Synthesis and fungicidal activity of tryptophan analogues – the unexpected calycanthaceous alkaloid derivatives

Abstract

A series of 21 N-protected tryptophan derivatives were synthesised from tryptophan in good yields. Their structures were characterised by IR, ¹H NMR, ¹³C NMR, DEPT (90° and 135°) and MS analysis. The synthesised compounds were evaluated against a wide variety of plant pathogen fungi. Compounds a19 and a21 displayed activity against Fusarium oxysporum (F. oxysporum), and compound a21 showed high activity against F. oxysporum and Eggplant Verticillium, with EC₅₀ values of 58.27 and 77.39 μg mL^-1, respectively. Considering that the bioassay of the title compounds was evaluated, effects of the chain alkyl substituents may contribute to the significant variations in fungicidal potency. Their structure-antifungal activity relationships were also discussed. These results will pave the way for further design, structural modification and development of calycanthaceous alkaloids as antimicrobial agents.