Trihydroxy-2-thiaquinolizidine derivatives as a new class of bicyclic glycosidase inhibitors

Article abstract of DOI:10.1016/j.tet.2005.02.002

Trihydroxy-2-thiaquinolizidines, a new class of bicyclic dideoxy-iminohexitol glycosidase inhibitor derivatives with nominally the d-gluco, l-ido, d-manno and l-gulo configurations were synthesized. X-ray analyses indicated that the preferred conformation for d-gluco and d-manno derivatives was a flat trans-fused system. Unlike deoxynojirimycin, the compound with d-gluco configuration was selective for α-glucosidases (yeast and rice) and showed no inhibitory activity towards β-glucosidase (almond), α-galactosidase (green coffee beans), α-galactosidase (E. coli) and α-mannosidase (jack bean), while the l-ido derivative was specific for β-glucosidase (almond).

Full text of DOI:10.1016/j.tet.2005.02.002

Tetrahedron 61 (2005) 3805–3811
Trihydroxy-2-thiaquinolizidine derivatives as a new class of
bicyclic glycosidase inhibitors
*
Li Gao and Rawle I. Hollingsworth
Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
Received 4 December 2004; revised 31 January 2005; accepted 1 February 2005
Abstract—Trihydroxy-2-thiaquinolizidines, a new class of bicyclic dideoxy-iminohexitol glycosidase inhibitor derivatives with nominally
the D-gluco, L-ido, D-manno and L-gulo configurations were synthesized. X-ray analyses indicated that the preferred conformation for D-gluco
and D-manno derivatives was a flat trans-fused system. Unlike deoxynojirimycin, the compound with D-gluco configuration was selective
for a-glucosidases (yeast and rice) and showed no inhibitory activity towards b-glucosidase (almond), a-galactosidase (green coffee beans),
a-galactosidase (E. coli) and a-mannosidase (jack bean), while the L-ido derivative was specific for b-glucosidase (almond).
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Despite their promise, glycosidase inhibitors such as
deoxynojirimycin 1 and castanospermine 2, (generally
known as iminoalditols or aza-sugars) have not realized
their full clinical potential. This is largely because of a lack
of commercially viable syntheses and difficulty in preparing
a comprehensive palette of variant structures. In some cases
such as deoxynojirimycin there is also the problem of too
low specificity.1,2 Iminoalditols are typically plant alkaloids
and many of the possible drug candidates are available in
only small exploratory amounts. The potential medical
applications for these compounds and their derivatives are
numerous and range from diabetes3–6 and other metabolic
disorders through antimicrobials,7–11 cancer,12 autoimmune
diseases,13–18 neurological19 and metabolic20,21 disorders.
Because of their rigidity and the added interaction of the
second ring, bicyclic systems such as castanospermine 2 and
swainsonine 3 are especially interesting.
As part of our ongoing work on the development of
strategies for the preparation of glycosidase inhibitors, we
explored the possibility of synthesizing analogs of deoxy-
nojirimycin 1 and related compounds in which O-6 were
replaced by a sulfur atom. We also envisaged bridging the
6-position to the ring nitrogen with a 2-carbon fragment to
form a trihydroxy-2-thiaquinolizidine ring system thus
increasing rigidity and lipophilicity. Such systems have
never been reported before but hold great promise because
the formation of a carbon–carbon bond is circumvented as
in 2 and 3. The presence of sulfur (closely related to oxygen)
Keywords: Glycosidase inhibitors; Aza-sugars; Iminoalditols; Glucosi-
at a position that is normally oxygenated is also a decided
dases; Mannosidases; Enzymology; Drugs.
advantage. If such systems could be reached using a general
strategy, analogs with differing configurations at the various
* Corresponding author. Tel.: C1 5173530613; fax: C1 5174321113;
e-mail: holling7@msu.edu
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.02.002

3806
L. Gao, R. I. Hollingsworth / Tetrahedron 61 (2005) 3805–3811
carbon centers and differing substitution patterns could be
made, increasing the chance of obtaining compounds with
useful therapeutic potential. The strategy could, in principle,
be extended to iminopentitol analogs. A total of four such
systems (4a, 4b, 5a, and 5b) were prepared corresponding to
the D-gluco, L-ido, D-manno, L-gulo configurations. The
synthesis is illustrated below in Scheme 1.
or imine by hydride (e.g., borane or cyanoborohydride)
should yield an amine which could then be cyclized to form
a lactam. Reduction of the lactam should yield the
thiaquinolizidine system.
