Shortcut to Fmoc-protected phosphinic pseudodipeptidic blocks

Article abstract of DOI:10.1021/ol051622y

(Chemical Equation Presented) A three-component condensation reaction of Fmoc-carbamate, aldehydes, and alkylphosphinic acids provides a new, direct, and efficient method for synthesizing Fmoc-protected phosphinic pseudodipeptidic blocks, directly usable

Full text of DOI:10.1021/ol051622y

ORGANIC
LETTERS
2005
Vol. 7, No. 18
4049-4052
Shortcut to Fmoc-Protected Phosphinic
Pseudodipeptidic Blocks
Magdalini Matziari and Athanasios Yiotakis*
Laboratory of Organic Chemistry, Department of Chemistry, UniVersity of Athens,
Panepistimiopolis Zografou 15771, Athens, Greece
yiotakis@chem.uoa.gr
Received July 11, 2005
ABSTRACT
A three-component condensation reaction of Fmoc-carbamate, aldehydes, and alkylphosphinic acids provides a new, direct, and efficient
method for synthesizing Fmoc-protected phosphinic pseudodipeptidic blocks, directly usable for solid-phase peptide synthesis.
Combinatorial chemistry is being increasingly applied for
the discovery of novel biologically active compounds. In this
context, multicomponent reactions are a powerful tool for
the rapid introduction of molecular diversity in terms of lead
identification and optimization.1 The three-component con-
densation reaction of trivalent phosphorus species, amides,
and aldehydes or ketones was first reported in 19742 and
later extended for the synthesis of R-aminophosphinic and
R-aminophosphonic acids.3 More recently, this type of
reaction has been applied in the synthesis of phosphinopep-
tide analogues of glutathionylspermidine.4
(1) Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.;
Keating, T. A. Acc. Chem. Res. 1996, 29, 123.
(2) Birum, G. H. J. Org. Chem. 1974, 39, 209.
(3) (a) Oleksyszyn, J.; Tyka, R.; Mastalerz, P. Synthesis 1978, 479. (b)
Oleksyszyn, J.; Subotkowska, L.; Mastalerz, P. Synthesis 1979, 985. (c)
Oleksyszyn, J.; Gruszecka, E. Tetrahedron Lett. 1981, 22, 3537. (d)
Oleksyszyn, J. J. Prakt. Chem. 1987, 329, 19.
(4) Chen, S.; Coward, J. K. J. Org. Chem. 1998, 63, 502.
(5) (a) Georgiadis, D.; Beau, F.; Czarny, B.; Cotton, J.; Yiotakis,
A.; Dive, V. Circ. Res. 2003, 93, 148. (b) Acharya, K. R.; Sturrock, E.
D.; Riordan, J. F.; Ehlers, M. R. W. Nat. ReV. Drug DiscoV. 2003, 2,
891.
Figure 1. Generic structure of phosphinic peptides.11a
(6) (a) Matziari, M.; Beau, F.; Cuniasse, P.; Dive, V.; Yiotakis, A. J.
Med. Chem. 2004, 47, 325. (b) Reiter, L. A.; Mitchell, P. G.; Martinelli, G.
J.; Lopresti-Morrow, L. L.; Yocum, S. A.; Eskra, J. D. Biorg. Med. Chem.
Lett. 2003, 13, 2331. (c) Schiodt, C. B.; Buchardt, J.; Terp, G. E.;
Christensen, U.; Brink, M.; Berger Larsen, Y.; Meldal, M.; Foged, N. T.
Curr. Med. Chem. 2001, 8, 967.
(7) Georgiadis, D.; Vazeux, G.; Llorens-Cortes, C.; Yiotakis, A.; Dive,
V. Biochemistry 2000, 39, 1152.
(8) Grembecka, J.; Mucha, A.; Cierpicki, T.; Kafarski, P. J. Med. Chem.
2003, 46, 2641.
(9) (a) Makaritis, A.; Georgiadis, D.; Dive, V.; Yiotakis, A. Chem. Eur.
J. 2003, 9, 2079. (b) Buchardt, J.; Schiodt, C. B.; Krog-Jensen, C.; Delaisse,
J. M.; Foged, N. T.; Meldal, M. J. Comb. Chem. 2000, 6, 624.
(10) (a) Dive, V.; Cotton, J.; Yiotakis, A.; Michaud, A.; Vassiliou, S.;
Jiracek J.; Vazeaux, G.; Chauvet, M.-T.; Cuniasse, P.; Corvol, P. Proc.
Natl. Acad. Sci. U.S.A. 1999, 96, 4330. (b) Jiracek. J.; Yiotakis, A.; Vincent,
B.; Checler, F.; Dive, V. J. Biol. Chem. 1996, 271, 19606.
Phosphinic peptides (Figure 1) are transition state analogue-
type inhibitors of Zn-metalloproteases. Replacement of the
scissile peptide bond with the hydrolytically stable P(O)-
(OH)CH2 moiety leads to highly potent and selective
inhibitors of various metalloproteases, e.g., angiotensin-
converting enzyme (ACE),5 matrixins (MMPs),6 aminopep-
tidase A (APA),7 leucine aminopeptidase,8 etc., using either
parallel or combinatorial chemistry strategies,9 both in
solution and on solid support.10
Resolution of three-dimensional structures of complexes
between Zn-metalloproteases and phosphinic peptide inhibi-
10.1021/ol051622y CCC: $30.25
© 2005 American Chemical Society
Published on Web 08/05/2005

