A moisture-tolerant route to unprotected \u03b1/\u03b2-amino acid N-carboxyanhydrides and facile synthesis of hyperbranched polypeptides

Zi-You Tian,Hua Lu,Zhengchu Zhang,Shuo Wang

doi:10.1038/s41467-021-25689-y

Zi-You Tian, Hua Lu + Show 2 more

Open Access

https://doi.org/10.1038/s41467-021-25689-y

Copy DOI

Abstract

A great hurdle in the production of synthetic polypeptides lies in the access of N-carboxyanhydrides (NCA) monomers, which requires dry solvents, Schlenk line/gloveboxe, and protection of side-chain functional groups. Here we report a robust method for preparing unprotected NCA monomers in air and under moisture. The method employs epoxy compounds as ultra-fast scavengers of hydrogen chloride to allow assisted ring-closure and prevent NCA from acid-catalyzed decomposition under moist conditions. The broad scope and functional group tolerance of the method are demonstrated by the facile synthesis of over 30 different α/β-amino acid NCAs, including many otherwise inaccessible compounds with reactive functional groups, at high yield, high purity, and up to decagram scales. The utility of the method and the unprotected NCAs is demonstrated by the facile synthesis of two water-soluble polypeptides that are promising candidates for drug delivery and protein modification. Overall, our strategy holds great potential for facilitating the synthesis of NCA and expanding the industrial application of synthetic polypeptides.

Highlights

A great hurdle in the production of synthetic polypeptides lies in the access of N-carboxyanhydrides (NCA) monomers, which requires dry solvents, Schlenk line/gloveboxe, and protection of side-chain functional groups
We concluded that HCl generated from the synthesis of NCA would cause the latter to rapidly decompose under hydrous conditions
Propose that NCA synthesis under mild, atmospheric conditions, without the need for moisture removal, could be achievable as long as HCl could be efficiently removed from the crude products before the HCl-catalyzed NCA decomposition taking place

Summary

Introduction

A great hurdle in the production of synthetic polypeptides lies in the access of N-carboxyanhydrides (NCA) monomers, which requires dry solvents, Schlenk line/gloveboxe, and protection of side-chain functional groups. Kramer and Deming achieved the notable breakthrough of purifying non-crystallizable NCAs via silica gel column chromatography in a glovebox[36] In another outstanding study, Fuse reported efficient NCA synthesis in a mixture of organic and aqueous solvents with the use of a microflow reactor, followed by a sequence of flash dilution, extraction, and purification[37]. Fuse reported efficient NCA synthesis in a mixture of organic and aqueous solvents with the use of a microflow reactor, followed by a sequence of flash dilution, extraction, and purification[37] Despite all these advances, the scalable, open-vessel, and moisture-tolerant synthesis of challenging NCAs without the burden of protecting functional side groups remains an urgent and unmet need

Methods

Results

Conclusion