invention further provides for methods of preparing compounds of general fromula I from compounds of general formula V:  
                         
 
         [0028]     wherein  
         [0029]     E, J, R1, R2 and B are as defined above.  
         [0030]     The protecting group of B when said nucleobase of B has an exocyclic amino function is also described above, and  
         [0031]     R3 may be H, alkyl, preferably (C1-C4) alkyl (such as methyl, ethyl, and t-butyl), or aryl.  
         [0032]     In another embodiment, the invention provides for compounds of general formula V and their preparation methods from compounds of general formula II:  
                         
 
         [0033]     wherein  
         [0034]     E, J, R1, R2 and R3 are as defined above.  
         [0035]     Also, the present invention provides compounds of formula II and their preparation methods.  
         [0036]     In another embodiment, the invention is directed to a method of making the compound of formula V, comprising coupling reaction of a compound of formula II with a nucleobase acetic acid moiety in the presence of non-nucleophilic organic base and a coupling reagent that is customarily used in peptide synthesis.  
         [0037]     The present invention further provides methods of preparing compounds of formula I from compounds of general formula IV:  
                         
 
         [0038]     wherein  
         [0039]     E, J, R1 and R2 are as defined above, and  
         [0040]     HX is organic or inorganic acid.  
         [0041]     The present invention also provides compounds of general formula IV and their free acid form, and their preparation methods.  
         [0042]     The present invention further provides methods of preparing compounds of general formula IV from compounds of general formula II.  
         [0043]     The invention is also directed to a method of making the compound of formula I, comprising coupling reaction of a compound of formula IV with a nucleobase acetic acid moiety in the presence of non-nucleophilic organic base and a coupling reagent that is customarily used in peptide synthesis.  
         [0044]     The invention is also directed to a method of making the compound of formula I, comprising cyclizing a compound of formula VI in the presence of a coupling reagent that is customarily used in peptide synthesis or mixed anhydride.  
                         
 
         [0045]     The entities represented by E, J, R1, R2, and B are as defined above. The protecting group of B when said nucleobase of B has an exocyclic amino function is also as set forth above.  
         [0046]     The invention is directed to a compound of formula II, for which its residues are defined as above. In particular, the R2 residue may be H or protected or unprotected side chain of natural α-amino acid. In other embodiments, the compound of formula II may have the following configuration: E is sulfur and R1 may be following general formula:  
                         
 
         [0047]     A1 , A2, A3, A4, A5, may be independently H, halogen such as F, Cl, Br or I, CF3, alkyl, preferably C1-C4 alkyl, nitro, nitrile, alkoxy, preferably C1-C4 alkoxy, halogenated (such as F, Cl, Br and I) alkyl, preferably halogenated C1-C4 alkyl, or halogenated (such as F, Cl, Br and I) alkoxy, preferably halogenated C1-C4 alkoxy, phenyl, or halogenated (such as F, Cl, Br and I) phenyl.  
         [0048]     The invention is also directed to a method of making the compound of formula II, comprising reacting thiadiazole-2-sulfonyl chloride, oxadiazole-2-sulfonyl chloride, thiazole-2-sulfonyl chloride, or oxazole-2-sulfonyl chloride derivative with N-(2-aminoethyl)glycine ester in the presence of non-nucleophilic organic base.  
         [0049]     The invention is further directed to a compound having formula IV and its free acid form. The residues for formula IV are as defined above. In particular, the R2 residue may be H or protected or unprotected side chain of natural α-amino acid. In other embodiments, the compound of formula IV may have the following configuration: R1 may be methyl, phenyl, 2-nitrophenyl, 4-nitrophenyl, 2-chloro-4-nitrophenyl, 4-chloro-2-nitrophenyl, 2,5-dichlorophenyl, or 2,4-dichlorophenyl; E is sulfur; J is nitrogen. In other embodiments, R1 may be H, methyl, or benzoyl; E is sulfur; J is C—CH3 or C—Ph.  
         [0050]     The invention is further directed to a method of making the compound of formula IV, comprising cyclizing a compound of formula III in the presence of a coupling reagent that is customarily used in peptide synthesis or mixed anhydride, followed by deprotection of a protection group such as t-Boc in acid.  
                         
 
         [0051]     The entities represented by E, J, R1, and R2 are as defined above.  
         [0052]     The invention is also directed to a method of making PNA oligomer, comprising linking together the compound of formula I.  
         [0053]     It is to be understood that the “R” groups, and E and J designations cited above apply to all of the compounds of formulae I-VI. It is also to be understood that the designations also apply to the compounds as they undergo the processes of the invention.  
         [0054]     These and other objects of the invention will be more fully understood from the following description of the invention, the referenced drawings attached hereto and the claims appended hereto. It is further to be understood that the chemical formulae as labeled in the figures serve as representative embodiments. The inventive chemical formulae are discussed throughout the specification. The recited chemical formulae in the figures are not meant to limit the scope of the recited compounds in any way. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0055]     The present invention will become more fully understood from the detailed description given herein below, and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein;  
         [0056]      FIG. 1  shows a chart of the chemical structures of naturally and non-naturally occurring nucleobases useful for DNA recognition.  
         [0057]      FIG. 2  shows another chart of the chemical structures of naturally and non-naturally occurring nucleobases useful for DNA recognition.  
         [0058]      FIG. 3  shows a schematic representation of the synthesis of protected backbone.  
         [0059]      FIG. 4  shows a schematic representation of the synthesis of protected piperazinone as a precursor for monomer.  
         [0060]      FIG. 5  shows a schematic representation of the synthesis of PNA monomer.  
         [0061]      FIG. 6  shows a schematic representation of the alternative synthesis of PNA monomer.  
         [0062]      FIG. 7  shows a schematic representation of the synthesis of PNA thymine monomer.  
         [0063]      FIG. 8  shows a schematic representation of the alternative synthesis of PNA thymine monomer.  
         [0064]      FIG. 9  shows a schematic representation of the synthesis of PNA cytosine monomer  
         [0065]      FIG. 10  shows a schematic representation of the synthesis of PNA adenine monomer.  
         [0066]      FIG. 11  shows a schematic representation of the synthesis of PNA guanine monomer.  
         [0067]      FIG. 12  shows a schematic representation of the PNA oligomer synthesis from PNA monomers.  
         [0068]      FIG. 13  shows HPLC result for synthesized oligomer (H2N-CGCTA-H) 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0069]     It is to be understood that the formulae depicted in the drawings are merely exemplified versions, and where a particular formula is referred to in the claims, the version discussed in the text of the specification is meant.  
         [0070]     In the present invention, 1,3,4-thiadiazole-2-sulfonyl, 1,3,4-oxadiazole-2-sulfonyl, thiazole-2-sulfonyl or oxazole-2-sulfonyl group of compounds having general formula I play an important role not only as protecting groups of amine of backbone but also as activating groups for coupling reaction. The monomers having described characteristics are useful for the synthesis of PNA oligomers by manual or automated synthesizer and the preparation of PNA oligomer library by combinatorial chemistry. Nucleobase B in the general formula I is naturally attached at the position found in nature, i.e., position 1 for thymine or cytosine, and position 9 for adenine or guanine, as well as for non-naturally occurring nucleobase (nucleobase analog), or nucleobase binding moiety. Some nucleobases and illustrative synthetic nucleobases are shown in  FIG. 1  and  FIG. 2 .  
         [0071]     Preparation of Protected Backbones  
         [0072]     The first step for the preparation of novel monomers having general formula I is synthesis of N-[2-(1,3,4-thiadiazole, 1,3,4-oxadiazole, thiazole or oxazole-2-sulfonylamino)-ethyl]-glycine derivatives having the formula II:  
                         
 
         [0073]     wherein E is sulfur and J is nitrogen for N-[2-(1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-glycine derivatives; E is oxygen and J is nitrogen for N-[2-(1,3,4-oxadiazole-2-sulfonylamino)-ethyl]-glycine derivatives; E is sulfur and J is C—R′ for N-[2-(thiazole-2-sulfonylamino)-ethyl]-glycine derivatives; E is oxygen and J is C—R′ for N-[2-(oxazole-2-sulfonylamino)-ethyl]-glycine derivatives; and R′, R1, R2, and R3 are as defined above.  
         [0074]     Derivatives having formula II are generally synthesized by selective reaction of primary amine of N-(2-aminoethyl)glycine derivatives with sulfonyl chloride compounds having the general formula:  
                         
 
         [0075]     wherein E is sulfur and J is nitrogen for 1,3,4-thiadiazole-2-sulfonyl chloride derivatives; E is oxygen and J is nitrogen for 1,3,4-oxadiazole-2-sulfonyl chloride derivatives; J is C—R′ and E is sulfur for thiazole-2-sulfonyl chloride derivatives; J is C—R′ and E is oxygen for oxazole-2-sulfonyl chloride derivatives; and R′, and R1 are as defined above.  
         [0076]     For an example of preparing derivatives having formula II, N-[2-(1,3,4-thiadiazole or thiazole-2-sulfonylamino)-ethyl]-glycine derivatives are synthesized by selective reaction of primary amine of N-(2-aminoethyl)glycine derivatives prepared by known methods (for instance, where R2 is H, see S. A. Thomson et al., Tetrahedron, 1995, 6179-6194; where R2 is a side chain of a protected or unprotected natural or unnatural amino acid, see A. Puschl et al., Tetrahedron Lett., 1998, 39, 4707-4710). 1,3,4-thiadiazole-2-sulfonyl chloride or thiazole-2-sulfonyl chloride derivatives are prepared from the corresponding 2-mercapto-1,3,4-thiadiazole or 2-mercapto-thiazole derivatives by the same procedure of synthesis of benzothiazole-2-sulfonyl chloride (E. Vedejs, et al., J. Am. Chem. Soc., 1996, 118, 9796-9797.).  
         [0077]     The coupling reaction for the preparation of N-[2-(1,3,4-thiadiazole, 1,3,4-oxadiazole, thiazole, or oxazole-2-sulfonylamino)-ethyl]-glycine derivatives is performed by slow addition of 1,3,4-thiadiazole-2-sulfonyl chloride, 1,3,4-oxadiazole-2-sulfonyl chloride, thiazole-2-sulfonyl chloride, or oxazole-2-sulfonyl chloride to a solution of N-(2-aminoethyl)-glycine derivatives in the presence of non-nucleophilic organic base at ambient temperature. Examples of solvents of above reaction include without limitation water, toluene, benzene, ethyl acetate, tetrahydrofuran, diisopropyl ether, diethyl ether, dichloromethane, chloroform, carbon tetrachloride, and acetonitrile. Preferred solvent is dichloromethane. Examples of non-nucleophilic organic bases include, but are not limited to, triethylamine, tripropylamine N,N-diisopropylethylamine, N-methylmorpholine, and N-ethylmorpholine. Preferred non-nucleophilic organic base is triethylamine. After completion of the reaction by monitoring by thin layer chromatography (TLC), the reaction mixture is washed with water, dried, and evaporated in reduced pressure to give the desired product.  
         [0078]     Preparation of 1-(1,3,4-thiadiazole, 1,3,4-oxadiazole, thiazole, or oxazole-2-sulfonyl)-piperazin-2-ones  
         [0079]     The first precursor synthons having formula IV for synthesis of monomers having general formula I are prepared from N-[2-(1,3,4-thiadiazole, 1,3,4-oxadiazole, thiazole, or oxazole-2-sulfonylamino)-ethyl]-glycine derivatives having the formula II by hydrolysis, protection of secondary amine, cyclization, and deprotection of protecting group of secondary amine ( FIG. 4 ).  
                         
