Synthesis and structure of 1-deoxy-1-phenyl-β-D-ribofuranose and its incorporation into oligonucleotides

Full text of DOI:10.1021/jo960091b

J . Org. Chem. 1996, 61, 3909-3911
3909
Syn th esis a n d Str u ctu r e of
1-Deoxy-1-p h en yl-â-D-r ibofu r a n ose a n d Its
In cor p or a tion in to Oligon u cleotid es
J asenka Matulic-Adamic,* Leonid Beigelman,
Stefan Portmann,† Martin Egli,† and Nassim Usman*
Department of Chemistry & Biochemistry, Ribozyme
Pharmaceuticals, Inc., 2950 Wilderness Place,
Boulder, Colorado 80301, and Department of Chemistry,
ETH, CH-8092 Zu¨rich, Switzerland
Received J anuary 16, 1996
Hammerhead ribozymes1 are one of the smallest
catalytic RNAs with sequence-specific endoribonuclease
activity. Their highly specific cleavage activity suggests
their use as therapeutic agents for the inhibition of gene
expression. As part of our studies2-5 on the molecular
mechanism of action of hammerhead ribozymes, we were
interested in the effect of incorporation of base-modified
nucleosides into the hammerhead domain as well as into
the RNA substrate. In particular, we were interested in
universal base analogs6 which behave indiscriminately
toward its opposite base, as well as in hydrophobic base
analogs and/or base analogs lacking hydrogen bonding
capability. We and others reported the incorporation of
abasic nucleoside analogs into ribozymes.3,7 Surprisingly,
several ribozymes containing 1-deoxy-D-ribofuranose in-
stead of uridine at the U4 and/or U7 position of the
catalytic core had cleavage activity.4 By designing ad-
ditional analogs that retain the close structural and steric
relationship of the natural bases, but are not likely to
form hydrogen bonds, we wanted to study their effect on
structure and activity in the hammerhead ribozyme.
The synthesis of C-aryl glycosides has recently received
increasing attention; however, good methods for attach-
ing fully carbocyclic aromatic moieties to a deoxyribo-
furanosyl and ribofuranosyl sugar are lacking. Recently,
Chaudhuri and Kool8 reported the high-yield synthesis
of deoxyribo-C-glycosides from 1-chloro sugars using
diarylcadmium and diarylzinc reagents. While the method
proved to be useful in the preparation of deoxyribo-C-
nucleosides, yields for the preparation of C-riboside
derivatives were poor.8,9 Millican and co-workers10 in-
corporated 1,2-dideoxy-1-phenyl-â-D-ribofuranose into oli-
gonucleotides and paired them against the natural bases;
in that study weak pairing was observed, the result was
attributed to poor base stacking. The three-step synthe-
F igu r e 1. Synthesis of 2′-O-tert-butyldimethylsilyl-5′-O-
dimethoxytrityl-3′-O-(2-cyanoethyl N,N-diisopropylphosphora-
midite)-1′-deoxy-1′-phenyl-â-D-ribofuranose. Reagents and con-
ditions: (i) PhLi/THF, -78 °C, (ii) Et3SiH/BF3‚Et2O/CH3CN,
-40 °C, (iii) 1 M TBAF/THF, (iv) 70% aqueous CH3COOH, (v)
DMT-Cl/DMAP/Et3N/Pyr, (vi) TBDMS-Cl/AgNO3/Pyr/THF, (vii)
P(OCE)(N-i-Pr2)Cl/ DIPEA/1-methylimidazole.
sis of 1-deoxy-1-phenyl-â-D-ribofuranose was reported11
from 2,3,5-tri-O-benzyl-D-ribose and phenylmagnesium
bromide. Recently Schweitzer and Kool12 reported the
synthesis and incorporation of hydrophobic isosteres of
the natural bases adenine and thymine in DNA and
examined their base-pairing properties. They found that
hydrophobic base analogs are significantly selective for
pairing with hydrophobic partners (by ∼20-fold) rather
than natural bases. In addition, they attributed desta-
bilization of the duplex upon introduction of the hydro-
phobic base to the cost of desolvation of the hydrophobic
partner and not to the weak stacking propensity of
hydrophobic bases.
