Characteristic alkaline catalyzed degradation of kotalanol, a potent α-glucosidase inhibitor isolated from Ayurvedic traditional medicine Salacia reticulata, leading to anhydroheptitols: another structural proof

Article abstract of DOI:10.1016/j.tet.2010.03.072

Stereochemical structure of kotalanol (2), a highly potent α-glucosidase inhibitor isolated from an Ayurvedic traditional medicine Salacia reticulata, was proved by alkaline catalyzed degradation of natural kotalanol (2), in which characteristic stereospecific cyclization of the degradative side chain leading to anhydroheptitols (10 and 11) was involved.

Full text of DOI:10.1016/j.tet.2010.03.072

Tetrahedron 66 (2010) 3717–3722
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Characteristic alkaline catalyzed degradation of kotalanol, a potent a-glucosidase
inhibitor isolated from Ayurvedic traditional medicine Salacia reticulata, leading
to anhydroheptitols: another structural proof
,
a
a
a
a
a
Osamu Muraoka a , Weijia Xie , Satomi Osaki , Ayumi Kagawa , Genzoh Tanabe , Mumen F.A. Amer ,
*
Toshie Minematsu a, Toshio Morikawa b, Masayuki Yoshikawa c
a School of Pharmacy, Kinki University, 3-4-1 Kowakae, Higashi-osaka, Osaka 577-8502, Japan
b Pharmaceutical Research and Technology Institute, Kinki University, 3-4-1 Kowakae, Higashi-osaka, Osaka 577-8502, Japan
c Kyoto Pharmaceutical University, 1 Shichono-cho, Misasagi, Yamashina-ku, Kyoto 607-8412, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Stereochemical structure of kotalanol (2), a highly potent
a-glucosidase inhibitor isolated from an
Received 4 November 2009
Received in revised form 17 March 2010
Accepted 19 March 2010
Ayurvedic traditional medicine Salacia reticulata, was proved by alkaline catalyzed degradation of natural
kotalanol (2), in which characteristic stereospecific cyclization of the degradative side chain leading to
anhydroheptitols (10 and 11) was involved.
Available online 24 March 2010
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
and 6 are reported to be the most active principals in aqueous
extracts of Salacia reticulata.2b,3a Most recently, through the in-
Over the years, inhibitors of carbohydrate-processing enzymes
viz. glycosidase inhibitors have received considerable attention in
the field of chemical and medicinal research. They have many po-
tential therapeutic applications because the glycosidase enzyme-
catalyzed hydrolysis of complex carbohydrates is a widespread
phenomenon in living systems.1 From roots and stems of a Salacia
species, which have traditionally been used for treatment of di-
abetes in Sri Lanka and India, the authors had isolated highly potent
tensive SAR studies directed toward the structural elucidation of 2,
Pinto and co-workers have accomplished the first total synthesis
of 2 by an elegant manner, proving its exact stereostructure.7 The
OH
OH OH OH
OH
3'
5'
7'
1'
S+
OH
-
S+ OSO3
OH
OH
-
1
5
OSO3
a
-glucosidase inhibitors, salacinol (1) and kotalanol (2).2 Their
a-
HO
HO
HO
HO
3
glucosidase inhibitory activities were revealed to be as high as
those of voglibose and acarbose, which are widely used clinically
these days.2 Besides, their structures are quite unique, bearing
thiosugar sulfonium sulfate inner salt comprised of 1-deoxy-4-
OH
HO
HO
salacinol (1)
kotalanol (2)
OH OH
OH
thio-D-arabinofranosyl cation and 1-deoxy-aldosyl-3-sulfate anion
OH
-
S+
S+ OSO3
OH
as shown in Figure 1. Thereafter, their analogs, ponkolanol (3) and
salaprinol (4),3a as well as O-desulfonated analogs (neosalacinol 5
and neokotalanol 6)4 were also isolated from several species of the
same genus (Fig. 1).
-
OSO3
HO
OH
OH
salaprinol (4)
OH OH OH
HO
HO
ponkoranol (3)
Because of their intriguing structure and high
a-glucosidase
OH
inhibitory activities, intensive structure–activity relationship (SAR)
studies have been reported,1,3,5 and through these studies, absolute
stereochemistry of 1,2a,c 3,3b and 46 was determined. While, ste-
reochemical structure of 2 has long been left unclarified, although 2
OH
OH
X-
X-
S+ OH
S+ OH
OH
4
HO
OH
salacinol de-O-sulfonate (5)
HO
OH
HO
kotalanol de-O-sulfonate (6)
* Corresponding author. e-mail address: muraoka@phar.kindai.ac.jp (O. Muraoka).
Figure 1.
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.03.072

3718
O. Muraoka et al. / Tetrahedron 66 (2010) 3717–3722
authors have also proved the stereostructure of 2 independently by
an alkaline catalyzed degradation of natural kotalanol 2, in which
characteristic cyclization of the degraded side chain into anhy-
droheptitols was observed. In this paper full details of the process
and the alternative synthesis of the degradative products are
described.
supported by HMBC correlations observed between a-carbons in
the tetrahydrofuran ring and appropriate protons as shown in
Scheme 1. Another deshielded signals (dC5 84.8 for 8, dC5 79.6 for 9)
suggested the presence of the sulfonyloxy moiety in the products.
The mass spectrum of the mixture run in a negative mode gave
a peak at m/z 273 corresponding to the sulfonate anion [MꢁNa]ꢁ.
The mixture was then subjected to an acid catalyzed methanolysis
to afford corresponding anhydroheptitols, 3,6-anhydro-
D-glycero-
1.1. Alkaline degradation of kotalanol (2)
D
-galacto-heptitol (10) and 4,7-anhydro- -glycero- -galacto-hepti-
D
D
tol (11), in good yield. 1H and 13C NMR spectra of 8, 9, 10, and 11
were summarized in Table 1. The physical and spectral properties of
11 were completely in accord with those of the authentic specimen
obtained via an alternative route as described in the next Section
1.2.
