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system where coupling constants of 5.3 Hz and 9.7 Hz indicated an axial proton (α) and
an equatorial hydroxyl group (β). The coupling constants of compound III compared
well to this with values of 3.84 Hz and 10.84 Hz indicating that the hydroxyl group at
position 3 in compound III was equatorial (β). This was supported by a NOESY
correlation between H-3 and H-5 indicating a 1,3-diaxial interaction between the two
protons.
The NOESY spectrum was then used to determine the configuration of the hydroxyl
group at C-11 as well as the methyl group situated at C-13. The methyl group CH3-20ax
showed a correlation to the proton at H-11 which puts this hydrogen in a beta/axial
position and the hydroxyl group in the alpha/equatorial position (Figure 18). It is for this
reason that the compound III has been named as ent-pimara-8(14),15-diene-3β,11α-diol.
The methyl group, CH3-17 was assigned to the equatorial (alpha) position as it showed
NOESY correlations with the H-12α proton at δΗ 1.82. The protons at H-12 was
assigned using values from the literature of similar compound, 3.3 (Meragelman et al.,
2003) (Table 20, page 117) as compound III in the literature does not distinguish
between the H-12 protons.
HO
H
3
2
4
19
1
18
5
H ax
20 ax
10
6
9
11
7
8
H
12
Figure 18: NOESY correlations for compound III
HO
H
H
14
15
13
16
17
115