Oxathiaphospholane approach to the synthesis of conjugates of amino acids methyl esters with nucleosides

Article abstract of DOI:10.1080/10426500212234

Based upon 1,3,2-oxathiaphospholane chemistry, 5′-O-derivatization of nucleosides with the O-methyl esters of amino acids was performed and corresponding conjugates were obtained in satisfactory yield.

Full text of DOI:10.1080/10426500212234

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Phosphorus, Sulfur, and Silicon and the Related
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Oxathiaphospholane Approach to the Synthesis
of Conjugates of Amino Acids Methyl Esters with
Nucleosides
Janina Baraniak a , Renata Kaczmarek a , Ewa Wasilewska a & Wojciech J. Stec a
a Department of Bioorganic Chemistry , Centre of Molecular and Macromolecular Studies
Polish Academy of Science, Department of Bioorganic Chemistry , Sienkiewicza 112, Łódź,
90-363, Poland
Published online: 27 Oct 2010.
To cite this article: Janina Baraniak , Renata Kaczmarek , Ewa Wasilewska & Wojciech J. Stec (2002) Oxathiaphospholane
Approach to the Synthesis of Conjugates of Amino Acids Methyl Esters with Nucleosides, Phosphorus, Sulfur, and Silicon and
the Related Elements, 177:6-7, 1667-1670, DOI: 10.1080/10426500212234
To link to this article: http://dx.doi.org/10.1080/10426500212234
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:1667–1670
C
Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
DOI: 10.1080/10426500290093504
OXATHIAPHOSPHOLANE APPROACH TO THE
SYNTHESIS OF CONJUGATES OF AMINO ACIDS
METHYL ESTERS WITH NUCLEOSIDES
Janina Baraniak, Renata Kaczmarek, Ewa Wasilewska,
and Wojciech J. Stec
Department of Bioorganic Chemistry, Centre of Molecular
and Macromolecular Studies Polish Academy of Science,
Department of Bioorganic Chemistry, Sienkiewicza 112,
90-363 Lo´dz´, Poland
(Received July 29, 2001; accepted December 25, 2001)
Based upon 1,3,2-oxathiaphospholane chemistry, 50-O-derivatization of
nucleosides with the O-methyl esters of amino acids was performed and
corresponding conjugates were obtained in satisfactory yield.
Keywords: Conjugates; N- and O-phosphorothioylated amino acids;
nuclesides; oxathiaphospholane ring opening condensation
In the light of early recognized importance of enzymatic O-
phosphorylation of hydroxyl groups of serine, threonine, or tyrosine in
the peptides sequence for their biological function,1 chemical phospho-
rylation of proteins become a matter of challenge for numerous chemical
establishment.
Independently, discovery of nucleoproteins in which the hydroxy
groups of L-amino acids serine, threonine, or tyrosine are conveniently
bound via phosphate linkages to 50-end of nucleic acids,2 initiated exten-
sive search for new methods of their chemical synthesis. On the other
side, natural products containing phosphoramidate linkage between
50-O-nucleoside and amino acid have been identified.3 Therefore, an
attention has been attracted to the development of a new method of
synthesis of nucleoside and amino acid conjugates via phosphoramidate
linkage.4 Accessibility of such hybrids has opened the door to the explo-
ration of peptide-oligonucleotide conjugates as antisense constructs.
In this laboratory, a novel method of synthesis of phosphodiesters
and phosphoramidoesters has been designed. This method is based
upon attachment of 1,3,2-oxathiaphospholane moiety to hydroxyl or
Address correspondence to J. Baraniak. E-mail: baraniak@bio.cbmm.lodz.pl
1667

