Application of in Situ FTIR for the Preparation of 17-α-Estradiol via Mitsunobu Reaction

Article abstract of DOI:10.1021/acs.oprd.5b00394

An efficient synthesis of 17-α-estradiol 1 is described. Utilization of in situ IR allowed for an online monitoring of the key Mitsunobu reaction and development of a safe and reliable synthesis of 17-α-estradiol 1 in 78% overall yield over three steps. Benzoylation of 17-β-estradiol 2 is conducted at high regioselectivity under phase-transfer catalysis (PTC) conditions, followed by a Mitsunobu reaction to invert the chiral center at C-17 and provide intermediate 5, containing the core structure of 17-α-estradiol 1. Finally, the desired active pharmaceutical ingredient (API) is prepared by saponification of the remaining esters.

Full text of DOI:10.1021/acs.oprd.5b00394

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Full Paper
Application of in Situ FTIR for the Preparation
of 17-#-estradiol via Mitsunobu Reaction
Flávio Sêga Pereira Cardoso, Gregory Mickle, Marco Antonio
da Silva, Patricia Tambarussi Baraldi, and Fabio Batista Ferreira
Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.5b00394 • Publication Date (Web): 14 Jan 2016
Downloaded from http://pubs.acs.org on January 19, 2016
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Application of in Situ FTIR for the Preparation of
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1
7ꢀαꢀestradiol via Mitsunobu Reaction
,†
†
†
†
Flávio S. P. Cardoso,* Gregory E. Mickle, Marco A. da Silva , Patricia T. Baraldi , and
‡
Fabio B. Ferreira
†
Libbs Farmacêutica Ltda., Rua Alberto Correia Francfort, 88, Embu das Artes, São Paulo,
Brazil
‡
Mettler Toledo Ind. e Com. Ltda, Av. Tamboré, 418, Barueri, São Paulo, Brazil
*Corresponding Author
Eꢀmail: flavio.cardoso@libbs.com.br
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TABLE OF CONTENTS GRAPHIC (TOC)
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ABSTRACT
An efficient synthesis of 17ꢀαꢀestradiol 1 is described. Utilization of in situ IR
allowed for an online monitoring of the key Mitsunobu reaction and development of a safe
and reliable synthesis of 17ꢀαꢀestradiol 1 in 78% overall yield over three steps.
Benzoylation of 17ꢀβꢀestradiol 2 is conducted in high regioselectivity under phase transfer
catalysis (PTC) conditions, followed by a Mitsunobu reaction to invert the chiral center at
Cꢀ17 and provide intermediate 5, containing the core structure of 17ꢀαꢀestradiol 1. Finally,
the desired API is prepared by saponification of the remaining esters.
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Keywords: 17ꢀαꢀestradiol, in situ FTIR, online analysis, Mitsunobu, phaseꢀtransfer catalysis
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INTRODUCTION
7ꢀαꢀestradiol 1 is a Cꢀ17ꢀepimer of the well known estrogen 17ꢀβꢀestradiol 2.
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Interestingly, 17ꢀαꢀestradiol has little to none of the feminizing activity associated with the
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βꢀsteroid. In fact, 17ꢀαꢀestradiol is a 5ꢀαꢀreductase inhibitor that exhibits influence on
human hair growth, and recently, studies towards its therapeutic use in neurodegenerative
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disorders such as Alzheimer's and Parkinson's diseases are being conducted.
Our interest in this area lies in the need to obtain 17ꢀαꢀestradiol on a multiꢀgram
scale. In principle, 17ꢀαꢀsteroids could be prepared through a stereoselective reduction of
the corresponding ketones at Cꢀ17. Nonetheless, the use of common reducing agents such
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as sodium borohydride leads to the 17ꢀβꢀsteroid. To circumvent this issue, research groups
have reported procedures to invert the chiral center of 17ꢀβꢀsteroids in order to obtain the αꢀ
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counterpart. For instance, Dodge and coꢀworkers successfully employed the Mitsunobu
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reaction for the S 2 displacement at Cꢀ17 of 17ꢀβꢀsteroids.
However, none of these
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reports describe the use of this strategy for the synthesis of 1 in greater than 300 g pilot
production scale. In this context, we present herein the synthesis of 17ꢀαꢀestradiol 1 through
a Mitsunobu reaction and scaleꢀup of the process.
