Ammonium Hydroxide → L-tert-Leucine

Participants

Reaction Conditions

Reaction Steps

In a 1 L beaker, 3.3 g of DL-tert-butylglycine (0.025 mol) was dissolved into 300 ml of water and the pH adjusted to 7.5-8.0 using concentrated NH4OH. The solution was transferred to a jacketed vessel and maintained at 25° C. Polypropylene glycol (1 ml) was added, and the mixture was agitated at 600 rpm. Oxygen gas was sparged via a metal frit at a flow rate of 1 L/min. The dissolved oxygen in the mixture was monitored using a calibrated oxygen electrode described in previous examples. Two milliliters of Catazyme (Novozymes) were preheated to 50° C. for 5 min and added to the mixture. Twenty grams of D-amino acid oxidase (500 units) were added to the mixture. An additional 1 ml of Catazyme (similarly preheated) was added to the reaction hourly following D-amino acid oxidase addition. When the DO2 returned to the initial reading, a sample was taken to determine the e.e. of L-tert-butylglycine by HPLC analysis. When the e.e. of L-tert-butylglycine was demonstrated to be >99%, the solution was decanted into a 2 L beaker. The final concentrations of trimethylpyruvate and residual L-tert-butylglycine were determined by HPLC analysis. The enzymes in the solution were removed by heating the solution to 90° C. and adding Celite® before filtering through a sintered glass funnel. The filtrate of the reaction was used directly in a subsequent reduction step, and L-tert-butylglycine was isolated by concentration and crystallization using standard methods.

Provenance & Evidence