652.9 μl (9 mmol) of thionyl chloride are added to a suspension of 2.06 g (4.6 mmol) of 2,4-bisbenzyloxy-5-[(N-methyl-N-butylamino) carbonyl]benzoic acid (5) in 20 ml of THF (dry), and the mixture is stirred for 15 min at 22° C. 10 ml of toluene are subsequently added, and the mixture is evaporated to dryness in vacuo at 40° C. The residue is dissolved in 20 ml of THF and added to a suspension of 800 mg (4.661 mmol) of 2,3-dihydro-1H-isoindol-5-ole hydrochloride in 30 ml of dichloromethane, 5 ml of THF and 1.7 ml (10 mmol) of N-ethyldiisopropylamine. After 2 h at 22° C., the mixture is evaporated and chromatographed over an RP18 column. Evaporation to dryness in vacuo gives 1.4 g (54%) of 2,4-bisbenzyloxy-N-butyl-5-(5-hydroxy-1,3-dihydroisoindole-2-carbonyl)-N-methylbenzamide as beige crystals, MW 564.7;
