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Complex Shift Reagent for 13C-NMR Studies on Carbohydrates.

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1;. calculated from (1). The close correlation between
I,,., and Zt, may be seen from Figure 1.
The residual variance of the regression plotted in Figure 1
amounts to V(I:+,)=O.00483eV2 at 4 = 22 degrees of freedom. A corresponding value of V(ZTvF) = 0.01128 eV2
(@=23)is obtained for a simple HMO model which does
not include bond localization (all p,,= p). The variance
Complex Shift Reagent for * 3C-NMR Studies
on Carbohydrates
By Wolfgang Voelter, Claus Biirvenich, and
Eberhard Breitmaier[*l
Application Of the pulse Fourier transform technique has
raised the sensitivity of NMR spectroscopy"! 13C-NMR
is consequently being employed increasingly for determination of configuration and conformation of carbohydratesf2'
and nucleosidesr3.'I.
The 13Csignals of carbohydrates are assigned by comparison of spectra of analogous compounds and on the basis of
the following,experimentally well-substantiated rules1'- 51 :
1. The resonances of deoxy carbon atoms appear at highest
2. The peaks of anomeric carbon atoms lie at lowest fieid.
3. A pyranose carbon atom having an axial hydroxyl group
is generally more strongly shielded than a corresponding
one with an equatorial hydroxyl group.
4. On changing a pyranose hydroxyl group from an
equatorial to an axial position the signals of y carbon atoms
having an axial hydrogen atom on the same side of the ring
are shifted upfield.
I [PI I exp
Fig. 1. Correlation between the vertical ionization potentials calculated
from (1)( l ; , J s l ( P I )calc.) and the experimental values (lv,J=I(PI)exp.).
The confidence limits shown refer to 90% security.
ratio F = 0.01 128/0.00483= 2.36 is greater than the critical
value F = 2.03 for 95% security, corresponding to degrees
of freedom I$1 =23 and &=22. This means that the regression (1) yields significantly better agreement with experiment than that based on orbital energies
calculated from an unperturbed HMO model.
However, it should be borne in mind that the improvement
of the correlation due to the perturbation term in (I),
i.e. the
significant reduction in residual variance, is smaller in the
present case than for the smaller n systems studied in the
preceding communication"]. This was to be expected since
the perturbation of the x-bond lengths due to removal of
an electron will become smaller with increasing size of the
rc system.
The regression shown in Figure 1 supports the assumption
that the first six bands (four bands for TR) in the PE spectra
of the hydrocarbons C,,H,, should be assigned to x orbitals. This assignment is also consistent with the band
shapes and relative band intensities, as will be reported
Received: March 6, 1972 [Z 639 IE]
German version: Angew. Chem. 84,551 (1972)
[I] Applications of Photoelectron Spectroscopy, Part 36. This work
is part of Project No. SR 2. 477. 71 of the Schweizerischer Nationalfonds.-Part 35: F . Brogli and E . Heilbronner, Theoret. Chim. Acta,
in press.
[2] G. Binsch, E . Heilbronner, and J . N. Murrell, Mol. Phys. I I , 305
(1966); G. Binsch and E. Heilbronner in A . Rich and N. Dacidson:
Structural Chemistry and Molecular Biology. Freeman, San Francisco
1968, p. 815.
131 H . Gotz and E . Heilbronner, Helv. Chim. Acta 44, 1365 (1961).
[ 4 ] D. W Turner, Proc. Roy. SOC.A 307, I 5 (1968).
[5] A . Streitwieser J r . and J . 1. Brauman: Supplemental Tables of
Molecular Orbital Calculations. Pergamon Press, Oxford 1965, Vol. 1.
Angew. Chem. internat. Edit. / Vol. I 1 (1972)
/ No. 6
5. Replacement of a hydroxyl hydrogen by a methyl group
shifts the signal of the ring carbon atom closest to the oxygen downfield by 6 to 12 ppm.
In the case of mutarotating sugars, recording the spectra
before and after mutarotational equilibration has proved
particularly valuable in signal assignment of anomeric
pairs''. '1.
A new means of investigating conformations and configurations of sugars or sugar residues has been found in
comparison of the 13C spectra of the sugar and its borate
complex. (Circular dichroism of molybdenum and copper
complexes can be employed for similar purposesf62
The use of borate as a complex shift reagent will be demonstrated for adenosine and 2'-deoxyadenosine.
As with molybdate ion[61,complex formation with borate
is pH dependent. In order to detect complex formation between borate and the sugar, the I3C signals of adenosine
( I ) are recorded with and without borate at various pH
values (cf. Figs. 1a and 1b).
The signals are assigned as in previous publication^'^'
Figure l a shows that the I3C signals of C-I' to C-5'
change by less than 0.5ppm between pH 1 and pH 10.
More pronounced shifts are observed for C-5 and for the
signals of the remaining adenyl-C atoms at low pH. In
[*] Doz. Dr. W. Voelter, Dip1.-Chem. C. Biirvenich, and
Doz. Dr E. Breitmaier
Chemisches Institut der Universitdt
74 Tiibingen, Wilhelmstrasse 33 (Germany)
chemical shifts of 2'-deoxyadenosine solutions with and
without borate are almost equal.
It may be seen from the above 13C study that borate is
particularly suitable as a complex shift reagent for the
detection of neighboring cis-hydroxyl groups in carbohydrate chemistry. The requisite information is obtained
without great experimental effort by measurement of sample
solutions adjusted to pH 10, once with addition of borate
and once without. Moreover, the method can be used for
elucidation of hitherto debatable structures in this class of
b [ ppml
Fig. l a . pH dependence of 13C signals of adenosine solutions. The
solution contained 30-270 mg of adenosine per 5 ml depending upon
Fig. 1b. pH dependence of 13C signals of adenosine-borate solutions.
