Tetrofuranose nucleoside phosphonic acids: Synthesis and properties

Article abstract of DOI:10.1135/cccc2011038

New isoelectronic, non-isosteric phosphonate analogues of nucleoside 5'-phosphates featuring the phosphorus moiety directly attached on the sugar ring in the C4' position are described. The analogues were synthesised by a nucleosidation reaction from tetr

Full text of DOI:10.1135/cccc2011038

Tetrofuranose Nucleoside Phosphonic Acids
503
TETROFURANOSE NUCLEOSIDE PHOSPHONIC ACIDS:
SYNTHESIS AND PROPERTIES
1
2
3
4,
Ivana POLÁKOVÁ , Miloš BUDĚŠÍNSKÝ , Zdeněk TOČÍK and Ivan ROSENBERG *
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i.,
1
Flemingovo 2, 16610 Prague 6, Czech Republic; e-mail: ivana.polakova@uochb.cas.cz,
2
3
4
budesinsky@uochb.cas.cz, tocik@uochb.cas.cz, ivan@uochb.cas.cz
Received February 9, 2011
Accepted March 4, 2011
Published online April 21, 2011
Dedicated to Professor Antonín Holý on the occasion of his 75th birthday.
New isoelectronic, non-isosteric phosphonate analogues of nucleoside 5′-phosphates featur-
ing the phosphorus moiety directly attached on the sugar ring in the C4′ position are de-
scribed. The analogues were synthesised by a nucleosidation reaction from tetrofuranosyl
phosphonate synthons and silylated nucleobases. The pyrimidine compounds with erythro
and threo configuration in both D- and L-series were prepared, and the structures were
assigned by NMR spectroscopy. The results of NMR conformational studies show that all cal-
culated conformers have a maximum pucker in the range typical for nucleosides. In all com-
pounds, the S-type conformer is preferred and is more significant in α-D-threo-compounds.
Studies on inhibition of thymidine phosphorylase revealed that one of the prepared phos-
phonic acids was a competitive inhibitor of the enzyme (Ki = 4 µM).
Keywords: Tetrofuranosyl phosphonate; Nucleotide analogues; NMR spectroscopy; Nucleo-
tides; Phosphorus; Oxidation; Synthesis design; Tetrofuranosyl phosphonate; Nucleotide
analogues; Sugar hydroxyphosphonates.
Numerous attempts have been made over past few decades to synthesise
suitable analogues of nucleotides that would be able to perform differently
in various biological processes and become therapeutically exploitable. The
search for novel analogues was governed, in addition to other factors, by
the necessity to overcome the susceptibility of the natural phosphoester
bond for cleavage by phosphomonoesterases. A prominent role belongs to
the nucleoside phosphonic acids containing a bridging P–C bond. Signifi-
cant effort devoted to the synthesis of these compounds and their biologi-
cal evaluation has led to the discovery of remarkable antiviral properties of
acyclic nucleoside phosphonic acids of general formula 1a (Fig. 1). Among
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© 2011 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc2011038

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Poláková, Buděšínský, Točík, Rosenberg:
them, Vistide (B = cytosine, R′ = CH2OH), Hepsera (B = adenine, R′ = H),
and Viread (B = adenine, R′ = CH3) are in clinical use for the treatment of
CMV-induced retinitis, hepatitis B, and HIV, respectively1–5
.
The biological activities of these compounds have stimulated additional
synthetic work, which has provided a number of novel compounds, such
as a 5-azacytosine derivative6,7 (1a, B = 5-azacytosine, R′ = CH2OH) efficient
against DNA viruses and a phosphonate GS-9219 (Gilead Sci, Ltd.) (1a, B =
2-amino-6-N-cyclopropylaminopurine, R′ = H), a prodrug of cytostatic
PMEG (1a, B = guanine, R′ = H) against leukaemia and non-Hodgkin’s lym-
phoma in dogs8. Recently, the prodrugs of phosphonate 1b 9,10 mimicking
the 2′,3′-dideoxydidehydronucleosides, were recognised as efficient com-
pounds against DNA viruses.
Attention was also devoted to the synthesis of the cyclic structures, such
as the pentofuranose and cyclopentane ring-containing phosphonate
nucleotide analogues11–17. Out of them, the compounds GS-9148 2a 18
,
2′-azido-2′-deoxyerythrose-based nucleoside phosphonate 2b 19, and 4′-sub-
stituted carbocyclic nucleoside phosphonate 2c 20 (R = C≡CH) have been
found to be efficient HIV-RT inhibitors. Surprisingly, diethyl esters of iso-
xazolidine nucleoside phosphonates 2d 21 were reported to be very potent
antiretroviral compounds although there was no proof of the mechanism
of action.
In contrast to the success in development of antiviral compounds against
DNA and retroviruses, the use of nucleoside phosphonates for treatment of
the RNA viruses, such as HCV, has not been fully explored16; however,
some potent HCV nucleoside inhibitors have been evaluated in clinical
studies22–25. The recently published substrate specificity study on HCV RNA
polymerase and diphosphoryl derivatives of several types of ribonucleoside
phosphonic acids revealed two chain terminators competing with ATP
(3a: X = O or CH2, Y = O, R = H)26. Compound 3b (PSI-7977, Pharmasset),
FIG. 1
Examples of nucleoside phosphonates with marked biological effects
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Tetrofuranose Nucleoside Phosphonic Acids
505
a very potent HCV RNA polymerase inhibitor containing phosphoester (not
phosphonate) moiety, is in phase II clinical development27. Despite impor-
tant achievements in the area of antivirals, the demand for novel sub-
stances with anticancer, antiviral, and other specific activities remains
strong. The chemistry of phosphonate analogues of nucleoside phosphates
is a fruitful, not yet fully explored field.
In our Laboratory, we have synthesised and evaluated a number of struc-
turally diverse nucleoside phosphonic acids such as 4a–4d (Fig. 2), differing
in the number of bridging atoms of the phosphoester mimic28–41. Some
nucleoside phosphonic acids exhibited interesting biological properties42–48
.
FIG. 2
Examples of structurally diverse nucleoside phosphonic acids
In continuation of our work, we attempted the synthesis of the addi-
tional compounds 9, 20, 34, and 50 related to the published adenine deriv-
ative 5 36. The compounds differ in the configuration on the asymmetric
centres of the sugar ring and nucleobases (Fig. 3).
FIG. 3
Phosphonic acids representing synthetic targets
RESULTS AND DISCUSSION
Preparation of D-Erythrofuranose Nucleoside Phosphonates
The nucleosidation reaction of of D-erythrofuranosylphosphonates 6
(newly prepared according to the published procedure36 providing a mix-
ture of both 2′,3′ regioisomers and anomers) with silylated uracil and thy-
mine in the presence of SnCl4 as a Lewis acid catalyst provided a low yield
of the protected derivatives 7a, 7b and 8a, 8b (Scheme 1). The free
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Poláková, Buděšínský, Točík, Rosenberg:
phosphonic acids 9a and 9b were easily obtained upon deprotection with
bromotrimethylsilane, followed by ammonia treatment (Scheme 1).
SCHEME 1
Preparation of nucleoside phosphonates with D-erythro configuration
Preparation of D-Threofuranose Nucleoside Phosphonates
Synthesis of the key synthon, D-threofuranosylphosphonate 17, was accom-
plished starting from 1,2:5,6-di-O-isopropylideneglucofuranose (10) which
was benzoylated to 11. Removal of the 5,6-O-isopropylidene group of 11
with 60% aqueous acetic acid, followed by periodate cleavage and
the addition of diethyl phosphite to aldehyde 13 (Scheme 2), proceeded
without difficulty to exclusively provide the desired R-epimer 14. As the
phosphite addition was performed in the presence of triethylamine, a par-
tial migration (ca. 25%) of the benzoyl group from the 3-OH onto 5-OH un-
der formation of 15 was observed. The migration of the benzoyl group
likely proceeded in an intramolecular manner through a six-membered in-
termediate. The attempt to achieve a reversed migration back to 3-hydroxyl
SCHEME 2
The path to the phosphonate precursor for nucleosidation in D-threo series
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Tetrofuranose Nucleoside Phosphonic Acids
507
using 5% Et3N in DCM led to a mixture of both benzoates 14 (26%) and 15
(23%), cyclic phosphonate 18 (36%), and several other undefined products
(15%). The formation of cyclic product 18 could be explained by an intra-
molecular transesterification. Phosphonate 14 was subjected to a cleavage-
oxidation step with HIO4 followed by acetylation to provide synthon 17 as
an α-anomer.
In contrast to D-erythrofuranosylphosphonate 6, the nucleosidation reac-
tion (Scheme 3) performed with D-threofuranosylphosphonate 17 and three
silylated pyrimidine nucleobases proceeded with good yields (approx. 50%).
The deprotection of 19a–19c with bromotrimethylsilane, followed by
ammonia treatment, afforded free phosphonic acids 20a–20c.
SCHEME 3
Preparation of nucleoside phosphonates with D-threo configuration
Preparation of L-Erythrofuranose Nucleoside Phosphonates
The synthesis of key synthon 32 started from methyl L-arabinoside (21).
The benzoylation with benzoyl chloride at –78 °C afforded the 5′-O-benzoyl
derivative 22 in very good yield of 76% (Scheme 4). Introduction of the iso-
propylidene group30 took place in relatively low yield, and the obtained
compound 23 with a free 3-hydroxyl group was reacted with benzyl
bromide–sodium hydride to provide compound 24. The 5-O-benzoyl moi-
ety was then removed under basic conditions whereby 3-O-benzyl-1,2-O-iso-
propylidene-β-L-arabinose (25) was obtained. This compound was subjected
to Moffatt oxidation and provided 5-aldehyde 26. The addition of diethyl
phosphite to the carbonyl group of 26 gave rise to a mixture of R- and S-
epimers 27 and 28, respectively, which were not separated (a ratio of minor
to major epimers, 22:78). The attempt to assign the 5R- and 5S-epimers by
NMR was not successful. Oxidation of the epimeric mixture of 27 and 28
with HIO4 afforded the phosphonate derivative 30. Similar to isomer 14
(Scheme 2), only the S-epimer 28 conformed to these conditions, while the
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Poláková, Buděšínský, Točík, Rosenberg:
R-epimer 27 underwent an oxidative decomposition. After acetylation of
free 1- and 3-hydroxyls of 30 to acetyl derivative 31, it was necessary to
oxidise the 3-O-benzyl group of compound 31 by RuO2 to the benzoyl
group, which was capable of providing the desired derivative 32. We en-
countered problems when monitoring the oxidation. On TLC analysis,
compounds 31 and 32 were not distinguishable, and information about the
course of reaction could only be obtained from HPLC or NMR verification.
SCHEME 4
The path to the phosphonate synthon 32 for nucleosidation in L-erythro series
The quantification of the conversion of 31 to 32 by UV detection was dif-
ficult. Because of the very different extinction coefficients of benzyl and
benzoyl derivatives, 31 and 32, the reaction mixture looked as if it con-
tained an apparent excess of compound 32 at all times. Interestingly, there
were no by-products observed with UV absorption and only starting com-
pound 31 and product 32 were identified in the reaction mixture. Thus,
compounds 31 and 32 were obtained in a mixture (27:73 by NMR). The
prolonged time of oxidation for an additional two days neither influenced
a ratio of 31 and 32 nor decreased the total amount of both compounds.
The nucleosidation reaction (Scheme 5) performed with the mixture of
the 2-O-benzoyl 32 and 2-O-benzyl 31 derivatives and the silylated uracil
surprisingly provided the 3-N-isomer 33a exclusively, however, the use of
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Tetrofuranose Nucleoside Phosphonic Acids
509
silylated thymine afforded the desired 1-N-isomer 33b though in a low
yield of 20%. The compounds 33a (the sole product obtained from the
nucleosidation reaction) was subsequently deprotected to yield phosphonic
acid 34 in 82% yield. The mechanism of exclusive formation of the 3-N-de-
rivative in case of only uracil and not thymine nucleobase remained un-
clear. We also examined the use of trimethylsilyl triflate as an alternative
Lewis acid in the nucleosidation reaction with silylated uracil, but in this
case, an unresolvable mixture of various products was obtained.
SCHEME 5
Preparation of nucleoside phosphonate with L-erythro configuration
Preparation of L-Threofuranose Nucleoside Phosphonates
To prepare the L-threofuranosylphosphonate 48 (Scheme 7) synthon, we
examined two synthetic pathways. The first pathway (Scheme 6) utilised
1,2-O-isopropylidene-L-xylose (35), which was easily accessible from L-
SCHEME 6
Sugar protections in the search for active species for phosphonylations and subsequent
nucleosidations in L-threo series
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Poláková, Buděšínský, Točík, Rosenberg:
xylose upon isopropylidenation, followed by a selective hydrolysis of the
3,5-O-isopropylidene group of 1,2:3,5-di-O-isopropylidene-L-xylose in 60%
aqueous acetic acid36. We further protected the 5-hydroxyl of 35 with an
allyloxycarbonyl group. The subsequent acylation of the formed compound
36 with benzoyl cyanide and methoxycarbonyltetrazole afforded the
3-O-benzoyl and 3-O-methoxycarbonyl derivatives 37 and 38, respectively.
The treatment of 37 and 38 with tetrakistriphenylphosphine palladium in
dichloromethane in the presence of tri-n-butylammonium formate to re-
move the allyloxycarbonyl moiety49 afforded in both cases almost quantita-
tive yield of the 5-O-acyl derivatives 40 and 41 instead of the desired
3-O-derivatives 39. In both cases, the complete 3→5 migration of benzoyl
and methoxycarbonyl groups occurred.
SCHEME 7
Pathway to the phosphonate precursor 48 for nucleosidations in L-threo series
An alternative route (Scheme 7) was contemplated, starting with direct
benzoylation of the 5-hydroxy group of compound 35 to provide derivative
40, which was easier than the one depicted in Scheme 6. The subsequent
benzylation of the 3-hydroxy group afforded compound 42, and the re-
moval of the 5-O-benzoyl group under basic conditions provided product
43. After Moffatt oxidation to the aldehyde 44 and the addition of diethyl
phosphite, only product 45 with an S-configuration on the C5 atom
formed. Oxidative treatment with HIO4 followed by acetylation afforded
47. The benzyl derivative was further oxidised with RuO2 to the final ben-
zoyl compound, 48, in a moderate yield. The separation of the benzyl 47
and benzoyl 48 derivatives was successfully performed. The nucleosidation
reaction (Scheme 8) proceeded in good yield, providing nucleoside phos-
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Tetrofuranose Nucleoside Phosphonic Acids
511
phonates 49a–49c, which were deprotected to yield free phosphonic acids
50a–50c.
SCHEME 8
Preparation of nucleoside phosphonates with L-threo configuration
Conformation of the Furanose Ring in 5, 9a, 9b, 20a–20c
It was realised that the compounds prepared in this work possessed specific
structural features, such as the “shortened” carbon backbone in the sugar
portion and the attachment of the phosphonate moiety directly to the
tetrofuranose ring. These properties were evaluated by determining their
prevailing conformational forms with an NMR study. Compounds 5, 9a,
9b, 20a–20c were selected for the measurement and computation, and they
represented several related configurational types differing in the orientation
of the nucleobase and adjacent hydroxy group (Fig. 4).
