Practical synthesis of an enantiomerically pure trans-4,5-disubstituted 2-pyrrolidinone via enzymatic resolution. Preparation of the LTB4 inhibitor BIRZ-227

Article abstract of DOI:10.1021/jo971605p

A practical synthesis of the enantiomerically pure BIRZ-227 (1), a LTB₄ inhibitor, has been developed. The key steps include the effective synthesis of the trans-diarylpyrrolidinone (±)-8 and the enzymatic resolution of N- acetoxymethyl pyrrolidinone (±)-10 by immobilized Lipase Novozym 435. Reduction of pyrrolidinone (+)-8 with borane and subsequent coupling with chlorobenzoxazole 2 furnished BIRZ-227 in high enantiomeric purity (99% ee). The overall process described herein required no chromatographic separation and is amenable to the preparation of multikilogram quantities of the desired drug candidate in a cost-effective manner.

Full text of DOI:10.1021/jo971605p

326
J . Org. Chem. 1998, 63, 326-330
P r a ctica l Syn th esis of a n En a n tiom er ica lly P u r e
tr a n s-4,5-Disu bstitu ted 2-P yr r olid in on e via En zym a tic Resolu tion .
P r ep a r a tion of th e LTB4 In h ibitor BIRZ-227†
Nathan K. Yee,* Laurence J . Nummy, Denis P. Byrne, Lana L. Smith, and Gregory P. Roth
Department of Chemical Development, Boehringer Ingelheim Pharmaceuticals, Inc., 900 Ridgebury Road,
P.O. Box 368, Ridgefield, Connecticut 06877-0368
Received August 28, 1997X
A practical synthesis of the enantiomerically pure BIRZ-227 (1), a LTB4 inhibitor, has been
developed. The key steps include the effective synthesis of the trans-diarylpyrrolidinone (()-8 and
the enzymatic resolution of N-acetoxymethyl pyrrolidinone (()-10 by immobilized Lipase Novozym
435. Reduction of pyrrolidinone (+)-8 with borane and subsequent coupling with chlorobenzoxazole
2 furnished BIRZ-227 in high enantiomeric purity (99% ee). The overall process described herein
required no chromatographic separation and is amenable to the preparation of multikilogram
quantities of the desired drug candidate in a cost-effective manner.
Sch em e 1
In tr od u ction
For at least 2 decades considerable research has been
centered on the discovery of compounds that inhibit the
arachidonic acid cascade. One particular strategy in-
volves the inhibition of leukotriene biosynthesis, and this
area has been well-reviewed in the literature.1 Several
years ago our inflammatory disease group discovered a
potent class of cis- and trans-diaryl pyrrolidines that
inhibit this biosynthetic pathway, specifically the syn-
thesis of leukotriene B4.2 Such compounds can be useful
for the treatment of inflammatory disorders such as
asthma, arthritis, inflammatory bowel disease, and pso-
riasis. During the preclinical evaluation of this series,
a potential clinical candidate, BIRZ-227 (1), emerged,
thus initiating the need for large quantities of enantio-
merically pure material for further development.
or six) were required to reach an acceptable enantiomeric
excess with a modest overall yield (∼10%). In addition,
the 1,3-dipolar cycloaddition step required reaction tem-
peratures below -60 °C, which is impractical for large-
scale production. These parameters initiated our decision
to find an alternative synthetic route that ultimately
could be demonstrated in the pilot plant. In this paper,
we will detail a large-scale synthesis of the enantiomeri-
cally pure BIRZ-227 (1).
Simple retrosynthetic analysis indicates that 1 can be
split into two subunits (Scheme 1), the benzoxazole 2 and
the chiral pyrrolidine 3. In the initial synthesis,2 1,3-
cycloaddition3 of an azaallyl anion with 4-methoxystyrene
furnished a racemic mixture of the cis- and trans-diaryl
pyrrolidines which could be separated after tedious
chromatography. Following reaction with a substituted
chlorobenzoxazole 2, milligram quantities were then
purified using chiral HPLC to furnish material for initial
biological assay. Multigram quantities of (+)-1 were
prepared through scaling up the 1,3-dipolar cycloaddition
chemistry and a method of resolving racemic 3 using (-)-
diacetone-2-keto-L-gulonic acid.4
Resu lts a n d Discu ssion
Syn th esis of Ra cem ic Su bstr a te. In a previous
paper5 we outlined a practical and general method for
the preparation of racemic trans-4,5-disubstituted 2-pyr-
rolidinones, which was based on Michael addition of a
Schiff base anion to a substituted cinnamate using phase
transfer catalysis (PTC) conditions.6 The one-pot proce-
dure to (()-8 started from commercially available 2-(ami-
nomethyl)pyridine (4, Scheme 2). The Schiff base 5 was
This protocol allowed for the synthesis of essentially
enantiomerically pure material but was limited for
additional scale-up since several recrystallizations (five
† Dedicated to Professors Robert M. Coates and Frederick E. Ziegler
on the occasion of their 60th birthday.