Kotalanol (2) was treated with sodium methoxide in methanol
at 50 ꢀC for 3 h. Concomitant with the corresponding thiosugar, 1,4-
dideoxy-1,4-epithio-
D
-arabinitol (7), a mixture of sodium salts
-glycero-
-galacto-heptitol 5-O-sulfonate (8) and sodium 4,7-anhydro-
of two anhydroheptitol sulfonates, sodium 3,6-anhydro-
D
D
D-
The formation of the major sulfonate 8 would be ascribed, as
shown in Scheme 2, to the nucleophilic attack of an alkoxide anion
at C-3 (intermediate A) to the epoxide moiety formed as an in-
termediate under the basic conditions (route a), while the minor
one 9 would be formed through the direct attack of an alkoxide ion
at C-40 to C10 methylene carbon of the side chain (route b).
glycero-D-galacto-heptitol 5-O-sulfonate (9), with a ratio of ca. 2:1,
was obtained as a hardly separable mixture in 95% yield. These
sulfonates 8 and 9 were characterized as shown in Scheme 1 on the
basis of intensive 2D NMR spectroscopic studies. Observed highly
deshielded signals (dC3 85.5 and dC6 81.2 for 8, dC4 80.7 & dC7 71.9 for
9) indicated the tetrahydrofuran ring formation, which was also
79.0
OH OH70.O5 H
OH
HO 1 OH
HO
67.8
S
1
OH
HO
53.3
85.5
O
3
O
81.2
71.9
72.8
69.3
3
+
69.9 OH
a
7
S+
+
61.7
5
OH
5
OH
-
HO7
OH
HO
OSO3
80.7
HO
OSO3Na77.5
8
7
HO
OSO3Na
84.8
79.6
OH
HO
9
(8 / 9 = ca. 2/1)
kotalanol (2)
b
OH
HO
HO
OH
1
1
O
3
O
7
3
+
OH
5
7
5
OH
HO
OH
HO
78.6
OH
10
HMBC
72.7
11
Scheme 1. Reagents and conditions: (a) NaOCH3, MeOH, 50 ꢀC; (b) 5% methanolic HCl, 50 ꢀC.
Table 1
1H and 13C NMR data for compounds 8 and 9 (500 MHz), 10 and 11 (700 MHz) in CD3OD
dH
dC
dH
dC
Compound 8
Compound 9
H-1a
H-1b
H-2
H-3
H-4
H-5
H-6
H-7a
H-7b
3.59 (dd, J¼11.2, 6.3)
3.66 (dd, J¼11.2, 5.5)
3.72 (ddd, J¼6.3, 5.5, 5.5)
3.68 (dd, J¼5.5, 5.5)
4.36 (dd, J¼5.5, 3.5)
4.70 (dd, J¼5.2, 3.5)
4.15 (ddd, J¼6.3, 5.2, 4.6)
3.73 (dd, J¼12.0, 6.3)
3.82 (dd, J¼12.0, 4.6)
64.6
3.63–3.68 (2H, m)
64.6
72.9
85.5
77.5
84.8
81.2
61.7
3.80 (ddd, J¼7.0, 6.0, 1.4)
3.95 (dd, J¼9.5, 1.4)
4.10 (dd, J¼9.5, 3.5)
4.88 (dd, J¼4.6, 3.5)
4.49 (ddd, J¼8.6, 7.7, 4.6)
3.60 (dd, J¼8.6, 8.6)
3.82 (dd, J¼8.6, 7.7)
71.7
69.3
80.7
79.6
72.8
71.9
Compound 10
Compound 11
H-1a
H-1b
H-2
H-3
H-4
H-5
H-6
H-7a
H-7b
3.60 (dd, J¼11.2, 6.4)
3.64 (dd, J¼11.2, 5.6)
3.74 (ddd, J¼6.4, 5.6, 3.0)
3.79 (dd, J¼3.8, 3.0)
4.09 (dd, J¼3.8, 2.6)
3.99 (dd, J¼4.4, 2.6)
4.02 (ddd, J¼6.0, 4.4, 4.4)
3.72 (dd, J¼11.6, 6.0)
3.78 (dd, J¼11.6, 4.4)
64.5
3.61 (dd, J¼11.1, 6.9)
3.636 (dd, J¼11.1, 6.0)
3.77 (ddd, J¼6.9, 6.0, 1.8)
3.92 (dd, J¼8.8, 1.8)
3.89 (dd, J¼8.8, 3.5)
4.19 (dd, J¼4.6, 3.5)
4.33 (ddd, J¼7.0, 7.0, 4.6)
3.640 (dd, J¼8.5, 7.0)
3.87 (dd, J¼8.5, 7.0)
64.6
72.9
86.1
80.2
78.6
82.6
61.8
72.3
70.1
81.4
72.7
73.2
72.1
1H chemical shift values (
d ppm) are followed by the multiplicity of the signal and the coupling constants (J/Hz).

O. Muraoka et al. / Tetrahedron 66 (2010) 3717–3722
3719
CH3O -
HO
H
O
OH OH
HO
OH
HO
O-
OH
OH OH
O
OH
route a
OH
CH3ONa
S
O
3
S+
OH
O
-
OSO3
OH
OH
OH
+
Na+
OSO3Na
HO
HO
OSO3Na
OSO3Na
OH
HO
2
A
OH
HO
8
7
Na+
-
OH OSO3
4'
OH
HO
OH OSO3Na
OH
OH
OH
1'
route b
OH
O
S+
HO
H
+
7
CH3O -
O
OH
2
9
OH
Scheme 2. Plausible mechanism for the formation of compounds 8 and 9.
1.2. Alternative synthesis of the degradation product (11)
yield. Selective deprotection of the TBS group in 18a was accom-
plished by using TBAF to give 1,2;3,4;5,6-tri-O-isopropylidene-
glycero- -galacto-heptitol (19a)in94%yield. Attemptedsulfonationof
19a with trifluoromethanesulfonic anhydride caused cyclization of
the resultant triflate (12) to afford 4,7-anhydro-1,2;5,6-di-O-iso-
D
-
In the course of synthetic studies8 on kotalanol (2), the authors
have encountered characteristic deprotective cyclo-etherification
of polyprotected heptitols to anhydroheptitols as shown in
Scheme 3. One of the anhydroheptitols thus derived from a heptitol
D
propylidene-D-glycero-D-galacto-heptitol (20) in 77% yield. The for-
derivative,
1,2;3,4;5,6-tri-O-isopropyridene-
D
-glycero-
D
-galacto-
mation of the tetrahydrofuran derivative 20 would be attributed to
stereospecific deprotective cyclo-etherification11 of 12 as shown in
Scheme 4. Acid catalyzed deprotection of tetrahydrofuran derivative
20 with 5% methanolic hydrogen chloride gave anhydroheptitol (11),
the spectroscopic properties of which were completely in accordance
with those of the degradation product (11).
heptitol 7-O-trifrate (12), was in accord with the degradative
product (11), which led to the unambiguous identification of the
product (11).
