An efficient synthesis of acyclic N7- and N9-adenine nucleosides via alkylation with secondary carbon electrophiles to introduce versatile functional groups at the C-1 position of acyclic moiety

Article abstract of DOI:10.1080/15257770500446816

The introduction of versatile functional groups, allyl and ester, at the C-1 position of the acyclic chain in acyclic adenine nucleosides was achieved for the first time directly by alkylation of adenine and N⁶-protected adenine. Thus, the C-1′

Full text of DOI:10.1080/15257770500446816

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An Efficient Synthesis Of Acyclic N7- and
N9-Adenine Nucleosides Via Alkylation
With Secondary Carbon Electrophiles to
Introduce Versatile Functional Groups At
the C-1 Position of Acyclic Moiety
Pravin L. Kotian a , V. Satish Kumar a , Tsu-Hsing Lin a , Yahya El-
Kattan a , Ajit Ghosh a , Minwan Wu a , Xiaogang Cheng a , Shanta
Bantia a , Yarlagadda S. Babu a & Pooran Chand a
a BioCryst Pharmaceuticals, Inc. , Birmingham, Alabama, USA
Published online: 07 Feb 2007.
To cite this article: Pravin L. Kotian , V. Satish Kumar , Tsu-Hsing Lin , Yahya El-Kattan , Ajit
Ghosh , Minwan Wu , Xiaogang Cheng , Shanta Bantia , Yarlagadda S. Babu & Pooran Chand (2006)
An Efficient Synthesis Of Acyclic N7- and N9-Adenine Nucleosides Via Alkylation With Secondary
Carbon Electrophiles to Introduce Versatile Functional Groups At the C-1 Position of Acyclic Moiety,
Nucleosides, Nucleotides and Nucleic Acids, 25:2, 121-140, DOI: 10.1080/15257770500446816
To link to this article: http://dx.doi.org/10.1080/15257770500446816
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Nucleosides, Nucleotides, and Nucleic Acids, 25:121–140, 2006
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770500446816
AN EFFICIENT SYNTHESIS OF ACYCLIC N7- AND N9-ADENINE
NUCLEOSIDES VIA ALKYLATION WITH SECONDARY CARBON
ELECTROPHILES TO INTRODUCE VERSATILE FUNCTIONAL
GROUPS AT THE C-1 POSITION OF ACYCLIC MOIETY
Pravin L. Kotian, V. Satish Kumar, Tsu-Hsing Lin, Yahya El-Kattan,
Ajit Ghosh, Minwan Wu, Xiaogang Cheng, Shanta Bantia,
Yarlagadda S. Babu, and Pooran Chand
BioCryst Pharmaceuticals, Inc.,
2
Birmingham, Alabama, USA
The introduction of versatile functional groups, allyl and ester, at the C-1 position of
2
the acyclic chain in acyclic adenine nucleosides was achieved for the first time directly by
alkylation of adenine and N6-protected adenine. Thus, the C-1ꢁ-substituted N9-adenine acyclic
nucleoside, adenine-9-yl-pent-4-enoic acid ethyl ester (11), was prepared by direct alkylation of ade-
nine with 2-bromopent-4-enoic acid ethyl ester (6), while the corresponding N7-regioisomer, 2-[6-
(dimethylaminomethyleneamino)-purin-7-yl]-pent-4-enoic acid ethyl ester (10), was obtained in one
step by the coupling of N, N-dimethyl-Nꢁ- (9H-purin-6-yl)-formamidine (9) with 2-bromopent-4-
enoic acid ethyl ester (6). The functional groups, ester and allyl, were converted to the desired
hydroxymethyl and hydroxyethyl groups, and subsequently to phosphonomethyl derivatives and cor-
responding pyrophosphorylphosphonates.
Keywords N7- and N9-Adenine nucleosides; N-Alkylation of adenine
INTRODUCTION
Acyclovir (1a) and ganciclovir (1b) are well-known purine-based acyclic
nucleoside drugs.[1−4] Extensive work has been done on phosphonomethyl
ether derivatives of purine acyclic nucleosides, such as PMEA (2a), PMPA
(2c), HPMPA (2e), FPMPA (2f), PMEDAP (2g), HPMPDAP (2h), PMEG
(3a), PMPG (3b), and HPMPG (3c).[5−11] This work resulted in two
Received 9 May 2005; accepted 1 August 2005.
The authors thank Drs. Charlie Bugg and Claude Bennett for their encouragement throughout
this work. The authors appreciate the assistance of Raman Krishnan at BioCryst Pharmaceuticals, Inc.,
for crystallizing compound 10 for X-ray crystallography, and Scott T. Griffin and Robin D. Rogers at the
University of Alabama in Tuscaloosa for getting the crystal structure of compound 10. We also thank Ken
Belmore for helpful discussions with NMR spectral data.
Address correspondence to P. Chand, BioCryst Pharmaceuticals, Inc., 2190 Parkway Lake Drive,
Birmingham, AL 35244, USA. E-mail: pchand@biocryst.com
121

122
P. L. Kotian et al.
Chart 1
FDA-approved drugs, adefovir dipivoxil (2b) for HBV and tenofovir diso-
proxil (2d) for HIV infections. The structure of compounds 1–3 are given
in Chart 1. The introduction of phosphonomethyl ether functionality in
place of phosphoric acid ester may be important because: a) it is expected
to be chemically and metabolically stable; b) the β-oxygen atom in phos-
phonomethyl ether functionality enhances the acidity of phosphonate and
brings its second pKa closer to that of phosphate ester; and c) the oxygen
atom in the immediate vicinity of phosphorus has been demonstrated to
play a critical role for the enzymatic phosphorylation and thus for antivi-
ral activity.[12,13] All these nucleosides are N9-substituted and either have no
substituent or have the substitution from the C-2ꢁ position in the acyclic part
of the molecule. In spite of the strong similarity in the structures of these
compounds, different modes of action and profiles of antiviral activity have
been reported for variously substituted acyclic structures. There are limited
numbers of reports in the literature on N7-acyclic nucleosides. The 6-deoxy
derivative of the N7-regioisomer of ganciclovir has been found to display
excellent antiherpes action.[14] Regarding the C-1ꢁ substitutions on N7- and
N9-derivatives, there are only a few literature references.[15−18] Therefore,
we were interested in exploring N7- and N9-substituted acyclic nucleosides
branching particularly from the C-1ꢁ position as possible antiviral agents.

