TABLE 1. Loa d in g of Am in o Alcoh ol
Use of Tr ich lor oa cetim id a te Lin k er in
Solid -P h a se P ep tid e Syn th esis
Fmoc AA
substitutiona
yield (%)b
glycinol
alaninol
D-alaninol
argininol (Pbf)
leucinol
phenylalaninol
D-phenylalaninol
prolinol
tryptophanol
lysinol (Boc)
threoninol (OtBu)
0.45
0.42
0.52
0.42
0.39
0.40
0.49
0.42
0.36
0.35
0.48
64.3
60.2
74.6
74.5
57.6
60.4
74.0
61.3
55.8
55.7
73.0
Liang Zeng Yan and J ohn P. Mayer*
Lilly Research Laboratories,
A Division of Eli Lilly and Company,
Lilly Corporate Center, Indianapolis, Indiana 46285
j.mayer@lilly.com
Received September 5, 2002
Abstr a ct: A solid-phase method for the preparation of
C-terminal amino-alcohol-containing peptides using acti-
vated Wang resin is presented. A diverse set of (fluorenyl-
methoxy)carbonyl (Fmoc) protected amino alcohols was
found to load rapidly and efficiently. The synthetic utility
of this approach was demonstrated through the direct
synthesis of the peptide drug octreotide with excellent yield
and purity. These results suggest that the use of trichloro-
acetimidate activated resins offers an attractive alternative
in the preparation of this class of peptides.
a
Substitution levels were determined as described in the text
and are expressed in millimoles substrate per gram polystyrene.
Yields are based on the percent of maximal theoretical substitu-
tion.
b
acid (DPTA) conjugated octreotide by (fluorenylmethoxy)-
carbonyl (Fmoc)/tBu strategy. Additionally, a creative
solution was provided by the Novartis group, which
involved the use of a cyclic acetal linkage between Fmoc-
threoninol and a 4-formylphenoxy resin in a solid-phase
synthesis of a radiotherapeutic analogue of octreotide.13
Rivier and co-workers recently reported a series of
C-terminal peptide alcohols as gonadotropin-releasing
hormone antagonists, prepared by using a solution-
coupling method to attach the amino acid alcohol to the
preassembled peptide fragment.14
The successful execution of a solid-phase procedure
requires the covalent attachment of the starting material
to a solid support, usually polystyrene or poly(ethylene
glycol), through an appropriate linker or “handle”. The
classic C-terminal anchoring strategy for peptide syn-
thesis pioneered by Merrifield based on benzyl and
benzhydrylamine linkers for Boc/Bzl chemistry1-3 as well
as the more labile alkoxybenzyl4 or 2,4-dimethoxyben-
zhydrylamine5 versions used in Fmoc/tBu protocols is
generally restricted in its application to the synthesis of
peptides with either free carboxyl or carboxyl amide
termini. While C-terminal anchoring permits modifica-
tions to the N-terminus of a peptide, modifications to the
C-terminus itself tend to be more challenging and may
require use of specialized linkers, prior cleavage from
support, or other indirect methods. An example of such
a modification is a C-terminal alcohol shared by the
antibacterial peptide alamethicin,6 a number of chole-
cystokinin antagonists, growth hormone secretagogues,7,8
and, most prominently, the growth hormone inhibitor
octreotide.9 Several specialized anchoring strategies have
been devised in order to synthesize octreotide and related
analogues by the solid-phase method. Albericio and co-
workers10 reported the use of an active carbonate resin
to anchor Boc-threoninol (OBzl) as part of a Boc/Bzl
synthetic strategy, while Arano et al.11 chose 2-chlorot-
rityl linker12 for attachment of the C-terminal threoninol
in their preparation of a diethylene-triaminepentacetic
The recent reports by Hanessian15 describing the use
of trichloroacetimidate modified resins in organic syn-
thesis demonstrated the straightforward preparation,
substrate loading, and facile cleavage as well as stability
of this linker strategy. These findings encouraged us to
investigate the application of trichloroacetimidate resins
in the solid-phase synthesis of peptides containing an
amino alcohol at the C-terminus.
