Concise and efficient synthesis of highly potent and selective dipeptidyl peptidase II inhibitors

Article abstract of DOI:10.1080/00397910701693633

Highly potent and selective DPP II inhibitors N'-(4-Chlorobenzyl)-N'- methyl-4-oxo-4-(1-piperidinyl)-1,3-(S)-butane-diamine dihydrochloride 1 and N'-(4-chlorobenzyl)-4-oxo-4-(1-piperidinyl)-1,3-(S)-butanediamine dihydrochloride 2 have been efficiently synthesized starting from L-glutamine. A short and high yielding route with simple isolation techniques has been disclosed. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701693633

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Concise and Efficient Synthesis of Highly
Potent and Selective Dipeptidyl Peptidase II
Inhibitors
Abdul M. Rasheed a , Rambabu Namala a , Narendra Manne a , Sreelatha
Vanjivaka a , Ravi Dhamjewar a & Gopalan Balasubramanian a
a Matrix Laboratories, Hyderabad, India
Version of record first published: 18 Jan 2008.
To cite this article: Abdul M. Rasheed, Rambabu Namala, Narendra Manne, Sreelatha Vanjivaka, Ravi
Dhamjewar & Gopalan Balasubramanian (2008): Concise and Efficient Synthesis of Highly Potent and
Selective Dipeptidyl Peptidase II Inhibitors, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 38:2, 162-169
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Synthetic Communicationsw, 38: 162–169, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701693633
Concise and Efficient Synthesis of Highly
Potent and Selective Dipeptidyl Peptidase II
Inhibitors
M. Abdul Rasheed, Rambabu Namala, Narendra Manne,
Sreelatha Vanjivaka, Ravi Dhamjewar,
and Gopalan Balasubramanian
Matrix Laboratories, Hyderabad, India
Abstract: Highly potent and selective DPP II inhibitors N0-(4-Chlorobenzyl)-N0-
methyl-4-oxo-4-(1-piperidinyl)-1,3-(S)-butane-diamine dihydrochloride 1 and N0-(4-
chlorobenzyl)-4-oxo-4-(1-piperidinyl)-1,3-(S)-butanediamine dihydrochloride 2 have
been efficiently synthesized starting from L-glutamine. A short and high yielding
route with simple isolation techniques has been disclosed.
Keywords: DPP II inhibitors, L-glutamine, Hoffmann rearrangement, reductive
amination
Dipeptidyl peptidases (DPPs) sequentially release dipeptides from polypep-
tides. Among these enzymes, DPP II (EC 3.4.14.2) and DPP IV (EC
3.4.14.5) cause the release of N-terminal dipeptides containing proline or
alanine at the penultimate position. DPP II and DPP IV are similar with
respect to their substrate specificity but differ in other aspects. DPP IV sub-
strates that have recently received special attention are incretins, a class of
hormones involved in glucose homeostasis. Inhibition of DPP IV prolongs
the in vivo half-life of these incretins (GLP 1 and GIP), and therefore, inhibi-
tors can be valuable in the treatment of type 2 diabetes. Several DPP IV inhibi-
tors are currently under clinical evaluation in this field.[1–3]
Received July 2, 2007
Address correspondence to M. Abdul Rasheed, GVK Bioscience, IDA, Nacharam,
Hyderabad 500076, India. E-mail: abdul.rasheed@gvkbio.com
162

Dipeptidyl Peptidase II Inhibitors
163
Scheme 1. Most potent and selective DPP-II Inhibitors.
RESULTS AND DISCUSSION
We were not successful in synthesizing sufficient quantities of DPP II inhibi-
tors 1 and 2 known in the literature[4] (Figure 1) for our ongoing research
aimed at developing new DPP IV inhibitors. In our hands, the process
suffered from low yields and many column purifications. At this point, we
felt it necessary to develop some other more practical and general route to syn-
thesize these inhibitors more efficiently. To start with, we selected the much
cheaper and abundantly available L-glutamine as our starting material,
whereas the original inventors started their synthesis with the much costlier
mono-Boc-protected L-2,4-diaminobutyric acid (Boc-L-Dab-OH). Our
synthesis started with L-glutamine 3, which was protected as its Boc derivative
4 by treatment with aq. NaOH and Boc anhydride in quantitative yields. The
Hoffmann rearrangement of the amide 4 with both [I,I-bis(triacetoxy)iodo]-
benzene (PIDA)[5a] and [I,I-bis(trifluoroacetoxy)iodo]benzene (PIFA)[5c]
resulted in low yields of the desired amine 5 and a substantial (ꢀ20–30%)
amount of the undesired cyclized product 6 (Scheme 1).
Having failed to enrich the yield of the desired compound 5, we envisaged
formation of amide 7 from carboxylic acid 4 followed by Hoffman rearrange-
ment reaction. Thus, the amide 4 on treatment with dicyclohexylcarbodiimide
(DCC) or N-ethyl-N0-(3-dimethylaminopropyl)carbodiimide (EDC) (both
showed similar results), HOBt, and piperidine in acetonitrile resulted in the
formation of the amide 7 in 80% yield (Scheme 2). Amide 7 on treatment
Figure 1. (a) NaOH/(BOC)2O, 08C to rt, 4 h 87%; (b) Phl(OAc)2, EtOAc, CH3CN,
H2O/Phl(OCOCF3)2, CH3CN, H2O, 58C to rt, 4 h.

