Design, synthesis, and biological evaluation of novel fluorinated ethanolamines

Article abstract of DOI:10.1002/chem.201102078

The preparation of novel fluorinated allylamines and their use as key fragments for the stereoselective synthesis of hydroxyethyl secondary amine (HEA)-type peptidomimetics is described. Our strategy employs chiral sulfinyl imines as synthesis intermediates, by treatment of hemiaminal precursors with two equivalents of vinylmagnesium bromide. The subsequent oxidation of the allylic amines to the corresponding epoxides was achieved by treatment with methyl(trifluoromethyl)dioxirane. Finally, epoxide ring opening with a range of nitrogen nucleophiles provided a library of HEA-derived peptidomimetics with a phenyldifluoromethylene moiety. The biological evaluation of these derivatives revealed compounds with remarkable BACE1 inhibitory activity. Docking studies revealed the influence of the fluorine atoms in the binding mode of the synthesized ligands. Furthermore, the biological evaluation of our final products and synthesis intermediates led to the discovery of compounds with antimicrobial activity against Mycobacterium and Nocardia species.

Full text of DOI:10.1002/chem.201102078

DOI: 10.1002/chem.201102078
Design, Synthesis, and Biological Evaluation of Novel Fluorinated
Ethanolamines
Santos Fustero,*[a, b] Ana C. CuÇat,[a] Sonia Flores,[a] Claribel Bꢀez,[a] Judit Oliver,[a]
Michael Cynamon,[c] Michael Gꢁtschow,[d] Matthias D. Mertens,[d] Oscar Delgado,[e]
Gary Tresadern,[e] and Andrꢂs A. Trabanco[e]
Abstract: The preparation of novel flu-
orinated allylamines and their use as
key fragments for the stereoselective
synthesis of hydroxyethyl secondary
amine (HEA)-type peptidomimetics is
described. Our strategy employs chiral
sulfinyl imines as synthesis intermedi-
ates, by treatment of hemiaminal pre-
cursors with two equivalents of vinyl-
magnesium bromide. The subsequent
oxidation of the allylic amines to the
corresponding epoxides was achieved
by treatment with methyl(trifluoro-
AHCTUNGTRENNGmUN ethyl)dioxirane. Finally, epoxide ring
compounds with remarkable BACE1
inhibitory activity. Docking studies re-
vealed the influence of the fluorine
atoms in the binding mode of the syn-
thesized ligands. Furthermore, the bio-
logical evaluation of our final products
and synthesis intermediates led to the
discovery of compounds with antimi-
crobial activity against Mycobacterium
and Nocardia species.
opening with a range of nitrogen nucle-
ophiles provided a library of HEA-de-
rived peptidomimetics with a phenyldi-
fluoromethylene moiety. The biological
evaluation of these derivatives revealed
Keywords: antimicrobials
·
BACE1 · ethanolamines · fluorine ·
peptidomimetics
Introduction
double the number of AD patients.[3] AD is characterized
by two major CNS pathologies: the occurrence of neurofi-
brillar tangles and amyloid plaques.
Alzheimerꢀs disease (AD) is a neurodegenerative disorder
of the central nervous system (CNS) that affects over 20 mil-
lion people worldwide.[1] It is the most common form of pro-
gressive dementia in the elderly population, and its symp-
toms include impairment of memory, cognition, reasoning
and gradual loss of bodily functions, which ultimately result
in death. Although the causes and progression of AD are
not well understood,[2] it has become a major health prob-
lem in all societies with long life expectancy. It is assumed
that in the year 2020, demographic changes could lead to
The amyloid cascade hypothesis states that the production
of the amyloid b (Ab) peptide and its subsequent aggrega-
tion and deposition in the form of plaques in the brain is the
fundamental cause of the disease.[4] Despite some controver-
sy, there is strong evidence that an anti-amyloid approach
(aimed at increasing Ab clearance or decreasing Ab produc-
tion or aggregation) could impair the progression of the dis-
ease.[5] As a consequence, many of the ongoing efforts from
the pharmaceutical industry are based on this hypothesis.
Ab peptides are a group of fragments derived from the b-
amyloid precursor protein (APP) through the sequential
action of two proteolytic enzymes (b- and g-secretases).[6] In
contrast to the complexity of other secretases, b-secretase
(BACE1, also named Asp2 or memapsin2) displays the pro-
totypical structure of aspartyl proteases. Following its iden-
tification in 1999,[7] it was shown that BACE1 has a large ex-
tracellular domain that contains the catalytic aspartic acids,
a transmembrane domain, and a short intracellular domain.
Based on successful drug discovery programs targeting re-
lated aspartyl proteases, in particular in the HIV and renin
fields, a range of potent BACE1 inhibitors of peptidic
nature were quickly identified by several groups from aca-
demia and industry.[8] Unfortunately, the development of
potent, CNS-active and therapeutically useful BACE1 inhib-
itors has remained an elusive goal to date. Peptidomimetics
lie at the center of the development of first-generation
BACE1 inhibitors. The substitution of readily hydrolyzable
peptide bonds by more robust subunits, such as the ethanol-
[a] Prof. Dr. S. Fustero, Dr. A. C. CuÇat, Dr. S. Flores, C. Bꢁez, J. Oliver
Departamento de Quꢂmica Orgꢁnica, Universidad de Valencia
46100 Burjassot (Spain)
Fax : (+34)963544939
E-mail: santos.fustero@uv.es
[b] Prof. Dr. S. Fustero
Laboratorio de Molꢃculas Orgꢁnicas
Centro de Investigaciꢄn Prꢂncipe Felipe
46012 Valencia (Spain)
[c] Prof. Dr. M. Cynamon
Department of Medicine, Syracuse VA Medical Center
SUNY Upstate Medical University
Syracuse, 13210 NY (USA)
[d] Prof. Dr. M. Gꢅtschow, M. D. Mertens
Pharmaceutical Institute, Pharmaceutical Chemistry I
University of Bonn, 53121 Bonn (Germany)
[e] Dr. O. Delgado, Dr. G. Tresadern, Dr. A. A. Trabanco
Neuroscience Medicinal Chemistry
Janssen Pharmaceutical Research and Development
45007 Toledo (Spain)
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FULL PAPER
amine moiety, is a strategy widely employed for improving
“drug-likeness”. Compound 1, resulting from collaboration
between Elan and Pfizer, is an example of a BACE1 inhibi-
tor incorporating the hydroxyethyl secondary amine (HEA)
isostere.[9]
We became particularly interested in 1 due to its extraor-
dinary potency and excellent cell permeability. As a further
exploration around the chemical space, we proposed the re-
placement of the hydrogen atoms at the benzylic position by
fluorine atoms.[10] This formal fluorine shift (from the aryl to
the benzylic position) was envisioned as a means of enhanc-
ing the pharmacological profile of the series (Scheme 1).
Our modular synthesis strategy should also allow stereo-
chemical permutations on the ethanolamine subunit.
our envisioned difluorobenzylethanolamines (Scheme 1)
against a panel of microorganisms could result in the iden-
tification of novel antibacterial agents.
To our knowledge, there are no examples of antimicrobial
or BACE1 inhibitors incorporating a phenyldifluoromethyl
substituent at the a-carbon of the hydroxyethyl secondary
amine (HEA). Based on these considerations, our group de-
signed a library of fluorinated ethanolamines following the
general retrosynthesis strategy shown in Scheme 2. The
Scheme 2. Retrosynthesis approach for the preparation of fluorinated
ethanolamines I.
ethanolamine moiety can be prepared by means of regiose-
lective opening of the fluorinated epoxide II through treat-
ment with benzylic amines. This epoxide, which contains the
entire carbon skeleton of the ethanolamines, might be ob-
tained by epoxidation of the allyl amine III. Taking into ac-
count that it is possible to prepare both chiral amines III,
the subsequent epoxidation should allow the preparation of
the four possible diastereoisomers of the final compounds I.
It is well-known that CF2 groups in benzylic positions im-
prove the stability of many substrates.[12] However, there are
few examples in the literature reporting the synthesis of flu-
orinated ethanolamines.[13] At first, we started with the prep-
aration of the aminoalcohols library (Figure 2). Structures
IV would then act as synthesis intermediates in the prepara-
tion of full-length analogues of the most potent example of
the HEA isostere inhibitors discovered by Elan/Pfizer (1).
Scheme 1. Design of analogues around the Elan/Pfizer chemical series.
The ethanolamine moiety is also present in marketed
drugs in other therapeutic areas, such as infectious diseases.
Ethambutol (2, Figure 1) is a bacteriostatic antimycobacteri-
al drug that belongs to the front-line agents that are recom-
mended by the World Health Organization (WHO) for the
treatment of tuberculosis (TB). It interferes with the biosyn-
thesis of the bacterial cell wall through inhibition of the
enzyme arabinosyl transferase, which affects the permeabili-
ty of the cell wall.[11] It was anticipated that the screening of
Figure 1. Biologically active ethanolamines.
Figure 2. Library of targeted fluorinated ethanolamines.
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S. Fustero et al.
Results and Discussion
Fluorinated imines are very useful synthons for the intro-
duction of nitrogen and fluorine atoms in complex struc-
tures.[14,15] In fact, trifluoromethyl imines have been previ-
ously used in the synthesis of protease inhibitors.[16] Our ap-
proach is based on the convenient functionalization of chiral
1-(difluorobenzyl)allylamine III, which is prepared through
a stereoselective vinylation of imine derivative VII. For the
introduction of the fluorine atoms we relied on the early
deoxofluorination of a suitable benzoylformate (Scheme 3).
Scheme 3. Synthesis scheme for fluorinated allylamines III.
We first considered using our previously reported tandem
protocol[17] for the racemic synthesis of the corresponding al-
lylamines III starting from p-methoxyphenyl (PMP) imines.
However, problems were encountered during the prepara-
tion of the required fluorinated starting materials. As an al-
ternative, we applied the diastereoselective protocol de-
scribed by Kuduk et al.[18] based on the use of Ellmanꢀs
chiral N-tert-butylsulfinimines.[19] This method avoids the
isolation of fluorinated N-tert-butylsulfinimines VII[20] and
allows for the preparation of the fluorinated chiral allyl
amines III with good yields and selectivities.
