Stereoselective synthesis of renin inhibitor BILA 2157 BS

Article abstract of DOI:10.1139/v99-233

We have developed a convergent and stereoselective synthesis of orally active renin inhibitor BILA 2157 BS. Three building blocks were used to generate the basic skeleton of the inhibitor. The key feature consisted of the late elaboration of the 2-amino-4-thiazolyl heterocycle from a vinylbromide precursor. The synthetic sequence, which required a total of 22 chemical steps, provided 0.6 kg of BILA 2157 BS in 7.3% overall yield.

Full text of DOI:10.1139/v99-233

739
Stereoselective synthesis of renin inhibitor BILA
2157 BS
Bruno Simoneau, Pierre Lavallée, Murray Bailey, Jean-Simon Duceppe,
Chantal Grand-Maître, Louis Grenier, William W. Ogilvie, Marc-André Poupart,
and Bounkham Thavonekham
Abstract: We have developed a convergent and stereoselective synthesis of orally active renin inhibitor BILA 2157 BS.
Three building blocks were used to generate the basic skeleton of the inhibitor. The key feature consisted of the late
elaboration of the 2-amino-4-thiazolyl heterocycle from a vinylbromide precursor. The synthetic sequence, which
required a total of 22 chemical steps, provided 0.6 kg of BILA 2157 BS in 7.3% overall yield.
Key words: renin, inhibitor, peptidomimetic, stereoselective synthesis.
Résumé: On a développé une synthèse convergente et stéréosélective de BILA 2157 BS, un inhibiteur de la rénine
actif oralement. Trois synthons ont été utilisés pour assembler le squelette de base de l’inhibiteur. L’élaboration tardive
de l’hétérocycle, le 2-amino-4-thiazolyl, à partir d’un précurseur bromovinyl a constitué l’étape clé de l’approche
utilisée. La synthèse, qui a requis un total de 22 transformations chimiques, a fourni 0.6 kg de BILA 2157 BS avec
7.3% de rendement.
Mots clés : rénine, inhibiteur, peptido-mimétique, synthèse stereosélective. Simoneau et al. 748
Introduction
mate model of hypertension. This compound was orally ac-
tive at a dose of 3 mg/kg in conscious sodium depleted
cynomolgus monkeys and possessed an outstanding oral
bioavailability of 40% in cynomolgus monkey. A large
amount of BILA 2157 BS was required for toxicity studies.
We report here an improved synthetic sequence for the prep-
aration of BILA 2157 BS on a 0.6 kg scale.
Renin, an aspartyl protease, catalyzes in the first and rate-
limiting step of the renin–angiotensin cascade (1). Renin
cleaves its substrate angiotensinogen to generate angiotensin
I, a decapeptide, that is in turn processed to angiotensin II
by the angiotensin converting enzyme (ACE). Angiotensin II
is one of the most potent vasoconstrictors known. The suc-
cess of ACE inhibitors in the treatment of hypertension has
been an incentive for the search for other modes of interven-
tion in the same cascade. Considerable efforts were invested
in the search for orally active renin inhibitors (1) and angio-
tensin II antagonists (2). Our own efforts led to the identifi-
cation of BILA 2157 BS, a potent and specific inhibitor of
human renin (3). This inhibitor exhibited IC50 values of 1.4
and 2.7 nM in human plasma renin assays at pH 6.0 and 7.4
respectively. BILA 2157 BS was selected as a candidate for
pre-development based on its high in vivo efficacy in a pri-
Discussion
BILA 2157 BS is a non-peptidic renin inhibitor that con-
tains four stereogenic centers. Three of them are located in
′
the transition state analog moiety (P1-P1) and one is located
on the P2-P3 butanediamide segment. A convergent approach
based on three key fragments was originally used in medici-
nal chemistry to provide the inhibitor in 23 steps and in
about 6% yield overall (Scheme 1). This synthetic approach,
developed for structure-activity relationship studies, was uti-
lized for the preparation of inhibitors on a relatively small
scale (from 100 mg to a few grams).
Received March 12, 1999. Published on the NRC Research
Press website on June 7, 2000.
In the analysis of the original synthesis (3), we realized
that some critical problems had to be considered and solved
for the preparation of hundreds of grams of BILA 2157 BS.
We considered that the fragments A and C (4, 5) could be
amenable to kilogram scale preparation using the existing
synthetic sequences. In contrast, the use of diazomethane in
the preparation of fragment B should preferably be avoided
on large scale. In addition, the use of the rather expensive
chiral oxazolidinone was also a pertinent question although
it provided high diastereoselectivity and could be recycled.
The major drawback of this synthesis was the concomitant
formation of the 2(S)-butanediamide epimer (5 to 10%) in
the coupling of the A-B acid unit to C, which made purifica-
tion of the trichloroethyl carbamate derivative, or BILA
This research article is dedicated with friendship and
admiration to Professor Stephen Hanessian on the occasion
of his 65th birthday.
B. Simoneau,1 P. Lavallée, M. Bailey, J.-S. Duceppe, C.
Grand-Maître, L. Grenier,2 W.W. Ogilvie, M.-A. Poupart,
and B. Thavonekham. Boehringer Ingelheim (Canada) Ltd.,
Bio-Méga Research Division, 2100 Cunard Street, Laval QC
H7S 2G5, Canada.
1Author to whom correspondence may be addressed.
Telephone: (450) 682-4640. Fax: (450) 682-4189.
e-mail: bsimoneau@lav.boehringer-ingelheim.com
2Present address: ProScript, Inc., 38 Sidney Street,
Cambridge, MA 02139, U.S.A.
Can. J. Chem. 78: 739–748 (2000)
© 2000 NRC Canada

740
Can. J. Chem. Vol. 78, 2000
Scheme 1. Original synthesis of BILA 2157 BS.
2157 BS itself, extremely difficult. Since these two com-
pounds were amorphous solids, chromatography was the
only solution for removal of this undesired side product. The
separation and purification could be achieved on a gram
scale but was considered to be impractical on large amounts.
The formation of salts of BILA 2157 BS did not produce
any crystalline salt and was complicated by the presence of
products resulting from N,O-acyl shift of the aminodiol por-
tion (6).3 A potential solution to the problem generated by
the presence of the 2(S)-butanediamide epimer came from
the observations made during the optimization of the P2
side-chain of the inhibitors. During these studies, we real-
ized that neutral side-chains such as cyclopropylmethyl or
thienylmethyl produced very low levels of the undesired
epimer at C-2 of the 4-oxo-4-substituted aminobutanoic ac-
ids. It was therefore decided to delay the introduction of the
2-amino-4-thiazolyl heterocycle until the end of the synthe-
sis while maintaining a convergent approach.
bromovinyl moiety could be easily converted into the corre-
sponding bromoketone with aqueous NBS (7) and finally
into the 2-amino-4-thiazolyl heterocycle with thiourea
(Hantzsch’s synthesis). For reason of expediency, the Evans’
alkylation method was retained for the control of the forma-
tion of the lone stereogenic center of B′. While this ap-
proach was sufficient for the short term and the scale of the
sequence, alternative strategies were examined in parallel to
address the long-term practicality and cost efficiency of in-
stalling this stereogenic center. The new global strategy used
for the preparation of BILA 2157 BS is outlined in
Scheme 2.
