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Can. J. Chem. Vol. 86, 2008
UV irradiations of trans-isohumulone were conducted with a
450 W Hanovia medium pressure mercury lamp, surrounded
by an aqueous solution of potassium chromate (1.44 ×
10–3 mol/L) and sodium carbonate (1.25 × 10–2 mol/L) (27).
Methanolic solutions were purged with nitrogen gas for
20 min prior to light exposure and maintained under nitro-
gen during the irradiation to minimize oxygen contamina-
tion. The solutions were stirred throughout the irradiation
procedures. Samples were withdrawn from the irradiation
vessel via syringe through a Teflon stopcock. Diethyl ether
was freshly distilled immediately prior to use. Solutions pre-
pared in diethyl ether were degassed by the freeze-pump-
thaw method (27). Sampling of these ether solutions was
performed at the conclusion of the irradiation to minimize
molecular oxygen contamination and loss of volatile com-
pounds.
7.0 Hz, 1H), 2.49 (dq, J = 7.0 Hz, 2H), 2.77 (dd, J = 7.0 Hz,
2H), 3.06 (dq, J = 7.0 Hz, 2H), 5.00 (t, J = 7.0 Hz, 1H), 5.14
(t, J = 7.0 Hz, 1H). 13C NMR δ: 17.9, 22.7, 25.4, 25.7, 26.1,
30.2, 46.0, 84.2, 110.1, 113.7, 115.4, 116.2, 135.2, 137.7,
175.8, 186.9, 191.1, 198.2. GC-MS: 363 (76%), 345 (78%),
327 (6%), 307 (3%), 295 (6%), 266 (3%), 223 (3%), 197
(3%), 166 (3%), 137 (4%), 109 (7%), 97 (7%), 85 (5%), 69
(100%), 57 (16%).
trans-Isohumulone3
Humulone was photo-isomerized by a literature method
(11) utilizing UV light from a medium pressure mercury
lamp that had passed through a uranium oxide glass filter.
The course of the irradiation was monitored by analytical
HPLC. Analysis by HPLC and GC-MS indicated the purity
to be greater than 97% after recrystallization.
1H NMR δ: 0.88 (d, J = 6.6 Hz, 3H), 0.91 (d, J = 6.6 Hz,
3H), 1.47 (s, 3H), 1.51 (s, 3H), 1.63 (s, 3H), 1.67 (s, 3H),
2.08 (m, 6.6, 1H), 2.27 (dt, J = 7.1 & 15 Hz, 1H), 2.52 (dt,
J = 7.1 & 15 Hz, 1H), 2.65 (d, J = 7.1 Hz, 2H), 2.98 (dd, J =
6.8 & 6.9 Hz, 1H), 3.27 (d, J = 7.2 Hz, 2H), 5.08 (t, J =
7.1Hz, 1H), 5.14 (t, J = 7.1 Hz, 1H). 13C NMR δ: 18.2, 18.7,
22.5, 23.1, 23.6, 25.9, 26.3, 38.8, 44.3, 55.8, 91.2, 110.6,
114.7, 120.3, 135.2, 136.4, 195.7, 198.2, 205.3, 207.1. GC-
MS: 363 (52%), 345 (44%), 327 (3%), 293 (15%), 277
(7%), 266 (5%), 238 (3%), 209 (5%), 197 (9%), 109 (3%),
97 (8%), 85 (5%), 69 (66%), 57 (11%), 41 (100%).
Qualitative analyses of products
Semi-preparative HPLC separations were accomplished
with a Waters instrument, employing a 10 mm × 300 mm
Supelco C18-nucleosil semi-preparative column. Samples
were introduced with a 500 uL sample loop and separated
with an eluent mixture of 80% acetonitrile, 20% water and
0.1% concentrated phosphoric acid. The NMR spectra were
obtained in CDCl3 with a Varian Mercury 400 NMR spec-
1
trometer at 400.09 MHz for H and 100.69 MHz for 13C.
1
The H and 13C NMR assignments were correlated with the
two-dimensional NMR techniques of gCOSY, gHSQC, and
gHMBC.
cis-Isohumulone
Humulone was isomerized to cis-isohumulone by a litera-
ture method (28). The material was isolated as a light yellow
oil from the reaction mixture and was purified by semi-
preparative HPLC.
