Improved photocontrol of ?±-chymotrypsin activity: Peptidomimetic trifluoromethylketone photoswitch enzyme inhibitors

Article abstract of DOI:10.1002/chem.200800082

A series of peptidomimetic trifluoromethylketones containing the photoisomerisable azobenzene group have been synthesised, photoisomerised and assayed against the serine protease ?±-chymotrypsin. All are inhibitors of the enzyme and exhibit up to a fivefold increase in activity on UV irradiation. Visible irradiation returns activity to close to that of the original sample. These results suggest the trifluoromethylketone group to be the best electrophilic enzyme binding group for use in photoswitch inhibitors of ?±-chymotrypsin. ? 2008 Wiley-VCH Verlag GmbH & Co. KGaA,.

Full text of DOI:10.1002/chem.200800082

DOI: 10.1002/chem.200800082
Improved Photocontrol of a-Chymotrypsin Activity: Peptidomimetic
Trifluoromethylketone Photoswitch Enzyme Inhibitors
David Pearson,[b] Nathan Alexander,[b] and Andrew D. Abell*[a, b]
Abstract: A series of peptidomimetic trifluoromethylketones containing the photo-
isomerisable azobenzene group have been synthesised, photoisomerised and as-
sayed against the serine protease a-chymotrypsin. All are inhibitors of the enzyme
and exhibit up to a fivefold increase in activity on UV irradiation. Visible irradia-
tion returns activity to close to that of the original sample. These results suggest
the trifluoromethylketone group to be the best electrophilic enzyme binding group
for use in photoswitch inhibitors of a-chymotrypsin.
Keywords:
enzymes
peptidomimetics · photochromism
azo compounds
molecular devices
·
·
·
Introduction
A number of important biological processes can be optically
controlled by incorporation of photochromic molecular
switches into biomolecules or biological ligands.[1–5] This bio-
logical photoswitching has potential applications in ad-
vanced technologies such as reversible biosensors, photoacti-
[1,2]
vated medicines and molecular devices. We
and others[4]
have developed a range of photoswitch inhibitors of the
serine protease a-chymotrypsin containing the photochro-
mic azobenzene group. UV-visible irradiation of these inhib-
itors induces E–Z photoisomerisation of the azobenzene
group, which results in a reversible change in inhibitor struc-
ture and hence enzyme affinity. For example, previously re-
ported photoswitch inhibitor a-ketoester 1 exhibits greater
activity as the Z-enriched state that results from UV irradia-
tion (inhibition constant, Ki, of 40 nm, compared with 80 nm
for the E-enriched state).[1] Boronate ester 2 was prepared
in an attempt to increase the extent of photoswitching, but
gave only semireversible photoswitching due to decomposi-
tion on irradiation with UV-visible light.[2]
The present study reports synthesis, enzyme assay and
photoisomerisation studies of trifluoromethylketone-based
photoswitch enzyme inhibitors 3–9. Compounds 3 and 4 are
based on previously reported inhibitors 1 and 2, respectively,
but with an alternative trifluoromethylketone inhibitory
group. This “warhead” is known to give potent inhibitors of
a-chymotrypsin, but is as yet unstudied with regards to pho-
toswitching, aside from a preliminary communication.[6]
Compounds 5–9 contain a sulfonamide linker, rather than
an amide, to provide improved stability towards enzyme-cat-
alysed hydrolysis. In addition, a halide substituent was in-
[a] Prof. A. D. Abell
School of Chemistry and Physics
The University of Adelaide
Adelaide, SA 5005 (Australia)
Fax : (+61)8-8303-4380
E-mail: andrew.abell@adelaide.edu.au
[b] Dr. D. Pearson, Dr. N. Alexander, Prof. A. D. Abell
Department of Chemistry
University of Canterbury
Christchurch (New Zealand)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200800082.
7358
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 7358 – 7365

FULL PAPER
cluded in compounds 6–9 to increase the effective size of
the photoswitch group and to provide a point for further
structural elaboration by means of Pd-catalysed coupling re-
actions. It was anticipated that an increase in effective size
of the photoswitch group would enhance enzyme photo-
switching, due to a greater difference in structure and shape
of the E and Z isomers. Furthermore, it was of interest to in-
vestigate the properties of photoswitch inhibitors containing
3’- and 4’-substituted azobenzene groups because related
linker groups are required for the surface attachment of
photoswitch inhibitors.[6] The substituents and substitution
positions of these compounds were varied to investigate re-
lationships between structure, activity and photoswitching,
particularly the effect of molecular structure on the relative
change in activity on photoisomerisation. Reported herein is
the synthesis and assay of compounds 3–9 against a-chymo-
trypsin in the following forms: as the stable E isomer, as a
Z-enriched photostationary state (PSS) resulting from UV
irradiation and as an E-enriched PSS resulting from visible
irradiation. Racemic samples of inhibitor are used for ease
of synthesis and, given that one enantiomer is invariably sig-
nificantly more active, to allow comparisons to be made.[2]
2, respectively. The monosubstituted azobenzene 3 was pre-
pared by coupling carboxylic acid 10[7,8] to racemic 11a[9]
using (benzotriazol-1-yloxy)tris(dimethylamino)phosphoni-
um hexafluorophosphate (BOP) to give 12, followed by oxi-
dation with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)
to give 3 in a yield of 87% (Scheme 1). The disubstituted
azobenzene 4 was prepared by coupling carboxylic acid 13[2]
to racemic 11b[9] using N-(3-dimethylaminopropyl)-N’-ethyl-
carbodiimide hydrochloride (EDCI) to give 14, followed by
oxidation with Dess–Martin periodinane to give
(Scheme 2).
4
Scheme 1. Synthesis of 3 (DIEA: N,N-diisopropylethylamine).
Scheme 2. Synthesis of 4.
Racemic sulfonamide 5 was prepared by coupling azoben-
zenesulfonyl chloride 15 to racemic 11a to give sulfonamide
16, followed by oxidation using TEMPO to give ketone 5 in
a yield of 80% (Scheme 3).
Results and Discussion
The 4-sulfonyl azobenzenes 6 and 7 (Scheme 4) and 3-sul-
fonyl azobenzenes 8 and 9 (Scheme 5) were synthesised
using an alternative approach. This involved coupling of rac-
emic 11a to an aryl amine, followed by condensation with a
Trifluoromethylketones 3 and 4 were synthesised as racemic
mixtures in a similar manner to the known inhibitors 1 and
Chem. Eur. J. 2008, 14, 7358 – 7365
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7359

A. D. Abell et al.
Scheme 3. Synthesis of 5.
Scheme 5. Synthesis of 8 and 9.
Table 1. E/Z compositions of azobenzenes 3–9 before and after irradia-
tions.
Cmpd
%Z isomer
before
irradiation
%Z isomer
after UV
irradiation
%Z isomer
after visible
irradiation
Decrease in
Z isomer after
visible irradiation
3
4
5
6
7
8
9
<5
<5
<5
7
11
8
78
93
68
77
90
89
86
18
16
17
14
20
18
12
4.3-fold
5.8-fold
4.0-fold
5.5-fold
4.5-fold
4.9-fold
7.2-fold
<5
tions were then irradiated with visible light (l>360 nm) to
1
give the E-enriched PSS (see Table 1). H NMR spectrosco-
Scheme 4. Synthesis of 6 and 7.
py was used to determine the E/Z compositions of samples
obtained from these irradiations. In all cases, the azoben-
zenes were initially (after synthesis and storage in the dark)
predominantly present as the E isomer. After UV irradia-
tion, compositions ranging from 68 to 93% Z isomer were
obtained (see Table 1). Visible irradiation gave PSS compo-
sitions of 12 to 20% Z isomer.
