A value-added use of volatile turpentine: antifungal activity and QSAR study of β-pinene derivatives against three agricultural fungi

Abstract

In consideration of turpentine and its analogues possessing some agricultural biological activity, persistent efforts to take advantage of renewable, abundant natural resources have been made. Three series of derivatives from β-pinene were synthesized and their fungicidal activities against Rhizoctonia solani, Fusarium graminearum, and Botrytis cinerea were investigated. Most of the synthesized compounds exhibited moderate to significant fungicidal activity. Among them, the acylthiourea derivatives from β-pinene showed more promising results than the other compounds. It was worth noting that compounds 7b and 7d displayed excellent fungicidal activity against Rhizoctonia solani, with IC₅₀ values of 2.439 and 1.857 μg mL⁻¹, which was close to or even better than the control triadimenol (1.945 μg mL⁻¹, a commercial fungicide). The structure–activity relationship (SAR) analysis indicated that the compounds with more net positive charge possessed better fungicidal activity. The quantitative structure–activity relationship (QSAR) model (R² = 0.9879, F = 348.41, S² = 0.0047) was obtained through the best multi-linear regression. The built model revealed a strong correlation of fungicidal activity against Rhizoctonia solani with the molecular features of the title compounds. Additionally, the SAR and QSAR studies showed that the introduction of an electron-withdrawing group, which can increase the positive charge, was favorable towards the fungicidal activity. These encouraging results may provide an alternative, promising use of β-pinene through the design and exploration of eco-friendly fungicides with low toxicity and high efficiency.