Histone deacetylase inhibitors through click chemistry

Article abstract of DOI:10.1021/jm8005355

Histone deacetylase inhibitors (HDACi) are a relatively new class of chemotherapy agents. Herein, we report a click-chemistry based approach to the synthesis of HDACi. Fourteen agents were synthesized from the combination of two alkyne and seven azido pre

Full text of DOI:10.1021/jm8005355

J. Med. Chem. 2008, 51, 7417–7427
7417
Histone Deacetylase Inhibitors through Click Chemistry
Jie Shen,†,| Robert Woodward,†,| James Patrick Kedenburg,† Xianwei Liu,‡ Min Chen,‡ Lanyan Fang,§ Duxin Sun,§ and
Peng George Wang*,†
Departments of Biochemistry and Chemistry, The Ohio State UniVersity, 876 Biological Sciences Building, 484 West 12th AVenue,
Columbus, Ohio 43210, DiVision of Pharmaceutics, School of Pharmacy, The Ohio State UniVersity, 500 West 12th AVenue,
Columbus, Ohio 43210, College of Life Science, Shandong UniVersity, Jinan, Shandong, 250100, P.R. China
ReceiVed May 8, 2008
Histone deacetylase inhibitors (HDACi) are a relatively new class of chemotherapy agents. Herein, we
report a click-chemistry based approach to the synthesis of HDACi. Fourteen agents were synthesized from
the combination of two alkyne and seven azido precursors. The inhibition of HDAC1 and HDAC8 was then
determined by in vitro enzymatic assays, after which the cytotoxicity was evaluated in the NCI human
cancer cell line screen. A lead compound 5g (NSC746457) was discovered that inhibited HDAC1 at an
IC50 value of 104 ( 30 nM and proved quite potent in the cancer cell line screen with GI50 values ranging
from 3.92 µM to 10 nM. Thus, this click HDACi design has provided a new chemical scaffold that has not
only revealed a lead compound, but one which is easily amendable to further structural modifications given
the modular nature of this approach.
Introduction
homologue of the hyperthermophilic bacterium Aquifex aeolicus
in 1999.22 In general, the active site is a tube-like pocket that
accommodates the side chain of client Lys residues. Located at
the bottom of this pocket is the Zn(II) cofactor, which acts as
a Lewis acid to catalyze hydrolysis of the acetylated Lys side
chain. The opening region (also called the cap region) of the
active site consists of multiple loops and is thus highly
malleable.
Posttranscriptional modifications of histones are important
processes in epigenetics.1-3 The reversible acetylation of Lys
residues,4-6 for example, can help control the remodeling status
of chromatin via charge-charge interactions between negatively
charged DNA and neutral or positively charged histones. The
removal and addition of these acetyl groups is catalyzed by the
enzymes histone deacetylase (HDACa) and histone acetyltrans-
ferase (HAT), respectively. In the past 10 years, studies on this
process have attracted an increasing amount of attention, due
in part to the observations that aberrant hypoacetylation of
histones frequently occurs in tumor cells, resulting in the
silencing of specific (tumor suppressor) genes.7 Accordingly,
clinical and biological studies have shown that inhibition of
HDACs can selectively inhibit cancer cell growth.8 It has also
been revealed that HDACs have a panel of nonhistone targets,
many of which are involved in tumorigenesis.9-17 All of these
features thus establish HDAC as an attractive target in cancer
chemotherapy.18-21
Thus far, 18 human HDAC subtypes have been identified
and accordingly divided into four classes based upon their
homology to yeast HDACs.20 Class I (yeast transcriptional
regulator RPD3) and II (yeast Hda 1) HDACs require a zinc
ion to mediate deacetylation and are therefore mechanistically
different from the class III (SIR2 yeast family) NAD+ dependent
HDACs. While HDAC 11 possesses similar catalytic activity
to classes I and II HDACs in terms of requiring a zinc ion, it
actually serves as the sole member of class IV due to low overall
sequence similarity with classes I and II.
From this elucidation of the structure of the HDAC active
site, progress on HDACi design has been greatly facilitated
(Figure 1). In most cases, the reported inhibitor is composed of
the following three moieties: a Zn(II) binding moiety, a spacer
moiety, and a “cap” moiety. Of the demonstrated Zn(II) binding
moieties, the hydroxamic acid (HA) functionality is the most
common. For example, the HA moiety exists in the naturally
occurring compound TSA as well as in the clinically approved
drug SAHA. In spite of the strong affinity of HA with Zn(II),
however, the in vivo efficacy of HA-containing HDACi is
impaired by the short clearance time of these agents.23-25
Therefore, non-HA HDACi design has been explored.26,27 These
non-HA moieties include electrophilic ketones (e.g., 1 in Figure
1), O-aminoanilides (e.g., MS-275), thiols (or the pro-drug
forms) (e.g.FK-228 and 2), and a variety of others. However,
in terms of binding affinity, none are as strong as HA. As for
the spacer moiety, proper length is the key factor in successful
HDAC inhibition. For example, for SAHA and its analogues,
six CH2 units are preferred, whereas chiral-center-and-HA-
containing HDACi (e.g., CHAPs and 3) prefer five CH2 units
between the HA and the chiral center.28-30 Similarly, chiral-
center-and-thiol-containing HDACi (e.g., 2) prefer five CH2
units in the spacer moiety. In addition to these length require-
ments, introduction of an unsaturated moiety within the spacer
region has also proved to be a valuable feature in enhancing
potency (e.g., TSA, MS275, (S)-HDAC-42 and 4). Such value
appears to arise from π-π stacking interactions between the
unsaturated moiety and two conserved Phe residues that occur
near the midpoint of the tube-like pocket (for HDAC8, they
are Phe152 and Phe208) in the 11 Zn(II) dependent human
HDACs.31 In regards to the “cap” moiety, a hydrophobic
substituent, especially an aromatic substituent, is frequently
In the case of the aforementioned Zn(II) dependent HDAC
isozymes, the active site structure was first revealed by a
* To whom correspondence should be addressed. Phone: (+1) 614-292-
9884. Fax: (+1) 614-688-3106. E-mail: wang.892@osu.edu.
†
Departments of Biochemistry and Chemistry, The Ohio State University.
Shandong University.
School of Pharmacy, The Ohio State University.
Authors who contributed equally to this paper.
‡
§
|
a Abbreviations: HDAC, histone deacetylase; HDACi, histone deacetylase
inhibitor; SAHA, Suberoylanilide hydroxamic acid; TSA, trichostatin A;
HA, hydroxamic acid.
10.1021/jm8005355 CCC: $40.75
2008 American Chemical Society
Published on Web 11/14/2008

7418 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23
Shen et al.
Figure 1. Current HDACi.
Figure 2. Combinatorial Design of HDACi via Click Chemistry.
incorporated. It should be noted that structure derivatization at
the “cap” region is a key strategy in current HDACi design
because topological differences are observed in the correspond-
ing “cap” regions of HDAC isozymes.
14 HDACi, a lead compound, 5g, was discovered that exhibited
an in vitro potency comparable to that of SAHA which was
clinically approved in 2007 as a chemotherapy agent.
Herein, we report a HDACi scaffold that is built upon a
Huisgen 1,3-dipolar cycloaddition of alkyne and azido precur-
sors (Figure 2). This reaction has been widely applied in
chemical synthesis in recent years in efforts to develop new
drugs.32-35 It is now recognized as the premier example of the
click reaction due to the convenient availability and high stability
of the alkyne and azide precursors, as well as the mild reaction
conditions and nearly quantitative yields. In our design, the
precursors corresponding to the “cap” moiety of the HDACi
contain an azido group, whereas the zinc chelating functionality
precursors contain an alkyne group. The “clicked” products have
a triazole ring in the spacer moiety, which may enhance the
HDAC binding affinity via π-π stacking interactions. We have
accordingly named these HDACi as click HDACi. Currently,
14 click HDACi (5a-f and 6a-f) have been prepared from
two alkyne precursors (7 and 8) and seven azido-substituted
precursors (9a-g) via this combinatorial approach. From these
Results and Discussion
The seven azido precursors 9a-g (Scheme 1) were synthe-
sized from the corresponding halide substrates 10a-g via
treatment with 0.5 M sodium azide in DMSO (Scheme 1).36
All products, with the exceptions of 9c and 9d, were obtained
after overnight stirring. In the case of 9e, however, the reaction
had to be carried out at 0 °C to provide satisfactory yields. For
9c and 9d, tetraethylammonium bromide was added to catalyze
the reactions, which were subsequently complete after two days.
Excluding 9e, all products could be used directly in the following
steps without column purification.
The preparation of the alkyne precursor 8 began with the
synthesis of the PMB-protected hydroxylamine 13 via estab-
lished procedures (Scheme 2).37 Subsequent amidation of 13
with the commercially available acid 14 provided intermediate
8 in 61% yield.

