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NMR assignment of iso‐ α ‐acids from isomerised extracts of Humulus lupulus L. cones
Author(s) -
Khatib Alfi,
Wilson Erica G.,
Kim Hye Kyong,
Supardi Moses,
Choi Young Hae,
Verpoorte Robert
Publication year - 2007
Publication title -
phytochemical analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 72
eISSN - 1099-1565
pISSN - 0958-0344
DOI - 10.1002/pca.991
Subject(s) - chemistry , humulus lupulus , epimer , electrospray ionization , mass spectrometry , chromatography , yield (engineering) , stereochemistry , materials science , food science , pepper , metallurgy
Iso‐ α ‐acids are known to contribute to the characteristic bitter taste of beer. Six iso‐ α ‐acids were isolated from a carbon dioxide extract of the cones of Humulus lupulus L. by centrifugal partition chromatography followed by separation through β ‐cyclodextrin binding. This method overcame the low yield issue of most isolation procedures that results from the low stability of these compounds to light and oxygen. Their full identification was performed using one‐ and two‐dimensional NMR spectrometry, including 1 H‐ and 13 C‐NMR, 1 H‐ 1 H COSY, HMQC and HMBC and electrospray ionisation mass spectrometry. The results confirmed the structures of the isolated compounds as trans ‐isocohumulone, cis ‐isocohumulone, trans ‐isohumulone, cis ‐isohumulone, trans ‐isoadhumulone and cis ‐isoadhumulone. Epimers can be easily distinguished by observing the chemical shift differences of the H‐5, H‐1′″, H‐2′″ and C‐5 signals and the different splitting pattern of H‐5 and H‐2″. Copyright © 2007 John Wiley & Sons, Ltd.