FIG. 4
The NMR-evaluated β-D-erythrose (5, 9a, 9b) and α-D-threose (20a–20c) nucleotide analogues
3
The J(H,H)s and PSEUROT program50, based on the concept of pseudo-
rotation51, were used to obtain information on conformation of furanose
ring. The NMR conformational studies showed that when nucleotides were
in solution, two preferred conformers (N- and S-type) of the furanose ring
were present in fast equilibrium and could be fully described by five param-
eters (phase angles P(N), P(S), puckering amplitudes (φm(N), φm(S)), and the
molar concentration of one conformer X(N) or X(S)). As there are only
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Poláková, Buděšínský, Točík, Rosenberg:
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Tetrofuranose Nucleoside Phosphonic Acids
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3
three J(H,H)s in the furanose ring in this case, the PSEUROT calculation
was started by assuming φm(N) = φm(S), and the values were changed in 2°
steps from 30 to 46°. The P(N), P(S), and X(N) were calculated to obtain a
3
best fit between the calculated and observed J(H,H) values. Table I shows
3
the observed J(H,H) values and the ranges of calculated combinations of
P(N), P(S), and X(N) that give an excellent agreement between the calcu-
3
lated and observed J(H,H)s (rms ≤ 0.001).
FIG. 5
Graphical presentation of the geometry optimisation of the N- and S-type conformers of com-
pounds 5, 9a, 9b and 20a–20c. The individual compounds are distinguished by colour: black,
5 and 20a; blue, 9a and 20b; red, 9b and 20c. The length of the lines indicates the relative
populations of conformers from PSEUROT calculations
FIG. 6
The energy-minimised conformations of thymine derivatives 9b and 20b with 8b-D-erythro and
α-D-threo configuration, respectively
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Poláková, Buděšínský, Točík, Rosenberg:
The results showed that all calculated conformers had a maximum pucker
Φm in the range typical for nucleosides, and all compounds indicated that
the S-type conformer was preferred (more significantly in α-D-threo-com-
pounds).
To verify if the calculated conformers corresponded to the energy min-
ima, molecular modeling was used. For each compound, we constructed
the model of its N- and S-type conformer using previously calculated
(PSEUROT) geometry parameters with a maximum pucker of φm = 38°. Each
molecule was allowed to “relax” without any restraints to optimize the ge-
ometry by energy minimisation (using the AMBER version of molecular me-
chanics in the HYPERCHEM 8.0 program). The calculated geometry data
(P(N), φm(N), P(S), φm(S)) were further used as the fixed input data in the
PSEUROT program for the estimation of the conformer populations ratio
(X(N):X(S) as the only variable. The results were summarised in Table I (in
red) and presented using the pseudorotation wheel in Fig. 5. It was con-
2
2
cluded that the S-conformer (type E to T1) was significantly preferred in
all six compounds and it existed in aqueous solution in a fast equilibrium
with a small amount of the N-conformer. The energy-minimised, preferred
S-type conformers of thymine derivatives 9b and 20b are shown in Fig. 6.
Inhibition of Thymidine Phosphorylase
Free phosphonic acids 9a, 9b, 20a–20c, 34, and 50a–50c were tested as po-
tential bi-substrate inhibitors of recombinant thymidine phosphorylase
(
dThdKm = 60 µM) (for methodology, see Experimental). It was found that
none of these analogues exerted any significant inhibition activity, except
for compound 34, which acted as a competitive inhibitor of thymidine
phosphorylase with a Ki value of 4 µM; compound 34 is a 3-N substituted
uracil derivative. Synthesis of the 1-N uracil derivative was not successfully
resolved to check and compare the inhibitory activity of both compounds.
CONCLUSION
The presented work described the synthesis of tetrofuranose nucleoside
phosphonic acids, the new isopolar phosphonate analogues of nucleoside
5′-phosphates. These analogues are distinguished for direct attachment of
the phosphoryl group to the C4 atom of the tetrofuranose ring. The key
synthons, erythro- and threo-configured tetrofuranosyl phosphonates in
the D- and L-series, were synthesised from pentofuranosyl 5′-hydroxy-
phosphonates through oxidative cleavage of the C1-C2 bond. Four such
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Tetrofuranose Nucleoside Phosphonic Acids
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synthons were prepared and found to yield desired compounds in the
nucleosidation reaction with silylated pyrimidine nucleobases. The course
of the reaction for particular tetrofuranose phosphonate synthons and
nucleobases was found to be far from uniform. Nevertheless, we were able
to prepare the representative compounds from all four groups, defined
by the variants of the tetrofuranosyl ring. NMR conformational studies
with a series of selected compounds, employing molecular modelling,
showed that with nucleotides in solution, the two preferred conformers
(N- and S-type) of the furanose ring were present in a fast equilibrium. All
calculated conformers had a maximum pucker Φm in a range typical for
nucleosides. In all compounds, the S-type conformer significantly prevailed
(especially in α-D-threo-compounds).
Free nucleoside phosphonic acids were subjected to screening for inhibi-
tion of human thymidine phosphorylase. Of the group, (4S)-[1-deoxy-1-
(uracil-3-yl)-β-L-erythrofuranos-4-yl]phosphonic acid was found to be com-
petitive inhibitor of the enzyme with a Ki value of 4 µM. Another com-
pound from the prepared series was found to inhibit human cytosolic and
mitochondrial pyrimidine specific 5′-nucleotidases but that recent data will
be published separately in a new context. The synthesis of diphosphoryl
derivatives of tetrose nucleoside phosphonic acids as NTP analogues and
a study with viral polymerases are underway.
EXPERIMENTAL
General
The solvents were evaporated at 30 °C in vacuo using a rotatory evaporator, and the prod-
ucts were dried over phosphorus pentoxide at 40–50 °C and 13 Pa. The course of the reac-
tions was checked by TLC on silica gel UV 254 foils (Merck), whereby the products were
detected by UV monitoring upon spraying with 1% ethanolic solution of 4-(4-nitrobenzyl)-
pyridine followed by heating and treating with gaseous ammonia (blue colour of diesters of
phosphonic acids), and by spraying with 10% aqueous sulfuric acid followed by heating
(sugar derivatives). For flash column chromatography, silica gel 40–60 µm (Fluka) was used.
The TLC and the preparative silica gel chromatography were carried out in the following
solvent systems (v/v): chloroform–ethanol 19:1 (C1), chloroform–ethanol 9:1 (C2), ethyl
acetate–acetone–ethanol–water 4:1:1:1 (H1), ethyl acetate–acetone–ethanol–water 6:1:1:1
(H3), 2-propanol–conc. aq. ammonia–water 7:1:2 (I), ethyl acetate–toluene 1:1 (T1) and
ethyl acetate–toluene 1:5 (T2). Analytical HPLC was performed on an LC 5000 liquid
chromatograph (INGOS, Czech Republic) with
a Luna C18 5 µm (4.6 × 150 mm;
Phenomenex) reversed phase column using a linear gradient of methanol in 0.1
M
triethylammonium acetate (TEAA) buffer. Preparative reversed-phase chromatography was
carried out on a spherical octadecyl silica gel column (25 × 250 mm, 20 to 40 µm), com-
pounds were eluted with a linear gradient of methanol in water at 10 ml min–1. Mass spec-
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Poláková, Buděšínský, Točík, Rosenberg:
tra (m/z), as well as HR-FAB MS, were recorded on a ZAB-EQ (VG Analytical) instrument
using FAB in both the positive and negative modes (ionisation by Xe, accelerating voltage
8 kV) with thioglycerol–glycerol (3:1) and 2-hydroxyethyldisulfide as matrices.
The 1H and 13C NMR spectra were measured on a Varian Unity 500 instrument (1H at
500 MHz, 13C at 125.7 MHz) or on a Bruker Avance 600 spectrometer (1H at 600 MHz,
13C at 150.9 MHz) in DMSO-d6 (referenced to the solvent signals δH 2.50 and δC 39.7),
CDCl3 (referenced to TMS), and D2O (referenced to DSS) at 20 °C. Proton signals in the
1H NMR spectra were assigned on the basis of chemical shifts, observed multiplicities, and
homonuclear 2D-COSY experiments. The exchange of hydroxyl protons for deuterium was
carried out using several drops of tetradeuterioacetic acid. Assignments of signals in the
13C NMR spectra were accomplished using J-modulated spectra (APT), and in some cases,
confirmed by 2D-1H,13C-HSQC and 2D-1H,13C-HBMC spectra.
Optical rotations were measured on an Autopol IV (Rudolph) instrument at 20 °C and
589 nm.
The thymidine phosphorylase activity was measured using an Infinite F500 (Tecan)
reader.
Synthetic Methods
Method A: Oxidative cleavage of pentofuranose 5′-hydroxyphosphonates and acetylation of
formed terofuranosylphosphonates. Periodic acid dihydrate (340 mg, 1.5 mmol) was added to a
solution of the respective pentofuranose 5′-hydroxyphosphonate (14, 28, 45; 1 mmol) in
50% aqueous dioxane (7 ml) and the reaction mixture was set aside at 50 °C in the dark for
2 days (TLC in C1). The solution was treated with Dowex 1x2 in acetate form (4 ml) under
stirring for 10 min to remove periodate and iodate anions. The resin was filtered off and
washed with methanol, and the combined filtrates were evaporated. The residue was
co-distilled several times with water to remove acetic acid, and finally treated with 0.1
M
TEAB (10 ml) for 20 min. The aqueous solution was evaporated to dryness, the crude
tetrofuranosylphosphonate (16, 30, 46) was co-distilled with pyridine, and treated with ace-
tic anhydride (0.42 ml, 4.4 mmol) and DMAP (7 mg, 0.06 mmol) in pyridine (4 ml) for
30 min (TLC in C1). The reaction mixture was quenched by the addition of water (0.4 ml)
at 0 °C, the solvent was evaporated in vacuo, and the acetyl derivative (17a, 17b, 31a,
31b, 47a, 47b) was purified on silica gel by elution with a linear gradient of ethyl acetate in
toluene.
Method B: Nucleosidation reaction. The nucleobase (4-N-benzoylcytosine, thymine, uracil; 4
mmol) in hexamethyldisilazane (HMDS; 12 ml, 56 mmol) was refluxed in the presence of a
catalytical amount of ammonium sulfate under stirring and exclusion of moisture overnight.
Volatile components were removed under reduced pressure and the resulting oil was
co-distilled twice with xylene and twice with acetonitrile to remove traces of HMDS. A solu-
tion of the sugar phosphonate (6, 17, 32, 48; 440 mg, 1 mmol) in acetonitrile (2 ml) was
then added via septum under argon to the silylated nucleobase followed by the addition of
tin tetrachloride (0.24 ml, 2 mmol) at –10 °C. The mixture was stored at r.t. for 12 h (TLC in
C1, H1). Into the reaction mixture, 2 M TEAB (2 ml) was added. The reaction was diluted
with chloroform and filtered through Celite, washed with chloroform, and the solvents were
removed under reduced pressure. The residue was purified on silica gel by elution with a lin-
ear gradient of ethanol in chloroform.
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Tetrofuranose Nucleoside Phosphonic Acids
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Method C: Oxidation of the benzyl group to the benzoyl group. Sodium periodate (900 mg, 4.2
mmol) and ruthenium(IV) oxide (3 mg, 0.02 mmol) was added at r.t. to the mixture of a
given phosphonate (31, 47; 1 mmol) and tetrachloromethane–acetonitrile– water (2:2:3; 35
ml). The reaction was set aside in the dark for 3 days (monitored by HPLC). The solution
was diluted with ethyl acetate, extracted twice with water, and the organic layers were dried,
evaporated, and finally purified on a silica gel column by a linear gradient of ethyl acetate
in toluene.
Method D: Removal of the protecting groups. Bromotrimethylsilane (0.66 ml, 5 mmol) was
added to a solution of the respective nucleotide (7a, 7b, 8a, 8b, 19a–19c, 33a, 33b,
49a–49c; 1 mmol) in acetonitrile (5 ml), the mixture was stored at r.t. for 48 h (TLC in C2,
H1 and I), and then concentrated in vacuo. Concentrated aqeuous ammonia (20 ml) was
added and the reaction was stored overnight. The solution was concentrated and the residue
was co-distilled several times with water. The phosphonic acid was obtained by purification
using chromatography on DEAE-Sephadex A-25 (HCO3)–. The compounds were eluted with
a linear gradient of 0 to 0.3 M TEAB. The fractions were pooled and evaporated and the resi-
due was co-distilled several times with methanol and then applied onto a C18 column (25 ×
300 mm). The products were eluted by a linear gradient of methanol in water (0 to 5%),
transformed into sodium salts on a column of Dowex 50 (Na+), and finally freeze-dried from
water.
Diethyl (4R)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(uracil-1-yl)-β-D-erythrofuranos-4-yl]-
phosphonate (7a) and Diethyl (4R)-[2-O-Acetyl-3-O-benzoyl-1-deoxy-1-(uracil-1-yl)-
β-D-erythrofuranos-4-yl]phosphonate (7b)
A mixture of phosphonates 7a, 7b was obtained from silylated uracil (630 mg, 5.6 mmol)
and the phosphonate 6 (410 mg, 0.9 mmol) according to the Method B. Yield 155 mg (17%,
white lyophilizate) of 7 (a:b = 63:37). HR-FAB calculated for C21H26N2O10P (M + H)+:
497.1325; found 497.1308. IR (CHCl3, cm–1): U: ν (NH-free) 3390w; ν (NH-bonded) 3171w, br;
ν (C=O) 1723s, 1699vs; ν (C=C) 1638w; ν (ring) 1460m, sh, 1391m, 1262s. –OAc: ν (C=O)
1752s; ν (C–O) 1229s, 1036s; γ (CCOO) 595w; δs (CH3) 1376m. OBz: β (C=O) 712m; ν (C–O)
1277s, sh, 964m; ν (=CH) 3065w, 3028m; ν (ring) 1603w, 1586w, 1493vw, 1445w, sh,
1317w, 1178w, 1068m, 686w. PO(OEt)2: ν (P=O) 1249s, νas (POCC) 1036s, 978m; δ (POC)
562m; βs (CH2) 1479w, sh; δas (CH3) 1454m; δas (CH3) 1163w, 1097m.
7a: 1H NMR (500 MHz, CDCl3): 8.385 bd, 1 H, J(NH,5) = 2.3 (NH); 8.21 dd, 1 H, J(6,5) =
8.3 (H-6); 7.97 m, 2 H, 7.59 m, 1 H and 7.45 m, 2 H (C6H5); 6.60 dd, 1 H, J(1′,2′) = 7.8 and
J(1′,3′) = 1.5 (H-1′); 5.88 dd, 1 H, J(5,6) = 8.3 and J(5,NH) = 2.3 (H-5); 5.85 ddd, 1 H, J(3′,2′) =
5.0, J(3′,4′) = 1.7 and J(3′,1′) = 1.5 (H-3′); 5.76 dd, 1 H, J(2′,1′) = 7.8 and J(2′,3′) = 5.0 (H-2′);
4.43 dd, 1 H, J(4′,3′) = 1.7 and J(4′,P) = 5.5 (H-4′); 4.31–4.21 m, 4 H and 1.42 t, 3 H, J = 7.0
and 1.415 t, 3 H, J = 7.0 (P(OEt)2); 2.13 s, 3 H (OAc).
7b: 1H NMR (500 MHz, CDCl3): 8.38 bd, 1 H, J(NH,5) = 2.3 (NH); 8.215 dd, 1 H, J(6,5) =
8.3 (H-6); 8.09 m, 2 H, 7.51 m, 1 H and 7.64 m, 2 H (C6H5); 6.54 dd, 1 H, J(1′,2′) = 8.1 and
J(1′,3′) = 1.6 (H-1′); 5.88 dd, 1 H, J(5,6) = 8.3 and J(5,NH) = 2.3 (H-5); 5.68 dd, 1 H, J(2′,1′) =
8.1 and J(2′,3′) = 5.1 (H-2′); 5.95 ddd, 1 H, J(3′,2′) = 5.1, J(3′,4′) = 1.4 and J(3′,1′) = 1.6 (H-3′);
4.52 dd, 1 H, J(4′,3′) = 1.4 and J(4′,P) = 5.75 (H-4′); 4.31–4.21 m, 4 H and 1.42 t, 3 H, J = 7.0
and 1.415 t, 3 H, J = 7.0 (P(OEt)2); 2.01 s, 3 H (OAc).
