Synthesis of 5'-C- and 2'-O-(bromoalkyl)-substituted ribonucleoside phosphoramidites for the post-synthetic functionalization of oligonucleotides on solid support

Article abstract of DOI:10.1002/1522-2675(20000607)83:6<1127::AID-HLCA1127>3.0.CO;2-B

The preparation of building blocks for the incorporation of 6'-O-(5- bromopentyl)-substituted β-D-allofuranosylnucleosides and 2'-O-[(3- bromopropoxy)methyl]-substituted ribonucleosides into oligonucleotide sequences is presented (Schemes 1 and 2). These reactive building blocks can be modified with a variety of soft nucleophiles while the (fully protected) sequence is still attached to the solid support. As an example of this strategy, we carried out some preliminary solid-phase substitution and conjugation reactions with DNA sequences containing a 2'-O-[(3- bromopropoxy)methyl]-substituted ribonucleoside (Scheme 3) and determined the pairing properties of duplexes obtained therefrom.

Full text of DOI:10.1002/1522-2675(20000607)83:6<1127::AID-HLCA1127>3.0.CO;2-B

Helvetica Chimica Acta ± Vol. 83 (2000)
1127
Synthesis of 5'-C- and 2'-O-(Bromoalkyl)-Substituted Ribonucleoside
Phosphoramidites for the Post-synthetic Functionalization of
Oligonucleotides on Solid Support
by Xiaolin Wu and Stefan Pitsch*
Laboratorium für Organische Chemie, ETH-Zentrum, Universitätstr. 16, CH-8092 Zürich
Dedicated to Prof. Dr. Frank Seela on the occasion of his 60th birthday
The preparation of building blocks for the incorporation of 6'-O-(5-bromopentyl)-substituted b-d-
allofuranosylnucleosides and 2'-O-[(3-bromopropoxy)methyl]-substituted ribonucleosides into oligonucleotide
sequences is presented (Schemes 1 and 2). These reactive building blocks can be modified with a variety of soft
nucleophiles while the (fully protected) sequence is still attached to the solid support. As an example of this
strategy, we carried out some preliminary solid-phase substitution and conjugation reactions with DNA
sequences containing a 2'-O-[(3-bromopropoxy)methyl]-substituted ribonucleoside (Scheme 3) and deter-
mined the pairing properties of duplexes obtained therefrom.
1. Introduction. ± Oligonucleotide conjugates and functionalized oligonucleotides
are versatile tools for structural, biological, and biophysical studies. To access a variety
of such oligonucleotide analogues within a short time, several solid-phase functional-
ization strategies have been developed. They are based on reactive, prefunctionalized
building blocks that, after their incorporation into oligonucleotides, can be function-
alized with a variety of different groups. The first examples of such ꢀconvertible
nucleosidesꢁ carried reactive nucleobases that, during deprotection with alkylamines,
afforded N-alkyl-substituted nucleosides [1]. Meanwhile, a few base analogues carrying
suitably protected reactive side chains have been developed; after liberation of their
reactive sites, these analogues can be modified, while the sequence is still fully
protected and attached to the solid support [2]. In this context, we recently reported a
method for the functionalization of the sugar moiety of oligonucleotides on the solid
support. Our approach was based on the incorporation of a 6'-O-(bromopentyl)-
substituted allofuranosyl-cytosine phosphoramidite into sequences followed by sub-
stitution of the Br-atom with a variety of soft nucleophiles [3]. Here we describe the
synthesis of the analogous 6'-O-(bromopentyl)-substituted allofuranosyl phosphora-
midites containing the three other canonical nucleobases uracil, adenine, and
guanosine.
Meanwhile, we have extended our concept and have prepared reactive 2'-O-[(3-
bromopropoxy)methyl]-substituted ribonucleoside building blocks that allow the
introduction of additional functionalities at the 2'-O-position of oligonucleotides. In
this first communication, we report the synthesis of such phosphoramidites containing
the four canonical nucleobases and base-pairing properties of some derivatives
obtained therefrom.

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Helvetica Chimica Acta ± Vol. 83 (2000)
2. Results and Discussion. ± 2.1. Synthesis of 6'-O-(Bromopentyl)-Substituted
Allofuranosyl Phosphoramidites. The 6'-O-(bromopentyl)-substituted b-d-allofurano-
syl nucleoside building blocks containing the nucleobases adenine, uracil, and guanine
were prepared from the prefunctionalized sugar building block 1 in analogy to the
synthesis of the corresponding cytosine-containing phosphoramidite that has been
reported in [3][4] (Scheme 1).
The nucleosidation of 1 was carried out under Vorbrüggen conditions with the in-
situ trimethylsilylated nucleobases uracil, N6-benzoyladenine, and N2-acetylguanine,
respectively; after aqueous workup, the products were desilylated, affording the
nucleosides 2, 3, and 4, respectively. Nucleoside formation with uracil proceeded
smoothly in the presence of SnCl4 in MeCN [5], and after treatment of the crude
product with HF and HCl in H2O/MeCN according to [4], the desilylated derivative 2
was obtained in a yield of 75%. With N6-benzoyladenine, a mixture of products was
obtained under a variety of nucleosidation and deprotection conditions. Nevertheless,
the nucleoside 3 could be isolated in a moderate yield of 45% by performing the
nucleosidation reaction with SnCl4 in MeCN [5] and the desilylation with CF3COOH/
H2O. The nucleosidation of 1 with N2-acetylguanine afforded, under various conditions,
always a mixture of the two isomeric N9- and N7-connected nucleosides, which could
not be separated. The best N9/N7 ratio was obtained with Me3Si-OTf in (CH2Cl)2
according to [5]. After desilylation of the crude products with HF and HCl in H2O/
MeCN [4], again an unseparable mixture of isomers was obtained in a moderate yield
of 40%. The dimethoxytritylation of the intermediates 2 ± 4, respectively, was carried
out with (MeO)2Tr-Cl in the presence of AgNO3 and sym-collidine (ˆ2,4,6-
trimethylpyridine) according to [4][6]. Without purification, the intermediates were
then directly O-debenzoylated under standard conditions with NaOH in THF/MeOH/
H2O [7]. The dimethoxytritylated uracil and adenine nucleosides 5 and 6 were obtained
in good yields of 87 and 92%, respectively. At this stage, the two regioisomeric N9- and
N7-connected guanine nucleosides 7 could be separated by chromatography (silica gel)
and were isolated in yields of 25 and 11%, respectively (based on 1)1). Introduction of
the 2'-O-[(triisopropylsilyloxy)methyl] ( ˆ tom) protecting group into the three
nucleosides was carried out under our general conditions, by first forming a cyclic
dibutyltin derivative with Bu2SnCl2/iPr2NEt and then treatment with tom-Cl at 808
[4][5][9]. Under these conditions, the three 2'-O-alkylated nucleosides 8 ± 10 were
obtained as major products that could be separated by chromatography (silica gel)
from the corresponding 3'-O-alkylated regioisomers 11 ± 132). Finally, the nucleosides
8 ± 10 were transformed into the phosphoramidites 14 ± 16 according to standard
procedures [5].
The connection of the nucleobase was determined by 13C-NMR spectroscopy according to [8].
The correct position of the tom group was determined by 1H-NMR spectroscopy according to [5].
Generally, within every pair of 5'-O-dimethoxytritylated, base-protected nucleosides with 2',3'-O-form-
aldehyde acetal-derived substituents known so far, we observed the following relationships: the 2'-O-
alkylated nucleosides are less polar and elute faster on chromatography (silica gel) than the corresponding
3'-O-alkylated regioisomers; the HÀC(1') signals of the former are further downfield, and the coupling
constants between HÀC(1')/HÀC(2') are smaller than the corresponding values of the latter.
1
)
)
2

Helvetica Chimica Acta ± Vol. 83 (2000)
Scheme 1a)
1129
a) For 2: 1) uracil, bis(trimethylsilyl)acetamide (BSA), then SnCl4, 2) HF, HCl in H2O/MeCN; for 3: N6-
benzoyladenine, BSA, then SnCl4, 2) CF3COOH, H2O; for 4: N2-acetylguanine, BSA, then Me3Si-OTf, 2) HF,
HCl in H2O/MeCN. b) (MeO)2Tr-Cl, AgNO3, sym-collidine, then NaOH in THF/MeOH/H2O. c) Bu2SnCl2,
i
iPr2NEt, then tom-Cl. d) (iPr2N)2PCl(OCH2CH2CN), Pr2NEt.
a) The synthesis of the analogous N4-acetylcytosine containing phosphoramidite is reported in [3] and [4].
2.2. Synthesis of 2'-O-[(3-Bromopropoxy)methyl]-Substituted Ribonucleosides.
The reactive, 2'-O-substituted ribonucleosides 25 ± 28 were prepared by alkylation of
the 5'-O-dimethoxytritylated, base-protected nucleosides 17 ± 20 with 1-bromo-3-
(chloromethoxy)propane (34) according to the conditions we developed for the
introduction of related, formaldehyde acetal based 2'-O-protecting groups [4][5][9].
The alkylating reagent 34 was prepared in two steps. From 3-bromopropanol the O,S-
acetal 33 was prepared with DMSO, Ac2O, and AcOH according to [10]. This
intermediate was then converted to 34 with SO2Cl2 according to [11]. Treatment of the
nucleosides 17 ± 20 first with Bu2SnCl2/iPr2NEt and then with the alkylating agent 34
afforded mixtures of the corresponding 2'-O- and 3'-O-alkylated nucleosides 21 ± 24
and 25 ± 28, respectively, which could be separated easily by chromatography (silica
gel)3). From the 2'-O-alkylated nucleosides 21 ± 24, the corresponding phosphorami-
dites 29 ± 32 were prepared according to standard procedures.
1
3
)
The correct position of the [(3-bromopropoxy)methyl] group was determined by H-NMR spectroscopy
according to [5]. See also Footnote 2.

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Helvetica Chimica Acta ± Vol. 83 (2000)
Scheme 2
i
i
a) Bu2SnCl2, Pr2NEt, then 34. b) (iPr2N)2PCl(OCH2CH2CN), Pr2NEt. c) DMSO, Ac2O, AcOH. d) SO2Cl2.
2.2. Solid-Phase Substitutions. Exploratory experiments were carried out to
investigate the potential for solid-support functionalization of oligonucleotides
containing 2'-O-[(3-bromopropoxy)methyl]substituted ribonucleosides and to collect
some information about the influence of such additional substituents on the pairing
behavior.
The 2'-O-[(3-bromopropoxy)methyl]-substituted cytidine phosphoramidite 32 was
incorporated into a tetradecameric DNA sequence at two positions, once near the 3'-
end ( ! 35) and once near the 5'-end ( ! 36), respectively (Scheme 3 and Table 1).
Under our conditions (which were developed for the assembly of RNA sequences
[3][9]), the coupling yields were >99% for the standard DNA phosphoramidites and
98% for the modified phosphoramidite 32 (Scheme 3). As a comparison and for
comparative duplex-stability studies, the corresponding DNA sequence 37 and the
complementary DNA and RNA sequences 38 and 39, respectively, were prepared as
well (Table 1).
Small portions of the immobilized oligonucleotides 35 and 36 were then treated
with 10m MeNH2 in H2O/EtOH 1:1 ( Scheme 3). In Fig. 1, the HPLC trace of such a
crude product is presented together with the chromatogram of the analogous
unmodified DNA sequence 37. According to this analysis, from sequence 35, a
dominant main product (with essentially the same retention time as the unmodified
DNA sequence 37) was formed, together with a small by-product. The main product

Helvetica Chimica Acta ± Vol. 83 (2000)
1131
Scheme 3
a) Oligonucleotide assembly, see Exper. Part. b) HSCH2COOH, iPr2NEt. c) HOBT, TBTU, iPr2NEt, l-
i
isoleucine allyl ester. d) HOBT, TBTU, iPr2NEt, MeNH2. e) HOBT, TBTU, Pr2NEt, histamine. f) MeNH2.

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Helvetica Chimica Acta ± Vol. 83 (2000)
Table 1. Characterization of Functionalized Oligonucleotides
d
Sequencea)
Product ratiob)
[%]
Yieldc)
[%]
Tm
)
[M À H]Àe
calc.
)
[8]
obs.
40 d(GGCGACCGACWGT)
41 d(GGWGACCGACCGT)
49 d(GGCGACCGACXGT)
50 d(GGXGACCGACCGT)
51 d(GGCGACCGACYGT)
52 d(GGYGACCGACCGT)
53 d(GGCGACCGACZGT)
37 d(GGCGACCGACCGT)
38 d(ACGGTCGGTCGCC)
39 r(ACGGUCGGUCGCC)
90
90
70
75
75
65
55
45
40
40
40
35
30
25
60
55
30
67
67
67
66
68
68
67
68
4078
4078
4152
4152
4232
4232
4265
3960
3952
4129
4081
4080
4153
4153
4234
4235
4265
3959
3951
4130
a) For the structure of W, X, Y, and Z, see Scheme 3. b) Area-% (HPLC, capillary electrophoresis (CE)) of
product signal. c) After purification by ion-exchange HPLC; by CE, the purity was estimated >95%. d) With
the RNA sequence 39 as complement; conditions: c (sequences) ˆ 1 ‡ 1 mm, 150 mm NaCl, 2 mm MgCl2, 1 0 mm
Tris ´ HCl (pH 7.4). e) MALDI-TOF-MS; matrix, 2,4-dihydroxyacetophenone (ammonium citrate) according
to [12].
Fig. 1. Reversed-phase HPLC traces from crude sequences: a) parent DNAsequence 37; b) (methylamino)-
substituted DNAsequence 40. Elution with A ! 20% B in 30 min, measured at 260 nm (see Exper. Part).
was isolated by prep. HPLC and identified by MALDI-TOF mass spectrometry as the
(methylamino)-substituted sequence 40 (Table 1).
Further solid-support functionalizations were carried out according to protocols
that we developed earlier [4] (Scheme 3). The immobilized sequences 35 and 36 were
treated with thioglycolic acid (ˆ mercaptoacetic acid) in the presence of iPr2NEt3, and
the resulting intermediates 42 and 43 (now containing a reactive carboxy group) were
treated under peptide-coupling conditions with MeNH2, histamine, and l-isoleucine
allyl ester, respectively. After deprotection of the intermediates 44 ± 48 with MeNH2 in
EtOH/H2O 1:1, the main products 49 ± 53 were isolated by HPLC and analyzed by

