Identification and Synthesis of 2-Heptanethiol, a New Flavor Compound Found in Bell Peppers

Article abstract of DOI:10.1021/jf035008h

2-Heptanethiol was identified for the first time as a constituent of red and green bell pepper extracts. The chemical structure of this new aroma compound was proposed on the basis of mass spectra and retention indices and confirmed by chemical synthesis and nuclear magnetic resonance spectroscopy measurements. Its aroma properties were described as sulfury, onion-like, and vegetable-like, reminiscent of bell pepper at lower concentrations, with an orthonasal detection threshold of 10 μg/L of water. No differences in odor note and threshold value were observed for the enantiomeric forms, which were prepared from enantiopure 2-heptanol by tosylation, followed by thioacetylation and reduction, giving the target thiol enantiomers.

Full text of DOI:10.1021/jf035008h

306 J. Agric. Food Chem. 2004, 52, 306−310
Identification and Synthesis of 2-Heptanethiol, a New Flavor
Compound Found in Bell Peppers‡
HERVEÄ SIMIAN,† FABIEN ROBERT, AND IMRE BLANK*
Nestle´ Research Center, P.O. Box 44, 1000 Lausanne 26, Switzerland
2-Heptanethiol was identified for the first time as a constituent of red and green bell pepper extracts.
The chemical structure of this new aroma compound was proposed on the basis of mass spectra
and retention indices and confirmed by chemical synthesis and nuclear magnetic resonance
spectroscopy measurements. Its aroma properties were described as sulfury, onion-like, and
vegetable-like, reminiscent of bell pepper at lower concentrations, with an orthonasal detection
threshold of 10 µg/L of water. No differences in odor note and threshold value were observed for the
enantiomeric forms, which were prepared from enantiopure 2-heptanol by tosylation, followed by
thioacetylation and reduction, giving the target thiol enantiomers.
KEYWORDS: Bell peppers; 2-heptanethiol; identification; GC-MS; NMR; synthesis; odor thresholds
INTRODUCTION
GC and sensory data revealed that green bell peppers were
characterized by the sensory attributes grassy, green bell pepper,
and fruity, which were closely related to 1-penten-3-one, (Z)-
3-hexanal, (Z)-3-hexanol, 3-isobutyl-2-methoxypyrazine, and
linalool (8).
The study of bell pepper’s volatile constituents has been the
subject of numerous publications. Up to now almost 200
volatiles have been reported (1), of which only a few are
reminiscent of bell pepper aroma, such as 3-isobutyl-2-meth-
oxypyrazine first identified by Buttery and co-workers (2). This
odorant has a characteristic green, bell pepper-like note and a
very low detection threshold of 2 ng/L water (2). Additional
odor-active compounds have been reported in fresh green bell
pepper on the basis of gas chromatography/olfactometry (GC/
O), e.g. 2-methylpropanal, 2- and 3-methylbutanal, 2,3-butane-
dione, 1-penten-3-one, hexanal, heptanal, â-ocimene, trans-3-
hepten-2-one, dimethyl trisulfide, and â-cyclocitral (3). More
recently, a systematic work characterized odor-active compounds
of sweet bell pepper powder of different origins (4). The authors
stressed the importance of â-ionone, 4-hydroxy-2,5-dimethyl-
3(2H)-furanone, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, and
2- and 3-methylbutanoic acid among more than 30 odorants
identified.
Volatile organic sulfur compounds obtained by enzymatic and
chemical reactions contribute to the aroma of many vegetables,
fruits, and food products (9, 10). In general, thiols and sulfides
belong to the most intense and characteristic aroma substances
with sulfury, vegetable-like, fruity notes perceived at low
concentrations. For example, (2R,3S)-3-mercapto-2-methyl-1-
pentanol found in fresh onions and dimethyl sulfide found in
cooked tomatoes show low odor thresholds of 0.03 and 0.3 µg/
kg of water, respectively (11, 12), and are character-impact
constituents of the respective vegetable. In bell peppers, only a
few odor-active sulfur compounds have been identified, such
as methional (4) and dimethyl trisulfide (3, 5). However, no
thiols have so far been reported as odorants of bell peppers.