Our synthetic approach to 1-deoxy-1-phenyl-â-D-ribo-
furanose (5) (Figure 1) was based on the work of Czer-
necki and Ville13 for the highly stereoselective prepara-
tion of 1-deoxy-1-phenyl-â-D-glucopyranose from 2,3,4,6-
tetra-O-benzyl-D-glucopyranolactone and phenyllithium.
The choice of protecting groups was crucial for this
approach:14 they must be compatible with a very reactive
organometallic reagent and at the same time withstand
the strongly acidic conditions during reduction with Et3-
SiH/BF3‚Et2O. Easily accessible 5-O-tert-butyldiphenyl-
silyl-2,3-O-isopropylidene-D-ribono-1,4-lactone (1)15 pro-
vided a suitable starting material for these transforma-
tions. The addition of PhLi to 1 using a slightly modified
procedure13 afforded after silica gel column chromatog-
raphy a 1:3 R/â16 mixture of lactols 2 in 71% yield.17 The
above mixture was subjected to reduction using Et3SiH
and BF3‚Et2O in CH3CN at -40 °C to yield the anomeric
† ETH.
(1) Uhlenbeck, O. C. Nature 1987, 328, 596-600.
(2) Usman, N.; Wincott, F.; Matulic-Adamic, J .; Beigelman, L. U.S.
Patent Appl. SN 08/116,177, 1993.
(3) Beigelman, L.; Karpeisky, A.; Usman, N. Bioorg. Med. Chem.
Lett. 1994, 4, 1715-1720.
(4) Beigelman, L.; Karpeisky, A.; Matulic-Adamic, J .; Gonzales, C.;
Usman, N. Nucleosides Nucleotides 1995, 14, 907-910.
(5) Beigelman, L.; McSwiggen, J .; Draper, K.; Gonzales, C.; J ensen,
K.; Karpeisky, A.; Modak, A.; Matulic-Adamic, J .; DiRenzo, A.; Hae-
berli, P.; Sweedler, D.; Tracz, D.; Grimm, S.; Wincott, F.; Thackray,
V.; Usman, N. J . Biol. Chem. 1995, 270, 25702-25708.
(6) Loakes, D.; Brown, D. M. Nucleic Acids Res. 1994, 22, 4039-
4043 and references cited therein.
(7) Fu, D.-J .; Benseler, F.; McLaughlin, L. W. J . Am. Chem. Soc.
1994, 116, 4591-4598.
(8) Chaudhuri, N. C.; Kool, E. T. Tetrahedron Lett. 1995, 36, 1795-
1798.
(9) Klein, R. S.; Kotick, M. P.; Watanabe, K. A.; Fox, J . J . J . Org.
Chem. 1971, 36, 4113-4116.
(10) Millican, T. A.; Mock, G. A.; Chauncey, M. A.; Patel, T. P.;
Eaton, M. A. W.; Gunning, J .; Cutbush, S. D.; Neidle, S.; Mann, J .
Nucleic Acids Res. 1984, 12, 7435-7453.
(11) Krohn, K.; Heins, H.; Wielckens, K. J . Med. Chem. 1992, 35,
511-517.
(12) Schweitzer, B. A.; Kool, E. T. J . Am. Chem. Soc. 1995, 117,
1863-1872.
(13) Czernecki, S.; Ville, G. J . Org. Chem. 1989, 54, 610-612.
(14) Piccirilli, J . A.; Krauch, T.; MacPherson, L. J .; Benner, S. A.
Helv. Chim. Acta 1991, 74, 397-406.
(15) Drew, M. G. B.; Mann, J .; Thomas, A. J . Chem. Soc., Perkin
Trans. 1 1986, 2279-2285.
(16) It should be noted that for hemiacetals 2 the prefix R refers to
the position of the glycosidic OH group relative to the configuration
at the reference C-atom (C4′ in 2; i.e., the phenyl moiety is in the
â-position).
S0022-3263(96)00091-6 CCC: $12.00 © 1996 American Chemical Society

3910 J . Org. Chem., Vol. 61, No. 11, 1996
Notes
mixture of protected phenyl ribosides. These anomers
were easily separated by flash silica gel chromatography
to yield the faster moving â-anomer 3 in 51% yield and
the slower moving R-anomer 4 in 13% yield. Some
cleavage of the TBDPSi group was observed under the
above reaction conditions. We believe that this cleavage
could be completely avoided by further lowering the
reaction temperature and/or shortening the reaction time.
