A versatile polymer-supported 4-(4-methylphenyl(chloro)methyl)phenoxy linker for solid-phase synthesis of pseudopeptides

Full text of DOI:10.1021/jo000315x

5048
J . Org. Chem. 2000, 65, 5048-5056
through hyperconjugative effects and hence, contributed
A Ver sa tile P olym er -Su p p or ted
to an accelerating effect on the subsequent acidolytic
cleavage reaction. To this end, the linker derivative 5-[4-
(phenyl(chloro)methyl)phenoxy]pentanoyl aminomethyl
polystyrene 1 was initially synthesized. Preliminary
investigations into linker-resin 1 showed good stability
and generic utility for anchoring a range of nucleophiles,
e.g. carboxylates, alcohols and hydroxylamines. However,
it was found that conditions such as 5% v/ v TFA in CH2-
Cl2 for 1 h were necessary for complete acidolytic release
of assembled hydroxamic acids and alcohols from the
solid support. Such acidolytic cleavage conditions were
harsher than we envisaged and this led to the design of
the new linker-resin 2.
4-(4-Meth ylp h en yl(ch lor o)m eth yl)p h en oxy
Lin k er for Solid -P h a se Syn th esis of
P seu d op ep tid es
Gail E. Atkinson, Peter M. Fischer,† and Weng C. Chan*
School of Pharmaceutical Sciences, University of
Nottingham, University Park, Nottingham NG7 2RD, U.K.,
and Cyclacel Ltd., J ames Lindsay Place,
Dundee DD1 5J J , Scotland, U.K.
weng.chan@nottingham.ac.uk
Received March 8, 2000
Solid-phase organic chemistry (SPOC) is now a mature
science and is used extensively as a tool for drug
discovery within the context of high throughput chemical
synthesis.1 A pivotal technology in any SPOC is the
linker-resin; hence, a multitude of such linker-resins have
been synthesized with the desired chemical properties
in mind, encompassing not only the range of ligation
methodologies, but also chemical orthogonality.2
Among the collection of linker-resins, the 2-chlorotrityl
chloride polystyrene3 and 4-[2,4-dimethoxyphenyl(hy-
droxy)methyl]phenoxymethyl polystyrene (Rink resin)4
have been extensively used for anchoring a plethora of
building blocks bearing nucleophilic functionalities. For
example, we recently reported the anchoring of polyamines
and N-Fmoc hydroxylamines, and following a series of
synthetic transformations afforded polyamine peptide
conjugates5 and hydroxamic acids,6 respectively. To
extend the scope of the Rink resin, the linker-solid
support is generally ‘activated′ by conversion to a halide6b,7a
or trifluoroacetate.7b,c However, in our hands, these
derivatives have to be prepared in situ, are unstable and
particularly susceptible to hydrolysis. This prompted us
to design and synthesize a comparatively more stable
Rink chloride analogue.
Structurally, the linker-resin 2 is analogous to the
previously established 1 but with the introduction of a
mildly electron-releasing methyl group at the para posi-
tion on the second aromatic ring. Such para-methyl
substituted aromatic systems have been similarly ex-
ploited,9 e.g. in comparison to the trityl group, 4-methyl-
trityl9a as an amide-protecting group for the side-chain
of asparagine and glutamine displays accelerated TFA-
mediated deprotection kinetics.
Herein, we report a facile and robust approach for the
synthesis of 5-[4-(4-methylphenyl(chloro)methylphenoxy]-
pentanoyl aminomethylated polystyrene 2 and highlight
its potential value for the synthesis of structurally diverse
pseudopeptides, via a range of challenging chemical
transformations. Thus, the synthesis of 2 involved first
Friedel-Crafts acylation of toluene with p-methoxyben-
zoyl chloride in the presence of anhydrous aluminum
chloride to yield 3 (Scheme 1).10 The presence of only the
Since the inherent instability of the Rink chloride resin
is primarily due to the excessive number of electron-
releasing aromatic methoxy groups, thus giving rise to a
highly polarized C-Cl bond, we envisaged that a corre-
sponding aromatic system containing a single para-
butoxy group8 would be sufficient to exhibit the desired
chemical properties. Furthermore, this structural modi-
fication was anticipated to stabilize the benzhydryl cation
1
para-substituted isomer was confirmed by both H NMR
and reversed-phase HPLC analysis. The aryl methyl
ether cleavage of 4-methoxy 4′-methylbenzophenone 3
was efficiently accomplished using a solution of boron
tribromide11 in dichloromethane, to afford the deprotected
handle 4-hydoxy 4′-methylbenzophenone. The desired
linker derivative 4 was then readily obtained in two
steps, specifically O-alkylation of 4-hydoxy 4′-methyl-
benzophenone with ethyl 5-bromopentanoate in the pres-
ence of anhydrous K2CO3, followed by saponification
using methanolic aqueous NaOH. In summary, the
synthesis of the desired handle 4 was accomplished in
* To whom correspondence should be addressed. Tel: +44 115
9515080. Fax: +44 115 9515078.
† Cyclacel Ltd.
(1) (a) Thompson, L. A.; Ellman, J . A. Chem. Rev. 1996, 96, 555-
600. (b) Patel, D. A.; Gordon, E. M. Drug Discovery Today 1996, 1,
134-144. (c) Schultz, J . S. Biotechnol. Prog. 1996, 12, 729-743.
(2) (a) Bunin, B. A. The Combinatorial Index, Academic Press:
London, 1998. (b) J ames, I. W. Tetrahedron 1999, 55, 4855-4946.
(3) Barlos, K.; Chatzi, O.; Gatos, D.; Stavropoulos, G. Int. J . Peptide
Protein Res. 1991, 37, 513-520.
(4) Rink, H. Tetrahedron Lett. 1987, 28, 3787-3790.
(5) Nash, I. A.; Bycroft, B. W.; Chan, W. C. Tetrahedron Lett. 1996,
37, 2625-2628.
(6) (a) Mellor, S. L.; McGuire, C.; Chan, W. C. Tetrahedron Lett.
1997, 38, 3311-3314. (b) Mellor, S. L.; Chan, W. C. Chem. Commun.
1997, 2005-2006.
(8) The 5-oxyvaleryl spacer has been successfully used in several
linker strategies: (a) Albericio, F.; Kneib-Cordonier, N.; Biancalana,
S.; Gera, L.; Masada, R. I.; Hudson, D.; Barany, G. J . Org. Chem. 1990,
55, 3730-3743. (b) Albericio, F.; Barany, G. Tetrahedron Lett. 1991,
32, 1015-1018. (c) Han, Y. X.; Bontems, S. L.; Hegyes, P.; Munson,
M. C.; Minor, C. A.; Kates, S. A.; Albericio, F.; Barany, G. J . Org. Chem.
1996, 61, 6326-6339.
(9) (a) Friede, M.; Denery, S.; Neimark, J .; Kieffer, S.; Gausepohl,
H.; Briand, J . P. Peptide Research 1992, 5, 145-147. (b) Aletras, A.;
Barlos, K.; Gatos, D.; Koutsogianni, S.; Mamos, P. Int. J . Peptide
Protein Res. 1995, 45, 488-496.
(10) Horner, L.; Medem, H. H. G. Chem. Ber. 1952, 85, 520-526.
(11) McOmie, J . F. W.; West, D. E. Org. Syntheses, Collect. Vol. V.
1973, 412-413.
(7) (a) Garigipati, R. S. Tetrahedron Lett. 1997, 38, 6807-6810. (b)
Brill, W. K.-D.; Schmidt, E.; Tommasi, R. A. Synth. Lett. 1998, 906-
908. (c) Tommasi, R. A.; Nantermet, P. G.; Shapiro, M. J .; Chin, J .;
Brill, W. K.-D.; Ang, K. Tetrahedron Lett. 1998, 39, 5477-5480.
10.1021/jo000315x CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/06/2000

Notes
J . Org. Chem., Vol. 65, No. 16, 2000 5049
Sch em e 1
Sch em e 2
four steps with an overall yield of typically 50%. Com-
pound 4 was then conveniently coupled to a solid support,
aminomethyl polystyrene, in quantitative yield. This was
then followed by two versatile solid-phase reactions.
First, sodium borohydride-mediated reduction of the
resin-bound benzophenone functionality to yield the
supported benzhydryl alcohol 6, which on repeated treat-
ment with excess Ph3P•Cl2 furnished the reactive polymer-
supported halide derivative 2. Conversely, the resin-
bound carbinol 6 was transformed to the chloride
derivative 2 using excess acetyl chloride in CH2Cl2,
though in marginally lower efficiency (ca. 90%). More-
over, in an approach similar to that outlined above and
using the high-substitution poly(ethylene glycol)-modified
aminomethyl polystyrene12 (NovaGel), we have also
readily achieved the synthesis of linker-derivatized solid
support, 5-[4-(4-tolyl(chloro)methyl)phenoxy]-pentanoyl
aminomethyl NovaGel.
with 2 to yield amino acyl resins 7 in excellent yields
(0.33-0.56 mmol g-1; 72-100% based on theoretical
chloride loading) (see Scheme 2). Furthermore, by em-
ploying a reversed-phase (RP)-HPLC based analytical
procedure, it was established that FmocAlaOH could be
released quantitatively by exposure of 7 (R ) Me) to
weakly acidic conditions, including 1% v/ v TFA in CH2-
Cl2 within 10 min or 25% v/ v 1,1,1,3,3,3-hexafluoropro-
pan-2-ol (HFIP) in CH2Cl2 within 1 h. This is in contrast
to the Fmoc-amino acid-modified linker-resin 1, which
under identical conditions did not allow complete aci-
dolysis of the benzhydryl ester bond. In addition, the
derivatized resin 7 (R ) Me) was effectively stable to
conditions such as 20% or 50% v/v trifluoroethanol in
CH2Cl2 (10-15% cleavage over 1 h), which are known to
caused complete acidolysis of O-(N-Fmoc-aminoacyl)oxy
2-chlorotrityl polystyrene3.