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Diethyl (4R)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(thymin-1-yl)-β-D-erythrofuranos-4-yl]-
phosphonate (8a) and Diethyl (4R)-[2-O-Acetyl-3-O-benzoyl-1-deoxy-1-(thymin-1-yl)-
β-D-erythrofuranos-4-yl]phosphonate (8b)
Phosphonates 8a and 8b were obtained from silylated thymine (1.1 g, 8.6 mmol) and
phosphonate 6 (950 mg, 2.1 mmol) according to the Method B. Yield 240 mg (22%, white
lyophilizate) of 8 (a:b = 74:26). HR-FAB calculated for C22H28N2O10P (M + H)+: 511.1482;
found 511.1473. IR (CHCl3, cm–1): T: ν (C=O) 1717s, 1696vs; ν (C=C) 1658w, sh; ν (ring)
1466w, 1435w, sh; δs (CH3) 1381w, sh. OAc: ν (C=O) 1752m; ν (C–O) 1249s, 1027s; δs (CH3)
1375w. OBz: ν (C=O) 1731s, sh; ν (C–O) 1261s; β (C=O) 711m; ν (ring) 1603w, 1586vw,
1493vw, 1453w, 1317w, 1178w, 1121m, 1070m, sh, 1027s, 1002w, sh, 686w. PO(OEt)2:
νas (POCC) 1038s, 1027s, 979w; δ (POC) 559w; δas (CH3) 1444w, sh; γs (CH2) 1391w; δas (CH3)
1164w, 1097m.
8a: 1H NMR (600 MHz, CDCl3): 8.00 q, 1 H, J(6,CH3) = 1.2 (H-6); 7.98 m, 2 H, 7.595 m,
1 H and 7.45 m, 2 H (OBz); 6.59 dd, 1 H, J(1′,2′) = 7.8 and J(1′,P) = 1.5 (H-1′); 5.86 ddd, 1 H,
J(3′,2′) = 5.1, J(3′,4′) = 1.7 and J(3′,P) = 7.0 (H-3′); 5.76 dd, 1 H, J(2′,1′) = 7.8 and J(2′,3′) = 5.1
(H-2′); 4.43 dd, 1 H, J(4′,3′) = 1.7 and J(4′,P) = 5.5 (H-4′); 4.25 m, 4 H, 1.42 t, 3 H and 1.38 t,
3 H (P(OEt)2); 2.12 s, 3 H (OAc); 1.98 d, 3 H, J(CH3,6) = 1.2 (CH3-5). 13C NMR (150.9 MHz,
CDCl3): 169.29 and 20.64 (OAc); 164.93, 133.86, 129.87(2), 128.63(2) and 128.31 (OBz);
162.94 (C-4); 150.50 (C-2); 135.56 (C-6); 112.42 (C-5); 85.56 d, J(C,P) = 2.9 (C-1′); 77.98 d,
J(C,P) = 168.1 (C-4′); 72.87 (C-2′); 70.91 d, J(C,P) = 10.1 (C-3′); 64.07 d, J(C,P) = 6.6, 63.51 d,
J(C,P) = 7.2, 16.47 d, J(C,P) = 5.7 and 16.46 d, J(C,P) = 5.7 (P(OEt)2).
8b: 1H NMR (600 MHz, CDCl3): 8.02 q, 1 H, J(6,CH3) = 1.2 (H-6); 7.98 m, 2 H, 7.595 m,
1 H and 7.45 m, 2 H (OBz); 6.54 dd, 1 H, J(1′,2′) = 8.0 and J(1′,P) = 1.5 (H-1′); 5.68 dd, 1 H,
J(2′,1′) = 8.0 and J(2′,3′) = 5.1 (H-2′); 5.95 ddd, 1 H, J(3′,2′) = 5.1, J(3′,4′) = 1.5 and J(3′,P) =
7.0 (H-3′); 4.52 dd, 1 H, J(4′,3′) = 1.5 and J(4′,P) = 5.7 (H-4′); 4.29 m, 4 H, 1.425 t, 3 H and
1.37 t, 3 H (P(OEt)2); 2.12 s, 3 H (OAc); 1.987 d, 3 H, J(CH3,6) = 1.2 (CH3-5).
(4R)-[1-Deoxy-1-(uracil-1-yl)-β-D-erythrofuranos-4-yl]phosphonic Acid (9a)
Phosphonic acid 9a was obtained from phosphonates 7a, 7b (60 mg, 0.12 mmol) according
to the Method D. Yield 28 mg (69%, white lyophilizate) of 9a, [α]20 –8.6. HR-FAB calculated
for C8H10N2O8P (M + H)+: 293.0175; found 293.0178. IR (KBr, cm–1): ν (OH, NH) 3423s, br,
3255m, br, sh, 2807w, br, ν (C–OH) 1117s, 1085s, ν (PO3)2– 972m, δ (PO3)2– 577m.
U: ν (C=O) 1697vs; ν (ring) 1637m, sh, 1466w, 1396w, 1273m; γ (=CH) 821w, 769w. 1H NMR
(600 MHz, D2O): 8.39 d, 1 H, J(6,5) = 8.1 (H-6); 6.04 dd, 1 H, J(1′,2′) = 7.0 and J(1′,P) = 1.2
(H-1′); 5.93 d, 1 H, J(5,6) = 8.1 (H-5); 4.42 bt, 1 H, J(2′,1′) = 7.0 and J(2′,3′) = 4.9 (H-2′);
4.39 ddd, 1 H, J(3′,2′) = 4.9, J(3′,4′) = 2.2 and J(3′,P) = 6.6 (H-3′); 4.05 dd, 1 H, J(4′,3′) = 2.2
and J(4′,P) = 5.6 (H-4′). 13C NMR (150.9 MHz, D2O): 167.04 (C-4); 152.87 (C-2); 143.50
(C-6); 103.19 (C-5); 87.73 d, J(C,P) = 3.2 (C-1′); 84.65 d, J(C,P) = 147.6 (C-4′); 75.47 d,
J(C,P) = 2.3 (C-2′); 72.27 d, J(C,P) = 5.7 (C-3′).
(4R)-[1-Deoxy-1-(thymin-1-yl)-β-D-erythrofuranos-4-yl]phosphonic Acid (9b)
Title phosphonic acid 9b was obtained from phosphonates 8a, 8b (120 mg, 0.23 mmol) ac-
cording to the Method D. Yield 65 mg (80 %, white lyophilizate) of 9b, [α]20 –12.8. HR-FAB
calculated for C9H12N2O8P (M + H)+: 307.0331; found 307.0336. IR (KBr, cm–1) ν (C–OH)
1122w, br, 1077w, br; ν (OH, NH) 3436vs, br; νas (PO3)2– 971w, br, δs (PO3)2– 597w.
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T: ν (C=O) 1700w, br; ν (ring) 1636m, br, 1476w, br, 1435w, br, sh, 1393w, br, 1273w, br.
1H NMR (600 MHz, D2O): 8.09 q, 1 H, J(6,CH3) = 1.2 (H-6); 6.04 dd, 1 H, J(1′,2′) = 6.8 and
J(1′,P) = 1.1 (H-1′); 4.41 ddd, 1 H, J(3′,2′) = 5.1, J(3′,4′) = 2.6 and J(3′,P) = 7.5 (H-3′); 4.38 dd,
1 H, J(2′,1′) = 6.8 and J(2′,3′) = 5.1 (H-2′); 4.09 dd, 1 H, J(4′,3′) = 2.6 and J(4′,P) = 5.2 (H-4′);
1.92 d, 3 H, J(CH3,6) = 1.2 (CH3-5). 13C NMR (150.9 MHz, D2O): 169.36 (C-4); 155.02 (C-2);
140.59 (C-6); 114.59 (C-5); 89.73 d, J(C,P) = 4.1 (C-1′); 85.40 d, J(C,P) = 152.4 (C-4′);
77.01 d, J(C,P) = 3.0 (C-2′); 73.82 d, J(C,P) = 5.6 (C-3′); 14.38 (CH3-5).
Diethyl (5R)-(3-O-Benzoyl-1,2-O-isopropylidene-α-D-xylofuranos-5-C-yl)-
phosphonate (14) and Diethyl (5R)-(5-O-Benzoyl-1,2-O-isopropylidene-
α-D-xylofuranos-5-C-yl)phosphonate (15)
1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (10; 31.9 g, 122 mmol) was treated with ben-
zoyl chloride (17 ml, 146 mmol) and triethylamine (34.2 ml, 244 mmol) in dichloro-
methane (146 ml) at 0 °C under exclusion of moisture (TLC in T1) overnight. The reaction
was quenched by addition of methanol (12 ml) and the solvent was evaporated in vacuo.
The residue was dissolved in chloroform and the organic layer was washed with water sev-
eral times. After evaporation of the solvent, the crude benzoyl derivative 11 was treated with
60% aqueous acetic acid (1500 ml) at r.t. for 3 days. The acid was evaporated in vacuo, the
residue taken into chloroform, and the organic layer was washed with saturated aqueous so-
lution of NaCl. The organic layer was washed with saturated aqueous solution of NaHCO3,
dried over anhydrous Na2SO4, and evaporated. Yield 29.4 g (74%; yellowish syrup) of
3-O-benzoyl-1,2-O-isopropylidene-α-D-glucofuranose (12). The saturated aqueous solution of
sodium periodate (23.5 g, 108 mmol) was then added at 0 °C to a stirred solution of this
compound (29.4 g, 90.5 mmol) in 70% aqueous acetone (905 ml) (TLC in C1). After 1 h, the
crystals of iodate were filtered off, the filter cake was washed with 70% aqueous acetone,
and the solvents were evaporated. The residue was dissolved in acetone, filtered once more,
evaporated, and co-distilled repeatably with toluene. To a solution of the formed aldehyde
in CH2Cl2 (90.5 ml), diethyl phosphite (23.5 ml, 181 mmol) and triethylamine (63.3 ml,
452 mmol) were added at 0 °C and the mixture was stirred overnight (TLC in C2). The reac-
tion mixture was then diluted with chloroform, filtered through Celite, and the filtrate was
extracted with water. The organic layer was dried over anhydrous Na2SO4. Chromatography
of the crude product on silica gel (elution with a linear gradient of 0–10% ethanol in chloro-
form) afforded a mixture of both regioisomeric phosphonates 14 and 15 (67:33). Yield
21.1 g (56%, colourless sirup). HR-FAB calculated for C19H28O9P (M + H)+: 431.1471; found
431.1453. IR (CHCl3, cm–1): ν (OH) 3573w, br, 3441w, br, 3251w, br. PO(OEt)2: ν (P=O)
1250s, sh; νas (POCC) 1050vs, 1026vs; ν (C–C) 974s, 963s; δ (POC) 554m, 543m; βs (CH2)
1478w; δas (CH3) 1453m; γs (CH2) 1395m, sh; δas (CH3) 1164s, 1096vs; νas (CH3) 2996s.
OBz: ν (C=O) 1726s; ν (C–O) 1269vs; β (C=O) 712s; ν (=CH) 3093w, 3065w, 3028m; ν (ring)
1602w, 1586w, 1493w, 1445w, 1316m, 1178s, 1112s, 1072vs, 1002m, sh, 686w, 617vs.
CMe2: δs (CH3) 1386m, 1377m; νs (CMe2) 861m; γs (CMe2) 521w.
14: 1H NMR (500 MHz, DMSO): 7.98 m, 2 H, 7.69 m, 1 H and 7.56 m, 2 H (C6H5); 5.98 d,
1 H, J(1,2) = 3.8 (H-1); 5.98 dd, 1 H, J(OH,5) = 7.4 and J(OH,P) = 5.3 (H-5); 5.31 bd, 1 H,
J(3,2) < 0.5 and J(3,4) = 2.8 (H-3); 4.66 bdd, 1 H, J(2,1) = 3.8, J(2,P) = 2.0 and J(2,3) < 0.5
(H-2); 4.40 ddd, 1 H, J(4,3) = 2.8, J(4,5) = 9.8 and J(4,P) = 8.9 (H-4); 4.06 m, 4 H, 1.24 t, 3 H,
J = 7.1 and 1.23 t, 3 H, J = 7.1 (P(OEt)2); 4.00 ddd, 1 H, J(5,4) = 9.8, J(5,OH) = 7.4 and
J(5,P) = 4.3 (H-5); 1.46 s, 3 H and 1.27 s, 3 H (1,2-OiPr). 13C NMR (125.8 MHz, DMSO):
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Poláková, Buděšínský, Točík, Rosenberg:
164.96, 133.77, 129.57(2), 129.55 and 128.93(2) (OBz); 111.47, 26.58 and 26.19 (1,2-OiPr);
105.11 (C-1); 81.92 (C-2); 77.87 d, J(C,P) = 3.5 (C-4); 76.33 d, J(C,P) = 10.4 (C-3); 63.99 d,
J(C,P) = 164.9 (C-5); 62.18 d, J(C,P) = 6.8, 61.95 d, J(C,P) = 6.7, 16.52 d, J(C,P) = 5.4 and
16.50 d, J(C,P) = 5.3 (P(OEt)2).
15: 1H NMR (500 MHz, DMSO): 7.98 m, 2 H, 7.69 m, 1 H and 7.55 m, 2 H (C6H5); 5.91 d,
1 H, J(1,2) = 3.6 (H-1); 5.49 dd, 1 H, J(5,4) = 10.0 and J(5,P) = 4.1 (H-5); 4.49 ddd, 1 H,
J(4,3) = 2.9, J(4,5) = 10.0 and J(4,P) = 8.5 (H-4); 4.42 bdd, 1 H, J(2,1) = 3.6, J(2,P) = 2.2 and
J(2,3) ≤ 0.5 (H-2); 4.06 m, 4 H, 1.19 t, 3 H, J = 7.2 and 1.16 t, 3 H, J = 7.2 (P(OEt)2); 4.04 bd,
1 H, J(3,2) ≤ 0.5 and J(3,4) = 2.9 (H-3); 1.43 s, 3 H and 1.26 s, 3 H (1,2-OiPr). 13C NMR
(125.8 MHz, DMSO): 163.76 d, J(C,P) = 2.0, 133.79, 129.54(2), 129.28 and 129.03(2) (OBz);
111.23, 26.91 and 26.31 (1,2-OiPr); 105.12 (C-1); 84.38 (C-2); 78.12 (C-4); 73.25 d, J(C,P) =
9.8 (C-3); 65.33 d, J(C,P) = 164.0 (C-5); 62.60(2) d, J(C,P) = 6.8, 16.37 d, J(C,P) = 5.2 and
16.32 d, J(C,P) = 5.5 (P(OEt)2).
Diethyl (4R)-(1,3-di-O-Acetyl-2-O-benzoyl-α-D-threofuranos-4-yl)phosphonate (17)
Phosphonate 17 was obtained from diethyl (5R)-(3-O-benzoyl-1,2-O-isopropylidene-α-D-xylo-
furanos-5-C-yl)phosphonate (14; 3.42 g, 8.0 mmol) according to the Method A. Yield 1.76 g
(49%, colourless sirup) of 17. HR-FAB calculated for C19H26O10P (M + H)+: 445.1264; found
445.1258. IR (CHCl3, cm–1): OBz: ν (C=O) 1730s; ν (C–O) 1266s, sh; β (C=O) 712s; ν (=CH)
3030m; ν (ring) 1603w, 1585w, 1493w, 1452w, 1317m, 1179m, 1297m, sh, 1100s, 686w.
