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

distinguished from the other resonances that occurred along with it. The C-9 carbon
resonance showed a HMBC correlation with H-7 and CH3-20 and the C-8 carbon
resonance showed a HMBC correlation to the H-7 resonance as well as the H-6
resonance. These correlations confirmed the assignments of H-6 and H-7 as well as C-8
and C-9.
The H-5, H-6 and H-7 resonances had the same slightly broadened singlet profile as that
of compound I and therefore the same stereochemistry would be prevalent here as well
with a 6β-ax, 7β-eq-dihydroxy form. The paramagnetic shift for the 3H-20 resonance is
also observed in compound II as well as for 3H-19β-ax methyl group which is more
deshielded at δH 1.62 than that of 3H-18 at δH 1.06.
Compound II was isolated previously from Mehrotra et al. (1989). Rasikari (2007) and
Hensch et al. (1975) report the 7α-axial-hydroxy isomer. However, the coupling
constants of JH-6, H-7 in both Rasikari (2007) and Hensch et al. (1975) are 2.0 Hz and
therefore we think that these compounds may also be the 7β-equatorial-hydroxy and not
the 7α-axial-hydroxy isomer. The NMR data of all three references are thus used for
comparison. The 1 H NMR data compare well, with a consistent 6-7 ppm difference for
Hensch et al. (1975). The 13 C NMR data compared well with that of Rasikari (2007). No
13 C NMR data is given in both Mehrotra et al. (1989) and Hensch et al. (1975).
Table 15: 1 H NMR data for compound I compared with three reference compounds
(CDCl3, 400MHz)
Position Moiety
Compound I
2.62, d
(J = 12.72 Hz)
Rasikari, 2007
(500MHz)
2.65, dt
(J = 12.8 Hz)
1 CH2
1.18 1.22, m
2 CH2
1.57
1.83
1.59, dt
(J = 13.4, 3.5 Hz)
1.85, qt
(J = 13.4, 3.5 Hz)
Continued on next page…..
(Mehrotra. et al.,
1989)
(80MHz)
(Hensch et al., 1975)
(60MHz)
2.64, m
109