X Abstract published in Advance ACS Abstracts, December 15, 1997.
(1) (a) Recent reviews: Musser, J . H.; Kreft, A. F. J . Med. Chem.
1992, 35, 2501. (b) Summers, J . B. Drug News Perspect. 1990, 3, 3517.
(2) (a) Pal, K.; Behnke, M.; Adams, J . US Patent 5594008, 1/14/97.
(b) Pal, K.; Behnke, M. L.; Tong, L. Tetrahedron Lett. 1993, 34, 6205.
(3) For 1,3-cycloaddition chemistry of azaallyl anion see: Pearson,
W. H.; Szura, D. P.; Postich, M. J . J . Am. Chem. Soc. 1992, 114, 1329.
(4) Roth, G. P.; Emmanuel, M.; Tong, L. Tetrahedron Asymmetry
1997, 8, 185.
(5) Yee, N. K. Tetrahedron Lett. 1997, 38, 5091 and references
therein.
(6) For phase transfer catalysis reactions of benzylidenebenzylamine
with cinnnamic acid derivatives, see: Potapov, V. M.; Gracheva, R.
A.; Sivova, N. A. Zh. Org. Khim. 1989, 25, 1876. For stereoselective
Michael additions of metal enolates of R-amino ester, see: (a) Tat-
sukawa, A.; Dan, M.; Ohbatake, M.; Kawatake, K.; Fukata, T.; Wada,
E.; Kanemasa, S.; Kakei, S. J . Org. Chem. 1993, 58, 4221. (b)
Kanemasa, S.; Uchida, O.; Wada, E. J . Org. Chem. 1990, 55, 4411.
S0022-3263(97)01605-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/23/1998

Preparation of the LTB4 Inhibitor BIRZ-227
J . Org. Chem., Vol. 63, No. 2, 1998 327
Sch em e 2
Sch em e 3
prepared from 4 and benzophenone in the presence of a
catalytic amount of p-toluenesulfonic acid under azeo-
tropic conditions. The PTC reaction was carried out by
direct addition of ethyl 4-methoxycinnamate, 5 mol % of
BnEt3NCl, and 0.5 equiv of aqueous 50% NaOH to the
above Schiff base at room temperature to form Michael
adduct 6.7 Acidic hydrolysis of 6 with aqueous HCl
followed by neutralizing the HCl salt of amino ester 7
with concentrated NH4OH afforded the desired 2-pyrro-
lidinone (()-8. On a 65 mol scale, 9.1 kg of (()-8 (52%
yield8 from 4, trans:cis ) 93:7) was obtained in the first
crop as a crystalline solid by a single crystallization
directly from the reaction mixture. The relative stereo-
chemistry of the corresponding pyrrolidine 3, prepared
by borane reduction of 8, was identical with that reported
previously.5
Even though the trans:cis ratio of (()-8 could be
enriched by recrystallization at this point, it was found
the undesired cis isomer can be easily removed in the
later stage of the synthesis and hence the product (()-8
(trans:cis ) 93:7) was used directly for the next step
without further purification.
En zym a tic Resolu tion a n d Sep a r a tion of th e
Resolved Mixtu r e. As mentioned earlier, chemical
resolution of (()-3 with (-)-diacetone-2-keto-L-gulonic
acid proved to be inefficient in terms of operation and
cost. At this point in our development of the process, we
explored the possibility of using enzymatic methods to
resolve a derivative of (()-8. Lipase-catalyzed enanti-
oselective hydrolysis of racemic N-acyloxymethyl-2-aze-
tidinones was previously reported.9 Limited reports have
appeared on an analogous resolution of 2-pyrrolidinone
derivatives.10 Therefore, we investigated this enzymatic
resolution strategy for (()-10 (Scheme 3).
The synthesis of racemic N-acyloxymethylated 2-pyr-
rolidinone (()-10 is straightforward. Hydroxymethyla-
tion (37% CH2O in H2O, TEA, THF)11 of (()-8 followed
by acylation (Ac2O, pyridine) gave the desired substrate
(()-10 in 96% yield. Our initial enzymatic resolution of
(()-10 was conducted according to the literature pro-
cedure,9a except that immobilized Novozym 43512 was
used (0.2 M in (i-Pr)2O-H2O, 50 wt % Novozym 435, rt).
(9) (a) Nagai, H.; Shiozawa, T.; Achiwa, K.; Terao, Y. Chem. Pharm.
