Development of a kilogram-scale synthesis of cis-LC15-0133 tartrate, a potent dipeptidyl peptidase IV inhibitor

Article abstract of DOI:10.1021/op800076r

(45)-N-Boc-4-fluoro-L-proline methyl ester (4) was prepared from the following sequence of reactions: esterification of trans-4-hydroxy-L-proline (2), Boc protection, and fluorination by DAST. Reaction of 4 with lithiated oxadiazole provided oxadiazolyl ketone 7. Deprotection of the Boc group of 7 and subsequent coupling with bromoacetyl bromide gave bromide 9. Coupling reaction of 9 with excess oxazolidine 16 provided coupled product 17. Unexpectedly, the stereogenic center of 17 was completely epimerized to a virtually 1:1 mixture of cis- and trans-17 at this stage. After the deprotection of the N,O-methylene acetal group of 17 using aqueous ammonium chloride, crystallization induced dynamic resolution (CIDR) of cis- and Awns-mixture of LC15-0133 (1) in the course of tartrate salt formation provided cis-LC15-0133 (1a) tartrate salt in 83% yield (>98% de).

Full text of DOI:10.1021/op800076r

Organic Process Research & Development 2008, 12, 626–631
Development of a Kilogram-Scale Synthesis of cis-LC15-0133 Tartrate, a Potent
Dipeptidyl Peptidase IV Inhibitor
Bong Chan Kim, Kyu-Young Kim, Hee Bong Lee,* and Hyunik Shin*
Chemical DeVelopment DiVision, LG Life Sciences, Ltd/ R&D Park, 104-1 Moonji-dong, Yusung-gu, Daejeon 305-380, Korea
Abstract:
(4S)-N-Boc-4-fluoro-
the following sequence of reactions: esterification of trans-4-
hydroxy- -proline (2), Boc protection, and fluorination by DAST.
L-proline methyl ester (4) was prepared from
L
Figure 1
Reaction of 4 with lithiated oxadiazole provided oxadiazolyl ketone
7. Deprotection of the Boc group of 7 and subsequent coupling
with bromoacetyl bromide gave bromide 9. Coupling reaction of
9 with excess oxazolidine 16 provided coupled product 17.
Unexpectedly, the stereogenic center of 17 was completely epimer-
ized to a virtually 1:1 mixture of cis- and trans-17 at this stage.
After the deprotection of the N,O-methylene acetal group of 17
using aqueous ammonium chloride, crystallization induced dynamic
resolution (CIDR) of cis- and trans-mixture of LC15-0133 (1) in
the course of tartrate salt formation provided cis-LC15-0133 (1a)
tartrate salt in 83% yield (>98% de).
Scheme 1. Medicinal chemistry route
Introduction
Type 2 diabetes (formerly noninsulin-dependent diabetes)
is a severe and increasingly prevalent disease.1 Diabetics may
suffer debilitating cardiovascular, eye, kidney, and nerve
damage, which are the result of glucose toxicity caused by their
hyperglycemia. A progressive reduction in insulin sensitivity
and insulin secretion are features of the disease, which eventu-
ally result in failure of the pancreatic islet cells and dependence
on exogenous insulin. The hormone glucagon-like peptide 1
(GLP-1) is a potent stimulator of endogenous insulin release.
GLP-1 has beneficial effects on islet ꢀ-cell function and insulin
sensitivity without induction of hypoglycemia.2 Unfortunately,
GLP-1 is rapidly degraded in vivo. Therefore, inhibition of
GLP-1 degradation by dipeptidyl peptidase IV (DPP-IV) has
emerged as a promising approach for the treatment of type 2
diabetes3 and has been aggressively pursued by numerous
laboratories. We are also involved in the discovery of potent
DPP-IV inhibitors, among which LC15-0133 (1) was chosen
as a development candidate on the basis of its potent activity
(Figure 1).4 Herein, we report an efficient and scalable synthesis
toward cis-LC15-0133 (1a) tartrate salt.
Result and Discussions
The medicinal chemistry route towards LC15-0133 (1) as
illustrated in Scheme 1 needs a couple of improvements for a
large-scale preparation, i.e. (1) increase of the moderate yields
of Weinreb amide formation and the preparation of oxadiazolyl
ketone 7 and (2) minimization of the side product 10 in the
* Author to whom correspondence may be sent. E-mail: hisin@lgls.com.
(1) Fact Sheet No. 138; World Health Organization: Geneva, 2002.
(2) Knudsen, L. B. J. Med. Chem. 2004, 47, 4128–4134.
