Synthesis of a glycosidic precursor of isomeric marmelo oxides, volatile components of quince fruit, Cydonia oblonga

Article abstract of DOI:10.1021/np970480g

Synthesis of (R)-8-hydroxy-2,7-dimethyl-(4E,6E)-octadienyl β-D- glucopyranoside (1), a glycosidic precursor of marmelo oxides, the volatile components of quince fruit, Cydonia oblonga Mill., was achieved starting from (S)-3-hydroxy-2-methylpropanoate (5).

Full text of DOI:10.1021/np970480g

J . Nat. Prod. 1998, 61, 551-554
551
Syn th esis of a Glycosid ic P r ecu r sor of Isom er ic Ma r m elo Oxid es, Vola tile
Com p on en ts of Qu in ce F r u it, Cyd on ia oblon ga
Takeshi Kitahara* and Hiroki Shimizu
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo,
1-1-1 Yayoi, Bunkyo-ku Tokyo 113-8657, J apan
Received October 29, 1997
Synthesis of (R)-8-hydroxy-2,7-dimethyl-(4E,6E)-octadienyl â-D-glucopyranoside (1), a glycosidic
precursor of marmelo oxides, the volatile components of quince fruit, Cydonia oblonga Mill.,
was achieved starting from (S)-3-hydroxy-2-methylpropanoate (5). The conjugated diene moiety
was constructed in one step by a Horner reaction, and the final glycosidation was executed via
the chloroimidate method.
Sch em e 1
In the past ten years an explosion of research activi-
ties in the study of the glycosidic precursors of flavor
substances has produced a number of publications
concerning the structures of these glycosides, their
occurrence, and their role in the plant kingdom. Gly-
cosides of more than 200 different aglycons, including
structurally diverse terpenoids and nonterpenoids, have
been characterized.1-4 To have enough of these glyco-
sides in essential-oil plants, to study their role they
must be obtained in adequate amounts, and it is, thus,
necessary to provide these amounts by chemical syn-
thesis.
In 1991, Schreier and co-workers isolated glycosidic
precursors 15 and 26 of marmelo oxides (3) and marmelo
lactones (4), the key flavor of the quince fruit, Cydonia
oblonga Mill. (Rosaceae)7 (Scheme 1). At almost the
same time, Na¨f and Velluz identified several acyclic
precursors of these flavors in the hydrolyzate of the
MeOH extract from the quince fruit.8 In the case of the
precursor 1 and marmelo oxide (3), the amount of
natural product was rather small and prompted us to
synthesize 1 in optically active form. We report herein
the synthesis of (R)-8-hydroxy-2,7-dimethyl-(4E,6E)-
octadienyl â-D-glucopyranoside (1) starting from readily
available methyl (S)-3-hydroxy-2-methylpropanoate (5).9
The ester 5 was converted to a siloxyalcohol (6) in two
steps, according to a known procedure.10 Tosylation of
6 was followed by treatment with NaCN to give the
nitrile 7 (85%). DIBAL reduction of 7 afforded the know
aldehyde 8 (78%).11 To introduce the conjugated diene
moiety in one step, we decided to use a Horner-type
reaction with the phosphonate 9, which we had pre-
pared for the synthesis of sirenin.12 As it happened,
reaction of the aldehyde 8 with the sodium salt of 9 in
THF smoothly gave the product 10 as an (E/Z) mixture
in a 2.5:1 ratio (85%). The ratio was improved to 10:1,
however, by using lithiophosphonate (n-BuLi-THF)
(53% yield). Finally, we achieved the ratio 8:1 and 98%
yield by using lithium diisopropylamide in THF. Sepa-
ration of the desired trans-isomer from the cis-isomer
was much easier at the next step. DIBAL reduction of
10 at -78 °C and simple chromatography furnished
pure dienol aglycon (11). Acetylation of 11 gave the
acetate 12, which was treated with tetrabutylammo-
nium fluoride (TBAF) to give the diol monoacetate 13
the substrate for glycosylation.
Initially we attempted modified Ko¨nigs-Knorr-type
glycosylation of 13 with 2,3,4,6-tetra-O-acetylglucosyl
bromide in the presence of mercuric cyanide,13 but the
reaction product was a complex mixture, and we were
unable to isolate the desired glycoside (14). It was
postulated that the conjugated diene was destroyed
under the procedure using mercuric ion. This result
prompted us to employ Schmidt’s glycosylation with
trichloroacetimidate (15).14 Treatment of the aglycon
13 with 15 in the presence of TMSOTf at low temper-
ature afforded the expected glycoside 14 in 52% yield.
