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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Synthetic approaches to the angucycline antibiotics

Osman, Hasnah, n/a January 2005 (has links)
The stereoselective synthesis of urdamycinone B (17) was achieved in a 21% overall yield from C-glycosyl-naphthoquinone 197. The key reaction was the Diels-Alder cycloaddition reaction of 197 and siloxydiene (�)-117 promoted by a chiral Lewis acid derived from (S)-3,3�-diphenyl-1,1�-binaphthalene-2,2�-diol (291), BH₃.THF and acetic acid. An effective kinetic resolution of (�)-117 occurred. Four cycloadducts 199a-d were formed in a ratio between 84:8:2:6 and 70:9:2:19. Aromatisation of the mixture by treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gave 200a and 200b in 4:1 ratio. A sequence of reactions involving deacetylation, conversion of a phenyldimethylsilyl group into a hydroxyl group and photooxidation gave a 4:1 mixture of urdamycinone B (17) and its C-3 epimer (154). Separation of these products was achieved by high performance liquid chromatography (HPLC). The C-glycosyl donor, 1,3,4-tri-O-acetyl-2,6-dideoxy-D-glucopyranose (204), was synthesised from readily accessible tri-O-acetyl-D-glucal (237) using two approaches. The first involved a sequence of deacetylation, tosylation, lithium aluminium hydride (LiAlH₄) reduction and acetylation to give di-O-acetyl-6-deoxy-D-glucal (242). The triphenylphosphine hydrogen bromide (TPPHBr) catalysed addition of acetic acid to 242 gave 204 in overall yields ranging from 0 to 32%. The step involving the reduction of the tosylate intermediate was the cause of the variable yields. The alternative synthesis started with the TPPHBr catalysed addition of benzyl alcohol to 237. Subsequent deacetylation, tosylation and reduction with LiAlH₄ gave benzyl 2,6-dideoxy-D-glucopyranoside (250). Acetylation and hydrogenolytic debenzylation gave 3,4-di-O-acetyl-2,6-dideoxy-D-glucopyranose (247). Acetylation gave 204 in 40% overall yield. A third approach to 204 involved selective tosylation of methyl α-D-mannopyranoside (258) and subsequent treatment with 2,2-dimethoxypropane under acidic conditions to give acetonide 255. LiAlH₄ reduction of the tosylate gave methyl 6-deoxy-2,3-O-isopropylidene-α-D-mannopyranoside (256). Acidic hydrolysis of 256 and subsequent acetylation afforded 1,2,3,4-tetra-O-acetyl-6-deoxy-α-D-mannopyranoside (260). Treatment of 260 with hydrogen bromide in acetic acid and subsequent reductive elimination with a zinc-copper couple gave 242. The addition of acetic acid catalysed by TPPHBr afforded 204 in 18% overall yield. The final synthesis of 204 started with thiophenyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside (269). A sequence of deacetylation, tosylation and LiAlH₄ reduction gave thiophenyl 2,3-O-isopropylidene-6-deoxy-α-D-mannopyranoside (274). The structure of 274 was confirmed from a single crystal X-ray diffraction study. Hydrolysis of the isopropylidene group of 274 and subsequent acetylation afforded thiophenyl 6-deoxy-2,3,4-tri-O-acetyl-α-D-mannopyrannoside (282). Treatment of 282 with iodine monobromide and subsequent reductive elimination with zinc-copper couple gave 242. The TPPHBr catalysed addition of acetic acid to 242 afforded 204 in 19% overall yield. Differentially protected C-glycosyl donor, 1,3-di-O-acetyl-4-O-benzyl-2,6-dideoxy-D-mannopyranose (265), was synthesised from 274. The benzylation of 274 gave thiophenyl 6-deoxy-2,3-O-isopropylidene-4-O-benzyl-α-D-mannopyranoside (276). Acidic hydrolysis followed by acetylation afforded thiophenyl 6-deoxy-1,2-di-O-acetyl-4-O-benzyl-α-D-mannopyranoside (278) which, upon bromination by iodine monobromide, gave thiophenyl 6-deoxy-1,2-di-O-acetyl-4-O-benzyl-α-D-mannopyranosyl bromide (279). The reductive elimination of 279 with zinc-copper couple gave 3-O-acetyl-4-O-benzyl-6-deoxy-D-glycal (264). The TPPHBr catalysed addition of acetic acid to 264 afforded 1,3-di-O-acetyl-4-O-benzyl-2,6-dideoxy-D-mannopyranose (265) in 16% overall yield from 274. The instabillity of bromide 279 affected the yield of 265. A C-glycosylation study of 2-naphthol 227 and 1,4-dimethoxy-5-hydroxynaphthalene (205) with 2-deoxy-glycosyl acetates was undertaken. Boron trifluoride diethyl etherate (BF₃.Et₂O) and scandium triflate [Sc(OTf)₃] proved effective promoters. For example, the glycosylation reaction of donor 265 and 227, promoted by 0.5 equivalents of Sc(OTf)₃, afforded C-glycoside 2-hydroxy-1-[3�-O-acetyl-4�-O-benzyl-2,6-dideoxy-β-D-manno-hexopyranosyl]-naphthalene (289) in 85% yield.
82

