The synthesis of azapeptidomimetic beta-lactam molecules as potential protease inhibitors.

Article abstract of DOI:10.1021/jo026280d

Synthetic methods for the construction of a novel peptidomimetic structure are reported. The structure incorporates a beta-lactam and an azapeptide in a peptide backbone with the intention of generating rationally designed substrate-based protease inhibitors. The beta-lactam is formed by subjecting serine or threonine-azapeptides to Mitsunobu reaction conditions. Importantly, the azapeptidomimetic beta-lactam structure permits extended binding inhibition and the synthetic methods to create tetrapeptidomimetic structures are described.

Full text of DOI:10.1021/jo026280d

Th e Syn th esis of Aza p ep tid om im etic â-La cta m Molecu les a s
P oten tia l P r otea se In h ibitor s
William P. Malachowski,* Chenyang Tie,† Katherine Wang,† and Robert L. Broadrup†
Department of Chemistry and Physics, The University of New England, Biddeford, Maine 04005, and
Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010-2899
wmalacho@brynmawr.edu
Received August 2, 2002
Synthetic methods for the construction of a novel peptidomimetic structure are reported. The
structure incorporates a â-lactam and an azapeptide in a peptide backbone with the intention of
generating rationally designed substrate-based protease inhibitors. The â-lactam is formed by
subjecting serine or threonine-azapeptides to Mitsunobu reaction conditions. Importantly, the
azapeptidomimetic â-lactam structure permits extended binding inhibition and the synthetic
methods to create tetrapeptidomimetic structures are described.
In tr od u ction
methyl ketones,8 are structurally limited in their ability
to generate so-called extended binding interactions (in-
teractions between the inhibitor and the target enzyme
on both sides of the scissile bond). Although there are a
few structurally related inhibitors4 that exploit interac-
tions on either side of the scissile bond, the majority of
protease inhibitors using these popular electrophilic
groups do not exploit extended binding to maximize in-
hibitor strength. An inhibitor design that uses a reactive,
electrophilic group, which is capable of forming extended
binding interactions, is shown in Figure 1. Use of the
reactive monocyclic â-lactam group as a serine9 and
cysteine9f,g,10 protease inhibitor has been reported, al-
though few of the reports are with peptidomimetic
structures. Otto and co-workers have reported9f,g pepti-
domimetic â-lactam serine and cysteine protease inhibi-
Peptidomimetic molecules represent valuable struc-
tures because they mimic certain properties of proteins,
such as three-dimensional structure, while conferring
unique properties, such as enhanced stability to degrada-
tion or inhibition of normal peptide processing. In
particular, peptidomimetic protease inhibitors, both natu-
ral and synthetic, have often initiated drug development
programs to identify therapeutic agents.1 Peptidomimetic
inhibitors of serine and cysteine proteases typically place
a reactive electrophilic functionality near the scissile
bond of a normal protease substrate. The electrophilic
group traps the nucleophilic serine hydroxyl group or
cysteine thiol at the active site, thereby terminating the
enzyme’s catalytic activities.
Interactions on both the prime and nonprime side2 of
the scissile bond of protease ligands have been shown to
enhance selectivity and catalytic activity with sub-
strates,3 and increase the strength of protease inhibitors.4
Four commonly used electrophilic groups, aldehydes,5
boronic acids,6 chloromethyl ketones,7 and trifluoro-
(4) (a) Imperiali, B.; Abeles, R. H. Biochemistry 1987, 26, 4474. (b)
Baggio, R.; Shi, Y.-Q.; Wu, Y.-q.; Abeles, R. H. Biochemistry 1996, 35,
3351. (c) Mookhtiar, K. A.; Marlowe, C. K.; Bartlett, P. A.; Van Wart,
H. E. Biochemistry 1987, 26, 1962. (d) Hu, L.-Y.; Abeles, R. H. Arch.
Biochem. Biophys. 1990, 281, 271. (e) Abato, P.; Conroy, J . L.; Seto, C.
T. J . Med. Chem. 1999, 42, 4001. (f) Chatterjee, S.; Dunn, D.; Tao, M.;
Welb, G.; Gu, Z.-Q.; Bihovsky, R.; Ator, M. A.; Simon, R.; Mallamo, J .
P. Bioorg. Med. Chem. Lett. 1999, 9, 2371. (g) Yamashita, D. S.; Smith,
W. W.; Zhao, B.; J anson, C. A.; Tomaszek, T. A.; Bossard, M. J .; Levy,
M. A.; Oh, H.-J .; Carr, T. J .; Thompson, S. K.; Ijames, C. F.; Carr, S.
A.; McQueney, M.; D’Alessio, K. J .; Amegadzie, B. Y.; Hanning, C. R.;
Abdel-Meguid, S.; DesJ arlais, R. L.; Gleason, J . G.; Veber, D. F. J .
Am. Chem. Soc. 1997, 119, 11351.
(5) (a) Umezawa, H.; Aoyagi, T.; Morishima, H.; Kunimoto, S.;
Matsuzaki, M.; Hamada, M.; Takeuchi, T. J . Antibiot. 1970, 23, 425.
(b) Verstraete, M. Haemostasis 1996, 26, 70.
(6) Kettner, C. A.; Shenvi, A. B. J . Bio. Chem. 1984, 259, 15106. (b)
Quan, M. L.; Wityak, J .; Dominguez, C.; Duncia, J . V.; Kettner, C. A.;
Ellis, C. D.; Liauw, A. Y.; Park, J . M.; Santella, J . B.; Knabb, R. M.;
Thoolen, M. J .; Weber, P. C.; Wexler, R. R. Bioorg. Med. Chem. Lett.
1997, 7, 1595.
(7) (a) Powers, J . C.; Gupton, B. F.; Harley, A. D.; Nishino, N.;
Whitley, R. J . Biochim. Biophys. Acta 1977, 485, 156. (b) Bode, W.;
Turk, D.; Karshikov, A. Protein Sci. 1992, 1, 426.
(8) (a) Imperiali, B.; Abeles, R. H. Biochemistry 1986, 25, 3760. (b)
Veale, C. A.; Bernstein, P. R.; Bohnert, C. M.; Brown, F. J .; Bryant,
C.; Damewood, J . R., J r.; Earley, R.; Feeney, S. W.; Edwards, P. D.;
Gomes, B.; Hulsizer, J . M.; Kosmider, B. J .; Krell, R. D.; Moore, G.;
Salcedo, T. W.; Shaw, A.; Silberstein, D. S.; Steelman, G. B.; Stein,
M.; Strimpler, A.; Thomas, R. M.; Vacek, E. P.; Williams, J . C.;
Wolanin, D. J .; Woolson, S. J . Med. Chem. 1997, 40, 3173.
* Address correspondence to this author at the Department of
Chemistry, Bryn Mawr College, 101 N. Merion Ave., Bryn Mawr, PA
19010-2899.
† Bryn Mawr College.
(1) For reviews on peptidomimetic enzyme inhibitors, see: (a)
Babine, R. E.; Bender, S. L. Chem. Rev. 1997, 97, 1359. (b) Leung, D.;
Abbenante, G.; Fairlie, D. P. J . Med. Chem. 2000, 43, 305. (c)
Whittaker, M.; Floyd, C. D.; Brown, P.; Gearing, A. J . H. Chem. Rev.
1999, 99, 2735. (d) Otto, H.-H.; Schirmeister, T. Chem. Rev. 1997, 97,
133.
(2) Prime and nonprime refers to terminology originally proposed
by I. Schechter and A. Berger (Biochem. Biophys. Res. Commun.
1967, 27, 157). The prime amino acids in a protease substrate ex-
tend in the carboxy terminal direction from the scissile bond starting
with P1′. The nonprime residues extend from the scissile bond in the
amino terminal direction beginning with P1. The subsites in the enzyme
associated with each amino acid position are denoted with S, e.g. S1′
or S1.
