Process development of a large-scale synthesis of TKA731: A tachykinin receptor antagonist

Article abstract of DOI:10.1021/op0341824

An efficient and chromatography-free large-scale synthesis of a tachykinin receptor antagonist TKA731 (1), utilizing the coupling of dipeptide 7 and 2-chloro-4(3H)-quinazolinone (13) as the key step, is described. The overall yield of 1 from BOC-L-3-(2-naphthyl)alanine (2) in six linear steps (total of eight steps) is 63%. This new convergent approach avoided the use of methyl iodide and the formation of methanethiol byproduct in the last step involving the construction of the quinazolinone ring in the original discovery synthesis. Four chromatographies were also eliminated. The main cause of the side reaction, leading to the urethane byproduct (I) formation and starting amino acid (2) liberation during the coupling of 2 with N-benzylmethylamine using well-known isobutyl chloroformate mediated mixed carboxylic-carbonic anhydride method, was found to be the symmetrical anhydride (III) formation from 2 as determined by the CO₂ offgas formation. A new procedure for the coupling of 2 with N-benzylmethylamine involving a reverse addition of 2 and the base to the coupling agent isobutyl chloroformate, followed by the addition of the amine, was developed that minimized the symmetrical anhydride formation. A novel, water-assisted N-methylation of 5 with dimethyl sulfate in the presence of sodium hydride in THF was also developed that eliminated the use of methyl iodide, silver oxide, and KCN. Deprotection of the BOC group in 6 with sulfuric acid circumvented the formation of diketopiperazine and tetrapeptide observed with HCl and trifluoroacetic acid, respectively.

Full text of DOI:10.1021/op0341824

Organic Process Research & Development 2004, 8, 330−340
Articles
Process Development of a Large-Scale Synthesis of TKA731: A Tachykinin
Receptor Antagonist
Mahavir Prashad,* Denis Har, Bin Hu, Hong-Yong Kim, Michael J. Girgis, Apurva Chaudhary, Oljan Repicˇ, and
Thomas J. Blacklock
Process Research and DeVelopment, Chemical and Analytical DeVelopment, NoVartis Institute for Biomedical Research,
One Health Plaza, East HanoVer, New Jersey 07936, U.S.A.
Wolfgang Marterer
Process Research and DeVelopment, Chemical and Analytical DeVelopment, NoVartis Pharma AG,
CH 4002 Basel, Switzerland
Abstract:
depicted in Scheme 1, which is a linear nine-step synthesis
with four chromatographies. Coupling of BOC-L-3-(2-
naphthyl)alanine (2) with N-benzylmethylamine in the pres-
ence of isobutyl chloroformate in dichloromethane gave
intermediate 3. Deprotection of Boc group in 3 with HCl
gas in dioxane afforded the hydrochloride salt 4. Coupling
of the free base of 4 with Boc-L-proline in the presence of
isobutyl chloroformate and 4-methylmorpholine in dichlo-
romethane yielded dipeptide 5. N-Methylation of dipeptide
5 was achieved with an excess of methyl iodide (8 equiv)
and silver oxide (4 equiv) in DMF at 60 °C followed by
workup using KCN. The resulting N-methylated derivative
6 was purified by silica gel chromatography. Deprotection
of 6 with HCl gas in dioxane yielded amine 7, that was then
treated with 2-methoxycarbonyl phenyl isothiocyanate in
dichloromethane to afford 8 in 90% yield after a chroma-
tography. Saponification of the methyl ester 8 with 5 N
aqueous NaOH in methanol afforded the acid 9, which was
treated with ammonium hydroxide in the presence of isobutyl
chloroformate and 4-methylmorpholine in dichloromethane
to furnish the amide 10 in 89% yield after a silica gel
chromatography. The last step, involving the construction
of the quinazolinone ring, was carried out by a treatment of
10 with an excess of methyl iodide in THF. Methanethiol
was produced as the byproduct in this cyclization reaction.
This afforded the drug substance 1 as an amorphous powder
in only 43% yield after a silica gel chromatography. The
overall yield of 1 was 31.6% from BOC-L-3-(2-naphthyl)-
alanine (2).
An efficient and chromatography-free large-scale synthesis of
a tachykinin receptor antagonist TKA731 (1), utilizing the
coupling of dipeptide 7 and 2-chloro-4(3H)-quinazolinone (13)
as the key step, is described. The overall yield of 1 from BOC-
L
-3-(2-naphthyl)alanine (2) in six linear steps (total of eight
steps) is 63%. This new convergent approach avoided the use
of methyl iodide and the formation of methanethiol byproduct
in the last step involving the construction of the quinazolinone
ring in the original discovery synthesis. Four chromatographies
were also eliminated. The main cause of the side reaction,
leading to the urethane byproduct (I) formation and starting
amino acid (2) liberation during the coupling of 2 with
N-benzylmethylamine using well-known isobutyl chloroformate
mediated mixed carboxylic-carbonic anhydride method, was
found to be the symmetrical anhydride (III) formation from 2
as determined by the CO2 offgas formation. A new procedure
for the coupling of 2 with N-benzylmethylamine involving a
reverse addition of 2 and the base to the coupling agent isobutyl
chloroformate, followed by the addition of the amine, was
developed that minimized the symmetrical anhydride formation.
A novel, water-assisted N-methylation of 5 with dimethyl sulfate
in the presence of sodium hydride in THF was also developed
that eliminated the use of methyl iodide, silver oxide, and KCN.
Deprotection of the BOC group in 6 with sulfuric acid
circumvented the formation of diketopiperazine and tetrapep-
tide observed with HCl and trifluoroacetic acid, respectively.
Introduction
Results and Discussion
TKA731 (1) is a potent and selective antagonist for the
human NK-1 tachykinin receptor.1 It is targeted for the
treatment of chronic inflammatory pain and diabetic neur-
opathy pain, and pain associated with angina, renal or billiary
colic, and menstruation. The discovery synthesis of 1 is
At the onset of this project we decided to modify the
discovery synthesis beyond intermediate 7 involving the
construction of quinazolinone ring to produce 1. This was
because of three chromatographies, use of methyl iodide,
methanethiol byproduct formation in the last cyclization step
of the amide 10 to 1, and poor yield. Thus, our goal was to
(1) Walpole, C. S. J.; Prashad, M.; Har, D. U.S. Patent 6,107,293, 2000.
330
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10.1021/op0341824 CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/17/2004

Scheme 1
develop an efficient and convergent synthesis of 1 that would
overcome these problems and would be practicable for large-
scale preparation in our pilot plant. Our strategy, as illustrated
in Scheme 2, was first to construct the quinazolinone ring
with a leaving group at the 2-position, as in 2-chloro-4(3H)-
quinazolinone (13),2 and then couple2,3 it with dipeptide 7
to afford the drug substance 1.
phosphorus oxychloride to 2,4-dichloroquinazoline (12)
followed by the selective hydrolysis of 12 with aqueous
NaOH to 13. However, scale-up of the known conditions4
for the dichlorination of 11 using N,N-dimethylaniline and
workup proved problematic since it led to the decomposition
of 12 back to 11 during quenching of the reaction mixture
and during the drying of the product. This prompted us to
develop alternative reaction and workup conditions for this
dichlorination step (Scheme 3).6 Thus, reaction of benzoyl-
eneurea (11) with phosphorus oxychloride (5 mL/g of 11)
in the presence of tripropylamine (2.15 equiv) at 102-105
°C for 3 h yielded a brown solution. Removal of phosphorus
oxychloride by distillation and an azeotrope with toluene
yielded a solution of 2,4-dichloroquinazoline (12) (Scheme
3) in toluene, which was quenched with water. Separation
of the organic layer followed by washing with 5% sodium
The synthesis of 13 from benzolyeneurea (11) was known
in the literature.4-6 It involved the dichlorination of 11 with
(2) DeRuiter, J.; Brubaker, A. N.; Millen, J.; Riley, T. N. J. Med. Chem. 1986,
29, 627-629.
