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New Method of Polypeptide Synthesis.

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an excess of concentrated sulfuric acid they yield the corresponding perfluoroalkanesulfinic acids. For CF,S( O)OH,
the 'H-NMR and 19F-NMR spectra provided the following data : 6, = - 11.0 ppm (singlet, external standard
(CH,),Si), 6, = 78.0 ppm (singlet, external standard CFCI,).
The most striking difference from the already well-known
perfluoroalkanesulfonic acids"] is in the IR spectra : on
comparing the spectra, the expected absence of an asymmetric (S=O) stretching vibration12' is observed in the
case of sulfinic acids. The spectrum of CF,S(O)OH shows
bands at 2900 (vs),2450 (s),1700 (s),1185 (vs)with shoulder
at 1160,1095 (vs), 850 (s), 750 (w), 635 (w), 587 (m), 480 (m),
and 440 (s)cm- The perfluoroalkanesulfinicacids investigated (CF,S(O)OH, b.p. 26-28 "C/O.l torr) could be
characterized by elemental analysis. They are water-clear
liquids that do not react with glass and can be vacuum
distilled without decomposition.
'.
Preparation of n-C4F9S(0)OH
Diethyl ether (1400 ml) and anhydrous hydrazine (22 g) are
transferred to a three-necked flask fitted with KPG stirrer,
dropping funnel, and reflux condenser (with drying tube).
n-C4F9S02F13.41(60 g) is added dropwise to the stirred
mixture at room temperature. A white precipitate is formed
and nitrogen is evolved. The ethereal phase is separated
from the precipitate and evaporated under vacuum. 12 g
of compound (2 b) remains. Concentrated sulfuric acid
(30 ml) is added to (2 b ) (10 g) and the resulting sulfinic
acid is distilled off under vacuum (oil-pump; flask temperature 60°C): b. p. 40-42°C at 0.05 torr; yield: 7.5 g.
Received: June 1,1971 [Z 497 IE]
German version: Angew. Chem. 83,890 (1971)
Publication delayed at author's request
[I] R . N . Haszeldine and J . M . Kidd, J. Chem. SOC.1954,4228; 1955,
2901 ; 7: Gramstad and R . N . Haszeldine, ibid. 1957,2640; J . Burden, I .
Farazmand, M . Stacey, and I: C . Tatlow, ibid. 1957,2514; R . M . Scribner,
J. Org. Chem. 31,3671 (1966).
[2] D. I: Sauer and J . M . Shreeue, Inorg. Chem. 10,358 (1971).
[3] !l Beyl, H . Niederpriim, and P . Voss, Liebigs Ann. Chem. 731, 58
( 1 970).
[4] H. W Roesky, Inorg. Nucl. Chem. Lett. 6, 807 (1970).
A New Route to Dewar-Benzenes
By Robert Weiss and Clemens Schlieifr'l
The thermal rearrangement of bicyclopropenyls ( I ) to
benzene derivatives discovered by Breslow['* is of considerable mechanistic and preparative interest. We have
investigated whether this reaction can be catalyzed by
transition metals.
If a solution of equimolar amounts of ( I ) and AgC104 in
anhydrous acetonitrile is heated to boiling, the occurrence
of the rearrangement ( I ) -(2) -(3) can be established
by 'H-NMR spectroscopy. After one hour's reaction the
singlet of the bridgehead protons of ( I ) at z=7.60 has
been completely replaced by a sharp singlet at r=5.78,
which we assign to the hitherto unknown 2,3,5,6-tetraphenyl-Dewar-benzene (,)I3]. The reaction can also be
followed in an NMR sample tube and proceeds quantitatively within the limits of detection of NMR; in particular,
no evidence is found for the formation of the intermediates
tetraphenylprismane and 1,2,3,4-tetraphenyl-Dewar-benzene assumed by Breslow['!
The class of rearrangements Dewar-benzene-benzene is
known to be catalyzed by transition metals['] ;accordingly,
compound (2) rearranges to (3) under the above conditions. The NMR spectrum indicates that (2) is accompanied
by 25% of (3). This finding also shows that the rearrangement ( I ) -(2) proceeds more rapidly than (2) j ( 3 ) .
(2) could be isolated pure by column chromatography on
basic A120, (yield 45 %) and characterized : 'H-NMR :
z=2.3-2.8(20 H/m);z=5.78(2H/s);UV:hm,,(CH,CN)=
292 nm (logs=4.38). For comparison : cis-stilbene has
h,,,(C,H,OH)=290
nm (10gs=4.0)[~~;
m.p. 156°C (Kofler bench); on melting it is converted into 1,2,4,5-tetraphenylbenzene (3) of m. p. 268 "C (identical with authentic
sample)[71;t1,2 for the thermal rearrangement (2) -+ (3) in
boiling CDCl, = 15.5 h.
