resonance (1H NMR) spectra were obtained on a FT-NMR (400 MHz)
Brucker apparatus spectrometer, and the chemical shifts are expressed
in δ ppm using TMS as an internal standard and J values are given in
Hz. The visible spectra were measured using a Pharmacia Biotech Spec-
trophotometer. The purity determination of the substrates and reaction
monitoring were accompanied by TLC using silica gel SIL G/UV 254 plates.