Two alangium alkaloids from Alangium lamarckii

Article abstract of DOI:10.1021/np0000163

Two new Alangium alkaloids, 1',2'-dehydrotubulosine (1) and alangine (2), were isolated from the dried fruits of Alangium lamarckii along with tubulosine (3), isotubulosine (4), deoxytubulosine, cephaeline, isocephaeline, psychotrine, neocephaeline, 10-O-

Full text of DOI:10.1021/np0000163

J . Nat. Prod. 2000, 63, 723-725
723
Tw o Ala n giu m Alk a loid s fr om Ala n giu m la m a r ckii
Atsuko Itoh, Yuki Ikuta, Takao Tanahashi,* and Naotaka Nagakura
Kobe Pharmaceutical University, Higashinada-ku, Kobe 658-8558, J apan
Received J anuary 14, 2000
Two new Alangium alkaloids, 1′,2′-dehydrotubulosine (1) and alangine (2), were isolated from the dried
fruits of Alangium lamarckii along with tubulosine (3), isotubulosine (4), deoxytubulosine, cephaeline,
isocephaeline, psychotrine, neocephaeline, 10-O-demethylcephaeline, 2′-N-(1′′-deoxy-1′′-â-D-fructopyran-
osyl)cephaeline, protoemetine, protoemetinol, salsoline, and alangiside. The structures of the new alkaloids
(1 and 2) were determined by spectroscopic and chemical means.
Alangium lamarckii Thwaites (Alangiaceae) is a decidu-
ous shrub of wide distribution in India and South East
Asia. The root, root-bark, and bark of this plant have been
used in the indigenous Indian systems of medicine for a
long time.1 Previous phytochemical studies of A. lamarckii
resulted in the isolation of numerous classes of alkaloids,
i.e., emetan, tubulosan, 3-ethyl-2H-benzo[a]quinolizine
(protoemetinol), and 8H-isoquino[2,1-b][2,7]naphthyridine-
8-one (alangimaridine).1 Recently, several new nitrogenous
glycosides closely related to the Alangium alkaloids were
isolated from the fruits of this plant.2-5 We have reexam-
ined the alkaloidal fraction of the fruits of A. lamarckii and
report here the isolation and characterization of two
additional novel Alangium alkaloids (1 and 2).
The dried and crushed fruits of A. lamarckii were
extracted with hot MeOH, and the MeOH extract was
successively partitioned between H2O/CHCl3 and H2O/
n-BuOH. The H2O layer was basified and extracted with
Et2O and then C2H4Cl2. The organic layers were separated
by a combination of chromatographic procedures, affording
alkaloids 1 and 2 along with the known compounds
tubulosine (3),6 isotubulosine (4),6 deoxytubulosine,6 ceph-
aeline,6 isocephaeline,6 psychotrine,6 10-O-demethyl-
cephaeline,7 protoemetinol,6 (()-salsoline,8 alangiside,9 neo-
cephaeline,7 2′-N-(1′′-deoxy-1′′-â-D-fructopyranosyl)ceph-
aeline,7 and protoemetine.6 The last three alkaloids were
isolated for the first time from this plant species.
Alkaloid 1 was obtained as an amorphous powder.
HREIMS revealed the molecular formula C29H35N3O3. It
3569, 1613, and 1516 cm-1. The signals for a methoxyl
group (δ 3.86) and two aromatic protons (δ 6.57 and 6.77)
in its 1H NMR spectrum, a NOESY correlation between
OMe (δ 3.86) and H-8 (δ 6.57) which correlated with H-7,
a fragment ion peak at m/z 230,10 and its 13C NMR
spectrum (see Experimental Section) all suggested that 2
contained a 9-methoxy-10-hydroxybenzo[a]quinolizine moi-
ety. Its 1H NMR spectrum showed signals for a terminal
vinyl group at δ 5.17, 5.23, and 5.60, signals for a hy-
droxymethyl group at δ 3.57 and 3.79, and a methine
proton at δ 2.35. COSY correlation between the methine
proton at δ 2.35 (H-14) and the hydroxymethyl proton at δ
3.57 (H-15), as well as HMBC correlations from H2-15 to
C-13 and C-2 and from H-13 to C-14 and C-15 defined the
side chain, and the sequence of correlations of H2-1 (δ 2.14),
H-2 (δ 1.68), H2-3 (δ 1.71-1.81), and H2-4 (δ 2.84) in the
COSY spectrum indicated the substitution at C-2.