Preliminary experiments with various substituted bicyclopropenyls suggest that the new rearrangements is of a
general nature. Mechanistic details are currently under
study.
Received: August 5,1971 [Z 491 IE]
German version: Angew. Chem. 83,887 (1971)
[I] R . Breslow, P. Gal, H . W. Chang, and L. J . Altmann, J. Amer. Chem.
SOC.87, 5139 (1965).
We propose the name "Breslow rearrangement" for this process.
[2] G. L. Closs, Advan. Alicyclic Chem. I , 90 (1966).
[3] These protons appear at r=6.18 [4] in the parent compound; the
additional deshielding in ( 3 ) is probably due to the anisotropic effect
of the flanking phenyl groups.
[4] E. E. van Tamelen and S. P. Pappas, J. Amer. Chem. SOC.85, 3297
(1963).
[ S ] H . Hogeuen and H . C . Volger, Recl. Trav. Chim. Pays-Bas 86, 830
(1967).
161 F. Wessely, H . Bauer, C . Chwala, J . Plaidinger, and R . Schonbeck,
Monatsh. Chem. 79, 596 (1948).
[7] W Dilthey and S . Hurtig, Chem. Ber. 67, 2005 (1934).
New Method of Polypeptide Synthesis
By Manfred Mutter, Hanspaul Hagenmaier, and
Ernst Buyer"'
J
H
(3)
p] Dr. R. Weiss and C. Schlierf
Organisch-chemisches Institut der Universitat
8 Miinchen 2, Karlstrasse 23 (Germany)
Angew. Chem. internat. Edit. / Vol. 10 (1971) 1 No. I1
The use of insoluble, polymeric carriers has simplified
peptide synthesis since the soluble reagents present in
excess can be removed by filtrationtiJ.However, the coupling reactions do not usually proceed quantitatively, thus
giving rise to failure sequences which can be separated
from the final product only with difficulty, if at
Moreover, synthesis on an insoluble carrier permits less
I*]
Dip].-Chem. M. Mutter, Doz. Dr. H. Hagenmaier, and
Prof. Dr. E. Bayer
Lehrstuhl fur Organische Chemie der Universitat
74 Tiibingen, Wilhelmstrasse 33 (Germany)
81 1
freedom regarding choice of solvents, protective groups,
and coupling method than peptide synthesis in solution.
Even the use of solid carriers having ordered surfaces
(“brush carriers”)l4~
’I or uncrosslinked polystyrenesL6-*I
cannot avoid these difficulties entirely.
We have now developed a synthesisin homogeneous phases
which permits a definite and simple separation of reagents
from the growing peptide chain. A solubilizing protective
group is bound to the C-terminal amino acid where it
remains for the duration of the synthesis. Polymeric protective groups can be chosen which make the molecule soluble
in the desired solvents. In practice, polyethylene glycol
residues which can form an ester-type bond with the Cterminal acid have proved particularly effective. The first
amino acid as well as the following ones can be linked in
homogeneous solution.
The decisive second step of the process, the separation of
the low-molecular-weight reagents from the growing peptide chain, which has polymeric character right from the
start owing to the protective group, is carried out by ultrafiltration (membrane filtrati~n)~’].
The synthesis has the following advantages : Synthesis and
removal of excess reagents in a homogeneous phase can
be carried out without the time-consuming separations of
“classical” peptide syntheses and the repeated washings of
the solid phase method; higher yields than when working
in heterogeneous phases ; possibility of removing incomplete sequences after each unsatisfactory coupling step ;
easy assessment of the coupling yield in aliquot amounts
(”F-NMRtxo1and radioactivity measurements especially
suitable); possibility of repeating a coupling step by any
other desired method if yields prove unsatisfactory ; possibility of condensing larger peptides bearing the macromolecular protective group“ ’]; possibility of automation,
including yield monitoring.
The technique will be explained on the basis of two syntheses of the tetrapeptide H-Ile-Ala-Val-Gly-OH.
1. Synthesis with tert-butyloxycarbonyl-protectedamino
acids by rhe anhydride method”]:
Esterification with the soluble carrier: Polyethylene glycol
(M. W. 20000) was used as soluble polymer. Esterification
is carried out with BOC-protected glycine and with I$’carbonyldiimidazole as coupling reagent“ 31.
Synthetic cycle: a) Preparation of the mixed anhydride of
isobutyl chloroformate and the BOC-protected amino acid
with addition of N-methylmorpholine[’21.b) Addition of
a three-fold excess of the mixed anhydride to the amino
component (polymer-peptide).c) After coupling : Removal
of protecting group by 4 N HCI in dioxane. d) Removal of
solvent by distillation and dissolution in water. e) Ultrafiltration to remove excess components and distillation to
remove water.
