Synthesis of Base Substituted 2-Hydroxy-3-(purin-9-yl)-propanoic Acids and 4-(Purin-9-yl)-3-butenoic Acids

Article abstract of DOI:10.1081/NCN-120026636

Alkylation of 6-chloropurine and 2-amino-6-chloropurine with bromoacetaldehyde diethyl acetal afforded 6-chloro-9-(2,2-diethoxyethyl)purine (3a) and its 2-amino congener (3b). Treatment of compounds 3 with primary and secondary amines gave the N⁶-substituted adenines (5a-5c) and 2,6-diaminopurines (5d-5f). Hydrolysis of 3 resulted in hypoxanthine (6a) and guanine (6b) derivatives, while their reaction with thiourea led to 6-sulfanylpurine (7a) and 2-amino-6-sulfanylpurine (7b) compounds. Treatment with diluted acid followed by potassium cyanide treatment and acid hydrolysis afforded 6-substituted 3-(purin-9-yl)- and 3-(2-aminopurin-9-yl)-2-hydroxypropanoic acids (8-10). Reaction of compounds 3 with malonic acid in aqueous solution gave exclusively the product of isomerisation, 6-substituted 4-(purin-9-yl)-3-butenoic acids (15).

Full text of DOI:10.1081/NCN-120026636

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Synthesis of Base Substituted 2-Hydroxy-3-(purin-9-yl)-
propanoic Acids and 4-(Purin-9-yl)-3-butenoic Acids
Petra Doláková a , Milena Masojídková a & Antonín Holý a b
a Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech
Republic , Praha, Czech Republic
b Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech
Republic , 6 Dejvice, Praha, 16610, Czech Republic
Published online: 19 Dec 2011.
To cite this article: Petra Doláková , Milena Masojídková & Antonín Holý (2003) Synthesis of Base Substituted 2-Hydroxy-3-
(purin-9-yl)-propanoic Acids and 4-(Purin-9-yl)-3-butenoic Acids, Nucleosides, Nucleotides and Nucleic Acids, 22:12,
2145-2160, DOI: 10.1081/NCN-120026636
To link to this article: http://dx.doi.org/10.1081/NCN-120026636
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NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS
Vol. 22, No. 12, pp. 2145–2160, 2003
Synthesis of Base Substituted 2-Hydroxy-3-(purin-9-yl)-
propanoic Acids and 4-(Purin-9-yl)-3-butenoic Acids#
z
*
´
´
´
´
´
´
Petra Dolakova, Milena Masojıdkova, and Antonın Holy
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the
Czech Republic, Praha, Czech Republic
ABSTRACT
Alkylation of 6-chloropurine and 2-amino-6-chloropurine with bromoacetalde-
hyde diethyl acetal afforded 6-chloro-9-(2,2-diethoxyethyl)purine (3a) and its
2-amino congener (3b). Treatment of compounds 3 with primary and secon-
dary amines gave the N6-substituted adenines (5a–5c) and 2,6-diaminopurines
(5d–5f). Hydrolysis of 3 resulted in hypoxanthine (6a) and guanine (6b) derivatives,
while their reaction with thiourea led to 6-sulfanylpurine (7a) and 2-amino-6-sulf-
anylpurine (7b) compounds. Treatment with diluted acid followed by potassium
cyanide treatment and acid hydrolysis afforded 6-substituted 3-(purin-9-yl)- and
3-(2-aminopurin-9-yl)-2-hydroxypropanoic acids (8–10). Reaction of compounds
3 with malonic acid in aqueous solution gave exclusively the product of isomer-
isation, 6-substituted 4-(purin-9-yl)-3-butenoic acids (15).
Key Words: Purines; Purine alkylation; Acyclic nucleosides; Malonic acid;
3-(Purin-9-yl)-2-hydroxypropanoic acids.
#In honor and celebration of the 70th birthday of Professor Leroy B. Townsend.
z
Republic).
Part of the Diploma Thesis (P.D.), Faculty of Sciences, Charles University Prague (Czech
´
´
*Correspondence: Antonın Holy, Institute of Organic Chemistry and Biochemistry, Academy
of Sciences of the Czech Republic, 6 Dejvice, Praha 16610, Czech Republic; Fax: 4202
220183560; E-mail: Holy@uochb.cas.cz.
2145
DOI: 10.1081/NCN-120026636
Copyright # 2003 by Marcel Dekker, Inc.
1525-7770 (Print); 1532-2335 (Online)
www.dekker.com

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Dolakova, Masojıdkova, and Holy
2146
INTRODUCTION
3-(Adenin-9-yl)-2-hydroxypropanoic acid (AHPA) (1a) is a powerful inactivator
of S-adenosyl-L-homocysteine hydrolase.[1] Hence it is endowed with a capacity to
interfere with proliferating cells and systems which require massive SAM-mediated
methylation reactions catalyzed by methyl transferases.[2] Thus, it manifested strong
chemosterilizing effect on certain insects,[3] on differentiation of plant root cells[4]
and, also, an antiviral effect directed against minus stranded RNA viruses and pox-
viruses. The antiviral activity was enhanced by esterification, which increased the
lipophilic character and penetrability of the compounds through the cell mem-
branes.[5] 2-Methylpropyl ester of AHPA (1b) was selected as the optimum candidate
for detailed investigation.[6] Its activity against vaccinia virus was higher compared
to the parent acid, which formed therefrom in the cell pool by cytosolic enzymes.
As expected, the target for AHPA action was the capping process (methylation of
50-end-guanine of viral mRNA).[7]
With the growing interest in compounds active against poxviruses we decided to
look more closely on the structureꢀactivity relationship in this field to find out
whether there is not any additional mechanism of antiviral action besides the
above-mentioned inhibition of methylation.
RESULTS
This article describes synthesis of racemic base-modified 3-(purin-9-yl)-2-hydro-
xypropanoic acids, mainly 6-substituted purine and 2-aminopurine derivatives.
Recently, we have prepared several optically active compounds of this type by enan-
tiospecific synthesis based on the alkylation of the bases with chiral oxiranecar-
boxylic acid esters.[8] In the present case, we are applying the cyanohydrin
synthesis from the appropriate 2-(purin-9-yl)ethanals, under the conditions used
for the original preparation of AHPA and its congeners.[9] The two key-compounds,
the 6-chloropurine (3a) and the 2-amino-6-chloropurine (3b) derivatives were synthe-
sized by treatment of the respective purine base with bromoacetaldehyde diethyl
acetal in the presence of NaH, Cs2CO3 or DBU in DMF. Under these conditions,
the alkylation was directed predominantly to the N9 position. The thus obtained
key-intermediates (3a) and (3b) were treated with the appropriate amine solution
(dimethylamine was replaced with dimethylammonium N,N-dimethylcarbamate).
The N6-substituted 9-(2,2-diethoxyethyl) adenines (5a–5c) or-2,6-diaminopurines
(5d–5f) were isolated and fully characterized. The DABCO-catalyzed alkaline hydro-
lysis of the 6-chloro derivatives (3a) and (3b) gave hypoxanthine (6a) and guanine
derivative (6b), while their treatment with thiourea afforded the 6-sulfanylpurine
(7a) and 2-amino-6-sulfanylpurine (7b) derivatives.[10]
To perform the cyanohydrin synthesis, the 2,2-diethoxyethyl derivatives (5a–5f,
6a–6b, 7a–7b) were first heated with dilute inorganic acid to form the free aldehydes
and the reaction mixtures were treated directly with KCN at neutral pH. Subsequent
hydrolysis with dilute HCl afforded the base-modified 2-hydroxy-3-(purin-9-yl)pro-
panoic acids (8a–8f, 9a–9b, 10a–10b). The deionized reaction products were finally
purified by anion exchange chromatography (Sch. 1).