The practical application of azobenzene photoswitches of
the type presented herein requires consideration of two dif-
ferent approaches to photoswitching:
nitrosobenzene to form the azobenzene moiety and oxida-
tion to give the trifluoromethylketone. In particular, com-
pounds 6 and 7 were prepared by coupling of 4-nitrosulfonyl
chloride 17 to 11a to give sulfonamide 18, catalytic reduc-
tion to 19, condensation with nitrosobenzenes 20[10,11] and
21[12,13] to give the azobenzenes 22 and 23, respectively, and
finally oxidation using TEMPO to give ketones 6 and 7, re-
spectively. Compounds 8 and 9 were similarly prepared,
using 3-nitrosulfonyl chloride 24 as starting material instead
of 17. All trifluoromethylketones were characterised as hy-
drates by using NMR spectroscopy in acetone containing
5% D2O (see the Experimental Section for details).
1) UV photoisomerisation of a purified E isomer to a Z-en-
riched PSS. This approach normally produces the largest
possible increase in the proportion of Z isomer, and
hence the largest change of activity on photoswitching,
since the starting E isomer can be obtained in a relative-
ly pure state (often <5% Z by chromatography or ther-
mal isomerisation in the dark). However, this approach
is not fully reversible over a short time period because
Next, azobenzenes 3–9 were photoisomerised by UV-visi-
ble irradiation. A solution of each compound was irradiated
with UV light (l=320–380 nm) to give the Z-enriched PSS
(see Table 1 for E/Z compositions). The Z-enriched solu-
7360
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 7358 – 7365

Photoswitch Enzyme Inhibitors
FULL PAPER
visible irradiation does not usually fully reconvert the Z
isomer to the E isomer. Over a longer timescale, the E
isomer can be thermally regenerated and can undergo
photoswitching of this type again.
bation of enzyme, substrate and inhibitor) since the initial
inhibition was weak. In all cases the Z isomer is the more
potent inhibitor, as has been observed previously for a-ke-
toester inhibitors of a-chymotrypsin.[1,16] This differs from
boronic acid based inhibitors of a-chymotrypsin and alde-
hyde inhibitors of calpain, which usually exhibit greater ac-
tivity as the E isomer.[2,4,17]
The solubility of inhibitors 3, 6, 7 and 9 in water was in-
sufficient to obtain an accurate IC50 value for the least
active composition(s) before irradiation; however, an IC50
could be obtained for the active Z-enriched sample of each
compound and for 3 and 7 after visible irradiation, which ex-
hibit 50% inhibition below the solubility limit. This solubili-
ty problem limits to some extent the amount of enzyme
photoswitching that can be measured by assay for these
compounds. For example, inhibitor 9, which is likely to give
good enzyme photoswitching based on its excellent photo-
2) Reversible photoisomerisation between the UV and visi-
ble PSSs. Although this approach does not modulate ac-
tivity as fully as irradiation of the purified E isomer, it
does provide potential for fast reversible photoswitching.
The second approach is likely to be the most useful in
practical switching applications. We describe the develop-
ment of the method used herein with an initial goal of defin-
ing those factors that maximise the relative difference (in E/
Z composition or enzyme activity) between the E- and Z-
enriched PSSs of the inhibitors, something that is currently
lacking in the literature. Photoisomerisation of the inhibitors
is carried out prior to addition of the protease given that in
situ photoswitching is known to result in poorer switching
and protease instability.[4]
A
switch inhibitors 6–8, can only be accurately stated as
having >2.2-fold change in activity on photoisomerisation.
The best enzyme photoswitch is 6, which exhibits a >4.7-
fold change in activity after UV or visible irradiation. As-
suming that the enzyme inhibition occurs by formation of a
1:1 enzyme–inhibitor complex (as expected for these elec-
trophilic transition-state mimics[18]), the observed change in
the IC50 value of such inhibitors on photoisomerisation is
limited to the relative change in the amount of the active Z
isomer. In cases in which the E isomer also inhibits the
enzyme, the actual change in the IC50 value will be less than
this maximum. Therefore, the maximum possible change in
activity for 6 is 5.5 times (see Table 1). The observed change
in activity (>4.7-fold) is close to this limit, which shows the
Z isomer to be significantly more active than the E isomer.
Therefore, the major limitation to enzyme photoswitching of
this compound is the incomplete isomerisation process be-
tween the E and Z forms.
Trifluoromethylketone 3 exhibited a 3.5-fold change in
enzyme activity between its E- and Z-enriched PSSs. In
comparison, 2-fold photoswitching was reported for 1, which
contains the same skeleton, but a different warhead group.[1]
Trifluoromethylketone 4 exhibited a 2.2-fold change in activ-
ity between the E- and Z-enriched PSSs. This represents a
significant improvement on the related 2, which is reported
to exhibit a less than 1.5-fold change in activity on photo-
switching and partially decomposed on irradiation.[2] In ad-
dition, the trifluoromethylketones presented herein general-
ly exhibit improved photo-
Of the compounds tested (Table 1), azobenzene 9 gave
the best photoswitching between UV and visible PSSs, with
7.2 times more Z isomer obtained after UV irradiation.
Compounds 4, 7 and 8 gave the largest proportion of Z
isomer after UV irradiation, but retained the largest propor-
tion of Z isomer after visible irradiation (see Table 1).
Either the Z isomers of these compounds are (relatively)
thermodynamically stable, or the p!p* electronic transition
involved in E!Z photoisomerisation[14] is relatively fav-
oured at both the UV and visible wavelengths used in this
study. It is unclear why this is the case, since the closely re-
lated compounds 6 and 9 do not similarly favour the Z
isomer.
Separate aliquots from each of three solutions (the initial
solution and the E- and Z-enriched PSSs) of racemic 3–9
were assayed for inhibition of a-chymotrypsin. All com-
pounds were inhibitors of a-chymotrypsin with micromolar
inhibition constants (see IC50 values in Table 2), and all
showed reversible photoswitching of enzyme activity. All
compounds were observed to initially exhibit weak inhibi-
tion, which subsequently increased over several minutes to
reach a higher steady-state level. This ꢁslow-tightꢁ binding
has been previously observed for trifluoromethylketone in-
hibitors, and is considered to occur due to an equilibrium
between the active ketone and a less-active hydrated
form.[15] The IC50 values were calculated using the final
steady-state rates of enzymatic reaction (after 8 min of incu-
switching (up to 5-fold changes
in IC50 value) compared with a-
ketoester and boronate ester
Table 2. a-Chymotrypsin inhibition constants (IC50) for compounds 3–9.
Cmpd IC50 before ir- IC50 after UV ir- IC50 after visible
Increase in activity
after UV irradiation
Decrease in activity
after visible irradiation
radiation [mm] radiation [mm]
irradiation [mm]
based inhibitors of a-chymo-
trypsin, which exhibit at best
only 3-fold changes in IC50
values on photoswitching.[1,2]
These favourable comparisons
suggest the trifluoromethylke-
tone to be a superior warhead
3
4
5
6
7
8
9
>65
32
46
>108
>86
46
16
13
10
23
17
8.5
27
56
28
31
>4.1-fold
2.5-fold
4.6-fold
>4.7-fold
>5.0-fold
5.4-fold
3.5-fold
2.2-fold
3.1-fold
>4.7-fold
3.8-fold
3.6-fold
>108
64
31
>60
>60
>2.2-fold
>2.2-fold
Chem. Eur. J. 2008, 14, 7358 – 7365
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7361

A. D. Abell et al.
for photoswitch inhibitor design. Further studies are re-
quired to directly compare structurally analogous a-ketoest-
ers and trifluoromethylketones.
