Published on Web 04/27/2004
Total Synthesis of TMC-95A and -B via a New Reaction
Leading to Z-Enamides. Some Preliminary Findings as to SAR
Songnian Lin,† Zhi-Qiang Yang,† Benjamin H. B. Kwok,‡ Michael Koldobskiy,‡
Craig M. Crews,‡,§,| and Samuel J. Danishefsky*,†,
Contribution from the Laboratory for Bioorganic Chemistry, Sloan Kettering Institute for Cancer
Research, 1275 York AVenue, New York, New York 10021, Department of Chemistry, Columbia
UniVersity, HaVemayer Hall, 3000 Broadway, New York, New York 10027, and Department of
Molecular, Cellular and DeVelopmental Biology, Pharmacology, and Chemistry, Yale UniVersity,
219 Prospect Street, New HaVen, Connecticut 06520-8103
Received January 11, 2004; E-mail: s-danishefsky@mskcc.org
Abstract: A full account of the total syntheses of proteasome inhibitors TMC-95A and -B is provided. A
key feature of the syntheses involved installation of a cis-propenylamide moiety by a thermal rearrangement
of an R-silylallyl amide. The scope and mechanism of the enamide-forming reaction are discussed. Also
provided are some preliminary results from SAR studies. It was found that simplified analogues can retain
the full potency of proteasome inhibition.
Introduction
In eukaryotic cells, degradation of key regulatory proteins
by the ubiquitin-proteasome pathway is crucial for many
important cellular processes, including cell cycle progression,
apoptosis, antigen presentation, and NF-κB activation.1,2 Selec-
tive proteasome inhibitors are of therapeutic potential for a
number of disorders, such as cancer, inflammation, and immune
diseases.3
TMC-95A (1a) and its diastereoisomers TMC-95B-D (1b-
d, Figure 1), recently isolated as fermentation products of
Apoispora montagnei,4 represent a new class of selective
proteasome inhibitors. Among their defining structural charac-
teristics are (i) the cyclic polypeptide array containing L-tyrosine,
L-asparagine, and highly oxidized L-tryptophan moieties, (ii) an
acylated (Z)-1-propenylamine substructure, and (iii) a 3-methyl-
2-oxopentanoic acid substructure in the form of an amidic
linkage to the tyrosine-like sector of the cyclic peptide.5
Biological studies showed that TMC-95A inhibited the chy-
motrypsin-like (CT-L), trypsin-like (TL), and post-glutamyl
peptide hydrolytic (PGPH) activities of the proteasome with IC50
Figure 1. Structures of TMC-95A-D.
values of 5.4, 200, and 60 nM, respectively.4 TMC-95B inhibited
these activities to the same extent as TMC-95A, while TMC-
95C and -D were 20-150 times weaker. The binding mode of
these inhibitors to the proteasome has been recently elucidated
by X-ray crystallography.6 Unlike other synthetic or natural
proteasome inhibitors,3b TMC-95A does not modify the N-
terminal catalytic threonine residue. It binds to the active sites
of the proteasome via characteristic hydrogen bonds. TMC-95A
also showed cytotoxic activities against human cancer cells
HCT-116 and HL-60 with IC50 values of 4.4 and 9.8 µM,
respectively.4
† Sloan-Kettering Institute for Cancer Research.
‡ Department of Molecular, Cellular and Developmental Biology, Yale
University.
The combination of structural novelty and potency, as well
as the unique inhibition mechanism of TMC-95A and -B has
served to generate considerable interest among synthetic organic
chemists. Not surprisingly, a variety of approaches have been
pursued by several research groups.7 Our group reported the
§ Department of Chemistry, Yale University.
| Department of Pharmacology, Yale University.
Columbia University.
(1) (a) Rock, K. L.; Gramm, C.; Rothstein, L.; Clark, K.; Stein, R.; Dick, L.;
Hwang, D.; Goldberg, A. L. Cell 1994, 78, 761-771. (b) Craiu, A.;
Gaczynska, M.; Akopoan, T.; Gramm, C. F.; Fenteany, G.; Gildberg, A.;
Rock, K. L. J. Biol. Chem. 1997, 272, 13437-13445.
(2) (a) Coux, O.; Tanaka, K.; Goldberg, A. L. Annu. ReV. Biochem. 1996, 65,
801-847. (b) Ciechanover, A. EMBO J. 1998, 17, 7151-7160.
(3) Myung, J.; Kim, K. B.; Crews, C. M. Med. Res. ReV. 2001, 21, 245-273.
(b) Kisselev, A. F.; Goldberg, A. L. Chem. Biol. 2001, 8, 739-758. (c)
Goldberg, A. L.; Rock, K. Nat. Med. 2002, 8, 338-340.
(4) Koguchi, Y.; Kohno, J.; Nishio, M.; Takahashi, K.; Okuda, T.; Ohnuki,
T.; Komatsubara, S. J. Antibiot. 2000, 53, 105-109.
(6) Groll, M.; Koguchi, Y.; Huber, R.; Kohno, J. J. Mol. Biol. 2001, 311, 543-
548.
(7) (a) Lin, S.; Danishefsky, S. J. Angew. Chem., Int. Ed. 2001, 40, 1967-
1970. (b) Inoue, M.; Furyama, H.; Sakazaki, H.; Hirama, M. Org. Lett.
2001, 3, 2863-2865. (c) Ma, D.; Wu, Q. Tetrahedron Lett. 2001, 42, 5279-
5281. (d) Albrecht, B. K.; Willians, R. M. Tetrahedron Lett. 2001, 42,
2755-2757. (e) Ma, D.; Wu, Q. Tetrahedron Lett. 2000, 41, 9089-9093.
(5) Kohno, J.; Koguchi, Y.; Nishio, M.; Nakao, K.; Kuroda, M.; Shimizu, R.;
Ohnuki, T.; Komatsubara, S. J. Org. Chem. 2000, 65, 990-995.
9
10.1021/ja049821k CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 6347-6355
6347