The chemical development of CI-972 and CI-1000: A continuous nitration, a MgCl2/Et3N-mediated C-alkylation of a chloronitropyrimidine, a catalytic protodediazotizatlon of a diazonium salt, and an air oxidation of an amine

Article abstract of DOI:10.1021/op000298d

Efficient, large-scale processes were developed for the preparation of the potent PNP inhibitors 2,6-diamino-3,5-dihydro-7-(3-thienylmethyl)-4H-pyrrolo[3,2-d]pyrimidin-4-one hydrochloride, monohydrate (1) and 2-amino-3,5-dihydro-7-(3-thienylmethyl)-4H-pyrrolo[3,2-d]pyrimidin-4-one hydrochloride, monohydrate (2). We report (1) a safe, continuous nitration process for the preparation of 2-amino-6-chloro-5-nitro-4-pyrimidinol (8a) and its stable diisopropylamine salt (8b), (2) the first MgCl₂/ Et₃N-mediated C-alkylation of a chloronitropyrimidine, (3) a rare catalytic protodediazotization of the diazonium salt 2-amino-4-oxo-7-thiophen-3-ylmethyl-4,5-dihydro-3H-pyrrolo[3,2-d]pyrimidine-6- diazonium chloride (14), (4) a single-step process to prepare 2 directly from 2-amino-6-hydroxy-5-nitro-a-(3-thienylmethyl)-4-pyrimidineacetonitrile (12) using a sponge nickel-catalyzed reduction, and (5) a method to convert the over-reduction by-product 2,5-diamino-6-(1-aminomethyl-2-thiophen-3-yl-ethyl)-pyrimidin-4-ol (16) into 2 using air oxidation.

Full text of DOI:10.1021/op000298d

Organic Process Research & Development 2001, 5, 216−225
The Chemical Development of CI-972 and CI-1000: A Continuous Nitration, A
MgCl2/Et3N-Mediated C-Alkylation of a Chloronitropyrimidine, A Catalytic
Protodediazotization of a Diazonium Salt, and an Air Oxidation of an Amine
Randall L. De Jong,* James G. Davidson, Gary J. Dozeman, Philip J. Fiore, Punam Giri, Margaret E. Kelly,
Timothy P. Puls, and Ronald E. Seamans
Pfizer Global Research and DeVelopment, Holland Laboratories, 188 Howard AVenue, Holland, Michigan 49424, U.S.A.
Abstract:
preparation of pure drug substance safely and in high yield
on a multikilogram scale.
Efficient, large-scale processes were developed for the prepara-
tion of the potent PNP inhibitors 2,6-diamino-3,5-dihydro-7-
(3-thienylmethyl)-4H-pyrrolo[3,2-d]pyrimidin-4-one hydrochlo-
ride, monohydrate (1) and 2-amino-3,5-dihydro-7-(3-thienylmeth-
yl)-4H-pyrrolo[3,2-d]pyrimidin-4-one hydrochloride, monohy-
drate (2). We report (1) a safe, continuous nitration process
for the preparation of 2-amino-6-chloro-5-nitro-4-pyrimidinol
(8a) and its stable diisopropylamine salt (8b), (2) the first MgCl2/
Et3N-mediated C-alkylation of a chloronitropyrimidine, (3) a
rare catalytic protodediazotization of the diazonium salt 2-amino-
4-oxo-7-thiophen-3-ylmethyl-4,5-dihydro-3H-pyrrolo[3,2-d]py-
rimidine-6-diazonium chloride (14), (4) a single-step process to
prepare 2 directly from 2-amino-6-hydroxy-5-nitro-r-(3-thie-
nylmethyl)-4-pyrimidineacetonitrile (12) using a sponge nickel-
catalyzed reduction, and (5) a method to convert the over-
reduction by-product 2,5-diamino-6-(1-aminomethyl-2-thiophen-
3-yl-ethyl)-pyrimidin-4-ol (16) into 2 using air oxidation.
The synthesis of 1 from thiophene-3-carboxaldehyde (4)
was completed in six synthetic steps. Knovenagel condensa-
tion of methyl cyanoacetate (3) and aldehyde 4 in isopropyl
alcohol (IPA) with catalytic diisopropylamine (DIPA) af-
forded the acrylate (5) in 93% yield (Scheme 1). The
condensation was originally run in toluene or dioxane with
piperidine; however, the acrylate 5 could only be obtained
in 86% yield if a second crop was recovered. Substituting
DIPA for piperidine improved the yield to 92%, but isolation
in two crops was still necessary. By using IPA and DIPA,
the acrylate 5 could be isolated in the same yield but in a
single crop (Table 1).
The acrylate 5 was converted to cyanoester 6 by catalytic
hydrogenation over 5% Pd on carbon in 89% yield. This
reduction was originally carried out using sodium cy-
anoborohydride in methanol. A more economical and safe
catalytic method in IPA was developed to give crystalline 6
of g99.7% purity (Table 2). IPA-wet acrylate 5 was
successfully reduced to 6 on 100 kg scale (batch 4), but we
found that the isolation of 5 could be avoided completely
by subjecting the Knovenagel reaction mixture directly to
the hydrogenation conditions, affording 6 in 79% overall
yield. This modification reduced the amount of solvent waste
by 50%.
Of particular concern from a safety and scale-up viewpoint
was the nitration of 2-amino-6-chloro-4-pyrimidinol (7). The
exothermic nitration (∆H ) -100.4 kJ/mol) of 7 required
the use of 90% nitric acid in sulfuric acid3 (Scheme 2). RSST
(reactive system screening tool) evaluation of the reaction
mixture showed an exothermic decomposition beginning at
70 °C, which reached nearly 2500 deg/min rate at 91 °C
and which peaked at 3260 deg/min rate at 245 °C. A large
amount of gas is evolved during this decomposition, resulting
in a maximum pressure rate of 515 psig/min at 98 °C. Clearly
Introduction
PNP inhibitors have been under investigation in our
Discovery Research program1 and in those of other compa-
nies2 for the treatment of rheumatoid arthritis and other
autoimmune diseases. In a recent effort toward introducing
the first PNP inhibitors into man the need for significant
amounts of material was required for toxicological, formula-
tion, and phase I clinical studies of 1 (CI-972) and its back-
up compound 2 (CI-1000). The similarities between these
compounds lent themselves nicely to a convergent synthesis
for their production.
(2) (a) Montgomery, J. A.; Niwas, S.; Rose, J. D.; Secrist, J. A., III; Babu, S.;
Bugg, C. E.; Erion, M. D.; Guida, W. C.; Ealick, S. E. J. Med. Chem. 1993,
36, 55. (b) Guida, W. C.; Elliot, R. D.; Thomas, H. J.; Secrist, J. A., III;
Babu, S.; Bugg, C. E.; Erion, M. D.; Ealick, S. E.; J. A.; Montgomery, J.
A. J. Med. Chem. 1994, 37, 1109. (c) Halazy, S.; Eggenspiller, A.; Ehrhard,
A.; Danzin, C. Bioorg. Med. Chem. Lett 1992, 2, 407. (d) Miles, R. W.;
Tyler, P. C.; Furneaux, R. H.; Bagdassarian, C. K.; Schramm, V. L.
Biochemistry 1998, 37, 8615. (e) Yokomatsu, T.; Hayakawa, Y.; Suemune,
K.; Kihara, T.; Soeda, S.; Shimeno, H.; Shibuya, S. Bioorg. Med. Chem.
Lett. 1999, 9, 2833.
Results and Discussion
Synthesis of 1. The general route to 1 was established
by medicinal chemists; however, significant modifications
to reagents and conditions were required to allow consistent
(3) (a) Temple, C., Jr.; Smith, B. H.; Montgomery, J. A. J. Org. Chem. 1975,
40, 3141. (b) Stuart, A.; West, D. W.; Wood, H. C. S. J. Chem. Soc. 1964,
4769.
(1) Sircar, J. C.; Kostlan, C. R.; Gilbertsen, R. B.; Bennett, M. K.; Dong, M.
K.; Cetenko, W. J. J. Med. Chem. 1992, 35, 1605.
