Syntheses and kinetic studies of cyclisation-based self-immolative spacers

Article abstract of DOI:10.1039/c7ob00121e

Kinetic analysis of the disassembly of self-immolative spacers based on cyclisation processes was performed. Five compounds were synthesized belonging to two different series, and their kinetic constants were determined. Electron-donating substituents gav

Full text of DOI:10.1039/c7ob00121e

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Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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Syntheses and kinetic studies of cyclisation-based self-immolative
spacers
Steve Huvelle,a Ahmed Alouane,a,b,c Thomas Le Saux,b,c Ludovic Jullien,*b,c Frédéric Schmidt*a
Received 00th January 20xx,
Accepted 00th January 20xx
Abstract Kinetic analysis of disassembly of self-immolative spacers based on cyclisation processes was performed. Five
compounds were synthesized belonging to two different series, and their kinetic constants were determined. Electron-
donating substituents gave a slight acceleration but the main effect was steric, and the Thorpe-Ingold effect was indeed
particularly effective. Comparison with the self-immolative spacers based on elimination processes showed that
cyclisations gave comparable or lower rate, but the corresponding spacers are more difficult to modulate.
DOI: 10.1039/x0xx00000x
www.rsc.org/
(like nitrogen or oxygen; less often sulfur13) which attacks an
electrophilic centre (classically a carbonyl) on another position of
the skeleton of the molecule14 (Scheme 1).
Introduction
Self-immolative spacers were introduced in 1981 by Katzellenbogen
et al1 as an original way to correlate the cleavage of two chemical
bonds. In a Medicinal Chemistry context, this strategy was proposed
to overcome limitations of prodrugs, classically made of two
moieties: an activator, reacting with an enzyme as a substrate, and
a bioactive compound, as a drug or a reporter. The introduction of
the spacer core consists of adding a third moiety designed to
release the effector after activation. The second bond is cleaved
spontaneously after cleavage of the trigger (scheme 1). A variety of
self-immolative spacers has been introduced over the years in the
literature2-4 and for instance used in cancer chemotherapy
(Adcetris®).5-8 In this strategy, the spontaneous release introduces a
second step with its own kinetic parameters. For most applications
(medicinal chemistry, analytical chemistry, materials or chemical
biology), the self-immolative step needs to be fast enough in order
to avoid release too far from the activation site. Our aim has been
to obtain comparative data on the kinetics of the self-immolative
To measure accurately the kinetics of the self-immolation step, a
general procedure was set up based on a fast and controlled
photoactivation; the fluorescence measurement of a reporter gave
then access to the kinetic constants.9-12 We have already published
comparative data on kinetic constants of various elimination-based
spacers (1,4 and 1,6) supported by aromatic10-11 or heteroaromatic
rings.12 In order to complete our comprehension of rate description
of self-immolative spacers, we measured the kinetics of cyclisation-
based spacers. Two main questions were addressed, the effect of
the nature of the spacer and the comparison between elimination
and cyclisation processes.
Results and discussion
Molecular design
step so that anyone can choose
a spacer suited to their
The structure of the targeted compounds was tripartite:
a
applications. Kinetics of some self-immolative spacers have been
studied during the past, especially for elimination-based releases.9-
photocleavable moiety, the self–immolative spacer, and a reporter
(fluorophore).
12
This is why we focused our present studies on the other class of
spacers exploiting cyclisation in a self-immolative step. In this series
of spacers, the activation step generates a nucleophilic heteroatom
A classical 4,5-dimethoxy-2-nitrobenzyl (also called 6-nitroveratryl)
group was used for the photocleavage step. This protecting group
(denoted PG in Scheme 1) has been reported to be selectively
cleaved by near-UV irradiation (365 nm), with excellent yield, and
allows a millisecond timescale resolution.10
Self-immolative spacers commonly reported in literature are mainly
based on phenyl cores, as aniline and phenol derivatives. The
nitrogen or oxygen atom, typically involved in a bond with various
protecting groups, triggers the self-immolation process. Here we
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used a phenol core, acting as a nucleophile during the elimination
step. Two representative series seemed particularly interesting for
cyclisation studies (scheme 1):
O
OH
O
OH
b)
a)
OH
- Trimethyl-lock derivatives13-18 via 6-exo-trig-cyclisation. These are
the most widely used cyclisation-based spacers
18
17
O
O
- 2-hydroxyphenyl carbamates (2-HPC) derivatives19 via 5-exo-trig
cyclisation. These derivatives are less popular but are good models
to study the influence of substituents on the self-immolation rate (4
substituents were selected: methoxy, nitro, H, bromide)
O
O
NO2
NO2
O
O
d)
e)
c)
OH
O
19
20
O
O
O
O
NO2
NO2
f)
O
O
O
O
Cl
OH
O
O
N
Cl
21
TML
Scheme 2: Synthesis of the trimethyl-lock derivative. Reagents and
conditions: a) 3.3-dimethylacrylic acid, methane sulfonic acid,
toluene, 85°C (99%); b) LiAlH4, THF, 0°C to rt (93%); c) 4,5-
dimethoxy-2-nitrobenzyl bromide, Cs2CO3, THF, rt (93%); d)
Pyridinium dichromate (PDC), CH2Cl2, rt (95%); e) NaClO2, NaH2PO4,
2-methyl-2-butene, acetone/tBuOH/water, rt (89%); f) 1. Phosgene,
THF, rt; 2. NEt3, 4-Dimethylaminopyridine (DMAP), DDAO, THF, rt
(quant.)
Scheme 1: Cyclisation-based spacers investigated, with a) trimethyl
lock and b) 2-HPC. PG=4,5-dimethoxy-2-nitrobenzyl; DDAO=1,3-
dichloro-9,9-dimethyl-9H-acridin-2(7)-one.
In order to analyse the stoichiometry and kinetics of cyclisation
reactions, we used 1,3-dichloro-9,9-dimethyl-9H-acridin-2(7)-one
(DDAO in Scheme 1) as a fluorescent reporter. This moiety does not
emit fluorescence in caged precursors, but emits strongly in the
red-wavelength region in the free phenol state.
Phenol-carbamate syntheses
The general synthesis of the 2-HPC (see scheme 3) derivatives
started by the aniline protection of the corresponding commercial
2-aminophenol with a Boc group. The selective protection of the
aniline function versus phenol came from a methanolysis step that
led to carbonate cleavage keeping the carbamate intact.
Etherification of the phenol position with 6-nitroveratryl bromide
was carried out under basic conditions, and then the Boc protecting
group was removed under acidic conditions using a 1:1 TFA:CH2Cl2
mixture. This liberated the free aniline which was then
monomethylated by iodomethane. Other methods of selective
monomethylation (such as reductive amination or use of a soft
Trimethyl-lock synthesis
The synthesis of the trimethyl-lock derivative (see scheme 2) began
by an esterification and an aromatic electrophilic substitution of
3,5-dimethylphenol with 3,3-dimethylacrylic acid under heating and
acidic conditions to form the corresponding dihydrocoumarine. The
lactone was then reduced by lithium aluminium hydride, leading to
the free alcohol. These two steps are common in trimethyl lock
derivatives syntheses. The following steps have been adapted to
produce our own compound. The phenol was engaged in an
etherification reaction with 6-nitroveratryl bromide, and then the
primary alcohol was successively oxidized to aldehyde and
carboxylic acid by, respectively, pyridinium dichromate and a
Pinnick oxidation. The acid was finally converted to acyl chloride by
phosgene and esterified by DDAO to give the desired ester with an
overall yield of 72%.
methylating
agent
like
dimethyl
carbonate)
showed
incompatibilities with our compounds. Finally, the secondary aniline
was treated with phosgene, and the resulting carbamoyl chloride
reacted with the phenol function of the DDAO to form the desired
carbamate (overall yield, from the commercial anilines: 32 to 47%,
depending on the substituents). These carbamates are constituted
of two rotamers (N-C bond).