Helvetica Chimica Acta ± Vol. 83 (2000)
1133
MALDI-TOF-MS (Table 1). According to HPLC and capillary electrophoresis (CE)
of the crude products, the efficiency of the overall functionalization procedures was in
the range of 55 ± 75%. Fig. 2 shows the CE chromatogram of the crude histamine-
substituted sequence 51 (Fig. 2,a); this sequence was formed in a overall efficiency of
ca. 75% and could be isolated in pure form by ion-exchange chromatography (Fig. 2,b).
Fig. 2. a) Capillary-electrophoresis (CE) trace of crude histamine-substituted sequence 51 (conditions, see [9],
measured at 260 nm); b) ion-exchange HPLC trace of crude 51 obtained from a preparative run (elution with
25% B ! 40% B in 30 min, measured at 260 nm) (see Exper. Part).
2.4. Thermal-Denaturation Study. In Table 1, the transition temperatures (Tm) of the
duplexes formed from the functionalized sequences 40, 41, and 49 ± 53 and the
complementary RNA sequence 39 are presented. Under physiological conditions
(150 mm NaCl, 2 mm MgCl2, pH 7.4), the modified duplexes had similar or slightly
lower Tm values than the unmodified duplex 37 ´ 39. A more detailed study was carried
out with the two histamine-substituted sequences 51 and 52 (Table 2). Their duplexes
with the complementary DNA sequence were significantly destabilized (as compared
to the corresponding unmodified DNA duplex 37 ´ 38). The DG0 values for duplex
formation of the modified DNA ´ RNA duplexes 51 ´ 39 and 52 ´ 39, respectively, were
more negative (DDG0 ˆ À0.9 and À2.8 kcal molÀ1, resp.) than the corresponding value
of the parent DNA ´ RNA duplex 37 ´ 39. In contrast to these results, the corresponding
DNA ´ DNA duplexes 51 ´ 38 and 52 ´ 38 showed more positive DG0 values than the
parent DNA ´ DNA duplex 37 ´ 38.
Fig. 3 illustrates the position of the additional imidazole moieties within the DNA ´
RNA duplexes 51 ´ 39 and 52 ´ 39, respectively. In duplex 51 ´ 39, the additional
functional group is near the 3'-end of the modified DNA sequence and is pointing into
solution, whereas in duplex 52 ´ 39, the additional functional group is near the 5'-end
and located within the minor groove of the duplex. The Tm values and the
thermodynamic data reflect a higher stability of the latter duplex, indicating a positive

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Helvetica Chimica Acta ± Vol. 83 (2000)
Table 2. Thermodynamic Parameters of Duplex Formationa)
b
Tm
)
DH0
[kcal molÀ1
TDS0 (298 K)
DG0 (298 K)
DDG0 (298 K)c)
[kcal molÀ1
]
[8C]
]
[kcal molÀ1
]
[kcal molÀ1
]
37 ´ 39
51 ´ 39
52 ´ 39
37 ´ 38
51 ´ 38
52 ´ 38
68.0
68.0
67.8
65.2
63.6
62.1
À 110.8
À 116.9
À 131.9
À 98.1
À 99.3
À 90.7
À 88.0
À 93.2
À 106.3
À 77.6
À 79.1
À 71.7
À 22.8
À 23.7
À 25.6
À 20.5
À 20.2
À 19.0
À 0.9
À 2.8
‡ 0.3
‡ 1.5
a) In 150 mm NaCl, 2 mm MgCl2, and 10 mm Tris ´ HCl (pH 7.4); thermodynamic parameters and transition
temperatures were determined according to [13] (the exper. error was estimated to be Æ5%).
c
b) c(sequences) ˆ 1 ‡ 1 mm. ) Difference between the DG0 value of the modified and the parent duplex.
interaction between the RNA strand 39 and the imidazole moiety on the modified
DNA strand 52 (located in the minor groove). In the analogous duplexes with the
complementary DNA strands, however, a duplex destabilization by the additional
imidazole moieties was observed, and this destabilization was more important when the
substituents were located in the minor groove. This difference is probably the
Fig. 3. Pictures of modified A-type DNA ´ RNA duplexes 51 ´ 39 and 52 ´ 39, illustrating the position of the
additional histamine substituent. The duplex was constructed with ꢀMacroModelꢁ, and the substituent was added
without further minimization.

Helvetica Chimica Acta ± Vol. 83 (2000)
1135
consequence of a disturbance of the hydration shell within the DNA ´ DNA duplex
52 ´ 384).
In conclusion, we present novel reactive building blocks that allow the introduc-
tion of a variety of functional groups by substitution and subsequent conjugation
on the solid phase according to [3]. These building blocks are fully compatible
with common procedures employed for the automated assembly of DNA and
RNA oligonucleotides and can be introduced by every desired position within a
sequence.
This work was supported by the ETH-Zürich and the Alfred-Werner-Stipendium. We thank Patrick A. Weiss
(Xeragon AG, Zürich) for providing us with reagents.
Experimental Part
General. Reagents and solvents from Fluka: (MeO)2Tr-Cl, tom-Cl, nucleosides 17 ± 20, BnSTet, and tom-
phosphoramidites [9] from Xeragon AG; standard DNA phosphoramidites (containing thymine, N6-(phenox-
yacetyl)guanine, N2-[(4-isopropylphenoxy)acetyl]guanine, and N4-acetylcytosine) and CPG supports from Glen
Research; N2-acetylguanine [15] and N6-benzoyladenine [16] were prepared according to published procedures.
Workup implies distribution of the reaction mixture between CH2Cl2 and sat. aq. NaHCO3 soln., drying
(MgSO4) of the org. layer, and evaporation. Column chromatography (CC): silica gel from Macherey & Nagel,
Al2O3 (act. III) from Woelm. TLC: precoated silica gel plates from Macherey & Nagel, stained by dipping into a
soln. of anisaldehyde (10 ml; Aldrich), H2SO4 soln. (10 ml), and AcOH (2 ml) in EtOH (180 ml) and
subsequent heating with a heat-gun. Reversed-phase HPLC: Aquapore RP 300, 4.6 Â 220 mm (Brownlee Labs);
eluent A 0.1m (Et3NH)OAc in H2O, pH 7, and eluent B MeCN; flow 1ml/min; detection at 260 nm, elution at
408. Ion-exchange HPLC: Mono Q HR 5/5 (Pharmacia); eluent A, 1 0 mm sodium phosphate in H2O, pH 11.5,
and eluent B, 1 0 mm sodium phosphate/1m NaCl in H2O, pH 11.5; flow 1 ml/min; detection at 260 nm, elution at
r.t. M.p.: uncorrected. UV Spectra: lmax (e) in nm. IR Spectra: nÄ in cmÀ1. NMR Spectra: chemical shifts d in ppm
and coupling constants J in Hz. FAB-MS: positive mode; 2-nitrobenzyl alcohol (NOBA) as matrix; m/z (rel.
%). MALDI-TOF-MS: according to [12]. Abbreviations: (MeO)2Tr-Cl ˆ 4,4'-dimethoxytrityl chloride, tom-
Cl ˆ (triisopropylsilyloxy)methyl chloride, BSA ˆ bis(trimethylsilyl)acetamide, BnSTet ˆ 1-(benzylthio)-1H-
tetrazole, HOBTˆ 1-hydroxy-1H-benzotriazole, TBTU ˆ O-(benzotriazole-1-yl)-N,N,N',N'-tetramethyluroni-
um tetrafluoroborate, CPG ˆ long-chain alkylamino controlled pore glass.
Thermal-Denaturation Studies. Absorbance vs. temperature profiles were recorded in fused quartz cuvettes
at 260 nm on a Cary Bio-1 spectrophotometer equipped with a Peltier temperature-controlling device. The
samples were prepared under sterile conditions from stock solns. of the oligonucleotide, 1m Tris ´ HCl buffer
(pH 7.4), 5m NaCl, and 50 mm MgCl2 and subsequently degassed. A layer of silicon oil was placed on the surface
of the soln. Prior to the measurements, each sample was briefly heated to 808. The curves were obtained with
both a cooling and heating ramp of 0.38/min. The transition temperatures (Tm) were obtained after
differentiation of the melting curves.
General Procedure (G.P.) for the Preparation of Phosphoramidites 14 ± 16 and 29 ± 32. At r.t., 0.3m
precursor nucleoside in CH2Cl2 was treated consecutively with 2.5 equiv. of iPr2NEt and 1.2 equiv. of
(iPr2N)2PCl(OCH2CH2CN). After 12 ± 16 h at r.t., the mixture was subjected to CC.
1-[6'-O-(5-Bromopentyl)-2',3'-di-O-benzoyl-b-d-allofuranosyl]uracil (2). A suspension of 1 [4] (3.2 g,
4.0 mmol), uracil (0.5 g, 4.4 mmol), and BSA (2.5 ml, 10 mmol) in MeCN (12 ml) was stirred at 608 for 30 min.
Then, SnCl4 (1.7 ml, 14 mmol) was added to the clear soln., which was kept at 608 for another 20 min. After
workup, the residue was dissolved in MeCN (80 ml), treated with conc. HCl soln. (0.8 ml) and 40% HF in H2O
(1.6 ml), and stirred at r.t. for 8 h. Workup and CC (silica gel, hexane/AcOEt 7:3! 3 :7) gave 2 (1.78 g, 75%).
White foam. TLC (hexane/AcOEt 3 :7): Rf 0.40. [a]2D5 ˆ À86.0 (c ˆ 1.0, CHCl3). UV (MeOH): 257 (12000), 251
(11700), 229 (29000), 216 (23300). IR (CHCl3): 3619w, 3392w, 3014m, 2975w, 3939w, 1727s, 1700s, 1602m,
1453m, 1392w, 1317m, 1262s, 1222m, 1178w, 1126m, 1094m, 1070w, 1046m, 877w. 1H-NMR (300 MHz, CDCl3):
1.47 ± 1.65 (m, BrCH2(CH2)2); 1.82 ± 1.89 (m, Br(CH2)3CH2); 3.23 (d, J ˆ 1.9, OHÀC(4')); 3.39 (t, J ˆ 6.9,
4
)
For the influence of one 2'-O-Me substituent within a DNA sequence on the minor-groove hydration, see
[14].