Initial feasibility studies with a number of diverse
Fmoc protected amino alcohols (obtained either com-
mercially or prepared according to the procedure of
Rodriquez et al.16 from the corresponding carboxylic
acids) confirmed the validity of this approach. Investiga-
tion of loading conditions including time, equivalents of
Lewis acid, and substrate indicated an optimized protocol
involving exposure of the resin to a 3-fold excess of the
Fmoc amino alcohol in dry THF in the presence of 0.2
equiv of BF3‚Et2O for 1 h. The loading performance for a
representative set of amino alcohols using the above set
(10) Alsina, J .; Chiva, C.; Ortiz, M.; Rabanal, F.; Giralt, E.; Albericio,
F. Tetrahedron Lett. 1997, 38, 883-886.
(11) Arano, Y.; Akizawa, H.; Uezono, T.; Akaji, K.; Ono, M.;
Funakoshi, S.; Koizumi, M.; Yokoyama, A.; Kiso, Y.; Saji, H. Biocon-
jugate Chem. 1997, 8, 442-446.
(12) Barlos, K.; Gatos, D.; Kallitsis, J .: Papaphotiou, G.; Sotiriou,
P.; Wenqing, Y.; Schafer, W. Tetrahedron Lett. 1989, 30, 3943.
(13) Albert, R.; Smith-J ones, P.; Stolz, B.; Simeon, C.; Knecht, H.;
Bruns, C.; Pless, J . Bioorg. Med. Chem. Lett. 1998, 8, 1207-1210.
(14) J iang, G.; Stalewski, J .; Galyean, R.; Dykert, J .; Schteingart,
C.; Broqua, P.; Aebi, A.; Aubert, M. L.; Semple, G.; Robson, P.;
Akinsanya, K.; Haigh, R.; Riviere, P.; Trojnar, J .; J unien, J . L.; Rivier,
J . E. J . Med. Chem. 2001, 44, 453-467.
(15) (a) Hanessian, S.; Xie, F. Tetrahedron Lett. 1998, 39, 733-736.
(b) Hanessian, S.; Xie, F. Tetrahedron Lett. 1998, 39, 737-740.
(16) Rodriguez, M.; Llinares, M.; Doulut, S.; Heitz, A.; Martinez, J .
Tetrahedron Lett. 1991, 32, 923-926.
(1) Merrifield, R. B. J . Am. Chem. Soc. 1963, 85, 2149-2154.
(2) Mitchell, A. R.; Erickson, B. W.; Ryabtsev, M. N.; Hodges, R. S.;
Merrifield, R. B. J . Am. Chem. Soc. 1976, 98, 7357-7362.
(3) Matsueda, G. R.; Stewart, J . M. Peptides 1981, 2, 45-50.
(4) Wang, S. S. J . Am. Chem. Soc. 1972, 95, 1328-1333.
(5) Rink, H. Tetrahedron Lett. 1987, 28, 3787-3790.
(6) Mueller, A. I.; Rudin, D. O. Nature 1968, 217, 713-719.
(7) Horwell, D. C.; Hughes, J .; Hunter, J . C.; Pritchard, M. C.;
Richardson, R. S.; Roberts, E.; Woodruff, G. N. J . Med. Chem. 1991,
34, 404-414.
(8) Ankerson, M.; J ohansen, N. L.; Madsen, K.; Hansen, B. S.; Raun,
K.; Nielson, K. K.; Thogersen, H.; Hansen, T. K.; Peschke, B.; Lau, J .;
Lundt, B. F.; Anderson, P. H. J . Med. Chem. 1998, 41, 3169-3704.
(9) Bauer, W.; Briner, U.; Dopfner, W.; Haller, R.; Huguenin, R.;
Marbach, P.; Petcher, T. J .; Pless, J . Life Sci. 1982, 31, 1133-1140.
10.1021/jo026405e CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/20/2002
J . Org. Chem. 2003, 68, 1161-1162
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