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We followed the same procedure as previously described.11 The
principle is to irradiate the compound at 365 nm and to follow the
liberation of the released DDAO by fluorimetry in a quartz cuvette
under temperature (293K) and pH control. The experimental data
were then fitted with the kinetic model to retrieve the values of k1
and k2. The results are reported in table 1.
pKa of the
phenol
Compound
k2 (min-1)
τ2 (min)
2-HPCN0
2
7.6 ± 0.1
(5.2 ± 0.5)10-2
(6.6 ± 0.5)10-2
(1.1 ± 0.3)10-1
(1.9 ± 0.2)10-1
(2.9 ± 0.3)10-1
(3.3 ± 0.3)10-1
19
15
9
(pH 5)
2-HPCNO
2
7.6 ± 0.1
10.0 ± 0.1
10.7 ± 0.1
10.8 ± 0.1
10.2 ± 0.1
(pH 8)
2-HPCBr
(pH 8)
2-HPCH
(pH 8)
2-HPC0CH
5
3
3.5
3
(pH 8)
TML
(pH 8)
Scheme 3: General synthesis of 2-HPC derivatives, with R as a para
substituent (H, Br, NO2, OCH3). Reagents and conditions: a) Boc2O,
K2CO3, THF, H2O, rt (96% to quant.); b) 4,5-dimethoxy-2-nitrobenzyl
bromide, Cs2CO3, THF, rt (71% to quant.); c) Trifluoroacetic acid
(TFA), CH2Cl2, rt (quant.); d) CH3I, K2CO3, DMF, rt (42 to 50%); e) 1.
Phosgene, THF, rt; 2. NEt3, DMAP, DDAO, THF, rt (quant.)
Table 1: Kinetic constants of trimethyl lock and 2-HPC derivatives. See Supporting
Information for equations and methods; where τ = 1/k2, k2 rate constant of the self-
immolation step. pKa determination was carried out by following absorbance of
protected aniline 1, 2, 3, 4 as a function of pH, applying the same method as in Alouane
et al.10-11
Cyclisation rates
Discussion
For the kinetic measurements, our working hypothesis was a two-
Results showed that cyclisation generally occurs in the minute
range, for both trimethyl lock and 2-HPC derivatives; disassembly
times were close to each other, showing only a factor of six
between the largest and the smallest. For the nitro derivative of 2-
HPC, which is the only derivative with a physiological pKa (7.6), we
did not observe any significant dependence on pH: kinetics at pH 5
and pH 8 are close, showing only a 20% difference.
step process as depicted in scheme 4. The first step is
a
photocleavage of the caged precursor, associated to k1, the rate
constant of uncaging, and the intramolecular cyclisation, where k2 is
the rate constant for the self-immolation step.
MeO
MeO
NO
O
O
OMe
CHO
MeO
The trimethyl lock was important because of the large number of
publications using it. The popularity of the trimethyl-lock is due to
the Thorpe-Ingold effect, which is supposed to allow rapid
intramolecular cyclisation. This steric effect is induced by the
unfavourable interaction between the methyl at the meta position
on the phenol core and the two geminal methyls on the alkyl chain
NO2
OH
O
O
O
DDAO
DDAO OH
DDAO
O
O
k1 (hv)
k2
(β position from ester). Because of this steric hindrance,
a
MeO
MeO
NO
O
N
conformation was favoured, making the carbonyl of the ester and
the phenol closer. This vicinity was already known to increase
drastically the cyclisation rate20 but the kinetics of the process was
still unknown. We measured only the rate constant of the TML, in
line with the huge interest to this linkage compared to other
carbonyl species (amide for instance).20 The measured lactonisation
time was around 3 min for this ester derivative.
O
OMe
CHO
R
MeO
NO2
OH
O
R
DDAO OH
N
O
N
O
DDAO
DDAO
k1 (hv)
k2
O
O
R
R = H, Br, NO2, OCH3
The 2-HPC series was chosen to study cyclisation rates of
carbamates, which are relatively resistant to enzymes such as
esterases or peptidases. The spacers have been modulated by
variation of the substituents on the phenol core. The results
Scheme 4: Kinetic models for disassembly from photoactivation to
self-immolation of trimethyl-lock (top) and 2-HPC (bottom)
derivatives.
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enabled us to determine the effects of the substituent and of the constants J in Hz; current notations are used for multiplicity (s:
protonation state on the kinetics of cyclisation. By lowering the pKa singlet; bs: broad singlet; d: doublet; dd: double doublet; t: triplet;
via a withdrawing group, the proportion of phenolate is increased; q: quadruplet; m: multiplet).
the phenolate anion is more nucleophilic than the phenol and so
able to accelerate the cyclisation process. We focused our attention
on the nitro derivative, which exhibits
a pKa close to the
Scheme 5: Numeration for C13 and H1 signals
physiological pH; in order to be in vivo/in vitro deprotonated. We
observed that the kinetics of the self-immolation did not change
significantly by deprotonating the nitrophenol, which led us to
conclude that the gain of nucleophilicity was partially compensated
by conjugation of the phenolate with the nitro group. More
generally, the most electron-donor the cycle has at para position
the faster the cyclisation occurs in line with an enhanced
nucleophilicity of the phenol: Compared to the H derivative (para-
hydrogen), we observed a relative acceleration with electron-donor
groups and a moderate slow-down with electron-withdrawing ones.
According to the literature, in both aliphatic21 and aromatic22
derivatives, nucleophilicity enhancement is a critical factor for the
cyclisation rate. Indeed, in every series (including ours, phenol-
based ones), electron-donating groups made the nucleophile
(oxygen or nitrogen in previously cited works) more reactive.
Adding this to other parameters, like decreasing pKa of the leaving
group, changing heteroatom, promoting cyclisation at high pH,
choosing a better electrophilic carbonyl, or increasing temperature,
various cyclisation-based spacer can be generated with half-times
close to the minute range, or even less.
General procedure
Aniline protection (1, 2, 3, 4)
To a solution of 2-aminophenol derivative (1 eq) in THF/water (1:1
proportion) was added K2CO3 (5 eq) and di-tert-butyl dicarbonate
(2.6 eq). After stirring for 4h at room temperature, the mixture was
neutralized (Acetic acid 100%, until pH 7), the organic layer was
diluted with EtOAc and washed with water and brine, then dried on
MgSO4, filtered and concentrated under reduced pressure. The
residue was resolubilized in MeOH and we added K2CO3 (5 eq) and
stirred at room temperature until no more evolution is observed (as
seen on TLC, between 1h30 and 4h). The same work-up than
previously was applied to obtain the crude product.
Eventually, this work and our previous ones11,12 show that self-
immolation in elimination-based spacers is much more rapid and
substituent sensitive than in cyclisation-based ones.
