A direct alkylation route to branched derivatives of suberoylanilide hydroxamic acid (SAHA), a potent non-selective inhibitor of histone deacetylases

Article abstract of DOI:10.1016/j.tet.2016.11.039

Alkylation of malonamic esters provides a direct approach to derivatives of suberoylanilide hydroxamic acid (SAHA) that are branched at the amide carbon atom, a location pivotal for enhancing biological and therapeutic activity. Alkylations use NaH in THF followed by addition of the ester of 6-bromohexanoic acid; no protection of the amidic NH group is necessary. By this means, carboxylic acid, ester, amide, hydroxymethyl and 2-benzimidazolyl branching units have been appended to the SAHA backbone. Routes to vary one of the branching units at a time have been developed.

Full text of DOI:10.1016/j.tet.2016.11.039

Tetrahedron 72 (2016) 8584e8592
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A direct alkylation route to branched derivatives of suberoylanilide
hydroxamic acid (SAHA), a potent non-selective inhibitor of histone
deacetylases
Jonathan A. Dines, Charles M. Marson*
Department of Chemistry, University College London, Christopher Ingold Laboratories, 20 Gordon Street, London WC1H OAJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Alkylation of malonamic esters provides a direct approach to derivatives of suberoylanilide hydroxamic
acid (SAHA) that are branched at the amide carbon atom, a location pivotal for enhancing biological and
therapeutic activity. Alkylations use NaH in THF followed by addition of the ester of 6-bromohexanoic
acid; no protection of the amidic NH group is necessary. By this means, carboxylic acid, ester, amide,
hydroxymethyl and 2-benzimidazolyl branching units have been appended to the SAHA backbone.
Routes to vary one of the branching units at a time have been developed.
Received 23 August 2016
Received in revised form
31 October 2016
Accepted 14 November 2016
Available online 15 November 2016
© 2016 Elsevier Ltd. All rights reserved.
Keywords:
Malonamic esters
Alkylation
Trifunctional compounds
Suberoylanilide hydroxamic acid
Histone deacetylase inhibitors
1. Introduction
early epigenetic studies, is marketed as Zolinza® for the treatment
of cutaneous T-cell lymphoma6; belinostat is used for the treatment
Hydroxamic acids1 play a pivotal role as inhibitors of metal-
dependent enzymes including matrix metalloproteinases and his-
tone deacetylases (HDACs).2e4 The hydrolytic action of histone
deacetylases requires coordination of a terminally acetylated lysine
residue, usually to zinc(II) in the catalytic site, prior to hydrolysis5;
this is inhibited by powerful metal chelators, including hydroxamic
acid derivatives compatible with the HDAC catalytic site, tunnel and
protein periphery. The extent of acetylation levels of terminal lysine
residues on histone protein is a major epigenetic regulator of gene
expression; up-regulation of HDACs results in aberrant gene
repression frequently associated with cancer. HDACs have also
recently been shown to affect DNA replication and DNA repair.3
Several HDAC inhibitors have entered clinical trials for the treat-
ment of cancers. HDAC inhibitors are also used in the treatment
Huntington's disease and show potential for the treatment of other
neurodegenerative diseases and inflammation.2e4
of peripheral T-cell lymphoma,7 and panobinostat for the treatment
of multiple myeloma.8 Currently, most HDAC inhibitors in clinical
trials are relatively nonselective among the nearly 20 known
mammalian HDAC isozymes. The provision of more selective HDAC
inhibitors with lower toxicity and greater potency are major unmet
needs in the area of HDAC therapy.9,10 The present work describes
the synthesis of branched hydroxamic acids, and in particular
branched analogues of SAHA, given its pivotal roles as a probe in
structural biology,11 in epigenetic studies,12 and its continued use as
an epigenetic anti-cancer agent.
2. Results and discussion
Branching of HDAC inhibitors in the region that bind to the
protein surface can enhance inhibitor potency and has been pre-
dicted to improve isozyme selectivity.13 The branched inhibitor 4
was found to be at least 6-fold more potent14 than SAHA in an
in vitro enzyme assay, and to be up to 20-fold more potent in
cellular antiproliferation assays against a panel of nine multiple
myeloma and non-Hodgkin's lymphoma cell lines.15 The greatly
increased overall inhibition of HDACs (pan-HDAC inhibition) su-
perior pre-clinical data compared to SAHA can be attributed to the
Hydroxamic acids are the largest class of HDAC inhibitors.2 Of
the four HDAC inhibitors approved by the FDA (Fig. 1), three are
hydroxamic acids: suberoylanilide hydroxamic acid (SAHA), used in
* Corresponding author.
E-mail address: c.m.marson@ucl.ac.uk (C.M. Marson).
http://dx.doi.org/10.1016/j.tet.2016.11.039
0040-4020/© 2016 Elsevier Ltd. All rights reserved.

J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
8585
O
H
H
H
N
N
N
OH
N
S
OH
H
O
O
O
O
¨
Zolinza
belinostat
(vorinostat,SAHA)
O
O
O
N
H
H
H
N
NH
S
O
S
N
H
NH
H
H
HN
N
O
OH
O
O
panobinostat
romidepsin
Fig. 1. FDA-approved HDAC inhibitors.
contacts made with the enzyme periphery by the additional anilide
moiety. Improvements to the first two steps of the route to the
branched hydroxamic acid 4 are here described (Scheme 1),
enabling a range of symmetrical malonamides to be synthesised in
two laboratory steps from the malonic acid 2.
conditions, cleavage of the tert-butyl group in ester 6 afforded the
desired carboxylic acid 9 which was selectively reduced with
NaBH4 in methanol to give the hydroxymethyl ester 10 (77%). This
ester underwent conversion into the corresponding hydroxamic
acid 11 by treatment with 5 equivalents of hydroxylamine in
methanolic KOH; although conversion was efficient, isolation
proved difficult, and only 12% was recovered.
Alkylation of N-disubstituted malonamides with linear alkyl
halides has been recently described.16,17 In contrast, few alkylations
of NH-malonamides have been described, which to our knowledge
have been limited to benzylic halides18,19 and diiodomethane,20
being activated halides rather than typical linear alkyl halides.
Notwithstanding that, the proposed route to branched derivatives
of SAHA was by alkylation of a suitable malonamic ester. The
strategy required the compatibility of the trifunctional compounds
with reagents and with a transformation of only one group per step,
for most sequences. The Boc-protected malonamic ester 5 was
selected for the start of the investigation since differential reaction
of the ester groups was expected to be reliable. Pleasingly, efficient
alkylation of malonamic ester 5 was accomplished by treatment
with NaH in THF followed by addition of ethyl 6-bromohexanoate
to give the key intermediate 6 in 74% yield (Scheme 2). This com-
pound provided access to a range of new trifunctional compounds,
including three hydroxamic acids: direct conversion of 6 into the C-
8 hydroxamic acid was achieved using excess aqueous hydroxyl-
amine in the presence of a methanolic solution of 1 M KOH and
affording 7 in 29% yield. Cleavage of the tert-butyl group in 1:1
TFA:dichloromethane afforded the carboxylic acid 8, unusual in
also containing amide and a hydroxamic acid units. Under similar
The benzimidazole ring system as a capping group for HDAC
inhibitors has shown potential in models of pancreatic cancer,22
and so was used in the present study as a representative hetero-
cycle. Having trifunctional acid 9 available in quantity, the intro-
duction of a range of amides at the branching position was feasible,
and hence a series of the corresponding hydroxamic acids should
be accessible. In a relatively challenging test of the protocol, the
carboxylic acid 9 was reacted with tert-butyl N-(2-aminophenyl)
carbamate
using
N-(3-dimethylaminopropyl)-N0-ethyl-
carbodiimide hydrochloride (EDC.HCl) and 1-hydroxybenzotriazole
monohydrate (HOBt), giving the malonamide 12 in 66% yield. Ring
closure was effected by heating in acetic acid at reflux, affording the
benzimidazole 13 (77%). However, direct conversion of ester 13 into
the desired hydroxamic acid 15 upon treatment with hydroxyl-
amine and KOH in aqueous methanol resulted in difficulties in
purification of the hydroxamic acid which was too polar for column
chromatography and could not be satisfactorily purified by
recrystallisation. This was circumvented by Boc-protection of 13 to
give 14 and treatment with the standard solution containing hy-
droxylamine. Concomitant conversion into the hydroxamate and
O
O
a
b
c
OEt
OEt
OEt
Br
t-BuO
HO
O
O
O
O
OBu-t
O
OH
1
2
O
O
O
O
O
O
d
H
e
OEt
OEt
N
Cl
N
N
OH
H
H
O
O
O
Cl
NH
NH
3
4
a
Scheme 1. Synthesis of a symmetrical bis-malonamide hydroxamic acid.14 Reagents and conditions: NaH (1.1 equiv.) first added to di-tert-butyl malonate (1 equiv.), THF, 20 ꢀC,
20 min then reflux, 16 h, 74%. bCF3CO2H (6 equiv.), CH2Cl2, 20 ꢀC, 16 h, 99%. cSOCl2 (6 equiv.), benzene, reflux, 2 h14 then, dPhNH2 (6 equiv.), pyridine (3 equiv.), CH2Cl2, 20 ꢀC, 17 h,
76%.14 eNaOMe, (3 equiv.) and HONH2 (2 equiv.), MeOH, 20 ꢀC, 16 h, 68%.14

8586
J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
O
O
O
H
N
a
b
OEt
N
N
H
N
OH
H
H
O
O
t-BuO
O
t-BuO
O
t-BuO
O
5
6
7
c
f
O
O
O
d
H
N
OEt
OEt
N
N
OH
N
H
H
H
O
O
O
HO
O
HO
O
HO
9
10
11
8
e
O
H
N
N
H
OH
O
HO
Scheme 2. Synthesis of branched derivatives of SAHA. Reagents and conditions: aNaH (1.1 equiv.), ethyl 6-bromohexanoate (1 equiv.), THF, 70 ꢀC, 18 h, 74%. b50% aqueous HONH2 (10
equiv.), 1 M KOH in MeOH, THF, 20 ꢀC, 1 h, 29%. c1:1 CF3CO2H:CH2Cl2, 20 ꢀC, 6 h, 80%. dClCO2Et (1.5 equiv.), Et3N (1.2 equiv), THF, 0 ꢀC, 30 min then NaBH4 (3 equiv.),21 MeOH, 10 ꢀC,
f
1.5 h, 77%. eAqueous 50% HONH2 (5 equiv.), 1 M KOH in MeOH, THF, 20 ꢀC, 1.5 h, 12%. 1:1 CF3CO2H:CH2Cl2, 20 ꢀC, 30 min, 80%.
