Design and synthesis of phosphotyrosine mimetics

Article abstract of DOI:10.1016/S0960-894X(03)00253-1

Selective inhibitors of protein tyrosine phosphatases (PTPases) are of great interest as therapeutic agents and research tools. Several phenylalanine derivatives (1, 2) designed as phosphotyrosine mimetics or irreversible active site inhibitors were successfully synthesized, then incorporated into a combinatorial library based on a peptidomimetic β-strand template.

Full text of DOI:10.1016/S0960-894X(03)00253-1

Bioorganic & Medicinal Chemistry Letters 13 (2003) 2083–2085
Design and Synthesis of Phosphotyrosine Mimetics
Zheng Yan,a Michael Kahn,b,c Maher Qabar,a Jan Urban,a Hwa-Ok Kima
and Mark A. Blaskovicha,*
aMolecumetics Ltd., 2023 120th Ave. N.E., Bellevue, WA 98005-2199, USA
bDepartment of Pathobiology, University of Washington, Seattle, WA 98195, USA
cPacific Northwest Research Institute, 720 Broadway, Seattle, WA 98122, USA
Received 28 August 2002; accepted 20 December 2002
Abstract—Selective inhibitors of protein tyrosine phosphatases (PTPases) are of great interest as therapeutic agents and research
tools. Several phenylalanine derivatives (1, 2) designed as phosphotyrosine mimetics or irreversible active site inhibitors were suc-
cessfully synthesized, then incorporated into a combinatorial library based on a peptidomimetic b-strand template.
# 2003 Elsevier Science Ltd. All rights reserved.
The protein tyrosine phosphatases (PTPases) play an
important role in controlling the status of tyrosine
phosphorylation and the regulation of cellular func-
tion.1 The ability to selectively inhibit tyrosine phos-
phatases holds enormous therapeutic potential for the
treatment of diseases such as diabetes, cancer and
osteoporosis.2 As a part of our ongoing research pro-
gram,3 we have designed and synthesized several phe-
nylalanine derivatives 1 and 2 (Fig. 1).4 The type-1
derivatives were designed to mimic a phosphorylated
tyrosine,5 while the type-2 derivatives include aryl sub-
stituents similar to a 1-benzothiopyran-1,1,4-trione
moiety, previously reported to be a selective irreversible
inhibitor of PTP1B.6
depicted in Scheme 1. The amino acid was esterified
with CDI and MeOH, followed by reduction of the
nitro group with SnCl2 and cyclization of the resulting
aminophenol 4 with phosgene to furnish 5. Compound
4 was also treated with TsCl in the presence of pyridine,
then cyclized with SO2Cl2 to afford 7. Both compounds
5 and 7 were then carefully hydrolyzed with LiOH to
the corresponding acids 1a and 1b.
The synthesis of the unusual amino acids 1 began with
commercially available Fmoc-l-Tyr-(3-NO2)-OH (3) as
Figure 1.
*Corresponding author at current address: CEPTYR, Inc., 22215 26th
Ave SE, Bothell, WA 98021, USA. Fax: +1-425-485-9026; e-mail:
mblaskovich@ceptyr.com
Scheme 1. (a) CDI in MeOH, rt, 85%; (b) SnCl2, EtOH, reflux, 88%; (c)
phosgene, THF, rt, 65%; (d) 0.2 M LiOH (aq), THF, 0 ꢀC, 61–62%; (e)
TsCl, Py, CH2Cl2, rt, 40%; (f) SO2Cl2, TEA, CH2Cl2, rt, 68%.
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00253-1

