1-Aminomethylisoquinoline-4-carboxylates as novel dipeptidylpeptidase IV inhibitors

Article abstract of DOI:10.1016/S0960-894X(00)00286-9

Structure-activity relationship within a series of 1-aminoalkylisoquinoline-4-carboxylates as inhibitors of DDP-IV is described. A primary aminomethyl group is required to maintain biological activity. Substitution of the isoquinoline at the 6- and 8-positions with methoxy groups increases potency to 53 times that of the lead compound SDZ 029-576. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00286-9

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1555±1558
1-Aminomethylisoquinoline-4-carboxylates as Novel
Dipeptidylpeptidase IV Inhibitors
Gary M. Coppola,* Y. Larry Zhang, Herbert F. Schuster, Mary E. Russell
and Thomas E. Hughes
Metabolic and Cardiovascular Diseases Research, Novartis Institute for Biomedical Research,
556 Morris Avenue, Summit, NJ 07901, USA
Received 10 March 2000; accepted 8 May 2000
AbstractÐStructure±activity relationship within a series of 1-aminoalkylisoquinoline-4-carboxylates as inhibitors of DPP-IV is described.
A primary aminomethyl group is required to maintain biological activity. Substitution of the isoquinoline at the 6- and 8-positions with
methoxy groups increases potency to 53 times that of the lead compound SDZ 029-576. # 2000 Elsevier Science Ltd. All rights reserved.
Diabetes mellitus is the sixth leading cause of death by
disease in the United States. The overall incidence of
noninsulin-dependent diabetes mellitus (Type 2 diabetes)
is approximately 20% of the United States population
over the age of 60, which translates to greater than 14
million people. Approximately 800,000 new cases are
diagnosed each year.1,2
dipeptidylpeptidase IV (DPP-IV), a highly specialized
aminopeptidase that removes dipeptides only from pro-
teins containing an N-terminal penultimate proline or
alanine.10 Therefore, agents that inhibit DPP-IV should
increase the circulation levels of endogenous GLP-1 and
ultimately lower blood glucose levels.11
As part of our high capacity screening e€orts, the iso-
quinoline derivative SDZ 029-576 (1) was identi®ed as an
inhibitor of DPP-IV. It is selective when compared to
PPCE, APP, and Trypsin and possesses a mixed inhibition
kinetic pro®le, which increases Km and reduces Vmax. A
preliminary SAR study explored some replacements of the
ester moiety and selected aryl substitutions but primarily
focused on the generation of a library of 4-acetic acid
amide derivatives of 1.12 Here we wished to further
explore the e€ects of subtle variations to the functional
groups at the 1- and 4-positions in addition to the oxy
substitution of the benzene ring in an e€ort to increase
potency of the lead structure.
Type 2 diabetes is a progressive disease characterized by
impaired insulin secretion by b-cells and glucagon secre-
tion by the a-cells as well as insulin resistance in skeletal
muscle and adipose tissue. This leads to increased fatty
acid ¯ux to the liver which stimulates lipoprotein produc-
tion. The resulting dislipidemia leads to macrovascular
complications such as atherosclerosis and stroke.
Recently, it has been demonstrated that injection of glu-
cagon-like peptide-1 (GLP-1) in man shows promise as a
therapeutic approach to Type 2 diabetes by its favorable
actions on insulin and glucagon secretion, peripheral
glucose disposal, and gastric emptying.3 6 GLP-1 is a 30
amino acid peptide secreted by endocrine (L) cells of the
distal intestinal mucosa in response to oral glucose
loads or mixed meals. GLP-1 reaches peak plasma con-
centrations within 15±30 min; however, it has been
shown that human plasma degrades the active GLP-1 (7±
36) amide to the terminally truncated inactive form
GLP-1 (9±36) amide with a half-life of about 1±2 min.7 9
Chemistry
The enzyme responsible for cleaving the N-terminal
His-Ala fragment from GLP-1 has been identi®ed as
The chain-shortened analogues where the carboxylate is
attached directly to the heterocycle were prepared by
*Corresponding author. E-mail: gary.coppola@pharm.novartis.com
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00286-9

