Efficient Synthesis of Azide-Bearing Cofactor Mimics

Article abstract of DOI:10.1021/jo035485z

8-Azido-5′-aziridmo-5′-deoxyadenosine (6), a novel cofactor mimic, was synthesized in nine steps from commercially available 2′,3′-isopropylideneadenosine in ～4% overall yield. Crucial to this success was a very unorthodox phthalimide cleavage procedure, C8 azidation prior to aziridination and late stage alkylation of the 5′ amino group with iodoethanol necessitated by the high degree of lability endowed by the aryl azide moiety. Aziridine 6 is envisioned as a useful biochemical tool by which to probe DNA and protein methylation patterns.

Full text of DOI:10.1021/jo035485z

“target” cytosine (bold) of 5′GCGC3′ is methylated prior
to reaction with 4 revealed no enzyme-specific alkylation
by 4.6 Thus, M.HhaI-mediated alkylation of 5′GCGC3′ with
SAM and 4 share the same regiochemistry. These find-
ings provide clear evidence of the importance of 5′ aziri-
dine adenylates as “cofactor mimics” of SAM as tools for
biology in the short term and potential therapeutic agents
in the long term. As a first step in developing these
agents as useful and broadly applicable biochemical tools,
we wished to equip 4 with a handle through which any
desired molecule (DNA damaging moiety, affinity matrix
handle, fluorophore, etc.) could be appended following
Mtase-dependent anchoring. Such a handle would need
to present a minimal disruption to cofactor-Mtase inter-
actions and be highly reactive in a chemoselective sense
following the enzymatic reaction. Most importantly, this
handle would need to be abiotic and capable of rapid
couplings to other reagents orthogonal to typical cellular
constituents.
An extensive body of literature now supports the im-
portance of the azido group as an abiotic handle capable
of undergoing highly efficient chemoselective couplings.7-20
Alkyl azides have been reported to react with o-meth-
oxycarbonyl-functionalized triarylphosphines to afford
amide-linked coupling products in what is now termed
the Staudinger ligation,7-16,20 and a wide array of azides
have been shown to be highly active participants in [2 +
3] Huisgen cycloadditions17-19,21 when presented with
alkynes. The latter reaction is representative of “click
chemistry”, a class of reactions nicely outlined by Sharp-
less and co-workers.21 Importantly, both reaction types
are amenable to complex biological mixtures.
Efficien t Syn th esis of Azid e-Bea r in g
Cofa ctor Mim ics
Lindsay R. Comstock and Scott R. Rajski*
University of WisconsinsMadison, School of Pharmacy,
777 Highland Avenue, Madison, Wisconsin 53705
srrajski@pharmacy.wisc.edu
Received October 9, 2003
Abstr act: 8-Azido-5′-aziridino-5′-deoxyadenosine (6), a novel
cofactor mimic, was synthesized in nine steps from com-
mercially available 2′,3′-isopropylideneadenosine in ∼4%
overall yield. Crucial to this success was a very unorthodox
phthalimide cleavage procedure, C8 azidation prior to aziri-
dination and late stage alkylation of the 5′ amino group with
iodoethanol necessitated by the high degree of lability
endowed by the aryl azide moiety. Aziridine 6 is envisioned
as a useful biochemical tool by which to probe DNA and
protein methylation patterns.
S-Adenosyl-L-methionine (SAM, 2)-dependent methy-
lation of nucleic acids and proteins is now recognized as
playing an absolutely vital role in the careful regulation
of gene transcription.1,2 Notably, flaws in activity and
expression levels of the eukaryotic DNA methyltrans-
ferase (Mtase) DNMT1 have been integrally linked to
oncogenic potential.2 Thus, the design and synthesis of
agents capable of exploiting such flawed traits of DNMT1
offers an attractive new means by which chemothera-
peutics might be devised. Substances capable of undergo-
ing transfer to nucleic acids and proteins in an Mtase-
dependent way also hold tremendous promise as bio-
chemical tools by which to dissect and understand
biological methylation. The advent of proteomics and its
goal of understanding how post-translational protein
modifications alter function lends significant credence to
the pursuit of substances that undergo Mtase-dependent
delivery to biomolecules, specifically components of the
transcriptional machinery. Our interests in the area of
cofactor mimicry are reflected by investigations into the
synthesis and biochemical study of 4 (Scheme 1) and
related congeners.
