First stereoselective synthesis of 2-deoxy-alpha-D-ribosyl-1-phosphate: novel application of crystallization-induced asymmetric transformation.

Article abstract of DOI:10.1021/jo025793h

A first stereoselective synthesis of bis(cyclohexylamine) 2-deoxy-alpha-D-ribosyl-1-phosphate has been achieved. The synthesis features a key crystallization-induced asymmetric transformation (AT) to generate a desired alpha-anomer in 99% yield at a 98.8:1.2 ratio of alpha/beta.

Full text of DOI:10.1021/jo025793h

F ir st Ster eoselective Syn th esis of
SCHEME 1
2
-Deoxy-r-D-r ibosyl-1-p h osp h a te: Novel
Ap p lica tion of Cr ysta lliza tion -In d u ced
Asym m etr ic Tr a n sfor m a tion
Hironori Komatsu* and Hirokazu Awano†
Catalysis Science Laboratory, Mitsui Chemicals, Inc., 1144
Togo, Mobara-shi, Chiba 297-0017, J apan
hironori.komatsu@mitsui-chem.co.jp
Received April 3, 2002
Abstr a ct: A first stereoselective synthesis of bis(cyclohexy-
lamine) 2-deoxy-R-D-ribosyl-1-phosphate has been achieved.
The synthesis features a key crystallization-induced asym-
metric transformation (AT) to generate a desired R-anomer
in 99% yield at a 98.8:1.2 ratio of R/â.
urgent need for a new concept for sugar 1-phosphate
synthesis that is applicable to the synthesis of 1.
Crystallization-induced asymmetric transformation
8
(
AT) is a promising methodology for syntheses of un-
9
10
natural amino acids, stereogenic heteroelements, and
other chiral molecules.11 Crystallization of one isomer
from an equilibrating diastereomeric mixture would
likely provide a realistic solution for syntheses of the
sugar 1-phosphates. However, this reaction requires
highly restrictive conditions. One requirement is the
faster interconversion of diastereomers than crystalliza-
tion of one diastereomer.10 The instability of 1 is based
Chemical synthesis of 2-deoxy-R-D-ribosyl-1-phosphate
1
(
1) has been an attractive target as a key substrate in
1
c,2
enzymatic preparations of 2′-deoxynucleosides that are
currently produced from natural resources such as DNA
in salmon milt. Large-scale production of 2′-deoxynucleo-
sides is the focus of growing attention for the develop-
ment of DNA-relating drugs due to the increased demand
of the starting raw materials. Since the known synthetic
on the rapid dephosphorylation to afford an oxonium
cation form under low pH1
a,12
that would accelerate the
3
interconversion between the R- and â-anomers. As il-
lustrated in Scheme 1, in the presence of water, the
oxonium cation form is rapidly hydroxylated to stop the
interconversion.13 It is also immediately transformed to
a furan derivative14 by dehydration and aromatization,
even at room temperature, that undergoes further deg-
methods of 2′-deoxynucleosides are not satisfactory in
yield and show low stereoselectivity at the anomeric
position, particularly the synthetic methods for purine
2
2
′-deoxynucleosides, the enzymatic conversion of 1 into
′-deoxynucleoside should be the most expedient strategy
4
for its practical manufacture. Even though several
methodologies in pyranosyl-1-phosphate or furanosyl-1-
phosphate chemistry have been reported during the past
1
5
radation dependent on the reaction conditions. Thus,
strict control of the anhydrous condition, low tempera-
ture, and proper pH will enable a rapid interconversion
suitable for AT for the synthesis of 1. Despite many
5
decades, to our knowledge, no application to the synthesis
6
of 1 has been demonstrated. Its extreme acid lability and
1
6
examples of acidic isomerization of sugar 1-phosphates,
lack of a neighboring group at the C2-position, important
for increasing the anomeric selectivity,5a have prevented
success. Only one application based on the known meth-
no further development according to this strategy has yet
been examined. Another requirement for AT is the
6
a
odology reported by MacDonald resulted in modest
selectivity and low yield.7 These results suggest the
(8) For a review, see: Caddick, S.; J enkins, K. Chem. Soc. Rev. 1996,
4
47.
