Reilly, Peter

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reilly@iastate.edu
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Reilly
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Peter

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MM# Modeling of Aldopentose Pyranose Rings

2002-01-01 , Dowd, Michael , Rockey, William , Reilly, Peter , French, Alfred , Reilly, Peter , Chemical and Biological Engineering

MM3 (version 1992, ϵ=3.0) was used to study the ring conformations of d-xylopyranose, d-lyxopyranose and d-arabinopyranose. The energy surfaces exhibit low-energy regions corresponding to chair and skew forms with high-energy barriers between these regions corresponding to envelope and half-chair forms. The lowest energy conformer is 4 C 1 for α- and β-xylopyranose and α- and β-lyxopyranose, and the lowest energy conformer is 1 C 4 for α- and β-arabinopyranose. Only α-lyxopyranose exhibits a secondary low-energy region (1 C 4) within 1 kcal/mol of its global minimum. Overall, the results are in good agreement with NMR and crystallographic results. For many of these molecules, skew conformations are found with relatively low energies (2.5 to 4 kcal/mol above lowest energy chair form). The 2 S O and 1 C 4conformers of crystalline benzoyl derivatives of xylopyranose are in secondary low-energy regions on the β-xylopyranose surface, within 3.8 kcal/mol of the global 4 C 1 minimum.

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Modeling of deoxy- and dideoxyaldohexopyranosyl ring puckering with MM3(92)

2001-10-01 , Rockey, William , Dowd, Michael , Reilly, Peter , Reilly, Peter , French, Alfred , Chemical and Biological Engineering

Extensive variations of the ring structures of three deoxyaldohexopyranoses, l-fucose, d-quinovose, and l-rhamnose, and four dideoxyaldohexopyranoses, d-digitoxose, abequose, paratose, and tyvelose, were studied by energy minimization with the molecular mechanics algorithm MM3(92). Chair conformers, 4C1 ind-quinovose and the equivalent 1C4 in l-fucose and l-rhamnose, overwhelmingly dominate in the three deoxyhexoses; in the d-dideoxyhexoses, 4C1 is again dominant, but with increased amounts of 1C4 forms in the α anomers of the three 3,6-dideoxyhexoses, abequose, paratose, and tyvelose and in both α and β anomers of the 2,6-dideoxyhexose d-digitoxose. In general, modeled proton–proton coupling constants agreed well with experimental values. Computed anomeric ratios strongly favor the β configuration except ford-digitoxose, which is almost equally divided between α and β configurations, and l-rhamnose, where the β configuration is somewhat favored. MM3(92) appears to overstate the prevalence of the equatorial β anomer in all three deoxyhexoses, as earlier found with fully oxygenated aldohexopyranoses.