Synthesis of new thiazole analogues of pyochelin, a siderophore of Pseudomonas aeruginosa and Burkholderia cepacia. A new conversion of thiazolines into thiazoles

Article abstract of DOI:10.1016/j.tet.2004.10.030

Three pyochelin analogues and their methyl esters all containing a thiazole ring have been synthesised from the same Weinreb amide key intermediate. One of these analogues called HPTT-COOH, a molecule released in the course of pyochelin and yersiniabactin biosynthesis, was efficiently synthesised using a new base induced conversion of the key compound 2′-(2-hydroxyphenyl)- 2′-thiazoline-4′-(N-methoxy,N-methyl) carboxamide into 2′-(2-hydroxyphenyl)-2′-thiazole-4′-(N-methoxy,N-methyl) carboxamide. Graphical Abstract

Full text of DOI:10.1016/j.tet.2004.10.030

Tetrahedron 60 (2004) 12139–12145
Synthesis of new thiazole analogues of pyochelin, a siderophore of
Pseudomonas aeruginosa and Burkholderia cepacia.
A new conversion of thiazolines into thiazoles
†
*
¨
Gaetan L. Mislin, Alain Burger and Mohamed A. Abdallah
´ ´ ´ ´
Laboratoire de Chimie Microbienne, Departement des Recepteurs et Proteines Membranaires UPR 9050 CNRS Ecole Superieure de
´
Biotechnologie de Strasbourg, Boulevard Sebastien Brant F-67400 Illkirch, France
Received 22 July 2004; revised 7 October 2004; accepted 7 October 2004
Abstract—Three pyochelin analogues and their methyl esters all containing a thiazole ring have been synthesised from the same Weinreb
amide key intermediate. One of these analogues called HPTT-COOH, a molecule released in the course of pyochelin and0 yersiniabacti0n
biosynthesis, was efficiently synthesised using a new base induced conversion of the key compound 20-(2-hydroxyphenyl)-2 -thiazoline-4 -
(N-methoxy,N-methyl) carboxamide into 20-(2-hydroxyphenyl)-20-thiazole-40-(N-methoxy,N-methyl) carboxamide.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
explore furthermore the influence of the C-40, C-200 and C-400
assymetric centers on iron chelation and transport.
Under iron deficient conditions, microorganisms synthesise
and excrete small molecules called siderophores which
strongly chelate iron (III) and transport it into the cell.1 In
Gram-negative bacteria, the ferrisiderophore is recognised
by a specific receptor in the outer membrane and the metal
ion is then transported into the cytoplasm by a proton-
motive force energised multiproteic system.2 Our interest is
focused on iron uptake systems in Pseudomonas aeruginosa
and Burkholderia cepacia.3 These bacteria are nosocomial
opportunistic pathogens, causing severe and often lethal
lung infections especially in cystic fibrosis patients. Both
In compounds 2 and 3, the thiazoline moiety was replaced
by a thiazole ring where C-40 and C-50 are both sp2, in
contrast to pyochelin. In analogue 4 by replacement of the
thiazolidine moiety with a thiazoline ring, C-40 and C-200
become sp2 and C-400 remains the only assymetric center
(Fig. 1).
In this paper we describe the synthesis of two thiazole
analogues of pyochelin 2 and 3 using the route developed in
our laboratory for the synthesis of natural pyochelin 1 via
P. aeruginosa and B. cepacia excrete pyochelin 1,4
a
hydroxyphenylthiazolinyl-thiazolidine type of siderophore
which chelates iron (III) with a 2:1 stoichiometry.5 We have
recently reported the synthesis and biological properties of
several synthetic pyochelin analogues and shown that both
the 40R and 40S enantiomers of pyochelin chelate and
transport iron(III) at very similar rates, suggesting that the
configuration at carbon C-40 has no effect on the biological
properties of pyochelin.6 These results prompted us to
synthesise the thiazole pyochelin analogues 2, 3 and 4 and to
Keywords: Pseudomonas; Siderophore; Pyochelin; Yersiniabactin; HPTT-
COOH; Thiazole; Thiazoline; Weinreb amide.
* Corresponding author. Tel.: C33 3 9024 4727; fax: C33 3 9024 4829;
e-mail: mislin@esbs.u-strasbg.fr
† Present address: Laboratoire de Chimie Bioorganique, UMR 6001 CNRS,
´
Universite de Nice Sophia Antipolis, Parc Valrose, F-06108 Nice Cedex
2, France.
Figure 1.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.030

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G. L. Mislin et al. / Tetrahedron 60 (2004) 12139–12145
the thiazole hydroxamate 5 (Fig. 2).7 We also report a new
conversion procedure of thiazolines into thiazoles which we
have applied to the synthesis of 4 a third thiazolic analogue
of pyochelin.
