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Are there activated esters that undergo amide bond formation with an amino group in a mild and selective fashion, other than NHS ester and Pentafluorophenyl ester? I am aware that there are many reagents to activate carboxylic acids to generate the amide bond. However, to my knowledge, only NHS ester and pentafluorophenyl esters are able to be isolated and characterized. Would there be any other alternatives?

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    $\begingroup$ Hydroxybenzotriazole (HOBt) ester $\endgroup$
    – Waylander
    Sep 29 at 11:10
  • $\begingroup$ @Waylander can it be isolated? $\endgroup$
    – chemrese
    Sep 29 at 11:12
  • $\begingroup$ best not to, besides being reactive they are potentially explosive ncbi.nlm.nih.gov/pmc/articles/PMC6259230 $\endgroup$
    – Waylander
    Sep 29 at 11:36
  • $\begingroup$ I edited the question $\endgroup$
    – chemrese
    Sep 29 at 15:53
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    $\begingroup$ The usual conditions use tertiary base. The phenol (pKa 7.1) is acidic enough to protonate your amine nucelophile and stop it acylating. See this review for further reading file:///C:/Users/marti/AppData/Local/Temp/2005-t-61-10827-852-tvorba-conh-vazby-jd.pdf $\endgroup$
    – Waylander
    Sep 30 at 6:49

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