Conversion test : Aliquots of the reaction mixture are
taken during coupling and analyzed by the ninhydrin
The coupling steps give yields in excess of 98%.
The coupling of alanine to valine, which is possible in yields
of only about 80% by the solid phase method, also gives a
yield of over 95%.
Cleavage from carrier and isolation : The tetrapeptide is
split off in the homogeneous phase by 0.05 N NaOH[’sJ
and isolated by ion-exchange chromatography on Dowex
X-50.
Ultrafiltration: The substance is dissolved in about 50 ml
of water (ca. 2% solution) and diafiltrated[16?The ultra812
filtrate is tested for amino acids with ninhydrin until no
positive reaction occurs. Hitherto, no membranes have
been used that are stable to organic solvents116!
2. Synthesis in aqueous solution with benzyloxycarbonylprotected amino acids and a water-soluble carbodiirnide:
Esterification with polyethylene glycol as described for
the anhydride method.
Synthetic cycle: a) The amino component is dissolved in a
small volume of water and coupled with a Z-protected
amino acid. A water-soluble carbodiimide, N-[2-(cycIohexyliminomethyleneimino)ethyl]-N-methylmorpholinium
p-toluene~ulfonate~‘~~,
is used as coupling reagent. Coupling component and Z-amino acid are used in threefold
excess. b) After coupling, an equal volume of methanol is
added to the aqueous solution and the protective group
removed by hydrogenation (Pd/activated charcoal). c)
Ultrafiltration as well as cleavage and isolation of the
tetrapeptide are carried out as described for the anhydride
method.
The new method combines the advantages of the Merrifield
solid phase synthesis and “classical” peptide synthesis. The
effect of macromolecular C-terminal protecting groups on
solubility and coupling opens up new preparative possibilities extending beyond the bounds of this method.
Received: September 17,1970 [Z 489 IE]
German version: Angew. Chem. 83,883 (1971)
Publication delayed at authors’ request
[I] R. B. Merrijield, J. Amer. Chem. SOC.85,2149 (1963).
[2] E . Buyer, H . Eckstein, K . Hagele, W A. Konig, W Briining, H . Hagenmaier, and W Purr, J. Amer. Chem. Soc. 92, 1735 (1970).
[3] E. Buyer in B. Weinstein: Peptides, Chemistry and Biochemistry.
Dekker, New York 1970, p. 99.
[4] E. Buyer ef al. in E. Scoffone: Peptides 1969. North-Holland Publ.
Comp., Amsterdam, 1971, p. 65.
[S] E . Buyer, G. Jung, I . H Q ~ U S and
Z , H . Sebaestian, Tetrahedron Lett.
1970,4503.
[6] B. Green and L. R. Garson, J. Chem. SOC.1969,401.
[7] M . M . Shemyakin, Yu. A. Ouchinnikou, and A . A . Kiryushkin, Tetrahedron Lett. 1965,2323.
[8] A . A . Kiryushkin, Yu. A. Ouchinnikov, I . V. Kozhevnikova, and
M . M . Shemyakin in: Proc. European 8th Peptide Symp. NorthHolland Publ. Comp., Amsterdam 1967, p. 100.
[9] H . Determann, Arch. Pharm. 303,117 (1970).
[lo] E . Bayer, P . Hunziker, and R. E. Sieuers, Nature 223, 179 (1969).
[I11 K.Schroder and E . Liibke: The Peptides. Vol. 11. Academic Press,
New York 1966.
[12] M . A. Zlak, Tetrahedron Lett. 1970,849.
[13] H . A . Staab, Angew. Chem. 71,194 (1959).
[14] S . Moore, D. H . Spackman, and W H . Stein,Anal. Chem. 30,1185
(1958).
[is] M . A . Zlak and C . S . Hollinden, Tetrahedron Lett. 1968, 1297.
[16] UM-2 filter produced by the AMICON company, mol. wt. limit
IOOO. See: Ultrafiltration with Diaflo Membranes. AMICON N.V.,
Oosterhout, Holland.
[17] D. G. Knorre and 7: N . Shubina, J. Gen. Chem. UdSSR 36, 671
(1966).
(CH3As),S,N,-A Novel
Arsenic-Sulfur-NitrogenHeterocycle
By Otto J . Scherer and Reinhard Wies“’
Formally, 3,7-dimethyl-1,5,2,4,6,8,3,7-dithia(1v)tetrazadiarsocine ( I ) can be visualized as tetrasulfur tetranitride (S4N4)
[‘I
Prof. Dr. 0. J. Scherer and Dip1.-Chem. R. Wies
Universitat Trier-Kaiserslautern and
Institut fur Anorganische Chemie der Universitat
87 Wurzburg, Landwehr (Germany)
Angew. Chem. internat. Edit. J Vol. 10 (1971) J No. I 1
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