1-Ethyl-3-(3'-dimethylaminopropyl)carbodiimide → Di-tert-butyl (2S)-2-[(3-{[5-oxido-4-(phenylsulphonyl)-1,2,5-oxadiazol-3-yl]-oxy}-propionyl)-amino]-pentanedioate

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Reaction Steps

A solution prepared from the compound B4 obtained in Step B of Example 1 (2.5 g-8 mmol), di-tert-butyl hydrochloride L-glutamate (2.36 g-8 mmol), EDCI (1.62 g-8 mmol), DIEA (1.32 ml-8 mmol) and HOBT (1.1 g-8 mmol) in 100 ml of anhydrous DMF is stirred for 72 hours at ambient temperature. The DMF is removed by distillation and then the residue is taken up in 100 ml of water and 100 ml of ethyl acetate. The organic phase is washed with 5% NaHCO3 solution and then with water, dried over Na2SO4 and evaporated to dryness. Purification by flash chromatography is carried out using a (90:10) dichloromethane/ethyl acetate mixture as eluant to yield the expected product in the form of a colourless oil.

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