New approach to preparation of N-acylphosphoramido(thio)(seleno)ates

Article abstract of DOI:10.1016/j.tetlet.2004.04.023

N-[2-(X)-1,3,2-Oxathiaphospholane] derivatives (X=S, Se, O) of carboxamides were prepared and their DBU-assisted reaction with alcohols led to the corresponding O-alkyl-N-acylphosphoramido(thio)(seleno)ates. Their structures were confirmed by MS analysis and ¹H and ³¹P NMR spectroscopy. Independently N-acylphosphoramidoselenoates were converted to N-acylphosphoramidates by treatment with tert-butylperoxytrimethylsilane. The oxathiaphospholane approach was also applied to the synthesis of derivatives having N-prolylphosphoramido(thio)(seleno)ate linkages on the 5′-OH group of AMP.

Full text of DOI:10.1016/j.tetlet.2004.04.023

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 4269–4272
New approach to preparation of
N-acylphosphoramido(thio)(seleno)ates
*
ꢀ
Janina Baraniak, Renata Kaczmarek, Ewa Wasilewska, Dariusz Korczynski
and Wojciech J. Stec
Department of Bioorganic Chemistry, Center of Molecular and Macromolecular Studies, Polish Academy of Sciences,
Sienkiewicza 112, 90-363 Łꢀodꢀz, Poland
Received 19 February 2004; revised 31 March 2004; accepted 6 April 2004
Available online
This work is dedicated to Professor P. Mastalerz on the occasion of his 75th birthday
Abstract—N-[2-(X)-1,3,2-Oxathiaphospholane] derivatives (X ¼ S, Se, O) of carboxamides were prepared and their DBU-assisted
reaction with alcohols led to the corresponding O-alkyl-N-acylphosphoramido(thio)(seleno)ates. Their structures were confirmed by
MS analysis and 1H and 31P NMR spectroscopy. Independently N-acylphosphoramidoselenoates were converted to N-acyl-
phosphoramidates by treatment with tert-butylperoxytrimethylsilane. The oxathiaphospholane approach was also applied to the
synthesis of derivatives having N-prolylphosphoramido(thio)(seleno)ate linkages on the 50-OH group of AMP.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Numerous studies on the synthesis of N-acylphosphor-
amidates were prompted by their use as potential
phosphorylating agents.1 However, their accessibility
has been limited by the low efficiency of synthetic pro-
cedures2 and unexpected reactivity, such as N fi O acyl
migration.3 Successful application of N-acylated oxaza-
phosphorinanes in the synthesis of enantiomerically
pure anticancer drugs such as ifosfamide and bromo-
fosfamide4 demonstrated their synthetic utility. Fur-
thermore, the discovery of natural products possessing
the N-acylphosphoramidate motif5 has attracted the
interest of several research establishments to the search
for the efficient methods for the synthesis of this class of
compounds.6
oxygen atom of the mixed anhydride bond in aa-AMP
was replaced by an NH-group.8 Subsequently, the same
group of researchers described the first synthesis of
phosmidosine, a natural product having N-prolyl-
phosphoramidate and O-methyl ester linkages on the 50-
O-phosphoryl residue of 8-oxoadenosine.9 Very recently
they also published the synthesis of a phosmidosine
analogue having an N-prolylphosphoramidothioate
linkage.10 It has been suggested that phosmidosine and
its related compounds can be considered as a novel class
of anticancer drugs targeting cell cycle regulation.
As a continuation of our efforts towards further devel-
opment of an oxathiaphospholane methodology beyond
applications in the stereocontrolled synthesis of P-chiral
analogues of oligonucleotides,11 phosphorothioylated
amino acids12 and, independently, conjugates of amino
acids with nucleoside-50-O-phosphorothioates,13 or
nucleoside phosphorothioylated polyols mimicking the
function of dinucleoside polyphosphates,14 we present
here a new route to O-alkyl-N-acylphosphoramido
(thio)(seleno)ates. To our knowledge, N-acylphosphor-
amidoselenoates are not described in the literature.
Recently Richards and co-workers synthesized b-
asparaginyladenylate as an inhibitor of asparagine syn-
thethase,7 while Sekine and co-workers in their elegant
studies utilizing phosphoramidite chemistry described
the synthesis of several aminoacyl-adenylates, where the
Keywords: Carboxamides; N-[2-Oxo(seleno)(thiono)-1,3,2-oxathia-
phospholanyl]carboxamides;
O-Alkyl-N-acylphosphoramido(thio)
(seleno)ates; tert-Butylperoxy-trimethylsilane; Prolylamido-AMP(S);
Oxathiaphospholane chemistry.
N-Oxathiaphosphitylation of carboxamides was the
initial step in the present approach towards the synthesis
of compounds containing N-acylphosphoramido
(thio)(seleno)ate linkages. Phenylacetamide (1a),
* Corresponding author. Tel.: +48-42-681-97-44; fax: +48-42-681-54-
83; e-mail: baraniak@bio.cbmm.lodz.pl
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.04.023

