Solution Conformation of the Antibiotic 3823A (Monensin A)‐Sodium Salt

Extensive double irradiation experiments allowed the almost complete unraveling and extraction of the parameters in the 1H‐nmr spectrum of Na+‐Monensin (1). From this it is concluded that the solution conformation is in its details highly similar to the crystal state of the Ag+ salt. Thus rings A and E are in a somewhat distorted chair, both rings B and D are in an envelope (with the flap at respectively C‐10 and C‐18) while ring C is in a 1514T(wist). An unusual high screening and consequently low rate of proton exchange was observed for some hydroxyl protons, especially in C6D6. The small couplings observed where OH‐protons are involved allow a further deeper insight in their spatial arrangement and in their participation as ligand and hydrogen bonding. Some differences with the solid state are noted here.