All eight possible mono-beta-D-glucosides of validoxylamine A. II. Biological activities.

The biological activities of all eight possible mono-beta-D-glucosides of validoxylamine A against Rhizoctonia solani were studied. The attachment of the D-glucosyl residue to validoxylamine A generally diminished the inhibitory activity against trehalase. The introduction of the D-glucosyl residue at the C-3 position did not cause serious loss in activity, while substitution at the C-6' position caused complete loss in trehalase inhibitory activity. Of the eight beta-D-glucosides, 4-O-beta-D-glucopyranosylvalidoxylamine A (4-O-beta-Glc-VA), 3-O-beta-Glc-VA and 5'-O-beta-Glc-VA exhibited very strong activity against R. solani in the "dendroid-test method". The antagonistic activity of sugars (1 mM) against validoxylamine A and 4-O-beta-Glc-VA was examined using the "dendroid-test method". The inhibitory effect of validoxylamine A on hyphal extension was not antagonized by any sugars tested, whereas that of 4-O-beta-Glc-VA was antagonized by beta-1,3- and beta-1,4-glucooligosaccharides. Of 2-O-, 3-O-, 4-O- and 7-O-beta-Glc-VAs, 7-O-beta-Glc-VA exhibiting the lowest activity was not antagonized by any beta-glucooligosaccharides tested. The inhibitory effect of 3-O- and 4-O-beta-Glc-VAs was antagonized by most beta-glucooligosaccharides. The uptake of 4-O-beta-Glc-VA into the mycelia was inhibited by laminaribiose and cellobiose but not by maltose.