Structure-activity relationships in a series of C2-substituted gluco-configured tetrahydroimidazopyridines as β-glucosidase inhibitors

Article abstract of DOI:10.1016/j.bmc.2011.02.043

Inhibition of glycoside hydrolases has widespread application in treatment of diabetes, viral infections, lysosomal storage diseases and cancers. Gluco-configured tetrahydroimidazopyridines are the most potent β-glucosidase inhibitors reported to date. Using transition state mimic strategy, a series of C2-substituted gluco-configured tetrahydroimidazopyridines were designed and synthesized. Compounds 3 (K_i = 0.64 nM) and 5 (K_i = 0.58 nM) showed stronger inhibitory potency against β-glucosidase. Maestro 9.1 was used to study the structure-activity relationships by docking the compounds into the β-glucosidase active sites. Crown Copyright

Full text of DOI:10.1016/j.bmc.2011.02.043

Bioorganic & Medicinal Chemistry 19 (2011) 2136–2144
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Structure–activity relationships in a series of C2-substituted gluco-configured
tetrahydroimidazopyridines as b-glucosidase inhibitors
Tiehai Li a, Lina Guo a, Yan Zhang a, Jiajia Wang a, Zhenxing Zhang a, Jing Li a, Wenpeng Zhang c, Jianping Lin a,
a,b,c,
Wei Zhao a, , Peng George Wang
⇑
⇑
a College of Pharmacy, Nankai University, Tianjin 300071, PR China
b State Key Laboratory of Elemento-organic Chemistry, Nankai University, Tianjin 300071, PR China
c Departments of Biochemistry and Chemistry, the Ohio State University, Columbus, OH 43210, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Inhibition of glycoside hydrolases has widespread application in treatment of diabetes, viral infections,
lysosomal storage diseases and cancers. Gluco-configured tetrahydroimidazopyridines are the most
potent b-glucosidase inhibitors reported to date. Using transition state mimic strategy, a series of
C2-substituted gluco-configured tetrahydroimidazopyridines were designed and synthesized. Com-
pounds 3 (Ki = 0.64 nM) and 5 (Ki = 0.58 nM) showed stronger inhibitory potency against b-glucosidase.
Maestro 9.1 was used to study the structure–activity relationships by docking the compounds into the
b-glucosidase active sites.
Received 13 January 2011
Revised 22 February 2011
Accepted 23 February 2011
Available online 26 February 2011
Keywords:
Glycosidase
Tetrahydroimidazopyridines
Inhibitors
Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
1. Introduction
glycosyl-enzyme intermediate. In the second step, the acid/base
carboxylate functions as a general base assistance to nucleophilic
Glycosidase inhibition is important not only for the insightful
understanding of enzyme mechanism, but also for questing prom-
ising therapeutics in treatment of disorders such as diabetes,1 viral
infections including HIV and influenza,2 metastatic cancer3 and
lysosomal storage diseases.4,5 The knowledge of the crystal struc-
ture of glycosidase and its complexes with known inhibitors pro-
attack by water, which hydrolyzes the glycosyl-enzyme intermedi-
ate.6,10 The transition state for enzymatic glycoside hydrolysis
displays sp2 hybridization with a partial positive charge predomi-
nantly located across the bond between the anomeric carbon and
endocyclic oxygen, and likely involves distortion of the pyranoside
to half-chair (4H3 and 3H4 or their equivalent 4E and 3E envelop
forms) or boat (2,5B or B2,5) conformations.11,12
vides
a
rich framework to design more potent inhibitors.6
Currently, more than 20,000 glycosidase sequences are known
and have been classified into over 100 glycosidase families based
upon amino-acid sequence similarity (http://www.cazy.org/).7
The b-glucosidases from Sweet almonds and Thermotoga maritima
(TmGH1) are both belonged to family GH1 of the CAZy system
which hydrolyze glycosides with net retention of anomeric config-
uration using a double-displacement mechanism in which a cova-
lent glycosyl-enzyme intermediate is formed.8,9 Subsequently, the
covalent intermediate is dissociated via a short-lived oxocarbenium
ion-like transition state (Fig. 1). The catalytic mechanism involves
two key catalytic carboxylates: an acid/base and a nucleophile. In
the first step, the acid/base carboxylate provides an acid-catalyzed
leaving group departure, simultaneously a nucleophilic attack by
the other residue is responsible for the formation of the covalent
Some of the most powerful glycosidase inhibitors are bicyclic
compounds which contain imidazole moieties, such as the glucoim-
idazole b-glucosidase inhibitors 1 and 2 (Fig. 2a).13,14 Both com-
pounds possess a nonhydrolyzable glycosidic C@N bond between
anomeric carbon of the ‘sugar’ and N1 of imidazole moieties, and
their anomeric carbons display sp2 hybridization. The conforma-
tions of both compounds in the ground state accurately mimic
the assumed flattened half-chair/envelope conformation of the su-
gar ring in the transition state resulting from fusion of the planar
imidazole ring to the ‘glycon’, and protonation of the imidazole ring
effectively imitates the charge distribution in the oxocarbenium ion
(Fig. 2b).15 Furthermore, both inhibitors also possess a lone pair
electrons in N1 atom of imidazole moieties for lateral ‘anti-
protonation’ by the acid/base residue.16 Compound 2 bearing C2
substituent with a phenethyl group shows that an aglycon mimick-
ing group in this position leads to stronger inhibition, and com-
pound 2 also is proposed to interact with active site residues in
the +1 subsite which would result in increasing potency and affin-
ity9,14,16 Gluco-configured tetrahydroimidazopyridine 1 showed
⇑
Corresponding authors. Tel./fax: +86 22 23507760 (W.Z.), tel./fax: +86 22
23506290 (P.G.W.).
E-mail addresses: wzhao@nankai.edu.cn (W. Zhao), pwang@nankai.edu.cn (P.G.
Wang).
0968-0896/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.02.043

T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
2137
Figure 1. Canonical retaining mechanism for b-glycoside hydrolysis via a short-lived oxocarbenium ion-like transition state.
Figure 2. (a) Structure of gluco-configured tetrahydroimidazopyridine 1 and phenethyl-substituted gluco-configured tetrahydroimidazopyridine 2; (b) proposed mechanism
of inhibition of b-glucosidase by tetrahydroimidazopyridine 1.
significant inhibition against b-glucosidase from Sweet almonds
(Ki = 100 nM).17 Provocatively, compound 2 with a phenethyl
group substituted at C2 displayed a 50 times stronger inhibition
(90%). Mono-deiodination of 11a by sequential treatment with
EtMgBr afforded the 2-iodo substituted imidazole 12a as a key
intermediate in 88% yield. Moreover, the structure of the com-
pound 12a was established by X-ray (Fig. 3). Then 12a was
subjected to Sonogashira coupling reaction, which was treated
with monosubstituted alkynes in the presence of Pd(PPh3)4, CuI
and Et3N. These reactions led to the corresponding coupling
products 13a–13i with yields ranging from 64% to 76%. Finally,
treatment of 10a and 13a–13i using H2 and Pd(OH)2/C resulted
in debenzylated products 1–11 with yields ranging from 42% to
72%.22
(Ki = 1.9 nM) than compound
1 against b-glucosidase from
Sweet almonds. Therefore, in our research, a novel series of
C2-substituted gluco-configured tetrahydroimidazopyridines were
designed and synthesized. Their inhibitory activities were evalu-
ated and structure–activity relationships were further investigated.