The chloride substitution levels were initially esti-
mated by exposing 2 to 0.05 M NaOH(aq) in 1,4-dioxane
Unexpectedly, in preliminary investigations, we noted
the necessity of a higher acid concentration (5% v/ v TFA
in CH2Cl2, 75 min) for the release of FmocArg(Pmc)OH
anchored to the linker resin 1. It was hypothesized that
during acid treatment, preferential protonation of the
side-chain guanidino functionality of Arg occurred, thus
retarding the rate of ester protonation that is close in
proximity. Consequently, the rate of acidolysis was
considerably retarded and is unique for the tethered
FmocArg(Pmc)OH residue. It was anticipated that the
new linker-resin 2, by virtue of the introduced 4′-methyl
group, would allow for a more rapid release of tethered
FmocArg(Pmc)OH. Indeed, acidolytic cleavage was com-
plete when the FmocArg(Pmc)-derivatized 7 was exposed
to milder acidic conditions (1% TFA for 75 min), but the
resin 7 was still relatively stable to 50% HFIP in CH2-
Cl2 (14% cleavage over 2 h). Intriguingly, we also found
that the 4-[2,4-dimethoxyphenyl(FmocArg(Pmc)-oxy)m-
ethyl]phenoxymethyl polystyrene (derived from Rink
resin4) on treatment with 50% v/ v HFIP in CH2Cl2 for 2
h resulted in only 14% cleavage of the ester bond.
(2:3 v/v) followed by back-titration with 0.01 M HCl(aq)
,
and using phenolphthalein as indicator. This typically
indicated chloride levels of 0.85-1.0 mmol g-1, which is
ca. 30% higher than expected (0.64 mmol g-1), hence
suggesting the presence of noncovalently bound chloride.
Based on subsequent experiments, we now routinely
estimate the ‘reactive′ chloride levels in 2 by condensing
with FmocAlaOH in the presence of DIEA, followed by
determination of Fmoc-substitution;6a accordingly, 0.58-
0.64 mmol g-1 chloride loading were typically obtained.
Significantly, using the “reactive” chloride loading as a
marker, the linker-resin 2 was observed to be stable when
stored at -20 °C over a period of two-to-three months.
Having established a facile synthetic route to linker-
resin 2, we proceeded to tether a range of O-nucleophiles.
Thus, in our initial investigations, a selection of N-Fmoc-
amino acids (e.g., Ala, Arg(Pmc), Glu(Ot-Bu), Trp(Boc),
Thr(t-Bu)), in the presence of DIEA, readily condensed
(12) Adams, J . H.; Cook, R. M.; Hudson, D.; J ammalamadaka, V.;
Lyttle, M. H.; Songster, M. F. J . Org. Chem. 1998, 63, 3706-3716.

5050 J . Org. Chem., Vol. 65, No. 16, 2000
Notes
Sch em e 3
The ability of the linker-resin 2 to anchor alcoholic
functionality was then illustrated by the tethering of
N-Fmoc-amino alcohols to yield derivatized resins 8 (R
) H, i-Pr, Bn, C,N-cyclic[-(CH2)3-]; 0.46-0.56 mmol g-1
,
82-100%, based on theoretical chloride loading) (Scheme
2). However, initial studies indicated that during the
TFA-mediated (1 or 5% TFA/CH2Cl2, in the presence of
triethylsilane) release of resin-bound FmocNH(CH2)2OH,
variable amounts of the byproduct FmocNH(CH2)2-
OCOCF3 were observed. Hence, following acidolytic
release, either FmocNH(CH2)2OH reacts with the trieth-
ylsilyl trifluoroacetate intermediate in a nucleophilic
manner to form the trifluoroacetate ester product, or the
ester is obtained directly via an acid-catalyzed esterifi-
cation reaction. The trifluoroacetylation of alcoholic
products during TFA treatment has previously been
observed, and a number of strategies have been devised
to overcome this undesired side-reaction.2,13 Thus, we
systematically evaluated several mild HCl-based cleav-
age reagents and concluded that 0.2 M HCl in CH2Cl2
for 75 min was most effective.
Furthermore, the ability of linker-resin 2 to anchor
hindered primary alcohols was illustrated by the attach-
ment of N-Fmoc-L-valinol to yield 8 (R ) i-Pr; 0.42-0.54
mmol g-1, 78-100%, based on a theoretical chloride
loading of 0.64 mmol g-1). This is in sharp contrast to
the condensation of N-Fmoc-L-valinol with 2-chlorotrityl
chloride polystyrene (0.46-0.51 mmol g-1, 58-63%, based
on an initial chloride loading of 1.05 mmol g-1), which
occurred in significantly lower efficiency and is compa-
rable to observations reported by Wenschuh et al.14
Attention was then directed to the application of the
linker-resin 2 for the selective O-anchoring of both
N-substituted and N-Fmoc protected hydroxylamines.
Thus, N-Fmoc protected hydroxylamines were tethered
onto 2 in high efficiency to yield derivatized resins 9
(FmocNHOH, 88%; FmocN(Pr)OH, 71%; FmocN(Me)OH,
84%, FmocN(Bn)OH, 65%; FmocN(cyclobutyl)OH, 50%)
(Scheme 2). Detailed evaluations established that Fmoc-
NHOH and FmocN(Pr)OH were released quantitatively
from 9 on treatment with 1% v/ v TFA in CH2Cl2 for 75
min at ambient temperature. Such mild acidolysis is
advantageous, since strong acidic reagents are known to
cause decomposition of the hydroxamic acid to the
corresponding acid. It should be noted however, that upon
exposure to 1% v/ v TFA in CH2Cl2 for a shorter time
period of 10 min, release of FmocNHOH and FmocN(Pr)-
OH from the linker-resin 9 were 74% and 88%, respec-
tively. In comparison, the FmocN(Pr)OH-derivatized
Rink resin4,6 upon treatment with 1% v/ v TFA in CH2-
Cl2 for 10 min yielded the required hydroxamic acid in
78% yield.
Sch em e 4
yield (99%) and purity (>90%, determined by RP-HPLC).
Such protected peptides per se are potentially useful
molecular tools, as well as useful building blocks for
convergent synthesis of proteins. The generic utility of
the derivatized linker-resin 7 was further illustrated by
the solid-phase synthesis of the acid-sensitive N-acyl
amino acid derivatives 11 and 12 (Scheme 3) in excellent
purities. Release of the protected peptide and derivatized
amino acids from the solid support was typically ac-
complished using extremely mild acidic conditions, 25%
v/ v HFIP in CH2Cl2 for 1 h, under which a range of
protecting groups, e.g. N-Boc and Ot-Bu remained intact.
The resin-bound alcohols 8, linked via the benzhydryl
ether functionality, also proved to be ideal starting
materials for the general solid-phase synthesis of various
modified alcohols, including the protected pseudopeptides
13 and 14 (Scheme 4). Following solid-phase reactions,
treatment of the resin products with 0.2 M HCl in CH2-
Cl2 for 75 min at ambient temperature afforded the
Collectively, we are confident that our new benzhydryl-
based linker retained many of the desired properties of
the parent Rink linker, but with the added advantage of
a highly stable and robust chloride intermediate 2. Thus,
we then subjected the derivatized linker-resins 7, 8 and
9 to a range of chemical transformations. In the first
instance, the resin 7 was successfully used for the
synthesis of the N,O-protected nonapeptide 10, using
standard Fmoc/t-Bu solid-phase strategy,15 in excellent
(13) (a) Leznoff, C. C.; Fyles, T. M. J . Chem. Soc., Chem. Commun.
1976, 251-252. (b) Deegan, T. L.; Gooding, O. W.; Baudart, S.; Porco,
J . A. Tetrahedron Lett. 1997, 38, 4973-4976.
(14) Wenschuh, H.; Beyermann, M.; Haber, H.; Seydel, J . K.; Krause,
E.; Bienert, M. J . Org. Chem. 1995, 60, 405-410.
(15) Fmoc Solid-Phase Peptide Synthesis: A Practical Approach;
Chan, W. C., White, P. D., Eds.; Oxford University Press: Oxford, 2000.

Notes
J . Org. Chem., Vol. 65, No. 16, 2000 5051
Sch em e 5
Sch em e 6
and reaction temperature to be of utmost importance.
Specifically, to the derivatized resin 15 in THF at 5 °C
was added successively the alcohol, Bu3P and TMAD. For
the pseudopeptide derivatives 16a -c, complete conver-
sion of the starting material 15 to the desired resin-
products were observed after 24 h (established by cleav-
age using 0.2 M HCl in CH2Cl2, and analysis by RP-
HPLC). However, for the aliphatic derivative 16d , ca.
10% of starting material remained even after 48 h
reaction time.
protected peptide alcohols in excellent yields and purities
(>99%). The solid-phase syntheses of fully protected or
acid-sensitive peptide alcohols, e.g., octreotide and pep-
taibols14 have been the focus of recent research due to
their unique biological properties. In summary, though
a number of useful linker-resins for anchoring alcoholic
functionality have been reported,14,16 the versatility of our
linker system makes it a valuable addition to the armory
of chemical tools.
Hydroxamic acid derivatives display a variety of phar-
maceutical properties, in particular the inhibition of the
matrix metalloproteinases (MMPs). These enzymes are
mediators for the breakdown of structural proteins of the
extracellular matrix and as such, have implications in a
variety of inflammatory and degenerative conditions.
Consequently, a number of solid-phase approaches for
high throughput synthesis of hydroxamic acids have been
reported.6,21 In the main, these synthetic methodologies21
are not adaptable for the synthesis of N-alkylhydroxamic
acids. Thus, due to the flexibility of our linker system,
we have also accomplished the solid-phase construction
of various modified hydroxamic acids, including the
hydroxamic acids 17 and 18 in good yields (Scheme 6).