2-Hydroxy-3-(purin-9-yl)propanoic Acids
2147
Scheme 1. (a) BrCH2CH(OEt)2,Cs2CO3=DMF, 100ꢁC; (b) R1R2NH or R1NH2, [or
(CH3)2NHþ(CH3)2N-COOꢂ]; (c) (1) Hþ, (2) KCN (3) Hþ; (d) DABCO, aq. K2CO3;
(e) thiourea.
In our earlier article,[9] we have discovered that the treatment of 9-(2,2-diethoxy-
ethyl)adenine (11a) with malonic acid in boiling aqueous solution does not afford
the expected 4-(adenin-9-yl)-2-butenoic acid (12) but gives exclusively the isomeric
4-(adenin-9-yl)-3-butenoic acid (13). We have postulated the mechanism of this

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Dolakova, Masojıdkova, and Holy
2148
isomerisation based on addition of water to the primary reaction product and its
subsequent elimination in either direction. It was considered plausible that the mark-
edly low water solubility of compound (13) could shift this equilibrium in favor of
this isomer. This speculation was supported by the fact that the homologue, 2-(ade-
nin-9-yl)-1,1-diethoxypropane (11b) gives with malonic acid in water the postulated
intermediate, 4-(adenin-9-yl)-3-hydroxypropanoic acid (14) as the only reaction pro-
duct. Having in hand the above series of 2,2-diethoxyethyl purines (5a–5f, 6a–6b, 7a–
7b) we have further investigated this reaction. However, in all cases examined solely
the 6-substituted 4-(purin-9-yl)-3-butenoic acids (15a–15j) were obtained, disregard-
ing the solubility of the product in the course of the reaction. Removal of excess
malonic acid and final purification were performed by ion exchange chromato-
graphy.
Untypical formation of b,g-unsaturated acids from malonic acid and aldehydes
was already described in the literature.[11] However, in all such cases the reaction was
performed in non-aqueous solvents in the presence of the tertiary base or, in the neat
tertiary base. Thus, to explain the formation of the b,g-unsaturated acids from 2,2-
diethoxyethyl purines and malonic acid in water we are suggesting the above water
addition-elimination mechanism. The driving force of this reaction could well be the
formation of the enamine product with extended p-orbital overlap involving the
heteroaromatic system (Sch. 2).
In conclusion, we have synthesized a series of base-substituted 2-hydroxy-3-
(purin-9-yl)propanoic acids by cyanohydrin synthesis from 3-(purin-9-yl)ethanals.
The latter compounds were obtained by transformations of 9-(2,2-diethoxyethyl)-6-
chloropurine or 2-amino-6-chloropurine prepared by alkylation of the bases with
bromoacetaldehyde diethyl acetal. The 2,2-diethoxyethyl derivatives give with
aqueous malonic acid 6-substituted 4-(purin-9-yl)-3-butenoic acids.
The biological examination of these compounds is not yet finished. However, we
have not encountered in this group any compound with prominent cytostatic activity
and=or antiviral activity against vaccinia virus.
Scheme 2. (a) CH2(COOH)2, H2O reflux.

2-Hydroxy-3-(purin-9-yl)propanoic Acids
EXPERIMENTAL
2149
Unless otherwise stated, solvents were evaporated at 40ꢁC=2 kPa and com-
pounds were dried overnight at 2 kPa over P2O5. Melting points were determined on
a Buchi Melting Point B-545 aparatus and are uncorrected. TLC was performed on
¨
plates of kieselgel 60 F254 (Merck) in systems S1 (chloroform-methanol 95:5), S2
(chloroform-methanol 9:1), S3 (ethyl acetate-acetone-ethanol-water 4:1:1:1) and
S4 (ethyl acetate-petroleum ether 1:1). Paper electrophoresis was performed on a
Whatman No. 3 MM paper at 40 V=cm for 1 h in 0.05 M triethylammonium hydro-
gencarbonate, pH 7.5; the electrophoretical mobilities were referenced to uridine
30-phosphate. NMR spectra were measured on an FT NMR spectrometer Varian
UNITY 500 (1H at 500 MHz and 13C at 125.7 MHz) in dimethyl sulfoxide-d6.
Chemical shifts (d ppm) and coupling constants (J, Hz) were obtained by the first-order
analysis of the spectra. Mass spectra were measured on a ZAB-EQ (VG Analytical)
spectrometer using FAB (ionization by Xe, accelerating voltage 8 kV, glycerol
matrix).
General Methods
Deionization of the Reaction Mixture. The solution of reaction products in water
(20–25 mL) was applied on a column of Dowex 50 ꢃ 8 (100 mL, Hþ form), and the
column was washed with water until the drop of the UV absorption (254 nm) and
acid reaction of the eluate. The standard elution rate was 3 mL=min. Elution was
continued with 10% ammonia, and the UV-absorbing eluate was collected and
evaporated.
Purification by Column Chromatography on Dowex 1 ꢃ 2. Unless stated other-
wise, 100 mL columns of Dowex 1 ꢃ 2 (acetate form) were used. The sample was dis-
solved in water (20–25 mL), alkalified with concentrated aqueous ammonia to pH 9–
9.5, and applied on the column. Elution with water (3 mL=min) was continued until
the drop of the initial UV absorption (254 nm) of the eluate. The column was then
eluted with a linear gradient of acetic acid.
6-Chloro-9-(2,2-diethoxyethyl)purine (3a) and 6-Chloro-7-(2,2-diethoxyethyl)pur-
ine (4a). To the stirred mixture of (2a) (7.7 g, 50 mmol) and cesium carbonate (8.1 g,
25 mmol) in DMF (150 mL) was added bromoacetaldehyde diethylacetal (11.6 mL,
75 mmol). The mixture was heated under stirring at 100ꢁC for 24 h with exclusion
of moisture. The reaction mixture was filtered while hot through Celite, taken down
at 50ꢁC=13 Pa and codistilled with toluene (3 ꢃ 50 mL) and ethanol (2 ꢃ 50 mL). The
residue was extracted with boiling chloroform (500 mL), filtered through Celite and
evaporated. The residue in methanol (200 mL) was treated with silica gel (150 mL),
evaporated and applied on a column of silica gel (600 mL) in ethyl acetate-petroleum
ether mixture (1:2). The column was eluted with ethyl acetate-petroleum ether mix-
ture (1:2–1:1). The crystallization from ethyl acetate-petroleum ether afforded 5.6 g
1
(42%) of compound (3a), white crystals, mp 85ꢁC, RF ¼ 0.66 (S1). H NMR: 8.79
(s, 1H, H–2); 8.62 (s, 1H, H–8); 4.89 (t, 1H, J(20,10) ¼ 5.0, H-20); 4.40 (d, 2H,

