EXPERIMENTAL SECTION General Experimental Procedures. NMR experiments were performed on the following NMR spectrometers: a Bruker AVANCE 400 equipped with a room-temperature 5 mm BBO autotune probe, a Bruker AVANCE 0 and/or a Bruker AVANCE-900 equipped with 5 TXI and TCI autotune probe, respectively, and a Bruker AVANCE 700 equipped with a 1.7 mm TXI cryoprobe. All NMR experiments were acquired nonspinning with the temperature controlled at 25 for all ID H and 2D oC (298 K). The H chemical shifts parts per million homonuclear H COSY spectra are expressed in solvent signal (o ppm) referenced to the residual protonated correlation (pyridine-d4) at 7.217 ppm. For the 2D heteronuclear data (HsQC and HMBC), spectra are expressed in parts