Chemoenzymatic Synthesis of (4 R ,7 R )‐Zingiberene Enables Construction of nor ‐Sesquiterpene Semiochemical Analogs

The wild tomato sesquiterpene (4 R ,7 R )‐zingiberene ( 6a ) acts as a potent repellent of the economically important agricultural pest, the silverleaf whitefly ( Bemisia tabaci ). While its biosynthesis is catalyzed by 7‐ epi ‐zingiberene synthase from the noncanonical terpene precursor (2 Z ,6 Z )‐farnesyl pyrophosphate ( 5a ), the precise enzymatic mechanism has remained undetermined. Using deuterated substrates generated chemoenzymatically, the 1,6‐cyclization mechanism was established to proceed via a 1,3‐hydride shift from the C1 position of the initial bisabolyl carbocationic intermediate. Product diversity was expanded by identifying two single residue switches within the G1/2 helix that govern enzyme fidelity, thereby redirecting product distributions to alternative C6‐cyclized zingiberenols as well as γ‐ and β‐curcumene. Applying this chemoenzymatic synthesis with alternative allyl alcohols plus isoprenol enabled the production and structural diversification of two novel nor ‐sesquiterpene analogs (C 14 /C 16 ), 13‐ nor ‐(4 R ,7 R )‐zingiberene ( 23 ) and 12‐ethyl‐13‐ nor ‐(4 R ,7 R )‐zingiberene ( 24 ). Notably, these syntheses were only possible because the tomato (2 Z ,6 Z )‐farnesyl pyrophosphate synthase overcomes conventional prenyltransferase substrate selectivity to catalyze chain extension via atypical secondary allyl carbocation intermediates. The catalytic promiscuity provides opportunities to engineer terpene products with diverse methyl‐branching patterns, providing the platform to investigate the molecular basis of terpene semiochemical activity needed for the development of broad‐spectrum repellents to sustainably manage insect pests in agriculture.