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Acylglycerols (=Glycerides) from the Glandular Trichome Exudate on the Leaves of Paulownia tomentosa
Author(s) -
Asai Teigo,
Hara Noriyuki,
Kobayashi Sawa,
Kohshima Shiro,
Fujimoto Yoshinori
Publication year - 2009
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200800456
Subject(s) - glyceride , chemistry , moiety , fatty acid , glycerol , trimethylsilyl , fatty alcohol , stereochemistry , organic chemistry
Chemical investigations of the glandular trichome exudates on the leaves of Paulownia tomentosa (Scrophulariaceae) led to the identification of the thirty acylglycerols (=glycerides) 1 – 30 , including five known ones ( 2, 3, 6, 9 , and 15 ) ( Fig. 1 ). Spectroscopic analysis combined with GC/MS studies of the glycerides and the liberated fatty acids, in the form of trimethylsilyl ether derivatives and trimethylsilylated methyl esters, respectively, established that the constituents belonged to 1,3‐di‐ O ‐acetyl‐2‐ O ‐(fatty acyl)glycerols, 1‐ O ‐acetyl‐2‐ O ‐(fatty acyl)‐ sn ‐glycerols, and 2‐ O ‐(fatty acyl)glycerols, wherein the fatty acyl moiety was either an eicosanoyl or an octadecanoyl group bearing OH and/or AcO groups at the 3‐, 3,6‐, 3,7‐, 3,8‐, or 3,9‐positions. The 1‐ O ‐acetyl‐2‐ O ‐[(3 R ,6 S )‐3‐(acetyloxy)‐6‐hydroxyeicosanoyl]‐ sn ‐glycerol ( 12 ; 20% of the total glycerides), 2‐ O ‐[(3 R ,8 R )‐3,8‐bis(acetyloxy)eicosanoyl]glycerol ( 17 ; 14%), 2‐ O ‐[(3 R ,9 R )‐3,9‐bis(acetyloxy)eicosanoyl]glycerol ( 18 ; 12%), and 2‐ O ‐[(3 R )‐3‐(acetyloxy)eicosanoyl]glycerol ( 10 ; 12%) were relatively abundant constituents. The configurations of the stereogenic centers of the fatty acyl moieties were determined by 1 H‐NMR analysis of the monoesters obtained from ( R )‐ and ( S )‐2‐(naphthalen‐2‐yl)‐2‐methoxyacetic acid (( R )‐ and ( S )‐2NMAOH and the hydroxy‐substituted fatty acid methyl esters ( Fig. 2 ). The configuration at C(2) of the glycerol moiety of the 1‐ O ‐acetyl‐2‐ O ‐(fatty acyl)glycerols was determined to be (2 S ) by chemical conversion of, e.g., G‐2 (= 2 / 3 1 : 10) to (+)‐3‐ O ‐[ tert ‐butyl)diphenylsilyl]‐ sn glycerol of known absolute configuration.