The synthetic approach to the hydroxamic acid deriva-
tive 17 was developed to provide a framework for rapid
access to structural analogues of the histone deacetylase
inhibitors, trichostatin A and suberoylanilide hydroxamic
acid,22 which display potent anti-tumor properties. N-
Moreover, the immobilized Fmoc-L-valinol derivative
8 was further elaborated to afford the sulfonamide
intermediate 15, via N-acylation with FmocNvaOH ac-
tivated as the 7-azabenzotriazol-1-yl ester17,18 and sulfo-
nylation of the Fmoc-liberated amine with para-meth-
oxybenzenesulfonyl chloride (Scheme 5). An aliquot of the
resin 15 was cleaved to characterize the intermediate and
assured the efficiency of the synthetic procedure. Sub-
sequently, the solid-phase N-alkylation of the sulfonam-
ide intermediate 15 was investigated extensively, and a
generic approach based on the Mitsunobu reaction19 was
developed. Recently, several new azodicarboxamides have
been introduced in order to improve the scope of the
original combination of DEAD and Ph3P in the Mitsu-
nobu reaction. In our studies, facile N-alkylation was ac-
complished by employing Tsunoda’s modified redox sys-
tem20 of N,N,N′,N′-tetramethylazodicarboxamide (TMAD)
and Bu3P. A variety of aryl/heteroarylmethyl and alkyl
alcohols as the alkylating component were investigated.
Expectedly, we found the order of introduction of reagents
(20) (a) Tsunoda, T.; Otsuka, J .; Yamamiya, Y.; Ito, S. Chem. Lett.
1994, 539-542. (b) Tsunoda, T.; Kawamura, Y.; Uemoto, K.; Ito, S.
Heterocycles 1998, 47, 177-179. (c) Tsunoda, T.; Ito, S. J . Synth. Org.
Chem. 1997, 55, 631-641. (d) Ngu, K.; Patel, D. V. J . Org. Chem. 1997,
62, 7088-7989. (e) Chaturvedi, S.; Otteson, K.; Bergot, J . Tetrahedron
Lett. 1999, 40, 8205-8209.
(16) (a) Thompson, L. A.; Ellman, J . A. Tetrahedron Lett. 1994, 35,
9333-9336. (b) Hsieh, H.-P.; Wu, Y.-T.; Chen, S.-T.; Wang, K.-T. Chem.
Commun. 1998, 649-650. (c) Wu, Y.-T.; Hsieh, H.-P.; Wu, C.-Y.; Yu,
H.-M.; Chen, S.-T.; Wang, K.-T. Tetrahedron Lett. 1998, 39, 1783-
1784. (d) Mergler, M.; Dick, F.; Gosteli, J .; Nyfeler, R. Tetrahedron
Lett. 1999, 40, 4663-4664.
(17) (a) Carpino, L. A. J . Am. Chem. Soc. 1993, 115, 4397-4398.
(b) Carpino, L. A.; El-Fahem, A.; Albericio, F. Tetrahedron Lett. 1994,
35, 2279-2282. (c) Carpino, L. A.; El-Fahem, A.; Minor, C. A.; Albericio,
F. J . Chem. Soc., Chem. Commun. 1994, 201-203. (d) Bofill, J . M.;
Albericio, F. Tetrahedron Lett. 1999, 40, 2641-2644.
(21) (a) Thouin, E.; Lubell, W. D. Tetrahedron Lett. 2000, 41, 457-
460. (b) Barlaam, B.; Hamon, A.; Maudet. M. Tetrahedron Lett. 1998,
39, 7865-7868. (c) Bauer, U.; Ho, W.-B.; Koskinen, A. M. P. Tetrahe-
dron Lett. 1997, 38, 7233-7236. (d) Richter, L. S.; Desai, M. C.
Tetrahedron Lett. 1997, 38, 321-322. (e) Chen, J . J .; Spatola, A. F.
Tetrahedron Lett. 1997, 38, 1511-1514. (f) Beckett, R. P.; Davidson,
A. H.; Drummond, A. H.; Huxley, P.; Whittaker, M. Drug Discovery
Today 1996, 1, 16-26. (g) Floyd, C. D.; Lewis, C. N.; Patel, S. R.;
Whittaker, M. Tetrahedron Lett. 1996, 37, 8045-8048.
(18) Albericio, F.; Bofill, J . M.; El-Faham, A.; Kates, S. A. J . Org.
Chem. 1998, 63, 9678-9683.
(19) (a) Mitsunobu, O. Synthesis 1981, 1-28. (b) Hughes, D. L.
Organic Reactions 1992, 42, 335-656.
(22) Finnin, M. S.; Donigian, J . R.; Cohen, A.; Richon, V. M.; Rifkind,
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188-193.

5052 J . Org. Chem., Vol. 65, No. 16, 2000
Notes
Sch em e 7
Sch em e 8
Attention was then focused on an unique class of
anomalous amino acid derivatives, namely the R,â-
dehydroamino acids, which are found in many natural
peptidic products that display interesting biological
activities.24 These unsaturated amino acid residues in-
troduce elements of conformational rigidity, as well as
reactive sites for Michael-type addition giving rise to
potentially complex macrocyclic structures. In view of our
particular interest in C-terminal dehydroamino acid
peptides, we have adapted our linker system for solid-
phase synthesis of these unique peptides. Our approach
is based on a recent disclosure by Wandless and co-
workers,25 in which treatment of threo-N-acyl-â-hy-
droxyamino acids with thionyl chloride lead to the
formation of cyclic sulfamidites that, under basic condi-
tions, eliminated SO2 stereospecifically to afford the
corresponding (Z)-N-acyldehydroamino acids in high
purity. Thus, Scheme 8 outlines a model study that was
carried out to establish a mild solid-phase synthetic
approach to (Z)-dehydroamino acid-containing pseudopep-
tides. The immobilized intermediate 7d was produced via
the attachment of FmocThrOH to linker-resin 2, within
24 h, in high efficiency (98%). Since in a preliminary
model experiment during which N-fluorenylmethoxycar-
bonylthreonylmorpholine amide reacted, over a period of
48 h, with linker-resin 2 in only ca. 10% efficiency, we
were confident that FmocThrOH would react preferen-
tially via the carboxylate and not the secondary alcohol
functionality. Following Fmoc-deprotection of 7d , acyla-
tion with activated 4-biphenylcarboxylic acid gave the
resin-bound N-acylthreonine intermediate. Accordingly,
in a one-pot procedure,25 treatment of the resin-bound
intermediate with SOCl2 and Et3N in THF/CH2Cl2 at -78
°C led first to the formation of the cyclic sulfamidite,
followed by elimination at 5 °C to furnish an immobilized
product, which on acidolysis provided the desired (Z)-4-
phenylbenzoyl dehydroaminoalanine 21 (75% purity).
The stereo-configuration of the purified pseudopeptide 21
Fmoc-N-methyl hydroxamic acid was tethered onto 2 in
good efficiency (83%), which on Fmoc-deprotection, was
acylated with carboxy-activated monomethyl suberate.
Saponification of the resin-bound ester intermediate with
0.5 M LiOH in MeOH/THF (cosolvent utilized to ensure
optimal swelling of insoluble polystyrene support), fol-
lowed by condensation with 4-methoxyaniline in the
presence of PyBOP18 yielded a resin product. Exposure
of this material to 1% v/ v TFA in CH2Cl2 furnished a
crude compound in high yield (94%), which was readily
purified to afford the hydroxamic acid 17 as a white solid.
The biaryl moiety, an important pharmacophore motif
present in many biologically active molecules, is syn-
thetically accessible through the well-established Suzuki
palladium-catalyzed cross-coupling reaction.23 Recently,
the Suzuki reaction has been developed extensively for
solid-phase organic chemistry as a method for parallel
synthesis of potential medicinal compounds.23c-h Accord-
ingly, we evaluated the robustness of our linker system
to Suzuki reaction conditions. Thus, FmocAlaOH was
condensed with the chloride linker-resin 2, and following
Fmoc-deprotection underwent acylation with activated
4-bromobenzoic acid (as the HOAt ester18) to yield the
intermediate benzhydryl ester resin 19 (Scheme 7). The
immobilized compound was then modified employing
Suzuki coupling of 2-thiopheneboronic acid under stan-
dard conditions (Pd(PPh3)4, DMF, 80 °C, 24 h) and in a
slight excess of base (2 M Na2CO3(aq.)), to afford upon
release from the solid-support, the biaryl modified amino
acid 20 in excellent crude yield and purity (>90%). Thus,
these results confirmed the stability of our new linker
system, in particular the 4-alkoxy 4′-methylbenzhydryl
ester functionality to both Suzuki conditions and basic
reagents.
(23) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483.
(b) Miyaura, N.; Yanagi, T.; Suzuki, A. Synthetic Communications
1981, 11, 513-519. (c) Lorsbach, B. A., Bagdanoff, J . T.; Miller, R. B.;
Kurth, M. J . J . Org. Chem. 1998, 63, 2244-2250. (d) Backes, B. J .;
Ellam, J . A. J . Am. Chem. Soc. 1994, 116, 11171-11172. (e) Guiles, J .
W.; J ohnson, S. G.; Murray, W. V. J . Org. Chem. 1996, 61, 5169-5171.
(f) Ruhland, B.; Bombrun, A.; Gallop, M. A. J . Org. Chem. 1997, 62,
7820-7826. (g) Frenette, R.; Friesen, R. W. Tetrahedron Lett. 1994,
35, 9177-9180. (h) Han, Y.; Giroux, A.; Lepine, C.; Laliberte, F.;
Huang, Z.; Perrier, H.; Bayly, C. I.; Young, R. N. Tetrahedron 1999,
55, 11669-11685.
1
was confirmed by H NMR.
