Acetylated methyl 1,2-dideoxyhex-1-enopyranuronates in density functional theory conformational studies

作者：Nowacki Andrzej; Liberek Beata^*

来源：Carbohydrate Research, 2013, 371: 1-7.

DOI：10.1016/j.carres.2013.01.009

• Glycuronal
• Mesomeric effect
• Half-chair conformation
• Allylic effect
• Vinylogous anomeric effect
• Quasi 1,3-diaxial interactions

Geometry optimizations at the B3LYP level and single point calculations at the MP2 level are reported for the H-4(5) and H-5(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 H-4(5) reversible arrow H-5(4) conformational equilibrium in both methyl 3,4-di-O-acetyl-D-glucuronal (shifted towards H-5(4)) and methyl 3,4-di-O-acetyl-D-galacturonal (shifted towards H-4(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-COOCH3 groups. Theoretical results are compared with assignments based on H-1 NMR studies.

• 出版日期2013-4-19