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Cyclopentadienyl Cobalt Complexes of Cobalta-pentalenes Products Formed by Reaction of (-Cyclopentadienylidene) Cobalt Complexes with Silylalkynes.

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obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft for
wissenschaftlich-technischeInformation mbH, D-W-7514 EggensteinLeopoldshafen 2 (FRG) on quoting the depository number CSD-56023,
the names of the authors, and the journal citation.
[13] R. Appel in 11 c], p. 160.
[14] 0. Wagner, G. Maas, M. Regitz, Angew. Chem. 1987, 99, 1328-1330;
Angew. Chem. Int. Ed. Engl. 1987,26, 1257-1259.
[15] E. Niecke, R. Streubel, M. Nieger, D. Stalke, Angew. Chem. 1989, 101,
1708-1710; Angew. Chem. Int. Ed. Engl. 1989, 28, 1673-1675.
1161 See for example M. Regitz. Chem. Rev. 1990, 90,191-213.
[17] Isolable compounds of the type 7 are known in carbon chemistry. They are
formed from the cyclodimerization of hut-2-yne with aluminum halides (P.
B. J. Driessen, H. Hogeveen, 1 Organomel. Chem. 1978, 156, 265-278) or
by oxidative ring opening of tetra-terl-butyltetrahedrane (G. Maier, R.
Emrich. K:D. Malsch, K.-A. Schneider, M. Nixdorf, H. Imgartinger,
Chem. Ber. 1985,118,2798-2810); in the latter case they have the character of homocyclopropenylium ions.
[18] F. Mathey, Chem. Rev. 1990, 90,997-1025.
E (zwitteri~n).[~]
With alkynes they do not react by insertion
of the alkyne into the c02-c1 bond,
c _
c 0-
l a , R' =H
l b , R' =Me
1c, R'S=Me,Et
Turquoise l a decomposes in the presence of but-2-yne,
hex-3-yne, bis(tert-butyl)acetylene, diphenylacetylene, or
bis(benzo-l,2-dioxaborolyl)acetylene at temperatures above
50 "C after a short time to form dark products that could not
be characterized. Bis(trimethylsi1yl)acetylene 2 a, on the other hand, reacts readily with the complexes 1 at 45 "C in a very
unusual reaction to form the binuclear complexes 4 with a
cobaltabicyclic ring system as ligand (Scheme 1). With
Cyclopentadienyl Cobalt Complexes of Cobaltapentalenes: Products Formed by Reaction
of (pCyclopentadienylidene) Cobalt Complexes
with Silylalkynes**
By Hubert Wadepohl,* Wolfgang Galm, Hans Pritzkow,
and Andreas Wolf
Dedicated to Professor Wolfgang Beck
on the occasion of his 60th birthday
Coupling reactions of metal-carbene complexes with alkynes are very important in chemical syntheses.['] Depending on the isolobal character of the relevant metal fragment,
metallacyclobutenes A or y3-vinylcarbene complexes B are
postulated as intermediates in these mechanistically still
largely unexplained reactions.['] In the Dotz reactiont3](that
is, the reaction of certain Fischer carbenes with alkynes) B or
an $-vinylcarbene complex C derived from the latter is carbonylated by a CO ligand. The resulting vinylketene complex can then react further, depending on the starting materials and the reaction conditions, to form one of numerous
possible types of products. Carbene complexes of the
Schrock type react with alkynes-with the insertion of the
alkynes into the M = C bonds-only as far as stage C.[41
c 0'
4- 7
Scheme 1. 2 a , R '= SiMe,;2b,R2 = SiEt,;2c,Rz =SiMe2tBu;3,R2= IBU;
4a, R' = H, R2 = R3 = SiMe,; 4b, R' = Me, R' = R3 = SiMe,; 4c, R: =
Me,Et, R' = R3 = SiMe,; 5a, R' = H, R' = SiEt,, R3 = SiMe,; Sa', R' =
H, R2 = SiMe,, R3 = SiEt,; 6a, R' = H, R2 = SiMe,rBu, R3 = SiMe,; 6a',
R' = H, R' = SiMe,, R3 = SiMe,tBu; 7a, R' = H, R' = rBu, R3 = SiMe,.