Introduction of Versatile Functional Groups at C-1 Position
123
Different approaches have been followed for the synthesis of N7 deriva-
tives of nucleosides. The N7 isomer of purine, 7-(α-D-ribofuranosyl)adenine,
isolated from pseudo-vitamin B12 was the first literature example of N7-
purine.[19a] The main problem for synthesis of N7 nucleosides is the pref-
erential alkylation at the N9 position of the purines and N7 is the minor
isomer.[19b] The N7-alkylated producthasbeenreportedtobeobtainedbyN7-
/N9-glycosyl transfer.[20] Detailed studies on N7 and N9 alkylation of guanine
have been conducted by Kjellberg and Johansson.[21] They have reported the
influence of the base, the alkylating agent, and the type of derivatization of
the purine moiety on relative formation of N7 and N9 isomers. Montgomery
and Thomas demonstrated the utility of removable blocking groups at N3 of
the adenine in the exclusive formation of 7-glycosyladenine in glycosylation
and transglycosylation reactions.[22] Hakimelahi has reported regioselective
alkylations at the N7 position in high yield by first tritylating adenine at
the N9 position and then alkylating the N7 position with concomitant self-
detritylation, which resulted in the desired N7-alkylated products.[23] Holy
and Okumura have demonstrated alkylation of N,N-dimethyl-Nꢁ-(9H-purin-
6-yl)-formamidine (9) with certain halogeno derivatives having electron-
withdrawing groups that lead selectively to N7-substituted nucleosides.[24−26]
Holy has reported that the preparation of C-1ꢁ-substituted analogues (N7 or
N9) with various electron-withdrawing functional groups in the C-1ꢁ position
is particularly difficult, since the elimination process during alkylation of the
heterocyclic base is strongly preferred.[24,26] The compounds with electron-
withdrawing groups at the C-1ꢁ position were prepared by Holy but in three
steps, which resulted in poor yield.[24,26] Since our main interest is in the
preparation of C-1ꢁ-substituted acyclic nucleosides (N7 and N9) having ester
and allyl functionalities suitable for transformation to hydroxymethyl and
hydroxyethyl groups, we were interested in developing an easy method for
direct alkylation of adenine; therefore, we reinvestigated the alkylation with
electron-withdrawing groups. The results of investigation of the alkylation of
adenine and N,N-dimethyl-Nꢁ-(9H-purin-6-yl)-formamidine with electron-
withdrawing substituent at the C-1ꢁ position using 2-bromopent-4-enoic acid
ethyl ester[27] (6) as our alkylating agent will be discussed in this article. The
conversion of allyl and ester functionalities to the desired hydroxyethyl and
hydroxymethyl functionalities and subsequently to phosphonomethyl deriva-
tives and corresponding pyrophosphorylphosphonates will also be discussed.
RESULTS AND DISCUSSION
Our objective is to have ester and allyl functionalities in the acyclic part of
the nucleoside at the C-1ꢁ position; therefore, we chose to use 2-bromopent-
4-enoic acid ethyl ester (6) as the alkylating agent so that both functionalities
can be introduced at the same time. These functional groups would be fur-
ther modified to the desired hydroxymethyl and hydroxyethyl groups. We
first attempted the synthesis of compound 7 (Scheme 1) using Hakimelahi’s

124
P. L. Kotian et al.
SCHEME 1
approach towards N7 alkylation from 9-trityl-9H-purin-6-ylamine (4) with 6
using lithium 2,2,6,6-tetramethyl piperidine as a base, which resulted in no
reaction. Our attempt to alkylate 3-(6-amino-purin-9-yl)-propionitrile (5) un-
der similar conditions also failed.
Holy has prepared the methyl ester of 10 from 9[28] in three steps: a) alky-
lation with chloroacetonitrile; b) alkylation of the active methylene group
with allyl bromide; and c) basic hydrolysis of the nitrile to the ester with
sodium methoxide in methanol.[24,26] We have followed the same concept
of alkylation, but we attempted to introduce allyl and ester functionalities at
the same time using 6 as the alkylating agent on 9 (Scheme 2). Various reac-
tion conditions, such as different bases (NaH and DBU), solvents (THF and
DMF), and the temperature, were examined for the alkylation of compound
9 with 6. The best results were obtained when NaH and 9 were heated at
100◦C in DMF for 1 h, followed by the addition of the electrophile 6 to the
anion at room temperature and stirring at room temperature for 16 h. This
reaction resulted in a mixture of N7 (10) and N9 (12) isomers in the ratio of 4

Introduction of Versatile Functional Groups at C-1 Position
125
SCHEME 2
to 1 and the N7-alkylated product 10 was isolated as a white solid by the filtra-
tion of the cold reaction mixture in 21% yield. The filtrate containing both
N9 and N7 isomers was concentrated and chromatography of the residue
gave the product, which on recrystallization further yielded 17% of the N7
derivative. The structure of N7 isomer was confirmed by X-ray crystallogra-
phy (Chart 2) and comparison of the NMR spectrum with the corresponding
methyl ester reported by Holy.[26] This method is much superior in terms of
number of steps, isolation of the product, and yield.
Chart 2

126
P. L. Kotian et al.
The methods of choice for the synthesis of the C-1ꢁ-substituted N9
nucleosides are through the Mitsunobu reaction and building of the purine
base.[29,30] In one case, the acetoxy group was used as the leaving group,
which is rather difficult to prepare compared to the bromo compounds.[31]
Holy prepared these types of compounds, again taking advantage of the ac-
tive methylene group of the side chain through condensation of aldehydes.
In our approach, direct alkylation of adenine 8 with 6 was achieved to pro-
duce compound 11 in DMF using sodium hydride as base, which is an easy
method and might become a method of choice for C-1ꢁ-substituted acyclic
nucleosides. Again, both allyl and ester groups are very useful for conversion
to other groups.
Further modifications of the ester to hydroxymethyl and allyl to hydrox-
yethyl were based upon known literature procedures. Reduction of the ester
group in 10 (Scheme 3) with sodium borohydride in MeOH gave the desired
hydroxymethyl product 13 in 52% yield, N6-deprotected 14 in 29% yield,
and N-methylated product 15 in 3% isolated yield, which were easily sepa-
rated by chromatography on a silica gel column. The NMR spectra of com-
pounds 13 and 14 match the NMR spectra of the same compounds reported
by Holy.[26] Compound 13 was hydrolyzed to compound 14 under basic
conditions.[26] Phosphonomethyl derivative 18 was prepared from 14 by the
reaction of sodium hydride and p-toluenesulfonyloxymethylphosphonate[32]
(16) to give 17 followed by TMSI-mediated hydrolysis. The phosphonic acid
18 thus obtained was converted to 19 using morpholine and DCC as the ac-
tivating reagent. Reaction of 19 with tri(n-butylammonium)pyrophosphate
furnished the pyrophosphorylphosphonate 20.[33] Ozonolysis of the termi-
nal alkene in compound 17 followed by reduction with NaBH4 gave the
desired alcohol 21, which was converted to the pyrophosphorylphosphonate
23 via the phosphonic acid 22 as described for compound 20.
Our next goal was to prepare compound 36 from 13. Protection of the
hydroxyl group in 13 (Scheme 4) with trityl followed by basic hydrolysis of
imine gave adenine derivative 24. The ozonolysis of 24 and the reduction
of the resultant ozonide occurred smoothly and 25 was isolated. Phospho-
nomethylation of 25 under similar conditions as used for 14 resulted in a
messy reaction and gave the phosphonate 26 only in 8% yield. We attempted
to run the same reaction sequence to improve the yield for compound 26 by
modifying the protecting groups on the hydroxyl, such as THP, TBDPS, and
MOM with no success.
To circumvent this problem, we decided to take an alternate convergent
approach through alkylation of compound 9 with the corresponding phos-
phonate 31 (Scheme 5). The phosphonate 31 was prepared from known com-
pound 27.[34] Alkylation of 27 with 16 using NaH as base gave 28, which upon
hydrolysis with 80% aqueous acetic acid gave 29. The primary hydroxyl group
of 29 was selectively protected with trityl to give compound 30, which on me-
sylation of the secondary hydroxyl group produced the desired alkylating

