Synthesis of 17-α-substituted estradiol-pyridin-2-yl hydrazine conjugates as effective ligands for labeling with Alberto's complex fac-[Re(OH2)3(CO)3]+ in water

Article abstract of DOI:10.1021/jo034780g

The development of ^99mTc-estradiol radiopharmaceuticals would be advantageous for the detection of estrogen receptor-positive breast tumors. Estradiol derivatives conjugated to organometallic tricarbonyl-Tc(I) and related Re(I) complexes are ca

Full text of DOI:10.1021/jo034780g

Syn th esis of 17-r-Su bstitu ted Estr a d iol-P yr id in -2-yl Hyd r a zin e
Con ju ga tes a s Effective Liga n d s for La belin g w ith Alber to’s
Com p lex fa c-[Re(OH2)3(CO)3]+ in Wa ter
J effrey B. Arterburn,*,† Cesear Corona,† Kalla Venkateswara Rao,† Kathryn E. Carlson,‡ and
J ohn A. Katzenellenbogen‡
Department of Chemistry and Biochemistry MSC 3C, New Mexico State University, P.O. Box 30001,
Las Cruces, New Mexico 88003, and Department of Chemistry, University of Illinois,
600 South Mathews Avenue, Urbana, Illinois 61801
jarterbu@nmsu.edu
Received J une 6, 2003
The development of 99mTc-estradiol radiopharmaceuticals would be advantageous for the detection
of estrogen receptor-positive breast tumors. Estradiol derivatives conjugated to organometallic
tricarbonyl-Tc(I) and related Re(I) complexes are capable of achieving high receptor binding affinity,
but effective methods for synthesizing radiolabeled complexes in water are not available. Our
interest in the synthesis of 2-hydrazinopyridines as ligands for Tc and Re led us to investigate
Pd-catalyzed amination reactions of halo-pyridine substrates with di-tert-butyl hydrazodiformate.
Both 2- and 4-substituted halo-pyridine substrates undergo C-N coupling with di-tert-butyl
hydrazodiformate to produce Boc-protected pyridine hydrazine derivatives. Only highly electrophilic
3-pyridine halides were converted to the hydrazine. The Boc-protected 5-bromopyridin-2-yl hydrazine
substrate 3 was prepared by regioselective substitution at the 2-position of 2,5-dibromopyridine.
This bifunctional chelate was attached to ethynyl or vinyl groups at the 17R position of estradiol,
using Sonogashira and Suzuki/Miyaura coupling reactions to synthesize 1 and 2 in high yields,
respectively. Deprotection of 1 under acidic conditions provided the hydrazine hydrochloride salt
25. The 17R-estradiol-tricarbonylrhenium(I) complex 4 was synthesized by labeling 25 with fac-
[Re(OH2)3(CO)3]+ in aqueous ethanol. This complex exhibited excellent stability and high receptor
binding affinity for the estrogen receptor, and it is a promising model for evaluation of the analogous
Tc-99m complexes as diagnostic imaging agents for breast tumors.
In tr od u ction
choice for diagnostic imaging due to its favorable nuclear
decay properties, a 6-h half-life, low cost, and availability
throughout the world. The discovery of kinetically stable,
substitution inert d6-technetium(I) complexes first dem-
onstrated the opportunities for organometallic complexes
in nuclear medicine.16,17 Current interest has focused on
developing a new generation of highly selective, target-
specific radiopharmaceuticals consisting of a metal com-
plex conjugated to an organic molecule that is a ligand
with high binding affinity for a receptor.18-25 The syn-
The kinetic and thermodynamic stability of certain
classes of organometallic complexes in aqueous, aerobic
environments contrasts with common assumptions that
relegate them to remain in the glovebox. These are
fascinating molecules with unique structural, electronic,
and chemical properties. Proponents of bioorganometallic
chemistry have realized this potential and pursued the
development of novel labeling agents, biochemical probes,
and new drugs.1-15 Technetium-99m is a radionuclide of
(9) Lo, H. C.; Leiva, C.; Buriez, O.; Kerr, J . B.; Olmstead, M. M.;
Fish, R. H. Inorg. Chem. 2001, 40, 6705-6716.
(10) Metzler-Nolte, N. Angew. Chem., Int. Ed. 2001, 40, 1040.
(11) J ackson, A.; Davis, J .; Pither, R. J .; Rodger, A.; Hannon, M. J .
Inorg. Chem. 2001, 40, 3964-3973.
* Address correspondence to this author. Phone: (505) 646-2738.
Fax: (505) 646-2649.
† New Mexico State University.
‡ University of Illinois.
(1) J aouen, G.; Vessieres, A.; Butler, I. S. Acc. Chem. Res. 1993, 26,
361-369.
(12) van Staveren, D. R.; Metzler-Nolte, N. Chem. Commun. 2002,
1406-1407.
(2) Salmain, M.; Gunn, M.; Gorfi, A.; Top, S.; J aouen, G. Bioconj.
Chem. 1993, 4, 425-433.
(13) Rodriguez, G.; Albrecht, M.; Schoenmaker, J .; Ford, A.; Lutz,
M.; Spek, A. L.; van Koten, G. J . Am. Chem. Soc. 2002, 124, 5127-
5138.
(14) Herebian, D.; Sheldrick, W. S. J . Chem. Soc., Dalton Trans.
2002, 966-974.
(15) Cadierno, V.; Conejero, S.; Gamasa, M. P.; Gimeno, J .; Rod-
riguez, M. A. Organometallics 2002, 21, 203-209.
(16) Abrams, M. J .; Davison, A.; J ones, A. G.; Costello, C. E.; Pang,
H. Inorg. Chem. 1983, 22, 2798-2800.
(17) J ones, A. G.; Abrams, M. J .; Davison, A.; Brodack, J . W.;
Toothaker, A. K.; Adelstein, S. J .; Kassis, A. I. Int. J . Nucl. Med. Biol.
1984, 11, 225-234.
(3) Severin, K.; Bergs, R.; Beck, W. Angew. Chem., Int. Ed. Engl.
1998, 37, 1635-1654.
(4) Fish, R. H. Coord. Chem. Rev. 1999, 186, 569-584.
(5) Grotjahn, D. B. Coord. Chem. Rev. 1999, 192, 1125-1141.
(6) J aouen, G.; Top, S.; Vessieres, A.; Alberto, R. J . Organomet.
Chem. 2000, 600, 23-36.
(7) Albrecht, M.; Rodriguez, G.; Schoenmaker, J .; vanKoten, G. Org.
Lett. 2000, 2, 3461-3464.
(8) Salmain, M.; Licandro, E.; Baldoli, C.; Maiorana, S.; Tran-Huy,
H.; J aouen, G. J . Organomet. Chem. 2001, 617, 376-382.
