A revision of the positive sign of the optical rotation and its maximum value of α-eudesmol

Article abstract of DOI:10.1016/S0031-9422(99)00299-X

The ether extract of the liverwort Porella perrottetiana afforded (-)- α-eudesmol, which showed an opposite sign of the optical rotation to that found in higher plants. Present work on the absolute configuration and an optical purity of (-)-α-eudesmol strongly suggested that the positive values (e.g. + 28.5°) described in many previous papers should be revised. Since the absolute configuration of (-)-α-eudesmol was identical to that of (+)- β-eudesmol found in the higher plants, it was apparent that the expression of the positive sign might be revised to (-)-α-eudesmol. The optical purity, reconfirmation of the absolute configuration and synthesis of (-)-α-eudesmol will be discussed.

Full text of DOI:10.1016/S0031-9422(99)00299-X

Phytochemistry 52 (1999) 689±694
A revision of the positive sign of the optical rotation and its
maximum value of a-eudesmol
Masao Toyotaa, Yumiko Yoneharaa, Isao Horibeb, Kazuyuki Minagawab,
Yoshinori Asakawaa,*
aFaculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima, 770-8514, Japan
bShionogi Research Laboratory, Shionogi and Co. Ltd., Fukushima-ku, Osaka, 553-0002, Japan
Received 29 March 1999; accepted 19 May 1999
Abstract
The ether extract of the liverwort Porella perrottetiana a€orded ( )-a-eudesmol, which showed an opposite sign of the optical
rotation to that found in higher plants. Present work on the absolute con®guration and an optical purity of ( )-a-eudesmol
strongly suggested that the positive values (e.g.+28.58) described in many previous papers should be revised. Since the absolute
con®guration of ( )-a-eudesmol was identical to that of (+)-b-eudesmol found in the higher plants, it was apparent that the
expression of the positive sign might be revised to ( )-a-eudesmol. The optical purity, recon®rmation of the absolute
con®guration and synthesis of ( )-a-eudesmol will be discussed. # 1999 Elsevier Science Ltd. All rights reserved.
Keywords: ( )-a-Eudesmol; Sesquiterpene alcohol; Absolute con®guration; Maximum optical rotation; Liverwort; Porella perrottetiana
1. Introduction
tation of a-eudesmol is positive (Table 1).
Furthermore, the maximum optical rotation is ambigu-
ous. Recently our work resulted in the isolation of
( )-a-eudesmol from the liverwort P. perrottetiana.
We report here the isolation and con®rmation of the
absolute con®guration of ( )-a-eudesmol and revision
of the value of optical rotation.
a-Eudesmol has been isolated from many species of
plant kingdom, including liverworts. The ®rst isolation
of a-eudesmol has been reported from Eucalyptus
species (McQuillin & Parrack, 1956). On the other
hand, the ®rst example of the isolation from the liver-
worts has been performed from Porella stephaniana as
a major constituent (Asakawa, Yamamura, Waki &
Takemoto, 1980). There are many publications, which
reported the isolation or detection of a-eudesmol from
essential oils of the plants. Recently, it was reported
that a-eudesmol possesses the P-type Ca2+ channel an-
tagonism (Kanemasa & Kagawa, 1999).
2. Results and discussion
The ether extract of the liverwort P. perrottetiana
(Mont.) Trev. was subjected to silica gel column chro-
matography followed by preparative HPLC to give a-
The absolute con®guration of (+)-a-eudesmol (1)
has been established by synthesis (Humber & Pinder,
1966; Humber, Pinder & Williams, 1967; Kutney &
Singh, 1984; Chen, Xiong, Zhou, Yang & Li, 1997). A
number of authors have indicated that the optical ro-
1
eudesmol (1). The H NMR spectrum of 1 was com-
pletely identical to that of a-eudesmol (Kutney &
Singh, 1984; Stoessl & Stothers, 1986; Schwartz &
Willbrand, 1985), but di€erent from the spectrum of
known isomers of a-eudesmol, 7-epi-a-eudesmol (2), 5-
epi-a-eudesmol (3), and 5-epi-7-epi-a-eudesmol (4)
(Raharivelomanana et al., 1998; Schwarz & Willbrand,
1985). Furthermore, the 13C NMR spectrum of 1 was
* Corresponding author. Tel.: +81-886-22-9611; fax: +81-886-55-
3051.
0031-9422/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S0031-9422(99)00299-X