Scheme 4. Preparation of enantiomerically enriched a-fluorinated allylic
amines 6 and ent-6.
The aldehyde required for the synthesis of the imines VII
is not commercially available. Thus, it had to be prepared as
the corresponding hemiacetal (4)[21] starting from ethyl ben-
zoyl formate (3) by a three-step sequence. As depicted in
Scheme 4, the treatment of 4 with (R)-tert-butanesulfin-
Scheme 5. Synthesis of p-brosylate 7.
A
ACHTUNGTRENNUNG(OEt)4 at 708C, overnight, yielded hemi-
A
able prior to the final coupling reaction. Hydrochloric acid
mediated removal of the N-tert-butanesulfinyl group[24] from
6, followed by treatment of the resulting ammonium salt
with benzyloxycarbonyl chloride in the presence of base and
(53% overall yield for the four-steps sequence from 3). The
unequivocal assignment of the stereochemistry of both epi-
mers was irrelevant since both afforded the desired allyl-
A
catalytic DMAP afforded carbamate 8 in 90% yield
(Scheme 6). Alternatively, treatment of the same ammonium
salt with Boc2O led to compound 9 (82%).
vinylmagnesium bromide in DCM at low temperature.[22]
The enantiomeric compound ent-5 was prepared in similar
yield following the same procedure by using (S)-tert-
Standard epoxidation methods, such as m-chloroperben-
zoic acid or lithium tert-butylhydroperoxide, failed with both
substrates 8 and 9, presumably due to the strong electron
withdrawing properties of the difluoromethylene group. The
in situ generation of a more reactive dioxirane, methyl(tri-
fluoromethyl)dioxirane, and subsequent treatment of allyl-
carbamate 8 in heterogeneous phase[25] afforded a 1.5:1 mix-
ture of two epoxide isomers (R,R)-10a and (R,S)-10b. These
were readily separated by chromatography on silica gel; this
resulted in a combined yield of 74%.[26] In order to confirm
butanesulACHTUNGTRENNUNGfinamide.
This strategy provided the chiral allylamines 6 and ent-6,
with high diastereoselectivities (20:1 d.r.).[23] The configura-
tion for these compounds was proposed according to the
model by Kuduk et al.,[18] and confirmed later by X-ray crys-
tal structure determination of the p-brosylate 7 (Scheme 5).
At this stage, it was necessary to remove the auxiliary
group in order to install a protecting group that would be
both compatible with the oxidation step and easily hydrolys-
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Fluorinated Ethanolamines
FULL PAPER
a similar experiment for oxazolidinone 13 exhibited correla-
tions of the CF2 group with the methylene group, which is in
agreement with a 4R,5R stereochemistry. The stereochemi-
cal determination was later confirmed by means of X-ray
diffraction analysis of 13 (see the Supporting Information).
The same reaction sequence was used with enantiomer
ent-6 to afford epoxides (S,S)-10a, (S,R)-10b, (S,S)-11a and
(S,R)-11b (Scheme 8). As in the previous synthesis se-
Scheme 6. Synthesis of epoxides 10 and 11 from allylic amine 6.
Scheme 8. Synthesis of epoxides 10 and 11 from allylic carbamate ent-6.
the preliminary stereochemical assignment, both epimers
(R,R)-10a and (R,S)-10b were converted separately into the
corresponding oxazolidinones 12 and 13, respectively, by
being heated in isopropanol with dibenzylamine; the crude
reaction mixture obtained was then treated with sodium hy-
dride in THF (Scheme 7).
quence, it was observed that when the bulkier Boc protect-
ing group was used, yields for the epoxidation were consis-
tently 10–30% lower than with the Cbz derivatives.
We then explored different reaction conditions for the ep-
oxide ring opening with m-iodobenzylamine using epoxide
(R,R)-11a as substrate. Bonnet-Delpon and co-workers have
recently shown that the ring opening of related fluorinated
aminoepoxides with nitrogen nucleophiles takes place with
excellent regiocontrol.[27] In our system, best yields were ob-
tained when the epoxide was refluxed in isopropanol to
afford the amino alcohol (2R,3S)-14a in excellent yield
(93%); this completed the ethanolamine core of the target
compound (Scheme 9). The other three Boc-protected dia-
stereoisomers were also treated under the same conditions
Scheme 7. Synthesis of oxazolidinones 12 and 13 for the stereochemical
assignment of epoxides 10. Key 1H–19F contacts extracted from HOESY
experiments are shown with the arrows.
The configurations of the resulting oxazolidinones were
determined according to the (1H–19F) contacts observed in
HOESY experiments. Oxazolidinone 12 showed a spatial
proximity between the CF2 group and H-5; this indicates
that the stereochemistry should be 4R,5S. At the same time,
Scheme 9. Epoxide ring-opening reaction of 10–11 to yield ethanolamines
14–15.
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S. Fustero et al.
to afford ethanolamines (2R,3R)-14b, (2S,3S)-14b and
(2S,3R)-14a in good yields. When the same conditions were
applied to Cbz-protected aminoepoxides 10, we were able to
prepare the four possible epoxide-opening isomers 15 in 64–
75% yield.
A small library of ethanolamines, in which variations fo-
cused on the nature of the nitrogen nucleophile, was pre-
pared by using the same protocol (Table 1).[28] The modifica-
tion of the halogen on the meta position of the benzylamine
or the introduction of an electron donating substituent
(entry 5) did not have a noticeable impact on the reaction
yield. Other types of amine that cleanly provide the desired
protected aminoalcohols are listed in Table 1 and include
heterocyclic ones (entries 6, 7, 10 and 11) and one example
of an aliphatic amine (entry 14).
With aminoalcohols 14 and 15 in hand, only the deprotec-
tion of the secondary amine and subsequent coupling with
5-methylisophthalic acid derivative 27[29] was required in
order to complete the synthesis of our BACE1 inhibitor ana-
logues. This two-step sequence proved to be troublesome.
Although it was not possible to obtain the unprotected ami-
noalcohols from Cbz derivatives 15, the acid-mediated de-
protection of Boc-intermediates 14 proceeded smoothly to
yield the corresponding trifluoroacetates. These were cou-
pled directly with 27 in the presence of EDCI and HOBt to
afford all the four possible stereoisomeric aminoalcohols in
moderate yields (26–53%, 2 steps; Scheme 10).[30]
In order to have a direct correlation in the BACE1 inhibi-
tory assays of our synthesized compounds, it was of interest
to have the Elan/Pfizer compound 1 in hand. Thus, we em-
barked on the synthesis of reference compound 1 and non-
fluorinated derivative 29. This would allow a more
detailed fluorine-focused structure–activity relation-
ship (SAR) study of this chemical series. The prepa-
ration of 1 and 29 was accomplished following an
alternative synthesis sequence, which started from
Table 1. Epoxide-opening reaction to yield ethanolamine-type products 16–26.
Entry
Epoxide
PG[a]
Amine
Compound
Yield
[%]
commercially available l-phenylalanine derivatives
30 and 31.
As shown in Scheme 11, the synthesis began with
1
2
3
4
5
G
Cbz
Cbz
Cbz
Cbz
Cbz
G
76
the preparation of methyl ketones 32 and 33
through the corresponding Weinreb amides in ex-
cellent yield (91–99%, 2 steps). According to our
strategy, these methyl ketones would then be a-bro-
minated prior to carbonyl reduction and base-medi-
ated epoxide formation. Disappointingly, methyl
ketone 33 could not be cleanly halogenated under a
range of conditions (NBS, NBS/KHSO4·SiO2, Br2/
AcOH). This problem could be circumvented by
performing the bromination on the silyl enol ether
(generated upon treatment of 33 with LiHMDS and
TMSCl).[31] The resulting bromoketone was directly
submitted to reductive conditions (NaBH4 in
EtOH)[32] to yield alcohol 35 almost exclusively
(95:5 d.r.) in acceptable yields (48%, 3 steps). The
bis-fluorinated bromohydrin 34 was obtained by fol-
lowing an identical three-step sequence in 58%
yield (95:5 d.r.). The stereochemical elucidation of
the reduction products was possible by comparing
61
74
60
84
6
7
Cbz
Cbz
83
65
8
9
Boc
Boc
75
65
1
the H NMR spectra and optical rotation data of 35
10
11
Boc
Boc
65
69
to that reported for the same compound by Rad-
datz et al.[32] The epoxides 36 and 37 were obtained
quantitatively upon treatment of the corresponding
bromohydrin precursors with potassium hydroxide
in ethanol. These intermediates were further elabo-
12
Boc
58
rated to our target compounds
1
and 29
(Scheme 12) following our developed epoxide
opening-amide formation strategy (vide supra).
13
14
15
G
Boc
Cbz
Cbz
G
21
81
65
BACE1 assays: Both the enzymatic and cellular ac-
tivity of our pair of difluorobenzyl analogues
(2R,3R)-28b and (2S,3S)-28b was evaluated
(Table 2). Our most potent analogue (2R,3R)-28b
[a] PG: protecting group.
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Fluorinated Ethanolamines
FULL PAPER
Docking studies were used to
understand how our HEA in-
hibitors bind and helped to ra-
tionalize the decreased activity
compared to the Elan/Pfizer
compound 1. The flexibility of
the BACE1 active site and es-
pecially the flexible active-site
flap often results in different
protein conformations depen-
AHCTUNGTERGdNNUN ing on the small molecule in-
hibitor.[33,34] Docking perfor-
mance and ranking for specific
chemotypes has been shown to
Scheme 10. Preparation of full-length analogues of Elan/Pfizer compound 1.
Scheme 12. Completion of the synthesis of reference compounds 1 and
29.
Scheme 11. Synthesis of epoxides 36 and 37 starting from carboxylic acids
30 and 31.
Table 2. Enzyme and cell activity of BACE1 inhibitors.
