Identification and synthesis of new volatile molecules found in extracts obtained from distinct parts of cooked chicken

Article abstract of DOI:10.1021/jf2023066

Several chicken parts (skin, fat, juice) were cooked in different ways (roasting, simmering) and investigated separately for their volatile composition. In-depth GC/MS analysis of the separate fractions revealed several unknown molecules. Mass spectra interpretation allowed us to identify nine molecules for the first time in chicken, including cyclic aldehydes, cyclic ketones, and new δ-lactones containing an unsaturated linear chain. Identification was confirmed by chemical synthesis followed by comparison of the mass spectra and linear retention indices. The natural occurrence of five of these molecules is reported here for the first time in a natural product.

Full text of DOI:10.1021/jf2023066

ARTICLE
pubs.acs.org/JAFC
Identification and Synthesis of New Volatile Molecules Found in
Extracts Obtained from Distinct Parts of Cooked Chicken
Estelle Delort,*,† Alain Velluz,† Eric Frꢀerot,† Mark Rubin,§ Alain Jaquier,† Simon Linder,^ Kirk F. Eidman,#
and Brian S. MacDougall#
†Firmenich SA, Corporate R&D Division, P.O. Box 239, CH-1211 Geneva 8, Switzerland
§Firmenich SA, Flavour Division, P.O. Box 148, CH-1217 Meyrin 2, Switzerland
^Firmenich SA, Corporate R&D Division, CH-1283 La Plaine, Switzerland
#Firmenich Inc., R&D Division, P.O. Box 5880, Princeton, New Jersey 08543, United States
S Supporting Information
b
ABSTRACT: Several chicken parts (skin, fat, juice) were cooked in different ways (roasting, simmering) and investigated separately
for their volatile composition. In-depth GC/MS analysis of the separate fractions revealed several unknown molecules. Mass spectra
interpretation allowed us to identify nine molecules for the first time in chicken, including cyclic aldehydes, cyclic ketones, and new
δ-lactones containing an unsaturated linear chain. Identification was confirmed by chemical synthesis followed by comparison of the
mass spectra and linear retention indices. The natural occurrence of five of these molecules is reported here for the first time in a
natural product.
KEYWORDS: chicken, Bresse chicken, poultry, roasted fat, cooked fat, roasted skin, roasted juice, aroma compounds, GC/MS
’ INTRODUCTION
may still contribute to the overall meaty aroma because of their
very low odor threshold. Gasser and Grosch identified 2-methyl-
3-furanthiol and its disulfide, bis(2-methyl-3-furyl) disulfide, as
well as 2-furfurylthiol and methional, as primary odorants of
chicken broth.5 Thialdine (2,4,6-trimethyl-5,6-dihydro-1,3,5-
dithiazine) and 2,4,6-trimethyl-1,3,5-trithiane were reported by
Tang et al. in fried chicken 6 and described as being useful for the
creation of chicken flavors.7 More recently, Werkhoff et al.
identified new alkyl-substituted 1,2,4-trithiolanes, as well as
new aliphatic sulfur-containing components.4
Heterocyclic compounds found in chicken, including furans,
thiophenes, pyrazines, thiazoles, pyridines, and trithiolanes, have
been reviewed by Shibamoto.8 Furans, especially 2-alkylfurans,
are known to be present in chicken meat and fat.6 Many
alkylpyrazines have been identified in chicken meat and recog-
nized as important trace flavor compounds for their roasted, nut-
like, or toasted character.2 Numerous thiazoles and some thio-
phenes have been reported in fried chicken by Tang et al.6 Several
pyridines have also been identified in chicken meat or fat.
2-Methylpyridine was identified by Horvat in 1976,9 and Tang
et al. later identified pyridine, 2-methylpyridine, 2-butylpyridine,
2-pentylpyridine, 3-ethylpyridine, and 4-ethylpyridine in fried
chicken.6
The complexity of the flavor of cooked meat results from the
large number of thermally induced reactions which can occur
during heating. In particular, the Maillard reaction and the
degradation of lipids account for the wide range of volatiles
found in cooked meat. The volatile composition of cooked and
roasted chicken meat has been extensively analyzed and reviewed
in the literature.1,2 The compounds identified in all types of meat
include the entire range of aroma chemicals, but those that
contribute highly to overall aroma range from aldehydes to
sulfur-containing components to heterocycles (furans, pyrroles,
pyrazines, thiazoles, thiophenes, oxazoles, pyridines).
Saturated and unsaturated aldehydes bearing 6ꢀ10 carbons
constitute the major part of the volatile compounds found in
cooked meat. Compared with beef meat, chicken meat contains a
higher proportion of unsaturated fatty acids in the triglycerides,
which produce more unsaturated volatile aldehydes upon de-
gradation. As these aldehydes generally have a strong green, fatty,
tallow aroma, they are thought to have a major role in the meat
aroma. In particular, 2,4-decadienal is well-known as a major
volatile component of cooked and roasted chicken, contributing
to its fatty aroma.1 An obvious oxidation product of 2,4-deca-
dienal, trans-4,5-epoxy-trans-2-decenal, was reported by Shi and
Ho as having “probably an important flavor contribution of fried
chicken”.2 Several dienals and trienals (C10ꢀC14) were also
isolated by Harker and Begemann in cooked chicken and com-
pared with model substances.3 Werkhoff et al. reported many
aroma-active compounds identified for the first time in chicken,
including 5-alkylcyclopentene-1-carbaldehydes and methyl-
branched long-chain saturated aliphatic aldehydes.4
Compared with chicken meat, the skin and dripping fat of
roasted chicken have been investigated less extensively. In 1986,
Noleau and Toulemonde quantified the volatile compounds
found in a roasted skin extract obtained by LikensꢀNickerson
Received: June 9, 2011
Accepted: September 18, 2011
Sulfur-containing components are generally found in smaller
Revised:
September 16, 2011
amounts in chicken meat than in beef meat, but some of them
Published: September 18, 2011
r
2011 American Chemical Society
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extraction.10 More than 200 compounds were identified and
quantified. Later, they isolated the volatiles of roasted chicken fat
by Leybold distillation.11 The analysis revealed a large amount of
aldehydes (59%) and acids (20%), whereas many alcohols,
ketones, and lactones were found in lower amounts. Esters,
furans, pyrazines, pyrroles, and thiazole were found in trace
amounts, and some compounds remained unidentified.
In the present study, aroma extracts of different tonalities were
obtained from distinct parts of cooked chicken (skin, fat, juice)
prepared with different cooking procedures. The volatile com-
position of each extract was analyzed by GC/MS with the aim of
better understanding the complexity of chicken flavor and
identifying new aroma molecules.
flux to volumes of about 30ꢀ200 μL. Fraction A-7 (40 mg) (eluted with
pentane:diethyl ether 50:50) had to be treated with deactivated alumina
to remove fatty acids before GC/MS analysis. Deactivated alumina was
obtained by thoroughly mixing with 4% of water and stirring for 2 h
using a rotavapor. Fraction A-7 was percolated through 650 mg of
deactivated alumina in a Pasteur pipet, resulting in A-7Al.
Preparation of Roasted Fat (LikensꢀNickerson): Extract D.
Roasted fat (56 g) in deionized water (560 mL) was codistilled with
pentane (150 mL) for 1 h 30 min at atmospheric pressure in Likensꢀ
Nickerson equipment. The organic phase was dried over MgSO4
and concentrated over a Vigreux column, yielding the “roasted fat
(LikensꢀNickerson),” extract D (20 mg).
Preparation of Roasted Juice Hydrodistillate: Extract E.
Roasted juice (1400 g) in deionized water (600 mL) was hydrodistilled
under reduced pressure by using the following program at 200 rpm:
25 mbar at 45 ꢀC for 1 h 15 min, 20ꢀ10 mbar at 55 ꢀC for 15 min. The
aqueous distillate was saturated with sodium chloride and extracted with
pentane:dichloromethane 2:1 (3 ꢁ 90 mL). The combined organic phase
was dried over MgSO4. The solvent was removed by using a Vigreux
column. The residual solvent was further removed under a gentle argon
flux, yielding the “roasted juice hydrodistillate,” extract E (ca. 2 g).
Preparation of Roasted Skin Hydrodistillate: Extract F. The
skin of four roasted chickens (220 g) was cut into small pieces, put into
deionized water (850 mL), and hydrodistilled under reduced pressure
with the following program at 200 rpm: 25 mbar at 43 ꢀC for 1 h, and
then 20ꢀ15 mbar at 50 ꢀC for 30 min. The aqueous distillate was
saturated with sodium chloride and extracted with pentane:dichloro-
methane 2:1 (3 ꢁ 90 mL). The combined organic phases were dried
over MgSO4. The solvent was removed by using a Vigreux column. The
residual solvent was further removed under a gentle argon flux, yielding
the “roasted skin hydrodistillate,” extract F (ca. 300 mg).
