title: Acetylated methyl 1,2-dideoxyhex-1-enopyranuronates in density functional theory conformational studies.
abstract: Geometry optimizations at the B3LYP level and single point calculations at the MP2 level are reported for the (4)H(5) and (5)H(4) conformations of methyl 3,4-di-O-acetyl-1,2-dideoxy-d-arabino-hex-1-enopyranuronate (methyl 3,4-di-O-acetyl-D-glucuronal), and methyl 3,4-di-O-acetyl-1,2-dideoxy-D-lyxo-hex-1-enopyranuronate (methyl 3,4-di-O-acetyl-D-galacturonal). Energy and geometry parameters are presented for the most stable optimized geometries. Conformational analysis of the acetoxy and methoxycarbonyl groups as well as the 1,2-unsaturated pyranoid ring is performed. It is demonstrated that both the acetoxy and methoxycarbonyl groups are planar and prefer cis over trans orientations with respect to the CO-O bond rotations. With regard to the AcO-R bond rotations some of the orientations are forbidden. The (4)H(5)⇌(5)H(4) conformational equilibrium in both methyl 3,4-di-O-acetyl-D-glucuronal (shifted towards (5)H4) and methyl 3,4-di-O-acetyl-D-galacturonal (shifted towards (4)H(5)) is the outcome of the competition between the vinylogous anomeric effect and quasi 1,3-diaxial interactions. It is demonstrated that the orientation of the 4-OAc group influences the strength of the quasi 1,3-diaxial interactions between 3-OAc and 5-COOCH(3) groups. Theoretical results are compared with assignments based on (1)H NMR studies.
authors: Faculty of Chemistry, University of Gdańsk, Sobieskiego 18, PL-80-952 Gdańsk, Poland.
authors: Andrzej
authors: A
authors: Nowacki
authors: Beata
authors: B
authors: Liberek
mesh_terms: D000107:Acetylation; D001688:Biological Products / Q000138:chemical synthesis*; D002236:Carbohydrate Conformation; D006027:Glycosides / Q000138:chemical synthesis*; D009844:Oligosaccharides / Q000138:chemical synthesis*; D011789:Quantum Theory
chemical_list: D001688:Biological Products; D006027:Glycosides; D009844:Oligosaccharides