On the Absolute Stereochemistry of Tolterodine: A Circular Dichroism Study

摘要

Tolterodine (>1) is a potent muscarinic receptor antagonist used in the treatment of overactive urinary bladder (OAB) syndrome. Tolterodine is chiral and it was patented, and is currently marketed, as the l-tartrate salt of the (R)-enantiomer. However, the existing literature does not offer an ultimate proof of a stereoselective mode of action of >1. A second open stereochemical issue concerns the absolute configuration (AC) of >1. Neither the original patents nor subsequent studies have established the AC of >1 in an unambiguous way, although the AC of the l-tartrate salt of >1 was assigned by X-ray diffractometry. Finally, neither electronic nor vibrational circular dichroism (ECD and VCD) spectra of >1 are reported so far. We performed a thorough ECD/VCD study of >1 in different solvents and at variable temperatures. Solvent and temperature dependence highlighted the existence of moderate flexibility which was confirmed by molecular modelling. ECD calculations with time-dependent density functional theory (TDDFT) accurately reproduced the experimental spectra and allowed us to confirm the AC of >1 in an independent way.