’ MATERIALS AND METHODS
Freshly distilled pentane (analytical grade, SDS, France) and diethyl
ether (analytical grade, SDS, France), dichloromethane (atrasol, SDS,
France) were used for sample preparation and fractionation. The Leybold
(or short-path, or thin-film) distillation unit was purchased from
Leybold-Heraeus (Oetikon, Switzerland) more than 30 years ago. A
similar apparatus is currently commercialized by ChemTech (Lockforf,
IL), model KDL-4.
Sample Preparation. A special variety of chicken, poulet de Bresse
AOC (Miꢀeral, France), was used for this study (AOC, “Appelation
d’Origine Contr^olꢀee,” is an official certification of origin and high quality
from the French Department of Agriculture). This chicken variety is
well-known for its gustative quality because of a high fat content. The
abdominal fat of 20 chickens was removed before they were roasted for
1 h in an oven at 180 ꢀC. After 30 min, the juice was regularly used to
baste the chicken, thereby increasing the grilling of the skin. After 1 h, the
dripping fat and the juice were collected and separated in a funnel to
provide both roasted fat (fatty fraction) and roasted juice (aqueous
phase). Cooked fat was obtained by gently simmering the abdominal
fat (2 kg) in a pan with 8% added water for 2 h. After filtration of the
brown residues, a yellow shiny oil was obtained. It was stored at ꢀ18 ꢀC
before Leybold distillation.
Fractionation of the Roasted Skin Hydrodistillate Extract
F. Roasted skin hydrodistillate (∼200 mg) was fractionated by flash
chromatography over silica gel (32ꢀ63, 60 Å, Brunschwig) with a
gradient pentane:diethyl ether, from 100:0 to 0:100, resulting in 97 tubes
of 5ꢀ10 mL, which were grouped according to qualitative odor evalua-
tion on a paper strip. The resulting 10 fractions, called F-1 to F-10, were
concentrated over a Vigreux column and a gentle argon flux.
Leybold Distillation of Cooked Fat: Extracts A, B, and C.
The cooked fat was gently melted in a water bath (50 ꢀC). Molecular
distillation of cooked fat (2 kg) was performed on Leybold laminar
distillation equipment at 60 ꢀC (0.06ꢀ0.03 mbar, 400 rpm) in 10
batches of 200 g. The oil feeding rate was about 100 mL/h. For each
batch, the coldfinger (ꢀ12 ꢀC) of the Leybold distillation unit was
rinsed with pentane (15 mL), and the combined batches were concen-
trated to 5 mL by using a Vigreux column to give the “cooked fat Leybold
distillate,” extract A. Similarly, the trap (ꢀ195 ꢀC) of the Leybold unit
was rinsed three times by using 15 mL of pentane, and the combined
rinses were dried over MgSO4 and concentrated to a volume of 2 mL by
using a Vigreux column to give the “cooked fat Leybold trap,” extract B.
For one batch, the volatiles were captured by solid-phase microextrac-
tion (SPME) for 15 min directly from the trap with a gray notched fiber
(DVB/CAR/PDMS, 1 cm, Supelco 57328-U) while the trap was
defrosting. The fiber was then desorbed in a gas chromatograph/mass
spectrometer (GCMS 6890/5972, Agilent, equipped with a polar Supel-
cowax10 capillary column) for 5 min, in splitless mode for 30 s. The
temperature program was as described in the following sections. The
extract obtained is called “cooked fat Leybold SPME,” extract C hereafter.
Fractionation of the Cooked Fat Leybold Distillate Extract
A. Cooked fat Leybold distillate extract A (1 g) was fractionated by
flash chromatography over silica gel (32ꢀ63, 60 Å, Brunschwig) with a
gradient of pentane/diethyl ether, from 100:0 to 0:100 in 111 tubes of
25ꢀ30 mL, which were grouped according to their qualitative odor
evaluation on a paper strip. The resulting 10 fractions, called A-1 to A-10,
were concentrated over a Vigreux column and then under a gentle argon
Odor Evaluations of the Extracts A, B, DꢀF and Fractions
A1ꢀ10 and F1ꢀ10. The extracts and fractions were evaluated on a
paper strip by expert flavorists who used in-house descriptors.
Cooked fat Leybold distillate extract A: “heavy, sweet, fatty, creamy”;
cooked fat Leybold trap extract B: “animal, honey, heavy, malty, lactonic,
cocoa”; roasted fat extract D: “roasted, fatty, pungent, malty, sweaty”;
roasted juice extract E: “grilled, fatty, cardboard, woody”; roasted skin
extract F: “typical, grilled, roasted skin”.
Flash chromatography fractions: A-1: “fresh, sulfury, grilled”; A-2:
“grilled, nutty ”; A-3: “fatty, green, aldehydic”; A-4: “sweet, nutty, pyrazinic,
paint, fatty, caramel”; A-5: “phenolic, animalic, dusty”; A-6: “peanut, fatty,
green, roasted”; A-7: “lactonic, peachy, creamy”; A-8: “sweet, creamy,
lactonic, caramel, creamy, burnt”; A-9: “cooked, creamy, coffee”; A-10:
“burnt, acidic”; F-1: “coal, hydrocarbon, petrol”; F-2: “weak”; F-3:
“sweet, fatty, cardboard”; F-4: “fishy, aldehydic, decanal-like,
citrus”; F-5: “coconut, creamy, lactonic”; F-6: “fatty, chicken skin, burnt,
pyrazinic”; F-7: “acetyl pyrazine-like, cereal”; F-8: “fruity, baked, coconut,
lactonic, burnt”; F-9: “acidic, sweaty, animalic, cooked”; F-10: “sweaty,
vegetable”.
GC/MS: General Conditions. GC/MS analyses were performed
on a GCMS 6890/5972 (Agilent) equipped with a polar column
Supelcowax10 capillary column (30 m ꢁ 0.25 mm, film thickness
0.25 μm); oven temperature program: 50 ꢀC, 5 min isotherm and then
5 ꢀC/min to 240 ꢀC; injector temperature 250 ꢀC; transfer line tem-
perature 250 ꢀC; carrier gas: helium, constant flow rate 1 mL/min; split
ratio 1:50. Analyses were repeated on a GCMS 6890/5973 (Agilent)
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equipped with a nonpolar column SPB-1 capillary column (30 m ꢁ
0.25 mm, film thickness 1 μm); oven temperature program: 60 ꢀC, 5 min
isotherm and then 5 ꢀC/min to 250 ꢀC; injector temperature 250 ꢀC;
transfer line temperature 250 ꢀC; carrier gas: helium, constant flow rate
1 mL/min; split ratio 1:50.
Phenomenex). Solvent A: heptane; solvent B: heptane/diethyl ether
(1/1). Gradient: 0% B, 1 min; 0ꢀ15% B in 12 min linear; 15% B
isocratic for 2.9 min; 15ꢀ100% B in 3.5 min, rinse for 7 min and
equilibration at 0% B for 15 min. Flow: 0.35 mL/min (initial pressure
was 240 bar). Detection: UV at 250 nm. The peaks seen at this
wavelength were collected and injected directly onto the GC/MS
(Varian). The peak corresponding to the unknown eluted as a
shoulder peak at 12.6 min, just before the higher peak of 2,4-
decadienal. Collection of the peak was made manually from five
injections of extract F.
Microchemical Reactions. Reduction of the carbonyl: 0.5 mL of
the collected peak solution was evaporated under a stream of nitrogen to
remove most of the diethyl ether. Ethanol (0.7 mL, to avoid phase
separation) and a few milligrams of sodium borohydride were added.
The vial was vortexed for 1 min and left standing for 1 h. The reaction
mixture was filtered over a PFTE syringe filter (0.45 μm) and injected
onto the GC/MS (Varian).
Reduction of the double bond(s): To the same reaction mixture was
added a few milligrams of 5% PdꢀC. Hydrogen was gently bubbled for
1 min and left standing for 15 min. The same operation was repeated
twice more. The reaction mixture was filtered and injected onto the GC/
MS (Varian).
Synthesis. Experimental Equipment. All moisture-sensitive reac-
tions were carried out under an argon atmosphere in oven- or flame-
dried glassware. Purification by flash chromatography was performed
over (done with) silica gel 32ꢀ63, 60 Å (Brunschwig). The yields of the
syntheses were not optimized. 1H and 13C NMR spectra were recorded
in CDCl3 on a Bruker DPX 400 spectrometer at 25 ꢀC, with tetra-
methylsilane as the internal standard. Standard gradient-selected COSY,
HSQC, and HMBC experiments were carried out on a Bruker Avance
500 spectrometer. Signal assignment was achieved by using Bruker
NMR software TopSpin 2.0 (s: singlet; d: doublet; t: triplet; m:
multiplet; brs: broad singlet; mc: centered multiplet).
Mass spectra were generated at 70 eV at a scan range from m/z:
27ꢀ350. Linear retention indices (LRIs) were determined after injec-
tion of a series of n-alkanes (C5ꢀC28) under identical conditions.