O
O
O
O
N
a
b
OEt
OEt
OEt
N
N
N
H
H
H
O
O
O
HO
O
NH
NH
9
12
13
BocHN
O
N
O
H
c
OEt
d
N
N
N
OH
H
H
O
O
NBoc
N
NH
15
14
Scheme 3. Synthesis of a branched 2-benzimidazolinyl derivative of SAHA. Reagents and conditions: atert-Butyl N-(2-aminophenyl)carbamate (1 equiv.), EDC.HCl (1.1 equiv.), HOBt
(1.1 equiv.), Et3N (2.2equiv), DMF, 20 ꢀC, 18 h, 66%. bTFA, reflux, 2 h, 75%. cDi-tert-butyl dicarbonate (1.5 equiv.), THF, 20 ꢀC, 7 d, 64% conversion. dAqueous 50% HONH2 (10 equiv.), 1 M
KOH in MeOH, THF, 20 ꢀC, 6 h, 50%.
cleavage of the Boc group occurred, affording in one laboratory step
the desired deprotected hydroxamic acid 15 in 50% yield. Scheme 3
established that differential amidation of 9 could be achieved, and
given that ester to hydroxamic acid conversion is tolerated by a
range of functional groups, is a likely general route to unsymmet-
rical malonamides and their corresponding hydroxamic acids.
Additionally, heterocyclisation involving the amide group should
permit a variety of heterocycles to be installed using well-
established ring-closures.
A more convergent approach to SAHA analogs containing
heterocyclic rings at the branch point than that of Scheme 3 could
be achieved if the order of reactions could be reversed, so that the
heterocycle is installed earlier on, as an acetate ester such as 17
(Scheme 4). This sequence would also be desirable when other
functionality present (or stereocentres) is incompatible with the
conditions for the formation of heteroaromatic rings, usually quite
harsh. The malonamic ester 16, formed by acylation of 1,2-
phenylenediamine with 3-tert-butoxy-3-oxopropanoic acid us-
ing N,N0-dicyclohexylcarbodiimide (DCC), underwent hetero-
cylisation in acetic acid at 90 ꢀC (96%) to give the benzimidazole
17. Boc-protection gave the derivative 18 (97%) which was
deprotonated using NaH in THF, and underwent alkylation using
ethyl 6-bromohexanoate, albeit in low yield (33%); the N-Boc
protected ester 19 underwent efficient conversion into the
hydroxamic acid, again accompanied by selective N-Boc-depro-
tection, to give the branched hydroxamic acid 20 in 67% yield.
These two strategies are complementary; different heterocycles
may be attached to the same amide using Scheme 3, but different
amides may also be attached to the same heterocycle using
Scheme 4.
For future comparison of biological activities of branched versus
non-branched hydroxamic acids, two linear hydroxamic acids were
prepared, the first being the parent compound 22 of the above
branched benzimidazole derivatives, synthesised succinctly ac-
cording to Scheme 5. For comparison with a heterocyclic analog of
SAHA constrained by annulation and lacking an NH group, which in
the case of SAHA is required for hydrogen-bonding with an aspar-
tate residue (Asp99 in HDAC1), pyrimidinone 25 was selected, since
it also contains a cyclic symmetrical malonamide motif (see
Scheme 6).

J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
8587
O
O
O
N
O
O
t-BuO
t-BuO
t-BuO
a
b
c
t-BuO
N
NH
O
NH
NBoc
H2N
OH
18
17
16
O
N
O
N
H
OEt
N
t-BuO
t-BuO
OH
O
O
d
e
NBoc
NH
20
19
a
Scheme 4. Synthesis of a branched hydroxamic acid with a 2-benzimidazolyl capping group. Reagents and conditions: 1,2-Phenylenediamine (1 equiv.), N,N0-dicyclohex-
ylcarbodiimide (1.1 equiv.), MeCN, 20 ꢀC, 20 min, 50%. bAcOH, 90 ꢀC, 1 h, 96%. cDi-tert-butyl dicarbonate (1.2 equiv.), THF, 20 ꢀC, 3 d, 97%. dNaH (1.1 equiv.), THF, 60 ꢀC, 18 h, 33%. e50%
aqueous HONH2 (10 equiv.), 1 M KOH in MeOH, THF, 20 ꢀC, 30 min, 67%.
H
OEt
N
OH
O
O
N
NH
N
NH
H2N
NH2
a
b
22
21
Scheme 5. Succinct synthesis of a linear hydroxamic acid with a 2-benzimidazolyl capping group. Reagents and conditions: aSuberic anhydride (1 equiv.), THF, 20 ꢀC, 20 min; then
b
4% conc. H2SO4 in EtOH, 29%. Aqueous 50% HONH2, 1 M KOH in MeOH, THF, 20 ꢀC, 6 h, 61%.
Attempts to form the pyrimidinone 24 via the diacid
dichloride of 2, or by activation of the carboxylic acid groups of 2
with ethyl chloroformate were unsuccessful. The synthesis of
pyrimidinone 24 was eventually accomplished by reaction of
(SAHA) that are branched alpha to the amide carbon atom, a loca-
tion pivotal for enhancing biological and therapeutic activity.
Deprotonation of malonamic esters was conveniently achieved
using NaH in THF followed by treatment with an ester of 6-
bromohexanoic acid; no protection of the amidic NH group was
necessary. By this means, carboxylic acid, ester, amide, hydrox-
ymethyl and 2-benzimidazolyl branching units have been appen-
ded to the SAHA backbone. A 2-benzimidazolyl unit can be added
by cyclisation, or alternatively by alkylation of a 2-benzimidazolyl
acetate. These complementary routes enable variation of either
branching unit at a time: the heterocyclic branching unit or alter-
natively the carboxy chain. Improvements to synthesis of branched
hydroxamic acids from malonyl derivatives have also been
23
diacid 2 with 2,4,6-trichlorophenol in the presence of POCl3 to
give the ester 23 which with N,N-diethyl-N0-phenylguanidine at
150 ꢀC underwent rapid conversion into the desired pyr-
imidinone 25.
3. Conclusion
Alkylation of malonamic esters has been shown to provide a
direct approach to derivatives of suberoylanilide hydroxamic acid
Cl
Cl
O
O
O
O
O
a
b
OEt
OEt
OEt
t-BuO
t-BuO
HO
Cl
O
O
O
O
O
HO
O
Cl
Cl
1
2
23
Cl
O
O
H
c
d
OEt
N
N
N
OH
O
O
N
N
OH
N
N
OH
24
25
a
Scheme 6. Synthesis of a SAHA analog constrained by annulation. Reagents and conditions: CF3CO2H (6 equiv.), CH2Cl2, 20 ꢀC, 24 h, 99%. b2,4,6-Trichlorophenol (2 equiv.), POCl3
c
(2.6 equiv.), 100 ꢀC, 5 h, 49%. N,N-Diethyl-N0-phenylguanidine (1 equiv.), 5 min, 150 ꢀC, 68%. dAqueous 50% HONH2 (10 equiv.), 1 M KOH in MeOH, THF, 20 ꢀC, 2 h, 51%.

8588
J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
achieved, and in addition the synthesis of a new SAHA derivative
constrained by heterocyclic annulation.
solution stirred for 24 h. The volatile material was then evaporated
to give the acid 2 (4.14 g, 99%) as a white crystalline solid, mp
71e73 ꢀC; IR nmax 2939, 2613,1705 cmꢂ1; 1H NMR (CDCl3, 300 MHz)
4. Experimental section
d
4.12 (2H, q, J ¼ 7.1 Hz, CH2CH3), 3.42 (1H, t, J ¼ 7.4 Hz, CH), 2.30
(2H, t, J ¼ 7.4 Hz, CH2COOEt), 1.98e1.85 (2H, m, CH2CH2COOEt),
1.65e1.52 (2H, m, CHCH2), 1.43e1.25 (4H, m, CHCH2CH2,
CHCH2CH2CH2), 1.18 (3H, t, J ¼ 7.1 Hz, CH2CH3); 13C NMR (CDCl3,
4.1. General
All moisture-sensitive reactions were performed under an at-
mosphere of nitrogen and the glassware was pre-dried in an oven
(130 ꢀC). Evaporation refers to the removal of solvent under
reduced pressure. Melting points were measured by a microscope
hot-stage Electrothermal 9100 apparatus. Infra-red (IR) spectra
were recorded on a Perkin-Elmer PE-983 spectrophotometer. 1H
NMR spectra were recorded on a Bruker AC300 (300 MHz) spec-
trometer or a Bruker AMX 500 (125 MHz) spectrometer; data are
75 MHz) d 174.6 (COOH), 174.5 (COOEt), 60.7 (CH2CH3), 51.5 (CH),
34.2 (CH2COOEt), 28.6 (CHCH2CH2CH2), 28.5 (CHCH2), 26.8
(CHCH2CH2), 24.5 (CH2CH2COOEt), 14.2 (CH2CH3); m/z (CI, %) 247
(MHþ, 31), 201 (21), 185 (100), 157 (27). Anal. Calcd for C11H18O6 C,
53.65; H, 7.37. Found: C, 53.48; H, 7.41.
