1608 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 8
Ni et al.
(3) Dower, W. J .; Barrett, R. W.; Gallop, M. A.; Needels, M. C.
Method of Synthesizing Diverse Collection of Oligomers. PCT
Application WO 93/06121.
(4) Brenner, S.; Lerner, R. A. Encoded Combinatorial Chemistry.
Proc. Natl. Acad. Sci. U.S.A. 1992, 89, 5181-5183.
of acetic anhydride and pyridine (each 10%, v/v, in NMP, 10
mL). The resin was thoroughly washed with NMP and CH2-
Cl2 and then subjected to one round of the tag addition cycle
described below.
(b) Th r ee-Step Ta g Ela bor a tion P r ocess (Sch em e 1b).
The Alloc protecting group was removed from the tag addition
sites by treatment of the resin with tetrabutylammonium azide
and Pd(0) as described above. After reaction with N-Alloc-
iminodiacetic anhydride (0.1 g, 0.5 mmol, 10 equiv relative to
free NH2) and DIEA (0.087 mL, 0.5 mmol) in NMP (5 mL) for
1 h, the resin suspension was drained and then treated with
an excess of pentafluorophenyl trifluoroacetate and pyridine
in NMP (1:1:1, total volume 3 mL) for 1 h. Subsequent
treatment of the polymer-supported OPfp ester with an
appropriate mixture of secondary amines completed one round
of the tagging cycle.
(5) For encoded synthesis using oligonucleotide tags, see: (a)
Needels, M. C.; J ones, D. G.; Tate, E. H.; Heinkel, G. L.;
Kochersperger, L. M.; Dower, W. J .; Barrett, R. W.; Gallop, M.
A. Generation and Screening of an Oligonucleotide-Encoded
Synthetic Peptide Library. Proc. Natl. Acad. Sci. U.S.A. 1993,
90, 10700-10704. (b) Nielsen, J .; Brenner, S.; J anda, K. D.
Synthetic Methods for the Implementation of Encoded Combi-
natorial Chemistry. J . Am. Chem. Soc. 1993, 115, 9812-9813.
(6) For encoded synthesis using amino acid tags, see: (a) Kerr, J .
M.; Banville, S. C.; Zuckermann, R. N. Encoded Combinatorial
Peptide Libraries Containing Non-Natural Amino Acids. J . Am.
Chem. Soc. 1993, 115, 2529-2531. (b) Nikolaiev, V.; Stierandova,
A.; Krchnak, V.; Seligmann, B.; Lam, K. S.; Salmon, S. E.; Lebl,
M. Peptide-Encoding for Structure Determination of Nonse-
quenceable Polymers Within Libraries Synthesized and Tested
on Solid-Phase Supports. Pept. Res. 1993, 6, 161-170. (c)
Krchnak, V.; Weichsel, A. S.; Cabel, D.; Lebl, M. Linear
Presentation of Variable Side-Chain Spacing in a Highly Diverse
Combinatorial Library. Pept. Res. 1995, 8, 198-205.
(7) For encoded synthesis using haloaromatic tags, see: (a) Ohlm-
eyer, M. H. J .; Swanson, R. N.; Dillard, L. W.; Reader, J . C.;
Asouline, G.; Kobayashi, R.; Wigler, M.; Still, W. C. Complex
Synthetic Chemical Libraries Indexed with Molecular Tags.
Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 10922-10926. (b) Nestler,
H. P.; Bartlett, P. A.; Still, W. C. A General Method for Molecular
Tagging of Encoded Combinatorial Chemistry Libraries. J . Org.
Chem. 1994, 59, 4723-4724.
