NMR assignment of iso-alpha-acids from isomerised extracts of Humulus lupulus L. cones.
Iso-alpha-acids are known to contribute to the characteristic bitter taste of beer. Six iso-alpha-acids were isolated from a carbon dioxide extract of the cones of Humulus lupulus L. by centrifugal partition chromatography followed by separation through beta-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''.
Khatib
Alfi
A
Division of Pharmacognosy, Section Metabolomics, Institute of Biology, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands.
Wilson
Erica G
EG
Kim
Hye Kyong
HK
Supardi
Moses
M
Choi
Young Hae
YH
Verpoorte
Robert
R
D000143:Acids / Q000737:chemistry; D003512:Cyclohexanones / Q000737:chemistry*; D005638:Fruit / Q000737:chemistry; D027582:Humulus / Q000737:chemistry* / Q000378:metabolism; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010936:Plant Extracts / Q000737:chemistry*; D013729:Terpenes / Q000737:chemistry*
D000143:Acids; D003512:Cyclohexanones; D010936:Plant Extracts; D013729:Terpenes