4.2.3. tert-Butyl 3-oxo-3-(phenylamino)propanoate (5)
Oxalyl chloride (11.7 g, 92.3 mmol) was added slowly to a stirred
solution of 3-tert-butoxy-3-oxopropanoic acid (4.93 g, 30.8 mmol)
in dichloromethane (300 mL) followed by DMF (10 drops). The
mixture was warmed to 40 ꢀC for 2 h then evaporated. The resulting
red oil was dissolved in dichloromethane (300 mL), and aniline
(3.09 g, 33.9 mmol) added, giving a precipitate. DMAP (4.14 g,
33.9 mmol) was added and the mixture was then stirred at 20 ꢀC for
2 h. The solvent was evaporated and the residue dissolved in ethyl
acetate (50 mL). The organic layer was washed with 2 M hydro-
chloric acid (2 ꢁ 30 mL) followed by saturated aqueous sodium
hydrogen carbonate (30 mL), then dried (MgSO4) and filtered. The
solvent was evaporated to leave a red oil which was purified by
column chromatography (3:7 ethyl acetate:40e60 petroleum
ether) to give ester 5 (6.92 g, 89%) as a white crystalline solid, mp
72e74 ꢀC; Rf (1:2 ethyl acetate:hexane) 0.57; IR nmax 3308, 3267,
reported in parts per million (d). Coupling constants (J) are given in
Hertz (Hz). The following abbreviations were used in signal as-
signments: singlet (s), broad singlet (br s), doublet (d), triplet (t),
quartet (q), and multiplet (m). 13C NMR spectra were recorded on
Bruker AMX300 (75 MHz), Bruker AMX400 (100 MHz) or Bruker
AMX 500 (125 MHz) spectrometers; data are reported in parts per
million (d), with CHCl3 as an internal standard. Mass spectra were
recorded on a VG7070H mass spectrometer with Finigan Incos II
data system at University College London. Optical rotations were
measured using a Perkin-Elmer 343 digital polarimeter. Thin-layer
chromatography was performed on Merck 0.2 mm aluminium-
backed silica gel 60 F254 plates and visualised by UV (254 nm) or
by staining with alkaline potassium permanganate spray and sub-
sequent heating. Flash column chromatography was performed
using Merck 0.040e0.063 mm, 230e400 mesh silica gel.
1721, 1556 cmꢂ1; 1H NMR (CDCl3, 300 MHz)
d 9.35 (1H, s, NH), 7.55
The following compounds were prepared according to the
(2H, d, J ¼ 8.0 Hz, 2,6-aryl), 7.29 (2H, dd, J ¼ 8.0, 7.5 Hz, 3,5-aryl),
literature: tert-butyl 3-oxo-3-(phenylamino)propanoate (5);14 tert-
7.08 (1H, t, J ¼ 7.5 Hz, 4-aryl), 3.36 (2H, s, CH2), 1.48 (9H, s, C(CH3)3);
butyl
N-(2-aminophenyl)carbamate;24
tert-butyl
3-
13C NMR (CDCl3, 75 MHz) 168.9 (COOBut), 163.8 (CONH), 137.7 (1-
d
oxopropanoate25; oxonane-2,9-dione26; bis(2,4,6-trichlorophenyl)
aryl), 128.9 (3,5-aryl), 124.4 (4-aryl), 120.1 (2,6-aryl), 82.9 (C(CH3)3),
42.9 (CH2), 28.0 ((CH3)3); m/z (CI, %) 235 (Mþ, 41), 179 (81), 162 (17),
119 (19), 93 (100). Anal. Calcd for C13H17NO3 C, 66.36; H, 7.28; N,
5.95. Found C, 66.35; H, 7.34; N, 5.98.
malonate;23 N,N-diethyl-N0-phenylguanidine.27
4.2. Synthesis
4.2.1. 6-Ethyl 1,1-bis(tert-butyl)hexane-1,1,6-tricarboxylate (1)
To a solution of di-tert-butyl malonate (5.0 g, 23.1 mmol) in dry
tetrahydrofuran (230 mL) was added sodium hydride (1.02 g of a
60% dispersion in mineral oil, 25.4 mmol). After stirring at 20 ꢀC for
20 min, ethyl-6-bromohexanoate (5.16 g, 23.1 mmol) was added
and the mixture was heated at reflux for 16 h. After allowing to cool,
the solvent was then evaporated and water (50 mL) added to the
residue. The mixture was extracted with diethyl ether (2 ꢁ 30 mL)
and the combined organic layers dried (MgSO4), filtered and
evaporated. Column chromatography (1:9 ethyl acetate:40e60 ꢀC
petroleum ether) of the oily residue gave ester 1 (6.11 g, 74%) as a
4.2.4. 1-tert-Butyl 8-ethyl-2-(phenylcarbamoyl)octanedioate (6)
Sodium hydride (773 mg of a 60% dispersion in oil, 19.3 mmol)
was added slowly to a stirred solution of tert-butyl 3-oxo-3-(phe-
nylamino)propanoate (5) (4.45 g, 17.57 mmol) in dry tetrahydro-
furan (175 mL) at 0 ꢀC. After stirring at 20 ꢀC for 20 min, ethyl 6-
bromohexanoate (3.92 g, 17.6 mmol) was added and the mixture
heated at 70 ꢀC for 18 h. After allowing to cool the solvent was
evaporated. The residue was taken up in ethyl acetate (50 mL) and
washed with 2 M hydrochloric acid (2 ꢁ 20 mL) then with brine
(20 mL), dried (MgSO4) and filtered. The residue was purified by
column chromatography (1:9 ethyl acetate:40e60 ꢀC petroleum
ether) to give the ester 6 (4.94 g, 74%) as pale yellow crystals, mp
65e66 ꢀC; Rf (1:2 ethyl acetate:hexane) 0.64; IR nmax 3307, 2944,
colourless oil; IR nmax 2935, 1732, 1369 cmꢂ1
300 MHz)
;
1H NMR (CDCl3,
d
4.04 (2H, q, J ¼ 7.1 Hz, CH2O), 3.02 (2H, t, J ¼ 7.6 Hz,
CH2COOEt), 2.20 (2H, t, J ¼ 7.5 Hz, CHCH2), 1.79e1.70 2H, m,
CH2CH2COOEt, 1.63e1.52 (2H, m, CHCH2CH2CH2), 1.38 (18H, s,
C(CH3)3), 1.34e1.25 (2H, m, CHCH2CH2), 1.17 (3H, t, J ¼ 7.1 Hz,
1726,1656,1554 cmꢂ1; 1H NMR (CDCl3, 300 MHz)
d 8.75 (1H, s, NH),
7.54 (2H, d, J ¼ 8.0 Hz, 2,6-aryl), 7.32 (2H, dd, J ¼ 8.0, 7.5 Hz, 3,5-
aryl), 7.10 (1H, t, J ¼ 7.5 Hz, 4-aryl), 4.11 (2H, q, J ¼ 7.1 Hz,
CH2CH3), 3.24 (1H, t, J ¼ 7.3 Hz, CH), 2.28 (2H, t, J ¼ 7.4 Hz, CH2COO),
2.00e1.90 (2H, m, CHCH2),1.68e1.57 (2H, m, CH2CH2COO),1.49 (9H,
s, (CH3)3, 1.44e1.32 (4H, m, CH2CH2CH2COO, CHCH2CH2), 1.24 (3H, t,
CH2CH3); 13C NMR (CDCl3, 75 MHz)
d 173.5 (COOEt), 168.8
(COOC(CH3)3), 81.1 (C(CH3)3), 60.1 (CH2CH3), 53.8 (CH), 34.1
(CH2COOEt), 28.7 (CHCH2), 28.3 (CH2CH2CH2COOEt), 27.8 (C(CH3)3),
26.8 (CHCH2CH2), 24.6 (CH2CH2COOEt), 14.2 (CH3CH2); m/z (CI, %)
381 (MHþ, 100), 269 (25), 247 (75), 201 (13); HRMS (M þ Na)þ calcd
for C19H34NaOþ6 381.2253. Found: 381.2260.
J ¼ 7.1 Hz, CH2CH3); 13C NMR (CDCl3, 75 MHz)
d 173.6 (COOEt), 172.0
(CONH), 167.0 (COOBut), 137.8 (1-aryl), 129.0 (3,5-aryl), 124.3 (4-
aryl), 119.9 (2,6-aryl), 82.7 (C(CH3)3), 60.2 (CH2CH3), 54.4 (CH),
34.2 (CH2COO), 31.5 (CHCH2), 28.6 (CH2CH2CH2CHOO), 28.0 (CH3)3),
26.9 (CHCH2CH2), 24.6 (CH2CH2COO), 14.2 (CH2CH3); m/z (EI, %) 377
(Mþ, 13), 322 (12), 258 (11), 179 (53), 161 (37), 93 (100). Anal. Calcd
for C21H31NO5 C, 66.82; H, 8.28; N, 3.71. Found C, 66.72; H, 8.32; N,
3.69.
4.2.2. 2-Carboxyoctanedioic acid 8-ethyl ester (2)
To a stirred solution of 6-ethyl 1,1-bis(tert-butyl) hexane-1,1,6-
tricarboxylate (1) (6.09 g, 17.0 mmol) in dichloromethane
(170 mL) was added trifluoroacetic acid (11.6 g, 102 mmol) and the

J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
8589
4.2.5. tert-Butyl 8-(hydroxyamino)-8-oxo-2-(phenylcarbamoyl)
octanoate (7)
(CH2CH2CH2COO), 26.5 (CHCH2CH2), 24.4 (CH2CH2COO), 14.1 (CH3);
m/z (EI, %) 321 (Mþ, 8), 277 (43), 232 (54), 179 (36), 135 (97), 93
(100). Anal. Calcd for C17H23NO5 C, 63.53; H, 7.21; N, 4.36. Found C,
63.08; H, 7.18; N, 3.92.