2. Results
The key feature of the reaction scheme is the oxidation of a
6-bromo b-glycoside to give a 6-bromo-5-ulosonic acid
alkyl ester (Scheme 1). This oxidation has been reported to
give the keto–ester functionality in high yield.22 Reaction of
this a-halo ketone with an a-aminothiol should lead to rapid
thioether formation and immediate cyclization to an aminal
which could quickly form an imine. Reduction of the aminal
The reaction sequence involved the preparation of a
peracylated 6-bromo-6-deoxy-glycoside 10 which was
obtained by selective conversion of the primary hydroxyl
group of methyl b-D-glucoside to a bromo-group followed
by treatment with pivaloyl chloride (trimethylacetyl
chloride) in pyridine to protect the remaining hydroxyl
groups. The pivaloyl group was selected over the acetyl
Scheme 1. Synthesis of trihydroxy-2-thiaquinolizidine derivatives. (i) Ph3P, CBr4, pyridine; (ii) PivCl, pyridine; (iii) CrO3, Ac2O, HOAc; (iv) HS(CH2)2NH2,
CH3OH; (v) NaCNBH3, CH3OH; (vi) Na2CO3, CHCl3; (vii) BH3–THF; (viii) NaOCH3, CH3OH.

L. Gao, R. I. Hollingsworth / Tetrahedron 61 (2005) 3805–3811
3807
group because of the partial deacylation of acetates by
aminoethanethiol, resulting in difficulty in purification and
low yield. Oxidation of 10 with chromium trioxide in acetic
acid afforded a 5-ulosonic acid ester 12. The oxidation of
acetylated b-glycopyranosides by chromium trioxide has
been reported by Angyal and James22 to afford 5-keto esters,
independent of the configurations on C2, C3, or C4.
The oxidation is specific to b-glycopyranosides, while
a-glycopyranosides are not attacked. Treatment of 12 with
2-aminoethanethiol yielded the aminal 14 directly which
underwent reduction by NaBCNH3 and cyclization to the
lactam 15a and the L-ido isomer 15b. There was some
variability in the actual amount of lactam 15b ranging from
traces to 2.5:1 in favor of the D-gluco analog. Reduction of
the lactams with borane and deacylation yielded the desired
compounds 4a and 4b.The final and intermediate products
were characterized by a very high degree of crystallinity.
Table 1 shows the inhibition constants (mM) for compounds
4a, 4b, 5a, and 5b. Compound 4a displayed competitive
inhibition against both yeast and rice a-glucosidase with Ki
of 330 and 900 mM, respectively. No inhibitory activity
towards b-glucosidase (almond), a-galactosidase (green
coffee beans), b-galactosidase (E. coli) and a-mannosidase
(jack bean) was observed. Compound 4b was tested against
a-glucosidase (yeast), b-glucosidase and a-mannosidase.
It showed an opposite inhibition pattern to compound 4a.
It only inhibits b-glucosidase with Ki value 1 mM without
inhibiting a-glucosidase and a-mannosidase. Compound 5a
and 5b were also tested for a-mannosidase (jack beans), but
no inhibition was observed.
3. Discussion
The synthetic strategy for the preparation of trihydroxy-2-
thiaquinolizidines proved to be quite efficient and direct.
The relative ease of preparation of these analogs and the
generality of the method open the possibility for the
preparation of a clinically relevant series of selective
inhibitory compounds. The inhibition results indicated that
compound 4a was active only against a-glucosidases. No
inhibition of b-glucosidases was observed. This is consist-
ent with the observation that deoxynojirimycin type
inhibitors with nitrogen atom at the ring oxygen position
are more selective for a-glucosidase.24–26 According to the
stereoelectronic requirements, in a-glycosidases, the posi-
tively charged leaving group and the lone pair of the ring
oxygen are positioned antiperiplanar and cooperatively
facilitate the glycosidic bond cleavage. Thus, oxocarbenium
ion can be formed directly, and this oxocarbenium ion with
positive charge at ring oxygen is an important transition
state for a-glucosidases. For b-glycosidases, the glycosidic
bond cleavage cannot receive aid form the lone pair of the
ring oxygen, so the ring could flip to a boat (17) or other
conformations (18) to facilitate the bond cleavage. Substrate
distortion is generally the case for b-glycosidases.27–31
The same reaction sequence was applied to methyl b-D-
mannopyranoside (7), and the D-manno lactam 16a and
L-gulo lactam 16b was obtained in 4:1 ratio in favor of the
D-manno lactam. Reduction of lactams and deprotection
yielded products 5a and 5b in good yields. X-ray analysis of
4a and 5a (Fig. 1) indicated two six-membered rings with
relaxed chair conformation for both D-gluco and D-manno
products. A trans-diequatorial type fusion between the rings
gives the molecules an overall flat geometry. The expected
intermediate oxocarbenium species is very flat because of
the double bond character between the ring oxygen and C-1.
