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Ethylene OxideЧX-Ray Structure Analysis (at 150 K) and ab initio Calculations.

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with k + l = 2 n + I, giving the location of the metal atom on a special
position The structure solution was completed using the DIRDIF system [IZ]. By virtue of the isostructuralism of the two complexes it was
possible to take the final coordinates from the converged Pt structure as
starting values for the refinement of the Pd structure. For refinement [ 131
hydrogen atoms were included in fixed, calculated positions, at convergence, the difference electroil density map showed no feature above 1.25
and 1 0 7 e k ' for M = Pd".Pt" respectively.Further details of the crystal
structure investigation are available on request from the Director of the
Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2 IEW. Any request should be accompanied by the full literature citation for this communication.
[lo] N. N. Greenwood, A. Earnshaw: Chemistry o f t h e Elements, Pergamon
Press 1984, p. 1497; R. D. Shannon, Acta Crystallogr. A32 (1976) 751.
[ I 11 For analogous N-donor tridentate macrocyclic complexes of Pt" see K.
Wieghardt, M. Koppen, W. Swiridoff, J. Weiss, J. Chem. Sor. Dalton
Trans. 1983. 1869.
1121 P. T. Beurskens, W. P. Bosman, H. M. Doesbury, Th. E. M. van den
Hark, P. A. J Prick, J. H. Noordik, G. Beurskens, R. 0. Could, V. Parthasarathai, D. I. R. D. 1. F . Applrcations of Direct Methods to Dgference
Structure Factor.s. University of Nijmegen, Netherlands 1983.
1131 G. M. Sheldrick: SHELX76, Program .for Crystal Structure Refinement.
University of Cambridge, 1976.
Ethylene Oxide-X-Ray Structure Analysis (at 150 K)
and a b initio Calculations**
By Peter Luger,* Chakib Zaki, Jurgen Buschmann, and
Ruiner Rudert
Dedicated to Professor George A . Jeflrey on the occasion
of his 70th birthday
In a series of studies on the structure of small, unsubstituted cyclic ethers we have so far determined the crystal
structures of tetrahydrofuran,"] oxetane,121and d i ~ x a n e . ' ~ ]
We have now been able to prepare crystals of ethylene oxide (oxirane). Its crystal structure and accompanying ab initio calculations are reported herein. Apart from in a conference report on the structure of c y ~ l o p r o p a n e , [no
~ ~ results of an X-ray structure analysis of a nonsubstituted
three-membered ring have so far been published. In the
works of Jeffrey et al.[5.61on ethylene oxide hydrate the
three-membered ring was treated with rigid geometry.
The ethylene oxide, which is gaseous at room ternperature (m.p. 161 K, b.p. 284 K), was crystallized in situ on a
Stoe four-circle diffractometer by a method described in
Refs. [ 1,2], and the intensity measurements were carried
out at 150 K."] After convergence of the refinement, a difference Fourier synthesis showed a residual electron-density maximum in the ring plane outside of the ring and
equidistant from the two C atoms (distance to the C-C
bond 70 pm), pointing to the existence of bent bonds in the
t h ree-mem bered ring.
In the crystal, the ethylene oxide molecule is, within the
estimated standard deviations, practically an equilateral
triangle (Fig. 1, top). The C - 0 bond (mean value 143.1 pm)
has about the same length as in the other cyclic ethers;
only in oxetane is it longer (146.0 pm). The C-C bond
length is shorter than that found for ethylene oxide by
other methods. It is also shorter than that found for a number of derivatives by other methods["] (Table I).
[*I
[**I
276
Prof. Dr. P. Luger, DipLPhys. C. Zaki, Dr. J. Buschmann,
Dipl.-Phys. R. Rudert
lnstitut fur Kristallographie der Freien Universitat
Takustr. 6, D-1000 Berlin 33
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
0 VCH Verlagsge~ellschajimbH, 0-6940 Wernherm. 1986
4
nQ
H-C-C ( m e a n ) = 1 1 5 ( 2 )
H-C-O(rnean) = 1 1 2 ( 2 )
,-,
Fig. I Top: Molecular structure of ethylene oxide in the cryatal at 150 K,
with bond lengths [pm] and angles ["I. Bottom: Stereoview of the crystal
structure of ethylene oxide in an x.y projection. C - H . . - 0contacts close to
or shorter than the van-der-Wads distances are shown as broken lines
(ORTEP [17]).
Table I. Bond lengths [pm] in ethylene oxide determined by various meth
ods.
C-0
c-c
C-H
Method
15615)
147.0( I )
147.013)
143.8(4)
144.9
147.0(18)
I05( 7)
108.3(2)
108.5(4)
9x3)
96 [a1
Electron diffraction
Microwave
spectroscopy
X-ray structure
analysis
Mean value [b]
Ref.
