An asymmetric synthesis of L-694,458, a human leukocyte elastase inhibitor, via novel enzyme resolution of β-lactam esters

Article abstract of DOI:10.1021/jo960618k

A convergent synthesis of [S-(R*,S*)]-2-[4-[(4-methylpiperazin-1-yl)carbonyl]phenoxy]-3,3-diet hyl-N-[1-[3,4-(methylenedioxy)phenyl]butyl]-4-oxo-1-azetidinecarboxami de (L-694,458, 1), a potent human leukocyte elastase inhibitor, was achieved via chiral synthesis of key intermediates: (S)-3,3-diethyl-4-[4'-[(N-methylpiperazin-1-yl)carbonylphenoxy]-2-azet idinone (2) and (R)-α-propylpiperonyl isocyanate (3). Synthesis of β-lactam 2 was achieved by a novel enantioselective lipase hydrolysis of ester 5 to produce (S)-3,3-diethyl-4-(4'-carboxyphenoxy)-2-azetidinone (6) (60% yield, three cycles, 93% ee) with isolation, epimerization, and recycling of the undesired (R)-ester 5. Isocyanate 3 was prepared by chiral addition of Zn(n-Pr)₂ to piperonal (98% yield, 99.2% ee), azide displacement and reduction to (R)-α-propylpiperonylamine (11) (58% yield, 85% ee), crystallization as the D-pyroglutamic acid salt (92% yield, 98.2% ee), and isocyanate formation (98% yield) with phosgene.

Full text of DOI:10.1021/jo960618k

J . Org. Chem. 1996, 61, 6575-6580
6575
An Asym m etr ic Syn th esis of L-694,458, a Hu m a n Leu k ocyte
Ela sta se In h ibitor , via Novel En zym e Resolu tion of
â-La cta m Ester s
Raymond J . Cvetovich,*,† Michel Chartrain,‡ Frederick W. Hartner, J r.,†
Christopher Roberge,‡ J oseph S. Amato,† and Edward J . J . Grabowski†
Departments of Process Research and Bioprocess Research and Development,
Merck Research Laboratories, P.O. Box 2000, Rahway, New J ersey 07065
Received April 2, 1996X
A convergent synthesis of [S-(R*,S*)]-2-[4-[(4-methylpiperazin-1-yl)carbonyl]phenoxy]-3,3-diethyl-
N-[1-[3,4-(methylenedioxy)phenyl]butyl]-4-oxo-1-azetidinecarboxamide (L-694,458, 1), a potent
human leukocyte elastase inhibitor, was achieved via chiral synthesis of key intermediates: (S)-
3,3-diethyl-4-[4′-[(N-methylpiperazin-1-yl)carbonylphenoxy]-2-azetidinone (2) and (R)-R-propylpip-
eronyl isocyanate (3). Synthesis of â-lactam 2 was achieved by a novel enantioselective lipase
hydrolysis of ester 5 to produce (S)-3,3-diethyl-4-(4′-carboxyphenoxy)-2-azetidinone (6) (60% yield,
three cycles, 93% ee) with isolation, epimerization, and recycling of the undesired (R)-ester 5.
Isocyanate 3 was prepared by chiral addition of Zn(n-Pr)2 to piperonal (98% yield, 99.2% ee), azide
displacement and reduction to (R)-R-propylpiperonylamine (11) (58% yield, 85% ee), crystallization
as the D-pyroglutamic acid salt (92% yield, 98.2% ee), and isocyanate formation (98% yield) with
phosgene.
In tr od u ction
and orally active HLE inhibitor and has been selected
for further development.7 Herein we report a convergent,
enantioselective synthesis suitable for large scale ap-
plication (Figure 1).
Human leukocyte elastase (HLE, EC 3.4.21.37) is a
serine protease which is stored in the azurophilic gran-
ules of polymorphonuclear leukocytes (PMNs). Upon its
release into extracellular space, HLE is capable of
hydrolyzing the connective tissue component elastin as
well as collagen. Excessive release of HLE or the
inhibition of its natural inhibitors has been implicated
in several disease processes.1 The controlled inhibition
of HLE, normally in balance with its natural inhibitors
R1-proteinase inhibitor (R1PI) and R2-macroglobulin (R2M),
by an exogenous low molecular weight inhibitor might,
therefore, have a positive therapeutic effect in the treat-
ment of emphysema,1a,2a rheumatoid arthritis,2b and
cystic fibrosis.2c Among the â-lactam-based inhibitors
reported,3-5 L-694,4586 (1) has been shown to be a
remarkably potent (Kobs/[I] ) 3.8 × 106 M-1 s-1), selective,
Resu lts a n d Discu ssion
A synthesis of L-694,458 (1), whose absolute configu-
ration was determined by X-ray analysis,6 logically
proceeds via the coupling of â-lactam 2 and isocyanate
3. Our initial preparation of chiral â-lactam 2 was
achieved via resolution of benzoic acid 6 (Scheme 1).
Racemic acid 6 was prepared by (1) displacement of the
propionate group of 3,3-diethyl-4-(propionyloxy)-2-azeti-
dinone8 (4) by benzyl 4-hydroxybenzoate (benzyl paraben)
and Cs2CO4 in 10% aqueous CH3CN to give crystalline
benzyl ester 5 (93% yield) followed by (2) hydrogen
transfer reduction using Pd/C and cyclohexene in EtOH
and crystallization from tert-butyl methyl ether (MTBE)
to give racemic acid 6 (82% yield). Racemic acid 6 was
† Department of Process Research.
‡ Department of Bioprocess Research and Development.
X Abstract published in Advance ACS Abstracts, September 1, 1996.
(1) (a) Snider, G. L. Protease-Antiprotease Imbalance in the Patho-
genesis of Emphysema and Chronic Bronchial Injury: A Potential
Target for Drug Development. Drug. Dev. Res. 1987, 10, 235. (b)
Weinbaum, G.; Giles, R. E.; Krell, R. D., Eds. Pulmonary Emphysema,
the Rationale for Intervention. Ann. N.Y. Acad. Sci. 1991, 624, 1. (c)
Bender, J . G.; van Epps, D. E.; Searles, R.; Williams, R. C., J r. Altered
Function of Synovial Fluid Granulocytes in Patients with Acute
Inflammatory Arthritis; Evidence for Action of Neutrophils and its
Mediation by a Factor Present in Synovial Fluid. Inflammation 1986,
10, 443.
(2) (a) J anoff, A. Elastases and Emphysema. Current Assessment
of the Protease-Antiprotease Hypothesis. Am. Rev. Respir. Dis. 1985,
132, 417. (b) J ackson, A. H.; Hill, S. L., Afford, S. C.; Stockley, R. A.
