Constituents of Lepidium meyenii ‘maca’
Ilias Muhammada,*, Jianping Zhaoa, D. Chuck Dunbara, Ikhlas A. Khana,b
aNational Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, School of Pharmacy,
University of Mississippi, University, MS 38677, USA
bDepartment of Pharmacognosy, Research Institute of Pharmaceutical Sciences, School of Pharmacy,
University of Mississippi, University, MS 38677, USA
Received 8 May 2001; received in revised form 23 August 2001
The tubers of Lepidium meyenii contain the benzylated derivative of 1,2-dihydro-N-hydroxypyridine, named macaridine, together
with the benzylated alkamides (macamides), N-benzyl-5-oxo-6E,8E-octadecadienamide and N-benzylhexadecanamide, as well as the
acyclic keto acid, 5-oxo-6E,8E-octadecadienoic acid. The structure elucidation of the isolated compounds was based primarily on 1D
and 2D NMR spectroscopic analyses, including1H–1H COSY,1H–13C HMQC,1H–13C HMBC and1H–1H NOESY experiments, as
well as from1H–15N NMR HMBC correlations for macaridine and N-benzylhexadecanamide. # 2002 Published by Elsevier
Keywords: Lepidium meyenii; Brassicaceae; 1,2-Dihydro-N-hydroxypyridine; Macaridine; Macamide; N-Benzyl-5-oxo-6E,8E-octadecadienamide; N-
Benzylhexadecanamide; 5-Oxo-6E,8E-octadecadienoic acid; 2D NMR;1H–15N NMR
Lepidium meyenii Walp. (Brassicaceae), commonly
known as ‘maca’, is a nutritionally valuable native Per-
uvian plant that is used in the Andean diet (Leon, 1964).
This plant was domesticated at least two centuries ago
in the Andean mountains, where natives used its tubers
as food and as a folk medicine. L. meyenii is known to
contain valuable nutritional ingredients (Dini et al.,
1994) and is used locally for the enhancement of fertility
and sexual behavior in men and women, and as a tradi-
tional remedy of menopausal symptoms. The aphrodi-
siac activity of L. meyenii after oral administration in
mice has recently been reported by Zheng et al. (2000).
Earlier chemical work on the roots of this plant yielded
mainly macaenes, macamides (alkamides), fatty acids,
sterols and benzyl isothiocyanate (Zheng et al., 2000).
However, other species of the genus Lepidium exhibit
the presence of flavonoids, flavonoid glycosides (Fursa
et al., 1970; KurKin et al., 1981) and alkaloids, includ-
ing the bis-benzyl imidazole derivatives from L. sativum
(Maier et al., 1998).
Several ‘maca’ dietary supplements1are currently
available in the United States for the nutritional supple-
ment of various sexual dysfunctions in men and women.
As part of our continuing program to isolate marker
compounds from traditional medicine and dietary sup-
plements (Ganzera et al., 2001; Muhammad et al., 2001
a,b), the present study deals with the isolation and char-
acterization of a 1,2-dihydro-N-hydroxypyridine deriva-
tive, macaridine (1), together with the hitherto unreported
(2), N-benzylhexadecanamide (3) and 5-oxo-6E,8E-
octadecadienoic acid (4), from the tubers of L. meyenii.
2. Results and discussion
The petroleum ether extract of L. meyenii tubers was
subjected to column chromatography (CC), followed by
a short flash-CC and centrifugal preparative TLC (see
0031-9422/02/$ - see front matter # 2002 Published by Elsevier Science Ltd.
Phytochemistry 59 (2002) 105–110
1Maca PureTM(Patent pending), Pure World Botanicals, Inc., 375
Huyler Street, South Hackensack, NJ 07606, USA, Web address
<http://www.madis.com/news/macapure_spec.html>; Maca 750TM,
Medicine Plants, Web address: <http://www.maca750.com>.