10.1021/jo034780g CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/14/2003
J . Org. Chem. 2003, 68, 7063-7070
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Arterburn et al.
thesis of rhenium analogues is important as stable
isotope models for the chemically similar technetium
complexes, and as Re-186,188 radiopharmaceuticals for
therapeutic applications.26-28 In this approach the organic
targeting groups are connected to a bifunctional chelate
that enables coordination of the transition metal. The
characteristics of an ideal bifunctional chelate for labeled
targeted radiopharmaceuticals include exceptionally strong
ligating ability, small size, and a nonpolar backbone. The
receptor ligand-chelate conjugate should undergo label-
ing in water and produce neutral complexes in high yield
and radiochemical purity.
however, the compounds investigated to date exhibit
relatively low binding affinity to ER.11,37,42-44
The remarkable synthesis of Alberto’s fac-[99mTc(OH2)3-
(CO)3]+ complex directly from [99mTcO4]- in water under
mild conditions has made this an important precursor
for radiopharmaceutical labeling with a variety of
chelators.45-51 A highly stable complex with 2-hydrazi-
nopyridine formed rapidly and quantitatively under
dilute (µM) concentrations, which indicates the potential
of this ligand class for producing radiopharmaceuticals
with high specific activity.47 Hydrazine ligands are also
known to form stable complexes with Tc/Re in higher
oxidation states.52-58 Hydrazinonicotinamide derivatives
have become important bifunctional ligands that can be
conjugated to substrates possessing an available amino
group.59-74
The importance of determining the estrogen receptor
(ER) content in breast tumors as a prerequisite for
effective treatment of this devastating disease and the
advantages associated with early detection have stimu-
lated great interest in 99mTc-estradiol radiopharmaceuti-
cals.19,29-32 Estradiol conjugates with pendant organo-
metallic cyclopentadienyl tricarbonyl complexes are ca-
pable of binding to ER with high affinity; however, no
satisfactory methods are available for the synthesis of
these radiopharmaceuticals directly in water.31-41 Estra-
diol derivatives possessing thioether ligands also form
tricarbonyl-technetium(I) and -rhenium(I) complexes;
(42) Reisgys, M.; Wust, F.; Alberto, R.; Schibli, R.; Schubiger, P. A.;
Pietzsch, H. J .; Spies, H.; J ohannsen, B. Bioorg. Med. Chem. Lett. 1997,
7, 2243-2246.
(43) Wust, F.; Spies, H.; J ohannsen, B. Tetrahedron Lett. 1997, 38,
2931-2932.
(44) Wust, F.; Carlson, K. E.; Katzenellenbogen, J . A.; Spies, H.;
J ohannsen, B. Steroids 1998, 63, 665-671.
(45) Alberto, R.; Schibli, R.; Egli, A.; Schubiger, A. P.; Abram, U.;
Kaden, T. A. J . Am. Chem. Soc. 1998, 120, 7987-7988.
(46) Alberto, R.; Schibli, R.; Waibel, R.; Abram, U.; Scubiger, A. P.
Coord. Chem. Rev. 1999, 192, 901-919.
(47) Alberto, R.; Schibli, R.; Schubiger, A. P.; Abram, U.; Pietzsch,
H.-J .; J ohannsen, B. J . Am. Chem. Soc. 1999, 121, 6076-6077.
(48) Schibli, R.; Bella, R. L.; Alberto, R.; Garcia-Garayoa, E.; Ortner,
K.; Abram, U.; Schubiger, P. A. Bioconj. Chem. 2000, 11, 345-351.
(49) Garcia, R.; Paulo, A.; Domingos, A.; Santos, I.; Ortner, K.;
Alberto, R. J . Am. Chem. Soc. 2000, 122, 11240-11241.
(50) Pietzsch, H.-J .; Gupta, A.; Reisgys, M.; Drews, A.; Seifert, S.;
Syhre, R.; Spies, H.; Alberto, R.; Abram, U.; Schubiger, P. A.;
J ohannsen, B. Bioconj. Chem. 2000, 11, 414-424.
(51) Correia, J . D. G.; Domingos, A.; Santos, I.; Alberto, R.; Ortner,
K. Inorg. Chem. 2001, 40, 5147-5151.
(18) Schwochau, K. Angew. Chem., Int. Ed. Engl. 1994, 33, 2258-
2267.
(19) Hom, R. K.; Katzenellenbogen, J . A. Nucl. Med. Biol. 1997, 24,
485-498.
(20) J ohannsen, B.; Spies, H. Transition Met. Chem. 1997, 22, 318-
320.
(21) J urisson, S. S.; Lydon, J . D. Chem. Rev. 1999, 99, 2205-2218.
(22) Liu, S.; Edwards, D. S. Chem. Rev. 1999, 99, 2235-2268.
(23) Dilworth, J . R.; Parrott, S. J . Chem. Soc. Rev. 1998, 27, 43-
55.
(24) Bandoli, G.; Dolmella, A.; Porchia, M.; Refosco, F.; Tisato, F.
Coord. Chem. Rev. 2001, 214, 43-90.
(52) Hirsch-Kuchma, M.; Nicholson, T.; Davison, A.; Davis, W. M.;
J ones, A. G. Inorg. Chem. 1997, 36, 3237-3241.
(25) Schibli, R.; Schubiger, P. A. Eur. J . Nucl. Med. Mol. Imaging
2002, 29, 1529-1542.
(53) Liu, S.; Edwards, D. S.; Harris, A. R.; Singh, P. R. Appl. Radiat.
Isot. 1997, 48, 1103-1111.
(26) Mirzadeh, S.; Knapp, F. F. J . J . Radioanal. Nucl. Chem. 1996,
203, 471-488.
(54) Rose, D. J .; Maresca, K. P.; Nicholson, T.; Davison, A.; J ones,
A. G.; Babich, J .; Fischman, A.; Graham, W.; DeBord, J . R. D.; Zubieta,
J . Inorg. Chem. 1998, 37, 2701-2716.
(27) Srivastava, S. C. In Current Directions in Radiopharmaceutical
Research and Development; Mather, S. J ., Ed.; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1996; p 63-79.
(28) Schubiger, P. A.; Alberto, R.; Smith, A. Bioconj. Chem. 1996,
7, 165-179.
(55) daCosta, M. T. A. R. S.; Dilworth, J . R.; Duarte, M. T.; daSilva,
J . J . R. F.; Galvao, A. M.; Pombeiro, A. J . L. J . Chem. Soc., Dalton
Trans. 1998, 2405-2410.