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Dolakova, Masojıdkova, and Holy
2150
J(10,20) ¼ 5.0, H-10); 3.64 and 3.45 (dq, 2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-
CH2); 1.01 (t, 6H, J(CH3,CH2) ¼ 7.1, CH3). 13C NMR: 152.32 (C-4); 151.74 (C-2);
149.15 (C-6); 148.04 (C-8); 130.64 (C-5); 99.26 (C-20); 62.59 (2C, O-CH2); 46.01
(C-10); 15.21 (2C, CH3). FAB MS, m=z: 271.2 [M þ H]. For C11H15N4O2Cl calcd:
C, 48.80; H, 5.58; N, 20.70; Cl, 13.10; O, 11.82%; found: C, 48.93; H, 5.60; N,
20.60; Cl, 13.19; O, 11.68%. Further elution of the column with ethyl acetate-petro-
leum ether (1:1) gave, after crystallization from ethyl acetate-petroleum ether, com-
1
pound (4a) (0.73 g, 5.5%), white crystals, mp ¼ 60ꢁC, RF ¼ 0.54. H NMR: 8.78
(s, 1H, H-2); 8.72 (s, 1H, H–8); 4.82 (t, 1H, J(20,10) ¼ 5.0, H-20); 4.59 (d, 2H,
J(10,20) ¼ 5.0, H-10); 3.64 and 3.42 (dq, 2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-
CH2); 0.99 (t, 6H, J(CH3,CH2) ¼ 7.1, CH3). 13C NMR: 161.57 (C-4); 151.87 (C-2);
151.63 (C-8); 142.51 (C-6); 122.45 (C-5); 100.40 (C-20); 63.23 (2C,O-CH2); 48.85
(C-10); 15.20 (2C, CH3). FAB MS, m=z: 271 [M þ H]. For C11H15N4O2Cl calcd:
C, 48.80; H, 5.58; N, 20.70; Cl, 13.10; O, 11.82%; found: C, 48.72; H, 5.54; N,
20.54; Cl, 13.18; O, 12.02%.
2-Amino-6-chloro-9-(2,2-diethoxyethyl)purine (3b) and 2-Amino-6-chloro-7-(2,2-
diethoxyethyl)purine (4b). These compounds were prepared from 2-amino-6-chlor-
opurine (2b) (8.5 g, 50 mmol) by the same procedure as compounds (3a) and (4a).
The silica gel column was eluted with chloroform (1 L) and then with chloroform-
methanol mixture (98:2). The crystallization from ethyl acetate-petroleum ether
afforded 8.5 g (59%) of compound (3b), white crystals, mp ¼ 139.2ꢁC, RF ¼ 0.54
1
(S1). H NMR: 8.04 (s, 1H, H–8); 6.94 (s, 2H, NH2); 4.80 (t, 1H, J(20,10) ¼ 5.4,
H-20); 4.13 (d, 2H, J(10,20) ¼ 5.4, H-10); 3.63 and 3.42 (dq, 2H, J(CH2, CH3) ¼ 7.1,
J(gem) ¼ 9.6, O-CH2); 1.025 (t, 6H, J(CH3,CH2) ¼ 7.1, CH3). 13C NMR: 160.00
(C-2); 154.43 (C-4); 149.45 (C-6); 143.73 (C-8); 123.14 (C-5); 99.37 (C-20); 62.48
(2C, O-CH2); 45.44 (C-10); 15.28 (2C, CH3). FAB MS, m=z: 286 [M þ H]. For
C11H16N5O2Cl calcd: C, 46.24; H, 5.64; N, 24.51; Cl, 12.41; O, 11.20%; found: C,
46.22; H, 5.75; N, 24.29; Cl, 12.25. O, 11.49%. Further elution of the column, and
crystallization from ethyl acetate-petroleum ether, afforded 1.7 g (12%) of compound
1
(4b), white crystals, mp ¼ 163ꢁC, RF ¼ 0.41 (S1). H NMR: 8.28 (s, 1H, H–8); 6.64
(brs, 2H, NH2); 4.76 (t, 1H, J(20,10) ¼ 5.4, H-20); 4.37 (d, 2H, J(10,20) ¼ 5.4, H-10);
3.63 and 3.39 (dq, 2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2); 1.01 (t, 6H,
J(CH3,CH2) ¼ 7.1, CH3). 13C NMR: 164.24 (C-4); 160.02 (C-2); 150.45 (C-8);
143.66 (C-6); 115.21 (C-5); 100.49 (C-20); 63.12 (2C, O-CH2); 48.64 (C-10); 15.27
(2C, CH3). FAB MS, m=z: 286 [M þ H]. For C11H16N5O2Cl calcd: C, 46.24; H,
5.64; N, 24.51; Cl, 12.41; O, 11.20%; found: C, 46.32; H, 5.75; N, 24.61; Cl, 12.42;
O, 10.90%.
9-(2,2-Diethoxyethyl)-6-(dimethylamino)purine (5a). The solution of compound
(3a) (4.1 g, 15 mmol) and dimethylamonium N,N-dimethylcarbamate (5.8 mL,
45 mmol) in acetonitrile (120 mL) was refluxed for 0.5 h with exclusion of moisture.
The mixture was evaporated and the residue codistilled with ethanol (2 ꢃ 50 mL).
The residue was dissolved in chloroform (100 mL) and washed with water
(3 ꢃ 50 mL) and the water was washed with chloroform (2 ꢃ 50 mL). Organic phase
was dried with MgSO4 and evaporated. The crystallization from ethyl acetate-petro-
leum ether afforded 4.54 g (95%) of compound (5a), white crystals, mp ¼ 65ꢁC,

2-Hydroxy-3-(purin-9-yl)propanoic Acids
2151
RF ¼ 0.75 (S1). 1H NMR: 8.22 (s, 1H, H–2); 8.07 (s, 1H, H–8); 4.83 (t, 1H,
J(20,10) ¼ 5.4, H-20); 4.23 (d, 2H, J(10,20) ¼ 5.4, H-10); 3.63 and 3.41 (dq, 2H,
J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2); 3.44 (brs, 6H, N-CH3); 1.02 (t, 6H,
J(CH3,CH2) ¼ 7.1, CH3). 13C NMR: 154.34 (C-6); 151.95 (C-2); 150.60 (C-4);
140.22 (C-8); 119.03 (C-5); 99.56 (C-20); 62.36 (2C, O-CH2); 45.40 (C-10); 39.00
(br, N-CH3); 38.00 (br, N-CH3); 15.22 (2C, CH3). FAB MS, m=z: 280 [M þ H].
For C13H21N5O2 calcd: C, 55.90; H, 7.58; N, 25.07; O, 11.45%; found: C, 55.74;
H, 7.69; N, 24.91; O, 11.66%.
2-Amino-9-(2,2-diethoxyethyl)-6-(dimethylamino)purine (5d). This compound
was prepared from compound (3b) (4.3 g, 15 mmol) by the procedure described for
compound (5a). Yield 4.07 g (92%), white crystals, mp ¼ 108–109ꢁC, RF ¼ 0.86
1
(S3). H NMR: 7.64 (s, 1H, H–8); 5.84 (brs, 2H, NH2); 4.76 (t, 1H, J(20,10) ¼ 5.5,
H-20); 4.04 (d, 2H, J(10,20) ¼ 5.5, H-10); 3.63 and 3.39 (dq, 2H, J(CH2, CH3) ¼ 7.0,
J(gem) ¼ 9.6, O-CH2); 3.37 (brs, 6H, N-CH3); 1.04 (t, 6H, J(CH3,CH2) ¼ 7.0,
CH3). 13C NMR: 159.70 (C-2); 154.85 (C-6); 153.03 (C-4); 137.05 (C-8); 113.41
(C-5); 99.67 (C-20); 62.31 (2C, O-CH2); 45.08 (C-10); 43.20 and 37.90 (N-CH3);
15.35, 2C (CH3). FAB MS, m=z: 295.2 [M þ H]. For C13H22N6O2 calcd: C, 53.05;
H, 7.53; N, 28.55; O, 10.87%; found: C, 53.00; H, 7.75; N, 28.51; O, 10.74%.
N 6-Substituted 6-Amino-9-(2,2-diethoxyethyl)purines and 2,6-Diamino-9-(2,2-
diethoxyethyl)purines. General procedure. A mixture of compound (3a) (2.17 g,
8 mmol) [for preparation of N 6-substituted 6-amino-9-(2,2-diethoxyethyl)purines]
or compound (3b) (2.28 g, 8 mmol) [for preparation of N 6-substituted 2,6-diamino-
9-(2,2-diethoxyethyl)purines], ethanol (80 mL) and primary or secondary amine (4
equivalents) was refluxed for 1–6 h with exclusion of moisture. The course of the
reaction was checked with TLC in systems S1 and S3. After completion, the mixture
was evaporated and the residue codistilled with ethanol (2 ꢃ 50 mL). The residue was
dissolved in chloroform (50 mL), washed with water (2 ꢃ 50 mL) and the water was
washed with chloroform (2 ꢃ 50 mL). Organic phase was dried with MgSO4 and
evaporated. The following compounds were prepared by this procedure:
6-(Cyclopropylamino)-9-(2,2-diethoxyethyl)purine (5b). Crystallized from ethyl
acetate-petroleum ether, yield 2.0 g (86%) of white crystals, mp ¼ 96.6ꢁC,
1
RF ¼ 0.46 (S2). H NMR: 8.25 (brs, 1H, H-2); 8.05 (s, 1H, H–8); 7.89 (brs, 1H,
NH); 4.84 (t, 1H, J(20,10) ¼ 5.4, H-20); 4.23 (d, 2H, J(10,20) ¼ 5.4, H-10); 3.63 and
3.41 (dq, 2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2); 3.04 (m, 1H, N-CH); 1.02
(t, 6H, J(CH3,CH2) ¼ 7.1, CH3); 0.72 and 0.61 (m, 2H, C-CH2). 13C NMR: 155.65
(C-6); 152.56 (C-2); 149.50 (C-4); 141.28 (C-8); 118.91 (C-5); 99.61 (C-20); 62.38 (2C,
O-CH2); 45.40 (C-10); 27.88 (N-CH); 15.28 (2C, CH3); 6.57 (2C, CH2). FAB MS,
m=z: 292.1 [M þ H]. For C14H21N5O2 calcd: C, 57.72; H, 7.26; N, 24.04; O,
10.98%; found: C, 57.63; H, 7.22; N, 23.96; O, 11.19%.
9-(2,2-Diethoxyethyl)-6-(pyrrolidin-1-yl)purine (5c). Crystallized from petro-
leum ether, yield 2.46 g (96%), white crystals, mp ¼ 59–61ꢁC, RF ¼ 0.56 (S1).
1H NMR: 8.20 (s, 1H, H–2); 8.04 (s, 1H, H–8); 4.83 (t, 1H, J(20,10) ¼ 5.4 (H-20);
4.22 (d, 2H, J(10,20) ¼ 5.4, H-10); 4.05 and 3.60 (m, 2H, N-CH2); 3.63 and 3.41

