γ-Glutamyl-peptides are frequently endowed with biological activities. In this work, "kokumi peptides" such as γ-glutamyl-methionine (1) and γ-glutamyl-(S)-allyl-cysteine (2), as well as the neuroprotective γ-glutamyl-taurine (3) and the antioxidant ophthalmic acid (4), were synthesized through an enzymatic transpeptidation reaction catalyzed by the γ-glutamyl transferase from Bacillus subtilis (BsGGT) using glutamine as the γ-glutamyl donor. BsGGT was covalently immobilized on glyoxyl-agarose resulting in high protein immobilization yield and activity recovery (>95%). Compounds 1-4 were obtained in moderate yields (19-40%, 5-10 g/L) with a variable purity depending on the presence of the main byproduct (γ-glutamyl-glutamine, 0-16%). To achieve process intensification and better control of side reactions, the synthesis of 2 was moved from batch to continuous flow. The specific productivity was 1.5 times higher than that in batch synthesis (13.7 μmol/min*g), but it was not accompanied by a paralleled improvement of the impurity profile.
Keywords: Bacillus subtilis; enzyme immobilization; flow chemistry; kokumi peptides; γ-glutamyl transferase.