Results
Fragment A was prepared using basically the same five-
step synthetic sequence that was used on small scale
(Scheme 3). The first three chemical steps were combined
into a one-pot procedure. Cyclohexanemethylamine was first
alkylated with ethyl 2-bromoacetate in the presence of Et3N
in THF. On a kilogram scale, the reagents were mixed at
As a result of this exercise, we selected synthon B′
(Scheme 2), which had a 2-bromo-2-propenyl substituent in
contrast to the synthon B utilized in the first approach. The
3 For a detailed analysis of N,O-acyl transfer on a related compound, see reference 6.
© 2000 NRC Canada

Simoneau et al.
741
Scheme 2. Retrosynthetic analysis of BILA 2157 BS.
Scheme 3. Synthesis of amine A. Reagents and conditions: (a) (c-C6H11)CH2NH2, Et3N, THF, 25°C then (BOC)2O, 25°C then aq. 2 N
NaOH, 25°C, 70%; (b) (CH3)3CCOCl, Et3N, THF then 2-pyr(CH2)2NHMe, 0 to 15°C; (c) 4 N HCl, dioxane, 25°C, 87% from 2.
–50°C but the reaction occurred smoothly at 25°C. The re-
sulting secondary amine was then transformed into the BOC
derivative by simple addition of (BOC)2O to the reaction
mixture. Finally, aqueous NaOH was introduced to saponify
the ethyl ester. Acid 2 was isolated in 70% yield by a simple
acid-base extraction procedure. The by-products generated
in the course of the three-step sequence consisted of
N-(cyclohexylmethyl)-N-(carboxymethyl)glycine (ca. 5%)
and tert-butyl N-(cyclohexylmethyl)carbamate (ca. 5%). The
former resulted from the double alkylation of cyclohexane-
methylamine by ethyl 2-bromoacetate and subsequent ester
hydrolysis while the second came from reaction of the re-
maining cyclohexanemethylamine with (BOC)2O. Both of
these by-products were easily eliminated in the extractive
work-up. The coupling of commercially available 2-[2-
(methylamino)ethyl]pyridine with the mixed anhydride de-
rived from acid 2 and pivaloyl chloride gave amide 3. After
cleavage of the BOC protective group of 3 with 4 N HCl in
dioxane and neutralization of the resulting hydrochloride
salt, amine A was isolated in 87% yield from acid 2. This
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742
Can. J. Chem. Vol. 78, 2000
Scheme 4. Preparation of fragment B′. Reagents and conditions: (a) LDA, THF, –78°C then CH2=CBrCH2Br, 64%; (b) 4 N HCl,
dioxane, 25°C, 82%; (c) (COCl)2, DMF cat., CH2Cl2, 0 to 25°C, 99%; (d) Lithium 4(S)-((CH3)2CH)-2-oxazolidinone, THF, –78°C;
(e) NaHMDS, THF, –78°C then BrCH2CO2t-Bu, 53% from 6; ( f ) 4 N HCl, dioxane, 25°C, 100%.
sequence produced 1.16 kg of A, a viscous oil, in 60% yield
overall. The crude product was of sufficient purity (>97% by
HPLC) for direct use in the assembly sequence.
having a 2-bromo-1-propenyl side-chain, the coupling of 10
and C should not produce large amounts of the 2(R)-butane-
diamide epimer as had been observed when a protected 2-
amino-4-thiazolylmethyl group was used. In the original
synthetic sequence (Scheme 1), the presence of this epimer
made the purification difficult even on a small scale. We
have therefore investigated many reagents for the coupling
of 10 and C and found, as expected, only a small amount of
the unwanted 2(R)-butanediamide epimer (<1%) in each
case. For convenience, TBTU was selected as the coupling
agent. Starting with 1.4 kg of 10 and 0.70 kg of C, the cou-
pling occurred smoothly with TBTU to give 1. In contrast to
BILA 2157 BS, 1 was crystalline and was purified by
recrystallization to give a 69% yield of highly pure material
(>98%, HPLC). In the process, the small amount of the
2(R)-epimer (ca. 0.5%) was completely removed and the
sole detectable impurity consisted of the corresponding
pyridine N-oxide (0.3%, HPLC). This impurity was probably
formed by oxidation with the peracid intermediate generated
in situ during the cleavage of the chiral auxiliary. In addition
to controlling the amount of the 2(R)-epimer, compound 1,
which had the basic skeleton of BILA 2157 BS, turned out
to be a very valuable crystalline intermediate.
The last requirement for the completion of the synthesis
was the transformation of the vinylbromide moiety present
in 1 into the 2-amino-4-thiazolyl heterocycle. Attempts to
generate the required bromoketone from 1 with aqueous
NBS in the presence of the diol resulted in a complex mix-
ture. The diol was therefore protected using 2-methoxypro-
pene in the presence of PPTS to give acetonide 11 in
quantitative yield.
Using acetonide 11, transformation of the vinylbromide
into bromoketone 12 occurred smoothly with NBS (7, 10) in
aqueous acetonitrile. The rather unstable bromoketone 12
was not isolated. Instead, the small excess of remaining NBS
in the reaction mixture was quenched by the addition of 2-
methoxypropene followed by treatment with thiourea to gen-
erate the 2-amino-4-thiazolyl ring, which was produced as
the hydrobromide salt. Upon heating to complete the hetero-
cycle formation, the HBr catalyzed the concomitant hydroly-
sis of the acetonide to provide BILA 2157 BS. This final
sequence, the formation of the bromoketone, the elaboration
of the heterocycle, and finally the hydrolysis of the acetonide
could be achieved efficiently in a one-pot operation. Using
acid-base extraction procedures and precipitation, BILA
2157 BS was obtained in 93% homogeneity as determined
Fragment B′ was prepared from tert-butyl acetate in six
steps as described in Scheme 4. The lithium enolate of tert-
butyl acetate was first alkylated with 2,3-dibromo-1-propene
at –78°C to provide tert-butyl 4-bromo-4-pentenoate (4) in
64% yield after purification by distillation. Treatment of es-
ter 4 with 4 N HCl in dioxane gave acid 5 in 82% yield. Al-
though it was not used for this particular synthesis, we found
that 5 could also be obtained in three steps (54% yield over-
all) from the alkylation of dimethyl malonate with 2,3-
dibromo-1-propene in the presence of sodium methoxide in
methanol, followed by the usual saponification and
decarboxylation reactions. Acid 5 was then converted into
acyl chloride 6 using oxalyl chloride.