(24) (a) Humphrey, J . M.; Chamberlin, A. R. Chem. Rev. 1997, 97,
2243-2266. (b) Schmidt, E.; Lieberknecht, A.; Wild, J . Synthesis 1998,
159-172.
(25) Stohlmeyer, M. M.; Tanaka, H.; Wandless, T. J . J . Am. Chem.
Soc. 1999, 121, 6100-6101.

Notes
In summary, we have developed a facile synthetic route
to the ‘fine-tuned′ benzhydryl chloride linker-resin 2 and
the robustness of the linker-resin to a range of advanced
organic synthetic transformations has been comprehen-
sively demonstrated. We envisaged that the linker de-
scribed herein would fill a significant niche in the arsenal
of chemical tools for solid-phase synthesis of both pep-
tides and modified pseudopeptides.
J . Org. Chem., Vol. 65, No. 16, 2000 5053
62.9 MHz) 195.33, 159.81, 142.82, 135.31, 132.81, 130.36, 130.05,
128.91, 115.11, 21.62.
Eth yl 5-[4-(4-Tolu oyl)p h en oxy]p en ta n oa te. 4-Hydroxy 4’-
methylbenzophenone (0.75 g, 3.52 mmol) and anhydrous K2CO3
(0.24 g, 1.76 mmol) were placed in a round-bottomed flask and
DMF (20 mL) was added. The reaction flask was sonicated for
15 min to aid the dissolution of K2CO3. Ethyl 5-bromopentanoate
(668 µL, 4.22 mmol) was then added, and the resultant mixture
was stirred at 50 °C for 72 h. TLC (ethyl acetate:hexane, 3:1)
analysis indicated that the reaction had gone to completion. The
reaction mixture was allowed to cool to room temperature and
the suspension was filtered and washed with DMF (10 mL). The
filtrate was evaporated to dryness in vacuo. The residue was
then dissolved in ethyl acetate (40 mL) and washed with aqueous
sodium hydrogen carbonate (2 × 30 mL), aqueous potassium
hydrogen sulfate (2 × 30 mL) and aqueous brine (2 × 30 mL).
The organic extract was dried and evaporated to dryness in
vacuo to afford the crude product (1.13 g, 95%) as a pale yellow
solid. Purification by flash column chromatography on silica gel,
eluting with 30% ethyl acetate in hexane, yielded the title
compound (0.89 g, 75%) as a white crystalline solid: mp 63-65
°C; APcI-MS+ m/z 341.2 (MH+), calc. 341.4; TLC (ethyl acetate:
hexane, 1:4); Rf ) 0.28; RP-HPLC 50-100% B in 20 min, tR 14.0
min; δH (CDCl3, 250 MHz) 7.80 (2 H, d, J 8.9 Hz), 7.68 (2 H, d,
J 8.2 Hz), 7.28 (2 H, d, J 7.8 Hz), 6.94 (2 H, d, J 8.9 Hz), 4.14 (2
H, q, J 6.9), 4.06 (2 H, t, J 5.3 Hz), 2.44 (3 H, s), 2.41 (2 H, t, J
7.0 Hz), 1.80-1.92 (4 H, m), 1.27 (3 H, t, J 7.1 Hz); δC (CDCl3,
62.9 MHz) 195.29, 173.31, 162.38, 142.51, 135.46, 132.36, 130.28,
129.93, 128.80, 113.85, 67.57, 60.31, 33.82, 28.47, 21.55, 21.52,
14.20. Anal. Calcd for C21H24O4: C, 74.10; H, 7.11%. Found: C,
73.98; H, 7.10%.
Exp er im en ta l Section
Gen er a l Meth od s. See the Supporting Information for
detailed information.
Aminomethylated polystyrene HL 200-400 mesh (AM resin),
aminomethyl NovaGel 100-200 mesh were purchased from CN
Biosciences UK Ltd., Nottingham, U.K Tetrahydrofuran (THF)
and dichloromethane were redistilled prior to use. All glassware
was oven-dried overnight prior to use. All resin products were
dried in vacuo over KOH pellets for 15 h. Reversed-phase high
performance liquid chromatography (RP-HPLC) was performed
on a Hypersil Pep5-C18 column (4.6 × 150 mm). Eluent detection
was monitored by UV absorbance at 220 nm. The linear elution
gradient was either 50 to 100% B in 20 min, 20 to 60% B in 25
min or 30 to 70% B in 25 min at 1.20 mL min-1 (A ) 0.06%
aqueous trifluoroacetic acid (TFA), B ) 0.06% TFA in 90%
aqueous acetonitrile.
P r ep a r a tion of 4-Meth oxy 4′-Meth ylben zop h en on e (3).
Aluminum chloride (2.00 g, 0.015 mol) and toluene (5 mL) were
placed in a two-necked flask, fitted with air-condenser and
dropping funnel, in an ice-bath (5 °C). To the stirred suspension
under argon was added dropwise p-methoxybenzoyl chloride
(1.71 g, 0.010 mol) in toluene (10 mL) via the dropping funnel.
The reaction mixture was stirred at 5 °C for a further 2 h, after
which TLC analysis (ethyl acetate: hexane, 1: 4) indicated that
the reaction had gone to completion. The reaction was quenched
by pouring the mixture into ice-water, and then washed with
1 M aqueous sodium hydroxide (3 × 30 mL). The organic phase
was separated and washed with aqueous potassium hydrogen
sulfate (2 × 40 mL), aqueous sodium hydrogen carbonate (3 ×
40 mL) and brine (2 × 40 mL). The organic extract was dried
(MgSO4) and evaporated to dryness in vacuo to afford the title
compound as a white solid (2.12 g, 94%). Typically, this material
was of sufficient purity: mp 91.3-91.9 °C (lit.10 92 °C); APcI-
MS+ m/z 227.1 (MH+), calcd 227.3; TLC (ethyl acetate:hexane,
1:4) Rf ) 0.32; RP-HPLC 50-100% B in 20 min, tR 10.0 min; δH
(CDCl3, 250 MHz) 7.82 (2 H, d, J 9.0 Hz), 7.69 (2 H, d, J 8.2
Hz), 7.28 (2 H, d, J 8.4 Hz), 6.97 (2 H, d, J 9.0 Hz), 3.89 (3 H, s),
2.45 (3 H, s); δC (CDCl3, 62.9 MHz) 195.33, 162.99, 142.59,
135.47, 132.40, 130.44, 129.97, 128.84, 113.45, 55.45, 21.59.
4-Hyd r oxy 4′-Meth ylben zop h en on e. 4-Methoxy 4’-meth-
ylbenzophenone 3 (1.00 g, 4.4 mmol) was dissolved in CH2Cl2
(10 mL) under argon, and cooled to -78 °C. A solution of 1 M
boron tribromide in CH2Cl2 (8.8 mL, 8.8 mmol) was added
carefully to the stirred solution. The reaction mixture was
allowed to attain room-temperature overnight (19 h) with
stirring, during which a clear brownish yellow solution was
obtained. A further quantity of boron tribromide (2.2 mL, 2.2
mmol) was added and the solution was stirred for a further 5 h.
The reaction mixture was then quenched by the careful addition
of ice-water (20 mL) and stirred for 15 min. A white solid was
obtained, which was dissolved by the addition of tert-butyl
methyl ether (60 mL). The organic phase was separated and
extracted with 2 M aqueous sodium hydroxide (2 × 30 mL). The
alkaline extract was washed with diethyl ether (2 × 30 mL),
neutralized with 2 M aqueous hydrochloric acid and a white
precipitate was formed, which was extracted into diethyl ether
(2 × 40 mL). The organic phase was washed with brine (2 × 30
mL), dried and concentrated in vacuo to afford the crude product
(0.90 g, 96%). The crude product was triturated with ice-cold
toluene to afford the title compound (0.78 g, 83%) as an off-white
solid: mp 167-169 °C (lit.10 175 °C); APcI-MS+ m/z 213.2 (MH+),
calcd 213.3; TLC (ethyl acetate:hexane, 1:1) Rf ) 0.51; RP-HPLC
50-100% B in 20 min, tR 5.6 min; δH (CDCl3, 250 MHz) 7.78 (2
H, d, J 8.8 Hz), 7.69 (2 H, d, J 8.2 Hz), 7.29 (2 H, d, J 8.5 Hz),
6.92 (2 H, d, J 8.8 Hz), 6.13 (1 H, br s), 2.45 (3 H, s); δC (CDCl3,
5-[4-(4-Tolu oyl)p h en oxy]p en ta n oic Acid (4). To a solution
of ethyl 5-[4-(4-toluoyl)phenoxy]pentanoate (0.80 g, 2.35 mmol)
in methanol (20 mL) was added 2 M aqueous sodium hydroxide
(20 mL). It was noted that upon addition of the aqueous NaOH,
the colorless solution turned cloudy and a precipitate was
formed. A further quantity of MeOH (10 mL) was added to aid
the dissolution of the ester. The mixture was vigorously stirred
at room-temperature overnight; TLC (ethyl acetate:acetic acid,
99:1) analysis indicated that the reaction had gone to completion.