164
M. A. Rasheed et al.
Scheme 2. (a) DCC or EDC, HOBt, Et3N, DMF, rt, 81% (b) Phl(OCOCF3)2, H2O,
CH3CN, rt, 83% (c) 4-Cl-PhCHO, NaCNBH3, AcOH, MeOH, 08C to rt, 85% (d) 3N
HCl/EtOAc, 08C to rt, 92–95% (e) Paraformaldehyde, NaCNBH3, AcOH, r.t 84%.
with both PIDA and PIFA in a suitable solvent system afforded amine 8 in
77% yield. The cyclization product 6 was not observed in either of these
two reactions. The amine, on reductive amination with 4-chlorobenzaldehyde
and NaCNBH3 in methanol, yielded compound 9 in 90% yield. Boc removal
from compound 9 with 3 N HCl in ethyl acetate at ambient temperature
afforded the desired dihydrochloride salt 1 in quantitative yields. Compound
9 on treatment with paraformaldehyde and NaCNBH3 in acetic acid–
methanol, afforded compound 10. The Boc deprotection of compound 10
with 3 N HCl in ethyl acetate afforded dihydrochloride salt 2 in 75% yield
(for two steps). The spectral data of compounds 1 and 2 are in excellent
agreement with the reported values.
In conclusion, we have demonstrated a more practical, nonchromato-
graphic, high-yielding, and shorter route for the synthesis of DPP II inhibitors
starting from the much cheaper and abundantly available L-glutamine.
EXPERIMENTAL
All chemicals were purchased from Sigma-Aldrich or Across. Solvents were
dried or distilled prior to use.
Characterization of all compounds was done with 1H NMR and mass spec-
trometry. 1H NMR spectra were recorded on a Bruker Avance 300 spectrometer

Dipeptidyl Peptidase II Inhibitors
165
(300 MHz). Electrospray (ESþ) mass spectra were acquired on an ion trap mass
spectrometer. Purity was verified using two diverse high performance liquid
chromatography (HPLC) systems using mass and ultra violet (UV) detection.
Reversed-phase HPLC was run on a Alliance Waters instrument (model 2695)
equipped with Inertsil ODS column 3 V, 250 ꢀ 4.6 mm, 5 mm, and UV
detector [20–80% acetonitrile (ACN) and phosphate buffer (pH ¼ 3), 40 min,
218 nm, 0.5 mL/min]. Elemental analyses were performed on a ThermoFinni-
gan instrument and were within 0.4% of the theoretical values.
(2S)-5-Amino-2-[(tert-butoxycarbonyl)amino]-5-oxopentanoic
Acid (4)
A solution of di-tert-butyl dicarbonate [(Boc)2O] (14.0 mL, 60 mmol) in
dioxane (40 mL) was added to an ice-cold, magnetically stirred solution of
L-glutamine 3 (5.84 g, 40 mmol) in 1 N sodium hydroxide (84 mL) by
means of an addition funnel. The two-phase mixture was stirred at 58C for
30 min and then allowed to warm to rt over 4 h, at which time thin-layer chrom-
atography (TLC) analysis showed completion of the reaction. The mixture was
concentrated to half its original volume by rotary evaporation at 358C, cooled
in an ice-water bath, acidified to pH 2–3 by the slow addition of 1 N potassium
bisulfate (90 mL), and then extracted with ethyl acetate. The combined extracts
were dried over anhydrous sodium sulfate, filtered, and concentrated under
reduced pressure to give Boc-L-glutamine 4 (8.6 g) as a colorless solid in
87% yield. Mp 48.0–49.88C; m/z (M þ 1) 247; 1H NMR (CDCl3) 300 MHz
d 6.36 (bs, 1H), 6.20 (bs, 1H), 5.65 (d, J ¼ 6.0 Hz, 1H), 4.35–4.20 (m, 1H),
2.60–2.36 (m, 2H), 2.25–2.0 (m, 2H), 1.44 (s, 9H). Elem. anal. for
C10H18N2O5: C, 39.98; H, 7.54; N, 11.32.
tert-Butyl-[(1S)-4-amino-4-oxo-1-(piperidin-1-ylcarbonyl)butyl]
Carbamate (5)
[I,I-Bis(triacetoxy)iodo]benzene (3.86 g, 12.0 mmol) was added to a stirred
mixture of compound 4 (2.46 g, 10.0 mmol), ethyl acetate (10 mL), aceto-
nitrile (10 mL), and water (10 mL) cooled at 108C and the reaction mixture
was gradually warmed to rt and stirred for 4 h. The volatiles were removed
with a rotary evaporator. The aqueous layer was extracted with EtOAc. The
combined organic layer was washed with brine, dried over anhydrous
Na2SO4, and evaporated under reduced pressure to obtain a crude reaction
mixture, which was purified by column chromatography to obtain
compound 5 (0.1 g) as a viscous liquid. m/z (M þ 1) 219; 1H NMR
(CDCl3) 300 MHz d 5.58 (bs, 1H), 4.35–4.25 (m, 1H), 3.5 (t, J ¼ 6.5 Hz,
1H), 2.50–2.40 (m, 1H), 2.10–2.0 (m, 1H), 1.28 (s, 9H). Compound 5 also
was isolated as off-white solid (0.12 g). m/z (M þ 1) 201; 1H NMR

