New method for GC/FID and GC-C-IRMS analysis of plasma free fatty acid concentration and isotopic enrichment.

A simple, direct and accurate method for the determination of concentration and enrichment of free fatty acids (FFAs) in human plasma was developed. The validation and comparison to a conventional method are reported. Three amide derivatives, dimethyl, diethyl and pyrrolidide, were investigated in order to achieve optimal resolution of the individual fatty acids. This method involves the use of dimethylamine/Deoxo-Fluor to derivatize plasma free fatty acids to their dimethylamides. This derivatization method is very mild and efficient, and is selective only towards FFAs so that no separation from a total lipid extract is required. The direct method gave lower concentrations for palmitic acid and stearic acid and increased concentrations for oleic acid and linoleic acid in plasma as compared to methyl ester derivative after thin-layer chromatography. The [(13)C]palmitate isotope enrichment measured using direct method was significantly higher than that observed with the BF(3)/MeOH-TLC method. The present method provided accurate and precise measures of concentration as well as enrichment when analyzed with gas chromatography combustion-isotope ratio-mass spectrometry.

Mild, efficient Friedel-Crafts acylations from carboxylic acids using cyanuric chloride and AlCl3.

A mild method for Friedel-Crafts acylation with aromatic and aliphatic carboxylic acids using cyanuric chloride, pyridine, and AlCl(3) was developed. Both inter- and intramolecular acylations were achieved at room temperature in high yield and in very short reaction times.

Liquid chromatography-mass spectrometric assay for quantitation of the short-chain fatty acid, 2,2-dimethylbutyrate (NSC 741804), in rat plasma.

2,2-Dimethylbutyrate (DMB) is a potential treatment for thalassemia and hemoglobinopathies. To facilitate pharmacokinetic evaluation of DMB, we developed an LC-MS assay and quantitated DMB in plasma of rats after an oral dose of 500mg/kg. After acetonitrile protein precipitation, DMB and dimethylvaleric acid (DMV) internal standard were derivatized to benzylamides, chromatographed on a Hydro-RP column with acetonitrile, water, and 0.1% formic acid, and detected by electrospray positive-mode ionization mass spectrometry. The assay was accurate (97-107%) and precise (3.4-6.2%) between 100 and 10,000ng/mL. Recovery from plasma was >62%. Plasma freeze-thaw and room temperature stability were acceptable.

Synthesis and mass spectrometry of benzoxazoline, dimethyloxazoline and 4-phenyloxazoline derivatives of polyunsaturated fatty acids.

Cyclic nitrogen moieties have proved to be of great value for the mass spectrometric location of double bonds in polyunsaturated fatty acids. However, their synthesis has traditionally required long reaction times and/or high temperatures. Recently, we introduced a one-pot, high-yield, mild and efficient method for the synthesis of various fatty acid amide derivatives. We have now extended this procedure to include the synthesis of benzoxazoline, dimethyloxazoline and 4-phenyloxazoline analogs of a series of fatty acids containing 18 to 22 carbon atoms and 0 to 6 double bonds. A comparison of the mass spectral properties of the three derivatives of these saturated and unsaturated fatty acids is described.

Ring-closing metathesis approach to dictyostatin.

[reaction: see text] An esterification/ring-closing metathesis approach to dictyostatin and discodermolide is introduced. The approach provides for facile fragment coupling of two main segments of these natural products at the C10-C11 alkene with high to complete Z-selectivity.

One pot direct synthesis of amides or oxazolines from carboxylic acids using Deoxo-Fluor reagent.

A mild and highly efficient one pot-one step condensation and/or condensation-cyclization of various acids to amides and/or oxazolines using Deoxo-Fluor reagents is described. Parallel syntheses of various free fatty acids with 2-amino-2, 2-dimethyl-1-propanol resulted with excellent yields.