Synthesis and dipeptidyl peptidase inhibition of N-(4-substituted-2,4-diaminobutanoyl)piperidines

Article abstract of DOI:10.1016/j.bmcl.2006.06.082

In this paper, we report the synthesis of diastereomerically pure N-(4-substituted-2,4-diaminobutanoyl)piperidines. These compounds were prepared to investigate the influence of the 4-substitution on the dipeptidyl peptidase II (DPP II) activity and selectivity of the parent N-(2,4-diaminobutanoyl)piperidine. The (4S)-methyl compound showed subnanomolar inhibition, comparable with the parent compound. The (4R)-methyl group or bigger substituents decreased the activity.

Full text of DOI:10.1016/j.bmcl.2006.06.082

Bioorganic & Medicinal Chemistry Letters 16 (2006) 4777–4779
Synthesis and dipeptidyl peptidase inhibition of
N-(4-substituted-2,4-diaminobutanoyl)piperidines
Anna Soroka,a Pieter Van der Veken,a Ingrid De Meester,b Anne-Marie Lambeir,b
b
b
a,
a
*
´
Marie-Berthe Maes, Simon Scharpe, Achiel Haemers and Koen Augustyns
aLaboratory of Medicinal Chemistry University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
bLaboratory of Medical Biochemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
Received 24 May 2006; revised 27 June 2006; accepted 28 June 2006
Available online 17 July 2006
Abstract—In this paper, we report the synthesis of diastereomerically pure N-(4-substituted-2,4-diaminobutanoyl)piperidines. These
compounds were prepared to investigate the influence of the 4-substitution on the dipeptidyl peptidase II (DPP II) activity and selec-
tivity of the parent N-(2,4-diaminobutanoyl)piperidine. The (4S)-methyl compound showed subnanomolar inhibition, comparable
with the parent compound. The (4R)-methyl group or bigger substituents decreased the activity.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Proline selective serine-type dipeptidyl peptidases
cleave off dipeptides from the amino terminus of
peptides or proteins with preferentially proline at the
penultimate position. Representative examples are
dipeptidyl peptidase II, IV, 8 and 9 (DPP II, DPP
IV, DPP8 and DPP9) and fibroblast-activation protein
a (FAPa). DPP IV is by far the best studied member
among these enzymes, and is currently a well-validated
target for the treatment of type 2 diabetes. Hence,
these peptidases are often referred to as DPP IV activ-
ity- and/or structure-homologues (DASH) proteins.
DPP II (EC 3.4.14.2) is less well studied. It is a 58-
kDa glycoprotein, active as a homodimer formed with
a leucine zipper motif and is identical to quiescent cell
proline peptidase (QPP, DPP7). It is widely found in
the human body and targeted to intracellular vesicles
but the natural substrates and physiological functions
are largely unknown. No sequence homology has been
found between DPP II and DPP IV. It shows, in con-
trast with the other DPPs, an optimum at acidic pH
but it cleaves, like DPP IV, N-terminal dipeptides from
oligopeptides with Ala or Pro at the penultimate posi-
tion.1,2 The kinetics of DPP II mediated hydrolysis of
chromogenic and fluorogenic dipeptide derivatives have
been characterized.3
The development of potent and selective inhibitors is a
very important item in research programmes on DPP
II. It is of utmost importance in the unraveling of the
biochemical and physiological functions of the enzyme
and in the disclosure of potential therapeutic properties
of its inhibition.
In a series of previous papers we reported a systematic
search for DPP II inhibitors.4,5 The optimal P1 group
appeared to be a piperidine unit and L-2,4-diaminobu-
tyric acid gave the best results as P2 building block.
Subnanomolar inhibitors were obtained when the
core structure, 2,4-diaminobutanoylpiperidine, was
N4-substituted with
a benzyl group such as in
UAMC00039 (N4-(4-chlorobenzyl)-2,4-diaminobutan-
oylpiperidine). This compound is not only a highly
potent inhibitor (Ki of 0.082 0.048 nM) of DPP II
but shows a high selectivity towards DPP IV and
DPP 8 (SI > 10000). UAMC00039 showed no toxicity
and good oral bioavailability.6
We further investigated the importance of the diamino-
butanoyl chain, more in particular the influence of 4-
substituents and prepared a set of 4-alkyl-derivatives
(1–7). These substitutions may indeed influence the flex-
ibility and lipophilicity of the compound and interfere in
the interaction with the active site of the enzyme. As well
(4R)- as (4S)-compounds were prepared.
Keywords: 2,4-Diaminoalkanoylpiperidines; Dipeptidyl peptidases;
DPP II; Inhibitors.
*
The 4-substituted 2,4-diaminobutyric acids were pre-
pared using the corresponding dehydroaminoacids as
Corresponding author. Tel.: +3238202717; fax: +3238202739; e-mail:
achiel.haemers@ua.ac.be
0960-894X/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.06.082

