Stereoselective synthesis of 1,2,3-triazolyl-functionalized isoxazolidines, via two consecutive 1,3-dipolar cycloadditions, as precursors of unnatural amino acids

Article abstract of DOI:10.1016/j.tetlet.2013.01.125

1,3-Dipolar cycloaddition of a (-)-menthone-derived nitrone to allyl bromide under microwave irradiation afforded, stereoselectively, the corresponding chiral isoxazolidine in 98% yield. After substitution of the bromine atom by an azide group (98% yield), another 1,3-cycloaddition with various alkynes led to a series of 1,2,3-triazolyl-functionalized isoxazolidines (85% yield). Removal of the chiral auxiliary under acid-catalysis appeared to be a limiting step toward 5-substituted isoxazolidines, which were isolated in modest yields. For a general and reliable access to 5-(triazolyl)methyl- substituted isoxazolidines, which are new compounds and valuable precursors of unnatural amino acids, performing the CuAAC cycloaddition as the final step is recommended.

Full text of DOI:10.1016/j.tetlet.2013.01.125

Tetrahedron Letters 54 (2013) 1967–1971
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Stereoselective synthesis of 1,2,3-triazolyl-functionalized isoxazolidines, via
two consecutive 1,3-dipolar cycloadditions, as precursors of unnatural amino
acids
Kaïss Aouadi a,b, , Sébastien Vidal a, Moncef Msaddek b, Jean-Pierre Praly a
⇑
a Université de Lyon, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, UMR CNRS 5246, Laboratoire de Chimie Organique 2—Glycochimie, Bâtiment Curien,
43 boulevard du, 11 Novembre 1918, F-69622 Villeurbanne, France
b Université de Monastir, Laboratoire de Synthèse Hétérocyclique, Chimie des Substances Naturelles, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5000 Monastir,
Tunisia
a r t i c l e i n f o
a b s t r a c t
Article history:
1,3-Dipolar cycloaddition of a (ꢀ)-menthone-derived nitrone to allyl bromide under microwave irradia-
tion afforded, stereoselectively, the corresponding chiral isoxazolidine in 98% yield. After substitution of
the bromine atom by an azide group (98% yield), another 1,3-cycloaddition with various alkynes led to a
series of 1,2,3-triazolyl-functionalized isoxazolidines (ꢁ85% yield). Removal of the chiral auxiliary under
acid-catalysis appeared to be a limiting step toward 5-substituted isoxazolidines, which were isolated in
modest yields. For a general and reliable access to 5-(triazolyl)methyl-substituted isoxazolidines, which
are new compounds and valuable precursors of unnatural amino acids, performing the CuAAC cycload-
dition as the final step is recommended.
Received 16 October 2012
Revised 21 January 2013
Accepted 30 January 2013
Available online 8 February 2013
Keywords:
Menthone
Chiral nitrone
1,3-Dipolar cycloaddition
Isoxazolidine
Ó 2013 Elsevier Ltd. All rights reserved.
1,2,3-Triazole
Click chemistry
Amino acids are building blocks essential for life, as their asso-
ciation through amide bonds leads to peptides and proteins. They
are the focus of many studies, in particular in the field of bioor-
ganic chemistry.1 The design of peptide analogues has therefore at-
1,3-dipolar cycloadditions of nitrones to alkenes is being investi-
gated intensely (Fig. 1).
