Solid-phase synthesis of 1,4-benzodiazepine-2,5-diones. Library preparation and demonstration of synthesis generality

Article abstract of DOI:10.1021/jo9622845

A general and expedient method has been developed for the solid-phase synthesis of 1,4-benzodiazepine-2,5-diones 1 from three commercially available components; anthranilic acids, α-amino esters, and alkylating agents. Reaction conditions have been developed to prepare either racemic compounds for lead identification efforts or optically pure compounds for lead optimization efforts. The incorporation of diverse functionality into the benzodiazepine products has also been demonstrated. On the basis of the scope and generality of the synthesis sequence, a library of 1,4-benzodiazepine-2,5-diones has been prepared from 11 alkylating agents, 12 anthranilic acids, and 19 α-amino esters (nine sets of enantiomeric pairs and glycine methyl ester hydrochloride). The library was prepared in a spatially separate format using a microtiter-based apparatus that is inexpensive and straightforward to construct from ordinary items found in an organic or bioorganic laboratory. The high quality of the 1,4-benzodiazepine-2,5-dione library has been demonstrated by evaluating representative compounds by HPLC analysis and ¹H NMR.

Full text of DOI:10.1021/jo9622845

1
240
J . Org. Chem. 1997, 62, 1240-1256
Solid -P h a se Syn th esis of 1,4-Ben zod ia zep in e-2,5-d ion es. Libr a r y
P r ep a r a tion a n d Dem on str a tion of Syn th esis Gen er a lity
†
Constantine G. Boojamra, Kristina M. Burow, Lorin A. Thompson, and J onathan A. Ellman*
Department of Chemistry, University of California, Berkeley, California 94720
Received December 9, 1996X
A general and expedient method has been developed for the solid-phase synthesis of 1,4-
benzodiazepine-2,5-diones 1 from three commercially available components; anthranilic acids,
R-amino esters, and alkylating agents. Reaction conditions have been developed to prepare either
racemic compounds for lead identification efforts or optically pure compounds for lead optimization
efforts. The incorporation of diverse functionality into the benzodiazepine products has also been
demonstrated. On the basis of the scope and generality of the synthesis sequence, a library of
1
,4-benzodiazepine-2,5-diones has been prepared from 11 alkylating agents, 12 anthranilic acids,
and 19 R-amino esters (nine sets of enantiomeric pairs and glycine methyl ester hydrochloride).
The library was prepared in a spatially separate format using a microtiter-based apparatus that
is inexpensive and straightforward to construct from ordinary items found in an organic or bioorganic
laboratory. The high quality of the 1,4-benzodiazepine-2,5-dione library has been demonstrated
1
by evaluating representative compounds by HPLC analysis and H NMR.
In tr od u ction
The preparation and evaluation of small-molecule
libraries has become an important part of the drug
1
-5
discovery process.
In these efforts, particular empha-
sis has been placed upon the preparation and evaluation
of libraries based upon priviledged templates. The
display of different functionality upon these templates
has previously provided a number of potent and specific
F igu r e 1. Benzodiazepine templates for library synthesis.
antibiotics12-19 as well as to the benzodiazepine receptor
6
drugs or candidates toward different therapeutic targets.
The 1,4-benzodiazepines are an important class of
priviledged templates, and numerous derivatives have
been identified that have selective activities against a
20
antagonist, flumazenil. Structures related to flumaze-
nil have experimental applications as ethanol-intoxica-
21-24
tion antagonists.
The 1,4-benzodiazepine-2,5-diones
7
diverse array of biological targets. A subset of the 1,4-
25
have also shown promise as herbicides. In addition, the
,4-benzodiazepine-2,5-dione core appears in a number
benzodiazepines, the 1,4-benzodiazepine-2,5-diones 1
1
(
Figure 1), is the focus of this work. Derivatives have
26-29
of natural products.
8
-11
shown promise as antithrombotics.
They serve as
precursors to the anthramycin family of antitumor
(9) Blackburn, B. K.; Lee, A.; Baier, M Atropisomeric GPIIbIIIa
antagonists. Presented at the 209th National Meeting of the American
Chemical Society, Anaheim, CA; American Chemical Society: Wash-
ington, DC, 1995; ORGN 280.
†
Present Address: Microcide Pharmaceuticals Inc., 850 Maude
Avenue, Mountain View, CA 94043.
(10) McDowell, R. S.; Blackburn, B. K.; Gadek, T. R.; McGee, L. R.;
Rawson, T.; Reynolds, M.; Robarge, K. D.; Somers, T. C.; Thorsett, E.
D.; Tischler, M.; Webb, R. R.; Venuti, M. C. J . Am. Chem. Soc. 1994,
116, 5077-5083.
X
Abstract published in Advance ACS Abstracts, February 1, 1997.
1) Thompson, L. A.; Ellman, J . A. Chem. Rev. 1996, 96, 555-600.
2) Choong, I. C., Ellman, J . A. Annu. Rep. Med. Chem. 1996, 31,
(
(
3
09-318.
3) Terrett, N. K.; Gardner, M.; Gordon, D. W.; Kobylecki, R. J .;
Steele, J . Tetrahedron 1995, 51, 8135-8173.
4) Gordon, E. M.; Barrett, R. W.; Dower, W. J .; Fodor, S. P. A.;
Gallop, M. A. J . Med. Chem. 1994, 37, 1385-1401.
5) Fr u¨ chtel, J . S.; J ung, G. Angew. Chem., Int. Ed. Engl. 1996, 35,
7-42.
6) Ariens, E. J .; Beld, A. J .; Rodrigues de Miranda, J . F.; Simonis,
(11) McDowell, R. S.; Gadek, T. R.; Barker, P. L.; Burdick, D. J .;
Chan, K. S.; Quan, C. L.; Skelton, N.; Strumble, M.; Thorsett, E. D.;
Tischler, M.; Tom, J . Y. K.; Webb, T. R.; Burnier, J . J . Am. Chem. Soc.
1994, 116, 5069-5076.
(
(
(12) Ishikura, M.; Mori, M.; Terashima, M.; Ban, Y. J . Chem. Soc.,
Chem. Commun. 1982, 741-742.
(
1
(13) Mori, M.; Uozumi, Y.; Kimura, M.; Ban, Y. Tetrahedron 1986,
42, 3793-3806.
(
A. M. In The Receptors: A Comprehensive Treaty; O’Brien, R. D., Ed.;
Plenum: New York, 1979; Vol. 1; pp 33-41.
(14) Reed, J . N.; Snieckus, V. Tetrahedron Lett. 1984, 25, 5505.
(15) Kaneko, T.; Wong, H.; Doyle, T. W. Tetrahedron Lett. 1983, 24,
5165-5168.
(
7) Selected 1,4-benzodiazepine therapeutic agents or promising
candidates: (a) Anxiolytics, hypnotics, and antiepileptics: Sternbach,
L. H. J . Med. Chem. 1979, 22, 1-7. (b) Cholecystokinin antagonists:
Evans, B. E. et al. J . Med. Chem. 1988, 31, 2235-2246. (c) Opioid
receptor antagonist: Romer, D. et al. Nature 1982, 298, 759-760. (d)
HIV Tat antagonist: Hsu, M.-C. et al. Science 1991, 254, 1799-1802.
(16) Stevens, R. V.; Cory, R. M.; Rossen, S. J . Chem. Soc., Chem.
Commun. 1975, 742.
(17) Confalone, P. N.; Huie, E. M.; Ko, S. S.; Cole, G. M. J . Org.
Chem. 1988, 53, 482-487.
(18) Pe n˜ a, M. R.; Stille, J . K. Tetrahedron Lett. 1987, 28, 6573-
6576.
(e) HIV reverse transcriptase inhibitor: Pauwels, R. et al. Nature 1990,
3
43, 470-474. (f) Platelet aggregating factor antagonist: Miyazawa,
(19) Pe n˜ a, M. R.; Stille, J . K. J . Am. Chem. Soc. 1989, 111, 5417-
S. et al. Chem. Pharm. Bull. 1992, 40(2), 521-523 (thienodiazepine
derivative). (g) Antipsychotics: Li e´ geois, J .-F. F.; Bruhwyler, J .; Damas,
J .; Nguyen, T. P.; Chleide, E. M. G.; Mercier, M. G. A.; Rogister, F. A.;
Delarge, J . E. J . Med. Chem. 1993, 36, 2107-2114. (h) Oxytocin
antagonist: MDDR MDL Drug Data Report data base. MDL Informa-
tion Systems, Inc., 14600 Catalina St., San Leandro, CA.
5424.
(20) Hunkeler, W. Chimia 1993, 47, 141-147.
(21) Suzdak, P. D.; Glowa, J . R.; Crawley, J . N.; Schwartz, R. D.;
Skolnick, P.; Paul, S. M. Science 1986, 234, 1243-1247.
(22) Polc, P.; Richards, J . G. Br. J . Pharmacol. 1985, 86, 465P.
(23) Malminiemi, O.; Korpi, E. R. Eur. J . Pharmacol. 1989, 169, 53-
60.
(
8) Webb, R. R.; Barker, P. R.; Baier, M.; Reynolds, M. E.; Robarge,
K. D.; Blackburn, B. K.; Tichler, M. H.; Weese, K. J . Tetrahedron Lett.
994, 35, 2113-2116.
(24) Bonetti, E. P.; Burkard, W. P.; Gabl, M.; Mohler, H.; Richards,
J . G. Br. J . Pharmacol. 1985, 86, 463P.
1
S0022-3263(96)02284-0 CCC: $14.00 © 1997 American Chemical Society

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1241
We3
0-32
and others33 have previously reported the
(Figure 1) is derived from glycine (R ) H). We did not
3
preparation of libraries of 1,4-benzodiazepines that be-
long to the 1,4-benzodiazepin-2-one class 2 (Figure 1).
Recently, we have also reported a high-yielding and
general method for the solid-phase synthesis of 1,4-
benzodiazepine-2,5-diones 1.34 The strategy comple-
ments our synthesis of structures 2 because it allows
consider palladium-catalyzed carbonylative insertion due
to the need for high temperatures and high pressures of
CO and poor yields.1
2,13,49-52
Finally, we chose not to
employ the aza-Wittig cyclization53 because this approach
would require the use of 2-azidobenzoic acids as one of
the components, few of which are commercially available.
1
much greater diversity to be introduced at the R site.
Two alternative solid-phase approaches to 1,4-benzodi-
Upon selecting lactamization as the cyclization method,
we then designed a sequence that relied on the incorpo-
ration of three different components, anthranilic acids
azepine-2,5-diones have now also been reported by other
researchers.3
5,36
Here, we describe further exploration
1
2
3
(
3
R ), alkylating agents (R ), and R-amino esters (R ). Over
of the generality of our chemistry and application of the
chemistry to the preparation of a 2508-member library
of benzodiazepines 1.
0 anthranilic acids, 50 R-amino esters with the ap-
propriate side-chain protection, and 100 alkylating agents
54
are commercially available. To expedite library genera-
tion, we required that incorporation of the anthranilic
acid derivatives be accomplished without prior protection
of either the aniline or carboxylic acid functionality.
Resu lts a n d Discu ssion
We sought to achieve three goals in designing an
approach to prepare libraries of 1,4-benzodiazepine-
,5-diones: (1) Several different building block sets
The optimized synthesis approach is shown in Scheme
1 and begins with the attachment of the R-amino ester
to the solid support, followed by acylation with an
anthranilic acid, base-catalyzed lactamization, alkylation,
and cleavage. A critical feature of the strategy is the
attachment to the support as an N-alkyl substituent 5,
which provides a tertiary amide lactamization precursor
6 (Scheme 1). Literature pertaining to the cyclizations
2
should be incorporated to provide rapid access to a large
number of diverse compounds. (2) The building blocks
used in the synthesis of the library should be readily
accessible and ideally commercially available to facilitate
rapid library synthesis. (3) The chemistry should be
compatible with the display of as much functionality as
possible including reactive functionality that is commonly
found in drugs.
In order to acheive these goals, literature regarding
the classical synthesis of 1,4-benzodiazepine-2,5-diones
indicated that closure of the seven-membered ring would
be the cornerstone of any approach. Ring closure via
lactamization was the most often used method and
clearly provided the highest yields and the most
of small peptides indicates that the presence of backbone
amide N-alkyl groups5
5-60
enhances the equilibrium cis/
trans ratio about these tertiary amides and, in a small
peptide cyclization precursor, greatly enhances the rate
6
0-63
of formation of cyclic peptide over dimer or oligomer.
1,4-Ben zodiazepin e-2,5-dion e Syn th esis Sequ en ce.
According to this strategy, (chloromethyl)polystyrene
(Merrifield resin) is derivatized by alkylation with the
sodium salt of 4-hydroxy-2,6-dimethoxybenzaldehyde (3)
generality.3
7-46
We rejected alkylative cyclizations,
since such closures are only precedented in the case
where the amino acid portion of the benzodiazepine 1
10,47,48
6
4,65
to provide resin-bound aldehyde 4 (Scheme 1).
R-amino ester is then loaded onto the support by reduc-
tive amination employing NaBH(OAc) in 1% acetic acid
An
3
(
(
25) Karp, G. M. J . Org. Chem. 1995, 60, 5814-5819.
26) White, J . D.; Haefliger, W. E.; Dimsdale, M. J . Tetrahedron
1
9
1
970, 26, 233-242.
27) Smith, H.; Wegfahrt, P.; Rapoport, H. J . Am. Chem. Soc. 1968,
0, 1668-1669.
28) Richter, H.; Winter, K.; Kousy, S. E.; Luckner, M. Pharmazie
974, 29, 506-510.
29) Martin, P. K.; Rapoport, H.; Smith, H. W.; Wong, J . L. J . Org.
Chem. 1969, 34, 1359-1363.
30) Bunin, B. A.; Plunkett, M. J .; Ellman, J . A. Methods Enzymol.
996, 267, 448-465.
31) Bunin, B. A.; Plunkett, M. J .; Ellman, J . A. Proc. Natl. Acad.
Sci. U.S.A. 1994, 91, 4708-4712.
32) Bunin, B. A.; Ellman, J . A. J . Am. Chem. Soc. 1992, 114,
0997-10998.
33) DeWitt, S. H.; Kiely, J . S.; Stankovic, C. J .; Schroeder, M. C.;
Cody, D. M. R.; Pavia, M. R. Proc. Natl. Acad. Sci. U.S.A. 1993, 90,
(47) Yamamoto, H.; Inaba, S.; Nakao, M.; Maruyama, I. Chem.
Pharm. Bull. 1969, 17, 400-403.
(
(48) Lee, C.-M. J . Heterocycl. Chem. 1964, 1, 235-238.
(49) Ishikura, M.; Mori, M.; Ikeda, T.; Terashima, M.; Ban, Y. J .
Org. Chem. 1982, 47, 2456-2461.
(
(
(50) Mori, M.; Ishikura, M.; Ikeda, T.; Ban, Y. Heterocycles 1981,
16, 1491-1494.
(
(51) Mori, M.; Purvaneckas, G. E.; Ishikura, M.; Ban, Y. Chem.
Pharm. Bull. 1984, 32, 3840-3847.
1
(
(52) Mori, M.; Kimura, M.; Uozumi, Y.; Ban, Y. Tetrahedron Lett.
1985, 26, 5947-5950.
(
(53) Eguchi, S.; Yamashita, K.; Matsushita, Y. Synlett 1992, 295-
296.
1
(
(54) Structure searches were performed using the Available Chemi-
cals Directory (ACD), MDL Information Systems, Inc., 14600 Catalina
St., San Leandro, CA 94577.
6
1
5
909-6913.
34) Boojamra, C. G.; Burow, K. M.; Ellman, J . A. J . Org. Chem.
995, 60, 5742-5743.
35) Goff, D. A.; Zuckermann, R. N. J . Org. Chem. 1995, 60, 5744-
745.
36) Moroder, L.; Lutz, J .; Grams, F.; Rudolph-B o¨ hner, S.; O¨ sapay,
G.; Goodman, M.; Kolbeck, W. Biopolymers 1996, 38, 295-300.
37) Cho, N. S.; Song, K. Y.; P a´ rk a´ nyi, C. J . Heterocycl. Chem. 1989,
6, 1807-1810.
38) Hoffmann, E.; J agnicinski, B. J . Heterocycl. Chem. 1966, 3,
48-351.
(
(55) Cavelier-Frontin, F.; P e` pe, G.; Verducci, J .; Siri, D.; J acquier,
R. J . Am. Chem. Soc. 1992, 114, 8885-8890.
(
(56) Dale, J .; Titlestad, K. J . Chem. Soc., Chem. Commun. 1969,
656-659.
(
(57) Pastuszak, J .; Gardner, J . H.; Singh, J .; Rich, D. H. J . Org.
Chem. 1982, 47, 2982-2987.
(
(58) Steiner, J . R.; Barnes, C. L. Int. J . Pept. Protein Res. 1988, 31,
212-219.
2
(
(59) Titlestad, K. Acta Chem. Scand., B 1977, 31, 641-661.
(60) J acquier, R.; Lazaro, R.; Raniriseheno, H.; Viallefont, P. Int. J .
Pept. Protein Res. 1987, 30, 22-32.
3
(
(
(
(
39) Carabateas, P. M.; Harris, L. S. J . Med. Chem. 1966, 9, 6-10.
40) Carabateas, P. M. U.S. Patent 3 415 814, 1968.
41) Carabateas, P. M. U.S. Patent 3 384 635, 1968.
42) Uskokovic, M.; Iacobelli, J .; Wenner, W. J . Org. Chem. 1962,
(61) Cavelier-Frontin, F.; Achmad, S.; Verducci, J .; J acquier, R.;
P e` pe, G. THEOCHEM 1993, 286, 125-130.
(62) Stewart, W. E.; T. H. Siddall, I. Chem. Rev. 1970, 70, 517-
2
7, 3606-3608.
551.
(
(
43) Uskokovic, M. R., Wenner, W. U.S. Patent 3 261 828, 1966.
44) Akssira, M.; Boumzebra, M.; Kasmi, H.; Dahdouh, A.; Roumes-
(63) Vitoux, B.; Aubry, A.; Cung, M. T.; Marraud, M. Int. J . Pept.
Protein Res. 1986, 27, 617-632.
tant, M. L.; Viallefont, P. Tetrahedron 1994, 50, 9051-9060.
45) Akssira, M.; Kasmi, H.; Dahdouh, A.; Boumzebra, M. Tetrahe-
dron Lett. 1992, 33, 1887-1888.
46) Akssira, M.; Boumzebra, M.; Kasmi, H.; Dahdouh, A.; Roumes-
tant, M. L.; Viallefont, P. Synth. Commun. 1993, 23, 2265-2272.
(64) Landi, J . J .; Ramig, K. Synth. Commun. 1991, 21, 167-171.
(65) In initial studies, a monomethoxy analog of the dimethoxy
linker described herein was initially employed. However, at the end
of the synthesis treatment with TFA resulted in release of the linker
from the support still covalently bound to the benzodiazepine.
(
(

