To a cold solution of 200 mg of 3′,4′,3′″,4′″-tetra-dehydro-3,2′,6′,2′″,6′″-Cbz-Neomycin (1 (3 from Example 4), 0.16 mmol) in 4.0 mL DMF was added 103 mg PyBOP (0.1972 mmol) and 1-(tert-butoxycarbonyl)-3-hydroxyazetidine-3-carboxylic acid (0.1972 mmol). The flask was then cooled to 0° C. and 47.8 μl DIPEA (0.2793 mmol) was added. The reaction was allowed to stir at room temperature overnight then LCMS was used to confirm product formation and the absence of starting material. The reaction was then quenched with 10-20 mL 1 M citric acid and desired product was extracted into 10 mL ethyl acetate. The organic layers were washed with a second 10 mL 1 M citric acid, brine and dried while stirring with MgSO4. Concentration under vacuum provided crude intermediate (2) that was used in the next reaction without further purification. MS: m/z (M+Na) calc: 1438.57, obs: 1438.4.