It is worth noting that when 5-O-tert-butyldimethylsilyl-
2,3-O-isopropylidene-D-ribono-1,4-lactone was used as the
starting material reduction as described above led to the
exclusive formation of 1,5-anhydro derivative 6.13 In this
case, because of the greater acid lability of the TBDMSi
ether compared to that of the TBDPSi ether, the cleavage
of the 5′-O-TBDMSi group occurred first, followed by
cyclization to give 6. Fully protected 3 was first treated
with 1.5 equiv of TBAF in THF to afford after silica gel
column chromatography the 5′-OH derivative quantita-
tively. The cleavage of the isopropylidene group using
boiling 70% aqueous AcOH for 30 min proceeded in a
quantitative manner to give the known 1-deoxy-1-phenyl-
â-D-ribofuranose (5).9
F igu r e 2.
interaction. The H6‚‚‚O4′ distance is 2.37 Å, the angle
at the hydrogen atom is 104°, and the angle C1′-O4′-
H6 is 85°.
Recent studies of the anomeric effect in a series of
pyrimidine C-nucleosides18,19 demonstrated the stronger
equatorial preference of the C-nucleoside base (the
absence of anomeric effect) in these compounds compared
to N-nucleosides. This feature makes phenyl riboside,
which might be considered a C-nucleoside analog, an
attractive analog to study the effect of sugar conformation
on ribozyme activity.
To incorporate the phenyl nucleoside into oligonucleo-
tides, we prepared phosphoramidite 10 in three steps
from 5. Protection of the 5′-hydroxyl group by dimethoxy-
tritylation was achieved under standard conditions (DMT-
Cl, DMAP, Et3N, Pyr)22 to afford, after silica gel column
purification, 5′-O-DMT-1′-deoxy-1′-phenyl-â-D-ribofura-
nose (7) in 75% yield. Selective protection of the 2′-
hydroxyl using tert-butyldimethylsilyl chloride proceeded
in the presence of AgNO3 and pyridine in THF23 to afford
a mixture of 2′-O-TBDMSi, 3′-O-TBDMSi, and some 2′,3′-
bis-O-TBDMSi derivatives. Careful separation of these
products using flash silica gel chromatography afforded
a faster running 3′-O-TBDMSi isomer 8 in 32% yield and
2′-O-TBDMSi isomer 9 in 35% yield. It is noteworthy
that the 3′-O-TBDMSi isomer is faster moving than the
2′-O-TBDMSi isomer, unlike the majority of silylated
nucleoside regioisomers. The 3′-isomer 8, when subjected
to 1% Et3N in MeOH, isomerizes to a 1:1 mixture of 2′-
and 3′-isomers from which an additional amount of the
desired 2′-isomer could be obtained. Phosphitylation of
9 using 2-cyanoethyl N,N-diisopropylchlorophosphora-
midite in the presence of N,N-diisopropylethylamine and
1-methylimidazole24 yielded the desired 3′-phosphora-
midite 10, 31P NMR in CDCl3 δ 149.1 & 146.6 ppm for
two P-diastereoisomers, respectively. No migration of the
TBDMSi group, under these conditions, was observed.
