Sulfonate Derivatives Containing a Kakuol Moiety as Potential Fungicidal Candidates: Design, Synthesis and Antifungal Activity Evaluation

As a part of our continuing exploration to discover new potential promising fungicide candidates, eighteen sulfonate derivatives (3a–3r) containing a kakuol moiety were designed and synthesized. Synthetic sulfonate derivatives were tested comprehensively for antifungal activities against four plant pathogenic fungi (Botrytis (B.) cinerea, Valsa (V.) mali, Fusarium (F.) graminearum, Sclerotinia (S.) sclerotiorum), and their structure activity relationships were summarized. Especially, derivatives 3i and 3j exhibited remarkable activity against V. mali, with the inhibition rates of 99.8 and 100%, which were slightly superior to that of carbendazim (98.9%), a reference fungicide. Moreover, derivatives 3a, 3k and 3q possess the broader antifungal spectrum against three tested plant pathogenic fungi with inhibition rates over 60%. Structure–activity relationship (SAR) analysis indicated that the introduction of 2-F or 3-F into the benzene ring would give rise to a remarkable increase of the antifungal activity against V. mali.