Synthesis of 4-substituted-3-aminopiperidin-2-ones: Application to the synthesis of a conformationally constrained tetrapeptide N-acetyl-Ser-Asp-Lys- Pro

Article abstract of DOI:10.1021/jo050736k

A new and practical synthetic strategy is developed for the synthesis of six-membered lactam-bridged dipeptides, 4-substituted-3-aminopiperidin-2-ones, featuring two key steps: (a) a diastereoselective addition of cuprate to (E)-α,β-unsaturated ester (3)

Full text of DOI:10.1021/jo050736k

Synthesis of 4-Substituted-3-aminopiperidin-2-ones: Application to
the Synthesis of a Conformationally Constrained Tetrapeptide
N-Acetyl-Ser-Asp-Lys-Pro
Sukeerthi Kumar, Ce´line Flamant-Robin, Qian Wang, Ange`le Chiaroni, and N. Andre´ Sasaki*
Institut de Chimie des Substances Naturelles, CNRS, 91198 Gif-sur-Yvette Cedex, France
andre.sasaki@icsn.cnrs-gif.fr
Received April 13, 2005
A new and practical synthetic strategy is developed for the synthesis of six-membered lactam-
bridged dipeptides, 4-substituted-3-aminopiperidin-2-ones, featuring two key steps: (a) a diaste-
reoselective addition of cuprate to (E)-R,â-unsaturated ester (3) and (b) racemization-free reductive
amination. On the basis of this methodology, conformationally constrained tetrapeptide N-acetyl-
Ser-Asp-Lys-Pro (AcSDKP) (2) has been successfully synthesized from 3-amino-4-vinylpiperidin-
2-one (22).
Introduction
Therefore, synthesis of novel Freidinger lactams is cur-
rently an area of intensive research in the field of peptide
and medicinal chemistry, and several types of Freidinger
lactams have been synthesized.4-7 Although 3-aminopi-
The design and synthesis of conformationally con-
strained peptidomimetics is an important approach in
searching for the bioactive compounds with improved
biological potency, selectivity, and metabolic stability
relative to endogenous linear peptides.1-3 Among the
numerous strategies developed for reducing the confor-
mational mobility, tethering the backbone side chain with
the neighboring amide nitrogen into a so-called “Fre-
idinger” lactam4 has proven useful for the design of a
variety of medicinally relevant enzyme inhibitors,5 es-
pecially in the case of the peptidase/protease inhibitors.6a
(5) (a) Samanen, J.; Hempel, J. C.; Narindary, D.; Regoli, D. In
Chemistry and Bilogy: Proceedings of the Tenth American Peptide
Symposium; Marshall, G. R., Ed.; ESCOM: Leiden, The Netherlands,
1988; pp 123-125. (b) Samanen, J.; Cash, T.; Narindray, D.; Brandeis,
E.; Adams, W., Jr.; Weideman, H.; Yellin, T. J. Med. Chem. 1991, 34,
3036-3043. (c) Ede, N.; Rale, I. D.; Hearn, M. T. W. Tetrahedron Lett.
1990, 31, 6071-6074.
(6) (a) Wolfe, M. S.; Dutta, D.; Aube´, J. J. Org. Chem. 1997, 62, 654-
663. Ref 6 cited in (b) Zydowky, T. M.; Dellaria, J. F., Jr.; Nellans, H.
N. J. Org. Chem. 1988, 53, 5607-5616. (c) Wolf, J.-P.; Rapoport, H. J.
Org. Chem. 1989, 54, 3164-3173. (d) Rodriguez, R.; Estiarte, M. A.;
Diez, A.; Rubiralta, M.; Colell, A.; Garcia-Ruiz, C.; Fernandes-C, J. C.
Tetrahedron 1996, 52, 7727-7736. (e) Rodriguez, R.; Deiz, A.; Rubi-
ralta, M.; Giralta, E. Heterocycles 1996, 43, 513-517. (f) Estiarte, M.
A.; de Souza, M. V. N.; Diez, A. Tetrahedron 1999, 55, 10173-10186.
(g) Estiarte, M. A.; Diez, A.; Rubiralta, M.; Jackson, R. F. W.
Tetrahedron 2001, 57, 157-161. (h) Piro, J.; Rubiralta, M.; Giralta,
E.; Diez, A. Tetrahedron Lett. 2001, 42, 871-873. (i) Koulocheri, S.
D.; Magiatis, P.; Haroutounian, S. A. J. Org. Chem. 2001, 66, 7915-
7918. (j) De Borggraeve, W. M.; Rombouts, F. J. R.; Van der Eycken,
E. V.; Toppet, S. M.; Hoornaert, G. J. Tetrahedron Lett. 2001, 42, 5693-
5695. (k) Hoffmann, T.; Waibel, R.; Gmeiner, P. J. Org. Chem. 2003,
68, 62-69. (l) Tanaka, K.; Nemoto, H.; Sawanishi, H. Tetrahedron:
Asymmetry 2005, 16, 809-815. (m) de Laszlo, S. E.; Bush, B. L.; Doyle,
J. J.; Greenlee, W. J.; Hangauer, D. G.; Halgren, T. A.; Lynch, R. J.;
Schorn, T. W.; Siegl. P. K. S. J. Med. Chem. 1992, 35, 833-846. (n)
Rodriguez, R.; Vinets, I.; Diez, A.; Rubiralta, M. Synth. Commun. 1996,
26, 3029-3059. (o) Weber, K.; Ohnmacht, U.; Gmeiner, P. J. Org.
Chem. 2000, 65, 7406-7416. (p) Piro, J.; Forns, P.; Blanchet, J.; Bonin,
M.; Micouin, L.; Diez, A. Tetrahedron: Asymmetry 2002, 13, 995-1004.
(7) Preliminary result dealing with the synthesis of 3-amino-4-
methylpiperdin-2-one has been published. Flamant-Robin, C.; Wang,
Q.; Sasaki, N. A. Tetrahedron Lett. 2001, 42, 8483-8484.
(1) (a) Olson, G. L.; Bolin, D. R.; Bonner, M. P.; Bos, M.; Cook, C.
M.; Fry, D. C.; Graves, B. J.; Hatada, M.; Hill, D. E.; Kahn, M.;
Madison, V. S.; Rusiecki, V. K.; Sarabu, R.; Sepinwall, J.; Vincent, G.
P.; Voss, M. E. J. Med. Chem. 1993, 3039-3049. (b) Hruby, V. J. Life
Sci. 1982, 31, 189. (c) Hruby, V. J.; Al-Obeidi, F.; Kazmierski, W.
Biochem. J. 1990, 268, 249. (d) Giannis, A.; Kolter, T. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1244-1267. (e) Gante, J. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1699-1720. (f) Liskamp, R. M. J. Recl. Trav. Chim.
Pays-Bas 1994, 113, 1-19.
(2) (a) Hruby, V. J. Nat. Rev. Drug Design 2002, 1, 847. (b) Nagai,
U.; Sato, K. Tetrahedron Lett. 1985, 26, 647. (c) Nagai, U.; Sato, K.;
Nakamura, R.; Kato, R. Tetrahedron 1993, 49, 3577.
(3) (a) Hanessian, S.; Smith-MacNaughton, G.; Lambort, H. G.;
Lubell, W. D. Tetrahedron 1993, 53, 12789. (b) Halab, L.; Gosselin,
F.; Lubell, W. D. Biopolymers, Pept. Sci. 2000, 55, 101.
(4) (a) Freidinger, R. M.; Veber, D. F.; Perlow, D. S.; Brooks, J. R.;
Saperstein, R. Science 1980, 210, 656-658. (b) Freidinger, R. M.;
Perlow, D.; Veber, D. F. J. Org. Chem. 1982, 47, 104-109. (c) Veber,
D. F.; Freidinger, R. M. Trends Neurosci. 1985, 392-396. (d) Fre-
idinger, R. M. In Peptide: Synthesis, Structure, Function; Rich, D. H.,
Gross, E., Eds.; Pierce Chemical Co.: Rockford, IL, 1981; pp 673-683.
(e) Freidinger, R. M. J. Med.Chem. 2003, 46, 1-14.
10.1021/jo050736k CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/22/2005
5946
J. Org. Chem. 2005, 70, 5946-5953

Synthesis of 4-Substituted-3-aminopiperidin-2-ones
SCHEME 2. Synthesis of Aldehydes 6a, 6b, and
6ca
FIGURE 1.
SCHEME 1. Retrosynthetic Analysis for
Lactam-Bridged Dipeptides
a Reagents and conditions: (i) R2CuLi (R ) CH3 for 4a; R )
CHdCH2 for 4c), (CH3)3SiCl, THF, -78 °C to room temperature;
PhMgBr, Cu(I) for 4b, (CH3)3SiCl, THF, -78 °C to room temper-
ature; (ii) LiAlH4, THF, room temperature, 2 h; (iii) (COCl)2,
DMSO, CH2Cl2, -78 °C; Et3N.
syn 4a and 4c, respectively,8 in good yields and with
excellent diastereofacial selectivities. Curiously, diphe-
nyllithium cuprate failed to react with 3 under identical
conditions. After much experimentation, it was found
that the 1,4-Michael addition of phenylmagnesium bro-
mide in the presence of Cu(I), according to Hruby,9
occurred smoothly. Under these conditions, the desired
syn 4b was obtained as a single diastereomer in 64%
isolated yield. Lithium aluminum hydride reduction of
esters 4a-4c10 and subsequent Swern oxidation of alco-
hols 5a-5c gave the corresponding aldehydes 6a-6c,
respectively.