OAc: ν (C=O) 1755vs; ν (C–O, P=O) 1257s, 1232vs, sh; γ (CCO) 602w; δs (CH3) 1370m.
PO(OEt)2: βs (CH2) 1479w; δas (CH3) 1444w; γs (CH2) 1393w; δas (CH3) 1164w, 1097s;
νas (POCC) 1046s, 1028vs, 963s; δ (POC) 574w. 1H NMR (500 MHz, CDCl3): 8.08 m, 2 H,
7.59 m, 1 H and 7.46 m, 2 H (OBz); 6.40 q, J(1,2) = 0.65, J(1,3) = 0.65 and J(1,P) = 0.7 (H-1);
5.72 dddd, J(3,2) = 1.6, J(3,4) = 5.8, J(3,1) = 0.65 and J(3,P) = 13.3 (H-3); 5.395 dt, J(2,1) =
0.65, J(2,3) = 1.6 and J(2,4) = 0.55 (H-2); 4.46 ddd, 1 H, J(4,3) = 5.8, J(4,P) = 4.3 and J(4,2) =
0.55 (H-4); 4.23 m, 4 H, 1.34 t, 3 H, J = 7.2 and 1.335 t, 3 H, J = 7.2 (P(OEt)2); 2.15 s, 6 H
(2 × OAc). 13C NMR (125.8 MHz, CDCl3): 169.18, 168.75, 20.96 and 20.70 (2 × OAc);
165.18, 133.69, 130.03(2), 128.70 and 128.48(2) (OBz); 63.40(2) d, J(CH2,P) = 6.5, 16.42 d,
J(CH3,P) = 5.5 and 16.39 d, J(CH3,P) = 5.5 (P(OEt)2); 99.58 d, J(1,P) = 12.6 (C-1); 76.24 d,
J(C,P) = 4.0 (C-3); 81.48 d, J(C,P) = 8.2 (C-2); 78.14 d, J(C,P) = 175.5 (C-4).
Diethyl (4R)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(uracil-1-yl)-α-D-threofuranos-4-yl]-
phosphonate (19a)
The title phosphonate was obtained from silylated uracil (3.1 g, 28 mmol) and the
phosphonate 17 (2.5 g, 5.6 mmol) according to the Method B. Yield 1.3 g (48%, white
lyophilizate) of 19a, [α]20 +55.6. HR-FAB calculated for C21H26N2O10P (M + H)+: 497.1325;
found 497.1303. IR (CHCl3, cm–1): OAc: ν (C=O) 1754s; ν (C–O) 1261s, 1029s; γ (CCOO)
600w; δs (CH3) 1377m. OBz: ν (C=O) 1727vs; β (C=O) 712s; ν (C–O) 1261s, 965m, sh;
ν (=CH) 3065w, 3026m; ν (ring) 1603w, 1586w, 1493w, 1453m, 1317w, 1179w, 1111s,
1071m, sh, 686w, 547w. U: ν (NH-free) 3389w; ν (NH-bonded) 3170w, br; ν (C=O) 1697vs;
ν (C=C) 1636w; ν (ring) 1425w, sh. PO(OEt)2: βs (CH2) 1480w, sh; δas (CH3) 1445w, sh;
γs (CH2) 1391m; δs (CH3) 1371m; δas (CH3) 1064w, 1097m; νas (POCC) 1048s, 1029s, 978m;
δ (POC) 571m. 1H NMR (600 MHz, DMSO): 7.99 m, 2 H, 7.71 m, 1 H and 7.56 m, 2 H
(C6H5); 7.80 d, 1 H, J(6,5) = 8.1 (H-6); 6.16 d, 1 H, J(1′,2′) = 4.6 (H-1′); 5.81 t, 1 H, J(2′,1′) =
4.6 and J(2′,3′) = 4.6 (H-2′); 5.78 ddd, 1 H, J(3′,4′) = 6.6, J(3′,P) = 13.1 and J(3′,2′) = 4.6
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(H-3′); 5.72 d, 1 H, J(5,6) = 8.1 (H-5); 4.88 dd, 1 H, J(4′,3′) = 6.6 and J(4′,P) = 1.5 (H-4′);
4.11 m, 4 H, 1.264 t, 3 H, J = 7.0 and 1.262 t, 3 H, J = 7.0 (P(OEt)2); 2.09 s, 3 H (OAc).
13C NMR (150.9 MHz, DMSO): 169.39 and 20.76 (OAc); 165.16, 134.27, 129.78(2), 129.09(2)
and 128.64 (OBz); 163.38 (C-4); 150.70 (C-2); 142.59 (C-6); 102.41 (C-5); 90.84 d, J(C,P) =
6.9 (C-1′); 79.41 d, J(C,P) = 7.1 (C-2′); 76.84 d, J(C,P) = 169.9 (C-4′); 74.76 d, J(C,P) = 4.4
(C-3′); 63.06 d, J(C,P) = 6.6, 62.93 d, J(C,P) = 6.6, 16.49 d, J(C,P) = 5.3 and 16.47 d, J(C,P) =
5.3 (P(OEt)2).
Diethyl (4R)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(thymin-1-yl)-α-D-threofuranos-4-yl]-
phoshonate (19b)
Phosphonate 19b was obtained from silylated thymine (1.02 g, 8.1 mmol) and phosphonate
17 (900 mg, 2.02 mmol) according to the Method B. Yield 600 mg (58%, white lyophilizate)
of 19b, [α]20 +71.0. HR-FAB calculated for C22H28N2O10P (M + H)+: 511.1482; found
511.1463. IR (CHCl3, cm–1): T: ν (NH-free) 3389w; ν (NH-bonded) 3185vw, br; ν (C=O)
1722vs, 1697vs; ν (C=C) 1659m, sh; ν (ring) 1465w, 1435w; δs (CH3) 1386w. OAc: ν (C=O)
1756m; ν (C–O) 1229s, 1029s; γ (CCOO) 602w; δs (CH3) 1370m. OBz: ν (C–O) 1261s;
β (C=O) 712m; ν (ring) 1603w, 1586w, 1494w, sh, 1452m, 1317w, 1179w, 1112m,
1072m, sh, 1001w, sh, 686w. PO(OEt)2: ν (P=O) 1247s, sh; νas (POCC) 1047s, 1029s, 976m;
δ (POC) 572w; δas (CH3) 1444w, sh; γs (CH2) 1393w, sh; δas (CH3) 1164w, 1097m. 1H NMR
(600 MHz, CDCl3): 8.67 bs, 1 H (NH); 8.07 m, 2 H, 7.60 m, 1 H and 7.46 m, 2 H (C6H5);
7.13 q, 1 H, J(6,CH3) = 1.2 (H-6); 6.14 d, 1 H, J(1′,2′) = 4.8 (H-1′); 5.94 ddd, 1 H, J(3′,4′) =
5.4, J(3′,P) = 12.7 and J(3′,2′) = 3.9 (H-3′); 5.76 ddd, 1 H, J(2′,1′) = 4.8, J(2′,3′) = 3.9 and
J(2′,P) = 0.8 (H-2′); 4.69 dd, 1 H, J(4′,3′) = 5.4 and J(4′,P) = 3.6 (H-4′); ~4.25 m, 4 H, 1.37 t,
3 H, J = 7.1 and 1.36 t, 3 H, J = 7.0 (P(OEt)2); 2.15 s, 3 H (OAc); 1.96 d, 3 H, J(CH3,6) = 1.2
(CH3-5). 13C NMR (150.9 MHz, CDCl3): 169.20 and 20.74 (OAc); 165.69, 133.86, 130.08(2),
128.57(2) and 128.37 (OBz); 163.36 (C-4); 150.00 (C-2); 136.44 (C-6); 111.70 (C-5); 91.25 d,
J(C,P) = 5.3 (C-1′); 79.88 d, J(C,P) = 5.4 (C-2′); 78.25 d, J(C,P) = 171.4 (C-4′); 75.80 d, J(C,P) =
6.2 (C-3′); 63.52 d, J(C,P) = 6.8, 63.42 d, J(C,P) = 6.9 and 16.45 d, J(C,P) = 5.4 (P(OEt)2);
12.60 (CH3-5).
Diethyl (4R)-[3-O-Acetyl-2-O-benzoyl-1-(4-N-benzoylcytosin-1-yl)-1-deoxy-
α-D-threofuranos-4-yl]phosphonate (19c)
The title phosphonate was obtained from silylated 6-N-benzoylcytosine (970 mg, 4.5 mmol)
and phosphonate 17 (500 mg, 1.12 mmol) according to the Method D. Yield 320 mg (48%,
white lyophilizate) of 19c, [α]20 +48.1. HR-FAB calculated for C28H31N3O10P (M + H)+:
600.1747; found 600.1754. IR (CHCl3, cm–1): OAc: ν (C=O) 1754m; ν (C–O) 1238s, sh,
1028s; γ (CCOO) 600w; δs (CH3) 1368m. OBz: ν (C=O) 1728m; β (C=O) 712m; ν (C–O)
1259s; ν (ring) 1316m, 1299w, 1112m, 1002w, 829w. NHBz: ν (NH) 3406w; ν (amide I)
1705m; ν (amide II) 1554m. OBz and NHBz: ν (C–H) 3092vw, 3066vw; ν (ring) 1603m,
1583w, 1497w, 1452w, 1180w, 1071m, sh, 1028s, 686w, 616vw. PO(OEt)2: ν (P=O) 1248s;
ν (POC) 1069s, 1028s, 976w; δ (POC) 567w; δas (CH3) 1445w; γs (CH2) 1392w; δas (CH3)
1165w, 1097m. –C: ν (C=O) 1674s; ν (ring) 1629m, 1480vs, 1404w, 1287m, sh. 1H NMR
(600 MHz, CDCl3): 8.78 b, 1 H (NH); 8.10 m, 2 H, 7.60 m, 1 H and 7.46 m, 2 H (O-Bz);
7.90 m, 2 H, 7.63 m, 1 H and 7.53 m, 2 H (N-Bz); 7.74 bd, 1 H, J(6,5) ~ 7.0 (H-6); 7.63 bd,
1 H, J(5,6) ~ 7.0 (H-5); 6.11 dd, 1 H, J(1′,2′) = 3.4 and J(1′,P) = 0.8 (H-1′); 5.95 ddd, 1 H,
J(3′,4′) = 5.4, J(3′,P) = 12.3 and J(3′,2′) = 3.4 (H-3′); 5.89 bt, 1 H, J(2′,1′) = 3.4 and J(2′,3′) =
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3.4 (H-2′); 4.89 dd, 1 H, J(4′,3′) = 5.4 and J(4′,P) = 3.3 (H-4′); 4.23 m, 4 H, 1.35 t, 3H, J = 7.0
and 1.34 t, 3 H, J = 7.0 (P(OEt)2); 2.13 s, 3 H (OAc). 13C NMR (150.9 MHz, CDCl3): 169.17
and 20.76 (OAc); 165.65, 133.76, 130.15(2), 128.51(2) (OBz); 133.36, 129.10(2), 128.58 and
127.54(2) (NBz); 154.65 (C-2); 145.80 (C-6); 94.80 (C-1′); 80.65 d, J(C,P) = 6.0 (C-2′);
80.03 d, J(C,P) = 181.5 (C-4′); 75.90 d, J(C,P) = 5.1 (C-3′); 63.48 d, J(C,P) = 6.8, 63.39 d,
J(C,P) = 6.8 and 16.45 d, J(C,P) = 5.6 (P(OEt)2).
(4R)-[1-Deoxy-1-(uracil-1-yl)-α-D-threofuranos-4-yl]phosphonic Acid (20a)
Phosphonic acid 20a was obtained from phosphonate 19a (300 mg, 0.6 mmol) according to
the Method D. Yield 160 g (80%, white lyophilizate) of 20a, [α]20 –3.2. HR-FAB calculated
for C8H9N2O8Na3P (M + Na)+: 360.9790; found 360.9786. IR (KBr, cm–1): ν (OH, NH)
3424s, br, 3109m, br, 2802m, br; ν (C=O) 1696vs, br; ν (C=C) 1625m, sh; ν (ring) 1470m,
1439m, 1400w, 1272m; γ (=CH) 766w; ν (C–OH) 1077s, br, 1062s, sh; νas (PO3)2– 978m;
νs (PO3)2– 912w, br; δs (PO32–) 584m. 1H NMR (600 MHz, D2O): 7.82 d, 1 H, J(6,5) = 8.1
(H-6); 5.89 d, 1 H, J(1′,2′) = 1.7 (H-1′); 5.84 d, 1 H, J(5,6) = 8.1 (H-5); 4.49 ddd, 1 H, J(3′,4′) =
2.2, J(3′,P) = 6.5 and J(3′,2′) = 1.9 (H-3′); 4.41 dd, 1 H, J(4′,3′) = 2.2, J(4′,2′) ~ 0.6 and J(4′,P) =
5.6 (H-4′); 4.22 m, 1 H, J(2′,1′) = 1.7, J(2′,3′) = 1.9, J(2′,4′) ~ 0.6 and J(2′,P) ~ 0.5 (H-2′).
13C NMR (150.9 MHz, D2O): 169.48 (C-4); 154.24 (C-2); 145.21 (C-6); 103.44 (C-5); 96.03 d,
J(C,P) = 3.8 (C-1′); 89.42 d, J(C,P) = 149.1 (C-4′); 83.70 d, J(C,P) = 1.8 (C-2′); 78.75 d, J(C,P) =
7.1 (C′-3).
(4R)-[1-Deoxy-1-(thymin-1-yl)-α-D-threofuranos-4-yl]phosphonic Acid (20b)
The title phosphonic acid was obtained from phosphonate 19b (190 g, 0.37 mmol) accord-
ing to the Method D. Yield 100 mg (77%, white lyophilizate) of 20b, [α]20 +9.5. HR-FAB cal-
culated for C9H12N2O8Na2P (M + H)+: 353.0127; found 353.0135. IR (KBr, cm–1): ν (C–OH)
1116m, br, 1078m, br; νas (PO3)2– 980w; δs (PO3)2– 596m. T: ν (C=O) 1692m, br; ν (ring)
1643m, br, 1473w, 1437w, 1399w, 1274w; γ (=CH) 769vw; δs (CH3) 1374w. 1H NMR
(600 MHz, D2O): 7.64 q, 1 H, J(6,CH3) = 1.2 (H-6); 5.88 t, 1 H, J(1′,2′) = 1.1 and J(1′,P) = 1.1
(H-1′); 4.475 dt, 1 H, J(3′,P) = 5.75, J(3′,4′) = 1.6 and J(3′,2′) = 1.5 (H-3′); 4.40 ddd, 1 H,
J(4′,3′) = 1.6, J(4′,2′) ~ 0.7 and J(4′,P) = 6.0 (H-4′); 4.15 m, 1 H, J(2′,1′) = 1.1, J(2′,3′) = 1.5 and
J(2′,4′) ~ 0.7 (H-2′); 1.89 d, 3 H, J(CH3,6) = 1.2 (CH3-5). 13C NMR (150.9 MHz, D2O): 167.63
(C-4); 152.11 (C-2); 138.15 (C-6); 110.17 (C-5); 94.12 d, J(C,P) = 3.0 (C-1′); 88.52 d, J(C,P) =
145.6 (C-4′); 81.91 (C-2′); 76.85 d, J(C,P) = 8.0 (C-3′); 12.92 (CH3-5).