The inhibitory activity of four trihydroxy-2-thiaquinolizi-
dines against a series of enzymes was tested. Enzymes were
assayed according to standard procedures23 by following the
hydrolysis of nitrophenyl glycosides spectrophotometrically
or by evaluating the reducing sugar formed in some
glucosidase assays. The enzymes used were a-glucosidase
(yeast and rice), b-glucosidase (almond), a-galactosidase
(green coffee beans), b-galactosidase (E. coli) and
a-mannosidase (jack beans).
Figure 1. X-ray structures of 7(S),8(R),9(R),10(S)-trihydroxy-2-thiaquinolizidine 4a and 7(R),8(R),9(R),10(S)-trihydroxy-2-thiaquinolizidine 5a showing the
trans-type ring junction and overall flat geometry.
Table 1. Inhibition constants (mM) for compounds 4a, 4b, 5a, and 5b
Enzymes
4a
4b
5a
5b
a-Glucosidase (yeast)
a-Glucosidase (rice)
b-Glucosidase (almond)
a-Galactosidase (green coffee beans)
b-Galactosidase (E. coli)
a-Mannosidase (jack beans)
0.33
0.9
ni
ni
ni
ni
—
—
—
—
—
ni
—
—
—
—
—
ni
—
1.0
—
—
ni
ni
ni, No inhibition observed in this concentration range; —, not determined.

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L. Gao, R. I. Hollingsworth / Tetrahedron 61 (2005) 3805–3811
Compound 4a, with its rigid bicyclic structure, is locked in
its trans-fused chair conformation, so it cannot flip or
change to other conformations. Therefore, it showed no
inhibition against b-glucosidase. In contrast, compound 4b
showed specific inhibition against b-glucosidase while no
inhibition for a-glucosidase. This is almost certainly due to
a difference in conformation to the D-gluco compound
brought about by flattening or ring inversion to place the
thiomethyl group in an equatorial position. Compound 4b
should be more stable in conformation 20 instead of
conformation 19. Conformation 20 corresponds to the one
that matches the transition state for a b-glycoside under-
going hydrolysis under stereoelectronic control.
activity against a-mannosidase (jack beans). This is
probably because of the rigid structure. It is also possible
that the second 6-member ring might interfere with any
change in ring geometry that might be necessary to facilitate
binding of the inhibitor to the active site of the enzyme.
Castanospermine is one of the most active bicyclic systems.
It showed poor activity against yeast a-glucosidase but
strongly inhibited the rice enzyme. However, it showed non-
selectivity by inhibiting almond b-glucosidase. It has
relatively flexible structure compared to 4a and 4b, and it
presented a twisted boat conformation of the 6-member ring
when bounded to Exo-b-(1,3)-gluconase.36 This distortion
cannot be made for compound 4a which has a trans-
diequatorial type fusion between the rings. Compound 22,
which is the slightly ring-expanded version of the potent
a-mannosidase inhibitor swainsonine (3) showed complete
loss of inhibition of a-mannosidase (Table 2). As a general
rule, decalin-type bicyclic systems show much reduced or
no inhibitory activity compared to their acyclic or
octahydroindene-type analogs. Therefore, one important
conclusion that can be made is that structural flexibility
leads to nonspecific inhibitory activity. Monocyclic systems
generally showed poor specificity by inhibiting both a-
and b-glycosidases because of their flexible structures.
Castanospermine (2) and the thiaquinolizidine described
here (4a) are the most impressive of the reported bicyclic
aza-type iminosugar derivatives with a nitrogen atom at the
ring junction. Compound 4a was superior against and
selective for a-glucosidases compared to castanospermine.
Thiaquinolizidines, therefore represent a significant
advancement in this area.
The activities and specificities of the known aza-bicyclic
systems and key monocyclic systems are shown in Table 2.
