Synthesis of [2′-2H1]-Ribonucleosides

Article abstract of DOI:10.1002/hlca.200490069

New syntheses of C(2′)-deuterated ribonucleosides have been accomplished starting either from 3,5-di-O-benzyl-1-O-methyl-α,β -D-ribofuranose (1b) or 2,3-O-isopropylidene-D-ribose (14), with >97 atom-% D incorporation in both cases. The former is suited to

Full text of DOI:10.1002/hlca.200490069

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Helvetica Chimica Acta Vol. 87 (2004)
Synthesis of [2'-2H1]-Ribonucleosides
by Andra¬s Fˆldesi*a), Mrinal K.Kundu a), Zolta¬n Dinyab), and Jyoti Chattopadhyayaa)
a) Department of Bioorganic Chemistry, Box 581, Biomedical Center, University of Uppsala,
SE-75123 Uppsala
b) Department of Organic Chemistry, L. Kossuth University, H-4010 Debrecen
(phone: ‡46184714929, fax: ‡4618554495, e-mail: andras@boc.uu.se)
New syntheses of C(2')-deuterated ribonucleosides have been accomplished starting either from 3,5-di-O-
benzyl-1-O-methyl-a,b-d-ribofuranose (1b) or 2,3-O-isopropylidene-d-ribose (14), with >97 atom-% D
incorporation in both cases. The former is suited to the demands of multiple-site deuteration or uniform 13C/
multiple 2H double labeling of the ribofuranose moiety, whereas the latter is particularly appropriate for single-
2
site H labeling for mechanistic studies of enzyme reactions.
1.Introduction.
Various physico-chemical techniques have been exploited in
order to correlate different structural motifs of oligo-DNA or oligo-RNA to their
specific biological functions. Amongst these, NMR spectroscopy is one of the most
powerful tools. The importance of NMR spectroscopy lies in its ability to provide the
desired structural information under quasi-physiological conditions. However, with
growing chain length, the usefulness of NMR spectroscopy becomes restricted due to
the increasing spectral overlap [1], intrinsic line broadening arising from decreased T2
relaxatioin [1], decreased sensitivity caused by slower tumbling rate [1], and the spin
diffusion that prevents accurate NOE volume measurements [2].
To tackle these problems, different isotope-labeling techniques have been reported
so far in the literature. Although either chemical or enzymatic introduction of 13C/15N
labels in the form of labeled monomers [3] into an oligo-RNA or oligo-DNA
substantially reduces the spectral overlap in heteronuclear multidimensional spectra
[4 6], the technique might be problematic for long oligomers for the following
reasons: i) 13C labeling decreases proton T2 relaxation time, which, in turn, decreases
the sensitivity of homonuclear J correlation techniques, ii) the syntheses of uniformly
13C-labeled 2'-deoxynucleosides is less elaborated [7 10] compared to the RNA
counterparts [11 13], iii) 13C-signal broadening and signal loss due to long pulse
sequences [14], iv) any enzymatic syntheses of labeled RNA [11 13] or DNA [7 10]
do not allow the labeling of a particular segment of interest except ligation of labeled
and natural stretches [15].
The early idea of using D labeling in NMR studies on oligonucleotides was based
primarily on suppressing part(s) of the 1H-NMR spectrum [16]. However, it was soon
found that site-specific or complete substitution of D for H in the sugar residues of
nucleosides [17] and the sequence-specific incorporation of these specifically deuter-
ated units into an oligomer not only simplifies spectral overcrowding, but enhances
resolution and sensitivity, as well as efficiently reduces the deleterious effect of

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743
relaxation. The cumulative effect is the facilitation of the structure elucidation as it has
been demonstrated for −the Uppsala NMR window× concept [18].
When introduced into uniformly 13C-labeled nucleoside blocks, D labels have a
positive effect on preserving the 13C magnetization during the long heteronuclear pulse
trains in NMR experiments with uniformly 13C-labeled RNAs [19]. Since the primary
source of 13C labels in the chemical synthesis of nucleosides with uniformly 13C-labeled
pentofuranose moiety is d-[13C6]glucose, the need for d-glucose-based deuteration
methods is fairly justified.
Besides NMR studies, investigations of the mechanisms of enzyme reactions have
posed a further great demand for specifically deuterated nucleosides [17a][20].
Additional need for these labeled molecules might arise from studying the possible
biological effect of the D substitution [21], which is an unexplored field for nucleosides
and its derivatives.
The
D
incorporation into ribonucleosides according to an oxida-
tionÀreductionÀinversion sequence at both nucleoside and sugar levels involves
various methods, which differ in orthogonality of the protecting groups as well as in the
type of the oxidation and reducing agents used [17a]. For example, the free C(2')ÀOH
of a 3',5'-bis-O-protected ribonucleoside (by either (tert-butyl)dimethylsilyl (TBDMS)
[22a,c,e] or 1,1,3,3-tetraisopropyldisiloxan-1,3-diyl group (TPDS) [18i][22b,e]) is
oxidized with CrO3/pyridine/Ac2O [18i][22a,b,e] or DMSO/Ac2O [22a] or DMSO/
oxalyl chloride [18i][22d] or DessÀMartin reagent to give the corresponding C(2')-oxo
nucleoside [22c][22e]. The subsequent reduction with LiAlD4 [22a] or NaBD4
[18i][22a][22c] gives predominantly the arabino-diastereoisomer [18i][22a,c,d] owing
to the preferential a-attack over the b-attack; the exact ratio of arabino vs. ribo
depends, however, on the nature of the nucleobase. Subsequently, the inversion of the
C(2')ÀOH with arabino-configuration affords the required protected [2'-2H1]ribonu-
cleoside [18i][22c].
This approach requires the careful choice of the protection for the C(3')ÀOH and
C(5')ÀOH groups. For example, the partial loss of the TPDS group during reduction of
an adenosine dervative [22b] complicated its usefulness for the preparation of the
target deuterionucleoside. Remarkable stereocontrol by the free C(5')ÀOH group has
been recently reported for 3'-O-TBDMS-2'-oxoadenosine and for a corresponding
base-modified analog, when the reducing agent sodium triacetoxyborodeuteride [22c]
is used to orchestrate a deuteride ion delivery from the b-face to give the ribo-product
with excellent stereocontrol (ca. 99%). However, the utility of this method for the
labeling of other nucleosides has not yet been corroborated. The 2'-2H labeling of
nucleosides by the above oxidationÀreduction sequence [22b] is further complicated
by the fact that it gives an intractable mixture of products for guanosine derivatives. For
the above reasons, clearly, D incorporation at C(2) at the sugar level, followed by
glycosylation to give ribonucleoside, is an attractive alternative procedure. The
oxidation of benzyl 3,4-O-isopropylidene-b-d-arabinopyranoside by CrO3/Ac2O/pyr-
idine, followed by reduction with LAD, furnished the [2'-2H1]ribopyranoside derivative
with high stereoselectivity (> 90%) [18i][22b]. A similar transformation commencing
with DessÀMartin oxidation of 1,3,5-tri-O-benzoyl-a-d-ribofuranose [23a], followed
by reduction with NaBD4 in presence of CeCl3, resulted in excellent stereoselectivity
2
but gave relatively poor D enrichment (92 94 atom-% H, which is considered to be

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Helvetica Chimica Acta Vol. 87 (2004)
insufficient for high-resolution NMR studies because of the interference by the
background residual proton resonance lines). The instability of the Bz protecting
groups during the reduction is an additional disadvantage of this methodology [23a]. A
further consideration for the incorporation of D at the nucleoside level especially for
the NMR studies is that the protecting-group manipulations for the D labeling are not
the same as for the preparation of the phosphoramidite building blocks for oligo-RNA
synthesis. Performing all protectionÀremovalÀreprotection steps with the individual
nucleosides can substantially diminish the overall yield as compared to the preparation
of the labeled sugar precursor. Hence, there is a good need for efficient alternative
syntheses, which can overcome most of the above disadvantages. In addition, the new
methodology should also be useful and practical for the multigram-scale preparation
of the deuterionucleosides for relatively large-scale oligo-RNA synthesis for NMR
work.
In our synthesis 2'-deoxy[2'(R/S),3',5'(R/S)-2H3]ribonucleosides, we introduced the
third D at C(2') through the reduction of the C(2)ˆO sugar resulting from the
oxidation of methyl 3,5-di-O-benzyl-a/b-d-[3,5(R/S)-2H2]ribofuranoside (1a;
Scheme 1) to give a mixture of predominantly arabino-and minor ribo-diastereoisom-
ers 2a (ca. 7:3 as estimated by 1H-NMR) [18i]. Similar stereoselectivity is exploited for
the synthesis of b-d-mannosides through the reduction of b-d-glycoside-2-uloses [24]
having 3-O-allyl or 3-O-benzyl groups vicinal to the CˆO function. In the subsequent
steps, the Bn groups of 2a were removed, and the resulting methyl [2,3,5(R/S)-
2H3]arabinofuranoside was separated from the corresponding ribo-component of 2a on
a Dowex OHÀ column, converted to the corresponding benzyl 3,4-O-ispropylidene-b-
d-arabinopyranoside, and deuterated at C(2) according to our oxidationÀreduction
procedure discussed earlier [22b]. This long sequence of reactions (ten steps from 2 to
9) decreased the yield of the labeled methyl ribofuranoside substantially (overall yield
of ca. 17% in ten steps), which is unacceptable for a building block to be used for
milligram-scale solid-phase synthesis of large oligo-DNA (>20mer) with one or two
NMR window(s) in the molecule for detailed solution-structure elucidation [18a,e,j].
We argued that if, upon appropriate protection of the C(2)ÀOH, the mixture of the
2
methyl 3,5-di-O-benzyl [2-2H1]arabino-and [2- H1]ribofuranosides 2b (arabino/ribo
7:3 by NMR) could be successfully separated, and then the inversion of the arabino-
diastereoisomer to ribo-analog could be achieved, it would constitute a much shorter
and practical synthetic protocol for the D labeling at C(2') of ribonucleosides. At this
point, we also considered, as an alternative, the scale-up of the single-step D/H
2
exchange reaction at C(2) (> 97 atom-% H) of 2,3-O-isopropylidene-a/b-d-ribofur-
anose [23b] in a mixture of 1,4-dioxane/Et3N/THF/2H2O at a reflux temperature. In this
paper, the synthetic details of these two alternative chemical syntheses of [2'-2H1]ri-
bonucleosides are reported.
2.Results and Discussion.
For the synthesis of the required nucleosides, we
wanted to take the advantage of a 2-O-acyl protection of the sugar precursor as in 11
(Scheme 1) during the glycosylation step, since this gives exclusively the b-anomer.
Also, due to the known difficulties [25] to remove the Bn protecting groups of a
nucleoside (specially with pyrimidine aglycones), a reasonable demand was to remove
these groups still at the sugar level (i.e., 8 ! 9). It is necessary to stress that the use of

