4-Amino-6-piperazin-1-yl-pyrimidine-5-carbaldehyde oximes as potent FLT-3 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2007.06.046

A series of 4-amino-6-piperazin-1-yl-pyrimidine-5-carbaldehyde oximes has been discovered and developed as potent FLT3 tyrosine kinase inhibitors. The series exhibited potent antiproliferative activity against both an FLT3 ITD-mutated human leukemic cell line as well as a wild-type FLT3 BaF₃ expressed cell line. The structure-activity relationship of this class of compounds is described.

Full text of DOI:10.1016/j.bmcl.2007.06.046

Bioorganic & Medicinal Chemistry Letters 17 (2007) 4861–4865
4-Amino-6-piperazin-1-yl-pyrimidine-5-carbaldehyde oximes
as potent FLT-3 inhibitors
Micheal D. Gaul,a,* Guozhang Xu,a Jennifer Kirkpatrick,b
Heidi Ottb and Christian A. Baumannb
aJohnson and Johnson Pharmaceutical Research and Development, L.L.C., 8 Clarke Drive, Cranbury, NJ 08512, USA
bJohnson and Johnson Pharmaceutical Research and Development, L.L.C., 665 Stockton Drive, Exton, PA 19341, USA
Received 29 May 2007; revised 11 June 2007; accepted 12 June 2007
Available online 14 June 2007
Abstract—A series of 4-amino-6-piperazin-1-yl-pyrimidine-5-carbaldehyde oximes has been discovered and developed as potent
FLT3 tyrosine kinase inhibitors. The series exhibited potent antiproliferative activity against both an FLT3 ITD-mutated human
leukemic cell line as well as a wild-type FLT3 BaF3 expressed cell line. The structure–activity relationship of this class of compounds
is described.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Normal hematopoiesis involves the regulation of prolif-
eration and differentiation in a number of cell types
from early stem cells to mature cells derived from ery-
throid, lymphoid, and myeloid lineages. This is a highly
regulated event and when unregulated can lead to a
number of myelodysplastic syndromes. The fms-like
tyrosine kinase 3 (FLT3), also known as fetal liver
kinase-2 (FLK-2) or human stem cell kinase-1 (STK-
1), is a receptor tyrosine kinase that is involved in the
differentiation of hematopoietic cells.1 The expression
of FLT3 is limited mainly to early hematopoietic stem
cells and myeloid and lymphoid progenitor cells.2 In
particular, FLT3 expression is limited to CD34+ fetal
liver and bone marrow stem cells,3 pre-B cells,4 and
peripheral dendritic cells. Activation of FLT3 is due to
binding of the endogenous FLT3 ligand (FLT3L) to
the extracellular portion of the receptor. FLT3L is
widely expressed in most tissues in the body including
many hematopoeitic cells.5
brane domain of the protein and specific point muta-
tions within the kinase activation loop.7 The ITD
mutation is found in approximately 25% of AML
patients and leads to constitutive activation via auto-
phosphorylation of the FLT3 receptor. Patients carrying
the FLT3 ITD mutation were found to have an increased
level of leukocytosis and a decreased overall survival time
as compared to patients without the activating mutation.8
Taken together the two activating mutations of FLT3 are
the most common genetic abnormality found in AML.
Therefore identification of a potent, selective FLT3
inhibitor that is potent against both the ITD mutation
as well as wild-type FLT3 kinase may provide a means
for therapeutic intervention in AML patients.
Recently it was reported that Tandutinib (Fig. 1) is a
dual PDGFR/FLT3 inhibitor9 that is currently under
clinical development in AML patients.10 We envisioned
that replacement of the quinazoline found in Tandutinib
with our recently reported 4-aminopyrimidine 5-carbox-
aldehyde oxime scaffold11 (Fig. 1) could lead to the iden-
tification of potent FLT3 tyrosine kinase inhibitors.
Herein, we report on the design, synthesis, and biologi-
cal activity of this new class of pyrimidine carbaldehyde
oxime FLT3 inhibitors.
FLT3 is expressed on blast cells in >90% of patients with
Acute Myeloid Leukemia (AML) and activating muta-
tions of FLT3 are present in approximately 30% of these
patients. There are currently two known mutations: an
internal tandem duplication (ITD)6 of the juxtamem-
The synthesis of the molecules is outlined in Scheme 1.