The p-cyclopentadienylidene dicobalt complexes 1 can be
described by the limiting structures D (carbene complex) and
Priv.-Doz. Dr. H. Wadepohl,'+' Dr. W. Galm, Dr. H. Pritzkow,
Dipl.-Chem. A. Wolf
Anorganisches Chemisches Institut der Universitat
Im Neuenheimer Feld 270, D-W-6900 Heidelberg (FRG)
['I Current address:
University of Oxford, Inorganic Chemistry Laboratory
South Parks Road, Oxford OX1 3QR (UK)
[**I This work was supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 247 of the Universitiit Heidelberg) and by the Fonds
der Chemischen Industrie.
Verlugsgesellsrhajt mbH. W-6940 Weinheim, 1992
bis(triethylsilyl)acetylene, 1 a does not react under similar
conditions; decomposition occurs above 60 "C.The unsymmetrically substituted bis(sily1)alkynes2 b, c react with 1 a to
give nonseparable mixtures of the stereoisomers Sa, 5a' and
6a, 6a', respectively. In both cases smaller amounts of the
complex 4 a with two trimethylsilyl groups in the cobaltabicyclic system are also formed. Only the product 7 a with the
trimethylsilyl group on the cobalt atom is obtained regioselectively from 1 a and 3.
The constitution of the novel blue-violet binuclear complexes 4-7 can be derived from the NMR spectra.[61The
singlet resonance signals displaced far downfield (6 = 9.911.l) for the metal-enyl hydrogen atom 7-H as well as the
broadened downfield "Si NMR signals (6 z 30-40) of the
silyl groups on the cobalt atoms are especially characteristic.
13CNMR signals for the quaternary carbon atoms C1
bound to the cobalt atom are not observed at all. The "car-
0570-0833~92/0808-1058$3.50+ .25/0
Angew. Chem. Int. Ed. Engl. 1992, 31, N o . 8
bene" carbon atoms are not detectable in the starting materials 1 either.I5.']
The complexes 4-7 can be described by limiting structures
such as F with y4-bonding of the metallabicyclic ring system
to the CpCo' group (Cp = y15-C,H,) as well as by zwitterionic formulations such as G . In the latter case the bicyclic
system should be $-coordinated to the [CpCo]' group. A
charge separation such as in G then appears to be energetically favorable if at the same time partial structures that
resemble the cobaltocenium cation are possible. This becomes clear, for example, in 1 (limiting structures D-E)
and the mononuclear complexes [(C,R,)Co(acenaphthyIene)] (8, R = H, Me),[*]both of which should be formulated
Fig. 1. Molecular structure of 4c. Hydrogen atoms of the Cp, CH,, and C,H,
groups are not shown. Selected bond lengths [A] and angles ["I with standard
deviations given in parentheses: Col-Cl 2.206(6), Col-C2 2.106(6), Col-C3
2.007(7), Col-C4 1.981(7), Col-C5 2.049(6), Co2-Sil 2.281(2), Co2-Cl
1.883(6), CO2-C7 1.877(7), C1-C2 1.462(8), C1-C5 1.433(8), C2-C3 1.410(9),
C2-C6 1.459(8), C3-C4 1.428(10), C4-C5 1.410(10), C6-C7 1.379(9); C5-Cl-C2
105.0(5), CZ-Cl-Co2 114.7(4), Cl-C2-C3 109.1(5), Cl-C2-C6 113.6(5), C2-C3C4 107.9(6), C3-C4-C5 107.9(6), Cl-C5-C4 109.9(6), Cl-C02-C7 81.9(3), C02C7-C6 122.0(5), C2-C6-C7 107.7(5),C5-Cl-Co2 140.2(5).