In past decades, the control of chemical processes through online analytical
technology has attracted both the academic and industrial communities. These methods are
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related to the concepts of Process Analytical Technology (PAT) and Quality by Design
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(
QbD) which are topics of high interest in the pharmaceutical industry. There are several
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reports demonstrating that the application of PAT technologies can improve the quality of
acquired data and enable a better understanding of the chemical processes, among them,
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IR, NIR, Raman , and quantitative NMR spectroscopy appear as important examples.
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Advantages on using these techniques include the avoidance of offline analysis (for
example, HPLC) and worker exposure to hazardous substances. In this contribution, we
describe the synthesis of 17ꢀαꢀestradiol using an in situ IR probe (ReactIR) and an
automated reactor (EasyMax) to study the key Mitsunobu reaction step.
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DISCUSSION
Aiming at the synthesis of 17ꢀαꢀestradiol, we devised the synthetic route presented
in Scheme 1. Protection of 17ꢀβꢀestradiol at Cꢀ3 followed by a Mitsunobu reaction at Cꢀ17
ultimately allows for global deprotection in the final step.
Scheme 1. Proposed synthetic route.
The preparation of 3ꢀbenzoylꢀ17ꢀβꢀestradiol 3 in large quantity by selective
protection of 17ꢀβꢀestradiol 2 at the Cꢀ3 oxygen was required prior to investigation of the
Mitsunobu reaction. To achieve this, we performed an acylation reaction using sodium
hydroxide and benzoyl chloride to furnish the desired product in 80% yield, although the
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formation of the undesired dibenzoate product 4 was also observed. Working towards a
cleaner reaction, which would preclude the formation of 4, we decided to investigate the
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effect of phase transfer catalysis (PTC) on this process. Our studies, presented in Table 1,
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focused on the selectivity of the reaction, expressed by the ratio between compounds 3 and
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. Initially, we performed an experiment employing 10 mol % of tetrabutylammonium
hydrogensulfate as a PTC catalyst, sodium hydroxide as a base, and a biphasic waterꢀ
dichloromethane solvent system. Gratifyingly, after 3 hours the starting material was
consumed and the desired product 3 was obtained with excellent selectivity (99.6/0.4 ratio,
Table 1, Entry 1). In a control experiment, without the catalyst, a lower selectivity was
observed confirming the importance of the PTC catalyst (Table 1, Entry 2). We also tested
potassium carbonate, a milder base, which proved to be suitable for this reaction (Table 1,
Entry 3). Additionally, an experiment employing 2 mol % of catalyst was conducted and
the product was obtained with excellent selectivity. When we tested tetraoctylammonium
bromide, an alternative PTC catalyst, the reaction presented lower selectivity (Table 1,
Entry 5). With the optimized conditions established (Entry 4), we performed a reaction with
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00 g of 17ꢀβꢀestradiol 2, affording the desired product 3 in 96% yield and 99.5% purity as
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determined by HPLC. Also of importance is the fact that 3 is a prohormone and this
reaction consists of an interesting alternative to prepare this product.
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Table 1. Optimization of the PTC benzoylation reaction
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With an optimized route to 3 established, we decided to explore the Mitsunobu
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reaction. Dodge and coꢀworkers reported that relatively acidic carboxylic acids, such as pꢀ
nitrobenzoic acid, are efficient nucleophiles for the acylation of sterically encumbered
secondary alcohols via Mitsunobu reaction. Using similar reaction conditions, 3ꢀbenzoylꢀ
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17ꢀβꢀestradiol 3 was treated with diisopropylazodicarboxylate (DIAD), 4ꢀnitrobenzoic
acid, and triphenylphosphine in toluene. After heating the reaction at 100 °C for 1.5 h the
product was isolated in 83% yield (Scheme 2).
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Scheme 2. Mitsunobu reaction of 3ꢀbenzoylꢀ17ꢀβꢀestradiol 3
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At the outset, HPLC was used as InꢀProcess Control (IPC) for this Mitsunobu
reaction, which requires long periods of analysis and verification of results (the
chromatography method takes approximately 65 minutes). To facilitate our process control,
we decided to monitor the reaction progress using an in situ FTIR probe instrument and an
automated reactor. This combination would give us valuable insight into the events
occurring throughout the process, such as temperature variations and chemical events.
