[CH2:1]([C:10]([OH:12])=[O:11])/[C:2](/[C:7]([OH:9])=[O:8])=[CH:3]\[C:4]([OH:6])=[O:5].C1N=CN(C(N2C=NC=C2)=O)C=1.FC(F)(F)S(O)(=O)=O.C1(SC)C=CC=CC=1.C1C(O)=CC=CC=1C.CCOCC>CN(C=O)C.FC(F)(F)C(O)=O.O>[C:10]([OH:12])(=[O:11])[CH:1]=[C:2]([CH2:3][C:4]([OH:6])=[O:5])[C:7]([OH:9])=[O:8]
Trans-aconitic acid (0.17 g, 1.0 mmol) and trifluoroacetic acid salt of β-Ala--Arg(Mts)--Leu--Asp(OBn)--Ser(Bn)--NH--iPr (SEQ ID NO:11) (3.23 g, 3.0 mmol) were condensed with CDI in DMF. The product was treated as in Example 73 to obtain the objective compound in the protected form (0.67 g, 0.22 mmol). The protected compound was dissolved in trifluoroacetic acid (10 ml), added with a trifuluoroacetic acid solution of 1M-trifluoromethanesulfonic acid/thioanisole/m-cresol with ice cooling at 0° C. and allowed to react for 1 hour to eliminate the protective group on the side chains and at the terminal of the peptide. The reaction mixture was poured into ether, and resulted oily precipitate was dissolved in distilled water, washed with ethyl acetate, passed through an anion-exchange resin column (Amberlite IRA400; C1 form) to convert the product into hydrochloride and lyophilized to obtain the objective aconitic acid (β-Ala--Arg--Leu--Asp--Ser--NH--iPr)3 (SEQ ID NO:11)3 (0.29 g, 0.15 mmol).
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