Reaction of crude acyl chloride 6 with the lithium salt of
4(S)-(1-methylethyl)-2-oxazolidinone provided acyl oxazo-
lidinone 7 which was used without any purification in the
Evans’ alkylation reaction (8). The sodium enolate of acyl
oxazolidinone 7 was treated with tert-butyl 2-bromoacetate
to give, after purification by crystallization, 8 in 53% yield
(from acid 5). The diastereomeric excess was greater than
99% as determined by HPLC. The high crystallinity of 8
(the compound crystallized from the reaction mixture as
soon as it was formed) and its ease of preparation facilitated
its use on a scale of hundreds of grams. Finally, the tert-
butyl ester was cleaved using 4 N HCl in dioxane to give
acid B′ in quantitative yield. A total of 1.27 kg of acid B′
was obtained in 28% yield overall from tert-butyl acetate.
Fragment C was prepared from N-BOC-cyclohexylalan-
inol using the five-step procedure described by Abbott scien-
tists (4, 5). The required 0.7 kg of C was obtained in two
batches in 25% overall yield. The cyanohydrin route was
preferred to the one using an osmylation reaction.
The assembly of the three fragments and the transforma-
tion of the bromovinyl moiety into the 2-amino-4-thiazolyl
heterocycle required six steps (Scheme 5). The mixed anhy-
dride generated by the treatment of acid B′ with iso-butyl
chloroformate at –40°C was treated with amine A to give 9.
Cleavage of the chiral auxiliary using LiOOH (9) at 0°C
provided the corresponding acid 10 in 77% yield for the two
steps. Acid 10 was contaminated with a small amount of the
chiral auxiliary (2% w/w), which was not detrimental to the
next step. The coupling of acid 10 and aminodiol C was the
key step of our synthetic strategy. We had envisaged that
© 2000 NRC Canada

Simoneau et al.
743
Scheme 5. Synthesis of BILA 2157 BS. Reagents and conditions: (a) ClCO2i-Bu, Et3N, THF, –40 to 25°C, 100%; (b) LiOOH, THF-
H2O, 0°C, 77%; (c) TBTU, i-Pr2NEt, C, MeCN, 0 to 25°C, 70%; (d) CH2=CMe(OMe), PPTS, CH2Cl2, 25°C; (e) NBS, aq. MeCN,
25°C; (f) thiourea, 25°C to ∆, 50% from 11.
by HPLC. Since the compound could not be purified fur-
ther by conventional extractive or crystallization procedures,
BILA 2157 BS was filtered through a column of silica gel.
A total of 0.59 kg of BILA 2157 BS of high purity (homo-
geneity >99% by HPLC) was obtained for a 50% yield from
1.
distinct chemical steps, a few multi-step one-pot operations
were implemented to generate BILA 2157 BS in 7.3% yield.
Nevertheless, this convergent and stereoselective synthesis
has to be further improved in a cost related fashion for
multikilogram scale. The most important issue concerns the
fragment B′. Alternatives for the use of an expensive chiral
auxiliary and three low temperature operations for its prepa-
ration are needed. Optimization of the reactions transform-
ing key crystalline intermediate 1 into BILA 2157 BS
should also help to facilitate final purification and eliminate
the sole chromatographic purification. Work is well under-
way to improve the 22-step sequence described here and the
results will be described elsewhere.
Conclusions
The original synthetic sequence leading to BILA 2157 BS
was improved in order to generate 0.6 kg of this renin inhib-
itor for preliminary toxicity studies. Three building blocks,
readily accessible from commercially available starting ma-
terials, were used to generate the basic skeleton of the inhib-
itor. The key modification consisted in the late stage
elaboration of the 2-amino-4-thiazolyl heterocycle from a
vinylbromide precursor. This modification allowed us to
eliminate the purification problems due to the formation of
the undesired 2-substituted butanediamide epimer in the
original sequence. A valuable advanced crystalline interme-
diate, compound 1, was also generated as a result of this
strategic decision. While the synthetic sequence required 22
Experimental section
All reactions were performed under a nitrogen atmosphere.
Reagents and anhydrous solvents were obtained from com-
mercial sources and were used without further purification
or treatment. Melting points were determined on an electro-
thermal Büchi 510 apparatus and are uncorrected. NMR
spectra were recorded on a Bruker AMX400 spectrometer.
© 2000 NRC Canada

744
Can. J. Chem. Vol. 78, 2000
Optical rotations were measured on a Perkin–Elmer 241
polarimeter. IR spectra were recorded on a Perkin–Elmer
781. Fast atom bombardment (FAB) mass spectra were de-
termined on a VG AutoSpec-Q or Kratos M550 apparatus at
the Université de Montréal mass spectrometry center.
Microanalyses were performed on a Carlo Erba 1100 or
Fisons EA 1108 instruments. Residual amounts of H2O were
quantified using the Karl Fisher method with a Metrohn 652
KF-coulometer. RP-HPLC analyses were performed on a
Waters 600-MS system (A: SupelcosilTM LC-ABZ; MeCN +
0.1% TFA–H2O + 0.1% TFA) and (or) a Waters 625 system
(B: Nova-PakTM C8 column; MeCN–NaH2PO4 50 mM,
pH 4.4) using a photodiode array detector.
1H NMR): 1H NMR (CDCl3) δ : (3:3:1:1 mixture of
rotamers) 8.60–8.58, 8.54 (m and d, J = 4.5 Hz, 1H), 7.64–
7.60 (m, 1H), 7.26–7.13 (m, 2H), 3.98, 3.90, 3.89, 3.80 (4s,
2H), 3.74–3.68 (m, 2H), 3.12–2.97, 2.93, 2.92 (m and 2s,
7H), 1.73–1.60 (m, 5H), 1.58–1.44 (m, 1H), 1.47, 1.45, 1.41,
1.40 (4s, 9H), 1.28–1.14 (m, 3H), 0.98–0.84 (m, 2H); MS
(FAB) m/z: 390 (MH+). The crude product was used directly
in the next step.
2-[(Cyclohexylmethyl)amino]-N-methyl-N-[2-(2-pyridinyl)ethyl]-
acetamide (A): To an ice-cold solution of crude 3 (2.16 kg,
4.59 mol) in 1,4-dioxane (1.5 L) was slowly added over
75 min a 4 N solution of HCl in 1,4-dioxane (4 L). The light
yellow suspension was stirred at ambient temperature for 3 h
leaving a gummy precipitate at the bottom of the flask. The
solvent was then removed and the precipitate solubilized in
H2O (7 L). The resulting solution was cooled to 0°C, ren-
dered basic with NaOH (550 g), and extracted with ether
(2 × 1.5 L) and EtOAc (3 × 1.5 L). The combined organic
extracts were washed with H2O (1 L), brine (1 L), dried
(Na2SO4), filtered, and concentrated under reduced pressure.
