L. Bayer (The Coca-Cola Company, Atlanta, GA) for helpful discussions and to Dr. T. Radford (The Coca-Cola Company, Atlanta, GA) for his help in preparation of the manuscript.

The resolution of racemic phenylalanine esters with esterases has been reexamined in relation to the development of a continuous process based on the use of hollow fiber/liquid membrane (SLM) reactors. The requirement for high enantioselectivity was met by phenylalanine isopropyl ester, whose (R)‐enantiomer was found refractory to the action of subtilisin Carlsberg, in water, pH 7.5, at 25 °C. The continuous feeding of (R, S)‐Phe‐O‐iPr‐HCl at 2 mm/h to 0.7 g/L subtilisin resulted in steady‐state reaction conditions that gave (S)‐Phe‐OH of 95% enantiomeric excess (ee) at the theoretical rate. The unreacted (R)‐Phe‐O‐iPr, which permeated out continuously, had 80% ee and was racemized quantitatively by heating with a salicylaldehyde catalyst in refluxing toluene. Doubling the feeding rate (4 mm/h) created excessive accumulation of (R)‐Phe‐O‐iPr in the reactor, which inhibited the enzyme through nonproductive binding, lowering the (S)‐Phe‐OH resolution rate to 68% of the theoretical rate. Similar experiments with (R, S)‐Phe‐OMe‐HCl gave (S)‐Phe‐OH of 9–48% ee, due to the enzymatic hydrolysis of (R)‐Phe‐OMe experienced during the runs. When α‐chymotrypsin was used for the continuous hydrolysis of (R, S)‐Phe‐O‐iPr, the isolated (S)‐Phe‐OH showed 67% ee, indicating that substantial hydrolysis of the (‐R)‐ester had occurred.

Das aus dem Osazon (I) entstehende Glucoson (II) reagiert mit dem Ketal (III) zu dem Imidazol (IV), dessen Deblockierung die im Titel genannte Verbindung (V) liefert.

No abstract