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Dolakova, Masojıdkova, and Holy
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(dq, 2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2); 1.97 and 1.91 (m, 2H, C-CH2);
1.025 (t, 6H, J(CH3,CH2) ¼ 7.1, CH3). FAB MS, m=z: 306 [M þ H]. For
C15H23N5O2 calcd: C, 59.00; H, 7.59; N, 22.93; O, 10.48; found: C, 58.93; H, 7.74;
N, 22.83; O, 10.50%.
2-Amino-6-(cyclopropylamino)-9-(2,2-diethoxyethyl)purine
(5e). Crystallized
from ethanol-ether, yield 1.92 g (78%), white crystals, mp ¼ 164.2ꢁC, RF ¼ 0.49
1
(S2). H NMR: 7.61 (s, 1H, H–8); 7.28 (brs, 1H, NH); 5.87 (brs, 2H, NH2); 4.76
(t, 1H, J(20,10) ¼ 5.4, H-20); 4.03 (d, 2H, J(10,20) ¼ 5.4, H-10); 3.63 and 3.39 (dq,
2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2); 3.03 (m, 1H, N-CH); 1.04 (t, 6H,
J(CH3,CH2) ¼ 7.1, CH3); 0.65 and 0.58 (m, 2H, C-CH2). 13C NMR: 160.41 (C-2);
156.02 (C-6); 150.00 (C-4); 137.78 (C-8); 113.21 (C-5); 99.74 (C-20); 62.32 (2C, O-
CH2); 45.06 (C-10); 27.00 (N-CH); 15.34 (2C, CH3); 6.55 (2C, CH2). FAB MS,
m=z: 307.1 [M þ H]. For C14H22N6O2 calcd: C, 54.89; H, 7.24; N, 27.43; O,
10.44%; found: C, 54.73; H, 7.37; N, 27.32; O, 10.58%.
2-Amino-9-(2,2-diethoxyethyl)-6-(pyrrolidin-1-yl)purine (5f). Crystallized from
ethyl acetate-petroleum ether, yield 2.2 g (88%) of white crystals, mp ¼ 110.4ꢁC,
1
RF ¼ 0.88 (S3), RF ¼ 0.14 (S4). H NMR: 7.61 (s, 1H, H–8); 5.80 (brs, 2H, NH2);
4.76 (t, 1H, J(20,10) ¼ 5.5, H-20); 4.03 (d, 2H, J(10,20) ¼ 5.5, H-10); 3.96 and 3.55
(m, 2H, N-CH2); 3.63 and 3.39 (dq, 2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2);
1.89 (m, 4H, C-CH2); 1.04 (t, 6H, J(CH3,CH2) ¼ 7.1, CH3). 13C NMR: 160.06
(C-2); 153.21 (C-6); 152.60 (C-4); 137.48 (C-8); 113.64 (C-5); 99.69 (C-20); 62.28
(2C, O-CH2); 48.20 and 47.00 (N-CH2); 45.02 (C-10); 25.15 a 24.00 (C-CH2); 15.35
(2C, CH3). FAB MS, m=z: 321.1 [M þ H]. For C15H24N6O2 calcd: C, 56.23; H,
7.55; N, 26.23; O, 9.98%; found: C, 56.06; H, 7.65; N, 25.97; O, 10.32%.
9-(2,2-Diethoxyethyl)hypoxanthine (6a). The solution of (3a) (2.17 g, 8 mmol),
K2CO3 (4.43 g, 32 mmol) and DABCO (1.8 g, 16 mmol) in water (25 mL) was stirred
at reflux for 2 h, neutralized by addition of Dowex 50 ꢃ 8, alkalified with 10% ammo-
nia and filtered. The resin was washed with water (200 mL) and 10% ammonia
(200 mL). The filtrate was evaporated. The residue was extracted with boiling ethyl
acetate, filtered, evaporated and applied on a silica gel column. The column was
eluted with ethyl acetate-methanol (90:10). The crystallization from ethyl acetate-
petroleum ether afforded 1.5 g (74%) of compound (6a), white solid, mp ¼ 172.3–
173.8ꢁC, RF ¼ 0.51 (S2). 1H NMR: 7.85 (s, 1H, H-2); 7.60 (s, 1H, H–8); 4.74
(t, 1H, J(20,10) ¼ 5.6, H-20); 4.07 (d, 2H, J(10,20) ¼ 5.6, H-10); 3.62 and 3.39 (dq, 2H,
J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2); 1.03 (t, 6H, J(CH2,CH3) ¼ 7.1, CH3).
13C NMR: 167.22 (C-6); 153.57 (C-2); 150.00 (C-4); 137.16 (C-8); 124.05 (C-5);
99.95 (C-20); 62.26 (2C, O-CH2); 45.33 (C-10); 15.33 (2C, CH3). FAB MS, m=z:
253 [M þ H]. For C11H16N4O3 calcd: C, 52.37; H, 6.39; N, 22.21; O, 19.03%; found:
C, 52.15; H, 6.49; N, 21.90; O, 19.46%.
9-(2,2-Diethoxyethyl)guanine (6b). The compound (3b) (1.7 g, 6 mmol), K2CO3
(3.32 g, 24 mmol) and DABCO (1.34 g, 12 mmol) were dissolved in water (20 mL)
and stirred at reflux for 1.5 h, neutralized with Dowex 50 ꢃ 8, alkalified with 10%
ammonia and filtered. The resin was washed with water (200 mL) and 10% ammonia