(8) As an alternative to molecularly based tags, two recent reports
describe the use of radiofrequency encodable microchips as
information storage media for combinatorial synthesis, i.e.: (a)
Moran, E. J .; Sarshar, S.; Cargill, J . F.; Shahbaz, M. M.; Lio,
A.; Mjalli, A. M. M.; Armstrong, R. W. Radio Frequency Tag
Encoded Combinatorial Library Method for the Discovery of
Tripeptide-Substituted Cinnamic Acid Inhibitors of the Protein
Tyrosine Phosphatase PTP1B. J . Am. Chem. Soc. 1995, 117,
10787-10788. (b) Nicolaou, K. C.; Xiao, X. -Y.; Parandoosh, Z.;
Senyei, A.; Nova, M. P. Radiofrequency Encoded Combinatorial
Chemistry. Angew. Chem., Int. Ed. Engl. 1995, 34, 2289-2291.
(9) In binary encoding, defined mixtures of tags are used to denote
the addition of a specific chemical building block in a particular
step of ligand synthesis (“binary” refers to the presence or
absence of tags in the mixture defining the two states that form
the basis of the synthesis code).
(10) The 18 amines, listed in order of increasing retention time of
their dansyl amides, are N-ethyl-N-butylamine, N-methyl-N-
hexylamine, N,N-dibutylamine, N-methyl-N-heptylamine, N-
butyl-N-pentylamine, N,N-dipentylamine; N-butyl-N-hepty-
lamine, N,N-dihexylamine, N-pentyl-N-octylamine, N-propyl-N-
decylamine, N-methyl-N-dodecylamine, N,N-bis[(2-ethyl)hexyl]-
amine, N,N-dioctylamine, N-butyl-N-dodecylamine, N-pentyl-N-
dodecylamine, N-hexyl-N-dodecylamine, N-heptyl-N-dodecy-
lamine, and N,N-didecylamine.
After treatment with Fmoc-Cl (0.6 g, 2.32 mmol) and DIEA
(0.4 mL, 2.32 mmol), a second repetition of the tag elongation
cycle gave phenylalanine resin encoded with a tag dimer. This
resin was then gently agitated with a 1.0 M solution of
benzaldehyde in trimethyl orthoformate (4 mL) for 4 h. The
resin was again filtered and washed with CH2Cl2 (2 × 3 mL).
[2 + 3] Cycloaddition of the imine was effected by addition of
a solution containing 1.0 M each of silver(I) nitrate, 3-buten-
2-one, and NEt3 in MeCN. The solution turned black after 5
min with plating of silver upon the walls of the vessel occurring
after 2 h. After 8 h the resin was filtered and washed with
saturated ammonium chloride (2 × 3 mL), MeOH (2 × 3 mL),
and CH2Cl2 (2 × 3 mL). The newly formed pyrrolidine amino
group was protected by 2 × 1 h treatments with an NMP
solution containing Fmoc-Cl and DIEA (2.0 M each) followed
by 2 × 1 h treatments with a pyridine solution containing
Fmoc-Cl (2.0 M). One further cycle of tag elongation gave the
fully encoded pyrrolidine resin. Spectrophotometric determi-
nation of dibenzofulvene released from a small aliquot of this
resin upon treatment with piperidine indicated a loading of
the Fmoc-protected pyrrolidine that was equivalent to the
initial loading of Fmoc-Phe. The pyrrolidine 9 was cleaved
from an aliquot of the resin upon treatment with a 10%
solution of trifluoroacetic acid in CH2Cl2 (2 mL) for 30 min
and characterized by HPLC and spectroscopic analysis: 1H
NMR (300 MHz, CDCl3) δ 7.80-7.01 (m, 10H), 4.54 (d, J )
6.9 Hz, 1H), 3.41-3.31 (m, 1H), 3.34 (ab q, J ) 14.0 Hz, 2H),
2.90 (dd, J ) 3.5, 14.3 Hz, 1H), 2.50 (dd, J ) 7.7, 14.3 Hz,
1H), 2.08 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 197.715,
152.754, 133.769, 132.851, 129.926, 129.911, 129.855, 129.782,
128.954, 127,601, 127.498, 126.955, 126.814, 120.662, 61.734,
55.725, 51.499, 49.348, 38.475, 29.694; MS (ESI) m/ z 324 [(M
+ H)+].
