Chemistry Reference
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synthesis of qinghaosu and its derivatives, and it will be mentioned in the following
sections. Somewhat late, Imakura et al. also reported that treatment of qinghaosu in
methanol or ethanol with TsOH or 14% hydrochloric acid afforded the methyl or
ethyl ester of 104 and 105, but in low yields.
113
5.3.3
Miscellaneous Chemical Reaction
5.3.3.1 Degradation in an Alkaline Medium
Qinghaosu is unstable in an alkaline medium; it may rapidly decompose in potas-
sium carbonate-methanol-water at room temperature to complicate the products,
among which an octa-hydro-indene 107 can be isolated in 10% yield.
26
It may
be necessary to pay attention to this property when handling the qinghaosu sample.
5.3.3.2 Pyrolysis
Qinghaosu is a stable compound in comparison with common peroxides; no decom-
position is observed even at its melting point at 156-157
C. However, pyrolysis
takes place at 190
C for 10 min, which provides a product mixture, from which
compounds 108 (4%), 28 (12%), and 15 (10%) can be separated.
114,115
It is inter-
esting that the latter two compounds are also the compositions of qinghao
(A. annua),
37,50
the metabolites of qinghaosu in vivo,
116,117
and the reaction pro-
ducts of qinghaosu and ferrous ion (vide infra) (Scheme 5-6).
5.3.4
Biotransformation
Microbial transformation study can serve as a model for the study of qinghaosu
metabolism in the mammalian and can unshed the new pathway to qinghaosu deri-
vatives. Therefore, several research groups have endeavored to transform qinghaosu
with different microbes and have found that the hydroxy group can be introduced in
some inactive carbon positions of qinghaosu.
It was reported in 1989 that qinghaosu can be transferred to deoxyqinghaosu
(14)byNocardia corallinaz and 3a-hydroxy-deoxyqinghaosu (15)byPenicilliam
O
H
K
2
CO
3
∆
O
1
MeOH-H
2
O
190 °C
O
HO
O
O
O
107
+
O
O
AcO
+
O
O
O
O
O
O
108
28
15
Scheme 5-6
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