(3) (a) Scrimager, S. T.; Hofmann, T. J . Biol. Chem. 1967, 242,
2528-2533. (b) Schechter, I.; Berger A. Biochem. Biophys. Res.
Commun. 1967, 27, 157. (c) Abramowitz, N.; Schechter, I.; Berger, A.
Biochem. Biophys. Res. Commun. 1967, 29, 862 (d) Atlas, D.; Levit,
S.; Schechter, I.; Berger, A. FEBS Lett. 1970, 11, 281.
10.1021/jo026280d CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/16/2002
8962
J . Org. Chem. 2002, 67, 8962-8969

Azapeptidomimetic â-Lactams
thesis, such as ester enolate-imine15 and ketene-imine
cycloadditions,16 are not well-suited for the synthesis of
C-3 amino, C-4 unsubstituted monocyclic â-lactams.17
Although recent structural studies18 with peptidomi-
metic monocyclic â-lactam compounds have indicated
â-turn character, the structures reported in the literature
have notable differences with those proposed in this
paper for the protease inhibitor design. For instance, one
structure with well-characterized â-turn character18a has
two quaternary R-carbons that further bias the peptido-
mimetic monocyclic â-lactam toward a folded secondary
structure.19 In addition, the prediction of inhibitor po-
tential from static structural studies is untenable if
enzymes bind substrates and inhibitors in a dynamic
process by an induced fit20 or by stabilization of confor-
mational ensembles,21 as is currently accepted.
F IGURE 1. Azapeptidomimetic â-lactams.
tors; however, the inhibitors do not exploit extended
binding interactions.
The inhibitor design shown in Figure 1 actually ac-
complishes extended binding by fusing azapeptides with
the monocyclic â-lactam. Azapeptides have also demon-
strated serine11 and cysteine12 protease inhibition. As the
fusion of two documented protease inhibitor functional-
ities, the azapeptidomimetic â-lactam inhibitor design in
Figure 1 represents a second generation of protease
inhibitor design. It is anticipated that the use of an
azapeptide in the P1′ position of the peptidomimetic
structure will make the â-lactam carbonyl more reactive.
The reactivity should be enhanced due to the polar effect
of the R-nitrogen and the associated stabilization of the
N-1 hydrazide leaving group on â-lactam cleavage.
In addition to affording enhanced reactivity of the
â-lactam ring and the potential for extended binding
interactions, it was anticipated that the use of an
azapeptide in the P1′ position would allow efficient
â-lactam synthesis. â-Lactam synthesis with acyl hy-
drazides has been reported,13 although not with azapep-
tides. Efficient â-lactam synthesis can be accomplished
under Mitsunobu conditions, due to the reduction in pKa
for the amide nitrogen in the acyl hydrazine.14
Resu lts a n d Discu ssion
A retrosynthetic analysis of the proposed azapeptido-
mimetic â-lactam inhibitors 1 (Scheme 1) focused our
attention on a core monocyclic â-lactam structure 2 that
could be extended in both the prime and nonprime
directions by the appropriate reactions. Prime residues
could be attached by reaction of a peptide isocyanate with
the N-1 hydrazine group, while nonprime residues would
be attached with standard peptide coupling reactions
with the C-3 amino group. Subjecting an appropriately
protected serine/threonine-azapeptide to Mitsunobu con-
ditions could provide the important monocyclic â-lactam
core 3. Peptide coupling of a protected derivative of serine
or threonine with an azapeptide would generate the
starting material 4 for the Mitsunobu cyclization reac-
tion.
Aza p ep tid e Syn th esis. The azapeptides were all
synthesized from carbamoylation of various alkyl hydra-
zine compounds. Methyl hydrazine is commercially avail-
able and therefore was used first to develop most of the
chemistry that follows. Reaction of methyl hydrazine with
benzyl chloroformate (Cbz-Cl) under Schotten-Bauman
conditions (Scheme 2) provided benzyl azaalanine 5.
Alternatively, reaction of methyl hydrazine with di-tert-
butyl dicarbonate (Boc2O) afforded the tert-butyl ester of
azaalanine 6.
There are many synthetic methods for â-lactam syn-
thesis, nevertheless the Mitsunobu cyclization reaction
was considered especially attractive for C-3 amino, C-4
unsubstituted â-lactams (Figure 1, R3 ) H), which was
one of the simplest inhibitors proposed and one of the
initial targets. More popular methods of â-lactam syn-
(9) (a) Firestone, R. A.; Barker, P. L.; Pisano, J . M.; Ashe, B. M.;
Dahlgren, M. E. Tetrahedron 1990, 46, 2255. (b) Knight, W. B.; Chabin,
R.; Green, B. Arch. Biochem. Biophys. 1992, 296, 704. (c) Yoakim, C.;
Ogilvie, W. W.; Cameron, D. R.; Chabot, C.; Guse, I.; Hache, B.; Naud,
J .; O’Meara, J . A.; Plante, R.; Deziel, R. J . Med. Chem. 1989, 32, 2882.
(d) Bulychev, A.; O’Brien, M. E.; Massova, I.; Teng, M.; Gibson, T. A.;
Miller, M. J .; Mobashery, S. J . Am. Chem. Soc. 1995, 117, 5938. (e)
Kuo, D.; Weidner, J .; Griffin, P.; Shah, S. K.; Knight, W. B. Biochem-
istry 1994, 33, 8347. (f) Achilles, K.; Schneider, M.; Schirmeister, T.;
Otto, H.-H. Pharmazie 2000, 55 (11), 798. (g) Achilles, K.; Schirmeister,
T.; Otto, H.-H. Arch. Pharm. 2000, 333 (8), 243.
(10) Skiles, J .; McNeil, D. Terahedront. Lett. 1990, 31, 7277.
(11) (a) Neumann, U.; Steinmetzer, T.; Barth, A.; Demut, H. U. J .
Enzymol. Inhib. 1991, 4, 213. (b) Powers, J . C.; Boone, R.; Carroll, D.
L.; Gupton, B. F.; Kam, C.-M.; Nishino, N.; Sakamoto, M.; Tuhy, P.
M. J . Biol. Chem. 1984, 259, 4288. (c) Gupton, B. F.; Carroll, D. L.;
Tuhy, P. M.; Kam, C.-M.; Powers, J . C. J . Biol. Chem. 1984, 259, 4279.
(d) Dorn, C. P.; Zimmerman, M.; Yang, S. S.; Yurewicz, E. C.; Ashe, B.
M.; Frankshun, R.; J ones, H. J . Med. Chem. 1977, 20, 1464. (e) Gray,
C. J .; Al-Dulaimi, K.; Khoujah, A. M.; Parker, R. C. Tetrahedron 1977,
33, 837. (f) Barker, S. A.; Gray, C. J .; Ireson, J . C.; Parker, R. C.;
McLaren, J . V. Biochem. J . 1974, 139, 555. (g) Powers, J . C.; Gupton,
B. F. Methods Enzymol. 1977, 46, 208.
It was considered important that the synthesis of the
proposed inhibitors allow for a variety of azapeptides in
the P1′ position. For this reason, the benzyl esters of
azavaline (7), azaleucine (8), and azaphenylalanine (9)
have been similarly generated from the reaction of benzyl
(15) (a) Hart, D.; Ha, D.-C. Chem. Rev. 1989, 89, 1447. (b) Brown,
M. J . Heterocycles 1989, 29, 2225.
(16) Georg, G. I.; Ravikumar, V. T. In The Organic Chemistry of
â-Lactams; Georg, G. I., Ed.; VCH Publishers: New York, 1993;
Chapter 6.
(17) One notable exception: Overman, L. E.; Osawa, T. J . Am. Chem.
Soc. 1985, 107, 1698.
(12) (a) Xing, R.; Hanzlik, R. P. J . Med. Chem. 1998, 41, 1344. (b)
Magrath, J .; Abeles, R. H. J . Med. Chem. 1992, 35, 4279. See also ref
4b.
(13) (a) Atherton, F. R.; Lambert, R. W. Tetrahedron 1983, 39, 2599.