Phosphoramidite 10 was incorporated, instead of U,
into the cleavage site of a 17-mer RNA substrate 5′-CAG
GGA UUU AUG GAG AU-3′ (cleavage site in bold). The
method of oligoribonucleotide synthesis, deprotection,
purification, and testing has been described.25,26 The
average stepwise coupling yields for all nucleotides were
The structure of 5 was confirmed by X-ray crystal-
lography20,27 and an ORTEP representation is shown in
Figure 2. The sugar pucker is in the C2′-endo conforma-
tion (pseudorotation angle P, 175.7°) and the backbone
torsion angles are γ -174.2° and δ 149.8°. The small
difference of 0.015 Å for the C4′-O4′ (1.422 Å) and O4′-
C1′ (1.427 Å) bond lengths is consistent with the absence
of an anomeric effect between the furanose oxygen and
the nucleobase. Similar differences were observed in the
crystal structures of other C-nucleosides.21 The S-type
sugar pucker puts the phenyl ring in a pseudoequatorial
conformation as expected for a sterically driven pseudo-
rotational equilibrium. The glycosidic torsion angle ø
(O4′-C1′-C1-C2, termed in analogy to pyrimidine
bases) in 5 is -171.7°. This generates a short 1‚‚‚4
contact between O4′ and the phenyl C6 of 2.76 Å. The
corresponding O4′-C1′-C1-C6 torsion angle is 8°. Thus,
there may be a weak C6-H6‚‚‚O4′ hydrogen-bonding
(17) 1H NMR (CDCl3) resonances for 2′,3′-O-isopropylidene groups
of 2: δ 1.68 (s) and 1.40 (s), ∆δ ) 0.28, R-isomer; 1.38 (s) and 1.25 (s),
∆δ ) 0.13, â-isomer. For the assignment of the anomeric configuration
of nucleosides based on ∆δ values, see: Tapiero, C.; Imbach, J .-L. In
Nucleic Acid Chemistry, Part 1; Townsend, L. B., Tipson, R. S., Eds.;
J . Wiley & Sons, Inc.: New York, 1978; pp 1055-1059. Ohrui, H.;
J ones, G. H.; Moffatt, J . G.; Maddox, M. L.; Christensen, A. T.; Byram,
S. K. J . Am. Chem. Soc. 1975, 97, 4602-4613.
(18) Thibaudeau, C.; Plavec, J .; Watanabe, K. A.; Chattopadhyaya,
J . J . Chem. Soc., Chem. Commun. 1994, 537-540.
(22) J ones, R. A. In Oligonucleotide Synthesis: A Practical Approach;
Gait, M. J ., Ed.; IRL Press: Oxford, 1984; p 27.
(19) O’Leary, D. J .; Kishi, Y. J . Org. Chem. 1994, 59, 6629-6636.
(23) Hakimelahi, G. H.; Proba, Z. A.; Ogilvie, K. K. Can. J . Chem.
1982, 60, 1106-1113.
(20) Crystals were obtained from
a saturated toluene solution
containing 5-10% EtOAc, and cooling to -18 °C. The space group was
P21 and the cell constants were a ) 6.736 Å, b ) 6.780 Å, c ) 11.085
(24) Tuschl, T.; Ng, M. M. P.; Pieken, W.; Benseler, F.; Eckstein, F.
Biochemistry 1993, 32, 11658-11668.
Å,
â
)
99.64°. Data were collected on an Enraf-Nonius CAD4
(25) Scaringe, S. A.; Franklyn, C.; Usman, N. Nucleic Acids Res.
1990, 18, 5433-5441.
diffractometer (Mo KR) and reduced to 1582 unique reflections (I g
2σ(I)). The structure was solved with direct methods using the program
SHELXS-86 and refined with the program SHELXL-93 (Sheldrick, G.
SHELXS-86, Universita¨t Go¨ttingen, Germany, 1986. Sheldrick, G.
SHELXL-93, Universita¨t Go¨ttingen, Germany, 1993). The final R-
factor was 5.45%.
(26) Wincott, F.; DiRenzo, A.; Shaffer, C.; Grimm, S.; Tracz, D.;
Workman, C.; Sweedler, D.; Scaringe, S.; Usman, N. Nucleic Acids Res.
1995, 23, 2677-2684.
(27) The author has deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, U.K.
(21) Thibaudeau, C; Plavec, J .; Chattopadhyaya, J . J . Am. Chem.
Soc. 1994, 116, 8033-8037 and references cited therein.

Notes
J . Org. Chem., Vol. 61, No. 11, 1996 3911
THF (3 mL, 3 mmol) was added. The reaction mixture was
stirred at rt for 30 min and then evaporated to a syrup. The
residue was applied to the silica gel column and eluted with
toluene followed by a 5-10% gradient of ethyl acetate in
hexanes. The 5′-O-desilylated product was obtained as a color-
less foam (0.68 g, 96% yield). This material was dissolved in
70% aqueous acetic acid and heated at 100 °C (oil bath) for 30
min. Evaporation to dryness under reduced pressure and
crystallization of the residual syrup from toluene afforded 5 (0.49
g, 94% yield), mp 120-121 °C (lit.9 mp 120-121 °C): 1H NMR
(DMSO-d6 + D2O) δ 7.47-7.31 (m, 5H, Ph), 4.63 (d, J 1′,2′ ) 7.0,
1H, H-1′), 3.95 (dd, J 3′,2′ ) 5.4, J 3′,4′ ) 3.7, 1H, H-3′), 3.89 (dd,
J 4′,5′ ) 4.4, 1H, H-4′), 3.76 (dd, J 2′,1′ ) 7.0, J 2′,3′ ) 5.4, 1H, H-2′),
3.61 (m, 2H, H-5′, H-5′′).