(4R)-[1-(Cytosin-1-yl)-1-deoxy-α-D-threofuranos-4-yl]phosphonic Acid (20c)
Phosphonic acid 20c was obtained from the phosphonate derivative 19c (150 mg,
0.25 mmol) according to the Method D. Yield 63 mg (75%, white lyophilizate) of 20c,
[α]20 +6.7. HR-FAB calculated for C8H11N3O7P (M + H)+: 292.0335; found 292.0322. IR (KBr,
cm–1): ν (C–OH) 1110m, br, 1079m, br; νas (PO32–) 979w; δs (PO32–) 584m, br. C: βs (NH2) +
ν (C=O) 1651s; ν (ring) 1605m, sh, 1530w, 1494w; ν (C-N) 1288w, br; γ (=CH) 787w.
1H NMR (600 MHz, D2O): 7.79 d, 1 H, J(6,5) = 7.6 (H-6); 6.03 d, 1 H, J(5,6) = 7.6 (H-5);
5.88 dd, 1 H, J(1′,2′) = 1.9 and J(1′,P) = 0.9 (H-1′); 4.48 ddd, 1 H, J(3′,4′) = 2.4, J(3′,P) = 7.0
and J(3′,2′) = 1.9 (H-3′); 4.42 ddd, 1 H, J(4′,3′) = 2.4, J(4′,2′) = 0.6 and J(4′,P) = 5.4 (H-4′);
4.22 tt, 1 H, J(2′,1′) = 1.9, J(2′,3′) = 1.9, J(2′,4′) = 0.6 and J(2′,P) = 0.9 (H-2′). 13C NMR
(150.9 MHz, D2O): 168.74 (C-4); 159.78 (C-2); 145.14 (C-6); 97.81 (C-5); 96.60 d, J(C,P) =
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3.9 (C-1′); 88.90 d, J(C,P) = 150.9 (C-4′); 83.96 d, J(C,P) = 2.3 (C-3′); 79.02 d, J(C,P) = 6.8
(C-2′).
Methyl 5-O-Benzoyl-β-L-arabinoside (22)
Methyl β-L-arabinoside (21; 1 g, 6.1 mmol) was treated with benzoyl chloride (0.84 ml,
7.1 mmol) and triethylamine (1.7 ml, 12 mmol) in dichloromethane (11.3 ml) at –78 °C un-
der exclusion of moisture (TLC in T1) for 18 h. The reaction was quenched by addition of
methanol (0.5 ml) and the solvents were evaporated in vacuo. The residue was dissolved in
chloroform and the organic layer was washed several times with saturated aqueous NaHCO3.
The crude product was purified on silica gel column with a linear gradient of ethanol in
chloroform. Yield 1.24 g (76 %, colourless sirup) of 22. HR-FAB calculated for C13H17O6
(M + H)+: 269.1025; found 269.1018. 1H NMR (500 MHz, DMSO): 7.99 m, 2 H, 7.67 m, 1 H
and 7.55 m, 2 H (OBz); 5.45 d, 1 H, J(OH,2) = 4.8 (OH-2); 5.36 d, 1 H, J(OH,3) = 5.3 (OH-3);
4.68 d, 1 H, J(1,2) = 2.0 (H-1); 4.49 dd, 1 H, J(5a,4) = 3.1 and J(5a,5b) = 11.9 (H-5a); 4.41 dd,
1 H, J(5b,4) = 6.0 and J(5b,5a) = 11.9 (H-5b); 4.01 ddd, 1 H, J(4,3) = 7.0, J(4,5a) = 3.1 and
J(4,5b) = 6.0 (H-4); 3.83 ddd, 1 H, J(2,1) = 2.0, J(2,OH) = 4.8 and J(2,3) = 4.0 (H-2); 3.80 ddd,
1 H, J(3,2) = 4.0, J(3,OH) = 5.3 and J(3,4) = 7.0 (H-3); 3.26 s, 3 H (OMe). 13C NMR (125.8 MHz,
DMSO): 165.77, 133.58, 129.70, 129.38(2) and 128.95(2) (OBz); 109.29 (C-1); 81.91 (C-2);
80.60 (C-4); 77.52 (C-3); 64.44 (C-5); 54.67 (OMe).
5-O-Benzoyl-1,2-O-isopropylidene-β-L-arabinose (23)
Copper sulfate (1.2 g, 7.4 mmol) followed by concentrated sulfuric acid (0.052 ml, 0.96 mmol)
were added to a solution of methyl-5-O-benzoyl-L-arabinoside (22; 1 g, 3.7 mmol) in acetone
(11.1 ml). The suspension was stirred overnight (TLC in C1). The reaction was set on pH 7
with the concentrated aqueous ammonia, diluted with chloroform and extracted with satu-
rated solution of aqueous sodium hydrogen carbonate. The organic layer was dried with an-
hydrous sodium sulfate and the solvents were evaporated. Yield 370 mg (37%, white
crystals) of 23, m.p. 138–141 °C, [α]20 –14.5. HR-FAB calculated for C15H19O6 (M + H)+:
295.1182; found 295.1178. IR (CHCl3, cm–1): ν (OH-free) 3611w; ν (OH-bonded) 3483w, br;
ν (C–OH) 1085s, sh. OBz: ν (C=O) 1720s; β (C=O) 713vs; ν (C–O) 1275vs; ν (=CH) 3092vs,
3065w, 3026m; ν (ring) 1603w, 1585w, 1493w, 1452m, 1317m, 1178m, 1110s, sh, 1070s,
1026s, 687w, 617vw. CMe2: δs (CH3) 1385m, 1377m; νs (CMe2) 859w; γs (CMe2) 517w;
δas 1019s. 1,3–Dioxolane: νs (COCOC) 1096s. 1H NMR (600 MHz, CDCl3): 8.06 m, 2 H,
7.57 m, 1 H and 7.44 m, 2 H (OBz); 5.97 d, 1 H, J(1,2) = 3.9 (H-1); 4.60 ddd, 1 H, J(2,1) =
3.9, J(2,3) = 1.0 and J(2,4) = 0.6 (H-2); 4.37 m, 1 H, J(3,2) = 1.0, J(3,4) = 2.6 and J(3,OH) =
4.6 (H-3); 4.31 tdd, 1 H, J(4,5a) ~ J(4,5b) = 6.2, J(4,3) = 2.6 and J(4,2) = 0.6 (H-4); 4.54 m,
2 H (H-5a + H-5b); 2.31 d, 1 H, J(OH,3) = 4.6 (OH-3); 1.57 bs, 3 H and 1.34 bs, 3 H
(1,2-OiPr). 13C NMR (150.9 MHz, CDCl3): 166.39, 133.22, 129.75(2), 129.63 and 128.38(2)
(OBz); 112.97, 26.93 and 26.10 (1,2-OiPr); 105.72 (C-1); 86.77 (C-2); 84.95 (C-4); 76.28
(C-3); 64.36 (C-5).
3-O-Benzyl-1,2-O-isopropylidene-β-L-arabinose (25)
The sugar derivative 23 (3.5 g, 12 mmol) was co-distilled with THF, then dissolved in 60 ml
THF, and sodium hydride (576 mg, 14.4 mmol) was added at 0 °C under argon atmosphere.
After 0.5 h, benzyl bromide (1.7 ml, 14.4 mmol) was added dropwise. The mixture was
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Poláková, Buděšínský, Točík, Rosenberg:
stirred overnight (TLC in T2). The mixture was diluted with chloroform (pH must be neu-
tral; adjustment with acetic acid) and extracted three times with water. The organic layer
was evaporated and the residue was purified on a silica gel column by elution with a linear
gradient of ethyl acetate in toluene. The so-obtained, pure intermediary product 24 was dis-
solved in a 0.05 M solution of sodium methoxide in dry methanol (30 ml). The reaction was
left to stand for 16 h (TLC in T1). The mixture was neutralized with solid CO2, evaporated,
and purified on a silica gel column by elution with a linear gradient of ethyl acetate in tolu-
ene. Yield 1.92 g (57%, white crystals) of 25, m.p. 73–77 °C, [α]20 –22.4. HR-FAB calculated
for C15H21O5 (M + H)+: 281.1389; found 281.1385. IR (CHCl3, cm–1): ν (OH) 3630w, sh,
3595w, 3500w, br; ν (C–OH) 1049s. OBn: νas (COC) 1076vs; ν (=CH) 3091w, 3068w; ν (ring)
1606w, 1588vw, 1497w, 1455m, 1027vs, 699s. 1,3-Dioxolane: δs (CH3) 1385s, 1376s;
νas (COCOC) 1163s, 1049s; δas (CH3) 1020s, sh; νs (CMe2) 864m; γs (CH2) 517w. 1H NMR
(600 MHz, CDCl3): 7.38–7.31 m, 5 H, 4.72 bd, 1 H, J(gem) = 12.0 and 4.495 bd, 1 H,
J(gem) = 12.0 (OBn); 5.99 d, 1 H, J(1,2) = 3.9 (H-1); 4.65 bd, 1 H, J(2,1) = 3.9 and J(2,3) ~ 0.6
(H-2); 4.28 ddd, 1 H, J(4,5a) = 5.2, J(4,5b) = 4.8 and J(4,3) = 3.6 (H-4); 4.02 dt, 1 H, J(3,2) ~
0.6, J(3,4) = 3.6 and J(3,5b) ~ 0.6 (H-3); 3.945 dd, 1 H, J(5a,4) = 5.2 and J(5a,5b) = 12.0
(H-5a); 3.86 bdd, 1 H, J(5b,4) = 4.8 and J(5b,5a) = 12.0, J(5b,3) ~ 0.6 (H-5b); 1.49 bs, 3 H and
1.33 bs, 3 H (1,2-OiPr). 13C NMR (150.9 MHz, CDCl3): 136.97, 128.64(2), 128.18, 127.71(2)
and 71.84 (OBn); 111.74, 26.75 and 26.25 (1,2-OiPr); 105.02 (C-1); 82.69 (C-3); 82.37 (C-2);
80.00 (C-4); 60.93 (C-5).
Diethyl (5R)-(3-O-Benzyl-1,2-O-isopropylidene-β-L-arabinofuranos-5-C-yl)-
phosphonate (27) and Diethyl (5S)-(3-O-Benzyl-1,2-O-isopropylidene-
β-L-arabinofuranos-5-C-yl)phosphonate (28)
Pyridine (0.45 ml, 5.6 mmol) followed by TFA (0.22 ml, 2.8 mmol) was added at r.t. to
a stirred solution of 3-O-benzyl-1,2-O-isopropylidene-β-L-arabinose (25; 1.5 g, 5.6 mmol) and
DCC (3.6 g, 16.8 mmol) in DMSO (22.4 ml) (TLC in C2). After 16 h, diethyl phosphite
(1.5 ml, 11.2 mmol) and trietylamine (3.9 ml, 28 mmol) were added and the mixture was
stirred overnight (TLC in C1). The reaction mixture was diluted with chloroform, filtered
through Celite, and the filtrate was extracted with water. The organic layer was dried over
anhydrous sodium sulfate. Chromatography of the crude product on silica gel (elution with
a linear gradient of 0–10% ethanol in chloroform) afforded the expected phosphonate. Yield
2.04 g (87%, white crystals) of a mixture of 27 and 28 (major epimer:minor epimer, 78:22),
m.p. 77–80 °C. HR-FAB calculated for C19H30O8P (M + H)+: 417.1678; found 417.1686. IR
(CHCl3, cm–1): ν (OH) 3550w, br; ν (C–OH) 1075s. PO(OEt)2: ν (P=O) 1245s; βs (CH2)
1479w; δas (CH3) 1454m; γs (CH2) 1393w, sh; δs (CH3) 1370w, sh; δas (CH3) 1164m, 1097s,
sh; νas (POCC) 1051s, 1028vs, 974m; δ (POC) 561w. 1,3–Dioxolan: δs (CH3) 1386m, 1377m;
νs (CMe2) 861w; γs (CMe2) 521w. OBn: ν (=CH) 3091vw, 3067w, 3029w; ν (ring) 1498w,
1287w, 699w.
Major epimer: 1H NMR (500 MHz, CDCl3): 7.37–7.26 m, 5 H, 4.67 d, 1 H, J(gem) = 11.6
and 4.59 d, 1 H, J(gem) = 11.6 (OBn); 5.91 d, 1 H, J(1,2) = 3.7 (H-1); 4.63 bd, 1 H, J(2,1) =
3.7 and J(2,3) ~ 0.5 (H-2); 4.48 ddd, 1 H, J(4,5) = 6.8, J(4,3) = 2.1 and J(4,P) = 5.6 (H-4);
4.42 dd, 1 H, J(3,2) ~ 0.5 and J(3,4) = 2.1 (H-3); 4.20 m, 4 H, 1.34 t, 3 H, J = 7.1 and 1.31 t,
3 H, J = 7.1 (P(OEt)2); 4.12 dt, 1 H, J(5,4) = 6.8, J(5,P) = 6.8 and J(5,OH) = 4.0 (H-5); 3.33 dd,
1 H, J(OH,5) = 4.0 and J(OH,P) = 12.6 (5-OH); 1.55 bs, 3 H and 1.32 bs, 3 H (1,2-OiPr).
13C NMR (150.9 MHz, CDCl3): 137.52, 128.39(2), 127.86(2), 127.81 and 71.89 (OBn);
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112.79, 26.77 and 25.95 (1,2-OiPr); 105.97 (C-1); 85.53 d, J(C,P) = 3.9 (C-4); 84.88 (C-2);
82.31 d, J(C,P) = 8.2 (C-3); 68.12 d, J(C,P) = 161.6 (C-5); 62.99 d, J(C,P) = 6.7, 62.87 d,
J(C,P) = 6.9, 16.46 and 16.42 (P(OEt)2).
Minor epimer: 1H NMR (500 MHz, CDCl3): 7.37–7.26 m, 5 H, 4.64 d, 1 H, J(gem) = 11.6
and 4.60 d, 1 H, J(gem) = 11.6 (OBn); 5.95 d, 1 H, J(1,2) = 4.0 (H-1); 4.68 dd, 1 H, J(2,1) =
4.0 and J(2,3) ~ 0.8 (H-2); 4.49 ddd, 1 H, J(4,5) = 6.5, J(4,3) = 2.1 and J(4,P) = 5.6 (H-4);
4.40 dd, 1 H, J(3,2) ~ 0.8 and J(3,4) = 2.1 (H-3); 4.20 m, 4 H, 1.34 t, 3 H, J = 7.1 and 1.31 t,
3 H, J = 7.1 (P(OEt)2); 4.06 dt, 1 H, J(5,4) = 6.5, J(5,P) = 9.5 and J(5,OH) = 5.6 (H-5); 2.93 dd,
1 H, J(OH,5) = 5.6 and J(OH,P) = 15.6 (5-OH); 1.53 bs, 3 H and 1.38 bs, 3 H (1,2-OiPr).
13C NMR (150.9 MHz, CDCl3): 137.30, 128.48(2), 127.93, 127.71(2) and 72.00 (OBn);
112.90, 26.92 and 26.10 (1,2-OiPr); 105.78 (C-1); 84.12 d, J(C,P) = 3.3 (C-4); 85.00 (C-2);
83.30 d, J(C,P) = 6.3 (C-3); 67.23 d, J(C,P) = 162.7 (C-5); 63.21 d, J(C,P) = 6.7, 62.64 d,
J(C,P) = 6.7, 16.48 and 16.44 (P(OEt)2).
