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 abstractmacrocyclization can be used to constrain peptides in their bioactive conformations , thereby supporting target affinity and bioactivity . in particular , for the targeting of challenging protein  
 protein interactions , macrocyclic peptides have proven to be very useful . 
 available approaches focus on the stabilization of helices , which limits their general applicability . here 
 we report for the first time on the use of ringclosing alkyne metathesis for the stabilization of an irregular peptide secondary structure . 
 a small library of alkynecrosslinked peptides provided a number of derivatives with improved target affinity relative to the linear parent peptide . 
 in addition , we report the crystal structure of the highestaffinity derivative in a complex with its protein target 1433. it can be expected that the alkynebased macrocyclization of irregular binding epitopes should give rise to new scaffolds suitable for targeting of currently intractable proteins . 
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