216
•
Vol. 5, No. 3, 2001 / Organic Process Research & Development
10.1021/op000298d CCC: $20.00 © 2001 American Chemical Society and The Royal Society of Chemistry
Published on Web 04/20/2001

Scheme 1
Table 3. Pilot plant lots of 8b
amount
yielda
(%)
purity
(HPLC, area %)
batch % nitric acid produced (kg)
1
2
3
4
90
98
98
90
25.7
44.4
49.1
76.8
78.2
44.2
45.9
82.2
91.1
99.7
93.6
96.6
a Corrected for purity
containing cold water. Typical residence time of the reaction
mixture in the tube was approximately 2.5 min. This system
offered several advantages: (1) the design was simple and
easily scaled as demand grew, (2) the process was much safer
than a batch process since only a small amount of nitration
reaction mixture was present at any given time, and (3) the
open-ended tube alleviated concerns of pressure build-up in
the event of gas evolution.
Several parameters including residence time, reactant
ratio, and reaction temperature had to be controlled to avoid
side reactions. If the residence time was too short, pyrimidine
7 remained. If the residence time was too long or if the
concentration of nitric acid too high, a dinitro impurity was
formed. It was also necessary to control the dissolution
temperature of pyrimidine 7 in sulfuric acid to avoid
hydrolysis of 7 to 2-amino-4,6-dihydroxypyrimidine (9). This
compound would then be nitrated, giving rise to nitrodiol
10 in the isolated product. After some optimization,5 pyri-
midine 7 could be prepared in 82% yield and 97% purity
(Table 3).
Table 1. Pilot plant lots of acrylate 5
amount
yielda
purity
batch solvent
base
produced (kg) (%) (VPC, area %)
1
2
3
4
5
toluene piperidine
toluene piperidine
toluene DIPA
21.4
29.5
44.1
83.0
85.5
91.7
92.6
-
100/99.4b
98.9/98.4b
98.0/99.6b
99.8
IPA
IPA
DIPA
DIPA
118.6
116.5c
99.4
a Not corrected for purity. b First crop/second crop. c Wet cake, carried on
directly into the next step.
Table 2. Pilot plant lots of cyanoester 6
amount
produced (kg)
yielda
(%)
purity
batch
(VPC, area %)
1
2
26.5
37.8
106.3
95.9
87.2
84.6
88.8
81.6c
99.7
99.7
99.9
99.9
3
4b
a Not corrected for purity. b Acrylate 5 wet cake carried on directly into
reduction. c Overall yield for Knovenagel condensation and catalytic reduction.
Scheme 2
For stability reasons 2-amino-6-chloro-5-nitro-4-pyrimi-
dinol (8a) was isolated as its diisopropylamine salt (8b).6
While the pyrimidinol 8a was difficult to dry and store
without some hydrolysis to the nitro diol 10, we found the
diisopropylamine salt to be stable for at least 4 years at
ambient temperature.
The coupling of cyanoester 6 with chloronitropyrimidinol
8a was originally carried out using NaH in DMF at 70 °C
overnight.1 This procedure was initially modified to use
K2CO3 in DMSO due to safety concerns associated with
NaH, and to improve the yield from 52 to 75-80%. Workup
involved filtering the reaction mixture (to remove excess
K2CO3 and KHCO3) into water followed by acidification with
hydrochloric acid to afford the crude cyanoester 11 as a
yellow solid. Foaming was a problem due to the clay-like
this reaction was not suitable for batch scale-up and was
run in quantities no larger than 22 L to prepare early lots of
material.
Due to the rapid rate of nitration and the desire for a small
reaction volume, continuous nitration seemed to be an ideal
alternative. A continuous method was developed wherein a
solution of the pyrimidine 7 in sulfuric acid was combined
with 90% nitric acid in a translucent Teflon tube.4 The flow
of each solution was controlled by means of a dual-head
metering pump while the temperature of the reaction was
moderated by immersion of the tube in a constant-temper-
ature bath. The tube outlet was connected to a quench tank
(5) Over the course of our scale-up work, two batches gave unexpectedly low
yields of 45% and 49% (batches 2 and 3). In those runs, 98% rather than
90% nitric acid was used. We postulate that the higher strength acid and
possibly higher reaction temperatures resulted in oxidative destruction of
the productsno UV absorbing impurities were found by HPLC.
(6) Several persons developed skin rashes and became sensitized to this material
over the course of this project. One must exercise care to minimize skin
contact when handling this compound.
(4) A manuscript detailing the development of this continuous nitration is under
preparation.
Vol. 5, No. 3, 2001 / Organic Process Research & Development
•
217

Scheme 3a
Table 4. Pilot plant lots of 11 and 12
amount
produced (kg)
yielda
(%)
purity
(HPLC, area %)
batch
Coupling Only Batches (11)
1b,c
2b,c
3b,c
4b,c
5b,c
6b,c
7b,e
8b,e
8.0
10.6
11.8
10.4
12.8
11.7
12.0
10.0
79.0
73.8
81.3
72.3
75.5
79.8
74.2
66.7
98.7
98.9
97.9d
98.4d
99.7d
100.3d
100.2d
97.4d,f
Hydrolysis Only Batches (12)
9
10
11
12
13
7.9
8.2
92.9
93.0
93.2
94.2
95.4
97.9
98.2
98.6
98.8
98.9
17.5
19.4
17.7
Combined Coupling and Hydrolysis Batches (12)
14b,e,g
15i
46.7
29.7
59.7
83.9h
93.2h
89.3h
94.2
96.0
95.4
16i
a a) K2CO3, DMSO, 70 °C. b) MgCl2, Et3N, CH3CN, 22 °C.
ND ) not determined. a Corrected for purity. b K2CO3/DMSO coupling. c 8a
used in coupling. d w/w %. e 8b used in coupling. f 2.1% 12 in product. g No
DMF purification of crude 11. h Overall yield for coupling and hydrolysis steps.
i MgCl2/Et3N/CH3CN coupling.
nature of the solid. Switching to 8b in the alkylation (Scheme
3) allowed reduction of the amount of K2CO3 from 2.0 to
1.05 mol equiv and eliminated the foaming problem. After
drying, the crude cyanoester 11 was purified by dissolving
in DMF and precipitating with water. Although the purifica-
tion achieved using this method was slight, it did reduce the
amount of residual DMSO in the product which, if not
removed, poisoned the catalyst in the next step.
The cyanoester 11 was hydrolyzed in about 90 min at
15-25 °C with aqueous NaOH. The addition of hydrochloric
acid resulted in decarboxylation to give the nitrile 12 in
93-95% yield. It was important that 12 be isolated in a
timely fashion due to its instability at low pH for extended
periods of time. We also found that some degradation of 12
occurred (up to 2-3%) as the material was dried.
Although this process was workable for pilot-scale
synthesis, it still had several drawbacks which needed to be
addressed: (1) The coupling of 6 and 8 consistently failed
to go to completion. HPLC analysis (area %) of a typical
K2CO3/DMSO coupling reaction mixture after 10 h at 70
°C showed 74% cyanoester 11, 4% nitrile 12, 11% nitro-
pyrimidinol 8, and 6% cyanoester 6. Unfortunately, further
heating did not result in the formation of more 11 but only
hydrolysis of 11 to 12. (2) Large amounts of aqueous waste
were generated in the work-up and reprecipitation of 11. (3)
DMSO was a safety concern because it (and whatever may
be dissolved in it) is readily absorbed through the skin. In
addition, traces of DMSO in 12 had been shown to be a
catalyst poison in the subsequent hydrogenation. (4) The
reprecipitation of 11 added extra isolation and drying steps
and removed the approximately 4% of usable nitrile 12 from
the cyanoester product 11.