* Corresponding author: Tel.: +1-662-915-1051; fax: +1-662-915-
E-mail address: email@example.com
Experimental) to give compounds 1–4. Compound 1,
analyzed for C13H13NO2by HRMS, gave a light pink
color with aqueous FeCl3, but was inactive with Dra-
gendorff’s reagent. The UV spectrum demonstrated a,b-
unsaturated carbonyl and benzyl chromophores at lmax
294 and 210 nm, respectively, and the IR spectrum
showed hydroxyl, conjugated aldehyde and aromatic
absorption bands [?max3385 (br.), 1658, 781 and 725
cm?1]. The1H NMR spectrum exhibited a deshielded
proton at ? 9.52 (1H, s; ?C-8180.2, d) for an aldehyde
group, two olefinic protons at ? 6.29 and 6.94 (each d,
J=4 Hz; ?C-6111.2, dC-5124.8) for a cis-disubstituted
double bond and five aromatic protons (? 6.98, 2H, d,
J=7.1 Hz; 7.22-7.29, 3H, m; ?C-9138.2, ?C-10,14126.2,
?C-11,13129.1, ?C-12128.0) for a monosubstituted ben-
zene ring. The13C NMR spectrum revealed two addi-
tional quaternary carbons at ?C-3142.5 and ?C-4133.2,
accounting for a C-3(4)-tetrasubstituted double bond.
In addition, the1H NMR spectrum demonstrated two
2H singlets at ? 4.54 (?C-257.0) and 5.73 (?C-848.9),
indicating the presence of two sets of isolated methylene
protons for –N–CH2–and C6H5–CH2– groups, respec-
tively. The deshielding of the C-8–CH2– protons was
due to benzylic and allylic groups, as well as the aniso-
tropic effect of C-7 carbonyl group. The13C NMR che-
mical shift value for the methylene carbon between
nitrogen and oxygen atoms (–N–CH2–O–) was found to
be highly deshielded (?C 80–83) (Linde et al., 1978;
Hatfield and Maciel, 1987) compared to that observed
for an N-methylene group (?C-257.0), which ruled out
the possibility of an alternative dihydrooxazepine-type
base structure. The1H–15N NMR HMBC experiment
established the presence of a single nitrogen atom at ?N
159.7, suggesting the presence of an hydroxylamino
group (–CH2–N(OH)–R), rather than an N–H group.
(Hatfield and Maciel, 1987; Witanowski et al., 1993;
Hadden et al., 1999) in a 1,2-dihydropyridine base
structure. The presence of an hydroxylamino group was
also supported by the HRMS using collision induced
dissociation in the ESI source, which clearly demon-
([C13H12NO]+, [M?OH]+, calc. for 198.0913) due to
the loss of OH?ion, while no such fragment ion was
observed under standard conditions. Furthermore, the
lack of an NH proton and oxygenated carbon in the1H
absence of a one bond correlation between the nitrogen
atom and the NH proton in the1H–15N NMR HMBC
spectrum (with no low pass filter) could only suggest
the presence of a hydroxyl group at the N-1 position.
The above spectral data suggested the presence of
benzyl and formyl groups in a 1,2-dihydro-N-hydroxy-
pyridine nucleus and the placement of the substituents
was established by gradient DQF-COSY, HMQC,
The COSY and HMQC experiments established the
systems –C–CH¼CH–R– and C6–H5–, while the HMBC
(Fig. 1) showed three-bond correlations between ?C-7
10,14126.5 and H2-8, and ?C-257.0 and H-6, confirming
the relative placements of the N-methylene, benzyl, for-
ion atm/z 198.0918
13C NMR spectra, respectively, as well as the
1H–13C HMBC and
1H–15N HMBC NMR
1H NMR spectral data and coupling constants (in parentheses, in Hz) for compounds 2–4a
1.61 br m
2.50 br t (7.3)
6.04 d (15.4)
7.09 dd (3.0, 9.7, 15.4)
0.87 t (7.0)
4.41 d (5.6)
7.24 d (8.4)
7.24 d (8.4)
5.76 br s
2.11 t (9.3)
0.81 t (6.9)
4.31 d (7.0)
7.17 d (8.0)
7.17 d (8.0)
1.18 br s, 1.94 m
6.03 br s
1.57 br m
2.49 br t (7.0)
6.03 d (15.5)
7.07 dd (2.8, 8.8, 15.5)
0.85 t (7.0)
aSpectra for 2–4 were recorded at 500 MHz in CDCl3.
bSuperimposed with other CH2protons.
