Myrioneurinol: a novel alkaloid skeleton from Myrioneuron nutans

Article abstract of DOI:10.1016/j.tet.2007.08.095

A new alkaloid, myrioneurinol (1), was isolated from the leaves of Myrioneuron nutans and its structure determined from spectral analysis, including mass spectrometry and 2D NMR. Myrioneurinol (1) presented an unprecedented fused tetracyclic skeleton. The

Full text of DOI:10.1016/j.tet.2007.08.095

Tetrahedron 63 (2007) 11244–11249
Myrioneurinol: a novel alkaloid skeleton
from Myrioneuron nutans
a
b
Van Cuong Pham,a,c, Akino Jossang, Thierry Sevenet,
*
ꢀ
Van Hung Nguyenc and Bernard Bodoa,
*
a
´
Laboratoire de Chimie et Biochimie des Substances Naturelles—UMR 5154 CNRS, Museum National d’Histoire Naturelle,
63 rue Buffon, 75005 Paris, France
bInstitut de Chimie des Substances Naturelles, CNRS—91198 Gif-sur-Yvette Cedex, France
cInstitute of Chemistry—Vietnamese Academy of Science and Technology, 18 Hoang Quoc Viet Road, Hanoi, Viet Nam
Received 19 July 2007; revised 24 August 2007; accepted 29 August 2007
Available online 1 September 2007
Abstract—A new alkaloid, myrioneurinol (1), was isolated from the leaves of Myrioneuron nutans and its structure determined from spectral
analysis, including mass spectrometry and 2D NMR. Myrioneurinol (1) presented an unprecedented fused tetracyclic skeleton. The absolute
configuration was established by the modified Mosher’s method, using (R)- and (S)-9-anthrylmethoxyacetic acid (9-AMAA). A plausible
biosynthetic pathway starting from L-lysine via D-piperideine was proposed for 1 in comparison with nitraramine biosynthesis and related
alkaloids.
Ó 2007 Elsevier Ltd. All rights reserved.
OH
1. Introduction
H
H
The Myrioneuron genus is a small one comprising about 15
species, which is distributed over south-east Asia and be-
longs to the Rubiaceae.1 The Rubiaceae is a large plant fam-
ily known to biosynthesize a great variety of alkaloids with
important pharmacological interests exemplified by quini-
ne2a–d and camptothecin.3a–c Myrioneuron nutans, a small
tree native in North-Viet Nam, was selected in the course
of a screening program of plants for their cytotoxicity
against tumor cells and also for the high content of alkaloids
depicted in this species. Furthermore, there was no previous
chemical study on this genus. The alkaloid extract showed
cytotoxic activity against KB cells with IC50 of 50 mg/mL.
Herein, we describe the isolation from M. nutans and the
structural determination, including absolute configuration
of a new alkaloid with a tetracyclic skeleton, myrioneurinol
(1) containing a 1,3-oxazine ring system. We previously
reported the isolation from M. nutans, the structure, and
the synthesis of two epimeric tricyclic 1,3-oxazines, myri-
oxazines A and B.4 Finally, a plausible biosynthetic pathway
for myrioneurinol (1) is proposed in comparison with related
alkaloids derived from lysine.
N
H
O
H
myrioneurinol (1)
2. Results and discussion
2.1. Isolation and structure determination
The dried and ground leaves (5 kg) of M. nutans were ex-
tracted with CH2Cl2 at pH 9 (NH4OH) and the crude alkaloid
obtained by acid–base purification of this extract was sepa-
rated by a combination of column chromatography to yield
myrioneurinol (1, 32 mg). Myrioneurinol 1 was obtained
as an optically active colorless solid, [a]2D0 +63 (c 1,
MeOH). In its ESI-MS, the protonated molecular ion was
observed at m/z 266.2149 (calcd 266.2120 for C16H28NO2,
[M+H]+), indicating the molecular formula C16H27NO2. IR
absorptions implied the presence of a hydroxyl group (n
3400 cmꢀ1). The 1D NMR (1H and 13C) spectra showed
11 methylenes, four methines, and one quaternary carbon,
in agreement with the molecular formula. The four degrees
of unsaturation were thus assigned to four rings.
