Studies of Laurencia Natural Products and Some Synthetic Bicyclic Molecules by X-Ray Analysis

Cameron, A. Forbes (1968) Studies of Laurencia Natural Products and Some Synthetic Bicyclic Molecules by X-Ray Analysis. PhD thesis, University of Glasgow.

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This thesis is divided into three sections. In Section I some theoretical aspects of the diffraction of X-rays by crystals and some techniques of X-ray structure analysis are introduced and discussed briefly. The structure analyses of two natural products are described in Section II and of three synthetic organic molecules containing bicyclic ring systems are described in Section III. The natural products described in Section II, laurencin and laurinterol, were both isolated from the Laurencia species of seaweed and were unusual as bromine-containing natural products. Unambiguous determination of their constitutions by chemical and spectroscopic techniques had proved impossible and no details of their stereochemistries were available. In each case the X-ray investigation has established the structure and both absolute stereochemistries were determined by consideration of anomalous dispersion effects. In the case of laurinterol, as a result of the determination of the absolute stereochemistry, the absolute stereochemistries of the chemically related compounds aplysin and aplysinol have been determined, and it has been proved that laurinterol, aplysin and aplysinol have the same absolute stereochemistry at their common centres as the natural products laurene and cuparene. This has allowed speculation on the possibility of a biological precursor common to all five compounds. The investigations of two bicyclo[2,2,2]octane derivatives and a bicyclo[3,2,2]nonene derivative have been described in Section III. There has been considerable controversy in the literature as to the conformation of the bicyclo[2,2,2]octane molecule, the possibilities being the eclipsed conformation as opposed to the staggered or twisted D3 conformation. The investigation of one of the bicyclo[2,2,2]octane derivatives was undertaken specifically to study this problem, and the results prove unambiguously that in the solid state the twisted or staggered D3 conformation is favoured with 5 dihedral angles between substituents on the bridges. The second bicyclo[2,2,2]-octane derivative was an adduct of unknown structure. The analysis has revealed the structure and the results show that despite the presence of many substituents and sp2 hybridised centres, the second bicyclo[2,2,2]octane skeleton reflects the same conformational trends as the first. The bicyclo[3,2,2]-nonene system was investigated because it was of conformational interest. In this case it has been shown that no twisting of the bicyclic ring system takes place, but that strain is relieved by ring-flattening with accompanying valency-angle distortions. The three conformations have been discussed in one chapter with an accompanying discussion of those strain effects which are generally considered to be conformation-determining.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1968
Depositing User: Enlighten Team
Unique ID: glathesis:1968-78466
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:21
Last Modified: 30 Jan 2020 15:21

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