Synthesis of new N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycines and N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycines esters

Article abstract of DOI:10.1080/00397910500191219

Following our efforts towards the synthesis of new potential inhibitors of Xanthine Dehydrogenase (XDH), we describe here a general method for the preparation of N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycines and N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycine esters

Full text of DOI:10.1080/00397910500191219

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Synthesis of New
N‐(5‐Oxo‐2,5‐dihydro)pyrrol‐3‐yl
Glycines and
N‐(5‐Oxo‐2,5‐dihydro)pyrrol‐3‐yl
Glycines Esters
Fabrice Jourdan a , Jens T. Kaiser b & David J. Lowe
c
a University of Bath, Department of Pharmacy and
Pharmacology, Claverton Down, Bath, UK
b Max Planck Institut für Biochemie, Martinsried,
Germany
c John Innes Centre, Department of Biological
Chemistry, Colney, Norwich, UK
Published online: 18 Aug 2006.
To cite this article: Fabrice Jourdan , Jens T. Kaiser & David J. Lowe (2005) Synthesis
of New N‐(5‐Oxo‐2,5‐dihydro)pyrrol‐3‐yl Glycines and N‐(5‐Oxo‐2,5‐dihydro)pyrrol‐3‐yl
Glycines Esters, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 35:18, 2453-2466
To link to this article: http://dx.doi.org/10.1080/00397910500191219
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Synthetic Communicationsw, 35: 2453–2466, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500191219
Synthesis of New N-(5-Oxo-2,5-
dihydro)pyrrol-3-yl Glycines and
N-(5-Oxo-2,5-dihydro)pyrrol-3-yl
Glycines Esters
Fabrice Jourdan
University of Bath, Department of Pharmacy and Pharmacology,
Claverton Down, Bath, UK
Jens T. Kaiser
Max Planck Institut fu¨r Biochemie, Martinsried, Germany
David J. Lowe
John Innes Centre, Department of Biological Chemistry,
Colney, Norwich, UK
Abstract: Following our efforts towards the synthesis of new potential inhibitors of
Xanthine Dehydrogenase (XDH), we describe here a general method for the prep-
aration of N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycines and N-(5-oxo-2,5-dihydro)pyr-
rol-3-yl glycine esters from glycine ethyl ester hydrochloride and various 4-hydroxy-
5-oxo-2,5-dihydro-1H-pyrrole-3-carboxylic acid esters and carbonitriles.
Keywords: Xanthine dehydrogenase, amino acid, 5-oxopyrrol-3-ylglycine
INTRODUCTION
Xanthine dehydrogenase (XDH) is a 290-kDa homodimeric enzyme that
catalyses the oxidation of hypoxanthine to xanthine and xanthine to uric
Received in the U.K. January 22, 2005
Address correspondence to Fabrice Jourdan, University of Bath, Department of
Pharmacy and Pharmacology, Claverton Down, Bath BA2 7AY, UK. E-mail: prsfj@
bath.ac.uk
2453

2454
F. Jourdan, J. T. Kaiser, and D. J. Lowe
acid.[1,2] Its crystal structure displays three major domains:[3] a 20-kDa
N-terminal domain containing two Fe-S clusters, a central 40-kDa FAD
domain, and a C-terminal 85-kDa molybdopterin-binding domain. XDH is a
target of drugs against gout and hyperuricemia.[4] The conversion of the
enzyme to its oxydase form xanthine oxidase (XO) has also been implicated
in diseases characterized by oxygen radical–induced tissue damage such as
postischemic reperfusion injury.[5] It has also been suggested that XO might
be associated with blood-pressure regulation.[6]
During the past decades, a number of inhibitors such as anthra-
quinones,[7] flavonoids,[8,9] xanthones,[10] caffeic esters,[11] pteridines,[12–14]
and purines[15–18] have been synthesized or isolated from plant sources.
However, allopurinol remains to date the only drug available for the
treatment of gout and hyperuricemia. As a consequence, the search for new
inhibitors of XDH remains a very important goal. Within this context, we
describe herein the results of our preliminary efforts toward the synthesis of
new 3-hydroxy-6-oxo-1,4,5,6-tetrahydro pyrrolo[3,4-b]pyrrole-2-carboxylic
acids (II, Figure 1). In particular, we describe a general procedure to access
new N-(5-oxo-2,5-dihydro)pyrrol-3-yl glycines and N-(5-oxo-2,5-dihydro)-
pyrrol-3-yl glycine esters from glycine ethyl ester hydrochloride and
various 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxylic acid esters
and carbonitriles.
RESULT AND DISCUSSION
To design new XDH/XO inhibitors, we have taken advantage of the recent
elucidation of bovine milk’s XDH/XO crystal structure. Our study, which
will be discussed elsewhere, led to a general model (I) described in
Figure 1. It is composed of two fused five-membered heterocyclic rings
(pyrrole, furan or thiophene rings). It was established that H-bond donor
(HBD) and acceptor (HBA) substituents are crucial, in particular those at
Figure 1. Design of XDH inhibitors. General model I and target molecules II and its
precursor III.

Synthesis of Esters
2455
positions 2 and 3. They interact in the binding site of XDH with the guani-
diium group of an arginine (Arg880), the carboxylate group of a glutamate
(Glu1261), and the hydroxyl group of a threonine (Thr1010). Although
some two- or three-heteroatom-containing rings were found to display
good interactions with the active site of the enzyme, they were usually less
promising. This was in general due to the fact that an increasing number
of heteroatoms in the heterocyclic backbone implicitly decreases the
number of H-bond donor/acceptor groups on the heterocyclic backbone.
Our study also showed that a phenylalanine (Phe914) interacts by
p-stacking with the aromatic ring of the substrate (e.g., salicylate in the
crystal structure).
Among the various possibilities of structures fitting our model I, we decided
to focus our attention on the synthesis of the 3-hydroxy-6-oxo-1,4,5,6-tetrahydro
pyrrolo[3,4-b]pyrrole-2-carboxylic acids II via the intermediate 4-amino-5-
oxo-2,5-dihydro-1H-pyrrole-3-carbonitriles or -3-carboxylic acid esters III,
the preparation of which are described in the literature.
The synthesis of the different 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-
3-carboxylic acid esters and carbonitriles 1a–d, 2a–e, and 3a–d
(Scheme 1) was achieved following different methods previously described
Scheme 1. Synthesis of the N-pyrrol-3-yl glycines 10–13.

