Abstract:
The present invention relates to a process for preparing haptens for immunoassay of phosphorothioate pesticides, which comprises the steps of reacting O-methyl(ethyl) dichlorothiophosphate with a phenolic compound to obtain O-methyl(ethyl) O-aryl chlorothiophosphate, and reacting the O-(methyl)ethyl O-aryl chlorothiophosphate thus obtained with aminocarboxylic acid to give desired haptens. In accordance with the present invention, haptens having a structure of O-methyl(ethyl) O-aryl N-(carboxyalkyl)phosphoramidothioate or O-methyl(ethyl) O-aryl N-alkyl-N-(carboxyalkyl)phosphoramidothioate can be simply prepared with a high yield by employing two-step processes in a cost-efficient manner.

Description:
RELATED APPLICATIONS 
     This application is a continuation under 35 U.S.C. § 365 (c) claiming the benefit of the filing date of PCT Application No. PCT/KR01/02301 designating the United States, filed Dec. 29, 2001. The PCT Application was published in English as WO 03/055895 A1 on Jul. 10, 2003. The contents of the international application No. PCT/KR01/02301 and the publication WO 03/055895 A1 are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for preparing haptens for immunoassay of phosphorothioate pesticides, more specifically, to a process for preparing haptens for immunoassay of organophosphorus phosphorothioate pesticides, by reacting O-methyl(ethyl) dichlorothiophosphate with a phenolic compound to obtain O-methyl(ethyl) O-aryl chlorothiophosphate, and reacting O-methyl(ethyl) O-aryl chlorothiophosphate thus obtained with aminocarboxylic acid. 
     2. Background of the Invention 
     Since Schrader&#39;s discovery of an organophosphorus compound possessing insecticidal activity in the 1930&#39;s, lots of organophosphorus pesticides with high biological activities have been actively developed in the art, in line with the movement of prohibiting the use of organochlorine pesticides. Nowadays, organophosphorus pesticides hold a large majority in current pesticides. Further, it is remarkable that about 100,000 of them have been identified to possess insecticidal activity, and more than 100 of them are commercially available. 
     Organophosphorus pesticides are classified into phosphate, phosphorothioate, phosphorothiolate, phosphorodithioate, phosphonate, phosphonothioate, phosphonodithioate, phosphorothiolothinate, and phosphoroamidate, depending on their chemical structures around a phosphorus atom (see: Table 1). Among them, phosphorothioate and phosphorodithioate are considered to be the most important pesticides in agriculture and have become the main subject of assaying residual pesticides. 
     The assay of residual pesticide has been carried out mainly by the aid of GC or HPLC, both of which have innate disadvantages that a time-consuming step of pre-treatment, high-priced machinery and tools, and labors with professional techniques are required and, in the case of GC, it is impossible to assay thermolabile material and in the case of HPLC, it is hard to assay pesticides having no chromophore. To solve these problems, many attempts to employ an immunoassay method for analysing residual pesticides, which was mainly used for assay of bio-components or a clinical diagnosis, began to be made in the 1970&#39;s. Immunoassay of residual pesticides is more favorable than the conventional methods in the points that: it is highly sensitive; pre-treatment of samples is not required; and, it costs a less deal since it allows the rapid assay of multiple samples in a simultaneous manner. 
     Immunoassay is based on the specific binding with a high affinity between antibodies and antigens. Thus, to develop immunoassay, an appropriate antigen should be prepared to generate antibodies against a substance to be assayed. However, low-molecular weight materials, such as pesticides, cannot serve as antigens in themselves and thus, antibodies cannot be generated. Under the circumstances, the need has been raised that haptens having a similar structure to pesticide and a functional groups capable of forming covalent bonds with proteins, should be synthesized for preparing pesticide-specific antigens. Also, synthesis of haptens has been required for preparing an enzyme tracer and a coating antigen, a competitor to be used for a competitive-immunoassay method. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Classification of organophosphorus pesticides 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Class 
                 Structure 
                 Example 
               