OR1 OR2 OR2
Thus, the side chain of kotalanol (2) was elucidated to be 7-
deoxy-D-glycero-D
-galacto-heptitol, a heptitol of 20S,30S,40R,50R,60S
OR2
R2O
OR2
or
OR2
EWGO
O
R2O
OR2
OR2
stereochemistry, and the exact stereochemistry of the side chain of
2 has been successfully proved. The present work has provided the
proof of the stereostructure of 2 in an independent manner, and the
results of these two works were totally consistent. In a previous
report by one of the authors2b was a transcription error with re-
O
O
or
OR1
OR2
OR2 OR2
R1O
OR2
OR2
R2O
OR2
OR2
OR2
spect to the d
value of the H50 proton as was indicated by Pinto and
EWG: electron withdrowing group
R = H, alkyl etc.
co-workers.7 In the present study the error has been corrected (dH
5.862b/4.86), and the 1H and 13C NMR spectroscopic data of nat-
ural kotalanol (2) in D2O and in CD3OD are also presented in Table 2.
Discrepancy on the specific rotation of 2 with the literature7 has
also been reexamined. Repeated measurements of optical rotation
Scheme 3. Charateristic deprotective cyclo-etherification of heptitols.
Thus, compound 11 was prepared as following. According to the
literature,9
-arabinose was converted to 3,4-O-isopropylidene-
-arabinopyranose (13). The Wittig reaction of 13 with tert-butox-
of 2 in MeOH in the present study gave inconsistent results, among
D
27
which the value corresponding to the one we had reported {[a]
D
D
þ11.5 (MeOH)}2b was involved. After careful refiltration of the so-
ycarbonylmethylenetriphenylphosphorane followed by treatment
of the resulting mixture with TBSCl afforded a mixture of corre-
sponding olefinic esters, tert-butyl (E)-7-O-tert-butyldimethylsilyl-
24
lution, we could obtain consistent and reproducible value of [a]
D
ꢁ6.9 (c 0.34, CH3OH), which was in good accordance with the
23
Pinto’s report {[
a]
ꢁ5.7 (c 0.7, MeOH)}.7 Thus, we attribute the
D
2,3-dideoxy-5,6-O-isopropylidene-D-arabino-hept-2-enoate (E-14)
discrepancy to our insufficient filtration of the solution, and to in-
visible particles, which might be caused by either the poor solu-
bility of kotalanol in MeOH or other concomitants introduced
and its Z-isomer (Z-14) in 41% and 35% yield, respectively. After the
ester moiety of E-14 was reduced with DIBAL, the resulting allyl
alcohol, (E)-7-O-tert-butyldimethylsilyl-2,3-dideoxy-5,6-O-isopro-
during the isolation. Aqueous solution of 2 gave reproducible spe-
pylidene-
dihydroxylation by osmium tetroxide to give a mixture of 7-tert-
butyldimethylsilyl-5,6-O-isopropylidene- -glycero- -galacto-hep-
titol (16a) and 1-tert-butyldimethylsilyl-2,3-O-isopropylidene-
glycero- -gulo-heptitol (16b) in 38% and 13% yield, respectively. The
structure of the major isomer 16a was confirmed by comparison of
D-arabino-hept-2-enitol (E-15) was subjected to
24
cific rotation {[
a
]
D
þ6.7 (c 0.30, H2O)}, which was in agreement
24
with the one {[a]
D
þ7.0 (c 0.6, H2O)} reported.7
D
D
D-
L
2. Experimental
2.1. General
its 13C NMR spectroscopic properties with those of
D-glycero-D-gal-
acto-heptitol10 (17a) afterdeprotectionof allthe protective groups of
16a by treatment with 1% hydrochloric acid. Acid catalyzed hydro-
lysis of the minor one (16b) also gave the corresponding heptitol,
Mps were determined on a Yanagimoto MP-3S micromelting
point apparatus, and mps and bps are uncorrected. IR spectra were
measured on either a Shimadzu IR-435 grating spectrophotometer
or a Shimadzu FTIR-8600PC spectrophotometer. NMR spectra were
recorded on a JEOL JNM-ECA 500 (500 MHz 1H, 125 MHz 13C) or
a JEOL JNM-ECA 700 (700 MHz 1H, 175 MHz 13C) spectrometer.
D
-glycero-L
-gulo-heptitol (17b), whose 13C NMR spectroscopic
properties were in accordance with those reported.10a From the
major isomer (16a) was obtained trisacetonide, 7-O-tert-butyldi-
methylsilyl-1,2;3,4;5,6-tri-O-isopropylidene-
D-glycero-D-galacto-
heptitol (18a) by treatment with excess (CH3)2C(OCH3)2 in 42%
Chemical shifts (d) and coupling constants (J) are given in parts per

3720
O. Muraoka et al. / Tetrahedron 66 (2010) 3717–3722
OH
OH
OH
OH
7
HO
HO
HO
HO
TBSO
5
1
h
h
3
OH
OH
O
t
OH
CO2 Bu
O
OH
17b
TBSO
16b
TBSO
O
OH
OH
a
b
c
+
OH
OH
OH
OH
OH
1
O
OH
E-15
O
O
O
HO
TBSO
HO
O
HO
HO
O
E-14
3
7
13
5
OH
+ Z-isomer (Z-14)
O
OH
O
OH
17a
16a
d
O
O
O
O
O
O
1
O
O
3
O
1
O
O
O
RO
7
O
O
+O
O
O
g
3
O
f
TfO
RO
11
O
4
7
O+
5
O
OH
O
O
O
O
O
O
O
O
O
O
O
O
O
O
20
18a : R = TBS
19a : R = H
e
12
D
C
t
Scheme 4. Reagents and conditions: (a) Ph3P]CHCO2 Bu, CH3CN, 60 ꢀC, then TBSCl, imidazole, 0 ꢀC; (b) DIBAL, toluene–THF, ꢁ15 ꢀC to rt; (c) OsO4, NMO, acetone–H2O, reflux; (d)
(CH3)2C(OCH3)2, TsOH, acetone, 0 ꢀC; (e) TBAF, THF–H2O, 70 ꢀC; (f) Tf2O, 2,6-lutidine, CH2Cl2, ꢁ15 ꢀC to 0 ꢀC; (g) 5% methanolic HCl, 60 ꢀC; (h) 1% aq HCl, MeOH, reflux.
Table 2
1H (600 MHz) and 13C (150 MHz) NMR data for kotalanol (2) in CD3OD and in D2O
In CD3OD
In D2O
dH
dC
dH
dC
H-1a
H-1b
H-2
H-3
H-4
3.81 (d-like, J¼2.8)
51.1
3.75 (d-like, J¼3.4)
47.8
4.60 (td, J¼2.8, 2.8)
4.43 (br d-like)
4.00 (m)
3.97 (m)
4.03 (m)
3.99 (dd, J¼13.4, 8.5)
4.08 (dd, J¼13.4, 3.8)
4.44 (m)
4.62 (dd, J¼8.6, 1.0)
4.04 (d-like, J¼10.3)
3.78 (dd, J¼9.6, 1.4)
3.95 (m)
79.0
79.9
73.0
60.8
4.61 (td, J¼3.4, 3.4)
76.8
77.8
70.0
59.1
4.33 (dd-like, J¼3.4, 3.4)
3.96 (ddd-like, J¼7.6, 5.5, 3.4)
3.83 (dd, J¼11.0, 7.6)
3.98 (dd, J¼11.0, 5.5)
3.78 (dd, J¼13.8, 7.6)
3.97 (dd, J¼13.8, 3.4)
4.32 (ddd, J¼8.2, 7.6, 3.4)
4.53 (d-like, J¼8.2)
H-5a
H-5b
H-10a
H-10b
H-20
53.3
50.8
67.8
79.0
69.9
70.5
71.8
65.1
66.2
78.4
68.0
68.7
70.0
63.3
H-30
H-40
3.86 (d-like, J¼10.3)
H-50
3.66 (dd, J¼10.3, 1.4)
3.85 (ddd-like, J¼7.6, 5.5, 1.4)
3.54 (dd, J¼11.6, 7.6)
3.56 (dd, J¼11.6, 5.5)
H-60
H-70a
H-70b
3.66 (dd, J¼11.2, 7.1)
3.69 (dd, J¼11.2, 6.0)
1H chemical shift values (
d ppm) are followed by the multiplicity of the signal and the coupling constants (J/Hz).
million and hertz, respectively. Low-resolution and high-resolution
mass spectra were recorded on a JEOL JMS-HX 100 spectrometer.
Optical rotations were determined with a JASCO P-2200 polarim-
eter. Column chromatography was effected over Fuji Silysia
Chemical silica gel BW-200. All the organic extracts were dried over
anhydrous sodium sulfate prior to evaporation.
2.3. Acid catalyzed methanolysis of degradation products 8
and 9
A mixture of two anhydroheptitol 5-O-sulfonates (8 and 9,
3.8 mg) was treated with 5% methanolic hydrogen chloride (0.6 ml)
at 50 ꢀC for 1.5 h. Removal of the solvent left a colorless oil (4.1 mg),
which on column chromatography (CHCl3–MeOH, 5:1) gave
a hardly separable ca. 2:1 mixture (2.4 mg, 95%) of 3,6-anhydro-D-
2.2. Alkaline degradation of kotalanol (2)
glycero-D-galacto-heptitol (10) and 4,7-anhydro-D-glycero-D-gal-
acto-heptitol (11). FABMS m/z: (pos.) 217 [MþNa]þ. 1H and 13C data
for compounds 10 and 11 extracted from NMR spectra of the mix-
ture were summarized in Table 1.
A mixture of kotalanol (2, 5.8 mg, 0.014 mmol), sodium meth-
oxide (36 mg, 0.67 mmol), and methanol (1.8 ml) was heated at
50 ꢀC for 3 h. After being cooled, the reaction mixture was neu-
tralized with amberlite IR-120 PLUS (Hþ form) and condensed to
give
a
colorless oil, which on column chromatography
2.4. (E)-7-O-tert-Butyl dimethylsilyl-2,3-dideoxy-5,6-O-
isopropylidene-D-arabino-hept-2-enoate (E-14) and its Z-
(CHCl3–MeOH, 5:1) gave thiosugar5b 7 (2.0 mg, 98%) and a hardly
separable ca. 2:1 mixture (3.8 mg, 95%) of sodium salts of
isomer (Z-14)
two anhydroheptitol sulfonates, sodium 3,6-anhydro-
galacto-heptitol 5-O-sulfonate (8) and sodium 4,7-anhydro-
D
-glycero-
D-
D
-glyc-
A mixture of 3,4-O-isopropylidene-D
-arabinopyranose9 (13,
ero-
D
-galacto-heptitol 5-O-sulfonate (9). FABMS m/z: (neg.) 273
2.77 g, 14.6 mmol), tert-butoxycarbonylmethylenetriphenylphos-
phorane (8.23 g, 21.9 mmol), and acetonitrile (30 ml) was heated at
60 ꢀC for 2 h. After removal of the solvent, the residue was
[MꢁNa]ꢁ. 1H and 13C data for 8 and 9 extracted from NMR spectra of
the mixture were summarized in Table 1.

O. Muraoka et al. / Tetrahedron 66 (2010) 3717–3722
3721
triturated with a mixture of n-hexane and diethyl ether (2:1). The
5.99 (1H, dtd, J¼15.7, 5.2, 1.2 Hz, H-2). 13C NMR (125 MHz, CDCl3)
d:
solidified material was filtered and washed with a mixture of n-
hexane and diethyl ether (2:1). The combined filtrate and washings
were condensed to give a pale yellow oil (8.5 g), which was then
silylated with tert-butyldimethylsilyl chloride (2.22 g, 14.7 mmol)
in dimethylformamide (40 ml) in the presence of imidazole (1.9 g,
27.6 mmol) at 0 ꢀC for 3 h. The reaction mixture was poured
into water, and the resulting mixture was extracted with a mixture
of n-hexane and diethyl ether (2:1). The extract was washed with
brine, and condensed to give a pale yellow oil (5.4 g), which on
column chromatography (n-hexane–acetone, 50:1) gave the title E-
olefinic ester (E-14, 2.41 g, 41%) and its Z-isomer Z-14 (2.05 g, 35%).
ꢁ5.45 [tBu(CH3)2Si], 18.3 [(CH3)3CMe2Si], 24.9/27.1 [C(CH3)2], 25.8
[(CH3)3CMe2Si], 61.7 (C-7), 63.1 (C-1), 69.3 (C-4), 77.3 (C-6), 79.7 (C-
5), 108.3 [C(CH3)2],130.8 (C-3), 130.9 (C-2).
2.6. Dihydroxylation of olefinic alcohol E-15
A mixtureof crude olefinic alcohol E-15 (1.24 g), 0.039 M aqueous
osmium tetroxide (4.8 ml, 0.19 mmol), N-methylmorphorine N-ox-
ide (874 mg, 7.46 mmol), and acetone (30 ml) was heated under
reflux for 4 h. After the reaction was quenched by the addition of
sodium sulfite (940 mg, 7.46 mmol), the resulting mixture was
condensed at reduced pressure. The residue was diluted with water
(10 ml) and extracted with ethyl acetate. The extract was condensed
to give a pale brown oil (1.73 g), which on column chromatography
(CHCl3/CHCl3–MeOH, 50:1) gave 7-tert-butyldimethylsilyl-5,6-O-
23
2.4.1. Olefinic ester E-14. Colorless oil. [
a]
þ0.30 (c 1.2, CHCl3). IR
D
(neat): 3352, 1601, 1458, 1381, 1250, 1219, 1072, 1049 cmꢁ1. 1H NMR
(500 MHz, CDCl3)
d
:
0.10 [6H, s, tBu(CH3)2Si], 0.90 [9H, s,
(CH3)3CMe2Si], 1.36/1.49 [each 3H, s, C(CH3)2], 1.48 [9H, s,
CO2C(CH3)3], 3.27 (1H, d, J¼6.3 Hz, C4–OH), 3.76 (1H, dd, J¼10.9,
3.7 Hz, H-7a), 3.94 (1H, dd, J¼10.9, 7.5 Hz, H-7b), 4.20 (1H, dd,
J¼6.3, 3.7 Hz, H-5), 4.23 (1H, ddd, J¼7.5, 6.3, 3.7 Hz, H-6), 4.54 (1H,
dddd, J¼6.3, 4.0, 3.7, 2.0 Hz, H-4), 6.10 (1H, dd, J¼15.8, 2.0 Hz, H-2),
isopropylidene-
E-14) and 1-tert-butyldimethylsilyl-2,3-O-isopropylidene-
ero- -gulo-heptitol (16b, 180 mg, 13% from E-14).
D
-glycero-
D
-galacto-heptitol (16a, 520 mg, 38% from
D-glyc-
L
23
2.6.1. Compound 16a. Waxy solid. Mp 80–81 ꢀC. [
CH3OH). IR (KBr): 3391,1437,1384,1254,1223,1111,1084,1034 cmꢁ1
1H NMR (500 MHz, CD3OD) : 0.11 [6H, s, tBu(CH3)2Si], 0.92 [9H, s,
a]
þ6.29 (c 0.97,
D
6.95 (1H, dd, J¼15.8, 4.0 Hz, H-3). 13C NMR (125 MHz, CDCl3)
d:
.
ꢁ5.50 [tBu(CH3)2Si], 18.2 [(CH3)3CMe2Si], 24.8/27.0 [C(CH3)2], 25.8
[(CH3)3CMe2Si], 28.1 [CO2C(CH3)3], 61.5 (C-7), 68.8 (C-4), 77.0 (C-6),
78.8 (C-5), 80.3 [CO2C(CH3)3], 108.5 [C(CH3)2], 123.5 (C-2), 145.6 (C-
3), 165.7 [CO2C(CH3)3]. FABMS m/z: (pos.) 425 [MþNa]þ.
d
(CH3)3CMe2Si], 1.35/1.46 [each 3H, s, C(CH3)2], 3.55 (1H, dd, J¼9.2,
1.4 Hz, H-3), 3.62 (2H, d, J¼6.3 Hz, H-1a and H-1b), 3.75 (1H, dd,
J¼9.2, 2.0 Hz, H-4), 3.88 (1H, dd, J¼10.9, 6.0 Hz, H-7a), 3.93 (1H, td,
J¼6.3,1.4 Hz, H-2), 3.95 (1H, dd, J¼10.9, 4.6 Hz, H-7b), 4.27 (1H, ddd,
J¼7.2, 6.0, 4.6 Hz, H-6), 4.49 (1H, dd, J¼7.2, 2.0 Hz, H-5). 13C NMR
24
2.4.2. Olefinic ester Z-14. Colorless oil. [
a
]
þ2.33 (c 0.90, CDCl3). IR
D
(neat): 3383, 1633, 1458, 1392, 1259, 1107, 1087, 1037 cmꢁ1. 1H NMR
(125 MHz, CD3OD)
d
: ꢁ5.18 [tBu(CH3)2Si],19.3 [(CH3)3CMe2Si], 25.2/
(500 MHz, CDCl3):
d:
0.11 [6H, s, tBu(CH3)2Si], 0.92 [9H, s,
27.3 [C(CH3)2], 26.4 [(CH3)3CMe2Si], 64.1 (C-7), 65.0 (C-1), 69.6 (C-4),
71.4 (C-2), 72.1 (C-3), 77.1 (C-5), 79.4 (C-6), 109.0 [C(CH3)2]. FABMS
m/z: (pos.) 389 [MþNa]þ.
(CH3)3CMe2Si], 1.36/1.53 [each 3H, s, C(CH3)2], 1.47 [9H, s,
CO2C(CH3)3], 3.88 (1H, dd, J¼11.3, 3.7 Hz, H-7a), 4.01 (1H, d, J¼4.9 Hz,
C4–OH), 4.03 (1H, dd, J¼11.3, 5.8 Hz, H-7b), 4.25 (1H, ddd, J¼6.6, 5.8,
3.7 Hz, H-6), 4.27 (1H, dd, J¼6.6, 2.3 Hz, H-5), 5.24 (1H, dddd, J¼7.3,
4.9, 2.3, 1.5 Hz, H-4), 5.77 (1H, dd, J¼11.8, 1.5 Hz, H-2), 6.28 (1H, dd,
23
2.6.2. Compound 16b. Waxy solid. Mp 69–70 ꢀC. [
a]
D
ꢁ5.94 (c 0.96,
CH3OH). IR (KBr): 3417, 1469, 1384, 1258, 1219, 1150, 1084, 1049 cmꢁ1
.
J¼11.8, 7.3 Hz, H-3). 13C NMR (150 MHz, CDCl3)
d
: ꢁ5.46/ꢁ5.43
1H NMR (500 MHz, CD3OD)
d: 0.10 [6H, s, Bu(CH3)2Si], 0.92 [9H, s,
t
[tBu(CH3)2Si], 18.4 [(CH3)3CMe2Si], 25.1/26.9 [C(CH3)2], 25.8
[(CH3)3CMe2Si], 28.1 [CO2C(CH3)3], 61.5 (C-7), 66.5 (C-4), 77.5 (C-6),
79.8 (C-5), 80.7 [CO2C(CH3)3], 108.4 [C(CH3)2], 121.8 (C-2), 148.8 (C-
3), 165.7 [CO2C(CH3)3]. FABMS m/z: (pos.) 425 [MþNa]þ.
(CH3)3CMe2Si], 1.34/1.46 [each 3H, s, C(CH3)2], 3.61 (1H, dd, J¼11.2,
6.3 Hz, H-7a), 3.65 (1H, dd, J¼11.2, 4.9 Hz, H-7b), 3.68 (1H, dd, J¼4.3,
4.0 Hz,H-5), 3.78(1H, ddd, J¼6.3, 4.9,4.0 Hz,H-6), 3.80(1H, dd,J¼11.2,
5.7 Hz, H-1a), 3.89 (1H, dd, J¼4.3, 4.3 Hz, H-4), 3.91 (1H, dd, J¼11.2,
5.2 Hz, H-1b), 4.21 (1H, dd, J¼6.6, 5.7, 5.2 Hz, H-2), 4.38 (1H, dd, J¼6.6,
2.5. (E)-7-O-tert-Butyldimethylsilyl-2,3-dideoxy-5,6-O-
4.3 Hz, H-3).13C NMR (125 MHz, CD3OD)
d
: ꢁ5.21/ꢁ5.16 [tBu(CH3)2Si],
isopropylidene-
D-arabino-hept-2-enitol (E-15)
19.3 [(CH3)3CMe2Si], 25.4/27.6 (C(CH3)2), 26.5 [(CH3)3CMe2Si], 63.8 (C-
1), 64.5 (C-7), 71.0 (C-4), 73.0 (C-5), 73.8 (C-6), 78.3 (C-3), 79.2 (C-2),
109.5 (C(CH3)2). FABMS m/z: (pos.) 389 [MþNa]þ.
To a solution of the olefinic ester E-14 (1.5 g, 3.73 mmol) in
tetrahydrofuran (50 ml) was added dropwise a 1 M solution of
diisobutylaluminum hydride in toluene (18 ml, 18 mmol) at ꢁ15 ꢀC.
After being stirred at ꢁ15 ꢀC for 1 h, the reaction mixture was
allowed to reach room temperature, and was stirred for 2 h. The
reaction was quenched with water (10 ml), and the resulting mix-
ture was diluted with ethyl acetate (50 ml). The deposited gel was
filtered through Celite and washed with ethyl acetate. The com-
bined filtrate and washings were condensed to give the title olefinic
alcohol (E-15, 1.24 g) as a colorless oil, which was used in the next
step without purification. Analytical sample of the olefinic alcohol
E-15 was obtained by means of column chromatography (n-hex-
ane–acetone, 20:1/10:1) of a small portion of the crude product.
2.7. Confirmation of stereochemistry of tetrols 16a and 16b
A mixture of tetrol 16a (10 mg, 0.027 mol), 1% hydrochloric acid
(0.2 ml), and methanol (0.6 ml) was heated under reflux for 1.5 h.
Condensation of the mixture left a colorless solid (5.8 mg), whose
13C NMR spectroscopic properties were in good accordance with
those of D-glycero-D
-galacto-heptitol (17a) reported.10a
Following the method used for the deprotection of 16a, tetrol
16b (10 mg, 0.027 mol) was treated with 1% hydrochloric acid.
Work-up in a manner similar to that used for the preparation of 17a
gave a colorless oil (5.8 mg), whose 13C NMR spectroscopic prop-
erties were in good accordance with those of
D-glycero-L-gulo-
23
2.5.1. Olefinic alcohol E-15. [
a
]
D
ꢁ8.84 (c 0.43, CDCl3). IR (neat):
heptitol (17b) reported.10a
3425, 1594, 1465, 1366, 1250, 1215, 1078 cmꢁ1. 1H NMR (500 MHz,
t
CDCl3)
d
: 0.10 [6H, s, Bu(CH3)2Si], 0.91 [9H, s, (CH3)3CMe2Si], 1.69
2.8. 7-O-tert-Butyldimethylsilyl-1,2;3,4;5,6-tri-O-
isopropylidene- -glycero- -galacto-heptitol (18a)
(1H, br s, OH), 1.37/1.49 [each 3H, s, C(CH3)2], 3.12 (1H, d, J¼5.5 Hz,
C4–OH), 3.77 (1H, dd, J¼10.9, 4.3 Hz, H-7a), 3.95 (1H, dd, J¼10.9,
6.9 Hz, H-7b), 4.11 (1H, dd, J¼6.6, 4.0 Hz, H-5), 4.16–4.20 (2H, m, H-
1a and H-1b), 4.20 (1H, ddd, J¼6.9, 6.6, 4.3 Hz, H-6), 4.39 (1H, dddd,
J¼5.5, 5.5, 4.0, 1.2 Hz, H-4), 5.88 (1H, ddt, J¼15.7, 5.5, 2.9 Hz, H-3),
D
D
A mixture of tetrol 16a (180 mg, 0.49 mmol), 2,2-dimethox-
ypropane (2 ml, 16 mmol), p-tosic acid (40 mg), and acetone (2 ml)
was stirred at 0 ꢀC for 2 h. After the reaction was quenched by the

3722
O. Muraoka et al. / Tetrahedron 66 (2010) 3717–3722
addition of aqueous sodium hydrogen carbonate (40 ml), the
resulting mixture was extracted with dichloromethane. The extract
was washed with brine, and condensed to give a pale yellow oil
(220 mg), which on column chromatography (n-hexane–acetone,
80:1/50:1/20:1) gave the title compound (18a, 92 mg, 42%).
J¼8.3, 6.9, Hz, H-1a), 4.02 (1H, d, J¼10.9 Hz, H-7b), 4.07 (1H, dd,
J¼8.3, 6.9 Hz, H-1b), 4.31 (1H, ddd, J¼6.9, 6.9, 4.3 Hz, H-2), 4.78 (1H,
dd, J¼6.0, 3.7 Hz, H-6), 4.82 (1H, dd, J¼6.0, 4.0 Hz, H-5). 13C NMR
(125 MHz, CDCl3) d: 24.6/25.2/26.0/26.4 [C(CH3)2], 66.1 (C-1), 69.1
(C-3), 73.2 (C-7), 76.5 (C-2), 80.6 (C-6) 80.7 (C-5), 82.4 (C-4), 109.2/
112.2 [C(CH3)2]. FABMS m/z: (pos.) 275 [MþH]þ.
26
2.8.1. Compound 18a. Colorless oil. [
a
]
D
þ31.3 (c 0.8, CHCl3). IR
(neat): 1462, 1373, 1250, 1219, 1157, 1072 cmꢁ1. 1H NMR (500 MHz,
CDCl3)
: 0.067/0.074 [each 3H, s, tBu(CH3)2Si], 0.89 [9H, s,
(CH3)3CMe2Si], 1.380(3H)/1.384(6H)/1.45(3H)/1.46(3H)/1.56(3H)
2.11. 4,7-Anhydro-D-glycero-D-galacto-heptitol (11)
d
A solution of the bisacetonide 20 (6.2 mg, 0.02 mmol) in 5%
methanolic hydrogen chloride (0.8 ml) was stirred at 60 ꢀC for 24 h.
Concentration of the mixture left the title compound 11 (4.4 mg) as
a pale yellow solid. Analytical sample was obtained by re-
crystallization from a mixture of diethyl ether and methanol.
[each s, C(CH3)2], 3.59 (1H, dd, J¼9.5, 4.0 Hz, H-7a), 3.78 (1H, dd,
J¼9.5, 9.5 Hz, H-7b), 3.81 (1H, dd, J¼7.7, 7.7 Hz, H-1a), 4.01 (1H, dd,
J¼7.7, 6.3 Hz, H-1b), 4.18 (1H, ddd, J¼9.5, 5.5, 4.0 Hz, H-6), 4.20 (1H,
m, H-3), 4.22 (1H, ddd, J¼7.7, 6.3, 3.8, Hz, H-2), 4.43 (1H, dd, J¼7.2,
7.2 Hz, H-4), 4.45 (1H, dd, J¼7.2, 5.5 Hz, H-5). 13C NMR (125 MHz,
: ꢁ5.55/ꢁ5.36 [tBu(CH3)2Si], 18.4 [(CH3)3CMe2Si], 25.08/
26
2.11.1. Compound 11. Colorless prisms. Mp 129–129.5 ꢀC. [
a]
CDCl3)
d
D
25.59/25.85/26.41/26.84/27.78 [C(CH3)2], 25.9 [(CH3)3CMe2Si], 62.1
(C-7), 66.4 (C-1), 75.2 (C-2), 75.3 (C-4), 75.7 (C-5) 76.4 (C-3), 76.8
(C-6), 108.5/109.1/109.7 [C(CH3)2]. FABMS m/z: (pos.) 469 [MþNa]þ.
ꢁ12.8 (c 0.46, CH3OH). IR (KBr): 3389, 1419, 1397, 1383, 1329, 1287,
1252, 1228, 1206, 1188, 1148, 1111, 1099, 1078, 1057, 1040 cmꢁ1
.
FABMS m/z: (pos.) 217 [MþNa]þ. FAB-HRMS m/z: 217.0684
(C7H14O6Na requires 217.0688). 1H and 13C NMR spectroscopic
properties of 11 were in accord with those of the product obtained
by alkaline degradation of kotalanol (2).
2.9. 1,2;3,4;5,6-Tri-O-isopropylidene-D-glycero-D-galacto-
heptitol (19a)
A mixture of compound 18a (70 mg, 0.16 mmol), a 1 M solution
of tetrabutylammonium fluoride in tetrahydrofuran (0.7 ml,
0.7 mmol), tetrahydrofuran (2 ml), and water (0.2 ml) was heated
at 70 ꢀC for 2 h. After being cooled, the mixture was poured into ice-
water (20 ml) and extracted with ethyl acetate. The extract was
washed with brine and condensed to give a pale yellow oil (67 mg),
which on column chromatography (n-hexane–ethyl acetate, 10:1)
gave the title compound (19a, 49 mg, 94%).
Acknowledgements
This work was supported by ‘High-Tech Research Center’
Project for Private Universities: matching fund subsidy from MEXT
(Ministry of Education, Culture, Sports, Science and Technology),
2007–2011 and also supported by a grant-in aid for scientific
research by the Japan Society for the Promotion of Science (JSPS).
References and notes
25
2.9.1. Compound 19a. Colorless oil. [
a
]
D
þ30.6 (c 0.8, CHCl3). IR
(neat): 3479, 1456, 1373, 1248, 1216, 1061, 1047 cmꢁ1
(700 MHz, CDCl3) : 1.384/1.385/1.40/1.47/1.52/1.58 [each 3H, s,
.
1H NMR
1. Recent review relevant to the present work: Mohan, S.; Pinto, B. M. Carbohydr.
Res. 2007, 342, 1551–1580.
d
2. (a) Yoshikawa, M.; Murakami, T.; Shimada, H.; Matsuda, H.; Yamahara, J.; Ta-
nabe, G.; Muraoka, O. Tetrahedron Lett. 1997, 38, 8367–8370; (b) Yoshikawa, M.;
Murakami, T.; Yashiro, K.; Matsuda, H. Chem. Pharm. Bull. 1998, 46, 1339–1340;
(c) Yoshikawa, M.; Morikawa, T.; Matsuda, H.; Tanabe, G.; Muraoka, O. Bioorg.
Med. Chem. 2002, 10, 1547–1554.
3. (a) Yoshikawa, M.; Xu, F.; Nakamura, S.; Wang, T.; Matsuda, H.; Tanabe, G.;
Muraoka, O. Heterocycles 2008, 75, 1397–1405; (b) Johnston, B. D.; Jensen, H. H.;
Pinto, B. M. J. Org. Chem. 2006, 71, 1111–1118.
