Efficient racemization of N‐phenylacetyl‐D‐glufosinate for L‐glufosinate production

Abstract

Most amino acids contain chiral centres and exist as both D‐enantiomer and L‐enantiomer. The optically pure enantiomer is often more valuable than the racemate. Enzymatic resolution provides an effective strategy to obtain optically pure amino acids but often results in large amounts of unwanted isomer. In this study, optically pure L‐glufosinate (L‐PPT) was obtained by coupling amidase‐mediated hydrolysis of N‐phenylacetyl‐D,L‐glufosinate with racemization of N‐phenylacetyl‐D‐glufosinate (NPDG), which exclusively exhibits effective herbicidal properties compared with its D‐enantiomer. To improve the yield of L‐PPT, the racemization reaction conditions were optimized, and through single‐factor experiments, the optimal reaction temperature, reaction time, and mole ratio of phenylacetic acid to NPDG were determined to be 150°C, 30 minutes, and 1.5, respectively. The response surface methodology was applied to further optimize the racemization conditions, and the final yield of L‐PPT reached 96.13% with optimum reaction temperature of 154°C, reaction time of 23 minutes, and phenylacetic acid/NPDG mole ratio of 1.7, respectively. Moreover, adding a small amount of acetic anhydride further raised the yield of L‐PPT to 97.02%.

Glufosinate‐ammonium: a review of the current state of knowledge

“…6 More recently, another method has been proposed to increase the proportion of L-phosphinothricin at up to 96% by coupling the amidase-mediated hydrolysis of N-phenylacetyl-D,L-phosphinothricin with racemization of N-phenylacetyl-Dphosphinothricin. 7 Field and laboratory experiments demonstrated that formulations with increased proportions of L-phosphinothricin provided similar levels of both grass and broadleaf weed control as well as lower crop injury for cotton and soybean compared to equivalent amounts of the L-isomer in the racemic mixture. 5 Glufosinate was first commercialized in the United States and Canada in 1993-1994 as a non-selective herbicide with broad spectrum of weed control.…”

“…The conversion of PPOB into L‐phosphinothricin can also be performed enzymatically through glutamate dehydrogenase, with optimized affinity for glufosinate 6 . More recently, another method has been proposed to increase the proportion of L‐phosphinothricin at up to 96% by coupling the amidase‐mediated hydrolysis of N ‐phenylacetyl‐D,L‐phosphinothricin with racemization of N ‐phenylacetyl‐D‐phosphinothricin 7 . Field and laboratory experiments demonstrated that formulations with increased proportions of L‐phosphinothricin provided similar levels of both grass and broadleaf weed control as well as lower crop injury for cotton and soybean compared to equivalent amounts of the L‐isomer in the racemic mixture 5…”

Highly Efficient Chemoenzymatic Synthesis of l-Phosphinothricin from N-Phenylacetyl-d,l-phosphinothricin by a Robust Immobilized Amidase

“…Unreacted N -phenylacetyl- d -phosphinothricin was added into a round bottom flask with phenylacetic acid in a mole ratio of 1:1.2. , The racemization reaction was performed in an oil bath at 140, 150, and 160 °C. After completion of the reaction, the racemic N -phenylacetyl- d , l -phosphinothricin was recycled as the substrate for second-round enzymatic hydrolysis.…”

“…The optical purity of L-phosphinothricin was determined on an Agilent C18 column after derivatization with o-phthalaldehyde/Nacety-L-cysteine using 50 mM ammonium acetate (pH 5.7)/methanol (90:10, v/v) as the mobile phase at a flow rate of 1.0 mL min −1 . 14 The eluent was monitored at 232 nm, and the column temperature was set at 40 °C. The retention times of L-and D-phosphinothricin were 10.39 and 12.71 min, respectively.…”

A Single‐Transaminase‐Catalyzed Biocatalytic Cascade for Efficient Asymmetric Synthesis of l‐Phosphinothricin

“…But, it often raised the problems of the complex synthesis process, high cost for the catalyst, and environmental pollution [5] . Recently, the biological method of synthesizing l ‐PPT has attracted more and more attention due to its advantages of low impact on the environmental, high rate of atom use, and high product yield, in which amidase, [6] nitrilase, [7] deacetylase, [8] amino acid dehydrogenase [9] and transaminase [10] were involved.…”