showed UV maxima at 230, 291, 328, and 370 nm, and IR
bands at 3432, 2833, 2748, 1612, and 1514 cm-1. Its 1H
NMR spectrum exhibited signals for an ethyl group at δ
1.00, 1.24-1.32, and 1.85, singlets for two aromatic protons
at δ 6.19 and 6.61, an AMX spin system for three aromatic
protons at δ 6.90, 6.92, and 7.28, and singlets for methoxyl
groups at δ 3.27 and 3.72. These spectral features were
similar to those of tubulosine (3), except for absence of the
H-1′ signal, which appeared at δ 4.12 in 3, suggesting that
1 was the 1′,2′-dehydrogenated analogue of tubulosine (3).
The proposed structure of 1 was consistent with its 13C
NMR spectrum, where C-1′ was observed at δ 166.4,
instead of at δ 48.4 in 3. Finally, 1 was treated with NaBH4
to afford 3 and isotubulosine (4). Thus, alkaloid 1 was
determined to be 1′,2′-dehydrotubulosine.
The second new alkaloid, 2, alangine, was obtained as a
white powder and analyzed for C18H25NO3 (HREIMS). It
showed UV maxima at 225 and 285 nm and IR bands at
The cis quinolizine ring junction was indicated by the
absence of Bohlmann bands in its IR spectrum and the
presence of a deshielded proton resonance at δ 4.07,
attributed to H-11b.11 The relative configurations of C-2,
* To whom correspondence should be addressed. Fax: +81-78-441-7546.
E-mail: tanahash@kobepharma-u.ac.jp.
10.1021/np0000163 CCC: $19.00
© 2000 American Chemical Society and American Society of Pharmacognosy
Published on Web 04/12/2000

724 J ournal of Natural Products, 2000, Vol. 63, No. 5
Notes
to 90:9:1) and preparative TLC (CHCl3/MeOH/NH4OH, 90:9:
1), affording protoemetine (4.8 mg), deoxytubulosine (83.9 mg),
protoemetinol (8.8 mg), neocephaeline (97.0 mg), 2′-N-(1′′-
deoxy-1′′-â-D-fructopyranosyl)cephaeline (25.5 mg), cephaeline
(1.39 g), and isocephaeline (109 mg). In the same way, the
following fractions were purified by a combination of MPLC
with CHCl3/MeOH/NH4OH (98:2:0.2 to 90:9:1) and preparative
TLC with CHCl3/MeOH/NH4OH (90:9:1) or C6H6/EtOAc/Et2NH
(2:7:1). Fraction 3 yielded deoxytubulosine (28.0 mg), neoceph-
aeline (28.6 mg), cephaeline (1.15 g), and isocephaeline (154
mg); fraction 4, 3 (224 mg), 4 (23.6 mg), 2′-N-(1′′-deoxy-1′′-â-
D-fructopyranosyl)cephaeline (4.7 mg), cephaeline (345 mg),
isocephaeline (899 mg), psychotrine (37.9 mg), and 10-O-
demethylcephaeline (24.5 mg); fraction 5, 3 (57.0 mg), 1 (10.9
mg), 4 (16.2 mg), cephaeline (10.2 mg), and isocephaeline (119
mg). The C2H4Cl2 layer (6.4 g) was also subjected to MPLC,
and elution with CHCl3/MeOH mixtures of the indicated that
the MeOH content gave 7 fractions: 1 (2%, 69.3 mg), 2 (2%,
245 mg), 3 (5%, 1.90 g), 4 (5-8%, 2.01 g), 5 (8%, 587 mg), 6
(8-20%, 826 mg), 7 (20%, 335 mg). Each fraction was purified
in a manner similar to that for the Et2O layer to yield
protoemetine (41.4 mg), cephaeline (1650 mg), isocephaeline
(985 mg), deoxytubulosine (26.1 mg), neocephaeline (16.1 mg),
2′-N-(1′′-deoxy-1′′-â-D-fructopyranosyl)cephaeline (74.9 mg),
psychotrine (596 mg), alangiside (96.0 mg), 3 (6.2 mg), 4 (3.4
mg), salsoline (2.8 mg), and 2 (3.0 mg). The known alkaloids
were identified by comparisons ([R]D, UV, IR, NMR, and MS)
with pure standards.
F igu r e 1. Selected NOESY correlations of 2.
