NMR spectra were obtained on a Bruker AV 400 (400/100
MHz), Bruker AMX 500 (500/125 MHz), JEOL JNM-ECA600 (600/150 MHz),
or Bruker AVANCE III 800 (800/200 MHz) spectrometer. Chemical shifts
are reported as parts per million (δ) relative to the solvent
peak. Coupling constants (J) are reported in hertz.
Mass spectra were recorded on a Thermo LCQ XP instrument. Optical
rotations were determined on Jasco III in appropriate solvent. UV
spectra were recorded on U-3000 made by Hitachi in methanol or water.
Infrared spectra were recorded on FT-IR (FTS-135) made by Bio-Rad.
Melting points were determined on a Buchan B-540 instrument and are
uncorrected. The crude compounds were purified by column chromatography
on a silica gel (Kieselgel 60, 70–230 mesh, Merck). Elemental
analyses (C, H, and N) were used to determine the purity of all synthesized
compounds, and the results were within ±0.4% of the calculated
values, confirming ≥95% purity.