1
242 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
Sch em e 1
in DMF. In order to minimize racemization, it is es-
sential in this step that preequilibration of the resin-
bound aldehyde and the R-amino ester be minimized
in DMF/THF (1:1) for 30 h followed by addition of an
appropriate alkylating agent provides a fully derivatized,
support-bound benzodiazepine 8. Complete cyclization
and alkylation (>95%) are observed according to this
reaction sequence as determined after cleavage of ben-
zodiazepines 8 from support. Cleavage is accomplished
in good yields and high purity by final treatment with
(
vide infra) before addition of the reducing agent to the
reaction mixture. We commonly employ two different
protocols for racemization free reductive amination. The
3
NaBH(OAc) can be premixed with resin-bound aldehyde
4
in 1% acetic acid in DMF followed by addition of an
TFA/Me
2 2
S/H O (90:5:5).
R-amino ester. Alternatively, the R-amino ester and
reductant can be premixed in 1% acetic acid in DMF
followed by addition of resin-bound aldehyde 4.
According to the above-described synthesis sequence,
the benzodiazepine products 1 are obtained without any
loss of optical purity at the stereocenter introduced by
the R-amino ester. Racemization in the reductive ami-
nation, anthranilic acid acylation, and cyclization steps
could readily be detected by chiral HPLC analysis. Less
than 1% racemization was observed for either benzodi-
azepine 1b or benzodiazepine 1c (Figure 2).
It was also necessary to show that no racemization
occurs in the alkylation step. Unfortunately, since enan-
tiomers of alkylated benzodiazepines separate poorly on
Pirkle chiral HPLC columns,68 it was necessary instead
to hydrolyze the benzodiazepine and analyze the chiral
integrity of the liberated amino acid. A sample of
benzodiazepine 1o (Figure 2) was heated at reflux in 6
N aqueous hydrochloric acid in order to liberate leucine.
The methyl ester was formed using thionyl chloride in
methanol, and separate aliquots of the amino ester were
then acylated with (+)-MTPA chloride and with (-)-
MTPA chloride. Gas chromatographic analysis indicated
a 97/3 ratio of amino acid enantiomers. The 3% minor
enantiomer most likely arose during the benzodiazepine
hydrolysis step69 and not in the course of benzodiazepine
synthesis.
Acylation of the resulting secondary amine 5 with
commercially available unprotected anthranilic acids
then provides the support-bound tertiary amide 6. Op-
timization of this acylation step required considerable
experimentation. For example, even the highly activated
azabenzotriazole-based reagents recently developed by
Carpino, such as HATU,66 gave poor reaction conversion.
Carbodiimides were the only coupling agents found to
efficiently effect this transformation. Furthermore, good
yields of acylated material were obtained only when the
carbodiimides were employed in conjunction with the
hydrochloride salt of a tertiary amine. EDC (1-ethyl-3-
[3-(dimethylamino)propyl] carbodiimide‚hydrochloride)
proved to be the most efficient reagent since it contains
an internal tertiary amine hydrochloride salt. To ensure
that complete acylation occurs, the resin is subjected
twice to this coupling procedure.
Solution studies indicated that base-catalyzed lactam-
ization would be the most general way of producing the
support-bound cyclic product 8 (R2 ) H). Ideally, cy-
clization would be accomplished under conditions suf-
Chirality is derived from the commercially available
R-amino ester starting materials. In some cases, the
D-enantiomer of the starting material is much more
expensive than the naturally occurring enantiomer or
may not be available from commercial sources. For lead
identification efforts it would be important to access both
enantiomers of the 1,4-benzodiazepine-2,5-dione products
in order to maximize the diverse display of functionality.
ficiently basic to provide the anilide anion 7 for subse-
quent alkylation to introduce the R2 components of
compounds 8 in the same reaction step. The lithium salt
of acetanilide proved to be an optimal base for effecting
these transformations. Because acetanilide has a pK
2
a
of
1.5 in DMSO,67 deprotonation and alkylation of amides,
esters, or carbamates does not occur since these func-
tionalities are all considerably more basic, with pK ’s
greater than 24 in DMSO. Treatment of 6 with this base
a
(
68) Pirkle, W. H.; Tsipouras, A. J . Chromatogr. 1984, 291, 291-
98.
(69) Benoiton, N. L. Quantitation and Sequence Dependence of
2
(
66) Carpino, L. A.; Elfaham, A.; Albericio, F. Tetrahedron Lett.
994, 35, 2279-2282.
67) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456-463.
1
Racemization in Peptide Synthesis. In The Peptides; Gross, E.; Meien-
hofer, J ., Eds.; Academic: New York, 1983; Vol. 5, pp 221-222.
(

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1243
F igu r e 2. Benzodiazepine products. Yields are of purified material and are based upon the amino ester loading levels of the
resin as determined according to the procedure described in the Experimental Section: (*) products formed under racemizing
†
conditions described in text from enantiopure starting materials; ( ) racemic products from commercially available racemic material.
We therefore chose to develop conditions whereby racemic
benzodiazepine products could be obtained under mild
conditions from the enantiomerically pure R-amino ester
starting materials. Complete racemization could be
accomplished, presumably by imine tautomerization, by
preequilibrating the R-amino ester‚HCl salt, 0.3 equiv of
P r od u cts a n d Yield s. We have synthesized a diverse
array of 1,4-benzodiazepine-2,5-diones to demonstrate the
versatility of the described synthesis sequence and to
determine which derivatives should be incorporated into
a library. We have been able to incorporate an array of
sterically and electronically diverse anthranilic acids,
both unfunctionalized and functionalized R-amino esters,
and a variety of alkylating agents.
i-Pr
2
EtN, and the resin-bound aldehyde 4 for 6 h before
. Chiral HPLC analysis of
addition of the NaBH(OAc)
3
benzodiazepine product 1c prepared using these initial
reductive amination conditions confirmed that complete
racemization had in fact occurred.
Simple amino acids work well in this protocol, as well
as those with functionalized side chains: Benzodiaz-
epines 1f, 1i, 1v, and 1n are derived from glutamic acid,

1
244 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
thienylalanine, tyrosine, and lysine, respectively. Com-
pound 1g is derived from glutamine. Glutamine methyl
ester, when incorporated without side-chain protection,
provided a succinimide side product resulting from side-
chain cyclization with the methyl ester. When the
dimethoxybenzhydrol group was used as a side-chain
protecting group, glutamine provided products in com-
parable yield to other amino acids.
Attempts to incorporate serine met with failure, as the
large majority of material isolated after attempting to
synthesize a serine-containing benzodiazepine was de-
rived from elimination of the â-hydroxyl group.71 The
incorporation of valine proceeds with low conversion due
to incomplete acylation in the anthranilic acid acylation
step as determined by recovery of significant amounts
of unacylated valine methyl ester after cleavage from
support.
epine 1d was cleaved from support, an aliquot of resin
was subjected to cross-coupling with p-methoxyben-
zeneboronic acid employing Pd(PPh
) as the catalyst in
3 4
THF at reflux to furnish 1u after cleavage from support.
Benzodiazepine 1v is an example of coupling reaction
with an alkylborane derived from B-hexyl-9-BBN (pre-
pared in situ by hydroboration) with a benzodiazepine
derived from 4-bromoanthranilic acid. We have also
explored Suzuki reactions employing conditions reported
7
0
7
5
by J ohnson in the synthesis of prostaglandin analogs
because the conditions reportedly allow reactions to be
performed at significantly lower temperatures. Product
1w was synthesized in 78% overall yield employing a
DMF/THF/H
no)ferrocenepalladium(II) chloride [PdCl
2
O solvent system and bis(diphenylphosphi-
(dppf)] as cata-
2
lyst. Heating the reaction mixture to 50 °C was required
in order to ensure reaction completion.
Libr a r y Syn th esis. The library was prepared pre-
dominantly to demonstrate that our synthetic method
proceeds with high fidelity, even when executed in a
parallel format. To this end, rigorous characterization
of representative members of the library was required,
and thus, a spatially separate parallel synthesis was
employed. The development of detailed structure-activ-
ity relationships upon biological evaluation of the spa-
tially separate library should also be straightforward.
The key to producing a high-quality library in a
parallel format requires the identification of the ap-
propriate solid support on which to synthesize the library,
and to a similar extent, the apparatus used to hold and
filter the support so that the synthesis can be performed
efficiently. There are a number of paradigms reported
in the literature for the spatially separate manipulation
We have been able to incorporate anthranilic acids
containing electron-rich (e.g., 1m ) and electron-poor
functionality (e.g. 1i), a host of halogenated structures
(
e.g., 1c,d ,n ,j), as well as heterocyclic analogs (1p ,t).
Unfortunately, attempts to alkylate 1t led to product that
was only 60% alkylated, presumably because the pK of
a
the anilide proton of the thienodiazepine 1t is slightly
higher than that of the other benzodiazepines synthe-
sized.
According to our synthesis strategy, the anthranilic
acids are employed without aniline protection. For the
compounds shown in Figure 2, no aniline acylation was
1
observed as determined by H NMR or TLC analysis of
the unpurified benzodiazepine products from support.
The presence of electron-donating functionality on the
anthranilic acid para with respect to the aniline does
result in significant acylation of the unprotected aniline.
In the case of 5-iodoanthranilic acid, the desired product
was contaminated with approximately 15-20% of higher
order oligomers, and 5-acetamidoanthranilic acid pro-
vided only oligomeric products.
7
6-78
of solid supports in the context of parallel synthesis.
Our most important selection criteria was that we employ
apparatus configured in a standard 96-well microtiter
format. A great deal of instrumentation has been
developed for the manipulation of materials in a micro-
titer format, e.g., multichannel pipet devices, filtration
units, and microtiter-based concentrators.
In order to further increase the diversity of the ben-
zodiazepine products, we have demonstrated the func-
Libr a r y Syn th esis Em p loyin g Ch ir on Mim otop es
P in Ap p a r a tu s. We intially employed the Chiron
tionalization of aryl bromide-containing benzodiazepines
with the Suzuki coupling reaction.72 This reaction is an
Mimotopes pin apparatus, originally developed by Geysen
ideal carbon-carbon bond-forming method for the syn-
thesis of compounds by combinatorial methods due to its
compatibility with a wide range of functionality and high
reaction yields. In addition, there are many commer-
cially available arylboronic acids, and alkylboranes can
readily be accessed through in situ hydroboration meth-
ods. There are now also a number of reports in the
literature of solid-phase applications of these reac-
for peptide epitope mapping.7
9-81
In this apparatus, 96
polyethylene pins are placed into a supporting block so
that each pin fits into a separate well of a 96-well
microtiter plate, thus allowing use of microtiter-based
instrumentation. In addition, we had previously pre-
3
0,31
pared a number of 1,4-benzodiazepin-2-one libraries
and a â-turn mimetic library82 employing this apparatus.
Unfortunately, we encountered two significant problems
with the Mimitopes apparatus in the synthesis of librar-
ies of 1,4-benzodiazepine-2,5-diones. First, the pins were
tions.2
,73,74
Benzodiazepines synthesized from 4- and 5-bromoan-
thranilic acids have been successfully subjected to Suzuki
cross-coupling reaction conditions. Before benzodiaz-
(75) J ohnson, C. R.; Braun, M. P. J . Am. Chem. Soc. 1993, 115,
1
1014-11015.
(
70) K o¨ nig, W.; Geiger, R. Chem. Ber. 1970, 103, 2041-2051.
(76) Dewitt, S. H.; Kiely, J . S.; Stankovic, C. J .; Schroeder, M. C.;
(71) In preliminary studies, good yields of 1,4-benzodazepine-2,5-
Cody, D. M. R.; Pavia, M. R. Proc. Natl. Acad. Sci. U.S.A. 1993, 90,
6909-6913.
diones incorporating serine were obtained by performing the cyclization
with pyridinium hydrochloride in DMF at 90 °C for 48 h. However,
the trifluoroacetic acid-mediated cleavage step resulted in significant
trifluoroacetylation of the primary hydroxyl. We have not previously
observed trifluoroacetylation of secondary alcohols or phenols during
the cleavage step. Benzodiazepines incorporating phenylalanine and
glycine were also prepared in good yield using these modified cycliza-
tion conditions.
(77) Geysen, H. M.; Meloen, R. H.; Barteling, S. J . Proc. Natl. Acad.
Sci. U.S.A. 1984, 81, 3998-4002.
(78) Meyers, H. V.; Dilley, G. J .; Durgin, T. L.; Powers, T. S.;
Winssinger, N. A.; Zhu, H.; Pavia, M. R. Mol. Diversity 1995, 1, 13-
20.
(79) Valerio, R. M.; Bray, A. M.; Maeji, N. J . Int. J . Pept. Protein
Res. 1994, 44, 158-165.
(80) Geysen, H. M.; Rodda, S. J .; Mason, T. J .; Tribbick, G.; Schoofs,
P. G. J . Immun. Methods 1987, 102, 259.
(
72) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2481.
(73) Backes, B. J .; Ellman, J . A. J . Am. Chem. Soc. 1994, 116,
1
9
1171-11172.
74) Frenette, R.; Friesen, R. W. Tetrahedron Lett. 1994, 35, 9177-
180.
(81) Maeji, N. J .; Bray, A. M.; Valerio, R. M.; Wang, W. Peptide Res.
1995, 8, 33-38.
(82) Virgilio, A. A.; Schurer, S.; Ellman, J . A. Tetrahedron, in press.
(

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1245
acids, 11 alkylating agents, and 10 R-amino esters (19 if
both enantiomers are counted). These are shown in
Figure 4.
The synthesis of the library was then carried out in a
split-split format. Equal portions of resin were first
derivatized with the 10 R-amino esters. The R-amino
esters derived from alanine, naphthylalanine, and thi-
enylalanine were loaded under the nonracemizing condi-
tions, since they were available in racemic form. Glycine
was also loaded under these conditions. The remaining
R-amino esters were loaded employing the racemizing
conditions. In every case, infrared spectroscopy indicated
complete disappearance of the aldehyde, which was
replaced by a strong ester carbonyl stretch. The flasks
were weighed, and equal portions of the product resin
mass was removed from each flask and placed into each
of 12 12-mL filter cartridges fitted with 70-µm hydro-
phobic polyethylene frits (available from Applied Separa-
tions). At the end of this splitting operation, 120 filter
cartridges had been charged with resin.
After the EDC-mediated acylations were performed
and the resins rinsed clean, the beads were suspended
as an isopycnic slurry83 in 3:2 dichloroethane/DMF.
Under isopycnic conditions, the solvated beads and the
solvent have the same density, and therefore, the beads
do not settle after agitation and remain evenly distrib-
uted for resin transfer. All of the resins in all 120 filter
cartridges were taken up in the same volume of this
mixture, and aliquots of equal volume were removed from
the cartridges and placed in the appropriately addressed
tubes in the multitube reaction apparatus. In this way,
approximately 15 mg dry weight of resin was transfered
to each tube. Given that the mixture was isopycnic and
equal volumes were added to all tubes, we expected the
number of moles of benzodiazepine precursor delivered
to each tube to be the same. A small portion of resin
was saved from each of the 120 filter cartridges in case
a particular benzodiazepine needed to be remade.
Two columns in every multitube plate were left empty,
providing an apparatus that was effectively 80 (10 × 8)
tubes per plate. Thus, after cleavage into a 96-well
microtiter plate, two columns would be left blank for
biological controls during assays. Sixteen multitube
plates, plus one that was only half full, were required.
These plates were transferred to small polypropylene bins
in a nitrogen bag (former pipet rack covers), and a 0.25
M solution of lithium acetanilide in 1:1 THF/DMF was
added to induce cyclization. After 48 h, each plate was
transferred to another bin that had been charged with a
DMF solution of 0.4 M alkylating agent. After 6 h, the
contents of the tubes were rinsed repeatedly and the
product benzodiazepines were cleaved into microtiter
wells.
F igu r e 3. Multitube parallel synthesis apparatus.
only available derivatized with amine functional groups.
This required that we reengineer our linker for attach-
ment through amine functionality. Of more serious
concern, we observed variable yields in 1,4-benzodiaz-
epine-2,5-dione synthesis on pins, indicating that sig-
nificant chemistry reoptimization would be necessary. We
therefore decided to explore alternative library synthesis
apparatus that would allow us to use commercially
available resin.
Libr a r y Syn th esis on Bea d s. The Diversomer ap-
paratus of DeWitt and co-workers allows the use of
polystyrene beads;33 however, it is not compatible with
a microtiter format. We therefore decided to design a
high-throughput parallel synthesis apparatus that could
be made quickly with relatively little expense and that
would be compatible with a microtiter format; it is shown
in schematic form in Figure 3. It consists of three parts,
a 96-hole (8 × 12) bracket, a series of 96 7-mm (outer
diameter) glass tubes, and hydrophobic polyethylene frits,
which have been sealed into one end of each of the tubes
by heating. Reagents are delivered into the tubes by
submerging them in a 96 2-mL well microtiter block. A
detailed account of the construction and use of this
apparatus is documented in the Experimental Section.
For the sake of simplicity, this will be referred to as the
multitube apparatus.
Several features of this apparatus make it attractive
for use in the context of parallel synthesis. Construction
is easy. It is made from ordinary items found in an
organic or bioorganic chemistry lab. In several days, 17
blocks (∼1500 discrete reaction tubes) can be constructed
for a total cost of under $500. Part or all of the apparatus
may be reused, depending on the conditions to which it
is subjected. Commercially available Beckman 2 mL
deep-well microtiter plates serve as reaction vessels.
Finally, the apparatus seems to be amenable to many
conditions that would be encountered over the course of
organic synthesis, e.g., acidic and basic conditions, as well
as compatibility with a range of protic and aprotic
solvents. Elevated temperatures may be a problem since
the polyethylene frits begin to deform around 60 °C.
Libr a r y Eva lu a tion . The integrity of the library was
evaluated in two ways. First, exact yields were obtained
by HPLC analysis for multiple benzodiazepines. For
these benzodiazepines the relative extinction coefficient
of the benzodiazepine to the internal standard nitrotolu-
ene was used to determine the quantity of material.
Syn th esis of a Libr a r y of 1,4-Ben zod ia zep in e-2,5-
d ion es. Each amino acid and each anthranilic acid that
were incorporated into our library were rigorously dem-
onstrated to provide 1,4-benzodiazepine-2,5-diones in
good to high yield (see, e.g., Figure 2). Every alkylating
agent was similarly evaluated, with the exception of the
1
Second, H NMR spectra were obtained from compounds
in 36 randomly chosen wells.
The first set of benzodiazepines evaluated were from
wells corresponding to structures whose UV absorbance
relative to the internal standard p-nitrotoluene had been
2
-(bromomethyl)naphthalene, which we considered equiva-
lent in reactivity to the other benzylic halides. Many
components were successfully tested in more than one
combination. Ultimately, we selected 12 anthranilic
(83) Zuckermann, R. N.; Kerr, J . M.; Siani, M. A.; Banville, S. C.
Int. J . Pept. Protein. Res. 1992, 40, 497-506.