2456
F. Jourdan, J. T. Kaiser, and D. J. Lowe
in the literature.[19–22] Their corresponding enamines 4a–d, 5a–e, and 6a–d
were obtained by treatment with ammonium acetate or potassium cyanate.[23]
Unfortunately, these enamines proved unreactive and could not be alkylated
with iodoacetic acid ethyl ester. On the other hand, the enols 1a–d, 2a–e, and
3a–d proved to react with glycine ethyl ester hydrochloride in refluxing
ethanol, although this nucleophilic substitution was found to be slow and
refluxing times of 3 to 4 days were required to obtain the target N-pyrrolyl
glycine esters 7a–d, 8a–e and 9a–d in good yields (65–85%). Various
attempts to obtain the target 3-hydroxy-6-oxo-1,4,5,6-tetrahydro pyrrolo[3,4-
b]pyrrole-2-carboxylic acid esters 14 from the (1-benzyl-4-cyano-2-oxo-2,5-
dihydro-1H-pyrrol-3-ylamino)-acetic acid ethyl ester (7d) and (1-benzyl-4-
ethoxycarbonyl-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid ethyl
esters (8d, 9d) failed. No reaction occurred by direct action of these starting
materials with bases (NaOH, NaH, BuLi) in dry THF. In parallel, we tried to
protect 8d with various protecting groups to subsequently carry out the intra-
molecular cyclization. Unfortunately the enamine could not be protected and
access to 14 following this route was abandoned.
Conversely, hydrolysis of the different ester groups was found to take
place selectively with good to excellent yields upon careful hydrolysis
of 7–9 with lithium hydroxide monohydrate. As expected, 7a–d were
deprotected in THF and water with at least 1 equivalent of base, leading to
the (4-cyano-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid 10a–d.
Compounds 8a–e afforded, following the same method, the monoacids
11a–e. Interestingly, in the case of the triesters 9a–d, selective hydrolyses
of the glycine ester occurred when strictly one equivalent of LiOH, H2O
was used. Two or more equivalents of the base directly led to the 4-(carboxy-
methyl-amino)-5-oxo-2,5-dihydro-1H-pyrrole-2,3-dicarboxylic acid 3-ethyl
ester 13a–d. The latter were also obtained by further hydrolyses of the mono-
esters 12a–d with an excess of lithium hydroxide. Furthermore, no hydrolysis
of the 3-carboxylic acid ester of the di- and triesters 8a–e and 9a–d and their
corresponding acids 11a–e, 12a–d, and 13a–d was found to be occur with
LiOH as well as with NaOH or KOH at room temperature. These selective
deprotections of the carboxylic acids can be used to functionalize the
N-pyrrolyl glycine at specific positions. This strategy is currently used in
our laboratory with the aim of preparing new peptidic structures analogous
to the antibiotic Microcin B17, a DNA gyrase inhibitor containing the
unnatural amino acids 2-aminomethyloxazol-4-carboxylic acids and 2-amino-
methylthiazol-4-carboxylic acids.
In conclusion, despite failing to obtain the target 3-hydroxy-6-oxo-
1,4,5,6-tetrahydropyrrolo[3,4-b]pyrrole-2-carboxylic acids as potential inhibitors
of XDH via 7a–d through 9a–d, we describe here a general method to access new
N-pyrrolyl glycines and glycine esters 7a–d through 13a–d. Moreover, the
selective deprotection of 9a–d to its monoacids 12a–d has proved very useful.
Indeed, these monoacids are currently used in our laboratory with the aim of
preparing new peptidomimetics.

Synthesis of Esters
2457
EXPERIMENTAL
Yields expressed are for isolated pure compounds (flash chromatography).
Their characterization was obtained by a combination of IR, NMR, MS, and
microanalysis. Infrared spectra were recorded on a FTIR-8300 Shimadzu
1
spectrometer in KBr with absorptions in cm21. H and 13C NMR spectra
were recorded on a JEOL JNM LA-400 spectrometer. Mass spectra were
recorded on a Kratos MS25 spectrometer.
General Method for the Synthesis of the N-Pyrrolyl Glycine Esters
7a–d, 8a–e, 9a–d
A solution of 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxylic acid
esters and carbonitriles 1a–d, 2a–e or 3a–d (1 mmol) and glycine ethyl
ester hydrochloride (5 mmol, 0.70 g) in 30 ml of ethanol was heated to
808C and the reaction monitored by TLC. When the reaction was complete
(3–4 days), the solution was cooled to room temperature, ethanol evaporated
under reduced pressure, and the residual solid was dissolved in ethyl acetate
(50 ml) and water (20 ml). The aqueous layer was extracted with another
30 ml of ethyl acetate, and the combined organic layers were washed with suc-
cessively with water and brine, dried over MgSO4, and the solvent evaporated
under reduced pressure. The residual oil/solid was purified by column
chromatography (hexane/ethyl acetate) to afford 7a–d, 8a–e or 9a–d.
(4-Cyano-1-methyl-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
ethyl ester 7a: White crystals; 175 mg (78%); mp ¼ 120–1218C; IR: 3307
(NH), 2198 (CN), 1749, and 1661 (C55O); 1H NMR (CDCl3) d: 5.97
(t, JH-H ¼ 5.9 Hz, 1H, NH), 4.28 (d, JH-H ¼ 5.9 Hz, 2H, NCH2CO2Et), 4.27
(q, JH-H ¼ 7.1 Hz, 2H, OCH2), 3.96 (s, 2H, CH2), 3.08 (s, 3H, CH3N), 1.32
(t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR (CDCl3) d: 168.6 (CO), 163.8 (CO),
146.3 (C3), 116.1 (CN), 74.6 (C4), 61.9 (CH2O), 50.5 (CH2), 44.4 (CH2),
29.8 (CH3N), 14.4 (CH3), 14.0 (CH3). Anal. calcd. for C10H13N3O3:
C, 53.80; H, 5.87; N, 18.82. Found: C, 53.72; H, 5.88; N, 18.78.
(4-Cyano-1-isobutyl-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
ethyl ester 7b: White crystals; 210 mg (79%); mp ¼ 82–838C; IR: 3310 (NH),
1
2197 (CN), 1748, and 1659 (C55O); H NMR (CDCl3) d: 5.89 (t, JH-H
5.9 Hz, 1H, NH), 4.30 (d, JH-H ¼ 5.9 Hz, 2H, NCH2CO2Et), 4.29 (q, JH-H
¼
¼
7.1 Hz, 2H, OCH2), 3.96 (s, 2H, CH2), 3.28 (d JH-H ¼ 7.8 Hz, 2H, NCH2),
1.96 (m, 1H, CH), 1.32 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 0.91 (d, JH-H ¼ 6.6 Hz,
6H, 2 Â rCH3); 13C NMR (CDCl3) d: 168.6 (CO), 164.0 (CO), 146.2 (C3),
116.2 (CN), 74.8 (C4), 62.0 (CH2O), 50.7 (CH2), 49.3(CH2), 44.5 (CH2), 27.6
(CH), 19.9 (2 Â CH3), 14.1 (CH3). Anal. calcd. for C13H19N3O3: C, 58.85;
H, 7.22; N, 15.84. Found: C, 58.63; H, 7.01; N, 15.59.
(4-Cyano-2-oxo-1-phenyl-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
ethyl ester 7c: White crystals; 210 mg (74%); mp ¼ 177–1788C; IR: 3322