In the H–1H COSY spectrum of 1, correlations between
CH2-3 (dH 1.50 and 1.72) and both CH2-2 (dH 2.61 and
3.22) and CH2-4 (dH 1.32 and 1.63) revealed the partial
1
* Corresponding authors. Tel.: +33 01 40793129; fax: +33 01 40793135
(B.B.); tel.: +84 04 7564995; fax: +84 04 8361283 (V.C.P.); e-mail
addresses: phamvc@ich.vast.ac.vn; bodo@mnhn.fr
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.08.095

V. C. Pham et al. / Tetrahedron 63 (2007) 11244–11249
11245
Table 1. NMR data for myrioneurinol (1) (CDCl3, 298 K), 1H NMR
16
15
14
(400.13 MHz), 13C NMR (75.47 MHz)
d
17
18
OH
Position
2
dC
dH
m
J (Hz)
6
4
a 5
3
7
8
A
B
44.9
—
20.4
—
19.7
—
36.2
47.6
37.0
31.0
—
27.1
69.5
73.4
—
86.7
—
34.2
—
20.4
—
26.6
—
23.0
—
65.1
—
3.22
2.61
1.72
1.50
1.63
1.32
—
ddd
ddd
m
m
ddd
br d
12.2; 11.0; 4.0
11.0; 4.8; 0.5
b
10
2
1N
9
c
3
4
13
11
O
13.3; 13.3; 3.0
13.3
Figure 1. 1H–1H COSY ( ) and selected 1H–13C HBMC correlations
▬
(H
C) for 1.
5
6
7
8
1.11
1.45
1.50
0.74
2.40
2.22
3.86
3.15
4.41
4.36
2.44
0.80
1.45
1.32
1.72
1.20
1.55
1.12
3.59
3.42
ddd
ddddd
ddd
ddd
ddddd
d
ddd
dd
dd
d
br d
dddd
m
m
m
10.5; 10.5; 3.0
12.1; 10.5; 6.0; 3.5; 3.5
12.1; 4.0; 3.5
12.1; 12.0; 12.0
12.0; 11.0; 10.6; 4.2; 4.0
11.0
10.8; 4.2; 1.0
10.8; 10.6
10.3; 1.0
structure A drawn with bold bonds in Figure 1. The 13C
chemical shifts of CH2-2 (dC 44.9) suggested its linkage to
the nitrogen atom. An other set of connectivities determined
the partial structure B: on one hand, CH2-14 (dH 0.80 and
2.44) was correlated to CH2-15 (dH 1.32 and 1.45), then
CH2-17 (dH 1.12 and 1.55) to CH2-16 (dH 1.20 and 1.72)
and finally CH2-15 and 16 were correlated between them-
selves, forming a –(CH2)4– spin system. On the other
hand, CH-9 (dH 2.40) had correlations with CH2-11 (dH
3.15 and 3.86), CH-10 (dH 2.22), and CH2-8 (dH 0.74 and
1.50). This one (CH2-8) was correlated to CH-7 (dH 1.45),
which was further correlated to both CH2-18 (dH 3.42 and
3.59) and CH-6 (dH 1.11) and finally this latter showed cor-
relation with CH2-17. The 13C chemical shifts of CH2-11 (dC
73.4) and CH2-18 (dC 65.1) suggested their direct linkage to
an oxygen atom, and those of CH-10 (dH 2.22 and dC 69.5) to
a nitrogen atom. A ‘W’ coupling (4J¼1 Hz) was depicted be-
tween H-11eq and H-13eq. The chemical shifts of CH2-13 (dC
86.7) indicated it was linked to both nitrogen and oxygen
atoms.
9
10
11
13
14
15
16
17
18
10.3
13.2
13.2; 13.2; 4.1; 1.0
m
m
dddd
dd
dd
10.5; 10.4; 9.8; 3.5
10.6; 3.5
10.6; 6.0
Thus, H-9 was axial on both b- and c-rings, indicating the
trans junctions of these two rings (Fig. 2). The proton H-6
showed two trans-diaxial coupling constants with H-7
(10.5 Hz) and H-17ax (10.5 Hz) and one cis coupling
(3.0 Hz with H-17eq), indicating its axial position on both
b- and d-rings and the axial position of H-7 on the b-ring.
Hence, the oxymethylene CH2-18 was equatorial on the
b-ring. Strong NOEs observed on the NOESY spectrum be-
tween H-10 and H-14ax, H-13ax, H-11ax, H-8ax, and H-6 and
between this latter one (H-6) and H-14ax, H-8ax, and H-16ax
allowed to determine their disposition on the same face of 1.