166
M. A. Rasheed et al.
(CDCl3) 300 MHz d 5.80 (bs, 1H), 5.09 (bs, 1H), 4.21–4.19 (m, 1H),
3.43–3.30 (m, 2H), 2.53–2.15 (m, 1H), 2.07–1.90 (m, 1H), 1.45 (s, 9H).
Elem. anal. for C9H18N2O4: C, 49.23; H, 8.36; N, 12.78.
tert-Butyl-[(1S)-4-amino-4-oxo-1-(piperidin-1-ylcarbonyl)butyl]
Carbamate (7)
Et3N (3.5 mL, 25 mmol), HOBt (2.4 g, 18 mmol), DCC (4.0 g, 18 mmol), and
piperidine (2 mL, 20 mmol) were sequentially added to a stirred solution of
Boc-L-glutamine 4 (4.0 g, 16.3 mmol) in DMF (33 mL) cooled at ice-bath
temperature. The reaction mixture was gradually warmed to rt and stirred
for 16 h. The reaction mixture was diluted with EtOAc and filtered through
a small pad of Celitew. The filtrate was washed with water and brine, then
dried over anhydrous Na2SO4. The solvent was evaporated under reduced
pressure to obtain a residue, which was triturated with ether, and the
combined ether fractions were evaporated under reduced pressure to obtain
the product, which was passed through a small pad of silica gel (60–120
mesh) using a 1:1 mixture of EtOAc and hexane to obtain compound 7
(5.5 g) in 81% yield as off-white solid. Mp 136.8–139.38C; m/z (M þ 1)
1
314; H NMR (CDCl3) 300 MHz d 6.57 (bs, 1H), 5.77 (d, J ¼ 8.0 Hz, 1H),
5.36 (bs, 1H), 4.65–4.55 (m, 1H), 3.61–3.48 (m, 4H), 2.43–2.22 (m, 2H),
2.10–2.0 (m, 1H), 1.75–1.40 (m, 7H), 1.44 (s, 9H). Elem. anal. for
C15H27N3O4: C, 57.28; H, 8.91; N, 13.27.
tert-Butyl-[(1S)-3-amino-1-(piperidin-1-ylcarbonyl)propyl]
Carbamate (8)
Deionized water (8 mL) was added to a stirred solution of [I,I-bis(trifluoroa-
cetoxy)iodo]benzene (3.36 g, 7.8 mmol) covered with aluminum foil in aceto-
nitrile (8 mL). A solution of carboxamide 7 (1.9 g, 6.0 mmol) in acetonitrile
(8 mL) was added, and the reaction mixture was stirred for 4 h. The aceto-
nitrile was removed with a rotary evaporator. The aqueous layer was cooled
to ice-bath temperature and acidified to pH 2–3 with 10 N HCl and
extracted with diethyl ether. The aqueous layer was cooled again to ice-bath
temperature, basified to pH 12–13 with 50% aq. NaOH solution, and
extracted with EtOAc. The combined organic layer was washed with brine,
dried over anhydrous Na2SO4, and evaporated under reduced pressure to
obtain amine 8 (1.4 g) as a viscous liquid in 83% yield. m/z (M þ 1) 286;
1H NMR (CDCl3) 300 MHz d 5.60 (d, J ¼ 8.4 Hz, 1H), 4.80–4.68 (m, 1H),
3.67–3.30 (m, 4H), 2.90–2.70 (m, 2H), 1.90–1.40 (m, 8H), 1.44 (s, 9H).
Elem. anal. for C14H27N3O3: C, 58.67; H, 9.64; N, 14.59.