(56) Perez-Lourido, P.; Romero, J .; Garcia-Vazquez, J . A.; Sousa, A.;
Maresca, K. P.; Zubieta, J . Inorg. Chem. 1999, 38, 1511-1519.
(57) Albertin, G.; Antoniutti, S.; Bacchi, A.; Ballico, G. B. B., E.;
Pelizzi, G.; Ranieri, M.; Ugo, P. Inorg. Chem. 2000, 39, 3265-3279.
(58) Mevellec, F.; Lepareur, N.; Roucoux, A.; Noiret, N.; Patin, H.;
Bandoli, G.; Porchia, M.; Tisato. F Inorg. Chem. 2002, 41, 1591-1597.
(59) Abrams, M. J .; J uweid, M.; TenKate, C. I.; Shwartz, D. A.;
Hauser, M. M.; Gaul, E. F.; Fucello, A. J .; Rubin, R. H.; Strauss, H.
W.; Fischman, A. J . J . Nucl. Med. 1990, 31, 2022-2028.
(60) Schwartz, D. A.; Abrams, M. J .; Hauser, M. Bioconj. Chem.
1991, 2, 333-336.
(29) Wust, F.; Spies, H.; J ohannsen, B. Bioorg. Med. Chem. Lett.
1996, 6, 2729-2734.
(30) Sugano, Y.; Katzenellenbogen, J . A. Bioorg. Med. Chem. Lett.
1996, 6, 361-366.
(31) Skaddan, M. B.; Katzenellenbogen, J . A. Bioconj. Chem. 1999,
10, 119-129.
(32) Mull, E. S.; Sattigeri, V. J .; Rodriguez, A. L.; Katzenellenbogen,
J . A. Bioorg. Med. Chem. Lett. 2002, 10, 1381-1398.
(33) Wenzel, M.; Klinge, C. J . Labeled Compd. Radiopharm. 1994,
34, 981-987.
(34) Top, S.; El Hafa, H.; Vessieres, A.; Quivy, J .; Vaissermann, J .;
Hughes, D. W.; McGlinchey, M. J .; Mornon, J . P.; Thoreau, E.; J aouen,
G. J . Am. Chem. Soc. 1995, 117, 8372-8380.
(35) Minutolo, F.; Katzenellenbogen, J . A. J . Am. Chem. Soc. 1998,
120, 13264-13265.
(61) Larson, S. K.; Solomon, H. F.; Caldwell, G.; Abrams, M. J .
Bioconj. Chem. 1995, 6, 635-.
(62) Edwards, D. S.; Liu, S. Transition Met. Chem. 1997, 22, 425-
426.
(63) Edwards, D. S.; Liu, S.; Harris, A. R.; Poirier, M. J .; Ewels, B.
A. Bioconj. Chem. 1999, 10, 803-807.
(36) Spradau, T. W.; Katzenellenbogen, J . A. Bioorg. Med. Chem.
Lett. 1998, 8, 3235-3240.
(64) Decristoforo, C.; Mather, S. J . J . Nucl. Biol. Med. 1999, 26, 389-
(37) Skaddan, M. B.; Wust, F. R.; Katzenellenbogen, J . A. J . Org.
Chem. 1999, 64, 8108-8121.
396.
(65) Rennen, H. J . J . M.; Boerman, O. C.; Koenders, E. B.; Oyen,
W. J . G.; Corstens, F. H. M. Nucl. Med. Biol. 2000, 27, 599-604.
(66) Liu, S.; Edwards, D. S.; Harris, A. R. Bioconj. Chem. 1998, 9,
583-595.
(67) Ono, M.; Arano, Y.; Uehara, T.; Fujioka, Y.; Ogawa, K.; Namba,
S.; Mukai, T.; Nakayama, M.; Saji, H. Bioconj. Chem. 1999, 10, 386-
394.
(68) Decristoforo, C.; Mather, S. J . Bioconj. Chem. 1999, 10, 431-
438.
(69) Edwards, D. S.; Liu, S.; Ziegler, M. C.; Harris, A. R.; Crocker,
A. C.; Heminway, S. J .; Barrett, J . A.; Bridger, G. J .; Abrams, M. J .;
Higgins, J . D. Bioconj. Chem. 1999, 10, 884-891.
(38) Skaddan, M. B.; Wust, F.; J onson, S.; Syhre, R.; Welch, M. J .;
Spies, H.; Katzenellenbogen, J . A. Nucl. Med. Biol. 2000, 27, 269-
278.
(39) Osella, D.; Cavigiolio, G.; Vincenti, M.; Vessieres, A.; Laios, I.;
Leclercq, G.; Napolitano, E.; Fiaschi, R.; J aouen, G. J . Organomet.
Chem. 2000, 596, 242-247.
(40) Le Bideau, F.; Salmain, M.; Top, S.; J aouen, G. Chem. Eur. J .
2001, 7, 2289-2294.
(41) Acylcyclopentadienyl Tc/Re tricarbonyl complexes have recently
been synthesized in H2O. Wald, J .; Alberto, R.; Ortner, K.; Candreia,
L. Angew. Chem., Int. Ed. 2001, 40, 3062-3066.
7064 J . Org. Chem., Vol. 68, No. 18, 2003

Estradiol-Pyridin-2-yl Hydrazine Conjugates
SCHEME 1
Our interest has focused on the synthesis of pyridin-
2-yl hydrazine derivatives of estradiol 1 and 2 as poten-
tial ligands for labeling with Alberto’s complex.75 We
report here the synthesis of 1 and 2 via palladium-
catalyzed C-C coupling of N,N′-di-tert-butyloxycarbonyl-
(5-bromopyridin-2-yl)-hydrazine 3. The tricarbonylrhe-
nium(I) complex 4 was synthesized in high yield from
[Re(OH2)3(CO)3]+ in water, and its binding affinity for the
estrogen receptor was determined. The chemical similar-
ity of Re to Tc suggests complex 4 should be an effective
model for Tc-99m-containing imaging agents for breast
cancer.
SCHEME 2
coupling reactions of halogenated pyridines with alkyne
and alkene derivatives, respectively. The selective cou-
pling of 17R-ethynylestradiol 5 with 2-chloro-5-iodopyri-
dine 6 to produce 7 was accomplished with use of
standard Sonogashira conditions as shown in Scheme
1.79-81 The mild conditions and functional group tolerance
of this reaction resulted in high product yields with use
of either the unprotected substrate 5a or the O-tert-
butyldimethylsilyl (TBS) derivative 5b.
