New constituents related to 3-methyl-2,4-nonanedione identified in green tea

Article abstract of DOI:10.1021/jf061738o

The volatile constituents of two exquisite green tea varieties, Kiyosawa tea from Japan and Long Jing tea from China, were investigated in order to identify new compounds responsible for the characteristic flavor of a green tea brew. The extracts were prepared by solid-phase extraction using Oasis-HLB-cartridges. Besides the common compounds of green tea chemistry, the already described compounds 3-methyl-2,4-nonanedione (1) and 3-hydroxy-3-methyl-2,4-nonanedione (2), products of degradation of furan fatty acids, as well as three new compounds related to compound 1 were identified. These were 1-methyl-2-oxopropyl hexanoate (3), 1-methyl-2-oxoheptyl acetate (4) and 2-butyl-4,5-dimethyl-3(2H)-furanone (5). Their syntheses and spectroscopic data are reported. Compound 2 increases the sweet, creamy aroma and the characteristic mouthfeel of a green tea flavor, compounds 3 and 4 contribute to its floral, juicy notes and compound 5 exhibits an interesting sweet, buttery flavor.

Full text of DOI:10.1021/jf061738o

J. Agric. Food Chem. 2006, 54, 9201−9205 9201
New Constituents Related to 3-Methyl-2,4-nonanedione
Identified in Green Tea
REGULA NAEF,† ALAINI JAQUIER,* ALAIN VELLUZ, AND BRUNO MAURER
Firmenich SA, Corporate R&D Division, P.O. Box 239, CH-1211 Geneva 8, Switzerland
The volatile constituents of two exquisite green tea varieties, Kiyosawa tea from Japan and Long
Jing tea from China, were investigated in order to identify new compounds responsible for the
characteristic flavor of a green tea brew. The extracts were prepared by solid-phase extraction using
Oasis-HLB-cartridges. Besides the common compounds of green tea chemistry, the already described
compounds 3-methyl-2,4-nonanedione (1) and 3-hydroxy-3-methyl-2,4-nonanedione (2), products of
degradation of furan fatty acids, as well as three new compounds related to compound 1 were
identified. These were 1-methyl-2-oxopropyl hexanoate (3), 1-methyl-2-oxoheptyl acetate (4) and
2-butyl-4,5-dimethyl-3(2H)-furanone (5). Their syntheses and spectroscopic data are reported.
Compound 2 increases the sweet, creamy aroma and the characteristic mouthfeel of a green tea
flavor, compounds 3 and 4 contribute to its floral, juicy notes and compound 5 exhibits an interesting
sweet, buttery flavor.
KEYWORDS: Green tea; Camellia sinensis; 3-methyl-2,4-nonanedione; 3-hydroxy-3-methyl-2,4-nonanedi-
one; 1-methyl-2-oxopropyl hexanoate; 1-methyl-2-oxoheptyl acetate; 2-butyl-4,5-dimethyl-3(2H)-furanone;
new constituents
INTRODUCTION
EXPERIMENTAL PROCEDURES
Materials. Long Jing tea was received from Zhejiang province
(China), and Kiyosawa (Sen-cha) was purchased from Betjeman &
Barton (Carouge/Switzerland). OASIS-HLB cartridges were obtained
from Waters Corporation (Milford, MA, 20 mL), filled with 1 g of the
polymer [poly(divinylbenzene-co-N-vinylpyrrolidone)]. Silica gel (35-
70 µm, SDS, France) was deactivated with 50% water.
Preparation of Tea Extracts. Tea leaves (50 g) were brewed in
demineralized water (500 mL) at 70 °C for 8 min. The leaves were
filtered off through a cotton plug. The tea infusion (350 mL) was
immediately cooled down to room temperature. An OASIS-HLB-
cartridge (20 mL/1 g) was conditioned as follows: under a slight
vacuum, methanol (10 mL) and then water (10 mL) were passed
through. The cooled tea was loaded under vacuum (water pump), and
then the cartridge was rinsed with water (100 mL) and with water
containing 5% methanol (10 mL). The tea extract was eluted with ether
(25 mL), which was dried and concentrated.