Previous reports strongly suggest a template effect of both
the metal ion and the configuration of the C-400 asymmetric
center, in the definition of the C-200 stereocenter.7c In our
hands, compounds 2, 3, 7 and 8 were isolated as mixtures of
two diastereoisomers a (200R, 400R) and b (200S, 400R) in
equimolar proportions. The relative configurations of the
stereocenters were unambiguously assigned by NOESY
experiments.7,11 When proton H-200 was saturated a marked
Overhauser effect with H-400 proton was observed for a
(200R, 400R) isomer (i.e. cis isomer) whereas no NOE was
observed for b (200S, 400R). In addition, using COSY and
1H–13C correlation it was then possible to assign the
chemical shifts of both diastereoisomers for 2, 3, 7 and 8
(Fig. 3).
Figure 2.
2. Results and discussion
The thiazole intermediate 5, was prepared from the known
Weinreb amide 67 which was used as starting material and
reacted under several different conditions. First attempts
performed using manganese dioxide under various con-
ditions yielded the expected thiazole intermediate 5 but in
poor to average yields. Better results were obtained when a
mixture of CBrCl3/DBU was used, giving compound 5 as a
single product in 87% yield.8 The Weinreb amide 5 was
then reduced with lithium aluminum hydride,9 into a very
labile aldehyde. This latter was straightforwardly condensed
with either (R)-cysteine or (R)-N-methylcysteine hydro-
chloride10 in the presence of potassium acetate leading to
the pyochelin analogues 3 and 2 respectively, both isolated
in 90% yield over two steps. Compounds 2 and 3 were
further converted into the corresponding methyl esters 7 and
8, both isolated in 85% yield, using trimethylsilyldiazo-
methane (Scheme 1).
Figure 3.
In the course of the synthesis of hydroxamic ester 5 we have
observed that if DBU was added a long time before CBrCl3,
the thiazole by-product 9 was isolated in significant amounts
along with thiazole 5. Moreover when CBrCl3 was omitted,
conversion of 6 into 9 proceeded sluggishly indicating that
the basic nature of DBU promotes the conversion of 6 into 9.
Other base/solvent combinations were tested (TMSOK/
THF, tBuOK/tBuOH, TBAF/THF, NaH/MeOH). The best
yields were obtained when an excess of sodium hydride in
dry methanol was used, where compound 6 was efficiently
converted into compound 9 in 70% isolated yield. A
plausible explanation of this result is illustrated in Scheme 2.
First the base abstracts the acidic proton of the Schiff base 6
giving the intermediate 10. Subsequent intramolecular
attack of the carbanion on the methoxy amide and release
of the methoxide anion affords the second intermediate 11.
Finally aromatisation and strain release favour the proton
elimination and the cleavage of the aziridone moiety to
yield compound 9 (Scheme 2).
Scheme 1. (i) DBU, CBrCl3, CH2Cl2, 20 8C. (ii) LiAlH4, THF, K40 to
K20 8C. (iii) (R)-cysteine or (R)-N-methylcysteine.HCl, AcOK, EtOH/
H2O, 20 8C. (iv) TMSCHN2, MeOH/CH2Cl2, 20 8C.
Pyochelin is usually extracted from culture broth or
synthesised as a mixture of diastereoisomers. Actually the
very labile C-200 position is readily epimerised in absence of
metal.
Scheme 2.

G. L. Mislin et al. / Tetrahedron 60 (2004) 12139–12145
12141
In addition, when hydroxamic esters 12 and 13, were treated
in the same conditions, conversion into the corresponding
2-arylthiazole-4-methylcarboxamides 14 and 15 proceeded
similarly, in very high yield. It is worthwhile pointing out
that the best yield was obtained with the derivatives bearing
the strongly electron withdrawing nitro group (Scheme 3).
Initially, the phenol function of compound 9 was protected
with silyl group. Both t-butyldimethylsilyl and
a
t-butyldiphenylsilyl groups were introduced in parallel
studies but the latter proved to be more suitable due to its
higher stability during the synthetic sequence.7 Thus,
compound 9 was treated with t-butyldiphenylsilyl chloride
in presence of triethylamine, leading quantitatively to the
corresponding silyl ether 17. Using the conditions reported
by Charette and co-workers,12 compound 17 was succes-
sively treated with triflic anhydride and with O-methyl-
cysteine hydrochloride, in the presence of pyridine, leading
to the expected tricyclic compound 18, isolated in 74% yield
(Scheme 4).
Scheme 3.
To the best of our knowledge this conversion of the Weinreb
amide is unprecedented and we wished to apply it to the
synthesis of other pyochelin thiazole analogues. In the
literature, such thiazole-4-methylcarboxamide structurally
related compounds were described recently as powerful
synthons in an approach to natural thiazolylthiazoline
compounds.12 In connection to this observation, thiazole 9
should be a good substrate for a straightforward synthesis of
molecules such as analogue 4. This compound, called
HPTT-COOH, was previously isolated and described as
an oxidised form of an hydrolytic intermediate in
the nonribosomal biosynthesis of pyochelin 1 and
yersiniabactin 16 (Fig. 4).13,14
Scheme 4. (i) TBDPSCl, NEt3, CH2Cl2, 20 8C. (ii) (a) (CF3SO2)2O,
pyridine, CH2Cl2, K30 to 20 8C. (b) O-Methylcysteine.HCl, pyridine, K30
to 20 8C.
