Novel practical synthesis of Kdn2en and its C-4 nitrogen-modified derivatives

Article abstract of DOI:10.1016/S0008-6215(99)00236-0

A practical synthesis of Kdn2en and 4-amino-4-deoxy-Kdn2en has been achieved via a key intermediate, methyl 4,5,7,8,9-penta-O-acetyl-2,6-anhydro- 3-deoxy-D-glycero-D-galacto-non-2-enonate, which has been prepared from Kdn in three steps in 91% overall yield. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0008-6215(99)00236-0

www.elsevier.nl/locate/carres
Carbohydrate Research 323 (2000) 1–6
Novel practical synthesis of Kdn2en and its C-4
nitrogen-modified derivatives
Xue-Long Sun 1, Noriko Sato, Toshitsugu Kai, Kimio Furuhata *
School of Pharmaceutical Sciences, Kitasato Uni6ersity, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
Received 11 May 1999; accepted 11 August 1999
Abstract
A practical synthesis of Kdn2en and 4-amino-4-deoxy-Kdn2en has been achieved via a key intermediate, methyl
4,5,7,8,9-penta-O-acetyl-2,6-anhydro-3-deoxy- -glycero- -galacto-non-2-enonate, which has been prepared from
D
D
Kdn in three steps in 91% overall yield. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Sialyl glycals; Kdn2en; 4-Acylamino-4-deoxy-; iso-Sialyl glycals
has been found to be a strong inhibitor of
1. Introduction
Kdnase [10]. A chemical method for prepara-
tion of Kdn on a large scale has been estab-
lished in our laboratory [11], and the synthesis
of Kdn2en can be achieved in 40–60% overall
yield from Kdn [12,13]. However, the labori-
ous chromatographic purification that is re-
quired after each reaction limits its large-scale
preparation. As a part of the work involved in
the clarification of the chemical and biological
properties of Kdn2en and the synthesis of
biologically active sialyl glycals, we herein re-
port a straightforward synthesis of Kdn2en
and its C-4 nitrogen-modified derivatives,
which we term as ‘iso-sialyl glycals’ (structures
1–5).
2,3-Dehydro-2-deoxy-sialic acids (Neu5-
Ac2en, Neu5Gc2en, and their acetates) are
widely distributed in nature [1] and display
interesting biological activities as transition-
state inhibitors of the enzyme, sialidase [2].
Recently, C-4 nitrogen-containing derivatives
of N-acetylneuraminic acid have been shown
to have significant in vivo activity against
influenza virus sialidase [3,4]. On the other
hand, sialyl glycals are also very important
precursors for the stereoselective a-glycosyla-
tion of sialic acid [5–9]. Consequently, devel-
opment of convenient routes to the glycals of
sialic acid and their derivatives is of particular
synthetic interest to many groups including
our own. 2,3-Dehydro-2-deoxy-Kdn (Kdn-
2en), which has not been isolated from nature,
* Corresponding author. Tel.: +81-3-3444-6161; fax: +
81-3-3444-2530.
E-mail address: furuhatak@pharm.kitasato-u.ac.jp (K. Fu-
ruhata)
2. Results and discussion
1 Present address: Frontier Research Program, The Institute
of Physical and Chemical Research (RIKEN), 2-1 Hirosawa,
Wako-shi, Saitama 351-01, Japan.