9) For most recent reports: (a) Kolarovic, A.; Berkes, D.; Baran,
(
*
To whom correspondence should be addressed. Tel: +81-475-23-
P.; Povazanec, F. Tetrahedron Lett. 2001, 42, 2579. (b) Boesten, W. H.
J .; Seerden, J .-P. G.; de Lange, B.; Dielemans, H. J . A.; Elsenberg, H.
L. M.; Kaptein, B.; Moody, H. M.; Kellogg, R. M.; Broxterman, Q. B.
Org. Lett. 2001, 3, 1121.
8
8
480. Fax: +81-475-23-8271.
†
Current address: 30 Asamuta-machi, Omuta-shi, Fukuoka 836-
610, J apan.
(
1) For an enzymatic synthesis, see: (a) Friedkin, M. J . Biol. Chem.
(10) For most recent reports: Vedejs, E.; Chapman, R. W.; Lin, S.;
Muller, M.; Powell, D. R. J . Am. Chem. Soc. 2000, 122, 3047.
(11) For most recent reports, see: (a) Kanomata, N.; Ochiai, Y.
Tetrahedron Lett. 2001, 42, 1045. (b) Olszewska, T.; Milewska, M. J .;
Gdaniec, M.; Maluszynska, H.; Polonski, T. J . Org. Chem. 2001, 66,
501.
1
2
950, 184, 449. (b) Friedkin, M.; Roberts, D. J . Biol. Chem. 1954, 207,
57. (c) Tarr, H. L. A. Can. J . Biochem. Physiol. 1958, 36, 517.
(
(
(
2) Friedkin, M. J . Biol. Chem. 1950, 184, 461.
3) For a review, see: Zorbach, W. W. Synthesis 1970, 7, 329.
4) Komatsu, H.; Awano, H.; Tanikawa, H.; Itou, K.; Ikeda, I.
Nucleosides Nucleotides Nucleic Acids 2001, 20, 1291.
5) For most recent reports on the preparation of sugar 1-phos-
phates: (a) Naundorf, A.; Natsch, S.; Klaffke, W. Tetrahedron Lett.
000, 41, 189. (b) Maryanoff, B. E.; Reitz, A. B.; Nortey, S. O.
Tetrahedron 1988, 44, 3093. (c) de Lederkremer, R. M.; Nahmad, V.
B.; Varela, O. J . Org. Chem. 1994, 59, 690.
(12) In ref 6b, it is reported that 2-deoxyribosyl-1-R-phosphate is
dephosphorylated within a few minutes at pH 4 at rt while ribosyl-1-
R-phosphate is stable under the same conditions. In our observation,
the pH for the stable state was more than 8.
(13) For a mechanism of acidic hydrolysis, see: Bunton, C. A.;
Humeres, E. J . Org. Chem. 1969, 34, 572 and references therein.
(14) For an example of pyrolytic elimination to a furan derivative,
see: Ness, R. K.; MacDonald, D. L.; Fletcher, J r., H. G. J . Org. Chem.
1961, 26, 2895.
(
2
(
6) (a) MacDonald, D. L.; Fletcher, J r., H. G. J . Am. Chem. Soc. 1961,
8
4, 1262. (b) Friedkin, M.; Kalckar, H. M. J . Biol. Chem. 1950, 184,
4
37.
(
7) The yield and the specific rotation of the product in ref 6a were
(15) When McDonald’s direct condensation with phosphoric acid
(see: MacDonald, D. L. J . Org. Chem. 1962, 27, 1107) was applied to
the synthesis of 1 starting from triacetyl 2-deoxyribose, the reaction
immediately turned to black tar right above the room temperature.
2
0
2
6% and [R] +23.6 (c 2, H O), respectively, after a preliminary
D
2
20
purification. An enzymatically prepared sample in ref 1c showed [R]
D
+
38.8 (c 2, H
2
O).