with considerable zwitterionic contributions. 4-7 are related
to xcomplexes of pentalene (H) on the one hand and to
TC complexes of dihydropentalenyl (I) on the other by the
isolobal series CpCoR e+ d7-ML,
CH and [CpCH, respectively. To our knowlCoR]- tir)d8-ML,
edge, at the present time only the latter are known, however,
they have q5-dihydropentalenyl ligands.["
Insight into the bonding is provided by an X-ray structural
analysis of 4c.['01The carbacyclic five-membered ring of the
cobaltapentalene ligand is bonded through all five carbon
atoms to the [($-C,Me,Et)Co] fragment (Fig. 1). The bond
between Col and C1, which is slightly displaced (0.07 A) from
the C2-C3-C4-C5 plane, is, at 2.206(6) A, longer than the
bonds between Col and the carbon atoms C2-C5. This
indicates a transition to the q4-coordination, as is also found
for the cyclopentadienylidene ligand in the binuclear complexes of type 1 (d(Co1 -Cl) = 2.186(6) (1 a["]), 2.204(5) A
(lb1"I), d(Col-C2 to C4) =1.98-2.04 and 1.99-2.06 A
(I b). It is striking that, in the planar CoC, five-membered
ring, both of the endocyclic Co-C bonds starting from C02
are very short and almost equal in length (1.88 A). This value
is comparable to the bond lengths Co2-C1 in 1 ( l a :
3.866(6) A,[111
l b : 1.872(5)
The length of formal CoC(sp2) single bonds, for example in the cobaltacyclopentadienes (cobaltoles) [ (11-C,H,R)(PPh,)Co(C,H,)]
(R = H,
COOMe),1'21 lies between 1.93 and 1.95 A. The C6-C7
bond is shorter than the remaining C-C bonds in the cobaltapentaiene. Overall, the structural data indicate that several
limiting structures such as F and G have to be taken into
account in a qualitative description of the bonding in the
dicobalt complexes 4-7.
Compared to the extremely air- and moisture-sensitive
starting compounds 1, 4-7 are much less reactive. They are
Angew. Chem. Int. Ed. Engl. 1992, 31, No. 8
0 VCH Verkugsgesekhafi mbH,
only moderately air-sensitive, can be chromatographed on
silica gel, and can be distilled or sublimed without decomposition under vacuum (oil pump) at about 100 "C. They do not
react with CO, even under pressure (30 bar, room temperature). The high stability of the cobaltabicyclic system is also
shown by the fact that hydrogenation of the formal C6-C7
double bond over a PdjC catalyst is not possible (1 bar H,,
room temperature).
The mechanism of formation of 4-7 can only be surmised
at the present time. We believe that oxidative addition of the
silylalkyne to the electron-rich C02 in 1 is probably one of
the first reaction steps.['31The o-alkynyl group that is thus
formed could attack the cyclopentadienylidene ligand at C2,
from which a [1,3] hydride shift to the enylic position (C7)
would be possible.
1 b : A solution of [Cp*Co(cyclopentadiene)](580 mg, 2.33 mmol) [14] and [CpCo(C,H,),] (440 mg, 2.44 mmol) [15] in petroleum ether (ca. 40 mL) was transferred to a 250 mL reaction flask, a slight vacuum was applied, and the solution
was left to stand at room temperature. The flask was flushed daily with argon
and slightly re-evacuated. After four days the deep-green reaction solution was
decanted off from the crude product which was recrystallized from toluene at
-20 "C. Yield 230 mg (25%) of dark-green 1b. M.p. 152 T ; correct C,H analysis.
'HNMR (200 MHz, [D,]toluene) 6 =1.2 (m. 2H, C,H,), 1.40 (s, 15H, Cp*),
3.0 (m. 2H, C,H,), 3.49 (br.s, 2H, CH), 3.85 ("t", 2H, CH), 4.67 (s, SH, Cp);
13C{'H} NMR (50 MHz, [D,]toluene, assignment by J-modulation test)
6 = 9.8 (C,Me,), 31.7 (C,H,), 79.4 (CH), 84.0 (Cp), 85.4 (CH), 90.7 (C,Me,);
MS (EI, 70 ev) m/z 382 (10 [ M - C2H4]+),260 (16, [Cp*Co(C,H,)]+), 259
(100, [Cp*CoCp]+),258 (23, [Cp*Co(C,H,)]+), 189 (18, [Cp2Co]+),133 (8,
[Cpi-2H]+), 124 (18, [CPCO]'), 59 (6, CO').
l c : Preparation from [(C,Me,Et)Co(cyclopentadiene)] [14] and [CpCo(C,H,),] analogous to 1b (yield 55 %).
4 a : A solution of l a (400 mg, 1.2 mmol) and t a (200 mg, 1.2 mmol) in toluene
(20 mL) was heated in a slight vacuum for three hours at 45 "C. After the
reaction solution was concentrated by evaporation to about 5 mL, the solution
was chromatographed on silica gel (eluent toluene). After the solvent was removed from the violet eluate, 440 mg (78% yield) of solid 3a was isolated.
