24th International Conference on Phosphorus Chemistry (ICPC24)

40 / 2023-08-11 21:31:42

Synthesis and herbicidal activity of Dimethyl-α-(substituted phenoxyacetoxy) alkylphosphine oxides

dimethyl-α-(substituted phenoxyacetoxy) alkylphosphine oxides,herbicidal activity

Phosphorus Material Chemistry and Applied Science > 2) Phosphorus chemistry in agriculture and food science

The herbicides glyphosate and glufosinate-ammonium, which possess phosphonate and hypophosphite structures, are extensively utilized globally, highlighting the significance of compounds containing "P-C" bonds in agricultural weed management. In our previous work, a series of alkylphosphonates with general structure I (Figure 1) were designed and synthesized. Among these alkylphosphonates, compound I-1 (clayfos) has been identified as the most efficacious against broadleaf weeds^[1]. To discover novel compounds with enhanced herbicidal activity or distinctive characteristics compared to clayfos, I-1 was selected as the lead structure for further structural optimization.

Methyl groups have a significant impact on the regulation of biological activity in small molecules, leading to notable alterations in the pharmacological properties of compounds, commonly referred to as the "Magic Methyl" effect^[2]. Therefore, a novel series of dimethylphosphine oxides II was designed by replacing the two methoxy groups linked to phosphorus of the lead compound I-1 with methyl groups. The synthesis of the compounds II involved the condensation of substituted phenoxyacetic acid with α-hydroxyphosphine oxide in the presence of CDI. Compound II was obtained with a high yield following post-treatment involving alkali washing, acid washing, and drying. This method is distinguished by its short reaction time, high atom utilization, and straightforward operation.

Their herbicidal activities, both pre-emergence and post-emergence, were assessed against a total of ten weed species, including three grass weeds and seven broadleaf weeds, within controlled greenhouse conditions. Similar to clacyfos, nearly all compounds II exhibited excellent post-emergence herbicidal efficacy against broadleaf weeds at a dosage of 150 g ai/ha, resulting in inhibition rates ranging from 80-100%. Remarkably, unlike clayfos, certain compounds also demonstrated remarkable pre-emergence herbicidal activity against the tested weeds. Notably, Compound II-23 displayed exceptional inhibitory activity against both grass and broadleaf weeds in both pre- and post-emergence treatments. Consequently, this novel class of dimethylphosphine oxides holds promise for the development of innovative herbicides and warrants further investigation.



Fig. 1 Design of the title compounds II.