Synthesis and desaturation of monofluorinated fatty acids 1
作者:Peter H. Buist、Kostas A. Alexopoulos、Behnaz Behrouzian、Brian Dawson、Bruce Black
DOI:10.1039/a701571b
日期:——
A series of monofluoro C16 and C18
fatty acids
have been synthesized and used as mechanistic probes for fatty acid
desaturation. Only fluoroolefinic products are obtained when these
compounds are processed by an in vivo Saccharomyces cerevisiae
ω9 desaturating system as determined by
1H-decoupled 19F NMR and GC–MS analysis. No
evidence for fluorohydrin formation has been found when either methyl
(R,S)-9- or 10-fluoropalmitate (stearate) 3a,b and
5a,b was incubated with the ω9 desaturase. On
desaturation α- and β-fluorine substituent
effects (kH/kF) of magnitude 6.2
and 2.4, respectively, have been measured by direct competition
experiments between 3a and 3b and between methyl 16-fluoropalmitate 3c
and 3b. These results do not support the involvement of discrete
hydroxylated and carbocationic intermediates in fatty acid desaturation.
Substantial apparent steric effects have been observed for
monofluorostearoyl substrates 5c–f bearing a fluorine distal from
the site of initial oxidation. In the case of
(R,S)-methyl 12-fluorostearate 5f, we show that both
enantiomers are desaturated at comparable rates.