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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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.
Relationship between artificially sweetened and sugar-sweetened cola beverage consumption during pregnancy and preterm delivery in a multi-ethnic cohort: analysis of the Born in Bradford cohort study.Petherick, E.S.; Goran, M.I.; Wright, J. (2014-02)The aim of this study was to investigate the relationship between the intake of sugar-sweetened (SS) and artificially sweetened (AS) cola beverages during pregnancy and the risk of preterm delivery (PTD). At baseline (2007–2010), 8914 pregnant women were recruited to the Born in Bradford birth cohort study at 24–28 weeks of pregnancy. Women completed a questionnaire describing their health and lifestyle behaviours, including their consumption of AS and SS cola beverages reported as cups per day, which were then linked to maternity records. The relationship between SS and AS cola beverage consumption was examined using logistic regression analyses. No relationship was observed between daily AS cola beverage consumption and PTD. Women who drank four cups per day of SS cola beverages had higher odds of a PTD when compared with women who did not consume these beverages daily. We conclude that high daily consumption of SS cola beverages during pregnancy is associated with increases in the rate of PTD.