Bull. 1993, 41, 1933; 1992, 40, 2227. (b) Csomos, P.; Kanerva, L. T.;
Bernath, G.; Fulop, F. Tetrahedron Asymmetry 1996, 7, 1789. (c)
Oumoch, S.; Rousseau, G. Bioorg. Med. Chem. Lett. 1994, 4, 2841.
(10) (a) Nakano, H.; Iwasa, K.; Okuyama, Y.; Hongo, H. Tetrahedron
Asymmetry 1996, 7, 2381. (b) J ouglet, B.; Rousseau, G. Tetrahedron
Lett. 1993, 34, 2307.
(11) Patthy, A.; Vezer, C. J . Heterocycl. Chem. 1989, 26, 133.
(12) Novozym 435 was purchased from Novo Nordisk Co.
(13) (a) The percent ee reported in the text refers only to the trans-
isomer. (b) Chiral HPLC column, Daicel Chiralpak AS (4.6 mm × 25
cm); mobile phase, 25% (v/v) absolute ethanol in hexane, isocratic, 1.0
mL/min; ambient temperature. Retention times: (4S,5R)-9, 11.65 min;
(4R,5S)-9, 13.09 min; (4S,5R)-10, 19.65 min; (4R,5S)-10, 24.58 min;
(+)/(-)-8, 32.15 min.
(7) Michael adduct 6 can be isolated and characterized see ref 5.
(8) The actual yield of (()-8 was estimated to be ∼70% by flash
column chromatography, see ref 5.

328 J . Org. Chem., Vol. 63, No. 2, 1998
Yee et al.
Sch em e 4
The progress of the reaction and the enantiomeric excess
of 9 and 10 were monitored by a chiral HPLC method.13
When completed, the desired (4R,5S)-10 was obtained in
32% yield (97% ee) after flash chromatography. Lipase
PS-3014 was also tested and succeeded in resolution of
10, but the isolation of product was problematic due to
the fact that the enzyme was not immobilized. Therefore,
the commercially available and inexpensive immobilized
Novozym 435 was preferred in the process development.
To achieve a process suitable for larger scale in terms
of safety, throughput, and cost, we screened a variety of
reaction parameters focusing on solvent, concentration,
enzyme load, and reaction temperature. The optimized
conditions (10-200 g scale) are realized as follows:
Substrate (()-10 was dissolved in methyl tert-butyl ether
(MTBE) at a 1.0 M concentration, and it was observed
that the use of 5 wt % of Novozym 435 and 3 equiv of
water were sufficient to achieve 62% conversion at 40
°C after 4 days. The enantiomeric enrichment of (4R,5S)-
10 was determined to be 97% ee while (4S,5R)-9 was 57%
ee. The desired (4R,5S)-10 was obtained in 35% yield
by flash chromatography. No attempt was made to
recycle the enzyme.
rectly from the aqueous layer and collected by filtration
to give pure material in 98% yield (trans:cis ) 97:3 by
1H NMR).
Syn th esis of BIRZ-227. Borane reduction (BH3-
THF, reflux) of (+)-8 to pyrrolidine was carried out
according to standard protocol15 (Scheme 4). The crude
pyrrolidine (2S,3R)-3 was treated with 0.5 equiv of oxalic
acid and its (2S,3R)-pyrrolidine oxalate salt (+)-11 was
isolated in 79% yield as a crystalline solid. At this point,
the undesired cis isomer of 11 was determined to be
present only at a level of 0.43% by HPLC.16 Attempted
reduction of (+)-8 by other reagents such as LiAlH4 or
Red-Al failed since the pyridine ring in (+)-8 was also
reduced. Condensation of free base of (2S,3R)-11 with
2,5-dichlorobenzoxazole (2, EtN(i-Pr)2, THF) gave BIRZ-
227 (1) in 84% yield (99% ee by chiral HPLC17 ) as
crystalline solids.
In the larger scale batch, 10.5 kg of crude (()-10 was
equally divided in three portions and the enzymatic
resolution was carried out in three 22 L flasks separately
using the above procedure (1.0 M in MTBE, 5 wt %
Novozym 435, 3 equiv of H2O, 40 °C). After 5 days, HPLC
analysis indicated that the reaction proceeded to 41%
conversion and the optical purity of 10 was 49% ee. An
additional 5 wt % Novozym 435 was added and the
reaction continued for another 5 days. At this point, the
reaction proceeded to 60% conversion [97.5% ee for
(4R,5S)-10 and 56.6% ee for (4S,5R)-9]. The reaction
mixture was simply filtered through a pad of Celite and
concentrated to afford the crude mixture (4R,5S)-10/
(4S,5R)-9 as a thick oil. The desired (4R,5S)-10 (2.6 kg,
36% yield, 97.5% ee) was isolated by silica gel chroma-
tography. The slower hydrolysis rate observed in these
batches can be attributed to the insufficient agitation by
the mechanical stirrer in the 22 L round-bottomed flask.
