Synthesis of Modified Carboxyl Binding Pockets of Vancomycin and Teicoplanin

Sixteen-membered macrocycle I (R = H) and 16+14 bicyclic compd. II, incorporating a terminal primary hydroxyl group in the peptide sequence, have been designed and synthesized. The syntheses feature the use of an efficient cycloetherification based on an intramol. SNAr reaction for the formation of biaryl ether bonds. Cyclization of a linear tetrapeptide, prepd. via a convergent [2+2] segment coupling, gave macrocycle I (R = Boc) (P configuration) as a single isolable atropisomer. Removal of the Boc protecting group afforded the modified carboxyl binding pocket of vancomycin (I; R = H). A sequential 2-fold intramol. SNAr reaction has been used to construct the model bicyclic system (i.e. II) of the D-O-E-F-O-G ring of teicoplanin. Cyclization conditions (CsF, DMF, room temp.) are sufficiently mild that the configuration of the racemization-prone arylglycine residue was not affected. Chiral amino acid and amino alc. building blocks were prepd. using Evans' asym. azidation method and Schollkopf's bislactim ether as a chiral glycine template. I showed interesting conformational properties compared to vancomycin and its binding with Ac-D-Ala was studied by NMR titrn. expts. A dissocn. const. (Kd = 5 * 10-4) was calcd. by a curve fitting method. II is currently the most advanced synthetic intermediate toward the total synthesis of teicoplanin. [on SciFinder (R)]