“…Alkenes and alkynes have been used to tag proteins, DNA, RNA, lipids, and sugars, enabling their labeling with tetrazine-fluorophore conjugates for imaging ( Agarwal et al., 2015 , Asare-Okai et al., 2014 , Busskamp et al., 2014 , Denk et al., 2014 , Kurra et al., 2014 , Lang et al., 2012a , Lang et al., 2012b , Nikic et al., 2014 , Patterson et al., 2014 , Pyka et al., 2014 , Selvaraj et al., 2015 , Uttamapinant et al., 2015 , Yang et al., 2012 ). However, while azide-alkyne reactions form the basis of strategies to enrich tagged biomolecules for their identification by mass spectrometry (MS) ( Bagert et al., 2016 , Chesarino et al., 2014 , Dieterich et al., 2006 , Dieterich et al., 2007 , Kleiner et al., 2015 , Smeekens et al., 2015 , Vanbeselaere et al., 2012 , Zhang et al., 2013 , Zheng et al., 2013 ), there are currently no methods for enriching and identifying biomolecules labeled with strained alkenes or alkynes through inverse electron-demand Diels-Alder reactions.…”