2. Chemistry
A successful synthetic strategy toward gluco-configured tetra-
hydroimidazopridine derivatives was shown in Scheme 1. Com-
3. Enzymatic assays
mercially available methyl
a-D-glucopyranoside 1a was applied
Inhibitory activities of C2-substituted gluco-configured tetrahy-
droimidazopyridines 1–11 were tested against b-glucosidase from
Sweet almonds. The Ki values were displayed in Table 1. Compound
2 with C2 substituted using a phenethyl group displayed a 50 times
stronger inhibition (Ki = 1.9 nM) than compound 1 (Ki = 100 nM).
Compound 3 bearing a 2,2-dimethylbutyl group at C2 showed a
156-fold higher potency (Ki = 0.64 nM) than compound 1. And
compound 5 with C2 substituted using a p-methyl-phenethyl
group (Ki = 0.58 nM) showed a 3-fold higher potency than com-
pound 2.
as the starting material, which was subjected to per-benzylation
using NaH and BnBr to afford methyl 2,3,4,6-tetra-O-benzyl-
alpha-D-glucopyranoside 2a.18 Subsequently, compound 2a was
treated with glacial acetic acid and sulphuric acid for hydrolyzing
glycosidic bond to give 2,3,4,6-tetra-O-benzyl-D-glucose 3a.19
After Swern oxidation of 3a with DMSO/Ac2O, tetrabenzylglucono-
lactone 4a was obtained with a high yield (96%).20 Ammonolysis of
4a with methanolic ammonia resulted in the hydroxy-amide 5a in
high yield (97%). Swern oxidation of 5a with DMSO/Ac2O gave the
corresponding keto amide 6a and isomers, which can be used for
next reaction without further purification. Reduction of 6a with so-
dium cyanoborohydride and formic acid afforded the lactam 7a,
and the two steps yield from 5a to 7a was 45%.21 Lactam 7a was
reacted with Lawesson’s reagent at 25 °C to afford thiolactam 8a
in 96% yield. Using Hg(OAc)2 activation of the thiolactam 8a, which
was treated with highly nucleophilic aminoacetaldehyde dimethyl
acetal to yield a mixture of the gluco-configurated amidine 9a and
manno-configurated amidine, which can be directly used for next
reaction without further purification. Cyclization of the crude ami-
dines with acidic condition (TsOHÁH2O) in the presence of addi-
tional H2O led to gluco-configurated imidazole 10a with 48%
overall yield from the thiolactam 8a.13
4. Structure–activity relationship
For C2-substituted gluco-configured tetrahydroimidazopyri-
dines in Table 1, compound 2 (with phenethyl, Ki = 1.9 nM) and 3
(with 2,2-dimethylbutyl, Ki = 0.64 nM) showed stronger inhibition
than their parent compound 1. Although compound 10
(Ki = 6.8 nM) and 11 (Ki = 3.5 nM) also displayed stronger inhibi-
tory potency than parent compound 1, their inhibitory potencies
were weaker than compounds 2 and 3. This suggested that hydro-
phobic substituted group at C2-position contributed to improving
the enzyme inhibitory activity. However, when the hydrophobic
chain on C2-substituted group became longer, the inhibitory
potency became weaker as the compound 4 (Ki = 10.7 nM) had a
Treatment of gluco-configurated imidazole 10a with excess NIS
resulted in the 2,3-diiodo substituted imidazole 11a in high yield

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T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
Scheme 1. Reagents and conditions: (a) NaH, BnBr, DMF, 0 °C?rt, 85%; (b) 80% AcOH, 1 M H2SO4, reflux, 60%; (c) Ac2O, DMSO, rt, 96%; (d) NH3, MeOH, 0 °C?rt, 97%; (e) Ac2O,
DMSO, rt; (f) NaCNBH3, HCOOH, MeCN, reflux, 45% (over two steps); (g) Lawesson’s reagent, toluene, 25 °C, 96%; (h) aminoacetaldehyde dimethyl acetal, THF, 0 °C; (i)
TsOHÁH2O, toluene, 65 °C, 48% (over two steps); (j) NIS, DMF, 80 °C, 90%; (k) 1 M EtMgBr, THF, 0 °C, 88%; (l) RCCH, Pd(PPh3)4, DMF, 80 °C, 64–76%; (m) H2, Pd(OH)2/C, EtOAc/
MeOH/H2O/AcOH, 42–72%.
lower inhibitory potency than compounds 2 and 3, which demon-
strated the length of the chain had a great effect on inhibition
against b-glucosidase. To find better inhibitors, we also introduced
substituents onto the 4-position of the phenyl as compared to the
compound 2. A fascinating discovery here was that introducing a
small electron-donating group improved the enzyme inhibitory
designed inhibitors with the b-glucosidase activity sites.23 Since
structure and sequence information of b-glucosidase from
Sweet almonds was yet unknown, structure of b-glucosidase from
the Thermotoga maritima (TmGH1) (PDB ID: 2J7D) was used as our
initial protein model for docking under the assumption that b-
glucosidase from Thermotoga maritima had similar active sites as
that from Sweet almonds because they both belonged to b-glucosi-
dase family 1.6,8 Figure 4 showed the best docked pose of com-
pound 5 (the best binder among the tested compounds in this
paper with a Ki of 0.58 nM) with the enzyme. In this simulated
structure, the sugar moiety of the inhibitor occupied the active site
of the enzyme, establishing hydrogen bond interactions mainly
with important residue N165, E351, E405. The sp2 hybridization
of carbon contributed to the pyranose ring adopting an envelope
(4E) conformation which was similar to the transition state. The
N1 atom of the imidazole moiety formed hydrogen bond with
the lateral ‘anti-protonating’ catalytic acid/base residue (E166).
The 4-methylphenethyl group stretched away from the active site,
potency, and introducing
a big electron-donating group or
electro-withdrawing group reduced the inhibition potency.
Compound 5 (Ki = 0.58 nM) showed a 3-fold inhibitory potency
increase than compound 2, while compound 6 (Ki = 2.0 nM) and
9 (Ki = 3.2 nM) showed slightly weaker potency than compound
2. Surprisingly, compound 7 (Ki = 24.5 nM) and 8 (Ki = 56.1 nm)
with big electron-donating group showed about 12-fold and
28-fold weaker potency respectively than compound 2, which
may be caused by the substitution groups that were too big to
make the inhibitors well accommodated into the enzyme pocket.
The Glide from Maestro 9.1 was used to perform the docking
simulation to study the structure–activity relationships of

T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
2139
Figure 4. The best docked pose of compound 5 against TmGH1 structure 2J7D.
Figure 3. X-ray crystal structure of the compound 12a.
