Under N2 atmosphere, 2.27 g 4,N-diethyl-4,5-dihydro-pyrazole-1-carboxamidine was dissolved in 30 mL dry DCM, and 5.17 ml DiPEA and 2.98 g of 4-(chlorosulfonyl)benzoic acid were added. The mixture was stirred overnight at room temperature and evaporated to dryness. The residue was purified by flash chromatography (first column with DCM/MeOH/NH4OH 92:7.5:0.5; second column with DCM/MeOH/Acetic acid 92:7.5:0.5) to yield 0.26 g (4%) of product (mono-DiPEA salt) as an off-white amorphous powder. 1H NMR (400 MHz, CDCl3) δ 0.98 (t, J=7.4 Hz, 3H), 1.27 (t, J=7.2 Hz, 3H), 1.53-1.81 (m, 2H), 3.15-3.30 (broad peak, 1H), 3.43-3.66 (broad peak, 3H), 4.01-4.20 (broad peak, 1H), 6.97 (br. s., 1H), 7.90 (d, J=8.1 Hz, 2H), 8.14 (d, J=8.1 Hz, 2H), 9.69 (br. s., 1H).