(b) Curran, W. V.; Ross, A. A.; Lee, V. J . J . Antibiotics 1988, 41, 1418.
(c) Iwagami, H.; Yasuda, N. Heterocycles 1990, 31, 529.
(18) (a) Palomo, C.; Aizpurua, J . M.; Benito, A.; Galarza, R.;
Khamrai, U. K.; Vazquez, J .; de Pascual-Teresa, B.; Nieto, P. M.;
Linden, A. Angew. Chem., Int. Ed. 1999, 38, 3056. (b) Linder, M. R.;
Podlech, J . Org. Lett. 1999, 1, 869. (c) Maier, T. C.; Frey, W. U.; Podlech,
J . Eur. J . Org. Chem. 2002, 2686. (d) Sreenivasan, U.; Mishra, R. K.;
J ohnson, R. L. J . Med. Chem. 1993, 36, 256.
(14) The lower pKa value is due to the polar effect of the R-nitrogen
and is significant enough that the dialkyl hydrazinodicarboxylate anion
can deprotonate the amide nitrogen creating a strong nucleophile.
Miller and co-workers have elegantly illustrated and exploited this fact
with related acyl hydroxamate compounds. See: Miller, M. J . Acc.
Chem. Res. 1986, 19, 49.
(19) (a) Karle, I. Acc. Chem. Res. 1999, 32, 693. (b) Venkatraman,
J .; Shankaramma, S. C.; Balaram, P. Chem. Rev. 2001, 101, 3131.
(20) Koshland, D. E. Proc. Natl. Acad. Sci. U.S.A. 1958, 44, 98.
(21) (a) Ma, B. Y.; Shatsky, M.; Wolfson, H. J .; Nussinov, R. Protein
Sci. 2002, 11, 184. (b) Bursavich, M. G.; Rich, D. H. J . Med. Chem.
2002, 45, 541.
J . Org. Chem, Vol. 67, No. 25, 2002 8963

Malachowski et al.
SCHEME 1
SCHEME 2
ethyl chloroformate) were tried. Subjecting pure serine-
azaalanine to Mitsunobu conditions,25 triphenylphos-
phine (Ph3P) and diethyl azodicarboxylate (DEAD), af-
forded cyclized â-lactam product 11, but the diethyl
hydrazinodicarboxylate side product was difficult to
separate. Use of di-tert-butyl azodicarboxylate (DBAD)
afforded easier chromatographic separations of the â-lac-
tam product and the di-tert-butyl hydrazinodicarboxylate
side product. Coupling of tert-butyl azaalanine (6) with
N-benzyloxycarbonyl-serine (N-Cbz-serine) also took place
in good yield and subsequent cyclization under Mit-
sunobu conditions was similarly efficient providing an
89% yield of 13. The use of the alternative protecting
group combination was intended to provide flexibility in
subsequent transformations that extended the â-lactam
core. A two-step procedure involving mesylation (meth-
anesulfonyl chloride, pyridine) of the serine alcohol of
10 followed by cyclization under mildly basic conditions
(K2CO3, acetone, reflux) provided only 33% yield of the
â-lactam product.26
SCHEME 3
SCHEME 4
Subsequent work has focused on applying the Mit-
sunobu conditions to a variety of analogues of serine-
azaalanine (Scheme 5). Consequently, serine-azavaline
(14), serine-azaleucine (16) and serine-azaphenylalanine
(18) have all been synthesized in good yield with EEDQ
coupling reactions. Subjecting each dipeptide to Mit-
sunobu conditions has been similarly efficient. In the
Mitsunobu cyclization of 14, 16, and 18, the choice of
dialkyl azodicarboxylate was adjusted to provide the
optimum conditions for chromatographic purification of
the â-lactam product, i.e., maximum separation between
the products (15, 17, and 19) and the dialkyl hydrazin-
odicarboxylate side product.
chloroformate with isopropyl hydrazine, isobutyl hydra-
zine, and benzyl hydrazine, respectively (Scheme 2).
Since isopropyl, isobutyl, and benzyl hydrazine are not
commercially available, literature methods were adapted
to generate these alkyl and alkaryl hydrazine derivatives.
Benzyl hydrazine was synthesized by direct reductive
amination between hydrazine and benzaldehyde (Scheme
3). The analogous reductive aminations with acetone and
isobutyraldehyde did not prove as effective, so a reductive
amination with ethyl carbazate was performed (Scheme
4).22 Hydrolysis of the ethyl carbamate afforded isopropyl
and isobutyl hydrazine.
â-La cta m Cor e Syn th esis. Coupling of benzyl azaala-
nine (5) with N-tert-butoxycarbonyl-serine (N-Boc-serine)
to yield 10 (Scheme 5) was most efficiently accomplished
with 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EE-
DQ),23 although a variety of agents (EDC,24 BOP, and
In addition to serine-azapeptides, threonine-azaalanine
has also been successfully cyclized (Scheme 5). Coupling
of N-Boc-threonine with benzyl azaalanine (5) was ac-
complished efficiently with EEDQ. Subjecting the dipep-
(22) Giegy, J . R. Monosubstituted Hydrazines. Swiss Patent 307,-
629, Aug. 16, 1955; Chem. Abstr. 1957, 51, 3113f.
(23) (a) Belleau, B.; Malek, G. J . Am. Chem. Soc. 1968, 90, 1651.
(b) Kiso, Y.; Yajima, H. J . Chem. Soc., Chem. Commun. 1972, 942.
(24) Abbreviations: EDC, 1-[3-(dimethylamino)propyl]-3-ethylcar-
bodiimide hydrochloride; BOP, benzotriazol-1-yloxytris(dimethylami-
no)phosphonium hexafluorophosphate.
(25) (a) Mitsunobu, O. Synthesis 1981, 1. (b) Hughes, D. L. Org.
React. 1992, 42, 337.
(26) The two-step procedure has been used as an alternative to
Mitsunobu conditions for serine hydroxamate cyclization to a â-lactam.
See: Floyd, D. M.; Fritz, A. W.; Cimarusti, C. M. J . Org. Chem. 1982,
47, 176.
8964 J . Org. Chem., Vol. 67, No. 25, 2002

Azapeptidomimetic â-Lactams
SCHEME 5
SCHEME 6
tide product 20 to Mitsunobu conditions (Ph3P, DBAD)
afforded a good yield of the â-lactam product.27
22 was fairly stable, but was usually reacted immediately
with leucine methyl ester isocyanate 23.28 Four different
conditions were explored for the isocyanate reaction with
the hydrazino derivative 22. Initially, when 22 and 23
were combined at room temperature, they failed to prov-
ide any product. Upon heating at 42 °C overnight, the
reaction did occur to afford a 70% yield of 24. The use of
triethylamine (Et3N), as a proton scavenger, allowed the
reaction to occur at room temperature to afford 72% yield
of the urea product 24. Finally, use of the acylation
catalyst 4,4′-(dimethylamino)pyridine (DMAP), in addi-
tion to Et3N, provided 24 in 100% yield.
E xt en sion of t h e Aza p ep t id om im et ic â-La ct a m
Cor e. Important to the inhibitor design was the potential
to test extended binding inhibitors. Consequently, the
next stage of the synthesis required methods to elaborate
the dipeptidomimetic â-lactam core, 3, into the tetrapep-
tidomimetic structures 1. Initially, the focus turned to
what was regarded as the more difficult step in the
process: carboxy terminal elaboration. Elaboration in the
amino terminal direction would occur with standard
peptide coupling procedures. To begin carboxy terminal
elaboration, deprotection of the benzyloxycarbonyl (Cbz)
group of 11 was accomplished uneventfully under hy-
drogenation conditions (Scheme 6, path A). The product
Deprotection of the amino-terminal Boc group with
trifluoroacetic acid (TFA) went smoothly to afford 25, the
TFA salt of the amine. However, coupling with N-acetyl-
alanine did not provide any product after column chro-
matography. There was some concern that the polarity
(27) Based on literature precedent with the Mitsunobu reaction of
acyl hydroxamates (see: Miller, M. J .; Mattingly, P. G.; Morrison, M.
