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New Route to -[(1E 3E)-dienyl]allenes via Butadiene-tricarbonyliron Complexes.

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ing C,,) is greater here than that observed in the crude
fullerene mixture obtained from the electric arc.171A typical
mass spectrum is shown in Figure 2. This indicates a
fullerene composition (in decreasing amounts) of C,, ( m / z
Experimental Procedure
In the evaporation of graphite in a high-frequency furnace (Huttinger IG 151
400, high-resistance version of a Hartley switch. 15 kW terminal power,
500 kHz) the following parameters were varied: a) graphite quality: purest
graphite (EK 966, Ringsdorff, Bonn), pyrolytic graphite (Ringsdorff, Bonn),
glassy carbon (Sigri, Meitingen); b) shape of the graphite bodies: tubes, cylinders, some slitted or laminated, some with cone-shaped cavities; c) thermal
isolation by one or two additional boron nitride tubes between the graphite
body and the water-cooled glass tube; d) water-cooling and inductor; e) type of
cooling gas (Ar, He) and the pressure of the cooling gas.
These investigations led to the following optimized procedure: The apparatus
(Fig. 1) was evacuated (lo-' hPa) and flushed a number of times and finally
heated in vacuum and then under a stream of inert gas (each heating lasted
20 min). The graphite body was heated quickly (over several min) to 2700 "C
and evaporated at this temperature under a weak helium stream (150 hPa). The
soot deposited on the inside of the PBN insulation tube never contained fullerenes. Most of the soot collected on the wall of the quartz tube and had a large
proportion of fullerene products. This soot was removed from the quartz tube
with a brush. The fullerenes were extracted from the soot with toluene yielding
a deep-red solution. The evaporation of 1 g of graphite in 10 min provided
80-120 mg of crude fullerenes.
New Route to a-[(l E,3E)-dienylJallenesvia
Butadiene-tricarbonylironComplexes* *
By Kurt Nunn, Paul Mosset, RenP Gree,* Rolf u! Saalfrank,*
Karl Peters, and Hans Georg von Schnering
Allenes are readily accessible from propargyl derivatives
through reactions with organocopper(1) reagents."] The
stereochemistry of this transformation results from an SN 2'
process, which usually favors anti-configurated products.[lm* ', 31 Organocopper(1) reagents of the type
[RCuX)M] (X = halogen, M = Li, MgX) are preferable in
this reaction since diorganocuprates [R,Cu)M] are known to
I k * '"I
racemize chiral allene~.[~*
Here, we report on our successful synthesis of acyclic cediThe introduction of
enylallenes 7,starting from complex l.[51
planar chirality by the Fe(CO),-organometallic moiety enables us to verify the stereochemical course of the propargyl-allene transformation, since a partial epimerization of
the allene part would generate two easily distinguishable
diastereoisomeric cc-(al1enylbutadiene)tricarbonylironcomplexes.
with
Reaction of butadienetricarbonyliron complex lfS1
1-lithioalkynes 2 in the presence of lithium bromide (THF,
-78 "C, 3 h) afforded +ex0 and $-endo alcohols 3 and 4L6I
in 73-82 and 10- 18 % yield, respectively, after easy separation by chromatography on silica gel (Scheme 1). Due to the
'",
Received: November 29, 1991 [Z50441E]
German version: Angew. Chem. 1992, 104, 240
R
CAS Registry numbers:
Fullerenes, 99685-96-8; graphite, 7782-42-5; He, 7440-59-7.
1
[l] a) H. W. Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl, R. E. Smalley,
Nature 1985, 318, 162-163; b) R. F. Curl, R. E. Smalley, Science 1988,
242, 1017-1022.
[2] H. W Kroto, Pure Appl. Chem. 1990, 62, 407-415; R. Ettl, J. Chao, F.
Diederich, L. Whetten, Nature 1991,353, 149-153; F. Diederich, R. Ettl,
Y Rnbin, R. L. Whetten, R. Beck, M. Alvarez, S. Anz, D. Sensharma, E
Wudl, K. C. Khemani, A. Koch, Science 1991,252,548-551; D. H. Parker. P. Wurz, K. Chatterjee, K. R. Lykke, J. E. Hunt, M. J. Pellin, J. C.