Entry
Assay (pIC50)
G
29
G
1
displayed nanomolar activity in the BACE1 enzymatic assay
(pIC50 =7.21) and caused notable reduction in the levels of
Abtotal and Ab42 produced in the cellular assay (pIC50 =
6.1). In accordance with the observation by Maillard et al.,[9]
the R configuration of the hydroxyl is important for BACE1
inhibition. Although the analogue that keeps the absolute
stereochemistry of the Elan/Pfizer lead compound, (2R,3R)-
28b, displayed nanomolar activity in the enzymatic assay
(IC50 =60.6ꢀ3.7 nm), its enantiomer (2S,3S)-28b was tenfold
less active. Interestingly, the potency of our analogues in the
cellular assay was comparable to the enzymatic assay; this
indicates that the difluorobenzyl moiety does not have a
detrimental effect on the cellular permeability of the sub-
strates. Direct comparison of our most potent analogue
(2R,3R)-28b with the non-fluorinated counterpart 29
showed a tenfold decrease in activity in both assays.
1
2
3
BACE1 enzymatic
cellular-human hAb42
cellular-human hAbTOT
8.43
7.51
7.49
8.63
7.54
7.52
be dependent on the protein structure used.[35] In essence,
docking molecules into a crystal structure solved with an in-
hibitor from a different chemical series presents difficulties
because most docking protocols are unable to predict the re-
quired enzyme flexibility. However, we can be relatively cer-
tain about the protein conformation due to the availability
of the X-ray structure for substrate 1 (PDB ID: 2IQG).
Molecule (2R,3R)-28b was docked into the BACE1 pro-
tein by using the GOLD[36] software according to the ap-
proach described in the Experimental Section. The docking
protocol was shown to reproduce the crystal structure bind-
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S. Fustero et al.
ing mode of five different BACE1–inhibitor complexes with
high accuracy. The best ranked binding pose for (2R,3R)-
28b is shown in Figure 3. Molecule (2R,3R)-28b shares the
Gln73 as previously described by Maillard et al.[9] Docking
of (2S,3S)-28b was also performed and resulted in a plausi-
ble binding pose (see the Supporting Information) in which
the change in configuration, particularly of the alcohol
carbon, resulted in the loss of interaction between the
ligand and Asp32; this likely contributes to the lower activi-
ty of this epimer.
The high potency of molecule (2R,3R)-28b suggests that
it has predominantly favorable interactions with the protein,
however, it is somewhat less active than 1. Examining the
binding mode in detail provides a possible explanation for
the lower potency. The difluoromethylene faces Asp32, and
the fluorine and carboxylate oxygen are as close as 2.7 ꢇ
(Figure 3b). The close proximity of these two electronega-
tive atoms is likely to have a slightly unfavorable contribu-
tion to the affinity of (2R,3R)-28b compared to 1.
Antimicrobial assays: Microorganisms including Gram posi-
tive and negative bacteria, as well as fungi, were tested by
using a disk diffusion susceptibility test, which is a semi-
quantitative method that allows for the determination of the
inhibition zone of microbial growth produced by each anti-
microbial agent tested. Mycobacterium is a genus known for
several of its pathogens (M. tuberculosis, M. leprae, and
M. ulcerans). These organisms are difficult to treat due to
their resistance to conventional drugs caused by the unusual
features of their cell walls. Therefore, in vitro evaluation of
the new fluorinated hydroxyethylamine backboned deriva-
tives was extended to other species of Mycobacterium and
Nocardia, a genus of bacteria closely related to Mycobacteri-
um. Ethambutol (2) was used as a positive control in the
susceptibility experiments. In addition, the ethambutol ana-
logue, SQ-109 (developed by Sequella, Inc.), a new drug
candidate with promising preliminary results, was also in-
cluded.[37] We initiated the studies with our full-length HEA
isosteres (2R,3R)-28b, (2S,3S)-28b. The results are shown in
Table 3, and are expressed as the diameter of growth inhibi-
tion around the disk impregnated with the compound
tested.
Figure 3. The docked binding mode of (2R,3R)-28b in the BACE1 pro-
tein active site. a) Negative (red) region of the electrostatic surface in-
cludes the catalytic aspartates, and in the foreground the active-site flap
is closed on top of the bound ligand. b) The interaction between CF2,
aminoalcohol and the catalytic aspartates with interatomic distances
in ꢇ.
Since the antimicrobial activity of our analogues was neg-
ligible, we decided to extend the screening to a series of in-
termediates of our synthesis route. The allylamine and epox-
ide-type intermediates studied (6 and (R,S)-10b, respective-
ly) did not show any evidence of growth inhibition, whereas
same binding mode as the crystal structure of the Elan/
Pfizer BACE1 inhibitor 1. Overall, the good performance of
the docking protocol on the validation set and the close
agreement between the docked pose for (2R,3R)-28b and
the X-ray structure of 1 provide high confidence in
the docking solution. The inhibitor binds at the
active site and forms the expected interaction with
the catalytic aspartates and the flexible flap (resi-
dues 69 to 76) in its closed conformation. The nega-
tive electrostatic charge on the surface of the bind-
ing site resulting from the aspartate amino acids
can be seen in Figure 3a. The alcohol of (2R,3R)-
28b forms a hydrogen bond with Asp32 while the
protonated amine makes hydrogen bonds with
Asp228. Further hydrogen bonds exist between the
N-terminal amide and the backbone NH of Thr232,
Table 3. Results of the disk diffusion susceptibility test (100 mg per disk) for com-
pounds (2R,3R)-28b, (2S,3S)-28b, 1, 29, EMB and SQ-109.
Product
N. far.[a]
N. asteroides M. kan.[b] M. kan.[b]
M. smeg.[c]
ATCC 3318 720
262
ATCC 35775 ATCC 19420
A
0
0
d.g.[e]
d.g.[e]
0
14
18
>55
54
11
0
17
24
50
55
0
0
9
E
14
15
16
0
1
29
EMB
SQ-109
d.g.[e]
11
19
27
15
n.a.[d]
40
n.a.[d]
[a] Nocardia farcinica. [b] Mycobacterium kansasii .[c] Mycobacterium smegmatis.
as well as the second amide carbonyl oxygen and [d] Not available. [e] Decreased growth around disk.
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Fluorinated Ethanolamines
FULL PAPER
the hydroxyethylamine backboned derivative (2R,3R)-15b
presented selective antimicrobial activity against some of
the microorganisms tested.[38] In particular, this compound
inhibited the growth of Mycobacterium smegmatis and Mi-
crococcus luteus, but not other Gram positive bacteria, such
as Staphylococcus aureus, or Gram negative bacteria, such
as Escherichia coli, or fungi, like Candida albicans. This se-
lectivity is interesting because it suggests a specific mecha-
nism of action on particular tar-
for antimicrobial activity was (2R,3R)-15b. Other analogues
were less active or even completely inactive.
A quantitative and more sensitive method was subse-
quently used to evaluate the in vitro activities of the best
candidates. Therefore, the determination of minimal inhibi-
tory concentration (MIC) by broth microdilution for all four
diastereoisomers (2R,3S)-15a, (2R,3R)-15b, (2S,3R)-15a,
(2S,3S)-15b, EMB and SQ-109 was carried out (Table 5).
gets of some species, as op-
Table 5. Minimal inhibitory concentration (MIC)[a] for compounds 15, EMB and SQ-109, determined by broth
microdilution.
posed to a nonspecific and gen-
eralized mechanism or toxicity
(Table 4).
Microorganism
(R,S)-15a
E
E
(S,S)-15b
EMB
SQ-109
M. kansasii T
M. kansasii ATCC 35775
M. kansasii P
N. farcinica 3318
N. farcinica 1
N. nova 1276
>256
32
128
32
16
16
16
8
>256
32
128
32
32
16
16
8
1
0.5
0.25
64
32
64
16
2
n.d.
8
8
2
The interesting results ob-
tained in the initial screening
prompted the study of other
structurally related molecules.
Therefore, the small library of
derivatives depicted in Table 1
was tested in order to study the
SAR. All the diastereoisomers
32
32
32
8
64
32
32
8
N. asteroides 1260
N. otitidiscaviarum S4953C
N. nova 10
16
256
32
8
32
8
16
64
64
256
8
128
128
128
128
8
4
4
8
16
16
8
N. asteroides 720
16
8
of compound 15, as well as mol- [a] MIC expressed in mgmLꢁ1. The lower MIC was displayed when there was a variation in the measured MIC
ecules with modifications in
values; n.d.: not determined.
Table 4. Results of the disk diffusion susceptibility test (50 mg per disk)
for compound (2R,3R)-15b.
It is interesting that the MICs for EMB (2) against
M. kansasii are considerably lower than those of the new
compounds 15 and even better than SQ-109. However, 2
was relatively inactive against Nocardia. Fluorinated etha-
nolamine compounds, especially (2R,3R)-15b and (2S,3S)-
15b, were more active against Nocardia than 2, with MICs
similar to that of SQ-109.
Entry
Microorganism
Zone
[mm]
1
2
3
4
5
6
7
8
9
10
11
12
13
Staphylococcus aureus (G+)
Escherichia coli (Gꢁ)
0
0
0
12
10
11
12
8
0
15
8
0
0
Candida albicans (Hongo)
Micrococcus luteus (G+)
Mycobacterium smegmatis 19420
Mycobacterium kansasii 262
Mycobacterium kansasii ATCC 35775
Mycobacterium marinum LCA-13
Mycobacterium avium complex (P)
Nocardia asteroides 720
Conclusion
In conclusion, the utilization of chiral sulfinyl imines as syn-
thesis intermediates, obtained by treatment of hemiaminal
precursors with two equivalents of vinylmagnesium bromide,
allowed for the preparation of enantiomerically enriched a-
fluorinated allylic amines with good diastereoselectivities
and yields. The subsequent oxidation of the allylic amines to
the corresponding epoxides, under treatment with in situ
generated methyl(trifluoromethyl)dioxirane, followed by ep-
oxide ring opening, provided a new family of fluorinated hy-
droxyethylamine-derived peptidomimetics with a phenyldi-
fluoromethyl moiety, a fluorinated isostere of phenylalanine.
The biological evaluation of these derivatives revealed a re-
markable BACE1 inhibitory activity but lower than the non-
fluorinated counterpart. Docking studies showed the fluo-
rine atoms to be in close proximity to an oxygen from
Asp32, which might account for this difference in potency.