Con clu sion
We have developed an effective synthesis of enantio-
merically pure BIRZ-227 (1) via an enzymatic resolution
method. The simple one-pot synthesis of racemic (()-8,
which involves the Schiff base formation, the PTC
Michael addition, hydrolysis, and cyclization, was ef-
ficient. A novel enzymatic resolution of its derivative (()-
10 and the following nonchromatographic separation of
the resolved mixture were devised and demonstrated on
a large scale. The chemical process described herein
should allow preparation of large quantities of the
leukotriene biosynthesis inhibitor 1.
Separation of the enzymatically resolved (4R,5S)-10/
(4S,5R)-9 mixture by column chromatography was not
desirable for large-scale production and an alternative
to such an operation is required. After the attempts to
separate the mixture through crystallization failed, we
investigated another approach taking advantage of the
different physical and chemical properties that (4R,5S)-
10 and (4S,5R)-9 exhibit. It was found that treatment
of a solution of the (4R,5S)-10/(4S,5R)-9 mixture in
methylene chloride with 1.0 M H3PO4 resulted in the
hydrolysis of (4S,5R)-9 to the corresponding pyrrolidinone
(4S,5R)-8, and the (4R,5S)-10 remained intact under
these conditions. Furthermore, the salt form of (4S,5R)-8
was extracted into the aqueous layer, and the (4R,5S)-
10 remained in the organic layer. Pure (4R,5S)-10 (>98%
purity) was obtained in 35% yield (97.5% ee) by concen-
trating the organic layer. Apparently the solubility
difference between the salt forms of (4R,5S)-10/(4S,5R)-8
in organic/aqueous layers accounts for their separation.
Exp er im en ta l Section
Gen er a l Meth od s. All melting points are uncorrected.
The H and 13C NMR spectra were recorded at 400 and 100.6
1
MHz, respectively. The elemental analyses were performed
by Quantitative Technologies Inc., Whitehouse, NJ . Solvents,
starting materials, and reagents were used as purchased
without further purification. Novozym 435 was purchased
from Novo Nordisk Co.
tr a n s-4-(4-Met h oxyp h en yl)-5-(2-p yr id yl)-2-p yr r olid i-
n on e (8). In a 50 gallon reactor, a solution of 2-(aminometh-
yl)pyridine (4, 7.05 kg, 65.1 mol), benzophenone (11.85 kg, 65.0
mol), and p-TsOH monohydrate (124 g, 0.65 mol) in toluene
(65 L) was heated at reflux. Azeotropic distillation of the
reaction mixture was carried out by continuous addition/
distillation of toluene (∼50 L) for 24 h. The reaction mixture
was cooled to rt and ethyl 4-methoxycinnamate (13.50 kg, 65.5
(15) Brown, H. C.; Choi, Y. M.; Narasimhan, S. J . Org. Chem. 1982,
47, 3153.
(16) HPLC column, Novapak C18 (3.9 mm × 15 cm); mobile phase,
MeCN/MeOH/aqueous phosphate, pH ) 2.0 (20:50:30); flow rate, 1.0
mL/min.
(17) Chiral HPLC column, chiralcel OD (4.6 mm × 25 cm); mobil
phase, 5% ethanol in hexane; flow rate, 1.0 mL/min; ambient temper-
ature. Retention times: (+)-(2S,3R)-1 (BIRZ-227), 12.39 min; (-)-
(2R,3S)-1, 14.05 min.
Hydrolysis of (4R,5S)-10 proceeded smoothly in a 1:1
mixture of concentrated NH4OH and MeOH at 45 °C.
After evaporation of MeOH, (+)-8 was crystallized di-
(14) Lipase PS-30 was purchased from Amano Co.