Hemminger, D. M. Grnen, L. M. Stock, J. Am. Chem. Soc. 1991, f f 3 ,
7499-7503.
[3] J. F. Stoddart, Angek'. Chem. 1991, f03, 71-72; Angen. Chem. Inr. Ed.
Engl. 1991,30,70; H. W. Kroto, A. W. Allaf, S. P. Balm, Chem. Rev. 1991,
91, 1213-1235.
[4] J. S. Miller, Adv. Muter. 1991, 3, 262-265; F. Diederich, R. L. Whetten,
Angen. Chem. 1991,103,695-697; Angew. Chem. Int. Ed. Engl. 1991,30,
678-680.
[5] T. G. Dietz, M. A. Duncan, D. E. Powers, R. E. Smalley, J. Chem. Phys.
1981, 74, 6511-6512; R. E. Haufler, Y. Chai, L. P. F. Chibante, J. Conceicao, C. Jin, L. S. Wang, S. Maruyama, R. E. Smalley, Mater. Res. Soc.
Symp. Proc. 1991,206, 627-637.
[6] J. B. Howard, J. McKinnon, Y Makarovsky, L. Laflleur, M. Elaine Johnson, Nature 1991, 352, 139-141.
[7] W. Kratschmer, K. Fostiropoulos, D. R. Huffman, Chem. Phys. Lett.
1990,170,167-170; W. Krbtschmer, L. D. Lamb, K. Fostiropoulos, D. R.
Huffman, Nature 1990, 347, 354-358; A. S. Koch, K. C. Khemani, F.
Wudl. J. Org. Chem. 1991, 56, 4543-4545.
[8] The temperature could be measured pyrometrically on the graphite surface
until soot formation started. Then the temperature was determined by
extrapolation based on the power data of the generator.
[9] The necessary inert conditions can be best obtained by the use of a watercooled quartz reaction tube, which is connected by a ground metal joint to
a gas-inlet valve and a valve to a vacuum pump. A balance must be made
between the power supplied to the inductor of the H F generator and the
power lost by the cooling water. The heat loss can be reduced substantially
by the use of a single- or double-walled insulation tube made of pyrolytic
boron nitride (PBN) which increases the temperature at the location ofthe
graphite body and reduces the temperature of the quartz surface. An additional effect of the PBN tube is seen in the creation of a larger hot reaction
zone (possible gas-phase deposition of fullerene on soot particles) and in
a chimney effect.
[lo] The mass spectra were recorded with a Concept 1H spectrometer (Kratos,
Manchesterl Ionization method: EI.
224
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VCH Verlugsgesellsehaf~ mhH. W-6940 Weinheim. 1992
Scheme 1. E
= C0,Me.
Reaction at -78 "C for 3 h.
stereoelectronic effects of the Fe(CO), moiety of 3, the
choice of an appropriate nucleofugal group was rather diffcult. Among numerous experiments, treatment of the alcohols 3 with phenyl chloroformate in the presence of pyridine
in THF, and in situr7]reaction of the resulting crude carbonates with six equivalents of (EtCuBr)MgBr . LiBr or (tBuTable 1. Snbstituents R for compounds 2-5 and 7 and the yields of 3-5 and
7.
2-5,7
a
b
C
d
e
R
Yield of 3 [ %]
Yield of 4 [YO]
Yield of 5 [%]
Yield of 7 ["A]
Ph
82
13
81
88
CH,Ph
82
13
nBu
80
12
55 [a]
77
tBu
76
10
23
SiMe,
73
SJI
-
-
15
72
18
[a] The reaction of 3c with (tBuCuBr)MgBr. LiBr furnished 5f in 77% yield.
[bl The reaction of 3e with (tBuCuBr)MgBr . LiBr yielded a complex mixture.
