Isolation and characterization of two new alkaloids, norpandamarilactonine-A and -B, from Pandanus amaryllifolius by spectroscopic and synthetic methods

Article abstract of DOI:10.1021/np010213h

Two new alkaloids, norpandamarilactonine-A (1) and -B (2), which have a pyrrolidinyl-α,β-unsaturated γ-lactone moiety as in the known pandamarilactonine alkaloids, were isolated from the leaves of Pandanus amaryllifolius. Their structures were determined

Full text of DOI:10.1021/np010213h

1224
J . Nat. Prod. 2001, 64, 1224-1225
Isola tion a n d Ch a r a cter iza tion of Tw o New Alk a loid s,
Nor p a n d a m a r ila cton in e-A a n d -B, fr om P a n d a n u s a m a r yllifoliu s by
Sp ectr oscop ic a n d Syn th etic Meth od s
Hiromitsu Takayama,*,† Tomotake Ichikawa,† Mariko Kitajima,† Maribel G. Nonato,‡ and Norio Aimi†
Graduate School of Pharmaceutical Sciences, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, J apan, and
Research Center for the Natural Sciences, University of Santo Tomas, Espana, Manila 1008, Philippines
Received April 24, 2001
Two new alkaloids, norpandamarilactonine-A (1) and -B (2), which have a pyrrolidinyl-R,â-unsaturated
γ-lactone moiety as in the known pandamarilactonine alkaloids, were isolated from the leaves of Pandanus
amaryllifolius. Their structures were determined by spectroscopic analysis and total synthesis.
The genus Pandanus (Pandanaceae) comprises about 600
species which are widely distributed in tropical and sub-
tropical regions. In a recent pharmacological survey, the
hypoglycemic effect of an extract of P. odorus was noted.1
During our chemical studies on the secondary metabolites
in Pandanus plants,2 we reported the isolation of pan-
damarilactonines-A (3) and -B (4), pyrrolidine alkaloids
from P. amaryllifolius. Roxb.3 Further investigation of the
minor bases in fresh leaves of this plant resulted in the
isolation of two additional alkaloids (1 and 2), whose
structure elucidation by spectroscopic and synthetic meth-
ods are described herein.
proton (δ 3.18, 1H, ddd, J ) 6.6, 6.6, 7.4 Hz, H-2′) on the
pyrrolidine ring correlated with the sp2 carbon at C-4 (δ
147.7) in the R,â-unsaturated γ-lactone ring. In addition,
the methine proton (δ 4.73) at C-5 (δ 83.8) in the γ-lactone
ring had connectivity between C-2′ and C-3′ in the pyrro-
lidine ring. All the above findings enabled us to describe
the molecular structure of the new alkaloid as 1, a
pyrrolidinyl-R,â-unsaturated γ-lactone skeleton, except for
the stereochemistry of the vicinal asymmetric centers at
C-5 and C-2′. Because of the lack of a γ-alkylidene-R,â-
unsaturated γ-lactone moiety as in the known alkaloids,
pandamarilactonines (3 and 4), we now name the new
alkaloid (1) norpandamarilactonine-A.
Alkaloid 2 was also obtained as an amorphous powder,
19
exhibiting [R]D 0° (c 0.70, CHCl3). The UV and mass
spectra, as well as the molecular formula obtained by HR-
FABMS, were almost identical to those of 1. The 1H and
13C NMR spectra were also very similar, indicating that 1
and 2 were diastereomeric at the C-5 and C-2′ positions.
To confirm the structures and relative stereochemistry
at C-5 and C-2′ in the new alkaloids, we planned the total
synthesis (Scheme 1). According to the procedure of Martin
et al.,4 compound 5 was prepared from 2-pyrrolidone and
3-methylfuran-2(5H)-one. The threo stereochemistry of the
major product (5) obtained by vinylogous Mannich coupling
reaction has been established by X-ray analysis.4 The
protecting group on the nitrogen in 5 was removed with
TMSI in CH3CN to give the secondary amine in 94% yield,
which was identical with the natural product, norpan-
damarilactonine-B (2), by direct comparison of the chro-
1
matographic behavior and high-resolution MS and H and
13C NMR spectra. Therefore, the relative stereochemistry
of norpandamarilactonine-A (1) was determined to be
erythro.
In summary, two new diastereomeric alkaloids (1 and
2) having a pyrrolidinyl-R,â-unsaturated γ-lactone skeleton
were isolated as minor constituents from a tropical me-
dicinal plant, Pandanus amaryllifolius. These interesting
molecules possessing the substructure of the known alka-
loids 3 and 4 were first characterized by spectroscopic
analysis and then the structures were confirmed by total
synthesis.
Compound 1 was obtained as an amorphous powder,
D
[R]19 0° (c 0.30, CHCl3), and high-resolution FABMS
analysis established the molecular formula as C9H13NO2.
The presence of an R-methyl-R,â-unsaturated γ-lactone
1
residue was shown by characteristic signals in the H and
13C NMR spectra [δ 7.13 (1H, ddd, J ) 0.8, 1.6, 1.6 Hz,
H-4), 4.73 (1H, ddd, J ) 1.6, 1.9, 6.6 Hz, H-5), 1.93 (3H); δ
174.3 (C-2), 130.7 (C-3), 147.7 (C-4), 83.8 (C-5), 10.7
(C-6)]. Using the residual four carbons (three methylenes
and one methine) and one nitrogen atom, a pyrrolidine ring
could be constructed. In the HMBC spectrum, the methine
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. Optical rotations
were measured on a J ASCO DIP-140 polarimeter. UV and IR
spectra were recorded on Hitachi U-3400 and J ASCO FT/IR-
230 spectrophotometers, respectively. EIMS and FABMS were
* To whom correspondence should be addressed. Tel and Fax: (81) 43
2902902. E-mail: htakayam@p.chiba-u.ac.jp.
† Chiba University.
‡ University of Santo Tomas.
10.1021/np010213h CCC: $20.00
© 2001 American Chemical Society and American Society of Pharmacognosy
Published on Web 08/08/2001