Helvetica Chimica Acta Vol. 87 (2004)
745
Scheme 1
i) Oxalyl chloride, DMSO in CH2Cl2, À708. ii) LiAlD4 in dry Et2O, r.t. iii) TolCl, pyridine, r.t. iv) NH3 in MeOH,
r.t. v) Tf2O, DMAP, Py, CH2Cl2, 08, 3 h. vi) Cesium propanoate, DMF, r.t. vii) Pd/C, H2 in EtOH, r.t. viii) Ac2O,
AcOH, conc. H2SO4, CH2Cl2, 08, 15 min. ix) Persilylated nucleobase, TMSOTf, ClCH2CH2Cl or toluene (12b),
heating. Ac ˆ Acetyl; Bn ˆ benzyl; Bz ˆ benzoyl; DMAP ˆ 4-(dimethylamino)pyridine; Dpc ˆ diphenylcar-
bamoyl; Prˆ propanoyl; TMSOTf ˆ trimethylsilyl trifluoromethanesulfonate; Tol ˆ 4-toluoyl (ˆ4-methylben-
zoyl); A ˆ adenin-9-yl; C ˆ cytidin-1-yl; G ˆ guanin-9-yl; U ˆ uracil-1-yl.
4-methoxybenzyl instead of Bn protection might overcome the pyrimidine-reduction
problem, since it involves a Ce3‡-promoted oxidation step [26], but its usefulness is yet
to be documented in nucleoside synthesis.
The first method introduces D to C(2) at the sugar level starting from 1,2 :5,6-di-O-
isopropylidene-a-d-glucose, from which the starting 3,5-O-protected methyl ribofur-
anoside derivative 1b (Scheme 1) is easily available in large quantity (15 g) in six steps
[27]. Compound 1b was subjected to Swern oxidation [28] with oxalyl chloride and
DMSO in dry CH2Cl2 at À708. The disappearance of the strong singlet at d 3.32 for the
1
anomeric Me group in the H-NMR spectrum for the b-anomer of 1b confirmed that
the oxidation was complete (the same signal at d 3.48 for the a-anomer of 1b overlaps
with other signals in the 1H-NMR spectrum of the ketone). Reduction with LAD in dry
Et2O afforded a diastereoisomeric C(2)-deuterated mixture 2b composed of arabino-
and ribofuranosides in a ratio of ca. 7:3 (64%), as evidenced by 1H-NMR. The arabino-
configuration in the main component is supported by the large upfield shift of C(1)
(from d 108.4 to 102.5). This mixture was successfully separated after 4-toluoylation at
C(2)ÀOH to afford methyl 3,5-di-O-benzyl-2-O-(4-toluoyl)-a-[2-2H1]ribofuranoside
(3) (26%) and methyl 3,5-di-O-benzyl-2-O-(4-toluoyl)-b-[2-2H1]arabinofuranoside (4)
(62%).
The composition of the starting C(1) epimeric mixture (b/a ca. 7:3) indicated again
[18i] that the arabino-derivative might be formed diastereospecifically from the b-

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Helvetica Chimica Acta Vol. 87 (2004)
anomer of 1b, whereas the ribo-compound arises from the a-anomer, i.e., the
configuration of the anomeric MeO group controls the diastereoselectivity by
specifically dictating the delivery of the deuteride ion from either a or b face. To
gain deeper insight into the stereochemical course of the reduction of the 2-oxo
compound diastereoisomer mixture of 1b was 2-O-(4-toluoyl)-protected, and the pure
anomers were separated. The 4-toluoyl group was removed, and the b-anomer of 1b
was subjected to DessÀMartin oxidation [17b][29]. Reduction of the ketone afforded a
mixture containing two compounds in a ratio of ca. 91:9. The whole mixture was again
4-toluoylated, and the two compounds were separated by short-column chromatog-
raphy (toluene/CH2Cl2 70 :30 (v/v) with MeOH gradient). The separated major
component proved to be the arabinoside 4, whereas the minor compound was identical,
by 1H-NMR, to the methyl 3,5-di-O-benzyl-2-O-(4-toluoyl)-b-d-ribofuranoside except
for bearing D at C(2). Similar oxidationÀreduction steps carried out with the a-
anomer gave ca. 4% of methyl 3,5-di-O-benzyl-a-arabinofuranoside as judged from the
analysis of the 1H-NMR spectrum of the crude mixture in comparison with the
literature data [30]. This reveals that the reduction is proceeding with a high
diastereoselectivity.
Compound 3 can be deprotected to the a-anomer of 9 (Scheme 1) to improve the
overall yield of the nucleoside precursor 11, as it has been shown in the preparation of
[2',3',4',5',5''-2H5]ribonucleosides [17b] but, in this study, it was used for exploring the
use of the MeO group at the anomeric center of the sugar for the glycosylation step.
However, a SnCl4-catalyzed synthesis of [2'-2H1]ribothymidine and the subsequent
deprotection proceeded with moderate yields (66 and 75%, resp.), hence this approach
was abandoned. As mentioned above, the goal of this work required the inversion of
configuration at C(2) of the arabino-compound 4 to give the ribo-counterpart 7. To
achieve this the 2-O-Tol group of compound 4 was removed by methanolic ammonia at
room temperature to afford arabinoside 5 (95%), followed by the conversion to the 2-
O-triflate derivative 6 (89%) upon treatment with 4-(dimethylamino)pyridine,
pyridine, and trifluoroacetic anhydride in dry CH2Cl2. In the absence of HÀC(2),
the presence of Tf moiety is corroborated by the appearance of a quadruplet 13C signal
at d 118.4 exhibiting the large J(C,F) coupling. Subsequently, compound 6 was
converted to the 2-O-propanoyl derivative 7 (73%) by displacement with cesium
propanoate in DMF at room temperature under an inert atmosphere [31]. The upfield
shift of the peak from d 4.99 to 4.87 for the corresponding anomeric proton HÀC(1)
proved that the reaction proceeded with an inversion of the configuration. Also, the
change of the appropriate 13C chemical-shift order for C(3) and C(4) (C(3) (d 80.8) >
C(4) (d 79.7) for the arabino-compound 6 to C(4) (d 80.3) > C(3) (d 77.7) for the ribo
compound 7), together with the large downfield shift of C(1) (Dd 5.9), corroborated
the ribo-configuration at C(2). An attempt to convert the deuterated 2-O-propanoyl-
ribofuranoside 7 to the 1-O-acetyl derivative via treatment with a Ac2O, AcOH, and
concentrated H2SO4 mixture in CH2Cl2 in order to achieve higher coupling yields with
the silylated nucleobases failed in our hand. This might be attributed to the presence of
the two Bn groups, which are most probably unstable in the strongly acidic medium.
Therefore, the 2-O-propanoyl group was cleaved upon treatment with methanolic
ammonia to furnish compound 8 (98%), followed by the removal of the Bn groups in a
catalytic hydrogenation process over 10% Pd/C in EtOH to afford the C(2)-deuterated