Correct C,H analysis; MS (EL 70eV) m/r 482 (32, M t ) , 409 (8,
[ M - SiMe,]'), 285 (42, [ M - SiMe, - CpCo]'), 189 (42, [Cp,Co]+), 124 (12,
[CpCo]'), 73 (30, [SiMe,]').
4b: is obtained in a similar manner to 4a, from 1 b and 2 a (yield 69%).
4c: A solution of 1 c (650 mg, 1.5 mmol) and 2a (280 mg, 1.6 mmol) in toluene
(40 mL) was heated in a slight vacuum for five hours at 60 "C. After the reaction
mixture was concentrated to 5 mL by evaporation, the solution was chromatographed twice on silica gel (eluent toluene). After the solvent was removed
W-6940 Weinheim. 1992
0570-0833/92/080S-1059$'3.50+ ,2510
from the violet eluate, 680mg (80% yield) of pure 3c was obtained and was
recrystallized from cyclopentane at -78 "C; yield 590 mg (69%); m.p. 124126°C. correct C,H analysis; MS (EI, 70eV) miz 566 (46, M ' ) , 493 (14,
[ M - SiMe,]+), 442 (13, [ M - CoCp]'), 369 (100, [M - CoCp - SiMe,]'),
273 (19, [(C,Me,Et)CoCplt).
5a,5a' (mixture of isomers): obtained similarly to 4a,from 1 a and 2b;yield
68% (mixture of 5a,5a' and a small amount of 4a).
6a,6a' (mixture of isomers): obtained similarly to 4% from la and 2c: yield
82% (mixture of 6a,6a' and a small amount of 4a).
7a:obtained similarly to 4a from la and 3 (yield 83%)
[ I 4 H. Yamazaki, Y Wakatsuki, J. Organornet. Chem. 1984,272,251-263.
[I31 The substitution of the ethylene ligand in 1 can take place dissociatively or
associatively. An q2-alkynecomplex would be a possible, but not a necessary intermediate stage. With Me,SnC,SnMe, as ligand there is evidence
for such a complex. However, with this alkyne 1 does not react to form a
complex of the type 4 (A. Wolf, Diplomarbeit, Universitat Heidelberg,
[I41 W. Galm, Dissertation, Universitat Heidelberg, 1990.
[15] K. Jonas, C. Kriiger, Angew. Chem. 1980,92,513-531;Angew. Chem. I n f .
Ed. Engl. 1980,19,520;K. Jonas, E.Deffense, D. Habermann, ibid. 1983,
95. 729 and 1983,22,716; Angew. Chem. Suppl. 1983,1005-1016.
Received: February 13, 1992 [Z 5187 IE]
German version: Angew. Chem. 1992, 104,1050
CAS Registry numbers:
la, 106250-11-7; 1 b. 141982-09-4;lc, 141982-10-7;Za,14630-40-1;Zb,2318397-3; 2c, 107474-01-1; 3, 14630-42-3; 421, 141982-11-8; 4b, 141982-12-9; 4c,
141982-18-5;5a, 141982-13-0;Sa', 141982-14-1 ; 6a, 141982-15-2;6a'. 14198216-3; 7a, 141982-17-4; C,Me,CoC,H,, 141982-19-6; C,Me,EtCoC,H,,
141982-20-9; C,H,Co(C,H,),, 69393-67-5.
[I] J. P. Collman, L. S. Hegedus, J. R. Norton, R. G. Finke, Principles and
Applications of Organotransition Metal Chemistry, University Science
Books, Mill Valley, 1987,chap. 16.
121 P. Hofmann, M. Hammerle, Angew. Chem. 1989,101, 940-942; Angew.
Chem. fnl. Ed. Engl. 1989,28,908, and references cited therein.
[3] K. H. Dotz, Angew. Chem. 1975,87, 672-673; Angew. Chem. f n t . Ed.
Engl. 1975, i4,644; ibid. 1984,96,573-594 and 1984,23,587.
[4] R. R. Schrock, Acc. Chem. Res. 1979,12,98-104.
[5] H. Wadepohl, H. Pritzkow, Angew. Chem. 1987,99, 132-134; Angew.
Chem. Int. Ed. Engl. 1987,26, 127.