tors has confirmed that these pseudopeptides interact with
residues on both sides of the scissile peptide bond.11b,c
However, such inhibitors should be not only potent but also
as selective as possible, to avoid unexpected interactions
among multiple zinc metalloproteases, an issue that could
be addressed by systematic investigation on the influence
of different side chains of the phosphinic inhibitors.
Solid-phase peptide synthesis (SPPS) has been successfully
applied in most cases, providing a powerful tool for the
development of phosphinic peptide libraries. As far as it
concerns the synthesis of the phosphinic pseudodipeptidic
block, numerous synthetic strategies have been developed
and reviewed,12 including building block approaches13 or
postmodification of phosphinopeptidic precursors.14,6a,9a None
of the above-mentioned methods are a panacea for all
situations, so new and improved methods are still needed.
deficient species such as an imine or an acrylic acid ester.
In the first case, phosphinic pseudo-amino acids can be
formed;15 phosphinic acids of type 2′ can be formed in the
second case.16 This general idea can find different applica-
tions depending on which masking bears the phosphorus
moiety.
During the course of this study, we became interested in
finding a synthetic pathway in which a masked phosphinic
acid of type 2 can attack an imine, thus creating the desired
17
dipeptidic block. The direct use of FmocNH2 and phos-
phinic acids of type 2 is superior to the corresponding method
that uses CbzNH2,18 since the building blocks obtained can
be used directly in SPPS. Phosphinic acids of type 2 are
synthesized according to reactions depicted in Scheme 2. It
In this Letter, we report a new method for the synthesis
of phosphinic building blocks, which can be used directly
in SPPS. The significant advantages of the present method,
as compared to the methods previously described in the
literature, are speed and simplicity. Synthesis of the Fmoc-
protected phosphinic dipeptidic blocks (Scheme 1) is achieved
Scheme 2. Synthesis of Compounds Type 2
Scheme 1. Synthesis of Fmoc-Protected Phosphinic Peptides
is worth mentioning that under the reaction conditions used
(5 equiv of bis(trimethylsilyl) phosphonite (BTSP) per 1
equiv of acrylate and high dilution), no disubstituted products
were observed. Compounds of type 2 and 2′ are isolated
using simple workup procedures, in a pure state, as confirmed
by NMR analysis. Acrylic acid esters were either prepared
using well-known procedures, e.g., alkylation of malonic acid
diethyl ester, selective saponification, and subsequent Kno-
evenagel condensation (reactions not shown), or were
commercially available.
Using this new method, phosphinic peptide building
blocks, bearing a variety of R1 and R1′ side-chains have been
synthesized in yields shown in Table 1. The aldehydes 1
(R1CHO) bear side-chains (R1) corresponding to those of
some natural amino acids. In this respect, phosphinic peptides
with R1 side-chains of glycine (3a), alanine (3b), valine (3c),
leucine (3d), isoleucine (3e), glutamic acid (3f), phenylgly-
cine (3g), serine (3h), and an analogue of histidine (3i) have
been synthesized. On the other hand, R1′ side-chains cor-
using mostly commercially available reagents, thus avoiding
multistep procedures, including laborious protection and
deprotection steps.
The basic step for synthesizing phosphinic dipeptidic
blocks is the formation of the P-C bond. Generally, this
type of reaction requires the activation of the P-moiety to
its trivalent form and subsequent attack to an electron-
(11) (a) Nomenclature based on that used in: Schechter, I.; Berger, A.
Biochem. Biophys. Res. Commun. 1967, 27, 157. (b) Gall, A.-L.; Ruff, M.;
Kannan, R.; Cuniasse, P.; Yiotakis, A.; Dive, V.; Rio, M.-C.; Basset, P.;
Moras, D. J. Mol. Biol. 2001, 307, 577. (c) Grams, F.; Dive, V.; Yiotakis,
A.; Yiallouros, I.; Vassiliou, S.; Zwilling, R.; Bode W.; Sto¨cker, W. Nature
Struct. Biol. 1996, 3, 671.
(12) (a) Yiotakis, A.; Georgiadis, D.; Matziari, M.; Makaritis, A.; Dive,
V. Curr. Org. Chem. 2004, 8, 1135. (b) Dive, V.; Georgiadis, D.; Matziari,
M.; Makaritis, A.; Beau, F.; Cuniasse, P.; Yiotakis, A. Cell. Mol. Life Sci.
2004, 61, 2010.
(13) (a) Yiotakis, A.; Vassiliou, S.; Jiracek, J.; Dive, V. J. Org. Chem.
1996, 61, 6601. (b) Campagne, J.-M.; Coste, J.; Guillou, L.; Heitz, A.; Jouin,
P. Tetrahedron Lett. 1993, 34, 4181. (c) Georgiadis, D.; Matziari, M.;
Yiotakis, A. Tetrahedron 2001, 57, 3471. (d) Miller, D. J.; Hammond, S.
M.; Anderluzzi, D.; Bugg, T. D. H. J. Chem. Soc., Perkin Trans. 1 1998,
131.
(14) (a) Matziari, M.; Georgiadis, D.; Dive, V.; Yiotakis, A. Org. Lett.
2001, 3, 659. (b) Georgiadis, D.; Matziari, M.; Vassiliou, S.; Dive, V.;
Yiotakis, A. Tetrahedron 1999, 55, 14635. (c) Kende, A. S.; Dong, H.-Q.;
Liu, X.; Ebetino, F. H. Tetrahedron Lett. 2002, 43, 4973.
(15) Baylis, E. K.; Campbell, C. D.; Dingwall, J. D. J. Chem. Soc., Perkin
Trans. 1 1984, 2845.
(16) (a) Boyd, E. A.; Regan, A. C.; James, K. Tetrahedron Lett. 1992,
33, 813. (b) Boyd, E. A.; Corless, M.; James, K.; Regan, A. C. Tetrahedron
Lett. 1990, 31, 2933.
(17) FmocNH2 is commercially available from Fluka or can be synthe-
sized as described in: Carpino, L. A.; Mansour, E. M. E.; Cheng, C. H.;
Williams, J. R.; MacDonald, R.; Knapczyk, J.; Carman, M.; Lopusinski,
A. J. Org. Chem. 1983, 48, 661.
(18) Chen, S.; Coward, J. K. Tetrahedron Lett. 1996, 37, 4335.
4050
Org. Lett., Vol. 7, No. 18, 2005