106 I. Muhammad et al./Phytochemistry 59 (2002) 105–110
myl and olefinic substituents at C-2–C-4 and C-5(6) posi-
tions, respectively. The HMBC also showed correlations
between ?C-3142.5 and ?H-24.54, as well as correlations
between ?C-4133.2 and ?H-66.29. This establishes the
position of ?C-257.0 between the nitrogen atom and C-3.
The assignment of the nitrogen atom at the N-1 position
was confirmed using an
which showed2J correlations between the signals at ?N-1
159.7, ?H-24.54 and ?H-66.29,3J correlations between
?N-1159.7 and ?H-56.94,4J correlations between ?N-1
159.7 and ?H-85.73; as well as5J correlations through
double bonds with ?H-79.52. From the foregoing data the
structure of 1, named macaridine, was assigned as shown.
1H–15N HMBC experiment
Alkamides 2 and 3 analyzed for the molecular formulas
C25H37NO2 and C23H39NO, respectively, by HRMS.
The alkamides were homogenous on TLC, but were
inactive with Dragendorff’s reagent. The UV spectrum
of 2 showed chromophores for a benzyl group and an
a,b-unsaturated ketone (lmax210, 274 nm), and the IR
spectrum exhibited absorption bands at ?max3311 and
1638 cm?1, for N–H and carbonyl group(s), respec-
tively. The NMR spectra revealed a carbonyl (?C
201.4), an amidecarbonyl
monosubstituted benzene ring (Tables 1 and 2), as well
as two disubstituted double bonds (?C 127.9, 143.4,
131.7, 146.1; each d; C-6–C-9, respectively), indicating
that compound 2 is a benzylamide of an oxo-octadeca-
dienoic acid. The
trans-coupled olefinic protons at ? 7.09 (ddd, J=3.0, 9.7,
15.4 Hz, H-7) and 6.04 (d, J=15.4 Hz, H-6), two other
olefinic protons between ? 6.14 and 6.12 (m, H-8 and H-
9), a primary methyl group at ? 0.87 (t, J= 7.0, H-18),
as well as 22 protons between ? 1.29–2.43, attributed to
eleven methylene groups. Due to the complexity of the
H-8 and H-9 signals, the coupling constants could not
be established. A 2D NMR1H–1H COSY experiment of
2 established the diene system –CH¼CH–CH¼CH–
CH2–, which was further substantiated by a series of
double resonance experiments. Thus, irradiation of the
protons at ? 6.12 and 6.14 (H-8 and H-9) resulted in a
doubletat? 7.09 (J=13 Hz, H-7), confirming the presence
of a trans-olefin at the C-6(7) position. The geometry of
1H NMR spectrum exhibited two
Fig. 1. 2D NMR1H–13C HMBC (broken lines) and COSY (solid
lines) correlations for compound 1.
13C NMR spectral data for compounds 2–4a
25.0–31.7 (6 t )
22.8–36.9 (11 t )
25.0–31.7 (6 t )
aSpectra for 2–4 were recorded at 125 MHz in CDCl3.
bMultiplicities were determined by DEPT 135?, also aided by 2D
NMR COSY and HMQC experiments.
I. Muhammad et al./Phytochemistry 59 (2002) 105–110107
the C-8(9) double bond was established as trans by using
2D NMR1H–1H NOESY experiment (vide infra; Fig. 2).