Treatment of 4-amino-6-chloropyrimidine-5-carboxal-
dehyde12 1 with N-Boc piperazine provided the pyrimi-
dine carboxaldehyde 2. Oxime formation utilizing
Keywords: FLT3 tyrosine kinase; Antiproliferative; Acute myeloid
leukemia.
*
Corresponding author. Tel.: +1 609 655 6902; fax: +1 609 655
6930; e-mail: mgaul@prdus.jnj.com
0960-894X/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.06.046

4862
M. D. Gaul et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4861–4865
H
N
H
N
O
O
N
N
N
N
O
R
O
O
O
1
N
R
N
N
N
N
H N
N
2
Tandutinib
Figure 1. Inhibitor design derived from reported FLT3 inhibitor.
H
N
O
H
Boc
N
H TFA
N
O
N
N
N
Z
R
4
O
Cl
O2N
Z
R
N
N
N
N
OHC
OHC
H2N
H3CO
d
H3CO
N
a
b,c
N
N
N
N
or
H2N
N
N
H2N
H2N
N
OCN
1
3
6-16
2
5
Z
R
Scheme 1. Reagents and conditions: (a) N-Boc piperidine, diisopropylethylamine, CH3CN, 100 ꢁC, 94%; (b) CH3ONH2 HCl, MeOH, 75 ꢁC, 75%; (c)
TFA/CH2Cl2 (1:1, v/v), rt, >95%; (d) 4 or 5, diisopropylethylamine, CH3CN, reflux, 47–70%.
O-methyl hydroxylamine to the E-isomer oxime
followed by subsequent removal of the N-Boc
protecting group provided the piperazinopyrimidine 3.
It should be pointed out that the E-isomer oxime13
was either the major or exclusive product obtained.
Treatment of piperazine 3 with either the o-nitrophenyl
ester carbamate14 4 or isocyanate reagent 5 under
similar conditions provided the desired final pyrimidines
6–16.
Our next objective was to study the effects of using a
variety of substituents off the oxime moiety. The synthe-
sis of the molecules is outlined in Scheme 2. Beginning
with the previously disclosed 2, deprotection of the N-
Boc group and subsequent acylation of the resulting
piperazine 17 with an appropriate o-nitrophenyl ester
carbamate14 4 provided the pyrimidine carboxaldehyde
18. Treatment of the aldehyde 18 with an appropriate
substituted hydroxylamine18 19 provided the desired
oxime pyrimidines 20–29. Table 2 summarizes the
FLT3 kinase and antiproliferative activities of this set
of compounds. Excellent activity was maintained when
the oxime substituent was increased in size to ethyl sub-
stitution as compared to the methyl oxime analogue
(compounds 27–29). The use of 2-(morpholin-1-yl)ethyl
side chain with an isopropoxy group as the R substitu-
ent 25 provided similar kinase and antiproliferative
activity as the corresponding methyl oxime 6. However
changing the oxime substituent to a more solubilizing
group diminished the activity in some compounds. Spe-
cifically changing the oxime substituent to 2-(morphol-
The oxime pyrimidines were evaluated for FLT3 tyro-
sine kinase inhibition15 as well as for antiproliferative
activity against two FLT3-driven cell lines: an MV4-
1116 line that is a human AML cell line expressing the
ITD activating mutation and
a wild-type FLT3
expressed BaF3 cell line.17 Our initial efforts focused
on developing the SAR of the para-substituted aryl urea
and the data are summarized in Table 1. Generally we
found that small, branched lipophilic substituents such
as isopropoxy, isopropyl, and pyrrolidin-1-yl provided
potent FLT3 enzyme inhibition as well as good antipro-
liferative activity in the FLT3-driven cell lines. Specifi-
cally, compounds 6, 10, and 12 provided potent
antiproliferative activity against the ITD mutation
MV4-11 cell line below 100 nM while maintaining excel-
lent activity against the wild-type FLT3-driven BaF3 cell
line. Not all substitutions were favorable; the use of
morpholin-4-yl or chlorine (compounds 8 and 14)
decreased activity against both the FLT3 kinase and
MV4-11 cells. It should be noted that each of the mole-
cules was tested against a parental BaF3 cell line to
determine general cytotoxic activity and all of the com-
pounds displayed <50% antiproliferative activity when
tested at 10 lM (data not shown), inferring that the
antiproliferative activity observed in the FLT3-driven
cell line was a result of FLT3 kinase inhibition.
in-1-yl)ethyl,
2-(methylsulfonamido)ethyl
or
3-
hydroxypropyl led to decreased activity in both FLT3
kinase inhibition as well as antiproliferative activity as
compared to the methyl oximes when R is either an iso-
propoxy group or pyrrolidin-1-yl.