Table 1
Inhibition constants Ki (nM) of gluco-configured tetrahydroimidazopridine derivatives against b-glucosidase from Sweet almonds
Compound
Ki (nM) (b-glucosidase from almonds)
1
2
100
1.9
3
4
5
0.64
10.7
0.58
6
2.0
7
8
9
24.5
56.1
3.2
10
11
6.8
3.5

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T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
6.1.1. Methyl 2,3,4,6-tetra-O-benzyl-
Benzyl bromide (9.19 mL, 77 mmol) was added to a stirred solu-
tion of methyl -D-glucopyranoside (3.0 g, 15 mmol) in anhydrous
a-D-glucopyranoside (2a)
a
DMF (30 mL). The reaction mixture was cooled to 0 °C and sodium
hydride (3.6 g, 90 mmol, 60% dispersion in oil) was then added
portion-wise. The mixture was then allowed to warm to room
temperature. After 17 h, TLC (petroleum ether/ethyl acetate = 5:1)
indicated complete conversion of starting material to a major prod-
uct (Rf = 0.50). The reaction mixture was quenched with methanol,
diluted with diethyl ether (200 mL) and washed with water
(100 mL). The aqueous phase was extracted with diethyl ether
(200 mL) and the combined organic was dried (Na2SO4), filtered
and concentrated in vacuo. The residue was purified by flash col-
umn chromatography (petroleum ether/ethyl acetate = 20:1) to
give 2a (7.2 g, 85%). 1H NMR (400 MHz, CDCl3): d 3.37 (s, 3H,
OCH3), 3.54–3.65 (m, 3H), 3.70–3.75 (m, 2H), 3.98 (t, J = 9.6 Hz,
1H), 4.45–4.48 (m, 2H), 4.58–4.67 (m, 3H), 4.78–4.84 (m, 3H),
4.98 (d, J = 10.8 Hz, 1H), 7.12–7.36 (m, 20H); 13C NMR (100 MHz,
CDCl3): d 55.20, 68.51, 70.08, 73.42, 73.51, 75.06, 75.78, 77.70,
79.87, 82.16, 98.24, 127.61, 127.71, 127.88, 127.93, 128.00,
128.17, 128.38, 128.42, 128.47, 137.95, 138.20, 138.29, 138.83;
HRMS (ESI) calcd for [C35H38O6+Na]+ 577.2561, found 577.2564.
Figure 5. 3D-Superimpostion the docked conformations of compound 4 (sticks
with baby blue), 5 (sticks with red), 7 (sticks with blue) into TmGH1 active site.
interacting with the solvent-exposed W295. 3D-Superimpostion
comparison of compounds 4, 5 and 7 was shown in Figure 5. The
octyl of compound 4 and the 2-(biphenyl-4-yl)ethyl of compound
7 protruded out of the active site onto the surface of TmGH1. The
octyl and 2-(biphenyl-4-yl)ethyl were more solvent exposed than
the 4-methylphenethyl of compound 5, which made 4 and 7 hav-
ing fewer productive contacts with the enzyme. Alternatively, the
conformational rigidity imposed by two ring system (compounds
7 and 8) did not allow the this type of inhibitor to adopt a confor-
mation that was either sufficiently close to that of the transition
state or one which maximized adventitious interactions with the
enzyme.
6.1.2. 2,3,4,6-Tetra-O-benzyl-D-glucopyranoside (3a)
A solution of methyl 2,3,4,6-tetra-O-benzyl-a-D-glucopyrano-
side 2a (3.7 g, 6.7 mmol) in 80% AcOH (100 mL) was added 1 M
H2SO4 (25 mL). After the solution was refluxed for 6 h, the reaction
mixture was neutralized by ice water containing 2.5 g NaOAc. This
mixture was concentrated to dryness on the rotoevaporator. Then
the mixture was suspended in water (100 mL) and the crude prod-
uct was extracted using CH2Cl2 (2 Â 100 mL), the extracts were
washed with saturated aqueous solutions of NaHCO3 (100 mL), fol-
lowed by saturated aqueous solutions of NaCl (100 mL), dried over
Na2SO4, filtered and concentrated to dryness. The crude product
was recrystallized with EtOAc, affording a white solid 3a (2.2 g,
60%). The white solid was used for the next step.
5. Conclusion
In summary, a series of C2-substituted gluco-configured tetra-
hydroimidazopyridines were synthesized as b-glucosidase inhibi-
tors. Compounds 3 (Ki = 0.64 nM) and 5 (Ki = 0.58 nM) showed
stronger inhibitory potency than parent compounds 1 and 2. The
structure–activity relationships indicated the hydrophobic chain
length of C2-substituted group could significantly affect the
inhibitory potency. For compound 2 derivatives, a small electron-
donating substituent group at the 4-position of the phenyl could
make inhibitors well accommodated into the enzyme pocket.
Overall, these new compounds represent a novel chemical scaf-
folds for developing highly potent and specific drugs.
6.1.3. 2,3,4,6-Tetra-O-benzyl-D-gluconolactone (4a)
Acetic anhydride (7.6 mL, 80 mmol) was added under argon
atmosphere to a solution of 2,3,4,6-tetra-O-benzyl-D-glucopyrano-
side 3a (2.2 g, 4 mmol) in anhydrous DMSO (11.4 mL, 160 mmol).
The mixture was stirred for 16 hours at ambient temperature.
TLC analysis showed complete conversion of starting material to
a major product Rf = 0.66 (petroleum ether/ethyl acetate = 5:1).
The reaction mixture was diluted with diethyl ether (150 mL),
washed thoroughly with water (2 Â 60 mL), 10% aqueous solution
of NaHCO3 (3 Â 50 mL), and twice with saturated NaCl (2 Â 50 mL)
solution. After drying on Na2SO4, the organic layer was concen-
trated in vacuo. The crude product was purified by silica gel col-
umn chromatography. Elution was performed with petroleum
ether/ethyl acetate = 25:1 to give 4a (2.06 g, 96%). 1H NMR
(400 MHz, DMSO-d6): d 3.67–3.74 (m, 2H), 3.89 (t, J = 6.4 Hz, 1H),
4.02 (t, J = 6.4 Hz, 1H), 4.37 (d, J = 6.4 Hz, 1H), 4.47–4.56 (m, 3H),
4.60–4.72 (m, 5H), 4.87 (d, J = 11.6 Hz, 1H), 7.22–7.36 (m, 20H);
13C NMR (100 MHz, DMSO-d6): d 68.29, 72.29, 72.37, 72.73,
75.29, 77.38, 77.57, 79.60, 127.57, 127.66, 127.71, 127.74, 127.79,
127.86, 128.24, 137.50, 137.60, 137.81, 137.86, 169.07; HRMS
(ESI) calcd for [C34H34O6+Na]+ 561.2248, found 561.2254.
6. Experimental section
6.1. Chemistry
All reagents were purchased from commercially sources and
were used without further purification. All solvents were avail-
able commercially dried or freshly dried and distilled prior to
use. Reactions were monitored by Thin Layer Chromatography
(TLC) using silica gel GF254 plates with detection by short wave
UV fluorescence (k = 254 nm) and staining with 10% phospho-
molybdic acid in EtOH. Column chromatography was conducted
by silica gel (200–300 mesh) with ethyl acetate and petroleum
ether (60–90 °C) or dichloromethane and methanol as eluent.