1
246 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
Ta ble 1. Yield s of Selected Ben zod ia zep in esa
entry
R1
R2
R3
yield (µmol)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
7-Cl
9-pyridyl
8-Me
benzyl
c-(C3H5)CH2 CH2C6H5
piperonyl
piperonyl
(CH2)2CO2H
4.8
3.6
2-thienylmethyl 3.3
CH2C6H5
CH2CH(CH3)2
7-Cl
2.4
2.8
1.8
not soluble
9-Br, 7-Me methyl
6-F
9-Br, 7-Me
8-Me
8-O2N
7-Cl
NH2COCH2 CH2C6H5
H
4-phenylBn CH2C6H4OH
c-(C3H5)CH2 2-thienylmethyl 2.0
ethyl
NH2COCH2 CH2C6H4OH
ethyl CH2C6H5
3,5-diMeBn 2-thienylmethyl 1.1
methyl
ethyl
CH2CH(CH3)2
b
2.4
1
1
1
1
1
1
1
1
(CH2)2CONH2
2.4
2.3
2.4
7-Cl
c
6-F
7-Cl
8-O2N
8-OMe
8-OMe
CH2-2-(C10H7)
CH2CH(CH3)2
H
CH3
2.6
2.4
4.0
9.7
2-MeOBn
benzyl
a
UV absorbances of the listed derivatives were determined
relative to the internal standard (p-nitrotoluene) were predeter-
mined (see Table 8). b This yield is based on the corresponding R
1
)
8-hexyl derivative, entry 13, Table 8 (Experimental Section).
The benzodiazepine in entry 12 coeluted with p-nitrotoluene.
c
Thus, 9-fluoreneone was used as an internal standard.
Ta ble 2. Eva lu a tion of Ben zod ia zep in es
UV ratio
of Bz/Std (µmol)
yield
entry R1
R2
7-Br c-(C3H5)CH2
R3
a
1
2
3
4
5
6
7
8
9
0
H
3.59
4.12
3.35
2.87
3.03
3.65
3.47
5.31
1.13
2.7
3.1
2.5
2.2
2.3
2.7
2.6
4.0
0.8
9.4
7-Br c-(C3H5)CH2 (CH2)4NH2
7-Br c-(C3H5)CH2 (CH2)2CO2H
7-Br c-(C3H5)CH2 CH2C6H4OH
7-Br c-(C3H5)CH2 CH2CH(CH3)2
7-Br c-(C3H5)CH2 CH2-(2-C10H7)
7-Br c-(C3H5)CH2 CH2C6H5
7-Br c-(C3H5)CH2 2-thienylmethyl
7-Br c-(C3H5)CH2 (CH2)2CONH2
7-Br c-(C3H5)CH2 CH3
1
12.5
a
UV ratio of benzodiazepine to the standard 4-nitrotoluene was
based upon the relative chromophore of a related benzodiazepine
prepared from 5-bromoanthranilic acid (entry 14, Table 8).
tions are most likely due to variations in the equimolar
distribution techniques for partitioning resin as described
previously rather than synthesis fidelity. Excluding
alanine, the average quantity produced is 2.7 µmol with
a standard deviation (σ
) of 0.9 µmol.
n
F igu r e 4. Components used in the synthesis of the 1,4-
We then evaluated a series of benzodiazepines from a
randomly chosen plate. All benzodiazepines in this plate
had been alkylated with (bromomethyl)cyclopropane. In
order to directly compare benzodiazepines incorporating
each of the different amino acids, we examined all the
benzodiazepines in this plate substituted at position 7
with a bromide (see Table 2). The chromophore of these
benzodiazepine-2,5-diones are dominated by the anthra-
nilic acid portion of the molecules; we therefore assumed
that the extinction coefficient of each derivative would
be approximately equal. The quantity of each benzodi-
azepine produced, with the exception of the benzodiaz-
epine derived from glutamine (Table 2, entry 9) and
alanine (Table 2, entry 10), fall within a factor of 2. The
average quantity produced is 2.5 µmol with a standard
deviation of 0.8 µmol.
For each of the compounds evaluated (with the excep-
tion of the glutamine-derived compounds), HPLC with
detection at 252 nm indicated that the desired product
was in all cases the major UV active peak and in most
cases (∼80%) the only observed UV active peak aside
from the internal standard. The dimethoxybenzhydrol
protecting group used to protect glutamine during ben-
benzodiazepine-2,5-dione library.
determined for purified derivatives prepared on a large
scale (see the Experimental Section). Yields were cal-
culated by delivery of a stock solution of the nitrotoluene
internal standard to the contents of a particular well,
followed by HPLC analysis. Results are presented in
Table 1. Entry 7 corresponds to a well that contained
insoluble product; the yield for this benzodiazepine is
omitted. However, an alkylated version of this benzodi-
azepine was obtained in 2.8 µmol yield (Table 1, entry
5
).
Relatively small quantities of the benzodiazepines with
a 6-fluoro substituent (Table 1, entries 6 and 13) were
produced. This is not unexpected given that the yield of
benzodiazepines made on a large scale with this anthra-
nilic acid were also low. The benzodiazepine derived from
alanine, Table 1, entry 17, was recovered in almost four
times the average quantity. Other alanine-containing
benzodiazepines appeared in equally high yield relative
to the nonalanine benzodiazepines. The benzodiazepine
represented by entry 1 (Table 1) was also produced in
greater than expected quantities. The observed varia-

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1247
zodiazepine synthesis to some extent complicated the
evaluation of these benzodiazepines by HPLC.
Novabiochem, or Advanced Chemtech. The anthranilic acids
were purchased from Aldrich, Lancaster, TCI America, or
Maybridge, through their American distributor, Ryan Scien-
tific. The synthesis of two anthranilic acids that are not
commercially available is described directly below this para-
graph. Anhydrous N,N-dimethylformamide (DMF) and an-
hydrous 1-methyl-2-pyrrolidinone (NMP) were purchased from
1
H NMR spectra of compounds from 36 randomly
chosen wells were obtained in order to evaluate the purity
of the components of the library and to characterize them
as well.84 On the basis of the H NMR spectra, the correct
benzodiazepine could be unequivocally assigned for 35
of the 36 wells. For 31 of the 35 wells the desired
benzodiazepine product was not contaminated with any
related material. For two of the wells the desired
benzodiazepine was contaminated with ∼25-35% of a
related compound, and for the final two wells the desired
benzodiazepine was contaminated with an equal amount
of a related impurity.
1
Aldrich. Tetrahydrofuran was distilled under N from sodium/
2
benzophenone immediately prior to use unless sieve-dried THF
was used (indicated when used). It was not necessary to use
distilled solvents for rinsing of resin. Flash column chroma-
tography was carried out using Merck 60 230-400-mesh silica
gel. Thin layer chromatography (TLC) analyses were per-
formed with Uniplate 250 µm silica gel plates from Analtech,
1
Newark, DE (catalog no. 21521). H NMR spectra were
obtained with a UCB Bruker AM-400 or AM-500 FT spec-
trometer. Proton-decoupled 13C spectra were obtained at 101
or 126 MHz with the same instruments with a line broadening
of 1.5 Hz. Chemical shifts are reported in ppm. Coupling
constants are reported in Hz. Unless otherwise noted, spectra
While in almost every case the only product related to
our benzodiazepine synthesis was the desired compound,
we found varying amounts of the plasticizer dioctylphtha-
late in some wells and varying amounts of another
unrelated aliphatic impurity in some wells. Efforts to
isolate and characterize this second impurity by extrac-
tive and chromatographic methods were unsuccessful.
were obtained in CDCl
standard at 7.25 ppm; spectra obtained in DMSO-d
referenced to the residual DMSO-d , 2.49 ppm; spectra ob-
tained in acetonitrile-d were referenced to residual acetoni-
trile-d at 1.94 ppm. NMR samples from the library were
obtained by dissolving the entire contents of the well in 0.75
mL of acetonitrile-d or methanol-d . Elemental analyses were
3
with residual CHCl
3
as an internal
6
were
5
3
2
Con clu sion
3
4
A general and expedient method for the solid-phase
synthesis of 1,4-benzodiazepine-2,5-diones has been de-
veloped. Three commerically available components, an-
thranilic acids, R-amino esters, and alkylating agents, are
employed to introduce functionality. Reaction conditions
were developed to prepare either racemic compounds for
lead identification efforts or optically pure compounds for
lead optimization efforts. The incorporation of diverse
functionality into the benzodiazepine products was dem-
onstrated, including the incorporation of amines, amides,
carboxylic acids, phenols, ethers, thiophenes, pyridines,
halogens, sulfones, and nitro groups. Limitations to the
chemistry were also identified.
performed by M-H-W Labs, Phoenix, AZ, or by the University
of California, Department of Chemistry Microanalytical Labo-
ratory. Chloromethylpolystyrene (1% cross-linked) resin was
obtained from Novabiochem, catalog no. 01-64-0007, 200-400
mesh size. (Aminomethyl)polystyrene was obtained from
Novabiochem or Bachem. A filtration cannula (Pharmacia,
Uppsala, Sweden) is useful for filtration of resins in round-
bottom flasks.
4
-Meth oxya n th r a n ilic Acid . This compound was pre-
pared according to a modified literature procedure from
4-methyl-3-nitroanisole (available from Aldrich) through the
intermediate 4-methoxy-2-nitrobenzoic acid.85 In 150 mL of
HOAc was suspended 9.74 g of 4-methoxy-2-nitrobenzoic acid
(49.4 mmol) in a round-bottom flask. To this was added 75
mL of EtOAc in order to help dissolve the starting material.
The solution was subsequently degassed by purging the
On the basis of the scope and generality of the
synthesis sequence, a library of 1,4-benzodiazepine-2,5-
diones was prepared from 11 alkylating agents, 12
anthranilic acids, and 19 R-amino esters (nine sets of
enantiomeric pairs and glycine methyl ester hydrochlo-
ride) to give 2508 total compounds, or 1320 spatially
separate compounds. In order to prepare the library, a
microtiter-based apparatus was developed that is inex-
pensive and straightforward to prepare from ordinary
items found in an organic or bioorganic laboratory. The
high quality of the benzodiazepine-2,5-dione library
prepared with this apparatus was demonstrated by
evaluating representative compounds by HPLC analysis
contents of the flask with N
of 10% Pd/C was added, and with vigorous stirring, the flask
was fitted with an H balloon and purged rapidly with this
gas. The contents of the flask were stirred at rt for 12 h under
2
for 30 min. A catalytic amount
2
1
atm of H
2
. The product and starting material had identical
R
f
values when TLC plates were eluted with 1:1 hexanes/
EtOAc. Completion was determined by the drastically differ-
ent appearance of the two compounds when TLC plates were
held under mixed short-wave UV light. The aniline was
extremely fluorescent, glowing blue on the TLC plate, while
the starting material was not. The heterogeneous mixture was
filtered through a plug of Celite, and the clear fluorescent
liquid was concentrated in vacuo. As the volume reduced, 5.85
g (35.0 mmol, 71%) of off-white needles precipitated, mp 165-
1
and H NMR.
1
67 °C (color change/decomposition begins, lit.18 mp 166 °C).
The reported solid-phase synthesis sequence, demon-
stration of scope and generality of the chemistry, and
methods for library synthesis should significantly expe-
dite lead identification or optimization efforts based upon
the 1,4-benzodiazepine-2,5-dione structure. In addition,
the described multitube apparatus should have broad
applicability to parallel synthesis efforts towards a range
of different applications.
A second crop of product could be isolated by further reducing
the volume of the supernatant. These combined crops of
product were used directly in the benzodiazepine synthesis
described below.
4-Br om oa n th r a n ilic Acid . This compound was prepared
from 4-amino-2-nitrobenzoic acid (available from Research
Plus) through the intermediate 4-bromo-2-nitrobenzoic acid.
To a solution of 4-amino-2-nitrobenzoic acid (1.00 g, 5.49 mmol)
in 48% aqueous HBr, which was cooled in an ice bath to 0 °C,
was added 16.4 mL of H
mmol) in 13.7 mL of H
NaNO was added dropwise to the solution of 4-amino-2-
2
O. A solution of NaNO
2
(0.38 g, 5.5
Exp er im en ta l Section
2
O was prepared. The solution of
2
Gen er a l Meth od s. Unless otherwise noted, materials were
obtained from commercial suppliers and used without further
purification. The R-amino esters were purchased from Bachem,
nitrobenzoic acid (still at 0 °C). The reaction mixture was
initially cloudy but after 5 min turned clear orange. In a
separate 500-mL, round-bottom flask was dissolved CuBr (1.04
g, 7.25 mmol) in 18 mL of 48% aqueous HBr. The flask was
(
84) Glutamine-containing benzodiazepines were not evaluated since
they were contaminated with the dimethoxybenzhyrol cleavage side
product.
(85) Ullman, F.; Dootson, P. Ber. Dtsch. Chem. Ges. 1918, 51, 9-24.