In order to determine kinase selectivity for this series
of FLT3 inhibitors a representative example was tested
against other Class III receptor tyrosine kinase class
comprising of PDGFRb, c-kit, and c-fms. Compound
6 was found to be a potent c-kit inhibitor with an
IC50 of 10.5 nM but was much less potent versus
PDGFRb (IC50 = 10.7 lM) and c-fms (IC50
=
1.28 lM). Compound 6 was also screened against a
diverse panel of 20 kinases at a fixed concentration

M. D. Gaul et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4861–4865
4863
Table 1. FLT3 kinase- and FLT3-mediated cellular antiproliferative activity of compounds 6–16
H
N
O
N
N
Z
R
H CO
3
N
N
H N
2
N
Compound
Z
R
FLT3 IC50 (lM)
MV4-11IC50 (lM)
BaF3 FLT3 IC50 (lM)
6
7
CH
CH
CH
N
–OCH(CH3)2
Piperidin-1-yl
Morpholin-4-yl
–O(cyclobutyl)
–CH(CH3)2
–O(cyclopentyl)
Pyrrolidin-1-yl
Cyclohexyl
–Cl
0.05
0.05
0.079
0.089
0.515
0.111
0.078
0.112
0.099
0.052
>1
0.017
0.153
0.105
0.104
0.008
0.068
0.312
0.012
0.11
8
0.34
9
0.075
0.015
0.018
0.003
0.099
1.37
10
11
12
13
14
15
16
CH
N
CH
CH
CH
CH
CH
–OPh
–N(CH3)2
0.001
0.014
0.086
0.472
0.102
0.058
H
N
H
N
O
O
N
H TFA
N
Boc
N
N
N
Z
R
Z
R
N
N
N
N
N
OHC
OHC
O
1
a
b
c
N
N
O
R
N
N
1
H N
2
R ONH
2 19
H N
N
H N
2
N
H N
N
2
2
17
18
20-29
2
Scheme 2. Reagents and conditions: (a) TFA/CH2Cl2 (1:1, v/v), rt, >95%; (b) 4, diisopropylethylamine, CH3CN, reflux, 32–70%; (c) 19, MeOH,
75 ꢁC, 50–60%.
Table 2. FLT3 kinase- and FLT3-mediated cellular antiproliferative activity of compounds 20–29
H
N
O
N
N
Z
R
O
1
R
N
N
H N
N
2
Compound
Z
R
R1
–CH2CH2NHSO2CH3
FLT3 IC50 (lM)
MV4-11 IC50 (lM)
BaF3 FLT3 IC50 (lM)
20
21
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
Pyrrolidin-1-yl
Pyrrolidin-1-yl
–OCH(CH3)2
Pyrrolidin-1-yl
–OCH(CH3)2
–OCH(CH3)2
–OCH(CH3)2
–OCH(CH3)2
Piperidin-1-yl
–O(cyclobutyl)
0.15
0.554
0.362
0.268
0.458
0.415
0.177
0.283
0.077
0.058
0.065
0.025
0.53
–CH2CH2(morpholin-1-yl)
–CH2CO(morpholin-1-yl)
–CH2CO(morpholin-1-yl)
–CH2CH2NHSO2CH3
–CH2CH2(morpholin-1-yl)
–CH2CH2CH2OH
–CH2CH3
0.165
0.062
0.041
0.146
0.036
0.26
22
23
0.187
0.066
0.028
0.081
0.072
0.022
0.026
0.063
24
25
26
2721
2821
2921
0.018
0.049
0.058
–CH2CH3
–CH2CH3
of 3 lM in the presence of 100 lM ATP.19 It was
observed that the compound was highly selective ver-
sus the kinase panel with the highest activity obtained
for FES and ALK (34% and 31% inhibition, respec-
tively). The series also displayed good in vitro micro-
somal stability when incubated in the presence of
human liver microsomes as demonstrated by examples
6, 7, 25, and 27 (78.5%, 69.2%, 82.9%, and 78.9% par-
ent compound remaining after 10 min of incubation,
respectively).