2-Hydroxy-3-(purin-9-yl)propanoic Acids
2153
(200 mL). The filtrate was evaporated. The crude product was crystallized from
water to afford 1.21 g (73%) of compound (6b), white solid, mp ¼ 277.7ꢁC (dec.),
1
RF ¼ 0.75 (S3). H NMR: d10.58 (s, 1H, NH); 7.60 (s, 1H, H–8); 6.46 (brs, 2H,
NH2); 4.73 (t, 1H, J(20,10) ¼ 5.4, H-20); 4.01 (d, 2H, J(10,20) ¼ 5.4, H-10); 3.63 a
3.39 (dq, 2H, J(CH2, CH3) ¼ 7.1, J(gem) ¼ 9.6, O-CH2); 1.04 (t, 6H,
J(CH3,CH2) ¼ 7.1, CH3). 13C NMR: d157.01 (C-2); 153.77 (C-6); 151.54 (C-4);
138.06 (C-8); 116.35 (C-5); 99.78 (C-20); 62.40 (2C, O-CH2); 45.32 (C-10); 15.31
(2C, CH3). FAB MS, m=z: 268.2 [M þ H]. For C11H17N5O3ꢄ1=2H2O calcd: C,
47.82; H, 6.57; N, 25.35; O, 20.27%; found: C, 47.73; H, 6.44; N, 25.16; O, 20.67%.
9-(2,2-Diethoxyethyl)-6-sulfanylpurine (7a). A solution of compound (3a)
(2.17 g, 8 mmol) and thiourea (1.9 g, 24 mmol) in ethanol (120 mL) was stirred at
reflux for 1.5 h, cooled and made basic with triethylamine. The crystalline product
was filtered, washed with ethanol and ether and dried. Yield 1.85 g (86%), white crys-
1
tals, mp ¼ 241-243ꢁC (dec.), RF ¼ 0.54 (S2). H NMR: d13.75 (brs, 1H, SH); 8.215
(s, 1H, H-2); 8.21 (s, 1H, H–8); 4.82 (t, 1H, J(20,10) ¼ 5.3, H-20); 4.26 (d, 2H,
J(10,20) ¼ 5.3, H-10); 3.62 and 3.43 (dq, 2H, J(CH2, CH3) ¼ 7.0, J(gem) ¼ 9.6, O-
CH2); 1.03 (t, 6H, J(CH3,CH2) ¼ 7.0, CH3). 13C NMR: d175.95 (C-6); 145.17 (C-2);
144.48 (C-4); 143.69 (C-8); 134.81 (C-5); 99.53 (C-20); 62.53 (2C, O-CH2); 45.74
(C-10); 15.26 (2C, CH3). FAB MS, m=z: 269.1 [M þ H]. For C11H16N4O2S calcd:
C, 49.24; H, 6.01; N, 20.88; O, 11.92; S, 11.95%; found: C, 49.03; H, 6.07; N,
20.73; O, 12.25%; S, 11.92%.
2-Amino-9-(2,2-diethoxyethyl)-6-sulfanylpurine (7b). This compound was pre-
pared from compound (3b) (1.71 g, 6 mmol) according to the above described proce-
dure for compound (7a). Yield 1.56 g (89%) of white crystals, not melting below
1
300ꢁC, RF ¼ 0.54 (S2). H NMR: d11.88 (s, 1H, SH); 7.80 (s, 1H, H–8); 6.81 (brs,
2H, NH2); 4.75 (t, 1H, J(20,10) ¼ 5.2, H-20); 4.03 (d, 2H, J(10,20) ¼ 5.2, H-10); 3.63
and 3.41 (dq, 2H, J(CH2, CH3) ¼ 7.0, J(gem) ¼ 9.6, O-CH2); 1.04 (t, 6H,
J(CH3,CH2) ¼ 7.0, CH3). 13C NMR: 175.01 (C-6); 153.19 (C-2); 148.22 (C-4);
141.13 (C-8); 128.06 (C-5); 99.57 (C-20); 62.45 (2C, O-CH2); 45.29 (C-10); 15.32
(2C, CH3). FAB MS, m=z: 284 [M þ H]. For C11H17N5O2S.1=2H2O calcd: C,
45.19; H, 6.21; N, 23.96; O, 13.68; S, 10.97%; found: C, 45.02; H, 6.11; N, 23.77;
O, 13.99; S, 11.11%.
N 6-Substituted 3-(6-Aminopurin-9-yl)-2-hydroxypropanoic acids and 3-(2,6-
Diaminopurin-9-yl)-2-hydroxypropanoic Acids. General procedure. A mixture of
N 6-substituted 6-amino- or 2,6-diamino-9-(2,2-diethoxyethyl)purine (5–7) (6mmol),
water (30 mL) and conc. hydrochloric acid (1.2mL) was heated for 4–8 h at 60ꢁC
until the reaction was complete (S2). After cooling to ꢂ5ꢁC (ice-salt mixture),
potassium cyanide (1.95 g, 30 mmol) was added under stirring, the mixture was
rapidly adjusted to pH 6–6.5 with acetic acid and stirred at 0ꢁC for 5 h and at room
temperature overnight. Concentrated hydrochloric acid (20 mL) was added, the
mixture was refluxed for 6 h, cooled, and evaporated. The residue was deionized
on Dowex 50 ꢃ 8 (see above), and purified by Dowex 1 ꢃ 2 column chromatography
(see above). Unless otherwise stated, the column was eluted with gradient of acetic

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Dolakova, Masojıdkova, and Holy
2154
acid (2 L, 0–0.5 M). The crude product was crystallized from water. The following
compounds were prepared by this procedure:
3-[6-(Dimethylamino)purin-9-yl]-2-hydroxypropanoic Acid (8a). Pale brown
1
solid, yield 76%, mp ¼ 232ꢁC (dec.), EUp ¼ 0.61. H NMR: 12.90 (brs, 1H, COOH);
8.22 (s, 1H, H–2); 8.07 (s, 1H, H–8); 5.90 (brs, 1H, OH); 4.46 (dd, 1H, J(10a,20) ¼ 3.9,
J(gem) ¼ 13.7, H-10a); 4.39 (dd, 1H, J(20,10a) ¼ 3.9, J(20,10b) ¼ 8.2, H-20); 4.27 (dd,
1H, J(10b,20) ¼ 8.2, J(gem) ¼ 13.7, H-10b); 3.46 (brs, 6H, N-CH3). FAB MS m=z:
252 [M þ H]. For C10H13N5O3ꢄ1=2H2O calcd: C, 46.15; H, 5.42; N, 26.91; O,
21.52%; found: C, 46.11; H, 5.39; N, 26.69; O, 21.81%.
3-[6-(Cyclopropylamino)purin-9-yl]-2-hydroxypropanoic Acid (8b). Crystallized
from water-acetone mixture, white solid, yield 80%, mp ¼ 245ꢁC (dec.), EUp ¼ 0.50.
1H NMR: 12.80 (brs, 1H, COOH); 8.24 (s, 1H, H–2); 8.04 (s, 1H, H–8); 7.90 (brs,
1H, NH); 5.90 (brs, 1H, OH); 4.46 (dd, 1H, J(10a,20) ¼ 3.6, J(gem) ¼ 13.7, H-10a);
4.40 (dd, 1H, J(20,10a) ¼ 3.6, J(20,10b) ¼ 8.0, H-20); 4.27 (dd, 1H, J(10b,20) ¼ 8.0,
J(gem) ¼ 13.7, H-10b); 3.05 (m, 1H, N-CH); 0.71 and 0.60 (m, 2H, C-CH2). 13C
NMR: 173.36 (C¼O); 155.66 (C-6); 152.44 (C-2); 149.30 (C-4); 141.56 (C-8); 68.72
(C-20); 46.39 (C-10); 24.02 (N-CH); 6.64 (2C, CH2). FAB MS m=z: 264 [M þ H].
For C11H13N5O3 calcd: C, 50.19; H, 4.98; N, 26.60; O, 18.23%; found: C, 49.86;
H, 4.98; N, 26.47; O, 18.69%.
2-Hydroxy-3-[6-(pyrrolidin-1-yl)purin-9-yl]propanoic Acid (8c). Pale brown
1
solid, yield 81%, mp ¼ 236ꢁC (dec.), EUp ¼ 0.54. H NMR: 12.80 (brs, 1H, COOH);
8.21 (s, 1H, H-2); 8.04 (s, 1H, H-8); 5.80 (brs, 1H, OH); 4.46 (dd, 1H, J(10a,20) ¼ 3.9,
J(gem) ¼ 13.8, H-10a); 4.39 (dd, 1H, J(20,10a) ¼ 3.9, J(20,10b) ¼ 8.1, H-20); 4.27 (dd,
1H, J(10b,20) ¼ 8.1, J(gem) ¼ 13.8, H-10b); 4.05 and 3.62 (m, 2H, N-CH2); 1.97 and
1.93 (m, 2H, C-CH2). 13C NMR: 173.28 (C¼O); 152.42 (C-6); 152.01 (C-2);
150.08 (C-4); 141.10 (C-8); 119.30 (C-5); 68.67 (C-20); 48.52 and 47.19 (N-CH2);
46.33 (C-10); 25.91 and 24.02 (C-CH2). FAB MS m=z: 278 [M þ H]. For
C12H15N5O3 calcd: C, 51.98; H, 5.45; N, 25.26; O, 17.31%; found: C, 51.90; H,
5.44; N, 25.02; O, 17.64%.
3-[2-Amino-6-(dimethylamino)purin-9-yl]-2-hydroxypropanoic Acid (8d). The
resin, after the elution by acetic acid, was stirred with boiling water (1 L), filtered
and the water was evaporated. The residue was crystallized from water to afford
1
white solid, yield 67%, mp ¼ 272ꢁC (dec.), EUp ¼ 0.47. H NMR: 7.63 (s, 1H, H-
8); 5.87 (brs, 2H, NH2); 4.33 (dd, 1H, J(20,10a) ¼ 3.9, J(20,10b) ¼ 8.4, H-20); 4.29
(dd, 1H, J(10a,20) ¼ 3.9, J(gem) ¼ 13.8, H-10a); 4.06 (dd, 1H, J(10b,20) ¼ 8.4,
J(gem) ¼ 13.8, H-10b); 3.35 (brs, 6H, N-CH3). FAB MS m=z: 267 [M þ H]. For
C10H14N6O3ꢄH2O calcd: C, 42.25; H, 5.67; N, 29.56; O, 22.51%; found: C, 42.16;
H, 5.75; N, 29.20; O, 22.89%.
3-[2-Amino-6-(cyclopropylamino)purin-9-yl]-2-hydroxypropanoic Acid (8e). White
1
solid, yield 82%, mp ¼ 258 – 260ꢁC (dec.), EUp ¼ 0.45. H NMR: 7.61 (s, 1H, H-8);
7.36 (brs, 1H, NH); 6.00 (brs, 1H, OH); 5.95 (brs, 2H, NH2); 4.33 (dd, 1H,
J(20,10a)¼ 3.8, J(20,10b) ¼ 8.4, H-20); 4.28 (dd, 1H, J(10a,20) ¼ 3.8, J(gem) ¼ 13.9,