Dipeptidyl Peptidase II Inhibitors
167
tert-Butyl-(S)-4-(4-chlorobenzylamino)-1-oxo-1-(piperidine-1-yl)
butan-2-yl Carbamate (9)
Acetic acid (1.0 mL, 17.5 mmol), 4-chlorobenzaldehyde (0.49 g, 3.5 mmol),
and NaCNBH3 (0.22 g, 3.5 mmol) were added to a stirred solution of 8
(1.0 g, 3.5 mmol) in methanol (14 mL) cooled at 08C. The reaction mixture
was gradually warmed to rt and stirred for 16 h. The volatiles were
removed under reduced pressure; the residue was diluted with 2 N HCl
(10 mL) and extracted with diethyl ether. The aqueous layer was cooled to
ice-bath temperature, basified to pH 12–13 with aq. 50% sodium hydroxide
solution, and extracted with ethyl acetate. The combined organic layer was
washed with water and brine, then dried over anhydrous Na2SO4. The
solvent was evaporated under reduced pressure to obtain compound 9
(1.2 g) as a viscous liquid in 85% yield. m/z (M þ 1) 410; 1H NMR
(CDCl3) 300 MHz d 7.32–7.18 (m, 4H), 5.63 (d, J ¼ 8.2 Hz, 1H), 4.75–
4.65 (m, 1H), 3.74 (d, J ¼ 6.2 Hz, 2H), 3.60–3.35 (m, 4H), 2.85–2.68
(m, 2H), 2.15–2.05 (m, 1H), 1.90–1.80 (m, 1H), 1.75–1.50 (m, 6H), 1.43
(s, 9H). Elem. anal. for C21H32ClN3O3: C, 61.62; H, 7.93; N, 10.36.
(3S)-N1-(4-Chlorobenzyl)-4-oxo-4-piperidin-1-ylbutane-1,3-
diamine (1)
3 N HCl (5 mL) was added to compound 9 (0.35 g, 0.86 mmol) placed at ice-
bath temperature, and the resultant mixture was stirred at rt for 2 h. The
volatiles were removed under reduced pressure, and the product was triturated
several times with diethyl ether to obtain compound 1 (0.31 g) in 95% yield.
1
m/z (M þ 1) 310; H NMR (DMSO-d6) 300 MHz d 9.85 (bs, 1H), 9.62 (bs,
1H), 8.40 (bs, 3H), 7.64 (d, J ¼ 8.5 Hz, 2H), 7.52 (d, J ¼ 8.5 Hz, 2H),
4.65–4.53 (m, 1H), 4.14 (bs, 2H), 3.60–3.34 (m, 4H), 3.17–3.03 (m, 1H),
3.03–2.90 (m, 1H), 2.30–2.05 (m, 2H), 1.68–1.40 (m, 6H). Elem. anal. for
C16H24ClN3O: C, 62.17; H, 7.97; N, 13.45.
tert-Butyl-(S)-4-(N-chlorobenzyl)-N-methylamino)-1-oxo-1-
(piperidine-1-yl)butan-2-yl Carbamate (10)
Paraformaldehyde (0.15 g) and NaCNBH3 (70 mg, 1.1 mmol) were added to a
stirred solution of compound 9 (0.15 g, 0.37 mmol) in methanol (1.5 mL) and
acetic acid (0.11 mL) cooled at 10–158C. The reaction mixture was stirred for
16 h, and the volatiles were removed under reduced pressure. The residue was
diluted with 2 N HCl (4 mL) and extracted with diethyl ether. The aqueous
layer was cooled to ice-bath temperature, basified to pH 12–13 with aq.
50% NaOH solution, and extracted with EtOAc. The combined organic

168
M. A. Rasheed et al.
layer were washed with brine and dried over anhydrous Na2SO4, and the
solvent was removed under reduced pressure to obtain compound 10
(0.13 g) in 84% yield as a viscous liquid. This compound was used for the
deprotection of the Boc group without further purification and
characterization.
(3S)-N1-(4-chlorobenzyl)-N1-methyl-4-oxo-4-piperidin-1-ylbutane-
1,3-diamine (2)
3 N HCl (1 mL) was added to compound 10 (0.1 g, 0.24 mmol) placed in a ice
bath, and the resultant mixture was stirred at rt for 2 h. The volatiles were
removed under reduced pressure, and the product was triturated several
times with diethyl ether to obtain compound 2 (0.11 g) in 92% yield. The
spectral data of this compound is in excellent agreement with the reported
compound.[4]
ACKNOWLEDGMENT
Authors thank Sreedhara Swamy and Ishtiyaque Ahmad for the in vitro
analysis of the compounds.
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