2458
F. Jourdan, J. T. Kaiser, and D. J. Lowe
(NH), 2203 (CN), 1747, and 1660 (C55O); 1H NMR (CDCl3) d: 7.68 (m, 2H,
Ph), 7.41 (m, 2H, Ph), 7.22 (m, 1H, Ph), 6.00 (t, JH-H ¼ 5.9 Hz, 1H, NH), 4.41
(s, 2H, CH2), 4.33 (d, JH-H ¼ 5.9 Hz, 2H, NCH2CO2Et), 4.30 (q, JH-
¼ 7.1 Hz, 2H, OCH2), 1.33 (t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR
H
(CDCl3) d: 168.6 (CO), 163.8 (CO), 146.3 (C3), 137.8, 129.3, 125.6 and
119.1 (Ph), 115.8 (CN), 74.9 (C4), 62.1 (CH2O), 49.0 (CH2), 44.4 (CH2),
14.1 (CH3). Anal. calcd. for C15H15N3O3: C, 63.15; H, 5.30; N, 14.73.
Found: C, 62.97; H, 5.33; N, 14.72.
(1-Benzyl-4-Cyano-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
ethyl ester 7d: White crystals; 230 mg (77%); mp ¼ 78–798C; IR: 3332
(NH), 2195 (CN), 1749, and 1660 (C55O); 1H NMR (CDCl3) d: 7.30
(m, 3H, Ph), 7.22 (m, 2H, Ph), 6.07 (t, JH-H ¼ 5.8 Hz, 1H, NH), 4.29 (d, JH-H
¼
5.8 Hz, 2H, NCH2CO2Et), 4.27 (q, JH-H ¼ 7.1 Hz, 2H, OCH2), 3.84 (s, 2H,
CH2), 1.31 (t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR (CDCl3) d: 168.6 (CO),
163.7 (CO), 146.0 (C3), 135.4, 128.9 and 128.0 (Ph), 116.0 (CN), 75.1 (C4),
62.0 (CH2O), 48.1 (CH2), 47.0 (CH2), 44.4 (CH2), 14.0 (CH3); Anal. calcd.
for C16H17N3O3: C, 64.20; H, 5.72; N, 14.04. Found: C, 64.18; H, 5.61;
N, 13.86.
4-(Ethoxycarbonylmethyl-amino)-1-methyl-5-oxo-2,5-dihydro-1H-pyrrole-
3-carboxylic acid ethyl ester 8a: White crystals; 225 mg (83%); mp ¼ 698C;
1
IR: 3347 (NH), 1750, 1702 and 1669 (C55O); H NMR (CDCl3) d: 6.83
(br, 1H, NH), 4.50 (d, JH-H ¼ 6.3 Hz, 2H, NCH2CO2Et), 4.14 (q, JH-H
¼
7.1 Hz, 2H, OCH2), 4.12 (q, JH-H ¼ 7.3 Hz, 2H, OCH2), 3.86 (s, 2H, CH2),
2.94 (s, 3H, CH3N), 1.21 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 1.18 (t, JH-H
¼
7.3 Hz, 3H, CH3); 13C NMR (CDCl3) d: 170.4 (CO), 165.1 (CO), 164.6
(CO), 145.9 (C4), 98.9 (C3), 60.6 (CH2O), 59.2 (CH2O), 49.0 (CH2), 43.7
(CH2), 29.1 (CH3N), 13.9 (CH3), 13.7 (CH3); Anal. calcd. for C12H18N2O5:
C, 53.33; H, 6.71; N, 10.36. Found: C, 53.31; H, 6.66; N, 10.27.
4-(Ethoxycarbonylmethyl-amino)-1-isobutyl-5-oxo-2,5-dihydro-1H-
pyrrole-3-carboxylic acid ethyl ester 8b: Yellow crystals; 230 mg (72%);
mp ¼ 488C; IR: 3328 (NH), 1748, 1698 and 1662 (C55O); 1H NMR
(CDCl3) d: 6.81 (br, 1H, NH), 4.52 (d, JH-H ¼ 6.3 Hz, 2H, NCH2CO2Et),
4.15 (q, JH-H ¼ 7.3 Hz, 2H, OCH2), 4.12 (q, JH-H ¼ 7.3 Hz, 2H, OCH2),
3.89 (s, 2H, CH2), 3.16 (d, JH-H ¼ 7.5 Hz, 2H, CH2), 1.90 (m, 1H, CH),
1.23 (t, JH-H ¼ 7.3 Hz, 3H, CH3), 1.19 (t, JH-H ¼ 7.3 Hz, 3H, CH3), 0.83
(d, JH-H ¼ 6.6 Hz, 6H, 2 Â CH3); 13C NMR (CDCl3) d: 170.6 (CO), 165.6
(CO), 164.9 (CO), 146.0 (C4), 99.3 (C3), 61.0 (CH2O), 59.6 (CH2), 50.1
(CH2), 48.0 (CH2), 44.7 (CH2), 27.4 (CH), 19.8 (2 Â CH3), 14.2 (CH3),
13.9 (CH3). Anal. calcd. for C15H24N2O5: C, 57.68; H, 7.74; N, 8.97.
Found: C, 57.43; H, 7.67; N, 9.01.
4-(Ethoxycarbonylmethyl-amino)-5-oxo-1-phenyl-2,5-dihydro-1H-pyrrole-
3-carboxylic acid ethyl ester 8c: White crystals; 275 mg (83%); mp ¼ 1048C;
1
IR: 3341 (NH), 1747, 1695 and 1665 (C55O); H NMR (CDCl3) d: 7.72
(m, 2H, ArH), 7.38 (m, 2H, ArH), 7.15 (m, 1H, ArH), 6.88 (br, 1H, NH), 4,62
(d, JH-H ¼ 6.2 Hz, 2H, NCH2CO2Et), 4.42 (s, 2H, CH2), 4.26 (q, JH-H
¼