The methyl ester of Kdn (6), prepared in
almost quantitative yield [14] by reaction of
0008-6215/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(99)00236-0

2
X.-L. Sun et al. / Carbohydrate Research 323 (2000) 1–6
Kdn with methanol containing Dowex-50
(H+), was dissolved in acetyl chloride, and the
reaction mixture was kept for 48 h at room
temperature. Concentration of the mixture
gave glycosyl chloride 7 in more than 96%
yield, with a trace of a-(methoxycarbonyl)-
furfuryl carbinol acetate (8). The crude pro-
duct 7 was dissolved in pyridine and stirred for
1 h at 50 °C to give the crude elimination
product, methyl 4,5,7,8,9-penta-O-acetyl-2,6-
dro-3,4-dideoxy-
D
-glycero-
D
-galacto- and
D
-
talo-non-2-enonates (10 and 11) from the
peracetate of Kdn methyl ester by reaction
with acetonitrile in the presence of trimethylsi-
lyl triflate (Me3SiOTf) at room temperature
[15,16]. We postulated that the reaction oc-
curred via an SN1 process like the Ritter reac-
tion via the peracetate of 2,3-unsaturated Kdn
methyl ester 9. Here, we performed the reac-
tion of 9 with acetonitrile and Me3SiOTf to
synthesize the 4-acetylamino-4-deoxy-Kdn2en
derivatives. Treatment of 9 with 2 equivalents
of Me3SiOTf in acetonitrile at 0 °C yielded
two epimers of methyl 5,7,8,9-tetra-O-acetyl-
anhydro-3-deoxy-
D
-glycero- -galacto-non-2-
D
enonate (9) after removal of pyridine by
concentration and pyridine hydrochloride by
trituration. This material could be purified by
silica gel column chromatography to yield
pure 9 in 91% overall yield. The physical data
for compound 9 and the intermediates were in
good agreement with those previously pub-
lished [12,14]. The advantages of this proce-
dure are the relatively inexpensive reagent
required and the easy workup. Moreover, ex-
cess acetyl chloride was recovered as a recy-
clable reagent. Deprotection of 9 with LiOH in
methanol and water afforded the expected
4-acylamino-2,6-anhydro-3,4-dideoxy-
D
-gly-
cero- -galacto- and -talo-2-enonates (10 and
D
D
11) in 88% yield. This result supported the
mechanism we had postulated, and it was
found that the formation of (4R)-configured
amide 11 was predominant over (4S)-
configured amide 10. Interestingly, a high re-
action temperature gave a high yield of the
products and appeared to favor the formation
of epimer 10 (Table 1). This agrees with the
results reported by Kok et al. using peracetyl
Kdn methyl ester [13]. In addition, similar
reactions of 9 with methoxyacetonitrile or
benzonitrile in the presence of Me3SiOTf at
room temperature afforded the respective 4-
compound 2,6-anhydro-3-deoxy-
D
-glycero- -
D
galacto-non-2-enonic acid (Kdn2en, 3) in 93%
yield (Scheme 1).
We have reported the preparation of methyl
5,7,8,9-tetra-O-acetyl-4-acetylamino-2,6-anhy-
Scheme 1.
Table 1
Ritter-type reaction of peracetyl Kdn2en methyl ester with Me3SiOTf (2.0 equiv) a
Run
Solvent
Temperature (°C)
Time (h)
Total yield (%)
Ratio (4S: to 4R)
1
2
3
4
5
CH3CN
CH3CN
CH3CN
CH3OCH2CN
C6H5CN
0
6
3
1
12
12
88
93
94
79
63
(1:8)
(1:6)
(1:1.1)
(1:1)
(1:1)
rt
70
rt
rt
a Isolated yield.

X.-L. Sun et al. / Carbohydrate Research 323 (2000) 1–6
3
Scheme 2.
the pyranoid ring has the same conformation
in the crystalline state as in solution.
acylamino-4-deoxy-Kdn2en derivatives (12–
15) in high yield.
In conclusion, a practical synthesis of
Kdn2en on a large scale, as well as iso-sialyl
glycal, 4-acetylamino-4-deoxy-Kdn2en and 4-
amino-4-deoxy-Kdn2en, was accomplished via
a key intermediate per-O-acetyl Kdn2en
methyl ester 9, which was prepared by a new
facile method from Kdn in high yield. Fur-
ther, selective deprotection of the N-acetyl
group was also established.
Next, selective deprotection of 10 and 11
was performed as follows. When 10 and 11
were subjected to 5% Ba(OH)2 at room tem-
perature, 4-acetylamino-4-deoxy-Kdn2en (4)
and 16 were formed in 85 and 75% yield,
respectively, whereas deprotection of 10 and
11 with 5% Ba(OH)2 at 90 °C afforded 4-
amino-4-deoxy-Kdn2en (6) and 17 in 63 and
71% yield, respectively (Scheme 2).
The structures of these products were eluci-
dated mainly by H NMR spectroscopy. The
Table 2
1
Crystal structure and refinement of compound 14 a
orientations of the 4-acylamino groups were
easily deduced from the values of the coupling
constants between H-3 and H-4, and H-4 and
H-5. For instance, the coupling constants J3,4
2.3–2.7 Hz and J4,5 8.4–9.3 Hz indicated the
(4S)-configuration for compounds 10, 12, and
14, whereas the coupling constants J3,4 5.1–
5.7 Hz and J4,5 4.8–5.1 Hz indicated (4R)-
configuration for compounds 11, 13, and 15.