Quantitative analyses of products
Samples were analyzed using an isocratic Waters HPLC
system with a tunable absorbance detector set to 270 nm.
Samples were introduced via a 10 uL injection loop and sep-
arated with a 250 mm × 4.6 mm Supelco ODS nucleosil an-
alytical column. The eluent system, composed of a mixture
of 600 mL of acetonitrile, 400 mL of distilled water, and
2 mL of concentrated phosphoric acid. Calibration curves
were prepared for each analyte using five different concen-
trations (ranging from 1% to 25% of the starting trans-
isohumulone concentration). The GC-MS analyses were per-
formed with a Varian Saturn 4-D GC-MS, equipped with a
DB-5 capillary column and a splitless injector. The tempera-
ture program of the GC began at 50 °C for 2 min, with the
temperature increased to 180 °C at 15 °C/min, then to
200 °C at 4 °C/min and finally to 230 °C/min at 1 °C. The
mass spectrometer scanned over the mass range of 33 to 550
mass units at 1 s intervals. Samples were analyzed in freshly
distilled, spectrophotometric grade diethyl ether. Calibration
curves were prepared for the analytes, using five different
concentrations (ranging from 0.5% to 50% of the typical
dehydro-humulinic acid concentration).
1H NMR δ: 0.94 (d, J = 6.2 Hz, 3H), 0.96 (d, J = 6.2 Hz,
3H), 1.52 (s, 3H), 1.56 (s, 3H), 1.59 (s, 3H), 1.63 (s, 3H),
2.13 (m, J = 6.2 Hz, 1H), 2.41 (dt, J = 7.2 Hz, 1H), 2.47 (dt,
J = 7.1 Hz, 1H), 2.60 (d, J = 7.1 Hz, 2H), 3.20 (dd, J =
7.1 Hz, 1H), 3.30 (d, J = 7.0 Hz, 2H), 5.01 (t, J = 7.0 Hz,
1H), 5.12 (t, J = 7.0 Hz, 1H). 13C NMR δ: 18.0, 18.3, 22.6,
22.7, 25.6, 59.9, 26.3, 37.1, 46.0, 50.3, 55.5, 87.7, 110.7,
114.7, 119.8, 119.9, 135.4, 136.9, 195.5, 200.6, 206.3,
206.9. GC-MS: 363 (84%), 346 (51%), 295 (11%), 266
(7%), 197 (19%), 137 (4%), 109 (3%), 97 (5%), 85 (9%), 69
(80%), 57 (14%), 41 (100%).
Dehydro-humulinic acid
A sample of trans-isohumulone was used to prepare
dehydro-humulinic acid by a literature method (29).
1H NMR δ: 0.95 (d, J = 7.0 Hz, 3H), 0.96 (d, J = 7.0 Hz,
3H), 1.63 (s, 3H), 1.70 (s, 3H), 2.11 (m, J = 7.0 Hz, 1H),
2.58 (d, J = 7.1 Hz, 1H), 3.02 (d, J = 7.0 Hz, 2H), 5.21 (t,
J = 7.0 Hz, 1H). 13C NMR δ: 17.7, 23.8, 25.2, 25.6, 48.9,
110.8, 116.7, 121.7, 136.2, 158.1, 161.3, 193.5, 198.1. GC-
MS: 265 (100%), 247 (9%), 209 (10%), 190 (13%), 175
(6%), 152 (10%), 95 (8%), 81 (13%), 79 (13%), 69 (19%),
55 (21%).
Preparation of compounds
Humulone
Humulone was isolated from a commercially available
non-isomerized hop extract provided by from the Research
and Development department of the Labatt Brewing Com-
pany. The procedure used is a literature method (11).
1H NMR δ: 0.97 (d, J = 7.0 Hz, 3H), 1.01 (d, J = 7.0 Hz,
3H), 1.53 (s, 3H), 1.69, (s, 6H), 1.74 (s, 3H), 2.15 (m, J =
Preparation of side chain products
PCC oxidations of primary alcohols to aldehydes
The pyridinium chlorochromate reagent was prepared by a
literature method (30).
© 2008 NRC Canada