690
M. Toyota et al. / Phytochemistry 52 (1999) 689±694
Table 1
The values of speci®c optical rotation of a-eudesmol (1)
the present species was satisfactorily close to that of
authentic sample, [a]D +2508(CHCl3) prepared from
(+)-b-eudesmol (6). (+)-b-Eudesmol and its deriva-
tive, d-selinene were recognized to be optically pure
state by their chiral capillary GC±mass analyses. On
the other hand, our present work resulted in the recon-
®rmation of the absolute con®guration of (+)-b-eudes-
mol, (6) [a ]D +57.78(CHCl3) {literature value; [a ]D
+58.08(CHCl3) (Varma & Bhattacharyya, 1964)} as
shown in ®gure by X-ray crystallographic analysis for
its crystalline derivative 7 (Toyota, Saito & Asakawa,
1999), although it has also been established by chemi-
cal means (Riniker et al., 1954). Judging from the evi-
dence, it was suggested that the absolute con®guration
of ( )-a-eudesmol accorded with that of (+)-b-eudes-
mol (6).
a
Source
[a]D
Eucalyptus macarthuri (McQuillin & Parrack, 1956)
Machilus kusanoi (McQuillin & Parrack, 1956)
Melaleuca uncinata (McQuillin & Parrack, 1956)
Leptospermum ¯avescens (McQuillin & Parrack, 1956)
Balsamorrhiza sagittata (McQuillin & Parrack, 1956)
Synthetic (Humber & Pinder, 1966)
+318
+31.48
+33.48
+38.98
+37.28
+28.58
+28.68
6.48
Synthetic (Kutney & Singh, 1984)
Porella stephaniana (Noma et al., 1996)
Porella perrottetianab
Syntheticb
6.98
8.08
a All these data were measured in CHCl3.
b Present work.
also identical to that of a-eudesmol (Stoessl
Stothers, 1986; Raharivelomanana, Bianchini,
&
The following experiments further con®rmed the ab-
solute con®guration of ( )-a-eudesmol. Osmium cata-
lyzed dihydroxylation of ( )-a-eudesmol gave a triol 8
and its isomer 9. The 1H NMR spectrum of triol 8
showed a proton signal at d 3.29 (1H, dd, J = 5,
12 Hz) due to an axial carbinyl proton at C-3. Triol 8,
having the equatorial hydroxyl group at C-3 was con-
verted to R (+)- and S ( )-a-methoxy-a-tri¯uoro-
methylphenyl acetic acid (MTPA) esters 10a and 10b,
respectively. The dD values between 10a and 10b are
displayed in Fig. 1. The values were applied to modi-
®ed Mosher's method (Ohtani, Kusumi, Kashman &
Kakisawa, 1991) and indicated the absolute con®gur-
ation of ( )-a-eudesmol. Furthermore, a-eudesmol
was obtained from (+)-b-eudesmol according to the
procedure as shown in Scheme 1. The CD spectrum of
11 obtained in the ®rst step showed DE 1.4 (at 288 nm
in methanol), which was identical to that of the
reported value (Humber, Pinder & Wails, 1968).
Finally, the optical rotation of the synthetic a-eudes-
mol, mp 87±898C had [a ]D 8.08(CHCl3, c 1.0).
Cambon, Azzard & Faure, 1995) and did not accord
with that of 7-epi-a-eudesmol (2) (Raharivelomanana
et al., 1998). The GC±mass analysis using capillary
column of 1 showed a single peak on the total ion
chromatogram (TIC). The optical rotation of 1 exhib-
ited a negative sign, which was opposite to that found
in higher plants. This suggested that compound 1 was
a-eudesmol. Liverworts often elaborate sesquiterpenes
enantiomeric to those found in higher plants
(Asakawa, 1995). However, further con®rmations of
the absolute con®guration and the optical purity of
( )-a-eudesmol, [a]D
6.98(CHCl3) were necessary,
since the optical rotation contrasted with the reported
values. The chiral GC±mass analysis using capillary
column b-DEX 120 showed a single peak on the TIC
and indicated ( )-a-eudesmol was in an optically pure
state.
Dehydration of ( )-a-eudesmol with p-toluenesulfo-
nic acid gave a hydrocarbon 5, whose spectral data
were identical to those of d-selinene derived from (+)-
b-eudesmol (6). The optical rotation of d-selinene, [a]D
+2628(CHCl3) derived from ( )-a-eudesmol found in
Further evidence which con®rmed the absolute con-
®guration of 1 was provided. ( )-a-Eudesmol (1), [a ]D
6.48(CHCl3, c 1.35) isolated from P. stephaniana was
Fig. 1. The dD values between (10a) and (10b) are given in Hz.