Spectral data (1H NMR, 13C NMR) of synthetic 14 were
entirely superimposable with those reported.5 Finally
transesterification of 14 with a catalytic amount of
NaOMe in MeOH yielded the target glycoside 1 in 77%
yield (Scheme 2).
In conclusion, the synthesis of (R)-8-hydroxy-2,7-
dimethyl-(4E,6E)-octadienyl â-D-glucopyranoside (1), a
glycosidic precursor of marmelo oxides, was completed
in 13% overall yield through 11 steps from methyl (R)-
2-hydroxypropanoate. As a substantial amount of the
synthetic glycoside (1) is now available, we plan to study
the chemical and physiological properties of 1. The
results of these studies will be reported in due course.
* To whom correspondence should be addressed. Tel: 81 3 3812 2111
ext. 5119. Fax: 81 3 5800 6865. E-mail: atkita@hongo.ecc.u-tokyo.ac.jp.
S0163-3864(97)00480-1 CCC: $15.00
© 1998 American Chemical Society and American Society of Pharmacognosy
Published on Web 04/08/1998

552 J ournal of Natural Products, 1998, Vol. 61, No. 4
Notes
Sch em e 2a
(R )-4-[(t er t -Bu t yld im e t h ylsilyl)oxy]-3-m e t h yl-
bu ta n -1-a l (8). To a solution of 7 (10.32 g, 1.49 mmol)
in CH2Cl2 (25 mL) was added dropwise DIBAL (1.01 M
in toluene 1.62 mL) at -78 °C under Ar. The mixture
was stirred at -30 °C for 4 h. The reaction mixture
was quenched with saturated NH4Cl solution, acidified
to pH 3 with 5% H2SO4 to hydrolize imine complex,
neutralized with saturated NaHCO3 solution, and ex-
tracted with ether. The combined organic layers were
washed with brine, dried (MgSO4), and concentrated in
vacuo. The residue was purified by SiO2 (8.4 g) chro-
matography [n-hexane-EtOAc (20:1)] to give 0.25 g
(77.7%) of the aldehyde 8 as a colorless oil: [R]18D +10.7°
(c 2.04, CHCl3); IR (film) νmax 2956 (s), 2713 (m, CHO),
1727 (s, CHO), 1471 (m), 1388 (m), 1255 (s), 1095 (s),
1
837 (s), 777 (s) cm-1; H NMR (90 MHz, CDCl3) δ 0.04
(6H, s, CH3-Si), 0.88 (9H, s, t-Bu-Si), 0.97 (3H, d, J )
6.6, CH3-3), 2.18 (1H, ddd, J ) 2.2, 6.9, 9.6 Hz, H-2a),
2.23 (1H, m, H-3), 2.48 (1H, ddd, J ) 2.2, 3.0, 9.6 Hz,
H-2b), 3.34 (1H, ddd, J ) 7.2, 9.8 Hz, H-4a), 3.53 (1H,
dd, J ) 4.7, 9.8 Hz, H-4b), 9.75 (1H, t, J ) 2.2 Hz, H-1);
anal. C 60.80%, H 11.09%; calcd for C11H24O2, C 61.06%,
H 11.18%.
(R)-8-[(ter t-Bu tyldim eth ylsilyl)oxy]-2,7-dim eth yl-
(2E,4E)-octa n d ien -1-ol (11). P r oced u r e A: Na H a s
th e ba se: To a suspension of NaH (60% in mineral oil,
120 mg, 3.0 mmol) in THF (7 mL) was added a solution
of 9 (0.578 g, 2.3 mmol) in THF (8 mL) with ice-cooling
under Ar. The mixture was further stirred for 2.5 h at
room temperature. To this was added a solution of 8
(0.25 g, 1.2 mmol) in THF below -10 °C. The mixture
was stirred at room temperature for 4 h. The reaction
mixture was quenched with H2O, and the mixture was
extracted with ether. The combined organic layer was
washed with brine, dried (MgSO4), and concentrated in
vacuo. The residue was purified by SiO2 (15 g) chro-
matography [n-hexane-EtOAc (20:1)] to give 0.31 g
(85%) of (E/Z) mixture [(E/Z) ) 2.5:1].
a
Key: (i) TBSCl, (i-Pr)2NEt, CH2Cl2, rt; (ii) DIBAL, PhCH3
0
°C; (iii) TsCl, Py, 4 °C then NaCN, DMSO, rt; (iv) DIBAL, CH2Cl2,
-30 °C; (v) 9, LDA, THF; rt; (vi) DIBAL, PhCH3 -78 °C then
chromatography; (vii) Ac2O, Py; (viii) TBAF, THF; (ix) 15, TMSOTf,
CH2Cl2, -78 °C; (x) NaOMe, MeOH.
