Correlation of Classification with Chemical constituents of particular Meliaceae species can be made only with great caution.
55 . . . . .
It has been said that general Statements of taxonomic significance can be made only if a systematic and thorough survey has been made as opposed to chance isolation of a few substances in a few plants.
Because the Chemistry of the meliaceae is still in its infancy, a generalization that can be of taxonomic importance cannot be made at present and will have to await further study. Our studies on three Khaya species have shown us clearly that plants of the same species are often chemically variable. Indeed we have been led by our findings to conclude that Chemical Variation is not due to macroclimatic conditions alone. In addition, even under
microclimatic conditions, it has been observed that two trees of the same species v/ithin a few yards from each other can Vary chemically.
However, this need not imply that a useful correlation will be
impossible, for what is regarded as being absent may well be present either in a small scale or not extracted in the usual way. Although successful isolation of Chemical compounds depends largely on skill and method, there is nevertheless an element of chance involved.
Since failure to detect a small concentration of a particular
30
reaching deductions that will be of taxonomic importance in this field may liave to wait tili better techniques are known which will lead to maximum Identification of a mixture. It is encouraging to know that extensive studies of the cucurbitacins
56
(familyCucurbitaceae) have very usefully complemented some other methods of taxonomy. The distribution and structural relationship of the
6 2
limonoids of the Rutaceae° have also enabled chemotaxonomic Classification to be raade.
The genus Khaya is the subject of this Thesis. There are six distinct Khaya species known to date and we have examined various
*+0
k757 58,75
parts of three of them (Khaya senegalensis, ’ ’^
y
Khaya37 59 60
ivorensis, ' Khaya grandifoliola^ 7 ’ ), and only the secds of two others (Khaya anthotheca
6l
and Khaya nyasica).The investigations carried out, the results obtained, and the deductions mado, will be described for each of the five species in compound present may obviously lead to a wrong conclusion, far
turn.
31
INVESTIGATION AND DSDUCTIONS
KHAYA SSNEGALENSIS
Khaya senegalensis (Desr) A. Juss grows in the savannah regions It is capable of attaining a height of over 100 ft. and a girth of nine feet. It is glabrous vvith grey scaly bark. The leaves are pinnate and the woody fruit encloses flat winged seed. The fruit which is four-carpelled seems capable of a subdivision into the thin walled and the thick-walled carpels. The locus of the treo is the beit extending fron Senegal to East Sudan and Uganda.
K t senegalensis has great reputation especially in West Africa as a potent drug to combat several diseases. The bark is the- raost commonly used. Several authors have described the various local uses of the tree and these can be surnraarised as follows:
Bark: Used as febrifuge, emraenagogue, vermifuge, emetic, anti-malarial, also for syphilis, ulcer and in local veterinary practice.
Flower: Used to treat stomach disorders and venereal diseases.
Seed: The crushed seed is used as an emraenagogue and the oil for anointing the body. Some early work on K. senegalensis has been reported but on the whole its Chemistry has not been satisfactorily treated. Oliver 52 recorded that K. senegalensis contains mineral
32
a saponin, lipids, and a small amount of bitter principles, which he and some earlier authors presumed might be the alkaloid cail-cedrine. Some of tho substances mentioned are probably present as fragments of larger molocules e.g. sucrose and sterol from a
glycoside. Dalziel reported that the bark from Northern Nigeria was shcv/n at the Imperial Institute (London) to contain no alkaloids, glucosides, er any resinous or crystalline neutral bodies. Ferreol 65 reported the isolation of nimbosterol, identical with ß-sitosterol.
Modern spectroscopic and analytical methods on which most of the work reported in this thosis depends have helped to clarify a lot of the rather confused picture in the literature. A lot of work in this dirc*ction will still be necessary before a full picture can emerge.
We have studied the extractives of various parts of trees of this species and have collected saraples from different places.
substances, oxalate, sterols, sucrose, starch, catechuic tannins,
Extraction of the timber of K. senegalensis with light
Petroleum gave a gum. From the chromatography of this gum, Bevan TIMBER
93 /
et al. have obtained two crystalline compounds (i) 7-d.eacetoxy- 7-oxokhivorin, and (ii) a compound melting at 88-100°
33
(CHClg). The chromatography on an old stock of extract obtained from the saine tree was repeated. The gum was dissolved in benzene and adsorbed on alumina. Elution with benzene-ethyl acetate (4:1) brought down a raixture found later to be about 85^ khayasin
(= 6-deoxyswietenolide isobutyrate) (L). The raixture ra.p. 114-116°, O l ß 25 - 163° was originally described as the low melting compound from K> seneganensis. 57 Elution with mcthanol gave 7-deacetyl-7- oxokhivorin ra.p. 225° identical in every respect with an authentic sample.
The first indication that the khayasin-containing raixture was impure was given by the marked difference in its melting point when it was crystallised from different solvents. It had a melting point 114-116° when crystallised from benzene and 87-90° from methylated spirit. The fact that it crystallised in either case with the
solvent of crystallisation, as shown by the i.r. and n.m.r. spectra, was not a satisfactory explanation for the difference. Molecular weight determination of a sample by the mass spectrometer confirmed the presence of impurities as there were still some peaks beyond 540, the molecular ion. The n.m.r. spectrum of the volatile acid showed the presence of what we originally thought was an acetate but which we now know to be a tiglate. This and another contaminant will be discussed.
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