2-Hydroxy-3-(purin-9-yl)propanoic Acids
2155
H-10a); 4.06 (dd, 1H, J(10b,20) ¼ 8.4, J(gem) ¼ 13.9, H-10b); 3.01 (m, 1H, N-CH); 0.65
and 0.57 (m, 2H, C-CH2). 13C NMR: 173.59 (C¼O); 160.11 (C-2); 155.97 (C-6); 150.00
(C-4); 138.21 (C-8); 113.32 (C-5); 68.91 (C-20); 46.11 (C-10); 28.45 (N-CH); 6.66 (2C,
CH2). FAB MS m=z: 279 [M þ H]. For C11H14N6O3ꢄ1=3H2O calcd: C, 46.48; H,
5.20; N, 29.56; O, 18.76%; found: C, 46.54; H, 5.22; N, 29.73; O, 18.51%.
3-[2-Amino-6-(pyrrolidin-1-yl)purin-9-yl]-2-hydroxypropanoic Acid (8f). The
Dowex 1 ꢃ 2 resin, after the elution with acetic acid, was stirred with boiling water
(1 L), filtered and the filtrate evaporated. The crude product was crystallized from
1
water. White solid, yield 51%, mp ¼ 275ꢁC (dec.), EUp ¼ 0.44. H NMR: 7.61 (s,
1H, H-8); 5.84 (brs, 2H, NH2); 4.30 and 4.05 and 4.00 (m, 1H, H-10and H-20);
3.70 (m, 4H, N-CH2); 1.90 (m, 4H, C-CH2). 13C NMR: 173.49 (C¼O); 159.87
(C-2); 153.20 (C-6); 152.40 (C-4); 137.82 (C-8); 113.78 (C-5); 68.85 (C-20); 46.03
(C-10). FAB MS m=z: 293 [M þ H]. For C12H16N6O3 calcd: C, 49.31; H, 5.52; N,
28.75; O, 16.42%; found: C, 49.04; H, 5.57; N, 28.60; O, 16.79%.
2-Hydroxy-3-[hypoxanthin-9-yl]propanoic Acid (9a). The Dowex 1 ꢃ 2 column
was eluted with gradient of acetic acid (2 L, 0–1 M). The resin was then stirred with
boiling water (1 L), filtered and stirred with hot acetic acid (1 L, 1.5 M). The aqueous
solutions were joined, evaporated and the residue has crystallized from water. White
1
crystals, yield 25%, mp ¼ 112.6ꢁC, EUp ¼ 0.72. H NMR: 12.60 (brs, 1H, COOH);
12.30 (brs, 1H, NH); 8.05 (s, 1H, H–2); 7.99 (s, 1H, H–8); 5.90 (brs, 1H, OH);
4.44 (dd, 1H, J(10a,20) ¼ 3.8, J(gem) ¼ 13.7, H-10a); 4.37 (dd, 1H, J(20,10a) ¼ 3.8,
J(20,10b) ¼ 8.3, H-20); 4.26 (dd, 1H, J(10b,20) ¼ 8.3, J(gem) ¼ 13.7, H-10b). 13C
NMR: 173.20 (C¼O); 156.85 (C-6); 148.67 (C-4); 145.69 (C-2); 141.15 (C-8);
123.90 (C-5); 68.87 (C-20); 46.66 (C-10). FAB MS m=z: 225 [M þ H]. For
C8H8N4O4ꢄH2O calcd: C, 39.67; H, 4.16; N, 23.13; O, 33.03; found: C, 39.53; H,
4.23; N, 22.93; O, 33.31%.
3-[Guanin-9-yl]-2-hydroxypropanoic Acid (9b). The Dowex 1 ꢃ 2 column was
eluted with gradient of acetic acid (2 L, 0–1.5 M). White solid, yield 27%, mp ¼ 292ꢁC
1
(dec.), EUp ¼ 0.66. H NMR: 12.50 (brs, 1H, COOH); 10.60 (brs, 1H, NH); 7.61 (s,
1H, H-8); 6.49 (brs, 2H, NH2); 5.90 (brs, 1H, OH); 4.31 (dd, 1H, J(20,10a) ¼ 3.9,
J(20,10b) ¼ 8.8, H-20); 4.25 (dd, 1H, J(10a,20) ¼ 3.9, J(gem) ¼ 13.9, H-10a); 4.04 (dd,
1H, J(10b,20) ¼ 8.8, J(gem) ¼ 13.9, H-10b). 13C NMR: 173.39 (C¼O); 157.01 (C-2);
153.74 (C-6); 151.42 (C-4); 138.38 (C-8); 116.43 (C-5); 68.83 (C-20); 46.14 (C-10).
FAB MS m=z: 240 [M þ H]. For C8H9N5O4ꢄ1=3H2O calcd: C, 39.19; H, 3.79; N,
28.56; O, 28.28; found: C, 39.30; H, 4.04; N, 28.18; O, 28.48%.
2-Hydroxy-3-[6-sulfanylpurin-9-yl]propanoic Acid (10a). DMF (5 mL) was
added to the reaction mixture to improve solubility. Crystallization from water
1
afforded yellow solid, yield 89%, mp ¼ 220ꢁC (dec.), EUp ¼ 0.88. H NMR: 13.74
(brs, 1H, SH); 12.50 (brs, 1H, COOH); 8.21 (s, 1H, H–2); 8.19 (s, 1H, H–8); 5.90
(brs, 1H, OH); 4.46 (dd, 1H, J(10a,20) ¼ 3.9, J(gem) ¼ 13.7, H-10a); 4.38 (dd, 1H,
J(20,10a) ¼ 3.9, J(20,10b) ¼ 8.2, H-20); 4.30 (dd, 1H, J(10b,20) ¼ 8.2, J(gem) ¼ 13.7, H-
10b). 13C NMR: 175.90 (C-6); 173.08 (C¼O); 145.11 (C-2); 144.47 (C-4); 143.88