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G. M. Coppola et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1555±1558
the acylation of 2 with phthaloylglycine followed by a
Bischler±Napieralski cyclization to 3 (n=1). Aromati-
zation with MnO2 then hydrazinolysis of the phthaloyl
group a€orded the products (Scheme 1). The free amine
was Boc-protected for puri®cation purposes then the Boc
group was removed to give pure 5. This general method
also allows for the preparation of the homologated
amine derivative 5c (n=2) simply by acylating 2 with 3-
phthalimidopropionic acid.13
ester produced the yellow crystalline 17 in good yield.
Reaction of 17 with ammonium hydroxide or propyl-
amine provided amides 18 and 19 in high yield.
Removal of the Boc group a€orded the desired products
(Scheme 4). Curtius rearrangement of 16 in the presence
of ethanol or t-butanol a€orded carbamates 23 and 24.
Removal of the Boc group from 23 gave amine 25,
which can be considered an analogue of 1 where the
CH2 of the acetic acid is replaced with NH.
The chain-lengthened analogue 11 was readily available
from 4b using Wittig methodology (Scheme 2). The
requisite aldehyde 7 was prepared by reduction of the ester
function of 4b to alcohol 6 followed by oxidation with
MnO2. A Horner±Emmons ole®nation of 7 furnished a,b-
unsaturated ester 8, which was then hydrogenated to
propionate 9. Removal of the Boc group furnished the
desired product 11.
Biology
Compound e€ects on DPP-IV activity in extracts of
human colonic carcinoma cells were assessed as described
by Hughes.14 In brief, the human colonic carcinoma cell
line Caco-2 was obtained from the American Type Cul-
ture Collection (ATCC HTB 37). Di€erentiation of the
cells to induce DPP-IV expression was accomplished as
described by Reisher.15 Cell extract is prepared from
cells solubilized in 10 mM Tris±HCl, 0.15 M NaCl, 0.04
t.i.u. aprotinin, 0.5% nonidet-P40, pH 8.0, which was
centrifuged at 35,000 g for 30 min at 4 ꢀC to remove cell
debris. The assay was conducted by adding 20 mg solu-
bilized Caco-2 protein, diluted to a ®nal volume of 125
N-methylated analogues 14 and 15 were prepared from the
1-chloromethylisoquinoline 13 according to previously
published procedures13 (Scheme 3).
Amides 21 and 22 were prepared from the versatile acid
intermediate 16. Activation of 16 as a p-nitrophenyl
Scheme 1. (a) N-Phthaloylglycine, Et3N, EDC, HOAt, DMF; (b) POCl3, DMF 80 ꢀC; (c) MnO2, benzene re¯ux; (d) N2H4, CH2Cl2:EtOH (10:1); (e)
BoC2O, Et3N, CH2Cl2; (f) HCl (g), EtOH:CH2Cl2 (8:2).
Scheme 2. (a) [(Et)2AlH2]Na, ether, 0±5 ꢀC (98%); (b) MnO2, CH2Cl2 (95%); (c) triethyl phosphonoacetate, NaH THF (47%); 9d) H2, 5% Pd/C,
EtOH (1 atm) (89%); (e) CF3COOH, CH2Cl2.
Scheme 3. (a) NCS, AlBN, CCl4; (b) methylamine or dimethylamine, THF.

G. M. Coppola et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1555±1558
1557
Scheme 4. (a) NaOH, EtOH, rt, 18 h (86%); (b) 4-nitrophenyltri¯uoroacetate, pyridine, rt, 18 h (62%); (c) NH4OH or propylamine, dioxane, 3 h;
(d) HCl (g), EtOH; (e) DPPA, Et3N, EtOH or t-BuOH, 80 ꢀC.
mL in assay bu€er (25 mM Tris±HCl pH 7.4, 140 mM
NaCl, 10 mM KCl, 1% bovine serum albumin) to
microtiter plate wells. The reaction was initiated by
adding 25 mL of 1 mM substrate (H-Alanine-Proline-
pNA; pNA is p-nitroaniline). The reaction was run at
room temperature for 10 min after which time a 19 mL
volume of 25% glacial acetic acid was added to stop the
reaction. Where indicated, compounds were added as 30
mL additions and the assay bu€er volume was reduced
to 95 mL. A standard curve of free p-nitroaniline was
generated using 0±500 mM solutions of free pNA in assay
bu€er. The curve generated was linear and was used for
interpolation of substrate consumption (catalytic activity
in nmoles substrate cleaved/min). The endpoint is deter-
mined by measuring absorbance at 405 nm in a Molecular
Devices UV Max microtiter plate reader. IC50 values were
calculated using a four-parameter logistic equation
(MicroCal Origin software package) in which the upper
and lower asymptotes were ®xed at 0 and 100, respectively.
Table 1. In vitro DPP-IV inhibitory activity of 1-aminoalk-
ylisoquinoline-4-carboxylates
Compd
R1
R2
R3
H
R4
n
di-Salt IC50 (mM)
5a
5b
5c
5d
5e
5f
5g
5h
5i
H
H
H
H
H
OCH3
OCH3 OCH3
OCH3 OCH3
OCH3
OEt
OCH3
OCH3
OCH3
H
H
H
H
H
H
H
H
OCH3
OCH3
H
1
1
2
1
1
1
1
1
1
1
1
HCl
HCl
TFA
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
207
3.4
746
6.7
4.7
8.4
14
0.32
2.4
OEt
OCH3
OPr
OH
H
H
H
H
OCH3
OCH3 OCH3 OCH3
H
H
5j
5k
18
1.1
OCH3 OCH3 OCH3
10
11
14
15
20
21
22
25
26a
27b
1
TFA
TFA
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
18
52.6
731
948
103
170
51.4
2.3
31.8
Within the series of compounds in Table 1 it is evident
that a primary amine is required for activity. Mono-
and di-methylated analogues 14 and 15 are not active.
Lengthening the carbon chain by one methylene (5c) also
reduces potency relative to 1. At the 4-position, chain
length is also important. Lengthening the chain by one
methylene unit (11) results in a 3-fold loss of activity
whereas shortening the chain (5b) increases potency by a
factor of ®ve. Replacing the ester with an acid (20), alde-
hyde (27) or primary amide (21) results in signi®cant loss
of activity whereas the methanol derivative 26 is only
about half as potent as 1.
277
17
aThis compound was prepared from 6 by removal of the Boc group
with HCl.
bThis compound was prepared from 7 by removal of the Boc group
with HCl.
is 53 times as potent as 1. It was also found that repla-
cing the methylene of the acetic acid of 1 with an NH
(25) increases potency 7-fold.
One can take advantage of the oxygenation pattern
around the benzene ring of the heterocycle to further
increase DPP-IV inhibitory activity in this series (Table 1).
The optimum substitution is 6,8-dimethoxy which
results in compound 5h with an IC50 of 0.32 mM which
References and Notes
1. American Diabetes Association, http://www.diabetes.org/
ada/facts.asp.

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