Novel sugar phosphorus ylides: Their synthesis, structure and reactivity. Synthesis of a series of sugar-derived phosphorus ylides from protected sugar derivatives and beta-oxo ylides as a route to novel alkynes and trioxo compounds.
AuthorSahabo, Nina Carole
KeywordSugar phosphorus ylides
ß,ß'-dioxo sugar-derived phosphorus ylides
The University of Bradford theses are licenced under a Creative Commons Licence.
InstitutionUniversity of Bradford
DepartmentSchool of Life Sciences
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AbstractHigher carbon chain sugars have gained increased interest recently; they are important building blocks of natural and unnatural products with biological properties. The synthesis of these higher sugar skeletons is commonly known to be achieved with the Wittig methodology which exploits phosphorus ylide chemistry. This method has been successfully used for the synthesis of the higher carbon sugars. The aim of this project was to synthesise ß,ß'-dioxo sugar-derived phosphorus ylides, a new class of ylides, as versatile intermediates to valuable higher carbon sugar derivatives and carbohydrate mimics. Model reactions were initially conducted; tetrahydro-2-furoic acid and tetrahydro-2H-pyran-4-carboxylic acid, compounds which are structurally similar to the precursor sugars, were identified as suitable model compounds. These compounds were converted to acyl chlorides and then converted to ß,ß'-dioxo phosphorus ylides precursors by acylation. The methodology proved successful and 8 examples were isolated. However, low yields were obtained due to the inevitable formation of triphenylphosphine oxide. The method was then extended to sugar derivatives, prepared using standard protecting group chemistry. It was found that acylation could be achieved using the simple acyl chloride route or peptide coupling methodology for sugar derivatives which were acid sensitive. ß,ß'-dioxo sugar-derived phosphorus ylides (16 examples) were successfully isolated in low yields. The oxidation and thermal reactivity of the ß,ß'-dioxo ylides were studied. Oxidation resulted in the successful synthesis of vicinal tricarbonyls, isolated as a mixture with the gem-diols (hydrates). The thermal decomposition of the ylides gave alkynes in moderate yields.
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Influence of changing patterns of sucrose consumption on industrial users. Response by manufacturers of soft drinks, biscuits, cereals, cakes confectionery, ice-cream, jams, canned products and other sugar-containing foods to the U. K. dietary guidelines that relate to sucrose consumption.Not named; Heasman , Michael Kenneth (University of BradfordPostgraduate School of Studies in Biomedical Sciences, 2010-02-10)Sugar is intrinsically linked with the modern food system. Large sections of the U. K. food industry are dependent on its use and functional qualities. Supplies of sucrose entering the food chain have declined 25% between the 1950's and 1980's and currently stand around 37 kg/person/year. Furthermore, U. K. dietary guidelines over the past 14 years have consistently suggested caution over how much sugar is eaten, especially in manufactured foods. Dietary guidelines such as the NACNE report (1983) recommend average sugar consumption should be no more than 20 kg/person/year. Currently, two-thirds of sugar supplies are bought for use in food and drink manufacture. Continued pressures on sugar consumption and negative consumer attitudes to sugar may be reflected in lost sales of sugar-containing foods. The available information on U. K. sugar consumption is critically assessed. Although the main sources of sugar supply are identified, individual sugar consumption is shown to vary by considerable amounts. The place of sucrose is examined in relation to other sweeteners and why and where sugars and sweeteners are used in food systems. The promotion of "no added sugar" and "sugar free" products is examined since the publication of the NACNE report to the end of 1987. To further test the impact of changing patterns of sugar consumption on food and drink manufacturers a national survey of manufacturers who use sugar was carried out in early 1988. This was an attitudinal postal questionnaire and responses to the issue of sugar, diet and health were analysed. Respondents bought an estimated 650,000 tonnes of sugar in 1986, around 45% of the total industrial market. While the survey aggregate were fully supportive of sucrose, respondents reported that the majority of consumers were worried about sugar being bad for health and were actively cutting down on individual intakes. There were significant differences to the issue of sugar, diet and health dependent on company size, whether a company manufactured for a retailer's own label and if products had already been marketed at a "healthy eating" segment. However, in general, while manufacturers considered consumer attitudes to sugar to be important they had to be put in the context of other factors. So far the impact of changing patterns of sugar consumption is not reflected in the total average industrial purchases of sugar, although substantial "sugar-free" and "sugar-reduced" product niches have been established.
Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 17. Preparation of aliphatic amino acid derived gamma-alkoxycarbonyl-amino-beta-oxo ylides and pyrolysis to give alpha,beta-acetylenic gamma-amino acid and GABA analoguesKarodia, Nazira; Aitken, R.A.; Massil, T.; Young, R.J. (2002)A series of eleven alpha-aminoacyl stabilised phosphorus ylides 9-19 have been prepared by condensation of N-alkoxycarbonyl protected amino acids with Ph3P=CHCO2Et using a carbodiimide peptide coupling reagent. Upon ash vacuum pyrolysis at 600 degreesC, these undergo extrusion of Ph3PO to give the corresponding, alpha,beta-acetylenic gamma-amino esters 21-29, 33 and 34 in moderate yield. In two cases the terminal alkynes 30 and 31 are also formed. The beta-aminoacyl ylide 20 from beta-alanine similarly gives the alpha,beta-acetylenic delta-amino ester 35 upon pyrolysis. Regioselective addition of HBr to the triple bond of one acetylenic ester 25 was observed giving a mixture of E and Z alpha-bromoacrylates 36. Hydrogenation of the N-Cbz acetylenic esters 21-23 and 33 results in N-deprotection and hydrogenation of the triple bond to afford the chiral GABA analogues 37-40 in 70 --> 95% ee as determined by F-19 NMR of their Mosher amides. Fully assigned C-13 NMR spectra of all the ylides and acetylenic ester derivatives are presented.
Synthesis, structure and pyrolysis of stabilised phosphonium ylides containing saturated oxygen heterocyclesAitken, R.A.; Karodia, Nazira; McCarron, H.B.; Rouxel, C.; Sahabo, Nina Carole; Slawin, A.M.Z. (2016-04)A range of twelve stabilised phosphonium ylides containing tetrahydrofuran, tetrahydropyran or 2,2- dimethyl-1,3-dioxolane rings have been prepared and fully characterised, including one X-ray structure determination of each type. The X-ray structures confirm the PvC and CvO functions to be syn and all the compounds undergo thermal extrusion of Ph3PO to give the corresponding alkynes. In some cases there is also competing loss of Ph3P to give different carbene-derived products and evidence has been obtained for the generation of 2-phenyloxete in this way. Raising the pyrolysis temperature leads in several cases to new secondary reactions of the alkyne products involving a sequence of alkyne to vinylidene isomerisation, intramolecular CH insertion, and retro Diels Alder reaction.