enzyme photoswitching (>4.7-fold) compared with previ-
ously reported reversible photoswitch inhibitors of a-chymo-
trypsin. Comparisons with known and related a-ketoesters
and boronate esters suggest the trifluoromethylketone war-
head to be the best for photoswitching in such inhibitors. In
addition, the 4’-halides 6–8 are better photoswitches than
the simple 5 that lacks a 4’-substituent. This implies that
photoswitching can be enhanced by increasing the effective
bulk of the photoswitch group. This is an important observa-
tion for the surface attachment of photoswitchable inhibitors
using a bulky linker substituent.[6] However, although the
surface attachment of inhibitors by means of a linker group
in the 3’- or 4’-position is expected to be generally favour-
A number of significant structure–activity photoswitching
relationships are evident on comparison of the structurally
related inhibitors 5–9. Firstly, the halide-substituted deriva-
tives 6–8 all exhibit improved photoswitching relative to the
unsubstituted analogue 5, with 6 being the best reversible
photoswitch inhibitor of a-chymotrypsin reported to date
(see above for discussion). This may be partially attributable
to an increase in the effective bulk of these photoswitching
groups leading to a greater change in molecular structure on
photoisomerisation. It is expected that halide 9 would also
give good photoswitching, but an accurate analysis was not
possible here due to its poor solubility. The 4-sulfonamide
series (5–7) allows comparison of the effect of different
groups at the 4’-position (denoted X; 5: X=H; 6: X=Br; 7:
X=I). Interestingly both PSSs of 5 are significantly more
potent than those of halides 6 and 7, which suggests that a
lack of steric bulk on the azobenzene provides a better fit to
the active site. However, the greatest change in enzyme ac-
tivity on photoswitching is exhibited by halides 6 and 7. This
is predominantly due to a greater amount of the more
active Z isomer in the irradiated PSS in these cases (com-
pare Tables 1 and 2). This is likely to be due to the electron-
withdrawing properties of the halide, which are known to
affect the energy levels involved in UV-visible absorban-
ces.[14] It is interesting to note that the smaller substituent of
8 (X=Br) relative to that of 9 (X=I) also results in im-
proved potency (see Table 2). However, the observed great-
er affinity of the bromide relative to the iodide contrasts
with the results obtained for 6 and 7, in which the larger
iodide 7 gives the greater potency. Photoswitching of 8 and
9 cannot be compared accurately due to the poor solubility
of 9.
A comparison of 4-substituted 6 and 7 with 3-substituted
8 and 9 also provides some interesting comparisons with re-
gards to enzyme affinity and photoswitching. In particular,
the 4-sulfonamido-4’-bromoazobenzene 6 is significantly less
potent than 3-sulfonamido-4’-bromoazobenzene 8, but ex-
hibits a larger change in activity on photoisomerisation.
Both bromides give similar changes in the proportion of Z
isomer on irradiation (see Table 1). Therefore, the differ-
ence in enzyme photoswitching is attributable to differences
in the “fit” of the inhibitors into the enzyme active site. In-
terestingly, the 4-sulfonamido-4’-iodoazobenzene 7 is more
potent than 3-sulfonamido-4’-iodoazobenzene 9, which dif-
fers from the results obtained for bromides 6 and 8. Howev-
er, again photoswitching cannot be compared due to the
poor solubility of 9.
A
pattern or substituent is evident. Ongoing studies are fo-
cused on improving photoswitching by optimising the size
and character of 4’ linker groups. Our findings provide an
important lead for the ongoing development of photoswitch-
able inhibitors of proteases for use in reversible biosensors,
photoactivated medicines and molecular devices.
Experimental Section
General: NMR spectra were obtained on a Varian INOVA spectrometer
1
operating at 500 MHz for H NMR, 126 MHz for 13C NMR and 282 MHz
for 19F NMR, or on a Varian UNITY 300 spectrometer operating at
300 MHz for 1H NMR and 75 MHz for 13C NMR (selected NMR spectra
are given in the Supporting Information). Two-dimensional NMR experi-
ments including COSY and HSQC were used to assign the spectra, and
were obtained on the Varian INOVA spectrometer operating at
500 MHz. For the racemic compounds, unless stated otherwise, the NMR
spectroscopy data given are for the major E isomer. Compounds 3–9
were characterized in their hydrated forms. Electrospray ionisation mass
spectrometry was performed on a Micromass LCT TOF mass spectrome-
ter operating in electrospray (ES) mode with 50% acetonitrile/H2O as
solvent. Electron impact ionisation (EI) mass spectroscopy was per-
formed on a Kratos MS80 mass spectrometer operating at 4 kV (acceler-
ating potential) and 70 eV (ionising potential). Anhydrous DMF was pur-
chased from Acros; anhydrous THF was distilled from sodium or potassi-
um; anhydrous CH2Cl2 was distilled from CaH2. EtOAc and AcOH were
distilled before use. HPLC-grade acetonitrile was purchased from BDH.
All other commercial reagents were used as received.
Photoisomerisation and enzyme assays: Photoisomerisation studies and
enzyme assays were carried out as has been reported previously,[2] except
that spectrophotometric assays were run for 10 min (instead of 5 min),
and the final steady-state rates were used to find IC50 values rather than
initial rates. E/Z ratios were determined based on the relative integrals
1
of well-separated peaks in the H NMR spectra, in particular those corre-
sponding to NH and azobenzene aromatic protons.
Synthesis
(E)-[N-(Benzyl-3,3,3-trifluoro-2-oxopropyl)-3-phenylazobenzamide] (3):
A solution of 12 (43 mg, 0.10 mmol), KBr (0.2 equiv) and TEMPO
(0.1 equiv) in CH2Cl2 (3.5 mL) was cooled to 08C. Buffered NaOCl
(5.25%, adjusted to pH 9 by addition of NaHCO3, 1.8 mL) was added
dropwise and the reaction mixture was stirred rapidly for 2 h. The mix-
ture was diluted with EtOAc, separated, washed with brine, dried over
MgSO4, filtered and concentrated. The crude product was purified by
column chromatography (EtOAc/CH2Cl2 1:9) followed by recrystallisa-
tion from MeOH/H2O to afford 3 (37 mg, 87%, 88% E isomer) as an
orange solid. M.p. 154–1568C; 1H NMR ([D6]acetone containing 5%
D2O, 500 MHz): d=8.18 (s, 1H), 7.99 (d, J=7.9 Hz, 1H), 7.90 (dd, J=
1.5, 8.2 Hz, 2H), 7.83 (d, J=7.7 Hz, 1H), 7.64–7.53 (m, 4H), 7.32 (d, J=
Conclusion
A series of trifluoromethylketone photoswitch inhibitors of
a-chymotrypsin has been developed and tested. The best
photoswitch, bromide 6, exhibits significantly improved
7362
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 7358 – 7365

Photoswitch Enzyme Inhibitors
FULL PAPER
7.2 Hz, 2H), 7.20 (t, J=7.5 Hz, 2H), 7.11 (t, J=7.4 Hz, 1H), 6.79 (d, J=
8.5 Hz, 1H; NH), 4.61 (dd, J=2.6, 11.8 Hz, 1H; CHCH2), 3.35 (dd, J=
3.0, 14.1 Hz, 1H; CHCHH), 3.07 ppm (dd, J=12.3, 13.7 Hz, 1H;
CHCHH); selected 1H NMR peaks for the minor Z hydrate isomer: d=
7.58 (d, J=8.1 Hz, 1H), 6.93–6.89 (m, 2H), 4.64 (d, J=11.6 Hz, 1H),
3.44–3.39 (m, 1H), 3.12–3.06 ppm (m, 1H); 13C NMR ([D6]acetone,
75 MHz): d=168.5 (CONH), 153.0, 139.3, 136.2, 132.4, 130.6, 130.2,
123.1, 128.9, 126.9, 126.0, 124.8 (q, J=289.7 Hz; CF3), 123.5, 122.3, 94.7
(q, J=29.9 Hz; C(OH)2), 56.8 (CHCH2), 34.0 ppm (CHCH2); 19F NMR
([D6]acetone, 282 MHz): d=ꢀ80.5 ppm (s, 3F); m/z (ES) calcd for
C23H21F3N3O3 [M++H]: 444.1535; found: 444.1528.
