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

3.4.1 Structural elucidation of Compounds I and II
2
19
1
4
O
20
18
9
10
5
11
6 7
OH
OH
12
14
8
R
13
16
15
O
17
I
II
R
OC(O)CH 3
Compound I is a yellow crystalline compound soluble in dichloromethane and methanol
with a melting point of 197 °C and an optical rotation of [α] 20 D +29° (c 0.0052g/100ml,
CHCl3) [Mehrotra et al., 1989, optical rotation = +23°]. The mass spectrum showed a
molecular ion peak at m/z 390 corresponding to a molecular formula of C22H30O6 and
fragment ion peaks at m/z 372 (M + - H2O) and 357 (M + - H2O - CH3). The IR spectrum
showed carbonyl stretching bands at 1734 cm -1 , O-H stretching bands at 3377 cm -1 ,
alkene stretching bands at 1641 cm -1 and C-H bending vibrations of the isopropyl group
at 1375 cm -1 . The UV spectrum showed a maximum absorbance at a wavelength of
275nm (log ε = 1.61).
The 1 H NMR spectrum of compound I showed deshielded methine resonances at δH 5.64
(H-7) and δΗ 4.30 (H-6) as well as a methine resonance of an isopropyl group (H-15) at
δΗ 3.14. One of the protons of the methylene group at C-1 resonating at δΗ 2.62 could
also be clearly seen as well as three methyl group resonances at δH 0.92 (3H-18ax), 1.62
(3H-20eq) and 2.02 (OC(O)CH3). Three other methyl groups were also present in the 1 H
NMR spectrum, but were not clearly distinguishingable as they overlapped with each
other. These were the methyl resonances at positions 16, 17 and 19 which occurred at
δH 1.18 and δH 1.23.
OH
104