The silylated compound 18 appeared to be unstable and was
therefore immediately deprotected with TBAF, leading to
the methylester 19, isolated in 79% yield. This ester was
converted into the expected HPTT-COOH 4 after saponi-
fication with lithium hydroxide in wet tetrahydrofurane.
This compound, which has been previously described in the
literature,13d was actually prepared from a multienzymatic
synthetic pathway and to the best of our knowledge the
present report is the first which describes a straightforward
efficient chemical synthetic access to HPTT-COOH
(Scheme 5).
Figure 4.
Scheme 5. (i) TBAF, THF, 20 8C. (ii) LiOH$H2O, THF/H2O, 25 8C.

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G. L. Mislin et al. / Tetrahedron 60 (2004) 12139–12145
3. Conclusion
for C12H12N2O3S: C, 54.53; H, 4.58; N, 10.60. Found: C,
54.73; H, 4.64; N, 10.53.
In conclusion we have synthesised in good overall yields,
three pyochelin analogues 2, 3 and 4 and their methyl
esters 7, 8 and 19, bearing all a thiazole moiety. During
the synthetic exploration, we have discovered a new
base induced conversion of 2-aryl-4,5-dihydrothiazole-
4-methoxymethylcarboxamide into the corresponding
2-arylthiazole-4-methylcarboxamide. This reaction was
applied to the synthesis of HPTT-COOH 4. The different
pyochelin analogues described herein might be useful tools
in order to investigate the pyochelin dependent iron uptake
systems from siderophore biosynthesis to the ferripyochelin
internalisation processes. Detailed analysis of pyochelin-
dependent iron transport should help us to develop a new
generation of antibiotics focused against emerging multi-
resistant strains of P. aeruginosa and B. cepacia.
0
4.1.2. -(2-Hydroxyphenyl)-40-(300-methyl-200,300,400,500-tet-
rahydro)-[200,40]bisthiazolyl-400-carboxylic acid (2) and
20-(2-hydroxyphenyl)-40-(200,300,400,500-tetrahydro)-[200,40]-
bisthiazolyl-400-carboxylic acid (3). To a solution of
Weinreb amide 5 (150 mg, 0.57 mmol) in dry THF
(8 mL), cooled down K60 8C, LiAlH4 (0.74 mL of a 1 M
solution in THF, 0.73 mmol, 1.30 equiv) was added
dropwise by syringe. The reaction temperature was allowed
to raise to K20 8C over 30 mn and then hydrolysed by
successive additions of saturated aqueous solution of NH4Cl
(12 mL) and 1 M aqueous solution of KHSO4 (5 mL). The
mixture was allowed to warm to room temperature and
vigorous stirring was applied until two phases were formed.
After extraction with Et2O (2!30 mL), the organic layers
were combined, dried over Na2SO4 and filtered before being
evaporated. The crude aldehyde, isolated as a yellow
powder, was very sensitive to oxidation and was used
directly for subsequent reactions. It was dissolved into a
mixture of ethanol (20 mL) and water (6 mL) and to this
solution were successively added, potassium acetate
(650 mg, 3.79 mmol, 6.65 equiv) and either (R)-N-methyl-
cysteine hydrochloride (207 mg, 1.21 mmol, 2.12 equiv) for
the synthesis of 2 or (R)-cysteine (255 mg, 2.11 mmol,
3.70 equiv) for 3. The mixture was then gently stirred in the
dark during one hour before being successively washed with
hexane (30 mL) and diluted with water (30 mL). This
aqueous layer was then acidified to pH 2.0 by addition of
solid citric acid before being extracted with CH2Cl2 (2!
35 mL). The organic layers were collected, dried over
Na2SO4, filtered and evaporated under reduced pressure.
The expected pyochelin analogues 2 (165 mg, yield: 90%)
and 3 (160 mg, yield: 90%) were respectively isolated as
yellow powders.
4. Experimental
4.1. General procedures
All reactions were carried out under argon. Solvents used
were of analytical grade purity. Amines were distilled and
stored on KOH before use. All reactions were monitored by
thin-layer chromatography (TLC) using Merck precoated
silica gel 60F254 (0.25 mm). Column chromatography
purifications were performed using Merck kieselgel 60
(63–200 mm). Melting points were determined with a Stuart
Scientific Bibby SMP3 apparatus. IR spectra were scanned
neat using a Perkin–Elmer Spectrum one spectro-
photometer. UV–visible spectra were measured on a
Kontron Uvikon 930 spectrophotometer. NMR spectra
were recorded either on a Bruker Avance 300 (300 MHz
for 1H and 75 MHz for 13C) or a Bruker Avance 400
instrument (400 MHz for 1H and 100 MHz for 13C).
Elemental analysis were performed at the Service
4.1.3. 20-(2-Hydroxyphenyl)-40-(300-methyl-200,300,400,500-
tetrahydro)-[200,40]bisthiazolyl-400-carboxylic acid (2).
Mp 100–103 8C. IR (neat) 3432, 2956, 2526, 1977, 1716,
1619, 1579, 1456, 1380, 1307, 1248, 1207, 1156, 1017, 948,
856, 821, 751. SM (ESK) m/z 321 (MKHC, 100), 643
(2MKHC, 8).