Reductive amination of aldehyde 6a with L-phenyla-
lanine methyl ester 7a (sodium triacetoxyborohydride,
THF) proceeded smoothly to provide secondary amine 8a
in 90% yield (Scheme 3). After N-protection of 8a with
CbzCl, the resulting carbamate 9a was subjected to Jones
oxidation to afford directly carboxylic acid 10a. Activation
of the carboxylic acid as pentafluorophenyl ester 11a
followed by tandem N-deprotection/lactamization under
catalytic hydrogenolysis conditions provided the desired
piperidin-2-one (12a)7 in 79% yield. Compound 12b was
prepared following the same synthetic scheme as de-
scribed above for 12a, starting from aldehyde 6b and
L-leucine methyl ester 7b (Scheme 3). The stereochem-
istry of 12a has been confirmed by X-ray analysis.
peridin-2-one is known, to the best of our knowledge a
few syntheses have been reported for 1,4-disubstituted-
3-aminopiperidin-2-one (1) (Figure 1).6l-o,7 We have been
interested in developing a short asymmetric synthesis
of this type of lactam based on the following reasoning.
The incorporation of a substituent at the C-4 position
would not only introduce an additional point of diversity
but also influence the conformation of the molecule by
modulating the bulkiness of the substituent as well as
the relative stereochemistry between C-3 and C-4. Be-
cause the side chains of amino acids often play important
roles in bioactivities of the peptide, we deemed it impor-
tant to develop a convergent synthesis that could allow
us to vary systematically the substituents (R, R1, R2) at
the periphery of the piperidin-2-one surrogate.
In this paper, we report a straightforward synthesis
of enantiomerically pure (3S,4R)-3-amino-4-alkyl(aryl)-
piperidin-2-ones in detail based on a strategy depicted
retrosynthetically in Scheme 1. In a forward sense,
lactam 1 was to be produced by a cycloamidation of amino
acid A that in turn could be obtained by a reductive
amination of amino aldehyde B and R-amino ester or
R-amino amide C. Compound B can be traced back to
Garner’s aldehyde, whereas C is commercially available.
The design and synthesis of a conformationally con-
strained analogue of N-acetyl-Ser-Asp-Lys-Pro (AcSDKP)
(2) based on this chemistry is also to be documented
(Figure 1).
Having developed the methodology for the synthesis
of lactam 12a and 12b, we turned our attention to the
synthesis of the 3-amino-4-vinylpiperidin-2-one system.
The presence of the vinyl function at the C-4 position of
the piperidin-2-one ring would allow us to introduce a
carboxylic acid required for the synthesis of the N-
AcSDKP analogue (Scheme 6) and other functionalities.
To further illustrate the generality of the present meth-
Results and Discussion
Synthesis of 4-Substituted-3-aminopiperidin-2-
one. Reductive amination of a suitably functionalized
amino aldehyde and an amino ester is the key step in
our planned synthesis of piperidin-2-one. The prerequi-
site amino aldehydes 6a-6c were synthesized following
literature procedure (Scheme 2). 1,4-Addition of lithium
dimethyl or divinyl cuprates to the enoate 3 derived from
serine in the presence of trimethylsilyl chloride furnished
(8) (a) Reetz, M. T. Angew. Chem., Int. Ed. Engl. 1991, 30, 1531-
1546. (b) Reetz, M. T. Chem. Rev. 1999, 1121-1162. (c) Hanessian S.;
Sumi, K. Synthesis 1991, 1083-1089. (d) Hanessian S.; Wang, W.; Gai,
Y. Tetrahedron Lett. 1996, 37, 7477-7480.
(9) Han, G.; Hruby, V. J. Tetrahedron Lett. 2001, 42, 4281-4283.
(10) Flamant-Robin, C.; Wang, Q.; Chiaroni, A.; Sasaki, N. A.
Tetrahedron 2002, 58, 10475-10484.
J. Org. Chem, Vol. 70, No. 15, 2005 5947

Kumar et al.
SCHEME 3. Synthesis of
SCHEME 4. Synthesis of
4-Substituted-3-aminopiperidin-2-one 12a and 12ba
3-Amino-4-vinylpiperidin-2-one 16a and 16ba
a Reagents and conditions: (i) NaBH(OAc)3, THF, room tem-
perature, 15 h; (ii) Cbz-Cl, Na2CO3, THF-H2O (3:1), room tem-
perature, 1 h; (iii) Jones reagent, acetone, 0 °C to room temper-
ature, 1 h; (iv) C6F5OH, EDC, CH2Cl2, 0 °C to room temperature,
2 h; (v) H2, 10% Pd/C, MeOH, 3 h.
a Reagents and conditions: (i) NaBH(OAc)3, THF, room tem-
perature, 15 h; (ii) Fmoc-Cl, 0.5M Na2CO3, THF-H2O (3:1), room
temperature, 3 h; (iii) Jones reagent, acetone, 0 °C to room
temperature, 3 h; (iv) (a) (C2H5)2NH, THF, 0 °C, 15 min, room
temperature, 6 h; (b) TBTU, HOBt, DIEA, DMF, room tempera-
ture, 24 h.
odology, a side chain functionalized amino acid, L-Lys-
(Cbz)OBn (7c), was employed as a reaction partner. Thus,
reductive amination of aldehyde 6c with L-Lys(Cbz)OBn
(7c) afforded amine 13a in 85% yield. Protection of the
secondary amine followed by Jones oxidation furnished
acid 15a in 73% yield. Removal of the Fmoc group with
diethylamine and subsequent intramolecular cyclization
(TBTU-HOBt-DIEA in DMF) provided lactam 16a in
88% yield (Scheme 4). Compound 16b was similarly
prepared in good overall yield.
Synthesis of Tetrapeptide 2, Analogue of N-
AcSDKP. The tetrapeptide N-acetyl-Ser-Asp-Lys-Pro
(AcSDKP), isolated from bone marrow,11 is present in
various tissues and biological fluids such as plasma,
urine, and circulating mononuclear cells of humans and
animals.12 It is recognized as a physiologic regulator of
hematopoiesis. It inhibits the proliferation of normal
hematopoietic stem cells and committed progenitors in
vivo as well as in vitro11,13 and consequently reduces the
damage to the stem cell compartment resulting from
treatment with chemotherapeutic agents or ionizing
radiations.14 It is well-known that AcSDKP is cleaved
from its precursor thymosin-â4, most likely by prolyl
oligopeptidase,15 and is hydrolyzed almost exclusively by
angiotensin converting enzyme (ACE) between the Asp-
Lys peptide bond.16 This tetrapeptide has a 4.5-min half-
life in the circulation and thus is probably released
continuously in its physiological condition.17 Another
novel biological function of AcSDKP as a mediator of
angiogenesis in vitro and in vivo was reported recently.18
(13) (a) Guigon, M.; Bonnet, D.; Lemoine, F.; et al. Exp. Hematol.
1990, 18, 1112-1115. (b) Bonnet, D.; Lemoine, F. M.; Pontvert-Delucq,
S.; Baillou, C.; Najman, A.; Guigon, M. Blood 1993, 82, 3307-3314.
(c) Cashman, J. D.; Eaves, A. C.; Eaves, C. J. Blood 1994, 84, 1534-
1542. (d) Jackson, J. D.; Yan, Y.; Ewel, C.; Talmage, J. E. Exp. Hematol.
1996, 24, 475-481. (e) Rousseau-Plasse, A.; Lenfant, M.; Potier, P.
Bioorg. Med. Chem. Lett. 1996, 4, 1113-1119. (f) Thierry, J.; Grillon,
C.; Gaudron, S.; Potier, P.; Riches, A.; Wdzieczak-Bakala, J. J. Pept.
Sci. 2001, 284-293.
(14) (a) Masse, A.; Ramirez, L. H.; Bindoula, G.; et al. Blood 1998,
91, 441-449. (b) Bogden, A. E.; Moreau, J. P.; Gamba-Vitalo, C.; et al.
Int. J. Cancer 1998, 76, 38-46. (c) Aidoudi, S.; Guigon, M.; Drouet,
V.; Caen, J. P.; Han, J. C. Int. J. Hematol. 1996, 68, 145-155. (d)
Watanabe, T.; Brown, G. S.; Kelsey, L. S. Exp. Hematol. 1996, 24, 713-
721.
(11) Lenfant, M.; Wdzieczak-Bakala, J.; Guittet, E.; Prome, J.-C.;
Sotty, D.; Frindel, E. Proc. Natl. Acad. Sci. U.S.A. 1989, 86, 779-782.