Furthermore, the1H NMR spectrum revealed five aro-
matic protons (? 7.24, 2H, d, J=8.4 Hz, H-30,70; 7.30,
3H, m, H-40-60), N-benzyl methylene protons at ? 4.41
(2H, d, J=5.6 Hz, H-10) and a broad one proton singlet
at ? 5.76, attributable to an N–H group. These spectral
data are in close agreement with those observed for N-
benzylhexadecanamide (3) (Tables 1 and 2). Thus, a
close comparison of the1H and13C NMR spectral data
of 2 with those of 3 led to the conclusion that indeed
compound 2 was a benzylated alkamide of oxo-octade-
The geometry of the double bonds at C-6(7) and C-
8(9) was inferred from 2D NMR
experiments, which showed cross peaks between H-4 (?
2.50) and H-7 (? 7.09). On the other hand, no NOESY
correlation was observed between H-7 and H-10 (?
2.13), while H-7 was correlated with H-9, suggesting E
configurations for both the olefins [at C-6(7) and C-
8(9)]. Furthermore, the NOESY spectrum showed cross
peaks between H-6 (? 6.04) and H-8 (centered at ? 6.14),
the latter proton being correlated with H-10 (? 2.13),
thereby confirming the assignment of a trans-C-8(9)
olefin. Other key NOESY correlations are depicted in
Fig. 2. Molecular modeling2indicated that the NOESY
correlation between H-7 and H-9 (2.4 A˚), and H-8 and
H-10 (2.3 A˚) are consistent with a trans C-8(9) double
bond. From the foregoing data alkamide 2 was assigned
The structure of alkamide 3 was unambiguously
established by rigorous 2D NMR COSY, HMQC, and
HMBC experiments. In addition, the placement of the
secondary amide group system (–CH2–NH–CO–CH2–)
in 3 was confirmed by a1H–15N NMR HMBC experi-
ment, which showed the
between the signals at ?N118.6 (–NH–CO–) and ?N-H
6.03, ?H-10 4.31, ?H-22.11, respectively.
Compound (4) displayed the molecular formula
C18H30O3from its HRMS, indicating four degrees of
(Tables 1 and 2) of 4 were found to be generally similar
to those observed for 2, except for the differences asso-
ciated with the absence of an N-benzyl group at C-1. Its
UV spectrum had a chromophore expected for an a, b-
unsaturated ketone (lmax274 nm), and the IR spectrum
showed a strong and broad carbonyl absorption band
(?max1708 cm?1). The13C NMR spectrum revealed car-
bonyl (?C201.5) and carboxylic acid (?C179.5) groups,
as well as two disubstituted double bonds (?C 128.2,
143.4 and ?C130.8, 146.0; each d), indicating that com-
pound 4 is an oxo-octadecadienoic acid. The pattern of
1H NMR chemical shift values of the four olefinic pro-
tons [? 7.07 (ddd, J=2.8, 8.8, 15.5 Hz, H-7), 6.03 (d,
J=15.5 Hz, H-6), 6.14 and 6.12 (each 1H, m; H-8 and
H-9)] were in clear agreement with those reported for a
6E,8E- diene system of 2, as well as the analogous E,E-
diene system of alkamides, isolated from Echinacae spp.
(Bauer et al., 1988). Structure 4 was unambiguously
established by detailed 2D NMR spectroscopic studies,
including the application of COSY, HMQC and HMBC
experiments. The HMBC experiment showed three-
bond correlations between ?C-5 201.5 and H-7, ?C-9
146.0 and H-7, ?C-8130.8 and H-6, and ?C-1179.5 and
H-3 (? 1.57), confirming the placement of carboxylic
acid, carbonyl and the two olefinic groups at the C-1, C-
5, C-6(7) and C-8(9) positions, respectively. In addition,
the HMBC revealed two-bond correlations between ?C-5
201.5 and H-4 (? 2.49), ?C-9146.0 and H-10 (? 2.13), and
?C-1179.5 and H-2 (? 2.29), which served to establish
structure 4 as 5-oxo-6E,8E-octadecadienoic acid.