Moreover, an X-ray crystallographic analysis
of 14 was conducted because only 14 afforded
good crystals on recrystallization from hex-
ane–ethyl acetate (Tables 2 and 3). An ORTEP
drawing in Fig. 1 shows that the conformation
of the pyranoid ring of 14 is a normal half
chair (6H5), with similar features to those of
other general glycals [17,18]. The absolute
configuration at C-4 was assigned as S. Fur-
Empirical formula
Space group
Z
C25H29NO12
P212121
4
Cell dimensions
,
a (A)
17.422(1)
28.225(2)
5.385(1)
2648(4)
,
b (A)
,
c (A)
3
,
V (A )
Crystal dimensions
(mm)
0.20×0.20×0.20
Dc (g cc−1
)
1.642
Radiation
Final agreement factors
R
Rw
graphite monochromated Cu Ka
6.8% (R=ꢀꢁFoꢂ−ꢂFcꢁ/ꢀꢂFoꢂ)
6.2% (Rw=[(ꢀw(ꢂFoꢂ−ꢂFcꢂ)/ꢀwFo2)]1/2
)
a The data were collected using the ꢀ−2q scan technique in the
range 2qB140.0°. Scans of (1.63+0.30 tan q)° were made at a speed
of 16.0° min−1. In total 2865 reflections were collected and cor-
rected for Lorentz and polarization factors but not for absorption.
The structure was elucidated by a direct method using TEXSAN [19].
The non-hydrogen atoms were refined anisotropically by full-ma-
trix least-squares refinement. A difference Fourier synthesis was
calculated, and the positions of all hydrogen atoms were found.
1
thermore, H NMR data for 14 indicated that

4
X.-L. Sun et al. / Carbohydrate Research 323 (2000) 1–6
Table 3
zation mass spectrometry (ESIMS) was mea-
sured on a Finnigan MATTSQ 700 mass spec-
trometer. Thin-layer chromatography (TLC)
was performed on Silica Gel 60-F254 (E.
Merck) and with detection by H2SO4 or
molybdenum blue reagent. Column chro-
matography was performed on Silica Gel-60
(E. Merck, and IATROBEADS, 6RS-8060).
4
,
Atomic coordinates (A×10 ) and equivalent temperature fac-
tors (Beq) for 14
Atom
x
y
z
Beq
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
0.4199(3)
0.5554(4)
0.4371(4)
0.4666(3)
0.5113(5)
0.3313(3)
0.3116(5)
0.2638(3)
0.2398(6)
0.1702(3)
0.0588(4)
0.6242(3)
0.6176(3)
0.4987(6)
0.4909(5)
0.5503(5)
0.5464(7)
0.4784(5)
0.4090(5)
0.3318(4)
0.2670(5)
0.1896(5)
0.4406(6)
0.4119(6)
0.4904(6)
0.3135(5)
0.2984(7)
0.2520(6)
0.2458(6)
0.1014(5)
0.0859(5)
0.6515(5)
0.7260(5)
0.7422(5)
0.8112(6)
0.8619(6)
0.7771(5)
0.8465(6)
0.2014(2)
0.2879(2)
0.2723(2)
0.0949(2)
0.0444(2)
0.1165(2)
0.0477(2)
0.2044(2)
0.2729(3)
0.1258(2)
0.1111(3)
0.1276(2)
0.1364(3)
0.2646(3)
0.2231(3)
0.2069(3)
0.1631(4)
0.1339(3)
0.1674(3)
0.1441(3)
0.1797(2)
0.1598(3)
0.3128(4)
0.0511(3)
0.0153(3)
0.0698(3)
0.0504(3)
0.2525(3)
0.2720(3)
0.1049(4)
0.0749(3)
0.1207(3)
0.0947(3)
0.0590(3)
0.0357(3)
0.0467(4)
0.1049(3)
0.0826(4)
0.358(1)
0.184(2)
0.058(2)
0.174(1)
0.425(1)
0.292(1)
0.500(1)
0.729(1)
0.976(2)
0.629(1)
0.436(2)
1.055(1)
0.638(2)
0.198(2)
0.361(2)
0.490(2)
0.638(2)
0.548(2)
0.554(2)
0.519(2)
0.492(2)
0.433(2)
3.8(3)
7.1(5)
6.0(4)
3.0(3)
7.1(5)
3.2(3)
7.3(5)
3.4(3)
11.6(7)
4.8(3)
7.1(5)
4.0(3)
3.8(4)
4.5(5)
3.3(4)
3.8(4)
3.3(5)
2.8(4)
2.8(4)
2.9(4)
2.7(4)
3.6(5)
8.4(8)
4.3(5)
6.3(6)
3.7(5)
5.5(6)
4.0(5)
3.4(4)
4.4(5)
5.8(6)
3.2(4)
3.1(4)
4.1(5)
5.7(6)
5.4(6)
4.2(5)
5.2(6)
Preparation of methyl 3-deoxy-
D
-glycero- -
D
galacto-2-nonulopyranosonate (6).—A mixture
of Kdn (5.00 g, 16.3 mmol) and Dowex-50
(H+) resin (5.00 g) in dry MeOH (100 mL)
was stirred for 18 h at room temperature (rt),
then filtered and washed with MeOH. The
filtrate was evaporated to dryness to give the
crude methyl ester 6 (5.13 g, 99.3%), which
was used directly without purification for the
O(9)
O(10)
O(11)
O(12)
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
1
next step. The H NMR spectrum was identi-
cal to that previously published [14].