In hypothesizing where best to equip 4 with an azide
moiety, we were struck by three realizations. First,
8-azidoadenosine (and aryl azides in general) undergoes
(3) Pignot, M.; Siethoff, C.; Linscheid, M.; Weinhold, E. Angew.
Chem., Int. Ed. 1998, 37, 2888.
(4) Pljevaljcic, G.; Pignot, M.; Weinhold, E. J . Am. Chem. Soc. 2003,
125, 3486.
(5) Pignot, M.; Siethoff, C.; Linscheid, M.; Weinhold, E. Eur. Patent
WO 00/06587, 2000.
The 5′ aziridine adenylate 4 is a substitute for SAM
(2) in the M.TaqI-catalyzed alkylation of adenine within
the recognition sequence 5′TCGA3′ (Scheme 1).3,4 Instead
of generating the N6-methylated dA residue, substrate
adenylation is accomplished via ring-opening of the
aziridine. This chemistry is tolerant of cofactor C8 modi-
fication and has been successfully used to fluorescently
tag short oligonucleotides and large plasmid substrates
in M.TaqI-dependent fashion.4 Cofactor 4 also undergoes
M.HhaI-dependent DNA attachment within the M.HhaI
recognition sequence 5′GCGC3′.5,6 Studies in which the
(6) Comstock, L. R. Unpublished results, 2002.
(7) Saxon, E.; Armstrong, J. I.; Bertozzi, C. R. Org. Lett. 2000, 2, 2141.
(8) Goon, S.; Bertozzi, C. R. J . Carbohydr. Chem. 2002, 21, 943.
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Am. Chem. Soc. 1999, 121, 4278.
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Bertozzi, C. R. J . Am. Chem. Soc. 2002, 124, 14893.
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Acad. Sci. U.S.A. 2002, 99, 19.
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(18) Qian, W.; Chan, T. R.; Hilgraf, R.; Fokin, V. V.; Sharpless, K.
B.; Finn, M. G. J . Am. Chem. Soc. 2003, 125, 3192.
(19) Speers, A. E.; Adam, G. C.; Cravatt, B. F. J . Am. Chem. Soc.
2003, 125, 4686.
(20) For some recent synthetic applications of Staudinger ligation,
see: (a) Nilsson, B. L.; Kiessling, L. L.; Raines, R. T. Org. Lett. 2000,
2, 1939. (b) Nilsson, B. L.; Hondal, R. J .; Soellner, M. B.; Dickson, K.
A.; Raines, R. T. J . Am. Chem. Soc. 2003, 125, 5268; (c) Soellner, M.
B.; Dickson, K. A.; Nilsson, B. L.; Raines, R. T. J . Am. Chem. Soc. 2003,
125, 11790.
* To whom correspondence should be addressed. Tel: 608-262-7582.
Fax: 608-262-5345.
(1) J akayama, J .; Rice, J . C.; Strahl, B. D.; Allis, C. D.; Grewal, S.
I. S. Science 2001, 292, 110. (b) Cheung, P.; Allis, C. D.; Sassone-Corsi,
P. Cell 2000, 103, 263. (c) Turner, B. M. Cell 2002, 111, 285. (d)
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10.1021/jo035485z CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/20/2004
J . Org. Chem. 2004, 69, 1425-1428
1425

SCHEME 1
much more facile Staudinger ligation with triarylphos-
phines than do alkyl azides.22 Second, aryl azides are very
effective photoaffinity reagents whose mechanism of
action continues to provide fertile ground for study and
which allow one to readily track ligand/protein interac-
tions and nucleic acid/protein interfaces.23 Indeed, 8-azi-
doadenosine and related adenylates represent one of the
most extensively studied classes of photoaffinity reagents
known.24 Finally, a small, but not insignificant amount
of work has demonstrated that C8 azido-SAM retains its
cofactor function.25 These considerations led us to un-
dertake the construction of 6, an azide bearing cofactor
mimic for applications in chemical biology to understand
SAM-dependent methylation.
