All reagents were purchased from Aldrich (Milwaukee, WI). The purity of compounds investigated were confirmed by 1H, 13C and 31P NMR spectroscopy at 400 MHz or 500 MHz performed on Varian (Palo Alto, CA) Unity spectrometers. High-resolution mass spectra were obtained at the University of Illinois Mass Spectrometry Laboratory. Cellulose thin layer chromatography (TLC) plates were visualized by using iodine or a sulphosalicylic acid-ferric chloride stain. The syntheses and characterization of 412 were described previously30 (link).