M. Toyota et al. / Phytochemistry 52 (1999) 689±694
691
1956; Stoessl & Stothers, 1986). Even when the purity
of a-eudesmol obtained from the mixture is 90%, it
still shows the positive sign, according to a calculation.
Previously reported positive values are due to the mix-
ture of ( )-a- and a very small amount of (+)-b-
eudesmol.
Scheme 1. Derivatization of ( )-a-eudesmol (1) from (+)-b-eudes-
mol (6).
biotransformed by the fungus Aspergillus cellulosae to
the a,b-unsaturated ketone 15 in 23.3% yield (Noma,
1
Hashimoto, Kikkawa & Asakawa, 1996). The H, 13C
NMR, UV and IR spectral data for the metabolite 15
were in excellent agreement with those of isopterocar-
polone (Kumar, Ravindrath & Seshadri, 1974; Kukla,
Kumar, Sanduja & Seshadri, 1976) and both optical
rotations {[a]D +47.08(CHCl3)} were satisfactorily
identical.
Consideration of these chemical and spectral data
led to the conclusion that the absolute con®guration of
( )-a-eudesmol is as shown in 1. The sign of the opti-
cal rotation for a-eudesmol possessing the absolute
con®guration of 1 is negative. It is strongly suggested
that the expression of the positive sign of a-eudesmol
should be revised to the negative value.
In certain cases, the natural product known as a-
eudesmol has been recognized to be a mixture of two
eudesmols, depending upon the source of the material.
Particularly, the isolation of ( )-a-eudesmol, [a]D
6.98(CHCl3) from a crystalline mixture including
Fortunately, since our material did not contain (+)-
b-eudesmol, it was easy to isolate ( )-a-eudesmol from
the liverwort P. perrottetiana. In many cases, a-eudes-
mol has been frequently encountered as a mixture of
isomers in higher plants, although it was found in the
liverwort P. perrottetiana as the major constituent
(Fig. 2). Therefore, this is the ®rst example of the iso-
(+)-b-eudesmol,
[a]D
+57.78(CHCl3)
{[a]D
+588(CHCl3) (Varma & Bhattacharyya, 1964)} and
removal of the last trace of (+)-b-eudesmol by crystal-
lization appeared to be dicult (McQuillin & Parrack,

692
M. Toyota et al. / Phytochemistry 52 (1999) 689±694
Fig. 2. Total ion chromatogram (TIC) of the ether extract of P. perrottetiana.
lation of ( )-a-eudesmol in a pure state from a natural
source. Whereas the speci®c rotation of the natural
product a-eudesmol have been recognized to be posi-
tive (e.g. +28.58) for many years, it is now clear that
the negative sign for its rotation is correct.
3.3. Plant material, extraction and isolation
P. perrottetiana (Mont.) Trev. (dry wt 17.7 g) was
collected in February 1995 at Katsuura-cho (altitude
460 m), Tokushima, Japan. The material was gently
washed with water, impurities removed and ground
mechanically, then extracted with Et2O for 1 week.
The crude Et2O extract (545 mg) was chromato-
graphed on silica gel to give ( )-a-eudesmol (1)
(46.6 mg; 8.6% in yield of the total extract). ( )-a-
Eudesmol (1): [a]D 6.98(CHCl3, c 2.33).
3. Experimental
3.1. General
TLC was carried out on silica gel precoated glass
plates with n-hexane±EtOAc (1:1 and 4:1). Detection
was with Godin reagent (Godin, 1954). For normal
phase column chromatography (CC), silica gel 60 (40±
63 or 63±200 mm) was used. The mixture of CH2Cl2±
MeOH (1:1) was used for CC on Sephadex LH-20 as
solvent.
3.4. Dehydration of ( )-a-eudesmol(1) and (+)-b-
eudesmol (6)
To a solution of ( )-a-eudesmol (10 mg) in benzene
(1 ml), p-toluenesulfonic acid (1 mg) was added and
the reaction mix was re¯uxed for 5 min. The mix was
puri®ed by prep-HPLC to give d-selinene (5) {5.2 mg,
[a]D +2628(CHCl3, c 0.15)}. d-Selinene (5) {19 mg,
[a]D +2508(CHCl3, c 1.9)} was obtained from (+)-b-
eudesmol (6) (30 mg) in the same manner. (+)-b-
Eudesmol (6), [a]D +57.78(CHCl3, c 1.32) was isolated
from the purchased crude drug, Atractylodes lancea
rhizome.
3.2. Spectral data
NMR spectra were recorded at 100, 75 or 50 MHz
1
for 13C and 400, 300 or 200 MHz for H. The tem-
perature programming of GC±mass analysis performed
from 508 isothermal for 3 min, then 50±2508 at 58
min 1, and ®nally isothermal at 2508 for 15 min.
Injection temp was 2508. A fused silica column coated
with DB-17 (30 m  0.25 mm id, ®lm thickness
0.25 mm) or b-DEX 120 (30 m  0.25 mm id, ®lm
thickness 0.25 mm) were used.
3.5. Osmium dihydroxylation of ( )-a-eudesmol (1)
To a solution of 1 (33 mg) in Et2O (1 ml), osmium
tetroxide (9 mg) and 30% H2O2 (0.3 ml) were added