Sputum Soluble Phase Proteins and Elastase Activity in Patients with
Cystic Fibrosis. J . Respir. Dis. 1984, 65, 114. (c) J anoff, A. In Neutral
Proteases of Human Polymorphonuclear Leukocytes; Havermann, K.,
J anoff, A. Eds.; Urban and Schwartzenberg: Baltimore, MD, 1978; pp
390-417
(3) Doherty, J . B.; Shah, S. K.; Finke, P. E.; Dorn, C. P., J r.; Hagman,
W. K.; Hale, J . J .; Kissinger, A. L.; Thompson, K. R.; Brause, K.;
Chandler, G. O.; Knight, W. B.; Maycock, A. L.; Ashe, B. M.; Weston,
H.; Gale, P.; Mumford, R. A.; Anderson, O. F.; Williams, H. R.; Nolan,
T. E.; Frankenfield, D. L.; Underwood, D.; Vyas, K. P.; Kari, P. H.;
Dahlgren, M. E.; Mao, J .; Fletcher, D. S.; Dellea, P. S.; Hand, K. M.;
Osinga, D. G.; Peterson, L. A.; Williams, D. T.; Metzger, J . M., Bonney,
R. J .; Humes, J . L.; Pacholok, S. P.; Hanlon, W. A.; Opas, E.; Stolk, J .;
Davies, P. Proc. Nat. Acad. Sci. U.S.A. 1993, 8727.
(4) Finke, P. E.; Shah, S. K.; Ashe, B. M.; Ball, R. G.; Blacklock, T.
J .; Bonney, R. J .; Brause, K. A.; Chandler, G. O.; Cotton, M.; Davies,
P.; Dellea, P. S.; Dorn, C. P., J r.; Fletcher, D. S.; O’Grady, L. A.;
Hagman, W. K.; Hand, K. M.; Knight, W. B.; Maycock, A. L.; Mumford,
R. A.; Osinga, D. G.; Sohar, P.; Thompson, K. R.; Weston, H. J . Med.
Chem. 1992, 35, 3731.
(5) (a) Shah, S. K.; Dorn, C. P., J r.; Finke, P. E.; Hale, J . J .; Hagman,
W. K.; Brause, K.; Chandler, G. O.; Kissinger, A. L.; Ashe, B. M.;
Weston, H.; Knight, W. B.; Maycock, A. L.; Dellea, P. S.; Fletcher, D.
S.; Hand, K. M.; Mumford, R. A; Underwood, D. J .; Doherty, J . B. J .
Med. Chem. 1992, 35, 3745. (b) Finke, P. E.; Shah, S. K.; Fletcher, D.
S.; Ashe, B. M.; Brause, K. A.; Chandler, G. O.; Dellea, P. S.; Hand, K.
M.; Maycock, A. L.; Osinga, D. G.; Underwood, D. J .; Weston, H.;
Davies, P.; Doherty, J . B. J . Med. Chem. 1995, 38, 2449.
(6) Finke, P. E.; Dorn, C. P., J r.; Kissinger, A. L.; Shah, S. K.; Ball,
R. G.; Chabin, R.; Davies, P.; Dellea, P. S.; Doherty, J . B.; Durette, P.
L.; Fletcher, D. S.; Griffen, P. R.; Green, B. G.; Hale, J . J .; Hanlon, W.
A.; Hand, K. M.; Humes, J . L.; Kieczykowski, G. R.; Klatt, T. D.; Lanza,
T. J .; Knight, W. B.; MacCoss, M.; Miller, D. S.; Mumford, R. A.;
Pacholok, S. G.; Peterson, L. P.; Poe, M.; Underwood, D. J .; Williams,
D. T.; Williams, H. R. Orally Active, Intracellular Inhibitors of Human
Leukocyte Elastase (HLE). Presented at the 22nd National Meeting
of the American Chemical Society, Chicago, 1995, MEDI 083.
(7) L-694,458 has been licensed to DuPont Merck Pharmaceutical
Company (DMP-777).
(8) Claus, M.; Grimm, D.; Prossel, G. Liebigs Ann. Chem. 1974, 539.
S0022-3263(96)00618-4 CCC: $12.00 © 1996 American Chemical Society

6576 J . Org. Chem., Vol. 61, No. 19, 1996
Cvetovich et al.
Ta ble 1. Effect of Ester Va r ia tion on Ra te of Acid
P r od u ction a n d Ster eosp ecificity w ith MB-5001 a n d
P S-800 Lip a ses
enzyme
MB-5001
mg/L (h)
PS-800
mg/L (h)
estera
% ee
% ee
methyl
26 (24)
36 (80)
2 (24)
85 (80)
21 (24)
48 (80)
32 (24)
58 (80)
43 (24)
72 (80)
85.5
88.6
87.8
86.8
37
88
91
95
propyl
hexyl
270 (24)
251 (80)
545 (24)
644 (80)
45 (24)
benzyl
60 (80)
F igu r e 1. L-694,458 (1) and key intermediates.
Sch em e 1. Syn th esis of (S)-â-La cta m 2
a
The isopropyl ester failed to hydrolyze with either lipase.
F igu r e 2. Rate of acid 6 production.
resolved by crystallization of the (S)-enantiomer as the
salt of (S)-R-methylbenzylamine (R-MBA) followed by
recrystallization from 2-propanol:acetonitrile. Maximum
recovery of acid (S)-6 was achieved by first crystallizing
and filtering the (R)-6:(R)-R-MBA salt. Treatment of
the mother liquour with (S)-R-MBA gave on crystalli-
zation the (S)-6:(S)-R-MBA salt directly. A recrystalli-
zation from 2-propanol:acetonitrile gave acid (S)-6:(S)-
R-MBA salt in 27% yield (based on racemic 6) in 96.4%
ee.
Greater efficiency in the production of the chiral acid
(S)-6 was a necessary and major goal of the synthesis.
Attempts to racemize either the (R)- or (S)-enantiomer
of acid 6 via displacement with either 4-hydroxybenzoic
acid or with the benzyl paraben gave mixtures of acid,
ester, and phenols (via displacement by the carboxylate
of 4-hydroxybenzoic acid). A kinetic enzymatic resolution
of the ester was proposed as an attractive alternative to
the classical salt resolution. The synthesis of optically
active â-lactams via enzyme resolution has been reported,
via the lipase hydrolysis of N-acyloxymethyl â-lactams.9
Our goal was to discover an enzyme to evoke a resolution
upon the hydrolysis of esters of â-lactam 5, an ambitious
goal involving an aromatic ring as spacer between the
prochiral center and the site of hydrolysis.
a rapid nonselective hydrolysis. After preliminary de-
velopment of the hydrolysis (pH, concentration, surfac-
tant, surfactant concentration, temperature), a variety
of esters were exposed to the selected enzymes (P.
aeruginosa lipase (MB-5001) and lipase PS-800), and
rates of acid 6 production and enantiomeric excess were
measured (see Table 1). While the P. aeruginosa lipase
showed sensitivity in the rate of acid production to the
type of ester, little differentiation was observed in the
overall enantioselectivity, with similar 85-88% ee values
observed. Hydrolysis using lipase PS-800 exhibited lower
production rates than P. aeruginosa lipase, but a sensi-
tivity to the ester structure was observed, with maximum
enantioselectivity occurring when the benzyl ester was
employed.