(3) (a) Mest, H.-J.; Mentlein, R. Diabetologia 2005, 48, 616–620. (b)
Weber, A. E. J. Med. Chem. 2004, 47, 4135–4141. (c) Drucker, D. J.
Expert Opin. InVest. Drugs 2003, 12, 87–100. (d) Augustyns, K.; Van
der Veken, P.; Senten, K.; Haemers, A. Expert Opin. Ther. Pat. 2003,
13, 499–510.
(4) (a) Lee, C.-S.; Koo, K. D.; Koh, J. S.; Kim, S.; Kim, D.-M.; Kim,
M.-J.; Kim, B. C.; Yoon, S. K.; Kim, S.; Yim, H. J.; Hur, G.-C.; Lee,
S. H.; Han, H. O.; Kim, K.-H.; Kim, G. T.; Kwon, O. H.; Kwon,
T.-S.; Lee, H. B.; Chung, H. K.; Kim, M.; Lim, D.; Kim, Y. C.; Kim,
S. PCT Int. Appl. WO2005037828, 2005. (b) Koo, K. D.; Kim, M. J.;
Kim, S.; Kim, K.-H.; Kong, S. Y.; Hur, G.-C.; Yim, H. J.; Kim, G. T.;
Han, H. O.; Kwon, O. H.; Kwon, T. S.; Koh, J. S.; Lee, C.-S. Bioorg.
Med. Chem. Lett. 2007, 17, 4167.
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10.1021/op800076r CCC: $40.75
2008 American Chemical Society
Published on Web 06/04/2008

Scheme 2. Direct conversion of 4 to 7
Scheme 3. Synthesis of LC15-0133 (1)
coupling of 8 with 9. In addition to those, unambiguous
determination of the chemical identity of 1 became a critical
issue in the later stage of chemical development because,
contrary to the belief that 1 would be a single diastereomer, it
turned out to be a mixture of cis- (1a) and trans-isomer (1b)
reflecting significant epimerization of the C-2 stereogenic center
in the course of the synthesis. Therefore, preparation of the
desired cis-LC15-0133 (1a) was urgently required for further
development.
product 13 with incomplete conversion. In contrast, use of
lithiated anion itself afforded desired ketone 7 in moderate
yield of 50-60% along with starting material and the tert-
alcohol 13 when the reaction temperature was raised up to
0 °C. After considerable experimentation, we found that the
optimal reaction temperature should be within the range of
-45 to -30 °C for the minimal formation of the side product
13, thus increasing the yield to 70%. As temperature was
raised above -20 °C, the chelated complex rapidly collapsed
to give ketone 7, which was immediately reacted with excess
lithiated oxadiazole (2.2 equiv) to lead to significant forma-
tion of the tertiary alcohol 13. After an extractive workup,
crude ketone 7 was readily solidified by triturating with
n-hexane in 67% yield contaminated with less than 5% of
trans-4-Hydroxy-L-proline (2) was converted to its methyl
ester under Fisher esterification conditions, which reacted with
Boc2O in the presence of triethylamine at ambient temperature
to provide the N-Boc proline ester 3 as a white solid in good
yield (82%). Fluorination under Middleton’s protocol5 using
(diethylamino)sulfur trifluoride (DAST, 1.1-1.2 equiv at -78
°C) provided fluoride 4 in 70% yield. Quick optimization
revealed that the reaction could also be executed at 0 °C and
the use of excess of DAST (1.9 equiv) could increase the yield
to 85% along with ∼5% of elimination byproduct. In the
medicinal chemical approach, the introduction of the oxadiazolyl
moiety6 to 4 was accomplished via a sequence of reactions:
(1) hydrolysis of the ester group of 4, (2) Weinreb amide
formation, and (3) addition of lithiated oxadiazole 6 in the
presence of MgBr2 ·OEt2. Since the overall yield of these steps
was ∼30-40%, it became imperative to increase the yield for
a large-scale preparation. To this end, we considered the
direct use of the ester functionality of 4 for the introduction
of the oxadiazolyl group on assumption that the hetero-
atoms of the oxadiazole fragment would play a similar role
as those of the Weinreb amide 11 in the stabilization of
tetrahedral intermediate 12 via chelation (Scheme 2). Initial
attempts for this assumption turned out to be disappointing:
Grignard-type oxadiazole anion7 generated from lithiated
oxadiazole in the presence of MgBr2 · OEt2 led to more side
1
13 by H NMR analysis.