´
d’Analyses de l’Institut de Chimie at Universite Louis
Pasteur of Strasbourg. Mass were performed on a Bruker
Daltonic MicroTOF mass spectrometer.
4.1.1. 20-(2-Hydroxyphenyl)-20-thiazole-40-(N-methoxy-
N-methyl) carboxamide (5). To a solution of 67 (521 mg,
1.96 mmol) and DBU (589 mL, 599 mg, 3.93 mmol,
2.00 equiv) in CH2Cl2 (20 mL), cooled to 0 8C was added
dropwise CBrCl3 (338 mL, 680 mg, 3.43 mmol, 1.75 equiv).
After 20 h of gentle stirring at 20 8C, the mixture was
adsorbed onto silica gel and filtered through a silica gel
column (30 g SiO2, hexane/acetone: 85/15). The expected
thiazole 5 (452 mg, yield: 87%) was isolated as a white
powder. Mp 111–114 8C, Rf 0.43 (hexane/acetone: 2/1), IR
(neat) 3167, 2925, 2160, 1634, 1583, 1478, 1399, 1378,
1275, 1219, 1183, 1153, 1132, 1070, 1037, 1006, 976, 934,
889, 837, 818, 798, 751, 743, 706, 663 cmK1. UV (MeOH)
214 (25240), 277 (10070), 323 (8320), 1H NMR (300 MHz,
CDCl3) d 3.44 (s, 3H), 3.82 (s, 3H), 6.92–6.97 (m,1H), 7.08
(dd, JZ8.2, 0.9 Hz, 1H), 7.36 (ddd, JZ8.8, 7.3, 1.6 Hz,
1H), 7.65 (dd, JZ7.9, 1.6 Hz, 1H), 8.03 (s, 1H), 11.96 (bs,
1H). 13C NMR (75 MHz, CDCl3) d 26.89, 61.86, 116.50,
117.89, 119.58, 123.78, 127.34, 132.34, 147.44, 161.56,
163.75, 168.57. MS (ESC) m/z 265 (MCHC, 100), 287
(MCNaC, 49), 551 (2MCNaC, 12), 582 (20). Anal. Calcd
4.1.4. (200R,400R)-20-(2-Hydroxyphenyl)-40-(300-methyl-
200,300, 400, 500-tetrahydro)-[200,40]bisthiazolyl-400carboxylic
carboxylic acid (2a). H NMR (400 MHz, CD3COCD3) d
1
2.63 (s, 3H), 3.34 (ABX, JAXZ6.6 Hz, JBXZ7.7 Hz, JAB
Z
11.0 Hz, 2H), 3.80 (dd, JZ7.7, 6.6 Hz, 1H), 5.35 (s, 1H),
6.94 (t, JZ7.6 Hz, 1H), 6.99 (d, JZ8.8 Hz, 1H), 7.33–7.39
(m, 1H), 7.69 (s, 1H), 7.72–7.77 (m, 1H). 13C NMR
(100 MHz, CD3COCD3) d 34.33, 41.50, 72.07, 73.00,
115.92, 117.72, 118.19, 120.45, 128.09, 132.74, 156.51,
157.28, 169.69, 172.00.
4.1.5. (200S,400R)-20-(2-Hydroxyphenyl)-40-(300-methyl-
200,300, 400,500-tetrahydro-[200,40]bisthiazolyl-400-carboxylic
acid (2b). 1H NMR (400 MHz, CD3COCD3) d 2.52 (s, 3H),
3.24 (dd, JZ10.4, 4.0 Hz, 1H), 3.46 (dd, JZ10.4, 6.8 Hz,
1H), 4.30 (dd, JZ6.8, 4.2 Hz, 1H), 5.62 (s, 1H), 6.94 (t, JZ
7.6 Hz, 1H), 6.99 (d, JZ8.8 Hz, 1H), 7.33–7.39 (m, 1H),
7.60 (s, 1H), 7.72–7.77 (m, 1H). 13C NMR (100 MHz,
CD3COCD3) d 33.13, 36.71, 69.38, 69.96, 116.08, 117.83,

G. L. Mislin et al. / Tetrahedron 60 (2004) 12139–12145
12143
118.24, 120.42, 128.04, 132.74, 156.31, 157.41, 169.74,
171.52.
114.26, 116.90, 117.77, 119.36, 127.01, 131.80, 155.27,
156.78, 169.46, 171.16.
4.1.6. 20-(2-Hydroxyphenyl)-40-(200,300,400,500-tetrahydro)-
[200,40]bisthiazolyl-400-carboxylic acid (3). Mp 165–
168 8C. IR (neat) 3119, 3062, 3021, 2161, 1641, 1615,
1573, 1479, 1429, 1361, 1336, 1311, 1292, 1270, 1248,
1200, 1167, 1145, 1127, 1068, 1036, 1023, 1010, 950, 933,
906, 866, 843, 831, 819, 772, 729, 682. SM (ESK) m/z 307
(MKHC, 100), 615 (2MKHC, 51).
