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Revised Assignment of 13C-NMR-Signals to Quarternary Carbons of the Amaryllidaceae Alkaloid Lycorin. Neuzuordnungen von 13C-NMR-Signalen zu quartren C-Atomen des Amaryllidaceae-Leitalkaloids Lycorin

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123
I3C-NMR-Signalsof Lycorin
Revised Assignment of 13C-NMR-Signalsto Quarternary Carbons of the
Amaryllidaceae Alkaloid Lycorin
Neuzuordnungen von 13C-NMR-Signalenzu quartaren C-Atomen des Amaryllidaceae-LeitalkaloidsLycorin
Marcus Spohn,Volker Brecht, and August W. Frahm'
k p t . of Pharmaceutical Chemistry, University of Freiburg i.Br.. Hermann-Herder-Str. 9, D-79 104 Freiburg, Germany
Received October 28,1993
The amaryllidaceae alkaloid Lycorin had been explored
'3C-NMR-spectroscopically in [D6]DMS01)and in [D4]methanol/CF3C02D2)since the 1980's. The latest paper
concerning this matter with reference to lit. l) in this journa13) with equivocal results from [D4]methanol solution
prompts us to publish the complete results of our reinvestigation. They are given in Tab. 1 compared to those from
Lit.')2)3).Poor solubility of the alkaloid required polar
NMR-solvents, three of which afforded sufficient concentrations with respect to the critical quarternary carbon signals.
The first systematic investigation to assign all I3C-NMR~ )
signals of Lycorin was performed by Evidence ec ~ 1 . by
means of time depending NOE measurements which are
extremely sensitive to traces of magnetic material in the
sample solution. We aspired an independent way of signal
shift assignment especially for the quarternary C-7a, C-9,
C-10, and C-1 la, with the LR-CH-coupling constants as a
decisive criterion via 2D-Long-Range-INEPT experiments.
As an outcome not only the results of Pundit et aL3)for C5, C-10, and C-1 l a have to be revised but also those of Evifor C-7a, C-9, C- 10, and C- l l a.
dente et
Tab. 1 Comparison of the "C-NMR shift values (ppm) for Lycorin
Lit')
Solvent
Ds-DMSO
Lit2)
CD30D/CF$OOD
(3 : 1)
own results
CDJODKF~COOD
(3: I )
Lit.3)
CDSOD
CDSOD
Carbon
4
28.2
30.3
30.33
29.30
28.36
llb
40.3
38.2
38.07
41.41
41.45
7
56.7
54.2
54.21
57.84
57.84
5
53.4
55.1
55.22
54.72
57.79
1lC
60.8
61.8
61.90
62.45
62.44
1
71.8
70.1
70.02
73-18
73.19
2
70.3
71.9
71.77
71.99
72.02
100.6
102.8
102.83
102.28
102.25
105.1
106.4
106.39
106.04
106.03
ocH20
11
8
107.1
108.8
108.83
108.21
108.19
3
118.5
122.9
122.78
119.15
119.15
7a
lla
129.8
129.7
130.6*
125.41
129.79
129.83
125.7*
130.45
130.42
129.8@
3a
9
141.8
137.9
137.84
136.50
137.09
145.7
149.2+
148.1+
148.04
148.17
148.14
149.67
148.20
143.7@
10
@
+*
145.3
wrong shift values
equal signed values may be interchanged
Arch. Pharm. (Weinheim) 327,123-124 (1994) 0 VCH VerlagsgesellschaftmbH, D-69451 Weinheim. 1994
0365-6233/94/0202-0123S 5.00 + .25/0
124
Spohn, Brecht, and Frahm
Results and Discussion
Three independent 2D-LR-INEPT experiments were run
using [D,]methanol/CF3COOD (3:l) as a solvent. In the
first two cases the 2 ~ c , H - and 3~c,Hcoupling constants of
8-H and 11-H were determined in the planar aromatic
system of the molecule. The third experiment gave evidence of the 2Jc,H- and 3JC.H- coupling constants arising
from the cycloaliphatic proton 11b-H interaction with the
quarternary aromatic carbons C-1 la and C-7a. In this case
the dependency of the 3Jc,H-couplingconstants from the dihedral angle of the coupling partners has to be considered.
The evaluation of the first experiment showed characteris~ 2 J ~ . 9 8 .=~ 3.3 Hz, 3 J ~ . 1 0 ; 8 . ~
tic values for 'Jc H < 3 J c , with
= 6.8 Hz and ' J c - ~ ~ =~ 6.6
; ~ -Hz
~ which allowed the
unequivocal assignment of the signals at 6 148.04 to carbon
9, at 6 149.67 to carbon-10 and at 130.45 to carbon l l a .
