METHODS OF PREPARATION OF L-GLUFOSINATE

Abstract

The present invention relates to a method for preparing L-glufosinate, CHARACTERIZED in that it comprises: reacting D-glufosinate with a D-amino acid oxidase (DAAO) enzyme to form PPO (2-oxo-4-(hydroxy(methyl)phosphinoyl)butyric acid) while aerated; and amination of the PPO to L-glufosinate by an L-amino acid dehydrogenase (LAAD) enzyme in the presence of an ammonia source, whereby at least 70% of the D-glufosinate is converted to L-glufosinate; and wherein the method is performed ex vivo.

Description

METHODS OF PREPARING L-GLUFOSINATE FIELD OF THE INVENTION Methods for producing a single stereoisomer of glufosinate are described, particularly for the production of L-glufosinate. BACKGROUND OF THE INVENTION The herbicide glufosinate is a non-selective, foliar-applied herbicide considered one of the safest herbicides from a toxicological and environmental standpoint. Current commercial methods for the chemical synthesis of glufosinate produce a racemic mixture of L-(and D-(glufosinate) (Duke et al., 2010 Toxins 2: 1943-(1962)). However, L-glufosinate (also known as phosphinothricin or (S)-2-amino-4-(hydroxy(methyl)phosphonoyl)butanoic acid) is much more potent than D-glufosinate (Ruhland et al. Res. 1: 29-(37)). Therefore, methods are needed to produce only or mainly the active form of L-glufosinate. Previously, no economically viable methods were available to generate pure L-glufosinate, or a mixture of D and L-glufosinate enriched for L-glufosinate. New and economically viable methods for the production of L-glufosinate are described. SUMMARY OF THE INVENTION Compositions and methods for preparing L-glufosinate are provided. The first step of the process involves the oxidative deamination of D-glufosinate to PPO (2-oxo-4-(hydroxy(methyl)phosphinoyl)butyric acid). The second step involves the specific amination of PPO to L-glufosinate, using an amine group from one or more amine donors. In some embodiments, the method comprises reacting D-glufosinate with a D-amino acid oxidase (DAAO) enzyme to form PPO (2-oxo-4-(hydroxy(methyl)phosphinoyl)butyric acid). followed by amination of PPO to L-glufosinate by a transaminase (TA) enzyme, using an amine group from one or more amine donors, while at least 70% of the D-glufosinate is removed and / or the yield of L-glufosinate is at least 85% of the input racemic glufosinate or at least 70 to 85% of the D-glufosinate is converted to L-glufosinate. In some embodiments, the unreacted amine donor from one reaction may be reused in other reaction rounds.Optionally, D-glufosinate is originally present (i.e., at the reaction stage) in a racemic mixture of D- and L-glufosinate. The DAAO enzyme must have an increased activity of approximately 3 µmol / min * mg or greater to drive the reaction. DAAO enzymes are available in the technique and can be modified or mutated to have the necessary increased activity required to drive the process. Thus, modified mutant enzymes from Rhodosporidium toruloides (UniProt P80324), Trigonopsis variabilis (UniProt Q99042), Neolentinus lepideus (GenBank KZT28066.1), Trichoderma reesei (GenBank XP 006968548.1), or Trichosporon oleaginosos (KLT40252.1) can be used in some modalities; the DAAO enzyme is a DAAO mutant based on the Rhodosporidium toruloides sequence. Although a number of mutations can be made and their effect on activity tested, the DAAO mutant in some forms may comprise mutations at positions 54, 56, 58, 213, and / or 238.For example, the DAAO mutant may comprise one or more of the following mutations at position 54: N54C, N54L, N54T, or N54V. The DAAO mutant may optionally comprise the following mutation at position 56: T56M. The DAAO mutant may optionally comprise one or more of the following mutations at position 58: F58A, F58G, F58H, F58K, F58N, F58Q, F58R, F58S, or F58T. Optionally, the DAAO mutant may comprise the following mutation at position 213: M213S. In some forms, the DAAO mutant may comprise one or more of the following combinations of mutations: F58K and M213S; N54T and T56M; N54V and F58Q; and / or N54V, F58Q, and M213S. In each case, the enzyme must have an activity equal to or greater than approximately 3 µmol / min*mg, greater than approximately 4 µmol / min*mg, or higher. A wild-type enzyme may be used in the methods of the invention provided that the enzyme has an activity level as indicated above.The TA enzyme may be a gabT transaminase from Escherichia coli (UniProt P22256). Alternatively, the TA enzyme may be a transaminase with the sequence identified according to Sequence ID No. 1. The TA enzyme may also be selected based on sequence similarity to Sequence ID No. 1 and / or mutated to improve its activity in the desired reaction. Thus, sequences possessing 80%, 85%, 90%, 95%, or more sequence identity with Sequence ID No. 1, based on the BLASTP alignment method, and retaining transaminase activity are covered by the present invention. Any DNA sequence encoding the enzyme sequence of Sequence ID No. 1 or its variants is also covered. or its variants are also included. The reaction step and the amination step can be carried out in a single or separate containers. In one configuration, all reagents are substantially added at the start of the reaction. Alternatively, the reagents for the reaction step and the reagents for the amination step are added to the container at different times. A method for selective weed control in a field containing a seeded crop or crops that may be optionally resistant to glufosinate is also described, comprising applying an effective amount of a composition comprising L-glufosinate in an enantiomeric excess greater than 90% over D-glufosinate to the field. A method for selective weed control in a field, weed control in other areas, defoliation of plants or crops, and / or desiccation of crops prior to harvest is also described, comprising applying an effective amount of a composition comprising L-glufosinate in an enantiomeric excess greater than 90% over D-glufosinate and more than 0.01% but less than 15% PPO to the field. Details of one or more embodiments are set forth in the drawings and the following description. Other features, objects, and benefits will become apparent from the description, drawings, and claims. Some compositions of the invention comprise D-glufosinate, PPO, and L-glufosinate. In such compositions, L-glufosinate is present at a concentration equal to or greater than 80%, 90%, 95%, 96%, 97%, 98%, or 99% by weight of the composition, based on the combined weight of D-glufosinate, PPO, and L-glufosinate. Other compositions comprise L-glufosinate at concentrations equal to or greater than 80% after isolation of L-glufosinate from the present reaction mixture. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic of an example of the conversion of D-glufosinate to L-glufosinate. The amine donor and keto acid product are examples and are not intended to be exhaustive. Figure 2 is a graph showing the concentrations of L-glufosinate (circles), D-glufosinate (triangles), and PPO (squares) during a one-step deracemization using the N54T, T56M, F58K, and M213S mutant variant Rhodosporidium toruloides DAAO and the gabT transaminase of E. coli DETAILED DESCRIPTION OF THE INVENTION Compositions and methods for the production of L-glufosinate (also known as phosphinothricin or (S)-2-amino-4-(hydroxy(methyl)phosphonoyl)butanoic acid) are provided. The methods comprise a two-step process, which can optionally occur in a single vessel and nearly simultaneously. The first step involves the oxidative deamination of L-glufosinate to PPO (2-oxo-4-(hydroxy(methyl)phosphonoyl)butyric acid). The second step involves the specific amination of PPO to L-glufosinate, using an amine group from one or more amine donors. By combining these two reactions, the proportion of L-glufosinate can be substantially increased in a racemic mixture of glufosinate. Thus, methods are provided for obtaining a composition consisting substantially of L-glufosinate. Since L-glufosinate is more potent than D-glufosinate, smaller amounts of the compound are needed to be effective as a herbicide. In one embodiment, according to the present, a composition comprising a mixture of L-glufosinate, PPO, and D-glufosinate is provided, wherein L-glufosinate is the predominant compound in the mixture of L-glufosinate, PPO, and D-glufosinate. This composition can be used directly as a herbicide since PPO can contribute herbicidal activity (EP0030424). In other embodiments, L-glufosinate can be purified or substantially purified and used as a herbicide. L-glufosinate compositions may comprise D-glufosinate, PPO, and L-glufosinate. Optionally, the amount of L-glufosinate is 80% or more, 85% or more, 90% or more, or approximately 95% or more, 97% or more, or 98% or more based on the combined weight of D-glufosinate, PPO, and L-glufosinate. Optionally, the amount of D-glufosinate is 10% or less, 5% or less, 2.5% or less, or 1% or less based on the combined weight of D-glufosinate, PPO, and L-glufosinate. Optionally, the amount of PPO is greater than 1% but less than 20%, less than 15%, less than 10%, or less than 5% based on the weight of D-glufosinate, PPO, and L-glufosinate. These compositions may optionally be presented as dry powders or dissolved in an aqueous or non-aqueous vehicle and may optionally contain other additional chemical ingredients. Optionally, the composition is prepared and used in an ex vivo setting. It is also recognized that L-glufosinate can be further isolated and used in formulations as a herbicide. Formulations are also described. The formulations comprise L-glufosinate ammonium in an amount of 10-30% by weight of the formulation; one or more additional components selected from the group consisting of sodium alkyl ether sulfate in an amount of 10-40% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5-2% by weight of the formulation; dipropylene glycol in an amount of 4-18% by weight of the formulation; and alkyl polysaccharide in an amount of 4-20% by weight of the formulation; and water as the remainder of the formulation. Optionally, the formulation comprises L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 31.6% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; dipropylene glycol in an amount of 8.6% by weight of the formulation; alkyl polysaccharide in an amount of 9.8% by weight of the formulation; and water in an amount of 36.75% by weight of the formulation. Optionally, the formulation comprises L-glufosinate ammonium in an amount of 24.5% by weight of the formulation; sodium alkyl ether sulfate in an amount of 31.6% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; dipropylene glycol in an amount of 8.6% by weight of the formulation; alkyl polysaccharide in an amount of 9.8% by weight of the formulation; and water in an amount of 24.5% by weight of the formulation. Optionally, the formulation comprises L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 15.8% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5% by weight of the formulation; dipropylene glycol in an amount of 4.3% by weight of the formulation; alkyl polysaccharide in an amount of 4.9% by weight of the formulation; and water in an amount of 62.25% by weight of the formulation.Optionally, the formulation comprises L-glufosinate ammonium in an amount of 24.5% by weight of the formulation; alkyl ether sulfate, sodium salt in an amount of 22.1% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1.0% by weight of the formulation; alkyl polysaccharide in an amount of 6.2% by weight of the formulation; and water in an amount of 46.2% by weight of the formulation. Although the methods can be used to produce substantially purified L-glufosinate in a batch reaction, it is recognized that a continuous procedure can be used. I. Synthesis methods Methods for converting D-glufosinate to L-glufosinate are provided. The methods described herein provide a means of converting a low-cost feedstock of a racemic mixture of D- and L-glufosinate into a more valuable product enriched in L-glufosinate. The conversion methods include two stages, which can be performed in one or more separate vessels. The first step is the oxidative deamination of D-glufosinate (which may be present in a racemic mixture of D- and L-glufosinate) to PPO (2-oxo4-(hydroxy(methyl)phosphinoyl)butyric acid). This step can be catalyzed by a D-amino acid oxidase (DAAO) enzyme, a D-amino acid dehydrogenase (DAAD) enzyme, or by chemical conversion. The second step is the specific amination of PPO to L-glufosinate, using an amine group from one or more amine donors.These amine donors can be selected from glutamate, L-glutamate, lysine, alanine, isopropylamine, sec-butylamine, phenylethylamine, and similar compounds. This step can be catalyzed by a transaminase (TA) enzyme, an L-amino acid dehydrogenase (LAAD) enzyme, or by chemical conversion. Substantially purified L-gufosinate compositions are obtained using the methods described herein. Figure 1 illustrates an example of the conversion of D-glufosinate to L-glufosinate. As indicated, the method comprises a two-stage process. According to the illustration, the first step is an oxidative deamination of D-glufosinate to PPO, and the second step is an amination of PPO to L-glufosinate. The first step, namely the oxidative deamination of D-glufosinate to PPO, can be catalyzed by several classes of enzymes or can occur non-enzymatically. These enzymes include DAAO, DAAD, and D-amino acid dehydratase. iviA / a / ¿u¿ i / un ózóz In one embodiment, a DAAO enzyme is used to catalyze the conversion of D-glufosinate to PPO. Such a reaction has the following stoichiometry: D-glufosinate + O2 + H2O => H2O2 + NH3 + PPO. Since the solubility of oxygen in the aqueous reaction buffer is typically low compared to that of glufosinate, for an efficient process, oxygen must be introduced throughout the entire time of the DAAO reaction. This contrasts with, for example, the Hawkes reaction according to U.S. Patent Nos. 7,723,576; 7,939,709; 8,642,836; and 8,946,507, where the reaction is carried out in a sealed vessel. Initially, D-glufosinate is present at a concentration of over 30 g / L up to a maximum of 140 g / L. The initial oxygen level is typically affected by the reaction temperature, but it is typically present at approximately 8 mg / L and is added throughout the reaction to ensure that a sufficient level of oxygen is available for the