Diethyl (4S)-(1,3-di-O-Acetyl-2-O-benzyl-β-L-erythrofuranos-4-yl)phoshonate (31)
The title phosphonate was obtained from the mixture of epimers 27 and 28 (2 g, 4.8 mmol)
according to the Method A. Yield 950 mg (46%, colourless sirup) of 31. 1H NMR (600 MHz,
CDCl3): 7.36–7.29 m, 5 H, 4.63 bd, 1 H, J(gem) = 11.6 and 4.58 bd, 1 H, J(gem) = 11.6
(OBn); 6.17 d, 1 H, J(1,2) = 2.0 and J(1,3) = 1.0 (H-1); 5.51 m, 1 H, J(3,1) = 1.0, J(3,2) = 4.8,
J(3,4) = 6.6 and J(3,P) = 12.8 (H-3); 4.32 ddd, 1 H, J(2,1) = 2.0, J(2,3) = 4.8 and J(2,4) = 0.5
(H-2); 4.40 m, 1 H, J(4,2) = 0.5, J(4,3) = 6.6 and J(4,P) = 1.4 (H-4); 4.18 m, 4 H, 1.33 dt, 3 H,
J(CH3,CH2) = 7.1, J(CH3,P) = 0.6 and 1.32 dt, 3 H, J(CH3,CH2) = 7.1, J(CH3,P) = 0.6 (P(OEt)2);
2.11 s, 3 H and 2.08 s, 3 H (2 × OAc). 13C NMR (150.9 MHz, CDCl3): 169.89, 169.65, 21.04
and 20.65 (2 × OAc); 136.96, 128.46(2), 128.10 and 127.79(2) (OBn); 98.88 d, J(1,P) = 1.8
(C-1); 79.73 d, J(2,P) = 5.7 (C-2); 76.19 d, J(4,P) = 172.0 (C-4); 71.73 d, J(3,P) = 5.1 (C-3);
63.39 d, J(C,P) = 6.6, 62.85 d, J(C,P) = 6.8 and 16.39(2) d, J(C,P) = 5.7 (P(OEt)2).
Mixture of Diethyl (4S)-(1,3-di-O-Acetyl-2-O-benzoyl-β-L-erythrofuranos-4-yl)-
phosphonate (32) and Diethyl (4S)-(1,3-di-O-Acetyl-2-O-benzyl-
β-L-erythrofuranos-4-yl)phoshonate (31)
Oxidation of the 2-O-benzyl group of diethyl (5S)-(1,3-di-O-acetyl-2-O-benzyl-L-erythro-
furanos-4-yl)phosphonate (31; 950 mg, 2.2 mmol) to 2-O-benzoyl was performed according
to the Method C. Yield 350 mg (~36%, colourless sirup) of a mixture of the desired 32 and
unreacted 31 (73:27).
32: HR-FAB calculated for C19H26O10P (M + H)+: 445.1264; found 445.1283. IR (CHCl3,
cm–1): OAc: ν (C=O) 1751vs; ν (C–O) 1232vs, sh; γ (CCOO) 598w; δs (CH3) 1370m. OBz:
ν (C=O) 1731s, sh; ν (C–O) 1270s; β (C=O) 712s; ν (=CH) 3092vw, 3064w, 3030m. ν (ring)
1603w, 1586w, 1494w, 1453w, 1317w, 1178m, 1071s, sh, 1109m, 697w, 617vw. PO(OEt)2:
ν (P=O) 1249s; βs (CH2) 1479w; δas (CH3) 1443w, 1437w; γs (CH2) 1393w; δas (CH3) 1164w,
1097m; νas (POCC) 1048s, 1028vs, 977m; δ (POC) 571w, 557w. 1H NMR (600 MHz, CDCl3):
8.04 m, 2 H, 7.62 m, 1 H and 7.48 m, 2 H (OBz); 6.34 m, 1 H, J(1,2) = 1.1, J(1,3) = 0.4 and
J(1,4) = 0.6 (H-1); 5.90 m, 1 H, J(3,1) = 0.4, J(3,2) = 4.6, J(3,4) = 8.0 and J(3,P) = 14.2 (H-3);
5.64 ddd, 1 H, J(2,1) = 1.1, J(2,3) = 4.6 and J(2,4) = 0.5 (H-2); 4.44 m, 1 H, J(4,1) = 0.6,
J(4,2) = 0.5, J(4,3) = 8.0 and J(4,P) = 0.9 (H-4); 4.22 m, 4 H, 1.355 dt, 3 H, J(CH3,CH2) = 7.1,
J(CH3,P) = 0.6 and 1.350 dt, 3 H, J(CH3,CH2) = 7.1, J(CH3,P) = 0.6 (2 × OEt); 2.15 s, 6 H (2 ×
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Poláková, Buděšínský, Točík, Rosenberg:
OAc). 13C NMR (150.9 MHz, CDCl3): 169.26, 169.10, 20.96 and 20.37 (2 × OAc); 164.90,
133.75, 129.80(2), 128.68 and 128.60(2) (OBz); 98.30 d, J(1,P) = 2.4 (C-1); 75.37 d, J(4,P) =
174.7 (C-4); 74.08 d, J(2,P) = 7.2 (C-2); 70.50 d, J(3,P) = 3.9 (C-3); 63.41 d, J(C,P) = 6.6,
62.98 d, J(C,P) = 6.8 and 16.43(2) d, J(C,P) = 5.7 (P(OEt)2).
Diethyl (4S)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(uracil-3-yl)-β-L-erythrofuranos-4-yl]-
phosphonate (33a)
Phosphonate 33a was obtained from silylated uracil (560 mg, 5 mmol) and the mixture of
sugar phosphonate 32 + 31 (700 mg, 1.6 56 mmol of 32) according to the Method B. Yield
240 mg (30%, white lyophilizate) of 33a. HR-FAB calculated for C21H26N2O10P (M + H)+:
497.1325; found 497.1340. IR (CHCl3, cm–1): OAc: ν (C=O) 1751s, sh; ν (C–O) 1231s;
γ (CCOO) 597w; δs (CH3) 1377m. OBz: ν (C=O) 1736vs; ν (C–O) 1271s, 963m, br; β (C=O)
712m; ν (ring) 1603w, 1585w, 1494w, sh, 1452w, 1314w, 1178w, 1110m, 1070s, 686w. U:
ν (NH) 3426w, 3318w, br, sh, 3245w, 3188w, 3109w, br; ν (C=O) 1736vs, 1680vs, sh,
1671vs; ν (C=C) 1643m, sh; ν (ring) 1477w, 1425w. PO(OEt)2: ν (P=O) 1248s; νas (POCC)
1050s, 1027vs, 978m; δ (POC) 564w; δas (CH3) 1444w, sh; γs (CH2) 1394w, sh; δas (CH3)
1164w, 1096m. 1H NMR (600 MHz, CDCl3 + DMSO 4:1): 11.16 bd, 1 H, J(NH,6) = 5.8 and
J(NH,5) = 1.5 (NH); 8.03 m, 2 H, 7.61 m, 1 H and 7.47 m, 2 H (OBz); 7.22 dd, 1 H, J(6,5) =
7.6 and J(6,NH) = 5.8 (H-6); 6.56 bd, 1 H, J(1′,2′) = 4.6 (H-1′); 6.03 dd, 1 H, J(2′,1′) = 4.6 and
J(2′,3′) = 5.0 (H-2′); 5.64 dd, 1 H, J(5,6) = 7.6 and J(5,NH) = 1.5 (H-5); 5.51 bd, 1 H,
J(OH,3′) ~ 7.0; 4.85 m, 1 H, J(3′,4′) = 8.0, J(3′,P) = 13.0, J(3′,OH) ~ 7.0 and J(3′,2′) = 5.0
(H-3′); 4.70 dd, 1 H, J(4′,3′) = 8.0 and J(4′,P) = 1.2 (H-4′); 4.21 m, 4 H, 1.363 t, 3 H, J = 7.0
and 1.354 t, 3 H, J = 7.0 (P(OEt)2). 13C NMR (150.9 MHz, CDCl3 + DMSO 4:1): 165.67,
133.16, 129.36(2), 128.78 and 128.16(2) (OBz); 163.00 (C-2); 151.10 (C-4); 140.37 (C-6);
100.52 (C-5); 85.43 (C-1′); 81.65 d, J(C,P) = 11.2 (C-2′); 79.68 d, J(C,P) = 169.2 (C-4′); 76.41
(C-3′); 62.46 d, J(C,P) = 6.5 and 16.17 d, J(C,P) = 4.7 (P(OEt)2).
Diethyl (4S)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(thymin-1-yl)-β-L-erythrofuranos-4-yl]-
phosphonate (33b)
Phosphonate 33b was obtained from silylated thymine (220 mg, 1.7 mmol) and the mixture
of sugar phosphonate 32 + 31 (190 mg, 0.42 mmol of 32) according to the Method B. Yield
40 mg (20%, white foam) of 33b. For C22H28N2O10P (M + H)+ calculated 511.1482, found
511.1495. IR (CHCl3, cm–1): T: ν (NH-free) 3391w; ν (NH-bonded) 3184w, br; ν (C=O) 1716s,
1696vs; ν (ring) 1655m, sh, 1466m, 1435w, sh; δs (CH3) 1376m. PO(OEt)2: ν (P=O) 1249s;
νas (POCC) 1055s, sh, 1038s, 979m; δ (POC) 560m; γs (CH2) 1391m; δas (CH3) 1163w,
1097m. OAc: ν (C=O) 1751s; ν (C–O) 1249s, 1027s; γ (CCOO) 596w; δs (CH3) 1376m. OBz:
ν (C=O) 1731s, sh; ν (C–O) 1262s, 961m; β (C=O) 711m; ν (=CH) 3064w, 3026m; ν (ring)
1603w, 1585w, 1495w, sh, 1453m, 1317w, 1178w, 1122m, 1073m, sh, 1027s, 686w, 615vw.
1H NMR (600 MHz, CDCl3): 8.40 bs, 1 H (NH); 8.00 q, 1 H, J(6,CH3) = 1.2 (H-6); 7.98 m,
2 H, 7.59 m, 1 H and 7.45 m, 2 H (OBz); 6.60 dd, 1 H, J(1′,2′) = 7.8 a J(1′,P) = 1.5 (H-1′);
5.86 ddd, 1 H, J(3′,4′) = 1.6, J(3′,P) = 6.9 and J(3′,2′) = 5.1 (H-3′); 5.76 dd, 1 H, J(2′,1′) = 7.8
and J(2′,3′) = 5.1 (H-2′); 4.42 dd, 1 H, J(4′,3′) = 1.6 and J(4′,P) = 5.2 (H-4′); 4.28 m, 2 H,
4.25 m, 2 H, 1.42 t, 3H, J(CH3,CH2) = 7.0 and 1.38 t, 3 H, J(CH3,CH2) = 7.0 (P(OEt)2); 2.12 s,
3 H (OAc); 1.98 q, 3 H, J(CH3,6) = 1.2 (CH3-5). 13C NMR (150.9 MHz, CDCl3): 169.29 and
20.63 (OAc); 164.92, 133.84, 129.87(2), 128.61(2) and 128.30 (OBz); 163.14 (C-4); 150.64
(C-2); 135.54 (C-6); 112.44 (C-5); 85.53 d, J(C,P) = 3.0 (C-1′); 77.95 d, J(C,P) = 168.1 (C-4′);
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72.85 d, J(C,P) = 1.4 (C-2′); 70.89 d, J(C,P) = 9.8 (C-3′); 64.07 d, J(C,P) = 6.6, 63.50 d,
J(C,P) = 7.2, 16.45 d, J(C,P) = 5.6 and 16.17 d, J(C,P) = 5.6 (P(OEt)2); 12.58 (CH3-5).
(4S)-[1-Deoxy-1-(uracil-3-yl)-β-L-erythrofuranos-4-yl]phosphonic Acid (34)
The title phosphonic acid was obtained from phosphonate mixture 33 (300 mg, 0.56 mmol)
according to the Method D. Yield 150 mg (82%, white lyophilizate) of 34, [α]20 +12.9.
HR-FAB calculated for C8H10N2O8Na2P (M + H)+: 338.9970; found 338.9979. IR (KBr, cm–1):
ν (CH, NH) 3427 vs, br, 3250m, br, sh; ν (C–OH) 1081s; νas (PO3)2– 975m; δ (PO3)2– 570m.
U: ν (C=O) 1717s, 1653vs; ν (C=C) 1601m, sh; γ (=CH) 815w, 769w. 1H NMR (600 MHz,
D2O): 7.48 d, 1 H, J(6,5) = 7.8 (H-6); 6.40 d, 1 H, J(1′,2′) = 5.3 (H-1′); 5.83 d, 1 H, J(5,6) = 7.8
(H-5); 4.825 dd, 1 H, J(2′,1′) = 5.3 and J(2′,3′) = 4.8 (H-2′); 4.38 ddd, 1 H, J(3′,2′) = 4.8,
J(3′,4′) = 6.5 and J(3′,P) = 10.0 (H-3′); 4.19 dd, 1 H, J(4′,3′) = 6.5 and J(4′,P) = 2.7 (H-4′).
13C NMR (150.9 MHz, D2O): 166.61 (C-4); 153.12 (C-2); 142.63 (C-6); 101.84 (C-5); 85.13 d,
J(C,P) = 5.7 (C-1′); 82.74 d, J(C,P) = 151.7 (C-4′); 78.82 d, J(C,P) = 7.1 (C-2′); 78.60 d, J(C,P) =
2.7 (C-3′).
1,2-O-Isopropylidene-α-L-xylofuranose (35)
Copper sulfate (16.3 g, 102 mmol) and then concentrated sulfuric acid (0.71 ml, 13.3 mmol)
were added to a solution of L-xylose (7.6 g, 51 mmol) in acetone (153 ml). The suspension
was stirred overnight (TLC in C1). The reaction was set to pH 7 using concentrated aqueous
ammonia, diluted with chloroform, and the solution was extracted with saturated solution
of aqueous sodium hydrogen carbonate. The organic layer was dried over anhydrous sodium
sulfate, and evaporated. To the crude 1,2;3,5-di-O-isopropylidene-α-L-xylofuranose, the 60%
aqueous acetic acid (500 ml) was added and the whole was set overnight. The reaction mix-
ture was evaporated and the residue co-distilled several times with water. The product was
purified on the Dowex 1 column in OH– form using the elution with water. Yield 8.4 g
(87%, yellow sirup) of 35, [α]20 +22.1. HR-FAB calculated for C8H14O5Na (M + Na)+:
213.0739; found 213.0730. IR (CHCl3, cm–1): ν (OH) 3587w, 3446m, br; ν (C–OH) 1076vs,
1041s. CMe2: δs (CH3) 1385s, 1376s; δas (CH3) 1014vs; νs (CMe2) 860m; γs (CMe2) 522m;
1,3–Dioxolane: νas (COCOC) 1164s, 1076vs; νs (COCOC) 1105s. 1H NMR (600 MHz,
DMSO): 5.79 dd, 1 H, J(1,2) = 3.8 and J(1,3) ~ 0.6 (H-1); 4.37 dd, 1 H, J(2,1) = 3.8 and
J(2,3) ~ 0.6 (H-2); 3.97 ddd, 1 H, J(4,3) = 2.8, J(4,5a) = 5.5 and J(4,5b) = 6.1 (H-4); 3.95 dt,
1 H, J(3,4) = 2.8, J(3,2) ~ 0.6 and J(3,1) ~ 0.6 (H-3); 3.60 dd, 1 H, J(5a,4) = 5.5, J(5a,5b) =
11.2 (H-5a); 3.49 dd, 1 H, J(5b,4) = 6.1, J(5b,5a) = 11.2 (H-5b); 1.35 s, 3 H and 1.22 s, 3 H
(1,2-OiPr). 13C NMR (150.9 MHz, DMSO): 110.48, 26.86 and 26.31 (1,2-OiPr); 104.45 (C-1);
81.56 (C-4); 85.25 (C-2); 73.56 (C-3); 58.97 (C-5).
