Amino acid chemistry is not my favorite; it's kind of... blah. Feels archaic somehow. But these amino acids are pretty funky - each fragment was formed with pretty standard chemistry (protections/deprotections and all). The N-N bonds were introduced with benzyl carbazate and t-butyl carbazate. The cyclization to form the leftmost-indicated piperazic ring occurred via Mitsunobu condition-induced Fmoc deprotection of the amine (which appears to be novel according to the article) followed by substitution of an alcohol, while the left occurred via Boc deprotection-induced displacement of a triflate and the top via Troc-deprotection induced displacement of a triflate. Don't forget the structures of these (the deprotection conditions used in the paper alongside):The most interesting part is the macrocyclization; rather than doing a macrolactonization between an acid or ester and an alcohol, the authors used a substitutive strategy by a carboxylate anion attacking a chlorine-turned-iodide leaving group to produce Piperazimycin A in 3.6% overall yield in 26 linear steps. Tight. Note the hexachloroacetone (HCA) used for chlorination in the Appel reaction instead of CCl4. Equally toxic reagent, but way cooler.