close

Вход

Забыли?

вход по аккаунту

?

Optical Activity of Chiral Dendritic Surfaces.

код для вставкиСкачать
COMMUNICATIONS
indicating metallic character. The hyperbolic PNS I,-Y**
bounds regions with very different degrees of valence electron
localization, that is of different bonding character. One has the
impression that the metallically conducting 3*.10, nets are separated by insulating hyperbolic layers.
The cubic phase RhBi, as a whole is isotropic. Nevertheless,
the atomic distribution and electronic structure show intrinsically a strongly anisotropic, layerlike structure. However, due to
the hyperbolic (non-Euclidean[’]) form of these layers, all anisotropic components are compensated in the crystal.
The formation of regions with very different localization of
the valence electrons and the resulting microscopic anisotropy
should influence the electro-kinetical properties and may
correlate to the superconductivity of the compound ( K =
2.9-3.4 K[”]).
Received December 9, 1994 [Z7566IE]
German version Angebt Chem 1995, 107, 1318-1320
Keywords : electron localization function . intermetallic phases .
periodic nodal surface . polyhedral nets
[l] F. Wagner. Dissertation, Universitit Sadrbrucken, 1993.
[2] Yu. Grin, U. Wedig. H. G. von Schnering, 11th Intern. Con/. Solid Compounds
of Trunsimn Elements, Abstracts. Wroclaw, 1994, p. 39.
[3] Yu. Grin, U. Wedig, F. Wagner, A. Savin, H. G. von Schnering. J Alloy5
Conip., submitted.
[4] V. P. Glagoleva, G. S . Zhdanov, Zh. Eksp. Teor. Pi;. 1956, 30, 248. Sov. Phys.
JETP (Engl. Trans.) 1956, 3, 155.
[S] P. I. Kripiakevich, Structure fjpes of rntermefallrc compoundr (Russian),
Nauka, Moskau, 1977, p. 118.
[6] E. Hellner, E. Koch, A. Reinhardt, Phys. Dufen/ Phys. Dara 1981.16-2,define
the frameworks using crystallographic point configurations of the space
groups. The connection of all positions of the site 24c (l/8 0 1/4) of the space
group lafd(No. 230) leads to fwo interpenetrating nets consisting offour-connected nodes. The nets are called + V and -V, both together--\/*. Each of the
four-connected nodes belongs to six rings, two three-membered and four tenmembered: 32.104 according to Wells [7].
I71 A. E Wells, Three-Dimensional Nets and Polyhedru, Wiley, New York, 1977,
p. 74K.
[8] H. G. von Schnering, R. Nesper, Aizgew. Chem. 1987,99,1097; Angew. Chem.
Int. Ed. Engt. 1987,26, 1059.
[9] H. G. von Schnering, R. Nesper, Z . Phys. 8. Condens. Matfer 1991,83, 407;
H. G. von Schnering, M. Oehme, G. Rudolf, Acra Chem. Scand. 1991,45,873.
1101 The PNS I,-Y** represents the zero points of the Fourier series built using
geometrical structure factors IS(112)l = IS(22O)l = I and their phases
a(112) = ~ ( 220)= 0 as coefficients under the consideration of the permutations of the space group Ia3d. The reduced form is ( c = cos, s = sin, X = 2nx,
Y = 2ny, z = 2x2): 0 = - 2[S2X C Y sz + sx s2Y c z + c x S Y s2Z] + c2x
c2Y c2Yc2Z c2Xc2Z. The description I,-Y** uses the symbols according
to [6] and shows that the point configurations I, and Y** were separated by
this PNS 181. All 16 points of the twofold body-centred lattice I are placed in
one labyrinth, which separates two other enantiomorph labyrinths. The 2 x
‘
8 points of the nets +Y* -Y* = Y** are located in the last two labyrinths.
[Ill A. H. Schoen, NASA Technical Note D-5541, Washington, D. C., 1970.
