Synthesis and NMR properties of positional isomers of methyl allenic fatty esters

Novel halo-oxo-allenic fatty ester derivatives from epoxidized methyl santalbate (methyl trans-11-octadecen-9-ynoate)

Methyl santalbate (methyl trans-11-octadecen-9-ynoate) from Sandal wood seed oil, Santalbum alum) was epoxidized to methyl trans-11,12-epoxy-octadec-9-ynoate (1). Treatment of compound 1 with tetrabutylammonium dihydrogentrifluoride, and boron trifluoride etherate gave the corresponding anti- (2a) (57%) and syn- (2b) (35%) fluorohydrin derivatives, respectively. These reactions were regio- and stereoselective in nature. The structures of the anti- and syn- isomers were confirmed by NMR spectroscopy. Ring opening of the epoxy system of compound 1 with lithium chloride gave the anti-chlorohydrin derivative (3) (89%). Oxidation of either compound 2a or 2b gave the same fluoro-keto acetylenic fatty ester (4) (75%), and compound 3 on chromic acid oxidation yielded the corresponding chloro-keto acetylene (5) (73%). Isomerization of compounds 4 and 5 with potassium carbonate in dichloromethane furnished the requisite fluoro-allenic (6) (63%, methyl 11-fluoro-12-oxo-9,10-octadecadienoate) and chloro-allenic (7) (80%, methyl 11-chloro-12-oxo-9,10-octadecadienoate) C(18) fatty esters. All products were confirmed by a combination of spectrometric and spectroscopic techniques.

Structure analysis of an allene-containing estolide tetraester triglyceride in the seed oil of Sebastiana commersoniana (Euphorbiaceae)

The seed oil of Sebastiana commersoniana (Euphorbiaceae) was separated into triglyceride and an estolide fraction by preparative thin-layer chromatography. The triglyceride band was characterized by spectroscopic methods, and its fatty acids have been analyzed by gas chromatography (GC) and GC-mass spectrometry (MS) as their methyl esters. Linolenic acid was the main fatty acid (65%). The estolide band was examined by a combination of spectroscopic and chromatographic methods (ultraviolet, infrared, nuclear magnetic resonance, fast atom bombardment-MS, GC-MS of the fatty acids before and after silylation) and was identified as a tetraglyceride, where one alpha-carbon of the triglyceride backbone was esterfied with 8-hydroxy-5,6-octadienoic acid, which itself was esterfied with trans-2,cis-4-decadienoic acid. The remaining positions of the triglyceride backbone were occupied by common fatty acids.