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Helvetica Chimica Acta ± Vol. 83 (2000)
BrCH2); 3.52 ± 3.57 (m, CH2O); 3.65 (br. d, J ꢀ 5.9, 2 HÀC(6')); 4.20 ± 4.23 (m, HÀC(5')); 4.37 (br. s,
HÀC(4')); 5.75 (dd, J ˆ 5.6, 7.5, HÀC(2')); 5.83 (d, J ˆ 8.1, HÀC(5)); 5.89 (dd, J ˆ 1.5, 5.6, HÀC(3')); 6.50
(d, J ˆ 7.5, HÀC(1')); 7.32 ± 7.61( m, 6 arom. H); 7.90 ± 8.04 (m, 4 arom. H, HÀC(6)); 8.18 (s, NHÀC(3)).
13C-NMR (75 MHz, CDCl3): 24.8 (t, Br(CH2)2CH2); 28.7 (t, BrCH2CH2); 32.5 (t, Br(CH2)3CH2); 33.7
(t, BrCH2); 71.0, 71.1 (2t, C(6'), CH2O); 71.4, 71.8, 74.0 (3d, C(2'), C(3'), C(5')); 84.6 (d, C(4')); 86.3 (br. d,
C(1')); 103.6 (d, C(5)); 123.4 (s, C(5)); 128.4, 128.5, 128.6, 129.8, 129.9 (5d, arom. C); 129.0, 133.71, 133.74 (3s,
‡
arom. C); 140.5 (d, C(6)); 150.7 (s, C(2)); 163.0 (s, C(4)), 165.3, 165.5 (2s, CO): FAB-MS: 1263 (26, [M2 ‡ H] ),
‡
‡
633 (10, [M ‡ H] ), 631(12, [ M ‡ H] ), 521(79), 519 (76). Anal. calc. for C 29H31BrN2O9 (631.48): C 55.16,
H 4.95, N 4.44; found: C 55.25, H 4.93, N 4.45.
N6-Benzoyl-9-[2',3'-di-O-benzoyl-6'-O-(5-bromopentyl)-b-d-allofuranosyl]adenine (3). A suspension of 1
[4] (3.2 g, 4.0 mmol), N6-benzoyladenine (1.14 g, 4.8 mmol), and BSA (3.5 ml, 14 mmol) in MeCN (12 ml) was
stirred at 608 for 1h. Then, SnCl 4 (1.9 ml, 20 mmol) was added to the clear soln., which was kept at 608 for
another 20 min. After workup, the residue was dissolved in CF3COOH/H2O 1:1 (80 ml) and stirred at r.t. for
12 h. Workup and CC (silica gel, hexane/AcOEt 8 :2 ! 4 :6) gave 3 (1.13 g, 45%). White foam. TLC (hexane/
AcOEt 3 :7): Rf 0.31. [a]2D5 ˆ À145.3 (c ˆ 1.0, CHCl3). UV (MeOH): 280 (21900), 254 (12600), 231 (32800). IR
(CHCl3): 3619w, 3014m, 2976w, 1730s, 1612m, 1590m, 1481w, 1457m, 1272s, 1245s, 1178w, 1123m, 1092m, 908w,
877w. 1H-NMR (300 MHz, CDCl3): 1.42 ± 1.52, 1.57 ± 1.66 (m, BrCH2(CH2)2); 1.78 ± 1.88 (m, Br(CH2)3CH2);
3.33 (t, J ˆ 6.8, BrCH2); 3.55 (t, J ˆ 6.2, CH2O); 3.69 ± 3.80 (m, 2 HÀC(6')); 4.28 ± 4.31( m, HÀC(5')); 4.67 (br. s,
HÀC(4')); 6.16 (dd, J ˆ 1.2, 5.0, HÀC(3')); 6.19 (d, J ˆ 2.5, OHÀC(5')); 6.35 ± 6.43 (m, HÀC(1'), HÀC(2'));
7.26 ± 7.65 (m, 9 arom. H); 7.79 ± 8.10 (m, 6 arom. H); 8.18 (s, HÀC(2)); 8.86 (s, HÀC(8)); 9.10 (br. s,
NHÀC(6)). 13C-NMR (75 MHz, CDCl3): 24.9 (t, Br(CH2)2CH2); 28.7 (t, BrCH2CH2); 32.6 (t, Br(CH2)3CH2);
33.7 (t, BrCH2); 70.8, 71.9, 73.7 (3d, C(2'), C(3'), C(5')); 71.1, 71.5 (2t, C(6'), CH2O); 87.2, 88.2 (br. d, C(1'),
C(4')); 123.4 (s, C(5)); 127.9, 128.5, 128.7, 128.9, 129.8, 133.0 (6d, arom. C); 128.3, 129.3, 133.5 (3s, arom. C);
133.7 (d, arom. C); 142.4 (d, C(8)); 150.4 (s, C(4)); 151.0 (s, C(6)); 152.6 (d, C(2)); 164.3, 164.8, 165.2 (3s, CO).
‡
‡
‡
‡
FAB-MS: 761(45, [ M ‡ H] ), 760 (100, M ), 759 (45, [M ‡ H] ), 758 (87, M ), 519 (58), 105 (64).
1-[6'-O-(5-Bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-b-d-allofuranosyl]uracil (5). suspension of
A
2
(1.78 g, 2.8 mmol), AgNO3 (476 mg, 2.8 mmol), and syn-collidine (0.93 ml, 7 mmol) in CH2Cl2 (10 ml) was
treated with (MeO)2Tr-Cl (1.42 g, 4.2 mmol) at r.t. for 1 h. After filtration and evaporation, the residue was
dissolved in an ice-cold soln. of THF/MeOH/H2O 5 :4 :1(40 ml), treated with 10 n aq. NaOH (0.8 ml), stirred at
r.t. for 30 min, neutralized with AcOH (0.48 ml), and concentrated to 10 ml. Workup and CC (silica gel, CH2Cl2
(‡2% Et3N) ! CH2Cl2/MeOH 97:3 (‡2% Et3N)) gave 5 (1.69 g, 87%). White foam. TLC (CH2Cl2/MeOH
92 :8): Rf 0.45. [a]D25 ˆ 31.8 (c ˆ 1.0, CHCl3): UV (MeOH): 269 (9500), 235 (21400), 227 (19700). IR (CHCl3):
3622w, 3390w, 3029m, 1691s, 1608s, 1509m, 1461m, 1391w, 1302w, 1253s, 1226m, 1178m, 1107m, 1036s, 909w,
877w, 828w. 1H-NMR (300 MHz, CDCl3): 1.55 ± 1.69 (m, BrCH2(CH2)2); 1.90 ± 1.94 (m, Br(CH2)3CH2); 3.17 ±
3.41( m, CH2O, 2 HÀC(6'), OH); 3.45 (t, J ˆ 6.5, BrCH2); 3.60 (br. s, HÀC(5')); 3.795, 3.798 (2s, MeO); 4.01
(dd, J ˆ 1.5, 7.5, HÀC(4')); 4.16 (dd, J ˆ 4.4, 5.6, HÀC(2')); 4.69 (dd, J ˆ 5.6, 7.5, HÀC(3')); 4.88 (d, J ˆ 8.1,
HÀC(5)); 5.86 (d, J ˆ 4.4, HÀC(1')); 6.82 ± 6.86 (m, 4 arom. H); 7.22 ± 7.53 (m, 9 arom. H, HÀC(6)). 13C-NMR
(75 MHz, CDCl3): 27.7 (t, Br(CH2)2CH2); 28.8 (t, BrCH2CH2); 32.2 (t, Br(CH2)3CH2); 33.8 (t, BrCH2); 55.3
(q, MeO); 70.7, 71.3, (2t, C(6')); 68.1, 71.5, 75.5 (3d, C(2'), C(3'), C(5)); 85.6 (d, C(4')); 87.9 (s, Ar2C(Ph)); 89.2
(d, C(1')); 103.6 (d, C(5)); 113.3, 113.4 (2d, arom. C); 127.1, 127.7, 128.1, 128.4, 130.1, 130.6 (6d, arom. C); 135.6,
135.9 (2s, arom. C); 140.2 (d, C(6)); 146.3 (s, arom. C); 150.3 (s, C(2)); 158.7, 158.8 (2s, MeOÀC); 163.1
‡
‡
(s, C(4)). FAB-MS: 747 (33), 746 (53), 727 (2, M ), 725 (2, M ), 303 (100).
N6-Benzoyl-9-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-b-d-allofuranosyl]adenine (6). A suspen-
sion of 3 (1.13 g, 1.5 mmol), AgNO (255 mg, 1.5 mmol), and sym-collidine (0.5 ml, 3.8 mmol) in CH2Cl2 (5 ml)
3
was treated with (MeO)2Tr-Cl (0.78 g, 2.3 mmol) at r.t. for 3 h. After filtration and evaporation, the residue was
dissolved in an ice-cold soln. of THF/MeOH/H2O 5 :4 :1(40 ml), treated with 10 n aq. NaOH (0.8 ml), stirred at
48 for 15 min, neutralized with AcOH (0.48 ml), and concentrated to 10 ml. Workup and CC (silica gel, CH2Cl2
(‡2% Et3N) ! CH2Cl2/MeOH 97:3 (‡2% Et3N)) gave 6 (1.13 g, 92%). Pale yellow foam. TLC (CH2Cl2/
MeOH 95 :5): Rf 0.29. [a]2D5 ˆ À14.0 (c ˆ 1.0, CHCl3). UV (MeOH): 278 (18800), 256 (11200), 232 (29100), 224
(27900). IR (CHCl3): 3622w, 3113w, 2975w, 1709m, 1611s, 1585w, 1509m, 1454m, 1299w, 1251s, 1179m, 1046s,
877w, 829w. 1H-NMR (300 MHz, CDCl3): 1.52 ± 1.60 (m, BrCH2(CH2)2); 1.83 ± 1.91 (m, Br(CH2)3CH2); 3.09 ±
3.13 (m, HÀC(6')); 3.18 ± 3.25 (m, CH2O, H'ÀC(6')); 3.43 (t, J ˆ 6.8, BrCH2); 3.64 ± 3.65 (m, HÀC(5')); 3.75,
3.76 (2s, MeO); 4.27 (dd, J ˆ 3.5, 5.0, HÀC(4')); 4.67 (dd, J ˆ 4.6, 5.3, HÀC(2')); 4.87 (br. t, J ꢀ 5.3, HÀC(3'));
5.96 (d, J ˆ 4.4, HÀC(1')); 6.70 ± 6.78 (m, 4 arom. H); 7.17 ± 7.61 (m, 12 arom. H); 7.96 (s, HÀC(2)); 8.01± 8.04
(m, 2 arom. H); 8.72 (s, HÀC(8)); 9.08 (br. s, NHÀC(6)). 13C-NMR (75 MHz, CDCl3): 24.8 (t, Br(CH2)2CH2);
28.8 (t, BrCH2CH2); 32.5 (t, Br(CH2)3CH2); 33.7 (t, BrCH2); 55.3 (q, MeO); 70.1, 71.1 (2t, C(6')); 70.0, 72.1, 74.7

Helvetica Chimica Acta ± Vol. 83 (2000)
1137
(3d, C(2'), C(3'), C(5)); 86.3 (d, C(4'), CH2O); 87.2 (s, Ar2CPh)); 89.3 (d, C(1')); 113.1 (d, arom. C); 123.0
(s, C(5)); 128.4 (s, arom. C); 126.9, 127.7, 127.9, 128.1, 128.9, 130.3, 130.4, 132.8 (8d, arom. C); 133.6, 136.2, 136.5
(3s, arom. C); 141.7 (d, C(8)); 145.9 (s, arom. C); 149.6 (s, C(4)); 151.2 (s, C(6)); 152.4 (d, C(2)); 158.6, 159.7
‡
‡
‡
‡
(2s, MeOÀC); 164.3 (s, CO). FAB-MS: 855 (22, [M ‡ H] ), 854 (37, M ), 853 (21, [M ‡ H] ), 852 (33, M ), 303
(100).
N2-Acetyl-9-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-b-d-allofuranosyl]guanine (N9-7) and N2-
Acetyl-7-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-b-d-allofuranosyl]guanine (N7-7). A suspension of
1 [4] (4.0 g, 5.0 mmol), N2-acetylguanine (1.6 g, 7.5 mmol), and BSA (6 ml, 25 mmol) in (CH2)Cl)2 (15 ml) was
stirred at 808 for 1h. Then Me 3SiÀOSO2CF3 (8.1ml, 45 mmol) was added to the clear soln., which was kept at
808 for another 4 h. After workup, the residue was dissolved in MeCN (100 ml), treated with conc. HCl soln.
(1ml) and 40% HF in H 2O (2 ml), and stirred at r.t. for 4 h. Workup and a filtration over silica gel gave a
mixture of N7- and N9-nucleoside derivatives. The mixture (1.53 g, 2.0 mmol) was dissolved in CH2Cl2 (12 ml)
and treated with sym-collidine (0.67 ml, 5 mmol), AgNO3 (340 mg, 2 mmol), and (MeO)2TrÀCl (1.2 g,
3.6 mmol). The suspension was stirred at r.t. for 4 h. After filtration and evaporation, the residue was dissolved
in an ice-cold soln. of THF/MeOH/H2O 5 :4 :1(50 ml), treated with 10 n aq. NaOH (1ml), stirred at 4 8 for
15 min, neutralized with AcOH (0.6 ml), and concentrated to 10 ml. Workup and CC (silica gel, CH2Cl2 (‡2%
Et3N) ! CH2Cl2/MeOH 97:3 (‡2% Et3N)) gave 42 (0.95 g, 25%) and 43 (0.56 g, 14%) as yellow foams.
Data of N9-7: TLC (CH2Cl2/MeOH 90 :10): Rf 0.32. [a]D25 ˆ À26.2 (c ˆ 1.0, CHCl3). UV (MeOH): 275
(9300), 236 (19000), 225 (16700). IR (CHCl3): 3620w, 3022m, 2937w, 1687m, 1609s, 1562m, 1509m, 1403m,
1375w, 1302m, 1252w, 1178w, 1118w, 1037s, 877w, 826w. 1H-NMR (300 MHz, CDCl3): 1.40 ± 1.47
(m, BrCH2(CH2)2); 1.80 ± 1.84 (m, Br(CH2)3)CH2); 2.30 (s, Ac); 3.02 ± 3.23 (m, CH2O, 2 HÀC(6')); 3.37
(t, J ˆ 6.7, BrCH2); 3.48 ± 3.52 (m, HÀC(5'), OH); 3.71, 3.73 (2s, MeO); 4.31± 4.33 ( m, HÀC(4')); 4.51± 4.54
(m, HÀC(3')); 4.73 ± 4.75 (m, HÀC(2')); 5.76 (d, J ˆ 5.6, HÀC(1')); 6.70 ± 6.76 (m, 4 arom. H); 7.13 ± 7.45
(m, 9 arom. H); 7.58 (s, HÀC(8)). 13C-NMR (75 MHz, CDCl3): 23.5 (q, MeCO); 24.8 (t, Br(CH2)2CH2); 28.7
(t, BrCH2CH2); 32.5 (t, Br(CH2)3CH2); 33.8 (t, BrCH2); 55.2 (q, MeO); 69.7, 70.9 (2t, C(6'), CH2O); 70.6, 72.4,
74.9 (3d, C(2'), C(3'), C(5')); 86.5 (d, C(4')); 87.2 (s, Ar2C(Ph)); 89.1( d, C(1')); 113.0 (d, arom. C); 120.7
(s, C(5)); 126.9, 127.7, 128.2, 128.3, 130.4, 130.5 (6d, arom. C); 136.2, 136.4 (2s, arom. C); 139.1 (d, C(8)); 145.9
(s, arom. C); 147.4 (s, C(4)); 148.2 (s, C(2)); 158.6, 158.7 (2s, MeOÀC), 172.2 (s, CO). FAB-MS: 809 (28, [M ‡
‡
‡
‡
‡
H] ), 808 (63, M ), 807 (34, [M ‡ H] ), 806 (54, M ), 303 (100).
Data of N7-7: TLC (CH2Cl2/MeOH 95 :5): Rf 0.29. [a]D25 ˆ 39.7 (c ˆ 1.0, CHCl3). UV (MeOH): 264 (14600),
255 (14300), 223 (32300). IR (CHCl3): 3622w, 3152w, 3013m, 2936w, 1679s, 1609s, 1548w, 1509m, 1444w, 1373m,
1301w, 1252s, 1178m, 1116m, 1038m, 877w, 829w. H-NMR (300 MHz, CDCl3): 1.45 ± 1.56 (m, BrCH2(CH2)2);
1
1.83 ± 1.87 (m, Br(CH2)3CH2); 2.39 (s, Ac), 3.16 ± 3.21 (m, CH2O, HÀC(6')); 3.39 (t, J ˆ 6.7, BrCH2); 3.36 ± 3.41
(m, H'ÀC(6')); 3.64 ± 3.69 (m, HÀC(5')); 3.75, 3.77 (2s, MeO); 4.24 (br. t, J ꢀ 5.0, HÀC(4')); 4.31(br. t, J ꢀ 4.0,
HÀC(3')); 4.66 (br. t, J ꢀ 5.3, HÀC(2')); 6.13 (d, J ˆ 4.3, HÀC(1')); 6.76 ± 6.81( m, 4 arom. H); 7.18 ± 7.50
(m, 9 arom. H); 7.85 (s, HÀC(8)), 11.02 (br. s, NHÀC(6)); 12.41 (br. s, HÀN(1)). 13C-NMR (75 MHz, CDCl3):
24.5 (q, MeCO); 24.8 (t, Br(CH2)2CH2); 28.7 (t, BrCH2CH2); 32.4 (t, Br(CH2)3CH2); 33.7 (t, BrCH2); 55.2
(q, MeO); 69.9, 71.0 (2t, C(6'), CH2O); 70.1, 72.1, 77.4 (3d, C(2'), C(3'), C(5')); 86.2 (d, C(4')); 87.3 (s, Ar2CPh);
91.5 (d, C(1')); 111.3 (s, C(5)); 113.0 (d, arom. C); 127.0, 127.8, 128.1, 128.3, 130.4, 130.5 (6d, arom. C); 136.1,
136.4 (2s, arom. C); 141.4 (d, C(8)); 145.9 (s, arom. C); 147.9 (s, C(4)); 153.4 (s, C(2)); 157.4 (s, C(6)), 158.6,
‡
‡
‡
158.7 (2s, MeOÀC), 173.5 (s, CO). FAB-MS: 809 (9, [M ‡ H] ), 808 (12, M ), 807 (12, [M ‡ H] ), 806 (19,
‡
M ), 303 (100).
1-[6'-O-(5-Bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-2'-O-{[(triisopropylsilyl)oxy]methyl}-b-d-allofurano-
syl]uracil (8) and 1-[6'-O-(5-Bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-3'-O-{[(triisopropylsilyl)oxy]methyl}-b-
d-allofuranosyl]uracil (11). A soln. of 5 (1.68 g, 2.4 mmol) and iPr2NEt (1.5 ml, 7 mmol) in (CH2Cl)2 (8 ml) was
treated with Bu2SnCl2 (729 mg, 2.4 mmol) at r.t. for 1.5 h. Then, the mixture was heated to 808, treated with tom-
Cl (700 mg, 3.1mmol), and stirred at 75 8 for 15 min. Workup and CC (silica gel, hexane/AcOEt (‡2% Et3N)
2 :8 ! 7:3 (‡2% Et3N)) gave 8 (1.0 g, 48%) and 11 (480 mg, 23%). White foams.
Data of 8: TLC (hexane/AcOEt 5 :5): Rf 0.59. [a]2D5 ˆ 31.2 (c ˆ 1.0, CHCl3). UV (MeOH): 268 (9200), 235
(22500), 226 (20700). IR (CHCl3): 3622w, 3391w, 3013m, 2945m, 1692s, 1608w, 1509m, 1462m, 1252s, 1224s,
1177w, 1038s, 996w, 881w. 1H-NMR (300 MHz, CDCl3): 1.05 ± 1.11 (m, iPr3Si); 1.43 ± 1.55 (m, BrCH2(CH2)2);
1.77 ± 1.87 (m, Br(CH2)3CH2); 3.12 ± 3.25 (m, 2 HÀC(6'), CH2O, OHÀC(3')); 3.40 (t, J ˆ 6.7, BrCH2); 3.49 ± 3.50
(m, HÀC(5')); 3.80 (s, MeO); 4.10 (dd, J ˆ 2.2, 4.0, HÀC(4')); 4.16 (br. t, J ˆ 5.6, HÀC(3')); 4.74 ± 4.77
(m, HÀC(3')); 4.97, 5.17 (2d, J ˆ 5.0, OCH2O); 5.06 (d, J ˆ 8.4, HÀC(5)); 5.98 (d, J ˆ 5.6, HÀC(1')); 6.81± 6.85
(m, 4 arom. H); 7.07 ± 7.51( m, 9 arom. H, HÀC(6)); 8.05 (br. s, HÀN(3)). 13C-NMR (75 MHz, CDCl3): 11.9
(d, Me2CH)3Si); 17.8 (q, (Me2CH)3Si); 24.8 (t, Br(CH2)2CH2); 28.7 (t, BrCH2CH2); 32.5 (t, Br(CH2)3CH2); 33.7

