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Inhibition of Photosynthesis Reactions by NH-Acidic Imidazoles and Benzimidazoles.

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acids: they dissolve in aqueous sodium carbonate and are
reprecipitated by acidification with HCI but d o not form
hydrochlorides. Their biological activity is related to their
pKa value.
We have studied the action of such compounds on oxidative
phosphorylation in isolated mitochondria from rat heart.
It was found that the benzimidazoles listed in the table have a n
uncoupling effect similar to that of 2,4-dinitrophenob They
inhibit the regulation of the mitochondria1 respiration by
adenosine diphosphate (ADP) and stimulate the respiration
beyond the state 3 rate 121. They also counteract the inhibition of the respiration caused by oligomycin and octylguanidine, and stimulate ATPase as well as or even better
than 2,4-dinitrophenol. The reduction of N A D in the electron transport of the mitochondria, which is dependent upon
ATP and linked to succinate, is inhibited.
As shown in the table, the uncoupling activity increases exponentially with the N-H acidity of the benzimidazoles.
N-Methylation leads to a complete loss of their action o n the
respiratory chain. Tetrachloro-2-trifluoromethylbenzimidazole effects complete uncoupling of oxidative phosphorylation at a concentration as low as 3 x 1O--SM. It is thus the
strongest uncoupler known to date.
stirred and chlorine is passed through for about 36 h at a rate
of 4 - 5 l/h. The solvent is removed in vacuum and the crude
crystalline residue is suspended in boiling water. More
chlorine is passed in until the conversion t o the tetrachloro
derivative is complete (after approx. 24 h). The end point of
the chlorination is determined by analysing a sample of the
reaction mixture by gas chromatography on Apiezon L at
250 " C with helium in a column 96 cm long. The product is
then filtered off and recrystallized from xylene. The yield of
colorless crystals, m.p. 269 "C, Amax = 223, 273, 290, and
301 m y (log E = 4.92, 3.94, 3.85, and 3.81), is above S 5 %.
Received: July 12th. 1965
[Z 27/851 IE]
German version: Angew. Chem. 77. 814 (19651
[ I ] K . H. Biichel, F. Korte, A . Trehst, and E. Pistorius, Angew.
Chem. 77, in press; Angew. Chem. internat. Edit. 4,789 (1965).
[2] J . E . Chuppell, Biochem. J. 90, 237 (1964).
[3] B. Chance and B. Hagihara: Proc. Vth Intern. Congr.
Biochem., Moscow 1961. Pergamon Press, London 1963.
Vol. 5, p. 3.
141 J. B. Chappefi,Biochem. J. 90, 225 (1964).
Inhibition of Photosynthesis Reactions by
NH-Acidic Imidazoles and Benzimidazoles
Uncoupling
concentration
b M / l I [bl
(I) TFB
( 2 ) 5-Chloro-TFB
(3) 5.6-Dichloro-TFB
( 4 ) 4,5,6-Trichloro-TFB
(5) 4,5,6,7-Tetrachloro-TFB
(6) N-Methyl-4.5.6trichloro-TFB
9.6
8.9
7.6
6.6
5.6
-
500
14
0.8
0.2
0.03
inactive
By Dr. K. H. Buchel and Prof. Dr. F. Korte
Shell Grundlagenforschung GmbH.,
SchloB Birlinghoven/Siegburg (Germany) and
Prof. Dr. A.Trebst and E. Pistorius
A bteilung Biochemie der Pflanzen, Pflanzenphysiologisches
Institut der UniversitPt Gottingen (Germany)
[a] In SO vol-% aqueous ethanol.
[bl The course of the respiration of rat heart mitochondria was measured
at 25 "C [3] using an oxygen electrode [4]. The mitochondria (2-3 mg
of protein) were suspended in 0.25 M sucrose/l.O mM ethylenediaminetetraaceticacid andthenadded to 3.7ml of amixturecontainingthefollowing components: 9.3 mmole of sucrose, 50 pmole of dipotassium
glutamate, and 20 pmole of MgClz. When state 4 respiration started,
0.4 vmole of A D P was added in order to obtain state 3 respiration. On
reattainment of state 4, a solution of the benzimidazole in ethanol was
added; an increase in respiratory activity was immediately observed.
More A D P was then added. When the second addition of A D P exhibits
no further effect on the respiratory activity, the phosphorylation system
is uncoupled.