1H NMR and 13C NMR were recorded with Bruker AV 400 spec-
6.1.4. 2,3,4,6-Tetra-O-benzyl-D-gluconamide (5a)
trometer at 400 MHz (1H NMR), 100 MHz
(
13C NMR) using
A solution of 2,3,4,6-tetra-O-benzyl-D-gluconolactone 4a (5.3 g,
10 mmol) in saturated methanolic ammonia (60 mL) was stirred at
0 °C for 2 h. TLC analysis showed complete conversion of starting
material to a major product Rf = 0.25 (petroleum ether/ethyl ace-
tate = 1:1). Subsequently, it was concentrated in vacuo. The residue
was recrystallized with EtOAc and hexane, resulting in a white
CDCl3, DMSO-d6 or CD3OD as solvents. Chemical shifts were re-
ported in d (ppm) from TMS internal standard (0.00 ppm). Cou-
pling constants were reported in hertz. High-resolution mass
spectra (HRMS) were obtained on
spectrometer.
a Varian QFT-ESI mass

T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
2141
solid 5a (5.4 g, 97%). 1H NMR (400 MHz, DMSO-d6): d 3.53 (dd,
J = 5.6 Hz, J = 10.0 Hz, 1H), 3.63–3.71 (m, 2H), 3.81–3.86 (m, 1H),
4.05–4.09 (m, 2H), 4.45–4.50 (m, 4H), 4.61–4.72 (m, 4H), 5.09 (d,
J = 5.2 Hz, 1H), 7.19–7.51 (m, 22H); 13C NMR (100 MHz, DMSO-
d6): d 69.79, 71.67, 72.34, 73.52, 74.94, 79.61, 80.30, 81.78,
127.19, 127.25, 127.33, 127.55, 127.61, 127.78, 127.95, 128.01,
128.13, 128.16, 137.81, 138.42, 138.83, 138.85, 172.51; HRMS
(ESI) calcd for [C34H37NO6+Na]+ 578.2513, found 578.2518.
82.47, 127.92, 128.03, 128.13, 128.24, 128.34, 128.42, 128.50,
128.62, 137.09, 137.39, 137.52, 200.42; HRMS (ESI) calcd for
[C34H35NO4S+Na]+ 576.2179, found 576.2183.
6.1.8. 2,3,4,6-Tetra-O-benzyl-1,5-dideoxy-1-[(2’,2’-
dimethoxyethyl)imino]-1,5-imino-D-glucitol (9a)
A solution of 2,3,4,6-tetra-O-benzyl-D-glucothionolactam 8a
(1.0 g, 1.8 mmol) in anhydrous THF (15 mL) was treated with
aminoacetaldehyde dimethyl acetal (l.0 mL, 9.3 mmol) and
Hg(OAc)2 (0.80 g, 2.5 mmol), and kept at 0 °C for 50 min. TLC anal-
ysis showed complete conversion of starting material to a major
product with Rf = 0.20 and a by-product with Rf = 0.18 (petroleum
ether/ethyl acetate = 1:2). The mixture was filtered, washed with
water, extracted with ethyl acetate, dried over Na2SO4 and concen-
trated in vacuum. The crude product was purified by silica gel col-
umn chromatography (petroleum ether/ethyl acetate = 1:1?1:5)
to afford a yellow oil which was a mixture of the gluco/manno-
configurated amidines (1.0 g).
6.1.5. 2,3,4,6-Tetra-O-benzyl-5-dehydro-5-oxo-D-gluconamide
(6a)
Acetic anhydride (10.3 mL, 0.108 mol) was added under ar-
gon atmosphere to
a solution of the compound 5a (3.0 g,
5.4 mmol) in anhydrous DMSO (20.6 mL, 0.216 mol). The mix-
ture was stirred for 8 h at room temperature. TLC analysis
showed complete conversion of starting material to a major
product with Rf = 0.5 (petroleum ether/ethyl acetate = 1:1). The
reaction mixture was diluted with diethyl ether (150 mL),
washed thoroughly with water (2 Â 60 mL), 10% aqueous solu-
tion of NaHCO3 (3 Â 60 mL), and twice with saturated NaCl
(2 Â 60 mL) solution. After drying on Na2SO4, the organic layer
was concentrated in vacuo to give a yellow syrup (2.6 g), which
can be directly used for next reaction without further
purification.
6.1.9. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-[(benzyloxy)-
methyl]-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine (10a)
A mixture of the gluco/manno-configurated amidines (1.0 g,
1.6 mmol) was dissolved in toluene (30 mL), treated with
TsOHÁH2O (0.95 g, 5.0 mmol) and H2O (1.0 mL), and stirred at
65 °C for 18 h. TLC analysis showed complete conversion of start-
ing material to a major product (Rf = 0.45, petroleum ether/ethyl
acetate = 1:1). Then the mixture was concentrated in vacuo, the
crude product was purified by silica gel column chromatography
(petroleum ether/ethyl acetate/Et3N = 500:80:10) affording a yel-
low syrup 10a (484.4 mg), and the yield of the two steps was
6.1.6. 2,3,4,6-Tetra-O-benzyl-D-gluconolactam (7a)
Formic acid (10.6 mL, 0.28 mol) was slowly added to a solution
of NaCNBH3 (0.59 g, 9.4 mmol) and the compound 6a (2.6 g,
4.7 mmol) in anhydrous acetonitrile (40 mL). The reaction mixture
was refluxed for 2.5 h. TLC analysis indicated the complete disap-
pearance of the starting material to
a major product with
48%. 1H NMR (400 MHz, CDCl3):
d
3.73 (dd, J = 5.6 Hz,
Rf = 0.63 (petroleum ether/ethyl acetate = 1:1). After cooling to
0 °C, the mixture was quenched by addition of aqueous HCl (1 M,
9.4 mL). After stirring for 15 min, the mixture was poured into a
stirred mixture of EtOAc:10% aqueous NaHCO3 solution (200 mL,
1:1). The aqueous layer was separated and extracted with EtOAc
(3 Â 100 mL). The organic fractions were combined and washed
with saturated aqueous NaCl (150 mL) solution. After drying on
Na2SO4, the organic layer was filtered and concentrated to dryness.
The residue was purified by flash column chromatography (petro-
leum ether/ethyl acetate = 5:1) to give a white solid 7a (1.31 g).
The two steps yield was 45%. 1H NMR (400 MHz, CDCl3): d 3.25
(t, J = 8.0 Hz, 1H), 3.50–3.61 (m, 3H), 3.91 (t, J = 8.0 Hz, 1H), 3.99
(d, J = 8.0 Hz, 1H), 4.41–4.50 (m, 3H), 4.71–4.78 (m, 2H), 4.82–
4.87 (m, 2H), 5.18 (d, J = 11.2 Hz, 1H), 5.97 (br s, 1H, NH), 7.17–
7.43 (m, 20H); 13C NMR (100 MHz, CDCl3): d 53.75, 70.02, 73.32,
74.63, 74.74, 77.08, 78.79, 82.31, 127.79, 127.88, 128.00, 128.13,
128.36, 128.41, 128.47, 128.55, 137.24, 137.53, 137.81, 138.00,
170.48; HRMS (ESI) calcd for [C34H35NO5+Na]+ 560.2407, found
560.2406.
J = 10.4 Hz, 1H), 3.83–3.87 (m, 2H), 4.08 (dd, J = 5.6 Hz,
J = 7.6 Hz, 1H), 4.18 (ddd, J = 2.8 Hz, J = 5.6 Hz, J = 8.0 Hz, 1H),
4.42–4.51 (m, 3H), 4.68 (d, J = 11.6 Hz, 1H), 4.75 (d, J = 6.0 Hz,
1H), 4.80–4.90 (m, 3H), 5.18 (d, J = 11.6 Hz, 1H), 7.04 (d,
J = 1.2 Hz, 1H), 7.12 (d, J = 1.2 Hz, 1H), 7.17–7.44 (m, 20H); 13C
NMR (100 MHz, CDCl3):
d 58.20, 68.39, 72.80, 73.29, 74.06,
74.21, 75.95, 81.84, 117.45, 127.63, 127.87, 127.91, 127.97,
128.02, 128.11, 128.21, 128.35, 128.48, 128.55, 128.96, 137.29,
137.58, 137.83, 138.18, 143.90; HRMS (ESI) calcd for
[C36H36N2O4+H]+ 561.2748, found 561.2752.