Histone Deacetylase Inhibitors through Click Chemistry
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23 7419
Scheme 1. Preparation of the Azido Precursors 9a-g
Scheme 2. Preparation of Alkyne Precursor 8
Scheme 3. Preparation of Alkyne Precursor 7
In contrast, synthesis of the alkyne precursor 7 (Scheme 3)
was initiated through conversion of the propiolic acid 15 to the
trans-iodopropenoic acid 16 in 75% yield according to reported
procedures.38 The synthesis of 18 from 16 utilized a known
route, which was employed to prepare the corresponding (Z)-
isomer.39 This route entailed initial protection of the acid 16
with MEMCl to furnish the ester 17 (86% yield). 18 was
subsequently obtained in 87% yield via a Sonogashira reaction.
Deprotection of 18 with HCl to afford 19 (quantitative), followed
by treatment with oxalyl chloride and a catalytic amount of
DMF, yielded an acid chloride intermediate. This acid chloride
was used directly in the next step in which DIPEA and 13 (2:
1) were added within 1 min at -10 °C to give 7 in 84% yield.
Such rapid addition of the amine 13 was necessary as slow
addition dramatically increased the yield of the byproduct 20.
Following preparation of these two libraries, a series of click
reactions between alkyne precursors 7 and 8 and the seven azido
precursors 9a-g were performed to afford intermediates 21a-g
and 22a-g (Scheme 4). In this combinatorial chemistry step,
the alkyne precursors were first desilylated with CsF (1 equiv).
Following workup, without purification, the crude desilylation
intermediates were treated with 9a-g in the presence of a Cu(I)
catalyst to give 21a-g and 22a-g. The purified products were
then treated with TFA to yield the click HDACi 5a-g and
6a-g. These final target compounds were purified by C-18
reverse phase column chromatography due to the presence of
an unidentified reddish impurity, which appeared upon addition
to normal phase silica gel.
To assess the biological activity of these 14 compounds, they
were first tested for inhibition of HDAC. Specifically, HDAC1
and HDAC8 were chosen for the preliminary screen. Selection
of these two isozymes stemmed from the previously reported
correlation between HDAC1 inhibition and cancer cell growth
inhibition,40-44 as well as the existence of preferences among
several HDAC inhibitors for HDAC1 or HDAC8.29,31,45,46
Accordingly, preliminary screening at a concentration of 0.50
µM (Table 1) was conducted. This screening revealed that one
of the compounds, 5g, possessed an inhibitory potency toward
HDAC1 that was quite similar to that of SAHA. In addition,
several other inhibitors (5a-5f, 6a, 6b, 6g) possessed activity
against HDAC1, albeit to a lesser extent than either SAHA or
5g. Of particular importance in this regard is 6g, given that it
showed only 10 ( 1% inhibition at the concentration tested.
This is notable due to the fact that it and 5g, which demonstrated
75 ( 5% inhibition, only differ in the length of the linker region.
This suggests that a longer linker length considerably aids
HDAC1 inhibition in this case.
While the aforementioned 10 compounds showed inhibition
against HDAC1, only five of the 14 (5a, 6a, 6b, 6d, 6g)
demonstrated any significant inhibition of HDAC8. Of these
five, four also possessed activity against HDAC1, with 6d being
the exception. Nonetheless, none of the inhibitors demonstrated
as high of a degree of inhibition of HDAC8 as that seen with
the inhibition of HDAC1 by SAHA and 5g.
Before better characterizing the activity of these compounds
against HDAC (Figure 3), a list of the 14 inhibitors was

7420 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23
Scheme 4. Combinatorial Syntheses of Click HDACi
Shen et al.
Table 1. Activity of All HDACi in the Human HDAC1 and HDAC8 Inhibition Testsa
SAHA
HDAC 1 72 ( 2 31 ( 4 10 ( 3 8 ( 2 13 ( 4 8 ( 2 15 ( 3 75 ( 5 18 ( 3 9 ( 1
HDAC 8 NS 12 ( 6 NS NS NS NS NS NS 12 ( 2 12 ( 2 NS 26 ( 3 NS NS 13 ( 2
5a
5b
5c
5d
5e
5f
5g
6a
6b
6c
6d
6e
6f
6g
NS NS
NS NS 10 ( 1
a The values given represent the percentage by which the HDAC activity was inhibited by a 0.50 µM HDACi treatment. All of the assays were repeated
at least three times. When the inhibition capacity was less than 5%, NS (meaning no significant inhibition) was assigned.
type of cancer, but rather cell line specific as the next most
sensitive renal cell line (TK-10) possesses a GI50 value of 495
nM.
Given the results of the NCI screen and the fact that 5g did
not show any significant inhibition of HDAC8 at the concentra-
tion used in the preliminary screen, a more detailed analysis of
HDAC1 inhibition was performed (Figure 3). It was found that
5g possesses an IC50 value against HDAC1 (104 ( 30 nM)
that is comparable to that found with SAHA (140 ( 65 nM).
Thus, taken together, the results of the enzyme and cell-based
assays provide support to the proposed correlation between the
cytotoxicity of HDAC inhibitors and the ability of these agents
to inhibit HDAC1. This notion is further supported by the NCI’s
preliminary cell inhibition studies on the six candidates which
were originally selected (Supporting Information). Those com-
pounds which demonstrated a high degree of HDAC1 inhibition
Figure 3. Comparison of HDAC1 inhibition by SAHA and 5g.
(SAHA and 5g) also exhibited high levels of potency in the
submitted to the National Cancer Institute (NCI) for acceptance
cell-based assay. In contrast, the weaker inhibitors of HDAC1
into the human cancer cell line screening program, which is
also generally exhibited reduced potency against cancer cells.
provided at no cost. Of the 14, only one, 5g, ultimately advanced
to the final five-dose screen. This selection for advancement
stemmed from the results of the single-dose preliminary screen
Conclusion
in which the percent inhibition of cell line growth was
determined through comparison to untreated samples as de-
scribed in detail in the Supporting Information. Furthermore,
in the five-dose screen (Figure 4), in which data for SAHA is
included to serve as a standard, 5g proved to be active against
each of the cancer cell lines in the screen, albeit to varying
extents. The differences among the cell lines, however, were
generally within or close to 1 order of magnitude. For example,
the GI50 values obtained against the various leukemia cell lines
all fell within the range of 0.249-2.99 µM. This same trend
appeared among the other cancer types for which the ranges
were as follows: nonsmall cell lung 0.199-2.26 µM, colon
0.347-2.07 µM, CNS 0.318-1.53 µM, melanoma 0.271-1.08
µM, ovarian 0.187-3.21 µM, renal 0.0100-2.38 µM, prostate
0.580-1.30 µM, and breast 0.180-3.92 µM. As can be seen,
the lower end of the range for the renal cancer cell lines is
noticeably lower than those of the other cancer types. Specif-
ically, the RXF 393 cell line possessed a GI50 < 10 nM. This
represents the lowest GI50 obtained across the 60 cell lines;
however, this low value does not appear to be specific to this
This paper highlights the utility of click chemistry in the
synthesis of HDACi. Through this approach, a combinatorial
strategy was employed that enabled generation of multiple
HDACi. Such combinatorial approaches greatly enhance the
efficiency of drug discovery as libraries of candidate molecules
can be obtained rapidly. This fact was highlighted by the
discovery of lead compound 5g, which was found to inhibit
HDAC1 with an IC50 ) 104 ( 30 nM while demonstrating no
significant inhibition of HDAC8 in preliminary testing. This
level of inhibition was found to be comparable to that exhibited
by the clinically approved drug SAHA (140 ( 65 nM).
Furthermore, 5g was also found to be active across all cell lines
in the NCI human cancer cell line screen, with GI50 values
ranging from 3.92 µM to 10 nM.
In summary, we have developed a click chemistry approach
to HDACi design, which has not only led to a potent lead
compound, but more importantly, one which is readily amend-
able to further derivatization. For example, functionalization of
the aromatic ring, replacement of the aromatic ring with a
heteroaromatic species, or introduction of a chiral center in the

Histone Deacetylase Inhibitors through Click Chemistry
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23 7421
Figure 4. Comparison of GI50 values from the NCI human cancer cell line screen for 5g and SAHA. Tested doses included 1 × 10-4, 1 × 10-5
,
1 × 10-6, 1 × 10-7, and 1 × 10-8 M. (a) Activity against leukemia and nonsmall cell lung cancer cell lines. (b) Activity against colon, central
nervous system (CNS) and prostate cancer cell lines. (c) Activity against melanoma and ovarian cancer cell lines. (d) Activity against renal and
breast cancer cell lines.
indicated field strengths. The high-resolution mass spectra were
collected at The Ohio State University Campus Chemical Instru-
mentation Center. The purities of click HDACi were analyzed by
HPLC (refer to the Supporting Information). The purity of the key
target compound 5g is 98.3%, with the purities of the other 13
target compounds all being higher than 96%. As for the HDAC1
and HDAC8 inhibition studies, the assay kits were obtained from
Biomol International LP. All assays were repeated at least three
times. Briefly, the assay was performed in two stages. In the first
stage, HDAC8 solution (15 µL, 1 U total), HDACi solution (10
µL), and HDAC8 substrate solution (25 µL) were added to the 96-
well microplate. The reaction proceeded at 30 °C for 45 min. The
second stage was initiated by the addition of 50 µL of developer,
which stopped HDAC activity and produced the fluorescent signal
(λex ) 350 nm; λem ) 450 nm). The cell line assays for the selected
six target compounds, 5b (NSC746454), 5e (NSC746455), 5f
(NSC746456), 5g (NSC746457), 6e (NSC746458), and 6g
“cap” moiety can all occur quite readily by incorporating these
features into the azide-containing fragment. This will allow
modifications to occur prior to the combinatorial step, thus
maintaining the modular nature of this approach. A large number
of new candidate molecules can therefore be rapidly prepared
via modification of the azide library.