13C NMR spectral data
Fig. 2. 2D NMR1H–1H NOESY correlations for compound 2.
2Molecular modeling was done using CS Chem3D Pro Version 5.0
MM2 molecular dynamics minimization followed by MM2 steric mini-
mization. The software was obtained from CambridgeSoft Corporation,
100 Cambridge Park Drive, Cambridge, MA 02140-2312, USA.
108 I. Muhammad et al./Phytochemistry 59 (2002) 105–110
This appears to be the first report of compounds 1–4
from a natural source. Various hydroxamic acid deriva-
tives were previously isolated, including benzoxazinoids-
cyclic hydroxamic acids from the genus Aphelandra (Bau-
meler et al., 2000) and fusarinines A and B from Fusarium
roseum (Sayer and Emery, 1968), but to our knowledge
there is no report regarding hydroxylamino-type deri-
vative, such as 1,2-dihydro-N-hydroxypyridines, as nat-
ural products. Furthermore, it is intriguing to note that
(including lepidine and lepidine B), analogous to ben-
zylated derivative 1,2-dihydro-N-hydroxypyridine (1),
were previously isolated from L. sativum (Bahroun and
Damak, 1985; Maier et al., 1998). Finally, several ben-
zylated alkamides (macamides) are currently regarded
as chemical markers for ‘maca’ dietary supplements
(Zheng et al., 2000), but to our knowledge macamides 2
and 3 appear to be new markers for L. meyenii (maca).
NMR spectra were acquired on a Bruker Avance
DRX-500 instrument at 500 MHz (1H) and 125 MHz
(13C), in CDCl3, using the residual solvent signal as int.
standard; Multiplicity determinations (DEPT 135?) and
2D NMR spectra (gradient DQF-COSY, HMQC, gra-
dient HMBC and NOESY) were acquired using stan-
dard Bruker pulse programs;15N NMR spectra were
recorded at 50.7 MHz using the HMBC pulse program
with no low pass filter; chemical shift values are repor-
ted relative to liquid NH3by calibrating nitromethane
to 380.2 ppm; HRMS were obtained by direct injection
using a Bruker Bioapex-FTMS with an Analytica Elec-
tro-Spray Ionization (ESI) source and the capillary vol-
tage was increased from 80 to 130 to generate collision
induced dissociation; TLC: silica gel GF254plates, sol-
vent: CH2Cl2:EtOAc (8:2); CC: flash-silica gel G (J.T.
Baker, 40 mM Flash); Centrifugal preparative TLC
(CPTLC, using Chromatotron1, Harrison Research
Inc. Model 8924): 1, 2 or 4 mm Si gel GF Chromato-
tronTMrotors, (Analtech, Inc.) using a N2flow rate of 4
ml min?1. The isolated compounds were visualized by
observing under UV-254 nm, followed by spraying with
anisaldehyde–H2SO4/neutral and acidic aqueous FeCl3/
and Dragendorff’s spray reagents.