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Figure 1 shows the in situ FTIR profile acquired from a laboratory scale reaction which is
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a 3ꢀD surface plot of the ConcIRT spectra acquired during the reaction as a function of
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time and wavelength. The high intensity peak observed at 1336 cm suggests that an
intermediate is formed and consumed during the process which will be discussed further in
detail.
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Figure 1. 3ꢀD surface plot of the ConcIRT spectra acquired during the Mitsunobu reaction
as a function of time and wavelength.
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The ReactIR software allows for data processing (ConcIRT module) which detects
the concentration of different “components” throughout the reaction (Figure 2). In this
experiment, three reaction components were identified and assigned based on their
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diagnostic IR signals: triphenylphosphine (signal at 1436 cm ), product 5 (ester carbonyl
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signals at 1724 cm and 1744 cm ) and an intermediate (signals at 1336 cm , 1596 cm
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and 1623 cm ). We suggest, based on literature data, that the intermediate could be the
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DIADꢀPPh complex (Figure 3). Furthermore, analysis of the ConcIRT spectrum profile
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when the intermediate is the major component reveals: a strong stretching signal at 1336
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cm , supporting the presence of a phosphorusꢀnitrogen bond; and signals at 1596 cm and
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623 cm , supporting the presence two different amide type carbonyls.
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Figure 2. ConcIRT trends profile during the Mitsunobu reaction progress.
Figure 3. Structure and ConcIRT spectrum profile of the proposed intermediate formed
during the Mitsunobu Reaction.
As illustrated in Figure 2, the addition of DIAD is concomitant with the
consumption of the triphenylphosphine (red trend line; 23ꢀ34 min) and the formation of the
intermediate (yellow trend line; 23ꢀ34 min). After a ~7 min hold time (34ꢀ39 min), the
reaction was heated to 100 °C leading to the disappearance of the intermediate (yellow
trend line; 39ꢀ49 min) and appearance of the product 5 (green trend line; 39ꢀ49 min).
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Another interesting feature is the variation of the reaction temperature, represented
by the purple trend line (Figure 2). As can be seen, the slow addition of DIAD (in 10
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portions) leads to an increase of the reaction temperature due to the exothermicity of the
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4,17
DIADꢀPPh complex formation (23ꢀ34 min). By the end of the addition, the intermediate
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concentration becomes constant, as represented by the plateau profile of the yellow line
trend (34ꢀ39 min). Next, we set the automated reactor to increase the reaction temperature
to 100 °C. Interestingly, the formation of the product 5 and the temperature ramp (green
and purple trend lines; 39ꢀ49 min) are almost coincident and the reaction is finished when
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the temperature reaches 100 °C. Thus, in contrast to the literature, this reaction requires
less than 1.5 h to complete, which allows for decreased energy use and may avoid impurity
formation. Actually, it shows that controlling the temperature rise to 100 °C will drive the
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reaction to completion within 5ꢀ10 minutes. Therefore, this online monitoring is useful as
an IPC for this specific step and we are able continue the process without a more time
demanding HPLC analysis and the need to collect a sample at 100 °C.
Aside from the control and understanding of the Mitsunobu reaction, efforts were
needed to achieve the isolation of 5 in high yield and purity. It is well known that
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triphenylphosphine oxide can be a problematic byꢀproduct from Mitsunobu reactions. To
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solve this issue, a variety of solvents were investigated to determine the optimal
crystallization conditions to purify 5. Among all solvents tested, we observed a very low
solubility of 5 in methanol, while triphenylphosphine oxide is highly soluble. This result
allowed for the removal of triphenylphosphine oxide from 5 using methanol and providing
the desired product in high purity.
To complete the synthesis, saponification of both esters and the isolation of 17ꢀαꢀ
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estradiol 1 were carried out. Reaction conditions employing aqueous sodium hydroxide in
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ethanol at reflux fully converted 5 to 17ꢀαꢀestradiol 1. Monitoring the reaction using the in
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situ FTIR instrument generated the ConcIRT trends profile illustrated in Figure 4. The
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conversion of the starting material 5 (blue trend line; carbonyl signals at 1719 cm and
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389 cm ) indicates a successful reaction (19ꢀ24 min). It is worth noting that the starting
material 5 is slightly soluble in ethanol resulting in low intensity peaks in the ConcIRT
trends profile (blue trend line). In addition, we can also track the formation of byꢀproducts
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with strong carbonyl IR peaks (red trend line; strong broad peak at 1650 cm ), which are
likely the carboxylic acids/carboxylates released during the saponification events.