Experimental Section
All solvents were dried with a solvent-purification system from
Innovative Technology, Inc. All reagents were obtained from
commercial sources and used without further purification. Analytical
TLC was carried out on silica gel 60 F254 aluminum-backed plates
(E. Merck). The 230-400 mesh size of the same absorbent was
utilized for all chromatographic purifications. The 200-400 mesh
silica gel 60 RP-18 (from EMD) was utilized to purify the target
click HDACi. 1H and 13C NMR spectra were recorded at the

7422 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23
Shen et al.
(NSC746459), were performed by the NIH.47 Cell lines tested
consisted of the following: CCRF-CEM, HL-60(TB), K-562,
MOLT-4, RPMI-8226, and SR (leukemia); A549/ATCC, EKVX,
HOP-62, HOP-92, NCI-H226, NCI-H23, NCI-H322 M, and NCI-
H460 (non-small cell lung cancer); COLO 205, HCT-116, HCT-
15, HT29, KM12, and SW-620 (colon cancer); SF-628, SF-295,
SF-539, SNB-19, SNB-75, and U251 (CNS cancer); LOX IMVI,
MALME-3M, M14, SK-MEL-28, SK-MEL-5, UACC-257, and
UACC-62 (melanoma); IGROV1, OVCAR-3, OVCAR-4, OVCAR-
5, OVCAR-8, and SK-OV-3 (ovarian cancer); 786-0, A498, ACHN,
CAKI-1, RXF 393, SN12C, TK-10, and UO-31 (renal cancer); PC-3
and DU-145 (prostate cancer); MCF7, NCI/ADR-RES, MDA-MB-
231/ATCC, HS578T, MDA-MB-435, BT-549, and T-47D (breast
cancer). Full experimental details are available free of charge via
the Internet at http://dtp.nci.nih.gov/branches/btb/ivclsp.html.48,49
(E)-N-Hydroxy-3-(1-(2-oxo-2-phenylethyl)-1H-1,2,3-triazol-4-
yl)acrylamide (5e). The crude product was purified via C-18 reverse
phase column chromatography (water:acetonitrile ) 6:1) to provide
a pale-colored solid (22 mg product 5e from 90 mg 21e, 35%). 1H
NMR (500 MHz, DMF-d7): δ 11.19 (s, 1H), 8.48 (s, 1H), 8.17 (d,
J ) 7.4 Hz, 2H), 7.80 (t, J ) 7.9 Hz, 1H), 7.67 (dd, J1 ) J2 )7.8
Hz, 2H), 7.62 (d, J ) 15.2, 1H), 6.85 (d, J ) 15.7 Hz, 1H), 6.34
(s, 2H). 13C NMR (125 MHz, DMF-d7): δ 192.2, 143.6, 134.4,
134.4, 129.2, 128.3, 127.7, 126.4, 119.8, 56.1 (one peak less due
to the overlap with solvent peak ∼ δ 162). HRMS (ESI) calcd for
C13H12N4O3Na [M + Na]+ 295.0807, found 295.0811.
(E)-N-Hydroxy-3-(1-(2-oxo-2-(phenylamino)ethyl)-1H-1,2,3-
triazol-4-yl)acrylamide (5f). The crude product was purified via
C-18 reverse phase column chromatography (water:acetonitrile:TFA
) 6:1:0.03) to provide a pink solid (67 mg 5f from 187 mg 21f,
1
71% yield). H NMR (500 MHz, DMF-d7): δ 10.60 (s, 1H), 8.49
General Procedure for the Preparation of Click HDACi
5a-g and 6a-g from 21a-g and 22a-g. Triisopropylsilane (3
mmol, 0.6 mL, 3 equiv), PMB protected substrate (21a-g or
22a-g, 1 mmol, 1.0 equiv), and TFA (2 mL) were added in
sequence to a reaction vessel containing DCM (40 mL). The mixture
was stirred at room temperature and monitored by TLC. Upon
completion, the reaction mixture was diluted with acetonitrile (100
mL) and then neutralized with DOWEX Marathon WBA anion
exchange resin (from Aldrich). The resin was washed additionally
with acetonitrile (50 mL × 2). The combined organic solution was
evaporated to provide a solid, which was purified to afford the final
product.
(s, 1H), 7.69 (d, J ) 7.5 Hz, 2H), 7.57 (d, J ) 15.7 Hz, 1H), 7.36
(apparent t, J ) 7.4 Hz, 2H), 7.12 (t, J ) 7.4 Hz, 1H), 6.81 (d, J
) 15.7 Hz, 1H), 5.51 (s, 2H). 13C NMR (125 MHz, CD3OD): δ
165.4, 144.5, 140.0, 129.9, 128.5, 127.2, 124.9, 120.8, 120.4, 53.6.
HRMS (ESI) calcd for C13H13N5O3Na [M + Na]+ 310.0916, found
310.0923.
(E)-3-(1-Cinnamyl-1H-1,2,3-triazol-4-yl)-N-hydroxyacryl-
amide (5g). The crude product was purified via C-18 reverse phase
column chromatography (water:acetonitrile ) 5:1) to provide a
1
white solid (96 mg 5g from 199 mg 21g, 70% yield). H NMR
(500 MHz, DMF-d7): δ 10.2 (br s, 1H), 8.48 (s, 1H), 7.58-7.48
(m, 3H), 7.37 (apparent t, J ) 7.4 Hz, 2H), 7.30 (t, J ) 7.1 Hz,
1H), 6.82 (d, J ) 16.0 Hz, 1H), 6.77 (d, J ) 15.8 Hz, 1H), 6.60
(E)-3-(1-Benzyl-1H-1,2,3-triazol-4-yl)-N-hydroxyacrylamide
(5a). The crude product was first dissolved with a minimal amount
of 5% methanol in DCM, after which the pure compound was
precipitated with hexanes (4× the original volume) as a slightly
pink solid (28 mg 5a from 100 mg 21a, 42% yield). 1H NMR (500
MHz, CD3OD): δ 8.15 (s, 1H), 7.50 (d, J ) 15.8 Hz, 1H),
7.42-7.28 (m, 5H), 6.62 (d, J ) 15.8 Hz, 1H), 5.60 (s, 2H). 13C
NMR (125 MHz, CD3OD): δ 165.8, 145.2, 136.7, 130.2, 129.8,
129.3, 125.7, 120.4, 55.1 (one peak less due to overlap ∼130).
HRMS (ESI) calcd for C12H12N4O2Na [M + Na]+ 267.0858, found
267.0860.
(dt, J1 ) 15.5 Hz, J2 ) 6.2 Hz,1H), 5.29 (d, J ) 6.1 Hz, 2H). 13
C
NMR (125 MHz, DMF-d7): δ 163.9, 144.9, 137.2, 129.7, 135.3,
129.2, 128.3, 127.8, 125.3, 124.5, 120.9, 52.8. HRMS (ESI) calcd
for C14H14N4O2Na [M + Na]+ 293.1014, found 293.1020.
1-Benzyl-1H-[1,2,3]triazole-4-carboxylic Acid Hydroxamide
(6a). The crude product was purified via C-18 reverse phase column
chromatography (water:acetonitrile ) 6:1) to provide a white solid
(16 mg 6a from 53 mg 22a, 47% yield). 1H NMR (500 MHz, DMF-
d7): δ 11.40-9.20 (bd s, 1H), 8.64 (s, 1H), 7.58-7.28 (m, 5H),
5.76 (s, 2H). 13C NMR (125 MHz, DMF-d7): δ 158.9, 143.1, 137.0,
129.9, 129.3, 129.1, 127.1, 54.4. HRMS (ESI) calcd for
C10H10N4O2Na [M + Na]+ 241.0701, found 241.0697.
1-Phenethyl-1H-[1,2,3]triazole-4-carboxylic Acid Hydroxa-
mide (6b). The crude product was purified via C-18 reverse phase
column chromatography (water:acetonitrile ) 6:1) to provide a
white solid (21 mg 6b from 63 mg 22b, 51% yield). 1H NMR (500
MHz, DMF-d7): δ 11.21 (s, 1H), 9.30 (s, 1H), 8.48 (s, 1H),
7.40-7.20 (m, 5H), 4.78 (t, J ) 7.3 Hz, 2H), 3.29 (t, J ) 7.3 Hz,
2H). 13C NMR (125 MHz, DMF-d7): δ 158.3, 141.9, 138.0, 129.0,
128.7, 126.9, 126.2, 51.3, 36.2. HRMS (ESI) calcd for
C11H12N4O2Na [M + Na]+ 255.0858, found 255.0862.