6.1.10. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-[(benzyloxy)-
methyl]-2,3-diiodo-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine
(11a)
A solution of 10a (2.0 g, 3.57 mmol) in DMF (40 mL) was treated
with N-iodosuccinimide (NIS) (8.0 g, 35.7 mmol) and kept at 80 °C
for 6 h. TLC analysis showed complete conversion of starting mate-
rial with Rf = 0.08 to a major product with Rf = 0.56 (petroleum
ether/ethyl acetate = 5:1). The reaction mixture was diluted with
Et2O (100 mL), washed with saturated aqueous NH4Cl solution
(2 Â 30 mL), 5% aqueous Na2S2O3 solution (30 mL) and water
(2 Â 30 mL), dried over Na2SO4, filtered and concentrated in vac-
uum. The crude product was purified by silica gel column chroma-
tography (petroleum ether/ethyl acetate = 1:0?10:1) affording a
yellow oil 11a (2.56 g, 90%). 1H NMR (400 MHz, CDCl3): d 3.64
(dd, J = 4.8 Hz, J = 9.2 Hz, 1H), 3.71 (t, J = 9.2 Hz, 1H), 4.08 (t,
J = 4.0 Hz, 1H), 4.33 (ddd, J = 2.4 Hz, J = 4.8 Hz, J = 8.0 Hz, 1H),
4.42–4.48 (m, 4H), 4.54–4.58 (m, 2H), 4.66–4.70 (m, 2H), 4.82 (d,
J = 11.6 Hz, 1H), 5.15 (d, J = 11.6 Hz, 1H), 7.19–7.43 (m, 20H); 13C
NMR (100 MHz, CDCl3): d 60.79, 69.33, 71.95, 72.18, 72.81, 72.95,
73.05, 73.14, 77.85, 81.24, 96.72, 127.64, 127.81, 127.88, 127.95,
128.00, 128.08, 128.15, 128.33, 128.48, 137.30, 137.39, 137.49,
138.06, 148.94; HRMS (ESI) calcd for [C36H34I2N2O4+H]+
813.0681, found 813.0687.
6.1.7. 2,3,4,6-Tetra-O-benzyl-D-glucothionolactam (8a)
2,3,4,6-Tetra-O-benzyl-D-gluconolactam 7a (2.15 g, 4.0 mmol)
and Lawesson’s reagent (1.62 g, 4.0 mmol) in toluene (60 mL)
was stirred at 25 °C for 28 h. TLC analysis showed complete con-
version of starting material to a major product (Rf = 0.27, diethyl
ether/ethyl acetate = 3:1). Then the mixture was concentrated in
vacuo, the crude product was purified by silica gel column chroma-
tography (diethyl ether/ethyl acetate = 5:1) to give a white solid 8a
(2.14 g, 96%). 1H NMR (400 MHz, CDCl3): d 3.37 (dd, J = 8.0 Hz,
J = 9.2 Hz, 1H), 3.57 (dd, J = 4.8 Hz, J = 9.2 Hz, 1H), 3.63 (dd,
J = 3.2 Hz, J = 9.2 Hz, 1H), 3.86–3.91 (m, 2H), 4.35 (d, J = 11.6 Hz,
1H), 4.43–4.49 (m, 4H), 4.58 (d, J = 11.6 Hz, 1H), 4.67 (d,
J = 11.6 Hz, 1H), 4.74 (d, J = 11.2 Hz, 1H), 5.02 (d, J = 11.6 Hz, 1H),
7.14–7.42 (m, 20H), 8.13 (br s, 1H, NH); 13C NMR (100 MHz,
CDCl3): d 55.93, 68.38, 72.54, 72.61, 72.79, 73.43, 78.41, 81.31,

2142
T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
6.1.11. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-[(benzyloxy)-
methyl]-2-iodo-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine (12a)
A solution of 11a (2.5 g, 3.13 mmol) in THF (25.0 mL) was treated
with a 1 M solution of EtMgBr in anhydrous THF (4.7 mL, 4.70 mmol),
stirred at 0 °C for 10 min. TLC analysis showed complete conversion
of starting material with Rf = 0.68 to a major product with Rf = 0.56
(petroleum ether/ethyl acetate = 4:1). The reaction mixture was trea-
ted with a saturated aqueous NH4Cl solution (10 mL) and extracted
with EtOAc (2 Â 40 mL). The organic fractions were combined, dried
over Na2SO4, filtered and concentrated in vacuum. The crude product
was purified by silica gel column chromatography (petroleum ether/
ethyl acetate = 20:1?15:1) to afford a white solid 12a (1.85 g, 88%).
1H NMR (400 MHz, CDCl3): d 3.68 (dd, J = 5.6 Hz, J = 10.4 Hz, 1H),
3.76- 3.82 (m, 2H), 4.06 (dd, J = 5.2 Hz, J = 6.8 Hz, 1H), 4.17 (ddd,
J = 2.4 Hz, J = 5.6 Hz, J = 8.0 Hz, 1H), 4.40–4.49 (m, 3H), 4.62 (d,
J = 11.2 Hz, 1H), 4.71–4.82 (m, 4H), 5.11 (d, J = 11.6 Hz, 1H), 7.09 (s,
1H), 7.15–7.41 (m, 20H); 13C NMR (100 MHz, CDCl3): d 58.36,
68.27, 72.61, 73.30, 73.41, 73.80, 73.98, 75.81, 81.29, 123.30,
127.63, 127.91, 127.99, 128.08, 128.18, 128.32, 128.46, 128.52,
128.59, 137.12, 137.47, 137.65, 138.05, 145.82; HRMS (ESI) calcd
for [C36H35IN2O4+H]+ 687.1714, found 687.1718.
J = 6.8 Hz, 3H), 1.23–1.61 (m, 9H), 2.40 (t, J = 6.8 Hz, 1H), 3.68
(dd, J = 5.6 Hz, J = 10.4 Hz, 1H), 3.77–3.82 (m, 2H), 4.05–4.19 (m,
2H), 4.40–4.49 (m, 3H), 4.62–4.71 (m, 2H), 4.75–4.83 (m, 3H),
5.11 (d, J = 11.6 Hz, 1H), 7.08–7.40 (m, 21H); 13C NMR (100 MHz,
CDCl3): d 14.12, 19.57, 22.60, 28.69, 28.71, 31.45, 58.31, 68.37,
72.64, 73.29, 73.50, 73.85, 74.03, 75.96, 81.70, 90.25, 120.66,
123.25, 127.86, 127.91, 128.00, 128.14, 128.18, 128.29, 128.47,
128.60, 137.25, 137.55, 137.77, 138.23, 143.61; HRMS (ESI) calcd
for [C44H48N2O4+H]+ 669.3687, found 669.3689.
6.1.12.4. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-(benzyloxymeth-
yl)-2-((4-methylphenyl)ethynyl)-5,6,7,8-tetrahydroimidazo[1,2-
a]pyridine (13d).