F IGURE 1.
aziridination. Thus, at the outset we envisioned construc-
tion of 6 through the agency of 7, which was readily
accessible by condensation of primary amine 8 with
methyl bromoacetate, reduction, oxazolidinone genera-
tion, and the sequence of C8 bromination followed by azi-
dation. Having generated gram quantities of 7, we sought
to unmask the 5′-ethanolamine moiety in preparation for
aziridination and 2′,3′-deprotection. Model studies of the
same transformation on material lacking the C8 azido
substituent showed 10% ethanolic NaOH27 to be very
effective at oxazolidinone cleavage. However, subjection
of 7 to these and a wide variety of related conditions, led
to significant decomposition processes.27-34 These diffi-
culties, compounded by complications involved with alter-
native protection strategies, ultimately proved insurmount-
able, thus forcing a reevaluation of synthetic approach.
We have previously reported on the utility of the Gab-
riel Cromwell reaction in forming the critical 5′-aziridine
of analogues of 4.26 An unfortunate limitation of this
chemistry is the absolute requirement for functionaliza-
tion of the R,â-dibromide starting material. This abro-
gates unsubstituted aziridine generation and thus would
not prove useful for generation of 6. In our laboratories,
we have reconciled the difficulty of 5′-aziridination via
alkylation of the 5′-aminoadenylate 8 (Figure 1) with
various bromoacetates followed by LiAlH4 reduction and
(23) Recent studies on the mechanism of aryl azide based photo-
cross-linking suggest that nitrene formation is sufficiently transient
so as to not directly contribute to cross-link formation. See: Buch-
mueller, K. L.; Hill, B. T.; Platz, M. S.; Weeks, K. M. J . Am. Chem.
Soc. 2003, 125, 10850.
(24) (a) Syed, S. K.; Kim, S.; Paik, W. K. Biochemistry 1993, 32,
2242. (b) Kaiser, I. I.; Kladianos, D. M.; VanKirk, E. A.; Haley, B. E.
J . Biol. Chem. 1983, 258, 1747. (c) Syed, S. K.; Kim, S.; Paik, W. K. J .
Protein Chem. 1993, 12, 603.
(25) (a) Reich, N. O.; Everett, E. A. J . Biol. Chem. 1990, 265, 8929.
(b) Kaiser, I. I.; Kladianos, D. M.; VanKirk, E. A.; Haley, B. E. J . Biol.
Chem. 1983, 258, 1747.
(22) Restituyo, J . A.; Comstock, L. R.; Petersen, S. G.; Stringfellow,
T.; Rajski, S. R. Org. Lett. 2003, 5, 4357.
(26) Comstock, L. R.; Rajski, S. R. Tetrahedron 2002, 58, 6019.
(27) Steinhagen, H.;Corey, E. J . Angew. Chem., Int. Ed. 1999, 38, 1928.
1426 J . Org. Chem., Vol. 69, No. 4, 2004

SCHEME 2a
SCHEME 3a
a
Reagents and conditions: (a) (1) phthalimide, PPh3, DEAD,
THF, rt, (2) 3:1:1 TFA/H2O/THF, rt, (3). TBSCl, imidazole, DMF,
rt, 60% three steps; (b) Br2, 0.5M NaOAc (pH 5.3), dioxane, rt,
79%; (c) NaN3, DMSO, 70 °C, 90%; (d) ethylenediamine, EtOH,
70 °C, 81%.
a
Reagents and conditions: (a) methyl bromoacetate, TEA, THF,
In re-engineering our path to 6, we again postulated
the importance of 5′-amine 8. Might the C8 azido ana-
logue of 8 permit 5′-amine alkylation and subsequent
ester reduction en route to ethanolamine incorporation?
