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Dependence of the Enantioselectivity on the Relative Concentration of Substrate in an NADH Model Reaction.

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constant are unsatisfactory parameters for most chemical
appIications”1.
The empirical Y-scale developed by Winstein, which is
based on solvolysis reactions, presently serves as a general
reference system. However, it is limited to polar media,
whereas the secondary polarity scales derived from spectroscopic data and linearly correlating with the Y-scale,
e. g. the ET(30) scale of Dimroth and Reichardt. can also be
applied in low polarity media.
The empirical polarity quantities are defined only for
the liquid phase; it should be checked, however, as to how
far an extension to solids is possible (see also .)]4l
The
phthalimides 1 and 2, which are also readily soluble in
low polarity media and, with their strong solvatochromism
in the fluorescence, are sensitive to polar solvation effects, can be used as models here.
S=28590 [kcal.nm.mol-’]
glasses investigated actually reflects the polarity of the medium can be shown with eq. (2),
S = &In (c,/c*
+
ET(30) = - 1.935, 160.4
ET(30) = - 1.81Sz + 155.7
Organic glasses, e. g. polymethylmethacrylate (Plexiglas)
are suitable model solids for the investigation of polarity,
since their spatial isotropism favors accuracy of measurement. We found that pure Plexiglas prepared by melting
granules shows only low polarity (ET(30)= 37.3) at 25 “C,
comparable to 1-chloropropane. Even a small residual
content of monomer noticeably increases the polarity; it
can be increased into the polarity range of 2-butanol
(ET(30)= 47.5) by addition of ca. 10% methanol.
Accordingly, solvatochromic dyes are just as influenced
by the medium in organic glasses as in liquids. That the
solvatochromism of the fluorescence of 1 or 2 in the
(2)
which quantitatively describes the polar behavior of binary
liquid mixtures[”]. cp is the molar concentration of the
more polar component and So the S-value of the less polar
component (here pure Plexiglas). E D and c* are the parameters of the equation.
Equation 2 also describes the polar behavior of solid
mixtures and holds both for solid copolymers (examples
see Fig. 1) as well as for low molecular additives to polymers (1,2-propanediol and 1,3-butanediol).
This finding is of interest for the directed preparation of
polymers having definite properties, for an understanding
of the action of softeners, and for the analysis of polymers.
It follows from these findings that the polarity of solid
matrices can be defined empirically in the same way as the
polarity of liquids (for a summary of previous works
see[‘’]).
Received: October 26, 1981 [Z 124 IE]
German version: Angew. Chern. 94 (1982) 452
The complete manuscript of this communication appears in:
Angew. Chern. Suppl. 198.2. 1138-1 144
(1)
The molar emission energy S is calculated analogously to
the ETvalues, from/2,,, of the fluorescence using eq. (1); S
correlates linearly with the ET(30) scale.
+ 1) + S o
CAS Registry numbers:
1, 2307-00-8: 2, 3676-85-5: plexiglas, 76416-69-8.
[2j C. Reichardt: Soluenf E/Jeca in Organic Chemisfry. Verlag Chemie.
Weinheim 1979.
[4] D. Walter, J . Prakf. Chem. 316 (1964) 604.
[lo] H. Langhals, Chern. Ber. 114 (1981) 2907.
1131 H. Langhals, Angew. Chern. and Angew. Chern. I n [ . Ed. Engl.. in press.
Dependence of the Enantioselectivity on the
Relative Concentration of Substrate in an
NADH Model Reaction**
By Naomichi Baba, Jun’ichi Oda, and
Yuzo Inouye*
Recently we found“] that the NADH model system I ,
which contains L-prolinamide as a chirality-inducing center, reduced ethyl 2-0x0-2-phenylacetate 2 (in presence of
Mg(CIO& at 50°C in anhydrous CH,CN) to give ( R ) ethyl mandelate in high enantiomeric excess (e. e. = 83%)[’]
and that the e.e. increased as the reaction proceeded. A
similar increase has also been reported in other examples[”
and was accounted for in terms of the feedback effect of
the oxidized nicotinamide, which accumulates during the
Ph,
,COOEt
$0
2
CH,Ph
conversion (Scheme 1): the oxidized form 4 interacts
(“feedback interaction”) with the reductant 3 uia chelative
mediation of metal ion and/or charge transfer interaction.
This may bring about specific blocking of one of the diastereotopic faces of the dihydropyridine ring (chiral selection), permitting easier access of the substrate carbonyl
0
[*] Prof. Dr. Y. Inouye, Dr. J. Oda, Dr. N. Baba
1 lnlrp/c*+l)
Fig. 1 . Linear relationship between S , (dye 1) and In(c,/c*+ 1) according to
eq. (2) for the copolymer of methyl methacrylate and 2-hydroxypropyl methacrylate.
Angew. Chem. Int. Ed. Engl. 21 (1982) No. 6
[**I
Institute for Chemical Research, Kyoto University
Uji, Kyoto-Fu 61 I (Japan)
We wish to express our thanks to Dr. Nobuyuki Sugita and Dr. Tadashi
Okamoto for their helpful advice on the kinetic treatments.
0 Verlag Chemie GmbH. 6940 Weinheirn. 1952
0270-0933/82/0606-043~S 02.50/0
433
compound to the other face, and thereby contributing
much towards increasing the enantiomeric excess in the later stages of the reduction.