3.2. Plant material
from Lima, Peru. A voucher specimen has been deposited
at the Herbarium of the University of Mississippi. The
material was collected, identified and provided by Frank
L. Jaksch Jr.
3.3. Extraction and isolation of compounds
Dried ground tubers of L. meyenii (1 kg) were perco-
lated successively at room temperature with petroleum
ether (60–80?), CHCl3and EtOH to yield 138, 21 and 25
g of crude extract, respectively. The dried petroleum
ether extract was re-extracted by percolation with
CHCl3(250 ml ?3) that afforded a 16 g CHCl3soluble
fraction. A portion of the CHCl3 fraction (4 g) was
subjected to flash-chromatography over Si gel (40 mM,
120 g), using n-hexane followed by increasing con-
centrations of EtOAc (30–70%) in n-hexane as eluent,
to give four fractions (A–D) after pooling by TLC ana-
lysis. Fraction A (110 mg) was subjected to short-flash
CC, using 2% EtOAc in CH2Cl2to give 4 (38 mg, Rf
0.68, silica gel, solvent: CH2Cl2:EtOAc, 8:2), while
fraction B (600 mg) was purified by repeated CPTLC
(2mm and 1 mm Si-gel GF disc), using 2% MeOH in
CH2Cl2to afford 2 (40 mg, Rf0.36,), followed by pal-
mitic acid (250 mg) and b-sitosterol (50 mg). Finally,
mixture C (80 mg) and D (800 mg) were separately
subjected to CPTLC (1 and 4 mm Si-gel GF disc), using
1% MeOH in CH2Cl2 and 10% EtOAc in CH2Cl2,
respectively, to yield 1 (15 mg, Rf0.56,) and 3 (10 mg, Rf
3.4. Macaridine (3-benzyl-1,2-dihydro-N-
Solid; UV lMeOH
(4.14) nm; IR ?film
1453, 1402, 1372, 1179, 1035, 725, 781 cm?1;1H NMR
(CDCl3) ? 9.52 (1H, s, H-7), 7.26 (2H, m, H-11,13), 7.22
(1H, m, H-12), 6.98 (2H, d, J=7.1 Hz, H-10,14), 6.94
(1H, d, J=4.0 Hz, H-5), 6.29 (1H, d, J=4.0 Hz, H-6),
5.73 (2H, s, H-8), 4.54 (2H, s, H-2);13C NMR (CDCl3)
?C180.2 (d, C-7), 142.5 (s, C-3), 138.2 (s, C-9), 133.2 (s,
C-4), 129.1 (d, C-11,13), 128.0 (d, C-12), 126.5 (d, C-
10,14), 124.8 (d, C-5), 111.2 (d, C-6), 57.0 (t, C-2), 48.9
(t, C-8); ESI–HRMS m/z 216.1021 ([M+H]+); (calc.
for [C13H13NO2+H]+, 216.10188).
(log ") 208 (4.07), 255 sh (3.76), 294
Max3385, br (OH), 1658 (CHO), 1494,
3.5. N-Benzyl-5-oxo-6E,8E-octadecadienamide (2)
Gum, UV lMeOH
Max3311 (N-H), 2928, 2845, 1638, 1545, 1239, 1000,
731, 697 cm?1; for1H NMR spectrum: Table 1; for13C
NMR spectrum: Table 2; ESI–HRMS m/z 384.3034
([M+H]+); (calc. for [C25H37NO2+H]+, 384.2903).
(log ") 210 (4.08), 276 (3.99) nm; IR
3.6. N-Benzylhexadecanamide (3)
Solid; UV lMeOH
(N-H), 2917, 2849, 1639, 1549, 1454, 730, 696 cm?1; for
1H NMR spectrum: Table 1; for13C NMR spectrum:
(log ") 208 (4.03) nm; IR ?film
I. Muhammad et al./Phytochemistry 59 (2002) 105–110 109
Table 2; ESI–HRMS m/z 346.3142 ([M+H]+); (calc for Download full-text
3.7. 5-Oxo-6E,8E-octadecadienoic acid (4)
Gum; UV lMeOH
for1H NMR spectrum: Table 1; for13C NMR spectrum:
Table 2; ESI–HRMS m/z 295.2319 ([M+H]+); (calc. for
(log ") 224 (3.70), 274 (3.49) nm; IR
Max3300–2800 (br), 2930, 2857, 1708, 1461, 1410 cm?1;
This work is supported in part by ChromaDex, Irvine,
CA and United States Department of Agriculture ARS
Specific Cooperative Agreement No. 58-64087-012. J.
Zhao thanks the China Scholarship Council for partial
Bahroun, A., Damak, M., 1985. Contribution to the study of Lepidium
sativum (Cruciferae). Structure of a new compound isolated from the
seed: lepidine. Journal of the Chemical Society of Tunisia 2, 15–24.