-11b, and -14 were suggested by the NOESY correlations
between H-11b and H-14 and between H-1 and H2-15
(Figure 1). This assumption was supported by comparative
studies of its 13C NMR spectral data with those of antirhine
(5).12 Biogenetic considerations that the non-dopamine
portion of 2 originated from secologanin, and thereby the
chirality of C-2 should be S, allowed assignment of the
absolute stereochemistry of 2. Thus, alangine was deter-
mined to be structure 2.
The occurrence of 1 and 2 is of great interest from the
viewpoint of biosynthesis of Alangium alkaloids.13 Alkaloid
1 could be derived from tubulosine (3) or isotubulosine (4).
Two plausible mechanisms could be proposed for the
formation of 3 and 4. Two epimeric alkaloids might be
independently biosynthesized through condensation of a
protoemetine type alkaloid with tryptamine (or serotonin)
in a manner similar to the biosynthesis of deacetylipecoside
and deacetylisoipecoside.14 Another possibility is an oxida-
tion-hydrogenation mechanism as observed in the conver-
sion of (S)-reticuline to (R)-reticuline via the 1,2-dehydro-
reticulinium ion.15 In the latter case 1 should be an
intermediate between 3 and 4. Alkaloid 1 could also be
oxidized to 1′,2′,3′,4′-tetradehydrotubulosine in Pogonopus
speciosus.16 On the other hand, alkaloid 2 is the first
compound with a new basic skeleton, which could be
formed from 6, a common intermediate to 10-O-demethyl-
protoemetinol (7).17
1′,2′-Deh yd r otu bu losin e (1): amorphous powder; [R]18
D
+2.1° (c 0.42, MeOH); UV (MeOH) λmax (log ꢀ) 230sh (4.20),
291 (3.69), 328 (4.04), 370sh (3.67) nm; CD (MeOH) λmax (∆ ꢀ)
211 (+8.7), 223 (-2.1) nm; IR (KBr) νmax 3432, 2833, 2748,
1612, 1514 cm-1; 1H NMR (CD3OD) δ 1.00 (3H, t, J ) 7.5 Hz,
H3-13), 1.17 (1H, dt, J ) 13.5, 11.5 Hz, H-1), 1.24-1.32 (3H,
m, H-12, H2-R), 1.55 (1H, m, H-3), 1.81 (1H, m, H-2), 1.85 (1H,
dqd, J ) 13.5, 7.5, 3.0 Hz, H-12), 2.03 (1H, ddd, J ) 13.5, 4.0,
3.0 Hz, H-1), 2.10 (1H, t, J ) 11.5 Hz, H-4), 2.50 (1H, m, H-6),
2.65 (1H, dt, J ) 14.0, 4.0 Hz, H-7), 2.96 (2H, m, H2-4′), 2.99-
3.18 (3H, m, H-6, H-7, H-11b), 3.11 (1H, dd, J ) 11.5, 4.0 Hz,
H-4), 3.27 (3H, s, 10-OMe), 3.72 (3H, s, 9-OMe), 3.78 (1H, m,
H-3′), 3.92 (1H, dt, J ) 15.0, 7.0 Hz, H-3′), 6.19 (1H, s, H-11),
6.61 (1H, s, H-8), 6.90 (1H, dd, J ) 8.5, 2.5 Hz, H-7′), 6.92
(1H, dd, J ) 2.5, 0.5 Hz, H-5′), 7.28 (1H, dd, J ) 8.5, 0.5 Hz,
H-8′); 13C NMR (CD3OD) δ 11.5 (C-13), 20.5 (C-4′), 24.5 (C-
12), 29.3 (C-7), 30.8 (C-R), 37.2 (C-1), 42.0 (C-2), 43.4 (C-3),
47.3 (C-3′), 53.6 (C-6), 56.1 (10-OMe), 56.4 (9-OMe), 61.8 (C-
4), 63.6 (C-11b), 104.0 (C-5′), 109.1 (C-11), 113.1 (C-8), 114.4
(C-8′), 118.7 (C-7′), 119.4 (C-4′a), 127.0 (C-5′a), 127.5 (C-7a),
130.3 (C-11a), 130.6 (C-9′a), 135.5 (C-8′a), 148.6 (C-10), 149.2
(C-9), 153.0 (C-6′), 166.4 (C-1′); NOESY correlations H-11/OMe
(δ 3.27); H-11/H-1 (δ 2.03); H-8/OMe (δ 3.78); H-8/H-7 (δ 2.65);
EIMS m/z 473 [M]+, 272, 270, 244, 201, 200, 192, 176, 146;
HR-EIMS m/z 473.2648 (calcd for C29H35N3O3, 473.2680).
