Synthesis and antiviral properties of aza-analogues of Acyclovir

Article abstract of DOI:10.1080/15257770601052281

Aza-analogues of Acyclovir were obtained from N-(2-pivaloyloxyethyl)-N- (pivaloyloxymethyl)-p-toluenesulfonamide via a one-pot base silylation/ nucleoside coupling procedure. The antiviral activities of all aza-nucleosides in vitro against a variety of vi

Full text of DOI:10.1080/15257770601052281

Nucleosides, Nucleotides, and Nucleic Acids, 26:51–64, 2007
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770601052281
SYNTHESIS AND ANTIVIRAL PROPERTIES OF AZA-ANALOGUES
OF ACYCLOVIR
Mariola Koszytkowska-Stawin´ ska, Katarzyna Kaleta, and Wojciech Sas
2
Faculty of Chemistry, Warsaw University of Technology, Warszawa, Poland
Erik De Clercq
Rega Institute for Medical Research, Catholic University of Leuven,
2
Leuven, Belgium
Aza-analogues of Acyclovir were obtained from N-(2-pivaloyloxyethyl)-N-(pivaloyloxymethyl)-
2
p-toluenesulfonamide via a one-pot base silylation/nucleoside coupling procedure. The antiviral
activities of all aza-nucleosides in vitro against a variety of viruses were evaluated. None of these
compounds displayed any specific antiviral effects.
Keywords Antiviral agents; Acyclic nucleosides; Aza-nucleosides; Acyclovir analogues
INTRODUCTION
Some acyclic nucleosides play a very important role in antiviral[1] and
antitumor[2] therapy; for example, Acyclovir, Ganciclovir, and their prodrugs
(e.g., Valacyclovir and Valganciclovir, respectively) are used for the clinical
treatment of herpes virus infections.[1,3] Consequently, various modifica-
tions have been made to the parent structures,[4,5] but there is a lack of
information on replacement of the oxygen atom by nitrogen. Generally
there is not much work on the synthesis and biological (i.e., antitumor,[6b,e,f]
antibacterial[6g] or antiviral[6o,p]) activities of acyclic nucleosides possessing
a nitrogen atom at the 2ꢁ-position, named acyclic aza-nucleosides. The
majority of them are aminoacid or peptide derivatives of pyrimidine nu-
cleobases, mostly 5-fluorouracil.[6]
Received 22 February 2006; accepted 22 June 2006.
This work was financially supported by Warsaw University of Technology. We thank Leentje
Persoons, Frieda De Meyer and Anita Van Lierde for excellent technical assistance with the antiviral
assays.
Address correspondence to Mariola Koszytkowska-Stawin´ska, Faculty of Chemistry, Warsaw Univer-
sity of Technology, ul. Noakowskiego 3, 00-664, Warszawa, Poland. E-mail: mkoszyt@ch.pw.edu.pl
51

52
M. Koszytkowska-Stawin´ska et al.
FIGURE 1 The general structure of aza-analogues of Acyclovir (A).
Recently, we have shown that acyclic aza-nucleosides may be obtained
easily from N -(pivaloyloxymethyl)sulfonamides through a one-pot base
silylation/nucleoside coupling procedure.[7] Using this methodology, we
successfully have accomplished the synthesis of aza–analogues of Ganciclovir.
Here, we describe the utility of this approach for the synthesis of aza-
analogues of Acyclovir (A) as well as the results of their antiviral screening
(Figure 1).
RESULTS AND DISCUSSION
Synthesis
As the first target we set up the synthesis of series of the aza–analogues
of Acyclovir possessing p-toluenesulfonyl substituent at the 2ꢁ-nitrogen
atom (Scheme 1, compounds of type 5). Thus, N -(2-hydroxyethyl)-p-
toluenesulfonamide[8] 1, readily available from 2-aminoethanol, was con-
verted into the key N -(pivaloyloxymethyl)sulfonamides 3a and 3b in two
steps through O-benzoylation or O-pivaloylation followed by the alkylation
with chloromethyl pivalate in the presence of potassium carbonate in dry
DMF at room temperature. The compounds 3a and 3b were obtained in
77% and 73% overall yield, respectively; crude 3 were pure enough to be
used for the synthesis of aza-nucleosides 4.
SCHEME 1 Reagents and conditions: (i) BzCl or PivCl, Py, rt, 1 day (2a, 90%; 2b, 91%); (ii) PivOCH2Cl,
K2CO3, DMF, rt, 5 days (3a, 85%; 3b, 80%); (iii) B(TMS)n or Bꢁ(TMS)n, Lewis acid; (iv) NH3 aq/MeOH.