reaction to proceed at its rate. Water is typically, but not necessarily, present at a concentration of over 500 g / L. Several DAAO enzymes are known in the art and can be used in the methods described herein, provided they are capable of accepting Dglufosinate as a substrate and provide sufficient activity to level and drive the reaction. The DAAO enzymes useful in the methods of the invention have an activity equal to or greater than approximately 3 µmol / min*mg, approximately 4 µmol / min*mg, or higher. A wild-type enzyme may be used in the methods of the invention provided the enzyme has an activity level as indicated. These DAAO enzymes that can be used in the method include those from Rhodosporidium toruloides, Trigonoypsis variabilis, Fusarium sp., Candida sp., Schizosaccharomyces sp., Verticillium sp., Neolentinus lepideus, Trichoderma reesei, Trichosporon oleaginosus, and similar species that have been modified to increase their activity.Any DAAO enzyme can be used as a starting enzyme, including those that have sequences corresponding to the accession numbers of. Swissprot numbers P80324, Q99042, P00371, and P24552 or SPTREMBL numbers Q9HGY3 and Q9Y7N4 or GenBank numbers KZT28066.1, XP_006968548.1, and KLT40252.1. The DAAO-encoding DNA sequences may be selected from the sequences established in EMBL A56901, RGU60066, Z50019, SSDA04, D00809, AB042032, RCDAAOX, A81420, and SPCC1450, or may be optimized with codons from the protein sequences listed above for optimal expression in the chosen expression host. U.S. Patent No. 8,227,228 describes DAAO enzymes from Candida intermedia. Such sequences are incorporated by reference. These enzymes can be modified to increase activity and used in the methods of the invention. Other DAAO enzymes can be identified in a variety of ways, including sequence similarity and functional screening. The DAAO enzyme may be a mutant DAAO enzyme capable of accepting D-glufosinate as a substrate. In Hawkes et al., Supra, a sequence-based DAAO mutant from Rhodosporidium toruloids (consisting of the F58K and M213S mutations) has been shown to accept D-glufosinate as a substrate (Hawkes et al., Plant Biotechnol J 9 (3): 301-(14). Other DAAO enzymes can be similarly modified to accept D-glufosinate and have increased activity, i.e., the activity necessary to drive the method of the invention. Likewise, known DAAO enzymes can be improved by mutagenesis, leading to the identification of new DAAO enzymes. In some embodiments, mutant enzymes can be prepared and tested using the methods described herein. Mutant DAAO enzymes (e.g., from Rhodotorula gracilis) may include one, two, three, or more mutations (e.g., four, five, six, seven, eight, nine, or ten or more mutations) at positions in the mutant sequence compared to the wild-type sequence. The DAAO mutant may optionally comprise mutations at positions 54, 56, 58, 213, and / or 238. In some embodiments, such mutants may comprise amino acid substitutions at positions 54 and 56 relative to the wild-type sequence. In other embodiments, these mutants may comprise amino acid substitutions at positions 54 and 58 relative to the wild-type sequence.In other embodiments, such mutants may include amino acid substitutions at positions 54, 213, and 238 with respect to the wild-type sequence. Optionally, at position 54, wild-type asparagine may be replaced with Ala, Cys, Gly, Ie, Ser, Leu, or, more preferably, Thr or Val. For example, the DAAO mutant may comprise one of the following mutations at position 54: N54C, N54L, N54T, or N54V. Optionally, at position 56, wild-type threonine may be replaced with Ala, Cys, Gly, Ie, Asn, Arg, Ser, Thr, Met, or Val. See U.S. Patent No. 7,939,709, which is incorporated herein by reference. For example, the DAAO mutant may comprise the T56M mutation. Additionally, at position 58, wild-type Phe can be replaced with Lys, Arg, Gln, Thr, Gly, Ser, Ala, Arg, Asn, or His. The DAAO mutant may optionally comprise one of the following mutations at position 58: F58A, F58G, F58H, F58K, F58N, F58Q, F58R, F58S, or F58T.In some forms, the DAAO mutant does not include a mutation at position 58. Optionally, at position 213, wild-type methionine is replaced with Arg, Lys, Ser, Cys, Asn, or Ala. In some examples, the DAAO mutant may include the M213S mutation. Optionally, at position 238, wild-type tyrosine is replaced with His, Ser, Gys, Asn, or Ala. In some forms, the DAAO mutant may comprise one or more of the following combinations of mutations: F58K and M213S; N54T and T56M; N54V and F58Q; N54C and F58H; N54T and F58T; N54T and F58G; N54T and F58Q; N54T and F58A; N54L and F58R; N54V and F58R; N54V and F58N; and / or N54V, F58Q, and M213S. In one modality, the DAAO mutant comprises mutations in other enzymes / υΊ DAAO in positions equivalent to positions 54, 56, 58, 213, and / or 238 of Rhodosporidium toruloides DAAO or Trigonopsis variabilis DAAO. Other suitable amino acid D oxidases may preferably be obtained from fungal sources. Such DAAO enzymes may be identified and tested for use in the methods of the invention. To determine whether the enzyme accepts D-glufosinate as a substrate, an oxygen electrode assay (Hawkes, 2011, supra), a colorimetric assay (Berneman A, Alves-Ferreira M, Coatnoan N, Chamond N, Minoprio P (2010) Medium / High Throughput D-Amino Acid Oxidase Colorimetric Method for Determination of D-Amino Acids. Application for Amino Acid Racemases. J. Microbial Biochem Technol 2: 139-146), and / or direct measurement (by high-performance liquid chromatography (HPLC), liquid chromatography, mass spectrometry (LC-MS), or similar) of product formation may be employed. The reaction catalyzed by the DAAO enzyme requires oxygen. In some embodiments, oxygen, oxygen-enriched air, an oxygen-enriched gas stream, or air is introduced into the reaction, either into the headspace or by bubbling gas through the reaction vessel, intermittently or continuously, to increase the reaction rate. Additionally, in other embodiments, optionally combined with bubbling gas through the reaction vessel, a pressurized reactor may be used. That is, the reactor may be sealed and allowed to consume O2. The use of a sealed chamber would limit steam emissions. When a DAAO enzyme catalyzes the conversion of D-glufosinate to PPO, hydrogen peroxide (H₂O₂) is released. This can be detrimental to the enzymes and other components of the biotransformation (e.g., products and / or substrates). Therefore, in one embodiment, an enzyme such as catalase can be used in addition to the DAAO enzyme to catalyze the removal of hydrogen peroxide. Catalase catalyzes the decomposition of hydrogen peroxide with the following stoichiometry: 2H2O2 => 2H2O + O2. In some formulations, hydrogen peroxide can be removed by catalyzed and uncatalyzed decomposition reactions. For example, hydrogen peroxide can be removed by an uncatalyzed decomposition reaction using increased heat and / or pH. Hydrogen peroxide can also be removed by a catalyzed decomposition reaction using, for example, transition metals and other agents, such as potassium iodide. In addition to removing hydrogen peroxide, the use of catalase also produces oxygen (O2). The oxygen produced by catalase can help facilitate the conversion of D-glufosinate to PPO using the enzyme DAAO, since DAAO requires oxygen to function. Other enzymes can be used to catalyze the conversion of D-glufosinate to PPO. For example, a DAAD enzyme that accepts D-glufosinate as a substrate can be used with the following stoichiometry: D-glufosinate + H20 + acceptor => NH3 + reduced acceptor + PPO. It is recognized that in methods using DAAD, the DAAD-catalyzed reaction may involve the recycling of redox cofactors. This entails the oxidation of the reduced acceptor so that it can accept more electrons from D-glufosinate. In one embodiment, an oxidative chemical deamination, in which an intermediate α-keto acid is produced from the parent amino acid, can be used in the methods described herein to convert D-glufosinate to L-glufosinate. Oxidative chemical deamination involves the conversion of an amine group to a keto group with concomitant release of ammonia, typically using metal ions such as copper or cobalt in an aqueous solution at temperatures between room temperature and the boiling point of the solution and at a pH ranging from approximately 4 to approximately 10. See, for example, Ikawa and Snell (1954) J. Am. Chem. Soc. 76 (19): 4900-4902, which is incorporated herein by reference. Substantially complete conversion (more than 70%, more than 75%, more than 80%, more than 85%, more than 90%, or more than 95%) of D-glufosinate to PPO can occur within 24 hours, within 18 hours, within 12 hours, within 8 hours, or less. The second step of the method described herein involves the conversion of PPO to L-glufosinate using a transaminase (TA) enzyme, an L-amino acid dehydrogenase (LAAD) enzyme, or by chemical conversion. In one embodiment, the method is a reaction catalyzed by a TA. A TA with the required stereospecificity that accepts PPO as a substrate catalyzes the amination of PPO to L-glufosinate with the following stoichiometry: PPO + amine donor => L-glufosinate + keto acid. If the reaction is carried out as a two-step process where Dglufosinate is substantially converted to PPO in the absence of an amine donor and / or transaminase, the initial amounts of PPO in the second step typically range from 10 g / L to 140 g / L; 20 g / L to 140 g / L; or from 30 g / L to 140 g / L. If the reaction is carried out as a one-step process, the initial amounts of PPO are typically less than 1 g / L, and the highest levels of PPO during the reaction are typically less than 25 g / L. The amine donor is initially present at a molar excess of 1 to 50 times the initial amount of racemic glufosinate. The transaminase enzymes (TAs) useful in the methods described herein include gabT transaminase from Escherichia coli (UniProt P22256; identified here as Sequence ID No. 3), which has been shown to catalyze the desired reaction with PPO as a substrate (Bartsch et al. (1990) Appl Environ Microbiol, 56(1): 7–12). Another enzyme has been developed to catalyze the desired reaction at a higher rate using isopropylamine as an amine donor (Bhatia et al. (2004) Peptide Revolution: Genomics, Proteomics & Therapeutics, Proceedings of the Eighteenth American Peptide Symposium, Ed. Michael Chorev and Tomi K. Sawyer, July 19). 23, 2003, pp. 47-48). A transaminase with the amino acid sequence of Seq. No. 1 also catalyzes the desired reaction with PPO and isopropylamine as substrate (Example 11). Additionally, the TA enzymes of numerous microorganisms, such as Streptomyces hygroscopicus, Streptomyces viridochromogenes, Candida albicans, and others, can be used in the practice of the methods described herein. In particular, see, for example, EP0249188 and U.S. Patent No. 5,162,212, which are incorporated herein by reference. When desired, the enzymes can be developed by mutagenesis to increase their activities. Mutant TA enzymes can be selected according to the desired activity using the assays described in Schulz et al., Appl Environ Microbiol. (1990) Jan. 56 (1): 1-6, and / or by direct measurement of the products by HPLC, LC-MS, or similar methods. Additional TA enzymes for use in the methods can be identified by selecting TA collections, such as those marketed by Prozomix Limited (Northumberland, UK), SyncoZymes (Shanghai, China), Evocatal (Monheim am Rhein, Germany), Codexis (CA), or Abcam (Cambridge, UK), for the desired activity. Alternatively, sequence similarity can be used to identify novel TA enzymes. Finally, TA enzymes can also be identified from organisms capable of catalyzing the desired reaction. Selecting an appropriate amine donor is important for the cost-effective conversion of D-glufosinate to L-glufosinate. A variety of factors must be considered, including donor cost, equilibrium thermodynamics, potential donor recovery, separation of the keto acid product from the desired L-glufosinate, and others. Consequently, TA enzymes that accept different amine donors can be used, including L-aspartate or racemic aspartate, L-glutamate or racemic glutamate, L-alanine or racemic alanine, L-phenylethylamine or racemic phenylalanine, L-glycine or racemic glycine, L-lysine or racemic lysine, L-valine or racemic valine, L-serine or racemic serine, L-glutamine or racemic glutamine, isopropylamine, sec-butylamine, ethanolamine, 2-aminobutyric acid, and diaminopropionic acid.In some forms, the amine donor is not aspartate or aspartic acid (e.g., L-aspartic acid, D-aspartic acid, racemic D, L-aspartic acid). In modalities where the amino donor is glutamate, the keto acid co-product resulting from the transamination reaction is α-ketoglutarate (also known as α-ketoglutaric acid or α-KG). α-Ketoglutarate can be isolated and / or purified using methods known to those skilled in the art, such as those described in EP Patent No. 0073711, CN Patent 10519873, CN Patent 105177065, CN Patent 104529755, and Zhan et al., Shipin Yu Shengwu, Jishu Xuebao, 32(10): 1043–1048 (2013), documents which are incorporated herein by reference in their entirety. The α-ketoglutarate produced and isolated can be used in a variety of applications, including in the synthesis of pharmaceutical agents, food additives, and biomaterials. Optionally, the α-ketoglutarate can be chemically converted to glutamate or racemic L-glutamate for reuse in the reaction. Chemical reductive amination involves the conversion of a ketone group to an amine group in an amine compound, typically by treating the ketone compound with a suitable amine in an organic solution. Suitable amines include, for example, methylamine or ammonia. Suitable organic solvents for use in the organic solution include tetrahydrofuran, ethanol, or dichloromethane (DCM). Reductive amination can be carried out at temperatures between room temperature and the boiling point of the solution. The resulting amine can then be reduced using a reducing agent in an organic solution. Suitable reducing agents include, for example, NaBH4, NaHB(OAc)3, or Na(CN)BH3. Suitable organic solvents for use in the organic solution include tetrahydrofuran, ethanol, or DCM. The reduction reaction can be carried out at temperatures between 0°C and the boiling point of the solution.Those skilled in the art will know that the process can be carried out in a single container or in multiple vessels, i.e., in separate