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-Oacetyl-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 bearingOH and/or AcO groups at the 3-, 3,6-, 3,7-, 3,8-, or 3,9-positions. The 1-O-acetyl-2-O-[(3R,6S)-3-(acetyloxy)-6-hydroxyeicosanoyl]-sn-glycerol (12; 20% of the total glycerides), 2-O-[(3R,8R)-3,8-bis(acetyloxy)eicosanoyl] glycerol (17; 14%), 2-O-[(3R,9R)-3,9-bis(acetyloxy)eicosanoyl]glycerol (18; 12%), and 2-O-[(3R)-3-(acetyloxy)eicosanoyl]glycerol (10; 12%) were relatively abundant constituents. The configurations of the stereogenic centers of the fatty acyl moieties were determined by 1H-NMR analysis of the monoesters obtained from (R)- and (S)-2-(naphthalen-2-yl)-2-methoxyacetic acid ((R)- and (S)-2NMA-OH 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 (2S) by chemical conversion of, e.g., G-2 (=2/3 1 :10) to (+)-3-O-[tert-butyl)diphenylsilyl]-sn glycerol of known absolute configuration.
ASJC Scopus subject areas
- Drug Discovery
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry