A general approach to the synthesis of dideoxy and trideoxyiminoalditols from β-D-glycosides

Article abstract of DOI:10.1016/S0008-6215(00)00124-5

Imino sugars (also called azasugars), a class of compounds of which the 1,5-dideoxy and 1,5,6-trideoxyiminoalditols are members, are important glycosidase inhibitors with very high potential as drugs. Their potential therapeutic applications range from the treatment of diabetes to cancer and AIDS. We present here a general method for the preparation of such compounds with the D-gluco and D-galacto configurations starting from β-D-glycosides. The procedure is especially appealing because of its high stereoselectivity and straightforwardness. The key steps are the selective oxidation of the glycosides to hexulosonic acids and reduction of the oxime derivatives to lactams, which are further reduced to the target compounds. The C-6 position can be deoxygenated during the reduction if it bears an acetoxy group. Trideoxy imino sugars are then produced. Deacetylation prior to oxime reduction gives dideoxy compounds. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0008-6215(00)00124-5

www.elsevier.nl/locate/carres
Carbohydrate Research 328 (2000) 467–472
A general approach to the synthesis of dideoxy and
trideoxyiminoalditols from b-
D-glycosides
Gabriela Pistia, Rawle I. Hollingsworth *
Department of Chemistry and Biochemistry, Michigan State Uni6ersity, East Lansing, MI 48824, USA
Received 20 January 2000; accepted 27 April 2000
Abstract
Imino sugars (also called azasugars), a class of compounds of which the 1,5-dideoxy and 1,5,6-trideoxyiminoaldi-
tols are members, are important glycosidase inhibitors with very high potential as drugs. Their potential therapeutic
applications range from the treatment of diabetes to cancer and AIDS. We present here a general method for the
preparation of such compounds with the
D
-gluco and
D
-galacto configurations starting from b-D-glycosides. The
procedure is especially appealing because of its high stereoselectivity and straightforwardness. The key steps are the
selective oxidation of the glycosides to hexulosonic acids and reduction of the oxime derivatives to lactams, which
are further reduced to the target compounds. The C-6 position can be deoxygenated during the reduction if it bears
an acetoxy group. Trideoxy imino sugars are then produced. Deacetylation prior to oxime reduction gives dideoxy
compounds. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Nitrogen heterocycles; Azasugars; Nojirimycin; 1,5-Imino-1,5-dideoxy alditols; 1,5-Imino-1,5,6-trideoxy alditols; Gly-
cosidase inhibitors
1. Introduction
literature. The first one involves enzymatic
aldol condensation of 3-azido-2-hydroxy-
propanal and dihydroxyacetone phosphate [5].
The second method is based on an asymmetric
Diels–Alder reaction of sorbaldehyde O-
methyloxime with a chiral chloronitroso
derivative of mannose [6]. The last approach
Over the last three decades there has been a
continued interest in natural and synthetic
imino sugars because of their high potency as
glycosidase inhibitors [1]. They proved to be
excellent drug candidates for diabetes [2], can-
cer [3] and HIV therapy [4]. This is why
chemists are still trying to develop simple and
general ways for their synthesis.
Our research has focused so far on the
synthesis of imino-dideoxy and -trideoxy
alditols.
We have been able to identify three chemi-
cal syntheses for 1,6-dideoxynojirimycin in the
uses protected 6-deoxy- -xylo-5-hexulose as
D
substrate for a double reductive amination [7].
Although these are important contributions,
they generally are not stereospecific for a
given sugar derivative, and the yields are be-
low 20%.
The literature contains many syntheses for
deoxynojirimycin and its analogues. These of-
ten utilize carbohydrates [8], lactones [9] or
other chiral pool sources [10] containing one
or more chiral centers as starting materials.
Enzymes [11] and bacteria [12] are also uti-
lized. One method worthy of special mention
* Corresponding author. Tel.: +1-517-3530613; fax: +1-
517-3539334.
E-mail address: rih@argus.cem.msu.edu (R.I. Hollings-
worth).
0008-6215/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(00)00124-5

468
G. Pistia, R.I. Hollingsworth / Carbohydrate Research 328 (2000) 467–472
is Behling’s short and enantiospecific synthesis
of deoxynojirimycin starting from -sorbose
we use here is based on the chromium trioxide
oxidation of glycosides to yield ketoaldonic
acid esters that are then converted to cyclic
imino sugars by reductive ring closure with a
nitrogen species. This paper focuses only on
compounds with the
configurations.
L
[13]. Its only drawback is that it cannot be
extended to other sugars. Wong’s aldolase-
promoted Diels–Alder reactions [14] between
dihydroxy acetone phosphate and a chiral N-
containing aldehyde can afford a variety of
deoxynojirimycin analogues, but the yields are
low, and it is not clear whether the enzyme is
available in sufficient quantity to allow large-
scale synthesis. The chemo-microbiological
method patented by Grabner and coworkers
[15] provides an elegant method for trans-
forming a sugar into its imino derivative by
reductive amination of an aldo-5-ulose ob-
tained by bacterial oxidation of glucose.
Again the extension of this method to deoxy
sugars and various substituted sugars is lim-
ited by the specificity of the organisms.
Here we present a general and simple new
synthesis for imino sugars. The routes start
from readily available b-glycosides and re-
quire just few steps with straightforward reac-
tion conditions. They allow access to
1,5-dideoxy- and 1,5,6-trideoxy-1,5-iminoaldi-
tols. The enantiochemistry does not have to be
induced but is derived from the starting sugar
and is, therefore, always close to 100%. Hence
the galacto isomers can be obtained simply by
using a galactoside. The method also allows
access to the 5-amino-5-deoxy-aldonic acid d-
lactams. They are excellent glycosidase in-
hibitors at concentrations 100 times lower
than most of the other inhibitors tested [5].
The gluco isomer has been made previously by
the oxidation of nojirimycin [5]. The approach
D-gluco and
D-galacto
2. Results and discussion
The oxidation of the anomeric carbon of
glycosides is well documented in patents and
papers. Examples are the microbiological oxi-
dation with Gluconobacter oxidans [15] or the
use of oxidants such as (Bu3Sn)2O [16] and
RuO4 with or without partial protection of the
hydroxyl groups. The chromium trioxide oxi-
dation we use here typically employs a large
excess of CrO3 [17], but we obtained excellent
results using only two equivalents. The perac-
etate of methyl b- -glucopyranoside 2a on
D
oxidation with chromium trioxide gave the
keto-ester 3a in quantitative yield (Scheme 1).
Our first attempts at reductive amination us-
ing NaCNBH3 and different amino-group
sources such as NH4OH, NH4Cl, NH4OAc
were unsuccessful. The use of the more nucle-
ophilic agent, hydroxylamine, yielded the ox-
ime 4a, which crystallized as a mixture of syn
and anti isomers in 95% yield. Reduction of
this oxime with hydrogen in the presence of
palladium-on-charcoal led to formation of the
5-amino-5-deoxy derivative, which sponta-
neously cyclized to form the d-lactam. The
hydrogenation conditions also led to reductive
Scheme 1. Preparation of 1,5,6-trideoxy-1,5-imino-D-glucitol (6a) and trideoxy galacitol, 1,5,6-trideoxy-1,5-imino-D-galacitol (6b).

G. Pistia, R.I. Hollingsworth / Carbohydrate Research 328 (2000) 467–472
469
proach should be general to any b-glycoside,
especially deoxy sugars and those with sub-
stituents such as ether groups, to give general
access to substituted or functionalized imi-
nosugars. The use of alkylamines instead of
hydroxylamine should give access to N-alky-
lated iminosugars. Further research in this
area is in progress and will be reported on
later.
Scheme 2. Preparation of 2,3,4,6-tetra-O-acetyl-5-amino-5-de-
oxy- -glucono-1,5-lactam (9).
3. Experimental
D
General methods.—Melting points were
measured on a Fisher–Johns melting point
apparatus. Optical rotations were measured
(u=589 nm) at room temperature (rt) using a
Perkin–Elmer 341 polarimeter in a 1 mL cell.
cleavage of the acetoxy group to form a 6-de-
oxy function. This preceded the reduction of
the oxime and allowed access to the 1,5,6-
trideoxyderivatives. Despite the presence of
both the syn and anti oximes, no -derivatives
L
1
The H and 13C NMR spectra were recorded
were formed. The desired isomer was formed
exclusively. Lactam 5a was formed quantita-
tively and was then reduced and deacetylated
with borane·THF, to give the 6-dideoxynojir-
imycin 6a in 84.8% total yield.
at 300 MHz on a Varian VXR spectrometer.
The HRMS FAB mass spectra were obtained
using a Jeol HX-110 double-focusing mass
spectrometer operating in positive ion mode.
Preparation of methyl 2,3,4,6-tetra-O-ace-
The same reaction sequence was applied to
tyl-i-
D
-glucopyranoside (2a).—The tetra-
methyl b- -galactopyranoside (1b), and while
D
acetate has been prepared from methyl
the first three reactions occurred with the
same high yields, the catalytic reduction was
accompanied by partial deacetylation, making
chromatographic separation necessary and
therefore decreasing the yield. Even so, this
method affords a convenient and high-yield
b- -glucopyranoside (1a), pyridine and Ac2O
D
according to standard procedures [18].
Preparation of methyl 2,3,4,6-tetra-O-ace-
tyl- -xylo-hex-5-ulosonate (3a).—To a soln
D
of 2a (7 g, 19.34 mmol) in AcOH (125 mL)
and Ac2O (10 mL), CrO3 (3.8 g, 38 mmol) was
added, and the suspension was stirred at 50 °C
for 2 h. The mixture was then poured slowly,
with stirring, into cold water (500 mL). The
water was extracted three times with CHCl3.
The combined CHCl3 layers were decolorized
with activated charcoal, filtered, and washed
with satd NaHCO3 soln and then with water.
After drying with Na2SO4 and rotary evapora-
tion of the solvent, the ketone 3a (7.25 g,
100%) was obtained as a colorless syrup: [h]D23
−2.4° (c 1.67, CH3Cl), lit. −5.8° (c 1.65,
route for preparing 1,6-dideoxy- -galactono-
D
jirimycin 6b.
Access to the 6-hydroxy derivatives (deoxy-
D-galacto and
D-gluconojirimycins) was read-
ily achieved by deacetylating the oxime with
hydrazine prior to reduction. The deacylation
yielded the acyl hydrazide 7 in quantitative
yield (Scheme 2). Catalytic hydrogenation of
the latter with Pd–C provided the d-lactam 8.
To facilitate isolation, 8 was reacetylated to 9,
which was recovered in 35% total yield by
chromatography. This can be reduced with
BH3·THF, using the previously indicated pro-
cedure to yield deoxynojirimycin.
In summary, we have developed a facile and
effective synthesis of 1,6-dideoxynojirimycin,
1,6-dideoxygalactonojirimycin and deoxyno-
jirimycin as well as the corresponding 5-
amino-5-deoxy-aldonic acid d-lactams using
b-glycosides as starting materials. This ap-
1
CH3Cl) [17]; H NMR (CDCl3) l 2.08 (s, 3 H,
OAc), 2.09 (s, 3 H, OAc), 2.10 (s, 3 H, OAc),
2.13 (s, 3 H, OAc), 3.70 (s, 3 H, OCH3), 4.73
(d, 1 H, J6a,6b 17.3 Hz, H-6a), 4.84 (d, 1 H,
H-6b), 5.26 (d, 1 H, J2,3 4.4 Hz, H-2), 5.43 (d,
13
1 H, J3,4 4.4 Hz, H-4), 5.65 (t, 1 H, H-3); C
NMR (CDCl3) l 20.1, 20.2, 20.3, 52.8, 66.4,
69.3, 69.6, 73.6, 167.0, 169.1, 169.3, 169.7,
197.0.

470
G. Pistia, R.I. Hollingsworth / Carbohydrate Research 328 (2000) 467–472
Preparation of methyl 2,3,4,6-tetra-O-ace-
tyl- -xylo-hex-5-ulosonate oxime (4a).—The
Preparation of 1,5,6-trideoxy-1,5-imino- -
D
D
glucitol (6a).—1 M BH3·THF (50 mL, 50
mmol) was added under N2 to a soln of 5a (5
g, 17.41 mmol) in THF (33 mL). The mixture
was stirred at rt for 1.5 h and then refluxed for
another 1.5 h. After cooling to rt, 9%
methanolic HCl (40 mL) was carefully added,
and the resulting soln was refluxed for 30 min.
The THF was removed by rotary evaporation,
and the reaction mixture was dissolved repeat-
edly in MeOH, followed by evaporation to
remove borates. Water was added to the dry
crude product and the soln was passed
through an anion-exchange resin (Amberlite
IR-45 OH-form) and then dried on the rotary
evaporator. To remove the last traces of bo-
rates, a soln of 1 M NaOH (15 mL) and
EtOH (6 mL) were added to the crude
product, and the mixture was stirred overnight
at rt. The EtOH was evaporated, and the aq
soln was lyophylized. A methanolic HCl soln
was added, which precipitated NaCl while the
methanolic soln was dried, to give product 6a
(2.43 g, 95%): [h]D23 +15.5° (c 1.88, H2O), lit.
ketone 3a (7 g, 18.61 mmol) was dissolved in
pyridine (16 mL), and the soln was cooled to
0 °C. Hydroxylamine hydrochloride (2 g,
28.77 mmol) was then added, and the soln was
stirred at 0 °C for 15 min, and then for an-
other 2 h at rt. The mixture was poured onto
ice and water and then extracted three times
with CHCl3. The combined CHCl3 layers were
subsequently washed with water, dried with
Na2SO4 and then evaporated. Crystallization
from hot EtOH gave white crystals of the
oxime 4a (6.9 g, 95%) as a 3:2 mixture of
syn–anti isomers:
1
Isomer 1: H NMR (CDCl3) l 1.93 (s, 3 H,
OAc), 1.94 (s, 3 H, OAc), 2.00 (s, 3 H, OAc),
2.01 (s, 3 H, OAc), 3.56 (s, 3 H, OCH3), 4.36
(d, 1 H, J6a,6b 12.4 Hz, H6-a), 4.72 (d, 1 H,
H6-b), 4.99 (d, 1 H, J3,4 2.6 Hz, H-4), 5.72
(dd, 1 H, J3,2 7.8 Hz, H-3), 6.28 (d, 1 H, H-2);
13C NMR (CDCl3) l 20.5, 20.4, 52.8, 61.3,
66.1, 69.5, 69.8, 149.9, 167.3, 169.4, 169.5,
170.1; HRFABMS (M+H+) calcd. 392.1193,
found 392.1198.
1
+13° (c 1.0, H2O) [7]; H NMR (D2O) l 1.25
Isomer 2: mp 121–122 °C; 1H NMR
(CDCl3) l 1.88 (s, 3 H, OAc), 1.89 (s, 3 H,
OAc), 1.98 (s, 3 H, OAc), 2.00 (s, 3 H, OAc),
3.56 (s, 3 H, OCH3), 4.82 (s, 2 H, H-6), 5.16
(d, 1 H, J3,4 2.6 Hz, H-4), 5.62 (d, 1 H, J3,2 8.5,
(d, 3 H, J5,6 6.3 Hz, H-6), 2.77 (dd, 1 H, J1a,1e
12.4 Hz, J1a,2 11.7 Hz, H-1a), 3.02 (m, 1 H,
H-5), 3.23 (dd, 1 H, J3,4 9.0 Hz, H-4), 3.33
(dd, 1 H, J1e,2 5.1 Hz, H-1e), 3.31 (dd, 1 H, J2,3
13
9.2 Hz, H-3), 3.63 (ddd, 1 H, H-2); C NMR
13
H-2), 5.78 (dd, 1 H, H-3); C NMR (CDCl3)
(D2O) l 17.5, 49.5, 55.2, 71.4, 76.7, 79.0.
Preparation of methyl 2,3,4,6-tetra-O-ace-
l 20.3, 20.4, 20.5, 52.8, 56.4, 69.8, 70.1, 70.4,
150.8, 167.2, 169.4, 169.6, 170.2, 170.3.
Preparation of 2,3,4-tri-O-acetyl-5-amino-
tyl-i-
D
-galactopyranoside (2b).—This com-
-galacto-
pound was prepared from methyl b-
D
5,6-dideoxy-
D
-glucono-1,5-lactam
(5a).—A
pyranoside hydrate (1b, 5 g, 24.63 mmol) us-
ing the same procedure described for the gluco
compound.
soln of 4a (6.9 g, 17.64 mmol) in glacial
AcOH (275 mL), containing 10% Pd–C (2.76
g), was hydrogenated in a Parr reactor under
a H2 pressure of 300–400 psi for 40 h at
55 °C. The reaction mixture was filtered
through Celite and washed with EtOH. The
solvent was rotary evaporated and the lactam
5a (5 g, 100%) was obtained as a light yellow
Preparation of methyl 2,3,4,6-tetra-O-ace-
tyl-L
-arabino-hex-5-ulosonate
(3b).—This
compound was prepared from 2b using the
same procedure as described for 3a, except
that the reaction time was 3 h. Yield was
100%: [h]2D3 −24.3° (c 1.4, CHCl3), lit. 12.0° (c
1
1
syrup: [h]2D3 +70.0° (c 1.56, CHCl3); H NMR
2.8, CHCl3) [18]; H NMR (CDCl3) l 2.06 (s,
(CDCl3) l 1.11 (d, 3 H, J5,6 6.3 Hz, H-6), 1.94
(s, 3 H, OAc), 1.98 (s, 3 H, OAc), 2.00 (s, 3 H,
OAc), 3.51 (m, 1 H, J4,5 9.7, Hz, H-5), 4.94 (t,
1 H, J2,3=J3,4 9.7 Hz, H-3), 4.96 (d, 1 H,
3 H, OAc), 2.10 (s, 3 H, OAc), 2.11 (s, 3 H,
OAc), 2.16 (s, 3 H, OAc), 3.71 (s, 3 H, OCH3),
4.80 (d, 1 H, J6a,6b 17.5 Hz, H-6a), 4.92 (d, 1
H, H-6b), 5.20 (d, 1 H, J2,3 8.7 Hz, H-2), 5.27
(d, 1 H, J3,4 2.4 Hz, H-4), 5.66 (dd, 1 H, H-3);
13C NMR (CDCl3) l 20.1, 20.2, 20.3, 20.4,
52.8, 67.1, 69.3, 69.5, 71.0, 167.0, 168.9, 169.4,
169.8, 198.1.
13
H-2), 5.40 (t, 1 H, H-4); C NMR (CDCl3) l
18.0, 20.3, 20.4, 48.7, 70.6, 70.9, 71.4, 166.7,
169.4, 169.6, 169.8; HRFABMS (M+H+)
calcd. 288.1083, found 288.1089.

G. Pistia, R.I. Hollingsworth / Carbohydrate Research 328 (2000) 467–472
471
(15 mL) for 5 h at rt. The mixture was poured
into cold water and extracted with CHCl3.
The CHCl3 layer was dried with Na2SO4.
Evaporation of the solvent gave crude product
(1.47 g), which was subjected to flash chro-
matography on silica (eluent: 2:1 hexane–ace-
tone) to give the peracetylated lactam 9 (0.5 g,
34% total yield from 4a) and its C-5 epimer,
Preparation of methyl 2,3,4,6-tetra-O-ace-
tyl- -arabino-hex-5-ulosonate oxime (4b).—
This compound was prepared from the ketone
-xylo
L
3b as described for the corresponding
D
compound. White crystals of 4b (85%) were
1
obtained as a mixture of syn–anti isomers: H
NMR (CDCl3) l: Isomer 1: 1.98 (s, 3 H,
OAc), 2.01 (s, 3 H, OAc), 2.08 (s, 3 H, OAc),
2.15 (s, 3 H, OAc), 3.70 (s, 3 H, OCH3), 4.82
(d, 1 H, J6a,6b 14.6 Hz, H6-a), 5.11 (d, 1 H,
H6-b), 5.35 (d, 1 H, J3,4 1.9 Hz, H-4), 5.68 (d,
1 H, J3,2 9.0, Hz, H-2), 5.84 (dd, 1 H, H-3);
13C NMR (CDCl3) l 20.2, 20.3, 20.4, 20.5,
52.6, 56.4, 68.7, 69.2, 69.6, 149.9, 167.5, 168.9,
169.3, 170.0, 170.3.
2,3,4,6-tetra-O-acetyl-5-amino-5-deoxy- -
L
idono-1,5-lactam in a 3:2 ratio.
Data for 9: mp 177–178 °C; [h]2D3 +88.6° (c
1.11, CHCl3), lit +104° (c 1.73, CHCl3) [5];
1H NMR (CDCl3) l 2.03 (s, 3 H, OAc), 2.06
(s, 3 H, OAc), 2.08 (s, 3 H, OAc), 2.10 (s, 3 H,
OAc), 3.75 (ddd, 1 H, J4,5 9.7 Hz, J5,6a 2.9 Hz,
J5,6b 6.5 Hz, H-5), 3.96 (dd, 1 H, J6a,6b 11.7
Hz, H6-b), 4.22 (dd, 1 H, H-6a), 5.06 (d, 1 H,
J3,2 9.5 Hz, H-2), 5.20 (t, 1 H, J3,4 9.5 Hz,
H-3), 5.53 (dd, 1 H, H-4), 6.48 (s, 1 H,
NH);13C NMR (CDCl3) l 20.5, 20.5, 20.5,
20.6, 52.4, 62.7, 67.2, 70.4, 70.5, 166.2, 169.4,
169.6, 170.0, 170.4. HRFABMS (M+H+)
calcd. 346.1060, found 346.1143.
Preparation of 1,5,6-trideoxy-1,5-imino- -
D
galactitol (6b).—This compound was pre-
pared from 4b (7.4 g, 18.92 mmol) as
described for the corresponding gluco com-
pound 5a. A total of 7.4 g of the crude
product was obtained, which was subjected to
borane reduction. The product was isolated as
described for the gluco isomer. Flash column
chromatography using a 6:1 CHCl3–EtOH
mixture gave product 6b (1.5 g, 30%): [h]D23
+27.0° (c 1.3, CHCl3), lit +49.0° (c 1,
Data for C-5 epimer of 9: [h]2D3 +3.1° (c
1
1.81, CHCl3); H NMR (CDCl3) l 1.98 (s, 3
H, OAc), 1.99 (s, 3 H, OAc), 2.00 (s, 3 H,
OAc), 2.02 (s, 3 H, OAc), 3.88 (m, 1 H, H-5),
4.04 (dd, 1 H, J6a,6b 11.4 Hz, J5,6b 6.3 Hz,
H6-b), 4.18 (dd, 1 H, J5,6a 3.9 Hz, H-6a), 5.15
(dd, 1 H, J4,5 9.5 Hz, J3,4 7.5 Hz, H-4), 5.15 (d,
1 H, J2,3 7.5 Hz, H-2), 5.39 (t, 1 H, H-3), 7.27
(s, broad, 1 H, NH);13C NMR (CDCl3) l 20.2,
20.3, 20.4, 50.0, 62.0, 68.0, 69.8, 70.0, 166.7,
169.3, 169.7, 170.3, 170.6.
1
CHCl3) [6b]; H NMR (D2O) l 1.21 (d, 3 H,
J5,6 6.6 Hz, H-6), 2.73 (t, 1 H, J1a,1e=J1a,2 11.9
Hz, H-1a), 3.30 (dd, 1 H, J1e,2 5.4 Hz, H-1e),
3.37 (m, 1 H, H-5), 3.50 (dd, 1 H, J2,3 9.6 Hz,
J3,4 3.1 Hz, H-3), 3.90 (d, 1 H, J4,5 3.1 Hz,
13
H-4), 3.91 (ddd, 1 H, H-2); C NMR (D2O) l
14.2, 46.1, 55.0, 64.4, 69.9, 73.1.
Preparation of 2,3,4,6-tetra-O-acetyl-5-
amino-5-deoxy- -glucono-1,5-lactam (9).—
D
The acetylated oxime 4a (1.5 g, 3.84 mmol)
was deacetylated with concomitant conversion
to the acyl hydrazide by treatment with anhyd
hydrazine (0.75 mL, 23.89 mmol) in EtOH (15
mL) at rt for 2 h. Evaporation of the solvent
gave crude 7: 1H NMR (D2O) l 4.18 (dd, 1 H,
J2,3 4.6 Hz, J3,4 7.0 Hz, H-3), 4.43 (d, 1 H,
J6a,6b 14.9 Hz, H-6a), 4.51 (d, 1 H, H-4), 4.53
Acknowledgements
This work was supported by the State of
Michigan Research Excellence Fund and by
the Synthon Corporation.
13
References
(d, 1 H, H-6b), 5.18 (d, 1 H, H-2); C NMR
(D2O) l 61.1, 69.1, 73.4, 73.5, 160.7, 173.4.
Compound 7 was hydrogenated in glacial
AcOH with 10%, Pd–C (0.4 g) at 50 °C and
300 psi pressure of H2 for 2 days. After filtra-
tion through Celite, the soln was dried on the
rotary evaporator, and the crude product was
acetylated with Ac2O (15 mL) and pyridine
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