In our work on the natural constituents of vegetables, we
investigated the odor-active compounds of red bell pepper. This
paper deals with the identification of a secondary alkanethiol,
a new odorant found in red bell pepper extracts, as well as its
sensory properties and synthesis.
Changes during drying of bell pepper have been studied by
Luning and co-workers (5). These authors reported on additional
bell pepper-like smelling compounds such as the monoterpene
∆-3-carene, which was particularly abundant in red bell pepper.
This typical bell pepper note had an increasing impact in turning
and mature samples, particularly in fresh and dried red, yellow,
and white bell peppers (6). In addition, 2-heptanone/heptanal
has been suggested to elicit bell pepper and cooked vegetable
notes in rehydrated bell peppers (7). Moreover, correlation of
EXPERIMENTAL PROCEDURES
Materials. The following chemicals were commercially available:
2-heptanol (>99%), p-toluenesulfonyl chloride (>99%), sodium
hydrogen sulfide monohydrate (NaSH, 97%), potassium thioacetate
(97%), lithium aluminum hydride (>99%) (Fluka, Buchs, Switzerland);
(R)-2-heptanol (>99%), (S)-2-heptanol (>99%), deuterochloroform (C2-
HCl3, >99%) (Aldrich, Buchs, Switzerland); ammonium chloride
(98%), hydrochloric acid (HCl, 37%), magnesium sulfate (98%), sodium
sulfate, silica gel 60 (Merck, Darmstadt, Germany). The solvents
pentane, ethyl acetate (EtOAc), methylene chloride, ethanol (EtOH),
toluene, pyridine, dimethylformamide (DMF), and diethyl ether (Et2O)
were from Merck and were freshly distilled prior to use.
‡ Dedicated to Professor Dr. Werner Grosch on the occasion of his 70th
birthday.
* To whom correspondence should be addressed. Telephone: +21/785-
8607. Fax: +21/785-8554. E-mail: imre.blank@rdls.nestle.com.
† Present address: Product Technology Center Orbe, 1350 Orbe,
Switzerland.
10.1021/jf035008h CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/03/2003

2-Heptanethiol in Bell Peppers
J. Agric. Food Chem., Vol. 52, No. 2, 2004 307
Scheme 1. Synthesis of 2-Heptanethiol and Its Dimerization upon Heat Treatmenta
a See the text for abbreviations and an explanation.
Scheme 2. Synthesis of Enantiopure (S)-2-Heptanethiol
Syntheses. The target compound was synthesized from 2-heptanol
1 as starting material using classical approaches (13) and two methods
to transform the intermediary tosylate 2 into the target thiol 4 (Scheme
1).
2-(p-Toluenesulfonyl)heptane (2). 2-Heptanol (1; 28 mL, 200 mmol,
1.0 equiv) dissolved in pyridine (135 mL) was placed in a 500-mL
flask and cooled to 0 °C. p-Toluenesulfonyl chloride (41.8 g, 220 mmol,
1.1 equiv) was slowly added and the mixture was stirred at room
temperature overnight. Toluene was added (200 mL), the reaction
mixture filtered, and the filtrate washed with toluene (200 mL). The
mother liquor was washed twice with an aqueous HCl solution (5 N,
200 mL). The organic layer was dried over magnesium sulfate and
concentrated under reduced pressure. After dry chromatography on silica
gel (eluent pentane/EtOAc, 9:1, v/v), 2-(p-toluenesulfonyl)heptane (2)
the addition, stirring was continued for another 0.5 h at room tem-
perature. First a saturated ammonium chloride solution (2 mL) and then
hydrochloric acid (2 N, 2 mL) were added at -10 °C for hydrolysis.
The organic phase was separated and the aqueous phase extracted with
diethyl ether (2 × 20 mL). The combined organic phases were dried
over sodium sulfate. The solvent was evaporated to furnish the racemic
target product 4 (91 mg, 82% yield).