Boc deprotection of 7 was carried out under typical reaction
conditions using anhydrous HCl to give the amine salt 14 in
excellent yield (Scheme 3). At the stage of bromoacetylation
of 14, the addition sequence of two reagents, bromoacetyl
bromide and triethylamine is very critical: attempted neutraliza-
tion of 14 by triethylamine instantly formed pyrrole 15 as a
major side product, whereas dropwise addition of triethylamine
to a stirred mixture of bromoacetyl bromide and 14 in CH2Cl2
at 0 °C afforded desired bromide 9 without any formation of
the byproduct 15 in good yield (85% in two steps overall).
According to the medicinal chemical route, the coupling of
bromide 9 with 2-amino-2-methyl-1-propanol (8) in CH2Cl2
provided a substantial amount of the intramolecular cyclized
byproduct 10 (Table 1, entry 2). To minimize this side reaction,
the influence of solvents and nucleophiles such as 16, 8, and
18 were tested, and the results are outlined in Table 1. In general,
the coupling reaction using 8 as a nucleophile in various solvents
(entries 1-5) proceeded rapidly to give the desired adduct 1
and a substantial amount of 10 with complete conversion within
1.0 h. Among the tested solvents, CH2Cl2 and EtOAc (entries
2 and 3) were marginally better than the rest. Change of the
(5) Middleton, W. J. J. Org. Chem. 1975, 40, 574.
(6) Ohmoto, K.; Yamamoto, T.; Horiuchi, T.; Kojima, T.; Hachiya, K.;
Hashimoto, S.; Kawamura, M.; Nakai, H.; Toda, M. Synlett 2001, 299.
(7) Ohmoto, K.; Yamamoto, T.; Okuma, M.; Horiuchi, T.; Imanishi, H.;
Odagaki, Y.; Kawabata, K.; Sekioka, T.; Hirota, Y.; Matsuoka, S.;
Nakai, H.; Toda, M. J. Med. Chem. 2001, 44, 1268.
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Table 1. Effect of solvent polarity and nucleophiles on the
coupling reaction
Scheme 4. Synthesis of trans-LC15-0133 (1b) ·HCl salt
At this stage, we carefully analyzed LC15-0133 (1) by HPLC
and unfortunately found that it was a virtually 1:1 mixture of
cis- and trans-diastereomers. Quick retrospective investigation
on the cause of this outcome was undertaken, and we found
that the epimerization at the carbonyl group-bearing stereogenic
center occurred in the coupling reaction of bromide 9 with 16.
To prove unequivocally the analytical HPLC and TLC results,10
independent syntheses of cis-LC15-0133 (1a) and trans-isomer
1b were carried out as in Scheme 4. Epimerization of cis-ketone
7 in the presence of 2.0 equiv of triethylamine over 12 h gave
an almost 1:1 diastereomeric mixture of 7, the diastereomers
of which were readily separated by column chromatography.
To avoid epimerization in the coupling with amine 18, the
ketone group of trans-7 was reduced and the formed hydroxyl
group was protected as acetate, which was transformed to 19
via deprotection of the Boc group and coupling with bro-
moacetyl bromide. Subsequent coupling of 19 with 18 pro-
ceeded smoothly to afford the coupled product, the amine group
of which was reacted with Boc2O in the presence of DMAP to
give 20. Deprotection of the acetyl group of 20 followed by
Dess-Martin oxidation gave N-Boc-, O-TBS-protected trans-
LC15-0133 (1b). Simultaneous deprotection of the Boc and the
TBS groups under acidic conditions gave trans-LC15-0133
(1b)·HCl salt. In the same manner, cis-LC15-0133 (1a)·HCl
a Yield was based on area % of HPLC. b 3.0 equiv of oxazolidine was used,
and 35% of starting bromide remained. c 6.0 equiv of oxazolidine was used.
nucleophile to TBS-protected aminoalcohol 18 led to significant
reduction of the side product 10 (entries 6 and 7) with
concomitant slow-down of the reaction rate. Use of the
oxazolidine 168 showed retarded reaction rate as well, compared
to that of 8 and 18: the starting bromide 8 was not completely
consumed in 24 h even with 3 equiv of 16 (entry 8). However,
although the reaction rate was retarded significantly, the side
product 10 was also dramatically reduced to 3.0% (entries 8
and 9). Therefore, we chose 16 as the optimal nucleophilic
partner, and after extensive experimentations, optimal conditions
were determined to use 6.0 equiv of oxazolidine 16 in
dichloroethane at ambient temperature in which 80% of
coupling product 17 was obtained along with only 3.5% of 10
(entry 9).
