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. 2019 Sep 25;9:13820. doi: 10.1038/s41598-019-49843-1

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Overview of the bio-orthogonal reactions, unnatural amino acids, and DNA modifications employed in this study. (a) Terminal alkynes (1) and azides (2) can form 1,4-disubstituted 1,2,3-triazoles in a 1,2-dipolar cycloaddition catalysed by copper. Azides can also react with strained alkynes such as DIBO/DBCO (3) in strain-promoted azide-alkyne cycloadditions that do not require a catalyst. Cyclopropenes (4) react with tetrazines (5) in inverse-electron-demand Diels-Alder reactions to diazanorcaradienes. (b) Lysine derivatives bearing alkyne, azide and cyclopropene moeities were introduced into PR65. (c) DNA oligonucleotides were modified with DBCO and tetrazine functional groups.