(R)- and (S)-2-Heptanethiol. Optically active 2-heptanethiols were
prepared from (S)- and (R)-2-heptanol using the reductive approach
(Scheme 2). The optical rotation of the target compounds, measured
in ethanol at 25 °C, was +33.7° (c ) 0.96) and -33.2° (c ) 0.83) for
(R)- and (S)-2-heptanethiol, respectively.
Isolation of Volatiles from Bell Peppers. Bell pepper (50 g, red or
green) was cut in small pieces and stirred in methylene chloride (100
mL) overnight at room temperature. After removing the solids by
filtration, crude extracts were obtained by high vacuum transfer using
the SAFE apparatus (14). The resulting clear extracts were dried over
sodium sulfate and concentrated on a Vigreux column (50 × 1 cm)
and by microdistillation (15) to 0.6 mL.
Extracts of cooked bell pepper were obtained by the simultaneous
distillation-extraction method (SDE) using methylene chloride as
solvent (16). Crude bell pepper (50 g, red or green) was cut in small
pieces and cooked in water (100 mL) for 2 h. The clear extracts
(1.3 mL for the green and 2.5 mL for red bell pepper) were dried over
sodium sulfate, and the resulting extracts were then concentrated to
0.7 mL on a Vigreux column and by microdistillation (15).
Gas Chromatography-Mass Spectrometry/Olfactometry (GC-
MS/O). Mass spectra of the synthesized compounds and their retention
indices were acquired using a gas chromatograph GC 5890 (Agilent,
Geneva, Switzerland) equipped with two splitless injectors heated at
260 °C and coupled with a quadrupole mass spectrometer MS 5970
(Agilent, Geneva, Switzerland) operating in the electron impact
ionization mode at 70 eV. Acquisitions were carried out over a mass
range of 10-350 Da. Separations were performed on a 100% dimethyl
polysiloxane apolar stationary phase (Ultra-1 PONA, 50 m × 0.20 mm
i.d., 0.5 µm film thickness, Agilent) and on a poly(ethylene glycol)
polar stationary phase (DB-Wax, 60 m × 0.25 mm i.d., 0.5 µm film
thickness, J&W, Folsom, CA). Helium was used as the carrier gas with
a constant flow rate of 0.6 and 1.0 mL/min, respectively. The oven
was programmed as follows: 20 °C (0.5 min), 70 °C/min to 60 °C,
4 °C/min to 240 °C. The temperature of the transfer line was held at
280 °C during the chromatographic run. Sniffing detection was
performed on both stationary phases. The same conditions were used
for the GC-MS analysis of bell pepper extracts.
1
was obtained as a colorless oil (40.8 g, 76% yield). H NMR (360
MHz, C2HCl3, δ/ppm): 0.82 (t, 3H, CH3, 3J ) 7.2 Hz), 1.12-1.23 (m,
6H, 3 CH2), 1.26 (d, 3H, CH3, 3J ) 6.3 Hz), 1.42-1.63 (m, 2H, CH2),
2.44 (s, 3H, CH3), 4.59 (qt, 1H, CH, 3J ) 6.1 Hz, 3J ) 6.35 Hz), 7.33
3
3
(d, 2H, J ) 8.3 Hz), 7.79 (d, 2H, J ) 8.3 Hz). 13C NMR (90 MHz,
C2HCl3, δ/ppm): 14.3 (CH3), 21.3 (CH3), 22.1 (CH3), 22.8 (CH2), 24.9
(CH2), 31.7 (CH2), 36.8 (CH2), 81.1 (O-CH), 128.1 (CdCH), 130.1
(CdCH), 135.0 (CdC), 144.8 (CdC).