Commercially available lipase PS-800 (Amano) was
selected for further development. Bioconversion of ester
5 to the acid 6 with lipase PS-800 was found to be
insensitive to pH in the range of 5-8, but highly
dependent on the surfactant concentration, the charge
of ester (the ester demonstrated limited solubility in the
broth, but the presence of excess solid was necessary to
keep the solution saturated with racemic ester), and the
charge of enzyme. The hydrolysis exhibited a decline in
acid production after 4 days (see Figure 2). The addition
of benzyl alcohol to an enzyme hydrolysis resulted in an
inhibition of hydrolysis. When racemic acid 6 was
exposed to the enzyme hydrolysis conditions in the
presence of benzyl alcohol, no production of benzyl ester
5 was detected. Inhibition of the PS-800 lipase due to
alcohol production was an effect observed with all of the
ester derivatives. The loss in rate of hydrolysis due to
production of alcohol was paralleled with gradually lower
ee (96-93%) as the hydrolysis was allowed to proceed
beyond 4 days, such that maximal productivity and
enantioselectivity were achieved at a 25% conversion of
racemic ester.
Racemic benzyl ester 5 was exposed to a series of
enzyme sources, and two promising candidates, Pseudomo-
nas aeruginosa lipase (MB5001) and lipase PS-800
(Amano), were identified. Some lipases (wheat germ,
Chromobacterium viscosum, Rhizopus arrhizus, Pseudomo-
nas sp., and pig pancreas) failed to effect hydrolysis over
a 20 h incubation at 28 °C, while pig liver esterase gave
(9) (a) Nagai, H.; Shiozawa, T.; Achiwa, K.; Terao, Y. Chem. Pharm.
Bull. J pn. 1992, 40, 2227. (b) J ouglet, B.; Rousseau, G. Tetrahedron
Lett. 1993, 34, 2307. (c) Nagai, H.; Shiozawa, T.; Achiwa, K.; Terao, Y.
Chem. Pharm. Bull. J pn. 1992, 41, 1933. (d) Oumoch, S.; Rousseau,
G. Bioorg. Med. Chem. Lett. 1994, 4, 2841. (e) J ones, J . B. Tetrahedron
1986, 42, 3351 (and references therein).

Asymmetric Synthesis of L-694,458
J . Org. Chem., Vol. 61, No. 19, 1996 6577
Sch em e 3. Syn th esis of (R)-Isocya n a te 3
Sch em e 2. En zym e Hyd r olysis of Ester 5
After considerable experimentation, the following pro-
cess was developed for optimal production of acid 6,
isolation and racemization of recovered ester 5, and
recovery and reuse of enzyme (Scheme 2). Racemic ester
5 was treated with lipase enzyme PS-80010 in aqueous
pH 7 phosphate medium in the presence of Triton X-100
and terminated at ∼25% conversion to acid (S)-6 (93%
ee). Insoluble, unreacted ester 5 was recovered by
filtration as a 70:30 mixture of R:S enantiomers, giving
a milky white filtrate. The isolated benzyl ester was
racemized in 90% yield via displacement with benzyl
4-hydroxybenzoate and Cs2CO4 in 10% aqueous acetoni-
trile. The PS-800 lipase enzyme was isolated by passage
of the filtrate through a 10 kD cartridge and washing
with water. Reuse of the enzyme indicated that the
lipase regained >90% of its original activity and all of
its enantioselectivity. Acid (S)-6 was isolated from the
second filtrate by salting (NaCl), pH adjustment (5.0,
with phosphoric acid), extraction with i-PrOAc, and
crystallization from MTBE. Racemized ester 5 was
hydrolyzed with recovered enzyme, and the isolation
procedure was repeated. This recycling procedure con-
tinued to provide chiral acid from racemized ester after
three cycles in a 60% overall yield based on ester 5
with retention of the activity and selectivity of the lipase
(93% ee).
(S)-Acid 6 was converted to amide 2 in 90% yield using
DCC with N-methylpiperazine. Crystallization provided
intermediate amide 2 in 66% yield with an increase in
optical purity to 99.4% ee, using (S)-acid 6 with optical
purity in the 93-96% ee range.
The preparation of the second fragment of the conver-
gent synthesis of L-694,458 is described. (R)-Isocyanate
3 was obtained from (S)-alcohol 9, which was prepared
via chiral addition of Zn(n-Pr)2 (mediated with titanium
isopropoxide and the bis-triflamide of (R,R)-1,2-diami-
nocyclohexane)11 to piperonal 7 in 98% yield and 99.2%
ee (Scheme 3). Alternatively, ketone 8 was reduced with
stoichiometric amounts of (S)-oxazaborolidine-borane
((S)-OAB-BH3) complex12 (S)-12 to give the alcohol (R)-9
in 97.5% ee. The desired (S)-enantiomer should then be
accessible by the reduction with (R)-OAB-BH3. (S)-
Alcohol 9 was reacted with diphenylphosphoryl azide13
in the presence of DBU to produce (R)-azide 10, which
was reduced to (R)-amine 11 with lithium aluminum
hydride in 57% yield and 85% ee. The loss of optical
purity of this benzylic alcohol was similar to the loss in
a reported13 example of a benzylic alcohol containing a
p-OCH3 vs an unsubstituted aromatic or p-CH3 substitu-
tion. The use of alternate bases, as well as the use of
Zn(N3)2,14 failed to improve upon this result. The optical
purity of (R)-amine 11 was upgraded to 98% ee by
crystallization as the D-pyroglutamic acid salt in 92%
yield. (R)-Amine 11 was then converted to the (R)-
isocyanate 3 in 98% yield and in 98.2% ee.
The coupling of (S)-â-lactam 2 and (R)-isocyanate 3 did
not proceed without added base. The use of powdered
K2CO3 generated 1-2% of the symmetrical urea 13, an
impurity that was difficult to remove during crystalliza-
tion (but could be removed by dissolving the product in
aqueous acetic acid and filtering the insoluble urea). The
addition of (S)-â-lactam 2 to (R)-isocyanate 3 was best
achieved in CH3CN in the presence of a catalytic amount
of DBU. The use of other solvents (MTBE, i-PrOAc) gave
the symmetrical urea 13 in 2-15% yield. L-694,458, 1,
was ultimately isolated and crystallized from MTBE in
80% yield and >99.5% de (SFC-HPLC).
An asymmetric and large scale synthesis of the potent
elastase inhibitor L-694,458 was achieved. A recyclable
enzymatic chiral synthesis of the â-lactam acid interme-
diate 6 was demonstrated, as well as a resolution of the
acid. The chiral piperonyl isocyanate 3 was prepared via
chiral addition of Zn(n-Pr)2 to piperonal, conversion of
alcohol 9 to azide 10, and reduction to amine 11.