Figure 4. ConcIRT trends profile during the saponification reaction.
Upon completion of the saponification reaction, neutralization with hydrochloric
acid leads to crystallization of 17ꢀαꢀestradiol 1. The crystallization of 17ꢀαꢀestradiol 1 from
the aqueous reaction medium furnished 17ꢀαꢀestradiol 1 hemiꢀhydrate, however, we desired
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the anhydrous API. Thus, we turned our attention to other solvents to crystallize 1. After
testing multiple solvents, ethyl acetate was the optimal choice to crystallize the desired
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pseudopolymorph, which is the anhydrous 17ꢀαꢀestradiol 1. It is important to mention that
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Xꢀray diffraction (XRD) was used to unambiguously differentiate the pseudopolymorphs.
With an improved understanding of this reaction sequence, we scaledꢀup the full
process on multiꢀgram scale (Scheme 3). Starting with 500 g of 17ꢀβꢀestradiol 2, the PTC
reaction is performed to give 3 in a dichloromethane solution. After solvent exchange
distillation to toluene, the Mitsunobu reaction is monitored by in situ IR and, after
completion, 5 is delivered as a white solid. The material 5 obtained is directly saponified to
give, after recrystallization, 378 g of 17ꢀαꢀestradiol 1 in 78% overall yield over three steps.
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Scheme 3. Threeꢀstep synthesis of 17ꢀαꢀestradiol 1.
CONCLUSION
In conclusion, we have developed an efficient threeꢀstep synthesis of 17ꢀαꢀestradiol
1 in 78% overall yield. We also developed an interesting regioselective approach to the
prohormone 17ꢀβꢀestradiol benzoate 3 under PTC conditions. The use of PAT tools enabled
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the monitoring of the formation and consumption of reaction intermediates, which is crucial
for a successful process development. Remarkably, the key Mitsunobu reaction goes to
completion in within 5ꢀ10 minutes rather than 1.5 hours, avoiding the formation of
impurities and diminishing energy consumption. The completion of the Mitsunobu reaction
was verified by the IR online analysis, which made the use of HPLC analysis unnecessary.
Therefore, the use of in situ FTIR coupled with an automated reactor was important for a
precise reaction progress control allowing for a safe and reliable scaleꢀup of this process.
On the basis of the success of this work, we intend to install a FTIR unit in our pilot plant
facilities.
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EXPERIMENTAL SECTION
General. All reagents and solvents were used as received without further
purification unless otherwise specified. Reactions were monitored and purity was assessed
1
by HPLC, using an Agilent 1260 series instrument. Proton nuclear magnetic resonance ( H
NMR) spectra were recorded using a Bruker 300 MHz spectrometer. Carbonꢀ13 nuclear
1
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magnetic resonance ( C NMR) spectra were recorded using a Bruker 300 spectrometer at
7
5 MHz. Infrared spectra were obtained on a PerkinElmer Spectrum One FTIR
ꢀ1
spectrometer at 1.0 cm resolution and are reported in wavenumbers. All in situ infrared
spectra were collected using a Mettler Toledo INꢀSITU FTIR, model ReactIR 15 equipped
with ATR Diamond Sensor Probe interfaced with Mettler EasyMax 102 Synthesis
Workstation.
Procedure for Data Presented in Figures 1 and 2. To a 100 mL EasyMax
cylindrical glass reactor equipped with mechanical stirring, temperature probe, and in situ
FTIR probe was added toluene (80 mL), and the online IR monitoring was started. The tips
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of the IR and temperature immersion probes were immersed at half depth of the solution
during the experiment, and 250 rpm agitation rate was used to ensure good mixing. The
jacket temperature (T mode) was maintained at 20 °C. To the mixture was added 3ꢀ
j
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benzoylꢀ17ꢀβꢀestradiol 3 (4.2 g, 11.2 mmol), triphenylphosphine (5.8 g, 22.1 mmol) and 4ꢀ
nitrobenzoic acid (22.1 g, 22.1 mmol), followed by addition of azodicarboxylic acid
diisopropyl ester (4.3 mL, 21.8 mmol) in ten portions over 10 minutes (the exothermicity of
the DIADꢀPPh complex formation is emphasized by the temperature variation illustrated
3
in Figure 3; 23ꢀ33 min). Next, the reaction temperature (T mode) was adjusted to 100 °C
r
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4
over 10 minutes when in situ FTIR indicated the reaction completion. Reference ConcIRT
spectrum profile of toluene was taken separately.
