found to be attached to C-20 with due to an observed HMBC
correlation with a carbon at dC 159.6 (C-20
). The measured CD
spectrum (see Supporting information) for compound 1 suggested
an absolute configuration at C-3 of S (negative Cotton effect near
306 nm and a positive Cotton effect near 240 nm (Versteeg et al.,
1999)) but close examination of the proton and carbon spectra
suggested that there could be some impurities. This suspicion was
further fueled by the fact that other isolated known isoflavans, 3–5,
in the same plant extract gave R absolute configuration. This is an
unusual observation and we thus have chosen to leave the absolute
configuration undetermined due to this ambiguity. Based on these
observations, compound 1 was characterized as 7-hydroxy-20
-
methoxy-[600,600-dimethylpyrano (200,300:40
,50
)]isoflavan and is being
reported here for the first time from natural source, and is