[Synthesis of three- and tetrapeptides catalyzed by subtilisin suspensions in organic solvents]

The behavior of subtilisin 72 in some aprotic solvents (acetonitrile, dioxane, and tetrahydrofurane) was studied. The enzyme was shown to be partially soluble in tetrahydrofurane, but it is rendered profoundly inactive in this solution. In acetonitrile and dioxane, subtilisin formed dilute suspensions whose activities were measured after dilution with water. Under these conditions, subtilisin suspended in acetonitrile manifested an activity that was an order of magnitude higher than that of its dioxane suspension, and this activity continued for a long time. Z-Ala-Ala-Leu-pNA was synthesized from Z-Ala-Ala-OCH3 and Leu-pNA under the catalysis by dilute suspension of subtilisin in acetonitrile. p-Nitroanilides of tetrapeptides, Z-Ala-Ala-P1-P'1-pNA, where P1 and P'1 were either Leu or Phe, were similarly synthesized in acetonitrile under catalysis by dilute subtilisin suspension at [S]:[E] = 10(5):1. p-Nitroanilides of tripeptides, Z-Ala-Ala-Leu-pNA, Z-Ala-Ala-Phe-pNA, and Z-Ala-Ala-Phe-NH2, were also synthesized in the presence of a concentrated subtilisin suspension at [S]:[E] = 10(3):1. It was shown that the increase in enzyme concentration resulted in the double coupling of nucleophile, and Z-Ala-Ala-Leu-Leu-pNA, Z-Ala-Ala-Phe-Phe-pNA, and Z-Ala-Ala-Phe-Phe-NH2 were obtained with 13, 33, and 40% yields, respectively. Therefore, such reaction systems can be used for creating long hydrophobic peptides whose synthesis in water-organic mixtures is difficult due to the poor solubility of starting components in aqueous buffer solutions.