Compared to deoxynojirimycin 1, compound 4a is a
relatively weak inhibitor, but it showed specificity for
a-glucosidase. No inhibitory activity towards b-glucosidase
(almond), a-galactosidase (green coffee beans), a-galacto-
sidase (E. coli) and a-mannosidase (jack bean) was
observed. One of the major problems with the use of
iminosugars and their derivatives as inhibitors is the lack of
specificity. Hence the last two entries in Table 2 have low Ki
values but show poor specificity. Compound 4a showed
very specific activity against a-glucosidase, and 4b showed
specificity against b-glucosidase. The specificity comes
from the structural rigidity, which prevents 4a from
distortion to boat or other conformations that are important
for mimicking the b-glucosidase transition state. Compound
4b is expected to exist in a conformation that favors
b-glucosidase inhibition. Compound 5a and 5b showed no
4. Conclusion
Trihydroxy-2-thiaquinolizidines are bicyclic systems where
reasonable inhibitory activity and absolute specificity for
one anomer were obtained. Although only modest inhibitory
activity was observed, the specificity is extremely high. This
is a very important point. For iminopentitol glycosidase
inhibitors, the general rule is that high inhibitory activity
always comes along with low specificity tremendously
limiting their utility as drugs. Modest inhibitors combined
Table 2. Comparison of inhibition activity Ki, mM (IC50, mM) for iminoalditol transition state analogs
Enzymes
4a
21
2132
2233
11
2334,35
a-Glucosidase
(yeast)
330
O1500
—
IC50O2000
12.6
w10
a-Glucosidase (rice)
b-Glucosidase
(almond)
900
ni
0.015
1.5
—
ni
—
IC50O2000
0.01
47
—
8
a-Galactosidase
(green coffee beans)
b-Galactosidase
(E. coli)
a-Mannosidase
(jack beans)
ni
ni
ni
—
—
—
ni
—
—
—
—
—
—
—
w10
w10
9
IC50O2000
—, Not determined; ni, no inhibition observed.

L. Gao, R. I. Hollingsworth / Tetrahedron 61 (2005) 3805–3811
3809
with efficient drug delivery strategies to keep local
5.3. Synthetic methods
concentrations high enough would constitute an excellent
therapeutic approach. This study also identifies a strategy
for changing the specificity of an inhibitor by inverting the
stereochemistry at a critical position to increase the stability
of inverted ring structures. The thiaquinolizidines described
here are relatively easily accessible. Their ease of
preparation and specificity therefore represent significant
potential for further therapeutic advancement.
5.3.1. Methyl 6-bromo-6-deoxy-b-D-glucopyranoside.37
(8) To a stirred solution of methyl b-D-glucopyranoside 6
(10.15 g, 50 mmol) in anhydrous pyridine (300 mL) at 0 8C
were added triphenylphosphine (26.2 g, 100 mmol) and
carbon tetrabromide (24.87 g, 75 mmol). The resulting
mixture was protected from moisture and stirred at 0 8C
for 10 min. It was then allowed to warm to 65 8C and was
stirred for an additional 4 h. Methanol (10 mL) was added to
decompose any excess reagent. The solvent was removed by
evaporation and the residue was purified by column
chromatography (CH2Cl2, followed by 20:1 CH2Cl2/
MeOH). Crystallization from methanol-hexanes afforded
white crystalline solid (10.96 g, 85%), mp 149–150 8C, lit.
mp38 154 8C, [a]D20 K27.68 (c 0.22, H2O).
5. Experimental
5.1. General procedures
Melting points were measured on a Ficher–Johns melting
point apparatus. Optical rotations were measured (lZ
589 nm) at room temperature using a Jasco P-1010
polarimeter. IR spectra were recorded on a FT-IR instru-
ment. The 1H (and 13C) NMR spectra were recorded at 500
(125.5) MHz on a Varian VXR spectrometer. The
HRFABMS mass spectra were obtained using a Jeol
HX-110 double-focusing mass spectrometer operating in
positive ion mode.