 
         [0080]     The entities represented by E, J, R1, R2, and HX may be as defined above.  
         [0081]     First, N-[2-(1,3,4-thiadiazole, 1,3,4-oxadiazole, thiazole, or oxazole-2-sulfonylamino)-ethyl]-glycine derivatives having the formula II are converted to corresponding acids by adding excess hydroxide ion source. Preferred R3 in the formula II is methyl or ethyl. Examples of hydroxide ion sources include, but are not limited to, lithium hydroxide, sodium hydroxide, and potassium hydroxide. Preferred hydroxide ion source is lithium hydroxide. The reaction mixture without work-up is then treated with a protecting group such as di-t-butyl dicarbonate to protect secondary amine to obtain a compound having the general formula III:  
                         
 
         [0082]     The entities represented by E, J, R1, and R2 are as defined above.  
         [0083]     Preferred hydrolysis reaction is carried out by adding an aqueous solution of lithium hydroxide (2 equivalent) to a solution of N-[2-(1,3,4-thiadiazole, 1,3,4-oxadiazole, thiazole, or oxazole-2-sulfonylamino)-ethyl]-glycine ester derivative at ambient temperature. After completion of the reaction by monitoring by thin layer chromatography (TLC), di-t-butyl dicarbonate (1.5 equivalent) and an aqueous solution of lithium hydroxide (additional 1 equivalent) are added to the reaction mixture. The reaction mixture is stirred for sufficient time. Then the excess di-t-butyl dicarbonate is removed by extraction with ethyl acetate. The aqueous solution is then acidified, extracted with dichloromethane, dried, and evaporated in reduced pressure to yield a solid. Examples of solvents of above reaction are aqueous tetrahydrofuran, aqueous dioxane, and aqueous 1,2-dimethoxyethane. Preferred solvent is aqueous tetrahydrofuran.  
         [0084]     Second, the cyclization reaction of carboxylic acids having general formula III and followed by deprotection of t-Boc produces piperazinone derivatives having general formula IV. The cyclization reaction occurs simultaneously during activation of carboxylic acid. The activation of carboxylic acid can be conducted by general coupling reagent for peptide synthesis at ambient temperature. Examples of coupling reagents include, but are not limited to, HATU, HOAt, HODhbt (L. A. Carpino et al., J. Am. Chem. Soc., 1993, 115, 4397-4398), HAPyU, TAPipU (A. Ehrlich et al., Tetrahedron Lett., 1993, 4781-4784), HBTU (V. Dourtoglou et al., Synthesis, 1984, 572-574), TBTU, TPTU, TSTU, TNTU (R. Knorr et al., Tetrahedron Lett., 1989, 1927-1930), TOTU, BOP (B. Castro et al., Tetrahedron Lett., 1975, 1219-1222), PyBOP (J. Coste et al., Tetrahedron Lett., 1990, 205-208), BroP (J. Coste et al., Tetrahedron Lett., 1990, 669-672), PyBroP (J. Coste et al., Tetrahedron Lett., 1991, 1967-1970), BOI (K. Akaji et al., Tetrahedron Lett., 1992, 3177-3180), MSNT (B. Blankemeyer-Menge et al., Tetrahedron Lett., 1990, 1701-1704), TDO (R. Kirstgen et al., J. Chem. Soc., Chem. Commun., 1987, 1870-1871), DCC, EDCI, CDI (H. A. Staab, Justus Liebigs Ann. Chem., 1957, 609, 75.), HOBt (W König et al., Chem. Ber., 1970, 103, 788, 2024, 2034), HOSu (E. Wünsch et al., Chem. Ber., 1966, 99, 110), NEPIS (R. B. Woodward et al.,. J. Am. Chem. Soc., 1961, 83, 1010), BBC (S. Chen et al., Tetrahedron Lett. 1992, 33, 647), BDMP (P, Li et al., Chem. Lett., 1999, 1163), BOMI (P, Li et al., Tetrahedron Lett., 1999, 40, 3605), AOP (L. A Carpino et al., Tetrahedron Lett., 1994, 35, 2279), BDP (S. Kim et al., Tetrahedron Lett., 1985, 26, 1341), PyAOP (F. Albericio et al., Tetrahedron Lett. 1997, 38, 4853), TDBTU (R. Knorr et al., Tetrahedron Lett. 1989, 30, 1927), BEMT (P. Li et al., Tetrahedron Lett. 1999, 40, 8301), BOP-Cl (J. Diago-Meseguer et al., Synthesis 1980, 547), BTFFH, TFFH (A. El-Faham et al. Chem. Lett., 1998, 671), CIP (K. Akaji, et al., Tetrahedron Lett., 1994, 35, 3315), DEPBT (H. Li et al. Organic Lett. 1999, 1, 91), Dpp-Cl (R. Ramage et al., J. Chem. Soc., Perkin Trans I, 1985, 461), EEDQ (B Belleau et al., J. Am. Chem. Soc., 1968, 90, 1651), FDPP (S Chen et al., Tetrahedron Lett., 1991, 32, 6711), HOTT, TOTT (M. A. Bailén et al., J. Org. Chem. 1999, 64, 8936), PyCloP (J. Coste et al., Tetrahedron Lett., 1991, 32, 1967 and J. Coste et al., J. Org. Chem., 1994, 59, 2437). The solvents may be selected from tetrahydrofuran, dichloromethane, chloroform, DMF, and N-methylpyrrolidone. Preferred solvent is DMF.  
         [0085]     Alternatively, the activation of carboxylic acid can be conducted by formation of mixed anhydride using alkyl chloroformate or alkanoyl chloride with non-nucleophilic organic base. Examples of anhydrous appropriate solvents include, but are not limited to, acetonitrile, chloroform, dichloromethane, 1,2-dimethoxyethane, diethyl ether, diisoproyl ether, and tetrahydrofuran. Preferred solvents are dichloromethane and tetrahydrofuran. The most preferred reaction temperature is in which the reaction mixture is allowed to slowly warm to 0° C. after completing addition of isobutyl chloroformate at −20° C.  
         [0086]     With reference to  FIG. 4 , the t-Boc group is deprotected in the presence of acid. Examples of acids include, but are not limited to, HCl, HBr, HF, HI, nitric acid, sulfuric acid, methanesulfonic acid, TFA, and trifluoromethanesulfonic acid. Preferred acid is TFA. The solvents used in the deprotection reaction may include without limitation dichloromethane, chloroform, carbon tetrachloride, ethyl acetate, toluene, and benzene. Preferred solvent is dichloromethane.  
         [0087]     Synthesis of PNA Monomer  
         [0088]     According to a method of this invention, PNA monomers having general formula I may be synthesized by at least two methods. With reference to  FIG. 5 , the first approach to PNA monomer syntheses is a method that introduces protected or unprotected nucleobase acetic acid moieties to protected linear backbone prior to cyclization reaction. Alternatively, PNA monomers may be synthesized by beginning with cylization of protected linear backbone, followed by deprotection of cyclized backbone and coupling of protected or unprotected nucleobase acetic acid moieties to create desired products.  
         [0089]     Method 1  
         [0090]     The linear moieties having general formula V are prepared from protected linear backbone having general formula II by acylation of nucleobase acetic acid moieties using coupling reagents as shown in  FIG. 5 .  
         [0091]     With reference to  FIG. 5 , the coupling reaction was conducted by addition of coupling reagent to the mixture of protected linear backbone having general formula II, nucleobase acetic acid moieties, and non-nucleophilic organic base in anhydrous appropriate solvent. Examples of coupling reagents include, but are not limited to, HATU, HOAt, HODhbt, HAPyU, TAPipU, HBTU, TBTU, TPTU, TSTU, TNTU, TOTU, BOP, PyBOP, BroP, PyBroP, BOI, MSNT, TDO, DCC, EDCI, CDI, HOBt, HOSu, NEPIS, BBC, BDMP, BOMI, AOP, BDP, PyAOP, TDBTU, BOP-Cl, CIP, DEPBT, Dpp-Cl, EEDQ, FDPP, HOTT, TOTT, PyCloP. Preferred coupling reagent is PyBOP or EDCI. Examples of non-nucleophilic organic bases include, but are not limited to, triethylamine, tripropylamine, N,N-diisopropylethylamine, N-methylmorpholine, and N-ethylmorpholine. Preferred non-nucleophilic organic base is N,N-diisopropylethylamine. Examples of anhydrous appropriate solvents include, but are not limited to, chloroform, dichloromethane, 1,2-dimethoxyethane, tetrahydrofuran, DMF, and N-methylpyrrolidone. Preferred solvent is DMF.  
                         
 
         [0092]     The entities represented by E, J, R1, R2, R3 and B are as defined above.  
         [0093]     Compounds having the general formula V are converted to corresponding acids such as formula VI by adding an excess of hydroxide ion source. Preferably, R3 may be a methyl or ethyl. Examples of hydroxide ion sources include, but are not limited to, lithium hydroxide, sodium hydroxide, and potassium hydroxide. Preferred hydroxide ion source is lithium hydroxide.  
                         
 
         [0094]     The entities represented by E, J, R1, R2, and B are as defined above.  
         [0095]     Further, with reference to  FIG. 5 , the cyclization reaction of carboxylic acids produces PNA monomers having the general formula I by simultaneous reaction during activation of carboxylic acid. The activation of carboxylic acid may be conducted by general coupling reagent for peptide synthesis at ambient temperature. Examples of coupling reagents include, but are not limited to, HATU, HOAt, HODhbt, HAPyU, TAPipU, HBTU, TBTU, TPTU, TSTU, TNTU, TOTU, BOP, PyBOP, BroP, PyBroP, BOI, MSNT, TDO, DCC, EDCI, CDI, HOBt, HOSu, NEPIS, BBC, BDMP, BOMI, AOP, BDP, PyAOP, TDBTU, BOP-Cl, CIP, DEPBT, Dpp-Cl, EEDQ, FDPP, HOTT, TOTT, PyCLoP. Preferred coupling reagent is EDCI or PyBOP. Examples of non-nucleophilic organic bases include, but are not limited to, triethylamine, tripropylamine, N,N-diisopropylethylamine, N-methylmorpholine, and N-ethylmorpholine. Preferred non-nucleophilic organic base is N,N-diisopropylethylamine. The solvents may be without limitation selected from tetrahydrofuran, dichloromethane, chloroform, DMF, or N-methylpyrrolidone. Preferred solvent is DMF. Alternatively, the activation of carboxylic acid can be conducted by formation of mixed anhydride using alkyl chloroformate or alkanoyl chloride with non-nucleophilic organic base. Examples of alkyl haloformates or alkanoyl chlorides include, but are not limited to, methyl chloroformate, ethyl chloroformate, propyl chloroformate, butyl chloroformate, isobutyl chloroformate, pivaloyl chloride, and adamantine carboxyl chloride. The most preferred acid chloride is isobutyl chloroformate. The cyclization reaction using isobutyl chloroformate is carried out by slowly adding isobutyl chloroformate to a reaction solution of carboxylic acid and non-nucleophilic organic base in an anhydrous appropriate solvent at a temperature between −30° C. and 10° C. Examples of non-nucleophilic organic bases include, but are not limited to, triethylamine, tripropylamine, N,N-diisopropylethylamine, N-methylmorpholine, and N-ethylmorpholine. Preferred non-nucleophilic organic base is N-methylmorpholine. Examples of anhydrous appropriate solvents include, but are not limited to, acetonitrile, chloroform, dichloromethane, 1,2-dimethoxyethane, diethyl ether, diisoproyl ether, and tetrahydrofuran. Preferred solvents are dichloromethane and tetrahydrofuran. Preferred reaction temperature is in which the reaction mixture is allowed to slowly warm to about 0° C. after completing addition of isobutyl chloroformate at −20° C.  
         [0096]     Method 2  
         [0097]     As an alternative method, PNA monomers according to this invention may be prepared by coupling of protected or unprotected nucleobase acetic acid moieties to cyclic precursor having the general formula IV:  
                         
 
         [0098]     The entities represented by E, J, R1, R2, and HX may be as defined above.  
         [0099]     With reference to  FIG. 6 , the coupling reaction of cyclic precursor with protected or unprotected nucleobase acetic acid moieties is carried out by using general coupling reagent for peptide synthesis and non-nucleophilic organic bases at ambient temperature. Examples of coupling reagents include, but are not limited to, HATU, HOAt, HODhbt, HAPyU, TAPipU, HBTU, TBTU, TPTU, TSTU, TNTU, TOTU, BOP, PyBOP, BroP, PyBroP, BOI, MSNT, TDO, DCC, EDCI, CDI, HOBt, HOSu, NEPIS, BBC, BDMP, BOMI, AOP, BDP, PyAOP, TDBTU, BOP-Cl, CIP, DEPBT, Dpp-Cl, EEDQ, FDPP, HOTT, TOTT, PyCloP. Preferred coupling reagent is PyBOP. Examples of non-nucleophilic organic bases include, but are not limited to, triethylamine, tripropylamine, N,N-diisopropylethylamine, N-methylmorpholine, and N-ethylmorpholine. Preferred non-nucleophilic organic base is N,N-diisopropylethylamine. The solvent may be without limitation tetrahydrofuran, dichloromethane, chloroform, DMF, or N-methylpyrrolidone. Preferred solvent is DMF.  
         [0100]     Nucleobases and Protecting Group  
         [0101]     Examples of nucleobases of this invention include, but are not limited to, adenine, cytosine, guanine, thymine, uridine, 2,6-diaminopurine, and naturally or non-naturally occurring nucleobases as depicted in  FIG. 1  and  FIG. 2 . Preferred nucleobases are adenine, cytosine, guanine, and thymine. Nucleobases may be protected by protecting group for the syntheses of PNA oligomers. Protecting groups may be, but are not limited to, Boc, adamantyloxycarbonyl, benzyloxycarbonyl (P. E. Nielsen et al., Science, 1991, 254, 1497-1500; M. Egholm et al., J. Am. Chem. Soc., 1992, 114, 9677-9679; M. Egholm et al., J. Am. Chem. Soc., 1992, 114, 1895-1897; M. Egholm et al., J. Chem. Soc. Chem. Commun., 1993, 800-801; K. L. Dueholm et al., J. Org. Chem., 1994, 59, 5767-5773; WO 92/20702), 4-methoxybenzyloxycarbonyl, 3,4-dimethoyxbenzyloxycarbonyl, benzhydryloxycarbonyl (U.S. Pat. No. 6,133,444), piperonyloxycarbonyl derivatives, 2-methylthioethoxycarbonyl (U.S. Pat. No. 6,063,569), Mmt (G. Breipohl et al., Bioorg. Med. Chem. Lett., 1996, 6, 665-670), or acid labile protecting group (T. W. Greene and P. G. M. Wuts, Protective Group in Organic Synthesis, 3rd Edition, pp 494˜653).  
         [0102]     Synthesis of T-Monomer  
         [0103]     T-monomer is a compound having general formula I-t:  
                         
 
         [0104]     The entities represented by E, J, R1, and R2 are as defined above.  
         [0105]     The precursor for T-monomer, (thymin-1-yl)-acetic acid (shown below), is prepared by known methods (K. L. Dueholm et. al., J. Org. Chem., 1994, 59, 5767-5773; WO 92/20702).  
                         
