Organic Process Research & Development
Article
(as required for desired pH, ∼124 g, 1.55 mol) was added at a
rate such that the temperature remained below 60 °C, to a final
pH of 6.0 (range 5.5−6.5). n-Propyl acetate (709 mL) was then
added, and the mixture was heated to 50 °C with stirring for 15
min. Stirring was halted, and the layers were allowed to settle
for 15 min. The lower phase (aqueous waste) was removed,
and the remaining product-containing organic phase was cooled
to 18 °C. Speck-free filtration was performed at this point.
While stirring, a vacuum of 100 mbar was applied, and
distillation was performed by heating the mixture (at this
pressure the distillation range was 21−30 °C) to a volume of
∼600 mL (7.5 mL/g β-keto-lactone 2). An additional portion
of n-propyl acetate (709 mL) was added, and vacuum
distillation at 100 mbar was resumed (the distillation range
was 34−41 °C) to a volume of ∼600 mL (7.5 mL/g β-keto-
lactone 2). Water content was measured by Karl Fischer
titration (spec NMT 0.15 wt %); then the mixture was heated
at ambient pressure to 102−103 °C and held at that
temperature (mild reflux) for 15 min. The solution was then
cooled to 80 °C at a rate of 0.5 °C/min and seeded with API 1
(0.14 g, 0.2 wt %; seeding was performed to ensure nucleation
and prevent occlusion of impurities in the crystal lattice (if
crystallization had already occurred, seeding could be omitted).
The slurry was stirred at 80 °C for 60 min, then cooled to 10
°C at a rate of 0.5 °C/min, and held at 10 °C for at least one
hour. The solids were collected by filtration, rinsing with two
portions of cold (10 °C) n-propyl acetate (36 L each). Drying
at 50 °C under a slow stream of nitrogen provides the API (1)
as a white solid (74.2 g, 147 mmol, 71.6% yield).
h, then isolated by filtration, rinsing with two portions of cold
(10 °C) n-propyl acetate (28 mL each, 2 mL/g). After drying in
a vacuum oven with nitrogen bleed at 50 °C, product was
obtained in ∼90% yield.
Characterization of Impurities 15 and 16. . Preparative
HPLC isolation of these impurities provided the following
characterization data:
(E)-2-(2-(5,7-Dimethyl-[1,2,4]triazolo[1,5-a]pyrimidin-2-
1
yl)vinyl)-5-(ethoxycarbonyl)-6-methylnicotinic acid (15): H
NMR (700 MHz, pyridine-d5): δ 10.02 (d, 1H, J = 15.5), 9.22
(s, 1H), 8.66 (d, 1H, J = 15.5), 6.60 (s, 1H), 4.30 (q, 2H, J =
7.2), 3.05 (s, 3H), 2.60 (s, 3H), 2.53 (s, 3H), 1.21 (t, 3H, J =
7.2).
13C NMR (175 MHz, pyridine-d5): δ 170.75, 166.20, 164.97,
164.83, 160.42, 156.27, 155.13, 146.58, 142.05, 134.97, 129.25,
126.10, 124.50, 110.67, 61.30, 25.38, 24.84, 16.62, 14.25.
HRMS (ESI+): m/z calcd for C19H20N5O4 (M + H)
382.15098; found 382.15158.
(R)-6-Cyclopentyl-6-(2-(2,6-diethylpyridin-4-yl)ethyl)-3-((5-
(2-(5,7-dimethyl-[1,2,4]triazolo[1,5-a]pyrimidin-2-yl)-2-hy-
droxyethyl)-7-methyl-[1,2,4]triazolo[1,5-a]pyrimidin-2-yl)-
methyl)-4-hydroxy-5,6-dihydro-2H-pyran-2-one (16c). One
of the four isomers (two regioisomers, each of which is a
mixture of two diastereomers at the newly formed secondary
alcohol) was isolated by preparative chromatography for full
characterization:
HRMS (ESI+): m/z calcd for C24H30N4O3ClS (M + H)
489.17217; found 489.17274.
