Total synthesis of Mauritines A, B, C, and F: Cyclopeptide alkaloids with a 1-4-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 (SNAr) 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 (IS)-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. (1R)-25 underwent the two-step syn-elimination much more easily than (IS)-22. A modified reductive deamination procedure via the diazonium intermediate was developed. A complete assignment of proton and carbon NMR spectroscopy signals for these natural products is reported for the first time.