Synthesis and Antifungal Activity of Novel Furan-2,4-dione Derivatives Containing Substituted Phenylhydrazine Moiety

Recent advances in the synthesis of naturally occurring tetronic acids

During the last decades the interest towards natural products containing the tetronic acid moiety augmented significantly, due to their challenging structures and to the wide range of biological activities they display. This increasing enthusiasm has led to noteworthy advances in the development of innovative methodologies for the construction of the butenolide nucleus. This review provides an overview of the progress in the synthesis of tetronic acid as a structural key motif of natural compounds, covering the last 15 years. Herein, the most representative synthetic pathways towards structurally diverse natural tetronic acids are grouped according to the strategy followed. The first part describes the functionalization of a preformed tetronic acid core by intermolecular reactions (cross-coupling reactions, nucleophilic substitution, multicomponent reactions) whereas the second part deals with intramolecular approaches (Dieckmann, cycloaddition or ring expansion reactions) to construct the heterocyclic core. This rational subcategorization allowed us to make some considerations about the best approaches for the synthesis of specific substrates, including modern intriguing methodologies such as microwave irradiation, solid phase anchoring, bio-transformations and continuous flow processes.

QSAR studies of phenylhydrazine-substituted tetronic acid derivatives based on the 1 H NMR and 13 C NMR chemical shifts

The quantitative structure-activity relationship models of 40 phenylhydrazine-substituted tetronic acid derivatives were established between the ¹ H nuclear magnetic resonance (NMR) and ¹³ C NMR chemical shifts and the antifungal activity against Fusarium graminearum, Botrytis cinerea, Rhizoctonia cerealis, and Colletotrichum capsici. The models were validated by R, R² , R_A² , variance inflation factor, F, and P values testing and residual analysis. It was concluded from the models that the ¹³ C NMR chemical shifts of C8, C10, C7, and the ¹ H NMR chemical shifts of Ha contributed positively to the activity against Fusarium graminearum, Botrytis cinerea, Colletotrichum capsici, and Rhizoctonia cerealis, respectively. The models indicated that decreasing the election cloud density of specific nucleuses in compounds, for example, by the substituting of electron withdrawing groups, would improve the antifungal activity. These models demonstrated the practical application meaning of chemical shifts in the quantitative structure-activity relationship study. Furthermore, a practical guide was provided for further structural optimization of the antifungal phenylhydrazine-substituted tetronic acid derivatives based on the ¹ H NMR and ¹³ C NMR chemical shifts.