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Natural Deuterium Distribution in Branched‐Chain Medium‐Length Fatty Acids is Nonstatistical: A Site‐Specific Study by Quantitative 2 H NMR Spectroscopy of the Fatty Acids of Capsaicinoids
Author(s) -
Markai Sandrine,
Marchand Patrice A.,
Mabon Françoise,
Baguet Evelyne,
Billault Isabelle,
Robins Richard J.
Publication year - 2002
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/1439-7633(20020301)3:2/3<212::aid-cbic212>3.0.co;2-r
Subject(s) - chemistry , deuterium , nuclear magnetic resonance spectroscopy , substrate (aquarium) , spectroscopy , stereochemistry , abundance (ecology) , fatty acid , isotopic labeling , organic chemistry , biology , ecology , physics , quantum mechanics , fishery
Quantitative 2 H NMR spectroscopy has been used to determine the natural abundance site‐specific 2 H isotopic content of 6,7‐dihydrocapsaicin ( 1 ) and capsaicin ( 2 ). Prior to analysis, the fatty acyl moieties were released as methyl 8‐methylnonanoate ( 3 ) and methyl E ‐8‐methylnon‐6‐enoate ( 4 ), respectively. A marked and similar nonstatisitical isotopic distribution of 2 H is observed for both fatty acids. Notably, it can be seen that: 1) the isobutyl portion of 3 is more impoverished in 2 H than the methylenic portion; 2) the isobutyl portion of 4 is more impoverished than that of 3 ; 3) an alternating pattern occurs in the ( 2 H/ 1 H) i between the C3 to C7 positions; and 4) the ethylenic hydrogens at C6 and C7 of 4 are, respectively, impoverished and unchanged relative to these positions in 3 . These observations are compatible with the proposed biosynthetic origins of the different parts of 1 and 2 , and with the view that 1 is a proximal precursor of 2 . Furthermore, it can be suggested that, firstly, the hydrogen atoms at C3 to C7 originate alternatively from the substrate and from the environment and, secondly, that the Δ 6 ‐ E desaturation is introduced by a mechanism closely mimicking that of the Z desaturation of higher plants.