Synthesis of Esters
2459
7.1 Hz, 2H, OCH2), 4.23 (q, JH-H ¼ 7.1 Hz, 2H, OCH2), 1.34 (t, JH-H ¼ 7.1 Hz,
3H, CH3), 1.29 (t, JH-H ¼ 7.3 Hz, 3H, CH3); 13C NMR (CDCl3) d: 170.6 (CO),
164.9 (CO), 164.5 (CO), 145.7 (C4), 138.6, 129.0, 125.0 and 119.3 (Ph), 99.4
(C3), 61.3 (CH2O), 60.0 (CH2), 48.0 (CH2), 44.5 (CH2), 14.4 (CH3), 14.1
(CH3). Anal. calcd. for C17H20N2O5: C, 61.44; H, 6.07; N, 8.43. Found: C,
61.21; H, 5.98; N, 8.42.
1-Benzyl-4-(Ethoxycarbonylmethyl-amino)-5-oxo-2,5-dihydro-1H-pyrrole-
3-carboxylic acid ethyl ester 8d: White crystals; 280 mg (81%); mp ¼ 778C;
IR: 3339 (NH), 1748, 1692 and 1669 (C55O); 1H NMR (CDCl3) d: 7.35–7.22
(m, 5H, ArH), 6.91 (br, 1H, NH), 4.63 (d, JH-H ¼ 6.5 Hz, 2H, NCH2CO2Et),
4.61 (s, 2H, CH2Ph), 4.23 (q, JH-H ¼ 7.3 Hz, 2H, OCH2), 4.18 (q, JH-H
¼7.3 Hz, 2H, OCH2), 3.86 (s, 2H, CH2), 1.28 (t, JH-H ¼ 7.3 Hz, 3H, CH3),
1.25 (t, JH-H ¼ 7.3 Hz, 3H, CH3); 13C NMR (CDCl3) d: 170.7 (CO), 165.4
(CO), 164.5 (CO), 145.9 (C4), 136.3, 128.7, 128.0 and 127.6 (Ph), 99.8
(C3), 61.1 (CH2O), 59.6 (CH2), 47.7 (CH2), 46.5 (CH2), 44.5 (CH2), 14.3
(CH3), 14.0 (CH3). Anal. calcd. for C18H22N2O5: C, 62.42; H, 6.40;
N, 8.09. Found: C, 62.46; H, 6.31; N, 8.05.
4-(Ethoxycarbonylmethyl-amino)-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxylic
acid ethyl ester 8e: White crystals; 180 mg (70%); mp ¼ 1388C; IR: 3351,
1
3188 (NH), 1753, 1699 and 1669 (C55O); H NMR (CD3COCD3) d: 7.62
(br, 1H, NH), 6.90 (br, 1H, NH), 4.47 (s, 2H, NCH2CO2Et), 4.06 (q, JH-H
¼
7.3 Hz, 2H, OCH2), 4.02 (q, JH-H ¼ 7.3 Hz, 2H, OCH2), 3.81 (s, 2H, CH2),
1.13 (t, JH-H ¼ 7.3 Hz, 3H, CH3), 1.10 (t, JH-H ¼ 7.3 Hz, 3H, CH3);
13C NMR (CD3COCD3) d: 171.5 (CO), 168.5 (CO), 165.8 (CO), 147.4
(C4), 102.0 (C3), 61.3 (CH2O), 60.0 (CH2O), 44.5 (CH2), 43.0 (CH2), 14.7
(CH3), 14.5 (CH3). Anal. calcd. for C11H16N2O5: C, 51.56; H, 6.29;
N, 10.93. Found: C, 51.43; H, 6.17; N, 10.83.
4-(Ethoxycarbonylmethyl-amino)-1-methyl-5-oxo-2,5-dihydro-1H-pyrrole-
2,3-dicarboxylic acid diethyl ester 9a: White crystals; 245 mg (71%);
1
mp ¼ 968C; IR: 3320 (NH), 1748, 1726, 1698 and 1659 (C55O); H NMR
(CDCl3) d: 7.19 (br, 1H, NH), 4.74 (m, 1H, NCH2CO2Et), 4.64 (s, 1H,
CH), 4.47 (m, 1H, NCH2CO2Et), 4.26–4.17 (m, 6H, 3 Â OCH2), 2.95
(s, 3H, CH3N), 1.29 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 1.28 (t, JH-H ¼ 7.1 Hz,
3H, CH3), 1.26 (t, JH-H ¼ 7.3 Hz, 3H, CH3); 13C NMR (CDCl3) d: 170.2
(CO), 168.7 (CO), 165.5 (CO), 164.5 (CO), 147.2 (C4), 99.4 (C3), 62.2
(CH), 61.7 (CH2O), 61.3 (CH2O), 59.9 (CH2O), 43.8 (CH2), 28.2 (CH3N),
14.3 (CH3), 14.1 (2 Â CH3). Anal. calcd. for C15H22N2O7: C, 52.63;
H, 6.48; N, 8.18. Found: C, 52.61; H, 6.37; N, 8.16.
4-(Ethoxycarbonylmethyl-amino)-1-isobutyl-5-oxo-2,5-dihydro-1H-
pyrrole-2,3-dicarboxylic acid diethyl ester 9b: Yellow oil; 290 mg (75%); IR:
3332 (NH), 1750, 1722, 1700 and 1661 (C55O); 1H NMR (CDCl3) d: 6.12 (br,
1H, NH), 4.61 (s, 1H, CH), 4.55 (m, 1H, NCH2CO2Et), 4.44 (m, 1H,
NCH2CO2Et), 4.16–4.04 (m, 6H, 3 Â OCH2), 3.40 [dd, JH-H ¼ 13.8 and
9.0 Hz, 1H, (CH3)2CHCH2N], 2.70 [dd, JH-H ¼ 13.8 and 6.3 Hz, 1H,
(CH3)2CHCH2N], 1.85 (m, 1H, (CH3)2CHCH2N), 1.20–1.12 (m, 9H,