Aza-Analogues of Acyclovir
53
SCHEME 2 Reagents and conditions: (i) a) CBz, BSA, MeCN, rt, 1 hour; b) 3a or 3b, TMSOTf, MeCN,
rt, 3 days; (ii) a) T or FU, BSA, MeCN, rt, 1 h; b) 3a, TMSOTf, MeCN, rt, 3 days; (iii) NH3 aq/MeOH,
70◦C, 5 days.
A one-pot base silylation/nucleoside coupling procedure was employed
for the synthesis of aza-analogues of Acyclovir 4, but the reaction conditions
varied somewhat depending on the sort of base employed (for details see
Schemes 2–4).[9] First the coupling of 3a and 3b with N 4-benzoylcytosine
(CBz) was examined (Scheme 2, path i). Thus, CBz was treated with N ,O-
bis(trimethylsilyl)acetamide (BSA) in dry acetonitrile at room temperature
for 1 hour, then the corresponding 3 and trimethylsilyl triflate (TMSOTf)
were added consecutively and the resulted mixture was kept at room
temperature for 3 days. The nucleoside 4CBz (R = Piv) was obtained in
much higher yield (64%) and it was more easily purified than 4ꢁCBz (R =
Bz, 25%); so for the next nucleoside couplings only O-pivaloyl sulfonamide
3a was utilized.
Under similar conditions 3a was condensed with thymine (T) or 5-
fluorouracil (FU) to give the corresponding aza-nucleosides 4T or 4FU in
67% or 78% yield, respectively (Scheme 2, path ii). Heating of 4CBz, 4T,
or 4FU with ammonium hydroxide in methanol at 70◦C (sealed tube) for 5
days afforded the deprotected nucleosides 5C, 5T, or 5FU, respectively; the
yields exceeded 60%.
The coupling of 3a with N 6–benzoyladenine (ABz) was conducted in
the presence of tin(IV) chloride (Scheme 3).[9] The mixture of regioi-
someric adenine N 9-(4ABz,9) and N7-derivative (4ABz,7) was obtained in
approximately 55% summary yield and variable N 9/N 7 ratio; this reaction
was repeated twice to yield, under the same conditions, the 4ABz,9/4ABz,7
mixtures in a 1.3/1 and 1/1.5 ratio, respectively.
To convert 4ABz,7 into 4ABz,9, the N7-isomer was heated in toluene at
80◦C in the presence of TMSOTf until the reaction was completed.[10]

54
M. Koszytkowska-Stawin´ska et al.
SCHEME 3 Reagents and conditions: i) a) ABz, BSA, MeCN, rt, 1 hour; b) 3a, SnCl4, MeCN, rt, 3 days;
(ii) TMSOTf, toluene, 80◦C, 2 hours (16%); (iii) NH3 aq/MeOH, 70◦C, 3 days.
SCHEME 4 Reagents and conditions: (i) a) GPac, BSA, CH2Cl2, 80◦C, 15 minutes; b) 3a, TMSOTf,
toluene, 80◦C, 1 hour; (ii) NH3 aq/MeOH, rt, 1 day; (iii) NH3 aq/MeOH, 70◦C, 7 days.

Aza-Analogues of Acyclovir
55
Under these conditions most of the substrate decomposed and 4ABz,9 was
obtained in low yield (16%). The deprotected derivative 5A9 or 5A7 was
obtained by heating 4ABz,9 or 4ABz,7 in methanol with ammonium hydroxide
at 70◦C for 3 days.
Since our previous attempts to obtain the guanine derived aza-
nucleosides using the procedure described above were unsuccessful,[7]
we employed the original Robins’ procedure[11] for the synthesis of the
corresponding guanine derivative 4GPac (Scheme 4). Thus, N 2-acetyl-O6-
(diphenylcarbamoyl)guanine (GPac) was silylated with BSA in dry ethylene
chloride before all volatile reagents were removed in vacuum. Silylated GPac
was dissolved in dry toluene and the coupling with 3a was conducted in the
presence of TMSOTf at 80◦C for 1 hour to afford the nucleoside 4GPac in
50% yield as a single N9-regioisomer.
The protecting groups were easily removed from the nucleobase moiety
by treatment of 4GPac with ammonium hydroxide in methanol at room
temperature to give compound 5G(Piv) in 80% yield (Scheme 4). To attain
5G we heated 4GPac with ammonium hydroxide in methanol at 70◦C.
However, in contrast to the deprotection of 4, after 7 days of heating we
obtained the 5G and 5G(Piv) mixture, in which the former nucleoside was
the minor component.
1D and 2D NMR Spectra
The structure of 4 and 5 was determined mostly on the basis of 1D and
2D NMR spectra. The N -1 linkage of the pyrimidine derivatives was evident,
1
but that of 4T was additionally proved by H–1H ROESY correlations; the
H-1ꢁ → H-6 interaction is shown in Figure 2.
An interesting feature in the 1H NMR spectrum of 5C is the existence of
two broad N-H singlets at 7.15 and 7.24 ppm. This phenomenon is probably
caused by the existence of 5C as the imino(4)-keto(2) tautomer, but not the
amino(4)-keto(2) one.[12] The elucidation of this problem would require
additional experiments.
The N -9 and N -7 isomers of the adenine aza-nucleosides 5A9 and 5A7
can be readily distinguished based on the 1H-13C HMBC correlations, which
FIGURE 2 The principal 1H-1H ROESY correlations observed in the spectrum of 4T.