(12) (a) Pradelles, P.; Frobert, Y.; Cre´minon, C.; Ivonine, H.; Frindel,
E. FEBS Lett. 1991, 289, 171-175. (b) Pradelles, P.; Frobert, Y.;
Cre´minon, C.; Liozon, E.; Masse´, A.; Frindel, E. Biochem. Biophys. Res.
Commun. 1990, 170, 986-993.
(15) (a) Grillon, C.; Reiger, K.; Bakala, J.; et al. FEBS Lett. 1990,
274, 30-34. (b) Wdzieczak-Bakala, J.; Fache, M.-P.; Lenfant, M.; et
al. Leukemia 1990, 4, 235-237. (c) Cavasin, M. A.; Rhaleb N-E.; Yang,
X.-P.; Carretero O. A. Hypertension 2004, 43, 1140-1145.
5948 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of 4-Substituted-3-aminopiperidin-2-ones
SCHEME 5. Synthesis of Tripepde 26aa
SCHEME 6. Synthesis of Tetrapeptide 2, Analogue
of N-AcSDKPa
a Reagents and conditions: (i) EDC, HOBt, CH2Cl2, room
temperature, 24 h, 85%; (ii) Et2NH, THF, 0 °C, then room
temperature, 3 h, 96%; (iii) Ac2O, Et3N, DMAP, CH2Cl2, room
temperature, 24 h, 86%; (iv) NaIO4, RuCl3, CH3CN-CCl4-H2O
(2:2:3), room temperpature, 24 h, 75%; (v) (a) CF3COOH, room
temperature, 3 h; (b) H2, Pd/C, MeOH, room temperature, 4 h
(54%).
a Reagents and conditions: (i) NaBH(OAc)3, THF, room tem-
perature, 15 h, 74%; (ii) Fmoc-Cl, 0.5 M Na2CO3, THF-H2O (3:1),
room temperature, 2 h, 92%; (iii) Jones reagent, acetone, 0 °C to
room temperature, 3 h, 57%; (iv) (a) (C2H5)2NH, THF, 0 °C, 15
min, room temperature, 6 h; (b) TBTU, HOBt, DIEA, DMF, room
temperature, 24 h, 71%; (v) 3 M HCl-EtOAc, -50 °C, 2 h, 0 °C, 1
h, 67%; (vi) Boc-L-Ser(OBn)OH, EDC, HOBt, CH2Cl2, room tem-
perature, 24 h, 80%; (vii) 3 M HCl-EtOAc, -50 °C, 2 h, 0 °C, 1 h,
70%; (viii) Ac2O, Et3N, DMAP, CH2Cl2, room temperature, 24 h,
51%; (ix) NaIO4, RuCl3, CH3CN-CCl4-H2O (2:2:3), room temper-
ature, 24 h.
was designed wherein the â-carbon of the aspartic acid
and the adjacent amide nitrogen of the lysine were
connected via ethylene linkage producing a piperidin-2-
one unit. It was expected that such a cyclic lactam motif
should render the molecule more resistant to in vivo
enzymatic degradation because the cyclic scaffold can
shelter the cleavable amide bond from degradative pep-
tidases.
From the viewpoint of synthesis, dipeptide 16b is
appropriately functionalized for the synthesis of a diverse
set of conformationally constrained peptides by elonga-
tion at both the N- and the C-terminals. However, for
the synthesis of the specifically targeted N-AcSDKP
analogue (2), a more convergent synthesis is developed
featuring a key reductive amination of the aldehyde 6c
with a tert-butyl ester of ω-N-Cbz-Lys-Pro (17) that is
synthesized from ω-N-Cbz-N-Fmoc-Lys19 and proline tert-
butyl ester. Reductive amination between aldehyde 6c
and dipeptide amine 17 took place without event to
produce compound 18 in 74% yield. Protection of the
AcSDKP may have potential for the clinical treatment
of deficient angiogenesis-related diseases.
To increase the metabolite stability of AcSDKP and to
probe the bioactive conformation of AcSDKP, lactam 2
(16) (a) Hanesworth, J. M.; Sardinia, M. F.; Krebs, L. T.; Hall, K.
L.; Harding, J. W. J. Pharmacol. Exp. Ther. 1993, 266, 1036-1042.
(b) Azizi, M.; Rousseau, A.; Ezan, E.; et al. J. Clin. Invest. 1996, 97,
839-844. (c) Rousseau, A.; Michaud, A.; Chauvet, M.-T.; et al. J. Biol.
Chem. 1995, 270, 3656-3661.
(17) Aziz, M.; Ezan, E.; et al. Hypertension 1997, 30, 1015-1019.
(18) (a) Liu, J.-M.; Lawrence, F.; Kovacevic, M.; Bignon, J.; Pa-
padimitriou, E.; Lallemand, J. Y.; Katsoris, P.; Potier, P.; Fromes, Y.;
Wdzieczak-Bakala, J. Blood 2003, 101, 3014-3020. (b) Wang, D.;
Carretero, O. A.; Yang, X.-Y.; Rhaleb, N.-E.; Liu, Y.-H.; Liao, T.-D.;
Yang, X.-P. Am. J. Physiol.: Heart Circ. Physiol. 2004, 287, H2099-
H2105.
(19) Beyermann, M.; Bienert, M.; Niedrich, H. J. Org. Chem. 1990,
55, 721-728.
J. Org. Chem, Vol. 70, No. 15, 2005 5949

Kumar et al.
secondary amine (FmocCl, THF-H2O, Na2CO3) followed
by Jones oxidation of the N-Boc oxazolidine afforded acid
20. Removal of the N-Fmoc function (Et2NH, THF)
varying both the aldehyde and the R-amino ester or the
R-amino amide inputs in the reductive amination step.
On the basis of this synthetic strategy, synthesis of an
N-AcSDKP analogue is documented.
i
followed by lactamization (TBTU, HOBt, Pr2NEt) fur-
nished piperidin-2-one (21) in 71% yield. Selective re-
moval of the N-Boc function without affecting the tert-
butyl ester was realized under mild acidic conditions (3
M HCl-EtOAc at -50 °C for 2 h then at 0 °C for 1 h).
Coupling of the resulting amine 22 with Boc-L-Ser(OBn)-
OH afforded tetrapeptide 23 that was then converted to
the N-Ac derivative by a sequence of selective N-depro-
tection and acetylation under classic conditions (51%).
Oxidative cleavage of the vinyl group under Sharpless
conditions20 afforded the desired compound 26a together
with the benzoate 26b (1:1 ratio) resulting from the
concomitant oxidation of the benzyl ether group. The
O-benzyl protected serine was selected with the hope to
achieve, at the final stage of the synthesis, the simulta-
neous deprotection of the O-Bn and N-Cbz functions.
Unforturnately, this seemingly trivial transformation
was found to be more difficult than one may expect.
Indeed, our attempts to cleave the O-benzyl ether and
the N-Cbz protective group under various hydrogenolysis
conditions varying the catalysts [Pd/C, Pd(OH)2] and the
solvents (MeOH, EtOAC, room temperature, 1 atm) gave
a mixture of O-benzyl ether product and hydroxyamine.
Unfortunately, when we forced the hydrogenolysis condi-
tion under pressure (60 psi) and forced transfer hydro-
genolysis (cyclohexene/EtOH, PdCl2, reflux and Zn/HCO2-
NH4, MeOH, rt), it resulted in complete decomposition
of the starting material and failed to produce the desired
tetrapeptide 2.
To surmount this problem, the synthesis was started
again using O-tert-butyl protected serine as the coupling
partner (Scheme 6). Thus, coupling of tripeptide amine
22, obtained by deprotection of the terminal primary
amine of 21, with N-Fmoc-L-Ser(OtBu) (27) under stan-
dard conditions (EDC, HOBt) afforded tetrapeptide 28
in 85% yield. Removal of the Fmoc protective group with
diethylamine and subsequent acetylation gave acetyl
tetrapeptide 30. Oxidation of double bonds according to
Sharpless proceeded smoothly in this case to provide the
corresponding carboxylic acid 31 in 75% yield. Simulta-
neous removal of the tert-butyl ester and the O-tert-butyl
ether from 31 under acidic conditions (TFA) followed by
hydrogenolysis of the crude diacid afforded tetrapeptide
2 in 54% yield. Tetrapeptide 2 was thus prepared starting
from R,â-unsaturated ester 3 in 13 steps with 4% overall
yield. The biological studies for tetrapeptide 2 are under
investigation and the results will be reported in due
course.
Experimental Section
General Procedure 1. Preparation of Aldehydes 6a-
c. To a solution of oxalyl chloride (9.34 mmol) in CH2Cl2 (15
mL) at -78 °C was added dropwise a solution of DMSO (20.33
mmol) in CH2Cl2 (15 mL). The resulting reaction mixture was
further stirred at the same temperature for another 15 min
before a solution of alcohols 5a-c (5.49 mmol) in CH2Cl2 (15
mL) was added dropwise over 15 min while the temperature
was kept at -78 °C. Stirring was continued for an additional
15 min followed by addition of Et3N (38.4 mmol), and the
reaction mixture was allowed to warm to room temperature.