Furthermore, the biological evaluation of our final products
and synthesis intermediates led to the discovery of com-
pounds with antimicrobial activity against Mycobacterium
and Nocardia species. Efforts directed towards the prepara-
tion of additional fluorinated analogues of protease inhibi-
Nocardia farcinica ATCC 3318
BCG Tice
Rhodococcus equi
other functional groups, were included in the study. Disk dif-
fusion susceptibility testing revealed that all four diastereo-
isomers were active against several Mycobacteria and Nocar-
dia species, especially N. asteroides 720, (2R,3R)-15b being
slightly better than the other three (see the Supporting In-
formation). Introduction of structural variability on the orig-
inal skeleton of 15 (compounds (2R,3S)-14a, (2R,3R)-14b,
(2S,3R)-14a, (2S,3S)-14b, 25a and 26b) gave products that
were inactive; this indicates that both the Cbz group and
iodine atom on the aromatic ring are important for the bio-
logical activity. Preparation and testing of other derivatives
with different aromatic substitutions on the amine (16a,
16b, 17a, 17b, 18b, 19b, 20b, 21a, 21b, 22a, 22b, 23b and
24b) confirmed that the most favorable combination tested
Chem. Eur. J. 2011, 17, 14772 – 14784
ꢆ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14779

S. Fustero et al.
measured. Abtotal and Ab42 were measured by sandwich AlphaLISA.
The AlphaLISA is a sandwich assay that requires biotinylated antibody
AbN/25 attached to streptavidin coated beads and antibody Ab4G8 or
cAb42/26 conjugated acceptor beads for the detection of Abtotal and
Ab42, respectively. In the presence of Abtotal or Ab42, the beads come
into close proximity. The excitation of the donor beads provokes the re-
lease of singlet oxygen molecules that triggers a cascade of energy trans-
fer in the acceptor beads, resulting in light emission. Light emission was
measured after 1 h incubation (excitation at 650 nm and emission at
615 nm). A best-fit curve was generated by a minimum sum of squares
method to the plot of %Controlmin versus compound concentration.
From this an IC50 value (inhibitory concentration causing 50% inhibition
of activity) was obtained.
tors bearing this moiety are currently underway in our labo-
ratories.
Experimental Section
General antimicrobial assays
Disk diffusion method: Compounds were screened for their in vitro anti-
microbial activities against several microorganisms (S. aureus
ATCC 29213 or ATCC 33591, E. coli ATCC 25922, M. luteus
ATCC 49732, M. smegmatis ATCC 19420, and C. albicans ATCC 14053)
by using frozen cell suspensions (0.5 McFarland units) in Mueller–Hinton
broth (BBL, BD, Sparks, MD, USA) with glycerol (20%). After being
thawed and mixed, a cotton-tipped swab was used to make a lawn of the
suspensions on Mueller–Hinton agar plates (BBL, BD, Sparks, MD,
USA). Solutions of the compounds in DMSO were spotted on blank
paper discs (6 mm; BBL, BD, Sparks, MD, USA) then placed on the agar
surface. The plates were incubated at 378C in ambient air, overnight,
prior to analysis of the zone of inhibition. Similar methodology was used
for the evaluation of activities against M. kansasii, N. asteroides, and
N. farcinica except that the suspension was at 3 McFarland units for
M. kansasii and 1 McFarland unit for the Nocardia sp. In addition, the
media used for M. kansasii was Middlebrook and Cohn 7H10 agar (BBL,
BD, Sparks, MD, USA). The plates were incubated at 378C in ambient
air for 7 days (M. kansasii) or 48–72 h (Nocardia sp.) prior to analysis of
the zone of inhibition.
Synthesis
N-[(1RS)-1-Ethoxy-2-phenyl-2,2-difluoroethyl]-(R)-tert-butylsulfinamide
(5): A solution of DMSO (19.6 mmol) in anhydrous CH2Cl2 (6 mL) was
added to a cooled (ꢁ608C) solution of oxalyl chloride (9.4 mmol) in
CH2Cl2 (6 mL). The mixture was stirred at the same temperature for a
few minutes, followed by dropwise addition of 2,2-difluoro-2-phenyletha-
nol (1.11 g, 7.8 mmol) in CH2Cl2 (20 mL). After the mixture was stirred
for 15 min, a solution of triethylamine (39.3 mmol) in CH2Cl2 (6 mL) was
added and stirring was continued for 5 min. The mixture was then al-
lowed to warm slowly to room temperature over 2 h. Then, ethanol
(15 mL) was added and stirring was continued for 3 h. The resulting mix-
ture was concentrated to afford a solid residue, which was suspended into
ethyl ether and filtered. The filtrate was evaporated under vacuum to
obtain a yellowish oil, which was used directly in the following step. 1-
Ethoxy-2,2-difluoro-2-phenylethanol (202 mg, 1.0 mmol), (R)-tert-butyl-
sulfinamide (1.0 mmol) and titanium tetra-ethoxide (5.0 mmol) were
added to a sealed tube. The resulting mixture was allowed to react at
708C, overnight. Then, the solution was diluted with ethyl acetate (5 mL)
and treated with water. The two phases were separated and the organic
extracts were washed with brine and dried over anhydrous Na2SO4. After
solvent evaporation under vacuum the 1H NMR spectra of the oily resi-
due indicated the presence of two diastereoisomers in a 3:1 relationship
(161 mg, 53% for the two steps). An analytical sample was purified by
chromatography with hexanes/ethyl acetate (2:1) as eluent. Major
isomer: yellow solid, m.p. 52–548C (CH2Cl2); ½aꢂ2D5 =ꢁ59.14 (c=1.0,
Broth microdilution method: Polystyrene 96-well round bottom plates
(Corning, Inc., Corning, NY, USA) were prepared with modified 7H10
broth (50 mL per well). The drugs were prepared at four times the maxi-
mum concentration tested in the first well, and then serially diluted two-
fold. To prepare the bacterial isolates the frozen cultures were thawed
and diluted to a final concentration of 1.25ꢈ105 CFU per mL (working
stock) in modified 7H10 broth (7H10 agar formulation with agar and
malachite green omitted). The actual inoculums were measured by titra-
tion and plating on 7H10 agar with OADC (10%). The agar plates were
incubated for 4 weeks in ambient air at 378C. Working stock (50 mL) was
added to each well. The microtiter plates were covered with SealPlate ad-
hesive sealing film (Excel Scientific, Wrightwood, CA, USA) and incu-
bated at 378C in ambient air for 18–21 days prior to analysis. The MIC
was defined as the lowest concentration of antimycobacterial agent yield-
ing no visible turbidity. Each isolate was tested in duplicate.
1
CHCl3); H NMR (CDCl3, 300 MHz): d=1.15 (t, J=6.9 Hz, 3H), 1.18 (s,
9H), 3.52 (dq, J=9.3, 6.9 Hz, 1H), 3.54 (d, J=10.2 Hz, 1H), 3.96 (dq, J=
9.3, 6.9 Hz, 1H), 4.72 (ddd, J=10.2, 8.5, 4.2 Hz, 1H), 7.40–7.44 (m, 3H),
7.49–7.50 ppm (m, 2H); 13C NMR (CDCl3, 75 MHz): d=14.6, 22.4, 56.8,
65.0, 89.1 (dd, JCF =35.2 Hz, JCF =32.5 Hz), 118.7 (t, JCF =248.4 Hz), 126.3
General BACE1 assays
(t,
J
CF =6.2 Hz), 128.0, 130.2, 133.1 ppm (t,
J
CF =25.4 Hz); 19F NMR
HF =8.5 Hz, 1F),
Enzymatic assay: BACE1 was assayed fluorimetrically on Monaco Safas
spectrofluorometer flx. The wavelength for excitation was 328 nm and
for emission 400 nm. The reactions were followed at 258C over 20 min.
A human recombinant BACE1 (Enzo Life Sciences, Lçrrach, Germany)
stock solution (500 mgmLꢁ1) was diluted 1:10 with assay buffer (20 mm
sodium acetate pH 4.5, 0.1% CHAPS, 0.1% Top Block). Inhibitor stock
solutions were prepared with DMSO. A stock solution (1 mm) of the sub-
(CDCl3, 282 MHz): d=ꢁ111.3 (dd,
J
FF =249.0 Hz,
J
ꢁ104.2 ppm (dd, JFF =249.0, JHF =4.2 Hz, 1F); HRMS (FAB) calcd for
C14H22F2NO2S [M+H+]: 306.1339, found: 306.1349. Minor isomer: yellow
solid; m.p. 45–478C (CH2Cl2); ½aꢂ2D5 =ꢁ12.05 (c=1.0, CHCl3), ꢁ12.05 (c=
1.0; CHCl3); 1H NMR (CDCl3, 300 MHz): d=1.09 (t, J=6.9 Hz, 3H),
1.23 (s, 9H), 3.40 (dq, J=9.3, 6.9 Hz, 1H), 3.76 (dq, J=9.3, 6.9 Hz, 1H),
4.05 (d, J=9.3 Hz, 1H), 4.77 (ddd, J=10.4, 9.3, 3.1 Hz, 1H), 7.42–7.44
(m, 3H), 7.55–7.57 ppm (m, 2H); 13C NMR (CDCl3, 75.5 MHz): d=14.6,
strate
Mca-Ser-Glu-Val-Asn-Leu-Asp-Ala-Glu-Phe-LysACTHNGUTERNNU(G Dnp)-OH
(Bachem, Bubendorf, Switzerland) was diluted 1:10 with DMSO (50%)
and 1:3 with ammonium acetate buffer (10 mm, pH 7.4). The final con-
centration of DMSO was 2.4%, and the final concentration of the sub-
strate was 2.5 mm. Assays were performed with a final concentration of
0.5 mgmLꢁ1 of BACE1. Assay buffer (905 mL), inhibitor solution and
DMSO in a total volume of 10 mL and BACE1 solution (10 mL) were
added to a cuvette, thoroughly mixed and incubated for 1 h at 258C. The
reaction was initiated by adding the substrate (75 mL). Experiments were
performed in duplicate with five different inhibitor concentrations. IC50
values were obtained from nonlinear regression according to the equa-
tion: v=v0/(1+[I]/IC50).