1121 G. Krier, M. van Schilfgaarde, T. A. Paxton, 0. Jepsen, 0. K. Andersen, Program TB-LMTO, unpublished.
1131 U. Barth, L. Hedin, J Phys. C 1972, 5, 1629.
[14] 0. K. Andersen, Z. Pawlowska, 0. Jepsen. Phys. Rev. B : Condens. Matter
1986, 34, 5253.
[IS] A. Savin, A. D. Becke. J. Flad, R. Nesper, H. Preuss, H. G. von Schnering,
Angew. Chem. 1991, 103, 421; Angen. Chem. In/. Ed. Engl. 1991, 30, 409.
116) A. Savin, 0.Jepsen, J. Flad, 0. K. Andersen, H. Preuss, H. G. von Schnering,
Angew. Chem. 1992,104, 186; Angen. Chem. Int. Ed. Engl. 1992, 31, 187.
1171 N. E. Alekseevskii,G. S. Zhdanov, N. N. Zhuravlev, Zh. Eksp. Teor. Fiz. 1955,
28. 237.
+
+
+
Optical Activity of Chiral Dendritic Surfaces**
Johan F. G. A. Jansen, H. W. I. Peerlings, Ellen M. M.
de Brabander-Van den Berg, and E. W. Meijer*
Macroscopic, nanoscopic, and mesoscopic chirality are
among the intriguing new key words in the studies of chiral
clusters, associated complexes, homo- and heterogeneous catalysts, and of many
Major drawbacks for these studies are, generally, the complexity of the materials under investigation and their lack of long-range order. Therefore, comprehensive studies of macroscopic chirality are primarily performed on single crystals and synthetic bilayers.[*]However, for
a better understanding of the chiroptical features of non-ordered structures, well-defined materials are required. Dendrimers are promising candidates for the preparation of well-defined chiral materials with nanoscopic dimensions.[31To the best
of our knowledge only chiral dendrimers of lower generations
have been prepared and no irregularities in the chiroptical properties of these enantiomerically pure dendrimers are reportmodified an amine-terminated
ed.[,- ’] Newkome et
dendrimer with enantiomerically pure tryptophane, whereas
Seebach et al.[sl prepared some dendrimers with a chiral core
and Chow et
prepared dendrimers with a chiral spacer.
Hudson and Damha”] synthesized a nucleic acid based chiral
dendrimer, Mitchell[’] a glutamic acid based dendrimer, while
Denkewalter disclosed a number of dendrimeric structures
based on amino acids.[’]
Larger chiral dendrimers with a more dense packing of
functional groups in the shell have not been studied so far.
Recently, we successfully prepared chiral structures of nanometer dimensions based on poly(propy1ene imine) dendrimers
(DAB-dendi--(NH,),,)[’ol that are terminated with amino acid
derivatives and we presented evidence that these compounds are
useful as dendritic “boxes” (DAB-dendr-(NH-&BOC-L-Phe),,;
Fig. I).[’ Due to the dense packing of the shell and the presence
of internal cavities, we are able to encapsulate a variety of guests
into these dendritic boxes; guests that are physically locked. The
synthesis of this and other amino acid modified dendrimers is
summarized in Scheme 1 . Here we report on the peculiar chiroptical properties of these dendritic boxes and discuss the structure
of highly curved chiral dendritic surfaces.
The investigation presented here was triggered by the observation that the specific optical rotation of the DAB-dendr(NH-t-BOC-L-Phe), decreases to almost zero on going from
dendrimers of the first generation ([a],, = - 1 1 ; c = 1, CHCI,)
with four end groups to dendrimers of the fifth generation
([a],, = - 0.1; c = 1, CHC1,) with 64 end groups. A more thorough investigation employing a variety of different amino acid
derivatives reveals that this decrease of optical rotation with
increasing generation is a general phenomenon for all the amino
acids studied (Table 1 ) . The most striking results are found for
the DAB-dendr-(NH-r-BOC-&-Z-L-Lys),,in which the [a],, value
decreases from - 28 (c = 1 , CHCI,) for the first generation dendrimer (x = 4) to 0 (c = 1 , CHCI,) for the fifth generation den[*] Prof. Dr. E. W. Meijer, Dr. J. F. G. A. Jansen, Ir. H. W. I. Peerlings
[**I
1206
0 VCH !4rlagsgeeellrchujt
mbH, 0-65451 Wernherm, 1955
Laboratory of Organic Chemistry
Eindhoven University of Technology
P. 0. Box 513, NL-5600 MB Eindhoven (The Netherlands)
Telefax: Int. code + (40)451036
Dr. E. M. M. de Brabander - Van den Berg
DSM Research. P. 0. Box 18, NL-6160 MD Geleen (The Netherlands).