Next, the deprotection of N,O-methylene acetal moiety of
17 was accomplished according to Falorni’s protocol (3 N HCl
in EtOAc) to give LC15-0133 (1)·HCl salt in good yield in a
laboratory scale.9 However, on a large laboratory scale (∼200
g), the deprotection reaction resulted in a number of byproducts,
which might be attributed to the incomplete removal of excess
HCl in the crude concentrate. Therefore, we examined several
deprotection conditions suitable for a pilot scale. Serendipi-
tously, aqueous NH4Cl was found to cleave effectively the N,O-
methylene acetal moiety of 17 at room temperature, and this
protocol was successfully applied to the preparation of LC15-
0133 (1) in a pilot scale.
1
salt was prepared. Through comparison with respective H
NMR spectra (Figure 2) and HPLC analysis of cis- and trans-
isomers, the story behind the epimerization was unambiguously
cleared: after the stage of the coupling reaction, all the
intermediates underwent rapid epimerization under neutral and
(8) Aqueous 4,4-dimethyloxazolidine (16, 75 wt %) is commercially
available from Aldrich. Oxazolidine 16 was extracted twice with
CH2Cl2 or dichloroethane (1.0 L and 500 mL, based on 1.0 L of 75%
aqueous oxazolidine) and used after concentration.
(9) Falorni, M.; Conti, S.; Giacomelli, G.; Cossu, S.; Soccolini, F.
Tetrahedron: Asymmetry 1995, 6, 287.
(10) Careful analysis of TLC showed two spots. However, upon isolating
them by preparative TLC, each isolated material turned out to be the
same mixture before purification. HPLC analysis was performed with
C1 column with CH3CN/H2O ) 3:97 containing 0.1% TFA as an
eluent at 254 nm; retention times of trans- and cis-1 were 10.9 and
17.8 min, respectively.
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1
Figure 2. Comparison of H NMR spectra of cis-1a·HCl, trans-1b·HCl, and a diastereomeric mixture of 1 ·HCl.
Scheme 5. Preparation of cis-LC15-0133 (1a) tartrate via CIDR
basic conditions. We speculate that the instant epimerization
might be facilitated significantly by proximity effect of the
internal amine as a base (see the transition structure A in Scheme
4). Thus, HPLC analysis of them should be carried out with an
acidic eluent containing 0.1% TFA.
tion (CIDR)11 methodology was successfully applied for the
preparation of ∼0.5 kg of cis-LC15-0133 (1a) tartrate salt in
83% yield from 1 with better than 98% de (Scheme 5).
In conclusion, we have established an efficient and scalable
synthetic route toward a potent DPP-IV inhibitor, cis-LC15-
0133 (1a). In the course of the study, we established direct
additions of lithiated oxadiazole to methyl ester 4 to render the
preparation of 7 more efficient, and judicious selection of
oxazolidine 16 as an equivalent of 2-amino-2-methyl-1-propanol
(8) led to minimal formation of the side product 10 at the
coupling reaction with bromide 9. Serendipitous discovery of
CIDR of a diastereomeric mixture of LC15-0133 (1) in the
course of tartaric acid salt formation led to the isolation of cis-
LC15-0133 (1a) tartrate salt as an exclusive product. This
finding implies that, when working with a stereochemically
labile compound, it would be a very useful strategy to consider
CIDR as a possible solution, particularly at the final stage of
the synthesis. Using the mentioned improvements, the kilogram-
scale synthesis of cis-1a tartrate salt was efficiently implemented
without any chromatographic purification in a total of 10 steps.
From the study on the X-ray crystallographic analysis of
the complex of DPP-IV and LC15-0133 (1), we knew that only
the cis form 1a is active. Moreover, to ensure consistent quality
control and provide clear description of the chemical identity
of the final API, we were required to develop a process to
prepare cis-LC15-0133 (1a) which is viable for a large-scale
operation. To this end, selective crystallization conditions for
the preparation of cis-LC15-0133 (1a) out of the cis- and trans-
mixture of 1 via salt formation with a variety of acids was
investigated. Among many acids tested, crystallization of 1 using
tartaric acid in acetonitrile provided highly crystalline tartrate
salt. To our surprise, the resulting crystal was found to be the
cis-isomer 1a exclusively in better than 98% de, which reflected
that in the course of crystallization of the cis- and trans-mixture
1 with tartaric acid, cis-1a tartrate salt was selectively crystal-
lized out with concomitant dynamic equilibration of the cis-
and trans-isomers. This crystallization-induced dynamic resolu-
(11) For an excellent review, see: Anderson, N. G. Org. Process Res. DeV.