Preparation of the LTB4 Inhibitor BIRZ-227
J . Org. Chem., Vol. 63, No. 2, 1998 329
mol), BnEt3NCl (744 g, 3.3 mol), and 50% (w/w) NaOH (2.65
kg, 33.1 mol) were added. The resulting mixture was stirred
at rt for 19 h. TLC analysis indicated the reaction was
completed. Hydrochloric acid (12 M, 19.5 L, 234 mol) and
water (15 L) were added at rt. The two-phase mixture was
stirred at rt for 20 h, and the layers were separated. The
organic layer was washed with water (2 × 10 L). The
combined aqueous layers were washed with toluene (2 × 25
L), mixed with toluene (87 L), and basified with concentrated
NH4OH (15 M, 19.2 L, 288 mol) at rt. This two-phase mixture
was stirred at rt for 18 h. The layers were separated, and the
aqueous layer was extracted with toluene (2 × 10 L). The
combined organic layers were washed with water (2 × 16.5 L)
and concentrated under house vacuum (jacket temperature,
65 °C). After ∼90 L of toluene was distilled, the mixture was
cooled to rt and stirred for 14 h. The crystalline solids were
collected by filtration and washed with toluene (12 L) to give
product 8 (9.1 kg, 52%) as crystalline solids (1H NMR indicated
that its purity was >98% and trans:cis ) 93:7): mp 118-119
°C; IR (KBr) 3190, 1695, 1511, 1250 cm-1. trans-8: 1H NMR
(400 MHz, CDCl3) δ 8.57 (d, J ) 4.6 Hz, 1H), 7.64 (dt, J ) 7.7
and 1.7 Hz, 1H), 7.22-7.25 (br s, 1H), 7.19 (m, 1H), 7.17-
7.15 (m, 3H), 6.86 (dd, J ) 6.8 and 1.8 Hz, 2H), 4.81 (d, J )
6.6 Hz, 1H), 3.79 (s, 3H), 3.62 (q, J ) 6.7 Hz, 1H), 2.86, 2.60
(ABq of d, J gem ) 17.0 Hz, J vic ) 9.0 Hz, 2H); 13C NMR (100.6
MHz, CDCl3) δ 177.5, 160, 159.1, 150, 137.3, 133.6, 128.9,
123.3, 121.3, 114.6, 67.1, 55.6, 48.2, 39.1. cis-8: 1H NMR (400
MHz, CDCl3) δ 8.40 (d, J ) 4.2 Hz, 1H), 7.40 (t, J ) 1.7 Hz,
1H), 7.17 (br.s, 1H), 7.01 (dd, J ) 6.8 and 4.6 Hz, 1H), 6.85 (d,
J ) 7.8 Hz, 1H), 6.76, 6.57 (ABq of d, J ) 6.7 and 1.8 Hz, 4H),
5.13 (d, J ) 7.6 Hz, 1H), 4.08 (q, J ) 7.9 Hz, 1H), 3.67 (s, 3H),
2.82, 2.74 (ABq of d, J gem ) 16.7 Hz, J vic ) 7.7 Hz, 2H); 13C
NMR (100.6 MHz, CDCl3) δ 179.3, 158.6, 158.4, 149.2, 136.5,
130.7, 129.2, 122.7, 121.8, 113.7, 64.3, 55.5, 45.5, 36.7. Anal.
Calcd for C16H16N2O2: C, 71.62; H, 6.01; N, 10.44. Found: C,
71.51; H, 5.97; N, 10.42.
1-Acet oxym et h yl-tr a n s-4-(4-m et h oxyp h en yl)-5-(2-p y-
r id yl)-2-p yr r olid in on e (10). A mixture of 8 (8.90 kg, 33.2
mol), triethylamine (4.76 kg, 47.0 mol), and aqueous formal-
dehyde (37% in H2O, 3.41 kg, 42.0 mol) in THF (26 L) was
stirred at rt for 4 days, at which point the HPLC analysis12
indicated that the reaction was completed. The reaction
mixture was concentrated to remove all volatiles. The residue
was treated with toluene (36 L) and the resulting suspension
was filtered to give ∼190 g of a crystalline solid, which was
identified by 1H NMR to be mainly the cis hydroxymethylated
pyrrolidinone 9 (trans:cis ) 7:93). The filtrate was concen-
trated to dryness and the residue was used directly for the
next step. An analytical sample was obtained by chromatog-
raphy. trans-9: 1H NMR (400 MHz, CDCl3) δ 8.62 (d, J ) 4.2
Hz, 1H), 7.66 (dt, J ) 7.7 and 1.8 Hz, 1H), 7.26 (t, J ) 8.8 Hz,
1H), 7.10 (d, J ) 7.7 Hz, 1H), 7.10, 6.83 (ABq, J ) 8.7 Hz,
4H), 5.09 (d, J ) 10.8 Hz, 1H), 4.96 (d, J ) 6.8 Hz, 1H), 4.30
(d, J ) 10.8 Hz, 1H), 3.77 (s, 3H), 3.54 (q, J ) 8.1 Hz, 1H),
2.99, 2.66 (ABq of d, J gem ) 17.1, J vic ) 9.1 and 8.5 Hz, 2H);
13C NMR (100.6 MHz, CDCl3) δ 175.8, 159.1, 158.4, 150.3,
137.5, 133.2, 128.6, 123.7, 123.3, 114.6, 70.4, 65.7, 55.6, 45.7,
39.4. cis-9: 1H NMR (400 MHz, CDCl3) δ 8.42 (d, J ) 4.2 Hz,
1H), 7.41 (dt, J ) 7.7 and 1.7 Hz, 1H), 7.05 (dd, J ) 7.3 and
5.4 Hz, 1H), 6.75 (d, J ) 6.8 Hz, 1H), 6.75, 6.60 (ABq, J ) 6.8
Hz, 4H), 5.22 (d, J ) 8.0 Hz, 1H), 5.12 (d, J ) 10.6 Hz, 1H),
4.55 (d, J ) 10.6 Hz, 1H), 4.02 (q, J ) 8.9 Hz, 1H), 3.70 (s,
3H), 3.02, 2.72 (ABq of d, J gem ) 16 Hz, J vic ) 10.3 and 8.4 Hz,
2H); 13C NMR (100.6 MHz, CDCl3) δ 176.7, 158.7, 157.2, 149.4,
136.4, 129.8, 129.3, 123.3, 122.9, 113.8, 67.7, 66.9, 55.5, 43.8,
36.2; HRMS m/z calcd for C17H19N2O3(MH)+ 299.1395, found
299.1396.