2-Heptanethiol (4). In a 50-mL flask equipped with a reflux
condenser, 2-(p-toluenesulfonyl)heptane (2; 10.0 g, 37 mmol, 1.0 equiv)
and sodium hydrogen sulfide monohydrate (7.0 g, 94 mmol, 2.5 equiv)
were stirred in dimethylformamide (25 mL) at 80 °C for 2 h. The
reaction mixture was diluted in brine (200 mL) and the aqueous layer
was extracted with diethyl ether (3 × 200 mL). The organic layers
were combined and washed with brine (5 × 200 mL), dried over
magnesium sulfate, and concentrated under reduced pressure. The
racemic target compound 4 was obtained after distillation (143 mbar,
1
120 °C) as a colorless oil (1.82 g, 40% yield). H NMR (360 MHz,
3
C2HCl3, δ/ppm): 0.82 (t, 3H, CH3, J ) 7.2 Hz), 1.27-1.38 (m, 6H,
3
3 CH2), 1.36 (d, 3H, CH3, J ) 6.7 Hz), 1.49-1.62 (m, 2H, CH2),
2.96 (tq, 1H, 3J ) 6.5 Hz, 3J ) 6.1 Hz). 13C NMR (90 MHz, C2HCl3,
δ/ppm): 14.5 (CH3), 23.0 (CH2), 26.0 (CH3), 27.5 (CH2), 31.9 (CH2),
36.0 (CH3), 41.3 (CH).
2-(Acetylthio)heptane (3). In a 50-mL flask equipped with a reflux
condenser, 2-(p-toluenesulfonyl)heptane (2; 4.0 g, 15 mmol, 1.0 equiv)
and potassium thioacetate (4.3 g, 38 mmol, 2.5 equiv) were stirred in
dimethylformamide (15 mL) at 80 °C for 2 h. The reaction mixture
was diluted in brine (100 mL) and the aqueous layer was extracted
with diethyl ether (3 × 100 mL). The organic layers were combined
and washed with brine (5 × 50 mL), dried over magnesium sulfate,
and concentrated under reduced pressure. Distillation (0.16 mbar,
1
35 °C) gave 3 as a colorless oil (2.2 g, 84% yield). H NMR (360
3
MHz, C2HCl3, δ/ppm): 0.89 (t, 3H, CH3, J ) 6.5 Hz), 1.27-1.41
3
(m, 6H, 3 CH2), 1.30 (d, 3H, CH3, J ) 6.8 Hz), 1.51-1.56 (m, 2H,
3
3
CH2), 2.31 (s, 3H,CH3); 3.55 (tq, 1 H, SCH, J ) 6.8 Hz, J ) 7.0
Hz). 13C NMR (90 MHz, C2HCl3, δ/ppm): 14.4 (CH3), 21.7 (CH3),
22.9 (CH2), 27.1 (CH2), 31.2 (CH3), 31.9 (CH2), 36.7 (CH2), 40.0 (CH),
196.6 (S-CdO).
Nuclear Magnetic Resonance (NMR) Spectroscopy. The samples
for NMR spectroscopy were prepared in Wilmad 528-PP 5 mm Pyrex
NMR tubes using deuterochloroform as solvent (0.7 mL). The NMR
spectra were acquired on a Bruker AM-360 spectrometer equipped with
a quadrinuclear 5 mm probe head, at 360.13 MHz for 1H and at 90.03
MHz for 13C under standard conditions (17). All chemical shifts are
cited in ppm relative to the solvent signal.
2-Heptanethiol Via 2-(Acetylthio)heptane. 2-(Acetylthio)heptane
(3; 0.146 g, 0.84 mmol) was diluted in dry diethyl ether (3 mL) and
added slowly (1.5 h) at -10 °C under nitrogen to a suspension of
lithium aluminum hydride (0.144 g) dissolved in dry diethyl ether
(2 mL). The temperature inside the flask did not exceed 5 °C. After

308 J. Agric. Food Chem., Vol. 52, No. 2, 2004
Simian et al.
Figure 1. GC−MS profile of a cooked red bell pepper extract obtained
on a nonpolar PONA capillary column. The unknown target compound is
marked with an arrow.
Polarimetry. Optical activity was measured in ethanol at 25 °C using
a Perkin-Elmer 241 polarimeter with a sodium lamp at 589 nm and a
slit of 1 mm. The cuvette length was 100 mm.