To a solution of 1-tert-butyl 8-ethyl 2-(phenylcarbamoyl)octa-
nedioate (6) (300 mg, 0.79 mmol) in tetrahydrofuran (8 mL) was
added 50% aqueous hydroxylamine (0.53 mL, 7.95 mmol) and 1 M
potassium hydroxide in methanol (2.37 mL, 2.37 mmol) dropwise.
The mixture was stirred at 20 ꢀC for 1 h then acidified with 2 M
hydrochloric acid. The solvent was evaporated to a volume of 5 mL
then water (20 mL) added. The aqueous mixture was extracted with
ethyl acetate (4 ꢁ 15 mL) and the combined yellow extracts dried
over Na2SO4. Evaporation of the solvent gave a yellow oil which was
purified by column chromatography (ethyl acetate) to give the
hydroxamic acid 7 (84 mg, 29%) as a yellow oil; Rf (1% methanol in
4.2.8. Ethyl 7-(hydroxymethyl)-8-oxo-8-(phenylamino)octanoate
(10)
To a stirred solution of 8-ethoxy-8-oxo-2-(phenylcarbamoyl)
octanoic acid (9) (300 mg, 0.94 mmol) in dry tetrahydrofuran
(3.0 mL) at 0 ꢀC was added triethylamine (114 mg, 1.13 mmol) and
ethyl chloroformate (152 mg, 1.40 mmol). The mixture was stirred
at 0 ꢀC for 30 min then filtered. The solid was washed with tetra-
hydrofuran (2 ꢁ 3 mL) and the combined filtrate was cooled to
10 ꢀC. Sodium borohydride (107 mg, 2.82 mmol) was added in one
portion, followed by dropwise addition of methanol (0.6 mL) over a
period of 1 h. After stirring for a further 30 min the reaction was
quenched by dropwise addition of 2 M hydrochloric acid, then
extracted with dichloromethane (2 ꢁ 10 mL). The combined
organic layers were dried (MgSO4), filtered and evaporated. The
residue was purified by column chromatography (3:2 ethyl
acetate:40e60 ꢀC petroleum ether) to give ester 10 (222 mg, 77%)
as a white crystalline solid, mp 132e134 ꢀC; IR nmax 2935, 2669,
ethyl acetate) 0.70; 1H NMR (CDCl3, 300 MHz)
d 9.02 (1H, s, NH),
7.52 (2H, d, J ¼ 7.7 Hz, 2,6-aryl), 7.26 (2H, dd, J ¼ 7.7, 7.5 Hz, 3,5-aryl),
7.06 (1H, t, J ¼ 7.5 Hz, 4-aryl), 3.27 (1H, t, J ¼ 7.0 Hz, CH), 2.13e2.03
(2H, m, CH2CONHOH), 1.95e1.83 (2H, m, CHCH2), 1.64e1.50 (2H, m,
CH2CH3CONHOH), 1.44 (9H, s, C(CH3)3), 1.40e1.25 (4H, m,
CHCH2CH2, CHCH2CH2CH2); 13C NMR (CDCl3, 75 MHz)
d 171.7
(COOC(CH3)3), 171.3 (CONHOH), 167.8 (CONHPh), 137.7 (1-aryl),
128.9 (3,5-aryl), 124.6 (4-aryl), 120.3 (2,6-aryl), 82.7 (C(CH3)3), 54.2
(CH), 32.5 (CH2CONHOH), 30.5 (CHCH2), 28.3 (CHCH2CH2CH2), 28.0
(C(CH3)3), 26.6 (CH2CH2CONHOH), 25.0 (CHCH2CH2); m/z (CI, %)
387 ((M þ Na)þ, 100), 365 (MHþ, 45), 328 (22), 309 (35). HRMS
calcd for C19H29N2O5 (M þ H)þ 365.2071. Found: 365.2079.
1684, 1408 cmꢂ1; 1H NMR (CDCl3, 300 MHz)
d 8.73 (1H, s, NH), 7.53
(2H, d, J ¼ 7.8 Hz, 2,6-aryl), 7.23 (2H, dd, J ¼ 7.8, 7.4 Hz, 3,5-aryl),
7.04 (1H, t, J ¼ 7.4 Hz, 4-aryl), 4.08 (2H, q, J ¼ 7.1 Hz, CH2CH3), 3.95
(1H, br s, OH), 3.73e3.53 (2H, m, CH2OH), 2.45 (1H, m, CH), 2.22
(2H, t, J ¼ 7.4 Hz, CH2COO), 1.56 (3H, CHCHH, CH2CH2COO),
1.40e1.18 (8H, m, CHCHH, CH2CH2CH2COO, CHCH2CH2, CH3); 13C
4.2.6. 8-(Hydroxyamino)-8-oxo-2-(phenylcarbamoyl)octanoic acid
(8)
To a solution of tert-butyl 8-(hydroxyamino)-8-oxo-2-(phenyl-
carbamoyl)octanoate (7) (170 mg, 0.47 mmol) in dichloromethane
(2 mL) was added trifluoroacetic acid (2 mL) and the mixture stir-
red for 30 min. Evaporation of the solvent gave a pale yellow solid
which was washed with cold diethyl ether then with dichloro-
methane to give the hydroxamic acid 8 (116 mg, 80%) as a white
solid, mp 150e152 ꢀC; Rf (5% methanol in ethyl acetate) 0.34; IR
nmax 2931, 2856, 1733, 1597, 1547 cmꢂ1; 1H NMR (CD3OD, 300 MHz)
NMR (CDCl3, 75 MHz) d 174.1 (COOEt), 174.1 (CONH), 138.1 (1-aryl),
128.8 (3,5-aryl), 124.2 (4-aryl), 120.2 (2,6-aryl), 63.5 (CH2OH), 60.4
(CH2CH3), 49.7 (CH), 34.2 (CH2COO), 29.0 (CH2CH2CH2COO), 28.7
(CHCH2), 26.9 (CHCH2CH2), 24.6 (CH2CH2COO), 14.2 (CH3); m/z (CI,
%) 308 (MHþ, 100), 262 (53), 197 (63), 169 (51). Anal. Calcd for
C17H25NO4 C, 66.43; H, 8.20; N, 4.56. Found C, 66.49; H, 8.34; N,
4.65.
d
7.55 (2H, d, J ¼ 7.6 Hz, 2,6-aryl), 7.30 (2H, dd, J ¼ 7.6, 7.3 Hz, 3,5-
4.2.9. N8-hydroxy-2-(hydroxymethyl)-N1-phenyloctanediamide
(11)
aryl), 7.09 (1H, t, J ¼ 7.3 Hz, 4-aryl), 3.44 (1H, t, J ¼ 7.1 Hz, CH), 2.07
(2H, t, J ¼ 6.8 Hz, CH2CONH), 2.02e1.86 (2H, m, CHCH2), 1.76e1.58
(2H, m, CH2CH2CONH), 1.53e1.30 (4H, m, CHCH2CH2,
To a stirred solution of ethyl 7-(hydroxymethyl)-8-oxo-8-(phe-
nylamino)octanoate (10) (600 mg, 1.95 mmol) in tetrahydrofuran
(20 mL) was added 50% aqueous hydroxylamine (0.64 mL,
9.76 mmol) and 1 M potassium hydroxide in methanol (3.9 mL,
3.9 mmol) and the resultant solution stirred for 1.5 h. Methanol was
evaporated from the yellow solution then 0.5 M hydrochloric acid
(10 mL) added. The hydroxamic acid 11 (70 mg, 12%) crystallised
from the aqueous solution as cream solid, mp 150e151 ꢀC; Rf (5%
methanol in ethyl acetate) 0.43; IR nmax 3398, 3291, 3185, 2920,
CHCH2CH2CH2); 13C NMR (CD3OD, 75 MHz)
d 173.4 (COOH), 173.0
(CONHPh), 170.4 (CONHOH), 139.6 (1-aryl), 129.9 (3,5-aryl), 125.5
(4-aryl), 121.4 (2,6-aryl), 54.4 (CH), 33.7 (CH2CONH), 30.2 (CHCH2),
29.9 (CHCH2CH2CH2), 28.1 (CH2CH2CONH), 26.3 (CHCH2CH2); m/z
(CI, %) 331 ((M þ Na)þ, 100), 309 (MHþ, 83). Anal. Calcd for
C
15H20N2O5 C, 58.43; H, 6.54; N, 9.09. Found C, 58.16; H, 6.51; N,
8.75.
1626 cmꢂ1; 1H NMR ((CD3)2SO, 300 MHz)
d 10.30 (1H, s, NH), 9.83
4.2.7. 8-Ethoxy-8-oxo-2-(phenylcarbamoyl)octanoic acid (9)
(1H, s, NHOH), 8.62 (1H, s, NH), 7.62 (2H, d, J ¼ 7.8 Hz, 2,6-aryl), 7.27
(2H, dd, J ¼ 7.8, 7.4 Hz, 3,5-aryl), 7.00 (1H, t, J ¼ 7.4 Hz, 4-aryl), 4.71
(1H, t, J ¼ 5.0 Hz, OH), 3.64e3.55 (1H, m, CHHOH), 3.45 (1H, td,
J ¼ 5.0, 10.2 Hz, CHHOH), 2.57e2.45 (1H, m, CH), 1.90 (2H, t,
J ¼ 7.3 Hz, CH2CONH), 1.54e1.35 (4H, m, CH2CH2CONH, CHCH2),
1.30e1.17 (4H, m, CHCH2CH2CH2, CHCH2CH2); 13C NMR ((CD3)2SO,
Trifluoroacetic acid (9 mL) was added to a solution of 1-tert-
butyl-8-ethyl-2-(phenylcarbamoyl)octanedioate (6) (1.33 g,
3.52 mmol) in dichloromethane (9 mL) and the solution stirred for
6 h. The solvent was evaporated and the residue washed with a 1:1
diethyl ether:40e60 ꢀC petroleum ether to give the acid 9 (0.91 g,
80%) as a white powder, mp 108e110 ꢀC; Rf (1:2 ethyl acetate:-
75 MHz)
d 173.0 (PhNHCO), 169.0 (CONHOH), 139.3 (1-aryl), 128.5
hexane) 0.67; IR nmax 3426, 3340, 2933, 1730, 1600 cmꢂ1
;
1H NMR
(3,5-aryl), 122.9 (4-aryl), 119.1 (2,6-aryl), 62.9 (CH2OH), 49.8 (CH),
32.2 (CH2CONH), 28.7 (CHCH2CH2CH2), 28.6 (CHCH2), 26.6
(CHCH2CH2), 25.0 (CH2CH2CONH); m/z (CI, %) ((M þ Na)þ, 100), 285
(17), 276 (15), 242,13 217.13 Anal. Calcd for C15H22N2O4 C, 61.21; H,
7.53; N, 9.52. Found: C, 60.71; H, 7.49; N, 9.39.