We would like to thank Prof. M. M. Green, Prof. M. Lahav, and Prof. R. J. M.
Nolte. as well as Dr. E. E. Havinga and Dr. M. H. P. van Genderen for valuable
discussions.
0570-0833lPSIi1lt-1206 S 10.00+ .25/0
Angeu. Chem. Int. Ed. EngI. 1995, 34, N o . I t
COMMUNICATIONS
Table 1. Selected specific rotations of modified poly(propy1ene imine) dendrimers.
Fig. 1 . Space-filling model of DAB-dendr-(NH-1-BOC-L-Phe),,; the l-BOC-L-Phe
end groups are given in red. while the core atoms are given in green, white, and blue.
drilner (x = 64). ~~~~~~i~ changes are also observed for L-(s)benzylcysteine and the L-tyrosine derivatives. For the smaller
amino acids (Ala, Val and Leu) the decrease in optical rotation
is less pronounced. As the number of chiral end groups per
weight unit is roughly independent of the generation (in each
new generation both the number of end groups and the moiecular weight double), the decrease in the [a], values with increasing generation is not due to the reduction of chiral chromophores.[’ 21 Furthermore neither concentration nor temperature effects are responsible for this decrease in optical activity,
as nearly identical rotations are observed for c = 0.1,1, and 4 in
chloroform at temperatures of 20 and 55 “C in the L-Phe dendrimer series. However, a significant solvent dependency of the
specific rotations was noticed for the lower generations and was
CH,CI,
E13N
DABdendr-(NH,)
R = CH,.CH(CH,),.CH,CH(CH,),,
CH,C&SCH,,
Scheme 1. Synthesis of the dendritic “box”, DAB-dendr-(NH-t-BOC-L-Phe),,
AnXrw. Cliem. Inr. Ed. Engl. 1995, 34. No. t 1
16
(3)
32
(4)
[ZID
I40
64
(5)
la],
- 25
-26
-33
- 14
- 39
-31
-27
-28
- 22
- 28
- 23
-21
-13
- 10
- 16
- 12
-11
-10
-2
+ 56
+ 42
+26
+13
+5
- 28
-8
-3
-1
0.0 [a]
-11
-1
-9
-1
-0.1 [a]
+lO[b]
+7
+2
+1
+0.1 [a]
+19[c]
+9
+1
-0.2
-0.1 [a]
Number a/ end groups
(generation)
4
(1)
BOC iimino arid
c = 1 (solvent)
IZID
(2)
[ZID
r-alanine (L-Ala)
(CHCI,)
r-valine (L-V~I)
(CH C131
L-leucine (L-Leu)
(CHCId
L-methionine (L-Met)
(CHCIJ
L-(S)-benzylcysteine
(CHCId
e-(Z)-L-lysine
(CHCIJ
L-phenylalanine (L-Phe)
(CHCI,)
D-phenylalanine (o-Phe)
(CHCI,)
L.tyrosine ( L - ~ y r )
(DMSO)
- 24
8
[a1 Error approximately kO.2. [bl In DMSO 1.
= - 13. [cl
In CHCL
I4 = + 15.
investigated in detail for the model compound N-t-BOC-L-Phepropylamide. Specific optical rotations were dependent on the
dielectric constant of the solvent, varying from [a], = 7.3 (c = 1 ,
toluene) to [a], = - 6.4 (c = 1, acetonitrile) for the model compound. The behavior of the corresponding dimeric model compound from diaminobutane and two L-Phe residues deviated
remarkably from all other ones. The dimer is only slightly soluble, indicative of intermolecular hydrogen bonding, and the
optical rotation is large (“ID = 22, c = 1, CHCI,; see Fig. 4).
