Stereochemical features of Lewis acid-promoted glycosidations involving 4'-spiroannulated DNA building blocks.
Tin tetrachloride-catalyzed glycosidation of persilylated nucleobases with acetate donor 6 in CH(2)Cl(2) solution followed by deprotection gave rise very predominantly to alpha-spironucleosides. These stereochemical assignments stem from the determination of NOE interactions and an X-ray crystallographic analysis of the latter product. Computational studies revealed that these results are consistent with the fact that the C5' substituent shields the beta-face of the oxonium ion involved in the coupling reaction while the C3' substituent is projected away from the alpha-underside. Attack from the more open direction is therefore kinetically favored. Entirely comparable calculations suggested that donor 19 should behave comparably. Experimentation involving this donor gave results consistent with this model although more equitable alpha/beta spironucleoside product ratios were seen when acetonitrile was employed as the reaction medium.
Paquette
Leo A
LA
Evans Chemical Laboratories, The Ohio State University, Columbus, Ohio 43210, USA. paquette.1@osu.edu
Seekamp
Christopher K
CK
Kahane
Alexandra L
AL
Hilmey
David G
DG
Gallucci
Judith
J
D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D018716:Molecular Mimicry; D015394:Molecular Structure; D013141:Spiro Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D017971:Tin Compounds / Q000737:chemistry
D006027:Glycosides; D013141:Spiro Compounds; D017971:Tin Compounds; C041694:stannic chloride; C004511:butenolide; D004247:DNA; D015107:4-Butyrolactone