Coupling of the intermediates was highly successful using
DBU in acetonitrile, and the final product was crystal-
lized in high diastereomeric purity.
(10) A full discussion of the enzyme hydrolysis will be the subject
of a future publication. Roberge, C.; Cvetovich, R. J .; Amato, J . S.;
Hartner, F.; Greasham, R.; Chartrain, M., to be submitted.
(11) Takahashi, H.; Kawakita, T.; Yoshioka, M.; Kobayashi, S.;
Ohno, M. Tetrahedron Lett. 1989, 30, 7095.
(12) Mathre, D. J ., Thompson, A. S., Douglas, A. W., Hoogsteen, K.,
Carroll, J . D., Corley, E. G., Grabowski, E. J . J . J . Org. Chem. 1993,
58, 2880.
(13) Thompson, A.; Humphrey, G.; DeMarco, A.; Mathre, D.;
Grabowski, E. J . J . J . Org. Chem. 1993, 58, 5886.
(14) Viaud, M. C.; Rollin, P. Synthesis 1990, 130.

6578 J . Org. Chem., Vol. 61, No. 19, 1996
Cvetovich et al.
9.5. To the mother liquors from the R,R salt crystallization
was added (S)-R-methylbenzylamine (850 mL). The slurry was
aged 16 h at room temperature. The S,S salt was filtered,
washed with i-PrOH:CH3CN (1:1, 5 L), and dried with a
nitrogen flow to give product as a wet cake (enantiomeric ratio,
S:R ) 77:23). Into i-PrOH:CH3CN (1:1, 80 L) was charged
the S,S diasteriomeric salt. The slurry was heated to reflux
to obtain a clear solution, which was cooled to room temper-
ature over 6 h and then aged 16 h. The S,S salt was filtered,
washed with i-PrOH:CH3CN (1:1, 6 L), and dried with a
nitrogen flow giving (S)-6:(S)-MBA salt (1.2 kg, 21.5% yield
from racemic acid, 96.4% ee). By recombining all the filtrates
and isolating the acid free of amine by extraction, a racemic
mixture of the acid is recovered which was resolved as above,
to give an additional 310 g of (S)-6:(S)-MBA salt, for a total
Exp er im en ta l Section
Gen er a l. HPLC analyses were performed using a Spectra-
Physics SP8700 ternary solvent delivery system. All reactions
were carried out in Pyrex glass vessels under an atmosphere
of N2, and solvents and reagents were dried where appropriate
over 3 Å molecular sieves prior to use. Other solvents and
reagents were used as received. Karl Fisher water analyses
were carried out on a Metrohm 684 KF coulometer. Optical
rotations were measured in a 1 dm cell. PS-800 lipase was
purchased from Amano (Troy, VA). High-resolution mass
spectroscopy studies were performed in the FAB mode. El-
emental analyses were performed by Quantitative Technolo-
gies Inc., Whitehouse, NJ . Dipropylzinc was obtained from
Akzo Chemicals, Inc.
isolated yield of 27%: [R]25 -78.6° (c ) 1.0, MeOH); mp )
3,3-Diet h yl-4-((4′-b en zylca r b oxy)p h en oxy)-2-a zet id i-
n on e (5). Into CH3CN:H2O (1:1, 40 L) were charged benzyl
4-hydroxybenzoate (6.03 kg, 26.4 mol) and Cs2CO4 (13 kg, 39.9
mol). The resulting two-phase mixture was heated to 30 °C,
and 3,3-diethyl-4-(propionyloxy)-2-azetidinone8 (4) (7 kg, 35.2
mol) was added dropwise over 60 min. The mixture was aged
for 90 min at 30-35 °C, cooled to rt, and partitioned with H2O
(19 L) and MTBE (19 L). The organic phase was washed with
H2O (3 × 19 L) and then concentrated in vacuo (40 °C, 28 in.
of Hg) to a volume of 10 L. The concentrate was diluted with
EtOH (10 L) and reconcentrated in vacuo. The batch was
diluted to a volume of 26 L with EtOH (20 L) and assayed by
HPLC. Ester 5 (16.8 kg, 295 g/L) was obtained in 93% yield
(based on benzyl paraben). HPLC: Altex Ultrasphere Octyl,
250 × 4.6 mm, 5 µm; CH3CN:H2O (with 0.1% H3PO4 in each),
gradient elution 50:50 to 90:10 over 30 min, 254 nm, 25 °C,
2.0 mL/min; tR {min} ester 5, 12.0; benzyl paraben, 5.4. Ester
5 can be crystallized from EtOH:H2O (1:1). Mp 78.5-80.9 °C.
1H NMR (250.13 MHz, CDCl3): δ 8.04 (m, 2H), 7.45-7.30 (om,
5H), 6.91-6.84 (om, 3H), 5.41 (s, 1H), 5.33 (s, 2H), 2.00-1.67
(om, 4H), 1.04 (t, J ) 7.5, 3H), 1.02 (t, J ) 7.4, 3H). 13C NMR
(62.89 MHz, CDCl3): δ 172.9, 165.7, 160.1, 135.9, 131.8 (2C),
128.4, 128.0, 127.9 (2C), 123.7, 115.0, 82.8, 66.4, 64.69, 23.5,
21.5, 8.7, 8.5. IR (film): 3270, 2915, 2840, 1770, 1716, 1606,
589
117.5-118.8 °C. NMR (250.13 MHz, CD3OD): δ 7.93 (br d, J
) 8.7, 1H), 7.6-7.32 (om, 5H), 6.90 (br d, J ) 8.7, 2H), 5.45
(s, 1H), 5.0 (br s, 1H), 4.42 (q, J ) 6.8, 1H), 1.97-1.58 (om,
4H), 1.61 (d, J ) 6.8, 3H), 1.05 (t, J ) 7.5, 3H), 1.01 (t, J )
7.5, 3H). 13C NMR (62.89 MHz, CD3OD): δ 175.7, 174.6, 159.9,
140.4, 132.5, 132.2 (2C), 130.2 (2C), 129.9, 127.6 (2C), 115.8
(2C), 84.1, 65.2, 52.2, 24.8, 22.9, 21.1, 9.4, 8.9. IR (film): λmax
3175, 3131, 1775, 1608, 1514, 1396, 1247 cm-1
.
Anal. Calcd for C22H28N2O4: C, 68.73; H, 7.34; N, 7.29.
Found: C, 68.6; H, 7.26; N, 7.28.
A sample of salt was partitioned between dilute phosphoric
acid and i-PrOAc and then crystallized from i-PrOAc after
partial concentration: [R]25
156.5-158 °C.
-115.8° (c 1.00, MeOH); mp
589
Following the same procedure, the (R)-6:(R)-MBA salt was
upgraded by recrystallization (94.6% ee): [R]25 +75.2° (c )
589
1.0, MeOH).
Anal. Calcd for C22H28N2O4: C, 68.73; H, 7.34; N, 7.29.