M. Toyota et al. / Phytochemistry 52 (1999) 689±694
693
and the reaction mixture was stirred for 24 h at room
temp. The mixture was chromatographed on Sephadex
LH-20 followed by prep.-HPLC to give triols 8
(4.0 mg) and 9 (3.0 mg), respectively.
2.7 mmol) in EtOAc (20 ml), ozone gas was introduced
at 788 until 6 was not detected on TLC. After remov-
ing excess ozone by bubbling in a N2 stream, triethyl-
amine (750 ml, 5.4 mmol) was added dropwise over
5 min. The cooling bath was then removed, and stir-
ring was continued at room temp for 2 h. The mix was
poured into ice water and extracted with EtOAc. The
organic extract was washed with brine, dried, and con-
centrated. The residue was puri®ed by chromatography
on silica gel using n-hex-EtOAc gradient to give 11
(495 mg).
3.6. Eudesm-3b,4b,11-triol (8)
1
Oil; [a ]D +1.78(CHCl3; c 1.4), H NMR (400 MHz;
CDCl3): d1.01 and 1.25 (each 3H, s), 1.21 (6H, s),
3.29 (1H, dd, J = 5, 12 Hz). 13C NMR (100 MHz;
CDCl3): d 18.5 (CH3), 21.4 (CH2), 22.2 (CH2), 25.0
(CH3), 26.8 (CH3), 27.2 (CH2), 27.5 (CH3), 33.3 (C),
39.1 (CH2), 43.3 (CH2), 49.8 (CH), 50.6 (CH), 73.1
(C), 74.1 (C), 75.9 (CH).
To a solution of 11 (394 mg, 1.76 mmol) in dry
DMF (2 ml) were added chlorotriethylsilane (384 ml,
2.29 mmol) and imidazole (240 mg, 3.52 mmol) at 08.
The reaction mixture was stirred at 08 for 3.5 h and
then poured into ice water. The mixture was extracted
with EtOAc, and the organic extract was washed with
brine, dried and concentrated. The residue was puri®ed
by silica gel chromatography using n-hex-EtOAc gradi-
ent to give 12 (574 mg).
3.7. Eudesm-3a,4a,11-triol (9)
1
Oil; [a ]D 31.08(CHCl3; c 1.0), H NMR (400 MHz;
CDCl3): d 0.88 and 1.12 (each 3H, s ), 1.21 (s, 6H),
3.61 (1H, t, J = 3 Hz). 13C NMR (100 MHz; CDCl3):
d 18.2 (CH3), 21.2 (CH2), 21.7 (CH3), 22.5 (CH2), 25.6
(CH2), 27.0 (CH3), 27.4 (CH3), 33.6 (CH2), 34.0 (C),
44.2 (CH2), 47.4 (CH), 49.9 (CH), 73.0 (C), 73.3 (C),
74.5 (CH).
To a solution of 12 (230 mg, 0.67 mmol) in dry
THF (4 ml) was added lithium diisopropylamide
(405 ml of 2 M heptane/tetrahydrofuran/ethylbenzene
solution, 0.81 mmol) at 788. After stirring for 20 min,
2-[N, N-bis(trifuruoromethylsulfonyl) amino]-5-chloro-
3.8. Esteri®cation of eudesm-3b,4b,11-triol (8) by R
(+) and S ( )-a-methoxy-a-
tri¯uoromethylphenylacetic acid (MTPA)
pyridine (Comins
& Dehghani, 1992) (318 mg,
0.81 mmol) in THF (1 ml) was added dropwise over
5 min. The mix was stirred at 408 for 30 min and
then quenched with ice water and extracted twice with
Et2O. The organic extracts were washed with brine,
combined, dried and concentrated. The residual oil
was puri®ed by silica gel chromatography using n-hex-
ane to give tri¯ate 13 (300 mg).
To a solution of 8 (1.5 mg) in dry CH2Cl2 (0.7 ml),
R (+)-MTPA (8.8 mg), DCC (5.5 mg) and DMAP