[*I Dr. R. Gree, Dr. P. Mosset
Laboratoire de Chimie Organique Biologique, CNRS URA 1467,ENSCR
Avenue du Gal Leclerc
35 700 Rennes-Beaulieu (France)
Prof. Dr. R. W. Saalfrank, K. Nunn
Institut fur Organische Chemie der Universitat Erlangen-Nurnberg
Henkestrasse 42, W-8520 Erlangen (FRG)
Dr. K. Peters, Prof. Dr. H . 4 . von Schnering
Max-Planck-Institut fur Festkorperforschung,
Heisenbergstrasse 1, W-7000 Stuttgart 80 (FRG).
[**I This work was supported by the Ministere des Affaires Etrangkres
Deutschen Akademischen Austauschdienst (MAEIDAAD) within the
framework of project-oriented promotion of the scientific exchange between France and Germany (PROCOPE). K. N. thanks the Freistaat
Bayern for a study grant.
0570-0833/92/0202-0224$3.50+ ,2510
Angew. Chem. Int. Ed. Engl. 31 (1992) N o . 2
C14
C14
5a-d
021
6
Scheme 2. E = CO,Me. a) CICO,Ph, pyridine, T H E 25°C. 10 min; b)
(EtCuBr)MgBr . LiBr. ether, -65 "C, 15 min; c) (rBuCuBr)MgBr. LiBr.
CuBr)MgBr . LiBr gave the highest yields for the a-(al1enylbutadiene)tricarbonyliron complexes 5 a-c or 5 f (81,
75, 55, and 77%)[*] (Scheme 2). Each of the allenes was
formed as a single isomer as judged by NMR (ds 2 95 %).
Starting from 3a or 4a, respectively, and (EtCuBr)MgBr .
LiBr, the a-allenylbutadienetricarbonyliron complexes 5 a
and 6 are formed (81 and 61 Oh,Scheme 2). Complexes 5a
and 6 are clearly different by NMR. The relative stereochemistry of the allene and organometallic moieties was unequivocally established by X-ray crystallography (Fig. l).[''
These results strongly support a formal 1,3-unti-substitution mechanism for the formation of acyclic allenes from
propargylic esters and organocopper(1) reagents.['"]
Fig. 1. Molecular structures of 5a (left) and 6 (right) in the solid state.
Decomplexation of 5a-c with ceric ammonium nitrate
removed the organometallic moiety to afford the air-sensitive colorless a-dienylallenes 7a-c (Scheme 3). The E,E
stereochemistry of the diene unit was established by 'H
NMR (J2,3 =15.3 Hz, J4,5 =14.8-15.0 Hz). Starting from
enantiomerically pure 5a-c should lead to chiral nonracemic a-dienyallenes 7 a- c provided that the decomplexation step is accomplished without racemization.
E
Scheme 3 . E
= C0,Me.
7a-c
a) 3.5 equiv ceric ammonium nitrate, MeOH, 0°C
To the best of our knowledge, this is the first example
where allenes are obtained in the presence of a butadienetri5a: M.p. = 86°C (light petroleum ether); IR (KBr): a [cm-'1 = 2050, 1995,
carbonyliron organometallic moiety. The excellent reactivity
l970,1935(sh),1705; 'HNMR(400MHz,CDC13):6 =1.17(dd, 1 H , J = 8.2,
of the carbonate leaving group compared to that of acetates
0 . 6 H ~H-C,), 1.21 (t, 3 H , J = 7 . 3 H z , H-Cl,),2.14(ddd, l H , J=lO.O, 8.9,
and benzoates must be emphasized. Furthermore, these a-dil.OHz, H-Cs), 2.47 (dqd, 1 H, J=15.7, 7.3, 3.5Hz, H-C,), 2.55 (dqd, 1 H,
J=15.7,7.3,3.SHz,H-C9),3.66(s,3H,OCH,),5.42(ddd,1H,J=8.9,5.2,enylallenes may be good substrates for sigmatropic rear0.6 Hz, H-C,), 5.66 (dt, 1 H, J =10.0, 3.5 Hz,H-C,), 5.84 (ddd, 1 H, J = 8.2,
rangements as shown by some studies in the retinoid
5.2. 1.0 Hz, H-C,), 7.21 (ddt. 1 H,para, arom., J = 8.0, 6.0, 1.5 Hz),7.28-7.38
field[''. 1' or provide an entry to natural products["] such as
(m. 4 H arom.); 13C NMR (100 MHz, CDCI,): 6 =12.08 (ClO), 23.10 (C9),
the antibiotic mycomicin['21 and its analogues.
