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

R 1
19
3
3
1
18
1
18
20
20
O
H
O
H
6 7
OH
6 7
OH
OH
OR 3
16
OR 2
16
13
O
CH 3
R1 R2 R3
(91) α-CH3 H H
(92) β-CH3 H H
(93) α-CH3 C(O)CH3 H
(94) β-CH3 C(O)CH3 H
(95) α−CH3 H C(O)CH3
(96) α−CH3 CH(O) H
(97) α−CH3 CH(O) C(O)CH3
(98) α−CH3 C(O)CH3 C(O)CH3
O
OCCH 3
O
CH 3
H
H
O
19
O
CH 3CO
3
CH 3COCH 2
O
3
1
18
20
1
O
H
20
O
H
6 7
OH
OCCH 3
(89) (90)
11
O
12
6 7
OH
(99)
14
OH
16
OH
13
O
O
OCCH 3
O
H
H
CH 3
CH 3
54