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. NMR spectra
were recorded at 90 MHz on J EOL J MN-EX90 in CDCl3
and 300 MHz on Bruker AC-300 in CDCl3 or MeOH-d4.
IR spectra were measured as films on a J ASCO A-102
spectrometer. HRMS measurements were performed on
a J EOL J MS-SX102/SX102. Optical rotations were
measured on a J ASCO DIP 371 polarimeter. Merck
Kieselgel 60 (Art. no. 7734) was used for column
chromatography.
P r oced u r e B: n -Bu Li a s th e ba se: To a solution
of 9 (3.9 g, 15.6 mmol) in THF (30 mL) was added a
solution of n-BuLi (1.59 M, 9.28 mL) in THF (70 mL)
with ice-cooling under Ar. The mixture was stirred for
3 h at room temperature. To this was added a solution
of 8 (1.98 g, 9.25 mmol) in THF (50 mL) below -10 °C.
The mixture was stirred at room temperature for 3.5 h.
The reaction mixture was poured into H2O and ex-
tracted with ether. The combined organic layer was
washed with saturated NaHCO3 solution and brine,
dried (MgSO4), and concentrated in vacuo. The residue
was purified by SiO2 (150 g) chromatography [n-hex-
ane-EtOAc (22:1)] to give 2.29 g (53%) of (E/Z) mixture
[(E/Z) ) 10:1].
P r oced u r e C: Lith iu m d iisop r op yla m id e a s th e
ba se: To a solution of 9 (4.5 g, 18 mmol) in THF (50
mL) was added a solution of lithium diisopropylamide
(0.44 M, 38.3 mL) in THF (25 mL) at -78 °C under Ar.
The mixture was stirred for 1 h at room temperature.
To this was added a solution of 8 (2.8 g, 12.9 mmol) in
THF (50 mL) at -78 °C. The mixture was stirred at
room temperature for 2 h. The reaction mixture was
quenched with saturated NH4Cl solution and extracted
with EtOAc. The combined organic layer was washed
with saturated NaHCO3 solution and brine, dried
(MgSO4), and concentrated in vacuo. The residue was
(R )-4-[(t er t -Bu t yld im e t h ylsilyl)oxy]-3-m e t h yl-
bu ta n en itr ile (7). To a solution of 6 (2.85 g, 1.88
mmol) in pyridine (12 mL) was added p-toluenesulfonyl
chloride (4.62 g, 24.5 mmol), and the mixture was stirred
for 12 h at 4 °C. The reaction mixture was poured into
H2O and extracted with ether. The organic layer was
washed with saturated CuSO4 solution, saturated NaH-
CO3 solution, and brine; dried (MgSO4), and concen-
trated in vacuo. To a solution of the residue in DMSO
(30 mL) was added NaCN (1.84 g, 37.6 mmol), and the
mixture was stirred for 3 h. The reaction mixture was
poured into ice-cooled H2O and extracted with ether.
The combined organic layer was washed with brine,
dried (MgSO4), and concentrated in vacuo. The residue
was purified by SiO2 (20 g) chromatography [n-hexane-
EtOAc (17:1)] to give 3.40 g (85%) of the nitrile 7 as a
colorless oil: [R]19D +19.1° (c 1.04, CHCl3); IR (film) νmax
2956 (s), 2246 (m, -CN), 1471 (s), 1390 (m), 1255 (s),
1
1101 (s), 1032 (m), 839 (s), 777 (s) cm-1; H NMR (90
MHz, CDCl3) δ 0.06 (6H, s, CH3-Si), 0.90 (9H, s, t-Bu-
Si), 1.04 (3H, d, J ) 6.7 Hz, CH3-3), 2.03 (1H, m, H-3),
2.29 (1H, dd, J ) 6.9, 16.6 Hz, H-2a), 2.41 (1H, dd, J )
5.6, 16.6 Hz, H-2b), 3.37 (1H, dd, J ) 7.3, 10.0 Hz, H-4a),
3.55 (1H, dd, J ) 4.6, 10.0 Hz); anal. C 61.75%, H
10.87%, N 6.61%; calcd for C11H23ON, C 61.91%, H
10.86%, N 6.56%.