45.38 (C2). 51.68 (OCH,), 60.11 (C5), 83.21, 84.54 (C3, C4), 98.66 (C6),
Table 2. Physical data for 5 a, 6, and 7 a
110.67 (CX), 126.15 (2 arom. CH), 127.14 (para-CH), 128.40 (2 arom. CH),
Experimental Procedure
135.82 (Carom.), 172.61 (C I ) , 206.37 (C7), 209.6 (CO-Fe); UV (MeCN): I,,,
[nm] ( E ) = 255 (41 000), 305 (sh, 9700); MS, EI: mjz of major fragments: 394
5 a : To a solution of LiCuBr, cooled at -65" [6equiv; prepared from lithium
( M e . 10%). 366 (Me-CO, 9), 363 (Me-OMe, 2), 338 (Me-2 CO, OS), 310
bromide (410 mg, 4.7 mmol) and cuprous bromide (680 mg, 4.7 mmol)] in THF
( M e - 3 CO. loo), 278 (19), 250 (59), 236 (26), 165 (40), 115 (24). 91 (21), 56 (55).
(10 mL) was added an solution (8 mL) of ethylmagnesium bromide in ether
6: M.p. 72°C (n-pentane); IR (Nujol): ij [cm-']= 2060,2000,1980,1700; 'H
[prepared from magnesium turnings (125 mg, 5.1 mmol) and bromoethane
NMR(400MHz,CDCl3):6=l.115(t,3H,J
=7.3Hz,H-ClO),l.l9(dd,lH,
(0.35 mL, 4.7 mmol)]. After 30 min at -65 "C, a solution of propargylic carJ=8.2,O.XHz,H-C2),2.07(ddd,lH,J=9.6,8.9,l.OHz,H-C5),2.465(dq,bonate was added. This was prepared by sequential addition of pyridine
2H,J=7.3,3.1Hz,H-C9),3.65(~,3H,OCH,),5.43(ddd,lH,J=8.9,5.1,
(0.165 mL, 2.05 mmol, 2.6 equiv) and phenyl chloroformate (0.13 mL,
0.8 Hz, H-C4), 5.67 (dt, 1 H, J = 9.6. 3.1 Hz, H-C6), 5.84 (ddd, 1 H, J = 8.2,
1.01 mmol, 1.3 equiv) to a stirred THF solution ( 5 mL) of propargylic alcohol
5.1, I .O Hz, H-C3), 7.30 (ddt, 1 H,para, arom., J = 8.0,6.0, 1.5 Hz), 7.30-7.48
3a (300 mg, 0.78 mmol) followed by 10min reaction at room temperature.
(m, 4 H arom.); "C NMR (100 MHz, CDC1,): 6 = 12.72 (C lo), 22.96 (C9),
After 15min reaction at -65°C between the carbonate and (EtCu45.47 (C2). 51.71 (OCH,), 59.86 (C5), 83.25, 84.28 (C3, C4), 98.19 (C6),
Br)MgBr LiBr, the reaction mixture was poured onto 25 ?4aqueous ammoni110.76 (C8). 126.18 (2 arom. CH), 127.18 (para, CH), 128.52 (2 arom. CH),
um chloride (100 mL) containing sodium cyanide (3 g). The resulting mixture
was extracted twice with ether, and the combined organic extracts were dried
135.70 (C arom.), 172.66 (C 1). 206.32 (C7); MS, EI, the same main fragments
as those for 5 a with very similar relative intensities.
with MgSO, and concentrated. Flash-chromatography of the remaining oily
residue on silica gel (45 g) with ether/petroleum ether (1:19) as eluent afforded
7 a : M.p. 74 'C (ether/petroleum ether 4: 1); IR (Nujol): 5 [cm- '1 = 1925, 1715,
the allene 5a as an orange oil which solidified on cooling.
