Solvents were of HPLC
grade, with chloroform stabilized with a hydrocarbon (amylene)
stabilizer. Optical rotations ([α]D) were obtained on a Perkin-Elmer
241 polarimeter in a 100 by 2 mm cell (units 10−1 deg cm2 g−1), while
ultraviolet (UV) absorption spectra were obtained using a Varian Cary
50 Bio UV−visible spectrophotometer. NMR experiments were
performed on a Varian INOVA 500 MHz NMR spectrometer. 1H
and 13C NMR spectra were referenced to the deuterated solvent peaks.
High-resolution mass spectrometric measurements were acquired on
an Agilent 6520 Accurate Mass Q-TOF instrument with internal
reference masses at 121.05087 and 922.00979, both to within 5 ppm.
High-performance liquid chromatography (HPLC) was performed
using a Varian ProStar 210/215 solvent delivery module equipped
with a Varian ProStar 325 UV−vis detector, operating under Star 6.41
chromatography workstation software. HPLC-DAD-MS(±) analysis
was carried out on an Agilent 1100 series separation module binary
pump system with a vacuum degasser, thermostat control (40 °C)
column compartment, well-plate autosampler, diode array detector,
and quadrupole mass detector. Equipment was under the control of
Agilent ChemStation (Revision A.10.02) software. Standard HPLCDAD-
MS gradient conditions were 0.5 mL/min gradient elution from
90% H2O (5% CH3CO2H)−MeCN to 100% MeCN over 20 min