5.3.2. Methyl 6-bromo-6-deoxy-2,3,4-tri-O-pivaloyl-b-D-
glucopyranoside (10). Pivaloylation of 8 (6.73 g, 26 mmol)
by trimethylacetyl chloride (28.8 mL, 32.4 mmol) in
pyridine (300 mL) at room temperature for 2 days afforded
an white solid 6 (11.2 g, 84%), mp 109–110 8C, [a]2D0 K2.48
(c 0.31, CHCl3). IR (CH3Cl) nmax 2971.7, 1745.6,
1
1140.9 cmK1. H NMR (500 MHz, CDCl3) d 5.29 (1H, t,
JZ9.5 Hz), 4.99 (2H, t, JZ9.7 Hz), 4.42 (1H, d, JZ
8.0 Hz), 3.70 (1H, m), 3.50 (3H, s), 3.39–3.12 (2H, m), 1.14
(9H, s), 1.13 (9H, s), 1.08 (9H, s); 13C NMR (125.5 MHz,
CDCl3) d 177.14, 176.63, 176.51, 101.36, 73.7, 71.9, 71.2,
70.8, 57.1, 38.8, 38.7, 30.6 ppm; HRFABMS (MCHC)
Calcd 509.1750, found 509.1736.
5.2. Inhibition assays
Inhibitory potency was determined by spectrophoto-
metrically measuring the residual hydrolytic activities of
the glycosidases against the corresponding nitrophenyl a- or
b-D-glycopyranoside. The glycosidases used were a-gluco-
sidase (yeast), a-glucosidase (rice), b-glucosidase (almond),
a-galactosidase (green coffee beans), b-galactosidase (E.
coli) and a-mannosidase (jack beans). All enzymes were
purchased from Sigma. Each assay was performed in a
phosphate or an acetate buffer at the optimal pH for each
enzyme. Inhibition studies (except rice a-glucosidase) were
performed by adding the inhibitor to a final concentration of
0.05–11 mM to the respective buffer solutions along with
enzyme. The solutions were incubated at 37 8C before
adding substrates to the reactions. The absorbance of
the resulting mixture was determined at 400 nm (for
p-nitrophenol).
5.3.3. Methyl 6-bromo-2,3,4-tri-O-pivaloyl-5-keto-ester
(12). To a solution of 10 (1 g, 1.96 mmol) in acetic acid
(100 mL) and acetic anhydride (10 mL), chromium trioxide
(1.18 g, 11.8 mmol) was added and the suspension was
stirred at room temperature for 3 h. The mixture was then
poured slowly into cold water (500 mL). The water was
extracted 5 times with CH2Cl2 and the combined organic
phase was washed with brine, saturated sodium bicarbonate
and dried (Na2SO4), concentrated. The resulting residue was
passed through a small pad of silica gel to give 12 as a
colorless oil (1 g, 97%), [a]2D0 C36.58 (c 0.12 CHCl3), IR
1
(CH2Cl2) nmax 2975.85, 1743.63, 1132.00 cmK1. H NMR
(500 MHz, CDCl3) d 5.72, (1H, t, JZ4.8 Hz), 5.57 (1H, d,
JZ4.5 Hz), 5.23 (1H, d, JZ5.0 Hz), 4.12 (1H, d, JZ
14.0 Hz), 4.01 (1H, d, JZ13.5 Hz), 3.72 (3H, s), 1.25 (9H,
s), 1.21 (9H, s), 1.18 (9H, s); 13C NMR (125.5 MHz, CDCl3)
d 194.5, 177.1, 176.9, 176.8, 167.1, 72.9, 70.2, 69.4, 52.7,
38.9, 38.8, 38.7, 31.6, 27.0, 26.9 ppm; HRFABMS (MC
HC) Calcd 523.1543, found 523.1530.
For rice a-glucosidase inhibition, maltose was used as the
substrate, and the assay was based on the glucose
oxidase/peroxidase enzyme procedure. In this assay, the
glucose released from maltose can be oxidized by glucose
oxidase to generate D-gluconic acid and hydrogen peroxide.
Under the catalysis of peroxidase, hydrogen peroxide reacts
with dianisidine to give the oxidized form which forms a
brown color. The absorbance of the solution was determined
at 500 nm for oxidized o-dianisidine. The assay was
performed in sodium acetate buffer at pH 4.0 at 37 8C.
The inhibitor was added to a final concentration of 0.4 and
8.9 mM to the substrate solution. The enzyme was added to
the solution at 37 8C, and the reaction was stopped after 10
and 30 min by adding dilute perchloric acid solution. The
glucose oxidase/peroxidase solution was pipetted into the
reaction mixture, and incubate at 37 8C for 30 min. The
absorbance of the solution was determined at 500 nm.
