M. J. Cryle, J. J. De Voss / Tetrahedron: Asymmetry 18 (2007) 547–551
551
0.24 lmol) were dissolved in CH2Cl2 (100 lL). Ibuprofen
Acknowledgement
acid chloride solution (50 lL) ((S)- or rac ibuprofen acid
chloride in CH2Cl2, 5 mg mLÀ1, 1.1 lmol) and pyridine
(50 lL) were added sequentially and the reaction left for
2 h at room temperature. The mixture was then concen-
trated to dryness under a stream of nitrogen before being
re-dissolved in diethyl ether (200 lL) for GC or GC–MS
analysis.
The authors are grateful to Professor S. K. Chapman for
donation of the relevant expression plasmids.
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The analysis of the products of fatty acid oxidation by
P450BM3 required not only resolution of enantiomers but
also the best possible separation of the regioisomers present
in the product mixture. The following GCMS programme
was therefore employed for C14–C16 fatty acids: 30 m DB-
5 column, splitless mode, 2.0 min sampling time; column
flow 2.5 mL minÀ1; total flow 46.4 mL minÀ1; injector
250 °C; detector 250 °C; oven 100 °C (1.0 min equilibra-
tion) hold for 2.0 min, ramp 16 °C minÀ1 to 300 °C and
hold for 20.5 min (total programme time 35.0 min).
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(S)-isomer 17.03 min, (R)-isomer 17.32 min; C14 x-2 (S)-
isomer 17.36 min, (R)-isomer 17.72 min; C14 x-1 (S)-isomer
17.64 min, (R)-isomer 18.06 min. Pentadecanoic acid turn-
over—C15 x-3 (S)-isomer 17.97 min, (R)-isomer 18.29 min;
C15 x-2 (S)-isomer 18.35 min, (R)-isomer 18.78 min; C15
x-1 (S)-isomer 18.71 min, (R)-isomer 19.15 min. Hexadeca-
noic acid turnover—C16 x-3 (S)-isomer 19.07 min, (R)-iso-
mer 19.46 min; C16 x-2 (S)-isomer 19.53 min, (R)-isomer
20.07 min; C16 x-1 (S)-isomer 19.96 min, (R)-isomer
20.50 min.
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The following GC–MS program was employed for the C12
fatty acid: 30 m DB-5 column, splitless mode, 2.0 min sam-
pling time; column flow 2.5 mL minÀ1; total flow 46.4 mL
minÀ1; injector 250 °C; detector 250 °C; oven 100 °C
(1.0 min equilibration) hold for 2.0 min, ramp 15 °C minÀ1
to 200 °C and hold for 8.0 min; ramp 9 °C minÀ1 to 315 °C
and hold for 15.6 min (total programme time 45.0 min).
Retention times: Dodecanoic acid turnover—C12 x-3 (S)-
isomer 26.11 min, (R)-isomer 26.44 min; C12 x-2 (S)-isomer
26.44 min, (R)-isomer 26.86 min; C12 x-1 (S)-isomer
26.77 min, (R)-isomer 27.18 min.
To improve the sensitivity of analyses, single ion monitor-
ing (SIM) can also be used, monitoring m/z 74, 206 and the
fragment caused by the loss of O-ibuprofen from the main
methylated fatty acid chain (e.g., m/z 213 for C12 FA,§ m/z
241 for C14 FA, m/z 255 for C15 FA, m/z 269 for C16 FA
(see Fig. 1).
§ FA—fatty acid.