✍ Scribed by Ludovic Drouin; E. Cristina Stanca-Kaposta; Priptal Saundh; Antony J. Fairbanks; Sebastian Kemper; Timothy D. W. Claridge; John P. Simons
No coin nor oath required. For personal study only.
The effect of carbon is subtle but sweet: The flexible C‐linkage in the newly synthesised C‐glycosyl mimetic, Manα(1,6)‐C‐ManαOPh allows OHπ bonding, both in the gas phase and in aqueous solution. This interaction is absent in the O‐linked disaccharide (see figure).magnified image
The intrinsic conformational preference of a newly synthesised glycomimetic, the __C‐__linked disaccharide Manα(1,6)‐C‐ManαOPh (1), has been determined in the gas phase at about 10 K by infrared ion dip spectroscopy coupled with density functional theory and ab initio calculations, and compared with its dynamical conformation in aqueous solution at 298 K by NMR spectroscopy. Comparisons are also made between these conformations and those of the corresponding O‐linked disaccharide 2 in the gas phase and the C‐linked disaccharide Manα(1,6)‐C‐ManαOMe (3) in the gas phase and in aqueous solution. The C‐ and O‐linked disaccharides 1 and 2 present quite distinct conformational preferences in the gas phase: inter‐glycosidic hydrogen bonding, seen in one of the two conformers populated in 2, is not seen in 1 which adopts a conformation (not populated in 2) with glycosidic dihedral angles (ϕ, ψ, ω) of −72°, 52° and 66°; supported in part by an OHπ hydrogen bond. This conformer is also strongly populated in an aqueous solution of 1 (and very weakly, of 3) together with a second conformer, with dihedral angles (ϕ, ψ, ω) of about −60°, 180° and 60°, not seen in the gas phase but by far the dominant conformer in an aqueous solution of 3. The C‐disaccharide 1 was tested as a potential inhibitor, but displayed no significant inhibitory activity against Jack Bean α‐mannosidase.
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