Development of the large-scale synthesis of tetrahydropyran glycine, a precursor to the HCV NS5A inhibitor BMS-986097

Article abstract of DOI:10.1021/acs.joc.7b01852

An efficient large-scale synthesis of acid 1, a penultimate precursor to the HCV NS5A inhibitor BMS-986097, along with the final API step are described. Three routes were devised for the synthesis of 1 at the various stages of the program. The third generation route, the one that proved scalable and is the main subject of this paper, features a one-step Michael addition of t-butyl 2-((diphenylmethylene)amino)acetate (24) to (E)-benzyl 4-(1-hydroxycyclopropyl)but-2-enoate (28) followed by cyclization and chiral separation to form 27c, the core skeleton of cap piece 1. The epimerization and chiral resolution of 27c followed by further synthetic manipulations involving the carbamate formation, lactone reduction and cyclization, afforded cyclopropyl pyran 1. A detailed study of diphenylmethane deprotection via acid hydrolysis as well as a key lactone to tetrahydropyran conversion, in order to avoid a side reaction that afforded an alternative cyclization product, are discussed. This synthesis was applied to the preparation of more than 100 g of the final API BMS-986097 for toxicology studies.

Full text of DOI:10.1021/acs.joc.7b01852

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Article
Development of large scale synthesis of tetrahydropyran
glycine, a precursor to the HCV NS5A inhibitor BMS-986097
Arvind Mathur, Bei Wang, Daniel Smith, Jianqing Li, Joseph Pawluczyk, Jung-Hui Sun, Michael Kwok Wong,
Subramaniam Krishnananthan, Dauh-Rurng Wu, Dawn Sun, Peng Li, Shiuhang Yip, Bang-Chi Cheng,
Phil S. Baran, Qi Chen, Omar D. Lopez, Zhong Yong, John A. Bender, Van N Nguyen, Jeffrey L Romine,
Denis R. St. Laurent, Gan Wang, John F Kadow, Nicholas A. Meanwell, Makonen Belema, and Rulin Zhao
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b01852 • Publication Date (Web): 06 Sep 2017
Downloaded from http://pubs.acs.org on September 7, 2017
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Development
Kadow, John; Viiv Healthcare, c/o Bristol-Myers Squibb
Meanwell, Nicholas; Bristol-Myers Squibb PRI, Department of Chemistry,
303; Bristol-Myers Squibb, Department of Chemistry, 303
Belema, Makonen; BMS,
Zhao, Rulin; Bristol-Myers Squibb Pharmaceutical Research and
Development
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Development of large scale synthesis of tetrahydropyran glycine, a precursor
to the HCV NS5A inhibitor BMS-986097
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Arvind Mathura, *, Bei Wanga, Daniel Smitha, Jianqing Lia, *, Joseph Pawluczyka, JungꢀHui Suna,
Michael Kwok Wonga, Subramaniam Krishnananthana, DauhꢀRurng Wua, Dawn Suna, Peng Lia,
Shiuhang Yipa, BangꢀChi Chena, Phil S. Baranb, Qi Chenc, Omar D. Lopezc, Zhong Yangc, John
A. Benderc, Van N. Nguyenc, Jeffrey L. Rominec, Denis R. St. Laurentc, Gan Wangc, John F.
Kadowc, Nicholas A. Meanwellc, Makonen Belemac , Rulin Zhaoa, *
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a
Discovery Chemistry, Research and Development, BristolꢀMyers Squibb Company, PO Box
4000, Princeton, NJ, 08543, USA
b Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La
Jolla, CA, 92037, USA
c Discovery Chemistry, BristolꢀMyers Squibb, Research and Development, 5 Research Parkway,
Wallingford, CT, 06492, USA
Abstract: An efficient large scale synthesis of acid 1, a penultimate precursor to the HCV NS5A
inhibitor BMS-986097, along with the final API step are described. Three routes were devised
for the synthesis of 1 at the various stages of the program. The 3rd generation route, the one that
proved scalable and is the main subject of this manuscript, features a one step Michael addition
of tꢀbutyl 2ꢀ((diphenylmethylene)amino)acetate 24 to (E)ꢀbenzyl 4ꢀ(1ꢀhydroxycyclopropyl)butꢀ
2ꢀenoate 28 followed by cyclization and chiral separation to form 27c, the core skeleton of cap
piece 1. Epimerization and chiral resolution of 27c followed by further synthetic manipulations
involving carbamate formation, lactone reduction and cyclization afforded cyclopropyl pyran 1.
A detailed study of diphenylmethane deprotection via acid hydrolysis as well as a key lactone to
tetrahydropyran conversion, in order to avoid a side reaction that afforded an alternative
cyclization product, are discussed. This synthesis was applied to the preparation of more than
100 g of the final API BMS-986097 for toxicology studies.
* Corresponding authors:
Eꢀmail address: Arvind.Mathur@bms.com (A. Mathur), Jianqing.Li@bms.com (J. Li),
Rulin.Zhao@bms.com (R. Zhao).
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1. Introduction
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Chronic hepatitis C virus (HCV) infection is a disease with a global prevalence affecting over
180 million individuals. Over the past decade, tremendous advances in HCV drug development
have been made that culminated in a number of approved drugs which demonstrated high cure
rates, shorter treatment duration and improved tolerance compared with the older standard of
care which included pegylated interferon and ribavirin.1 Inhibiting HCV NS5A, a protein with
no known enzymatic function, is an approach to the suppression of virus replication that has
emerged as a critical element of all currently approved therapeutic regimens that rely upon
combinations of small molecule HCV inhibitors.1ꢀ2 During our efforts to identify HCV NS5A
inhibitors with improved profiles, BMS-986097 was identified as a highly potent compound that
was selected as the lead candidate for further evaluation.3 Over 100 grams of this compound was
required to support preclinical toxicology studies.
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Scheme 1. BMS-986097 synthesis disconnection
2. Results and discussion
BMS-986097 was prepared by coupling core precursor 2 and cyclopropyl pyran 1 (Scheme
1). Three independent routes were devised to acid 1 during the discovery and early stage
characterizations of BMS-986097, the 3rd one proving most amenable to scale up.
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The 1st generation route to acid 1, devised as part of a broader structureꢀactivity relation
investigation that necessitated access to all the stereoisomers of 1, is outlined in Scheme 2. It
was envisioned that a HornerꢀWadsworthꢀEmmons (HWE) coupling of pyranone 9 with a
glycine phosphonate ester derivative followed by an asymmetric hydrogenation of the resultant
E/Zꢀmixture 10 would provide an entry to the targeted stereoisomers (see Scheme 2). The
preparation of pyranone 9 started from the readily available ester 3, and elaboration to the acidꢀ
and baseꢀsensitive βꢀketoester 5 was conducted according to a literature precedent.4 A
combination of standard reduction and protection steps afforded silyl ether 6, setting the stage for
a key cyclopropanation step. Of note, the silylation step was much slower than expected,
requiring a reaction time in excess of two days to reach completion. Kulinkovich
cyclopropanation proved robust, and treatment of the resultant cyclopropanol with pꢀTsOH acid
effected both hemiacetal exchange and desilylation, resulting in alcohol 7 of unknown
stereochemical composition although inconsequential for the current purpose.5 Reductive
removal of the methoxy moiety of 76 followed by a standard Swern oxidation afforded the key
ketone progenitor 9 in a good overall yield.
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HWE condensation of 9 with Nꢀbenzyloxycarbonyl(dimethoxyphosphinyl) glycine methyl
ester in the presence of tetramethyl guanidine gave low yield of the α,βꢀdidehydroamino ester 10
as an inseparable mixture of E/Z isomers. Alternate conditions were briefly examined (such as
changing the base or the solvent) but did not provide a measurable impact on the efficiency of
the reaction. It is noteworthy that a side product, not fully characterized but believed to be a
close structural analog of the targeted product 10, was also isolated. Asymmetric hydrogenation
of E/Z mixture 10 under Burk’s condition provided a diastereomeric mixture of 11a and 11b,
which was readily separable on an AD chiral column.7 Hydrogenolysis of the individual
stereoisomers in the presence of dimethyl carbonate followed by a standard ester hydrolysis
afforded acids 12 and 1, whose absolute stereochemical assignment was made as described
below.