Experimental
145(5)
1 4 3 4I)
143.4(2)
143.1(4)
144. I
144.3(13)
-
ab-mitio catcularions
143.3
147.0
146.9
145.9
145.9
140.1
139.9
143.7
148.3
147.4
147.4
146.1
146.4
145.3
145.2
146.3
108.8
107.1
107.1
106.9
107.1
107.7
107.8
108.7
(STO-3G)
( H F/3-2 I G)
(H F/3-2 1 G*)
(HF/4-3 IG)
(HFI6-31G)
(HF/6-3 1G*)
(H F/6-3 I C**)
(MP2/6-31Gt)
[a] rigid body" correction [14-16] with the temperature parameters of all
atoms. The results of this correction should be regarded with some care,
since only isotropic temperature factors are available for the hydrogen
atoms. [b] Average values from twelve X-ray and neutron diffraction studies
on ethylene oxide derivatives carried out after 1975 (source: Cambridge Data
File [Ill).
A complete optimization of the geometry by a b initio
calculations["I was carried out at the MP2/6-31G* level,
and the results were compared with those of earlier calculations (Table 1). Compared to the results of the X-ray
structure analysis, which indicated that all bonds in the
ring are almost of the same length, the MP2/6-31G* calculations gave the same C-0 bond lengths, but a longer C-C
bond length.
In the crystal lattice of ethylene oxide (Fig. I), two intermolecular C-H.. .O contacts fall within the van-derWaals distance (van-der-Waals radii of 152 pm for 0 and
0570-0833/86/0303-0276 $ 02.50/0
Angew. Chern. Int. Ed. Engl 25 (1986) No. 3
120 pm for H are a~sumed"~1).
Contacts of this sort were
also observed in the crystal structure of oxetane.I2'
Received: October 21, 1985;
revised: December 13, 1985 [Z 1503 IE]
German version: Angew. Chem. 98 (1986) 254
CAS Registry number.
Oxirdne, 75-2 1-8
[I] P. Luger. J. Buschmann, Angew. Chem. 95 (1983) 423; Angew Chem. I n t .
Ed. Engl. 22 (1983) 410; Angew. Chem. Suppl. 1983. 537.
12) P. Luger. J. Buschmann, J. Am. Chem. Soc. 102 (1984) 71 18.
[3] J. Buschmann, P. Luger, E. Muller, Absrr. 8th Eur. Crystdogr. Meet..
Liege 1983, p. 133
[4] D. Nijveldt, A. Vos, A. F. Cameron, Abstr. 7/11 Eur. Crysfallagr. Meet.,
Jerusalem 1982, p. 153.
IS] R. K. McMullan, G. A. Jeffrey, J. Chem. Pfiys. 42 (1965) 2725.
[6] F. Hollander, G. A. Jeffrey, J. Chem. Phys. 66 (1977) 4699.
[7] Crystallographic data for ethylene oxide at 150 K: a=464.5(4),
b=840.7(6), c=666.4(7) pm, p= 100.00(8)", space group P2,/n, 2 = 4 ,
R =0.048 for 339 observed reflections (Stoe four-circle dilfractometer,
Ni-filtered Cux,. radiation, o-20 scan, 2 8 < 113'). Further details of
the crystal structure investigation are available on request from the
Fachinformationszentrum Energie, Physik, Mathematik GmbH. D-7514
Eggenstein-Leopoldshafen 2, on quoting the depository number C S D
5 1 792, the names of the authors, and the full citation of the journal.
IS] P. G. Ackermann. J. E. Mayer, J. Chem. Pfiys. 4 (1936) 377.
191 T. E. Turner, J . A. Howe, J. Chem. Phys. 27 (1957) 974.
[la] Ch. Hirose, Bull. Chem. Soc. Jpn. 47(1974) 1311.
[ I l l 0. Kennard, D. G. Watson, W. G . Town, J. Chem. SOC.12 (1972) 14.
[I21 J. S. Binkley, M. J. Frisch, D. J . DeFrees, K. Raghavachari, R. A. Whiteside, H. B. Schelgel, E. M. Fluder, J. A. Pople: Gaussian 82. Users
Manuol. Department of Chemistry, Carnegie-Mellon University, Pittsburgh, PA, USA 1983.
1131 A. Bondi, J. Cl~em.Phys. 68 (1964) 441.
[I41 V. Schomaker, K. N. Trueblood, Acta CrystaNogr. 8 2 4 (1968) 63.
[IS] C Scheringer, Acra CrysfaNogr.A 2 8 (1972) 616.
[ 161 C. Scheringer, Acra Crystallogr. A 34 (1978) 428.
[I71 C . K. Johnson: ORTEP. Report ORNL-5138. Oak Ridge National Laboratory. TN, USA 1976.
[I81 W. A. Lathan, L. Rddom, P. C. Hariharan, W. J. Hehre, J. A. Pople, Top.
Curr. Chem. 40 (1973) I.
