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Determination of Connectivities via Small Proton-Carbon Couplings with a New Two-Dimensional NMR Technique.

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[l I Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Energie Physik Mathematik,
D-7514 Eggenstein-Leopoldshafen2, on quoting the depository number
CSD 50864, the names of the authors, and the journal citation.
[I; rac-4: a=18.397(3), b = 18.397(3), c=9.712(2)A;
V=3287.0A3
( - 100°C); tetragonal, P42,c; Z = 8 ; C16H25N03;~caIc=1.129
(- 1OO"C),
peXp=
1.10 (20°C) g/cm3; R3 diffractometer (Nicolet); 29/9 scan;
M o K ~ ,- 100°C; 2058 [F>u(F)] from 2246 independent reflections
(Smrx=2S0),R,=0.038 [ w = 1/u2(F)l;G. M. Sheldrick: SHELXTL, An
Integrated System for Solving, Refining and Displaying Crystal Structures from Diffraction Data, Universitat Gdttingen, 1983.
1\31 Extremely good solubility in and readily eluted from silica gel by apolar
solvents; bathochromic shift of the IR absorption bands for the enol
acetate group.
[I41 H. Kessler, C. Griesinger, J. Lautz, Angew. Chem. 96 (1984) 434; Angew.
Chem. Int. Ed. Engl. 23 (1984) 444.
[I51 Confirmed by the N-cyclohexylamide of the pyruvic acid formed on
ozonolysis and by ready conversion under mild transesterification conditions of the enol acetate rac-3 into the two diastereomeric racemic
mixtures of the respective ketones.
[I61 G. Quinkert in W. Bartmann, E. Winterfeldt: StereoselectiveSynthesis of
Natural Products, Workshop Conferences Hoechst, Vol. 7, Excerpta Medica, Amsterdam 1979, p. 151, and literature cited therein.
Compared to conventional H,C-COSY, the H,C-COLOC
sequence has the advantage of an easy optimization of the
A , and A2 delays for development of small couplings by
INEPT measurements[']. Because of the constant length of
the pulse sequence, the parameters so determined are also
valid for the whole 2D experiment. In addition, an improved signal-to-noise ratio results from the pulse sequence shortened by t , and the homonuclear broad-band
decoupling in tlrs1.
The following two examples demonstrate the application of the new technique. On irradiation of rac-(1,2,3,4,5pentamethyl-6-oxo-2,4-cyclohexadienyl) acetate (rac-6acetoxy-2,3,4,5,6-pentamethyl-2,4-cyclohexadien-l-one)
in
the presence of cyclohexylamine as protic nucleophile, the
two adducts rac-117] and ra~-2[~,''
are formed. An NMRspectroscopic characterization of the two isomers by 2DINADEQUATE is not very attractive because of the large
Determination of Connectivities via
Small Proton-Carbon Couplings
with a New Two-Dimensional NMR Technique**
By Horst Kessler*, Christian Griesinger, and Jorg Lautz
The scalar spin-spin couplings observable in NMR spectra are brought about by bonding and thus provide information about atomic linkages. Hitherto, only carbon-carbon (INADEQUATE)['] or proton-proton couplings
(H,H-COSY)[" have been used for establishing the connectivity of carbon atoms in organic compounds (Fig. 1). If
1-c-c1 t-7 i?i
A\
c-c
c-c
c-c
INADEQUATE
H,H-COSY
H,C - COSY
Relayed-H,C-COSY
c-c-x-c-c
H,C-COLOC
Fig. 1. NMR spectroscopic methods for locating carbon linkages
proton couplings are used, this information is obtained in
an indirect way via an additional H,C-COSY spectrumL3].
If relevant signals overlap, the relayed H,C-COSY technique14] often enables an unequivocal assignment. Herein
we describe the use of two-dimensional heteronuclear shift
correlation via small couplings (H,C-COLOC =
Correlation spectroscopy via Long range Couplings). The
conventional H,C-COSY pulse sequence[31has the disadvantage that the intensity of the cross peaks not only depends on 'JCH and 3JcHcouplings of differing sizes but
also on couplings between the protons themselves and the
direct CH coupling ('JCH). An optimization of the parameters prior to carrying out the two-dimensional experiment
is not possible in the conventional sequence. We therefore
propose the following pulse sequence H,C-COLOC['], in
which the evolution time ( t , ) is incorporated in the time in
which H,C-couplings develop ( A , ) :
[*I
[**I
Prof. Dr. H. Kessler, C. Griesinger, J. Lautz
Institut fur Organische Chemie der Universitat
Niederurseler Hang, D-6000 Frankfurt am Main 50 (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie. C. G. thanks the Studienstiftung
des Deutschen Volkes.