1138
Helvetica Chimica Acta ± Vol. 83 (2000)
(t, BrCH2); 55.3 (q, MeO); 69.7, 70.9 (2t, CH2O, C(6')); 69.3, 72.6, 81.2 (3d, C(2'), C(3'), C(5')); 85.8, 86.0 (2d,
C(1'), C(4')); 87.8 (s, Ar2C(Ph)); 90.5 (t, OCH2O); 102.3 (d, C(5)); 113.2, 113.3 (2d, arom. C); 127.1, 128.0,
130.2, 130.6 (4d, arom. C); 135.8, 135.9 (2s, arom. C); 140.2 (d, C(6)); 146.3 (s, arom. C); 150.2 (s, C(6)); 158.7,
‡
‡
‡
‡
158.8 (2s, MeOÀC); 162.9 (s, C(4)). FAB-MS: 913 (7, M ), 912 (4, [M À H] ), 911 (7, M ), 910 (4, [M À H] ),
303 (100).
Data of 11: TLC (hexane/AcOEt 5 :5): Rf 0.48. [a]2D5 ˆ À41.5 (c ˆ 1.0, CHCl3). UV (MeOH): 268 (7800),
235 (21700), 227 (20200). IR (CHCl3): 3620w, 3391w, 3018m, 2945m, 1716m, 1694s, 1608w, 1509m, 1462m,
1390w, 1299w, 1252s, 1226m, 1178s, 1076m, 1036s, 881w. 1H-NMR (300 MHz, CDCl3): 1.10 ± 1.14 (m, iPr3Si);
1.44 ± 1.54 (m, BrCH2(CH2)2); 1.83 ± 1.87 (m, Br(CH2)3CH2); 3.10 ± 3.20 (m, HÀC(6'), CH2O); 3.31± 3.38
(m, HÀC(5'), H'ÀC(6')); 3.41( t, J ˆ 6.8, BrCH2); 3.79, 3.80 (2s, MeO); 3.80 (d, J ˆ 7.5, OHÀC(2')); 4.08 ± 4.11
(m, HÀC(4')); 4.18 ± 4.19 (m, HÀC(2')); 4.70 (dd, J ˆ 2.2, 5.9, HÀC(3')); 4.94, 5.20 (2d, J ˆ 5.7, OCH2O); 5.19
(d, J ˆ 7.8, HÀC(5)); 5.85 (d, J ˆ 7.5, HÀC(1')); 6.81± 6.86 ( m, 4 arom. H); 7.21± 7.49 ( m, 9 arom. H, HÀC(6'));
8.44 (br. s, HÀN(3)). 13C-NMR (75 MHz, CDCl3): 11.9 (d, (Me2CH)3Si); 17.8 (q, (Me2CH)3Si); 24.8
(t, Br(CH2)2CH2); 28.9 (t, BrCH2CH2); 32.5 (t, Br(CH2)3CH2); 33.6 (t, BrCH2); 55.3 (q, MeO); 69.7, 70.9 (2t,
CH2O, C(6)); 71.0, 72.9, 79.2 (3d, C(2'), C(3'), C(5')); 84.6, 87.1(2 d, C(4'), C(1')); 87.8 (s, Ar2C(Ph)); 90.7
(t, OCH2O); 102.5 (d, C(5)); 113.2, 113.3 (2d, arom. C); 127.1, 128.0, 130.3, 130.5 (4d, arom. C); 135.8, 136.1
(2s, arom. C); 140.2 (d, C(6)); 146.2 (s, arom. C); 150.5 (s, C(6)); 158.7, 158.8 (2s, MeOÀC), 162.8 (s, C(4)).
‡
‡
‡
‡
FAB-MS: 913 (3, M ), 912 (4, [M À H] ), 911 (6, M ), 910 (5, [M À H] ), 303 (100).
N6-Benzoyl-9-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-2'-O-{[(triisopropylsilyl)oxy]methyl}-b-d-
allofuranosyl]adenine (9) and N6-Benzoyl-9-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-3'-O-{[(triiso-
propylsilyl)oxy]methyl}-b-d-allofuranosyl]adenine (12). As described for 8/11, with 6 (1.05 g, 1.0 mmol),
iPr2NEt (0.7 ml, 4 mmol), (CH2Cl)2 (8 ml), Bu2SnCl2 (334 mg, 1.1 mmol), and tom-Cl (291 mg, 1.3 mmol).
Workup and CC (silica gel, hexane/AcOEt (‡2% Et3N) 2 :8 ! 8 :2 (‡2% Et3N)) gave 9 (0.45 g, 45%) and 12
(0.20 g, 20%) as pale yellow foams.
Data of 9: TLC (hexane/AcOEt 4 :6): Rf 0.56. [a]2D5 ˆ À46.1( c ˆ 1.0, CHCl3). UV (MeOH): 278 (19400),
257 (11900), 233 (32000), 226 (31100). IR (CHCl3): 3620w, 3016s, 2945m, 2869w, 1708m, 1611m, 1584w, 1509m,
1456s, 1391w, 1300m, 1250s, 1177m, 1048s, 881w, 862w. 1H-NMR (300 MHz, CDCl3): 0.97 ± 1.10 (m, iPr3Si);
1.46 ± 1.56 (m, BrCH2(CH2)2); 1.84 ± 1.88 (m, Br(CH2)3CH2); 3.05 ± 3.18 (m, HÀC(6'), CH2O, OHÀC(3')); 3.29
(dd, J ˆ 4.0, 10.3, H'ÀC(6')); 3.43 (t, J ˆ 6.8, BrCH2); 3.67 (br. s, HÀC(5')); 3.775, 3.781(2 s, MeO); 4.39 (dd, J ˆ
2.3, 5.6, HÀC(4')); 4.72 ± 4.77 (m, HÀC(2'), HÀC(3')); 4.83, 5.02 (2d, J ˆ 4.6, OCH2O); 6.07 (d, J ˆ 6.0,
HÀC(1')); 6.78 ± 6.82 (m, 4 arom. H); 7.21± 7.61( m, 12 arom. H); 7.80 (s, HÀC(2)); 8.01± 8.03 ( m, 2 arom. H);
8.64 (s, HÀC(8)); 9.02 (br. s, NHÀC(6)). 13C-NMR (75 MHz, CDCl3): 11.8 (d, (Me2CH)3Si); 17.8 (q, (Me2CH)3Si);
24.9 (t, Br(CH2)2CH2); 28.8 (t, BrCH2CH2); 32.6 (t, Br(CH2)3CH2); 33.7 (t, BrCH2); 55.3 (q, MeO); 69.1, 70.7
(2t, CH2O, C(6)); 70.3, 72.3, 80.8 (3d, C(2'), C(3'), C(5')); 85.2, 86.9 (2d, C(1'), C(4')); 87.2 (s, Ar2C(Ph)); 90.8
(t, OCH2O); 113.1 (d, arom. C); 123.5 (s, C(5)); 126.9, 127.7, 127.8, 128.9; 130.3, 130.4, 132.8 (7d, arom. C); 133.7,
136.7, 136.8 (3s, arom. C); 142.4 (d, C(8)); 146.1 (s, arom. C); 149.5 (s, C(4)); 151.7 (s, C(6)); 152.6 (d, C(2));
‡
‡
‡
158.3 (s, MeOÀC); 164.6 (s, CO). FAB-MS: 1040 (51, [M ‡ H] ), 1039 (30, M ), 1038 (40, [M ‡ H] ), 1037
‡
(35, M ), 303 (100).
Data of 12: TLC (hexane/AcOEt 4 :6): Rf 0.40. [a]2D5 ˆ À54.3. UV (MeOH): 278 (16200), 257 (10800), 233
(30000), 226 (29400). IR (CHCl3): 3621w, 3014w, 2973w, 2869w, 1710m, 1611m, 1585w, 1509m, 1456m, 1390w,
1301m, 1250s, 1178w, 1038s, 880w, 829w. 1H-NMR (300 MHz, CDCl3): 1.09 ± 1.11 (m, iPr3Si); 1.42 ± 1.57
(m, BrCH2(CH2)2); 1.84 ± 1.88 (m, BrCH2)3CH2); 3.02 ± 3.31( m, 2 HÀC(6'), CH2O); 3.41( t, J ˆ 6.8, BrCH2);
3.59 ± 3.62 (m, HÀC(5')); 3.77, 3.78 (2s, MeO); 3.99 (d, J ˆ 6.9, OHÀC(2')); 4.49 ± 4.55 (m, HÀC(3'), HÀC(4'));
4.66 ± 4.70 (m, HÀC(2')); 4.95, 5.23 (2d, J ˆ 4.6, OCH2O); 5.84 (d, J ˆ 6.9, HÀC(1')); 6.78 ± 6.84 (m, 4 arom. H);
7.21± 7.69 ( m, 12 arom. H); 7.82 (s, HÀC(2)); 8.01± 8.03 ( m, 2 arom. H); 8.61( s, HÀC(8)); 9.02 (br. s,
NHÀC(6)). 13C-NMR (75 MHz, CDCl3): 11.9 (d, (Me2CH)3Si); 17.8 (q, (Me2CH)3Si); 24.9 (t, Br(CH2)2CH2);
28.9 (t, BrCH2CH2); 32.6 (t, Br(CH2)3CH2); 33.7 (t, BrCH2); 55.3 (q, MeO); 68.7, 70.7 (2t, CH2O, C(6')); 72.2,
72.6, 81.0 (3d, C(2'), C(3'), C(5')); 83.8 (d, C(4')); 87.3 (s, Ar2C(Ph)); 89.0 (d, C(1')); 91.0 (t, OCH2O); 113.2
(d, arom. C); 123.4 (s, C(5)); 126.9 (s, arom. C); 127.7, 127.8, 128.2, 128.9, 130.3, 132.7 (6d, arom. C); 133.7, 136.7,
136.8 (3s, arom. C); 142.3 (d, C(8)); 146.2 (s, arom. C); 149.4 (s, C(4)); 151.8 (s, C(6)); 152.5 (d, C(2)); 158.7
‡
‡
‡
(s, MeOÀC); 164.3, 170.8 (2s, CO). FAB-MS: 1040 (57, [M ‡ H] ), 1039 (39, M ), 1038 (44, [M ‡ H] ), 1037
‡
(42, M ), 303 (100).
N2-Acetyl-9-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-2'-O-{[(triisopropylsilyl)oxy]methyl}-b-d-
allofuranosyl]guanine (10). As described for 8/11, with 7 (0.45 g, 0.58 mmol), Pr2NEt (0.4 ml, 2.3 mmol),
i
(CH2Cl)2 (2 ml), Bu2SnCl2 (176 mg, 0.58 mmol), and tom-Cl (130 mg, 0.58 mmol). Workup and CC (silica gel,
hexane/AcOEt (‡2% Et3N) 3 :7 ! AcOEt (‡2% Et3N)) gave 10 (0.31g, 55%). Pale yellow foam. TLC