1620; 'HNMR(400MHz,CDCI3):S =1.14(t,3H,J=7.3Hz,H-C10),2.49
(dqd,lH,J=15.5,7.3,3.3H~,H-C9),2.52(dqd,lH,J=15.5,7.3,3.3Hz, 7 a : To a solution of complex 5a (93 mg, 0.24 mmol) cooled to O'C in anhyH-C9),3.74(~,3H,OCH,),5.875(d,2H,J=15.3H~,H-C2),6,32(dt,lH,
drous methanol ( 5 mL) was added portionswise over 15 min ceric ammonium
J=10.5. 3.3 Hz, H-C6),6.36(dd, 1 H, J=14.8, 11.0Hz,H-C4), 6.48(dd, 1 H,
nitrate (448 mg, 0.82 mmol, 3.5 equiv). After stirring for a further 10 minutes
J=14.8. 10.5H2, H-C5). 7.22 (ddt, 1 H, para, arom., J=7.5, 6.6, 1.4Hz),
at 0 "C, the reaction mixture was diluted with ether and water. The aqueous
7.28-7.40 (m, 4 H arom. and H-C3, dd, 6 =7.325, J = l S . 3 , 11.0Hz); I3C
phase was extracted with ether and combined organic extracts were washed
NMR (100 MHz, CDCI,): 6 =12.48 (CIO), 23.10 (C9). 51.50 (OCH,), 98.16
with brine. Drying (MgSO3, concentration, and flash-chromatography of the
119.96 (C4), 126.23(2arom. CH), 127.23 (para, CH), 128.51
(C6), 109.85 (CS),
remaining residue with etherlpetroleum ether (1:9 and then 1:4) as eluents
(2 arom. CH), 128.61 (C2), 135.60 (Carom.), 137.14 (C5), 144.46 (C3), 167.53
yielded 7a (53 mg, 88 %) as a white solid which gradually turned yellow upon
(Cl). 211.14(C7); UV(MeCN): A,,,[nm](&) = 255(11000),300(49000);MS,
exposure to air.
El: m / z of major fragments: 254 ( M e , 65%) 239 (Me-Me, 6), 225 (Me-Et, 9),
The physical data of compounds 5a, 6, and 7 a are listed in Table 2.
223 (M@-OMe.16). 207 (19). 195 (81). 179 (62), 165 (IOO), 117 (62), 91 (95),77
Received: July 5, 1991 [Z 4772 IE]
(28).
German version: Angew. Chem. 1992, 104. 228
Angeh. Chem. In!. Ed. Engl. 31 (1992) No. 2
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Verlag~gesellschaftmbH, W-6940 Weinheim, 1992
0570-0833/92j0202-0225$3.50+.2S/O
225
[I] a) P. Ortiz de Montellano, J. Chem. Sac. Chem. Commun. 1973, 709; b)
P. Vermeer, J. Meijer, C. De Gra d, H. Schreurs. Rec. Fav. Chim. PaysBas 1974, 93, 46; c) A. Alexakis, J. F. Normant, J. Viliieras. J. Molecular
Catalysis 1975/1976, 1, 43; d) G. Tadema, P. Vermeer, J. Meijer, L.
Brandsma, Rec. Trav. Chim. Pays-Bas 1976, 95, 66; e) A. Alexakis, A.
Commercon, J. Villieras. J. F. Normant, Tefrahedron Lett. 1976, 2313; f )
The Cltemislry o f ' A l h e s , Vol. 1-3, (Ed.: S. R. Landor), Academic, London, 1982; g) A. C. Oehlshlager, E. Cryzewska, Tetrohedron Lett. 1983,
24, 5587; h) H. F. Schuster, G. M. Coppola: ANenes in Organic Synthesis,
Wiley, New York, 1984, i) C. Sahlberg, A. Claesson. J. Org. Chem. 1984,
49. 4120, and references cited therein; j) T. C. Norman, A. R. de Lara,
W. H. Okamura, Tetrahedron Lett. 1988,29,1251; k) C. J. Elsevier, P. Vermeer. J. Org. Chem. 1989,54, 3726, and references cited therein; 1) K. M.
Wu, M. M. Midland, W. H. Okamura, ibid. 1990,55, 4381, and references
cited therein; m) A. Alexakis. I. Marek. P. Mangeney, J. F. Normant, J.