In addition, the correlation of H-3ax with H-14eq and of H-7
with both H-4ax and H-9ax was observed. Complete NOE
analysis indicated the chair conformation for the four rings
(a–d) of 1 and the relative configuration shown in Figure 2.
Myrioneurinol (1) was characterized by a new alkaloid tetra-
cyclic skeleton, including an 1,3-oxazine ring, which can be
compared to the tricyclic alkaloid myrioxazine A, as they
have in common the tricyclic a-, b-, and c-ring system.4
The 2J and 3J HMBC correlations of the C-5 quaternary car-
bon (dC 36.2) with, on one hand, the protons of CH2-17,
CH2-15, CH2-14, CH-10, CH-9, CH-7, and CH-6 of the
B-fragment and, on the other hand, with the protons at
CH2-4, and CH2-3 of A-fragment provided the connection
between the two substructures. Quaternary carbon C-5 was
linked to C-6, C-10, and C-14 of B-fragment, as well as to
C-4 of A-fragment (Fig. 1).
This structure was supported by the correlations of both CH-
10 (dH 2.22) and CH2-4 (dH 1.32 and 1.63) protons with C-14
carbon (dC 34.2). Cross peaks of CH2-2 (dH 2.61 and 3.22)
with C-10 carbon (dC 69.5) indicated their linkage through
a nitrogen atom, resulting in a decahydroquinoline moiety.
Finally, C-13 (dC 86.7) was correlated to CH2-11 (dH 3.15
and 3.86), CH-10 (dH 2.22), and CH2-2 (dH 2.61 and 3.22)
protons, indicating its direct linkage to N-1 nitrogen and
O-12 oxygen, and closing thus an 1,3-oxazine ring. Taking
into account the molecular formula, the methylene at CH2-
18 was connected to a hydroxyl group and the gross planar
structure of 1 was thus established as indicated in Figure 1.
H
15
16
H
H
H
14
17
H
3
d
H
The relative stereochemistry of 1 was deduced from the
5
1
4
6
NOE correlations and the values of the H–1H vicinal cou-
H
H
b
a
N
H
H
pling constants: H-10 and H-9 presented a large reciprocal
coupling constant (J¼11.0 Hz), indicative of their trans-
diaxial disposition on the cyclohexane b-ring in the chair
form (Table 1). Moreover, H-9 showed two other trans-
diaxial coupling constants (J¼10.6 and 12.0 Hz with
H-11ax and H-8ax, respectively) and two small couplings
(J¼4.2 and 4.0 Hz with H-11eq and H-8eq, respectively).
H
2
10H
9
OH
H
18
7
13
H
H
H
H
8
c
O
H
12
11
H
H
Figure 2. Selected NOE interactions for 1.

11246
V. C. Pham et al. / Tetrahedron 63 (2007) 11244–11249
+1.30
+0.54
2.1.1. Determination of absolute configuration of myrio-
neurinol (1) by derivation with (R)- and (S)-9-anthryl-
methoxyacetic acid (9-AMAA). If the absolute
stereochemistry of chiral secondary alcohols could be deter-
mined by MTPA or MPA (Mosher’s method),5a–h they are
not recommended for b-chiral primary alcohols. However,
Reguera and co-workers have demonstrated that absolute
configuration of such b-chiral primary alcohol can be estab-
lished by using 9-anthrylmethoxyacetic acid (9-AMAA)
instead of MTPA.6a–e
+0.28
+0.29
+0.21
OR
-0.06
H
H
+0.30
-0.67
+0.47
N
H
H-0.17
-0.38
-0.14
R= (S)-AMAA or (R)-AMAA
O
Figure 3. Some significant D(d(R)-9-AMAA-myrioneurinolꢀd(S)-9-AMAA-myrioneuri-
nol) values of the two esters 11 and 12.