Water (50 mL) was then added, and the aqueous layer was
extracted with CH2Cl2. The organic layers were washed with
1 M HCl, H2O, saturated NaHCO3, and brine, successively,
and then dried over Na2SO4. The filtered solution was con-
centrated under reduced pressure to give aldehydes 6a-c,
which were used directly for the next reaction without further
purification.
(4S,1′R)-2,2-Dimethyl-4-(1′-methyl-3′-oxopropyl)oxazo-
lidine-3-carboxylic Acid tert-Butyl Ester (6a). General
procedure 1 was followed using alcohol 5a (1.50 g, 5.49 mmol)
to give 1.43 g (96%) of 6a as a yellow oil: 1H NMR (300 MHz,
CDCl3) δ 9.75 (bs, 1H), 4.00-3.72 (m, 3H), 2.74-2.54 (m, 2H),
2.32-2.12 (m, 1H), 1.72-1.42 (m, 15H), 0.93 (d, J ) 6.7 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 202.2, 201.8, 153.0, 152.8,
94.3, 94.0, 80.2, 64.1, 60.9, 46.0, 45.7, 29.9, 28.3, 26.7, 26.3,
23.9, 22.4, 17.0, 16.7; MS (ESI) m/z 272 [M + H]+, 294 [M +
Na]+.
General Procedure 2. Preparation of Amines 8a, 8b,
13a, 13b, and 18. To a solution of the aldehydes 6a-c (1.0
mmol) and the amines 7a-d and 17 (1.1-1.3 mmol) in THF
(15 mL) was added sodium triacetoxyborohydride (1.1-1.4
mmol). The reaction mixture was stirred at room temperature
under Ar for 15 h. The reaction was quenched by addition of
aqueous saturated NaHCO3, and the reaction mixture was
extracted with ethyl acetate. The combined organic extracts
were washed with brine and then dried over Na2SO4. Purifica-
tion of the crude residue by flash column chromatography
provided amines 8a, 8b, 13a, 13b, and 18.
(4S,1′R,1′′S)-4-[3′-(1′′-Methoxycarbonyl-2′′-phenylethyl-
amino)-1′-methylpropyl]-2,2-dimethyloxazolidine-3-car-
boxylic Acid tert-Butyl Ester (8a). General procedure 2 was
followed using aldehyde (6a) (653 mg, 2.41 mmol) and L-Phe-
OMe (7a) (518 mg, 2.89 mmol). Chromatography with heptane/
ethyl acetate (2:1) gave 942 mg (90%, two rotamers) of 8a as
a yellow oil: [R]D +29 (c 3.40, CHCl3); IR (neat) ν 3328, 3027,
3020, 3012, 2979, 2953, 2878, 1732, 1686, 1495, 1476, 1455,
1435, 1392, 1366, 1255, 1172 cm-1; 1H NMR (300 MHz, CDCl3)
δ 7.31-7.12 (m, 5H), 3.89-3.76 (m, 3H), 3.63 (s, 3H), 3.51 (t,
J ) 7.2 Hz, 1H), 2.94 (d, J ) 7.2 Hz, 2H), 2.68 (dt, J ) 5.1,
10.8 Hz, 1H), 2.49-2.35 (m, 1H), 2.05-1.80 (m, 1H), 1.68-
1.41 (m, 16H), 1.25 (m, 1H), 0.83 (d, J ) 7.2 Hz, 3H); 13C NMR
(75 MHz, CDCl3) δ 175.0, 152.9, 152.5, 137.3, 129.1, 128.3,
126.6, 94.0, 93.6, 79.8, 79.5, 65.0, 64.5, 63.1, 61.9, 51.5, 46.4,
39.7, 33.7, 33.3, 32.0, 28.4, 26.9, 26.3, 24.3, 16.3; MS (ESI) m/z
435 [M + H]+, 457 [M + Na]+, 473 [M + K]+. Anal. Calcd for
C24H38N2O5: C, 66.33; H, 8.81; N, 6.45. Found: C, 66.09; H,
8.84; N, 6.47.
Conclusion
In summary, we developed a concise synthesis of
4-substituted-3-aminopiperidin-2-one that can be con-
sidered as a conformationally constrained dipeptide. The
synthesis is highly convergent and features a key reduc-
tive amination of the R-amino ester and the functional-
ized aldehyde, derived from serine. A variety of substit-
uents can be installed adjacent to the ring nitrogen by
(4S,1′R,1′′S)-4-{3′-[Benzyloxycarbonyl-(1′′-methoxycar-
bonyl-2′′-phenylethyl)amino]-1′- methylpropyl}-2,2-di-
methyloxazolidine-3-carboxylic Acid tert-Butyl Ester
(9a). To a solution of amine (8a) (205 mg, 0.47 mmol) and 0.5
M Na2CO3 (2 mL, 1 mmol) in THF-water (6 mL, 3:1) was
added dropwise benzyl chloroformate (0.08 mL, 0.52 mmol),
and the resulting mixture was vigorously stirred at room
temperature for 1 h. The reaction mixture was diluted with
(20) Carlsen, P. H.; Katsuki, T.; Martin, V. S.; Sharpless, K. B. J.
Org. Chem. 1981, 46, 3936-3938.
5950 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of 4-Substituted-3-aminopiperidin-2-ones
water and extracted with ethyl acetate, and the combined
organic layers were washed with brine and then dried over
Na2SO4. The crude product obtained upon concentration was
purified by flash column chromatography on silica gel with
heptane/ethyl acetate (6:1) and gave 226 mg (85%, two
rotamers) of 9a as an oil: [R]D -57 (c 2.10, CHCl3); IR (CHCl3)
ν 3028, 3013, 2980, 2879, 1741, 1686, 1476, 1455, 1393, 1377,
31.3, 28.3, 14.7; MS (ESI) m/z 709 [M + H]+, 731 [M + Na]+,
747 [M + K]+, 1417 [2M + H]+; HRMS calcd for C35H37F5N2O8-
Na (M + Na) 731.2368, found 731.2378.
(2S,3′S,4′R)-2-(3′-tert-Butoxycarbonylamino-4′-methyl-
2′-oxopiperidin-1′-yl)-3-phenylpropionic Acid Methyl Es-
ter (12a). A suspension of ester 11a (345 mg, 0.49 mmol) in
MeOH (20 mL) containing a catalytic amount of 10% Pd-C
(52 mg) was hydrogenated at atmospheric pressure for 3 h.
The catalyst was removed by filtration through Celite. The
filtrate was concentrated under reduced pressure and purifica-
tion by flash column chromatography on silica gel with
heptane/ethyl acetate (4:1) gave 151 mg (79%, two rotamers)
of 12a as white crystals: mp 112-113 °C; [R]D -59 (c 2.80,
CHCl3); IR (CHCl3) ν 3440, 3019, 2981, 2933, 2875, 1739, 1713,
1367, 1257, 1174, 1085 cm-1 1H NMR (300 MHz, CDCl3) δ
;
7.39-7.04 (m, 10H), 5.21-5.06 (m, 2H), 4.36-4.15 (m, 1H),
3.84-3.52 (m, 6H), 3.38-3.02 (m, 3H), 2.87-2.72 (m, 1H), 1.45
(s, 9H), 1.85-1.35 (m, 8H), 1.17-0.95 (m, 1H), 0.83 (d, J )
6.6 Hz, 1.7H), 0.73 (d, J ) 6.8 Hz, 1.3H); 13C NMR (75 MHz,
CDCl3) δ 171.3, 155.9, 155.5, 137.9, 137.8, 129.2, 128.5, 128.3,
128.2, 128.1, 128.0, 126.7, 126.6, 94.0, 93.6, 80.0, 79.6, 67.4,
67.3, 65.2, 62.3, 61.8, 61.7, 52.3, 47.2, 46.6, 36.3, 35.3, 33.9,
33.7, 31.1, 30.5, 28.5, 27.1, 26.5, 24.4, 22.9, 16.1, 15.9; MS (ESI)
m/z 569 [M + H]+, 591 [M + Na]+, 607 [M + K]+; HRMS calcd
for C32H45N2O7 (M + H) 569.3226, found 569.3202.
General Procedure 3. Preparation of 10a, 10b, 15a,
15b, and 20. Jones reagent (2.67 M, 1.1 mL, 2.98 mmol) was
added to a solution of 9a, 9b, 14a, 14b, and 19 (0.99 mmol) in
acetone (10 mL) at 0 °C under argon. After stirring at room
temperature for 3 h, the reaction was quenched by addition of
2-propanol. The reaction mixture was further stirred for 15
min, neutralized with saturated aqueous NaHCO3 to pH 4-5,
and extracted with ethyl acetate. The combined organic layers
were washed with brine, dried, and evaporated under reduced
pressure. Flash column chromatography on silica gel yielded
acids 10a, 10b, 15a, 15b, and 20.