Using an N-borononitrone, generated in situ from the corre-
sponding O-silylated oxime and boron trifluoride diethyl etherate,
Tamura and co-workers14 reported an access to 3,5-disubstituted
isoxazolidines, with an unsubstituted nitrogen atom initially
linked to the boron species (Fig. 1). The racemic cycloadducts were
obtained regioselectively with average to high cis/trans selectivity.
tracted significant interest and synthetic unnatural a-amino acids
have found many applications,2 for example, as starting materials
for the total synthesis of natural products,3 as chiral auxiliaries,4
as ligands for metal-catalyzed reactions,5 or for the design of drugs
or bioactive molecules.6 1,3-Dipolar cycloadditions of alkenes with
nitrones produce substituted isoxazolidines, obtained as racemic
mixtures7 or with stereoinduction if chirality is present, generally
in either the dipole or the dipolarophile.8 Cycloaddition of chiral
nitrones to alkenes creates either two stereogenic centers in the
case of terminal alkenes (Fig. 1), or three if using disubstituted al-
kenes. Isoxazolidines offer a general route to natural and unnatural
amino acids,9 through opening of the isoxazolidine ring, usually by
reductive cleavage of the weak N–O bond. Consequently, isoxazoli-
dines have been used as key intermediates for the synthesis of var-
ious natural products,10 or antifungal,11 anti-tuberculosis,12 and
antiviral agents.13 As a consequence, the synthetic potential of
a-Substituted ester nitrones were studied by Dujardin and co-
workers15 as dipoles reacting with vinyl ethers to afford racemic
mixtures in high yields (63–97%) and with good stereocontrol.
Using a chiral auxiliary linked either to the alkene (N-vinyloxazoli-
din-2-one16 or vinyl ether17), or to the nitrone,17 the same group
reported enantioselective approaches showing modest to high
selectivities. Most of these examples used achiral nitrones, among
which, N-benzyl-ethoxy-carbonyl nitrone16 was a readily accessi-
ble acyclic glycine equivalent. Acyclic chiral nitrones,17 which exist
as E and Z isomers, lead to isoxazolidines with modest stereocon-
trol. Blandin and co-workers18 and others9g,h have reported the
use of a cyclic chiral nitrone as a glycine equivalent for the enantio-
selective synthesis of c-hydroxy a-amino acids. In such cases, high
and even complete stereocontrol can be achieved with cyclic chiral
nitrones, as observed for menthone-based chiral nitrones, for
example (ꢀ)-1 (Fig. 1).19
⇑
Corresponding author. Address: ISSAT Gabès, Rue Amor El Khatab, Gabès 6029,
Tunisia. Tel.: +216 23 75 52 65; fax: +216 75 39 23 90.
E-mail address: kaiss_aouadi@yahoo.com (K. Aouadi).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.01.125

1968
K. Aouadi et al. / Tetrahedron Letters 54 (2013) 1967–1971
BF2
R4
N
CO2Et
O
R4 = Ph, n-C4H9, (CH2)4OCH3
R1 = R2 = H
R
Tamura et al.14
3 = CO2Et
CH2Ph
N
O
R4
R4
CO 2Me
R4
N
O
O
Du jardin et al.15
N
R3
R2
This work
R3
O
CH3
R1 = CH2Ph
R1 = COMe
R2 = CONHMe
R3 = H
N
R4 = OEt, Ot-Bu
(
)-1
R2 = CO2Me
R4 = CH2Br
R1
R3 = OMe, OEt, OBn,
O(CH2)2CO2Me
R4 = CH2N3,
Ar
N
CH2
N
N
R1 = R2
R3 = H
=
N
Me
Blandin et al. 18
O
Amino acids obtained
based on our
synthetic
R4 = CH2OAc, CH2OH,
methodology
O
N
Ph, n-B uO, CO 2Et
R4
N
Me
O
Re f. 9 c
Ref. 9f
Ref. 9e
Re f. 9 g
HO
OH
CH2OMe
CO2
CH2Cl
R
ClH2C