4864
M. D. Gaul et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4861–4865
14. p-Nitrophenyl ester carbamates were prepared from the
corresponding anilines by treating with 1 equiv p-nitro-
phenylchloroformate and 1 equiv diisopropylethylamine.
15. FLT3 kinase assay protocol. To determine the activity of
the compounds in an in vitro kinase assay, inhibition of
the isolated kinase domain of the human FLT3 receptor
(aa 571–993) was performed using the following fluores-
cence polarization (FP) protocol. The FLT3 fluorescence
polarization assay utilizes the fluorescein-labeled phos-
phopeptide and the anti-phosphotyrosine antibody
included in the Panvera Phospho-Tyrosine Kinase Kit
(Green) supplied by Invitrogen. The FLT3 kinase reaction
is incubated at room temperature for 30 min under the
following conditions: 10 nM FLT3 571–993, 20 lg/mL
poly Glu4Tyr, 150 lM ATP, 5 mM MgCl2, 1% compound
in DMSO. The kinase reaction is stopped with the
addition of EDTA. The fluorescein-labeled phosphopep-
tide and the anti-phosphotyrosine antibody are added and
incubated for 30 min at room temperature and polariza-
tion was read.
In summary, we have described a new class of oxime
pyrimidines20 as potent inhibitors of FLT3 kinase. In
addition the compounds show excellent antiproliferative
activity against both a FLT3 ITD-mutated human leu-
kemic cell line as well as a wild-type FLT3 cell line. A
variety of small lipophilic substitutions off the phenyl
urea head group such as isopropoxy, pyrrolidin-yl, and
isopropyl were preferred substituents. Substitution off
the oxime side chain exhibited either the same or less
activity as compared to the parent methyl oxime. Fur-
ther studies with this series of molecules will be reported
in due course.
Acknowledgment
We thank Malini Dasgupta for conducting the human
liver microsomal stability studies.
16. MV4-11 cell-based assay: (a) Quentmeier, H.; Reinhardt,
J.; Zaborski, M.; Drexler, H. G. Leukemia 2003, 17, 120;
(b) MV4-11 (ATCC No. CRL-9591) cells were plated at
10,000 cells per well in 100 ll of RPMI media containing
penn/strep, 10% FBS, and 0.2 ng/ml GM-CSF. Com-
pound dilutions or 0.1% DMSO (vehicle control) is added
to cells and the cells are allowed to grow for 72 h at
standard cell growth conditions (37 ꢁC, 5% CO2). To
measure total cell growth an equal volume of CellTiterGlo
reagent (Promega Madison, WI) was added to each well,
according to the manufacturer’s instructions, and lumi-
nescence was quantified. Total cell growth was quantified
as the difference in luminescent counts (relative light units,
RLU) of cell number at Day 0 compared to total cell
number at Day 3 (72 h of growth and/or compound
treatment). All IC50 values are calculated in GraphPadP-
rism using non-linear regression analysis with a multipa-
rameter (variable slope) equation.
References and notes
1. (a) Matthews, W.; Jordan, C. T.; Wiegand, G. W.;
Pardoll, D.; Lemischka, I. R. Cell 1991, 65, 1143; (b)
Rosnet, O.; Marchetto, S.; deLapeyriere, O.; Birn-
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Mattei, M. G.; Marchetto, S.; Birnbaum, D. Genomics
1991, 2, 380.
2. (a) Small, D.; Levenstein, M.; Kim, E.; Carow, C.;
Amin, S.; Rockwell, P.; Witte, L.; Burrow, C.; Ratacj-
zak, M. Z.; Gewirtz, A. M. Proc. Natl. Acad. Sci. U.S.A.
1994, 91, 459; (b) Brasel, K.; Escobar, S.; Anderberg, R.;
de Vries, P.; Gruss, H. J.; Lyman, S. D. Leukemia 1995,
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D.; Baumhueter, S.; Carroll, K. J.; Hooley, J.; Bauer, K.;
Matthews, W. Blood 1994, 84, 2422.