∼97-98%. The presence of the phenyl nucleotide was
confirmed by nucleoside compositional analysis.5 The
substrate containing the phenyl nucleoside, 5′-CAG GGA
UUP AUG GAG AU-3′, was cleaved by the hammerhead
ribozyme, 5′-UCU CCA UCU GAU GAG GCC GAA AGG
CCG AAA AUC CCU-3′, ca. 10 times slower than the
U-containing substrate. Contributions of altered sugar
conformations, anomeric effect, and hydrophobic interac-
tions to the change of the cleavage rate in a series of
substrates containing pyrimidine analogs incorporated
at the cleavage site are under investigation and will be
reported in due course.
3′-O-t er t -Bu t yld im e t h ylsilyl-5′-O-d im e t h oxyt r it yl-1′-
d eoxy-1′-p h en yl-â-D-r ib ofu r a n ose (8) a n d 2′-O-ter t-Bu -
tyld im eth ylsilyl-5′-O-d im eth oxytr ityl-1′-d eoxy-1′-p h en yl-
â-D-r ibofu r a n ose (9). Compound 5 (770 mg, 3.7 mmol) was
5′-O-dimethoxytritylated according to the standard procedure22
to yield, after silica gel column chromatography (0.5-2% gradi-
ent of ethyl acetate in hexanes), 1.4 g (75% yield) of 5′-O-
dimethoxytrityl derivative 7 as a yellowish foam: 1H NMR δ
7.43-6.81 (m,18 H, Ph), 4.80 (d, J 1′,2′ ) 6.3, 1H, H-1′), 4.18 (dd,
Exp er im en ta l Section
Gen er a l. All reactions were carried out under a positive
pressure of argon in anhydrous solvents. Commercially avail-
able reagents and anhydrous solvents were used without further
purification. 2,3-O-Isopropylidene-D-ribono-1,4-lactone was pur-
chased from Aldrich. 1H (400.075 MHz) and 31P (161.947 MHz)
NMR spectra were recorded in CDCl3, unless stated otherwise,
and chemical shifts in ppm refer to TMS and H3PO4, respec-
tively. J values are in hertz. Analytical thin-layer chromatog-
raphy (TLC) was performed with Merck Art. 5554 kieselgel 60
F254 plates and flash column chromatography using Merck
0.040-0.063 mm silica gel 60. Elemental analyses were per-
formed by MHW Laboratories, Phoenix, AZ.
J 3′,OH ) 3.9, J 3′,4′ ) 8.7, 1H, H-3′), 4.13 (dd, J 4′,5′ ) 4.2, J 4′,3′
)
8.7, 1H, H-4′), 4.08 (dd, J 2′,1′ ) 6.3, J 2′,OH ) 5.8, 1H, H-2′), 3.79
(s, 6H, OMe), 3.47 (dd, J 5′,4′ ) 4.2, J 5′,5′′ ) 10.1, 1H, H-5′), 3.37
(dd, J 5′′,4′ ) 4.0, J 5′′,5′ ) 10.1, 1H, H-5′′), 2.48 (d, J OH,2′ ) 5.8, 1H,
2′-OH), 2.43 (d, J OH,3′ ) 3.9, 1H, 3′-OH). Anal. Calcd for
C
32H32O6: C, 74.98; H, 6.29. Found: C, 75.17; H, 6.15.