transformations. Additionally, those skilled in the art will recognize that the described procedure will yield racemic amino material when possible. The use of a chiral reducing agent such as RuCl2[(S)-BINAP] and hydrogen gas or a latent source of hydrogen gas, or achiral hydride-based reducing agents in the presence of chiral ligands such as (S)-(or (R)-VAPOL in a ratio between 1:1 and 1:0.05, can produce enantiomerically pure and / or amino-enriched material. See, for example, Mignonac (1921) Compt. Rend. 172:223 and G. Li, Y. Liang, J.C. Antilla (2007) J. Am. Chem. Soc., 129:5830-5831. A wild-type transaminase that accepts a desired amine donor can be identified, or a transaminase that does not normally accept a desired amine donor can evolve to accept the desired substrate. Optionally, the transaminase is not an aspartate transaminase. Optionally, the transaminase is not a 4-aminobutyrate:2-ketoglutarate transaminase. In some embodiments, the transaminase is not a combined enzyme system that includes a specific PPT transaminase and a glutamate:oxaloacetate transaminase. Other enzymes that catalyze the conversion of PPO to L-glufosinate include LAAD enzymes or amine reductases that accept PPO as a substrate. Such LAAD enzymes use the following stoichiometry: NH3 + reduced acceptor + PPO => L-glufosinate + H2O + acceptor. LAAD-catalyzed reactions can include the recycling of the redox cofactor, which involves reducing the oxidized acceptor so that it can donate more electrons to PPO. Chemical reductive amination, in which an amino group is produced from the parent keto compound, can also be used to produce glufosinate when no chiral reagent or ligand is used, or L-glufosinate when a chiral reagent or ligand is used. Chemical reductive amination can be affected as previously described. The substantially complete conversion of PPO to L-glufosinate can occur within 24 hours, within 18 hours, within 12 hours, within 8 hours, or within 4 hours. Substantially complete, in this context, means that the conversion of PPO to L-glufosinate is greater than approximately 70%, greater than approximately 75%, greater than approximately 80%, greater than approximately 85%, greater than approximately 90%, greater than approximately 95%, greater than approximately 98%, or greater than approximately 99%. If the reaction takes place in a single container, the TA enzyme can be added with the DAAO enzyme or it can be incorporated later, for example, after the DAAO enzyme has catalyzed some or substantially all of the oxidative deamination. Enzymes can be added to a reaction using a variety of methods. One approach is to express the enzyme(s) in microorganisms such as E. coli, S. cerevisiae, P. pastoris, and others, and add the whole cells to the reactions as whole-cell biocatalysts. Another approach is to express the enzyme(s), lyse the microorganisms, and add the cell lysate. Another method involves purifying, or partially purifying, the enzyme(s) from a source and adding pure or partially purified enzymes to the reaction. If multiple enzymes are required for a reaction, the enzymes can be expressed in one or more microorganisms, including the expression of all the enzymes within a single microorganism. An additional approach, which can be combined with the approaches described above, is to immobilize the enzyme(s) on a support (examples of strategies are described in Datta et al. (2013) Biotech. Feb; 3(1): (1-9). As described in Datta et al., and without limitation, enzymes, either individually or in combination, can be adsorbed, covalently or non-covalently bound, or trapped within natural or synthetic polymers or inorganic supports, including aggregates of the enzyme(s) themselves. Once immobilized, the enzyme(s) and support can be dispersed in a bulk solution or incorporated into beds, columns, or any number of similar approaches for interaction between the reaction solution and the enzyme(s). Since aeration is important for the DAAO reaction under consideration, bubble columns or similar structures can be used for enzyme immobilization.As examples, the reaction mixture may flow through a column of immobilized enzymes (flow reaction), be added to a fixed-bed column of immobilized enzymes, allowed to react, and then removed from the bottom or top of the reaction vessel (plug flow), or be added to dispersed immobilized enzymes and allowed to react, with the immobilized enzymes then removed by filtration, centrifugation, or similar means (batch). Thus, any method for immobilizing the enzymes may be employed in the methods of the invention. DAAO, TA, and / or other reactions can occur in a buffer. Examples of buffers commonly used in biotransformation reactions include Tris, phosphate, or any of Good's buffers, such as 2-(N-morpholino)ethanesulfonic acid (MES); N-(2-(acetamido)iminodiacetic acid (ADA); Piperazine-(N,N'-bis(2-(ethanesulfonic) (PIPES); N-(2-(acetamido)-(2-(aminoethanesulfonic acid (ACES); 3-(N-(morpholino) propanesulfonic acid (MOPS); N, N-(Bis (2-(hydroxyethyl)-(2-(aminoethanesulfonic acid (BES); 4-(2(hydroxyethyl)-(1-(piperazinoethanesulfonic acid (HEPES); 3-(bis) (2-(hydroxyethyl)amino)-(2(hydroxypropane-(1-(sulfonic acid (DIPSO);Acetamidoglycine, 3-(N-(tris(hydroxymethyl)methylamino(2-(hydroxypropanesulfonic acid (TAPSO), piperazine-(N,N'-bis(2-(hydroxypropanesulfonic acid)-(2-(hydroxypropanesulfonic acid) (HEPPSO), 3-[4-(2-(hydroxyethyl)-(1-(piperazinyl]propanesulfonic acid (HEPPS), tricine, glycinamide, bicine, or 3-([[1,3-dihydroxy-(-(hydroxymethyl)propan-(2-(yl)amino]-(propane-(1-(sulfonic acid (TAPS)). Further examples of lamp recipes can be found in Whittall, J. and Sutton, PW (eds) (2012) Front Matter, in Practical Methods for Biocatalysis and Biotransformations 2, John Wiley & Sons, Ltd. Chichester, UK. In some formulations, ammonia can act as a buffer. One or more organic solvents can also be added to the reaction. Surprisingly, the reactions of DAAO, TA, and / or others can occur with or without low levels (less than 1 mM) of added buffer (other than ammonium, which may be optionally present due to the addition of racemic glufosinate ammonium). In particular, immobilized DAAO and TA can be stable and active in the presence of less than 1 mM phosphate buffer and without any other buffer except the ammonium present due to the addition of racemic glufosinate ammonium. Racemic glufosinate starter material can be provided in several forms. Various salts of racemic glufosinate, such as ammonium and hydrochloride, or the zwitterion, can be used. Racemic glufosinate may be in the form of a solid powder (such as a powder with a purity of over 80%, 85%, 90%, or 95%) or an aqueous solution (such as a solution of approximately 50% racemic glufosinate). In some forms, the reaction occurs within the defined pG range, which can range from pH 4 to pH 10 (e.g., between pH 6 and pH 9, as approximately a pH between 7.5 and 8). In some formulations, the reaction occurs at a defined temperature. The temperature can be maintained at a point between room temperature and the boiling point of the solvent, most typically between room temperature and 50°C. As indicated, the methods described herein provide a substantially pure L-glufosinate composition (as opposed to a racemic mixture of L(glufosinate) and D-(glufosinate)). Substantially pure L-glufosinate means that more than approximately 70%, more than approximately 75%, more than approximately 80%, more than approximately 85%, more than approximately 90%, more than approximately 95%, more than approximately 96%, more than approximately 97%, more than approximately 98%, or more than approximately 99% of the D-glufosinate has been converted to L-glufosinate, resulting in a composition that contains more than approximately 80%, more than approximately 85%, more than approximately 90%, more than approximately 95%, more than approximately 96%, more than approximately 97%, more than approximately 98%, or more than approximately 99% L-glufosinate relative to the sum of D-glufosinate and L-glufosinate present in the composition. In one embodiment, L-glufosinate is not isolated from the biotransformation mixture, and a composition comprising D-glufosinate, PPO, and L-glufosinate is obtained. This composition shall contain at least 80% L-glufosinate by weight of the sum of L-glufosinate, D-glufosinate, and PPO, and at least 90% L-glufosinate by weight of the sum of the components. This composition may be used directly as a herbicide composition or as an ingredient in a formulated herbicide product. Alternatively, some or all of the components other than L-glufosinate can be removed from the biotransformation mixture, the optionally concentrated mixture, and then the mixture can be used directly (and / or with the addition of various adjuvants) for weed prevention or control. The biotransformation mixture, in some cases, can be used directly (and / or with the addition of various adjuvants) for weed prevention or control. Additional steps can be added to further purify L-glufosinate. Such additional purification and isolation methods include ion exchange, extraction, salt formation, crystallization, and filtration; each can be used multiple times in a suitable combination. Enzymes can be removed by simple filtration if supported, or if free in solution by ultrafiltration, the use of adsorbents such as Celite, cellulose, or carbon, or denaturation through various techniques known to those skilled in the art. Ion exchange processes effect the separation of solutes by selective adsorption onto resins chosen for this purpose. Because the products and impurities must be dissolved in a single solution before adsorption, concentration of the purified product stream by evaporation or distillation is usually required before isolation. Examples of the use of ion exchange for purification are described in Schultz et al., and EP0249188 (A2). Purification can be achieved by forming an insoluble L-glufosinate salt through the addition of a suitable acid, including hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, and similar acids. Similarly, purification can be achieved by adding a suitable base to form an insoluble salt. Useful bases include alkali metal hydroxides, carbonates, sulfates, and phosphates. Other nitrogen-containing bases may be used, including ammonia, hydroxylamine, isopropylamine, triethylamine, tributylamine, pyridine, 2-picoline, 3-picoline, 4-picoline, 2,4-lutidine, 2,6-lutidine, morpholine, N-methylmorpholine, 1,8-diazabicyclo[5.4.0]undec-7-ene, and dimethylethanolamine. It may be advantageous to concentrate the mixture or add a solvent (or both) to maximize yield and optimize the purity of the desired salt.Suitable solvents for this purpose include those in which the solubility of the desired salt is very low (such solvents are often called antisolvents). L-glufosinate salts can be transformed into glufosinate forms suitable for formulation by standard methods known to those skilled in the art. Alternatively, L-glufosinate can be isolated as a zwitterion. ivIA / a / ¿u¿ i / un US patent 9,255,115 B2 describes how the hydrochloric acid salt of L-glufosinate can be converted to the zwitterionic form using a sodium hydroxide or sodium methoxide base and then crystallized from an aqueous alcohol solvent to yield L-glufosinate with relatively high purity. This method has the advantage of producing crystalline L-glufosinate that is non-hygroscopic and therefore maintains higher purity compared to amorphous L-glufosinate when exposed to moisture over time. Other L-glufosinate salts are known in the art. US 5,767,309 and US 5,869,668 disclose the use of chiral alkaloid bases to form diastereomeric salts with racemic glufosinate. Purification is achieved because the L-glufosinate salt precipitates from the solution in a much greater quantity than the corresponding D-glufosinate salt. Therefore, this method could be used with the present invention to obtain L-glufosinate with a high enantiomeric excess, if desired. Optionally, purification can be achieved by first crystallizing one or more impurities, removing the impurities by filtration, and then purifying the L-glufosinate from the resulting filtrate by forming a salt as described above. This is advantageous if the unreacted amine donor can be partially or completely isolated and used in downstream reactions. Similarly, the unreacted PPO that is partially or completely isolated can be recycled for use in subsequent reactions. Extraction can be used to purify the product. Document DE 3920570 C2 describes a process in which excess glutamic acid (used as the amine donor) is precipitated by adjusting the pH of the solution from 3.7 to 4.2 with sulfuric acid. After filtering the glutamic acid, the pH of the filtrate is reduced to 1–2, after which further impurities are extracted in a solvent. Following extraction and concentration, ammonia is added to the aqueous solution to a pH of 5–7, after which ammonium sulfate precipitates. The ammonium sulfate is separated by filtration, and the resulting filtrate is concentrated to provide the ammonium salt of L-glufosinate. Isolating L-glufosinate or its salts may be desirable, for example, for shipping solids to the formulation or use site. Typical industrial isolation methods, such as filtration and centrifugation, can be used. The isolated product often requires the removal of water, volatile impurities, and solvents (if present), and typical industrial drying equipment can be used for this purpose. Examples of such equipment include ovens, rotary drum dryers, agitated dryers, etc. In some cases, using a spray dryer may be advantageous. It is not necessary to produce a solid product after purification. This can be advantageous if the L-glufosinate formulation is produced at the same site used for L-glufosinate production. L-glufosinate and many of its salts are readily soluble in water, and water is a convenient liquid to use in product formulation. For example, the amine donor is isolated by filtration, and the resulting filtrate is concentrated by distillation. The pH of the filtrate can be adjusted to a desired value, and the resulting solution can be used as mixed with the formulation ingredients. In another example, a suspension of L-glufosinate or one of its salts can be prepared as described above and isolated by filtration. The solid could be dissolved directly on the filter by adding water or a suitable solvent to obtain an L-glufosinate solution. II. Compositions