Four undescribed plant growth inhibitory indole derivatives, colletotriauxins A-D (1-4), along with two known analogues indole-3-acetic acid (IAA) (5) and its amide indole-3-acetamide (6), were isolated from the phytopathogenic fungus Colletotrichum gloeosporioides NRRL 45420. Their structures were elucidated by NMR and MS analyses. 1 and 2 are rhamnosides of indole-3-ethanol (tryptophol) and its methylated derivative, respectively. In the structures of 3 and 4, the two terminal hydroxyl groups of hexitol and pentane-1,2,3,4,5-pentol are connected with indole-3-(2-methyl)-acetyl and acetyl moieties. Compounds 1-6 inhibit Lepidium sativum seedling growth. The inhibition activities of colletotriauxins for stem growth were even stronger than IAA, with compounds 3 and 4 as the most active ones. These results suggested that colletotriauxins could serve as potential candidates as herbicides.
Keywords: Colletotrichum gloeosporioides; colletotriauxins A−D; phytopathogenic fungus; plant growth inhibitors.