| dc.contributor.author | Namazi, Hassan. | en_US |
| dc.date.accessioned | 2014-10-21T12:34:58Z | |
| dc.date.available | 1997 | |
| dc.date.issued | 1997 | en_US |
| dc.identifier.other | AAINQ24757 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55495 | |
| dc.description | Dialkylstannylene acetals are known to be very useful intermediates for the regioselective preparation of monosubstituted derivatives of diols and polyols and are widely used during syntheses of complex carbohydrates. The factors that influence the regioselectivity of reactions of different dialkylstannylene acetals of three cis-1,2-diols on pyranose rings, namely methyl 4,6-O-benzylidene-$\alpha$- scD-mannopyranoside (34) and methyl 4,6-O-benzylidene- $\alpha$- and $\beta$- scD-allopyranoside (54 and 60), were investigated in detail. Dialkylstannylene acetals of compound 34 react at O-2 or O-3 depending on reaction conditions, while those of compounds 54 and 60 react only at O-2. It was shown by $\sp{119}$Sn NMR spectroscopy that dialkylstannylene acetals of compound 34 exist in chloroform-d solutions mainly as mixtures of a dimer and a trimer, those of compound 54 are mixtures of two dimers, while those of compound 60 are mainly one dimer. The structures of these species were determined. The factors influencing reaction regioselectivity for these intermediates include the nature of the species present in solution and the reactivities of the oxygen atoms in the different species present. | en_US |
| dc.description | Clustering of oligosaccharide molecules on cell surfaces are important for their biological activity. Methodology was developed for the regioselective preparation of small non-glycosidically linked clusters in high yields from dibutylstannylene acetal intermediates. Many different small clusters were formed by linking a number of different monosaccharides via ester linkages formed by reaction with a wide variety of di- or tri-functional electrophiles. | en_US |
| dc.description | Cyclodextrins are very useful as complexing agents for drugs and other biologically active molecules and there has been intense interest in preparing modified derivatives. Methods have been developed that give by far the highest yields known of two substituted derivatives that have been widely used in syntheses, namely heptakis-(6-O-tert-butyldimethylsilyl)-2-O-p-toluenesulfonyl-$\beta$-cyclodextrin (114) and heptakis-(6-O-tert-butyldimethylsilyl-2-O-p-toluenesulfonyl)-$\beta$-cyclodextrin (118). Dimeric silylated $\beta$-cyclodextrins (119-121) were also prepared but broadening in their NMR spectra limited precise determination of their structures. Evidence was obtained from variable temperature $\sp1$H NMR spectra that the hydrogen bonding in compound 118 is very unusual. The two different types of hydroxyl hydrogens are both extremely reluctant to exchange with each other and, at the same time, are involved in rapid exchange between "flip-flop" hydrogen-bonding sites. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1997. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Chemistry, Organic. | en_US |
| dc.title | Novel regioselective syntheses of carbohydrate clusters and beta-cyclodextrin derivatives and studies of the reactions of dialkylstannylene acetals of carbohydrate-derived cis-1,2-diols. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