(2.0 mg) were added and the reaction mixture was stir-
red for 48 h. To the mix, H2O was added and the sol-
ution was washed with 1N HCl, saturated NaHCO3
and NaCl. After evaporation, the CH2Cl2 layer was
puri®ed by prep.-TLC to give R (+)-MTPA ester 10a
(0.9 mg). S ( )-MTPA ester 10b (1.2 mg) of 8 was
obtained by S ( )-MTPA in the same manner.
To a solution of 13 (303 mg, 0.64 mmol) in dry
THF (2 ml) was added HMPA (508 mg, 2.8 mmol)
and methyl zinc iodide (1.29 ml of 1.1 M THF sol,
1.41 mmol) at room temp. After stirring for 10 min,
the reaction mix was heated to 608 and tetrakis(triphe-
nylphosphine) palladium (0) (22 mg, 0.02 mmol) was
added. After being heated at 608 for 10 min and then
cooled, the mix was poured into ice water and
extracted with Et2O. The organic extract was washed
with brine, dried and concentrated. Puri®cation by
silica gel chromatography using n-hexane gave ole®n
14 (203 mg) (Tamura, Ochiai, Nakamura & Yoshida,
1986).
3.9. R (+)-MTPA ester 10a
1H NMR (400 MHz; CDCl3): d 0.92, 0.99, 1.55 and
1.58 (each 3H, s), 3.54 and 3.57 (each 3H, brs ), 4.75
(1H, dd, J = 5, 12 Hz), 7.38 (m, 3H), 7.42 (m, 3H),
7.53 (m, 4H).
3.10. S ( )-MTPA ester 10b
To a solution of 14 (203 mg, 0.60 mmol) in dry
THF (2 ml) was added tetrabutylammonium ¯uoride
(0.90 ml of 1 M THF solution, 0.90 mmol) dropwise
at room temp. After being stirred for 18 h, the mix
was poured into ice water and extracted with EtOAc.
The residue was puri®ed by silica gel chromatography
using n-hex-EtOAc gradient to give ( )-a-eudesmol (1)
(133 mg). Recrystallization from pentane gave an ana-
lytically pure sample.
1H NMR(400 MHz; CDCl3): d 0.97, 1.02, 1.57 and
1.58 (each 3H, s), 3.51 and 3.52 (each 3H, brs ), 4.72
(1H, dd, J = 5, 12 Hz), 7.39 (m, 3H), 7.43 (m, 3H),
7.52 (m, 3H).
3.11. Synthesis of ( )-a-eudesmol (1)
To a solution of crude (+)-b-eudesmol (6) (600 mg,

694
M. Toyota et al. / Phytochemistry 52 (1999) 689±694
3.12. Compound 11
Acknowledgements
Mp. 120±1218, [a ]D +5.58(CHCl3; c 0.5), IRnmax
We thank Dr M. Mizutani (Hattori Botanical
Laboratory, Nichinan, Miyazaki, Japan) for his con®r-
mation of our identi®ed species. This work was sup-
ported by a Grand-in-Aid for Scienti®c Research (B)
(No. 08459026) from the Ministry of Education,
Science, Sports and Culture.
cm 1(CHCl3): 3609, 2944, 2848, 1703, 1466, 1384,
1249. DE288
1.36 (MeOH). EIMS m/z (rel. int.):
224[M]+, 111(100), Anal. Calcd. For C14H24O2: C
74.95, H 10.78 found: C 74.67, H 10.70, 1H NMR
(300 MHz; CDCl3): d 0.77 (3H, s), 1.20 and 1.21 (each
3H, s), 2.21 (1H, m ), 2.33 (2H, m ). 13C NMR
(75 MHz; CDCl3): d 17.0, 21.5, 21.9, 22.7, 26.7, 27.4,
39.4, 40.4, 40.8, 41.3, 48.4, 57.4, 72.7, 213.0
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1
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