Notes
J ournal of Natural Products, 2001, Vol. 64, No. 9 1225
Sch em e 1
recorded on J EOL J MS-AM20 and J EOL J MS-HX110 mass
spectrophotometers, respectively. The 1H and 13C NMR, COSY,
HMQC, HMBC, and NOE were recorded on J EOL J NM A-500
and J EOL J NM ECP600 spectrometers. The chemical shifts
are given in δ (ppm) and coupling constants in Hz. Kieselgel
60 (Merck, 70-230 and 230-400 meshes) and a silica gel
prepacked column (Kusano CPS-HS-221-05) were used for
column chromatography.
P la n t Ma ter ia l. The fresh leaves of P. amaryllifolius were
purchased at a flower market in Bangkok (Thailand) and
identified by Dr. Kittisak Likhitwitayawuid, Department of
Pharmacognosy, Faculty of Pharmaceutical Sciences, Chula-
longkorn University, Thailand. A voucher specimen was
deposited at the Herbarium of the Faculty of Pharmaceutical
Sciences, Chiba University.
(1H, dddd, J ) 1.6, 1.9, 3.0, and 6.6 Hz, H-5), 3.20 (1H, ddd,
J ) 6.6, 7.1, and 7.4 Hz, H-2′), 2.98 (1H, ddd, J ) 5.8, 7.1 and
12.9 Hz, H-5′), 2.91 (1H, ddd, J ) 6.6, 7.7, and 14.3 Hz, H-5′),
1.93 (3H, s, H3-6), 1.87 (1H, dddd, J ) 3.0, 7.4, 10.7, and 15.4
Hz, H-3′), 1.81 (1H, m, H-4′), 1.74 (1H, m, H-4′), 1.56 (1H, dddd,
J ) 5.2, 6.9, 7.1 and 15.4 Hz, H-3′); 13C NMR (CDCl3, 150 MHz)
δ 174.1 (C-2), 146.6 (C-4), 131.2 (C-3), 84.3 (C-5), 60.2 (C-2′),
46.5 (C-5′), 26.8 (C-3′), 25.1 (C-4′), 10.7 (C-6); FABMS (NBA)
m/z 168 [M + H]+; HRFABMS (NBA) m/z 168.1030 (calcd for
C9H14NO2: 168.1025).
Syn th esis of Nor p a n d a m a r ila cton in e-B (2). To a solu-
tion of diastereomerically pure carbamate (5) (30.6 mg, 0.1
mmol), which was prepared according to the procedure by
Martin,4 in CH3CN (1 mL), was added TMSI (43 µL, 0.3 mmol)
at -10 °C under argon. The reaction mixture was stirred at
the same temperature for 15 min and then stirred at 0 °C for
15 min. The reaction mixture was poured into a chilled solution
of 1 N HCl, and the whole mixture was extracted with Et2O.
The aqueous layer was basified with 1 N NaOH, and the
mixture was extracted with CHCl3 three times. The combined
organic layers were washed with H2O, dried over MgSO4, and
evaporated to give 2 (16 mg, 94%), which was identical to
natural norpandamarilactonine-B by comparison of their
Extr a ction a n d Isola tion of Alk a loid s. Fresh young
leaves (8.0 kg) of P. amaryllifolius were macerated with EtOH
(20 L) three times and filtered. The combined filtrates were
concentrated under reduced pressure to give a crude extract
(201 g), which was then partitioned between Et2O and 5%
aqueous H2SO4. The water-soluble fraction was alkalinized
with concentrated NH4OH (pH 10) and exhaustively extracted
with CHCl3. The organic layer was dried over MgSO4 and