A.; Kerwin, J . F., J r. J . Am. Chem. Soc. 1980, 102, 7026), the â-carbon
of L-threonine should undergo inversion of configuration. However, the
stereochemistry at C-4 of the azetidinone in 21 could not be determined
due to spectral broadening from rotamers.
(28) (a) Nowick, J . S.; Powell, N. A.; Nguyen, T. M.; Noronha, G. J .
Org. Chem. 1992, 57, 7364. (b) Tsai, J . H.; Takaoka, L. R.; Powell, N.
A.; Nowick, J . S. Org. Synth. 2000, 78, 220.
J . Org. Chem, Vol. 67, No. 25, 2002 8965

Malachowski et al.
TABLE 1. P ep tid e Cou p lin g Con d ition s to 28
extend the dipeptidomimetic â-lactam core into a tet-
rapeptidomimetic â-lactam structure.
Con clu sion
A flexible and efficient synthesis of azapeptidomimetic
â-lactams has been accomplished. The current synthetic
sequence provides ample opportunity to further modify
side chain groups in positions on both sides of the scissile
bond. As illustrated with threonine, the use of different
â-substituted serine derivates will provide alternative P1
side chains. The P1′ side chain can be modified by the
use of different azapeptides in a manner analogous to
the use of azavaline, azaleucine, and azaphenylalanine.
Finally, the use of alternative amino acids or amino ester
isocyanates will afford different groups in the P2 and P2′
positions. In addition, the potential exists, in the current
scheme, for even longer extension with the use of polypep-
tides in place of N-Ac-Phe or peptide isocyanates31 for
leucine methyl ester isocyanate. The flexibility of the syn-
thesis and the efficiency of the â-lactam synthesis is cur-
rently being exploited to generate and test potential pro-
tease inhibitors. Inhibition studies will be forthcoming.
of the tetrapeptidomimetic and the absence of a chro-
mophore in the product made purification by silica gel
column chromatography difficult. Consequently, the next
attempt coupled N-acetyl-phenylalanine (N-Ac-Phe) to
the amine and afforded a 44% yield of 26 after column
chromatographic purification. The product 26 represents
a tetrapeptidomimetic â-lactam molecule capable of
presenting P2, P1, P1′, and P2′ side chains to a protease
enzyme.
The disappointingly low yield for the final step in path
A was partially attributed to the presence of the TFA salt
that can compete with the carboxylic acid component for
carbodiimide in coupling reactions. Deprotection of the
Exp er im en ta l Section
Gen er a l Meth od s. Unless otherwise stated, all air- or
moisture-sensitive reactions were performed with magnetic
stirring in oven-dried glassware under an argon or nitrogen
atmosphere using dry, distilled solvents. Tetrahydrofuran
(THF) was dried over microwave-activated 4-Å molecular
sieves. Methylene chloride (CH2Cl2), ethyl acetate (EtOAc), and
triethylamine (Et3N) were distilled from calcium hydride.
Methanol was dried over Mg and distilled. All other com-
mercially obtained reagents were used as received. The 3.0 M
HCl solution in EtOAc was generated by bubbling HCl gas
into a cooled (-15 °C) solution of EtOAc. All reactions were
monitored by thin-layer chromatography (TLC) using silica gel
60 Å K6F (0.25 mm) or silica gel 60 Å 5-17 mym particle size
(0.25 mm) precoated glass-backed plates. TLC was visualized
with UV light (254 nm), iodine, or ninhydrin. Flash chroma-
tography was performed with the indicated solvent system
using 0.040-0.060 mm silica gel (230-400 mesh) or silica gel
60 Å (200-400 mesh). Concentration refers to the removal of
solvent with a rotary evaporator at normal aspirator pressure
followed by further evacuation with a two-stage mechanical
pump. Yields refer to chromatographically and spectroscopi-
cally pure compounds, except as otherwise indicated. All
melting points were determined with an open capillary. 1H and
13C NMR spectra were recorded at 300 MHz. Chemical shifts
were reported in δ values relative to tetramethylsilane in 1H
NMR and the solvent peak in 13C NMR. Elemental analyses
were conducted by Quantitative Technologies Inc., White-
house, NJ .
29
Boc group of 24 with BBr3 afforded the HBr salt, but
the subsequent coupling reaction with N-Ac-Phe did not
proceed as desired. Bubbling HCl gas through an ethyl
acetate solution of 24 at low temperature (-45 °C) led to
decomposition of the â-lactam. It also appeared that the
methyl ester of leucine was being cleaved under the
strong acid reaction conditions.
Rather than consume more of precious compound 24
and to avoid potential cleavage problems with the methyl
ester of leucine, deprotection of the Boc group was tested
on compound 11. Treatment of 11 with 3.0 M HCl in ethyl
acetate (EtOAc) afforded the HCl salt of the amine 27
(Scheme 6, path B) in quantitative yield. Peptide coupling
with N-Ac-Phe and EDC was accomplished in 61% yield.
A study of this peptide coupling reaction was undertaken
with a variety of peptide coupling reagents (Table 1). The
optimum conditions used EDC with 1-hydroxy-7-azaben-
zotriazole (HOAt) to provide a 74% yield of 28. Depro-
tection of 28 under hydrogenation conditions afforded 29,
which underwent reaction with leucine isocyanate (23)
at room temperature in the presence of Et3N (57% yield)
or in the presence of Et3N and DMAP (59% yield) to
afford 26.
Surprisingly, the intermediates in the second pathway
were significantly less soluble in many organic solvents
than the intermediates in the first pathway. This solubil-
ity problem contributed to lower yields in the hydrogena-
tion reaction and the conversion of 29 to 26 in the second
pathway. Although the deprotection procedure for the Boc
group and the subsequent coupling with N-Ac-Phe was
improved in path B, the hydrogenolytic deprotection of
the Cbz group and the coupling reaction with 23 were
not as efficient in path B as in path A. In the final
analysis, both paths had a similar overall yield, 44% for
path A and 35% for path B, for the four-step sequence to
Com m en t on th e Com p iled Sp ectr a l Da ta . For several
of the compounds reported (10-21), substantial peak broaden-
ing was seen presumably due to rotamers; however, high-
temperature NMR studies did not improve peak resolution.
Ben zyl Aza a la n in e (5). Methyl hydrazine (7.0 mL, 132
mmol) was dissolved in CH2Cl2 (140 mL) and cooled to 0 °C.
(30) Coupling reagent abbreviations: EEDQ, 2-ethoxy-1-ethoxycar-
bonyl-1,2-dihydroquinoline; HOBt, 1-hydroxybenzotriazole hydrate;
PyBOP, benzotriazol-1-yl-N-oxy-tris(dimethylamino)phosphonium hexa-
fluorophosphate; HATU, N-[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]-
pyridino-1-ylmethylene]-N-methylmethanaminium hexafluorophos-
phate N-oxide; i-BCF, isobutylchloroformate.
(31) (a) Nowick, J . S.; Holmes, D. L.; Noronha, G.; Smith, E. M.;
Nguyen, T. M.; Huang, S.-L. J . Org. Chem. 1996, 61, 3929. (b) Nowick,
J . S.; Holmes, D. L.; Noronha, G.; Smith, E. M.; Nguyen, T. M.; Huang,
S.-L.; Wang, E. H. J . Org. Chem. 1998, 63, 9144.
(29) Mattiingly, P. G.; Miller, M. J . J . Org. Chem. 1981, 46, 1557.