               
                   
                   
               
               
                   
                 Phosphate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Dichlorvos 
               
               
                   
                   
               
               
                   
                 Phosphorothioate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Parathion 
               
               
                   
                   
               
               
                   
                 Phosphorothiolate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Omethoate 
               
               
                   
                   
               
               
                   
                 Phosphorodithioate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Malathion 
               
               
                   
                   
               
               
                   
                 Phosphonate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 trichlorfon 
               
               
                   
                   
               
               
                   
                 Phosphonothioate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 EPN 
               
               
                   
                   
               
               
                   
                 Phosphonodithioate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Fonfos 
               
               
                   
                   
               
               
                   
                 Phosphorothiolothionate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Ethoprop 
               
               
                   
                   
               
               
                   
                 Phosphoroamidate 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Dimefox 
               
               
                   
                   
               
             
          
         
       
     
     In general, haptens used for immunoassay of phosphorothioate pesticides have a chemical structure as following: 
                                
wherein,
         R 1  is methyl or ethyl group;   R 2  is aryl group;   R 3  is hydrogen or alkyl group; and,   R 4  is alkylidene group.       

     Among the above haptens, haptens having the structure in which R 3  is hydrogen and R 4  is di- or pentamethylene group have been synthesized so far. The haptens having the structure in which R 3  is hydrogen and R 4  is dimethylene group have been synthesized by a process comprising the steps of: (i) reacting 3-aminopropanoic acid (1) with benzylchloroformate to obtain 3-(benzyloxycarbonylamino)propanoic acid (2); (ii) reacting 3-(benzyloxycarbonylamino)propanoic acid (2) thus obtained with tert-butanol in the presence of dicyclohexalcarbodiimide(DCC) to obtain tert-butyl 3-(benzyloxycarbonylamino)propanoate (3); (iii) eliminating amino protective group from tert-butyl 3-(benzyloxycarbonylamino)propanoate (3) thus obtained by way of hydrogenation using a catalyst to obtain tert-butyl-3-aminopropanoate (4); (iv) reacting tert-butyl 3-aminopropanoate (4) thus obtained with O-methyl dichlorothiophosphate (5) to obtain tert-butyl 3-[chloro(methoxyl)phosphorothioylamino]propanoate (6); (v) reacting tert-butyl 3-[chloro(methoxyl) phosphorothioylamino]propanoate thus obtained with a sodium salt of phenol (7) to obtain tert-butyl 3-[methoxy(aryloxy)phosphorothioylamino]propanoate (8); and, (vi) removing tert-butyl protective group from tert-butyl 3-[methoxy(aryloxy)phosphorothioylamino]propanoate (8) with an aid of trifluoroacetic acid(TFA) to obtain 3-[methoxy(aryloxy)phosphorothioylamino]propanoic acid (9). 
     
       
                 
         
             
             
         
      
     