5-O-Allyloxycarbonyl-1,2-O-isopropylidene-α-L-xylofuranose (36)
1,2-O-Isopropylidene-α-L-xylofuranose 35 (1 g, 5.3 mmol) was repeatedly co-evaporated with
dichloromethane and then dissolved in a 1:1 dichlormethane–pyridine mixture (10 ml).
After cooling of the solution to –78 °C, allyloxycarbonyl chloride (0.58 ml, 5.5 mmol) was
added. The reaction was monitored on TLC in T1 system using a 10% H2SO4 detection. After
30 min, the reaction was quenched with methanol (0.2 ml), diluted with chloroform, and
the whole was extracted with water. The organic washings were evaporated and the crude
product was purified on silica gel using a linear gradient of ethyl acetate in toluene. Yield
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Poláková, Buděšínský, Točík, Rosenberg:
1.0 g (68%, white foam) of 36, [α]20 +5.0. HR-FAB calculated for C12H19O7 (M + H)+:
275.1131; found 275.1134. IR (CHCl3, cm–1): ν (OH) 3603w, br, 3441m, br; ν (C–OH)
1076vs. CMe2: δs (CH3) 1385s, 1376s; δas (CH3) 1011vs; νs (CMe2) 860m; γs (CMe2) 522w.
1,3–Dioxolane: νas (COCOC) 1164s, 1076vs; νs (COCOC) 1105s. Carbonyl: ν (C=O) 1746m;
νas (OCO) 1268s, 1258s. Vinyl: ν (C=C) 1649vw; νas (=CH2) 3090vw; βs (=CH2) 1410w;
β (=CH) 1294m; γs (=CH2) 906w. 1H NMR (500 MHz, DMSO): 5.93 ddt, 1 H, J = 17.25,
10.5, 5.5 (2×), 5.33 dq, 1 H, J = 17.25 and 1.5 (3×), 5.25 dq, 1 H, J = 10.5 and 1.5 (3×) and
4.61 dt, 2 H, J = 5.5 and 1.5 (2×) (O-CH2-CH=CH2); 5.86 d, 1 H, J(1,2) = 3.7 (H-1); 5.46 d,
1 H, J(OH,3) = 4.4 (OH-3); 4.41 dd, 1 H, J(2,1) = 3.7 and J(2,3) = 0.6 (H-2); 4.30 m (H-4);
4.19 m, 1 H and 4.16 m, 1 H (H-5a + H-5b); 4.04 m, 1 H (H-3); 1.38 bs, 3 H and 1.23 bs,
3
H
(1,2-OiPr). 13C NMR (125.8 MHz, DMSO): 154.44, 68.10, 132.31 and 118.58
(O-CO-O-CH2-CH=CH2); 110.86, 26.83 and 26.24 (1,2-OiPr); 104.76 (C-1); 85.10 (C-2);
78.16 (C-4); 73.86 (C-3); 66.42 (C-5).
5-O-Allyloxycarbonyl-1,2-O-isopropylidene-3-O-methoxycarbonyl-α-L-xylofuranose (38)
A solution of methoxycarbonyl chloride was added dropwise, under exclusion of atmo-
spheric moisture and 0 °C, to a solution of tetrazole (1.4 g, 20 mmol) in THF (60 ml) and
triethylamine (2.8 ml, 20 mmol). The mixture was left to react for 3 h. After filtering off the
deposited triethylamine hydrochloride, a solution of 5-O-allyloxycarbonyl-1,2-O-isopropyl-
idene-α-L-xylofuranose (36; 1.1 g, 4 mmol) in THF (28 ml) and DMAP (1.7 g, 16 mmol) was
added to the obtained filtrate (which contained methoxycarbonyl tetrazolide). The reaction
was monitored on TLC (system T1) and the detection was carried out by spraying with
a 10% H2SO4 solution. Upon quenching of the reaction (18 h) with methanol (0.64 ml), the
mixture was diluted with chloroform and the whole was extracted several times with 10%
aqueous solution of citric acid and once with water. The combined organic washings were
evaporated and the residue was chromatographed on silica gel using a linear gradient of
ethyl acetate in toluene. Yield 0.86 g (93%, white crystals) of 38, m.p. 112–117 °C, [α]20
+4.8. HR-FAB calculated for C14H21O9 (M + H)+: 333.1186; found 333.1178. IR (CHCl3,
cm–1): CMe2: δs (CH3) 1385w, 1376m; δas (CH3) 1026m; νs (CMe2) 859w. 1,3-Dioxolane:
νas (COCOC) 1163m, 1069m; νs (COCOC) 1095m. Carbonyl: ν (C=O) 1753vs; νas (OCO)
1279vs, 1261vs; δs (CH3) 1444m. Vinyl: ν (C=C) 1650vw; νas (=CH2) 3089vw; βs (=CH2)
1414w; β (=CH) 1293s; γs (=CH2) 913w. 1H NMR (500 MHz, CDCl3): 5.95 bd, 1 H, J(1,2) =
3.7, J(1,3) ~ 0.6 and J(1,4) ~ 0.6 (H-1); 5.93 ddt, 1 H, J = 17.2, 10.4, 5.8 (2×), 5.37 dq, 1 H,
J = 17.2 and 1.5 (3×), 5.28 dq, 1 H, J = 10.4 and 1.5 (3×) and 4.63 dt, 2 H, J = 5.8 and
1.5 (2×) (O-CH2-CH=CH2); 5.13 dt, 1 H, J(3,4) = 3.0, J(3,2) ~ 0.6 and J(3,1) ~ 0.6 (H-3);
4.61 bd, 1 H, J(2,1) = 3.7 and J(2,3) ~ 0.6 (H-2); 4.53 ddd, J(4.3) = 3.0, J(4,5a) = 6.1 and
J(4,5b) = 5.8 (H-4); 4.37 m, 2 H (H-5a + H-5b); 3.82 s, 3 H (OCO-OCH3); 1.51 bs, 3 H and
1.32 bs, 3 H (1,2-OiPr). 13C NMR (125.8 MHz, CDCl3): 154.64, 68.75, 131.31 and 119.08
(O-CO-O-CH2-CH=CH2); 154.59 and 55.33 (O-CO-OCH3); 112.45, 26.65 and 26.20 (1,2-OiPr);
104.79 (C-1); 83.15 (C-2); 79.48 (C-3); 76.46 (C-4); 64.43 (C-5).
5-O-Benzoyl-1,2-O-isopropylidene-α-L-xylofuranose (40)
Route A: To a solution of 5-O-allyloxycarbonyl-1,2-O-isopropylidene-α-L-xylofuranose (36;
1.1 g, 4 mmol) in dry acetonitrile (30 ml) containing 0.112 ml (0.8 mmol, 0.2 equiv.) of
triethylamine, benzoyl cyanide (1.051 g, 8 mmol, 2 equiv.) was added at 0 °C and the mix-
ture was left to react at r.t. for 8 h (TLC checking in T1). The solvent was evaporated and
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the residue containing the 3′′-O-benzoyl derivative 40 was processed by flash chromatography
on silica gel using a linear gradient of ethyl acetate in toluene to afford the 3′-O-benzoyl de-
rivative 37 (1.29 g, 85%), HR-FAB calculated for C19H22O8 (M + H)+: 379.1348; found
379.1360), as amorphous solid which was submitted for further reaction. The so-obtained
product (3.4 mmol) was co-evaporated with toluene and dichloromethane, and dissolved in
the latter (15 ml). To the solution, triphenylphosphine (0.34 g, 1.27 mmol), tetrakistri-
phenylphosphinepalladium (0.25 g, 0.21 mmol) and butylammonium formate (1.10 ml,
9.2 mmol) were added, and the reaction was set to proceed (TLC checking in T1) until dis-
appearance of the starting material (16 h). The mixture was evaporated in vacuo and the res-
idue was chromatographed on silica gel using a linear gradient of ethyl acetate in toluene.
Yield 0.90 g (90%, sirup, based on 37) of 40.
Route B: 1,2-O-Isopropylidene-α-L-xylofuranose (35; 860 mg, 4.5 mmol) was treated with
benzoyl chloride (0.53 ml, 4.5 mmol) and pyridine (7.8 ml, 55 mmol) in dichloromethane
(31 ml) at –78 °C under exclusion of moisture (TLC in T1) overnight. The reaction was
quenched by addition of methanol (1 ml) and the solvent was evaporated in vacuo. The res-
idue was dissolved in chloroform and the organic layer was washed several times with satu-
rated aqueous NaHCO3. The crude product was purified on a silica gel column using a linear
gradient of ethanol in chloroform. Yield 1.17 g (88%, colorless sirup) of 40. HR-FAB calcu-
lated for C15H19O6 (M + H)+: 295.1182; found 295.1173. 1H NMR (500 MHz, DMSO):
7.98 m, 2 H, 7.67 m, 1 H and 7.54 m, 2 H (OBz); 5.89 d, 1 H, J(1,2) = 3.7 (H-1); 5.49 d, 1 H,
J(OH,3) = 5.0 (OH-3); 4.47 m, 1 H and 4.36 m, 1 H (H-5a + H-5b); 4.455 dd, 1 H, J(2,1) = 3.7
and J(2,3) ~ 0.5 (H-2); 4.34 m, 1 H (H-4); 4.13 ddd, 1 H, J(3,4) = 3.6, J(3,2) ~ 0.5 and
J(3,OH) = 5.0 (H-3); 1.40 s, 3 H and 1.25 s, 3 H (1,2-OiPr). 13C NMR (125.8 MHz, DMSO):
165.79, 133.57, 129.78, 129.40(2) and 128.94(2) (OBz); 110.84, 26.86 and 26.23 (1,2-OiPr);
104.78 (C-1); 85.17 (C-2); 78.35 (C-4); 73.91 (C-3); 63.32 (C-5).
1,2-O-Isopropylidene-5-O-methoxycarbonyl-α-L-xylofuranose (41)
Triphenylphosphine (0.23 g, 0.86 mmol), tetrakistriphenylphosphinepalladium (0.17 g,
0.14 mmol), and butylammonium formate (0.74 ml, 6.2 mmol) were added to a solution of
compound 38 (0.77 g, 2.3 mmol) in dichloromethane (12 ml). The reaction was followed on
TLC in the system T1 and the detection was done by spraying with a 10% H2SO4 solution.
After completion of the reaction (16 h), the mixture was evaporated in vacuo and the resi-
due was chromatographed on silica gel using a linear gradient of ethyl acetate in toluene.
Yield 0.60 g (92%, white crystals) of 41, m.p. 130–135 °C, [α]20 +7.5. HR-FAB calculated for
C
10H17O7 (M + H)+: 249.0974; found 249.0971. IR (CHCl3, cm–1): ν (OH) 3617w, 3580w, sh,
3492m, br; ν (C–OH) 1076vs. CMe2: δs (CH3) 1385s, 1376s; δas (CH3) 1015vs; νs (CMe2) 860s;
γs (CMe2) 520m. 1,3-Dioxolane: νas (COCOC) 1164vs, 1076vs; νs (COCOC) 1109s.
Methoxycarbonyl: ν (C=O) 1747vs, br; νas (OCO) 1281vs, br; δs (CH3) 1444vs. 1H NMR
(500 MHz, CDCl3): 5.93 bd, 1 H, J(1,2) = 3.7 and J(1,3) ~ 0.6 (H-1); 4.20 ddt,1 H, J(3,4) =
2.25, J(3,OH) = 4.6, J(3,2) ~ 0.6 and J(3,1) ~ 0.6 (H-3); 4.56 bd, 1 H, J(2,1) = 3.7 and J(2,3) ~
0.6 (H-2); 4.50 m, 1 H (H-5a); 4.325 m, 2 H (H-4 + H-5b); 3.815 s, 3 H (O-COOCH3);
2.82 bd, 1 H, J(OH,3) = 4.6 (OH-3); 1.50 bs, 3 H and 1.32 bs, 3 H (1,2-OiPr). 13C NMR
(125.8 MHz, CDCl3): 156.26 and 55.27 (O-CO-OCH3); 111.93, 26.75 and 26.16 (1,2-OiPr);
104.67 (C-1); 85.06 (C-2); 77.95 (C-4); 74.44 (C-3); 64.10 (C-5).
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530
Poláková, Buděšínský, Točík, Rosenberg:
Diethyl (5S)-(3-O-Benzyl-1,2-O-isopropylidene-α-L-xylofuranos-5-C-yl)phoshonate (45)
The sugar derivative 40 (3 g, 10 mmol) was co-distilled with THF, then dissolved in 44 ml
THF, and sodium hydride (480 mg, 12 mmol) was added at 0 °C under argon atmosphere.
After 0.5 h, benzyl bromide (6.5 ml, 12 mmol) was added dropwise. The mixture was stirred
overnight (TLC in T2), then diluted with chloroform (pH must be neutral) and extracted
three times with water. The organic layer was evaporated and the residue was purified on a
silica gel column by elution with a linear gradient of ethyl acetate in toluene. The pure
product 42 was dissolved in 0.05 M solution of sodium methoxide in dry methanol (60 ml).
The reaction was set overnight (TLC in T1). The mixture was neutralized with solid CO2,
evaporated, and purified on a silica gel column by elution with a linear gradient of ethyl
acetate in toluene. Yield 2.2 g (78%, yellowish sirup) of 3-O-benzyl-1,2-O-isopropylidene-
α-L-xylofuranose (43), [α]20 +67.4. HR-FAB calculated for C15H21O5 (M + H)+: 281.1389;
found 281.1385. This compound was used for further reaction without any additional char-
acterization.
Pyridine (0.13 ml, 1.6 mmol) followed by TFA (0.064 ml, 0.8 mmol) was added at r.t. to a
stirred solution of 3-O-benzyl-1,2-O-isopropylidene-α-L-xylofuranose (43; 430 mg, 1.6 mmol)
and DCC (1.1 g, 4.8 mmol) in DMSO (6.4 ml) (TLC in C2). After 16 h, diethyl phosphite
(0.42 ml, 3.2 mmol) and trietylamine (1.12 ml, 8 mmol) were added and the whole was
stirred overnight (TLC in C1). The reaction mixture was diluted with chloroform and fil-
tered through Celite. The filtrate was then extracted with water and the organic layer was
dried over anhydrous sodium sulfate. Chromatography of the crude product on silica gel
(elution with a linear gradient of 0–10% ethanol in chloroform) afforded the expected
phosphonate. Yield 480 mg (75%, colourless sirup) of 45, [α]20 +29.5. HR-FAB calculated for
C
19H30O8P (M + H)+: 417.1678; found 417.1674. IR (CHCl3, cm–1): ν (OH)3451w, br, 3240w, br;
OBn: ν (=CH) 3092w, 3068w, 3027m; ν (ring) 1604vw, 1588vw, 1498w, 1456m, 699m;
νas (CH2) 2911m; νs (CH2) 2872w. 1,3-Dioxolane: δs (CH3) 1386m, 1376m; νas (COCOC)
1132m, sh, 1075vs; νs (COCOC) 1098s, sh; νs (CMe2) 859w; γs (CMe2) 523m. PO(OEt)2:
ν (P=O) 1245s, br; βs (CH2) 1478w; δas (CH3) 1444w; γs (CH2) 1394m, sh; δas (CH3) 1164s,
1098s, sh; νas (POCC) 1049vs, 1028vs, 974s; δ (POC) 567m. 1H NMR (600 MHz, CDCl3):
6.00 bd, 1 H, J(1,2) = 3.8 (H-1); 7.37–7.30 m, 5 H, 4.72 d, 1 H, J(gem) = 10.8 and 4.65 d,
1 H, J(gem) = 10.8 (OBn); 4.60 d, 1 H, J(2,1) = 3.8 and J(2,3) ~ 0 (H-2); 4.41 m, 1 H, J(4,3) =
3.2 (H-4); 4.39 d, 1 H, J(3,4) = 3.2, J(3,2) ~ 0 (H-3); 4.37 m, 1 H (H-5); 4.23 m, 2 H, 4.19 m,
2 H, 1.353 t, 3 H, J = 7.0 and 1.347 t, 3 H, J = 7.0 (P(OEt)2); 4.14 b, 1 H (OH-5′); 1.50 bs,
3 H and 1.32 bs, 3 H (1,2-OiPr). 13C NMR (150.9 MHz, CDCl3): 136.76, 128.52(2), 128.16,
127.98(2) and 72.83 (OBn); 117.80, 26.67 and 26.16 (1,2-OiPr); 104.77 (C-1); 84.37 d,
J(C,P) = 3.9 (C-3); 81.98 (C-2); 77.16 d, J(C,P) = 11.8 (C-4); 67.44 d, J(C,P) = 161.0 (C-5);
63.23 d, J(C,P) = 7.1, 62.48 d, J(C,P) = 7.1, 16.47 d, J(C,P) = 5.6 and 16.41 d, J(C,P) = 5.6
(P(OEt)2).