8966 J . Org. Chem., Vol. 67, No. 25, 2002

Azapeptidomimetic â-Lactams
Sodium hydroxide (1.0 M, 106 mL) was added slowly and the
biphasic mixture was stirred rapidly for 5 min. Benzyl chlo-
roformate (14.4 mL, 101 mmol) was added dropwise and the
reaction was slowly warmed to room temperature and stirred
for 4 h. The reaction solution was separated and the organic
layer was washed with H2O and brine, dried with Na2SO4,
filtered, and concentrated in vacuo. Purification of the crude
oil by distillation (bp 104-134 °C, 0.2 mmHg) provided pure
product as a yellow oil (10.01 g, 55% yield). 1H NMR, 13C NMR,
and IR spectra matched a previous report of benzyl azaalanine
(1-methyl-1-benzyloxycarbonylhydrazine).32
ter t-Bu tyl Aza a la n in e (6). Di-tert-butyl dicarbonate (1.55
g, 7.10 mmol) was dissolved in MeOH (10 mL) and treated
with methyl hydrazine (0.50 mL, 9.4 mmol). The reaction was
stirred for 40 min and then concentrated in vacuo to afford a
yellow oil (0.868 g, 83% yield). 1H NMR, 13C NMR, and IR
spectra matched a previous report of tert-butyl azaalanine
(1-methyl-1-tert-butoxycarbonylhydrazine).30
Ben zyl N-(ter t-Bu t oxyca r b on yl)-L-ser in e-a za a la n in e
(10). N-Boc-serine (1.10 g, 5.35 mmol) was suspended in
CH2Cl2 (10 mL) and cooled to 0 °C. Benzyl azaalanine (917
mg, 5.09 mmol) was added as a CH2Cl2 solution (5 mL). The
reaction was cooled to -12 °C and EEDQ (1.52 g, 6.11 mmol)
was added as a CH2Cl2 solution (5 mL). The reaction was
slowly warmed to room temperature and stirred overnight. The
reaction was concentrated in vacuo and loaded on a silica gel
column. The product was eluted with 1:1 hexanes/EtOAc to
afford an opaque oil (1.26 g, 67% yield). 1H NMR (CDCl3) δ
9.32 (br s, 1 H), 7.31 (s, 5 H), 5.91 (br s, 1 H), 5.11 (s, 2 H),
4.33 (br s, 1 H), 3.91-3.67 (m, 2 H), 3.17 (s, 3 H), 1.41 (s, 9 H).
13C NMR (CDCl3) δ 170.8, 156.4, 155.6, 135.4, 128.3, 128.0,
127.6, 80.1, 68.1, 62.8, 54.4, 37.7, 28.0. IR (neat) 3428, 3305,
1722, 1676 cm-1
.
ter t-Bu tyl N-(Ben zyloxyca r bon yl)-L-ser in e-a za a la n in e
(12). The reaction procedure was identical with that for benzyl
N-(Boc)-L-serine-azaalanine (10) except N-Cbz-serine and 6
were used. The reaction afforded a 78% yield of 12, a colorless
Ben zyl Aza va lin e (7). Ethyl carbazate (10.4 g, 0.100 mol)
and acetone (5.8 g, 0.100 mol) were heated to reflux temper-
ature for 12 h in CH3OH (150 mL). Methanol was removed in
vacuo to yield a solid hydrazone (14.2 g, 98% yield) that was
used immediately in the next step. The hydrazone was
dissolved in ethanol (150 mL) and reduced at atmospheric
pressure under hydrogen in the presence of 3% Pt/C (500 mg).
The catalyst was removed by filtration through Celite and the
solvent was evaporated to give ethyl 2-isopropylcarbazate (11.5
g, 80% yield). The carbazate (11.5 g, 79 mmol) and 30% NaOH
(53 mL) were heated to reflux for 12 h. The reaction was cooled
to room temperature and CH2Cl2 (100 mL) was added. The
biphasic mixture was cooled to 0 °C and benzyl chloroformate
(8.7 mL, 61 mmol) was added dropwise. The mixture was
stirred at 0 °C for 30 min, then warmed to room temperature
and stirred overnight. The organic layer was washed with
water and brine, dried with Na2SO4, filtered, and concentrated.
The residue was purified by silica gel column chromatography
(eluted with 1:1 hexanes/EtOAc) to give 7, 8.1 g (64% yield),
1
oil. H NMR (CDCl3) δ 8.76 (br s, 1 H), 7.31 (s, 5 H), 5.92 (d,
1 H, J ) 7.1 Hz), 5.10 (s, 2 H), 4.29 (br s, 1 H), 3.96 (d, 1 H, J
) 6.7 Hz), 3.09 (s, 3 H), 1.43 (s, 9 H). 13C NMR (CDCl3) δ 170.4,
156.2, 155.6, 135.8, 128.3, 128.0, 127.8, 82.0, 66.9, 62.6, 54.9,
37.9, 27.9. IR (neat) 3436, 3283, 1729, 1691 cm-1
.
Ben zyl N-(ter t-Bu toxycar bon yl)-L-ser in e-azavalin e (14).
The reaction procedure was identical with that for benzyl
N-(Boc)-L-serine-azaalanine (10) except azavaline was used
instead of azaalanine. The reaction afforded a white foam 14
in 79% yield. 1H NMR (CDCl3) δ 8.13 (br s, 1 H), 7.33 (s, 5 H),
5.50 (br s, 1 H), 5.15 (s, 2 H), 4.44 (br s, 1 H), 4.18 (br s, 1 H),
3.98 (br s, 1 H), 3.60 (br s, 1 H), 1.44 (s, 9 H), 1.14 (d, 6 H, J
) 6.4 Hz). 13C NMR (CDCl3) δ 172.0, 155.8, 135.9, 128.7, 128.4,
128.1, 80.7, 68.4, 63.0, 54.6, 50.4, 28.4, 19.9. IR (CDCl3) 3432,
2983, 1699 cm-1
.
Ben zyl N-(ter t-Bu t oxyca r b on yl)-L-ser in e-a za leu cin e
(16). The reaction procedure was identical with that for benzyl
N-(Boc)-L-serine-azaalanine (10) except azaleucine was used
in place of azaalanine. The reaction afforded a white foam 16
in 75% yield. 1H NMR (CDCl3) δ 8.79 (br s, 1 H), 7.33 (s, 5 H),
5.64 (br s, 1 H), 5.14 (s, 2 H), 4.24 (br s, 1 H), 4.10 (br s, 1 H),
3.96 (br s, 1 H), 3.64 (br s, 1 H), 3.36 (s, 2 H), 1.89 (s, 1 H),
1.43 (s, 9 H), 0.90 (s, 6 H). 13C NMR (CDCl3) δ 171.4, 156.8,
155.8, 135.7, 128.6, 128.3, 128.0, 80.6, 68.6, 63.2, 57.9, 54.7,
1
as an opaque liquid. H NMR (CDCl3) δ 7.34 (s, 5 H), 5.15 (s,
2 H), 4.32 (m, 1 H), 3.67 (s, 2 H), 1.12 (d, 6 H, J ) 6.6 Hz). 13
C
NMR (CDCl3) δ 157.3, 136.8, 128.6, 128.2, 128.0, 67.5, 48.7,
19.6. IR (CDCl3) 1689 cm-1
.
Ben zyl Aza leu cin e (8). The reaction procedure was identi-
cal with that for benzyl azavaline (7), except isobutyraldehyde
was used in place of acetone. The yield of the hydrazone was
94% and the hydrogenation product, ethyl 2-isobutylcarbazate,
was obtained in 91% yield. The final step to afforded compound
28.3, 26.9, 20.0. IR (CDCl3) 3432, 2982,1698 cm-1
.