Threshold Determination. Orthonasal detection thresholds were
determined in water (Vittel) by seven panelists. Eight samples were
presented in order of decreasing concentrations (a factor of 10 between
samples) to estimate the range of threshold concentration. Threshold
values were determined by a triangle test using a series of four
concentrations (a factor of 2.5 between samples). Threshold values
correspond to more than 70% of correct answers.
RESULTS AND DISCUSSION
Investigation of Raw and Cooked Bell Peppers. In this
work we focused on the volatile composition of red bell peppers.
GC-O analysis performed on two capillary columns revealed
a powerful and very typical red bell pepper-like note detected
at RI(PONA) ) 953 and RI(DB-Wax) ) 1170. The compound
was also described as sulfury and fruity. The abundance of this
compound was relatively high, as shown in Figure 1, obtained
by GC-MS of a cooked red bell pepper extract on the nonpolar
capillary column. Luning and co-workers (5) also found a
compound by GC-O having bell pepper-like notes at RI(CP-
Wax 52CB) ) 1152, which is close to the unknown compound
found in this study. Surprisingly, the authors associated the
strong red/green bell pepper-like, rubbery notes with ∆-3-carene,
which has been described in the literature as terpene-like (18).
Indeed, our panel used the descriptors terpenic, limonene-like,
and slightly lemon-like for ∆-3-carene, which was baseline
separated from the unknown bell pepper-like smelling odorant.
Therefore, additional experiments were performed to clarify
the identity of the bell pepper-like odorant. Figure 2 shows the
GC-MS profiles of the raw (SAFE extraction) and cooked
(SDE extraction) red and green bell peppers and confirms the
presence of the unknown compound in all four extracts.
Surprisingly, higher amounts of the thiol were found in cooked
samples. It was about 4 times more concentrated in the red bell
pepper than in the green variety. However, this compound was
already detected at a low concentration level in raw red and
green bell pepper.
Figure 2. GC−MS profile of liquid bell pepper extracts obtained on a
polar DB−Wax capillary column: A, cooked red bell pepper; B, raw red
bell pepper; C, cooked green bell pepper; D, raw green bell pepper.
Identification of 2-Heptanethiol. The corresponding peaks
on polar and nonpolar capillary columns revealed identical mass
spectra (Figure 3), thus confirming that only one specific
molecule was imparting this typical note. Interpretation of the
mass spectrum indicated the presence of an even fragment at
m/z 98, which may stem from the mass at m/z 132 by loss of
Figure 3. Mass spectrum of the unknown compound.
H2S. Another main indication for a sulfur compound was the
presence of an intense ion at m/z 61, generally associated with
a C2H5S fragment. Assuming that 132 Da was the molecular

2-Heptanethiol in Bell Peppers
J. Agric. Food Chem., Vol. 52, No. 2, 2004 309
weight of the unknown compound, the isotopic distribution of
the molecular peak was M + 1 (m/z 133) ) 14.5% and M + 2
(m/z 134) ) 3.6%. The value measured at M + 2 was close to
the typical isotopic abundance of one sulfur atom (4.4%). This
is consistent with the fragment at m/z 61 and a loss of 34 Da
corresponding to H2S. Consequently, the formulas C6H12OS and
C7H16S were found to be coherent with the MS spectrum.
Table 1. Thiols Synthesized and Their Sensory Properties
compound
odor description
thresholdc
10
(R,S)-2-heptanethiol
bell pepper, fruity, vegetables
(sulfury, onion, mushroom)b
fruity (4), sweet (4), tropical (4),
fresh (2), floral (1)
2-heptanethiola
nd
10
10
(R)-2-heptanethiol
(S)-2-heptanethiol
bell pepper, fruity, vegetables
(sulfury, onion, mushroom)b
bell pepper, fruity, vegetables
(sulfury, onion, mushroom)b
Moreover, the significant fragment at m/z 61 (C2H5S+), as
the result of an R-cleavage of the mercaptan, suggested a
secondary thiol containing an adjacent methyl group, which is
also indicated by m/z 117 ([M - 15]+). The remaining part of
the molecule was supposed to be a C4H7O or a C5H11 with m/z
71. The base peak at m/z 57 is typical for an ethyl ketone
(MeCH2COR′) or an alkyl group with four carbons with or
without ramifications (MeC3H6R′) with R′ ) C3H7S (due to
the loss of 75 Da). After combining the two moieties of the
molecule, a mass of 14 Da, corresponding to a methylene group,
was still missing. Thus, the following hypothetical formulas can
be proposed: MeCH2COCH2CH(Me)SH or MeC4H8CH(Me)-
SH. The only way to associate a secondary thiol and an ethyl
ketone with the formula C6H12OS is 5-mercapto-3-hexanone.