C-alkylation of chloronitropyrimidines. In general, chloroni-
tropyrimidines are readily coupled with nitrogen nucleo-
philes,8 but carbon-based nucleophiles are much more
resistant to this reaction. This chemistry should prove useful
in preparing other pyrrolo[3,2-d]pyrimidines.9
This method offered several advantages over the K2CO3/
DMSO procedure: (1) the MgCl2/Et3N/CH3CN reaction is
complete in only 3 h at 25 °C versus 10 h at 70 °C, (2) the
lower coupling temperature is safer for handling 8 due to
decomposition concerns,10 (3) the purification of 11 is no
longer necessary, and the material can be used as a wet cake
in the hydrolysis step, (4) the problematic solvent DMSO is
eliminated, (5) the product 12 was obtained as a more
crystalline, better filtering solid due to the elimination of
traces of DMSO, (6) the overall yield from 8 was 93 versus
84% for the combined step 4/5 DMSO process and 73% for
the original NaH/DMSO process.
One drawback of using MgCl2/Et3N for the coupling of
6 and 8b was the formation of a new impurity (17) in
approximately 3% yield, which resulted from addition of
(7) Rathke and Cowan report the use of these conditions to acylate diethyl
malonate or ethyl acetoacetate with acid chlorides. Rathke, M. W.; Cowan,
P. J. J. Org. Chem. 1985, 50, 2622.
(8) For some recent examples of amine additions to 8a, see: (a) Bailey, S. W.;
Chandrasekaran, R. Y.; Ayling, J. E. J. Org. Chem. 1992, 57, 4470. (b)
Ogawa, K.; Nishii, M.; Inagaki, J.; Nohara, F.; Saito, T.; Itaya, T.; Fujii, T.
Chem, Pharm. Bull. 1992, 40, 1315. (c) Baxter, A. D.; Penn, C. R.; Storer,
R.; Weir, N. G.; Woods, J. M.; Nucleosides Nucleotides 1991, 10, 393. (d)
Haddow, J.; Suckling, C. J.; Wood, Hamish C. S. J. Chem Soc., Perkin
Trans 1 1989, 1297. (e) Nair, M. G.; Murthy, B. R.; Patil, S. D.; Kisliuk,
R. L.; Thorndike, J.; Gaumont, Y.; Ferone, R.; Duch, D. S.; Edelstein, M.
P.; J. Med. Chem. 1989, 32, 1277. (f) Boyle, P. H.; Hughes, E. M.; Khattab,
H. A.; Lockhart, R. J. Tetrahedron Lett. 1987, 28, 5331. (g) Lever, O. W.,
Jr.; Vestal, B. R. J. Heterocycl. Chem. 1986, 23, 901.
We were encouraged to discover that 6 and 8 could be
cleanly coupled using Rathke-type conditions7 of MgCl2
(1.5-1.7 mol) and Et3N (2.0-2.2 mol) in acetonitrile at
ambient temperature (Table 4). As far as we know, this is
the only example of using Lewis acid conditions to effect
(9) Amarnath, V.; Madhav, R. Synthesis, 1974, 837.
(10) Accelerated rate calorimetry (ARC) analysis of the K2CO3/DMSO reaction
mixture showed an exotherm beginning at 91 °C along with a rapid
exothermic decomposition at 166 °C.
218
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Vol. 5, No. 3, 2001 / Organic Process Research & Development

Table 5. Pilot plant lots of 1
Scheme 4a
amount
produced (kg)
yielda
(%)
purity
(HPLC, w/w %)
batch
1
2
3
4
5
6
4.6
3.3
13.9
12.6
11.9
23.6
53.7
37.6
64.7
60.9
62.0
62.1
101.8
99.6
100.1
99.4
100.6
98.9
a a) 1. H3PO2, CuSO4, IPA, H2O 2. NaOH; 3. chromatography and
recrystallization. b) 1. H2, 5% Pd/C, IPA, H2O, HCl; 2. NaNO2; 3. aqueous HCl
recrystallization.
a Overall yield for reduction, cyclization, and recrystallization.
roborate salt was the most stable of the salts prepared. The
chloride salt was the most reactive and the most attractive
due to cost. DSC analysis of the chloride and tetrafluorobo-
rate salts showed the onset of exothermic decomposition at
130 and 150 °C, respectively. As an added precaution the
diazonium salts were handled and stored as wet cakes for
safety reasons.13
Many known protodediazotization methods including
H3PO2,14,15 PPh3/MeOH,16 isoamyl nitrite/DMF,17 NaBH4,18
Et3SiH,19 Zn/EtOH,20 Al(O-iPr)3/IPA, alkaline formalde-
hyde,21 PhSH,22 and SmI2 were evaluated to reduce diazo-
nium salt 14 to 2. Hypophosphorus acid (H3PO2) reduction,
although not especially clean, showed the most promise
initially; therefore, we directed our development efforts on
this method for making the first small batches of 2. We found
that addition of 5-10 mol % of CuSO414b improved the rate
of reduction and that addition of IPA to the reaction mixture
helped to control foaming. Since the reaction was exothermic,
H3PO2 was generally added to a cold slurry (0 °C) of the
diazonium salt, which was then slowly warmed to 15 °C
and held there until the reduction was complete.
Purification of 2 obtained from this reduction proved to
be difficult. Crude 2 was dark in color and contained salts
and tarry materials (typical yield of material was 115% with
a purity of 60-70% by w/w HPLC). In addition, a small
amount of 1 that was formed proved to be very difficult to
remove. We explored recrystallization (in conjunction with
several different carbon treatments), extraction, Sohlet
extraction, and carbon absorption/deabsorption (2 is tightly
bound to carbon, especially Calgon ADP carbon), but column
chromatography was ultimately needed to prepare the first
two lots of acceptable 2 (Table 6).
diisopropylamine to 8. Fortunately, the formation of 17 did
not affect the isolation or purity of 1 or 2. We prepared
bulkier amine salts (diisopropylethylamine 8c, diphenylamine
8d, dicyclohexylamine 8e, and triethylamine 8f 11) of 8 and
found the dicyclohexylamine salt to be the most promising
in light of cost, preparation yield, stability toward amine
addition, and overall yield to 11. Interestingly, we also found
that using 8e in the coupling with 6 required warmer
temperatures (45-55 °C) to give complete reaction in a
reasonable time (2-5 h).
The final conversion of nitrile 12 to 1 was accomplished
in two steps (Scheme 3). The nitro group was hydrogenated
over 5% palladium on carbon, giving intermediate amino-
nitrile 13, which when refluxed with methanolic HCl cyclized
to 1. Crude 1 was isolated and recystallized from either
aqueous acetonitrile or aqueous methanol to afford 1 as the
monohydrate, monohydrochloride salt in 61-65% overall
yield from 12 after some optimization (Table 5). Since 1 is
weakly basic, the addition of hydrochloric acid in the
recrystallization was necessary to obtain the full 1:1 hydrogen
chloride salt.
Synthesis of 2. Compound 1 (CI-972) was the first PNP
inhibitor tested in man, but poor efficacy prompted the de-
cision to develop the back-up compound 2 (CI-1000), which
exhibited better solubility and PNP binding. Because we had
a suitable synthesis of 1 as well as sizable quantities of 1 on
hand, we initially looked for a method to prepare 2 from 1.
We opted to investigate a diazotization/reductive cleavage
sequence to prepare the initial lots of 2 (Scheme 4).
The diazonium chloride, tetrafluoroborate, hexafluoro-
phosphate, and hydrogen sulfate salts of 1 were prepared
using standard literature procedures.12 The hexafluorophos-
phate salt was cost-prohibitive, while the hydrogen sulfate
salt was not stable enough for long-term use. The tetrafluo-
In our search for a cleaner method of reduction we
discovered that catalytic hydrogenation over Pd on carbon
was a viable method for preparing 2 from 14. Church23 et
al. reported that the diazonium salt of 9-amino-7-nitro-6-
(13) On one occasion, removal of some dry diazonium chloride salt from a filter
funnelsscraping with a metal spatulasresulted in rapid decomposition,
giving a black foam.
(14) (a) Kornblum, N. Organic Reactions; John Wiley and Sons Inc.: New York,
1944; Vol. II, pp 277-282. (b) Kornblum, N.; Cooper, G. D.; Taylor, J. E.
J. Am. Chem. Soc. 1950, 72, 3013.
(15) Patai, S. Chemistry of Diazonium and Diazo Groups Pt 2; Wiley: New
York, 1978; pg 564.