56
M. Koszytkowska-Stawin´ska et al.
FIGURE 3 The principal 1H-13C HMBC correlations observed in the spectra of 5A9 and 5A7.
are shown in Figure 3. The N9-linkage in 5A9 was proved by H−1ꢁ → C-4
HMBC correlation and the N 7-one in 5A7 by the H-1ꢁ → C–5 interaction.[13]
The N -9 alkylation pattern at guanine derivative 5G(Piv) was proved by
H-1ꢁ → C-4 HMBC correlation (Figure 4).[13]
Antiviral Activity
The compounds 4T, 5 (T, C, FU, A9, A7, G(Piv), and G) were evaluated
in vitro against a variety of viruses in different host cell cultures:
(a) Vero cell cultures: parainfluenza-3 virus, reovirus-1, Sindbis virus, Cox-
sackie B4 virus and Punta Toro virus;
(b) E6SM cell cultures: herpes simplex virus-1 (KOS), herpes simplex virus-
2 (G), herpes simplex virus-1 (TK − KOS ACVr), vaccinia virus and
vesicular stomatitis virus;
(c) HeLa cell cultures: vesicular stomatitis virus, Coxsackie B4 virus and
respiratory syncytial virus.
FIGURE 4 The principal 1H-13C HMBC correlations observed in the spectrum of 5G(Piv).

Aza-Analogues of Acyclovir
57
Brivudin, (S)-9-(2,3-Dihydroxypropyl)adenine, Ribavirin, Acyclovir, and
Ganciclovir were used as the reference compounds. The following minimum
cytotoxic concentration values[14] were estimated for tested azanucleosides:
(i) Vero cell cultures: 200 µM for all compounds; (ii) E6SM cell cultures:
>200 µM for 4T and 5 (T, C, FU, A9, A7 and G); (iii) HeLa cell cultures:
>200 µM for 4T and 5 (T, C, FU, A9, A7 and G); (iv) E6SM or HeLa
cell cultures: 200 µM or 40 µM for compound G(Piv); respectively.[15] No
specific antiviral effects were noted for any of the compounds against any of
the viruses evaluated.
EXPERIMENTAL
General
Acetonitrile and dimethylformamide were dried prior to use according
to known procedures. Reagent and solvents were obtained from Sigma-
Aldrich, Poland. High resolution mass spectra (Electrospray Ionisation, ESI)
were performed at Laboratory of Mass Spectrometry, Institute of Organic
Chemistry, Polish Academy of Science (Warsaw) on Mariner spectrometer in
positive ionization mode (samples were loop injected in methanol solution).
The IR spectra were recorded at Division of Organic Chemistry, Faculty
of Chemistry, Warsaw University of Technology, on a Specord M80 (Carl-
Zeiss Jena) spectrometer in KBr disc; absorption maxima (νmax) are given
in cm−1. Elemental analyses were performed at Department of Analytical
Chemistry, Warsaw University of Technology, on a Perkin Elmer 2400
1
apparatus. H- and 13C-NMR spectra of all compounds were recorded at
Division of Organic Chemistry, Faculty of Chemistry, Warsaw University of
Technology, on a Varian Gemini 200 spectrometer (1H at 200 MHz, 13C
1
at 50 MHz). H and 13C chemical shifts are reported in ppm relative to
the solvent signals: CDCl3, δH(residual CHCl3) 7.26 ppm, δC 77.16 ppm or
DMSO-d6, δH(residual DMSO) 2.50 ppm, δC 39.52 ppm; signals are quoted
as “s” (singlet), “d” (doublet), “t” (triplet), “dt” (doublet of triplets), “m”
(multiplet), and “sbr” (broad singlet). Coupling constants J are reported in
Hz. 1H-13C HMBC (Heteronuclear Multiple Bond Correlation) and 1H–1H
ROESY (Rotational nuclear Overhauser Effect SpectroscopY) spectra were
measured at Division of Homogenous Catalysis and Organometallic Chem-
istry, Faculty of Chemistry, Warsaw University of Technology, on a Varian
Gemini 400 spectrometer in DMSO-d6. Precoated Merck silica gel 60 F254
(0.2 mm) plates were used for thin-layer chromatography (TLC), and the
spots were detected under UV light (254 nm). Column chromatography
was performed using silica gel (200−400 mesh) purchased from Merck Ltd.
(Poland).
The anhydrous MgSO4 was employed as a drying agent. Solvents were
distilled off under reduced pressure on the rotating evaporator.

