Conformational aspects of 6-N-aryl-glycosides: X-ray and vibrational spectroscopic studies

Abstract

This study investigates the structural and conformational features of novel 6-N-aryl-galactosides, specifically 4-halo-6-deoxy-1,2:3,4-di-O-isopropylidene-6-N-phenylamino-α-d-galactopyranosides, using a combination of spectroscopic techniques. Comparative analyses were performed using single-crystal X-ray diffraction, FT-IR, and FT-Raman vibrational spectroscopy to elucidate structural similarities and differences among the derivatives. Two crystallographically independent molecules were observed in the asymmetric unit of the p‑chloro compound, and four in that of the p-fluoro compound, all exhibiting close structural resemblance. Key inter- and intramolecular interactions governing crystal packing and conformational variability were identified. The 6-C substituent displayed notable flexibility in the solid state. Unlike the typical perpendicular orientation in C1-substituted glycosides, the C6-N-galactosides exhibited a planar arrangement of the aromatic and sugar rings. The pyranose ring adopted an °S₂ twist-boat conformation, as confirmed by torsional analysis. These interactions also led to distinct supramolecular assemblies in the p‑chloro and p-fluoro derivatives.