Building blocks for ribozyme mimics: Conjugates of terpyridine and bipyridine with nucleosides

Article abstract of DOI:10.1021/jo9518213

The incorporation of the 2,2':6',2''-terpyridyl (terpy) complex of Cu(II) into a deoxyoligonucleotide has led to a functional mimic of ribozymes. The resulting mimic can cleave target RNA in a sequence-directed manner by a hydrolytic mechanism. Here we describe the synthesis and characterization of four modified nucleoside phosphoramidite reagents (7, 10, 14, and 18) that contain pendant 2,2'-bipyridine or terpy ligands. The ligands are attached either to the nucleobase (7, 10) or to the sugar (14, 18). Nucleobase modification was carried out at the C-5 position of 2'-deoxyuridine (dU). One route to sugar modification was performed by synthesis of 18, a 1'-functionalized analog of dU based on 1-[3-deoxy-β-D-psicofuranosyl]uracil. Another route to sugar functionalization resulted in 14, a 2'-C-alkyl derivative of adenosine. These modified nucleosides are building blocks for ribozyme mimics. They are designed to deliver hydrolytically active metal complexes across either the major groove (7, 10) or the minor groove (14, 18) of an RNA/DNA duplex.

Full text of DOI:10.1021/jo9518213

2314
J . Org. Chem. 1996, 61, 2314-2321
Bu ild in g Block s for Ribozym e Mim ics: Con ju ga tes of Ter p yr id in e
a n d Bip yr id in e w ith Nu cleosid es
J ames K. Bashkin,* J in Xie, Andrew T. Daniher, UmaShanker Sampath, and
J effrey L.-F. Kao†
Department of Chemistry, Washington University, St. Louis, Missouri 63130-4899
Received October 9, 1995X
The incorporation of the 2,2′:6′,2′′-terpyridyl (terpy) complex of Cu(II) into a deoxyoligonucleotide
has led to a functional mimic of ribozymes. The resulting mimic can cleave target RNA in a
sequence-directed manner by a hydrolytic mechanism. Here we describe the synthesis and
characterization of four modified nucleoside phosphoramidite reagents (7, 10, 14, and 18) that
contain pendant 2,2′-bipyridine or terpy ligands. The ligands are attached either to the nucleobase
(7, 10) or to the sugar (14, 18). Nucleobase modification was carried out at the C-5 position of
2′-deoxyuridine (dU). One route to sugar modification was performed by synthesis of 18, a 1′-
functionalized analog of dU based on 1-[3-deoxy-â-D-psicofuranosyl]uracil. Another route to sugar
functionaliztion resulted in 14, a 2′-O-alkyl derivative of adenosine. These modified nucleosides
are building blocks for ribozyme mimics. They are designed to deliver hydrolytically active metal
complexes across either the major groove (7, 10) or the minor groove (14, 18) of an RNA/DNA
duplex.
In tr od u ction
among the first well-defined metal complexes found to
cleave RNA hydrolytically.9 Our mechanistic studies
have shown that aqueous Cu(II) terpyridine promotes
both the transesterification and hydrolysis of RNA sub-
strates.10 By linking bipyridine and terpyridine moieties
to molecular recognition elements, we hoped to prepare
sequence-specific RNA cleavage agents that operate via
biocompatible hydrolytic pathways.11 On the basis of this
design, we recently reported1 the first example of a
wholly-synthetic ribozyme mimic. This mimic comprises
a 17-mer DNA oligonucleotide with a covalently attached
terpy ligand that is incorporated as a side chain on an
internal nucleotide residue. Our design combines the
binding specificity of the oligonucleotide with the hydro-
lytic activity of aqueous terpyridyl Cu(II). This approach
allowed us to achieve sequence-specific cleavage of a 159-
mer RNA fragment of the HIV gag gene mRNA. Re-
cently, other examples of sequence-specific hydrolytic
cleavage of RNA by synthetic reagents have been
reported.12-16
We report a series of four DNA building blocks (7, 10,
14, and 18) for the synthesis of ribozyme mimics,
sequence-specific reagents for the hydrolytic cleavage of
RNA. These ribozyme mimics contain a deoxyoligonucle-
otide, designed to form a sequence-specific RNA/DNA
duplex by Watson-Crick base-pairing, and a pendant
metal complex designed to cleave the target RNA. Our
nucleoside phosphoramidites incorporate 2,2′-bipyridine
(bipy) or 2,2′:6′,2′′-terpyridine (terpy) ligands, allowing
the synthesis of deoxyoligonucleotides that can deliver
hydrolytically-active metal complexes to a complemen-
tary RNA strand. The bipy and terpy ligands are
attached either to nucleobases or sugar moieties, to allow
attack across either the major groove (7, 10) or the minor
groove (14, 18) of an RNA/DNA duplex. A preliminary
account of the synthesis of 7 has been reported, along
with the successful cleavage of RNA by an oligodeoxy-
nucleotide incorporating 7.1
Metal bipy and terpy complexes have been used for a
variety of applications in nucleic acid research. Fluo-
rescent, redox-active, ruthenium-bipyridine complexes
have been used to label DNA.2,3 Platinum terpy com-
plexes have been used to intercalate into DNA and to
modify DNA in a covalent manner.4,5 Bipyridine and
terpyridine complexes of metal ions have also played an
important role in the development of RNA hydrolysis
agents.6-8 The Cu(II) complexes of these ligands were
One of our main goals since 1986 has been the
preparation of catalytically active ribozyme mimics that
may serve as catalytic antisense reagents for the control
of viral gene expression. The desired catalytic cycle
involves (1) binding of the ribozyme mimic to the RNA
target, (2) cleavage of the RNA, and (3) release of the
cleaved RNA fragments to regenerate the catalyst.
(8) Morrow, J . R.; Trogler, W. C. Inorg. Chem. 1988, 27, 3387-3394.
(9) Stern, M. K.; Bashkin, J . K.; Sall, E. D. J . Am. Chem. Soc. 1990,
112, 5357-5358.
† High Resolution NMR Facility, Department of Chemistry.
X Abstract published in Advance ACS Abstracts, March 1, 1996.
(1) (a) Bashkin, J . K.; Frolova, E. I.; Sampath, U. J . Am. Chem. Soc.
1994, 116, 5981-5982. (b) Bashkin, J . K.; Sampath, U.; Frolova, E. I.
Appl. Biochem. Biotechnol. 1995, 54, 43-56.
(10) Bashkin, J . K.; J enkins, L. A. J . Chem. Soc., Dalton Trans.
1993, 3631-3632.