22.5, 57.1, 64.9, 87.7 (dd, JCF =36.7 Hz, JCF =32.2 Hz), 118.6 (t, JCF
=
249.2 Hz), 126.5 (t,
JCF =6.4 Hz), 128.1, 130.2, 133.0 ppm (t, JCF
=
25.4 Hz); 19F NMR (CDCl3, 282.4 MHz): d=ꢁ113.0 (dd, JFF =251.9 Hz,
J
HF =10.4 Hz, 1F), ꢁ103.0 ppm (dd, JFF =249.0, JHF =3.1 Hz, 1F); HRMS
(FAB) calcd for C14H22F2NO2S [M+H+]: 306.1339, found: 306.1335.
N-[(1RS)-1-Ethoxy-2-phenyl-2,2-difluoroethyl]-(S)-tert-butylsulfinamide
(ent-5): When using (S)-tert-butylsulfinamide, similar results were ob-
tained. The alcohol (1.9 g) was converted to a mixture of both hemiami-
nals, which upon chromatography gave 1.0 g (27%) of the major isomer;
½aꢂ2D5 =+71.07 (c=1.0, CHCl3); and 351 mg (10%) of the minor isomer:
½aꢂ2D5 =+16.85 (c=1.0, CHCl3).
Cellular AlphaLISA assay in SKNBE2 cells: In two AlphaLISA assays
the levels of Abtotal and Ab42 produced and secreted into the medium
of human neuroblastoma SKNBE2 cells are quantified. The assay is
based on the human neuroblastoma SKNBE2 expressing the wild-type
Amyloid precursor protein (hAPP695). The compounds were diluted and
added to these cells, incubated for 18 h and then Ab42 and Abtotal were
(R)-tert-Butylsulfinyl-[(1R)-1-(phenyldifluoromethyl)allyl]amine
(6):
Vinyl magnesium bromide solution in toluene (1m; 21.7 mL) was added
to a solution of both hemiaminals (5) (2.66 g, 8.7 mmol) in CH2CH2
(95 mL) at ꢁ608C. The mixture was allowed to warm slowly while being
stirred until ꢁ258C was reached, at which point disappearance of the
14780
www.chemeurj.org
ꢆ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14772 – 14784

Fluorinated Ethanolamines
FULL PAPER
starting material was observed. The mixture was treated with aqueous
ammonium chloride and extracted with CH2CH2. The combined organic
extracts were washed with brine and dried over anhydrous Na2SO4. After
solvent evaporation under vacuum the residue was subjected to chroma-
tography with hexanes/ethyl acetate (4:1) as eluent to give the allylamine
6 as a yellowish oil (2.2 g, 85%) as a mixture of diastereomers 20:1 as in-
dicated by 1H and 19F NMR spectroscopy; ½aꢂ2D5 =ꢁ101.49 (c=1.0,
Benzyloxycarbonyl-[(1S)-1-(phenyldifluoromethyl)allyl]amine
(ent-8):
Allylamine ent-6 (1.3 g) afforded N-Cbz-allylamine ent-8 (970 mg, 68%);
½aꢂ2D5 =ꢁ9.18 (c=1.0, CHCl3).
(R)-tert-Butyl 1,1-difluoro-1-phenylbut-3-en-2-ylcarbamate (9): HCl (4m)
in dioxane (8.7 mL) was added to a solution of allylamine 6 (1.00 g,
3.5 mmol) in anhydrous methanol (21.6 mL) and the resulting mixture
was stirred for 2 h. Then, the solvent was evaporated under vacuum and
the white residue was suspended into dioxane (21.6 mL). This solution
was treated successively with K2CO3 (10.4 mmol), di-tert-butyl dicarbon-
ate (3.5 mmol) and a catalytic amount of DMAP (0.1 mmol). After being
stirred at room temperature for 52 h the mixture was treated with brine
to separate the phases. The aqueous layer was extracted with ethyl ace-
tate and the combined organic phases were washed with brine and dried
over anhydrous Na2SO4. After the solvent was evaporated under reduced
pressure, the oily residue was subjected to chromatography with hexanes/
diethyl ether (7:1) as eluent to afford the allyl amine 9 as a white solid
(805 mg, 82%); m.p. 49–518C (CH2Cl2); ½aꢂ2D5 =+23.67 (c=1.0, CHCl3);
1H NMR (300 MHz, CDCl3): d=1.37 (s, 9H), 4.80–4.85 (m, 1H), 4.82
(brs, 1H), 5.28 (d, J=9.3 Hz, 1H), 5.29 (d, J=18.0 Hz, 1H), 5.80–5.89
(m, 1H), 7.40–7.43 (m, 3H), 7.47–7.50 ppm (m, 2H); 13C NMR
(75.5 MHz, CDCl3): d=27.3, 57.8 (t, JCF =28.1 Hz), 85.1, 118.8, 120.9 (t,
1
CHCl3); H NMR (CDCl3, 300 MHz): d=1.19 (s, 9H), 3.57 (d, J=3.0 Hz,
1H), 4.27–4.38 (m, 1H), 5.32 (d, J=16.8 Hz, 1H), 5.36 (d, J=9.9 Hz,
1H), 5.62 (ddd, J=16.8, 9.9, 7.7 Hz, 1H), 7.40, 7.47 ppm (m, 5H);
13C NMR (CDCl3, 75.5 MHz): d=22.4, 56.0, 63.4 (t, JCF =28.9 Hz), 120.9
(t, JCF =249.5 Hz), 122.9, 126.1 (t, JCF =6.3 Hz), 128.3, 130.3 (t, JCF
=
4.0 Hz), 130.4 (t, JCF =1.7 Hz), 133.7 ppm (t, JCF =26.4 Hz); 19F NMR
(CDCl3, 282.4 MHz): d=ꢁ107.3 (dd, JFF =244.3 Hz, JHF =13.0 Hz, 1F),
ꢁ103.4 ppm (dd, JFF =244.3 Hz, JHF =7.9 Hz, 1F); HRMS (FAB) calcd
for C14H20F2NOS [M+H+]: 288.1234, found: 288.1235.
(S)-tert-Butylsulfinyl-[(1S)-1-(phenyldifluoromethyl)allyl]amine (ent-6):
When using a mixture of hemiaminals ent-5 (1.35 g), allylamine ent-6
(1.05 g, 85%) were obtained after chromatography; ½aꢂ2D5 =+105.20 (c=
1.0, CHCl3).
N-(4-Bromophenyl)sulfonyl-[(1R)-1-(phenyldifluoromethyl)allyl]amine
(7): HCl (4m) in dioxane (0.87 mL) was added to a solution of allylamine
6 (100 mg, 0.3 mmol) in anhydrous methanol (2.2 mL), and the resulting
mixture was stirred for 2 h. Then, the solvent was evaporated under
vacuum and the white residue was suspended into dioxane (2.2 mL). This
solution was treated successively with K2CO3 (1.0 mmol), (4-bromophe-
nyl)sulfonyl chloride (1.7 mmol) and a catalytic amount of 4-dimethyl-
J
CF =249.4 Hz), 125.7 (t, JCF =6.2 Hz), 128, 130.0, 130.9 (t, JCF =2.9 Hz),
134.4 (t, JCF =25.7 Hz), 146.7 ppm; 19F NMR (CDCl3, 282.4 MHz): d=
ꢁ106.5 (dd, JFF =251.6 Hz, JHF =10.4 Hz, 1F), ꢁ105.3 ppm (dd, JFF
=
251.6 Hz, JHF =11.3 Hz, 1F); HRMS (ESI+) calcd for C15H19F2NNaO2
[M+Na+]: 306.1282, found: 306.1284.
(S)-tert-Butyl 1,1-difluoro-1-phenylbut-3-en-2-ylcarbamate (ent-9): Allyl-
amine ent-6 (1.7 g) afforded N-Boc-allylamine ent-9 (430 mg, 41%);
½aꢂ2D5 =ꢁ20.78 (c=1.0, CHCl3).
