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S. Price et al. / Bioorg. Med. Chem. Lett. 17 (2007) 370–375
O
O
d
b, e, f
S
HN
S
N
S
N
S
a
CN
CN
CN
R
R
Me2N
NHOH
N
N
N
2
4a-f
6a-j
1
b, c
j, e, f or k
N
N
S
CO2Me
CO2Me
BocHN
N
N
h, i
g
l
5
HN
S
R1
N
S
CO2Me
CO2Me
N
R2/H
N
N
OMe
3
7
S
m, n
MeO
8
Scheme 1. Reagents and conditions: (a) EtOH, hydrazine hydrate (1.1 equiv), reflux, 16 h (89%); (b) 1 M NaOH, reflux, 2 h (52–97%); (c) MeOH,
i
concd HCl, reflux, 16 h (93%); (d) RX (1.2 equiv), K2CO3, DMF, 70 °C, 16 h (43–90%); (e) Pr2NEt (2.5 equiv), DMF, H2NOTHP (1.1 equiv),
HATU (1.1 equiv) (60–95%); (f) pTSA, MeOH (23–85%); (g) BocHN(CH2)2Br (1.1 equiv), K2CO3, DMF, 70 °C, 16 h (88%); (h) CF3CO2H, CH2Cl2;
(i) R1CHO (0.9 equiv), MeOH, 16 h, then NaBH4, 2 h (50–73% two steps); (j) LiOH, H2O, CH3CN, 16 h (quant); (k) NH2OHÆHCl (5 equiv), KOH,
MeOH, 16 h (25–65%); (l) (MeO)2CHCH2Br (1.2 equiv), K2CO3, DMF, 90 °C, 16 h (60%); (m) 1 M HCl, THF, lW 150 °C, 100 s (80%); (n)
R1R2NH (1.1 equiv), Na(OAc)3BH, CH2ClCH2Cl, 16 h (65–80%).
a variety of aromatic aldehydes to yield tethered
carbomethoxythiophenes 7. Acidic deprotection of the
dimethyl acetal 8 to liberate the corresponding aldehyde,
followed by reductive amination conditions using
tetrahydroisoquinoline, provided the desired intermedi-
ate carbomethoxythiophene 7 from which compound
6i was obtained. Conversion of the carbomethoxythi-
ophenes 7 to the desired hydroxamic acids 6g–j was
achieved by ester hydrolysis, followed by the same
coupling and deprotection conditions used for the
1-N-alkylated cyanothiophenes 4a–f, or directly by
treating with basic hydroxylamine.
pound 6g by a methylene group to furnish the pheneth-
ylamino-tethered analogue 6h resulted in reduced
activity in the HDAC assay, but no loss of potency in
the cellular assay. Cyclisation of the secondary amino
group of compound 6g onto the aromatic ring by an eth-
yl linker, compound 6i, provided a marginal increase in
activity in the HDAC assay, and a 3-fold increase in
activity in both cell proliferation assays.
Encouraged by the promising activity of the unsub-
stituted phenyl-tethered analogues 6a–i, we next focused
our attention on investigating the effect of functionalis-
ing the phenyl rings of compounds 6g, and 6f, respective-
ly. Table 2 includes a selection of compounds synthesised
to investigate aromatic ring substitution SAR.
All compounds were initially tested in a primary HDAC
enzyme assay,11 and those possessing sub-micromolar
activity were then simultaneously evaluated in MCF-7
and MDA-MB231 cell-based proliferation assays.12
The aminoethyl-tethered compounds 6j–r were pro-
duced using the existing synthetic methodology as out-
lined in Scheme 1. However, a modified synthetic
route was required to make further acetamide-tethered
hydroxamic acids that would enable the use of commer-
cially available aromatic amines (Scheme 2).13
The benzyl-tethered compound 6a possessed a 5-fold
increase in HDAC potency over ADS100380, both in
the HDAC and the MCF-7 cell proliferation assays.
Increasing the linker length of compound 6a by a
methylene group, compound 6b, led to a minor increase
in HDAC activity, whereas increasing the linker length
by two methylene units, compound 6c, provided more
than a 4-fold increase in activity. Both compounds 6b
and 6c display corresponding increases in activity in
the MCF-7 cell proliferation assays. Replacement of a
methylene group in the tether of compound 6c with an
oxygen atom, compound 6d, had little effect on the
activity. Homologation of the tether of compound 6d
with a methylene group, compound 6e, provided no
further increase in activity in the HDAC assay, but a
2-fold increase in anti-proliferative activity in the
MDA-MB231 cell-based assay. Introducing an acetam-
ide moiety between the phenyl and pyrazole ring sys-
tems, compound 6f, afforded the most potent three-
atom tether identified. Compound 6g was designed to
incorporate a basic amino group into a four-atom
tether, a transformation that retained similar activity
to the non-basic tethered analogue 6e in the HDAC
and MCF-7 assays. Homologation of the tether of com-
The carbomethoxythiophene 3 was alkylated with tert-
butyl bromoacetate to provide compound 9. The tert-
butyl ester 9 was readily hydrolysed and the resulting
acid was coupled with a variety of aromatic amines to
give compounds of the generic structure 10. Standard
conditions were then used to convert the methyl carbox-
ylate to the corresponding hydroxamic acids 6s–w.
The benzodioxole analogue 6j was one of the first substi-
tuted phenyl-tethered analogues to be prepared and test-
ed. Compound 6j indicated that phenyl substitution was
tolerated, and provided potent HDAC and cell prolifer-
ation IC50 values. The introduction of a para-methoxy
substituent to compound 6g afforded analogue 6k that
possessed a 3-fold increase in HDAC activity. However,
the 3,4-bis-methoxy substituted phenyl compound 6l
lost almost an order of magnitude in potency in both
HDAC and cellular proliferation assays. 5,6-Fused ring
systems attached either by the five- or the six-membered