The alkene derivative 8a was synthesized in 85% yield
by addition of vinylmagnesium chloride in the presence
of cerium(III) chloride to TBS-protected estrone.82 The
standard Heck reaction conditions used to couple 8a with
2-chloro-5-iodo pyridine 6 gave the desired product 9a
in 24% yield, as shown in Scheme 2. Replacing PPh3 with
the bulky phosphine ligand (o-tolyl)3P resulted in a
modest improvement in the yield of 9a to 45%. These
relatively low yields with the Heck reaction prompted us
to investigate the Suzuki/Miyaura coupling procedure.83,84
The vinyl boronic acid derivative 8b was prepared
according to the literature procedure from ethynylestra-
diol and catechol borane, followed by hydrolysis.85 The
Suzuki coupling of 8b with 2-chloro-5-iodo pyridine 6 was
Resu lts a n d Discu ssion
The 17R-position of estradiol was chosen for conjuga-
tion to the pyridin-2-yl hydrazine group, based on
previous examples that demonstrated large groups
could be introduced without compromising binding
affinity.11,34,40,44,76-78 We designed our synthetic approach
to the protected pyridin-2-yl hydrazine derivatives 1 and
2 with the expectation of using palladium-catalyzed cross-
(70) Babich, J . W.; Coco, W. G.; Barrow, S.; Fischman, A. J .; Femia,
F. J .; Zubieta, J . Inorg. Chim. Acta 2000, 309, 123-136.
(71) Liu, S.; Edwards, D. S.; Ziegler, M. C.; Harris, A. R.; Heming-
way, S. J .; Barrett, J . A. Bioconj. Chem. 2001, 12, 624-629.
(72) Rennen, H. J . J . M.; van Eerd, J . E.; Oyen, W. J . G.; Corstens,
F. H. M.; Edwards, D. S.; Boerman, O. C. Bioconj. Chem. 2002, 13,
370-377.
(73) Liu, S.; Harris, A. R.; Williams, N. E.; Edwards, D. S. Bioconj.
Chem. 2002, 13, 881-886.
(79) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 4467-4470.
(74) Graham, K. A. N.; Wang, Q.; Eisenhut, M.; Haberkorn, U.; Mier,
W. Tetrahedron Lett. 2002, 43, 5021-5024.
(80) Grosshenny, V.; Romero, F. M.; Ziessel, R. J . Org. Chem. 1997,
62, 1491-1500.
(75) Arterburn, J . B.; Rao, K. V.; Perry, M. C. Angew. Chem., Int.
Ed. 2000, 39, 771-772.
(81) Arterburn, J . B.; Rao, K. V.; Perry, M. C. Tetrahedron Lett.
2000, 41, 839-842.
(76) Amouri, H. I.; Vessieres, A.; Vichard, D.; Top, S.; Gruselle, M.;
J aouen, G. J . Med. Chem. 1992, 35, 3130-3135.
(77) Foy, N.; Stephan, E.; J aouen, G. Tetrahedron Lett. 2000, 41,
8089-8092.
(82) Imamoto, T.; Takiyama, N.; Nakamura, K.; Hatajima, T.;
Kamiya, Y. J . Am. Chem. Soc. 1989, 111, 4392-4398.
(83) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483.
(84) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002, 58,
9633-9695.
(78) Lee, C. Y.; Hanson, R. N. Tetrahedron 2000, 56, 1623-1629.
J . Org. Chem, Vol. 68, No. 18, 2003 7065

Arterburn et al.
accomplished with Pd(PPh3)4/CsF.86 The reaction pro-
gressed slowly at 70 °C and produced 9b in 65% yield.
Heating the reaction to 90 °C for 6 h improved the yield
of 9b to 84%.
TABLE 1. Cou p lin g of P yr id in e Ha lid es w ith DTBHz
Hyd r a zin e Syn th esis. Various attempts at direct
nucleophilic substitution of the chloride in derivatives 7
and 9 with hydrazine were unsuccessful, and under
forcing conditions reduction of the alkene/alkyne groups
was observed.87 These results were consistent with our
expectations for low SNAr reactivity in the absence of
additional electron-withdrawing substituents on pyridine.
Our efforts were then directed toward the application of
catalytic methods for C-N bond formation with pyridin-
2-yl halide substrates. Recent developments in methods
for the catalytic amination of aryl halides have greatly
facilitated arylamine synthesis,88-93 and there has been
interest in extending these methods for the synthesis of
hydrazines.75,81,94-101 Halogenated pyridines were origi-
nally found to be unsuitable substrates for Pd-catalyzed
amination with use of first generation catalysts. The
amination of pyridyl substrates with aryl- and alky-
lamines was accomplished with use of chelating ligands
or sterically hindered monodentate biphenylphosphine
ligands.92,102-105 We recently reported that Hartwig’s
conditions for catalytic amination using Pd2(dba)3, 1,1′-
bis(diphenylphosph1ino)ferrocene (dppf), and Cs2CO3
were suitable for the amination of 2-halo-pyridines with
di-tert-butyl hydrazodiformate 10.106 To further define the
scope of reactivity of halo-pyridine substrates in the Pd-
catalyzed amination with 10, we conducted a series of
experiments using compounds 11a -i (Table 1).
yields with bromide 11b reflect the general reactivity
trend for Pd-catalyzed amination of aryl-bromides > aryl-
chlorides. 2,5-Dibromopyridine 11c was selectively ami-
nated at the 2-position to give 3. This demonstrates the
greater reactivity of the bromide ortho to the nitrogen
atom. The reaction of 2-chloro-5-iodopyridine 6 under
these conditions resulted in a complex mixture that was
not characterized further. Iodopyrazine 11d underwent
catalytic amination to produce the hydrazine product 12d
in excellent yield. Similarly, 4-bromopyridine 11e was
converted to hydrazine 12e in high yield. In contrast, the
attempted amination of 3-bromopyridine 11f with 10 was
The amination of 2-chloropyridine 11a and 2-bromopy-
ridine 11b with 10 produced the hydrazine 12a in 70%
and 85% yields, respectively. The consistently higher
(85) Nakatsuka, I.; Ferreira, N. L.; Eckelman, W. C.; Francis, B.
E.; Rzeszotarski, W. J .; Gibson, R. E.; J agoda, E. M.; Reba, R. C. J .
Med. Chem. 1984, 27, 1287-1291.
(86) Collet, S.; Danion-Bougot, R.; Danion, D. Synth. Commun. 2001,
31, 249-255.
(87) Corey, E. J .; Mock, W. L.; Pasto, D. J . Tetrahedron Lett. 1961,
347-352.
(88) Hartwig, J . F. Angew. Chem., Int. Ed. 1998, 37, 2046-2067.
(89) Hartwig, J . F. Acc. Chem. Res. 1998, 31, 852-860.
(90) Wolfe, J . P.; Wagaw, S.; Marcoux, J . F.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805-818.