(11) Bashkin, J . K. In Bioinorganic Chemistry of Copper; Karlin,
K. D., Tyeklar, Z., Eds.; Chapman and Hall: New York, 1993; pp 132-
139.
(2) Telser, J .; Cruickshank, K. A.; Schanze, K. S.; Netzel, T. L. J .
Am. Chem. Soc. 1989, 111, 7221-7226.
(3) Telser, J .; Cruickshank, K. A.; Morrison, L. E.; Netzel, T. L.;
Chan, C. J . Am. Chem. Soc. 1989, 111, 7226-7232.
(4) Peyratout, C. S.; Aldridge, T. K.; Crites, D. K.; McMillen, D. R.
Inorg. Chem. 1995, 34, 4484-4489.
(5) Wang, A. H.-J .; Nathans, J .; van der Marel, G. A.; van Boom, J .
H.; Rich, A. Nature (London) 1978, 276, 471-474.
(6) Bashkin, J . K.; J enkins, L. A. Comments Inorg. Chem. 1994, 16,
77-93.
(7) Linkletter, B.; Chin, J . Angew. Chem., Int. Ed. Engl. 1995, 34,
472-474.
(12) Magda, D.; Miller, R. A.; Sessler, J . L.; Iverson, B. L. J . Am.
Chem. Soc. 1994, 116, 7439-7440.
(13) Matsumura, K.; Endo, M.; Komiyama, M. J . Chem. Soc., Chem.
Commun. 1994, 2019-2020.
(14) Hall, J .; Huesken, D.; Pieles, U.; Moser, H. E.; Haener, R. Chem.
Biol. 1994, 185-190.
(15) Hovinen, J .; Guzaev, A.; Azhayeva, E.; Azhayev, A.; Lonnberg,
H. J . Org. Chem. 1995, 60, 2205-2209.
(16) Komiyama, M.; Inokawa, T.; Yoshinari, K. J . Chem. Soc., Chem.
Commun. 1995, 77-78.
0022-3263/96/1961-2314$12.00/0 © 1996 American Chemical Society

Building Blocks for Ribozyme Mimics
J . Org. Chem., Vol. 61, No. 7, 1996 2315
Sch em e 1
Failure to release the RNA fragments would result in
product inhibition. The DNA building blocks reported
here form part of our strategy for avoiding product
inhibition and achieving turnover. As depicted in Scheme
1a, cleavage at an internal residue in the RNA/DNA
duplex decreases the stability of the duplex and allows
the product fragments to be displaced by a new substrate
molecule. This occurs because RNA-DNA binding con-
stants depend on the length (and sequence) of the duplex.
As shown in Scheme 1b, cleavage outside the duplex
region has no significant effect on RNA-DNA binding,
and the product cannot be released efficiently from the
“catalyst”. The reagents described here allow incorpora-
tion of hydrolytic agents at internal sites in the ribozyme
mimic. As we have shown, this strategy can achieve the
desired cleavage in the duplex region, which is an
important feature of our plans to achieve catalytic
turnover.1
Resu lts a n d Discu ssion
Our general route to deliver bipy and terpy complexes
across the major groove of an RNA/DNA duplex is shown
in Schemes 2 and 3. The reagents 4-(4-aminobutyl)-4′-
methyl-2,2′-bipyridine 317 and terpy derivative 218 are
each linked to nucleotides via reaction with active ester
derivatives. Alkylamino terpyridine and bipyridine were
coupled to 2′-deoxyuridine C-5 carboxyethyl nucleoside
1.19 The resulting nucleosides 5 and 8 were protected
Sch em e 2a
and phosphitylated to yield phosphoramidite reagents 7
and 10, which are suitable for automated DNA synthe-
sis.20 Compound 7 has been used to prepare a 17-mer
oligonucleotide that has shown ribozyme-like activity.1
The bipyridine reagent 10 complements the series of
nucleoside-bipyridine conjugates reported previously.21,22
FABMS and HRMS were obtained for compounds 5-7
and 8-10. NMR assignments of these compounds are
provided in the Experimental Section.
Two complementary approaches were explored for the
delivery of catalytic reagents across the minor groove.
Both the 1′- and 2′-position of nucleosides point into the
minor groove of an A-form double helix. Scheme 4 shows
a
EDC‚HCl, DMSO, rt, 24 h; (b) pyridine, DMT-Cl, 26 h; (c)
iPr2NEt, THF, â-cyanoethyl N,N-diisopropylchlorophosphona-
midite, 9 h.
(17) Ciana, L. D.; Hamachi, I.; Meyer, T. J . J . Org. Chem. 1989, 54,
1731-1735.
(18) Manuscript in preparation.
(19) Bashkin, J . K.; Gard, J . K.; Modak, A. S. J . Org. Chem. 1990,
55, 5125-5132.
(20) Gait, M. J . Oligonucleotide Synthesis: A Practical Approach;
IRL Press: Oxford, UK, 1984.
(21) Modak, A. S.; Gard, J . K.; Merriman, M. C.; Winkeler, K. A.;
Bashkin, J . K.; Stern, M. K. J . Am. Chem. Soc. 1991, 113, 283-291.
(22) Wang, G.; Bergstrom, D. E. Tetrahedron Lett. 1993, 34, 6721-
6724.
the preparation of the 2′-functionalized adenosine phos-
phoramidite 14. By analogy with a reported procedure,23
we deprotonated adenosine with NaH/DMF at -5 °C and
alkylated the resulting mixture of anions with alkyl
(23) Manoharan, M.; J ohnson, L.; Tivel, K.; Springer, R.; Cook, P.
D. Bioorg. Med. Chem. Lett. 1993, 3, 2765-2770.

2316 J . Org. Chem., Vol. 61, No. 7, 1996
Bashkin et al.
Sch em e 3a
Sch em e 4a
a
(a) EDC‚HCl, DMF, rt, 30 h; (b) pyridine, DMT-Cl, 6 h; (c)
iPr2NEt, THF, â-cyanoethyl N,N-diisopropylchlorophosphona-
midite, 5 h.
a
(a) NaH, DMF, 24 h, -5 °C; (b) DMT-Cl, pyridine, overnight;
halide 4. Nucleoside 11a , the desired 2′-alkylated prod-
uct, was isolated in 18% yield along with unreacted 4.
The mixture of the analogous 3′ isomer 11b and ad-
ditional 11a was isolated in 8% yield. The 5′-sugar
hydroxyls of this mixture were protected by treatment
with dimethoxytrityl chloride (DMT-Cl) and the resultant
mixture was conveniently separated into the 2′-O-isomer
(12a ) and 3′-O-isomer (12b) on a basic alumina column
(<5% 3′-O-alkylated product was isolated).