(CDCl3, 300 MHz) 10.17 (1H, br s, OH), 9.05 (1H, s, NH), 7.50 (2H, d,
d
J ¼ 7.8 Hz, 2,6-aryl), 7.30 (2H, dd, J ¼ 7.8, 7.3 Hz, 3,5-aryl), 7.14 (1H, t,
J ¼ 7.3 Hz, 4-aryl), 4.12 (2H, q, J ¼ 7.1 Hz, CH2CH3), 3.47 (1H, t,
J ¼ 6.2 Hz, CH), 2.29 (2H, t, J ¼ 7.3 Hz, CH2COO), 2.06e1.95 (2H, m,
CHCH2), 1.68e1.53 (2H, m, CH2CH2COO), 1.48e1.30 (4H, m,
CH2CH2CH2COO, CHCH2CH2), 1.24 (3H, t, J ¼ 7.1 Hz, CH3); 13C NMR
4.2.10. Ethyl 8-(2-(tert-butoxycarbonylamino)phenylamino)-8-
oxo-7-(phenylcarbamoyl)-octanoate (12)
(CDCl3, 75 MHz) d 175.1 (COOH), 174.6 (COOEt), 169.1 (CONH), 136.7
(1-aryl), 129.1 (3,5-aryl), 125.5 (4-aryl), 120.8 (2,6-aryl), 60.9
(CH2CH3), 52.2 (CH), 34.1 (CH2COO), 31.1 (CHCH2), 28.3
To a stirred solution of 8-ethoxy-8-oxo-2-(phenylcarbamoyl)
octanoic acid (9) (1.0 g, 3.11 mmol) in DMF (30 mL) was added tert-

8590
J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
butyl 2-aminophenylcarbamate (648 mg, 3.11 mmol), triethyl-
amine (692 mg, 6.84 mmol), EDC.HCl (657 mg, 3.42 mmol) and
HOBt (462 mg, 3.42 mmol). The mixture was stirred for 18 h then
evaporated and water (50 mL) added to the residue. The mixture
was extracted with ethyl acetate (2 ꢁ 25 mL) and the combined
organic layers were washed with water (15 mL), saturated aqueous
ammonium chloride (15 mL) and lastly with saturated aqueous
sodium hydrogen carbonate (15 mL). The organic layer was dried
(MgSO4), filtered and evaporated to give a yellow oil which was
purified by column chromatography (1:2 40e60 ꢀC petroleum
ether: ethyl acetate) to give amide 12 (1.05 g, 66%) as a white solid,
used without further purification.
(CI, %) 516 ((M þ Na)þ, 49), 494 (MHþ, 92), 394 (28), 335 (100), 276
(19). HRMS (MH)þ calcd for C28H36N3Oþ5 494.2649. Found:
494.2650.
4.2.13. 2-(1H-Benzo[d]imidazol-2-yl)-N8-hydroxy-N1-
phenyloctanediamide (15)
To a stirred solution of tert-butyl 2-(8-ethoxy-1,8-dioxo-1-
(phenylamino)octan-2-yl)-1H-benzo[d]imidazole-1-carboxylate
(14) (210 mg, 0.43 mmol) in tetrahydrofuran (4 mL) was added 50%
aqueous hydroxylamine (0.28 mL, 4.25 mmol) followed by drop-
wise addition of 1 M potassium hydroxide in methanol (1.29 mL).
The pale yellow solution was stirred for 6 h then evaporated. Water
(10 mL) was added to the residue followed by saturated aqueous
ammonium chloride (10 mL) and the precipitate collected by
filtration. The solid was recrystallised from ethanol to give the
hydroxamic acid 15 (81 mg, 50%) as a white crystalline solid, mp
184e185 ꢀC; IR nmax 3261, 3093, 2924, 1637 cmꢂ1; 1H NMR (CD3OD,
4.2.11. Ethyl 7-(1H-benzo[d]imidazol-2-yl)-8-oxo-8-(phenylamino)
octanoate (13)
To a solution of ethyl 8-(2-(tert-butoxycarbonylamino)phenyl-
amino)-8-oxo-7-(phenylcarbamoyl)octanoate
(12)
(0.88
g,
1.72 mmol) in dichloromethane (9 mL) was added trifluoroacetic
acid (9 mL). The solution was heated at reflux for 2 h. The solvent
was evaporated and the residue recrystallised from a mixture of
ethyl acetate and 40e60 ꢀC petroleum ether to give ester 13
(505 mg, 75%) as a white crystalline solid, mp 211e212 ꢀC; Rf (1:1
ethyl acetate:hexane) 0.49; IR nmax 3284, 2926, 1734, 1666 cmꢂ1; 1H
300 MHz) d 7.75e7.45 (4H, m, 2,6-aryl, 4,7-benzimidazolyl), 7.27
(2H, t, J ¼ 7.5 Hz, 3,5-aryl), 7.24e7.18 (2H, m, 5,6-benzimidazolyl),
7.06 (1H, t, J ¼ 7.5 Hz, 4-aryl), 4.20e4.00 (1H, m, CH), 2.28e1.97 (4H,
m, CHCH2, CH2CONH), 1.68e1.50 (2H, m, CH2CH2CONH), 1.48e1.30
(4H, m, CHCH2CH2, CHCH2CH2CH2); 13C NMR ((CD3)2SO, 125 MHz)
d
169.3 (PhNHCO), 169.3 (CONHOH), 152.7 (2-benzimidazolyl),
NMR (CDCl3, 300 MHz)
d
11.95 (1H, s, NH), 11.47 (1H, s, NH), 7.66
142.7 (benzimidazolyl),138.9 (1-aryl),134.6 (benzimidazolyl),128.7
(3,5-aryl), 123.5 (4-aryl), 121.8 (benzimidazolyl), 121.0 (benzimi-
dazolyl), 119.3 (benzimidazolyl), 118.3 (benzimidazolyl), 111.3
(benzimidazolyl), 47.8 (CH), 32.2 (CH2CONHOH), 31.1 (CHCH2), 28.4
(CHCH2CH2CH2), 26.8 (CHCH2CH2), 25.0 (CH2CH2CONHOH). Anal.
Calcd for C21H24N4O3.0.5H2O C, 64.75; H, 6.47; N, 14.39. Found C,
65.18; H, 6.36; N, 14.13.
(3H, m, 2,6-aryl, 7-benzimidazolyl), 7.48 (1H, m, 4-benzimidazolyl),
7.25 (4H, m, 3,5-aryl, 5,6-benzimidazolyl), 7.10 (1H, t, J ¼ 7.4 Hz, 4-
aryl), 4.65 (1H, t, J ¼ 7.7 Hz, CH), 4.02 (2H, q, J ¼ 7.1 Hz, CH2CH3),
2.32 (1H, m, CHCHH), 2.15 (1H, m, CHCHH), 1.99 (2H, t, J ¼ 7.5 Hz,
CH2COO), 1.36 (4H, m, CHCH2CH2, CH2CH2COO), 1.19 (5H, m,
CH2CH2CH2COO, CH2CH3); 13C NMR (CDCl3, 75 MHz)
d 173.5 (COO),
170.8 (NHCO), 153.3 (2-benzimidazolyl), 142.1 (7a-benzimidazolyl),
138.2 (1-aryl), 134.2 (3a-benzimidazolyl), 129.0 (3,5-aryl), 124.7 (4-
aryl), 123.2 (7-benzimidazolyl), 122.4 (4-benzimidazolyl), 120.4
(2,6-aryl), 118.3 (6-benzimidazolyl), 111.7 (5-benzimidazolyl), 60.1
(CH2CH3), 48.3 (CH), 34.0 (CH2COO), 33.6 (CHCH2), 28.5
(CH2CH2CH2COO), 27.2 (CHCH2CH2), 24.5 (CH2CH2COO), 14.2
(CH2CH3); m/z (CI, %) 394 ((M þ H)þ, 100), 293 (58), 274 (23). Anal.
Calcd for C23H27N3O3 C, 70.21; H, 6.92; N, 10.68. Found C, 70.17; H,
7.01; N, 10.79.