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. UV spectra were
recorded on a Shimadzu UV-240 spectrophotometer and IR
spectra on a Shimadzu FTIR-8200 spectrophotometer. Optical
rotations were measured on a J asco DIP-370 digital polarim-
eter and CD spectra on a Shimadzu-AVIV 62 A DS circular
dichroism spectrometer. 1H (500 MHz) and 13C (125 MHz)
NMR spectra were recorded on a Varian VXR-500 spectrom-
eter with TMS as an internal standard. MS and HRMS were
obtained with a Hitachi M-4100 mass spectrometer. MPLC
was carried out with Wakogel FC-40. TLC was performed on
precoated Kieselgel 60F254 plates (Merck).
P la n t Ma ter ia l. The dried fruits of Alangium lamarckii,
collected in India, were purchased from Mikuni, Osaka, J apan.
A voucher specimen (KPFY-921) is deposited in our laboratory.
Extr a ction a n d Isola tion . The dried fruits (4.5 kg) of A.
lamarckii were crushed and extracted with hot MeOH, and
the extracts were fractionated as described previously.2 A part
(426 g) of the residue (556 g) from the H2O layers was
redissolved in H2O, basified with Na2CO3, and extracted with
Et2O and C2H4Cl2 successively. The residue (8.8 g) from the
Et2O layer was subjected to MPLC, and elution with CHCl3/
MeOH mixtures of the indicated MeOH content gave 5
fractions: 1 (2%, 171 mg), 2 (2-5%, 2.49 g), 3 (8%, 1.75 g), 4
(10-15%, 2.44 g), 5 (20-25%, 192 mg). Fraction 1 was purified
by preparative TLC (CHCl3/MeOH/NH4OH, 85:15:1.5) to afford
protoemetine (15.2 mg) and deoxytubulosine (11.6 mg). Frac-
tion 2 was purified by MPLC (CHCl3/MeOH/NH4OH, 98:2:0.2
Ala n gin e (2): amorphous powder; [R]30 -0.95° (c 0.21,
D
MeOH); [R]23 -2.5° (c 0.20, CHCl3); UV (MeOH) λmax (log ꢀ)
D
225sh (3.74), 285 (3.45) nm; CD (MeOH) λmax (∆ ꢀ) 206 (-4.8),
219 (+1.4), 235 (+0.7) nm; IR (KBr) νmax 3569, 2975, 1613,
1516, 1457 cm-1; 1H NMR (CDCl3) δ 1.68 (1H, m, H-2), 1.71-
1.81 (2H, m, H2-3), 2.14 (2H, m, H2-1), 2.35 (1H, m, H-14), 2.71
(1H, m, H-7), 2.84 (2H, m, H2-4), 3.07 (1H, m, H-6), 3.09 (1H,
m, H-7), 3.19 (1H, m, H-6), 3.57 (1H, dd, J ) 10.5, 7.5 Hz,
H-15), 3.79 (1H, dd, J ) 10.5, 4.5 Hz, H-15), 3.86 (3H, s, OMe),
4.07 (1H, m, H-11b), 5.17 (1H, ddd, J ) 17.0, 1.5, 0.5 Hz, H-12),
5.23 (1H, dd, J ) 10.0, 1.5 Hz, H-12), 5.60 (1H, ddd, J ) 17.0,
10.0, 9.5 Hz, H-13), 6.57 (1H, s, H-8), 6.77 (1H, s, H-11); 13C
NMR (CDCl3) δ 25.0 (C-7), 27.4 (C-3), 31.0 (C-2), 31.5 (C-1),
47.8 (C-4), 49.0 (C-14), 50.7 (C-6), 55.9 (OMe), 56.8 (C-11b),
63.5 (C-15), 111.0 (C-8), 111.2 (C-11), 118.8 (C-12), 124.5 (C-
7a), 127.0 (C-11a), 138.1 (C-13), 144.5 (C-10), 145.7 (C-9);
NOESY correlations H-1/H-11; H2-7/H-8; H2-15/H2-1; H-11b/
H-14; H-14/H-12 (δ 5.23); OMe/H-8; H-12 (δ 5.17)/H-14; EIMS
m/z 303 [M]+, 302, 272, 232, 230, 191, 178, 176; HREIMS m/z
303.1858 (calcd for C18H25NO3, 303.1836).
