Department of Chemistry
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Item Allelochemicals from Sorghum Bicolor that Stimulate Feeding by the Larvae of the Stem Borer Chilo Partellus(University of Ghana, 1988-08) Torto, B.Feeding bioassays with cellulose acetate discs impregnated with the hexane, ethyl acetate and methanol extracts of the leaf-whorls of field grown plants of sorghum cultivars IS 18363 (susceptible) and IS 2205 (resistant) showed that the methanol extracts were most stimulatory to the feeding of the third-ins tar larvae of Chilo partellus. Ethyl acetate extracts were intermediate in stimulatory activity whilst hexane extracts were the least stimulatory. Extracts of the more susceptible cultivar were more stimulatory than those of the more resistant cultivar and those of the whorls of the 3 week old plants were more stimulatory to larvae than those of the 6 week old plants. The phagostimulatory compounds in the ethyl acetate extracts were phenolic, p-hydroxybenzaldehyde and phydroxybenzoic acid being the major components and ferulic and caffeic acids being in minor amounts. p-Coumaric acid was also present in minor amounts but was non-stimulatory at all the doses tested. p-Hydroxybenzaldehyde was a more potent feeding stimulant for the larvae relative to some of its possible theoretical biogenetic analogues. Limited structure-activity studies with some hydroxybenzoic acids and their corresponding cinnamic acids showed that the former were more stimulatory to the feeding of the larvae than the latter and that oxygen substitution in the benzene ring was crucial for activity. The phagostimulatory compounds in the methanol extracts were phenolic, identical to those in the ethyl acetate extracts, and sugars. The sugars which were identified in the extracts comprised sucrose, fructose, glucose and xylose. The feeding response of larvae to these sugars followed the order sucrose » glucose fructosei xylose was non-stimulatory. Comparison of the activities of sucrose with mixtures of glucose and fructose showed that the high activity of the disaccharide is due to its total structure and not to a summation of its monosaccharide moieties. Sugars synergised with phenolics to give enhanced feeding response of the third-instar larvae. Chromatographic analyses of the extracts showed that stimulatory and non-stimulatory components in the extracts differed quantitatively rather than qualitatively in the whorls of the two cultivars at the two growth stages. This may have implication in resistance screening and breeding programmes.Item Targeting of Tlck-Coupled Liposome to Simian Virus 40 Transformed Mouse Fibroblasts(University of Ghana, 1984-08) Ankrah, N.A.; Wei R.; Flechtner W.T.; University of Ghana, College of Basic and Applied Sciences, School of Physical and Mathematical Sciences, Department of Chemistry.N-a-tosyl-L-lysyl-chloromethyl ketone (TLCK) has been coupled to ara-C or colchicine encapsulated liposomes via glutaraldehyde treated liposomal phosphatidylethanolamine (Lp-G-TLCK) or sodium metaperiodate oxidized oligosaccharide side chain of liposomal digoxin (Lp-D-TLCK). TLCK has been shown to react with specific histidine residue at the active site of such protein as trypsin and has high binding affinity for simian virus 40 and polyoma virus transformed fibroblasts. A 20-minute exposure of cells to Lp-G-TLCK containing ara-C impaired the growth of tumor cells (SVT2 ) for up to two days, but did not impair the growth of normal cells (Balb/C 3T3). However, at 50-minute exposure, the Lp-G-TLCK containing ara-C impaired the growth of Balb/C 3T3 cells at day one but recovered by the second day. The SVT2 cells, on the other hand, did not recover from the cytotoxic effect of Lp-GTLCK, containing ara-C during the second day. The underivatized liposome (Lp-PE) containing ara-C was cytotoxic to both Balb/C 3T3 and SVT2 cells at 20 or 50 minute exposure periods. The Lp-D containing ara-C, at 20 to 60-minute exposure, slightly impaired the growth of SVT2 and Balb/C 3T3 cells at day one. Such cytotoxic effect was, however, not observed by the second and third days of growth. In contrast, Lp-D-TLCK containing ara-C impaired the growth of SVT^ cells while the growth of Balb/C 3T3 cells was nearly indistinguishable from control cells over a threeday period. Thus TLCK selectively enhanced ara-C encapsulated Lp-D-TLCK SVT2 cell cytotoxicity. Lp-D-TLCK containing colchicine, while impairing the growth of Balb/C 3T3 cells, was particularly cytotoxic to SVT2 cells, indicating that colchicine may be an unsuitable anti-tumor drug for use in a culture system with normal cells in their exponential growth phase. The uptake of Lp—D—TLCK by SVT2 cells was higher than the uptake by Balb/C 3T3 cells. With respect to underivatized liposome (Lp-D) the uptake by Balb/C 3T3 cells was higher than the uptake by SVT2 cells, indicating that TLCK enhanced liposome reaction with SVT2 cells and may retard reaction with the Balb/C 3T3 cells.