(3) Ogawa, N.; Yoshida, T.; Aratani, T.; Koshinaka, E.; Kato, H.; Ito, Y. Chem.
Pharm. Bull. 1988, 36, 2955-2967.
(4) Lacefield, W. B. U.S. Patent 3,956,495, 1976.
(5) Lange, N. A.; Roush, W. E.; Asbeck, H. J. J. Am. Chem. Soc. 1930, 52,
3696-3702.
(6) Scarborough, H. C.; Lawes, B. C.; Minielli, J. L.; Compton, J. L. J. Org.
Chem. 1962, 27, 957-961.
Vol. 8, No. 3, 2004 / Organic Process Research & Development
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331

Scheme 2
ethyl acetate. Three issues needed to be addressed with the
coupling conditions of 2 with N-benzylmethylamine for the
large-scale synthesis of TKA731 (1). First, we had to replace
4-methylmorpholine with a base that could be extracted from
the aqueous layer to address the disposal concerns with the
aqueous layer. Second, to avoid a solvent exchange, ethyl
acetate required replacement with a solvent that was compat-
ible with aqueous HCl in the next deprotection step. Finally,
since multiple additions of isobutyl chloroformate and
N-benzylmethylamine were necessary to recycle in situ the
liberated starting material 2 due to the urethane (I, Scheme
4) byproduct formation during the coupling reaction, and to
drive the reaction to completion to 3, our goal was also to
develop a procedure that would avoid such multiple additions
and make the procedure more convenient for large scale.
Byproduct urethane I did not present any purification
problems as it was easily removed in the mother liquor during
the isolation of crystalline 4 after the deprotection step. Since
the next deprotection step is carried out under acidic
conditions in toluene, we decided to replace the ethyl acetate
in the coupling step with toluene. 4-Methylmorpholine was
replaced by N,N-dimethylbenzylamine as the base, because
it could be easily extracted with heptane or toluene from
the aqueous layer after basification (and recycled). The
coupling reaction could also be satisfactorily carried out at
-10 °C instead of -15 °C. Further optimization of the
coupling reaction of 2 with N-benzylmethylamine proved to
be quite interesting. The formation of the urethane byproduct
I could either be due to the aminolysis at the undesired
carbonyl9,10-15 of the mixed carboxylic-carbonic anhydride
intermediate II with N-benzylmethylamine, or due to the
symmetrical anhydride III formation,12 leaving unconsumed
isobutyl chloroformate in the reaction mixture to react with
N-benzylmethylamine (Scheme 4). In both cases, the reaction
would also result in the liberation of the starting material 2.
To avoid the multiple additions of reagents and make the
process more convenient for large scale, it became necessary
for us to understand the mechanism of the urethane byproduct
I formation and the liberation of the starting material 2. We
recently reported the development of a novel method using
the formation of CO2 offgas as the probe for elucidating the
mechanism of the formation of I and liberation of the starting
material 2.16,17 This method was based on the rationale that
the symmetrical anhydride III formation would be ac-
companied by the formation of an equivalent amount of CO2
during the first step involving the preparation of mixed
carboxylic-carbonic anhydride II from 2. This was because
initially formed II can react further with 2, present in excess,
Scheme 3
hydroxide and water gave a neutral organic layer. Concentra-
tion of the organic layer and addition of heptane yielded 2,4-
dichloroquinazoline (12) as a white solid in 75% yield.
Hydrolysis of 12 with 2 N sodium hydroxide afforded pure
2-chloro-4(3H)-quinazolinone (13)2 in 98% yield. Intermedi-
ate 13 is unstable at room temperature and must be stored
in a refrigerator. One of the drawbacks with the preparation
of 2,4-dichloroquinazoline (12) was the use of excess of
phosphorus oxychloride and its removal by distillation. To
circumvent these problems, we developed an improved
process for the dichlorination of 11 that involved the
treatment of 11 with phosphorus oxychloride (2.3 equiv) and
tripropylamine (2.05 equiv) in refluxing toluene. The reaction
mixture was quenched by reverse addition to water to furnish
a biphasic mixture. Workup and concentration of the organic
layer, and recrystallization of the crude product from heptane,
afforded 12 in 87.6% yield.
The first two steps of the synthesis of intermediate
dipeptide 7 were identical to those utilized in the synthesis
of NKT343.7,8 In connection with the synthesis of NKT343,
we reported9 the details of our early results on the process
development of 4 from the coupling of BOC-L-3-(2-naph-
thyl)alanine (2) with N-benzylmethylamine in the presence
of isobutyl chloroformate and 4-methylmorpholine in ethyl
acetate under the well-known two-step conventional condi-
tions, followed by the deprotection of 3 with HCl gas in
(10) Sole, N.; Torres, J. L.; Anton, J. M. G.; Valencia, G.; Reig, F. Tetrahedron
1986, 42, 193-198.
(11) Chen, F. M. F.; Lee, Y.; Steinauer, R.; Benoiton, N. L. Can. J. Chem. 1987,
65, 613-618.
(12) Chen, F. M. F.; Benoiton, N. L. Can. J. Chem. 1987, 65, 619-625.
(13) Thaler, A.; Seebach, D.; Cardinaux, F. HelV. Chim. Acta 1991, 74, 617-
627.
(14) Chen, F. M. F.; Steinauer, R.; Bentoin, N. L. J. Org. Chem. 1983, 48, 2939-
(7) Ko, S. Y.; Walpole, C. WO 96/18643, 1996.
2941.
(8) Walpole, C.; Ko, S. Y.; Brown, M.; Beattie, D.; Campbell, E.; Dickenson,
F.; Swan, S.; Hughes, G. A. Lemaire, M.; Lerpiniere, J.; Patel, S.; Urban,
L. J. Med. Chem. 1998, 41, 3159-3173.
(9) Prashad, M.; Prasad, K.; Repicˇ, O.; Blacklock, T. J.; Prikoszovich, W. Org.
Process Res. DeV. 1999, 3, 409-415.
(15) Bodanszky, M.; Tolle, J. Int. J. Pept. Protein Res. 1977, 10, 380-384.
(16) Chaudhary, A.; Girgis, M. J.; Prashad, M.; Hu, B.; Har, D.; Repicˇ, O.;
Blacklock, T. J. Tetrahedron Lett. 2003, 44, 5543-5546.
(17) Chaudhary, A.; Girgis, M. J.; Prashad, M.; Hu, B.; Har, D.; Repicˇ, O.;
Blacklock, T. J. Org. Process Res. DeV. 2003, 7, 888-895.
