The crude acid 20a (410 mg, 1.09 mmol) was dissolved in DMF (1.5 ml) and DCM (4.5 ml) followed by addition of EDAC (417 mg, 2.18 mmol) at room temperature. The mixture was allowed to incubate with stirring at room temperature. After 10 min, DMAP (133 mg, 1.09 mmol) was added followed by another 20 min incubation at room temperature. Subsequently, a pre-mixed solution of cyclopropanesulfonic acid amide (527 mg, 4.36 mmol) and DBU (663 mg, 4.36 mmol) in DMF (2 ml) and DCM (2 ml) was added followed by heating in the microwave to 100° C. for 30 min. The resulting red solution was concentrated in vacuo and re-dissolved in EtOAc (20 ml). The organic phase was washed with 1 M HCl (aq) (3×10 ml) and brine (10 ml), dried (MgSO4) and filtered. The solvent was evaporated in vacuo to yield the crude sulfonamide which was further purified by chromatography (Silica, EtOAc/MeOH, 97.5:2.5) to afford the title compound (403 mg, 77%); LC/MS, >95%, m/z (ESI+)=482(MH+)
