Abstract
The effect of different leaving groups on the substitution versus elimination outcomes with C-5 d-glucose derivatives was investigated. The stereochemical configurations of 3-O-benzyl-1,2-O-iso-propyl-idene-5-O-methane-sulfonyl-6-O-tri-phenyl-methyl-α-d-gluco-furan-ose, C36H38O8S (3) [systematic name: 1-[(3aR,5R,6S,6aR)-6-benz-yloxy-2,2-di-methyl-tetra-hydro-furo[2,3-d][1,3]dioxol-5-yl)-2-(trit-yloxy)ethyl methane-sulfonate], a stable inter-mediate, and 5-azido-3-O-benzyl-5-de-oxy-1,2-O-iso-propyl-idene-6-O-tri-phenyl-methyl-β-l-ido-furan-ose, C35H35N3O5 (4) [systematic name: (3aR,5S,6S,6aR)-5-[1-azido-2-(trit-yloxy)eth-yl]-6-benz-yloxy-2,2-di-methyl-tetra-hydro-furo[2,3-d][1,3]dioxole], a substitution product, were examined and the inversion of configuration for the azido group on C-5 in 4 was confirmed. The absolute structures of the mol-ecules in the crystals of both compounds were confirmed by resonant scattering. In the crystal of 3, neighbouring mol-ecules are linked by C-H⋯O hydrogen bonds, forming chains along the b-axis direction. The chains are linked by C-H⋯π inter-actions, forming layers parallel to the ab plane. In the crystal of 4, mol-ecules are also linked by C-H⋯O hydrogen bonds, forming this time helices along the a-axis direction. The helices are linked by a number of C-H⋯π inter-actions, forming a supra-molecular framework.
Highlights
The effect of different leaving groups on the substitution versus elimination outcomes with C-5 d-glucose derivatives was investigated
In the crystal of 3, neighbouring molecules are linked by C—HÁ Á ÁO hydrogen bonds, forming chains along the b-axis direction
In our development of novel iminosugars (Simone et al, 2012; Soengas et al, 2012; Reed et al, 2013), we viewed the installation of a C-5 disposed double bond and the ability to stereoselectively substitute at C-5 as critical to analogue development
Summary
Nucleophilic substitution reactions and their competition with elimination are mechanistically complex processes in carbohydrate systems (Latham et al, 2017; Monnier et al, 2008; Kroh et al, 2008; Hayase et al, 2002; Jin et al, 2008; Chheda et al, 2007; Reza et al, 2014; Srokol et al, 2004; Chuntanapum & Matsumura, 2010; Stemann et al, 2013). In our development of novel iminosugars (Simone et al, 2012; Soengas et al, 2012; Reed et al, 2013), we viewed the installation of a C-5 disposed double bond (through elimination) and the ability to stereoselectively substitute at C-5 (through substitution) as critical to analogue development. To effect these transformations in an orthogonal manner (Fig. 1), we probed the nature of the C-5 leaving group through the introduction of a mesylate (2) and a triflate moiety (3), which could be either displaced or eliminated. Reaction conditions to afford the regioselective elimination product/s with a C-4/C-5 and/or a C-5/C-6 disposed double bond are currently under investigation
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