Ben zyl N-(ter t-Bu t oxyca r b on yl)-L-ser in e-a za p h en yl-
a la n in e (18). The reaction procedure was identical with that
for benzyl N-(Boc)-L-serine-azaalanine (10) except azaphenyl-
alanine was used instead of azaalanine. The reaction afforded
1
8 (opaque liquid) in an 82% yield. H NMR (CDCl3) δ 7.33 (s,
5 H), 5.14 (s, 2 H), 4.07 (s, 2 H), 3.23 (d, 2 H, J ) 7.2 Hz), 2.0
(m, 1 H), 0.87 (d, 6 H, J ) 6.5 Hz). 13C NMR (CDCl3) δ 157.8,
136.6, 128.5, 128.0, 127.9, 67.5, 57.8, 26.8, 19.8. IR (CDCl3)
1
a white foam 18 in 56% yield. H NMR (CDCl3) δ 8.92 (br s, 1
H), 7.27-7.23 (m, 10 H), 5.68 (br s, 1 H), 5.10 (s, 2 H), 4.66 (s,
2 H), 4.15 (br s, 1 H), 3.98 (br s, 1 H), 3.76 (br s, 1 H), 3.51 (br
s, 1 H), 1.33 (m, 9 H). 13C NMR (CDCl3) δ 169.7, 154.5, 134.7,
134.3, 128.3, 127.3, 127.1, 126.7, 126.6, 79.1, 67.3, 61.7, 53.5,
1691 cm-1
.
Ben zyl Aza p h en yla la n in e (9). Benzaldehyde (11.7 mL,
115 mol) and hydrazine (3.6 mL,115 mmol) were dissolved in
CH3OH (150 mL). The mixture was reduced at atmospheric
hydrogen pressure in the presence of 10% Pd/C (2 g). The
catalyst was removed by filtration through Celite and the
solvent was evaporated to give benzylhydrazine (11.1 g, 91
mmol) in 79% yield. Benzylhydrazine was dissolved in 100 mL
of CH2Cl2, then cooled to 0 °C. Sodium hydroxide (1 M, 74 mL)
was added and benzyl chloroformate (10 mL, 70 mmol) was
added dropwise. The mixture was stirred at 0 °C for 30 min,
then warmed to room temperature and stirred overnight. The
organic layer was washed with water and brine, dried with
Na2SO4, filtered, and concentrated. The residue was purified
by silica gel column chromatography (eluted with 1:1 hexanes/
EtOAc) to give 9 (6.77 g, 38% yield) as an opaque liquid. 1H
NMR (CDCl3) δ 7.34-7.22 (m, 10 H), 5.18 (s, 2 H), 4.60 (s, 2
H), 4.04 (br s, 2 H). 13C NMR (CDCl3) δ 157.6, 137.3, 136.4,
128.5, 128.3, 128.2, 128.1, 128.0, 127.5, 67.8, 54.5. IR (CDCl3)
52.9, 27.7. IR (CDCl3) 3431, 2983, 1699 cm-1
.
Ben zyl N-(ter t-Bu t oxyca r bon yl)-L-t h r eon in e-a za a la -
n in e (20). The reaction procedure was identical with that for
benzyl N-(Boc)-L-serine-azaalanine (10) except N-(Boc)-L-threo-
nine was used instead of N-(Boc)-L-serine. The reaction af-
1
forded an opaque/cloudy yellow oil 20 in 93% yield. H NMR
(CDCl3) δ 8.97 (s, 1 H), 7.33 (s, 5 H), 5.76 (br s, 1 H), 5.14 (s,
2 H), 4.27 (2 br s, 2 H), 3.60 (br s, 1 H), 3.24 (s, 3 H), 1.44 (s,
9 H), 1.26 (br s, 3 H). 13C NMR (CDCl3) δ 170.8, 156.4, 156.1,
135.6, 128.4, 128.1, 127,9, 80.3, 68.2, 67.6, 58.1, 38.3, 28.2, 19.5.
IR (CDCl3) 3428, 2983, 1720, 1699 cm-1
.
1-[(N-Met h yl,N-b en zyloxyca r b on yl)-a m in o]-3-[(ter t-
bu toxycar bon yl)am in o]-2-azetidin on e (11). Benzyl N-(Boc)-
L-serine-azaalanine (7.15 g, 19.5 mmol) was combined with
Ph3P (5.62 g, 21.4 mmol) in THF (250 mL) and the homoge-
neous solution was treated with DBAD (4.93 g, 21.4 mmol).
The DBAD was added in three portions allowing the yellow
color of the reaction solution to fade with each addition. After
being stirred overnight at room temperature, the reaction was
1689 cm-1
.
(32) Brosse, N.; Pinto, M.-F.; J amart-Gregoire, B. J . Org. Chem.
2000, 65, 4370.
J . Org. Chem, Vol. 67, No. 25, 2002 8967

Malachowski et al.
concentrated in vacuo and subjected to silica gel chromatog-
raphy (eluted with 2:1 hexanes/EtOAc). A white crystalline
solid, 6.00 g (88% yield), was obtained which was further
purified by recrystallization (EtOAc/Hex) for analysis. Mp
1-[(N-Meth yl)a m in o]-3-[(ter t-bu toxyca r bon yl)a m in o]-
2-azetidin on e (22). 1-[(N-Methyl,N-benzyloxycarbonyl)amino]-
3-[(tert-butoxycarbonyl)amino]-2-azetidinone (11, 200 mg, 0.573
mmol) was dissolved in methanol (8 mL) and Pd/C (20 mg)
was added. The reaction atmosphere was purged with hydro-
gen (3×) and the reaction was left stirring under hydrogen
for 2 h. The reaction mixture was filtered through Celite and
concentrated to afford 129 mg (100% yield) of 22. Mp 158-
159.5 °C. 1H NMR (CDCl3) δ 5.43 (d, 1 H, J ) 6.9 Hz), 4.62
(bs, 1 H), 4.10 (d, 1 H, J ) 4.9 Hz), 3.70 (t, 1 H, J ) 5.0 Hz),
3.37 (dd, 1 H, J ) 5.0, 2.2 Hz), 2.70 (d, 3 H, J ) 5.0 Hz), 1.44
(s, 9 H). 13C NMR (CDCl3) δ 166.2, 155.0, 80.3, 54.6, 51.4, 36.5,
28.2. IR (CDCl3) 3442, 1769, 1717, 1508, 1370, 1249, 1164
cm-1. Anal. Calcd for C9H17N3O3: C, 50.21; H, 7.96; N, 19.53.
Found: C, 50.16; H, 7.95; N, 19.27.
1
99-101 °C. H NMR (CDCl3) δ 7.36 (s, 5 H), 5.35 (br s, 1 H),
5.16 (s, 2 H), 4.70 (br s, 1 H), 3.77 (br s, 1 H), 3.49 (br s, 1 H),
3.19 (s, 3 H), 1.44 (s, 9 H). 13C NMR (CDCl3) δ 166.3, 154.7,
135.4, 128.6, 128.4, 128.0, 80.5, 68.4, 55.2, 51.7, 36.1, 28.2. IR
(CDCl3) 3433, 1790, 1717 cm-1. Anal. Calcd for C17H23N3O5:
C, 58.44; H, 6.63; N, 12.03. Found: C, 58.49; H, 6.69; N, 11.99.
1-[(N-Meth yl,N-ter t-bu toxycar bon yl)am in o]-3-[(ben zyl-
oxyca r bon yl)a m in o]-2-a zetid in on e (13). The reaction pro-
cedure was identical with that for 11 except 12 was used to
1
afford an 89% yield of the product 13. Mp 109.5-111 °C. H
NMR (CDCl3) δ 7.34 (s, 5 H), 5.51 (br s, 1 H), 5.12 (s, 2 H),
4.72 (br s, 1 H), 3.79 (br s, 1 H), 3.53 (s, 1 H), 3.12 (s, 3 H),
1.46 (s, 9 H). 13C NMR (CDCl3) δ 165.6, 155.5, 153.7, 135.8,
128.5, 128.3, 128.1, 82.3, 67.3, 55.4, 51.4, 35.8, 28.1. IR (CDCl3)
3437, 1792, 1717 cm-1. Anal. Calcd for C17H23N3O5: C, 58.44;
H, 6.63; N, 12.03. Found: C, 58.54; H, 6.70; N, 11.91.
