Ethyl orthoformate → 2-[6-(4-Methyl-piperazin-1-ylmethyl)-benzoimidazol-1-yl]-4-phenyl-thiazole-5-carboxylic acid ethyl ester

To a mixture of 2-[2-amino-5-(4-methyl-piperazin-1-ylmethyl)-phenylamino]-4-phenyl-thiazole-5-carboxylic acid ethyl ester (VII.1a) from previous step and 0.2 mL of acetic acid was added 0.2 mL of triethyl orthoformate. The reaction mixture was heated to 60 degrees for 1 hour, and then concentrated under reduced pressure. The residue was diluted with 10 mL of water and 2 mL of saturated sodium bicarbonate and then extracted three times with 5 mL of dichloromethane. The combined organic layers were washed with brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluting with methanol-dichloromethane (gradient 0:100-10:90) to give 0.041 g of 2-[6-(4-methyl-piperazin-1-ylmethyl)-benzoimidazol-1-yl]-4-phenyl-thiazole-5-carboxylic acid ethyl ester (I.1a) as a white solid.