4.1.12. (200S,400R)-20-(2-Hydroxyphenyl)-40-(300-methyl-
200,300, 400,500-tetrahydro)-[200,40]bisthiazolyl-400-carboxylic
acid methyl ester (7b). 1H NMR (400 MHz, CDCl3) d 2.50
(s, 3H), 3.20 (dd, JZ10.8, 4.6 Hz, 1H), 3.46 (dd, JZ10.5,
6.7 Hz, 1H), 3.80 (s, 3H), 4.20 (dd, JZ6.6, 4.1 Hz, 1H),
5.54 (s, 1H), 6.90 (m, 1H), 7.05 (m, 1H), 7.27 (s, 1H), 7.32
(m, 1H), 7.61 (d, JZ10.5 Hz, 1H). 13C NMR (75 MHz,
CDCl3) d 33.71, 36.61, 52.13, 68.36, 69.26, 113.95, 117.74,
119.37, 127.01, 131.80, 156.13, 156.70, 169.57, 171.69.
4.1.7. (200R,400R)-20-(2-Hydroxyphenyl)-40-(200,300,400,500-
tetra hydro)-[200,40]bisthiazolyl-400-carboxylic acid (3a).
1H NMR (400 MHz, CD3SOCD3) d 3.01 (dd, JZ10.0,
9.0 Hz, 1H), 3.39 (dd, JZ10.0, 7.0 Hz, 1H), 3.93 (dd, JZ
9.0, 7.0 Hz, 1H), 5.73 (s, 1H), 6.92–7.02 (m, 2H), 7.28–7.33
(m, 1H), 7.72 (s, 1H), 8.06 (dd, JZ7.9, 1.6 Hz, 1H), 11.14
(bs, 1H). 13C NMR (100 MHz, CD3SOCD3) d 38.33, 65.33,
66.99, 116.45, 116.56, 118.82, 119.45, 127.34, 131.08,
155.42, 163.66, 172.64, 174.52.
4.1.13.
20-(2-Hydroxyphenyl)-40-(200,300,400,500-tetra-
hydro)-[200,40]bisthiazolyl-400-carboxylic acid methyl-
ester (8). Mp 80–83 8C. IR (neat) 3482, 3272, 3101, 3000,
2949, 1732, 1619, 1582, 1475, 1431, 1402, 1377, 1332,
1304, 1265, 1203, 1175, 1157, 1137, 1037, 1005, 974, 948,
925, 880, 845, 821, 790, 743, 721, 700. (ESC) m/z 323
(MCHC, 100).
4.1.8. (200S,400R)-20-(2-Hydroxyphenyl)-40-(200,300,400,500-
tetra hydro)-[200,40]bisthiazolyl-400-carboxylic acid (3b).
1H NMR (400 MHz, CD3SOCD3) d 3.06 (dd, JZ10.2,
5.8 Hz, 1H), 3.31 (dd, JZ10.1, 6.8 Hz, 1H), 4.31 (dd, JZ
6.4, 5.9 Hz, 1H), 5.89 (s, 1H), 6.92–7.02 (m, 2H), 7.28–7.33
(m, 1H), 7.56 (s, 1H), 8.01 (dd, JZ7.9, 1.2 Hz, 1H), 11.22
(bs, 1H). 13C NMR (100 MHz, CD3SOCD3) d 38.00, 64.94,
66.90, 114.75, 116.56, 118.60, 119.43, 127.39, 131.08,
154.92, 164.13, 171.19, 172.21.
4.1.14. (200R,400R)-20-(2-Hydroxyphenyl)-40-(200,300,400,500-
tetra hydro)-[200,40]bisthiazolyl-400-carboxylic acid
methyl ester (8a). H NMR (300 MHz, CDCl3) d 3.11–
1
3.19 (m, 1H), 3.40–3.52 (m, 1H), 3.84 (s, 3H), 4.04 (m, 1H),
5.71 (s, 1H), 6.88–6.95 (m, 1H), 7.04–7.08 (m, 1H), 7.29–
7.37 (m, 1H), 7.31 (d, JZ0.5 Hz, 1H), 7.59–7.64 (m, 1H),
11.76 (bs, 1H). 13C NMR (100 MHz, CDCl3) d 32.83, 52.73,
65.80, 66.94, 114.11, 116.72, 117.91, 119.54, 127.24,
132.19, 152.67, 155.90, 170.10, 171.23.
4.1.9. 20-(2-Hydroxyphenyl)-40-(300-methyl-200,300,400,500-
4.1.15. (200S,400R)-20-(2-Hydroxyphenyl)-40-(200,300,400,500-
tetrahydro)-[200,40]bisthiazolyl-400-carboxylic
acid
tetra hydro)-[200,40]bisthiazolyl-400-carboxylic acid
methyl ester (8b). H NMR (300 MHz, CDCl3) d 3.11–
1
methyl ester (7) and 20-(2-hydroxyphenyl)-40-(200,300,
400,500-tetrahydro)-[200,40]bisthiazolyl-400-carboxylic acid
methylester (8). To a solution of 2 (77 mg, 0.24 mmol) or
3 (70 mg, 0.23 mmol) in a mixture of CH2Cl2 (8 mL) and
MeOH (3 mL), trimethylsilyldiazomethane (480 mL of an
approx. 2 M solution in hexane, 0.91 mmol, 4.00 equiv) was
added dropwise in four successive injections (every 20 mn).
