Synthesis And Biological Activities Of 1,2,3-Thiadiazole-Containing Heterocyclic Derivatives

Plant disease caused by fungi is a serious threat to agriculture and horticulture all over the world. Traditional fungicides play a critical role in the plant protection by killing or controlling target fungi directly, sometimes caused adverse effects to the environment, and often led to the fungicide resistance too. Hence, from both academic and practical points of view, it is very important to develop new environment-benign fungicides for plant protection. Plant activators (also called elicitors) themselves and their metabolites had no distinct direct fungicidal activity, they induce the immunological system of the plant to produce a broad spectrum of systemic acquired resistance by altering the physiological status of the host plants and, therefore, are among the most attractive directions in modern green pesticide development. However, only a limited number of commercial elicitors are available; the most successful elicitor commercialized is acibenzolar-S-methyl (BTH). Tiadinil (TDL) is another successful elicitor commercialized for disease control.1,2,3-Thiadiazole has been found as the crucial moiety in these elicitors. In this dissertation, series of 1,2,3-thiadiazole derivatives (62 compounds) are designed and synthesized with the active group 1,2,3-thiadiazole as a parent, namely:(1) A series of compounds in which 1,2,3-thiadiazole ring were connected with N-substituted amino-1,3,4-thiadiazole scaffolds; (2) A series of compounds in which 1,2,3-thiadiazole ring were connected with 1,2,4-triazole-3-thiodone scaffolds; (3) A series of hydrazone and hydrazide derivatives containing 1,2,3-thiadiazole moiety. Their potential systemic acquired resistance as elicitors was also evaluated. Bioassay results indicated that the N-substituted amino-1,3,4-thiadiazole derivatives had no notable in vitro fungicidal activities, while the compound A08 showed certain induction activity. 1,2,4-Triazole-3-thiodone derivatives had no obvious in vitro fungicidal activities, but several compounds showed certain induction activities for plants against Phytophthora infestans and Corynespora cassiicola; for example, compound B01 had a satisfactory induction activity against Phytophthora infestans. Among twenty evaluated 1,2,3-thiadiazole acylhydrazone derivatives, no remarkable in vitro fungicidal activities was observed; however, several compounds (e.g. D07 and D09) were found to be satisfactory in plant activating. 1,2,3-Thiadiazole hydrazides had no in vitro and in vivo fungicidal activities.