Nitroveratryl coupling (5, 6, 7, 8)
Conclusions
4,5-dimethoxy-2-nitrobenzyl bromide (1 eq) was introduced in a
solution containing the carbamate (1 eq), and Cs2CO3 (1.5 eq) in
THF. The mixture was stirred overnight at room temperature, and
then neutralized to pH 7 by HCl 1M, washed with water then brine,
dried on MgSO4, filtered and evaporated. After purification on silica
gel column chromatography, the corresponding ether was obtained.
We investigated the self-immolation kinetics of common
cyclisation-based self-immolative spacers. They exhibited release-
times within the 1-10 minute range at room temperature. Steric
effects were more stringent than electronic ones to modulate the
self-immolation rate. The comparison between cyclisation and
elimination-driven self-immolation rates (as reported by Alouane et
al)11,12 further suggested the later mechanism to have more
potential for modulating kinetics.
Aniline deprotection (9, 10, 11, 12
The protected aniline (1
)
eq)
was
solubilized
in
Experimental
dichloromethane/trifluoroacetic acid (1:1 volume ratio) and stirred
at room temperature for 30 min. After evaporation, the residue was
taken up in EtOAc and washed with aqueous K2CO3 solution, water,
and brine, then dried on MgSO4, filtrated and the solvent was
removed in vacuo. The unprotected secondary anilines were
isolated without further purification.
The commercially available chemicals were used without further
purification. Anhydrous solvents were freshly distilled before use.
Low actinic glassware and aluminium film were used for all
experiments involving compounds bearing the nitroveratryl moiety.
Column chromatography (CC): silica gel 60 (0.040-0.063mm) Merck.
Analytical and thin layer chromatography (TLC): Merck silica gel 60
F-254 precoated plates; detection by UV (254 and 365 nm). 1H NMR
spectra were recorded at 300 MHz. 13C NMR spectra were recorded
at 75 MHz with complete proton decoupling; chemical shifts (δ) in
ppm related to protonated solvent as internal reference (1H: CHCl3
in CDCl3, 7.26 ppm; 13C: 13CDCl3 in CDCl3, 77.0 ppm; Coupling
Aniline methylation (13, 14, 15, 16)
The secondary anilines ( 1 eq), K2CO3 (1.5 eq), and iodomethane (1
eq) in DMF were stirred at room temperature under argon until
reaction showed no more evolution on TLC. The solvent was
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removed and the residue was solubilized in EtOAc. The organic layer The aniline 9 was directly obtained pure as a deeply red solid (427
was washed with water several times, brine; and finally dried on mg, quantitative yield) rf 0.18 (30% EtOAc/cyclohexane); mp 187°C;
MgSO4, filtrated and concentrated to dryness. The secondary IR (cm-1) 3368, 2922, 2851, 1783, 1514; δH 3.92 (3H, s, OCH3 (1)),
anilines were obtained after purification by column chromatography 3.97 (3H, s, OCH3 (2)), 5.62 (1H, s, H7), 7.15 (1H, d, 9.12 Hz, H6), 7.36
on silica gel.
(1H, s, H13), 7.81 (1H, s, H10), 8.13 (1H, d, 2.55 Hz, H3), 8.26 (1H, dd,
2.58/9.06 Hz, H5); δC 56.6 (OCH3 (1) & (2)), 68.1 (C7), 108.2 (C3),
109.5 (C5 & C13), 111.1 (C6), 114.8 (C8), 127.4 (C10), 136.9 (C2), 139.5
(C4), 142.5 (C9), 148.3 (C11), 150.1 (C1), 154 (C12); m/z 196, 350, 545
[M+H]+. HRMS, calculated: m/z 350.0910, found: m/z 350.0982
([M+H]+).
Coupling with DDAO (2-HPC)
To a solution of N-methylaniline (1 eq) in anhydrous THF, was
carefully injected an excess of phosgene 30% in toluene (500 µL)
under argon. The mixture was stirred at room temperature for 20
min. The remaining phosgene was eliminated by an argon flux
(warning, highly toxic) then the solution was added to a solution of
2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-N-methyl-5-
nitroaniline (13)
1,3-dichloro-7-hydroxy-9,9-dimethylacridin-2(9H)-one
(0.055
mmol), 4-dimethylaminopyridine (0.055 mmol) and an excess of
triethylamine (1 mL), in THF. The resulting solution was stirred
under argon at room temperature overnight. The solvent was
evaporated, then the residue was taken up in dichloromethane; the
organic phase was washed with a solution of K2CO3, water and
brine; dried on MgSO4, filtrated and concentrated in vacuo. The final
carbamates were purified by HPLC using 80 to 90% gradient of
CH3CN/water/0.1% TFA, Waters XBridge® Prep C18 5µm OBD™ 30 x
150mm Column.
The aniline 13 was obtained after purification by column
chromatography on silica gel (15% EtOAc/cyclohexane) as a yellow
solid (170 mg, 40%); rf 0.23 (20% EtOAc/cyclohexane); mp 197°C; IR
(cm-1) 3424, 2921, 2851, 1271, 1219; δH 2.96 (s, 3H, NCH3), 3.90 (s,
3H, OCH3 (1)), 3.98 (s, 3H, OCH3 (2) ), 5.62 (s, 2H, H7), 6.78 (d, 1H, J=
9 Hz, H6), 7.03 (s, 1H, H13), 7.43 (d, 1H, J= 3 Hz, H3), 7.58 (dd, 1H, J=
3/ 9 Hz, H5), 7.77 (s, 1H, H10); δC 30.2 (NCH3), 56.5 (OCH3 (1) & (2)),
68.2 (C7), 103.9 (C3),108.3 (C5), 109.7 (C13), 109.9 (C6/C8), 113 (C10),
127.2 (C2), 139.7 (C9), 143.1 (C11), 148.4 (C12), 148.9 (C1), 153.9 (C4);
m/z 196, 364 [M+H]+. HRMS, calculated: m/z 364.1100, found: m/z
364.1141 ([M+H]+).
tert-butyl (2-hydroxy-5-nitrophenyl)carbamate (1)
The carbamate 1 was obtained without purification as a dark yellow
powder (330 mg, 99%); rf 0.57 (40% EtOAc/cyclohexane); mp 111°C;
IR (cm-1) 3264, 1765, 1530, 1151; δH 1.54 (s, 9H, tBu), 3.81 (bs, 1H,
OH), 7.9 (dd, 1H, J= 2.67/8.91 Hz, H6), 8.06 (d, 1H, J= 2.64, H3), 8.11
(dd, 1H, 2.70/8.94 Hz, H5), 8.23 (bs, 1H, NH); δC 28.2 (tBu), 85.2 (Cq
Boc), 117.2 (C3), 121.1 (C6), 126.2 (C5), 126.8 (C2), 151.8 (C4), 153.4
(C=O), 158.6 (C1); m/z 155, 199, 377 [M+Na]+. HRMS, calculated:
m/z 277.0793, found: m/z 277.0792 ([M+Na]+), 278.0825
([MN15+Na]+).