4,5,6,7-Tetruchloro-2-trijl1~orornethylbenziiniduzole
A solution of 93 g (0.5 mole) of 2-trifluoromethylbenzimidazole in dichlorobenzene is heated at 120 ' C . The solution is
Imidazoles and benzimidazoles containing strongly electronegative substituents, e.g. halogens or trifluoromethyl or
nitro groups, are strongly acidic at the N H group and
sometimes exhibit good herbicidal properties. Since some
herbicides, c. g. urea derivatives, aminotriazines, and uracils,
inhibit the fixation of carbon and release of oxygen by
photosynthesis, we have examined the effects of our herbicidal
heterocycles on photosynthesis reactions in isolated chloroplasts.
The table shows that these substances inhibit the electron
transport in photosynthesis. The compounds with the highest
activity have a high NH-acidity [I]. N-Alkylation of the
acidic secondary amino group, e . g . t o give ( l o ) , causes a
reduction in the inhibitory effect. The imidazole anion is
probably the species responsible for the effect. Since the
release of oxygen is inhibited at concentrations which are
insufficient to affect cyclic photophosphorylation, the blockage
Table 1. Relationships between the pKa (in SO % aqueous ethanol) of some substituted imidazoles and benzimidazoles and their inhibitory
action ( ~ 1 5= ~minus the logarithm of the molar concentration which produces a 5 0 % inhibition) on the release of oxygen and the cyclic
photophosphorylation during photosynthesis in isolated chloroplasts [31.
~
-iberation of oxygen
Hill reaction with
Compound
PKa
-
(2)
(3)
(4)
( 5)
(6)
(7)
(8)
(9)
(10)
&
4-ChloroTFB
5,6-DichloroTFB
4,5,6-TrichloroTFB
4,5,6,7-TetrachloroTFB
4,5,6,7-TetrabromoTFB
5,6-DinitroTFB
2,4,5-Trihromoimidazole
2,4,5-Triiodoimidazole
N-Methyl-4,5.6-trichloroTFB
Angew. Chem. internut. Edit. Vol. 4 (1965) /
No. 9
PI50
SO % inhibn.
at [ylmll
PISO
198
2.91
9.6
!8
3.28
8.2
7.6
6.6
5.6
10
0.34
0.44
0.9
I .7
0.3
0.5
0.4
10
4.34
5.88
5.82
5.5
4.1
6.9
8.0
-
5.56
5.47
5.96
5.79
6.05 (51
4.48
87
4.8
3.3
2.9
2.9
3.4
24
7.8
3.40
4.73
4.93
5.05
5.24
4.91
4.11
4.76
789
occurs in the region of the second light reaction of photosynthesis (photo-oxidation of water), for this is not required
for cyclic phosphorylation. Higher concentrations - generally
about ten times greater - cause inhibition of the cyclic
photophosphorylation, i. e. formation of ATP, as well (see
Table). In this respect, the imidazoles and benzimidazoles
described here differ from the herbicides of the urea and
triazine types, which only affect the cyclic phosphorylation
at extremely high concentrations, if at all. The inhibition of
the formation of ATP by the benzimidazoles is due to an
uncoupling and not to a disturbance of the cyclic electron
transport, because photosynthetic reduction of NADP by an
artificial electron donor (diaminodurol/ascorbate [2]) is not
inhibited even by much higher concentrations of herbicide.
Hence the electron transport in the region of the first light
reaction is unaffected.
The benzimidazole derivatives listed in the table were
prepared by condensation of the correspondingly substituted
o-phenylenediamines with excess trifluoroacetic acid at
80-100 O C or by substitution of 2-trifluoromethylbenzimidazole (I) [61. Compound ( 6 ) was made by bromination of ( I )
with a twofold molar excess of bromine in boiling water.
Compound (7) is obtained in 6 0 % yield by nitrating ( I ) with
By Dr. B. Fell and Dipl.-Chem. J. M. J. Tetteroo
Institut fur Technische Chemie, Tecbnische Hochschule,
Aachen (Germany)
During hydrocarboxylation 111 of higher n-alkynes under
normal pressure to give qB-unsaturated carboxylic acids,
the length of the inhibition time and the rate of the reaction
depend on the intensity of the incident light [2]. We have
found that if the reaction is carried out in ultraviolet light,
open-chain or cyclic mono-olefins can also be converted into
the corresponding carboxylic acids in good conversions and
high yields, although these compounds can otherwise seldom
be hydrocarboxylated. The results obtained are shown in the
table. Each charge comprised 0.25 mole of olefin, 0.15 mole
of nickel carbonyl, 5 moles of water, 0.5 mole of HCI (added
in the form of concentrated hydrochloric acid), and 200 ml of
acetone. The ultraviolet radiation source was a 7 0 watt Q 81
immersion lamp from Messrs. Quarzlampen GmbH, Hanau
(Germany); the reaction temperature was 55-60 "C.