The solutions contained 30-270 mg of adenosine per 5 ml and 100 mg
of boric acid.
6-substituted purines protonation occurs initially at N-I
(pK 2-4)['].
Proton addition hardly affects the electron
density on C-5 ; the resonances of C-2, C-4, and C-6 are
shifted upfield and that of C-8 downfield (Figs. 1a and 1b).
The upfield shift of the C-2 and C-6 signals on monoprotonation can be explained in terms of the rule found by Pugmire and
for six-membered heterocyclics. The pH
dependence of the 13Cresonances observed with pyrimidine
does not apply to C-5 of the purine system.
Figure 1b represents the pH dependence of the 3Csignals
of adenosine-borate solutions. The resonances of the
adenyl-C atoms are almost identical with those in Figure
1a. The signals of C-2' and C-3', however, are shifted downfield by about 6 ppm in the presence of borate at pH > 6.
Complex formation of neighboring cis-hydroxyl groups
on C-2 and C-3' with borate can thus be unequivocally
detected by I3C-NMR spectroscopy. Whereas the signal
of C-5' is hardly affected by complex formation, the signals
of C-I' and C-4' adjacent to C-2' and C-3' exhibit a slight
but readily detectable downfield shift.
In the absence of a hydroxyl group on C-2' the ribose
residue can no longer form chelates with borate. The 13C
The 'H-broad band decoupled Fourier transform 'jCNMR spectra were recorded with a Bruker HFX 90 multinuclear spectrometer. The (deoxy)-adenosineand (deoxy)adenosine-borate solutions were adjusted to the desired
pH values by addition of sodium hydroxide or hydrochloric acid of various molarities.
Received: April 10,1972 [Z 641 IE]
German version: Angew. Chem. 84,589 (1972)
[l] E. Breitmaier, G. Jung, and W Voelter,Angew. Chem. 83,659 (1971);
Angew. Chem. internat. Edit. 10, 673 (1971).
[2] D. E. Dorman and J . D. Roberts, J. Amer. Chem. SOC.92, 1355
(1970); A. S . Perlin, B. Casu, and H. J . Koch, Can. J. Chem. 48, 2596
(1970); E. Breitmaier, G . Jung, and 19: Voelter, Chimia 25, 362 (1971);
E. Breitmaier, W Voelter, G. Jung, and C . Tanzer, Chem. Ber. 104,1147
(197 1).
[3] A. J . Jones, D. M . Grant, M . W Winkley, and R . K. Robins, J. Amer.
Chem. SOC.92, 4079 (1970); E . Breitmaier, G . Jung, and W Voelter,
Chimia 26, 136 (1972).
[4] E. Breirrnaier and W Voelter, Hoppe-Seylers Z. Physiol. Chem., in
[5] W Voelter, E. Breitmaier, and G . Jung, Angew. Chem. 83, 1012
(1971); Angew. Chem. internat. Edit. 10,935 (1971).
161 W Voelter, Hoppe-Seylers Z . Physiol. Chem. 350, 15 (1971); W
Voelter, E. Bayer, R. Records,E. Bunnenberg, and C. Djerassi, Chem.
Ber. 102, 1005 (1969); W Voelter, G. Kuhfittig, and E. Bayer, Angew.
Chem. 82,985 (1970); Angew. Chem. internat. Edit. 9,964 (1970).
[7] H . Bauer, Diplomarbeit, Universitat Tiibingen 1972; H . Vergin,
H . Bauer, G . Kuhfittig, and W Voelter, 2. Naturforsch, in press.
[8] A. M . Fiskin and M . Beer, Biochemistry 4, 1289 (1965).
[9] R. J . Pugmire and D. M . Grant, J. Amer. Chem. SOC.90,697 (1968).
[lo] E. W Malcolm, J . W Green, and H. A. Swenson, J. Chem. SOC.
Synthesis, Kinetics, and Luminescencel*'"'~
By WaIdemar Adam and Hans-Christian Steinmetzer"'
Five years ago a-peroxylactones (1) were postulated for
the first time as active precursors in the bioluminescence
of the firefly[31and of Cypridina k i l g e n d ~ r f i i [ ~This
~ I . was
confirmed in the latter case by "0 labeling[4! In the fireflyrs1 and in Renillar6I,however, an u-hydroperoxide (2)
is responsible for bioluminescence. a-Peroxylactones are
also suspected as luminescence-initiating species in the
reaction of acridinium salts with H202['] and of ketenes
with singlet oxygen['I.
p] Prof. Dr. W. Adam and Dr. H.-Chr. Steinmetzer
Chemistry Department, University of Puerto Rico
Rio Piedras, Puerto Rico 00931 (USA)
[**I Cyclic peroxides, Part 26.-Part 25: W Adam and L. Szendrey,
Tetrahedron Lett., in press. This work was supported by the National
Science Foundation, the Petroleum Research Fund of the American
Chemical Society, the Research Corporation, and the A. P. Sloan
Foundation. H.-Chr. S t . is indebted to the Deutsche Forschungsgerneinschaft for a traveling grant.
Angew. Chem. internal. Edit. 1 Vol. I 1 (1972) / N o . 6
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complex, nmr, reagents, 13c, carbohydrate, studies, shifr
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