 
         [0106]     With reference to  FIG. 7 , the compounds of general formula V-t are prepared by coupling reaction of (thymin-1-yl)-acetic acid with 1,3,4-thiadiazole or thiazole-2-sulfonyl group protected backbone ester having general formula II in the presence of coupling reagent to afford the compound having general formula:  
                         
 
         [0107]     The entities represented by E, J, R1, R2, and R3 are as defined above.  
         [0108]     Preferred R3 is methyl or ethyl.  
         [0109]     The compounds having the general formula V-t are converted to corresponding acids by adding an excess hydroxide ion source to afford the compound having general formula VI-t.  
                         
 
         [0110]     The entities represented by E, J, R1, and R2 are as defined above.  
         [0111]     With reference to  FIG. 7 , the cyclization reaction of carboxylic acids produces PNA T-monomers having general formula I-t by simultaneous reaction during activation of carboxylic acid. The activation of carboxylic acid may be conducted by general coupling reagent for peptide synthesis or mixed anhydride. The reaction conditions and reagents are the same as described above.  
         [0112]     Alternatively, as seen in  FIG. 8 , PNA T-monomers can be prepared by coupling (thymin-1-yl)-acetic acid to piperazinone derivatives having general formula IV. The reaction conditions and reagents are the same as described above.  
         [0113]     Synthesis of C-Monomer  
         [0114]     C-monomer is a compound having general formula I-c:  
                         
 
         [0115]     The entities represented by E, J, R1, R2, R3, and R4 are as defined above.  
         [0116]     The precursors for PNA C-monomers, suitably protected (cytosin-1-yl)-acetic acids (shown below), are prepared by the known methods such as described in U.S. Pat. No. 6,133,444; U.S. Pat. No. 6,063,569; Dueholm, et al., J. Org. Chem., 1994, 59, 5767-5773; and WO 92/20702, which are incorporated by reference herein in their entirety, or modifications thereof.  
                         
 
         [0117]     R4 may be benzyl, benzhydryl, 4-methoxybenzyl, or piperonyl derivatives.  
         [0118]     With reference to  FIG. 9 , PNA C-monomer is prepared by coupling reaction of suitably protected (cytosin-1-yl)-acetic acids with a 1,3,4-thiadiazole or thiazole-2-sulfonyl group protected backbone ester having general formula II in the presence of coupling reagent to afford the compound having general formula:  
                         
 
         [0119]     The entities represented by E, J, R1, R2, R3, and R4 are as defined above.  
         [0120]     The compounds having the general formula V-c are converted to corresponding acids by adding an excess of hydroxide ion source to obtain a compound having general formula VI-c:  
                         
 
         [0121]     The entities represented by E, J, R1, R2, and R4 are as defined above.  
         [0122]     With reference to  FIG. 9 , the cyclization reaction of carboxylic acids produces PNA monomers having the general formula I-c by simultaneous reaction during activation of carboxylic acid. The activation of carboxylic acid may be conducted by general coupling reagent for peptide synthesis or mixed anhydride. The reaction conditions and reagents are the same as described above.  
         [0123]     Alternatively, PNA C-monomer can be prepared by coupling suitably protected (cytosin-1-yl)-acetic acids to piperazinone derivatives having general formula IV. The reaction conditions and reagents are the same as described above.  
         [0124]     Synthesis of A-monomer  
         [0125]     A-monomer is a compound having general formula I-a:  
                         
 
         [0126]     The entities represented by E, J, R1, R2, and R4 are as defined above.  
         [0127]     The precursors for PNA A-monomers, suitably protected (adenin-9-yl)-acetic acids (shown below), are prepared by the known methods such as described in U.S. Pat. No. 6,133,444; and S. A. Thomson et al., Tetrahedron, 1995, 6179-6194, which are incorporated by reference herein in their entirety, or modifications thereof.  
                         
 
         [0128]     R4 is selected from benzyl, benzhydryl, 4-methoxybenzyl, and piperonyl derivatives.  
         [0129]     With reference to  FIG. 10 , PNA A-monomer is prepared by coupling reaction of suitably protected (adenin-9-yl)-acetic acids with a 1,3,4-thiadiazole or thiazole-2-sulfonyl group protected backbone ester having general formula II in the presence of coupling reagent to obtain the compound having general formula V-a:  
                         
 
         [0130]     The entities represented by E, J, R1, R2, R3, and R4 are as defined above.  
         [0131]     The compounds having the general formula V-a are converted to corresponding acids by adding an excess hydroxide ion source to afford the compound having general formula VI-a:  
                         
 
         [0132]     The entities represented by E, J, R1, R2, and R4 are as defined above.  
         [0133]     With reference to  FIG. 12 , the cyclization reaction of carboxylic acids produces PNA monomers having the general formula I-a by simultaneous reaction during activation of carboxylic acid. The activation of carboxylic acid can be conducted by general coupling reagent for peptide synthesis or mixed anhydride. The reaction conditions and reagents are the same as described above.  
         [0134]     Alternatively, PNA A-monomer can be prepared by coupling suitably protected (adenin-9-yl)-acetic acids to piperazinone derivatives having general formula IV. The reaction conditions and reagents are the same as described above.  
         [0135]     Synthesis of G-Monomer  
         [0136]     G-monomer is a compound having general formula I-g:  
                         
 
         [0137]     The entities represented by E, J, R1, R2, and R4 are as defined above.  
         [0138]     The precursors for PNA G-monomers, suitably protected (guanin-9-yl)-acetic acids (shown below), are prepared by the known methods such as described in U.S. Pat. No. 6,172,226, or modifications thereof.  
                         
 
         [0139]     R4 may be benzyl, benzhydryl, 4-methoxybenzyl, or piperonyl derivatives.  
         [0140]     With reference to  FIG. 11 , PNA G-monomer is prepared by coupling reaction of suitably protected (guanin-9-yl)-acetic acids with a 1,3,4-thiadiazole or thiazole-2-sulfonyl group protected backbone ester having general formula II in the presence of coupling reagent to afford the compound having general formula V-g:  
                         
 
         [0141]     The entities represented by E, J, R1, R2, R3, and R4 are as defined above.  
         [0142]     The compounds having the general formula V-g are converted to corresponding acids by adding an excess hydroxide ion source to afford the compound having general formula VI-g:  
                         
 
         [0143]     The entities represented by E, J, R1, R2, and R4 are as defined above.  
         [0144]     With reference to  FIG. 11 , the cyclization reaction of carboxylic acids produces PNA monomers having the general formula I-g by simultaneous reaction during activation of carboxylic acid. The activation of carboxylic acid can be conducted by general coupling reagent for peptide synthesis or mixed anhydride. The reaction conditions and reagents are the same as described above.  
         [0145]     Alternatively, PNA G-monomer can be prepared by coupling suitably protected (guanin-9-yl)-acetic acids to piperazinone derivatives having general formula IV. The reaction conditions and reagents are the same as described above.  
         [0146]     Synthesis of PNA Oligomers  
         [0147]     Various combinatorial synthetic methods already reported in chemical literature are generally applicable to PNA oligomer synthesis using the monomers of this invention. These methods include, but are not limited to, solid phase synthesis and solution phase synthesis. After the PNA monomers have been synthesized in the manner described above, PNA oligomers are constructed by solid phase synthesis on a suitable support material such as, but not limited to, polystyrene, polyoxyethylene-modified polystyrene, such as, for example CLEAR®, Tentagel® or Controlled Pore Glass, which is provided with anchoring group which latently contains cleavable amine functional group. In solid phase synthesis, the first PNA monomer of this invention is incorporated by coupling reaction to solid support. The next step is systematic elaboration of desired PNA oligomer sequence. This elaboration includes repeated deprotection/coupling/capping cycles. The backbone protecting group on the last coupled monomer, 1,3,4-thiadiazole-2-sulfonyl or thiazole-2-sulfonyl group is quantitatively removed by treatment with suitable thiol in the presence of organic base to liberate terminal free amine. Once the synthesis of PNA oligomer has been completed, the oligomers are cleaved from the solid support and nucleobase protecting groups are simultaneously removed by incubation for 1-2 h. at about room temperature in TFA containing cresol as a cation scavenger.  
         [0148]     Following is an example of a general reaction cycle that may be used for the synthesis of PNA oligomers, and is not meant to limit the invention in any way, such as in the sequence of steps, since any oligomer synthesis method may be generally used so long as the inventive PNA monomer is employed.  
         [0149]     1. Removing protecting group from resin to activate amine functional group.  
         [0150]     2. Incorporating amino-acid, linker, or PNA monomer having terminal protected amine group to resin.  
         [0151]     3. Washing.  
         [0152]     4. Capping with acetic anhydride in the presence of organic base.  
         [0153]     5. Washing.  
         [0154]     6. Cleavage over reacted acetyl group in sulfonamide.  
         [0155]     7. Washing.  
         [0156]     8. Deprotecting sulfonyl group.  
         [0157]     9. Washing.  
         [0158]     10. Adding monomer.  
         [0159]     11. Returning to No. 3 and repeating No. 4-No. 11.  
         [0160]     In the course of the coupling reaction of monomer for the oligomer synthesis reaction, the acylating reaction can be accelerated by using a catalyst such as but not limited to mercury acetate, tetramethylammonium fluoride, tetraethylammonium fluoride, tetrabutylammonium fluoride, benzyltrimethylammonium fluoride, cesium fluoride, tributylphosphine, triphenylphosphine. Preferred catalyst is tetrabutylammonium fluoride. Also, the reaction rate depends on the solvent used and reaction temperature. Examples of solvents include, but are not limited to, DMF, N-methylpyrrolidone, dimethoxyethane, dichloromethane, 1,2-dichloroethane, DMSO, tetrahydrofuran, hexamethylphophoramide, tetramethylene sulfone, isopropyl alcohol, ethyl alcohol, and mixture of solvents. Preferred solvent is DMF. The N-terminal amino protecting group is cleaved by using thiol with organic base in solvent. Examples of thiols include, but are not limited to, C2˜C20 alkanethiol, 4-methoxytoluenethiol, 4-methylbenzenethiol, 3,6-dioxa-1,8-octanethiol, 4-chlorotoluenethiol, benzylmercaptane, N-acetylcysteine, N-(t-Boc)cysteine methyl ester, methyl 3-mercaptopropionate, 4-methoxybenzenethiol. Examples of organic bases include, but are not limited to, triethylamine, N,N-diisopropyethylamine, piperidine, N-methylmorpholine, and 1,8-diazabicyclo[5,4,0]undec-7-one. Preferred organic base is N,N-diisopropylethylamine.  
         [0161]     List of abbreviations. 
    t-Boc tert-Butyloxycarbonyl     AOP O-(7-azabenzotriazol-1-yl)-tris(dimethylamino)phosphonium     BBC 1-benzotriazol-1-yloxy-bis(pyrrolidino)uronium hexafluorophosphate     BDMP 5-(1H-benzotriazol-1-yloxy)-3,4-dihydro-1-methyl 2H-pyrrolium hexachloroanitimonate     BDP benzotriazol-1-yl diethyl phosphate     BEMT 2-bromo-3-ethyl-4-methyl thiazolium tetrafluoroborate     BTFFH bis(tetramethylenefluoroformamidinium) hexafluorophosphate     BOMI benzotriazol-1-yloxy-N,N-dimethylmethaniminium hexachloroantimonate    
 
         [0170]     BOI 2-(benzotriazol-1-yl)oxy-1,3-dimethyl-imidazolinium hexafluorophosphate 
    BOP benzotriazolyl-1-oxy-tris(dimethylamino)phophonium hexafluorophosphate     BOP—Cl bis(2-oxo-3-oxazolidinyl)phosphinic chloride     BroP bromotris(dimethylamino)phophonium hexafluorophosphate     CDI carbonyldiimidazole     CIP 2-chloro-1,3-dimethylimidazolidinium hexafluorophosphate     DMF dimethylformamide     DCC 1,3-dicyclohexylcarbodiimide     DEPBT 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one     Dpp-Cl diphenylphosphinic chloride     EDCI 1-ethyl-3-(3′-dimethylaminopropyl)carbodiimide hydrochloride     EEDQ 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline     Fmoc 9-fluorenylmethyloxycarbonyl     FDPP pentafluorophenyl diphenylphosphinate     HAPyU O-(7-azabenzotriazol-1-yl)-1,1,3,3-bis(tetramethylene)uranium hexafluorophosphate     HATU O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluranium hexafluorophosphate     HBTU O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluranium hexafluorophosphate     HOBt hydroxybenzotriazole     HOAt 1-hydroxy-7-azabenzotriazole     HODhbt 3-hydroxy-3,4-dihydro-4-oxo-1,2,3-benzotriazine     HOSu hydroxysuccinimide     HOTT S-(1-oxido-2-pyridinyl)-1,1,3,3-tetramethylthiouronium hexafluorophosphate     MSNT 2,4,6-mesitylenesulfonyl-3-nitro-1,2,4-triazolide     Mmt 4-methoxyphenyldiphenylmethyl     NEPIS N-ethyl-5-phenylisoxazolium-3′-sulfonate     PyAOP 7-azobenzotriazolyoxytris(pyrrolidino)phosphonium hexafluorophosphate     PyBOP benzotriazolyl-1-oxy-tripyrrolidinophosphonium hexafluorophosphate     PyBroP bromotripyrrolidinophosphonium hexafluorophosphate     PyCloP chlorotris(pyrrolydino)phophonium hexafluorophosphate     TAPipU O-(7-azabenzotriazol-1-yl)-1,1,3,3-bis(pentamethylene)uranium tetrafluoroborate     TBTU O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluranium tetrafluoroborate     TDO 2,5-diphenyl-2,3-dihydro-3-oxo-4-hydroxythiophene dioxide     TFA trifluoroacetic acid     TFFH tetramethylfluoroformamidinium hexafluorophosphate     TOTT S-(1-oxido-2-pyridinyl)-1,1,3,3-tetramethylthiouronium tetrafluoroborate     TDBTU 2-(3,4-dihydro-4-oxo-1,2,3-benzotriazin-3-yl)-1,1,3,3-tetramethyluronium     tetrafluoroborate     TNTU O-[(5-norbonene-2,3-dicarboximido)-1,1,3,3-tetramethyluronium tetrafluoroborate     TOTU O-[(cyano(ethoxycarbonyl)methylene)amino]-1,1,3.3-tetramethyluronium tetrafluoroborate     TPTU O-(1,2-dihydro-2-oxo-1-pyridyl-1,1,3,3-tetramethyluronium tetrafluoroborate     TSTU O-(N-succinimidyl)-1,1,3,3-tetramethyluronium tetrafluoroborate    
 