1
248 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
fitted with a magnetic stir bar and was cooled to 0 °C. The
diazonium salt of 4-amino-2-nitrobenzoic acid was transferred
to an addition funnel and was added dropwise with vigorous
stirring to the solution of CuBr, generating a deep purple
solution. Caution must be used when working up diazonium-
mmol) was dissolved, also with gentle stirring. Alternatively,
the reductant and the R-amino ester may be premixed in the
same volume of 1% HOAc in DMF and the same mass of dry
resin 4. An aliquot of this resin was removed after 20 min
and rinsed with DMF (7 × 20 mL), CH
2
Cl
2
(7 × 20 mL), and
forming reactions. HNO
may decompose, producing NO
2
is not stable in aqueous solution and
. NO is an insidious poison
finally, CH
3
OH (3 × 10 mL). The aldehyde stretch was no
2
2
longer observed. This procedure was repeated at 60 min to
ensure that there were no additional changes in the IR
and exposure to it may be deadly. Appropriate precautions
should be taken. The contents of the reaction flask were
concentrated in vacuo (not quite to dryness) and slurried in
spectrum. The bulk of the resin was then rinsed with CH
OH (1 × 10 mL), DMF (7 × 20 mL), CH Cl (7 × 20 mL), and
finally, CH
3
-
2
2
2
00 mL of EtOAc and 1 N aqueous HCl. The phases were
3
OH (3 × 10 mL). The resin was dried in vacuo to
-1
separated, and the aqueous layer was extracted again with
EtOAc (2 × 100 mL). The combined organic layers were dried
and concentrated in vacuo to a green solid (the color presum-
ably due to residual copper salts). The green solid was
dissolved in 50 mL of EtOAc and decolorized on a Florisil plug
a constant weight IR (KBr) 1736 cm (s).
Ra cem izin g P r oced u r e for th e Loa d in g of r-Am in o
Ester s 5. A general procedure is described for loading of any
R-amino ester hydrochloride to support-bound aldehyde 4
when racemic product is desired from scalemic R-amino ester.
In a three-neck, 250-mL, round-bottom flask was placed a
small magnetic stir bar and 1% HOAc in DMF (50 mL). In
this solvent mixture was suspended 6.00 g of aldehyde-
derivatized resin 4. To this was added the R-amino ester
(eluting with excess EtOAc). Concentration in vacuo yielded
4
-bromo-2-nitrobenzoic acid as a yellow solid (0.80 g, 60%
yield). This diazotization was scaled up, and the product
bromide was carried on without further purification to gener-
ate 4-bromoanthranilic acid according to literature procedure.86
In a large, round-bottom flask charged with 130 mL of
hydrochloride of choice (22.2 mmol) and distilled i-Pr EtN
2
(0.859 g, 6.66 mmol). The system was stirred gently for 6 h,
concentrated NH
4
OH was dissolved 4-bromo-2-nitrobenzoic
after which time NaBH(OAc) (4.70 g, 22.2 mmol) was added.
3
acid (6.52 g, 26.5 mmol). In a separate conical flask was
dissolved 65 g (160 mmol) of ammonium iron(II) sulfate in 130
It may be necessary to pulverize the chunks that form in this
reagent before addition. The suspension was stirred gently
mL of H
2
O. This light green solution was added to the solution
for 36 h, at which point CH OH was added to the resin to
3
of 4-bromo-2-nitrobenzoic acid with magnetic stirring. On
contact, the light green solution became dark green and then
rust colored. The mixture was heated at reflux for 2 min and
cooled. The rust-colored suspension was filtered though a pad
quench the excess reductant and dissolve the borate salts that
were present. The solution was then removed from the resin
via filtration cannula and the resin rinsed with DMF (7 × 50
mL), CH Cl (7 × 50 mL), and finally, CH OH (3 × 20 mL).
2
2
3
of Celite, which was then rinsed with water and aqueous NH
4
-
The resin was dried to a constant weight in vacuo, and IR
(KBr) indicated that the aldehyde carbonyl stretch had been
OH. The dark brown filtrate was acidified with concentrated
aqueous HCl, and the resulting pink turbid suspension was
extracted with EtOAc (3 × 200 mL). The combined organic
-
1
replaced by an ester carboxyl stretch (∼1740 cm ).
Deter m in a tion of Resin Su bstitu tion Level. The load-
ing of resin-bound R-amino esters is quantitated by acetylation
of the free amine of 5 followed by cleavage with subsequent
determination of the mass balance of the silica gel purified
product. A typical experiment follows: A 50-mL flame-dried
round-bottom flask was charged with a magnetic stir bar and
2
layers were washed with H O, dried, and concentrated in
vacuo. The resulting residue was decolorized on a silica plug,
eluting with 1% HOAc in 2:1 hexanes/EtOAc. Concentration
in vacuo of the eluant provided 3.3 g (62% yield) of a slightly
8
6
brown solid, mp 222-223 °C (lit. mp 222 °C). Anal. Calcd
for C NO Br: C, 38.92; H, 2.80; N, 6.48. Found: C, 39.17;
7
H
6
2
20 mL of a mixture of pyr/Ac O (2:1) and a catalytic amount
2
H, 2.80; N, 6.59.
of 4-(dimethylamino)pyridine (DMAP). To this flask, with
gentle stirring, was added ∼0.500 g of R-amino ester resin.
The flask was fitted with a rubber septum, equipped with an
Ar inlet, and gently heated to no more than 50 °C. After 12
h, the solution was removed from the resin by filtration
cannula and the resin was washed with DMF (7 × 20 mL),
CH Cl (7 × 20 mL), and finally, CH OH (3 × 10 mL), which
Ald eh yd e-Der ived P olystyr en e 4. To a flame-dried, 2-L,
three-neck, round-bottom flask fitted with a mechanical stirrer
and an Ar inlet were added 15.3 g (84.2 mmol) of 4-hydroxy-
2
,6-dimethoxybenzaldehyde87 and DMF (800 mL). The solu-
tion was degassed by bubbling Ar through it for 30 min. Under
a gentle positive Ar flow, 1.92 g (79.9 mmol) of 95% NaH was
added slowly in ∼0.5 g aliquots. The addition of NaH was
complete in 15 min. An off-white/yellow solid slowly precipi-
2
2
3
desolvates the resin. The resin was then dried in vacuo to a
constant weight, and a known mass was presolvated in 10 mL
of CH Cl and stirred with a magnetic stir bar for 5 min. A
tated as the solution turned dark red. As H
solution was continually purged with a stream of Ar. After
0 min, H evolution ceased, and Merrifield resin (chloro-
methylpolystyrene, 1% divinylbenzene, 31.7 g, loading level
2
evolved, the
2
2
filtration cannula was then used to remove the CH Cl , and
2
2
3
2
care was taken not to accidentally remove any resin from the
flask as the cannula was removed. The resin was then treated
with 20 mL of a solution of TFA/Me S/H O (90:5:5) and stirred
-1
0
.76 mmol g , 24.1 mmol) added, and the Ar purge continued
2
2
for 15 min. The contents were stirred mechanically for 36 h
while being heated at 50 °C. The DMF suspension was diluted
for a minimum of 12 h. After 12 h, the contents of the flask
were filtered into a round-bottom flask, and the resin and filter
paper were repeatedly washed with CH Cl and then CH OH.
with CH
The resin was then rinsed with DMF/CH
DMF (5 × 500 mL), CH Cl (7 × 500 mL), and CH
00 mL). The salmon-colored resin was dried in vacuo to a
3
OH (200 mL) and filtered with a filtration cannula.
OH 1:1 (2 × 500 mL),
OH (4 ×
2
2
3
3
The filtrate was concentrated in vacuo, and the product
N-acetyl R-amino ester was purified by flash column chroma-
tography and the mass balance obtained. The above acetyla-
tion procedure was performed on phenylalanine methyl ester
resin (0.500 g), and 0.420 g of the acetylated resin was cleaved
as described above. Silica gel purification eluting with 2:1-
1:1 hexanes/EtOAc yielded 34.5 mg (0.156 mmol) of clear oil
(that later solidified). The loading is therefore determined to
2
2
3
4
constant weight of 33.4 g. A strong aldehyde carbonyl stretch
was observed in the IR (KBr) spectrum of this resin: 1690
-
1
cm
.
Ra cem iza tion -F r ee Loa d in g of a n r-Am in o Ester To
Obta in Solid Su p p or t 5. This procedure may be used for
racemization-free loading of an R-amino ester hydrochloride
to support-bound aldehyde 4. A 50-mL round-bottom flask was
charged with 1% HOAc in DMF (20 mL) and a magnetic stir
bar. To the flask was added 0.500 g of aldehyde-derived resin
-
1
be 0.156 mmol/0.420 g resin or 0.37 mmol g resin. An
identical experiment performed on leucine-derived resin from
the same lot of 4 showed the resin to be substituted at 0.36
-1
mmol g resin. Such loadings are typical when starting with
4
and NaBH(OAc)
turbid suspension. It may be necessary to pulverize the
chunks in commercially available NaBH(OAc) before addition.
The suspension was stirred gently, and an R-amino ester (3.00
3
(0.636 g, 3.00 mmol), generating a white,
commercially available Merrifield resin that is functionalized
-1
at a loading of ∼0.7 mmol g . Such a loading experiment was
performed every time a new lot of aldehyde-derived resin was
synthesized, and all yields are based on loading levels obtained
in this manner.
3
(
(
86) Leggate, P.; Dunn, G. E. Can. J . Chem. 1965, 43, 1158-1174.
87) Landi, J . J .; Ramig, K. Synth. Commun. 1991, 21, 167-171.
Gen er a l P r oced u r e for Syn th esis of 1,4-Ben zod ia z-
ep in e-2,5-d ion es 1. A typical procedure for the generation

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1249
of 1,4-benzodiazepine-2,5-diones follows. In an oven-dried, 50-
mL, round-bottom flask with a dry magnetic stir bar was
placed 0.500 g (0.185 mmol) of R-amino ester resin 5. The flask
was fitted with a rubber septum, and 5 mL of N-methylpyr-
rolidinone (NMP) was added. Once the resin was solvated (3
min), 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide‚HCl
ride, and acetic acid. The scalemic R-amino ester was loaded
according to the nonracemizing conditions. Cleavage of 0.170
g (0.0595 mmol) of this resin by stirring in 20 mL of 90:5:5
TFA/Me
gravity filtration, rinsing of the resin and filter paper with
CH Cl
2 2
S/H O for 36 h yielded a crude yellow residue after
2
2
(4 × 15 mL) and CH OH (2 × 10 mL), and concentra-
3
(EDC, 0.425 g, 2.22 mmol) was added. It may be necessary to
tion. Silica gel chromatography eluting with 3:1 hexanes/
EtOAc provided 15.9 mg (0.053 mmol, 89% yield) of an
amorphous glass. IR (KBr): 3425, 3232, 3067, 2932, 1685,
pulverize the chunks that form in this reagent before addition.
After the solution became saturated in EDC (most of the EDC
will dissolve over the course of 5 min), the anthranilic acid of
choice was slowly added (1.85 mmol). It is imperative that the
EDC and resin be allowed to mix thoroughly before addition
of anthranilic acid and that the anthranilic acid be added
slowly. This minimizes side reactions that can occur with the
unprotected aniline functionality. The reaction mixture was
stirred gently for 8-12 h. For some anthranilic acids (4-Cl,
-
1
1
1652, 1479, 1432, 1353, 1221, 1128, 828, 700 cm
.
H NMR
(400 MHz, DMSO-d ): δ 2.85 (dd, 1, J ) 9.2, 14.3), 3.11 (dd,
6
1, J ) 5.1, 14.3), 3.92-3.98 (m, 1), 7.11 (d, 1, J ) 8.9), 7.18 (t,
1, J ) 7.2), 7.24 (t, 2, J ) 7.2), 7.30 (d, 2, J ) 7.4), 7.57 (dd, 1,
J ) 2.3, 8.7), 7.61 (d, 1, J ) 2.5), 8.65 (d, 1, J ) 6.1), 10.51 (s,
1). 13C NMR (101 MHz, CDCl
, one drop CD OD): δ 34.0, 53.7,
3
3
122.5, 126.7, 127.0, 128.6, 129.1, 130.5, 133.0, 134.5, 136.1,
+
+
4
-NO
2
), a precipitate formed as the reaction proceeded. The
167.7, 171.1. HRMS (FAB ) m/ e: 301.0741 (MH
Cl requires 301.0744). Anal. Calcd for C16
16 14 2 2
C H N O -
precipitate was so fine that it was easily removed during the
rinses with the filtration cannula. The resin was rinsed with
H
13
O
2
N
2
Cl: C,
63.91; H, 4.36; N, 9.32. Found: C, 63.71; H, 4.45; N, 9.15.
Ben zod ia zep in e 1c. The support-bound benzodiazepine
was prepared according to the above procedure from 4-chlo-
roanthranilic acid, (S)-leucine methyl ester hydrochloride, and
acetic acid. The scalemic R-amino ester was loaded according
to the nonracemizing conditions. Cleavage of 0.350 g (0.123
DMF (7 × 20 mL), CH
2
Cl
2
(7 × 20 mL), and finally CH
3
OH (3
×
10 mL). The acylation and rinsing were repeated (2 h is
adequate) to ensure reaction completion, and the resin was
dried to a constant weight in vacuo. Nitro-containing anthra-
nilic acids may require a third subjection. Cyclization and
alkylation were then accomplished in one pot: The acylated
resin 6 was placed in a 50-mL, round-bottom flask fitted with
a small, magnetic stir bar and purged gently with Ar for 5
min. In a separate flame-dried, 50-mL, round-bottom flask
was placed a magnetic stir bar and acetanilide (4.44 mmol),
followed by 7.5 mL of THF. This flask was purged with Ar
for 5 min. The flask was then cooled in a dry ice/acetone bath
to -78 °C. A fraction of the compound may precipitate on
cooling (this does not affect the reaction). A hexanes solution
of n-BuLi (1.48 mL, 2.5 M, 3.7 mmol) was added dropwise over
mmol) of this resin by stirring in 20 mL of 90:5:5 TFA/Me S/
2
H O for 36 h yielded a crude yellow residue after gravity
2
filtration, rinsing of the resin and filter paper with CH Cl (4
2
2
× 15 mL) and CH OH (2 × 10 mL), and concentration. Silica
3
gel chromatography eluting with 2:1 hexanes/EtOAc provided
29 mg (0.109 mmol, 89% yield) of a white powder, mp 244-
248 °C (decomposition begins). IR (KBr): 3427, 3164, 2967,
-1
1
1664, 1604, 1473, 1427, 1216 (w), 1098 (w), 828 cm
. H NMR
(400 MHz, DMSO-d ): δ 0.76 (d, 3, J ) 6.5), 0.85 (d, 3, J )
6
6.5), 1.54 (t, 2, J ) 7.0), 1.65-1.70 (m, 1), 3.62-3.67 (m, 1),
1
0 min with rapid stirring. The suspension became slightly
yellow and sometimes turned into a gelatin over the course of
0 min. DMF (7.5 mL) was then added to homogenize the
7.13 (s, 1), 7.26 (m, 1), 7.74 (d, 1, 8.5), 8.49 (d, 1, J ) 5.6),
10.45 (s, 1). 13C NMR (101 MHz, DMSO-d ): δ 21.5, 22.8, 23.8,
6
3
36.1, 50.1, 120.2, 123.8, 125.0, 132.3, 136.3, 138.1, 166.8, 171.5.
Anal. Calcd for C H O N Cl: C, 58.55; H, 5.67; N, 10.50.
solution. After all solids dissolved, the mixture was stirred
at -78 °C for another 15 min, warmed to rt, and then
transferred via metal cannula into the flask containing the
resin (which was under Ar at rt). The suspension was stirred
gently at rt for 30 h under an Ar atmosphere. Alkylating agent
1
3
15
2
2
Found: C, 58.67; H, 5.81; N, 10.46.
Ben zod ia zep in e 1d . The benzodiazepine was prepared
according to the above procedure from 5-bromoanthranilic acid,
(S)-leucine methyl ester hydrochloride, and EtI. The scalemic
R-amino ester was loaded according to the racemizing condi-
tions. Cleavage of 0.500 g (0.170 mmol) of this resin by stirring
in 20 mL of 90:5:5 TFA/Me S/H O for 36 h yielded a crude
(7.40 mmol) was added via syringe, and stirring was continued
until the suspension no longer turned pH paper dark green
or blue. This typically took 3-6 h. The alkylating solution
was removed via filtration cannula and the resin was rinsed
2
2
yellow residue after gravity filtration, rinsing of the resin and
with DMF (7 × 20 mL), CH
2
Cl
2
(7 × 20 mL), and finally CH
3
-
filter paper with CH Cl (4 × 15 mL) and CH OH (2 × 10 mL),
2
2
3
OH (3 × 10 mL) and dried in vacuo to a constant weight. The
and concentration. Silica gel chromatography, eluting with
4:1-3:1 hexanes/EtOAc yielded, 41.0 mg (0.121 mmol) of an
amorphous white solid (71% yield). IR (KBr): 3441 (b), 2967,
benzodiazepines were then cleaved from support. A known
2 2 2 2
mass of resin was swelled with CH Cl . The CH Cl was
-
1
1
removed with a filtration cannula, taking care not to lose any
resin on the cannula as it was removed from the flask. The
benzodiazepines made by this method are cleaved and char-
acterized below.
Ben zod ia zep in e 1a . The support-bound benzodiazepine
was prepared according to the above procedure from anthra-
nilic acid and (R)-alanine methyl ester hydrochloride, and
acetic acid was substituted for an alkylating agent. The
scalemic R-amino ester was loaded according to the nonrace-
mizing conditions. Cleavage of 0.314 g (0.107 mmol) of this
1670, 1598 (w), 1440, 1396 (w), 1256 (w), 1124 (w) cm
.
H
NMR (400 MHz, DMSO-d ): δ 0.73 (d, 3, J ) 6.3), 0.82 (d, 3,
6
J ) 6.3), 0.99 (t, 3, J ) 6.6), 1.57-1.74 (m, 3), 3.59-3.71 (m,
2), 4.03-4.10 (m, 1), 7.44 (d, 1, J ) 9.2), 7.74-7.80 (m, 2), 8.67
1
3
(d, 1, J ) 5.8). C NMR (101 MHz, DMSO-d ): δ 13.1, 21.7,
6
22.8, 23.8, 36.3, 42.2, 50.1, 117.7, 125.0, 131.6, 131.7, 134.8,
138.6, 166.2, 169.3. Anal. Calcd for C15 Br: C, 53.11;
19 2 2
H O N
H, 5.65; N, 8.26. Found: C, 52.89; H, 5.61; N, 8.12.
Ben zod ia zep in e 1e. The support-bound benzodiazepine
was prepared according to the above procedure from 4-meth-
oxyanthranilic acid (vide supra), glycine methyl ester hydro-
chloride, and 2-methoxybenzyl chloride. The R-amino ester
was loaded according to the nonracemizing conditions. Cleav-
age of 0.392 g (0.128 mmol) of this resin by stirring in 20 mL
of 90:5:5 TFA/Me S/H O for 36 h yielded a crude yellow residue
resin in 20 mL of 90:5:5 TFA/Me
yellow residue after gravity filtration, rinsing of the resin and
filter paper with CH Cl
2 2
S/H O for 36 h yielded a crude
2
2
(4 × 15 mL) and CH OH (2 × 10 mL),
3
and concentration. Silica gel chromatography eluting with 2:1
EtOAc/hexanes provided 15.7 mg (0.083 mmol, 77% yield) of
2
2
a fine, white, amorphous powder. IR (KBr): 3272, 3173, 3060,
after gravity filtration, rinsing of the resin and filter paper
1
2
919, 1705, 1675, 1478, 1408, 755 cm-1
.
H NMR (400 MHz,
with CH Cl2 (4 × 15 mL) and CH OH (2 × 10 mL), and
2
3
DMSO-d
6
): δ 1.21 (d, 3, J ) 6.8), 3.76-3.82 (m, 1), 7.08 (d, 1,
concentration. Silica gel chromatography eluting with 5:1
EtOAc/hexanes followed by neat ethyl acetate after product
began to elute provided 16.9 mg (0.052 mmol, 40% yield) of a
white fluffy powder, mp 99-100 °C. IR (KBr): 3435, 2935,
8
7
.0), 7.20 (t, 1, J ) 7.1), 7.47-7.51 (m, 1), 7.71 (dd, 1, J ) 1.5,
.9), 8.39 (d, 1, J ) 5.1), 10.3 (s, 1).
1
3
C NMR (101 MHz,
DMSO-d
36.7, 167.7, 172.2. HRMS (FAB ) m/ e: 191.0822 (MH
requires 191.0821).
Ben zod ia zep in e 1b. The support-bound benzodiazepine
6
): δ 13.8, 47.3, 120.9, 123.8, 126.2, 130.4, 132.2,
+
+
-1
1
1
1642, 1608, 1660, 1248, 1118, 1096 cm . H NMR (400 MHz,
C
10
H
11
N
2
O
2
DMSO-d ): δ 3.52 (b s, 1), 3.67 (s, 3), 3.73 (s, 3), 3.80 (b s, 1),
6
4.85 (d, 1, J ) 15.6), 5.20 (d, 1, J ) 16.6), 6.77-6.83 (m, 2),
6.87-6.89 (m, 2), 7.02 (d, 1, J ) 7.4), 7.16 (d, 1, J ) 7.6), 7.56
(d, 1, J ) 8.5), 8.56 (t, 1, J ) 5.1). 13C NMR (101 MHz, DMSO-
was prepared according to the above procedure from 5-chlo-
roanthranilic acid, (S)-phenylalanine methyl ester hydrochlo-