1
0.1021/jo025793h CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/18/2002
J . Org. Chem. 2002, 67, 5419-5421
5419

SCHEME 2a
a
Reagents and conditions: (a) 3.5 equiv of o-H3PO4, 1.2 equiv
of nBu3N, 4 Å MS, acetonitrile, -5 °C, R-3/â-3 ) 98.5:1.5; (b) 3.5
equiv of Bu3N; (c) cyclohexylamine, 99%; (d) cyclohexylamine,
F IGURE 1. Time-course of crystallization-induced asym-
metric transformation in various solvents in the presence of
orthophosphoric acid (3 equiv) and tri(n-butyl)amine (1
equiv): acetonitrile (O), 4-methyl-2-pentanone (]), 2-butanone
(×), 2-butanone, after 20 h of reaction time with 1 equiv of
orthophosphoric acid, 2 equiv of orthophosphoric acid was
added (+).
n
MeOH, 92% (85% for recrystallization).
specific crystallization of the target diastereomer.10
A
proper salt formation of the phosphate and selection of
a crystallizable protective group for the sugar hydroxyl
groups can be key factors to apply AT to sugar 1-phos-
phate syntheses. Here, we report a novel application of
AT to the first stereoselective synthesis of 1.
As depicted in Scheme 2, reaction of chlorosugar 2,
prepared from 2-deoxy-D-ribose according to the reported
method,17 with orthophosphoric acid (3.5 equiv) and tri-
or pyridine in lieu of tri(n-butyl)amine. In acetonitrile,
the reaction resulted in the highest selectivity (a 98.5:
1
.5 ratio of R-3/â-3) as a consequence of solidification of
the reaction mixture. Increased acidity accelerated the
reaction as shown in Figure 1 [compare the result of (×)
with (+)]. When 1.2 equiv of orthophosphoric acid was
initially used in 2-butanone, the R-3/â-3 ratio was 71:29
even after 20 h of reaction time, and no crystallization
was observed. However, immediately after the addition
of 2.3 equiv of orthophosphoric acid into the reaction
mixture, the crystallization of 4 out of the reaction
solution occurred, and subsequently increased the selec-
tivity to a 89:11 ratio of R-3/â-3 within 3 h.
(n-butyl)amine (1.2 equiv) in various solvents in the
1
8
presence of 4 Å molecular sieves (pellets) at -5 °C
initially produced R-phosphate (R-3) and â-phosphate (â-
3
) in a ratio of 49:51 with no anomeric selectivity
according to HPLC analysis. The result reflects the low
selectivity observed in a previous report.6 The reaction
a
N
proceeds by S 2 displacement of Cl by phosphoric acid
with inversion at the anomeric carbon of 2, but rapid
anomerization of 2 in polar solvents results in low
selectivity.19 However, the possibility of a complete inver-
sion followed by rapid anomerization of the resulting â-3
cannot be excluded. Under acidic conditions due to excess
phosphoric acid, equilibration between R-3 and â-3 oc-
curred, gradually inclining to the thermodynamically
more stable R-3. In DMF solvent, the reaction equili-
brated at a ca. 2:1 ratio of R-3/â-3. In 4-methyl-2-
pentanone, the ratio was further upgraded by crystalli-
zation of mono(tributylamine) phosphate (4) out of the
reaction solution, giving R-3 and â-3 at a ratio of 91:9.
Clear evidence of AT is shown in Figure 1. In various
solvents, the R-anomer ratio increased dependent on the
reaction time. However, beyond the ratio of ca. 2:1 (R-3/
â-3), the selection of amine and solvent was crucial for
the induction of the R/â selectivity at the anomeric
position. AT was not observed using either triethylamine
Since mono(tributylamine) phosphate (4) was too labile
to isolate directly from the reaction mixture, 3.5 equiv
of tri(n-butyl)amine was added to neutralize the reaction
mixture before the workup.12 The resulting bis(tributy-
lamine) phosphate (5) was stable enough for an aqueous
workup. Extraction with 4-methyl-2-pentanone followed
by rinsing of the organic phase with water to remove
phosphate impurities was performed. From the organic
solution, phosphate 6 was isolated as a bis(cyclohexy-
lamine) salt in 99% yield, and the R- and â-anomer ratio
was 98.8:1.2 in HPLC assay. The resulting 6 contained
no phosphate impurities according to 31P NMR analysis.
Without further purification, 6 was debenzoylated by
using cyclohexylamine in methanol at room temperature
to afford bis(cyclohexylamine) salt of the desired 2-deoxy-
R-D-ribosyl-1-phosphate (1) in 92% yield. The resulting
phosphate (1) contained no phosphate impurities accord-
ing to 3 P NMR analysis, and its specific rotation indi-
1
cated [R]25
+37.3 (c 3, H
2
O).7 Recrystallization from
D
(
16) (a) MacDonald, D. L. Carbohydr. Res. 1966, 3, 117. (b) Perchem-
lides, P.; Osawa, T.; Davidson, E. A.; J eanloz, R. W. Carbohydr. Res.