332
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Scheme 4
to afford the symmetrical anydride III, isobutanol, and CO2,
leaving some of isobutyl chloroformate unconsumed. Thus,
if the CO2 formation were observed during the formation of
mixed carboxylic-carbonic anhydride II (before amine
addition), then the urethane I would form as a result of the
reaction of unconsumed isobutyl chloroformate with N-
benzylmethylamine. Otherwise, its origin must be aminolysis
at the undesired carbonyl in II. Thus, by quantifying the
amount of CO2 formed during the preparation of II, one can
also determine whether there was any aminolysis at the
undesired carbonyl in II. This would ascertain whether both
effects are operating and to what extent. The reaction of 2
with isobutyl chloroformate in the presence of N,N-dimeth-
ylbenzylamine led to a significant amount of CO2 formation,
indicating the formation of 17.5% of symmetrical anhydride
III along with II. Only a minor (<2.0%) amount of
aminolysis at the undesired carbonyl in II was observed.16,17
These results were consistent with the amount of liberated
amino acid 2 at the end of the reaction as determined by
HPLC. Formation of substantial amounts of CO2 in the first
step clearly demonstrated that the formation of the urethane
I and liberation of the starting material 2 was mainly due
to the symmetrical anhydride III formation during the
preparation of II. No corresponding isobutyl ester of 2 was
detected, suggesting that liberated isobutanol did not react
with II to produce CO2. tert-Butyloxycarbonyl protecting
group on nitrogen is known18 to prevent the formation of
oxazolinone that would have resulted in CO2 production from
II. We reasoned that the symmetrical anhydride formation,
and in turn the multiple additions of reagents to recycle in
situ the liberated starting material 2, could be avoided by
reverting the order of addition of isobutyl chloroformate and
2. One-stage conditions19 involving the addition of isobutyl
chloroformate to a solution of 2, N-methylbenzylamine, and
4-methylmorpholine in THF led to ∼30% of 2, again
requiring multiple additions of isobutyl chloroformate to
drive the reaction to completion. We have thus developed a
new procedure that involves a reverse addition of 2 and N,N-
dimethylbenzylamine in toluene to a solution of isobutyl
chloroformate in toluene, followed by the addition of
N-benzylmethylamine. These conditions led to completion
of the reaction and avoided the multiple additions of isobutyl
chloroformate. Only 1.9% of symmetrical anhydride III
formed under these conditions during the reaction of 2 with
isobutyl chloroformate as determined by CO2 analysis and
confirmed by measuring liberated 2. Such a reverse addition
of the amino acid to isobutyl chloroformate has not been
reported previously in the peptide-coupling chemistry, and
it represents a new methodology that is racemization free.
These newly developed conditions were successfully scaled
up in our pilot plant on 63.0-kg scale of 2.
Our previously reported process for the deprotection of
the BOC group in 3 utilized HCl gas in ethyl acetate.9 The
reaction mixture required concentration to remove HCl gas,
and the hydrochloride salt 4 was isolated by filtration. Our
goal was to avoid the use of HCl gas and the concentration
of the reaction mixture on production scale. We found that
the deprotection of the BOC group in 3 could be carried out
with concentrated aqueous HCl at 65 °C in toluene. Only
∼1% of over-hydrolysis of the amide 3 to L-3-(2-naphthyl)-
alanine was observed under these conditions. The hydro-
chloride salt that crystallized during the reaction was isolated
by filtration. Thus, use of HCl gas and the concentration of
the reaction mixture were eliminated. This afforded 4 in
93.4% yield (in two steps from 2) with >99% purity and
>99.5% enantiopurity. These deprotection conditions were
successfully scaled up in the pilot plant with a crude solution
of 3 in toluene from 63.0-kg scale of 2.
Our improvements7,9 of the discovery synthesis conditions
for the coupling of the free base from 4 with BOC-L-proline
with isobutyl chloroformate in ethyl acetate in the presence
of 4-methylmorpholine cleanly afforded dipeptide 5 without
any urethane byproduct formation that would be due to
(18) Bodanszky, M.; Klausner, Y. S.; Ondetti, M. A., Eds. Peptide Synthesis;
John Wiley & Sons: New York, London, Sydney, Toronto, 1976; pp 140.
(19) Shieh, W. C.; Carlson, J. A.; Shore, M. E. Tetrahedron Lett. 1999, 40, 7167-
7170.
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333

Scheme 5
aminolysis of the wrong carbonyl group in mixed carboxy-
lic-carbonic anhydride. We further optimized these condi-
tions for the manufacturing scale. In an analogy to the
coupling of 2 with N-benzylmethylamine, ethyl acetate was
replaced by toluene and 4-methylmorpholine by N,N-
dimethylbenzylamine. Thus, the free base from the HCl salt
4 was generated in toluene by a treatment with NaOH. The
resulting solution of the free base 4 was used directly in the
coupling reaction with BOC-L-proline in the presence of
isobutyl chloroformate and N,N-dimethylbenzylamine to
afford a solution of 5 in toluene. Since ∼40% of toluene
was well tolerated in the next N-methylation step, crude 5
was used for N-methylation after concentration. These
coupling conditions were successfully scaled up in the pilot
plant on 33.0-kg scale of 4 to afford 5 in quantitative yield.
The next step was the N-methylation of dipeptide 5 to 6.
The discovery synthesis conditions were not suitable for
scale-up in our pilot plant. The use of excess of methyl iodide
(8.0 equiv) and silver oxide (4.0 equiv), followed by workup
that involved distillative removal of methyl iodide using a
-78 °C cold trap and washing with KCN, was both
hazardous and uneconomical. Dimethyl sulfate was selected
as the suitable methylating agent to replace methyl iodide
because it is high boiling, and any excess of this reagent
could be safely destroyed with ammonium hydroxide. We
recently reported an efficient and practical N-methylation of
amino acid derivatives with dimethyl sulfate in the presence
of sodium hydride and a catalyic amount of water.20 Reaction
of water with sodium hydride generated highly reactive dry
sodium hydroxide, which led to much faster reaction rates
than powdered sodium hydroxide itself. No reaction was
observed without water. Thus, N-methylation of crude 5 with
dimethyl sulfate (1.8 equiv) in THF in the presence of sodium
hydride (2.0 equiv) and catalytic amounts of water (>0.1
equiv) at 8-15 °C afforded the N-methylated dipeptide 6 in
excellent yield which was used crude in the next step. The
reaction mixture was quenched with ammonium hydroxide
to destroy the excess of dimethyl sulfate and extracted with
toluene. No epimerization was observed at 8-15 °C,
however, ∼10% epimerization was observed at 30 °C. We
found that any residual ethyl acetate in crude 5 inhibited the
N-methylation, but 40% of toluene (of the desired volume
of THF) in 5 did not affect the N-methylation.
hydride (1.7 equiv), and dimethyl sulfate (1.54 equiv) in THF
at 10 °C for 3 h. Initially, the reaction was carried out by
the sequential addition of water, a solution of 5 in THF, and
dimethyl sulfate to a suspension of sodium hydride in THF
and was scaled up to a multikilogram scale in the pilot plant.
However, these reaction conditions were not addition-
controlled. We recognized that the safest way to perform
the N-methylation was to add a solution of 5, dimethyl
sulfate, and water in THF to a suspension of sodium hydride
in THF. These addition-controlled conditions were found to
be both safer and epimerization/racemization free as con-
firmed by a chiral HPLC.20 Finally, 6 was isolated by a
crystallization from a mixture of toluene and heptane in 86%
yield with 99% purity and >99.5% enantiopurity. These
N-methylation conditions were successfully scaled up in the
pilot plant with a crude solution of 5 in toluene (containing
48.0 kg of 5) obtained from 33.0-kg scale of 4 to afford 6 in
86.5% yield (in two steps from 4).