1
250 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
d
1
6
): δ 45.0, 45.7,55.1, 55.5, 107.6, 110.6, 111.4, 119.9, 121.7,
24.3, 128.1, 128.4, 131.4, 141.3, 156.7, 161.5, 167.7, 169.1.
C, 66.25; H, 5.56; N, 8.58.
residue after gravity filtration, rinsing of the resin and filter
paper with CH
2
Cl
2
(4 × 15 mL) and CH OH (2 × 10 mL), and
3
Anal. Calcd for C18
Found: C, 66.20; H, 5.61; N, 8.32.
H
18
O
4
N
2
:
concentration. Silica gel chromatography eluting with 3:1
hexanes/EtOAc provided 43.6 mg (0.121 mmol, 81% yield) of
an amorphous yellow powder. A small aliquot of this product
was taken up in a drop of ethyl acetate and precipitated by
addition of hexanes. The supernatant was decanted from the
product yielding a fine yellow crystals, mp 173 °C (decomposi-
tion begins). IR (KBr): 3472, 3260, 3096, 2934, 1669, 1527,
Ben zod ia zep in e 1f. The support-bound benzodiazepine
was prepared according to the above procedure from 5-chlo-
roanthranilic acid, H-(S)-Glu(t-Bu)-OMe‚HCl, and benzyl bro-
mide. The scalemic R-amino ester was loaded according to the
nonracemizing conditions. Cleavage of 0.528 g (0.169 mmol)
-1
1
of this resin by stirring in 20 mL of 90:5:5 TFA/Me
6 h yielded a crude yellow residue after gravity filtration,
rinsing of the resin and filter paper with CH Cl
(4 × 15 mL)
and CH
2
S/H
2
O for
1442, 1347, 1232 (w), 1155 (w), 697 cm
. H NMR (400 MHz,
3
DMSO-d ): δ 0.08-0.15 (m, 2), 0.31-0.35 (m, 2), 0.80-0.88
6
2
2
(m, 1), 3.19 (dd, 1, J ) 8.1, 15), 3.29-3.34 (m, 1), 3.73 (dd, 1,
J ) 6.5, 14.5), 3.97 (dd, 1, J ) 6.2, 14.2), 4.06 (dd, 1, J ) 7.5,
14.6), 6.87-6.90 (m, 1), 6.92-6.94 (m, 1), 7.28 (dd, 1, J ) 1.2,
5.1), 7.90 (d, 1, J ) 8.6), 8.10 (dd, 1, J ) 2.1, 8.6), 8.33 (d, 1,
3
OH (2 × 10 mL), and concentration. Silica gel
chromatography eluting with 60:40:1 hexanes/EtOAc/HOAc
provided 32.5 mg (0.087 mmol, 52% yield) of an amorphous
white powder. IR (KBr): 3432, 3272, 2919, 2849, 1670, 1441,
1
3
6
J ) 2.0), 9.08 (d, 1, J ) 6.4). C NMR (101 MHz, DMSO-d ):
-
1
1
1
207, 730 cm
.
H NMR (400 MHz, DMSO-d
6
): δ 1.85-1.92
δ 3.1, 3.9, 9.8, 28.1, 50.9, 53.7, 118.9, 120.1, 124.6, 126.7, 131.1,
+
(
4
7
m, 1), 2.00-2.07 (m, 1), 2.28-2.34 (m, 2), 3.85-3.90 (m, 1),
135.2, 139.3, 140.4, 149.5, 166.1, 169.3. HRMS (FAB ) m/ e:
+
.93 (d, 1, J ) 16.0), 5.33 (d, 1, J ) 16.0), 7.06 (d, 2, J ) 7.1),
.18-7.25 (m, 3), 7.49 (d, 1, J ) 8.4), 7.56-7.59 (m, 2), 8.80
372.1027 (MH
C
18
H
18
N
3
O
4
S requires 372.1018).
Ben zod ia zep in e 1j. The support-bound benzodiazepine
was prepared according to the above procedure from 6-fluo-
roanthranilic acid, (S)-phenylalanine methyl ester hydrochlo-
ride, and iodoacetamide. The scalemic R-amino ester was
loaded according to the nonracemizing conditions. Cleavage
of 0.340 g (0.120 mmol) of this resin by stirring in 20 mL of
1
3
(
4
1
d, 1, J ) 5.8). C NMR (101 MHz, DMSO-d ): δ 23.5, 29.8,
6
9.5, 51.0, 124.7, 126.7, 127.1, 128.5, 128.9, 129.7, 131.4, 131.8,
17 4 2
37.0, 138.0, 166.3, 170.0, 174.0. Anal. Calcd for C19H O N -
Cl: C, 61.22; H, 4.60; N, 7.52. Found: C, 61.22; H, 4.76; N,
.35.
Ben zod ia zep in e 1g. The support-bound benzodiazepine
was prepared according to the above procedure from 5-chlo-
7
90:5:5 TFA/Me
after gravity filtration, rinsing of the resin and filter paper
with CH Cl
2 2
S/H O for 36 h yielded a crude yellow residue
7
0
roanthranilic acid, H-(S)-Gln(Dod)-OMe‚HCl, and ethyl io-
dide. The scalemic R-amino ester was loaded according to the
nonracemizing conditions. Cleavage of 0.464 g (0.142 mmol)
2
2
(4 × 15 mL) and CH OH (2 × 10 mL), and
3
concentration. Silica gel chromatography, eluting with 3:100
i-PrOH/EtOAc, yielded 25.0 mg (0.073 mmol) of an amorphous
yellow solid (62% yield). IR (KBr): 3276, 3157, 1678, 1618,
of this resin by stirring in 20 mL of 90:5:5 TFA/Me
6 h yielded a crude yellow residue after gravity filtration,
rinsing of the resin and filter paper with CH Cl
(4 × 15 mL)
and CH
2 2
S/H O for
-
1
1
3
1473, 1394, 1242, 1032, 1006, 755, 703, 624 cm
.
H NMR
2
2
(400 MHz, DMSO-d
6
): δ 2.91 (dd, 1, J ) 9.4, 14.3), 3.07 (dd,
3
OH (2 × 10 mL), and concentration. Silica gel
1, J ) 4.9, 14.3), 4.02-4.07 (m, 1), 4.24 (d, 1, J ) 16.7), 4.43
(d, 1, J ) 16.8), 7.11-7.18 (m, 4), 7.24 (t, 2, J ) 7.1), 7.29 (d,
chromatography eluting with 2:1 hexanes/EtOAc provided 31.0
mg (0.100 mmol, 70% yield) of an amber powder. It was
necessary to weight this powder out immediately; it was
extraordinarily hygroscopic and visibly liquefied with atmo-
spheric water within minutes after isolation. IR (KBr): 3427,
3
cm
1
3
1
3
2, J ) 7.0), 7.52-7.57 (m, 2), 8.82 (d, 1, J ) 7.3). C NMR
(101 MHz, DMSO-d ): δ 33.3, 51.0, 53.4, 113.1 (d, J FC ) 21.4),
6
117.8 (d, J FC ) 15.3), 118.1, 126.3, 128.1, 129.2, 132.3 (d, J FC
) 10.4), 137.7, 141.6, 159.5 (d, J FC ) 258), 163.3, 169.1, 170.1.
+
+
208, 2933, 1669, 1602, 1444, 1207, 1133, 1028, 826, 801, 721
HRMS (FAB ) m/ e: 342.1252 (MH
18 17 3 3
C H N O F requires
-
1
1
.
H NMR (400 MHz, DMSO-d
6
): δ 1.00 (t, 3, J ) 7.0),
342.1254).
.79-1.84 (m, 1), 1.93-1.97 (m, 1), 2.13 (t, 2, J ) 7.2), 3.64-
.72 (m, 2), 4.06-4.12 (m, 1), 6.72 (b s, 1), 7.25 (b s, 1), 7.52
Ben zod ia zep in e 1k . The support-bound benzodiazepine
was prepared according to the above procedure from 5-fluo-
roanthranilic acid, (R)-alanine methyl ester hydrochloride, and
3,5-dimethylbenzyl bromide. The scalemic R-amino ester was
loaded according to the nonracemizing conditions. Cleavage
of 0.433 g (0.143 mmol) of this resin by stirring in 20 mL of
1
3
(
(
d, 1, J ) 9.3), 7.63-7.66 (m, 2), 8.72 (d, 1, J ) 5.8). C NMR
101 MHz, DMSO-d
6
): δ 13.1, 23.6, 30.6, 42.1, 51.4, 124.8,
1
28.7, 129.7, 131.5, 131.9, 138.0, 166.2, 169.3, 173.6. HRMS
+
+
(FAB ) m/ e: 310.0961 (MH
14 17 3 3
C H N O Cl requires 310.0958).
Ben zod ia zep in e 1h . The support-bound benzodiazepine
90:5:5 TFA/Me
after gravity filtration, rinsing of the resin and filter paper
with CH Cl
2 2
S/H O for 36 h yielded a crude yellow residue
was prepared from 4-nitroanthranilic acid, (S)-leucine methyl
ester hydrochloride, and EtI according to the above procedure.
The scalemic R-amino ester was loaded according to the
racemizing conditions. This benzodiazepine required a third
subjection in the EDC-mediated acylation step. Cleavage of
2
2
(4 × 15 mL) and CH OH (2 × 10 mL), and
3
concentration. Silica gel chromatography eluting with 2:1
hexanes/EtOAc provided 29.1 mg (0.892 mmol, 62% yield) of
an amorphous off-white powder. IR (KBr): 3434, 2925, 1665,
-1
1
0
5
.450 g (0.153 mmol) of this resin by stirring in 20 mL of 90:
:5 TFA/Me S/H O for 36 h yielded a crude yellow residue after
6
1492, 1451, 1197 cm . H NMR (400 MHz, DMSO-d ): δ 1.26
2
2
(d, 3, J ) 6.7), 2.14 (s, 6), 3.93-3.98 (m, 1), 4.80 (d, 1, J )
16.0), 5.30 (d, 1, J ) 16.0), 6.65 (s, 2), 6.78 (s, 1), 7.35-7.41
gravity filtration, rinsing of the resin and filter paper with
CH Cl
1
3
2
2
(4 × 15 mL) and CH
3
OH (2 × 10 mL), and concentra-
(m, 2), 7.52 (dd, 1, J ) 4.6, 8.9), 8.78 (d, 1, J ) 5.7). C NMR
tion. Silica gel chromatography, eluting with 3.5:1 hexanes/
EtOAc, yielded 43.0 mg (0.141 mmol, 92% yield) of a white
solid: mp 179.5-180.5 °C. IR (KBr): 3427 (b), 3204, 3098,
6
(101 MHz, DMSO-d ): δ 14.0, 20.8, 47.4, 49.3, 115.2 (d, J FC )
23.8), 119.0 (d, J FC ) 23.2), 124.4, 125.1 (d, J FC ) 7.6), 128.4,
132.0 (d, J FC ) 7.6), 135.7, 137.0, 137.4, 158.9 (d, J FC ) 243),
+
+
2
8
)
3
960, 2868, 1703, 1670, 1539, 1440, 1354, 1249, 1223, 1131,
166.3, 170.8. HRMS (FAB ) m/ e: 327.1502 (MH
C
19
H
20
N
2
O
2
F
-
1
1
02, 742 cm
6.1), 0.83 (d, 3, J ) 6.1), 1.03 (t, 3, J ) 7.0), 1.57-1.65 (m,
), 3.65-3.68 (m, 1), 3.75-3.82 (m, 1), 4.15-4.20 (m, 1), 7.93
d, 1, J ) 8.5), 8.11 (d, 1, J ) 8.5), 8.22 (s, 1), 8.85 (d, 1, J )
.
H NMR (400 MHz, DMSO-d
6
): δ 0.72 (d, 3, J
requires 327.1509).
Ben zod ia zep in e 1l. The support-bound benzodiazepine
was prepared according to the above procedure from 5-chlo-
roanthranilic acid, (S)-phenylalanine methyl ester hydrochlo-
ride, and allyl bromide. The scalemic R-amino ester was
loaded according to the nonracemizing conditions. Cleavage
of 0.319 g (0.111 mmol) of this resin by stirring in 20 mL of
(
1
3
5
3
1
1
.9). C NMR (101 MHz, DMSO-d
6.1, 42.1, 49.9, 117.9, 119.8, 131.1, 135.0, 140.0, 149.4, 165.1,
69.3. Anal. Calcd for C15 : C, 59.00; H, 6.27; N,
6
): δ 13.0, 21.5, 22.7, 23.7,
19 4 3
H O N
3.76. Found: C, 58.97; H, 6.48; N, 13.69.
Ben zod ia zep in e 1i. The support-bound benzodiazepine
was prepared according to the above procedure from 4-ni-
troanthranilic acid, 3-(2-thienyl)-D,L-alanine methyl ester
hydrochloride, and (bromomethyl)cyclopropane. Racemic R-ami-
no ester was loaded according to the nonracemizing conditions.
Cleavage of 0.390 g (0.150 mmol) of this resin by stirring in
90:5:5 TFA/Me
after gravity filtration, rinsing of the resin and filter paper
with CH Cl
2 2
S/H O for 36 h yielded a crude yellow residue
2
2
(4 × 15 mL) and CH OH (2 × 10 mL), and
3
concentration. Silica gel chromatography, eluting with 4:1
hexanes/EtOAc, yielded 33.6 mg (0.098 mmol) of an amorphous
white solid (89% yield). IR (KBr): 3447 (b), 3072, 3033, 2940,
-
1
1
1670, 1479, 1440, 1354 cm
6
. H NMR (400 MHz, DMSO-d ):
2
2 2
0 mL of 90:5:5 TFA/Me S/H O for 36 h yielded a crude yellow
δ 2.91 (dd, 1, J ) 8.9. 14.2), 3.12 (dd, 1, J ) 5.45, 14.2), 4.01-

