SYNTHESIS OF ENANTIOMERIC N-(2-PHOSPHONOMETHOXYPROPYL) DERIVATIVES OF PURINE AND PYRIMIDINE BASES. I. THE STEPWISE APPROACH

Article abstract of DOI:10.1135/cccc19951196

The (R)- and (S)-N-(2-phosphonomethoxypropyl) derivatives of purine and pyrimidine bases (PMP derivatives) exhibit very high activity against retroviruses.This paper describes the synthesis of enantiomeric 9-(2-phosphonomethoxypropyl)adenines (I and XXVII), 9-(2-phosphonomethoxypropyl)-2,6-diaminopurines (II and XXXI), 9-(2-phosphonomethoxypropyl)guanines (III and XXIX) and 1-(R)-(2-phosphonomethoxypropyl)cytosine (XIX) by alkylation of N-protected N-(2-hydroxypropyl) derivatives of the corresponding bases with bis(2-propyl) p-toluenesulfonyloxymethylphosphonate (X), followed by stepwise N- and O-deprotection of the intermediates.The key intermediates, N-(2-hydropxypropyl) derivatives IX and XXV, were obtained by alkylation of the appropriate heterocyclic base with (R)- or (S)-2-(2-tetrahydropyranyloxy)propyl p-toluenesulfonate (VII or XXIII) ans acid hydrolysis of the resulting N-<2-(2-tetrahydropyranyloxy)propyl> derivatives VIII and XXII.The chiral synthons were prepared by tosylation of (R)- or (S)-2-(2-tetrahydropyranyloxy)propanol (VI or XXI) available by reduction of enantiomeric alkyl 2-O-tetrahydropyranyllactates V and XXI with sodium bis(2-methoxyethyoxy)aluminum hydride.This approach was used for the synthsis of cytosine, adenine and 2,6-diaminopurine derivatives, while compounds derived from guanine were prepared by hydrolysis of 2-amino-6-chloropurine intermediates.Cytosine derivative IXe was also synthesized by alkylation of 4-methoxy-2-pyrimidone followed by ammonolysis of the intermediate IXf.

Full text of DOI:10.1135/cccc19951196

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SYNTHESIS OF ENANTIOMERIC N-(2-PHOSPHONOMETHOXYPROPYL)
DERIVATIVES OF PURINE AND PYRIMIDINE BASES. I.
THE STEPWISE APPROACH*
Antonin HOLY and Milena MASOJIDKOVA
Institute of Organic Chemistry and Biochemistry,
Academy of Sciences of the Czech Republic, 166 10 Prague 6, Czech Republic
Received March 10, 1995
Accepted May 25, 1995
The (R)- and (S)-N-(2-phosphonomethoxypropyl) derivatives of purine and pyrimidine bases (PMP
derivatives) exhibit very high activity against retroviruses. This paper describes the synthesis of
enantiomeric 9-(2-phosphonomethoxypropyl)adenines (I and XXVII), 9-(2-phosphonomethoxypropyl)-
2,6-diaminopurines (II and XXXI), 9-(2-phosphonomethoxypropyl)guanines (III and XXIX) and 1-(R)-
(2-phosphonomethoxypropyl)cytosine (XIX) by alkylation of N-protected N-(2-hydroxypropyl)
derivatives of the corresponding bases with bis(2-propyl) p-toluenesulfonyloxymethylphosphonate
(X), followed by stepwise N- and O-deprotection of the intermediates. The key intermediates, N-(2-
hydroxypropyl) derivatives IX and XXV, were obtained by alkylation of the appropriate heterocyclic
base with (R)- or (S)-2-(2-tetrahydropyranyloxy)propyl p-toluenesulfonate (VII or XXIII) and acid hy-
drolysis of the resulting N-[2-(2-tetrahydropyranyloxy)propyl] derivatives VIII and XXII. The chiral
synthons were prepared by tosylation of (R)- or (S)-2-(2-tetrahydropyranyloxy)propanol (VI or XXI)
available by reduction of enantiomeric alkyl 2-O-tetrahydropyranyllactates V and XXI with sodium
bis(2-methoxyethoxy)aluminum hydride. This approach was used for the synthesis of cytosine,
adenine and 2,6-diaminopurine derivatives, while compounds derived from guanine were prepared by
hydrolysis of 2-amino-6-chloropurine intermediates. Cytosine derivative IXe was also synthesized by
alkylation of 4-methoxy-2-pyrimidone followed by ammonolysis of the intermediate IXf.
In the course of our systematic structure–activity studies on acyclic phosphonate
analogs of nucleotides containing a phosphonomethylether functional group, we dis-
covered recently a significant antiviral activity of a new group of compounds, N-(2-
phosphonomethoxypropyl) derivatives of heterocyclic bases, the so-called
PMP-derivatives of adenine (I), 2,6-diaminopurine (II) and guanine3,4 (III). This dis-
covery is important from the following two viewpoints: In N-(2-phosphonomethoxy-
ethyl) derivatives (PME-derivatives5–8) substitution with an alkyl, cycloalkyl or
arylalkyl group in position β to the heterocyclic base led so far to loss of activity9,10
* This approach was reported previously in a preliminary form1,2
.
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
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(except for the (S)-hydroxymethyl5,10 and (S)-fluoromethyl11 derivatives). The biologi-
cal effect of these compounds concerns retroviruses (the group involving HIV, causing
AIDS) and is thus different from the parent PME-derivatives which are active both
against retroviruses and DNA viruses. The second interesting feature is the finding11
that for those derivatives of heterocyclic bases, where the biological effect of the acy-
clic phosphonates is limited to only one enantiomer, its absolute configuration in the
PMP-derivatives (in this case R) corresponds to that of the active enantiomer of their
hydroxymethyl analogs5,8 as well as fluoromethyl analogs (S-enantiomers)11,*, although
the specificity of their biological effect is principally different.
The first findings of the interesting biological properties of these compounds gave
impetus to extensive studies of their optimal preparation, stress being put particularly
on the enantiomeric purity of the products, general applicability to various heterocyclic
systems and accessibility and enantiomeric purity of the starting chiral material. The
only optimal type of starting chiral material, accessible in both enantiomeric forms, is
lactic acid or its esters.
The first synthetic variant, described in this paper, is the stepwise approach that
consists in introduction of the phosphonomethyl group into a heterocyclic base deriva-
tive with preformed side chain bearing one hydroxyl functionality. We made use of our
previous experience with the synthesis of N-(3-hydroxy-2-phosphonomethoxypropyl)
derivatives12.
The first phase of the synthesis was focused on the preparation of N-(2-hydroxypro-
pyl) derivatives of heterocyclic bases. We rejected the apparently simplest chiral
methyloxiranes as synthons because of their unsuitable physical properties and limited
* The formal difference in the designation is due to different preferences of the methyl, hydroxymethyl
and fluoromethyl groups in the Cahn–Ingold–Prelog notation.
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accessibility13; as the key synthon we have chosen the tosyl derivative of 1,2-propane-
diol, protected on the secondary hydroxyl. The commercially accessible 2-methylpropyl
ester of D-(–)-lactic acid (IV) was converted into the tetrahydropyranyl derivative V
which was reduced with sodium bis(2-methoxyethoxy)lithium aluminum hydride to
give (R)-2-(2-tetrahydropyranyloxy)propanol (VI) in high yield. Tosylation of VI under
usual conditions afforded the tosyl derivative VII. This compound was used for alkylation
of heterocyclic bases; according to our former experience, in most cases we alkylated
the unprotected heterocyclic base in the presence of half equivalent of cesium carbo-
nate. Under such conditions the alkylation reactions proceeded rapidly and with high
regiospecificity. In this way, we alkylated adenine, 2,6-diaminopurine and cytosine to
obtain the respective 2-O-tetrahydropyranyl derivatives VIIIa, VIIIb and VIIIe (Scheme 1).