(2S,3R,1′S)-5-[Benzyloxycarbonyl-(1′-methoxycarbonyl-
2′-phenylethyl)amino]-2-tert-butoxycarbonylamino-3-
methyl Pentanoic Acid (10a). General procedure 3 was
followed using 9a (565 mg, 0.99 mmol). Flash column chro-
matography with CH2Cl2/ethyl acetate (5:1) gave 477 mg (89%,
two rotamers) of 10a: [R]D -65 (c 2.50, CHCl3); IR (CHCl3) ν
3674, 3440, 3029, 3019, 2981, 1705, 1498, 1476, 1455, 1429,
1368, 1229, 1162 cm-1; 1H NMR (300 MHz, CDCl3) δ 8.31 (bs,
1H), 7.39-7.00 (m, 10H), 5.20-5.05 (m, 3H), 4.43-4.35 (m,
0.5H), 4.27-4.04 (m, 1.5H), 3.74 (s, 1.5H), 3.55 (s, 1.5H), 3.36-
3.08 (m, 3H), 3.01-2.83 (m, 0.5H), 2.70-2.62 (m, 0.5H), 2.05-
1.90 (m, 1H), 1.45-0.64 (m, 14H); 13C NMR (75 MHz, CDCl3)
δ 176.2, 175.9, 171.4, 171.3, 156.8, 156.2, 156.0, 155.8, 137.9,
137.6, 136.5, 136.0, 129.3, 128.5, 128.1, 126.8, 126.6, 80.0, 67.7,
67.3, 62.6, 62.4, 56.9, 56.7, 52.3, 46.9, 46.3, 36.0, 34.9, 32.9,
32.7, 31.9, 31.7, 28.3, 14.3; MS (ESI) m/z 543 [M + H]+, 565
[M + Na]+, 581 [M + K]+. Anal. Calcd for C29H38N2O8: C,
64.19; H, 7.06; N, 5.16. Found: C, 63.92; H, 7.27; N, 4.79.
1
1651, 1499, 1166 cm-1; H NMR (250 MHz, CDCl3) δ 7.31-
7.15 (m, 5H), 5.11-4.97 (m, 2H), 3.72 (s, 3H), 3.75-3.64 (m,
1H), 3.36 (dd, J ) 5.6, 14.3 Hz, 1H), 3.26-2.99 (m, 3H), 1.86-
1.65 (m, 2H), 1.44 (s, 9H), 1.51-1.33 (m, 1H), 1.00 (d, J ) 6.1
Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 170.8, 170.3, 156.4,
136.8, 128.7, 128.5, 126.7, 79.3, 58.9, 57.2, 52.2, 43.8, 34.2, 34.0,
29.3, 28.2, 18.8; MS (CI) m/z 391 [M + H]+; HRMS calcd for
C21H31N2O5 (M + H) 391.2232, found 391.2243.
(4S,1′S,1′′′S)-4-{1′-[2′′-(1′′′-Benzyloxycarbonyl-5′′′-ben-
zyloxycarbonylaminopentylamino)ethyl]allyl}-2,2-di-
methyloxazolidine-3-carboxylic Acid tert-Butyl Ester
(13a). General procedure 2 was followed using L-Lys(Cbz)OBn
(7c) (1.43 g, 3.87 mmol) and aldehyde 6c (996 mg, 3.52 mmol).
Flash column chromatography with heptane/ethyl acetate (2:
1) gave 1.89 g (85%, two rotamers) of 13a: [R]D +12 (c 1.90,
CHCl3); IR (neat) ν 3691, 3452, 3069, 3020, 3015, 2981, 2939,
2881, 1723,1687, 1515, 1455, 1393, 1378, 1367, 1238, 1172
cm-1; 1H NMR (300 MHz, CDCl3) δ 7.36-7.30 (m, 10H), 5.69-
5.48 (m, 1H), 5.19-4.95 (m, 6H), 4.94-4.81 (m, 1H), 3.94-
3.70 (m, 3H), 3.20 (t, J ) 6.4 Hz, 1H), 3.12 (q, J ) 6.2 Hz,
2H), 2.68-2.58 (m, 1H), 2.56-2.44 (m, 1H), 2.38-2.26 (m, 1H),
1.46 (s, 9H), 1.65-1.24 (m, 14H); 13C NMR (75 MHz, CDCl3) δ
175.4, 156.4, 152.9, 152.8, 139.3, 136.7, 135.9, 128.6, 128.5,
128.4, 128.1, 117.3, 116.8, 94.2, 93.7, 80.0, 79.7, 66.6, 66.4, 65.4,
61.6, 60.9, 46.5, 45.7, 40.9, 33.1, 30.7, 30.4, 29.7, 28.5, 27.1,
26.4, 24.5, 23.0, 22.7, 22.9; MS (ESI) m/z 638 [M + H]+, 660
[M + Na]+. Anal. Calcd for C36H51N3O7: C, 67.79; H, 8.06; N,
6.59. Found: C, 67.59; H, 8.31; N, 6.43.
General Procedure 4. Preparation of 14a, 14b, and 19.
To a cooled (0 °C) solution of amines 13a, 13b, and 18 (0.5
mmol) and 0.5 M Na2CO3 (2 mL, 1 mmol) in THF-water (20
mL, 3:1) was added 9-fluorenylmethyl chloroformate (0.55
mmol) in one portion, and the resulting mixture was vigorously
stirred at room temperature for 3 h. The reaction mixture was
diluted with water, extracted with ethyl acetate, and the
combined organic layers were washed with brine and then
dried over Na2SO4. The residue obtained upon concentration
was purified by flash column chromatography on silica gel to
give 14a, 14b, and 19.
(2S,3R,1′S)-5-[Benzyloxycarbonyl-(1′-methoxycarbonyl-
2′-phenylethyl)amino]-2-tert-butoxycarbonylamino-pen-
tafluorophenyl-3-methyl Pentanoate (11a). To a solution
of acid 10a (271 mg, 0.50 mmol) in CH2Cl2 (10 mL) at 0 °C
was added EDC (118 mg, 0.60 mmol). After stirring at that
temperature for 10 min, pentafluorophenol (112 mg, 0.60
mmol) was added and stirring was continued at room tem-
perature for 2 h. The reaction mixture was diluted with water
and extracted with ethyl acetate, and the combined organic
extracts were washed with brine and then dried over Na2SO4.
The crude residue obtained upon concentration was purified
by flash column chromatography on silica gel with heptane/
ethyl acetate (6:1) and gave 272 mg (77%, two rotamers) of
11a as white crystals: mp 81-82 °C; [R]D -65 (c 1.80, CHCl3);
IR (CHCl3) ν 3443, 3019, 2956, 1786, 1708, 1521, 1456, 1437,
(4S,1′S,1′′′S)-4-(1′-{2′′-[(1′′′-Benzyloxycarbonyl-5′′′-ben-
zyloxycarbonylaminopentyl)-(9H-fluoren-9-ylmethoxy-
carbonyl)amino]ethyl}allyl)-2,2-dimethyloxazolidine-3-
carboxylic Acid tert-Butyl Ester (14a). General procedure
4 was followed using 13a (231 mg, 0.36 mmol). Flash column
chromatography with heptane/ethyl acetate (4:1) gave 294 mg
(97%, two rotamers) of 14a: [R]D -2 (c 1.70, CHCl3); IR (CHCl3)
ν 3452, 3069, 3020, 2983, 2940, 2876, 1689, 1515, 1477, 1453,
1
1393, 1378, 1367 cm-1; H NMR (300 MHz, CDCl3) δ 7,79-
1368, 1228, 1144, 998 cm-1 1H NMR (300 MHz, CDCl3) δ
;
7,70 (m, 2H), 7.58-7.46 (m, 2H), 7.44-7.19 (m, 14H), 5.69-
5.32 (m, 1H), 5.18-4.85 (m, 7H), 4.64-4.28 (m, 3H), 4.22-
3.93 (m, 1H), 3.85-3.55 (m, 3H), 3.22-2.93 (m, 4H), 2.33-
2.12 (m, 1H), 2.08-1.91 (m, 1H), 1.85-1.62 (m, 1H), 1.44-
1.41 (2s, 9H), 1.58-1.22 (m, 12H); 13C NMR (75 MHz, CDCl3)
δ 171.1, 170.7, 156.3, 155.7, 152.7, 152.0, 143.8, 141.3, 138.5,
138.4, 136.6, 135.5, 128.5, 128.4, 128.2, 128.0, 127.6, 127.0,
126.9, 125.0, 124.8, 119.9, 117.3, 116.8, 94.0, 93.5, 79.9, 79.7,
67.1, 66.7, 66.4, 65.4, 65.3, 60.5, 60.1, 59.8, 47.3, 47.2, 46.2,
46.1, 45.5, 40.7, 29.6, 29.4, 29.3, 28.9, 28.3, 27.1, 26.4, 24.3,
7.37-7.04 (m, 10H), 5.29-5.08 (m, 3H), 4.63-4.48 (m, 1H),
4.09-4.01 (m, 1H), 3.77 (s, 1.5H), 3.57 (s, 1.5H), 3.47-3.24
(m, 2.5H), 3.21-3.11 (m, 0.5H), 2.78-2.56 (m, 1H), 2.26-2.03
(m, 1H), 1.47 (s, 9H), 1.53-1.40 (m, 1H), 1.35-1.02 (m, 1H),
0.96 (d, J ) 6.3 Hz, 1.5H), 0.81 (d, J ) 6.6 Hz, 1.5H); 13C NMR
(75 MHz, CDCl3) δ 171.4, 168.5, 168.4, 155.7, 155.5, 142.6,
141.3, 139.8, 139.5, 139.3, 138.0, 137.7, 136.5, 136.2, 129.3,
128.6, 128.4, 128.1, 126.8, 126.7, 80.4, 67.6, 67.4, 63.0, 62.3,
57.5, 57.4, 52.5, 52.3, 46.8, 46.3, 36.1, 34.9, 32.7, 32.6, 31.5,
J. Org. Chem, Vol. 70, No. 15, 2005 5951

Kumar et al.