5′-O-ter t-Bu t yld ip h en ylsilyl-2′,3′-O-isop r op ylid en e-1′-
d eoxy-1′-p h en yl-â-D-r ibofu r a n ose (3). To a stirred solution
of 5-O-tert-butyldiphenylsilyl-2,3-O-isopropylidene-D-ribono-1,4-
lactone (1)15 (12 g, 28 mmol) in dry THF (70 mL) cooled to -78
°C was added phenyllithium (2 M solution in cyclohexane/ether
70/30, 15 mL, 30 mmol) dropwise. The reaction mixture was
stirred at -78 °C for 2 h and at rt for 4 h, then quenched with
cold water, and extracted with ether (×3). The combined organic
layers were dried (Na2SO4) and evaporated to a syrup under
reduced pressure. Silica gel column chromatographic purifica-
tion using a 3-10% gradient of ethyl acetate in hexanes afforded
2 as a syrup (R/â16 1:3 mixture) (10 g, 71%): 1H NMR for
R-anomer δ 7.80-7.38 (m, Ph), 4.95 (d, J 2′,3′ ) 5.2, H-2′), 4.63
(d, J 3′,4′ ) 7.3, H-3′), 4.48 (s, OH-1′), 4.34 (m, H-4′), 3.99 (dd,
J 5′,4′ ) 3.4, J 5′,5′′ ) 11.4, H-5′), 3.91 (dd, J 5′′,4′ ) 3.4, J 5′′,5′ ) 11.4,
H-5′′), 1.68 (s, Me), 1.40 (s, Me), 1.08 (s, t-Bu), â-anomer δ 7.80-
7.38 (m, Ph), 4.93 (d, J 2′,3′ ) 5.7, H-2′), 4.68 (d, J 3′,2′ ) 5.7, H-3′),
4.42 (s, OH-1′), 4.45 (m, H-4′), 3.96 (dd, J 5′,4′ ) 3.8, J 5′,5′′ ) 11.2,
H-5′), 3.78 (dd, J 5′′,4′ ) 3.6, J 5′′,5′ ) 11.2, H-5′′), 1.38 (s, Me), 1.25
(s, Me), 1.12 (s, t-Bu).
Compound 7 was treated with tert-butyldimethylsilyl chloride
under the conditions described by Hakimelahi et al.,23 and the
reaction mixture was purified by the silica gel column chroma-
tography (1-2% gradient of ethyl acetate in hexanes) to afford
faster moving 3′-O-TBDMSi isomer 8 as a foam (0.55 g, 32%):
1H NMR (CDCl3 + D2O) δ 7.62-6.89 (m, 18 H, Ph), 4.85 (d, J 1′,2′
) 6.2, 1H, H-1′), 4.30 (dd, J 3′,2′ ) 5.7, J 3′,4′ ) 4.2, 1H, H-3′), 4.13
(m, 1H, H-4′), 4.01 (app t, J 2′,1′ ) 6.2, 1H, H-2′) 3.86 (s, 6H, OMe),
3.56 (dd, J 5′,4′ ) 3.2, J 5′,5′′ ) 10.3, 1H, H-5′), 3.27 (dd, J 5′′,4′ ) 3.9,
J 5′′,5′ ) 10.3, 1H, H-5′′), 0.93 (s, 9H, t-Bu), 0.09 (s, 3H, Me), 0.00
(s, 3H, Me). Anal. Calcd for C38H46O6Si: C, 72.81; H, 7.40.
Found: C, 72.77; H, 7.26.
The slower migrating 2′-O-TBDMSi isomer 9 was then eluted
to give, upon evaporation, a white foam (0.60 g, 35%): 1H NMR
(CDCl3 + D2O) δ 7.59-6.88 (m,18 H, Ph), 4.81 (d, J 1′,2′ ) 7.2,
1H, H-1′), 4.27 (m, 1H, H-4′), 4.22 (dd, J 2′,1′ ) 7.2, J 2′,3′ ) 5.4,
1H, H-2′), 4.15 (dd, J 3′,2′ ) 5.4, J 3′,4′ ) 2.6, 1H, H-3′), 3.87 (s, 6H,
OMe), 3.60 (dd, J 5′,4′ ) 3.0, J 5′,5′′ ) 10.3, 1H, H-5′), 3.35 (dd, J 5′′,4′
) 3.6, J 5′′,5′ ) 10.3, 1H, H-5′′), 0.93 (s, 9H, t-Bu), 0.12 (s, 3H,
Me), 0.05 (s, 3H, Me). Anal. Calcd for C38H46O6Si: C, 72.81;
H, 7.40. Found: C, 72.97; H, 7.22.