To investigate this, commercially available 2′,3′-isopro-
pylideneadenosine was converted to the bis-silyl ether 10
using Mitsunobu chemistry reported by Kolb and co-
workers35 and subsequent isopropylidene cleavage with
aqueous TFA36 followed by reaction with TBSCl and
imidazole.37 Phthalimide 10 was derived from 9 in 60%
overall yield in a fashion not requiring chromatography
(Scheme 2). Bromination at the 8-position was accom-
rt, 80%; (b) 2-iodoethanol, toluene, 70 °C, 34%; (c) PPh3, DEAD,
THF, reflux, 58%; (d) Bu4NF, THF, 0 °C, 60%.
assortment of haloethanols. Previous efforts had shown
that alkylation of 5′-aminoadenylates with oxirane is very
difficult to control leading most often to dialkylated
materials. This, in combination with reports by Brown
and Chen of effective amine alkylations with haloethyl-
hydrins, deterred us from investigating epoxide aminoly-
sis as a means of ethanolamine installation.41,42 We
ultimately chose to alkylate 13 with 2-iodoethanol to yield
ethanolamine adenylate 15 (Scheme 3). Optimization of
the reaction was necessary to avoid undesired bis-
alkylated material, and careful control of time, solvent,
and number of equivalents of iodoethanol proved vital
to the success of this transformation. The yield for
alkylation is low (34%) but is partly offset by facile
recovery and recycling of 13 (37%) following column
chromatography. Having successfully obtained 15, aziri-
dination was accomplished using Mitsunobu chemistry
to yield 16 in a 58% yield.43 Finally, TBS ether cleavage
was effected using Bu4NF to yield the 8-azido-5′-aziri-
dino-5′-deoxyadenosine (6) in 60% yield.44
In conclusion, we have completed the synthesis of the
novel 8-azido-5′-aziridino-5′-deoxyadenosine. By virtue of
the known biochemistry of 4, we propose that 6 and
related substances will allow the conversion of biological
methyltransferases into azidases. In light of the abiotic
nature of the azido group and its utility as a photoaffinity
agent, participation in Staudinger ligation chemistries
and [2 + 3] cycloadditions with acetylenes, 6 represents
a potentially important new tool for those at the chem-
istry-biology interface. The methodology reported here
is highly amenable to generation of analogues of 6. Such
synthetic efforts, as well as those to investigate the bio-
chemistry of 6, are ongoing and will be reported shortly.
38
plished with Br2 under mildly acidic conditions in 79%
yield to render 11, which was then converted to azide39
12 in 90% yield. Interestingly, phthalimide cleavage
efforts using hydrazine hydrate and other well-known
procedures failed to produce primary amine 13 with suit-
able efficiencies. An alternative procedure utilizing ethyl-
enediamine40 afforded the versatile C8 azido 5′-amine 13
in 81% yield.
With 13 in hand, the stage was now set for ultimate
aziridination. As predicted based on earlier experiences,
alkylation of 13 with methyl bromoacetate proceeded
smoothly in 80% yield. Disappointingly, however, reduc-
tion of 14 with DIBALH, as well as numerous other
milder reductants, failed to yield the obligate ethanola-
mine moiety. As with previous attempts to deprotect oxa-
zolidinone 7, the azide proved to be a clear liability.
Motivated by the reductive liability posed by the C8 azide
of 14, we next pursued 5′-alkylation of 13 with an
(28) Evans, D. A.; Weber, A. E. J . Am. Chem. Soc. 1987, 109, 7151.
(29) Evans, D. A.; Wu, L. D.; Wiener, J . J . M.; J ohnson, J . S.; Ripin,
D. H. B.; Tedrow, J . S. J . Org. Chem. 1999, 64, 6411.
(30) Ishizuka, T.; Kunieda, T. Tetrahedron Lett. 1987, 28, 4185.
(31) Showalter, H. D. H.; Angelo, M. M.; Berman, E. M.; Kanter, G.
D.; Ortwine, D. F.; Ross-Kesten, S. G.; Sercel, A. D.; Turner, W. R.;
Werbel, L. M.; Worth, D. F.; Elslager, E. F.; Leopold, W. R.; Shillis, J .
L. J . Med. Chem. 1988, 31, 1527.
Exp er im en ta l Section
(32) Heiker, F. R.; Schueller, A. M. Carbohydr. Res. 1990, 203, 314.
