Antibacterial and Fungicidal Activities of Some 1,2-Bis(diphenylphosphine oxide)ethanes Against Plant Phytopathogens

The search for new classes of agrochemicals is a key task of modern agrochemistry due to the growing resistance of phytopathogens and stricter environmental requirements for pesticides. In this work, the antimicrobial activity of a number of synthesized α,β-bis(diphenylphosphinoxide)ethanes against economically significant phytopathogens was investigated. Antimicrobial activity was assessed by serial micro-dilution in broth to determine the minimum inhibitory (MIC) and fungicidal/bactericidal (MFC/MBC) concentrations. To assess the effect of solubility on biological activity, studies were conducted in two solvent systems: 5 and 50% aqueous ethanol. In a system with 5% ethanol, most compounds showed no activity against Fusarium graminearum and Alternaria alternata fungi. However, with an increase in ethanol concentration to 50%, compounds [1-(2-fluorophenyl)ethane-1,2-diyl]bis(diphenylphosphine oxide) and (1-phenylhexane-1,2-diyl)bis(diphenylphosphine oxide) demonstrated pronounced fungicidal activity against F. graminearum (MIC = 312 μg/mL). The highest antibacterial activity was recorded for (1-phenylhexane-1,2-diyl)bis(diphenylphosphine oxide), especially against the gram-negative bacterium Erwinia carotovora (MIC = 19 μg/mL), which significantly exceeds the performance of the reference drug chloramphenicol (MIC = 312 μg/mL). Thus, the compounds studied, especially bisphosphine oxide with a long alkyl substituent, have demonstrated high potential as antibacterial agents. The dependence of their fungicidal activity on solubility was revealed. [1-(2-Fluorophenyl)ethane-1,2-diyl]bis(diphenylphosphine oxide) is a promising leader structure for the further development of new plant protection products.