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A. Soroka et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4777–4779
O
O
O
H
N
O
R
OMe
R
R
Cbz
R
OCH3
a
b
c
d
OH
N
H
NH
NH
NH
Boc
Boc
Boc
NH
Boc
O
O
O
H
N
H
H
N
N
Cbz
OCH3
Cbz
OH
Cbz
N
d
g
e
f
R
R
R
NH
NH
NH
Boc
Boc
Boc
O
O
O
H
N
H
N
H2N
R
g
h
N
N
i
Cbz
Cbz
R
N
Cl
R
Cl
NH
NH2
NH
Scheme 1. Reagents: R=Me, Et, sec-But, iso-Pro, Bz. (a) N,O-dimethylhydroxylamine hydrochloride, TBTU, TEA, DMF; (b) LiAlH4, THF; (c)
methyl 2-benzyloxycarbonylamino-2-(dimethoxyphosphoryl)-acetate, DBU, DCM; (d) H2, R,R [Rh(COD)DIPAMP]+BF4À, EtOH, 3 Bar; (e) 75%
KOH/MeOH; (f) piperidine, TBTU, TEA, DMF; (g) TFA/DCM (1:1); (h) p-chlorobenzaldehyde, NaCNBH3, AcOH, MeOH; (i) 33% HBr/AcOH.
intermediates (Scheme 1; (2S,4S) shown). The latter
are common starting materials for the synthesis of
unnatural amino acids7 and were prepared through a
Horner–Wadsworth–Emmons reaction.8 This method
was already used for the synthesis of protected 2,4-
diaminobutyric acid.9 Another literature described
method used a diketopiperazine-derived dehydroamino
acid for the stereoselective synthesis of substituted 2,4-
diamino acids.10 We used the commercially available
methyl 2-benzyloxycarbonylamino-2-dimethoxyphos-
phoryl acetate and the corresponding (S)- or (R)-
Boc-protected aminoaldehydes as starting compounds.
The latter were prepared from the corresponding ami-
no acids by a lithium aluminium hydride reduction of
after Boc-deprotection with trifluoroacetic acid. At
this stage the (2S)-compounds were purified until
100% de by chromatography and finally Z-deprotected
by hydrobromic acid/acetic acid.
A set of compounds were prepared with methyl-,
ethyl-, isopropyl-, sec-butyl and benzyl substituents
(Table 1). All compounds were evaluated as
described for their ability to inhibit DPP II, DPP IV
and DPP 8 and their IC50s compared with reference
compound UAMC00039.5 Results are summarized in
Table 1.
Following conclusions can be drawn from the results
obtained:
their
N-methoxy-N-methylamides.
Stereoselective
hydrogenation of the a,b-unsaturated amino acids
with an optically active homogeneous catalyst was
used. As (2R)-diaminobutyric acid amides were found
to be poorly active DPP II inhibitors, we focused on
the (2S)-configuration and used R, R [Rh(COD)DIP-
AMP]+BF4À as a catalyst11 and obtained (2S)-com-
pounds with a % de of about 80. The piperidyl
amides were obtained by TBTU coupling after hydro-
lysis of the methyl ester and the final N-benzyl com-
pounds were prepared by reductive amination with
p-chlorobenzaldehyde and sodium cyanoborohydride
• The (4S)-methyl-(2S)-compound (1) shows about the
same activity as the reference compound. The corre-
sponding (2S,4R)-compound (2) is about 100 times
less active. The (4S)-methyl group does not hinder
the inhibitor–enzyme interaction and keeps the inhib-
itor in its active conformation.
• Larger substituents at the 4-position decrease the
activity: the (4S)-ethyl-(2S)-compound (3) and the
(4S)-benzyl-(2S)-compound (6) are about 5 times less
active. Isopropyl- and sec-butyl substitutions (com-
Table 1. Biological data
Entry
R1
Stereochemistry
DPP IIa
DPP IVa
DPP 8a
1
CH3
CH3
C2H5
i-Pr
s-Bu
Bn
2S,4S
2S,4R
2S,4S
2S,4R
2S,4R
2S,4S
2S,4R
2S
0.00062 0.00003
0.057 0.004
325 16
>250
>100
148 16
65
2
2
3
4b
0.0034 0.0002
0.019 0.001
0.084 0.006
>100
>100
>100
>100
>500
>125
5
234 31
>125
>125
6
0.0038 0.0002
0.0465 0.0133
0.00022 0.00002
7
Bn
H
UAMC000395
196
8
142 17
a IC50 (lM); the errors shown are the errors on the fit.
b (4R) of compounds 4, 5 corresponds to (4S) of compounds 1, 3, 6.