23.5, 22.6; MS (ESI) m/z 860 [M + H]+, 882 [M + Na]+. Anal.
Calcd for C51H61N3O9: C, 71.22; H, 7.15; N, 4.89. Found: C,
71.07; H, 7.22; N, 4.75.
3.42 (m, 2H), 3.32-3.03 (m, 2H), 2.26-1.32 (m, 10H), 1.41 (s,
9H); 13C NMR (75 MHz, CDCl3) δ 171.1, 170.4, 156.6, 156.1,
143.9, 143.8, 141.2, 136.8, 128.4, 128.1, 127.9, 127.7, 127.0,
125.1, 119.9, 81.5, 66.9, 66.4, 59.6, 52.1, 47.1, 47.0, 40.4, 31.9,
29.1, 28.9, 27.9, 24.9, 21.5; MS (ESI) m/z 678 [M + Na]+;
HRMS calcd for C38H45N3O7Na (M + Na) 678.3155, found
678.3149.
To a solution of Fmoc-L-Lys(Cbz)-ProOBut (5.20 g, 7.94
mmol) in dry THF (50 mL) at 0 °C was added dropwise
diethylamine (20 mL) under Ar during 15 min and the reaction
mixture was stirred at room temperature for 3 h. Solvent was
removed by evaporation under reduced pressure, and purifica-
tion by flash column chromatography on silica gel with
heptane/ethyl acetate (1:1) and then CH2Cl2/MeOH (20:1) gave
3.00 g (87%) of 17 as an oil: [R]D -37 (c 2.10, CHCl3); IR (neat)
ν 3300, 2932, 2873, 1713, 1633,1530, 1445, 1366, 1245, 1150,
1092, 1025, 981, 847 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.42-
7.18 (m, 5H), 5.81 (m, 1H), 5.06 (s, 2H), 4.41-4.26 (m, 1H),
3.68-3.38 (m, 3H), 3.27-3.06 (m, 2H), 2.28-1.30 (m, 12H),
1.40 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 174.0, 171.3, 156.6,
136.9, 128.4, 128.0, 127.9, 81.2, 66.3, 59.6, 52.5, 46.6, 40.5, 34.5,
29.8, 29.5, 27.9, 24.9, 22.2; MS (ESI) m/z 434 [M + H]+, 456
[M + Na]+; HRMS calcd for C23H35N3O5Na (M + Na) 456.2474,
found 456.2458.
(2S,3S,1′′S)-3-{2′-[(1′′-Benzyloxycarbonyl-5′′-benzyloxy-
carbonylaminopentyl)-(9H-fluoren-9-ylmethoxycarbonyl)-
amino]ethyl}-2-tert-butoxycarbonylaminopent-4-enoic
Acid (15a). General procedure 3 was followed using 14a (322
mg, 0.38 mmol). Flash column chromatography with heptane/
ethyl acetate (2:1) gave 227 mg (73%, two rotamers) of 15a:
[R]D -4 (c 1.10, CHCl3); IR (CHCl3) ν 3445, 3069, 3021, 2957,
2871, 1706, 1500, 1477, 1453, 1420, 1369, 1224, 1160 cm-1
;
1H NMR (300 MHz, CDCl3) δ 7.79-7.66 (m, 2H), 7.57-7.43
(m, 2H), 7.41-7.16 (m, 14H), 5.66-5.30 (m, 1H), 5.23-4.84
(m, 8H), 4.63-3.92 (m, 5H), 3.27-2.88 (m, 4H), 2.64-2.22 (m,
1H), 2.07-1.02 (m, 17H); 13C NMR (75 MHz, CDCl3) δ 174.2,
171.2, 170.7, 156.8, 156.4, 156.2, 155.7, 143.9, 143.7, 141.3,
138.5, 135.6, 135.5, 128.8, 128.5, 128.2, 128.1, 127.6, 127.0,
124.8, 124.5, 120.0, 119.0, 118.7, 79.9, 66.8, 66.7, 60.3, 59.9,
56.7, 47.3, 47.2, 45.2, 45.1, 44.3, 44.2, 40.9, 40.8, 30.3, 30.2,
29.8, 28.3, 23.6, 23.5; MS (ESI) m/z 834 [M + H]+, 856 [M +
Na]+, 872 [M + K]+. Anal. Calcd for C48H55N3O10: C, 69.13;
H, 6.65; N, 5.04. Found: C, 69.17; H, 6.64; N, 5.18.
General Procedure 5. Preparation of 16a, 16b, and 21.
To a solution of acids 15a, 15b, and 20 (0.24 mmol) in dry
THF (2 mL) at 0 °C was added dropwise diethylamine (10 mL)
under argon during 15 min, and the reaction mixture was
stirred at room temperature for 6 h. The solvent was evapo-
rated to dryness. To a solution of the oil obtained above in dry
DMF (25 mL) were added TBTU (0.72 mmol), HOBt (0.72
mmol), and DIEA (0.96 mmol), and the reaction mixture was
stirred at room temperature for 24 h. The reaction was
quenched by addition of water, and the reaction mixture was
extracted with ethyl acetate. The organic layers were washed
with 1 N KHSO4, H2O, saturated NaHCO3, and brine and then
dried over Na2SO4 and evaporated. Flash column chromatog-
raphy on silica gel gave 16a, 16b, and 21.
(2S,3′S,4′S)-6-Benzyloxycarbonylamino-2-(3′-tert-bu-
toxycarbonylamino-2′-oxo-4′-vinylpiperidin-1′-yl)-hex-
anoic Acid Benzyl Ester (16a). General procedure 5 was
followed using 15a (200 mg, 0.24 mmol). Flash column
chromatography with heptane/ethyl acetate (3:1) gave 125 mg
(88%, two rotamers) of 16a: [R]D -21 (c 0.70, CHCl3); IR
(CHCl3) ν 3449, 3020, 2983, 2937, 2868, 1714, 1655, 1507,
1455, 1438, 1368, 1326, 1265, 1167 cm-1; 1H NMR (300 MHz,
CDCl3) δ 7.38-7.30 (m, 10H), 5.76 (ddd, J ) 8.0, 10.3, 16.9
Hz, 1H), 5.19-4.94 (m, 8H), 4.88 (bs, 1H), 4.05 (m, 1H), 3.28-
3.12 (m, 4H), 2.40-2.27 (m, 1H), 2.06-1.92 (m, 2H), 1.82-
1.60 (m, 2H), 1.43 (s, 9H), 1.58-1.21 (m, 4H); 13C NMR (75
MHz, CDCl3) δ 170.8, 170.6, 156.5, 156.2, 138.6, 136.7, 135.4,
128.6, 128.4, 128.2, 128.0, 116.0, 79.5, 66.9, 66.4, 56.4, 55.2,
43.6, 41.6, 40.5, 29.2, 28.3, 27.8, 27.5, 23.2; MS (ESI) m/z 594
[M + H]+, 616 [M + Na]+, 632 [M + K]+. Anal. Calcd for
C33H43N3O7: C, 66.76; H, 7.30; N, 7.08. Found: C, 66.48; H,
7.61: N, 6.99.
(2S,2’S,3’’S,4’’S)-1-[2’-(3’’-Amino-2’’-oxo-4’’-vinyl-piperi-
din-1’’-yl)-6’-benzyloxycarbonylamino-hexanoyl]-pyrro-
lidine-2-carboxylic Acid tert-Butyl Ester (22). To a solu-
tion of 21 (399 mg, 0.60 mmol) in ethyl acetate (9 mL) was
added concentrated HCl (3 mL) at -50 °C, and the reaction
mixture was stirred at that temperature for 2 h and then
stirred at 0 °C for 1 h. The reaction mixture was neutralized
with a saturated solution of NaHCO3 and then extracted with
ethyl acetate. The organic layers were combined and washed
with brine, dried over Na2SO4, and evaporated under reduced
pressure. Flash column chromatography with CH2Cl2 and then
CH2Cl2/MeOH (20:1) gave 260 mg (67%) of 22 as an oil: [R]D
-91 (c 1.10, CHCl3); IR (neat) ν 3329, 2977, 2935, 2874, 1720,
1643, 1532, 1487, 1440, 1393, 1367, 1248, 1153, 1094, 1025,
1
919, 845, 753, 698 cm-1; H NMR (300 MHz, CDCl3) δ 7.37-
7.25 (m, 5H), 5.81-5.58 (m, 1H), 5.51-5.41 (m, 1H), 5.40-
5.26 (m, 1H), 5.24-4.99 (m, 4H), 4.37-4.26 (m, 1H), 3.78-
3.55 (m, 2H), 3.43-3.30 (m, 2H), 3.28-3.11 (m, 3H), 2.83-
2.58 (bs, 2H), 2.43-2.24 (m, 1H), 2.21-1.23 (m, 12H), 1.40 (s,
9H); 13C NMR (75 MHz, CDCl3) δ 171.3, 171.2, 168.7, 156.5,
139.2, 136.8, 128.4, 128.0, 128.0, 116.7, 81.3, 66.4, 59.8, 55.9,
53.6, 47.2, 44.6, 41.7, 40.6, 29.3, 29.1, 28.2, 27.9, 27.5, 24.8,
22.6; MS (ESI) m/z 557 [M + H]+, 579 [M + Na]+; HRMS calcd
for C50H44N4O6Na (M + Na) 579.3159, found 579.3167.