[6] ' H N M R (200 MHz, C,D,) 4% 6 = 0.09 (s, 9H, SiMe,), 0.35 (s, 9H,
SiMe,), 4.26 (t. 1H, CH), 4.33 (5, 5H, Cp(Col)), 4.62 (dd, 1H, CH), 4.78
Synthesis of (2-Arylindol-3-y1)acetamides
as Probes of Mitochondria1 Steroidogenesis-A New
Mechanism for GABA, Receptor Modulation""
By Alan P. Kozikowski,* Dawei Ma, Elena Romeo,
James Auta, Vissilios Papadopoulos, Guliu Puiu,
Erminio Costa, and Alessandro Guidotti
Binding studies,''] molecular biological studies,['' and
steroid biosynthesis studiesr3'have revealed the presence in
the central nervous system (CNS) of a structurally and functionally distinct class of benzodiazepine binding sites located
on the outer mitochondrial surface. These receptors bind
benzodiazepines and non-benzodiazepine derivatives such as
imidazopyridines (Alpidem) and other ligands including the
peptide DBI. This peptide is present in the pe(dd,lH,CH),4.85(~,5H,Cp(C02)),11.00(~,1H,CH);4b:6=0.ll(~,
9H,SiMe,),0.38(s,9H,SiMe,),1.42(s,15H,Me),3.91(t,1H,CH),4.18ripheral and CNS cells that contain this mitochondrial rec e p t ~ r [ ~it ]binds
with high affinity (lo-' M) and stimulates
(d, 1 H, CH). 4.36 (dd, 1 H, CH), 4.93 (s, 5H, Cp), 10.95 (s, 1 H, CH); 4c:
6 = 0.12 (s, 9H , SiMe,), 0.39 (s, 9H, SiMe,), 0.72 (t, 3H, CH,CH,), 1.43
mitochondrial steroidogenesis in vitro.['I In order to adhere
(d. 6H, CH,), 1.47 (d, 6H, CH,), 2.05 (q, 2H, CH,CH,). 3.93 (t, 1 H, CH),
to the classical nomenclature that names a receptor from the
4.20 (d, 1 H, CHI, 4.40 (d, 1 H, CH), 4.94 (s, 5H, Cp), 10.96 (s, 1H, CH);
ligand, we have termed this receptor the mito5a: 6 = 0.08 (s, 9H , SiMe,), 0.44 (9, 6H, Si(CH,CH,),), 1.19 (t. 9 H ,
chondrial DBI receptor (MDR).['] This MDR is thus to be
Si(CH,CH,),), 4.27 (t, I H , CH), 4.36 (s, 5H, Cp), 4.65 (d, 1 H, CH), 4.77
(d. 1 H. CH), 4.83 ( s , 5H, Cp), 11.01 (s, 1 H, CH); 5a': 6 = 0.35 (s, 9H,
distinguished from the neuronal benzodiazepine binding
SiMe,), 0.56 (q, 6H, Si(CH,CH,),), 1.05 (t. 9 H , Si(CH,CH,),), 4.25 (t,
located predominantly on the extracellular domain of
1 H. CHI, 4.34 (s, 5H, Cp), 4.63 (d, l H , CH), 4.83 (d, 1H, CH), 4.86 ( s ,
the type A receptor for y-aminobutyric acid (GABA, recep5H, Cp), 11.06 (s, I H , CH); 6a:6 = 0.03 (5, 9H, SiMe,), 0.39 (s, 6H,
tor), sites which when occupied serve to modulate the
SiMe,), 1.11 (s, 9H, tBu), 4.28 (t. 1H, CH), 4.37 (s, 5H. Cp), 4.58 (d. 1 H,
CH), 4.76 (d. 1H, CH), 4.80 (s, 5H,Cp), 11.31 (s, 1 H, CH); 6a': 6 = 0.12
GABA-dependent conformational transitions in the associ(s, 9H. SiMe,), 0.31 (s, 6H, SiMe,), 0.99 (s, 9H, tBu), 4.27 (t, 1 H, CH),
ated chloride ion channel.r6]
4.34 ( s , 5H, Cp), 4.59 (d, l H , CH), 4.78 (d, I H , CH), 4.81 (s, 5H, Cp),
11.08(s,1H,CH);7a:6=0.11(s,9H,SiMe,),1.34(s,9H,tBu),4.26(t, Neurosteroid precursors are synthesized in mitochondria
1 H, CHL4.36 (s, 5H, Cp), 4.49 (d, l H , C H ) , 4.78 (d, 1 H, CH), 4.86 ( s,
under the regulation of the mitochondrial benzodiazepine re5 H, Cp), 9.94 (s, 1H, CH); ',C{'H} NMR (50 MHz, C,D,) 4a: 6 = 0.23