(E)-N-Hydroxy-3-(1-phenethyl-1H-1,2,3-triazol-4-yl)acryl-
amide (5b). The crude product was purified via C-18 reverse phase
column chromatography (water: acetonitrile ) 5:1) to provide 5b
as a white solid (65 mg 5b from 174 mg 21b, 55% yield). 1H NMR
(500 MHz, DMF-d7): δ 8.32 (s, 1H), 7.48 (d, J ) 15.7 Hz, 1H),
7.36-7.20 (m, 5H), 6.74 (d, J ) 15.7 Hz, 1H), 4.73 (t, J ) 7.3
Hz, 2H), 3.27 (t, J ) 7.3 Hz, 2H). 13C NMR (125 MHz, CD3OD):
δ 163.9, 144.4, 139.0, 129.9, 129.6, 128.5, 127.8, 125.5,120.6, 52.0,
37.1. HRMS (ESI) calcd for C13H14N4O2Na [M + Na]+ 281.1014,
found 281.1017.
(E)-N-Hydroxy-3-(1-(3-phenylpropyl)-1H-1,2,3-triazol-4-yl)-
acrylamide (5c). The crude product was purified via C-18 reverse
phase column chromatography (water:acetonitrile ) 5:1) to provide
a pale-colored solid (35 mg product 5c from 100 mg 21c, 50%
yield). 1H NMR (500 MHz, CD3OD): δ 8.15 (s, 1H), 7.51 (d, J )
15.8 Hz, 1H), 7.30-7.24 (m, 2H), 7.21-7.15 (m, 3H), 6.62 (d, J
) 15.8 Hz, 1H), 4.42 (t, J ) 7.2 Hz, 2H), 2.64 (t, J ) 7.5 Hz, 2H),
2.41 (tt, J1 ) J2 ) 7.4 Hz, 2H). 13C NMR (125 MHz, CD3OD): δ
165.9, 144.9, 142.0, 129.7, 129.6, 129.4, 127.4, 125.8,120.2, 51.0,
33.6, 33.0. HRMS (ESI) calcd for C14H16N4O2Na [M + Na]+
295.1171, found 295.1168.
1-(3-Phenyl-propyl)-1H-[1,2,3]triazole-4-carboxylic Acid Hy-
droxamide (6c). The crude product was purified via C-18 reverse
phase column chromatography (water:acetonitrile ) 6:1) to provide
1
a white solid (31 mg 6c from 63 mg 22c, 74% yield). H NMR
(500 MHz, DMF-d7): δ 11.27 (s, 1H), 9.38 (s, 1H), 8.61 (s, 1H),
7.36-7.20 (m, 5H), 4.54 (t, J ) 7.1 Hz, 2H), 2.66 (t, J ) 7.7 Hz,
2H), 2.26 (tt, J1 ) J2 ) 7.1 Hz, 2H). 13C NMR (125 MHz, DMF-
d7): δ 159.1, 142.8, 142.0, 129.4, 127.0, 126.9, 55.7, 50.5, 33.2,
32.7. HRMS (ESI) calcd for C12H14N4O2Na [M + Na]+ 269.1014,
found 269.1014.
(E)-N-Hydroxy-3-(1-(2-phenoxyethyl)-1H-1,2,3-triazol-4-yl)-
acrylamide (5d). The crude product was purified via C-18 reverse
phase column chromatography (water:acetonitrile ) 6:1) to provide
1-(2-Phenoxy-ethyl)-1H-[1,2,3]triazole-4-carboxylic Acid Hy-
droxamide (6d). The crude product was purified via C-18 reverse
phase column chromatography (water:acetonitrile ) 6:1) to provide
1
a white solid (69 mg 5d from 163 mg 21d, 61% yield). H NMR
1
(500 MHz, DMF-d7): δ 8.52 (s, 1H), 7.52 (d, J ) 15.8 Hz, 1H),
7.38-7.24 (m, 2H), 7.07-6.92 (m, 3H), 6.79 (d, J ) 15.7 Hz,
1H), 4.91 (t, J ) 5.0 Hz, 2H), 4.51 (t, J ) 5.0 Hz, 2H). 13C NMR
(125 MHz, DMF-d7): δ 163.8, 159.3, 144.7, 130.6, 128.3, 126.0,
122,2, 120.8,115.7, 67.3 50.6. HRMS (ESI) calcd for C13H14N4O3Na
[M + Na]+ 297.0964, found 297.0966.
a white solid (15 mg 6d from 40 mg 22d, 56% yield). H NMR
(500 MHz, DMF-d7): δ 10.60-9.90 (bd s, 1H), 8.65 (s, 1H),
7.34-7.28 (m, 2H), 7.00-6.94 (m, 2H), 4.95 (t, J ) 5.1 Hz, 2H),
4.53 (t, J ) 5.1, 2H). 13C NMR (125 MHz, DMF-d7): δ 159.4,
159.1, 143.0, 130.6, 127.6, 122.2, 115.7, 67.3, 50.7. HRMS (ESI)
calcd for C11H12N4O2Na [M + Na]+ 271.0807, found 271.0807.

Histone Deacetylase Inhibitors through Click Chemistry
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23 7423
1-(2-oxo-2-Phenyl-ethyl)-1H-[1,2,3]triazole-4-carboxylic Acid
Hydroxyamide (6e). The crude product was purified via C-18
reverse phase column chromatography (water:acetonitrile ) 7:1)
to provide a white solid (56 mg 6e from 116 mg 22e, 72% yield).
1H NMR (500 MHz, DMF-d7): δ 11.40-9.20 (bd s, 2H), 8.62 (s,
1H), 8.16 (d, J ) 7.3 Hz, 2H), 7.78 (t, J ) 7.4 Hz, 1H), 7.65 (dd,
J1 ) J2 ) 7.8 Hz, 2H), 6.38 (s, 2H). 13C NMR (125 MHz, DMF-
d7): δ 192.9, 159.1, 143.0, 135.5, 135.3, 130.1, 129.3, 128.9, 57.3.
HRMS (ESI) calcd for C11H10N4O3Na [M + Na]+ 269.0651, found
269.0629.
1-Phenylcarbamoylmethyl-1H-[1,2,3]triazole-4-carboxylic Acid
Hydroxyamide (6f). The crude product was purified via C-18
reverse phase column chromatography (water:acetonitrile ) 7:1)
to provide a white solid (45 mg 6f from 120 mg 22f, 55% yield).
1H NMR (500 MHz, DMF-d7): δ 10.77 (s, 1H), 10.50-10.00 (bd
s, 1H), 8.65 (s, 1H), 7.70 (d, J ) 7.4 Hz, 2H), 7.35 (dd, J1 ) J2 )
7.9 Hz, 2H), 7.11 (t, J ) 7.4 Hz, 1H), 5.57 (s, 2H). 13C NMR (125
MHz, DMF-d7): δ 165.3, 159.1, 142.8, 140.1, 129.9, 128.8, 124.8,
120.4, 53.6. HRMS (ESI) calcd for C11H11N5O3Na [M + Na]+
284.0760, found 284.0743.
1-(3-Phenyl-allyl)-1H-[1,2,3]triazole-4-carboxylic Acid Hy-
droxyamide (6g). The crude product was purified via C-18 reverse
phase column chromatography (water:acetonitrile ) 5:1) to provide
a white solid (21 mg 6 from 62 mg 22 50% yield). 1H NMR (500
MHz, DMF-d7): δ 10.60-9.80 (bd s, 2H), 8.61 (s, 1H), 7.53 (d, J
) 7.6 Hz, 2H), 7.38 (dd, J1 ) J2 ) 7.5 Hz, 2H), 7.31 (t, J ) 7.3
Hz, 1H), 6.79 (d, J ) 15.9, 1H), 6.62 (td, J1 ) 15.7 Hz, J2 ) 6.6
Hz, 1H), 5.33 (d, J ) 6.5, 2H). 13C NMR (125 MHz, DMF-d7): δ
159.4, 159.1, 143.0, 130.6, 127.6, 122.2, 115.7, 67.3, 50.7. HRMS
(ESI) calcd for C12H12N4O2Na [M + Na]+ 267.0858, found
267.0855.
amount of DMF were added. The mixture was stirred at room
temperature for 2 h. The solution was then placed in an ice bath,
and most of the acidic gases (HCl and SO2) were removed under
vacuum (∼20 bar) to give a yellow solution. Freshly dried DCM
(10 mL) was then added (solution A). The amine 13 (950 mg, 5.0
mmol, 1.0 equiv) and DIPEA (2.8 mL, 16.1 mmol, 3.2 equiv) were
added to a second reaction vessel containing DCM (50 mL)
(solution B). Solution B was cooled to 0 °C, after which solution
A was added within 1 min. The mixture was then stirred for 30
min at 0 °C. The reaction mixture was poured onto ice-cold 0.1 N
HCl (200 mL) before DCM (200 mL) was also added. The organic
layer was additionally washed with ice-cold 0.1 N HCl twice (2 ×
100 mL). The DCM solution was dried with Na2SO4, and the
solvent was evaporated. The crude product was purified via flash
column chromatography (hexanes:ethyl acetate, 85:15 to 80:20) to
1
provide 8 as pale-colored oil (0.85 g, 61%). H NMR (500 MHz,
CDCl3): δ 8.43 (bd s, 1H), 7.32 (d, J ) 8.5 Hz, 2H), 6.89 (dd, J )
8.5 Hz, 2H), 4.85 (s, 2H), 3.80 (s, 3H), 0.20 (s, 9H). 13C NMR
(125 MHz, CDCl3): δ 160.1, 151.0, 131.0, 126.9, 114.0, 95.0, 94.4,
78.2, 55.3, 0.8. HRMS (ESI) calcd for C14H19NO3SiNa [M + Na]+
300.1032, found 300.1033.
