title: Experimental and computational investigation of the uncatalyzed rearrangement and elimination reactions of isochorismate.
abstract: The versatile biosynthetic intermediate isochorismate decomposes in aqueous buffer by two competitive pathways, one leading to isoprephenate by a facile Claisen rearrangement and the other to salicylate via elimination of the enolpyruvyl side chain. Computation suggests that both processes are concerted but asynchronous pericyclic reactions, with considerable C-O cleavage in the transition state but relatively little C-C bond formation (rearrangement) or hydrogen atom transfer to the enolpyruvyl side chain (elimination). Kinetic experiments show that rearrangement is roughly 8-times more favorable than elimination. Moreover, transfer of the C2 hydrogen atom to C9 was verified by monitoring the decomposition of [2-(2)H]isochorismate, which was prepared chemoenzymatically from labeled shikimate, by (2)H NMR spectroscopy and observing the appearance of [3-(2)H]pyruvate. Finally, the isotope effects obtained with the C2 deuterated substrate are in good agreement with calculations assuming pericyclic reaction mechanisms. These results provide a benchmark for mechanistic investigations of isochorismate mutase and isochorismate pyruvate lyase, the enzymes that respectively catalyze the rearrangement and elimination reactions in plants and bacteria.
authors.affiliation: Laboratory of Organic Chemistry, ETH Zürich, CH-8093 Zürich, Switzerland.
authors.forename: Michael S
authors.initials: MS
authors.lastname: DeClue
authors.forename: Kim K
authors.initials: KK
authors.lastname: Baldridge
authors.forename: Peter
authors.initials: P
authors.lastname: Kast
authors.forename: Donald
authors.initials: D
authors.lastname: Hilvert
mesh_terms: D002826:Chorismate Mutase / Q000737:chemistry / Q000378:metabolism; D002827:Chorismic Acid / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D053138:Cyclohexenes; D003903:Deuterium / Q000737:chemistry; D006358:Hot Temperature; D007553:Isotope Labeling; D007700:Kinetics; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D007652:Oxo-Acid-Lyases / Q000737:chemistry / Q000378:metabolism
chemical_list: D053138:Cyclohexenes; C052985:isochorismic acid; D003903:Deuterium; D007652:Oxo-Acid-Lyases; C075960:chorismate pyruvate lyase; D002826:Chorismate Mutase; D002827:Chorismic Acid