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1251
4
1
7
7
6
1
1
6
.06 (m, 1), 4.40 (dd, 1, J ) 5.4, 16.5), 4.59 (dd, 1, J ) 4.7,
6.5), 5.01-5.09 (m, 2), 5.68-5.77 (m, 1), 7.14-7.18 (m, 1),
.23 (t, 2, J ) 7.1), 7.29 (d, 2, J ) 7.1), 7.47 ( d, 1, J ) 8.8),
.57 (d, 1, J ) 2.6), 7.62 (dd, 1, J ) 2.6, 8.8), 8.86 (d, 1, J )
stirring in 20 mL of 90:5:5 TFA/Me
crude yellow residue after gravity filtration, rinsing of the resin
and filter paper with CH Cl
2 2
S/H O for 36 h yielded a
2
2
(4 × 15 mL) and CH OH (2 × 10
3
mL), and concentration. Silica gel chromatography eluting
with 2:1 hexanes/EtOAc provided 28.8 mg (0.090 mmol, 69%
yield) of an amorphous white powder. IR (KBr): 3432, 3072,
1
3
.4). C NMR (101 MHz, DMSO-d
24.5, 126.3, 128.1, 128.7, 129.3, 129.6, 131.1, 131.8, 133.0,
37.6, 138.3, 166.3, 169.4. Anal. Calcd for C19 Cl: C,
6
): δ 33.6, 49.1, 53.6, 116.7,
-
1
H
17
O
2
N
2
2919, 1664, 1559, 1426, 1401, 1226, 1097, 786, 752, 700 cm
.
6.96; H, 5.03; N, 8.22. Found: C, 66.83; H, 5.20; N, 8.18.
Ben zod ia zep in e 1m . The support-bound benzodiazepine
1
H NMR (400 MHz, DMSO-d ): δ 0.00-0.02 (m, 1), 0.15-0.18
6
(m, 1), 0.28-0.31 (m, 2), 0.92-0.96 (m, 1), 2.94 (dd, 1, J ) 9.0,
14.0), 3.16 (dd, 1, J ) 4.9, 14.0), 3.98-4.05 (m, 3), 7.16-7.18
was prepared according to the above procedure from 4-meth-
oxyanthranilic acid (vide supra), (S)-leucine methyl ester
hydrochloride, and (bromomethyl)cyclopropane. The scalemic
R-amino ester was loaded according to the racemizing condi-
tions. Cleavage of 0.428 g (0.145 mmol) of this resin by stirring
(
m, 1), 7.23 (t, 2, J ) 7.1), 7.30-7.36 (m, 3), 8.07 (d, 1, J )
13
6
.7), 8.63 (d, 1, J ) 2.9), 8.85 (d, 1, J ) 6.1). C NMR (101
MHz, DMSO-d ): δ 2.9, 3.6, 10.1, 33.6, 48.4, 53.7, 120.9, 124.3,
26.3, 128.1, 129.4, 137.6, 139.5, 150.5, 151.2, 166.3, 169.7.
Anal. Calcd for C19 C, 71.10; H, 5.96; N, 13.07.
6
1
in 20 mL of 90:5:5 TFA/Me
yellow residue after gravity filtration, rinsing of the resin and
filter paper with CH Cl OH (2 × 10 mL),
(4 × 15 mL) and CH
and concentration. Silica gel chromatography, eluting with
:1-2:1 hexanes/EtOAc, yielded 36.0 mg (0.114 mmol) of a
white solid (79% yield), mp 133-135 °C. IR (KBr): 3434 (b),
2 2
S/H O for 36 h yielded a crude
19 2 3
H O N :
Found: C, 71.10; H, 6.18; N, 12.92.
2
2
3
Ben zod ia zep in e 1q. The support-bound benzodiazepine
was prepared according to the above procedure from 4-methyl-
anthranilic acid, 3-(2-thienyl)-D,L-alanine methyl ester hydro-
chloride, and piperonyl chloride. The racemic R-amino ester
was loaded according to the nonracemizing conditions. Cleav-
age of 0.332 g (0.085 mmol) of this resin by stirring in 20 mL
4
3
1
0
)
(
184, 3079, 2954, 1664, 1611, 1453, 1381, 1262, 1223, 1124,
-
1
1
032, 841, 795 cm
.10 (m, 2), 0.27-0.31 (m, 2), 0.72 (d, 3, J ) 6.3), 0.81 (d, 4, J
6.3), 1.57-1.68 (m, 3), 33.57-3.67 (m, 2), 3.83 (s, 3), 3.99
dd, 1, J ) 7.4, 14.5), 6.91 (dd, 1, J ) 2.1, 8.7), 7.01 (d, 1, J )
6
. H NMR (400 MHz, DMSO-d ): δ 0.05-
of 90:5:5 TFA/Me
after gravity filtration, rinsing of the resin and filter paper
with CH Cl OH (2 × 10 mL), and
(4 × 15 mL) and CH
concentration. Silica gel chromatography eluting with 3:1-
:1 hexanes/EtOAc provided 23.5 mg (0.056 mmol, 66% yield)
of an off-white amorphous powder. IR (KBr): 3448, 3283,
2 2
S/H O for 36 h yielded a crude yellow residue
1
3
2
2
3
2
.1), 7.62 (d, 1, J ) 8.6), 8.41 (d, 1, J ) 5.8). C NMR (101
): δ 13.0, 13.7, 19.9, 31.7, 32.7, 33.8, 46.4, 60.2,
0.8, 65.5, 118.1, 121.9, 132.8, 140.9, 151.2, 171.8, 177.4, 179.9.
MHz, DMSO-d
6
6
2
+
+
HRMS (FAB ) m/ e: 317.1858 (MH
17.1865).
Ben zod ia zep in e 1n . The support-bound benzodiazepine
18 25 2 3
C H N O requires
-
1 1
2
927, 1665, 1649, 1612, 1500, 1438, 1248, 1041, 696 cm . H
NMR (400 MHz, DMSO-d ): δ 2.31 (s, 3), 3.17 (dd, 1, J ) 8.2,
5.0), 3.33-3.37 (m, 1), 3.90-3.95 (m, 1), 4.83 (d, 1, J ) 15.5),
3
6
1
5
1
was prepared according to the above procedure from 5-chlo-
roanthranilic acid, H-Lys(Boc)-OMe‚HCl, and allyl bromide.
The scalemic R-amino ester was loaded according to the
racemizing conditions. Cleavage of 0.405 g (0.137 mmol) of
.25 (d, 1, J ) 15.5), 5.94 (s, 2), 6.56 (b d, 1, J ) 8.0), 6.60 (d,
, J ) 1.4), 6.74 (d, 1, J ) 7.9), 6.89 (dd, 1, J ) 3.5, 5.0), 6.93
(
b s, 1), 7.09 (b d, 1, J ) 7.9), 7.29 (dd, 1, J ) 1.2, 5.1), 7.32 (b
13
this resin by stirring in 20 mL 90:5:5 of TFA/Me
h yielded a crude yellow residue after gravity filtration, rinsing
of the resin and filter paper with CH Cl
(4 × 15 mL) and CH
OH (2 × 10 mL), and concentration. Silica gel chromatography
eluting with 90:10:1 CH Cl /CH OH/NH OH provided 28 mg
0.087 mmol, 63% yield) of a viscous glass. IR (thin film):
2
S/H
2
O for 36
s, 1), 7.46 (d, 1, J ) 7.98), 8.74, (d, 1, J ) 6.2). C NMR (101
MHz, DMSO-d
6
): δ 20.9, 28.2, 49.2, 54.0, 100.9, 107.3, 108.1,
-
120.3, 123.0, 124.6, 126.6, 126.7, 127.1, 129.3, 131.0, 137.7,
2
2
3
+
138.9, 139.6, 142.3, 146.2, 147.3, 167.4, 169.7. HRMS (FAB )
+
m/ e: 420.1136 (M
C
23
H
20
N
2
O
4
S requires 420.1144).
2
2
3
4
(
Ben zod ia zep in e 1r . The support-bound benzodiazepine
was prepared according to the above procedure from 3-methyl-
anthranilic acid, (S)-leucine methyl ester hydrochloride, and
3
7
1
1
177, 3079, 2940, 1670, 1598, 1572, 1486, 1446, 1367, 1210,
-
1
1
36 cm
.
3
H NMR (400 MHz, CD OD): δ 1.37-1.40 (m, 1),
.40-1.48 (m, 1), 1.48-1.52 (m, 2), 1.72-1.79 (m, 1), 1.90-
.97 (m, 1), 2.66 (t, 2, J ) 7.0), 3.80 (t, 1, J ) 6.5), 4.46 (dd, 1,
4
-bromobenzyl bromide. The scalemic R-amino ester was
loaded according to the nonracemizing conditions. Cleavage
of 0.355 g (0.112 mmol) of this resin by stirring in 20 mL of
J ) 5.5, 16.3), 4.60 (dd, 1, J ) 5.0, 16.3), 5.11-5.15 (m, 2).
5
7
2
1
.78-5.84 (m, 1), 7.47 (d, 1, J ) 8.8), 7.58 (dd, 1, J ) 2.6, 8.8),
9
0:5:5 TFA/Me
after gravity filtration, rinsing of the resin and filter paper
with CH Cl
2 2
S/H O for 36 h yielded a crude yellow residue
13
.73 (d, 1, J ) 2.5). C NMR (101 MHz, DMSO-d ): δ 24.0,
6
8.9, 31.9, 41.5, 51.5, 53.8, 117.7, 125.7, 130.3, 132.1, 132.5,
33.6, 134.0, 140.1, 169.4, 171.6. HRMS (FAB ) m/ e: 322.1319
2
2
(4 × 15 mL) and CH OH (2 × 10 mL), and
3
+
concentration. Silica gel chromatography eluting with 4.5:1
hexanes/EtOAc provided 34.5 mg (0.083 mmol, 74% yield) of
an amorphous white powder. IR (KBr): 2966, 1654, 1637,
+
(MH
C
16
H
21
N
3
O
2
Cl requires 322.1322).
Ben zod ia zep in e 1o. The support-bound benzodiazepine
was prepared according to the above procedure from 4-chlo-
roanthranilic acid, (S)-leucine methyl ester hydrochloride, and
EtI. The scalemic R-amino ester was loaded according to the
racemizing conditions. Cleavage of 0.440 g (0.150 mmol) of
this resin by stirring in 20 mL of 90:5:5 TFA/Me
h yielded a crude yellow residue after gravity filtration, rinsing
of the resin and filter paper with CH Cl -
3
OH (2 × 10 mL), and concentration. Silica gel chromatogra-
phy, eluting with 3:1 hexanes/EtOAc, yielded 33.0 mg (0.112
mmol) of an amorphous off-white powder (75% yield). IR
-1
1
1
560, 1542, 1508, 1090, 832, 803 cm
.
H NMR (400 MHz,
DMSO-d
6
): δ 0.68 (d, 3, J ) 6.4), 0.78 (d, 3, J ) 6.4), 1.54 (t,
2
, 6.9), 1.59-1.66 (m, 1), 2.40 (s, 3), 3.56 (q, 1, J ) 6.5), 4.22
(
d, 1, J ) 14.7), 5.31 (d, 1, J ) 14.6), 6.94 (d, 2, J ) 8.2), 7.31
2 2
S/H O for 36
(t, 1, J ) 7.5), 7.33 (d, 2, J ) 8.2), 7.43 (d, 1, J ) 7.9), 7.49 (d,
1
, J ) 7.6), 8.47 (d, 1, J ) 6.0). Anal. Calcd for C21
Br: C, 60.73; H, 5.58; N, 6.74. Found: C, 60.90; H, 5.69; N,
.65.
Ben zod ia zep in e 1s. The support-bound benzodiazepine
was prepared according to the above procedure from 3-bromo-
-methylanthranilic acid, leucine methyl ester hydrochloride,
23 2 2
H N O -
2
2
(4 × 15 mL) and CH
6
-
1
1
(
(
KBr): 3441 (b), 2967, 1689, 1657, 1598, 1440 cm
400 MHz, DMSO-d ): δ 0.73 (d, 3, J ) 6.3), 0.82 (d, 3, J )
.3), 0.98 (t, 3, J ) 7.0), 1.45-1.65 (m, 3), 3.61 (m, 1), 3.70 (m,
), 4.13 (m, 1), 7.39 (d, 1, J ) 8.3), 7.58 (s, 1), 7.68 (d, 1, 8.3),
. H NMR
5
6
and iodomethane. The scalemic R-amino ester was loaded
according to the nonracemizing conditions. Cleavage of 0.248
g (0.073 mmol) of this resin by stirring in 20 mL of 90:5:5 TFA/
6
1
8
2
1
1
3
.62 (d, 1, 5.8). C NMR (101 MHz, DMSO-d
6
): δ 13.0, 21.6,
2.8, 23.8, 36.3, 42.0, 50.1, 122.5, 125.7, 128.8, 131.1, 136.5,
Me
2
S/H
2
O for 36 h yielded a crude yellow residue after gravity
Cl (4
+
+
40.4, 166.8, 169.4. HRMS (FAB ) m/ e: 295.1212 (MH
Cl requires 295.1213).
P yr id od ia zep in e 1p . The support-bound benzodiazepine
filtration, rinsing of the resin and filter paper with CH
2
2
C
15
H
20
N
2
O
2
× 15 mL) and CH OH (2 × 10 mL), and concentration. Silica
3
gel chromatography eluting with 3:1-2:1 hexanes/EtOAc
provided 21.5 mg (0.064 mmol, 88% yield) of an amorphous
white powder. Two compounds eluted separately from each
other. On standing, the second to elute converted into the first.
The two compounds are atropisomers, which results from
substitution at the 3-position. Equilibration occurs to provide
was prepared according to the above procedure from 2-ami-
nopyridine-3-carboxylic acid, (S)-phenylalanine methyl ester
hydrochloride, and (bromomethyl)cyclopropane. The scalemic
R-amino ester was loaded according to the nonracemizing
conditions. Cleavage of 0.398 g (0.130 mmol) of this resin by

1
252 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
the most stable atropisomer. Gilman88,89 and Blackburn have
9
dried, round-bottom flask was dissolved 9-BBN dimer (0.506
g, 2.02 mmol) in 7 mL of THF. A dry stir bar was introduced
into the flask, and the contents were cooled with stirring to 0
°C. Over the course of 7 min was added 1-hexene (0.65 mL,
5.2 mmol) via syringe. The reaction mixture was warmed to
rt and stirred for 6 h. This solution was then transferred via
cannula into a 50-mL, round-bottom flask containing the resin
derivatized with the benzodiazepine (0.70 g, 0.24 mmol) that
was presolvated in 7 mL of THF and 5 mL of 2 N aqueous
K
CO . The flask was fitted with a reflux condenser and a
2 3
needle passed through the top of the condenser into the
solution. The solution was then degassed by bubbling Ar
through it for 20 min. A catalytic amount of Pd(PPh ) was
3 4
previously detailed atropisomerism in benzodiazepine deriva-
-
1
1
tives. IR (KBr): 3271, 2955, 1667, 1447, 1108, 779 cm
NMR (500 MHz, DMSO-d ): δ 0.73 (d, 3, J ) 5.5), 0.79 (d, 3,
J ) 5.5), 1.59 (m, 3), 2.35 (s, 3), 3.16 (s, 3), 3.61 (m, 1), 7.50 (s,
.
H
6
1
3
1
d
1
), 7.77 (s, 1), 8.65 (d, 1, J ) 5.5). C NMR (125 MHz, DMSO-
): δ 20.3, 22.2, 23.0, 24.4, 36.3, 37.6, 50.7, 119.1, 129.3, 132.9,
37.4, 137.6, 139.1, 167.2, 171.2. HRMS (FAB ) m/ e: 339.0705
MH
Th ien od ia zep in e 1t. The support-bound benzodiazepine
was prepared according to the above procedure from 3-amino-
-(4-chlorobenzenesulfonyl)thiophene-2-carboxylic acid, D,L-
homophenylalanine methyl ester hydrochloride, and HOAc.
The racemic R-amino ester was loaded according to the
nonracemizing conditions. Cleavage of 0.323 g (0.101 mmol)
6
+
+
(
15 20 2 2
C H N O Br requires 339.0708).
4
then added and purging continued for 10 min. The reaction
mixture was stirred with a magnetic stirrer for 20 h while
being heated at reflux. The solution was removed from the
resin by filtration cannula, and the resin was rinsed with DMF
of this resin by stirring in 20 mL of 90:5:5 TFA/Me
6 h yielded a crude yellow residue after gravity filtration,
rinsing of the resin and filter paper with CH Cl
(4 × 15 mL)
and CH
2 2
S/H O for
3
(7 x 20 mL), CH
mL). The resin was dried in vacuo to a constant weight, and
0.418 g (0.137 mmol) was cleaved by stirring in 20 mL of 90:
2
Cl
2
(7 × 20 mL), and finally CH OH (3 × 10
3
2
2
3
OH (2 × 10 mL), and concentration. Silica gel
chromatography eluting with 2:1 hexanes/EtOAc provided 42.3
mg (0.092 mmol, 90% yield) of an amorphous white powder.
5:5 TFA/Me
the resin and filter paper with excess CH
2
S/H
2
O for 36 h. Gravity filtration and rinsing of
Cl and CH OH
IR (KBr): 2900, 1715, 1654, 1561, 1502, 1355, 1220, 1155,
2
2
3
1
1
1
3
091, 750, 667, 615 cm-1
.
H NMR (400 MHz, DMSO-d
6
): δ
yielded a crude yellow solid upon evaporation in vacuo. Silica
gel chromatography 2:1 hexanes/EtOAc yielded 55.2 mg (0.106
mmol, 77% yield) of white solid, mp 176-178 °C. IR (KBr):
3430 (b), 3100, 3026, 2927, 1657, 1612, 1517, 1443, 1385, 1224,
.76-1.85 (m, 1), 1.96-2.05 (m, 1), 2.51-2.64 (m, 2), 3.63-
.69 (m, 1), 7.10 (d, 2, J ) 7.0), 7.15 (d, 1, J ) 7.1), 7.23 (t, 2,
J ) 7.1), 7.73 (d, 2, J ) 8.6), 7.99 (d, 2, J ) 8.6), 8.68 (d, 1, J
1
3
-1
1
)
4.7), 8.86 (s, 1), 9.43 (s, 1). C NMR (101 MHz, DMSO-d
δ 30.0, 31.2, 52.2, 125.9, 126.2, 128.2, 128.3, 129.1, 130.0, 130.5,
33.4, 139.1, 139.4, 139.5, 141.1, 162.3, 168.8. Anal. Calcd
for C21 Cl: C, 54.72; H, 3.72; N, 6.08. Found: C,
4.88; H, 3.90; N, 5.87.
Ben zod ia zep in e 1u . This is a Suzuki cross-coupling
6
)
1174, 1130, 1008, 834, 757, 698 cm
.
H NMR (400 MHz,
DMSO-d ): δ 0.79 (t, 3, J ) 6.5), 1.17-1.22 (m, 6), 1.50 (t, 2,
6
1
J ) 6.5), 2.56 (t, 2, J ) 7.5), 2.83 (dd, 1, J ) 8.6, 14.2), 3.07
(dd, 1, J ) 5.5, 14.3), 3.89 (q, 1, J ) 6.0), 5.00 (d, 1, J ) 15.9),
5.39 (d, 1, J ) 15.9), 6.62 (d, 2, J ) 8.4), 7.06 (d, 1, J ) 8.0),
17 2 4 2
H N O S
5
7
.10 (d, 2, J ) 8.4), 7.15 (d, 2, J ) 8.1), 7.30-7.34 (m, 2), 7.42
(
2
t, 2, J ) 7.6), 7.46 (d, 1, J ) 7.9), 7.51 (d, 2, J ) 8.2), 7.59 (d,
product. In a 100-mL round-bottom flask was suspended 0.500
g (0.180 mmol) of the resin from which 1d was cleaved in 30
mL of THF. After the resin had completely solvated (5 min),
1
3
, J ) 7.2), 8.66 (d, 1, J ) 6.2), 9.2 (s, 1). C NMR (101 MHz,
): δ 13.8, 21.9, 28.1, 30.2, 31.0, 32.9, 34.8, 49.1, 54.2,
14.9, 122.1, 125.7, 126.4, 126.5, 127.3, 127.4, 127.5, 127.8,
28.8, 129.4, 130.3, 136.6, 138.8, 139.0, 139.5, 146.9, 155.8,
67.5, 170.2. Anal. Calcd for C35 : C, 78.92; H, 6.81;
DMSO-d
6
1
1
1
2
2 3
N aqueous K CO (5 mL) was added to the flask generating
a biphasic liquid. With magnetic stirring, 4-methoxyben-
zeneboronic acid (0.281 g, 1.85 mmol) was added, and the flask
was fitted with a reflux condenser. A long needle was dropped
through the reflux condenser, and the system was purged with
36 3 2
H O N
N, 5.26. Found: C, 78.74; H, 6.84; N, 5.07.
Ben zod ia zep in e 1w . This is a Suzuki cross-coupling
product. The support-bound benzodiazepine, prepared accord-
ing to the above procedure from 5-bromoanthranilic acid,
leucine methyl ester hydrochloride (nonracemizing reductive
amination conditions), and (bromomethyl)cyclopropane, was
suspended (0.500 g, 0.180 mmol) in 4 mL of THF, 4 mL of
3 4
Ar. After 30 min, Pd(PPh ) (0.100 g, 0.086 mmol) was added,
and the suspension was purged with Ar for another 15 min.
The purge needle was removed, and the system was heated
at reflux for 18 h under 1 atm of Ar. The yellow/orange
solution was removed from the resin by filtration cannula, and
the resin was rinsed with DMF (7 × 20 mL), CH
mL), and finally CH
OH (3 × 10 mL). The resin was dried in
vacuo to a constant weight, and 0.320 g (0.106 mmol) was
cleaved by stirring in 20 mL of 90:5:5 TFA/Me S/H O for 36
h. Gravity filtration and rinsing of the resin and filter paper
with excess CH Cl and CH OH yielded a crude yellow solid
2
Cl
2
(7 × 20
DMF, and 1 mL of H
solvated (5 min), CsCO
2
O. After the resin had completely
3
(0.61 g, 1.87 mmol) was added to the
3
flask. With magnetic stirring, 4-methoxybenzeneboronic acid
(0.577 g, 3.80 mmol) was added, followed by addition of
2
2
[PdCl
2
gently to 55 °C for 12 h under 1 atm of N . The black solution
(dppf)]75 (0.100 g, 0.122 mmol). The solution was heated
2
2
2
3
upon evaporation in vacuo. Silica gel chromatography 2:1
hexanes/EtOAc yielded 24.0 mg (0.066 mmol, 62% yield) of
white solid, mp 202-204 °C (phase change and subsequent
decomposition). IR (KBr): 3454 (b), 3177, 3046, 2960, 1690,
was removed from the resin by filtration cannula and was
rinsed with a solution of saturated KCN in DMSO (in order
to remove the Pd) followed by DMF (7 × 20 mL), CH
2
Cl
2
(7 ×
20 mL), and finally CH
3
OH (3 × 10 mL). Caution! Extreme
-
1 1
1
664, 1611, 1493, 1453, 1256, 1183, 1117, 1032, 828 cm . H
NMR (400 MHz, DMSO-d ): δ 0.74 (d, 3, J ) 6.1), 0.82 (d, 3,
J ) 6.0), 1.03 (t, 3, J ) 6.8), 1.60-1.69 (m, 3), 3.62-3.68 (m,
), 3.71-3.79 (m, 1), 3.80 (s, 3), 4.07-4.14 (m, 1), 7.04 (d, 2, J
8.1), 7.52 (d, 1, J ) 8.3), 7.67 (d, 2, J ) 8.1), 7.84-7.87 (m,
care should be used during rinsing with KCN in DMSO. This
mixture is toxic and may be deadly on skin contact. Appropri-
ate precautions should be taken. Rinses should be disposed of
accordingly. The resin was dried in vacuo to a constant
weight, and 0.450 g (0.144 mmol) was cleaved by stirring in
6
1
)
1
3
2
2
1
), 8.59 (d, 1, J ) 5.8). C NMR (101 MHz, DMSO-d
6
): δ 13.1,
20 mL of 90:5:5 TFA/Me
residue after gravity filtration, rinsing of the resin and filter
paper with CH Cl
2 2
S/H O for 36 h yielded a crude yellow
1.7, 22.7, 23.8, 36.4, 42.1, 50.2, 55.1, 114.5, 123.1, 126.4, 127.7,
29.6, 130.2, 130.6, 136.7, 137.8, 159.2, 167.5, 169.3. Anal.
2
2
(4 × 15 mL) and CH OH (2 × 10 mL), and
3
Calcd for C22
1.99; H, 7.00; N, 7.43.
Ben zod ia zep in e 1v. The support-bound benzodiazepine
H
26
O
3
N
2
: C, 72.11; H, 7.15; N, 7.64. Found: C,
concentration. Silica gel chromatography eluting with 2:1
hexanes/EtOAc provided 44.0 mg (0.112 mmol, 78% yield) of
a white powder, mp 85-86 °C. IR (KBr): 2953, 1654, 1555,
7
-
1
was prepared according to the above procedure from 4-bro-
moanthranilic acid, H-(S)-Tyr(t-Bu)-OMe‚HCl, and 4-phenyl-
benzyl bromide. The scalemic R-amino ester was loaded
according to the nonracemizing conditions. A Suzuki reaction
was then performed with B-hexyl-9-BBN. In a 10-mL, flame-
1486, 1444, 1364, 1246, 1180, 1025, 870, 828, 668, 553 cm .
1
H NMR (400 MHz, DMSO-d ): δ 0.10 (m, 2), 0.31 (m, 2), 0.74
6
(d, 3, J ) 6.3), 0.82 (m, 4), 1.59-1.67 (m, 3), 3.61-3.80 (m, 2),
3.80 (s, 3), 4.04 (dd, 1, J ) 14.4, 7.6), 7.03, (d, 2, J ) 8.8), 7.57
(d, 1, J ) 8.5), 7.68 (d, 2, J ) 8.8), 7.86 (dd, 1, J ) 8.5, 2.4),
1
3
7
.88 (d, 1, J ) 2.25), 8.61 (d, 1, J ) 6.1). C NMR (101 MHz,
DMSO-d ): δ 3.5, 4.3, 10.4, 22.2, 23.2, 24.3, 36.9, 50.6, 51.1,
5.7, 115.0, 124.2, 126.9, 128.2, 129.9, 130.9, 131.1, 137.2,
138.6, 159.7, 168.1, 170.3. Anal. Calcd for C24 : C,
73.44; H, 7.19; N, 7.14. Found: C, 73.19; H, 6.96; N, 7.14.
6
(
88) Gilman, N. W.; Rosen, P.; Early, J . V.; Cook, C.; Todaro, L. J .
J . Am. Chem. Soc. 1990, 112, 3969-3978.
89) Gilman, N. W.; Rosen, P.; Earley, J . V.; Cook, C. M.; Blount, J .
F.; Todaro, L. J . J . Org. Chem. 1993, 58, 3285-3298.
5
28 2 3
H N O
(