C(CH3)2], 2.50 (1H, br s, OH), 3.67 (1H, dd, J¼11.8, 5.0 Hz, H-7a), 3.71
(1H, dd, J¼11.8, 5.6 Hz, H-7b), 3.75 (1H, dd, J¼8.0, 6.6 Hz, H-1a), 4.09
(1H, dd, J¼8.0, 6.6 Hz, H-1b), 4.16 (1H, dd, J¼6.2, 4.0 Hz, H-5), 4.218
(1H, ddd, J¼6.2, 5.6, 5.0 Hz, H-6), 4.223 (1H, dd, J¼6.6, 6.6 Hz, H-3),
4.35 (1H, dd, J¼6.6, 4.0 Hz, H-4), 4.36 (1H, ddd, J¼6.6, 6.6, 6.6 Hz, H-
2). 13C NMR (175 MHz, CDCl3)
d: 25.33/25.34/25.53/26.58/26.61/
4. (a) Ozaki, S.; Oe, H.; Kitamura, S. J. Nat. Prod. 2008, 71, 931–934; (b) Oe, H.;
Ozaki, S. Biosci. Biotechnol. Biochem. 2008, 72, 1962–1964; (c) Minami, Y.; Kur-
iyama, C.; Ikeda, K.; Kato, A.; Takebayashi, K.; Adachi, I.; Fleet, W. J. G.; Ketta-
wan, A.; Okamoto, T.; Asano, N. Bioorg. Med. Chem. 2008, 16, 2734–2740; (d)
Muraoka, O.; Xie, W.; Tanabe, G.; Amer, M. F. A.; Minematsu, T.; Yoshikawa, M.
Tetrahedron Lett. 2008, 49, 7315–7317; (e) Tanabe, G.; Xie, W.; Ogawa, A.;
Minematsu, T.; Yoshikawa, M.; Muraoka, O. Bioorg. Med. Chem. Lett. 2009, 19,
2195–2198; (f) Tanabe, G.; Yoshikai, K.; Hatanaka, T.; Yamamoto, M.; Shao, Y.;
Minematsu, T.; Muraoka, O.; Wang, T.; Matsuda, H.; Yoshikawa, M. Bioorg. Med.
Chem. 2007, 15, 3926–3973.
5. (a) Nasi, R.; Patrick, B. O.; Sim, L.; Rose, D. R.; Pinto, B. M. J. Org. Chem. 2008, 73,
6172–6181; (b) Muraoka, O.; Yoshikai, K.; Takahashi, H.; Minematsu, T.; Lu, G.;
Tanabe, G.; Wang, T.; Matsuda, H.; Yoshikawa, M. Bioorg. Med. Chem. 2006, 14,
500–509; (c) Matsuda, H.; Yoshikawa, M.; Morikawa, T.; Tanabe, G.; Muraoka,
O. J. Trad. Med. 2005, 22, 145–153; (d) Muraoka, O.; Ying, S.; Yoshikai, K.;
Matsuura, Y.; Yamada, E.; Minematsu, T.; Tanabe, G.; Matsuda, H.; Yoshikawa,
M. Chem. Pharm. Bull. 2001, 49, 1503–1505 and references cited therein.
6. Tanabe, G.; Sakano, M.; Minematsu, T.; Matusda, H.; Yoshikawa, M.; Muraoka,
O. Tetrahedron 2008, 64, 10080–10086.
7. Jayakanthan, K.; Mohan, S.; Pinto, B. M. J. Am. Chem. Soc. 2009, 131, 5621–5626.
8. Tanabe, G.; Matsuoka, K.; Minematsu, T.; Morikawa, T.; Ninomiya, K.; Matsuda,
H.; Yoshikawa, M.; Murata, H.; Muraoka, O. J. Pharm. Soc. Jpn. 2007, 127, 129–130.
9. Ireland, R. E.; Courtney, L.; Fizsimmons, B. J. J. Org. Chem. 1983, 48, 5186–5198.
10. (a) Angyal, S. J. Carbohydr. Res. 1984, 126, 15–26; (b) Lewis, D. J. Chem. Soc.,
Perkin Trans. 2 1986, 467–470; (c) Ishizu, T.; Winarno, H.; Tsujino, E.; Morita, T.;
Shibuya, H. Chem. Pharm. Bull. 2002, 50, 489–492.
11. Similar mode of deprotective cyclo-etherification has been reported for the
carbohydrate-derived allylic alcohols, see Cribu´ , R.; Cumpstey, I. Chem. Commun.
2008, 1246–1248.
27.4 [C(CH3)2], 61.8 (C-7), 66.2 (C-1), 74.2 (C-4), 75.00 (C-2), 75.02
(C-5), 77.6 (C-6), 78.2 (C-3), 109.0/109.8/110.0 [C(CH3)2]. FABMS m/
z: (pos.) 355 [MþNa]þ.
2.10. 4,7-Anhydro-1,2;5,6-di-O-isopropylidene-
-galacto-heptitol (20)
D-glycero-
D
A solution of compound 19a (20 mg, 0.06 mmol) was added to
a mixture of trifluoromethanesulfonic anhydride (100 l, 0.6 mol),
m
m
lutidine (0.35 ml, 3 mmol), and dichloromethane (1 ml) at ꢁ15 ꢀC,
and the reaction mixture was stirred at 0 ꢀC for 5 h. After addition
of aqueous sodium hydrogen carbonate (5 ml), the resulting mix-
ture was extracted with ethyl acetate. The extract was washed with
brine and condensed to give a brown oil (50 mg), which on column
chromatography (chloroform) gave the title compound (20,
12.7 mg, 77%).
26
2.10.1. Compound 20. Colorless oil, [
a
]
ꢁ36.5 (c 0.6, CHCl3). IR
D
(neat): 3472, 1456, 1373, 1255, 1209, 1159, 1105, 1087, 1058 cmꢁ1. 1H
NMR (500 MHz, CDCl3) : 1.35/1.39/1.46/1.49 [each 3H, s, C(CH3)2],
d
2.52 (1H, br s, OH), 3.42 (1H, dd, J¼8.6, 4.0 Hz, H-4), 3.50 (1H, dd,
J¼10.9, 3.7 Hz, H-7a), 3.87 (1H, dd, J¼8.6, 4.3 Hz, H-3), 3.96 (1H, dd,