         [0211]     This invention is more specifically illustrated by following Examples, which are not meant limit the invention, unless otherwise noted.  
       EXAMPLES  
     Example 1  
     N-{2-[5-(4-Chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine Ethyl Ester  
       [0212]     To a solution of N-(2-aminoethyl)-glycine ethyl ester 2HCl (1.4 g, 6.4 mmol), prepared as described by Will (D. W. Will et al.,  Tetrahedron,  1995, 51, 12069.), in dichloromethane (50 mL) was added 5-(4-chlorophenyl)-1,3,4-thiadiazole-2-sulfonyl chloride (1.5 g, 5.1 mmol) at 0° C. Then triethylamine (2.7 mL) was slowly added. The resulting reaction mixture was stirred for additional 2 h. at room temperature and washed with water (30 mL). The organic layer was dried over MgSO 4  and filtered. The filtrate was concentrated, followed by column chromatography to give the title compound (1.1 g, 2.7 mmol, 53%) as a solid.  1 H NMR (500 MHz; DMSO-d 6 ) δ 8.08 (d, 2H), 7.66 (d, 2H), 4.03 (q, 2H), 3.26 (s, 2H), 3.15 (t, 2H), 2.64 (t, 2H), 1.14 (t, 3H).  
       Example 2  
     N-[2-(5-Phenyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-glycine Ethyl Ester  
       [0213]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-phenyl-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (500 MHz; DMSO-d 6 ) δ 8.05 (d, 2H), 7.60-7.56 (m, 3H), 4.02 (q, 2H), 3.26 (s, 2H), 3.16 (t, 2H), 2.64 (t, 2H), 1.14 (t, 3H).  
       Example 3  
     N-{2-[5-(2,5-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine Ethyl Ester  
       [0214]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-(2,5-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (500 MHz ; DMSO-d 6 ) δ 8.27 (s, 1H), 7.80 (d, 1H), 7.75 (d, 1H), 4.03 (q, 2H), 3.35 (s, 2H), 3.21 (t, 2H), 2.71 (t, 2H), 1.15 (t, 3H).  
       Example 4  
     N-{2-[5-(4-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine Ethyl Ester  
       [0215]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-(4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (400 MHz ; DMSO-d 6 ) δ 8.42 (d, 2H), 8.27 (d, 2H), 6.40 (brs, 2H), 4.05 (q, 2H), 3.35 (s, 2H), 3.21 (t, 2H), 2.71 (t, 2H), 1.15 (t, 3H).  
       Example 5  
     N-{2-[5-(2-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine Ethyl Ester  
       [0216]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-(2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (MHz; DMSO-d 6 ) δ 8.16 (d, 1H), 7.81-7.78 (m, 3H), 4.02 (q, 2H), 3.34 (s, 2H), 3.21 (t, 2H), 2.70 (t, 2H), 1.15 (t, 3H).  
       Example 6  
     N-{2-[5-(2-Chloro-4-nitro-phenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine Ethyl Ester  
       [0217]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-(2-chloro-4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (500 MHz; DMSO-d 6 ) δ 8.60 (d, 1H), 8.54 (d, 1H), 8.40 (dd, 1H) 4.05 (q, 2H), 3.27 (s, 2H), 3.19 (t, 2H), 2.67 (t, 2H), 1.16 (t, 3H).  
       Example 7  
     N-{2-[5-(2,4-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-ethyl glycine Ethyl Ester  
       [0218]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-(2,4-dichloro-phenyl)-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (400 MHz ; DMSO-d 6 ) δ 8.29 (d, 1H), 7.98 (d, 1H), 7.70 (dd, 1H), 5.65 (brs, 1H), 4.05 (q, 2H), 3.28 (s, 2H), 3.19 (t, 2H), 2.67 (t, 2H), 1.17 (t, 3H).  
       Example 8  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine Ethyl Ester  
       [0219]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (500 MHz; DMSO-d 6 ) δ 8.40 (d, 1H), 8.05 (dd, 1H), 8.02 (d, 1 H) 4.07 (q, 2H), 3.30 (s, 2H), 3.19 (t, 2H), 2.67 (t, 2H), 1.18 (t, 3H).  
       Example 9  
     N-[2-(5-methyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-glycine ethyl Ester  
       [0220]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-methyl-1,3,4-thiadiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H HMR (500 MHz; DMSO-d 6 ) δ 4.07 (q, 2H), 3.27 (s, 2H), 3.09 (t, 2H), 2.82 (s, 3H), 2.62 (t, 2H), 1.18 (t, 3H).  
       Example 10  
     N-[2-(4-Methyl-thiazole-2-sulfonylamino)-ethyl]-glycine Ethyl Ester  
       [0221]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 4-methyl-thiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (500 MHz ; DMSO-d 6 ) δ 7.68 (s, 1H), 4.07 (q, 2H), 3.26 (s, 2H), 3.02 (t, 2H), 2.58 (t, 2H), 2.43 (s, 3H), 1.18 (t, 3H).  
       Example 11  
     N-[2-(5-Benzoyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-glycine Ethyl Ester  
       [0222]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-benzoyl-4-phenyl-thiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (500 MHz; DMSO-d 6 ) δ 7.46 (d, 2H), 7.36-7.24 (m, 4H), 7.19-7.11 (m, 4H), 4.05 (q, 2H), 3.28 (s, 2H), 3.19 (t, 2H), 2.66 (t, 2H), 1.16 (t, 3H).  
       Example 12  
     N-[2-(5-methyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-glycine Ethyl Ester  
       [0223]     The title compound was synthesized by the reaction of N-(2-aminoethyl)-glycine ethyl ester 2HCl with 5-methyl-4-phenyl-thiazole-2-sulfonyl chloride as per the procedure of example 1.  1 H NMR (500 MHz; DMSO-d 6 ) δ 7.68 (d, 2H), 7.51 (t, 2H), 7.44 (t, 1H), 4.05 (q, 2H), 3.26 (s, 2H), 3.10 (t, 2H), 2.64 (s, 3H), 2.63 (t, 2H), 1.16 (t, 3H).  
       Example 13  
     N-{2-[5-(4-Chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0224]     To the solution of N-{2-[5-(4-Chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester (4.05 g, 10 mmol) in 30 mL of DMF, were added 1.68 g (11 mmol) of 1-hydroxybenzotriazole monohydrate, 2.27 g (11 mmol) of dicyclohexylcarbodiimide and 1.84 g (10 mmol) of (thymin-1-yl)-acetic acid. The reaction mixture was stirred for 3 hours at room temperature. The precipitated dicyclohexylurea was filtered off and the filtrate was concentrated in vacuo, followed by column chromatography on silica gel to give the title compound (4.85 g, 8.5 mmol, 85%).  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.28 (s, 0.6H), 11.26 (s, 0.4H), 9.15 (brs, 0.6H), 9.00 (brs, 0.4H), 8.07 (d, 2H), 7.67 (d, 2H), 7.31 (s, 0.6H), 7.24 (s, 0.4H), 4.65 (s, 1.2H), 4.47 (s, 0.8H), 4.31 (s, 0.8H), 4.16 (q, 0.8H), 4.06 (q, 1.2H), 4.03 (s, 1.2H), 3.55 (t, 1.2H), 3.45-3.38 (m, 2H), 3.23 (t, 0.8H), 1.73 (s, 3H), 1.21 (t, 1.2H), 1.16 (t, 1.8H).  
       Example 14  
     N-[2-(5-Phenyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0225]     The title compound was synthesized by the reaction of N-[2-(5-phenyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-glycine ethyl ester with (thymin-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.28 (s, 0.6H), 11.26 (s, 0.4H), 9.08 (brs, 1H), 8.05 (d, 2H), 7.66-7.57 (m, 3H), 7.32 (s, 0.6H), 7.24 (s, 0.4H), 4.65 (s, 1.2H), 4.47 (s, 0.8H), 4.32 (s, 0.8H), 4.16 (q, 0.8H), 4.06 (q, 1.2H), 4.04 (s, 1.2H), 3.56 (t, 1.2H), 3.43-3.38 (m, 2H), 3.24 (t, 0.8H), 1.73 (s, 3H), 1.21 (t, 1.2H), 1.16 (t, 1.8H).  
       Example 15  
     N-{2-[5-(2,5-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0226]     The title compound was synthesized by the reaction of N-{2-[5-(2,5-dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with (thymin-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.27 (s, 0.6H), 11.25 (s, 0.4H), 9.13 (brs, 1H), 8.26 (d, 0.4H), 8.25 (d, 0.6H), 7.81-7.74 (m, 2H), 7.32 (s, 0.6H), 7.23 (s, 0.4H), 4.63 (s, 1.2H), 4.47 (s, 0.8H), 4.32 (s, 0.8H), 4.16 (q, 0.8H), 4.06 (q, 1.2H), 4.04 (s, 1.2H), 3.55 (t, 1.2H), 3.45-3.38 (m, 2H), 3.25 (t, 0.8H), 1.73 (s, 3H), 1.22 (t, 1.2H), 1.16 (t, 1.8H).  
       Example 16  
     N-{2-[5-(4-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0227]     The title compound was synthesized by the reaction of N-{2-[5-(4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with (thymin-1-yl)-acetic acid as per the procedure of example 13.  
         [0228]      1 H NMR (500 MHz; DMSO-d 6 ) δ 11.20 (s, 1H), 8.37 (d, 2H), 8.24 (d, 2H), 7.49 (s, 1H), 4.82 (s, 1.7H), 4.45 (s, 0.3H), 4.42 (s, 0.3H), 4.13 (q, 0.3H), 4.04 (q, 1.7H), 4.01 (s, 1.7H), 3.39 (t, 1.7H), 3.28 (t, 0.3H), 3.16 (t, 1.7H), 3.03 (t, 0.3H), 1.74 (s, 3H), 1.21 (t, 0.6H), 1.16 (t, 2.4H).  
       Example 17  
     N-{2-[5-(2-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0229]     The title compound was synthesized by the reaction of N-{2-[5-(2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with (thymin-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.29 (s, 0.6H), 11.28 (s, 0.4H), 9.21 (brs, 0.6H), 9.10 (brs, 0.4H), 8.26-8.21 (m, 1H), 7.97-7.89 (m, 3H), 7.33 (d, 0.6H), 7.26 (d, 0.4H), 4.68 (s, 1.2H), 4.45 (s, 0.4H), 4.33 (s, 0.8H), 4.18 (q, 0.8H), 4.08 (q, 1.2H), 4.07 (s, 1.2H), 3.59 (t, 1.2H), 3.47-3.40 (m, 2H), 3.28 (t, 0.8H), 1.74 (s, 3H), 1.24 (t, 1.2H), 1.18 (t, 1.8H).  
       Example 18  
     N-{2-[5-(2-Chloro-4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0230]     The title compound was synthesized by the reaction of N-{2-[5-(2-chloro-4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with (thymin-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.28 (s, 0.6H), 11.25 (s, 0.4H), 9.16 (brs, 1H), 8.62-8.57 (m, 1H), 8.54-8.48 (m, 1H), 8.42-8.36 (m, 1H), 7.33 (s, 0.6H), 7.24 (s, 0.4H), 4.66 (s, 1.2H), 4.47 (s, 0.8H), 4.33 (s, 0.8H), 4.18 (q, 0.8H), 4.08 (q, 1.2H), 4.06 (s, 1.2H), 3.57 (t, 1.2H), 3.45-3.40 (m, 2H), 3.28 (t, 0.8H), 1.75 (s, 1.8H), 1.74 (s, 1.2H), 1.24 (t, 1.2H), 1.18 (t, 1.8H).  
       Example 19  
     N-{2-[5-(2,4-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0231]     The title compound was synthesized by the reaction of N-{2-[5-(2,4-dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with (thymin-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.28 (s, 0.6H), 11.27 (s, 0.4H), 9.11 (brs, 1H), 8.28 (d, 0.6H), 8.27 (d, 0.4H), 8.00 (d, 0.6H), 7.98 (d, 0.4H), 7.72-7.68 (m, 1H), 7.33 (s, 0.6H), 7.25 (s, 0.4H), 4.66 (s, 1.2H), 4.48 (s, 0.8H), 4.33 (s, 0.8H), 4.18 (q, 0.8H), 4.08 (q, 1.2H), 4.06 (s, 1.2H), 3.57 (t, 1.2H), 3.45-3.39 (m, 2H), 3.26 (t, 0.8H), 1.75 (s, 3H), 1.25 (t, 1.2H), 1.17 (t, 1.8H).  
       Example 20  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine Ethyl Ester  