1-[(N-Meth yl)-N-(ca r bon yl-L-(m eth ylleu cyl))a m in o]-3-
[(ter t-bu toxyca r bon yl)a m in o]-2-a zetid in on e (24). Hydra-
zine derivative 22 (573 mg, 2.67 mmol) was dissolved in CH2Cl2
(40 mL), cooled to 0 °C, and treated with leucine isocyanate,
methyl ester 23 (830 mg, 4.85 mmol) dissolved in CH2Cl2 (25
mL), Et3N (0.950 mL, 6.82 mmol), and DMAP (69 mg, 0.565
mmol). The reaction was stirred for 22 h, then the reaction
solution was concentrated and subjected to column chroma-
tography (gradient: 1:1 hexane/EtOAc to EtOAc). The product
24 was obtained as a white crystalline solid (1.030 g, 100%
1-[(N-Isop r op yl,N-ben zyloxyca r bon yl)a m in o]-3-[(ter t-
bu toxyca r bon yl)a m in o]-2-a zetid in on e (15). The reaction
procedure was identical with that for 11 except serine-
azavaline 14 was used in place of 10 and DEAD was used
instead of DBAD. The DEAD was added slowly dropwise to
allow the yellow color of the reaction to fade. Column chro-
matography was performed with 3:1 hexanes/EtOAc. The
â-lactam 15 was isolated as a white solid in 71% yield. Mp
95-96 °C. 1H NMR (CDCl3) δ 7.41-7.31 (m, 5 H), 5.15 (s, 2
H), 4.79 (br s, 1 H), 4.37 (br s, 1 H), 3.78 (br s, 1 H), 3.44 (br
s, 1 H), 1.44 (s, 9 H), 1.20 (d, 6 H, J ) 6.6 Hz). 13C NMR (CDCl3)
δ 168.6, 154.9, 154.1, 135.6, 128.8, 128.7, 128.2, 80.5, 68.5, 55.4,
1
yield), mp 136-8 °C. H NMR (CDCl3) δ 7.07 (d, 1 H, J ) 8.2
Hz), 5.63 (d, 1 H, J ) 7.1 Hz), 4.42 (q, 1 H, J ) 7.8 Hz), 4.31
(m, 1 H), 3.80 (m, 2 H), 3.70 (s, 3 H), 3.12 (s, 3 H), 1.71 (m, 3
H), 1.44 (s, 9 H), 0.93 (t, 6 H, J ) 6.0 Hz). 13C NMR (CDCl3)
δ 173.7, 165.9, 156.8, 154.8, 81.3, 55.8, 52.4, 52.0, 48.3, 40.4,
34.4, 28.2, 24.9, 22.8, 21.7. IR (CDCl3) 3460, 3354, 1793, 1736,
1706, 1671, 1508, 1471, 1370, 1254, 1165 cm-1. Anal. Calcd
for C17H30N4O6: C, 52.84; H, 7.83; N, 14.49. Found: C, 52.96;
H, 7.85; N, 14.42.
55.6, 50.4, 28.3, 20.5. IR (CDCl3) 3438, 2983, 1792, 1716 cm-1
.
Anal. Calcd for C19H27N3O5: C, 60.46; H, 7.21; N, 11.13.
Found: C, 60.05; H, 7.12; N, 10.91.
1-[[N-Meth yl,N-(ca r bon yl-L-(m eth ylleu cyl))]a m in o]-3-
a m in o-2-a zetid in on e, Tr iflu or oa ceta te Sa lt (25). Trifluo-
roacetic acid (1.0 mL) was added to 24 (155 mg) dissolved in
CH2Cl2 (5 mL) and anisole (0.5 mL) at 0 °C. The reaction was
warmed to room temperature and stirred for 3.5 h. Concentra-
tion of the reaction solution afforded a viscous light-orange
oil. The crude trifluoroacetate salt 25 was in excess of a
quantitative yield (186 mg) and was used immediately in the
next coupling reaction.
1-[(N-Isob u t yl,N-b en zyloxyca r b on yl)a m in o]-3-[(ter t-
bu toxyca r bon yl)a m in o]-2-a zetid in on e (17). The reaction
procedure was identical with that for 11 except serine-
azaleucine 16 was used in place of 10 and DEAD was used
instead of DBAD. Column chromatography was performed
with 3:1 hexanes/EtOAc. The â-lactam 17 was isolated as a
white solid in 75% yield. Mp 94-96 °C. 1H NMR (CDCl3) δ
7.40-7.33 (m, 5 H), 5.16 (s, 2 H), 4.74 (br s, 1 H), 3.78 (br s, 1
H), 3.37 (br s, 1 H), 3.31 (d, 2 H, J ) 7.4 Hz), 1.95-1.84 (m, 1
H), 1.43 (s, 9 H), 0.93 (d, 6 H, J ) 6.5 Hz). 13C NMR (CDCl3)
δ 167.1, 154.9, 135.6, 128.7, 128.5, 128.0, 80.4, 68.5, 56.4, 55.1,
1-[(N-Meth yl,N-ben zyloxyca r bon yl)a m in o]-3-a m in o-2-
a zetid in on e, Hyd r och lor id e Sa lt (27). 1-[(N-Methyl,N-tert-
butoxycarbonyl)amino]-3-[benzyloxycarbonylamino]-2-azetid-
inone (11, 243 mg, 0.695 mmol) was treated with 3.0 M HCl
in EtOAc (2.32 mL) at room temperature for 0.5 h. The reaction
solution was concentrated in vacuo with a bath temperature
maintained below 35 °C. Coevaporation with toluene and
chloroform provided a white solid 7 (195 mg, 99% yield), mp
53.0, 28.3, 27.1, 19.8. IR (CDCl3) 3439, 2966, 1792, 1717 cm-1
.
Anal. Calcd for C20H29N3O5: C, 61.36; H, 7.47; N, 10.73.
Found: C, 61.31; H, 7.60; N, 10.62.
1-[(N-Ben zyl,N-ben zyloxyca r bon yl)a m in o]-3-[(ter t-bu -
toxyca r bon yl)a m in o]-2-a zetid in on e (19). The reaction pro-
cedure was identical with that for 11 except serine-azaphen-
ylalanine 18 was used and column chromatography was
performed with 3:1 hexanes/EtOAc. The â-lactam 19 was
1
176-7 °C dec. H NMR (CD3OD) δ 7.40-7.33 (m, 5 H), 5.22
(s, 2 H), 4.92 (s, 3 H), 4.54 (dd, 1 H, J ) 5.6, 2.4 Hz), 3.96 (t,
1 H, J ) 5.8 Hz), 3.75 (dd, 1 H, J ) 6.0, 2.4 Hz), 3.23 (s, 3 H).
13C NMR (CD3OD) δ 163.1, 156.5, 137.1, 129.6, 129.5, 129.2,
1
isolated as a white solid in 48% yield. Mp 97-98 °C. H NMR
69.8, 53.7, 36.5. IR (KBr) 3700-2300, 1793, 1725 cm-1
.
(CDCl3) δ 7.34-7.31 (m, 10 H), 5.20 (s, 2 H), 4.95 (br s, 1 H),
4.71 (s, 2 H), 4.61 (br s, 1 H), 3.39 (br s, 1 H), 3.10 (br s, 1 H),
1.41 (s, 9 H). 13C NMR (CDCl3) δ 165.5, 153.6, 153.4, 134.5,
134.3, 127.6, 127.4, 127.1, 126.7, 79.4, 67.6, 54.1, 52.5, 51.9,
27.1. IR (CDCl3) 3440, 2983, 1791, 1717 cm-1. Anal. Calcd for
1-[(N-Meth yl,N-ben zyloxycar bon yl)am in o]-3-[(N-acetyl-
L-ph en ylalan in e)am in o]-2-azetidin on e (28). N-Acetyl-phen-
ylalanine (265 mg, 1.28 mmol) was dissolved in DMF (3.5 mL)
and the solution was cooled to 0 °C and treated with EDC
(245 mg, 1.28 mmol) and 1-hydroxy-7-azabenzotriazole (HOAt,
140 mg, 1.02 mmol). Ten minutes later, a DMF solution (2.0
mL) of 27 (289 mg, 1.02 mmol) was added, followed shortly
thereafter by Et3N (0.440 mL, 3.16 mmol). After warming to
room temperature and stirring overnight, the reaction solution
was diluted with EtOAc, washed with 5% KHSO4 (twice), 5%
NaHCO3 (twice), water, and brine, dried with MgSO4, filtered,
and concentrated. The oil was subjected to column chroma-
tography (5% MeOH/CH2Cl2) to affford a white foam (332 mg,
C
23H27N3O5: C, 64.93; H, 6.40; N, 9.88. Found: C, 64.70; H,
6.24; N, 9.93.