Alternatively, some analyses were performed on a Varian 300-MS
triple quadruple GC/MS system equipped with a CombiPal autosampler,
two split/splitless injectors, a VF-WAXms column (30 m ꢁ 0.25 mm,
film thickness 0.25 μm) and a VF-1 ms column (30 m ꢁ 0.25 mm, film
thickness 0.25 μm) installed on each of the injectors connected to the
transfer line (methyl deactivated fused silica tubing, 0.25 mm ꢁ 30 cm)
via a fused silica Y connector (Supelco, PA, PN 23631). VF-1 and VF-
WAX columns are equivalent to the widely used DB-1 and DB-Wax
columns. The transfer line temperature was set at 250 ꢀC, and the ion
source temperature was set at 175 ꢀC. The GC conditions were as
follows: injector temperature 250 ꢀC; both columns were operated at a
constant flow of 0.7 mL/min; oven temperature program: 40 ꢀC held for
5 min, 5 ꢀC/min to 240 ꢀC and held for 10 min, total run time 55 min;
split ratio 1:5; injection volume: 1 μL. MS parameters at electron
ionization (EI) mode: electron energy 70 eV, mass range m/z 29 to m/z
450, scan time 0.25 s. MS parameters at chemical ionization (CI) mode:
CI gas pressure 3.00 Torr, mass range m/z 60 to m/z 350, and scan time
0.1 s for single ion monitoring (SIM).
Identification of Components. The volatile compounds were
identified by GC/MS (see Supporting Information) and confirmed by
comparison of their mass spectra and LRIs with those of reference
samples. If only one method was applied (MS data alone or LRI alone),
the identification was “tentative”. These reference samples were pur-
chased from Fluka-Sigma-Aldrich (Buchs, Switzerland), Acros Organics
(Geel, Belgium), or SDS Carlo-Erba (Val de Reuil, France), or synthe-
sized in-house using standard procedures. The structures of all reference
samples were unequivocally confirmed in-house by NMR spectroscopy.
The synthetic procedures and characterizations of all newly identified
molecules in chicken are given in detail hereafter.
2-Propyl-1-cyclopentanone 2. A solution of ethyl cyclopentanone-2-
carboxylate 1 (Aldrich, 24 g, 0.157 mol, 1 equiv) in THF (200 mL) was
added dropwise during 20 min to a mechanically stirred mixture of NaH
(60% oil dispersion: 6.8 g, 0.17 mol, 1.1 equiv) in THF (300 mL)
maintained between 15 ꢀC and 25 ꢀC. After a further 15 min at room
temperature, a solution of 1-iodopropane (53.4 g, 0.314 mol, 2 equiv) in
THF (200 mL) was added dropwise during 10 min. The mixture was
then heated at reflux during 3 days. The cooled mixture was poured into
cold sat. aq NH4Cl (200 mL) and extracted (diethyl ether). Workup and
concentration in vacuo afforded a residual oil (24.6 g) to which was added
concd aq HCl (140 mL). The mixture was then heated at reflux (ca. 95 ꢀC)
during 20 h. The reaction was monitored by GC. The cooled mixture was
poured into iceꢀwater (250 mL) and extracted (diethyl ether). Workup
and bulb-to-bulb distillation in vacuo (110ꢀ120 ꢀC/8 mbar) afforded 2
(17 g, 88% yield) as a colorless oil (bp: 67ꢀ70 ꢀC/18 mbar).
High-Resolution Gas Chromatography Time-of-Flight
Mass-Spectrometry (HR GC-TOF-MS). Roasted juice hydrodistil-
late, extract E, was injected on a GCT Premier (Waters, Milford, MA)
with a SPB-1 column (30 m ꢁ 0.25 mm, film thickness 1.0 μm film,
Supelco). Oven: 60 ꢀC for 5 min, 5 ꢀC/min to 250 ꢀC; injector tem-
perature 250 ꢀC; transfer line temperature 250 ꢀC; carrier gas: helium;
constant flow rate 1.0 mL/min; split ratio 1:10; injection volume: 1.0 μL.
The acquisition time was set to 0.5 s with an interscan delay of 0.01 s over
a mass range of 1ꢀ350 Da. Spectra were recorded with an electron energy
of 70 eV, emission current of 612 μA, trap current of 200 μA, and source
temperature of 200 ꢀC. Calibration was performed by using heptacosa
(perfluorotributylamine, MS grade, Apollo Scientific Ltd., Bradbury,
UK). Calibration data were collected for 1 min in centroid mode. A total
of 60 spectra were summed to generate a 16-point calibration curve from
m/z 69 to 614 Da. The curve was fitted to a second-order polynomial
such that the standard deviation of the residuals was 0.001 amu or lower.
Heptacosa was continuously introduced into the ion source, and the ion
m/z 218.9856 was used as a lock mass. Mass spectra and molecular
formula were obtained by using MassLynx software (Waters). The
difference δ between the exact mass calculated from the molecular
formula and that measured is calculated by the software and expressed
in ppm: δ = (Mmeasured ꢀ Mcalculated)/Mcalculated ꢁ 106.
1H NMR: (400 MHz, CDCl3): δ 0.91 (t, J = 7.2, 3 H); 1.18ꢀ1.45 (m,
3 H); 1.46ꢀ1.58 (m, 1 H); 1.68ꢀ1.84 (m, 2 H); 1.94ꢀ2.35 (m, 5 H).
13C NMR (100 MHz, CDCl3): δ 14.0 (q); 20.8 (t); 20.8 (t); 29.6 (t);
31.9 (t); 38.2 (t); 49.0 (d); 221.5 (s). MS (EI, 70 eV), m/z (%):
126(11); 67(6); 85(6); 84(100); 83(34); 70(7); 69(9); 67(8); 56(11);
55(33); 53(6); 43(4); 42(20); 41(28); 39(19).
2-Propyl-1-cyclopentanone p-Toluenesulfonylhydrazone 4. A solu-
tion of 2 (15 g, 0.119 mol, 1 equiv) and p-tolylsulfonylhydrazide (24.4 g,
0.131 mol, 1.1 equiv) in EtOH (180 mL) containing concd aq HCl
(0.2 mL) was heated at reflux during 8 h. The yellow reaction mixture
was cooled to room temperature and concentrated in vacuo to afford
an yellow oil (43.1 g). Crystallization (diethyl ether:pentane 60:40)
afforded 4 (26.1 g, 75% yield) as white crystals.
Semipreparative Normal Phase High-Performance Liquid
Chromatography (NP-HPLC). NP-HPLC experiments were per-
formed on an Agilent 1100 system equipped with a quaternary pump,
a single wavelength UV detector, and an autosampler (loop of 100
1H NMR: (400 MHz, CDCl3): δ 0.84 (t, J = 7.2 Hz, 3 H); 1.10ꢀ1.34
(m, 4 H); 1.54ꢀ1.68 (m, 2 H); 1.78ꢀ1.98 (m, 2 H); 2.04ꢀ2.16 (m,
1 H); 2.21ꢀ2.48 (m, 2 H); 2.43 (s, 3 H); 7.30 (d, J = 8.5 Hz, 2H); 7.85
2
μL). The column was a Luna Silica (3 μm, 150 ꢁ 1.0 mm;
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(d, J = 8.5 Hz, 2H). 13C NMR: (100 MHz, CDCl3): δ 14.1 (q); 20.4 (t);
21.6 (q); 22.6 (t); 28.1 (t); 31.2 (t); 34.1 (t); 44.5 (d); 128.1 (d); 129.4
(d); 135.6 (s); 143.8 (s); 169.8 (s).
2-Pentyl-1-cyclopentanone p-Toluenesulfonylhydrazone 5. The
same procedure was used as for compound 4, using 2-pentyl-1-cyclo-
pentanone 3 as starting material (available in house, 14.3 g, 92.9 mmol,
1 equiv) and giving white crystals of 2-pentyl-1-cyclopentanone p-tolue-
nesulfonylhydrazone 5 (18.8 g, 63% yield).
84(100); 83(39); 70(6); 69(20); 68(30); 67(8); 57(6); 56(76); 55(70);
53(11); 51(6); 43(12); 42(36); 41(78); 39(50).
(Z)-N0-(2-Ethylcyclopentylidene)-4-methylbenzenesulfonohydrazide
9. The same procedure was used as for compound 4, using 2-ethyl cyclo-
pentanone 8 as starting material (6.65 g, 59.4 mmol, 1 equiv) and giving
(Z)-N0-(2-ethylcyclopentylidene)-4-methylbenzenesulfonohydrazide 9 as
1
a yellow powder (12.3 g, 74% yield). H NMR and 13C NMR were
identical to those described in ref 12.
