Organic Letters
Letter
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(11) For the use of more conformationally constrained macrocycles,
see: (a) allo-Threonine: Carney, D. W.; Schmitz, K. R.; Truong, J. V.;
Sauer, R. T.; Sello, J. K. J. Am. Chem. Soc. 2014, 136, 1922−1929. (b) 4-
Methylpipecolic acid: Socha, A. M.; Tan, N. Y.; LaPlante, K. L.; Sello, J.
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253.
(14) Skwarczynski, M.; Kiso, Y. Curr. Med. Chem. 2007, 14, 2813−
2823 and references therein.
oriented and rapid approach for analogue synthesis than can be
achieved through macrolactamization based strategies. Further
investigations on the generality of this approach for the
formation of other depsipeptide and macrocyclic natural
products as well as mechanistic studies will be reported in due
course.
ASSOCIATED CONTENT
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S
* Supporting Information
Full experimental details and characterization data for all
compounds including copies of 1H and 13C NMR spectra. This
material is available free of charge via the Internet at http://pubs.
(15) (a) Cochrane, J. R.; Yoon, D. H.; McErlean, C. S. P.; Jolliffe, K. A.
Beilstein J. Org. Chem. 2012, 8, 1344−1351. (b) Cochrane, J.; McErlean,
C. S. P.; Jolliffe, K. A. Org. Lett. 2010, 12, 3394−3397.
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Tetrahedron Lett. 2002, 43, 7535−7539.
AUTHOR INFORMATION
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Corresponding Author
(17) Mukaiyama, T.; Izumi, J.; Miyashita, M.; Shiina, I. Chem. Lett.
1993, 907−910.
Notes
(18) Ishihara, K.; Kubota, M.; Kurihara, H.; Yamamoto, H. J. Org.
Chem. 1996, 61, 4560−4567.
(19) (a) Shiina, I.; Fujisawa, H.; Ishii, T.; Fukada, Y. Heterocycles 2000,
52, 1105−1123. (b) Shiina, I.; Fukada, Y.; Ishii, T.; Fujisawa, H.;
Mukaiyama, T. Chem. Lett. 1998, 831−832.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(20) For the direct macrolactonization of seco acids using Hf(OTf)4,
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́ ́
see: de Leseleuc, M.; Collins, S. K. ACS Catal. 2015, 5, 1462−1467.
The authors are grateful for financial support through a Natural
Science and Engineering Research Council (NSERC) of Canada
Discovery Grant and a Canadian Institutes of Health Research
(CIHR) Institute of Infection and Immunity - Emerging Team
Grant (XNE-86945) (P.I.: Walid Houry) and an NSERC PGS-
D2 scholarship to J.D.G. E.d.S. thanks the Conselho Nacional de
(21) For the use of Ln(III) salts in combination with anhydrides and
related derivatives for the intermolecular esterification of alcohols, see:
(a) Dalpozzo, R.; De Nino, A.; Maiuolo, L.; Oliverio, M.; Procopio, A.;
Russo, B.; Tocci, A. Aust. J. Chem. 2007, 60, 75−79. (b) Procopio, A.;
Dalpozzo, R.; De Nino, A.; Maiuolo, L.; Russo, B.; Sindona, G. Adv.
Synth. Catal. 2004, 346, 1465−1470. (c) Dalpozzo, R.; De Nino, A.;
Maiuolo, L.; Procopio, A.; Nardi, M.; Bartoli, G.; Romeo, R. Tetrahedron
Lett. 2003, 44, 5621−5624. (d) Kluger, R.; Cameron, L. L. J. Am. Chem.
Soc. 2002, 124, 3303−3308.
́
́
Desenvolvimento Cientıfico e Tecnologico/CNPq - Brazil for
scholarship support.
(22) For chemoselective monoesterification studies of polyols using
lanthanides, see: (a) Dhiman, R. S.; Kluger, R. Org. Biomol. Chem. 2010,
8, 2006−2008. (b) Tzvetkova, S.; Kluger, R. J. Am. Chem. Soc. 2007, 129,
15848−15854. (c) Cameron, L. L.; Wang, S. C.; Kluger, R. J. Am. Chem.
Soc. 2004, 126, 10721−10726. (d) Clarke, P. A.; Kayaleh, N. E.; Smith,
M. A.; Baker, J. R.; Bird, S. J.; Chan, C. J. Org. Chem. 2002, 67, 5226−
5231. (e) Clarke, P. A. Tetrahedron Lett. 2002, 43, 4761−4763.
(23) Initial attempts to macrolactonize the corresponding threonine
and allo-threonine analogues of 12a using these conditions were both
unsuccessful, but alternative conditions are currently under inves-
tigation.
(24) THF and MeCN were also found to be suitable solvents for the
macrolactonization of 12a in the presence of 30 mol % Dy(OTf)3, giving
13a in 87% and 92% isolated yield, respectively.
(25) Tic = (3S)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid.
(26) The antibacterial evaluation of these analogues is in progress and
will be the subject of a full report.
(27) Attempts to replace the Pip moiety with other groups including
azetidine-2-carboxylic acid, MeVal or MeLeu, or replacement of the
adjacent Pro residue with trans-4-hydroxyproline(t-Bu) or Oic
((2S,3aS,7aS)-octahydroindole-2-carboxylic acid) were not tolerated.
(28) NMR experiments in CD2Cl2 were carried out in order to
establish the role of the lanthanide salt during ester formation. The
mixed anhydride derived from Cbz-Pro-OH and MNBA was exposed to
excess MeOH (∼40 equiv) in the presence/absence of La(OTf)3 (30
mol %). Methyl ester formation in the presence of La(OTf)3 occurred
cleanly and in less than 2 h, whereas in the absence of lanthanide salt
required at least 12 h. Furthermore, the latter experiment results in an
unselective ∼1:1 mixture of the expected ester and starting material
(Cbz-Pro-OH). For experimental details, see Supporting Information.
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