After 16 h stirring at 20 8C, the mixture was evaporated and
chromatographed on a silica gel column (5 g SiO2, hexane/
Et2O: 1/1) leading respectively to methyl esters 7 (71 mg,
yield: 85%) or 8 (63 mg, yield: 84%) isolated respectively
as an orange oil and an yellow solid. Before NMR
measurements, these compounds were purified again on
preparative thin layer chromatography (eluent: Et2O).
3.19 (m, 1H), 3.40–3.52 (m, 1H), 3.83 (s, 3H), 4.27 (t, JZ
6.6 Hz, 1H), 5.94 (s, 1H), 6.88–6.95 (m, 1H), 7.04–7.08 (m,
1H), 7.22 (d, JZ0.9 Hz, 1H), 7.29–7.37 (m, 1H), 7.59–7.64
(m, 1H), 11.95 (bs, 1H). 13C NMR (75 MHz, CDCl3) d
38.42, 52.73, 64.64, 66.30, 112.62, 116.86, 117.80, 119.45,
127.13, 132.02, 152.67, 156. 75, 170.10, 171.83.
4.1.16. 20-(2-Hydroxyphenyl)-thiazole-40-N-methyl car-
boxamide (9). To a solution of 6 (469 mg, 1.76 mmol) in
MeOH (50 mL) stirred at 23 8C was added portionwise NaH
(220 mg of a 60% w/w dispersion in mineral oil, 132 mg,
5.52 mmol, 3.13 equiv). After 20 mn of gentle stirring, the
mixture was carefully hydrolysed with saturated aqueous
NH4Cl (5 mL), diluted with water (50 mL) and extracted
with EtOAc (50 mL). The organic layer was dried over
Na2SO4, filtered and adsorbed onto silica gel before being
filtered through a silica gel column (30 g SiO2, cyclohexane/
Et2O: 1/1). The resulting pale yellow solid was then
crystallised from hot cyclohexane/ethanol leading to the
expected methylamide 9 (286 mg, yield: 70%) isolated as a
white solid. Mp 172–174 8C, Rf 0.51 (CH2Cl2/MeOH: 95/5),
IR (neat) 3397, 3113, 3050, 2949, 2735, 2577, 1650, 1602,
1486, 1457, 1412, 1378, 1322, 1306, 1278, 1261, 1247,
1209, 1157, 1107, 1036, 984, 948, 921, 847, 834, 802, 777,
749, 720, 693 cmK1. UV (MeOH) 214 (28455), 223
4.1.10. 20-(2-Hydroxyphenyl)-40-(300-methyl-200,300, 400,500-
tetra hydro)-[200,40]bisthiazolyl-400carboxylic acid methyl
ester (7). IR (neat) 3108, 3043, 2992, 2950, 2850, 2790,
1737, 1619, 1580, 1475, 1456, 1436, 1400, 1346, 1269,
1250, 1216, 1201, 1155, 1057, 1018, 947, 909, 857, 821,
739. (ESC) m/z 337 (MCHC, 100).
4.1.11. (200R,400R)-20-(2-Hydroxyphenyl)-40-(300-methyl-
200,300, 400,500-tetrahydro)-[200,40]bisthiazolyl-400carboxylic
acid methyl ester (7a). 1H NMR (400 MHz, CDCl3) d 2.59
(s, 3H), 3.20 (dd, JZ11.0, 6.2 Hz, 1H), 3.33 (dd, JZ10.8,
9.2 Hz, 1H), 3.69 (dd, JZ9.2, 6.1 Hz, 1H), 3.76 (s, 3H),
5.20 (s, 1H), 6.90 (m, 1H), 7.05 (m, 1H), 7.32 (m, 1H), 7.48
(s, 1H), 7.60 (d, JZ10.5 Hz, 1H), 12.00 (bs, 1H). 13C NMR
(75 MHz, CDCl3) d 32.76, 41.49, 52.46, 71.11, 72.43,
1
(20855), 277 (10870), 323 (10678), H NMR (300 MHz,
CDCl3) d 3.05 (d, JZ5.0 Hz, 3H), 6.86 (bs, 1H), 6.96 (ddd,
JZ7.9, 7.1, 1.1 Hz, 1H), 7.08 (dd, JZ8.3, 0.8 Hz, 1H), 7.38
(ddd, JZ8.6, 7.36, 1.5 Hz, 1H), 7.65 (dd, JZ7.9, 1.7 Hz,

12144
G. L. Mislin et al. / Tetrahedron 60 (2004) 12139–12145
1H), 8.10 (s, 1H), 11.16 (bs, 1H). 13C NMR (75 MHz,
CDCl3) d 26.32, 116.39, 117.79, 120.05, 121.79, 127.60,
132.57, 148.00, 156.17, 162.00, 169.52. SM (ESC) m/z 235
(MCHC, 26), 257 (MCNaC, 100), 491 (2MCNaC, 20),
522 (29). Anal. Calcd for C11H10N2O2S: C, 56.39; H, 4.30;
N, 11.96. Found: C, 56.51; H, 4.63; N, 11.73.
