Fatty acids. VII. The gas-liquid chromatographic properties of all dimethylene interrupted methyl cis,cis-octadecadienoates

First total synthesis of (5Z,9Z)-(+/-)-2-methoxy-5,9-octadecadienoic acid, a marine derived methoxylated analog of taxoleic acid

The first total synthesis for the sponge derived (5Z,9Z)-(+/-)-2-methoxy-5,9-octadecadienoic acid, an analog of taxoleic acid, was accomplished in seven steps and in a 10% overall yield. It was again corroborated that the best strategy to prepare these cis,cis dimethylene interrupted double bonds is the double-alkyne bromide coupling reaction of 1,5-hexadiyne, which provides the advantage of achieving a 100% cis stereochemical purity for both double bonds after hydrogenation under Lindlar conditions. The alpha-methoxy functionality was best prepared via the Mukaiyama reaction of (4Z,8Z)-heptadecadienal with trimethylsilyl cyanide and triethylamine followed by acid hydrolysis. Selective methylation of the hydroxyl group of (5Z,9Z)-(+/-)-2-hydroxy-5,9-octadecadienoic acid was achieved with sodium hydride/methyl iodide when tetrahydrofuran was used as solvent. Complete spectral data is presented, for the first time, for this unusual marine alpha-methoxylated fatty acid.

Changes in lipid content, fatty acid composition and lipoprotein lipase activity in dry goat omental adipose tissue according to tissue site

Water and lipid contents, fatty acid distribution, and lipoprotein lipase activity were determined in 11 samples taken from the Omentum Majus of five dry Alpine goats. Samples were chosen to standardize sampling sites using geometric guide marks representative of different adipose tissue sites. Sample location explained between 20% and 30% of the total variance in water and lipid contents and in lipoprotein lipase activity, and from 5.5% to 45.4% of the total variance in fatty acid distribution. Increased sample thickness was associated with an increase in lipid content and in saturated fatty acid percentages. Samples taken in proximity of the omentum tissue attached to the rumen and abomasum had the highest content. We furthermore found that the levels of 18:2n-6, 18:1n-7, and of branched chain fatty acids were high close to a pila of the rumen which also corresponded to high lipoprotein lipase activity. Concomitant high levels of 16:1n-7, 17:1n-8, and 18:1n-9 may reflect high levels of delta 9 desaturase activity.

Fractionation of fish oil fatty acid methyl esters by means of argentation and reversed-phase high-performance liquid chromatography, and its utility in total fatty acid analysis

The utility of reversed-phase and argentation high-performance liquid chromatography (HPLC) as pre-fractionation methods in fatty acid analysis is discussed. Both HPLC modes were applied to cod liver oil fatty acid methyl esters. Apart from positional isomers, the fractions obtained by reversed-phase HPLC were analysed by gas-liquid chromatography and appear to be free of the usually occurring "critical pairs". The mechanism of retention of the fatty acid methyl esters on low-loaded silver nitrate-impregnated silicas is discussed. It is shown that argentation HPLC is a rapid semi-preparative pre-fractionation method for highly unsaturated fatty esters with 3-6 double bonds.

Fatty acids. XIII. The gas-liquid chromatographic behaviour of dimethylene-interrupted methyl cis-octadecenynoates

All of the dimethylene-interrupted methyl cis-octadecenynoate isomers, except the delta13c,17a isomer, have been prepared by partial hydrogenation of the corresponding methyl octadecadiynoate. Gas-liquid chromatographic analysis of the octadecenymoates has been carried out on Carbowax 20M, DEGA, DEGS, FFAP and Silar 10C stationary phases. The delta3,7 isomers decompose on chromatography. The equivalent chain lengths of all of the remaining methyl cis-octadecenynoates are reported.

Fatty acids, Part X. Raman spectra of all dimethylene interrupted methyl cis, cis-octadecadienoates and octadecadiynoates

The Raman spectra of all the dimethylene interrupted methyl cis, cis-octadecadienoates and octadecadiyonates have been studied. The Raman band positions and their relative intensities for the v(C=C),v(C=C),v(C-H) and beta (CH2) modes are recorded. The height intensity of the bands arising from v(C=C) relative to v(C=O) provides a means of determining the number of cis-ethylenic bonds in a mono-ester. In the acetylenic series, the intensity of the bands arising from v(C=C) relative to v(C=O) failed to indicate with certainty the number of acetylenic bonds in the mono-esters studied, due to the weak intensity of the band due to v(C=O). However a better correlation between the relative intensities of the v(C=C) and beta (CH2) bands is established instead. An attempt to correlate the areas under the bands due to v(C=C), (C=C), (C=O) and beta (CH2) failed to produce any significant results. The Raman spectra of the methyl octadec-cis-10-en-5-ynoate and methyl octadeca-5, 10-diynoate are also recorded.

Fatty acids. VII. Gas-liquid chromatographic properties of all dimethylene interrupted methyl trans,trans-octadecadienoates

All the dimethylene interrupted trans,trans-octadecadienoic acids were synthesised by lithium metal-ammonia reduction of the corresponding octadecadiynoic acids, except for the detla2t,6t isomer, which was obtained by the isomerisation of the delta2c,6c isomer. The gas-liquid chromatographic behaviour of the methyl esters was studied on polar [Carbowax 20M, FFAP, DEGA, DEGS, Silar 10C (recently renamed as Apolar 10) and SP 2330], semi-polar (XE-60), and non-polar (SE-30, OV101 and Apiezon L) stationary phases. The equivalent chain length of each isomer is recorded (including the delta2t,6c isomer) and the possibility of separation of these isomers is discussed.