(c) i. TMS-Cl; ii. benzoyl chloride; iii. 2 M NH4OH; (d) iPr2NEt,
THF, â-cyanoethyl N,N-diisopropylchlorophosphonamidite
long-range carbon-proton coupling to H13 and H19,
respectively. The C4, C5, and C6 carbons of the adenine
base were unambiguously assigned based on their mul-
tiple-bond correlation to ribose H1′, or to adenine H2 and
NH2 (Figure 2b). Of particular importance, multiple
bond 13C-1H couplings were observed between C10 and
H2′, as well as between C2′ and H10, indicating that 11a
has a C2′-O-C10 connection. The result is consistent
with the observed C2′ chemical shift, which is 11.9 ppm
downfield from C3′, indicating that substitution has
occurred at the C2′ site of 11a . Moreover, the presence
For compounds 11a , 12a , and 12b, the sites of alky-
lation were unambiguously identified via COSY, HMQC,
and HMBC NMR studies. 1H chemical shifts of 11a were
assigned by analysis of COSY (Figure 1) and HOHAHA
1
spectra. Spin propagation and the H-1H connectivities
of sugar (H1′ to H5′, H5"), and of the bipyridine-linker
arm (H10 to H13, H15 to H16, and H15′ to H16′) were
3
identified through vicinal J H-H coupling. Long-range
coupling via the sugar H1′ enabled assignment of the
nonexchangeable H8 proton of the adenine subunit. The
1
presence of four-bond H-1H coupling of methyl-H19 to
H15′ and H17′, and coupling of H13 to H15 and H17,
facilitated an unambiguous assignment of the two pyri-
dine residues. To complete the assignment of the 13C
spectrum and confirm the adenosine-bipyridine connec-
tion, HMQC and HMBC spectra (Figure 2, parts a and
b) were obtained. The one-bond carbon correlations to
the attached protons were determined by HMQC, which
included all of the sugar carbons, the CH2 and CH
carbons of the bipyridine-linker arm, and two aromatic
carbons, C2 and C8, bearing nonexchangeable protons
of the adenine subunit. Quaternary carbons C14 and
C14′ of the bipyridine were determined by HMBC through
of the strong cross peak between a hydroxyl proton and
H3′, and the lack of such coupling to H2′ in the COSY
spectrum, further confirm the structure of 11a . Com-
pounds 12a and 12b were confirmed by the same
1
strategy, and complete 13C and H chemical shift assign-
ments are listed in the Experimental Section.

Building Blocks for Ribozyme Mimics
J . Org. Chem., Vol. 61, No. 7, 1996 2317
F igu r e 1. The 500 MHz COSY spectrum of 11a in DMSO-d6. A 500 × 2048 data matrix with 16 scans per t1 value was acquired.
The long-range 1H-1H couplings are drawn in brackets.
F igu r e 2. Expansion of (a) HMQC, and (b) HMBC spectra of 11a . Multiple bond 13C-1H correlations allow unambiguous
assignment of the quaternary carbons and establish the ribose and bipyridine-linker arm connection.
The 5′-OH of the pure 2′-O-isomer 11a was protected
with DMT-Cl to give 12a in 58% yield. The modified
nucleoside 12a was then N-6-benzoyl-protected using the
“J ones” transient protection20 to give 13 in 27% yield.
Phosphitylation gave phosphoramidite 14 in 50% yield.
starting from D-fructose.24,25 Protection of the 5′-OH with
DMT-Cl gave nucleoside 16. 16 was coupled to the
terpyridine amine 2 using carbonyl diimidazole,25 result-
ing in the two products 17a and 17b. Nucleoside 17a
was then converted to phosphoramidite 18.20 Initially,
The synthesis of the C1′-functionalized terpy nucleo-
side phosphoramidite 18 is given in Scheme 5. The
starting nucleoside 15 was synthesized in six steps
(24) Holy, A. Nucleic Acids Res. 1974, 1, 289-298.
(25) Ono, A.; Dan, A.; Matsuda, A. Bioconjugate Chem. 1993, 4, 499-
508.

2318 J . Org. Chem., Vol. 61, No. 7, 1996
Bashkin et al.
Sch em e 5a
stituents located at the C-5 position of 2′-deoxyuridine
mimic the methyl group of thymidine: they point away
from the A-T hydrogen bonds and across the major
groove, toward the opposite strand. Appropriate DNA
derivatives functionalized at the C-5 position can be
prepared via the Heck reaction. Here we reported the
preparation of 2′-deoxyuridine phosphoramidite reagents
with pendant bi- and terpyridine ligands. We also
investigated alternative sites of chemical modifications
of nucleotides that involve the delivery of catalytic
reagents across the minor groove.25,27 We were particu-
larly interested in placing hydrolysis agents on the
nucleosides so that when the modified oligonucleotides
hybridize with target RNA, the functionalities would
reside in the minor groove of the heteroduplex, proximal
to the 2′-hydroxyl group of the RNA strand. We pre-
sented two methods to tether bipyridine and terpyridine
ligands in the minor groove. One approach led to an
analog of 2′-deoxyuridine that was functionalized at the
C1′ sugar position. In a second approach, a butyl linker
was attached to the 2′-O-position of adenosine.23 Gener-
ally, alkoxy modifications in the 2′-position of the ribose
ring significantly increase the binding affinity of the
oligomer to the RNA target and provide resistance to
nucleases.28 The effectiveness of 7 in forming active
ribozyme mimics has already been demonstrated.1 Work
is ongoing to prepare ribozyme mimics with 10, 14, and
18, and to assess the relative hydrolytic capabilities of
major and minor groove attack.
a
(a) Pyridine, DMT-Cl, 24 h; (b) carbonyldiimidazole, 2, CH2Cl2;
Exp er im en ta l Section
(c) â-cyanoethyl N,N-diisopropylchlorophosphonamidite, Et3N,
CH2Cl2, 30 min.
Gen er a l. FAB mass spectra were recorded by the Wash-
ington University Resource for Biomedical and Bio-organic
Mass Spectrometry, Department of Chemistry, Washington
University. Thin-layer chromatography (TLC) was performed
on Baker-Flex aluminum oxide IB-F plates, Baker-Flex silica
gel IB2-F plates, and Merck DC-Fertigplattern RP-18 F254
S
plates. Column (flash) chromatography was performed on
basic alumina (Selecto Scientific, 23-75) or silica gel (Selecto
Scientific, 40 µ). Reverse phase (RP) column chromatography
was performed using Fisher Prep Sep-C18 extraction columns.