162.94, 166.50, 171.41. SM (ESC) m/z 559 (MCHC, 100),
581 (MCNaC, 20), 1117 (2MCHC, 23), 1139 (2MCNaC,
50).
4.1.19. 20-(2-Hydroxyphenyl)-400,500-dihydro-[200,40]bis
thiazolyl-400-carboxylic acid methyl ester (19). To a
stirred solution of 18 (840 mg, 1.50 mmol) in CH2Cl2
(40 mL), TBAF (1.70 mL, 1 M solution in THF, 1.70 mmol,
1.20 equiv) was added dropwise at 20 8C. After 20 mn, the
mixture was adsorbed onto silica gel then filtered through a
silica gel column (20 g SiO2, pentane/Et2O: 7/3 then
pentane/Et2O: 3/7). The phenolic compound 19 (376 mg,
yield: 79%) was isolated as a white solid. Mp 100–102 8C,
Rf 0.61 (Et2O), IR (neat) 3296, 3123, 3067, 3009, 2954,
2160, 1978, 1719, 1622, 1600, 1584, 1506, 1478, 1443,
1427, 1330, 1304, 1258, 1211, 1172, 1158, 1110, 1030, 997,
971, 931, 896, 840, 827, 788, 743, 699, 684 cmK1. UV
4.1.17. 20-[2-(t-Butyldiphenylsilyloxy)-phenyl]-thiazole-
40-N-methylcarboxamide (17). To a solution of methyl-
amide 9 (161 mg, 0.69 mmol) dissolved in a 3:1 mixture of
CH2Cl2 and NEt3 (4 mL) at 20 8C was added TBDPSCl
(500 mL, 537 mg, 1.95 mmol, 2.84 equiv). After 16 h of
gentle stirring, the mixture was evaporated under reduced
pressure. The crude product was filtered through a silica gel
column (20 g SiO2, cyclohexane/EtOAc: 90/10 then cyclo-
hexane/EtOAc: 80/20) leading to the expected protected
phenol 17 (330 mg, yield: 100%) isolated as a white foam.
Mp 130–133 8C, Rf 0.70 (Et2O), IR (neat) 3643, 3340, 3076,
2950, 2932, 2856, 2161, 1978, 1655, 1636, 1579, 1539,
1496, 1449, 1427, 1404, 1392, 1361, 1290, 1239, 1222,
1189, 1163, 1112, 1052, 1031, 1017, 988, 944, 923, 890,
859, 826, 807, 775, 758, 746, 736, 706, 693, 681 cmK1. UV
1
(MeOH) 218 (41800), 281 (24600), 325 (16800), H NMR
(300 MHz, CDCl3) d 3.71 (ABX, JAXZ9.1 Hz, JBX
Z
9.7 Hz, JABZ11.2 Hz, 2H), 3.86 (s, 3H), 5.32 (t, JZ9.5 Hz,
1H), 6.93–6.96 (m, 1H), 7.08 (dd, JZ8.2, 0.93 Hz, 1H),
7.36 (ddd, JZ8.6, 7.3, 1.6 Hz 1H), 7.61 (dd, JZ7.9, 1.5 Hz,
1H), 8.02 (s, 1H), 11.53 (bs, 1H). 13C NMR (75 MHz,
CDCl3) d 35.17, 52.88, 78.47, 116.23, 118.02, 118.68,
119.65, 127.32, 132.47, 147.36, 156.73, 164.82, 169.06,
171.02. SM (ESC) m/z 321 (MCHC, 60), 343 (MCNaC,
100), 641 (2MCHC, 19), 663 (2MCNaC, 83), 694 (9).
Exact mass calcd for C30H31N2O3S2Si (MCHC): 321.0368,
found: 321.0406.
1
(MeOH) 213 (50223), 289 (13000), 308 (12130), H NMR
(300 MHz, CDCl3) d 1.13 (s, 9H), 3.06 (d, JZ5.1 Hz, 3H),
6.55 (dd, JZ7.9, 1.6 Hz, 1H), 6.89–6.99 (m, 2H), 7.36–7.46
(m, 6H), 7.53 (bs, 1H), 7.74–7.77 (m, 4H), 8.19–8.22 (m,
1H), 8.21 (s, 1H). 13C NMR (75 MHz, CDCl3) d 19.38,
26.03, 26.48, 120.52, 121.28, 123.15, 123.38, 128.01,
129.25, 130.16, 130.48, 131.87, 135.30, 149.22, 153.08,
162.15, 162.95. SM (ESC) m/z 473 (MCHC, 50), 495
(MCNaC, 91), 967 (2MCNaC, 100). Anal. Calcd for
C27H28N2O2SSi: C, 68.61; H, 5.97; N, 5.93. Found: C,
68.28; H, 6.22; N, 5.42.