(E)-[N-(Benzyl-3,3,3-trifluoro-2-oxopropyl)-4-(4-iodophenylazo)benzene-
sulfonamide] (7): A solution of 23 (88 mg, 0.15 mmol), KBr (0.2 equiv)
and TEMPO (0.1 equiv) in EtOAc/CH2Cl2 2:1 (15 mL) was cooled to
08C. Buffered NaOCl (5.25%, adjusted to pH 9 by addition of NaHCO3,
7.5 mL) was added dropwise and the reaction mixture was stirred rapidly
for 3 h. The biphasic mixture was diluted with EtOAc, separated, washed
with brine, dried over MgSO4, filtered and concentrated. The crude prod-
uct was recrystallised from MeOH/H2O to afford the hydrate of 7
(53 mg, 60%, >95% E isomer) as an orange solid. M.p. 154–1568C;
1H NMR ([D6]acetone, 500 MHz): d=8.05 (d, J=8.5 Hz, 2H), 7.79 (d,
J=8.5 Hz, 2H), 7.73 (d, J=8.6 Hz, 2H), 7.58 (d, J=8.6 Hz, 2H), 7.22
(brs, 1H; NH), 7.05 (dd, J=1.8, 7.0 Hz, 2H), 6.93 (m, 3H), 6.26 (brs,
2H), 3.93 (d, J=10.5 Hz, 1H; CHCH2), 3.24 (dd, J=2.2, 14.3 Hz, 1H;
CHCHH), 2.73 ppm (dd, J=11.3, 14.3 Hz, 1H; CHCHH); 13C NMR
([D6]acetone, 75 MHz): d=154.0, 152.4, 144.3, 139.4, 138.4, 129.9, 128.8,
128.0, 126.7, 125.2, 124.4 (q, J=289.2; CF3), 123.5, 99.2, 94.0 (q, J=
29.8 Hz; C(OH)2), 61.2 (CHCH2), 35.9 ppm (CHCH2); 19F NMR
([D6]acetone, 282 MHz): d=ꢀ79.0 ppm (s, 3F); m/z (EI) calcd for
C22H17F3IN3O3S [M+]: 586.9987; found: 586.9992.
(E)-tert-Butyl-2-oxo-2-(4-{[4-(4,4,4-trifluoro-3-oxo-1-phenylbutan-2-ylcar-
bamoyl)phenyl]diazenyl}benzylamino)ethyl carbamate (4): A solution of
14 (7.0 mg, 0.011 mmol) and Dess–Martin periodinane (34 mg, 7 equiv)
in CH2Cl2 (0.5 mL) was stirred for 3 h, diluted with EtOAc (50 mL),
washed with Na2S2O3 (0.25m in saturated NaHCO3, 50 mL), saturated
NaHCO3 (2”50 mL), brine (50 mL), dried over MgSO4 and concentrat-
ed. The crude material was purified by column chromatography (EtOAc/
CH2Cl2 4:1) to give 4 (3.0 mg, 44%, >95% E isomer) as an orange solid.
M.p. 122–1258C; 1H NMR ([D6]acetone, 500 MHz): d=7.99 (s, 1H),
7.89–7.85 (m, 6H), 7.52 (d, J=8.1 Hz, 2H), 7.33 (d, J=7.2 Hz, 2H), 7.24
(t, J=7.6 Hz, 2H), 7.16 (t, J=7.3 Hz, 1H), 6.41 (s, 1H), 4.55–4.46 (m,
3H), 3.80 (d, J=5.6 Hz, 2H), 3.37 (dd, J=14.1, 3.0 Hz, 1H), 3.21–3.15
(E)-[N-(Benzyl-3,3,3-trifluoro-2-oxopropyl)-3-(4-bromophenylazo)ben-
A
and TEMPO (0.1 equiv) in CH2Cl2 (0.5 mL) was cooled to 08C. Buffered
NaOCl (5.25%, adjusted to pH 9 by addition of NaHCO3, 0.25 mL) was
added dropwise and the reaction mixture was stirred rapidly for 2 h. The
biphasic mixture was diluted with EtOAc, separated, washed with brine,
dried over MgSO4, filtered and concentrated. The crude product was pu-
rified by flash chromatography (EtOAc/CH2Cl2 1:9) followed by recrys-
tallisation from MeOH/H2O to give the hydrate of 8 (18 mg, 83%,
(m, 1H), 1.40 ppm (s, C
(CH3)3, 9H); 13C NMR ([D6]acetone, 75 MHz):
R
d=170.6, 169.7, 155.1, 152.3, 144.8, 139.5, 136.7, 130.1, 129.5, 129.2, 129.0,
127.2, 123.8, 123.3, 95.4 (q, J=29.9 Hz, C(OH)2), 79.4, 58.6, 44.8, 43.0,
33.7, 28.5 ppm; m/z (ES) calcd for C32H37F3N5O6 [M++CH5O]: 644.2696;
found: 644.2717.
>95%
E
isomer) as an orange solid. M.p. 86–888C; 1H NMR
(E)-[N-(Benzyl-3,3,3-trifluoro-2-oxopropyl)-4-phenylazobenzenesulfon-
amide] (5): A solution of 15 (50 mg, 0.11 mmol), KBr (0.2 equiv) and
([D6]acetone, 500 MHz): d=7.94 (d, J=7.9 Hz, 1H), 7.89 (d, J=8.7 Hz,
2H), 7.79 (d, J=8.8 Hz, 3H), 7.62 (d, J=7.9 Hz, 1H), 7.50 (t, J=7.9 Hz,
1H), 6.98 (d, J=7.2 Hz, 2H), 6.83 (t, J=7.4 Hz, 2H), 6.77 (t, J=7.3 Hz,
1H), 3.96 (dd, J=2.5, 11.0 Hz, 1H; CHCH2), 3.19 (dd, J=2.6, 14.3 Hz,
1H; CHCHH), 2.64 ppm (dd, J=11.1, 14.3 Hz, 1H; CHCHH); 13C NMR
([D6]acetone, 75 MHz): d=152.4, 151.8, 143.8, 138.4, 133.3, 130.6, 129.8,
129.5, 128.7, 127.4, 127.2, 126.3, 125.3, 120.2, 94.1 (q, J=29.7 Hz;
C(OH)2), 61.4 (CHCH2), 36.0 ppm (CHCH2); 19F NMR ([D6]acetone,
282 MHz): d=ꢀ78.9 ppm (s, 3F); m/z (ES) calcd for C22H2079BrF3N3O4S
[M++H]: 558.0310; found: 558.0302.