17. wt FLT3 BaF3 cell-based assay. BaF3 FLT3 cells were
maintained in RPMI 1640 with 10% FBS, penn/strep, and
10 ng/ml of FLT ligand at 37 ꢁC, 5% CO2. BaF3 FLT3
cells (2 · 105) were plated in 96-well dishes in RPMI 1640
with 0.5% serum and 0.01 ng/mL IL-3 for 16 h prior to 1 h
compound or DMSO vehicle incubation. Cells were
treated with 100 ng/mL Flt ligand (R&D Systems Cat#
308-FK) for 10 min at 37 ꢁC. Cells were pelleted, washed,
and lysed in 100 ll lysis buffer (50 mM Hepes, 150 mM
NaCl, 10% Glycerol, 1% Triton X-100, 10 mM NaF,
1 mM EDTA, 1.5 mM MgCl2, 10 mM Na-pyrophosphate)
supplemented with phosphatase (Sigma Cat # P2850) and
protease inhibitors (Sigma Cat # P8340). Lysates were
cleared by centrifugation at 1000g for 5 min at 4 ꢁC. Cell
lysates were transferred to white wall 96-well microtiter
(Costar # 9018) plates coated with 50 ng/well anti-FLT3
antibody (Santa Cruz Cat # sc-480) and blocked with
SeaBlock reagent (Pierce Cat # 37527). Lysates were
incubated at 4 ꢁC for 2 h. Plates were washed 3· with
200 ll/well PBS/0.1% Triton X-100. Plates were then
incubated with 1:8000 dilution of HRP-conjugated anti-
phosphotyrosine antibody (Clone 4G10, Upstate Biotech-
nology Cat # 16-105) for 1 h at room temperature. Plates
were washed 3· with 200 ll/well PBS/0.1% Triton X-100.
Signal detection with Super Signal Pico reagent (Pierce
Cat # 37070) was done according to manufacturer’s
instruction with a Berthold microplate luminometer. All
data points are an average of triplicate samples. The total
relative light units (RLU) of Flt ligand stimulated FLT3
phosphorylation in the presence of 0.1% DMSO control
was defined as 0% inhibition and 100% inhibition was the
4. Rosnet, O.; Schiff, C.; Pebusque, M. J.; Marchetto, S.;
Tonnelle, C.; Toiron, Y.; Birg, F.; Birnbaum, D. Blood
1993, 82, 1110.
5. Brasel, K.; Escobar, S.; Anderberg, R.; de Vries, P.; Gruss,
H. J.; Lyman, S. D. Leukemia 1995, 9, 1212.
6. Nakao, M.; Yokota, S.; Iwai, T.; Kaneko, H.; Horiike, S.;
Kashima, K.; Sonoda, Y.; Fujimoto, T.; Misawa, S.
Leukemia 1996, 10, 1911–1918.
7. (a) Yamamoto, Y.; Kiyoi, H.; Nakano, Y.; Suzuki, R.;
Kodera, Y.; Miyawaki, S.; Asou, N.; Kuriyama, K.; Yaga-
saki, F.; Shimazaki, C.; Akiyama, H.; Saito, K.; Nishimura,
M.; Motoji, T.; Shinagawa, K.; Takeshita, A.; Saito, H.;
Ueda, R.; Ohno, R.; Naoe, T. Blood 2001, 97, 2434; (b) Abu-
Duhier, F. M.; Goodeve, A. C.; Wilson, G. A.; Care, R. S.;
Peake, I. R.; Reilly, J. T. Br. J. Haematol. 2001, 113, 983.
8. Levis, M.; Small, D. Leukemia 2003, 17, 1738–1752.
9. Pandey, A.; Volkots, D. L.; Seroogy, J. M.; Rose, J. W.;
Yu, J. C.; Lambing, J. L.; Hutchaleelaha, A.; Hollenbach,
S. J.; Abe, K.; Giese, N. A.; Scarborough, R. M. J. Med.
Chem. 2002, 45, 3772–3793.