6,8-dichloro-9,9-dimethyl-7-oxo-7,9-dihydroacridin-2-yl(2-
((4,5-dimethoxy-2-nitrobenzyl)oxy)-5-
nitrophenyl)(methyl)carbamate (2-HPCNO2
)
The crude product was purified by column chromatography on silica
gel (100% dichloromethane) to give the final carbamate 2-HPCNO2
(38.4 mg, quantitative yield) as a yellow solid; rf 0.14 (20%
EtOAc/cyclohexane); mp 216°C; IR (cm-1) 2922, 2851, 1787, 1656,
1254, 1220; δH 1.67 (s, 6H, CH3 DDAO), 3.42 (s, 3H, NCH3), 3.90 (s,
3H, OCH3 (1)), 4 (s, 3H, OCH3 (2)), 5.71 (s, 2H, H7), 6.88 (d, 1H, J= 8.1
Hz, H6), 6.9 (s, 1H, H13), 7.31 (s, 1H, H22), 7.35 (d, 1H, J= 4.32 Hz, H5),
7.5 (s, 1H, H25), 7.84 (d, 1H, J= 4.32 Hz, H3), 8.34 (s, 2H, H15/H26),
8.37 (s, 1H, H10); δC 26.5 (CH3 DDAO), 30.9 (NCH3), 56.5/56.9 (OCH3
1 and 2), 68.3 (C3), 108.2 (C5), 108.3 (C3), 108.4 (C13), 112.8 (C15),
119.7 (C6), 121.2 (C25), 124.8 (C26), 125.7 (C2), 131.8 (C8), 133 (C10),
135.6 (C19/C21), 138.4 (C9), 136.8 (C4/C24), 138.4 (C16), 139.4
(C11/C12), 148.5 (C18), 149.8 (C14), 153.5 (C22), 153.6 (C23), 158.5 (C1),
173.1 (C20), 207 (C=O carbamate); m/z 196, 289, 371, 447, 697
[M+H]+. HRMS, calculated: m/z 697.1096, found: m/z 697.1105
([M+H]+), 699.1088 (MCl37+H]+).
tert-butyl
(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-5-
nitrophenyl)carbamate (5)
The crude product was purified by column chromatography on silica
gel (20% EtOAc/cyclohexane) to give the ether 5 as a dark red solid
(548 mg, 94%) rf 0.23 (20% EtOAc/cyclohexane); mp 122°C; IR (cm-1)
2979, 1785, 1519; δH 1.36 (9H, s, tBu), 3.97 (3H, s, OCH3 (1)), 4.03
(3H, s, OCH3 (2)), 5.65 (1H, s, H7), 7.15 (1H, d, 9.12 Hz, H6), 7.36 (1H,
s, H13), 7.81 (1H, s, H10), 8.13 (1H, d, 2.55 Hz, H3), 8.26 (1H, dd,
2.58/9.06 Hz, H5); δC 27.8 (CH3 Boc), 56.4-57.2 (OCH3 (1) & (2)), 67.8
(C7), 83.4 (Cq Boc), 108 (C3), 108.5 (C13), 111.9 (C5), 125.4 (C6), 125.5
(C2), 127.4 (C8), 129.2 (C10), 138.3 (C9), 141.5 (C11), 148.1 (C4), 150.8
(C=O Boc), 154.7 (C12), 158 (C1); m/z 196, 472 [M+Na]+. HRMS,
calculated: m/z 472.1334, found: m/z 472.1326 ([M+Na]+).
tert-butyl (2-hydroxyphenyl)carbamate (2)
The carbamate 2 was obtained as a dark yellow powder (919 mg,
96%); rf 0.7 (40% EtOAc/cyclohexane); mp 142°C; IR (cm-1) 3284,
1690, 1147; δH 1.53 (s, 9H, tBu), 6.77 (bs, 1H, OH), 6.85 (d, 1H, J=
14.7 Hz, H6), 6.94 (d, 1H, 14.6 Hz, H4), 6.98 (d, 1H, 9.2 Hz, H5), 7.15
(d, 1H, 7.5 Hz, H3); δC 28.3 (CH3 Boc), 82.1 (Cq Boc), 118.9 (C6), 120.8
2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-5-nitroaniline (9)
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(C4), 121.4 (C2), 125.7 (C3/5), 147.5 (C1), 155.1 (C=O Boc); m/z 176, mg, quantitative yield) as
Journal Name
a
yellow solid; rf 0.27 (20%
232 [M+Na]+. HRMS, calculated: m/z 232.0917, found: m/z EtOAc/cyclohexane); mp 160°C; IR (cm-1) 3382, 2915, 2850, 2813,
232.0943 ([M+Na]+).
1710, 1502; δH 1.58 (s, 6H, CH3 DDAO), 3.32 (s, 3H, NCH3), 3.82 (s,
3H, OCH3 (1)), 3.95 (s, 3H, OCH3 (2)), 5.52 (s, 2H, H7), 6.58 (d, 1H, J=
tert-butyl
(2-((4,5-dimethoxy-2- 1.32 Hz, H5), 6.61 (d, 1H, J= 1.32 Hz, H4), 6.75 (d, 1H, J= 7.62 Hz, H6),
6.87 (s, 1H, H22), 6.93 (d, 1H, J= 7.89 Hz, H3), 7.11 (s, 1H, H26), 7.21
nitrobenzyl)oxy)phenyl)carbamate (6)
(s, 1H, H13), 7.22 (s, 1H, H25), 7.38 (s, 1H, H15), 7.44 (s, 1H, H10); δC
The crude product was purified by column chromatography on silica 27.8 (CH3 DDAO), 30.5 (NCH3), 32.8 (C17), 56.4 (OCH3 (1) & (2)), 68.1
gel (20% EtOAc/cyclohexane) to give the ether 6 as a light yellow (C7), 109.7 (C13), 118.8 (C15), 118.9 (C8), 119.5 (C6), 120.1 (C26), 120.4
solid (376.1 mg, quantitative yield); rf 0.3 (20% EtOAc/cyclohexane); (C25), 121.5 (C4), 122.1 (C2), 122.3 (C10), 126.4 (C3/5), 129.4 (C21),
mp 137°C; IR (cm-1) 3452, 2943, 2897, 1730, 1221, 1150; δH 1.52 (s, 129.9 (C19), 136.9 (C9), 139.3 (C11), 140.8 (C24), 144.6 (C16), 145.9
9H, tBu), 3.92 (s, 3H, OCH3 (1)), 3.96 (s, 3H, OCH3 (2)), 5.54 (s, 2H, (C12), 147.2 (C18), 148.1 (C1), 151.2 (C22), 158.8 (C14), 164.6 (C23),
H7), 6.84 (dd, 1H, J= 1.26/14.7 Hz, H6), 6.9 (dd, 1H, J= 1.3/14.1 Hz, 170.2 (C20); m/z 196, 345, 652 [M+H]+. HRMS, calculated: m/z
H4), 6.95 (dd, 1H, J= 1.3/14 Hz, H5), 7.12 (bs, 1H, NH), 7.18 (s, 1H, 652.1146, found: m/z 652.1252 ([M+H]+), 654.1235 (MCl37+H]+).
H13), 7.77 (s, 1H, H10), 8.07 (d, 1H, J= 7 Hz, H3); δC 28.5 (CH3 Boc),
55.9 (OCH3 (1) & (2)), 67.7 (C7), 82.3 (Cq Boc), 109.5 (C13), 118.7 (C8),
119.1 (C6), 121 (C4), 121.6 (C2), 122.2 (C10), 125.9 (C3/5), 136.5 (C9),
tert-butyl (2-hydroxy-5-methoxyphenyl)carbamate (3)
139.1 (C11), 145.7 (C12), 147.7 (C1), 155.3 (C=O Boc); m/z 196, 305, The carbamate 3 was obtained as a dark red oil (555.1 mg,
349, 405 [M+H]+, 427 ([M+Na]+. HRMS, calculated: m/z 405.1617, quantitative); rf 0.77 (40% EtOAc/cyclohexane); IR (cm-1) 3225,
found: m/z 405.1661 ([M+H]+).
