N-PROTECTION OF AMINO-ACID DERIVATIVES CATALYZED BY IMMOBILIZED PENICILLIN-G ACYLASE

The introduction of a N-alpha-phenylacetyl moiety into glycine, methio nine and aspartic acid derivatives using immobilized penicillin G acyl ase (PGA) as catalyst was studied. High synthetic yields (86-97%) were obtained in biphasic systems under thermodynamic control using fully carboxy-protected derivatives of amino acids such as H-Gly-OMe, H-Gly- OBzl, H-Met-OEt, H-Asp(OBu(t))-OMe, H-Asp(OMe)-OMe and H-Asp(OBzl)-OBz l. Moderate yields (50-62%) were obtained for the N-alpha protection o f beta-carboxy free, alpha-carboxy esters aspartic acid such as H-Asp- OMe and H-Asp-OBzl in methanol/buffer mixtures under kinetic control. The synthesis of some phenylacetyl derivatives on a preparative scale under the optimum conditions is also described.