(16) Yasui, S.; Fujii, M.; Kawano, C.; Nishimura, Y.; Ohno, A. Tetrahedron
Lett. 1991, 32, 5601.
(17) Doyle, M. P.; Dellaria, J. F.; Siegfried, B.; Bishop, S. W. J. Org. Chem.
1977, 42, 3494.
(11) Brown, R.; Joseph, M.; Leigh, T.; Swain, M. J. Chem. Soc., Perkin Trans.
1 1977, 9, 1003.
(12) The salts were generally prepared at 0-5 °C in water using 2-3 mol equiv
of acid and 1.2-1.4 mol equiv of sodium nitrite. The resulting slurry was
then warmed to ambient temperature and the diazonium salt isolated by
filtration.
(18) Hendrickson, J. B. J. Am. Chem. Soc. 1961, 83, 1251.
(19) Nakayama, J.; Yoshida, M.; Simamura, O. Tetrahedron 1970, 26, 4609.
(20) Roe, A.; Graham, J. R. J. Am. Chem. Soc. 1952, 74, 6297.
(21) Brewster, R. Q.; Poje, J. A. J. Am. Chem. Soc. 1939, 61, 2418.
(22) Shono, T.; Matsumura, Y.; Tsubata, K. Chem. Lett. 1979, 1051.
Vol. 5, No. 3, 2001 / Organic Process Research & Development
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219

Table 6. Lab and pilot plant lots of 2
able to selectively reduce the nitrile functionality of 13 to
the imine 15 faster than rearrangement to 1, and to cyclize
15 with loss of ammonia to give 2 faster than further
reduction to give triamine 16.
reduction
method
amount
produced (kg)
yield
(%)
purity
batch
(HPLC, w/w %)
1a
2a
3a
4a
5d
6d
H3PO2
H3PO2
H2, Pd/C
H2, Pd/C
sponge Ni
sponge Ni
19 g
250 g
212 g
11.4 kg
2.3 kg
30.8 kg
17.0b
37.1b
53.1b
51.1b
50.0e
59.7e
99.8c
99.8c
99.4
100.5
99.3
We were encouraged that initial results using hydrogen
and a sponge nickel catalyst showed some desired product,28
but high levels of 1 and 16 were also present.29 Stepwise
reduction using Pd/C to first reduce the nitro moiety followed
by sponge nickel reduction to reduce the nitrile was only
slightly more successful. We found that the relative product
ratio of 2, 1, and 16 was dependent on pH, temperature,
catalyst type, hydrogen pressure, and solvents used (including
water). The best ratio of products was obtained using one
molar equivalent of potassium carbonate and Activated
Metals sponge nickel catalyst A-5000 in methanol at 50 psig
hydrogen pressure. The reaction was cleaner if the batch was
kept below 30 °C for the initial nitro group reduction and
then warmed to 40-50 °C for the nitrile reduction and
cyclization. Analysis of the reaction mixture after the
reduction was complete typically showed (HPLC area %):
65-70% 2, 9-11% 1, and 18-20% 16. Unfortunately,
purifying 2 of this quality was tedious and low-yielding.
However, a key observation was made that the HPLC area
% of 2 seemed to increase slightly in reaction mixtures from
which catalyst had been filtered and left standing overnight.
We confirmed that 16 was being air oxidized to the desired
product 2 and exploited this transformation by bubbling air
through the reaction mixture (after catalyst filtration) at 20-
30 °C for several hours (Scheme 6).30 Charcoal proved to
be the best additive for increasing the oxidation rate, but
longer times were still required as the reaction scale
increased. Since crude 2 from the sponge nickel reduction
is typically dark-colored, the addition of carbon to the
oxidation step eliminated a second recrystallization which
was usually needed to remove color.
99.7
a Using diazotization/reduction of 1. b Overall yield from 1. c Area %. d Using
sponge nickel reduction of 12. e Overall yield from 12.
demethyl-6-deoxytetracycline could be reduced to the cor-
responding hydrocarbon using 10% Pd on carbon in the
presence of formaldehyde and hydrogen. We are not aware
of any other reported examples of protodediazonation using
palladium on carbon and hydrogen alone.
The catalytic reduction of 14 to 2 was typically run in
mixtures of water and alcoholic solvents under 50 psig
hydrogen pressure24 at 20-30 °C in the presence of
hydrochloric acid.25 Work-up consisted of filtering the
reaction mixture and diluting with water. Most of the alcohol
was removed by distillation and the product isolated by
filtration. Aqueous isopropyl alcohol was superior to aqueous
methanol with a 3:1 ratio of isopropyl alcohol to water being
optimal.26 Palladium was found to be a better catalyst than
Pt, Rh, Ru, or sponge nickel.
Again, preparing colorless 2 free of 1 was difficult. The
problem of removing 1 was finally accomplished by treating
the reduction filtrate with a small amount of NaNO2 to
cleanly diazotize any 1 present into the water-soluble
derivative 14, which was then left behind in the aqueous
filtrate when 2 was isolated. Unfortunately, this diazotization
added to our already difficult color problem. This problem
was partially solved (at the expense of significant yield loss)
by resorting to multiple recrystallizations from dilute HCl
and Calgon pulverized ADP carbon.27 Nevertheless, even
after two recrystallizations, the product was off-white to pale
yellow in color. Two lots of 2 were prepared from 1 using
this chemistry in 51-53% yield (Table 6).
Another advantage of the air oxidation was that the
troublesome impurity 1 in the product stream was degraded
during the oxidation period. Compound 2 is quite stable to
strongly acidic and basic conditions; however, 1 readily
decomposes under basic conditions to by-products which are
easily removed in the final recrystallization. As a result, the
Although the diazotization/reduction route provided a
necessary short-term solution, we knew that this process was
not attractive for long-term production for a number of
reasons: (1) unstable intermediates, (2) a low-yielding final
step, (3) high cost, and (4) large waste volumes. We reasoned
that an attractive alternate route would convert nitrile 12 to
2 directly, thereby eliminating two synthetic steps (Scheme
5). However, due to the fact that several competing reaction
pathways are possible, the key to our success required being
(28) Elliot and co-workers who were also developing similar PNP inhibitors at
the time reported that Raney nickel reduction of 12 gave detectable levels
of 2, but due to extensive decomposition products it was not amendable to
isolation. Elliott, A. J.; Kotian, P. L.; Montgomery, J. A.; Walsh, D. A.
Tetrahedron Lett. 1996, 37, 5829.
(29) Hicks, J. L. J. Labelled Cmpds. Radiopharm. 1995, 34, 1029.
(30) The oxidation may be nickel-catalyzedsrunning the reaction mixture through
a column of Duolite C-467 ion-exchange resin, which efficiently removes
nickel, completely stopped the oxidation. Concentration of the eluent from
the ion-exchange column and analysis of the resulting solid by ICP showed
7.5 times less nickel than solid obtained by concentration of the reduction
mixture. All other metals analyzed for by ICP (Fe(II), Mn(I), Mo(I), Cr-
(III), Zn(III), Al(III), and Cu(I)) were found at similar or greater levels in
the Duolite-treated solid. Many metal additives (Fe, Fe(acac)3, FeSO4, RhCl3,
PdCl2, ZnF2, CuCl, CuCl2, Cu(OAc)2, Na2MoO4, 12MoO3‚1/3H3PO4, NiCl2,
Ni(OH)2, Ni(acac)2, Ni peroxide, (Ph3P)2NiCl2, Al-Ni, Al(OiPr)3, AcAl-
(OH)2‚1/3H3BO3, AlCl3, and Al foil) and oxidizing agents (Na2S2O8/AgNO3,
Oxone, BaMnO4, H2O2, NaClO, 3,5-di-tert-butyl-1,2-benzoquinone, MMPP,
NaIO4, and CAN) were evaluated in an attempt at improving the oxidation
with respect to rate and purity; however, they were either ineffective or
resulted in decomposition of 16 without conversion to 2. The use of Cu(II)
salts did increase the rate of air oxidation, but the reaction mixtures became
very dark.
(23) Church, R. F. R.; Schaub, R. E.; Weiss, M. J. J. Org. Chem. 1971, 36, 723.
Church notes that this reduction is unusual.