Found: C, 69.0; H, 7.29; N, 7.27.
En zym e Hyd r olysis of Ben zyl Ester 5. Racemic ester 5
(43 g) was added to a phosphate-buffered aqueous solution (1.5
L) of Triton X-100 (2.7 g) and stirred (200 rpm) at 37 °C.
Lipase PS-800 (12 g) was added, and the mixture was agitated
for 96 h. The enzyme hydrolysis mixture, containing benzyl
ester and enzyme in suspension and carboxylic acid (8.09 g,
by HPLC assay) in solution, was filtered through a coarse
sintered glass funnel that was overlaid with filter paper. The
filtered ester 5 was washed with H2O (3 × 200 mL), dried,
and set aside for racemization. The combined aqueous sus-
pension of the enzyme hydrolysis medium was pumped (Cole-
Parmer Masterflex centrifugal pump) at ∼300 mL/min through
a Millipore PLTK Prep/Scale-TFF 1 ft2 10 kD regenerated
cellulose filter cartridge. The retentate return line was
restricted to allow a permeate flow of ∼700 mL/h. The final
reduction in volume was followed by a dilution to 250 mL with
H2O and recirculation of the enzyme slurry through the filter.
The enzyme slurry was removed and drained from the filter,
and fresh H2O (250 mL) was recirculated through the filter
(twice) to recover the enzyme. The combined aqueous enzyme
washes were set aside for assay and reuse. Assay of the
recovered aqueous enzyme suspension (olive oil hydrolysis)15
indicated that 90% activity of enzyme was recovered. The
permeate (3 L) was adjusted to pH 5.0 with H3PO4, NaCl (1.2
kg) was added, and the mixture was extracted with i-PrOAc
(3 × 200 mL). The combined extracts were washed with H2O
(200 mL), azeotropically dried by distillation, and filtered to
remove inorganic solids. This material was evaporated, and
the concentrate was crystallized from MTBE (100 mL). The
slurry was filtered, washed with MTBE, and dried to give 7.0
g of acid (S)-6. The mother liquors were concentrated to 15
mL, aged for 5 h, filtered, washed with MTBE, and dried to
give an additional 1.02 g of acid (S)-6. The first and second
crops were assayed (HPLC) and found to be 91 wt % and 96
wt % pure, respectively, with a 93% ee by chiral SFC-HPLC
assay. Isolated acid 6 (6.4 g) was dissolved in i-PrOH:CH3-
CN (1:1, 120 mL) and warmed to 55 °C. (S)-R-Methylbenzyl-
amine was added, and crystallization began immediately. The
1508, 1273, 1243, 1053 cm-1
.
Anal. Calcd for C21H23NO4: C, 71.37; H, 6.56; N, 3.96.
Found: C, 71.22; H, 6.45; N, 3.92.
3,3-Dieth yl-4-(4′-ca r boxyp h en oxy)-2-a zetid in on e (6).
To benzyl ester 5 (7.0 kg, 20.5 mol) in EtOH (15 L) were added
cyclohexene (10 L) and 5% Pd/C (500 g). The reaction was
stirred at reflux for 2 h. The mixture was filtered through
Solka-Floc (1 kg), and the cake was washed with EtOH (2 ×
1 L). The EtOH solution was evaporated in vacuo (30 °C, 29
in. of Hg) to a volume of 10 L. The concentrate was diluted
with MTBE (5 L) and reconcentrated in vacuo to a slurry.
MTBE (5 L) was added, and the product was filtered, washed
with MTBE (10 L), and dried with a nitrogen flow giving 4.38
kg of acid 6 for an 82% yield. Mp: 168.5-170.7 °C. HPLC
assay: Altex Ultrasphere Octyl, 250 × 4.6 mm, 5 µm; CH3-
CN:H2O (with 0.1% H3PO4 in each), gradient elution 50:50 to
90:10 over 30 min, 254 nm, 25 °C, 2 mL/min; tR {min} acid 6,
2.3; ester 5, 12.0. 1H NMR (250.13 MHz, CD3OD): δ 7.99 (d,
J ) 8.9, 2H), 6.98 (d, J ) 8.9, 2H), 5.50 (s, 1H), 4.99 (br s,
exchangeable H), 1.96-1.68 (om, 4H), 1.04 (t, J ) 7.6, 3H),
1.00 (t, J ) 7.6, 3H). 13C NMR (62.89 MHz, CD3OD): δ 175.6,
169.4, 161.7, 133.0 (2C), 125.5, 116.3 (2C), 83.8, 65.3, 24.8, 22.9,
9.4, 8.9. IR (film): λmax 3220, 2915, 2840, 1717, 1692, 1605,
1238 cm-1
.
Anal. Calcd for C14H17NO4: C, 63.87; H, 6.51; N, 5.32.
Found C, 63.62; H, 6.54; N. 5.23.
Resolu tion of Acid 6. Racemic acid 6 (3.9 kg, 14.8 mol)
was dissolved in i-PrOH:CH3CN (1:1, 70 L) at 70 °C. (R)-R-
Methylbenzylamine (883 mL) was added. The solution was
cooled to room temperature over 4 h, and the slurry was aged
16 h at room temperature. The R,R salt was filtered, washed
with i-PrOH:CH3CN (1:1, 7 L), and dried with a nitrogen flow
to give 1.88 kg with an enantiomeric ratio R:S ) 80:20. The
desired (S)-enantiomer was enriched in the mother liquors as
a 76:24 mixture. Chiral SFC-HPLC: Chiracel OD(H), 250 ×
4.6 mm, 28 vol % EtOH (containing 20 mM HClO4) modifier,
1.0 mL/min, 300 bar, 35 °C, 248 nm; tR {min} (S)-6, 7.6; (R)-6,
(15) Tiez, N.; Rex-Astles, J .; Shuey, D. Clin. Chem. 1989, 35, 1688.

Asymmetric Synthesis of L-694,458
J . Org. Chem., Vol. 61, No. 19, 1996 6579
slurry was aged 18 h at 20 °C, cooled to 2 °C, filtered, washed
with i-PrOH:CH3CN (1:1, 20 mL), and dried (in vacuo, 45 °C,
25 in. of Hg) to give (S)-6:(S)-MBA salt (8.4 g, 90% yield, 96.1%
ee). Chiracel OD(H), 250 × 4.6 mm; 28 vol % EtOH (contain-
ing 20 mM HClO4) modifier, 1.0 mL/min, 300 bar, 35 °C, 248
nm; tR {min} (S)-6, 7.6; (S)-5, 8.3; (R)-6, 9.5; (R)-5, 11.6.