The discovery synthesis conditions for the deprotection
of 6 to 7 utilized HCl gas in dioxane. Dioxane is a toxic
solvent and was not deemed suitable for scale-up in our pilot
plant. Further optimization proved particularly onerous. On
the basis of our previous experience, dioxane was first
replaced by ethyl acetate. The deprotection of 6 with HCl
gas in ethyl acetate was satisfactory on a small scale;
however, a scale-up of these conditions led to a significant
loss in the yield (only 50%). Other byproducts, which were
isolated by silica gel chromatography, were identified as
diastereoisomers of diketopiperazine (IV, Scheme 5) formed
by an intramolecular cyclization.21 N-Benzylmethylamine
was also isolated from this reaction. These results were in
sharp contrast to those obtained with the deprotection of des-
methyl analogue 5 in our NKT343 synthesis,7,9 which gave
excellent yield of the deprotected compound without the
formation of any diketopiperazine byproducts. This marked
difference in intramolecular transamidative cyclization be-
havior between 5 and 6 can be attributed to the differences
It was imperative to optimize the above reaction around
the amount of water and to further design N-methylation
conditions that were addition-controlled to improve process
safety for large scale. We determined the optimized amount
of water to be 0.2 equiv (including residual water in 5 as
determined by Karl Fischer analysis). The reaction was very
slow with 0.125 equiv of water affording only 5% conversion
in 2 h at 10 °C. With 0.165 equiv of water, the reaction was
complete in 4 h, while with 0.2 equiv it required 2 h. Fastest
reaction rates were observed with 0.25 equiv of water leading
to completion of the reaction in 30 min. An excess of water
(0.752 equiv) slowed the reaction as it required 4 h. The
final reaction conditions utilized water (0.2 equiv), sodium
(20) Prashad, M.; Har, D.; Hu, B.; Kim, H. Y.; Repicˇ, O.; Blacklock, T. J. Org.
Lett. 2003, 5, 125-128.
(21) Dinsmore, C.; Beshore, D. C. Tetrahedron 2002, 58, 3297-3312.
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Figure 2.
formation of tetrapeptide impurities IV in the laboratory
experiments failed under a variety of conditions. Because
of this problem and the fact that trifluoroacetic acid is not a
preferred reagent in excess for manufacturing scale, we
needed to develop alternative conditions for the deprotection
of 6. We next investigated the deprotection of 6 with sulfuric
acid in toluene. No reaction was observed with 10% sulfuric
acid at 55 °C; however, the deprotection was complete in 3
h with 50% sulfuric acid at 52 °C. Dilution of the reaction
mixture with isopropyl acetate and basification with sodium
hydroxide gave the organic layer, which was treated with
heptane to afford crystalline 7 in 87.3% yield. The 1.0:2.0:
6.0 ratio of toluene, isopropyl acetate, and heptane (per gram
of the starting material 6 used) was important for the
crystallization, and up to 4.0% of water was well tolerated.
These conditions scaled up well in the pilot plant on 65.0-
kg scale of 6 to afford 7 in 89.0% yield with excellent purity.
No tetrapeptide impurities V and VI were detected by HPLC.
The optimized synthesis of 7 for the large-scale is depicted
in Scheme 6.
Before studying the coupling of dipeptide 7 and 13, we
first decided to develop a crystallization procedure for the
drug substance 1. This was because the drug substance 1
was initially an amorphous material, and it was purified by
a silica gel chromatography both by the discovery chemists
and us. Elimination of the silica gel chromatography was
highly desirable for production scale. Additionally, the drug
substance also retained solvents such as, ethyl acetate,
toluene, and heptane. Initially, crystallization of 1 was
effected from 2-propanol-water (1:1 v/v) and ethanol-water
(1.25:1.0 v/v) using seeds23 of analogous NKT343 (Figure
2),9 affording crystalline TKA731 (1) as confirmed by X-ray
powder diffraction. These seeds of 1 were then used in
subsequent crystallizations. We decided to use the ethanol-
water mixture for further work.
Figure 1.
in the conformations of dipeptides 5 and 6 due to the
N-methyl group. The intramolecular diketopiperazine forma-
tion from a dipeptide amide and an ester is known.22
Dipeptide 6 was stable after its isolation. Formation of a
mixture of two diastereomers of the diketopiperazine led us
to speculate that chloride from HCl may be catalyzing this
cyclization. We next investigated the deprotection of 6 with
trifluoroacetic acid that gave satisfactory results. For early-
phase development we had decided not to isolate the
N-methylated intermediate 6 and use the toluene solution in
the next deprotection step, as we had found that toluene was
a suitable solvent for the deprotection. Thus, treatment of a
solution of 6 in toluene with trifluoroacetic acid (7.5 equiv)
followed by basification with aqueous sodium hydroxide,
extractive workup with isopropyl acetate, and recrystalliza-
tion from isopropyl acetate and heptane furnished 7 in 67%
yield (overall from 4 in three steps) in high purity. The pH
during basification required adjustment to 10-12 as below
this pH, 7 was contaminated with its TFA salt. Scale-up of
these conditions to a multikilogram scale in our pilot plant,
however, led to the formation of a new tetrapeptide impurity
(1.2%) that was a mixture of two diastereomers (V and VI;
Figure 1) as indicated by LC-MS. The identity of one of
the diastereomers was confirmed by comparison of its HPLC
chromatogram with that of an authentic sample of V prepared
from 7. The quality of 7, so obtained, afforded the drug
substance 1 of the desired purity. Attempts to induce the
Scheme 6
Vol. 8, No. 3, 2004 / Organic Process Research & Development
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335

Scheme 7
With two key intermediates 7 and 13 in hand, and having
defined the conditions for the crystallization of TKA731 (1),
we were ready to carry out the key and final coupling step.
Having known that 2-chloro-4(3H)-quinazolinone (13) is
unstable at room temperature as it hydrolyzes to benzoyl-
eneurea (11), achieving a consistent quality of 13 could prove
problematic. Thus, we needed to develop a robust process
for this key coupling step of 7 with 13 that will tolerate the
varying purity of 13 (due to varying amount of 11). Since
benzoyleneurea (11) is not soluble in toluene and can be
easily removed by filtration, we selected toluene as the
solvent for this coupling reaction. Thus, treatment of 7 with
13 (1.1 equiv) in toluene at 85 °C in the presence of
triethylamine (1.5 equiv) afforded the reaction mixture that
was filtered to remove triethylamine hydrochloride and any
benzoyleneurea (11). The resulting toluene filtrate was
washed with citric acid solution, water, and sodium bicar-
bonate to afford a solution of crude TKA731 (1). Concentra-
tion of the toluene solution followed by a solvent exchange
with ethanol and crystallization from ethanol and water
mixture (1.25:1.0 v/v) afforded pure and crystalline TKA731
(1) in 88% yield with >99.0% purity (Scheme 7). Thus, the
silica gel chromatography used for 1 was eliminated. We
found that 13 of the lower purity, containing up to 12% of
11, afforded the drug substance 1 of the desired quality.
These conditions were scaled-up in our pilot plant on a 23.4-
kg scale of 7 to afford 1 in 89.1% yield with >99.5% purity.
To ascertain the enantiopurity of 1, other three diastereo-
isomers of TKA731 (VII, VIII, and IX, Figure 3) were also
synthesized from appropriate enantiomerically pure amino
acids using the same synthesis. A chiral HPLC analysis of
1 suggested that product produced according to our optimized
synthesis contained only 0.04% of D,L-isomer (VIII).
Figure 3.