TEMPO (0.1 equiv) in CH2Cl2 (4.0 mL) was cooled to 08C. Buffered
NaOCl (5.25%, adjusted to pH 9 by addition of NaHCO3, 2.0 mL) was
added dropwise and the reaction mixture was stirred rapidly for 2 h. The
mixture was diluted with EtOAc, separated, washed with brine, dried
over MgSO4, filtered and concentrated. The crude product was purified
by flash chromatography (EtOAc/petroleum ether 3:7) followed by re-
crystallisation from MeOH/H2O to give
5 (40 mg, 80%, >95% E
isomer) as fluffy orange needles. M.p. 99–1108C (decomp); 1H NMR
([D6]acetone, 500 MHz): d=8.01 (dd, J=1.5, 7.7 Hz, 2H), 7.73 (d, J=
8.5 Hz, 2H), 7.65 (m, 3H), 7.59 (d, J=8.4 Hz, 2H), 7.23 (d, J=9.0 Hz,
1H; NH), 7.06 (m, 2H), 6.94 (m, 3H), 6.28 (s, 1H; OH), 6.23 (s, 1H;
OH), 3.93 (m, 1H; CHCH2), 3.24 (dd, J=2.3, 14.3 Hz, 1H; CHCHH),
2.74 ppm (dd, J=11.3, 14.3 Hz, 1H; CHCHH); 13C NMR ([D6]acetone,
75 MHz): d=154.6, 153.4, 143.7, 138.5, 132.8, 130.3, 130.0, 129.0, 128.3,
127.0, 124.7 (q, J=289.2 Hz; CF3), 123.8, 123.6, 94.2 (q, J=29.4 Hz;
C(OH)2), 61.7 (CHCH2), 36.2 ppm (CHCH2); 19F NMR ([D6]acetone,
282 MHz): d=ꢀ78.9 ppm (s, 3F); m/z (EI) calcd for C22H18F3N3O3S
([M+], ketone): 461.1021; found: 461.1031.
(E)-[N-(Benzyl-3,3,3-trifluoro-2-oxopropyl)-3-(4-iodophenylazo)benzene-
sulfonamide] (9): A solution of 28 (24 mg, 40 mmol), KBr (0.2 equiv) and
TEMPO (0.1 equiv) in CH2Cl2 (0.5 mL) was cooled to 08C. Buffered
NaOCl (5.25%, adjusted to pH 9 by addition of NaHCO3, 0.25 mL
CH2Cl2) was added dropwise and the reaction mixture was stirred rapidly
for 2 h. The biphasic mixture was diluted with EtOAc, separated, washed
with brine, dried over MgSO4, filtered and concentrated. The crude prod-
uct was purified by flash chromatography (EtOAc/CH2Cl2 1:9), followed
by recrystallisation from aqueous MeOH/H2O to give the ketone/hydrate
mixture 9 (19 mg, 81%, >95% E isomer) as an orange solid. M.p. 109–
1128C; 1H NMR ([D6]acetone containing 5% D2O, 500 MHz): d=8.02
(d, J=8.5 Hz, 2H), 7.95 (d, J=7.8 Hz, 1H), 7.80 (s, 1H), 7.75 (d, J=
8.5 Hz, 2H), 7.61 (d, J=7.9 Hz, 1H), 7.51 (t, J=7.8 Hz, 1H), 6.98 (d, J=
7.4 Hz, 2H), 6.84 (t, J=7.5 Hz, 2H), 6.77 (t, J=7.4 Hz, 1H), 3.96 (dd, J=
2.2, 11.0 Hz, 1H; CHCH2), 3.18 (dd, J=2.4, 14.2 Hz, 1H; CHCHH),
2.64 ppm (dd, J=11.3, 14.1 Hz, 1H; CHCHH); 13C NMR ([D6]acetone,
75 MHz): d=152.6, 152.5, 143.6, 139.5, 138.4, 130.7, 129.9, 129.6, 128.8,
127.6, 127.2, 125.3, 124.6 (q, J=289.2 Hz; CF3), 120.4, 99.0, 94.4 (q, J=
29.6 Hz; C(OH)2), 61.6 (CHCH2), 36.1 ppm (CHCH2); 19F NMR
([D6]acetone, 282 MHz): d=ꢀ78.9 ppm (s, 3F); m/z (ES) calcd for
C22H20F3IN3O4S [M++H]: 606.0171; found: 606.0165.
(E)-[N-(Benzyl-3,3,3-trifluoro-2-oxopropyl)-4-(4-bromophenylazo)ben-
G
(0.2 equiv) and TEMPO (0.1 equiv) in EtOAc/CH2Cl2 (2:1, 15 mL) was
cooled to 08C. Buffered NaOCl (5.25%, adjusted to pH 9 by addition of
NaHCO3, 7.5 mL) was added dropwise and the reaction mixture was
stirred rapidly for 3 h. The biphasic mixture was diluted with EtOAc, sep-
arated, washed with brine, dried over MgSO4, filtered and concentrated.
The crude product was recrystallised from MeOH/H2O to give 6 (57 mg,
70%, >95% E isomer) as an orange solid. M.p. 140–1418C; 1H NMR
([D6]acetone, 500 MHz): d=7.96 (d, J=8.7 Hz, 2H), 7.84 (d, J=8.7 Hz,
2H), 7.74 (d, J=8.6 Hz, 2H), 7.59 (d, J=8.6 Hz, 2H), 7.23 (brs, 1H;
NH), 7.05 (dd, J=1.9, 7.1 Hz, 2H), 6.93 (m, 3H), 6.30–6.20 (m, 2H), 3.93
(d, J=9.9 Hz, 1H; CHCH2), 3.25 (dd, J=2.4, 14.3 Hz, 1H; CHCHH),
2.73 ppm (dd, J=11.3, 14.3 Hz, 1H; CHCHH); 13C NMR ([D6]acetone,
75 MHz): d=154.2, 152.1, 144.4, 138.6, 133.5, 130.1, 128.9, 128.2, 126.9,
126.6, 125.5, 124.6 (q, J=289.1 Hz; CF3), 123.7, 94.2 (q, J=29.9 Hz;
C(OH)2), 61.5 (CHCH2), 36.1 ppm (CHCH2); 19F NMR ([D6]acetone,
282 MHz): d=ꢀ79.0 ppm (s; 3F); m/z (ES) calcd for C22H2079BrF3N3O4S
[M++H]: 558.0310; found: 558.0311.
(E)-[N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-3-phenylazobenz-
A
0.39 mmol), 11a[9] (100 mg, 0.40 mmol) and BOP (180 mg, 0.40 mmol) in
CH2Cl2 (5.0 mL) was stirred at RT under an inert atmosphere. After
5 min, DIEA (140 mL, 0.80 mmol) was added dropwise. The resulting so-
lution was stirred for a further 16 h then diluted with EtOAc (20 mL),
washed with 10% aqueous HCl, saturated aqueous NaHCO3, brine, dried
over MgSO4, filtered and concentrated. Recrystallisation from aqueous
Chem. Eur. J. 2008, 14, 7358 – 7365
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7363

A. D. Abell et al.
acetone gave 12 (160 mg, 98%, >95% E isomer) as an orange powder.