SCHEME 1
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
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As a second alternative for the preparation of the cytosine derivative VIIIe we checked
also the ammonolysis of the 4-methoxy-2-pyrimidone derivative VIIIf prepared by alky-
lation of 4-methoxy-2-pyrimidone under standard conditions. We have found, however, that
the regiospecificity of alkylation of cytosine with the synthon VII is sufficiently high,
so that this indirect alternative offers no particular advantage. Acid hydrolysis with a
mineral acid afforded the N-(2-hydroxypropyl) derivatives IXa, IXb and IXe in high
purity. In addition to these compounds, we synthesized the guanine derivative IXd by
alkylation of 2-amino-6-chloropurine with the synthon VII. The reaction gave predomi-
nantly the 9-isomer VIIIc (we did not isolate pure 7-isomer), which on acid hydrolysis
of the C–Cl bond afforded, with simultaneous removal of the tetrahydropyranyl group,
(R)-9-(2-hydroxypropyl)guanine (IXd). The structure of the obtained compounds fol-
1
lowed unequivocally from their H NMR spectra.
Prior to the condensation with synthon12 X, the amino groups of the heterocyclic
bases should be protected. Therefore, we converted adenine and guanine into the
N-benzoyl derivatives XI and XIII, cytosine and 2,4-diaminopurine into amidines XV.
These derivatives were condensed with tosyl derivative X in the presence of an excess
(3 equivalents) of sodium hydride, and the protecting groups were then removed by
methanolysis. Deionization of the crude mixtures afforded bis(2-propyl) esters of (R)-
PMP-derivatives XII, XIV, XVI and XVIII, which were finally subjected to transsilyla-
tion with bromotrimethylsilane and subsequent hydrolysis. The obtained compounds
I–III and XIX were isolated by ion-exchange chromatography and crystallized in their
zwitterionic form (Scheme 2).
The same procedures were used in the preparation of (S)-PMP-derivatives, where the
starting compound was ethyl L-(+)-lactate (XX). Pyranylation, followed by reduction of
the tetrahydropyranyl derivative XXI, and subsequent tosylation of the protected diol
XXII afforded the (S)-synthon XXIII. Alkylation of bases with this synthon led to tetra-
hydropyranyl derivatives XXIV which were cleaved with acid to give the desired (S)-(2-
hydroxypropyl) derivatives XXV (Scheme 3). In this series, the described method was
used for the preparation of derivatives of adenine (XXVa) and 2,6-diaminopurine
(XXVb); the guanine derivative XXVd was obtained again via the 2-amino-6-chloro-
purine intermediate XXIVc (vide supra).
In the further step we made use of the same strategy: conversion of the adenine and
guanine derivatives into the N-benzoyl derivatives XXVI and XXVIII which were con-
densed with the reagent X in the presence of sodium hydride. For 2,6-diaminopurine we
have chosen the amidine protection method (N-benzoyl derivatives of this base are very
stable toward methanolysis): this led to compound XXX as the starting compound for
the condensation. After condensation with compound X and removal of the protecting
groups, the crude diesters were deionized on a cation-exchanger and finally their ester
functionalities were hydrolyzed after transsilylation with bromotrimethylsilane. Also in
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SCHEME 2
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
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this case the final (S)-PMP-derivatives XXVII, XXIX and XXXI were obtained in the
zwitterion form (Scheme 4).
In addition to sufficient characterization of the 2-hydroxypropyl and N-benzoyl deri-
vatives in both enantiomeric series, the structure of the phosphonates of the PMP-series
was confirmed by 1H NMR spectra of their salts. The spectra proved the presence of all
the three characteristic groupings in the molecule (heterocyclic base, methyl and phos-
phonomethyl groups). Their electrophoretical mobility in a weakly alkaline medium
corresponds to dissociation to the second degree and their UV spectra are compatible
with the corresponding chromophore. Their homogeneity was checked by HPLC; the
chromatographic parameters were identical for both enantiomers and were in accord
with those of compounds prepared by other methods2,14. The absolute values of [α]D
were identical within the experimental error for both enantiomers. The optical purity
was limited by that of the starting esters of D-(+)- and L-(–)-lactic acid*.
SCHEME 3
* The value of [α]D (–11.06° (neat)) for ethyl L-(–)-lactate is identical with the published15 value
(–11.3°) whereas the value for isobutyl D-(+)-lactate (+17.25°) is significantly higher than the
published15 one (+15.2°).
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EXPERIMENTAL
If not stated otherwise, the solutions were evaporated at 40 °C/2 kPa and the compounds were dried
at 13 Pa over phosphorus pentoxide. Melting points were determined on a Kofler block and are un-
corrected.
Thin-layer chromatography was carried out on Silufol UV254 plates (Kavalier, Votice, Czech Republic) in
the systems S1 chloroform, S2 chloroform–methanol (4 : 1) and S3 chloroform–methanol (95 : 5).
Preparative TLC was performed on loose layers (40 × 17 × 0.4 cm) of silica gel with fluorescent
indicator (Kavalier, Votice, Czech Republic). Column chromatography on silica gel (30 µm) was carried
out with material of the same origin. Paper electrophoresis was performed on Whatman No 3 MM
paper at 40 V/cm (1 h) in 0.05 M triethylammonium hydrogen carbonate, pH 7.5. Electrophoretic
mobilities (EUp) are referred to uridine 3′-phosphate.
SCHEME 4
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
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Deionisation of the reaction mixtures was effected on columns of Dowex 50 X 8 (100–200 mesh,
H+ form); after application of the mixture, the column was washed with water until the UV absorp-
tion at 254 nm dropped to the original value. The compounds were then eluted with 2.5% aqueous
ammonia.
1H NMR spectra were measured on Varian UNITY-200 (200 MHz) and Varian UNITY-500 (500 MHz)
spectrometers in (CD3)2SO with tetramethylsilane as internal standard or in D2O with sodium 3-(tri-
methylsilyl)propanesulfonate (DSS) as internal standard. Mass spectra were measured on a ZAB-EQ
(VG Analytical) spectrometer by the EI (electron energy 70 eV) and FAB (ionization Xe, accelera-
ting voltage 8 kV) techniques.
Starting Materials and Reagents
Sodium bis(2-methoxyethoxy)aluminum hydride (70% solution in toluene, Synhydride) was pur-
chased from Spolana, Neratovice (Czech Republic), dimethylformamide, acetonitrile, 2-methylpropyl
D-(+)-lactate, ethyl L-(–)-lactate, 3,4-dihydropyran, chlorotrimethylsilane, benzoyl chloride and Celite
were obtained from Merck (Germany), cytosine, adenine and cesium carbonate from Fluka (Switzerland),
2-aminoadenine from Tokyo Kasei Co. (Japan) and 2-amino-6-chloropurine from Mack (Germany).
Bromotrimethylsilane and 4-dimethylaminopyridine were purchased from Aldrich (Germany). Di-
methylformamide and acetonitrile were dried by distillation from phosphorus pentoxide and stored
over molecular sieves. Hydrogen chloride in dimethylformamide was prepared by introduction of dry
HCl into dimethylformamide under ice-cooling, followed by dissolution of the obtained crystalline
product by addition of dimethylformamide.
