Coupled methyl group epimerization and reduction by polyketide synthase ketoreductase domains.
Ashish Garg1, Chaitan Khosla, David E Cane
1Department of Chemistry, Brown University , Providence, Rhode Island 02912-9108, United States.
Abstract:
Incubation of [2-(2)H]-(2S,3R)-2-methyl-3-hydroxypentanoyl-SACP ([2-(2)H]-1a) with the epimerizing ketoreductase domain EryKR1 in the presence of a catalytic amount NADP(+) (0.05 equiv) resulted in time- and cofactor-dependent washout of deuterium from 1a, as a result of equilibrium isotope exchange of transiently generated [2-(2)H]-2-methyl-3-ketopentanoyl-ACP. Incubations of [2-(2)H]-(2S,3S)-2-methyl-3-hydroxy-pentanoyl-SACP with RifKR7 and with NysKR1 also resulted in time-dependent loss of deuterium. By contrast, incubations of [2-(2)H]-(2R,3S)-2-methyl-3-hydroxypentanoyl-SACP and [2-(2)H]-(2R,3R)-2-methyl-3-hydroxypentanoyl-SACP with the non-epimerizing ketoreductase domains EryKR6 and TylKR1, respectively, did not result in any significant washout of deuterium. The isotope exchange assay directly establishes that specific polyketide synthase ketoreductase domains also have an intrinsic epimerase activity, thus enabling mechanistic analysis of a key determinant of polyketide stereocomplexity.
Related Concept Videos
α-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview
Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview
Protecting Groups for Aldehydes and Ketones: Introduction
Aldehydes and Ketones to Alkanes: Wolff–Kishner Reduction
Phase I Reactions: Reductive Reactions