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Scheme 2. 1st generation route to cap piece 1
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Although the 1st generation route was straightforward and provided gram quantities of acid 1,
which covered the initial material demand for BMS-986097 and other associated structureꢀ
activity relation studies, the route was deemed unsuitable for scale up. Specifically, it suffered
from a poor yield at a late stage (see the HWEꢀcoupling step), it was lengthy, and most of the
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intermediates were purified by chromatography. To insure material delivery within targeted
timelines, two new routes to acid 1 were devised in parallel by two subꢀgroups where one
primarily focused on streamlining the 1st generation route while the second one investigated
more differentiated disconnections.
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A 2nd generation route was thus devised that supplied pyranone 9 in half the number of steps
compared to the 1st generation route (see Scheme 3). Phosphorane 14 and cyclopropanol 16, both
of which were prepared in one step from commercially available materials, were condensed
under DeanꢀStark conditions (in order to remove the ethanol byproduct) to afford enone 17 in a
good although variable yield when done by different individuals (Range: 44ꢀ88%; average:
68%). Treatment of 17 with an Amberlystꢀ15 resin in acetonitrile effected both desilylation and
cyclization. Copperꢀcatalyzed Schollkopf condensation8 of the resultant pyranone 9 with ethyl
isocyanoacetate provided a mixture of esters 18a and 18b (in a 3:2 ratio) in a combined yield
(69%) that was more than twice that of the corresponding HWEꢀcoupling step in the 1st
generation route. The E/Z isomers separation was challenging but achievable under both flash
column and SFC conditions, the latter method proving relatively the more efficient method due
to a greater distinction in retention times. E/Zꢀstereochemical assignments were readily made
based on NOE interactions between the formamide NꢀH signal and that of the differentiated
allylic protons. Asymmetric hydrogenation of a clean sample of 18b under Burk’s condition
afforded 19 in 95% yield and 98.6% stereochemical excess, and 19 was elaborated through a
combination of formamide deprotection and methyl carbamate formation to afford ester 20 in
88% yield. Of note, since the complete removal of 18a from 18b was problematic when
processing on scale, the batches that were submitted to the chiral hydrogenation step contained
varying but low (<5%) levels of 18a, whose hydrogenation resulted in the presence of
diastereomer 12 as a contaminant. In addition, although not investigated closely, one could not
rule out the possibility of some optical erosion at the αꢀcarbon center during the subsequent
hydrolysis step. Thus, the material obtained from the hydrolysis of ester 20 was submitted to a
chiral SFC purification to afford carboxylic acid 1 in 71% yield and in 98.7ꢀ99.1% SFC purity
although containing 0.32ꢀ0.42% of diastereomer 12 and ≤ 0.2% of the remaining two
stereoisomers combined. [Reference: As an example, one preꢀSFC crude sample obtained from
the hydrolysis step exhibited a stereoisomer ratio of 85.0% (1) : 3.3% (12) : 4.5% (for the
remaining two stereoisomers) whereas another sample exhibited a corresponding ratio of 91% :
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3.1% : 4.4%]. Compound 18a was processed separately in a similar manner to afford a sample of
the undesired isomer 12 for analytical purpose. Also, in both the current case as well as the 1st
generation route, utilization of the enantiomer of the chiral hydrogenation catalyst provided
samples of the remaining two stereoisomers of 1 with (R)ꢀconfiguration at the αꢀcarbon center,
which, along with a sample of 12, enabled the discussed optical purity assessments of 1.
Absolute stereochemical assignment of acid 12 was made based on single crystal Xꢀray analysis
done on its amide derivative with (S)ꢀ1ꢀ(naphthalenꢀ2ꢀyl)ethanꢀ1ꢀamine. Factoring in this Xꢀray
result, the E/Z assignment made for 18b/18a above and the established stereochemical induction
of the utilized catalyst, the absolute stereochemistry of 1 was deduced.
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The feasibility of converting the formamide precursor 18a into the desired 18b via cis/trans
double bond isomerization was briefly investigated. Although the interconversion was
demonstrated utilizing subꢀstoichiometric amount of Nꢀbromosuccinimide in CH2Cl2, the double
bond was unfortunately susceptible to migration into the tetrahydropyran ring, resulting in an
impurity that was difficult to separate.
The preparation and elaboration of pyranone 9 in the 2nd generation route resulted in a
substantial improvement over the 1st generation route (reduced step count for its preparation and
a higher yield for the installation of the glycine moiety). Yet, this route had some drawbacks: the
silyl and the phosphorane moieties of 14, which constituted ~72% of its mass, required the
processing of a significant and unproductive mass before reaching pyranone 9; the Wittig and the
desilylativeꢀcyclization steps needed to be done in batches as their yields suffered on scale; and,
for reasons not apparent, the desilylation of 15 required variable time for completion depending
on sourcing of material; and, 18b was formed as a minor component and its separation from its
isomer 18a was a challenge. Despite these drawbacks, this route delivered sufficient quantity of
acid 1 to generate BMS-986097 in a mass output that was >10ꢀfold greater than what was
achieved through the 1st route.
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Scheme 3. 2nd generation route to cyclopropyl pyran 1
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In a parallel campaign, a distinct 3rd generation route was devised that proved more scalable
and thus was critical in securing the requisite mass of BMS-986097 to support advanced
preclinical characterizations including toxicological assessments. A detailed discussion of this
route is provided below.
Alternate retrosynthetic analysis revealed additional routes to 1 that pivoted off of a Michael
addition approach for introducing the glycine element to potential precursors to the
tetrahydopyran moiety. Among them, two strategies, outlined in Scheme 4, were selected for
further
investigation.
A
Michael
addition
reaction
using
tertꢀbutyl
2ꢀ
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((diphenylmethylene)amino)acetate 24 as the masked amino acid function was chosen to
construct the skeleton of 1 in both routes since similar enantioselective Michael additions have
been reported previously in the literature. 9 The tertꢀbutyl ester was preferred to other esters for
the Michael addition since a tertꢀbutyl ester can not only survive the Kulinkovich reaction but
also is less prone to potential racemization in the downstream baseꢀcatalyzed saponification step.
The main difference between Route A and Route B is the relative sequencing of the Kulinkovich
reaction and the Michael addition.
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Scheme 4. Retrosynthetic analyses of t-butyl ester 21, a precusor of acid 1
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Scheme 5. Route A: Michael addition followed by Kulinkovich reaction
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Route A (Scheme 5) was first investigated. Michael addition of commercially available 24 to
25 in the presence of DBU furnished 23 in 86% yield but of undetermined stereochemical
composition. However, the subsequent Kulinkovich reaction afforded only a 10% yield of 22.
Scheme 6. Route B: Kulinkovich reaction followed by Michael addition
Given the initial disappointing results of the Kulinkovich reaction in Route A, our attention
was shifted to Route B (Scheme 6). Compound 31 was prepared based on literature procedures
via a Kulinkovich reaction of 3 with ethylmagnesium bromide in the presence of
tetraisopropoxytitanium.10 Hydrolysis of the acetal with 0.1 eq. of pꢀtoluenesulfonic acid in a
mixture of THF/water (6:1) and subsequent olefination with 29 proceeded cleanly to give 28 in
70ꢀ80% yield under typical HWE reaction conditions11 in a oneꢀpot operation. Michael addition
of 24 to 28 in CH3CN with DBU as the catalyst gave the four stereoisomers 27a-d as a roughly
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equimolar mixture which were resolved by chiral preparative SFC. Based on the SFC/UV
retention times along with the SFC/CD signs and intensities, it was determined that peak 1 and
peak 2 were a pair of enantiomers, while peak 3 and peak 4 were the alternate pair of
enantiomers (Figure 1). However, without an authentic sample in hand, it was not feasible to
determine which peak corresponded to the desired isomer 27b. In order to establish this
unambiguously, all four isomers were elaborated separately to the final step. In this paper, we
will only show the synthetic schemes using the desired stereoisomer 27b to demonstrate the
downstream chemistry.