Helvetica Chimica Acta Vol. 87 (2004)
747
methyl ribofuranoside 9 (98%). The spectral data were compared to those of its natural
counterpart. The presence of a singlet at d 4.83 for HÀC(1) and a doublet at d 4.1
(J(3,4) ˆ 6.9 Hz) for HÀC(3) obviated that more than 97 atom-% isotope incorpo-
ration has indeed taken place at C(2). Also, a low-intensity triplet (arising from the
distribution of signal intensity and longer relaxation) was observed at d 73.6 in the 1H-
decoupled 13C-NMR spectrum as a result of C,D coupling. Subsequently, compound 9
was 4-toluoylated to afford compound 10 (98%), followed by a treatment with a
mixture of Ac2O, AcOH, and concentrated H2SO4 in CH2Cl2 [18i] to obtain the
required 1-O-acetyl-2,3,5-tri-O-(4-toluoyl)-a/b-d-[2-2H1]ribofuranose (11) (99%).
From this anomeric mixture, the b-anomer was crystallized from MeOH to give an
1
analytical sample. When its H-NMR spectrum is compared to the spectrum of the
natural counterpart (Fig. 1,a and b), the lack of HÀC(2) signal at d 5.75 and the
appearance of the HÀC(3) signal as a doublet at d 5.86 establish the > 97 atom-% D
incorporation as measured by integrating the residual HÀC(2) signal. The specific-
optical-rotation measurement also established the identity of this compound (specific
optical rotation for b-anomer of 11: ‡ 62, for authentic sample: ‡ 63).
The second method introduces the D label at C(2) starting from d-ribose. It has
been reported from our laboratory [23b] that, on small scale (1 mmol), it is possible to
obtain > 97 atom-% diastereospecific exchange of the H at C(2) of 2,3-O-
ispropylidene-ribose to D upon equilibration in dioxane/THF/Et3N/2H2O at elevated
temperature. We herein report on specific conditions optimized for scaling up this
exchange reaction to a level suitable for production of nucleosides for oligomer
synthesis (ca. 22 mmol), which, upon several steps of synthetic manipulations, gave the
4-toluoylated ribose derivative 11 to be used for subsequent coupling with nucleobases
(Scheme 2). The starting 2,3-O-acetonide 14 was prepared in a protic-acid-catalyzed
reaction of d-ribose with acetone [32] in 78% yield. For the multigram-scale exchange
of the ribofuranose 14, it was dissolved in ca. 3.5 ml/mmol of the mixture of dioxane/
THF/Et3N/2H2O, instead of 20 ml/mmol [23b], and the 2H2O amount was reduced from
4.6 ml/mmol [23b] to 0.73 ml/mmol, and the mixture was then heated at ca. 908 for 5 d.
The reaction proceeded without formation of detectable amount of side products to
furnish the deuterated sugar 15 (99% yield). The deuteration level was found to be >
97 atom-% as determined from the 1H-NMR spectrum. The deuterated ribose
derivative 15 was converted to the labeled methyl ribofuranoside 16 (99%) by
deprotection of the isopropylidene group in 80% aqueous AcOH, followed by
glycosylation in MeOH in the presence of catalytic amount of concentrated H2SO4.
Scheme 2
i) Dioxane/THF/Et3N/D2O (24 :24 :12 :16 ml), 908, 5 d. ii) 80% aq. AcOH, 908, 24 h. iii) MeOH, conc. H2SO4,
48, 12 h. iv) TolCl, Py, r.t. Tol ˆ 4-Toluoyl.

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Helvetica Chimica Acta Vol. 87 (2004)
Fig. 1. Expanded regions of the 270-MHz 1D-1H NMR spectra of 1-O-acetyl-2,3,5-tris-O-(4-toluoyl)-b-d-[2-
2H1]ribose (11b) (a) and its natural-abundance counterpart (b), 2',3',5'-tris-O-(4-toluoyl)-[2'-2H1]uridine (12a)
(c) and its natural-abundance counterpart (d), N2-acetyl-O6-(diphenylcarbamoyl)-2',3',5'-tris-O-(4-toluoyl)[2'-
2H1]guanosine (12b) (e) and its natural-abundance counterpart (f)

Helvetica Chimica Acta Vol. 87 (2004)
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This ribose derivative 16 was 4-toluoylated by 4-methylbenzoyl chloride in dry pyridine
to give the fully protected 17 (93%), which was further converted to 11 by the
acetylation procedure as described for 10 [18i].
The coupling reactions with the persilylated uracil, N2-acetyl-O6-(diphenylcarba-
moyl)guanine, N6-benzoyladenine, and N4-benzoylcytosine nucleobases were carried
out according to well-established methods [33] to give the fully protected C(2)-
deuterated nucleosides 12a 12d (88, 73, 85, and 70%, resp.). Comparison of their
1H-NMR spectra with those of the corresponding protected natural nucleosides
(Fig. 1,c f, and Fig. 2,a d) evidences that no D-exchange reaction has taken place
during the coupling process. The protecting groups were removed by treatment with
NH3 in MeOH to produce the target [2'-2H1]ribonucleosides 13a 13d (99, 85, 82, and
90%, resp.). The purity and the high-level isotope enrichment of these compounds are
1
evidenced again upon comparison of their H-NMR spectra with those of authentic
natural counterparts (Fig. 2,e and f, and Fig. 3, and Exper. Part). The identity of the
nucleosides 13a 13d was further corroborated by high-resolution mass spectrometry,
IR spectroscopy, as well as by optical-rotation measurements (see Exper. Part for
details). It is interesting to note herein that, in the IR spectra of these monodeuterated
carbohydrate and nucleoside analogues, no absorptions were observed in the region of
the CÀD stretching (2300 2000 cmÀ1) [34], even when films of the neat compounds
were used as samples.
3.Conclusions. Two new syntheses of C(2')-deuterated ribonucleosides have been
devised. Starting from 1-O-methyl-3,5-di-O-benzyl-a/b-d-ribofuranose (1), it has been
found that i) Swern oxidation is suitable for complete oxidation of the C(2)ÀOH as a
cheaper alternative to the DessÀMartin periodinane oxidation; ii) the reduction
proceeds with high diastereoselectivity governed by the anomeric MeO group; iii) the
present method substantially improves the overall yield from arabino-2 to ribo-9 (from
17 to 36%) as compared to the previous C(2)-deuterations [18i][22b] through benzyl
arabinopyranoside; iv) the method is fully compatible with sequential multiple D
incorporation (> 97 atom-%) and with the ul-13C-labeled d-glucose-based 2H/13C
double labeling. The second method uses 2,3-O-isopropylidene-d-ribose (14) as
starting material, and a large-scale exchange process gives > 97 atom-% D
incorporation in a single equilibration step. Because of its simplicity, it is well-suited
for C(2') single-site labeling for exploring mechanistic aspects of enzyme reactions.
Thanks are due to the Swedish Natural Science Research Council (NFR contract No. K-KU 12067-300 to A.
F. and K-AA/Ku04626-321 to J. C.), Philip Morris USA Inc. (to J. C.) and Carl Tryggers Styftelse (to A. F.) for
generous financial support.
Experimental Part
General. CH2Cl2 and 1,2-dichloroethane were refluxed with P2O5, followed by distillation under N2 and
kept over molecular sieves (3 ä). Pyridine was refluxed on CaH2 overnight, followed by distillation and stored
over molecular sieves (3 ä). The chromatographic separations were performed on Merck G60 silica gel. TLC
was performed on Merck pre-coated silica gel 60 F254 glass backed plates in following systems: A) toluene/
CH2Cl2/MeOH 7:3 :0.1 (v/v/v), B) AcOEt/cyclohexane 1:1 (v/v), C) AcOEt/cyclohexane 70 :30 (v/v), D)
AcOEt/PrOH/H2O 30 :18 :6 (v/v/v), E) AcOEt, F) MeOH/CH2Cl2 10 :90 (v/v), G) petroleum ether/AcOEt
8 :2. 1H-NMR Spectra: at 270.17 MHz, with TMS or MeCN (for D2O solns., set at 2.0 ppm) as internal

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Fig. 2. Expanded regions of the 270-MHz 1D-1H-NMR spectra of N6-benzoyl-2',3',5'-tris-O-(4-toluoyl)[2'-
2H1]adenosine (12c) (a) and its natural-abundance counterpart (b), N6-benzoyl-2',3',5'-tris-O-(4-toluoyl)[2'-
2H1]cytidine (12d) (c) and its natural-abundance counterpart (d), [2'-2H1]uridine (13a) (e) and its natural-
abundance counterpart (f)

Helvetica Chimica Acta Vol. 87 (2004)
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Fig. 3. Expanded regions of the 270-MHz 1D-1H NMR spectra of [2'-2H1]guanosine (13b) (a) and its natural-
abundance counterpart (b), [2'-2H1]adenosine (13c) (c) and its natural-abundance counterpart (d), [2'-2H1]cy-
tidine (13d) (e) and its natural-abundance counterpart (f)