(91) Frost, C. G.; Mendonca, P. J . Chem. Soc., Perkin Trans. 1 1998,
2615-2623.
(92) Yang, B. H.; Buchwald, S. L. J . Organomet. Chem. 1999, 576,
125-146.
(93) Prim, D.; Campagne, J . M.; J oseph, D.; Andrioletti, B. Tetra-
hedron 2002, 58, 2041-2075.
unsuccessful under these conditions. Related substrates
possessing a similar meta-substituted halide, such as
5-bromopyrimidine 11g and 4-bromoisoquinoline 11h ,
also failed to produce the corresponding hydrazine prod-
ucts. The electron-deficient substrate 2-nitro-5-bromopy-
ridine 11i underwent C-N coupling to form the hydra-
zine product 12i in low yield. Bromobenzene 13, which
typically functions as an effective arylating agent for Pd-
catalyzed aminations with alkyl- and arylamines, did not
react with 10 under these conditions. The electron-
deficient aryl substrate 4-nitrobromobenzene 14 was
converted to the hydrazine product 15 in 63% yield.
These results demonstrate the regioselectivity of the
Pd/dppf-catalyzed amination reaction of 10 for 2- or
4-halo-pyridine substrates. Positions 2 and 4 are also the
most reactive in nucleophilic substitution reactions due
to stabilization of the intermediate addition products by
localization of electron density on nitrogen. The failure
(94) Hartwig, J . F. Angew. Chem., Int. Ed. 1998, 37, 2090-2093.
(95) Wagaw, S.; Yang, B. H.; Buchwald, S. L. J . Am. Chem. Soc.
1998, 120, 6621-6622.
(96) Wang, Z.; Skerlj, R. T.; Bridger, G. J . Tetrahedron Lett. 1999,
40, 3543-3546.
(97) Wagaw, S.; Yang, B. H.; Buchwald, S. L. J . Am. Chem. Soc.
1999, 121, 10251-10263.
(98) Stieber, F.; Grether, U.; Waldmann, H. Angew. Chem., Int. Ed.
1999, 38, 1073-1077.
(99) Wolfe, J . P.; Tomori, H.; Sadighi, J . P.; Yin, J .; Buchwald, S. L.
J . Org. Chem. 2000, 65, 1158-1174.
(100) Song, J . J .; Yee, N. K. Org. Lett. 2000, 2, 519-521.
(101) Song, J . J .; Yee, N. K. Tetrahedron Lett. 2001, 42, 2937-2940.
(102) Wagaw, S.; Buchwald, S. L. J . Org. Chem. 1996, 61, 7240-
7241.
(103) Wagaw, S.; Rennels, R. A.; Buchwald, S. L. J . Am. Chem. Soc.
1997, 119, 8451-8458.
(104) Cheng, J .; Trudell, M. L. Org. Lett. 2001, 3, 1371-1374.
(105) Wolfe, J . P.; Ahman, J .; Sadighi, J . P.; Singer, R. A.; Buchwald,
S. L. Tetrahedron Lett. 1997, 38, 6367-6370.
(106) Arterburn, J . B.; Rao, K. V.; Ramdas, R.; Dible, B. R. Org.
Lett. 2001, 3, 1351-1354.
7066 J . Org. Chem., Vol. 68, No. 18, 2003

Estradiol-Pyridin-2-yl Hydrazine Conjugates
SCHEME 3
SCHEME 4
SCHEME 5
of 3-bromopyridine substrates under the catalytic reac-
tion conditions was not anticipated, since these sub-
strates have previously been used in Pd-catalyzed C-N
coupling reactions with nucleophilic amines and hydra-
zones.90 Numerous investigations have identified that
electron-withdrawing groups on aryl substrates increased
the rates of reductive elimination to form C-N, C-S, and
C-O bonds. These electronic effects are also evident in
the amination with weak N-nucleophiles. Sulfoximine
and amides react efficiently with electrophilic aryl bro-
mides and poorly with electron-rich aryl halides.107,108
This emphasizes the importance of matching weak N-
nucleophiles with electrophilic substrates in Pd-catalyzed
C-N coupling reactions.
SCHEME 6
The results from Table 1 can be rationalized by
considering resonance effects in the putative pyridine-
Pd intermediates. The intermediates resulting from
oxidative addition of 2- and 4-pyridine halides are capable
of localizing electron density on nitrogen. These reso-
nance effects enhance the electrophilicity of the hetero-
cycle, and increase the reactivity for C-N bond formation
with the weak nucleophile 10. Similar stabilizing reso-
nance effects are not possible for substitution at the
3-position. The more electrophilic 2-nitro-5-bromopyri-
dine 11i functions in the C-N coupling due to stabiliza-
tion of the developing charge by the nitro group. The
interplay of similar resonance effects is also consistent
with our observations that 4-nitrobromobenzene 14 was
coupled with 10 under these conditions, whereas no
reaction occurred with bromobenzene.
Syn th esis of 17r-(p yr id in -2-yl)-h yd r a zin e Estr a -
d iol Der iva tives 1 a n d 2. The catalytic amination of
the TBS-protected estradiol derivative 7b with 10 under
these conditions produced hydrazine 1b in a moderate
36% yield, as shown in Scheme 3. Estrone 20 was also
isolated from the reaction product mixture in 25% yield,
and similar amounts of starting 7b were recovered.
Control reactions established that estrone was produced
by a competing fragmentation of the tertiary propargyl
alcohol under these mildly basic, anhydrous conditions.
This fragmentation is analogous to reported cleavage
reactions of propargylic alcohols under basic conditions.109
The unprotected derivative 7a possesses an acidic phenol
group and precipitated as the potassium salt under these
reaction conditions. The reaction of the simple model
2-chloropyridine substrate 21 under the standard condi-
tions produced the corresponding hydrazine product 22
in an improved 67% yield, as shown in Scheme 4. These
results indicate the incompatibility of tertiary propargylic
alcohol substrates under the C-N coupling conditions.
No reaction of alkene derivative 9b with 10 was
observed under these C-N coupling conditions. The
model substrate 23, which lacks a tertiary allylic alcohol
group, produced hydrazine 24 in 57% yield, as shown in
Scheme 5. These results demonstrate the incompatibility
of the C-N coupling reaction of 10 with allylic alcohol
9b. We then investigated the direct coupling of a pro-
tected pyridine hydrazine group as an alternative ap-
proach for the synthesis of 1 and 2. The protected
hydrazine derivative 3 was coupled with 17R-ethyn-
ylestradiol 5a with use of standard Sonogashira condi-
tions to afford the estradiol pyridine hydrazine derivative
1 in 85% yield, as shown in Scheme 6.