Individual resin beads were selected at random for decoding
as described above.
(11) The time required to effect this acidic hydrolysis can be reduced
to ∼20 min by irradiation of the sealed capillary tube in a
domestic microwave oven.
Ack n ow led gm en t. We thank J ung Lee and Caryn
Schunk for assistance in the preparation of several
tagging monomers.
(12) Holmes, C. P.; J ones, D. G. Reagents for Combinatorial Organic
Synthesis: Development of a New o-Nitrobenzyl Photolabile
linker for Solid Phase Synthesis. J . Org. Chem. 1995, 60, 2318-
2319.
(13) Ruhland, B.; Bhandari, A.; Gordon, E. M.; Gallop, M. A. Solid-
Supported Combinatorial Synthesis of Structurally Diverse
â-Lactams. J . Am. Chem. Soc. 1996, 118, 253-254.
Su p p or tin g In for m a tion Ava ila ble: Spectroscopic and
analytical data characterizing the 18 N-Boc-N-[(dialkylcar-
bamoyl)methyl]glycine tag monomers 4a -r (38 pages). Order-
ing information is given on any current masthead page.
(14) Murphy, M. M.; Schullek, J . R.; Gordon, E. M.; Gallop, M. A.
Combinatorial Synthesis of Highly Functionalized Pyrro-
lidines: Identification of
a Potent Angiotensin Converting
Enzyme Inhibitor from a Mercaptoacyl Proline Library. J . Am.
Chem. Soc. 1995, 117, 7029-7030.
(15) Holmes, C. P.; Chinn, J . P.; Look, G. C.; Gordon, E. M.; Gallop,
M. A. Strategies for Combinatorial Organic Synthesis: Solution
and Polymer-Supported Synthesis of 4-Thiazolidinones and
4-Metathiazanones Derived from Amino Acids. J . Org. Chem.
1995, 60, 7328-7333.
(16) The Fmoc protecting group is stable under these conditions;
see: Shapiro, G.; Buechler, D. Mild and Rapid Azide-Mediated
Palladium Catalyzed Cleavage of Allylester Based Protecting
Groups. Tetrahedron Lett. 1994, 35, 5421-5424.
(17) By contrast, the rates of aminolysis of resin-bound pentafluo-
rophenyl esters are highly dependent on the steric bulk of the
secondary amine nucleophile, and thus, in the second approach,
the relative composition of mixtures of tagging amines must be
modulated to reflect these kinetic differences.
Refer en ces
(1) (a) Gallop, M. A.; Barrett, R. W.; Dower, W. J .; Fodor, S. P. A.;
Gordon, E. M. Applications of Combinatorial Technologies to
Drug Discovery. 1. Background and Peptide Combinatorial
Libraries. J . Med. Chem. 1994, 37, 1233-1251. (b) Gordon, E.
M.; Barrett, R. W.; Dower, W. J .; Fodor, S. P. A.; Gallop, M. A.
Applications of Combinatorial Technologies to Drug Discovery.
2. Combinatorial Organic Synthesis, Library Screening Strate-
gies, and Future Directions. J . Med. Chem. 1994, 37, 1385-1401.
(c) Terrett, N. K.; Gardner, M.; Gordon, D. W.; Kobylecki, R. J .;
Steele, J . Combinatorial Synthesis - The Design of Compound
Libraries and their Application to Drug Discovery. Tetrahedron
1995, 51, 8135-8173. (d) Gordon, E. M.; Gallop, M. A.; Patel,
D. V. Strategy and Tactics in Combinatorial Organic Synthesis.
Applications to Drug Discovery. Acc. Chem. Res. 1996, 29, 144-
154.
(18) This is a significant limitation with the amino acid-based coding
schemes previously described.
(2) Furka, A.; Sebestyen, F.; Asgedom, M.; Dibo, G. General Method
for Rapid Synthesis of Multicomponent Peptide Mixtures. Int.
J . Pept. Protein Res. 1991, 37, 487-493.
J M960043J