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Helvetica Chimica Acta Vol. 87 (2004)
standards. 13C-NMR Spectra: at 67.9 MHz, with the central peak of CDCl3 (76.9 ppm), (D6)DMSO (39.6 ppm),
or MeCN (1.3 ppm) as references. Chemical shifts (d) in ppm, coupling constants in Hz; signal assignments for
each compound were achieved by 2D-NMR experiments (1H,1H-COSY, 1H,13C-HETCOR, COLOC) with
standard software. 13C Multiplicities and overlapping quaternary signals were identified by APT experiments.
Assignments were also corroborated by comparison with literature data. EI-MS (pos.): at a resolution of R ˆ
8000.
3,5-Di-O-benzyl-1-O-methyl-b-d-[2-2H1]arabino/a-d-[2-2H1]ribofuranose (2b). A soln. of DMSO (4.6 ml,
65.1 mmol) in CH2Cl2 (15 ml) was added slowly to a mixture of oxalyl chloride (3.7 ml, 42.3 mmol) and dry
CH2Cl2 (15 ml) at À708, followed by the dropwise addition of a soln. of 1b (11.25 g, 32.7 mmol) in CH2Cl2
(35 ml), and the resulting mixture was stirred for 4 h at the same temp. To quench the reaction, Et3N (23 ml,
163 mmol) was added at À708, and then the mixture was allowed to reach r.t., followed by the addition of H2O
and extraction with CH2Cl2. The combined org. layer was successively washed with brine, dried (MgSO4), and
concentrated. The crude residue was dissolved in dry Et2O (100 ml), and LAD (0.8 g, 19 mmol) was added at 08,
and the mixture was extracted with CH2Cl2. The org. phase was concentrated, and the residue was purified by
column chromatography (CC) to yield 2b (7.2 g, 64%). Rf (G) 0.27, 0.29. 1H-NMR (CDCl3): 7.34 7.27
(m, 2 PhCH2); 4.88, 4.86 (2s, HÀC(1) (a and b)); 4.77 4.56 (m, 2 PhCH2); 4.26 4.22, 4.16 4.06 (m, HÀC(4)
(a and b)); 3.84, 3.78 (2d, HÀC(3) (a and b)); 3.54 3.52 (m, CH2(5)); 3.47, 3.41 (s, MeO (a and b)). 13C-NMR
(CDCl3): 137.9, 129.7, 129.6, 128.2, 127.8, 127.62, 127.6 (PhCH2); 102.5 (C(1)); 84.5 (C(3)); 80.7 (C(4)); 72.3
‡
‡
(PhCH2); 71.9 (C(5)); 71.7 (CH2); 55.3 (MeO). HR-EI-MS (pos.): 345.1693 (M , C20H232HO5 ; calc. 345.1686).
Methyl 3,5-Di-O-benzyl-2-O-(4-methylbenzoyl)-a-d-[2-2H1]ribofuranoside (3) and Methyl 3,5-Di-O-ben-
zyl-2-O-(4-methylbenzoyl)-b-d-[2-2H1]arabinofuranoside (4). Compound 2b (7.2 g, 20.8 mmol) was co-evapo-
rated with dry Py and dissolved in the same solvent (100 ml). 4-Methylbenzoyl chloride (3.2 ml, 24 mmol) was
added dropwise at ice-bath temp., and the mixture was stirred overnight allowing it to warm to r.t. Cold sat. aq.
NaHCO3 soln. was added, and the mixture was stirred for 30 min. It was extracted with CH2Cl2, and the org.
phase was dried (MgSO4). After removing the solvent under reduced pressure, the crude product was subjected
to CC to afford 3 (2.52 g, 26%) and 4 (6.0 g, 62%).
Data of 3: Rf (B) 0.60. [a]2D6 ˆ ‡98 (c ˆ 0.67, CHCl3). IR (neat): 3082, 3059, 3025, 2998, 2917, 2858, 1712,
1608, 1492, 1449, 1406, 1360, 1286, 1204, 1178, 1153, 1100, 1018, 908, 839. 1H-NMR (CDCl3): 8.03 7.23 (m, Tol,
2 PhCH2); 5.21 (s, HÀC(1)); 4.73 4.43 (m, 2 PhCH2); 4.30 4.24 (m, HÀC(4)); 4.10 (d, J(3,4) ˆ 4.5, HÀC(3));
3.52 3.33 (m, CH2(5)); 3.47 (s, MeO); 2.42 (s, MeC6H4). 13C-NMR (CDCl3): 166.0 (CˆO, Tol); 143.8, 137.8,
129.9 (Tol); 129.0, 128.3, 128.2, 128.0, 127.6 (PhCH2); 102.1 (C(1)); 81.5 (C(4)); 75.2 (C(3)); 73.4, 72.9 (PhCH2);
69.4 (C(5)); 55.7 (MeO); 21.6 (MeC6H4). HR-EI-MS (pos.): 463.2109 (M , C28H292HO6 ; calc. 463.2106).
Data of 4: Rf (G) 0.54. [a]2D5 ˆ À91 (c ˆ 0.24, CHCl3). IR (neat): 3082, 3060, 3032, 2924, 2860, 1718, 1610,
1492, 1452, 1408, 1360, 1288, 1208, 1179, 1145, 1110, 1028, 910, 839. 1H-NMR (CDCl3): 7.94 7.21 (m, Tol,
PhCH2); 5.21 (s, HÀC(1)); 4.70 4.59 (m, 2 PhCH2); 4.34 (d, J(3,4) ˆ 5.6, HÀC(3)); 4.26 4.19 (m, HÀC(4));
3.65 3.54 (m, CH2(5)); 3.28 (s, MeO); 2.42 (s, MeC6H4). 13C-NMR (CDCl3): 165.8 (CˆO, Tol); 143.9, 137.9,
137.6, 129.8, 129.0, 128.3, 127.7, 127.62, 127.6, 126.6 (PhCH2, Tol); 101.3 (C(1)); 81.3 (C(3)); 79.6 (C(4)); 73.3
‡
‡
‡
(PhCH2); 72.0 (C(5)); 71.98 (PhCH2); 55.2 (MeO); 21.6 (MeC6H4). HR-EI-MS (pos.): 463.2110 (M ,
C28H292HO6 ; calc. 463.2106).
‡
Methyl 3,5-Di-O-benzyl-b-d-[2-2H1]arabinofuranoside (5). Methanolic ammonia was added to 4 (6.0 g,
12.94 mmol), and the soln. was stirred at r.t. for 2 d. Removal of solvent and purification by silica-gel CC gave 5
(4.23 g, 95%). Rf (G) 0.29. [a]2D5 ˆ À49 (c ˆ 0.32, CHCl3). IR (neat): 3459, 3084, 3060, 3030, 2920, 2859, 1494,
1452, 1362, 1308, 1202, 1156, 1095, 1049, 1029, 1010, 910, 852, 819. 1H-NMR (CDCl3): 7.34 7.25 (m, 2 PhCH2);
4.86 (s, HÀC(1)); 4.77 4.52 (m, 2 PhCH2); 4.17 4.11 (m, HÀC(4)); 3.84 (d, J(3,4) ˆ 5.4, HÀC(3)); 3.55 3.52
(d, J(4,5) ˆ 5.7, CH2(5)); 3.41 (s, MeO). 13C-NMR (CDCl3): 137.9, 137.8, 128.2, 127.54, 127.5, 127.47 (PhCH2);
102.5 (C(1)); 84.4 (C(3)); 80.6 (C(4)); 73.1 (PhCH2); 71.9 (C(5)); 71.7 (PhCH2); 55.2 (MeO). HR-EI-MS
(pos.): 345.1695 (M , C20H232HO5 ; calc. 345.1687).
‡
‡
Methyl 3,5-Di-O-benzyl-2-O-(trifluoromethylsulfonyl)-b-d-[2-2H1]arabinofuranoside (6). Compound 5
(4.18 g, 12.10 mmol) was co-evaporated with dry pyridine, and it was dissolved in dry CH2Cl2 (90 ml), followed
by the addition of DMAP (5.18 g, 42.4 mmol) and pyridine (9 ml). The mixture was cooled to 08, and Tf2O
(2.8 ml, 16.96 mmol) was added dropwise, and the resulting mixture was stirred at the same temp. for 3 h. The
mixture was poured into cold sat. NaHCO3 soln. The org. layer was separated, and the H2O phase was extracted
with CH2Cl2. The combined org. extract was dried (MgSO4) and concentrated. The residue was purified by CC
to give 6 (5.18 g, 90%). Rf (G) 0.59. [a]D27 ˆ À64 (c ˆ 0.74, CHCl3). 1H-NMR (CDCl3): 7.35 7.20 (m, 2 PhCH2);
4.99 (s, HÀC(1)); 4.76 4.47 (m, 2 PhCH2); 4.29 (d, J(3,4) ˆ 5.4, HÀC(3)); 4.17 4.11 (m, HÀC(4)); 3.58 3.44
(m, CH2(5)); 3.38 (s, MeO). 13C-NMR (CDCl3): 137.6, 136.8, 128.4, 128.3, 127.7, 127.6 (PhCH2); 118.4

