Combinatorial Synthesis of Sulfonate Derivatives of α/β-Naphthol as Anti- Oomycete Agents

Background: Developing new, efficient, and environment-friendly small molecule fungicides is the key to effectively prevent and control plant pathogenic oomycetes. α/β-Naphthol is an important raw material for drug synthesis. Due to its special structure, α/β-naphthol and its analogs possess significant biological activity. The preparation and anti-oomycete activity of novel sulfonate derivatives based on α/β-naphthol against Phytophthora capsici have not been reported yet. Methods: Thirty-two sulfonate derivatives of α/β-naphthol (4a-p and 5a-p) were prepared. The structure of all title compounds was identified by ¹H NMR, MS, and m.p. The anti-oomycete activity of 4a-p and 5a-p against P. capsici was determined using the mycelial growth rate method. Results: With our ongoing research aimed at the discovery and development of fungicidal agents, 4a-p and 5a-p were designed and synthesized, and their anti-oomycete activity against P. capsici was evaluated in vitro. Two compounds 4a and 5a were found to have good anti-oomycete activity against P. capsici, and their corresponding EC50 values were 63.41 and 65.21 mg/L, respectively. Conclusion: It has been observed that the substituent R in these derivatives is aliphatic, which is very important for maintaining their anti-oomycete activity. The results lay a foundation for further design and development of sulfonate derivatives of α/β-naphthol as fungicidal agents. The structure- fungicidal activity relationship of α/β-naphthol derivatives is under investigation in our laboratory.