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Figure 1. SFC/CD analysis of racemic 27a-d.
We envisioned that reduction of 27b followed by deprotection and carbamate formation
would provide 21b (Scheme 7). The reduction of 27b was studied under a variety of conditions
(BH3ꢀBF3, NaBH4ꢀBF3 and NaBH4).12 The major product had a molecular weight consistent
with 32 by LC/MS. However, detailed NMR studies revealed that the isolated product was
pyrrolidine 35. The most likely mechanism of producing 35 from 27b is depicted in Scheme 7.
Upon NaBH4 reduction, the ringꢀchain tautomer of alcohol 33, aldehyde 34, undergoes an
intramolecular reductive amination to yield 35.
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Scheme 7. Five membered ring formation as a side reaction
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This issue was circumvented by converting diphenylmethanimine 27b to its carbamate 39b
prior to lactone reduction (Scheme 8). The diphenylmethane protecting group was removed
under acidic conditions.13 Conversion of 27b to 39b was achieved in quantitative yield with high
purity through a number of operations without any column purification. Hydrolysis of 27b with
2 eq. HCl in a mixture of THF and water generated a mixture of ringꢀopened amino acid 36b and
lactone 37b. The byꢀproduct benzophenone was removed by extraction with heptane. The
neutralized aqueous layer (pH 7.5) containing 36b and 37b was treated with 2 eq. of dimethyl
dicarbonate to give a mixture of carbamates 38b and 39b. After ethyl acetate extraction and
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concentration, this mixture was heated neat at 50 C under vacuum overnight. During this
process, 38b underwent intramolecular cyclization to give pure lactone 39b as a colorless oil in
98% yield.
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Scheme 8. Acid hydrolysis approach to carbamate 39b
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The direct reduction of lactone 39b to tetrahydropyran 21b was studied under various
conditions as summarized in Scheme 9.12 Unfortunately, no desired product 21b was obtained.
The best result, with an isolated yield amounting to only 50%, came from reduction of 39b to
diol 40b using NaBH4 in a mixture of THF and water after stirring for 18 hours. Upon study of
the LCMS spectral data, it was discovered that the overꢀreduced triol 41 was also formed in the
reaction. This compound was difficult to detect due to its weak UV absorption properties and
was washed away during the work up due to its high aqueous solubility. Fortunately, triol 41 was
formed only slowly and in order to limit this overꢀreduction, the reaction was monitored by
LCMS and quenched immediately at the first sign of the formation of triol 41 (around 3.5 h
reaction time). Under these optimized conditions, the yield of diol 40b was significantly
increased to 95%.
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Scheme 9. Reduction of lactone 39b to diol 40b
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We next turned our attention to the synthesis of 21b via the cyclization of diol 40b (Scheme
9). Initially we tried a mesylate14 as the leaving group for cyclization which resulted in only 10%
conversion to the desired product 21b (Scheme 10). The main product isolated was 43 which
arises from mesylation of both alcohols to give intermediate 42 that is unable to cyclize to form
the six membered ring, but instead undergoes five membered ring formation to give 43.
Attempts to control the amount of bisꢀmesylation formation were unsuccessful and thus attention
turned to a search for an alternative leaving group.
To our delight, when the mesylate was replaced by a tosylate,15 the yield of the twoꢀstep,
oneꢀpot cyclization was increased to 72%. Compared to the mesylate, the tosylate is more UV
active which greatly facilitated reaction monitoring. In addition, a tosylate is bulkier which
contributes to the increased selectivity for monoꢀtosylation. Thus, the formation of the five
membered ring side product was avoided. In practice, since the commercially available TsCl
contains a small amount of TsOH, 1.1 eq. of TsCl was added at 0 oC. The reaction was carefully
monitored and warmed to room temperature. After LCMS indicated that all of the diol 41b was
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transformed to the monoꢀtosylate 44, the reaction mixture was warmed to 38 C overnight to
promote the cyclization of 44 to 21b.
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Scheme 10. One-pot cyclization and hydrolysis to 1
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With 21b inꢀhand, our attention turned to the deprotection of the tertꢀbutyl ester. We
immediately experienced the acid sensitive nature of the cyclopropylpyran moiety in 21b. Under
strongly acidic conditions such as TFA or 4 N HCl in dioxane, 21b gave significant ring opened
side products, whereas milder formic acid conditions gave a much cleaner profile. Hydrolysis of
tꢀbutyl ester 21b using formic acid (50 eq.) went smoothly at rt to give the coveted cyclopropyl
pyran 1 in 94% yield. No epimerization was observed during the reaction and workꢀup. It is
critical to remove traces of formic acid in 1 before the next coupling reaction with 2 in order to
minimize a formylation side reaction.
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Scheme 11. Michael addition and SFC purification
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With compound 1 and its three other stereoisomers synthesized from 21a-d inꢀhand, we were
able to correlate the stereochemical configuration of each SFC peak. As mentioned earlier, the
Michael addition of 24 to 28 was conducted in CH3CN with DBU catalysis to give all four
isomers: 27a (Peak 1), 27b (Peak 2), 27c (Peak 3), 27d (Peak 4) with an equal ratio (Scheme 11).
Using this condition, a low yield of 27b was obtained, in part due to the challenges associated
with the chiral separation of four isomers. Applying chiral separation on other later
intermediates or compound 1 proved to be impractical due to their weak UV absorbances.
Therefore it was necessary to develop a more efficient stereoselective synthesis and separation
protocol of intermediate 27. To this end, the asymmetric Michael addition9 was considered and
attempted employing a commercially available chiral ligand, bis((3aS,8aR)ꢀ3a,8aꢀdihydroꢀ8Hꢀ
indeno[1,2ꢀd]oxazolꢀ2ꢀyl)methane and different bases such as Ba(OꢀtꢀBu)2 and Ca(OꢀMe)2
under the conditions described by Kobayashi and coꢀworkers.9a Unfortunately, none gave any
enantioselectivity, but good diastereoselectivity in this case. It was envisioned that in the
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absence of a chiral ligand but at low temperatures under the same conditions would also result in
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diastereoselectivity. Indeed, the Michael addition of 24 to 28 catalyzed by 0.025 to 0.1
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equivalent of lithium bis(trimethylsilyl)amide in THF at 5 C to rt followed by simultaneous
cyclization gave a racemic mixture of 27c and 27d with 1:1 ratio and no 27a and 27b were
detected.
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The mixture of 27c and 27d was first isolated as a white solid in 86% yield by crystallization
from 10% toluene in heptane after aqueous workꢀup and the two compounds were readily
separated by SFC. Although 27c is not the desired isomer, it can be epimerized in the presence
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of DBU in acetonitrile at 80 C to give a 1:1 ratio of 27b and 27c. The mixture of 27b and 27c
can also be separated readily by SFC.
With these data in hand, we developed the following sequence of procedures to produce the
desired isomer 27b (peak 2):
1) Conduct the Michael addition at low temperature to prepare isomers 27c and 27d.
2) Separate isomer 27c from 27d by SFC.
3) Epimerize 27c to give a mixture of 27b and 27c.
4) Isolate the isomer 27b from the mixture of 27b/27c and recover 27c
5) Cycle back 27c through steps 3 and 4.
Thus, after performing the Michael addition, the racemic mixture of 27c and 27d was
separated by SFC in 85% recovery yield of 27c, which was then converted to a 1:1
diastereomeric mixture of 27b and 27c by treatment with DBU in acetonitrile under reflux. The
desired stereoisomer 27b was isolated by SFC in 72% recovery yield. The undesired 27c was
recycled to recover additional mass of 27b.
Following this new procedure (Scheme 12), 86 g of optically pure cyclopropyl pyran 1 was
prepared and coupled with amine core 2 to give 107 g of the final compound in 94% yield
with >99% purity.16
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Scheme 12. Scale-up scheme for BMS-986097
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3. Summary
Three routes were developed to prepare the cap acid precursor 1 of BMS-986097. The third
route, which overcame the scalability limitation of the first two, features a oneꢀpot synthesis of
α,βꢀunsaturated ester 28 followed by a diastereoselective Michael addition, cyclization and DBU
catalyzed epimerization to afford lactone 27b, and highly efficient conversion of 27b to the
cyclopropyl pyran 1 through acid catalyzed deprotection, carbamate formation, lactone reduction,
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tosylation, cyclization and final hydrolysis. This route generated sufficient amount of acid 1 for
coupling with amine core 2 to provide over 100 g of BMS-986097 with >99% purity for
toxicology studies.