     It has been known that O-alkyl O-aryl N-(2-carboxyalkyl)phosphoramidothioates synthesized by the above process is can be a haptens highly preferable for generating antibodies for phosphothioate pesticides. However, the said process has revealed shortcomings that it is very complicated, time- and cost-consuming and poorly yielded, since the said method goes through a process comprising total six steps or seven steps provided a step of preparing a sodium salt of phenol is added. 
     Under the circumstances, there are strong reasons for developing a process for preparing haptens for immunoassay of phosphothioate pesticide in a more efficient manner. 
     SUMMARY OF THE INVENTION 
     The present inventors have made an effort to develop an efficient process for preparing haptens for immunoassay of phosphothioate pesticide, and found that haptens having a structure of O-methyl(ethyl) O-aryl N-(carboxyalkyl)phosphoramidothioate or O-methyl(ethyl) O-aryl N-alkyl-N-(carboxyalkyl)phosphoramidothioate can be prepared by the process comprising the steps of: reacting O-methyl(ethyl) dichlorothiophosphate with a phenolic compound to obtain O-methyl(ethyl) O-aryl chlorothiophosphate; and, reacting O-methyl(ethyl) O-aryl chlorothiophosphate thus obtained with aminocarboxylic acid whose carboxylic group is not protected. 
     A primary object of the present invention is, therefore, to provide a process for preparing haptens for immunoassay of organophosphorus phosphorothioate pesticides. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A process for preparing haptens for immunoassay of organophosporous phosphorothioate pesticides comprises the steps of: (i) reacting a compound (10) with a phenolic compound ( 11 ) and K 2 CO 3  in acetonitrile at 4° C. for 30 to 90 min to obtain a compound (12); and, (ii) reacting the compound (12) with a compound (13) and KOH in methanol at 4° C. for 3 to 5 min to obtain a compound (14). The phosphorothioate pesticides includes fenthion, fenitrothion, parathion, parathion-methyl, bromophos-methyl, bromophos-ethyl, chlorpyrifos, chlorpyrifos-methyl, diazinon, isofenphos and pyrimiphos-methyl. 
     
       
                 
         
             
             
         
      
         
         
           
             wherein,
           R 1  is methyl or ethyl group;   R 2  is aryl group;   R 3  is hydrogen or alkyl group; and,   R 4  is alkylidene polymethylene or substituted polymethylene group.   
         
           
         
       
    
     The present invention is further illustrated in the following examples, which should not be taken to limit the scope of the invention. 
     EXAMPLE 1 
     Preparation of Haptens for Immunoassay of Phosphorothioate Pesticides 
     O-methyl(ethyl) O-aryl chlorothiophosphate, which was obtained by reacting O-methyl(ethyl) dichlorothiophosphate with phenol, was reacted with aminocarboxylic acid to give a hapten for immunoassay of phosphorothioate pesticides: to 46 mmol of O-methyl(ethyl) dichlorothiophosphate (10) dissolved in 30 mL of acetonitrile was added 45 g of ground K 2 CO 3  and 42 mmol of phenol (11) dissolved in 30 mL of acetonitrile, and the mixture was stirred for 1 hour at room temperature. Then, the reaction mixture was filtered with cellite, the solvent was evaporated from the filtrate, and the remnant was subject to silica-gel column chromatography equilibrated with benzene/hexane (1:1, v/v) or hexane/ethylacetic acid (10:1, v/v), to obtain oily compound of O-methyl(ethyl) O-aryl chlorothiophosphate (12). 
     A solution of 2.1 mmol of O-methyl(ethyl) O-aryl chlorothiophosphate (12) thus obtained in 3 mL of methanol, cooled in ice-water bath, was stirred for 3 to 5 min with a gradual addition of 5.2 mmol (292 mg) of KOH and 2.6 mmol of aminocarboxylic acid (13) dissolved in 1.7 mL of methanol. In a case that aminocarboxylic acid is hydrochloride, the molar ratio of KOH to aminocarboxylic acid was three. The reaction solution was poured into a separatory funnel, and the product was extracted with the addition of 1N HCl and chloroform. The extract was dehydrated over MgSO 4 , the solvent was evaporated, and the remnant was subject to silica-gel column chromatography equilibrated with chloroform:ethylacetic acid:acetic acid (65:35:1, v/v/v), to obtain a compound (14) for the immunoassay of phosphorothioate pesticide. In the following chemical reaction scheme, R 1  is methyl or ethyl group, R 2  is aryl group, R 3  is hydrogen or alkyl group, and R 4  is alkylidene polymethylene or substituted polymethylene group. 
     