Scaleꢀup. Preparation of compound (5). To a suspension of estradiol hemiꢀhydrate
2
(500.1 g, 1.78 mol) in DCM (4.4 L) and water (4.4 L) in a 25 L reactor, was added
potassium carbonate (761.1 g, 5.51 mol) and tetrabutylammonium hydrogensulfate (12.5 g,
36.67 mmol). Next, benzoyl chloride (258.2 g, 1.84 mol) was slowly added over 30 minutes
at room temperature. The reaction mixture was stirred at room temperature for 1.5 hours
when HPLC analysis indicated <1% of 2. The organic layer was separated and washed with
water (3 x 4 L). The dichloromethane solution of 3 was transferred to a 20 L fourꢀneck
roundꢀbottom flask and used in the next step. The dichloromethane solution of 3 was
distilled to total volume of 0.5 L. Next, 14.5 L of toluene was added and 1.4 L of solvent
was distilled under vacuum. The obtained solution of 3 in toluene was allowed to cool to 25
°
C. Triphenylphosphine (963.1 g, 3.67 mol) and 4ꢀnitrobenzoic acid (613.4 g, 3.67 mol)
were added. Azodicarboxylic acid diisopropyl ester (742.3 g, 3.67 mol) was added over 30
minutes while maintaining the internal temperature below 25 °C. Next, the internal reaction
temperature was increased to 100 °C over 30 minutes when in situ FTIR indicated reaction
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completion. The toluene solution was distilled under vacuum to 1 L total volume. The
concentrated toluene solution was allowed to cool to 25 °C and the vessel was charged with
15 L of methanol resulting in a white slurry. The slurry was cooled to 0ꢀ5 °C and stirred for
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hour. Next, it was vacuum filtered and washed with cold methanol (0.5 L). The filter cake
was dried in a 65 °C vacuum oven for 12 hours and 5 was isolated as a white crystalline
solid (876.9 g) to be submitted to the next step without further purification. MP: 194ꢀ197
1
ºC. H NMR (300 MHz, DMSOꢀd ) 8.36 (tt, J = 9.0, 2.4 Hz, 2H), 8.24 (tt, J = 9.0, 2.1 Hz,
6
2H), 8.13 – 8.10 (m, 2H), 7.75 (tt, J = 7.5, 1.2 Hz, 1H), 7.61 (t, J = 7.5 Hz, 2H), 7.36 (d, J =
8
.4 Hz, 1H), 7.00 (td, J = 8.4, 2.4 Hz, 2H), 5.07 (d, J = 6.0 Hz, 1H), 2.87 (bs, 2H), 2.41 –
2
.33 (m, 3H), 1.96 – 1.87 (m, 2H), 1.78 – 1.66 (m, 4H), 1.52 – 1.35 (m, 4H), 0.87 (s, 3H).
1
3
C NMR (75 MHz, CDCl ) δ 165.6, 164.4, 150.6, 148.9, 138.3, 137.8, 136.3, 133.6, 130.8,
3
1
2
30.3, 129.8, 128.7, 126.6, 123.7, 121.8, 118.9, 83.9, 49.8, 45.6, 44.0, 38.8, 32.3, 30.4,
9.8, 28.0, 26.1, 24.6, 16.9. IR (Neat): 2908, 1745, 1716, 1601, 1527, 1494, 1349, 1258,
ꢀ1
1132, 1061, 1016, 703 cm . Anal. Calcd For C H NO : C, 73.13; H, 5.94; N, 2.66.
32
31
6
Found: C, 73.13; H, 5.96; N, 2.59.