(R)-2-(2-Tetrahydropyranyloxy)propanol (VI)
To a mixture of 2-methylpropyl D-(+)-lactate (IV, 100 ml, 0.66 mol) and 3,4-dihydropyran (70 ml)
was added 6 M solution of HCl in dimethylformamide (4 ml). After standing overnight at ambient
temperature (calcium chloride tube), silver carbonate (20 g) was added and the suspension was
stirred at room temperature for 3 h. The mixture was filtered, the solid washed with ether and the
filtrate concentrated in vacuo. Distillation in vacuo afforded 120 g (79%) of 2-tetrahydropyranyl deri-
vative VI, b.p. 85–90 °C/13 Pa.
This product was dissolved in ether (170 ml) and the solution was added dropwise during 1 h to
a stirred and gently refluxing solution of sodium bis(2-methoxyethoxy)aluminum hydride (70% toluene
solution, 227 g) in ether (700 ml) under exclusion of moisture. After stirring for 2 h, the mixture was
decomposed by successive addition of ethyl acetate (100 ml) and water (115 ml). The suspension was
filtered through a layer of Celite, the solid was washed with dioxane (200 ml) and the filtrate was
concentrated in vacuo. The residue was dissolved in ether (300 ml), dried over magnesium sulfate,
filtered, evaporated and distilled in vacuo. Yield 79.3 g (95%) of alcohol VI, b.p. 82–83 °C/13 Pa.
For C8H16O3 (160.2) calculated: 59.98% C, 10.07% H; found: 60.04% C, 10.17% H.
(R)-2-(2-Tetrahydropyranyloxy)propyl p-Toluenesulfonate (VII)
A solution of p-toluenesulfonyl chloride (107.5 g, 0.56 mol) in pyridine (300 ml) was added during
30 min to a stirred and ice-cooled solution of alcohol VI (80.1 g, 0.5 mol) and 4-dimethylaminopy-
ridine (2 g) in pyridine (750 ml). The mixture was stirred at 0 °C for 3 h under exclusion of moisture
and then set aside at 0 °C overnight. Water (20 ml) was added and, after standing for 1 h, the mix-
ture was concentrated in vacuo at 30 °C to a half. After addition of ethyl acetate (2 l), the mixture
was extracted with water (3 × 300 ml) and the organic phase was evaporated in vacuo. The residue
was codistilled with toluene (4 × 250 ml) until the pyridine was completely removed and the remaining
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oil was chromatographed on a column of silica gel in chloroform. Yield 144 g (92%) of colourless
oily tosylate VII, RF 0.60 (S1). For C15H22O5S (314.4) calculated: 57.30% C, 7.05% H, 10.20% S;
found: 57.22% C, 7.30% H, 10.01% S.
(S)-2-(2-Tetrahydropyranyloxy)propanol (XXII)
To a mixture of ethyl L-(–)-lactate (XX, 50 g, 0.42 mol) and 3,4-dihydropyran (70 ml) was addded 6 M
solution of hydrogen chloride in dimethylformamide and the mixture was allowed to stand under
exclusion of moisture at room temperature overnight. The further work-up was executed as described
for compound VI. Distillation in vacuo afforded 85.5 g (100%) of colourless oily product XXI, b.p.
101–105 °C/2 kPa.
This product was dissolved in ether (200 ml) and the solution was added dropwise during 30 min
under exclusion of moisture to a stirred solution of Synhydride (200 g) in ether (500 ml) (reflux
condenser). After stirring for 2 h, the mixture was decomposed by successive addition of ethyl ace-
tate (70 ml) and water (100 ml). Further work-up was the same as described for compound VI. Yield
69.2 g (96%) of compound XXII, b.p. 85–87 °C/13 Pa. For C8H16O3 (160.2) calculated: 59.98% C,
10.07% H; found: 59.80% C, 10.14% H.
(S)-2-(2-Tetrahydropyranyloxy)propyl p-Toluenesulfonate (XXIII)
A solution of p-toluenesulfonyl chloride (91 g, 0.477 mol) in pyridine (300 ml) was added during 30 min
under stirring and ice-cooling to a solution od compound XXII (67.3 g, 0.42 mol) and 4-dimethylamino-
pyridine (2 g) in pyridine (600 ml). The mixture was stirred for 3 h at 0 °C under exclusion of mois-
ture and then set aside at 0 °C overnight. Further work-up was the same as described for compound
VII; yield 122 g (93%) of compound XXIII as a thick oil, RF 0.60 (S1). For C15H22O5S (314.4) cal-
culated: 57.30% C, 7.05% H, 10.20% S; found: 57.15% C, 7.22% H, 10.52% S.
(R)-9-[2-(2-Tetrahydropyranyloxy)propyl]adenine (VIIIa)
A solution of tosyl derivative VII (31.4 g, 0.1 mol) in dimethylformamide (100 ml) was added drop-
wise during 20 min to a stirred suspension of adenine (13.5 g, 0.1 mol) and cesium carbonate (16.4 g,
0.05 mol) in dimethylformamide (300 ml), pre-heated to 100 °C. The mixture was heated at 100 °C
for 16 h under exclusion of moisture. The solvent was evaporated in vacuo and the residue was ex-
tracted with hot chloroform (1 l total). The extract was filtered through Celite. The filtrate was con-
centrated in vacuo and the residue was crystallized from ethanol (ether added to turbidity) to give
compound VIIIa (7.3 g). Another portion (4.9 g) of the product was obtained from the mother liquors
by chromatography on silica gel (300 ml) and subsequent crystallization from ethanol. Total yield 12.2 g
(44%) of VIIIa, m.p. 171–172 °C, RF 0.55 (S2). For C13H19N5O2 (277.3) calculated: 56.30% C, 6.91% H,
25.26% N; found: 56.57% C, 6.71% H, 25.41% N. 1H NMR spectrum (200 MHz): 8.14 s, 1 H and
8.04 s, 1 H (H-2 and H-8); 7.20 br s, 2 H (NH2); 4.23 dd, 1 H, J(1′a,2′) = 3.2, J(gem) = 13.7 (H-1′a);
4.11 dd, 1 H, J(1′b,2′) = 7.1, J(gem) = 13.7 (H-1′b); 4.06, m, 1 H (H-2′); 1.12 d, 3 H, J(3′,2′) = 6.1
(H-3′); tetrahydropyranyl: 4.28 dd, 1 H, J = 2.9 and 4.4 (H-2″); 3.72 ddd, 1 H, J = 3.9, 7.8 and 11.2
and 3.34 ddd, 1 H, J = 4.9, 5.1 and 11.2 (H-6″); 1.20–1.65 m, 6 H (2 × H-3″, 2 × H-4″, 2 × H-5″).
(R)-9-(2-Hydroxypropyl)adenine (IXa)
A solution of tetrahydropyranyl derivative VIIIa (7.0 g, 25.2 mmol) in 0.25 M sulfuric acid (150 ml)
was set aside at room temperature overnight and then neutralized with saturated barium hydroxide
solution. The suspension was heated to 80 °C, filtered through Celite and the solid was washed with
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
1205
boiling water (1 l). Evaporation of the filtrate in vacuo and crystallization of the residue from ethanol
(ether added to turbidity) afforded 4.1 g (85%) of compound IXa, m.p. 202 °C, RF 0.40 (S2). For
C8H11N5O (193.2) calculated: 49.73% C, 5.74% H, 36.25% N; found: 49.59% C, 5.54% H, 36.29% N.