4270
J. Baraniak et al. / Tetrahedron Letters 45 (2004) 4269–4272
oxytrimethylsilane (t-BuOOSiMe3).15a The 31P NMR
O
C
O
C
S
S
i
1
1
spectrum of the reaction mixture recorded after 2 h
contained a peak at around 40 ppm, indicating the for-
mation of 6a,c. It is worth mentioning that the common
oxidant t-BuOOH, which was successfully used for the
oxidation of PIII oxathiaphospholane derivatives of
nucleosides,16 provided 6a,c low yields accompanied by
unidentified side products, as detected by 31P NMR.
Subsequently, compounds 4a–d, 5a and 6a,c, after
treatment with alcohols such as methanol, benzyl alco-
hol or 3-hydroxypropionitrile in the presence of DBU,
provided the corresponding, O-alkyl-N-acylphosph-
P
Cl
R
NH2
+
R
NH
P
O
O
3a-d
1a-d
2
O
X
P
O
X
P
S
ii
iii
1
1
2
R
C
NH
R
C
NH
OR
O
-
O
X = S 4a-d
X = Se 5a
X = O 6a,c
X = S
X = Se
X = O 11a,12c
7-9a-d
10a
Scheme 1. Reagents: (i) Py, 12 h; or DIPEA, CH2Cl2 (ii) S8 or Se or
t-BuOOSiMe3; (iii) R2OH, DBU.
oramidothioates
7–9,
O-alkyl-N-acylphosphoro-
selenoamidates 10a, or O-alkyl-N-acylphosphor-
amidates 11a and 12c, respectively (Scheme 1). All
compounds 7–12 were isolated from the reaction
mixture by silica gel column chromatography and were
characterized by 31P NMR and FAB-MS analysis (Table
2). The yields of N-acylphosphoramidothioate and
N-acylphosphorselenoamidate derivatives 7–10 are
presented in Table 2 and reflect the efficiency of the last
step as depicted in Scheme 1. However, in the case of
11a and 12c the overall yields are provided because
crude compounds 6a,c were converted into the final
products without isolation of these intermediates. All
attempts to purify 6a,c were unsuccessful due to their
instability on silica gel.
benzamide (1b), acetamide (1c) and nicotinamide (1d)
have been used as representative carboxamides. Thus,
1a–d were treated with 2-chloro-1,3,2-oxathiaphospho-
lane (2) in pyridine. The resulting PIII intermediates 3a–d,
after treatment with elemental sulfur or selenium, gave
compounds 4a–d and 5a, respectively (Scheme 1). The
reactions were monitored by 31P NMR and were com-
plete within 12 h, and the final products, either 4a–d or
5a, were isolated by silica gel column chromatography in
1
40–93% yields. Their structures were confirmed by H
NMR, 31P NMR and FAB-MS analyses (Table 1).
To obtain 2-oxo-1,3,2-oxathiaphospholane derivatives
6a,c, we carried out the reaction between carboxamides
1a,c and 2 for 3 h in the presence of bis(N,N-diisoprop-
yl)ethylamine in methylene chloride. The resulting PIII
derivatives 3a,c were treated at 0 ꢁC with tert-butylper-
An alternative route leading to N-acylphosphoramidate
utilized 2-seleno-1,3,2-oxathiaphospholane derivative
5a. Its DBU-assisted reaction with methanol afforded
Table 1. The physicochemical characteristics of compounds 4–6 prepared via Scheme 1
Entry
Compound
R1
X
31P NMR (d, ppm)a
FAB-MS (M)1 ) m( =z)
Yield (%)
1
2
3
4
5
6
7
4a
4b
4c
4d
5a
6a
6c
PhCH2
Ph
CH3
S
89.3
90.3
88.9
89.9
79.2b
42.5
41.3
273
256
196
259
320
––
72
93
55
42
40
75c
57c
S
S
C5H4N
PhCH2
PhCH2
CH3
S
Se
O
O
––
a The spectra were measured on a 200 MHz spectrometer.
b
1
The coupling constant JPSe ¼ 910 Hz.
c Based on 31P NMR.
Table 2. The physicochemical characteristics of compounds 7–12 prepared via Scheme 1
Entry
Substrate
Product
No.
X
R1
R2
31P NMR
(d, ppm)a
FAB-MS (M)1)
(m=z)
Yield (%)
1
4a
4b
4c
4d
4a
4b
4a
4b
5a
6a
6c
7a
7b
S
PhCH2
Ph
CH3
CH3
CH3
48.6
48.2
48.8
48.7
48.3
48.9
48.3
48.6
40.6b
)6.0
)7.2
244
230
168
23197
320
306
283
269
290
228
228
92
85
97
2
S
3
7c
7d
S
CH3
CH3
4
S
C5H4N
PhCH2
Ph
5
8a
8b
S
PhCH2
PhCH2
96
96
79
81
70
39
20
6
S
7
9a
9b
S
PhCH2
Ph
CH2CH2CN
CH2CH2CN
CH3
8
S
9
10a
11a
12c
Se
O
O
PhCH2
PhCH2
CH3
10
11
CH3
PhCH2
a The spectra were measured on a 200 MHz spectrometer.
b
1
The coupling constant JPSe ¼ 778 Hz.

