(2-Methyl-thiazol-4-yl)-methanol (168, 670 mg, 5.2 mmol) is dissolved in 12 ml of dry THF under argon, followed by addition of 4-Hydroxy-indole-1,2-dicarboxylic acid 1-tert-butyl ester 2-ethyl ester (102, see example 42, 1.58 g, 5.2 mmol), triphenylphosphine (1.63 g, 6.2 mmol).) and the solution is cooled to 0° C. A 40% solution of ethyl azadicarboxylate in toluene (2.7 ml, 6.2 mmol) is added dropwise and the mixture is stirred for 2.5 h at 0° C. The solvents are removed under reduced pressure and the residue is dissolved in ethyl acetate and washed with sodium hydrogencarbonate solution and brine. The organic layers are dried over sodium sulphate, filtrated and evaporated. The crude product is purified by flash chromatography (silica gel, ethyl acetate/hexanes 3:7)