       
                 
         
             
             
         
      
     
     EXAMPLE 2 
     Synthesis of Haptens for Immunoassay of Phosphorothioate Pesticides 
     By employing the method of Example 1, haptens with various substituents (R 1 , R 2 , R 3  and R 4 ) were synthesized for immunoassay of phosphorothioate pesticides such as parathion-methyl, chlorpyrifos and isofenphos. Various structures of haptens for immunoassay of phosphorothioate pesticide are shown in Table 2 below, where Ph and Pyr represent benzene ring and pyridinyl group, respectively. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Various structures of haptens for immunoassay of phosphorothioate pesticides 
               
             
          
           
               
                   
                 Phosphorothioate pesticides 
                 R 1   
                 R 2   
                 R 3   
                 R 4   
               
               
                   
                   
               
             
          
           
               
                 A 
                 parathion-methyl 
                 CH 3   
                 Ph-p-NO 2   
                 H 
                 —(CH 2 ) 3 — 
               
               
                 B 
                 parathion-methyl 
                 CH 3   
                 Ph-p-NO 2   
                 H 
                 —(CH 2 ) 5 — 
               
               
                 C 
                 parathion-methyl 
                 CH 3   
                 Ph-p-NO 2   
                 CH 3   
                 —(CH 2 ) 3 — 
               
               
                 D 
                 chlorpyrifos 
                 CH 3 CH 2   
                 Pyr-(3,5,6-trichloro) 
                 H 
                 —(CH 2 ) 3 — 
               
               
                 E 
                 chlorpyrifos 
                 CH 3 CH 2   
                 Pyr-(3,5,6-trichloro) 
                 H 
                 —(CH 2 ) 5 — 
               
               
                 F 
                 chlorpyrifos 
                 CH 3 CH 2   
                 Pyr-(3,5,6-trichloro) 
                 CH 3   
                 —(CH 2 ) 3 — 
               
               
                 G 
                 isofenphos 
                 CH 3 CH 2   
                 Ph-o-CO 2 CH(CH 3 ) 2   
                 H 
                 —CH(CH 3 )CH 2 — 
               
               
                   
               
             
          
         
       
     
