A Study of an 8-Aminoquinoline-Directed C(sp2)-H Arylation Reaction on the Route to Chiral Cyclobutane Keto Acids from Myrtenal

Design, synthesis, antifungal evaluation and mechanism study of myrtenal derivatives as potential laccase inhibitors

BACKGROUND

To develop novel natural product-derived fungicides, four series of myrtenal oxadiazole/thiadiazole-hydrazide/amide derivatives were designed, synthesized and evaluated for their inhibitions toward several crop pathogenic fungi/oomycetes.

RESULTS

In the in vitro antifungal experiments, some myrtenal derivatives showed good antifungal activity against Botryosphaeria dothidea, Sclerotinia sclerotiorum and Fusarium graminearum. Among them, compound 6d exhibited the best antifungal activity against B. dothidea, with EC50 value of 0.052 mg/L, which was significantly stronger than carbendazim (EC50 = 0.40 mg/L). In vivo antifungal activity assay on apple fruits and branches showed that 6d displayed significant protective and curative effects, both superior to carbendazim. In the preliminary antifungal mechanism study, 6d can damage the surface morphology of mycelia, destroy the integrity and permeability of cell membrane, increase intracellular ROS content, thereby inhibiting the growth of B. dothidea. Compound 6d also significantly inhibited laccase with IC50 value of 8.45 μM, much stronger than cysteine and PMDD-5Y. Molecular docking also confirmed the binding affinity and interaction mode of 6d with laccase.

CONCLUSION

This study presented a promising lead compound for the study on novel laccase inhibitors as fungicidal agrochemicals, which demonstrated significant anti-B. dothidea activity and laccase inhibitory activity. © 2025 Society of Chemical Industry.

Construction of carbazole-based unnatural amino acid scaffolds via Pd(II)-catalyzed C(sp3)-H functionalization

We report the synthesis of carbazole-based unnatural α-amino acid and non-α-amino acid derivatives via a Pd(II)-catalyzed bidentate directing group 8-aminoquinoline-aided β-C(sp³)-H activation/functionalization method. Various N-phthaloyl, DL-, L- and D-carboxamides derived from their corresponding α-amino acids, non-α-amino acids and aliphatic carboxamides were subjected to the β-C(sp³)-H functionalization with 3-iodocarbazoles in the presence of a Pd(II) catalyst to afford the corresponding carbazole moiety installed unnatural amino acid derivatives and aliphatic carboxamides. Carbazole motif-containing racemic (DL) and enantiopure (L and D) amino acid derivatives including phenylalanine, norvaline, leucine, norleucine and 2-aminooctanoic acid with anti-stereochemistry and various non-α-amino acid derivatives including GABA have been synthesized. Removal of the 8-aminoquinoline directing group, deprotection of the phthalimide moiety and the preparation of carbazole amino acid derivatives containing free amino- and carboxylate groups are shown. The carbazole motif is prevalent in alkaloids and biologically active molecules and functional materials. Thus, this work on the synthesis of carbazole-based unnatural amino acid derivatives would enrich the libraries of unnatural amino acid derivatives and carbazoles.