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Isolation and structure of a new galactolipid from oat seeds
Author(s) -
Hamberg Mats,
Liepinsh Edvards,
Otting Gottfried,
Griffiths William
Publication year - 1998
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-998-0215-9
Subject(s) - galactolipid , glycolipid , chemistry , chromatography , avena , nuclear magnetic resonance spectroscopy , molecule , stereochemistry , biochemistry , phospholipid , organic chemistry , biology , membrane , ecology
Seeds of oat ( Avena sativa L.) were recently shown to contain significant quantities of a new hydroxy acid, (15 R )‐hydroxy‐(9 Z )‐(12 Z )‐octadecadienoic acid (trivial name, avenoleic acid). In the present work, avenoleate was found to be mainly (63%) localized in the glycolipid fraction of oat seed lipids. Fractionation of the glycolipids by thin‐layer chromatography and reversed‐phase high‐performance liquid chromatography revealed the presence of a main molecular species which accounted for 20% of the total avenoleate content of oat seeds. Structural studies by chemical methods and mass spectrometry demonstrated that the avenoleate‐containing glycolipid was a galactolipid assembled of one molecule of avenoleic acid, two molecules of linoleic acid, two molecules of D‐galactose, and one molecule of glycerol. Degradation of the new galactolipid by chemical and enzymatic methods demonstrated the localization of acyl chains, i.e., linoleate at sn ‐1 and linoleoylavenoleate at sn ‐2. Nuclear magnetic resonance spectroscopy gave independent support for this structure and also demonstrated that the two galactoses formed an α‐ d ‐galactopyranosyl‐1‐6‐β‐ d ‐galactopyranosyl moiety which was bound to the sn ‐3 position. Based on these experiments, the new galactolipid could be formulated as 1‐[(9′ Z ),(12′ Z )‐octadecadienoyl]‐2‐[(15″ R )‐{9″′ Z ), (12″′ Z )‐octadecadienoyloxy}‐(9″ Z ),(12″ Z )‐octadecadienoyl]‐3‐(α‐ d ‐galactopyranosyl‐1‐6‐β‐ d ‐galactopyranosyl)‐glycerol. Quantitatively, the amount of the avenoleate‐containing galactolipid was of the same order of magnitude as those of individual molecular species of digalactosyldiacylglycerol containing nonoxygenated acyl chains. The content of the new galactolipid in oat seeds was 0.5–0.6 mg per g of seed.