R
R = NH2
CO2
Me O
R = OH
H2N
OH
NH3
OH
OH
NH3
47% (4 steps)
CH3
CO 2
46% (4 steps)
CO2
OH
CH2OH
R = all yl thioglucoside
OH
48% (3 steps)
NH3
OH
OH NH3
OH
NH3
O
CO2
HO
HO
S
CO 2
OH NH3
OH
52% (3 steps)
21% (5 steps)
56% (3 steps)
Figure 1. 2,3,5-Trisubstituted isoxazolidines: selected recent synthetic strategies14,15,18 and our approaches toward unnatural amino acids.9c,9e–g
In a previous work, we described the synthesis of enantiopure
tiopure (2S,3R,4R)-9d or (2S,3S,4R)-4-hydroxyisoleucine,9g and
4(S)-4-hydroxy-
-ornithine.9f As the simultaneous creation of
several stereogenic centers impacts favorably on atom economy,
these cycloaddition routes are advantageous as compared, for
4,5-dihydroxylated amino acids by cycloaddition of chiral
nitrones derived from menthone with racemic 3-substituted
1-butenes. This process afforded a ꢁ4:1 mixture of the two
cycloadducts as epimers depending on the 3-substituent on
the alkene.9c In contrast, the cycloaddition of nitrone (ꢀ)-1 to
L
example, with a multi-step route from
D-glucose to analogues
of (2S,3R,4S)-4-hydroxyisoleucine, a naturally-occurring insulino-
tropic amino acid.20 With these considerations in mind, we rea-
soned that the cycloadducts obtained could be elaborated further
by the application of a simple and high-yielding protocol from
the panel of methods referred to as ‘click-chemistry’.21 We re-
(Z)-but-2-en-1,4-diol produced
a
single cycloadduct.9e The
stereoselectivity was also excellent with a series of allyl O- and
S-glycosides affording the corresponding carbohydrate-based
isoxazolidines.9f Nevertheless, the reaction carried out under sim-
ilar conditions with (Z)-pent-2-en-1-ol afforded two regioisomers
in 38% and 60% yield,9e while the cycloaddition of chiral nitrone
(ꢀ)-1 with (E)-1,4-dichlorobut-2-ene afforded a major diastereo-
isomer in 70% yield (Fig. 1).9g
port herein
a stereoselective synthesis of isoxazolidines by
the 1,3-dipolar cycloaddition of nitrone (ꢀ)-1, derived from
(ꢀ)-menthone, with allyl bromide (Scheme 1) and subsequent
formation of 1,2,3-triazole moieties22 by Cu(I)-catalyzed azide–
alkyne cycloaddition (CuAAC) applied to an azidomethyl inter-
mediate. The popular CuAAC methodology23 was chosen for its
simplicity and efficiency in coupling suitable units through for-
mation of a triazole ring. Its application to various alkyne deriv-
atives allowed for the rapid generation of a small library of
1,2,3-triazolyl-functionalized isoxazolidines that might be of
interest as unprecedented polyheterocyclic motifs, or as precur-
sors of unnatural amino acids.24
Nitrone (ꢀ)-1, and its enantiomer derived from (+)-menthone,19
are glycine equivalents8g,h which provide a convenient and rapid
access to c-hydroxy a-amino acids, with very high regio- and ste-
reocontrol upon reaction with terminal,9c,f or symmetrically disub-
stituted alkenes.9e Inevitably, asymmetric disubstituted alkenes
raise regioselectivity issues.9d,g
Our previous Letters showed the potential of stereocontrolled
cycloadditions to access unnatural amino acids9c,9e such as enan-

K. Aouadi et al. / Tetrahedron Letters 54 (2013) 1967–1971
1969
N
Br
N
3
N
O
N
N
3
H
R
H
N
O
O
O
O
NH CH
N
N
3
N
O
O
NH CH
N
O
3
N
N
N
H
COC
O
3
H
COC
3
O
4
2
7a-f
6
(
)-1
Scheme 1. Retrosynthetic scheme for the preparation of 5-substituted isoxazolidines.