(24) The pressure increases over the course of the reaction presumably due to
the formation of a mole of N2 and HCl.
(25) The addition of HCl is not required, but it does appear to increase the rate
of reaction. We added excess acid primarily to obtain the full 1:1 HCl salt
of the weakly basic 2.
(26) A higher percentage of water resulted in a faster reduction rate, but more
impurities were formed.
(27) ADP carbon was found to be superior to the 15 or more carbons that were
evaluated.
220
•
Vol. 5, No. 3, 2001 / Organic Process Research & Development

Scheme 5
Scheme 6
catalytic hydrogenation was developed, and an air oxidation
of by-product 16 to product 2 was discovered and exploited.
Experimental Section
General. All reagents, solvents, and processing aids were
from commercially available sources and used as received
unless otherwise noted. Proton NMR spectra were obtained
from either a Varian Gemini 200 spectrometer operating at
200 MHz for proton (1H) and at 50 MHz for carbon (13C),
from a Bruker AM250 spectrometer operating at 250 MHz
for proton (1H) and at 63 MHz for carbon (13C), or from a
Varian Unity 400 spectrometer operating at 400 MHz for
proton (1H) and at 100 MHz for carbon (13C). Chemical shifts
are reported in ppm using Me4Si or residual nondeuterated
solvent as reference. IR spectra were measured on an Analect
DS-20 or AQS-20 spectrometer with strong absorbances
reported in wavenumbers (cm-1).
addition of NaNO2, which was used in the diazotization/
reduction method to remove residual 1 and which gave rise
to color in the final product, was no longer needed. Using
this process, two lots of 2 were prepared on pilot scale in
50-60% overall yield from 12 (Table 6).
Although sponge nickel catalyst is inexpensive, the
biggest drawback in using this reduction methodology was
the heavy loading of catalyst required. We typically used a
75% catalyst loading (by weight). If the loading of catalyst
was decreased (single or multiple dose) the reduction failed
to go to completion; if increased, the level of 16 also
increased.
It also should be noted that there are hazards associated
with the use of sponge nickel. On one occasion, a rapid
decomposition occurred as sponge nickel was being added
to a nitrogen-purged hydrogenation Vessel containing nitrile
12 and potassium carbonate. Black carbonaceous material,
yellow powder, gas, and smoke were generated. It was
concluded that the sponge nickel became hot on contact with
air which in turn ignited 12. It is noteworthy that this ignition
occurred even with standard nitrogen inertion procedures.
To circumvent problems in subsequent runs, a slurry of 12
and potassium carbonate in methanol was charged to a sealed,
nitrogen-purged vessel containing the sponge nickel catalyst.
No further problems were encountered.
The sponge nickel reduction route offers several advan-
tages over the diazotization/reduction route toward preparing
2: (1) six versus eight steps, (2) a 40% increase in yield,
(3) 33-50% reduction in waste, (4) stable intermediates, (5)
chemistry not affected by traces of DMSO, (6) 50% decrease
in cost, and (7) no changes to the final purification step. The
last benefit was especially important in maintaining consistent
physical properties of the drug substance over the course of
development.
Methyl 2-Cyano-3-(thienyl)acrylate (5). To a cold (0-5
°C) solution of thiophene-3-carboxaldehyde (74.3 kg, 663
mol), methyl cyanoacetate (65.7 kg, 663 mol), and isopropyl
alcohol (305 L) was slowly added a solution of diisopropy-
lamine (8.3 kg, 82 mol) in isopropyl alcohol (42 L) followed
by a 10 L isopropyl alcohol rinse. An exotherm to 40 °C
was observed during the diisopropylamine addition, and 5
began to crystallize. The slurry was cooled to 20-25 °C,
stirred for 3 h, and then cooled to 0-10 °C for 1 h. The
solid was collected on a centrifuge and washed with cold
isopropyl alcohol (120 L) and vacuum-dried at 45-50 °C
to a constant weight, affording acrylate 5 (118.6 kg, 93%
yield) as an off-white crystalline solid. VPC assay: 99.8%
(area) (DB-5, 15 m, 50 °C (5 min) to 280 °C (10 min) @ 15
°C/min, injector temp 150 °C, detector temp 300 °C, 10:1
1
split). H NMR (CDCl3) δ 8.23 (m, 1H), 8.19 (ddd, J )
0.6, 1.3, 2.9 Hz, 1H), 7.86 (ddd, J ) 0.5, 1.3, 5.2, 1H),
7.47 (ddd, J ) 0.6, 3.0, 5.2, 1H), 3.93 (s, 3H); 13C NMR
(CDCl3) δ 163.5, 148.1, 136.0, 134.6, 127.9, 127.8, 116.1,
100.9, 53.5.
Methyl 2-Cyano-3-(thienyl)propionate (6). From 5. The
hydrogenation was carried out in two part lots. A mixture
of acrylate 5 (60 kg, 310.5 mol), 5% Pd/C (11 kg, Johnson
Matthey type 87L, 50% water wet) and isopropyl alcohol
(526 L) was hydrogenated under 50 psig hydrogen at 50 °C
for 18 h. After cooling the mixture to ambient temperature
the catalyst was removed by filtration and washed with
isopropyl alcohol (75 L). The combined filtrate was con-
centrated by vacuum distillation until 300-318 kg of
distillate had been collected. The product solution was cooled
Conclusions
Efficient, large-scale processes for the preparation of 1
and 2 were developed and proven on pilot scale. In this effort
a safe, high-yielding continuous nitration of 7 was developed,
a MgCl2-mediated alkylation of a chloronitropyrimidine (8)
was discovered, a protodediazotization sequence using
Vol. 5, No. 3, 2001 / Organic Process Research & Development
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221

to 25 °C and held for the second part lot. A second batch of
acrylate 5 (58.5 kg, 302.8 mol) was hydrogenated over 5%
Pd/C (10.7 kg) in isopropyl alcohol (513 L) in a similar
fashion (50 psig hydrogen, 50 °C, 22 h). After cooling, the
mixture was filtered and the catalyst washed with isopropyl
alcohol (73 L). The filtrate and wash were combined with
the first part lot and concentrated by vacuum distillation until
300-318 kg of distillate has been collected. The solution
was cooled to 0-5 °C over 2 h to precipitate the product
and held for at least 1 h. The crystalline solid was collected
on a centrifuge, washed with isopropyl alcohol (51 L), and
vacuum-dried at 25 °C to a constant weight to give
cyanoester 6 (106.3 kg, 89% yield) as a white solid. VPC
assay: 99.9% (area) (DB-5, 15m, 50 °C (5 min) to 280 °C
(10 min) @ 15 °C/min, injector temp 150 °C, detector temp
mixture stirred at 25 °C for about 30 min. After cooling to
0 °C the bright yellow solid was collected on a centrifuge
and rinsed with isopropyl alcohol (200 L). The product was
dried (21 °C, 2 mmHg, at least 24 h) to a constant weight to
afford pyrimidine 8b (76.8 kg, 81.6% yield corrected for
residual IPA 0.7% (w/w) and purity) as a bright yellow
powder. HPLC assay 96.6% (area), (Zorbax CN, 5 µm, 250
× 4.6 mm, 1.0 mL/min, 225 nm, 15% CH3CN:85% 0.036
M Et3N in H2O pH ) 3 with concentrated H3PO4). 1H NMR
(DMSO-d6) δ 6.6 (br s, 4H), 3.33 (septet, J ) 6.6 Hz, 2H),
1.19 (d, J ) 6.6 Hz, 12H); 13C NMR (DMSO-d6) δ 161.2,
161.1, 150.2, 123.4, 46.4, 19.3; IR (1% KBr pellet) 3447,
3318, 3220, 3184, 3176, 3034, 2989, 2873, 1646, 1597, 1556,
1466, 1448, 1394, 1356, 1332, 1245, 1022, 910, 844, 794.
