cursor phosphates in the reaction mixture, the yield is low
in most cases. (ii) For triphosphorylation in solution, the
phosphoramidates and phosphorodichloridates are needed to
be synthesized first. (iii) Extensive purification of interme-
diates and final products from the reagents are required. (iv)
These strategies involve protection and deprotection reactions
for carbohydrates and lead in most cases to low overall yield
due to the lack of regioselectivity. (v) The synthesis of
dithiodiphosphate and trithiotriphosphate derivatives from the
corresponding diphosphate and triphosphate derivatives in
solution phase often leads to the incorporation of two sulfur
atoms (disulfurization) on the terminal phosphorus atom.
To solve one or more of these problems, we report the
solid-phase diphosphorylation, dithiodiphosphorylation, tri-
phosphorylation, and trithiotriphosphorylation of unprotected
carbohydrates and nucleosides. This strategy offered several
advantages. (i) The main advantage of this chemical proce-
dure was that it produced one type of monosubstituted
derivatives. Similar reactions in solution phase yield a mix-
ture of polysubstituted products. (ii) The alcohols (unpro-
tected nucleosides and carbohydrates) were mixed with an
immobilized reagent and were thereby “captured” as an im-
mobilized compound. Washing the support allowed for re-
moval of unreacted reagents and guaranteed that no unreacted
starting materials remained. (iii) This approach made use of
the presence of reagents on a rigid solid support having a
hindered structure, thereby allowing for the regioselective
reaction. The most reactive hydroxyl group of carbohydrates
and nucleosides reacted selectively with hindered polymer-
bound reagents when an excess of carbohydrates and
nucleoside was used. (iv) Reactions using this strategy
offered the advantage of facile isolation and the recovery of
products. The linkers remained trapped on the resins, which
facilitated the separation of the monosubstituted final prod-
ucts by filtration. (v) This method was used for synthesis of
four classes of compounds, carbohydrate and nucleoside
diphosphates, triphosphates, dithiodiphosphates, and trithiot-
riphosphates, from the same polymer-bound linker.
Scheme 1. Synthesis of Diphosphitylating (6) and
Triphosphitylating Reagents (7)
were determined by nuclear magnetic resonance spectra (1H
NMR, 13C NMR, 31P NMR) and high-resolution time-of-
flight electrospray mass spectrometry. Stability studies using
spectroscopic methods showed that the compounds remained
stable even after 2 weeks storage at -20 °C.
Our research on the development of polymer-bound
linkers8 and the synthesis of monophosphates and mono-
thiophosphates9 revealed that the p-acetoxybenzyl alcohol
is a good linker for attachment to solid-phase resins and
application in a variety of reactions. Two polymer-bound
linkers containing the p-acetoxybenzyl alcohol were selected
and synthesized from aminomethyl polystyrene resin in
multiple-step reactions.9 The polymer-bound linkers included
aminomethyl polystyrene resin linked through amide bond
with p-acetoxybenzyl alcohol (8A) and aminomethyl poly-
styrene resin linked through reduced amide bond with
p-acetoxybenzyl alcohol (8B) (Scheme 2).
Two classes of aminomethyl polystyrene resin-bound
linkers of p-acetoxybenzyl alcohol, 8A (3.05 g, 0.87 mmol/
g) and 8B (3.75 g, 0.72 mmol/g), were subjected to reactions
with the diphosphitylating reagent (6, ∼10 mmol) in the
presence of 1H-tetrazole to produce the corresponding
polymer-bound diphosphitylating reagents (9A and 9B).
Several unprotected nucleosides (e.g., thymidine (a), uridine
(b), 3′-azido-3′-deoxythymidine (c), adenosine (d)) and
carbohydrates (e.g., R,â-D-mannose (e), â-D-galactopyranose
(f), â-D-fructopyranose (g), melibiose (h)) (1.28 mmol) were
reacted with the polymer-bound reagents (9A and 9B) in the
presence of 1H-tetrazole to yield 11a-h and 12a-h,
respectively. Oxidation with tert-butyl hydroperoxide or
sulfurization with Beaucage’s reagent (3H-1,2-benzotrithiole-
3-one-1,1-dioxide),10 followed by removal of the cyano-
ethoxy group with DBU, afforded the corresponding polymer-
bound diphosphodiesters, 23a-h and 24a-h, or diphospho-
dithioesters, 25a-h and 26a-h. The cleavage of polymer-
bound compounds was carried out under acidic conditions
(TFA). The crude products had a purity of 69-91% and were
purified by using small C18 Sep-Pak cartridges and appropri-
ate solvents to afford nucleoside and carbohydrate diphos-
Scheme 1 illustrates the synthesis of diphosphitylating and
triphosphitylating reagents (6 and 7). Phosphorus trichloride
(1, 20 mmol) was reacted with 3-hydroxypropionitrile (2, 1
equiv) to yield 2-cyanoethylphosphorodichloridite (3). No
base was required in this reaction since generated HCl was
insoluble in acetonitrile and was bubbled out under dry
nitrogen at atmospheric pressure. The subsequent reaction
of 3 with diisopropylamine (20 mmol, 1 equiv) afforded
2-cyanoethyldiisopropylphosphoramidochloridite (4). Addi-
tion of water (1 equiv) gave the intermediate 5 that was
reacted with 4 (1 equiv) or 3 (0.5 equiv) to yield the
diphosphitylating (6, 97%) and triphosphitylating (7, 94%)
reagents, respectively. The chemical structures of 6 and 7
(5) (a) Ludwig, J. Acta Biochim. Biophys. Acad. Sci. Hung. 1981, 16,
131-133. (b) Burgess, K.; Cook, D. Chem. ReV. 2000, 100, 2047-2059.
(c) De´saubry, L.; Shoshani, I.; Johnson, R. A. Tetrahedron Lett. 1995, 36,
995-996. (d) Shoshani, I.; Laux, W. H. G.; Perigaud, C.; Gosselin, G.;
Johnson, R. A. J. Biol. Chem. 1999, 274, 34742-34744.
(6) Bettendorff, L.; Nghiem, H.-O.; Wins, P.; Lakaye, B. Anal. Biochem.
2003, 322, 190-197 and references cited therein.
(8) (a) Ahmadibeni, Y.; Parang, K. Org. Lett. 2005, 7, 1955-1958. (b)
Parang, K. Bioorg. Med. Chem. Lett. 2002, 12, 1863-1866. (c) Parang,
K.; Fournier, E. J.-L.; Hindsgaul, O. Org. Lett. 2001, 3, 307-309.
(9) Ahmadibeni, Y.; Parang, K. J. Org. Chem. 2005, 70, 1100-1103.
(10) Iyer, R. P.; Egan, W.; Regan, J. B.; Beaucage, S. L. J. Am. Chem.
Soc. 1990, 112, 1253-1254.
(7) Wu, W.; Meyers, C. L. F.; Borch, R. F. Org. Lett. 2004, 6, 2257-
2260.
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