DMT-Cl, 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide
(EDC), carbonyl diimidazole, EtN(iPr)2, â-cyanoethyl N,N-
diisopropylchlorophosphonamidite, adenosine, NaH, Et3N,
Me3SiCl, benzoyl chloride, and all anhydrous solvents were
purchased from Aldrich. All starting materials were dissolved
in dry pyridine and evaporated under reduced pressure. This
process was repeated twice to remove traces of moisture.
During workup, all compounds were dried over anhydrous Na2-
SO4 or MgSO4. All reactions were done under N2 or Ar.
Deoxyu r id in e-C3-S-ter p yr id in e 5. A pear-shaped two-
neck flask was charged with 5-(2-carboxyethyl)-2′-deoxyuridine
(1)19 (601.0 mg, 2.0 mmol), EDC (306 mg, 2.0 mmol), and dry
DMSO (2.0 mL) and stirred for 0.5 h. To this was added the
amine 218 (324 mg, 1.0 mmol), and the reaction was stirred at
room temperature for 24 h. The reaction mixture was then
evaporated and redissolved in CHCl3, and the product 5 (455.2
mg, 74.9%) precipitated by adding hexanes. Analytically pure
material was obtained by RP chromatography with 50% CH3-
in order to achieve exclusive coupling at C1′, we at-
tempted a published procedure25 to protect the 3′ and 5′
hydroxyl groups of 15 with 1,3-dichloro-1,1,3,3-tetraiso-
propyldisiloxane (TIPDSCl2). However, in our hands, the
diprotected analog of 15, 3′,5′-O-(1,1,3,3-tetraisopropyl-
1,3-disiloxanediyl)-3′-deoxypsicouridine, was isolated as
a very minor product. Recently, Hovinen reported simi-
lar results with this protection reaction.26 Therefore, we
performed the synthesis of 17a as shown in Scheme 5,
without protecting the 3′ and 5′ positions. The desired
product 17a (25.8%) and the disubstituted product 17b
(34.8%) were separated by basic alumina chromatogra-
phy.
1
CN/H2O: Rf 0.245 (50% CH3CN/H2O on RP plates); H NMR
(300 MHz, CD3OD/CDCl3) δ 1.83 (m, 2H, H11); 2.09 (m, 2H,
H2′); 2.31-2.47 (m, 4H, H7 and H8); 3.08 (t, 2H, H10, J )
7.41 Hz); 3.22 (t, 2H, H12); 3.59 (dd, 1H, J ) 12.09, 3.78 Hz,
H5′); 3.67 (dd, 1H, J ) 12.09, 3.24 Hz, H5′); 3.76 (q, 1H, H4′,
J ) 3.36 Hz); 4.26 (ddd, 1H, J ) 5.12, 3.27, 3.27 Hz, H3′′);
6.12 (t, 1H, H1′, J ) 6.74 Hz); 7.35 (ddd, 2H, H19, J ) 6.24,
Con clu sion s
According to one of our working hypotheses, a ribozyme
mimic′s “active site” should reside adjacent to a phos-
phodiester and/or 2′-hydroxyl of the target RNA without
seriously disrupting Watson-Crick base pairing. Sub-
(27) Manoharan, M.; Guinosso, C. J .; Cook, P. D. Tetrahedron Lett.
1991, 32, 7171-7174.
(28) Boiziau, C.; Larrouy, B.; Sproat, B. S.; Toulme, J . J . Nucleic
Acids Res. 1995, 23, 64-71.
(26) Hovinen, J .; Azhayev, A.; Guzaev, A.; Lonnberg, H. Nucleosides
Nucleotides 1995, 14, 329-332.

Building Blocks for Ribozyme Mimics
J . Org. Chem., Vol. 61, No. 7, 1996 2319
4.89, 1.17 Hz); 7.68 (s, 1H, H6); 7.86 (ddd, 2H, H18, J ) 7.59,
7.59, 1.77 Hz); 8.11 (s, 2H, H14); 8.47 (m, 2H, H17, J ) 8.1
Hz); 8.54 (ddd, 2H, H20, J ) 5.01 Hz); 13C NMR (75.1 MHz,
CD3OD/CDCl3) ppm 24.21 C7, 28.81 C11, 29.39 C10, 35.49 C8,
39.15 C12, 41.27 C2′, 62.67 C5′, 71.94 C3′, 86.15 C1′, 88.62
C4′, 113.77 C5, 118.56 C14, 122.93 C17, 125.36 C19, 138.60
C18, 138.82 C6, 149.84 C20, 151.96 2CO, 152.77 C13, 156.05
C16, 156.71 C15, 165.51 4CO, 174.77 9CO; UV-vis (concn )
2.25 × 10-4 M, MeOH/0.02 M NH4OAc) λmax 277 nm (ꢀ )
32680); FAB HRMS m/ z C30H33O6N6S (M)+: calcd 605.2182,
found 605.2175; MS (FAB) m/ z 627 (18 [M + Na]+), 605 (40
[M + H]+), 550 (7), 511 (9), 489 (11), 478 (25), 456 (40), 388
(13), 340 (13), 323 (39), 307 (30), 303 (32), 292 (39), 289 (24),
13C NMR (125 MHz, DMSO-d6) ppm 83.6 C1′, 40.5 C2′, 70.5
C3′, 87.3 C4′, 61.4 C5′, 150.3 2CO, 163.3 4CO, 112.6 C5, 136.5
C6, 22.8 C7, 34.1 C8, 38.1 C10, 28.7 C11, 27.2 C12, 34.1 C13,
152.4 and 148.2 C14 and C14′, 124.3 and 125.0 C15 and C15′,
148.9 and 148.7 C16 and C16′, 121.4 and 120.6 C17 and C17′,
154.7 C18 and C18′, 171.1 19CO; FAB HRMS m/ z C27H34N5O6
(M + H)+: calcd 524.2431, found 524.2501.
DMT-d eoxyr u id in e-C4-bip yr id in e 9. Nucleoside 8 (600
mg, 1.146 mmol) and DMT-Cl (465.0 mg, 1.375 mmol) were
dissolved in pyridine (10 mL) and allowed to stand at rt for
5-6 h. After the reaction was quenched with MeOH, the
reaction mixture was concentrated to dryness. The residue
was dissolved in CH2Cl2 (100 mL) and washed with H2O (2 ×
25 mL), and the organic layer was dried and concentrated.
Purification was accomplished by chromatography on basic
alumina (10% MeOH/CH2Cl2). Final product 9 was obtained
as a white foam (450.0 mg, 48%): Rf 0.44 (10% MeOH /CH2-
279 (25), 266 (100), 233 (19), 224 (17). Anal. Calcd for C30H32
-
O6N6S: C, 59.58; H, 5.33; N, 13.89; S, 5.30. Found: C, 56.92;
H, 5.17; N, 13.82; S, 5.39.