Helvetica Chimica Acta Vol. 87 (2004)
753
(q, J(C,F) ˆ 319.7, CF3); 100.3 (C(1)); 80.8 (C(3)); 79.7 (C(4)); 73.4, 72.5 (2 PhCH2); 71.3 (C(5)); 55.4 (MeO).
‡
‡
HR-EI-MS (pos.): 477.1184 (M , C21H22 2HF3O7S ; calc. 477.1179).
3,5-Di-O-benzyl-1-O-methyl-2-O-propanoyl-b-d-[2-2H1]ribofuranose (7). Cesium propionate (2.9 g,
14.1 mmol) was added to a soln. of 6 (5.18 g, 10.85 mmol) in dry DMF (60 ml), and the mixture was stirred
for 36 h at r.t. The solvent was removed under reduced pressure, and H2O was added. After extraction with
CH2Cl2 and removal of volatile material, the residue was separated by silica-gel CC to give 7 (3.2 g, 73%). Rf
(G) 0.54. [a]2D7 ˆ ‡14 (c ˆ 0.71, CHCl3). IR (neat): 3082, 3060, 3030, 2920, 2855, 1735, 1494, 1452, 1418, 1360,
1275, 1188, 1140, 1099, 1068, 1012, 982, 950, 910, 879. 1H-NMR (CDCl3): 7.33 7.25 (m, 2 PhCH2). 4.87
(s, HÀC(1)); 4.61 4.38 (m, 2 PhCH2); 4.25 4.19 (m, HÀC(4)); 4.12 (d, J(3,4) ˆ 7.6, HÀC(3)); 3.63 3.47
(dq, CH2(5)); 3.33 (s, MeO); 2.4 (q, CH2O); 1.13 (t, Me). 13C-NMR (CDCl3): 173.5 (CˆO); 138.1, 137.4, 128.2,
127.8, 127.7, 127.5 (PhCH2); 106.2 (C(1)); 80.3 (C(4)); 77.7 (C(3)); 73.1, 72.9 (2 PhCH2); 71.1 (C(5)); 54.9
(CH2O); 27.3 (MeO); 8.9 (MeCH2). HR-EI-MS (pos.): 401.1955 (M , C23H272HO6 ; calc. 401.1949).
Methyl 3,5-Di-O-benzyl-b-d-[2-2H1]ribofuranoside (8). Compound 7 (2.7 g, 6.73 mmol) was treated with
methanolic ammonia under stirring at r.t. for 30 h. Usual workup, followed by removal of solvent on a rotary
evaporator and washing with H2O, gave chromatographically homogeneous compound 8 (2.3 g, 99%). Rf (G)
0.27. [a]2D7 ˆ À29 (c ˆ 0.71, CHCl3). IR (neat): 3459, 3082, 3060, 3026, 2920, 2859, 1494, 1452, 1362, 1204, 1158,
1085, 1063, 910, 873, 810. 1H-NMR (CDCl3): 7.38 7.48 (m, 2 PhCH2); 4.86 (s, HÀC(1)); 4.57 (2s, 2 PhCH2);
4.26 4.20 (m, HÀC(4)); 4.07 (d, J(3,4) ˆ 6.2, HÀC(3)); 3.54 (d, J(4,5) ˆ 5.3, CH2(5)); 3.31 (s, MeO).
13C-NMR (CDCl3): 138.0, 137.0, 128.5, 128.2, 127.5 (PhCH2); 108.4 (C(1)); 80.5 (C(4)); 79.4 (C(3)); 73.2
‡
‡
(PhCH2); 72.7 (PhCH2); 71.5 (C(5)); 54.9 (MeO). HR-EI-MS (pos.): 345.1692 (M , C20H232HO5 ; calc.
345.1687).
‡
‡
Methyl b-d-[2-2H1]ribofuranoside (9). The Bn groups of 8 (2.1 g, 6.08 mmol) were cleaved with Pd/CÀH2
(450 mg) in EtOH (40 ml) over 3 h at r.t. The reagent was filtered through Celite, and the filtrate was evaporated
to dryness to afford 9 (980 mg, 98%). Rf (D) 0.58. [a]2D6 ˆ À38 (c ˆ 0.15, H2O). 1H-NMR (D2O): 4.83
(s, HÀC(1)); 4.08 (d, J(3,4) ˆ 6.9, HÀC(3)); 3.98 3.92 (m, HÀC(4)); 3.76 3.51 (dq, J(4,5) ˆ 3.3, J(4,5') ˆ 6.4,
J(5,5') ˆ 12.2, CH2(5)); 3.33 (s, MeO). 13C-NMR (D2O): 107.7 (C(1)); 82.7 (C(4)); 73.6 (t, J(C,D) ˆ 24, C(2));
70.5 (C(3)); 62.6 (C(5)); 54.9 (MeO). HR-EI-MS (pos.): 165.0748 (M , C6H112HO5 ; calc. 165.0747).
‡
‡
1-O-Methyl-2,3,5-tris-O-(4-methylbenzoyl)-b-d-[2-2H1]ribofuranose (10). Compound
9 (980 mg,
5.93 mmol) was co-evaporated with dry pyridine twice and dissolved in the same solvent (50 ml). 4-
Methoxybenzoyl chloride (2.6 ml, 19.52 mmol) was added dropwise in an ice-bath under stirring. The mixture
was kept for 15 h allowing it to warm to r.t. Sat. aq. NaHCO3 soln. was added and stirred for 3 h. The compound
was extracted with CH2Cl2 from H2O. Evaporation under reduced pressure gave chromatographically
homogeneous 10 (2.97 g, 96%). Rf (C) 0.82. [a]2D6 ˆ ‡75 (c ˆ 0.17, CHCl3). 1H-NMR (CDCl3): 7.98 7.20
(m, 3 MeC6H4; 5.83 (d, J(3,4) ˆ 6.8, HÀC(3)); 5.13 (s, HÀC(1)); 4.74 4.67 (m, HÀC(4), HÀC(5)); 4.52 4.45
(dd, HÀC(5)); 3.40 (s, MeO); 2.40, 2.39, 2.36 (3s, 3 MeC6H4). 13C-NMR (CDCl3): 166.2, 165.3, 165.2 (3 CˆO,
Tol); 144.0, 143.9, 143.6, 129.7, 129.6, 129.0, 128.9, 126.9, 126.5, 126.2 (Tol); 106.3 (C(1)); 79.0 (C(4)); 72.1
‡
‡
(C(3)); 64.5 (C(5)); 55.2 (MeO); 21.5 (Me, Tol). HR-EI-MS (pos): 519.2009 (M , C30H292HO8 ; calc. 519.2004).
1-O-Acetyl-2,3,5-tris-O-(4-methylbenzoyl)-a/b-d-[2-2H1]ribofuranose (11). A cold mixture of Ac2O
(3.2 ml), AcOH (2.6 ml), and conc. H2SO4 (0.5 ml) was added dropwise to a soln. of 10 (2.98 g, 5.74 mmol)
in dry CH2Cl2 (15 ml) at 08, and the mixture was stirred for 15 min. Cold sat. aq. NaHCO3 soln. was added slowly,
and stirring was maintained for 3 h. The Ac derivative was extracted with CH2Cl2 from the H2O phase and dried
(MgSO4). The solvent was evaporated, and co-evaporation with toluene furnished 11 (3.1 g, 99%). The b-
anomer was crystallized from MeOH as a white solid (1.87 g, 59%). Rf (C) 0.75. [a]2D6 ˆ ‡62 (c ˆ 1.04, CHCl3).
For natural 11: [a]2D8 ˆ ‡63. IR (KBr): 3060, 3036, 3005, 2919, 2858, 1750, 1725, 1715, 1619, 1408, 1370, 1300,
1280, 1209, 1177, 1110, 1092, 1070, 973. 1H-NMR (CDCl3): 7.98 7.10 (m, 3 MeC6H4); 6.40 (s, HÀC(1)); 5.86
(d, J(3,4) ˆ 6.8, HÀC(3)); 4.78 4.71 (m, HÀC(4), HÀC(5)); 4.51 4.44 (m, HÀC(5)); 2.41, 2.39, 2.37 (3s,
3 MeC6H4); 2.00 (s, MeCO). 13C-NMR (CDCl3): 169.0 (MeCO); 165.9, 165.3, 164.9 (CˆO, Tol); 144.3, 144.2,
143.8, 129.8, 129.7, 129.1, 128.9, 126.8, 126.0, 125.9 (MeC6H4); 98.3 (C(1)); 80.0 (C(4)); 71.0 (C(3)); 63.5 (C(5));
‡
‡
21.5 (MeC6H4); 20.8 (MeCO). HR-EI-MS (pos.): 547.1960 (M , C31H292HO9 ; calc. 547.1953).
2',3',5'-Tris-O-(4-methylbenzoyl)[2'-2H1]uridine (12a). Uracil (292 mg, 2.60 mmol) was suspended in
hexamethyldisilazane (4.7 ml), and Me3SiCl (0.5 ml) was added. The mixture was stirred at 1208 under N2
for 4 h. The volatile materials were evaporated, and residue was kept on an oil pump for 20 min. Compound 11
(1.10 g, 2.01 mmol) was dissolved in dry ClCH2CH2Cl (25 ml), and this soln. and TMSOTf (0.5 ml) were added
to the persilylated nucleobase. The reaction was kept overnight at 358 under N2. Workup with sat. aq. NaHCO3
soln. and separation on a silica-gel column gave 12a (1.06 g, 88%). White foam. Rf (E) 0.74. [a]2D6 ˆ À74 (c ˆ
0.75, CHCl3). IR (KBr): 3060, 3035, 2950, 2920, 1720, 1685, 1609, 1451, 1380, 1376, 1270, 1210, 1180, 1157, 1129,