       1 H NMR analysis revealed that the synthesized haptens have the same spectrum as those of the structures of haptens shown in Table 2. In  1 H NMR spectrum, the value of chemical shift (ppm) is given relative to internal tetramethylsilane and the values of coupling constant (J) is expressed in Hz and s, d, t, q, qn, sp, ar and m represent singlet, doublet, triplet, quartet, quintet, septet, aromatic and multiplet, respectively. 
     EXAMPLE 2-1 
     Synthesis of Hapten A 
     By employing the method of Example 1, hapten A(R 1 =methyl, R 2 =ρ-nitrophenyl, R 3 =hydrogen and R 4 =(CH 2 ) 3  was synthesized: to 4.59 g (28 mmol) of O-methyl dichlorothiophosphate dissolved in 20 mL of acetonitrile was added 20 g of ground K 2 CO 3  and 3.00 g (22 mmol) of 4-nitrophenol dissolved in 15 mL of acetonitrile, and the mixture was stirred for 1 hour at room temperature. Then, the reaction mixture was filtered with cellite, the solvent was evaporated solvent from the filtrate, and the remnant was subject to silica-gel column chromatography equilibrated with benzene/hexane (1:1, v/v) to obtain oily compound of O-methyl O-(4-nitrophenyl)chlorothiophosphate. The yield of the compound was 70% and its NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ8.28(2H, d, J=6.1, ar), 7.42(2H, d, J=7.2, ar), 4.03(3H, d, J=16.5, CH 3 OP) 
     A solution of 500 mg (1.9 mmol) of O-methyl O-(4-nitrophenyl)chlorothiophosphate thus obtained in 3 mL of methanol, cooled in ice-water bath, was stirred for 3 to 5 min with a gradual addition of 274 mg (4.9 mmol) of KOH and 229 mg (2.2 mmol) of aminobutyric acid in 1.7 mL of methanol. The reaction solution was poured into a separatory funnel, and the product was extracted with an addition of 1N HCl and chloroform. The extract was dehydrated over MgSO 4,  the solvent was evaporated, and the remnant was subject to silica-gel column chromatography equilibrated with chloroform:ethylacetic acid:acetic acid (65:35:1, v/v/v), to obtain a hapten A of Table 2. The yield of hapten A was 81% and its NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ8.24 (2H, d, J=8.9, ar), 7.38 (2H, d, J=8.3, ar), 3.81 (3H, d, J=14.1, CH 3 OP), 3.47 (1H, dxt, J=14.8 &amp; 7.0, NH), 3.17 (2H, dxq, J=13.6 &amp; 6.9, NCH 2 ), 2.46 (2H, t, J=7.0, CH 2 CO 2 ), 1.88 (2H, qn, J=7.0, CH 2 CH 2 CH 2 ) 
     EXAMPLE 2-2 
     Synthesis of Hapten B 
     By employing the method of Example 1, hapten B(R 1 =methyl, R 2 =ρ-nitrophenyl, R 3 =hydrogen and R 4 =(CH 2 ) 5 ) was synthesized: a solution of 500 mg (1.9 mmol) of O-methyl O-(4-nitrophenyl)chlorothiophosphate in 3 mL of methanol, cooled in ice water bath, was stirred for 3 to 5 min with a gradual addition of 274 mg (4.9 mmol) of KOH and 291 mg (2.2 mmol) of 6-aminocaproic acid in 1.7 mL of methanol. Then, hapten B was synthesized in a similar manner as in Example 2-1, whose yield was 88% and NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ8.24 (2H, d, J=8.9, ar), 7.37 (2H, dxd, J=9.2 &amp; 1.4, ar), 3.81 (3H, d, J=14.2 CH 3 OP), 3.34 (1H, dxt, J=15.5 &amp; 6.8, NH), 3.09 (2H, dxq, J=13.8 &amp; 6.9, NCH 2 ), 2.37 (2H, t, J=7.3, CH 2 CO), 1.68 (2H, qn, J=7.6, NHCH 2 CH 2 ), 1.56 (2H, m, CH 2 CH 2 CO), 1.40 (2H, m, (CH 2 ) 2 CH 2 CH 2 (CH 2 ) 2 ) 
     EXAMPLE 2-3 
