Antibacterial diterpenes and their fatty acid conjugates from rice leaves.

ABSTRACT

Six structurally oryzalide-related compounds, oryzadione (1), 2, 3, 4, 5 and 6, were isolated from a neutral fraction of the extract of healthy leaves using a bacterial leaf blight-resistant cultivar of a rice plant, "Norin-27", as a group of antimicrobial substances. Their structures were determined by spectroscopic studies to be kaurane analogues and kaurane analogues conjugated with fatty acids, i.e., 1 ent-15,16-epoxy-kauran-2,3-dione (enol form ent-15,16-epoxy-2-hydroxy-kauran-1-en-3-one), 2 ent-15,16-epoxy-3beta-hydroxy-kauran-2-one, 3 ent-15,16-epoxy-3-oxa-kauran-2-one, 4 ent-15,16-epoxy-3beta-myristoyloxy-kauran-2-one, 5 ent-15,16-epoxy-3alpha-palmitoyloxy-kauran-2-one, and 6 ent-15,16-epoxy-2beta-palmitoyloxy-kauran-2-one.