This decision was confirmed by characteristic values for
2Jc.H< 3 J ~with
, ~ 2JC.Ioll.H= 3.4 Hz, 3J~.9;.,.~ = 7.1 Hz and
with 3JC.7a;l
I.H = 7.4 Hz allowing the additional assignment
of the signal at 6 = 125.41 for carbon 7a
Tab. 2 'J,,,-
C-9
C-I0
C-7a
C-lla
c-I1
and 'JC." values (Hz) for Lycorin
H-8
H-11
H-llb
J' = 3.3
'J = 7.1
2J = 3.4
'J = 7.4
-
-
-
-
-
-
-
'J = 2.4
'J =5.3
'J=2.1
ca. 1 lo"
ca. 2.8
-
-
ca. 100"
ca. 1.9
'J =6.8
3J =6.6
-
Dihedral
angle
calc.
'J-values
Lit.2
The third 2D-LR-INEPT measurement delivered interesting C,H-coupling constants for the interaction between the
cycloaliphatic proton l l b and the carbons 7a, l l a , and 11
with 2Jc,H> 3Jc,Horiginating from the dependency of the
dihedral angle of the coupling partners. On these reasons
the signal at 6 = 106.39 is assigned to C-11 coupled to
1 lb-H with a dihedral angele of about 100" approximately
and a coupling constant of 3JC-II;IIbH
= 2.0 Hz (calculated
value 1.9 Hz according to Wasylishen and SchaefeP)).
For reasons given above the signal at 6 = 125.41 is
assigned to carbon 7a with a 3Jc,H= 2.4 Hz for a dihedral
angle of 110" between the coupling partners. The signal at
6 = 130.45 is assigned to carbon l l a by its significant two
Arch. Pharm. (Weinheim) 327,123-124 (1994)
bond interactions with 2Jc~lla;llbH= 5.3 Hz,which agrees
with results of Hunsen and Jucobsen5)for 2Jc,H-values in
toluene.
The evaluation of the 2D-LR-INEPT-experiments afforded complete assignment of all I3C-NMR-signalsof Lycorin
which necessitates a revision of often cited chemical shifts
for the quarternary carbons 7a, 9,10, and 1 l a 2).
Switching from [D4]methanol/CF3COOD (3: 1) to pure
[D4]methanol as a solvent the solubility of Lycorin decreases remarkably therewith requiring prolongated acquisition time to gain low noise 13C-NMR spectra with unequivocal signals for the quarternary carbons. Disregarding this
requirement leads to wrong assignments for C-10 and C1 l a as well as for C-5 3).
The use of the solvent [D,]DMSO for assignment and differentiation of the Lycorin-13C-NMR-signals is not commendable. Important signals such as C-7a, C-1 l a or C-9, C10 cannot be distinguished clearly. The best solvent for
complete signal differentiation is CD30D/CF3COOD (3: 1)
(Tab. 1).
Financial support for this work from Fonds der Chemischen Industrie is
gratefully acknowlegded.
Experimental Part
Selective 2D-INEPT spectra were obtained using a Varian Unity 300
spectrometer. Pulse sequencies see lit.@.Lycorin samples were prepared as
CD30D/CF3C02D (3:l) and CD'OD solutions (c = 0.3 M and c = 0.03 M,
respectively). &values are given in ppm downfield from TMS (TMS =
O.O), measured from internal CD30D and corrected by using the equation
& = &-,OD - 49.0 ppm. The measurement conditions were as follows:
I 3 ms P 90' pulse
Observe pulse with:
2s
Pulse delay:
Refocussing delay:
62.5 ms
Acquisition time:
62 ms
Soft decoupler power:
I3 dB
Spectral width:
16.5 kHd4 kHz
Data points:
4 K/256
Effective resolution:
8.0 Hz/0.15 Hz
Heteronuclear-LR-Coupling Constant: 8 Hz
Accumulation of FLD's in reversed
gated decoupled mode:
32 pulses/32 increments
Total experimental time:
48.8 min
Probe temperature:
27°C
Sample tube:
5 mm
References
1
A.A. Ali, H. Kating, A.W. Frahm, A.M. El-Moghazi, M.A. Ramadan.
Phyrochemisrry 1981,20, 1121-1123.
2
A. Evidente, M.R. Cicala, I. Guidicianni, G. Randazzo, R. Ricco,
Phytochemistry 1983.22, 581-584.
3
4
5
6
B.Sener, S . Koniikol, C. Kruk, U.K. Pandit, Arch. Phorm. (Weinheim)
1993,326,61-62.
R. Wasylishen, T. Schaefer, Can. J. Chem. 1973,51,961-973.
M. Hansen, H.J. Jakobsen. J . Magn. Res. 1975.20.520-529.
T. Jippo, 0. Kamo, K. Nagayama, J. Magn.Res. 1986.66.344-348.
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signalen, 13c, alkaloid, quartren, quarternary, nmr, signali, leitalkaloids, neuzuordnungen, lycorine, atomen, revised, amaryllidaceae, des, assignments, von, carbon
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