2006, 10, 683.
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Experimental Section
addition, the mixture was heated to 90 °C, and Ti(O-i-Pr)4 (140
g, 1 mol%) was added slowly. After 1.5 h at the same
temperature, the reaction mixture was heated to 115 °C for 4 h
with azeotropic distillation using a Dean-Stark separator (∼2.5
L of distilled water was collected). After cooling to 56 °C, the
reaction mixture was filtered through a pad of Celite, and the
filtrate was concentrated under reduced pressure to give a waxy
solid. Trituration of the residue with n-hexane (5 L) and filtration
afforded 2,2-dimethylpropanohydrazide (4.32 kg, 75%) as a
N-Boc-trans-4-hydroxy-L-proline Methyl Ester (3). To a
stirred slurry of trans-4-hydroxy-L-proline (2, 2.3 kg, 17.5 mol)
in methanol (9.4 kg) was added portionwise thionyl chloride
(2 kg, 0.96 equiv) using a feeding pump over 1 h at 5 °C. During
the addition, the reaction temperature was slowly warmed to
34 °C. After the completion of the addition, the resulting slurry
was heated to 60 °C and stirred for 24 h to give a clear light-
brown solution. The mixture was evaporated under reduced
pressure to give methyl ester as a light-brown solid containing
a small amount of methanol, which was used in the next step
without further purification. Boc2O (4.3 kg, 1.12 equiv) was
added portionwise to a stirred suspension of crude methyl ester
in dichloromethane (25 kg). To the mixture was added slowly
a solution of triethylamine (5.0 L, 2.04 equiv) in CH2Cl2 (10
kg). When most of staring material was consumed by TLC
analysis (approximately 3.5 h), the reaction mixture was
quenched with 1 N HCl solution (11 kg). The organic layer
was separated and evaporated under reduced pressure to give a
brown viscous liquid. n-Hexane (6.0 L) was added to the
concentrate, and the resulting slurry was vigorously stirred at
ambient temperature. Filtration of the formed solid and drying
with N2 purge gave alcohol 3 as an off-white solid (3.5 kg,
14.3 mol, 81.5%). 1H NMR (a mixture of rotamers, 400 MHz,
CDCl3) δ 1.38 (s, 3.6 H), 1.44 (s, 5.4H), 1.75 (br s, 1H,), 2.08
(m, 1H), 2.30 (m, 1H), 3.46 (br d, J ) 11.8 Hz, 0.4 H), 3.56
(br d, J ) 11.8 Hz, 0.6 H), 3.65 (dd, J ) 4.4, 11.8 Hz, 1H),
3.74 (s, 3H), 4.40 (t, J ) 8.0 Hz, 0.6 H), 4.44 (t, J ) 8.0 Hz,
0.4 H), 4.50 (br s, 1H). 13C NMR (100 MHz, CDCl3) δ 28.5,
28.7, 38.6, 39.3, 52.4, 52.5, 54.9, 55.0, 57.9, 58.3, 69.3, 70.0,
80.6, 80.7, 154.4, 155.0, 173.9, 174.1.
1
white solid. H NMR of (400 MHz, CDCl3) δ 1.21 (s, 9H),
3.92 (br s, 2H), 7.29 (br s, 1H).
Catalytic amount of p-toluenesulfonic acid monohydrate (140
g, 2 mol%) was added to a stirred mixture of 2,2-dimethylpro-
panohydrazide (4.30 kg, 37 mol) and trimethyl orthoformate
(5.0 L, 1.23 equiv) at ambient temperature (16 °C). The reaction
mixture was heated to 70 °C. After 2 h, the temperature was
raised to 106 °C to remove methanol via a Dean-Stark
separator. The resulting brown solution was distilled under
reduced pressure (55-60 mmHg) to give a tert-butyl-1,3,4-
oxadiazole12 (6, 3.70 kg, 28.5 mol, 75%) as a colorless liquid.1H
NMR (500 MHz, CDCl3) δ 1.45 (s, 9H), 8.32 (s, 1H). 13C NMR
(125 MHz, CDCl3) δ 28.2, 32.4, 152.9, 173.3.
tert-Butyl-(2S,4S)-2-[(5-tert-butyl-1,3,4-oxadiazol-2-yl)car-
bonyl]-4-fluoropyrrolidine-1-carboxylate (7). To a stirred
solution of oxadiazole (6, 1.9 kg, 15 mol) in THF (20 L) was
added slowly 6.0 L of n-BuLi (2.5 M in hexane) under positive
N2 pressure over 4 h, maintaining the reaction temperature
below -60 °C (After ∼2.0 h, the reaction mixture changed to
an off-white slurry due to the formation of lithiated oxadiazole).
