Total synthesis of mauritines A, B, C, and F: cyclopeptide alkaloids with a 14-membered paracyclophane unit.

A unified strategy for the synthesis of mauritines A (5), B (6), C (7), and F (10) has been developed based on a key intramolecular nucleophilic aromatic substitution reaction (S(N)Ar) for the formation of the strained 14-membered paracyclophane. It was demonstrated that the outcome of the cycloetherification is independent of the stereochemistry of the peptide backbone and that both (1R)-16 and (1S)-16 cyclized smoothly to provide the corresponding macrocycle. On the other hand, dehydration of the secondary benzylic alcohol, via the phenylselenide intermediate, is configuration dependent.

Strained-cyclophane-induced beta-turn template: design, synthesis, and spectroscopic characterization.

[structure: see text] Three tetrapeptides incorporating a 14-membered (R(i+1), S(i+2)) cycloisodityrosine at the i + 1 and i + 2 positions were designed and synthesized. Conformational analysis by (1)H NMR and CD spectra as well as molecular modeling indicated that they all adopt a beta-turn conformation. While the CD spectrum of compound 2 is characteristic of the typical type-II beta-turn (maximum at approximately 200 nm and a minimum at approximately 220 nm), that of 1a (atropisomer of 2) is opposite in sign to the expected spectrum of the type-II beta-turn.

A rapid access to biaryl ether containing macrocycles by pairwise use of Ugi 4CR and intramolecular S(N)Ar-based cycloetherification.

[reaction: see text] From readily accessible starting materials, macrocycles with an endo aryl-aryl ether bond are synthesized in only two operations by combination of the Ugi four-component reaction and an intramolecular S(N)Ar reaction. The nitro group serves as an activator for the macrocyclization and provides a handle for the introduction of functional group diversity. A Ugi reaction promoted by ammonium chloride in aprotic solvent is documented for the first time.