Notes
J ournal of Natural Products, 1998, Vol. 61, No. 4 553
purified by SiO2 (160 g) chromatography [n-hexane-
EtOAc (22:1)] to give 3.99 g (98%) of (E/Z) mixture
[(E/Z) ) 8:1].
1.77 (3H, s, CH3-2), 2.00 (1H, dt, J ) 7.3, 14.1 Hz, H-6a),
2.08 (3H, s, CH3-acetyl), 2.25 (1H, dt, J ) 7.0, 14.1 Hz,
H-6b), 3.49 (2H, qui, J ) 5.3 Hz, H-8), 4.50 (2H, s, H-1),
5.73 (1H, dt, J ) 7.5, 15.0 Hz, H-5), 6.04 (1H, d, J )
10.9 Hz, H-3), 6.27 (1H, dd, J ) 10.9, 15.0 Hz, H-4);
anal. C 67.89%, H 9.50%; calcd for C12H20O3, C 67.78%,
H 9.47%.
To a solution of this (1.72 g, 5.50 mmol) in toluene
(70 mL) was added dropwise DIBAL (1.99 mL 1.01 M
toluene solution) at -78 °C under Ar. The mixture was
stirred at -78 °C for 2 h and quenched with MeOH.
After temperature was raised to 0 °C, Rochelle salt
solution was added, and the mixture was extracted with
ether. The combined organic layers were washed with
saturated NaHCO3 solution and brine, dried (MgSO4),
and concentrated in vacuo. The residue was purified
by SiO2 (15 g) chromatography [n-hexane-EtOAc
(R)-8-Acet oxy-2,7-d im et h yl-(4E,6E)-oct a d ien yl
2′,3′,4′,6′-Tetr a -O-a cetyl-â-D-glu cop yr a n osid e (14).
To a solution of 13 (0.1 g, 0.471 mmol) and O-(2,3,4,6-
t et r a -O-a cet yl-R-D-glu copyr a n osyl)t r ich lor oa cet o-
imidate (15) (0.8 g, 1.602 mmol) with molecular sieves
AW 300 (0.5 g), in CH2Cl2 (9 mL) was added dropwise
TMSOTf (16.5 µL, d ) 1.23, 4.51 mmol) at -78 °C under
Ar. After 3 h stirring at -78 °C, triethylamine was
added, and the mixture was allowed to stand at ambient
temperature. The reaction mixture was filtered. The
filtrate was diluted with H2O and extracted with ether.
The combined organic layer was washed with brine,
dried (MgSO4), and concentrated in vacuo. The residue
was purified by chromatography on SiO2 (40 g) [n-hex-
ane-ether (6:1)] to give 0.135 g (53%, 0.289 mmol) of
(20:1)] to give 1.26 g (80%) of 11 as a colorless oil: [R]27
D
+4.58° (c 2.30, CHCl3); IR(film) νmax 3324 (br s, OH),
3035 (w), 2955 (s), 1660 (w), 1625 (w), 1471 (m), 1388
(m), 1254 (m), 1097 (s), 1007 (m), 969 (m), 837 (s), 775
(s) cm-1; 1H NMR (300 MHz, CDCl3) δ 0.04 (6H, s, CH3-
Si), 0.88 (3H, d, J ) 6.7 Hz, CH3-7), 0.90 (9H, s, t-Bu-
Si), 1.32 (1H, t, J ) 5.8 Hz, -OH), 1.70 (1H, m, H-7),
1.78 (3H, s, CH3-2), 1.90 (1H, dt, 7.5, 13.9 Hz, H-6a),
2.23 (1 H, dt, J ) 6.5, 13.9 Hz, H-6b), 3.42 (2H, d, J )
6.1 Hz, H-8), 4.05 (2H, d, J ) 5.8 Hz, H-1), 5.68 (1H, dt,
J ) 7.5, 14.9 Hz, H-5), 6.03 (1H, d, J ) 10.5 Hz, H-3),
6.25 (1H, dd, J ) 10.5, 14.9 Hz, H-4); anal. C 67.22%,
H 11.30%; calcd for C16H32O2Si, C 67.55%, H 11.34%.
