Journal of Lipid Research, Vol 21, 326-338, Copyright © 1980 by Lipid Research, Inc.
Proton nuclear magnetic resonance identification and discrimination of side chain isomers of phytosterols using a lanthanide shift reagent
T Iida, T Tamura and T Matsumoto
Proton nuclear magnetic resonance (1H-NMR) spectra at 90 MHz were measured
for a number of side chain isomers of phytosterols (sterols with a C8H17
side chain, and delta 24-, 24-methylene, delta 22-, 24- ethylidene,
24-methly, 24-ethyl, 24-methyl-delta 22-, 24-ethyl delta 22- , and
24-ethyl-delta 22,25(27)-sterols) with or without a lanthanide shift
reagent, tris[1,1,1,2,2,3,3 - heptafluoro - 7,7 - dimethyloctane - 4,6 -
dionato]ytterbium, Yb(fod)3, and the effect of Yb(fod)3 on the side chain
methyl protons is discussed. The change of the chemical shifts induced
Yb(fod)3 for the side chain methyls was expressed in terms of the induced
shift ratios (ISR values), i.e., the ratios of the induced chemical shifts
of the respective side chain methyls to that of the fastest moving side
chain methyl. The ISR values were sentitive to minor structural and
stereochemical differences, but almost independent of ring structures and
of substrate concentrations, thus providing confirmatory evidence for the
side chain structures. Also, the Yb(fod)3- induced spectral patterns
observed in the high-field methyl region bore the fingerprints of the side
chain structures. Several isomeric pairs of sterols, which differ only in
the geometry of double bonds or the absolute configuration at C-24 in the
side chain, i.e., cis- and trans-isomers of delta 22-and 24-ethylidene
sterols, 24R/alpha- and 24S/beta-methyl sterols, 24R/alpha- and
24S/beta-ethyl sterols, and 24S/alpha- and 24R/beta-ethyl-delta 22-sterols,
could be differentiated from each other under the influence of Yb(fod)3,
even though they were measured at 90 MHz.
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