       [0232]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with (thymin-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.29 (s, 0.6H), 11.28 (s, 0.4H), 9.20 (brs, 1H), 8.41-8.40 (m, 1H), 8.07-7.97 (m, 2H), 7.33 (s, 0.6H), 7.26 (s, 0.4H), 4.67 (s, 1.2H), 4.48 (s, 0.8H), 4.33 (s, 0.8H), 4.18 (q, 0.8H), 4.08 (q, 1.2H), 4.06 (s, 1.2H), 3.58 (t, 1.2H), 3.46-3.40 (m, 2H), 3.28 (t, 0.8H), 1.75 (s, 3H), 1.24 (t, 1.2H), 1.18 (t, 1.8H).  
       Example 21  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(benzhydryloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine Ethyl Ester  
       [0233]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [4-N-(benzhydryloxycarbonyl)-cytosin-1-yl]-acetic acid as per the procedure of example 13.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.97 (s, 1H), 9.16 (brs, 1H), 8.40 (d, 0.6H), 8.38 (d, 0.4H), 8.06-7.94 (m, 2H), 7.91 (d, 0.6H), 7.85 (d, 0.4H), 7.45 (d, 4H), 7.37 (t, 4H), 7.29 (t, 2H), 6.96-6.93 (m, 1H), 6.80 (s, 1H), 4.81 (s, 1.2H), 4.63 (s, 0.8H), 4.36 (s, 0.8H), 4.18 (q, 0.8H), 4.07 (s, 1.2H), 4.06 (q, 1.2H), 3.61 (t, 1.2H), 3.48-3.40 (m, 2H), 3.27 (t, 0.8H), 1.25 (t, 1.2H), 1.17 (t, 1.8H).  
       Example 22  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(benzhydryloxycarbonyl)-adenin-9-yl]-acetyl}-glycine Ethyl Ester  
       [0234]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [6-N-(benzhydryloxycarbonyl)-adenin-9-yl]-acetic acid as per the procedure of example 13.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.90 (s, 0.45H), 10.89 (s, 0.55H), 9.30 (brs, 0.55H), 9.12 (brs, 0.45H), 8.59 (s, 0.45H), 8.58 (s, 0.55H), 8.39 (d, 0.55H), 8.38 (d, 0.45H), 8.34 (s, 0.55H), 8.33 (s, 0.45H), 8.02-7.97 (m, 1H), 7.92 (d, 0.55H), 7.89 (d, 0.45H), 7.53 (d, 4H), 7.38 (t, 4H), 7.29 (t, 2H), 6.83 (s, 1H), 5.39 (s, 1.1H), 5.18 (s, 0.9H), 4.48 (s, 0.9H), 4.23 (q, 0.9H), 4.09 (s, 1.11H), 4.03 (q, 1.11H), 3.73 (t, 1.11H), 3.54 (t, 1.11H), 3.45 (t, 0.9H), 3.29 (t, 0.9H), 1.27 (t, 1.35H), 1.15 (t, 1.65H).  
       Example 23  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(benzhydryloxycarbonyl)-guanin-9-yl]-acetyl}-glycine Ethyl Ester  
       [0235]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [2-N-(benzhydryloxycarbonyl)-guanin-9-yl]-acetic acid as per the procedure of example 13.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.65 (brs, 1H), 11.25 (s, 0.45H), 11.23 (s, 0.55H), 9.20 (brs, 1H), 8.39 (s, 1H), 8.03-7.91 (m, 2H), 7.82 (s, 0.55H), 7.80 (s, 0.45H), 7.46 (d, 4H), 7.38 (t, 4H), 7.30 (dt, 2H), 6.87 (s, 1H), 5.15 (s, 1.1H), 4.96 (s, 0.9H), 4.47 (s, 0.9H), 4.22 (q, 0.9H), 4.10 (s, 1.1H), 4.09 (q, 1.1H), 3.69 (t, 1.1H), 3.52 (t, 0.9H), 3.45 (t, 1.1H), 3.29 (t, 0.9H), 1.26 (t, 1.35H), 1.16 (t, 1.65H).  
       Example 24  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(4-methoxybenzyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine Ethyl Ester  
       [0236]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [4-N-(4-methoxybenzyloxycarbonyl)-cytosin-1-yl]-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.69 (s, 1H), 9.21 (brs, 0.6H), 9.09 (brs, 0.4H), 8.40 (s, 1H), 8.07-7.96 (m, 2H), 7.92 (d, 0.6H), 7.86 (d, 0.4H), 7.36 (d, 2H), 7.02 (d, 0.6H), 7.01 (d, 1H), 6.94 (d, 2H), 5.12 (s, 2H), 4.81 (s, 1.2H), 4.64 (s, 0.8H), 4.37 (s, 0.8H), 4.18 (q, 0.8H), 4.08 (s, 1.2H), 4.08 (q, 1.2H), 3.76 (s, 3H), 3.62 (t, 1.2H), 3.47 (t, 1.2H), 3.43 (t, 0.8H), 3.28 (t, 0.8H), 1.24 (t, 1.2H), 1.17 (t, 1.8H).  
       Example 25  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(4-methoxybenzyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine Ethyl Ester  
       [0237]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [6-N-(4-methoxybenzyloxycarbonyl)-adenin-9-yl]-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.56 (s, 1H), 10.59 (s, 0.55H), 9.31 (brs, 0.55H), 9.11 (brs, 0.45H), 8.57 (s, 0.45H), 8.56 (s, 0.55H), 8.40 (d, 0.55H), 8.39 (d, 0.45H), 8.31 (s, 0.55H), 8.30 (s, 0.45H), 8.03-7.99 (m, 1H), 7.93 (d, 0.55H), 7.91 (d, 0.45H), 7.39 (d, 1H), 6.95 (d, 2H), 5.38 (s, 1.1H), 5.17 (s, 0.9H), 5.14 (s, 2H), 4.48 (s, 0.9H), 4.23 (q, 0.9H), 4.08 (s, 1.1H), 4.07 (q, 1.1H), 3.76 (s, 3H), 3.72 (t, 1.1H), 3.54 (t, 1.1H), 3.45 (t, 0.9H), 3.29 (t, 0.9H), 1.27 (t, 1.35H), 1.15 (t, 1.65H).  
       Example 26  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(4-methoxybenzyloxycarbonyl)-guanin-9-yl]-acetyl}-glycine Ethyl Ester  
       [0238]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [2-N-(4-methoxybenzyloxycarbonyl)-guanin-9-yl]-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.39 (brs, 0.45H), 11.36 (brs, 0.55H), 9.20 (brs, 1H), 8.39 (s, 1H), 8.01 (d, 1H), 7.95 (d, 0.55H), 7.92 (d, 0.45H), 7.82 (s, 0.55H), 7.79 (s, 0.45H), 7.37 (d, 2H), 6.95 (d, 2H), 5.17 (s, 2H), 5.13 (s, 1.1H), 4.93 (s, 0.9H), 4.45 (s, 0.9H), 4.21 (q, 0.9H), 4.08 (s, 1.1H), 4.07 (q, 1.1H), 3.76 (s, 3H), 3.66 (t, 1.1H), 3.49 (t, 1.1H), 3.43 (t, 0.9H), 3.28 (t, 0.9H), 1.25 (t, 1.35H), 1.16 (t, 1.65H).  
       Example 27  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(piperonyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine Ethyl Ester  
       [0239]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [4-N-(piperonyloxycarbonyl)-cytosin-1-yl]-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.71 (s, 1H), 9.22 (brs, 0.6H), 9.08 (brs, 0.4H), 8.40 (s, 1H), 8.07-7.96 (m, 2H), 7.92 (d, 0.6H), 7.86 (d, 0.4H), 7.02 (d, 0.6H), 7.00 (d, 0.4H), 6.99 (s, 1H), 6.91 (s, 2H), 6.02 (s, 2H), 5.08 (s, 2H), 4.81 (s, 1.2H), 4.64 (s, 0.8H), 4.37 (s, 0.8H), 4.18 (q, 0.8H), 4.08 (s, 1.2H), 4.08 (q, 1.2H), 3.62 (t, 1.2H), 3.47 (t, 1.2H), 3.43 (t, 0.8H), 3.28 (t, 0.8H), 1.24 (t, 1.2H), 1.17 (t, 1.8H).  
       Example 28  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(piperonyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine Ethyl Ester  
       [0240]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with [6-N-(piperonyloxycarbonyl)-adenin-9-yl]-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.60 (s, 0.45H), 10.59 (s, 0.55H), 9.31 (brs, 0.55H), 9.11 (brs, 0.45H), 8.58 (s, 0.45H), 8.57 (s, 0.55H), 8.40 (d, 0.55H), 8.39 (d, 0.45H), 8.32 (s, 0.55H), 8.31 (s, 0.45H), 8.03-7.98 (m, 1H), 7.93 (d, 0.55H), 7.90 (d, 0.45H), 7.05 (s, 1H), 6.95 (d, 1H), 6.91 (d, 1H), 6.02 (s, 2H), 5.38 (s, 1.1H), 5.17 (s, 0.9H), 5.11 (s, 2H), 4.48 (s, 0.9H), 4.23 (q, 0.9H), 4.08 (s, 1.1H), 4.07 (q, 1.1H), 3.73 (t, 1.1H), 3.54 (t, 1.1H), 3.45 (t, 0.9H), 3.30 (t, 0.9H), 1.27 (t, 1.35H), 1.15 (t, 1.65H).  
       Example 29  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(piperonyloxycarbonyl)-guanin-9-yl]-acetyl}-glycine Ethyl Ester  
       [0241]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester with N-{[2-N-(piperonyloxycarbonyl)-guanin-9-yl]-acetic acid as per the procedure of example 13.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.37 (brs, 0.4H), 11.35 (brs, 0.6H), 9.20 (brs, 1H), 8.39 (s, 1H), 8.03-7.99 (m, 1H), 7.95 (d, 0.6H), 7.92 (d, 0.4H), 7.82 (s, 0.6H), 7.79 (s, 0.4H), 7.01 (s, 1H), 6.94 (d, 1H), 6.91 (d, 1H), 6.02 (s, 2H), 5.14 (s, 3.2H), 4.93 (s, 0.8H), 4.45 (s, 0.8H), 4.21 (q, 0.8H), 4.08 (s, 1.2H), 4.07 (q, 1.2H), 3.65 (t, 1.2H), 3.48 (t, 1.2H), 3.43 (t, 0.8H), 3.27 (t, 0.8H), 1.25 (t, 1.2H), 1.16 (t, 1.8H).  
       Example 30  
     N-[2-(5-Benzoyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine Ethyl Ester  
       [0242]     The title compound was synthesized by the reaction of N-[2-(5-benzoyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-glycine ethyl ester with N-(thymine-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.26 (s, 0.6H), 11.24 (s, 0.4H), 8.90 (brs, 0.6H), 8.78 (brs, 0.4H), 7.72 (d, 2H), 7.58-7.53 (m, 1H), 7.47-7.43 (m, 2H), 7.38-7.32 (m, 2H), 7.31-7.22 (m, 4H), 4.61 (s, 1.2H), 4.48 (s, 0.8H), 4.32 (s, 0.8H), 4.15 (q, 0.8H), 4.06 (s, 1.2H), 4.05 (q, 0.8H), 3.56 (t, 1.2H), 3.44 (t, 2H), 3.30 (t, 0.8H), 1.72 (s, 1.8H), 1.71 (s, 1.2H), 1.21 (t, 1.2H), 1.15 (t, 1.8H).  
       Example 31  
     N-[2-(5-Methyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine Ethyl Ester  
       [0243]     The title compound was synthesized by the reaction of N-[2-(5-methyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-glycine ethyl ester with N-(thymine-1-yl)-acetic acid as per the procedure of example 13.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.26 (s, 1H), 8.58 (brs, 0.6H), 8.50 (brs, 0.4H), 7.68 (d, 2H), 7.53-7.47 (m, 3H), 7.46-7.40 (m, 2H), 7.27 (s, 0.6H), 7.25 (s, 4H), 4.60 (s, 1.2H), 4.47 (s, 0.8H), 4.29 (s, 0.8H), 4.13 (q, 0.8H), 4.05 (q, 0.8H), 4.04 (s, 1.2H), 3.52 (t, 1.2H), 3.40 (t, 0.8H), 3.34 (t, 1.2H), 3.17 (t, 0.8H), 2.64 (s, 3H), 1.72 (s, 3H), 1.20 (t, 1.2H), 1.15 (t, 1.8H).  
       Example 32  
     N-{2-[5-(4-Chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine  
       [0244]     N-{2-[5-(4-Chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester (2.85 g, 5.0 mmol) was suspended in the mixture solvent of 10 mL of tetrahydrofuran and 20 mL of water. Lithium hydroxide monohydrate (0.84 g, 20 mmol) was added and the reaction mixture was stirred for 10 min at room temperature. After completion of the reaction by monitoring by thin layer chromatography (TLC), 20 mL of water was added and then the reaction mixture was acidified with 1N HCl solution adjusting the pH between 3.0 and 3.5. The precipitated solid was filtered, washed with water, and dried by blowing nitrogen gas to give the title compound (2.44 g, 4.5 mmol, 90%).  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.28 (s, 0.5H), 11.24 (s, 0.5H), 8.09-8.05 (m, 2H), 7.68-7.65 (m, 2H), 7.31 (s, 0.5H), 7.24 (s, 0.5H), 4.64 (s, 1H), 4.44 (s, 1H), 4.13 (s, 1H), 3.95 (s, 1H), 3.54 (t, 1H), 3.45-3.38 (m, 2H), 3.25 (t, 1H), 1.73 (s, 1.5H), 1.71 (s, 1.5H)  
       Example 33  
     N-[2-(5-Phenyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-N-[(thymin-1-yl)-acetyl]-glycine  