2084
Z. Yan et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2083–2085
Table 1. Yields of 9, 11 and 2 (%)
The synthesis of the title compounds 2 is described in
Scheme 2. Starting material 8a was commercially avail-
able, while the synthesis of 8b has been previously
reported.7 The 4,4,7-trimethyl-4H-naphthalen-1-one 8c
was prepared from gem-dimethyl carboxylic acid 128 via
treatment with TFAA in TFA (Scheme 3). Resulting
ketone 13 was deprotonated with LHMDS and sele-
nated with PhSeBr, followed by oxidative elimination to
afford 8c. The synthesis of 8d required the intermediate
15, prepared from 149 by reaction with SO2Cl2, then
quinoline (Scheme 4). The thioenol 15 was then treated
with H2O2 to give 8d in 76% yield.
8
9
11
2
a: X=O, Y=CO
b: X=S, Y=CO
c: X=CMe2, Y=CO
d: X=O, Y=SO2
61
53
66
50
42
54
59
60
100
90
86
68
Table 2. Screening results for inhibition of tyrosine phosphatases
Finally, the desired benzyl bromides 9 were obtained in
moderate yield by benzylic bromination of 8 with NBS
in the presence of AIBN. With the starting materials 9
in hand, we adopted O’Donnell’s protocol10 to synthe-
size 2 (Scheme 2). The glycine Schiff base 10, derived
from benzophone imine and glycine methyl ester, was
benzylated with 9 to give 11 in 42–60% yield. For the
final step, imino methyl ester 11 was treated with 1 N
HCl to provide the title compounds 2 in good to excel-
lent yields (Table 1).
Compd
R
PTP1B % TC-PTP % LAR % CD45 %
inhibition inhibition inhibition inhibition
(100 mM, (100 mM, (100 mM, (100 mM,
10 mM)
10 mM)
10 mM)
10 mM)
16a
16b
16c
16d
2,5-F2-Bn
4-PhO-Ph
PhCH(Me)CH2 95, 55
cHexCH2 70, 40
95, 0
100, 75
100, 85
100, 85
90, 20
20, 10
50, 25
70, 50
50, 10
10, 0
50, 5
70, 20
55, 15
70, 20
The phosphotyrosine mimetics were successfully incor-
porated into a library containing triazolopyridazine
b-strand templates11 via solid-phase synthesis. Pre-
liminary screening for inhibition of four phosphatases
(CD45, LAR, TCPP, and PTP1B) was accomplished by
flourometric assays, using 6,8-difluoro-4-methy-
lumbelliferyl phosphate (DiFMUP, Molecular Probes)
as substrate.12 Some derivatives exhibited moderate
potency (up to 85% inhibition at 10 mM sample con-
centration) and selectivity against the tyrosine phos-
phatases assayed (see Table 2), with the type 2d
phosphotyrosine mimetic providing the best activity.13
Acknowledgements
The authors are grateful to Dr. H. Nakanishi for helpful
discussions.
References and Notes
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Scheme 2. (a) NBS/AIBN, CCl4; (b) 10% NaOH(aq), CH2Cl2,
nBu4N+HSO-4; (c) 1 N HCl.
Scheme 3. (a) TFAA, TFA, 0 ꢀC to rt, 63%; (b) (i) LHMDS, PhSeBr,
À78 ꢀC, THF, 86%; (ii) 30% H2O2, AcOH, THF, 80%.
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4. A preliminary account of this research was presented at the
221st ACS Meeting, San Diego, CA, April 2001; Abstr.
MEDI-32.
Scheme 4. (a) SO2Cl2, CH2Cl2, reflux, then quinoline, 150 ꢀC, 50%;
(b) 30% H2O2, AcOH, reflux, 76%.

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12. Samples were preincubated with 0.2 units/mL enzyme in
buffer (100 mM HEPES, 1 mM EDTA, 5 mM DTT, 0.05%
Tween-20, 0.01% BSA) for 20 min at rt in black 96-well plates.
DiFMUP was then added (final concentration 3.6 mM for
PTP1B, 2.1 mM for TCPTP, 15 mM for LAR and 200 mM for
CD45) and the plates read on a Fluoroskan (abs. 358, em.
452).
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13. Regretfully, further analysis of the enzymatic inhibition
was not possible due to the termination of the operations of
Molecumetics. The mode of inhibition of compounds con-
taining the purported irreversible inhibitor 2d is of particular
interest, as are IC50 or Ki values for the most active com-
pounds against the various enzymes in order to determine
selectivity.