Compositions comprising the reaction products described above are also described. In some embodiments, the composition substantially includes L-glufosinate and acceptable cationic or anionic salt forms such as hydrochloride, ammonium, or isopropylammonium salts. In some embodiments, the composition comprises a mixture of L-glufosinate, PPO, and D-glufosinate. Optionally, L-glufosinate is the predominant compound among L-glufosinate, PPO, and D-glufosinate.For example, L-glufosinate may be present in the composition in an amount of at least 80% by weight of the sum of L-glufosinate, PPO, and D-glufosinate, at least 85 % by weight of the sum of L-glufosinate, PPO, and D-glufosinate, at least 90% by weight of the sum of L-glufosinate, PPO, and D-glufosinate, at least 95% by weight of the sum of L-glufosinate, PPO, and D-glufosinate, at least 96% by weight of the sum of L-glufosinate, PPO, and D-glufosinate, at least 97% by weight the sum of L-glufosinate, PPO, and D-glufosinate D-glufosinate, at least 98% by weight of the sum of L-glufosinate, PPO, and Dglufosinate, or at least 99% by weight of the sum of L-glufosinate, PPO, and D-glufosinate. The composition may include PPO in an amount of up to 20% by weight of the sum of L-glufosinate, PPO, and D-glufosinate. Optionally, the composition includes between 0.001% and 20% PPO (for example, between 0.05% and 15% or between more than 0.01% and less than 5% PPO). For example, the composition may include PPO in an amount of less than 20%, less than 19%, less than 18%, less than 17%, less than 16%, less than 15%, less than 14%, less than 13%, less than 12%, less than 11%, less than 10%, less than 9%, less than 8%, less than 7%, less than 6%, less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, less than 0.5%, less than 0.1%, or less than 0.01% by weight of the sum of the masses of L-glufosinate, PPO, and D-glufosinate. D-Glufosinate may be present in the composition in an amount of 15% or less by weight of the sum of L-glufosinate, PPO, and D-glufosinate. For example, D-glufosinate may be present in an amount of 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 9% or less, 8% or less, 7% or less, 8% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, or 0.5% or less by weight of the sum of L-glufosinate, PPO, and D-glufosinate. In some formulations, the composition may contain small amounts (e.g., approximately 10% or less, approximately 8% or less, approximately 5% or less, approximately 2% or less, or approximately 1% or less by weight of the composition) of D-glufosinate. In some formulations, the composition may contain small amounts (e.g., approximately 15% or less, approximately 10% or less, approximately 8% or less, approximately 5% or less, approximately 2% or less, or approximately 1% or less by weight of the composition) of PPO. The compositions described herein are useful for application to a sown field for weed prevention or control. The composition can be formulated as a liquid that is sprayed onto the field. L-glufosinate is provided in the composition in effective quantities. According to this document, effective amount means between approximately 10 grams of active ingredient per hectare and approximately 1,500 grams of active ingredient per hectare; for example, between approximately 50 grams and approximately 400 grams, or between approximately 100 grams and approximately 350 grams. In some formulations, the active ingredient is L-glufosinate.For example, the amount of L-glufosinate in the composition may be approximately 10 grams, approximately 50 grams, approximately 100 grams, approximately 150 grams, approximately 200 grams, approximately 250 grams, approximately 300 grams, approximately 350 grams, approximately 400 grams, approximately 500 grams, approximately 550 grams, approximately 600 grams, approximately 650 grams, approximately 700 grams, approximately 750 grams, approximately 800 grams, approximately 850 grams, approximately 900 grams, approximately 950 grams, approximately 1,000 grams, approximately 1,050 grams, approximately 1,100 grams, approximately 1,150 grams, approximately 1,200 grams, approximately 1,250 grams, approximately 1,300 grams, approximately 1,350 grams, approximately 1,400 grams, approximately 1,450 grams, or approximately 1,500 grams L-glufosinate per hectare. The herbicide compositions (including concentrates that require dilution before application to plants) described herein contain L-glufosinate (i.e., the active ingredient), optionally some D-glufosinate and / or residual PPO, one or more adjuvant components in liquid or solid form. Compositions are prepared by mixing the active ingredient with one or more adjuvants, such as diluents, extenders, vehicles, surfactants, organic solvents, wetting agents, or conditioning agents, to provide a composition in the form of a finely divided solid, pellet, solution, dispersion, or emulsion. Thus, the active ingredient may be used with an adjuvant, such as a finely divided solid, a liquid of organic origin, water, a wetting agent, a dispersing agent, an emulsifying agent, or any suitable combination thereof. From the standpoint of economy and convenience, water is the preferred diluent. However, not all compounds are resistant to hydrolysis, and in some cases this may dictate the use of non-aqueous solvent media, as will be advised by a person skilled in the art.Optionally, one or more additional components may be incorporated into the composition to produce a formulated herbicide composition. These formulated herbicide compositions may include L-glufosinate, carriers (e.g., diluents and / or solvents), and other components. The formulated composition includes an effective amount of L-glufosinate. Optionally, the L-glufosinate may be present in the form of L-glufosinate ammonium. The L-glufosinate ammonium may be present in an amount ranging from 10% to 30% by weight of the formulated composition. For example, L-glufosinate ammonium may be present in an amount of 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30% by weight of the formulated composition. Optionally, L-glufosinate ammonium is present in an amount of 12.25% or 24.5%. In some examples, the formulated composition may include one or more surfactants. A suitable surfactant for use in the formulated composition includes sodium alkyl ether sulfate. The surfactant may be present in an amount of 10% to 40% by weight of the formulated composition. For example, the surfactant may be present in an amount of 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, or 40% by weight of the formulated composition. Optionally, sodium alkyl ether sulfate is present in an amount of 11.05%, 15.8%, 22.1%, or 31.6%. The formulated composition may optionally include one or more solvents (e.g., organic solvents). Optionally, the solvent may be 1-methoxy-2-propanol, dipropylene glycol, ethylene glycol, or mixtures thereof. The single or multiple solvents may be present in an amount ranging from 0.5% to 20% by weight of the formulated composition. For example, the total amount of solvents in the composition may be present in amounts ranging from 0.5% to 18%, 5% to 15%, or 7.5% to 10% by weight of the formulated composition. Optionally, the solvent may include a combination of two solvents. For example, the solvents in the formulation may include 1-methoxy-2-propanol and dipropylene glycol. The 1-methoxy-2-propanol may be present, for example, in amounts ranging from 0.5% to 2% by weight of the formulated composition. For example, 1-methoxy-2-propanol may be present in the amount of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0% by weight of the formulated composition. Optionally, 1-methoxy-2-propanol is present in an amount of 0.5% or 1.0% by weight of the formulated composition. Dipropylene glycol may be present in an amount of between 4% and 18% by weight of the formulated composition. For example, dipropylene glycol may be present in an amount of 4%, 6%, 8%, 10%, 12%, 14%, 16%, or 18% by weight of the formulated composition. Optionally, dipropylene glycol is present in an amount of 4.3% or 8.6% by weight of the formulated composition. The formulated composition may also include one or more polysaccharide humectants. Examples of suitable polysaccharide humectants include, for example, alkyl polysaccharides, pentoses, high fructose corn syrup, sorbitol, and molasses. The polysaccharide humectant, such as an alkyl polysaccharide, may be present in the formulated composition in an amount ranging from 4% to 20% by weight. For example, the total amount of polysaccharide humectant in the composition may be present in an amount of 4% to 18%, 4.5% to 15%, or 5% to 10% by weight. In some examples, the total amount of polysaccharide humectant, such as alkyl polysaccharide, present in the formulated composition may be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18%. Optionally, the alkyl polysaccharide may be present in an amount of 3.2%, 4.9%, 6.2%, or 9.8%. A diluent may also be included in the formulated composition. Suitable diluents include water and other aqueous components. Optionally, diluents are supplied in the quantity necessary to produce compositions ready for packaging or use. In one example, the formulated composition includes L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 31.6% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; dipropylene glycol in an amount of 8.6% by weight of the formulation; alkyl polysaccharide in an amount of 9.8% by weight of the formulation; and water in an amount of 36.75% by weight of the formulation. In another example, the formulated composition includes L-glufosinate ammonium in an amount of 24.5% by weight of the formulation; sodium alkyl ether sulfate in an amount of 31.6% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; dipropylene glycol in an amount of 8.6% by weight of the formulation; alkyl polysaccharide in an amount of 9.8% by weight of the formulation; and water in an amount of 36.75% by weight of the formulation. In another example, the formulated composition includes L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 15.8% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5% by weight of the formulation; dipropylene glycol in an amount of 4.3% by weight of the formulation; alkyl polysaccharide in an amount of 4.9% by weight of the formulation; and water in an amount of 62.25% by weight of the formulation. In another example, the formulated composition includes L-glufosinate ammonium in an amount of 24.5% by weight of the formulation; sodium alkyl ether sulfate in an amount of 22.1% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; alkyl polysaccharide in an amount of 6.2% by weight of the formulation; and water in an amount of 46.2% by weight of the formulation. In another example, the formulated composition includes L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 22.1% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; alkyl polysaccharide in an amount of 6.2% by weight of the formulation; and water in an amount of 58.45% by weight of the formulation. In another example, the formulated composition includes L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 11.05% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5% by weight of the formulation; alkyl polysaccharide in an amount of 3.1% by weight of the formulation; and water in an amount of 73.1% by weight of the formulation. Other components suitable for use in the formulated compositions provided herein are described in U.S. Patents Nos. 4,692,181 and 5,258,358, which are incorporated herein by reference. The herbicide compositions described herein, particularly soluble liquids and powders, may contain, as other adjuvant components, one or more surfactants in sufficient quantities to make a given composition readily dispersible in water or oil. The incorporation of a surfactant into the compositions greatly increases their effectiveness. Surfactants, as defined herein, include wetting agents, dispersing agents, suspending agents, and emulsifying agents. Anionic, cationic, and nonionic surfactants may be used with equal ease. Suitable wetting agents include alkylbenzene and alkylnaphthalene sulfonates, sulfated fatty alcohols, acid amines or amides, long-chain acid esters of sodium isothionate, sodium sulfosuccinate esters, petroleum sulfonates of sulfated or sulfonated fatty acid esters, sulfonated vegetable oils, ditertiary acetylenic glycols, polyoxyethylene derivatives of alkylphenols (particularly isooctylphenol and nonylphenol), and polyoxyethylene derivatives of higher fatty acid mono-esters of hexitol anhydrides (e.g., sorbitan). Examples of dispersants include methyl cellulose, polyvinyl alcohol, sodium lignin sulfonates, polymeric alkyl naphthalene sulfonates, sodium naphthalene sulfonate, polymethylene bisnaphthalene sulfonate, and sodium N-methyl-N-(long chain acid) laurates. Water-dispersible powder compositions may be prepared containing one or more active ingredients, an inert solid diluent, and one or more wetting and dispersing agents. Inert solid extenders are usually of mineral origin, such as natural clays, diatomaceous earth, and synthetic minerals derived from silica and the like. Examples of such extenders include kaolinite, attapulgite clay, and synthetic magnesium silicate. The water-dispersible powders described herein may optionally contain from approximately 5 to approximately 95 parts by weight of active ingredient (e.g., from approximately 15 to 30 parts by weight of active ingredient), from approximately 0.25 to 25 parts by weight of wetting agent, from approximately 0.25 to 25 parts by weight of dispersant, and from 4.5 to approximately 94.5 parts by weight of inert solid extender, all parts by weight of the total composition.When necessary, between approximately 0.1 and 2.0 parts by weight of the solid inert extender may be replaced by a corrosion inhibitor or anti-foaming agent or both. Aqueous suspensions can be prepared by dissolving or by mixing and grinding an aqueous suspension of a water-insoluble active ingredient in the presence of a dispersing agent to obtain a concentrated suspension of very finely divided particles. The resulting concentrated aqueous suspension is characterized by its extremely small particle size, so that when diluted and sprayed, the coverage is very uniform. Emulsifiable oils are usually solutions of an active ingredient in water-immiscible or partially water-immiscible solvents