Concerning the secondary thiol with the formula C7H16S, five
possible formulas were conceivable, but 2-methyl-2-hexanethiol
could be excluded because the R-cleavage gives a strong peak
at m/z 75 associated with the fragment C3H7S+ (CMe2SH+).
a Odor description adapted from ref 22. The odor strength of each descriptor
was scored from 0 (none) to 5 (strong). b Odor description at a higher concentration
(about 1 mg/L). c Detection threshold in µg/L of water was obtained by orthonasal
measurements performed by seven panelists (nd ) not determined).
Sensory Properties. The odor properties of 2-heptanethiol
are summarized in Table 1. Racemic 2-heptanethiol showed a
low orthonasal detection threshold value of 10 µg/L of water.
This threshold is similar to the well-known hydrogen sulfide,
having a sulfury, egg-like note (9). In high dilution, i.e. about
10-times the threshold, racemic 2-heptanethiol was mainly
described as bell pepper-like, fruity, and vegetable-like. At
higher concentrations (100-1000 times the threshold), the odor
description was completely different: sulfury, onion-like, with
some mushroom note. However, no significant difference was
observed between the two enantiomers (Table 1). In the
literature, the odor of 2-heptanethiol has been described as sweet,
fruity, tropical (sulfury), and floral, however, without indicating
the threshold value (22). The authors stressed the unique odor
of this compound and 2-octanethiol compared to other 1- and
2-alkylthiols.
The bell pepper-like note previously associated with 2-hep-
tanone/heptanal and ∆-3-carene (5-7) was most likely provoked
by 2-heptanethiol, considering its physical, chemical, and
sensorial properties. On the other hand, 2-heptanol and 2-hep-
tanone were detected in all extracts as possible precursors
functionalized in position 2 and owning the same C7 carbon
chain. 2-Heptanone was present in higher amounts in raw green
bell pepper than in red bell pepper (data not shown), which is
in agreement with literature data (5). The same ratio was
observed in cooked bell peppers but at higher concentrations.
On the contrary, all samples contained the same low level of
2-heptanol. 2-Heptanethiol might be formed through the me-
tabolism of the plant without any effect of the ripening because
of the similar amounts found in raw green and red bell peppers.
Alternatively, it might be generated during the cooking process
from a precursor that is probably present in higher amount in
the mature bell pepper compared to the green sample.
In conclusion, 2-heptanethiol was identified in red bell pepper
extracts using combined analytical and synthetic approaches.
Its sensory properties suggest that this new flavor compound
plays a role in imparting the characteristic red bell pepper note
in low concentrations. It may find applications in bell pepper
or vegetable flavor compositions.
Consequently, the four possible isomers were synthesized.
Only the 2-heptanethiol showed exactly the same mass spectra
and retention indices on both columns as the odorant isolated
from bell peppers. The sensory properties of the synthetic
compound were confirmed by GC-sniffing by three panelists
with four repetitions each. 2-Heptanethiol is a new nature-
identical component never described in food before. It has been
cited as a constituent of crude oil distillate (19), natural gas
(20), and in a Japanese patent focusing on asymmetric synthesis
of optically active thioesters and thiols (21).