10. Levis, M.; Small, D. Curr. Pharm. Des 2004, 10, 1183.
11. Huang, S.; Li, R.; Connolly, P. J.; Xu, G.; Gaul, M. D.;
Emanuel, S.; LaMontagne, K. R.; Greenberger, L. M.
Biorg. Med. Chem. Lett. 2006, 20, 6063.
12. Gomtsyan, A.; Didomenico, S.; Lee, C. H.; Matulenko,
M. A.; Kim, K.; Kowaluk, E. A.; Wismer, C. T.; Mikusa,
J.; Yu, H.; Kohlhaas, K.; Jarvis, M. F.; Bhagwat, S. S.
J. Med. Chem. 2002, 45, 3639–3648.
13. Pallavinci, M.; Moroni, B.; Bolchi, C.; Clementi, F.;
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M. D. Gaul et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4861–4865
4865
total RLU of lysate in the basal state. All IC50 values are
calculated in GraphPadPrism using non-linear regression
analysis with a multiparameter (variable slope) equation.
18. Prepared by the following 2-step protocol:
J = 8.94 Hz, 2H), 6.45 (br, 1H), 4.46 (m, 1H), 3.96 (s, 3H),
3.58 (m, 4H), 3.42 (m, 4H), 1.30 (d, J = 6.06 Hz, 6H); LC/
MS (ESI) calcd for C20H28N7O3 (MH)+ 414.2, found
414.2.
Ph
Ph
Compound 25. A mixture of 4-(6-amino-5-formyl-pyrim-
idin-4-yl)-piperazine-1-carboxylic acid (4-isopropoxy-phe-
nyl)-amide (Ref. 18) (20.9 mg, 0.054 mmol) and O-(2-
Ph
Ph
1
R Cl
6N HCl
1
R ONH
2
N
N
KOH
1
OH
Gaul, M.D.; Xu, G.; Baumann, C.A. PCT Int. Appl. WO
OR
morpholin-4-yl-ethyl)-hydroxylamine
dihydrochloride
salt (Ref. 18) (12 mg, 0.054 mmol) in MeOH (1 mL)
was heated at 100 ꢁC for 0.5 h and the solvent was
removed. The residue was partitioned between EtOAc
and water. The organic extracts were dried with Na2SO4,
evaporated, and the residue was purified by preparative
TLC (5% MeOH/EtOAc) to yield compound 25. 1H
NMR (CD3OD) d 8.24 (s, 1H), 8.08 (s, 1H), 7.21 (d,
J = 8.79 Hz, 2H), 6.83 (d, J = 9.03 Hz, 2H), 4.52 (m,
1H), 4.34 (t, J = 5.63 Hz, 2H), 3.71 (t, J = 4.84 Hz, 4H),
3.63 (m, 4H), 3.43 (m, 4H), 2.75 (t, J = 5.60 Hz, 2H),
2.57 (t, J = 4.96 Hz, 4H), 1.28 (d, J = 6.05 Hz, 6H); LC/
MS (ESI) calcd for C25H37N8O4 (MH)+ 513.2, found
513.3.
2006/135719 A1 20061221, 2006.
19. Upstate Cell Signaling Solutions, Charlottesville, VA.
20. Compounds 6–16 and 20–29 were characterized by 1H
NMR and LC/MS. Representative experimental proce-
dures.
Compound 6. To a mixture of 4-amino-6-piperazin-1-yl-
pyrimidine-5-carbaldehyde O-methyl-oxime trifluoroace-
tic acid salt
3 (Ref. 18) (23 mg, 0.066 mmol) and
(4-isopropoxy-phenyl)-carbamic acid 4-nitro-phenyl ester
4 (22.8 mg, 0.072 mmol) in CH3CN (1.5 mL) was added
DIEA (17 mg, 0.13 mmol). The mixture was heated at
reflux with stirring for 3 h and the solvents were evapo-
rated under reduced pressure. The residue was purified by
flash column chromatography on silica gel (EtOAc as
eluent) to afford Compound 6. 1H NMR (CDCl3)d 8.19 (s,
1H), 8.12 (s, 1H), 7.21 (d, J = 8.93 Hz, 2H), 6.81 (d,
21. Compounds 27–29 were prepared as outlined in Scheme 1
using O-ethylhydroxylamine hydrochloride in place of O-
methylhydroxylamine hydrochloride in step B.