(2S,2’S,3’’S,4’’S,2’’’S)-1-{2’-[3’’-(3’’’-Benzyloxy-2’’’-tert-bu-
toxycarbonylamino-propionylamino)-2’’-oxo-4’’-vinyl-pi-
peridin-1’’-yl]-6’-benzyloxycarbonylamino-hexanoyl}-pyr-
rolidine-2-carboxylic Acid tert-Butyl Ester (23). To a
solution of 22 (250 mg, 0.45 mmol) and Boc-L-Ser(OBn)OH (145
mg, 0.49 mmol) in CH2Cl2 (25 mL) was added EDC (103 mg,
0.54 mmol) and HOBt (72 mg, 0.54 mmol), and the reaction
mixture was stirred at room temperature under Ar for 24 h.
Water was added, and the reaction mixture was extracted with
CH2Cl2. The organic extracts were washed with 1 N KHSO4,
H2O, saturated NaHCO3, and brine, successively, and then
dried over Na2SO4 and evaporated under reduced pressure.
The crude residue obtained was purified by flash column
chromatography with heptane/ethyl acetate (4:1 then 2:1) to
give 303 mg (80%) of 23 as white crystals: mp 55-56 °C; [R]D
-59 (c 1.00, CHCl3); IR (CHCl3) ν 3445, 3015, 2983, 2934, 2871,
1714, 1681, 1644, 1515, 1487, 1455, 1393, 1368, 1236, 1156,
1100, 1025, 923, 844 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.38-
7.22 (m, 10H), 7.19-7.06 (m, 1H), 5.76-5.58 (m, 1H), 5.52-
5.35 (m, 1H), 5.33-5.19 (m, 2H), 5.15-4.89 (m, 4H), 4.61-
4.43 (m, 2H), 4.39-4.23 (m, 2H), 4.14-3.98 (m, 1H), 3.93-
3.72 (m, 2H), 3.70-3.27 (m, 4H), 3.25-3.07 (m, 2H), 2.64-
2.41 (m, 1H), 2.66-1.12 (m, 12H), 1.44 (s, 9H), 1.42 (s, 9H);
13C NMR (75 MHz, CDCl3) δ 171.2, 170.7, 169.0, 168.8, 156.5,
(2S,2’S)-1-(2’-Amino-6’-benzyloxycarbonylamino-hex-
anoyl)-pyrrolidine-2-carboxylic Acid tert-Butyl Ester
(17). To a solution of L-Pro-OBut (1.83 g, 10.70 mmol) and
Fmoc-L-Lys(Cbz)OH (4.50 g, 8.90 mmol) in CH2Cl2 (25 mL) was
added EDC (2.00 g, 10.70 mmol) and HOBt (1.44 g, 10.70
mmol), and the reaction mixture was stirred at room temper-
ature under Ar for 24 h. Water was added, and the reaction
mixture was extracted with CH2Cl2. The organic extracts were
washed with 1 N KHSO4, H2O, saturated NaHCO3, and brine,
successively, and then dried over Na2SO4 and evaporated
under reduced pressure. The crude residue obtained was
purified by flash column chromatography with heptane/ethyl
acetate (4:1 then 2:1) to give 5.25 g (89%) of Fmoc-l-Lys(Cbz)-
Pro-OBut: [R]D -36 (c 1.60, CHCl3); IR (neat) ν 3296, 2941,
1713, 1637, 1524, 1446, 1366, 1241, 1149, 1092, 1030, 914, 842
1
cm-1; H NMR (300 MHz, CDCl3) δ 7.73 (d, J ) 7.4 Hz, 2H),
7.57 (d, J ) 7.3 Hz, 2H), 7.43-7.19 (m, 9H), 5.88 (d, J ) 8.1
Hz, 1H), 5.44 (bs, 1H), 5.06 (s, 2H), 4.59-4.04 (m, 5H), 3.74-
5952 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of 4-Substituted-3-aminopiperidin-2-ones
155.4, 138.4, 137.6, 136.9, 128.4, 128.1, 128.0, 127.8, 116.2,
81.3, 80.0, 73.3, 70.0, 66.4, 59.8, 54.8, 53.9, 47.1, 42.7, 41.3,
40.6, 29.3, 29.1, 28.3, 27.9, 24.8, 22.8; MS (ESI) m/z 856 [M +
Na]+; HRMS calcd for C45H63N5O10Na (M + Na) 856.4473,
found 856.4487.
cm-1; 1H NMR (300 MHz, CD3OD) δ 7.28-7.12 (m, 10H), 5.19
(t, J ) 7.6 Hz, 1H), 4.95 (s, 2H), 4.82-4.68 (m, 4H), 4.53 (t, J
) 5.2 Hz, 1H), 4.42 (s, 2H), 4.25-4.15 (m, 1H), 3.71-3.62 (m,
1H), 3.59 (d, J ) 5.3 Hz, 2H), 3.49-3.16 (m, 4H), 3.07-2.93
(m, 2H), 2.18-1.14 (m, 13H), 1.88 (s, 3H), 1.34 (s, 9H); 13C
NMR (75 MHz, CD3OD) δ 175.8, 173.2, 173.0, 172.0, 170.4,
169.9, 158.9, 139.3, 138.5, 129.5, 129.4, 128.9, 128.8, 128.7,
82.7, 74.2, 71.0, 67.3, 61.6, 55.8, 54.5, 53.8, 48.4, 44.7, 43.0,
41.5, 30.5, 30.2, 29.1, 28.3, 26.9, 25.8, 24.0, 22.6; MS (ESI) m/z
816 [M + Na]+; HRMS calcd for C41H55N5O11Na (M + Na)
816.3796, found 816.3770.
(2S,2’S,3’’S,4’’S,2’’’S)-1-{2’-[3’’-(2’’’-Amino-3’’’-benzyloxy-
propionylamino)-2’’-oxo-4’’-vinyl-piperidin-1’’-yl]-6’-ben-
zyloxycarbonylamino-hexanoyl}-pyrrolidine-2-carbox-
ylic Acid tert-Butyl Ester (24). This compound was prepared
following the same procedure as described for 22 starting from
23 (380 mg, 0.46 mmol). Flash column chromatography with
CH2Cl2 and then CH2Cl2/MeOH (20:1) gave 234 mg (70%, two
rotamers): [R]D -81 (c 1.00, CHCl3); IR (CHCl3) ν 3452, 3377,
3022, 3016, 2948, 2868, 1716, 1643, 1517, 1454, 1393, 1368,
1228, 1205, 1154, 1095, 1027, 990, 923, 843 cm-1; H NMR (300
MHz, CDCl3) δ 7.95-7.82 (m, 1H), 7.40-7.22 (m, 10H), 5.76-
5.58 (m, 1H), 5.50-4.91 (m, 6H), 4.56-4.14 (m, 4H), 3.90-
3.08 (m, 9H), 2.58-1.19 (m, 16H), 1.42 (s, 9H); 13C NMR (75
MHz, CDCl3) δ 172.9, 171.2, 169.4, 169.3, 156.5, 138.6, 137.8,
136.8, 128.4, 128.1, 128.0, 127.7, 116.1, 81.3, 73.1, 72.2, 66.4,
59.7, 55.0, 53.9, 47.1, 43.2, 41.2, 40.6, 29.3, 29.1, 28.4, 28.0,
24.8, 22.8; MS (ESI) m/z 756 [M + Na]+, 734 [M + H]+; HRMS
calcd for C40H57N5O8 (M + H) 734.4129, found 734.4103.
