C[O:2]C(=O)CCCCC(O)=O.[CH2:12]1[CH2:17][CH2:16][CH:15]([N:18]=[C:19]=[N:20][CH:21]2[CH2:26][CH2:25][CH2:24][CH2:23][CH2:22]2)[CH2:14][CH2:13]1.ON1C(=O)CCC1=O>CN(C1C=CN=CC=1)C.CN(C=O)C>[C:19]([NH:18][CH:15]1[CH2:14][CH2:13][CH2:12][CH2:17][CH2:16]1)([NH:20][CH:21]1[CH2:26][CH2:25][CH2:24][CH2:23][CH2:22]1)=[O:2]Step 1, Compound 4: Adipic acid monomethyl ester is treated with one molar equivalent of DCC, DMAP and N-hydroxysuccinimide in DMF for 30 min. To this a molar equivalent of the compound obtained from Step 3a (Example 1) is added and stirred at ambient temperature for 8 h. Dicylcohexylurea formed during the course of the reaction is filtered off and the product is extracted into ethyl acetate, washed with sodium bicarbonate solution followed by standard workup. The methyl ester thus obtained is treated with LiOH in THF/water to obtain compound 4.
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