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Cyclization of Unsaturated Fatty Acids.

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plished with the system propionic acid/water/carbon tetrachloride in a flow apparatus specially developed for this
purpose [21. The resulting kinetic data are plausible if the
boundary layer reaction occurring on transfer of a caroxylic
acid is formulated as a series of three individual reaction
stepsW For the passage through the boundary layer from
water to carbon tetrachloride, these steps are:
1) Adsorption of the carboxylic acid molecule, which exists
as the monomer in water;
2) dimerization of the adsorbed molecules; and
3) desorption of the dimer into the cc14 phase.
The same processes occur in the reverse order on passage in
the opposite direction. The dependence of the rate constants
on the length of the fatty acid residues lends support to the
above interpretation. This dependence corresponds quantitatively to established adsorption phenomena.
Lecture at Stuttgart (Germany) on January 9. 1969 IVB 194 IEI
German version: Angew. Chem. 81,401 (1969)
[*] Priv.-Doz. Dr. W. Nitsch
Institut fur Technische Chemie der Technischen Hochschule
8 Miinchen, Arcisstrasse 21 (Germany)
[I] H . Furst and W. Nirsch, unpublished.
[2] W. Nitsch and K. Matschke, Chemie-1ng.-Techn. 40, 625
(1968).
[3] W. Nitsch, Chemie-1ng.-Techn. 38, 525 (1966).
Cyclization of Unsaturated Fatty Acids
By V. Wc(f[*1
The cyclization of 9,12,15-c,c.c- (linolenic acid), of 9,12,15t,t,t- (linolenelaidic acid), of 9,11,13-c,i,t- (a-eleostearic acid),
and of 9,11,13-t,t,t-octadecatrienecarboxylicacid (p-eleostearic acid) has been studied in alkaline diethylene glycol
solutions at 180-220 ‘C. An alkali-induced ionic reaction
occurs in which the non-conjugated acids undergo allylic rearrangement, whereas cis-trans rearrangement and doublebond shifts are observed in systems already containing two
or three conjugated double bonds or in cases in which such
conjugated systems are formed.
The a,y,c-t,c,t-triene formed in this manner is cyclized in a
thermal multi-center process to give 5,6-disubstituted 1,3cyclohexadiene. Compounds of this kind occur in equilibrium
with all conceivable cyclohexadienes and cyclohexenes having
conjugated semi-cyclic double bonds. About 10% of the cyclic dienes form o-substituted aromatic carboxylic acids. The
aromatization proceeds by loss of either two hydrogen
atoms, or one hydrogen atom and one side chain, or two side
chains. Interpretation of the mechanism is greatly facilitated
by the diverse but highly characteristic distribution of the
lengths of the alkyl and ester side chains for each of the
acids investigated.
Lecture at Freiburg (Germany) on January 24, 1969 IVB 195 1El
German version: Angew. Chem. 8, 402 (1969)
[*I Prof. Dr. V. Wolf
Unilever Forschungslaboratorium
2 Hamburg 50, Behringstrasse 154 (Germany)
New Investigations of the Biosynthesis of
Flavonoids
By H. Grisebach [*I
trans-Cinnamic acid which is formed from L-phenylalanine
by the enzyme phenylalanine-ammoniumlyase is an important precursor for the formation of flavonoids. Its hydroxylation to 4-hydroxycinnamic acid Cp-coumaric acid) is catalyzed by a microsome fraction from peas“]. This enzyme belongs to the mixed-function hydroxylyases; it could be shown
392
that the H atom originally in the para-position migrates into
the ortho-position to the hydroxyl group (“NIH shift”). A
similar reaction occurs in the biosynthesis of several flavonoids.
Further hydroxylation ofp-coumaric acid, giving caffeic acid,
can be catalyzed by an enzyme (or several enzymes) of phenolase type[21. This enzyme, purified from spinach beet, can
also hydroxylate several flavonoids at the 3’-position of the
B-ring.
According to our results, chalcones are the central intermediates in the biosynthesis of flavonoids. The enzyme chalcone-flavanone-isomerase, first enriched by E. Wong, has been
found to be present in all plants so far studied. The substrate
specificity of several isoenzymes, which are found in plants,
were investigated. It remains unsolved whether the further
changes start from the chalcone or the flavanone precursors.
Kinetic experiments with the pair [“C]chalcone-[3H]flavanone have been carried out in this connection.
Coumestanes and related natural products are biogenetically
to be counted among the isoflavones since, like isoflavanones, the latter can be converted into coumestanes. Coumestrol and a new coumestane have been isolated from Mung
bean (PhaseoIus aureus).
Dihydrodaidzein can be converted into daidzein in seedlings
of the Mung bean. Dihydroisoflavones are, however, probably not intermediates in the biosynthesis of isoflavones. The
fate of the hydrogen was studied in the conversion of 7,4‘dihydroxyt2- 14C-3 -3Hzjflavanone and 5,7,4‘- trihydroxy[2-14C-2-3H]flavanone; the H atom on C-2 is retained but a
H atom is lost from C-3.
Work by W. Burr in our Institute indicates that some isoflavones and coumestrols in Cicer arietinum and Phaseolus
aureus undergo a turnover whose biological half-life is of the
order of 50 hours. Thus synthetic and degradative reactions
will have to be considered in future studies of the metabolism
of these compounds.
Lecture at Berlin on February 24, 1969 IVB 197 1El
German version: Angew. Chem. 81,403 (1969)
[*I Prof. Dr. H. Grisebach
Biologisches Institut I1 der Universitat
78 Freiburg, Schanzlestrasse 9/11 (Germany)
[l] D. W. Russel and E. E. Conn, Arch. Biochem. Biophys.,
No. 1 2 2 ; ~ 256
.
(1967).
[2] P. F. T . Vuughan and V . S. Butt, Biochem. J., in press.
Investigation of Binding of Inhibitors to
Ribonuclease by NMR Spectroscopy
By H . Ruterjans [*I
Hitherto, high-resolution nuclear resonance spectra have
been little used for the structural analysis of such macromolecules. The signals are broad and overlap because of the small
mobility of the individual molecular groups. Only a limited
number of the signals in the N M R spectra can be unequivocally assigned to particular protons of the protein. As example
can be cited the signals of the C-2 protons of the histidineirnidazole rings, which are shifted beyond the spectral region
of the remaining protons to lower field. Furthermore, the
signals of these protons shift about 1.0 ppm to higher field
during the deprotonation to the uncharged imidazole ring; if
the chemical shift of the imidazole C-2 protons is plotted
against the p H value, “titration curves” and p K values of the
histidines are obtained.
In the case of bovine pancreatic ribonuclease A, different pK
values are obtained for the four histidines present in the enzyme. From N M R investigations on carboxyalkyl derivatives
of RNase A and on the subtilisin-cleaved enzyme (RNase S),
these pK values can be assigned to the histidines 12, 48, 105,
and 119 of the polypeptide chainrll. The pK values of the
histidines 12 and 119 of the active site are unusually low; they
increase by about 1.0 and 0.7 respectively if the NaCl concenAngew. Chem. internat. Edit. 1 Vol. 8 (1969) 1 No. 5
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