The aim of this thesis was the synthesis of gossypol derivatives for biological testing against melanoma and psoriasis. The bis-Schiff s bases of (-)-gossypol and (+ )-gossypol with the following amino acid esters were prepared, isolated, and characterised (yields indicated in brackets); L-phenylalanine methyl ester {( -), 39%; (+), 31 %}, L-tyrosine ethyl ester {(-), 16%; (+), 21%}, L-tryptophan methyl ester {(-), 25%; (+), 25%}, D-tryptophan methyl ester {(-), 24%; (+), 24%}. The half-Schiff's bases of (-)-gossypol and (+ )-gossypol were prepared by the partial hydrolysis of the corresponding bis-Schiff's base; L-phenylalanine methyl ester {( -), 51 %; (+), 13%}, L- tyrosine ethyl ester {( -), 28%; (+), 72%}, L-tryptophan methyl ester {( -), 29%}. An analytical HPLC method was developed for monitoring of these reactions and the determination of the diastereoisomeric purity of the Schiff s bases. The (-)-gossypol and (+)-gossypol enantiomers were prepared in 95% and 91.5% yields by the complete hydrolysis of (-)-gossypol bisel-tyrosine ethyl ester) Schiff's base and (+)-gossypol biseL-phenylalanine methyl ester) Schiff's base, respectively. Racemic gossypolone was prepared in 59% yield by ferric chloride oxidation of gossypol. The synthesis of an individual gossypolone atropisomer was attempted by an oxidative dimerisation reaction, but an unidentified C-C or C-O coupling product was obtained. Two chiral stationary phases were prepared - APS-Hypersil silica coated with CDMPC, and Fluka silica coated with CDMPC. The former was packed into an analytical column, which proved effective for the chiral separation of gossypol atropisomers, but did not give reproducible resolution of the gossypolone atropisomers. Gossypol and some of its derivatives were tested for antipsoriatic activity against a highly proliferating human keratinocyte (HPV -16) cell line, using an MIT viability assay. The most potent inhibitor of psoriatic cell proliferation was (_)_ gossypol (GIso = 5 flM), followed by racemic gossypol, (+)-gossypol, the halfSchiff s bases and racemic gossypolone, with the bis-Schiff s bases being the least active. Gossypol and some of its derivatives were tested as inhibitors of liposomal peroxidation. All compounds tested showed similar antioxidant activity and were more potent than propyl gallate, which was included as an antioxidant standard. Two gossypol half-Schiffs bases were screened for anti-tumour activity against the NCI cell line panel. The most sensitive cell lines to (-)-gossypol half(Lphenylalanine methyl ester) Schiffs base included the melanoma cell lines, SKMEL- 2 and SK-MEL-28, and the most sensitive to (-)-gossypol half(L-tyrosine ethyl ester) Schiffs base included SK-MEL-2. As a result of its activity in the keratinocyte assay, and favourable toxicological profile, gossypol can be regarded as a possible candidate for the treatment of psonaslS. The feasibility of formulating racemic gossypol into a topical preparation was, therefore, investigated. Pre-formulation studies showed; higher gossypol solubility in oily rather than aqueous vehicles, compatibility with commonly used excipients, instability to oxidising conditions, photosensitivity, and preferential partition into organic phases. Racemic gossypol was then formulated into a cream dosage form, which was relatively stable on storage below 40°C, and showed permeation through an artificial membrane in vitro.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:404670 |
| Date | January 2003 |
| Creators | Fife, Ingvar Andre Joseph |
| Publisher | King's College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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