R1
=CHO'
R2
6
R
4
3
":
,CHO'
R2
R
5
R
Acid/Mercaptoethanol/Hydrogenase**
By Ichiro Okura*, Nguyen Kim-Thuan, and
Makoto Takeuchi
Aside from zinc porphyrin complexes[z1almost exclusively ruthenium complexes have been used as sensitizers
in studies on the photo-induced cleavage of water'']. We
report here on the use of the manganese(i1) meso-tetraphenylporphyrintrisulfonic acid complex (Mn"-TPP(S03H)3)
as photosensitizer for the photo-induced reduction of
methyl vioiogen (N,N'-dimethylbipyridinium dichloride,
MV2+); photochemically facile redox reactions are possible with manganese porphyrin and phthalocyanin comp l e ~ e s ~ ~Since
'.
the reduced form of methyl viologen
(MV+) in the presence of a catalyst liberates H, from water, we attempted carrying out this reaction with the system
H H
R
Photochemical Evolution of H2 in the System Methyl
Viologen/Mn"-meso-Tetraphenylporphyrintrisulfonic
P2
6
Mn"-TPP(S03H)~/MV2~/mercaptoethanol/hydrogenase.
Scheme I. Hypothetical pathway of the asymmetric reduction with nicotinamide derivatives 3 using a feedback interaction between 3 and 4.
The feedback mechanism can be described by eqs. (a)(c):
Mn"TPP(SO,H), was generated in situ from the corresponding Mn"' complex, which was synthesized from
TPP(SO,H), and Mn(OAc), in CH,OH. The hydrogenase
from D. vulgaris was purified according to Yagi's methodI4l; the hydrogenase solution had the ability to generate
8.5 x lo-' mol of hydrogen using the reaction system: hydrogenase (0.1 mL)
MV2+ (8.1 x lo-' mol)
Na2SZO4
( 2 x lo-' mol) in 3 mL of a 0.02 M phosphate buffer (pH 7)
at 30°C for 20 min. Irradiation (150W tungsten lamp,
/z > 390 nm) of a buffered (Tris-HCI, pH 7) aqueous solution of Mn"'-TPP(S03H),, MV2+, and mercaptoethanol
under anaerobic conditions at 30°C led to formation of
MV+ (characteristic absorption at 395 and 605 nm); as
shown in Figure 1 the formation of MV+ first sets in after
an induction period, and then increases with time. During
the induction period the concentration of Mn"'TPP(SO,H), drops rapidly (rapid decrease in intensity of
the band at ;1=467 nm), with concomitant formation of
Mn"-TPP(SO,H),, which shows a strong absorption at
/2=435 nm: Aeration (introduction of oxygen) leads to immediate reconversion of the Mn"-complex into the Mn"'complex.
+
where A = MgZ+-activated[61, chiral NADH model 3;
C =oxidized species 4 ; B =hypothetical intermediate 5 ;
S=substrate 6; P=product. The e.e. can be calculated
using eq. (d):
e. e. =
(m- n ) K + m - (n- r n ) J K ( 1 - [S]/[S,])- ' In[([S]/[S,]
(d)
+ K)( 1 + K ) - '1
where, m and n represent the optical yield of PI and Pz,
respectively, with the assumption that n > m ; I =
k l ( k l - k 3 ) - ' and K=k3(kl-k3)-'. Eq. (d) shows that the
e. e. should increase monotonically with increasing initial
concentration of the substrate ([S,]);moreover, as is found,
an increase in e.e. is also to be expected with decreasing
[ S ] towards the end of the reaction.
In accord with predictions, a significant increment in
e.e. (from 46 to 76%) was observed in the reduction of 2
upon increase of the substrate initial concentration from
to l o - ' M.
This constitutes the first example in which the enantioselectivity is dependent on the initial concentration of substrate. It seems very likely that a similar feedback interaction between products and reactants may sometimes be operative in other asymmetric systems. Accordingly, it might
possibly be used as a probe for studying the mechanisms
of other reactions.
+
4
i
i
i
1
0
Received: June 10, 1981 [Z 102 IEI
German version: Anyew. Chem. 94 (1982) 465
The complete manuscript of this communication appears in:
Anyew. Chem. Suppl. 1982. 1021-1027
[I] N. Baba, J. Oda, Y. Inouye, J. Chem. SOC.Chem. Commun. 1980, 815.
[2] a) A. Ohno, T. Kimura, S. Oka, Y. Ohnishi, Tetrahedron Lett. 1978. 757.
b) T. Makino, T. Nunozawa, N. Baba, J. Oda, Y. Inouye, J. Chem. SOC.
Perkin Trans. 11980, 7.
[6] A. Ohno, H. Yamamoto, T. Okamoto, S. Oka, Y. Ohnishi, Bull. Chem.
SOC.Jpn. 50 (1977) 2385.
434
0 Verlay Chemie GmbH. 6940 Weinheim. I982
0
10
t lminl
-
20
Fig. I. Change of concentration of Mn"l-TPP(SOIH)7 (0). Mn"TPP(SO,H), (a), and MV' ( 0 )on irradiation of 6 mL of an aqueous solution of 1.31 x l o - " mol Mn"'-TPP(S03H)3, 8 . 1 2 ~lo-' mol MV'+, and
5.43 x
mol mercaptoethanol at 30°C.
[*I
Dr. 1. Okura, Dr. N. Kim-Thuan, M. Takeuchi
Department of Chemical Engineering, Tokyo institute of Technology
Meguro-ku, Tokyo, 152 (Japan)
[**I We thank Prof. T. Keii and Prof. Y. Ono for stimulating and helpful discussions.
0570-0833/82/0606-0434 $02.50/0
Angew. Chem. Int. Ed. En& 21 (1982) No. 6
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