After completion of the addition, the reaction mixture was stirred
for 40 min and cooled to -70 °C. A solution of methyl ester
4 (1.75 kg, 7.0 mol) in THF (2.0 L) was added over 1.5 h to a
stirred slurry of lithiated oxadiazole, maintaining the reaction
temperature below -60 °C. After the completion of the addition,
the reaction temperature was warmed slowly to -30 °C over
2 h. After completion of the reaction was confirmed by 1H NMR
analysis, the reaction mixture was quenched by an aqueous
NH4Cl solution (3 kg of NH4Cl and 15 kg of H2O). The organic
layer was separated and concentrated under reduced pressure
to give a brown-colored oil, which was vigorously triturated
with n-hexane (3.0 L) to give ketone 7 (1.6 kg, 4.68 mol, 67%)
as a white solid, including less than 5% of tertiary alcohol 13
on the basis of NMR analysis. 1H NMR (500 MHz, CDCl3) δ
1.36 (s, 4.5H), 1.47 (s, 4.5H), 1.49 (s, 9H), 2.57-2.74 (m, 2
H), 3.74 (m, 1H), 3.93 (m, 1H), 5.32-5.42 (m, 1H). 13C NMR
(125 MHz, CDCl3) δ 28.0, 28.3, 29.6, 32.7, 32.8, 36.4 (d, 2JCF
(4S)-N-Boc-cis-4-fluoro-L-proline Methyl Ester (4). Di-
ethylaminosulfur trifluoride (DAST) (4.5 kg, 1.9 equiv) was
added dropwise using a feeding pump to a stirred solution of 3
(3.5 kg, 14.2 mol) in dichloromethane (50 kg) at -2 °C. During
the addition, a slight exotherm was observed that resulted in a
temperature increase to 7.8 °C. After completion of the addition,
the mixture was slowly warmed to ambient temperature and
stirred for 14 h. To the mixture was added over 5 h saturated
aqueous NaHCO3 solution at 0 °C. The organic layer was
separated and the aqueous layer was extracted again with 8.0
kg of dichloromethane. The combined organic layer was
concentrated under reduced pressure to give the crude brown
oil 4 (3.29 kg), which was directly used for the next step without
further purification. 1H NMR (a mixture of rotamers, 400 MHz,
CDCl3) δ 1.44 (s, 5H), 1.49 (s, 4H), 2.25-2.55 (m, 2H),
3.56-3.93 (m, 2H), 3.75 (s, 3H), 4.43 (d, J ) 9.2 Hz, 0.5H),
2
2
) 21.5 Hz), 37.3 (d, JCF ) 21.5 Hz), 53.1 (d, JCF ) 23.9
Hz), 53.4 (d, 2JCF ) 23.9 Hz), 61.9, 62.0, 80.7, 91.9 (d, 1JCF
)
4.55 (d, J ) 9.2 Hz, 0.5H), 5.20 (br d, J ) 52.8 Hz, 1H). 13
C
176.5 Hz), 92.2 (d, 1JCF ) 176.5 Hz), 153.2, 153.9, 169.7, 175.4,
2
NMR (125 MHz, CDCl3) δ 27.7, 27.9, 36.1 (d, JCF ) 21.5
Hz), 36.9 (d, 2JCF ) 21.5 Hz), 51.6, 51.7, 52.4 (d, 2JCF ) 23.9
Hz), 52.6 (d, 2JCF ) 23.9 Hz), 56.8, 57.2, 79.6, 79.7, 90.8 (d,
1
175.6, 183.6, 184.0. Spectroscopic data of 13: H NMR (500
MHz, CDCl3) δ 1.41 (s, 9H), 1.43 (s, 9H), 1.51 (s, 9H),
2.61-2.79 (m, 2H), 3.53 (dd, J ) 13.2, 23.6 Hz, 1H), 3.73
(ddd, J ) 4.9, 13.2, 30.6 Hz, 1H), 5.01 (dm, J ) 54.4 Hz, 1H),
5.16 (dd, J ) 3.2, 9.6 Hz, 1H), 7.81 (br s, 1H); 13C NMR (125
1JCF ) 176.5 Hz), 91.9 (d, JCF ) 176.5 Hz), 153.2, 153.5,
1
171.4, 171.8.