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1253
Ra cem iza tion Stu d y. Benzodiazepine 1c was prepared
Ta ble 3. Am ou n ts Used for th e Loa d in g r-Am in o Ester s
according to the racemization-free procedure described previ-
u n d er Ra cem iza tion Con d ition s
6
8
ously. HPLC analysis (chiral column, D-phenylglycine de-
rivatized silica, 5% i-PrOH in isooctane eluant, 4 mL/min flow
rate, UV detection at 262 nm) of benzodiazepine 1c, prepared
under racemization-free conditions, indicated a single enan-
total
amino FW concn vol mmol mass i-Pr EtN reductant
2
label ester (g/mol) (M) (mL) ester (g)
(mL)
(g)
L
F
Y
E
Q
K
Leu
Phe
Tyr
Glu
Gln
Lys
181.7 0.15
215.7 0.15
287.8 0.15
253.8 0.15
422.9 0.15
296.8 0.15
50
50
50
50
50
50
7.50 1.36
7.50 1.62
7.50 2.16
7.50 1.90
7.50 3.17
7.50 2.23
0.393
0.393
0.393
0.393
0.393
0.393
1.59
1.59
1.59
1.59
1.59
1.59
tiomer, t
also prepared by allowing preequilibration in the reductive
amination step for 6 h in the presence of i-Pr EtN. Analysis
R
) 45.4 min. A fully racemized sample of 1c was
2
of the racemized sample under the same HPLC conditions
indicated two well-separated peaks of approximate equal area,
t ) 41.8, 44.8 min, confirming that complete racemization
R
had occurred.
holes. Before the tubes cooled, a thermally resistant cloth was
used to wipe away the excess polyethylene from around the
outside of the tube. After these tubes cooled, they were
introduced manually into the bracket creating a reactor of 12
× 8 (96) spatially separate reaction tubes per bracket, leaving
most of the tube below the bracket. Only ∼1/4 in. was left
above the bracket. It was useful to let the brackets sit in a
desiccator that had been charged with 50 mL of THF for 30
min prior to inserting the filter tubes. This helped to swell
the plastic, allowing for easy insertion. On standing for 2 h
on the bench top, the plastic shrinks and seals around the
tubes. This apparatus is shown in schematic form in Figure
3.
An additional HPLC study was performed with 1b, synthe-
sized from the more racemization-prone phenylalanine.90 Ben-
zodiazepine 1b was prepared according to the racemization-
free procedure described previously. A racemized sample of
1
b was also prepared. This racemized sample served as an
5
HPLC standard. HPLC analysis (chiral column, D-phenyl-
glycine derivatized silica, 4% i-PrOH in hexanes eluant, 9.99
mL/min flow rate, UV detection at 252 nm) of benzodiazepine
1
b, prepared under racemization-free conditions indicated a
major enantiomer, t ) 29.5 min and a trace of a second (<
%), t ) 35.7 min. Analysis of the racemized sample under
the same conditions indicated two well-separated peaks, t
0.5 min and t ) 35.8 min.
Benzodiazepine 1o was also prepared employing racemiza-
R
1
R
R
)
3
R
Libr a r y Syn th esis. Cou p lin g of Lin k er to Su p p or t. In
an oven-dried, two-neck, 2000-mL round-bottom flask, fitted
with an oven-dried mechanical stirring arm, was dissolved
tion-free conditions. To verify that during and after alkylation
significant racemization was not able to occur, we heated
benzodiazepine 1o in 6 N aqueous HCl at reflux for 12 h in
order to liberate the amino acid portion of this benzodiazepine.
The liquid was evaporated in vacuo to a yellow residue that
-1
18.56 g (182.2 g mol , 102 mmol) of 4-hydroxy-2,6-dimethoxy-
benzaldehyde87 in 400 mL of dry DMF. The solution was
purged with Ar for 20 min. To this solution, with cooling to 0
°C, under constant positive Ar pressure, was added 2.45 g
-
1
was subsequently dissolved in 10 mL of CH
3
OH. To this
(24.00 g mol , 97 mmol) of 95% NaH in four aliquots. The
mixture was added SOCl (28 mL, 0.40 mmol). The mixture
2
dark orange solution evolved H (g) rapidly and turned a turbid
2
was heated at reflux for 3 h, and the volatile contents of the
flask were removed in vacuo. The yellow residue was then
blood red color and then finally became cloudy orange in
appearance. After the evolution of H ceased, the suspension
2
dissolved in 10 mL of CH
into two round-bottom flasks. One portion was treated with
drops of (R)-R-methoxy-R-(trifluoromethyl)phenylacetic acid
chloride, (R)-MTPA chloride, and 5 drops of Et N, and the
other portion was treated with 5 drops of (S)-MTPA chloride
and 5 drops of Et N. After the reactions were allowed to
proceed for 12 h, the reaction solutions were each washed with
N aqueous HCl (3 × 2 mL), 5% aqueous K CO (2 × 2 mL),
saturated aqueous NaHCO (2 mL), and brine (2 mL). The
organic layers were dried over MgSO , and the crude residues
2
Cl
2
and partitioned in equal volumes
was purged continuously with Ar under vigorous mechanical
stirring and was simultaneously allowed to warm to rt. After
20 min, 50.0 g (34.5 mmol of chloride) of Merrifield resin (200-
400 mesh chloromethylpolystyrene, 1% divinylbenzene cross-
5
3
-
link, 0.69 mmol Cl /g resin) was added with constant gentle
3
mechanical stirring under gentle positive pressure of Ar,
taking care not to let the Ar flow blow the resin out of the
flask as it was being added. The mixture was then heated to
100 °C for 30 min and cooled to 50 °C where it was allowed to
stir under an atmosphere of Ar for 36 h. The resin was rinsed
1
2
3
3
4
were purified on a silica plug, eluting with 1:1 hexanes/EtOAc.
The diastereomeric ratio of the products formed was evaluated
by capillary GC analysis (HP-1, 150-200 °C, 1 deg/min ramp,
with 2:1 DMF/MeOH (3 × 500 mL), DMF (7 × 375 mL), CH -
2
Cl (7 × 400 mL), and finally MeOH (4 × 300 mL). After being
2
dried in vacuo, the resin had assumed the tan color of the
linker aldehyde. A strong aldehyde carbonyl stretch was
2
0 psi). The sample prepared from the (R)-MTPA chloride
indicated a major diastereomer (t ) 26.0 min, 97%) of (R)-
MTPA-(S)-Leu-OMe, and a minor diastereomer (t ) 27.0 min,
%). The sample prepared from (S)-MTPA chloride indicated
a minor diastereomer of (R)-MTPA-(S)-Leu-OMe (t ) 26.0
min, 3%) and a major diastereomer (t ) 27.1 min, 97%). This
-
1
R
observed in the IR (KBr) spectrum of this resin: 1690 cm .
R
Red u ctive Am in a tion s, Ra cem izin g P r oced u r e. In
each of six tared 100-mL round-bottom flasks was placed 3.5
g of aldehyde resin. To this was added 50 mL of 1% HOAc in
DMF. After the resin had solvated (5 min), one R-amino ester
(amounts are found in Table 3) was added to each flask, which
was then labeled with the code for that particular R-amino
ester. To each flask was then added a catalytic amount of
3
R
R
experiment demonstrates that racemization occurred to a
maximum extent of 3% in this leucine-derived benzodiazepine.
It is most likely that the racemization occurs in the benzodi-
6
9
azepine hydrolysis step and not during the benzodiazepine
synthesis.
i-Pr EtN (0.291 g, 2.25 mmol). The mixtures were secured on
2
a shaker table and allowed to agitate for 9 h. The reductant,
Con str u ction of Mu ltitu be Ap p a r a tu s. The apparatus
consists of three parts: a bracket, a tube, and a filter frit. The
bracket, which secured the individual reactor tubes in place,
was made by sawing off the top ∼1/6 in. of 96 1-mL well
microtiter plates. The individual reaction tubes were made
by cutting 1500 identical 2 in. pieces of 7 mm (outer diameter)
glass tubing using a diamond-bladed glass saw with a 2-in.
stop to ensure uniformity. The filter frits were introduced onto
each of these by heating one end in a Bunsen burner until
yellow-hot and melting it directly into a 70 µm hydrophobic
polyethylene filter disk (purchased from Applied Separations,
catalog no. 2427), taking the time to ensure that the entire
bottom of the tube was sealed, with no obvious large pores or
NaBH(OAc) (1.59 g, 7.50 mmol), was then added. After 6 h,
3
an IR spectrum of the resin containing H-Leu-OMe‚HCl
indicated that the reaction had proceeded to completion. The
resins were washed with 1:1 DMF/MeOH (1 × 30 mL), DMF
(7 × 30 mL), CH Cl (7 × 30 mL), and MeOH (4 × 20 mL). A
2
2
Kim Wipe was inserted into the mouth of each flask and the
resins dried in a vacuum desiccator for 18 h. Infrared spectra
(KBr) were obtained, and all resins showed a strong ester
-
1
carbonyl absorbance at ∼1740 cm
.
Red u ctive Am in a tion s, Non r a cem izin g Loa d in g of
Ra cem ic r-Am in o Ester s a n d Glycin e. Into four tared 100-
mL round-bottom flasks was aliquoted 3.5 g of the aldehyde
resin. To each of them was added 50 mL of DMF and 0.5 mL
of HOAc. Upon addition of the acetic acid, the resin turned
3
from bright orange to yellow. NaBH(OAc) (1.59 g, 7.50 mmol)
(
90) Kov a´ cs, J . In The Peptides; Gross, E., Meienhofer, J ., Eds.;
Academic: New York, 1980; Vol. 2, pp 485-539.
was added and dissolved, followed immediately by the R-amino

1
254 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
Ta ble 4. Am ou n ts Used for th e Loa d in g r-Am in o Ester s
top and placed upright in a box on a shaker table. After 12 h
of agitation, the filter cartridges were rinsed, 12 at a time,
using a Visiprep filter cartridge filtration apparatus obtained
from Supelco (catalog no. 5-7030). The rinses consisted of
soaking the resin in each cartridge with DMF (5 mL) as many
times as was needed until the supernatant that was removed
was colorless. Each resin sample was then soaked for 5 min
u n d er Ra cem iza tion -F r ee Con d ition s
amino
FW
concn total vol
mass reductant
label ester (g/mol) (M)
(mL)
mmol (g)
(g)
G
A
U
X
Gly
Ala
2-Nal 245.3
2-Thi 221.7
125.6
139.6
0.15
0.15
0.15
0.15
50
50
50
50
7.50 0.94
7.50 1.05
7.50 1.84
7.50 1.66
1.59
1.59
1.59
1.59
in CH
2
Cl
2
(5 × 5 mL). The acylation and rinsing was repeated
in an identical manner, with the exception that an additional
rinse with MeOH (3 × 5 mL) was performed at the end. All
Ta ble 5. Distr ibu tion of r-Am in o Ester -Der iva tized
1
20 filter cartridges were sealed at the top with a 14/20 rubber
Resin by Ma ss
septum and dried in a vacuum desiccator overnight.
Resin Distr ibu tion , Cycliza tion , a n d Alk yla tion . The
cartridges were removed from the vacuum desiccator, and a
mixture of 3:2 1,2-dichloroethane/DMF was found to be isopyc-
nic83 with respect to the resins in a randomly chosen cartridge.
Since each cartridge had a structurally unique resin-bound
benzodiazepine precursor, there was concern that 3:2 dichlo-
roethane/DMF might not be isopycnic with respect to the
contents of all the cartridges. This was found not to be the
case. In particular, for each cartridge after dilution, no visible
settling of the resin was observed over 10 s. We felt that this
was sufficient to ensure that removal of equal volume aliquots
from 120 equal total volume slurries would allow for equimolar
distribution.
amino
ester
FW
(g/mol)
recovered
mass (g)
0.9/12 of resin
to each cartridge (g)
label
L
F
Y
E
Q
K
G
A
U
X
Leu
Phe
Tyr
Glu
Gln
Lys
Gly
Ala
2-Nal
2-Thi
181.7
215.7
287.8
253.8
422.9
296.8
125.6
139.6
245.3
221.7
3.55
3.79
3.95
3.92
4.21
3.88
3.59
3.64
3.93
3.84
0.266
0.284
0.296
0.294
0.316
0.291
0.268
0.273
0.295
0.288
Ta ble 6. Am ou n ts Used for th e An th r a n ilic Acid
Acyla tion Step
The contents of every cartridge were suspended in excess
3
:2 dichloroethane/DMF and agitated on a vortex mixer until
anthranilic
completely solvated. The liquid was removed by suction, the
cartridge bottom was stoppered with an 8 mm white rubber
septum, and 2 mL of 3:2 dichloroethane/DMF was delivered
by a Pipetman. Aliquots of 240 µL of the contents of each
cartridge were transfered to 10 separate reaction tubes. The
volume was delivered as 2 × 120 µL portions to help average
out any variation. Aliquoting was performed with a Pipetman,
fitted with tips whose ends had been cropped to provide a
wider bore to accommodate free passage of polymer beads.
Enough extra resin in each cartridge remained to remake at
least one benzodiazepine if necessary.
A total of 16.5 multitube plates were filled, and each of these
plates was blotted on a terry cloth towel, which helped to draw
solvent out of the tubes. Several polypropylene covers from
pipet tip racks (referred to as polypropylene bins) were then
used as small solvent reservoirs and filled with DMF. Each
multitube plate was submerged in DMF 1 in. high (2 × 1 min).
The filter bottoms were blotted on terry cloth towels in between
rinses. Several large polypropylene tubs were then filled 1
in. high with THF, and the tubes were submerged and soaked
acid
FW
concn vol
mass
EDC
label
A
(abbr Ant)
(g/mol) (M) (mL) mmol (mg) (mg, M)
anthranilic
acid (Ant)
4-Cl Ant
5-Cl Ant
6-F Ant
3-Me Ant
4-Br Ant
5-Br Ant
4-MeO Ant
4-nitro Ant
4-Me Ant
137.1
0.35
3.0
1.05
144 247, 0.43
B
C
D
E
F
G
H
I
171.6
171.6
155.1
151.7
216.0
216.0
167.2
182.1
151.7
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.05
1.05
180 247, 0.43
180 247, 0.43
162 247, 0.43
159 247, 0.43
227 247, 0.43
227 247, 0.43
175 247, 0.43
191 247, 0.43
159 247, 0.43
242 247, 0.43
145 247, 0.43
J
K
L
3-Br, 5-Me Ant 230.1
3-pyridine Ant 138.1
esters (amounts are shown in Table 4). The flasks were
secured on the shaker table. As the reduction proceeded, the
color of the resin became even lighter. After 3 h, the resins
were given the same rinse sequence described in the preceding
experimental procedure and were dried in vacuo for 12 h, and
IR (KBr) spectra were obtained. All resins showed a strong
(
3 × 30 min), allowing the tubes to drain in between soakings.
The multitube plates were then submerged quickly in THF
-
1
ester carbonyl stretch at ∼1740 cm
.
(
3×) and blotted on terry cloth towels in between rinses. The
Acylations were performed in 120 12-mL filter cartridges
with 70 µm hydrophobic polyethylene frits, purchased from
Applied Separations (catalog no. 2427). In order to deliver an
equimolar amount of resin-bound R-amino ester into each of
these reaction vessels, the total mass of each of the R-amino
ester-derivatized resins was obtained based on the tare of the
round-bottom flasks. This total mass was then divided by 12
plates were then soaked in 4-Å sieve-dried THF for 36 h in an
N glove bag over 4-Å sieves.
2
Cyclizations were performed using lithiated acetanilide in
a THF/DMF solution: In a 2-L, oven-dried, round-bottom flask,
fitted with a large magnetic stir bar, was placed 500 mL of
4-Å sieve-dried THF. To this was added 55.0 g (407 mmol,
135.2 g mol-1) of acetanilide. The acetanilide had been dried
(
corresponding to acylation with 12 anthranilic acids). In order
in vacuo overnight. This solution was cooled to -78 °C, and
to have a small amount of resin left over, this quantity was
then multiplied by 0.9. These masses are shown in the last
column of Table 5. The resin corresponding to each R-amino
ester was then distributed into 12 filter cartridges according
to the mass in the right most column of Table 5. The total
number of filter cartridges was 120; each was labeled in
duplicate according to the R-amino ester resin contained within
and the anthranilic acid to be acylated.
the flask was purged with dry N . With rapid stirring,
2
n-butyllithium (2.5 M in hexanes, 150 mL, 375 mmol) was
added dropwise by syringe over the course of 1.5 h. As the
addition proceeded, a white solid precipitated from the reaction
mixture. After n-BuLi addition was complete, the contents of
the flask were warmed to rt as solids continued to precipitate.
Once at rt, 1 L of dry DMF was added over 30 min. All solids
dissolved. The flask containing the 0.25 M cyclization cocktail
Acyla tion of Resin -Bou n d r-Am in o Ester s. The bottom
2
was moved into an N glovebag.
of each of the 120 12-mL filter cartridges was sealed with an
8
2
Into each of 17 of the 40 small polypropylene bins was
poured between 75 and 100 mL of the cyclization cocktail. Each
of the multitube plates was removed from the 4-Å sieve/THF
bin, blotted on a terry cloth towel, which had dried over night
mm rubber septum and to each of them was added 1-methyl-
-pyrrolidinone (NMP, 3 mL) and the coupling agent EDC (see
Table 6 for amounts). Some EDC remained undissolved until
the anthranilic acid was added. Before addition of the an-
thranilic acid, the mixture of EDC, NMP, and resin was
agitated on a vortex mixer for 10 s. The anthranilic acid (Table
in a N
2
glovebag, and transferred into the small polypropylene
bins containing the 75-100 mL of cyclization cocktail.
A
multichannel pipet device was then used to remove cyclization
cocktail from the bottom of the polypropylene reaction bins
and drop it down from the tops of the reactor tubes in order
6
) was then added and immediately vortexed to homogeneity.
The cartridges were sealed with a 14/20 rubber septum at the

