Solid phase synthesis of a trypsin inhibitor isolated from the Cucurbitaceae Ecballium elaterium

The synthesis of a 28-residue peptide isolated from Ecballium elaterium of the Cucurbitaceae family which strongly inhibits trypsin activities (Ka = 8.10(-11)M), using BOP as the coupling reagent in a solid phase procedure is presented. This micro protein contains three disulfide bridges in its sequence and was obtained after oxidation of the six half-cystine residues either by air or with the use of carboethoxysulfenyl chloride. After purification by semi-preparative HPLC, the synthetic product was shown by trypsin inhibition tests to be identical with the trypsin inhibitor EETI II isolated from Ecballium elaterium.