S(N)Ar-based cycloetherification methodology: application in the synthesis of heterodectic macrocyclic peptides with endo aryl-aryl and aryl-alkyl ether bonds.

The endo aryl-aryl and aryl-alkyl ether bonds exist in a number of biologically important macrocyclic natural products, such as vancomycin family glycopeptide antibiotics (1-3), antitumor series RA I-XIV (4), K-13 (5), OF4949 (6), piperazinomycin (7), cyclopeptide alkaloids (8,9), nonpeptidic diarylheptanoids (10), and so on. Peptidomimetics incorporating, such structural features, have also been designed and synthesized as potential inhibitors of ACE (11), anti-HIV agents (12) and so on. From the view point of synthesis design (15), macrocyclization via formation of aryl-aryl or aryl-alkyl ether bond is unique, since it tackles two difficult synthetic problems, i.e., formation of ether bond and ring closure by a single operation. Intramolecular Ullmann ether synthesis (16), oxidative coupling reaction (17), and so forth, have been employed for the synthesis of type A (Fig. 1) compounds. Ring closure via the formation of aryl-aryl (type A) (18) and aryl-alkyl ether bonds (type B, Fig. 1) (19) by way of intramolecualr S(N)Ar reaction (20) will be the focus of this chapter. Figure 1.