       [0245]     The title compound was synthesized by the reaction of N-[2-(5-phenyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-N-[(thymin-1-yl)-acetyl]-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.28 (s, 0.55H), 11.25 (s, 0.45H), 9.05 (brs, 1H), 8.05 (d, 2H), 7.68-7.57 (m, 3H), 7.32 (s, 0.55H), 7.24 (s, 0.45H), 4.64 (s, 1.1H), 4.46 (s, 0.9H), 4.20 (s, 0.9H), 3.97 (s, 1.11H), 3.54 (t, 1.11H), 3.45-3.37 (m, 2H), 3.24 (t, 0.9H), 1.74 (s, 1.1H), 1.73 (s, 0.9H)  
       Example 34  
     N-{2-[5-(2,5-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine  
       [0246]     The title compound was synthesized by the reaction of N-{2-[5-(2,5-dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.27 (s, 0.6H), 11.24 (s, 0.4H), 9.13 (brs, 1H), 8.26 (d, 0.4H), 8.25 (d, 0.6H), 7.82-7.25 (m, 2H), 7.32 (s, 0.6H), 7.24 (s, 0.4H), 4.62 (s, 1.2H), 4.45 (s, 0.8H), 4.20 (s, 0.8H), 3.97 (s, 1.2H), 3.54 (t, 1.2H), 3.43-3.37 (m, 2H), 3.26 (t, 0.8H), 1.73 (s, 3H).  
       Example 35  
     N-{2-[5-(4-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine  
       [0247]     The title compound was synthesized by the reaction of N-{2-[5-(4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 12.85 (brs, 1H), 11.29 (s, 0.5H), 11.25 (s, 0.5H), 8.43-8.39 (m, 2H), 8.36-8.32 (m, 2H), 7.33 (s, 0.5H), 7.25 (s, 0.5H), 4.65 (s, 1H), 4.47 (s, 1H), 4.22 (s, 1H), 3.98 (s, 1H), 3.56 (t, 1H), 3.42 (t, 2H), 3.27 (t, 1H), 3.03 (t, 0.3H), 1.75 (s, 1.5H), 1.74 (s, 1.5H).  
       Example 36  
     N-{2-[5-(2-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine  
       [0248]     The title compound was synthesized by the reaction of N-{2-[5-(2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 12.95 (brs, 1H), 11.30 (s, 0.55H), 11.28 (s, 0.45H), 9.22 (brs, 0.55H), 9.08 (brs, 0.45H), 8.27-8.23 (m, 1H), 7.99-7.89 (m, 3H), 7.34 (s, 0.55H), 7.27 (s, 0.45H), 4.67 (s, 1.1H), 4.48 (s, 0.9H), 4.24 (s, 0.9H), 4.00 (s, 1.1H), 3.57 (t, 1H), 3.47-3.41 (m, 2H), 3.33 (t, 0.9H), 1.75 (s, 3H),  
       Example 37  
     N-{2-[5-(2-Chloro-4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine  
       [0249]     The title compound was synthesized by the reaction of N-{2-[5-(2-chloro-4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.28 (s, 0.55H), 11.24 (s, 0.45H), 9.26 (brs, 1H), 8.62-8.57 (m, 1H), 8.55-8.48 (m, 1H), 8.43-8.36 (m, 1H), 7.34 (s, 0.55H), 7.24 (s, 0.45H), 4.65 (s, 1.1H), 4.46 (s, 0.9H), 4.20 (s, 0.9H), 3.99 (s, 1.1H), 3.56 (t, 1.1H), 3.46-3.39 (m, 2H), 3.29 (t, 0.9H), 1.75 (s, 1.1H), 1.73 (s, 0.9H)  
       Example 38  
     N-{2-[5-(2,4-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine  
       [0250]     The title compound was synthesized by the reaction of N-{2-[5-(2,4-dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.28 (s, 0.5H), 11.25 (s, 0.5H), 9.23 (brs, 1H), 8.29 (d, 0.5H), 8.27 (d, 0.5H), 7.99 (d, 0.5H), 7.97 (d, 0.5H), 7.72-7.67 (m, 1H), 7.34 (s, 0.5H), 7.25 (s, 0.5H), 4.65 (s, 1H), 4.46 (s, 1H), 4.17 (s, 1H), 3.99 (s, 1H), 3.56 (t, 1H), 3.45-3.38 (m, 2H), 3.28 (t, 1H), 1.73 (s, 3H).  
       Example 39  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine  
       [0251]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.29 (s, 0.5H), 11.27 (s, 0.5H), 9.28 (brs, 1H), 8.41-8.39 (m, 1H), 8.06-7.97 (m, 2H), 7.33 (s, 0.5H), 7.26 (s, 0.5H), 4.66 (s, 1H), 4.47 (s, 1H), 4.19 (s, 1H), 3.99 (s, 1H), 3.57 (t, 1H), 3.46-3.39 (m, 2H), 3.29 (t, 1H), 1.75 (s, 1H), 1.74 (s, 1H)  
       Example 40  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(benzhydryloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine  
       [0252]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(benzhydryloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.95 (brs, 1H), 9.16 (brs, 1H), 8.39 (d, 0.45H), 8.37 (d, 0.55H), 8.06-7.94 (m, 2H), 7.91 (d, 0.45H), 7.84 (d, 0.55H), 7.45 (d, 4H), 7.37 (t, 4H), 7.29 (t, 2H), 6.94 (d, 0.45H), 6.90 (d, 0.55H), 6.80 (s, 1H), 4.79 (s, 0.9H), 4.58 (s, 1.11H), 4.07 (s, 0.9H), 3.98 (s, 1.1H), 3.56 (t, 1.1H), 3.46 (t, 0.9H), 3.41 (t, 1.1H), 3.30 (t, 0.9H)  
       Example 41  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(benzhydryloxycarbonyl)-adenin-9-yl]-acetyl}-glycine  
       [0253]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(benzhydryloxycarbonyl)-adenin-9-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.89 (s, 1H), 8.57 (s, 0.4H), 8.56 (s, 0.6H), 8.38 (d, 0.4H), 8.35 (d, 0.6H), 8.34 (s, 0.4H), 8.32 (s, 0.6H), 8.01-7.91 (m, 1.4H), 7.82 (d, 0.6H), 7.54 (d, 4H), 7.38 (t, 4H), 7.29 (t, 2H), 6.83 (s, 1H), 5.37 (s, 0.8H), 5.11 (s, 1.2H), 4.12 (s, 1.2H), 3.97 (s, 0.8H), 3.78 (t, 0.8H), 3.54 (t, 0.8H), 3.44 (t, 1.2H), 3.33 (t, 1.2H).  
       Example 42  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(benzhydryloxycarbonyl)-guanin-9-yl]-acetyl}-glycine  
       [0254]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(benzhydryloxycarbonyl)-guanin-9-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.20 (brs, 1H), 8.38 (d, 0.3H), 8.35 (d, 0.7H), 8.04-7.79 (m, 3H), 7.81 (d, 1H), 7.46 (d, 4H), 7.37 (t, 4H), 7.28 (dt, 2H), 6.86 (s, 0.3H, 6.85 (s, 0.7H), 5.13 (s, 0.6H), 4.89 (s, 1.4H), 4.02 (s, 1.4H), 3.96 (s, 0.6H), 3.66 (t, 0.6H), 3.51 (t, 0.6H), 3.44 (t, 1.4H), 3.34 (t, 1.4H)  
       Example 43  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(4-methoxybenzyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine  
       [0255]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(4-methoxybenzyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.71 (brs, 1H), 8.40 (s, 0.5H), 8.38 (s, 0.5H), 8.07-7.96 (m, 2H), 7.92 (d, 0.5H), 7.85 (d, 0.5H), 7.36 (d, 2H), 7.02 (d, 0.5H), 6.98 (d, 0.5H), 6.94 (d, 2H), 5.11 (s, 2H), 4.80 (s, 1H), 4.59 (s, 1H), 4.09 (s, 1H), 3.98 (s, 1H), 3.76 (s, 3H), 3.59 (t, 1H), 3.47 (t, 1H), 3.42 (t, 1H), 3.30 (t, 1H).  
       Example 44  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(4-methoxybenzyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine  
       [0256]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(4-methoxybenzyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.56 (s, 1H), 8.57 (s, 0.45H), 8.56 (s, 0.55H), 8.39 (d, 0.45H), 8.38 (d, 0.55H), 8.31 (s, 0.45H), 8.30 (s, 0.55H), 8.02-7.96 (m, 1H), 7.93 (d, 0.45H), 7.87 (d, 0.55H), 7.39 (d, 2H), 6.95 (d, 2H), 5.37 (s, 0.9H), 5.14 (s, 2H), 5.13 (s, 1.1H), 4.27 (s, 1.11H), 4.00 (s, 0.9H), 3.76 (s, 3H), 3.71 (t, 0.9H), 3.54 (t, 0.9H), 3.44 (t, 1.1H), 3.31 (t, 1.1H).  
       Example 45  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(4-methoxybenzyloxycarbonyl)-guanin-9-yl]-acetyl}-glycine  
       [0257]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(4-methoxybenzyloxycarbonyl)-guanin-9-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.38 (s, 1H), 11.35 (brs, 1H), 9.30 (brs, 0.5H), 9.12 (brs, 0.5H), 8.39 (s, 1H), 8.01 (d, 1H), 7.95 (d, 0.5H), 7.92 (d, 0.5H), 7.82 (s, 0.5H), 7.79 (s, 0.5H), 7.37 (d, 2H), 6.95 (d, 2H), 5.17 (s, 2H), 5.11 (s, 1H), 4.92 (s, 1H), 4.34 (s, 1H), 4.01 (s, 1H), 3.76 (s, 3H), 3.65 (t, 1H), 3.50 (t, 1H), 3.42 (t, 1H), 3.30 (t, 1H).  
       Example 46  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(piperonyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine  
       [0258]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(piperonyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.71 (brs, 1H), 8.40 (s, 1H), 8.07-7.95 (m, 2H), 7.92 (d, 0.5H), 7.85 (d, 0.5H), 7.00 (d, 0.5H), 6.99 (s, 1H), 6.98 (d, 0.5H), 6.91 (s, 2H), 6.02 (s, 2H), 5.08 (s, 2H), 4.80 (s, 1H), 4.60 (s, 1H), 4.15 (s, 1H), 3.99 (s, 1H), 3.60 (t, 1H), 3.46 (t, 1H), 3.42 (t, 1H), 3.29 (t, 1H).  
       Example 47  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(piperonyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine  
       [0259]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(piperonyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.59 (s, 1H), 8.57 (s, 0.45H), 8.56 (s, 0.55H), 8.39 (d, 0.45H), 8.37 (d, 0.55H), 8.32 (s, 0.45H), 8.30 (s, 0.55H), 8.02-7.96 (m, 1H), 7.93 (d, 0.45H), 7.86 (d, 0.55H), 7.05 (s, 1H), 6.96 (d, 1H), 6.91 (d, 1H), 6.02 (s, 2H), 5.37 (s, 0.9H), 5.13 (s, 1.11H), 5.12 (s, 2H), 4.21 (s, 1.11H), 3.99 (s, 0.9H), 3.71 (t, 0.9H), 3.54 (t, 0.9H), 3.44 (t, 1.1H), 3.32 (t, 1.1H).  
       Example 48  
     N-{2-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(piperonyloxycarbonyl)-guanin-9-yl]-acetyl}-glycine  
       [0260]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(piperonyloxycarbonyl)-guanin-9-yl]-acetyl}-glycine ethyl ester as per the procedure of example 32.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.50 (brs, 1H), 11.35 (s, 1H), 8.39 (s, 1H), 8.03-7.94 (m, 2.5H), 7.90 (d, 0.5H), 7.82 (s, 0.5H), 7.79 (s, 0.5H), 7.01 (s, 1H), 6.93 (d, 1H), 6.91 (d, 1H), 6.02 (s, 2H), 5.14 (s, 2H), 5.11 (s, 1H), 4.91 (s, 1H), 4.24 (s, 1H), 4.00 (s, 1H), 3.65 (t, 1H), 3.50 (t, 1H), 3.42 (t, 1H), 3.30 (t, 1H).  
       Example 49  
     N-[2-(5-Benzoyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine  
       [0261]     The title compound was synthesized by the reaction of N-[2-(5-benzoyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.25(s, 0.55H), 11.21 (s, 0.45H), 8.96 (brs, 1H), 7.72 (d, 2H), 7.58-7.53 (m, 1H), 7.47-7.43 (m, 2H), 7.38-7.32 (m, 2H), 7.31-7.22 (m, 4H), 4.60 (s, 1.1H), 4.46 (s, 0.9H), 4.17 (s, 0.9H), 3.99 (s, 1.1H), 3.54 (t, 1.1H), 3.44 (t, 2H), 3.31 (t, 0.9H), 1.73 (s, 1.65H), 1.71 (s, 1.35H).  
       Example 50  
     N-[2-(5-Methyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine  
       [0262]     The title compound was synthesized by the reaction of N-[2-(5-methyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine ethyl ester as per the procedure of example 32.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.26 (s, 1H), 8.61 (brs, 0.55H), 8.56 (brs, 0.45H), 7.68 (d, 2H), 7.53-7.47 (m, 2H), 7.46-7.40 (m, 1H), 7.27 (s, 0.55H), 7.24 (s, 45H), 4.58 (s, 1.1H), 4.45 (s, 0.9H), 4.17 (s, 0.9H), 3.97(s, 1.1H), 3.49 (t, 1.1H), 3.38 (t, 0.9H), 3.33 (t, 1.1H), 3.17 (t, 0.9H), 2.63 (s, 3H), 1.73 (s, 3H).  
       Example 51  
