For example, several groups have reported synthetic limitations when working with various strained alkynes due to the 5-endo-dig cycloisomerization, and protecting these strained alkynes with (MeCN)4CuBF4 should increase the number of synthetic strategies available. This (MeCN)4CuBF4 protection may also be effective in protecting DBCO peptides after resin cleavage and ether precipitation, as suggested by the 10 and 50 equiv. (MeCN)4CuBF4 data shown in Figure . The larger quantities of (MeCN)4CuBF4 in the cleavage solution appear to allow DBCO to remain protected after resin cleavage, as 6-azidohexanoic acid did not efficiently react with DBCO in aqueous conditions. Liberation of copper from the DBCO peptides could be accomplished with aqueous ammonia, EDTA, or metal scavengers, as reported by the Hosoya group. As other metal salts have been demonstrated to complex with cycloalkyne rings, these may also be able to protect against acid-mediated degradation.