Evaluation of the efficiency of Pd/H2-catalyzed benzylic H/D exchange of dehydroabietinal with D2O and synthesis of a tritium-labeled analogue

Dehydroabietinal (DA) has been identified as an important signaling molecule in systemic acquired resistance in plants. Deuterium and tritium‐labeled DA were synthesized to confirm its role in signaling and to further elucidate the mechanism by which DA induces systemic acquired resistance. Pd/H2‐catalyzed exchange of benzylic hydrogen atoms of DA with 2H‐H2O or 3H‐H2O was conducted with >97% label incorporation for 2H‐DA and a specific activity of 12.6 mCi/mmol for 3H‐DA synthesized from 90 mCi/mmol 3H‐H2O. The extent of deuterium labeling at each benzylic position was determined via an inverse‐gated 13C NMR experiment. C7 and C15 were 87% and 81% labeled, respectively. Isotope‐induced chemical shift changes at C6 were used to approximate the amount of singly (66%) and doubly (17%) labeled 2H‐DA at C7. Results also indicated that two of the three benzylic protons in DA underwent facile exchange. Exchange at the remaining position was likely hampered by steric interactions of nearby methyl groups at the surface of the Pd catalyst. Pd/H2‐catalyzed exchange of benzylic hydrogen atoms of dehydroabietinal (DA) with 2H‐H2O or 3H‐H2O was conducted with >97% label incorporation for 2H‐DA and a specific activity of 12.6 mCi/mmol for 3H‐DA. The extent of deuterium labeling at each benzylic position was determined via an inverse‐gated 13C NMR experiment. C7 and C15 were 87% and 81% labeled, respectively. Isotope‐induced chemical shift changes at C6 were used to approximate the amount of singly (66%) and doubly (17%) labeled 2H‐DA at C7.