General Procedure to Prepare the Azido Precursors 9a-g.
An alkyl halide 10a-g (1.5 g, 1.0 equiv) was added to a reaction
vessel containing a solution of NaN3 in DMSO (1.1 equiv, 0.5 M).
The reaction was monitored by NMR analysis. Upon completion
of the reaction, water (50 mL) was added and the product was
extracted with ether (3 × 50 mL). The combined organic layers
were washed with water (2 × 50 mL) and brine (50 mL) and dried
with magnesium sulfate. The organic solvent was removed to
provide the azido compound. For 9c and 9d, a catalytic amount of
tetraethylammonium bromide (0.05 mol%, 0.005 equiv) was added.
The spectral data were in agreement with those reported.36,50-53
(Azidomethyl)benzene (9a). From 10a (1.5 g, 11.3 mmol, 1.0
equiv), 9a was obtained in 95% yield as a colorless liquid. 1H NMR
(500 MHz, CDCl3): δ 7.75-7.40 (m, 5H), 4.35 (s, 2H).36
(2-Azidoethyl)benzene (9b). From 10b (1.5 g, 10.2 mmol, 1.0
equiv), 9b was obtained in 93% yield as a colorless liquid. 1H NMR
(500 MHz, CDCl3): δ 7.33 (t, J ) 7.2 Hz, 2H), 7.26 (d, J ) 7.1
Hz, 1H), 7.23 (d, J ) 7.2 Hz, 2H), 3.51 (t, J ) 7.3 Hz, 2H), 2.91
(t, J ) 7.3 Hz, 2H).50,51
(3-Azidopropyl)benzene (9c). From 10c (1.5 g, 9.30 mmol, 1.0
equiv), 9c was obtained in 90% yield as a colorless liquid. 1H NMR
(500 MHz, CDCl3): δ 7.30 (t, J ) 7.3 Hz, 2H), 7.24-7.16 (m,
3H), 3.29(t, J ) 7.3 Hz, 2H), 2.71 (t, J ) 7.6 Hz, 2H), 1.92 (tt, J1
) J2 ) 7.2 Hz, 2H).50,51
(2-Azidoethoxy)benzene (9d). From 10d (1.5 g, 9.2 mmol, 1.0
equiv), 9d was obtained in 95% yield as a colorless liquid. 1H NMR
(500 MHz, CDCl3): δ 7.34-7.28 (m, 2H), 7.02-6.97 (m, 1H),
6.95-6.89 (m, 2H), 4.16 (d, J ) 5.0 Hz, 2H), 3.60 (d, J ) 5.0 Hz,
2H). 13C NMR (125 MHz, CDCl3): δ 158.4, 129.8, 121.6, 114.8,
67.1, 50.4.
(E)-N-(4-Methoxybenzyloxy)-5-(trimethylsilyl)pent-2-en-4-
ynamide (7). The acid 19 (168 mg, 1.0 mmol, 1.0 equiv) was added
to a reaction vessel containing DCM (3 mL). To this solution, oxalyl
chloride (130 µL, 1.6 mmol, 1.6 equiv) and a trace amount of DMF
were added. The mixture was stirred at room temperature for 1 h.
The solvent was then removed under vacuum to afford a
yellow-reddish syrup. DCM (4 mL) was added, and the flask was
cooled to 0 °C (solution A). The amine 13 (285 mg 1.5 mmol, 1.5
equiv) and N,N-diisopropylethylamine (DIPEA) (0.52 mL, 3.0
mmol, 3.0 equiv) were added to a second reaction vessel containing
DCM (10 mL) (solution B). Solution B was cooled to 0 °C, after
which solution A was added within 1 min. The mixture was stirred
for one-half hour at 0 °C. The reaction mixture was then poured
into ice-cold 0.1 N HCl (20 mL), after which DCM (20 mL) was
added. The organic layer was additionally washed with ice-cold
0.1 N HCl (2 × 20 mL). The DCM solution was dried with Na2SO4,
and the solvent was evaporated. The crude product was purified
via flash column chromatography (hexanes:ethyl acetate, 87:13 to
1
83:17) to provide pure 7 as a white oil (253 mg, 84%). H NMR
(500 MHz, CD3CN): δ 9.44 (bd s, 1H), 7.33 (d, J ) 8.6 Hz, 2H),
6.92 (d, J ) 8.6 Hz, 2H), 6.64 (d, J ) 15.5 Hz, 1H), 6.17 (d, J )
14.2 Hz, 1H), 4.79 (s, 2H), 3.79 (s, 3H), 0.20 (s, 9H). 13C NMR
(125 MHz, CD3CN): δ 163.0, 161.0, 132.3, 132.0, 128.7, 121.4,
114.8, 103.2, 102.8, 78.4, 55.9, -0.33. HRMS (ESI) calcd for
C16H21NO3SiNa [M + Na]+ 326.1188, found 326.1193.
(E)-N-(4-Methoxybenzyloxy)-5-(trimethylsilyl)-N-((E)-5-(tri-
methylsilyl)pent-2-en-4-ynoyl)pent-2-en-4-ynamide (20). Com-
pound 20 was a byproduct obtained during the preparation of 7.
1H NMR (500 MHz, CD3CN): δ 7.25 (d, J ) 8.6 Hz, 2H), 6.90 (d,
J ) 8.7 Hz, 2H), 6.88 (d, J ) 15.9 Hz, 1H), 6.48 (d, J ) 16.0 Hz,
1H), 6.34 (d, J ) 15.9 Hz, 1H), 6.12 (d, J ) 16.0 Hz, 1H), 5.00 (s,
1H), 3.78 (s, 1H), 0.22 (s, 9H), 0.18 (s, 9H). 13C NMR (125 MHz,
CD3CN): δ 161.3, 160.8, 149.0, 131.1, 131.0, 129.7, 129.6, 128.8,
116.4, 114.8, 108.2, 103.1, 103.1, 101.6, 77.8, 55.9, -0.30, -0.51.
HRMS (ESI) calcd for C24H31NO4Si2Na [M + Na]+ 476.1689,
found 476.1683.
2-Azido-1-phenylethanone (9e). From 10e (1.5 g, 8.0 mmol,
1.0 equiv), 9e was obtained in 75% yield after flash column
chromatography (2-5% ether in hexanes) as a colorless liquid. 1H
NMR (500 MHz, CDCl3): δ 7.91-7.88 (m, 2H), 7.65-7.60 (m,
1H), 7.53-7.48 (m, 2H), 4.56 (s, 2H).52
2-Azido-N-phenylacetamide (9f). From 10f (1.5 g, 8.5 mmol,
1
1.0 equiv), 9f was obtained in 90% yield as a colorless liquid. H
NMR (500 MHz, CDCl3): δ 8.00 (bd s, 1H), 7.54 (d, J ) 8.6 Hz,
2H), 7.35 (dd, J1 ) 8.4 Hz, J2 ) 7.5 Hz, 2H), 7.16 (d, J ) 8.6 Hz,
1H), 4.15 (s, 2H).53
2-Azido-N-phenylacetamide (9g). From 10g (1.5 g, 9.4 mmol,
1.0 equiv), 9g was obtained in 87% yield as a colorless liquid. 1H
NMR (500 MHz, DMSO-d6): δ 7.51-7.47 (m, 2H), 7.38-7.31
(m, 2H), 7.31-7.26 (m, 1H), 6.71 (d, J ) 15.8 Hz, 1H), 6.39 (dt,
J1 ) 15.8 Hz, J2 ) 6.6 Hz, 1H), 4.04 (d, J ) 6.6 Hz, 2H).36
O-(4-Methoxybenzyl)hydroxylammonium Chloride (13). N-
Hydroxyphthalimide 11 (4.9 g, 30 mmol, 1.0 equiv) and potassium
carbonate (5.0 g, 36 mmol, 1.2 equiv) were added to a reaction
vessel containing DMF (100 mL). To this solution, 1-(chlorom-
ethyl)-4-methoxybenzene (PMBCl) (4.7 mL, 33 mmol, 1.1 equiv)
N-(4-Methoxybenzyloxy)-3-(trimethylsilyl)propiolamide (8).
Commercially available acid 14 (710 mg, 5.0 mmol, 1.0 equiv)
was added to a reaction vessel containing DCM (10 mL). To this
solution, oxalyl chloride (430 µL, 5.5 mmol, 1.1 equiv) and a trace

7424 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23
Shen et al.
was added. The reaction continued overnight at room temperature.