DMT-d eoxyu r id in e-C3-S-ter p yr id in e 6. Deoxyuridine-
C3-S-terpyridine 5 (557 mg, 0.921 mmol) was dissolved in
anhydrous pyridine (3.0 mL). DMT-Cl (474.5 mg, 1.406 mmol)
in dry pyridine (1.0 mL) was added, and the reaction mixture
was stirred for 26 h at rt. The mixture was then quenched
with CH3OH and concentrated. The residue was dissolved in
CH2Cl2 and extracted with H2O, and the organic layer was
dried and concentrated. Chromatography on a basic alumina
column (12-30% MeOH/CH2Cl2) gave 6 (549 mg, 65.7%) as a
white foam after evaporation: Rf 0.438 (15% MeOH/CH2Cl2
1
Cl2 on basic alumina); H NMR (500 MHz, CD3OD) δ 6.24 (t,
1H, H1′), 2.27 (m, 2H, H2′), 4.42 (m, 1H, H3′), 3.98 (m, 1H,
H4′), 3.10 (m, 2H, H5′), 7.54 (s, 1H, H6), 2.15 (m, 4H, H7 and
H8), 3.38 (t, 2H, H10), 1.40-1.63 (b, 4H, H12 and H11), 2.70
(t, 2H, H13), 7.37 (dd, 2H, H15 and H15′), 8.47 (dd, 2H, H16
and H16′), 8.07 (dd, 2H, H17 and H17′), 2.45 (s, 3H, H19), 3.73
(s, 6H, OCH3); 13C NMR (125 MHz, CD3OD) ppm 87.1 C1′, 41.9
C2′, 73.4 C3′, 88.64 C4′, 65.6 C5′, 155.3 2CO, 166.3 4CO, 115.0
C5, 139.1 C6, 25.1 C7, 36.5 C8, 175.0 9CO, 40.6 C10, 30.7 C11,
29.3 C12, 36.5 C13, 152.8 and 151.1 C14 and C14′, 126.8 and
126.2 C15 and C15′, 150.6 and 150.7 C16 and C16′, 123.7 and
124.2 C17 and C17′, 157.7 and 157.8 C18 and C18′, 21.9 C19,
1
on basic alumina); H NMR (300 MHz, CDCl3) δ 1.8 (m, 2H,
H11); 2.1-2.4 (m, 6H, H2′, H7 and H8); 3.05 (t, 2H, H10); 3.2-
3.5 (ddd, 2H, H5′ and m, 2H, H12); 3.75 (s, 6H, H26-DMT-
OCH3); 4.05 (q, 1H, H4′); 4.50 (ddd, 1H, H3′); 6.35 (t, 1H, H1′
and t, 1H(exch), C9-amide NH); 6.7 (d, 4H, H23); 7.15-7.35
(m, 5H, H27-30 and d, 4H, H24) 7.4 (m, 2H, H19); 7.49 (s,
1H, H6); 7.82 (ddd, 2H, H18); 8.25 (s, 2H, H14); 8.55 (m, 2H,
H17); 8.62 (ddd, 2H, H20); 13C NMR (75.1 MHz, CDCl3) ppm
23.33 C7, 27.80 C11, 28.10 C10, 35.07 C8, 38.03 C12, 40.45
C2′, 50.44 (MeOH), 55.14 C26 (DMT-OCH3), 63.57 C5′, 71.81
C3′, 84.64 C1′, 85.89 C21, 86.49 C4′, 113.15, 113.36 C5, 117.67
C14, 121.52, 123.95 C17, 126.95, 127.88, 128.01, 129.99,
135.39, 135.45, 136.97, 144.41, 148.80 C20, 150.39 C2, 151.10
C13, 154.72 C15, 155.56 C16, 158.48, 163.94 C4, 172.03 C9;
FAB HRMS m/ z C51H51O8N6S (M)+: calcd 907.3489, found
907.3488; MS (FAB) m/ z 907.4 (19 (M + H)+), 758.4 (8), 550.6
(9), 303.2 (50), 154.1 (100).
56.4 OCH3
C48
(DMT), 89.0 C(Ph)(PhOMe)2; FAB HRMS m/ z
H51N5O8 (M + H)+: calcd 826.3737, found 826.3802.
DMT-deoxyu r idin e-C4-bipyr idin e ph osph or am idite 10.
To a solution of 9 (400.0 mg, 0.504 mmol) and EtN(iPr)2 (0.195
mL, 0.804 mmol) in dry THF (2.0 mL) was added â-cyanoethyl
N,N-diisopropylchlorophosphonamidite (143.1 mg, 0.605 mmol).
The reaction was complete in 4 h at rt. The reaction mixture
was evaporated to dryness. The residue was purified by
chromatography on basic alumina (3% MeOH/CH2Cl2). Final
product 10 was obtained as a white foam (376.0 mg, 73%): Rf
0.41 (5% MeOH/CH2Cl2 on basic alumina); 31P NMR (75.1
MHz, CD3CN, referenced to 85% H3PO4) ppm 141.959, 141.656;
FAB HRMS m/ z C57H68N7O9P (M + H)+: calcd 1026.4894,
found 1026.4897.
DMT-d eoxyu r id in e-C3-S-t er p yr id in e P h osp h or a m i-
d ite 7. Nucleoside 6 (549.0 mg, 0.605 mmol) was dissolved
in dry THF (4.5 mL) under N2. Then EtN(iPr)2 (0.156 g, 1.21
mmol, 0.21 mL) was added to the reaction vessel at -4 °C in
an ice bath. To this cold reaction mixture was added â-cya-
noethyl N,N-diisopropylchlorophosphonamidite (151.2 mg,
0.635 mmol, 0.143 mL). The reaction mixture was stirred for
2 h from -4 to 0 °C. TLC of the reaction mixture showed
presence of the starting nucleoside. A second equivalent of
EtN(iPr)2 and â-cyanoethyl N,N-diisopropylchlorophosphona-
midite was added and stirred for 9.0 h at 5-15 °C. After the
reaction was complete, the solvent was evaporated by flushing
with a steady stream of N2. The residue was dissolved in CH2-
Cl2, loaded on to a basic alumina column, and eluted with
0-5% MeOH in CH2Cl2 to give pure product 7 (581 mg,
86.7%): Rf 0.345 (5% MeOH/CH2Cl2 on basic alumina); 31P
NMR (CD3CN, referenced to 85% H3PO4) ppm 149.62, 149.59.
FAB HRMS m/ z C60H68O9N8SP (M)+: calcd 1107.4567, found
1107.4532; MS (FAB) m/ z 1107.5 (2 (M + H)+), 958.5 (2), 890.4
(2), 803.3 (1), 585.2 (2), 489.2 (2), 303.1 (100), 201.1 (5).