     N-[2-(5-Methyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-N-(tert-butoxycarbonyl)-glycine  
       [0263]     To a solution of N-[2-(5-methyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-glycine ethyl ester (616 mg, 2 mmol) in tetrahydrofuran (10 mL) was added a solution of LiOH monohydrate (252 mg , 6 mmol) dissolved in water (3 mL). After stirring for 1 hour at room temperature, di-t-butyl dicarbonate (655 mg, 3 mmol) was added to the reaction mixture. The resulting reaction mixture was stirred for 30 min. After completion of the reaction by monitoring by thin layer chromatography (TLC), tetrahydrofuran was removed in vacuo. The residual solution was washed with ethyl ether (100 mL). The aqueous layer was acidified to pH 3 by adding 2N HCl and extracted with dichloromethane (50 mL). The organic layer was dried over MgSO 4  and filtered. The filtrate was concentrated in vacuo to afford the desired product (690 mg, 91%).  1 H NMR (500 MHz ; DMSO-d 6 ) δ 8.82 (brs, 1H), 3.84 (s, 1H), 3.81 (s, 1H), 3.28 (t, 2H), 3.21˜3.16 (m, 2H), 2.82 (s, 3H), 1.38 (s, 4.5H), 1.33 (s, 4.5H).  
       Example 52  
     N-[2-(4-Methyl-thiazole-2-sulfonylamino)-ethyl]-N-(tert-butoxycarbonyl)-glycine  
       [0264]     The title compound was synthesized by the reaction of N-[2-(4-methyl-thiazole-2-sulfonylamino)-ethyl]-glycine ethyl ester as per the procedure of example 51.  1 H NMR (400 MHz; DMSO-d 6 ) δ 12.50 (brs, 1H), 8.29 (s, 0.5H), 8.27 (s, 0.5H), 7.59 (s, 1H), 3.72 (s, 1H), 3.69 (s, 1H), 3.14 (t, 2H), 3.06˜2.98 (m, 2H), 2.34 (s, 3H), 1.27 (s, 4.5H), 1.23 (s, 4.5H).  
       Example 53  
     N-{2-[5-(4-chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-(tert-butoxycarbonyl)-glycine  
       [0265]     The title compound was synthesized by the reaction of N-{2-[5-(4-chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine ethyl ester as per the procedure of example 51.  1 H NMR (500 MHz; DMSO-d 6 ) δ 9.01 (brs, 1H), 8.11-8.08 (m, 2H), 7.68 (d, 2H), 3.84 (s, 1H), 3.80 (s, 1H), 3.30-3.23 (m, 4H), 1.38 (s, 4.5H), 1.30 (4.5H).  
       Example 54  
     1-(5-methyl-1,3,4-thiadiazole-2-sulfonyl)-piperazin-2-one, trifluoroacetic Acid Salt  
       [0266]     To a solution of N-[2-(5-methyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-N-(tert-butoxycarbonyl)-glycine (760 mg, 2 mmol) in dichloromethane (10 mL) was added dicyclohexyl carbodiimide (516 mg, 2.5 mmol). After stirring for 2 hours at room temperature, the precipitate was removed by filtration. The filtrate was concentrated to approximately 3 mL and cooled to 0° C. To a cold solution was added trifluoroacetic acid (2 mL). The mixture was stirred for 2 hours at the same temperature and ethyl ether (10 mL) was slowly added. The precipitated product was filtered, washed with ethyl ether, and dried in vacuo to afford white solid (602 mg, 80%).  1 H-NMR (500 MHz; DMSO-d 6 ) δ 10.13 (brs, 2H), 4.16 (t, 2H), 3.95 (s, 2H), 3.54 (t, 2H), 2.87 (s, 3H).  
       Example 55  
     1-(4-methyl-thiazole-2-sulfonyl)-piperazin-2-one, Trifluoroacetic Acid Salt  
       [0267]     The title compound was synthesized by the reaction of N-[2-(4-methyl-thiazole-2-sulfonylamino)-ethyl]-N-(tert-butoxycarbonyl)-glycine as per the procedure of example 54.  1 H NMR (400 MHz; DMSO-d 6 ) δ 9.20 (brs, 2H), 7.94 (s, 1H), 4.08 (t, 2H), 3.94 (s, 2H), 3.52 (t, 2H), 2.46 (s, 3H).  
       Example 56  
     1-[5-(4-Chlorophenyl)-1,3,4-thiadiazole-2-sulfonyl]-piperazin-2-one, Trifluoroacetic Acid Salt  
       [0268]     The title compound was synthesized by the reaction of N-{2-[5-(4-chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-(tert-butoxycarbonyl)-glycine as per the procedure of example 54.  1 H NMR (500 MHz ; DMSO-d 6 ) δ 9.37 (brs, 2H), 8.15 (d, 2H), 7.70 (d, 2H), 4.14 (t, 2H), 3.98 (s, 2H), 3.56 (t, 2H), 1.41 (s, 9H).  
       Example 57  
     1-[5-(4-Chlorophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0269]     1-Ethyl-3-(3′-dimethylaminopropyl)carbodiimide hydrochloride (0.21 g, 1.1 mmol) was added to the solution of N-{2-[5-(4-chlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-glycine (0.54 g. 1.0 mmol) in 5 mL of DMF,. The reaction mixture was stirred for 3 hours at room temperature. Water (50 mL) was added to the reaction mixture. Then the precipitated solid was filtered, washed with water and dried by blowing nitrogen gas to give the title compound (0.45 g, 0.86 mmol, 86%)  
         [0270]      1 H NMR (500 MHz; DMSO-d 6 ) δ 11.29 (s, 0.6H), 11.28 (s, 0.4H), 8.13 (d, 2H), 7.68 (d, 2H), 7.33 (s, 0.6H), 7.27 (s, 0.4H), 4.66 (s, 1.2H), 4.57 (s, 0.8H), 4.43 (s, 0.8H), 4.29 (s, 1.2H), 4.16 (t, 1.2H), 4.02 (t, 0.8H), 3.94 (t, 1.2H), 3.84 (t, 0.8H), 1.74(s, 3H).  
       Example 58  
     1-(5-Phenyl-1,3,4-thiadiazole-2-sulfonyl)-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0271]     To a solution of N-[2-(5-phenyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-N-[(thymin-1-yl)-acetyl]-glycine (1.02 g, 2 mmol) in tetrahydrofuran (50 mL) was added N-methylmorpholine (3.3 mL, 3 mmol) and then the mixture was cooled to −20° C. After stirring for 5 min at the same temperature, isobutyl chloroformate (3.4 mL, 26 mmol) was added to the reaction mixture. The resulting mixture was slowly warmed to 0° C. for 1 hour. Then the reaction mixture was evaporated in vacuo and dissolved in a mixture of ethyl acetate and acetonitrile. The solution was washed with brine and dried over sodium sulfate and filtered. The filtrate was evaporated in vacuo and triturated with tetrahydrofuran-ethyl ether (1/1, v/v) to precipitate solid. The solid was filtered off, washed with ethyl ether, and dried in vacuo to give the titled compound (883 mg, 90%).  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.30 (s, 0.6H), 11.29 (s, 0.4H), 8.10 (d, 2H), 7.68-7.57 (m, 3H), 7.33 (s, 0.6H), 7.27 (s, 0.4H), 4.66 (s, 1.2H), 4.58 (s, 0.8H), 4.43 (s, 0.8H), 4.30 (s, 1.2H), 4.17 (t, 1.2H), 4.02 (t, 0.8H), 3.95 (t, 1.2H), 3.85 (t, 0.8H), 1.73(s, 3H).  
       Example 59  
     1-[5-(2,5-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0272]     The title compound was synthesized by the reaction of N-[2-(5-phenyl-1,3,4-thiadiazole-2-sulfonylamino)-ethyl]-N-[(thymin-1-yl)-acetyl]-glycine as per the procedure of example 57.  1 H  
         [0273]     NMR (500 MHz; DMSO-d 6 ) δ 11.30 (s, 0.6H), 11.28 (s, 0.4H), 8.31 (s, 1H), 7.85-7.75 (m, 2H), 7.33 (s, 0.6H), 7.27 (s, 0.4H), 4.66 (s, 1.2H), 4.58 (s, 0.8H), 4.43 (s, 0.8H), 4.30 (s, 1.2H), 4.18 (t, 1.2H), 4.04 (t, 0.8H), 3.95 (t, 1.2H), 3.85 (t, 0.8H), 1.74 (s, 3H).  
       Example 60  
     1-[5-(4-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0274]     The title compound was synthesized by the reaction of N-{2-[5-(4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine as per the procedure of example 57.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.30(s, 0.6H), 11.29 (s, 0.4H), 8.44-8.39(m, 4H), 7.34(s, 0.6H), 7.25(s, 0.4H), 4.69(s, 1.2H), 4.59(s, 0.8H), 4.45(s, 0.8H), 4.31 (s, 1.2H), 4.18(t, 1.2H), 4.05(t, 0.8H), 3.97(t, 1.2H), 3.86(t, 0.8H), 1.75(s, 3H).  
       Example 61  
     1-[5-(2-Nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0275]     The title compound was synthesized by the reaction of N-{2-[5-(2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.31(s, 1H), 8.27-8.24(m, 1H), 7.99-7.90 (m, 3H), 7.35(s, 0.6H), 7.30(s, 0.4H), 4.69(s, 1.2H), 4.61 (s, 0.8H), 4.49 (s, 0.8H), 4.35 (s, 1.2H), 4.21(t, 1.2H), 4.07(t, 0.8H), 3.98 (t, 1.2H), 3.88 (t, 0.8H), 1.75(s, 3H).  
       Example 62  
     1-[5-(2-Chloro-4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0276]     The title compound was synthesized by the reaction of N-{2-[5-(2-chloro-4-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.31 (s, 0.6H), 11.29 (s, 0.4H), 8.65-8.55 (m, 2H), 8.44-8.37 (m, 1H), 7.34 (s, 0.6H), 7.28 (s, 0.4H), 4.68 (s, 1.2H), 4.59 (s, 0.8H), 4.45 (s, 0.8H), 4.32 (s, 1.2H), 4.20 (t, 1.2H), 4.06 (t, 0.8H), 3.97 (t, 1.2H), 3.87 (t, 0.8H), 1.75(s, 3H).  
       Example 63  
     1-[5-(2,4-Dichlorophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0277]     The title compound was synthesized by the reaction of N-{2-[5-(2,4-dichlorophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine as per the procedure of example 57.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.30 (s, 0.6H), 11.29 (s, 0.4H), 8.35 (d, 1H), 8.02 (s, 1H), 7.72 (d, 1H), 7.34 (s, 0.6H), 7.28 (s, 0.4H), 4.68 (s, 1.2H), 4.59 (s, 0.8H), 4.45 (s, 0.8H), 4.31 (s, 1.2H), 4.19 (t, 1.2H), 4.05 (t, 0.8H), 3.96 (t, 1.2H), 3.87 (t, 0.8H), 1.75 (s, 3H).  
       Example 64  
     1-(4-methyl-thiazole-2-sulfonyl)-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0278]     To 3 mL of DMF, were added 0.30 g (0.8 mmol) of 4-(4-methyl-thiazole-2-sulfonyl)-piperazin-2-one trifluoroacetic acid salt, 0.147 g (0.8 mmol) of (thymin-1-yl)-acetic acid and 0.458 g of PyBOP. The reaction mixture was stirred for 4 hours at room temperature. Almost of the solvent was removed in vacuo and the residue was dissolved in methylene chloride. The solution was washed with saturated sodium bicarbonate solution, water, 1N HCl, water and brine sequencially. The organic layer was concentrated and column chromatographed on silicagel to give 0.19 g (56%) of the title compound.  
         [0279]      1 H NMR (500 MHz; DMSO-d 6 ) δ 11.33 (s, 0.6H), 11.31 (s, 0.4H), 7.90 (d, 1H), 7.35 (s, 0.6H), 7.28 (s, 0.4H), 4.66 (s, 1.2H), 4.58 (s, 0.8H), 4.39 (s, 0.8H), 4.25 (s, 1.2H), 4.13 (t, 1.2H), 3.98 (t, 0.8H), 3.90 (t, 1.2H), 3.79 (t, 0.8H), 2.45 (s, 3H), 1.74 (s, 3H).  
       Example 65  
     1-(5-Methyl-1,3,4-thiadiazole-2-sulfonyl)-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0280]     The title compound was synthesized by the reaction of 4-(5-methyl-1,3,4-thiadiazole-2-sulfonyl)-piperazin-2-one trifluoroacetic acid salt with (thymin-1-yl)-acetic acid as per the procedure of method B described in example 64,  
         [0281]      1 H NMR (500 MHz; DMSO-d 6 ) δ 11.31 (s, 1H), 7.34 (s, 0.6H), 7.28 (s, 0.4H), 4.66 (s, 1.2H), 4.58 (s, 0.8H), 4.41 (s, 0.8H), 4.28 (s, 1.2H), 4.14 (t, 1.2H), 3.99 (t, 0.8H), 3.92 (t, 1.2H), 3.82 (t, 0.8H), 2.86 (s, 3H), 1.74 (s, 3H).  
