L-glufosinate ammonium, also known as left-turning ammonium glufosinate (L-glufosinate), was first discovered in the fermentation product of the soil actinomycete Streptomyces hygroscopicus var. jinggangensis. In plants, it is metabolized into L-glufosinate and two amino acid molecules. It is a natural herbicide containing the C-P-C structure, and its significance in terms of environmental friendliness and safety far surpasses chemical synthetic herbicides such as paraquat, glyphosate, and regular glufosinate-ammonium.

L-glufosinate belongs to the phosphinic acid herbicide class, and its mode of action is similar to that of glufosinate-ammonium. Ammonium glufosinate is a racemic mixture of D- and L-glufosinate, with only L-glufosinate exhibiting herbicidal activity. It acts on glutamine synthetase in plant cells, inhibiting L-glutamine synthesis, leading to the accumulation of cytotoxic ammonium ions, disruption of ammonium metabolism, amino acid deficiency, chlorophyll degradation, and suppression of photosynthesis, ultimately killing weeds completely.


 

Synthesis Routes:
The primary synthesis methods for L-glufosinate ammonium include asymmetric synthesis, racemate separation, and biocatalysis. The industrial-scale production methods mainly involve asymmetric synthesis and racemate separation.

1) Asymmetric synthesis starts with chiral raw materials to synthesize optically pure L-glufosinate. In 2007, Meiji Seika Co. reacted B-aminophosphonate ester aldehyde with primary amine to produce an imine compound. Using the Jacobsen catalyst, the imine undergoes asymmetric Strecker reaction with trimethylsilyl cyanide. Hydrolysis of the resulting compound yields L-glufosinate. This process is complex, involves expensive chiral separation reagents, and has a theoretical yield of only 50% with low single-step separation rates.

2) Racemate separation involves the chiral separation of racemic DL-glufosinate or its derivatives to isolate D- and L-isomers, resulting in optically pure L-glufosinate. During the separation process, N-decyl-glufosinate hydrolyzes to produce L-glufosinate, catalyzed by Pseudomonas sp. zjut126. This method has multiple steps, low yields, and expensive chiral starting materials, making it less suitable for large-scale preparation.

3) Biocatalysis: Starting with DL-glufosinate, R-selective ω-transaminase converts D-glufosinate into 2-carbonyl-4-[hydroxy(methyl)phosphinoyl]butyric acid, while L-glufosinate remains unreacted. Glutamate dehydrogenase then uses 2-carbonyl-4-[hydroxy(methyl)phosphinoyl]butyric acid as a starting material to asymmetrically synthesize L-glufosinate, producing optically pure L-glufosinate.

Environmental Acute Toxicity:

A 10% L-glufosinate ammonium soluble solution has an oral LD50 of 282 mg a.i./kg b.w. for quail, categorizing it as "toxic."

For silkworms, a 10% L-glufosinate ammonium soluble solution has an LC50 of 186 mg a.i./L, also classified as "toxic."

For earthworms, the LC50 for a 10% L-glufosinate ammonium soluble solution is >100 mg a.i./kg dry soil, categorized as "low toxicity."

The oral LD50 for bees is 19.5 μg a.i./bee, while the contact LD50 is 40.0 μg a.i./bee, both considered "low toxicity" for bees in 48-hour acute oral and contact tests.

For ladybugs, the LC50 (pre-adults) is 167 g a.i./ha, with a maximum recommended field dose of 600 g a.i./ha. The safety factor for ladybugs is 0.278, resulting in a
"high-risk" classification for ladybugs in a 24-hour test.
 

Uses of L-Glufosinate Ammonium:

1. Weed Control in Agriculture: L-Glufosinate ammonium is widely used in agriculture to control weeds in various crops, including corn, soybeans, cotton, and more. Its non-selective nature makes it effective against both grassy and broadleaf weeds, providing farmers with a versatile tool for weed management.

2. Non-GMO Crop Desiccation: In addition to weed control, Glufosinate is used to desiccate non-genetically modified (non-GMO) crops like potatoes, wheat, and barley. By applying this herbicide before harvest, farmers can promote even ripening and facilitate a more efficient harvesting process.

3. Forest and Non-Agricultural Use: Glufosinate ammonium is not limited to agricultural applications. It is also employed in forestry to manage unwanted vegetation in reforestation efforts. Furthermore, it finds use in non-agricultural settings such as railway tracks and industrial sites to control vegetation that can impede operations.