Studies of the synthesis of cyclodextrins with novel stereochemistry

Tahanpesar, Elham. 2007. Studies of the synthesis of cyclodextrins with novel stereochemistry. PhD Thesis, Cardiff University.

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Abstract

Proton-deuterium exchange of the carbinol hydrogens of gluco-, manno- and galacto-methyl- ot-D-pyranosides with deuterium oxide catalysed by ultrasonicated Raney nickel had low regioselectivity. 4,6-0-Benzylidene-methyl-cc-D-glucopyranoside underwent deuteration at C- 2 and C-3 and cleavage of the benzylidene group, whereas 4,6-O-isopropylidene-methyl-a-D- glucopyranoside was deuterated exclusively at C-2 (2H-NMR), which provides a rapid and economical route to 2- 2Hi -methyl-a-D-glucopyranoside. The diol moiety of 4,6-0-benzylidene-methyl-a-D-glucopyranoside was cleaved under aqueous (sodium periodate), and non-aqueous (periodic acid) conditions to give a D-erythritol in high yield (80%, 90%). Application of similar conditions to heptakis{6-0-tert- butyldimethylsilyl)-p-cyclodextrin failed to give an isolable product. The epoxides methyl 2,3-anhydro-4,6-(9-benzylidene-methyl-a-D-mannopyranoside and /z67ta£w(2,3-anhydro)-f3-cyclomannin were prepared via the C2-tosylates. Both reacted with 4-ter/-butylbenzylthiol at the 3-position. The cyclomannin gave an adduct with xQ&,-altro stereochemistry as determined by NMR and the homogeneity was established by MALDI-MS (M+K+, m/z 3109.5, Ci6iH26602sS7Si7K). The mannopyranoside similarly reacted with L- cysteine to give a 4Ci-a//ro-amino acid sugar adduct, but the cyclomannin failed to react. The benzylidene-, isopropylidene- glucopyranosides and the silylated cyclodextrin mentioned above underwent allylation with allyl bromide, to give 2,3-di-O-allyl-glucopyranosides and heptakis(2,3-di-0-allyl)-p-CD respectively. Ring closing metathesis (RCM) with Grubb's 2nd generation catalyst of the allylated cyclodextrin yielded a complex mixture, but the allylated glucopyranosides yielded the cyclo-octenes, which were hydrogenated. Unexpectedly, the benzylidene protecting group was partially cleaved during RCM. All NMR spectra were assigned by correlation methods.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
ISBN:	9781303209284
Date of First Compliant Deposit:	30 March 2016
Last Modified:	12 Feb 2016 23:12
URI:	https://orca.cardiff.ac.uk/id/eprint/54588

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