Synthesis of prenylated cysteines from serine derivatives

Article abstract of DOI:10.1039/a700428a

Prenylated cysteines are prepared by the reaction of serine β-lactone with prenyl thiolate.

Full text of DOI:10.1039/a700428a

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis of prenylated cysteines from serine derivatives
William W. Epstein*† and Zhaolin Wang
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA
Prenylated cysteines are prepared by the reaction of serine
b-lactone with prenyl thiolate.
The serine b-lactone 5 was prepared by reaction of Boc-serine
with triphenylphosphine and diethyl azodicarboxylate
(
DEAD).12
Prenylation, a recently discovered post-translational modifi-
Although there are two possible ways of opening the
1–5
13
cation of proteins, has become a topic of substantial interest.
Prenylation involves covalent attachment of either farnesyl
15) or geranylgeranyl (C20) isoprenoids to conserved car-
b-lactone as shown in Scheme 2, alkyl–oxygen cleavage
occurred when farnesyl thiolate, prepared by the reaction of
farnesyl thiol with sodium hydride, was used to give the desired
stereochemically pure prenylated cysteines 6a¶ and 6b in
52–60% yield. It should be noted that acyl–oxygen fission
occurred when triethylamine was used as the base to give
thioester 7 as the major product (61%). With 6b in hand, the
dipeptide 9∑ with two geranylgeranylated cysteines was pre-
(C
boxy-terminal cysteine residues by a family of prenyltransfe-
rase enzymes. Three types of carboxy-terminal cysteine se-
quences are substrates for this modification. The major class of
these proteins has a CAAX motif (where C is a cysteine, A is
usually an aliphatic amino acid and X is an amino acid that
determines whether a protein is farnesylated or geranyl-
geranylated). The second and third types of proteins have CXC
or CC motifs, respectively, in which both cysteines are
geranylgeranylated. Subsequent to prenylation, proteins con-
taining the CAAX motif are further processed by proteolytic
removal of the three terminal amino acids (AAX) followed by
methylation of the prenylcysteine carboxy group. Prenylation is
common for many physiologically important proteins. Since
oncogenic forms of Ras proteins require farnesylation for their
ability to transform cells, inhibition of farnesylation has become
a very attractive target for anti-cancer drug design.
OR1
OMe
Me
+
R2
BocHN
HS
O
1a R1 = P(O)(OPh)2
b R1 = SO2C6H4Me-4
2a R2 = C10H17
b R2 = C15H25
Et3N
S
R2
2
a or 2b
OMe Me
OMe
6
Since Kamiya et al. first synthesized farnesylcysteine,
BocHN
BocHN
Et3N
several methods for the preparation of prenylated cysteines and
peptides have been reported.7 These methods are based on
alkylation of the sulfhydryl group of cysteine with prenyl
halides. Despite the success achieved, there are two potential
problems for prenylation of cysteine by this alkylation ap-
proach. Since basic conditions are generally required, free
amino, hydroxy and carboxylate moieties, and especially other
sulfide anions, are potential competing nucleophiles which can
lead to major side reactions. The second and less important
problem is that the required allylic prenyl halides are hard to
purify. These potential difficulties led us to explore a new route
to prenylated cysteines. Here we report a method for the
synthesis of prenylated cysteines from a suitable serine
precursor.
O
O
–9
4a R2 = C10H17
b R2 = C15H25
3
Scheme 1
S
R
OH Me
BocHN
2a or 2b, NaH
THF
O
6a R = C10H17
b R = C17H25
O
2
a, Et3N
BocHN
O
H
OH
S
Our initial synthetic plan was based on activation of the
serine hydroxy group and subsequent displacement with a
prenyl thiol. N-Boc-O-diphenylphosphoryl-l -serine methyl
ester 1a and N- Boc-O-tosyl-l -serine methyl ester 1b were
prepared from Boc-l -serine methyl ester. The required prenyl
thiols 2a and 2b were prepared from the C15 and C20 prenyl
chlorides.10 The low yields and lack of regiospecificity in the
preparation of C15 and C20 prenyl halides were circumvented by
THF
5
BocHN
R
O
Me
7
R = C10H17
Scheme 2
11
using the method of Collington and Meyers. Treatment of
serine derivatives 1a and 1b with prenyl thiol 2a‡ or 2b in the
presence of triethylamine yielded racemic prenylated cysteine
6b
S
O
R
4§ (Scheme 1). The isolation of 3 suggested to us that
OMe Me
Me
, THF
Cl
O
H2N
b-elimination may be the initial step of the reaction followed by
Michael addition of the anion of 2a or 2b to the a,b-unsaturated
substrate 3 to give the observed racemic mixture.
In order to avoid the above stereochemical problems, we
turned to an alternative sequence. The synthetic methodology
developed by Arnold et al.12 for the preparation of b-substituted
alanines and their derivatives seemed applicable to our problem.
Thus we undertook the synthesis of prenylated cysteines by the
stereospecific opening of serine b-lactone with prenyl thiols.
Me
O
S
R
O
H
N
Me
BocHN
OMe Me
O
R
S
Scheme 3
Chem. Commun., 1997
863