The attempted Heck reaction of the vinyl estradiol
derivative 8a with the protected pyridine hydrazine
derivative 3 was unsuccessful, and some decomposition
of 3 was observed. Employing the Suzuki conditions for
coupling the estradiol vinyl boronic acid 8b with 3 with
use of Pd(PPh3)4/CsF gave a 40% yield of the desired
(107) Bolm, C.; Hildebrand, J . P. J . Org. Chem. 2000, 65, 169-175.
(108) Yin, J .; Buchwald, S. L. Org. Lett. 2000, 2, 1101-1104.
(109) (a) Boyal, D.; Lopez, F.; Sasaki, H.; Frantz, D.; Carreira, E.
M. Org. Lett. 2000, 2, 4233-4236. (b) Crisp, G. T.; J iang, Y. L. Synth.
Commun. 1998, 28, 2571-2576.
J . Org. Chem, Vol. 68, No. 18, 2003 7067

Arterburn et al.
SCHEME 7
SCHEME 8
The elimination reaction producing 26 removes the 17â-
hydroxyl group, which is crucial for ER binding; there-
fore, this compound was not investigated further. Hy-
drogenation of the alkene in 2 would be expected to
facilitate the deprotection by preventing the formation
of conjugated diene. This derivative would also be of
interest for further evaluation.
Syn th esis of Tr ica r bon yl-Re(I) Com p lex 4. The
tricarbonylrhenium(I) complex [Et4N]2[ReCl3(CO)3]was
prepared from [Bu4N][ReO4] as reported in the litera-
ture.110 This complex undergoes rapid hydrolysis of the
chloride ligands in water, and is an effective precursor
for fac-[Re(OH2)3(CO)3]+ in situ. The resulting complex
was mixed with the estradiol-hydrazine hydrochloride 25
in ethanol, acidified with 2 M HCl (aq), and stirred at
ambient temperature for 30 h, as shown in Scheme 8.
The product tricarbonylrhenium(I) complex 4 was iso-
lated as a light pink solid in 92% yield after precipitation
from H2O. The complex was purified by chromatography
on silica gel eluted with 5% CH3OH/CH2Cl2 and obtained
in 71% yield.
product 2. Under these conditions, protodeboronation of
the boronic acid occurred as a side reaction to give 17R-
vinylestradiol in 34% yield. The yield of 2 was improved
significantly to 83% with use of PdCl2(dppf) in DMF with
aqueous Na2CO3, as shown in Scheme 7. A second portion
of catalyst was added after 4 h to complete the conver-
sion.
A variety of hydrolysis conditions were investigated for
the removal of the Boc-protecting groups from 1 and 2.
The hydrolysis of 1 was incomplete with use of 10%
trifluoroacetic acid in 2-propanol at 60 °C. A complicated
mixture was obtained from 1 with use of 20% trifluoro-
acetic acid in CH2Cl2 at ambient temperature. The
deprotection of 1 was accomplished by using 20% con-
centrated HCl in ethanol (v/v) at ambient temperature
for 6 h to produce the hydrochloride salt 25 in 95% yield.
The salt 25 was stored at 4 °C and found to be stable as
a solid without observable decomposition after two
months. Solutions of 25 in DMSO exhibited decomposi-
tion with extended storage.
The structure of complex 4 is supported by spectral and
elemental analysis data. The complex exhibits UV/vis
absorption maxima at 273 and 330 nm. The 13C NMR
spectra exhibited three distinct resonances for the car-
bonyl peaks at δ 198.8, 198.0, and 193.5. The FT-IR
absorbances at 2029, 1919, and 1898 cm-1 also confirm
the presence of carbonyl groups. The 13C NMR signals of
the o-pyridine positions were shifted significantly down-
field upon formation of the complex, such that C-1 shifted
by 4.8 ppm, and C-5 by 4.0 ppm, relative to 25. The
p-pyridine position C3 shifted downfield by 1.8 ppm.
These results are consistent with coordination of the
pyridine nitrogen to the electrophilic tricarbonylrhenium-
The HCl/EtOH hydrolysis conditions were then used
with the allylic alcohol substrate 2, but the deprotection
was incomplete and the product mixture contained
significant amounts of the dehydration product 26. The
1
(I) complex. The H NMR revealed sharp signals for the
phenol and 3° alcohol at δ 9.29 and 4.55, respectively,
and three distinct hydrazine protons in acetone-d6 that
exchanged with D2O. The internal hydrazine N-H ap-
peared at δ 7.88, while the two terminal hydrazine
protons appeared at δ 7.98 and 6.58 as doublets with a
geminal coupling constant J ) 8.8 Hz. This assignment
was verified by decoupling experiments in which irradia-
tion of the signal at δ 7.98 collapsed the peak at δ 6.58
to a singlet. These data demonstrate that the diaste-
reotopic terminal hydrazine hydrogen atoms do not
interconvert on the NMR time scale. This observation is
consistent with expectations for a kinetically stable
octahedral d6 Re(I) configuration. The coordination en-
vironment of the metal complex is chiral and complex 4
C16-H of the conjugated diene in 26 appeared as a
1
characteristic vinyl signal at δ 5.94 in the H NMR, and
the other vinyl hydrogens were observed at δ 6.64 and
7.10 with J ) 8.0 Hz. Complete deprotection of 2 was
accomplished with use of 25% concentrated HCl in ethyl
acetate (v/v) at ambient temperature for 1.5 h, but
produced the conjugated diene 26 in 97% yield instead
of the desired allylic alcohol. Further attempts to depro-
tect 2 without elimination of the sensitive allylic alcohol
under milder hydrolysis conditions were unsuccessful.
(110) Alberto, R.; Schibli, R.; Egli, A.; Schubiger, P. A.; Herrmann,
W. A.; Artus, G.; Abram, U.; Kaden, T. A. J . Organomet. Chem. 1995,
492, 217-224.
7068 J . Org. Chem., Vol. 68, No. 18, 2003

Estradiol-Pyridin-2-yl Hydrazine Conjugates
exists as two diastereomers. The distance of the chiral
steroid appendage from the stereogenic complex mini-
mizes the energy difference between the diastereomers
and leads to a single set of pyridine 1H and 13C NMR
signals. Attempts to grow single crystals suitable for
X-ray analysis have not been successful. The proposed
structure with the pyridine-N and terminal hydrazine-N
oriented trans to the carbonyls is analogous to the
recently reported X-ray structure of a similar picoly-
lamine complex [ReBr(CO)3(2-pyridine-CH2NH2)].111 Com-
plex 4 was stable for weeks without observable decom-
position as a solid and in solutions of acetone or DMSO
exposed to air and moisture.