4.2.14. tert-Butyl 3-(2-aminophenylamino)-3-oxopropanoate (16)
To a solution of 3-tert-butoxy-3-oxopropanoic acid (200 mg,
1.25 mmol) and 1,2-phenylenediamine (135 mg, 1.25 mmol) in
acetonitrile (5 mL) was added a solution of DCC (283 mg,
1.37 mmol) in acetonitrile (2 mL) and the reaction stirred for
20 min. The white suspension was filtered and the filtrate evapo-
rated to leave a dark yellow oil which was purified by column
chromatography (1:1 ethyl acetate:40e60 ꢀC petroleum ether)
followed by recrystallisation from a mixture of ethyl acetate and
40e60 ꢀC petroleum ether to give amide 16 (155 mg, 50%) as a
white crystalline solid, mp 122e123 ꢀC; Rf (1:1 ethyl acetate:hex-
4.2.12. tert-Butyl 2-(8-ethoxy-1,8-dioxo-1-(phenylamino)octan-2-
yl)-1H-benzo[d]imidazole-1-carboxylate (14)
Di-tert-butyl dicarbonate (403 mg, 1.85 mmol) was added to a
stirred solution of ethyl 7-(1H-benzo[d]imidazol-2-yl)-8-oxo-8-
(phenylamino)octanoate (13) (484 mg, 1.23 mmol) in tetrahydro-
furan (12 mL). The solution was stirred at 20 ꢀC for 7 d. Evaporation
gave a residue was purified by column chromatography (1:4 ethyl
acetate:40e60 ꢀC petroleum ether) to give recovered 13 (220 mg,
45%) and ester 14 (210 mg, 35%) as a colourless oil; Rf (1:3 ethyl
acetate:hexane) 0.40; IR nmax 3319, 2936, 1732, 1600 cmꢂ1; 1H NMR
ane) 0.48; IR nmax 3428, 3318, 1718, 1655 cmꢂ1
;
1H NMR (CDCl3,
300 MHz) 8.89 (1H, s, NH), 7.29e7.25 (1H, m, 3-aryl), 7.09e7.02
d
(1H, m, 5-aryl), 6.84e6.77 (2H, m, 4,6-aryl), 3.59 (2H, br s, NH2),
3.40 (2H, s, CH2), 1.50 (9H, s, (CH3)3); 13C NMR (CDCl3, 75 MHz)
d
169.1 (COOBut), 164.2 (CONH), 140.6 (2-aryl), 127.2 (4-aryl), 125.3
(6-aryl), 123.8 (1-aryl), 119.3 (5-aryl), 117.7 (3-aryl), 83.1 (C(CH3)3),
42.0 (CH2), 28.0 ((CH3)3). Anal. Calcd for C13H18N2O3 C, 62.38; H,
7.25; N, 11.19. Found C, 62.29; H, 7.28; N, 11.13.
(CDCl3, 300 MHz)
d 9.46 (1H, s, NH), 7.94e7.89 (1H, m, 7-
benzimidazolyl), 7.82e7.77 (1H, m, 4-benzimidazolyl), 7.57 (2H, d,
J ¼ 8.5 Hz, 2,6-aryl), 7.39e7.35 (2H, m, 5,6-benzimidazolyl), 7.28
(2H, t, J ¼ 7.5 Hz, 3,5-aryl), 7.04 (1H, t, J ¼ 7.5 Hz, 4-aryl), 4.82 (1H, t,
J ¼ 7.2 Hz, CH), 4.07 (2H, q, J ¼ 7.1 Hz, CH2CH3), 2.38e2.25 (4H, m,
CHCH2, CH2COO), 1.72 (9H, s, C(CH3)3), 1.69e1.57 (2H, m,
CH2CH2COO), 1.55e1.35 (4H, m, CHCH2CH2, CHCH2CH2CH3), 1.21
4.2.15. tert-Butyl 2-(1H-benzo[d]imidazol-2-yl)acetate (17)
tert-Butyl 3-(2-aminophenylamino)-3-oxopropanoate (16)
(70 mg, 0.28 mmol) was dissolved in acetic acid (0.15 mL) and the
solution heated to 90 ꢀC for 1 h. After allowing to cool the solvent
was evaporated and the residue recrystallised from a mixture of
ethyl acetate and 40e60 ꢀC petroleum ether to give ester 17 (62 mg,
96%) as a white crystalline solid, mp 158e161 ꢀC; Rf (1:1 ethyl
(3H, t, J ¼ 7.1 Hz, CH2CH3); 13C NMR (CDCl3, 75 MHz)
d 173.7
(COOEt), 168.1 (CONH), 154.1 (COOBut), 149.2 (2-benzimidazolyl),
141.7 (7a-benzimidazolyl), 138.2 (1-aryl), 132.6 (3a-benzimida-
zolyl), 128.9 (3,5-aryl), 125.0 (6-benzimidazolyl), 124.5 (5-
benzimidazolyl), 124.1 (4-aryl), 119.9 (7-benzimidazolyl), 119.7
(2,6-aryl), 115.2 (4-benzimidazolyl), 86.7 (C(CH3)3), 60.2 (CH2CH3),
48.1 (CH), 34.2 (CH2COO), 33.5 (CHCH2), 28.9 (CHCH2CH2CH2), 28.1
(C(CH3)3), 27.0 (CHCH2CH2), 24.7 (CH2CH2COO), 14.3 (CH2CH3); m/z
acetate:hexane) 0.38; IR nmax 2984, 1722, 1435 cmꢂ1
(CDCl3, 300 MHz)
10.0 (1H, br s, NH), 7.56 (2H, dd, J ¼ 6.0, 3.2 Hz,
4,7-benzimidazolyl), 7.22 (2H, dd, 6.0, 3.2 Hz, 5,6-
benzimidazolyl), 3.99 (2H, s, CH2), 1.46 (9H, s, (CH3)3); 13C NMR
(CDCl3, 75 MHz)
169.0 (COOBut), 147.8 (2-benzimidazolyl), 138.3
;
1H NMR
d
J
¼
d
(3a,7a-benzimidazolyl), 122.5 (4,7-benzimidazolyl), 115.0 (5,6-
benzimidazolyl), 82.7 (C(CH3)3), 35.7 (CH2), 28.0 ((CH3)3). Anal.

J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
8591
Calcd for C13H16N2O2 C, 67.22; H, 6.49; N, 12.06. Found C, 67.10; H,
6.97; N, 11.97.
(15 mL) was added to the oily residue and the mixture neutralised
with 1 M hydrochloric acid. On cooling, the precipitate was
collected by filtration, air-dried and recrystallised from aqueous
ethanol to give the hydroxamic acid 20 (508 mg, 67%) as a white
crystalline solid, mp 110e115 ꢀC; Rf (5% methanol in ethyl acetate)
4.2.16. tert-Butyl 2-(2-tert-butoxy-2-oxoethyl)-1H-benzo[d]
imidazole-1-carboxylate (18)
To a stirred solution of tert-butyl 2-(1H-benzo[d]imidazol-2-yl)
acetate (17) (3.37 g, 14.5 mmol) in tetrahydrofuran (33 mL) was
added di-tert-butyl dicarbonate (3.80 g, 17.4 mmol) and the solu-
tion stirred at 20 ꢀC for 3 d. Evaporation gave a residue that was
subjected to column chromatography (1:4 ethyl acetate:40e60 ꢀC
petroleum ether) to give ester 18 (4.68 g, 97%) as a colourless
viscous oil which solidified on standing to a white solid, mp
82e83 ꢀC; Rf (1:1 ethyl acetate:hexane) 0.60; IR nmax 2979, 1750,
0.58; IR nmax 3341, 2934, 1704, 1650 cmꢂ1
300 MHz)
NH), 7.54 (1H, d, J ¼ 7.6 Hz, 7-benzimidazolyl), 7.44 (1H, d,
7.0 Hz, 4-benzimidazolyl), 7.19e7.08 (2H, m, 5,6-
;
1H NMR ((CD3)2SO,
d
12.31 (1H, br s, OH), 10.32 (1H, br s, NH), 8.65 (1H, br s,
J
¼
benzimidazolyl), 3.80 (1H, t, J ¼ 7.7 Hz, CH), 2.06e1.97 (2H, m,
CHCH2), 1.90 (2H, t, J ¼ 7.3 Hz, CH2CONH), 1.52e1.43 (2H, m,
CH2CH2CONH), 1.37 (9H, s, C(CH3)3), 1.33e1.24 (4H, m, CHCH2CH2,
CHCH2CH2CH2); 13C NMR ((CD3)2SO, 75 MHz)
d
170.2 (COO), 169.0
1729 cmꢂ1 1H NMR (CDCl3, 300 MHz)
; d 7.93e7.87 (1H, m, 7-
(CONH), 151.7 (2-benzimidazolyl), 142.8 (7a-benzimidazolyl), 134.4
benzimidazolyl), 7.74e7.67 (1H, m, 4-benzimidazolyl), 7.38e7.28
(3a-benzimidazolyl), 121.8
benzimidazolyl), 118.4
(7-benzimidazolyl), 120.9
(5-benzimidazolyl), 111.1
(4-
(6-
(2H, m, 5,6-benzimidazolyl), 4.19 (2H, s, CH2), 1.68 (9H, s, (CH3)3),
1.43 (9H, s, (CH3)3); 13C NMR (CDCl3, 300 MHz)
d
167.9 (NCOO),
benzimidazolyl), 80.8 (C(CH3)3), 46.8 (CH), 32.1 (CH2CONH), 30.5
(CHCH2), 28.2 (CHCH2CH2CH2), 27.6 (C(CH3)3), 26.5 (CH2CH2CONH),
24.9 (CHCH2CH2); m/z (EI, %) 384 ((M þ Na)þ, 100), 362 (54), 329
(79), 306 (36), 176 (99), 154 (99). HRMS (M þ Na)þ calcd for
149.7 (CH2COO), 148.9 (2-benzimidazolyl), 142.1 (3a-benzimida-
zolyl), 132.9 (7a-benzimidazolyl), 124.6 (7-benzimidazolyl), 124.1
(4-benzimidazolyl),
119.8
(5-benzimidazolyl),
114.9
(6-
benzimidazolyl), 85.7 (C(CH3)3), 81.7 (C(CH3)3), 39.1 (CH2), 28.0
((CH3)3), 28.0 ((CH3)3). Anal. Calcd for C18H24N2O3 C, 65.04; H, 7.28;
N, 8.43. Found C, 65.02; H, 7.26; N, 8.30.
C
19H27N3NaOþ4 384.1899. Found: 384.1906.
4.2.19. Ethyl 7-(1H-benzo[d]imidazol-2-yl)heptanoate (21)
A solution of oxononane-2,9-dione (3.0 g, 19.2 mmol) in tetra-
hydrofuran (15 mL) was added dropwise to a stirred solution of 1,2-
phenylenediamine (2.08 g, 19.2 mmol) in tetrahydrofuran (30 mL)
and the brown solution stirred for 45 min. Evaporation gave a
residue which was dissolved in a solution of 4% by volume of
concentrated sulfuric acid in ethanol (190 mL), previously prepared
by slow addition of sulfuric acid to cold ethanol (CAUTION!). The
orange solution was heated at 90 ꢀC for 16 h then allowed to cool
and quenched with saturated aqueous sodium hydrogen carbonate.
