The Chemistry of Some Naturally Occurring Compounds Containing Condensed Alicyclic Ring Systems: An Investigation into the Structure of the Triterpene α-Amyrin

155 Pages·04.561 MB·English

by  Ruff, Stefan Udo

THE CHEMISTRY
of
SOME NATURALLY OCCURRING COMPOUNDS
CONTAINING CONDENSED ALICYCLIC RING SISTEMS
An Investigation into the Structure
of the Triterpene
OC-AMIR IN
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T H E S I S
presented to
THE UNIVERSITY OF GLASGOW
FOR THE DEGREE OF
DOCTOR of PHILOSOPHY
B Y
STEFAN UDO RUFF
ACKNOWLEDGEMENTS
The author would like to express his most sincere
gratitude to Professor F.S. Spring for his friendly
and helpful interest and many words of encouragement
throughout these investigations. He would also thank
Dr. J. MacLean for the liberality with which he gave
of his fund of practical experience, and, finally, he
would thank Dr. G.T* Newbold for much assistance in
the interpretation of spectrographic data.
C O N T E N T S
Page
HISTORICAL
Introduction .................. 1
Dehydrogenation ............................ 3
The Environment of the Double Bond . . . . • 7
The relative Positions of the Double Bond
and the Hydroxyl Group • . . . ......... 12
Ring Fissions in Oc-Amyrin • . . . . • • • • 1 7
THEORETICAL
Introduction • • • • • • • • ........... . . . 2S
The Oxidation of oc-Amyradienol • • • • • • • 3 1
The Chemistry of 1- 0£-Amyradiene • • • • • • 49
Oxidative Degradation of Ring A • • • • • • • 5 9
The Oxidation of iso- od-Amyrenonyl
Derivatives with Selenium Dioxide . . . • 73
Conclusion ........................... • . . S i
EXPERIMENTAL
BIBLIOGRAPHY
H I S T O R I C A L
N«B. Arabic numerals in parentheses refer to the
Bibliography, Roman numerals to the formulae in the text.
INTRODUCTION
The pentacyclic triterpenes ©c- and ^-arayrin con­
stitute the main neutral, non-volatile fraction of the
resin obtained from Manila Elemi, and were first isolated
by Rose (1) in 1&35* A large number of other triterpenes
(alcohols and acids) occur naturally in the saps of a wide
variety of plants, and many of these bear a close struc­
tural relationship to one or other of the amyrins. Thus
-boswellic acid (2), oleanolic acid (3), glycyrrhetic
acid (4), erythrodiol (3), basseol (6), gypsogenin (7)
and hederagenin ($) have all been converted to ^9-amyrin
or one of its derivatives, and similarly ursolic acid (9)
and ^9-boswellic acid (10) have been shown to be closely
related to o^-amyrin.
In 1&$7 Vesterberg (11) separated the two isomeric
amyrins by utilising the difference in solubility of the
acetates, and differential solution of various esters
ha s remained the standard method of separation of ©£-
*•*»
and y$-amyrin.
A very complete summary of the chemistry of the tri­
terpenes is given elsewhere (12, 13 )• In the present
dissertation the author will confine himself to a discussion
2
of the chemistry of 06-amyrin, and previous work will
be described with particular reference to its bearing on
the experimental results obtained by the author.
m
3
DEHY DROGENATIQN
The first evidence as to the nature of the carbon
skeleton of both the amyrins was obtained by dehydroge­
nation, using sulphur or selenium at an elevated tempera­
ture. Oxidative experiments had already been carried
out by Vesterberg (14), but these did not give conclusive
results which could be interpreted at the time. Simi­
larly bromination experiments (15) and the oxidation of
the bromo-derivatives so formed had not yielded any fur­
ther information. In 1929 Ruzicka (16) clearly showed
the presence in oc-amyrin of an unreactive double bond
which could not be hydrogenated though it did undergo
ozonolysis. The presence of the secondary hydroxyl group
had been proved at a very early stage in the investigations
(17)* Since ordinary methods of degradation, which would
allow a step-wise reconstruction of the basic skeleton,
had not been successful, Ruzicka (16) studied drastic heat
treatment. Dry distillation yielded a number of hydro­
carbons which were separated by fractional distillation
and some of which could be dehydrogenated with sulphur or
selenium to naphthalene type compounds. The amyrins
themselves (as a mixture of the two isomers) were therefore
subjected to dehydrogenation with the same reagents and
4
one of the products obtained was finally identified as a
trimethylnaphthalene (Sapotalene, I). In 1932 Ruzicka
(IS) subjected various other triterpenes to the same
treatment and identified many of the reaction products
by synthesis. It was not, however, till 1937 that 06-
amyrin was dehydrogenated (19). Among the reaction
products was the naphthalene derivative (I) first obtained
in 1929, l:2:5:6-tetramethylnaphthalene (II) and 1:5:6-
trimethyl- /) -naphthol (III).
The isolation of this last product clearly placed
the hydroxyl group at position 2 of the picene skeleton
(IV) which had been suggested by Ruzicka (20) who ob­
tained a picene homologue on dehydrogenation of various
triterpenes. The isolation of this same hydrocarbon by
Spring (19) from 06-amyrin showed that this, too, had
the basic hydropicene structure. Though allowance had
to be made for the possibility of migration of the methyl
groups during the process of dehydrogenation, the isola­
tion of the products listed above gave some indication
of their possible location.