Published on Web 04/05/2002
Total Synthesis of A-315675: A Potent Inhibitor of Influenza
Neuraminidase
Stephen Hanessian,* Malken Bayrakdarian, and Xuehong Luo
Contribution from the Department of Chemistry, UniVersite´ de Montre´al,
C.P. 6128, Succursale Centre-Ville, Montre´al, Que´bec H3C 3J7, Canada
Received November 29, 2001
Abstract: A concise, stereocontrolled, and practical synthesis of a neuraminidase inhibitor consisting of a
highly functionalized D-proline scaffold is described. Key features involve a stereocontrolled addition of a
propiolate ester to a chiral nonracemic nitrone derived originally from D-serine and the manipulation of
acyclic and cyclic motifs en route to the target in 12.8% overall yield over 22 steps. Several crystalline
intermediates were suitable for single-crystal X-ray analysis.
Introduction
After replication, new virus particles are released with the aid
of a second glycoprotein, neuraminidase,8 which cleaves
Headlines announcing the approach of the “flu season” are
causes of major health concerns affecting millions of people
worldwide. Despite major efforts at thwarting annual epidemics,
the prospects of morbidity and mortality resulting from such
respiratory tract infections are significant.1 Until recently,
therapeutic options against the influenza virus consisted of
vaccination,2 and the use of two closely related drugs, aman-
tadine or rimantadine.3 However, mutations in the antigenic
components of viral surface proteins have curtailed the wide-
spread use of anti-flu vaccines except for a segment of the
population. While effective against influenza A virus, the utility
of amantadine or rimantadine has been hampered by the rapid
emergence of resistance in viral strains, and the lack of efficacy
against influenza B virus.4 Their specific activity against
influenza A virus has been attributed to an ion channel blocking
of a specific viral protein.
terminal N-acetyl neuraminic acid units from the cell surface
glycoconjugate, thus sparing the virus from being entrapped by
aggregation. The infective virus will then propagate through
the respiratory tract, a process that is also facilitated by further
neuraminidase-mediated cleavages at the mucosal level.6a,9 The
catalytic action of neuraminidase is therefore responsible for
the replication, infectivity, and propagation of the influenza
virus. Elegant X-ray crystallographic10 structural studies have
revealed that the catalytic active site of influenza neuraminidases
A and B, consisting of 18 amino acid residues is highly
conserved.
The realization that N-acetyl neuraminic acid (NANA) 1 is a
weak inhibitor of the enzyme led to the design of closely related
analogues, such as the 2,3-didehydro analogue DANA (2), which
is about 1000 times more active as an inhibitor (Figure 1).11
The structural information on the enzyme has spurned several
new inhibitors of which two are presently marketed. Zanamivir
(Relenza) (3), a 4-deoxy-4-guanidino analogue of 2, is admin-
istered by nasal inhalation, since it is of low bioavailability when
given orally, and it is rapidly eliminated.12 Tamiflu (Oselta-
mivir)13 is a carbocyclic ester analogue of GS-4071 that is highly
The influenza RNA virus expresses two glycoproteins on its
surface that are essential for its replication and infectivity.5 The
cycle of infection starts in the epithelial cells of the upper
respiratory tract by binding of virus particles to cell surface
receptor glyconconjugates, which is followed by endocytosis.6
The viral glycoprotein hemagglutinin7 mediates the binding to
the receptor on the host cell and the process of endocytosis.
(7) (a) Sauter, N. K.; Hanson, J. E.; Click, G. D.; Brown, J. H.; Crowther, R.
L.; Park, S. J.; Skehel, J. J.; Wiley, D. C. Biochemistry 1992, 31, 9609. (b)
Mammen, M.; Dahmann, G.; Whitesides, G. J. Med. Chem. 1995, 38, 4179.
(8) Colman, P. M. In The Influenza Viruses: Influenza Virus Neuraminidase,
Enzyme and Antigen; Krug, R. M., Ed.; Plenum: New York, 1989, pp
175-218. Colman, P. M. Protein Sci. 1994, 3, 1657.
* Address correspondence to this author. Phone: (514) 343-6738. Fax:
(1) (a) Monto, A. S.; Iacuzio, I. A.; La Montagne, J. R. J. Infect. Dis. 1997,
176, 51. (b) Service, R. F. Science 1997, 275, 756. (c) Saul, H. New Scientist
1995, 26. (d) Lui, K.-J.; Kendal, A. P. Am. J. Public Health 1987, 77, 712.
(e) Glezen, W. P. Epidemiol. ReV. 1982, 4, 25.
(2) Hayden, F. G.; Belshe, R. B.; Clover, R. D.; Hay, A. J.; Oakes, M. G.;
Soo, N. N. Engl. J. Med. 1989, 321, 1696.
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1985, 4, 3021.
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1995, 69, 1099. (c) Klenk, H.-D.; Rott, R. AdV. Virus Res. 1988, 34, 247.
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(10) (a) Burmeister, W. P.; Ruigrok, R. W. H.; Cusack, S. EMBO J. 1992, 11,
49. (b) Bossart-Whitaker, P.; Carson, M.; Babu, Y. S.; Smith, C. D.; Laver,
W. G.; Air, G. M. J. Mol. Biol. 1993, 232, 1069. (c) Varghese, J. H.;
Colman, P. M. J. Mol. Biol. 1995, 221, 473. (d) Janakiraman, M. N.; White,
C. L.; Laver, W. G.; Air, G. M.; Luo, M. Biochemistry 1994, 33, 8172. (e)
Varghese, J. N.; McKimm-Breschkin, J. L.; Caldwell, J. B.; Kortt, A. A.;
Colman, P. M. Proteins: Struct. Funct. Genet. 1992, 14, 327. (f) Tulip,
W. R.; Varghese, J. N.; Laver, W. G.; Colman, P. M. J. Mol. Biol. 1992,
227, 122. (g) Varghese, J. N.; Epa, V. C.; Colman, P. M. Protein Sci. 1995,
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J. AM. CHEM. SOC. 2002, 124, 4716-4721
10.1021/ja0126226 CCC: $22.00 © 2002 American Chemical Society