0 1 n h 2 so 4 twice with saturated nahco 3 and once with brine the organic layer was then dried over mgso 4 filtered and concentrated in vacuo the residue was then purified on silica get using 5 methanol in dcm as eluent to provide pure methyl ester 2 3 equivalents of lithium iodide was added to 1 equivalent of the methyl ester in pyridine and the mixture heated at reflux for 8 hours the reaction was concentrated in vacuo and the residue was partitioned between etoac and 1n hcl the aqueous layer was extracted three times with etoac and the combined organic layers were washed with 1m nahco 3 dried over mgso 4 and concentrated in vacuo the residue was dissolved in nmm and the solution concentrated in vacuo the residue was taken up in dcm and then washed three times with 1n hcl the organic layer was dried over mgso 4 and concentrated in vacuo to provide the benzoic acid in high enough purity to be used without further purification 1 equivalent of the acid 2 equivalents of commercially available u03b2 boc diaminopropionic acid methyl ester 2 equivalents of edc 1 equivalent of hobt and 3 equivalents of dipea were dissolved.