Preparation of 17ꢀαꢀestradiol (1). The above obtained 5 (876.9 g) is suspended in
ethanol (10 L) in a 20 L fourꢀneck roundꢀbottom flask. Next, a sodium hydroxide solution
(prepared with 661.3 g of NaOH in 3.4 L of water) is added at room temperature. The
reaction mixture is then stirred at reflux for 30 minutes when HPLC analysis indicated <1%
of 5. Once complete, 3 L of water is added and distilled by azeotropic distillation to 10 L
total volume. Next, 6.5 L of water is added and distilled by azeotropic distillation to 14 L
total volume. The concentrated solution was allowed to cool to 25 °C and the pH adjusted
to 6ꢀ7 using 20 % acetic acid (4.0 L). The resulting slurry was aged for 1 h at room
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temperature and filtered. The solid obtained was dissolved in ethyl acetate (12 L) under
reflux. The solution was filtered and distilled under vacuum to total volume of 3 L. The
slurry was cooled to 0ꢀ5 °C, stirred for 1 hour and filtered. The obtained solid was washed
with cold ethyl acetate (0.5 L) and dried at 65 °C vacuum oven for 4 hours to give 17ꢀαꢀ
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estradiol 1 as a white solid (378.4 g, 78%). MP: 222ꢀ226 ºC. H NMR (300 MHz, DMSOꢀ
d6) δ 8.97 (s, 1H), 7.06 (d, J = 8.4 Hz, 1H), 6.50 (dd, J = 8.4, 2.7 Hz, 1H), 6.43 (d, J = 2.7
Hz, 1H), 4.32 (s, 1H), 3.58 (d, J = 5.7 Hz, 1H), 2.78 – 2.64 (m, 2H), 2.30 – 2.24 (m, 1H),
1
3
2.10 – 1.99 (m, 2H), 1.83 – 1.09 (m, 10H), 0.61 (s, 3H). C NMR (75 MHz, DMSOꢀd ) δ
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54.8, 137.1, 130.5, 126.1, 114.9, 112.7, 78.0, 47.2, 45.0, 43.4, 32.1, 31.5, 29.3, 27.9, 26.0,
3.9, 17.0. IR (Neat): 3309, 2912, 1602, 1472, 1287, 1236, 1032, 925, 871 cmꢀ1. Anal.
Calcd For C H O : C, 79.37; H, 8.88. Found: C, 79.40; H, 9.19.
1
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2
AUTHOR INFORMATION
Corresponding author
*
Eꢀmail: flavio.cardoso@libbs.com.br
Notes
The authors declare no competing financial interest.
ACKNOLEDGEMENTS
The authors would like to thank the Mettler Toledo team in Brazil for providing the
equipment as well as supporting us during the study.
ASSOCIATED CONTENT
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Supporting Information. Full characterization (1H, 13CꢀNMR, and IR) for compounds 4
and 5, as well as XRD data and additional ConcIRT data. This information is available free
of charge via the Internet at http://pubs.acs.org.
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ABREVIATIONS
PTC, phaseꢀtransfer catalysis; QbD, Quality by Design; PAT, process analytical
technology; HPLC, High Performance Liquid Chromatography; NMR, nuclear magnetic
resonance; IR, infrared; NIR, nearꢀinfrared; DIAD, diisopropylazodicarboxylate; XRD, Xꢀ
ray diffraction; API, active pharmaceutical ingredient; IPC, InꢀProcess Control.
REFERENCES
1
. (a) Moos, W. H.; Dykens, J. A.; Howell, N. Drug Dev. Res. 2008, 69, 177ꢀ184; (b)
Dykens, J. A.; Moos, W. H.; Howell, N. Ann. N. Y. Acad. Sci. 2005, 1052, 116ꢀ135.
(c) Moos, W. H.; Dykens, J. A.; Nohynek, D.; Rubinchik, E.; Howell, N. Drug Dev.
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Tetrahedron Letters 2015, 56, 4096–4100; (f) Shi, X.; Shen, C.; Yao, J.; Nie, L.;
Quan, N. Tetrahedron: Asymmetry 2010, 21, 277.
4. (a) Swamy, K. C. K. Khumar, N. N. B.; Balaraman, E.; Kumar, K. V. P. P. Chem.
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(
c) Fletcher, S. Org. Chem. Front., 2015, 2, 739–752; (d) Mitsunobu, O.; Yamada,
Y. Bulletin of the Chemical Society of Japan 1967, 40, 2380–2382; (e) Mitsunobu,
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. (a) Caron, S.; Thomson, N. M. J. Org. Chem. 2015, 80, 2943–2958; (b) Chanda, A.;
Daly, A. M.; Foley, D. A.; LaPack, M. A.; Mukherjee, S.; Orr, J. D.; Reid, G. L.;
Thompson, D. R.; Ward, H. W. Org. Process Res. Dev. 2015, 19, 63−83.