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M. Koszytkowska-Stawin´ska et al.
p-Toluenesulfonamides (2). mixture of N -(2-hydroxyethyl)-p-
A
toluenesulfonamide 1[8] (5 g, 23 mmol), acid chloride (25 mmol) and
pyridine (10 cm3) was kept at room temperature for 1 day. The mixture
was diluted with water (20 cm3) and then chloroform (60 cm3) was added.
After 1 hour stirring organic layer was separated, washed subsequently with
water, 10% HCl aq (3 × 20 cm3), water and dried. Solvent was distilled off
to give 2a or 2b.
N-(2-Pivaloyloxyethyl)-p-toluenesulfonamide (2a). Yield 90% (6.3 g,
crude), mp 54–56◦C. The crude product was used in the next step without
purification. An analytical sample was crystallized from hexane-ethyl acetate
mixture (1/1, v/v). δH (CDCl3) 1.15 (9H, s) 2.42 (3H, s), 3.22 (2H, dt,
3
3
3
3J H-H = 6.0, J
= 5.2), 4.07 (2H, t, J H-H = 5.2), 4.96 (1H, t, J H-H =
H-H
6.0, NH), 7.30 (2H, m), 7.74 (2H, m). δC (CDCl3) 21.65, 27.22, 38.89,
42.52, 62.82, 127.16, 129.96, 137.03, 143.82, 178.53; νmax 3304, 2976, 1720,
1324, 1156, 1284; HRMS m/z calcd for C14H21NO4NaS 322.1084 (M+Na)+.
Found: 322.1098.
N-(2-Benzoyloxyethyl)-p-toluenesulfonamide (2b). 6.7 g (91%), mp.
107–109◦C [hexane-ethyl acetate mixture (1/1, v/v)]. δH (CDCl3) 2.37 (3H,
s, CH3), 3.37 (2H, dt, 3J H-H = 6.0, 3J H-H = 5.0), 4.33 (2H, t, 3J H-H = 5.0), 5.20
(1H, t, 3J H-H = 6.0, NH), 7.23 (m, 2H), 7.40 (m, 2H), 7.56 (m, 1H), 7.74 (m,
2H), 7.94 (m, 2H). δC (CDCl3) 21.66, 42.56, 63.49, 127.15, 128.56, 129.52,
129.81, 129.94, 133.47, 136.98, 143.78, 166.48; νmax 3272, 1700, 1288. Anal.
calcd for C16H17NO4S: C 60.17, H 5.37, N 4.39. Found: C 60.19, H 5.35, N
4.40.
N-(Pivaloyloxymethyl)sulfonamides (3). Chloromethyl pivalate (2.26 g,
15 mmol, 2.16 cm3) was added to a stirred mixture of p-toluenesulfonamide
2 (5 mmol), anhydrous potassium carbonate (2.77 g, 20 mmol) and dry
DMF (3 cm3). The mixture was left at room temperature for 5 days and then
was poured into ice-cold water (10 cm3). 1 was extracted with methylene
chloride (3 × 10 cm3). The extracts combined were washed with water and
dried. Solvent was distilled off to give 3a or 3b.
N-(2-Pivaloyloxyethyl)-N-(pivaloyloxymethyl)-p-toluenesulfonamide
(3a). Yield 85% (1.75 g, crude), mp 49–52◦C. An analytical sample was
crystallized form hexane. δH (CDCl3) 0.99 (9H, s), 1.21 (9H, s), 2.42 (3H,
3
3
s), 3.44 (2H, t, J H-H = 5.6), 4.24 (2H, t, J H-H = 5.6), 5.54 (2H, s), 7.29
(2H, m), 7.75 (2H, m). δC (CDCl3) 21.60, 26.86, 27.27, 38.84, 45.35, 62.55,
72.38, 127.68, 129.83, 137.07, 144.05, 178.03, 178.37; νmax 2924, 1728, 1464,
1384, 1156. Anal. calcd for C20H31NO6S: C 58.09, H 7.56, N 3.39. Found C
57.96, H 7.51, N 3.43.
N-(2-Benzoyloxyethyl)-N-(pivaloyloxymethyl)-p-toluenesulfonamide
(3b). Yield 80% (1.86 g, crude), mp 67–70◦C. An analytical sample was
crystallized form hexane. δH (CDCl3) 1.00 (9H, s), 2.40 (3H, s), 3.60 (2H,
3
3
t, J H-H = 5.6), 4.50 (2H, t, J H-H = 5.6), 5.60 (2H, s), 7.32–7.67 (5H, m),
7.77 (2H, m), 8.02 (2H, m). δC (CDCl3) 21.62, 26.89, 38.84, 45.52, 62.99,