967, 3, 463.
17) (a) Hoffer, M. Chem. Ber. 1960, 93, 2777. (b) Wang, Z.-X.; Duan,
aqueous methanol-diethyl ether afforded analytically
1
pure 1 as bis(cyclohexylamine) salt in 85% yield, and its
(
25
specific rotation was improved to [R]
D
2
+41.4 (c 3, H O)
W.; Wiebe, L. I.; Balzarini, J .; De Clercq, E.; Knaus, E. E. Nucleosides
Nucleotides Nucleic Acids 2001, 20, 11.
that was comparable with the reported value of the
(
18) Fine powder molecular sieves was not suitable to induce the
desired crystallization of the target diastereomer (4).
19) For a mechanism of S 2 attack of nucleoside bases to 2, see:
Hubbard, A. J .; J ones, A. S.; Walker, R. T. Nucleic Acids Res. 1984,
2, 6827.
sample synthesized by an enzymatical degradation of 2′-
1,7
deoxyguanosine. The structure was confirmed by spec-
(
N
1
13
31
troscopic methods ( H, C, and P NMR and IR), mass
spectral analysis, and elemental analysis in comparison
1
5
420 J . Org. Chem., Vol. 67, No. 15, 2002

with commercially available 1 [bis(cyclohexylamine) salt]
that was enzymatically prepared.
Crystallization-induced asymmetric transformation has
been applied to the stereoselective synthesis of bis-
Hz), 7.455 (2H, ddd, J ) 2.2, 2.2, 8.8 Hz), 5.98 (1H, ddd, J )
0.8, 5.1, 6.3 Hz), 5.46 (1H, ddd, J ) 1.8, 3.3, 7.7 Hz), 4.65 (1H,
ddd, J ) 4.2, 4.2, 4.2 Hz), 4.62 (1H, dd, J ) 4.2, 11.5 Hz), 4.51
2
0
(
1H, dd, J ) 4.2, 11.5 Hz), 2.96 (2H, m), 2.56 (1H, dddd, J )
.8, 5.1, 7.7, 14.4 Hz), 2.37 (1H, dddd, J ) 0.8, 0.8, 1.8, 14.4
Hz), 1.98 (4H, m), 1.76 (4H, m), 1.61 (2H, m), 1.28-1.1 (8H, m),
1.17 (2H, m); NMR δ (100 MHz, CD OD) 167.1, 166.8, 140.7,
140.6, 132.5, 132.2, 129.9, 129.8, 101.1 (d, J ) 4.1 Hz), 83.0, 76.9,
5.9, 51.2, 41.3 (d, J ) 6.6 Hz), 32.8, 26.1, 25.6; NMR δ (162
OD) 1.35; MS [APCI (-)] m/z 489 (M - 2) ; HPLC t
4.8 min (R-isomer); t 18.0 min (â-isomer) [column: YMC Pack
AM312 (ODS-AM) (150 cm × 6.0 mm) (from YMC, Co. Ltd.),
mobile phase: 10 mM NaH PO
0
(
cyclohexylamine) 2-deoxy-R-D-ribosyl-1-phosphate (1)
that is a key compound for the enzymatic preparation of
2
C
3
1
c,2
′-deoxynucleosides. Further modification to establish
6
P
a more practical and scalable method is under investiga-
tion and will be reported elsewhere.
-
MHz, CD
3
R
1
R
2
4
-MeOH (35:65), flow rate: 1.0
Exp er im en ta l Section
mL/min, UV wavelength: 254 nm, column temperature: 40 °C],
R-3/â-3 ) 98.8:1.2.
Gen er a l Meth od s. Melting points are uncorrected. The 1
NMR chemical shifts are described as δ values in ppm relative
H
Syn th esis of Bis(cycloh exyla m in e) 2-Deoxy-R-D-r ibosyl-
1-p h osp h a te (1). A solution of 6 (7.05 g, 10.2 mmol) and
cyclohexylamine (2.92 mL, 25.6 mmol) in MeOH (106 mL) was
stirred at rt for 72 h. The reaction mixture was concentrated at
10 °C, and EtOH was added. The resulting precipitates were
collected, rinsed with EtOH, and dried in vacuo at rt to give
1
3
to TMS as an internal standard. The C NMR chemical shifts
are reported as δ values in ppm relative to methanol. The 31
NMR chemical shifts are described as δ values in ppm downfield
from 85% H PO as an external standard.
