university of kwazulu-natal faculty of science and agriculture school ...

esonance at δΗ 5.29 and two oxygenated methine resonances at δΗ 3.33 (d, J = 2.28 Hz)
which overlapped with the solvent peaks and δΗ 3.93, a broad doublet of triplets
respectively.
The two characteristic olefinic resonances at δC 127.95 (CH=) and δC 138.66 (C=)
suggested an urs-12-ene skeleton. However the tertiary methyl group (3H-28) which is
usually present at C-17 in urs-12-ene triterpenes was replaced by a carboxylic acid group
evidenced by the carbonyl resonance of the carboxyl group at δC 180.88. The C-17
carbon resonance overlapped with the resonances of the deuterated methanol solvent
peak between δ 47 and δ 48 and showed HMBC correlations to a methylene and methine
resonance at δΗ 2.57 (2H-16) and δΗ 2.49 (H-18), respectively. The proposed resonance
for quartenary carbon C-17, falls within the range as documented for similar compounds
4.1, 4.4 and 4.5 (Table 23).
The two proton resonances at δH 3.93 and δH 3.33 were attributed to H-2ax and H-3eq
respectively based on a comparison with the C-17 methylated compounds, where H-2 and
H-3 are axial and equatorial respectively (Lontsi et al., 1992) and where H-2 and H-3 are
both axially situated (Lontsi et al., 1998). Our compound compared favourably with the
H-2ax and H-3eq configuration. The corresponding carbon resonances at δC 65.90 (C-2)
and δC 78.70 (C-3) are deshielded owing to the oxygenation at these carbons.
In addition to C-2 and C-3, a further deshielded carbon resonance at δC 72.18 suggested
the presence of another oxygenated group. This carbon resonance was however
quaternary and was placed at C-19 with a hydroxyl and methyl attached to it. Literature
supported this assignment as C-19 in the literature with the same substitution pattern
resonates between δ 71 and δ 74, Table 22 (da Graca Rocha et al., 2007; Fang et al.,
1991; Lontsi et al., 1992; 1998).
The C-3 carbon resonance showed HMBC correlations to two tertiary methyl resonances,
3H-23eq (δΗ 0.98) and 3H-24ax (δΗ 0.86) whose corresponding methyl proton resonances
121