[α]D –40.8° (c 0.5, 0.1 M HCl). 1H NMR spectrum (200 MHz): 8.14 and 8.05 2 × s, 2 × 1 H (H-2
and H-8); 7.23 br s, 2 H (NH2); 5.05 d, 1 H, J(OH,CH) = 4.2 (OH); 3.97–4.13 m, 3 H (H-1′ and
H-2′); 1.06 d, 3 H, J(3′,2′) = 5.6 (H-3′).
(R)-9-(2-Hydroxypropyl)-2,6-diaminopurine (IXb)
(R)-2-(2-Tetrahydropyranyloxy)propyl p-toluenesulfonate (VII) (32.8 g, 0.104 mol) was added to a
suspension of 2,6-diaminopurine (15 g, 0.1 mol) and cesium carbonate (16.4 g, 0.05 mol) in di-
methylformamide (250 ml), pre-heated to 100 °C, and the mixture was stirred at 100 °C for 20 h.
After evaporation at 50 °C/13 Pa, the residue was extracted with boiling chloroform (3 × 300 ml).
The extract was filtered, the filtrate concentrated in vacuo and chromatographed on a column of
silica gel (500 ml). The product was eluted with chloroform–methanol (95 : 5) and crystallized from
ethyl acetate (ether added to turbidity). Yield of (R)-9-[2-(2-tetrahydropyranyloxy)propyl]-2,6-di-
aminopurine (VIIIb) was 14.2 g (49%), m.p. 150–152 °C, RF 0.30 (S2). For C13H20N6O2 (292.3) cal-
culated: 53.41% C, 6.90% H, 28.76% N; found: 53.27% C, 7.02% H, 28.77% N.
A solution of compound VIIIb (11.7 g, 0.04 mol) in 0.25 M sulfuric acid (400 ml) was set aside at
room temperature overnight, neutralized with ammonia, concentrated in vacuo, applied onto a column
of Dowex 50 X 8 (250 ml, H+ form) and the column was washed with water until the UV absorption
dropped to the original value. Then the column was eluted with dilute (1 : 10) aqueous ammonia and
the UV-absorbing eluate was concentrated in vacuo. Crystallization of the residue from ethanol af-
forded 9-(R)-(2-hydroxypropyl)-2,6-diaminopurine (IXb) (6.5 g, 78%), m.p. 192 °C, RF 0.22 (S2). [α]D
–40.7° (c 0.5, 0.1 M HCl). For C8H12N6O (208.2) calculated: 46.15% C, 5.81% H, 40.37% N; found:
1
45.97% C, 5.72% H, 40.56% N. H NMR spectrum (200 MHz): 7.62 s, 1 H (H-8); 6.65 and 5.77, 2 × br s,
2 × 2 H (NH2); 5.05 br, 1 H (OH); 3.90 dd, 1 H, J(1′a,2′) = 3.9, J(gem) = 13.7 (H-1′a); 3.80 dd, 1 H,
J(1′b,2′) = 7.6, J(gem) = 13.7 (H-1′b); 3.95 m, 1 H (H-2′); 1.04 d, 3 H, J(3′,2′) = 6.1 (H-3′).
(R)-9-[2-(2-Tetrahydropyranyloxy)propyl]-2-amino-6-chloropurine (VIIIc)
A solution of (R)-2-(2-tetrahydropyranyloxy)propyl p-toluenesulfonate (VII) (42.0 g, 0.134 mol) in
dimethylformamide (100 ml) was added dropwise during 30 min to a suspension of 2-amino-6-
chloropurine (18.6 g, 0.11 mol) and cesium carbonate (17.9 g, 0.055 mol) in dimethylformamide (350 ml),
which had been pre-heated to 100 °C for 30 min. The mixture was heated at 100 °C for 6 h under
stirring and exlusion of moisture. After evaporation at 50 °C/13 Pa, the residue was extracted with
boiling chloroform (3 × 300 ml). The extract was filtered through Celite, the solvent was evaporated
in vacuo and chromatographed on a column (500 ml) of silica gel in chloroform. The UV-absorbing
product fractions were combined, taken down in vacuo and the residue was dried in vacuo. (R)-9-[2-
(2-Tetrahydropyranyloxy)propyl]-2-amino-6-chloropurine (VIIIc) was obtained as an amorphous
foam (10.7 g, 31%), RF 0.64 (S2). For C13H18ClN5O2 (311.8) calculated: 50.08% C, 5.82% H,
1
11.37% Cl, 22.47% N; found: 49.92% C, 6.08% H, 11.44% Cl, 22.54% N. H NMR spectrum (200 MHz):
8.06 s, 1 H (H-8); 4.01 dd, 1 H, J(1′a,2′) = 7.3, J(gem) = 14.2 (H-1′a); 3.94 dd, 1 H, J(1′b,2′) = 5.4,
J(gem) = 14.2 (H-1′b); 3.42 m, 1 H (H-2′); 1.06 d, 3 H, J(3′,2′) = 5.4 (H-3′); tetrahydropyranyl: 5.07 dd,
1 H, J = 2.9, and 8.3 (H-2″); 4.02 m and 3.80 m, 2 H (H-6″); 1.30–1.90 m, 6 H (other CH2).
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(R)-9-(2-Hydroxypropyl)guanine (IXd)
A solution of compound VIIIc (10 g, 0.032 mol) in 1 M hydrochloric acid (200 ml) was refluxed with
stirring for 1 h. After cooling, the mixture was made alkaline with ammonia and evaporated in vacuo
to dryness. Crystallization of the residue from water (a little charcoal added) afforded (R)-9-(2-hy-
droxypropyl)guanine (IXd) (6.0 g, 91%), m.p. 255 °C. [α]D –35.7° (c 0.5, 0.1 M HCl), RF 0.13 (S2).
For C8H11N5O2 (209.2) calculated: 45.92% C, 5.30% H, 33.48% N; found: 46.02% C, 5.25% H, 33.41% N.
1H NMR spectrum (200 MHz): 10.80 br, 1 H (NH); 7.61 s, 1 H (H-8); 6.74 br s, 2 H, (2-NH2); 5.05 br,
1 H (OH); 3.93 m, 1 H (H-2′); 3.89 dd, 1 H, J(1′a,2′) = 3.7, J(gem) = 13.4 (H-1′a); 3.78 dd, 1 H,
J(1′b,2′) = 7.8, J(gem) = 13.4 (H-1′b); 1.03 d, 3 H, J(3′,2′) = 6.1 (H-3′).
(R)-1-[2-(2-Tetrahydropyranyloxy)propyl]cytosine (VIIIe)
A mixture of cytosine (8.5 g, 76 mmol), cesium carbonate (13 g, 40 mmol), p-toluenesulfonate VII
(24 g, 76 mmol) and dimethylformamide (300 ml) was heated at 100 °C under stirring and exclusion
of moisture, filtered while hot through Celite, and the solvent was evaporated in vacuo. The residue
was chromatographed on a column of silica gel (300 ml) in chloroform. The product was eluted with
chloroform–methanol (95 : 5). The product fractions were combined, concentrated in vacuo and the
residue was crystallized from ethyl acetate (with ether added to turbidity). Yield 4.6 g (18 mmol,
24%) of (R)-1-[2-(2-tetrahydropyranyloxy)propyl]cytosine (VIIIe), m.p. 259–260 °C. For C12H19N3O3
(253.3) calculated: 56.89% C, 7.57% H, 16.59% N; found: 55.80% C, 7.72% H, 16.85% N. 1H NMR
spectrum (200 MHz) (mixture of diastereomers, 3 : 1), major isomer: 7.52 d, 1 H, J(5,6) = 7.3 (H-6);
6.98 br s, 2 H (NH2); 5.73 d, 1 H, J(5,6) = 7.3 (H-5); 3.72–4.01 m, 3 H (H-1′ and H-2′); 1.13 d, 3 H,
J = 6.1 (H-3′); tetrahydropyranyl: 4.36 br t, 1 H, J = 3.2 (H-2″); 3.26–3.54 m, 2 H (H-6″); 1.20–1.70 m,