Am. Chem. SOC.
1990, 112, 8042; n) 0. W. Gooding. C. C. Beard, D. Y
Jackson, D. L. Wren, G. F. Cooper, J. Org. Chem. 1991, 56. 1083, and
referencescited therein; o) A. Alexakis, I. Marek, P. Mangeney, J. F. Normant, Tetrahedron 1991, 47. 1677.
C. J. Elsevier, J. Meijer. H. Westmijre, P. Vermeer. L. A. van Dijck, J.
Chem. Sac. Chem. Commun. 1982, 84.
For examples where both syn and anti processes occur see [Im,o].
A. Claesson, L.-I. Olsson, J. Chem. Sac. Chem. Commun. 1979, 524.
Although we worked with racemic compounds, all the representations are
made for clarity as if this study was performed starting with (R&I.
Furthermore, the complex 1 can he easily resolved, see A. Monpert,
J. Martelli, R. G r k , R. Carrie, Tetrahedron Lett. 1981, 22, 1961.
For this terminology see N. A. Clinton, C. P. Lillya, J. Am. Chem. Soc.
1970,92, 3058.
The intermediate carbonates could not he isolated since they were quickly
oxidized by air contact and had therefore to be used in situ.
A limitation of this reaction was observed since 5d was obtained in 23%
yield and was moreover the only allenic compound of this study which was
not enough pure for microanalysis. The reaction of 3 e with (EtCuBr)MgBr . LiBr yielded a complex mixture.
Crystal data for 5a: monoclinic. space group: P2,/c,a = 9.495(4),
6 = 18.705(7), c = 11.262(3) A,
= 107.70(3)', M = 394.21, V =
~ , radiation. 4795 measured
1906.(1) A3,Z = 4, P.,,,~ = 1.347 g ~ m - Mo,.
reflections, 4405 unique reflections, 3745 reflections with F > 3 a ( F ) . Fullmatrix least-squares refinement gave R = 0.042, R, = 0.040. Crystal data
for 6a: orthorhombic, space group: Pna2,, a =19.610(5), h =
1 3 . 5 6 6 ( 6 ) , ~ = 1 4 . 7 7 7 ( 6 ) A , M = 3 9 4 . 2 1V, = 3 9 3 1 . ( 3 ) A 3 , Z = 8 . ~ I s , L d =
1.332 gcm-'. Mo,, radiation. 5062 measured reflections, 4721 unique reflections, 3774 reflections with F > 3 u ( F ) . Full-matrix least-squares refinement gave R = 0.048, R , = 0.042. Program used: Siemens SHELXTL
PLUS (Micro Vax 11). Further details may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fiir wissenschaftlich-technische Information mbH, W-7514 Eggenstein-Leopoldshafen 2 (FRG). on
quoting the depository number CSD-55 335, the names of the authors, and
the journal citation.
[lo] a) J. Sueiras, W. H. Okamura, J. Am. Chem. Soc. 1980, f02, 6255: h)
W. H. Okamura, M. L. Curtin, Synlert 1990,l and references cited therein.
I
Chem. Res. 1981, (M) 2869; (S) 244.
[I11 G. Balme, M. Malacria, J. Gore, .
[I21 W. D. Celmer. I. A. Solomons, J. Am. Chem. Soc. 1952 74, 1870, 2245,
3838; ihid. 1953, 75, 1372, 3430. For a clinical use of mycomycin, see
F. Fraschini et al. Drugs E.up. Clin. Res. 1988, 14, 253.
Ion-Spray Mass Spectrometry of Lipopeptide
Vaccines **
By Jorg W Metzger, Werner Beck, and Giinther Jung*
Dedicated to Professor Michael Hanack on the occasion
of his 60th birthday
Ion spray (IS) is a soft ionization method in which a solution of the analyte is sprayed with compressed air through a
capillary that is held at several kilovolts.['] The high electric
field and nebulization causes the formation of highly
[*] Prof. Dr. G. Jung, Dr. J. W. Metzger, Dipl. Chem. W. Beck
Institut fiir Organische Chemie der Universitit
[**I
226
Auf der Morgenstelle 18, D-W-7400 Tubingen (FRG).