J. Baraniak et al. / Tetrahedron Letters 45 (2004) 4269–4272
4271
N-acylphosphoramidoselenoate 10a, which was oxidized
in situ to 11a in 42% overall yield by treatment with
t-BuOOSiMe3 (Scheme 2).15b
Tr
N
Tr
N
-
X
P
O
O
C
X
P
O
C
S
AdeBz
OBz
2
i
O
+
NH
O
NH
17
H
H
O
BzO
15 X = Se
16 X = S
These results prompted us to synthesize nucleotides
containing an acylphosphoramidate linkage. Prolyl-
amido-AMP7 and prolylamido-AMPS became our tar-
get molecules. N-Trityl protected prolinamide (13)8 was
used as the substrate because the 2-thiono-1,3,2-oxa-
thiaphospholane derivative of unprotected prolinamide
underwent an intramolecular cyclization in the presence
of DBU (data not shown). Thus, 13 was allowed to react
with 2 in pyridine, and the resulting PIII intermediate
was oxidized in situ by treatment with t-BuOOSiMe3
(Scheme 3). However, examination of the reaction
mixture by 31P NMR revealed that the oxidation leading
to 14 was inefficient and the desired product was
accompanied by several unidentified side products. As
the 2-oxo-1,3,2-oxathiaphospholane derivatives are rel-
atively unstable in the presence of silica gel, an attempt
to prepare prolylamido-AMP via the oxidation of
N-phosphoramidoselenoate derivatives, as already
described for the synthesis of 10a, was undertaken.
18 X = Se
21 X = S
ii
iii, iv
H
Tr
-
S
-
O
O
C
H
O
P
N
N
AdeBz
OBz
2
Ade
C
NH
P
O
O
NH
O
O
H
O
O
HO
OH
BzO
22
19
iii, iv
H
N
-
O
C
H
O
P
Ade
O
NH
O
O
HO
OH
20
Scheme 4. Reagents and conditions: (i) DBU, CH3CN, 12 h;
(ii) 4 equiv t-BuOOSiMe, CH2Cl2, 12 h; (iii) NH4OH; (iv) 50%
CF3CO2H, CH2Cl2, 1 h.
for a phosphoramidate function. The structure of com-
pound 19 was confirmed by FAB mass spectrometry
after its isolation in 42% yield. Finally, removal of the
benzoyl protecting groups of 19 with aqueous ammonia
followed by treatment with 50% trifluoroacetic acid
(removal of the trityl group) provided the prolylamido-
AMP (20) in 52% yield. The structure of isolated
product 20 was confirmed by 1H and 31P NMR analyses
and MALDI-TOF mass spectrometry.19
Thus, reaction between N-Tr-prolinamide (13) and 2
performed in the presence of black selenium gave, after
1h, the expected product 15 (Scheme 3), which was
isolated by column chromatography in 72% yield.17 No
side products were observed in this case, albeit extending
the reaction time led to decomposition, as evidenced by
31P NMR. The condensation of N-(N-Tr-L-prolinam-
ido)-20-seleno-1,3,2-oxathiaphospholane (15) with N6,
0
N6,O2 ,O3 -tetrabenzoyladenosine (17) was carried out in
the presence of DBU and the product 18 (Scheme 4),
was obtained as a mixture of diastereoisomers.18 Then
18 was oxidized in situ by treatment with 4 equiv of t-
BuOOSiMe3. The reaction was monitored by 31P NMR
and gave signals at: 42.8 and 41.7 ppm corresponding to
diastereomers at the phosphoroselenoate function, and
appearance of a resonance at ca. )5 ppm, characteristic
Prolylamido-AMPS was obtained via a two-step pro-
cess. N-Tr-prolinamide 13 was reacted with 2 in the
presence of elemental sulfur providing the oxathia-
phospholane derivative 16 in 68% yield.20 Subsequent
DBU activated ring-opening condensation of 16 with 17
gave compound 21 (Scheme 4). Removal of the benzoyl
and trityl protecting groups afforded prolylamido-
AMPS (22) in 47% yield.21
Se
P
O
C
O
C
O
In summary, we have developed a new approach to the
preparation of O-alkyl-N-acylphosphoramidates and O-
alkyl-N-acylphosphoramidothioates that is based on
oxathiaphospholane chemistry. Our efficient and facile
preparation gives N-[2-oxo(seleno)(thiono)-1,3,2-oxa-
thiaphospholane] derivatives of carboxamides (4–6, 15,
16), that were used for DBU-assisted condensation with
various alcohols providing products with an N-acyl-
phosphoramido(thio)(seleno)ate linkage. Furthermore
we have demonstrated that N-acylphosphoramidosele-
noates can be converted to their parent N-acylphosph-
oramidates by treatment with t-BuOOSiMe3. Although
N-acylphosphoramidates could be obtained directly
from N-(2-oxo-1,3,2-oxathiaphospholane) derivatives
(Table 2, entries 10 and 11), the synthesis of oxo
derivatives was not always efficient as in the case of 14.
Therefore, an alternative route via seleno derivatives 5
and 15, was elaborated. To our best knowledge N-acyl-
phosphoramidoselenoates have not yet been described
in the literature. These compounds after isolation from
the reaction mixture can be stored under vacuum for
S
i
PhCH2
PhCH2
PhCH2
NH
5a
NH
P
OMe
-
O
Se
10a
ii
O
C
O
P
NH
OMe
-
O
11a
Scheme 2. Reagents and conditions: (i) MeOH, DBU, CH3CN, 3 h;
(ii) 2 equiv t-BuOOSiMe3, 1 2 h.
Tr
N
Tr
N
O
C
H
X
P
O
C
S
i
NH
NH2
+ 2
H
O
14 X = O
13
15 X = Se
16 X = S
Scheme 3. Reagents: (i) t-BuOOSiMe3 or Se or S8.