Helvetica Chimica Acta ± Vol. 83 (2000)
1139
(AcOEt): Rf 0.24. [a]2D5 ˆ À15.5 (c ˆ 1.0, CHCl3). UV (MeOH): 282 (10900), 276 (11600), 260 (13200), 246
(11600), 231 (26100). IR (CHCl3): 3215w, 3027m, 2945w, 2868m, 1704s, 1609m, 1559m, 1509m, 1464m, 1418s,
1374w, 1298m, 1251s, 1176w, 1118s, 1037m, 996w, 831w. 1H-NMR (300 MHz, CDCl3): 1.01 ± 1.07 (m, iPr3Si);
1.42 ± 1.51 (m, BrCH2(CH2)2); 1.82 ± 1.84 (m, Br(CH2)3CH2); 2.12 (s, Ac); 2.95 (dd, J ˆ 3.1, 10.3, HÀC(6'));
3.13 ± 3.17 (m, CH2O, OHÀC(3')); 3.24 (dd, J ˆ 4.3, 10.3, H'ÀC(6')); 3.39 (t, J ˆ 6.8, BrCH2); 3.60 ± 3.62
(m, HÀC(5')); 3.77, 3.78 (2s, MeO); 4.23 (dd, J ˆ 3.1, 3.4, HÀC(4')); 4.51± 4.55 ( m, HÀC(2')); 4.82 ± 4.83 (m,
HÀC(3')); 4.89, 5.07 (2d, J ˆ 5.0, OCH2O); 5.85 (d, J ˆ 6.9, HÀC(1')); 6.74 ± 6.79 (m, 4 arom. H); 7.20 ± 7.54
(m, 9 arom. H, HÀC(8)); 8.43 (br. s, NHÀC(6)); 11.95 (s, HÀN(1)). 13C-NMR (75 MHz, CDCl3): 11.8
(d, (Me2CH)3Si); 17.8 (q, (Me2CH)3Si); 24.4 (q, MeCO); 24.8 (t, Br(CH2)2CH); 28.7 (t, BrCH2CH2); 32.5
(t, Br(CH2)3CH2); 33.8 (t, BrCH2); 55.3 (q, MeO); 69.9, 70.8 (2t, CH2O, C(6)); 72.5, 77.2, 81.5 (3d, C(2'), C(3'),
C(5')); 85.2, 86.1(2 d, C(1'), C(4')); 87.2 (s, Ar2C(Ph)); 90.9 (t, OCH2O); 113.2, 113.3 (2d, arom. C); 121.6
(s, C(5)); 127.1, 127.9, 128.2, 128.4, 130.4, 130.5, (6d, arom. C); 136.3, 136.4 (2s, arom. C); 137.5 (d, C(8)); 146.1
(s, arom. C); 147.0 (s, C(4)); 148.5 (s, C(2)); 155.7 (s, C(6)); 158.7 (s, MeOÀC); 171.2 (s, CO). FAB-MS: 994 (3,
‡
‡
M ), 992 (3, M ), 693 (20), 691 (17), 303 (100).
1-[6'-O-(5-Bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-2'-O-{[(triisopropylsilyl)oxy]methyl}-b-d-allofurano-
syl]uracil 3'-(2-Cyanoethyl Diisopropylphosphoramidite) (14). According to the G.P., with
8 (170 mg,
0.17 mmol). CC (Al2O3, hexane/AcOEt 6 :4 ! 3 :7) gave 14 (184 mg, 94%; 1:1 mixture of diastereoisomers).
White foam. TLC (hexane/AcOEt 6 :4): Rf 0.39. UV (MeCN): 269 (9700), 238 (23100), 226 (19100). IR
(CHCl3): 3408w, 3019w, 2965m, 2868w, 2360w, 1719m, 1694s, 1608m, 1509m, 1462m, 1386w, 1302w, 1252m,
1218m, 1178m, 1117w, 1036m, 980w, 882w, 828w. 1H-NMR (300 MHz, CDCl3): 0.95 ± 1.05 (m, iPr3Si); 1.10 ± 1.22
(m, (Me2CH)2N); 1.37 ± 1.42 (m, BrCH2(CH2)2); 1.70 ± 1.81 (m, Br(CH2)2CH2); 2.53 (t, J ˆ 6.7, 0.5 H,
OCH2CH2CN); 2.54 (t, J ˆ 6.2, 0.5 H, OCH2CH2CN); 2.62 (t, J ˆ 6.2, 1H, OCH 2CH2CN); 2.97 ± 3.11
(m, CH2O); 3.35 ± 3.67 (m, BrCH2, HÀC(5'), 2 HÀ(6'), (Me2CH)2N); 3.80 (s, MeO); 4.30 ± 4.36
(m, HÀC(2'), HÀC(4')); 4.68 ± 4.81( m, HÀC(3')); 4.87, 4.92, 4.94, 4.97 (4d, J ˆ 5.0, OCH2O); 5.23 (d, J ˆ 8.1,
HÀC(5)); 6.00 (d, J ˆ 5.8, 0.5 H, HÀC(1')); 6.01( d, J ˆ 7.5, 0.5 H, HÀC(1')); 6.81± 6.85 ( m, 4 arom. H); 7.06 ±
7.49 (m, 9 arom. H, HÀC(6)); 8.21(br. s, HÀN(3)). 13C-NMR (75 MHz, CDCl3): 12.0 (d, (Me2CH)3Si); 17.8 (q,
(Me2CH)3Si); 20.2, 20.4, (2t, J ˆ (C,P) ˆ 6.1, OCH2CH2CN); 23.5 (t, Br(CH2)2CH2); 24.48, 24.50, 24.63, 24.69,
24.73, 24.74 (6q, Me2CHN); 28.7, 28.8 (2t, BrCH2CH2); 32.4, 32.6 (2t, Br(CH2)3CH2); 33.6, 33.7 (2t, BrCH2); 43.4,
43.6 (2d, J(C,P) ˆ 4.9, Me2CHN); 55.4 (q, MeO); 57.7 (t, (C,P) ˆ 18.3, OCH2CH2CN); 58.7 (t, J(C,P) ˆ 15.8,
OCH2CH2CN); 68.8, 69.2, 71.6, 71.7 (4t, CH2O, C(6')); 70.7, 70.8, 70.9, 72.5 (4d, C(2'), C(3'), C(5')); 84.6, 85.6,
86.4, 87.0 (4d, C(1'), C(4')); 87.77, 87.81(2 s, Ar2C(Ph)); 89.3, 89.7 (2t, OCH2O); 102.5 (d, C(5)); 113.4, 113.5 (2d,
arom. C); 117.8, 118.0 (2s, CN); 127.3, 128.1, 128.5, 130.5, 130.8, 130.9 (6d, arom. C); 136.28, 136.32, 136.42
(3s, arom. C); 141.0 (d, C(6)); 146.2, 146.3 (2s, arom. C); 150.3 (s, C(4)); 162.9 (2s, C(6)); 159.0, 159.1
‡
‡
(2s, MeOÀC). 31P-NMR (121 MHz, CDCl3): 150.7, 151.4. FAB-MS: 1114 (6, [M ‡ H] ), 1113 (10, M ), 1112
‡
‡
(7, [M ‡ H] ), 1111 (11, M ), 303 (100).
N6-Benzoyl-9-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-2'-O-{[(triisopropylsilyl)oxy]methyl}-b-d-
allofuranosyl]adenine 3'-(2-Cyanoethyl Diisopropylphosphoramidite) (15). According to the G.P. with 9
(560 mg, 0.17 mmol). CC (Al2O3, hexane/AcOEt 8 :2 ! 6 :4) gave 15 (605 mg, 90%; a 1:1 mixture of
diastereoisomers). Pale yellow foam. TLC (hexane/AcOEt 5 :5): Rf 0.52. UV (MeCN): 277 (20400), 258
(14200), 234 (33300), 224 (31400). IR (CHCl3): 3406w, 3067w, 2945m, 2867w, 1709m, 1611s, 1545m, 1509m,
1457s, 1365w, 1300w, 1250w, 1179m, 1120m, 1082m, 980w, 932w, 828w. 1H-NMR (300 MHz, CDCl3): 0.75 ± 0.81
(m, iPr3Si); 1.21 ± 1.27 (m, (Me2CH)2N); 1.45 ± 1.50 (m, BrCH2(CH2)2); 1.72 ± 1.84 (m, Br(CH2)3CH2); 2.53 ±
2.57 (m, OCH2CH2CN); 2.94 ± 2.97 (m, 1H, OC H2CH2CN); 3.05 ± 3.11 (m, CH2O); 3.25 ± 3.28 (m, 1 H,
OCH2CH2CN); 3.36 ± 3.42 (m, 1H, BrCH 2); 3.48 ± 3.55 (m, 1H, BrCH 2); 3.66 ± 3.74 (m, 2 HÀC(6'),
(Me2CH)2N); 3.78 (s, MeO); 3.81± 3.87 ( m, HÀC(5')); 4.60 ± 4.94 (m, HÀC(2'), HÀC(3'), HÀC(4'), OCH2O);
5.98 (d, J ˆ 7.4, 0.5 H, HÀC(1')); 6.02 (d, J ˆ 7.4, 0.5 H, HÀC(1')); 6.81± 6.85 ( m, 4 arom. H); 7.21± 7.61
(m, 12 arom. H); 7.89, 7.91 (2s, HÀC(2)); 8.00 ± 8.02 (m, 2 arom. H); 8.58, 8.61(2 s, HÀC(8)); 9.02 (br. s,
NHÀC(4)). 13C-NMR (75 MHz, CDCl3): 11.9 (d, (Me2CH)3Si); 17.5 (q, (Me2CH)3Si); 20.2, 20.3 (2t, J(C,P) ˆ
6.8, CH2CN); 23.6 (t, Br(CH2)2CH2); 24.51, 24.55, 24.61, 24.70, 24.72 (5q, Me2CHN); 28.90, 28.96
(2t, BrCH2CH2); 32.4, 32.5 (2t, Br(CH2)3CH2); 33.8, 34.0 (2t, BrCH2); 43.4 (d, J ˆ (C,P) ˆ 12.1, Me2CHN);
45.1( d, J(C,P) ˆ 4.9, Me2CHN); 55.3 (q, MeO); 57.9, 58.4 (2t, J(C,P) ˆ 17.7, O CH2CH2CN); 67.8, 68.0, 70.5, 70.6
(4t, CH2O, C(6')); 72.0, 72.3, 72.8, 73.0, 75.9, 76.4 (6d, C(2'), C(3'), C(5')); 84.0, 84.7, 87.6, 88.0 (4d, C(1'), C(4'));
87.0 (s, Ar2C(Ph)); 89.1, 89.5 (2t, OCH2O); 113.0 (d, arom. C); 117.7, 117.8 (2s, CN); 123.6 (d, C(5)); 127.0, 127.8,
128.6, 128.9, 130.2, 130.4, 130.5, 133.8 (8d, arom. C); 132.8, 136.8, 136.9, 137.0, 137.1 (5s, arom. C); 143.2, 143.3
(2d, C(8)); 145.8 (s, arom. C); 149.4 (s, C(4)); 151.3, 151.5 (2s, C(6)); 152.6 (d, C(2)); 158.6 (s, MeOÀC); 164.4