Synthesis of 1,4-Benzodiazepine-2,5-diones
J . Org. Chem., Vol. 62, No. 5, 1997 1255
Ta ble 7. Am ou n ts Used for th e Alk yla tion Step a
Ta ble 8. Rela tive Ch r om op h or es of Ben zod ia zep in es to
Nitr otolu en e Sta n d a r d a
alkylating
agent
FW
d
concn
mass, vol
(g, mL)
label
(g/mol) (g/mL) (M)
mol
R1
R2
R3
entry
factor
A
B
C
D
E
F
G
H
none (AcOH)
methyl iodide
ethyl iodide
60.05 1.049 0.40 0.030 1.80, 1.72
141.94 2.280 0.40 0.030 4.26, 1.86
155.97 1.513 0.40 0.030 4.68, 3.09
1
2
3
4
5
6
7
8
9
10
11
12
3
4
5
6
17
18
19
7-Cl
7-Cl
9-pyridyl
8-MeO
8-NO2
7-Cl
ethyl
benzyl
c-(C3H5)CH2
2-MeOBn
ethyl
(CH2)2CONH2
(CH2)2CO2H
CH2C6H5
0.37
0.38
0.55
0.39
0.24
0.35
0.30
0.25
0.26
0.40
0.53
0.37
0.20
0.25
0.28
4-Phbenzyl bromide 247.13
0.40 0.030 7.41 g
0.40 0.030 5.18 g
0.40 0.030 5.97 g
0.40 0.030 4.70 g
H
piperonyl chloride
3,5-dimethylBnBr
o-MeOBnCl
(bromomethyl)-
cyclopropane
2-(bromomethyl)-
naphthalene
benzyl bromide
iodoacetamide
170.60
199.10
156.61
CH2CH(CH3)2
CH2C6H5
2-thienylmethyl
CH2C6H5
2-thienylmethyl
CH2CH(CH3)2
CH2C6H5
CH2CH(CH3)2
CH2C6H4OH
CH2CH(CH3)2
CH2C6H4OH
CH2C6H5
H
8-Me
7-Cl
piperonyl
piperonyl
c-(C3H5)CH2
methyl
NH2COCH2
H
4-phenylBn
ethyl
NH2COCH2
ethyl
135.00 1.410 0.40 0.030 4.05, 2.87
8-O2N
9-Br, 7-Me
6-F
9-Br, 7-Me
8-hexyl
7-Br
7-Cl
-
8-MeO
6-F
I
221.10 0.40 0.030 6.63 g
J
K
171.04 1.438 0.40 0.030 5.13, 3.57
187.96 0.40 0.030 5.64 g
1
1
1
1
a
Amounts are calculated on the basis of a volume of stock
solution of 75 mL.
b
12.4
to ensure that the resin was properly bathed in the cyclization
cocktail. These cyclization conditions were maintained for 40
h, over which time the volume of the cyclization cocktail had
reduced and some white solid had precipitated.
Solutions of the alkylating agents (0.4 M, 75 mL) were
prepared in the remaining dry polypropylene bins employing
the amounts shown in Table 7. With the exception of 3,4-
benzyl
3,5-diMeBn
methyl
CH3
2-thienylmethyl
CH2-2-(C10H7)
0.42
0.46
0.24
7-Cl
a
Correction factors by which HPLC ratios of benzodiazepine
to internal standard (p-nitrotoluene) would need to be multiplied
to obtain the actual ratio of benzodiazepine to standard. UV
absorbance detection was monitored at 252 nm. A sample calcula-
(
methylenedioxy)benzyl (piperonyl) chloride and 2-methoxy-
tion appears in the Experimental Section. b The benzodiazepine
benzyl chloride, the liquid alkylating agents were eluted from
a plug of basic alumina prior to use. The solid alkylating
agents were used without any further purification or prepara-
tion, except 3,5-dimethylbenzyl bromide. This solid was
dissolved in a minimal volume of hexanes and eluted from a
plug of basic alumina prior to use. The 3,4-(methylenedioxy)-
benzyl chloride (piperonyl chloride) and 2-methoxybenzyl
chloride were obtained from Trans World Chemicals as 50%-
in entry 16 coeluted with p-nitrotoluene. This factor was mea-
sured relative to 9-fluoreneone.
device and reconcentrated. When brought to dryness, the
bottom of each well had a small orange or yellow pellet. The
wells with glutamine-containing benzodiazepines had red
pellets at the bottom, the color presumably derived from the
dimethoxybenzhydrol protecting group.
Deter m in a tion of Yield s by 1H NMR Com bin ed w ith
HP LC w ith UV Detection . The correction factors found in
Table 8 were all calculated according to the following protocol.
p-Nitrotoluene (∼2 mg) and the selected benzodiazepine (∼4
by-weight solutions in CH
2 2 3
Cl , stabilized with CaCO . These
solutions were passed through a 0.2-µm nylon syringe tip filter
and concentrated in vacuo without heating prior to use.
The resin blocks were removed from the cyclization cocktail,
blotted on a terry cloth towel, and transferred to the bins
containing the alkylating agents. A multichannel pipet device
was used to bathe each of the wells in the solution. The
multitube plates were configured such that only one alkylating
agent was used for each of eight multitube plates. For the
remaining eight plates only two alkylating agents were used.
Alkylation reactions were therefore straightforward to perform
since they were carried out in bins rather than requiring that
the stock solutions be aliquoted into individual wells of
microtiter plates. Alkylations were allowed to continue for
6
mg) were dissolved in DMSO-d . The exact ratio of the
benzodiazepine (Bz) to the internal standard (Std) was deter-
1
mined by H NMR integration. A portion of the mixture was
then injected onto an analytical RP-HPLC column (ramp 40-
100% MeOH in H O over 40 min, UV detection at 252 nm) to
2
obtain the ratio of UV responses of the benzodiazepine relative
to the internal standard. With this information the correction
factor (C) could be calculated:
C ) (Std/Bz)HPLC × (Bz/Std)NMR
6
-8 h. The multitube plates were blotted on towels until all
the alkylation cocktails had drained and transferred to bins
containing DMF to soak.
In order to determine the exact quantity of a benzodiazepine
in the library, the following protocol was used. The well from
the library corresponding to the desired benzodiazepine was
The multitube plates were then repeatedly submerged in
at least 1 in. of DMF and allowed to soak for at least 5 min.
This was repeated five times with blotting in between each
rinse. The plates were then rinsed in the same manner with
THF and then allowed to soak overnight in THF-filled polypro-
diluted with 1.00 mL of a solution of 1:2:0.5 MeOH/CH CN/
3
1,2-dichloroethane. This solvent mixture was used instead of
DMSO to allow for easy reconcentration. The contents of the
well were repeatedly drawn up into a pipet to ensure that
everything had dissolved. A Pipetman was used to transfer
10 µL from the well to a small vial. A solution of the internal
pylene bins in an N
2
glovebag. After 12 h, they were blotted
on terry cloth towels and given three quick rinses by submerg-
ing them in THF, 1 in. deep. Although probably not necessary,
they were soaked overnight again in THF. After 12 h, they
-
1
standard p-nitrotoluene (0.1 mg mL ) was added so as to
deliver 0.03 µmol (41.1 µL) of the internal standard. This
sample was mixed thoroughly after addition of five drops of
DMF. Injection onto RP-HPLC, with ramp and UV detection
as above, provides the ratio of benzodiazepine to standard. The
ratio of benzodiazepine to standard by UV absorbance and the
correction factor (C) are then used to calculate the quantity of
the benzodiazepine: (Bz/Std)HPLC × C (correction factor) × 0.03
µmol (quantity of Std).
were all soaked in CH
2
Cl
2
(7 × 20 min) to remove the THF.
Clea va ges. Into every well (except in the first and last
columns, which were left blank for controls during biological
assay) of 17, 96 2-mL well microtiter plates was added ∼1 mL
3 2 2
of 90:5:5 TFA/(CH ) S/H O by glass pipet. The tubes of the
multitube plates were slowly submerged into the cleavage
cocktail, taking care not to accidentally force TFA up over the
edges of each well as the tubes filled. Cleavages were allowed
to proceed for 36-40 h. The plates were removed slowly,
allowing liquid to drain into the wells, and immediately
submerged into a second plate, charged with a rinse cocktail
Full characterization has previously been provided for most
of the benzodiazepines evaluated above. Complete character-
ization for an additional five benzodiazepines that had been
synthesized on large scale during the development of this
synthetic methodology and that were used in library yield
calculation follows.
3
of 1:1 dichloroethane/CH CN. The plate with the TFA mixture
were concentrated in a J ouan microtiter plate concentrator.
After all the TFA was removed, the rinse cocktails from the
appropriate wells were combined using a multichannel pipet
Ben zod ia zep in e (Ta ble 8, En tr y 16). IR (KBr): 3272,
-
1
1
2943, 1654, 1602, 1460, 1400, 1240, 1129, 761, 703 cm
.
H

1
256 J . Org. Chem., Vol. 62, No. 5, 1997
Boojamra et al.
NMR (400 MHz, DMSO-d ): δ 0.99 (t, 3, J ) 7.0), 2.90 (dd, 1,
6
Ben zod ia zep in e (Ta ble 8, En tr y 18). IR (thin film):
-
1
1
J ) 8.9, 14.2), 3.11 (dd, 1, J ) 5.4), 14.1), 3.68-3.74 (m, 1),
2916, 1672, 1611, 1468, 1390, 1233 cm
. H NMR (400 MHz,
3
2
7
d
.79-3.85 (m, 1), 4.11-4.16 (m, 1), 7.14-7.16 (m, 1), 7.22 (dd,
, J ) 7.1, 7.5), 7.27-7.31 (m, 3), 7.47 (d, 1, J ) 7.9), 7.56-
DMSO-d ): δ 2.14 (s, 6) 3.20 (dd, 1, J ) 8.0, 14.9), 3.33-3.39
6
(m, 1), 4.08-4.13 (m, 1), 4.89 (d, 1,J ) 16.0), 5.27 (d, 1, J )
16.0), 6.69 (b s, 2), 6.80 (b s, 1), 6.90-6.92 (m, 1), 6.94-6.95
(m, 1), 7.11 (t, 1, J ) 9.0), 7.28-7.31 (m, 2), 7.46-7.51 (m, 1),
1
3
.60 (m, 2), 8.68 (d, 1, J ) 6.2). C NMR (101 MHz, DMSO-
6
): δ 13.0, 33.6, 42.1, 53.9, 122.7, 125.6, 126.3, 128.1, 129.3
1
3
(b), 129.9, 132.2, 137.9, 139.1, 167.5, 169.3. Anal. Calcd for
9.07 (d, 1, J ) 7.1). C NMR (126 MHz, DMSO-d
28.4, 49.8, 54.2, 113.8 (d, J FC ) 21.5), 118.9, 119.1 (d, J FC
15.0), 124.7, 125.0, 127.1, 128.8, 132.7 (d, J FC ) 10.0), 137.1,
37.8, 139.8, 141.0 (b), 159.9 (d, J FC ) 252.9), 163.7, 170.3.
6
): δ 21.1,
C
18
H
18
N
2
O
2
: C, 73.45; H, 6.16; N, 9.52. Found: C, 73.40; H,
)
5
.98; N, 9.39.
1
Ben zod ia zep in e (Ta ble 8, En tr y 15). IR (KBr): 2965,
+
+
677, 1519, 1440, 1368, 1210, 1137, 841 cm-1
1
HRMS (FAB ) m/ e: 409.1377 (MH
09.1386).
HP LC Con d ition s. The same conditions were used both
23 2 2
C H22FN O S requires
1
.
H NMR (400
4
MHz, DMSO-d
6
): δ 2.78 (dd, 1, J ) 9.3, 14.3), 2.98 (dd, 1, J )
5
.0, 14.4), 3.87-3.90 (m, 1), 4.22 (d, 1, J ) 16.8), 4.41 (d, 1, J
when evaluating yields and when determining the correction
factors (C). The samples were prepared as described im-
)
7
1
16.8), 6.61 (d, 2, J ) 8.4), 7.06 (d, 2, J ) 8.4), 7.17 (b s, 1),
.35 (d, 1, J ) 8.8), 7.56 (d, 1, J ) 2.6), 7.59 (b s, 1), 7.62 (dd,
13
mediately above. Samples were injected at 40% MeOH in H
on an analytical C-18 reversed-phase HPLC column, ramp 40-
00% MeOH in H O over 40 min, UV detection at 252 nm.
However, an isocratic solvent system of 70% MeOH in H
2
O
, J ) 2.6, 8.8), 8.72 (d, 1, J ) 6.3), 9.22 (s, 1). C NMR (101
): δ 32.7, 50.8, 53.7, 114.9, 124.5, 127.5, 128.7,
29.5, 130.2, 130.7, 131.8, 139.2, 155.9, 166.2, 169.3, 169.9.
MHz, DMSO-d
1
6
1
2
+
+
2
O
HRMS (FAB ) m/ e: 374.0910 (MH
18 17 3 4
C H N O Cl requires
was used in order to minimize slight chromophore variation
compared with entry 13, Tables 3 and 4. The correction factors
of these benzodiazepines were used interchangeably in yield
calculations since they only differ in the length of the C-8 alkyl
group.
3
74.0908).
Ben zod ia zep in e (Ta ble 8, En tr y 8). IR (KBr): 3256,
2
9
883, 1669 (s), 1560, 1488, 1438, 1351, 1244, 1190, 1101, 1042,
-
1
1
32, 812 cm
.
6
H NMR (400 MHz, DMSO-d ): δ 2.94 (dd, 1,
J ) 8.9, 14.0), 3.15 (dd, 1, J ) 5.2, 14.0), 4.04-4.09 (m, 1),
4
1
7
.81, (d, 1, J ) 15.6), 5.27 (d, 1, J ) 15.5), 5.94 (b s, 2), 6.54 (d,
, J ) 7.7), 6.59 (s, 1), 6.75, (d, 1, J ) 7.8), 7.17 (t, 1, J ) 7.1),
.23 (t, 2, J ) 7.1), 7.31 (d, 2, J ) 7.1), 7.51-7.53 (m, 2), 7.58
Ack n ow led gm en t. The NIH (GM50353) and Bur-
roughs Wellcome Fund provided support for this re-
search. J .A.E. is an Alfred E. Sloan Foundation Fellow
and Eli Lilly Grantee. K.M.B. also gratefully acknowl-
edges the J ean Dreyfus Boissevain Undergraduate
Scholarship for Excellence in Chemistry, sponsored by
the Camille and Henry Dreyfus Foundation. Reaction
database searches were performed with ISIS (from
MDL, Inc., 14600 Catalina St., San Leandro, CA 94577).
1
3
(d, 1, J , 8.5), 8.90 (d, 1, J ) 6.3). C NMR (101 MHz, DMSO-
d
1
1
6
): δ 33.6, 49.1, 53.6, 101.0, 107.3, 108.2, 120.4, 124.9, 126.4,
28.1, 128.8, 129.4, 129.8, 130.7, 131.5, 131.8, 137.7, 137.9,
+
+
46.3, 147.4, 166.2, 169.9. HRMS (FAB ) m/ e: 434.1038 (M
Cl requires 434.1033).
Ben zod ia zep in e (Ta ble 8, En tr y 19). IR (KBr): 3060,
24 19 2 4
C H N O
-1
1
2
931, 1664, 1432, 1123, 826 cm
. H NMR (400 MHz, DMSO-
d
6
): δ 3.05 (dd, 1, J ) 8.74, 14.2), 3.28-3.31 (m, 4), 4.05-4.10
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
(
8
m, 1), 7.44-7.46 (m, 4), 7.53-7.56 (m, 1), 7.63 (dd, 1, J ) 3.3,
library members (3 pages). This material is contained in
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, and can be ordered from the
ACS; see any current masthead page for ordering information.
1
3
.8), 7.76-7.83 (m, 4), 8.88 (d, 1, J ) 6.3). C NMR (126 MHz,
): δ 33.9, 35.0, 53.6, 124.2, 125.5, 126.0, 127.3, 127.4,
27.6, 127.7, 127.8, 128.7, 129.3, 130.2, 131.7, 131.8, 132.8,
DMSO-d
1
1
6
+
35.4, 139.6, 166.3, 170.1. HRMS (FAB ) m/ e: 365.1049
+
(MH
C
21
H
18
N
2
O
2
Cl requires 365.1057).
J O9622845