Guth and Grosch mentioned 3-methyl-2,4-nonanedione (1)
(Figure 1) for the first time as off-flavor in reversed soybean
oil (1). The same authors identified it as a compound with
beneficial odor contribution in tea (2). In addition to its previous
identification in dry spinach (3), we found it in fresh spinach
leaves and described its organoleptic properties (4). Very
recently, Kumasawa et al. (5) protected its use in green tea with
a patent, and recently, it got the FEMA-number 4057 which
opened its use in flavor creations. Amado et al. (6-8) published
a series of investigations about its light-induced oxidation and
autoxidation in model reactions as well as in green tea and
established its relationship with furan fatty acids. The structure
of 3-hydroxy-3-methyl-2,4-nonanedione (2) (Figure 1) was
proposed on the basis of its mass and infrared spectra (8).
GC-MS Analysis. GC-MS was performed on a GC 6890 (Agilent,
Palo Alto, CA) equipped with a 30 m × 0.25 mm i.d. fused silica
Supelcowax polar capillary column, film thickness 0.25 µm, held at
50 °C for 5 min, then increased at 5 °C/min. to 240 °C, coupled to a
MS 5972 (Agilent) or on a GC 6890 equipped with a 30 m × 0.25
mm i.d. SPB-1 apolar column, film thickness 1 µm, held at 60 °C for
5 min, then increased at 5 °C/ min. to 250 °C, coupled to a MS 5971
(Agilent). The carrier gas was He (63 kPa) for both systems. The mass
spectra in the electron impact mode (EI) were measured at 70 eV in a
scan range from 35 to 300.
In the present study, extracts of brews of Chinese Long Jing,
a famous green tea from Zhejiang province, and of Japanese
Kiyosawa tea, a rare Japanese “Sen-cha” from a small tea
garden, were prepared by solid-phase extraction and analyzed
in search of compounds which would contribute to the char-
acteristic green, woody, and haylike flavor of green tea. The
structures of the new compounds were established by interpreta-
tion of the mass spectra and were confirmed by syntheses. Their
organoleptic properties were evaluated.
1
NMR Spectra. H and 13C NMR spectra were recorded in CDCl3
on a Bruker DPX 400 instrument with tetramethylsilane as internal
standard, δ ) 0.00 ppm (coupling constants J in Hz). Pulse sequence:
power-gated decoupled 13C experiments with 30° excitation pulse
(decoupling scheme WALTZ16); multiplicity was obtained from
* To whom correspondence should be addressed. Phone: +41 22 780
34 70. Fax: +41 22 780 33 34. E-mail: alain.jaquier@firmenich.com.
† Present address: Achermattstrasse 4, CH-6423 Seewen, Switzerland.
E-mail: rfnaef@bluewin.ch.
10.1021/jf061738o CCC: $33.50
© 2006 American Chemical Society
Published on Web 11/04/2006

9202 J. Agric. Food Chem., Vol. 54, No. 24, 2006
Naef et al.
Figure 1. Compounds related to 3-methyl-2,4-nonandione (1).
Spectroscopic data of 6 were consistent with literature data (10)
(()-1-Acetyl-1-methyl-2-oxoheptyl dimethyl phosphate (7). In a dried
flask, hexanoyl chloride (21.52 g, 0.16 mol, Fluka) was added dropwise
at room temperature to 6 (33.6 g, 0.16 mol). The reaction mixture was
stirred at 80 °C overnight (19 h) and became dark brown. Volatile
byproducts were distilled off from 65 to 83 °C at 0.26 Torr, using a
Vigreux column, and the residue which contained the desired product
was bulb-to-bulb distilled (180 °C/0.15 Torr). Compound 7 (14.22 g)
in a purity of ca. 80% by GC-MS was recovered (yield: 30%). A
byproduct which was isolated by chromatography on deactivated silica
gel using pentane with 10% ether as solvent was characterized as (()-
2-butyl-4,5-dimethyl-3(2H)-furanone (5, purity: >95%). Analytical data
follow for 7. MS: m/z 294 (M+•, 0), 252 (3), 196 (28), 127 (100), 109
Figure 2. Diketone 1 and its enol.
DEPT90 and DEPT135 experiments, with 1 s recycle delay, 26000 Hz
sweep width, 32768 data-points, and 1.5 Hz line-broadening. CoSY,
13C,1H HSQC, and 13C,1H HMBC-experiments were performed on a
Bruker ADVANCE 500 MHz at 25 °C under standard conditions with
coherence selection by gradients and a number of increments of 256.
Linear Retention Indices (RI). RI were determined after injection
of a series of n-alkanes under the same conditions.