Deoxyu r id in e-C4-bip yr id in e 8. Nucleoside 1 (1.000 mg,
3.330 mmol), compound 317 (535.0 mg, 2.215 mmol), and the
coupling agent EDC (635.0 mg, 3.330 mmol) were dissolved
in dry DMF (1.8 mL). After stirring at rt for 30 h, the reaction
mixture was concentrated to dryness. The residue was applied
to a C-18 RP column. Elution with 20% CH3CN/H2O gave the
desired compound 8 (950 mg, 82%): Rf 0.30 (40% CH3CN/H2O
Ad en osin e-C4-bip yr id in e 11a . To a suspension of ad-
enosine (5.34 g, 20 mmol) in dry DMF (180 mL) was added
NaH (50% mineral oil dispersion, 1.24 g, 26 mmol, washed
with benzene) at -5 °C. After stirring for 1 h, (4-bromobutyl)-
bipyridine 4 (7.00 g, 24 mmol) in dry DMF (10 mL) was added
dropwise to the reaction mixture over 50 min. The reaction
was allowed to stand for 24 h at -5 °C. After quenching with
ice-water (10 mL), the reaction mixture was concentrated to
an oil. The oil was dissolved in H2
O (140 mL) and extracted
with CH2Cl2 (3 × 25 mL). The organic layer was dried and
concentrated to give the crude mixture. The residue was
purified by chromatography on basic alumina (5% MeOH/CH2-
Cl2). Final product 11a was obtained as a white solid (1.678
1
g, 18.0%): Rf 0.47 (5% MeOH /CH2Cl2 on basic alumina); H
NMR (600 MHz, DMSO-d6) δ 6.09 (d, 1H, H1′), 4.57 (t, 1H,
H2′), 4.41 (t, 1H, H3′), 4.09 (t, 1H, H4′), 3.78 and 3.63 (m, 2H,
H5′), 8.23 (s, 1H, H2), 8.48 (s, 1H, H8), 3.68 and 3.48 (m, 2H,
H10), 1.56 (m, 2H, H11), 1.64 (m, 2H, H12), 2.65 (t, 2H, H13),
2.49 (s, 3H, H19), 7.21 (dd, 1H, H15), 7.34 (dd, 1H, H15′), 8.60
(dd, 1H, H16), 8.61 (dd, 1H, H16′), 8.27 (d, 1H, H17), 8.30 (d,
1H, H17′); 13C NMR (150 MHz, DMSO-d6) ppm 86.1 C1′, 80.9
C2′, 69.0 C3′, 86.4 C4′, 61.5 C5′, 152.4 C2, 149.0 C4, 156.1 C5,
119.3 C6, 139.7 C8, 69.3 C10, 28.5 C11, 26.3 C12, 34.1 C13,
152.0 C14, 147.7 C14′, 123.9 C15, 124.7 C15′, 148.9 C16, 148.8
C16′, 120.4 C17, 121.2 C17′, 155.2 C18 and C18′, 20.6 C19;
FAB HRMS m/ z C25H30N7O4 (M + H)+: calcd 492.2359, found
492.2369.
DMT-aden osin e-C4-bipyr idin e 12a. Nucleoside 11a (2.825
g, 5.75 mmol), Et3N (1.13 mL), and DMT-Cl (2.337 g, 6.89
mmol) were dissolved in pyridine (50 mL) and allowed to stand
at rt for 5-6 h. After quenching with CH3OH, the reaction
mixture was concentrated to dryness. The residue was dis-
solved in CH2Cl2 (200 mL) and washed with H2O (3 × 25 mL).
1
on RP plates); H NMR (500 MHz, DMSO-d6) δ 6.20 (t, 1H,
H1′), 2.28 (m, 2H, H2′), 4.27 (m, 1H, H3′), 3.79 (m, 1H, H4′),
3.00 (m, 2H, H5′), 7.85 (s, 1H, H6), 2.09 and 2.54 (m, 4H, H7
and H8), 2.70 (t, 2H, H13), 1.40-1.70 (b, 4H, H12 and H11),
3.60 (m, 2H, H10), 7.30 (d, 2H, H15 and H15′), 8.59 (m, 2H,
H16 and H16′), 8.27 (s, 2H, H17 and H17′), 2.45 (s, 3H, H19);

2320 J . Org. Chem., Vol. 61, No. 7, 1996
Bashkin et al.
The organic layer was dried, concentrated, and chromato-
graphed on basic alumina (4% MeOH/CH2Cl2). Final product
12a was obtained as a yellow solid (2.65 g, 58%): Rf 0.34 (2%
MeOH/CH2Cl2 on basic alumina); 1H NMR (600 MHz, CD2-
Cl2) δ 6.14 (d, 1H, H1′), 4.50 (m, 2H, H2′ and H3′), 4.23 (t, 1H,
H4′), 3.48 and 3.43 (m, 2H, H5′), 8.24 (s, 1H, H2), 8.05 (s, 1H,
H8), 3.67 (m, 2H, H10), 1.64 (m, 2H, H11), 1.75 (m, 2H, H12),
2.68 (t, 2H, H13), 2.43 (s, 3H, H19), 7.09 (dd, 1H, H15), 7.13
(dd, 1H, H15′), 8.50 (dd, 1H, H16), 8.47 (dd, 1H, H16′), 8.25
(d, 1H, H17), 8.26 (d, 1H, H17′), 3.50 (s, 6H, OMe3); 13C NMR
(150 MHz, CD2Cl2) ppm 87.4 C1′, 81.9 C2′, 70.2 C3′, 84.2 C4′,
63.6 C5′, 153.3 C2, 149.9 C4, 156.1 C5, 120.4 C6, 139.5 C8,
71.2 C10, 29.3 C11, 26.9 C12, 35.2 C13, 152.3 C14, 148.5 C14′,
124.2 C15, 124.9 C15′, 149.3 C16, 149.1 C16′, 121.3 C17, 122.2
C17′, 156.3 C18 and C18′, 21.2 C19, 55.7 OCH3(DMT), 86.8
C(Ph)(PhOMe)2; FAB HRMS m/ z C46H48N7O6 (M + H)+: calcd
794.3666, found 794.3657.