Ra cem iza tion of (R)-3,3-Dieth yl-4-[4-(ben zylca r boxy)-
p h en oxy]-2-a zetid in on e (5). Benzyl ester 5 (49.5 g), recov-
ered from enzyme hydrolyses as a 70:30 mixture of R:S
enantiomers, was added to 10% aqueous CH3CN (165 mL) and
warmed to 50 °C to give a homogeneous solution. Benzyl
paraben (0.38 g) and Cs2CO3 (0.5 g) were added, and the
mixture was aged at 50-55 °C for 6 h. After the solution was
cooled to room temperature, H2O (500 mL) and MTBE (100
mL) were added. The aqueous phase was extracted with
MTBE (100 mL), and the combined organic phases were
washed with saturated aqueous NaCl (50 mL), concentrated
in vacuo (40 °C, 28 in. of Hg) to a volume of ∼80 mL, diluted
with EtOH (75 mL), reevaporated to ∼80 mL, and then diluted
with EtOH to a 150 mL volume, whereupon the benzyl ester
began to slowly crystallize after seeding. H2O (100 mL) was
added dropwise over 1 h, and the mixture was aged for 1 h,
filtered, washed with 33% (v/v) aqueous EtOH (100 mL), and
then dried in vacuo (45 °C, 20 h) to give 45.2 g of crystalline
racemic ester 5 (98.7 wt % by HPLC assay, see above, 90%
yield).
4.12 mol) in toluene (1.9 L) was added while a temperature of
∼0 °C was maintained. The mixture was stirred at 0 °C for
2-4 h; then the reaction was quenched by the slow addition
of cold 2 N HCl (8.8 L) while a temperature of <5 °C was
maintained. The aqueous layer was extracted with a 1:1
mixture of hexanes:toluene (2 L). The combined organic layers
3
were washed with aqueous NaHCO (1.5 L) and 10% aqueous
NaCl (1.5 L). The organic layer was dried with Na2SO4 (700
g) and was filtered to provide a solution of alcohol 9 (784 g,
4.03 mol) in 98% yield and 99.2% ee. Chiral HPLC assay:
Chiralcel-OD, 250 × 4.6 mm, 280 nm, i-PrOH:hexane, isocratic
7.5:92.5, 1.5 mL/min; tR {min} (R)-9, 5.3; (S)-9, 7.5. HPLC
assay: Zorbax Phenyl, 250 × 4.6 mm, 5 µm, 210 nm; CH3CN:
0.1% H3PO4, gradient, 50:50 at t ) 0 min, 90:10 at t ) 18 min,
1.0 mL/min; tR {min} 9, 5.8; 7, 3.8 min; toluene, 7.7. A sample
was concentrated for analysis. 1H NMR (250.13 MHz): δ 6.82
(s, 1H), 6.74 (s, 2H), 5.91 (s, 2H), 4.53 (t, J ) 6.64, 1H), 2.39
(br s, 1H), 1.80-1.51 (om, 2H), 1.45 (om, 2H), 0.90 (t, J ) 7.3,
3H). 13C NMR (62.89 MHz): δ 147.5, 146.6, 139.0, 119.2,
107.8, 106.3, 100.8, 74.0, 41.0, 18.9, 13.8. IR (film): λmax 3381,
2857, 1504, 1487, 1442, 1244, 1040, 939, 811 cm-1. HRMS:
[M+] ) 1 94.0952 (calcd ) 194.0943).
(R)-r-P r op ylp ip er on yla m in e (11). In a Pyrex glass ves-
sel, alcohol 9 (1.20 kg, 6.2 mol) in toluene (12 L) was cooled to
5 °C. Diphenylphosphoryl azide (1.60 L, 7.42 mol) was added;
then DBU (1.11 L) was added at such a rate as to maintain a
temperature of e5 °C. The reaction was allowed to warm to
rt over 2-3 h, forming two liquid layers upon 16 h of aging.
[Caution: Tests have shown that azide 10 and toluene solutions
of the azide are shock sensitive and undergo exothermic
decomposition beginning at ∼50 °C.] The two liquid layers
were diluted with H2O (7 L) and separated. The aqueous layer
was extracted with toluene (1 L); then the combined organic
extracts were washed sequentially with H2O (7 L), cold 1 N
aqueous HCl (4 L), H2O (4 L), and 10% aqueous NaCl (4 L).
The organic layer was dried with anhydrous Na2SO4 and
filtered. On a large scale, no attempt was made to concentrate
the azide solution. HPLC conditions: Inertsil Phenyl, 250 ×
4.6 mm; 5 µm; 210 nm; CH3CN:0.1% H3PO4, gradient 50:50
at t ) 0 min, 90:10 at t ) 18 min, 1.0 mL/min; tR {min} 9, 5.9;
toluene 7.8; (PhO)2P(O)N3, 9.3; 10, 11.4. To dry THF (6.3 L)
cooled to 10 °C was added a 1 M LAH/THF solution (6.0 L).
An azide 10 solution was added to the LAH over ∼2 h at such
a rate as to maintain the temperature at 23 ( 2 °C. The
reaction was aged until gas evolution (N2) ceased (6 h). Then
the reaction mixture was cooled to 0 °C, and the excess LAH
was quenched by the slow addition of H2O (400 mL). A 17.5
wt % aqueous potassium sodium tartrate solution (8 L) was
added to the reaction, and the mixture was stirred at room
temperature for 16 h. The aqueous layer was extracted with
toluene (2 L), and the combined organic phases were washed
with H2O (7 L). The organic phase was extracted with cold 1
N HCl (7 L). The aqueous phase was adjusted to pH 13 with
25 wt % aqueous NaOH and then extracted with toluene (4
L). After the toluene layer was washed with 10% aqueous
NaCl (4 L) and dried with anhydrous Na2SO4 (500 g), it was
filtered and concentrated to give amine 11 as an oil (740 g,
57% yield of (R)-11 over two steps, 85% ee). HPLC assay:
Inertsil ODS-2, 250 × 4.6 mm, 5 µm; 210 nm; CH3CN:10 mM
pH 6.5 potassium phosphate buffer:MeOH; gradient 36:60:6
at t ) 0 min, 64:30:6 at t ) 12 min, 67:27:6 at t ) 18 min,
74:20:6 at t ) 19 min, 74:20:6 at t ) 25 min; 1.0 mL/min; 30
°C; tR {min} 11, 5.0; toluene, 14.7. The ratio of enantiomers
was determined by either of two Chiral HPLC methods: (1)
Chiralcel OD-R, 250 × 4.6 mm, 238 nm, CH3CN:0.1% HClO4;
isocratic 15:85; 1.0 mL/min; 23 °C; tR {min} (R)-11, 7.3; (S)-
11, 15.0; alternatively, (2) SFC HPLC: Chiracel OD(H); 250
× 4.6 mm; 238 nm; 22% MeOH modifier (containing 0.1 vol %
of 70% HClO4); 1 mL/min; 35 °C; 300 Bar; tR{min}: (R)-11,
6.1; (S)-11, 8.8. Azide 10. 1H NMR (300.133 MHz, CDCl3): δ
6.81 (d, J ) 1.6, 1H), 6.80 (d, J ) 7.9, 1H), 6.75 (dd, J ) 7.9,
1.6, 1H), 5.99 (s, 2H), 4.34 (t, J ) 7.3, 1H), 1.86-1.61 (m, 2H),
1.45-1.24 (m, 2H), 0.92 (t, J ) 7.3, 3H). 13C NMR (75.469
MHz, CDCl3): δ 148.0, 147.4, 133.7, 120.6, 108.2, 107.0, 101.2,
66.0, 38.2, 19.5, 13.7. Amine 11: 1H NMR (250.13 MHz,
CDCl3): δ 6.76 (s, 1H), 6.66 (s, 2H), 5.83 (s, 2H), 3.73 (t, J )
Racemized ester was resubmitted to enzyme hydrolysis,
using recycled enzyme, and identical results were achieved.