M.p. 187–1888C; 1H NMR ([D6]acetone, 500 MHz): d=8.28 (t, J=
1.6 Hz, 1H), 8.03 (dd, J=1.7, 7.8 Hz, 2H), 7.95 (dd, J=1.2, 8.0 Hz, 2H),
7.92 (d, J=7.8 Hz, 1H), 7.64–7.57 (m, 4H), 7.36 (d, J=7.4 Hz, 2H), 7.27
(t, J=7.6 Hz, 2H), 7.17 (t, J=7.4 Hz, 1H), 4.67 (m, 1H; CHCH2), 4.44
(m, 1H; CHOH), 3.26 (dd J=3.6, 14.2 Hz, 1H; CHCHH), 3.16 ppm (dd,
J=10.8, 14.2 Hz, 1H; CHCHH); 13C NMR ([D6]acetone): d=167.0
(CO), 153.2, 139.2, 136.9, 132.5, 130.6, 130.2, 129.1, 127.1, 126.4 (q, J=
283.2 Hz; CF3), 125.9, 123.6, 122.4, 72.0 (q, J=28.6 Hz; CHOH), 52.8
(CHCH2), 35.6 ppm (CHCH2); 19F NMR (CDCl3, 282 MHz): d=
ꢀ74.4 ppm (d, J=7.4 Hz, 3F); m/z (ES) calcd for C23H21F3N3O2
vacuum for 5 min then stirred under a hydrogen atmosphere for a further
16 h, filtered through a mixture of Celite and MgSO4 and concentrated
to give 19 (1.2 g, 99%) as a pale yellow solid. M.p. 175–1808C; 1H NMR
([D6]acetone, 500 MHz): d=7.17–7.12 (m, 5H), 7.05 (dd, J=3.0, 6.5 Hz,
2H), 6.51 (d, J=8.7 Hz, 2H), 6.20 (d, J=7.8 Hz, 1H; NH), 5.73 (d, J=
6.9 Hz, 1H; OH), 5.38 (s, 2H; ArNH2), 4.40 (m, 1H; CHOH), 3.65 (m,
1H; CHCH2), 2.92 (dd, J=3.5, 14.5 Hz, 1H; CHCHH), 2.80 ppm (dd, J=
10.2, 14.5 Hz, 1H; CHCHH); 13C NMR ([D6]acetone, 75 MHz): d=153.1,
138.2, 130.0, 129.4, 129.0, 127.2, 127.0, 126.1 (q, J=283.3 Hz; CF3), 113.9,
71.7 (q, J=28.8 Hz; CHOH), 55.8 (CHCH2), 34.9 ppm (CHCH2);
19F NMR ([D6]acetone, 282 MHz): d=ꢀ74.1 ppm (d, J=8.1 Hz, 3F); m/z
(EI) calcd for C16H17F3N2O3S [M+]: 374.0912; found: 374.0900.
A
(E)-tert-Butyl-2-oxo-2-(4-{[4-(4,4,4-trifluoro-3-hydroxy-1-phenylbutan-2-
ylcarbamoyl)phenyl]diazenyl}benzylamino)ethyl carbamate (14): DIEA
(9.0 mL, 6.7 mg, 1 equiv) was added to
(E)-[N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-4-(4-bromophenylazo)-
benzenesulfonamide] (22): A suspension of 19 (200 mg, 0.60 mmol) and
4-bromonitrosobenzene 20[10,11] (110 mg, 0.60 mmol) in AcOH (2.4 mL)
was stirred at 1008C for 4 h. The reaction mixture was cooled to RT then
diluted with H2O/CH2Cl2 (1:1, 50 mL). Solid Na2CO3 was added until ef-
fervescence ceased and the aqueous layer was basic to litmus. The aque-
ous layer was back-extracted with CH2Cl2 and the combined organics
were washed with 10% aqueous HCl, saturated aqueous NaHCO3 then
brine, dried over MgSO4, filtered and concentrated. Purification by
column chromatography (EtOAc/CH2Cl2 1:9) gave 22 (210 mg, 64%,
a
solution of 13[2] (20 mg,
0.049 mmol), 11b[9] (11 mg, 1 equiv), EDCI (10 mg, 1 equiv) and HOAt
(7.0 mg, 1 equiv) in DMF (3.0 mL), and the resulting mixture was stirred
for 16 h, diluted with EtOAc (50 mL), washed with H2O (50 mL”2),
brine (50 mL), dried over MgSO4 and concentrated. The crude product
was purified by flash chromatography (EtOAc/CH2Cl2 3:2) to give 14
(15 mg, 50%, >95% E isomer) as an orange solid. M.p. 182–1858C;
1H NMR ([D6]acetone, 500 MHz): d?7.98 (d, J=8.5 Hz, 2H), 7.83–7.96
(m, 6H), 7.50 (d, J=8.0 Hz, 2H), 7.37 (d, J=7.4 Hz, 2H;
CHCHCHCHCH), 7.30 (t, J=7.4 Hz, 2H; CHCHCHCHCH), 7.21 (t,
J=7.4 Hz, 1H; CHCHCHCHCH), 4.72 (m, 1H), 6.35–6.40 (m, 2H), 4.53
(d, J=6.0 Hz, 2H), 4.23 (m, 1H), 3.84 (d, J=5.7 Hz, 2H), 3.17 (m, 2H;
1
>95% E isomer) as an orange solid. M.p. 135–1388C (MeOH); H NMR
([D6]acetone, 500 MHz): d=7.94 (d, J=8.6 Hz, 2H), 7.83 (d, J=8.6 Hz,
2H), 7.78 (d, J=8.5 Hz, 2H), 7.60 (d, J=8.5 Hz, 2H), 7.04 (m, 3H), 7.00
(m, 3H), 5.91 (d, J=6.9 Hz, 1H; OH), 4.44 (m, 1H; CHOH), 3.81 (m,
1H; CHCH2), 2.95 (dd, J=3.0, 14.4 Hz, 1H; CHCHH), 2.89 (s, 2H;
H2O), 2.83 ppm (dd, J=10.9, 14.6 Hz, 1H; CHCHH); 13C NMR
([D6]acetone, 75 MHz): d=154.6, 152.2, 143.7, 138.1, 133.5, 130.0, 129.1,
128.2, 126.1, 126.8, 126.0 (q, J=283.5 Hz; CF3), 125.6, 123.9, 73.6 (q, J=
28.9 Hz; CHOH), 56.7 (CHCH2), 34.8 ppm (CHCH2); 19F NMR
([D6]acetone, 282 MHz): d=ꢀ74.2 ppm (d, J=8.0 Hz, 3F); m/z (EI)
calcd for C22H1979BrF3N3O3S [M+]: 541.0283; found: 541.0280.
CHCH2), 1.42 ppm (s, 9H; C
(CH3)3); 13C NMR ([D6]acetone, 126 MHz):
R
d=170.7, 167.3, 154.9, 152.3, 144.5, 138.9, 137.4, 130.2, 129.3, 129.2, 128.9,
127.4, 123.8, 123.3, 79.4, 70.5 (q, J=29.5 Hz; CHOH), 52.2, 44.8, 43.0,
37.9, 28.5 ppm; m/z (ES) calcd for C31H35F3N5O5 [M++H]: 614.2602;
found: 614.2590.
(E)-[N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-4-phenylazobenzene-
sulfonamide] (16): DIEA (0.39 mL, 2.2 mmol) was added to a stirred sus-
pension of 15 (290 mg, 1.0 mmol) and 11a (290 mg, 1.1 mmol) in CH2Cl2
(10 mL). The resulting solution was heated at reflux for 4 h, cooled and
then concentrated. The residue was dissolved in EtOAc, washed with
10% aqueous HCl, saturated aqueous NaHCO3 and brine, dried over
MgSO4, filtered and concentrated to give 16 (47 mg, quantitative, >95%
(E)-[N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-4-(4-iodophenylazo)-
benzenesulfonamide] (23): A suspension of 19 (130 mg, 0.34 mmol) and
4-iodonitrosobenzene 21[12,13] (79 mg, 0.34 mmol) in AcOH (1.5 mL) was
stirred at 1008C for 4 h. The reaction mixture was cooled to RT then di-
luted with water/CH2Cl2 (1:1, 50 mL). Solid Na2CO3 was added until ef-
fervescence ceased and the aqueous layer was basic to litmus. The aque-
ous layer was back-extracted with CH2Cl2 and the combined organics
washed successively with 10% aqueous HCl, saturated aqueous NaHCO3
and brine, dried over MgSO4, filtered and concentrated. Purification by
column chromatography (EtOAc/CH2Cl2 1:9) gave 23 (130 mg, 67%,
E
isomer) as an orange solid. M.p. 143–1448C (MeOH); 1H NMR
(CDCl3, 500 MHz): d=8.12 (dd, J=1.7, 7.9 Hz, 2H), 7.90 (d, J=8.5 Hz,
2H), 7.74 (m, 5H), 7.18 (m, 3H), 7.14 (m, 3H), 6.02 (d, J=6.9 Hz, 1H;
OH), 4.57 (m, 1H; CHOH), 3.93 (m, 1H; CHCH2), 3.08 (dd, J=3.1,
14.4 Hz, 1H; CHCHH), 2.96 ppm (dd, J=10.8, 14.4 Hz, 1H; CHCHH);
13C NMR ([D6]acetone, 75 MHz): d=154.7, 153.3, 143.3, 138.1, 132.9,
130.2, 130.0, 129.0, 128.3, 127.1, 126.0 (q, J=283.5 Hz; CF3), 123.8, 123.7,
73.6 (q, J=28.8 Hz; CHOH), 56.7 (CHCH2), 34.8 ppm (CHCH2);
19F NMR ([D6]acetone, 282 MHz): d=ꢀ74.2 ppm (d, J=8.0 Hz, 3F); m/z
(EI) calcd for C22H20F3N3O3S [M+]: 463.1178; found: 463.1191.