6 H (additional CH2 groups).
(R)-1-(2-Hydroxypropyl)cytosine (IXe)
Procedure A. A solution of compound VIIIe (4.0 g, 16 mmol) in 0.25 M sulfuric acid (50 ml) was
set aside overnight at room temperature. The mixture was neutralized with saturated barium hydroxide
solution, heated to 80 °C and filtered through Celite. The precipitate was washed with boiling water
(500 ml) and the filtrate was evaporated in vacuo to dryness. The residue was codistilled with etha-
nol (200 ml) and crystallized from ethanol (ether added) to give 2.5 g (94%) of (R)-1-(2-hydroxy-
propyl)cytosine (IXe), m.p. 246 °C, RF 0.17 (S2), [α]D –107.0° (c 0.5, 0.1 M HCl). For C7H11N3O2
1
(169.2) calculated: 49.69% C, 6.55% H, 24.84% N; found: 49.48% C, 6.70% H, 24.70% N. H NMR
spectrum (500 MHz): 7.45 d, 1 H, J(5,6) = 7.3 (H-6); 7.04 and 6.98 2 × br s, 2 × 1 H (NH2); 5.61 d,
1 H, J(5,6) = 7.3 (H-5); 4.88 br, 1 H (OH); 3.82 m, 1 H (H-2′); 3.73 dd, 1 H, J(1′a,2′) = 3.9, J(gem)
= 13.2 (H-1′a); 3.31 dd, 1 H, J(1′b,2′) = 8.0, J(gem) = 13.2 (H-1′b); 1.08 d, 3 H, J(3′,2′) = 6.3 (H-3′).
Procedure B. 4-Methoxy-2-pyrimidone (12.6 g, 0.1 mol) was added at 0 °C to a stirred suspension
of sodium hydride (4.0 g of 60% dispersion in paraffin, 0.1 mol) in dimethylformamide (300 ml) and
the mixture was stirred at 0 °C for 1 h (calcium chloride tube). To the resulting solution p-toluene-
sulfonate VII (31.4 g, 0.1 mol) in dimethylformamide (100 ml) was added and the stirred mixture
was heated at 80 °C for 8 h under exclusion of moisture. After evaporation in vacuo, the residue was
extracted with boiling chloroform (3 × 200 ml), the extract was filtered through Celite and the sol-
vent was evaporated in vacuo. The residue was chromatographed on a column of silica gel (300 ml).
The product fractions were combined, taken down in vacuo and dried in vacuo. Yield 16.9 g (63%)
of (R)-1-[2-(2-tetrahydropyranyloxy)propyl]-4-methoxy-2-pyrimidone (VIIIf) as an amorphous foam.
This product was heated with methanolic ammonia (500 ml, saturated at 0 °C) at 110 °C for 8 h in
an autoclave. The suspension was then evaporated in vacuo and the remaining compound VIIIe was
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
1207
heated with 0.25 M sulfuric acid (300 ml) at 70 °C for 5 h. The mixture was neutralized with am-
monia, filtered through Celite and the filtrate was concentrated in vacuo. The obtained solution was
deionized on a column of Dowex 50 X 8 (250 ml; H+ form) and the UV-absorbing ammonia eluate
was taken down in vacuo. Crystallization from ethanol afforded 7.8 g (73%) of (R)-1-(2-hydroxy-
propyl)cytosine (IXe), identical with the product obtained according to procedure A.
(S)-9-[2-(2-Tetrahydropyranyloxy)propyl]adenine (XXIVa)
A solution of (S)-2-(2-tetrahydropyranyloxy)propyl p-toluenesulfonate (XXIII) (31.4 g, 0.1 mol) in
dimethylformamide (200 ml) was added dropwise during 30 min to a stirred mixture of adenine (13.5 g,
0.1 mol), cesium carbonate (16.4 g, 0.05 mol) and dimethylformamide (400 ml) that had been pre-
heated to 100 °C. The mixture was heated at 100 °C for 6 h under stirring and exclusion of moisture.
The solvent was evaporated in vacuo and the residue was extracted with boiling chloroform (3 × 300 ml).
The extract was filtered through Celite and the filtrate was taken down in vacuo. Crystallization of
the residue from ethanol afforded (S)-9-[2-(2-tetrahydropyranyloxy)propyl]adenine (XXIVa) (13.2 g,
48%), m.p. 172 °C, RF 0.55 (S2). For C13H19N5O2 (277.3) calculated: 56.30% C, 6.91% H, 25.26% N;
1
found: 56.46% C, 6.82% H, 25.57% N. H NMR spectrum (200 MHz): 8.14 and 8.04 2 × s, 2 × 1 H
(H-2 and H-8); 7.20 br s, 2 H (NH2); 4.23 dd, 1 H, J(1′a,2′) = 3.2, J(gem) = 13.7 (H-1′a); 4.11 dd,
1 H, J(gem) = 13.7, J(1′b,2′) = 7.1 (H-1′b); 4.06 m, 1 H (H-2′); 1.12 d, 3 H, J(3′,2′) = 6.1 (H-3′);
tetrahydropyranyl: 4.28 dd, 1 H, J = 2.9 and 4.4 (H-2″); 3.72 ddd, 1 H, J = 3.9, 7.8, 11.2 and 3.34 ddd,
1 H, J = 4.9, 5.1 and 11.2 (H-6″); 1.20–1.65 m, 6 H (additional CH2).
(S)-9-(2-Hydroxypropyl)adenine (XXVa)
A solution of compound XXIVa (13 g, 0.047 mol) in 0.25 M sulfuric acid (300 ml) was set aside at
ambient temperature overnight. The mixture was neutralized with saturated barium hydroxide solu-
tion, heated to 80 °C and filtered through Celite. The precipitate was washed with boiling water (500 ml)
and the filtrate was taken down in vacuo. The dry residue was crystallized from ethanol to give 7.7 g
(85%) of compound XXVa, m.p. 202 °C, RF 0.40 (S2). For C8H11N5O (193.2) calculated: 49.73% C,
5.74% H, 36.25% N; found: 49.59% C, 5.54% H, 36.29% N. [α ]D +41.0° (c 0.5, 0.1 M HCl).
1H NMR spectrum (200 MHz): 8.14 and 8.05 2 × s, 2 × 1 H (H-2 and H-8); 7.23 br s, 2 H (NH2);
5.05 brd, 1 H, J(OH,CH) = 4.2 (OH); 3.97–4.13 m, 3 H (H-1′ and H-2′); 1.06 d, 3 H, J(3′,2′) = 5.6
(H-3′).