(S)-3,3-Dieth yl-4-(4′-((N-m eth ylp ip er a zin -1-yl)ca r bon -
yl)p h en oxy)-2-a zetid in on e (2). (S)-6:(S)-MBA salt (3.30 kg,
8.58 mol, 96.4% ee) was suspended in i-PrOAc (30 L). H2O (1
L) was added. To this mixture, maintained at 25 °C was added
a 1 N aqueous H3PO4 solution (11.8 L) dropwise until all the
solids were dissolved, and a constant pH of 2.0 was achieved.
NaCl (1.0 kg) was added, and the phases were separated. The
i-PrOAc solution was concentrated in vacuo to ∼16 L (KF ∼8
mg/mL) whereupon acid (S)-6 began to crystallize. i-PrOAc
(10 L) was added, and the solution was dried by azeotropic
distillation in vacuo to KF ) 0.4 mg/mL. The mixture was
warmed to 55 °C, N-methylpiperazine (1.05 kg, 10.46 mol) and
HOBT (146 g, 1.08 mol) were added, and then a solution of
DCC (2.97 kg, 14.4 mol) in i-PrOAc (3 L) was added over 5
min. The reaction temperature was adjusted to 48-50 °C and
aged for 1.5 h. The reaction mixture was cooled to 18 °C and
filtered. The cake was washed with i-PrOAc (3 L), and the
filtrate was concentrated in vacuo to a volume of ∼8 L.
Crystallization began during distillation. The mixture was
aged for 18 h at 18 °C and 2 h at 10 °C and then filtered and
washed with cold i-PrOAc (3 L). The cake was dried with a
stream of nitrogen for 40 h to give â-lactam 2 (1.98 kg, 99.5
area %, 66% isolated yield) as a white crystalline solid. Chiral
SFC assay showed that the crystallization enriched the (S)-
enantiomer (solids, 99.4% ee; mother liquour, 87.2% ee).
HPLC assay: Inertsil C8, 250 × 4.6 mm, 5 µm; CH3CN:H2O
(with 0.1% H3PO4); gradient elution 3:97 to 80:20 over 20 min,
248 nm, 25 °C, 2.0 mL/min; tR{min} â-lactam 2, 7.9; 6, 14.2.
Chiral SFC HPLC assay: Chiralcel OD(H), 250 × 4.6 mm, 20%
MeOH (containing 0.1% TEA) modifier; 1.0 mL/min, 300 bar,
248 nm; tR {min} (S)-2, 7.3, (R)-2, 10.1. [R]25 -81.2° (c )
589
5.0, MeOH). 1H NMR (250.13 MHz): δ 8.09 (s, 1H), 7.23 (d,
J ) 8.7, 2H), 6.72 (d, J ) 8.7, 2H), 5.14 (s, 1H), 3.75-3.10 (br
m, 4H), 2.43-2.00 (br m, 4H), 2.13 (s, 3H), 1.88-1.51 (om, 4H),
0.91-0.81 (om, 6H). 13C NMR (62.89 MHz): δ 172.6, 169.5,
157.3, 128.8, 128.5, 115.1, 82.7, 64.0, 54.4, 45.5, 23.4, 21.3, 8.6,
8.3. Mp: 117.5-120.7 °C. IR (film): 3550, 3200, 2915, 2840,
1767, 1607, 1462, 1437, 1237, 1053 cm-1
.
Anal. Calcd for C19H27N3O3: C, 66.06; H, 7.88; N, 12.16.
Found: C, 66.00; H, 8.12; N, 12.10.
(S)-r-P r op ylp ip er on yl Alcoh ol (9). Titanium(IV) isopro-
poxide (226 mL) was charged to a slurry of (R,R)-1,2-diami-
nocyclohexane ditrifluoromethanesulfonamide11 (29.6 g) in
toluene (1.25 L) at room temperature. The mixture was heated
to 40 °C for 20 min and then cooled to 20 °C. In a separate
flask, Zn(n-Pr)2 (850 g, 5.60 mol) was added to cold (-5 °C)
hexanes (5.6 L). The titanium catalyst mixture was added to
the Zn(n-Pr)2 solution; then a solution of piperonal (7, 619 g,

6580 J . Org. Chem., Vol. 61, No. 19, 1996
Cvetovich et al.
6.9, 1H), 1.62-1.46 (om, 2H), 1.41 (br s, 2H), 1.36-1.07 (m,
2H), 0.83 (t, J ) 7.3, 3H). 13C NMR (62.896 MHz, CDCl3): δ
147.4, 146.0, 140.7, 119.2, 107.7, 106.3, 100.5, 55.5, 41.6, 19.4,
13.7. IR (film): λmax 3330, 2956, 1486, 1440, 1245, 1040, 937,
810 cm-1. HRMS: [M+] ) 193.1073 (calcd ) 193.1103).
Op tica l P u r ifica tion of (R)-r-P r op ylp ip er on yla m in e
(11). A solution R-propylpiperonylamine (11) (1.523 kg, 7.88
mol, 85% ee) in EtOAc (30.5 L) and EtOH (1.5 L) was heated
to 50-55 °C. D-Pyroglutamic acid (150 g) was added, and the
solution was seeded with amine/D-pyroglutamic acid salt (5
g). Additional D-pyroglutamic acid (769 g) was added in
portions over 30 min as the salt crystallized. The mixture was
allowed to cool to 20-22 °C over 2-3 h and was aged for 16 h.