2-tert-Butyl-1,3,4-oxadiazole (6). To a stirred solution of
5.02 kg of pivalic acid (49.13 mol) in 5.0 L of toluene and 8.0
L of n-butanol was added NH2NH2 monohydrate (80% purity,
51% of hydrazine, 1.15 equiv). During the addition, the reaction
temperature rose from 18 to 32 °C. After completion of the
2
MHz, CDCl3) δ 28.0, 28.2, 32.3, 32.4, 35.3 (d, JCF ) 22.9
2
Hz), 54.6 (d, JCF ) 25.0 Hz), 62.7, 74.3, 82.8, 90.5 (1JCF
)
177.7 Hz), 158.4, 162.9, 164.4, 173.9, 174.4.
(12) Please refer to ref 7.
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[(2S,4S)-1-(Bromoacetyl)-4-fluoropyrrolidin-2-yl](5-tert-
butyl-1,3,4-oxatriazol-2-yl)methanone (9). To a stirred solu-
tion of ketone 7 (2.28 kg, 8.26 mol) in ethyl acetate (20 L) was
added a solution of saturated HCl in ethyl acetate (20 L) at
ambient temperature, and the resulting mixture was stirred for
∼1.5 h. The color of the reaction mixture slowly changed to
dark purple. Concentration of the mixture afforded amine salt
14 (2.18 kg, > 95%) as a dark purple-colored solid, which was
used in next step without purification.1H NMR (500 MHz,
CDCl3) δ 1.48 (s, 9H), 2.82-3.16 (m, 2H), 3.82-4.05 (m, 2H),
5.40 (dm, J ) 52.8 Hz, 1H), 5.70 (d, J ) 9.6 Hz, 1H), 9.20 (br
s, 1H), 11.10 (br s, 1H).
To a mixture of amine salt 7 (1.0 kg, 3.6 mol) and
bromoacetyl bromide (0.35 L, 1.1 equiv based on ketone 7) in
dichloromethane (15 L) was added slowly triethylamine (10.6
L, 2.1 equiv) at 0 °C. After completion of the addition, the
reaction temperature was warmed to 20 °C over 40 min. The
mixture was washed with 0.5 N HCl solution (20 L) and
saturated aqueous NaHCO3 solution (20 L) in sequence. The
organic layer was concentrated to give bromide 9 (1.15 kg, 88%)
as a light purple-colored solid.1H NMR (500 MHz, CDCl3) δ
1.46 (s, 7H), 1.50 (s, 2H), 2.60-2.86 (m, 2H), 3.56 (d, J )
11.0 Hz, 0.2H), 3.76 (d, J ) 11.0 Hz, 0.2H), 3.85 (d, J ) 11.0
Hz, 0.8H), 3.93 (d, J ) 11.0 Hz, 0.8H), 3.85-4.14 (m, 2H),
5.27 (dm, J ) 52.0 Hz, 0.2H), 5.38 (dm, J ) 52.0 Hz, 0.8H),
5.59 (d, J ) 10.4 Hz, 0.2H), 5.61 (d, J ) 10.4 Hz, 0.8H).
Spectroscopic data of pyrrole 15: 1H NMR (500 MHz, CDCl3)
δ 1.50 (s, 9H), 6.42 (m, 1H), 7.21 (m, 1H), 7.70 (br s, 1H),
10.0 (br s, 1H).
To s stirred solution of 17 in cosolvents of 4.22 kg of
CH2Cl2, 20.8 kg of methanol, and 3.20 kg of H2O was added
640 g of NH4Cl (12.0 mol) at ambient temperature (21 °C).
After stirring for 2.5 h, the reaction mixture was diluted with
20 kg of H2O and 30 kg of CH2Cl2. The pH of the heteroge-
neous mixture was adjusted to 8.0 with triethylamine (220 g),
and the organic layer was separated. The separated aqueous
layer was re-extracted with 15 kg of CH2Cl2, and the combined
organic layer was concentrated under reduced pressure to give
crude LC15-0133 (1) as a waxy light brown-colored solid.