Water (500 mL) and benzene (500 mL) were then added. The
aqueous layer was additionally extracted with benzene (2 × 100
mL). The combined organic layers were washed with sat. NaHCO3
solution (3 × 200 mL) and dried with magnesium sulfate. Crude
12 was obtained after removal of the solvent and was directly
employed in the next step. To this crude product in methanol (500
mL), hydrazine monohydrate was added (4.5 mL, 92.5 mmol, 3.1
equiv). The mixture was stirred overnight at room temperature. TLC
analysis indicated the presence of a new compound. Upon comple-
tion of the reaction, the solution pH was adjusted to 2 via the
addition of aqueous 2 M HCl. The mixture was cooled in an ice
bath for 1 h, after which the white precipitate (byproduct) was
removed. The solvent was removed, and the residue/syrup was
partitioned between DCM (200 mL) and ammonium bicarbonate
solution (pH ) 8, 200 mL). The organic layer was dried with
Na2SO4. Addition of 1 M HCl in ether then caused the product 13
to precipitate as a white solid (4.3 g, 75.6% yield for two steps).
Spectral data were in agreement with those reported.37 1H NMR
(500 MHz, DMSO-d6): δ 11.10 (bd s, 3H), 7.35 (d, J ) 8.6 Hz,
2H), 6.96 (d, J ) 8.6 Hz, 2H), 4.97 (s, 2H), 3.76 (s, 3H).
(E)-3-Iodopropenoic acid (16). Propiolic acid 15 (10 mL, 162.0
mmol, 1.0 equiv) was added over 1 min to a reaction vessel
containing a solution of CuI (200 mg, 1.1 mmol, 0.007 equiv) and
HI (40 mL, initially 57%, 303.2 mmol, 1.9 equiv). The reaction
mixture was immediately immersed in a preheated oil bath (130
°C) for 30 min. The reaction was then cooled to room temperature
over a 15 min period. A white precipitate formed, after which the
solution was kept at room temperature for another 15 min. The
liquid was removed by filtration, and the solid was washed water
(3 × 70 mL). Following a period of drying, the pure iodoacid 16
was obtained as white needles (23.9 g, 75%). 1H NMR (500 MHz,
CDCl3): δ 10.54-8.66 (bd s, 1H), 8.07 (d, J ) 14.9 Hz, 1H), 6.88
(d, J ) 14.9 Hz, 1H). Spectral data were in agreement with those
reported.38
time it was monitored by TLC (5% MeOH in dichloromethane, Rf
) 0.10). The solution was then concentrated and the residue
partitioned between water (250 mL) and CH2Cl2 (100 mL). The
water was further extracted with CH2Cl2 (2 × 100 mL). The
combined organic layers were washed with brine, dried over
MgSO4, and concentrated to give 2.01 g (∼100%) of the crude
acid 19 as pale-yellow solid. The crude product was pure enough
1
for NMR analysis. H NMR (500 MHz, CDCl3): δ 0.20 (s, 9H),
6.22 (d, J ) 15.9 Hz, 1H), 6.80 (d, J ) 15.9 Hz, 1H), 12.5-11.0
(bd s, 1H). 13C NMR (125 MHz, CDCl3): δ -0.34, 101.1, 107.1,
127.6, 130.4, 171.4. HRMS (ESI) calcd for C8H12O2SiNa [M +
Na]+ 191.0502, found 191.0504.
General Procedure for the Preparation of 21a-g. The alkyne
precursor 7 (152 mg, 0.5 mmol, 1.0 equiv) was added to a reaction
vessel containing THF (5 mL) and MeOH (5 mL). Cesium fluoride
(91 mg, 0.6 mmol, 1.2 equiv) was then added, after which the
reaction was monitored by TLC analysis. The desilylation inter-
mediate was slightly more polar than the reactant. Upon disap-
pearance of the reactant, the solvent was removed, followed by
partitioning between DCM (50 mL) and brine (50 mL). A trace
amount of acetic acid was added to neutralize the aqueous solution.
The brine phase was additionally extracted with DCM (2 × 50
mL). The combined DCM solution was dried with Na2SO4, and
the solvent was removed. The obtained white solid was dissolved
with THF (10 mL). To this solution, the azido compound 9a-g
(0.75 mmol, 1.5 equiv), catalyst CuIP(OEt)3 (7 mg, 0.02 mmol,
0.04 equiv), and one drop of DIPEA were added sequentially. The
reaction continued overnight at room temperature and was moni-
tored by TLC analysis. Frequently, more and more white precipitate
(product) formed as the reaction progressed. The solvent was
removed, and the residue was partitioned between DCM (50 mL)
and 1% CuSO4 aqueous solution (50 mL). The aqueous layer was
additionally extracted with DCM (2 × 50 mL). The combined DCM
layers were dried with Na2SO4. After removal of the solvent, the
crude product was purified via flash column chromatography to
afford the final product 21a-g.
(E)-3-(1-Benzyl-1H-1,2,3-triazol-4-yl)-N-(4-methoxybenzyl-
oxy) Acrylamide (21a). A white solid was obtained (87%, 158
mg 21a product from 0.5 mmol 7) via flash column chromatography
(MeOH:DCM, from 1.2:100 to 1.5:100). 1H NMR (500 MHz,
CD2Cl2 and CD3OD): δ 7.91 (s, 1H), 7.50 (d, J ) 15.7 Hz, 1H),
7.42-7.28 (m, 7H), 6.90 (d, J ) 8.4 Hz, 2H), 6.54 (d, J ) 15.7
Hz, 1H), 5.56 (s, 2H), 4.84 (s, 2H), 3.79 (s, 3H). 13C NMR (125
MHz, CD2Cl2 and CD3OD): δ 164.8, 160.8, 144.5, 135.4, 131.6,
129.7, 129.4, 129.2, 128.7, 128.3, 125.0, 119.6, 114.4, 78.5, 55.6,
54.8. HRMS (ESI) calcd for C20H20N4O3Na [M + Na]+ 387.1433,
found 387.1431.
(2-Methoxyethoxy)methyl-(2E)-3-iodoprop-2-enoate (17).
K2CO3 (3.42 g, 24.8 mmol, 1.2 equiv) and 2-methoxyethoxymethyl
chloride (MEMCl) (3.2 mL, 27.6 mmol, 1.3 equiv) were added to
a reaction vessel containing a solution of E-iodopropenoic acid 16
(4.2 g, 21.2 mmol, 1.0 equiv) in DMF (20 mL). The mixture was
stirred at ambient temperature for 1 h, poured onto water (20 mL),
and then extracted with ether (3 × 20 mL). The combined organic
layers were washed with water, brine, dried over MgSO4, and
concentrated. Flash column chromatography (hexanes:ethyl acetate,
1
20:1 to 10:1) provided 5.2 g (86%) of 17 as a colorless oil. H
NMR (500 MHz, C6D6): δ 7.62 (d, J ) 14.8 Hz, 1H) 6.62 (d, J )
14.8 Hz, 1H), 5.13 (s, 2H), 3.49 (t, J ) 4.7 Hz, 2H), 3.18 (t, J )
4.7 Hz, 2H), 3.04 (s, 3H). 13C NMR (125 MHz, C6D6): δ 163.1,
136.6, 100.2, 89.9, 71.8, 69.9, 58.7. HRMS (ESI) calcd for
C7H11IO4Na [M + Na]+ 308.9600, found 308.9605.
(E)-N-(4-Methoxybenzyloxy)-3-(1-phenethyl-1H-1,2,3-triazol-
4-yl) Acrylamide (21b). A white solid was obtained (97% yield,
184 mg 21b from 0.5 mmol 7) via flash column chromatography
(MeOH:DCM, from 0.8:100 to 1.5:100). 1H NMR (500 MHz,
DMF-d7): δ 11.28 (s, 1H), 8.36 (s, 1H), 7.56 (d, J ) 15.7 Hz, 1H),
7.40 (d, J ) 8.5 Hz, 2H), 7.35-7.20 (m, 5H), 6.98 (d, J ) 8.6 Hz,
2H), 6.72 (d, J ) 15.5 Hz, 1H), 4.89 (s, 2H), 4.74 (t, J ) 7.3 Hz,
2H), 3.83 (s, 3H), 3.27 (t, J ) 7.3 Hz, 2H). 13C NMR (125 MHz,
DMF-d7): δ 164.1, 161.0, 144.2, 138.9, 131.9, 129.9, 129.6, 129.6,
129.4, 127.7, 125.8, 120.2, 114.7, 78.1, 56.0, 52.0, 37.0. HRMS
(ESI) calcd for C21H22N4O3Na [M + Na]+ 401.1590, found
401.1585.
