Synthesis of o-brominated diaryl ethers using symmetrical iodonium salts: application to the synthesis of Bastadin precursors
Elias .. Couladouros*, Vassilios .. Moutsos, and Emmannuel N. Pitsinos
Department of Chemistry, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece
Organic and Bioorganic Chemistry Laboratory, NCSR Demokritos, 15310 Ag. Paraskevi Attikis, PO Box 60228, Athens, Greece
E-mail: ecoula@chem.demokritos.gr
Dedicated to Professor Anastasios Varvoglis on the occasion of his 65th birthday
(received 10 Sep 03; accepted 18 Nov 03; published on the web 06 Jan 04)
Abstract
The coupling of o-brominated phenols with symmetrical iodonium salts for the construction of the corresponding diaryl ethers was studied. Bis-(2-benzyloxy-5-formyl-phenyl)-iodonium bromide 6b, only once mentioned in the literature, was fully characterized and tested for the synthesis of Bastadin related diaryl ethers.
Keywords: Bastadins, iodonium salt, synthesis, natural products
Introduction
Diaryl ether is the common structural feature of many natural products with significant biological activity. Vancomycin is the most prominent example, since it is a very potent antibiotic and constitutes the last defense of science against the penicillin resistant Staphylococcus aureus.1 Bastadins, a family of linear or macrocyclic bis-diaryl ether tetrapeptides possessing brominated aryl units and unique a-oximinino amide bonds, are yet another example.2
Despite recent advances in the synthesis of diaryl ethers,3 the efficient preparation of o- halogenated derivatives continues to constitute a synthetic challenge with which we were faced in the course of ongoing research towards the synthesis of Bastadins. We would like to report herein results related to our studies on the construction of the o-brominated diaryl ether moiety of these natural products, based on the coupling of phenols with triazenes or iodonium salts.
0
