[C:1]([CH2:4][C:5]1[CH:14]=[CH:13][C:8]([C:9]([O:11][CH3:12])=[O:10])=[C:7]([O:15][CH3:16])[CH:6]=1)([OH:3])=[O:2].[Br:17]Br.CCCCCC>CC(O)=O>[Br:17][C:14]1[C:5]([CH2:4][C:1]([OH:3])=[O:2])=[CH:6][C:7]([O:15][CH3:16])=[C:8]([CH:13]=1)[C:9]([O:11][CH3:12])=[O:10]Methyl 4-carboxymethyl-2-methoxybenzoate 10c (12.7 g, 0.0567 mol) was dissolved in glacial AcOH (100 mL) and bromine (3.2 mL, 0.0624 mol, 1.1 eq) was added drop wise via a syringe, while maintaining the internal temperature between 20-25° C. After stirring for 4 h at RT, the AcOH was evaporated and the orange oil co-evaporated twice with toluene to give an orange solid. This material was triturated with CH2Cl2 and some of the precipitated product was removed by filtration. The rest of the product which remained in the filtrate was then concentrated, loaded on a silica gel column and eluted with 1% AcOH in EtOAc:hexane (6:4 ratio). The product was further purified by a second chromatography and re-crystallization from EtOAc:hexane to give pure methyl 5-bromo-4-carboxymethyl-2-methoxybenzoate as white solid 10d (total amount 9 g, 52% yield).
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