     Synthesis of Hapten C 
     By employing the method of Example 1, hapten C(R 1 =methyl, R 2 =ρ-nitrophenyl, R 3 =methyl and R 4 =(CH 2 ) 3  was synthesized: a solution of 202 mg (0.76 mmol) of O-methyl O-(4-nitrophenyl)chlorothiophosphate in 1.5 mL of methanol, cooled in ice-water bath, was stirred for 5 min with a gradual addition of 207 mg (3.7 mmol) of KOH and 154 mg (1.0 mmol) of 4-(methylamino)butyric acid(salt of hydrochloride) in 1.5 mL of methanol. Then, hapten C was synthesized in a similar manner as in Example 2-1, whose yield was 70% and its NMR data was as follows: 
       1 H NMR (400 MHz, CDCl 3 ): δ8.23 (2H, d, J=9.0, ar), 7.31 (2H, d, J=9.0, ar), 3.76 (3H, d, J=14.1, CH 3 OP), 3.36 (2H, dxq, NCH 2 ), 2.86 (3H, d, J=11.0, CH 3 N), 2.40 (2H, t, J=7.5, CH 2 CO 2 ), 1.89 (2H, qn, J=7.0, CH 2 CH 2 CH 2 ) 
     EXAMPLE 2-4 
     Synthesis of Hapten D 
     By employing the method of Example 1, hapten D(R 1 =ethyl, R 2 =3,5,6-trichloro-2-pyridyl, R 3 =hydrogen and R 4 =(CH 2 ) 3 ) was synthesized: to 3.52 g (20 mmol) of O-ethyl dichlorothiophosphate dissolved in 20 mL of acetonitrile was added 10 g of ground K 2 CO 3  and 3.00 g (15 mmol) of 3, 5, 6-trichloro-2-pyridinol dissolved in 5 mL of acetonitrile, and the mixture was stirred for 1 hour at room temperature. Then, the reaction mixture was filtered with cellite, the solvent was evaporated, and the remnant was subject to silica-gel column chromatography equilibrated with benzene/hexane (1:1, v/v) solvent to obtain oily compound of O-ethyl O-(3, 5, 6-trichloro-2-pyridyl)chlorothiophosphate. The yield of the said compound was 65% and its NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ7.91 (1H, d, J=1.3, ar), 4.52 (2H, qxd, J=11.0 &amp; 7.1, CH 2 CH 3 ), 1.51 (3H, txd, J=7.1 &amp; 1.1, CH 2 CH 3 ) 
     A solution of 0.50 g (1.5 mol) of O-ethyl O-(3, 5, 6-trichloro-2-pyridyl)chlorothiophosphate thus obtained was dissolved in 3 mL of methanol, cooled in ice-water bath, was stirred for 3 to 5 min with a gradual addition of 0.205 g (3.23 mmol) of KOH and 0.166 g (1.6 mmol) of aminobutyric acid in 1.7 mL of methanol. Then, hapten D was synthesized in a similar manner as in Example 2-1, whose yield was 54% and its NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ7.85 (1H, d, J=0.9, ar), 4.34 (2H, qxd, J=9.5 &amp; 7.1, CH 2 CH 3 ), 3.54 (1H, dxt, J=11.4 &amp; 6.6, NH), 3.25 (2H, dxq, J=13.1 &amp; 6.8, NHCH 2 ), 2.51 (2H, t, J=7.2, CH 2 CO 2 ), 1.93 (2H, qn, J=6.9, CH 2 CH 2 CH 2 ), 1.41 (3H, t, J=7.1, CH 2 CH 3 ) 
     EXAMPLE 2-5 
     Synthesis of Hapten E 
     By employing the method of Example 1, hapten E(R 1 =ethyl, R 2 =3,5,6-trichloro-2-pyridyl, R 3 =hydrogen and R 4 =(CH 2 ) 5  was synthesized: a solution of 0.50 g (1.5 mol) of O-ethyl O-(3, 5, 6-trichloro-2-pyridyl)chlorothiophosphate in 3 mL of methanol, cooled in ice-water bath, was stirred for 5 min with a gradual addition of 0.205 g (3.2 mmol) of KOH and 0.210 g (1.6 mmol) of 6-aminocaproic acid in 1.7 mL of methanol. Then, hapten E was synthesized in a similar manner as in Example 2-1, whose yield was 53% and its NMR data was as follows: 
       1 H NMR(250 MHz, CDCl 3 ): δ7.87 (1H, d, J=1.0, ar), 4.36 (2H, qxd, J=9.6 &amp; 7.1, CH 2 CH 3 ), 3.47 (1H, dxt, J=12.2 &amp; 6.5, NH), 3.19 (2H, dxq, J=13.8 &amp; 6.9, NHCH 2 ), 2.40 (2H, t, J=7.3, CH 2 CO 2 ), 1.50 (6H, m, CH 2 (CH 2 ) 3 CH 2 ), 1.43 (3H, t, J=7.1, CH 2 CH 3 ) 