Estr ogen Recep tor Bin d in g Affin ity of 4. The
estrogen binding affinity of complex 4 was measured at
0 °C by a competitive radiometric binding assay, using
either cytosol estrogen receptor preparation from lamb
uterus or purified human estrogen receptors (ERR or
ERâ), and [3H]estradiol as tracer.112 Affinities are ex-
pressed as relative binding affinity (RBA) values, where
estradiol has a value of 100. Complex 4 exhibited a high
binding affinity for ERR (RBA ) 38), though its affinity
for ERâ and lamb uterine ER was somewhat lower
(RBA’s of 5.0 and 5.9, respectively). This affinity com-
pares favorably with other reported estradiol-derived
tricarbonyl-Re(I) complexes, measured in uterine cytosol
or whole cell extract preparations of ER. The sterically
demanding 17R-ethynylpyridine mercaptan complex 27
for 4 is also higher than the cyclopentadienyl-Re(CO)3
complexes substituted in the 17R- and 7R-positions of
estradiol 29 and 30 that have binding affinities of 16 and
29, respectively.34,37
Con clu sion s
We have described the synthesis of pyridine hydrazine
derivatives using Pd-dppf catalyzed C-N coupling of di-
tert-butyl hydrazodiformate. The amination reaction was
successful for 2- and 4-halo-pyridine substrates, but
3-halo-pyridines required an additional electron-with-
drawing nitro group for activation. 2-Chloropyridine-
estradiol conjugates were synthesized with use of Sono-
gashira and Suzuki/Miyaura procedures, but the pro-
pargylic and allylic alcohol groups were not compatible
with the alkaline Pd-catalyzed C-N coupling conditions.
The syntheses of novel estradiol pyridine hydrazine
derivatives 1 and 2 were accomplished by using 3 as a
protected bifunctional chelate in catalytic C-C coupling
procedures. The Re(I)-tricarbonyl complex 4 was synthe-
sized directly in water from the hydrazine hydrochloride
salt, and exhibited a very high RBA for ER. These results
highlight the potential of this structural class of com-
pounds for labeling with Tc-99m to provide new imaging
agents for ER+ breast cancers.
Exp er im en ta l Section
17r-[6-(N ,N ′-Bis-t er t -b u t yloxyca r b on yl-h yd r a zin o-
p yr id in -3-yleth yn yl)]-estr a -1,3,5(10)-tr ien e-3,17â-d iol (1).
A solution of Pd(OAc)2 (12 mg, 0.05 mmol) and PPh3 (27 mg,
0.1 mmol) in diethylamine (5 mL) under an argon atmosphere
was stirred for 10 min. CuI (19 mg, 0.1 mmol) and 3 (234 mg,
1 mmol) were added. After the mixture was stirred for 5 min,
17R-ethynylestradiol 5a (296 mg, 1 mmol) was added and the
solution was stirred for 4 h at 55 °C. The volatiles were
removed in vacuo, and the residue was chromatographed (5%
CH3OH/CH2Cl2) to yield 1 (452 mg, 75%) as a yellow solid.
Mp 172-173 °C. IR (KBr) 3419, 2932, 1730, 1290, 1154 cm-1
.
1H NMR (CDCl3, 400 MHz,) δ 8.45 (s, 1H), 7.71 (s, 2H), 7.15
(d, J ) 8 Hz, 1H), 7.07 (s, 1H,), 6.62 (d, J ) 8 Hz, 1H), 6.56 (s,
1H), 5.10 (s, 1H), 2.82 (s, 2H), 2.50-1.60 (m, 14H), 1.52 (s,
9H), 1.45 (s, 9H), 0.93 (s, 3H). 13C NMR (CDCl3, 100 MHz) δ
154.9, 153.9, 152.9, 152.4, 150.1, 140.2, 137.8, 131.8, 126.3,
117.9, 116.9, 115.3, 112.9, 96.2, 83.2, 82.1, 81.6, 80.2, 49.9, 47.7,
43.6, 39.5, 39.0, 33.1, 29.6, 28.1, 28.0, 27.2, 26.4, 22.9, 12.9.
Anal. Calcd for C35H45N3O6‚0.5H2O: C, 68.60; H, 7.57; N, 6.86.
Found: C, 68.48; H, 7.30; N, 6.57.
17r-[6-(N ,N ′-Bis-t er t -b u t yloxyca r b on yl-h yd r a zin o-
p yr id in -3-yl-(E)-eth en yl)]-estr a -1,3,5(10)-tr ien e-3,17â-d i-
ol (2). A Shlenck tube was charged with 5a (300 mg, 0.88
mmol) and 3 (407.6 mg, 1.05 mmol). PdCl2(dppf)‚CH2Cl2 (28.7
mg, 0.035 mmol) was added in a glovebox. The tube was
purged with argon and the contents were dissolved in DMF
(4.4 mL). To the stirred solution was added degassed 2 M Na2-
CO3(aq) (2.2. mL) and the mixture was heated to 80 °C with
stirring. After 4 h PdCl2(dppf)‚CH2Cl2 (28.7 mg, 0.035 mmol)
in DMF (0.75 mL) was added to the reaction mixture, which
was then stirred with heating for 20 h. Volatiles were removed
in vacuo. The residue was dissolved in EtOAc, filtered through
Celite, washed with water, and dried over Na2SO4. Removal
of solvent yielded a brown solid that was purified by flash
chromatography (5% MeOH/CH2Cl2) to yield 2 (440 mg, 83%)
as a white solid. Mp 189-190 °C. IR (KBr) 3385, 2931, 1728,
exhibited a low RBA ) 1.5.11 The dithioether tricarbon-
ylrhenium(I) complex 28 also showed low affinity for the
estrogen receptor with RBA ) 2.5.44 The observed RBA
(111) Banerjee, S. R.; Levadala, M. K.; Lazarova, N.; Wei, L.;
Valliant, J . F.; Stephenson, K. A.; Babich, J . W.; Maresca, K. P.;
Zubieta, J . Inorg. Chem. 2002, 41, 6417-6425.
(112) (a) Katzenellenbogen, J . A.; J ohnson, H. J . J .; Myers, H. N.
Biochemistry 1973, 12, 4085-4092. (b) Carlson, K. E.; Choi, I.; Gee,
A.; Katzenellenbogen, B. S.; Katzenellenbogen, J . A. Biochemistry 1997,
36, 14897-14905. (c) Stauffer, S. R.; Coletta, C. J .; Tedesco, R.; Sun,
J .; Katzenellenbogen, B. S.; Katzenellenbogen, J . A. J . Med. Chem.
2000, 43, 4934-4947.
1480, 1154 cm-1 1H NMR (CDCl3, 400 MHz) δ 8.38 (s, 1H),
.