2460
F. Jourdan, J. T. Kaiser, and D. J. Lowe
3 Â CH3), 0.82 (d, JH-H ¼ 6.6 Hz, 3H, CH3), 0.74 (d, JH-H ¼ 6.8 Hz, 3H,
CH3); 13C NMR (CDCl3) d: 170.7 (CO), 169.4 (CO), 166.1 (CO), 165.8
(CO), 147.8 (C4), 99.9 (C3), 62.1 (CH2O), 61.6 (CH2O), 61.4 (CH), 60.3
(CH2O), 49.3 (CH2), 44.3 (CH2), 27.6 (CH), 20.2 (2 Â CH3), 14.5 (CH3),
14.3 (CH3) 14.2 (CH3). Anal. calcd. for C18H28N2O7: C, 56.24; H, 7.34;
N, 7.29. Found: C, 56.01; H, 7.32; N, 7.14.
4-(Ethoxycarbonylmethyl-amino)-5-oxo-1-phenyl-2,5-dihydro-1H-pyrrole-
2,3-dicarboxylic acid diethyl ester 9c: White solid; 330 mg (82%);
1
mp ¼ 928C; IR: 3328 (NH), 1750, 1720, 1697 and 1658 (C55O); H NMR
(CDCl3) d: 7.47 (m, 2H, ArH), 7.27 (m, 2H, ArH), 7.11 (m, 1H, ArH), 6.72
(br, 1H, NH), 5.26 (s, 1H, CH), 4.65 (m, 1H, NCH2CO2Et), 4.43 (m, 1H,
NCH2CO2Et), 4.14 (q, JH-H ¼ 7.1 Hz, 2H, OCH2), 4.12 (q, JH-H ¼ 7.2 Hz,
2H, OCH2), 3.97 (q, JH-H ¼ 7.1 Hz, 2H, OCH2), 1.21 (t, JH-H ¼ 7.2 Hz, 3H,
CH3), 1.18 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 0.98 (t, JH-H ¼ 7.1 Hz, 3H, CH3);
13C NMR (CDCl3) d: 170.0 (CO), 168.3 (CO), 164.4 (CO), 164.2 (CO),
146.7 (C4), 136.2, 128.8, 126.0 and 121.7 (Ph), 99.2 (C3), 61.5 (CH2O),
61.3 (CH), 61.1 (CH2O), 59.9 (CH2O), 43.9 (CH2), 14.0 (CH3), 13.9 (CH3)
13.6 (CH3). Anal. calcd. for C20H24N2O7: C, 59.40; H, 5.98; N, 6.93.
Found: C, 59.12; H, 5.93; N, 6.78.
1-Benzyl-4-(Ethoxycarbonylmethyl-amino)-5-oxo-2,5-dihydro-1H-
pyrrole-2,3-dicarboxylic acid diethyl ester 9d: Yellow oil; 310 mg (74%); IR:
1
3339 (NH), 1748, 1723, 1698 and 1660 (C55O); H NMR (CDCl3) d: 7.25–
7.12 (m, 5H, ArH), 6.89 (br, 1H, NH), 4.81 (d, JH-H ¼ 15.2 Hz, 1H, CH2Ph),
4.57 (m, 1H, NCH2CO2Et), 4.46 (m, 1H, NCH2CO2Et), 4.44 (s, 1H, CH),
4.15–3.90 (m, 7H, 3 Â OCH2 and CH2Ph), 1.18 (t, JH-H ¼ 7.1 Hz, 3H,
CH3), 1.12 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 1.10 (t, JH-H ¼ 7.0 Hz, 3H, CH3);
13C NMR (CDCl3) d: 171.1 (CO), 170.7 (CO), 166.0 (CO), 165.8 (CO),
147.3 (C4), 136.2, 129.0, 128.7 and 128.2 (Ph), 99.6 (C3), 62.1 (CH2O),
61.7 (CH2O), 60.5 (CH), 60.3 (CH2O), 45.7 (CH2), 44.9 CH2), 14.4 (CH3),
14.3 (CH3) 14.2 (CH3). Anal. calcd. for C21H26N2O7: C, 60.28; H, 6.26;
N, 6.69. Found: C, 60.04; H, 6.12; N, 6.72.
General Method for the Hydrolysis of the N-Pyrrolyl
Glycine Esters 7a–d, 8a–e, 9a–d
A solution of 7a–d, 8a–e, or 9a–d (0.5 mmol) in 10 ml of THF and 10 ml of
water was stirred at room temperature with 1 equivalents of lithium hydroxide
monohydrate (0.50 mmol, 21 mg) and the reaction monitored by TLC. When
the reaction was complete (30 min to 1 h), the solution extracted with ethyl
acetate (50 ml). The aqueous layer was then made acidic with a ꢀ1M
aqueous solution of NH4Cl and extracted with ethyl acetate (3 Â 20 ml),
and the combined organic layers were successively washed with water and
brine, dried over MgSO4, and the solvent evaporated under reduced
pressure. The residual oil/solid was purified by column chromatography

Synthesis of Esters
2461
(hexane/ethyl acetate) and/or recrystallized to afford 10a–d, 11a–e, or
12a–d.
Compounds 13a–d were obtained directly from 9a–d or from 12a–d
using 3 to 5 equivalents of LiOH; H2O and following the method described
previously. They were purified by column chromatography (hexane/ethyl
acetate/methanol) and/or recrystallized (hexane/ethyl acetate).
(4-Cyano-1-methyl-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
10a: White crystals; 85 mg (87%); mp ¼ 131–1328C; IR: 3410–3035 (OH,
1
NH), 2198 (CN), 1733, and 1661 (C55O); H NMR (CD3COCD3) d: 6.42
(t, JH-H ¼ 6.4 Hz, 1H, NH), 5.47 (br, 1H, OH), 4.30 (d, JH-H ¼ 6.4 Hz, 2H,
NCH2CO2H), 4.00 (s, 2H, CH2), 3.01 (s, 3H, CH3N); 13C NMR
(CD3COCD3) d: 170.7 (CO), 164.5 (CO), 147.6 (C3), 116.9 (CN), 75.1
(C4), 50.9 (CH2), 44.5 (CH2), 29.7 (CH3N). Anal. calcd. for C8H9N3O3:
C, 49.23; H, 4.65; N, 21.53. Found: C, 49.02; H, 4.38; N, 21.46.
(4-Cyano-1-isobutyl-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
10b: White crystals; 110 mg (93%); mp ¼ 192–1938C; IR: 3405–3040
1
(OH, NH), 2196 (CN), 1738, and 1660 (C55O); H NMR (CD3COCD3) d:
6.38 (t, JH-H ¼ 6.4 Hz, 1H, NH), 5.09 (br, 1H, OH), 4.25 (d, JH-H ¼ 6.4 Hz,
2H, NCH2CO2H), 4.00 (s, 2H, CH2), 3.23 (d, JH-H ¼ 7.5 Hz, 2H, CH3N),
1.96 (m, 1H, CH), 0.84 (d, JH-H ¼ 6.8 Hz, 6H, 2 Â CH3); 13C NMR
(CD3COCD3) d: 170.8 (CO), 164.8 (CO), 147.4 (C3), 117.0 (CN), 75.2
(C4), 51.0 (CH2), 49.7 (CH2), 44.6 (CH2), 28.2 (CH), 20.2 (2 Â CH3).
Anal. calcd. for C11H15N3O3: C, 55.69; H, 6.37; N, 17.71. Found: C, 55.57;
H, 6.24; N, 17.71.
(4-Cyano-2-oxo-1-phenyl-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
10c: White crystals; 115 mg (89%); mp ¼ 219–2208C; IR: 3435–3050
1
(OH, NH), 2202 (CN), 1734, and 1658 (C55O); H NMR (CD3COCD3) d:
7.82 (m, 2H, Ph), 7.42 (m, 2H, Ph), 7.20 (m, 1H, Ph), 6.59 (t, JH-H
6.3 Hz, 1H, NH), 5.51 (br, 1H, OH), 4.55 (s, 2H, CH2), 4.36 (d, JH-H
6.3 Hz, 2H, NCH2CO2H); 13C NMR (CD3COCD3) d: 170.6 (CO), 163.6
(CO), 147.1 (C3), 139.5, 129.9, 125.9 and 119.9 (Ph), 116.6 (CN), 75.7
(C4), 49.5 (CH2), 44.4 (CH2). Anal. calcd. for C13H11N3O3: C, 60.70;
H, 4.31; N, 16.33. Found: C, 60.52; H, 4.13; N, 16.16.
¼
¼
(1-Benzyl-4-cyano-2-oxo-2,5-dihydro-1H-pyrrol-3-ylamino)-acetic acid
10d: White crystals; 118 mg (87%); mp ¼ 186–1878C; IR: 3430–3060
1
(OH, NH), 2195 (CN), 1736, and 1659 (C55O); H NMR (CD3COCD3) d:
7.33 (m, 3H, Ph), 7.24 (m, 2H, Ph), 6.47 (t, JH-H ¼ 6.4 Hz, 1H, NH), 5.19
(br, 1H, OH), 4.38 (s, 2H, CH2), 4.18 (d, JH-H ¼ 6.4 Hz, 2H, NCH2CO2H),
3.92 (s, 2H, CH2); 13C NMR (CD3COCD3) d: 170.7 (CO), 163.7 (CO),
146.9 (C3), 136.5, 128.8, 127.8 and 127.7 (Ph), 116.7 (CN), 73.3 (C4), 47.9
(CH2), 46.1 (CH2), 44.0 (CH2); Anal. calcd. for C14H13N3O3: C, 61.99;
H, 4.83; N, 15.49. Found: C, 61.97; H, 4.86; N, 15.31.
4-(Carboxymethyl-amino)-1-methyl-5-oxo-2,5-dihydro-1H-pyrrole-3-
carboxylic acid ethyl ester 11a: White crystals; 105 mg (87%); mp ¼ 91–
1
928C; IR: 3390–3055 (OH, NH), 1738, 1701 and 1670 (C55O); H NMR