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Dolakova, Masojıdkova, and Holy
2156
(C-8); 134.99 (C-5); 68.72 (C-20); 46.72 (C-10). FAB MS m=z: 241 [M þ H]. For
C8H8N4O3S.H2O calcd: C, 37.21; H, 3.90; N, 21.69; O, 24.78; S, 12.41%; found:
C, 37.59; H, 3.77; N, 21.74; O, 24.51; S, 12.39%.
3-[2-Amino-6-sulfanylpurin-9-yl]-2-hydroxypropanoic Acid (10b). DMF (5 mL)
was added to the reaction mixture to improve solubility. The resin was, after the elu-
tion by acetic acid, stirred with boiling water (1 L), filtered and then stirred with hot
acetic acid (1 L, 1 M) and filtered. Water and acetic acid were evaporated. The resi-
due has crystallized from water to afford yellow solid, yield 27%, mp ¼ 284ꢁC (dec.),
1
EUp ¼ 0.63. H NMR: 12.90 (brs, 1H, SH); 11.88 (brs, 1H, COOH); 7.79 (s, 1H,
H-8); 6.82 (brs, 2H, NH2); 5.90 (brs, 1H, OH); 4.32 (dd, 1H, J(20,10a) ¼ 3.9,
J(20,10b) ¼ 8.7, H-20); 4.26 (dd, 1H, J(10a,20) ¼ 3.9, J(gem) ¼ 14.0, H-10a); 4.07 (dd,
1H, J(10b,20) ¼ 8.7, J(gem) ¼ 14.0, H-10b). 13C NMR: 174.95 (C-6); 173.24 (C¼O);
153.15 (C-2); 148.14 (C-4); 141.37 (C-8); 128.20 (C-5); 68.60 (C-20); 46.12 (C-10).
FAB MS m=z: 256 [M þ H]. For C8H9N5O3S.1=3H2O calcd: C, 36.78; H, 3.73; N,
26.81; O, 20.41; S, 12.27%; found: C, 37.19; H, 3.70; N, 26.51; O, 20.49; S, 12.11%.
N 6-Substituted 4-(6-Aminopurin-9-yl)-3-butenoic Acids. General procedure.
A mixture of N 6-substituted 6-amino-9-(2,2-diethoxyethyl)purine (5a–5c) (2 mmol)
and malonic acid (8 mmol) in water (15 mL) was stirring at reflux for 24–32 h. The
course of the reaction was checked by TLC in S1 and by electrophoresis. The reac-
tion mixture was cooled to r.t. and the crystalline product was filtered, washed with
water and ether and dried over P2O5. The following compounds were prepared:
4-[6-(Dimethylamino)purin-9-yl]-3-butenoic Acid (15a). White crystals, yield
1
0.28 g (60%), mp ¼ 222.8ꢁC, EUp ¼ 0.57. H NMR: 12.43 (brs, 1H, COOH); 8.46
(s, 1H, H-2); 8.25 (s, 1H, H–8); 7.20 (dt, 1H, J(10,20) ¼ 14.5, J(10,30) ¼ 1.3, H-10);
6.63 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.4, H-20); 3.24 (dd, 2H, J(30,20) ¼ 7.4,
J(30,10) ¼ 1.3, H-30); 3.37 (brs, 6H, CH3). 13C NMR: 172.64 (C¼O); 154.36 (C-6);
152.49 (C-2); 149.44 (C-4); 137.48 (C-8); 123.19 (C-10); 119.62 (C-5); 113.70 (C-20);
43.50 and 37.55 (N-CH3); 35.12 (C-30). FAB MS, m=z: 248 [M þ H]. For
C11H13N5O2 calcd: C, 53.44; H, 5.30; N, 28.32; O, 12.94%; found: C, 53.33; H,
5.37; N, 28.15; O, 13.15%.
4-[6-(Cyclopropylamino)purin-9-yl]-3-butenoic Acid (15b). Pale yellow crystals,
yield 0.36 g (70%), mp ¼ 239ꢁC (dec.), EUp ¼ 0.52. 1H NMR: 12.47 (brs, 1H, COOH);
8.44 (s, 1H, H-2); 8.30 (s, 1H, H–8); 8.01 (brs, 1H, N-H); 7.20 (dt, 1H, J(10,20) ¼ 14.5,
J(10,30) ¼ 1.3, H-10); 6.66 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.4, H-20); 3.24 (dd, 2H,
J(30,20) ¼ 7.4, J(30,10) ¼ 1.3, H-30); 3.02 (m, 1H, N-CH); 0.73 and 0.62 (m, 2H, C-
CH2). 13C NMR: 172.66 (C¼O); 156.02 (C-6); 153.14 (C-2); 149.50 (C-4); 138.74
(C-8); 123.41 (C-10); 119.62 (C-5); 113.63 (C-20); 35.15 (C-30); 27.00 (N-CH); 6.61
(C-CH2). FAB MS, m=z: 260 [M þ H]. For C12H13N5O2 calcd: C, 55.59; H, 5.05;
N, 27.01; O, 12.34%; found: C, 55.33; H, 5.17; N, 27.39; O, 12.11%.
4-[6-(Pyrrolidin-1-yl)purin-9-yl]-3-butenoic Acid (15c). White crystals, yield
1
0.37 g (64%), mp ¼ 213ꢁC (dec.), EUp ¼ 0.58. H NMR: 12.45 (brs, 1H, COOH);
8.42 (s, 1H, H-2); 8.24 (s, 1H, H–8); 7.20 (dt, 1H, J(10,20) ¼ 14.5, J(10,30) ¼ 1.3,

2-Hydroxy-3-(purin-9-yl)propanoic Acids
2157
H-10); 6.64 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.4, H-20); 4.01 and 3.62 (m, 2H, N-
CH2); 3.24 (dd, 2H, J(30,20) ¼ 7.4, J(30,10) ¼ 1.3, H-30); 1.95 and 1.91 (m, 2H, C-
CH2). 13C NMR: 172.68 (C¼O); 152.90 (C-2); 152.62 (C-6); 149.12 (C-4); 137.99
(C-8); 123.30 (C-10); 119.80 (C-5); 113.53 (C-20); 48.64 and 47.21 (N-CH2); 35.14
(C-30); 25.96 and 23.90 (C-CH2). FAB MS, m=z: 274 [M þ H]. For
C13H15N5O2.2H2O calcd: C, 50.48; H, 6.19; N, 22.64; O, 20.69%; found: C, 50.77;
H, 6.23; N, 22.64; O, 20.36%.
4-(Hypoxanthin-9-yl)-3-butenoic Acid (15d). The mixture of compound (6a)
(1.13 g, 4.5 mmol) and malonic acid (1.89 g, 18 mmol) in water (30 mL) was refluxed
for 24 h and cooled to r.t. The crystalline product was filtered, washed with water
and acetone. Recrystallization from water afforded 0.59 g (59%) of white solid,
1
mp ¼ 294ꢁC (dec.), EUp ¼ 0.63. H NMR: 12.47 (brs, 2H, COOH and N-H); 8.42
(s, 1H, H-2); 8.11 (s, 1H, H–8); 7.16 (dt, 1H, J(10,20) ¼ 14.5, J(10,30) ¼ 1.5, H-10);
6.58 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.4, H-20); 3.25 (dd, 2H, J(30,20) ¼ 7.4,
J(30,10) ¼ 1.5, H-30). 13C NMR: 172.49 (C¼O); 156.69 (C-6); 147.35 (C-4); 146.43
(C-2); 138.13 (C-8); 124.67 (C-5); 122.99 (C-10); 115.00 (C-20); 35.00 (C-30). FAB
MS, m=z: 221 [M þ H]. For C9H8N4O3 calcd: C, 49.09; H, 3.66; N, 25.45; O,
21.80%; found: C, 48.97; H, 3.65; N, 25.28; O, 22.10%.
4-(6-Sulfanylpurin-9-yl)-3-butenoic Acid (15e). The solution of compound (7a)
(1.9 g, 7 mmol) and malonic acid (3 g, 28 mmol) in water (40 mL) was refluxed for
5 h. The reaction mixture was evaporated and deionized on a column of Dowex
50 ꢃ 8 (see above). The crude solid was dissolved in water (10 mL), alkalified with
ammonia and applied on a column of Dowex 1 ꢃ 2 (acetate form). The column
was eluted with water (500 mL), gradient of acetic acid (2 L, 0–1 M) and then with
formic acid (500 mL, 1 M). The UV absorbing fraction of the last eluate was evapo-
rated and codistilled with water (3 ꢃ 50 mL). The crystallization from water afforded
1
0.52 g (30%) of compound (15e). Yellow solid, mp ¼ 225ꢁC (dec.), EUp ¼ 0.86. H
NMR: 13.90 (brs, 1H, SH); 12.50 (brs, 1H, COOH); 8.62 (s, 1H, H-2); 8.25 (s,
1H, H–8); 7.18 (dt, 1H, J(10,20) ¼ 14.5, J(10,30) ¼ 1.5, H-10); 6.61 (dt, 1H,
J(20,10) ¼ 14.5, J(20,30) ¼ 7.4, H-20); 3.26 (dd, 2H, J(30,20) ¼ 7.4, J(30,10) ¼ 1.5, H-30).
13C NMR: 176.18 (C-6); 172.46 (C¼O); 145.80 (C-2); 143.02 (C-4); 140.83 (C-8);
135.61 (C-5); 122.68 (C-10); 115.79 (C-20); 35.00 (C-30). FAB MS, m=z: 237
[M þ H]. For C9H8N4O2S.2=3H2O calcd: C, 43.54; H, 3.79; N, 22.57; O, 17.19; S,
12.91%; found: C, 43.37; H, 3.69; N, 22.77; O, 17.08; S, 13.09%.
N 6-Substituted 4-(2,6-Diaminopurin-9-yl)-3-butenoic Acids. General procedure.
A
mixture of N 6-substituted 2,6-diamino-9-(2,2-diethoxyethyl)purine (5f–5h)
(6 mmol) and malonic acid (24 mmol) in water (35 mL) was refluxed for 19–25 h,
the course of the reaction was checked on TLC (S2) and by electrophoresis. The
reaction mixture was evaporated, deionized on Dowex 50 ꢃ 8 (see above). The crude
product was purified by Dowex 1 ꢃ 2 column chromatography (see above), the
column was eluted with gradient of acetic acid (2 L, 0–0.5 M). The UV absorbing
eluate was evaporated and codistilled with water (3 ꢃ 50 mL). The subsequent