444
0 Verlag Chemie GmhH, 0-6940 Weinheim, 1984
1
2
amounts of substance necessary for the measurement and
the large spectral range of the "C-NMR signals (ca.
150 ppm) with various 'Jcc coupling constants. Techniques which are designed for the measurement of carbons
directly bonded to protons cannot be used because of the
missing protons at the olefinic carbons. In the COLOC
spectrum of rac-1, elucidation of the constitution via determination of the connectivities is possible (Fig. 2): Cross
peaks are visible for all cases where the carbon atoms couple with protons via several bonds.
It is convenient to start the interpretation of the spectrum with the downfield carbonyl signals. Signal 7 shows
only one cross peak with the signal of the protons of the
methyl group f. The latter do not couple with any other
olefinic C-atom; f can thus be assigned to the acetyl moiety. The carbonyl carbon 1 couples with the protons of the
methyl group a, which, in turn, exhibit couplings with the
olefinic C-atoms 3 and 2. Of these, only C3 couples with
the protons of the methyl group c, which are easily identified as a doublet in the 'H-NMR spectrum. C5 also couples
with c. The signals 5 and 6 form cross peaks with d and e.
It follows from the cross-sections through C5 and C6 (not
shown here) that the cross peaks of C5 with d and of C6
with e are the most intense. C,H couplings via two and
three bonds are, of course, of the same order of magnitude; however, it is seen from the higher intensity of 2-a
and 3-b compared to 2-b and 3-a that in the case of the parameters chosen here, the geminal coupling is more developed than the vicinal coupling. The protons of the methyl
groups d and e can also be assigned under these assumptions. The experiment thus enables the sequencing and assignment of the signals of all the olefinic carbon atoms and
methyl protons. Hence, all the requirements for determining the configuration at the two double bonds by NOE difference spectroscopy are fulfilled' ' Noteworthy is the
sharpness of the cross peaks 3-c an< 5-c, which results
from homonuclear proton decoupling.
0570/0833/84/0606-0444 $02.50/0
Angew. Chem. Int. Ed. Engl. 23 (1984) No. 6
-
-1.8
~~~
.
-
I
,v
----,
170
160
lk0
,
~~.
..
140
130
,.,
_I_
'"i
110
-&(%I
Received: February 24, 1984;
revised: March 22, 1984 [Z 722 IE]
German version: Angew. Chem. 96 (1984) 434
Fig. 2. Section of the H,C-COLOC spectrum of ruc-1 for the olefinic carbon
atoms and the carbonyl groups, in the proton region of the methyl groups.
Spectrometer: Bruker WH 270. Measuring conditions: 150 mg in 2 m L
CDCI,/C6D6 ( 5 : 1); A1=A2=40 ms; spectral width in wl=1850 Hz, in
w2=3625 Hz. Total duration of a scan 1.5 s. 140 increments of 1 K with 192
scans each. Total recording time: 12 h. The phases of the 90"-'H--pulsewere
cycled independently of one another in 90" steps with respect to the receiver
phase ( b l = k x 9 0 " , @ d e , = - k x 9 0 0 , k=O,1,2 ,... and @,=mx9Oo,
@ d e l = - m x 9 0 " , m = 0 , 1,2,... ; @ 2 = @ 4 = @ 5 = O ) .
[I] A. Bax, R. Freeman, T. A. Frenkiel, M. H. Levitt, J. Mugn. Reson. 43
(1981) 478.
[2] W. P. Aue, E. Bartholdi, R. R. Emst, J. Chem. Phys. 64 (1976) 2229; A.
Bax, R. Freeman, J. Mugn. Reson. 44 (1981) 542.
[3] A. A. Maudsley, R. R. Ernst, Chcm. Phys. Lett. 50 (1977) 368; G. A.
Morris, L. D. Hall, J. Am. Chem. Soc. 103 (1981) 4703.
[4] G. Eich, G. Bodenhausen, R. R. Ernst, J. Am. Chem. Soc. 104 (1982)
3731; P. H. Bolton, G. Bodenhausen, Chem. Phys. Lett. 89 (1982) 139;
H. Kessler, M. Bernd, H. Kogler, J . Zarbock, 0.W. Sorensen, G. Bodenhausen, R. R. Ernst, J. Am. Chem. SUC.105 (1983) 6944.
