Enzymatic construction of highly strained carbocycles
Small carbocycles are structurally rigid and possess high intrinsic energy due to their ring strain. These features lead to broad applications but also create challenges for their construction. We report the engineering of hemeproteins that catalyze the formation of chiral bicyclobutanes, one of the most strained four-membered systems, via successive carbene addition to unsaturated carbon-carbon bonds. Enzymes that produce cyclopropenes, putative intermediates to the bicyclobutanes, were also identified. These genetically encoded proteins are readily optimized by directed evolution, function in Escherichia coli, and act on structurally diverse substrates with high efficiency and selectivity, providing an effective route to many chiral strained structures. This biotransformation is easily performed at preparative scale, and the resulting strained carbocycles can be derivatized, opening myriad potential applications.
© 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. This is an article distributed under the terms of the Science Journals Default License. Received for publication November 8, 2017. Accepted for publication February 6, 2018. We thank D. K. Romney, S. C. Hammer, and S.-Q. Zhang for helpful discussions and comments on the manuscript; C. K. Pier, O. F. Brandenberg, and A. M. Knight for sharing hemeprotein variants; K. Ding (D. J. Anderson Lab, Caltech) and J. Li (R. H. Grubbs Lab, Caltech) for generous donation of materials and reagents; S. C. Virgil and the Caltech Center for Catalysis and Chemical Synthesis, N. Torian and the Caltech Mass Spectrometry Laboratory, and M. K. Takase, L. M. Henling, and the Caltech X-ray Crystallography Facility for analytical support; and B. M. Stoltz for use of polarimeter and chiral gas chromatography equipment. Funding: Supported by NSF Division of Molecular and Cellular Biosciences grant MCB-1513007; Ruth L. Kirschstein NIH Postdoctoral Fellowship F32GM125231 (X.H.); and NSF Graduate Research Fellowship grant DGE-1144469 and the Donna and Benjamin M. Rosen Bioengineering Center (R.K.Z.). R.K.Z. is a trainee in the Caltech Biotechnology Leadership Program. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funding organizations. Author contributions: conceptualization, K.C.; methodology, K.C.; validation, K.C. and X.H.; formal analysis, K.C., X.H., S.B.J.K., and R.K.Z.; writing (original draft), K.C. and F.H.A.; writing (review and editing), X.H., S.B.J.K., and R.K.Z.; funding acquisition, F.H.A.; supervision, F.H.A. Competing interests: K.C., X.H., and S.B.J.K. are inventors on patent application (CIT-7744-P) submitted by California Institute of Technology that covers biocatalytic synthesis of strained carbocycles. Data and materials availability: All data are available in the main text or the supplementary materials. Plasmids encoding the enzymes reported in this study are available for research purposes from F.H.A. under a material transfer agreement with the California Institute of Technology. Crystallographic coordinates and structure factors have been deposited with the Cambridge Crystallographic Data Centre (www.ccdc.cam.ac.uk) under reference number 1815089 for compound 4d.
Supplemental Material - aar4239_Chen_SM.pdf
Accepted Version - nihms-983961.pdf