Olefin
Light
Cyclohexene
Darkness
Daylight
Ultraviolet
Ultraviolet
n- 1-0ctene
Darkness
Daylight
Ultraviolet
Ultraviolet
6
Daylight
Ultraviolet
Ultraviolet
6
cis-n-4-Octene
HNO3 (sp. gr. = 1.52) at 60-70°C and recrystallization from
xylene. The N-methyl derivative (10) is formed by treating
the sodium salt of (4) with methyl iodide in acetonitrile at
50 "C. The trihaloimidazoles (8) and (9) were made according
to [7].
Received: July 12th, 1965
[ Z 39/864 IEl
German version: Angew. Chem. 77, in press.
[I] A similar relationship between the half-neutralization potential of substituted N-phenyl amides and the inhibition of the
Hill reaction was recently observed: N.D. Camper and D. E.
Morefund, Biochem. biophysica Acta 94, 383 (1965).
[Z] A.Trebst and E. Pistoriirs, 2. Naturforsch. 206, 143 (1965).
[3] Duplicate experiments were carried out on 3 ml samples
containing chloroplast fragments (PlsLfrom spinach [41, 0.2 mg
of chlorophyll), 8 0 pmole of tris buffer at pH 8.0, 5 pnole of
MgC12, 10 p o l e of potassium phosphate, lOpnole of ADP, and
either 20 pmole of K3[Fe(CN)6] or 0.3 pmole of vitamin K3.
The mixtures were exposed to 35000 lux for 15 min under
nitrogen. The oxygen produced was determined manometrically
and the amount of ATP formed was determined enzymatically
with phosphoglycerokinase, triose phosphate dehydrogenase,
phosphoglyceric acid, and NADH2. The control value for the
oxygen production without addition of inhibitor was 1300 mm3
per mg of chlorophyll per h.
[4] M. B. AIIen, F. R . Whatley, and D. I. Arnon, Biochim. biophysics Acta 32, 32 (1959).
[S] The pI50 of (9) is relatively high in consideration of its PKa,
but this is because [9) is more lipophilic than (8). Better correlations between the PKa and pI50 are generally obtained by
inclusion of partition coefficients.
[6] Synthesis of (Sj ; K . H . Biichei, F. Korte, and R. B . Beechey,
Angew. Chem. 77, 814 (1965); Angew. Chem. internat. Edit. 4,
788 (1965).
[71 J. E. Bafuban and F. L. Pyman, J. Chem. SOC.(London) 121,
947 (1922); H. Punly and K . Gunderrnann, Ber. dtsch. chem.
Ges. 41, 3999 (1908).
790
Photo-initiated Hydrocarboxylation of
Mono-olefins
6
6
9
6
9
No reaction
A mixture of isomeric
nonanoic acids [a]
9.1
86.5
98
70
70
17
[a] 37 % 1-nonanoic acid, 61 % 2-nonanoic acid, 1 % 3-nonanoic acid,
and 1 % 4-nonanoic acid.
[b] 2 % 2-nonanoic acid, 3.5 % 3-nonanoic acid, and 94.5 % 4-nonanoic
acid.
The unconverted olefin is partly isomerized. For example,after
hydrocarboxylation of I-octene in daylight, the unconverted
olefin consists of 87.1 % starting material, 2.8 % cis-2-octene,
and 10.1 % trans-2-octene. After irradiation with ultraviolet
light, however, the percentages are 28.8, 13.6, and 57.6 %,
respectively. After the reaction with cis-4-octene, the unchanged olefin comprises 9 2 % starting material, 5 % transn-4-octene, and 3 trans-n-3-octene.
Received: July 19th, 1965
[ Z 26/850 IE]
German version: Angew. Chem. 77, 813 (1965)
[ I ] W. Reppe et al., Liebigs Ann. Chem. 582, 1 (1963); E. R. H.
Jones, T. Y . Shen, and M. C. Whiting, 5. chem. Soc. (London)
19S1,766.
[2] J. M. J . Tetteroo, Doctorate Thesis, Technische Hochschule
Aachen, 1965.
N-(2,4-Dinitrophenyloxycarbonyl)amino Esters New N-Activated Amino-Acid Derivatives
By Dr. J. Gante
lnstitut fur Organische Chemie der Freien Universitat Berlin
(Germany)
Reaction of amino esters with bis-(2,4-dinitrophenyl) carbonate [ 1] in a molar ratio of 1: 1 in anhydrous ethyl acetate
or ethyl acetate/ether (1 :2 v/v) at ro3m temperature followed
by precipitation with petroleum ether gives the N-(2,4dinitrophenyloxycarbony1)amino esters ( l o ) - ( l d ) .
Angew. Chem. internat. Edit./ Vol. 4(1965) No. 9
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