[Enzymetic synthesis and characterization of a carnosine analogue in non-aqueous solvent]

Carnosine (beta-Ala-L-His) has high antioxidant activity, and it is widely used in biology, chemical engineering, medicine and other fields. Its analogue syntheised in non-aqueous solvent and catalyzed by enzymes is high-effective but low-price, so it has great prospect. Here, we synthesized a carnosine analogue imidazole 4(5)-alanylamide-5(4)-carboxylic acid with imidazole-4,5-dicarboxylic acid and L-Alanine as substrates, alpha-chymotrypsin as catalyst in tetrahydrofuran (THF) solvent. Based on the orthogonal experiments, the optimized synthetic conditions are 4,5-dicarboxylic acid: L-alanine = 1:3 (m/m), alpha-chymotrypsin: substrates (4,5-dicarboxyl acid and L-alanine) = 1:200 (m/m), pH 8 phosphate buffer:THF = 1.6:10 (V/V), reaction temperature 35 degrees C, time 1.5 h. We separated the product with silica gel G60 thin-layer chromatography (TLC), and a new spot appeared at Rf (ratio to front) = 0.81; then the new spot was purified and characterized with UV spectra, high performance liquid chromatogram (HPLC) and 13C NMR (13C nuclear magnetic resonance). The UV spectra shows a new absorption peak at 310 nm, and the peak in 253 nm is largely strengthened; HPLC reserve times are all 4.5 min at 253 nm, 310 nm, 330 nm; 13C NMR shows 8 carbons. Combing with the catalytic mechanism of alpha-chymotrypsin, structure of the analogue is confirmed, i.e., imidazole 4(5)-alanylamide-5(4)-carboxylic acid.