Determination of the absolute stereochemistry at the C16 orthoester of everninomicin antibiotics; A novel acid-catalyzed isomerization of orthoesters

The absolute stereochemistry at C16 orthoester center of Ziracin (1) was unequivocally established via a novel acid-catalyzed orthoester isomerization. Structures of the resulting isomers 2 and 3 were determined by chemical degradation and extensive spectroscopic analyses. This novel isomerization was successfully extended to other related everninomicins (11-13), thus completing the entire structural assignment of everninomicin antibiotics. (C) 1997 Elsevier Science Ltd.