Red u ction of 1′,2′-Deh yd r otu bu losin e (1). A methanolic
solution (1 mL) of 1′,2′-dehydrotubulosine (1) (4.9 mg) was

Notes
J ournal of Natural Products, 2000, Vol. 63, No. 5 725
(4) Itoh, A.; Tanahashi, T.; Nagakura, N. Phytochemistry 1997, 46, 1225-
1229.
stirred with NaBH4 (75 mg) for 10 min at room temperature.
The mixture was then diluted with H2O and extracted with
CHCl3, and the extract was washed, dried, and concentrated.
The residue (5.0 mg) was purified by preparative TLC (CHCl3/
(5) Itoh, A.; Tanahashi, T.; Nagakura, N. Heterocycles 1998, 48, 499-
505.
(6) Wiegrebe, W.; Kraamer, W. J .; Shamma, M. J . Nat. Prod. 1984, 47,
397-408.
(7) Itoh, A.; Ikuta, Y.; Baba, Y.; Tanahashi, T.; Nagakura, N. Phytochem-
istry 1999, 52, 1169-1176.
(8) Achari, B.; Ali, E.; Ghosh Dastidar, P. P.; Sinha, R. R.; Pakrashi, S.
C. Planta Med. 1980, Suppl., 5-7.
(9) Shoeb, A.; Raj, K.; Kapil, R. S.; Popli, S. P. J . Chem. Soc., Perkin
Trans. 1 1975, 1245-1248.
(10) J ohns, S. R.; Lamberton, J . A.; Occolowitz, J . L. Aust. J . Chem. 1967,
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(11) Weniger, B.; Anton, R.; Varea, T.; Quirion, J .-C.; Bastida, J .; Garcia,
R. J . Nat. Prod. 1994, 57, 287-290.
(12) Kan-Fan, C.; Brillanceau, M. H.; Husson, H. P. J . Nat. Prod. 1986,
49, 1130-1132.
(13) Bhakuni, D. S.; J ain, S.; Chaturvedi, R. J . Chem. Soc., Perkin Trans.
1 1983, 1949-1952.
MeOH/NH4OH, 85:15:1.5) to give 3 (1.7 mg) and 4 (1.1 mg).
1
UV, IR, H NMR, EIMS, optical rotation ([R]27 -60° (c 0.16,
D
MeOH)), and CD ((MeOH) λmax (∆ ꢀ) 229 (-9.5), 242 (+1.6)
nm) spectra of 3 were identical with those of the authentic
tubulosine. UV, IR, 1H NMR, EIMS, optical rotation ([R]27
D
-74° (c 0.10, MeOH)), and CD ((MeOH) λmax (∆ ꢀ) 220 (-15.5),
241 (+2.6) nm) spectra of 4 were identical with those of the
authentic isotubulosine.
Ack n ow led gm en t. Our thanks go to Dr. M. Sugiura (Kobe
Pharmaceutical University) for the NMR spectra and to Dr.
K. Saiki (Kobe Pharmaceutical University) for the MS meas-
urements.
(14) De-Eknamkul, W.; Ounaroon, A.; Tanahashi, T.; Kutchan, T. M.;
Zenk, M. H. Phytochemistry 1997, 45, 477-484.
(15) De-Eknamkul, W.; Zenk, M. H. Phytochemistry 1992, 31, 813-821.
(16) Ito, A.; Lee, Y.-H.; Chai, H.-B.; Gupta, M. P.; Farnsworth, N. R.;
Cordell, G. A.; Pezzuto, J . M.; Kinghorn, A. D. J . Nat. Prod. 1999,
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Refer en ces a n d Notes
(1) Fujii, T.; Ohba, M. In The Alkaloids. Chemistry and Pharmacology;
Brossi, A., Ed.; Academic Press: New York, 1983; Vol. 22, Chapter
1, pp 1-50.
(17) Ali, E.; Sinha, R. R.; Achari, B.; Pakrashi, S. C. Heterocycles 1982,
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(2) Itoh, A.; Tanahashi, T.; Nagakura, N. J . Nat. Prod. 1995, 58, 1228-
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(3) Itoh, A.; Tanahashi, T.; Nagakura, N. Phytochemistry 1996, 41, 651-
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NP0000163