along with a surfactant. Suitable solvents for the active ingredient as described herein include water-immiscible hydrocarbons and ethers, esters, or ketones. Emulsifiable oil compositions generally contain between 5 and 95 parts of active substance, approximately 1 to 50 parts of surfactant, and approximately 4 to 94 parts of solvent, all parts being by weight based on the total weight of emulsifiable oil. The compositions described herein may also contain other additives, fertilizers, plant growth regulators, pesticides, and similar products used as adjuvants or in combination with any of the adjuvants described above. The compositions described herein may also be mixed with other materials, such as fertilizers, other plant growth regulators, etc., and applied in a single application. In each of the formulation types described here, for example liquid and solid, the concentration of the active ingredients is the same. In some embodiments, the composition may include α-ketoglutarate as the main component. α-Ketoglutarate is an important dicarboxylic acid and one of the main intermediate compounds in the tricarboxylic acid cycle and amino acid metabolism. α-Ketoglutarate can be isolated from the reaction mixture by methods such as those described in French Patent No. 07199, incorporated herein by reference. The α-ketoglutarate composition can be formulated with pharmaceutical excipients and carriers, food additives, or components used to form biomaterials. The α-ketoglutarate composition can be used in a variety of applications, including in the synthesis of pharmaceutical agents, food additives, and biomaterials, as described in L. et al., Bioprocess Biosyst Eng. 39: 967-976 (2016). It is recognized that herbicidal compositions can be used in combination with other herbicides. The herbicidal compositions of the present invention are often applied together with one or more other herbicides to control a wider variety of undesirable vegetation. When used in conjunction with other herbicides, the claimed compounds may be formulated with the other herbicide or herbicides, tank-mixed with the other herbicide or herbicides, or applied sequentially with the other herbicide or herbicides. Some of the herbicides that can be used in conjunction with the compounds of the present invention include: amide herbicides such as allidochlor, beflubutamide, benzadox, benzipram, bromobutide, cafenstrole, CDEA, chlortamycin, ciprazole, dimethenamide, dimethenamide-P, diphenamide, epronaz, etnipromide, fentrazamide, flupoxam, fomesafen, halosafen, isocarbamide, isoxabene, napropamide, naptalam, pethoxamide, propylamide,quinonamide and tebutam; anilide herbicides such as chloranocryl, cisanilide, clomeprop, cypromid, diflufenican, etobenzanid, fenasulam, flufenacet, flufenican, mefenacet, mefluidide, metamifop, monalide, naproanilide, pentanechlor, picolinaphene and propanil; arylalanine herbicides such as benzoylprop, flamprop and flamprop-M; chloroacetanilide herbicides such as acetochlor, alachlor, butachlor, butenachlor, delachlor, diethyl, dimetachlor, metazachlor, metolachlor, S-metolachlor, pretylachlor, propachlor, propisochlor, prinachlor, terbuchlor, thenylchlor and xylchlor; Sulfonanilide herbicides such as benzofluor, perfluidone, pirimisulfan, and profluazole; Sulfonamide herbicides such as asulam, carbasulam, fenasulam, and oryzalin; Antibiotic herbicides such as bilanafos; Benzoic acid herbicides such as chloramben, dicamba, 2,3,6-TBA and tricamba; pyrimidinyloxybenzoic acid herbicides such as bispyribac and piriminobac; pyrimidinylthiobenzoic acid such as pyritiobac; italic acid herbicides such as chlorotics; picolinic acid herbicides such as aminopyralid, clopyralid and picloram; quinolinecarboxylic acid herbicides such as quinclorac and quinmerac; arsenic herbicides such as cacodylic acid, CMA, DSMA, hexaflurate, MAA, MAMA, MSMA, potassium arsenite and sodium arsenite; benzoylcyclohexanedione herbicides such as mesotrione, sulcotrione, tefuryltrione and tembotrione; benzofuranyl alkylsulfonate herbicides such as benfuresate and etofumesate; Carbamate herbicides such as asulam, carboxazole chlorprocarb, dichlorate, fenasulam, karbutylate and terbucarb; Carbanylate herbicides such as barban, BCPC, carbasulam, carbetamide, CEPC, chlorbufam, chlorpropham, CPPC, desmedifam, phenisopham, phenmedipham, phenmedipham-ethyl, profam and swep; Cyclohexenes oxime herbicides such as alloxidim, butroxidim, clethodim, cloproxidim,Cycloxidim, profoxidim, sethoxidim, tepraloxidim, and tralcoxidim; Cyclopropylisoxazole herbicides such as isoxachlortole and isoxaflutole; Dicarboximide herbicides such as benzphendizone, cynidon-ethyl, flumezine, flumiclorac, flumioxazine, and flumipropine; Dinitroaniline herbicides such as benfluralin, butralin, dinitramine, ethalfluralin, fluchloralin, isopropalin, metalpropalin, nitralin, oryzalin, pendimethalin, prodiamine, profluralin, and trifluralin; Dinitrophenol herbicides such as dinophenate, dinoprop, dinosam, dinoseb, dinoterb, DNOC, ethynophene, and medinoterb; Diphenyl ether herbicides such as ethoxyphene; Nitrophenyl ether herbicides such as acifluorfen, aclonifen, bifenox, chlormethoxyfen, chlormitrofen, etnipromid, fluorodifen, fluoroglycofen, fluoronitrofen, fomesafen, furiloxyfen, halosafen, lactofen, nitrofen, nitrofluorfen, and oxyfluorfen; Dithiocarbamate herbicides such as dazomet and metam; Halogenated aliphatic herbicides such as alorac, chloropon, and dalapon.flupropanate, hexachloroacetone, iodomethane, methyl bromide, monochloroacetic acid, SMA and TCA; Imidazolinone herbicides such as imazamethabenz, imazamox, imazapic, imazapyr, imazaquin and imazethapyr; Inorganic herbicides such as ammonium sulfamate, borax, calcium chlorate, copper sulfate, ferrous sulfate, potassium azide, potassium cyanate, sodium azide, sodium chlorate and sulfuric acid; Nitrile herbicides such as bromobonyl, bromoxynyl, chloroxynyl, dichlorobenyl, iodobonyl, ioxynyl and pyraclonil; Organophosphate herbicides such as amiprophos-methyl, anilophos, bensulide, bilanaphos, butamiphos, 2,4-DEP, DMPA, EBEP, phosamine, glyphosate, and piperophos; Phenoxy herbicides such as bromophenoxime, chlormeprop, 2,4-DEB, 2,4-DEP, diphenopenten, disul, erbon, etnipromid, fentheracol, and triphopsime; Phenoxyacetic herbicides such as 4-CPA, 2,4-D, 3,4-DA, MCPA, MCPA-thioethyl, and 2,4,5-T; Phenoxybutyric herbicides such as 4-CPB, 2,4-DB, 3,4-DB, MCPB, and 2,4,5-TB; Phenoxypropionic herbicides such as cloprop, 4-CPP, and dichlorprop.dichlorprop-P, 3,4-DP, phenoprop, mecoprop and mecoprop-P; Herbicides ariloxi fenoxi propiónicos como chlorazifop, clodinafop, clofop, cyhalofop, diclofop, fenoxaprop, fenoxaprop-P, fenthiaprop, fluazifop, fluazifop-P, haloxifop, haloxifop-P, isoxapyrifop, metamifop, propaquizafop, quizalofop, quizalofop-P y triphop; Phenylidenediamine herbicides such as dinitramine and prodiamine; Pyrazolid herbicides such as benzofenap, pyrazolinate, pyrasulfotol, pyrazoxifen, pyroxasulfona and topramezona; pyrazolylphenyl herbicides such as fluazolate and piraflufen; Pyridazine herbicides such as credazine, pyridafol and pyridate; Pyridazine herbicides such as brompirazon, chloridazon, dimidazon, flufenpir, metflurazon, norflurazon, oxapirazon and pidanon; Pyridine herbicides such as aminopyralid, cliodinate, clopyralid, dithiopir, fluroxypyr, haloxidine, picloram, picolinafen, piriclor,tiazopir and triclopir; Pyrimidinadiamine herbicides such as iprimidam and tioclorim; quaternary ammonium herbicides such as ciperquat, dietaamquat, dibenzoquat, diquat, morfamquat and paraquat; herbicides de tiocarbamato tales como butilato, cicloato, di-alato, EPTC, esprocarb, etiolato, isopolinato, metiobencarb, molinato, orbencarb, ινΐΛ / a / zuz i / un ozoz pebulato, prosulfocarb, piributicarb, sulfallato, tiobencarb, tiocarbazil, tri-alato y vemolato;herbicidas de tiocarbonato tales como dimexano, EXD y proxan; thiourea herbicides such as metiuron; triazine herbicides such as dipropetrina, triaziflam and trihidroxidriazina; herbicides of clorotriazina such as atrazina, clorazina, cyanazina, cyprazina, eglinazina, ipazina, mesoprazina, prociazina, proglinazina, propazina, subutilazina, simazina, terbutilazina and trietazina; herbicides of metoxytriazina such as atraton, metometon, prometon, secbumeton,simeton and terbumeton; methylthiotriazine herbicides such as ametrine, aziprothrin, cyanathrin, desmethrin, dimetamethrin, metoprothrin, promethrin, simetrine and terbutryne; triazinone herbicides such as ametridione, amibuzin, hexazinone, isomethiozin, metamitron and metribuzin; triazole herbicides such as amitrol, cafenstrol, epronaz and flupoxam; triazolone herbicides such as amicarbazone, bencarbazone, carfentrazone, flucarbazone, propoxycarbazone, sulfentrazone and thiencarbazone-methyl; triazolopyrimidine herbicides such as chloransulam, diclosulam, florasulam, flumetsulam, metosulam, penoxsulam and piroxsulam; uracil herbicides such as butafenacil, bromacil, flupropacil, isocil, lenacil and terbacil; 3-feiluracils; urea herbicides such as benzthiazuron, cumiluron, cycloron, dichloralurea, diflufenzopyr, isonoruron, isouron, metabenzthiazuron, monisouron and noruron; phenylurea herbicides such as anisuron, buturon, chlorbromuron, cloreturon, chlorotoluron,cloroxuron, daimuron, difenoxuron, dimefuron, diuron, fenuron, fluometuron, fluotiuron, isoproturon, linuron, methiuron, methyldimuron, metobenzuron, metobromuron, methoxuron, monolinuron, monuron, neburon, parafluron, fenobenzuron, siduron, tetrafluron y thidiazuron; pyrimidinylsulfonylurea herbicides such as amidosulfur, azimsulfur, bensulfur, chlorimur, cyclosulfamur, ethoxysulfur, flazasulfur, flucetosulfur, flupyrsulfur, foramsulfur, halosulfur, imazosulfur, mesosulfur, nicosulfur, orthosulfamur, oxasulfur, primisulfur, pyrazosulfur, rimsulfur, sulfometur, sulfosulfur and trifloxysulfur; triazinylsulfonylurea herbicides such as chlorsulfur, cinosulfur, etametsulfur, iodosulfur, metsulfur, prosulfur, thifensulfur, triasulfur, tribenur, triflusulfur and tritosulfur; thiadiazolylurea herbicides such as iviA / a / ¿u¿ i / ui butyuron, ethidimuron, tebutyuron,thiazafluron and thidiazuron; and unclassified herbicides such as acrolein, allyl alcohol, aminocyclopyrachlor, azaphenidine, benazoline, bentazone, benzobicyclon, butidazole, calcium cyanamide, cambendichlor, chlorfenac, chlorfenprop, chlorflurazole, chlorflurenol, cinmethyl, clomazone, CPMF, cresol, ortho-dichlorobenzene, dimepiperate, endothal, fluoromidine, fluridone, flurochloridone, flurtamone, flutiacet, indanophan, metazole, methyl isothiocyanate, nipiraclofen, OCH, oxadiargil, oxadiazon, oxaziclomefon, pentachlorophenol, pentoxazone, phenylmercury acetate, pinoxaden, prosulfalin, pyribenzoxim, pyriftolid, quinoclamine, rodetanine, sulglicapin, thidiazimin, tridiphane, trimeturon, tripropindan, and tritac. The herbicidal compositions of the present invention can also be used in conjunction with glyphosate or 2,4-D in crops tolerant to glyphosate or 2,4-D. In general, it is preferred to use the compositions of the invention in combination with herbicides that are selective for the treated crop, complementing the spectrum of weeds controlled by these compositions at the application rate employed. Furthermore, it is generally preferred to apply the compositions of the invention and other complementary herbicides simultaneously, either in combination or as a tank mix. III. Methods of use of L-glufosinate compositions The compositions described herein may be used in methods for selectively controlling weeds in a field or any other area, including, for example, a railway line, lawn, golf course, etc., where weed control is desired. Optionally, the field or area may contain a glufosinate-resistant crop or crops. The methods may include applying an effective amount of a composition comprising L-glufosinate as described herein to the field. The compositions described herein are useful for application to a planted field for weed prevention or control. The composition may be formulated as a liquid that is sprayed onto a field. The L-glufosinate is provided in the composition in effective amounts.According to this document, effective amount means between approximately 10 grams of active ingredient per hectare and approximately 1,500 grams of active ingredient per hectare; for example, between approximately 50 grams and approximately 400 grams, or between approximately 100 grams and approximately 350 grams. In some formulations, the active ingredient is L-glufosinate.For example, the amount of L-glufosinate in the composition may be approximately 10 grams, approximately 50 grams, approximately 100 grams, approximately 150 grams, approximately 200 grams, approximately 250 grams, approximately 300 grams, approximately 350 grams, approximately 400 grams, approximately 500 grams, approximately 550 grams, approximately 600 grams, approximately 650 grams, approximately 700 grams, approximately 750 grams, approximately 800 grams, approximately 850 grams, approximately 900 grams, approximately 950 grams, approximately 1,000 grams, approximately 1,050 grams, approximately 1,100 grams, approximately 1,150 grams, approximately 1,200 grams, approximately 1,250 grams, approximately 1,300 grams, approximately 1,350 grams, approximately 1,400 grams, approximately 1,450 grams, or approximately 1,500 grams L-glufosinate per hectare. IV. Examples of Modalities Examples of modalities include: 1. A method of preparing L-glufosinate, comprising: react D-glufosinate with a D-amino acid oxidase (DAAO) enzyme to form PPO (2-oxo-4-(hydroxy(methyl)phosphinoyl)butyric acid); and amination of PPO to L-glufosinate by a transaminase (TA) enzyme, using an amine group from one or more amine donors, while at least 70% of the D-glufosinate is converted to L-glufosinate. 2. The Modality 1 method, in which the amine donor is ML / a / ZUZ 1 ÓZÓZ selected from the group consisting of glutamate, L-glutamate, alanine, sec-butylamine, phenylethylamine, glycine, lysine, valine, serine, glutamine, isopropylamine, ethanolamine, 2-aminobutyric acid, and diaminopropionic acid, or any amine or secondary amino acid. 3. The Modality 1 method, in which D-glufosinate is originally present in a racemic mixture of D- and L-glufosinate or salts thereof. 