3.3. NMR analysis of the rotamers of swertiajaponin (3)
and swertisin (6)
Swertiajaponin (3) and swertisin (6) are both 6-C-glucosyl-
flavones with 7-methoxyl group. As Table 1 shows, two sets of
signals appeared in their 1
H- and 13C NMR spectra of 3 and 6,
and their intensities are approximately 9:8 in DMSO-d6. The
interconversion of two conformations were also examined to
run both 1
H and 13C at 0C in d-methanol, which exhibited
more significant changes in their chemical shifts at H-3 and H-
8, and with an intensities ratios at about 4:3. Davoust et al [9]
and Rayyan et al [11] indicated that rotamers of flavonoid 6-Cglucoside
resulted in the steric hindrance from the ortho
methoxyl substituent at C-7 which restricted rotation around
the C(sp3
)-C(sp2
) glucosyl-flavone linkage (C-6-C-100).