A yellow solid (139.7 mg, 69%, Rf = 0.49,
petroleum ether/ethyl acetate = 4:1). 1H NMR (400 MHz, CDCl3):
d 2.35 (s, 3H), 3.73 (dd, J = 5.6 Hz, J = 10.4 Hz, 1H), 3.81–3.85 (m,
2H), 4.10 (dd, J = 5.2 Hz, J = 6.8 Hz, 1H), 4.20 (ddd, J = 2.8 Hz,
J = 5.6 Hz, J = 8.0 Hz, 1H), 4.43–4.51 (m, 3H), 4.63 (d, J = 11.2 Hz,
1H), 4.74–4.86 (m, 4H), 5.17 (d, J = 12.0 Hz, 1H), 7.12–7.45 (m,
25H); 13C NMR (100 MHz, CDCl3): 21.55, 58.33, 68.30, 72.72,
73.33, 73.60, 73.82, 74.02, 75.89, 81.45, 120.27, 121.65, 127.63,
127.93, 128.00, 128.08, 128.11, 128.19, 128.34, 128.49, 128.59,
129.03, 131.49, 137.17, 137.46, 137.67, 138.11, 138.15, 144.04;
HRMS (ESI) calcd for [C45H42N2O4+H]+ 675.3217, found 675.3219.
6.1.12. General procedure for synthesis of compounds 13a–13i
A mixture of 12a (201.8 mg, 0.3 mmol), Pd(PPh3)4 (17.3 mg,
0.015 mmol), Et3N (0.22 mL, 1.5 mmol), CuI (5.7 mg, 0.03 mmol)
and monosubstituted alkynes 13a–13i (0.9 mmol) in DMF
(6.0 mL) was stirred at 80 °C for 3 h under argon atmosphere. TLC
analysis showed complete conversion of starting material to a ma-
jor product. The reaction mixture was cooled to room temperature,
diluted with Et2O (25 mL), washed with a saturated aqueous NH4Cl
solution (3 Â 10 mL), dried over Na2SO4, filtered and concentrated
in vacuum. The crude product was purified by silica gel column
chromatography to give the pure product.
6.1.12.5. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-(benzyloxymeth-
yl)-2-[(4-methoxyphenyl)ethynyl]-5,6,7,8-tetrahydroimi-
dazo[1,2-a]pyridine (13e).
A yellow solid (149.2 mg, 72%,
Rf = 0.37, petroleum ether/ethyl acetate = 4:1). 1H NMR (400 MHz,
CDCl3): d 3.73 (dd, J = 5.6 Hz, J = 10.4 Hz, 1H), 3.81–3.85 (m, 5H),
4.10 (dd, J = 5.6 Hz, J = 7.2 Hz, 1H), 4.20 (ddd, J = 2.8 Hz, J = 5.6 Hz,
J = 8.0 Hz, 1H), 4.43–4.51 (m, 3H), 4.64 (d, J = 11.2 Hz, 1H), 4.73–
4.86 (m, 4H), 5.17 (d, J = 11.6 Hz, 1H), 6.85–6.87 (m, 2H), 7.16–
7.49 (m, 23H); 13C NMR (100 MHz, CDCl3): 55.30, 58.29, 68.31,
72.70, 73.32, 73.84, 74.04, 75.91, 81.56, 113.90, 115.51, 121.43,
127.61, 127.92, 127.96, 128.00, 128.07, 128.11, 128.18, 128.34,
128.48, 128.58, 133.06, 137.18, 137.47, 137.69, 138.13, 144.01,
159.45; HRMS (ESI) calcd for [C45H42N2O5+H]+ 691.3167, found
691.3174.
6.1.12.1.
methyl]-2-(2-phenylethynyl)-5,6,7,8-tetrahydroimidazo[1,2-
a]pyridine (13a). A yellow solid (150.6 mg, 76%, Rf = 0.49,
(5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-[(benzyloxy)-
petroleum ether/ethyl acetate = 4:1). 1H NMR (400 MHz, CDCl3):
d 3.73 (dd, J = 5.6 Hz, J = 10.4 Hz, 1H), 3.82–3.85 (m, 2H), 4.11
(dd, J = 5.2 Hz, J = 7.2 Hz, 1H), 4.20 (ddd, J = 2.8 Hz, J = 5.6 Hz,
J = 7.6 Hz, 1H), 4.44–4.51 (m, 3H), 4.64 (d, J = 11.2 Hz, 1H), 4.73–
4.86 (m, 4H), 5.17 (d, J = 11.6 Hz, 1H), 7.16–7.55 (m, 26H); 13C
NMR (100 MHz, CDCl3): d 58.30, 68.29, 72.67, 73.31, 73.60, 73.79,
73.99, 75.89, 81.44, 83.29, 89.20, 121.85, 123.37, 127.60, 127.90,
127.97, 128.08, 128.15, 128.22, 128.32, 128.46, 128.56, 131.54,
137.14, 137.44, 137.65, 138.07, 144.11; HRMS (ESI) calcd for
[C44H40N2O4+H]+ 661.3061, found 661.3067.
6.1.12.6. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-(benzyloxymeth-
yl)-2-(biphenyl-4-ylethynyl)-5,6,7,8-tetrahydroimidazo[1,2-
a]pyridine (13f).
A yellow solid (154.7 mg, 70%, Rf = 0.42,
petroleum ether/ethyl acetate = 4:1). 1H NMR (400 MHz, CDCl3):
d 3.74 (dd, J = 5.6 Hz, J = 10.8 Hz, 1H), 3.82–3.86 (m, 2H), 4.11
(dd, J = 5.2 Hz, J = 6.8 Hz, 1H), 4.22 (ddd, J = 2.8 Hz, J = 5.6 Hz,
J = 7.6 Hz, 1H), 4.44–4.52 (m, 3H), 4.65 (d, J = 11.2 Hz, 1H), 4.74–
4.87 (m, 4H), 5.17 (d, J = 12.0 Hz, 1H), 7.17–7.18 (m, 2H), 7.25–
7.63 (m, 28H); 13C NMR (100 MHz, CDCl3): 58.32, 68.32, 72.67,
73.31, 73.62, 73.79, 73.98, 75.91, 81.46, 121.91, 122.31, 126.92,
127.01, 127.54, 127.60, 127.90, 127.97, 128.08, 128.15, 128.32,
128.46, 128.57, 128.83, 131.94, 137.16, 137.45, 137.65, 138.08,
140.45, 140.68, 144.15; HRMS (ESI) calcd for [C50H44N2O4+H]+
737.3374, found 737.3366.
6.1.12.2.
methyl]-2-(3,3-dimethylbut-1-ynyl)-5,6,7,8-tetrahydroimidazo-
[1,2-a]pyridine (13b). yellow solid (138.3 mg, 72%,
(5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-[(benzyloxy)-
A
Rf = 0.42, petroleum ether/ethyl acetate = 4:1). 1H NMR (400 MHz,
CDCl3): d 1.32 (s, 9H), 3.71 (dd, J = 5.2 Hz, J = 10.4 Hz, 1H), 3.78–
3.83 (m, 2H), 4.08 (dd, J = 5.2 Hz, J = 6.8 Hz, 1H), 4.16 (ddd,
J = 2.8 Hz, J = 5.2 Hz, J = 7.6 Hz, 1H), 4.42–4.50 (m, 3H), 4.61 (d,
J = 11.2 Hz, 1H), 4.70–4.80 (m, 4H), 5.10 (d, J = 11.6 Hz, 1H), 7.12
(s, 1H), 7.14–7.40 (m, 20H); 13C NMR (100 MHz, CDCl3): d 27.97,
31.01, 58.04, 68.32, 72.45, 73.24, 73.64, 73.89, 76.14, 81.63,
120.85, 127.52, 127.87, 127.93, 127.98, 128.05, 128.28, 128.44,
128.53, 137.26, 137.54, 137.71, 138.24, 143.46; HRMS (ESI) calcd
for [C42H44N2O4+H]+ 641.3374, found 641.3377.