14 as a viscous, colorless oil: [R]23 -6.6° (c 1.15,
D
CHCl3); IR (film) νmax 3030 (w), 2959 (m), 1757 (s,
acetate), 1434 (w), 1372 (m), 1227 (s), 1173 (m), 1039
(s), 980 (w), 906 (w), 756 (m) cm-1; 1H NMR (300 MHz,
CDCl3) δ 0.87 (3H, d, J ) 6.7 Hz), 1.61 (3 H, s, CH3-7),
1.77-2.24 (18H, H-2, H-3, and 5 acetates), 3.28 (1H, dd,
J ) 7.0, 9.5 Hz, H-1a), 3.69 (1H, ddd, J ) 2.3, 4.6, 12.2
Hz, H-5′), 3.72 (1H, dd, J ) 5.9, 9.5 Hz, H-1b), 4.14 (1H,
dd, J ) 2.3, 12.2 Hz, H-6′a), 4.26 (1H, dd, J ) 4.6, 12.2
Hz, H-6′b), 4.46 (1H, d, J ) 8.0 Hz, H-1′), 4.50 (2H, s,
H-8), 4.98-5.23 (3H, H-2′, H-3′, and H-4′), 5.68 (1H, dt,
J ) 7.3, 14.9 Hz, H-4), 6.03 (1H, d, J ) 10.7 Hz, H-6),
6.23 (1H, dd, J ) 10.7, 14.9 Hz, H-5); 13C NMR (300
MHz, CDCl3) δ 14.3, 16.1, 20.5-20.8, 33.4, 36.4, 61.9,
68.4, 69.8, 71.3, 71.7, 72.7, 74.5, 101.0, 127.4, 128.1,
130.0, 133.13, 169.1, 169.6, 170.0, 170.5, 171.0; anal. C
57.56%, H 7.06%; calcd for C26H38O12, C 57.42%, H
7.06%.
(R)-2,7-Dim eth yl-8-[(ter t-bu tyldim eth ylsilyl)oxy]-
(2E,4E)-octa d ien yl Aceta te (12). To a solution of 11
(0.14 g, 0.492 mmol) in pyridine (3 mL) was added
dropwise Ac2O (2 mL) with ice cooling. After stirring
for 3 h at room temperature, the reaction mixture was
poured into cold H2O and extracted with ether. The
combined organic layer was washed with saturated
CuSO4 solution, saturated NaHCO3 solution, and brine;
dried (MgSO4), and concentrated in vacuo. The residue
was purified by chromatography on SiO2 (5 g) [n-hex-
ane-EtOAc (17:1)] to give 0.161 g (quant.) of the acetate
12 as a colorless oil: [R]19 +4.3° (c 0.50, CHCl3; IR-
D
(film) νmax 2955 (s), 1744 (s, acetate), 1660 (w), 1623 (w),
1471 (m), 1374 (m), 1227 (s), 1095 (s), 1021 (m), 967 (m),
837 (s), 776 (s) cm-1; 1H NMR (300 MHz, CDCl3) δ 0.04
(6H, s, CH3-Si), 0.87 (3H, d, J ) 6.7 Hz, CH3-7), 0.90
(9H, s, t-Bu-Si), 1.68 (1H, m, H-7), 1.70 (3H, s, CH3-2),
1.91 (1H, dt, J ) 7.5, 13.9 Hz, H-6a), 2.08 (3H, s, acetyl),
2.25 (1H, dt, J ) 6.8, 13.9 Hz, H-6b), 3.51 (2H, d, J )
6.0 Hz, H-8), 4.50 (2H, s, H-1), 5.71 (1H, dt, J ) 8.3,
12.7 Hz, H-5), 6.04 (1H, d, J ) 10.9 Hz, H-3), 6.23 (1H,
dd, J ) 10.9, 12.7 Hz, H-4); anal. C 66.05%, H 10.40%;
calcd for C18H34O3Si, C 66.21%, H 10.49%.