The slurry was filtered, and the cake was washed with a
mixture of EtOAc (5 L) and EtOH (0.25 L). The cake was
dissolved in a mixture of toluene (6 L) and cold 2.5% aqueous
NaOH (15 L). The toluene layer was washed with 10%
aqueous NaCl (3 L), dried with anhydrous Na2SO4 (500 g),
filtered, and concentrated to give amine 11 as an oil (1.315
kg, 92% yield, 98.2% ee). (R)-R-Propylpiperonylamine D-
[S-(R*,S*)]-2-[4-[(4-Meth ylp ip er a zin -1-yl)ca r bon yl]p h e-
n oxy]-3,3-d ieth yl-N-[1-(3,4-(m eth ylen ed ioxy)p h en yl)bu -
tyl]-4-oxo-1-a zetid in eca r boxa m id e (1). A slurry of (S)-â-
lactam 2 (1.77 kg, 5.12 mol) and (R)-isocyanate 3 (1.12 kg, 5.11
mol) in CH3CN (23.5 L) was cooled to 4 °C. DBU (76 g, 0.5
mol) dissolved in CH3CN (0.5 L) was added to the mixture over
1 min with cooling. The mixture was aged for a total of 60
min and then poured into a stirring mixture of H2O (100 L,
containing 1 wt % sodium chloride) and i-PrOAc (50 L). The
organic phase was washed with H2O (2 × 20 L, containing 1
wt % sodium chloride) and then saturated aqueous sodium
chloride (10 L). The organic phase was concentrated in vacuo
to 40 L, diluted with i-PrOAc (20 L), and reconcentrated to
∼6 L. The concentrate was diluted with MTBE (4 L),
reconcentrated, and diluted with MTBE (4 L). The product
was crystallized by being heated to reflux and cooled to 0 °C.
The mixture was aged for 1 h and filtered. The cake was
washed with cold (-10 °C) MTBE (6 L) and dried at rt with a
nitrogen flow for 18 h, to give L-694,458 (1, 2.25 kg, >99.5%
de) as a crystalline white solid. HPLC assay: Inertsil C8, 250
× 4.6 mm; 5 µm; CH3CN:H2O (0.1% HClO4); gradient: 25:75
to 100:0 over 20 min; 2.0 mL/min, 230 nm, 25 °C; tR {min} 2,
3.6; L-694,458,1, 9.9; 3, 13.8. Chiral SFC HPLC assay:
Chiralcel OD(H), 250 × 4.6 mm, MeOH (containing 0.1% TEA)
modifier; gradient (8-32%, rate 1%/min); 30 min, 300 bar, 1.0
mL/min, 35 °C, 230 nm; tR {min} (R,R)-diastereomer, 11.65
min; (R,S)-diastereomer, 12.19 min; L-694,458, 1 (S,R), 14.76
pyroglutamic acid salt. Mp: 106.5-107.5 °C, [R]25 -17.7°
405
(c ) 1.0, MeOH). 1H NMR (250.13 MHz, CDCl3): δ 8.2 (br s,
3H), 7.82 (s, 1H), 6.92 (s, 1H), 6.8-6.7 (om, 2H), 5.91 (s, 2H),
3.95 (dd, J ) 9.3, 5.5, 1H), 3.76 (m, 1H), 2.28-2.05 (om, 3H),
1.96-1.70 (om, 3H), 1.27-1.02 (om, 2H), 0.83 (t, J ) 7.1, 3H).
13C NMR (62.896 MHz, CDCl3): δ 179.2, 178.1, 148.0, 147.6,
132.0, 121.3, 108.2, 107.5, 101.2, 58.4, 55.0, 36.9, 30.6, 25.4,
19.0, 13.6.
min; (S,S)-diastereomer, 20.37 min. [R]25 +57.7° (c ) 5.0,
589
Anal. Calcd for C16H22N2O5: C, 59.62; H, 6.88; N, 8.69.
Found: C, 59.48; H, 6.87; N, 8.63.
MeOH). Mp: 117.5-118.8 °C. 1H NMR (399.872 MHz, CD3-
CN): δ 7.39 (m, 2H), 7.27 (m, 2H), 6.88 (d, J ∼7, 1H), 6.87 (s,
1H), 6.82 (m, 2H), 5.97 (s, 2H), 5.79 (s, 1H), 4.74 (q, J ) 7.0,
1H), 3.54 (v br s, 4H), 2.36 (br s, 4H), 2.26 (s, 3H), 1.97 (m,
1H), 1.89-1.69 (om, 5H), 1.44-1.21 (om, 2H), 1.06 (t, J ) 7.5,
3H), 0.95 (t, J ) 7.2, 3H), 0.93 (t, J ) 7.2, 3H). 13C NMR
(100.558 MHz, CD3CN): δ 172.9, 170.1, 159.0, 150.2, 148.9,
147.7, 137.9, 131.9, 129.8 (2C), 118.05 (2C), 108.9, 107.6, 102.3,
86.8, 65.2, 55.7 (2C), 54.8, 48 (v br, 2C), 46.2, 43 (v br), 39.4,
24.0, 21.8, 20.2, 14.0, 9.2, 8.8. IR (film): λmax 3350, 1770, 1710,
(R)-r-P r op ylp ip er on yl Isocya n a te (3). To a solution of
(R)-11 (1.16 kg, 6.14 mol) in toluene (24 L) was added 12 N
HCl (582 mL) over 5-10 min to form a thick slurry. The slurry
was azeotropically dried using a Dean-Stark trap. When the
distillate was clear, additional toluene (2.4 L) was distilled.
The mixture was then allowed to cool to 100 °C, and a solution
of phosgene in toluene (1.93 M, 9.54 L) was added over 1 h
while a temperature of 100 °C was maintained. The resulting
homogeneous solution was heated at 100 °C for an additional
20 min, cooled to 0 °C, washed with 5% NaHCO3 (1 × 18 L, 2
× 9 L) and H2O (2 × 9 L), and then dried with Na2SO4 (2.4
kg). The mixture was filtered, and the filtrate was concen-
trated to give isocyanate 3 as an oil (1.346 kg, 98% yield).
HPLC assay: Inertsil ODS-2, 250 × 4.6 mm; 5 µm; 210 nm;
CH3CN:10 mM pH 6.5 potassium phosphate buffer:MeOH;
isocratic, 64:30:6, 1.0 mL/min; tR {min} 11, 4.9; 3, 10.4. 1H
NMR (250.13 MHz, CDCl3): δ 6.81-6.71 (om, 3H), 5.96 (s, 2H),
4.49 (dd, J ) 8.0, 6.0, 1H), 1.88-1.64 (om, 2H), 1.52-1.26 (om,
2H), 0.94 (t, J ) 7.4, 3H). 13C NMR (75.469 MHz, CDCl3): δ
147.9, 147.1, 135.5, 119.2, 108.1, 106.2, 101.2, 58.9, 41.7, 19.4,
13.5. IR (film): λmax 2980, 2950, 2890, 2270, 1510, 1495, 1500,
1250, 1040, 935, 810 cm-1. HRMS: [M+] ) 219.0880 (calcd )
219.0895).
1630, 1295, 1230 cm-1
.
Anal. Calcd for C31H40N4O6: C, 65.94; H, 7.14; N, 9.92.
Found: C, 65.85; H, 7.20; N, 9.84.
Ack n ow led gm en t. We are grateful to Ms. Debbie
Zink for providing us with the high-resolution mass
spectra.
Su p p or t in g In for m a t ion Ava ila b le: 1H NMR and 13C
NMR spectra for compounds 1-3, 4-6, and 9-11 (19 pages).
This material is contained in libraries on microfiche, im-
mediately follows this article in the microfilm version of this
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J O960618K