2857, 1726, 1150; δH 3.66 (s, 3H, methoxy), 6.14 (dd, 1H, J=
2.94/8.94 Hz, H5), 6.36 (d, 1H, J= 2.91 Hz, H3), 6.58 (d, 1H, J= 8.58
Hz, H6); δC 55.6 (OCH3 phenol), 106.3 (C3), 110 (C6), 118.2 (C5), 126.3
(C2), 140.3 (C1), 153.5 (C4); m/z 140 [M+H]+, 206, 262 [M+Na]+.
2-((4,5-dimethoxy-2-nitrobenzyl)oxy)aniline (10)
The aniline 10 was obtained as
a
yellow solid (137.7 mg, HRMS, calculated: m/z 262.1091, found: m/z 262.1050 ([M+Na]+).
quantitative yield); rf 0.24 (30% EtOAc/cyclohexane); mp 115°C; IR
(cm-1) 3453, 2946, 2907, 1221, 1151; δH 3.90 (s, 3H, OCH3 (1)), 3.93
tert-butyl
(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-5-
(s, 3H, OCH3 (2)), 5.49 (s, 2H, H7), 6.64 (dd, 1H, J= 1.3/14.7 Hz, H6), methoxyphenyl)carbamate (7)
6.69 (dd, 1H, J= 1.28/13.7 Hz, H4), 6.76 (dd, 1H, J= 1.3/14 Hz, H5),
6.8 (dd, 1H, J= 1.7/14.2 Hz, H3), 7.25 (s, 1H, H13), 7.72 (s, 1H, H10); δC The crude product was purified by column chromatography on silica
56.1 (OCH3 (1) and (2)), 68.1 (C7), 109.7 (C13), 118.9 (C8), 119.5 (C6), gel (50% dichloromethane/cyclohexane) to give the ether 7 as a red
121.5 (C4), 122.1 (C2), 122.3 (C10), 126.4 (C3/5), 136.9 (C9), 139.3 solid (485.5 mg, 71%); rf 0.33 (20% EtOAc/cyclohexane); mp 143°C;
(C11), 145.9 (C12), 148.1 (C1); m/z 196, 305 [M+H]+. HRMS, IR (cm-1) 3451, 2975, 2904, 2863, 1712, 1271; δH 1.49 (s, 9H, tBu),
calculated: m/z 305.1093, found: m/z 305.1131 ([M+H]+).
3.68 (s, 3H, methoxy), 6.47 (dd, 1H, J= 2.88/8.70 Hz, H5), 6.78 (d, 1H,
J= 8,5 Hz, H6), 7.12 (d, 1H, J= 2.6 Hz, H3); δC 28.3 (CH3 Boc), 55.6
(methoxy), 81.8 (Cq Boc), 106.5 (C3), 110.2 (C6), 118.4 (C5), 126.5
(C2), 140.5 (C1), 152.5 (C=O Boc), 153.7 (C4); m/z 140, 196, 335, 379
2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-N-methylaniline (14)
The aniline 14 was obtained after purification by column [M+H]+, 457 [M+Na]+. HRMS, calculated: m/z 435.1789, found: m/z
chromatography on silica gel (15% EtOAc/cyclohexane) as an orange 435.1763 ([M+H]+).
solid (60 mg, 48%); rf 0.36 (20% EtOAc/cyclohexane); mp 130°C; IR
(cm-1) 2976, 2999, 1215; δH 2.9 (s, 3H, NCH3), 3.90 (s, 3H, OCH3 (1)),
2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-5-methoxyaniline (11)
3.95 (s, 3H, OCH3 (2)), 4.32 (bs, 1H, NH), 5.51 (s, 2H, H7), 6.58 (d, 1H,
J= 1.32 Hz, H5), 6.61 (d, 1H, J= 1.32 Hz, H4), 6.65 (d, 1H, J= 7.62 Hz, The aniline 11 was obtained as a red solid (m= 639 mg, quantitative
H6), 6.93 (d, 1H, J= 7.89 Hz, H3), 7.21 (s, 1H, H13), 7.44 (s, 1H, H10); δC yield); rf 0.35 (30% EtOAc/cyclohexane); mp 117°C; IR (cm-1) 3193,
30.5 (NCH3), 56.4 (OCH3 (1) & (2)), 68.1 (C7), 109.7 (C13), 118.9 (C8), 2918, 2863, 1208; δH 3.67 (s, 1H, methoxy), 3.82 (s, 1H, OCH3 (1) ),
119.5 (C6), 121.5 (C4), 122.1 (C2), 122.3 (C11), 126.4 (C3/5), 136.9 (C9), 3.91 (s, 1H, OCH3 (2) ), 5.4 (s, 2H, H7), 6.78 (dd, 1H, J= 2.3/8.9 Hz,
139.3 (C11), 145.9 (C12), 148.1 (C1); m/z 196, 319 [M+H]+. HRMS, H5), 6.85 (d, 1H, 8.9 Hz, H6), 6.99 (d, 1H, 2.3 Hz, H3), 7.12 (s, 1H, H13),
calculated: m/z 319.1249, found: m/z 319.1288 ([M+H]+).
7.65 (s, 1H, H10), 11.08 (bs, 2H, NH2); δC 55.5 (methoxy), 56.5 (OCH3
(1) and (2)), 68.7 (C7), 102.3 (C3), 102.5 (C5), 108 (C6), 109.5 (C8),
114.3 (C10/C13), 129.9 (C2), 139.2 (C4), 140.2 (C1), 148.8 (C9), 153.9
(C12), 155.2 (C11); m/z 154, 182, 196, 335, 357 [M+H]+. HRMS,
calculated: m/z 335.1165, found: m/z 335.1239 ([M+H]+).
6,8-dichloro-9,9-dimethyl-7-oxo-7,9-dihydroacridin-2-yl(2-
((4,5-dimethoxy-2-nitrobenzyl) oxy)phenyl)(methyl)carbamate
(2-HPCH)
The crude product was purified by column chromatography on silica
2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-5-methoxy-N-
gel (100% dichloromethane) to give the carbamate 2-HPCH (110.4 methylaniline (15)
6 | J. Name., 2012, 00, 1-3
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7.03 (dd, 1H, J= 2.31/8.61 Hz, H5), 7.11 (s, 2H, H3/H13), 7.77 (s, 1H,
The aniline 15 was obtained after purification by column H10), 8.3 (bs, 1H, NH); δC 28.3 (tBu), 56.4 (OCH3 (1) & (2)), 68.3 (C7),
chromatography on silica gel (15% EtOAc/cyclohexane) as a yellow 81.1 (Cq Boc), 108.2 (C13), 109 (C4), 113.3 (C6), 114.7 (C3), 121.4 (C2),
solid (148.9 mg, 45%); rf 0.51 (20% EtOAc/cyclohexane); mp 153°C; 125.1 (C8), 129.6 (C10), 139.1 (C9), 145.1 (C11), 148.2 (C11), 152.3
IR (cm-1) 3406, 2929, 1516; δH 3.87 (s, 3H, NCH3), 3.76 (s, 3H, (C=O Boc), 154 (C12); m/z 196, 385, 427, 483 [M+H]+. HRMS,
methoxy), 3.92 (s, 3H, OCH3 (1)), 3.96 (s, 3H, OCH3 (2)), 5.46 (s, 2H, calculated: m/z 483.0668, found: m/z 483.0766 ([M+H]+), 485.0738
H7), 6.1 (dd, 1H, J= 3.00/9.00 Hz, H5), 6.24 (d, 1H, J= 2.8 Hz, H3), 6.67 (MBr81+H]+).