Diethyl (4S)-(1,3-Di-O-acetyl-2-O-benzyl-α-L-threofuranos-4-yl)phosphonate (47)
The title phosphonate was obtained from diethyl (5S)-(3-O-benzyl-1,2-di-O-isopropylidene-
α-L-xylofuranos-5-C-yl)phosphonate (45; 1 g, 2.4 mmol) according to the Method A. Yield
940 mg (91%, colourless syrup) of 47. HR-FAB calculated for C19H28O9P (M + H)+: 431.1471;
found 431.1467. IR (CHCl3, cm–1): OBn: ν (=CH) 3091vw, 3067w, 3030w; ν (ring) 1604vw,
1497w, 1455w, 699w; νas (CH2) 2912w, νs (CH2) 2871w. OAc: ν (C=O) 1749s, ν (C–O) 1255s, sh,
1229vs; γ (CCOO) 604w; δs ((CH3) 1374m. PO(OEt)2: βs (CH2) 1478w; δas (CH3) 1443w;
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Tetrofuranose Nucleoside Phosphonic Acids
531
γs (CH2) 1393w; δas (CH3) 1164w, 1103m; ν (POCC) 1043vs, 1029vs; δ (POC) 575w. 1H NMR
(500 MHz, CDCl3): 7.38–7.28 m, 5 H, 4.80 d, 1 H, J(gem) = 12.0 and 4.67 d, 1 H, J(gem) =
12.0 (OBn); 6.30 p, 1 H, J(1,2) = 0.5; J(1,3) = 0.6; J(1,4) = 0.4 and J(1,P) = 0.8 (H-1); 3.98 m,
1 H, J(2,1) = 0.5, J(2,3) = 1.0 and J(2,P) = 0.5 (H-2); 5.56 m, 1 H, J(3,4) = 5.0, J(3,2) = 1.0,
J(3,1) = 0.6 and J(3,P) = 13.2 (H-3); 4.44 m, 1 H, J(4,3) = 5.0, J(4,1) = 0.4 and J(4,P) = 4.5
(H-4); 2.105 s, 3 H (1-OAc); 2.07 s, 3 H (3-OAc); ~4.18 m, 4 H, 1.305 td, 3 H, J(CH3,CH2) =
7.1 and J(CH3,P) = 0.4 and 1.27 td, 3 H, J(CH3,CH2) = 7.1 and J(CH3,P) = 0.4 (P(OEt)2).
13C NMR (125.8 MHz, CDCl3): 169.15 and 20.88 (1-OAc); 169.71 and 21.02 (3-OAc); 136.97,
128.38(2), 127.90(3) and 71.67 (OBn); 100.72 d, J(C,P) = 12.1 (C-1); 86.25 d, J(C,P) = 6.9
(C-2); 78.55 d, J(C,P) = 174.1 (C-4); 76.41 d, J(C,P) = 4.2 (C-3); 63.46 d, J(C,P) = 6.5, 63.40 d,
J(C,P) = 6.3, 16.35 d, J(C,P) = 5.7 and 16.32 d, J(C,P) = 5.8 (P(OEt)2).
Diethyl (4S)-(1,3-Di-O-acetyl-2-O-benzoyl-α-L-threofuranos-4-yl)phosphonate (48)
The title phosphonate was obtained from diethyl (4S)-(1,3-O-acetyl-2-O-benzyl-L-threo-
furanos-4-yl)phosphonate (47; 6 g, 14 mmol) according to the Method C. Yield 2.5 g (40%,
colourless sirup) of 48. HR-FAB calculated for C19H26O10P (M + H)+: 445.1264; found
445.1279. IR (CHCl3, cm–1): OAc: ν (C=O) 1755s; ν (C–O) 1232s, sh; γ (CCOO) 603w;
δs (CH3) 1370w. OBz: ν (C=O) 1729m; ν (C–O) 1270s; β (C=O) 712m; ν (=CH) 3033w;
ν (ring) 1585vw, 1494vw, 1444w, 1317w, 1179w, 1110m, 1070m, sh, 855w, 687w, 617vw.
PO(OEt)2: ν (P=O) 1261s; νas (POCC) 1045s, 1028vs; ν (C–C) 963m; δ (POC) 574w; νas (CH3)
2990w, sh; βs (CH2) 1479vw; δas (CH3) 1452w; γs (CH2) 1393w; δas 1163w, 1097m. 1H NMR
(500 MHz, CDCl3): 8.09 m, 2 H, 7.59 m, 1 H and 7.46 m, 2H (OBz); 6.40 m, 1 H, J(1,2) =
0.6, J(1,3) = 0.65 and J(1,4) = 0.4 (H-1); 5.72 m, 1 H, J(3,1) = 0.65, J(3,2) = 1.6, J(3,4) =
5.8 and J(3,P) = 13.3 (H-3); 5.40 dt, 1 H, J(2,1) = 0.6, J(2,3) = 1.6 and J(2,P) = 0.6 (H-2);
4.46 ddd, 1 H, J(4,1) = 0.4, J(4,3) = 5.8 and J(4,P) = 4.3 (H-4); 4.24 m, 4 H and 1.34 dt, 6 H,
J(CH3,CH2) = 7.1, J(CH3,P) = 0.4 (2 × OEt); 2.15 s, 6 H (2 × OAc). 13C NMR (125.8 MHz,
CDCl3): 169.20, 168.77, 20.98 and 20.71 (2 × OAc); 165.20, 133.71, 130.05(2), 128.71 and
128.49(2) (OBz); 99.60 d, J(1,P) = 12.6 (C-1); 81.50 d, J(2,P) = 8.2 (C-2); 79.25 d, J(3,P) = 4.0
(C-3); 78.15 d, J(4,P) = 175.3 (C-4); 63.42(2) d, J(C,P) = 6.7, 16.43 d, J(C,P) = 5.5 and 16.40 d,
J(C,P) = 5.8 (P(OEt)2).
Diethyl (4S)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(uracil-1-yl)-α-L-threofuranos-4-yl]-
phosphonate (49a)
The title phosphonate was obtained from silylated uracil (2.14 g, 19 mmol) and the
phosphonate 48 (2.1 g, 4.8 mmol) according to the Method B. Yield 1.3 g (57%, white
lyophilizate) of 49a, [α]20 –40.0. HR-FAB calculated for C21H26N2O10P (M + H)+: 497.1325;
found 497.1332. IR (CHCl3, cm–1): U: ν (NH-free) 3389w; ν (NH-bonded) 3171w, br; ν (C=O)
1727vs, 1697vs; ν (C=C)1635m; ν (ring) 1480w, sh, 1427w, sh. OAc: ν (C=O) 1756s, sh;
ν (C–O) 1232vs, sh; γ (CCOO) 600w; δs (CH3) 1376m, 1372m. OBz: ν (C–O) 1260vs, β (C=O)
712s; ν (=CH) 3064w, 3027m; ν (ring) 1603w, 1586w, 1493w, 1453s, 1317m, 1179m, 1111s,
1071s, sh, 686w, 617vw. PO(OEt)2: ν (P=O) 1250vs, sh; νas (POCC) 1047vs, 1029vs, 978s;
δ (POC) 572m; δas (CH3) 1444m, sh; γs (CH2) 1391m; δas (CH3) 1164m, 1097s. 1H NMR
(600 MHz, CDCl3): 8.82 bs, 1 H (NH); 8.07 m, 2 H, 7.60 m, 1 H and 7.46 m, 2 H (OBz);
7.32 d, 1 H, J(6,5) = 8.2 (H-6); 6.11 d, 1 H, J(1′,2′) = 4.5 (H-1′); 5.93 ddd, 1 H, J(3′,4′) = 5.4,
J(3′,P) = 12.6 and J(3′,2′) = 3.8 (H-3′); 5.81 d, 1 H, J(5,6) = 8.2 (H-5); 5.74 m, 1 H, J(2′,1′) =
4.5, J(2′,3′) = 3.8 and J(2′,P) = 0.9 (H-2′); 4.71 dd, 1 H, J(4′,3′) = 5.4 and J(4′,P) = 3.7 (H-4′);
Collect. Czech. Chem. Commun. 2011, Vol. 76, No. 5, pp. 503–536

532
Poláková, Buděšínský, Točík, Rosenberg:
~4.25 m, 4 H, 1.362 t, 3 H, J(CH3,CH2) = 7.0 and 1.358 t, 3 H, J(CH3,CH2) = 7.0 (P(OEt)2);
2.15 s, 3 H (OAc). 13C NMR (150.9 MHz, CDCl3): 169.21 and 20.73 (OAc); 165.68, 133.89,
130.09(2), 128.58(2) and 128.32 (OBz); 162.68 (C-4); 149.86 (C-2); 140.81 (C-6); 103.13
(C-5); 91.91 d, J(C,P) = 7.2 (C-1′); 80.14 d, J(C,P) = 5.4 (C-2′); 78.61 d, J(C,P) = 171.6 (C-4′);
75.78 d, J(C,P) = 6.2 (C-3′); 63.55 d, J(C,P) = 6.8, 63.42 d, J(C,P) = 6.8 and 16.45(2) d,
J(C,P) = 5.6 (P(OEt)2).
Diethyl (4S)-[3-O-Acetyl-2-O-benzoyl-1-deoxy-1-(thymin-1-yl)-α-L-threofuranos-4-yl]-
phosphonate (49b)
The title phosphonate was obtained from silylated thymine (1.23 g, 9.8 mmol) and phos-
phonate 48 (900 mg, 2.4 mmol) according to the Method B. Yield 480 mg (47%, white
lyophilizate) of 49b, [α]20 –55.5. HR-FAB calculated for C22H28N2O10P (M + H)+: 511.1482;
found 511.1490. IR (CHCl3, cm–1): T: ν (NH) 3389w; ν (C=O) 1723vs, 1697vs; ν (C=C)
1657m, sh; ν (ring) 1465m, 1435w; δs (CH3) 1387m. OAc: ν (C=O) 1756s; ν (C–O) 1245s, sh,
1029vs; δs (CH3) 1370m; γ (CCOO) 600w. OBz: ν (C=O) 1723vs; ν (C–O) 1261s; ν (ring)
1603w, 1586w, 1493w, 1452m, 1317m, 1179m, 1112m, 1029vs, 1072m, sh, 1002m, sh;
β (C=O) 712s. PO(OEt)2: ν (P=O) 1245s, sh; νas (POCC) 1048s, 1029vs, 977m; δ (POC) 572w;
δas (CH3) 1444w, sh; γs (CH2) 1394w, sh; δas (CH3) 1164w, 1097m. 1H NMR (600 MHz,
CDCl3): 8.24 bs, 1 H (NH); 8.07 m, 2 H, 7.61 m, 1 H and 7.46 m, 2 H (OBz); 7.13 q, 1 H,
J(6,CH3) = 1.2 (H-6); 6.15 d, 1 H, J(1′,2′) = 4.8 (H-1′); 5.93 ddd, 1 H, J(3′,2′) = 3.95, J(3′,4′) =
5.4 and J(3′,P) = 12.7 (H-3′); 5.75 bdd, 1 H, J(2′,1′) = 4.8, J(2′,3′) = 3.95 and J(2′,P) < 1 (H-2);
4.68 dd, 1 H, J(4′,3′) = 5.4 and J(4′,P) = 3.7 (H-4′); 4.25 m, 4 H, 1.37 t, 3 H, J(CH3,CH2) = 7.1
and 1.34 t, 3 H, J(CH3,CH2) = 7.1 (P(OEt)2); 2.16 s, 3 H (OAc); 1.97 d, 3 H, J(CH3,6) = 1.2
(5-CH3). 13C NMR (150.9 MHz, CDCl3): 169.20 and 20.75 (OAc); 165.71, 133.89, 130.10(2),
128.59(2) and 128.37 (OBz); 163.11 (C-4); 149.89 (C-2); 136.38 (C-6); 111.73 (C-5); 91.23
(C-1′); 79.89 d, J(2′,P) = 5.3 (C-2′); 78.28 d, J(4,P) = 171.3 (C-4′); 75.82 d, J(3′,P) = 6.5 (C-3′);
63.52 d, J(C,P) = 6.8, 63.42 d, J(C,P) = 6.9 and 16.47(2) d, J(C,P) = 5.6 (P(OEt)2); 12.61
(5-CH3).
Diethyl (4S)-[3-O-Acetyl-2-O-benzoyl-1-(4-N-benzoylcytosin-1-yl)-
1-deoxy-α-L-threofuranos-4-yl]phosphonate (49c)
The title phosphonate was obtained from silylated 4-N-benzoylcytosine (0.97 g, 4.5 mmol)
and the phosphonate 48 (0.5 g, 1.12 mmol) according to the Method B. Yield 370 mg (55%,
white lyophilizate) of 49c, [α]20 –36.5. HR-FAB calculated for C28H31N3O10P (M + H)+:
600.1747; found 600.1722. IR (CHCl3, cm–1): OAc: ν (C=O) 1754m; ν (C–O) 1239s, sh,
1028s; γ (CCOO) 600w; δs (CH3) 1368m. OBz: ν (C=O) 1728m; β (C=O) 712m; ν (C–O)
1259s; ν (ring) 1316m, 1298m, 1112m, 1002w, 829w. NHBz: ν (NH) 3406w; ν (amide I)
1705m; ν (amide II) 1554m. OBz and NHBz: ν (=CH) 3092vw, 3066vw, 3027w; ν (ring)
1603m, 1583w, 1497w, sh, 1452w, 1180w, 1071m, sh, 1028s, 686w, 616vw. PO(OEt)2:
ν (P=O) 1248s; νas (POCC) 1049s, 1028s, 976w; δ (POC) 567w; δas (CH3) 1445w; γs (CH2)
1392w; δas (CH3) 1165w, 1097m. C: ν (C=O) 1674s; ν (ring) 1629m, 1480vs, 1404w,
1285m, sh. 1H NMR (600 MHz, CDCl3 + DMSO 9:1): 10.22 bs, 1 H (NH); 8.09 m, 2 H,
7.61 m, 1 H and 7.47 m, 2 H (OBz); 8.01 m, 2 H, 7.60 m, 1 H and 7.51 m, 2 H (NBz);
7.845 bd, 1 H, J(6,5) = 7.5 (H-6); 7.64 bd, 1 H, J(5,6) = 7.5 (H-5); 6.16 d, 1 H, J(1′,2′) = 3.3
(H-1′); 5.91 m, 2 H (H-3′ and H-4′); 4.94 dd, 1 H, J(2′,1′) = 3.3 and J(2′,3′) = 5.0 (H-2);
Collect. Czech. Chem. Commun. 2011, Vol. 76, No. 5, pp. 503–536