1
(12), 79 (2), 43 (15); H NMR: 0.89 (t, J ) 6, 3H); 1.20-1,35 (m,
4H); 1.56 (m, 2H); 1.84 (s, 3H); 2.27 (s, 3H); 2.62 (m, 2H); 3.85 (dd,
J ) 10, 6H); 13C NMR: 204.5 (s); 202.2 (s); 93.1 (s); 54.7 (q); 54.6
(q); 37.5 (t); 31.1 (t); 25.6 (q); 22.8(t); 22.4 (t); 20.3 (q); 13.9(q); 31P
NMR: -1.9(s), (ref 85% H3PO4). Analytical data follow for 5. MS:
m/z 168 (M+•, 18), 125 (60), 112 (100), 97 (4), 83 (8), 54 (13), 43 (3);
1H NMR: 0.91 (t, J ) 6, 3H); 1.38 (m, 4H); 1.62 (m, 1H); 1.66 (s,
3H); 1.91 (m, 1H); 2.19 (s, 3H); 4.33(dd, J ) 7.5 and 3.7, 1H); 13C
NMR: 205.2 (s); 184.7 (s); 110.8 (s); 84.7 (d); 31.0 (t); 26.9 (t); 22.4
(t); 14.9 (q); 13.9 (q); 5.6 (q). RI polar: 1792; RI apolar: 1277; UV: 272
Syntheses. 3-Methyl-2,4-nonanedione (1). See Figure 2. Using the
method of Adams and Hauser (9), 2-butanone was acylated with
hexanoic anhydride using stoichiometric amounts of BF3‚AcOH. A
mixture of â-diketone 1 and the corresponding enol 1a in a ratio 3:1
was obtained (yield 53%). Analytical data follow for 1. MS: m/z 170
(M+•, 3), 155 (1), 152 (1), 127 (1), 114 (4), 99 (78), 86 (5), 71 (40), 55
1
(12), 43 (100); H NMR: was consistent with previous reports (1);
13C NMR: 207.4 (s); 205.2 (s); 61.7 (d); 41.7 (t); 31.3 (t); 28.5 (q);
23.2 (t); 22.4 (t); 13.9 (q); 12.7 (q); RIpolar: 1725; RIapolar: 1211.
Analytical data follow for 1a. MS: m/z 170 (M+•, 10), 155 (7), 152
(5), 137 (2), 127 (6), 114 (14), 99 (100), 85 (4), 71 (15), 55 (10), 43
nm (ꢀ ) 6181) in EtOH; IR (neat): 1698, 1613 cm-1
.
(()-3-Hydroxy-3-methyl-2,4-nonanedione (2). In a flask, 7 (7.35 g
at 80% purity, 20 mmol), H2O (6.25 mL) and toluene (30 mL) were
refluxed for 2 h. After the reaction mixture was cooled to room
temperature, the water phase was separated, saturated with NaCl and
extracted with toluene (3x). The combined organic extracts were dried
over MgSO4. The solvent was removed using a Rotavapor and the
residue (6.33 g) purified on deactivated silica gel using pentane/10%
ether as solvent to give pure 2 (1.97 g, yield: 53%). Analytical data
follow for 2. MS was consistent with literature (8); 1H NMR: 0.88 (t,
J ) 6.5, 3H); 1.26 (m, 4H); 1.54 (m, 2H); 1.53 (s, 3H); 2.23 (s, 3H);
2.49 (m, 1H); 2.66 (m, 1H); 4.73 (s, 1H); 13C NMR: 209.6 (s); 207.4
(s); 87.6 (s); 36.8 (t); 31.2 (t); 24.6 (q); 23.1 (t); 22.7 (q); 22.4 (t); 13.9
(q). RI polar: 1712; RI apolar: 1201.
1
(66). H NMR: consistent with literature data (1). 13C NMR: 193.5
(s); 190.3 (s); 104.4 (s); 35.9 (t); 31.6 (t); 25.0 (t); 23.5 (q); 22.5 (t);
14.0 (q); 12.6 (q). RIapolar: 1295. The compound was unstable on a
polar column.
3-Hydroxy-3-methyl-2,4-nonanedione (2). See Figure 3. This com-
pound was prepared using the general method of Raminez et al. (10)
for analogous structures.
2,2,2-Trimethoxy-4,5-dimethyl-1,3,2-dioxaphosphole (6). In a dried
flask, 2,3-butanedione (17.20 g, 0.20 mol, Fluka) was added very slowly
(exothermic!) at 0-5 °C to trimethyl phosphite (27.28 g, 0.22 mol).
The reaction mixture was stirred at room temperature overnight and
then distilled (40-47 °C/0.1 Torr) using a Vigreux column to give
pure 6 (35.04 g, yield: 83%).