The solution was evaporated to dryness in vacuo, and the
resulting white solid was dissolved in water (50 mL) and washed
with tert-butyl methyl ether (2 × 30 mL). The aqueous extract
was acidified to pH 2 with 2 M aqueous HCl and a precipitate
was obtained, which was extracted into tert-butyl methyl ether
(3 × 40 mL). The organic extract was washed with brine (2 ×
30 mL), dried and concentrated in vacuo to afford a crude
product (0.69 g, 94%). The crude product was triturated with
hexane to afford the title compound (0.63 g, 86%) as a white
crystalline solid: mp 128-130 °C; APcI-MS+ m/z 313.1 (MH+),
calcd 313.4; TLC (ethyl acetate:acetic acid, 99:1) Rf ) 0.45; RP-
HPLC 50-100% B in 20 min, tR 7.2 min; δH (CDCl3, 250 MHz)
7.80 (2 H, d, J 8.9 Hz), 7.68 (2 H, d, J 8.2 Hz), 7.27 (2 H, d, J 7.8
Hz), 6.94 (2 H, d, J 8.9 Hz), 4.06 (2 H, t, J 5.6 Hz), 2.47 (2 H, t,
J 6.8 Hz), 2.44 (3 H, s), 1.81-1.89 (4 H, m); δC (CDCl3, 62.9 MHz)
195.44, 179.21, 162.36, 142.61, 135.43, 132.43, 130.33, 129.98,
128.84, 113.87, 67.53, 33.50, 28.38, 21.59, 21.29; Calcd for
C19H20O4: C, 73.06; H, 6.45%. Found: C, 73.21; H, 6.35%.
5-[4-(4-Tolu oyl)p h en oxy]p en t a n oyl Am in om et h yla t ed
P olystyr en e (5). Amino-methylated resin (0.5 g, 0.40 mmol,
loading 0.80 mmol g-1) was swollen in CH2Cl2 (3 mL) for 15 min.
5-[4-(4-Toluoyl)phenoxy]pentanoic acid 4 (0.375 g, 1.20 mmol),
HOAt (0.163 g, 1.20 mmol) and N,N-diisopropylcarbodiimide
(DIPCDI) (207 µL, 1.32 mmol) were then added to the resin
suspension. DMF (3 mL) was added to aid stirring and the
reaction mixture was stirred for 3 h at room temperature. A
further quantity of aminomethylated resin (0.325 g, 0.26 mmol)
was added to the reaction mixture and stirred for a further
24 h. The derivatized resin was filtered, washed successive-
ly with DMF, CH2Cl2 and hexane, and dried in vacuo to afford
5-[4-(4-toluoyl)phenoxy]pentanoyl aminomethylated polysty-
rene (1.25 g, quantitative yield): IR (KBr) 2922, 1651 and 1601
cm-1
.
5-[4-(4-Tolyl(h yd r oxy)m eth yl)p h en oxy]p en ta n oyl Am i-
n om eth yla ted P olystyr en e (6). 5-[4-(4-Toluoyl)phenoxy]pen-
tanoyl aminomethylated polystyrene 5 (1.20 g, 0.78 mmol;
expected loading 0.648 mmol g-1) was swollen in DMF (10 mL)

5054 J . Org. Chem., Vol. 65, No. 16, 2000
Notes
and MeOH (2 mL). Sodium borohydride (0.295 g, 7.8 mmol) was
added portionwise over a period of 30 min. The suspension was
then stirred at room temperature overnight. The resin was
filtered, washed successively with DMF, CH2Cl2 and MeOH, and
dried in vacuo to yield the title compound (0.96 g, 80%): IR (KBr)
Nin -ter t-Bu toxyca r bon yl-NR-(3-p ip er id in -1-ylp r op ion yl)-
L-tr yp top h a n (12). The amino acid derivative FmocTrp(Boc)-
OH (0.158 g, 0.1 mmol) was reacted with 2 (0.156 g, 0.10 mmol,
0.64 mmol g-1) to yield the derivatized resin 7 (0.184 g, 90%;
Fmoc-substitution 0.45 mmol g-1, 91% efficiency). The resin
product was placed in a reaction column and swollen in DMF
for 4 h. The resin was then washed with DMF (10 min, 2.5 mL
min-1), Fmoc-deprotected by treatment with 20% v/ v piperidine
in DMF and finally washed with DMF (10 min, 2.5 mL min-1),
after which excess DMF was removed. 1-Piperidinepropionic acid
(0.05 g, 0.32 mmol), HOAt (0.04 g, 0.32 mmol) and DIPCDI (50
µL, 0.32 mmol) in DMF (1 mL) was added to the resin, and the
mixture was gently stirred at room temperature for 16 h. The
resin was then washed with DMF (10 min, 2.5 mL min-1),
3322, 3025, 2921, 1657 and 1602 cm-1
.
5-[4-(4-Tolyl(ch lor o)m eth yl)p h en oxy]p en ta n oyl a m in o-
m eth yla ted p olystyr en e (2). 5-[4-(4-Tolyl(hydroxy)methyl)-
phenoxy]pentanoyl aminomethylated polystyrene 6 (0.96 g, 0.62
mmol, expected loading 0.648 mmol g-1) was suspended in CH2-
Cl2 (8 mL) and dichlorotriphenylphosphorane (Ph3P•Cl2) (2.00
g, 6.20 mmol) was added portionwise over a period of 15 min.
THF (2 mL) was added to aid the stirring of the resin. The
reaction mixture was stirred at room temperature for 24 h. The
resin was filtered and washed repeatedly with CH2Cl2 and
hexane, and dried in vacuo (1.08 g). The resin was retreated
with Ph3P•Cl2 (1.00 g, 3.10 mmol) in CH2Cl2 (6 mL) and THF (2
mL). Following gently stirring for 24 h at room temperature,
the resin was filtered, washed repeatedly with CH2Cl2 and
hexane, and dried in vacuo to afford the desired title linker-
followed by 20% v/ v piperidine in DMF (5 min, 2.5 mL min-1
)
and finally washed with DMF (10 min, 2.5 mL min-1). The resin
was filtered, washed successively with DMF, CH2Cl2 and MeOH,
and dried in vacuo to yield the desired resin product (0.164 g,
93%), was suspended in CH2Cl2 (3.75 mL) and HFIP (1.25 mL)
was added. The mixture was left at room temperature for 1 h.
The cleavage mixture was then filtered, and washed with CH2-
Cl2 (5 mL), CH2Cl2:MeOH (1:1, 10 mL) and MeOH (5 mL). The
filtrate was evaporated to dryness in vacuo to yield a crude
product (0.033 g, 100%; >95% when analyzed by RP-HPLC).
Purification by recrystallization from ethyl acetate:hexane af-
forded the title compound (0.026 g, 79%) as a white crystalline
solid: mp 135 °C; ES-MS+ m/z 444.4 (MH+), calcd 444.5; RP-
HPLC 50-100% B in 20 min, tR 4.8 min; δH (CDCl3, 250 MHz)
8.03 (1 H, d, J 8.2 Hz), 7.62 (1 H, d, J 7.4 Hz), 7.52 (1 H, d, J 7.1
Hz), 7.45 (1 H, s), 7.14-7.22 (2 H, m), 4.68 (1H, br m), 3.15-
3.28 (2 H, m), 2.60-2.69 (14 H, m), 1.62 (9 H, s); δC (CDCl3,
62.9 MHz) 176.10, 168.86, 149.88, 131.59, 123.89, 122.08, 119.63,
117.25, 114.98, 83.23, 54.86, 53.15, 31.83, 28.19, 28.15, 27.55,
22.53, 22.20. Anal. Calcd for C24H33N3O5‚1/4(CF3)2CHOH: C,
61.22; H, 6.95; N, 8.65%. Found: C, 61.07; H, 7.51; N, 8.75%.
2-(N-(9-F lu or en ylm eth oxyca r bon yl)-O-ter t-bu tyl-L-ser i-
n yl)a m in oeth a n ol (13). To a mixture of 5-[4-(4-tolyl(chloro)-
methyl)phenoxy]pentanoyl aminomethylated polystyrene 2 (0.10
g, 0.06 mmol, expected loading 0.64 mmol g-1) and N-Fmoc-
aminoethanol (0.054 g, 0.192 mmol) in ClCH2CH2Cl (DCE; 3 mL)
and THF (1 mL) was added DIEA (0.10 mmol). The suspension
was then gently agitated at room temperature for 24 h. The resin
was filtered, washed successively with DMF, CH2Cl2 and MeOH,
and dried in vacuo to yield the required resin 8 (0.096 g, 83%;
Fmoc substitution 0.453 mmol g-1, 82% efficiency). The deriva-
tized resin product (0.065 g, 0.03 mmol) was placed in a reaction
column and swollen in DMF for 3 h. The resin underwent Fmoc-
deprotection by treatment with 20% v/ v piperidine in DMF and
finally washed with DMF (10 min, 2.5 mL min-1), after which
excess DMF was removed. FmocSer(t-Bu)OH (0.115 g, 0.30
mmol) and HATU (0.114 g, 0.30 mmol) were dissolved in DMF
(1 mL) and DIEA (104 µL, 0.60 mmol) was added. After ca. 1
min, the mixture was added to the resin and the reaction
mixture was stirred at room temperature for 3 h. The resin was
then washed with DMF (10 min, 2.5 mL min-1), filtered, washed
successively with DMF, CH2Cl2 and MeOH, and dried in vacuo
to give the desired functionalized resin (0.067 g, 94%; Fmoc-
substitution 0.426 mmol g-1, 100% efficiency). The derivatized
resin product (17.7 mg) was suspended in CH2Cl2 (3 mL) and
0.5 M HCl in CH2Cl2 (2 mL) was added, followed by H2O (50
µL) and triethylsilane (50 µL). The resin was vigorously stirred
at room temperature for 1.5 h. The suspension was then filtered
and the resin washed with CH2Cl2 (2 × 5 mL) and MeOH:CH2-
Cl2 (1:1, 5 mL). The combined filtrates were evaporated to
dryness in vacuo to afford the title compound (4.1 mg, quantita-
tive): RP-HPLC analysis (50-100% B in 20 min) estimated the
purity to be >99%; ES-MS+ m/z 449.6 (MNa+), 427.7 (MH+),
calcd 427.5; RP-HPLC 50-100% B in 20 min, tR 6.8 min; δH
(CDCl3, 250 MHz) 7.77 (2 H, d, J 6.9 Hz), 7.60 (2 H, d, J 7.1
Hz), 7.27-7.41 (4 H, m), 6.90 (1 H, br s), 5.73 (1 H, br s), 4.43 (2
H, d, J 6.8), 4.23 (2 H, m), 3.82 (1 H, dd, J 8.6, 3.6 Hz), 3.71-
3.73 (2 H, m), 3.37-3.44 (3 H, m), 1.20 (9 H, s).
resin (0.88 g, 91%): IR (KBr) 3025, 2922, 1657 and 1602 cm-1
.