>95%
E
isomer) as an orange solid. M.p. 149–1508C; 1H NMR
([D6]acetone, 500 MHz): d=8.05 (d, J=8.5 Hz, 2H), 7.79 (d, J=8.5 Hz,
2H), 7.78 (d, J=8.4 Hz, 2H), 7.60 (d, J=8.4 Hz, 2H), 7.04 (m, 3H), 7.00
(m, 3H), 4.44 (m, 1H; CHOH), 3.80 (m, 1H; CHCH2), 2.95 (dd, J=2.9,
14.4 Hz, 1H; CHCHH), 2.83 ppm (dd, J=10.9, 14.4 Hz, 1H; CHCHH);
13C NMR ([D6]acetone, 75 MHz): d=154.5, 152.6, 143.7, 139.6, 138.1,
130.0, 129.0, 128.3, 127.1, 126.0 (q, J=283.4 Hz; CF3), 125.5, 123.8, 99.3,
73.6 (q, J=28.7 Hz; CHOH), 56.7 (CHCH2), 34.8 ppm (CHCH2);
19F NMR ([D6]acetone, 282 MHz): d=ꢀ74.26ppm (d, J=7.9 Hz, 3F);
m/z (EI) calcd for C22H19F3IN3O3S [M+]: 589.0144; found: 589.0155.
N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-4-nitrobenzenesulfonamide
(18): DIEA (0.38 mL, 2.2 mmol) was added to a stirred suspension of 4-
nitrobenzenesulfonyl chloride (230 mg, 1.00 mmol) and 11a[9] (280 mg,
1.10 mmol) in CH2Cl2 (10 mL). The resulting solution was heated at
reflux under an inert atmosphere for 4 h, cooled and concentrated. The
residue was redissolved in EtOAc, successively extracted with 10% aque-
ous HCl, saturated aqueous NaHCO3 and brine, dried over MgSO4, fil-
tered and concentrated. Flash chromatography (CH2Cl2) of the crude ma-
terial gave 18 (400 mg, quantitative) as a pale yellow solid. M.p. 129–
1318C; 1H NMR ([D6]acetone, 500 MHz): d=8.05 (d, J=8.9 Hz, 2H),
7.61 (d, J=8.9 Hz, 2H), 7.28 (d, J=8.3 Hz, 1H; NH), 7.01–6.95 (m, 5H),
5.93 (d, J=6.9 Hz, 1H; OH), 4.44 (m, 1H; CHOH), 3.80 (m, 1H;
CHCH2), 2.94 (dd, J=2.9, 14.4 Hz, 1H; CHCHH), 2.78 ppm (dd, J=
11.2, 14.4 Hz, 1H; CHCHH); 13C NMR ([D6]acetone, 75 MHz): d=150.2,
147.0, 138.0, 130.0, 129.0, 128.3, 126.9, 125.8 (q, J=283.5; CF3), 124.8,
73.9 (q, J=29.0 Hz; CHOH), 56.1 (CHCH2), 34.7 ppm (CHCH2);
19F NMR ([D6]acetone, 282 MHz): d=ꢀ74.2 ppm (d, J=8.0 Hz, 3F).
N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-3-nitrobenzenesulfonamide
(25): DIEA (0.37 mL, 2.1 mmol) was added to a stirred suspension of 3-
nitrobenzenesulfonyl chloride 24 (220 mg, 1.00 mmol) and 11a[9] (270 mg,
1.1 mmol) in CH2Cl2 (10 mL). The resulting solution was heated at reflux
for 4 h, cooled and then concentrated. The residue was redissolved in
EtOAc, washed with 10% aqueous HCl, saturated aqueous NaHCO3 and
brine, dried over MgSO4, filtered and concentrated. Flash chromatogra-
phy (CH2Cl2) of the crude material gave 25 (400 mg, 99%) as a pale
yellow solid. M.p. 116–1188C; 1H NMR (CDCl3, 500 MHz): d=8.26 (d,
J=8.2 Hz, 1H), 8.12 (s, 1H), 7.78 (d, J=7.9 Hz, 1H), 7.48 (t, J=8.0 Hz,
1H), 6.97–6.94 (m, 3H), 6.85 (dd, J=2.8, 6.3 Hz, 2H), 5.44 (d, J=8.1 Hz,
1H; NH), 4.55 (m, 1H; CHOH), 3.62–3.73 (m, 2H), 2.97 (dd, J=3.3,
14.4 Hz, 1H; CHCHH), 2.68 ppm (dd, J=11.6, 14.4 Hz, 1H; CHCHH);
13C NMR (CDCl3, 75 MHz): d=148.2, 140.6, 136.0, 132.1, 130.0, 128.8,
128.6, 127.0, 126.7, 124.1 (q, J=283.3 Hz; CF3), 122.0, 72.7 (q, J=
4-Amino-N-(1-benzyl-3,3,3-trifluoro-2-hydroxypropyl)benzenesulfon-
ACHTREUNG
7364
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 7358 – 7365

Photoswitch Enzyme Inhibitors
FULL PAPER
30.1 Hz; CHOH), 56.3 (CHCH2), 34.2 ppm (CHCH2); 19F NMR (CDCl3,
282 MHz): d=ꢀ74.7 ppm (d, J=7.4 Hz, 3F).
8.6 Hz, 2H), 7.61 (d, J=7.8 Hz, 1H), 7.54 (t, J=7.8 Hz, 1H), 7.05 (d, J=
8.2 Hz, 1H; NH), 7.01 (d, J=7.1 Hz, 2H), 6.93 (t, J=7.3 Hz, 2H), 6.87
(t, J=7.2 Hz, 1H), 5.90 (d, J=6.9 Hz, 1H; OH), 4.47 (m, 1H; CHOH),
3.82 (m, 1H; CHCH2), 2.94 (dd, J=2.9, 14.4 Hz, 1H; CHCHH),
2.82 ppm (dd, J=10.9, 14.4 Hz, 1H; CHCHH); 13C NMR ([D6]acetone,
75 MHz): d=152.8, 152.5, 143.0, 139.6, 138.0, 130.8, 129.8, 129.7, 128.9,
127.7, 127.2, 126.0 (q, J=283.4 Hz; CF3), 125.4, 120.6, 99.1, 73.6 (q, J=
28.7 Hz; CHOH), 56.8 (CHCH2), 34.8 ppm (CHCH2); 19F NMR
([D6]acetone, 282 MHz): d=ꢀ74.2 ppm (d, J=8.0 Hz, 3F); m/z (EI)
calcd for C22H19F3IN3O3S [M+]: 589.0144; found: 589.0146.