(S)-9-(2-Hydroxypropyl)-2,6-diaminopurine (XXVb)
A mixture of 2,6-diaminopurine (5 g, 33 mmol), cesium carbonate (5.1 g, 16.5 mmol), p-toluene-
sulfonate XXIII (13.5 g, 0.43 mol) and dimethylformamide (100 ml) was heated at 100 °C for 16 h
and worked up as described for compound XXIVa. The product-containing fraction on evaporation
gave XXIVb (5.6 g, 19.1 mmol, 58%) which was dissolved in 0.25 M sulfuric acid (100 ml) and left
to stand overnight at ambient temperature. The solution was neutralized with saturated solution of
barium hydroxide, heated to 80 °C, filtered through Celite and the precipitate was washed with boiling
water (500 ml). The filtrate was taken down in vacuo and the residue crystallized from ethanol. Yield
3.65 g (53% related to the base) of compound XXVb, m.p. 191–192 °C, RF 0.22 (S2). [α]D +41.2° (c 0.5,
0.1 M HCl). For C8H12N6O (208.2) calculated: 46.15% C, 5.81% H, 40.37% N; found: 46.08% C,
5.74% H, 40.18% N. Its 1H NMR spectrum was identical with that of the (R)-enantiomer IXb.
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Holy, Masojidkova:
(S)-9-[2-(2-Tetrahydropyranyloxy)propyl]-2-amino-6-chloropurine (XXIVc)
A mixture of 6-amino-2-chloropurine (18.6 g, 0.11 mol), cesium carbonate (17.9 g, 0.055 mol) and
dimethylformamide (350 ml) was heated at 100 °C. A solution of compound XXIII (42.1 g, 0.134 mol)
in dimethylformamide (100 ml) was added and the mixture was heated at 100 °C for 6 h under stir-
ring and exclusion of moisture. After evaporation at 40 °C/13 Pa, the residue was extracted with
boiling chloroform (3 × 300 ml), filtered and the solvent was evaporated in vacuo. Column chroma-
tography of the residue on silica gel (300 ml) in chloroform afforded 10.65 g (31%) of the 9-isomer
XXIVc as an amorphous foam, RF 0.64 (S2). For C13H18ClN5O2 (311.8) calculated: 50.08% C, 5.82% H,
1
11.37% Cl, 22.47% N; found: 50.32% C, 5.88% H, 11.51% Cl, 22.32% N. H NMR spectrum (200 MHz):
8.06 s, 1 H (H-8); 4.01 dd, 1 H, J(1′a,2′) = 7.3, J(gem) = 14.2 (H-1′a); 3.94 dd, 1 H, J(1′b,2′) = 5.4,
J(gem) = 14.2 (H-1′b); 3.42 m, 1 H (H-2′); 1.06 d, 3 H, J(3′,2′) = 5.4 (3′-H); tetrahydropyranyl: 5.17 dd
and 4.63 dd, total 1 H (ratio 7 : 1), J = 2.9 and 8.3, or 2.4 and 6.3 (H-2″); 4.02 m and 3.80 m, total
2 H (H-6″); 1.30–1.90 m, 6 H (other CH2 groups).
Further elution and precipitation with ether from ethyl acetate gave 5.7 g (17%) of an amorphous
product which, according to its NMR spectrum, was a mixture of isomers (RF 0.48 (S3)) with the
7-isomer probably predominating.
(S)-9-(2-Hydroxypropyl)guanine (XXVd)
Compound XXIVc (10.4 g, 33.3 mmol) was refluxed for 1 h with a mixture of 2 M hydrochloric acid
(100 ml) and dioxane (100 ml). After cooling, the mixture was neutralized with ammonia and taken
down. Crystallization from water afforded 5.7 g (77%) of (S)-9-(2-hydroxypropyl)guanine (XXVd),
m.p. 256 °C, RF 0.13 (S2). [α]D +36.2° (c 0.5, 0.1 M HCl). For C8H11N5O2 (209.2) calculated: 45.92% C,
5.30% H, 33.48% N; found: 45.88% C, 5.25% H, 33.41% N. The 1H NMR spectrum (200 MHz) was
identical with that of the (R)-enantiomer IXd.
(R)-9-(2-Hydroxypropyl)-N6-benzoyladenine (XI)
Chlorotrimethylsilane (26 ml) was added to a suspension of (R)-9-(2-hydroxypropyl)adenine (IXa)
(5.8 g, 30 mmol) in pyridine (160 ml) and the mixture was stirred at room temperature for 1 h. Ben-
zoyl chloride (20 ml) was added and stirring was continued for another 2 h at room temperature.
After cooling with ice, ice-cold water (30 ml) was added during 15 min, followed by concentrated
aqueous ammonia (70 ml). The mixture was concentrated in vacuo and the residue was codistilled
with ethanol (3 × 150 ml) and crystallized from boiling water. Recrystallization from ethanol afforded
7.8 g (87%) of (R)-9-(2-hydroxypropyl)-N6-benzoyladenine (XI), m.p. 227 °C, RF 0.45 (S2). [α]D –21.7°
(c 0.5, DMF). For C15H15N5O2 (297.3) calculated: 60.59% C, 5.09% H, 23.56% N; found: 60.73% C,
5.28% H, 23.47% N. 1H NMR spectrum (200 MHz): 8.73 and 8.42, 2 × s, 2 × 1 H (H-2 and H-8);
7.30–8.10 m, 6 H (arom. H and NH); 4.05–4.30 m, 3 H (H-1′ and H-2′); 1.11 d, 3 H, J(3′,2′) = 5.6
(H-3′).
(S)-9-(2-Hydroxypropyl)-N6-benzoyladenine (XXVI)
The benzoyl derivative XXVI was prepared analogously as compound XI from (S)-9-(2-hydroxy-
propyl)adenine (XXVa) (6.8 g, 35 mmol); yield 4.4 g (43%), m.p. 230 °C. The combined mother
liquors were evaporated and the residue was stirred with ethanol (150 ml) for 30 min, and filtered.
The ethanolic extract was evaporated in vacuo and the residue was extracted with chloroform (2 × 150 ml).
After evaporation of the solvent, the residue was chromatographed on a column of silica gel (200 ml).
The product was eluted with chloroform–ethanol (9 : 1). The product fractions were combined, the
solvent evaporated in vacuo and the residue was crystallized from ethyl acetate (light petroleum
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
1209
added to turbidity) to give further crop (3.0 g) of the same product; total yield 7.4 of compound
XXVI, m.p. 230 °C, RF 0.45 (S2). [α]D +25.2° (c 0.5, 0.1 M HCl). For C15H15N5O2 (297.3) calculated:
1
60.59% C, 5.09% H, 23.56% N; found: 60.63% C, 5.16% H, 23.30% N. The H NMR spectrum was
identical with that of the (R)-isomer.
(R)-9-(2-Hydroxypropyl)-N2-benzoylguanine (XIII)
The benzoyl derivative XIII was prepared analogously as the compound XI from (R)-9-(2-hydroxy-
propyl)guanine (IXd) (2.5 g, 12 mmol). After evaporation of pyridine, the residue was stirred with a
mixture of water (200 ml) and ethyl acetate (200 ml). The mixture was filtered, the crystalline product
was washed with water, ethyl acetate, ether, and dried in vacuo. Yield 2.4 g (57%), m.p. 276 °C, RF 0.33
(S2). [α]D –28.4° (c 0.5, DMF). For C15H15N5O3 . 2 H2O (349.4) calculated: 51.56% C, 5.49% H,
20.05% N; found: 51.28% C, 5.62% H, 20.24% N. 1H NMR spectrum (500 MHz): 12.30 and 11.90
2 × br, 2 × 1 H (NH); 8.05 m, 2 H and 7.50–7.70 m, 3 H (arom. H); 7.95 s, 1 H (H-8); 5.05 d, 1 H,
J(2′,OH) = 4.9 (2′-OH); 4.05 dd, 1 H, J(1′a,2′) = 3.4, J(gem) = 12.5 (H-1′a); 4.01 br m, 1 H (H-2′);
3.96 dd, 1 H, J(1′b,2′) = 7.1, J(gem) = 12.5 (H-1′b); 1.09 dd, 3 H, J(3′,2′) = 6.1 (H-3′).