(2-Methoxyethoxy)methyl-(2E)-5-(trimethylsilyl)pent-2-en-4-
ynoate (18). Pd(PPh3)2Cl2 (0.56 g, 0.80 mmol, 0.8 equiv) and CuI
(0.31 g, 1.63 mmol, 0.1 equiv) were added to a reaction vessel
containing a solution of the iodide 17 (4.65 g, 16.3 mmol, 1.0 equiv)
in Et3N (60 mL). The solution was degassed with argon. Trimeth-
ylsilylacetylene (3.8 mL, 29.3 mmol, 1.8 equiv) was then added
and the solution was stirred for 1 h. The mixture was poured into
sat. NH4Cl (200 mL) and extracted with ether (3 × 100 mL). The
combined organic layers were washed with brine, dried over
MgSO4, and concentrated. The thick oily residue was subjected to
flash column chromatography (hexanes:ethyl acetate, 20:1 to 13:
(E)-N-(4-Methoxybenzyloxy)-3-(1-(3-phenylpropyl)-1H-1,2,3-
triazol-4-yl)acrylamide (21c). A white solid was obtained (95%
yield, 186 mg 21c from 0.5 mmol 7) via flash column chromatog-
raphy (MeOH:DCM, from 0.8:100 to 1.5:100). 1H NMR (500 MHz,
DMF-d7): δ 11.29 (s, 1H), 8.49 (s, 1H), 7.60 (d, J ) 15.7 Hz, 1H),
7.40 (d, J ) 8.5 Hz, 2H), 7.35-7.30 (m, 2H), 7.30-7.25 (m, 2H),
7.25-7.20 (m, 1H), 6.98 (d, J ) 8.6 Hz, 2H), 6.75 (d, J ) 15.5
Hz, 1H), 4.90 (s, 2H), 4.50 (t, J ) 7.3 Hz, 2H), 3.83 (s, 3H), 2.67
(t, J ) 7.3 Hz, 2H), 2.25 (t, J ) 7.3 Hz, 2H). 13C NMR (125 MHz,
DMF-d7): δ 164.1, 161.0, 144.5, 142.2, 131.9, 129.7, 129.6, 129.5,
127.2, 125.8, 120.3, 114.8, 78.1, 56.0, 50.4, 33.3, 32.8 (one peak
1
1) to yield 3.6 g (87%) of 18 as a pale oil. H NMR (500 MHz,
CDCl3): δ 6.77 (d, J ) 16.0 Hz, 1H), 6.23 (d, J ) 16.0 Hz, 1H),
5.38 (s, 2H), 3.77(m, 2H), 3.53(m, 2H), 3.36 (s, 3H), 0.20 (s, 9H).
13C NMR (125 MHz, CDCl3): δ 165.1, 130.6, 126.0, 105.9, 101.1,
89.8, 71.5, 69.6, 59.1, -0.43. HRMS (ESI) calcd for C12H20O4SiNa
[M + Na]+ 279.1029, found 279.1032.
(E)-5-(Trimethylsilyl)pent-2-en-4-ynoic acid (19). MEM-
protected 18 (3.07 g, 12.0 mmol, 1.0 equiv) and 3N HCl (12 mL)
were added to a reaction vessel containing THF (150 mL). The
reaction was stirred at room temperature for 3 days, during which

Histone Deacetylase Inhibitors through Click Chemistry
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23 7425
less due to overlap). HRMS (ESI) calcd for C22H24N4O3Na [M +
1-Benzyl-1H-[1,2,3]triazole-4-carboxylic Acid (4-Methoxy-
benzyloxy)-amide (22a). A white solid was obtained (83% yield,
60 mg 22a from 0.212 mmol 8) via flash column chromatography
(MeOH:DCM, from 0.5:100 to 0.8:100). 1H NMR (500 MHz,
DMF-d7): δ 11.76 (bd s, 1H), 8.72 (s, 1H), 7.60-7.25 (m, 7H),
6.96 (d, J ) 7.3 Hz, 2H), 5.77 (s, 2H), 4.95 (s, 2H), 3.82 (s, 3H).
13C NMR (125 MHz, DMF-d7): δ 161.0, 159.1, 142.8, 137.1, 131.8,
130.0, 129.5, 129.3, 127.7, 114.7, 78.5, 56.0, 54.5. HRMS (ESI)
calcd for C18H18N4O3Na [M + Na]+ 361.1277, found 361.1263.
1-Phenethyl-1H-[1,2,3]triazole-4-carboxylic Acid (4-Methoxy-
benzyloxy)-amide (22b). A white solid was obtained (95% yield,
63 mg 22b from 0.189 mmol 8) via flash column chromatography
(MeOH:DCM, from 0.5:100 to 0.75:100). 1H NMR (500 MHz,
DMF-d7): δ 11.69 (bd s, 1H), 8.56 (s, 1H), 7.42 (d, J ) 8.6 Hz,
2H), 7.32-7.20 (m, 5H), 6.96 (d, J ) 8.7 Hz, 2H), 4.93 (s, 2H),
4.77 (t, J ) 7.3 Hz, 2H), 3.81 (s, 3H), 3.28 (t, J ) 7.4 Hz, 2H).
13C NMR (125 MHz, DMF-d7): δ 161.0,142.4, 138.8, 131.8, 129.9,
129.6, 129.3, 127.8, 127.7, 114.8, 78.5, 56.0, 52.2, 37.0. HRMS
(ESI) calcd for C19H20N4O3Na [M + Na]+ 375.1433, found
375.1425.
1-(3-Phenyl-propyl)-1H-[1,2,3]triazole-4-carboxylic Acid (4-
Methoxy-benzyloxy)-amide (22c). A white solid was obtained
(67% yield, 53 mg 22c from 0.212 mmol 8) via flash column
chromatography (MeOH:DCM, from 0.5:100 to 0.6:100). 1H NMR
(500 MHz, DMF-d7): δ 11.74 (bd s, 1H), 8.69 (s, 1H), 7.45 (d, J
) 8.4 Hz, 2H), 7.36-7.20 (m, 5H), 6.98 (d, J ) 8.5 Hz, 2H), 4.97
(s, 2H), 4.54 (t, J ) 7.0 Hz, 2H), 3.83 (s, 3H), 2.67 (t, J ) 7.7 Hz,
2H), 2.27 (tt, J1 ) J2 ) 7.4 Hz, 2H). 13C NMR (125 MHz, DMF-
d7): δ 161.0, 159.2, 142.6, 142.1, 131.8, 129.5, 129.3, 127.6, 127.2,
114.8, 78.5, 56.0, 50.7, 33.3, 32.8 (one less peak due to overlap).
HRMS (ESI) calcd for C20H22N4O3Na [M + Na]+ 389.1590, found
389.1585.
1-(2-Phenoxy-ethyl)-1H-[1,2,3]triazole-4-carboxylic Acid (4-
Methoxy-benzyloxy)-amide (22d). A white solid was obtained
(56% yield, 44 mg 22d from 0.212 mmol 8) via flash column
chromatography (MeOH:DCM, from 0.5:100 to 1.0:100). 1H NMR
(500 MHz, DMF-d7): δ 11.81-11.72 (bd s, 1H), 8.73 (s, 1H), 7.44
(d, J ) 8.6 Hz, 2H), 7.31 (t, J ) 8.0 Hz, 2H), 7.01-6.95 (m, 5H),
4.98-4.94 (m, 4H), 4.54 (t, J ) 5.2 Hz, 2H), 3.82 (s, 3H). 13C
NMR (125 MHz, DMF-d7): δ 161.0, 159.4, 159.1, 142.6, 131.8,
130.7, 129.3, 128.2, 122.3, 115.7, 114.7, 78.5, 63.7, 56.0, 50.8.
HRMS (ESI) calcd for C19H20N4O4Na [M + Na]+ 391.1382, found
391.1379.
1-(2-oxo-2-Phenyl-ethyl-1H-[1,2,3]triazole-4-carboxylic Acid
(4-Methoxy-benzyloxy)-amide (22e). A pale-yellow solid was
obtained (76% yield, 74 mg 22e from 0.265 mmol 8) via flash
column chromatography (MeOH:DCM, from 0.25:100 to 1:100).
1H NMR (500 MHz, DMF-d7): δ 11.83 (s, 1H), 8.69 (s, 1H), 8.17
(d, J ) 7.6 Hz, 2H), 7.78 (t, J ) 7.3 Hz, 1H), 7.65 (dd, J1 ) J2 )
7.5 Hz, 2H), 7.46 (d, J ) 8.2 Hz, 2H), 6.99 (d, J ) 8.2 Hz, 2H),
6.39 (s, 2H), 4.99 (s, 2H), 3.84 (s, 3H). 13C NMR (125 MHz, DMF-
d7): δ 192.9, 161.0, 159.2, 142.6, 135.6, 135.4, 131.9, 130.1, 129.5,
129.3, 114.8, 78.5, 57.4, 56.0 (one less peak due to overlap). HRMS
(ESI) calcd for C19H18N4O4Na [M + Na]+ 389.1266, found
389.1218.
Na]+ 415.1746, found 415.1745.
(E)-N-(4-Methoxybenzyloxy)-3-(1-(2-phenoxyethyl)-1H-1,2,3-
triazol-4-yl)acrylamide (21d). A white solid was obtained (89%
yield, 176 mg 21d from 0.5 mmol 7) via flash column chroma-
1
tography (MeOH:DCM, from 1.0:100 to 2.0:100). H NMR (500
MHz, DMF-d7): δ 11.26 (s, 1H), 8.55 (s, 1H), 7.61 (d, J ) 15.7
Hz, 1H), 7.40 (d, J ) 8.3 Hz, 2H), 7.36-7.27 (m, 2H), 7.06-6.90
(m, 5H), 6.77 (d, J ) 14.8 Hz, 1H), 4.91 (t, J ) 5.0 Hz, 2H), 4.89
(s, 2H), 4.51 (t, J ) 5.1 Hz, 2H), 3.83 (s, 3H). 13C NMR (125
MHz, DMF-d7): δ 164.2, 161.0, 159.4, 144.5, 131.9, 130.6, 129.6,
129.5, 126.5, 122.3, 120.4, 115.7, 114.8, 78.1, 67.4, 56.0, 50.6.