1H NMR: (400 MHz, CDCl3): δ 0.87 (t, J = 7.2 Hz, 3 H); 1.10ꢀ1.35
(m, 8 H); 1.54ꢀ1.68 (m, 2 H); 1.77ꢀ1.98 (m, 2 H); 2.04ꢀ2.16
(m, 1 H); 2.22ꢀ2.48 (m, 2 H); 2.43 (s, 3 H); 7.29 (d, J = 8.1 Hz,
2 H); 7.57 (brs, 1H); 7.86 (d, J = 8.1, 2 H). 13C NMR: (100 MHz,
CDCl3): δ 14.1 (q); 21.6 (q); 22.6 (t); 22.6 (t); 26.9 (t); 28.1 (t); 31.2
(t); 31.9 (t); 32.0 (t); 44.7 (d); 128.1 (d); 129.4 (d); 135.6 (s); 143.8
(s); 169.8 (s).
5-Ethyl 1-cyclopentene-1-carbaldehyde 10. To a ꢀ60 ꢀC solution of
9 (4.5 g, 16.1 mmol, 1 equiv) in N,N,N0,N0-tetramethylethylenediamine
(40.5 mL) and THF (13.5 mL) was added n-butyllithium (40.5 mL of
1.6 M in hexane, 64.8 mmol, 4 equiv) over 45 min. The reaction was
allowed to reach 0 ꢀC and was stirred for 1.5 h until it changed from deep
red to brownish-green. At ꢀ15 ꢀC, DMF (4.5 mL, 58.0 mmol, 3.6 equiv)
was added and was reacted for another 40 min at 5ꢀ10 ꢀC. The reaction
was poured onto 3.2 N HCl (190 mL) at 0 ꢀC and was extracted with
diethyl ether. The organic phase was washed with brine, dried over
Na2SO4, and concentrated to 40 mL; a GC/MS with decane as the
internal standard showed about 430 mg of 10 (GC purity 46%).
1H NMR (400 MHz, CDCl3): δ 0.87 (t, J = 7.4 Hz, 3H); 1.36ꢀ
1.25 (m, 1H); 1.85ꢀ1.69 (m, 2H); 2.19ꢀ2.10 (m, 1H); 2.64ꢀ2.45 (m,
2H); 2.96ꢀ2.91 (m, 1H); 6.85ꢀ6.83 (m, 1H); 9.77 (s, 1H). 13C NMR
(100 MHz, CDCl3): δ 11.4 (q); 25.8 (t); 29.1 (t); 32.2 (t); 43.5 (d);
150.5 (s); 153.9 (d); 190.1 (d). MS (EI, 70 eV), m/z (%): 124(53); 109
(28); 95(72); 93(11); 91(9); 81(14); 79(9); 77(8); 67(100); 65(17);
55(8); 41(22); 39(18).
3-(5-Ethyl-1-cyclopentenyl)-N-methoxy-N-methylacrylamide 11.
Diethyl (N-methoxy-N-methylcarbamoylmethyl) phosphate (2.51 g,
12 mmol, 4 equiv) was added to a suspension of sodium methoxide
(972 mg, 18 mmol, 6 equiv) in THF (42 mL) at room temperature. A
solution of 35 mL of 10 (about 375 mg, 3 mmol, 1 equiv) and THF
(12 mL) was added. A water bath was used to keep the reaction below
30 ꢀC (slightly exothermic) for 1 h. The usual workup with dichloro-
methane as extraction solvent gave 4.2 g of crude product. The Weinreb
amide 11 (405 mg, 65%) was obtained with a purity of 93% by flash chro-
matography (30% AcOEt in cyclohexane).
5-Propyl-1-cyclopentene-1-carbaldehyde 6. A 1.6 M hexane solu-
tion of n-butyllithium (64 mL, 102 mmol, 3 equiv) was added dropwise
during 30 min to a stirred solution of 4 (10 g, 34 mmol, 1 equiv) in N,N,
N0,N0-tetramethylethylenediamine (TMEDA, 75 mL) and THF
(15 mL) at ꢀ45 ꢀC under nitrogen. The deep-red solution was allowed
to reach 10 ꢀC during 1 h and then maintained at 15ꢀ18 ꢀC for a further
75 min. Recooling to ꢀ5 ꢀC (brown-green mixture) was followed by the
dropwise addition of DMF (puriss., 6 g, 82 mmol, 2.4 equiv). A tem-
perature rise to 8 ꢀC with the appearance of a brown precipitate was
observed. The reaction mixture was then stirred at 10 ꢀC during 20 min.
Dilution with 10% aq NaCl (100 mL) was followed by extraction (diethyl
ether). The combinedorganic phase was washedwith cold 5% aqHCl and
then sat. aq NaCl. Workup, concentration in vacuo, flash chromatography
(cyclohexane:ethyl acetate 95:5), and bulb-to-bulb distillation in vacuo
(bp: 60ꢀ70 ꢀC/2.5 mbar) afforded 6 (0.25 g, 5% yield), a colorless oil.
LRI (SWax) 1518, LRI (SPB-1) 1106. In natural extract: LRI
1
(SWax) 1516; LRI (SPB-1) 1105. H NMR: (400 MHz, CDCl3): δ
0.90 (t, J = 7.2 Hz, 3H); 1.14ꢀ1.42 (m, 3 H); 1.66ꢀ1.81 (m, 2H); 2.15
(mc, 1H); 2.42ꢀ2.66 (m, 2 H); 2.92ꢀ3.02 (m, 1 H); 6.82 (mc, 1 H);
9.76 (s, 1 H). 13C NMR (100 MHz, CDCl3): δ 14.2 (q); 20.6 (t); 29.7
(t); 32.2 (t); 35.5 (t); 42.0 (d); 150.9 (s); 153.7 (d); 190.0 (d). MS (EI,
70 eV), m/z (%): 138(30); 123(15); 110(13); 109(33); 96(27);
95(48); 81(25); 79(18); 67(100); 41(27). HR-GC-TOF-MS: 138.1046
(C9H14O, +0.7 ppm).
5-Pentyl-1-cyclopentene-1-carbaldehyde 7. The same procedure was
used as for compound 6, using 2-pentyl-1-cyclopentanone p-toluenesul-
fonylhydrazone 5 (11 g, 34.1 mmol, 1 equiv) as starting material and giving
7 (1.55 g, 27% yield) as a pale-yellow oil (bp: 100ꢀ110 ꢀC/0.8 mbar).
LRI (SWax) 1732, LRI (SPB-1) 1308. In natural extract: LRI (SWax)
1725; LRI (SPB-1) 1309. 1H NMR: (400 MHz, CDCl3): δ 0.88 (mc, 3
H); 1.16ꢀ1.38 (m, 7 H); 1.67ꢀ1.83 (m, 2 H); 2.08ꢀ2.21 (m, 1 H);
2.42ꢀ2.66 (m, 2H); 2.91ꢀ3.02 (m, 1 H); 6.82 (mc, 1 H); 9.76 (s, 1 H).
13C NMR: (100 MHz, CDCl3): δ 14.1 (q); 22.7 (t); 27.1 (t); 29.7 (t);
32.0 (t); 32.2 (t); 33.2 (t); 42.2 (d); 151.0 (s); 153.5 (d); 190.0 (d). MS
(EI, 70 eV), m/z (%): 166(21); 137(10); 124(33); 123(18); 110(22);
109(25); 96(37); 95(49); 81(32); 79(24); 67(100); 41(36). HR-GC-
TOF-MS: 166.1359 (C11H18O, +0.6 ppm).
1H NMR (500 MHz, CDCl3): δ 0.90 (t, J = 7.5 Hz, 3H); 1.38ꢀ1.28
(m, 1H); 1.68ꢀ1.60 (m, 1H); 1.80ꢀ1.74 (m, 1H); 2.10ꢀ2.04 (m, 1H);
2.40ꢀ2.33 (m, 1H); 2.51ꢀ2.43 (m, 1H); 2.86ꢀ2.82 (m, 1H); 3.27 (s,
3H); 3.71 (s, 3H); 6.13 (t, J = 2.9 Hz, 1H); 6.39 (d, J = 15.7 Hz, 1H);
7.45 (d, J = 15.7 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 11.4 (q);
25.8 (t); 29.3 (t); 31.8 (t); 32.5 (q); 45.0 (d); 61.7 (q); 115.2 (d); 139.2
(d); 139.4 (d); 144.9 (s); 167.7 (s). MS (EI, 70 eV), m/z (%): 209(6);
150 (16); 149(100); 131(21); 121(10); 119(5); 107(10); 105(9);
93(17); 91(29); 79(18); 77(10); 65(8); 55(25).
(E)-3-(5-Ethylcyclopent-1-enyl)acrylaldehyde 12. To a solution of
the Weinreb amide 11 (250 mg, 1.14 mmol, 1 equiv) in diethyl ether
(2 mL) kept at ꢀ15 ꢀC was added LiAlH4 (43 mg in 2 mL of diethyl
ether) portionwise. The reaction was stirred at ꢀ15 ꢀC for 30 min. The
amide had completely reacted, as observed by GC/MS. Then diethyl
ether (5 mL) was added, and the reaction was poured into cold 1%
KHSO4 (4 mL). The usual workup gave a crude product (199 mg), which
was purified by flash chromatography (3% diethyl ether in pentane) to
give pure 12 (61 mg, 34% yield).