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4. Experimental section
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4.1 General
All reagents were obtained from Aldrich and used without further purification unless
otherwise stated. All reactions were performed under a nitrogen atmosphere. All reactions were
monitored by a Shimadzu LC/MS system using the following method: Phenomenex C18 column
10 ꢁm 4.6 mm × 50 mm. Solvent: A = 10% methanol/90% water with 0.1% TFA; B = 90%
methanol/10% water with 0.1% TFA. Gradient: 0ꢀ100% B over 4 min. Flow: 4 mL/min,
wavelength: 220 nm. HPLC analyses were performed using a Shimadzu system (model SPD
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10AV). Optical rotations were measured using a polarimeter in the solvent specified. All H
NMR and 13C NMR spectra were recorded on a Bruker 400 or 500 MHz spectrometer using
DMSOꢀd6 or CDCl3 as the solvent. HRMS were measured with electrospray ionization (ESI). All
the a/b/c/d stereoisomeric designations below derive their assignments from the relative
stereochemistry established in structures 27. Also of note, the compound designated as acid 1 in
text is the same as the compound noted as acid 1b below.
4.2. Benzyl (E)ꢀ4ꢀ(1ꢀhydroxycyclopropyl)butꢀ2ꢀenoate (28)
To a solution of 1ꢀ(2,2ꢀdimethoxyethyl) cyclopropanol (31)10 (244 g, 1669 mmol) in a
mixture of THF and H2O (6:1 ratio, 3.5 L) at room temperature was added pꢀtoluenesulfonic acid
(28.7 g, 167 mmol). The solution was stirred for 24 h, and then potassium carbonate (461 g,
3338 mmol) and benzyl 2ꢀ(dimethoxyphosphoryl)acetate (431 g, 1669 mmol) was added. After
the mixture was stirred for another 24 h, the solution was concentrated in vacuo. The residue
was dissolved in EtOAc (1 L) and the resulting solution was washed with brine (500 mL). The
organic layer was dried over Na2SO4, filtered and concentrated in vacuo to give the crude
product which was purified by flash chromatography to afford alkene 28 (334 g, 1438 mmol, 86%
1
yield) as a yellow oil. H NMR (400 MHz, CDCl3):) δ 7.41ꢀ7.34 (m, 5H), 7.17ꢀ7.04 (m, 1H),
6.04 (dt, J = 15.7 and 1.5 Hz, 1H), 5.20 (s, 2H), 2.50ꢀ2.45 (m, 2H), 2.25ꢀ2.16 (m, 1H), 0.86ꢀ0.80
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(m, 2H), 0.58ꢀ0.51 (m, 2H); C NMR (101 MHz, CDCl3): δ 166.2, 145.8, 136.0, 128.6, 128.3,
128.3, 123.6, 66.3, 54.6, 41.1, 13.3; HRMS(ESIꢀFTMS): m/z calcd for C14H16O3 [M + H]+:
232.1099, found: 233.1170.
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4.3. tertꢀButyl 2ꢀ((diphenylmethylene)amino)ꢀ2ꢀ(5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate (27)
To a N2 flushed 5 L threeꢀnecked round bottom flask was added tertꢀbutyl 2ꢀ
((diphenylmethylene)amino)acetate (24) (120 g, 406 mmol) and a solution of alkene 28 (118 g,
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406 mmol) in THF (1.2 L). The solution was cooled with an ice bath to 5 C and a solution of
lithium bis(trimethylsilyl)amide (1 M in THF, 20.31 mL, 20.31 mmol) was added slowly. The
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reaction mixture was stirred below 10 C for an hour and then allowed to warm to 15 C over a
period of 2 h. The reaction mixture was quenched with a saturated solution of NH4Cl (1.5 L), the
organic phase separated and the aqueous layer extracted with EtOAc (600 mL). The combined
organic layers was washed with brine, dried over Na2SO4, filtered and concentrated in vacuo to
afford the crude product (220 g) as a yellow semiꢀsolid which was crystallized from 10% toluene
in heptane (2.2 L) (from 55 oC to 0 oC) to give a 1:1 mixture of 27c and 27d (146 g, 348 mmol,
86 % yield) as a white solid.
The above mixture was separated by SFC to give the first eluting compound 27c (62 g, 148
mmol, 85% recovery yield) as a white solid and the later eluting compound 27d (61 g, 145 mmol,
84% recovery) as a white solid. Preparative chiral SFC conditions: Luxꢀcelluloseꢀ4 (5 x 25 cm, 5
o
µm), 12% methanol in CO2, 250 mL/min, 220 nm, 40 C, 100 bar BPR, 100 mg/mL in
acetonitrile, 2 mL/ 2.75 min stack injection. Analytical condition: Luxꢀcelluloseꢀ4 (0.46 x 25 cm,
5 µm), 3 mL/min, 10 % methanol in CO2, 40 oC, 210 nm, 100 bar BPR.
Racemization of the αꢀcarbon center of compound 27c to afford a mixture of 27b and 27c. A
solution of 27c (46 g, 110 mmol) and 1,8ꢀdiazabicyclo[5.4.0]undecꢀ7ꢀene (16.40 mL, 110 mmol)
in CH3CN (250 mL) was heated at reflux for 16 h. After cooling to rt, the solvent was removed
under reduced pressure and the residue partitioned between EtOAc and water (2 L, 1:1). The
organic phase was separated, washed with water (2 x 1 L), brine (1 L), dried over Na2SO4,
filtered and concentrated in vacuo to give a mixture of 27b and 27c as an oil (43 g, 102 mmol, 93%
yield).
Preparative chiral SFC conditions to separate a mixture of 27b and 27c: Chiralpak IC (3 x 25
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cm, 5 µm), 10% methanol in CO2, 200 mL/min, 220 nm, 45 C, 100 bar BPR, 220 mg/mL in
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acetonitrile:DCM (1:1), 2 mL/3.1 min stack injection. Analytical condition: Chiralpak IC (0.46
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x 25 cm, 5 µm), 10% methanol in CO2, 3 mL/min, 40 C, 220 nm, 100 bar BPR. The first
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eluting compound 27b was obtained as a white solid (15.4 g, 36.7 mmol, 72% recovery). The
second eluting compound 27c was obtained as a white solid (15 g, 35.8 mmol, 70% recovery).
Using the similar procedure, we can obtain pure 27a by racemization of the αꢀcarbon center
of compound 27d to a mixture of 27a and 27d, followed by chiral SFC separation.
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4.4. tertꢀButyl (R)ꢀ2ꢀ((diphenylmethylene)amino)ꢀ2ꢀ((S)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate
(27a).
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[α]D = 112.17 (c = 4.00, MeOH). H NMR (400 MHz,CDCl3): δ 7.66 (d, J = 7.7 Hz, 2H),
7.51ꢀ7.34 (m, 6H), 7.22ꢀ7.16 (m, 2H), 3.91 (d, J = 4.5 Hz, 1H), 2.91 (ddd, J = 9.3, 6.3 and 4.6
Hz, 1H), 2.59ꢀ2.52 (m, 1H), 2.43ꢀ2.35 (m, 2H), 1.82 (dd, J = 14.0 and 6.5 Hz, 1H), 1.45 (s, 9H),
1.12ꢀ1.03 (m, 2H), 0.87ꢀ0.77 (m, 1H), 0.71ꢀ0.63 (m, 1H); 13C NMR (101 MHz, CDCl3): δ 172.8,
172.3, 169.6, 139.1, 136.4, 130.7, 128.9, 128.8, 128.6, 128.1, 127.7, 81.8, 68.3, 62.2, 34.7, 33.8,
30.7, 28.1, 12.4, 11.9; Anal. Calcd for C26H29NO4: C, 74.44; H, 6.97; N, 3.34; Found: C 74.47, H
6.83, N 3.39; HRMS (ESIꢀFTMS): m/z calcd for C26H30NO4 [M + H]+: 420.2175; found:
420.2171.