the crude product (()-10 (13.63 kg, 96% yield from 8 based on
21% (w/w) content of MTBE in the crude product). An
analytical sample was obtained by chromatography: mp 66-
68 °C; IR (KBr) 2832, 1739, 1699, 1514, 1399 cm-1. trans-10:
1H NMR (400 MHz, CDCl3) δ 8.66 (d, J ) 4.4 Hz, 1H), 7.66
(dt, J ) 7.6 and 1.8 Hz, 1H), 7.26 (dd, J ) 8.0 and 4.0 Hz,
1H), 7.12 (d, J ) 7.7 Hz, 1H), 7.09, 6.84 (ABq, J ) 8.7 Hz,
4H), 5.61 (d, J ) 10.6 Hz, 1H), 4.83 (d, J ) 10.6 Hz, 1H), 4.79
(d, J ) 6.3 Hz, 1H), 3.79 (s, 3H), 3.61 (q, J ) 7.7 Hz, 1H),
3.06, 2.68 (ABq of d, J gem ) 17.3 Hz, J vic ) 7.1 and 7.9 Hz,
2H), 1.98 (s, 3H); 13C NMR (100.6 MHz, CDCl3) δ 175.9, 171.0,
159.1, 158.1, 150.7, 137.2, 133.4, 128.4, 123.7, 123.3, 114.6,
70.7, 65.9, 55.6, 45.4, 38.5, 21.0. cis-10: 1H NMR (400 MHz,
CDCl3) δ 8.48 (d, J ) 4.2 Hz, 1H), 7.38 (dt, J ) 7.6 and 1.6
Hz, 1H), 7.06 (dd, J ) 8.0 and 4.3 Hz, 1H), 6.75, 6.61 (ABq, J
) 8.6 Hz, 4H), 6.69 (d, J ) 7.8 Hz, 1H), 5.61 (d, J ) 10.6 Hz,
1H), 5.10 (d, J ) 8.1 Hz, 1H), 4.95 (d, J ) 10.6 Hz, 1H), 4.02
(m, 1H), 3.70 (s, 3H), 3.13, 2.68 (ABq of d, J gem ) 16.6 Hz, J vic
) 12.0 and 8.3 Hz, 2H), 1.99 (s, 3H); 13C NMR (100.6 MHz,
CDCl3) δ 177.0, 171.3, 158.8, 156.9, 149.7, 136.2, 129.3, 123.6,
123.0, 113.8, 68.1, 66.7, 55.5, 43.7, 35.0, 21.1; HRMS m/z calcd
for C19H21N2O4(MH)+ 341.1501, found 341.1501. See (+)-10
for elemental analysis.
E n zym a t ic R esolu t ion of (()-10, (4R,5S)-1-Acet oxy-
m et h yl-4-(4-m et h oxyp h en yl)-5-(2-p yr id yl)-2-p yr r olid i-
n on e [(+)-10]. The enzymatic resolution of the above crude
product (()-10 (13.63 kg) was carried out in three separate
22 L flasks by equally dividing the substrate. The reaction
conditions were all identical in these three batches (A-C).