The residue was further dried under reduced pressure
(0.5 mm Hg, 6 h) to afford the amine A as a brownish oil
(1.16 kg, 84% from 2) contaminated with 1,4-dioxane (0.3%
1,1-Dimethylethyl N-(carboxymethyl)-N-(cyclohexylmethyl)car-
bamate (2): To a cold (–50°C) solution of Et3N (1398 g,
13.88 mol) and cyclohexanemethylamine (783 g, 6.91 mol)
in THF (4 L) was added ethyl 2-bromoacetate (1.156 kg,
6.91 mol) over 5 min. The cold bath was removed and after
25 min the mixture was diluted with THF (4 L). Stirring was
maintained for an additional 2.5 h at room temperature. Af-
ter cooling to 10°C, (BOC)2O (1.52 kg, 6.98 mol) was added
at such a rate so as to maintain the internal temperature be-
low 25°C. After 2 h, a solution of NaOH (1.10 kg) in H2O
(4.5 L) was added slowly, followed by MeOH (800 mL), and
the mixture was left stirring overnight. The volatiles were re-
moved under reduced pressure, the oily residue was diluted
with water (8 L), and the mixture washed with hexane (2 ×
4 L). The aqueous solution was acidified with citric acid
(1.27 kg) and extracted with EtOAc (3 × 2 L). The combined
organic extracts were washed successively with 10% citric
acid solution (1 L), water (3 L), and brine (2 L). The solu-
tion was then dried (MgSO4) and concentrated under re-
duced pressure to give acid 2 (1.32 kg, 70%) as a yellow
solid: mp 78.5–80.5°C; IR (KBr) νmax: 3120–2540, 1730,
1690 cm–1; 1H NMR (CDCl3) δ : (1.3:1.0 mixture of
rotamers) 3.97, 3.90 (2s, 2H), 3.11 (broad d, J = 6.4 Hz,
2H), 1.73–1.67 (m, 5H), 1.56–1.47 (m, 1H), 1.47, 1.43 (2s,
9H), 1.27–1.14 (m, 3H), 0.94–0.89 (m, 2H); 13C NMR
(CDCl3) δ : 175.6, 175.1, 156.5, 155.5, 80.5, 80.3, 54.7,
54.5, 49.8, 49.2, 37.1, 36.9, 30.8, 30.7, 28.3, 28.2, 26.4,
25.8; MS (CI) m/z: 272 (MH+). Anal. calcd. for C14H25NO4:
C 61.99, H 9.20, N 5.16; found: C 61.99, H 9.45, N 5.26.
1
w/w determined by H NMR): IR (film) νmax: 3520–3300,
1
1650, 1590 cm–1; H NMR (CDCl3) δ : (1.2:1.0 mixture of
rotamers) 8.46, 8.42 (2 broad d, J = 4.8 Hz, 1H), 7.54–7.49
(m, 1H), 7.12–7.02 (m, 2H), 3.67, 3.58 (2t, J = 7.0 Hz, 2H),
3.24, 3.14 (2s, 2H), 2.93 (t, J = 7.0 Hz, 2H), 2.86, 2.77 (2s,
3H), 2.41 (broad s, 1H), 2.32, 2.18 (2d, J = 6.7 Hz, 2H),
1.70–1.54 (m, 5H), 1.39–1.28 (m, 1H), 1.19–1.03 (m, 3H),
0.88–0.76 (m, 2H); MS (FAB) m/z: 290 (MH+). Anal. calcd.
for C17H27N3O + 4.0% (w/w) H2O (and accounting for 1,4-
dioxane content): C 67.79, H 9.47, N 13.92; found: C 67.69,
H 9.50, N 13.77. RP-HPLC (A) indicated 98.4% homogene-
ity. The material was kept at 4°C, in darkness, and under an
inert atmosphere.
1,1-Dimethylethyl 4-bromo-4-pentenoate (4): A solution of
tert-butyl acetate (581 g, 5.00 mol) in THF (350 mL) was
added dropwise over 45 min to a cold (–78°C) solution of
LDA — prepared at –30°C from n-BuLi (2.5 M in hexanes,
2.20 L, 5.50 mol) and i-Pr2NH (771 mL, 5.50 mol) — in
THF (2.2 L). After stirring at –78°C for 45 min, a solution
of 2,3-dibromopropene (620 mL, 6.00 mol) (filtered on neu-
tral alumina and dried over 4 Å molecular sieves) in THF
(600 mL) was slowly added over 2 h while the temperature
was maintained below –60°C. After 3.5 h, a saturated solu-
tion of NH4Cl (1 L) was added and the mixture was allowed
to warm to room temperature and stirred for an additional
12 h. The reaction mixture was partitioned between ether
(500 mL) and H2O (1.5 L) and the aqueous phase was ex-
tracted with Et2O (2 × 250 mL). The combined organic ex-
tracts were washed with H2O (3 × 100 mL), 2 N HCl
solution (5 × 150 mL), brine (2 × 300 mL), dried (MgSO4
and charcoal), filtered over a pad of Celite®, and concen-
trated under reduced pressure to give a red-brown oil. Distil-
lation of the oily residue using a short Vigreux column
afforded the expected ester 4 as a colorless oil (749 g, 64%),
contaminated with 2% of 2,3-dibromopropene: bp 55–65°C
1,1-Dimethylethyl N-[2-[methyl[2-(2-pyridinyl)ethyl]amino]-
2-oxoethyl]-N-(cyclohexylmethyl)carbamate (3): To an ice-
cold solution of acid 3 (1.31 kg, 4.84 mol) in THF (8 L) was
added Et3N (745 mL, 5.34 mol) over a period of 5 min. The
mixture was stirred until the temperature reached 5°C and
then, trimethylacetyl chloride (565 g, 4.69 mol) was added
dropwise over 45 min. After stirring the pale yellow suspen-
sion at 5–10°C for 1 h, 2-[(2-methylamino)ethyl]pyridine
(625 g, 4.58 mol) was added slowly over 45 min. The mix-
ture was stirred at 15°C for 2.5 h, then diluted with H2O
(4 L) and extracted with EtOAc (7 × 1 L). The combined or-
ganic extracts were washed with saturated NaHCO3 solution
(2 × 1 L), H2O (1 L), brine (2 × 1 L), dried (MgSO4), fil-
tered, and concentrated under reduced pressure. The residue
was further dried under reduced pressure overnight to afford
3 as a viscous liquid (2.16 kg, 121% mass recovery) contain-
ing H2O (1.74% w/w) and EtOAc (2% w/w, determined by
1
at 0.5 mm Hg; IR (film) νmax: 1735, 1635 cm–1; H NMR
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Simoneau et al.