According to this regard, (R)- and (S)-9-AMAA were pre-
pared by a modified method of the previously reported
paper.6b Compound 4 was obtained in 65% yield from an-
thracene (2) by reaction with ethyl oxalyl chloride following
with NaBH4. Methylation of 4 with MeI and Ag2O afforded
5, which was hydrolyzed to yield the free acid 6. Racemic
resolution of 9-AMAA 6 was performed by its derivation
with (ꢀ)-menthol to afford 7 and 8. These two diastereo-
isomers (S)-9-AMAA-(ꢀ)-menthyl (7) and (R)-9-AMAA-
(ꢀ)-menthyl (8) were separated by column chromatography
and their structure were determined from comparison of
their NMR data and optical rotations with those reported
in the literature.6b (S)-AMAA (9) and (R)-AMAA (10) ob-
tained from hydrolysis of the corresponding menthyl esters
(7 and 8) in basic conditions were esterified with myrio-
neurinol (1) to yield two diastereoisomers 11 and 12, respec-
tively (Scheme 1).
2.2. Biosynthesis of myrioneurinol (1)
Retroanalysis of myrioneurinol (1) shows piperidineringsub-
stitutions, which are characteristic for D-piperideine derived
(from lysine) polycyclic alkaloids. Nitraria alkaloids such
as nitramine and sibirine, and also lupin alkaloids such as lu-
pinine, sparteine, andmatrine, aregoodexamplesforproducts
derived from D-piperideine. A hypothetical biosynthetic
pathway for lupin alkaloids was previously reported, in which
the amino enamine 13 resulting from lysine could be immedi-
ately hydrolyzed to afford the intermediate 14. From this
intermediate, a number of lupin alkaloids such as lupinine
and sparteine are biosynthesized. However, the amino en-
amine 13 could be also transformed to the key intermediate
15.7a–d Addition of a third D2-piperideine unit to 15, followed
by cyclisation leads to intermediate 16 (Scheme 2). Com-
pound 16 could be, on one hand, transformed to nitraramine
with ring inversion leading to a ring conformation (17) where
the hydroxyl at C-7 and the piperideine ring at C-11 are in a
1,3-diaxial disposition. This facilitates the formation of the
two successive aminal bonds by cyclisation process. On the
other hand, compound 16 could be deoxygenated to afford
the diimine 18, which could be hydrolyzed and oxidized
into the dialdehyde 19. The enol form of 19 could cyclise to
afford the amino dialdehyde 21. In the last step, 21 is reduced
and condensed with formaldehyde to complete the myrio-
neurinol biosynthesis (Scheme 2). Note that no ring inversion
of the intermediate 14 is needed for the myrioneurinol (1)
The resulting esters 11 and 12 were analyzed by NMR
and the DdRꢀS (d(R)-9-AMA-myrioneurinolꢀd(S)-9-AMA-myrioneurinol
)
values were calculated. These values were positive on the
upside of the molecule whereas they were negative on the
other side, except for H-8 (Fig. 3). By using Mosher’s mod-
eq
el,5a–c,6b the absolute configuration of the chiral carbon C-7
was determined as S. According to the relative configuration
established from 3JH–H coupling constants and NOE interac-
tions, the absolute configuration of myrioneurinol (1) was
determined as 5R,6R,7S,9R,10S.
O
O
O
O
O
OH
OMe
OMe
EtO
EtO
EtO
HO
a
b
c
d
2
3
5
6
4
O
O
OMe
OMe
(-)-Menthol-O
(-)-Menthol-O
+
e
7
8
f
f
O
O
O
O
OMe
OMe
OMe
OMe
(Myrioneurinol)-O
HO
g
HO
(Myrioneurinol)-O
g
11
9
10
12
Scheme 1. (a) Ethyl oxalyl chloride, CH2Cl2, 25 ꢁC, 12 h, 86%; (b) NaBH4, MeOH, 0 ꢁC, 12 h, 85%; (c) MeI, Ag2O, CH2Cl2, 25 ꢁC, 24 h, 67%; (d) LiOH, THF/
MeOH/H2O (3:1:1), 0–25 ꢁC, 4 h, 71%; (e) (ꢀ)-menthol, DCC, DMAP, CH2Cl2, 25 ꢁC, 24 h, 32% for 7 and 29% for 8; (f) 2 N NaOH, EtOH, 25 ꢁC, 12 h, 62%
for 9 and 51% for 10; (g) myrioneurinol (1), DCC, DMAP, CH2Cl2, 25 ꢁC, 24 h, 38% for 11 and 31% for 12.