This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 323).
0 VCH
Vcrlagsgesellschajt mhH, W-6940 Weinheim. 1992
charged droplets from which predissolved ions are emitted
directly into the gas phase. Two models for the mechanism of
ion production from charged droplets are at present under
discussion : ion evaporation['] and Rayleigh disintegrat i ~ n . [The
~ ] pneumatic nebulization assists droplet formation
effecting a more stable ion current and therefore allows
higher flow rates"] than the closely related electr~spray[~l
technique. IS ionization takes place at atmospheric pressure
(atmospheric pressure ionization mass spectrometry, APIMS). After ejection from the liquid the ions are sampled
through a small orifice into the mass spectrometer. As no
heat is applied, ion spray mass spectrometry ( I S M S ) provides a highly sensitive method for molecular mass determination of thermolabile molecules like peptides and
proteins.[*]
For routine analysis of a polypeptide or a protein the
sample is dissolved and continuously introduced into the IS
source at flow rates up to 200 pLmin- '.Sensitivity increases
with decreasing flow rate. IS mass spectra of peptides or a
protein consist of a series of peaks arising from singly and
multiply charged, protonated molecular ions [ M + nH]"+.
For most peptides and proteins the multiplicity is related to
the number of basic lysine, arginine, and histidine residues in
addition to the N-terminal a-amino group.[', Each peak in
the spectrum constitutes an independent measure of the mass
of the parent species; from each pair of adjacent peaks the
molecular mass can be calculated.['I Therefore mass assignment can be made with greater precision and more confidence than is possible with singly charged ions. The effective
mass range of any analyzer is increased by a factor equal to
the number of charges on an ion. This opens the intriguing
possibility to determine molecular masses of biomolecules in
the kD range with quadrupole analyzers.
The increasing importance of synthetic lipopeptide vaccines for immunological screening['] and the lack of a simple
and reliable routine method for the characterization of these
compounds were the reasons for this study. The synthetic
vaccines investigated consist of the three-chain lipoamino
acid N-palmitoyl-S-[2,3-bis(palmitoyloxy)-propyl]-(R)-cysteine (tripalmitoyl-S-glycerylcysteine,
Pam,Cys-OH ; molecular mass 910.5 u)['l and selected partial sequences (B- and
T-cell epitopes containing 15-25 amino acids) of viral
proteins.['' We found IS-MS to be an extremely valuable
tool for characterizing these compounds and their precursors. As common aqueous solvent mixtures cannot be used
for the analysis of these highly lipophilic, water-insoluble
compounds, we evaluated the possibility of using organic
solvent mixtures for IS-MS.[''] Smaller lipopeptides of this
kind, for example, the amphiphilic lipohexapeptide
Pam,Cys-Ser-(Lys),["I or related lipoids["I we could analyze by field-desorption mass spectrometry and plasma desorption mass spectrometry. Matrix-assisted laser desorpt i ~ n [ ' has
~ ] also be proven to be a powerful method for the
mass determination of large lipophilic compounds.
Lipopeptide vaccines"] are usually built up by solid-phase
peptide synthesis (Merrifield synthesis). The lipoamino acid
Pam,Cys-OH is attached to the antigenic determinant either
N-terminally in the last coupling step"' or C-terminally
beginning the synthesis with Pam,Cys-Lys(Fmoc)-OH
(Fmoc = 9-fluorenylmethoxycarbonyl) as a resin-bound
building block.[141A third possibility is to introduce 0,O'dipalmitoyl-S-glyceryl-cysteinewithin a peptide chain using
an N,-Fmoc protected derivative." Thus, the partial sequence 135-154 of 0 , K foot-and-mouth disease virus
VP 1 ['I, an icosapeptide, was built up on an acid-labile resin
using FmocltBu strategy. This epitope contains three
arginine residues, which were introduced by using Fmoc-Ar-
0570-0833i92i0202-0226 S 3.50+ .25/0
Angew. Chem. Int. Ed. Engl. 31 (1992) No. 2
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tricarbonyliron, allenes, dienyl, complexes, new, via, route, butadiene
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