Introduction of Versatile Functional Groups at C-1 Position
127
SCHEME 3
reagent 31. Alkylation of compound 9 with phosphonate 31 using NaH as
base resulted in slightly improved yield of 18% of the desired N7 derivative
32. The majority of alkylation occurred at N9 position in this case, and 15%
of 33 and 18% of 34 were isolated. The decrease in yield for the formation of
N7 compound 32 may be due to several reasons, such as the steric bulk of the
alkylating reagent, low reactivity of the secondary carbon since the mesylate

128
P. L. Kotian et al.
SCHEME 4
is a poor leaving group compared to bromo, and the absence of the electron-
withdrawing group at the C-1ꢁ position. Hydrolysis of compound 32 gave a
compound whose NMR and TLC matches with compound 26 prepared in
Scheme 4. Compound 26 was converted to pyrophosphorylphosphonate 36
via the phosphonic acid 35 as described for compound 20.
BIOLOGICAL ACTIVITY
Compounds 18, 20, 22, 23, 35, and 36 were evaluated for antiviral activity
against HCV in replicon assay but showed poor activity.
EXPERIMENTAL
Unless otherwise stated, all reagents and solvents were purchased from
1
Aldrich and used as received. H NMR and 13C NMR were recorded on a
Bruker 300 MHz instrument. Chemical shifts (δ) are reported in parts per mil-
lion (ppm) referenced to TMS at 0.00 or respective deuterated solvent peak.
31P NMR chemical shifts are reported with respect to D3PO4 in D2O as the ex-
ternal standard. Coupling constants (J) are reported in Hertz. IR spectra were
obtained from films on NaCl plates for oils or KBr pellets for solids with a scan
range of 4000–500 cm−1 on an FT-IR spectrometer (BioRad FTS-3500GX).
Mass spectra data were acquired on a Waters ZMD mass spectrometer coupled

Introduction of Versatile Functional Groups at C-1 Position
129
SCHEME 5
with a Waters System 2695 for loading of the samples in ES positive or negative
mode. UV spectroscopy was carried out on an Agilent 8453 spectrophotome-
ter. For the calculation of the concentration of phosphonates in solution by
UV, the reported value of 7-β-D-ribofuranosyl-7H-purin-6-amine was taken
as reference. The elemental analysis (C, H, and N) were performed by
Atlantic Microlab in Norcross, Georgia. The TLC solvent systems CMA-80
and CMA-50 refers to chloroform:methanol:conc. NH4OH (80:18:2) and

130
P. L. Kotian et al.
chloroform:methanol:conc. NH4OH (50:40:10), respectively. The non-UV
active compounds were visualized by charring the TLC plate sprayed with
ammonium molybdate cesium sulfate spray prepared by dissolving conc.
H2SO4 (22.4 mL), CeSO4 (45 mgs), (NH4)6Mo7O24·4 H2O (7 g) in water
in 100 mL volumetric flask. The olefin compounds were visualized by us-
ing KMnO4 spray. Ozonolysis was performed using ozone generated by an
ozonolyzer from Yanco Industries. Purification by flash column chromatog-
raphy was performed on a Combiflash Sq16X manufactured by Isco using
the appropriate solvent system as described in the experimental procedures.
N,N -Dimethyl-Nꢀ-(9H-purin-6-yl)-formamidine (9).
This was prepared
by slight modification of the literature procedure.[28] To a mixture of adenine
(43.8 g, 0.32 mol) and N,N-dimethylformamide dineopentyl acetal (150 g,
0.65 mol) was added DMF (150 mL) and heated at reflux for 1 h. Additional
DMF (75 mL) was added to make the reaction mixture homogeneous and
again heated at reflux for 1 h. The reaction mixture was cooled to room
temperature and allowed to stand at room temperature for 16 h. The solid
obtained was collected by filtration, washed with ethyl acetate (25 mL), and
dried under vacuum to furnish 43.22 g (70%) of 9 as a white solid; mp 252–
1
255◦C; UV (MeOH) λmax 308 nM; H NMR (DMSO-d6): δ 13.00 (bs, 1H),
8.89 (s, 1H), 8.44 (s, 1H), 8.28 (s, 1H), 3.19 (s, 3H), 3.14 (s, 3H); MS (ES+)
191.59 [100% (M+1)+]. Anal. Calcd for C8H10N6: C, 50.52; H, 5.30; N, 44.18.
Found: C, 50.50; H, 5.23; N, 44.02.
2-[6-(Dimethylamino-methyleneamino)-purin-7-yl]-pent-4-enoic Acid
Ethyl Ester (10).
To a suspension of NaH (60% suspension in mineral oil,
10.06 g, 0.26 mol) in DMF (700 mL) was slowly added 9 (47.5 g, 0.25 mol)
using a solid addition funnel at room temperature. The reaction mixture
became homogeneous after stirring for 10 min at room temperature and
was then heated at 100◦C for 1 h and cooled to room temperature. To this
anion, 6 was added (43 mL, 0.29 mol) dropwise at room temperature and
stirred for 16 h. The solid precipitated out and was collected by filtration and
washed with ether and hexane (100 mL each) to furnish 17 g (21%) of 10
as a white solid. The filtrate was concentrated and purified by flash column
chromatography on silica gel, eluting with 0 to 7.5% methanol in chloroform.
The appropriate fraction was collected together and concentrated and the
residue was recrystallized from ethanol (75 mL) to give 13.65 g (17%) of
additional 10 as a white solid; mp 174–175◦C; UV (MeOH) λmax 320 nm;
1H NMR (DMSO-d6): δ 8.89 (s, 1H), 8.43 (s, 2H), 5.91 (m, 1H), 5.77–5.60
(m, 1H), 4.93 (d, J = 10.0 Hz, 2H), 4.10 (q, J = 7.0 Hz, 2H), 3.20 (s, 3H),
3.19–3.09 (m, 2H), 3.08 (s, 3H), 1.08 (t, J = 7.0 Hz, 3H); 13CNMR (CDCl3) : δ
14.16, 35.09, 35.99, 41.11, 59.16, 61.74, 116.97, 118.91, 133.80, 146.76, 152.30,
154.88, 156.96, 161.17, 169.8; IR (KBr) 3452, 3045, 2958, 2903, 2397, 1885,