1,3-Dipolar cycloaddition of allyl bromide with nitrone (ꢀ)-119
in toluene under microwave irradiation at 110 °C afforded com-
pound 2 in 98% yield as a single isomer (Scheme 1). The regioselec-
tivity was similar to that observed for various terminal alkenes,
with attack on the terminal methylene by the electrophilic carbon
of the dipole, presumably due to both steric and electronic rea-
sons.9c,f,19c The stereoselectivity results from the approach of allyl
bromide from the less hindered face of nitrone (ꢀ)-1 (opposite to
the isopropyl group), the reaction taking place via a transition state
placing the bromomethyl group away from the spirocyclic nitrone
according to an exo-approach (Scheme 2). This was deduced from a
2D NOESY experiment, which showed strong correlations between
protons H3–H4, H40–H5, and H5–H12, and weak nuclear Overhaus-
er effects between protons H3–H40 and H4–H5. Other correlations
observed between H3 and both H13 and H15 were also in agree-
ment with the stereochemistry proposed for 2 (Fig. 2).
strong
Br
6
H4'
weak
H
H4
5
4
strong
H
1
O
3
2
medium
medium
N
strong
H
13
15
14
O
7
N
H
8
9
11
12
10
16
When the brominated cycloadduct 2 was treated under acidic
conditions to remove the chiral auxiliary, the isoxazolidine 3 was
obtained in an unexpectedly poor yield. Consequently, following
our synthetic plan, the bromide 2 was converted into the corre-
sponding azido-functionalized isoxazolidine 4 by nucleophilic sub-
stitution in excellent yield. Azide 4 was converted in high yields
into a series of 1,2,3-triazoles 5a–f by means of CuAAC reactions
under microwave irradiation.23 Acid treatment of compounds
5a–c and 5f led to cleavage and formation of compounds 7a–c
and 7f in 34, 32, 29, and 39% yields, respectively (Table 1), while
5d and 5e, which both contain electron-rich and bulky moieties re-
mained unchanged under the conditions applied. To overcome the
Figure 2. Characteristic NOESY correlations of compound 2.
limitations previously mentioned, we undertook the acidic cleav-
age of the chiral auxiliary in 4 to afford the N-acetylated isoxazol-
idine 6 in 45% yield. Treatment of isoxazolidine 6 with various
terminal alkynes under CuAAC conditions afforded, uneventfully,
a series of six 1,4-disubstituted 1,2,3-triazoles 7a–f in good yields.
The low yield (25%) observed for the acidic cleavage of the
chiral auxiliary in bromide 2 was unexpected, but was close to that
recorded for the same step (33%) in the case of the cycloadduct de-
rived from allylic alcohol.9f When converting 2 into isoxazolidine 3,
N
N
N
Br
N3
Br
allyl bromide
R
H
H
H
H
O
O
O
5a 84%
5b 86%
5c 88%
5d 87%
5e 84%
5f 88%
O
N
N
N
O
O
O
N
a
b
98%
c
C
O
N
N
N
R
CH
98%
N
2
4
5a-f
(
)-1
% from 5
7a 34%
7b 32%
7c 29%
7d NR
25% d
45% e
f
R
R
N
N
CH3
Br
N3
N
7e NR
a
b
c
; d
; e
; f
7f 39%
R
O2N
H3CO
NHCH3
NHCH3
O
O
NHCH3
O
c
N
COCH3
N
COCH3
N
H3CO
CH3
% from 6
7a 79%
7b 80%
7c 78%
7d 71%
7e 76%
7f 82%
R
C
CH
O
O
COCH3
O
O
3
6
7a-f
H3CO
O
Scheme 2. Synthesis of functionalized isoxazolidines. Reagents and conditions: (a) toluene, MW, 110 °C, 2 h; (b) NaN3, DMF, 70 °C, 6 h; (c) iPr2NEt, CuI, MW, DMF, 110 °C,
15 min; (d) AcOH, Ac2O, cat. H2SO4, 50 °C, 6 h; (e) AcOH, Ac2O, cat. H2SO4, 50 °C, 10 h; (f) see Table 1.