2-Amino-4-chloro-6-hydroxy-5-nitro-pyrimidine, Di-
isopropylethylamine Salt (8c). To a slurry of pyrimidine
8a (10 g, 0.052 mol) in IPA (100 mL) was added diisopro-
pylethylamine (9.1 mL, 0.052 mol). The yellow mixture was
heated to 78 °C for 1 h and then cooled to 15 °C. The solid
was filtered, washed with IPA (150 mL), and dried under
vacuum to a constant weight to afford pyrimidine 8c (9.3 g,
56% yield) as a bright yellow powder (HPLC assay 94%
(area)). The filtrates were concentrated to afford a second
crop of 8c (4.0 g, 24% yield) as a bright yellow solid (HPLC
assay 89% (area), Zorbax SB CN, 5 µm, 250 × 4.6 mm, 1.0
mL/min, 225 nm, 50% CH3OH:50% 0.05 M NH4H2PO4 in
H2O pH ) 3 with concentrated H3PO4).
2-Amino-4-chloro-6-hydroxy-5-nitro-pyrimidine,Diphen-
ylamine Salt (8d). Prepared as for 8c (0.14 mol) but using
diphenylamine afforded pyrimidine 8d (24.2 g, 44% yield)
as a pale yellow powder (HPLC assay 87% (area)).
2-Amino-4-chloro-6-hydroxy-5-nitro-pyrimidine, Di-
cyclohexylamine Salt (8e). Prepared as for 8c (0.63 mol)
but using dicyclohexylamine and heating to 50 °C afforded
pyrimidine 8e (219.5 g, 94% yield) as a bright yellow powder
(HPLC assay 94% (area)).
2-Amino-r-cyano-6-hydroxy-5-nitro-r-(3-thienylmethyl)-
4-pyrimidineacetic acid, Methyl Ester (11). K2CO3/DMSO
Process. A mixture of pyrimidine 8a hydrate (8.8 kg, 53.8
mol), cyanoester 6 (9.5 kg, 48.7 mol), and dry milled
K2CO3 (13.1 kg, 94.8 mol) in DMSO (76 kg) was heated to
70 °C for 10 h. Celite (1.5 kg) was added and the mixture
filtered at 60-65 °C into water (270 L) and ice (52 kg),
washing the filter cake with DMSO (23 kg). The mixture
was slowly acidified to pH 4.0 using 18% HCl (7.5 L). The
resulting solid was collected, washed with water (325 L),
and dried under vacuum to a constant weight (60 °C, H2O
(KF) 2.1%) to afford crude cyanoester 11 (12.8 kg) as a light
yellow solid. The crude cyanoester 11 was dissolved in DMF
(23 kg) and treated with carbon (0.5 kg, Darco G-60) and
Celite (0.5 kg) for 1 h at ambient temperature. The mixture
was filtered and the filter cake rinsed with acetone (55 kg).
With efficient agitation, water (347 L) was added to the
combined filtrates and the resulting slurry cooled to 10-15
°C for 2 h. The solid was collected on a centrifuge, washed
with water (200 L), and dried under vacuum to a constant
weight (60 °C, H2O (KF) 1.2%) to afford cyanoester 11 (11.7
kg, 80% yield) as a light yellow solid. HPLC assay: 100.3%
1
300 °C, 10:1 split). H NMR (DMSO-d6) δ 7.48 (dd, J )
4.9, 3.0 Hz,1H), 7.34 (m, 1H), 7.05 (dd, J ) 4.9, 1.1 Hz,
1H), 4.52 (t, J ) 6.6 Hz, 1H), 3.73 (s, 3H), 3.21 (d, J ) 6.6
Hz, 2H); 13C NMR (DMSO-d6) δ 166.3, 136.2, 128.2, 126.3,
123.3, 117.0, 53.1, 38.1, 29.2.
From Thiophene-3-carboxaldehyde. To a cooled solu-
tion (12 °C) of thiophene-3-carboxaldehyde (11.1 g, 0.1 mol),
methyl cyanoacetate (9.9 g, 0.1 mol), and isopropyl alcohol
(75 mL) was added diisopropylamine (0.2 g, 0.002 mol).
After the initial exotherm of 2 °C subsided, the mixture was
allowed to stir at ambient temperature for 3 h. Then 5% Pd/C
(3.0 g, 50% water wet, Johnson Matthey type 87L) was
added and the mixture subjected to hydrogen at 50 psig and
50 °C overnight. The catalyst was removed by filtration and
washed with isopropyl alcohol. The combined filtrate was
concentrated to approximately a 40 mL volume and seeded.
The resulting slurry was cooled in an ice bath for about 1 h.
The solid was filtered, washed with cold isopropyl alcohol,
and air-dried to afford cyanoester 6 (15.4 g, 79% yield) as
a white solid.
2-Amino-4-chloro-6-hydroxy-5-nitro-pyrimidine, Di-
isopropylamine Salt (8b). The continuous nitration was
carried out in a Teflon tube immersed in a constant-
temperature bath and connected to an aqueous quench tank.
The flow and mixing of the pyrimidine/sulfuric acid and
nitric acid solutions were controlled by means of a dual-
head metering pump.
2-Amino-4-chloro-6-hydroxypyrimidine (45 kg, 309.3
mol) was dissolved in sulfuric acid (290 kg) while maintain-
ing the temperature below 15 °C. After the addition was
complete, the solution was held at approximately 15 °C.
Water (1000 L) was charged to a 2000 L quench tank and
cooled to 0-5 °C. Nitric acid (90%, 60 kg, 958.8 mol) and
the pyrimidine/sulfuric acid solution were combined in the
tube at a flow rate ratio of 4.4:1 over 7 h. The bath
temperature was held at 45 °C. The product mixture in the
quench tank was maintained at <6 °C. After the pyrimidine
solution was consumed, the pale yellow solid in the quench
tank was collected on a centrifuge and washed with water
(400 L) and isopropyl alcohol (200 L), affording pyrimidine
8a as an isopropyl alcohol wet cake. 8a was combined with
isopropyl alcohol (700 L) and agitated to a smooth mixture.
Diisopropylamine (47 kg, 473.7 mol) was added and the
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Vol. 5, No. 3, 2001 / Organic Process Research & Development

(w/w), 99.2% (area), (Zorbax CN, 5 µm, 250 × 4.6 mm,
1.0 mL/min, 225 nm, 30% CH3CN:70% 0.036 M Et3N in
H2O pH ) 3 with concentrated H3PO4), DMSO 0.05% (w/
w). H NMR (DMSO-d6) δ 12.2 (br s, 1H), 8.7 (br s, 1H),
7.47 (dd, J ) 4.9, 3.0 Hz, 1H), 7.4 (br s, 1H), 7.39 (m, 1H),
was collected on a centrifuge, washed with water (150 L),
and dried under vacuum to a constant weight (50-55 °C,
13 mmHg) to afford nitrile 12 (29.7 kg, 93.1% yield
corrected for purity) as a yellow solid (HPLC assay 96.0%
(area)).
1
7.02 (dd, J ) 4.9, 1.3 Hz, 1H), 3.67 (m, 5H).
2,6-Diamino-3,5-dihydro-7-(3-thienylmethyl)-4H-pyr-
rolo[3,2-d]pyrimidin-4-one Hydrochloride, Monohydrate;
CI-972; (1). To a 400 L stainless steel hydrogenator was
charged 5% Pd/C (3.0 kg, 50% water-wet, Johnson Matthey
type 21R), potassium carbonate (12.6 kg, mol), nitrile 12
(17.7 kg, mol), and methanol (250 L). The mixture was
hydrogenated under 50 psig hydrogen pressure at 20-35 °C
for 6.75 h. The reaction mixture was filtered and the catalyst
cake washed with methanol (70 L). The combined filtrate
was cooled to 15-20 °C, and a 20% HCl in methanol
solution was slowly added (35 kg, pH ) 3.5 using a 0-6
pH test strip). The precipitated potassium chloride was
removed by filtration and the cake rinsed with methanol (35
L). More 20% methanolic HCl solution (18.2 kg) was added
to the combined filtrate, which was then heated to reflux
for 5 h. The solution was concentrated by vacuum distillation
to a batch volume of 175 L to partially crystallize the product.
The slurry was cooled to 0-5 °C and held for at least 1 h.