V. C. Pham et al. / Tetrahedron 63 (2007) 11244–11249
11247
H3O+
N
N
lupin alkaloids
lysine
H2
H2
O
N
H3N
14
13
HO
7
OH
N
O
N
NH
C-alkylation
O
11
ring inversion
cyclisation
N
N
N
H
N
N
15
16
17
nitraramine
H
H
H
H
H3O+
-NH3, [O]
cyclisation
OH
[H]
O
HCHO
O
O
N
N
N
N
H
O
N
H
H2
O
HO
O
N
18
19
myrioneurinol
20
21
Scheme 2. Plausible biosynthetic pathway for myrioneurinol (1) and related alkaloids.
formation. This is a difference in the biosynthetic pathways of
myrioneurinol (1) and nitraramine.
of Botany, VAST, Viet Nam. The dried and ground leaves
(5 kg) were alkalinized with aqueous NH4OH (10%) and
extracted with CH2Cl2. After evaporation to dryness, the
CH2Cl2 crude extract was suspended in an aqueous 5%
HCl solution and then extracted with CH2Cl2. The crude
alkaloid extract obtained after solvent removing under re-
duced pressure was chromatographed over silica gel column
and eluted with a gradient of CH2Cl2/MeOH (from 1/0 to
0/1) to provide myrioneurinol (1, 32 mg).
2.3. Biological activities’ evaluation
When evaluated for its cytotoxic and antimalarial activities,
myrioneurinol (1) induced weak inhibition on KB cell pro-
liferation with IC50 of 26 mg/mL. However, it showed a stron-
ger activity in antimalarial assay on Plasmodium falciparum
(IC50: 11 mg/mL), suggesting that its moderate antimalarial
activity was not due to its cytotoxicity.
4.3. Natural compound characterization
4.3.1. Myrioneurinol (1). C16H27NO2; colorless microcrys-
talline solid (Et2O/EtOH); mp: 145–146 ꢁC; [a]D20 +63.2 (c 1,
MeOH); IR (KBr) nmax (cmꢀ1): 3400, 2929, 2859, 1468,
1450, 1380, 1280, 1180, 1166, 1134, 1032, 742, 704;
ESI-MS (TOF), m/z: 266.2149 [M+H]+ (calcd 266.2120
for C16H28NO2); ESI-MSMS (TOF) on [M+H]+ ion, m/z:
266 [M+H]+, 236, 218, 206, 187, 176, 173, 159, 145, 131,
119, 110, 107, 105, 93, 79, 70, 67, 56, 44.
3. Conclusion
This paper describes the isolation and absolute structure de-
termination of the tetracyclic alkaloid, myrioneurinol (1)
showing a new skeleton. The absolute configuration was
established by analysis of its derivatives with (R)- and (S)-
9-AMAA, which were resolved from racemic form through
their esters with (ꢀ)-menthol. Retroanalysis of structure of
1 allows to suggest its biosynthesis from D-piperideine
derived from lysine.
4.4. Procedures for preparation of compounds 3–12
4.4.1. Ethyl (9-anthryl)glyoxylate (3). To a solution of an-
thracene (8 g, 44 mmol) in anhydrous CH2Cl2 (150 mL) was
added ethyl oxalyl chloride (5.1 mL, 49 mmol) at 0 ꢁC. The
resulting solution was stirred for 1 h and then warmed to
25 ꢁC for 12 h. Water (100 mL) was added and the organic
layer was separated. The aqueous solution was extracted
with CH2Cl2 (2ꢂ100 mL). The combined extracts were
washed with 5% NaHCO3 and water, and dried over
MgSO4. The solvent was removed under diminished pres-
sure and the crude was purified by silica gel column chroma-
tography (n-hexane/EtOAc) to afford 3 (10.5 g, 86% yield).
ESI-MS m/z 279 [M+H]+.
4. Experimental section
4.1. General
Melting points were determined on a Reichert microscope
and were uncorrected. Optical rotations were measured on
a Perkin Elmer 341 Kontron spectrophotometer. ESI-mass
spectra were performed on an API Q-STAR PULSAR i of
Applied Biosystems. 13C spectra were recorded on a Bruker
AC 300 spectrometer operating at 300.13 and 75.43 MHz.
1H 1D and 2D NMR spectra were recorded on a Bruker
Avance 400 spectrometer operating at 400.13 MHz. For
HMBC experiments the delay (1/2J) was 70 ms and for
the NOESY experiments the mixing time was 150 ms.