1970
K. Aouadi et al. / Tetrahedron Letters 54 (2013) 1967–1971
Table 1
Acid cleavage of the chiral auxiliary in compounds 5a–f
Entry
Substrate
Conditionsa
Time (h)
Product
Yieldb (%)
N
N
N
H
O2N
O
1
A
6
19
19
7a
34
N
O
5a
N
N
N
N
H
H3C
O
2
3
4
5
6
A
7b
32
N
O
5b
N
N
N
N
H
H3CO
O
A
7c
29
N
5c
O
N
NRc
NRc
N
A
B
6
24
7d
7d
N
CH3
N
H
H3CO
O
N
O
5d
N
N
N
N
H
H3CO
O
A
6
7e
NRc
N
O
5e
N
N
N
N
O
O
H
O
A
8
7f
39
N
5f
O
N
a
b
c
Conditions: (A) AcOH, Ac2O, cat. H2SO4, 55 °C; (B) AcOH, Ac2O, cat. HCl (37%), 75 °C.
Yields are of the isolated product after silica gel column chromatography.
NR no reaction, starting material unchanged.
TLC analysis showed one mobile spot for 3, plus one spot on the
baseline for unidentified highly polar products. Acidic cleavage of
the menthone in 4 led to 6 in a 45% yield. As we observed much
better yields (reaching ꢁ90%) for the cleavage of the chiral auxil-
iary in related cycloadducts,25 we do not at present have a general
explanation for the disappointing yields observed in the present
study. To prepare the desired 1,2,3-triazolyl-substituted isoxazoli-
dines 7a–f from the azido-functionalized isoxazolidine 4, the best
two-step route involved initial acidic removal of the menthone
moiety to deliver azide 6 and subsequent CuAAC coupling with ter-
minal alkynes, which proceeded well in all the attempted reac-
tions. The approach reported herein represents another entry to

K. Aouadi et al. / Tetrahedron Letters 54 (2013) 1967–1971
1971
triazole-linked heterocycles24 that can be elaborated further to tri-
azole-linked amino acids, by cleavage of the N–O bond,9c–g and
saponification.25
6. (a) Couty, F.; Evano, G.; Varga-Sanchez, M.; Bouzas, G. J. Org. Chem. 2005, 70,
9028–9031; (b) Wang, L.; Schultz, P. G. Angew. Chem., Int. Ed. 2005, 44, 34–66;
(c) Tsantrizos, Y. S. Acc. Chem. Res. 2008, 41, 1252–1263.
7. Singh, R.; Singh Bhella, S.; Sexana, A. K.; Shanmugavel, M.; Faruk, A.; Ishar, M. P.
S. Tetrahedron 2007, 63, 2283–2291.
8. For selected references see : (a) Grigor’ev, I. A. In Nitrile Oxides, Nitrones, and
Nitronates in Organic Synthesis; Feuer, H., Ed., 2nd ed.; Wiley-Interscience, 2008;
pp 129–434; For recent reviews on asymmetric 1,3-dipolar cycloadditions, see
In conclusion, the cycloaddition of a chiral nitrone to allyl bro-
mide led to a single isoxazolidine in 98% yield. Substitution with an
azide group opened a rapid access through CuAAC reactions to a
series of six heterocycles possessing a 4-substituted-(1,2,3-triazol-
yl)methyl moiety linked to an isoxazolidine. As the acidic cleavage
of the menthone chiral auxiliary was found to be a limiting step,
access to the desired triazolylmethyl 2,3,5-trisubstituted isoxazoli-
dines appeared to be more efficient when the CuAAC step was ap-
plied after cleavage of the chiral auxiliary. The ring-opening of
substituted isoxazolidines to afford amino acids being well docu-
mented, further developments of this strategy for synthesizing tri-
azole-based unnatural amino acids are now under investigation
and will be reported in due course.
:
(b) Pellissier, H. Tetrahedron 2007, 63, 3235–3285; (c) Gothelf, K. V.;
Jorgensen, K. A. Chem. Rev. 1998, 98, 863–909; Stereocontrolled cycloaddition
with chiral nitrones are documented, see : (d) Stanley, L. M.; Sibi, M. P. Chem.