2462
F. Jourdan, J. T. Kaiser, and D. J. Lowe
(DMSO-d6) d: 8.96 (br, 1H, OH), 6.95 (br, 1H, NH), 4.48 (s, 2H,
NCH2CO2H), 4.19 (q, JH-H ¼ 7.1 Hz, 2H, CH2O), 3.97 (s, 2H, CH2), 3.00
(s, 3H, CH3N), 1.28 (t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR (DMSO-d6) d:
174.4 (CO), 167.4 (CO), 166.4 (CO), 148.3 (C4), 100.2 (C3), 60.9
(CH2O), 50.7 (CH2), 45.1 (CH2), 29.9 (CH3N), 14.3 (CH3); Anal. calcd.
for C10H14N2O5: C, 49.58; H, 5.83; N, 11.56. Found: C, 49.26; H, 5.61;
N, 11.23.
4-(Carboxymethyl-amino)-1-isobutyl-5-oxo-2,5-dihydro-1H-pyrrole-3-
carboxylic acid ethyl ester 11b: White crystals; 120 mg (84%); mp ¼ 93–
1
948C; IR: 3395–3045 (OH, NH), 1742, 1700 and 1665 (C55O); H NMR
(CDCl3) d: 8.59 (br, 1H, OH), 6.75 (br, 1H, NH), 4.49 (d, JH-H ¼ 6.4 Hz,
2H, NCH2CO2H), 4.12 (q, JH-H ¼ 7.1 Hz, 2H, CH2O), 3.90 (s, 2H, CH2),
3.15 (d, JH-H ¼ 7.5 Hz, 2H, CH2N), 1.88 (m, 1H, CH), 1.20 (t, JH-H
¼
7.1 Hz, 3H, CH3), 0.81 (d, JH-H ¼ 6.6 Hz, 6H, 2 Â CH3); 13C NMR (CDCl3)
d: 174.4 (CO), 166.4 (CO), 165.5 (CO), 146.2 (C4), 100.2 (C3), 60.3
(CH2O), 50.8 (CH2), 48.8 (CH2), 44.7 (CH2), 28.0 (CH), 20.1 (2 Â CH3),
14.5 (CH3). Anal. calcd. for C13H20N2O5: C, 54.92; H, 7.09; N, 9.85.
Found: C, 54.75; H, 6.78; N, 9.81.
4-(Carboxymethyl-amino)-5-oxo-1-phenyl-2,5-dihydro-1H-pyrrole-3-
carboxylic acid ethyl ester 11c: White crystals; 130 mg (85%); mp ¼ 158–
1
1598C; IR: 3400–3050 (OH, NH), 1741, 1698 and 1665 (C55O); H NMR
(CDCl3) d: 8.76 (br, 1H, OH), 7.72 (m, 2H, Ph), 7.38 (m, 2H, Ph), 7.18
(m, 1H, Ph), 6.78 (br, 1H, NH), 4.52 (d, JH-H ¼ 6.3 Hz, 2H, NCH2CO2H),
4.44 (s, 2H, CH2), 4.23 (q, JH-H ¼ 7.3 Hz, 2H, CH2O), 1.28 (t, JH-H
¼
7.3 Hz, 3H, CH3); 13C NMR (CDCl3) d: 173.9 (CO), 166.1 (CO), 165.4
(CO), 145.9 (C4), 138.6, 128.9, 125.0 and 119.2 (Ph), 100.3 (C3), 60.8
(CH2O), 48.3 (CH2), 46.4 (CH2), 14.4 (CH3). Anal. calcd. for C15H16N2O5:
C, 59.21; H, 5.30; N, 9.21. Found: C, 59.03; H, 5.07; N, 9.18.
1-Benzyl-4-(carboxymethyl-amino)-5-oxo-2,5-dihydro-1H-pyrrole-3-
carboxylic acid ethyl ester 11d: White crystals; 125 mg (79%); mp ¼ 119–
1
1208C; IR: 3410–3070 (OH, NH), 1739, 1697 and 1668 (C55O); H NMR
(CDCl3) d: 9.36 (br, 1H, OH), 7.28–7.14 (m, 5H, Ph), 6.82 (br, 1H, NH),
4.58 (d, JH-H ¼ 6.4 Hz, 2H, NCH2CO2H), 4.54 (s, 2H, CH2Ph), 4.10 (q, JH-H
¼
7.1 Hz, 2H, CH2O), 3.80 (s, 2H, CH2), 1.18 (t, JH-H ¼ 7.1 Hz, 3H, CH3);
13C NMR (CDCl3) d: 174.9 (CO), 165.7 (CO), 165.2 (CO), 146.0 (C4),
136.1, 128.8, 128.1 and 127.8 (Ph), 100.2 (C3), 59.9 (CH2O), 47.2 (CH2),
46.7 (CH2), 44.1 (CH2), 14.3 (CH3). Anal. calcd. for C16H18N2O5: C, 60.37;
H, 5.70; N, 8.80. Found: C, 60.16; H, 5.49; N, 8.74.
4-(Carboxymethyl-amino)-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxylic acid
ethyl ester 11e: White crystals; 85 mg (74%); mp ¼ 152–1538C; IR: 3375–
1
3050 (OH, NH), 1743, 1700 and 1668 (C55O); H NMR (DMSO-d6) d:
8.65 (br, 1H, OH), 6.97 (br, 1H, NH), 4.34 (d, JH-H ¼ 6.9 Hz, 2H,
NCH2CO2H), 4.13 (q, JH-H ¼ 7.3 Hz, 2H, CH2O), 3.80 (s, 2H, CH2), 1.18
(t, JH-H ¼ 7.3 Hz, 3H, CH3); 13C NMR (DMSO-d6) d: 172.5 (CO), 167.4
(CO), 165.0 (CO), 150.2 (C4), 100.1 (C3), 60.5 (CH2O), 44.0 (CH2), 42.7