(S)-9-(2-Hydroxypropyl)-N2-benzoylguanine (XXVIII)
The reaction with (R)-9-(2-hydroxypropyl)guanine (IXd) (5.0 g, 24 mmol) was executed as described
for compound XI. After evaporation of pyridine, the residue was stirred with a mixture of water (200 ml)
and ethyl acetate (200 ml). The mixture was filtered, the crystalline product was washed with water,
ethyl acetate, ether, and dried in vacuo. Yield of the chromatographically pure (S)-9-(2-hydroxy-
propyl)-N2-benzoylguanine (XXVIII) was 3.4 g (40%), RF 0.33 (S2), m.p. 278 °C. [α]D +28.1° (c 0.5,
DMF). For C15H15N5O3 . 2 H2O (349.4) calculated: 51.56% C, 5.49% H, 20.05% N; found: 51.48% C,
1
5.41% H, 20.05% N. The H NMR spectrum was identical with that of compound IXd.
(R)-9-(2-Phosphonomethoxypropyl)adenine (I)
A mixture of (R)-9-(2-hydroxypropyl)-N6-benzoyladenine (XI) (3.0 g, 10 mmol) and bis(isopropyl)
p-toluenesulfonyloxymethylphosphonate (X) (4.2 g, 12 mmol) was codistilled with dimethylform-
amide (2 × 25 ml) at 40 °C/13 Pa. The residue was again dissolved in dimethylformamide (50 ml)
by gentle warming, cooled with ice, and sodium hydride (60% dispersion, 1.2 g, 30 mmol) was
added. The mixture was stirred under exclusion of moisture at room temperature for 48 h, 0.1
M
methanolic sodium methoxide was added (150 ml) and the mixture was set aside under exclusion of
moisture at room temperature overnight. After neutralization by addition of Dowex 50 X 8 (H+ form),
the mixture was made alkaline with triethylamine, filtered and the ion exchanger was washed with
methanol (200 ml). The filtrate was evaporated in vacuo, the residue was dissolved in water (200 ml)
and extracted with ether (2 × 100 ml). The aqueous phase was concentrated in vacuo to about 100 ml
and this solution was applied onto a column of Dowex 50 X 8 (250 ml). The column was washed
with 20% aqueous methanol till the UV absorption of the eluate dropped to the original value. The
crude product XII was then eluted with dilute (1 : 10) aqueous ammonia and the UV-absorbing eluate
was taken down in vacuo. The residue was codistilled with ethanol (2 × 50 ml) and dried at 13 Pa
over phosphorus pentoxide. Yield of crude bis(isopropyl) ester XII was 3.0 g; RF 0.55 (S2).
This residue was dissolved in a mixture of acetonitrile (50 ml) and bromotrimethylsilane (5 ml).
The mixture was set aside under exclusion of moisture at room temperature overnight and the reac-
tion was monitored by paper electrophoresis of a hydrolyzed sample. The mixture was taken down in
vacuo and water (100 ml) was added. After 30 min the mixture was made alkaline with ammonia and
again taken down in vacuo. The residue was deionized on a column of Dowex 50 as described above
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Holy, Masojidkova:
and the ammonia eluate of the product was evaporated to dryness. The residue was again dissolved
in water (50 ml) by adjusting the pH to 9–10, and this solution was applied onto a column of Dowex
1 X 2 (250 ml, acetate form), pre-equilibrated with 0.02 M acetic acid. The column was washed with
the same eluent until the UV absorption dropped and then with linear gradient of 0.02–1 M acetic
acid (1 l each). The product was eluted at concentration 1 M and the product fraction was taken down
in vacuo. The residue was codistilled with water (3 × 50 ml) and then dissolved in a minimum
amount of boiling water, three parts of ethanol were added and the mixture was left to crystallize.
Yield of (R)-9-(2-phosphonomethoxypropyl)adenine (I) was 1.35 g (47%), m.p. 279 °C, [α]D –21.2°
(c 0.5, 0.1 M HCl). For C9H14N5O4P . H2O (305.3) calculated: 35.40% C, 5.29% H, 22.94% N,
1
10.17% P; found: 35.28% C, 5.37% H, 23.03% N, 10.17% P. EUp 0.80. H NMR spectrum (200 MHz,
D2O + NaOD): 8.25 s, 1 H (H-2); 8.09 s, 1 H (H-8); 4.35 dd, 1 H, J(1′a,2′) = 4.4, J(gem) = 14.4
(H-1′a); 4.22 dd, 1 H, J(1′b,2′) = 5.1, J(gem) = 14.4 (H-1′b); 3.97 m, 1 H (H-2′); 3.57 dd, 1 H,
J(P,CHa) = 9.5, J(gem) = 12.4 (P-CHa); 3.46 dd, 1 H, J(P,CHb) = 9.3, J(gem) = 12.4 (P-CHb); 1.11 d,
3 H, J(3′,2′) = 6.3 (H-3′).
(S)-9-(2-Phosphonomethoxypropyl)adenine (XXVII)
The title compound was prepared in the same manner as described for compound I from 3.57 g (12 mmol)
of compound XXVI, yield 1.9 g (56%), m.p. 276–278 °C, [α]D +21.2° (c 0.5, 0.1 M HCl). For
C9H14N5O4P . H2O (305.3) calculated: 35.40% C, 5.29% H, 22.94% N, 10.17% P; found: 35.33% C,
1
5.56% H, 23.14% N, 10.00% P. Electrophoretic mobility and H NMR spectrum were identical with
those of the (R)-isomer I.
(R)-9-(2-Phosphonomethoxypropyl)-2,6-diaminopurine (II)
(R)-9-(2-Hydroxypropyl)-2,6-diaminopurine (IXb) (2.1 g, 10 mmol) was dissolved in a warm mixture
of dimethylformamide (40 ml) and dimethylformamide dimethyl acetal (25 ml). After standing at am-
bient temperature overnight under exclusion of moisture, the mixture was taken down at 40 °C/13 Pa.
The residue was codistilled with dimethylformamide (2 × 20 ml) and then mixed with 50% aqueous
pyridine (50 ml) and finely crushed dry ice (about 20 g). After 30 min the mixture was evaporated
at 40 °C/13 Pa and the residue was codistilled with pyridine (4 × 25 ml). Bis(isopropyl) p-toluene-
sulfonyloxymethylphosphonate (X) (4.2 g, 12 mmol) was added, the mixture was codistilled with di-
methylformamide (2 × 25 ml) and the residue was dissolved in dimethylformamide (40 ml) and
cooled to –10 °C. Sodium hydride (60% dispersion, 1.2 g, 30 mmol) was added and the mixture was
stirred under exclusion of moisture at room temperature for 48 h. After decomposition with acetic
acid (1.8 ml, 30 mmol), the solvent was evaporated in vacuo and the residue was dissolved in dilute
(1 : 1) aqueous ammonia (100 ml). The solution was set aside at room temperature overnight, evaporated
in vacuo and the residue was deionized on a column of Dowex 50 as described for compound I. After
cleavage with bromotrimethylsilane, the mixture was again deionized on the same ion-exchanger. The
obtained ammonium salt was dissolved in hot water (50 ml) and under stirring acidified with 1
M
hydrochloric acid to pH 3.5. The crystalline product was collected, washed successively with water,
ethanol, ether, and dried in vacuo. Yield 1.4 g (46%) of (R)-9-(2-phosphonomethoxypropyl)-2,6-
diaminopurine (II), m.p. 287 °C. [α]D –26.1° (c 0.5, 0.1 M HCl). For C9H15N6O4P (302.3) calculated:
1
35.75% C, 5.00% H, 27.80% N, 10.27% P; found: 35.93% C, 5.02% H, 27.59% N, 10.28% P. H NMR
spectrum (500 MHz, D2O + NaOD): 7.94 s, 1 H (H-8); 4.17 dd, 1 H, J(1′a,2′) = 4.4, J(gem) = 14.6
(H-1′a); 4.09 dd, 1 H, J(1′b,2′) = 5.4, J(gem) = 14.6 (H-1′b); 3.93 m, 1 H (H-2′); 3.54 dd, 1 H,
J(P,CHa) = 9.3, J(gem) = 12.2 (P-CHa); 3.45 dd, 1 H, J(P,CHb) = 9.3, J(gem) = 12.2 (P-CHb); 1.12 d,