Rev. 2008, 108, 2887–2902; (e) Fišera, L. Top. Heterocycl. Chem. 2007, 7, 287–
323; (f) Brandi, A.; Cardona, F.; Cicchi, S.; Cordero, F. M.; Goti, A. Chem. Eur. J.
2009, 15, 7808–7821; For enantiopure cyclic nitrones, see: (g) Revuelta, J.;
Cicchi, S.; Goti, A.; Brandi, A. Synthesis 2007, 485–504; for nitrone-based chiral
glycine equivalents, see: (h) Baldwin, S. W.; Long, A. Org. Lett. 2004, 6, 1653–
1656.
9. (a) Tamura, O.; Shiro, T.; Ogasawara, M.; Toyao, A.; Ishibashi, H. J. Org. Chem.
2005, 70, 4569–4577; (b) Cordero, F. M.; Bonollo, S.; Machetti, F.; Brandi, A. Eur.
J. Org. Chem. 2006, 3235–3241; (c) Aouadi, K.; Vidal, S.; Msaddek, M.; Praly, J.-P.
Synlett 2006, 3299–3303; (d) Aouadi, K.; Jeanneau, E.; Msaddek, M.; Praly, J.-P.
Synthesis 2007, 3399–3405; (e) Aouadi, K.; Jeanneau, E.; Msaddek, M.; Praly, J.-
P. Tetrahedron: Asymmetry 2008, 19, 1145–1152; (f) Aouadi, K.; Msaddek, M.;
Praly, J.-P. Tetrahedron 2012, 68, 1762–1768; (g) Aouadi, K.; Jeanneau, E.;
Msaddek, M.; Praly, J.-P. Tetrahedron Lett. 2012, 53, 2817–2821.
10. Jones, R. C. F.; Martin, J. N. The Chemistry of Heterocyclic Compounds In
Synthetic Applications of 1,3-Dipolar Cycloaddition Chemistry Toward Heterocycles
and Natural Products; Padwa, A., Pearson, W. H., Eds.; Wiley: New York, 2002;
Vol. 59, pp 1–81.
11. Kumar, K. R. R.; Mallesha, H.; Rangappa, K. S. Arch. Pharm. Pharm. Med. Chem.
2003, 336, 159–164.
12. Kumar, R. S.; Perumal, S.; Shetty, K. A.; Yogeeswari, P.; Sriram, D. Eur. J. Med.
Chem. 2010, 45, 124–133.
13. Loh, B.; Vozzolo, L.; Mok, B. J.; Lee, C. C.; Fitzmaurice, R. J.; Caddick, S.; Fassati,
A. Chem. Biol. Drug Des. 2010, 75, 461–474.
14. Morita, N.; Fukui, K.; Irikuchi, J.; Sato, H.; Takano, Y.; Okamoto, I.; Ishibashi, H.;
Tamura, O. J. Org. Chem. 2008, 73, 7164–7174.
Acknowledgments
Région Rhône-Alpes is gratefully thanked for financial support
(via SRESR2007-2010/Cluster de Recherche 2009 n 5/Chimie:
Molécules Bioactives) and a stipend to K. A. (via CMIRA ACCUEIL
PRO 2010 program). Other supports from University Claude-
Bernard Lyon 1 and CNRS are also acknowledged. The authors
thank Dr. F. Albrieux, C. Duchamp, and N. Henriques from the
Centre Commun de Spectrométrie de Masse (ICBMS UMR-5246)
for their assistance and access to mass spectrometry facilities.
15. Nguyen, T. B.; Beauseigneur, A.; Martel, A.; Dhal, R.; Laurent, M.; Dujardin, G. J.
Org. Chem. 2010, 75, 611–620.