A study of Glycosides in grapes and wines of Vitis vinifera cv. Shiraz / Patrick George Iland.

Iland, Patrick G. January 2001 (has links)
Includes a list of publications co-authored by the author during the preparation of this thesis. / Bibliography: leaves 103-111. / vi, 111 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Studies the links between grape composition, wine composition and wine sensory properties. Developed a new method of measuring glycoside concentration in grapes (glycosyl-glucose assay) and a modified measurement of wine colour density in red wine. These were used to analyse samples of Shiraz grapes and wines from a comprehensive vineyard irrigation trial. Glycosyl-glucose concentrations shows promise for the prediction of wine composition and flavor intensity. / Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 2001
83

Biosynthesis and translocation of secondary metabolite glycosides in the grapevine Vitis vinifera L.

Gholami, Mansour. January 1996 (has links) (PDF)
Copies of author's previously published articles inserted. Bibliography: leaves 121-144. This study investigates the site of biosynthesis of flavour compounds in the grapevine. Most of the secondary metabolites, including flavour compounds, are glycosylated and stored in plant tissues as glycosides. The chemical properties of these compounds, especially their water solubility, suggests that glycosides might be forms of translocated secondary metabolites in plants.
84

Hot water-soluble glycosides: location in the tissue of Populus grandidentata bark

Erickson, Richard L. 01 January 1969 (has links)
No description available.
85

The effect of the glycon and hydroxyl orientation on alkali-oxygen degradations of methyl glycosides

Hearne, David O. (David Oliver) 01 January 1978 (has links)
No description available.
86

Effect of a 2-O-acetyl substituent on the stereoselectivity of Koenigs-Knorr reactions involving 1,2-cis-glucopyranosyl bromides.

Wallace, Jerry E. 01 January 1975 (has links)
No description available.
87

Mechanisms of alkaline glycosidic bond cleavage in 1,5-anhydro-4-O-

Henderson, Margaret Esther 01 January 1986 (has links)
see pdf
88

Ketone sensitized photochemical degradation of 2-methoxy-6-methyltetrahydropyran

Babcock, Bruce William, January 1980 (has links) (PDF)
Thesis (Ph. D.)--Institute of Paper Chemistry, 1980. / Includes bibliographical references (p. 52).
89

The alkaline degradation of 1,5-anhydro-2,3,6-tri-O-methyl-cellobiitol

Wylie, Thomas R., January 1979 (has links) (PDF)
Thesis (Ph. D.)--Institute of Paper Chemistry, 1979. / Includes bibliographical references (p. 68-69).
90

Alcoholyses of 2,3,4-tri-O-acetyl-[alpha]-D-xylopranosyl bromide and 2,3,4,6-tetra-O-acetyl-[alpha]-D-galactopyranosyl bromide

Counts, K. M. January 1974 (has links) (PDF)
Thesis (Ph. D.)--Institute of Paper Chemistry, 1974. / Includes bibliographical references (leaves 81-84).

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