ACHTUNGTRENNUNGaminopyridine (DMAP; 0.05 mmol). After being stirred at room temper-
ature for 18 h the mixture was treated with brine and the phases were
separated. The aqueous layer was extracted with ethyl acetate and the
combined organic phases were washed with brine and dried over anhy-
drous Na2SO4. After the solvent was evaporated under reduced pressure,
the oily residue was subjected to chromatography with hexanes/ethyl
ether (6:1) as eluent to afford the allylic amine 7 as a white solid (92 mg,
66%); m.p. 94–968C (CH2Cl2); ½aꢂ2D5 =+4.12 (c=1.0, CHCl3); 1H NMR
(300 MHz, CDCl3): d=4.47 (tddt, J=11.6, 9.6, 6.0, 2.1 Hz, 1H), 5.13 (d,
J=9.6 Hz, 2H), 5.24 (d, J=18.0 Hz, 1H), 5.25 (d, J=10.2 Hz, 1H), 6.75
(ddd, J=18.0, 10.2, 6.0 Hz, 1H), 7.40–7.43 (m, 3H), 7.47–7.50 ppm (m,
2H); 13C NMR (75.5 MHz, CDCl3): d=61.4 (t, JCF =30.6 Hz), 120.2 (t,
Benzyl
[(R,R)-10a] and benzyl (R)-2,2-difluoro-1-[(S)-oxiran-2-yl]-2-phenyl-
ethylcarbamate [(R,S)-10b]: solution of allylamine (951 mg,
(R)-2,2-difluoro-1-[(R)-oxiran-2-yl]-2-phenylethylcarbamate
G
A
8
3.0 mmol) in acetonitrile (26 mL) was treated with an aqueous solution
of Na2EDTA·2H2O (13 mL; 4ꢈ10ꢁ4 m). The solution was cooled at 08C
and trifluoroacetone (1 mL) was added. Then, NaHCO3 (52.8 mmol) and
oxone (17.0 mmol) were added successively. After 3 h of continued stir-
ring the solution was filtered. The filtrate was extracted with CH2Cl2,
washed with brine and dried over anhydrous Na2SO4. After the solvent
was eliminated under vacuum, the residue was subjected to chromatogra-
phy with hexanes/diethyl ether in a gradient of polarity (10:1–6:1) to
afford 441 mg (44%) of 10a and 308 mg (31%) of 10b. Isomer (R,R)-
10a: white solid, m.p. 68–708C (CH2Cl2); ½aꢂ2D5 =+4.38 (c=1.0, CHCl3);
1H NMR (CDCl3, 300 MHz): d=2.36 (dd, J=4.5, 2.4 Hz, 1H), 2.61 (t,
J=4.5 Hz, 1H), 3.18–3.22 (m, 1H), 4.52 (td, J=12.0, 9 Hz, 1H), 4.97 (d,
J=9.0 Hz, 1H), 5.03 (s, 2H), 7.24–7.54 ppm (m, 10H); 13C NMR (CDCl3,
75.5 MHz): d=42.5, 48.0 (t, JCF =3.6 Hz), 55.0 (t, JCF =29.3 Hz), 67.3,
121.1 (t, JCF =249.2 Hz), 125.6 (t, JCF =6.4 Hz), 127.9, 128.2, 128.5, 128.5,
J
J
CF =249.4 Hz), 120.6, 125.7 (JCF =6.2 Hz), 127.5, 128.4, 128.4, 130.1 (t,
CF =2.9 Hz), 130.3, 132.1, 133.5 (t, JCF =25.7 Hz), 139.6 ppm; 19F NMR
(CDCl3, 282.4 MHz): d=ꢁ104.4 ppm (d,
JHF =11.6 Hz, 2F); HRMS
ACHTUNGTRENNUNG
Benzyloxycarbonyl-[(1R)-1-(phenyldifluoromethyl)allyl]amine (8): HCl
(4m) in dioxane (1.8 mL) was added to a solution of allylamine 6
(200 mg, 0.7 mmol) in anhydrous methanol (4.5 mL) and the resulting
mixture was stirred for 2 h. Then, the solvent was evaporated under
vacuum and the white residue was suspended in dioxane (4.5 mL). This
solution was treated successively with K2CO3 (2.1 mmol), benzoyl chlo-
ride (3.5 mmol) and a catalytic amount of DMAP (0.1 mmol). After
being stirred at room temperature for 18 h the mixture was treated with
brine to separate the phases. The aqueous layer was extracted with ethyl
acetate and the combined organic phases were washed with brine and
dried over anhydrous Na2SO4. After the solvent was evaporated under
reduced pressure, the oily residue was subjected to chromatography with
hexane/ethyl ether (4:1) as eluent to afford the allylic amine 8 as a white
solid (202 mg, 91%); m.p. 64–668C (CH2Cl2); ½aꢂ2D5 =+21.14 (c=1.0,
CHCl3); 1H NMR (CDCl3, 300 MHz): d=4.83–5.00 (m, 1H), 5.08 (s,
1H), 5.08 (s, 2H), 5.29 (d, J=12.0 Hz, 1H), 5.30 (d, J=16.2 Hz, 1H),
5.84 (ddd, J=16.2, 10.2, 5.4 Hz, 1H), 7.30–7.37 (m, 5H), 7.37–7.50 ppm
(m, 5H); 13C NMR (CDCl3, 75.5 MHz): d=58.5 (t, JCF =29.3 Hz), 67.1,
119.2, 120.7 (t, JCF =258.4 Hz), 125.7 (t, JCF =6.3 Hz), 128.0, 128.2, 128.3,
130.4, 133.9 (t,
J
CF =25.9 Hz), 135.9, 156.0 ppm; 19F NMR (CDCl3,
282.4 MHz): d=ꢁ104.9 ppm (d, JHF =12.0 Hz, 2F). HRMS (EI+) calcd
for C18H17F2NO3 [M+]: 333.1177, found: 333.1182. Isomer (R,S)-10b:
white solid, m.p. 92–948C (CH2Cl2); ½aꢂ2D5 =ꢁ8.05 (c=1.0, CHCl3);
1H NMR (CDCl3, 300 MHz): d=2.65–2.76 (m, 2H), 3.11–3.16 (m, 1H),
4.27–4.37 (m, 1H), 4.98–5.15 (m, 1H), 5.06 (s, 2H), 7.26–7.56 ppm (m,
10H); 13C NMR (CDCl3, 75.5 MHz): d=43.9, 48.9 (t, JCF =3.4 Hz), 57.8
(t, JCF =29.3 Hz), 67.4, 120.9 (t, JCF =247.6 Hz), 125.4 (t, JCF =6.3 Hz),
128.0, 128.3, 128.6, 128.6, 130.6, 133.8 (t, JCF =25.9 Hz), 135.8, 155.7 ppm;
19F NMR (CDCl3, 282.4 MHz): d=ꢁ106.8 (dd,
JFF =251.7 Hz, JHF =
12.5 Hz, 1F), ꢁ104.9 ppm (d, JFF =251.7 Hz, JHF =13.4 Hz, 1F); HRMS
(EI+) calcd for C18H17F2NO3 [M+]: 333.1177, found: 333.1175.
Benzyl
(S)-2,2-difluoro-1-[(S)-oxiran-2-yl]-2-phenylethylcarbamate
[(S,S)-10a] and benzyl (S)-2,2-difluoro-1-[(R)-oxiran-2-yl]-2-phenylethyl-
carbamate [(S,R)-10b]: Allylamine ent-8 (965 mg) was converted to a
mixture of both diastereomeric epoxides, which after chromatography af-
forded isomer (S,S)-10a (307 mg, 30%); ½aꢂ2D5 =ꢁ4.98 (c=1.0, CHCl3),
and isomer (S,R)-10b (441 mg, 44%); ½aꢂ2D5 =+13.04 (c=1.0, CHCl3).
128.5, 130.2 (t,
JCF =1.4 Hz), 130.6 (t, JCF =2.6 Hz), 134.1 (t, JCF =
25.6 Hz), 136.0, 155.6 ppm; 19F NMR (CDCl3, 282.4 MHz): d=ꢁ106.9
(dd, 2JFF =247.2 Hz, JHF =12.7 Hz, 1F), ꢁ104.5 ppm (dd, JFF =247.7 Hz,
tert-Butyl
(R)-2,2-difluoro-1-[(R)-oxiran-2-yl]-2-phenylethylcarbamate
J
HF =11.9 Hz, 1F); HRMS (EI+) calcd for C18H17F2NO2 [M+]: 317.1227,
[(R,R)-11a] and tert-butyl (R)-2,2-difluoro-1-[(S)-oxiran-2-yl]-2-phenyl-
found: 317.1229.
ethylcarbamate [(R,S)-11b]:
A
solution of allylamine
9
(631 mg,
Chem. Eur. J. 2011, 17, 14772 – 14784
ꢆ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14781

S. Fustero et al.
2.23 mmol) in acetonitrile (17 mL) was treated with an aqueous solution
of Na2EDTAꢈ2H2O (8.42 mL; 4ꢈ10ꢁ4 m). The solution was cooled at
08C and trifluoroacetone (4.5 mL) was added. Then, NaHCO3
(35.6 mmol) and oxone (11.1 mmol) were added successively. After 3 h of
continued stirring the solution was filtered. The filtrate was extracted
with CH2Cl2, washed with brine and dried over anhydrous Na2SO4. After
the solvent was eliminated under vacuum, the residue was subjected to
chromatography with hexane/ethyl ether in a gradient of polarity (10:1–
6:1) to afford 187 g (28%) of (R,R)-11a, and 277 g (42%) of (R,S)-11b.
Isomer (R,R)-11a: white solid; m.p. 65–678C (CH2Cl2); ½aꢂ2D5 =+8.16 (c=
1.0, CHCl3); 1H NMR (300 MHz, CDCl3): d=1.32 (s, 9H), 2.51 (dd, J=
4.5, 2.4 Hz, 1H), 2.70 (dd, J=4.5, 4.5 Hz, 1H), 3.28–3.29 (m, 1H), 4.78
(d, J=10.2 Hz, 1H), 7.42–7.45 (m, 3H), 7.50–7.53 ppm (m, 2H);
13C NMR (75.5 MHz, CDCl3): d=28.0, 42.4, 48.0 (t, J=3.2 Hz), 54.3 (t,
J=29.1 Hz), 80.2, 121.2 (t, J=249.3 Hz), 125.6 (t, J=6.3 Hz), 128.4,
130.2, 134.2 (t, J=25.4 Hz), 155.1 ppm; 19F NMR (CDCl3, 282.4 MHz):
282.4 MHz): d=ꢁ108.2 (d, JFF =251.3 Hz, 1F), ꢁ102.3 ppm (d, JFF
=
251.3 Hz, 1F); HRMS (EI+) calcd for C25H24F2N2O2 [M+]: 422.1805,
found: 422.1817.
tert-Butyl (2R,3S)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phe-
nylbutan-2-ylcarbamate [(2R,3S)-14a]: 3-Iodobenzylamine (0.18 mmol)
was added to a solution of epoxide (R,R)-11a (48 mg, 0.16 mmol) in an-
hydrous isopropanol (1 mL) at room temperature and the resulting mix-
ture was warmed to 708C until complete consumption of epoxide was ob-
served by TLC. Then, the solvent was evaporated under vacuum and the
crude obtained was purified by chromatography with hexane/AcOEt
(2:1) as eluent to afford 74 mg of the coupling compound (2R,3S)-14a,
(87%) as colorless oil; ½aꢂ2D5 =ꢁ17.99 (c=1.0, CHCl3); 1H NMR
(300 MHz, CDCl3): d=1.34 (s, 9H), 2.58 (dd, J=12.0, 9.0 Hz, 1H), 2.67
(dd, J=12.0, 4.5 Hz, 1H), 3.65 (d, J=13.5 Hz, 1H), 3.72 (d, J=13.5 Hz,
1H), 4.01 (dd, J=9.0, 4.5 Hz, 1H), 4.06–4.16 (m, 1H), 5.28 (d, J=
10.2 Hz, 1H), 7.03 (t, J=7.5 Hz, 1H), 7.19 (d, J=7.5 Hz, 1H), 7.41–
7.62 ppm (m, 7H); 13C NMR (75.5 MHz, CDCl3): d=28.1, 51.4, 52.6, 56.5
d=ꢁ106.0 (dd, JFF =250.5 Hz, JHF =11.9 Hz, 1F), ꢁ104.4 ppm (dd, JFF
=
250.5 Hz, HF =11.6 Hz, 1F); HRMS (FAB) calcd for C15H20F2NO3
J
(t, JCF =28.2 Hz), 65.7, 79.9, 94.4, 121.8 (t, JCF =249.3 Hz), 125.6 (t, JCF
=
[M+H+]: 300.1411, found: 300.1402. Isomer (R,S)-11b: white solid; m.p.