Aza-Analogues of Acyclovir
59
72.48, 127.73, 128.56, 129.84, 133.32, 137.01, 144.09, 166.38, 178.07; νmax
2976, 1720, 1732, 1452, 1268. Anal. calcd for C22H27NO6S: C 60.95, H 6.28,
N 3.23. Found: C 61.01, H 6.26, N 3.31.
General procedure for the coupling of pyrimidine nucleobases and
N6-benzoyladenine with 3. Nucleobase, BSA, Lewis acid and 3 were used
in the following molar ratios: (i) 2.0/4.0/1.66/1.0 for the preparation of
4CBz, 4ꢁCBz, and 4T, (ii) 2.0/4.0/3.0/1.0 for the preparation of 4FU and
4A9/4A7. TMSOTf was used as Lewis acid for all couplings except for the
reaction with ABz where SnCl4 was employed. The mixture of nucleobase
(2.0 mmol), BSA (814 mg, 4 mmol, 1 cm3), and dry acetonitrile (10 cm3)
was stirred at room temperature under an argon atmosphere for 1 hour.
Then the solution of 3 (1.0 mmol) in dry acetonitrile (1 cm3) and Lewis
acid (in an amount depending on the kind of base) were added successively.
The reaction mixture was left at room temperature for 3 days, then ethyl
acetate (50 cm3) and saturated solution of sodium bicarbonate (1 cm3) were
added successively and the resulting mixture was stirred for 1 hour. The
mixture was filtered through a Celite pad. The organic phase was separated,
washed with water, brine, and dried. The solvent was distilled off. Crude 4
was purified by flash chromatography.
4-(Benzoylamino)-1-[N-(2-benzoyloxyethyl)-p-toluenesulfonylaminome-
thyl]-1H-pyrimidin-2-one (4ꢁCBz). Yield 25% (contaminated with pivalic
acid, ca. 20 mol%) (chloroform-acetone, 85/15, v/v). δH (CDCl3) 1.22
3
(9H, s, pivalic acid), 2.27 (3H, s, CH3) 3.85 (2H, t, J H-H = 5.4, H-3ꢁ), 4.48
(2H, t, 3J H-H = 5.4, H-4ꢁ), 5.48 (2H, s, H-1ꢁ), 7.14 (1H, d, 3J H-H = 7.4, H-5),
7.30–7.61 (10H, m, Ph), 7.85–7.98 (4H, m, Ph), 8.04 (2H, m, Ph), 8.07 (1H,
3
d, J H-H = 7.4, H-6). δC (CDCl3) 21.50 (CH3), 27.12 (pivalic acid), 38.47
(pivalic acid), 48.07, 61.81, 62.64, 97.55, 126.86, 128.17, 128.32, 128.77,
129.65, 130.02, 132.81, 133.06, 133.21, 136.26, 144.35, 148.75, 155.78
163.53, 167.10, 184.01 (pivalic acid). νmax 3382, 1620, 1520; HRMS m/z
calcd for C28H26N4O6NaS (M+Na)+ 569.1465. Found: 569.1496.
4-(Benzoylamino)-1-[N-(2-pivaloyloxyethyl)-p-toluenesulfonylaminome-
thyl]-1H-pyrimidin-2-one (4CBz). Yield 64% (methylene chloride–methanol,
99/1, v/v), mp 151–156◦C. δH (CDCl3) 1.17 [9H, s, (CH3)3C-], 2.39 (3H,
s), 3.77 (2H, t, 3J H-H = 5.4, H-3ꢁ), 4.19 (2H, t, 3J H-H = 5.4, H-4ꢁ), 5.42 (2H,
3
s, H-1ꢁ), 7.28 (1H, d, J H-H = 7.4, H-5), 7.49–7.63 (7H, m, Ph), 7.90 (2H,
m, Ph), 8.05 (1H, d, 3J H-H = 7.4, H-6), 8.73 (1H, s, NH). δC (CDCl3) 21.66,
27.30, 38.81, 48.35, 62.40, 62.52, 97.18, 126.88, 127.73, 129.21, 130.19,
133.48, 136.67, 144.49, 148.70, 162.91; 178.22. νmax 3064, 2972, 1728, 1668,
1628, 1556, 1484, 1368, 1324, 1256, 1156; Anal. Calcd for C26H30N4O6S: C
59.30, H 5.74, N 10.64. Found C 59.14, H 5.70, N 9.81.
1-[N-(2-Pivaloyloxyethyl)-p-toluenesulfonylaminomethyl]-5-methyl-1H,
3H-pyrimidin-2,4-dione (4T). 67% (methylene chloride–methanol, 97/3,
v/v), mp 145–149◦C. δH (CDCl3) 1.15 [9H, s, (CH3)3C-], 1.89 (3H, d,
3
4J H-H = 1.4, CH3), 2.41 (3H, s, CH3), 3.65 (2H, t, J H-H = 5.6, H-3ꢁ), 4.15

