Issue 6, 2024, Issue in Progress

Cross aldol OPAL bioconjugation outcompetes intramolecular hemiaminal cyclisation of proline adjacent N-terminal α-oxo aldehydes at acidic pH

Abstract

Novel methods to construct small molecule–protein bioconjugates are integral to the development of new biomedicines for a variety of diseases. C–C linked bioconjugates are increasingly desirable in this application due to their in vivo stability and can be accessed through cross aldol bioconjugation of reactive α-oxo aldehyde handles easily introduced at the N-terminus of proteins by periodate oxidation. We previously developed an organocatalyst-mediated protein aldol ligation (OPAL) for chemical modification of these reactive aldehydes, but the efficiency of this method was limited when a proline residue was directly adjacent to the N-terminus due to intramolecular hemiaminal formation. Herein we explore the competition between this cyclisation and the OPAL modification and demonstrate bioconjugation can be favoured through use of acidic pH for both oxidation and OPAL, and optimisation of reaction conditions and organocatalyst. We then showcase the utility of this acidic-OPAL in modification of the cholera toxin B-subunit (CTB), a homo-pentameric protein of biomedical promise.

Graphical abstract: Cross aldol OPAL bioconjugation outcompetes intramolecular hemiaminal cyclisation of proline adjacent N-terminal α-oxo aldehydes at acidic pH

Supplementary files

Article information

Article type
Paper
Submitted
22 Dec 2023
Accepted
12 Jan 2024
First published
24 Jan 2024
This article is Open Access
Creative Commons BY license

RSC Adv., 2024,14, 3723-3729

Cross aldol OPAL bioconjugation outcompetes intramolecular hemiaminal cyclisation of proline adjacent N-terminal α-oxo aldehydes at acidic pH

A. Tufail, S. Akkad, N. E. Hatton, N. D. J. Yates, R. J. Spears, T. Keenan, A. Parkin, N. Signoret and M. A. Fascione, RSC Adv., 2024, 14, 3723 DOI: 10.1039/D3RA08776J

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