Ba tch A: A suspension of the crude product (()-10 (4.54
kg, 10.55 mol), water (561 g, 31.17 mol), and Novozym 435
(188 g, 5 wt % based on the substrate) in MTBE (11 L) was
stirred at 40 °C. The reaction was monitored by HPLC
(Chiralpak AS).13 After 5 days, it was observed that the
reaction proceeded at 41% conversion and the optical purity
of (+)-10 was 49% ee. At this point, additional 5 wt %
Novozym 435 (188 g) was added and the reaction continued
for another 5 days. The HPLC analysis indicated that the
optical purity of (+)-10 was 97.5% ee (60% conversion). The
reaction mixture was cooled to rt and filtered through a pad
of Celite. The cake was washed with MTBE (5 × 1 L). The
combined filtrates were concentrated to dryness to give the
crude product (+)-10/(-)-9 (3.60 kg) as a thick oil. The crude
product (+)-10/(-)-9 (3.60 kg) was purified by flash chroma-
tography on silica gel (15 kg) eluted with EtOAc-hexane (4:
1) to give pure (+)-10 (1.28 kg, 36% yield, 97.5% ee) as
crystalline solids. In the batch B, 1.30 kg (36%) of (+)-10 was
obtained in the same manner: mp 76-78 °C; [R]25D ) +156.7°
(c ) 1.0, CHCl3); 1H and 13C NMR spectra were identical with
(()-10 as described above. Anal. Calcd for C19H20N2O4: C,
67.05; H, 5.92; N, 8.23. Found: C, 67.14; H, 5.94; N, 8.16
The nonchromatographic separation of (+)-10/(-)-9 was
performed as follows. A solution of the enzymatically resolved
crude product (+)-10/(-)-9 [19.5 g, 58.8 mmol, prepared from
20.0 g of (()-10] in methylene chloride (100 mL) was washed
with 1.0 M H3PO4 (5 × 60 mL), at which point the HPLC
analysis indicated there was no (-)-9 present in the organic
layer. The organic layer was dried (MgSO4) and concentrated
to give 7.06 g (35%) of (+)-10 as crystalline solids. The optical
purity (97.5% ee) and chemical purity (>98%) were determined
by a chiral HPLC method.13
(4R,5S)-4-(4-Meth oxyp h en yl)-5-(2-p yr id yl)-2-p yr r olid i-
n on e [(+)-9]. A solution of (+)-10 (1.28 kg, 3.76 mol) in MeOH
(3.4 L) was treated with concentrated NH4OH (3.4 L) at rt.
The reaction mixture was heated to 45 °C and stirred at 45
°C for 6 h. The HPLC analysis indicated that the reaction
was complete. The reaction mixture was evaporated to remove
most of MeOH, and the crystalline solids were precipitated
during this period. The solids were collected by filtration and
the cake was washed with water (1 L). This product was dried
in an oven at rt overnight to afford 840 g (98%) of (+)-8 as
crystalline solids (its purity was determined to be >99% by
The above residue was mixed with pyridine (7.95 kg, 100.6
mol) and acetic anhydride (9.00 kg, 88.2 mol) at rt. The
reaction mixture was stirred at rt for 22 h and then quenched
with water (1.2 L). The mixture was concentrated to dryness
and the residue was dissolved in toluene (40 L). This solution
was washed with water (6 × 10 L), at which point the aqueous
layer was pH ) 5, and concentrated to dryness. The residue
was redissolved in MTBE (30 L) and then concentrated to give
1
HPLC and the trans:cis ratio ) 98:2 by H NMR): mp 144-
1
146 °C; [R]25 ) +151.5° (c ) 1.01, CHCl3); H and 13C NMR
D
spectra were identical with (()-8 as described above.

330 J . Org. Chem., Vol. 63, No. 2, 1998
Yee et al.
(2S,3R )-2-(2-P yr id yl)-3-(4-m e t h yoxyp h e n yl)p yr r oli-
d in e Hem ioxa la te (11). In a 22 L flask, 2-pyrrolidinone (+)-8
(731 g, 2.73 mol) was added to a BH3-THF solution (1.0 M,
9.4 L, 9.4 mol) at rt over 2 h. Gases evolved during this period
and the internal temperature arose to 42 °C at the end. The
reaction mixture was heated at reflux overnight (16 h). The
mixture was then cooled to rt, quenched with MeOH (850 mL),
and concentrated to dryness by rotavap. The resulting residue
was dissolved in MeOH (2 L) and evaporated; such treatment
was repeated twice. The residue was dissolved in MeOH (6
L) and treated with a solution of HCl (462 g, 12.6 mol) in
MeOH (3 L). The mixture was heated at reflux for 2 h and
then evaporated to dryness. The residue was redissolved in
MeOH (2 L) and evaporated; such treatment was repeated
twice. The residue was dissolved in aqueous 2.4 N HCl (5 L)
and the aqueous layer was washed with toluene (3 × 3 L).
The aqueous layer was mixed with toluene (3.5 L) and basified
with 50% NaOH (∼1.4 kg) until pH ) 13 (internal temperature
was kept below rt by cooling). The layers were separated, and
the aqueous layer was extracted with toluene (2 × 3 L). The
combined organic layers were filtered and concentrated to
dryness to yield crude pyrrolidine (633 g) as an oil. 1H NMR
analysis indicated this crude product contained 4.5 wt % of
toluene and trans:cis ) 97:3.
2-[1-(2S,3R)-2-(2-P yr id yl)-3-(4-m eth yoxyp h en yl)p yr r o-
lid in yl]-5-ch lor oben zoxa zole (1, BIRZ-227). Pyrrolidine
salt (+)-11 (652 g, 2.18 mol) was dissolved in water (5.5 L)
and mixed with toluene (5.5 L). The mixture was stirred at 0
°C as a 50% NaOH solution was added until pH ) 13. The
layers were separated, and the aqueous layer was extracted
with toluene (2 × 2.5 L). The organic layers were combined,
washed with water (3 × 1 L), and concentrated to dryness.