(d, 1H, J= 8.9 Hz, H6), 7.24 (s, 1H, H13), 7.75 ( s, 1H, H10); δC 30.3
(NCH3), 56.1 (methoxy), 56.4 (OCH3 (1) & (2)), 70.1 (C7), 107 (C3),
110.7 (C6), 113.4 (C13), 118.9 (C5), 127 (C2), 127.8 (C8) 129.9 (C10), (12)
140.4 (C9), 140.9 (C1), 142.4 (C11), 154.2 (C4), 156.6 (C12); m/z 152,
5-bromo-2-((4,5-dimethoxy-2-nitrobenzyl)oxy)aniline
349 [M+H]+. HRMS, calculated: m/z 349.1355, found: m/z 349.1393 The aniline 18 was obtained as a dark red solid (955.1 mg,
([M+H]+).
quantitative yield); rf 0.23 (30% EtOAc/cyclohexane); mp 142°C; IR
(cm-1) 3366, 2917, 2884, 1271, 1192; δH 3.64 (bs, 2H, NH2) ; 3.92 (s,
3H, OCH3 (1)) ; 3.95 (s, 3H, OCH3 (2)) ; 5,49 (s, 2H, H7) ; 6,62 (d, 1H,
oxy)-5- J= 8.58 Hz, H6) ; 6.75 (1H, dd, 2.19/8.52 Hz, H5), 6.86 (1H, d, 2.22 Hz,
H3), 7.17 (1H, s, H13), 7.74 (1H, s, H10); δC 56.4 (OCH3 (1) & (2)), 68.0
(C7), 108.1 (C13), 109.4 (C4), 114.1 (C3), 114.4 (C6), 118.0 (C5), 121.0
6,8-dichloro-9,9-dimethyl-7-oxo-7,9-dihydroacridin-2-yl(2-
((4,5-dimethoxy-2-nitrobenzyl)
methoxyphenyl)(methyl)carbamate (2-HPCOCH3
)
The crude product was purified by column chromatography on silica (C8), 128.9 (C10), 138.0 (C2), 139.3 (C9), 144.7 (C11), 148.0 (C1), 153.9
gel (100% dichloromethane) to give the final carbamate 2-HPCOCH3 (C12); m/z 196, 383 [M+H]+. HRMS, calculated: m/z 383.0144, found:
(44.4 mg, quantitative yield) as a brown solid; rf 0.27 (20% m/z 383.0234 ([M+H]+), 385.0217 (MBr81+H]+).
EtOAc/cyclohexane); mp 103°C; IR (cm-1) 2924, 2801, 1726, 1657,
1235; δH 1.58 (s, 6H, CH3 DDAO), 3.31 (s, 3H, NCH3), 3.77/3.81 (s,
5-bromo-2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-N-
6H, OCH3 (1) & (2)), 3.91 (s, 3H, methoxy), 5.46 (s, 2H, H7), 6.87 (m, methylaniline (16)
3H, H3/H5/H6), 6.97 (d, 1H, J= 3Hz, H15), 7.03 (s, 1H, H25), 7.38 (s, 1H,
H13), 7.44 (d, 1H, J= 9Hz, H26), 7.51 (s, 1H, H22), 7.74 (s, 1H, H10); δC The aniline 16 was obtained after purification by column
29.7 (CH3 DDAO), 39.1 (NCH3), 56.9/56.5/55.8 (OCH3 (1)&(2), chromatography on silica gel (15% EtOAc/cyclohexane) as a yellow
methoxy), 67.7 (C7), 106.6 (C3/C5), 108 (C13), 108.6 (C6), 113.4 (C15), solid (496 mg, 50%); rf 0.26 (20% EtOAc/cyclohexane); mp 170°C; IR
113.9 (C25), 114.9 (C26), 120 (C2), 121.5 (C8), 121.5 (C9), 129 (C21), (cm-1) 2922, 28.47, 1209, 1155; δH:2.88 (3H, s, NCH3), 3.91 (3H, s,
132.1 (C19), 132.9 (C10), 135.4 (C16), 137.2 (C9), 138.2 (C16), 138.6 OCH3 (1)), 3.96 (3H, s, OCH3 (2)), 5.50 (2H, s, H7), 6.60 (1H, d, J= 8.46
(C11), 139.2 (C12), 139.4 (C1), 140.3 (C18), 147.4 (C14), 148 (C22), 149.6 Hz, H6), 6.76 (1H, d, J= 8.31 Hz, H5), 6.82 (1H, s, H3), 7.15 (1H, s, H13),
(C23), 154.1 (C4), 154.4 (C=O carbamate), 173.1 (C=O DDAO); m/z 7.75 (1H, s, H10).; δC 30.4 (NCH3), 56.5 (OCH3 (1) & (2)), 68.3 (C7),
149, 448, 682 [M+H]+. HRMS, calculated: m/z 682.1251, found: m/z 108.0 (C13), 109.5 (C3), 113.0 (C4), 115.4 (C6), 119.1 (C5), 129.0 (C8),
682.1356 ([M+H]+), 684.1341 (MCl37+H]+).
139.4 (C10), 140.6 (C9), 144.5 (C2), 148.3 (C11/C1), 154.1 (C12); m/z
196, 397 [M+H]+. HRMS, calculated: m/z 397.0300, found: m/z
397.0392 ([M+H]+), 399.0373 (MBr81+H]+).
tert-butyl (5-bromo-2-hydroxyphenyl)carbamate (4)
The carbamate 4 was obtained as a red solid (750 mg, quantitative
6,8-dichloro-9,9-dimethyl-7-oxo-7,9-dihydroacridin-2-yl(5-
yield); rf 0.74 (40% EtOAc/cyclohexane); mp 135°C; IR (cm-1) 3262, bromo-2-((4,5-dimethoxy-2-nitrobenzyl)oxy)
2978, 1691, 1150; δH 1.52 (s, 9H, tBu), 6.65 (s, 1H, H3), 6.82 (d, 1H, phenyl)(methyl)carbamate (2-HPCBr)
J= 8.58 Hz, H6), 7.11 (dd, 1H, J= 3.87/8.49 Hz, H5), 7.33 (s, 1H, OH),
7.87 (bs, 1H, NH); δC 28.2 (CH3 Boc), 82.6 (Cq Boc), 112.4 (C4), 120 The crude product was purified by column chromatography on silica
(C6), 123.8 (C3), 127.1 (C2), 128.1 (C5), 146.4 (C1), 154.6 (C=O Boc); gel (100% dichloromethane) to give the carbamate 2-HPCBr (24.1
m/z 187, 231 [M+H]+, 310 [M+Na]+. HRMS, calculated: m/z mg, quantitative yield) as
a dark green solid; rf 0.31 (20%
310.0037, found: m/z 310.0048 ([M+Na]+), 312.0029 (MBr81+Na]+).