4.5 tertꢀButyl (S)ꢀ2ꢀ((diphenylmethylene)amino)ꢀ2ꢀ((R)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate
(27b)
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[α]D = ꢀ110.98 (c = 4.20, MeOH); H NMR (400 MHz, CDCl3): δ 7.65 (d, J = 7.6 Hz,
2H), 7.49ꢀ7.32 (m, 6H), 7.20ꢀ7.14 (m, 2H), 3.90 (d, J = 4.5 Hz, 1H), 2.95ꢀ 2.85 (m, 1H), 2.58ꢀ
2.50 (m, 1H), 2.42ꢀ 2.33 (m, 2H), 1.80 (dd, J = 13.9 and 6.5 Hz, 1H), 1.50ꢀ1.43 (m, 9H), 1.1 ꢀ
1.02 (m, 2H), 0.86ꢀ0.76 (m, 1H), 0.70ꢀ0.61 (m, 1H); 13C NMR (101 MHz,CDCl3) δ 172.8, 172.3,
169.6, 139.1, 136.4, 130.7, 128.9, 128.8, 128.6, 128.1, 127.7, 81.8, 68.3, 62.2, 34.7, 33.8, 30.7,
28.1, 12.4, 11.9; Anal. Calcd for C26H29NO4: C, 74.44; H, 6.97; N, 3.34; Found: C 74.29, H 6.78,
N 3.35. HRMS (ESIꢀFTMS): m/z calcd for C26H30NO4 [M + H]+: 420.2175; found 420.2171.
4.6.
tertꢀButyl
(R)ꢀ2ꢀ((diphenylmethylene)amino)ꢀ2ꢀ((R)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀ
yl)acetate (27c).
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[α]D20 = +110.28 (c = 4.00, MeOH); 1H NMR (400 MHz, CDCl3): δ 7.66 (d, J = 7.6 Hz, 2H),
7.49ꢀ .33 (m, 6H), 7.20ꢀ7.13 (m, 2H), 3.94 (d, J = 4.5 Hz, 1H), 3.00ꢀ2.86 (m, 2H), 2.80ꢀ2.69 (m,
1H), 1.89 (dd, J = 13.7 and 9.5 Hz, 1H), 1.54ꢀ1.42 (m, 10H), 1.07ꢀ0.97 (m, 2H), 0.68 ꢀ 0.54 (m,
2H);13C NMR (101 MHz,CDCl3): δ 172.8, 171.7, 169.5, 139.0, 136.4, 130.7, 128.9, 128.8, 128.6,
128.1, 127.7, 81.9, 68.4, 61.9, 34.7, 32.6, 31.9, 28.1, 12.0, 12.0; Anal. Calcd for C26H29NO4: C,
74.44; H, 6.97; N, 3.34; Found: C 74.55, H 6.90, N 3.22; HRMS (ESIꢀFTMS): m/z calcd for
C26H30NO4 [M + H]+: 420.2175; found 420.2168.
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4.7. tertꢀButyl (S)ꢀ2ꢀ((diphenylmethylene)amino)ꢀ2ꢀ((S)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate
(27d)
[α]D20 = ꢀ109.29 (c = 6.85, MeOH); 1H NMR (400 MHz, CDCl3): δ 7.66 (d, J = 7.7 Hz, 2H),
7.49ꢀ7.33 (m, 6H), 7.19ꢀ7.13 (m, 2H), 3.94 (d, J = 4.6 Hz, 1H), 3.00ꢀ2.86 (m, 2H), 2.81ꢀ2.68 (m,
1H), 1.89 (dd, J = 13.8 and 9.3 Hz, 1H), 1.54ꢀ1.48 (m, 1H), 1.45 (s, 9H), 1.08ꢀ0.97 (m, 2H),
0.68ꢀ0.54 (m, 2H); 13C NMR (101 MHz, CDCl3): δ 172.8, 171.7, 169.5, 139.0, 136.4, 130.7,
128.9, 128.8, 128.6, 128.1, 127.7, 81.9, 68.4, 61.9, 34.7, 32.6, 31.9, 28.1, 12.0, 12.0; Anal. Calcd
for C26H29NO4: C, 74.44; H, 6.97; N, 3.34; Found: C 73.94, H 6.88, N 3.33; HRMS (ESIꢀFTMS):
m/z calcd for C26H30NO4 [M + H]+: 420.2175; found 420.2168.
4.8. tertꢀButyl 2ꢀ((diphenylmethylene)amino)ꢀ2ꢀ(5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate (39).
General procedure: To a solution of 27 (32.5 g, 72 mmol) in THF (97 mL) at 0 oC was added
a solution of HCl (12 N, 12 mL) and ice (70 g). After stirring the solution at rt for 20 min, the
reaction mixture was extracted with heptane (2 x 250 mL). The aqueous layer was separated and
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neutralized to pH 7ꢀ7.5 with NaHCO3 (15.11 g, 180 mmol) at 0 C and solution of dimethyl
dicarbonate (19.30 g, 144 mmol) in EtOAc (97 mL) was added. The reaction mixture was stirred
at rt for 1 h. The aqueous layer was adjusted to pH = 1 and extracted with EtOAc (3 x 200 mL).
The combined organic extracts were dried over Na2SO4 and evaporated to give an oil. The crude
product was dissolved in THF (100 mL) and a solution of LiOH (1 M in water, 144 mL, 144
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mmol) was added at 0 C. The reaction mixture was stirred at 0 C for 15 mins. The aqueous
layer was acidified to pH = 1 and then extracted with EtOAc (3 x 200 mL). The combined
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4.9. (R)ꢀtertꢀbutyl 2ꢀ((diphenylmethylene)amino)ꢀ2ꢀ((S)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate
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[α]D = ꢀ51.63 (c = 3.11, CH2Cl2); H NMR (400 MHz, CDCl3ꢀ): δ 5.31 (br d, J = 7.9 Hz,
1H), 4.39ꢀ4.24 (m, 1H), 3.73 (s, 3H), 2.79ꢀ2.63 (m, 2H), 2.61ꢀ2.50 (m, 1H), 1.93 (dd, J = 13.9
and 9.5 Hz, 1H), 1.56 (br d, J = 5.6 Hz, 1H), 1.50 (s, 9H), 1.15ꢀ1.03 (m, 2H), 0.80ꢀ0.73 (m, 1H),
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0.63ꢀ0.54 (m, 1H); C NMR (126 MHz, CDCl3): δ 171.6, 169.8, 157.0, 83.4, 61.7, 56.9, 52.7,
34.9, 33.1, 30.6, 28.1, 12.3, 12.0; Anal. Calcd for C15H23NO6: C, 57.50; H, 7.40; N, 4.47; Found:
C 57.59, H 7.13, N 4.45. HRMS (ESIꢀFTMS): m/z calcd for C15H23NNaO6 [M + Na]+: 336.1423;
found 336.1417.
4.10. (S)ꢀtertꢀbutyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((R)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate
(39b)
[α]D20 = +50.77 (c = 6.12, CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 5.31 (br d, J = 7.8 Hz,
1H), 4.37ꢀ4.25 (m, 1H), 3.71 (s, 3H), 2.77ꢀ2.62 (m, 2H), 2.60ꢀ2.48 (m, 1H), 1.91 (dd, J = 14.0
and 9.4 Hz, 1H), 1.56 (dd, J = 13.7 and 5.6 Hz, 1H), 1.48 (s, 9H), 1.12ꢀ1.01 (m, 2H), 0.78ꢀ0.71
(m, 1H), 0.61ꢀ0.53 (m, 1H); 13C NMR (101 MHz, CDCl3): δ 171.6, 169.8, 157.0, 83.4, 61.7, 56.9,
52.7, 34.9, 33.1, 30.6, 28.1, 12.3, 12.0; Anal. Calcd for C15H23NO6: C, 57.50; H, 7.40; N, 4.47;
Found: C 57.79, N 4.48, H 7.13. HRMS(ESIꢀFTMS): m/z calcd for C15H23NNaO6 [M + Na]+:
336.1423; found 336.1417.