5.3.4. Lactam (15a) and (15b). A solution of 7 (7 g,
13.4 mmol) and 2-aminoethanethiol (1.24 g, 16.1 mmol) in
methanol (250 mL) was stirred at room temperature for 1 h,
followed by addition of sodium cyanoboron hydride (1.26 g,
20 mmol). The reaction mixture was stirred overnight and
sodium carbonate was added to facilitate the lactam
cyclization. After stirred for several hours, the suspension
was filtered and acetic acid (2 mL) was added and
concentrated. The residue was purified by column chroma-
tography (10:1 hexanes/acetone) to yield two lactam
diastereomers 15a and 15b (4.64 g, 73.6%), the ratio is
2.5:1.

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L. Gao, R. I. Hollingsworth / Tetrahedron 61 (2005) 3805–3811
Lactam 15a (3.31 g, 52.6%) was given as a white solid, mp
188–190 8C, [a]D20 C12.68 (c 0.1 CHCl3), IR (CHCl3) nmax
(84%). 1H NMR (500 MHz, D2O) d 3.91 (1H, d, JZ2 Hz),
3.75 (1H, d, JZ2.5 Hz), 3.73 (1H, d, JZ2.5 Hz), 3.571 (2H,
dd, JZ11.8, 5.8 Hz), 3.569 (1H, d, JZ1.5 Hz), 3.46 (3H, s),
3.43 (1H, m); 13C NMR (125.5 MHz, D2O) d 101.41, 74.89,
72.83, 70.47, 68.96, 57.24, 32.95 ppm.
1744.54, 1685.34 cmK1 1H NMR (500 MHz, CDCl3) d
.
5.53 (1H, t, JZ10.5 Hz), 5.30 (1H, d, JZ11.0 Hz), 5.19
(1H, dd, JZ10.5, 8 Hz), 4.94 (1H, dt, JZ13.5, 3 Hz), 3.53
(1H, ddd, JZ9.8, 8.4, 3.4 Hz), 2.87 (1H, td, JZ14.3,
2.5 Hz Hz), 2.66 (1H, td, JZ13.0, 3.0 Hz), 2.61–2.49 (3H,
m); 1.21 (9H, s), 1.17 (9H, s), 1.12 (9H, s); 13C NMR
(125.5 MHz, CDCl3) d 177.4, 177.1, 176.6, 164.3, 70.4,
69.4, 67.8, 60.2, 44.7, 38.9, 38.7, 31.8, 27.1, 26.6 ppm.
HRFABMS (MCHC) calcd 472.2369, found 472.2379.
5.3.8. Methyl 6-bromo-6-deoxy-2,3,4-tri-O-pivaloyl-b-D-
mannopyranoside (11). The title compound was obtained
as white solid (80%), mp 130–132. H NMR (500 MHz,
1
CDCl3) d 5.41 (1H, dd, JZ3, 0.75 Hz), 5.24 (1H, t, JZ
10 Hz), 5.08 (1H, dd, JZ10, 3 Hz), 4.57 (1H, d, JZ1 Hz),
3.68 (1H, m), 3.49 (3H, s), 3.47–3.39 (2H, m), 1.24 (9H, s),
1.15 (9H, s), 1.09 (9H, s); 13C NMR (125.5 MHz, CDCl3) d
177.28, 177.22, 176.80, 99.74, 73.82, 70.85, 68.31, 68.21,
57.18, 39.06, 38.84, 38.75, 31.08, 27.16, 27.04, 27.02 ppm.
HRFABMS (MCHC) Calcd 509.1750, found 509.1748.
Lactam 15b (1.33 g, 21.0%) was given as a white solid, mp
179–181 8C. IR (CH2Cl2) nmax 1741.07, 1679.15,
1
1137.70 cmK1; H NMR (500 MHz, CDCl3) d 5.76 (1H, t,
JZ10.3 Hz), 5.27 (1H, dd, JZ11.5, 6.3 Hz), 4.78 (1H, m),
4.02 (1H, ddd, JZ11.8, 6.3, 2.0 Hz), 3.07 (1H, t, JZ
12.3 Hz), 2.98–2.88 (3H, m), 2.50 (1H, d, JZ13.0 Hz), 2.35
(1H, m), 1.20 (9H, s), 1.17 (9H, s), 1.14 (9H, s); 13C NMR
(125.5 MHz, CDCl3) d 177.4, 176.8, 163.7, 67.7, 67.0, 59.2,
47.1, 38.9, 38.7, 27.7, 27.1, 27.1, 27.0, 26.3 ppm.
