Substrate-Determined Diastereoselectivity in an Enzymatic Carboligation

Area of Science:

• Enzymology
• Organic Chemistry
• Spectroscopy

Background:

• Thiamine diphosphate-dependent enzymes are crucial for C-C bond formation, yielding chiral alcohols.
• Carbohydrate-modifying enzymes like YerE play roles in biological transformations.

Purpose of the Study:

• To investigate the stereoselectivity of carboligations catalyzed by YerE using vibrational circular dichroism (VCD) spectroscopy.
• To understand the factors governing the high stereochemical outcome of YerE-catalyzed reactions.

Main Methods:

• Utilized vibrational circular dichroism (VCD) spectroscopy to analyze stereochemical outcomes.
• Employed (R)- and (S)-3-methylcyclohexanone as non-physiological substrates for YerE.
• Determined diastereomeric ratios (dr) of the reaction products.

Main Results:

• YerE catalyzed the formation of R,R-configured tertiary alcohol from (R)-3-methylcyclohexanone with dr >99:1.
• YerE catalyzed the formation of S,S-configured tertiary alcohol from (S)-3-methylcyclohexanone with dr >99:1.
• Demonstrated that YerE can follow either an R- or S-specific pathway depending on the substrate enantiomer.

Conclusions:

• YerE exhibits exceptionally high stereoselectivity in carboligation reactions.
• The observed stereoselectivity is attributed to the substrate's conformational preference for a low-energy state.
• This study provides insights into enzyme-substrate interactions and stereochemical control in biocatalysis.