Monte Carlo MM3(96) conformational analyses of N,N'-dimethylylaramide, N,N'-dimethyl-L-arabinaramide and their 2,3,4-tri-O-acetyl derivatives: Some comparisons

CARB 83

Michael R. Hinton, Michael.Hinton@umontana.edu1, Michael K. Dowd, mkdowd@nola.srrc.usda.gov2, Brian Nicholson, b.nicholson@waikato.ac.nz3, and Donald E. Kiely, donkiely@selway.umt.edu1. (1) Shafizadeh Rocky Mountain Center for Wood and Carbohydrate Chemistry, Department of Chemistry, University of Montana, Missoula, MT 59801, (2) Southern Regional Research Center, U. S. Department of Agriculture, 1100 Robt. E. Lee Blvd, New Orleans, LA 70124, (3) Department of Chemistry, University of Waikato, Hamilton, New Zealand
Converging Monte Carlo conformational analyses of N,N'-dimethylxylaramide, N,N'-dimethyl-L-arabinaramide and their 2,3,4-tri-O-acetyl derivatives were carried out using a novel Monte Carlo search method in conjunction with MM3(96). Six starting conformations of each molecule were fully energy-minimized using MM3's block diagonal/full matrix optimization option at multiple dielectric constants. Torsion angles were driven in increments of 120º. A new conformer was defined as differing from any other conformer by a torsion angle of > 2.5º, generating 26x1018 possible solutions for the more complex tri-O-acetyl derivatives. Conformer populations were calculated according to a partition function and complimentary statistical formula. Theoretical average 1H vicinal coupling constants were then compared to experimental values obtained in appropriate NMR solvents. Calculated low energy structures were compared to the x-ray structures of these aldaramides as illustrated in the Figure.

 

General Posters
6:00 PM-8:00 PM, Tuesday, August 21, 2007 BCEC -- Exhibit Hall - B2, Poster

Division of Carbohydrate Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007