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

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).