112–1148C (CH2Cl2); ½aꢂD25 =ꢁ5.6 (c=1.0, CHCl3); 1H NMR (300 MHz,
CDCl3): d=1.35 (s, 9H), 2.67 (dd, J=4.5, 2.1 Hz, 1H), 2.73 (dd, J=4.5,
4.5 Hz, 1H), 3.10–3.20 (m, 1H), 4.85 (d, J=10.2 Hz, 1H), 7.43–7.45 (m,
3H), 7.50–7.53 ppm (m, 2H); 13C NMR (75.5 MHz, CDCl3): d=28.0,
43.8, 49.0 (t, J=3.2 Hz), 57.1 (t, J=25.6 Hz), 80.4, 121.0 (t, J=247.9 Hz),
125.5 (t, J=6.3 Hz), 128.4, 130.3, 134.1 (t, J=25.4 Hz), 154.8 ppm;
6.3 Hz), 127.2, 128.2, 130.0, 130.2, 134.8 (t, JCF =25.8 Hz), 136.2, 136.9,
142.0, 155.5 ppm; 19F NMR (CDCl3, 282.4 MHz): d=ꢁ104.3 (dd, JHF
=
14.4 Hz, 1F), ꢁ104.3 ppm (dd, JHF =13.0 Hz, 1F); HRMS (FAB) calcd
for C22H28F2IN2O3 [M+H+]: 533.1113, found: 533.1092.
tert-Butyl (2S,3R)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phe-
nylbutan-2-ylcarbamate [(2S,3R)-14a]: Following the same procedure,
epoxide (S,S)-11a (35 mg) afforded, after chromatography, 56 mg (90%)
of (2S,3R)-14a; ½aꢂ2D5 =+22.57 (c=1.0, CHCl3).
19F NMR (CDCl3, 282.4 MHz): d=ꢁ106.4 (dd,
JFF =251.6 Hz, JHF =
11.6 Hz, 1F), ꢁ104.8 ppm (dd, JFF =251.6 Hz, JHF =13.8 Hz, 1F); HRMS
tert-Butyl (2R,3R)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phe-
nylbutan-2-ylcarbamate [(2R,3R)-14b]: Epoxide (R,S)-11b (21.5 mg;
0.07 mmol) was converted to (2R,3R)-14b (35.6 mg, 93%). White solid;
m.p. 100–1028C (CH2Cl2); ½aꢂ2D5 =ꢁ10.25 (c=1.0, CHCl3); 1H NMR
(300 MHz, CDCl3): d=1.22 (brs, 1H), 1.34 (s, 9H), 2.31 (brs, 1H), 2.75–
2.84 (m, 2H), 3.69 (d, J=13.8 Hz, 1H), 3.74 (d, J=13.8 Hz, 1H), 3.89
(dd, J=9.2, 4.7 Hz, 1H), 4.32–4.49 (m, 1H), 5.46 (d, J=9.6 Hz, 1H), 7.05
(t, J=7.5 Hz, 1H), 7.26 (d, J=7.5 Hz, 1H), 7.38–7.45 (m, 3H), 7.45–7.53
(m, 2H), 7.58 (d, J=7.9 Hz, 1H), 7.65 ppm (s, 1H); 13C NMR
(75.5 MHz, CDCl3): d=28.1, 50.8, 53.1, 58.9 (t, JCF =27.2 Hz), 67.9, 80.1,
94.4, 121.6 (t, JCF =248.9 Hz), 125.4 (t, JCF =6.0 Hz), 127.3, 128.3, 130.0,
130.2, 135.0 (t, JCF =25.4 Hz), 136.1, 137.0, 142.2, 155.8 ppm; 19F NMR
(CDCl3, 282.4 MHz): d=ꢁ104.6 (dd, JFF =249.6 Hz, JHF =11.6 Hz, 1F),
ꢁ101.8 ppm (dd, JFF =249.6 Hz, JHF =16.4 Hz, 1F); HRMS (FAB) calcd
for C22H28F2IN2O3 [M+H+]: 533.1113, found: 533.1113.
(FAB) calcd for C15H20F2NO3 [M+H+]: 300.1411, found: 300.1407.
tert-Butyl
[(S,S)-11a] and tert-butyl (S)-2,2-difluoro-1-[(R)-oxiran-2-yl]-2-phenyl-
ACHTUNGTRENNUNGethylcarbamate [(S,R)-11b]: Allylamine ent-4 (325 mg) led to a mixture
(S)-2,2-difluoro-1-[(S)-oxiran-2-yl]-2-phenylethylcarbamate
of both diastereomeric epoxides, which upon chromatography afforded
35 mg (10%) of isomer (S,S)-11a; ½aꢂ2D5 =ꢁ7.32 (c=1.0, CHCl3); and
67 mg (20%) of isomer (S,R)-11b; ½aꢂ2D5 =+6.13 (c=1.0, CHCl3).
A
ACHTUNGERTN(NUNG phenyl)methyl]oxazo-
ACHTUNGTRENNUNG
containing epoxide (R,R)-10a (25 mg, 0.075 mmol) dissolved in anhy-
drous isopropanol (1 mL) at room temperature. The resulting mixture
was heated to 708C and allowed to react for 5 h. The solvent was then re-
moved under vacuum and the oily residue was subjected to chromatogra-
phy on silica gel and eluted with hexanes/AcOEt (2:1) in order to elimi-
nate the extra amine. The crude mixture was dissolved in THF (1 mL)
and treated at 08C with NaH (0.75 mmol; previously washed with hex-
anes to eliminate the mineral oil and dried, in vacuo). The resulting solu-
tion was stirred at room temperature for 12 h. After hydrolysis with
water, the organics were extracted twice with CH2Cl2, washed with brine
and dried over anhydrous Na2SO4. Evaporation of the solvent gave a res-
idue that was purified on silica gel by using hexanes/diethyl ether (10:1),
to give oxazolidinone (12) as a white solid (25.2 mg, 80%); m.p. 132–
1358C (CH2Cl2); ½aꢂ2D5 =ꢁ11.08 (c=1.0, CHCl3); 1H NMR (300 MHz,
CDCl3): d=2.60 (dd, J=14.0, 4.6 Hz, 1H), 2.72 (dd, J=14.0, 6.3 Hz,
1H), 3.57 (s, 4H), 3.72 (td, J=11.3, 3.6 Hz, 1H), 4.62 (ddd, J=6.3, 4.6,
3.6 Hz, 1H), 5.50 (brs, 1H), 7.23–7–35 (m, 12H), 7.38–7.49 ppm (m, 3H);
13C NMR (75.5 MHz, CDCl3): d=55.1, 59.4, 60.1 (t, JCF =31.8 Hz), 75.0,
119.7 (t, JCF =247.6 Hz), 125.5 (t, JCF =6.3 Hz), 127.3, 128.4, 128.8, 129.2,
tert-Butyl (2S,3S)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phe-
nylbutan-2-ylcarbamate [(2S,3S)-14b]: Following the same procedure, ep-
oxide (S,R)-11b (67 mg) afforded, after chromatography, 86 mg (72%) of
(2S,3S)-14b; ½aꢂD25 =+11.32 (c=1.0, CHCl3).
Benzyl (2R,3S)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phenyl-
butan-2-ylcarbamate [(2R,3S)-15a]: 3-Iodobenzylamine (0.18 mmol) was
added to a solution of epoxide (R,R)-10a (40 mg, 0.12 mmol) in anhy-
drous isopropanol (0.5 mL) at room temperature and the resulting mix-
ture was warmed to 708C until complete consumption of epoxide was ob-
served by TLC. Then, the solvent was evaporated under vacuum and the
crude obtained was purified by chromatography with hexanes/ethyl ace-
tate (2:1) as eluent affording the coupling compound (2R,3S)-15a as a
yellow solid (55 mg, 81%); m.p. 85–878C (CH2Cl2); ½aꢂ2D5 =ꢁ20.82 (c=
1.0, CHCl3); 1H NMR (CDCl3, 300 MHz): d=2.34 (brs, 2H), 2.58 (dd,
J=12.3, 9.3 Hz, 1H), 2.68 (dd, J=12.3, 4.5 Hz, 1H), 3.67 (s, 2H), 4.01
(dd, J=9.3, 4.3 Hz, 1H), 4.18 (td, J=13.7, 10.3 Hz, 1H), 5.04 (d, J=
12.3 Hz, 1H), 5.09 (d, J=12.3 Hz, 1H), 5.59 (d, J=10.3 Hz, 1H), 7.03 (t,
J=7.7 Hz, 1H), 7.19 (d, J=7.7 Hz, 1H), 7.26–7.60 ppm (m, 13H);
13C NMR (CDCl3, 75.5 MHz): d=51.4, 52.6, 57.2 (t, JCF =28.0 Hz), 65.7,
67.1, 94.5, 121.7 (t, JCF =250.9 Hz), 125.6 (t, JCF =6.4 Hz), 127.2, 127.9,
128.2, 128.4, 128.5, 128.5, 130.2, 134.6 (t, JCF =25.0 Hz), 136.2, 136.3,
137.0, 141.9, 156.3 ppm; 19F NMR (CDCl3, 282.4 MHz): d=ꢁ104.7 (dd,
130.8, 132.5 (t,
J
CF =25.6 Hz), 138.6, 158.0 ppm; 19F NMR (CDCl3,
282.4 MHz): d=ꢁ109.8 ppm (dd, JHF =10.9, 16.1 Hz, 2F); HRMS (FAB)
calcd for C25H24F2N2O2 [M+H+]: 423.1884, found: 423.1887.
