Preparation of cyclohexene isotopologues and stereoisotopomers from benzene

Abstract

The hydrogen isotopes deuterium (D) and tritium (T) have become essential tools in chemistry, biology and medicine1. Beyond their widespread use in spectroscopy, mass spectrometry and mechanistic and pharmacokinetic studies, there has been considerable interest in incorporating deuterium into drug molecules1. Deutetrabenazine, a deuterated drug that is promising for the treatment of Huntington’s disease2, was recently approved by the United States’ Food and Drug Administration. The deuterium kinetic isotope effect, which compares the rate of a chemical reaction for a compound with that for its deuterated counterpart, can be substantial1,3,4. The strategic replacement of hydrogen with deuterium can affect both the rate of metabolism and the distribution of metabolites for a compound5, improving the efficacy and safety of a drug. The pharmacokinetics of a deuterated compound depends on the location(s) of deuterium. Although methods are available for deuterium incorporation at both early and late stages of the synthesis of a drug6,7, these processes are often unselective and the stereoisotopic purity can be difficult to measure7,8. Here we describe the preparation of stereoselectively deuterated building blocks for pharmaceutical research. As a proof of concept, we demonstrate a four-step conversion of benzene to cyclohexene with varying degrees of deuterium incorporation, via binding to a tungsten complex. Using different combinations of deuterated and proteated acid and hydride reagents, the deuterated positions on the cyclohexene ring can be controlled precisely. In total, 52 unique stereoisotopomers of cyclohexene are available, in the form of ten different isotopologues. This concept can be extended to prepare discrete stereoisotopomers of functionalized cyclohexenes. Such systematic methods for the preparation of pharmacologically active compounds as discrete stereoisotopomers could improve the pharmacological and toxicological properties of drugs and provide mechanistic information related to their distribution and metabolism in the body.

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Fig. 1: Methods for the deuteration of benzene.
Fig. 2: Formation of tungsten-bound cyclohexene from benzene.
Fig. 3: Synthesis of isotopologues and stereoisotopomers of the cyclohexene complex 7.
Fig. 4: Examples of functionalized cyclohexene isotopomer complexes.

Data availability

All data are available in the main text and Supplementary Information, including NMR spectra, experimental details, crystallographic information, DFT calculations, rotational spectroscopy and HRMS data. Supplementary crystallographic data for this paper (4, 7, 9 (X-ray) and 45 (neutron)) can be obtained from the Cambridge Crystallographic Data Centre at www.ccdc.cam.ac.uk/structures (CCDC 1885723-1885725 and 1972890).

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Acknowledgements

We acknowledge the assistance of E. Ashcraft in collecting HRMS data. The work was funded by the National Institutes of Health (1R01GM132205-01) and the University of Virginia. The single-crystal neutron diffraction experiment performed on TOPAZ using resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory, under contract number DE-AC05-00OR22725 with UT-Battelle, LLC.

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W.D.H., J.A.S. and K.B.W. conceived the project. K.D.W., W.D.H. and J.A.S. designed the experiments. J.A.S. and K.S.W. prepared the samples and collected NMR and HRMS data. D.A.D. carried out X-ray molecular structure determinations. B.H.P., P.J.K. and R.E.S. conceived and ran the rotational spectroscopy experiments. E.K.P. and K.S.W. carried out DFT calculations. J.A.S. and W.D.H. wrote the manuscript. X.W. collected and processed neutron diffraction data.

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Correspondence to W. Dean Harman.

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This file contains Supplementary Materials A-N, which includes Supplementary Figures S1-S15 and Supplementary Tables S1-S4.

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Smith, J.A., Wilson, K.B., Sonstrom, R.E. et al. Preparation of cyclohexene isotopologues and stereoisotopomers from benzene. Nature 581, 288–293 (2020). https://doi.org/10.1038/s41586-020-2268-y

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