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The primary mode of action of L-glufosinate is through its inhibition of the plant enzyme glutamine synthetase, leading to the disruption of L-glutamine synthesis. This results in the accumulation of toxic ammonia, disturbance in ammonia metabolism, depletion of amino acids, breakdown of chlorophyll, and the inhibition of photosynthesis, ultimately leading to the death of targeted weeds.

With the long-term and extensive use of glyphosate, many weeds such as *Eleusine indica*, *Conyza canadensis*, and *Ipomoea triloba* have developed resistance to it. In 2015, the International Agency for Research on Cancer classified glyphosate as a probable human carcinogen. Additionally, chronic animal feeding studies found an increased incidence of liver and kidney tumors, leading some countries, such as France and Germany, to ban its use. As a result, the demand for glufosinate has surged, with sales growing from $450 million in 2012 to $1.05 billion in 2020, making it one of the fastest-growing non-selective herbicides. 

Compared to traditional glufosinate, L-glufosinate is more than twice as active. Since 2018, some Chinese companies have registered L-glufosinate as a technical product and formulation in China. The promotion of L-glufosinate has the potential to reduce the amount of herbicide applied by 50%, thereby directly reducing 1 ton of the ineffective D-glufosinate component for every 1 ton of L-glufosinate used. This reduction aligns with national policies aimed at reducing pesticide use and improving agricultural efficiency.

Synthesis Methods of L-glufosinate

There are three primary methods for synthesizing L-glufosinate: asymmetric synthesis, racemate resolution, and biocatalysis. Among these, asymmetric synthesis and racemate resolution are the main industrial-scale production methods. 

1. Asymmetric Synthesis:

   Asymmetric synthesis starts with chiral raw materials to produce optically pure L-glufosinate. In 2007, Meiji Seika developed a process where β-phosphonate aldehyde reacts with a primary amine to form an imine compound. This undergoes an asymmetric Strecker reaction, catalyzed by Jacobsen's catalyst, followed by hydrolysis to produce L-glufosinate. The enantiomeric excess (e.e.) of this process can reach up to 94%. However, the method is complex, requires expensive chiral reagents, and yields only 50%.

2. Racemate Resolution:

   This method separates D- and L-glufosinate from racemic DL-glufosinate or its derivatives. In 2018, a process was reported where *Pseudomonas sp. zjut126* catalyzed the hydrolysis of N-decanoyl-glufosinate to produce L-glufosinate with an e.e. value of over 95.2%. However, the high cost of raw materials and the multi-step nature of this process limit its industrial application.

Biocatalysis for L-glufosinate Synthesis

Biocatalysis offers several advantages, including strict stereoselectivity, mild reaction conditions, and high yields, making it a promising alternative to traditional chemical synthesis. 

1. Dehydrogenase Mutant Method:

   Professor Xue Yaping’s team from Zhejiang University of Technology discovered a mutated dehydrogenase enzyme from *Thiopseudomonas denitrificans*, which catalyzes the deracemization of DL-glufosinate to produce L-glufosinate. The D-glufosinate is converted into an intermediate compound, while L-glufosinate remains intact. This method enhances the efficiency of existing deracemization techniques. 

2. ω-Transaminase Method:

   In 2021, Professor Yang Lirong’s team from Zhejiang University developed a novel transaminase enzyme from *Bacillus sp.* YM-01. This enzyme can deracemize DL-glufosinate by converting D-glufosinate into an intermediate product, leaving L-glufosinate untouched. This process avoids the formation of toxic hydrogen peroxide and improves raw material utilization.

3. Multi-Enzyme Cascade Reaction:

   In 2022, China’s first large-scale L-glufosinate biomanufacturing process was developed through a multi-enzyme cascade system. This process was jointly developed by Yongnong Bio and East China University of Science and Technology, under the leadership of Professor Wei Dongzhi. The method uses multiple enzymes to catalyze DL-glufosinate into L-glufosinate with nearly 100% efficiency, marking a breakthrough in green pesticide manufacturing. 

Future Prospects

Since 1995, major companies like Bayer and Syngenta have promoted glufosinate-resistant and multi-resistant genetically modified crops. By 2018, more than 26 countries had commercially planted these crops, with soybeans being the largest genetically modified herbicide-resistant crop. In 2020, glufosinate demand for genetically modified crops reached 12,000 tons, accounting for 26% of total demand.

With the growing commercialization of genetically modified crops, the demand for glufosinate is expected to rise significantly. By 2025, the demand for genetically modified crops is projected to reach 34,000 tons, representing 36% of total glufosinate demand. In comparison to traditional glufosinate, L-glufosinate offers higher efficacy, requires lower dosages, and is suitable for glufosinate-resistant genetically modified crops. Given its enhanced activity and reduced environmental impact, L-glufosinate is poised to replace traditional herbicides like glyphosate and paraquat, making it an essential product in the rapidly expanding herbicide market.

In conclusion, L-glufosinate stands out as a more efficient and environmentally friendly herbicide, with broad applications in both conventional agriculture and genetically modified crop cultivation. Its potential to reduce herbicide application rates while maintaining high efficacy makes it a valuable tool in the sustainable management of agricultural weeds. As the demand for non-selective herbicides continues to grow, L-glufosinate will likely play an increasingly important role in global agriculture.