P
3
4
Syn th esis of Bis(cycloh exyla m in e) 3′,5′-O-Bis(4-ch lo-
r oben zoyl)-2-d eoxy-R-D-r ibosyl-1-p h osp h a te (6). A mixture
2
5
3.87 g (92%) of crude 1 as a colorless solid: [R]
O). The crude 1 (495 mg, 1.20 mmol) was recrystallized from
MeOH-Et O at -15 °C and dried in vacuo at rt for 2 days to
give 423 mg (85%) of 1 as a colorless solid: mp 168-169 °C dec;
D
37.3 (c 3.0,
of 98% o-H
and 4 Å MS (10 g, pellets) in CH
overnight. 3′,5′-O-Bis(4-chlorobenzoyl)-2-deoxy-R-D-ribosyl 1-chlo-
3
PO
4
(6.92 g, 6.92 mmol), Bu
3
N (5.51 mL, 23.1 mmol),
H
2
3
CN (80 mL) was stirred at rt
2
1
7
25
-1
ride (2) (8.5 g, 19.8 mmol) was added at -5 °C, and the reaction
[R]
D
41.4 (c 3.0, H
2
O); IR (KBr) 2940, 2725, 2239, 1631 cm
;
mixture was stirred for 23 h. Bu N (16.5 mL, 69.3 mmol) was
3
NMR δ
H
(400 MHz, D
2
O) 5.60 (1H, dd, J ) 5.2, 5.2 Hz), 4.07
added at -5 °C. The molecular sieves were filtered off, and the
(1H, ddd, J ) 2.9, 3.6, 7.2 Hz), 4.04 (1H, ddd, J ) 3.6, 3.6, 3.6
Hz), 3.56 (1H, dd, J ) 3.6, 12.2 Hz), 3.45 (1H, dd, J ) 3.6, 12.2
Hz), 2.99 (2H, m), 2.20 (1H, ddd, J ) 5.2, 7.2, 14.4 Hz), 1.93
(1H, ddd, J ) 1.3, 2.9, 14.4 Hz), 1.83 (4H, m), 1.64 (4H, m), 1.50
filtrate was concentrated at rt. The residue was dissolved in
4
-methyl-2-pentanone and rinsed with purified water three
times. After filtration of the organic phase to remove very fine
impurities, cyclohexylamine (5.66 mL, 49.5 mmol) was added
at 0 °C, and the mixture was stirred for 2 h. The resulting
precipitates were collected, rinsed with 4-methyl-2-pentanone
and acetone successively, and dried in vacuo at 40 °C to give
(2H, m), 1.26-1.1 (8H, m), 1.12 (2H, m); NMR δ
O) 100.2 (d, J ) 4.1 Hz), 86.7, 72.0, 62.4, 51.1, 42.5 (d, J )
(162 MHz, D O) 1.48; MS [APCI
C
(100 MHz,
D
2
5.0 Hz), 31.1, 25.1, 24.6; NMR δ
P
2
-
(-)] m/z 213 (M - 1) . Anal. Calcd: C, 49.50; H, 9.04; N, 6.79;
2
5
1
4
δ
3.5 g (99%) of 6 as a colorless solid: mp 179-180 °C dec; [R]
D
P, 7.51. Found: C, 49.26; H, 8.81; N, 6.64; P, 7.29.
-
1
5.6 (c 1.23, methanol); IR (KBr) 2938, 2859, 1721 cm ; NMR
(400 MHz, CD OD) 8.05 (2 H, ddd, J ) 2.2, 2.2, 8.8 Hz), 7.99
2 H, ddd, J ) 2.2, 2.2, 8.8 Hz), 7.456 (2 H, ddd, J ) 2.2, 2.2, 8.8
Su p p or tin g In for m a tion Ava ila ble: Spectral data of
compounds 1 [bis(cyclohexylamine) salt] and 6. This material
is available free of charge via the Internet at http://pubs.acs.org.
H
3
(
(20) Available from Sigma-Aldrich Co.
J O025793H
J . Org. Chem, Vol. 67, No. 15, 2002 5421