Synthesis of Esters
2463
(CH2), 14.7 (CH3). Anal. calcd. for C9H12N2O5: C, 47.37; H, 5.30; N, 12.28.
Found: C, 47.41; H, 5.25; N, 12.20.
4-(Carboxymethyl-amino)-1-methyl-5-oxo-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid diethyl ester 12a: White crystals; 125 mg (80%);
mp ¼ 103–1048C; IR: 3370–3110 (NH, OH), 1742, 1725, 1698 and 1658
1
(C55O); H NMR (CDCl3) d: 9.92 (br, 1H, OH), 6.79 (br, 1H, NH), 4.66
(m, 1H, NCH2CO2H), 4.61 (s, 1H, CH), 4.51 (m, 1H, NCH2CO2H), 4.21
(q, JH-H ¼ 7.3 Hz, 2H, CH2O), 4.18 (q, JH-H ¼ 7.1 Hz, 2H, CH2O), 2.87
(s, 3H, CH3N), 1.29 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 1.27 (t, JH-H ¼ 7.3 Hz,
3H, CH3); 13C NMR (CDCl3) d: 174.0 (CO), 168.7 (CO), 165.8 (CO),
164.6 (CO), 146.8 (C4), 99.3 (C3), 61.8 (CH2O), 61.5 (CH), 60.2 (CH2O),
44.0 (CH2), 28.2 (CH3N), 14.2 (CH3), 14.1 (CH3). Anal. calcd. for
C13H18N2O7: C, 49.68; H, 5.77; N, 8.91. Found: C, 49.66; H, 5.78; N, 8.85.
4-(Carboxymethyl-amino)-1-isobutyl-5-oxo-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid diethyl ester 12b: White crystals; 135 mg (76%);
mp ¼ 77–788C; IR: 3360–3100 (NH, OH), 1745, 1722, 1699 and 1661
1
(C55O); H NMR (CDCl3) d: 9.79 (br, 1H, OH), 7.12 (br, 1H, NH), 4.76
(m, 1H, NCH2CO2H), 4.73 (s, 1H, CH), 4.57 (m, 1H, NCH2CO2H), 4.22
(q, JH-H ¼ 7.1 Hz, 2H, CH2O), 4.20 (q, JH-H ¼ 7.1 Hz, 2H, CH2O), 3.53
(dd, JH-H ¼ 13.9 and 8.7 Hz, 1H, CH2N), 2.82 (dd, JH-H ¼ 13.9 and 6.3 Hz
1H, CH2N), 1.95 (m, 1H, CH), 1.28 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 1.26
(t, JH-H ¼ 7.1 Hz, 3H, CH3), 0.93 (d, JH-H ¼ 6.6 Hz 3H, CH3), 0.84
(d, JH-H ¼ 6.8 Hz, 3H, CH3); 13C NMR (CDCl3) d: 174.4 (CO), 168.9 (CO),
166.0 (CO), 164.4 (CO), 146.4 (C4), 99.1 (C3), 61.8 (CH2O), 61.2 (CH),
60.0 (CH2O), 49.1 (CH2), 43.8 (CH2), 27.1 (CH), 20.0 (CH3), 19.6 (CH3),
14.1 (CH3), 14.0 (CH3). Anal. calcd. for C16H24N2O7: C, 53.92; H, 6.79;
N, 7.86. Found: C, 53.75; H, 6.51; N, 7.80.
4-(Carboxymethyl-amino)-5-oxo-1-phenyl-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid diethyl ester 12c: White crystals; 155 mg (82%);
mp ¼ 144–1458C; IR: 3350–3105 (NH, OH), 1743, 1720, 1700 and 1660
1
(C55O); H NMR (CDCl3) d: 10.20 (br, 1H, OH), 8.55 (br, 1H, NH), 7.46
(m, 2H, Ph), 7.25 (m, 2H, Ph), 7.12 (m, 1H, Ph), 5.28 (s, 1H, CH), 4.69
(m, 1H, NCH2CO2H), 4.48 (m, 1H, NCH2CO2H), 4.15 (q, JH-H ¼ 7.1 Hz,
2H, CH2O), 3.97 (q, JH-H ¼ 7.1 Hz, 2H, CH2O), 1.21 (t, JH-H ¼ 7.1 Hz, 3H,
CH3), 0.99 (t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR (CDCl3) d: 174.7 (CO),
168.5 (CO), 168.0 (CO), 164.4 (CO), 146.4 (C4), 136.1, 129.0, 126.3 and
122.1 (Ph), 99.3 (C3), 61.8 (CH2O), 61.6 (CH), 60.3 (CH2O), 44.0 (CH2),
14.1 (CH3), 13.8 (CH3). Anal. calcd. for C18H20N2O7: C, 57.44; H, 5.36;
N, 7.44. Found: C, 57.37; H, 5.21; N, 7.29.
1-Benzyl-4-(carboxymethyl-amino)-5-oxo-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid diethyl ester 12d: White crystals; 170 mg (87%); mp ¼
102–1038C; IR: 3360-3095 (NH, OH), 1741, 1722, 1699 and 1659 (C55O);
1H NMR (CDCl3) d: 10.21 (br, 1H, OH), 7.35–7.22 (m, 5H, Ph), 7.04 (br,
1H, NH), 4.95 (d, JH-H ¼ 15.1Hz, 1H, CH2Ph), 4.80 (m, 1H, NCH2CO2H),
4.60 (m, 1H, NCH2CO2H), 4.58 (s, 1H, CH), 4.16 (q, JH-H ¼ 7.1 Hz, 2H,

