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Organometallic palladium reagents for cysteine bioconjugation


Reactions based on transition metals have found wide use in organic synthesis, in particular for the functionalization of small molecules1,2. However, there are very few reports of using transition-metal-based reactions to modify complex biomolecules3,4, which is due to the need for stringent reaction conditions (for example, aqueous media, low temperature and mild pH) and the existence of multiple reactive functional groups found in biomolecules. Here we report that palladium(ii) complexes can be used for efficient and highly selective cysteine conjugation (bioconjugation) reactions that are rapid and robust under a range of bio-compatible reaction conditions. The straightforward synthesis of the palladium reagents from diverse and easily accessible aryl halide and trifluoromethanesulfonate precursors makes the method highly practical, providing access to a large structural space for protein modification. The resulting aryl bioconjugates are stable towards acids, bases, oxidants and external thiol nucleophiles. The broad utility of the bioconjugation platform was further corroborated by the synthesis of new classes of stapled peptides and antibody–drug conjugates. These palladium complexes show potential as benchtop reagents for diverse bioconjugation applications.

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Figure 1: Organometallic palladium reagents for cysteine modification.
Figure 2: The substrate scope of cysteine arylation using organometallic palladium reagents.
Figure 3: Protein modification using the developed palladium reagents.
Figure 4: Peptide stapling and antibody drug conjugate formation using palladium-based reagents.


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Financial support for this work was provided by the National Institutes of Health (GM-58160; GM-110535; postdoctoral fellowship for A.M.S., 1F32GM101762), the MIT start-up fund (B.L.P.), a Damon Runyon Cancer Research Foundation Award (B.L.P.) and the Sontag Foundation Distinguished Scientist Award (B.L.P.). C.Z. is the recipient of the George Büchi Research Fellowship and the Koch Graduate Fellowship in Cancer Research of MIT. We thank R. J. Collier (Harvard) for contributing select laboratory equipment used in this study. We thank the Biological Instrument Facility of MIT for providing the Octet BioLayer Interferometry System (NSF S10 OD016326). We are indebted to the NERCE facility (U54A1057159) for expressing the toxin proteins. We thank M. Lu and A. Rabideu for help with cell assays. The Varian 300 spectrometer used for portions of this work was purchased with funds from NSF (grant CHE-9808061). The departmental X-ray diffraction instrumentation was purchased with the help of funding from NSF (CHE-0946721). We are grateful to P. Müller (MIT) for X-ray crystallographic analysis of 1A–OTf˙CH3CN and to A. Rancier (Merck) for the ICP-MS analysis.

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S.L.B. conceived the idea of using palladium(ii) reagents for bioconjugation; E.V.V., C.Z., A.M.S., B.L.P. and S.L.B. designed the research; E.V.V. and C.Z. conducted the majority of the experimental work; and A.M.S. conducted initial feasibility experiments. E.V.V. and C.Z. wrote the manuscript. All authors commented on the final draft of the manuscript and contributed to the analysis and interpretation of the data.

Corresponding authors

Correspondence to Bradley L. Pentelute or Stephen L. Buchwald.

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Competing interests

MIT has patents on the ligand used in this paper from which S.L.B. and former co-workers receive royalty payments.

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This file contains Supplementary Text and Data, Supplementary Tables 1-7, Supplementary Figures 1-16 and Supplementary References. (PDF 6807 kb)

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Vinogradova, E., Zhang, C., Spokoyny, A. et al. Organometallic palladium reagents for cysteine bioconjugation. Nature 526, 687–691 (2015).

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