Summary
An efficient and chromatography-free large-scale synthe-
sis of a tachykinin receptor antagonist TKA731 (1), utilizing
the coupling of dipeptide 7 and 2-chloro-4(3H)-quinazolinone
(13) as the key step, is described. The overall yield of 1
from BOC-L-3-(2-naphthyl)alanine (2) in six linear steps
(total of 8 steps) is 63%. This new convergent approach
avoided the use of methyl iodide and the formation of
methanethiol byproduct in the last step involving the
construction of the quinazolinone ring in the original
discovery synthesis. Four chromatographies were also elimi-
nated. The main cause of the side reaction, leading to the
urethane byproduct (I) formation and starting amino acid
(2) liberation during the coupling of 2 with N-benzylmethy-
lamine using well-known isobutyl chloroformate-mediated
mixed carboxylic-carbonic anhydride method, was found
to be the symmetrical anhydride III formation from 2 as
determined by the CO2 offgas formation. A new procedure
for the coupling of 2 with N-benzylmethylamine involving
a reverse addition of 2 and the base to the coupling agent
isobutyl chloroformate, followed by the addition of the
amine, was developed that minimized the symmetrical
anhydride formation. A novel, water-assisted N-methylation
of 5 with dimethyl sulfate in the presence of sodium hydride
in THF was also developed that eliminated the use of methyl
iodide, silver oxide, and KCN. Deprotection of the BOC
group in 6 with sulfuric acid circumvented the formation of
diketopiperazine and tetrapeptide observed with HCl and
trifluoroacetic acid, respectively.
(22) Franzen, H. M.; Bessidskaia, G.; Abedi, V.; Nilsson, A.; Nilsson, M.; Olsson,
L. Org. Process Res. DeV. 2002, 6, 788-797.
(23) Myerson, A. S., Ed. Handbook of Industrial Crystallization; Butterworth-
Heinemann: Boston, 1993; pp 39 and 46.
336
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Vol. 8, No. 3, 2004 / Organic Process Research & Development

Experimental Section
(This process was satisfactorily scaled up on 63.0-kg scale
of BOC-L-3-(2-naphthyl)alanine in 100% assumed yield).
(S)-3-(2-Naphthyl)alanyl-N-benzyl-N-methylamide Hy-
drochloride (4). A Mettler-Toledo LabMax reactor, equipped
with 2-L glass vessel, pitched-blade impeller, RTD sensor,
addition funnel, nitrogen inlet/outlet, and a reflux condenser,
was charged with a solution of BOC-(S)-3-(2-naphthyl)-
alanyl-N-benzyl-N-methyl amide (3) in toluene (310.0 mL,
272.0 g) containing (68.0 g of 3, 162.3 mmol). The solution
was warmed to an internal temperature at 67 ( 3 °C (jacket
temperature: 67-70 °C) over a period of 30 min, and
concentrated hydrochloric acid (37%, 67.5 mL, 811.0 mmol)
was added over a period of 45 min, while maintaining the
internal temperature at 67 ( 3 °C (jacket temperature: 67-
70 °C) to give a slurry. The reaction mixture was stirred at
67 ( 3 °C for an additional 8 h. The reaction mixture was
cooled to an internal temperature at 20-23 °C over a period
of 1 h and stirred for an additional 1 h at this temperature.
The solids were collected by filtration, and the vessel was
rinsed with toluene (100.0 mL), which was used to wash
the filter cake. The filter cake was then washed with fresh
toluene (50.0 mL) and dried at 60-65 °C in vacuo to afford
(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide hydro-
chloride (4, 53.8 g, 93.4% in two steps).9 This intermediate
is a weak-to-moderate skin sensitizer. The major byproduct
in this deprotection step was tert-butyl chloride as determined
1H and 13C NMR spectra were recorded on a Bruker FT-
NMR spectrometer at 300 and 75 MHz, respectively. Melting
points were measured on a Buchi 533 melting point ap-
paratus. Enantiopurity of 1 was determined by a chiral HPLC
method using a Phenomenex Chirex 3012, 4.6 mm × 150
mm column using a mixture of hexanes/1,2-dichloroethane/
ethanol (50:15:5) as the mobile phase at a flow rate of 1.0
mL/min and UV detector (272 nm) at room temperature. The
retention times of L,D (VII), D,L (VIII), D,D (IX) diastere-
oisomers and TKA731 (1) were 26.2, 33.8, 57.5, and 67.1
min, respectively.
BOC-(S)-3-(2-Naphthyl)alanyl-N-benzyl-N-methyl
Amide (3). A Mettler-Toledo LabMax reactor, equipped
with 1-L glass vessel, pitched-blade impeller, RTD sensor,
addition funnel, nitrogen inlet/outlet, and distillation setup
was charged with BOC-L-3-(2-naphthyl)alanine (2, 51.2 g,
162.3 mmol) and toluene (130.0 mL). The suspension was
cooled to an internal temperature at 20 ( 2 °C, and N,N-
dimethylbenzylamine (29.64 g, 219.3 mmol) was added over
a period of 10 min, while maintaining the internal temper-
ature at 20 ( 2 °C (jacket temperature 17 ( 3 °C). The
addition funnel was washed with toluene (5.2 mL), and the
wash was added to the reaction mixture. This solution was
held for further use.
A Mettler-Toledo LabMax reactor, equipped with a clean
1-L glass vessel, pitched-blade impeller, RTD sensor, addi-
tion funnel, nitrogen inlet/outlet, and distillation setup was
charged with toluene (390.0 mL) and isobutyl chloroformate
(28.86 g, 211.3 mmol). The solution was cooled to an internal
temperature of -12 ( 2 °C, and the above-prepared solution
of BOC-L-3-(2-naphthyl)alanine (2) and N,N-dimethylben-
zylamine in toluene was added over a period of 40 min, while
maintaining an internal temperature at -12 ( 3 °C (jacket
temperature -15 ( 3 °C). The addition funnel was washed
with toluene (2 × 5.2 mL) and added to the reaction mixture.
The slurry was stirred at -12 ( 2 °C for an additional 30
min, and a solution of N-benzylmethylamine (24.6 g, 203.0
mmol) in toluene (15.6 mL) was added over a period of 30
min, while maintaining an internal temperature at -12 ( 2
°C (jacket temperature -15 ( 3 °C). The addition funnel
was washed with toluene (2 × 5.2 mL) and added to the
reaction mixture. The reaction mixture was stirred at -12
( 2 °C for 30 min and then warmed to an internal
temperature at 21 ( 2 °C over a period of 35 min (the
completion of the reaction was monitored by HPLC). The
reaction mixture was quenched by addition of 1 N H2SO4
(125.0 mL) and stirred for 10 min. The organic layer was
separated and washed sequentially with water (125.0 mL),
5% aqueous sodium bicarbonate (125.0 mL), and water
(125.0 mL). The organic layer was concentrated at a jacket
temperature of 65 ( 5 °C in vacuo (150 mbar) to collect
340 mL (∼309.0 g) of solvent and obtain a solution of BOC-
(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methyl amide in toluene
(3, 310.0 mL, 272.0 g). This solution (containing 68.0 g of
3, assumed 100% yield) was held at an internal temperature
of 21-23 °C under nitrogen for the next step.
1
by H NMR and GC analysis of the toluene filtrate. About
10-11% of isobutene was also detected in offgases.
(This process was satisfactorily scaled up on 63.0-kg scale
of BOC-L-3-(2-naphthyl)alanine (2) to afford 94% yield of
4 in two steps).