Introduction of Versatile Functional Groups at C-1 Position
131
1735, 1634, 1584, 1545, 1425 cm−1; MS (ES+) 339.45 [100% (M + Na)]. Anal.
Calcd for: C15H20N6O2: C, 56.95; H, 6.37; N, 26.56. Found: C, 56.99; H, 6.48;
N, 26.48. The filtrate was a mixture of 10 and 12.
In a separate experiment on 1 mmol scale, the reaction mixture on pu-
rification by silica gel chromatography yielded both N7 (10) and N9 (12)
isomers in the ratio of 4 to 1 and in 48% overall yield. The structure of 12
was confirmed by the following data 12, UV (MeOH) λmax 308 nm; 1H NMR
(DMSO-d6): δ 8.9 (s, 1H), 8.38 (s, 1H), 8.33 (s, 1H), 5.74–5.58 (m, 1H), 5.46
(dd, J = 10.5 and 5.0 Hz, 1H), 4.98 (dd, J = 7.5 and 1.5 Hz, 1H), 4.91 (d,
J = 10.5 Hz, 1H), 4.14 (q, J = 7.0 Hz, 2H), 3.18 (s, 3H), 3.11 (s, 3H), 3.11–
2.93 (m, 2H), 1.13 (t, J = 7.0 Hz, 3H); 13CNMR (DMSO-d6) : δ 14.26, 34.85,
55.26, 55.92, 61.96, 119.15, 125.24, 133.38, 142.47, 151.92, 152.19, 158.39,
159.44, 169.38; IR (KBr) 3458, 3078, 2982, 2926, 2813, 1443, 1633, 1564,
1418, 1348, 1270, 1205, 1115, 1013 cm−1; MS (ES+) 317.54 [100% (M+1)+].
Anal. Calcd for: C15H20N6O2·0.25 H2O: C, 55.37; H, 6.51; N, 25.83. Found:
C, 55.78; H, 6.42; N, 25.77.
2-(6-Amino-purin-9-yl)-pent-4-enoic Acid Ethyl Ester (11).
A suspen-
sion of NaH (95%, 0.21 g, 8.5 mmol) and adenine (1.13 g, 8.38 mmol)
in DMF (20 mL) was sonicated for 10 min and heated at 100◦C for 2 h and
then cooled to room temperature. To the anion formed was added 6 (2.18 g,
10.5 mmol) in DMF (2.5 mL) dropwise at room temperature and stirred
for 16 h and concentrated. The residue on purification by flash column
chromatography eluting with 0 to 7.5% methanol in chloroform gave 1.33
g (60%) of 11 as a white solid; mp 130–134◦C; UV (MeOH) λmax 260 nm;
1H NMR (DMSO-d6) : δ8.22 (s, 1H), 8.10 (s, 1H), 7.26 (bs, 2H), 5.75–5.58
(m, 1H), 5.38 (dd, J = 10.5 and 5.0 Hz, 1H), 4.98 (d, J = 17.5, 1H), 4.94
(d, J = 10.5 Hz, 1H), 4.12 (q, J = 7.0 Hz, 2H), 3.18–2.90 (m, 2H), 1.14 (t,
J = 7.0 Hz, 3H); 13CNMR (DMSO-d6) : δ 14.27, 34.82, 55.85, 61.93, 118.72,
119.10, 133.41, 140.55, 149.90, 152.82, 156.31, 169.46; IR (KBr) 3319, 3162,
2982, 2675, 1899, 1744, 1678, 1605, 1576, 1476, 1420, 1198, 1155 cm−1; MS
(ES+) 284.50 [100% (M + Na)+]. Anal. Calcd for: C12H15N5O2: C, 55.16; H,
5.79; N, 26.80. Found: C, 54.93; H, 5.89; N, 26.78.
Nꢀ-[7-(1-Hydroxymethyl-but-3-enyl)-7H-purin-6-yl]-N, N-dimethyl-form-
amidine (13), 2-(6-Amino-purin-7-yl)-pent-4-en-1-ol (14), 2-(6-Methylamino-
purin-7-yl)-pent-4-en-1-ol (15).
To a solution of 10 (18.96 g, 60 mmol)
in methanol (600 mL) was added sodium borohydride (3.42 g, 90 mmol)
portionwise at −5◦C over a period of 2 h and further stirred for 1 h at
−5◦C. Additional sodium borohydride (0.43 g, 12 mmol) was added in
two installments over a period of 2 h and the mixture stirred at 0◦C for
an additional 6 h and quenched with glacial acetic acid (18.9 mL, 320
mmol). After stirring for 30 min at room temperature, the reaction mixture

