[NH2:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[CH:4][CH:3]=1.[OH-].[Na+].C([O-])([O-])=O.[Na+].[Na+].Cl[C:20]1[C:25](CC=O)=[C:24]([CH3:29])[CH:23]=[CH:22][C:21]=1[S:30]([O-:33])(=[O:32])=[O:31].C1C[O:37][CH2:36][CH2:35]1>O.C(OCC)C>[S:30]([O:33][CH2:35][C:36]([NH:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[CH:4][CH:3]=1)=[O:37])([C:21]1[CH:20]=[CH:25][C:24]([CH3:29])=[CH:23][CH:22]=1)(=[O:31])=[O:32]A mixture of p-aminobenzoic acid (92 mg, 0.67 mmol) and NaOH (27 mg, 0.67 mmol) in water (6 ml) was stirred at room temperature for 10 min until all of the solid material had dissolved. Na2CO3 (59 mg, 0.5561 mmol) was then added and the mixture cooled to 0° C. A solution of 2-chloro-2-oxoethyl-4-methylbenzenesulfonate (4, 200 mg, 0.8044 mmol) in THF (2 ml) was injected rapidly and the resulting solution allowed to warm to room temperature and stirred for 2 h. Then reaction mixture was poured into a separating funnel containing diethyl ether. The phases were separated and the aqueous phase washed with a further portion of diethyl ether. The aqueous phase was acidified to pH 1 by addition of 1N HCl solution and the product extracted into ethyl acetate. The ethyl acetate was washed twice with 1N HCl solution and the organic phase was dried (Na2SO4), filtered and the solvent removed in vacuo. The resulting pale orange solid was recrystallized from chloroform/MeOH (20:1) affording 5 as a white powder (146 mg, 62%). δH (400 MHz, DMSO) 2.37 (3H, s, Me), 4.70 (2H, s, CH2), 7.46 (2H, d, J=8 Hz, ArH), 7.59 (2H, d, J=8.6 Hz, ArH), 7.82 (2H, d, J=8 Hz, ArH), 7.87 (2H, d, J=8.6 Hz, ArH), 10.39 (1H, s, NH), 12.72 (1H, CO2H); δc (100.6 MHz, DMSO) 21.8, 68.0, 119.4, 126.4, 128.5, 130.9, 131.1, 132.7, 142.7, 146.0, 164.4, 167.5; MS (ES+) 349.7 (100%, [M+H]+), 371.7 (40%, [M+Na]+); MS (ES−) 347.9 (100%, [M−H]−); HRMS [M−H]− requires 348.05473, found 348.05334.
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