Scheme 3. Solid-Phase Elongation of Phosphinic Peptides
Table 1. Yields and Side-Chains of Compounds 3
entry
R1
R1′
yields (%)
3a
3b
3c
3d
3e
3f
3g
3h
3i
H
CH3
PhCH2
56
57
55
62
61
60
73
67
69
58
54
42
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
PhCH2
(CH3)2CHCH2
CH3
(CH3)2CH
(CH3)2CHCH2
CH3CH2(CH3)CH
CH3OOCCH2CH2
Ph
PhCH2OCH2
4-imidazole
CH3
3j
3k
3l
Ph
(CH3)2CHCH2
H
respond to those of phenylalanine (3a-i), leucine (3j),
alanine (3k), and glycine (3l). The yields of pure products
are given in Table 1.
Compounds 3b-k, possess two stereogenic centers,
namely, four diastereoisomers, two pairs of enantiomers, in
approximately the same amount, as indicated by RP-HPLC
analyses and 31P NMR. Separation of the four stereoisomers
can be achieved by RP-HPLC using a chiral column and
the suitable gradient. Alternatively, when blocks 3b-k are
incorporated into a peptide sequence, their separation is easily
accomplished using a conventional RP column, as shown
below in Figure 2 for compound 4. Though the proposed
methods gave satisfactory results in our hands with regard
to yield and purity of the obtained product, except the original
Rosenmund reduction, which provided quantitative and pure
product.24 4(5)Formylimidazole (entry 3i) was prepared by
oxidation of the corresponding alcohol using MnO2.25
An additional advantage of the present method is the
synthesis of phosphinic dipeptides bearing a glutamyl residue
in the P1 position (entry 3f). As already reported,14b Michael-
type additions of aspartyl or glutamyl aminophosphinic acids
to acrylates fail. Up to now, phosphinic peptides bearing an
aspartyl or glutamyl residue in this position were prepared
by postmodification using oxidation of a phenyl group to
carboxylic acid. Obviously, this method cannot be applied
when aryl groups are present in other positions of the
phosphinic block. The method proposed here provides a new
synthetic route to synthesize such blocks.
Figure 2. HPLC chromatogram of compound 4.
synthetic procedure is not stereoselective, it provides the four
diastereoisomers of the phosphinic peptide in nearly the same
amount, which is convenient, especially when the inhibitory
effect of each diasteroisomer is not known, and any of them
can be active.
In addition, phosphinic peptides containing a glycine
residue in the P1 position (entry 3a) can be directly
synthesized by this method, while the synthesis of the
corresponding aminophosphinic acid reported in the literature
requires laborious workup and the yield is low.26
Most of the aldehydes used were commercially available,
except those in entries 3f and 3i. It is interesting to note that
a variety of synthetic methods leading to methyl 4-oxobu-
tanoate (entry 3f) are reported, including ozonolysis,19 acetal
hydrolysis,20 oxidation with PCC,21 reduction with triethyl-
silane,22 and modified Rosenmund reduction.23 None of these
Finally, a protocol for SPPS elongation of the phosphinic
blocks synthesized has been established (Scheme 3). Phos-
phinic peptides of type 3, which bear a free carboxylate
group, are readily applicable for use in SPPS.
(22) Pham, T.; Lubell, W. D. J. Org. Chem. 1994, 59, 3676.
(23) Ku, T. W.; McCarthy, M. E.; Weichman, B. M.; Gleason, J. G. J.
Med. Chem. 1985, 28, 1847.
(19) Taylor, W. G. J. Org. Chem. 1981, 46, 4290.
(24) Hershberg, E. B.; Cason, J. Organic Syntheses; Wiley: New York,
1955; Collect. Vol. III, p 627.
(25) Su, Q.; Wood, J. L. Synth. Commun. 2000, 30, 3383.
(26) Buchardt, J.; Ferreras, M.; Krog-Jensen, C.; Delaisse´, J. M.; Foged,
N. T.; Meldal, M. Chem. Eur. J. 1999, 5, 2877.
(20) Simoneau, B.; Savard, J.; Brassard, P. J. Org. Chem. 1985, 50, 5434.
(21) (a) Gannet. P. M.; Nagel, D. L.; Reilly, P. J.; Lawson, T.; Sharpe,
J.; Toth, B. J. Org. Chem. 1988, 53, 1064. (b) Gutman, A. L.; Boltanski,
A. J. Chem. Soc., Perkin Trans. 1 1989, 47.
Org. Lett., Vol. 7, No. 18, 2005
4051