HRMS (ESI) calcd for C21H22N4O4Na [M + Na]+ 417.1539, found
417.1543.
(E)-N-(4-Methoxybenzyloxy)-3-(1-(2-oxo-2-phenylethyl)-1H-
1,2,3-triazol-4-yl)acrylamide (21e). A pale-yellow solid was
obtained (38% yield, 110 mg 21e from 0.73 mmol 7) via flash
column chromatography (MeOH:DCM, from 1.5:100 to 2:100). 1H
NMR (500 MHz, DMF-d7): δ 11.30 (s, 1H), 8.48 (s, 1H), 8.17 (d,
J ) 7.4 Hz, 2H), 7.78 (t, J ) 7.4 Hz, 1H), 7.72-7.62 (m, 3H),
7.41 (d, J ) 8.3 Hz, 2H), 6.99 (d, J ) 8.5 Hz, 2H), 6.80 (d, J )
15.6 Hz, 1H), 6.35 (s, 2H), 4.91 (s, 2H), 3.83 (s, 3H). 13C NMR
(125 MHz, DMF-d7): δ 192.3, 163.4, 160.2, 143.8, 134.8, 134.6,
131.1, 129.3, 128.9, 128.7, 128.6, 126.9, 119.7, 114.0, 77.3, 56.4,
55.3. HRMS (ESI) calcd for C21H20N4O4Na [M + Na]+ 415.1382,
found 387.1378.
(E)-N-(4-Methoxybenzyloxy)-3-(1-(2-oxo-2-(phenylamino)-
ethyl)-1H-1,2,3-triazol-4-yl)acrylamide (21f). A white solid was
obtained (92%, 187 mg product 21f from 0.5 mmol 7) via flash
column chromatography (MeOH:DCM, from 2.5:100 to 3.5:100).
1H NMR (500 MHz, DMF-d7): δ 11.29 (s, 1H), 10.60 (s, 1H), 8.53
(s, 1H), 7.69 (d, J ) 8.0 Hz, 2H), 7.65 (d, J ) 15.7 Hz, 1H), 7.41
(d, J ) 8.4 Hz, 2H), 7.36 (dd, J1 ) 7.6 Hz, J2 ) 8.4 Hz, 2H), 7.12
(t, J ) 7.4 Hz, 1H), 6.98 (d, J ) 8.6 Hz, 2H), 6.78 (d, J ) 15.7
Hz, 1H), 5.52 (s, 2H), 4.90 (s, 2H), 3.83 (s, 3H). 13C NMR (125
MHz, DMF-d7) δ 164.6, 163.4, 160.2, 143.6, 139.3, 131.1, 129.2,
128.9, 128.7, 126.8, 124.1, 119.6, 114.0, 77.3, 55.2, 52.8 (one peak
less due to the overlap). HRMS (ESI) calcd for C21H21N5O4Na [M
+ Na]+ 430.1491, found 430.1492.
(E)-3-(1-Cinnamyl-1H-1,2,3-triazol-4-yl)-N-(4-methoxybenzyl-
oxy)acrylamide (21g). A white solid was obtained (86% yield, 216
mg product 21g from 150 mg 7) via flash column chromatography
(MeOH:DCM, from 1.0:100 to 2.0:100). 1H NMR (500 MHz,
DMF-d7): δ 11.29 (s, 1H), 8.52 (s, 1H), 7.62 (d, J ) 15.7 Hz, 1H),
7.53 (d, J ) 7.3 Hz, 2H), 7.42-7.36 (m, 4H), 7.31 (tt, J1 ) 7.3
Hz, J2 ) 2.0 Hz, 1H), 6.98 (d, J ) 8.6 Hz, 2H), 6.78 (m, 2H), 6.61
(td, J1 ) 15.8 Hz, J2 ) 6.3 Hz, 1H), 5.30 (d, J ) 6.1 Hz, 2H), 4.89
(s, 2H), 3.83 (s, 3H). 13C NMR (125 MHz, DMF-d7): δ 164.1,
161.0, 144.7, 137.3, 135.4, 131.9, 129.8, 129.7, 129.4, 129.3, 127.8,
125.7, 124.5, 120.4, 114.8, 78.1, 56.0, 52.8. HRMS (ESI) calcd
for C22H22N4O3Na [M + Na]+ 413.1590, found 413.1581.
General Procedure for the Preparation of 22a-g. The alkyne
precursor 8 (589 mg, 2.12 mmol, 1.0 equiv) was added to a reaction
vessel containing THF (50 mL) and MeOH (50 mL). Cesium
fluoride (322 mg, 2.12 mmol, 1.0 equiv) was then added, after which
the reaction was monitored by TLC analysis. The desilylation
intermediate was slightly more polar than 8. Upon the disappearance
of 8, the solution was split into 10 equal fractions. These fractions
were used directly in the ensuing reactions as workup led to
degradation of the alkyne. To each fraction of the alkyne solution,
the azido compound 9a-g (0.32 mmol, 1.5 equiv), catalyst
CuIP(OEt)3 (10 mg, 0.028 mmol, 0.1 equiv), and one drop of
DIPEA were added sequentially. The reaction was allowed to
proceed to completion by stirring overnight at room temperature.
The solvent was removed, and the residue was partitioned between
DCM (50 mL) and 1% CuSO4 aqueous solution (50 mL). The
aqueous phase was additionally extracted with DCM (2 × 50 mL).
The combined organic fractions were then dried (Na2SO4). After
removal of the solvent, the crude product was purified via flash
column chromatography.
1-Phenylcarbamoylmethyl-1H-[1,2,3]triazole-4-carboxylic Acid
(4-Methoxy-benzyloxy)-amide (22f). The crude product was
dissolved in a minimal amount of 5% MeOH in DCM. The pure
compound was then precipitated via addition of hexane (2:1 )
hexane:solution). Following centrifugation (5000 rpm, 5 min), the
supernatant was removed and the solid was sonicated in the presence
of a 1% EDTA aqueous solution. The solution was then filtered to
afford the pure compound (81% yield, 82 mg 22f from 0.265 mmol
8). 1H NMR (500 MHz, DMF-d7): δ 11.90-11.70 (bd s, 1H), 10.65
(s, 1H), 8.72 (s, 1H), 7.69 (d, J ) 8.0 Hz, 2H), 7.45 (d, J ) 8.5
Hz, 2H), 7.36 (dd, J1 ) J2 ) 7.8 Hz, 2H), 7.12 (t, J ) 7.3 Hz,
1H), 6.98 (d, J ) 8.5 Hz, 2H), 5.57 (s, 2H), 4.98 (s, 2H), 3.83 (s,
3H). 13C NMR (125 MHz, DMF-d7): δ 165.2, 161.0, 159.2, 142.4,
140.0, 131.8, 129.4, 129.3, 124.9, 120.4, 114.8, 78.5, 56.0, 53.7
(one less peak due to overlap). HRMS (ESI) calcd for
C19H19N5O4Na [M + Na]+ 404.1335, found 404.1319.

7426 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 23
Shen et al.
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1-(3-Phenyl-allyl)-1H-[1,2,3]triazole-4-carboxylic Acid (4-
Methoxy-benzyloxy)-amide (22g). A white solid was obtained
(80% yield, 62 mg of 22g from 0.212 mmol 8) via flash column
chromatography (MeOH:DCM, from 0.25:100 to 0.5:100). 1H NMR
(500 MHz, DMF-d7): δ 11.76 (s, 1H), 8.69 (s, 1H), 7.54 (d, J )
7.4 Hz, 2H), 7.44 (d, J ) 8.6 Hz, 2H), 7.38 (dd, J1 ) J2 ) 7.5 Hz,
2H), 7.31 (t, J ) 7.3 Hz, 1H), 6.97 (d, J ) 8.5 Hz, 2H), 6.80 (d,
J ) 15.9 Hz, 1H), 6.63 (td, J1 ) 15.8 Hz, J2 ) 6.6 Hz, 1H), 5.34
(d, J ) 6.5, 2H), 4.96 (s, 2H), 3.82 (s, 3H). 13C NMR (125 MHz,
DMF-d7): δ 161.0, 159.1, 142.7, 137.3, 135.6, 131.8, 129.8, 129.4,
129.3, 127.8, 127.5, 124.4, 114.7, 78.5, 56.0, 53.0. HRMS (ESI)
calcd for C20H20N4O3Na [M + Na]+ 387.1433, found 387.1430.
Acknowledgment. This project was supported by The Ohio
State University (support to Peng George Wang). The Cell Line
Studies were performed by the NIH.
Supporting Information Available: Proton and carbon NMR
spectra of new compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
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