The solid was collected on a centrifuge, washed with
isopropyl alcohol (80 L) and dried (50 °C) to afford 1 (14.9
kg, 62.1% yield) as a tan solid. The material was recrystal-
lized from aqueous acetonitrile (1:2, 482 L) and carbon (2.6
kg, Calgon ADP pulverized, 12 L water rinse) at 70 °C. After
complete dissolution the carbon was removed by filtration
and washed with aqueous acetonitrile (1:2, 27 L). Hydro-
chloric acid (9.0 kg, 37% HCl, 15.3 L water) was added to
the combined filtrate and the solution cooled to 5-10 °C
for at least 1 h. The product was collected on a centrifuge,
washed with water (31 L), dried (50 °C) to a constant weight,
and milled to afford 1 (11.9 kg, 60% yield) as a white solid.
HPLC assay: 100.6 (w/w), 99.5% (area) (Zorbax CN, 5 µm,
250 × 4.6 mm, 1.0 mL/min, 225 nm, 15% CH3CN:85%
0.036 M Et3N in H2O pH ) 3 with concentrated H3PO4),
chloride 11.43% (w/w), water 6.83% (w/w). 1H NMR
(DMSO-d6) δ 12.9 (br s, 1H), 11.5 (br s, 1H), 11.1 (s, 1H),
7.7 (s, 2H), 7.4 (m, 1H), 7.3 (m, 1H), 7.1 (m, 1H), 5.9 (br
s, 2H), 3.8 (s, 2H); 13C NMR (DMSO-d6) δ 128.5, 125.8,
120.7, 150.8, 148.7, 147.3, 141.2, 133.7, 101.3, 89.7, 21.7;
IR (1.0% KBr pellet) 3454, 3311, 3213, 3167, 3076, 2993,
1686, 1618, 1552, 1433, 1408, 1304, 748.
MgCl2/Et3N/CH3CN Process Using 8e. To a mixture of
cyanoester 6 (5.3 g, 0.027 mol) and pyrimidine 8e (10.0 g,
0.027 mol) in CH3CN (150 mL) was added MgCl2 (3.8 g,
0.040 mol), resulting in a 5 °C exotherm. Et3N (7.5 mL,
0.054 mol) was added and the orange mixture heated to 50
°C for 3 h. The batch was poured into aqueous HCl (11.3
mL of 37% HCl and 500 mL of water) and cooled to ambient
temperature. The solid was filtered, washed with water (200
mL), and dried under vacuum to a constant weight to afford
cyanoester 11 (8.1 g, 86% yield) as a pale yellow powder
(HPLC assay 91% (area)).
2-Amino-6-hydroxy-5-nitro-r-(3-thienylmethyl)-4-py-
rimidineacetonitrile (12). K2CO3/DMSO Process. To a
cooled mixture (10-15 °C) of cyanoester 11 (22.0 kg, 63.0
mol) in water (264 L) was added 50% NaOH (22 kg, mol)
over 10 min, keeping the temperature <20 °C. After 3 h at
10-15 °C, the solution was acidified to pH 4 by addition of
37% HCl (29 kg). Without delay the resulting solid was
collected on a centrifuge, washed with water (110 L), and
dried under vacuum to a constant weight (45-50 °C, H2O
(KF) 1.1%) to afford nitrile 12 (17.7 kg, 97% yield) as a tan
solid. HPLC assay: 94.9% (area) (Zorbax CN, 5 µm, 250
× 4.6 mm, 1.0 mL/min, 225 nm, 30% CH3CN:70% 0.05%
1
Et3N in H2O pH ) 3 with concentrated H3PO4). H NMR
(DMSO-d6) δ 12.1 (br s, 1H), 8.4 (br s, 1H), 7.52 (dd, J )
4.9, 3.0 Hz, 1H), 7.4 (br s, 1H), 7.37 (m, 1H), 7.06 (dd, J )
4.9, 1.3 Hz, 1H), 4.67 (dd, J ) 9.3, 5.8 Hz, 1H), 3.26 (dd,
J ) 14.0, 5.8 Hz, 1H), 3.19 (dd, J ) 14.0, 9.4 Hz, 1H); 13
C
NMR (DMSO-d6) δ 160.3, 156.31, 156.28, 136.7, 128.2,
127.3, 126.6, 123.3, 118.8, 37.4, 32.3; IR (1.0% KBr pellet)
3429, 3322, 3219, 1641, 1578, 1485, 1329, 1296, 1219, 847,
789, 766.
MgCl2/Et3N/CH3CN Process. To a mixture of cyanoester
6 (20.5 kg, 105.0 mol) and pyrimidine 8b (34.0 kg, 116.5
mol) in CH3CN (133 kg) was added MgCl2 (16.6 kg, 174.3
mol) in portions over 45 min, maintaining the temperature
below 8 °C (a jacket temperature of -15 °C was used during
the addition). Et3N (23.5 kg, 232.2 mol) was then added,
resulting in an exotherm from 8 to 23 °C. The batch was
stirred at 23-25 °C for 3 h and then slowly quenched into
aqueous HCl (23.1 kg 37% HCl, 551 L water), rinsing the
reaction vessel with acetonitrile (20 L). The resulting solid
was collected on a centrifuge and washed water (100 L) to
give cyanoester 11 (98.8 kg, HPLC assay 96.4% (area)) as
a pale yellow, water-wet solid.
The wet cyanoester 11 was combined with water (289 L)
and stirred to an even suspension. After cooling to 10-15
°C, sodium hydroxide (50% aqueous, 30.4 kg, 379 mol)
was added and the dark brown solution stirred at 15-25
°C for 1.5 h. Hydrochloric acid (37%, 37.6 kg, final pH )
3.5) was added to the batch, while maintaining the temper-
ature at 10-20 °C. Without delay, the resulting solid product
2-Amino-3,5-dihydro-7-(3-thienylmethyl)-4H-pyrrolo-
[3,2-d]pyrimidin-4-one Hydrochloride, Monohydrate; CI-
1000; (2). From 1 Using Diazotization and Hypophos-
phorus Acid Reduction. To a cold (0-5 °C) slurry of 1
(294.7 g, 0.93 mol), water (2.2 L), and hydrochloric acid
(37%, 156 mL, 1.86 mol) was slowly added (to control
foaming) a solution of sodium nitrite (90.1 g, 1.31 mol) in
water (285 mL), keeping the temperature between 5 and 10
°C. The mixture was carefully warmed to 20 °C and held at
that temperature for 3 h. The solid was collected on a
Bu¨chner funnel, washed with water (2 × 285 mL), and pulled
dry using a rubber dam to give the diazonium chloride salt
14 (753 g) as a bright yellow, water-wet solid.
Vol. 5, No. 3, 2001 / Organic Process Research & Development
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223

To a mixture of water-wet 14, deionized water (1.5 L),
CuSO4 (13.8 g, 0.086 mol), and isopropyl alcohol (215 mL)
at 0-5 °C was added 50% aqueous H3PO2 (896 mL, 8.65
mol) over 18 minsthe temperature increased from 4 to 8
°C over the course of the addition. The mixture was warmed
to 15 °C (15 min) and held at that temperature for 1.75 h.
The batch was neutralized to a pH of 6.9 by the addition of
50% NaOH (512 mL), while keeping the temperature at 15-
20 °C. The solid was filtered, washed with water (500 mL),
and dried in vacuo at 50 °C for at least 24 h to afford crude
2 freebase (364 g) as a brown solid. The crude 2 freebase
was purified by flash chromatography (6 in. diameter column,
7 kg 60 Å 230-400 mesh silica gel) eluting with CH2Cl2/
CH3OH/NH4OH (16:1:0.05 to 6:1:0.05) to afford 2 freebase
(63.5 g) as a white solid.
