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Isolation and characterisation of an unexpected byproduct in the regioselective butane diacetal protection of α-methyl galactopyranoside

Isolation and characterisation of an unexpected byproduct in the regioselective butane diacetal protection of α-methyl galactopyranoside
Isolation and characterisation of an unexpected byproduct in the regioselective butane diacetal protection of α-methyl galactopyranoside
The regioselective protection of both methyl galactopyranoside anomers at the 2 and 3-positions as the butane diacetal (BDA) is well known. Here we describe the formation of an unexpected byproduct, which mainly occurs when α-methyl galactopyranoside is reacted with 2,3-butanedione under BF3•OEt2 catalysis. The structure of the byproduct, which did not arise from anomerisation to the β-anomer or from BDA formation at the galactopyranoside 3,4-positions, was elucidated by NMR and X-ray crystallographic analysis, and proved to be the expected BDA protected galactopyranoside, but in which the stereochemistry of both its BDA acetal centres are inverted. Interestingly, the conformation of the resulting six-membered BDA ring was distorted to a skew boat conformation in order to maintain anomeric stabilisation.
Galactose, Butane diacetal, regioselective, Conformation
0008-6215
14-17
Fontenelle, Clement Q.
929410b0-7dcb-4c83-a9f7-ef2be8e81fbb
Kuppala, Ramakrishna
c92bd85a-9009-4d33-99ca-a9ee3b457d44
Light, Mark
cf57314e-6856-491b-a8d2-2dffc452e161
Linclau, Bruno
19b9cacd-b8e8-4c65-af36-6352cade84ba
Fontenelle, Clement Q.
929410b0-7dcb-4c83-a9f7-ef2be8e81fbb
Kuppala, Ramakrishna
c92bd85a-9009-4d33-99ca-a9ee3b457d44
Light, Mark
cf57314e-6856-491b-a8d2-2dffc452e161
Linclau, Bruno
19b9cacd-b8e8-4c65-af36-6352cade84ba

Fontenelle, Clement Q., Kuppala, Ramakrishna, Light, Mark and Linclau, Bruno (2018) Isolation and characterisation of an unexpected byproduct in the regioselective butane diacetal protection of α-methyl galactopyranoside Carbohydrate Research, 455, pp. 14-17. (doi:10.1016/j.carres.2017.10.023).

Record type: Article

Abstract

The regioselective protection of both methyl galactopyranoside anomers at the 2 and 3-positions as the butane diacetal (BDA) is well known. Here we describe the formation of an unexpected byproduct, which mainly occurs when α-methyl galactopyranoside is reacted with 2,3-butanedione under BF3•OEt2 catalysis. The structure of the byproduct, which did not arise from anomerisation to the β-anomer or from BDA formation at the galactopyranoside 3,4-positions, was elucidated by NMR and X-ray crystallographic analysis, and proved to be the expected BDA protected galactopyranoside, but in which the stereochemistry of both its BDA acetal centres are inverted. Interestingly, the conformation of the resulting six-membered BDA ring was distorted to a skew boat conformation in order to maintain anomeric stabilisation.

Text BDA paper_v11_corrected_headings - Accepted Manuscript
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Accepted/In Press date: 29 October 2017
e-pub ahead of print date: 6 November 2017
Published date: 2 January 2018
Keywords: Galactose, Butane diacetal, regioselective, Conformation

Identifiers

Local EPrints ID: 415924
URI: http://eprints.soton.ac.uk/id/eprint/415924
ISSN: 0008-6215
PURE UUID: cddbf0f5-27f9-445b-8474-7d0a1ed5defa
ORCID for Mark Light: ORCID iD orcid.org/0000-0002-0585-0843
ORCID for Bruno Linclau: ORCID iD orcid.org/0000-0001-8762-0170

Catalogue record

Date deposited: 28 Nov 2017 17:31
Last modified: 03 Jan 2018 17:31

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Contributors

Author: Clement Q. Fontenelle
Author: Ramakrishna Kuppala
Author: Mark Light ORCID iD
Author: Bruno Linclau ORCID iD

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