The residue was dissolved in toluene (2 L) and evaporated.
Such treatment was repeated again. 1H NMR analysis
indicated that the crude pyrrolidine (723 g, trans:cis ) 99.6:
0.4) contained 22 wt % of toluene. Chiral HPLC analysis
showed its optical purity was 97% ee.
A solution of 2,5-dichlorobenzoxazole (2, 374 g, 1.99 mol) in
THF (4.8 L) was stirred at rt as a solution of the above crude
pyrrolidine (723 g, 2.22 mol) in THF (4.8 L) and also diiso-
propylethylamine (541 g, 4.18 mol) were added. The reaction
mixture was stirred at rt for 2 h and TLC analysis indicated
that the reaction was complete. The mixture was evaporated
to dryness. The residue was redissolved in EtOAc (2.4 L) and
then evaporated; such treatment was repeated again. The
residue was diluted with EtOAc (2.4 L) and extracted with
water (1.2 L). The layers were separated, and the aqueous
layer was extracted with EtOAc (2 × 1.2 L). The combined
organic layers were washed with water (2 × 1.2 L) and
concentrated to dryness. A single crystallization of the residue
in cyclohexane (2 L) afforded the desired product 1 (739 g, 84%
yield, 99% ee): mp 90-92 °C; [R]25D ) +46.97°; IR (KBr) 2833,
The above crude product was dissolved in 2-propanol (2 L)
and evaporated; such treatment was repeated again. The
residue was dissolved in 2-propanol (2.4 L) and the solution
was stirred and heated to 60 °C as a solution of oxalic acid
dihydrate (152 g, 1.2 mol) in 2-propanol (915 mL) and water
(34 mL) was added. The mixture was heated at reflux for 15
min, and cooled to rt overnight (13 h). The crystalline product
was collected by filtration, and the cake was rinsed with
2-propanol (2 × 1 L) and dried under vacuum to afford
pyrrolidine hemioxalate salt (+)-11 (652 g, 79% yield, trans:
1
1641, 1512, 1246 cm-1; H NMR (400 MHz, CDCl3) δ 8.60 (d,
J ) 4.2 Hz, 1H), 7.62 (dt, J ) 7.6 and 1.8 Hz, 1H), 7.30 (d, J
) 2.0 Hz, 1H), 7.21-7.13 (m, 4H), 7.04 (d, J ) 8.4 Hz, 1H),
6.92 (dd, J ) 8.5 and 2.0 Hz, 1H), 6.86 (dd, J ) 7.1 and 1.8
Hz, 2H), 5.19 (d, J ) 5.2 Hz, 1H), 4.13 (m, 2H), 3.40 (s, 3H),
3.71 (q, J ) 6.3 Hz, 1H), 2.52 (m, 1H), 2.22 (m, 1H); 13C NMR
(100.6 MHz, CDCl3) δ 161.8, 160.7, 158.9, 150.1, 148.0, 145.1,
136.9, 133.7, 129.5, 128.4, 122.8, 121.8, 120.4, 116.8, 114.5,
cis ) 99.6:0.4): mp 184-185.5 °C; [R]25 ) +135.31° (c ) 1.0,
D
MeOH); IR (KBr) 1595, 1514, 1311, 1251 cm-1; 1H NMR (400
MHz, DMSO-d6) δ 8.56 (d, J ) 4.4 Hz, 1H), 7.67 (t, J ) 7.5
Hz, 1H), 7.32 (dd, J ) 7.1 and 5.1 Hz, 1H), 7.13, 6.82 (ABq, J
) 8.5 Hz, 4H), 7.03 (d, J ) 7.8 Hz, 1H), 4.50 (d, J ) 10.2 Hz,
1H), 3.67 (s, 3H), 3.35 (m, 3H), 2.34 (m, 1H), 2.09 (m, 1H); 13
C
109.6, 70.8, 55.6, 52.3, 48.9, 32.5. Anal. Calcd for C23H20
-
NMR (100.6 MHz, DMSO-d6) δ 166.3, 158.8, 158.2, 149.9,
137.7, 133.0, 129.4, 124.0, 123.4, 114.7, 69.6, 55.8, 51.9, 46.0,
35.2. Anal. Calcd for C17H19N2O3: C, 68.21; H, 6.40; N, 9.36.
Found: C, 68.15; H, 6.38; N, 9.32.
ClN3O2: C, 68.06; H, 4.97; N, 10.35. Found: C, 67.95; H, 4.96;
N, 10.42.
J O971605P