2464
F. Jourdan, J. T. Kaiser, and D. J. Lowe
CH2O), 4.15 (d, JH-H ¼ 15.1Hz, 1H, CH2Ph), 4.06 (q, JH-H ¼ 7.1 Hz, 2H,
CH2O), 1.22 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 1.20 (t, JH-H ¼ 7.1 Hz, 3H, CH3);
13C NMR (CDCl3) d: 174.6 (CO), 168.2 (CO), 167.7 (CO), 164.6 (CO),
146.1 (C4), 136.2, 129.0, 128.8 and 128.2 (Ph), 99.5 (C3), 61.5 (CH2O), 61.1
(CH), 60.1 (CH2O), 45.5 (CH2), 43.9 (CH2), 14.3 (CH3), 14.1 (CH3). Anal.
calcd. for C19H22N2O7: C, 58.46; H, 5.68; N, 7.18. Found: C, 58.29; H, 5.33;
N, 7.02.
4-(Carboxymethyl-amino)-1-methyl-5-oxo-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid 3-ethyl ester 13a: White crystals; 110 mg (77%);
mp ¼ 111–1128C; IR: 3410–3100 (NH, 2 Â OH), 1741, 1720, 1699 and
1660 (C55O); 1H NMR (CD3COCD3) d: 9.04 (br, 2H, 2 Â OH), 7.30
(br, 1H, NH), 4.66 (m, 1H, NCH2CO2H), 4.62 (s, 1H, CH), 4.56 (m, 1H,
NCH2CO2H), 4.13 (q, JH-H ¼ 7.1 Hz, 2H, CH2O), 2.89 (s, 3H, CH3N),
1.18 (t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR (CD3COCD3) d: 172.0 (CO),
170.3 (CO), 166.2 (CO), 165.3 (CO), 146.3 (C4), 99.4 (C3), 62.8
(CH), 60.3 (CH2O), 44.0 (CH2), 28.2 (CH3N), 14.5 (CH3). Anal. calcd.
for C11H14N2O7: C, 46.16; H, 4.93; N, 9.79. Found: C, 45.98; H, 4.77;
N, 9.61.
4-(Carboxymethyl-amino)-1-isobutyl-5-oxo-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid 3-ethyl ester 13b: White crystals; 140 mg (85%); mp ¼ 84–
858C; IR: 3390–3090 (NH, 2 Â OH), 1745, 1720, 1698 and 1660 (C55O); 1H
NMR (CDCl3) d: 9.95 (br, 2H, 2 Â OH), 7.14 (br, 1H, NH), 4.74 (s, 1H, CH),
4.62 (m, 2H, NCH2CO2H), 4.18 (q, JH-H ¼ 7.1 Hz, 2H, CH2O), 3.60 (dd, JH-H
¼
13.9 and 9.0 Hz, 1H, CH2N), 2.89 (dd, JH-H ¼ 13.9 and 6.3 Hz, 1H, CH2N),
1.98 (m, 1H, CH), 1.26 (t, JH-H ¼ 7.1 Hz, 3H, CH3), 0.88 (d, JH-H ¼ 6.6 Hz
3H, CH3), 0.83 (d, JH-H ¼ 6.8 Hz 3H, CH3); 13C NMR (CDCl3) d: 172.7
(CO), 171.6 (CO), 166.0 (CO), 165.0 (CO), 145.3 (C4), 98.7 (C3), 61.0
(CH), 60.6 (CH2O), 49.2 (CH2), 44.6 (CH2), 27.2 (CH), 20.1 (CH3), 19.7
(CH3), 14.1 (CH3). Anal. calcd. for C14H20N2O7: C, 51.22; H, 6.14;
N, 8.53. Found: C, 50.97; H, 6.01; N, 8.45.
4-(Carboxymethyl-amino)-5-oxo-1-phenyl-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid 3-ethyl ester 13c: White crystals; 150 mg (86%);
mp ¼ 151–1528C; IR: 3380–3095 (NH, 2 Â OH), 1741, 1717, 1700 and
1
1659 (C55O); H NMR (CDCl3) d: 10.15 (br, 2H, 2 Â OH), 7.30 (m, 2H,
Ph), 7.26 (m, 2H, Ph), 7.12 (m, 1H, Ph), 6.98 (br, 1H, NH), 5.13 (s, 1H,
CH), 4.73 (m, 1H, NCH2CO2H), 4.51 (m, 1H, NCH2CO2H), 4.13 (q, JH-H
¼
7.1 Hz, 2H, CH2O), 1.15 (t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR (CDCl3) d:
172.4 (CO), 172.0 (CO), 166.3 (CO), 166.0 (CO), 144.7 (C4), 136.0, 128.8,
126.1 and 121.7 (Ph), 98.5 (C3), 62.2 (CH), 61.0 (CH2O), 44.2 (CH2), 14.0
(CH3). Anal. calcd. for C16H16N2O7: C, 55.17; H, 4.63; N, 8.04. Found:
C, 55.04; H, 4.39; N, 7.97.
1-Benzyl-4-(carboxymethyl-amino)-5-oxo-2,5-dihydro-1H-pyrrole-2,3-
dicarboxylic acid 3-ethyl ester 13d: White crystals; 175 mg (96%);
mp ¼ 120–1218C; IR: 3400–3075 (NH, OH), 1740, 1718, 1700 and 1660
1
(C55O); H NMR (CDCl3) d: 10.34 (br, 2H, OH), 7.32–7.21 (m, 5H, Ph),

Synthesis of Esters
2465
7.08 (br, 1H, NH), 5.10 (d, JH-H ¼ 15.0 Hz, 1H, CH2Ph), 4.64 (m, 2H,
NCH2CO2H), 4.56 (s, 1H, CH), 4.18 (d, JH-H ¼ 15.0 Hz, 1H, CH2Ph), 4.16
(q, JH-H ¼ 7.1 Hz, 2H, CH2O), 1.25 (t, JH-H ¼ 7.1 Hz, 3H, CH3); 13C NMR
(CDCl3) d: 174.9 (CO), 172.3 (CO), 165.5 (CO), 164.9 (CO), 147.0 (C4),
135.1, 128.8, 128.5 and 128.1 (Ph), 98.9 (C3), 60.7 (CH2O), 59.6 (CH),
45.5 (CH2), 44.1 (CH2), 14.0 (CH3). Anal. calcd. for C17H18N2O7: C, 56.35;
H, 5.01; N, 7.73. Found: C, 56.32; H, 4.88; N, 7.64.
ACKNOWLEDGMENTS
We gratefully acknowledge the European Community (Grant HPRN-CT-
1999-00084) and the BBSRC for financial support. We also thank Professor
Chris Pickett for helpful discussions and suggestions.
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