Direct deuteration of hinokitiol and its mechanistic study.

Hinokitiol has a broad antibacterial activity against bacteria and fungi. While its biosynthetic pathway has been intensively studied, its dynamics in natural environments, such as biodegradation pathway, remain unclear. In this study, the authors report a direct deuterium labeling of hinokitiol as a traceable molecular probe to serve those studies. Hinokitiol was subjected to the H2-Pd/C-D2O conditions and deuterated hinokitiol was obtained with excellent deuteration efficiencies and in moderate yield. The 1H and 2H NMR spectra indicated that all ring- and aliphatic hydrogens except that on C-6 were substituted by deuterium. According to the substrate scope and computational chemistry, deuteration on tropolone ring was suggested to proceed via D+-mediated process, and which was supported by the results of the experiment with trifluoroacetic acid and Pd(TPP)4. On the other hand, the deuteration on aliphatic group was predicted to be catalyzed by Pd(II) species.