754
Helvetica Chimica Acta Vol. 87 (2004)
1111, 1092, 1019. 1H-NMR (CDCl3): 8.47 (br. d, NH); 8.00 7.15 (m, 3 MeC6H4); 7.41 (d, HÀC(6)); 6.34 (s,
HÀC(1')); 5.84 (d, J(3',4') ˆ 4.1, HÀC(3')); 5.58 (dd, HÀC(5)); 4.85 4.60 (m, HÀC(4'), CH2(5)); 2.43, 2.41,
2.38 (3s, 3 MeC6H4). 13C-NMR (CDCl3): 166.0, 165.3, 165.2 (3 CˆO); 162.0 (C(4)); 149.7 (C(2)); 144.60, 144.53,
144.48 (MeC6H4); 139.3 (C(6)); 129.9, 129.8, 129.6, 129.4, 129.2, 126.3, 125.8, 125.5 (MeC6H4); 103.3 (C(5)); 87.4
‡
(C(1')); 80.7 (C(4')); 71.0 (C(3')); 63.5 (C(5')); 21.6 (3 MeC6H4). HR-EI-MS (pos.): 599.2022 (M ,
C33H292HN2O9 ; calc. 599.2014).
‡
N2-Acetyl-O6-(diphenylcarbamoyl)2',3',5'-tris-O-(4-methylbenzoyl)[2'-2H1]guanosine (12b). N2-Acetyl-O6-
(diphenylcarbamoyl)guanine (1.16 g, 3.0 mmol) was suspended in dry ClCH2CH2Cl (10.0 ml) and N,N-
bis(trimethylsilyl)acetamide (1.5 ml) was added. The mixture was heated at ca. 908 under N2 for 1 h. The volatile
materials were evaporated, and, after co-evaporation with dry toluene, the residue was kept on an oil pump for
20 min. Compound 11 (1.1 g, 2.01 mmol) was added in dry toluene (12.0 ml) to the persilylated nucleobase,
followed by TMSOTf (0.8 ml). The mixture was kept at ca. 838 for 5.5 h, then the reaction was quenched by
adding sat. aq. NaHCO3 soln., from which the product was extracted with CH2Cl2. The org. phase was dried
(MgSO4), and the solvent was evaporated. The product was separated by CC to yield 12b (1.29 g, 73%). Off-
white foam. Rf (E) 0.75. [a]2D6 ˆ À36 (c ˆ 1.03, CHCl3). IR (KBr): 3092, 3059, 3036, 2946, 2915, 1720, 1609, 1588,
1
1508, 1489, 1449, 1408, 1369, 1268, 1210, 1176, 1091, 1058, 1018, 979. H-NMR (CDCl3): 8.10 (br. s, NH); 8.06
(s, HÀC(8)); 7.93 7.13 (m, 2 Ph, 3 MeC6H4); 6.34 (s, HÀC(1')); 6.21 (d, HÀC(3')); 4.9 4.7 (m, HÀC(4'),
CH2(5)); 2.47 (s, MeCO)); 2.41, 2.37 (2s, 3 MeC6H4). 13C-NMR (CDCl3): 170.0 (MeCO); 166.1, 165.2, 165.0
(3 CˆO, Tol); 156.3 (C(6)); 154.3 (C(4)); 152.2 (C(2)); 150.0 (Ph2NCO); 144.6, 144.4, 144.1 (Tol); 142.1 (C(8));
141.6 (Ph2NCO); 129.7, 129.5, 129.2, 129.1, 126.9, 126.4, 125.9, 125.5 (Ph2NCO, MeC6H4); 121.1 (C(5)); 87.0
‡
(C(1')); 80.7 (C(4')); 71.2 (C(3')); 63.4 (C(5')); 25.0 (MeCO); 21.6 (MeC6H4). HR-EI-MS (pos.): 875.3034 (M ,
C49H412HN6O10 ; calc. 875.3025).
‡
N6-Benzoyl-2',3',5'-tris-O-(4-methylbenzoyl)[2'-2H1]adenosine (12c). N6-Benzoyladenine (180 mg,
0.75 mmol) was condensed with 11 (273 mg, 0.5 mmol) at ca. 758 as described for 12a to give 12c (310 mg,
85%). White foam. Rf (E) 0.68. [a]2D6 ˆ À97 (c ˆ 0.27, CHCl3). IR (KBr): 3059, 3035, 2918, 1721, 1608, 1580,
1506, 1479, 1450, 1407, 1266, 1177, 1089, 1019. 1H-NMR (CDCl3): 9.01 (s, NH); 8.72 (s, HÀC(8)); 8.17
(s, HÀC(2)); 8.01 7.15 (m, Ph, 3 MeC6H4); 6.50 (s, HÀC(1')); 6.20 (d, J(3',4') ˆ 4.5, HÀC(3')); 4.93 4.64
(m, HÀC(4'), CH2(5)); 2.42, 2.41, 2.37 (3s, 3 MeC6H4). 13C-NMR (CDCl3): 166.1, 165.3, 165.1 (3 CˆO, Tol) ;
164.3 (PhCO); 152.9 (C(2)); 151.6 (C(6)); 149.6 (C(4)); 144.6, 144.5, 144.1 (Tol); 141.4 (C(8)); 133.5, 132.7 (Bz);
129.8, 129.7, 129.2, 129.16, 129.1, 128.8, 127.7, 126.5, 125.9, 125.5 (Tol, Bz); 123.4 (C(5)); 86.7 (C(1')); 81.1 (C(4'));
‡
‡
71.3 (C(3')); 63.3 (C(5')); 21.6 (MeC6H4). HR-EI-MS (pos.): 726.2557 (M , C41H342HN5O8 ; calc. 726.2548).
N4-Benzoyl-2',3',5'-tris-O-(4-methylbenzoyl)[2'-2H2]cytidine (12d). N4-Benzoylcytosine (162 mg,
0.75 mmol) and 11 (273 mg, 0.5 mmol) were condensed according to the procedure described above at 708
for 7 h. Workup and purification afforded 12d (245 mg, 70%). White foam. Rf (E) 0.72. [a]2D6 ˆ À68 (c ˆ 0.43,
CHCl3). IR (KBr): 3060, 3026, 2948, 2918, 1715, 1669, 1622, 1608, 1548, 1478, 1402, 1388, 1310, 1263, 1175, 1121,
1
1091, 1019. H-NMR (CDCl3): 8.01 7.84 (m, 9 H, HÀC(6), MeC6H4, Ph); 7.62 7.48 (m, 3 H, Ph); 7.31 7.15
(m, 7 H, HÀC(5), MeC6H4, Ph); 6.51 (s, HÀC(1')); 5.87 (d, J(3',4') ˆ 4.8, HÀC(3')); 4.87 4.65 (m, HÀC(4'),
CH2(5')); 2.44, 2.40, 2.38 (3s, 3 MeC6H4). 13C-NMR (CDCl3): 166.0, 165.2, 165.1 (CˆO, Tol); 162.3 (C(4)); 153.4
(C(2)); 144.41, 144.37, 144.32 (Tol); 143.9 (C(6)); 133.1, 129.9, 129.8, 129.6, 129.4, 129.1, 128.9, 127.5, 126.4, 125.8,
125.7 (MeC6H4, Ph); 97.3 (C(5)); 88.9 (C(1')); 80.8 (C(4')); 70.8 (C(3')); 63.4 (C(5')); 21.6 (MeC6H4). HR-EI-
MS (pos.): 702.2444 (M , C40H342HNO39 ; calc. 702.2436).
‡
‡
[2'-2H1]Uridine (13a). Nucleoside 12a (0.61 g, 1.02 mmol) was dissolved in methanolic ammonia (50 ml)
and stirred at r.t. overnight. The solvent was evaporated, the residue was dissolved in H2O and extracted 3 times
with CH2Cl2 and then with Et2O. Evaporation of the aq. phase gave 13a (248 mg, 1.01 mmol; 99%). [a]2D6 ˆ ‡9
(c ˆ 0.2, H2O) ([a]2D6 (natural uridine ˆ ‡10). IR (KBr): 3340, 3105, 2959, 2920, 2798, 1776, 1670, 1463, 1418,
1385, 1357, 1318, 1267, 1226, 1180, 1161, 1108, 1082, 1071, 1049, 1025, 960, 940, 930, 900, 870, 849, 829, 761.
1H-NMR (D2O): 7.78 (d, J(5,6) ˆ 8.1, HÀC(6)); 5.83 (s, HÀC(1')); 5.81 (d, HÀC(5)); 4.15 (d, HÀC(3')); 4.08
4.04 (m, HÀC(4')); 3.69 (ddd, J(5',4') ˆ 2.9, J(5',5'') ˆ 12.8, J(5'',4') ˆ 4.3, CH2(5)). 13C-NMR (D2O): 166.0
(C(4)); 151.1 (C(2)); 141.7 (C(6)); 102.1 (C(5)); 89.2 (C(1')); 84.0 (C(4')); 69.2 (C(3')); 60.6 (C(5')). HR-EI-MS
(pos.): 245.0759 (M , C9H112HN2O6 ; calc. 245.0758).
‡
‡
[2'-2H1]Guanosine (13b). Compound 12b (630 mg, 0.72 mmol) was deprotected by stirring in methanolic
ammonia (25 ml) for 3 days at r.t. After evaporation of MeOH, the residue was dissolved in H2O, and extracted
with CH2Cl2 (3Â) and then with Et2O. Evaporation of the aq. phase left 13b (0.173 g, 85%). White solid. The
sample for analysis was recrystallized from H2O. [a]2D6 ˆ À36 (c ˆ 0.04, H2O) ([a]D26 (for natural guanosine ˆ
À37). IR (KBr): 3420, 3320, 3218, 3140, 2929, 2748, 1683, 1625, 1592, 1531, 1480, 1408, 1360, 1315, 1241, 1172,
1083, 1045, 1012, 910, 890, 865, 828, 778, 690. 1H-NMR ((D6)DMSO 508): 8.00 (s, HÀC(8)); 6.54 (br. s, NH2);