7.76 (d, J ) 8 Hz, 1H), 7.65 (s, 1H), 7.13 (d, 8 Hz, 1H), 7.00 (s,
1H), 6.68-6.45 (m, 4H), 4.70 (s, 1H), 2.82 (m, 2H), 2.40-1.60
(m, 14H), 1.52 (s, 9H), 1.46 (s, 9H), 0.99 (s, 3H). 13C NMR
J . Org. Chem, Vol. 68, No. 18, 2003 7069

Arterburn et al.
(CDCl3, 100 MHz) δ 155.0, 154.3, 153.2, 152.4, 145.9, 137.8,
137.1, 134.7, 131.7, 130.4, 128.1, 126.2, 123.1, 118.6, 115.4,
112.9, 84.2, 82.8, 81.4, 49.6, 47.6, 43.6, 39.6, 37.1, 32.6, 31.4,
29.6, 28.1, 27.4, 26.3, 23.4, 14.2. Anal. Calcd for C35H47N3O6‚
0.5H2O: C, 68.38; H, 7.87; N, 6.83. Found: C, 67.99; H, 7.99;
N, 6.57.
(d, J ) 2.4 Hz, 1H), 4.59 (s, 1H), 3.00 (s, 1H), 2.80-2.74 (m,
2H), 2.55-2.20 (m, 2H), 2.05-1.80 (m, 3H), 1.79 (m, 4H), 1.40
(m, 4H), 0.93 (s, 3H). 13C NMR (acetone-d6, 100 MHz) δ 198.78,
197.99, 193.51, 160.16, 156.30, 152.69, 143.00, 138.83, 132.41,
127.45, 116.42, 114.08, 112.78, 109.10, 97.44, 81.36, 80.22,
51.19, 48.89, 45.04, 41.09, 40.41, 34.54, 28.59, 27.83, 24.04,
13.82. Anal. Calcd for C28H29ClN3O5Re: C, 47.42; H, 4.12; N,
5.92; Cl, 5.00. Found: C, 47.42; H, 4.39; N, 6.03; Cl, 5.04.
Estr ogen Recep tor Bin d in g. Binding affinities of each
compound for ERR and ERâ, and uterine cytosol were deter-
mined in a radiometric competitive binding assay, using [3H]-
estradiol as tracer and charcoal dextran to adsorb free tracer
(uterine cytosol ER)112a or hydroxylapatite to adsorb ligand-
receptor complex (human ERR and ERâ).112b,112c Receptor
preparation was either lamb uterine cytosol, which consists
of nearly exclusively ERR,113 or human ERR and ERâ, ex-
pressed in baculovirus and purified (PanVera, Madison, WI).
Values given represent the mean of 2-3 repeat determinations
which have a coefficient of variation of 0.3.
N,N′-Bis-ter t-bu tyloxyca r bon yl-(5-br om o-p yr id in -2-yl)-
h yd r a zin e (3). A Schlenk tube was charged with Pd2(dba)3
(37 mg, 0.04 mmol), dppf (67 mg, 0.12 mmol), Cs2CO3 (352 mg,
1 mmol), and 10 (186 mg, 0.8 mmol) in a drybox. The tube
was purged with argon, then toluene (2 mL) and 2,5-dibro-
mopyridine (388.2 mg, 1 mmol) were added. The reaction
mixture was heated at 100 °C with stirring until 10 had been
consumed, as judged by TLC. The reaction mixture was cooled,
diluted with CH2Cl2, washed with water, concentrated under
vacuum, and chromatographed (10% EtOAc/Hex) to yield 3
(792 mg,85%) as a white solid. Mp 75-77 °C. IR (KBr) 3212,
1730, 1582, 1462, 1156, 838 cm-1. 1H NMR (CDCl3, 400 MHz)
δ 8.43 (d, J ) 2.2 Hz, 1H), 7.78 (dd, J ) 8 Hz, 2.2 Hz, 1H),
7.75 (d, J ) 8 Hz, 1H), 7.32 (s, 1H), 1.52 (s, 9H), 1.47 (s, 9H).
13C NMR (CDCl3, 100 MHz) 154.8, 152.9, 152.2, 148.5, 139.80,
Ack n ow led gm en t. The authors thank the US-
AMRC Breast Cancer Research Program DAMD17-97-
1-7120 (to J .B.A.) and National Institutes of Health (GM
08136 to J .B.A. and CA25563 to J .A.K.) for support of
this work. C.C. was supported by NIH/RISE (GM61222).
119.5, 116.1, 82.9, 81.6, 28.1. FAB MS (M + 1) calcd for C15H22
BrN3O4 388.0871, found 388.0853.
-
Tr icar bon yl-ch lor o-[(6-(h ydr azin o-pyr idin -3-yleth yn yl)-
est r a -1,3,5(10)-t r ien e-3,17â-d iol-17r-yl)]-r h en iu m (I) (4).
[ReCl3(CO)3][NEt4]2 (230 mg, 0.36 mmol) was stirred in 4 mL
of H2O for 1 h. To the solution was added 25 (116 mg, 0.24
mmol) in absolute ethanol (8 mL) as a clear yellow solution
and 2 M HCl(aq) (4 mL), then the mixture was allowed to stir
for 30 h. The product was precipitated by the addition of 90
mL of cold H2O and was collected by vacuum filtration. The
resulting product was purified by flash chromatography (10%
MeOH/CH2Cl2) to yield (130 mg, 75%) 4 as a pink solid. IR
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal methods, experimental methods for compounds 7a ,b, 9b,
12a -i, 15, 16, and 21-26 as well as 1H NMR and 13C NMR
spectra of compounds 1-4, 7a ,b, 9b, 12a -i, 15, 16, and 21-
26. This material is available free of charge via the Internet
at http://pubs.acs.org.
(KBr) 3254, 2029, 1919, 1898, 1625, 1503 cm-1 1H NMR
.
J O034780G
(acetone-d6, 400 MHz) δ 9.32 (s, 1H), 8.34 (d, J ) 2 Hz, 1H),
7.98 (d, J ) 8.8 Hz, 1H), 7.91 (s, 1H), 7.73 (dd, J ) 8.8, 2.0
Hz, 1H), 7.10 (d, J ) 8.4 Hz, 1H), 7.02 (d, J ) 8.8 Hz, 1H),
6.64 (d, J ) 8.8 Hz, 1H), 6.58 (dd, J ) 8.4, 2.4 Hz, 1H), 6.52
(113) Pettersson, K.; Gustafsson, J . A. Annu. Rev. Physiol. 2001,
63, 165-192.
7070 J . Org. Chem., Vol. 68, No. 18, 2003