LRI (SWax) 1853; LRI (SPB-1) 1296. In natural extract: LRI (SWax)
1855; LRI (SPB-1) 1299. 1H NMR (400 MHz, CDCl3): δ 0.90 (t, J =
7.5 Hz, 3H); 1.34ꢀ1.21 (m, 1H); 1.66ꢀ1.56 (m, 1H); 1.84ꢀ1.77 (m,
1H); 2.16ꢀ2.06 (m, 1H); 2.46ꢀ2.38 (m, 1H); 2.57ꢀ2.48 (m, 1H);
2.84ꢀ2.79 (m, 1H); 6.10 (dd, J = 15.8, 7.8 Hz, 1H); 6.31 (t, J = 2.8 Hz,
1H); 7.24 (d, J = 15.8 Hz, 1H); 9.56 (d, J = 7.8 Hz, 1H). 13C NMR
(100 MHz, CDCl3): δ 11.5 (q); 25.7 (t); 29.2 (t); 32.1 (t); 44.9 (d);
128.5 (d); 143.2 (d); 145.1 (s); 148.4 (d); 194.5 (d). MS (EI, 70 eV),
m/z (%): 150 (42); 135 (5); 122 (20); 121 (100); 107(18); 103
(19); 94 (62); 93 (54); 91 (92); 79 (27); 77 (88); 65 (23); 63 (8); 55
2-Ethyl Cyclopentanone 8. Ethyl 2-oxocyclopentanecarboxylate 1
(Aldrich, 25 g, 160 mmol, 1 equiv), potassium carbonate (66 g, 423
mmol, 2.4 equiv), and ethyl iodide (37.5 g, 240 mmol, 1.5 equiv) in
acetone (250 mL) were refluxed for 5 h. The reaction medium was
filtered and evaporated. Then concd HCl (100 mL) was poured onto it,
and the reaction was refluxed for 20 h, cooled, and extracted with
heptane. The usual workup and distillation in vacuo with a Vigreux
column yielded 8 (6.65 g, 37% yield, bp 53 ꢀC/10 Torr).
1H NMR: (AMX 360 MHz, CDCl3): δ 0.94 (t, J = 7.2, 3 H); 1.26ꢀ1.38
(m, 1 H); 1.48ꢀ1.59 (m, 1 H); 1.71ꢀ1.84 (m, 2 H); 1.94ꢀ2.35 (m, 5 H).
13C NMR (90 MHz, CDCl3): δ 11.9 (q); 20.7 (t); 22.7 (t); 29.0 (t); 38.3
(t); 50.6 (d); 221.4 (s). MS (EI, 70 eV), m/z (%): 112(30); 97(5); 85(5);
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Figure 1. Extraction of the chicken parts (skin, fat, juice) investigated separately for their volatile composition. A = cooked fat Leybold distillate extract;
B = cooked fat Leybold trap extract; C = cooked fat Leybold solid-phase microextraction (SPME) extract; D = roasted fat (LikensꢀNickerson) extract;
E = roasted juice hydrodistillate extract; F = roasted skin hydrodistillate extract.
(18); 53 (12); 51 (13); 41 (15); 39 (24). HR-GC-TOF-MS: 150.1044
(C10H14O, ꢀ0.7 ppm).
2-pentyl-2,3-epoxy-1-cyclopentanone 18 (11.85 g, 35% yield, purity
GC/MS 95%, bp: 103.6 ꢀC/6.4 mbar).
(E)-2-Butylidene-1-cyclopentanone 14. To a 500-mL flask under
argon were added pyrrolidine (17.75 g, 0.25 mol), water (15.5 mL,
0.85 mol), and methyl tert-butyl ether (MTBE, 85 mL). The reaction
mixture was cooled down with an ice bath, and acetic acid (15.00 g,
0.25 mol) was introduced dropwise within 30 min. Cyclopentanone 13
(84.00 g, 1.00 mol, 1 equiv) was added within 10 min and after an
additional 10 min, butyraldehyde (89.28 g, 1.24 mol, 1.2 equiv) was added
dropwise within 30 min. The reaction mixture was stirred for another
10 min and then refluxed for 4 h. MTBE was added, and the organic phase
was separated and washed with HCl 20%, brine, H2O/brine 1/1, and
NaHCO3 sat/brine 1/1, dried over MgSO4, and concentrated. The
residue was distilled over a Vigreux column under vacuum, giving (E)-2-
butylidene-1-cyclopentanone 14 (43.96 g, 32% yield, purity GC/MS:
89%, bp: 86ꢀ90 ꢀC/5.8 mbar).
1H NMR (CDCl3, 400 MHz): δ 0.89 (t, J = 6.9 Hz, 3H); 1.24ꢀ1.44
(m, 6H); 1.72ꢀ2.14 (m, 4H); 2.24ꢀ2.41 (m, 2H); 3.78ꢀ3.80 (m, 1H).
13C NMR (100 MHz, CDCl3): δ 13.9 (q); 22.3 (t); 22.4 (t); 24.1 (t);
31.7 (t); 31.9 (t); 63.0 (d); 63.7 (s); 210.8 (s).
3-Butyl-2-hydroxy-2-cyclopenten-1-one 19. A solution of 2-butyl-
2,3-epoxy-1-cyclopentanone 17 (7.77 g, 50 mmol, 1 equiv) in acetic acid
(35 mL) containing sulfuric acid (0.49 mL) was heated at 55 ꢀC for 2 h.
After removal of acetic acid in vacuo, the residue was diluted with diethyl
ether and extracted with NaOH 5% (2ꢁ). The alkaline solution was
acidified with HCl 10%, extracted with diethyl ether, washed with brine,
dried over MgSO4, and concentrated. The residue was purified by flash
chromatographybyusingpentane/diethyl ether 70/30. Inorder tofurther
remove traces of acetic acid, the fractions were washed with aq NaHCO3
sat., dried over MgSO4, and concentrated, giving 3-butyl-2-hydroxy-2-
cyclopenten-1-one 19 (1.00 g, 13% yield, purity GC/MS 99%).
LRI (SWax) 2097; LRI (SPB-1) 1288. In natural extract: LRI (SWax)
2095; LRI (SPB-1) 1287. 1H NMR (CDCl3, 400 MHz): δ 0.94 (t, J =
7.3 Hz, 3H); 1.32ꢀ1.43 (m, 2H); 1.51ꢀ1.59 (m, 2H); 2.39ꢀ2.47
(m, 6H); 6.39 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 13.8 (q); 22.7
(t); 25.2 (t); 28.4 (t); 29.0 (t); 31.9 (t); 148.6 (s); 148.8 (s); 203.4 (s).
MS (EI, 70 eV), m/z (%): 154 (16); 125(43); 112(100); 111(30);
99(27); 83(14); 70(8); 55(30); 41(12). HR-GC-TOF-MS: 154.0994
(C9H14O2, ꢀ2.6 ppm).
1H NMR (CDCl3, 400 MHz): δ 0.94 (t, J = 7.2 Hz, 3H); 1.40ꢀ1.58
(m, 2H); 1.89ꢀ1.98 (m, 2H); 2.10ꢀ2.16 (m, 2H); 2.33 (t, J = 7.7 Hz,
2H); 2.56ꢀ2.62 (m, 2H); 6.52ꢀ6.58 (m, 1H). 13C NMR (100 MHz,
CDCl3): δ 13.9 (q); 19.8 (t); 21.7 (t); 26.8 (t); 31.7 (t); 38.6 (t); 136.1
(d); 137.4 (s); 207.2 (s).
2-Butyl-2-cyclopenten-1-one 15. In a flask under argon, (E)-2-buty-
lidene-1-cyclopentanone 14 (34.5 g, 0.25 mol) and iodine (35 mg,
0.14 mmol) were heated at 160 ꢀC for 2 h. The mixture was distilled by
using a Vigreux column under vacuum, giving 2-butyl-2-cyclopenten-1-one
15 (27.76 g, 80% yield, purity GC/MS: 92%, bp: 90ꢀ92 ꢀC/12 mmHg).
1H NMR (CDCl3, 400 MHz): δ 0.91 (t, J = 7.2 Hz, 3H); 1.28ꢀ1.39
(m, 2H); 1.41ꢀ1.51 (m, 2H); 2.13ꢀ2.20 (m, 2H); 2.37ꢀ2.41 (m, 2H);
2.54ꢀ2.59 (m, 2H); 7.29ꢀ7.32 (m, 1H). 13C NMR (100 MHz, CDCl3):
δ 13.9 (q); 22.5 (t); 24.5 (t); 26.5 (t); 29.9 (t); 34.6 (t); 146.5 (s); 157.3
(d); 210.0 (s).
2-Hydroxy-3-pentyl-2-cyclopenten-1-one 20. The same procedure
was usedasfor compound19, using 2-pentyl-2,3-epoxy-1-cyclopentanone
18 (11.61 g, 69.1 mmol) as starting material and giving 2-hydroxy-3-
pentyl-2-cyclopenten-1-one 20 (1.92 g, 17% yield, purity GC/MS 99%).