The peculiar behavior of symmetric dipeptides is the subject of
many recent studies.[’31Finally, we have demonstrated that the
protected amino acids do not
undergo racemization in the
coupling method employed;
analysis of the amino acids after acid-catalyzed hydrolysis
of the modified dendrimers by
HPLC using chiral stationary
phases revealed an enantiomeric excess of greater than
96 Yo.
Circular dichroism (CD)
and optical rotatory dispersion (ORD) studies in conjunction with UV/Vis absorption spectroscopy have been
performed to gain a better insight into the peculiar chiroptical effects observed. The restricted solubility of the
dendritic boxes hampers the
use of the entire spectral
range. Most of the Cotton effects (CEs) present in the CD
spectra of the lower generations decrease with generation; the results of the L- and
D-Phe series are given in Figand other amino acid derivatives.
ure 2. Both the CE of the car-
8 VCH Ver~agsgesellschafimbH, 0-69451 Weinheim, fYY5
o570-OR33~YS;ltf1-1207
.$ 1O.fJfl+ .25!0
1207
COMMUNICATIONS
~~
-51
-1 0
-15l
Fig. 4. Specific optical rotation of camphor sulfonic acid modified dendrimers (A)
and L-Phe modified dendrimers (m), both measured in CHCI, (c = 1)
Fig. 2. Dependence of the specific ellipticity $ [deg cm2g-'1 on the wavelength for
D- and L-Phe modified dendrimers in CHCI,,
bamate chromophore at A,,, = 240 nm and the CEs of the
phenyl chromophore at 2 = 250-270 nm are influenced strongly by the generation, while some (diminished) residual optical
activity remains for the amide chr~mophore.['~]
The decrease in
the CEs is accompanied by some small changes in the UV/Vis
spectra, indicative of changes in conformation. Similar chiroptical effects are observed for dendrimers modified with other
amino acids. Since the L-Tyr series has limited solubility, ORD
spectra are taken in dimethylsulfoxide (DMSO) and compared
with those of the 4- and 64-~-Phederived dendrimer (Fig. 3:
note the change of sign in the rotation of the L-Phe series;
negative in CHCI, and positive in DMSO)
Fig. 3. Dependence of the specific rotation [a] [deg cm2g- '1 on the wavelength for
the L-Tyr modified dendrimers in DMSO.
The optical behavior of the amino acid modified dendrimers
is in sharp contrast with the optical rotations found for chiral
dendrimers with more rigid end groups. The rigid dendritic camphor sulfonamides (Fig. 4) and camphanic amides have almost
identical rotations ([a], = 23; c = 1, CHCI, and [a], = - 18;
1208
0 VCH Veriagsgesellschafi m b H , 0-69451
Weinheim,1995
c = 1, CHCl,, respectively) for all generations. Furthermore,
the corresponding N-propyl camphor sulfonamide model compound showed a specific rotation independent of solvent
([a]D= 25; c = 1, CHCI,).
A number of phenomena other than trivial ones, like racemization or concentration effects, can explain the remarkable observations presented above for the amino acid modified dendrimers. A decreasing/vanishing optical activity of dendrimers
is observed for dendrimers with chiral end groups; whose optical activity is susceptible to changes in the local environment.