60
M. Koszytkowska-Stawin´ska et al.
(2H, t, 3J H-H = 5.6, H-4ꢁ), 5.23 (2H, s, H-1ꢁ), 7.29 (2H, m, Ph), 7.37 (1H, q,
4J H-H = 1.4, H-6), 7.62 (2H, m, Ph), 9.39 (1H, s, NH). δC (CDCl3) 12.38,
21.60, 27.20, 38.74, 47.58, 60.43, 62.12, 111.45, 126.83, 130.12, 136.88,
139.60, 144.53, 151.55, 164.38, 178.15. νmax 3340, 1724, 1656, 1500, 1322,
1152. Anal. calcd for C20H27N3O6S: C 54.90, H 6.22, N 9.60. Found: C
54.62, H 6.18, N 9.47.
1-[N-(2-Pivaloyloxyethyl)-p-toluenesulfonylaminomethyl]-5-fluoro-1H,
3H-pyrimidin-2,4-dione (4FU). 78% (hexane-ethyl acetate, 1/1, v/v), mp
170–179◦C. δH (CDCl3) 1.16 [9H, s, (CH3)3C-], 2.44 (3H, s, CH3) 3.64 (2H,
t, 3J H-H = 5.6, H-3ꢁ), 4.14 (2H, t, 3J H-H = 5.6, H-4ꢁ), 5.24 (2H, s, H-1ꢁ), 7.33
(2H, m, Ph), 7.66 (2H, m, Ph), 7.76 (1H, d, 3J H-F = 5.6), 8.86 (1H, s, NH).
δC (DMSO-d6) 20.96, 26.78, 38.81, 47.91, 60.98, 61.73, 126.71, 128.69 (d,
1
2J C-F = 33.4), 136.55, 139.23 (d, J C-F = 221.0), 143.94, 149.79, 157.13 (d,
2J C-F = 26.2), 177.16. νmax 3220, 1718, 1693, 1343, 1162, 1088. Anal. calcd
for C19H24FN3O6S C 51.69, H 5.48, N 9.52. Found: C 51.19, H 5.23, N 9.20.
6-(Benzoylamino)-9-[N-(2-pivaloyloxyethyl)-p-toluenesulfonylaminome-
thyl]-9H-purine (4ABz,9). Yield 31% (the second run 23%) (methylene
chloride-acetone, 98/2, v/v), mp 45–49◦C. δH (CDCl3) 1.14 [9H, s,
3
(CH3)3C-], 2.31 (3H, s, CH3), 3.71 (2H, t, J H-H = 5.6, H-3ꢁ), 4.21 (2H, t,
3J H-H = 5.6, H-4ꢁ), 5.77 (2H, s, H-1ꢁ), 7.13–7.51 (9H, m, Ph), 7.97 (2H, m,
Ph), 8.20 (1H, s), 8.64 (1H, s), 9.32 (1H, s, NH). δC (CDCl3) 21.50, 27.16,
38.72, 47.01, 55.71, 62.07, 122.47, 126.67, 127.93, 128.84, 129.95, 132.83,
133.56, 136.41, 143.37, 144.42, 149.61, 152.03, 152.87, 164.79, 178.13. νmax
3408, 1620, 1520. HRMS m/z calcd for C27H31N6O5S 551.2071 (M+H)+.
Found 551.2067.
6-(Benzoylamino)-7-[N-(2-pivaloyloxy-ethyl)-p-toluenesulfonylaminome-
thyl]-7H-purine (4ABz,7 ). Yield 23% (the second run 34%) (methylene
chloride-acetone, 98/2, v/v), mp 72–74◦C. HRMS m/z calcd for
C27H30N6O5NaS 573.1891 (M+Na)+. Found 573.1903. Signals in 1H–
and 13C–NMR spectra were broad, so their interpretation was impossible.
The rearrangement of 4ABz,7 . The mixture of 4ABz,7 (50 mg, 0.1 mmol),
TMSOTf (38 mg, 31 µl, 0.17 mmol) and toluene (20 cm3) was heated
in sealed tube at 80◦C for 2 hours. Ethyl acetate (10 cm3) and saturated
solution of sodium bicarbonate (1 cm3) were added successively and the
resulting mixture was stirred for 1 hour. The mixture was filtered through
a Celite pad. The organic phase was separated, washed with water, brine,
and dried. The solvent was distilled off. The residue was purified by flash
chromatography (methylene chloride-acetone, 98/2, v/v) to give 4ABz,9
(8 mg, 16%), mp 44–49◦C. The 1H– and 13C–NMR spectra were consistent
with those determined previously.
2-(Acetylamino)-6-(diphenylcarbamoyl)-9-[N-(2-pivaloyloxyethyl)-p-tol-
uenesulfonylaminomethyl]-9H-purine (4GPac). The mixture of GPac
(680 mg, 2 mmol), BSA (814 mg, 4 mmol, 1 cm3) and dry ethylene chloride
(10 cm3) was heated at 80◦C under an argon atmosphere in a sealed tube for