[I91 R. A. Whiteside, M. J. Frisch, J. A. Pople (Eds.): Carnegie-Mellon Quantum Chemistry Archive. 3rd edit., Carnegie-Mellon University, Pittsburgh, PA, USA 1983.
[20] B. A. Hess, Jr., L. J. Schaad, P. L. Polavarapu, J. Am. Chem. Soc. I06
(1984) 4348.
Synthesis of N-(l-Carboxy-5-arninopentyl)dipeptides
as Inhibitors of Angiotensin Converting Enzyme**
By Riidiger Escher and Peter Biinning*
N-Carboxymethyldipeptides have gained great importance in recent years as inhibitors of angiotensin converting enzyme (ACE) in the treatment of hypertension and
conjestive heart failure."' In the form of N-( 1-carboxy-5aminopentyl)dipeptides, these inhibitors are, moreover,
valuable tools for biochemical studies on ACE; owing to
their functional &-aminogroup they are suitable, after coupling to a gel matrix, as ligands for an affinity chromatography of the enzyme. The following synthetic routes provide access to these N-substituted dipeptides: reductive
amination of a-keto acids o r reaction of primary amines
with a-bromo-, a-methanesulfonyloxy-, o r a-trifluoromethanesulfonyloxy-carboxylicesters 2. However, only the
[ * ] Pri\ .-l)oz. Dr. P. Biinning, Lebensmittelchem. R. Escher
['"I
Biochemisches lnstitut der Universitat
Hermann-Herder-Str. 7, D-7800 Freiburg (FRG)
This work was supported by the Deutsche Forschungsgerneinschaft and
the Fonds der Chemischen Industrie. We wish to thank Dr. H . Urboch.
Dr R H m n m y , Dr. F. Effenberger. and Mrs. U. Burkard for their valuable help with this work.
Angew Chrm Int. Ed. Engl. ZS 11986) No. 3
reaction of esters 2 with amino acid derivatives furnish Nsubstituted a-aminocarboxylates 3 in high yield via
Walden inversion.[*' I n this way, a series of N-( I-carboxy5-aminopentyl)glycyl- and N-( 1-carboxy-5-aminopentyl)alanyl-amino acids, 6a and 6b respectively, were synthesized.
0
0
II
HO-CH-C-OBzl
I
(CF~SO,)ZO
II
CF,SO,O-CH-C-OBZI
I
>
C&SN
R'
1
R1
0 NH,
II I
H~CO-C-CH-(CH~)~-NH-BOC
2
0
>
2
0
II
I1
H3CO-C-7H-NH-CH-C-OX
1
3, X = Bzl
H,/Pd
4 , X = H
H N CH-C-OR3
-1
I1
*
Rz 0
4
1 ) NoOH
0
0
II
0
1
I
H,CO-C-CH-NH-CH-C-NH-CH-C-OR3
ll
0
0
I/
II
0
II
HO-C-CH-NH-CH-C-NH-CH-C-OH
5
2) CF3COOH
I
I
I
R2
NH,
6
Scheme I . Synthesis of N-( I-carboxy-5-aminopenty1)dipeptides
6. Bzl = benzyl, Boc=butoxycarbonyl. a , R ' = H ; b, R'=CH,.
The synthesis of the N-( I-carboxy-5-aminopenty1)dipeptides 6 is outlined in Scheme 1. For the synthesis of the
glycyl derivatives 6a and the L-alanyl derivatives 6b, benzyl glycolate l a and benzyl D-laCtate l b were allowed to
react with trifluoromethanesulfonic acid anhydride/pyridine to give 2a and 2b, respectively. The low stability of the
ester 2a necessitated careful reaction with two equivalents
of N"-Boc-~-lysinemethyl ester, whereupon one equivalent
served as base for buffering of the liberated trifluoromethanesulfonic acid. In contrast, for the reaction of the ester
2b, equimolar amounts of N"-Boc-L-lysine methyl ester
could be employed, with triethylamine as base. The benzyl
group was removed from the products 3 by catalytic hydrogenation; subsequent condensation of 4 with amino
acid esters by the propylphosphonic anhydride methodl'l
furnished the protected dipeptide derivatives 5. Hydrolysis of the esters with sodium hydroxide and cleavage of the
Boc group with trifluoroacetic acid then afforded the active ACE inhibitors 6 (Table 1).
Investigation of the inhibition of ACE by the compounds 6 showed that the
values vary over a range
from 5500 nmol/L for the weakest inhibitor, 6al, to 10
nmol/l for the strongest inhibitor, N-( I-carboxy-5-aminopentyl)-~-alanyl-~-alanine,
6b2 (Table 1).
The inhibitors were coupled to a Sepharose 6B matrix
(Pharmacia, Freiburg) according to the carbodiimide
method15'via a spacer, which was synthesized from 1,4-bis
0 VCH Verlag.~gesellscha~
mbH. 0-6940 Weinheim, 1986
0570-0833/86/0303-0277 $ 02.50/0
277
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