Although it seems that the use of phosphinic blocks
protected at the hydroxyphosphinyl function is a safer
choice,13a,c utilization of EDC as the coupling reagent ensures
short reaction times and lack of byproducts. As shown in
Figure 2, all four diasteroisomers of compound 4 can be
separated by HPLC.
In conclusion, we have presented a new and very efficient
method for the direct synthesis of Fmoc-protected phosphinic
building blocks, which can be used directly in SPPS. To our
knowledge, it is the first time that FmocNH2 is used in this
type of reaction. The reaction is mild and versatile. Most of
the reagents used are commercially available. Workup and
isolation procedures are simple, and yields are satisfactory.
The proposed method can give rise to a large number of
combinations between R1 and R1′ side chains of phosphinic
peptides and allows the synthesis even of capricious se-
quences.
Acknowledgment. This work was supported in part by
the European Commission (FP5RDT, QLK3-CT02-02136
and FP6RDT, LSHC-CT-2003-503297) and by funds from
the Laboratory of Organic Chemistry and Special Account
for Research Grants of National Athens University (NKUA).
Supporting Information Available: Detailed experi-
mental procedures, spectroscopic and analytical data for all
compounds, copies of 1H, 13C, and 31P NMR and MS spectra,
and HPLC chromatograms for compounds 3a-l. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OL051622Y
4052
Org. Lett., Vol. 7, No. 18, 2005