The chloride substitution level was estimated by exposing 2 to
0.05 M aqueous NaOH in 1,4-dioxane followed by back-titration
using 0.01 M aqueous HCl. This typically indicated chloride
levels of 0.85-1.0 mmol g-1, which is ca. 30% higher than
expected (0.64 mmol g-1), hence suggesting the presence of
noncovalent bound chloride. The chloride linker-resin 2 (100 mg)
on treatment with FmocAlaOH (62 mg, 0.192 mmol) in the
presence of DIEA, afforded 5-[4-(4-tolyl(N-Fmoc-Ala-O)-methyl)-
phenoxy]pentanoyl amino-methylated polystyrene 7 (0.54 mmol
g-1). Based on a Fmoc-echo methodology, the chloride substitu-
tion was estimated to be 0.63 mmol g-1
.
Ad d ition of N-F m oc-P r otected Am in o Acid s to th e
Ben zh yd r yl Ch lor id e Lin k er -P olystyr en e 2. 5-[4-(4-Tolyl-
(chloro)methyl)phenoxy]pentanoyl aminomethylated polystyrene
2 (0.064 mmol, theoretical loading 0.64 mmol g-1) and N-Fmoc-
protected amino acid (0.192 mmol) were suspended in DCM (2
mL). Following the addition of DIEA (0.128 mmol), the resultant
mixture was stirred gently at room temperature for 24 h. The
resin was filtered, washed successively with DMF, DCM and
MeOH, and dried in vacuo.
Boc-Lys(Boc)-Ala-Abu -Ar g(P m c)-Ar g(P m c)-Leu -P h e-Gly-
Ala -OH (10). 5-[4-(4-Tolyl(N-Fmoc-Ala-O)-methyl)phenoxy]pen-
tanoyl aminomethylated polystyrene 7 (95 mg, 0.05 mmol; 0.54
mmol g-1) placed in a reaction column was allowed to swell in
DMF (1 mL) for 18 h, and then Fmoc-deprotected using 20%
v/ v piperidine in DMF (2.5 mL min-1). The resin was washed
with DMF (10 min, 2.5 mL min-1) and the peptide sequence Boc-
Lys(Boc)-Ala-Abu-Arg(Pmc)-Arg(Pmc)-Leu-Phe-Gly was assembled
using the LKB Biolynx 4175 manual peptide synthesizer.
Sequential acylation reactions were carried out at ambient
temperature for 1.5 h using appropriate N-Fmoc-protected amino
acids [Fmoc-Gly-OH, 74 mg; Fmoc-Phe-OH, 97 mg; Fmoc-Leu-
OH, 88 mg; Fmoc-Arg(Pmc)-OH, 166 mg; Fmoc-Abu-OH, 81 mg;
Fmoc-Ala-OH, 78 mg; Fmoc-Lys(Boc)-OH, 117 mg; 0.25 mmol]
and carboxyl-activated using TBTU (80 mg, 0.25 mmol), HOBt
(38 mg) and DIEA (87 µL, 0.50 mmol). Repetitive N-Fmoc-
deprotection was achieved using 20% v/v piperidine in DMF (6
min, 2.5 mL min-1). After the final N-Fmoc-deprotection, the
terminal amine group was Boc-protected with di-tert-butyl
dicarbonate (218 mg, 1.0 mmol). The assembled N-Boc-peptidyl-
resin was filtered and washed successively with DMF, CH2Cl2
and MeOH and dried in vacuo (131 mg, 79%). The resin product
was suspended in CH2Cl2 (3.75 mL) and HFIP (1.25 mL) was
added. The mixture was left at room temperature for 1 h. The
cleavage mixture was then filtered to remove residual resin and
washed with CH2Cl2 (5 mL), CH2Cl2:MeOH (1:1, 10 mL) and
MeOH (5 mL). The filtrate was evaporated to dryness in vacuo,
the residual material redissolved in acetonitrile (10 mL) and the
solution evaporated to dryness in vacuo; and the process was
repeated twice. The peptide was precipitated with water, filtered,
washed with water, air-dried overnight, and dried in vacuo to
afford the title compound as a white crystalline solid (21 mg,
99%, purity >95%): mp 187-189 °C; RP-HPLC 50-100% B in
20 min, tR 18.4 min; ES-MS+ m/z 1736.8 (MH+), calcd 1737.1.
Anal. Calcd for C83H130N16O20S2‚1/4(CF3)2CHOH: C, 52.86; H,
6.74; N, 11.27%. Found: C, 53.00; H, 6.96; N, 11.04%.
Boc-Lys(Boc)-Ala -Abu -Ar g(P bf)-Ar g(P bf)-Leu -P h e-Asp -
(Ot-Bu )-P r o[ψCH2OH] (14). The chloride resin 2 (0.10 g, 0.064
mmol, 0.64 mmol g-1), suspended in DCE:THF (3:1; 4 mL), was
derivatized with N-Fmoc-L-prolinol (0.062 g, 0.192 mmol; (S)-
N-(9-fluorenylmethoxycarbonyl)-2-pyrrolidinylmethanol) in the

Notes
J . Org. Chem., Vol. 65, No. 16, 2000 5055
presence of DIEA (0.1 mmol) for 48 h, to yield the resin 8 (0.095
g, 81%; Fmoc-substitution 0.531 mmol g-1, 98% efficiency). The
resin product (0.094 g, 0.05 mmol) was placed in a reaction
column, swollen in DMF for 18 h, and Fmoc-deprotected using
20% v/ v piperidine in DMF. The resin was then washed with
DMF (10 min, 2.5 mL min-1) and the peptide sequence Boc-Lys-
(Boc)-Ala-Abu-Arg(Pbf)-Arg(Pbf)-Leu-Phe-Asp(Ot-Bu) was then
assembled using the LKB manual peptide synthesizer. Sequen-
tial acylation reactions were carried out at ambient temperature
for 1.5 h using appropriate N-Fmoc-protected amino acids [Fmoc-
Asp(Ot-Bu)-OH, 103 mg; Fmoc-Phe-OH, 97 mg; Fmoc-Leu-OH,
88 mg; Fmoc-Arg(Pbf)-OH, 162 mg; Fmoc-Abu-OH, 81 mg; Fmoc-
Ala-OH, 78 mg; Fmoc-Lys(Boc)-OH, 117 mg; 0.25 mmol] and
carboxyl-activated using TBTU (80 mg, 0.25 mmol), HOBt (38
mg, 0.25 mmol) and DIEA (87 µL, 0.50 mmol). Repetitive
N-Fmoc-deprotection was achieved using 20% v/v piperidine in
DMF (6 min, 2.5 mL min-1). After the final N-Fmoc-deprotection,
the terminal amine group was Boc-protected with di-tert-butyl
dicarbonate (218 mg, 1.0 mmol). The assembled N-Boc-protected
peptidyl-resin was filtered, washed successively with DMF, CH2-
Cl2 and MeOH, and dried in vacuo (150 mg, 88%). The deriva-
tized resin product was suspended in 0.2 M HCl in CH2Cl2 (10
mL) and vigorously stirred at room temperature for 1.5 h. The
suspension was then filtered and the resin washed with CH2-
Cl2 (2 × 5 mL) and MeOH:CH2Cl2 (1:1, 5 mL). The combined
filtrates were evaporated to dryness in vacuo to afford the title
compound as a white solid (105 mg, quantitative yield; purity
estimated using RP-HPLC >99%): mp 225-227 °C; ES-MS+ m/z
1835.4 (MH+), calcd 1835.3; RP-HPLC 20-60% B in 25 min, tR
14.8 min. Anal. Calcd for C89H140N16O21S2•HCl: C, 57.14; H,
7.60; N, 11.98%. Found: C, 57.21; H, 7.68; N, 11.41%.
N-(4-Meth oxyben zen esu lfon yl)-L-n or valin yl-L-valin ol De-
r iva tized Lin k er -Resin (15). A solution of N-Fmoc-L-valinol
(0.062 g, 0.19 mmol; (S)-N-(9-fluorenylmethoxy-carbonyl)-2-
amino-3-methylbutanol) and DIEA (0.10 mmol) in DCE:THF (3:
1; 4 mL) was reacted with the chloride linker-resin 2 (0.10 g,
0.064 mmol, 0.64 mmol g-1) for 72 h to yield the derivatized resin
8 (0.105 g, 90%; Fmoc-substitution 0.50 mmol g-1, 92% ef-
ficiency). It should be noted that after a 24 h reaction period,
the Fmoc-substitution value of the derivatized resin was 0.42
mmol g-1 (78%). The derivatized resin product was placed in a
reaction column and swollen in DMF for 4 h. The resin was then
washed with DMF (10 min, 2.5 mL min-1), Fmoc-deprotected
by treatment with 20% v/ v piperidine in DMF and finally
washed with DMF (10 min, 2.5 mL min-1), after which excess
DMF was removed. FmocNvaOH (0.217 g, 0.64 mmol) and
HATU (0.243 g, 0.64 mmol) were dissolved in DMF (1 mL) and
DIEA (223 µL, 1.28 mmol) then added. After ca. 1 min, the
mixture was added to the resin and the resultant mixture stirred
at room temperature for 16 h. The resin was then washed with
DMF (10 min, 2.5 mL min-1) and dried in vacuo to afford the
title resin.
N-Ben zyl-N-(4-m et h oxyb en zen esu lfon yl)-L-n or va lin yl-
L-va lin ol (16a ). The above derivatized resin 15 (142 mg, 0.06
mmol) was swollen in dry THF (2 mL) for 16 h under nitrogen.