(2S)-2-[[[(1S)-2-[Methyl(phenylmethyl)amino]-1-(2-
naphthalenylmethyl)-2-oxoethyl]amino]carbonyl]-1-pyr-
rolidinecarboxylic acid 1,1-Dimethylethyl Ester (5). A
Mettler-Toledo LabMax reactor, equipped with a 1-L glass
vessel, pitched-blade impeller, RTD sensor, addition funnel,
nitrogen inlet/outlet, and distillation setup was charged with
(S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide hydro-
chloride (4, 65.8 g, 185.4 mmol) and toluene (400.0 mL).
To the stirring suspension was added 5% sodium hydroxide
solution (280.0 mL, 294.6 g) over a period of 10 min, while
maintaining the internal temperature at 22 ( 3 °C. The
suspension was stirred for 1 h until all the solids dissolved.
The organic layer was separated, washed with 20% sodium
chloride solution (140.0 mL, 158.0 g), and filtered through
a line filter. The vessel was washed with toluene (28.0 mL),
and the wash was line filtered and mixed with the batch.
The combined filtrates were concentrated in vacuo (150 (
10 mbar) at an internal temperature of 57 ( 5 °C (jacket
temperature: 68 ( 3 °C) to collect 320-350.0 mL of solvent
to obtain (S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide
free base (140.0 mL, 135.5 g). This solution was held for
further use.
A Mettler-Toledo LabMax reactor, equipped with a 1-L
glass vessel, pitched-blade impeller, RTD sensor, addition
funnel, nitrogen inlet/outlet, and distillation setup was
charged with BOC-L-proline (42.3 g, 196.5 mmol) and
toluene (295.0 mL). To the stirring suspension was added
Vol. 8, No. 3, 2004 / Organic Process Research & Development
•
337

N,N-dimethylbenzylamine (33.8 g, 250.0 mmol) over a
period of 10 min, while maintaining the internal temperature
at 22 ( 3 °C (jacket temperature: 20 ( 3 °C). The addition
funnel was washed with toluene (6.0 mL), and the wash was
added to the reaction mixture. The reaction mixture was
stirred to obtain a clear solution. The solution was cooled to
an internal temperature at -12 ( 3 °C (jacket temperature:
-15 ( 3 °C), and isobutyl chloroformate (27.1 g, 198.4
mmol) was added over a period of 30 min, while maintaining
the internal temperature at -12 ( 3 °C (jacket temperature:
-15 ( 3 °C). The addition funnel was washed with toluene
(3 × 4.0 mL), and the washes were added to the reaction
mixture. The resulting suspension was stirred at an internal
temperature at -12 ( 3 °C (jacket temperature: -15 ( 3
°C) for an additional 30 min. The above prepared solution
of (S)-3-(2-naphthyl)alanyl-N-benzyl-N-methylamide free
base (140.0 mL, 135.5 g) was then added at a constant rate
over a period of at least 60 min, while maintaining the
internal temperature at -12 ( 3 °C (jacket temperature: -15
( 3 °C). The addition funnel was washed with toluene (3 ×
6.0 mL), and the washes were added to the reaction mixture.
The reaction mixture was stirred at this temperature for an
additional 30 min and then warmed to an internal temperature
at 22 ( 3 °C over a period of 45 min. The reaction mixture
was stirred at an internal temperature of 22 ( 3 °C for an
additional 15 min, and 1 N sulfuric acid (180.0 mL) was
added to the reaction mixture, while maintaining the internal
temperature at 22 ( 3 °C. The stirring was continued for an
additional 5-10 min, and the organic layer was separated.
The organic layer was washed sequentially with water (180.0
mL), 8% aqueous sodium bicarbonate (180.0 mL), and water
(180.0 mL). The organic layer was concentrated in vacuo
(150 ( 10 mbar) at an internal temperature at 55 ( 5 °C
(jacket temperature: 68 ( 3 °C) to collect 340-370 mL of
solvent to obtain (2S)-2-[[[(1S)-2-[methyl(phenylmethyl)-
amino]-1-(2-naphthalenylmethyl)-2-oxoethyl]amino]carbonyl]-
1-pyrrolidinecarboxylic acid 1,1-dimethylethyl ester (5, 145.0
mL, 149.0 g containing 95.6 g of 5 based on 100% theoretical
yield). This solution was held at an internal temperature of
21-23 °C under nitrogen for further use.
internal temperature at 10 ( 3 °C. The addition funnel was
washed with tetrahydrofuran (3 × 4.9 mL), and the washes
were added to the reaction mixture. The reaction mixture
was stirred at an internal temperature of 10 ( 3 °C for 3 h.
Ammonium hydroxide (28-30%, 54.6 mL, 49.14 g) was
added to the reaction mixture over a period of 30 min, while
maintaining the internal temperature at 10 ( 3 °C. The
mixture was stirred at this temperature for 1 h, and water
(72.6 mL) and toluene (182.0 mL) were added. After stirring
for 10 min at 20 ( 3 °C, the organic layer was separated
and washed with water (91.0 mL). The organic layer was
concentrated in vacuo (150 ( 10 mbar) at an internal
temperature of 28-45 °C (jacket temperature 33-49 °C) to
collect ∼ 375 mL of solvent to obtain a solution of crude
(2S)-2-[[methyl[(1S)-2-[methyl(phenylmethyl)amino]-1-(2-
naphthalenylmethyl)-2-oxoethyl]amino]carbonyl]-1-pyrrolidi-
necarboxylic acid 1,1-dimethylethyl ester (6, 220.0 mL) in
toluene. This solution was heated to an internal temperature
of 57 ( 2 °C (jacket temperature 62-64 °C) over a period
of 10 min, and heptane (392.7 mL) was added over a period
of 30 min, while maintaining the internal temperature at 57
( 2 °C (jacket temperature 59-62 °C). Immediately, pure
(2S)-2-[[methyl[(1S)-2-[methyl(phenylmethyl)amino]-1-(2-
naphthalenylmethyl)-2-oxoethyl]amino]carbonyl]-1-pyrroli-
dinecarboxylic acid 1,1-dimethylethyl ester (6) seeds (35.3
mg) were added, and the mixture was cooled to an internal
temperature of 21 ( 2 °C (jacket temperature 18-22 °C)
over a period of 1 h, and the stirring was continued at this
temperature for an additional 10 h. The solids were collected
by filtration. The vessel and filter cake were washed with a
mixture of toluene and heptane (1:5 v/v, 500.0 mL). The
filter cake was washed with a fresh mixture of toluene and
heptane (1:5 v/v, 59.0 mL) in two equal portions of 29.5
mL each. The solid was dried at 45-50 °C in vacuo to obtain
pure (2S)-2-[[methyl[(1S)-2-[methyl(phenylmethyl)amino]-
1-(2-naphthalenylmethyl)-2-oxoethyl]amino]carbonyl]-1-pyr-
rolidinecarboxylic acid 1,1-dimethylethyl ester (6, 41.4 g,
1
86.0% in two steps): mp 126-129 °C; H NMR (CDCl3)
mixture of rotamers δ 1.71-2.23 (m, 4H), 2.31-2.52 (m,
9H), 2.67-2.76 (m, 3H), 2.77-3.07 (m, 1H), 3.08-3.23 (m,
3H), 3.30-3.75 (m, 3H), 4.24-4.72 (m, 3H), 5.78-5.95 (m,
1H), 6.59-6.79 (m, 2H), 6.83-7.12 (m, 3H), 7.33-7.48 (m,
3H), 7.65-7.82 (m, 4H); [R]d -177.3 (c ) 2.54, CH3OH);
Calc for C32H39N3O4: C, 72.50; H, 7.36; N, 7.93%. Found:
C, 72.39, H, 7.53; N, 7.92%.