132
P. L. Kotian et al.
was concentrated to dryness and the residue purified by flash column
chromatography on silica gel column eluting with 0 to 25% methanol in
chloroform to furnish, first 10 (3.11 g, 16%), followed by 13 (8.46 g, 52%),
15 (0.4 g, 3%), and 14 (3.83 g, 29%).
1
13, White solid; mp 155–156◦C; UV (MeOH) λmax 314 nm; H NMR
(DMSO-d6): δ 8.91 (s, 1H), 8.43 (s, 1H), 8.41 (s, 1H), 5.72 (m, 1H), 5.36 (m,
1H), 5.03 (t, J = 5.6 Hz, 1H), 4.96 (d, J = 16.6 Hz, 1H), 4.91 (d, J = 10.0
Hz, 1H), 3.93 (m, 1H), 3.78 (m, 1H), 3.21 (s, 3H), 3.11 (s, 3H), 2.73 (m,
2H); IR (KBr) 3271, 3090, 2926, 2870, 2356, 1633, 1688, 1547, 1391, 1350
cm−1; MS (ES+) 275.51 [100% (M + 1)+]. Anal. Calcd for: C13H18N6O: C,
56.92; H, 6.61; N, 30.64. Found: C, 57.01; H, 6.65; N, 30.48.
14, Off-white solid; mp 186–188◦C; UV (MeOH) λmax 271 nm; 1H NMR
(DMSO-d6): δ8.38 (s, 1H), 8.17 (s, 1H), 6.90 (s, 2H), 5.72 (m, 1H), 5.29 (bs,
1H), 5.05 (d, J = 17.0 Hz, 1H), 4.97 (d, J = 10.0 Hz, 1H), 4.83 (m, 1H), 3.73
(bs, 2H), 2.71 (m, 2H); IR (KBr) 3393, 3302, 3145, 2914, 2845, 2762, 1909,
1641, 1603, 1552, 1469, 1392, 1319 cm−1; MS (ES+) 220.56 [100% (M + 1)+].
Anal. Calcd for: C10H13N5O·0.15 H2O: C, 54.09; H, 6.04; N, 31.56. Found:
C, 54.28; H, 5.97; N, 31.28.
15, Off-white solid; mp 180–181◦ C; UV (MeOH) λmax 277 nm; 1H NMR
(DMSO-d6): δ 8.34 (s, 1H), 8.26 (s, 1H), 6.94 (bs, 1H), 5.78–5.62 (m, 1H),
5.28 (t, J = 5.0 Hz, 1H), 5.04 (d, J = 17.0 Hz, 1H), 4.96 (d, J = 10.0 Hz, 1H),
4.88–4.77 (m, 1H), 3.72 (t, J = 5.0 Hz, 2H), 2.95 (d, J = 4.5 Hz, 3H), 2.81–
2.62 (m, 2H); IR (KBr) 3380, 3112, 2913, 2862, 1611, 1561, 1471, 1393, 1352,
1227 cm−1; MS (ES+) 234.55 [100% (M + 1)+]. Anal. Calcd for: C11H15N5O:
C, 56. 64; H, 6.48; N, 30.02. Found: C, 56.67; H, 6.43; N, 30.11.
[2-(6-Amino-purin-7-yl)-pent-4-enyloxymethyl]-phosphonic Acid Diiso-
propyl Ester (17).
A slurry of NaH (60%, suspension in mineral oil, 0.87
g, 21.68 mmol) and 14 (3.8 g, 17.34 mmol) in DMF (175 mL) was sonicated
for 10 min at room temperature and stirred for an additional 30 min. To the
anion formed was added 16[23] (7.89 g, 22.55 mmol) in DMF (25 mL) drop-
wise at room temperature and stirred for 16 h. The reaction was quenched
with glacial acetic acid (1.62 mL, 27 mmol) and concentrated. The residue
was purified by flash column chromatography on silica gel eluting with 0 to
25% methanol in chloroform to give 1.48 g (22%) of 17 as a beige solid; mp
120–126◦C; UV (MeOH) λmax 272 nm; 1H NMR (DMSO-d6): δ8.40 (s, 1H),
8.16 (s, 1H), 6.89 (bs, 2H), 5.79–5.63 (m, 1H), 5.12–4.94 (m, 3H), 4.54–4.39
(m, 2H), 3.96 (dd, J = 10.0 and 7.0 Hz, 1H), 3.85 (dd, J = 10.0 and 3.5 Hz,
1H), 3.77 (d, J = 8.0 Hz, 2H), 2.79–2.57 (m, 2H), 1.13 (d, J = 6.2 Hz, 6H),
1.08 (2 d, J = 6.2 Hz, 6H); 31P NMR (DMSO-d6) δ19.87; IR (KBr) 3335, 3158,
2981, 2935, 1655, 1603, 1550, 1584, 1474, 1389, 1256, 1093 cm−1; MS (ES+)
420.42 [100% (M + Na)+]. Anal. Calcd for: C17H28N5O4P: C, 51.38; H, 7.10;
N, 17.62. Found: C, 51.38; H, 7.02; N, 17.67. Unreacted 14 (2.41 g, 64%) was
recovered from the column.

Introduction of Versatile Functional Groups at C-1 Position
133
[2-(6-Amino-purin-7-yl)-pent-4-enyloxymethyl]-phosphonic acid (18). To
a solution of 17 (0.25 g, 0.63 mmol) in DMF (5 mL) at 0◦C was added TMSI
(0.89 mL, 6.29 mmol) and allowed to stir at room temperature for 16 h. The
reaction was cooled to 0◦C and again added TMSI (0.89 mL, 6.29 mmol) and
stirred at room temperature for an additional 24 h. The reaction mixture
was quenched with methanol (10 mL) and neutralized with triethylamine
and concentrated to dryness under vacuum. The residue was purified by
flash column chromatography using Combiflash Sq16X on 10 g silica gel,
eluting with 0 to 100% methanol in CMA-50 to furnish 63 mg (32%) of 18
(calculated on the basis of UV absorption concentration in water of the
purified product); UV (water) λmax 272 nm; 1H NMR (D2O): δ 8.48 (s, 1H),
8.25 (s, 1H), 5.79–5.62 (m, 1H), 5.08–4.89 (m, 4H), 4.12–3.96 (m, 2H), 3.67
(m, 1H), 2.80 (t, J = 7.0 Hz, 2H). 31P NMR (D2O) δ 16.20; MS (ES+) 314.4
[100% (M + 1)+].
Pyrophosphorylphosphonate of [2-(6-amino-purin-7-yl)-pent-4-enyloxy-
methyl]-phosphonic acid (20).
A solution of N,Nꢁ-dicyclohexylcarbo-
diimide (0.33 g, 1.61 mmol) in tert-butyl alcohol (20 mL) was added to a
stirred solution of 18 (63 mg, 0.20 mmol) and morpholine (0.26 g, 3.02
mmol) in aqueous tert-butyl alcohol (1:1; 40 mL) over a period of 15 min.
The mixture was then heated at reflux for 5 h and morpholine (0.26 g, 3.02
mmol) and N,Nꢁ-dicyclohexylcarbodiimide (0.33 g, 1.61 mmol) in tert-butyl
alcohol (20 mL) were again added and further heated at reflux for 20 h. The
reaction mixture was concentrated to dryness to give crude 19 [MS (ES+)
383.0 (100%; M + 1)], which was used as such for the next step. Crude 19
was dissolved in DMSO (25 mL) and tri-n-butylammonium pyrophosphate
(1.6 M tri-n-butylamine/1 M pyrophosphate, 0.67 g, 1.41 mmol) added to
it. After stirring at room temperature for 3.5 days, the reaction mixture was
triturated twice with ether (100 mL) and the ethereal phase removed by
decantation. The residue was washed once more with ether (100 mL) and
traces of ether removed under vacuum. The residue obtained was dissolved
in water (10 mL) and filtered to remove insoluble material. The filtrate was
purified by diethylaminoethyl (DEAE) weak anion with a Sepharose FF col-
umn (50 g) using triethylammonium hydrogen carbonate (TEAB) as buffer
0 to 0.1 M in water (700 mL). The product was found contaminated with py-
rophosphate and trisodium metaphosphate by 31P NMR spectrum analysis.
The crude product obtained was dissolved in water (2 mL) and applied on
a column of Dowex 1X2 (Cl-form; 100 mL), elution with linear gradient of
0–0.4 mol L−1 lithium chloride in 0.01 mol L−1 hydrochloric acid (500 mL).
The relevant product fractions were combined, neutralized with 0.5 mol L−1
lithium hydroxide to pH 6.7–6.8, and concentrated under vacuum to dry-
ness. The thick suspension was mixed with ethanol (30 mL) and centrifuged.
The sediment obtained was washed with ethanol and dried under vacuum