HRFABMS (MCHC) calcd 472.2369, found 472.2371.
5.3.9. Methyl 6-bromo-2,3,4-tri-O-pivaloyl-5-keto-ester
(13). The title compound was obtained as a colorless oil
(91%). 1H NMR (500 MHz, CDCl3) d 5.73 (1H, dd, JZ8.5,
3 Hz), 5.71 (1H, d, JZ2.5 Hz), 5.01 (1H, d, JZ9 Hz), 4.13
(1H, d, JZ14 Hz), 4.00 (1H, d, JZ13.5 Hz) 3.69 (3H, s),
1.24 (9H, s), 1.21 (9H, s), 1.15 (9H, s); 13C NMR
(125.5 MHz, CDCl3) d 194.78, 176.90, 176.85, 176.59,
167.76, 73.16, 68.99, 68.85, 52.75, 38.91, 38.81, 38.69,
38.91, 38.81, 38.69, 31.38, 26.96, 26.86, 26.84 ppm.
HRFABMS (MCHC) Calcd 523.1543, found 523.1545.
5.3.5. 7(S),8(R),9(R),10(S)-Trihydroxy-2-thiaquinolizi-
dine (4a). A solution of lactam 15a (2 g, 4.24 mmol) and
BH3–THF (20 mL, 1.5 M) in anhydrous THF (30 mL) was
refluxed for 4 h and the TLC and NMR showed the
completion of the reduction. The solvent was removed and
methanol was added and the mixture concentrated 3 times.
The residue was dissolved in methanol (30 mL), followed
by addition of NaOMe (0.15 g, 2.8 mmol). The reaction was
stirred for 8 h to remove remaining ester groups and
concentrated. The residue was applied to an ion exchange
column (Dowex 50WX8-400, 30 g), which was washed
with water (50 mL) and eluted with NH4OH (50 mL). The
elution was concentrated and purified by column chroma-
tography (15:1 CH2Cl2/MeOH) to afford a white solid
(0.62 g, 71%), mp 235–237 8C; [a]2D0 C20.28 (c 0.06 H2O);
IR (KBr) nmax 3355.78, 3275.61 cmK1; 1H NMR (500 MHz,
CDCl3) d 3.50 (1H, ddd, 11.0, 9.1, 4.9 Hz), 3.25 (1H, t, JZ
9.3 Hz), 3.12 (1H, dt, JZ12.5, 3.0 Hz), 3.06 (1H, t, JZ
9.5 Hz), 2.93 (1H, dt, JZ14.0, 2.5 Hz), 2.84 (1H, dd, JZ
11.5, 5.0 Hz), 2.75 (1H, td, JZ13.0, 3.0 Hz), 2.52 (1H, m),
2.45 (1H, t, JZ12.3 Hz), 2.43 (1H, m), 2.19 (1H, t, JZ
11.3 Hz), 2.13 (1H, td, JZ10.0, 2.5 Hz); 13C NMR
(125.5 MHz, CDCl3) d 77.9, 74.1, 68.5, 65.6, 59.4, 55.7,
29.3, 26.3 ppm. HRFABMS (MCHC) calcd 206.0851,
found 206.0849.
5.3.10. Lactam 16a. The title compound was obtained as
white solid (65%), mp 136–138. 1H NMR (500 MHz,
CDCl3) d 5.67 (1H, d, JZ3.5 Hz), 5.39 (1H, m), 5.01 (1H,
m), 4.99 (1H, t, JZ3 Hz), 3.66 (1H, dt, JZ11.5, 2 Hz), 2.99
(1H, m), 2.85 (1H, td, JZ13, 2 Hz), 2.74 (1H, td, JZ13,
2.5 Hz), 2.59 (1H, dt, JZ13.5, 2 Hz), 2.46 (1H, m), 1.22
(9H, s), 1.21 (9H, s), 1.20 (9H, s); 13C NMR (125.5 MHz,
CDCl3) d 176.94, 176.86, 176.36, 163.27, 69.43, 68.18,
66.51, 62.75, 46.54, 38.91, 38.85, 38.81, 31.06, 27.18,
27.08, 26.98, 26.66 ppm. HRFABMS (MCHC) calcd
472.2369, found 472.2366.
