Communications
opening of cryptophycins 5a–c or by a CrpTE-catalyzed
Keywords: cryptophycins · macrolactonization ·
safety-catch linkers · solid-phase synthesis · thioesterases
.
hydrolysis of the solid-phase-bound substrates 4a–c, as
previously observed.[9a]
After the first enzymatic cleavage of substrates 4a–c, a
second round of activation and incubation with CrpTE
yielded only minor quantities (< 1 mg) of cryptophycins 5a–
c. This result is in accordance with previous observations that
substrates bound to solid support are only partially accessible
to enzymes.[2b] Unlike reported examples for release and
macrolactamization of peptides from solid support, treatment
of substrates 4a–c with a base (e.g. DIPEA or 4-dimethyl-
aminopyridine) did not lead to a macrolactonized product.[15]
All CrpTE substrates tested in this study were enzymati-
cally cleaved from the solid support and cyclized. CrpTE
displays remarkable tolerance towards selected variations in
unit B. The substitution of an ester for an amide between
units C and D was also tolerated by CrpTE. Along with the
previously reported tolerance of CrpTE for structural
variations within b-alanine (unit C), these results indicate
that CrpTE is a versatile tool for chemoenzymatic synthesis
of diverse unitB and unitC cryptophycin analogues using this
method.
b) M. A. Marahiel, T. Stachelhaus, H. D. Mootz, Chem. Rev.
[3] a) J. D. Umarye, T. Leßmann, A. B. García, V. Mamane, S.
b) T. Leßmann, H. Waldmann, Chem. Commun. 2006, 3380 –
[4] a) R. E. Schwartz, C. F. Hirsch, D. F. Sesin, J. E. Flor, M.
Chartrain, R. E. Fromtling, G. H. Harris, M. J. Salvatore, J. M.
Golakoti, I. Ohtani, G. M. L. Patterson, R. E. Moore, T. H.
Corbett, F. A. Valeriote, L. Demchik, J. Am. Chem. Soc. 1994,
116, 4729 – 4737; c) T. Golakoti, J. Ogino, C. E. Heltzel, T. L.
Husebo, C. M. Jensen, L. K. Larsen, G. M. L. Patterson, R. E.
Moore, S. L. Mooberry, T. H. Corbett, F. A. Valeriote, J. Am.
To our knowledge, this is the first report of alkylated
acylsulfonamides as suitable enzyme substrates. In addition,
this is the first example of macrolactone formation using
solid-phase techniques. Combined with the advantages of
solid-phase synthesis this enzymatic approach is an efficient
and fast method for preparing cryptophycin natural products
and related analogues. Owing to the evident versatility of
CrpTE, as also shown here, this solid-phase approach can be
used to generate rapidly a multitude of new cryptophycin
analogues in sufficient yields for bioactivity analysis. In
addition, this solid-phase chemoenzymatic approach should
be suitable for the synthesis of other macrocyclic and linear
natural products.
[5] C. D. Smith, X. Zhang, S. L. Mooberry, G. M. L. Patterson, R. E.
Moore, Cancer Res. 1994, 54, 3779 – 3784.
[6] J. Liang, R. E. Moore, E. D. Moher, J. E. Munroe, R. S. Al-Awar,
D. A. Hay, D. L. Varie, T. Y. Zhang, J. A. Aikins, M. J. Martinelli,
C. Shih, J. E. Ray, L. L. Gibson, V. Vasudevan, L. Polin, K.
White, J. Kushner, C. Simpson, S. Pugh, T. H. Corbett, Invest.
[7] Recent reviews: a) S. Eißler, A. Stoncius, M. Nahrwold, N.
Sewald, Synthesis 2006, 3747 – 3789; b) M. Eggen, G. I. Georg,
[8] N. A. Magarvey, Z. Q. Beck, T. Golakoti, Y. Ding, U. Huber,
T. K. Hemscheidt, D. Abelson, R. E. Moore, D. H. Sherman,
[9] a) Z. Q. Beck, C. C. Aldrich, N. A. Magarvey, G. I. Georg, D. H.
Experimental Section
Activation and CrpTE-mediated macrolactonization of solid-phase-
bound substrates: The substrates 3a–c on safety-catch PEGA resin
(approximately 0.2 mmol) were washed with several portions of N-
methylpyrrolidinone (NMP). The swollen resin was treated with
NMP (5 mL), DIPEA (11 equiv), and iodoacetonitrile (25 equiv),
which was filtered through a plug of basic alumina prior to use. The
reaction flask was shielded from light and agitated for 24 h at 358C.
Resin was washed sequentially with NMP (5 5 mL), DMF (5
5 mL), water (5 5 mL) and pH 8 phosphate buffer (3 5 mL).
CrpTE (3 mL, 60 mm in 25 mm phosphate buffer, pH 8) was added,
and the enzyme–resin mixture was left to stand for 4 h at 238C. Next,
the resin was washed with water (2 5 mL) and dichloromethane (5
5 mL). After extraction of the aqueous filtrate with dichloromethane,
the combined organic extracts and filtrates were dried over MgSO4,
filtered, and concentrated under vacuum. Purification by flash
chromatography or RP-HPLC yielded the cryptophycins 5a–c and
the seco-cryptophycins 6a–c.
Meldal, F.-I. Auzanneau, O. Hindsgaul, M. M. Palcic, J. Chem.
[12] M. Eggen, C. J. Mossman, S. B. Buck, S. K. Nair, L. Bhat, S. M.
[13] The use of standard tris(hydroxymethyl)aminomethane (TRIS)
buffer leads to significant formation of a cryptophycin–TRIS
adduct, as determined by mass spectrometry. Non-nucleophilic
buffer systems circumvented this problem.
[14] Similar arenastatin analogues with an amide bond between
units C and D have been reported: a) N. Murakami, W. Wang, N.
Ohyabu, T. Ito, S. Tamura, S. Aoki, M. Kobayashi, I. Kitagawa,
Narumi, E. Ohtani, S. Kamada, S. Aoki, N. Okada, S. Nakagawa,
b) P. C. de Visser, N. M. A. J. Kriek, P. A. V. van Hooft, A.
Van Schepdael, D. V. Filippov, G. A. van der Marel, H. S. Over-
Received: August 10, 2007
Published online: November 2, 2007
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 9298 –9300
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