Bauer, R., Remiger, P., Wagner, H., 1988. Alkamides from the roots
of Echinaceae purpurea. Phytochemistrry 27, 2339–2342.
Baumeler, A., Hesse, M., Werner, C., 2000. Benzoxazinoids-cyclic
hydroxamic acids, lactams and their corresponding glucosides in the
genus Aphelandra (Acanthaceae). Phytochemistry 53, 213–222.
Dini, A., Migliuolo, G., Rastrelli, L., Saturnino, P., Schettino, O.,
1994. Chemical composition of Lepidium meyenii. Food Chemistry
Fursa, N.S., Litvinenko, V.I., Krivenchuk, P.E., 1970. Flavonol gly-
cosides of Lepidium latifolium and Lepidium draba. Rastitel’nye
Resursy 6, 567–571.
Ganzera, M., Muhammad, I., Khan, R., Khan, I.A., 2001. Improved
methods for the determination of oxindole alkaloids in Uncaria
tomentosa by high performace liquid chromatography. Planta Med-
ica 67, 447–450.
Hadden, C.E., Kaluzny, B.D., Robins, R.H., Martin, G.E., 1999.
Effects of N-oxidation on the15N chemical shifts in the Strychnos
alkaloids strychnine and brucine. Magnetic Resonance Chemistry
Hatfield, G.R., Maciel, G.E., 1987. Solid-state NMR study of the
hexamethylene-tetramine curing of phenolic resin. Macromolecules
KurKin, V.A., Zapesochnaya, G.G., Krivenchuk, P.E., 1981. Flavo-
noids of Orobus vernus, Lepidium draba and Lepidium ruderale.
Chemistry of Natural Compounds (Khim. Prir. Soedin.) 5, 661–
Leon, T., 1964. The ‘Maca’ (Lepidium meyenii): a little known food
plant from Peru. Economic Botany 18, 122–127.
Linde, V.H., Oelschla ¨ ger, H., Czirwitzky, C., 1978. Umwandlung des
Tetrahydro-1,3-oxazines in 1,3,5-Tris(3-hydroxypropyl)-hexahydro-
1,3,5-triazin—einStabilita ¨ tsproblem.
Research) 28 (I), 937–940.
Maier, U.H., Gundlach, H., Zenk, M.H., 1998. Seven imidazole alka-
loids from Lepidium sativum. Phytochemistry 49, 1791–1795.
Muhammad, I., Dunbar, D.C., Khan, R.A., Ganzera, M., Khan, I.A.,
2001. Investigation of Un ˜ a De Gato. 7-Deoxyloganic acid and15N
NMR spectroscopic studies on pentacyclic oxindole alkaloids from
Uncaria tomentosa. Phytochemistry 57, 781–785.
Muhammad, I., Khan, I.A., Fischer, N.H., Fronczek, F.R., 2001. Two
stereoisomeric pentacyclic oxindole alkaloids from Uncaria tomen-
tosa: uncarine C and uncarine E. Acta Crystallographica Section C,
Crystal Structure Communication C 57, 480–482.
Sayer, J.M., Emery, T.F., 1968. Structures of the naturally occur-
ring hydroxamic acids, fusarinines A and B. Biochemistry 7,
Witanowski, M., Stefaniak, L., Webb, G.A., 1993. Nitrogen NMR
spectroscopy. In: Webb, G.A. (Ed.), Annual Reports on NMR
Spectroscopy, Vol. 25. Academic Press, CA, pp. 167–182.
Zheng, B.L., He, K., Kim, C.H., Rogers, L., Shao, Y., Huang, Z.Y.,
Lu, Y., Yan, S.J., Qien, L.C., Zheng, Q.Y., 2000. Effect of a lipidic
extract from Lepidium meyenii on sexual behavior of mice and rats.
Urology 55, 598–602.
110 I. Muhammad et al./Phytochemistry 59 (2002) 105–110