LRI (SWax) 2195; LRI (SPB-1) 1390. In natural extract: LRI (SWax)
2197; LRI (SPB-1) 1389. 1H NMR (CDCl3, 400 MHz): δ 0.90 (t, J =
7.1 Hz, 3H); 1.28ꢀ1.38 (m, 2H); 1.52ꢀ1.60 (m, 2H); 2.40ꢀ2.46 (m,
6H); 6.40 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 14.0 (q); 22.4
(t); 25.2 (t); 26.5 (t); 28.6 (t); 31.8 (t); 31.9 (t); 148.8 (s); 148.9 (s);
203.5 (s). MS (EI, 70 eV), m/z (%): 168(18); 125(46); 112(100);
111(26); 99(34); 83(10); 55(25); 41(11). HR-GC-TOF-MS: 168.1146
(C10H16O2, ꢀ2.4 ppm).
2-Butyl-2,3-epoxy-1-cyclopentanone 17. A solution of 2-butyl-2-
cyclopenten-1-one 15 (21.61 g, 157 mmol, 1 equiv) and aqueous
hydrogen peroxide 30% (45 mL, 470 mmol, 3 equiv) in methanol
(200 mL) was cooled to 15 ꢀC. Then 6 N aqueous sodium hydroxide
(13 mL, 79 mmol, 0.5 equiv) was added dropwise within 45 min under
stirring. During the addition, the temperature was kept at 15ꢀ25 ꢀC.
The resulting mixture was stirred for 3 h at room temperature, poured
into water (250 mL), extracted with diethyl ether, dried over MgSO4,
and concentrated. The residue was distilled by using a Vigreux column
under vacuum, giving 2-butyl-2,3-epoxy-1-cyclopentanone 17 (7.9 g,
33% yield, purity GC/MS 98%, bp: 87ꢀ89 ꢀC/6.8 mbar).
(8Z)-8-Tetradecen-5-olide 28. To a solution of trimethyl 4-bro-
moorthobutyrate 24 (Aldrich, 16.32 g, 72.0 mmol, 2.8 equiv) in diethyl
ether (120 mL) at ꢀ78 ꢀC was added tert-butyllithium (1.7 M in pentane,
76.32 mL, 130.0 mmol, 5 equiv) dropwise over 45 min. The reaction
mixture was stirred at ꢀ78 ꢀC for 1 h and then at 0 ꢀC for 50 min. After
recooling to ꢀ78 ꢀC, (4Z)-decenal 21 (Acros, 3.96 g, 25.7 mmol, 1 equiv)
was added dropwise over 5 min. The resulting light-yellow slurry was
stirred at ꢀ78 ꢀC for 30 min followed by 90 min at 0 ꢀC. A 5% aq AcOH
solution was added dropwise to the reaction mixture, followed by stirring
at 0 ꢀC for 40 min. The mixture was extracted with diethyl ether, dried
over MgSO4, and concentrated. The residue was purified by flash
chromatography (pentane/diethyl ether: 7/3). The resulting crude
1H NMR (CDCl3, 400 MHz): δ 0.90 (t, J = 6.9 Hz, 3H); 1.29ꢀ1.44
(m, 4H); 1.72ꢀ2.15 (m, 4H); 2.24ꢀ2.41 (m, 2H); 3.78ꢀ3.80 (m, 1H).
13C NMR (100 MHz, CDCl3): δ 13.9 (q); 22.3 (t); 22.8 (t); 23.8 (t);
26.6 (t); 31.7 (t); 63.0 (d); 63.7 (s); 210.9 (s).
2-Pentyl-2,3-epoxy-1-cyclopentanone 18. The same procedure
was used as for compound 17, using 2-pentyl-2-cyclopenten-1-one 16
(available in house, 30.40 g, 200 mmol) as starting material and giving
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25 (2.85 g, 11.1 mmol, 1 equiv), KOH (1.85 g, 33.3 mmol, 3 equiv), H2O
(2.9 mL), and ethanol (16.5 mL) were refluxed for 2 h. After removal of
ethanol, the residue was dissolved in water and concd H2SO4 until it
reached pH 1. The mixture was extracted with diethyl ether, washed with
brine, dried over MgSO4, concentrated, and purified by flash chroma-
tography by using pentane/diethyl ether 60/40, giving 28 (1.35 g, 54%
yield, purity GC/MS 96%).
LRI (SWax) 2653; LRI (SPB-1) 1855. In natural extract: LRI (SWax)
2662; LRI (SPB-1) 1852. 1H NMR (CDCl3, 400 MHz): δ 0.89 (t, J =
6.8 Hz, 3H); 1.18ꢀ1.39 (m, 6H); 1.46ꢀ2.63 (m, 10H); 2.36ꢀ2.63 (m,
2H); 4.26ꢀ4.32 (m, 1H); 5.29ꢀ5.45 (m, 2H). 13C NMR (100 MHz,
CDCl3): δ 14.1 (q); 18.5 (t); 22.6 (t); 22.7 (t); 27.2 (t); 27.8 (t); 29.4
(t); 29.5 (t); 31.5 (t); 35.8 (t); 79.9 (d); 128.0 (d); 131.4 (d); 1759);
55(49); 54(68); 41(40). MS (EI, 70 eV), m/z (%): 224 (2); 121(4);
110(100); 95(28); 82(31); 81(100); 68(43); 67(49); 55(39); 54(42);
41(36). HR-GC-TOF-MS: 224.1785 (C14H24O2, +4.0 ppm).
(8E)-8-Tetradecen-5-olide 29. The same procedure was used as
for compound 28, using (4E)-decenal 22 (Acros, 3.96 g, 25.7 mmol,
1 equiv) as starting material and giving 29 (1.07 g, 37% yield, purity GC/
MS 99%).
2H); 4.25ꢀ4.32 (m, 1H); 5.32ꢀ5.40 (m, 1H); 5.42ꢀ5.49 (m, 1H). 13
C
NMR (100 MHz, CDCl3): δ 14.1 (q); 18.5 (t); 22.5 (t); 27.8 (t); 27.9
(t); 29.2 (t); 29.5 (t); 31.4 (t); 32.5 (t); 35.7 (t); 79.8 (d); 128.5 (d);
131.8 (d); 171.9 (s). MS (EI, 70 eV), m/z (%): 224 (2); 121(4);
110(100); 95(28); 82(31); 81(71); 68(46); 67(47); 55(41); 54(46);
41(37). HR-GC-TOF-MS: 224.1782 (C14H24O2, +2.7 ppm).
(6E)-6-Tetradecen-5-olide 30. The same procedure was used as for com-
pound 28, using (2E)-decenal 23 (Alfa Aesar, 5.00 g, 32.5 mmol, 1 equiv) as
starting material and giving 30 (1.45 g, 20% yield, purity GC/MS 99%).
LRI (SWax) 2738; LRI (SPB-1) 1900. In natural extract: LRI (SWax)
2744; LRI (SPB-1) 1896. 1H NMR (CDCl3, 400 MHz): δ 0.86ꢀ
0.91 (t, J = 6.9 Hz, 3H); 1.21ꢀ1.42 (m, 10H); 1.60ꢀ2.09 (m, 6H);
2.42ꢀ2.62 (m, 2H); 4.74ꢀ4.79 (m, 1H); 5.45ꢀ5.52 (m, 1H);
5.73ꢀ5.80 (m, 1H). 13C NMR (100 MHz, CDCl3): δ 14.1 (q); 18.2
(t); 22.7 (t); 28.4 (t); 28.9 (t); 29.1 (t); 29.1 (t); 29.5 (t); 31.8 (t); 32.2 (t);
80.8 (d); 127.9 (d); 134.6 (d); 171.5 (s). MS (EI, 70 eV), m/z (%): 224
(2); 164(11); 154(16); 136(20); 125(85); 112(41); 97(100); 84(46);
83(56); 70(52); 55(64), 42 (45); 41 (40). HR-GC-TOF-MS: 224.1786
(C14H24O2, +4.5 ppm).