745
(200 MHz, CDCl3) δ : 5.63 (dt, J = 1.7, 1.1 Hz, 1H), 5.43 (d,
J = 1.7 Hz, 1H), 2.72 (t, J = 7.4 Hz, 2H), 2.48 (td, J = 7.4,
1.1 Hz, 2H), 1.45 (s, 9H); MS (CI) m/z: 235/237 (MH+).
Similarly, starting with twice the amount of tert-butyl ace-
tate (1.16 kg, 10.0 mol), 1.63 kg (69%) of 4 was obtained.
tional 15 min at –78°C and for 2.5 h at room temperature.
The mixture was diluted with H2O (4 L) and saturated
NaHCO3 solution (2 L) and extracted with Et2O (4 × 1.5 L).
The combined organic extracts were washed with water (2 ×
800 mL), brine (1.5 L), dried (MgSO4), filtered, and the sol-
vent evaporated under reduced pressure. The residue was
further dried under reduced pressure (0.5 mm Hg, 15 h) to
4-Bromo-4-pentenoic acid (5): A 4 N HCl solution in 1,4-
dioxane (4.8 L, 19.2 mol) was added to ester 4 (1.48 kg,
6.30 mol) while stirring under inert atmosphere. After 18 h
an additional portion of 4 N HCl in 1,4-dioxane (800 mL,
3.20 mol) was introduced. After stirring for an additional
24 h, the solvent was removed under reduced pressure, the
residue was dissolved in Et2O (3 L), and the solution washed
with 2 N NaOH (4 × 1 L). The combined aqueous washings
were acidified with 6 N HCl (1.4 L, 8.4 mol) to pH 2 and
extracted with a 5:1 mixture of Et2O:EtOAc (3 × 1.2 L). The
combined organic extracts were washed with brine (1 L),
dried (MgSO4), filtered, and the solvent evaporated under re-
duced pressure. The residue was co-evaporated with hexane
and dried under reduced pressure to give acid 5 as a tan
solid (919 g, 82%): IR (KBr) νmax: 3130–2900 (broad),
1
afford 7 as a yellow solid (1.42 kg, 98%). H NMR (CDCl3)
δ : 5.66 (broad d, J = 1.7 Hz, 1H), 5.44 (d, J = 1.7 Hz, 1H),
4.42 (ddd, J = 8.3, 3.8, 3.2 Hz, 1H), 4.28 (dd, J = 9.1,
8.3 Hz, 1H), 4.21 (dd, J = 9.1, 3.2 Hz, 1H), 3.29–3.12 (m,
2H), 2.80 (broad t, J = 7.5 Hz, 2H), 2.36 (sept d, J = 7.0,
3.8 Hz, 1H), 0.91 (d, J = 7.0 Hz, 3H), 0.87 (d, J = 7.0 Hz,
3H). The material was used in the subsequent reaction with-
out further purification. Similarly, a second run starting with
532 g of 6 (2.69 mol) produced 710 g of 7 (92%), identical
to the material described above.
3-[4-Bromo-2(S)-[2-(1,1-dimethylethoxy)-2-oxoethyl]-1-oxo-
4-pentenyl]-4(S)-(1-methylethyl)-2-oxazolidinone (8): To
a
cold (–78°C) solution of crude acyl oxazolidinone 7
(1.42 kg, 4.90 mol) in dry THF (3 L) was added dropwise a
1 M solution of NaHMDS in THF (5.5 L, 5.50 mol) over a
2 h period. After stirring mechanically for 1.5 h at –78°C, a
solution of tert-butyl 2-bromoacetate (900 mL, 5.57 mol) in
THF (1 L) was added dropwise over 1.5 h. The mixture was
stirred for an additional 1.5 h and a saturated NaHCO3 solu-
tion (4 L) was introduced. After warming to room tempera-
ture, the THF extract was removed and the aqueous extract
was extracted with EtOAc (2 × 2 L). The combined organic
solutions (THF and EtOAc) were concentrated under re-
duced pressure to give a solid residue which was suspended
in hexane (3 L) and filtered. The material was washed with
H2O (2 × 1 L), hexane (2 × 1.5 L), filtered, and dried under
reduced pressure over P2O5. The solid was dissolved in
CH2Cl2 (3.5 L), the solution was filtered through a
microglass filter, and concentrated under reduced pressure to
a semi-solid mass. After dilution with hexane (3.5 L), the re-
sulting crystals were filtered and dried under reduced pres-
sure to afford 8 as small white needles (1.02 kg, 53%): mp
1
1715, 1635 cm–1; H NMR (CDCl3) δ : 10.57 (broad s, 1H),
5.67 (q, J = 1.0 Hz, 1H), 5.46 (d, J = 1.0 Hz, 1H), 2.78 (t,
J = 7.3 Hz, 2H), 2.66 (td, J = 7.3, 1.0 Hz, 2H); MS
(CI) m/z: 179/181 (MH)+. The product was used directly in
the next step. Alternatively, TFA (490 mL, 6.40 mol) was
added over 60 min to an ice-cold solution of 4 (748 g, 3.18
mol) in CH2Cl2 (1 L). The mixture was stirred at 25°C for
48 h then was concentrated under reduced pressure. The res-
idue was diluted with Et2O (2 L) and the solution was
extracted with aqueous 2 N NaOH (5 × 400 mL). The com-
bined aqueous extracts were rendered acidic with 6 N HCl
(500 mL) and extracted with Et2O (4 × 500 mL). The com-
bined ethereal extracts were washed with H2O (3 × 300 mL)
and brine (300 mL), dried (Na2SO4), filtered, and concen-
trated under reduced pressure. The residue was dissolved in
toluene and concentrated under reduced pressure to give 5
(488 g, 86%) as a yellowish solid: analytical data identical
to those described above.
121–122.5°C; [α]D25 + 49.8° (c 1.28, CHCl3); IR (KBr) νmax
:
4-Bromo-4-pentenoyl chloride (6): To a cold (0°C) solution
of the crude acid 5 (918 g, 5.13 mol) in CH2Cl2 (2.0 L) con-
taining DMF (0.5 mL) was added oxalyl chloride (490 mL,
5.60 mol) over a period of 3 h. After stirring for 18 h at
room temperature, the solvent was removed under reduced
pressure and the residue dried under reduced pressure
(0.5 mm Hg, 1.5 h) to afford crude acyl chloride 6 as a liq-
1
1770, 1735, 1705, 1640 cm–1; H NMR (CDCl3) δ : 5.67
(broad s, 1H), 5.50 (d, J = 1.6 Hz, 1H), 4.51–4.44 (m, 1H),
4.42 (ddd, J = 8.1, 3.8, 3.2 Hz, 1H), 4.27 (dd, J = 9.2,
8.1 Hz, 1H), 4.22 (dd, J = 9.2, 3.2 Hz, 1H), 2.87 (broad dd,
J = 14.5, 6.4 Hz, 1H), 2.73 (dd, J = 16.5, 9.1 Hz, 1H), 2.56
(broad dd, J = 14.5, 7.6 Hz, 1H), 2.52 (dd, J = 16.5, 5.1 Hz,
1H), 2.38 (sept d, J = 7.0, 3.8 Hz, 1H), 1.42 (s, 9H), 0.93 (d,
J = 7.0 Hz, 3H), 0.91 (d, J = 7.0 Hz, 3H); 13C NMR
(CDCl3) δ : 173.9, 170.4, 153.5, 129.9, 119.8, 80.8, 63.3,
58.8, 42.4, 38.5, 36.5, 28.2, 28.0, 18.4, 14.6; MS (FAB) m/z:
404/406 (MH+). Anal. calcd. for C17H26NO5Br: C 50.50, H
6.48, N 3.46; found: C 50.20, H 6.50, N 3.49. The
diastereomeric purity was found to be >99% when assessed
by HPLC using a chiral column (CHIRALPAK® AS, Daicel
Chem. Co.; 0.5% EtOH in hexane). A second run starting
with 707 g (2.44 mol) of 7 yielded 514 g (52%) of 8.