Supplementary data
16. Nguyen, T. B.; Vuong, T. M. H.; Martel, A.; Dhal, R.; Dujardin, G. Tetrahedron:
Asymmetry 2008, 19, 2084–2087.
17. Nguyen, T. B.; Martel, A.; Dhal, R.; Dujardin, G. Org. Lett. 2008, 10, 4493–4496.
18. Thiverny, M.; Philouze, C.; Chavant, P.-Y.; Blandin, V. Org. Biomol. Chem. 2010, 8,
864–872.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.01.
125.
19. (a) Altenbach, H.-J.; Kottenhahn, M.; Vogt, A.; Matthäus, M.; Grundler, A.;
Hahn, M. DE 19533617 A1, 1997; Chem. Abstr. 1997, 126, 264352f.; (b) Vogt, A.;
Altenbach, H.-J.; Kirschbaum, M.; Hahn, M. G.; Matthäus, M. S. P.; Hermann, A.
R. EP 976721, 2000; Chem. Abstr. 2000, 132, 108296j.; (c) Westermann, B.;
Walter, A.; Flörke, U.; Altenbach, H.-J. Org. Lett. 2001, 3, 1375–1378.
20. Aouadi, K.; Lajoix, A.-D.; Gross, R.; Praly, J.-P. Eur. J. Org. Chem. 2009, 61–71.
21. Meldal, M.; Tornøe, C. W. Chem. Rev. 2008, 108, 2952–3015.
22. Huisgen, R. In 1,3-Dipolar Cycloaddition Chemistry; Padwa, A., Ed.; Wiley: New
York, 1984.
23. (a) Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67, 3057–3064;
(b) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem., Int.
Ed. 2002, 41, 2596–2599; (c) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew.
Chem., Int. Ed. 2001, 40, 2004–2021; (d) Bouillon, C.; Meyer, A.; Vidal, S.;
Jochum, A.; Chevolot, Y.; Cloarec, J.-P.; Praly, J.-P.; Vasseur, J. J.; Morvan, F. J.
Org. Chem. 2006, 71, 4700–4702; (e) Cecioni, S.; Lalor, R.; Blanchard, B.; Praly,
J.-P.; Imberty, A.; Matthews, S. E.; Vidal, S. Chem. Eur. J. 2009, 15, 13232–13240.
24. Nasir Baig, R. B.; Varma, R. S. Chem. Commun. 2012, 48, 5853–5855.
25. Cecioni, S.; Aouadi, K.; Praly, J.-P. unpublished results.
References and notes
1. Chemistry of Peptide Synthesis; Leo Benoiton, N., Ed.; CRC Press Taylor & Francis:
Boca Raton, 2005.
2. (a) Bhat, S. V.; Nagasampagi, B. A.; Sivakumar, M. Chem. Nat. Prod. Springer
2005, 317–393; (b) Xie, J.; Schultz, P. G. Nat. Rev. Mol. Cell Biol. 2006, 7, 775–
782; (c) Neumann, H.; Peak-Chew, S. Y.; Chin, J. W. Nat. Chem. Biol. 2008, 4,
232–234; Zuend, S. J.; Coughlin, M. P.; Lalonde, M. P.; Jacobsen, E. N. Nature
2009, 461, 968–970.
3. Liao, X. W.; Liu, W.; Dong, W. F.; Guan, B. H.; Chen, S. Z.; Liu, Z. Z. Tetrahedron
2009, 65, 5709–5715.
4. Bueno, M. P.; Cativiela, C. A.; Mayoral, J. A.; Avenoza, A. J. Org. Chem. 1991, 56,
6551–6555.
5. (a) Cowen, B. J.; Miller, S. J. J. Am. Chem. Soc. 2007, 129, 10988–10989; (b)
Tsogoeva, S. B. Eur. J. Org. Chem. 2007, 1701–1716; (c) Micskei, K.; Patonay, T.;
Caglioti, L.; Pályi, G. Chem. Biodiversity 2010, 7, 1660–1669.