Preparation of methyl 4,5,7,8,9-penta-O-
C(8)
C(9)
acetyl - 2 - chloro - 2,3 - dideoxy -
D
- glycero - -
D
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
−0.107(3)
0.634(2)
0.828(2)
0.309(2)
0.065(2)
0.711(2)
0.534(1)
0.606(2)
0.833(2)
0.849(2)
0.807(2)
0.982(2)
0.959(2)
0.777(3)
0.624(2)
0.606(2)
galacto-2-nonulopyranosonate (7).—A reac-
tion vessel containing the crude methyl ester 6
(5.13 g, 18 mmol) in acetyl chloride (50 mL)
was stoppered and left for 48 h at rt, then
evaporated to dryness and coevaporated three
times with toluene to give crude 7 (8.90 g,
3. Experimental
General methods.—Melting points were
measured on Yanaco melting-point apparatus
without correction. Optical rotations were de-
termined with a HORIBA SEPA-200 polar-
1
imeter. H NMR spectra were recorded at 270
MHz (JEOL EX-270) on solution in CDCl3,
CD3OD (internal Me4Si, l 0), or D2O (inter-
nal 3-trimethylsilyl-2,2,3,3-d4-propionic acid
sodium salt, l 0). High-resolution fast-atom
bombardment mass spectrometry (HR-
FABMS) was measured on a JEOL JMS-HX-
110 mass spectrometer. Electrospray ioni-
Fig. 1. ORTEP view of 14.

X.-L. Sun et al. / Carbohydrate Research 323 (2000) 1–6
5
under reduced pressure gave a residue that
was purified by silica gel chromatography (5:1
hexane–acetone) to yield methyl 5,7,8,9-tetra-
O - acetyl - 4 - acetylamino - 2,6 - anhydro - 3,4-
96%), which was used directly without purifi-
1
cation for the next step. The H NMR spec-
trum was identical to that published [14].
Preparation of methyl 4,5,7,8,9-penta-O-
dideoxy-
(10) and methyl 5,7,8,9-tetra-O-acetyl-4-acetyl-
amino-2,6-anhydro-3,4-dideoxy- -glycero- -
D
-glycero- -galacto-non-2-enonate
D
acetyl-2,3-dideoxy-
D
-glycero- -galacto-non-2-
D
enopyranosonate (9).—Crude 7 (8.90 g, 17
mmol) was dissolved in pyridine (100 mL),
and the reaction mixture was stirred for 1 h at
50 °C, then evaporated to dryness. The residue
was treated with EtOAc to remove the precip-
itated pyridine hydrochloride, and then con-
centrated to give the desired product as a
slightly yellow solid in 98% yield (8.11 g). It
was further purified on a silica gel column
with 4:3 hexane–acetone to afford 9 (8.03 g,
D
D
talo-non-2-enonate (11); methyl 5,7,8,9-tetra-
O-acetyl-2,6-anhydro-3,4-dideoxy-4-methoxy-
acetylamino-
D
-glycero- -galacto-non-2-eno-
D
nate (12) and methyl 5,7,8,9-tetra-O-acetyl-
2,6 - anhydro - 3,4 - dideoxy - 4 - methoxyacetyl-
amino-
D
-glycero- -talo-non-2-enonate (13);
D
methyl 5,7,8,9-tetra-O-acetyl-2,6-anhydro-4-
benzoylamino - 3,4 - dideoxy - - glycero - -
D
D
1
galacto-non-2-enonate (14) and methyl 5,7,8,
9-tetra-O-acetyl-2,6-anhydro-4-benzoylamino-
97%). The H NMR spectrum was identical to
that published [12].