The mixture was evaporated and water (20 mL) was added. This
mixture was extracted with ethyl acetate (3 ꢁ 20 mL) and the
combined organic layers were dried (MgSO4), filtered and evapo-
rated to give a brown oil which was purified by column chroma-
tography (1:4 ethyl acetate:40e60 ꢀC petroleum ether) to give an
cream solid. Recrystallisation from diethyl ether afforded the ester
21 (1.52 g, 29%) as white needles, mp 95e97 ꢀC; Rf (1:1 ethyl ace-
4.2.17. 1-tert-Butyl, 8-ethyl 2-(1-(tert-butoxycarbonyl)-1H-benzo
[d]imidazol-2-yl)octanedioate (19)
Sodium hydride (337 mg of a 60% dispersion in mineral oil,
14.0 mmol) was added to a stirred solution of tert-butyl 2-(2-tert-
butoxy-2-oxoethyl)-1H-benzo[d]imidazole-1-carboxylate
(18)
(4.24 g, 12.8 mmol) in dry tetrahydrofuran (130 mL). The suspen-
sion was stirred for a further 30 min, then ethyl 6-bromohexanoate
(3.13 g, 14.0 mmol) added and the mixture stirred at 60 ꢀC for 18 h.
A further portion of sodium hydride (337 mg, 14.0 mmol) was then
added (with effervescence) and stirring continued at 60 ꢀC for 4 h.
After allowing to cool the solvent was evaporated and ethyl acetate
(80 mL) added. The suspension was washed with saturated aqueous
ammonium chloride (40 mL), dried (MgSO4), filtered and evapo-
rated to give a brown oil which was purified by column chroma-
tography (15:85 ethyl acetate:40e60 ꢀC petroleum ether) to give
ester 19 (2.01 g, 33%) as a yellow oil; Rf (1:2 ethyl acetate:hexane)
tate:hexane) 0.42; IR nmax 2934, 1720, 1175, 1026 cmꢂ1
(CDCl3, 300 MHz)
10.78 (1H, br s, NH), 7.54 (2H, dd, J ¼ 6.0, 3.2 Hz,
4,7-benzimidazolyl), 7.20 (2H, dd, 6.0, 3.2 Hz, 5,6-
;
1H NMR
0.53; IR nmax 2978, 1731, 1453 cmꢂ1
;
1H NMR (CDCl3, 300 MHz)
d
d
7.88e7.83 (1H, m, 7-benzimidazolyl), 7.73e7.68 (1H, m, 4-
J
¼
benzimidazolyl), 7.28e7.23 (2H, m, 5,6-benzimidazolyl), 4.39 (1H,
dd, J ¼ 6.1, 8.3 Hz, CH), 4.05 (2H, q, J ¼ 7.1 Hz, CH2CH3), 2.36e2.09
(4H, m, CHCH2, CH2COO), 1.66 (9H, m, (CH3)3), 1.65e1.57 (2H, m,
CH2CH2COO), 1.55e1.43 (4H, m, CHCH2CH2, CHCH3CH3CH2), 1.40
(9H, m, (CH3)3), 1.18 (3H, t, J ¼ 7.1 Hz, CH2CH3); 13C NMR (CDCl3,
benzimidazolyl), 4.10 (2H, q, J ¼ 7.1 Hz, CH2CH3), 2.93 (2H, t,
J ¼ 7.6 Hz, NCCH2), 2.21 (2H, t, J ¼ 7.4 Hz, CH2COO), 1.89e1.77 (2H,
m, CH2CH2COO), 1.58e1.47 (2H, m, NCCH2CH2), 1.39e1.19 (7H, m,
NCCH2CH2CH2, CH2CH2CH2COO, CH3); 13C NMR (CDCl3, 75 MHz)
d
174.0 (COO), 155.5 (2-benzimidazolyl), 138.6 (3a,7a-benzimida-
75 MHz)
d
173.6 (COOEt),170.5 (CHCOOBut),153.5 (NCOO),149.1 (2-
zolyl), 122.0 (4,7-benzimidazolyl), 114.6 (5,6-benzimidazolyl), 60.3
(CH2CH3), 34.2 (CH2COO), 29.2 (NCCH2), 28.8 (NCCH2CH2), 28.6
(CH2CH2CH2COO), 28.1 (NCCH2CH2CH2), 24.7 (CH2CH2COO), 14.2
(CH3); m/z (CI, %) 275 ((M þ H)þ, 100), 229 (6), 187 (4). Anal. Calcd
for C16H22N2O2 C, 70.04; H, 8.08; N, 10.21. Found C, 69.87; H, 8.07;
N, 10.12.
benzimidazolyl), 142.1 (7a-benzimidazolyl), 132.8 (3a-benzimida-
zolyl), 124.4 (7-benzimidazolyl), 124.0 (4a-benzimidazolyl), 120.0
(5-benzimidazolyl), 115.0 (6-benzimidazolyl), 85.5 (C(CH3)3), 81.2
(C(CH3)3), 60.0 (CH2CH3), 48.2 (CH), 34.2, (CH2COO), 29.8 (CHCH2),
28.9 (CHCH2CH2CH2), 28.1 ((CH3)3), 27.8 ((CH3)3), 27.5 (CHCH2CH2),
24.7 (CH2CH2COO), 14.2 (CH2CH3); m/z (EI, %) 497 (MHþ, 34), 441
(33), 397 (57), 297 (100), 251 (86). HRMS (M þ Na)þ calcd for
4.2.20. 7-(1H-Benzo[d]imidazol-2-yl)-N-hydroxyheptanamide (22)
To a stirred solution of ethyl 7-(1H-benzo[d]imidazol-2-yl)
heptanoate (21) (1.20 g, 4.37 mmol) in tetrahydrofuran (40 mL) was
added 50% aqueous hydroxylamine (2.89 mL, 43.7 mmol) followed
by slow addition of 1 M potassium hydroxide in methanol
(6.56 mL). The mixture was stirred at 20 ꢀC for 2 h then evaporated.
To the yellow residue was added water (60 mL) then the solution
was acidified with 2 M hydrochloric acid to give a white precipitate.
After filtering, the product was washed with water, methanol and
lastly with diethyl ether to give the hydroxamic acid 22 (696 mg,
61%) as a white solid, mp 226e227 ꢀC; Rf (1% methanol in ethyl
C
26H38N2NaOþ6 497.2628. Found: 497.2620.
4.2.18. tert-Butyl 2-(1H-benzo[d]imidazol-2-yl)-8-
(hydroxyamino)-8-oxooctanoate (20)
To a stirred solution of 1-tert-butyl 8-ethyl 2-(1-(tert-butox-
ycarbonyl)-1H-benzo[d]imidazol-2-yl)octanedioate (19) (1.0 g,
2.11 mmol) in tetrahydrofuran (20 mL) was added 50% aqueous
hydroxylamine (1.39 mL, 21.1 mmol) followed by dropwise addition
of 1 M potassium hydroxide in methanol (6.33 mL). The mixture
was stirred for 30 min then the solvent was evaporated. Water

8592
J.A. Dines, C.M. Marson / Tetrahedron 72 (2016) 8584e8592
acetate) 0.16; IR nmax 3284, 2930, 2324, 1642 cmꢂ1
;
1H NMR
4.2.23. 6-(2-(Diethylamino)-4-hydroxy-6-oxo-1-phenyl-1,6-
((CD3)2SO, 300 MHz) 10.33 (1H, s, NH), 8.67 (1H, s, NH), 7.51e7.30
d
dihydropyrimidin-5-yl)-N-hydroxy-hexanamide (25)
(2H, m, 4,7-benzimidazolyl), 7.13e7.05 (2H, m, 5,6-benzimidazolyl),
2.77 (2H, t, J ¼ 7.5 Hz, NNCCH2), 1.92 (2H, t, J ¼ 7.3 Hz, CH2CO),
1.78e1.68 (2H, m, NNCCH2CH2), 1.54e1.42 (2H, m, CH2CH2CO),
1.38e1.23 (4H, m, CH2CH2CH2CH2CO, CH2CH2CH2CO); 13C NMR
To a stirred solution of ethyl 6-(2-(diethylamino)-4-hydroxy-6-
oxo-1-phenyl-1,6-dihydropyrimidin-5-yl)hexanoate (24) (250 mg,
0.62 mmol) in tetrahydrofuran (6 mL) was added 50% aqueous
hydroxylamine (0.41 mL, 6.23 mmol) followed by dropwise addi-
tion of 1 M potassium hydroxide in methanol (1.87 mL). The
mixture was stirred for 5 min then evaporated and water (20 mL)
added to the residue. The mixture was neutralised with 1 M hy-
drochloric acid then extracted with ethyl acetate (4 ꢁ 20 mL). The
combined organic layers were dried (Na2SO4), filtered and evapo-
rated to give an orange oil which was purified by column chro-
matography (ethyl acetate) to give the hydroxamic acid 25 (124 mg,
51%) as an orange oil; Rf (1% methanol in ethyl acetate) 0.45; IR nmax
((CD3)2SO, 75 MHz)
(7a-benzimidazolyl), 139.4 (3a-benzimidazolyl), 126.4 (7-
benzimidazolyl), 125.9 (4-benzimidazolyl), 123.1 (6-
d 174.2 (CO), 160.2 (2-benzimidazolyl), 148.4
benzimidazolyl), 115.8 (5-benzimidazolyl), 37.3 (NNCCH2), 33.6
(CH2CO), 33.5 (NNCCH2CH2), 33.4 (CH2CH2CH2CO), 32.5
(CH2CH2CH2CH2CO), 30.1 (CH2CH2CO); m/z (CI, %) 262 ((M þ H)þ,
100), 242 (57), 201 (9). Anal. Calcd for C14H19N3O2 C, 64.35; H, 7.33;
N, 16.08. Found C, 64.36; H, 7.51; N, 15.89.
