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A series of carbohydrate derivatives were prepared and their structural determination was made by NMR spectroscopy. The molecular structures of 1,2-<I>O</I>-isopropylidene-5-<I>O-p-</I>tosyl-α-D-xylofuranose (1) and 1,2-<I>O</I>-isopropylidene-3,5-di-<I>O</I>-<I>p-</I>tosyl-α-D-xylo-furanose (2) was determined by X-ray single-crystal diffraction. All the carbohydrate derivatives were used as precursors for the synthesis of stannylated carbohydrate derivatives. The synthesis of these stannylated carbohydrate derivatives were carried out using two methods: (i) the reaction of triphenylstannyl-lithium with derivatised and protected (or partially protected) carbohydrates and (ii) hydrostannation of alkenyl or allylic substituted carbohydrates using triphenyltin hydride. The solution structures of the triorganotin-carbohydrate derivatives were investigated by <SUP>1</SUP>H, <SUP>13</SUP>C and <SUP>119</SUP>Sn NMR spectroscopy. In solution all the triorganotin-carbohydrate derivatives were shown to contain four-coordinate tin atoms. Reactions of 1,4:3,6-dianhydro-2,5-di-<I>O-p</I>-tosyl-D-glucitol (3) with triphenylstannyl-lithium resulted in the synthesis of (2S,1'R)-(-)-2-[1-hydroxyl-2-(triphenylstannyl)ethyl]-2,5-dihydrofuran (4). Structural elucidation was performed by 1D and 2D NMR experiments as DEPT, HMQC, HMBC, <SUP>1</SUP>H/<SUP>1</SUP>H COSY, <SUP>1</SUP>H/<SUP>1</SUP>H Long-Range COSY and NOESY NMR experiments. (2R,1'R)-(+)-2-[1-hydroxyl-2-(triphenylstannyl)ethyl]-2,5-dihydrofuran (5) was obtained from reaction of 1,4:3,6-dianhydro-2,5-di-<I>O-p-</I>tosyl-D-mannitol (6) with triphenylstannyl-lithium. Complete assignment of the <SUP>119</SUP>Sn NMR spectra to the different tin atoms of methyl 2,3-di-<I>O</I>-[(dimethylphenylstannyl)methyl]-4,6-<I>O</I>-benzylidene-α-D-glucopyranoside (7) and methyl 2,3-di-<I>O-</I>[(triphenylstannyl)methyl]-4,6-<I>O-</I>benzylidene-α-D-glucopyranoside (8) was obtained from a sequence of single frequency tin decoupling experiments. Complete assignment of the <SUP>119</SUP>Sn NMR spectra for 3-[(triphenylstannyl)propyl] 5-deoxy-2,3-<I>O</I>-isopropylidene-5-C-triphenylstannyl-β-D-ribofuranoside (9) was aided with two dimensional correlation by application of the gradient-heteronuclear multiple quantum coherence method (gs-HMQC) for <SUP>1</SUP>H-<SUP>119</SUP>Sn correlation.

Our research has been based on the biosynthetic pathway to <i>N</i>-linked glycoproteins, species which are comprised of an oligosaccharide moiety attached to the side-chain nitrogen atom of an asparagines residue in a peptide. In order to effectively study the steps involved in the biosynthesis of lipid-linked oligosaccharides and their subsequent transfer to a nascent protein in cotranslational modification processes, it is essential to have a source of pure dolichols in quantities sufficient to allow the synthesis of both biosynthetic intermediates and synthetic analogues in the pathways responsible for the biogenesis of glycoproteins. Since supplies of naturally occurring dolichols are scarce and they are difficult to synthesise, a number of lipid substrates were prepared as synthetic analogues of naturally occurring dolichyl phosphate. (Fig. 6302A) The synthesis and biological testing of lipids 1 and 2 are reported. The result of a study of the fluorescence of lipid 1 is also presented. Work towards the preparation of lipid 3 is detailed. Many of the enzymes involved in the biosynthesis of <i>N-</i>linked glycoproteins have already been isolated and characterised, however, some of those enzymes involved in the early stages of <i>N</i>-glycan biosynthesis remain unidentified. In order to gain more information about the unknown mannosyltransferases that are active in the early stages of <i>N</i>-glycan biosynthesis, a phytanyl-linked monosaccharide (glucosamine), 4, and disaccharide (chitobiose), 5, were prepared.  (Fig. 6302B) The syntheses of chitobiose phosphate from commercially available chitobiose octaacetate is reported. Details of the preparation of <i>N</i>-acetyl glucosaminyl phosphate from commercially available <i>N</i>-acetyl glucosamine are pretend. The lipid moiety, phytanyl phosphate, was derived from commercially available phytol. The manner in which phytanyl phosphate was coupled to both the monosaccharide phosphate and the disaccharide phosphoryl species is detailed and results of subsequent biological testing are reported. Finally, work towards the preparation of a fluorescently-labelled asparagine-linked chitobiosyl substrate, 6, is reported.

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Several dihydrochalcone glucosides have been synthesised and their potential value as possible sweetening agents have been assessed. Some of these dihydrochalcone glucosides were isolated as gums. These were the glucosides of 4'-hydroxydihydrochalcone; 4,4'-dihydroxy-dihydrochalcone; 3,4'-dihydrozy-4-methoxydihydrochalcone; 4'-hydroxy-3,4-dimethoxydihydrochalcone and 4'-hydroxy-2-methoxydihydrochalcone. Two more of these compounds were obtained as solids, however. These were: 4,4'-dihydroxydihydrochalcone as a pale yellow, waxy sol.id and 4'-hydroxy-3,4-methylenedioxydihydrochalcone as a white, crystalline solid. All these dihydrochalcone glucosides were found to be non-sweet. The dihydrochalcone aglycone 3,4'-dihydroxy-4-niethoxydihydrochal-cone produced an enhanced sweetness sensation when added to 5% w/v solutions of either glucose, sorbitol or mannitol. Naringin dihydrochalcone and Neohesperidin dihydrochalcone were prepared and their sweetness characteristics were assessed in Quosh and Chekwate Orange Drinks. These sweeteners produced a delayed sweet-ness effect, a gasp effect and their sweetnesses were of a lingering, cloying nature. In Quosh Orange Drink the sweetness equivalence of neohesperidin dihydrochalcone was found to be 3.8 X saccharin at the concentration used. The corresponding figure for naringin dihydrochal-cone was 0.19 X saccharin. In Chekwate Orange Drink the sweetness equivalences for neohesperidin and naringin dihydrochalcones were 6.4 and 0.21 X saccharin, respectively. It is suggested that the glucose and rhamnose constituents of the neohesperidose moiety in neohesperidin dihydrochalcone adopt the CI conformation as it interacts with the human taste-bud receptor. This conformation would allow two pairs of OH groups to adopt the gauchoconformation so that the inter-hydroxyl distance is ca. 3A. If the IC conformation were adopted, only one hydroxyl pair would adopt the gauche conformation with attendant diminution in sweetness intensity. Attempts to prepare dihydrochalcone disaccharides from simple starting materials were unsuccessful. The compounds investigated weret: 4-hydroxyacetophenone-4-B-neohesperidoside; 4-hydroxyacetophenone-4-B-sophoroside; 4-hydroxyacetophenone-4-B-laminaribioside and 4-hydroxy-acetophenone-4-maltoside.