3,4-dideoxy-
D
-glycero- -talo-non-2-enonate
D
2,6-Anhydro-3-deoxy-
D
-glycero- -galacto-
D
(15). Physical data of all products were identi-
non-2-enonic acid (3).—To a solution of 9
(107 mg, 0.227 mmol) in MeOH (10 mL), was
added LiOH·H2O (57 mg, 1.36 mmol, 6 equiv)
dissolved in water (2 mL). After stirring for 1
h at rt, the reaction mixture was acidified to
pH 4 by adding cation-exchange resin
(Dowex-50 (H+)) at 0 °C. The resin was
filtered off, and the filtrate was evaporated to
dryness. Chromatography of the residue on
Sephadex LH-20 with methanol afforded 3 (57
mg, 93%) as an amorphous powder; [h]D20
cal to those published [15,16].
4-Acetylamino-2,6-anhydro-3,4-dideoxy- -
D
glycero-
acetylamino-2,6-anhydro-3,4-dideoxy-
cero- -talo-non-2-enonic acid (16).—A solu-
D
-galacto-non-2-enonic acid (4) and 4-
D
-gly-
D
tion of 10 (160 mg, 0.34 mmol) in 5% aq
barium hydroxide (20 mL) was stirred for 5 h
at rt. The mixture was brought to pH 6.0 by
addition of 1 N H2SO4 at 0 °C and filtered
through Celite. The filtrate was brought to pH
10 by addition of 1 N NaOH and evaporated
to dryness in vacuo at 60 °C. The residue was
partially dissolved in water (40 mL), and the
insolubles were removed by filtration. The
filtrate was eluted through Amberlite IRC-50
(H+) resin (20 mL), which was washed with
water (40 mL), and the combined filtrate was
lyophilized to give 4 (84 mg, 85%). Compound
16 was prepared from 11 in 75% yield as
described for 4.
1
−134° (c 0.78, D2O); H NMR (300 MHz,
D2O): l 5.92 (d, 1 H, J3,4 2.7 Hz, H-3), 4.39
(dd, 1 H, J4,5 7.8 Hz, H-4), 4.14 (dd, 1 H, J5,6
10.8 Hz, J6,7 1.2 Hz, H-6), 3.84 (m, 3 H, H-7,
8, 9), 3.75 (dd, 1 H, H-5), 3.64 (dd, 1 H, J9,9%
11.4 Hz, J8,9% 6.0 Hz, H-9%). 13C NMR (75
MHz, D2O): l 69.73 (C-9), 70.05 (C-5), 70.17
(C-7), 71.83 (C-4), 72.72 (C-8), 79.59 (C-6),
114.79 (C-3), 146.09 (C-2), 168.29 (C-1).
FABMS m/z: 273 [M++1] (m-NBA as
matrix).
Compound 4: amorphous powder; [h]D20
1
+33° (c 0.33, H2O); H NMR (300 MHz,
General procedure for the Ritter-type reac-
tion.—A soln of Me3SiOTf (0.2 mL, 1 mmol)
in the appropriate nitrile (Table 1) (1 mL) was
added to a solution of 9 (267 mg, 0.50 mmol)
in the same nitrile (10 mL) at 0 °C. The mix-
ture was stirred at rt for 3 h until the starting
material was no longer detectable by TLC
(CHCl3 –MeOH). Potassium carbonate (150
mg, 2 equiv) was then added, and the mixture
was stirred for a further 15 min. Solids were
filtered off, and concentration of the filtrate
D2O): l 5.51 (d, 1 H, J3,4 2.4 Hz, H-3), 4.63
(dd, 1 H, J4,5 8.7, Hz, H-4), 4.18 (br. d, 1 H,
J6,5 10.2 Hz, H-6), 3.91 (dd, 1 H, J9,9% 12.0, J9,8
2.7 Hz, H-9), 3.94–3.88 (m, 2 H, H-7, 8), 3.80
(dd, 1 H, H-5), 3.68 (dd, 1 H, J9%,8 5.7 Hz,
H-9%), 2.03 (s, 3 H, NHAc). 13C NMR (75
MHz, D2O): l 25.50 (COCH3), 53.88 (4-C),
66.59 (9-C), 69.19 (5-C), 71.15 (7-C), 73.43
(8-C), 80.23 (6-C), 109.42 (3-C), 151.18 (2-C),
172.45 (1-C), 178.02 (COCH3). FABMS m/z:
292 [M++1] (m-NBA as matrix).

