Application of RDC enhanced NMR spectroscopy in structural analysis of thiacalix[4]arene derivatives

Abstract

Thiacalix[4]arene spirodienone was rearranged into the corresponding phenoxathiin-based macrocycle. Alkylation of this inherently chiral system to achieve its immobilization led to a mixture of only two (out of four theoretically possible) stereoisomers. As standard NOE and dynamic NMR experiments did not lead to unambiguous determination of the structures we applied the Residual Dipolar Coupling constant (RDC) method. Poly-γ-ethyl-L-glutamate (PELG) and poly-γ-benzyl-L-glutamate (PBLG) were found to be easily applicable lyotropic liquid crystalline alignment media for the conformational analysis of thiacalixarene derivatives. Using these media the 1,2-alternate and the partial cone conformations were determined unequivocally.