(33) Hanessian, S.; Ninkovic, S. J . Org. Chem. 1996, 61, 5418.
(34) Katz, S. J .; Bergmeier, S. C. Tetrahedron Lett. 2002, 43, 557.
(35) Kolb, M.; Danzin, C.; Barth, J .; Claverie, N. J . Med. Chem. 1982,
25, 550.
(36) Fei, L.; Austin, D. L. Org. Lett. 2001, 3, 2273.
(37) Allerson, C. R.; Chen, S. L.; Verdine, G. L. J . Am. Chem. Soc.
1997, 119, 7423.
(38) Urata, H.; Miyagoshi, H.; Yumoto, T.; Akagi, M. J . Chem. Soc.,
Perkin Trans. 1 1999, 1833.
(39) Holmes, R. E.; Robins, R. K. J . Am. Chem. Soc. 1965, 87, 1772.
(40) Kanie, O.; Crawley, S. C.; Palcic, M. M.; Hindsgaul, O. Carbo-
hydr. Res. 1993, 243, 139.
5′-P h th a lim id e-5′-d eoxy-2′,3′-bis(O-ter t-bu tyld im eth ylsi-
lyl)a d en osin e (10). To 2′,3′-isopropylideneadenosine (9) (24.46
g, 79.64 mmol) in 275 mL of dry THF were added phthalimide
(41) Bataille, P.; Paterne, M.; Brown, E. Tetrahedron: Asymmetry
1998, 9, 2181.
(42) Deng, S. L.; Liu, D. Z.; Huang, J . M.; Chen, R. Y. Synthesis
2001, 11, 1631.
(43) Lindstrom, U. M.; Somfai, P. Synthesis 1997, 109.
(44) Van der Wende, E. M.; Carnielli, M.; Roelen, H. C. P. F.;
Lorenzen, A.; von Frijtag Drabe Kunzel, J . K.; IJ zerman, A. P. J . Med.
Chem. 1998, 41, 102.
J . Org. Chem, Vol. 69, No. 4, 2004 1427

(11.68 g, 81.91 mmol) and PPh3 (20.89 g, 79.64 mmol). After the
mixture was stirred at rt for 10 min, DEAD (13.87 g, 79.64 mmol)
was added to the slurry and the mixture stirred an additional
2.5 h. The white precipitate was filtered off and washed with
200 mL of cold Et2O to yield product that was taken forward.
5′-Phthalimide-5′-deoxy-2′,3′-isopropylideneadenosine (22.0 g,
50.41 mmol) was dissolved in 500 mL of 3:1:1 TFA/H2O/THF
and stirred at rt for 2 h. The solvent was evaporated in vacuo
and co-stripped with EtOH (×3). The resulting material was
-0.07 (s, 3H), -0.39 (s, 3H); 13C NMR (CDCl3) δ 154.1, 151.9,
150.2, 146.0, 118.3, 88.0, 87.0, 73.3, 73.1, 43.8, 26.0, 25.7, 18.2,
17.9, -4.3, -4.4, -4.5, -5.2; HRFAB calcd for C22H41N9O3Si2
(M + H+) 536.295, obsd 536.2970.