1668
J. Baraniak et al.
amino-groups and their P-oxidation or P-sulfurization, providing inter-
mediate like 1 (Eq. 1, Y O, S).
(1)
If R carries chiral auxiliary, compound of type 1 may be separated
into diastereomers. DBU-assisted 1,3,2-oxathiaphospholane ring open-
ing condensation of 1 with alcohols provides in high yields phospho-
rothioate diesters or phosphorothioate amidoesters, respectively, and
if diastereomerically pure 1 is used, aforementioned compound can
be prepared in stereocontrolled manner. Examples of successful ap-
plication of OTP methodology to the synthesis of phosphorothioate
diesters and amidoesters are numerous and include the first stereo-
controlled synthesis of oligo(nucleoside phosphorothioate)s,5 dinucle-
oside N30-P50 phosphates and phosphorothioates,6 dinucleoside 30,50-
boranophosphates,7 or bis-adenosylphosphorothioylated polyols.8
In this communication we wish to present our recent results
on 1,3,2-oxathiaphosphorothioylation of O-methyl esters of amino
acids. Their treatment with an equimolar amount of 2-chloro-1,3,2-
oxathiaphospholane (2) in pyridine solution in the presence of ele-
mental sulfur provided 2-N-(carbomethoxyaminoacido)-[2-thiono-1,3,
2-oxathiaphospholanes] (1, Y S, R1X amino acid O-methyl ester).
Compounds 1 were isolated from the reaction mixture by silica gel col-
umn chromatography with satisfactory yields and were characterized
by means of 1H NMR, 31P NMR, and FAB-MS analysis (Table I).
TABLE I The Physicochemical Characteristics of Compounds
1a–g and 4b, 4d
31P NMR
[ppm]
FAB-MS
[M-1]
Yield
[%]
Comp.
Z
1a
1b
1c
1d
1e
1f
1g
4b
4d
CH3
CH2Ph
96.7; 97.3
96.5; 95.6
97.7; 96.1
96.5; 95.5
105.6; 105.5
104.0; 103.9
100.52
241
316
313
355
356
370
432
523
562
83
89
80
75
62
92
73
87
92
CH2CH2COOMe
CH2-indoyl-3
CH2
CH(CH3)
CH2C6H4
CH2Ph
58.5; 58.2
58.5; 58.4
CH2-indoyl-3

Oxathiaphospholane Approach
1669
Compounds 1 were subjected to the DBU-assisted ring-opening con-
densation process by means of 50-hydroxyl group of nucleosides. The
cleavage of endocyclic P S bond was followed by fast elimination of
episulfide leading to nucleosido-50-aminoacidophosphoramidothioates
(4). DBU is the reagent of choice for acceleration of the 1,3,2-
oxathiaphospholane ring opening condensation process, although the
bases, such as imidazole or DMAP, can be used as the catalysts for this
condensation.
Elaborated procedure has been applied first for the synthesis of phos-
phorothioate conjugates of amino acids with antiviral nucleosides.9 It
has been known from the literature that the higher the activity against
HIV-1 replication in PBMCs cells, then the parent, AZT, exhibits phos-
phate derivatives of L-tryptophan and L-phenylalanine.10 Therefore,
phosphorothioate analogues 4b and 4d have been obtained.
AZT and 20,30-dideoxythymidine (D4T) were chosen as antiviral
nucleosides8 (Eq. 2).
(2)
In the case of tryptophan, diastereomeric OTP derivatives 1d were sep-
arated via crystallization, and the absolute configuration at phosphorus
atom of diastereomer absorbing at lower field in 31P NMR spectrum has
been assigned by X-ray analysis as RP. Therefore, compound 4d pre-
pared from RP-1d has SP-configuration. At present, phosphorothioate
conjugates of amino acids with AZT and D4T (4) are tested as inhibitors
of HIV-1 transcriptase.11
The second type of conjugates involves phosphodiester linkage be-
tween 50-hydroxyl group of nucleoside and hydroxyl group of amino
acid side chains. The O-oxathiaphospholane derivatives of appropri-
ately amino- and carboxyl-protected threonine and tyrosine (1e–g) were
condensed with nucleosides (Eq. 3).
(3)

1670
J. Baraniak et al.
The essential problem in the synthesis of that type of conjugate is
their stability under basic conditions, casually used for the removal of
nucleoside-protecting groups.9 Compounds 4 were treated with conc.
aqueous ammonia for 24 h. The desired removal of benzoyl protecting
group was accompanied by concomitant conversion of carboxymethyl
into carboxamide function; decomposition of phosphorothioate linkage
involving 50-O-nucleoside and hydroxyl side chain of aforementioned
amino acids were not observed.
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