4. The method of Modality 1, wherein the DAAO enzyme is selected from the enzyme of Rhodosporidium toruloides or Trigonopsis variabilis, Neolentinus lepideus, Trichoderma reesei, or Trichosporon oleaginosus. In one modality, the Rhodosporidium toruloides DAAO enzyme is UniProt P80324. In one modality, the Trigonopsis variabilis DAAO enzyme is UniProt Q99042. In one modality, the Neolentinus lepideus DAAO enzyme is KZT28066.1. In one modality, the Trichoderma reesei DAAO enzyme is XP_006968548.1. In one modality, the Trichosporon oleaginosus DAAO enzyme is KLT40252.1. 5. The Modality 1 method, in which the DAAO enzyme is a DAAO mutant. 6. The Modality 5 method, in which the DAAO mutant is a DAAO mutant based on the Rhodosporidium toruloids sequence. 7. The Modality 5 method, wherein the DAAO mutant comprises one or more mutations at positions 54, 56, 58, 213, and 238. 8. The Modality 7 method, in which the mutation at position 54 is selected from the group consisting of N54C, N54L, N54T, and N54V. 9. The Modality 7 method, in which the mutation at position 56 is T56M. 10. The Modality 7 method, in which the mutation at position 58 is selected from the group consisting of F58A, F58G, F58H, F58K, F58N, F58Q, F58R, F58S, and ινΐΛ / a / zuz i / un ózóz F58T. 11. The Modality 7 method, in which the mutation at position 213 is M213S. 12. The Modality 5 method, wherein the DAAO mutant comprises the F58K and M213S mutations. 13. The Modality 5 method, wherein the DAAO mutant comprises mutations at positions 54 and 56. 14. The Modality 5 method, wherein the DAAO mutant comprises the N54T and T56M mutations. 15. The Modality 5 method, wherein the DAAO mutant comprises the F58Q or F58H mutations. 16. The Modality 5 method, wherein the DAAO mutant comprises the N54V and F58Q mutations. 17. The Modality 5 method, wherein the DAAO mutant comprises the N54V, F58Q, and M213S mutations. 18. The Modality 1 method, in which the TA enzyme is a gabT transaminase from Escherichia coli. In one modality, the Escherichia coli gabT transaminase enzyme is UniProt P22256. 19. The Modality 1 method, in which the TA enzyme is encoded by Seq. ID No. 1. 20. The Mode 1 method, in which the reaction step and the amination step are performed in a single container. 21. The Modality 20 method, in which all reagents are substantially incorporated at the beginning of the reaction. 22. The Modality 20 method, in which the reagents for the reaction step and the reagents for the amination step are incorporated into the container at different times. 23. The Modality 1 method, in which the reaction step and the amination step are performed in separate containers. 24. A composition comprising D-glufosinate, PPO, and L-glufosinate. 25. The composition of modality 24, in which the amount of L-glufosinate is 90% or greater based on the total amount of D-glufosinate, PPO, and L-glufosinate. 26. The method of Modality 1 in which a solid is obtained that has the composition of modality 25. 27. The Modality 1 method in which a solution of Lglufosinate is obtained for use in a formulation having herbicidal activity. 28. A formulation comprising L-glufosinate ammonium in an amount of 10-30% by weight of the formulation; one or more additional components selected from the group consisting of sodium alkyl ether sulfate in an amount of 10-40% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5-2% by weight of the formulation; dipropylene glycol in an amount of 4-18% by weight of the formulation; and alkyl polysaccharide in an amount of 4-20% by weight of the formulation; and water as the remainder of the formulation. 29. The composition of modality 28, wherein the formulation comprises: L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 31.6% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; dipropylene glycol in an amount of 8.6% by weight of the formulation; alkyl polysaccharide in an amount of 9.8% by weight of the formulation; and water in an amount of 36.75% by weight of the formulation. 30. The composition of modality 28, wherein the formulation comprises: L-glufosinate ammonium in an amount of 24.5% by weight of the formulation; sodium alkyl ether sulfate in an amount of 31.6% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; dipropylene glycol in an amount of 8.6% by weight of the formulation; alkyl polysaccharide in an amount of 9.8% by weight of the formulation; and water in an amount of 24.5% by weight of the formulation. 31. The composition of modality 28, wherein the formulation comprises: L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 15.8% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5% by weight of the formulation; dipropylene glycol in an amount of 4.3% by weight of the formulation; alkyl polysaccharide in an amount of 4.9% by weight of the formulation; and water in an amount of 62.25% by weight of the formulation. 32. A formulation comprising L-glufosinate ammonium in an amount of 10-30% by weight of the formulation; one or more additional components selected from the group consisting of sodium alkyl ether sulfate in an amount of 10-40% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5-2% by weight of the formulation; and alkyl polysaccharide in an amount of 3-10% by weight of the formulation; and water as the remainder of the formulation. 33. The composition of modality 32, wherein the formulation comprises: L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 22.1% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; alkyl polysaccharide in an amount of 6.2% by weight of the formulation; and water in an amount of 58.45% by weight of the formulation. 34. The composition of modality 32, wherein the formulation comprises: L-glufosinate ammonium in an amount of 24.5% by weight of the formulation; sodium alkyl ether sulfate in an amount of 22.1% by weight of the formulation; 1-methoxy-2-propanol in an amount of 1% by weight of the formulation; alkyl polysaccharide in an amount of 6.2% by weight of the formulation; and water in an amount of 46.2% by weight of the formulation. 35. The composition of modality 32, wherein the formulation comprises: L-glufosinate ammonium in an amount of 12.25% by weight of the formulation; sodium alkyl ether sulfate in an amount of 11.05% by weight of the formulation; 1-methoxy-2-propanol in an amount of 0.5% by weight of the formulation; alkyl polysaccharide in an amount of 3.1% by weight of the formulation; and water in an amount of 73.1% by weight of the formulation. 36. A method for selectively controlling weeds in an area comprising: applying an effective amount of a composition comprising L-glufosinate in an enantiomeric excess greater than 90% over D-glufosinate to the area. 37. The Modality 36 method, in which the amount of the composition is applied to less than 400 grams of the sum of L-glufosinate and D-glufosinate per hectare. 38. A method for selectively controlling weeds in an area comprising: Apply an effective amount of a composition comprising L-glufosinate in an enantiomeric excess greater than 90% over D-glufosinate to the area and more than 0.01% but less than 10% PPO to the area. 39. The Modality 38 method in which the amount of the composition is applied to less than 400 grams of the sum of L-glufosinate, D-glufosinate and PPO per hectare. 40. A method for selectively controlling weeds in an area containing a seed-planted crop or glufosinate-resistant crops, comprising: Apply an effective amount of a composition comprising L-glufosinate in an enantiomeric excess greater than 90% over D-glufosinate and more than 0.01% but less than 10% PPO to the field. The following examples are for illustrative purposes only and are not exhaustive. EXAMPLES Example 1: Purification of the DAAO enzyme The coding sequence of a Rhodosporidium toruloides DAAO mutant (e.g., comprising an MMARIRL leader sequence and the F58K and M213S mutations) was cloned into the pET14b vector to enable the expression of a 6xHis-tagged N protein. This pET14b-RgDAAO plasmid was transformed into BL21 (BE3) trxB pLysS cells. The wild-type Rhodosporidium toruloides DAAO sequence is described in Section 2. To purify the DAAO enzyme, cells were cultured in 400 ml of autoinducer medium (LB broth base with trace elements, Formedium) at 30°C for 20–24 hours. The cells were collected in pre-cooled centrifuges and cuvettes, washed with cold water, centrifuged again, and stored at -80gC until purification. The cell pellets were then thawed in lysis buffer (50 mM potassium phosphate, pH 8.0, 20 mM imidazole, and 1% Sigma protease inhibitor cocktail (EDTA)) at a volume of 5 mL of lysis buffer per 1 g of cell pellet. While on ice, the cells were sonicated four times for 30 seconds at an amplitude of 10. The cell lysate was clarified by centrifugation and then added to cobalt resin (HisPur Cobalt, ThermoScientific) at four times the bed volume. The cell lysate was incubated for 1 hour, with gentle shaking, at room temperature. The resin was added to a column and washed twice with five bed volumes of wash buffer (50 mM Kpi, pH 8.0, 20 mM imidazole). Elution was performed four times with one bed volume of elution buffer (Kpi 50 mM, imidazole 200 mM). Example 2: Colorimetric determination of DAAO activity DAAO activity was determined similarly to that described by Berneman et al. In summary, 100 µL of substrate and HRP (0.1 mg / ml HRP, Sigma P8375, and the desired amount of D-glufosinate or racemic D / L-glufosinate in 50 mM potassium phosphate, pH 8) were added to a Brand UV microtube. 50 µL of dyes (60 µg / ml TBHBA, Sigma 439533, and 1 mg / ml 4-aminoantipyrine, Sigma A4382, in 50 mM potassium phosphate, pH 8) were then added, followed by 50 µL of enzyme mixture (desired DAAO concentration in 100 mM potassium phosphate, pH 8). The reaction was monitored in a spectrophotometer at 510 nm for an appropriate time to determine the enzyme kinetics. Although no flavin adenine dinucleotide (FAD) was added to the DAAO purification or the reaction, this reagent may be optionally included.Two example variants of Rhodosporidium toruloids DAAO mutants, AC201 (containing F58K and M213S) and AC263 (containing N54T, T56M, F58K, and M213S), purified according to Example 1, were tested using this assay and were shown to produce hydrogen peroxide, demonstrating their activity in the oxidation of D-glufosinate. AC201 and AC263 have similar Vmax, but AC263 has a lower KM. Example 3: Purification of transaminases To purify, for example, Escherichia coli gabT transaminase (http: / / www.uniprot.org / uniprot / P22256), the gene from E. coli K12 strain ER2925 was amplified and cloned into pET-14b to generate a 6xHis-terminally labeled version. This plasmid was then transformed into BL21 (DE3) cells for induction. After induction in autoinducer media, the cells were lysed by sonication, and the 6xHis-labeled enzyme was purified as described in Example 1. Example 4: Demonstration of transaminase activity In a non-limiting example, the source of PPO for a transamination assay can be D-glufosinate or racemic D / L-glufosinate that has been converted to PPO by DAAO. In the first step, 39 mM racemic D / L-glufosinate was incubated with 0.5 mg / ml of DAAO from purified Rhodosporidium toruloides F58K M213S and 10 pg / ml catalase in 50 mM potassium phosphate buffer, pH 8, for 20 hours at 30°C. This resulted in the conversion of most of the D-glufosinate in PPO. Subsequently, gabT from purified E. coli was added at 20 µg / ml, and L-glutamate at 50 mM was added as the amine donor. At relevant points, the samples were interrupted by boiling for 10 minutes followed by precipitation with an equal volume of acetonitrile. Individual chemical species were resolved by HPLC using a Chirobiotic T2 column and quantified by comparison with authentic standards. The combination of a DAAO mutant variant and a transaminase resulted in enhanced enantiomeric enrichment, starting at 0% for L-glufosinate over D-glufosinate (i.e., equal D-glufosinate and L-glufosinate) and progressing to 92% enantiomeric enrichment. These results demonstrate that E. coli gabT has transaminase activity, and this assay can be used to determine the activity of any number of potential mutant and / or wild-type transaminases. Example 5: Des racemization of racemic D / L-glufosinate in one vessel The reactions were designed similarly to that in Example 4. The system (5.45 mL, 30°C) was run in phosphate buffer at pH 7.3. It was observed that 50 mM phosphate buffer at pH 8.0 was inadequate to buffer the amino acid additions and that the unadjusted pH after amino acid additions in this system was pH 6.4. The pH was adjusted using 1 M of the base salt K₂HPO₄ in a volume of 5.45 mL, meaning that the initial concentration of the starting substrate per addition was 275 mM. The following reagents were incorporated essentially simultaneously with the start of the reaction: 271 mg of D,L-glufosinate, 420 mg of glutamate, 15 mg of AC₂₆₃ DAAO, 50 pg of catalase, and 1.0 mg of E. coli gab T transaminase. Figure 2 shows that, when all reagents were added, the amount of D-PPT (D-glufosinate) decreased with only a modest accumulation of PPO.This result indicates efficient deracemization of D / L-glufosinate to L-glufosinate by the enzyme pair RgDAAO / EcgabT. Example 6: Demonstration of enhanced DAAO enzymes Using protein mutagenesis strategies as described, enhanced DAAO enzymes and variants were identified. The enzymes were assayed according to the procedures described below. Mother solutions: The following stock solutions were prepared: a 20 mg / ml stock solution of 2,4,6-tribromo-3-hydroxybenzoic acid (TBHBA) in DMSO; and a 100 mg / ml stock solution of 4-aminoantipyrine (4-AAP) in water. The following enzyme stock solution was prepared: a 1 mg / ml stock solution of horseradish peroxide (HRP) type 6 in potassium phosphate buffer at pH 8.0. The following substrate stock solution was prepared: varying concentrations of amino acid D or DL ​​in potassium phosphate buffer at pH 8.0. Reaction mixtures: The following reaction mixtures were prepared: Mixture A is a combination of the substrate and the HRP enzyme. Solutions were prepared for each substrate concentration to be tested using reaction buffer. The solutions were twice the final substrate concentration and 0.2 mg / ml for the HRP solution. Mixture B is a mixture of dyes. To 5 ml of reaction buffer, 120 µL of TBHBA solution and 400 µL of 4-AAP solution were added. Mixture C is a mixture of enzymes. A 0.1 mg / ml solution of DAAO was prepared in reaction buffer. The final reaction concentration was 25 pg / ml. / υΊ Protocol: A spectrophotometer was used at a wavelength of 510 nm, which corresponds to the maximum