Enzymatic Synthesis of Agmatine by Immobilized Escherichia coli Cells with Arginine Decarboxylase Activity

A new method for the enzymatic synthesis of agmatine by immobilized Escherichia coli cells with arginine decarboxylase（ADC） activity was established and a series of optimal reaction conditions was set down. The arginine decarboxylase showed the maximum activity when the pyridoxal phosphate（PLP） concentration was 50 mmol/L, pH=7 and 45 °C. The arginine decarboxylase exhibited the maximum production efficiency when the substrate concentration was 100 mmol/L and the reaction time was 15 h. It was also observed that the appropriate concentration of Mg2＋, especially at 0.5 mmol/L promoted the arginine decarboxylase activity; Mn2＋ had little effect on the arginine decarboxylase activity. The inhibition of Cu2＋ and Zn2＋ to the arginine decarboxylase activity was significant. The immobilized cells were continuously used 6 times and the average conversion rate during the six-time usage was 55.6%. The immobilized cells exhibited favourable operational stability. After optimization, the maximally cumulative amount of agmatine could be up to 20 g/L. In addition, this method can also catalyze D,L-arginine to agmatine, leaving the pure optically D-arginine simultaneously. The method has a very important guiding significance to the enzymatic preparation of agmatine.

Highly selective kinetic resolution of D/L-syn-p-sulfone phenylserine catalyzed by D-threonine aldolase in two-phase ionic solvent

In the chemical synthesis of L-syn-p-methylsulfoxide phenylserine ethyl ester(D-ethyl ester),L-tartaric acid or enzymatic resolution is employed to resolve the racemate,and thus obtain the target compound,and the remaining isomer can be recycled to obtain the raw material.In this study,high-purity L-syn-p-methylsulfoxide phenylserine(L-syn-MPS)was obtained.The kinetics of the D-threonine aldolase enzymatic hydrolysis reaction reveals that D-syn-p-sulfoxylphenylserine resolves well in[BMIM][BF 4]ionic solvents.The D/L-syn-MPS racemate was resolved using a two-phase ionic solvent[BMIM][NTf 2]to afford L-syn-MPS(ee(enantiomeric excess)>99%)and a white solid in 41.7%yield.Therefore,this system is suitable for the separation of insoluble aldehydes and successfully avoids the condensation of hydroxyl aldehydes to form D-anti-MPS.

Preparation of Optically Active Alkoxy-serines from Amino-amide Racemate Catalyzed by Escherichia coli Cells with Peptidase B Activity

Alkoxy-L-serines are useful for peptide syntheses. The demand for alkoxy-L-serines in the pharmaceutical industries continues to increase because of their multiple physiological effects. In this research, an improved method for alkoxy-L-serines synthesis is reported. A series of substrates, DL-fl-alkoxy-a-amino propionamides, was used for the synthesis of alkoxy-serines catalyzed by Escherichia coli cells with peptidase B（PepB） activity. The results show that PepB has a high resolution activity with DL-fl-alkoxy-a-amino propionamides as substrate. Reaction conditions were optimized, i.e., DL-β-methoxy-a-amino propionamide as substrate at pH=9.0, 40 ℃ and 14 h, and the optimal reaction concentration is 400 mmol/L. The results also show that divalent metal cations exhibit different effects on the PepB activity, for example, Zn2＋ and Cu2＋ can obviously inhibit the activity of PepB, whereas Co2＋, Ca2＋, Mn〉 and Mg2＋ at low concentrations can activate PepB. This research provides access to enantiomerically enriched and valuable alkoxy-L-serines from a simple amino-amide racemate.