4.11. (R)ꢀtertꢀbutyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((R)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate
(39c).
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[α]D = ꢀ25.19 (c = 4.35, CH2Cl2); H NMR (500 MHz, CDCl3): δ 5.39 (br d, J = 7.5 Hz,
1H), 4.38 (br dd, J = 7.5, 3.7 Hz, 1H), 3.70 (s, 3H), 2.75ꢀ2.61 (m, 1H), 2.59ꢀ2.42 (m, 2H), 2.09ꢀ
1.95 (m, 1H), 1.73 (br dd, J = 14.2 and 5.5 Hz, 1H), 1.50 (s, 9H), 1.11ꢀ1.00 (m, 2H), 0.79ꢀ0.68
(m, 1H), 0.66ꢀ0.59 (m, 1H); 13C NMR (126 MHz, CDCl3): δ 171.7, 169.5, 157.1, 83.6, 62.0, 56.9,
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52.7, 34.8, 32.0, 31.2, 28.0, 12.0. HRMS (ESIꢀFTMS): m/z calcd for C15H23NNaO6 [M + Na]+:
336.1423; found 336.1417.
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4.12. (S)ꢀtertꢀbutyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((S)ꢀ5ꢀoxoꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate
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(39d)
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[α]D = +23.29 (c = 4.13, CH2Cl2); H NMR (400 MHz, CDCl3): δ 5.41 (br d, J = 8.1 Hz,
1H), 4.44ꢀ4.34 (m, 1H), 3.72 (s, 3H), 2.72 (dt, J = 10.4, 5.2 Hz, 1H), 2.61ꢀ2.41 (m, 2H), 2.08ꢀ
1.99 (m, 1H), 1.75 (br dd, J = 14.2 and 5.6 Hz, 1H), 1.51 (s, 9H), 1.15ꢀ1.00 (m, 2H), 0.81ꢀ0.71
(m, 1H), 0.67ꢀ0.59 (m, 1H); 13C NMR (101 MHz, CDCl3): δ 171.7, 169.5, 157.1, 83.6, 62.0, 56.9,
52.7, 34.8, 32.0, 31.2, 28.1, 12.1, 12.0. HRMS (ESIꢀFTMS): m/z calcd for C15H23NNaO6 [M +
Na]+: 336.1423; found 336.1417.
4.13.
tertꢀButyl
5ꢀhydroxyꢀ3ꢀ((1ꢀhydroxycyclopropyl)methyl)ꢀ2ꢀ((methoxycarbonyl)amino)
pentanoate (40)
General procedure: to a solution of 40 (22.5 g, 71.8 mmol) in THF (225 mL) at 0 °C cooled
with an ice bath was added dropwise a solution of NaBH4 (10.89 g, 288 mmol) in H2O (45.1 mL).
The temperature of the reaction mixture was kept below 10 °C during the addition and then
warmed up to rt and stirred for 3.5 h. The solution was diluted with aqueous NaHCO3 (200 mL)
and the aqueous layer extracted with EtOAc (3 X 300 mL). The combined organic layer was
dried over Na2SO4 overnight and concentrated to give the diol product 40 (21.7g, 68.4 mmol, 95 %
yield), which was used in the next step without further purification.
4.14. tertꢀButyl (2R,3R)ꢀ5ꢀhydroxyꢀ3ꢀ((1ꢀhydroxycyclopropyl)methyl)ꢀ2ꢀ((methoxycarbonyl)
amino)pentanoate (40a)
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[α]D = ꢀ70.58 (c = 6.25, CH2Cl2); H NMR (400 MHz, DMSOꢀd6): δ 7.22 (d, J = 8.4 Hz,
1H), 5.02 (s, 1H), 4.42 (t, J = 4.8 Hz, 1H), 4.17 (dd, J = 8.3, 3.8 Hz, 1H), 3.54 (s, 3H), 3.48ꢀ3.38
(m, 2H), 2.33 (br d, J = 3.5 Hz, 1H), 1.74ꢀ1.60 (m, 1H), 1.52ꢀ1.37 (m, 12H), 0.60ꢀ0.49 (m, 2H),
0.34 (s, 2H); 13C NMR (101 MHz, DMSOꢀd6): δ 171.5, 157.4, 80.9, 59.3, 56.7, 52.5, 51.9, 38.7,
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34.8, 33.4, 28.2, 14.4, 13.0. HRMS(ESIꢀFTMS): m/z calcd for C15H27NNaO6 [M + Na]+:
340.1736; found 340.1727.
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tertꢀButyl
(2S,3S)ꢀ5ꢀhydroxyꢀ3ꢀ((1ꢀhydroxycyclopropyl)methyl)ꢀ2ꢀ((methoxycarbonyl)
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amino)pentanoate (40b)
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[α]D = +71.39 (c = 2.42, CH2Cl2); H NMR (500 MHz, DMSOꢀd6): δ 7.22 (d, J = 8.2 Hz,
1H), 5.03 (s, 1H), 4.42 (t, J = 4.8 Hz, 1H), 4.18 (dd, J = 8.3, 3.9 Hz, 1H), 3.55 (s, 3H), 3.47 ꢀ
3.40 (m, 2H), 2.33 (br dd, J = 8.5 and 4.7 Hz, 1H), 1.69 (br dd, J = 13.4 and 6.3 Hz, 1H), 1.51ꢀ
1.37 (m, 12H), 0.61ꢀ0.50 (m, 2H), 0.38ꢀ0.29 (m, 2H); 13C NMR (126 MHz, DMSOꢀd6): δ 171.5,
157.4, 80.9, 59.3, 56.6, 52.5, 51.9, 38.7, 34.8, 33.4, 28.2, 14.3, 13.0; HRMS(ESIꢀFTMS): m/z
calcd for C15H27NNaO6 [M + Na]+: 340.1736; found 340.1728.
4.16
tertꢀButyl
(2R,3S)ꢀ5ꢀhydroxyꢀ3ꢀ((1ꢀhydroxycyclopropyl)methyl)ꢀ2ꢀ((methoxycarbonyl)
amino)pentanoate (40c)
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[α]D = ꢀ28.04 (c = 4.35, CH2Cl2); H NMR (500 MHz, CDCl3): δ 5.73 (br d, J = 8.1 Hz,
1H), 4.64 (br dd, J = 8.3, 2.1 Hz, 1H), 3.77ꢀ3.73 (m, 2H), 3.71 (s, 3H), 3.44 (br s, 1H), 2.51 (td, J
= 6.7, 2.9 Hz, 1H), 2.26 (br s, 1H), 1.88 (br dd, J = 14.6, 7.3 Hz, 1H), 1.50 (s, 11H), 1.41ꢀ1.32
(m, 1H), 0.88ꢀ0.77 (m, 2H), 0.53ꢀ0.44 (m, 2H); 13C NMR (126 MHz, CDCl3): δ 171.2, 157.5,
82.6, 60.4, 56.8, 54.4, 52.5, 39.0, 36.5, 33.1, 28.1, 14.2, 14.2, 14.1; HRMS(ESIꢀFTMS): m/z
calcd for C15H27NNaO6 [M + Na]+: 340.1736; found 340.1728.
4.17. tertꢀButyl (2S,3R)ꢀ5ꢀhydroxyꢀ3ꢀ((1ꢀhydroxycyclopropyl)methyl)ꢀ2ꢀ((methoxycarbonyl)
amino)pentanoate (40d)
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[α]D = +23.71 (c = 6.25, CH2Cl2); H NMR (400 MHz, DMSOꢀd6): δ 7.21 (d, J = 8.4 Hz,
1H), 5.01 (s, 1H), 4.50 (t, J = 4.9 Hz, 1H), 4.25 (dd, J = 8.4, 3.8 Hz, 1H), 3.54 (s, 3H), 3.41 (qd,
J = 11.0, 4.3 Hz, 2H), 2.46 ꢀ 2.32 (m, 1H), 1.58ꢀ1.32 (m, 13H), 0.57ꢀ0.47 (m, 2H), 0.38ꢀ0.18 (m,
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2H); C NMR (101 MHz, DMSOꢀd6): δ 171.8, 157.5, 80.8, 59.3, 57.3, 52.5, 51.8, 39.1, 34.4,
33.5, 28.2, 13.3, 13.2; HRMS(ESIꢀFTMS): m/z calcd for C15H27NNaO6 [M + Na]+: 340.1736;
found 340.1728.