absorbance for 4-AAP / TBHBA and is the point at which the extinction coefficient is 29400 M⁻¹ cm⁻¹. The temperature for the tests was 30°C. The reaction kinetics were obtained by measuring every minute for 15 minutes. Between measurements, 20 seconds of orbital shaking at normal intensity were performed, followed by 10 seconds of settling time. Using a 96-cavity plate, the following mixtures (with replicates) were added in the following order using multichannel: 100 ul of mixture A, 50 ul of mixture B, and 50 ul of mixture C. Measurements were started immediately after the enzyme addition. Enzyme kinetics were measured as described, plotted on a Michaelis-Menten chart, and used to calculate Vmax and KM. For the Ac302 variant (54V, 58Q, 213S), Vmax was 4.2 µmol / min * mg. This analysis was completed for a number of DAAO enzyme variants like the above, except that Mixture C was 0.2 mg / ml of DAAO solution and this final reaction concentration of DAAO was 50 pg / ml. As shown in Table 1 below, the variant mutant DAAO enzymes exhibited a range of activities: ivIA / a / ¿u¿ i / un Table 1: Variant Mutations Vmax Ac302) (% of Ac263 54T, 56M, 58K, 213S 33 AC302 54V, 580,2138 100 Ac305 54C, 58H, 213S 88 Ac309 54T, 58T, 213S 71 Ac312 54T,58G, 213S 74 Ac314 54T, 58Q,213S 99 Ac316 54T, 58S, 213S 75 Ac318 54T, 58A, 213S 71 Ac319 54L, 58R, 213S 64 Ac320 54V, 58R, 213S 76 Ac322 54V, 58N,213S 79 Example 7: Deracemization of racemic D / L-glufosinate to a reaction size of 5 I. The scale of deracemization is increased using approaches familiar to those skilled in the art. The reagents and their relative ratios are substantially similar to Example 5, but the quantities are significantly larger. Instead of tubes on stirrers, the reactions are carried out in jacketed reactors with stirring, including, optionally, air or oxygen bubbling from the broth or headspace. These reactors vary in size from less than 10 mL of reaction to tens or hundreds of thousands of liters. Stirring speeds are chosen to increase mixing and reaction rate while minimizing energy consumption and shear. In one example, the reaction was carried out on a 5 L scale. The system (5 L, 30 °C) was operated in 200 mM phosphate buffer at pH 8.0 in a jacketed reactor with stirring. The following reagents were added almost simultaneously with the start of the reaction: 300 mM D,L-glufosinate, 900 mM glutamate, 7.5 g AC302 DAAO, 0.2 g catalase, and 1.0 g E. coli gab T transaminase. In addition, 500 mL of isopropanol were added to control foaming. During the course of the reaction, air was introduced at 0.3 VVM (volumes of air per volume of reaction mixture per minute). HPLC analysis of the reaction showed that equilibrium was reached within 8 hours, with an enantiomeric excess of L-glufosinate over D-glufosinate of more than 99% and an L-glufosinate to PPO ratio of 90% and 10%. This result indicates efficient deracemization of D / L-glufosinate to L-glufosinate by the RgDAAO / EcgabT enzyme pair on a larger scale. Example 8: Impact of oxygen on reaction rate Although jacketed reactors with agitation or immobilized columns typically allow some oxygen transfer, the rate of oxygen uptake provided by passive aeration is insufficient for an efficient process. In one example, a reaction was carried out in the same vessel as in Example 7 under substantially identical conditions, but under a reduction (0.01 VVM), with twice the volumetric amount of AC3O2 DAAO (3 g / L vs. 1.5 g / L) and without isopropanol. In this case, the reaction took more than 60 hours to reach equilibrium, demonstrating the critical importance of aeration for an efficient reaction. Example 9: Co-lnmobilization of DAAO and TA The enzymes DAAO and TA were co-immobilized on controlled-porosity glass beads with EziG (EnginZyme). 100 mg of EziG type 3 beads were shaken at room temperature with 3 mL of a solution containing 16 mg of purified DAAO AC330 and 1.6 mg of purified gabT in 50 mM potassium phosphate buffer, pH 7.5, 0.5 M NaCl, and 20 mM imidazole in a 50 mL Falcon tube. After 30 minutes, the beads were centrifuged, the immobilization solution was removed, and the beads were washed three times with 10 mL of 100 mM potassium phosphate buffer, pH 7.5. The reaction was initiated by adding all other components to the washed beads. The reaction mixture contained 300 mM D / L-glufosinate, 900 mM L-glutamic acid, 50 pg of catalase, and 198 mM potassium phosphate in 2.5 mL. The reaction was incubated at 30°C with shaking (250 rpm) in a 50 mL tube covered with parafilm with through-holes for gas exchange. After 1 hour, D-glufosinate depletion and L-glufosinate formation were determined by HPLC, and these rates were calculated. After 6 hours, the beads were centrifuged, the reaction mixture was removed, and the beads were washed 3 times with 10 mL of 100 mM potassium phosphate buffer, pH 7.5. The beads were then stored at 42°C for 18 hours before repeating the reaction, for a total of 15 times, after which the retained activity was more than 50% of the initial activity. Example 10: Effect of the buffer on the reaction When using the enzymes AC302 DAAO and E. coli gabT TA, a phosphate buffer >50 mM is required for full activity. A 100 mL reaction was incubated at 30°C with shaking (250 rpm) in a 500 mL flask covered with Parafilm. An air pump was used to bubble air through the reaction for the first 5 hours. The air pump was then removed for overnight incubation to allow the reaction to stop bubbling, and fresh Parafilm with air holes was used for gas exchange. The reaction mixture contained 300 mM D / Lglufosinate, 905 mM L-glutamic acid, 80 mg of AC302 DAAO (0.8 mg / mL), 14.5 mg of gabT (0.145 mg / mL), 2 mg of catalase, and isopropanol as an antifoaming agent (initial concentration of 10%; additional isopropanol was added at 2 h (2 mL), 3 h (1 mL), 3.5 h (1 mL), and 4 h (2 mL)). 500 µL of 1N NaOH (added before the enzymes) was used to adjust the pH to between approximately 6 and approximately 7.The pH remained at approximately 7 throughout the reaction without further adjustment. Due to the potassium phosphate in the common enzyme buffer, the final mixture was 45 mM phosphate buffer. When compared to a similar reaction with 200 mM phosphate buffer, the reaction rate was 50–60% of that of the reaction with the 200 mM buffer. When using immobilized AC302 DAAO and E. coli gabT TA enzymes, less than 1 mM phosphate buffer is sufficient for full activity. Immobilized proteins were prepared, and the reaction was run as in Example 9 for the buffered reaction. Additionally, immobilized proteins were prepared, and reactions were run as in Example 9 for the pH 7 reaction, except that sodium hydroxide was used to adjust the reaction pH to 7, along with phosphate buffer (the residual phosphate buffer from the enzyme storage buffer is less than 1 mM). This work demonstrated that the initial reaction rates for both DAAO and the combined DAAO and gabT reactions are very similar with and without the addition of phosphate buffer when using immobilized enzymes. Example 11: Isopropylamine as an amine donor Isopropylamine can be used as an amine donor for the conversion of PPO to L-glufosinate with the use of an appropriate TA. PPO was converted to L-glufosinate in a reaction with the following components: • 0.25 mg / ml TA encoded by Sec. ID #1 • 25 mM PPO • 0.2 mM pyridoxal phosphate • 250 mM isopropylamine (pH at 8 with H3PO4), • 100 mM Kphos buffer pH 8.0 The reaction was incubated at 25–30°C for 30 hours with gentle shaking (250 rpm). At 0 hours, the amount of L-glufosinate measured by HPLC was 0 mM, at 20 hours it was 14 mM, and at 30 hours it was 18 mM. This demonstrates that the enzyme encoded by Id. of Sec. No. 1 can convert PPO to L-glufosinate. Example 12: Lysine as an amine donor Lysine can be used as an amine donor for the conversion of PPO to L-glufosinate with the use of an appropriate TA. PPO was converted to L-glufosinate in a reaction with the following components: 0.4 mg / ml of gabT (purified as in Example 3) • PPO 25 mM (pH adjusted to 8 with NaOH) ινΐΛ / a / zuz i / un ózóz Pyridoxal phosphate 0.2 mM • L-lysine dihydrochloride 75 mM (pH adjusted to 8 with NaOH) • 100 mM Kphos buffer pH 8.0 The reaction was incubated at 30°C for 20 hours with shaking (250 rpm). L-glufosinate was formed at a rate of 0.4 mM / h for 20 hours. This demonstrates that L-lysine can be used to convert PPO to L-glufosinate. Example 13: Purification and isolation of L-glufosinate Several batches were prepared following the procedure described in Example 9, but on a larger scale. After removing the beads, each batch was heated to 90°C for at least 10 minutes, and after cooling to 20–25°C, it was filtered to remove a small amount of solids. 37% HCl was added dropwise to each individual batch to precipitate the glutamic acid. The amount of 37% HCl added was approximately 10% of the batch volume. The resulting white solid was removed by filtration. The batches were combined and concentrated under vacuum to an oil containing approximately 153 grams of L-glufosinate. The oil was diluted with five volumes of water and 37% HCI was added to adjust the solution to pH 1. The solution was sequentially treated with two portions each of approximately 3.0 kg of previously washed DOWEX 50WX8 cation exchange resin.In each treatment, the solution was allowed to mix with the resin for 30 minutes, after which the resin was isolated on a filter. Both resin portions were combined and washed first with water and then eluted with 4M NH4OH. The eluent was concentrated under vacuum to an oil; PPO and 2-oxoglutarate were not present in the oil. Approximately 100 grams of the oil were diluted with water, and aqueous ammonium hydroxide was added until the pH was approximately 9. 1.0 kg of pre-washed DOWEX Monosphere anion exchange resin (hydroxide form) was added to the batch, and the mixture was stirred for approximately 40 minutes. An equal amount of pre-washed DOWEX Monosphere resin was loaded onto a glass column. The DOWEX resin suspension in water was added to the column over the pre-washed resin.800 mL of water were charged into the column, followed by 0.1 N acetic acid, which was allowed to flow through the column until all the glutamic acid had eluted, as determined by HPLC. 4 N acetic acid was then added to the column until all the L-glufosinate had eluted, as determined by HPLC. The L-glufosinate solution was concentrated under vacuum. The resulting oil was diluted with water and concentrated under vacuum to a minimum volume twice. Methanol was added until a clear solution was obtained, and an equal volume of heptane was added. The mixture was concentrated under vacuum to a minimum volume, and the procedure was repeated. The remaining 168 grams of oil recovered from the cation exchange treatment were treated similarly to yield a final total of 108 grams of crude L-glufosinate. The ratio of L-glufosinate to glutamic acid was over 99:1 as determined by NMR.The resulting solid was mixed with aqueous ammonium hydroxide and concentrated to dryness to yield 111 grams of L-glufosinate ammonium. Neither methanol nor acetic acid were detected by NMR analysis of the product. It should be understood that the terminology used is intended to describe certain modalities only and is not intended to be limiting. The scope of the invention is limited only by the appended claims. Unless otherwise indicated, all scientific and technical terms used have the same meaning as they commonly have for a person skilled in the art to which this invention pertains. When a range of values ​​is provided, it is understood that every intermediate value, up to one-tenth of the lower limit unless the context clearly indicates otherwise, between the lower and upper limits of that range and any other stated or intermediate limits, is covered by the invention. The lower and upper limits of these smaller intervals may independently be included within the smaller intervals and are also included within the invention, subject to any limits specifically excluded within the stated interval.When the stated range includes one or both of the limits, the ranges that exclude either or both of those included limits are also included in the invention. Certain ranges are presented herein with numerical values ​​preceded by the term "approximately." The term "approximately" is used herein to provide literal support for the exact number it precedes, as well as for a number that is close to or approximately the number it precedes. In determining whether a number is close to or approximately a specifically stated number, the number close to or approximately an unstated number may be a number that, in the context where it is presented, provides the substantial equivalent of the specifically stated number. All publications, patents, and patent applications cited in this specification are incorporated herein by reference to the same extent as if each publication, patent, or patent application were specifically and individually incorporated by reference. Furthermore, each cited publication, patent, or patent application is incorporated herein by reference to disclose and describe the subject matter in relation to which the publications are cited. Mention of any publication is deemed to predate the filing date and should not be construed as an admission that the invention described herein is not entitled to precede such publication by virtue of prior invention. In addition, the publication dates provided may differ from the actual publication dates, which should be independently confirmed. It should be noted that claims may be drafted to exclude any optional elements. As such, this statement is intended to serve as a precedent for the use of such exclusive terminology as "only" and its variants in relation to the statement of the elements of the claim, or the use of a negative limitation. As will be evident to those skilled in the art upon reading this description, each of the individual embodiments described and illustrated herein has individual components and features that can be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the invention. Any claimed method may be carried out in the order of events cited or in any other logically possible order.Although any of the methods and materials similar or equivalent to those described in this document may also be used in the practice or testing of the invention, representative illustrative methods and materials will be set out below.