EtOAc/cyclohexane); mp 146°C; IR (cm-1) 2923, 1728, 1658, 1222; δH
1.67 (s, 6H, CH3 DDAO), 3.38 (s, 3H, NCH3), 3.88 (s, 3H, OCH3 (1)),
tert-butyl
(5-bromo-2-((4,5-dimethoxy-2- 3.99 (s, 3H, OCH3 (2)), 5.57 (s, 2H, H7), 6.93 (d, 1H, J = 9Hz, H5), 7.03
(s, 1H, H13), 7.09 (d, 1H, J= 6 Hz, H3), 7.39 (s, 1H, H6), 7.52 (m, 3H,
nitrobenzyl)oxy)phenyl)carbamate (8)
H25/H26/H15), 7.60 (s, 1H, H10), 7.82 (s, 1H, H22); δC 25.6/26.4 (CH3
The crude product was purified by column chromatography on silica DDAO), 29.7 (NCH3), 56.5 (OCH3 (1)), 56.9 (OCH3 (2)), 67.6 (C17), 68
gel (20% EtOAc/cyclohexane) to give the ether as a brown solid (C7), 108.2 (C13), 108.4 (C4), 113.5 (C6), 114.7 (C15), 119.8 (C26), 121.4
(1.23 g, 94%); rf 0.34 (20% EtOAc/cyclohexane); mp 148°C; IR (cm-1) (C25), 128 (C3), 131.6 (C8), 132.3 (C5), 132.7 (C2), 135.6 (C21), 137.3
3452, 2976, 2927, 1726; δH 1.52 (s, 9H, tBu), 3.92 (s, 3H, OCH3 (1)), (C19), 138.2 (C24), 138.7 (C16), 139.3 (C11), 140.2 (C12/C23), 148.2 (C18),
3.97 (s, 3H, OCH3 (2)), 5.53 (s, 2H, H7), 6.69 (d, 1H, J= 8.70 Hz, H6), 149.6 (C14/C22), 152.6 (C1), 153.9 (C9), 154.4 (C=O carbamate), 173.1
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(C20); m/z 397, 730 [M+H]+. HRMS, calculated: m/z 730.0260, found: (6H, s, H10/H11), 2.21 (3H, s, H7), 2.24 (2H, t, J= 7.24 Hz, H12), 2.51
m/z 730.0358 ([M+H]+), 732.0333 (MBr81+H]+), 734.0319 (3H, s, H8, 3.57 (2H, t, J= 7.23 Hz, H13), 3.94 (3H, s, OCH3 (1)), 3.97
(MCl37Br81+H]+).
(3H, s, OCH3 (2)), 5.50 (2H, s, H14), 6.58 (2H, s, H4/H6), 7.37 (1H, s,
H20), 7.78 (1H, s, H17); δC 21.0 (C7), 26.2 (C8), 32.7 (C10/C11), 40.5 (C9),
46.0 (C12), 56.5 (OCH3 (1) & (2)), 61.5 (C13), 69.4 (C14), 108.5 (C20),
110.6 (C6), 114.0 (C4), 129.0 (C15), 130.6 (C2), 131.4 (C17), 137.1 (C3),
138.3 (C5), 139.3 (C16), 148.5 (C18), 154.3 (C1), 158.8 (C19); m/z 196,
318, 404, 421 [M+H]+. HRMS, calculated: m/z 404.2028, found: m/z
404.2069 ([M+H]+).
4,4,5,7-Tetramethyl-2-chromanone (17)
3,5-dimethylphenol (500 mg, 4.09 mmol) and 3,3-dimethylacrylic
acid (409,5 mg, 4.09 mmol) were dissolved in toluene (15 mL). Then
methyl sulfonic acid was added (2.92 mL, 20.45 mmol). The mixture
was stirred for 4 h under argon at 85°C. After solvent evaporation,
the reaction mixture was diluted with EtOAc and washed with
3-(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-4,6-dimethylphenyl)-
K2CO3 (1M) solution, water and brine; and finally dried over 3-methylbutanal (20)
anhydrous magnesium sulphate. The solvent was removed under
To
a
solution of 3-(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-4,6-
vacuum affording a yellow oil (827 mg, 99%); rf 0.72 (30%
EtOAc/cyclohexane); IR (cm-1) 2966, 1766; δH 1.42 (6H, s, H10/H11),
2.25 (3H, s, H7), 2.45 (3H, s, H8), 2.56 (2H, s, H12), 6.72 (2H, d, J= 4.86
Hz, H4/H6); δC 20.9 (C7), 23.9 (C8), 28.2 (C10/C11), 35.5 (C9), 46.0 (C12),
117.0 (C6), 126.9 (C4), 130.1 (C3), 136.6 (C2), 138.2 (C5), 152.0 (C1),
169.3 (C13); m/z 175, 205 [M+H]+. HRMS, calculated: m/z 205.1184,
found: m/z 205.1222 ([M+H]+).
dimethylphenyl)-3-methylbutan-1-ol (714.9 mg, 1.77 mmol, 1 eq) in
10 mL of dichloromethane was added pyridinium dichromate (2.66
g, 7.08 mmol, 4 eq). The mixture was stirred under argon for 24h,
then treated by NH4Cl, water and brine; dried over MgSO4, filtrated
and concentrated in vacuo. The crude product was purified by
column chromatography (20% EtOAc/cyclohexane) to give the
aldehyde as an orange solid (675 mg, 95%); rf 0.51 (30%
EtOAc/cyclohexane); mp 106 °C; IR (cm-1) 2919, 1721, 1275; δH 1.62
(6H, s, H10/H11), 2.16 (3H, s, H7), 2.51 (3H, s, H8), 2.97 (2H, s, H12),
3.90 (3H, s, OCH3 (1)), 3.94 (3H, s, OCH3 (2)), 5.47 (2H, s, H14), 6.52
(1H, s, H4), 6.58 (1H, s, H6), 7.20 (1H, s, H20), 7.74 (1H, s, H17), 9.54
(1H, s, H13); δC 21.0 (C7), 26.2 (C8), 32.3 (C10/C11), 39.2 (C9), 57.1
(OCH3 (1) & (2)), 69.2 (C14), 108.5 (C20), 110.2 (C6), 113.9 (C4), 128.9
(C15), 129.9 (C2), 130.2 (C17), 137.4 (C3), 138.0 (C5), 139.3 (C12), 148.4
(C18), 154.4 (C1), 157.8 (C19), 204.1 (C13); m/z 196, 338, 384, 402, 419
[M+H]+. HRMS, calculated: m/z 402.1872, found: m/z 402.1911
([M+H]+).
2-(4-hydroxy-2-methylbutan-2-yl)-3,5-dimethylphenol (18)
To a solution of 4,4,5,7-Tetramethyl-2-chromanone (500 mg, 2.45
mmol) in anhydrous THF (10 mL) in an ice bath was added lithium
aluminium hydride (766.6 mg, 12.12 mmol) portion wise. The
heterogeneous mixture was allowed to warm at room temperature
and stirred 1h30 under argon. The excess of LiAlH4 was neutralized
with NH4Cl at 0°C, then the suspension was filtrated on Celite 535;
the resulting filtrate was diluted by EtOAc and treated by HCl 1M,
water and brine; and finally dried on MgSO4, filtrated and
concentrated in vacuo. The crude product was purified on silica gel
column chromatography, giving the alcohol 18 as an off-white
3-(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-4,6-dimethylphenyl)-
powder (479 mg, 94%); rf 0.35 (30% EtOAc/cyclohexane); mp 78°C; 3-methylbutanoic acid (21)
IR (cm-1) 3508; δH (CD3OD) 1.55 (6H, s, H10/H11), 2.17 (3H, s, H7), 2.27
3-(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-4,6-dimethylphenyl)-3-
(2H, t, J= 6.24 Hz, H12), 2.48 (3H, s, H8), 3.62 (2H, dd, J= 7.24/14.61
Hz, H13), 6.34 (1H, s, H4), 6.45 (1H, bs, OH), 6.49 (1H, s, H6); δC
(CD3OD) 20.6 (C7), 26.0 (C8), 32.1 (C10/C11), 45.2 (C12), 61.9 (C13),
113.6 (C6), 127.2 (C4), 136.7 (C2), 138.4 (C3), 139.9 (C5), 156.1 (C1);
m/z 123, 189, 209 [M+H]+, 231 [M+Na]+. HRMS, calculated: m/z
209.1497, found: m/z 209.1531 ([M+H]+).