6
X.-L. Sun et al. / Carbohydrate Research 323 (2000) 1–6
Compound 16: amorphous powder; [h]D20
(dd, 1 H, J4,5 5.1, J5,6 9.6 Hz, H-5), 4.23 (dd, 1
H, J6,7 1.2 Hz, H-6), 4.12 (t, 1 H, H-4), 3.94
(ddd, 1 H, J8,7 9.3, J8,9% 6.3, J8,9 2.7 Hz, H-8),
3.91 (dd, 1 H, J9,9%12.3 Hz, H-9), 3.86 (dd, 1
H, H-7), 3.69 (dd, 1 H, H-9%). 13C NMR (75
MHz, D2O): l 49.44 (C-4), 64.88 (C-5), 66.45
(C-9), 71.56 (C-7), 73.43 (C-8), 76.57 (C-6),
102.24 (C-3), 153.95 (C-2), 171.32 (C-1).
FABMS m/z: 250 [M+ +1] (m-NBA as
matrix).
1
−163° (c 0.33, H2O). H NMR (300 MHz,
D2O): l 5.75 (d, 1 H, J3,4 5.7 Hz, H-3), 4.71
(dd, 1 H, J4,5 4.8, Hz, H-4), 4.11 (dd, 1 H, J6,5
9.9 Hz, H-5), 4.06 (dd, 1 H, J6,7 1.2 Hz, H-6),
3.94 (dd, 1 H, J8,9 2.7, J8,7 9.1, J8,9% 6.6 Hz,
H-8), 3.90 (dd, 1 H, J9,9% 11.7 Hz, H-9), 3.83
(dd, 1 H, H-7), 3.69 (dd, 1 H, H-9%), 2.04 (s, 3
H, NHAc). 13C NMR (75 MHz, D2O): l 25.45
(COCH3), 47.76 (C-4), 66.51 (C-9), 67.93 (C-
5), 71.66 (C-7), 73.62 (C-8), 76.90 (C-6),
107.62 (C-3), 151.05 (C-2), 171.78 (C-1),
177.65 (COCH3). FABMS m/z: 292 [M++1]
(m-NBA as matrix).
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4-Amino-2,6-anhydro-3,4-dideoxy-
-galacto-non-2-enonic acid (5) and 4-amino-
2,6-anhydro-3,4-dideoxy- -glycero- -talo-non-
D-glycero-
D
D
D
2-enonic acid (17).—A solution of 10 (123 mg,
0.26 mmol) in 5% aq barium hydroxide (20
mL) was stirred for 5 h at 90 °C. The mixture
was brought to pH 6.0 by addition of 1 N
H2SO4 at 0 °C and filtered through Celite. The
filtrate was brought to pH 10 by addition of 1
N NaOH and evaporated to dryness in vacuo
at 60 °C. The residue was partially dissolved
in water (40 mL), and the precipitate was
removed by filtration. The filtrate was eluted
through Amberlite IRC-50 (H+) resin (20
mL), which was washed with water (40 mL),
and the combined filtrate was lyophilized to
give 5 (41 mg, 63%).
Compound 17 was prepared from 11 in 71%
yield as described for 5.
Compound 5: amorphous powder; [h]D20
1
−5.7° (c 0.28, H2O); H NMR (300 MHz,
D2O): l 5.83 (d, 1 H, J3,4 2.4 Hz, H-3), 4.26
(br. d, 1 H, J6,5 10.2 Hz, H-6), 4.14 (dd, 1 H,
J4,5 8.7 Hz, H-4), 4.02 (dd, 1 H, H-5), 4.01–
3.90 (m, 3 H, H-7, 8, 9), 3.71 (dd, 1 H, J9,9%
11.7, J9%,8 5.9 Hz, H-9%). 13C NMR (75 MHz,
D2O): l 55.04 (C-4), 66.49 (C-9), 67.62 (C-5),
70.83 (C-7), 73.19 (C-8), 79.89 (C-6), 102.98
(C-3), 153.69 (C-2), 171.90 (C-1). FABMS
m/z: 250 [M++1] (m-NBA as matrix).
Compound 17: amorphous powder; [h]D20
1
−141° (c 0.21, H2O); H NMR (300 MHz,
[19] TEXRAY: Structure Analysis Package, Molecular Struc-
ture Corporation, 1985.
D2O): l 5.77 (d, 1 H, J3,4 5.1 Hz, H-3), 4.32