. (a) am Ende, D.; Bronk, K. S.; Mustakis, J.; O’Connor, G.; Santa Maria, C. L.;
Nosal, R.; Watson, T. J. N. J. Pharm. Innovation 2007, 2, 71−87; (b) Kouri, T.;
Davis, B. Pharm. Eng. 2012, 32, 1–10; (c) Rubin, A. E.; Tummala, S.; Both, D. A.;
Wang, C.; Delaney, E. J. Chem. Rev. 2006, 106, 2794−2810.
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7. Eisenbeis, S. A.; Chen, R.; Kang, M.; Barrila, M.; Buzon, R. Org. Process Res. Dev.
015, 19, 244−248.
. Palucki, M.; Lin, Z.; Sun, Y. Org. Process. Res. Dev. 2005, 9, 141−148.
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9. Hao, H.; Mark, B.; Yun, H.; Weiyi, S.; Steven, F.; Barbara, W.; Brian, G. Org.
Process Res. Dev. 2012, 16, 35−41.
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0. (a) Do, N. M.; Olivier, M. A.; Salisbury, J. J.; Wager, C. B. Anal. Chem. 2011, 83,
766−8771; (b) Drexler, M. T., Foley, D. A., Ward, H. W., Clarke, H. J. Org.
Process Res. Dev. 2015, 19, 1119ꢀ1127.
8
11. Starks, C. M., Liotta, C. L., Halpern, M. E. PhaseꢀTransfer Catalysis, Chapman &
Hall, New York, 1994.
12. Raviña, E. The Evolution of Drug Discovery: From Traditional Medicines to
Modern Drugs, John Wiley & Sons, Weinheim, 2011, pp 175.
1
3. Diisopropylazodicarboxylate (DIAD) was selected over diethylazodicarboxylate
(DEAD) due to safety conditions and commercial availability.
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4. To generate this graphic, the ConcIRT data was treated using second derivative and
the solvent ConcIRT spectrum (toluene) was removed.
15. ConcIRT is a chemometric treatment based on curve resolution that, in some cases,
provides a concentration profile (“component”) and calculates the spectra
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(“ConcIRT spectrum profile”) of transient species in a reaction medium, as
observed in this study.
16. See Supporting Information for ConcIRT spectrum profile.
17. For mechanistic studies on the Mitsunobu reaction see: (a) Schenk, S.; Weston, J.;
Anders, E. J. Am. Chem. Soc. 2005, 127, 12566 –12576; (b) Camp, D.; Jenkins, I.
D. J. Org. Chem. 1989, 54, 3045– 3049; (c) Camp, D.; Jenkins, I. D. J. Org. Chem.
1989, 54, 3049 –3054; (d) Hughes, D. L.; Reamer, R. A.; Bergan, J. J.; Grabowski.
E. J. J. J. Am. Chem. Soc., 1988, 110, 6487–6491.
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8. Pretsch, E.; Bühlmann, P.; Affolter, C. Structure Determination of Organic
Compounds: Tables of Spectral Data, Springer, New York, 2000, pp 330.
19. During the DIAD addition, the temperature was controlled by a set jacket
temperature (T mode). See Supporting Information for a comparison between the
j
jacket temperature and reaction temperature.
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0. The effect of temperature on product formation was also evaluated at lower
temperatures. See Supporting Information for a ConcIRT trends profile at 50 °C and
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0 °C showing the different reaction rates in each set temperature.
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1. The solubilities of 5 and triphenylphosphine oxide in different solvents at reflux
temperature are presented on the Supporting Information.
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2. Huffman, M. N.; Lott, M. H.; Tillotson, A. J. Biol. Chem, 1955, 217, 103ꢀ106.
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3. To generate this graphic, the solvent ConcIRT spectrum (ethanol) was subtracted
from the data.
24. As proved by an offline HPLC analysis.
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5. (a) Zhurova, E. A.; Zhurov, V. V.; Chopra, D.; Stash, A. I.; Pinkerton, A.A. J. Am.
Chem. Soc., 2009, 131, 17260–17269; (b) Busetta, B.; Barrans, Y., Precigoux, G.,
Hospital, M. Acta Cryst., 1976, B32, 1290–1292.
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6. See Supporting Information for full details.
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