... Experimental Section NMR spectra were recorded on a Varian XL-200 or Varian XL-300 (1H NMR, 200 or 300 MHz; lSC NMR, 50.31 or 75.43 MHz) spectrometer. Chemical shift values are reported in parts per million. ... 3468 Journal of Medicinal Chemistry, 1993, Vol. ...