Analysis was performed on an HP1100 system (Hewlett–Packard) equipped with an HP1100 quaternary pump, an HP1100
degassing device, a 20- ll injection loop (Rheodyne, Cotati, CA) and an HP1100 UV-detector set at 245 nm. The HPLC was controlled by a personal computer running Agilent ChemStation software for LC and LC/MS systems.