6.1.12.7. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-(benzyloxymeth-
yl)-2-((4-fluoroph-enyl)ethynyl)-5,6,7,8-tetrahydroimidazo[1,2-
a]pyridine (13g).
A yellow solid (136.4 mg, 67%, Rf = 0.50,
petroleum ether/ethyl acetate = 4:1). 1H NMR (400 MHz, CDCl3):
d 3.73 (dd, J = 5.6 Hz, J = 10.4 Hz, 1H), 3.81–3.85 (m, 2H), 4.10
(dd, J = 5.2 Hz, J = 7.2 Hz, 1H), 4.21 (ddd, J = 2.8 Hz, J = 5.6 Hz,
J = 8.0 Hz, 1H), 4.43–4.51 (m, 3H), 4.63 (d, J = 11.2 Hz, 1H), 4.73–
4.86 (m, 4H), 5.15 (d, J = 11.6 Hz, 1H), 7.00–7.04 (m, 2H), 7.16–
7.42 (m, 21H), 7.50–7.53 (m, 2H); 13C NMR (100 MHz, CDCl3): d
58.33, 68.32, 72.69, 73.29, 73.53, 73.79, 73.97, 75.82, 81.31,
115.41, 115.63, 121.85, 127.62, 127.92, 127.97, 128.08, 128.14,
128.32, 128.46, 128.56, 133.36, 133.44, 137.13, 137.40, 137.60,
6.1.12.3. (5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-(benzyloxymeth-
yl)-2-(oct-1-ynyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine
(13c).
A yellow solid (143.3 mg, 70%, Rf = 0.39, petroleum
ether/ethyl acetate = 4:1). 1H NMR (400 MHz, CDCl3): d 0.89 (t,

T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
2143
138.02, 144.13, 161.12; HRMS (ESI) calcd for [C44H39FN2O4+H]+
679.2967, found 679.2973.
J = 8.0 Hz, 1H), 3.67–3.76 (m, 2H), 3.82 (dd, J = 4.0 Hz, J = 12.0 Hz,
1H), 4.05 (dd, J = 2.4 Hz, J = 12.0 Hz, 1H), 4.37 (d, J = 7.6 Hz, 1H),
6.90 (s, 1H); 13C NMR (100 MHz, CD3OD): d 24.30, 29.71, 31.14,
44.82, 61.43, 62.75, 69.31, 69.76, 76.69, 114.17, 144.11, 146.84;
HRMS (ESI) calcd for [C14H24N2O4+H]+ 285.1809, found 285.1810.
6.1.12.8.
(benzyloxymethyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-2-
yl)propiolamide (13h). yellow solid (137.1 mg, 65%,
N-Phenyl-3-(5R,6R,7S,8S)-6,7,8-Tris(benzyloxy)-5-
A
Rf = 0.39, petroleum ether/ethyl acetate = 4:1). 1H NMR (400 MHz,
CDCl3): d 3.70 (dd, J = 6.0 Hz, J = 10.4 Hz, 1H), 3.79–3.83 (m, 2H),
4.09 (dd, J = 5.6 Hz, J = 6.4 Hz, 1H), 4.21 (ddd, J = 2.8 Hz, J = 6.0 Hz,
J = 8.0 Hz, 1H), 4.41–4.50 (m, 3H), 4.62 (d, J = 11.2 Hz, 1H), 4.69–
4.82 (m, 4H), 5.11 (d, J = 11.6 Hz, 1H), 7.13–7.17 (m, 3H), 7.26–
7.47 (m, 21H), 7.54–7.56 (m, 2H), 7.82 (br s, 1H); 13C NMR
(100 MHz, CDCl3): d 58.64, 68.18, 72.76, 73.34, 73.45, 73.83,
73.98, 75.65, 80.52, 81.03, 84.39, 119.73, 121.46, 124.70, 125.83,
127.79, 127.98, 128.02, 128.08, 128.13, 128.23, 128.41, 128.52,
128.66, 129.12, 136.92, 137.28, 137.49, 137.60, 137.77, 144.92,
151.11; HRMS (ESI) calcd for [C45H41N3O5+H]+ 704.3119, found
704.3114.
6.1.13.4. (5R,6R,7S,8S)-5-(Hydroxymethyl)-2-octyl-5,6,7,8-tetra-
hydroimidazo[1,2-a]pyridine-6,7,8-triol (4).
A white solid
(42.5 mg, 68%). 1H NMR (400 MHz, CD3OD): d 0.80 (t, J = 6.8 Hz,
3H), 1.20–1.23 (m, 10H), 1.48–1.53 (m, 2H), 2.39–2.43 (m, 2H),
3.57 (t, J = 8.0 Hz, 1H), 3.66–3.75 (m, 2H), 3.82 (dd, J = 4.0 Hz,
J = 12.0 Hz, 1H), 4.05 (dd, J = 2.4 Hz, J = 12.0 Hz, 1H), 4.36 (d,
J = 8.0 Hz, 1H), 6.89 (s, 1H); 13C NMR (100 MHz, CD3OD): d 14.47,
23.76, 29.13, 30.45, 30.54, 30.62, 33.09, 61.52, 62.66, 69.36,
69.85, 76.76, 114.39, 143.80, 146.86; HRMS (ESI) calcd for
[C16H28N2O4+H]+ 313.2122, found 313.2115.
6.1.13.5. (5R,6R,7S,8S)-5-(Hydroxymethyl)-2-(4-methylpheneth-
yl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine-6,7,8-triol
6.1.12.9. N-(3,5-Dichlorophenyl)-2,2-dimethyl-4-((5R,6R,7S,8S)-
6,7,8-tris(benzyloxy)-5-(benzyloxymethyl)-5,6,7,8-tetrahydro-
(5).
A white solid (45.2 mg, 71%). 1H NMR (400 MHz, CD3OD):
d 2.18 (s, 3H), 2.70–2.81 (m, 4H), 3.59 (t, J = 8.4 Hz, 1H), 3.71 (t,
J = 8.4 Hz, 1H), 3.77–3.85 (m, 2H), 4.05 (dd, J = 2.4 Hz, J = 12.0 Hz,
1H), 4.43 (d, J = 8.0 Hz, 1H), 6.95–7.01 (m, 5H); 13C NMR
(100 MHz, CD3OD): d 21.10, 30.30, 36.04, 61.13, 63.20, 69.11,
69.33, 76.34, 115.66, 129.32, 130.03, 136.57, 139.56, 140.88,
146.99; HRMS (ESI) calcd for [C17H22N2O4+H]+ 319.1652, found
319.1658.
imidazo[1,2-a]pyridin-2-yl)but-3-yn-amide (13i).