To this suspension at 5 °C was added successively benzyl alcohol
(124 µL, 1.2 mmol), tributylphosphine (148 µL, 0.6 mmol) and
N,N,N′,N′-tetramethylazodicarboxamide (TMAD; 103 mg, 0.6
mmol). The resultant mixture was then agitated at room
temperature under nitrogen for 24 h. The resin was filtered,
washed successively with THF, DMF, CH2Cl2 and MeOH, and
dried in vacuo to yield the transformed resin product (139 mg,
88%). The resin product (119 mg) was treated with 0.2 M HCl
in CH2Cl2 (10 mL) to afford the crude product (18.0 mg, 84%;
>95% when analyzed by RP-HPLC), which was purified by
preparative RP-HPLC to afford the title compound as a colorless
oil (11.25 mg, 63% based on 18.0 mg crude compound, 52%
theoretical): ES-MS+ m/z 463.0 (MH+), calcd 463.6; RP-HPLC
50-100% B in 20 min, tR 8.8 min; δH (CDCl3, 250 MHz) 7.72 (2
H, d, J 9.0 Hz), 7.27-7.38 (5 H, m), 6.96 (2 H, d, J 9.0 Hz), 6.62
(1 H, br d, J 6.6 Hz), 4.65 (1 H, d, J 15.3 Hz), 4.23 (1 H, d, J
15.3 Hz), 4.11 (1 H, dd, J 6.7, 8.1 Hz), 3.88 (3 H, s), 3.61 (1 H,
dd, J 3.1, 11.3 Hz), 3.49 (1 H, dd, J 6.9, 11.3 Hz), 3.32-3.36
(1 H, m), 1.91-1.97 (2 H, m), 1.62-1.68 (1 H, m), 1.40-1.45
(2 H, m), 0.89 (3 H, d, J 6.8 Hz), 0.81 (3 H, d, J 6.8 Hz), 0.72 (3
H, t, J 7.2 Hz); δC (CDCl3, 62.9 MHz) 171.61, 163.18, 136.63,
131.35, 129.36, 129.11, 128.61, 128.49, 128.01, 114.29, 114.22,
77.21, 64.37, 60.29, 58.38, 55.68, 52.93, 48.57, 30.47, 29.04, 19.63,
19.12, 18.67, 13.66; HRMS (FAB) calcd for C24H35N2O5S (MH+):
463.226669, found 463.228820.
N-(2-Th ien ylm et h yl)-N-(4-m et h oxyben zen esu lfon yl)-L-
n or va lin yl-L-va lin ol (16b). The derivatized resin 15 (185 mg,
0.07 mmol) was swollen in dry THF (3 mL) for 16 h under
nitrogen. To this suspension at 5 °C was added successively
2-thiophenemethanol (132.6 µL, 1.40 mmol), tributylphosphine
(173 µL, 0.70 mmol) and TMAD (121 mg, 0.70 mmol). The
resultant mixture was then agitated at room temperature under
nitrogen for 24 h. The resin was filtered, washed successively
with THF, DMF, CH2Cl2 and MeOH, and dried in vacuo to yield
the transformed resin product (190 mg, 97%). The resin (190
mg) was treated with 0.2 M HCl in CH2Cl2 (10 mL) to afford
the crude product (25.3 mg, 79%; >95% when analyzed by RP-
HPLC), which was purified by preparative RP-HPLC to afford
the title compound as a white semisolid (20.18 mg, 80% based
on 25.3 mg crude compound, 63% theoretical): ES-MS+ m/z
469.1 (MH+), calcd 469.6; RP-HPLC 50-100% B in 20 min, tR
8.0 min; δH (CDCl3, 250 MHz) 7.68 (2 H, d, J 9.0 Hz), 7.24-7.27
(1 H, m), 7.06 (1 H, m), 6.94 (2 H, d, J 8.9 Hz), 6.92-6.96 (1 H,
m), 6.68 (1 H, br d, J 6.9 Hz), 4.70 (1 H, d, J 16.0 Hz), 4.59 (1 H,
d, J 16.0 Hz), 4.10 (1 H, dd, J 8.6, 6.2 Hz), 3.68 (3 H, s), 3.63-
3.67 (1 H, m), 3.47-3.58 (2 H, m), 1.93-2.07 (2 H, m), 1.61-
1.73 (1 H, m), 1.49-1.58 (2 H, m), 0.91 (3 H, d, J 6.8 Hz), 0.86
(3 H, d, J 6.8 Hz), 0.72 (3 H, t, J 7.1 Hz); δC (CDCl3, 62.9 MHz)
171.65, 163.19, 139.57, 131.23, 129.41, 128.48, 126.78, 126.52,
114.22, 77.20, 64.30, 60.40, 58.23, 55.66, 42.76, 30.67, 29.05,
19.54, 19.21, 18.66, 13.60; HRMS (FAB) calcd for C22H33N2O5S2
(MH+): 469.183091, found 469.181357.
Su ber oyl 4-Meth oxya n ilid e N-Meth ylh yd r oxa m ic Acid
(17). The chloride linker resin 2 (0.10 g, 0.064 mmol, 0.64 mmol
g-1), suspended in CH2Cl2:THF (2:1; 3 mL) was treated with
N-Fmoc-N-methylhydroxylamine (0.069 g, 0.256 mmol) in the
presence of DIEA (0.128 mmol) for 72 h to yield the required
resin 9a (0.093 g, 83%; Fmoc substitution 0.466 mmol g-1, 84%
efficiency). The resin product (0.092 g, 0.043 mmol) was placed
in a reaction column and swollen in DMF for 5 h. The resin was
then washed with DMF (10 min, 2.5 mL min-1), Fmoc-depro-
tected by treatment with 20% v/ v piperidine in DMF and finally
washed with DMF (10 min, 2.5 mL min-1), after which excess
DMF was removed. To the resin was added a DMF (1 mL)
solution containing monomethyl suberate (77 µL, 0.43 mmol),
HATU (0.163 g, 0.43 mmol) and DIEA (150 µL, 0.86 mmol), and
the mixture was stirred at room temperature for 18 h. Following
washing the resin with DMF (10 mL), excess DMF was expelled,
a solution of 0.5 M LiOH in MeOH/THF (3:5; 1 mL) was added
and the resultant mixture was stirred at ambient temperature
for 24 h. The resin product was extensively washed with DMF
(20 min, 2.5 mL min-1), and was then added a solution of
benzotriazol-1-yloxytris(pyrrolidino)phosphonium hexafluoro-
phosphate (PyBOP; 0.034 g, 0.065 mmol) in DMF (1 mL) followed
by 4-methoxyaniline (0.053 g, 0.43 mmol). Following stirring at
room temperature for 1 h, a further aliquot of PyBOP (0.022 g,
0.043 mmol) was added and the mixture was stirred for a further
20 h. The resin was filtered, washed successively with DMF,
CH2Cl2 and MeOH, and dried in vacuo (0.085 g, 91%). Treatment
of the derivatized resin (97 mg) with 1% TFA in CH2Cl2 (5 mL)
for 75 min afforded the crude product as a beige solid (11.25
mg, 94%; >95% when analyzed by RP-HPLC). The crude
compound was purified by preparative RP-HPLC to afford the
title compound as a white solid (6.64 mg, 60% based on 11.25
mg compound purified, 55% theoretical): mp 135 °C; RP-HPLC
20-60% B in 25 min, tR 11.6 min; δH (CDCl3:CD3OD, 250 MHz)
7.44 (2 H, d, J 9.1 Hz), 6.86 (2 H, d, J 9.1 Hz), 3.80 (3 H, s), 2.46
(2 H, t, J 7.4 Hz), 2.33 (2 H, t, J 7.5), 1.59-1.74 (4 H, m), 1.37-
1.40 (4 H, m); δC (CDCl3:CD3OD, 62.9 MHz) 174.75, 172.60,
156.00, 131.21, 121.65, 113.78, 55.23, 36.61, 35.63, 31.66, 28.37,
28.32, 25.16, 24.16; HRMS (FAB) calcd for C16H25N2O4 (MH+):
309.181433, found 309.183703.
N-(N-Ben zyl-N-(4-m eth oxyben zen esu lfon yl)-L-leu cyl) N-
Cyclobu tylm eth yl Hyd r oxa m ic Acid (18). The chloride linker
resin 2 (0.10 g, 0.064 mmol, 0.64 mmol g-1) was treated with
N-Fmoc-N-cyclobutylmethylhydroxylamine (0.083 g, 0.256 mmol)
in the presence of DIEA (0.128 mmol) for 72 h to yield the
required resin 9c (0.094 g, 80%; Fmoc substitution 0.243 mmol
g-1, 50% efficiency). The derivatized resin product (0.092 g, 0.022

5056 J . Org. Chem., Vol. 65, No. 16, 2000
Notes
mmol) was placed in a reaction column and swollen in DMF for
3 h. The resin underwent Fmoc-deprotection by treatment with
20% v/ v piperidine in DMF and finally washed with DMF (10
min, 2.5 mL min-1), after which excess DMF was removed. A
solution of FmocLeuOH (0.078 g, 0.22 mmol), HOAt (0.03 g, 0.22
mmol) and DIPCDI (34.4 µL, 0.22 mmol) in DMF (1 mL) was
then added to the resin, and the mixture was gently stirred at
room temperature for 24 h. The resin was then washed with
DMF (10 min, 2.5 mL min-1), followed by 20% v/ v piperidine in
DMF (5 min, 2.5 mL min-1), and finally washed with DMF (10
min, 2.5 mL min-1). A solution of 4-methoxybenzenesulfonyl
chloride (0.036 g, 0.176 mmol) in DMF (1 mL) was added to the
resin, followed by DIEA (7.6 µL, 0.44 mmol) and the resultant
suspension was gently agitated at room temperature for 24 h.