Aza-Analogues of Acyclovir
61
15 minutes. The solvent and BSA were removed in vacuum and the residue
was dissolved in dry toluene (20 cm3). Compound 3a (413 mg, 1.0 mmol) in
dry toluene (1 cm3) and TMSOTf (378 mg, 310 µl, 1.7 mmol) were added
to this solution, successively. The reaction mixture was heated at 80◦C for 1
hour. Ethyl acetate (50 cm3) and saturated solution of sodium bicarbonate
(1 cm3) were added to reaction mixture cooled to room temperature. The
resulting mixture was stirred for 1 hour at room temperature. The mixture
was filtered through a Celite pad. The organic phase was separated from the
filtrate and washed with water, brine, and dried. The solvent was distilled
off. 4GPac was purified by flash chromatography (chloroform–acetone,
95/5, v/v). Yield 50%, mp 64–67◦C. δH (CDCl3) 1.13 [9H, s, (CH3)3C-],
3
2.23 (3H, s, CH3), 2.34 (3H, s, CH3), 3.75 (2H, t, J H-H = 5.6, H-3ꢁ), 4.25
3
(2H, t, J
= 5.6, H-4ꢁ), 5.59 (2H, s, H-1ꢁ) 7.05–7.43 (14H, m, Ph), 8.07
H-H
(1H, s, H-8), 8.65 (1H, s, NH). δC (CDCl3) 21.30, 24.96, 27.10, 38.65, 47.32,
55.92, 61.96, 120.28, 126.49, 126.95, 129.16, 129.77, 136.24, 141.64, 144.25,
150.23, 152.17, 154.87, 155.98, 169.73, 178.25. νmax 2928, 1721, 1334, 759,
736.
Procedure for a deprotection of 4. The mixture of 4 (1.0 mmol), conc.
NH3 aq (2 cm3) and MeOH (4 cm3) was heated in a sealed tube at 70◦C
for 3–7 days (for details see Schemes 2–4) till a substrate was not detected
(TLC). Then solvent was distilled off and a residue was purified by flash
chromatography.
4-Amino-1-[N-(2-hydroxyethyl)-p-toluenesulfonylaminomethyl]-1H-pyri-
midin-2-one (5C). Yield 65% (chloroform–methanol, 9/1, v/v), mp
131–139◦C. δH (DMSO-d6) 2.39 (3H, s, CH3) 3.41 (4H, m, H-3ꢁ, H-4ꢁ), 4.77
(1H, sbr, OH), 5.14 (2H, s, H-1ꢁ), 5.69 (1H, d, 3J H-H = 7.7, H-5), 7.15 (1H,
3
sbr, NH), 7.24 (1H, sbr, NH), 7.37 (2H, m, Ph), 7.57 (2H, d, J H-H = 7.7,
H-6), 7.77 (2H, m, Ph). δC (DMSO-d6) 20.96, 50.49, 59.61, 61.51, 93.92,
126.74, 129.20, 129.76, 136.78, 143.43, 145.23, 155.85, 166.04; νmax 3336,
2928, 1664, 1640, 1500, 1332, 1152. HRMS m/z calcd for C14H19N4O4S:
(M+H)+ 339.1122. Found: 339.1138.
1-[N-(2-Hydroxyethyl)-p-toluenesulfonylaminomethyl]-5-methyl-1H,3H-
pyrimidin-2,4-dione (5T). Yield 64% (chloroform–methanol, 98/2, v/v),
mp 204–206◦C. δH (DMSO-d6) 1.73 (3H, s, CH3), 2.38 (3H, s, CH3), 3.37
(2H, m, H-3ꢁ), 3.45 (2H, m, H-4ꢁ), 4.81 (1H, m, OH), 5.15 (1H, s, H-1ꢁ), 7.38
(3H, m, H-6, Ph), 7.69 (2H, m, Ph), 11.26 (1H, sbr, NH). δC (DMSO-d6)
11.96, 20.96, 50.85, 59.77, 60.51, 108.76, 126.71, 129.77, 136.81, 140.09,
143.57, 151.07, 163.94; νmax 3405, 3029, 1718, 1695, 1439, 1340, 1278, 1160,
1136. Anal. calcd for C15H19N3O5S: C 50.98, H 5.42, N 11.98. Found: C
50.84, H 5.27, N 11.64.
1-[N-(2-Hydroxyethyl)-p-toluenesulfonylaminomethyl]-5-fluoro-1H,3H-
pyrimidin-2,4-dione (5FU). Yield 63% (chloroform-acetone, 85/15, v/v),
mp 196–202◦C. δH (DMSO-d6) 2.39 (3H, s, CH3), 3.40 (4H, m, H-3ꢁ, H-4ꢁ),
4.85 (1H, sbr, OH), 5.14 (2H, s, H-1ꢁ), 7.41 (2H, m, Ph), 7.72 (2H, m,