     EXAMPLE 2-6 
     Synthesis of Hapten F 
     By employing the method of Example 1, hapten F(R 1 =ethyl, R 2 =3,5,6-trichloro-2-pyridyl, R 3 =methyl and R 4 =(CH 2 ) 3 ) was synthesized: 0.50 g (1.5 mol) of O-ethyl O-(3, 5, 6-trichloro-2-pyridyl)chlorothiophosphate in 3 mL of methanol, cooled in ice-water bath, was stirred for 5 min with a gradual addition of 0.31 g (4.8 mmol) of KOH and 0.166 g (1.6 mmol) of 4-(methylamino)butyric acid(salt of hydrochloride) in 1.7 mL of methanol. Then, hapten F was synthesized in a similar manner as in Example 2-1, whose yield was 54% and its NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ7.82 (1H, s, ar), 4.36 (2H, qxd, J=8.7 &amp; 7.1, CH 2 CH 3 ), 3.33 (2H, m, NCH 2 ), 2.87 (3H, d, J=12.3, CH 3 N), 2.46 (2H, t, CH 2 CO 2 ), 1.93 (2H, qn, CH 2 CH 2 CH 2 ), 1.43 (3H, t, J=7.1, CH 2 CH 3 ) 
     EXAMPLE 2-7 
     Synthesis of Hapten G 
     By employing the method of Example 1, hapten G(R 1 =ethyl, R 2 =2-(isopropyloxycarbonyl)phenyl, R 3 =hydrogen and R 4 =CH(CH 3 )CH 2 ) was synthesized: to 2.96 g (17 mmol) of O-ethyl dichlorothiophosphate dissolved in 10 mL of acetonitrile was added 5 g of ground K 2 CO 3  and 1.96 g (11 mmol) of isopropyl salicylate dissolved in 20 mL of acetonitrile, and the mixture was stirred for 40 min at room temperature. Then, the reaction mixture was filtered with cellite, the solvent was evaporated, and the remnant was subject to silica-gel column chromatography equilibrated with hexane/ethylacetatic acid (10:1, v/v) to obtain oily compound of O-ethyl O-[(2-isopropyloxycarbonyl)phenyl]chlorothiophosphate. The yield of the said compound was 61% and its NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ7.93 (1H, dxd, J=7.7 &amp; 1.2, ar), 7.55 (1H, dxd, J=8.5 &amp; 1.5, ar), 7.48 (1H, txt, J=8.4 &amp; 1.6, ar), 7.32 (1H, txt, J=7.5 &amp; 1.5, ar), 5.25 (1H, sp, J=6.3, (CH 3 ) 2 CH), 4.48 (2H, q, J=7.1, CH 2 CH 3 ), 1.47 (3H, t, J=7.1, CH 2 CH 3 ), 1.38 (6H, d, J=6.3, CH(CH 3 ) 2 ) 
     A solution of 67 mg (0.21 mol) of O-(2-isopropyloxycarbonyl)phenyl]chlorothiophosphate in 0.2 mL of methanol, cooled in ice-water bath, was stirred for 5 min with a gradual addition of 31 mg (0.55 mmol) of KOH and 26 mg (0.25 mmol) of DL-aminobutyric acid in 0.26 mL of methanol. The reaction solution was poured into a separatory funnel, and the product was extracted with an addition of 1N HCl and chloroform. The extract was dehydrated over MgSO 4,  the solvent was evaporated, and the remnant was subject to silica-gel column chromatography equilibrated with chloroform:ethylacetic acid:acetic acid (29:9:1, v/v/v), to obtain a hapten G of Table 2. The yield of hapten G thus obtained was 66% and its NMR data was as follows: 
       1 H NMR(300 MHz, CDCl 3 ): δ7.81 (1H, dxd, J=8.9 &amp; 1.2, ar), 7.60 (1H, dxqn, J=8.2 &amp; 1.5, ar), 7.48 (1H, txt, J=7.9 &amp; 1.8, ar), 7.21 (1H, txt, J=7.5 &amp; 1.1, ar), 5.25 (1H, sp, J=6.2, (CH 3 ) 2 CH), 4.29 (1H, q, J=9.5, NHCH), 4.20 (2H, q, J=7.1, CH 2 CH 3 ), 3.97 (1H, sp, J=6.0, NHCH), 2.45 (2H, t, J=6.3, CH 2 CO 2 ), 1.38 (3H, t, J=7.0, CH 2 CH 3 ), 1.37 (6H, d, J=6.2, CH(CH 3 ) 2 ), 1.31 (3H, CHCH 3 )