We are prompted to propose an explanation based on the fact
that the outer surface (shell) of these dendrimers exhibit a highly
dense solidlike packing in solution, as has been demonstrated by
I3C NMR relaxation measurements.["I The rigidity of the shell
is probably enhanced by multiple hydrogen bonding of the
amide and carbamate groups in the shell. This rigid, close packing will lead to a number of conformations that are frozen. Due
to the sensitivity of the chiroptical properties of the amino acid
derivatives to the molecular environment and, hence, to conformational disorder, it is hypothesized that an internal compensation effect of different chiral conformers in the dendritic surface
causes the vanishing or decreasing optical activity of the dendrimers. Chiral conformers with a non-equilibrium conformation are formed, forced by the dense packing in the shell. This
explanation is related to the discussions by Green and Garetz
on how the configurational stereochemistry of polymers can
lead to vanishing optical activities by compensation among
diastereomeric states.['51
As these dendritic structures are highly organized, it is tempting to suggest that the conformational disorder in the shell is
limited to the presence of only two frozen conformations with a
kind of pseudo-enantiomeric relationship and almost opposite
CD and ORD for both pseudo-enantiomers. It is well documented that the density of racemic crystals is higher than that of
conglomerates['61 and the most dramatic differences are found
for amino acid derivatives." 'I A pseudo mirror-image relation
of conformers of enantiomerically pure compounds has been
observed in X-ray studies of a number of crystals.["' We have
performed a variety of preliminary studies using scalemic mixtures to evaluate this pseudo-enantiomer hypothesis, but a detailed interpretation is lacking.["' However, it is apparent from
our results that the highly curved surface does not allow the
packing of all amino acid derivatives into their preferred lowest
energy conformations. This effect is probably strengthened by
multiple hydrogen bonding.[*']
The constant optical rotation of the camphor sulfonamide
and camphanic amide dendrimers of different generations is in
$ iO.OO+ .25/O
0570-0833/95/fiti-i2U8
Angew. Chem. I n t . Ed. Engl. 1995, 34, N o . if
COMMUNICATIONS
full agreement with the insensitivity of its rotation with respect
to changes in the molecular environment. The constant [XI,
value does not imply that the camphor sulfonamide and camphanic amide shells are not densely packed nor that they do not
possess frozen-in conformations. However, in these densely
packed surfaces the frozen-in conformations all have the same
optical activity and no internal compensation effects are operative here. Also the number and strength of the hydrogen bonds
in these cases will be lower than in the case of the amino acid
derived dendrimers. Further research to elucidate the reasons
for the observations presented here are in progress. It is foreseen
that research on chiral dendrimers with highly packed shells will
yield important information for this type of curved structures;
structures that are so prominently present in nature.
Received: November 8. 1994
Revised version: January 26, 1995 [Z74591E]
German version: Angen.. Chem. 1995, 107, 1321 - 1324
Keywords: chirality . chiroptical studies . circular dichroism
dendrimers stereochemistry
M. M. Green, 8. A . Garetz, Terruhedron Lert. 1984, 25. 2831
0. Wallach. Jusrus Liebies Ann. Chem. 1895. 286. 90-143
C.
1 P. Brock, W. B. Schweizer, J. Dunitz, J. Am. Chem. Soc. 1991, 113, 98119820
I. Weissbuch, F. Frolow, L. Addadi, M. Lahav. L. Leiserowitz, J Am. Chem.
Soc. 1990. 112, 7718-7724.
In order to discriminate between disorder and pseudo-ceiitrosymmetry, we
performed experiments using scalemic mixtures of D-Phe and L-Tyr in the
formation of the fifth-generation box. In sharp contrast to the [.IDvalues of 0
for the pure o-Phe or L-Tyr, we found [.ID = + 16 (c = 1 , DMSO) for the 50: 50
scalemic mixture of D-Phe and L-Tyr, and optical rotations between + 16 and
0 for the other mixtures studied. The trend observed is indicative for some kind
of pseudo-centrosymmetric ordering in the shell. in which in the case of the
S O : 50 scalemic mixture both units can adopt their preferred conformation and
still the most dense packing is formed.
This conclusion seems at first glance to be in contrast with "la coupe du roi"
in which both chiral halves are of the same handedness, however a chiral
dendritic surface possesses molecular chirality while "la coupe du roi" has only
macroscopic chirality, see K. Mislow, Bull. Sur. Chim. Fr. 1994, 131, 534-538.
.
[l] a) F. Ciardclli. Encylopediu qf'Poljmer Science und Enginering. Vol10. Wiley,
New York, 1987. p 463; h) J. M. Lehn, Angew. Chem. 1988, 100, 91-116:
AnReii. Chrm. In[. Ed. EngI. 1988. 27, 89-112; c) M. Kitamura, S. Okada, S.