(()-1-Methyl-2-oxopropyl hexanoate (3). This compound was
synthesized by analogy to the method of Long (11) (Figure 4).
Figure 3. Synthesis of compounds 2 and 5.

New Compounds in Green Tea
J. Agric. Food Chem., Vol. 54, No. 24, 2006 9203
Figure 4. Syntheses of compounds 3 and 4.
Sodium Hexanoate (10). NaOH (20 g, 0.5 mol) in H2O (80 mL)
was introduced into a flask cooled in an ice/water bath. Hexanoic acid
(8, 58.0.g, 0.5 mol) was added dropwise. After warming to room
temperature the mixture (pH 8) was washed with ether to remove any
free acid. The sticky salt was dried and reduced to a fine powder with
a mortar.
temperature for 2 h. Then, pentylmagnesium chloride (11), prepared
under standard conditions (53 mmol) in THF (20 mL), was added
dropwise at -10 °C. After 15 min, the reaction mixture was cooled to
-20 °C, and 2-acetoxy-propanoyl chloride (12), prepared according
to Plieninger et al. (13) with thionyl chloride at 90 °C, was added
dropwise. The reaction was stopped after 1.5 h, and the mixture was
hydrolyzed with 1 N HCl at -10 °C, extracted with ether, washed
with brine, dried over MgSO4, and concentrated. The crude residue
(8.76 g) was decolorized with active charcoal and distilled at 108-
111 °C/12 mmHg to give 3.74 g of compound 4 (purity 95%).
Analytical data follow for 4. MS: m/z 186 (M+•, 1), 144 (2), 130 (3),
Ester 3. Sodium salt 10 (13.8 g, 0.1 mol), hexanoic acid (8, 23.2 g,
0.2 mol), and 3-chloro-2-butanone (9, 10.65 g, 0.1 mol) were heated
at 130 °C for 7 h. The reaction mixture was cooled to room temperature.
Ether was added, and the mixture was cooled with an ice bath. Saturated
aqueous Na2CO3 was added, and the mixture was stirred for 15 min.
The two phases were separated, and the aqueous phase was extracted
with ether. The combined organic phases were washed with water, dried
with MgSO4, and concentrated. The residue (7.16 g) was distilled at
67-72 °C at 12 mmHg using a Vigreux column to give compound 3
(9.59 g, 90% purity). Analytical data follow for 3. MS: m/z 186 (M+.,
1), 168 (0.5), 143 (8), 130 (2), 99 (85), 88 (4), 71 (38), 55 (10), 43
(100); 1H NMR: 0.91 (t, J ) 6.5, 3H); 1.33 (m, 4H); 1.40 (d, J ) 6.5,
3H); 1.66 (m, 2H); 2.17 (s, 3H); 2.39 (m, 2H); 5.08 (q, 1H); 13C
NMR: 205.8 (s); 173.2 (s); 74.7 (d); 34.0 (t); 31.3 (t); 25.7 (q); 24.5
(t); 22.3 (t); 16.0 (q); 13.9 (q); RIpolar: 1714; RIapolar: 1233.
1
126 (2), 99 (40), 87 (8), 71 (20), 55 (4), 43 (100); H NMR: 0.89 (t,
J ) 6, 3H); 1.30 (m, 4H); 1.39 (d, J ) 6.5, 3H); 1.60 (quint, 2H); 2.14
(s, 3H); 2.47 (m, 2H); 5.09 (q, J ) 6.5, 1H); 13C NMR: 207.9 (s);
170.5 (s); 74.7 (d); 38.2 (t); 31.3 (t); 22.9 (t); 22.4 (t); 20.8 (q); 16.2
(q); 13.9 (q). RIpolar: 1703; RIapolar: 1227.
RESULTS AND DISCUSSION
It is well-known that the flavor of tea extracts prepared by
simultaneous distillation extraction (SDE) is always too rich in
floral notes due to high amounts of terpenic alcohols such as
linalool, geraniol, nerolidol, and phenylethanol formed by the
hydrolysis of their glycosides under SDE conditions (14, 15).
Therefore, our extracts of fresh tea brews were prepared by
(()-1-Methyl-2-oxoheptyl Acetate (4). See Figure 4. This compound
was prepared by partially following a general method of Cahiez and
Metais (12). In a flask dried with the flame under argon, a solution of
MnCl4Li2 was prepared by stirring anhydrous MnCl2 (6.93 g, 55 mmol)
and anhydrous LiCl (4.68 g, 110 mmol) in THF (80 mL) at room
Figure 5. (A) GC−MS profile of an extract of Long Jing green tea. (B) GC−MS profile of an extract of Kiyosawa green tea. Both samples were analyzed
on the Supelcowax column. BHT is an impurity of ether used for the extraction of the resin.