3-Amino-N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)benzenesulfon-
A
0.75 mmol) in EtOAc (50 mL). The suspension was rapidly stirred under
vacuum for 3–5 min then stirred under a hydrogen atmosphere for a fur-
ther 16 h, filtered through a mixture of Celite and MgSO4 and concen-
trated to give 26 (270 mg, 95%) as a foamy off-white solid. M.p. 131–
1348C (EtOAc); 1H NMR (CDCl3, 500 MHz): d=7.15–7.02 (m, 4H),
6.89 (dd, J=2.5, 6.0 Hz, 2H), 6.85 (d, J=7.7 Hz, 1H), 6.73 (d, J=8.0 Hz,
1H), 6.67 (s, 1H), 5.37 (d, J=8.0 Hz, 1H; NH), 4.46 (m, 1H; CHOH),
3.90 (br, 2H; ArNH2), 3.68 (m, 1H; CHCH2), 2.92 (dd, J=3.6, 14.4 Hz,
1H; CHCHH), 2.68 ppm (dd, J=10.7, 14.4 Hz, 1H; CHCHH); 13C NMR
(CDCl3, 75 MHz): d=147.2, 139.2, 136.2, 130.0, 129.2, 128.6, 126.9, 124.5
(q, J=283.6 Hz; CF3), 119.6, 116.5, 112.9, 72.0 (q, J=29.2 Hz; CHOH),
55.7 (CHCH2), 34.4 ppm (CHCH2); 19F NMR (CDCl3, 282 MHz): d=
ꢀ74.1 (d, J=8.0 Hz, 3F); m/z (ES) calcd for C16H18F3N2O3S [M++H]:
375.0990; found: 375.0991.
Acknowledgements
Financial support from the Royal Society of New Zealand Marsden
Fund, ARC (DP0771901), and TEC Bright Future Scheme (scholarship
for D.P.) are gratefully acknowledged.
(E)-[N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-3-(4-bromophenylazo)-
benzenesulfonamide] (27): A suspension of 26 (100 mg, 0.30 mmol) and
20 (56 mg, 0.30 mmol) in AcOH (1.2 mL) was stirred at 1008C for 4 h.
The reaction mixture was cooled to RT then diluted with water/CH2Cl2
(1:1, 50 mL). Solid Na2CO3 was added until effervescence ceased and the
aqueous layer was basic to litmus. The aqueous layer was back-extracted
with CH2Cl2 and the combined organics washed successively with 10%
aqueous HCl, saturated aqueous NaHCO3 and brine, dried over MgSO4,
filtered and concentrated. Purification by column chromatography
(EtOAc/CH2Cl2 1:9) gave 27 (120 mg, 76%, >95% E isomer) as an
[1] A. J. Harvey, A. D. Abell, Tetrahedron 2000, 56, 9763.
[2] D. Pearson, A. D. Abell, Org. Biomol. Chem. 2006, 4, 3618.
[3] M. A. Wainberg, B. F. Erlanger, Biochemistry 1971, 10, 3816.
[4] P. R. Westmark, J. P. Kelly, B. D. Smith, J. Am. Chem. Soc. 1993,
115, 3416.
[5] J. Auernheimer, C. Dahmen, U. Hersel, A. Bausch, H. Kessler, J.
Am. Chem. Soc. 2005, 127, 16107.
[6] D. Pearson, A. J. Downard, A. Muscroft-Taylor, A. D. Abell, J. Am.
Chem. Soc. 2007, 129, 14862.
[7] P. Jacobson, Justus Liebigs Ann. Chem. 1909, 367, 329.
[8] C. J. Byrne, D. A. R. Happer, M. P. Hartshorn, H. K. J. Powell, J.
Chem. Soc. Perkin Trans. 2 1987, 1649.
[9] N. P. Peet, J. P. Burkhart, M. R. Angelastro, E. L. Giroux, S. Mehdi,
P. Bey, M. Kolb, B. Neises, D. Schirlin, J. Med. Chem. 1990, 33, 394.
[10] S. Tollari, M. Cuscela, F. Porta, J. Chem. Soc. Chem. Commun. 1993,
1510.
[11] A. Defoin, Synthesis 2004, 706.
[12] D. A. Fletcher, B. G. Gowenlock, K. G. Orrell, J. Chem. Soc. Perkin
Trans. 2 1997, 2201.
1
orange solid. M.p. 140–1418C; H NMR ([D6]acetone, 500 MHz): d=8.02
(d, J=7.9 Hz, 1H), 7.93 (d, J=8.7 Hz, 2H), 7.89 (s, 1H), 7.83 (d, J=
8.7 Hz, 2H), 7.61 (d, J=7.9 Hz, 1H), 7.55 (t, J=6.1 Hz, 1H), 7.05 (d, J=
8.2 Hz, 1H; NH), 7.01 (d, J=7.2 Hz, 2H), 6.93 (t, J=7.3 Hz, 2H), 6.88
(m, J=7.3 Hz, 1H), 5.92 (d, J=6.9 Hz, 1H; OH), 4.46 (m, 1H; CHOH),
3.82 (m, 1H; CHCH2), 2.94 (dd, J=3.0, 14.4 Hz, 1H; CHCHH) 2.82 ppm
(dd, J=10.9, 14.4 Hz, 1H; CHCHH); 13C NMR ([D6]acetone, 75 MHz):
d=152.9, 152.1, 143.0, 138.0, 133.5, 130.9, 129.9, 129.7, 128.9, 127.7, 127.3,
126.5, 126.0 (q, J=283.5 Hz; CF3), 125.5, 120.6, 73.6 (q, J=28.8 Hz;
CHOH), 56.8 (CHCH2), 34.8 ppm (CHCH2); 19F NMR ([D6]acetone,
282 MHz): d=ꢀ74.2 ppm (d, J=8.0 Hz, 3F); m/z (EI) calcd for
C22H1979BrF3N3O3S [M+]: 541.0283; found: 541.0278.
(E)-[N-(1-Benzyl-3,3,3-trifluoro-2-hydroxypropyl)-3-(4-iodophenylazo)-
benzenesulfonamide] (28): A suspension of 26 (100 mg, 0.30 mmol) and
21 (70 mg, 0.30 mmol) in AcOH (1.2 mL) was stirred at 1008C for 4 h.
The reaction mixture was cooled to RT then diluted with water/CH2Cl2
(1:1, 50 mL). Solid Na2CO3 was added until effervescence ceased and the
aqueous layer was basic to litmus. The aqueous layer was back-extracted
with CH2Cl2 and the combined organics washed successively with 10%
aqueous HCl, saturated aqueous NaHCO3 and brine, dried over MgSO4,
filtered and concentrated. Purification by column chromatography
(EtOAc/CH2Cl2 1:9) gave 28 (140 mg, 77%, >95% E isomer) as an
[13] E. Bamberger, Ber. Dtsch. Chem. Ges. 1895, 245.
[14] H. Rau in Photochromism: Molecules and Systems (Eds.: H. Dꢂrr,
H. Bouas-Laurent), Elsevier, Amsterdam, 1990, p. 165.
[15] K. Brady, R. H. Abeles, Biochemistry 1990, 29, 7608.
[16] A. J. Harvey, A. D. Abell, Bioorg. Med. Chem. Lett. 2001, 11, 2441.
[17] A. D. Abell, M. A. Jones, A. T. Neffe, S. G. Aitken, T. P. Cain, R. J.
Payne, S. B. McNabb, J. M. Coxon, B. G. Stuart, D. Pearson, H. Y.-Y.
Lee, J. D. Morton, J. Med. Chem. 2007, 50, 2916.
[18] B. Imperiali, R. H. Abeles, Biochemistry 1986, 25, 3760.
1
orange solid. M.p. 134–1378C; H NMR ([D6]acetone, 500 MHz): d=8.04
(d, J=8.7 Hz, 2H), 8.02 (d, J=7.9 Hz, 1H), 7.89 (s, 1H), 7.77 (d, J=
Received: January 15, 2008
Published online: July 7, 2008
Chem. Eur. J. 2008, 14, 7358 – 7365
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7365