Synthesis of Florasulam Stable Isotopes to Enable Identification of Degradants by Mass Spectrometry for Re‐registration Studies

Florasulam is a triazolopyrimidine herbicide that controls broadleaf and grass weeds in cereal crops and turf. It acts as an acetolactase synthase (ALS) inhibitor, blocking the synthesis of essential amino acids required for plant growth. Due to its potency, florasulam is effective at very low application rates making it cost-effective with reduced environmental off-target effects. As is common practice, florasulam has been subject to periodic reviews by regulatory agencies during re-registration requirements since its introduction into the market in 1998. The goal of these reviews is to ensure that the herbicide carries out its intended use without creating adverse side effects to humans and the environment. Since scientific methods are continually evolving and being developed, global regulatory agencies can require additional studies to address data gaps for pesticide renewals. During this re-registration process for florasulam, new environmental fate studies were conducted to meet new European Food Safety Authority (EFSA) guidelines. Consequently, florasulam-[triazole(¹³C,¹⁵N₂)] and florasulam-[phenyl(¹³C₆)] stable isotopes were synthesized to support the re-registration process.