A. Soroka et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4777–4779
4779
2. Augustyns, K.; Van der Veken, P.; Haemers, A. Exp.
Opin. Ther. Patents 2005, 15, 1387.
3. Maes, M.-B.; Lambeir, A.-M.; Gilany, K.; Senten, K.;
Van der Veken, P.; Leiting, B.; Augustyns, K.;
´
Scharpe, S.; De Meester, I. Biochem. J. 2005, 386,
315.
4. Senten, K.; Van der Veken, P.; De Meester, I.; Lambeir,
´
A.-M.; Scharpe, S.; Augustyns, K. J. Med. Chem. 2003,
pounds 4, 5) afford lower inhibitory activities. The
lower activity for (4R) compounds is confirmed by
benzyl compound 7.
• The selectivity of N-(2,4-diaminobutanoyl)piperidines
towards DPP II is confirmed: each compound shows a
selectivity index of >1000 over DPP IV and DPP 8.
These results will be used in the investigation of the
active site of DPP II and its interaction with inhibitors.
46, 5005.
5. Senten, K.; Van der Veken, P.; De Meester, I.; Lambeir,
´
A.-M.; Scharpe, S.; Haemers, A.; Augustyns, K. J. Med.
Chem. 2004, 47, 2906.
6. Maes, M.-B.; Lambeir, A.-M.; Van der Veken, P.; De
´
Acknowledgments
Winter, B.; Augustyns, K.; Scharpe, S.; De Meester, I.
Adv. Exp. Med. Biol. 2006, 575, 73.
7. Bonauer, C.; Walenzyk, T.; Ko¨nig, B. Synthesis 2006,
1.
8. Schmidt, U.; Griesser, H.; Leitenberger, V.; Lieberkn-
echt, A.; Mangold, R.; Meyer, R.; Riedl, B. Synthesis
1992, 487.
This work was supported by the Fund of Scientific
Research, Flanders. P. Van der Veken and M.-B. Maes
are fellows of the Fund of Scientific Research, Flanders.
The authors are grateful to W. Bollaert and N. Lamoen
for technical assistance.
9. Shin, C.; Obara, T.; Segami, S.; Yonezawa, Y. Tetrahe-
dron Lett. 1987, 28, 3827.
10. Park, N. G.; Lee, S.; Maeda, H.; Aoyagi, H.; Kato, T.
Bull. Chem. Soc. Jpn 1989, 62, 2315.
References and notes
11. Schmidt, U.; Lieberknecht, A.; Kazmaier, U.; Griesser,
H.; Jung, G.; Metzger, J. Synthesis 1991, 49.
1. Augustyns, K.; Van der Veken, P.; Senten, K.; Haemers,
A. Curr. Med. Chem. 2005, 12, 971.