4.4.2. ( )-Ethyl a-hydroxy-a-(9-anthryl) acetate (4). A
solution containing 4 (9.5 g, 34.17 mmol) in MeOH
(50 mL) was treated with NaBH4 (1.3 g, 34.17 mmol) at
0 ꢁC. The reaction mixture was stirred for 5 h. Saturated
aqueous solution of NH4Cl (50 mL) was added, and then
the mixture solution was warmed to 25 ꢁC and extracted
with CH2Cl2 (3ꢂ50 mL). The combined organic extracts
4.2. Plant material and extraction
M. nutans Drake was collected in North-Viet Nam in June
2000 and a specimen (VN 700) was deposited in the Institute

11248
V. C. Pham et al. / Tetrahedron 63 (2007) 11244–11249
were washed with water and dried over MgSO4. The solvent
was removed under diminished pressure. The crude was
chromatographed on silica gel column and eluted with gra-
dient mixture of n-hexane/EtOAc to provide 4 (8.1 g, 85%
1H), 7.49 (m, 4H), 7.78 (d, 7.7 Hz, 2H), 8.44 (s, 1H), 8.57
(d, 8.4 Hz, 2H); 13C NMR (CDCl3, 75.47 MHz): 16.5,
20.6, 21.7, 23.4, 26.5, 31.1, 33.9, 39.9, 46.6, 57.4, 75.4,
77.3, 124.5, 124.9, 126.3, 126.9, 129.0, 130.6, 131.4,
170.2; ESI-MS m/z 405.2365 [M+H]+.
1
yield): mp 107 ꢁC; H NMR (CDCl3, 300 MHz): 0.97 (t,
7.1 Hz, 3H), 4.12 (q, 7.1 Hz, 2H), 6.55 (s, 1H), 7.28 (m,
4H), 7.99 (d, 7.8 Hz, 2H), 8.32 (d, 8.7 Hz, 2H), 8.45 (s,
1H); 13C NMR (CDCl3, 75.47 MHz): 13.8, 62.2, 68.1,
123.8, 124.8, 126.5, 128.5, 129.1, 129.2, 130.3, 131.5,
175.1; ESI-MS m/z 281 [M+H]+.
Compound 8: [a]2D0 ꢀ55.1 (c 0.002, EtOH); 1H NMR
(CDCl3, 300 MHz): ꢀ0.08 (d, 5.9 Hz, 3H), 0.05 (d,
2.5 Hz, 3H), 0.09 (m, 1H), 0.5–2.1 (m, 8H), 3.48 (s, 3H),
4.53 (br dd, 3.3 and 10.6 Hz, 1H), 6.25 (s, 1H), 7.49 (m,
4H), 8.01 (d, 7.6 Hz, 2H), 8.45 (s, 1H), 8.59 (d, 8.5 Hz,
2H); 13C NMR (CDCl3, 75.47 MHz): 14.3, 16.4, 21.3,
22.0, 23.1, 25.9, 31.8, 34.7, 45.2, 50.8, 57.9, 61.4, 71.8,
77.4, 124.8, 125.0, 126.8, 127.1, 130.2, 130.8, 131.4,
171.2; ESI-MS m/z 405.2378 [M+H]+.
4.4.3. ( )-Ethyl a-methoxy-a-(9-anthryl) acetate (5). To
a solution containing 4 (6 g, 21.42 mmol) and MeI (6 mL)
in anhydrous CH2Cl2 (50 mL) was added Ag2O (5.9 g,
25.4 mmol). The reaction mixture was stirred at 25 ꢁC for
12 h and then water (50 mL) was added. The solution mix-
ture was extracted with CH2Cl2 (3ꢂ50 mL). The combined
organic extracts were washed with water and dried over
MgSO4. The solvent was evaporated under diminished pres-
sure and the crude was purified over silica gel column chro-
matography (n-hexane/EtOAc), giving 5 (4.2 g, 67% yield):
mp 79 ꢁC; 1H NMR (CDCl3, 300 MHz): 1.02 (t, 7.1 Hz, 3H),
3.39 (s, 3H), 4.10 (q, 7.1 Hz, 2H), 6.25 (s, 1H), 7.49 (m, 4H),
8.01 (dd, 0.5 and 8.3 Hz, 2H), 8.45 (s, 1H), 8.55 (d, 8.8 Hz);
13C NMR (CDCl3, 75.47 MHz): 13.9, 57.4, 61.3, 77.2,
124.4, 124.9, 126.4, 127.4, 129.1, 129.2, 130.6, 131.5,
171.3; ESI-MS m/z 295 [M+H]+.