3192, 2932, 1616, 1522 cmꢂ1
;
1H NMR (CD3OD, 300 MHz)
4.2.21. 6-Ethyl 1,1-bis(2,4,6-trichlorophenyl)hexane-1,1,6-
tricarboxylate (23)
d
7.62e7.38 (3H, m, 3,4,5-aryl), 7.27 (2H, d, J ¼ 7.0 Hz, 2,6-aryl), 3.08
(4H, q, J ¼ 7.0 Hz, N(CH2CH3)2), 2.36 (2H, t, J ¼ 7.5 Hz, CH2CO), 2.07
(2H, t, J ¼ 7.5 Hz, CCH2), 1.62 (2H, dt, J ¼ 15.0, 7.5 Hz, CH2CH2CO),
1.57e1.25 (4H, m, CH2CH2CH2CH2CO, CH2CH2CH2CO), 0.80 (6H, t,
A mixture of 2-carboxyoctanedioic acid 8-ethyl ester (2) (1.34 g,
5.44 mmol) and 2,4,6-trichlorophenol (2.15 g, 10.9 mmol) in
phosphorus oxychloride (2.17 g, 14.4 mmol) was heated to 100 ꢀC
for 5 h. After allowing to cool, water (10 mL) was added. The
mixture was extracted with ethyl acetate (2 ꢁ 10 mL) and the
combined organic layers were washed with saturated aqueous
sodium hydrogen carbonate (10 mL) and then with brine (10 mL).
The organic layer was dried (MgSO4), filtered and the solvent
evaporated to give a brown oil which was purified by column
chromatography (5:95 ethyl acetate:40e60 ꢀC petroleum ether) to
give ester 23 as a colourless oil (1.61 g, 49%); Rf (1:9 ethyl aceta-
J ¼ 7.0 Hz, N(CH2CH3)2); 13C NMR (CD3OD, 75 MHz)
d 173.2 (4-
pyrimidyl), 167.7 (CONHOH), 167.2 (6-pyrimidyl), 160.0 (2-
pyrimidyl), 139.9 (1-aryl), 130.3 (3,5-aryl), 130.2 (2,6-aryl), 129.3
(4-aryl), 95.8 (5-pyrimidyl), 46.0 (N(CH2CH3)2), 33.7 (CH2CO), 30.0
(CH2CH2CH2CO), 29.0 (CH2CH2CH2CH2CO), 26.7 (CH2CH2CO), 23.9
(CCH2), 12.9 (N(CH2CH3)2); m/z (CI, %) 411 ((M þ Na)þ, 100), 389
(MHþ, 65), 321 (17), 192 (70). HRMS calcd for C20H29N4Oþ4 (MHþ)
389.2183, found 389.2198.
te:hexane) 0.55; IR nmax 2937, 1769, 1731, 1566 cmꢂ1
;
1H NMR
(CDCl3, 300 MHz) 7.44e7.37 (4H, m, 3,5-aryl), 4.13 (2H, q,
d
Acknowledgment
J ¼ 7.1 Hz, CH2CH3), 4.05 (1H, t, J ¼ 7.4 Hz, COCHCO), 2.38e2.24 (4H,
m, CHCH2, CH2CO2Et), 1.77e1.58 (4H, m, CH2CH2CO2Et, CHCH2CH2),
1.57e1.40 (2H, m, CHCH2CH2CH2), 1.25 (3H, t, J ¼ 7.1 Hz, CH2CH3);
We are grateful for generous support by the Mandeville Trust
(studentship to JAD).
13C NMR (CDCl3, 75 MHz)
d 173.5 (COOEt), 164.6 (COOAr), 142.4 (1-
Ar), 132.6 (4-Ar), 129.5 (Ar) 128.8 (Ar), 60.3 (CH2CH3), 50.7 (CH),
34.1 (CH2COOEt), 29.2 (CHCH2), 28.6 (CH2CH2CH2COOEt), 27.0
(CHCH2CH2), 24.6 (CH2CH2COOEt), 14.1 (CH3CH2); m/z (CI, %) 626
(18), 211 (26), 176 (100). HRMS calcd for C23H20Cl6NaO6 (M þ Na)þ
624.9289, found 624.9275.
References
1.. Codd R. Coord Chem Rev. 2008;252:1387.
ꢀ
2.. Lopez JE, Sullivan ED, Fierke CA. ACS Chem Biol. 2016;11:706.
3.. Stengel KR, Hiebert SW. Antiox Redox Signal. 2015;23:99.
4.. Marson CM. Anti Cancer Agents Med Chem. 2009;9:661.
5.. Lombardi PM, Cole KE, Dowling DP, Christianson DW. Curr Opin Struct Biol.
2011;21:735.
6.. Mottamal M, Zheng S, Huang TL, Wang G. Molecules. 2015;20:3898.
7.. Poole RM. Drugs. 2014;74:1543.
8.. Fenichel MP. J Nat Cancer Inst. 2015;107:165.
9.. Mack GS. Nat Biotechnol. 2010;28:1259.
10.. Benedetti R, Conte M, Altucci L. Antiox Redox Signal. 2015;23:99.
11.. Finnin MS, Donigian JR, Cohen A, Richon VM, Rifkind RA, Marks PA. Nature.
1999;401:188.
12.. Amodio N, Stamato MA, Guila AM, et al. Mol Cancer Ther. 2016;15:1364.
13.. Wang D-F, Helquist P, Wiech NL, Wiest O. J Med Chem. 2005;48:6936.
14.. Joel, S. P.; Marson, C. M; U.S. Pat. Appl. 2010/0160392 Queen Mary & Westfield
College, University College London, Barts and London NHS Trust, 24.06.10.
15.. Maharaj L, Marson CM, Middleton BJ, et al. Br J Haematol. 2013;163:135.
16.. Drouhin P, Hurst TE, Whitwood AC, Taylor RJK. Tetrahedron. 2015;71:7124.
17.. Bixa T, Hunter R, Andrijevic A, Petersen W, Su H, Dhoro F. J Org Chem. 2015;80:
762.
4.2.22. Ethyl 6-(2-(diethylamino)-4-hydroxy-6-oxo-1-phenyl-1,6-
dihydropyrimidin-5-yl)-hexanoate (24)
A stirred mixture of 6-ethyl 1,1-bis(2,4,6-trichlorophenyl)hex-
ane-1,1,6-tricarboxylate (23) (1.40 g, 2.31 mmol) and N,N-diethyl-
N0-phenylguanidine (443 mg, 2.31 mmol) was heated to 150 ꢀC for
5 min. After allowing to cool to room temperature the viscous
brown oil was purified by column chromatography (1:1 ethyl ace-
tate:hexane) to give the ester 24 (635 mg, 68%) as a pale yellow oil;
Rf (1:1 ethyl acetate:hexane) 0.27; IR nmax 2935, 1730, 1595,
1524 cmꢂ1; 1H NMR (CDCl3, 300 MHz)
d
7.36 (2H, t, J ¼ 7.4 Hz, 3,5-
aryl), 7.28 (1H, t, J ¼ 7.4 Hz, 4-aryl), 7.19 (2H, d, J ¼ 7.4 Hz, 2,6-aryl),
4.02 (2H, q, J ¼ 7.1 Hz, OCH2CH3), 2.97 (4H, q, J ¼ 6.9 Hz,
N(CH2CH3)2), 2.33 (2H, t, J ¼ 7.5 Hz, CCH2), 2.20 (2H, t, J ¼ 7.5 Hz,
CH2COOEt), 1.63e1.53 (2H, m, CH2CH2COOEt), 1.50e1.40 (2H, m,
CCH2CH2), 1.36e1.25 (2H, m, CCH2CH2CH2), 1.15 (3H, t, J ¼ 7.1 Hz,
OCH2CH3), 0.75 (6H, t, J ¼ 7.0 Hz, N(CH2CH3)2); 13C NMR (CDCl3,
18.. Gopalakrishnan B, Babu SA, Padmavathi R. Tetrahedron. 2015;71:8333.
19.. Adediran SA, Cabaret D, Lohier J-F, Wakselman M, Pratt RF. Bioorg Med Chem
Lett. 2004;14:5117.
20.. Braeuniger H, Stens B. Pharmazie. 1963;18:585.
75 MHz)
d 174.1 (COOEt), 165.1 (4-pyrimidinyl), 163.7 (6-
21.. Polla MO, Tottie L, Norden C, et al. Bioorg Med Chem. 2004;12:1151.
22.. Wang T, Sepulveda M, Gonzales P, Gately S. Bioorg Med Chem Lett. 2013;23:
4790.
23.. Varga M, Kapui Z, Batori S, et al. Eur J Med Chem. 2003;38:421.
24.. Seto CT, Mathias JP, Whitesides GM. J Am Chem Soc. 1993;115:1321.
25.. Shelkov R, Nahmany M, Melman A. J Org Chem. 2002;67:8975.
26.. Mai A, Esposito M, Sbardella G, Massa S. Org Prep Proc Int. 2001;33:391.
27.. Schotte, H. Ger. Pat. 514248, Schering Kahlbaum AG, 30.12.10.
pyrimidinyl), 155.5 (2-pyrimidinyl), 138.1 (1-aryl), 128.9 (3,5-aryl),
128.8 (2,6-aryl), 128.0 (4-aryl), 95.1 (5-pyrimidinyl), 60.1 (CH2CH3),
44.6 (N(CH2CH3)2), 34.4 (CH2COOEt), 29.1 (CCH2CH2CH2), 27.9
(CHCH2CH2), 24.9 (CH2CH2COOEt), 23.1 (CCH2), 14.2 (CH2CH3), 12.4
(N(CH2CH3)2); m/z (EI, %) 401 (Mþ, 2), 291 (27), 171 (59), 125 (100);
HRMS calcd for C22H31N3O4 401.2314. Found: 401.2311.