(R)-8-H yd r oxy-2,7-d im et h yl-(4E,6E)-oct a d ien yl
â-D-Glu cop yr a n osid e (1). To a solution of 16 (0.0152
g, 0.028 mmol) in MeOH (0.5 mL) was added sodium
methoxide (0.45 mg, 0.008 mmol) with ice-cooling. After
stirring 17 h, Amberlyst (0.06 g) was added and filtered.
The residue was concentrated in vacuo to give 0.0072 g
(77.4% 0.0217 mmol) of 1 as a highly viscous and
slightly yellow oil: [R]21 -15.5° (c 0.31, CH3OH); IR
D
(film) νmax 3390 (br s, OH), 2875 (s), 1633 (m), 1454 (m),
1379 (m), 1260 (m), 1165 (m), 1032 (s), 893 (m) cm-1
;
(R)-8-Hydr oxy-2,7-dim eth yl-(2E,4E)-octadien yl Ac-
eta te (13). To a solution of 12 (0.604 g, 1.85 mmol) in
THF (5 mL) was added a solution of TBAF (1.34 mL, d
) 0.903 THF solution, 4.63 mmol) below 0 °C. After
warming to room temperature, the mixture was poured
into H2O and extracted with ether. The combined
organic layer was washed with saturated NaHCO3
solution and brine, dried (MgSO4), and concentrated in
vacuo. The residue was purified by chromatography on
SiO2 (6.7 g) [n-hexane-EtOAc (10:1)] to give 0.391 g
1H NMR (300 MHz, CD3OD) δ 0.81 (3H, d, J ) 6.7 Hz,
CH3-2), 1.17 (1H, -OH), 1.64 (3H, s, CH3-7), 1.75 (1H,
m, H-2), 1.91 (1H, dt, J ) 7.3, 15.4 Hz, H-3a), 2.20 (1H,
dt, J ) 7.3, 13.4 Hz, H-3b), 3.04-3.29 (4H, H-1a, H-5′,
H-6′), 3.54-3.62 (3H, H-2′, H-3′, and H-4′), 3.74 (1H,
dd, J ) 1.6, 12.3 Hz, H-1b), 3.85 (2H, s, H-8), 4.11 (1H,
d, J ) 7.7 Hz, H-1′), 5.58 (1H, dt, J ) 7.3, 14.7 Hz, H-4),
5.90 (1H, d, J ) 10.8 Hz, H-6), 6.20 (1H, dd, J ) 10.8,
14.7 Hz, H-5); 13C NMR (300 MHz, CD3OD) δ 14.2, 17.0,
35.1, 37.9, 62.8, 71.7, 75.2, 75.7, 77.9, 78.1, 104.7, 126.1,
129.0, 133.2, 136.1; HRFABMS m/z 332.1807 [M+] (calcd
for C16H28O7, 332.1835).
(quant.) of 13 as a colorless oil: [R]21 +3.9° (c 2.05,
D
CHCl3); IR (film) νmax 3419 (br s, OH), 3035 (w), 3025
(m), 2958 (s), 1739 (s, acetate), 1455 (m), 1375 (m), 1236
1
(s), 1024 (s), 970 (m) cm-1; H NMR (300 MHz, CDCl3)
Ack n ow led gm en t. We thank Prof. P. Schreier and
δ 0.94 (3H, d, J ) 6.9 Hz, CH3-7), 1.73 (1H, m, H-7),
Prof. P. Winterhalter for the generous gift of the

554 J ournal of Natural Products, 1998, Vol. 61, No. 4
Notes
(5) Lutz, A.; Winterhalter, P.; Schreier, P. Tetrahedron Lett. 1991,
82, 5943-5944.
authentic sample and the copies of spectra. We are
grateful to Dr. J . Hasegawa, Kanegafuchi Chemical
Industry Co., Ltd., for his kind supply of methyl (S)-
(+)-3-hydroxy-2-methylpropanoate. This work is partly
supported by a Grant-in-Aid for Scientific Research from
the J apanese Ministry of Science, Education, Culture
and Sport (no. 09460056).
(6) Winterhalter, P.; Lutz, A.; Schreier, P. Tetrahedron Lett. 1991,
32, 3669-3670.
(7) Tsuneya, T.; Ishikawa, M.; Shiota, H.; Shiga, M. Agric. Biol.
Chem. 1980, 44, 957-958; 1983, 47, 2495-2502.
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4389-4392.
Refer en ces a n d Notes
(1) Stahl-Biskup, E. Flavour Fragr. J . 1987, 2, 75-82.
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NP970480G