4.4.6. (D)-(S)-a-Methoxy-a-(9-anthryl) acetic acid—(S)-
AMAA (9). To a solution of 7 (0.5 g, 1.2 mmol) in 3 mL of
a mixture of EtOH/H2O (1:1) was treated with NaOH
(96 mg, 2.4 mmol) at 25 ꢁC. The reaction mixture was
stirred for 12 h and then 1 N HCl was slowly added until
pH 7. The mixture was extracted with CH2Cl2 (3ꢂ15 mL).
The combined organic extracts were washed with water
and dried over MgSO4. The solvent was removed under di-
minished pressure and the crude was chromatographed on
silica gel column (CH2Cl2/MeOH) to provide 9 (197 mg,
62% yield): [a]2D0 +131.2 (c 0.001, EtOH).
4.4.4. ( )-a-Methoxy-a-(9-anthryl) acetic acid (6). To a so-
lution of 5 (3.5 g, 11.9 mmol) in a mixture of THF/MeOH/
H2O (3:1:1, 30 mL) was added LiOH (0.6 g, 23.8 mmol) at
0 ꢁC. The resulting mixture was stirred for 3 h and then
warmed to 25 ꢁC for 1 h. To this solution mixture, 1 N
HCl was slowly added until pH 7. The volatile layer was re-
moved under diminished pressure. The mixture solution was
extracted with EtOAc (4ꢂ50 mL). The combined organic
extracts were washed with water and dried over MgSO4.
The solvent was removed under diminished pressure, the
crude was chromatographed on silica gel column, and eluted
with a gradient mixture of CH2Cl2/MeOH to afford 6 (2.2 g,
71% yield): mp 188 ꢁC; 1H NMR (CDCl3, 300 MHz): 3.36
(s, 3H), 6.28 (s, 1H), 7.49 (m, 4H), 8.01 (dd, 0.5 and
8.2 Hz, 2H), 8.46 (d, 8.8 Hz, 2H), 8.49 (s, 1H); ESI-MS
m/z 267 [M+H]+.
4.4.7. (L)-(R)-a-Methoxy-a-(9-anthryl) acetic acid—
(R)-AMAA (10). Compound 10 (176 mg, 51% yield) was
obtained from 8 (0.55 g, 1.3 mmol) according to the proce-
dure for 9: [a]2D0 ꢀ128.2 (c 0.001, EtOH).
4.4.8. Myrioneurinol-(S)-AMAA (11). A solution of
myrioneurinol (1, 5 mg, 0.019 mmol) and (S)-AMAA (9,
10 mg, 0.038 mmol) in anhydrous CH2Cl2 (1 mL) was
treated with DCC (5.9 mg, 0.028 mmol) and a small crystal
of DMAP. The resulting solution was stirred at 25 ꢁC for
24 h. The solvent was removed and the crude was purified
by prep. TLC to afford 11 (3.7 mg, 38% yield): [a]D20
+76.4 (c 0.01, MeOH); 1H NMR (CDCl3, 400 MHz):
ꢀ0.28 (ddd, 12.9, 11.7, 3.8 Hz, H-6), ꢀ0.17 (m, H-16ax),
ꢀ0.07 (ddd, 13.2, 13.2, 4.3 Hz, H-14ax), 0.05 (ddd, 12.6,
12.6, 12.6 Hz, H-8ax), 0.50 (m, H-17ax), 0.75 (ddd, 12.6,
3.8, 3.8 Hz, H-8eq), 0.79 (m, H-17eq), 0.89 (m, H-4ax), 1.01
(m, CH2-15), ꢀ1.05 (m, H-16eq), 1.14 (ddddd, 12.6, 11.7,
4.3, 3.8, 3.2 Hz, H-7), 1.25 (m, H-4eq), 1.29 (d, 11.1 Hz),
1.31 (m, H-3eq), 1.50 (m, H-3ax), 1.98 (m, H-9), 2.03 (m,
H-14eq), 2.47 (br dd, 11.7, 4.3 Hz, H-2eq), 2.65 (dd, 10.7,
10.7 Hz, H-11ax), 3.00 (ddd, 11.7, 11.7, 3.9 Hz, H-2ax),
3.44 (s, OMe), 3.48 (dd, 10.7, 3.7 Hz, H-11eq), 3.59 (dd,
11.0, 3.2 Hz, H-18a), 4.17 (d, 10.2 Hz, H-13ax), 4.25 (dd,
11.0, 4.3 Hz, H-18b), 4.31 (d, 10.2, H-13eq), 6.28 (s, 1H),
7.49 (m, 2H), 7.53 (m, 2H), 8.02 (br d, 8.3 Hz, 2H), 8.48
(s, 1H), 8.60 (br d, 8.3 Hz, 2H).
