Synthetic chemists often exploit the high enantioselectivity of lipases to prepare pure enantiomers of primary alcohols, but the molecular basis for this enantioselectivity is unknown. The crystal structures of two phosphonate transition-state analogs bound to Burkholderia cepacia lipase reveal this molecular basis for a typical primary alcohol: 2-methyl-3-phenyl-1-propanol. The enantiomeric alcohol moieties adopt surprisingly similar orientations, with only subtle differences that make it difficult to predict how to alter enantioselectivity. These structures, along with a survey of previous structures of enzyme bound enantiomers, reveal that binding of enantiomers does not involve an exchange of two substituent positions as most researchers assumed. Instead, the enantiomers adopt mirror-image packing, where three of the four substituents at the stereocenter lie in similar positions. The fourth substituent, hydrogen, points in opposite directions.
Bibliographical noteFunding Information:
We thank Dr. Alexandra Weissfloch for initial synthesis of racemic inactivators, the Natural Sciences and Engineering Research Council of Canada (NSERC) for financial support, Dr. Miroslaw Cygler for helpful discussions, and Peter Bernhardt for preparing the PyMol figures. A.M. thanks Les Fonds Québécois de la Recherche sur la Nature et les Technologies for two postgraduate fellowships and Mr. Tobie Généreux-Vincent and Dr. Mohamed Naim for insightful discussions and precious help.