Structures of Oryzalic Acid B and Three Related Compounds, a Group of Novel Antibacterial Diterpenes, Isolated from Leaves of a Bacterial Leaf Blight-Resistent Cultivar of Rice

Abstract

Oryzalic acid B and its related compounds (A, B and C) were isolated from healthy flag leaves of a bacterial leaf blight-resistant cultivar of rice as a group of novel antibacterial compounds. Their structures were determined to be ent-kaurane or ent-kaurene analogues by chemical and spectroscopic studies ; i.e., oryzalic acid B, ent-15-hydroxy-2, 3-secokauren-2, 3-dioic acid (Fig.1-I) ; compound A, ent-15, 16-epoxy-2, 3-dihydroxy-kaurane (II) ; compound B, ent-2, 3, 15-trihydroxy-kaurene (III) ; compound C, ent-15, 16-epoxy-kauran-3-one (IV).