Lanthanide-Induced Chemical Shifts and the Relative Stereochemistry of Multistriatin, 2,4-Dimethyl-5-ethyl-6,8-dioxabicyclo[3.2.1]octane

The ¹H NMR spectra of the four diastereomers of multistriatin, 2,4-dimethyl-5-ethyl-6,8-dioxabicyclo[3.2.1]octane (1α-δ), and of frontalin, 1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane (2), were recorded in the presence of the europium paramagnetic shift reagent d₂₇-tris(2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato)europium(III) [(Eu(fod)₃]. The binding of Eu(fod)₃ to each substrate was investigated by comparing observed shift ratios' with those calculated for lanthanide atom positions about each of the oxygen atoms in 1α-δ and in 2. The calculations indicated that for each of these dioxabicyclo[3.2.1] octanes, substrate binding occurred preferentially at one oxygen atom, and that the location of the lanthanide atom was related to steric hindrance about the two potential binding sites. Comparisons of the observed shift ratios for each isomer of 1 with the calculated shift ratios of all isomers of 1 verified the relative stereochemical assignments for these isomers. A correlation between the shift reagent binding site and the biological activity of 1α-δ was observed.