3 H J(3′,2′) = 6.3 (H-3′). EUp 0.70.
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Enantiomeric Derivatives of Purine and Pyrimidine Bases
1211
(S)-9-(2-Phosphonomethoxypropyl)-2,6-diaminopurine (XXXI)
The title compound was prepared in 33% yield from (S)-9-(2-hydroxypropyl)-2,6-diaminopurine
(IXb) (2.1 g, 10 mmol) in the same manner as its (R)-enantiomer II. M.p. 275–278 °C, EUp 0.70. [α]D
+28.5° (c 0.5, 0.1 M HCl). For C9H15N6O4P (302.3) calculated: 35.75% C, 5.00% H, 27.80% N,
1
10.27% P; found: 35.56% C, 5.08% H, 27.99% N, 10.18% P. The H NMR spectrum was identical
with that of its (R)-enantiomer.
(R)-9-(2-Phosphonomethoxypropyl)guanine (III)
The reaction was performed with (R)-9-(2-hydroxypropyl)-N2-benzoylguanine (XIII) (2.5 g, 7 mmol)
and bis(2-propyl) p-toluenesulfonyloxymethylphosphonate (X; 2.9 g, 8.4 mmol) in dimethylformamide
(30 ml). After standing for 24 h at room temperature, methanol (100 ml) was added and the mixture
was set aside at room temperature overnight under exclusion of moisture. The mixture was neu-
tralized with Dowex 50 X 8 (H+ form) and filtered. The filtrate was worked up as described for com-
pound I. Chromatography on Dowex 1 X 2 and subsequent crystallization from water gave 0.90 g
(43%) of (R)-9-(2-phosphonomethoxypropyl)guanine (III), m.p. 286 °C. [α]D –26.1° (c 0.5, 0.1
M
HCl). For C9H14N5O5P (303.3) calculated: 35.64% C, 4.65% H, 23.10% N, 10.23% P; found: 35.35% C,
4.58% H, 23.24% N, 10.40% P. 1H NMR spectrum (500 MHz, D2O + NaOD): 7.90 s, 1 H (H-8);
4.21 dd, 1 H, J(1′a,2′) = 4.6, J(gem) = 14.5 (H-1′a); 4.15 dd, 1 H, J(1′b,2′) = 5.5, J(gem) = 14.5
(H-1′b); 3.99 m, 1 H (H-2′); 3.56 dd, 1 H, J(P,CHa) = 9.3, J(gem) = 12.4 (P-CHa); 3.48 dd, 1 H,
J(P,CHb) = 9.2, J(gem) = 12.4 (P-CHb); 1.14 d, 3 H, J(3′,2′) = 6.2 (H-3′).
(S)-9-(2-Phosphonomethoxypropyl)guanine (XXIX)
The reaction of compound XXVIII (1.57 g, 5 mmol) with bis(isopropyl) p-toluenesulfonyloxymethyl-
phosphonate (X) (2.1 g, 6 mmol) was performed as described for the preparation of the (R)-enantiomer III.
Compound XXIX was obtained as the free acid by crystallization from water in 43% yield (0.65 g),
m.p. 287 °C. [α]D +26.3° (c 0.5, 0.1 M HCl). For C9H14N5O5P (303.3) calculated: 35.64% C, 4.65% H,
1
23.10% N, 10.23% P; found: 35.72% C, 4.54% H, 23.06% N, 10.29% P. The H NMR spectrum was
identical with that of the (R)-enantiomer III.
(R)-1-(2-Phosphonomethoxypropyl)cytosine (XIX)
A mixture of (R)-1-(2-hydroxypropyl)cytosine (IXe) (1.7 g, 10 mmol), dimethylformamide (40 ml)
and dimethylformamide dimethyl acetal (15 ml) was stirred overnight and then evaporated at
40 °C/13 Pa. The work-up with aqueous pyridine and dry ice was carried out as described for com-
pound II. The obtained compound XVII was mixed with p-toluenesulfonyloxyphosphonate (X; 4.2 g,
12 mmol), the mixture was dried by codistillation with dimethylformamide and the reaction with so-
dium hydride was carried out as described for compound II. After addition of 0.1 M methanolic so-
dium methoxide (100 ml), the mixture was allowed to stand overnight at room temperature, then
neutralized with Dowex 50 X 8 (H+ form), and filtered. The ion exchanger on the filter was washed
with methanol (200 ml), the filtrate was concentrated and the residue was deionized under standard
conditions. The obtained compound XVIII was treated with bromotrimethylsilane as described for
compound I. After deionization, the product was chromatographed on Dowex 1 X 2 (vide supra) in
a linear gradient of acetic acid (1 l of water and 1 l of 0.3 M acetic acid). The product fraction was
taken down in vacuo, the residue was codistilled with water (3 × 50 ml) and crystallized from
aqueous ethanol to give 0.90 g (19%) of (R)-1-(2-phosphonomethoxypropyl)cytosine, m.p. 261 °C,
EUp 0.70. [α]D –108.1° (c 0.5, 0.1 M HCl). For C8H14N3O5P (263.3) calculated: 36.50% C, 5.36% H,
1
15.97% N, 11.79% P; found: 36.43% C, 5.39% H, 16.05% N, 11.82% P. H NMR spectrum (500 MHz,
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

1212
Holy, Masojidkova:
D2O, NaOD): 7.66 d, 1 H, J(5,6) = 7.3 (H-6); 6.00 d, 1 H, J(5,6) = 7.3 (H-5); 3.98 dd, 1 H, J(1′a,2′) = 3.4,
J(gem) = 14.2 (H-1′a); 3.84 m, 1 H (H-2′); 3.73 dd, 1 H, J(1′b,2′) = 7.6, J(gem) = 14.2 (H-1′b); 3.68 dd,
1 H, J(P,CHa) = 9.5, J(gem) = 13.2 (P-CHa); 3.50 dd, 1 H, J(P,CHb) = 9.5, J(gem) = 13.2 (P-CHb);
1.21 d, 3 H, J(3′,2′) = 6.1 (H-3′).
The authors are obliged to Dr J. Kohoutova for measuring the mass spectra, to Mrs J. Krelinova for
the measurement of optical rotations and to the Analytical Laboratory (Dr V. Pechanec, Head) for
elemental analyses. The excellent technical assistance of Mrs B. Novakova is gratefully acknowledged.
This program was supported by the Grant Agency of the Czech Republic (Grant No. 203/93/0118), the
Grant Agency of the Academy of Sciences (Grant No. 455407) and by the Gilead Sciences (Foster City,
CA, U.S.A.).
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