8-Azid o-5′-e t h a n ola m in e -5′-d e oxy-2′,3′-b is(O-t er t -b u -
tyldim eth ylsilyl)aden osin e (15). To 8-azido-5′-amino-5′-deoxy-
2′,3′-bis(O-tert-butyldimethylsilyl)adenosine (13) (0.479 g, 0.8940
mmol) in 9.78 mL of toluene was added 2-iodoethanol (0.261 g,
1.5198 mmol). The reaction was stirred at 70 °C for 7.5 h. An
aqueous workup was performed (NaHCO3, EtOAc, brine), and
the organic layer was dried over Na2SO4 and evaporated in
vacuo. Column chromatography (2:1:1 EtOAc/CH2Cl2/MeOH)
yielded 15 (0.178 g, 34%) and recovered starting material (0.179
g, 37%): mp 134 °C dec; 1H NMR (CDCl3) δ 8.18 (s, 1H), 6.03
(bs, 2H), 5.73 (d, J ) 6.4 Hz, 1H), 5.08 (dd, J ) 6.4, 4.8 Hz, 1H),
4.35 (dd, J ) 4.8, 2.4 Hz, 1H), 4.18 (m, 1H), 3.70 (t, J ) 5.6 Hz,
2H), 3.64 (m, 2H), 3.01 (dd, J ) 12.0, 6.4 Hz, 1H), 2.94 (dd, J )
12.0, 3.2 Hz, 1H), 2.84 (ddt, J ) 36.0, 12.4, 5.6 Hz, 2H), 0.93 (s,
9H), 0.76 (s, 9H), 0.11 (s, 3H), 0.10 (s, 3H), -0.12 (s, 3H), -0.43
(s, 3H); 13C NMR (CDCl3) δ 153.9, 151.9, 150.2, 146.2, 118.4,
88.0, 85.4, 73.9, 72.9, 60.8, 51.4, 50.9, 26.1, 25.8, 18.3, 18.0, -4.2,
-4.35, -4.37, -5.2; HRFAB calcd for C24H45N9O4Si2 (M + H+)
580.321, obsd 580.3210.
8-Azid o-5′-a zir id in o-5′-d eoxy-2′,3′-bis(O-ter t-bu tyld im e-
th ylsilyl)a d en osin e (16). To PPh3 (0.1242 g, 0.4737 mmol) in
4.74 mL of THF at 0 °C was added DEAD (0.0825 g, 0.4737
mmol). The components were stirred until TLC indicated
complete consumption of PPh3. The mixture was added to
8-azido-5′-ethanolamine-5′-deoxy-2′,3′-bis(O-tert-butyldimethyl-
silyl)adenosine (15) (0.1831 g, 0.3158 mmol) in 4.22 mL of THF.
The reaction was warmed to rt and heated at reflux for 4 h. An
aqueous workup was performed (NaHCO3, EtOAc, brine), and
the organic layer was dried over Na2SO4 and evaporated in
vacuo. Column chromatography (6:1 EtOAc/CH2Cl2) yielded 16
(0.1026 g, 58%): mp 151 °C dec; 1H NMR (CDCl3) δ 8.21 (s, 1H),
5.77 (d, J ) 6.0 Hz, 1H), 5.73 (s, 2H), 5.22 (d, J ) 6.0, 4.8 Hz,
1H), 4.46 (dd, J ) 4.8, 3.2 Hz, 1H), 4.15 (m, 1H), 2.80 (dd, J )
12.0, 5.6 Hz, 1H), 2.31 (dd, J ) 12.0, 3.6 Hz, 1H), 1.70 (m, 2H),
1.16 (m, 2H), 0.94 (s, 9H), 0.78 (s, 9H), 0.13 (s, 3H), 0.12 (s, 3H),
-0.08 (s, 3H), -0.35 (s, 3H); 13C NMR (CDCl3) δ 153.8, 151.9,
150.6, 146.4, 118.4, 88.0, 85.2, 74.1, 72.4, 63.3, 27.6, 27.3, 26.1,
25.8, 18.3, 18.0, -4.2, -4.3, -4.4, -5.0; HRFAB calcd for
C24H43N9O3Si2 (M + H+) 562.311, obsd 562.3100.