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4.18. tertꢀButyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ(4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate (21)
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To a solution of diol 40 (25.4 g, 80 mmol), triethylamine (55.8 mL, 400 mmol) and DMAP
(0.977 g, 8.00 mmol) in CH2Cl2 (267 mL) at 8 °C cooled with an ice bath was added 4ꢀ
methylbenzeneꢀ1ꢀsulfonyl chloride (15.25 g, 80 mmol). The ice bath was removed after
completion of the addition. After 1 h, another portion of TsCl (2.29 g, 12.0 mmol) was added at
8 °C. The solution was stirred for 1 h, cooled with an ice bath and then heated at 38 °C for 24 h.
The reaction mixture was washed sequentially with H2O, saturated NaHCO3 and brine. The
organic layer was dried over MgSO4 and concentrated under reduced pressure. The residue was
purified by flash chromatography (0ꢀ40% acetone/hexane) to give tetrahydropyran 22 (17.31 g,
57.8 mmol, 72.3 % yield).
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4.19. (R)ꢀtertꢀButyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((R)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate (21a)
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[α]D = ꢀ63.12 (c = 5.10, CH2Cl2); H NMR (500 MHz, DMSOꢀd6): δ 7.48 (d, J = 8.2 Hz,
1H), 3.82 (t, J = 7.9 Hz, 1H), 3.78ꢀ3.73 (m, 1H), 3.54 (s, 3H), 3.39ꢀ3.33 (m, 1H), 2.04 (br d, J =
7.6 Hz, 1H), 1.79 (br t, J = 12.3 Hz, 1H), 1.52 (br d, J = 13.9 Hz, 1H), 1.41 (s, 9H), 1.39ꢀ1.33 (m,
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1H), 1.01 (br d, J = 11.4 Hz, 1H), 0.73ꢀ0.65 (m, 1H), 0.53ꢀ0.44 (m, 2H), 0.32ꢀ0.25 (m, 1H); C
NMR (126 MHz, DMSOꢀd6): δ 171.2, 157.3, 81.2, 65.8, 59.4, 59.2, 52.0, 36.8, 34.6, 29.0, 28.2,
12.6, 11.2; HRMS (ESIꢀFTMS): m/z calcd for C15H25NNaO5 [M + Na]+: 322.1630; found
322.1624.
4.20. (S)ꢀtertꢀButyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((S)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate (21b)
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[α]D = +66.82 (c = 2.40, CH2Cl2); H NMR (400 MHz, CDCl3): δ 5.24 (br d, J = 7.9 Hz,
1H), 4.26 (br dd, J = 8.0, 5.0 Hz, 1H), 3.90 (ddd, J = 11.1, 4.6, 1.8 Hz, 1H), 3.71 (s, 3H), 3.53 (td,
J = 11.6, 2.5 Hz, 1H), 2.27ꢀ2.11 (m, 1H), 2.04ꢀ1.93 (m, 1H), 1.71ꢀ1.62 (m, 1H), 1.50 (s, 10H),
0.99ꢀ0.82 (m, 2H), 0.66 (dddd, J = 10.8, 6.4, 4.7 and1.9 Hz, 1H), 0.57ꢀ0.49 (m, 1H), 0.29 (ddd, J
= 10.0, 6.5 and 4.8 Hz, 1H); 13C NMR (101 MHz, CDCl3): δ 170.7, 156.8, 82.4, 66.3, 59.0, 58.1,
52.4, 38.5, 33.7, 28.7, 28.1, 12.6, 11.4; HRMS (ESIꢀFTMS): m/z calcd for C15H26NO5 [M + H]+:
300.1811; found 300.1815.
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4.21. (R)ꢀtertꢀButyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((S)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate (21c)
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[α]D20 = +7.86 (c = 4.35, CH2Cl2); 1H NMR (500 MHz, DMSOꢀd6): δ 7.50 (br d, J = 8.4 Hz,
1H), 3.86 (dd, J = 8.1 and 6.9 Hz, 1H), 3.80ꢀ3.69 (m, 1H), 3.55 (s, 3H), 3.38ꢀ3.33 (m, 1H), 2.06
(br d, J = 6.7 Hz, 1H), 1.74 (t, J = 12.4 Hz, 1H), 1.55ꢀ1.41 (m, 2H), 1.40 (s, 9H), 1.02 (dd, J =
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13.0 and 2.2 Hz, 1H), 0.73ꢀ0.66 (m, 1H), 0.53ꢀ0.44 (m, 2H), 0.33ꢀ0.27 (m, 1H); C NMR (126
MHz, DMSOꢀd6): δ 171.0, 157.3, 81.2, 66.1, 59.1, 59.0, 52.0, 36.9, 35.0, 28.2, 12.5, 11.4.
HRMS(ESIꢀFTMS): m/z calcd for C15H25NNaO5 [M + Na]+: 322.1630; found 322.1623.
4.22. (S)ꢀtertꢀButyl 2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((R)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetate (21d)
[α]D20 = ꢀ7.52 (c = 3.80, CH2Cl2); 1H NMR (500 MHz, DMSOꢀd6): δ 7.50 (br d, J = 8.4 Hz,
1H), 3.86 (dd, J = 8.1 and 6.9 Hz, 1H), 3.79ꢀ3.71 (m, 1H), 3.55 (s, 3H), 3.37ꢀ3.32 (m, 1H), 2.11ꢀ
1.96 (m, 1H), 1.75 (t, J = 12.4 Hz, 1H), 1.52ꢀ1.41 (m, 2H), 1.40 (s, 9H), 1.02 (dd, J = 13.0 and
2.3 Hz, 1H), 0.74ꢀ0.65 (m, 1H), 0.54ꢀ0.45 (m, 2H), 0.34ꢀ0.27 (m, 1H); 13C NMR (126 MHz,
DMSOꢀd6): δ 171.0, 157.3, 81.2, 66.1, 59.2, 59.0, 52.0, 36.9, 35.0, 28.2, 12.5, 11.4. HRMS (ESIꢀ
FTMS): m/z calcd for C15H25NNaO5 [M + Na]+: 322.1630; found 322.1624.
4.23. 2ꢀ((Methoxycarbonyl)amino)ꢀ2ꢀ(4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetic acid (1)
A solution of tetrahydropyran 21b (41.5 g, 139 mmol) in formic acid (319 g, 6931 mmol)
was stirred at rt for 46 h. The formic acid was removed by distillation in vacuo at 37 °C
(external temperature). The remaining clear viscous oil was treated with toluene (50 mL), and
distilled again to remove residual formic acid and toluene. This process was repeated three more
times. The viscous oil (42.7 g) was treated with saturated NaHCO3 (250 mL) with stirring for 30
min. The basic solution was washed with ether (2 x 150 mL, 1 x 100 mL). The basic solution
was treated with 1 N HCl until pH about 2. The acidic solution was extracted with 2ꢀMeꢀTHF (6
x 200 mL) until the aqueous layer indicated an absence of the desired product. (Note: after each
extraction, 1N HCl was added to the aqueous layer to adjust pH to 2ꢀ3). The combined organic
extracts were dried over MgSO4, filtered, evaporated, and dried under vacuum to give 35.8 g of 1.
The NMR indicated that the ratio of formic acid to product was 1:80. The material was treated
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with toluene and sonicated to afford a clear solution. The excess of toluene was removed by
distillation. The remaining viscous oil was treated with CH2Cl2 (120 mL), concentrated, and
then treated with ether (50 mL) and dried in vacuo to give 1 (31.74 g, 130 mmol, 94% yield) as a
white foam.
