One bond C-13 C spin-couplings ( 1 J CC ) were measured on crystalline samples of Clabeled compounds using a JEOL ECX-300 solid-state FT-NMR spectrometer operating at a 1 H frequency of 300 MHz and equipped with a 3.2-mm magic angle spinning (MAS) probe, as previously described. Briefly, 20-50 mg of each sample (30-60 w/w %) was mixed with KBr as an internal reference for magic angle calibration. The MAS frequency was set to 15.9 or 16 kHz. To check the sample identity and purity, 1D cross polarization (CP) MAS C NMR spectra were recorded on each sample using a 1.97 μs 1 H 90 o pulse and a 1.5 ms contact time, and 32 scans were collected on the sample. For measurement of C-13 C spin-couplings, the reference signals (S o ) were obtained using a single-band selective 180 o Gaussian function, and the Jmodulated signals (S) were obtained using a double-band selective 180 o Gaussian function multiplied by a cosine wave. The total spin-echo delay was increased from 5 to 56 ms in 3-ms increments. Spectra were collected with spectral windows of 300 ppm, a total of 8 scans, and a 20 s relaxation delay. The data were processed using JEOL Delta v5.0.4.4 NMR processing software. Signal intensities were measured to give the intensity ratios of the J-modulated to reference signals (S/S o ), which were plotted against the total echo interval. Three or more measurements were made on each sample. (A), 2 (B), 1 (C), 2 (D), 3 (E), 4