brought up in
a 1:1:1 EtOAc/CH2Cl2/PE (petroleum ether)
mixture, and the product was filtered off as a solid and washed
to yield product (20.0 g). The resulting product was dissolved in
110 mL of dry DMF, followed by the addition of imidazole (34.4
g, 505.3 mmol) and TBSCl (16.7 g, 111.0 mmol). The reaction
was stirred at rt for 3 h, followed by aqueous workup (NH4Cl
(×2), EtOAc, brine). The organic layer was dried over Na2SO4
and evaporated in vacuo, which provided 10 (29.86 g, 60%): mp
1
163-166 °C; H NMR (CDCl3) δ 8.14 (s, 1H), 8.08 (s, 1H), 7.83
(m, 2H), 7.68 (m, 2H), 6.53 (bs, 2H), 5.85 (d, J ) 5.6 Hz, 1H),
5.12 (dd, J ) 5.6, 4.4 Hz, 1H), 4.32 (td, J ) 6.4, 2.8 Hz, 1H),
4.24 (m, 1H), 4.20 (dd, J ) 14.0, 6.4 Hz, 1H), 3.92 (dd, J ) 14.0,
6.4 Hz, 1H), 0.85 (s, 9H), 0.73 (s, 9H), 0.02 (s, 3H), -0.01 (s,
3H), -0.06 (s, 3H), -0.33 (s, 3H); 13C NMR (CDCl3) δ 168.3,
160.0, 152.9, 149.8, 140.5, 134.3, 132.0, 123.5, 120.7, 89.3, 82.9,
74.0, 73.8, 40.3, 25.84, 25.79, 18.1, 17.9, -4.4, -4.6, -4.8, -5.1;
HRMALDI calcd for C30H44N6O5Si2 (M + H+) 625.29, obsd
625.283.
8-Bromo-5′-phthalimide-5′-deoxy-2′,3′-bis(O-tert-butyldime-
th ylsilyl)a d en osin e (11). To 5′-phthalimide-5′-deoxy-2′,3′-bis-
(O-tert-butyldimethylsilyl)adenosine (10) (4.150 g, 6.641 mmol)
in 100 mL of 7:4 dioxane/0.5 M NaOAc (pH 5.3) was added Br2
(2.122 g, 13.282 mmol). The reaction was stirred at rt for 3 h,
followed by aqueous workup (Na2S2O3, CH2Cl2, brine). The
organic layer was dried over Na2SO4 and evaporated in vacuo.
Column chromatography (1:1 hexanes/EtOAc) provided 11 (3.680
g, 79%): mp 89-93 °C; 1H NMR (CDCl3) δ 8.03 (s, 1H), 7.81 (m,
2H), 7.69 (m, 2H), 6.31 (bs, 2H), 5.96 (d, J ) 6.8 Hz, 1H), 5.63
(dd, J ) 6.8, 4.4 Hz, 1H), 4.47 (dd, J ) 4.4, 1.6 Hz, 1H), 4.36
(dd, J ) 14.0, 8.4 Hz, 1H), 4.27 (m, 1H), 3.93 (dd, J ) 14.0, 4.4
Hz, 1H), 0.85 (s, 9H), 0.75 (s, 9H), 0.04 (s, 3H), -0.02 (s, 3H),
-0.06 (s, 3H), -0.42 (s, 3H); 13C NMR (CDCl3) δ 168.4, 154.7,
152.7, 150.9, 134.2, 132.1, 128.7, 123.4, 120.6, 90.3, 84.1, 74.0,
71.4, 39.7, 25.9, 25.8, 18.2, 17.9, -4.4, -4.7, -5.1, -5.2;
HRMALDI calcd for C30H43BrN6O5Si2 (M + H+) 703.20, obsd
703.200.
8-Azid o-5′-a zir id in o-5′-d eoxya d en osin e (6). To 8-azido-5′-
aziridine-5′-deoxy-2′,3′-bis(O-tert-butyldimethylsilyl)adenosine
(16) (0.0593 g, 0.1055 mmol) in 3.5 mL of THF at 0 °C was added
Bu4NF (0.0552 g, 0.2110 mmol). The reaction was stirred cold
for 1 h and evaporated in vacuo. Column chromatography (2:
1:1 EtOAc/CH2Cl2/MeOH) yielded 6 (0.0211 g, 60%): mp 155
°C dec; 1H NMR (DMSO-d6) δ 8.10 (s, 1H), 7.23 (bs, 2H), 5.66
(d, J ) 5.6 Hz, 1H), 5.40 (bs, 1H), 5.20 (bs. 1H), 4.98 (m, 1H),
4.24 (m, 1H), 3.95 (m, 1H), 2.60 (dd, J ) 12.4, 4.8 Hz, 1H), 2.25
(dd, J ) 12.4, 7.2 Hz, 1H), 1.52 (m, 2H), 1.09 (m, 2H); 13C NMR
(DMSO-d6) δ 154.3, 151.9, 149.8, 144.4, 116.8, 87.3, 83.9, 71.5,
70.6, 62.7, 26.7, 26.1; HRFAB calcd for C12H15N9O3 (M + H+)
334.138, obsd 334.1377.