(This process was scaled up on 48.0-kg scale of crude 5
obtained from 33.0 kg of 4 to afford 86.5% yield of 6 in
two steps).
N-Methyl-N-[(1S)-2-[methyl(phenylmethyl)amino]-1-
(2-naphthalenylmethyl)-2-oxoethyl]-(2S)-2-pyrrolidnecar-
boxamide (7). A Mettler-Toledo LabMax reactor, equipped
with a 1-L glass vessel, pitched-blade impeller, RTD sensor,
addition funnel, nitrogen inlet/outlet, and distillation setup
was charged with (2S)-2-[[methyl[(1S)-2-[methyl(phenyl-
methyl)amino]-1-(2-naphthalenylmethyl)-2-oxoethyl]amino]-
carbonyl]-1-pyrrolidinecarboxylic acid 1,1-dimethylethyl es-
ter (6, 60.0 g, 113.27 mmol) and toluene (60.0 mL). The
suspension was heated to an internal temperature of 78 (
(This process was scaled-up on 33.0-kg scale of 4 in 100%
assumed yield of 5).
(2S)-2-[[Methyl[(1S)-2-[methyl(phenylmethyl)amino]-
1-(2-naphthalenylmethyl)-2-oxoethyl]amino]carbonyl]-1-
pyrrolidinecarboxylic Acid 1,1-Dimethylethyl Ester (6).
A Mettler-Toledo LabMax reactor, equipped with a 1-L
glass vessel, pitched-blade impeller, RTD sensor, addition
funnel, nitrogen inlet/outlet, and distillation setup was
charged with sodium hydride (6.188 g, 154.7 mmol, 60%
dispersion in mineral oil) and tetrahydrofuran (295.0 mL).
To the suspension, cooled to an internal temperature at 10
( 3 °C, was added a solution of crude (2S)-2-[[[(1S)-2-
[methyl(phenylmethyl)amino]-1-(2-naphthalenylmethyl)-2-
oxoethyl]amino]carbonyl]-1-pyrrolidinecarboxylic acid 1,1-
dimethylethyl ester solution (5, containing 46.93 g product,
91.0 mmol) as prepared above, tetrahydrofuran (90.9 mL),
dimethyl sulfate (17.71 g, 140.4 mmol), and of water (0.3276
g, 18.2 mmol) over a period of 1 h while maintaining an
338
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Vol. 8, No. 3, 2004 / Organic Process Research & Development

3 °C (jacket temperature ) 83 ( 3 °C) over a period of 1 h
to obtain a clear solution. The resulting solution was cooled
to an internal temperature of 53 ( 3 °C over a period of 30
min, and 50% sulfuric acid (66.0 g) was added over a period
of 40 min, while maintaining the internal temperature at 53
( 3 °C (mild exothermic reaction with gas evolution). The
mixture was stirred at this temperature for an additional 2-4
h. The mixture was cooled to an internal temperature of 17
( 3 °C over a period of 30 min, and water (120.0 mL) and
isopropyl acetate (120.0 mL) were added sequentially. The
mixture was stirred at 17 ( 3 °C for 5 min, and 10% sodium
hydroxide solution (300.0 g) was added over a period of 40
min to adjust the pH to 11-13, while maintaining an internal
temperature at 17 ( 3 °C. After the mixture stirred at this
temperature for 10 min, the organic layer was separated and
washed with 10% sodium chloride solution (60.0 g). The
organic layer was line-filtered to a clean Mettler-Toledo
LabMax reactor, equipped with 1-L glass vessel, pitched-
blade impeller, RTD sensor, addition funnel, nitrogen inlet/
outlet, and reflux condenser. The solution was heated to an
internal temperature of 83 ( 3 °C over a period of 60 min,
and heptane (360.0 mL) was added over 40 min, while
maintaining the internal temperature above 75 °C. The
mixture was cooled at a rate of 0.5 °C/min, and pure
N-methyl-N-[(1S)-2-[methyl(phenylmethyl)amino]-1-(2-naph-
thalenylmethyl)-2-oxoethyl]-(2S)-2-pyrrolidnecarboxamide
seeds (7, 36.0 mg) were added at an internal temperature of
66 ( 3 °C. The mixture was cooled to an internal temperature
of 22 ( 3 °C over a period of 1 h and 30 min (cooling rate
) 0.5 °C/min), and the stirring was continued at this
temperature for an additional 14 h. The solids were collected
by filtration, washed with a mixture of isopropyl acetate and
heptane (1:4 v/v; 80.0 mL) in two equal portions of 40.0
mL each, and dried at 45-50 °C in vacuo to afford pure
N-methyl-N-[(1S)-2-[methyl(phenylmethyl)amino]-1-(2-naph-
thalenylmethyl)-2-oxoethyl]-(2S)-2-pyrrolidnecarboxamide
was added over a period of 1 h at a rate that maintains the
internal temperature below 65 °C (an exothermic reaction).
The addition funnel was washed with toluene (10.0 mL),
and the wash was added to the reaction mixture. The mixture
was slowly heated to an internal temperature of 85 °C, and
after 10 min, to 108-110 °C. The mixture was stirred at
108-110 °C for 4 h to obtain a clear brown-yellow solution.
The reaction mixture was cooled to an internal temperature
of 40 °C and added to warm (35-40 °C) water (1.5 L) with
nitrogen pressure over a period of 30-40 min, while
maintaining an internal temperature below 45 °C. The first
vessel was washed with toluene (0.8 L) and added to the
reaction mixture. After stirring for an additional 30 min, the
bottom aqueous layer was discarded, and the organic layer
(with rag layer) was filtered over Cellflock-Polster (20.0 g).
The filter cake was washed with toluene (20.0 mL) and water
(40.0 mL). The aqueous layer was removed from the
combined filtrates, and the organic layer was washed with
water (2 × 400.0 mL) (the pH of the aqueous layer was
>3). The organic layer was dried by azeotropic removal of
water at 70 °C (external temperature) under vacuum (200
mbar). The organic layer was concentrated at 55 °C (external
temperature) under vacuum (50 mbar) until no more solvent
distilled. To the residue was added heptane (2.4 L), and the
mixture was heated to an internal temperature at 90 °C to
obtain a brown solution. The solution was cooled to an
internal temperature at 70 °C, and seeds of 2,4-dichloro-
quinazoline (12, 0.2 g) were added. The mixture was slowly
cooled to room temperature (21-23 °C) and stirred at this
temperature for ∼14 h. The mixture was cooled to 0-10 °C
and stirred at this temperature for 1 h. The solid was collected
by filtration, washed with heptane (450.0 mL), and dried at
40 °C in vacuo to afford pure 2,4-dichloroquinazoline (12,
251.0 g, 87.6%): mp 118-120 °C.4 Store this material in a
refrigerator.
