FIGR ID=jo070155qn00002> figures/jo070155qn00002.gif" ALIGN="left" HSPACE=5> |
The absolute con
figurations (ACs) o
f the iridoid natural products, plumericin (
1) and isoplumericin (
2),have been re-investigated using vibrational circular dichroism (VCD) sp
ectroscopy, el
ectronic circulardichroism (ECD) sp
ectroscopy, and optical rotatory dispersion (ORD). Comparison o
f DFT calculationso
f the VCD sp
ectra o
f 1 and
2 to the experimental VCD sp
ectra o
f the natural products, (+)
-1 and (+)
-2,leads unambiguously to the AC (1
R,5
S,8
S,9
S,10
S)-(+)
for both
1 and
2. In contrast, comparison o
f time-dependent DFT (TDDFT) calculations o
f the ECD sp
ectra o
f 1 and
2 to the experimental sp
ectra o
f(+)
-1 and (+)
-2 does not permit de
finitive assignment o
f their ACs. On the other hand, TDDFT calculationso
f the ORD o
f (1
R,5
S,8
S,9
S,10
S)
-1 and
-2 over the range o
f 365-589 nm are in excellent agreementwith the experimental data o
f (+)
-1 and (+)
-2, con
firming the ACs derived
from the VCD sp
ectra.Thus, the ACs initially proposed by Albers-Schönberg and Schmid are shown to be corr
ect, and theopposite ACs r
ecently derived
from the ECD sp
ectra o
f 1 and
2 by Els&
auml;sser et al. are shown to beincorr
ect. As a result, the ACs o
f other iridoid natural products obtained by chemical correlation with
1and
2 are not in need o
f revision.