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Helvetica Chimica Acta ± Vol. 83 (2000)
‡
‡
(s, CO). 31P-NMR (121 MHz, CDCl3): 150.5, 151.4. FAB-MS: 1240 (5, [M ‡ H] ), 1239 (7, M ), 1238 (6, [M ‡
‡
‡
H] ), 1237 (8, M ), 303 (100).
N2-Acetyl-9-[6'-O-(5-bromopentyl)-5'-O-(4,4'-dimethoxytrityl)-2'-O-{[(triisopropylsilyl)oxy]methyl}-a-d-
allofuranosyl]guanine 3'-(2-Cyanoethyl Diisopropylphosphoramidite) (16). According to the G.P., with 10
(170 mg, 0.17 mmol). CC (Al2O3, hexane/AcOEt 6 :4 to 3 :7) gave 16 (164 mg, 80%; 1:1 mixture of
diastereoisomers). Pale yellow foam. TLC (hexane/AcOEt 2 :8): Rf 0.50. UV (MeCN): 276 (13500), 270
(13000), 239 (24500), 228 (22200). IR (CHCl3): 3213w, 3012m, 2945m, 2868w, 2361w, 1695s, 1609s, 1559w,
1509m, 1464m, 1403w, 1371m, 1301m, 1252s, 1179m, 1127m, 1036s, 981w, 882w, 828w. 1H-NMR (300 MHz,
CDCl3): 0.90 ± 1.07 (m, iPr3Si); 1.11 ± 1.42 (m, (Me2CH)2N, BrCH2(CH2)2); 1.72 ± 1.79 (m, Br(CH2)3CH2); 2.15,
2.17 (2s, MeCO); 2.74 ± 2.78 (m, OCH2CH2CN); 2.98 ± 3.15 (m, CH2O); 3.35 ± 3.61( m, OCH2CH2CN, BrCH2,
2 HÀC(6'), (Me2CH)2N); 3.763, 3.767, 3.774, 3.778 (4s, MeO); 3.88 ± 3.91( m, HÀC(5')); 4.22 ± 4.42
(m, HÀC(2'), HÀC(4')); 4.62 ± 4.92 (m, HÀC(3'), OCH2O); 5.80 (d, J ˆ 5.3, 0.5 H, HÀC(1')); 5.96 (d, J ˆ 7.5,
0.5 H, HÀC(1')); 6.74 ± 6.84 (m, 4 arom. H); 7.21± 7.53 ( m, 9 arom. H); 9.03 ± 9.11 (m, NHÀC(2)); 11.96 ± 12.07
(m, HÀN(1)). 13C-NMR (75 MHz, CDCl3): 11.9 (d, (Me2CH)3Si); 17.9 (q, (Me2CH)3Si); 20.3, 20.4 (2t, J(C,P) ˆ
7.2, OCH2CH2CN); 24.3 (q, MeCO); 24.8 (t, Br(CH2)2CH2); 24.46, 24.51, 24.59, 24.64 (4q, Me2CHN); 28.6, 28.7
(2t, BrCH2CH2); 32.4, 32.6 (2t, Br(CH2)3CH2); 33.6, 33.7 (2t, BrCH2); 43.4, 43.5 (2d, J(C,P) ˆ 11.1, Me2CHN);
55.3 (q, MeO); 57.8 (t, J(C,P) ˆ 8.7, OCH2CH2CN); 58.7 (t, J(C,P) ˆ 18.8, OCH2CH2CN); 68.7, 69.2, 70.9, 71.2
(4t, CH2O, C(6')); 74.3, 74.5, 77.2, 78.1, 87.4, 87.9 (6d, C(2'), C(3'), C(5')); 84.9, 85.3 (2d, C(4')); 87.4, 87.9 (2d,
C(1')); 87.3 (s, Ar2C(Ph)); 90.4, 90.6 (2t, OCH2O); 113.3 (d, arom. C); 117.7, 117.8 (2s, CN); 122.2 (d, C(5));
127.3, 127.4, 128.1, 128.4, 128.5, 128.7, 130.4 (7d, arom. C); 135.4, 135.5, 136.1 (3s, arom. C); 137.8, 138.4
(2d, C(8)); 145.5, 146.1 (2s, arom. C); 147.7, 147.8 (2s, C(4)); 148.7, 148.9 (2s, C(2)); 155.2, 155.3 (2s, C(6)); 158.8,
‡
158.9 (2s, MeOÀC); 170.1 (s, CO). 31P-NMR (121 MHz, CDCl3): 150.4, 150.0. FAB-MS: 1195 (4, [M ‡ H] ),
‡
‡
‡
1194 (6, M ), 1193 (4, [M ‡ H] ), 1192 (5, M ), 303 (100).
1-Bromo-3-[(methylthio)methoxy]propane (33). A soln. of 3-bromopropanol (8.8 g, 0.1mol), DMSO
(108 ml, 1.8 mol), Ac2O (94 ml, 1.0 mol), and AcOH (68 ml, 1.2 mol) was kept at r.t. for 7 days. Extraction
(hexane/sat. NaHCO3 soln.) and distillation (758/10 Torr) gave 33 (10 g, 50%). Yellow liquid. 1H-NMR
(300 MHz): 1.98 ± 2.03 (m, CH2); 2.14 (s, MeS); 3.37 (t, J ˆ 6.5, BrCH2); 3.51( t, J ˆ 5.4, CH2O); 4.63
(s, OCH2S). 13C-NMR (75 MHz): 29.9 (t, CH2); 31.6 (q, MeS); 32.2 (t, BrCH2); 66.5 (t, CH2O); 74.4 (t, OCH2S).
1-Bromo-3-(chloromethoxy)propane (34). SO2Cl2 (4.3 ml, 0.1mol) was added dropwise to a soln. of 33
(10 g, 0.05 mol) in CH2Cl2 (240 ml) at 08. The soln. was stirred at r.t. for 1h. Evaporation and distillation (53 8/
0.3 Torr) gave 34 (4.7 g, 42%). Yellow liquid. 1H-NMR (300 MHz): 2.02 ± 2.10 (m, CH2); 3.43 (t, J ˆ 6.4,
BrCH2); 3.61( t, J ˆ 5.0, CH2O); 4.63 (s, ClCH2O). 13C-NMR (75 MHz): 30.1( t, CH2); 32.7 (t, BrCH2); 66.5
(t, CH2O); 82.0 (t, ClCH2O).
2'-O-[(3-Bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)uridine (21) and 3'-O-[(3-Bromopropoxy)-
i
methyl]-5'-O-(4,4'-dimethoxytrityl)uridine (25). A soln. of 17 (1.1 g, 2.0 mmol) and Pr2NEt (1.4 ml, 8 mmol)
in (CH2Cl)2 (6 ml) was treated with Bu2SnCl2 (608 mg, 2.0 mmol) at r.t. for 1h. Then the mixture was heated to
708, treated with 34 (488 mg, 2.6 mmol), and stirred at 708 for 15 min. Workup and CC (silica gel, hexane/AcOEt
(‡2% Et3N) 5 :5 ! AcOEt (‡2% Et3N)) gave 21 (530 mg, 38%) and 25 (418 mg, 30%) as pale yellow foams.
Data of 21: TLC (hexane/AcOEt 7:3): Rf 0.55. [a]2D5 ˆ 17.1 ( c ˆ 1.0, CHCl3). UV (MeOH): 264 (9700), 256
(9500), 233 (22900), 227 (22300). IR (CHCl3): 3391w, 3018m, 2959w, 1691s, 1608w, 1510m, 1461w, 1390w, 1299w,
1276w, 1253m, 1221m, 1178m, 1102w, 1036m, 909w, 830w. 1H-NMR: 2.07 ± 2.15 (m, CH2); 2.67 (br. s,
OHÀC(3')); 3.50 (t, J ˆ 6.4, BrCH2); 3.54 ± 3.78 (m, CH2O, 2 HÀC(5')); 3.80 (s, 2 MeO); 4.07 ± 4.09
(m, HÀC(4')); 4.26 (dd, J ˆ 2.8, 5.3, HÀC(2')); 4.47 ± 4.49 (m, HÀC(3')); 4.90, 5.00 (2d, J ˆ 6.9, OCH2O);
5.29 (d, J ˆ 8.1, HÀC(5)); 6.01( d, J ˆ 2.8, HÀC(1')); 6.82 ± 6.87 (m, 4 arom. H); 7.22 ± 7.40 (m, 9 arom. H); 7.96
(d, J ˆ 8.1, HÀC(6)). 13C-NMR (75 MHz, CDCl3): 30.1( t, CH2); 32.4 (t, BrCH2); 55.3 (q, MeO); 62.1, 66.1 (2t,
CH2O, C(5')); 74.6, 75.4, 81.9 (3d, C(2'), C(3'), C(4')); 87.1( s, Ar2C(Ph)); 89.6 (d, C(1')); 95.5 (t, OCH2O); 102.5
(d, C(5)); 113.3 (d, arom. C); 127.3, 128.1, 128.2, 128.4, 130.1 (5d, arom. C); 135.1, 135.2 (2s, arom. C); 140.0
‡
(d, C(6)); 144.2 (s, arom. C); 150.7 (s, C(2)); 158.8 (s, MeOÀC); 163.2 (s, C(4)). FAB-MS: 699 (6, [M ‡ H] ),
‡
‡
‡
698 (11, M ), 697 (7, [M ‡ H] ), 696 (12, M ), 303 (100).
Data of 25: TLC (hexane/AcOEt 3 :7): Rf 0.43. [a]2D5 ˆ 27.1( c ˆ 1.0, CHCl3). UV (MeOH): 264 (9700), 257
(9400), 234 (22100), 227 (21300). IR (CHCl3): 3556w, 3390w, 2959w, 1690s, 1608w, 1510m, 1461m, 1391w, 1300w,
1253s, 1226m, 1177m, 1101m, 1036m, 909w, 830w. 1H-NMR: 2.02 ± 2.06 (m, CH2); 3.37 ± 3.70 (m, OHÀC(2'),
BrCH2, CH2O, 2 HÀC(5')); 3.80 (s, 2 MeO); 4.25 ± 4.32 (m, HÀC(2'), HÀC(3'), HÀC(4')); 4.74, 4.78 (2d, J ˆ
6.8, OCH2O); 5.37 (d, J ˆ 8.4, HÀC(5)); 5.95 (d, J ˆ 3.4, HÀC(1')); 6.83 ± 6.86 (m, 4 arom. H); 7.24 ± 7.39
(m, 9 arom. H); 7.83 (d, J ˆ 8.1, HÀC(6)); 8.91(br. s, HÀN(3)). 13C-NMR (75 MHz, CDCl3): 30.3 (t, CH2); 32.4
(t, BrCH2); 55.3 (q, MeO); 61.7, 66.4 (2t, CH2O, C(5')); 69.0, 80.0, 83.5 (3d, C(2'), C(3'), C(4')); 87.2

Helvetica Chimica Acta ± Vol. 83 (2000)
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(s, Ar2C(Ph)); 87.7 (d, C(1')); 95.3 (t, OCH2O); 102.3 (d, C(5)); 113.3 (d, arom. C), 127.2, 128.1, 128.2, 130.1,
130.2 (5d, arom. C); 128.4, 135.1, 135.2 (3s, arom. C); 140.0 (d, C(6)); 144.3 (s, arom. C); 150.2 (s, C(2)); 158.7,
‡
‡
158.8 (2s, MeOÀC); 163.3 (s, C(4)). FAB-MS (NOBA, pos. mode): 699 (12, [M ‡ H] ), 698 (9, M ), 697 (8,
‡
‡
[M ‡ H] ), 696 (14, M ), 303 (100).
N6-Acetyl-2'-O-[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)adenosine (22) and N6-Acetyl-3'-O-
[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)adenosine (26). As described for 21/25, with 18 (1.5 g,
2.5 mmol), iPr2NEt (1.7 ml, 10 mmol), (CH2Cl)2 (10 ml), Bu2SnCl2 (0.75 g, 2.5 mmol), and 34 (630 mg,
3.6 mmol). Workup and CC (silica gel, hexane/AcOEt (‡2% Et3N) 8 :2 ! AcOEt/EtOH 9 :1( ‡2% Et3N))
gave 22 (941mg, 51%) and 26 (370 mg, 20%) as pale yellow foams.
Data of 22: TLC (AcOEt/EtOH 9 :1): Rf 0.54. [a]2D5 ˆ 1.3 (c ˆ 1.0, CHCl3). UV (MeOH): 272 (17900), 253
(12500), 234 (18400). IR (CHCl3): 3374w, 3028w, 2934w, 1728w, 1703m, 1608s, 1588m, 1509m, 1463m, 1375w,
1297m, 1251m, 1233m, 1208s, 1177m, 1098m, 1037m, 91 w3, 829w. 1H-NMR: 1.80 ± 1.98 (m, CH2); 2.16
(s, MeCO); 2.78 (d, J ˆ 5.0, OHÀC(3')); 3.37 (t, J ˆ 6.5, BrCH2); 3.41± 3.67 ( m, CH2O, 2 HÀC(5')); 3.78
(s, MeO); 4.25 ± 4.28 (m, HÀC(4')); 4.53 ± 4.56 (m, HÀC(3')); 4.83 (s, OCH2O); 4.94 (dd, J ˆ 5.0, 5.4,
HÀC(2')); 6.23 (d, J ˆ 5.4, HÀC(1')); 6.78 ± 6.83 (m, 4 arom. H); 7.19 ± 7.44 (m, 9 arom. H); 8.18 (s, HÀC(2));
8.61( s, HÀC(8)); 8.66 (br. s, NHÀC(6)). 13C-NMR (75 MHz, CDCl3): 25.6 (q, MeCO); 29.9 (t, CH2); 32.2
(t, BrCH2); 55.3 (q, MeO); 63.1, 66.3 (2t, CH2O, C(5')); 78.2, 80.1, 84.1 (3d, C(2'), C(3'), C(4')); 87.1
(s, Ar2C(Ph)); 89.5 (d, C(1')); 95.9 (t, OCH2O); 113.4 (d, arom. C); 127.0, 127.9, 128.1, 130.1 (4d, arom. C);
128.4, 135.5, 135.6 (3s, arom. C); 141.6 (d, C(8)); 144.4 (s, arom. C); 149.4 (s, C(4)); 151.0 (s, C(6)); 152.5
‡
‡
‡
‡
(d, C(2)); 158.6 (s,MeOÀC). FAB-MS: 765 (47, [M ‡ H] ), 764 (100, M ), 763 (59, [M ‡ H] ), 762 (94, M ),
303 (51).
Data of 26: TLC (AcOEt/EtOH 9 :1): Rf 0.43. [a]2D5 ˆ À5.7 (c ˆ 1.0, CHCl3). UV (MeOH): 271(18200),
253 (13500), 234 (24700), 229 (24300). IR (CHCl3): 3373w, 3016m, 2935w, 1729w, 1704m, 1609s, 1588m, 1509m,
1
1462m, 1375w, 1296m, 1252m, 1226m, 1206s, 1177m, 1086w, 1036m, 91 2w, 833w. H-NMR (300 MHz, CDCl3):
2.04 ± 2.08 (m, CH2); 2.61( s, MeCO); 3.17 ± 3.71 (m, BrCH2, CH2O, 2 HÀC(5')); 3.77, 3.78 (2s, MeO); 4.09
(br. s, OHÀC(2')); 4.37 ± 4.39 (m, HÀC(4')); 4.48 (dd, J ˆ 3.4, 5.0, HÀC(3')); 4.80, 4.84 (2d, J ˆ 6.7, OCH2O);
4.82 ± 4.88 (m, HÀC(2')); 6.04 (d, J ˆ 5.6, HÀC(1')); 6.73 ± 6.82 (m, 4 arom. H); 7.16 ± 7.38 (m, 9 arom. H); 8.19
(s, HÀC(2)); 8.62 (s, HÀC(8)); 8.71(br. s, NHÀC(6)). 13C-NMR (75 MHz, CDCl3): 25.7 (q, MeCO); 30.1
(t, CH2); 32.4 (t, BrCH2); 55.2 (q, MeO); 63.0, 66.0 (2t, CH2O, C(5')); 74.4, 77.0, 83.2 (3d, C(2'), C(3'), C(4'));
86.7 (s, Ar2C(Ph)); 89.4 (d, C(1')); 95.7 (t, OCH2O); 113.2 (d, arom. C); 122.1 (s, C(5)); 127.0, 127.9, 128.1, 130.1
(4d, arom. C); 135.5, 135.6 (2s, arom. C); 141.5 (d, C(8)); 144.4 (s, arom. C); 149.3 (s, C(4)); 152.3 (s, C(6));
‡
‡
‡
‡
158.6 (s, MeOÀC). FAB-MS: 765 (34, [M ‡ H] ), 764 (67, M ), 763 (34, [M ‡ H] ), 762 (64, M ), 303 (100).
N2-Acetyl-2'-O-[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)guanosine (23) and N2-Acetyl-3'-O-
[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)guanosine (27). As described for 21/25, with 19 (1.57 g,
2.5 mmol), iPr2NEt (1.7 ml, 10 mmol), (CH2Cl)2 (10 ml), Bu2SnCl2 (760 mg, 2.5 mmol), and 34 (470 mg,
2.5 mmol). Workup and CC (silica gel, hexane/AcOEt (‡2% Et3N) 5 :5 ! AcOEt (‡2% Et3N)) gave 23
(1.18 g, 60%) as a pale yellow foam and 0.1 g of a mixture of by-products. From this mixture,27 was isolated by
prep. TLC (CH2Cl2/MeOH 9 :1) as a pale yellow foam.
Data of 23: TLC (AcOEt/EtOH 9 :1): Rf 0.48. [a]2D5 ˆ 1.5 (c ˆ 1.0, CHCl3). UV (MeOH): 275 (13000), 271
(12900), 235 (26700), 226 (25200). IR (CHCl3): 3369w, 3222w, 3022m, 2935w, 1703s, 1674s, 1563m, 1509m,
1
1463w, 1411m, 1301w, 1253m, 1226s, 1178w, 1095m, 1036m, 996w, 830w. H-NMR: 1.76 (s, MeCO); 1.94 ± 1.97
(m, CH2); 3.18 (br. s, OHÀC(3')); 3.22 ± 3.73 (m, BrCH2, CH2O, 2 HÀC(5')); 3.75, 3.76 (2s, MeO); 4.21(br. s,
HÀC(4')); 4.23 (br. s, HÀC(3')); 4.74, 4.80 (2d, J ˆ 6.8, OCH2O); 5.07 ± 5.10 (m, HÀC(2')); 5.70 (d, J ˆ 6.2,
HÀC(1')); 6.75 ± 6.84 (m, 4 arom. H); 7.15 ± 7.50 (m, 9 arom. H); 7.87 (s, HÀC(8)); 8.73 (s, NHÀC(6)); 11.94
(s, HÀN(1)). 13C-NMR (75 MHz, CDCl3): 23.7 (q, MeCO); 30.1( t, CH2); 32.2 (t, BrCH2); 55.3 (q, MeO); 63.8,
66.1(2 t, CH2O), C(5')); 70.5, 78.9, 84.3 (3d, C(2'), C(3'), C(4')); 86.5 (d, C(1')); 87.1( s, Ar2C(Ph)); 95.7
(t, OCH2O); 113.3 (d, arom. C); 122.0 (s, C(5)); 127.2, 128.1, 128.4, 130.1 (4d, arom. C); 135.5, 135.9 (2s,
arom. C); 139.0 (d, C(8)); 144.9 (s, arom. C); 147.2 (s, C(4)); 148.4 (s, C(4)); 155.6 (s, C(6)); 158.8 (s, MeOÀC);
‡
‡
‡
‡
171.9 (s, CO). FAB-MS: 781(36, [ M ‡ H] ), 780 (52, M ), 779 (18, [M ‡ H] ), 778 (69, M ), 303 (100).
Data of 27: TLC (AcOEt/EtOH 9 :1): Rf 0.40. 1H-NMR: 1.64 ± 1.67 (m, CH2); 1.79 (s, MeCO); 3.11 ± 3.16
(m, HÀC(5')); 3.26 ± 3.58 (m, BrCH2, CH2O, H'ÀC(5')); 3.74, 3.76 (2s, MeO); 4.10 ± 4.12 (m, HÀC(4')); 4.30 ±
4.33 (m, OCH2O); 4.45 ± 4.48 (m, HÀC(3')); 4.51(br. d, J ˆ 5.0, OHÀC(2')); 4.98 ± 5.02 (m, HÀC(2')); 6.00
(d, J ˆ 6.5, HÀC(1')); 6.71± 6.83 ( m, 4 arom. H); 7.10 ± 7.46 (m, 9 arom. H); 7.81( s, HÀC(8)); 8.92 (br. s,
NHÀC(6)); 11.95 (br. s, HÀN(1)). 13C-NMR (75 MHz, CDCl3): 23.6 (q, MeCO); 30.2 (t, CH2); 31.6 (t, BrCH2);
55.1( q, MeO); 62.4, 64.8 (2t, CH2O, C(5')); 68.7, 74.9, 82.6 (3d, C(2'), C(3'), C(4')); 86.9 (d, C(1')); 87.9
(s, Ar2C(Ph)); 94.8 (t, OCH2O); 113.2 (d, arom. C); 123.8 (s, C(5)); 128.0, 128.2, 128.5, 130.1 (4d, arom. C);