Synthesis of 2-Heptanethiol. The target compound was
synthesized from 2-heptanol 1 by activating the hydroxyl
function with p-toluenesufonyl chloride (TsCl), followed by two
approaches to release the thiol from the intermediate tosylate 2
(Scheme 1). 2-Heptanethiol (4) was obtained either by a direct
nucleophilic substitution of 2 with sodium hydrogen sulfide
(NaSH) or with potassium thioacetate (KSAc) followed by
reduction of the thioester 3. With sodium hydrogen sulfide as
nucleophile, the conversion was excellent, but the yield was
not satisfactory, most likely due to the instability of the target
thiol 4 that easily oxidized to the corresponding disulfide 5 upon
distillation (Scheme 1). On the contrary, with potassium
thioacetate as nucleophile, the nucleophilic substitution led to
2-(acetylthio)heptane 3 in good yields. Reduction with lithium
aluminum hydride resulted in the target thiol.
The synthesis procedure chosen for secondary thiols and
thioesters led to racemic mixtures. Both enantiomers of 2-hep-
tanethiol were prepared to evaluate their sensory properties. The
acetylthio approach was employed using commercially available
pure (R)- and (S)-2-heptanol as starting materials. The two
enantiomers were obtained in 56% and 45% overall yield,
respectively. To keep the optical purity, the nucleophilic
substitution should be an SN2 reaction. Polarimetric measure-
ments indicated that no racemization occurred during nucleo-
philic substitution. The optical rotation of the target compounds
was +33.7° (c ) 0.96, EtOH) and -33.2° (c ) 0.83, EtOH)
for (R)- and (S)-2-heptanethiol, respectively. Due to Walden
inversion, (S)- and (R)-2-heptanethiol were obtained from (R)-
and (S)-2-heptanol, respectively (Scheme 2).
ACKNOWLEDGMENT
We are grateful to Mrs. Francia Acre Vera for the NMR
measurements and Dr. Elizabeth Prior for critical proofreading
of the manuscript.
NOTE ADDED AFTER ASAP
The original posting of December 3, 2003, contained an
incorrect version of Figure 2. The correct version of this figure
is included in the posting as of December 5, 2003.

310 J. Agric. Food Chem., Vol. 52, No. 2, 2004
Simian et al.
(13) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis;
Wiley: New York, 1967; Vol. 1, p 1179.
LITERATURE CITED
(14) Engel, W.; Bahr, W.; Schieberle, P. Solvent assisted flavor
evaporation. A new and versatile technique for the careful and
direct isolation of aroma compounds from complex food
matrixes. Eur. Food Res. Technol. 1999, 209, 237-241.
(15) Bemelmans, J. M. H. Review of isolation and concentration
techniques. In Progress in FlaVour Research; Land D. G.,
Nursten H. E., Eds.; Applied Sciences: London, 1979; pp 79-
88.
(1) Nijssen, L. M.; Visscher, C. A.; Maarse, H.; Willemsens, L. C.
Volatile Compounds in Food, 7th ed.; TNO Nutrition and Food
Research Institute: Zeist, 1996; p 26.1.
(2) Buttery, R. G.; Seifert, R. M.; Guadagni, D. G.; Ling, L. C.
Characterization of some volatile constituents of bell peppers.
J. Agric. Food Chem. 1969, 17, 1322-1327.
(3) van Ruth, S. M.; Roozen, J. P. Gas chromatography/sniffing port
analysis and sensory evaluation of commercially dried bell
peppers (Capsicum annuum) after rehydration. Food Chem. 1995,
54, 165-170.
(4) Zimmermann, M.; Schieberle, P. Important odorants of sweet
bell pepper powder (Capsicum annuum cv. annuum): Differ-
ences between samples of Hungarian and Moroccan origin. Eur.
Food Res. Technol. 2000, 211, 175-180.
(5) Luning, P. A.; de Rijk, T.; Wichers H. J.; Roozen, J. P. Gas
chromatography, mass spectrometry, and sniffing port analyses
of volatile compounds of fresh bell peppers (Capsicum annuum)
at different ripening stages. J. Agric. Food Chem. 1994, 42, 977-
983.