(2S,2’S,3’’S,4’’S,2’’’S)-1-{2’-[3’’-(2’’’-Amino-3’’’-tert-butoxy-
propionylamino)-2’’-oxo-4’’-vinyl-piperidin-1’’-yl]-6’-ben-
zyloxycarbonylamino-hexanoyl}-pyrrolidine-2-carbox-
ylic Acid tert-Butyl Ester (29). This compound was prepared
according to the procedure described for 17 starting from 28
(278 mg, 0.40 mmol). Flash column chromatography with CH2-
Cl2/ethyl acetate (1:1) and then CH2Cl2/MeOH (20:1) gave 203
mg (96%) of 29 as white crystals: mp 53-55 °C; [R]D -84 (c
0.50, CHCl3); IR (neat) ν 3319, 2972, 2932, 2871, 1716, 1632,
1518, 1435, 1391, 1364, 1245, 1194, 1150, 1082, 1020, 914, 845
1
cm-1; H NMR (300 MHz, CDCl3) δ 7.92 (d, J ) 8.3 Hz, 1H),
7.37-7.23 (m, 5H), 5.78-5.61 (m, 1H), 5.38-5.27 (m, 1H), 5.24
(t, J ) 7.6 Hz, 1H), 5.11-4.96 (m, 4H), 4.33 (dd, J ) 4.2, 9.0
Hz, 1H), 4.20 (t, J ) 9.7 Hz, 1H), 3.91-3.71 (m, 1H), 3.65-
3.48 (m, 4H), 3.43-3.30 (m, 2H), 3.26-3.05 (m, 2H), 2.22-
2.08 (m, 1H), 2.05-1.80 (m, 5H), 1.77-1.61 (m, 2H), 1.57-
(2S,2’S,3’’S,4’’S,2’’’S)-1-{2’-[3’’-(2’’’-Acetylamino-3’’’-ben-
zyloxy-propionylamino)-2’’-oxo-4’’-vinyl-piperidin-1’’-yl]-
6’-benzyloxycarbonylamino-hexanoyl}-pyrrolidine-2-car-
boxylic Acid tert-Butyl Ester (25). To a stirred solution of
amine 24 (1.25 g, 1.71 mmol) in dry CH2Cl2 were added
triethylamine (0.31 mL, 2.22 mmol), a catalytic amount of
DMAP (5 mg), and acetic anhydride (0.21 mL, 2.22 mmol). The
reaction mixture was stirred at room temperature overnight
under an argon atmosphere. The reaction was quenched by
the addition of several drops of MeOH. The reaction mixture
was extracted with dichloromethane and the combined organic
extracts were washed with 1 N KHSO4, a saturated solution
of NaHCO3, and brine and then dried over Na2SO4. The solvent
was removed under reduced pressure, and the residue was
purified by HPLC (CH3CN:H2O, 45:55, Colonne Symmetry, 250
× 4.6 mm, C 18) to give 675 mg (51%) of 25 as white crystals:
mp 61-62 °C; [R]D -60 (c 0.50, CHCl3); IR (CHCl3) ν 3301,
1.47 (m, 2H), 1.41 (s, 9H), 1.37-1.24 (m, 2H), 1.17 (s, 9H); 13
C
NMR (75 MHz, CDCl3) δ 173.1, 171.2, 169.4, 169.2, 156.5,
138.7, 136.8, 128.4, 128.1, 128.0, 116.0, 81.3, 73.3, 66.4, 63.8,
59.7, 55.4, 53.9, 53.9, 47.2, 47.1, 43.2, 41.2, 40.6, 29.3, 29.1,
28.4, 27.9, 27.5, 24.8, 22.8; MS (ESI) m/z 700 [M + H]+, 722
[M + Na]+; HRMS calcd for C37H57N5O8Na (M + Na) 722.4105,
found 722.4133.
(3S,4R,2′S,1′′S,2′′′S)-3-(2′-Acetylamino-3′-hydroxy-pro-
pionylamino)-1-[5′′-amino-1′′-(2′′′-carboxy-pyrrolidine-
1′′′-carbonyl)-pentyl]-2-oxo-piperidine-4-carboxylic Acid
(2). Acid 31 (80 mg, 0.11 mmol) was treated with trifluoroacetic
acid (5 mL) at 0 °C, and the reaction mixture was stirred at
room temperature for 3 h. The volatile was evaporated under
reduced pressure to dryness. A suspension of crude diacid in
MeOH (10 mL) containing a catalytic amount of 10% Pd-C
(18 mg) was hydrogenated at atmospheric pressure for 3 h.
The catalyst was removed by filtration through Celite. The
filtrate was concentrated under reduced pressure, and the
crude residue obtained was purified by reversed phase HPLC
(Colonne Hypercarb debit 1 mL/min, eluted with CH3CN/0.5%
CF3COOH (85%) and H2O/0.5% CF3COOH (15%)) to give 27
mg (54%) of tetrapeptide 2 as white solid: mp 94-96 °C; [R]D
-93 (c 0.25, H2O); IR (neat) ν 2951, 1631, 1435, 1180, 1129,
2931, 1718, 1631, 1522, 1437, 1366, 1244, 1150, 915, 843 cm-1
;
1H NMR (300 MHz, CDCl3) δ 7.41-7.23 (m, 11H), 6.59-6.67
(m, 1H), 5.75-5.56 (m, 1H), 5.42-5.33 (m, 1H), 5.31-5.22 (m,
1H), 5.11-4.92 (m, 4H), 4.68-4.57 (m, 1H), 4.55-4.50 (s, 2H),
4.36-4.27 (m, 1H), 4.15-3.08 (m, 9H), 2.64-2.45 (m, 1H),
2.23-1.20 (m, 12H), 1.97 (s, 3H), 1.42 (s, 9H); 13C NMR (75
MHz, CDCl3) δ 171.2, 170.4, 170.2, 168.9, 168.7, 156.5, 138.4,
137.5, 136.8, 128.4, 128.0, 127.9, 127.9, 116.2, 81.3, 73.4, 69.5,
66.4, 59.7, 54.7, 53.9, 52.2, 47.1, 42.7, 41.3, 40.6, 29.3, 29.1,
28.4, 28.1, 27.9, 24.8, 23.2, 22.8; MS (ESI) m/z 798 [M + Na]+;
HRMS calcd for C42H57N5O9Na (M + Na) 798.4054, found
798.4049. Anal. Calcd C42H57N5O9: C, 65.01; H, 7.40; N, 9.03.
Found: C, 64.58; H, 7.25; N, 8.66.
838, 798, 721 cm-1 1H NMR (300 MHz, D2O diaoxane as
;
reference) δ 5.19 (t, J ) 6.9 Hz, 1H), 4.46-4.30 (m, 3H), 3.77
(dd, J ) 4.7, 11.5 Hz, 2H), 3.57 (t, J ) 6.4 Hz, 2H), 3.41 (dt, J
) 3.9, 12.5 Hz, 1H), 3.32-3.20 (m, 1H), 3.06 (dt, J ) 3.8, 11.2
Hz, 1H), 2.93 (t, J ) 7.5 Hz, 2H), 2.33-2.12 (m, 2H), 2.06-
1.89 (m, 6H), 1.86-1.54 (m, 4H), 1.42-1.14 (m, 3H); 13C NMR
(75 MHz, CD3OD) δ 176.0, 174.4, 171.6, 169.8, 169.2, 163.0
(q, J ) 35 Hz), 116.0 (q, J ) 291 Hz), 61.2, 59.8, 55.6, 55.2,
52.1, 47.6, 43.0, 42.2, 39.3, 28.9, 27.1, 26.4, 24.9, 24.5, 22.0,
21.8; MS (ESI) m/z 514 [M + H]+; HRMS calcd for C22H36N5O9-
Na (M + H) 514.2513, found 514.2546.
(2S,2’S,3’’S,4’’R,2’’’S)-3-(2’-Acetylamino-3’-benzyloxy-
propionylamino)-1-[5’’-benzyloxycarbonylamino-1’’-(2’’’-
tert-butoxycarbonyl-pyrrolidine-1’’’-carbonyl)-pentyl]-2-
oxo-piperidine-4-carboxylic Acid (26a). Acetyl lactam 25
(150 mg, 0.19 mmol) was dissolved in carbon tetrachloride (2
mL), acetonitrile (2 mL), and distilled water (3 mL). To this
biphasic solution were added sodium metaperiodate (213 mg,
0.76 mmol) and a catalytic amount of ruthenium trichloride
hydrate (1 mg, 2.2 mol %), and the reaction mixture was
stirred vigorously at room temperature under an argon
atmosphere for 24 h. Then, 10 mL of CH2Cl2 was added, and
the phases were separated. The upper aqueous phase was
extracted three times with CH2Cl2. The combined organic
extracts were dried over Na2SO4 and then concentrated.
Purification by reversed phase HPLC (Colonne Hypercarb
debit 1 mL/min, eluted with CH3CN/CH2Cl2/2% CH3COOH)
gave 55 mg (36%) of 26a as white solid: mp 88-89 °C; [R]D
-88 (c 1.00, CHCl3); IR (neat) ν 3304, 2926, 1713, 1632, 1530,
1443, 1366, 1247, 1150, 1095, 1026, 982, 915, 842, 733, 696
Acknowledgment. S.K. thanks CNRS for a post-
doctoral fellowship.
Supporting Information Available: General information
and all spectroscopic data for compounds 6b, 6c, 8b, 9b, 10b,
11b, 12b, 13b, 14b, 15b, 16b, 18, 19, 20, 21, 28, 30, and 31;
X-ray crystallographic data (CIF) and ORTEP drawing for
compound 12a; copies of 1H NMR and 13C NMR spectra. This
material is available free of charge via the Internet at
http://pubs.acs.org.
JO050736K
J. Org. Chem, Vol. 70, No. 15, 2005 5953