[5] H. Kessler, C. Griesinger, J. Zarbock, H. R. Loosli, J . Mugn. Reson. 57
(1984) 331.
[6] G. A. Morris, R. R. Freeman, J. Am. Chem. Soc. 101 (1979) 760.
[7] G. Quinkert, U.-M. Billhardt, E. F. Paulus, J. W. Bats, H. Fuess, Angew.
Chem. 96 (1984) 422; Angew. Chem. lnt. Ed. Engl. 23 (1984) 442.
[8] A. J. Waring, M. R. Morris, M. M. Islam, J . Chem. Soc. C 1971, 3274.
(91 For the application of this technique see, e.g., H. Kessler, G. Zimmermann, H. Forster, J. Engel, G. Oepen, W. S . Sheldrick,Angew. Chem. 93
(1981) 1085; Angew. Chem. Int. Ed. Engl. I2 (1981) 1053.
[lo] H. Kogler, 0. W. Sorensen, G. Bodenhausen, R. R. Ernst, J. Magn. Reson. 55 (1983) 157.
[Ill H. Kessler, C. Griesinger, W. Bermel, unpublished.
The spectrum of rac-2 (Fig. 3) reveals the presence of
two conformers in solution, of which the dominating one
has the conformation determined in the crystal. This was
1 7
3 45
6
proven by dissolution at - 80°C in CD2C12and immediate
'H-NMR
The conformation occurring on
warming the solution is formed through steric hindrance of
rotation about the single bond between C4 and C5['I. The
H,C-COLOC spectrum of the dominating conformation
can be interpreted completely analogously to that of the
isomeric rac-1.
The method presented here, which employs H,C-couplings via two and three bonds, can be used with advantage for the assignment of quaternary carbon atoms, whose
environment is thus also determinable. For its application
to aliphatic carbon atoms we recommend the use of a lowpass J filter"'] for suppressing the direct C-H cross signals["]. The new pulse sequence enables a convenient and,
other than the conventional H,C-COSY sequence, effective
optimization of the delay for the whole experiment. It is
especially suitable, therefore, for the investigation of complex molecules, where intensity maximization is of importance due to scarcity of substance or short relaxation
times.
The sensitivity of the experiment described here, like
that in the relayed H,C-COSY technique, can be rated between that of H,C-COSY and 2D-INADEQUATE.
a
d
Pigments from the Cap Cuticle of the Bay Boletus
(Xerocomus badius)" *
C
f
e
I
I
tl.8
v
b
3-b;
14-b
2.0
I
170
160
150
140
130
'
By Bert Steffan and Wolfgang Steglich*
Dedicated to Professor Sir Derek Barton on the occasion
of his 65th birthday
The bay boletus [Xerocornus badius (Fr.) Kuhn. ex Gilb.],
highly prized as an edible fungus, has a chocolate-brown
pileus. The pigments contained therein are apparently
present in the form of salts, since addition of a small
amount of hydrochloric acid i s necessary for their extrac-
4---66C3c)
Fig. 3. Section of the H,C-COLOC spectrum of ruc-2. Spectrometer: Bruker
AM 500. Measuring conditions: 240 mg in 2 mL C6D6.A1=60 ms, A2=40
ms; spectral width in a,=3800 Hz, in w2=6670 Hz. Total duration per scan
1.5 s. 180 increments of 4 K with 128 scans each. Total recording time: 10 h.
Other than for the spectrum in Figure 2, the phase of the 90"-13C-pulsewas
also cycled with respect to the receiver phase ( @ 5 = n x 90", &,=n x 90",
n = O , l,2, ...; @,=g,=O). This led to a better suppression of spectral artefacts.
Angew. Chem. Int. Ed. Engl. 23 (1984) No. 6
[*I Prof. Dr. W. Steglich, Dr. B. Steffan
Institut fur Organische Chemie und Biochemie der Universitat
Gerhard-Domagk-Strasse I , D-5300 Bonn 1 (FRG)
[**I Fungal Pigments, Part 44. This work was supported by the Deutsche
Forschungsgemeinschaft. We thank Dr. M. Schmitz, Bonn, for recording
the X-ray emission spectra and Dr. C. Wo/f, Bruker, Karlsruhe for highfield NMR measurements.-Part 43: W. Steglich, B. Oertel, Sydowia
Ann. Mycol., in press.
0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984
0570/0833/84/0606-0445 $02.50/0
445
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