Dicyclohexylcarbodiimide → 4-{5-[Bis-(chloroethyl)-amino]-1-methyl-1H-benzimidazol-2-yl}butyric acid 2-dodecyl ester

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A 250 mL three neck round bottom flask was equipped with an overhead stirrer, thermocouple, temperature controller and nitrogen sweep then charged with 10.0 g (25.34 mmol) of bendamustine hydrochloride, 4.77 g (5.75 mL, 25.6 mmol, 1.01 eq) of 2-dodecanol, 5.3 g (25.6 mmol, 1.01 eq) of dicyclohexylcarbodiimide (DCC), 100 mL of MDC and 0.31 g (2.54 mmol, 0.1 eq) of DMAP. The reaction was stirred at room temperature overnight at which time an in process analysis indicated the reaction was complete. Solids were removed by vacuum filtration and washed with 25 mL of MDC. The filtrate was diluted with 200 mL of MDC then washed with 4% aqueous sodium bicarbonate solution (1×500 mL) before drying over sodium sulfate, filtering and concentrating to dryness in vacuo to an off-white solid. This solid was triturated with 25 mL of MDC and the solid impurities were removed by vacuum filtration and washed with 5 mL of MDC. The filtrate was concentrated to dryness in vacuo to yield the crude product which was shown to contain residual 2-dodecanol by 1H NMR. The crude product was chromatographed using 100 g of silica gel 60, 230-400 mesh, eluting with first 1 L of heptanes, then 500 mL of 3:1 heptane/EtOAc, 500 of 2:1 heptane/EtOAc and finally 500 mL of 1:1 heptane/EtOAc collecting 100 mL fractions. Product containing fractions were combined and concentrated to dryness in vacuo to yield 5.35 g (10.16 mmol, 40%) of the product as a light purple viscous oil with an HPLC purity of 99.5 A %. 1HNMR (400 MHz, DMSO-d6) δ 7.31 (d, J=8.76 Hz, 1H), 6.93 (d, J=2.28 Hz, 1H), 6.78 (dd, J=2.36, 8.76 Hz, 1H), 4.8 (m, 1H), 3.7 (s, 8H), 3.65 (s, 3H), 2.82 (t, J=7.4 Hz, 2H), 2.42 (t, J=7.36 Hz, 2H), 2.00 (m, 2H), 1.50 (m, 2H), 1.25 (s, b, 16H), 1.14 (d, J=6.24, 2H), 0.84 (t, J=6.68 Hz, 3H).

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