5.3.11. Lactam 16b. The title compound was obtained as
white solid (16%), mp 182–184. 1H NMR (500 MHz,
CDCl3) d 5.65 (1H, d, JZ2.5 Hz), 5.34 (1H, t, JZ5 Hz),
5.31 (1H, m), 5.04 (1H, dt, JZ8.5, 3 Hz), 3.77 (1H, m), 2.79
(1H, td, JZ13.5, 2 Hz), 2.68 (2H, m), 2.53 (1H, m), 2.39
(1H, dt, JZ13.5, 2 Hz), 1.25 (9H, s), 1.20 (9H, s), 1.18 (9H,
s); 13C NMR (125.5 MHz, CDCl3) d 177.12, 176.66, 176.23,
165.11, 67.13, 66.90, 66.34, 58.60, 44.57, 39.14, 38.94,
38.85, 28.78, 27.19, 27.11, 27.04 ppm. HRFABMS (MC
HC) calcd 472.2369, found 472.2367.
5.3.6. 7(S),8(R),9(R),10(R)-Trihydroxy-2-thiaquinolizi-
dine (4b). The title compound was obtained by the same
method as 4a from lactam 15b (75% from 15b). H NMR
1
5.3.12. 7(R),8(R),9(R),10(S)-Trihydroxy-2-thiaquinolizi-
dine (5a). The title compound was obtained as white solid
(73% from 16a), mp 144–145. 1H NMR (500 MHz, D2O) d
3.93 (1H, m), 3.43 (1H, dd, JZ10, 3.5 Hz), 3.35 (1H, t, JZ
9.5 Hz), 3.06 (1H, dt, JZ12.5, 3 Hz), 2.90 (1H, dt, JZ8.5,
2.5 Hz), 2.81–2.74 (2H, m), 2.51–2.44 (2H, m), 2.39–2.32
(2H, m), 2.05 (1H, t, JZ9 Hz); 13C NMR (125.5 MHz, D2O) d
73.90, 71.15, 67.48, 66.24, 59.37, 55.87, 28.77, 26.02 ppm.
HRFABMS (MCHC) calcd 206.0851, found 206.0851.
(500 MHz, D2O) d 3.51–2.42 (2H, m), 3.06 (2H, d, JZ
10.0 Hz), 2.90 (4H, dd, JZ26.0, 12.5 Hz), 2.82 (2H, t, JZ
10.5 Hz), 2.60 (2H, dd, JZ12.0, 4 Hz), 2.20 (2H, d, JZ
14.0 Hz). HRFABMS (MCHC) calcd 206.0851, found
206.0849.
Manno-derivatives were obtained in the same fashion as
gluco-derivatives.
5.3.7. Methyl 6-bromo-6-deoxy-b-D-mannopyranoside
(9). The title compound was obtained as a white solid
5.3.13. 7(R),8(R),9(R),10(R)-Trihydroxy-2-thiaquinolizi-
dine (5b). The title compound was obtained by the same

L. Gao, R. I. Hollingsworth / Tetrahedron 61 (2005) 3805–3811
3811
1
way as 51a (71% from 16b). H NMR (500 MHz, D2O) d
13. Kino, I.; Inamura, N.; Klakahara, K.; Kiyoto, S.; Goto, T.;
Terano, H.; Kohsaka, M. J. Antibiot. 1985, 38, 936.
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15. Elbein, A. D. FASEB J. 1991, 5, 3055.
3.97 (1H, m), 3.87 (1H, s), 3.69 (1H, d, JZ2.0 Hz), 3.10
(1H, d, JZ12.5 Hz), 2.84 (2H, dd, JZ13.5, 11.0 Hz), 2.76
(1H, m), 2.61 (2H, m), 2.44 (2H, t, JZ11.0 Hz), 2.36 (1H, d,
JZ14.0 Hz). 13C NMR (125.5 MHz, D2O) d 72.1, 70.5,
64.3, 60.4, 56.8, 54.4, 28.4, 26.0. HRFABMS (MCHC)
calcd 206.0851, found 206.0850.
16. Goss, P. E.; Baker, M. A.; Carver, J. P.; Dennis, J. W. Clin.
Cancer Res. 1995, 1, 935.
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Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication numbers CCDC 231490. Copies of the data can
be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [fax: C44 1223
36033 or e-mail: deposit@ccdc.cam.ac.uk].
18. Elbein, A. D.; Molyneux, R. J. In Iminosugars as Glycosidase
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We thank Dr Don Ward for assistance with the X-ray
structure determination.
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