First, we revisited the reported NMR data of bradyoxetin, a putative cell density factor of Bradyrhizobium japonicum, and found some inconsistencies in the proposed structure. To elucidate the correct structure, we synthesized model oxetane compounds and confirmed that the NMR data of the synthetic compounds did not match those of the reported bradyoxetin. After reinterpreting the reported NMR data, we concluded that bradyoxetin must be chloramphenicol. Next, some derivatives of 2-hydroxy-4-((methylamino)(phenyl)methyl)cyclopentanone (HMCP), which is a putative quorum-sensing molecule of Ralstonia solanacearum, were synthesized. The NMR spectra of the synthesized compounds were completely different from those of the reported natural products. Based on theoretical studies, including the estimation of 1 H and 13 C NMR chemical shifts using density functional theory calculations, we confirmed the correctness of the structure of the synthesized compound. These results strongly suggest that the proposed structure of HMCP could be incorrect.

The enantioselective synthesis of zealexin A1, a sesquiterpene phytoalexin isolated from maize Zea mays is described for the first time. Our methodology for the total synthesis of zealexin A1 involved the stereoselective construction of the stereogenic center via enzymatic resolution followed by Johnson–Claisen rearrangement. The absolute configuration of the natural product was determined through gas chromatography analyses for the methyl esters for both synthetic and natural zealexin A1.