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Helvetica Chimica Acta ± Vol. 83 (2000)
135.1, 135.6 (2s, arom. C); 138.7 (d, C(8)); 144.9 (s, arom. C); 147.9 (s, C(4)); 148.4 (s, C(4)); 155.5 (s, C(6));
‡
‡
158.7 (s, MeOÀC); 172.1 (s, CO). FAB-MS: 780 (10, M ), 778 (8, M ), 653 (4), 561(5), 303 (100).
N4-Acetyl-2'-O-[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)cytidine (24) and N4-Acetyl-3'-O-
[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)cytidine (28). As described for 21/25, with 20 (1.47 g,
2.5 mmol), iPr2NEt (1.7 ml, 10 mmol), (CH2Cl)2 (10 ml), Bu2SnCl2 (760 mg, 2.5 mmol), and 34 (610 mg,
3.3 mmol). Workup and CC (silica gel, hexane/AcOEt (‡2% Et3N) 7:3 ! AcOEt/EtOH 9 :1( ‡2% Et3N))
gave 24 (833 mg, 45%) and 28 (370 mg, 20%) as pale yellow foams.
Data of 24: TLC (AcOEt/EtOH 9 :1): Rf 0.63. [a]2D5 ˆ 40.9 (c ˆ 1.0, CHCl3). UV (MeOH): 299 (6600), 290
(6100), 283 (6500), 278 (6000), 271 (5800), 236 (26700), 226 (23300). IR (CHCl3): 3401w, 3011m, 2961w, 1723m,
1661s, 1610m, 1554m, 1504m, 1462s, 1362m, 1306m, 1252m, 1224s, 1206w, 1177m, 1102m, 1036m, 909w, 829w.
1H-NMR: 2.06 ± 2.14 (m, CH2); 2.22 (s, MeCO); 2.71( d, J ˆ 9.3, OHÀC(3')); 3.48 (t, J ˆ 6.4, BrCH2); 3.52 ± 3.74
(m, CH2O, 2 HÀC(5')); 3.81, 3.82 (2s, MeO); 4.11 ± 4.13 (m, HÀC(4')); 4.24 (br. d, J ꢀ 5.0, HÀC(2')); 4.43 ± 4.46
(m, HÀC(3')); 4.95, 5.17 (2d, J ˆ 6.5, OCH2O); 5.99 (s, HÀC(1')); 6.85 ± 6.89 (m, 4 arom. H); 7.08 ± 7.44
(m, 9 arom. H, HÀC(5)); 8.47 (d, J ˆ 7.4, HÀC(6)); 9.21(br. s, NHÀC(4)). 13C-NMR (75 MHz, CDCl3): 24.9
(q, MeCO); 30.4 (t, CH2); 32.5 (t, BrCH2); 55.3 (q, MeO); 61.0, 66.3 (2t, CH2O, C(5')); 68.0, 80.2, 83.2 (3d, C(2'),
C(3'), C(4')); 87.1( s, Ar2C(Ph)); 89.5 (d, C(1')); 95.2 (t, OCH2O); 96.7 (d, C(5)); 113.4 (d, arom. C); 127.2,
128.0, 128.1, 128.4, 130.2 (5d, arom. C); 135.2, 135.5, (2s, arom. C); 144.3 (s, arom. C); 144.7 (d, C(6)); 155.3
‡
‡
(s, C(2)); 158.7 (s, MeOÀC); 162.8 (s, C(4)); 170.4 (s, CO). FAB-MS: 740 (92, [M ‡ H] ), 739 (45, M ), 738
‡
‡
(74, [M ‡ H] ), 737 (14, M ), 303 (100).
Data of 28: TLC (AcOEt/EtOH 9 :1): Rf 0.53. [a]2D5 ˆ 11.8 (c ˆ 1.0, CHCl3). UV (MeOH): 299 (5600), 290
(5100), 284 (5400), 271 (4700), 236 (23300), 227 (20900). IR (CHCl3): 3400w, 3012m, 2960w, 1724m, 1658m,
1610w, 1554m, 1510m, 1482s, 1444w, 1382m, 1307m, 1252s, 1177m, 1114m, 1036m, 909w, 830w. 1H-NMR
(300 MHz, CDCl3): 2.01± 2.06 ( m, CH2); 2.24 (s, MeCO); 3.35 ± 3.67 (m, BrCH2, OCH2, 2 HÀC(5'),
OHÀC(2')); 3.81( s, 2 MeO); 4.27 ± 4.39 (m, HÀC(2'), HÀC(3'), HÀC(4')); 4.70, 4.77 (2d, J ˆ 6.8, OCH2O);
5.94 (d, J ˆ 2.8, HÀC(1')); 6.84 ± 6.88 (m, 4 arom. H); 7.16 ± 7.39 (m, 9 arom. H, HÀC(5)); 8.31( d, J ˆ 7.5,
HÀC(6)); 9.16 (br. s, NHÀC(4)). 13C-NMR (75 MHz, CDCl3): 25.0 (q, MeCO); 30.2 (t, CH2); 32.4 (t, BrCH2);
55.3 (q, MeO); 61.7, 65.9 (2t, CH2O, C(5')); 74.9, 75.5, 82.4 (3d, C(2'), C(3'), C(4')); 87.0 (s, Ar2C(Ph)); 92.2
(d, C(1')); 95.4 (t, OCH2O); 96.7 (d, C(5)); 113.3 (d, arom. C); 128.0, 128.1, 128.4, 130.3 (4d, arom. C); 135.2,
135.3 (2s, arom. C); 144.1 (d, arom. C); 144.6 (d, C(6)); 155.7 (s, C(2)); 158.8 (s, MeOÀC); 162.6 (s, C(4)); 170.0
‡
‡
‡
‡
(s, CO). FAB-MS: 740 (38, [M ‡ H] ), 739 (25, M ), 738 (38, [M ‡ H] ), 737 (11, M ), 303 (100).
2'-O-[(3-Bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)uridine 3'-(2-Cyanoethyl Diisopropylphos-
phoramidite) (29). According to the G.P., with 21 (373 mg, 0.53 mmol). CC (Al2O3, hexane/AcOEt 8 :2 to
3 :7) gave 29 (434 mg, 91%; 1:1 mixture of diastereoisomers). Pale yellow foam. TLC (hexane/AcOEt 5 :5):
Rf 0.42. UV (MeCN): 265 (22300), 236 (20900), 225 (18200). IR (CHCl3): 3390w, 3026s, 2973w, 2360w, 1806m,
1697s, 1608w, 1509m, 1458w, 1414w, 1395w, 1251s, 1178w, 1098w, 1034m, 1004m, 835w. 1H-NMR (300 MHz,
CDCl3): 1.03 ± 1.29 (m, (Me2CH2N); 2.07 ± 2.13 (m, CH2); 2.43 (t, J ˆ 6.4, 1H, OCH 2CH2CN); 2.66 (t, J ˆ 6.0,
1H, OCH 2CH2CN); 3.40 ± 3.77 (m, 2 HÀC(5'), OCH2CH2CH2Br, OCH2CH2CN, (Me2CH)2N); 3.80, 3.83
(2s, MeO); 4.18 ± 4.19, 4.26 ± 4.28 (2m, HÀC(4')); 4.37 ± 4.39, 4.42 ± 4.45 (2m, HÀC(2')); 4.52 ± 4.58
(m, HÀC(3')); 4.82 ± 4.93 (m, OCH2O); 5.24 (d, J ˆ 8.4, 0.5 H, HÀC(5)); 5.28 (d, J ˆ 8.1, 0.5 H, HÀC(5));
6.05 (d, J ˆ 3.7, 0.5 H, HÀC(1')); 6.09 (d, J ˆ 4.0, 0.5 H, HÀC(1')); 6.82 ± 6.86 (m, 4 arom. H); 7.24 ± 7.42
(m, 9 arom. H); 7.90, 7.96 (2d, J ˆ 8.1, HÀC(6)). 13C-NMR (75 MHz, CDCl3): 20.3 (br. t, CH2CN); 24.5 (br. q,
Me2CHN); 30.4 (t, CH2); 32.6 (t, BrCH2); 43.2, 43.3 (2 br. d, Me2CHN); 55.3 (q, MeO); 58.1, 58.2 (2t, J(C,P) ˆ
18.5, OCH2CH2CN); 61.5, 63.9, 65.9, 66.2 (4t, CH2O, C(5')); 68.0, 70.4, 73.9, 75.5, 82.7, 82.8 (6d, C(2'), C(3'),
C(4')); 87.1 , 87.2 (d2, C(1')); 87.7, 87.8 (2s, Ar2C(Ph)); 95.0 (t, OCH2O); 102.5, 102.6 (2d, C(5)); 113.3
(s, arom. C); 117.4, 117.6 (2s, CN); 127.2, 128.0, 128.2, 128.3, 130.3 (5d, arom. C); 134.9, 135.1, 135.2
(3s, arom. C); 140.0 (d, C(6)); 144.2, 144.3 (2s, arom. C); 150.06, 150.13 (2s, C(2)); 158.8 (s, MeOÀC); 162.9
‡
‡
(s, C(4)). 31P-NMR (121 MHz, CDCl3): 150.5, 151.2. FAB-MS: 900 (7, [M ‡ H] ), 899 (16, M ), 898 (8, [M ‡
‡
‡
H] ), 897 (21, M ), 595 (68), 593 (64), 303 (100).
N6-Acetyl-2'-O-[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)adenosine 3'-(2-Cyanoethyl Diiso-
propylphosphoramidite) (30). According to the G.P., with 22 (705 mg, 0.87 mmol). CC (Al2O3, hexane/AcOEt
6 :4 to 9 :1) gave 30 (760 mg, 92%; 1:1 mixture of diastereoisomers). Pale yellow foam. TLC (hexane/AcOEt
2 :8): Rf 0.35. UV (MeCN): 271 (19300), 254 (14700), 236 (22300), 229 (20800). IR (CHCl3): 3014m, 2974w,
2337w, 1806m, 1706w, 1610s, 1590w, 1509m, 1462m, 1412w, 1373w, 1252s, 1180m, 1097m, 1035m, 1003w, 839w.
1H-NMR (300 MHz, CDCl3): 1.06 ± 1.29 (m, (Me2CH)2N); 1.78 ± 1.96 (m, CH2); 2.39 (t, J ˆ 5.6, 0.8 H,
OCH2CH2CN); 2.60 (s, MeCO); 2.65 (t, J ˆ 5.6, 1.2 H, OCH2CH2CN); 3.27 ± 3.73 (m, 2 HÀC(5'), CH2O,
BrCH2, OCH2CH2CN, (Me2CH)2N); 3.77, 3.78 (2s, MeO); 4.32 ± 4.35 (m, 0.6 H, HÀC(4')); 4.40 ± 4.42