Compound 2 (9 g, 17.8 mmol) was dissolved in dry acetonitrile
(170 mL) and the solution cooled to -40 °C. Et3SiH (5.7 mL,
36 mmol) was added followed by the dropwise addition of BF3‚
Et2O (2.49 mL, 20 mmol). The mixture was stirred at -40 °C
for 1 h and, after warming to rt, quenched with saturated
aqueous K2CO3 (18 mL). The aqueous mixture was extracted
with ether and the organic layer dried (Na2SO4) and evaporated
to a syrup. Silica gel column chromatography (0.5-3% gradient
of ethyl acetate in hexanes) afforded 3 as a white foam (4.4 g,
2′-O-ter t-Bu t yld im et h ylsilyl-5′-O-d im et h oxyt r it yl-3′-O-
(2-cya n oeth yl N,N-d iisop r op ylp h osp h or a m id ite)-1′-d eoxy-
1′-p h en yl-â-D-r ibofu r a n ose (10). Compound 9 (0.87 g, 1.4
mmol) was phosphitylated under the conditions described by
Tuschl et al.,24 and the product was isolated by silica gel column
chromatography using 0.5% ethyl acetate in toluene (1% Et3N)
for elution (0.85 g, 74% yield): 31P NMR δ 149.1 (s), 146.6 (s).
Anal. Calcd for C47H63N2O7PSi: C, 68.25; H, 7.68; N, 3.39.
Found: C, 68.21; H, 7.49; N, 3.26.
51% yield): 1H NMR δ 7.82-7.36 (m,15 H, Ph), 4.99 (d, J 1′,2′
)
5.4, 1H, H-1′), 4.89 (dd, J 3′,2′ ) 6.4, J 3′,4′ ) 4.0, 1H, H-3′), 4.61
(dd, J 2′,1′ ) 5.4, J 2′,3′ ) 6.4, 1H, H-2′), 4.29 (m, 1H, H-4′), 4.03
(dd, J 5′,4′ ) 3.4, J 5′,5′′ ) 11.2, 1H, H-5′), 3.97 (dd, J 5′′,4′ ) 3.9, J 5′′,5′
) 11.2, 1H, H-5′′), 1.71 (s, 3H, Me), 1.44 (s, 3H, Me), 1.15 (s,
9H, t-Bu). Anal. Calcd for C30H36O4Si: C, 73.73; H, 7.42.
Found: C, 73.68; H, 7.45.
Ack n ow led gm en t. We thank Anthony DiRenzo for
ribozyme synthesis, Carolyn Gonzalez for ribozyme
cleavage experiments, and David Sweedler for nucleo-
side compositional analysis.
The slower moving R-anomer 4 was isolated as a syrup (1.1
g, 13% yield): 1H NMR δ 7.77-7.34 (m,15 H, Ph), 5.39 (d, J 1′2′
) 4.1, 1H, H-1′), 5.07 (d, J 3′,2′ ) 6.0, 1H, H-3′), 4.95 (dd, J 2′,1′
4.1, J 2′,3′ ) 6.0, 1H, H-2′), 4.39 (m, 1H, H-4′), 4.00 (dd, J 5′,4′
)
)
Su p p or tin g In for m a tion Ava ila ble: Coordinates for the
structure of 1-deoxy-1-phenyl-â-D-ribofuranose (5) (6 pages).
This material is contained in libraries on microfiche, im-
mediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS; see any current
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3.8, J 5′,5′′ ) 11.1, 1H, H-5′), 3.88 (dd, J 5′′,4′ ) 3.6, J 5′′,5′ ) 11.1,
1H, H-5′′), 1.53 (s, 3H, Me), 1.38 (s, 3H, Me), 1.18 (s, 9H, t-Bu).
Anal. Calcd for C30H36O4Si: C, 73.73; H, 7.42. Found: C, 73.73;
H, 7.30.
1′-Deoxy-1′-p h en yl-â-D-r ibofu r a n ose (5). Compound 3 (1
g, 2.1 mmol) was dissolved in THF (20 mL), and 1 M TBAF in
J O960091B