Suga, R. Noyori. J Am. Chem. Soc. 1989, 111.4028-4036; d) M. Kitamura,
R. Noyori. Angcw. Chem. 1991. 103. 34 - 5 5 ; Angen.. Chem. In[. Ed. Engl. 1991,
30.49.- 76; e) T. Katsuki. K. B. Sharpless. J. A m . Chem. SOC.1980,102,59745976: f ) D. K. Mitchell. J.-P. Sauvage, Angew Chem. 1988, 100, 985-987:
A n p r . C%rm.fnr. Ed. h g l . 1988.27. 930-933; g) H. Ringsdorf, B. Schlarh,
J. Venzmer. dnd. 1988, 100. 117-162 and 1988, 27, 113-158: h) D. Seebach,
ihd. 1990. 102. 1363-1409 and 1990.29, 1320-1366.
(21 a ) L. Addadi, 2. Berkovitch-Yellin. I. Weisshuch. M. Lahav, L. Leiserowitz, in
Top. Srrrwchem. 1986, 16, 1: h) T. Kunitake, N. Nakashima. S. Hayashida. K.
Yonemori. Chem. Lrrl. 1979. 1413; c) T. Kunitake, N. Nakashima. M. Shimomurlt. Y Okahata. K. Kano. T. Ogawa. J. Am. Chon. SOC.1980, 1/12, 6642;
d ) N. Nakashima. R. Ando. T. Muramtsu, T. Kunitake, Lungmuir 1994. 10,
232
[3] a ) D. A Tomdlia. A. Naylor, W. A. Goddard, Ange". Chem. 1990. 102, 119157. Angeiv. ('hem. f n t . Ed. EngI. 1990,29,138-175; h ) G . R.Newkome, C. N.
Moorfield. G. R. Baker, A. L. Johnson. R. K. Behera, J. Org. Chem. 1992.57.
358 362: c) Z. Xu. J. S . Moore, Angew. Chrm. 1993,105.1394-1396: Angew.
('hrtn. I n / . 6 1 . Engl. 1993, 32, 1354-1357; d ) C. Worner. R. Mulhaupt. ibid.
367-1370and 1993.32.1306-1308e)K. L. Woo1ey.C. J. Hawker.
chet, J. Am. Chem. Soc. 1991, 113, 4252-4261: f) K. L. Wooley,
C . J. Hawker. J. M. J. Frechet, Angew. Chem. 1994. 106, 123-126; Angekv.
Chcn?. fn!. E d Enx/. 1994. 33. 82-85; g) T. M. Miller, T. X. Neenan. E. W.
Kwock, S . M . Stein. J. Am. Cheni. Soc. 1993. 115. 356-357: h) J. Issherner, R.
Moors, E Vogtle, Angew. Chem. 1994, 106,2507-2514; Angew. Chem. fnr. Ed.
Engl. 1994, 33. 2413-2420.
(41 G . R. Newkome. X. Lin, C. D . Weis, Tetruhrdron Asynimerry 1991, 2, 957960
[S] a ) D. Seehach. J.-M. Lapierre, K. Skohridis. G. Greiveldrnger, Angew. Chem.
1994. 106, 457- 458; Angew. Chem. f n r . Ed. Engl. 1994. 33, 440-442; Helv.
Chini. AcIu 1994, 77. 1673-1688.
[6] a) H:F. Chow, L. E Fok, C. C. Mak. E'trahedron Lett. 1994,3S, 3547--3550:
h) H:F. ('how, C. C. Mak. J. Chrm. SOC.Perkin Trans. f1994, 2223.
(71 R. H . E. Hudson, M. J. Damha. 1 Am. Chem. Soc. 1993. 115, 2119-2124.
[XI L. W. Twyman, A. E. BceLer. J. C. Mitchell, Tetrahedron Lerr. 1994, 35. 4423.