CH3OH was added to quench the reaction and the mixture
was concentrated to give an orange-yellow residue. The
residue was dissolved in CH2Cl2 and washed with H2O. The
CH2Cl2 layer was dried; chromatography on silica (2-5% CH3-
CH2OH/CH2Cl2) gave pure product (2.5 g, 28.8%) which was
evaporated to a white foam: Rf 0.154 (5% MeOH/CH2Cl2 on
1
silica); H NMR (300 MHz, CD3OD) δ 2.3 (dd, 1H, H2a′, J )
0.835, 4.95 Hz), 2.7 (dd, 1H, H2b′, J ) 2.00, 4.97 Hz), 3.12
(dq, 2H, H5′, J ) 1.48, 3.55, 5.62 Hz), 3.65 (s, 6H, OCH3), 3.75
(q, 2H, H6′, J ) 3.91, 6.98 Hz), 4.09 (m, 1H, H4′), 4.15 (m, 1H,
H3′), 5.32 (d, 1H, H5, J ) 2.74 Hz), 7.84 (d, 1H, H6, J ) 2.75
Hz); 13C NMR (75.1 MHz, CDCl3) ppm 44.05 C2′, 55.12 OCH3,
63.27 and 64.91 C5′ and C6′, 72.85 C3′, 100.83 C1′, 89.12 C4′,
100.14 C5, 141.38 C6, 150.55 C2, 164.43 C4; FAB HRMS m/ z
C31H32N2O8 (M)+: calcd 560.2158 found 560.2181.
DMT-n u cleosid e-C1′-C3-S-ter p yr id in e 17a . Nucleoside
16 (0.420 g, 0.75 mmol) and carbonyl diimidazole (0.195 g, 1.2
mmol) were dissolved in dry CH2Cl2 (6.25 mL) and stirred for
50 min. H2O (22 mL) was added, and the mixture was
extracted with CH2Cl2 (3 × 30 mL). The organic layers were
combined, dried, and filtered. Terpyridine amine 2 (0.680 g,
2.10 mmol) was then added to the filtrate (100 mL) and stirred
for 13 h at rt. The solution was concentrated to 50 mL by
blowing Ar into the flask. The reaction was stirred for another
2 days and concentrated to dryness. The residue was dissolved
in CH2Cl2 and washed with H2O. The organic layer was
chromatographed on basic alumina (10% CH3OH/CH2Cl2).
After evaporation, product 17a was obtained as a white foam
(0.176 g, 25.8%). The disubstituted product 17b (0.328 g,
34.8%) also was obtained. Data for 17a : Rf 0.209 (MeOH/CH2-
DMT-a d en osin e-C4-bip yr id in e 12b: 1H NMR (600 MHz,
CD2Cl2) δ 5.95 (d, 1H, H1′), 4.81 (t, 1H, H2′), 4.18 (t, 1H, H3′),
4.23 (t, 1H, H4′), 3.28 and 3.42 (m, 2H, H5′), 8.22 (s, 1H, H2),
7.98 (s, 1H, H8), 3.59 (m, 2H, H10), 1.65 (m, 2H, H11), 1.73
(m, 2H, H12), 2.70 (t, 2H, H13), 2.42 (s, 3H, H19), 7.11 (dd,
2H, H15 and H15′), 8.49 and 8.45 (dd, 2H, H16 and H16′),
8.26 (d, 2H, H17 and H17′), 3.76 (s, 6H, OMe3); 13C NMR (150
MHz, CD2Cl2) ppm 89.8 C1′, 74.0 C2′, 78.8 C3′, 82.5 C4′, 63.6
C5′, 153.3 C2, 140.0 C4, 155.9 C5, 120.5 C6, 139.7 C8, 70.9
C10, 29.5 C11, 27.1 C12, 35.3 C13, 152.4 C14, 148.5 C14′, 124.9
and 124.3 C15 and C15′, 149.3 and 149.1 C16 and C16′, 122.1
and 121.3 C17 and C17′, 156.3 C18 and C18′, 21.3 C19, 55.6
OCH3(DMT), 86.9 C(Ph)(PhOMe)2; FAB HRMS m/ z C46H48N7O6
(M + H)+: calcd 794.3666, found 794.3657.
1
Cl2 on basic alumina); H NMR (300 MHz, CDCl3) δ 1.94 (m,
DMT-a d en osin e(NH-Bz)-C4-bip yr id in e 13. Nucleoside
12a (158.7 mg, 0.2 mmol) in dry pyridine (5 mL) was cooled
in an ice bath. Me3SiCl (0.127 mL, 1.0 mmol) was added,
followed (after 30 min) by 5 equivalents of benzoyl chloride
(0.116 mL, 1.0 mmol). The reaction mixture was stirred at rt
for about 3 h. Cold water (4 mL) was added, followed by 4
mL of concentrated aqueous NH3 (after 5 min), to give
approximately 2 M ammonia solution. The mixture was
stirred for another 30 min and concentrated to dryness. The
residue was dissolved in CH2Cl2 (100 mL) and washed with
H2O (2 × 25 mL). The organic layer was dried, concentrated,
and chromatographed on basic alumina (75% hexane/CH2Cl2).
Final product 13 was obtained as a pale yellowish solid (80
2H, H11), 2.78 (m, 2H, H2′), 3.15 (m, 4H, H10 and H12), 3.30
(m, 2H, H5′), 3.72 (s, 6H, OCH3), 4.35 (m, 2H, H4′ and H3′),
4.49 (d, 1H, H6a′, J ) 3.85 Hz), 4.65 (d, 1H, H6b′, J ) 3.85
Hz), 5.42 (d, 1H, H5, J ) 2.8 Hz), 5.91 (t, 1H, C9-NH, J ) 1.9
Hz), 7.75 (d, 1H, H6, J ) 2.8 Hz), 7.83 (m, 2H, H18 and H18′),
8.25 (m, 2H, H14 and H14′), 8.56 (m, 2H, H17 and H17′, J )
2.5 Hz), 8.65 (d, 2H, H20 and H20′, J ) 1.5 Hz); 13C-NMR (75.1
MHz, CDCl3) ppm 27.52 C11, 28.51 C10, 39.83 C12, 44.29 C2′,
55.13 OMe, 63.08 and 66.21 C5′ and C6′, 72.45 C3′, 98.16 C1′,
86.60 C4′, 100.61 C5, 123.98 C17 and C17′, 117.62 C14 and
C14′, 126.92 C19 and C19′, 137.01 C18 and C18′, 141.17 C6,
148.91 C20 and C20′, 150.11 C2, 151.09 C13, 155.65 C16 and
C16′, 154.80 C15 and C15′, 156.08 C9, 163.79 C4; FAB HRMS
m/ z C50H48N6O9S (M + H)+: calcd 909.3203, found 909.3298.