4.4.5. (L)-Menthyl (D)-(S)-a-methoxy-a-(9-anthryl)
acetate (7) and (L)-menthyl (L)-(R)-a-methoxy-a-(9-
anthryl) acetate (8). A solution of 7 (1.5 g, 5.6 mmol) and
(ꢀ)-menthol (1.1 g, 7.0 mmol) in anhydrous CH2Cl2
(20 mL) was treated with DCC (1.2 g, 5.6 mmol) and
DMAP (0.1 g, 0.8 mmol) at 25 ꢁC. The resulting solution
was stirred for 24 h and then 50 mL water was added. The
mixture was extracted with CH2Cl2 (3ꢂ50 mL). The com-
bined extracts were washed with water and dried over
MgSO4. The crude obtained after removing the solvent
was chromatographed on silica gel column and eluted with
a mixture of cyclohexane/CH2Cl2 to afford 7 (0.72 g, 32%
yield) and 8 (0.65 g, 29% yield).
4.4.9. Myrioneurinol-(R)-AMAA (12). Compound 12
(2.1 mg, 31% yield) was obtained from (R)-AMAA (10,
1
3.5 mg): [a]2D0 +8.6 (c 0.01, MeOH); H NMR (CDCl3,
Compound 7: [a]2D0 ꢀ5.8 (c 0.002, EtOH); 1H NMR (CDCl3,
300 MHz): 0.44 (q, 9 Hz, 1H), 0.5–2.0 (m, 8H), 0.64 (d,
6.7 Hz, 3H), 0.75 (d, 7.2 Hz, 3H), 0.84 (d, 7.2 Hz, 3H),
3.38 (s, 3H), 4.73 (br dd, 3.1 and 9.8 Hz, 1H), 6.25 (s,
400 MHz): ꢀ0.62 (ddd, 12.2, 12.2, 12.2 Hz, H-8ax), 0.02
(m, H-6), 0.71 (m, H-17ax), 0.95 (m, H-4ax), 1.01 (m,
H-3ax), 1.08 (m, H-7), 1.13 (m, H-16ax), 1.15 (m, H-10),
1.21 (m, H-3eq), 1.22 (m, H-8eq), 1.29 (m, CH2-15), 1.81

V. C. Pham et al. / Tetrahedron 63 (2007) 11244–11249
11249
Aimi, N.; Nishimura, M.; Miwa, A.; Hoshino, H.; Sakai, S. I.;
Haginiwa, J. Tetrahedron Lett. 1989, 54, 4991.
ꢀ
4. Pham, V. C.; Jossang, A.; Chiaroni, A.; Sevenet, T.; Bodo, B.
Tetrahedron Lett. 2002, 43, 7565.
(m, H-9), 2.27 (dd, 11.0, 11.0 Hz, H-11ax), 3.34 (br d,
11.0 Hz, H-11eq), 3.45 (m, CH2-2), 3.56 (dd, 11.1, 4.1 Hz,
H-18a), 4.09 (m, H-18b), 4.24 (m, CH2-13), 6.29 (s, 1H),
7.51 (m, 4H), 8.13 (m, 2H), 8.58 (m, 3H).
5. (a) Dale, J. A.; Dull, D. L.; Mosher, H. S. J. Org. Chem. 1969, 34,
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Acknowledgements
The authors thank Mr. D.C. Dao and Mr. A. Gramain for
plant collection and its botanical determination, Mr. Lionel
Dubost for ESI-MS measurement, and Dr. A. Blond for
recording 2D NMR spectra. The CNRS is gratefully ac-
knowledged for doctoral fellowship supporting (V.C.P.).
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