4-Methyl-2-pentylpyridine 32. A 50-mL reactor under argon was
charged with 2-bromo-4-methylpyridine 31 (2.0 g, 11.6 mmol, 1 equiv)
and THF (10 mL). The reaction was cooled to ꢀ78 ꢀC, and Pd-
(dppf)2Cl2 (0.18 g, 0.232 mmol, 2 mol % cat., dppf: 1,10-di(diphenyl-
LRI (SWax) 2690; LRI (SPB-1) 1873. In natural extract: LRI (SWax)
2691; LRI (SPB-1) 1871. 1H NMR (CDCl3, 400 MHz): δ 0.88 (t, J =
6.8 Hz, 3H); 1.20ꢀ1.37 (m, 6H); 1.48ꢀ2.23 (m, 10H); 2.40ꢀ2.62 (m,
Figure 2. Continued
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Figure 2. Mass spectra of new molecules identified in chicken and compared with those of the synthetic reference: (a) 5-propyl-1-cyclopentene-1-
carbaldehyde 6; (b) 5-pentyl-1-cyclopentene-1-carbaldehyde 7; (c) high-resolution GC-TOF-MS obtained on 12 in chicken extract E; (d) (E)-3-(5-
ethylcyclopent-1-enyl)acrylaldehyde 12; (e) 3-butyl-2-hydroxy-2-cyclopenten-1-one 19; (f) 2-hydroxy-3-pentyl-2-cyclopenten-1-one 20; (g) (8Z)-8-
tetradecen-5-olide 28; (h) (8E)-8-tetradecen-5-olide 29; (i) (6E)-6-tetradecen-5-olide 30; (j) 4-methyl-2-pentylpyridine 32.
phosphine)ferrocene) was added, followed by 3.0 N pentylmagnesium
bromide (10 mL, 17.4 mmol, 1.5 equiv). The reaction was allowed to
warm to 0 ꢀC until the starting material was consumed. The reaction was
quenched with saturated ammonium chloride solution (20 mL) and
extracted with ethyl acetate (20 mL). The ethyl acetate layer was
extracted with 1 N aqueous HCl (20 mL) to extract the pyridine
product from neutral organics. The aqueous acid layer was neutralized
with 1 N NaOH and extracted with ethyl acetate (20 mL). The
ethyl acetate layer was washed with brine and dried on anhydrous
sodium sulfate. The product phase was filtered and concentrated on
the rotary evaporator to give 4-methyl-2-pentylpyridine 32 (850 mg,
44.9% yield).
LRI (SWax) 1677 LRI (SPB-1) 1286. In natural extract: LRI (SWax)
1682; LRI (SPB-1) 1294. 1H NMR: 0.89 (t; 3H); 1.34 (m; 4 H); 1.72
(m; 2 H); 2.30 (s; 3 H); 2.72 (dd; 2 H); 6.91 (d; 1 H); 6.96 (s; 1 H); 8.37
(d; 1H). 13C NMR (100 MHz, CDCl3): δ 14.0 (q); 21.0 (q); 22.6 (t);
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Table 1. Linear Retention Indices (on Polar and Nonpolar Columns) and Relative Abundance in the Different Extracts of the New
Molecules Identified in the Present Studya,b
compd
LRIexp SWax
LRIexp SPB‑1
A
B
C
D
E
F
LRIref SWax
LRIref SPB‑1
6
1516
1725
1855
2095
2197
2662
2691
2744
1682
1105
1309
1299
1287
1389
1852
1871
1896
1294
_
_
_
tr
_
_
_
_
_
_
_
_
_
0.32
_
0.18
0.54
1.55
_
_
_
1518
1732
1853
2097
2195
2682
2707
2757
1702
1106
1308
1296
1288
1390
1855
1873
1900
1286
7
_
12
19
20
28
29
30
32
0.69
_
0.85
_
2.87
_
tr(A-7Al)
tr
_
tr
0.15
_
_
tr(A-7Al)
tr
_
_
_
_
_
_
_
tr(A-7Al)
_
_
_
_
tr(A-6)
_
_
_
_
a A = cooked fat Leybold distillate extract; B = cooked fat Leybold trap extract; C = cooked fat Leybold solid-phase microextraction extract; D = roasted
fat (LikensꢀNickerson) extract; E = roasted juice hydrodistillate extract; F = roasted skin hydrodistillate extract. The abundances are given in relative
percentage of the integration of the total ion current and are therefore not quantitative data. LRIexp: LRI measured in chicken extract; LRIref: LRI of
synthesized product; tr: trace: <0.1%; tr(X-Y): compound identified in the fraction Y after fractionation on SiO2 of extract X. b The linear retention
indices of the synthesized references are given in the right columns.
Scheme 1. Synthesis of 5-Propyl-1-cyclopentene-1-carbal-
dehyde 6 and 5-Pentyl-1-cyclopentene-1-carbaldehyde 7a
reflected the typicity of the starting materials. The evaluations are
given in Materials and Methods. In particular, the sweet, creamy
character of the cooked abdominal fat was clearly present in
extract A, evaluated as “heavy, sweet, fatty, creamy”. The roasted
skin extract F was “typical of grilled, roasted skin”.
The volatile composition of each extract was analyzed by GC/
MS. The complete results are given in Supporting Information.
Aldehydes (in particular alkanals (E)-2-alkenals, dienals) were
the major components of the different fractions. Interestingly,
some chemical families or molecules tended to be characteristic
of some extracts in which they were found in high amounts. In
particular, alcohols (e.g., 1-octen-3-ol, 1-hexanol, and (2Z)-
octenol) and ketones (e.g., 1-hydroxy-2-heptanone and 2-decan-
one) were found in higher amounts in roasted skin extract F as
compared with the other extracts. Phenylacetaldehyde, 1-hepta-
nol, and 4-butanolide were found in higher amounts in cooked fat
Leybold trap extract B. A compound that was newly identified as
(2E)-3-(5-ethyl-1-cyclopentenyl)propenal 12 (see the following)
was found in all extracts, with a higher abundance in roasted skin
extract F. Even if these differences between extracts can also
result from the different cooking procedures or from the extrac-
tion method, they likely reflect, at least in part, the typicity of the
distinct chicken parts.
a Reagents and conditions: (i) NaH, 1-iodoalcane, THF; (ii) concd aq
HCl; (iii) TsNHNH2, EtOH, HCl cat., reflux; (iv) n-BuLi, TMEDAꢀ
THF, and then DMF.
29.7 (t); 31.7 (t); 38.3 (t); 121.9 (d); 123.6 (d); 147.2 (s); 148.9 (d);
162.3 (s). MS (EI, 70 eV), m/z (%): 134(24); 120(25); 108(8);
107(100); 106(7); 77(5); 65(4); 39(4). HR-GC-TOF-MS: 163.1363
(C11H17N, +1.2 ppm).
General Procedure for New Compound Evaluation. The
new compound was diluted with propylene glycol in order to provide a
10% solution. This solution was then diluted using a 0.3% aqueous
solution of NaCl. Three flavorist experts evaluated the taste properties of
the new compounds using in-house descriptors.
Fractionation of cooked fat Leybold distillate (extract A) and
roasted skin hydrodistillate (extract F) by chromatography on
silica gel enabled us to detect many additional trace components,
which may be keys in the aroma of these fractions. The odor
evaluations of all resulting fractions are given in Materials and
Methods. Many pyrazines were found in trace amounts in roasted
skin extract F, resulting from Maillard reactions on the skin during
roasting. Compared with roasted juice, which contained a series of
γ-lactones (from 4-butanolide to 4-dodecanolide), cooked fat
Leybold distillate A contained mainly long-chain δ-lactones
(>C12), including the previously unknown lactones described
hereafter. Trace amounts of pyridines were also detected in
extract A after fractionation. Short chain pyridines (C2 to C5)
were identified in roasted juice extract E, whereas traces of longer
chain pyridines (C4 to C7) were found in cooked fat extract A.
In-depth GC/MS analysis of these extracts and fractions
revealed the presence of several unknown molecules, generally
present in only trace amounts in several extracts or fractions. The
’ RESULTS AND DISCUSSION
Preparation and GC/MS Analysis of Aroma Extracts from
Different Parts (Skin, Fat, and Juice) of Chicken. To maximize
our chance of finding new molecules, we investigated distinct
parts of top-quality chicken (Poulet de Bresse AOC from France)
obtained under different conditions (cooking or roasting). These
distinct parts had to be extracted with techniques appropriate to
their nature (solid or liquid, water or oil phase) (Figure 1).
Leybold distillation (or molecular distillation, or thin-film dis-
tillation) was applied to the cooked fat. During this distillation,
the most volatile compounds were captured in a trap at ꢀ200 ꢀC
and were subsequently analyzed by GC/MS and SPME-GC/MS.
Simultaneous distillation extraction (LikensꢀNickerson) was
applied to the roasted fat. The roasted juice and the roasted skin
were both extracted by hydrodistillation under reduced pressure.
The odor of the resulting extracts was evaluated by expert
flavorists, who agreed that the aroma of the resulting extracts
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Scheme 2. Synthesis of (E)-3-(5-Ethyl 1-cyclopentenyl)propenal 12a
a Reagents and conditions: (i) K2CO3, EtI, acetone, reflux; (ii) concd aq HCl, reflux 20 h; (iii) TsNHNH2, EtOH, HCl cat., reflux; (iv) n-BuLi,
TMEDAꢀTHF, and then DMF; (v) diethyl (N-methoxy-N-methylcarbamoylmethyl) phosphate, MeONa, THF; (vi) LiAlH4, Et2O.
Scheme 3. Synthesis of 3-Butyl-2-hydroxy-2-cyclopenten-1-one 19 and 2-Hydroxy-3-pentyl-2-cyclopenten-1-one 20a
a Reagents and conditions: (i) butyraldehyde, pyrrolidine, MTBE; (ii) I2, 160 ꢀC; (iii) H2O2, MeOH; (iv) acetic acid, sulfuric acid.