NMR (700 MHz, CD3CN):
The 1D proton spectrum shows the expected chemical shifts,
multiplicities, and integrations that are consistent with
1H NMR (500 MHz, (CD3)2SO): δ 10.90 (br s, 1H), 7.04 (s,
1H), 6.91 (s, 2H), 3.84 (d, 1H, J = 16.4), 3.72 (d, 1H, J = 16.1),
2.80 (d, 1H, J = 17.6), 2.64 (q, 4H, J = 7.5), 2.59−2.55 (m,
3H), 2.52 (s, 3H), 2.43 (s, 3H), 2.41 (m, 1H), 2.15 (m, 2H),
1.69 (m, 2H), 1.57 (m, 5H), 1.38 (m, 1H), 1.16 (t, 6H, J = 7.6).
13C NMR (125 MHz, (CD3)2SO): δ 166.91, 166.66, 165.12,
163.53, 161.98, 154.90, 151.24, 146.19, 119.17, 110.02, 98.17,
81.44, 45.72, 36.83, 33.01, 30.44, 29.12, 26.50, 26.28, 25.40,
25.34, 24.32, 23.20, 16.07, 13.86.
1
Structure 16c. The D carbon spectrum is consistent based
upon chemical shift. The 2D spectra show the expected
1H−13C and 1H−1H correlations. Key homonuclear and
heteronuclear correlations are indicated in Figure 2. Proton
and carbon assignments are tabulated in Table 5. The
secondary alcohol center at position 38 was not determined.
HRMS (ESI+): m/z calcd for C29H38N5O3 (M + H)
504.2975; found 504.2963.
Anal. Calcd for C29H37N5O3: C, 69.16; H, 7.40; N, 13.91.
Found: C, 69.18; H, 7.60; N, 13.93.
AUTHOR INFORMATION
■
Corresponding Authors
Reprocessing Procedure (if needed to meet purity
specifications). API 1 (14.0 g, 40 mmol) and THF (55 mL,
4 mL/g) were combined and the resulting slurry was heated to
60 °C with stirring until homogeneous. If desired, a speck-free
filtration could be performed at this stage. To the THF solution
was added n-propyl acetate (69 mL, 5 mL/g), and this solution
was cooled to 17 °C (crystallization may occur during this cool
down). Vacuum (100 mbar) was applied, and the solution was
distilled, with occasional addition of n-propyl acetate to
maintain a constant volume of 112−126 mL (8−9 mL/g)
during distillation. Approximately 140 mL (10 mL/g) of n-
propyl acetate was required during the distillation. Distillation
was halted when the solution had reached a temperature of ∼42
°C. When distillation was complete, additional n-propyl acetate
was added to a total volume of 140 mL (10 mL/g), and the
resulting solution was heated to 102−103 °C. This temperature
(reflux) was maintained for 15 min, then cooled to 80 °C at a
rate of 0.5 °C/min. Seeding with pure API (30 mg, 0.2 wt %)
was done unless crystallization had already initiated. The slurry
was maintained at 80 °C for 2 h, and then cooled to 10 °C at a
rate of 0.5 °C/min. The slurry was stirred at 10 °C for at least 3
Present Addresses
§Tetraphase Pharmaceuticals, 480 Arsenal Street, Suite 110,
Watertown, MA 02472.
∥Canterbury Christ Church University, North Holmes Road,
Canterbury, Kent, UK.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank John Lucas and Brian Conway for
experiments related to the Mannich-Hydrogenation approach
(Scheme 6), Anil Rane and Donna Brown for preparation of
14C-labelled β-keto-lactone (2), and Silke Wunderwald, Ron
Morris, Mark Zell, and Todd Zelesky for characterization of
impurities 15 and 16.
REFERENCES
■
(1) Li, H.; Tatlock, J.; Linton, A.; Gonzalez, J.; Jewell, T.; Patel, L.;
Ludlum, S.; Drowns, M.; Rahavendran, S. V.; Skor, H.; Hunter, R.; Shi,
K
dx.doi.org/10.1021/op400237j | Org. Process Res. Dev. XXXX, XXX, XXX−XXX