(6) Luning, P. A.; Ebbenhorst-Seller, T.; de Rijk, T.; Roozen, J. P.
Effect of hot-air-drying on flavour compounds of bell peppers
(Capsicum annuum). J. Sci. Food Agric. 1995, 68, 355-365.
(7) van Ruth, S. M.; Roozen, J. P.; Cozijnsen, J. L.; Posthumus, M.
A. Volatile compounds of rehydrated French beans, bell peppers
and leeks. Part II. Gas chromatography/sniffing port analysis and
sensory evaluation. Food Chem. 1995, 54, 1-7.
(8) Luning, P. A.; Yuksel, D.; Roozen, J. P. Sensory attributes of
bell peppers (Capsicum annuum) correlated with the composition
of volatile compounds. In Trends in FlaVour Research; Maarse,
H., van der Heij, D. J., Eds.; Developments in Food Science,
Vol. 35; Elsevier Science: Amsterdam, 1994; pp 241-248.
(9) Blank, I. Sensory relevance of volatile organic sulfur compounds
in food. In Heteroatomic Aroma Compounds; Reineccius G. A.,
Reineccius T. A., Eds.; ACS Symposium Series 826; American
Chemical Society: Washington, DC, 2002; pp 25-53.
(10) Boelens, M. H.; van Gemert, L. J. Volatile character-impact sulfur
compounds and their sensory properties. Perfumer FlaVorist
1993, 18, 29-39.
(16) Nickerson G. B.; Likens, S. T. Gas chromatographic evidence
for the occurrence of hop oil components in beer. J. Chromatogr.
1966, 21, 1-5.
(17) Lin, J.; Welti, H. D.; Arce Vera, F.; Fay, L. B.; Blank, I.
Synthesis of deuterated volatile lipid degradation products to be
used as internal standards in isotope dilution assays. 1. Alde-
hydes. J. Agric. Food Chem. 1999, 47, 2813-2821.
(18) Tairu, A. O.; Hofmann, T.; Schieberle, P. Identification of the
key aroma compound in dried fruits of Xylopia aethiopica. In
PerspectiVes on new crops and new uses; Janick, J., Ed.; ASHS
Press: Alexandria, 1999; pp 474-478.
(19) Coleman, H. J.; Thomson, C. J.; Hopkins, R. L.; Rall, H. T.
Identification of thiols in a Wasson, Texas, crude oil distillate
boiling from 111° to 150°. J. Chem. Enginer. Data 1965, 10,
80-84.
(20) Vol’tsov, A. A.; Lyapina, N. K. Organosulfur compounds of
condensates from Orenburg and Sovkhoznensk deposits. Khim.
Tekhnol. TopliV Masel 1980, 4, 37-40 (in Russian; Chem. Abstr.
1980, 93, 50013).
(21) Maejima, Y.; Yoshiwara, M.; Komori, H.; Kondo, S.; Fujiwara,
H.; Yoneda, A. Optically active thioesters and optically active
thiols derived from them. Japanese Patent Application JP
55139355 A2, 31.10.1980 (in Japanese, Chem. Abstr. 1981, 94,
120897).
(22) Sakoda, Y.; Hayashi, S. Relationship of odour and chemical
structure in 1- and 2-alkyl alcohols and thiols. In AdVances in
FlaVours and Fragrances; Swift, K. A. D., Ed.; Special
Publication no. 277; Royal Society of Chemistry: Cambridge,
2002; pp 15-24.
(11) Widder, S.; Sabater Lu¨ntzel, C.; Dittner, T.; Pickenhagen, W.
3-Mercapto-2-methylpentan-1-ol, a new powerful aroma com-
pound. J. Agric. Food Chem. 2000, 48, 418-423.
(12) Buttery, R. G.; Teranishi, R.; Ling, L. C.; Turnbaugh, J. G.
Quantitative and sensory studies on tomato paste volatiles. J.
Agric. Food Chem. 1990, 38, 336-340.
Received for review September 4, 2003. Revised manuscript received
October 16, 2003. Accepted October 26, 2003.
JF035008H