methylbutanal (116 mg, 0.29 mmol) was dissolved in 10 mL of
acetone/tert-butanol/water (17:12:3) mixture, then 2-methyl-2-
butene (208 µL, 1.96 mmol, 6.75 eq), sodium chlorite (137.7 mg,
1.52 mmol, 5.25 eq), and sodium dihydrogenophosphate (53 mg,
0.44 mmol, 1.5 eq) were added. The mixture was stirred overnight,
and then neutralized by NH4Cl. The organic phase was diluted by
EtOAc, treated by water and dried on MgSO4. After filtration,
evaporation and purification on silica gel (40% EtOAc/cyclohexane),
the acid was obtained as a light yellow powder (107.6 mg, 89%); rf
0.40 (40%EtOAc/cyclohexane); mp 120 °C; IR (cm-1) 2927, 1711,
1275; δH 1.79 (6H, s, H10H/11), 2.26 (3H, s, H8), 2.37 (3H, s, H7), 3.64
(2H, s, H12), 3.76 (3H, s, OCH3 (1)), 3.90 (3H, s, OCH3 (2)), 5.61 (2H, s,
H14), 6.65 (1H, s, H4), 6.68 (1H, s, H6), 7.40 (1H, s, H20), 7.68 (1H, s,
H17); δC 19.2 (C7), 21.4 (C8), 26.0 (C9), 32.3 C10/C11), 40.1 (C12), 57.1
(OCH3 (1) & (2)), 69.3 (C14), 108.4 (C20), 110.0 (C6), 114.0 (C4), 128.8
(C15), 130.4 (C2), 130.7 (C17), 136.6 (C3), 138.2 (C5), 139.2 (C16), 148.3
(C18), 154.3 (C1), 158.1 (C19), 177.7 (C13); m/z 196, 318, 418 [M+H]+,
435 [M+NH4]+. HRMS, calculated: m/z 418.1821, found: m/z
418.1860 ([M+H]+).
3-(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-4,6-dimethylphenyl)-
3-methylbutan-1-ol (19)
K2CO3 (559.8 mg, 4.05 mmol, 1.5 eq) was added to a solution of 2-
(4-hydroxy-2-methylbutan-2-yl)-3,5-dimethylphenol
(563
mg,
2.7mmol, 1 eq) in DMF (12 mL). After 2 min, 4,5-dimethoxy-2-
nitrobenzyl bromide (740mg, 2.7mmol, 1 eq) was added. The
mixture was stirred under argon overnight, then treated by an
aqueous solution of K2CO3, water and brine; dried on MgSO4,
filtrated and evaporated. The crude product was purified on silica
gel column chromatography (40% EtOAc/cyclohexane) to give the
ether as an orange solid (879 mg, 81%); rf 0.17 (30%
EtOAc/cyclohexane); mp 86°C; IR (cm-1) 3326, 2969, 1274; δH 1.58
8 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C7OB00121E
ARTICLE
6,8-dichloro-9,9-dimethyl-7-oxo-7,9-dihydroacridin-2-yl-3-(2-
((4,5-dimethoxy-2-nitrobenzyl)oxy)-4,6-dimethylphenyl)-3-
methylbutanoate (TML)
Acknowledgements
The ComUE Paris Sciences et Lettres (PSL) is acknowledged for
financial support to SH.
Christine Gaillet and Stéphanie Deville-Foillard are
acknowledged for respectively NMR measurements and HPLC.
To
a
solution of 3-(2-((4,5-dimethoxy-2-nitrobenzyl)oxy)-4,6-
dimethylphenyl)-3-methylbutanoic acid (15 mg, 0.036 mmol, 1 eq)
in anhydrous THF (5 mL), was injected an excess of phosgene 30% in
toluene (300 µL) under inert atmosphere. The mixture was stirred at
room temperature for 45 min. The remaining phosgene was
eliminated by an argon flux; this solution was then added to a
solution of 1,3-dichloro-7-hydroxy-9,9-dimethylacridin-2(9H)-one
(11.1 mg, 0.036 mmol), 4-dimethylaminopyridine (4.4 mg, 0,036
mmol) and an excess of triethylamine (1 mL) in THF (5mL). The
resulting solution was stirred under argon at room temperature
overnight. The solvent was evaporated, then the residue was taken
up in dichloromethane; the organic phase was washed water and
brine; dried on MgSO4, filtrated and concentrated in vacuo. The
ester was purified by HPLC using 80 to 90% gradient of
CH3CN/water/0.1% TFA, Waters XBridge® Prep C18 5µm OBD™ 30 x
150mm Column, to give the pure product as a deep dark green solid
(25 mg, quantitative yield); rf 0.40 (40%EtOAc/cyclohexane); mp
220°C; IR (cm-1) 2918, 1754, 1621; δH 1.71 (s, 6H, CH3 DDAO), 2.21 (s,
2H, H7), 2.57 (s, 2H, H8), 3.09 (s, 2H, H19), 4.01 (s, 6H, OCH3 (1) &
(2)), 5.56 (s, 2H, H9), 6.55-7.82 (m, 7H, ArH); δC 11 (C7), 14.1 (C8),
20.7 (C16), 23 (C17), 23.7/25.8 (CH3 DDAO), 38.9 (C18), 56.4 (OCH3 1
and 2), 68.2 (C9), 70.1 (C19), 108.1 (C2), 109.7 (C3/C5), 128.5 (C4),
128.8 (C15/C23), 129.8 (C10), 130.9 (C14/C13), 132.4 (C6), 147.9
(C1/C11), 153.7 (C25/C27), 167.8 (C26), 187.8(C=O ester); m/z 350, 447,
647, 707 [M+H]+. HRMS, calculated: m/z 707.1819, found: m/z
707.1922 ([M+H]+), 709.1911 (MCl37+H]+).
Notes and references
1
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3
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All kinetic experiments have been performed in CH3CN/0.1 M
Britton-Robinson buffer23 1:1 (v:v). All solutions were prepared
using water purified through a Direct-Q 5 (Millipore, Billerica, MA).
UV-Visible Absorption: UV/Vis absorption spectra were recorded in
1 cm × 1 cm quartz cuvettes (Hellma) on a diode array UV/Vis
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with a Peltier cell holder (TLC50, Quantum Northwest, Shoreline,
WA). Solutions for fluorescence measurements were adjusted to 10
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This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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DOI: 10.1039/C7OB00121E
ARTICLE
Journal Name
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10 | J. Name., 2012, 00, 1-3
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Organic & Biomolecular Chemistry
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DOI: 10.1039/C7OB00121E
Hit the lights: Photochemical activation has
permitted to determine precisely disassembly
times of cyclisation-based self-immolative
spacers. Results confirmed high differences
with previously studied elimination-based self-
immolative spacers.
S. Huvelle, A. Alouane, T. Le Saux, L. Jullien,* F.
Schmidt*