134
P. L. Kotian et al.
at room temperature to furnish desired triphosphate 20 (8.5 mg, 8.5%); UV
(water) λmax 271 nm; 1H NMR (D2O): δ 8.24 (s, 1H), 8.00 (s, 1H), 5.56–5.40
(m, 1H), 4.85–4.71 (m, 3H), 3.92 (dd, J = 3.7 and 10.4 Hz, 1H), 3.83 (dd,
J = 7.9 and 10.4 Hz, 1H), 3.60 (d, J = 8.1 Hz, 2H), 2.58 (t, J = 7.5 Hz, 2H);
31PNMR (D2O) δ 9.25 (dt, J = 8.9 and 25.2 Hz, 1P), −4.10 (d, J = 19.3 Hz,
1P), −19.63 (dd, 19.3 and 25.2 Hz, 1P); MS (ES+) 498.06 [100% (M+1)+].
Anal. Calcd for: C11H14Li4N5O10P3·5 H2O·LiCl: C, 20.98; H, 3.85; N, 11.13.
Found: C, 21.36; H, 3.88; N, 10.89.
[2-(6-Amino-purin-7-yl)-4-hydroxy-butoxymethyl]-phosphonic acid diiso-
propyl ester (21).
A solution of 17 (0.98 g, 2.46 mmol) in methanol:water
(4:1, 25 mL) was cooled to −78◦ C and oxygen slowly bubbled through it for
5 min. The reaction mixture was then ozonized for 1 h or until all starting
material disappeared as evidenced by TLC analysis. To this reaction mixture
at −78◦ C was added sodium borohydride (0.37 g, 9.87 mmol) in three por-
tions over a period of 1 h and then allowed to warm to room temperature for
16 h and quenched with acetic acid (2.9 mL, 49.35 mmol). After stirring for
10 min at room temperature, the mixture was concentrated and the residue
obtained was purified by flash column chromatography using Combiflash
Sq16X on 40 g silica gel, eluting with 0 to 10% methanol in chloroform
to furnish 0.5 g (51%) of 21 as a white solid; mp 138◦C; UV (MeOH) λmax
1
271 nm; H NMR (DMSO-d6): δ 8.42 (s, 1H), 8.17 (s, 1H), 6.86 (bs, 2H),
5.03–4.92 (m, 2H), 4.54–4.36 (m, 2H), 4.01 (dd, J = 10.0 and 7.0 Hz, 1H),
3.89 (dd, J = 10.0 and 3.0 Hz, 1H), 3.75 (d, J = 8.0 Hz, 2H), 3.52–3.40 (m
1H), 3.33–3.22 (m, 1H), 2.14–1.97 (m, 2H), 1.13 (d, J = 6.0 Hz, 6H), 1.08
(2d, J = 6.0 Hz, 6H); 31P NMR (DMSO-d6): δ 19.86; MS (ES+) 402.44 [100%
(M + 1)+]. Anal. Calcd for: C16H28N5O5P: C, 47.87; H, 7.03; N, 17.44. Found:
C, 48.03; H, 7.03; N, 17.17.
[2-(6-Amino-purin-7-yl)-4-hydroxy-butoxymethyl]-phosphonic acid (22).
Prepared from 21 (0.18 g, 0.44 mmol) using the same procedure as de-
scribed for 18 to give 66.3 mg (46%) of 22 (calculated on the basis of UV
absorption concentration in water of the purified product); UV (water) λmax
1
272 nm; H NMR (D2O): δ 8.24 (s, 1H), 7.99 (s, 1H), 4.78–4.68 (m, 1H),
3.80–3.69 (m, 2H), 3.43–3.29 (m, 3H), 3.20–3.12 (m, 1H), 2.00 (q, J = 6.78
Hz, 2H). 31P NMR (D2O) δ 16.25; MS (ES+) 318.4 [100% (M + 1)+].
Pyrophosphorylphosphonate of [2-(6-amino-purin-7-yl)-4-hydroxy-buto-
xymethyl]-phosphonic acid (23).
Prepared from 22 (63 mg, 0.20 mmol)
using the same procedure as described for 20 to give 23 (37 mg, 37%); UV
(water) λmax 271;1H NMR (D2O): δ 8.61 (s, 1H), 8.39 (s, 1H), 5.11–5.02 (m,
1H), 4.12–4.09 (m, 1H), 4.04–3.98 (m, 1H), 3.82–3.78 (m, 2H), 3.73–3.66
(m, 1H), 3.51–3.44 (m, 1H), 2.35–2.28 (m, 2H); 31P NMR (D2O): δ 9.09 (dt,
J = 10.0 and 24.5 Hz, 1P), −9.56 (d, J = 20.7 Hz, 1P), −22.02 (dd, J = 19.3

Introduction of Versatile Functional Groups at C-1 Position
135
and 24.5 Hz, IP); MS (ES+) 502.17 [100% (M + 1)+]. Anal. Calcd for: C10H14
Li4N5O11P3·4 H2O·0.25 LiCl: C, 20.56; H, 3.80; N, 12.00. Found: C, 20.85;
H, 4.00; N, 11.70.
7-(1-Trityloxymethyl-but-3-enyl)-7H-purin-6-ylamine (24).
To a solu-
tion of 13 (0.29 g, 1.07 mmol) in pyridine (10 mL) was added trityl chloride
(0.75 g, 2.67 mmol) and DMAP (0.012 g, 0.1 mmol) and stirred at room tem-
perature for 2 days. The reaction mixture was concentrated and the residue
dissolved in methanol (10 mL) and an aqueous NaOH solution (1N, 5 mL,
5 mmol) added. After stirring for 2 days at room temperature, the mixture
was concentrated and the residue purified by flash column chromatography
using Combiflash Sq16X (on 10 g silica gel), eluting with 0 to 10% methanol
in chloroform to furnish 0.3 g (61%) of 24 as a white solid; mp 210◦C (dec);
UV (MeOH) λmax 271 nm; 1H NMR (DMSO-d6): δ 8.50 (s, 1H), 8.21 (s, 1H),
7.23–7.16 (m, 9H), 7.11–7.04 (m, 6H), 6.88 (bs, 2H), 5.76–5.60 (m, 1H),
5.14–5.04 (m, 2H), 4.97 (dd, J = 10.0 and 2.0 Hz, 1H), 3.22 (dd, J = 10.0
and 3.0 Hz, 1H), 3.13 (dd, J = 10.0 and 5.0 Hz, 1H), 3.02–2.89 (m 1H),
2.86–2.74 (m, 1H); MS (ES+) 484.42 [100% (M + Na)]. Anal. Calcd for:
C29H27N5O·0.75 H2O : C, 73.32; H, 6.05; N, 14.74. Found: C, 73.40; H, 5.79;
N, 14.81.
3-(6-Amino-purin-7-yl)-4-trityloxy-butan-1-ol (25).
Ozonolysis of 24 was
accomplished the same way as described for 21 to give 25 in 53% yield as a
white solid; 1H NMR (DMSO-d6): δ 8.50 (s, 1H), 8.21 (s, 1H), 7.23–7.15 (m,
9H), 7.12–7.05 (m, 6H), 6.82 (bs, 2H), 5.02 (bs, 1H), 4.74 (t, J = 5.0 Hz,
1H), 3.49–3.37 (m, 2H), 3.29–3.15 (m, 2H), 2.40–2.34 (m, 1H), 2.16–2.01
(m, 1H); MS (ES+) 488.38 [100% (M + Na)+].
[3-(6-Amino-purin-7-yl)-4-trityloxy-butoxymethoxymethyl]-phosphonic
acid diisopropyl ester (26) from 25.
A slurry of NaH (60%, suspension
in mineral oil, 0.015 g, 0.38 mmol) and 25 (0.14 g, 0.3 mmol) in DMF
(3 mL) was sonicated for 10 min at room temperature and stirred for an
additional 30 min at 50◦C. To the anion formed was added 16 dropwise
at room temperature (0.133 g, 0.38 mmol) in DMF (1 mL). The reaction
mixture was stirred at room temperature for 2.5 h and at 50◦C for 1 h, then
cooled to room temperature and quenched with glacial acetic acid (0.022
mL, 0.38 mmol). The reaction mixture was concentrated to dryness and the
residue taken in chloroform (10 mL) and washed with water (2 × 10 mL).
The organic layer was separated, dried over MgSO4, concentrated to dryness,
and the residue purified by flash column chromatography using Combiflash
Sq16X on 10 g silica gel, eluting with 0 to 100% CMA-80 in chloroform to
give 0.015 g (8%, 27% based upon recovered starting material) of 26 as
1
oil; H NMR (DMSO-d6): δ 8.57 (s, 1H), 8.21 (s, 1H), 7.23–7.15 (m, 9H),

