Modeling of deoxy- and dideoxyaldohexopyranosyl ring puckering with MM3(92).
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, 4C(1) in D-quinovose and the equivalent 1C(4) in L-fucose and L-rhamnose, overwhelmingly dominate in the three deoxyhexoses; in the D-dideoxyhexoses, 4C(1) is again dominant, but with increased amounts of 1C(4) forms in the alpha anomers of the three 3,6-dideoxyhexoses, abequose, paratose, and tyvelose and in both alpha and beta 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 beta configuration except for D-digitoxose, which is almost equally divided between alpha and beta configurations, and L-rhamnose, where the beta configuration is somewhat favored. MM3(92) appears to overstate the prevalence of the equatorial beta anomer in all three deoxyhexoses, as earlier found with fully oxygenated aldohexopyranoses.
Rockey
W M
WM
Department of Chemical Engineering, Iowa State University, Ames, IA 50011, USA.
Dowd
M K
MK
Reilly
P J
PJ
French
A D
AD
D000465:Algorithms; D002236:Carbohydrate Conformation; D003837:Deoxy Sugars / Q000737:chemistry*; D003847:Deoxyglucose / Q000737:chemistry; D005643:Fucose / Q000031:analogs & derivatives* / Q000737:chemistry; D006601:Hexoses / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D012210:Rhamnose / Q000737:chemistry; D012984:Software; D013816:Thermodynamics
D003837:Deoxy Sugars; D006601:Hexoses; D005643:Fucose; C009616:tyvelose; C022880:paratose; C023708:abequose; D003847:Deoxyglucose; C020615:digitoxose; D012210:Rhamnose