1
uid (1003 g, 99%): H NMR (CDCl3) δ : 5.71 (broad d, J =
1.9 Hz, 1H), 5.51 (d, J = 1.9 Hz, 1H), 3.19 (t, J = 7.2 Hz,
2H), 2.82 (broad t, J = 7.2 Hz, 2H). The material was used
directly in the next step. Similarly, a second run starting with
about half the quantity of 5 (487 g, 2.72 mol) gave 533 g of
6 (99%), identical to the material obtained above.
3-(4-Bromo-1-oxo-4-pentenyl)-4(S)-(1-methylethyl)-2-oxa-
zolidinone (7): To a cold (–78°C) solution of 4(S)-(1-
methylethyl)-2-oxazolidinone (642 g, 4.97 mol) and Ph3CH
(300 mg, as indicator) in dry THF (9 L) was added dropwise
n-BuLi (2.5 M in hexanes, 2.05 L, 5.12 mol) until a pink
color appeared. After stirring the suspension for 1 h, crude
acyl chloride 6 (1001 g, 5.07 mol) was added via cannula
over a 1.5 h period. Stirring was maintained for an addi-
3-[4-Bromo-2(S)-(carboxymethyl)-1-oxo-4-pentenyl]-4(S)-
(1-methylethyl)-2-oxazolidinone (B′): Ester 8 (1.48 kg, 3.67
mol) was dissolved in 4 N HCl 1,4-dioxane (8.8 L, 35.2
mol) and the solution was stirred at room temperature for
© 2000 NRC Canada

746
Can. J. Chem. Vol. 78, 2000
20 h. The yellow solution was concentrated to half volume
by partial evaporation of the solvent under reduced pressure
and then poured into water (40 L). The white solid formed
was filtered and re-dissolved in Et2O (10 L). The solution
was washed with brine (3 × 1 L), treated with anhydrous
MgSO4 and charcoal, and filtered through a pad of Celite®.
The pale yellow filtrate was concentrated under reduced
pressure to give a white solid which, after drying under re-
duced pressure for 3 h, afforded B′ as an amorphous product
(1.27 kg, 100% mass recovery, containing 2.47% w/w of
1,4-dioxane): mp 124–125°C; 1H NMR (CDCl3) δ : 5.70
(broad s, 1H), 5.54 (d, J = 1.6 Hz, 1H), 4.54–4.48 (m, 1H),
4.43 (ddd, J = 7.9, 3.5, 3.2 Hz, 1H), 4.30–4.22 (m, 2H),
2.89 (dd, J = 17.4, 10.2 Hz, 1H), 2.86 (dd, J = 14.1, 5.1 Hz,
1H), 2.64 (dd, J = 17.4, 4.3 Hz, 1H), 2.53 (dd, J = 14.1,
8.6 Hz, 1H), 2.37 (sept d, J = 7.0, 3.5 Hz, 1H), 0.91 (d, J =
7.0 Hz, 3H), 0.89 (d, J = 7.0 Hz, 3H); MS (FAB) m/z:
348/350 (M+). Anal. calcd. for C13H18NO5Br (+ 2.47% w/w
1,4-dioxane): C 45.08, H 5.32, N 3.92; found: C 45.15, H
5.69, N 3.62.
concentrated under reduced pressure to remove the THF.
The aqueous extract was extracted with EtOAc (6 × 1 L) and
the combined organic extracts were extracted with saturated
NaHCO3 (8 × 500 mL). The combined aqueous extracts con-
taining the carboxylic acid sodium salt were extracted manu-
ally with ether (7 × 750 mL) and then submitted to
continuous extraction with Et2O (4 L) for 17 h. All the or-
ganic extracts were combined and evaporated to dryness al-
lowing recovery of the chiral auxiliary. The aqueous extracts
were acidified with solid citric acid to pH 3 and extracted
with EtOAc (4 × 1 L). The combined organic extracts were
washed with brine (2 × 600 mL), treated with anhydrous
MgSO4 and charcoal, filtered through Celite®, and concen-
trated under reduced pressure. The resulting gummy residue
was further dried at 45°C under reduced pressure for 8 h to
afford acid 10 as a yellow glassy solid (1.51 kg, 77%) con-
taminated with EtOAc (2.5% w/w) and residual chiral auxil-
1
iary (2.5% w/w): H NMR (CDCl3) δ : 10.00 (broad s, 1H),
8.62, 8.58, 8.55, 8.53 (4d, J = 4.4, 4.8, 5.1, 5 Hz, 1H), 7.73–
7.66 (m, 1H), 7.33–7.17 (m, 2H), 5.74, 5.69, 5.63 (3s, 1H),
5.50, 5.47, 5.45 (3 broad s, 1H), 4.09–3.85 (m, 2H), 3.77–
3.60 (m, 2H), 3.25–3.04 (m, 5H), 2.98, 2.97, 2.94, 2.90 (4s,
3H), 2.99–2.88, 2.74–2.67 and 2.51–2.30 (m, 4H), 1.76–1.44
(m, 6H), 1.27–1.13 (m, 3H), 0.95–0.85 (m, 2H); MS
(FAB) m/z: 508/510 (MH+). Homogeneity was determined
to be 97.8% (chiral auxiliary not detected by UV) by RP-
HPLC (A). This acid (10) was used directly in the subse-
quent reaction.
3-[4-Bromo-2(S)-[2-[(cyclohexylmethyl)[2-[methyl[2-(2-py-
ridinyl)ethyl]amino]-2-oxoethyl]amino]-2-oxoethyl]-1-oxo-
4-pentenyl]-4(S)-(1-methylethyl)-2-oxazolidinone (9): Et3N
(1.02 L, 7.30 mol) was added in one portion to a solution of
B′ (1.27 kg, 3.65 mol) in dry THF (5 L). The mixture was
cooled to –45°C and iso-butyl chloroformate (497 mL, 3.83
mol) was added dropwise over a 30 min period while main-
taining the temperature below –40°C. After stirring for
30 min, a solution of amine A (1.16 kg, 3.99 mol, 1.1 equiv.)
in dry THF (2 L) was added dropwise over 45 min and the
resulting mixture was stirred at room temperature for 2.5 h.