The resin was filtered, washed successively with DMF, CH2Cl2
and MeOH, and dried in vacuo to yield the desired resin product
(0.088 g, 95%). A batch of the derivatized resin (0.079 g, 0.017
mmol) was allowed to swell in dry THF (2 mL) for 16 h in a
round-bottomed flask under nitrogen. To this suspension was
added benzyl alcohol (35 µL, 0.34 mmol) and tributylphosphine
(42 µL, 0.17 mmol) at 0 °C, followed by TMAD (0.03 g, 0.17
mmol). The mixture was allowed to reach ambient temperature
and stirred under nitrogen for 24 h. The supernatant was
removed and the resin was washed with THF (2 × 3 mL). The
resin in THF (2 mL) was re-alkylated in the same manner with
the above quantities of reagents and stirred for 16 h at room
temperature. The resin was filtered, washed successively with
THF, DMF, CH2Cl2 and MeOH, and dried in vacuo to give the
required resin (0.074 g, 84%). Treatment of the derivatized resin
(74 mg) with 1% TFA in CH2Cl2 (5 mL) for 75 min afforded the
crude product as a colorless oil (6.2 mg, 83%; >80% when
analyzed by RP-HPLC). The crude compound was purified by
preparative RP-HPLC to afford the title compound (5.3 mg, 85%
based on 6.2 mg compound purified, 71% theoretical): ES-MS+
m/z 474.9 (MH+), calcd 475.62; RP-HPLC 50-100% B in 20 min,
tR 13.6 min; δH (CDCl3, 250 MHz) Mixtures of Z/E isomers 7.70
(0.67 H, d, J 8.7 Hz), 7.64 (1.33 H, d, J 8.8 Hz), 7.24-7.33 (5 H,
m), 6.96 (0.67 H, d, J 8.6 Hz), 6.93 (1.33 H, d, J 8.7 Hz), 4.95
(0.67 H, dd, J 5.2, 9.2 Hz), 4.85 (0.33 H, m), 4.57, 4.78 (0.67 H,
2 × d, J 16.3 Hz), 4.37, 4.75 (1.33 H, 2 × d, J 16.2 Hz), 3.87 (3
H, s), 3.53-3.59 (1.33 H, m), 3.46, 3.97 (0.67 H, m), 2.59-2.68
(1 H, m), 1.82-1.92, 2.02-2.09 (6 H, m), 1.69-1.79 (1 H, m),
1.25 (1 H, m), 0.88-1.16 (1 H, m), 0.65, 0.83 (2.4 H, 2 × d, J 6.6
Hz), 0.60, 0.73 (3.6 H, 2 × d, J 6.6 Hz); δC (CDCl3, 62.9 MHz)
163.11, 129.57, 128.29, 128.16, 127.21, 114.18, 77.20, 55.65,
53.13, 52.74, 52.18, 48.64, 47.71, 38.35, 33.21, 26.02, 24.79,
22.64, 21.71, 18.44; HRMS (FAB) calcd for C25H35N2O5S (MH+):
475.226669, found 475.225401.
4-(2-Th ien yl)ben zoyl-L-a la n in e (20). The FmocAlaOH-de-
rivatized resin 7 (105 mg, 0.054 mmol; Fmoc-substitution 0.541
mmol g-1, 100% efficiency) was placed in a reaction column and
swollen in DMF for 4 h. The resin was then washed with DMF
(10 min, 2.5 mL min-1), Fmoc-deprotected by treatment with
20% v/ v piperidine in DMF and finally washed with DMF (10
min, 2.5 mL min-1), after which excess DMF was removed. A
mixture of 4-bromobenzoic acid (0.043 g, 0.216 mmol), HOAt
(0.029 g, 0.216 mmol) and DIPCDI (34 µL, 0.216 mmol) in DMF
(1 mL) was added to the resin and the mixture was gently stirred
at room temperature for 16 h. The resin was then washed with
DMF (10 min, 2.5 mL min-1). The resin was filtered, washed
successively with DMF, CH2Cl2 and MeOH, and dried in vacuo
to yield the desired resin product 19 (102 mg, 98%). The resin
19 (102 mg, 0.05 mmol) was allowed to swell in DMF for 1 h in
a round-bottomed flask. To the resin suspension was added
2-thiopheneboronic acid (21.0 mg, 0.165 mmol) and 2 M aqueous
Na2CO3 solution (103 µL, 0.206 mmol) and the mixture was
deoxygenated under a stream of nitrogen for 5 min. Recently
prepared tetrakis(triphenylphosphine)palladium(0) (6.4 mg, 0.0055
mmol) was then added, and the resultant mixture was stirred
under nitrogen at 80 °C for 24 h. The mixture was filtered when
hot, the resin washed sequentially with DMF (20 mL), DMF/
H2O (1:1, 40 mL), DMF (20 mL), THF (20 mL) and MeOH (20
mL), and dried in vacuo to afford the required resin product (101
mg, 98%). Treatment of the derivatized resin (100 mg) using 1%
TFA in CH2Cl2 (5 mL) for 75 min yielded the crude product as
a pale yellow solid (13.61 mg, 90%; >95% when analyzed by RP-
HPLC). The crude compound was purified by preparative RP-
HPLC to afford the title compound as a white solid (10.45 mg,
77% based on 13.6 mg compound purified, 70% theoretical): mp
191-193 °C; RP-HPLC 50-100% B in 20 min, tR 3.6 min; δH
(CDCl3:CD3OD, 250 MHz) 7.84 (2 H, d, J 8.6 Hz), 7.69 (2 H, d,
J 8.6 Hz), 7.42 (1 H, dd, J 1.1, 3.6 Hz), 7.36 (1 H, dd, J 1.1, 5.1
Hz), 7.12 (1 H, dd, J 3.6, 5.1 Hz), 4.72 (1 H, br q, J 7.2 Hz), 1.56
(3 H, d, J 7.2 Hz); δC (CDCl3:CD3OD, 62.9 MHz) 166.97, 142.82,
137.55, 132.11, 128.12, 127.69, 125.90, 125.55, 124.12, 48.26,
17.92; HRMS (FAB) calcd for C14H14NO3S (MH+): 276.069440,
found 276.069310.
(Z)-2-(4-P h en ylben zoylam in o)bu t-2-en oic Acid (21). Fmoc-
ThrOH (66 mg, 0.192 mmol) was reacted with 2 (100 mg, 0.064
mmol, 0.64 mmol g-1) to yield the derivatized resin 7d (106 mg,
90%; Fmoc-substitution 0.525 mmol g-1, 98% efficiency). The
resin product was placed in a reaction column and swollen in
DMF for 16 h. The resin was then washed with DMF (10 min,
2.5 mL min-1), Fmoc-deprotected by treatment with 20% v/ v
piperidine in DMF and finally washed with DMF (10 min, 2.5
mL min-1), after which excess DMF was removed. A DMF (1
mL) solution containing 4-biphenylcarboxylic acid (44 mg, 0.22
mmol), HOAt (30 mg, 0.22 mmol) and DIPCDI (34.4 µL, 0.22
mmol) was added to the resin (105 mg, 0.055 mmol), and the
mixture was gently stirred at room temperature for 4 h. The
resin was then washed with DMF (10 min, 2.5 mL min-1), 20%
v/ v piperidine in DMF (6 min, 2.5 mL min-1) and finally DMF
(10 min, 2.5 mL min-1). The resin was filtered, washed succes-
sively with DMF, CH2Cl2 and MeOH, and dried in vacuo to yield
the desired resin product (101 mg, 98%). A portion of the
â-hydroxyamino acid derivatized resin (87 mg, 0.046 mmol) was
swollen in CH2Cl2 (0.5 mL) and THF (0.5 mL) in a two-necked
round-bottomed flask for 1 h under a nitrogen atmosphere. The
solution was cooled to -78 °C, and triethylamine (192 µL, 1.38
mmol) followed by thionyl chloride (16 µL, 0.184 mmol) were
carefully added to the resin suspension. The mixture was stirred
at -78 °C for 1 h, after which a further quantity of thionyl
chloride (16 µL, 0.184 mmol) was added, and the stirred mixture
was gradually warmed to -50 °C over a period of 1.5 h. The
mixture was then stirred at 5 °C for 2.5 h. The resin was filtered,
washed successively with DMF, CH2Cl2 and MeOH, and dried
in vacuo to afford the required resin (84 mg, 96%). Treatment
of the derivatized resin (84 mg) with 1% TFA in CH2Cl2 for 15
min afforded the crude product as an off-white solid (14.04 mg;
>75% when analyzed by RP-HPLC). The crude compound was
purified by preparative RP-HPLC to afford the title compound
as a white solid (6.59 mg, 52%): mp 204-206 °C (dec); RP-HPLC
50-100% B in 20 min, tR 4.4 min; δH (CDCl3:CD3OD, 250 MHz)
7.98 (2 H, d, J 8.5 Hz), 7.71 (2 H, d, J 8.5 Hz), 7.64 (2 H, m),
7.45 (3 H, m), 6.98 (1 H, q, J 7.2 Hz), 1.87 (3 H, d, J 7.2 Hz); δC
(CDCl3:CD3OD, 62.9 MHz) 166.55, 166.06, 144.72, 139.76,
134.55, 132.29, 128.79, 127.95, 127.90, 127.13, 127.05, 14.62;
HRMS (CI) calcd for C17H15NO3 (M+): 281.105194, found
281.105881.
Ack n ow led gm en t. G.E.A. would like to acknowl-
edge the BBSRC, U.K., and Cyclacel Ltd., U.K., for the
funding of a CASE studentship.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails and spectral data for aminomethyl NovaGel derivatiza-
tion studies, 11, 16c, 16d and intermediate compounds;
general procedures for attachment of O-nucleophiles to 2;
general procedures for cleavage experiments and RP-HPLC
analysis. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O000315X