136
P. L. Kotian et al.
7.08–7.04 (m, 6H), 6.83 (bs, 2H), 5.02 (bs, 1H), 4.61–4.44 (m, 2H), 3.64 (d,
J = 7.0 Hz, 1H), 3.50 (t, J = 5.0 Hz, 1H), 3.29–3.08 (m, 4H) 2.36–2.09 (m,
2H), 1.21–1.14 (m, 12H); 31P NMR (DMSO-d6): δ 20.76; 1H NMR (CDCl3):
δ 8.49 (s, 1H), 8.22 (s, 1H), 7.33–7.25 (m, 15H), 5.70 (bs, 2H), 4.99–4.88
(m, 1H), 4.78–4.62 (m, 2H), 3.62 (dd, J = 9.0 and 5.0 Hz, 2H), 3.59–3.54
(m, 2H), 3.42 (t, J = 5.0 Hz, 2H), 2.44–2.18 (m, 2H), 1.36–1.25 (m, 12H);
31P NMR (CDCl3): δ 19.73; MS (ES+) 644.40 [100% (M + 1)+]. Unreacted
25 (0.1 g, 72%) was recovered from the column.
26 from 32. To a solution of 32 (0.075 g, 0.11 mmol) in methanol (2.5 mL)
was added conc. NH4OH (5 mL) and stirred at room temperature for 3
days. Additional conc. NH4OH (5 mL) and MeOH (0.5 mL) were added
and stirred for 24 h and the process was repeated once more. The reaction
mixture was concentrated under vacuum to furnish a residue, which was
triturated with hexane and filtered to furnish 0.03 g (42%) of 26 as a white
solid. All spectral data are the same as given above.
(3,4-Dihydroxy-butoxymethyl)-phosphonic acid diisopropyl ester (29).
A suspension of NaH (60%, suspension in mineral oil, 2.52 g, 63 mmol)
in DMF (40 mL) was treated at room temperature with 2-(2,2-dimethyl-
[1,3]dioxolan-4-yl)-ethanol[32] (27) (3.06 g, 21 mmol) in DMF (10 mL) and
thereactionmixturefurtherstirredfor1h. Totheanionformed 16wasadded
dropwise at room temperature (7.35 g, 21 mmol) in DMF (10 mL) and stirred
for 16 h before quenching with glacial acetic acid (3.75 mL, 62.5 mmol). The
reaction mixture was diluted with water (200 mL) and extracted with ethyl
acetate (3 × 75 mL). The organic layers were combined, washed with water
(2 × 75 mL) and brine (75 mL), and dried over MgSO4. After filtration,
the filtrate was concentrated to furnish [2-(2,2-dimethyl-[1,3]dioxolan-4-yl)-
ethoxymethyl]-phosphonic acid diisopropyl ester (28, 4 g, 59%) as an oil;
MS (ES+) 347.39 [100% (M + Na)+]. The product obtained was pure by
TLC analysis to be used for the next step. To 28 obtained above was added
80% acetic acid (150 mL) and stirred at room temperature for 16 h and
concentrated to give an oily residue, which was purified by flash column
chromatography on silica gel, eluting with 0 to 7.5% methanol in chloro-
form to furnish 1.24 (36%) of 29 as an oil; 1H NMR (DMSO-d6): δ 4.64–4.55
(m, 2H), 4.49 (dd, J = 11.5 and 5.5 Hz, 2H), 3.68 (d, J = 8.5 Hz, 2H), 3.57
(dd, J = 7.5 and 6.0 Hz, 2H), 3.53–3.43 (m, 1H), 3.32–3.18 (m, 2H), 1.76–
1.64 (m, 1H), 1.47–1.36 (m, 1H), 1.23 (dd, J = 6.0 and 2.5 Hz, 12H); 31P
NMR (DMSO-d6): δ 21.02.
(3-Hydroxy-4-trityloxy-butoxymethyl)-phosphonic acid diisopropyl ester
(30).
Toasolutionof 29(1.24g, 4.37mmol)inpyridine(40mL)wasadded
trityl chloride (1.34 g, 4.8 mmol) and DMAP (0.1 g, 0.44 mmol) and stirred at
room temperature for 2 days. The reaction mixture was concentrated and the