H2O (7 L) was added and the mixture was extracted with
EtOAc (6 × 1 L). The combined organic extracts were
washed successively with a 10% citric acid solution (6 ×
500 mL), H2O (2 × 1 L), saturated NaHCO3 solution (3 ×
1 L), and brine (2 × 1 L). The solution was treated with an-
hydrous MgSO4 and charcoal, filtered through a pad of
Celite®, and concentrated under reduced pressure to give
amide 9 as a yellow gum (2.27 kg, 100%): 1H NMR
(CDCl3) δ : (3:3:1:1 mixture of rotamers) 8.61, 8.55, 8.51
(3d, J = 4.1, 4.8, 3.8 Hz, 1H), 7.68–7.58 (m, 1H), 7.24–7.11
(m, 2H), 5.72, 5.67, 5.64 (3s, 1H), 5.52, 5.51, 5.48, 5.46 (4d,
J = 1.6, 1.3, 1.3, 1.6 Hz, 1H), 4.57–4.47 (m, 1H), 4.45–4.40
(m, 1H), 4.28–4.17 (m, 2H), 4.17–3.68 (m, 4H), 3.50–3.30
and 3.19–2.83 (m, 5H), 2.97, 2.95, 2.90, 2.87 (4s, 3H),
2.75–2.54 (m, 2H), 2.43–2.36 (m, 1H), 2.15–2.07 (m, 1H),
1.76–1.45 (m, 6H), 1.29–1.15 (m, 3H), 0.95–0.85 (m, 8H);
MS (FAB) m/z: 619/621 (MH+). The material was used di-
rectly in the subsequent reaction.
N4-(Cyclohexylmethyl)-N4-[2-[methyl[2-(2-pyridinyl)ethyl]amino]-
2-oxoethyl]-N1-[1(S)-(cyclohexylmethyl)-2(R),3(S)-dihydroxy-
5-methylhexyl]-2(S)-(2-bromo-2-propenyl)butanediamide (1):
A mixture of acid 10 (1394 g, 2.74 mol), aminodiol C
(704.5 g, 2.89 mol), and TBTU (880.4 g, 2.74 mol, 1 equiv.)
was dissolved in MeCN (7 L) and cooled to 0–5°C under an
inert atmosphere before i-Pr2NEt (1433 mL, 8.23 mol) was
added portionwise over a 15 min period raising the tempera-
ture to 15°C. The bath was removed and the mixture was
stirred at room temperature for 2 h. Water (8 L) was added
and the mixture was extracted with EtOAc (6 × 650 mL).
The combined organic extracts were washed successively
with 10% citric acid solution (6 × 1 L), water (6 × 1 L), sat-
urated NaHCO3 solution (4 × 1 L), and brine (2 × 1 L). The
organic solution was treated with anhydrous MgSO4 and
charcoal, and filtered through a pad of Celite®. The solution
was filtered twice through a pad of silica gel and washed
with EtOAc (2 × 5 L). The combined organic filtrates were
concentrated under reduced pressure to give a 6 L solution
which was left at room temperature overnight to allow crys-
tallization. The solid was filtered, washed with hexane (3 ×
1 L), and dried overnight under reduced pressure to afford a
first crop of 1 as white micro-needles (1.20 kg, 59.9%): mp
2(S)-(2-Bromo-2-propenyl)-4-[(cyclohexylmethyl)[2-[methyl[2-
(2-pyridinyl)ethyl]amino]-2-oxo-ethyl]amino]-4-oxobutanoic acid
(10): To a mechanically stirred solution of the crude tertiary
amide 9 (2269 g, 3.65 mol) in a 6:1 THF:H2O mixture
(16 L) cooled to 0°C, was added a 30% H2O2 solution
(2042 mL, 18.31 mol). After 10 min, LiOH•H2O (384 g,
9.16 mol) was added and the mixture was stirred vigorously
for 40 min. A Na2SO3 solution (2552 g in 5.7 L of H2O) was
slowly added over 40 min while keeping the temperature be-
low 25°C. After stirring for an additional 15 min to ensure
complete neutralization of the peroxide, the solution was
1
139–141°C; H NMR (DMSO-d6) δ : (1.7:1.0:1.0 mixture of
rotamers) 8.54–8.51, 8.48 (m and d, J = 4.8 Hz, 1H), 7.75–
7.67 (m, 2H), 7.33–7.19 (m, 2H), 5.77, 5.71, 5.68 (3s, 1H),
5.42, 5.40, 5.38 (s and 2d, J = 1.5, 1.5 Hz, 1H), 4.61
(broad s, 1H), 4.51 (broad s, 1H), 4.21–3.88 (m, 3H), 3.70–
3.54 (m, 2H), 3.10–2.85, 2.84, 2.80 (m and 2 s, 10H), 2.70–
2.65 (1H), 2.52–2.05 (m, 3H), 1.76–1.10 (m, 23H), 0.92–
0.70 (m, 4H), 0.86 (d, J = 6.6 Hz, 3H), 0.79 (d, J = 6.6 Hz,
3H); MS (FAB) m/z: 733/735 (MH+). Anal. calcd. for
© 2000 NRC Canada

Simoneau et al.
747
C38H61N4O5Br: C 62.20, H 8.38, N 7.63; found: C 61.54, H
8.48, N 7.66. Homogeneity was determined to be 98.6% by
RP-HPLC (A), with 0.3% of the corresponding pyridine
N-oxide derivative. This first crop of 1 was used directly in
the subsequent reaction sequence leading to BILA 2157 BS.
Concentration of the mother liquors under reduced pres-
sure gave a solid residue that was filtered and washed suc-
cessively with a 1:1 EtOAc–hexane mixture (2 L) and then
hexane (3 L). The solid was dissolved in hot EtOAc (1 L),
the solution was filtered through Celite®, and stored at 0–5°C
overnight. The crystalline white solid was filtered, washed
with hexane, and dried under reduced pressure to afford an
impure crop of intermediate 1 (281 g): mp 132–133°C.