View Article Online
pared by coupling of 5b with geranylgeranylated cysteine
39.90, 39.83, 29.90, 28.62, 28.54, 26.92, 26.70, 25.91, 17.89, 16.37, 16.21
(HRMS FAB): calc. for C23H NO S, 424.2522. Found, 424.2503).
14
methyl ester 8 via the mixed anhydrides method. Dipeptide 9
may serve as an important model compound to study ger-
anylgeranylated Rab proteins.2
39
4
1
∑
5
4
3
Selected data for 9: H NMR (300 MHz, CDCl ): d 7.13 (d, J 6.9 Hz, 1 H),
.36 (brs, 1 H), 5.28–5.17 (m, 2 H), 5.11–5.07 (m, 6 H), 4.80–4.67 (m, 1 H),
.30 (brs, 1 H), 3.23–3.07 (m, 4 H), 3.00–2.80 (m, 2 H), 2.10–1.98 (m, 24
In summary we have described a practical and novel route to
stereospecifically synthesize prenylated cysteines from serine
b-lactone. The optical purity and simplicity of this approach to
prenylated cysteines are attractive features compared with
H), 1.68 (s, 6 H), 1.60 (s, 18 H), 1.47 (s, 9 H); (HRMS CI): calc. for
882.5978. Found 882.5811).
52 86 2 5 2
C H N O S
References
8
previous methods.
1
C. Marshall, Science, 1993, 259, 1865; M. S. Brown and J. L. Goldstein,
Nature, 1993, 366, 14.
2
3
S. Clarke, Annu. Rev. Biochem., 1992, 61, 355.
P. J. Casey, J. Lipid. Res., 1992, 33, 1731.
Footnotes
†
‡
E-mail: Epstein@chemistry.utah.edu
All new compounds described herein have been fully characterized by H
4 W. R. Schafer and J. Rine, Annu. Rev. Genet., 1992, 30, 209.
5 H. C. Rilling, E. Breunger, W. W. Epstein and P. F. Crain, Science,
1990, 247, 318; C. C. Farnsworth, M. H. Gelb and J. A. Glomset,
Science, 1990, 247, 320.
6 Y. Kamiya, A. Sakurai, S. Tamura, N. Takahashi, E. Tsuchiya, K. Abe
and S. Fukui, Agric. Biol. Chem., 1979, 43, 363.
7 M. J. Brown, P. D. Milano, D. C. Lever, W. W. Epstein and
C. D. Poulter, J. Am. Chem. Soc., 1991, 113, 3176.
8 C. C. Yang, C. K. Marlowe and R. Kania, J. Am. Chem. Soc., 1991, 113,
3177.
9 C. B. Xue, J. M. Becker and F. Naider, Tetrahedron Lett., 1992, 33,
1435.
10 E. C. Horning, Org. Synth., 1955, Coll. Vol. 2, 363.
11 E. W. Collington and A. I. Meyers, J. Org. Chem., 1971, 36, 3044.
12 L. D. Arnold, T. H. Kalantar and J. C. Vederas, J. Am. Chem. Soc., 1985,
107, 7105.
1
1
3
and C NMR spectral, HRMS and elemental analyses. Selected data for 2a:
1
H NMR (300 MHz, CDCl
3
): d 5.35 (m, 1 H), 5.10 (m, 2 H), 3.16 (dd, J 7.5,
0
3
1
2
1
1
§
.6 Hz, 2 H), 2.11–1.97 (m, 8 H), 1.68 (d, J 0.9 Hz, 3 H), 1.66 (d, J 0.9 Hz,
1
3
H), 1.60 (s, 6 H), 1.40 (t, J 7.2 Hz, 1 H); C NMR (75 MHz, CDCl
3
): d
37.50, 135.30, 131.29, 124.31, 123.72, 123.28, 39.68, 39.38, 26.70, 26.27,
5.69, 22.11, 17.68, 16.02, 15.77; nmax(neat)/cm2 2966.7, 2926.2, 1446.7,
1
381.1 (Calc. for C15
H26S: C, 75.56; H, 10.99. Found: C, 75.43; H,
1.03%).
1
Selected data for 4a: H NMR (300 MHz, CDCl ): d 5.31 (d, J 6.6 Hz, 1
3
H), 5.21 (t, J 7.8 Hz, 1 H), 5.11–5.06 (m, 2 H), 3.76 (s, 3 H), 3.18 (t, J 8.1
Hz, 2 H), 2.95–2.81 (m, 2 H), 2.07–2.00 (m, 8 H), 1.68 (d, J 1.2 Hz, 3 H),
1
3
1
.67 (d, J 1.2 Hz, 3 H), 1.60 (s, 6 H), 1.45 (s, 9 H); C NMR (75 MHz,
CDCl ): d 171.94, 155.39, 140.16, 135.57, 131.51, 124.52, 123.93, 119.87,
0.27, 53.45, 52.67, 39.90, 39.83, 33.86, 30.23, 28.51, 26.92, 26.62, 25.91,
7.89, 16.34, 16.22. (Calc. for C24 41NO S: C, 65.57; H, 9.40; N, 3.19.
3
8
1
H
4
13 H. Shao, S. H. Wang, C. W. Lee, G. Osapay and M. Goodman, J. Org.
Chem., 1995, 60, 2956.
14 J. R. Vaughan, Jr. and R. L. Osato, J. Am. Chem. Soc., 1952, 73,
3547.
Found: C, 65.63; H, 9.47; N, 3.15%).
¶
1
Selected data for 6a: H NMR (300 MHz, CDCl
3
): d 5.35 (m, 1 H), 5.23
(t, J 7.8 Hz, 1 H), 5.09 (t, J = 6.9 Hz, 2 H), 4.48 (brs, 1 H), 3.21 (m, 2 H),
2
3
1
.93 (m, 1 H), 2.09–2.00 (m, 8 H), 1.68 (d, J 0.9 Hz, 3 H), 1.67 (d, J 1.2 Hz,
1
3
Received in Corvallis, OR, USA, 20th January 1997; Com.
7/00428A
H), 1.60 (s, 6 H),1.46 (s, 9 H); C NMR (75 MHz, CDCl
3
): d 170.00,
55.74, 140.11, 135.44, 131.46, 124.52, 124.01, 119.73, 80.03, 54.17,
864
Chem. Commun., 1997