Diethyl ether (6.0 L) was added, and the resulting slurry was
vigorously stirred for 1.0 h. Filtration and drying with N2 purge
overnight provided LC15-0133 (1) (680 g, 58% from 9) as an
off-white solid. 1H NMR (cis- and trans-diastereomeric mixture,
500 MHz, CDCl3) δ 1.00 (s, 2H), 1.01 (s, 2H), 1.07 (s, 2H),
1.45 (s, 9H), 2.24 (dddd, J ) 3.7, 10.4, 14.4, 39.7 Hz, 0.7H),
2.56-2.79 (m, 1.3H), 3.05 (d, J ) 11.7 Hz, 0.8H), 3.13 (d, J
) 11.7 Hz, 0.8H), 3.22-3.43 (m, 2.1H), 3.53 (d, J ) 16.0 Hz,
0.3H), 3.79-4.02 (m, 2H), 5.36 (dm, J ) 52.0 Hz, 0.3H), 5.41
(dm, J ) 52.0 Hz, 0.7H), 5.42 (dd, J ) 8.0, 9.8 Hz, 0.7H),
5.61 (dd, J ) 1.5, 10.0 Hz, 0.3H). 13C NMR (125 MHz, CD3OD
with 0.1% TFA) δ 19.4, 19.6, 27.0, 32.6, 35.1 (d, 2JCF ) 20.3
Hz), 42.2, 52.8 (d, 2JCF ) 25.0 Hz), 60.3, 62.6, 65.3, 92.4 (1JCF
) 180.0 Hz), 160.0, 164.6, 175.7, 181.9; MS(ESI) m/z 371 (M
+ H).
cis-LC15-0133 (1a) Tartrate Salt. To a solution of LC15-
0133 (1) (410 g, 1.1 mol) in methanol (2.0 L) was added L-(+)-
tartaric acid (167 g, 1.0 equiv) at ambient temperature (18 °C).
After the mixture became a homogeneous brown-colored
solution, methanol was removed under reduced pressure to give
a waxy solid. To the residue was added 3.0 L of CH3CN. On
dissolving the solid, crystals began to form. After 1.0 h, the
resulting solid was filtered and dried with N2 purge overnight
to provide cis-LC15-0133 (1a) tartrate salt (475 g, 83%, 98%
de) as an off-white solid.1H NMR (400 MHz, CD3OD with
0.1% TFA) δ 1.27 (s, 0.65H), 1.28 (s, 0.65H), 1.34 (s, 4.7H),
1.46 (s, 7H), 1.47 (s, 2H), 2.65-2.88 (m, 2H), 3.52-3.68 (m,
2H), 3.81-4.08 (m, 3.2H), 4.15 (d, J ) 16.5 Hz, 0.8H), 4.52
(s, 2H), 5.31 (dm, J ) 52.0 Hz, 0.2H), 5.39 (dm, J ) 52.0 Hz,
0.8H), 5.53 (d, J ) 9.8 Hz, 0.6H), 5.58 (m, 0.8H). 13C NMR
(125 MHz, CD3OD with 0.1% TFA) δ 19.4, 19.6, 27.0, 32.6,
35.1 (d, 2JCF ) 21.5 Hz), 42.2, 52.8 (d, 2JCF ) 25.0 Hz), 60.4,
62.6, 65.3, 72.1, 92.4 (1JCF ) 180.0 Hz), 159.9, 164.7, 173.5,
175.8, 182.0; MS(ESI) m/z 371 (M + H).
LC15-0133 (1). A mixture of bromide 9 (1.15 kg, 3.17 mol)
and oxazolidine 16 (4.5 kg, 4.8 equiv based on 9) in dichlo-
romethane (10 L) was stirred at ambient temperature (25 °C).
After 14 h, TLC showed that approximately 5-10% of starting
bromide 9 was not consumed. Additional oxazolidine 16 (1.8
kg, 1.9 equiv) was added, and the mixture was stirred for 4 h.
To the reaction mixture was added CH2Cl2 (10 kg) and H2O
(15 kg). The organic layer was separated, and the separated
aqueous layer was re-extracted with 6.0 kg of CH2Cl2. The
combined organic layer was concentrated under reduced pres-
sure to provide a cis- and trans-diastereomeric mixture 17 as
1
brown-colored viscous oil. H NMR (cis- and trans-mixture,
500 MHz, CDCl3) δ 1.00 (s, 2H), 1.01 (s, 2H), 1.07 (s, 2H),
2.24 (dddd, J ) 3.7, 10.4, 14.4, 39.7 Hz, 0.7H), 2.56-2.79
(m, 1.3H), 3.05 (d, J ) 11.7 Hz, 0.8H), 3.13 (d, J ) 11.7 Hz,
0.8H), 3.22-3.43 (m, 2.1H), 3.53 (d, J ) 16.0 Hz, 0.3H),
3.79-4.02 (m, 2H), 5.36 (dm, J ) 52.0 Hz, 0.3H), 5.41 (dm,
J ) 52.0 Hz, 0.7H), 5.42 (dd, J ) 8.0, 9.8 Hz, 0.7H), 5.61 (dd,
J ) 1.5, 10.0 Hz, 0.3H).
Received for review March 31, 2008.
OP800076R
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