Several lots of 2 freebase prepared as described above
were recrystallized together: To a solution of 2 freebase (238
g), water (12.3 L), and 37% HCl (595 mL) at reflux was
added carbon (23.5 g, Calgon ADP pulverized) in water (100
mL). After refluxing for 30 min the mixture filtered through
Celite and washed with hot water (500 mL). The combined
filtrate was cooled to 0-5 °C and held for 2 h. The
precipitate was filtered, washed with water (500 mL), and
dried to a constant weight (50 °C, 24-48 h) to afford 2
(250.3 g, 37.1% overall yield from 1) as a white solid. HPLC
assay 99.8% (w/w) (Zorbax CN, 5 µm, 250 × 4.6 mm, 1.0
mL/min, 225 nm, 15% CH3CN:85% 0.036 M Et3N in H2O
pH ) 3 with concentrated H3PO4), chloride 11.77% (w/w),
water 7.13% (w/w). 1H NMR (DMSO-d6) δ 12.6 (br s, 1H),
12.33 (d, J ) 2.6 Hz, 1H), 7.94 (s, 2H), 7.44 (dd, J ) 4.9,
3.0 Hz, 1H), 7.28 (m, 2H), 7.08 (dd, J ) 4.9, 1.2 Hz, 1H),
3.9 (s, 2H); 13C NMR (DMSO-d6) δ 151.9, 151.3, 140.8,
130.6, 128.5, 127.6, 126.1, 121.3, 111.1, 110.2, 21.9; IR
(1.0% KBr pellet) 3099, 2932, 2868, 1703, 1667, 1481, 1389,
1129, 1063, 825, 759, 731, 702. Anal. Calcd for C11H10N4-
OS?HCl?H2O: C, 43.40; H, 4.44; N, 18.40; S, 10.50.
Found: C, 43.22; H, 4.10; N, 18.28; S, 10.79.
30 °C. The mixture was filtered and the catalyst cake washed
with isopropyl alcohol (75 L). The filtrate was transferred
to a second reactor, followed by an isopropyl alcohol rinse
(75 L), and cooled to 0-5 °C. The remaining diazonium
chloride salt 14 was reduced in the same manner and
combined with the first-part lot. After warming the combined
filtrates to 20-25 °C, they were treated with ADP carbon
(7.2 kg), sodium nitrite (0.5 kg), and Celite (4.0 kg). The
mixture was agitated for about 1 h and filtered, and the
carbon cake was rinsed with methanol (400 L). The filtrate
was diluted with water (160 L) and the batch concentrated
by vacuum distillation to one-quarter of its original volume
(approximately 160 L of volume remained). More water (100
L) was charged to the mixture, and the distillation continued
until less than 5% isopropyl alcohol and methanol were
detected in the distillate (1.7% MeOH and 2.4% IPA were
detected in this batch. A volume of about 200 L remained
in the still). The resulting mixture was cooled to 0-5 °C
for at least 1 h and the crude product collected on a centrifuge
and washed with cold (0-5 °C) water (150 L), yielding crude
2 (19.3 kg) as a wet (LOD 23%), light brown solid.
The crude 2 was combined with water (500 L), 37% HCl
(19.5 kg), carbon (3.3 kg, Calgon ADP pulverized), and
Celite (2.0 kg) and heated to reflux. After about 20 min, the
mixture was filtered and the cake rinsed with hot (95 °C)
water (50 L). The combined filtrates were cooled to 0-5
°C and held for at least 1 h. The precipitate was collected
on a centrifuge and rinsed with cold water (150 L) to afford
2 (18.7 kg) as light gold colored needles (LOD 32%).
The material was recrystallized a second time for color
in a similar fashion using water (460 L) 37% hydrochloric
acid (15.3 kg), ADP carbon (1.3 kg), and Celite (1.0 kg).
The product was collected on a centrifuge, washed with water
(150 L), dried to a constant weight (50-55 °C, 28 in. Hg,
at least 24 h), and milled to give 2 (11.4 kg, 51% yield from
1) as a pale yellow solid (HPLC assay 100.5% (w/w), 99.7%
(area), chloride 11.86% (w/w), 6.14% water (w/w)).
From 1 Using Diazotization and Catalytic Hydrogena-
tion. To a cold (0-5 °C) slurry of 1 (23.4 kg, 74.1 mol),
water (240 L), and hydrochloric acid (37%, 14.9 kg, 151.2
mol) was slowly added (40 min) a solution of sodium nitrite
(7.9 kg, 114.5 mol) in water (20 L), keeping the temperature
at <4 °C. The mixture was carefully warmed to 20-25 °C
over about an hour and held at that temperature for about
an hour. The solid was collected on a centrifuge and the
cake washed with water (90 L) to give the diazonium chloride
salt 14 (63.5 kg) as a bright yellow, water-wet solid.
Hydrogenation of the diazonium salt 14 was carried out
in two-part lots: To a 400 L glass-lined hydrogenator was
charged approximately one-half of the water-wet 14, 5%
Pd/C (3.5 kg, 50% water-wet, Johnson Matthey type 87L),
isopropyl alcohol (225 L), water (75 L), and 37% hydro-
chloric acid (18.7 kg). The mixture was hydrogenated at 50
psig31 over 2 h, while maintaining the temperature at 20-
From 12 Using Sponge Nickel Reduction. To an inerted
800 L stainless steel hydrogenator containing sponge nickel
catalyst (37.5 kg, Activated Metals type A-5000) was charged
a mixture of nitrile 12 (50 kg, 171.6 mol), potassium
carbonate (23.7 kg, 171.6 mol), and methanol (378 L),
followed by a methanol rinse (50 L). The mixture was cooled
to 5-15 °C, and the mixture was hydrogenated under 50
psig hydrogen, while maintaining the temperature at <30
°C. After the initial exotherm subsided (about 1.25 h), the
mixture was warmed to 40-50 °C and the hydrogenation
continued for an additional 18 h. The mixture was filtered
onto carbon (4.4 kg Calgon ADP pulverized) and Celite (4.4
kg) using methanol (171 L) as a catalyst cake wash. Air was
gently sparged through the filtrate with agitation at 20-30
°C for 72 h. The mixture was then filtered and the cake
washed with methanol (100 L). The orange filtrate was
diluted with water (1345 L) and 37% hydrochloric acid (50.7
kg) and the solution concentrated by atmospheric distillation
until a batch temperature of 98-100 °C was obtained (6 h).
The solution was cooled to 0-5 °C and held for at least 1
h. The precipitate was collected on a centrifuge and washed
(31) Presumably due to the formation of hydrogen chloride and nitrogen during
the reduction, the batch pressure actually increases as the hydrogen is
consumed. During this hydrogenation the pressure was relieved twice from
60 to 50 psig and once from 60 to 5 psig, followed by repressurizing to 50
psig with hydrogen. The hydrogenation was essentially complete after 1 h.
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with water (100 L) to afford crude 2 (41.7 kg, HPLC assay
>99% (area)) as dark brown needles.
chloride 11.94% (w/w), water 6.09% (w/w), nickel <10
ppm).
Recrystallization for Color. The crude 2 was dissolved
at reflux in water (1470 L) and 37% hydrochloric acid (23.7
kg) and then treated with a slurry of carbon (3.6 kg, Calgon
ADP pulverized) and Celite (3.6 kg) in water (20 L). After
15 min the mixture was filtered hot and the carbon cake
washed with boiling water (150 L). The combined aqueous
filtrate was cooled to 0-5 °C and held for at least 1 h. The
precipitate was collected on a centrifuge, washed with water
(100 L), and dried to a constant weight (50-55 °C, 29 in.
Hg) to afford 2 (30.8 kg, 60% yield) as an off-white solid.
HPLC assay: 99.1% (w/w), 99.7% (area) (Lichrosorb RP8,
5 µm, 250 × 4.6 mm, 1.1 mL/min, 225 nm, 26% CH3CN:
74% 0.02M NH4OAc in H2O pH ) 6.8 with NH4OH),
Acknowledgment
We thank Mr. J. Van De Vusse, Mr. G. Flores, and Mr.
D. Wehrmeyer for their many practical contributions both
in the laboratory and in the pilot plant. We also thank Dr.
D. Belmont and Dr. J. Zeller for their valuable scientific
input. We gratefully acknowledge the analytical support of
Dr. T. Zennie, Mr. T. Wilcox, and Mr. K. Speaks and also
Mr. F. Mauro for process hazard evaluation. Finally, we also
thank Dr. D. Butler, Dr. M. Hoekstra, and Ms. S. Dokter
for assistance in preparing this manuscript.
Received for review September 23, 2000.
OP000298D
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