9204 J. Agric. Food Chem., Vol. 54, No. 24, 2006
Naef et al.
lead to the esters 3 and 4. The same type of rearrangements
was observed by House et al. (18) when they treated â-diketones
with peracids. Another example of a Baeyer-Villiger oxidation
occurring in natural products is menthone lactone, which is
formed from menthone and has been identified in Mentha
piperita (19). Ester 3 is already known as a constituent of the
pawpaw fruit (20), where it can be considered as an ester
between hexanoic acid and acetoine, both common compounds
of fruit flavors. To our knowledge, ester 4 is a new natural
product.
Furanone 5 was identified in our Long Jing tea extract as
well as in a sample of white tea (Yin Zen) in very tiny amounts
(unpublished results). It was also obtained as a byproduct of
the reaction depicted in Figure 3. Its structure could be
unambiguously determined by its 13C NMR value at 205.2 ppm
together with CoSY, 13C,1H HMBC, and 13C,1H HSQC experi-
ments, the UV absorption at 272 nm (ꢀ ) 6181) characteristic
for conjugated ketones, the IR-band (at 1700 cm-1 for R,â-
unsaturated cyclopentanones), and the mass spectrum (M+• 168,
M+• - 56). Compound 5 exhibits a strong buttery, sweet, and
creamy flavor.
Figure 6. Formation of compounds 3 and 4.
solid-phase extraction and truly represented their original
organoleptic properties.
2,3-Octanedione and hydroxy-bovolide, both reported to form
in the photo-oxidation of furan fatty acids as well (7, 8), were
additionally identified in our Long Jing extract.
In green tea processing, the fresh tea leaves undergo a slight
fermentation which induces the degradation of nonvolatile
constituents such as carotenes, amino acids, and fatty acids into
flavor-active volatile compounds. Then, the enzymatic activity
is stopped either by steaming or pan-firing before the leaves
are dried. General knowledge about the complex chemistry of
the tea flavor is summarized by Yamanishi (16). In the present
paper, only the newly identified compounds will be described
in detail.
The extract of Long Jing tea (Figure 5A), a pan-fired tea,
had a delicate, green, slightly toasted, slightly spinachlike, floral,
and sweet flavor and contained the so-called primary compounds
(Z)-3-hexen-1-ol, linalool and its oxides, benzyl alcohol, phe-
nylethanol, and geraniol, and especially jasmone and methyl
jasmonate.
The extract prepared from Kiyosawa tea (Figure 5B), a
steamed tea, exhibited a fresh, floral, green, slightly vegetable-
like, and haylike aroma. Its main component was indole. Further
components were the carotenoids â-cyclocitral, 2-hydroxy-2,6,6-
trimethylcyclohexanone, â-ionone, and dihydroactinidiolide
together with (Z)-3-hexen-1-ol, benzyl alcohol, linalool, and
linalool oxide, the primary products, which are already present
in extracts of fresh, unprocessed tea leaves (17).
Intrigued by the results of Amado and co-workers (7, 8) who
investigated the photo-oxidative degradation of furan fatty acids
in green tea and other dried vegetables, we concentrated our
research on products they found so far, and indeed, compounds
1 and 2 were present in both extracts. In order to corroborate
the structure of compound 2, a synthetic sample was prepared
following a method of Ramirez et al. (10) (Figure 3). Addition
of 2 to tea flavors improved their sweet, creamy, buttery notes
and enhanced the typical mouthfeel of green tea.
In spite of the abundance of investigations published on the
constituents of tea, the flavor of freshly brewed green tea still
conceals many secrets. Nevertheless, combining the use of
untraditional methods for the preparation of extracts with
sophisticated GC-MS-analysis supported by synthetic work
allowed the identification of three new compounds in tea, among
them the two new structures 4 and 5, with interesting chemical
structures and new organoleptic properties which help to
increase the quality of ready-to-drink tea beverages, an increas-
ingly important market in the flavor industry.
ACKNOWLEDGMENT
We thank Drs. E. Fre´rot, L. Wu¨nsche, and R. Snowden for the
critical review of the manuscript and R. Brauchli for the help
in the interpretation of the NMR-spectra.
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Received for review June 21, 2006. Revised manuscript received August
23, 2006. Accepted August 25, 2006.
JF061738O