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4.24. (R)ꢀ2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((R)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetic acid (1a)
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[α]D = ꢀ75.55 (c = 3.75, CH2Cl2); 1H NMR (500 MHz, DMSOꢀd6): δ 12.76ꢀ12.54 (m, 1H),
7.44 (br d, J = 8.4 Hz, 1H), 3.85 (t, J = 7.9 Hz, 1H), 3.78ꢀ3.70 (m, 1H), 3.57ꢀ3.50 (m, 3H), 3.43ꢀ
3.27 (m, 1H), 2.04 (dtd, J = 11.5, 7.8 and 3.8 Hz, 1H), 1.78 (t, J = 12.2 Hz, 1H), 1.53 (br d, J =
12.1 Hz, 1H), 1.35 (qd, J = 12.5, 4.6 Hz, 1H), 1.05 (br d, J = 11.6 Hz, 1H), 0.73ꢀ0.65 (m, 1H),
0.52ꢀ0.43 (m, 2H), 0.35ꢀ0.26 (m, 1H); 13C NMR (126 MHz, DMSOꢀd6): δ 173.5, 157.3, 65.9,
59.2, 59.0, 51.9, 36.5, 34.7, 29.2, 12.6, 11.2; HRMS(ESIꢀFTMS): m/z calcd for C11H18NO5 [M +
H]+: 244.1185; found 244.1178.
4.25. (S)ꢀ2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((S)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetic acid (1b) (Note:
This is the same as acid 1 in text)
[α]D20 = +78.31 (c = 5.04, CH2Cl2); 1H NMR (400 MHz, DMSOꢀd6): δ 12.64 (br s, 1H), 7.46
(br d, J = 8.3 Hz, 1H), 3.85 (br t, J = 7.9 Hz, 1H), 3.75 (br dd, J = 11.1 and 2.8 Hz, 1H), 3.54 (s,
3H), 3.36 (br t, J = 10.8 Hz, 1H), 2.03 (ddd, J = 11.4, 7.6 and 3.7 Hz, 1H), 1.78 (br t, J = 12.2 Hz,
1H), 1.53 (br d, J = 12.7 Hz, 1H), 1.43ꢀ1.28 (m, 1H), 1.05 (br d, J=11.9 Hz, 1H), 0.74ꢀ0.64 (m,
1H), 0.53ꢀ0.42 (m, 2H), 0.30 (br dd, J = 9.5 and 2.9 Hz, 1H); 13C NMR (101 MHz, DMSOꢀd6): δ
173.5, 157.3, 65.9, 59.2, 58.9, 51.9, 36.5, 34.7, 29.2, 12.6, 11.2. HRMS(ESIꢀFTMS): m/z calcd
for C11H18NO5 [M + H]+: 244.1185; found 244.1178.
4.26. (R)ꢀ2ꢀ((methoxycarbonyl)amino)ꢀ2ꢀ((S)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)acetic acid (1c)
[α]D20 = +13.40 (c = 3.75, CH2Cl2); 1H NMR (500 MHz, DMSOꢀd6): δ 12.64 (s, 1H), 7.47 (d,
J = 8.5 Hz, 1H), 3.92 (dd, J = 8.2, 6.9 Hz, 1H), 3.79ꢀ3.69 (m, 1H), 3.55 (s, 3H), 3.36ꢀ3.30 (m,
1H), 2.14ꢀ2.00 (m, 1H), 1.77 (t, J = 12.4 Hz, 1H), 1.57ꢀ1.39 (m, 2H), 1.02 (dd, J = 13.0 and 2.1
Hz, 1H), 0.73ꢀ0.65 (m, 1H), 0.53ꢀ0.44 (m, 2H), 0.34ꢀ0.26 (m, 1H); 13C NMR (126 MHz, DMSOꢀ
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d6): δ 173.3, 157.4, 66.1, 59.0, 58.6, 51.9, 36.6, 35.2, 28.2, 12.5, 11.3; HRMS(ESIꢀFTMS): m/z
calcd for C11H18NO5 [M + H]+: 244.1185; found 244.1179.
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[α]D20 = ꢀ15.70 (c = 2.19, CH2Cl2). 1H NMR (400 MHz, DMSOꢀd6): δ 12.64 (br s, 1H), 7.47
(d, J = 8.6 Hz, 1H), 3.92 (dd, J = 8.3, 6.8 Hz, 1H), 3.79ꢀ3.71 (m, 1H), 3.55 (s, 3H), 3.38ꢀ3.29 (m,
1H), 2.15ꢀ2.00 (m, 1H), 1.77 (t, J = 12.0 Hz, 1H), 1.57ꢀ1.38 (m, 2H), 1.02 (dd, J = 13.0 and 2.3
Hz, 1H), 0.72ꢀ0.65 (m, 1H), 0.53ꢀ0.44 (m, 2H), 0.35ꢀ0.26 (m, 1H); 13C NMR (101 MHz, DMSOꢀ
d6): δ 173.3, 157.4, 66.1, 59.0, 58.7, 52.0, 36.7, 35.2, 28.2, 12.5, 11.3; HRMS(ESIꢀFTMS): m/z
calcd for C11H18NO5 [M + H]+: 244.1185; found 244.1178.
4.27.
Dimethyl
((1S,1'S)ꢀ((2S,2'S,5S,5'S)ꢀ([1,1'ꢀbiphenyl]ꢀ4,4'ꢀdiylbis(1Hꢀimidazoleꢀ5,2ꢀ
diyl))bis(2ꢀmethylpyrrolidineꢀ5,1ꢀdiyl))bis(2ꢀoxoꢀ1ꢀ((S)ꢀ4ꢀoxaspiro[2.5]octanꢀ7ꢀyl)ethaneꢀ2,1ꢀ
diyl))dicarbamate (BMS-986097)
To a solution of chiral acid 1 (28.3 g, 107 mmol) in DMSO (486 mL) was added 2ꢀ
hydroxypyridine 1ꢀoxide (HOPO) (11.87 g, 107 mmol) and EDC (22.34 g, 117 mmol). The light
yellow solution was stirred at rt for 100 mins before adding 4,4'ꢀbis(2ꢀ((2S,5S)ꢀ5ꢀ
methylpyrrolidinꢀ2ꢀyl)ꢀ1Hꢀimidazolꢀ5ꢀyl)ꢀ1,1'ꢀbiphenyl, 4 HCl, 5.65 H2O (2) (34.0 g, 48.6 mmol)
and DIPEA (40.8 g, 316 mmol). The yellow solution was maintained at 25 °C and stirred for 16
h before pouring into 2.5 kg of ice water with mechanical stirring. The resulting white
suspension was stirred for 4 h. The white solid was filtered off, washed with H2O (500 mL), and
dried under house vacuum overnight to give a wet white solid (265 g). This was dissolved in
CH2Cl2 (750 mL) and the layers separated. The organic layer was washed with H2O (6 x 200
mL), dried over MgSO4, and evaporated to give 47.7 g of a light brown solid. The crude
material was purified by flash chromatography (0ꢀ15% MeOH/DCM) to give BMS-986097 (41.1
20
1
g, 45.5 mmol, 93.7% yield, 99.1% HPLC purity). [α]D = ꢀ73.61 (c = 3.62, MeOH). H NMR
(500 MHz, DMSOꢀd6): δ 11.84 (br s., 1H), 7.85 (d, J = 7.3 Hz, 1H), 7.77 (d, J = 6.3 Hz, 2H),
7.67 (br s, 3H), 7.57 (d, J = 7.9 Hz, 1H), 7.49 (br. s, 1H), 5.01 (t, J = 8.2 Hz, 1H), 4.75 (br. s, 1H),
4.16ꢀ3.96 (m, 2H), 3.67 (d, J = 7.6 Hz, 1H), 3.54 (s, 4H), 3.18 (t, J = 11.2 Hz, 1H), 2.55 (s, 1H),
2.26 (br s, 2H), 2.10ꢀ1.95 (m, 3H), 1.80 (d, J = 5.4 Hz, 1H), 1.65 (t, J = 12.1 Hz, 1H), 1.57 (d, J
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