Helvetica Chimica Acta Vol. 87 (2004)
755
5.82 (s, HÀC(1')); 4.22 (d, J(3',4') ˆ 3.6, HÀC(3')); 4.03 3.99 (m, HÀC(4')); 3.78 3.63 (ddd, J(5',4') ˆ 3.9,
J(5',5'') ˆ 11.8, J(5'',4') ˆ 3.9, CH2(5)). 13C-NMR ((D6)DMSO): 157.3 (C(6)); 153.9 (C(2)); 151.8 (C(4)); 136.3
‡
(C(8)); 117.0 (C(5)); 86.8 (C(1')); 85.6 (C(4')); 70.7 (C(3')); 61.7 (C(5')). HR-EI-MS (pos.): 284.0983 (M ,
C10H122HN5O5 ; calc. 284.0979).
‡
[2'-2H1]Adenosine (13c). Nucleoside 13c (70 mg, 82%) was obtained as white powder after deprotection of
12c (230 mg, 0.32 mmol) in methanolic ammonia. [a]2D6 ˆ À53 (c ˆ 0.17, H2O). [a]2D6 (natural adenosine) ˆ
À60). IR (KBr): 3430, 3320, 3160, 2918, 1651, 1642, 1601, 1573, 1474, 1417, 1380, 1338, 1291, 1245, 1208, 1177,
1
1158, 1110, 1105, 1086, 1078, 1050, 1028, 960, 970, 880, 835, 791, 749. H-NMR (D2O): 8.21 (s, HÀC(8)); 8.08
(s, HÀC(2)); 5.95 (s, HÀC(1')); 4.34 (d, J(3',4') ˆ 3.2, HÀC(3')); 4.23 4.19 (m, HÀC(4')); 3.88 3.73
(ddd, J(5',4') ˆ 2.7, J(5',5'') ˆ 12.9, J(5'',4') ˆ 3.5, CH2(5)). 13C-NMR (D2O): 155.3 (C(6)); 152.2 (C(2)); 148.3
(C(4)); 140.6 (C(8)); 119.1 (C(5)); 88.2 (C(1')); 85.8 (C(4')); 70.5 (C(3')); 61.5 (C(5')). HR-EI-MS (pos.):
‡
‡
268.1036 (M , C10H122HN5O4 ; calc. 268.1030).
[2'-2H1]Cytidine (13d). Compound 12d (220 mg, 0.31 mmol) was stirred overnight in methanolic ammonia,
followed by removal of MeOH. Dissolving the residue in H2O, and successive washings with CH2Cl2 (3Â) and
Et2O afforded 13d (68.2 mg, 90%). [a]2D6 ˆ ‡32 (c ˆ 0.08, H2O). ([a]2D7 (natural cytidine) ˆ ‡33). IR (KBr):
3340, 3200, 2920, 2715, 1640, 1600, 1521, 1483, 1398, 1370, 1282, 1242, 1206, 1152, 1120, 1082, 1040, 1025, 965, 882,
858, 780. 1H-NMR (D2O): 7.77 (d, J(5,6) ˆ 7.6, H ÀC(6)); 5.98 (d, HÀC(5)); 5.82 (s, HÀC(1')); 4.13
(d, J(3',4') ˆ 5.9, HÀC(3')); 4.08 4.03 (m, HÀC(4')); 3.89 3.70 (ddd, J(5',4') ˆ 3.0, J(5',5'') ˆ 12.7, J(5'',4') ˆ
4.3, CH2(5)). 13C-NMR (D2O): 166.1 (C(4)); 157.5 (C(2)); 141.5 (C(6)); 96.0 (C(5)); 90.1 (C(1')); 83.6 (C(4'));
69.1 (C(3')); 60.6 (C(5')). HR-EI-MS (pos.): 244.0922 (M , C9H122HN3O5 ; calc. 244.0918).
‡
‡
2,3-O-Isopropylidene-a/b-d-[2-2H1]ribose (15). 2,3-O-Isopropylideneribofuranose (14; 4.18 g, 22.0 mmol)
was co-evaporated with D2O and dissolved in dioxane/THF/Et3N/D2O (24 :24 :12 :16 ml (v/v/v/v)). The soln.
was heated at 908 for 5 d, and evaporation gave 15 (4.18 g, 99%). Brown oil. Rf (F) 0.53. 1H-NMR (CDCl3): b-
Anomer: 5.39 (s, HÀC(1)); 4.84 (s, HÀC(3)); 4.40 4.37 (m, HÀC(4)); 3.75 3.66 (m, CH2(5)); 1.49, 1.32 (2s,
2 Me)); a-Anomer: 5.42 (s, 0.12 H, HÀC(1)); 4.74 (d, J(3,4) ˆ 2.2, 0.12 H, HÀC(3)); 4.19 4.16 (m, 0.12 H,
HÀC(4)); 3.75 3.66 (m, 0.24 H, CH2(5)); 1.58, 1.40 (2s, 0.72 H, 2 Me). 13C-NMR (CDCl3): b-Anomer: 111.8
(Me2C); 102.5 (C(1)); 87.5 (C(4)); 81.6 (C(3)); 63.2 (C(5)); 26.2, 24.6 (2 Me); a-Anomer: 113.8 (Me2C); 96.9
(C(1)); 81.3 (C(4)); 80.9 (C(3)); 61.2 (C(5)); 25.9, 24.6 (2 Me). HR-EI-MS (pos.): 191.0907 (M , C8H132HO5
;
‡
‡
calc. 191.0904).
Methyl a/b-d-[2-2H1]Ribofuranoside (16). Compound 15 (4.18 g, 21.9 mmol) was dissolved in 80% aq.
AcOH (150 ml), and the soln. was stirred at 908 for 24 h. The solvent was evaporated, and residual AcOH was
removed by co-evaporation with H2O. The oil obtained was dissolved in dry MeOH (60 ml), and a few drops of
conc. H2SO4 were added at 08. The soln. was kept in refrigerator at 48 overnight, then neutralized passing
through an Amberlist A-21 column (OHÀ form) with MeOH as an eluent. Removal of the solvent left 16 (3.58 g,
99%). Thick, light-yellow syrup. Rf (b and a; D) 0.59, 0.42. 1H-NMR (D2O): 4.92 (s, 0.3 H, HÀC(1) (a)); 4.83
(s, 1 H, HÀC(1) (b)); 4.10 3.91 (m, 2.6 H (b), HÀC(3) (a), HÀC(4) (a), HÀC(4) (b), HÀC(3) (b)); 3.76
3.50 (m, 2.6 H, CH2(5) (a), CH2(5) (b)); 3.36 (s, 0.9 H, Me (a)); 3.33 (s, 3 H, Me (b)). 13C-NMR (D2O): b-
Anomer: 108.1 (C(1)); 83.0 (C(4)); 70.9 (C(3)); 62.9 (C(5)); 55.3 (Me); a-Anomer: 103.3 (C(1)); 84.7 (C(4));
‡
‡
69.8 (C(3)); 61.7 (C(5)); 55.6 (Me). HR-EI-MS (pos.): 165.0756 (M , C6H112HO5 ; calc. 165.0748).
1-O-Methyl-2,3,5-tris-O-(4-methylbenzoyl)-a/b-d-[2-2H1]ribofuranose (17). Compound 16 (3.58 g,
21.8 mmol) was co-evaporated with dry pyridine and dissolved in pyridine (150 ml). 4-Methylbenzoyl chloride
(9.6 ml, 72.6 mmol) was added in 5 portions at 08, and the mixture was stirred overnight. It was poured into sat.
aq. NaHCO3 soln. and stirred for 2 h, followed by extraction with CH2Cl2. Solvents were evaporated, and the
residue was co-evaporated with toluene. The oily residue was subjected to CC to afford 17 (10.67 g, 93%). Rf (C)
0.81. 1H-NMR (CDCl3): 8.05 7.09 (m, 15.6 H, MeC6H4 (a ‡ b)); 5.83 (d, J(3,4) ˆ 6.7, HÀC(3) (b)); 5.68
(d, J(3,4) ˆ 3.3, 0.3 H, HÀC(3) (a)); 5.37 (s, 0.3 H, HÀC(1) (a)); 5.13 (s, HÀC(1) (b)); 4.74 4.45 (m, 3.9 H)
HÀC(4) (a), HÀC(4) (b), CH2(5) (a), CH2(5) (b)); 3.47 (s, 0.9 H, MeO (a)); 3.40 (s, MeO (b)); 2.46 2.36
(m, 11.7 H, Me (a ‡ b)). 13C-NMR (CDCl3): b-Anomer: 166.2, 165.3, 165.2 (CˆO); 144.1, 144.0, 143.6, 129.7,
129.6, 129.4, 128.9, 127.0, 126.5, 126.2 (MeC6H4); 106.3 (C(1)); 79.1 (C(4)); 72.1 (C(3)); 64.5 (C(5)); 55.2
(MeO); 21.5 (Me); a-Anomer: 166.1, 165.9, 165.4 (CˆO); 145.4, 143.8, 130.5, 129.9, 129.0, 126.8, 126.4, 126.1
(MeC6H4); 101.8 (C(1)); 79.5 (C(4)); 70.5 (C(3)); 63.8 (C(5)); 55.6 (MeO); 21.7 (Me). HR-EI-MS (pos.):
519.2010 (M , C30H292HO8 ; calc. 519.2004).
‡
‡