8-Azido-5′-ph th alim ide-5′-deoxy-2′,3′-bis(O-ter t-bu tyldim e-
th ylsilyl)a d en osin e (12). To 8-bromo-5′-phthalimide-5′-deoxy-
2′,3′-bis(O-tert-butyldimethylsilyl)adenosine (11) (2.138 g, 3.038
mmol) in 25.7 mL of DMSO was added NaN3 (0.790 g, 12.152
mmol). The reaction was stirred at 70 °C for 7 h, followed by
aqueous workup (NaHCO3, EtOAc, brine). The organic layer was
dried over Na2SO4 and evaporated in vacuo. Column chroma-
tography (5:1 PE/EtOAc) yielded 12 (1.820 g, 90%): mp 95-97
1
°C; H NMR (CDCl3) δ 8.03 (s, 1H), 7.82 (m, 2H), 7.70 (m, 2H),
5.78 (dd, J ) 6.8 Hz, 1H), 5.43 (dd, J ) 6.8, 4.4 Hz, 1H), 5.33
(bs, 2H), 4.43 (dd, J ) 4.4, 0.8 Hz, 1H), 4.27 (dd, J ) 18.4, 7.6
Hz, 1H), 4.26 (m, 1H), 3.93 (dd, J ) 18.4, 8.8 Hz, 1H), 0.85 (s,
9H), 0.75 (s, 9H), 0.04 (s, 3H), -0.02 (s, 3H), -0.06 (s, 3H), -0.36
(s, 3H); 13C NMR (CDCl3) δ 168.4, 153.8, 151.9, 150.6, 146.2,
134.2, 132.1, 123.5, 118.2, 87.5, 83.7, 74.0, 71.7, 39.8, 25.9, 25.8,
18.2, 18.0, -4.4, -4.4, -4.7, -5.2; HRFAB calcd for C30H43N9O5-
Si2 (M + H+) 666.300, obsd 666.2991.
Ack n ow led gm en t. We thank our colleagues Scott
G. Petersen and Rachel L. Weller for very helpful
discussions, the American Foundation for Pharmaceuti-
cal Education (AFPE) and Burroughs-Wellcome Trust
Fund for a New Investigator in Pharmacy Award
(administered by American Association of Colleges of
Pharmacy), and University of Wisconsin Graduate
School and School of Pharmacy for generous startup
funding.
8-Azid o-5′-a m in o-5′-d eoxy-2′,3′-bis(O-ter t-bu tyld im eth yl-
silyl)a d en osin e (13). To 8-azido-5′-phthalimide-5′-deoxy-2′,3′-
bis(O-tert-butyldimethylsilyl)adenosine (12) (1.820 g, 2.733 mmol)
in 84.7 mL of EtOH was added ethylenediamine (0.821 g, 13.665
mmol). The reaction was stirred at 70 °C for 6 h and solvent
evaporated in vacuo. Column chromatography on silica pre-
treated with 1% TEA (4:2:1 EtOAc/CH2Cl2/MeOH) yielded 13
(1.190 g, 81%): mp 150 °C dec; 1H NMR (CDCl3) δ 8.23 (s, 1H),
5.75 (d, J ) 6.4 Hz, 1H), 5.59 (bs, 2H), 5.09 (dd, J ) 6.0, 4.4 Hz,
1H), 4.40 (dd, J ) 4.4, 2.4 Hz, 1H), 4.05 (m, 1H), 3.93 (m, 2H),
2.70 (bs, 2H), 0.95 (s, 9H), 0.79 (s, 9H), 0.13 (s, 3H), 0.12 (s, 3H),
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal methods and 1H and 13C NMR spectra for compounds 6,
10-13, 15, 16. This material is available free of charge via
the Internet at http://pubs.acs.org.
J O035485Z
1428 J . Org. Chem., Vol. 69, No. 4, 2004