4.1.20. 20-(2-Hydroxyphenyl)-400,500-dihydro-[200,40]bis
thiazolyl-400-carboxylic acid (HPTT-COOH) (4). To a
solution of ester 19 (80 mg, 0.25 mmol) in THF (5 mL) and
water (2 mL) was added powdered LiOH$H2O (24 mg,
0.58 mmol, 2.30 equiv). After two hours of gentle stirring at
room temperature (25 8C) the mixture was diluted with
water (20 mL) and washed with Et2O (20 mL) before being
acidified to pH 2.0 with 0.5 N HCl solution. After
evaporation under reduced pressure, the resulting pale
yellow solid was extracted twice with hot ethanol. The
combined organic layers were dried over Na2SO4, filtered
and evaporated under reduced pressure. The resulting pale
yellow powder was then recrystallised from MeOH yielding
HPTT-COOH 4 (70 mg, yield: 91%) isolated as a light beige
powder. Mp 220 8C (dec), Rf 0.69 (CH2Cl2/iPrOH/HCOOH:
66/33/1). IR (neat) 3514, 3379, 3094, 3028, 1713, 1672,
1616, 1502, 1475, 1394, 1361, 1314, 1292, 1271, 1251,
1224, 1194, 1180, 1165, 1141, 1053, 1036, 1019, 957, 941,
920, 900, 846, 826, 816, 783, 765, 757, 740, 703, 681,
661 cmK1, 1H NMR (300 MHz, CD3SOCD3) d 3.61 (ABX,
JAXZ8.2 Hz, JBXZ9.7 Hz, JABZ11.3 Hz, 2H), 5.29 (dd,
JZ8.2, 9.6 Hz, 1H), 6.95–7.01 (m, 1H), 7.08 (d, JZ8.2 Hz,
1H), 7.34 (ddd, JZ8.4, 7.1, 1.6 Hz 1H), 8.13 (dd, JZ7.9,
1.6 Hz, 1H), 8.31 (s, 1H), 11.20 (bs, 1H), 12.99 (sl, 1H). 13C
NMR (75 MHz, CD3SOCD3) d 34.32, 78.39, 116.46,
118.78, 119.62, 122.04, 127.37, 131.47, 146.78, 155.04,
162.93, 163.76, 171.86. SM (ESK): 305 (MKHC, 100),
611 (2MK2HC, 95).
4.1.18. 20-[2-(t-Butyldiphenylsilyloxy)-phenyl]-400,500-di
hydro-[200,40]bisthiazolyl-400-carboxylic acid methyl
ester (18). To a solution of 17 (330 mg, 0.71 mmol) in
CH2Cl2 (5 mL) cooled to K30 8C, was added pyridine
(218 mL, 215 mg, 2.71 mmol, 3.87 equiv). After 5 mn, Tf2O
(183 mL, 305 mg, 1.08 mmol, 1.55 equiv) was added
dropwise by syringe. The mixture was allowed to warm to
21 8C and stirred gently for 2 h. The resulting orange
solution was cooled down again to K30 8C before pyridine
(218 mL, 215 mg, 2.71 mmol, 3.87 equiv) and O-methyl-
cysteine hydrochloride (186 mg, 1.08 mmol, 1.55 equiv)
were successively introduced. After 15 mn stirring at
K30 8C, the mixture was warmed up to room temperature
and stirred overnight. The mixture was then adsorbed onto
silica gel before being purified by chromatography on a
silica gel column (20 g SiO2, cyclohexane/EtOAc: 8/2)
leading to compound 18 (289 mg, yield: 74%) isolated as an
unstable deliquescent colorless solid. Rf 0.86 (Et2O), IR
(neat) 3073, 2930, 2858, 1742, 1674, 1598, 1577, 1535,
1493, 1472, 1449, 1429, 1391, 1362, 1326, 1289, 1240,
1219, 1197, 1173, 1111, 1049, 1009, 973, 901, 882, 821,
804, 758, 735, 699, 1H NMR (300 MHz, CDCl3) d 1.08 (s,
9H), 3.70 (ABX, JAXZ9.0 Hz, JBXZ9.7 Hz, JAB
Z
11.3 Hz, 2H), 3.86 (s, 3H), 5.36 (t, JZ9.3 Hz, 1H), 6.52
(dd, JZ8.2, 1.1 Hz, 1H), 6.86–6.99 (m, 2H), 7.36–7.48 (m,
4H), 7.75–7.78 (m, 6H), 8.18 (s, 1H), 8.32 (dd, JZ7.9,
2.0 Hz, 1H). 13C NMR (75 MHz, CDCl3) d 14.14, 26.51,
34.95, 52.80, 78.51, 120.27, 121.37, 121.49, 123.12, 128.01,
129.71, 130.13, 130.40, 131.87, 135.32, 147.82, 152.97,
Acknowledgements
We acknowledge the Centre National de la Recherche

G. L. Mislin et al. / Tetrahedron 60 (2004) 12139–12145
12145
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Scientifique (C.N.R.S) and the association Vaincre la
Mucoviscidose for financial support.
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