All NMR experiments were performed on a Bruker 500.13 MHz
FT-NMR spectrometer (Bruker, Bremen, Germany) interfaced with
a BBO 5 mm-1H probe operating at 25 C, and the chemical shifts
were referenced to tetramethylsilane (0 ppm) and the residual solvent
signal (CDCl3: d H 7.26, d C 77.0; MeOD: d H 3.0, d H 5.0, and d
C 50.0). The samples were dissolved in 600 lL of CDCl3 or MeOD
containing 1 mM tetramethylsilane (TMS) and transferred to
5-mm NMR tubes for analysis.