Peptide synthesis in aqueous–organic media catalyzed by proteases from latex of Araujia hortorum (Asclepiadaceae) fruits

An enzymatic preparation containing cysteine phytoproteases belonging to the papain family and isolated from the latex of Araujia hortorum Fourn. (Asclepiadaceae) fruits was used as catalyst of the synthesis of the bitter dipeptide precursor Z-Ala-Phe-OMe in aqueous–organic media. Considering the good stability and activity of araujiain in different media, N,N-dimethylformamide (with low water content) and mixtures of the Tris–HCl buffer (0.1 M, pH 8.5) and hexane, ethyl acetate or propanone in 50:50 ratio were selected to perform the synthesis of that peptide. The araujiain-catalyzed synthesis was carried out at 40 °C using 2-mercaptoethanol as activator, TEA as neutralizing agent of the amino component (Phe-OMe·HCl) and different carboxylic components (Z-Ala, Z-Ala-OMe and Z-Ala-pNo). Under these conditions, araujiain only was able to form peptide bonds in biphasic media. The highest dipeptide conversion was obtained in the kinetically controlled synthesis using p-nitrophenyl ester derivative as carboxylic component in 50% (v/v) ethyl acetate. It is noteworthy that araujiain was unable to form oligopeptides derivatives, showing a good selectivity towards the synthesis of Z-Ala-Phe-OMe. For this reason and in general terms, araujiain constituted a new catalyst for the synthesis of small peptides.