Crystal polymorphism of Methyl 2,3,4-tri-O-acetyl-1-O- (trichloroacetimidoyl)-α-d-glucopyranouronate

The polymorphism of the glycoside donor methyl 2,3,4-tri-O-acetyl-1-O- (trichloroacetimidoyl)-α-d-glucopyranouronate (1) has been investigated. Two polymorphic forms (labelled Forms I and II) have been elucidated and fully characterised by DSC, PXRD and single crystal analysis, both crystallizing in the space group P2₁. Form I was obtained by crystallization from a wide range of solvents, while Form II was obtained only from ethyl acetate or isopropanol on certain occasions. Unit cell dimensions for Form I are a 14.0292(12), b 8.9641(8), c 16.8580(14) Å, β 94.285(2), and for Form II a 11.266(3), b 6.8889(17), c 13.921(4) Å, β 101.161(6). Z' is 2 for Form I and 1 for Form II. Form I displays two moderate intermolecular hydrogen bonds in the unit cell whereas Form II shows no moderate hydrogen-bonding motifs. All three molecules in the two polymorphs differ significantly in their conformations, especially with respect to the methyl carboxylate and trichloroacetimidoyl groups.