1-[(N-Meth yl,N-ben zyloxyca r bon yl)a m in o]-3-[(ter t-bu -
toxyca r bon yl)a m in o]-4-m eth yl-2-a zetid in on e (21). The
reaction procedure was identical with that for 11 except
threonine-azaphenylalanine 20 was used. The product was
eluted with 1:1 hexanes/EtOAc to afford a yellow oil in 76%
1
yield. H NMR (CDCl3) δ 7.40 (s, 5 H), 5.11 (s, 2 H), 4.27 (br
s, 1 H), 4.21 (br s, 1 H), 3.80 (br s, 1 H), 3.24 (s, 3 H), 1.44 (s,
12 H). 13C NMR (CDCl3) δ 165.2, 154.9, 135.4, 129.4, 128.3,
127.9, 80.3, 68.4, 61.8, 61.5, 28.2, 27.7, 16.5. IR (CDCl3) 3321,
1
74% yield). H NMR (CD3OD) δ 7.76 (br s, 1 H), 7.33 (s, 5 H),
7.28-7.15 (m, 5 H), 6.77 (d, 1 H, J ) 8.0 Hz), 5.13 (s, 2 H),
4.77 (q, 1 H, J ) 7.3 Hz), 4.62 (br s, 1 H), 3.69 (br s, 1 H), 3.54
2972, 1780, 1706 cm-1
.
8968 J . Org. Chem., Vol. 67, No. 25, 2002

Azapeptidomimetic â-Lactams
(s, 1 H), 3.18 (s, 3 H), 3.09 (dd, 1 H, J ) 13.9, 6.4 Hz), 2.95
(dd, 1 H, J ) 13.9, 7.6 Hz), 1.89 (s, 3 H). 13C NMR (CDCl3) δ
172.1, 170.4, 165.7, 154.8, 136.3, 135.5, 129.2, 128.5, 128.4,
128.3, 127.9, 126.9, 68.3, 54.4, 54.0, 49.7, 38.6, 38.2, 22.9. IR
CH2Cl2 solution (3 mL), followed shortly thereafter by the
addition of Et3N (0.120 mL, 0.861 mmol) and DMAP (9.0 mg,
0.074 mmol). The reaction was warmed to room temperature
and stirred overnight. The reaction solution was concentrated
and the crude product was purified by column chromatography
(CH2Cl2, then 5% MeOH/CH2Cl2) to afford 96 mg (59% yield)
(CDCl3) 3425, 3304, 1787, 1721, 1671 cm-1
.
1-[(N-Meth yl)a m in o]-3-[(N-a cetyl-L-p h en yla la n in e)a m -
in o]-2-a zetid in on e (29). Compound 28 (213 mg, 0.486 mmol)
was combined with 10% palladium on carbon (20 mg) in
CH3OH (7 mL) and the reaction atmosphere was purged with
H2 (3×). The reaction was stirred at room temperature under
a static H2 atmosphere for 0.5 h. Filtration through Celite and
concentration in vacuo provided a white solid (121 mg, 82%
1
of a white solid. H NMR (CDCl3) δ 7.94 (d, 1 H, J ) 6.7 Hz),
7.29-7.13 (m, 6 H), 7.00 (d, 1 H, J ) 7.9 Hz), 4.73 (dd, 1 H, J
) 13.4, 8.1 Hz), 4.37-4.28 (m, 2 H), 3.77 (t, 1 H, J ) 4.8 Hz),
3.71 (m, 1 H), 3.65 (s, 3 Hz), 3.19 (dd, 1 H, J ) 14.1, 5.2 Hz),
3.09 (s, 3 H), 2.91 (dd, 1 H, J ) 14.0, 8.5 Hz), 1.88 (s, 3 H),
1.77-1.58 (m, 3 H), 0.91 (dd, 6 H, J ) 9.6, 5.8 Hz). 13C NMR
(CDCl3) δ 174.3, 172.5, 170.9, 166.1, 157.1, 136.5, 129.0, 128.4,
126.8, 55.2, 53.8, 52.4, 52.0, 47.5, 40.0, 37.2, 34.3, 24.8, 23.0,
22.8, 21.3. IR (CDCl3) 3434, 3345, 1787, 1736, 1671, 1536,
1
yield). H NMR (CD3OD) δ 7.30-7.17 (m, 5 H), 4.65 (dd, 1 H,
J ) 5.2, 2.3 Hz), 4.58 (dd, 1 H, J ) 8.7, 5.9 Hz), 3.64 (t, 1 H,
J ) 5.1 Hz), 3.42 (dd, 1 H, J ) 4.9, 2.3 Hz), 3.12 (dd, 1H, J )
13.8, 5.9 Hz), 2.88 (dd, 1 H, J ) 13.8, 8.8), 2.61 (s, 3 H), 1.89
(s, 3 H). 13C NMR (CD3OD) δ 174.0, 173.1, 168.1, 138.3, 130.3,
129.5, 127.8, 56.0, 54.4, 39.0, 35.9, 22.4. IR (CDCl3) 3285, 1765,
1253, 1202, 1046 cm-1
.
Ack n ow led gm en t. We gratefully acknowledge fi-
nancial support from the National Science Foundation
(RUI CHE-9710479), Bryn Mawr College, and the
University of New England. We thank the Faculty for
the Future Program sponsored by the GE Fund for a
fellowship for K.W. The authors recognize important
preliminary work by Scott Cyr and Ian Paquette. The
authors acknowledge helpful suggestions from Dr. Timo-
thy M. Ramsey of Novartis Pharma. The authors thank
Prof. J ames K. Coward of the University of Michigan
and Prof. Frank Mallory of Bryn Mawr College for their
assistance in the preparation of the manuscript.
1643, 1542 cm-1
.
1-[[N-Meth yl,N-(ca r bon yl-L-(m eth ylleu cyl))]a m in o]-3-
[(N-acetyl-L-phenylalanyl)amino]-2-azetidinone (26).Method
A (p a th A): The trifluoroacetate salt 25 (161 mg, 0.402 mmol)
was dissolved in THF (5 mL) and CH2Cl2 (5 mL) and cooled to
0 °C. The amine was sequentially treated with Et3N (0.290
mL, 2.08 mmol), HOBt (69 mg, 0.511 mmol), N-acetyl-phen-
ylalanine (127 mg, 0.613 mmol), and EDC (127 mg, 0.662
mmol). The reaction solution was allowed to slowly warm to
room temperature while stirring overnight. The reaction
mixture was concentrated to remove THF, dissolved in EtOAc,
and washed sequentially with 10% citric acid (twice), saturated
NaHCO3 (twice), water, and brine. The organic layer was dried
with MgSO4, filtered, and concentrated. The resulting residue
was purified by column chromatography (EtOAc followed by
5% MeOH/CH2Cl2) to afford 84 mg (44% yield) of a white solid.
Meth od B (p a th B): Hydrazine derivative 29 (105 mg, 0.345
mmol) was suspended in CH2Cl2 (5 mL) and cooled to 0 °C.
Leucine isocyanate (138 mg, 0.807 mmol) was added as a
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of 7-10, 12, 14, 16, 18, 20, 21, and 26-29. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O026280D
J . Org. Chem, Vol. 67, No. 25, 2002 8969