Claims

1. A method for preparing L-glufosinate, CHARACTERIZED in that it comprises: reacting D-glufosinate with a D-amino acid oxidase (DAAO) enzyme to form PRO (2-oxo-4-(hydroxy(methyl)phosphinoyl)butyric acid); and amination of the PPO to L-glufosinate by means of an L-amino acid dehydrogenase (LAAD) enzyme using ammonia, wherein at least 70% of the D-glufosinate is converted to L-glufosinate.

2. The method of claim 1, CHARACTERIZED in that the D-glufosinate is originally present in a racemic mixture of D- and L-glufosinate or salts thereof.

3. The method of claim 1, CHARACTERIZED in that the DAAO enzyme is selected from the enzyme of Rhodosporidium toruloids (UniProt P80324), Trigonopsis variabais (UniProt Q99042), Neolentinus lepideus (KZT128066.1), Trichoderma reesei (XP 006968548.1), or Trichosporon oleaginosus (KLT40252.1).

4. The method of claim 1, CHARACTERIZED in that the DAAO enzyme is a DAAO mutant.

5. The method of claim 4, CHARACTERIZED in that the DAAO mutant is a DAAO mutant based on the Rhodosporidium toruloids sequence.

6. The method of claim 4, CHARACTERIZED in that the DAAO mutant comprises one or more mutations at positions 54, 56, 58, 213 and 238, using Seq. Id. No. 2 as the reference sequence.

7. The method of claim 6, CHARACTERIZED in that the mutation at position 54 is selected from the group consisting of N54C, N54L, N54T and N54V.

8. The method of claim 6, CHARACTERIZED in that the mutation at position 56 is T56M.

9. The method of claim 6, CHARACTERIZED in that the mutation at position 58 is selected from the group consisting of F58A, F58G, F58H, F58K, F58N, F58Q, F58R, F585S and F58T.

10. The method of claim 6, CHARACTERIZED in that the mutation at position 213 is M213S.

11. L-glufosinate obtained by a method of claim 1.