evaporated to give a crude alkaloidal fraction (10.03 g). A
portion of the crude base (1.63 g) was roughly separated by
silica gel flash column chromatography using a CHCl3-MeOH/
CHCl3 gradient to give seven fractions. The 10% MeOH/CHCl3
eluate was rechromatographed over SiO2 using the same
solvent to give 6 mg of norpandamarilactonine-A (1) and 33
mg of norpandamarilactonine-B (2).
1
chromatographic behaviors, UV, H and 13C NMR, and mass
spectra.
Ack n ow led gm en t. This work was supported in part by a
Grant-in-Aid (No. 10877349) for Scientific Research from the
Ministry of Education, Science, Sports, and Culture, J apan.
Nor p a n d a m a r ila cton in e-A (1): amorphous powder; [R]19
D
Refer en ces a n d Notes
0° (c 0.30); UV (MeOH) λmax (log ꢀ) 274 (0.44), 252 (0.35), 207
(2.29) nm; IR (neat) νmax 1750 (lactone) cm-1; 1H NMR (CDCl3,
600 MHz) δ 7.13 (1H, ddd, J ) 0.8, 1.6 and 1.6 Hz, H-4), 4.73
(1H, ddd, J ) 1.6, 1.9 and 6.6 Hz, H-5), 3.18 (1H, ddd, J )
6.6, 6.6 and 7.4 Hz, H-2′), 2.96 (1H, ddd, J ) 6.3, 6.3 and 10.4
Hz, H-5′), 2.93 (1H, ddd, J ) 6.8, 6.8 and 10.4 Hz, H-5′), 1.93
(3H, s, H3-6), 1.84-1.92 (1H, m, H-3′), 1.72-1.90 (2H, m, H2-
4′), 1.63 (1H, dddd, J ) 6.3, 6.3, 6.6 and 12.9 Hz, H-3′); 13C
NMR (CDCl3, 150 MHz) δ 174.3 (C-2), 147.7 (C-4), 130.7 (C-
3), 83.8 (C-5), 60.4 (C-2′), 47.1 (C-5′), 27.9 (C-3′), 25.6 (C-4′),
10.7 (C-6); FABMS (NBA) m/z 168 [M + H]+; HRFABMS
(NBA) m/z 168.1039 (calcd for C9H14NO2, 168.1025).
(1) (a) Peungvicha P.; Thirawarapan S. S.; Watanabe H. Biol. Pharm.
Bull. 1996, 19, 364-366. (b) Peungvicha P.; Thirawarapan S. S.;
Watanabe H. J pn. J . Pharmacol. 1998, 78, 395-398. (c) Peungvicha
P.; Temsiririrkkul, R.; Prasain, J . K.; Tezuka, Y.; Kadota, S.;
Thirawarapan S. S.; Watanabe H. J . Ethnopharmacol. 1998, 62, 79-
84.
(2) (a) Nonato, M. G.; Garson, M. J .; Truscott, R. J . W.; Carver, J . A.
Phytochemistry 1993, 34, 1159-1163. (b) Takayama, H.; Kuwajima,
T.; Kitajima, M.; Nonato, M. G.; Aimi, N. Heterocycles 1999, 50, 75-
78. (c) Takayama, H.; Kuwajima, T.; Kitajima, M.; Nonato, M. G.;
Aimi, N. Nat. Med. 1999, 53, 335. (d) Takayama, H.; Ichikawa, T.;
Kitajima, M.; Aimi, N.; Lopez, D.; Nonato, M. G. Tetrahedron Lett.
2001, 42, 2995-2996.
(3) Takayama, H.; Ichikawa, T.; Kuwajima, T.; Kitajima, M.; Seki, H.;
Aimi, N.; Nonato, M. G. J . Am. Chem. Soc. 2000, 122, 8635-8639.
(4) Martin, S. F.; Barr, K. J .; Smith, D. W.; Bur, S. K. J . Am. Chem. Soc.
1999, 121, 6990-6997.
Nor p a n d a m a r ila cton in e-B (2): amorphous powder; [R]19
D
0° (c 0.70); UV (MeOH) λmax (log ꢀ) 274 (0.36), 253 (0.29), 207
(2.58) nm; IR (neat) νmax 1750 (lactone) cm-1; 1H NMR (CDCl3,
600 MHz) δ 7.02 (1H, ddd, J ) 1.4, 1.7 and 3.0 Hz, H-4), 4.79
NP010213H