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© 2021 Wiley-VCH GmbH In this Research Article, a related patent by Hill et al. was not cited. The main text should accordingly be revised as detailed below, with the missing citation included as Ref. [41]. The authors are grateful to the reader who pointed out the missing citation and apologize for not discovering and citing this patent in the original report. Include Ref. [41] in paragraph 1: “Through the formation of stable pre-activated precursor oligonucleotides, a simple process,[41] more controlled ligation can occur in reagent-free, mild buffered conditions.” Revise paragraph 2 as follows: “Structurally related carbamate,[24–26] thiourea,[27] urea,[26] and squaramides[28] have been introduced into oligonucleotides during solid phase synthesis by iterative coupling or as phosphoramidite dinucleotides. Interestingly, all of these backbones could be derived from unmodified or minimally modified oligonucleotides where the terminal 5′- or 3′-hydroxy groups are replaced by amino groups. Furthermore, the reagents (for example, 1,1′-carbonyldiimidazole (CDI) and squarate ester) used to generate these linkages become progressively less reactive upon each nucleophilic addition–elimination step,[29] allowing oligonucleotides to be pre-activated prior to ligation with another strand. Of these linkages, only the squaramide has been explored in a chemical ligation context mostly in a dual step pre-activation (pH 7.2) and template-dependent ligation (pH 9.2) system.[41] The resulting squaramide linkage was shown to be read-through by polymerases (Herculase II and Phusion DNA polymerases),[41] with the replication compared to unmodified oligonucleotides being described as ‘slightly less efficient’. Here we extensively study amine-based chemical ligation strategies and demonstrate their practical application.” Add Ref. [41] and a short text to paragraph 3: “On the other hand, squaramide- and urea-linked oligonucleotide ligation proceeded well using squarate ester and CDI, respectively (71 % and 46 %, respectively, Figure 2B; consistent with previous reports for the squaramide[41]).” Add Ref. [41] and an additional sentence to paragraph 5: “… was present (Figure 2E). These results support previous reports,[41] which showed quantitative pre-activation around pH 7 and good subsequent ligation at pH 9. Finally, the 5′-amino pre-activated oligonucleotides gave slightly lower ligation efficiency (80 % vs. 88 % for the pre-activated 3′-amino oligonucleotide, Figure 2D, a full summary of squaramide ligation efficiency can be found in Table S10 in the Supporting Information), most likely due to the 3′-amino group being a more sterically hindered nucleophile.” Revise the second sentence of paragraph 7: “(…, respectively assuming 100 % PCR efficiency; see also Ref. [41] for information on the performance of Herculase II and Phusion DNA polymerases in this context).”.

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Angewandte Chemie - International Edition

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