RP-HPLC (A) indicated 92% homogeneity. The solid was
dissolved in EtOAc (3 L) and the resulting solution was fil-
tered twice through a pad of silica gel and washed with
EtOAc (2 × 600 mL). The combined organic filtrates were
concentrated under reduced pressure to give a 1 L solution
which was left at room temperature overnight to allow crys-
tallization. The solid was filtered, washed with hexane, and
dried over P2O5 under reduced pressure to afford a second
crop of 1 as a white powder (189 g, 9.5%): mp 140–142°C;
[α]2D5 –27.1° (c 1.03, MeOH); IR (KBr) νmax: 3450, 3280,
1655, 1630 cm–1; 1H NMR and MS identical to those of first
crop of 1. Anal. calcd. for C38H61N4O5Br: C 61.82, H 8.38,
N 7.63; found: C 61.82, H 8.44, N 7.63. RP-HPLC (A) indi-
cated 99.2% homogeneity.
with charcoal, filtered through a pad of Celite®, and brought
to pH 9 by addition of solid NaOH (290 g). The mixture was
extracted with CHCl3 (3 × 2 L) and the combined organic
extracts were washed with H2O (3 × 1.5 L) and brine (2 ×
1 L). The solution was filtered through a pad of silica gel
(G-60, 500 g) and the pad was washed with CHCl3
(500 mL). The combined filtrate and washing solutions were
evaporated under reduced pressure to give 930 g of crude
BILA 2157 BS (93% homogeneity by RP-HPLC, A). This
crude product was purified in 6 portions by flash chromatog-
raphy (silica gel G-60, 6 kg) using a gradient of MeOH in
EtOAc (5 to 20%) as eluent. Following RP-HPLC analysis,
fractions containing pure product were combined and the
solvent was evaporated to dryness. The residue (603.6 g)
was dissolved in EtOAc (2 L) and the solution was filtered
through a microfiber filter. After evaporation of the solvent,
the residue was co-evaporated with MeOH (2 × 1.5 L) and
then dissolved in MeOH (700 mL). The brown solution was
added dropwise over a 1 h period to a mixture of water
(30 L) and ice (5 L) under vigorous mechanical stirring. The
resulting precipitate was filtered, air dried overnight, and
then dried under reduced pressure for 48 h to afford BILA
2157 BS as an off-white amorphous solid (518 g, 44%): mp
92–97°C; [α]2D5 –26.0° (c 1.02, MeOH); IR (KBr) νmax
:
3600–3040, 1645 (broad) cm–1; 1H NMR (DMSO-d6) δ :
(1:1:1:1 mixture of rotamers) 8.54–8.51, 8.48 (m and d, J =
4.8 Hz, 1H), 7.75–7.67 (m, 1H), 7.59, 7.56, 7.53 (3d, J =
9.0, 9.9, 9.6 Hz, 1H), 7.33–7.19 (m, 2H), 6.77, 6.73 (2s,
2H), 6.18, 6.17, 6.10, 6.06 (4s, 1H), 4.64–4.61, 4.59, 4.56
(m and 2d, J = 6.6, 6.6 Hz, 2H), 4.18, 4.17, 4.11, 4.09–4.01,
3.88, 3.85 (3d, m and 2d, J = 17.8, 16.2, 16.5, 17.8,
16.2 Hz, 3H), 3.69–3.51 (m, 2H), 3.10–2.80 (m, 7H), 2.90,
2.89, 2.83, 2.80 (4s, 3H), 2.74–2.62 (m, 1H), 2.51–2.32,
2.24, 2.14, 2.02 (m and 3dd, J = 15.8, 7.8 Hz, J = 16.1,
5.7 Hz, J = 15.8, 5.7 Hz, 3H), 1.78–1.05 (m, 23H), 0.90–
0.69 (m, 4H), 0.86 (d, J = 6.9, 3H), 0.77 (d, J = 6.6 Hz,
3H); MS (FAB) m/z: 727 (MH+). Anal. calcd. for
C39H62N6O5S + 1.53% (w/w) H2O: C 63.45, H 8.63, N
11.39; found: C 63.03, H 8.64, N 11.31. RP-HPLC analysis
indicated homogeneities of 99.9% (A) and 99.6% (B). An
additional amount of BILA 2157 BS (73.0 g, 6%) was ob-
tained after purification by flash chromatography of the mixed
N4-(Cyclohexylmethyl)-N4-[2-[methyl[2-(2-pyridinyl)ethyl]-
amino]-2-oxoethyl]-N1-[1(S)-(cyclohexylmethyl)-2(R),3(S)-dihy-
droxy-5-methylhexyl]-2(R)-[(2-amino-4-thiazolyl)methyl]butan-
ediamide (BILA 2157 BS): To a solution of butanediamide
intermediate 1 (1.20 kg, 1.63 mol) in CH2Cl2 (6.5 L), was
added 2-methoxypropene (783 mL, 8.18 mol) followed by a
catalytic amount of PPTS (41.0 g, 163 mmol). The mixture
was stirred at room temperature for 15 h. The solvent was
evaporated under reduced pressure and the residue was co-
evaporated with Et2O (3 × 1 L). The oily residue was dis-
solved in EtOAc (2.5 L) and washed successively with H2O
(2 × 500 mL) and saturated NaHCO3 solution (2 × 500 mL).
The solution was treated with anhydrous MgSO4 and char-
coal, and filtered through a pad of Celite®. The filtrate was
concentrated under reduced pressure to afford the corre-
sponding crude acetonide derivative 11 as a yellow gum
(1.35 kg, 107% mass recovery). RP-HPLC (B) analysis indi-
cated homogeneity of 94%. The crude product was used im-
mediately in the subsequent reaction.
1
fractions: mp 88–94°C; [α]2D5 –25.5° (c 1.03, MeOH); IR, H
NMR and MS identical to those described above. Anal. calcd.
for C39H62N6O5S + 0.78% (w/w) H2O: C 63.93, H 8.62, N
11.47; found: C 63.96, H 9.02, N 11.29. RP-HPLC analysis
indicated homogeneities of 99.9% (A) and 99.6% (B).
To a solution of crude acetonide 11 (1.35 kg, 1.63 mol) in
a mixture of MeCN (12 L) and H2O (3 L) protected from
light, was added NBS (349 g, 1.96 mol) in two portions at
10 min intervals. The mixture was stirred for 50 min and
treated with 2-methoxypropene (31.0 mL, 0.33 mol) to neu-
tralize the excess NBS. After 5 min, thiourea (156 g, 2.04
mol) was added in one portion. After 15 min, the mixture
was heated to 60–65°C under reduced pressure to distill off
5 L of MeCN while completing the hydrolysis of the
acetonide (4.5 h). Water (4 L) was then added and the mix-
ture was left stirring at room temperature overnight. The re-
maining MeCN was removed under reduced pressure and the
solution was washed successively with TBME (8 × 2 L),
EtOAc (8 × 2 L), and CH2Cl2 (8 × 2 L). The aqueous solu-
tion containing BILA 2157 BS as its HBr salt was treated
Acknowledgements
The authors would like to thank Dr. Karl Grozinger and
Dr. John Landi of Boehringer Ingelheim Pharmaceuticals
Inc. for the preparation of the N-BOC derivative of amine C,
and Colette Boucher, Sylvain Bordeleau and Serge Valois
for analytical support.
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