Introduction of Versatile Functional Groups at C-1 Position
137
residue purified by flash column chromatography using Combiflash Sq16X
on 40 g silica gel, eluting with 0 to 10% methanol in chloroform to furnish
1.72 g (75%) of 30 as an oil; 1H NMR (DMSO-d6): δ 7.43–7.18 (m, 15H), 4.77
(d, J = 5.7 Hz, 1H), 4.65–4.52 (m, 2H), 3.80–3.70 (m, 1H), 3.66 (d, J = 8.5
Hz, 2H), 3.61–348 (m, 2H), 3.00–2.90 (m, 1H), 2.81–2.74 (dd, J = 8.7 and
5.7 Hz, 1H), 1.86–1.72 (m 1H), 1.55–1.41 (m, 1H), 1.26–1.19 (m, 12H); MS
(ES+) 549.39 [100% (M + Na)+].
Methanesulfonic acid 3-(diisopropyloxy-phosphorylmethoxy-1-trityloxy-
methyl-propyl ester (31).
To a solution of 30 (1.72 g, 3.3 mmol), tri-
ethylamine (0.7 mL, 4.95 mmol) and DMAP (0.02 g, 0.17 mmol) in
dichloromethane (33 mL) at 0◦C was added methanesulfonyl chloride (0.32
mL, 8 mmol) and the mixture allowed to warm to room temperature and
stirred for 16 h. After quenching the reaction mixture with aqueous HCl
(0.2 N, 25 mL), the organic layer was separated and washed with brine (25
mL), dried over MgSO4, filtered, and the filtrate concentrated. The residue
obtained was purified by flash column chromatography using Combiflash
Sq16X on 40 g silica gel, eluting with 0 to 5% methanol in chloroform to
furnish 1.68 g (84%) of 31 as an oil; 1H NMR (DMSO-d6): δ 7.44–7.23 (m,
15H), 4.85–4.75 (m, 1H), 4.65–4.47 (m, 2H), 3.64 (d, J = 8.5 Hz, 2H), 3.59–
3.44 (m, 2H), 3.28 (dd, J = 10.5 and 3.5 Hz, 1H), 3.16 (s, 3H), 3.13–3.06 (m,
1H), 1.44 (q, J = 6.0 Hz, 2H), 1.26–1.17 (m, 12H); 31P NMR (DMSO-d6): δ
20.70; MS (ES+) 627.30 [35% (M + Na)+].
{3-[6-(Dimethylamino-methyleneamino)-purin-7-yl]-4-trityloxy-butoxy-
methyl}-phosphonic acid diisopropyl ester (32); {3-[6-(dimethylamino-
methyleneamino)-purin-9-yl]-4-trityloxy-butoxymethyl}-phosphonic acid di-
isopropyl ester (33); [3-(6-amino-purin-9-yl)-4-trityloxy-butoxymethyl]-phos-
phonic acid diisopropyl ester (34).
To a suspension of NaH (60%,
suspension in mineral oil, 0.044 g, 1.1 mmol) in DMF (5 mL) was added at
room temperature 9 (0.19 g, 1.0 mmol) and the reaction mixture heated at
100◦C for 1 h. After cooling to room temperature, the anion formed (0.2 N
solution in DMF, 3.5 mL, 0.7 mmol) was added to 31 (0.43 g, 0.71 mmol) in
DMF (1 mL) and heated at 100◦C for 4 h. The reaction mixture was cooled
to room temperature and quenched with glacial acetic acid (0.15 mL, 2.5
mmol), diluted with water (10 mL), and extracted with chloroform (2 × 10
mL). The combined organic layers were washed with water (10 mL) and
brine (10 mL) and then dried over MgSO4. After filtration, the filtrate was
concentrated and the residue obtained was purified very carefully by flash
column chromatography using Combiflash Sq16X on 10 g of silica gel,
eluting with 0 to 10% methanol in chloroform to give first 33 (0.075 g, 15%)
as an oil followed by 34 (0.080 g, 18%) as an oil and 32 (0.090 g, 18%) as an
oil.
32, 1H NMR (CDCl3): δ 8.62 (s, 2H), 8.25 (s, 1H), 7.23–7.08 (m, 15H),
4.80–4.63 (m, 3H), 3.56 (d, J = 8.0 Hz, 2H), 3.55–3.41 (m, 3H), 3.12 (s,

138
P. L. Kotian et al.
6H), 3.02–2.79 (m, 2H) 2.42–2.22 (m, 1H), 1.39–1.19 (m, 12H); 31P NMR
(CDCl3): δ 20.43; MS (ES+) 721.36 [100% (M + Na)+].
33, 1H NMR (CDCl3): δ9.00 (s, 1H), 8.41 (s, 1H), 8.07 (s, 1H), 7.25–7.08
(m, 15H), 4.85 (bs, 1H), 4.80–4.64 (m, 2H), 3.72 (t, J = 9.0 Hz, 1H), 3.55
(d, J = 8.0 Hz, 2H), 3.45–3.34 (m, 3H), 3.28 (s, 3H), 3.22 (s, 3H), 2.63–2.45
(m, 1H) 2.33–2.10 (m, 1H), 1.46–1.18 (m, 12H); 31P NMR (CDCl3): δ 20.40;
MS (ES+) 721.34 [100% (M + Na)+].
34, 1H NMR (CDCl3): δ 8.21 (s, 1H), 7.96 (s, 1H), 7.25–7.14 (m, 15H),
5.57 (bs, 2H), 4.90–4.65 (m, 3H), 3.69 (t, J = 9.0 Hz, 1H), 3.57 (d, J = 8.0 Hz,
2H), 3.54–3.12 (m, 3H), 2.63–2.45 (m, 1H) 2.31–2.11 (m, 1H), 1.47–1.18 (m,
12H); 31P NMR (DMSO-d6): δ 20.64; MS (ES+) 666.36 [100% (M + Na)+].
[3-(6-Amino-purin-7-yl)-4-hydroxy-butoxymethyl]-phosphonic acid (35).
Prepared from 26 (0.14 g, 0.22 mmol) using the same procedure as described
for 18 to give 26.8 mg (38%) of 35 (calculated on the basis of UV absorption
concentration in water of the purified product); 1H NMR (D2O): δ 8.18 (s,
1H), 7.89 (s, 1H), 4.74–4.64 (m, 1H), 3.79 (d, J = 5.1 Hz, 2H), 3.43–3.33 (m,
2H), 3.25–3.18 (m, 2H), 2.12–2.06 (m, 1H), 1.98–1.87 (m, 1H); MS (ES+)
318.34 [100% (M + 1)+].
Pyrophosphorylphosphonate of [3-(6-amino-purin-7-yl)-4-hydroxy-but-
oxymethyl]-phosphonic acid (36).
Prepared from 35 (26.82 mg, 0.084
mmol) as described for 20 to afford 36 (7.5 mg, 17.6%); UV (water) λmax
1
272 nM; H NMR (D2O): δ 8.37 (s, 1H), 8.13 (s, 1H), 4.87–4.77 (m, 1H),
3.94–3.88 (m, 2H), 3.66–3.54 (m, 2H), 3.45–3.29 (m, 2H), 2.32–2.19 (m,
1H), 2.14–2.03 (m, 1H), 31P NMR (D2O): δ 9.09 (d, J = 24.5 Hz, 1P), −3.85
(d, J = 19.3 Hz, 1P), −19.21 (t, J = 24.5 Hz, 1P).
CONCLUSION
We have developed an easy method to introduce allyl and ester function-
alities at the C-1ꢁ position of acyclic N7 or N9 nucleosides. These functional
groups are very versatile and may be converted to the desired functional
groups. These methods open a new area for the development of C-1ꢁ-
branched N7- and N9-acyclic nucleosides.
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