17b: Rf 0.389 (MeOH/CH2Cl2 on basic alumina); 1H NMR (300
MHz, CDCl3) δ 1.86-1.98 (m, 4H, H11 H11′), 2.86 (m, 2H, H2′),
3.05-3.30 (m, 10H, H10 and H10′ and H12 and H12′ and H5′),
3.70 (s, 6H, OCH3), 4.48 (m, 2H, H4′ and H3′), 4.64 (d, 1H,
H6a′), 5.20 (m, 1H, H6b′), 5.39 (d, 1H, H5, J ) 2.8 Hz), 6.20
(t, 1H, NH, J ) 1.7 Hz), 6.34 (t, 1H, NH, J ) 1.7 Hz), 7.68 (d,
1H, H6, J ) 2.8 Hz), 7.78 (m, 4H, H18 and H18′ and H18′′
and H18′′′), 8.20 and 8.26 (s and s, 4H, H14 and H14′ and H14′′
and H14′′′), 8.50-8.54 (m, 4H, H17 and H17′ and H17′′ and
1
mg, 27%): Rf 0.50 (CH2Cl2 on basic alumina); H NMR (300
MHz, CD3OD) δ 6.00 (d, 1H, H1′), 4.50 (t, 1H, H2′), 4.38 (t,
1H, H3′), 4.05 (t, 1H, H4′), 3.20 (m, 2H, H5′), 8.30 (s, 1H, H2),
8.40 (s, 1H, H8), 3.50 (m, 2H, H10), 1.60-1.50 (m, 4H, H11
and H12), 2.50 (t, 2H, H13), 2.30 (s, 3H, H19), 7.00 (dd, 2H,
H15 and H15′), 8.22 (m, 2H, H16 and H16′), 7.85 (d, 2H, H17
and H17′), 3.50 (s, 6H, OMe3); 7.65 (d, 1H, from Bz), 7.30-
7.40 (m, 4H, from Bz); 13C NMR (75 MHz, CD3OD) ppm 90.5
C1′, 84.1 C2′, 72.4 C3′, 87.3 C4′, 65.9 C5′, 154.8 C2, 152.1 C4,
156.3 C5, 130.0 C6, 146.1 C8, 73.2 C10, 31.6 C11, 29.3 C12,
37.4 C13, 147.7 C14 and C14′, 127.7 and 126.9 C15 and C15′,
151.6 and 151.5 C16 and C16′, 124.5 and 125.2 C17 and C17′,
158.0 C18 and C18′, 22.8 C19, 57.2 OCH3(DMT), 89.3 C(Ph)-
(PhOMe)2, 188.3 COPh; FAB HRMS m/ z C53H51N7O7 (M +
H)+: calcd 898.3928, found 898.3913.
DMT-p h osp h or a m id ite-a d en osin e-bip yr id in e 14. To a
solution of 13 (200.0 mg, 0.223 mmol) and EtN(iPr)2 (0.195
mL, 0.804 mmol) in dry THF (2.0 mL) was added â-cyanoethyl
N,N-diisopropylchlorophosphonamidite (143.1 mg, 0.605 mmol).
The reaction was complete in 4 h at rt and was evaporated to
dryness. The residue was chromatographed on basic alumina
(3% MeOH/CH2Cl2). Final product 14 was obtained as a white
foam (120 mg, 50%): Rf 0.30 (3% MeOH/CH2Cl2 on basic
alumina); 31P NMR (75.1 MHz, CD3CN, referenced to TMP)
ppm 148.2, 147.6; FAB HRMS m/ z C62H68N9O8P (M + H)+:
calcd 1098.5007, found 1098.4979.
H17′′′), 8.63 (m, 4H, H20 and H20′ and H20′′ and H20′′′); 13
C
NMR (75.1 MHz, CDCl3) ppm 27.45 and 27.77 C11 and C11′,
28.51 C10 and C10′, 39.77 and 39.85 C12 and C12′, 42.16 C2′,
55.02 OMe, 63.08 and 66.21 C5′ and C6′, 75.72 C3′, 86.52 C4′,
98.02 C1′, 100.27 C5, 117.36 and 117.43 C14 and C14′ and
C14′′ and C14′′′, 123.81 C17 and C17′ and C17′′ and C17′′′,
126.83 C19 and C19′ and C19′′ and C19′′′, 136.79 C18 and C18′
and C18′′ and C18′′′, 141.49 C6, 148.78 C20 and C20′ and C20′′
and C20′′′, 150.01 C2, 150.81 and 150.89 C13 and C13′, 154.63
C15 and C15′ and C15′′ and C15′′′, 155.44 and 155.48 C16 and
C16′ and C16′′ and 16′′′, 156.03 C9, 163.90 C4; FAB HRMS
m/ z C69H65N10O10S2 (M)+: calcd 1257.4326, found 1257.4327.
DMT-p h osp h or a m id ite-C1′-C3-S-ter p yr id in e 18. Nu-
cleoside 17 (45 mg, 0.0495 mmol) was dissolved in dry CH2Cl2
(0.768 mL). To this solution was added Et3N (0.247 mmol,
0.035 mL) and â-cyanoethyl N,N-diisopropylchlorophospho-
namidite (0.099 mmol, 0.022 mL). The reaction was stirred
for 20 min at rt and quenched with saturated Na2CO3 solution
(ca. 2 mL). The aqueous layer was extracted 3× with ethyl
acetate. The organic layers were combined, dried, filtered, and
concentrated to give a residue. The residue was chromato-
graphed on basic alumina (0-3% MeOH/CH2Cl2) to give pure
DMT-n u cleosid e-C1′ 16. Triol nucleoside 15 (4.0 g, 15.5
mmol) and DMT-Cl (5.248 g, 15.49 mmol) were dissolved in
45 mL of dry pyridine. The reaction was cooled to -20 °C and
allowed to warm to rt while stirring for 22 h. TLC showed
that some starting material remained. More DMT-Cl (1.05 g,
3.10 mmol) was added to the solution and stirred for 4 h.

Building Blocks for Ribozyme Mimics
J . Org. Chem., Vol. 61, No. 7, 1996 2321
product 18 (0.030 g, 55%) as a white foam after evaporation:
Rf 0.488 (5% MeOH/CH2Cl2, on basic alumina); 31P NMR (75.1
MHz, CD3COCD3, referenced to TMP) ppm 146.195, 146.121;
FAB HRMS m/ z C59H67N8O10SP (M)+: calcd 1110.4438, found
1110.4477.
administered by the American Chemical Society, for
partial support of this research.
Su p p or tin g In for m a tion Ava ila ble: Details of 2D NMR
experiments (2 pages). This material is contained in libraries
on microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
Ack n ow led gm en t. This work was supported in part
by NSF Grant CHE-9318581. Acknowledgment is also
made to the donors of The Petroleum Research Fund,
J O9518213