[9] a) R. G. Denkewalter. J. F. Kolc, W. J. Lukasavage. US-A 4410688, 1983
[('hrm. Ahsrr. 1984. 100. 103907p]; h) R. G . Denkewalter, J. F. Kolc. W. J.
Lukasavage. US-A 4289872, 1981 [Chem. Abstr. 1985, 102,79324q1.
[lo] E. M . M. den Brabander-van den Berg. E. W. Meijer, Angen. Chem. 1993,105.
1 3 7 0 ~1372; Angew. Chem. In!. Ed. Engl. 1993. 32, 1308-1311.
[11] J. F. G. A. Jansen, E. M. M. den Brabander-van den Berg, E. W. Meijer, Sciewe. 1994, 266, 1226-1229.
[12] The 1x1, values of the dendrimers of all generations are comparable to the
Fpecitic optical rotation per chiral group. In the class of chiral dendrimers with
a chiral core and achiral branches it i s obvious that the optical rotation decreases with generation (51.
[13] D. 0. McDonnald. W. C. Still, J Am. Chem. SOC.1994, 116, 11550-11553:
b) S H. Gellman, G. P. Dado. G.-B. Liang. B. R. Adams, J. Am. Chem. SOC.
1991. 113. 1164.
[14] A similar decrease in optical activity, although not as pronounced, is found for
the amidc ahsorption in trifluoroethanol. In this solvent. however, neither the
aromatic nor the carhamate absorption could he detected with CD.
Anjirii.. C'bvm. lnt. Ed. E n d 1995, 34, No. 11
[15]
[16]
~ 7
Facile Synthesis and Solid-state Structure
of a Benzylic Amide [2]Catenane**
Andrew G. Johnston, David A. Leigh,* Robin J.
Pritchard, and Michael D. Deegan
The synthesis of interlocked molecular rings, catenanes, is one
of the greatest challenges in preparative chemistry." - 31 Large
macromolecular catenane structures (10' D) are found in DNA,
where they appear to act as intermediates during the replication,
transcription, and recombination p;oce~ses,[~~
and are probably formed in small quantities in some polymerization reactions
by the chance threading of growing molecular chains through
large rings.c61Recently the structural characteristics of smaller
catenanes (lo3 D) have earmarked them, together with their
relatives the rotaxanes, as key elements in the development of
components for nanoscale electronic devices and molecular machines such as molecular shuttles, switches, and information
storage systems.[3* Here we report the serendipitous formation
of a new amide-based [2]catenane (1) prepared in one step from
two commercially available starting materials (see Scheme 2).
The catenane is obtained in 20 % yield (remarkable for an eightmolecule condensation) following a chromatography-free purification procedure simple enough to be performed in a wellequipped high school or undergraduate laboratory. The
structure of 1 has been confirmed by N M R spectroscopy, mass
spectrometry, and, in particular, by X-ray crystallography,
which reveals a beautiful self-assembled system held together by
networks of inter- and intramolecular hydrogen bonds and perfectly tessellating n-stacking interactions between four aromatic
rings. Each catenane consists of two identical, interlocked, 26membered rings with an internal cavity of 4 x 6 A, making 1 the
smallest interlocked ring system yet isolated.
[*I Dr. I).A. Leigh, A. G. Johnston, Dr. R. J. Pritchard
Department of Chemistry
University of Manchester Institute of Science and Technology
Sackville St., Manchester M60 1QD (UK)
Telefax: Int. code (161)200-4539
M. D. Deegan
Gas Research Centre, British Gas PLC
Loughhorough (UK)
[**I We thank Dr. J. P. Smart for useful discussions and advice, and S. Davey, M.
Bolgar. and Prof. S . Gaskell for mass spectral data. This work was carried out
through the support of a British Gas Scholarship award (to A. G. J).
8 VCH firiugsgesellschafr nibH, 0-69451 Weinheim, 1995
+
+
0570-0833l95llIl/-l2093 10.00 .25/0
1209
Документ
Категория
Без категории
Просмотров
0
Размер файла
943 Кб
Теги
chiral, dendriticum, optical, surface, activity
1/--страниц
Пожаловаться на содержимое документа