756
Helvetica Chimica Acta Vol. 87 (2004)
REFERENCES
[1] K. W¸thrich, −NMR of Proteins and Nucleic Acids×, John Wiley & Sons, New York, 1986.
[2] G. Varani, F. Aboul-ela, F. H.-T. Allain, Progr. Nucl. Magn. Res. Spectrosc. 1996, 29, 51.
[3] a) J. Milecki, J. Labelled Compd. Radiopharm. 2002, 45, 307; b) I. M. Lagoja, P. Herdewijn, Synthesis 2002,
301; c) J. Cromsight, J. Schleucher, T. Gustafsson, J. Kihlberg, S. Wijmenga, Nucleic Acids Res. 2002, 30,
1639; d) N. Ouwerkerk, J. van Boom, J. Lugtenburg, J. Raap, Eur. J. Org. Chem. 2002, 2356; e) I. M. Lagoja,
S. Pochet, V. Boudou, R. Little, E. Lescrinier, J. Rozenski, P. Herdewijn, J. Org. Chem. 2003, 68, 1867; f) E.
Kawashima, K. Umabe, T. Sekine, J. Org. Chem. 2002, 67, 5142; g) J. Milecki, A. Fˆldesi, A. Fischer, R. W.
Adamiak, J. Chattopadhyaya, J. Labelled Compd. Radiopharm. 2001, 44, 763; h) Y. Saito, A. Nyilas, L. A.
Agrofoglio, Carbohydr. Res. 2001, 331, 83; i) J.-L. Abad, A. J. Shallop, B. L. Gaffney, R. A. Jones,
Biopolymers 1998, 48, 57.
[4] S. S. Wijmenga, B. N. M. van Buuren, Progr. Nucl. Magn. Res. Spectrosc. 1998, 32, 287.
[5] T. Dieckmann, J. Feigon, Curr. Opin. Struct. Biol. 1994, 4, 745.
[6] A. Pardi, Methods Enzymol. 1995, 261, 350.
[7] D. P. Zimmer, D. M. Crothers, Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 3091.
[8] J. M. Louis, R. G. Martin, G. M. Clore, A. M. Groneborn, J. Biol. Chem. 1998, 273, 2374.
[9] D. E. Smith, J.-Y. Su, F. M. Jucker, J. Biomol. NMR 1997, 10, 245.
[10] J. E. Masse, P. Bortmann, T. Dieckmann, J. Feigon, Nucleic Acids Res. 1998, 26, 2618.
[11] E. P. Nikonowicz, A. Sirr, P. Legault, F. M. Jucker, L. M. Baer, A. Pardi, Nucleic Acids Res. 1992, 20, 4507.
[12] R. T. Batey, J. L. Battiste, J. R. Willamson, Methods Enzymol. 1995, 261, 300.
[13] J. R. Wyatt, M. Chastain, J. D. Puglisi, Bio Techniques 1991, 11, 764.
[14] P. B. Moore, Acc. Chem. Res. 1995, 28, 251.
[15] a) J. Xu, J. Lapham, D. M. Crothers, Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 43; b) G. Mer, W. J. Chazin, J.
Am. Chem. Soc. 1998, 120, 607; c) I. Kim, P. J. Lukavsky, J. D. Puglisi, J. Am. Chem. Soc. 2002, 124, 9338.
[16] a) F. S. Ezra, C. H. Lee, N. S. Kondo, S. S. Danyliuk, R. H. Sarma, Biochemistry 1977, 16, 1977; b) C. K.
Brush, M. P. Stone, T. M. Harris, Biochemistry 1988, 27, 115; c) C. K. Brush, M. P. Stone, T. M. Harris, J.
Am. Chem. Soc. 1988, 110, 4405; d) L. Arnold, M. Pressova, D. Saman, M. Vogtherr, S. Limmer, Collect.
Czech. Chem. Commun. 1996, 61, 389; e) C. Cheong, C. Lee, Bull. Korean Chem. Soc. 1995, 16, 383; f) J.
Yang, L. Silks, R. Wu, N. Isern, C. Unkefer, M. A. Kennedy, J. Magn. Reson. 1997, 129, 212; g) E. P.
Nikonowicz, K. Kalurachchi, E. DeJong, FEBS Lett. 1997, 415, 109; h) E. P. Nikonowicz, M. Michnicka, E.
DeJong, J. Am. Chem. Soc. 1998, 120, 3813; i) X. Huang, P. Yu, E. LeProust, X. Gao, Nucleic Acids Res.
1997, 25, 4758.
[17] a) A. Fˆldesi, A. Trifonova, M. K. Kundu, J. Chattopadhyaya, Nucleosides Nucleotides Nucleic Acids 2000,
19, 1615; b) A. Fˆldesi, A. Trifonova, Z. Dinya, J. Chattopadhyaya, J. Org. Chem. 2001, 66, 6560; c) M. K.
Kundu, A. Trifonova, A. Fˆldesi, Z. Sinya, J. Chattopadhyaya, Nucleosides Nucleotides Nucleic Acids 2001,
20, 1333; d) D. MacDonald, P. Lu, J. Am. Chem. Soc. 2002, 124, 9722; e) B. Chen, E. R. Jamieson, T. D.
Tullius, Bioorg. Med. Chem. Lett. 2002, 12, 3093; f) P. Chirakul, S. T. Sigurdsson, Org. Lett. 2003, 5, 917;
g) M. K. Kundu, A. Fˆldesi, J. Chattopadhyaya, Helv. Chim. Acta 2003, 86, 633.
[18] a) S.-I. Yamakage, T. V. Maltseva, F. P. Nilson, A. Fˆldesi, J. Chattopadhyaya, Nucleic Acids Res. 1993, 21,
5005; b) P. Agback, T. V. Maltseva, S.-I. Yamakage, F. P. R. Nilson, A. Fˆldesi, J. Chattopadhyaya, Nucleic
Acids Res. 1994, 22, 1404; c) A. Fˆldesi, S.-I. Yamakage, F. P. R. Nilson, T. V. Maltseva, J. Chattopadhyaya,
Nucleic Acids Res. 1996, 24, 1187; d) C. Glemarec, J. Kufel, A. Fˆldesi, T. V. Maltseva, A. Sandstrom, L.
Kirsebom, J. Chattopadhyaya, Nucleic Acids Res. 1996, 24, 2022; e) A. Fˆldesi, S.-I. Yamakage, T. V.
Maltseva, F. P. R. Nilson, P. Agback, J. Chattapadhyaya, Tetrahedron 1995, 51, 10065; f) T. V. Maltseva, A.
Fˆldesi, J. Chattopadhyaya, Magn. Reson. Chem. 1998, 36, 227; g) T. V. Maltseva, A. Fˆldesi, J.
Chattopadhyaya, J. Chem. Soc., Perkin Trans. 2 1998, 2689; h) T. V. Maltseva, A. Fˆldesi, J. Chattopad-
hyaya, Magn. Reson. Chem. 1999, 37, 203; i) A. Fˆldesi, T. V. Maltseva, Z. Dinya, J. Chattopadhyaya,
Tetrahedron 1998, 54, 14487; j) T. V. Maltseva, A. Fˆldesi, J. Chattopadhyaya, Tetrahedron 1998, 54, 14515.
[19] J. A. M. T. C. Cromsigt, J. Schleucher, K. Kidd-Ljunggren, S. S. Wijmenga, J. Biomol. Struct. Dyn. 2000, S2, 211.
[20] a) S. Salowe, J. M. J. Bollinger, M. Ator, J. Stubbe, J. McCracken, J. Peisach, M. C. Samano, M. J. Robins,
Biochemistry 1993, 32, 12749; b) I. Saito, Pure Appl. Chem. 1992, 64, 1305; c) S. J. Baker, D. W. Young, J.
Labelled Compd. Radiopharm. 2000, 43, 1023.
[21] D. Wade, Chem. Biol. Interact. 1999, 117, 191.
[22] a) F. Hansske, D. Madej, M. J. Robins, Tetrahedron 1984, 40, 125; b) J.-C. Wu, H. Bazin, J. Chattopadhyaya,
Tetrahedron 1987, 43, 2355; c) V. Samano, M. J. Robins, J. Org. Chem. 1990, 55, 5186; d) M. E. Perlman,

Helvetica Chimica Acta Vol. 87 (2004)
757
Nucleosides Nucleotides 1993, 12, 73; e) M. J. Robins, S. Sarker, V. Samano, S. F. Wnuk, Tetrahedron 1997,
53, 447.
[23] a) G. P. Cook, M. M. Greenberg, J. Org. Chem. 1994, 59, 4704; b) M. K. Kundu, A. Fˆldesi, J.
Chattopadhyaya, Collect. Czech. Chem. Commun. Symp. Ser. 2 1999, 47.
¬
¬
¬
¬
¬
¬
¬
¬
[24] J. Kerekgyarto, J. Rako, Agoston, Gy. Gyemant, Z. Szurmai, Eur. J. Org. Chem. 2000, 3931.
[25] T. Chen, M. M. Greenberg, Tetrahedron Lett. 1998, 39, 1103.
[26] a) B. Classon, P. J. Garegg, B. Samuelsson, Acta Chem. Scand., Ser. B 1984, 38, 419; b) R. Johansson, B.
Samuelsson, J. Chem. Soc., Perkin Trans. 1 1984, 2371.
[27] G. Ritzmann, R. S. Klein, D. H. Hollenberg, J. J. Fox, Carbohydr. Res. 1975, 39, 227.
[28] a) A. J. Mancuso, S.-L. Huang, D. Swern, J. Org. Chem. 1978, 43, 2480; b) A. J. Mancuso, D. Swern,
Synthesis 1981, 165.
[29] D. B. Dess, C. J. Martin, J. Org. Chem. 1983, 48, 4155.
[30] R. R. Gadikota, C. S. Callam, T. L. Lowary, Org. Lett. 2001, 3, 607.
[31] W. H. Kruizinga, B. Strijtveen, R. M. Kellog, J. Org. Chem. 1981, 46, 4321.
[32] a) N. A. Hughes, P. R. H. Speakman, Carbohydr. Res. 1965, 1, 171; b) B. Kaskar, G. L. Heise, R. S.
Michalak, B. R. Vishnuvajjala, Synthesis 1990, 1031.
[33] a) H. Vorbr¸ggen, G. Hˆfle, Chem. Ber. 1981, 114, 1256; b) H. Vorbr¸ggen, K. Krolikiewicz, B. Bennua,
Chem. Ber. 1981, 114, 1234; c) M. J. Robins, R. Zou, Z. Guo, S. F. Wnuk, J. Org. Chem. 1996, 61, 9207.
[34] S. Abbate, G. Conti, A. Naggi, Carbohydr. Res. 1991, 210, 1.
Received October 25, 2003