A
ACHTUNGERTN(NUNG phenyl)methyl]oxazo-
ACHTUNGTRENNUNG
converted to oxazolidinone 13 (80%) as a white solid; m.p. 146–1488C
(CH2Cl2); ½aꢂ2D5 =ꢁ4.48 (c=1.0, CHCl3); 1H NMR (300 MHz, CDCl3):
d=2.94 (d, J=14.7 Hz, 1H), 3.01 (dd, J=14.7, 9.3 Hz, 1H), 3.51 (d, J=
13.8 Hz, 2H), 3.76 (d, J=13.8 Hz, 2H), 3.95 (dt, J=18.9, 7.5 Hz, 1H),
4.81 (ddd, J=18.9, 7.5, 2.4 Hz, 1H), 5.08 (brs, 1H), 7.13–7.43 ppm (m,
15H); 13C NMR (75.5 MHz, CDCl3): d=52.0 (t, JCF =3.5 Hz), 53.1, 58.7,
78.9, 120.2 (t, JCF =250.3 Hz), 125.3 (t, JCF =6.3 Hz), 127.0, 128.2, 128.8,
129.0, 131.0, 133.2 (t, JCF =25.6 Hz), 139.0, 158.1 ppm; 19F NMR (CDCl3,
J
FF =249.1 Hz, JHF =14.4 Hz, 1F), ꢁ103.4 ppm (dd, JFF =249.1 Hz, JHF
=
13.0 Hz, 1F); HRMS (EI+) calcd for C25H25F2IN2O3 [M+]: 566.0878,
found: 566.0865.
Benzyl (2S,3R)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phenyl-
butan-2-ylcarbamate [(2S,3R)-15a]: Epoxide (S,S)-10a (50 mg) afforded
14782
www.chemeurj.org
ꢆ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14772 – 14784

Fluorinated Ethanolamines
FULL PAPER
58 mg of (2S,3R)-15a after chromatography (68%); ½aꢂ2D5 =+18.80 (c=
7.38–7.42 (m, 4H), 7.48–7.52 (m, 4H), 7.89 ppm (d, J=9.3 Hz, 1H);
13C NMR (75.5 MHz, CDCl3): d=11.0, 11.4, 20.7, 21.3, 21.9, 46.4, 50.6,
51.0, 53.1, 58.3 (t, JCF =28.0 Hz), 67.6, 94.4, 121.4 (t, JCF =248.8 Hz),
122.4, 122.4, 125.4 (t, JCF =6.2 Hz), 127.4, 128.4, 128.4, 130.2, 130.3, 134.0,
135.0 (t, JCF =25.7 Hz), 136.3, 137.6, 137.6, 139.0, 141.6, 167.5, 170.9 ppm;
19F NMR (CDCl3, 282.4 MHz): d=ꢁ104.7 (dd, J=250.2, 13.0 Hz, 1F),
ꢁ100.4 ppm (dd, J=250.2, 15.5 Hz, 1F); HRMS (FAB) calcd for
C32H39F2IN3O3 [M+H+]: 678.2004, found: 678.2004.
N1-[(2S,3S)-1,1-Difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phenylbu-
tan-2-yl]-5-methyl-N3,N3-dipropylisophthalamide [(2S,3S)-28b]: Follow-
ing the same procedure, (2S,3S)-14b (160 mg) afforded, after chromatog-
raphy, 108.6 mg (26%) of (2S,3S)-28b; ½aꢂ2D5 =+27.40 (c=1.0, CHCl3).
1.0, CHCl3).
Benzyl (2R,3R)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phenyl-
butan-2-ylcarbamate [(2R,3R)-15b]: Following the same procedure, ep-
oxide (R,S)-10b (112 mg) afforded 142 mg of (2R,3R)-15b (75%); yellow
solid; m.p. 109–1118C (CH2Cl2); ½aꢂ2D5 =ꢁ16.80 (c=1.0, CHCl3); H NMR
1
(300 MHz, CDCl3): d=2.69 (dd, J=12.6, 5.4 Hz, 1H), 2.75 (dd, J=12.6,
3.9 Hz, 1H), 3.53 (d, J=13.5 Hz, 1H), 3.59 (d, J=13.5 Hz, 1H), 3.81 (dd,
J=5.4, 3.9 Hz, 1H), 4.34–4.48 (m, 1H), 4.86 (d, J=12.3 Hz, 1H), 4.97 (d,
J=12.3 Hz, 1H), 6.25 (d, J=10.3 Hz, 1H), 6.90 (t, J=7.8 Hz, 1H), 7.10–
7.54 ppm (m, 13H); 13C NMR (75.5 MHz, CDCl3): d=49.8, 52.1, 58.9 (t,
J
CF =28.0 Hz), 66.1, 66.4, 93.5, 120.4 (t, JCF =248.4 Hz), 124.4 (t, JCF
=
6.4 Hz), 126.3, 126.9, 127.1, 127.4, 127.5, 129.2, 129.2, 133.8 (t, JCF
=
25.7 Hz), 135.1, 135.2, 136.0, 140.9, 155.7 ppm; 19F NMR (CDCl3,
282.4 MHz): d=ꢁ104.9 (dd,
J
FF =250.2 Hz,
JHF =11.6 Hz, 1F),
ꢁ102.0 ppm (dd, JFF =250.2 Hz, JHF =15.8 Hz, 1F); HRMS (EI+) calcd
for C25H25F2IN2O3 [M+]: 566.0878, found: 566.0876.
Acknowledgements
Benzyl (2S,3S)-1,1-difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phenyl-
butan-2-ylcarbamate [(2S,3S)-15b]: Epoxide (S,R)-10b (36 mg) gave
43 mg (70%) of (2S,3S)-15b after chromatography; ½aꢂ2D5 =+15.60 (c=
1.0, CHCl3).
The authors thank the Ministerio de Educaciꢄn y Ciencia (CTQ2007-
61462/BQU) and Generalitat Valenciana (GVPRE/2008/382) for finan-
cial support. S.F. thanks Ministerio de Educaciꢄn y Ciencia for a Predoc-
toral Fellowship (FPU Programme); C.B. thanks Generalitat Valenciana
for a Predoctoral Fellowship (S. Grisolia Programme). M.G. and M.D.M.
thank Dr. U. Neumann, Basel, for advice.
N1-[(2R,3S)-1,1-Difluoro-3-hydroxy-4-(3-iodobenzylamino)-1-phenylbu-
tan-2-yl]-5-methyl-N3,N3-dipropylisophthalamide [(2R,3S)-28a]: A solu-
tion of trifluoroacetic acid (15%) in CH2Cl2 (3.6 mL) was added at 08C
to compound (2R,3S)-14a (160 mg, 0.1 mmol). The reaction was stirred
for 3 h at 08C and then concentrated under reduced pressure to give the
amine trifluoroacetate salt as a colorless oil. The crude salt was redis-
solved in dry CH2Cl2 (3 mL) and cooled to 08C. This solution was treated
successively with triethylamine (0.57 mmol), 27 (0.11 mmol), HOBt
0.20 mmol) and EDC (0.20 mmol). The mixture was stirred at 08C for 1 h
and then allowed to warm slowly to room temperature, overnight. The
resulting solution was treated with citric acid (10%; 3 mL) and EtOAc
(3 mL) and the aqueous layer was washed with EtOAc (3ꢈ3 mL). The
combined organic layers were washed sequentially with saturated aque-
ous NaHCO3 and brine, dried over saturated aqueous Na2SO4 and the
solvent evaporated under reduced pressure, to give a yellowish oily resi-
due. Subsequent chromatography on silica gel provided (2R,3S)-28a as a
colorless oil (61 mg, 30%); ½aꢂ2D5 =ꢁ15.38 (c=1.0, CHCl3); 1H NMR
(300 MHz, CDCl3): d=0.74 (t, J=6.6 Hz, 3H), 0.98 (t, J=6.6 Hz, 3H),
1.45–1.61 (m, 2H), 1.62–1.80 (m, 2H), 2.08 (brs, 2H), 2.40 (s, 3H), 2.56
(dd, J=12.6, 9.9 Hz, 1H), 2.72 (dd, J=12.6, 4.3 Hz, 1H), 3.12 (t, J=
6.6 Hz, 2H), 3.45 (t, J=7.8 Hz, 2H), 3.66 (d, J=13.8 Hz, 1H), 3.71 (d,
J=13.8 Hz, 1H), 4.05–4.11 (m, 1H), 4.71 (dt, J=14.2, 10.0 Hz, 1H), 6.91
(d, J=10.0 Hz, 1H), 7.01 (t, J=7.7 Hz, 1H), 7.20 (d, J=7.7 Hz, 1H), 7.28
(s, 1H), 7.38–7.45 (m, 3H), 7.49 (s, 1H), 7.53–7.61 ppm (m, 5H);
13C NMR (75.5 MHz, CDCl3): d=11.0, 11.5, 20.7, 21.3, 21.9, 46.5, 50.7,
51.3, 52.2, 55.2 (t, JCF =27.5 Hz), 65.6, 94.5, 121.7 (t, JCF =249.5 Hz),
122.2, 125.6 (t, JCF =6.2 Hz), 127.2, 128.4, 128.4, 130.3, 130.3, 130.4, 133.9,
134.6 (t, JCF =25.4 Hz), 136.5, 137.1, 137.8, 139.0, 141.2, 167.1, 170.9 ppm;
19F NMR (CDCl3, 282.4 MHz): d=ꢁ104.7 (dd, J1 =249.3 Hz, J2 =12.9 Hz,
1F), ꢁ102.3 ppm (dd, J1 =249.3 Hz, J2 =14.0 Hz, 1F); HRMS (FAB)
calcd for C32H39F2IN3O3 [M+H+]: 678.2004, found: 678.2011.
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[26] Surprisingly, there was negligible stereochemical induction from the
N-containing stereocenter, even at the lowest temperature that the
solvent system allowed (ꢁ158C).
Received: July 6, 2011
Published online: November 24, 2011
14784
www.chemeurj.org
ꢆ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14772 – 14784