2-Chloro-4(3H)-quinazolinone (13). A 3-L, four-necked,
round-bottomed flask, equipped with a mechanical stirrer,
digital thermometer, addition funnel, nitrogen inlet-outlet,
and cooling bath was charged with a solution of sodium
hydroxide (2 N, 840.0 mL). The solution was cooled to an
internal temperature at 17-19 °C, and 2,4-dichloroquinazo-
line (12, 112.0 g, 562.7 mmol) was added in three equal
portions of 37.33 g each at 10-15 min intervals. The
resulting slurry was stirred at 21-24 °C for 4 h to obtain a
solution. Water (560.0 mL) was added over 5-10 min, while
maintaining the internal temperature at 21-24 °C. After
stirring for 5-10 min, glacial acetic acid (140.0 mL) was
added with efficient stirring over 20-25 min, while main-
taining the internal temperaure at 21-24 °C. The solid was
collected by filtration, washed with water (3 × 400 0.0 mL),
and dried at 50-52 °C under vacuum for 24 h (to obtain a
constant weight) to afford pure 2-chloro-4(3H)-quinazolinone
(13, 100.0 g, 98.4%) as a white solid: mp 219-221 °C.2
Coupling of 7 and 13. (2S)-1-(3,4-dihydro-4-oxo-2-
quinazolinyl)-N-methyl-N-[(1S)-2-[methyl(phenylmethyl)-
amino]-1-(2-naphthalenylmethyl)-2-oxoethyl]-2-pyrrolidin-
ecarboxamide (1). A Mettler-Toledo LabMax reactor, equipped
with a 1-L glass vessel, pitched-blade impeller, RTD sensor,
1
(7, 42.5 g, 87.3%) as a white solid: mp 117-120 °C; H
NMR (CDCl3) mixture of rotamers δ 1.26-2.12 (m, 4H),
2.59-3.17 (m, 8H), 3.48-3.89 (m, 2H), 4.36-4.81 (m, 2H),
5.89-6.05 (m, 1H), 6.69-6.90 (m, 2H), 6.92-7.16 (m, 3H),
7.30-7.49 (m, 3H), 7.63-7.79 (m, 4H); [R]d -147.5 (c )
2.92, CH3OH); Calc for C27H31N3O2: C, 75.43; H, 7.22; N,
9.78%. Found: C, 75.35, H, 7.37; N, 9.81%.
This intermediate is a skin sensitizer. The major byproduct
in this deprotection step was tert-butyl alcohol as determined
1
by H NMR of the toluene layer after the reaction.
(This process was satisfactorily scaled-up on 65.0-kg scale
of 6 to afford 89% yield of 7).
2,4-Dichloroquinazoline (12). A 5-L, four-necked, round-
bottomed flask, equipped with a mechanical stirrer, digital
thermometer, addition funnel, condenser with nitrogen inlet-
outlet and heating mantle was charged with benzoyleneurea
(11, 200.0 g, 1.233 mol) and toluene (800.0 mL). Phosphorus
oxychloride (435.0 g, 2.84 mol) was added with stirring at
20 °C, and the addition funnel was washed with toluene (10.0
mL), which was added to the reaction mixture. After stirring
at 20 °C for 15 min, the mixture was heated to an internal
temperature of 55 °C, and tripropylamine (363.0 g, 2.53 mol)
Vol. 8, No. 3, 2004 / Organic Process Research & Development
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339

addition funnel, nitrogen inlet/outlet, and distillation setup
was charged with (2S)-N-methyl-N-[(1S)-2-[methyl(phenyl-
methyl)amino]-1-(2-naphthalenylmethyl)-2-oxoethyl]-2-pyr-
rolidinecarboxamide (7, 42.96 g, 100.0 mmol), 2-chloro-
4(3H)-quinazolinone (13, 19.87 g, 110.0 mmol), toluene
(644.0 mL), and triethylamine (15.18 g, 150.0 mmol). The
suspension was heated to an internal temperature at 85 ( 2
°C over a period of 1 h and stirred at this temperature for an
additional 2.5 h. The reaction mixture was cooled to an
internal temperature at 20-25 °C over a period of 1 h and
stirred at this temperature for additional 30 min. The reaction
mixture was filtered, and the filter cake was washed with
toluene (2 × 65.0 mL). The combined filtrates were
sequentially washed with 20% citric acid solution (100.0
mL), water (100.0 mL), 8% aqueous sodium bicarbonate
solution (100.0 mL), and water (100.0 mL). The organic layer
was line-filtered. The separatory funnel was washed with
toluene (20.0 mL), and the wash was combined with the
filtered organic layer. The organic layer was transferred to
a 2-L, four-necked, round-bottomed flask, equipped with a
mechanical stirrer, digital thermometer, addition funnel,
nitrogen inlet-outlet, and heating mantle and concentrated
in vacuo to collect ∼660 mL of solvent to obtain less than
140 mL of a solution. Ethanol (920.0 mL, 200 proof) was
added, and the solution was concentrated in vacuo to collect
∼500 mL of solvent to obtain a solution or light slurry (∼550
mL). This process was repeated twice more with 400.0 mL
of ethanol (200 proof) each time to collect ∼400.0 mL of
solvent each time to obtain a light slurry (∼550 mL). The
reaction mixture was heated to an internal temperature at
73-78 °C (external temperature 85-95 °C) over a period
of 15 min to obtain a clear solution (Note: adjust the volume
to approximately 550 mL.), and water (400.0 mL) was added
over a period of 30 min, while maintaining an internal
temperature at 72-78 °C. The solution was cooled to an
internal temperature at 20-25 °C over a period of 2 h with
efficient stirring. A solid crystallized at ∼65 °C. The resulting
suspension was stirred at 20-25 °C for an additional 6 h.
The solids were collected by filtration, washed with a mixture
of ethanol and water (1:1 v/v; 480.0 mL) in two equal
portions of 240 mL each, dried at 60-65 °C in vacuo to
afford pure (2S)-1-(3,4-dihydro-4-oxo-2-quinazolinyl)-N-
methyl-N-[(1S)-2-[methyl(phenylmethyl)amino]-1-(2-naph-
thalenylmethyl)-2-oxoethyl]-2-pyrrolidinecarboxamide (1,
50.96 g, 88%): mp 175-176 °C; 1H NMR (CDCl3) mixture
of rotamers δ 1.80-2.30 (m, 4H), 2.68 (s, 0.59 × 3H, major
N-CH3), 2.74 (s, 0.41 × 3H, minor N-CH3), 2.80-3.0 (m,
1H), 3.35 (m, 3H), 3.50-3.90 (m, 3H), 4.33 (d, 1H, J )
14.9 Hz), 4.45-4.52 (m, 1H), 4.86 (m, 0.41 × 1H, minor
CH), 5.0 (m, 0.59 × 1H, major CH), 5.80 (m, 1H), 6.60-
7.70 (m, 15H), 7.95 (m, 1H), 10.60 (bs, 1H); [R]d -255.8
(c ) 1.0, CH3OH); Calc for C35H35N5O3: C, 73.28; H, 6.15;
N, 12.21%. Found: C, 72.91, H, 6.28; N, 12.13%.
(This process satisfactorily scaled-up on 23.4-kg scale of
7 to afford 89% yield of 1).
Acknowledgment
We thank Mr. Richard Tarapata and Mr. Erwin Waldvogel
for their project-management support; Dr. D. Munch and Ms.
J. Li for the chiral HPLC method; Dr. D. Drinkwater for
LC-MS; and all the chemical operators, Dr. Ratna Shekhar,
Mr. Paul Lee, Mr. Peter Sands, Dr. Joanna Szewczyk, Ms.
Dana Wambser in the pilot plant for scale-up of procedures;
and Mr. Peter Gysi in the pilot plant in Basel for producing
13.
Received for review December 3, 2003.
OP0341824
340
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Vol. 8, No. 3, 2004 / Organic Process Research & Development