ceptors. The glial cells probably constitute the most important
(SiMe,), 6.99 (SiMe,), 81.63 (Cp), 87.15 (Cp), 68.32 (CH), 77.13 (CH),
steroidogenic cells in the brain, and evidence indicates that
83.56 (CH), 79.29 (C7), 141.93 (C), 222.25 (C); 4c:6 = 1.85 (SiMe,), 7.05
they produce pregnenolone and perhaps]'] dehydroepiandro(SiMe,), 9.70 (CH,), 9.83 (CH,), 14.41 (CH,), 18.96 (CH,), 71.65 (CH),
sterone sulfate, 3cc-hydroxy-5a-pregnan-20-one(3a-OH( C ) . 138.68 (C), 162.10 (C), 219.94 (C); 7a: 6 =7.03 (SiMe,), 31.15
DHP), and 3a,21-dihydroxy-5a-pregnan-20-one
(CCH,), 36.05 (CCH,), 68.81 (CH), 76.83 (CH), 79.15 (C7), 81.48 (Cp),
locat83.05 (CH), 87.13 (Cp), 146.47 (C), 219.15 (C); 29Si{1H}NMR(40 MHz,
ed on the transmembrane domain of the heterooligomeric
C,D,, INEPT) 4a:6 = -15.00, 30.2 (br); 5a: 6 = -7.1, 30.6 (br); 5a':
6 = -15.1, 38.5 (br); 7a:6 = 29.5 (br).
integral membrane protein functioning as the GABA, recep171 This can presumably be attributed to relaxation effects due to coupling
tor, thereby modulating the responsiveness of the GABA,
with the 59C0nucleus.
receptor. These MDR receptors would therefore appear to
[XI K. Jonas, J. Organomet. Chem. 1990,400, 165-184.
an intriguing new, but indirect, pharmacological ap191 a) T. J. Katz, M. Rosenberger, J . Am. Chem. Soc. 1963,85,2030-2031;
b)T. J. Katz, J. J. Mrowca, J. Am. Chem. Soc. 1967,89, 1105-1111.
proach to modulation of the GABA, receptor complex
[I01 Monoclinic. space group P2,ia, a =14.336(10), b = 15.493(8), c =
(Fig. 1).
14.658(10)8,p =113.64(5)", V = 2982 A', Z = 4, Stoe-Siemens four-cirAt present, the isoquinolinecarboxamide PKI 1195 is the
cle diffractometer (Mo,, radiation, graphite monochromator, w-scan,
only compound known to possess high affinity for the MDR
3' < 28 < 50", empirical absorption correction), 2875 independent reflections with ( I > 2 4 0 , all non-hydrogen atoms anisotropic, all H-atoms of
without binding to other known neurotransmitter recepthe cobaltapentalene localized in difference Fourier syntheses and refined
R = 0.054; R, = 0.054, w-' = (u*(F)+ 0.0003 F z )
(SHELX-76 [G. M. Sheldrick, University of Cambridge 19761). Further
details of the crystal structure investigation may be obtained from the
Fachinformationszentrum Karlsruhe, Gesellschaft for wissenschaftlichtechnische Information mbH, D-W-7514 Eggenstein-Leopoldshafen2
(FRG) on quoting the depository number CSD-56207, the names of the
authors, and the journal citation.
[ l l ] H. Wadepohl, W. Galm, H. Pritzkow, A. Wolf, unpublished.
Verlagsgesellschafi mbH. W-6940 Weinheim, 1992
[*] Prof. A. P. Kozikowski, Dr. D. Ma
Neurochemistry Research, Mayo Clinic Jacksonville
4500 San Pablo Road, Jacksonville, FL 32224 (USA)
E. Romeo, M. D., Dr. J. Auta, Dr. V. Papadopoulos, Dr. G. Puia.
E. Costa, M. D., A. Guidotti, M. D.
Fidia-Georgetown Institute for the Neurosciences
This work was supported by the Fidia Research Foundation.
Angew. Chem. Int. Ed. Engl. 1992,31,No. 8
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