Scheme 4. Synthesis of the New δ-Lactones (8Z)-Tetradecen-5-olide 28, (8E)-tTetradecen-5-olide 29, and (6E)-Tetradecen-5-
olide 30 Identified in Chicken Fata
a Reagents and conditions: (i) 24, t-BuLi, Et2O (ꢀ78 ꢀC); (ii) 5% aq AcOH (0 ꢀC); (iii) KOH, EtOH; (iv) H2SO4.
elucidation of their structure was further investigated, as de-
scribed hereafter.
identification. All newly identified compounds have been synthe-
sized to confirm their occurrence in chicken. Their MS, their
LRIs on polar and nonpolar columns, and their relative abun-
dances in the different extracts are given in Figure 2 and Table 1.
Identification of Cyclic Aldehydes 6, 7, and 12 in Roasted
Juice. A series of rarely described cyclic aldehydes, 5-n-alkyl-1-
cyclopentene-1-carbaldehyde (C2 to C5), was identified in roasted
juice. In 1993, 5-methyl-, 5-ethyl-, and 5-butyl-1-cyclopentene-1-
carbaldehyde were identified for the first time by Werkhoff et al. in
Identification and Synthesis of New Volatile Compounds.
Identification of the structure of unknowns based solely on mass
spectra interpretation is challenging. Although many unknowns
could be elucidated during this work via mass spectra interpreta-
tion, others remained unidentified. Their mass spectra and LRIs
are given in Supporting Information. For certain compounds
such as 12, additional microchemical techniques helped in the
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Journal of Agricultural and Food Chemistry
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chicken.4 In our study, two additional members of this chemical class
were identified, namely, 5-propyl-1-cyclopentene-1-carbaldehyde 6
and 5-pentyl-1-cyclopentene-1-carbaldehyde 7. Compounds 6
and 7 were recently tentatively identified by Madruga et al. in
goat meat but had not been confirmed by synthesis.13 In our
study, 6 and 7 were prepared from the corresponding 2-alkylcy-
clopentanones by using the Shapiro reaction (Scheme 1). The
comparison of their mass spectra and LRIs (both on polar and
nonpolar phase) confirmed their occurrence in chicken.
One unknown compound was found in significant amount in
all fractions. This unknown had a mass spectrum very similar to
that of 2,4,7-decatrienal. All isomers of 2,4,7-decatrienal, ob-
tained as described in ref 14, eluted after the unknown product
on the polar GC column. The same spectrum had already been
obtained by Schroll et al. during an analysis of hen meat and
hypothesized as corresponding to an unspecified isomer of 2,4,7-
decatrienal.15 As given in Figure 2c, high-resolution GC-TOF-
MS indicated C10H14O (150.1031, ꢀ1.4 mDa) as the molecular
formula, therefore containing four double-bond equivalents.
Interestingly, the fragment m/z 121.0659 (C8H9O, +0.6 mDa)
corresponded to a loss of an ethyl group rather than a loss of
CHO. The product was purified from the extract F by using NP-
HPLC purification, yielding a diluted solution of pure unknown
compound on which we performed microchemical reactions to
determine the number of double bond(s) and ring(s). The
reduction with sodium borohydride gave a product with a
molecular ion at m/z 152. Then catalytic hydrogenation gave a
Scheme 5. Synthesis of 4-Methyl-2-pentylpyridine 32a
a Reagents: (i) n-C5H11MgBr, Pd(dppf)2Cl2.
Figure 3. Molecules newly identified in chicken and their flavor description (in salted water 0.3%). *First natural occurrence.
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product whose nominal mass had to be determined by negative-
CI GC/MS, using ammonia as reagent gas. The nominal mass of
m/z 156 so obtained indicated the presence of one ring. By using
all the information, the product was identified as penal (E)-3-(5-
ethylcyclopent-1-enyl)acrylaldehyde 12. This was confirmed by
chemical synthesis (Scheme 2) after comparison of both MS
spectra and LRIs. To the best of our knowledge, this new
aldehyde has never been identified in a natural product. The
formation of such cyclic aldehydes is not yet fully understood.
They may come from degradation of either linolenic acid or
cyclic fatty acids. Cyclopentyl and cyclohexyl fatty acids are
known to form during the frying of fat.16
Identification of New Hydroxyketones 19 and 20 in Cooked
Fat. The analysis of cooked fat revealed a series of uncommon
cyclic ketones, namely, 3-alkyl-2-hydroxy-2-cyclopenten-1-
ones. 3-Ethyl-2-hydroxy-2-cyclopenten-1-one was found in the
cooked fat Leybold trap extract B, and the longer homologues
hypothesized as 3-butyl-2-hydroxy-2-cyclopenten-1-one 19 and
2-hydroxy-3-pentyl-2-cyclopenten-1-one 20 were found in the
cooked fat distillate A. They were synthesized for confirmation
by acid-catalyzed rearrangement of 2,3-epoxy-2-alkylcyclopen-
tanones, obtained by alkaline hydrogen peroxide oxidation of
the corresponding 2-alkylcyclopent-2-en-1-ones (Scheme 3).17
Previously, they were only reported in smoke condensate of
cigarettes.18
Identification of New Lactones 28, 29, 30 in Cooked Fat. The
fractionation of the cooked fat Leybold distillate extract A by
flash chromatography provided 10 fractions that were evaluated
on paper strips and are described as given in Materials and
Methods. In particular, fraction A-7 had a “lactonic, peachy,
creamy” odor. This fraction contained mainly fatty acids (from
C10 to C18), which rendered the detection of minor components
difficult. An alumina treatment enabled us to selectively remove
the acids and subsequently detect many minor volatile compounds,
in particular δ- and γ-lactones. In particular, three unidentified
trace compounds were hypothesized as (8Z)-8-tetradecen-5-
olide, (8E)-8-tetradecen-5-olide, and (6E)-6-tetradecen-5-olide
on the basis of their MS fragmentation. These three new lactones
28ꢀ30 were confirmed by synthesis via cyclization of the corre-
sponding 5-hydroxyesters (Scheme 4).19 Their natural occurrence
is reported here for the first time. Their enantiomeric distribution
was not investigated in the present study.
Identification of 2-Pentyl-4-methylpyridine 32 in Cooked
Fat. A series of 2-alkylpyridines (C4 to C7) and 3-alkylpyridines
(C2 and C5) were found in trace amounts in roasted juice, as
well as in fractions A-6 and A-7 obtained after fractionation on
silica gel of the cooked fat Leybold distillate extract A. Although
most of these alkyl pyridines have already been identified by
Buttery et al. in the basic fraction of a roasted lamb fat extract,20
only a few of them have already been reported in chicken.6,10
Moreover, the taste enhancer properties of 2-pentyl, 2-hexyl,
and 2-heptylpyridine were discovered,21 as described recently.22
In the present study, 2-pentyl-4-methylpyridine 32 was tenta-
tively identified in fraction A-6 and confirmed by synthesis
(Scheme 5).
hydroxyketones 19 and 20, together with 3-ethyl-2-hydroxy-2-
cyclopenten-1-one, may contribute to the caramellic note of
roasted chicken. Because of their creamy and milky character,
the new lactones 28ꢀ30 may impart creaminess to the overall
aroma of cooked fat. Interestingly, 2-pentyl-4-methylpyridine
32 possesses a natural green, spicy-bell pepper odor, which
represents a novel aspect of green notes for perfumery appli-
cations.23
This study gives new insight into the aroma complexity of the
poulet de Bresse. The extraction of different parts of chicken
obtained under different cooking conditions provided extracts
having different molecular compositions. Although the volatiles
found in chicken meat have already been widely investigated for
many years, our approach allowed us to discover new molecules.
The in-depth GC/MS analysis of the separate fractions revealed
several trace unknown molecules. MS interpretation and micro-
chemical reactions allowed us to identify nine molecules for the
first time in chicken. They were all confirmed by chemical
synthesis after comparison of their mass spectra and LRIs. The
natural occurrence of five of them is reported here for the
first time.
’ ASSOCIATED CONTENT
S
Supporting Information. Volatile composition of chicken
b
extracts AꢀF. ThismaterialisavailablefreeofchargeviatheInternet
at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: +41 22 780 35 32. Fax: +41 22 780 22 11. E-mail:
estelle.delort@firmenich.com.
’ ACKNOWLEDGMENT
The chickens were cooked by Nicolas Maire. We thank him
and Dr. Robert Wagner for fruitful discussions. Mr. Robert
Brauchli is acknowledged for his help in the interpretation of
NMR spectra.
’ ABBREVIATIONS
DMF, dimethylformamide; EI, electron ionization; GC/MS, gas
chromatograph mass spectrometer; LRIs, linear retention in-
dices; MTBE, methyl tert-butyl ether; NP-HPLC, normal phase
high-performance liquid chromatography; SPME, solid-phase
microextraction; THF, tetrahydrofuran;BuLi, butyllithium; TOF,
time-of-flight
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