´ ´
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Dolakova, Masojıdkova, and Holy
2158
crystallization afforded these compounds:
4-[2-Amino-6-(dimethylamino)purin-9-yl]-3-butenoic Acid (15f). White solid,
crystallized from water, yield 0.95 g (54%), mp ¼ 241ꢁC (dec.), EUp ¼ 0.47. 1H
NMR: 12.30 (brs, 1H, COOH); 8.06 (s, 1H, H-8); 7.00 (dt, 1H, J(10,20) ¼ 14.5,
J(10,30) ¼ 1.2, H-10); 6.44 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.4, H-20); 6.00 (brs, 2H,
NH2); 3.36 (brs, 6H, N-CH3); 3.18 (dd, 2H, J(30,20) ¼ 7.4, J(30,10) ¼ 1.2, H-30). 13C
NMR: 172.74 (C¼O); 159.68 (C-2); 154.62 (C-6); 151.83 (C-4); 134.09 (C-8);
123.39 (C-10); 113.86 (C-5); 111.90 (C-20); 40.29 and 37.90 (N-CH3); 35.22 (C-30).
FAB MS, m=z: 263 [M þ H]. For C11H14N6O2 calcd: C, 50.38; H, 5.38; N, 32.04;
O, 12.20%; found: C, 50.21; H, 5.35; N, 31.92; O, 12.52%.
4-[2-Amino-6-(cyclopropylamino)purin-9-yl]-3-butenoic Acid (15 g). White solid,
crystallized from water-acetone mixture, yield 0.9 g (50%), mp ¼ 247ꢁC (dec.),
1
EUp ¼ 0.41. H NMR: 12.43 (brs, 1H, COOH); 8.18 (s, 1H, H-8); 7.50 (brs, 3H,
N-H); 7.00 (d, 1H, J(10,20) ¼ 14.4, H-10); 6.49 (dt, 1H, J(20,10) ¼ 14.4, J(20,30) ¼ 7.4,
H-20); 3.19 (d, 2H, J(30,20) ¼ 7.4, H-30); 2.95 (m, 1H, N-CH); 0.80 and 0.68 (m,
2H, C-CH2). 13C NMR: 172.63 (C¼O); 157.5 (C-2); 153.00 (C-6); 149.99 (C-4);
123.14 (C-10); 113.26 (C-5); 112.84 (C-20); 35.19 (C-30); 24.11 (N-CH); 7.08 (2C,
CH2). FAB MS, m=z: 275 [M þ H]. For C12H14N6O2.3=2H2O calcd: C, 47.84; H,
5.69; N, 27.89; O, 18.58%; found: C, 48.15; H, 5.33; N, 27.76; O, 18.76%.
4-[2-Amino-6-(pyrrolidin-1-yl)purin-9-yl]-3-butenoic Acid (15 h). White solid,
crystallized from water-ethanol mixture, yield 0.6 g (35%), mp ¼ 259ꢁC, EUp ¼ 0.39.
0.39. 1H NMR: 12.40 (brs, 1H, COOH); 8.01 (s, 1H, H-8); 7.00 (dt, 1H,
J(10,20) ¼ 14.5, J(10,30) ¼ 1.0, H-10); 6.44 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.1, H-20);
5.92 (brs, 2H, NH2); 3.95 and 3.55 (m, 2H, N-CH2); 3.17 (d, 2H, J(30,20) ¼ 7.1,
H-30); 1.91 (m, 4H, C-CH2). 13C NMR: 172.78 (C¼O); 160.27 (C-2); 153.13 (C-6);
151.54 (C-4); 134.48 (C-8); 123.51 (C-10); 114.14 (C-5); 111.61 (C-20); 48.60 and
47.50 (N-CH2); 35.25 (C-30); 25.50 and 25.0 (C-CH2). FAB MS, m=z: 289
[M þ H]. For C13H16N6O2ꢄ1=2H2O calcd: C, 52.52; H, 5.76; N, 28.27; O, 13.45%;
found: C, 52.79; H, 5.73; N, 28.17; O, 13.31%.
4-(Guanin-9-yl)-3-butenoic Acid (15i). This compound was prepared by the
same procedure as compound (15d) from compound (6b) (1.2 g, 4.5 mmol), white
1
solid, yield 0.63 g (60%), mp ¼ 306ꢁC (dec.), EUp ¼ 0.52. H NMR: 12.45 (brs, 1H,
COOH); 10.71 (s, 1H, N-H); 8.02 (s, 1H, H-8); 6.93 (dt, 1H, J(10,20) ¼ 14.5,
J(10,30) ¼ 1.5, H-10); 6.56 (brs, 2H, NH2); 6.41 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.4,
H-20); 3.17 (dd, 2H, J(30,20) ¼ 7.4, J(30,10) ¼ 1.5, H-30). 13C NMR: 172.69 (C¼O);
156.85 (C-2); 154.11 (C-6); 150.31 (C-4); 135.08 (C-8); 123.19 (C-10); 117.06 (C-5);
113.03 (C-20); 35.17 (C-30). FAB MS, m=z: 236 [M þ H]. For C9H9N5O3 calcd: C,
45.96; H, 3.86; N, 29.78; O, 20.41%; found: C, 45.61; H, 3.89; N, 29.74; O, 20.76%.
4-(2-Amino-6-sulfanylpurin-9-yl)-3-butenoic Acid (15j). This compound was
prepared from compound (7b) (0.98 g, 7 mmol) by the same procedure as the com-
pound (15e). Crystallization from water afforded 0.76 g (42%) of yellow solid,
mp¼ 259ꢁC (dec.), EUp ¼ 0.67. 1H NMR: 12.48 (brs, 1H, COOH); 12.01 (s, 1H, SH);

2-Hydroxy-3-(purin-9-yl)propanoic Acids
2159
8.21 (s, 1H, H-8); 6.94 (dt, 1H, J(10,20) ¼ 14.5, J(10,30) ¼ 1.0, H-10); 6.88 (brs, 2H, NH2);
6.46 (dt, 1H, J(20,10) ¼ 14.5, J(20,30) ¼ 7.4, H-20); 3.19 (dd, 2H, J(30,20) ¼ 7.4,
J(30,10) ¼ 1.0, H-30). 13C NMR: 175.30 (C-6); 172.55 (C¼O); 153.43 (C-2); 146.80
(C-4); 138.13 (C-8); 128.65 (C-5); 122.84 (C-10); 113.86 (C-20); 35.14 (C-30). FAB
MS, m=z: 252 [M þ H]. For C9H9N5O2S.1=2H2O calcd: C, 41.53; H, 3.87; N, 26.91;
O, 15.37; S, 12.32%; found: C, 41.87; H, 3.83; N, 26.53; O, 15.34; S, 12.43%.
ACKNOWLEDGMENTS
This study was performed as a part of research project # 4055905 of the Institute
of Organic Chemistry and Biochemistry. It was supported by the Programme of Tar-
geted Projects of the Academy of Sciences of the Czech Republic (# S4055109), by
´
the Rene Descartes Prize-2001 of the European Commission, by COST programme
13.20 of the Ministry of Education of the Czech Republic and by Gilead Sciences
(Foster City, CA, USA). The authors’ thanks are due to Professor E. De Clercq
and his group in the Rega Institute, Katholic University Leuven (Belgium) for the
evaluation of antiviral activity, to Dr.I. Votruba of the Institute of Organic Chem-
istry and Biochemistry for the estimation of cytostatic activity and to the staff of
the mass spectrometry and analytical departments of this Institute (Head, K.Ubik)
for elemental analyses and measuring of mass spectra.
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Received July 25, 2003
Accepted August 29, 2003