       Example 66  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-[(thymin-1-yl)-acetyl]-piperazin-2-one  
       [0282]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-[(thymin-1-yl)-acetyl]-glycine as per the procedure of example 57.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.31 (s, 1H), 8.42 (s, 1H), 8.05 (d, 1H), 8.01 (d, 1H), 7.35 (s, 0.6H), 7.29 (s, 0.4H), 4.69 (s, 1.2H), 4.61 (s, 0.8H), 4.48 (s, 0.8H), 4.37 (s, 1.2H), 4.21 (t, 1.2H), 4.07 (t, 0.8H), 3.98 (t, 1.2H), 3.88 (t, 0.8H), 1.76(s, 3H).  
       Example 67  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[4-N-(benzhydryloxycarbonyl)-cytosin-1-yl]-acetyl}]-piperazin-2-one  
       [0283]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(benzhydryloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (400 MHz; DMSO-d 6 ) δ 8.42 (s, 1H), 8.06-7.95 (m, 2H), 7.90 (d, 0.6H), 7.86 (d, 0.4H), 7.46 (d, 4H), 7.37 (t, 4H), 7.29 (t, 2H), 6.96 (d, 1H), 6.80 (s, 1H), 4.83 (s, 1.2H), 4.76 (s, 0.8H), 4.52 (s, 0.8H), 4.35 (s, 1.2H), 4.21 (t, 1.2H), 4.06 (t, 0.8H), 4.01 (t, 1.2H), 3.87 (t, 0.8H).  
       Example 68  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[6-N-(benzhydryloxycarbonyl)-adenin-9-yl]-acetyl}]-piperazin-2-one  
       [0284]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(benzhydryloxycarbonyl)-adenin-9-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.89 (s, 1H), 8.60 (s, 1H), 8.43 (s, dH), 8.33 (d, 0.6H), 8.31 (d, 0.4H), 8.07-7.98 (m, 2H), 7.53 (d, 4H), 7.38 (t, 4H), 7.29 (t, 2H), 6.83 (s, 1H), 5.41 (s, 1.2H), 5.31 (s, 0.8H), 4.63 (s, 0.8H), 4.35 (s, 1.2H), 4.27 (t, 1.2H), 4.12-4.07 (m, 2H), 3.90 (t, 0.8H).  
       Example 69  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[2-N-(benzhydryloxycarbonyl)-guanin-9-yl]-acetyl}]-piperazin-2-one  
       [0285]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(benzhydryloxycarbonyl)-guanin-9-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (400 MHz; DMSO-d 6 ) δ 11.26 (s, 1H), 8.43 (s, 1H), 8.06-7.93 (m, 2H), 7.81 (d, 1H), 7.46 (d, 4H), 7.38 (t, 4H), 7.30 (t, 2H), 6.86 (s, 1H), 5.17 (s, 1.2H), 5.09 (s, 0.8H), 4.60 (s, 0.8H), 4.36 (s, 1.2H), 4.25 (t, 1.2H), 4.10-4.05 (m, 2H), 3.89 (t, 0.8H).  
       Example 70  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[4-N-(4-methoxybenzyloxycarbonyl)-cytosin-1-yl]-acetyl}]-piperazin-2-one  
       [0286]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(4-methoxybenzyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.69 (s, 1H), 8.42 (s, 1H), 8.40 (s, 1H), 8.07-7.96 (m, 2H), 7.90 (d, 0.6H), 7.87 (d, 0.4H), 7.36 (d, 2H), 7.03 (d, 1H), 6.94 (d, 2H), 5.11 (s, 2H), 4.83 (s, 1.2H), 4.75 (s, 0.8H), 4.52 (s, 0.8H), 4.35 (s, 1.2H), 4.21 (t, 1.2H), 4.06 (t, 0.8H), 4.01 (t, 1.2H), 3.88 (t, 0.8H), 3.76 (s, 3H).  
       Example 71  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[6-N-(4-methoxybenzyloxycarbonyl)-adenin-9-yl]-acetyl}]-piperazin-2-one  
       [0287]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(4-methoxybenzyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.57 (s, 1H), 8.59 (s, 0.6H), 8.58 (s, 0.4H), 8.43 (s, 0.4H), 8.42 (s, 0.6H), 8.31 (s, 0.6H), 8.29 (s, 0.4H), 8.04-8.00 (m, 2H), 7.39 (d, 2H), 6.95 (d, 2H), 5.40 (s, 1.2H), 5.31 (s, 0.8H), 5.14 (s, 2H), 4.63 (s, 0.8H), 4.35 (s, 1.2H), 4.28 (t, 1.2H), 4.11 (t, 1.2H), 4.08 (t, 0.8H), 3.90 (t, 0.8H), 3.76 (s, 3H).  
       Example 72  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[2-N-(4-methoxybenzyloxycarbonyl)-guanin-9-yl]-acetyl}]-piperazin-2-one  
       [0288]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(4-methoxybenzyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.38 (brs, 1H), 8.42 (s, 1H), 8.08-7.99 (m, 2H), 7.82 (s, 0.6H), 7.80 (s, 0.4H), 7.38 (d, 2H), 6.95 (d, 2H), 5.18 (s, 2H), 5.15 (s, 1.2H), 5.07 (s, 0.8H), 4.60 (s, 0.8H), 4.35 (s, 1.2H), 4.25 (t, 1.2H), 4.12-4.05 (m, 2H), 3.89 (t, 0.8H), 3.76 (s, 3H).  
       Example 73  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[4-N-(piperonyloxycarbonyl)-cytosin-1-yl]-acetyl}]-piperazin-2-one  
       [0289]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[4-N-(piperonyloxycarbonyl)-cytosin-1-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (400 MHz; DMSO-d 6 ) δ 10.71 (s, 1H), 8.42 (s, 1H), 8.07-7.95 (m, 2H), 7.91 (d, 0.6H), 7.87 (d, 0.4H), 7.02 (d, 1H), 6.99 (s, 1H), 6.91 (s, 2H), 6.02 (s, 2H), 5.08 (s, 2H), 4.84 (s, 1.2H), 4.76 (s, 0.8H), 4.52 (s, 0.8H), 4.35 (s, 1.2H), 4.21 (t, 1.2H), 4.06 (t, 0.8H), 4.02 (t, 1.2H), 3.88 (t, 0.8H).  
       Example 74  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[6-N-(piperonyloxycarbonyl)-adenin-9-yl]-acetyl}]-piperazin-2-one  
       [0290]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[6-N-(piperonyloxycarbonyl)-adenin-9-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 10.60 (s, 1H), 8.59 (s, 0.6H), 8.58 (s, 0.4H), 8.43 (s, 0.4H), 8.42 (s, 0.6H), 8.31 (s, 0.6H), 8.30 (d, 0.4H), 8.08-7.99 (m, 2H), 7.05 (s, 1H), 6.95 (d, 1H), 6.92 (d, 1H), 6.02 (s, 2H), 5.40 (s, 1.2H), 5.31 (s, 0.8H), 5.11 (s, 2H), 4.63 (s, 0.8H), 4.35 (s, 1.2H), 4.28 (t, 1.2H), 4.12 (t, 0.8H), 4.08 (t, 1.2H), 3.90 (t, 0.8H).  
       Example 75  
     1-[5-(4-Chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonyl]-4-{[2-N-(piperonyloxycarbonyl)-guanin-9-yl]-acetyl}]-piperazin-2-one  
       [0291]     The title compound was synthesized by the reaction of N-{2-[5-(4-chloro-2-nitrophenyl)-1,3,4-thiadiazole-2-sulfonylamino]-ethyl}-N-{[2-N-(piperonyloxycarbonyl)-guanin-9-yl]-acetyl}-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.38 (brs, 1H), 8.42 (s, 1H), 8.09-7.99 (m, 2H), 7.82 (s, 0.6H), 7.80 (s, 0.4H), 7.01 (s, 1H), 6.93 (d, 1H), 6.91 (d, 1H), 6.03 (s, 2H), 5.14 (s, 3.2H), 5.07 (s, 0.8H), 4.59 (s, 0.8H), 4.35 (s, 1.2H), 4.24 (t, 1.2H), 4.10-4.05 (m, 2H), 3.88 (t, 0.8H).  
       Example 76  
     1-(5-Benzoyl-4-phenyl-thiazole-2-sulfonyl)-4-(thymine-1-yl-acetyl)-piperazin-2-one  
       [0292]     The title compound was synthesized by the reaction of N-[2-(5-benzoyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.30(s, 0.6H), 11.29 (s, 0.4H), 7.76-7.72 (m, 2H), 7.59 (t, 1H), 7.47 (d, 2H), 7.40 (t, 2H), 7.34-7.26 (m, 4H), 4.66 (s, 1.2H), 4.60 (s, 0.8H), 4.47 (s, 0.8H), 4.33 (s, 1.2H), 4.20 (t, 1.2H), 4.06 (t, 0.8H), 3.95 (t, 1.2H), 3.84 (t, 0.8H), 1.73 (s, 1.65H), 1.74 (s, 3H).  
       Example 77  
     1-(5-methyl-4-phenyl-thiazole-2-sulfonyl)-4-(thymine-1-yl-acetyl)-piperazin-2-one  
       [0293]     The title compound was synthesized by the reaction of N-[2-(5-methyl-4-phenyl-thiazole-2-sulfonylamino)-ethyl]-N-(thymine-1-yl-acetyl)-glycine as per the procedure of example 57.  1 H NMR (500 MHz; DMSO-d 6 ) δ 11.30 (s, 0.6H), 11.29 (s, 0.4H), 7.69 (d, 2H), 7.52 (t, 2H), 7.45 (t, 1H), 7.32 (s, 0.6H), 7.27 (s, 0.4H), 4.66 (s, 1.2H), 4.58 (s, 0.8H), 4.42 (s, 0.8H), 4.28 (s, 1.2H), 4.17 (t, 1.2H), 4.03 (t, 0.8H), 3.92 (t, 1.2H), 3.81 (t, 0.8H), 2.68 (s, 3H), 1.74 (s, 3H).  
         [0294]     Solid Phase Synthesis of PNA Oligomer  
         [0295]     General Procedure  
         [0296]     PNA oligomer synthesis was conducted manually on a CLEAR-Base resin (Peptide international) which is a cross linked ethylate acrylate resin with amine functionality. The resin was coupled with PAL linker (5-[4-(9-fluorenylmethoxycarbonyl)amino-3,5-dimethoxyphenoxy]pentanoic acid (Advanced ChemTech) by using HBTU as a coupling reagent in DMF. The resulting resin was treated with 20% piperidine in DMF to activate the amine functional group of PAL linker for PNA oligomer synthesis. The PNA oligomer was synthesized according to the following synthesis cycle. All reactions and washes of the resin were performed in a fritted syringe reactor.  
         [0297]     Following is a non-limiting general procedure for solid phase synthesis of PNA oligomer:  
         [0298]     1. Coupling with 10 equiv. of appropriate monomer (0.4 M in 0.5M acetic acid in DMF) for 2 h.  
         [0299]     2. Washing with DMF 3 times.  
         [0300]     3. Capping with acetic anhydride (5% acetic anhydride and 6% lutidine in DMF) for 5 mm.  
         [0301]     4. Washing with DMF 2 times.  
         [0302]     5. Cleavage over reacted acetyl group in sulfonamide with piperidine (1.0 M in DMF) for 5 min.  
         [0303]     6. Washing with DMF 3 times.  
         [0304]     7. Deprotection of thiazole or thiadiazole-2-sulfonyl group with 4-methoxybenzenethiol for 15 min.  
         [0305]     8. Washing with DMF 3 times  
         [0306]     After removal of the final thiazole or thiadiazole-2-sulfonyl group, the resin is washed with DMF 3 times and dichloromethane 2 times and dried. The removal the protecting group of exocyclic amine and cleavage from the resin was performed in one step by treatment with 25% m-cresol in TFA for 1.5 h. The resin is filtered off and washed with TFA. Almost TFA of the combined filtrate is removed by blowing a steady stream of nitrogen. Then the residue was suspended with ethyl ether and centrifuged. The supernatant is carefully decanted off. The residue of crude PNA oligomer is washed one more time by suspension with ethyl ether, centrifuge, and removal of supernatant. The crude PNA oligomer is analyzed with HPLC and confirmed by Matrix Assisted Laser Desorption-Time of Flight (MALDI-TOF).  
       Example 78  
     Synthesis of PNA Oligomer Sequence H 2 N-CGCTA-H  
       [0307]     The title sequence was synthesized manually by the above general procedure using monomer of general formula I, wherein E is sulfur; J is nitrogen; R1 is 4-chloro-2-nitro-phenyl; R2 is H; and the protecting group of exocyclic amine of nucleobases (A, C, and G) is benzhydryloxycarbonyl.  FIG. 13  shows HPLC profile. MALDI-TOF MS: 1352.5 (M+H).  
         [0308]     Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention specifically described herein. Such equivalents are intended to be encompassed in the scope of the claims.