Helvetica Chimica Acta ± Vol. 83 (2000)
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(m, 0.4 H, HÀC(4')); 4.65 ± 4.67 (m, HÀC(3')); 4.69 ± 4.85 (m, OCH2O); 5.08 ± 5.13 (m, HÀC(2')); 6.19 (d, J ˆ
5.9, 0.4 H, HÀC(1')); 6.21( d, J ˆ 1.5, 0.6 H, HÀC(1')); 6.76 ± 6.83 (m, 4 arom. H); 7.19 ± 7.44 (m, 9 arom. H);
8.19, 8.20 (2s, 1H, H ÀC(2)); 8.59, 8.61(2 s, 1H, H ÀC(8)); 8.68 (br. s, NHÀC(6)). 13C-NMR (75 MHz, CDCl3):
20.2, 20.4 (2t, J(C,P) ˆ 7.1, CH2CN); 24.3, 24.4, 24.5, 24.7 (4q, Me2CHN); 25.7 (q, MeCO); 30.1( t, CH2); 32.3
(t, BrCH2); 43.1, 43.4 (2d, J(C,P) ˆ 6.9, Me2CHN); 55.3 (q, MeO); 58.1, 58.9 (2t, J(C,P) ˆ 13.9, OCH2CH2CN);
63.0, 66.0 (2t, CH2O, C(5')); 71.1, 71.3, 71.7, 71.9, 83.8, 83.9 (6d, C(2'), C(3'), C(4')); 86.7, 86.8 (2d, C(1')); 87.0
(s, Ar2C(Ph)); 95.1, 95.2 (2t, OCH2O); 113.2 (d, arom. C); 117.4, 117.6 (2s, CN); 122.2 (s, C(5)); 127.0
(s, arom. C); 127.9, 128.2, 128.3, 130.1, 130.2 (5d, arom. C); 135.5, 135.6 (2s, arom. C); 141.9 (d, C(8)); 144.4,
144.5 (2s, arom. C); 149.2 (s, C(4)); 151.2 (s, C(6)); 152.4 (d, C(2)); 158.6, 158.7 (s, MeOÀC); 170.1 (s, CO). 31P-
‡
‡
‡
NMR (202 MHz, CDCl3): 150.9, 151.1. FAB-MS: 965 (16, [M ‡ H] ), 964 (38, M ), 963 (11, [M ‡ H] ), 962 (37,
‡
M ), 787 (34), 785 (35), 303 (100).
N2-Acetyl-2'-O-[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)guanosine 3'-(2-Cyanoethyl Diiso-
propylphosphoramidite) (31). According to the G.P. with 23 (990 mg, 1.27 mmol). CC (silica gel, hexane/
AcOEt (‡2% Et3N) 6 :4) ! AcOEt (‡2% Et3N) gave 31 (1.03 mg, 83%; 1 :1 mixture of diastereoisomers).
Pale yellow foam. TLC (hexane/AcOEt 1:9): Rf 0.51. UV (MeCN): 281 (12900), 269 (11800), 238 (23700), 224
(19600). IR (CHCl3): 3385w, 3020s, 2973m, 2241w, 1806w, 1701s, 1608m, 1560m, 1509m, 1494w, 1412m, 1301w,
1253s, 1178m, 1126w, 1094m, 1034s, 1002w, 835w. 1H-NMR (300 MHz, CDCl3): 1.00 ± 1.19 (m, (Me2CH)2N);
1.59, 1.74 (2s, MeCO); 1.86 ± 1.94 (m, CH2); 2.31( t, J ˆ 6.2, 1H, OCH 2CH2CN); 2.72 ± 2.78 (m, 1 H,
OCH2CH2CN); 3.17 ± 3.19 (m, HÀC(5')); 3.26 ± 3.29 (m, BrCH2); 3.42 ± 3.66 (m, H'ÀC(5'), CH2O,
(Me2CH)2N); 3.75, 3.76, 3.77 (3s, MeO); 4.23, 4.34 (2 br. s, HÀC(4')); 4.52 ± 4.61( m, HÀC(3')); 4.64 ± 4.80
(m, OCH2O); 5.13 ± 5.22 (m, HÀC(2')); 5.86 (d, J ˆ 6.5, 0.5 H, HÀC(1')); 5.98 (d, J ˆ 8.5, 0.5 H, HÀC(1'));
6.77 ± 6.82 (m, 4 arom. H); 7.19 ± 7.55 (m, 9 arom. H); 7.79, 7.83 (2s, HÀC(8)); 8.60, 8.46 (2 br. s, NHÀC(2));
11.88 (br. s, HÀN(1)). 13C-NMR 75 MHz, CDCl3): 20.2 (m, CH2CN); 23.5, 23.6 (2q, MeCO); 24.5, 24.6, 24.7
(3q, Me2CHN); 30.1( t, CH2); 32.4, 32.5 (2t, BrCH2); 43.1, 45.4 (2d, J(C,P) ˆ 12.2, Me2CHN); 55.4 (q, MeO);
57.4 (t, J(C,P) ˆ 19.5, OCH2CH2CN); 59.0 (t, J(C,P) ˆ 13.4, OCH2CH2CN); 63.6, 63.8 (2t, C(5')); 66.0, 66.2 (2t,
CH2O); 70.7 (d, J(C,P) ˆ 17.1); 71.8 (d, J(C,P) ˆ 13.4); 76.4, 76.8 (2d); 84.5 (d, C(2'), C(3'), C(4')); 86.1, 88.0
(d, C(1')); 86.5, 86.8 (2s, Ar2C(Ph)); 95.0 (t, OCH2O); 113.4, 113.5 (2d, arom. C); 117.7, 118.3 (2s, CN); 122.2,
122.9 (2s, C(5)); 127.35, 127.42, 128.26, 128.33, 128.4, 130.3, 130.4 (7d, arom. C); 135.7, 135.9, 136.0, 136.4
(4s, arom. C); 138.3, 139.5 (2d, C(8)); 144.9, 145.3 (2s, arom. C); 147.1, 147.5 (2s, C(4)); 148.4, 148.7 (2s, C(2));
155.8 (s, C(6)); 159.0 (s, MeOÀC); 171.8, 171.9 (2s, CO). 31P-NMR (121 MHz, CDCl3): 150.4, 150.8. FAB-MS:
‡
‡
‡
‡
981(16, [ M ‡ H] ), 980 (38, M ), 979 (10, [M ‡ H] ), 978 (36, M ), 787 (40), 785 (38), 303 (100).
N2-Acetyl-2'-O-[(3-bromopropoxy)methyl]-5'-O-(4,4'-dimethoxytrityl)cytidine 3'-(2-Cyanoethyl Diisopro-
pylphosphoramidite) (32). According to the G.P., with 24 (566 mg, 0.77 mmol). CC (silica gel, hexane/AcOEt
6 :4 ! 2 :8) gave 32 (639 mg, 89%; 1:1 mixture of diastereoisomers). Pale yellow foam. TLC (hexane/AcOEt
1:9): Rf 0.40. UV (MeCN): 304 (6600), 290 (5600), 283 (6100), 237 (27900), 226 (22700), IR (CHCl3): 3401w,
3011m, 2969m, 2361w, 1722m, 1664m, 1609w, 1555m, 1509m, 1482s, 1383w, 1307m, 1251m, 1179m, 1120m,
1035m, 980w, 830w. 1H-NMR (300 MHz, CDCl3): 0.99 ± 1.29 (m, (Me2CH)2N); 2.08 ± 2.18 (m, CH2); 2.205, 2.213
(2s, MeCO); 2.40, 2.61(2 t, J ˆ 6.2, OCH2CH2CN); 3.41± 3.76 ( m, 2 HÀC(5'), CH2O, BrCH2, OCH2CH2CN,
(Me2CH)2N); 3.81, 3.82 (2s, MeO); 4.22 ± 4.53 (m, HÀC(2'), HÀC(3'), HÀC(4')); 4.89 ± 5.01( m, OCH2O);
6.06 (s, 0.5 H, HÀC(1')); 6.09 (d, J ˆ 1.5, 0.5 H, HÀC(1')); 6.80 ± 6.98 (m, 4 arom. H); 6.95 (d, J ˆ 7.6, 0.5 H,
HÀC(5)); 7.00 (d, J ˆ 7.5, 0.5 H, HÀC(5)); 7.23 ± 7.44 (m, 9 arom. H); 8.42 (d, J ˆ 7.5, 0.5 H, HÀC(6)); 8.52
(d, J ˆ 7.8, 0.5 H, HÀC(6)); 9.09, 9.13 (2 br, s, NHÀC(4)). 13C-NMR (75 MHz, CDCl3): 20.2, 20.4 (2t, J(C,P) ˆ
6.9, CH2CN); 24.4, 24.5, 24.6, 25.0 (4q, Me2CHN, MeCO); 30.7 (t, CH2); 32.8 (t, BrCH2); 43.1, 43.3 (2d, J(C,P) ˆ
7.0, Me2CHN); 55.2 (q, MeO); 58.2 (t, J(C,P) ˆ 15, OCH2CH2CN); 60.6, 61.0, 65.2, 66.1 (4t, CH2O, C(5')); 69.1,
76.6, 78.6, 79.1, 82.0, 86.4 (6d, C(2'), C(3'), C(4')); 87.08, 87.15 (2s, Ar2C (Ph)); 89.8 (d, C(1')); 94.9, 95.1(2 t,
OCH2O); 96.4 (d, C(5)); 113.3 (d, arom. C); 117.4 (s, CN); 127.3, 128.0, 128.4, 130.1, 130.3 (5d, arom. C); 128.3,
135.1, 135.2, 135.3 (4s, arom. C); 144.1, 144.2 (2s, arom. C); 144.9 (d, C(6)); 155.2 (s, C(2)); 158.8 (s, MeOÀC);
‡
160.6 (s, C(4)); 170.1 (s, CO). 31P-NMR (202 MHz, CDCl3): 150.2, 151.3. FAB-MS: 941 (11, [M ‡ H] ), 940 (18,
‡
‡
‡
M ), 939 (11, [M ‡ H] ), 938 (17, M ), 303 (100).
Assembly of Oligonucleotides. Automated 1.0-mmol syntheses (ꢀtrityl-offꢁ mode) were carried out on a Gene
Assembler (Pharmacia) by the following protocol: 1) 1.5 min detritylation with 4% CHCl2COOH in (CH2Cl)2;
2) 2.5 min coupling with the appropriate phosphoramidites (0.12 ml of 0.1m soln. in MeCN) and BnSTet (0.36 ml
of a 0.35m soln. in MeCN); 3) 1min capping with a 1:1mixture of Ac 2O/2,6-lutidine/THF 1:1:8 and 16% 1-
methyl-1H-imidazole in THF; 4) 0.5 min oxidation with I2/H2O/pyridine/THF 2 :2 :20 :75. According to the
trityl-assay, the average coupling yields were 99.7% for standard DNA phosphoramidites, 99.3% for tom-
protected phosphoramidites [9], and ca. 98% for phosphoramidite 32.

1144
Helvetica Chimica Acta ± Vol. 83 (2000)
Oligonucleotides 37 and 38. The assembled, immobilized sequences were treated with 12m aq. MeNH2
(0.5 ml) and 8m MeNH2/EtOH (0.5 ml). The suspension was shaken for 2 h at r.t. After centrifugation, the
supernatant was evaporated, and the resulting crude oligonucleotides were purified by ion-exchange HPLC.
After desalting of the pooled product-containing fractions, 80 OD260nm (60%) of 37 and 75 OD260nm (55%) of 38,
resp., were obtained (Table 1).
Oligonucleotide 39. As described for 37 or 38, but after the MeNH2 treatment, the residue was treated with
1m Bu4NF ´ 3H2O/THF (0.5 ml); after 12 h at r.t., 1m aq. Tris ´ HCl (pH 7.4; 0.5 ml) was added, and the clear soln.
was desalted on a Sephadex G-10 column (H2O as eluent). The product-containing fractions were collected,
evaporated, and purified by ion-exchange chromatography. After desalting of the pooled product-containing
fractions, 40 OD260nm (30%) of 39 were obtained (Table 1).
Oligonucleotides 40 and 41. As described for 37 and 38, but only with 1/10 of the solid support 35 or 36 (ca.
0.1 mmol each), resp. After ion-exchange chromatography and desalting of the pooled product-containing
fractions, 6 OD260nm (45%) of 40 and 5 OD260nm (40%) of 41, resp., were obtained (Table 1).
Oligonucleotides 49 ± 53. Under Ar, ca. 80% of the solid support 35 or 36 (ca. 0.8 mmol each) was shaken
with 1m thioglycolic acid/2m iPr2NEt/DMF (1ml). After 14 h at r.t., the solid suppport was collected by
centrifugation and washed 3 Â with DMF ( ! 35 and 36, resp.). About 1/3 of the solid support (ca. 0.25 mmol
each) was treated with a soln. of HOBT (14 mg, 0.1mmol), TBTU (32 mg, 0.1mmol), iPr3NEt (34 ml,
0.2 mmol), and 0.8 mmol of an amine (MeNH2, histamine, or l-isoleucine allyl ester) in DMF. The suspension
was shaken for 4 h at r.t., collected by centrifugation, and washed 2 Â with DMF and EtOH, resp. Deprotection
and purification were carried out as described for 37 and 38. From 35, 1 5OD260nm (40%) of 49, 1 2OD260nm (35%)
of 51, and 9 OD260nm (25%) of 53 were obtained with MeNH2, histamine, and l-isoleucine allylester, resp.
(Table 1). From 36, 1 4OD260nm (40%) of 50 and 11 OD260nm (30%) of 53 were obtained with MeNH2 and
histamine, resp. (Table 1).
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[15] H. Hrebabecky, J. Farkas, in ꢀNucleic Acid Chemistryꢁ, Vol. 1, J. Wiley & Sons, New York, 1978.
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Received February 22, 2000