62
M. Koszytkowska-Stawin´ska et al.
3
Ph), 7.91 (1H, d, J H-F = 5.6), 11.75 (1H, sbr, NH). δC (DMSO-d6) 20.96,
51.19, 59.75, 61.12, 126.78, 128.76 (d, 2J C-F = 34.15), 129.85, 136.52, 139.29
1
2
(d, J C-F = 229.10), 143.74, 149.70, 157.24 (d, J C-F = 25.75). νmax 3432,
2999, 2850, 1741, 1727, 1699, 1664, 1447, 1336, 1156, 1138. Anal. calcd
for C14H16FN3O5S: C 47.05, H 4.51, N 11.76. Found: C 47.01, H 4.43,
N 11.62.
6-Amino-9-[N-(2-hydroxyethyl)-p-toluenesulfonylaminomethyl]-9H-puri-
ne (5A9). Yield 65% (chloroform-methanol, 99/1, v/v), mp 210–215◦C. δH
(DMSO-d6) 2.39 (3H, s, CH3), 3.49 (4H, m), 4.98 (1H, sbr, OH), 5.67 (2H,
s, H-1ꢁ), 7.27 (4H, m, Ph, NH2), 7.58 (2H, m, Ph), 8.06 (1H, s, H-8), 8.11
(1H, s, H-2). δC (DMSO-d6) 20.92 (CH3), 50.26 (C-3ꢁ), 55.98 (C-1ꢁ), 59.59
(C-4ꢁ), 118.30 (C-5), 126.61 (Carom-H), 129.57 (Carom-H), 136.47 (Carom),
140.70 (C–8), 143.48 (Carom), 149.31 (C–4), 152.67 (C-2), 155.96 (C–6).
νmax 3441, 1656, 1375, 1150. HRMS m/z calcd for C15H19N6O3S (M+H)+
363.1234. Found: 363.1216.
6-Amino-7-[N-(2-hydroxyethyl)-p-toluenesulfonylaminomethyl]-7H-puri-
ne (5A7). Yield 76% (chloroform-methanol, 99/1, v/v), mp 226–231◦C.
δH (DMSO-d6) 2.42 (3H, s, CH3), 3.07 (2H, m, H-3ꢁ), 3.19 (2H, m,
H-4ꢁ), 4.79 (1H, sbr, OH), 5.83 (2H, s, H-1ꢁ), 7.00 (2H, s, NH2), 7.46
(2H, m, Ph), 7.78 (2H, m, Ph), 8.22 (1H, s, H-2), 8.31 (1H, s, H-8). δC
(DMSO-d6) 21.00 (CH3), 49.00 (C-3ꢁ), 59.67 (C-4ꢁ), 60.34 (C-1ꢁ), 110.30
(C-5), 126.97 (Carom-H), 130.15 (Carom-H), 135.13 (Carom), 144.25 (Carom),
146.01 (C-8), 151.38 (C-6), 152.70 (C-2), 160.27 (C-4). νmax 3199, 3096,
2874, 1655,. HRMS m/z calcd for C15H18N6O3NaS (M+Na)+ 385.1059.
Found: 385.1064.
2-Amino-9-[N-(2-pivaloyloxyethyl)-p-toluenesulfonylaminomethyl]-9H-
purin-6-one [5G(Piv)] Yield 80% (chloroform-methanol, 95/5, v/v), mp
230◦C (dec), δH (DMSO-d6) 1.09 [9H, s, (CH3)3C-], 2.35 (3H, s, CH3), 3.68
(2H, t, 3J H–H = 4.8, H-3ꢁ), 4.18 (2H, t, 3J H–H = 4.8, H-4ꢁ), 5.47 (2H, s, H-1ꢁ),
6.41 (2H, sbr, NH2), 7.31 (2H, m, Ph), 7.52 (1H, s, H-8), 7.59 (2H, m, Ph),
10.53 (1H, sbr, NH). δC (DMSO-d6) 20.89 (CH3), 26.79 [(CH3)3C], 37.95
[(CH3)3C], 46.80 (C-3ꢁ), 54.92 (C-1ꢁ), 61.49 (C-4ꢁ), 116.09 (C-5), 126.57
(Carom-H), 129.63 (Carom-H), 136.39 (Carom), 136.90 (C-8), 143.53 (Carom),
151.01 (C-4), 153.63 [C-2(6)], 156.53 [C-6(2)], 177.28 (C O). νmax 2928,
1721, 1334, 759, 736. HRMS m/z calcd for C20H26N6O5NaS (M+Na)+
485.1578. Found: 485.1600.
2-Amino-9-[N-(2-hydroxyethyl)-p-toluenesulfonylaminomethyl]-9H-pur-
in-6-one (5G). Yield 9% (chloroform-methanol, 95/5, v/v). δH (DMSO-d6)
2.36 (3H, s, CH3), 3.40 (4H, m, H-3ꢁ, H-4ꢁ), 4.84 (1H, sbr, OH), 5.46 (2H, s,
H−1ꢁ), 6.45 (2H, sbr, NH2), 7.32 (2H, m, Ph), 7.60 (3H, m, Ph, H-8), 10.68
(1H, sbr, NH). δC (DMSO-d6) 20.95, 49.78, 55.48, 59.62, 116.13, 126.73,
129.62, 136.52, 137.04, 143.43, 151.10, 153.71, 156.70. HRMS m/z calcd for
C15H18N6O4NaS (M+Na)+ 401.1002. Found: 401.0985.

Aza-Analogues of Acyclovir
63
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