4272
J. Baraniak et al. / Tetrahedron Letters 45 (2004) 4269–4272
8. (a) Moriguchi, T.; Asai, N.; Wada, T.; Seio, K.; Sasaki, T.;
Sekine, M. Tetrahedron Lett. 2000, 41, 5881–5884; (b)
Moriguchi, T.; Yanagi, T.; Kuniomori, M.; Wada, T.;
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months and they can be considered either as interme-
diates for the corresponding phosphoramidates or by
virtue of P-chirality, N-acylphosphoramidoselenoates
can serve as new stereochemical tools in mechanistic and
biological studies. It is worth mentioning that the role of
selenium in biological systems is of increasing interest.22
Besides its biological functions, there are numerous
physical, spectroscopic and biological studies of proteins
and other macromolecules, which are facilitated by the
incorporation of a selenium atom.23
11. (a) Stec, W. J.; Grajkowski, A.; Karwowski, B.; Ko-
ꢀ
bylanska, A.; Koziołkiewicz, M.; Misiura, K.; Okruszek,
A.; Wilk, A.; Guga, P.; Boczkowska, M. J. Am. Chem. Soc.
1995, 117, 12019–12029; (b) Stec, W. J.; Karwowski, B.;
Boczkowska, M.; Guga, P.; Koziołkiewicz, M.; Sochacki,
M.; Wieczorek, M.; Błaszczyk, J. J. Am. Chem. Soc. 1998,
120, 7156–7167; (c) Guga, P.; Stec, W. J. In Current
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Sons: New York, 2003; Vol. 4, pp 1–28.
Acknowledgements
These studies were supported financially by the State
Committee for Scientific Research (KBN), grant PBZ-
KBN 059/T09/06 to J.B. The authors are grateful to
Dr. S. Patterson for his assistance in preparation of the
manuscript.
ꢀ
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R.; Wasilewska, E.; Stec, W. J. Phosphorus Sulfur Silicon
2002, 177, 1667–1670.
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1
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