A yellow
solid (165.9 mg, 68%, Rf = 0.30, petroleum ether/ethyl ace-
tate = 4:1). 1H NMR (400 MHz, CDCl3): d 1.85 (s, 6H), 3.70–3.82
(m, 3H), 4.06–4.18 (m, 2H), 4.43–4.50 (m, 3H), 4.61–4.79 (m,
5H), 5.08 (d, J = 11.6 Hz, 1H), 6.55 (br s, 1H), 7.15–7.65 (m, 24H);
13C NMR (100 MHz, CDCl3): d 28.48, 49.96, 58.30, 68.27, 72.59,
73.29, 73.43, 73.68, 73.87, 75.94, 81.22, 85.19, 91.13, 122.17,
125.71, 127.63, 127.97, 128.04, 128.33, 128.47, 128.56, 131.18,
135.36, 137.15, 137.40, 137.56, 137.62, 137.99, 138.10, 143.88,
163.89; HRMS (ESI) calcd for [C48H45Cl2N3O5+H]+ 814.2809, found
814.2809.
6.1.13.6. (5R,6R,7S,8S)-5-(Hydroxymethyl)-2-(4-methoxyphen-
ethyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine-6,7,8-triol
(6).
A white solid (42.8 mg, 64%). 1H NMR (400 MHz, CD3OD):
d 2.78 (m, 4H), 3.57–3.66 (m, 4H), 3.72–3.86 (m, 3H), 4.06 (dd,
J = 2.4 Hz, J = 11.6 Hz, 1H), 4.48 (d, J = 8.4 Hz, 1H), 6.72–6.74 (m,
2H), 7.01–7.03 (m, 2H), 7.14 (s, 1H); 13C NMR (100 MHz, CD3OD):
d 29.37, 35.23, 55.62, 60.83, 63.72, 68.81, 68.89, 75.96, 114.87,
116.54, 130.37, 134.03, 138.77, 146.99, 159.66; HRMS (ESI) calcd
for [C17H22N2O5+H]+ 335.1602, found 335.1602.
6.1.13. General procedure for synthesis of compounds 1–11
A solution of 13a–13i (0.2 mmol) in EtOAc/MeOH/H2O (3:1:1,
2.5 mL) was treated with AcOH (2.5 mL) and Pd(OH)2/C (100 mg),
hydrogenated at 6 bar for 56 h at room temperature, filtered
through Celite, and washed with MeOH/H2O (9:1, 25 mL). The
combined filtrates were concentrated in vacuum, the residue was
purified by silica gel column chromatography to give the pure
product.
6.1.13.7.
methyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine-6,7,8-triol
(7).
A white solid (37.1 mg, 48%). 1H NMR (400 MHz, CD3OD):
(5R,6R,7S,8S)-2-(2-(Biphenyl-4-yl)ethyl)-5-(hydroxy-
d 2.75–2.90 (m, 4H), 3.61 (t, J = 8.4 Hz, 1H), 3.73 (t, J = 8.4 Hz, 1H),
3.79–3.86 (m, 2H), 4.05 (dd, J = 2.0 Hz, J = 11.6 Hz, 1H), 4.45 (d,
J = 8.0 Hz, 1H), 7.00–7.06 (m, 3H), 7.18–7.32 (m, 4H), 7.41–7.48
(m, 3H); 13C NMR (100 MHz, CD3OD): d 29.96, 35.80, 61.10,
63.30, 69.09, 69.26, 76.28, 115.92, 127.84, 128.02, 128.16, 129.34,
129.85, 130.00, 139.84, 140.33, 140.39, 141.74, 142.30, 147.07;
HRMS (ESI) calcd for [C22H24N2O4+H]+ 381.1809, found 381.1811.
6.1.13.1. (5R,6R,7S,8S)-5-(Hydroxymethyl)-5,6,7,8-tetrahydro-
imidazo[1,2-a]pyridine-6,7,8-triol
(1).
A
white
solid
(24.8 mg, 62%). 1H NMR (400 MHz, CD3OD): d 3.59 (t, J = 8.4 Hz,
1H), 3.72 (t, J = 8.4 Hz, 1H), 3.78–3.87 (m, 2H), 4.09 (dd,
J = 2.4 Hz, J = 12.0 Hz, 1H), 4.39 (d, J = 8.4 Hz, 1H), 6.94 (s, 1H),
7.21 (s, 1H). 13C NMR (100 MHz, CD3OD): d 61.39, 62.84, 69.31,
69.79, 76.69, 118.68, 128.99, 147.79. HRMS (ESI) calcd for
[C8H12N2O4+H]+ 201.0870, found 201.0873.
6.1.13.8. (5R,6R,7S,8S)-2-((4-Cyclohexyl)phenethyl)-5-(hydroxy-
methyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine-6,7,8-triol
6.1.13.2.
(5R,6R,7S,8S)-5-(Hydroxymethyl)-2-(2-phenylethyl)-
(8).
A solution of 13f (147.3 mg, 0.2 mmol) in EtOAc/MeOH/
5,6,7,8-tetrahydroimidazo[1,2-a]pyridine-6,7,8-triol (2).
A
H2O (3:1:1, 2.5 mL) was treated with AcOH (2.5 mL) and
Pd(OH)2/C (100 mg), hydrogenated at 8 bar for 68 hours at room
temperature, filtered through Celite and washed with MeOH/H2O
(9:1, 25 mL). The combined filtrates were concentrated in vacuum,
the residue was purified by silica gel column chromatography
(CH2Cl2/MeOH = 10:1) affording a white solid (32.5 mg, 42%). 1H
NMR (400 MHz, CD3OD): d 1.27–1.38 (m, 4H), 1.61–1.73 (m, 6H),
2.35–2.49 (m, 1H), 2.73–2.79 (m, 4H), 3.59 (t, J = 8.4 Hz, 1H), 3.71
(t, J = 8.4 Hz, 1H), 3.77–3.84 (m, 2H), 4.05 (dd, J = 2.0 Hz,
J = 12.0 Hz, 1H), 4.43 (d, J = 8.0 Hz, 1H), 6.99–7.01 (m, 5H). 13C
NMR (100 MHz, CD3OD): d 27.31, 28.07, 30.05, 30.35, 35.81,
36.08, 45.68, 61.16, 63.19, 69.12, 69.35, 76.38, 115.59, 127.83,
129.33, 140.05, 141.02, 147.00. HRMS (ESI) calcd for
[C22H30N2O4+H]+ 387.2278, found 387.2276.
white solid (42 mg, 69%). 1H NMR (400 MHz, CD3OD): d 2.79–
2.83 (m, 2H), 2.90–2.94 (m, 2H), 3.68 (t, J = 8.4 Hz, 1H), 3.77–3.84
(m, 2H), 3.91 (dd, J = 3.6 Hz, J = 12.0 Hz, 1H), 4.13 (dd, J = 2.0 Hz,
J = 12.0 Hz, 1H), 4.48 (d, J = 7.6 Hz, 1H), 6.97 (s, 1H), 7.12–7.26
(m, 5H); 13C NMR (100 MHz, CD3OD): d 31.34, 36.87, 61.53,
62.68, 69.37, 69.87, 76.75, 114.76, 126.88, 129.32, 129.44, 143.01,
143.28, 147.03; HRMS (ESI) calcd for [C16H20N2O4+H]+ 305.1496,
found 305.1492.
6.1.13.3.
methyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine-6,7,8-triol
(3).
A white solid (39.8 mg, 72%). 1H NMR (400 MHz, CD3OD):
d 0.86 (s, 9H), 1.42–1.46 (m, 2H), 2.39–2.44 (m, 2H), 3.57 (t,
(5R,6R,7S,8S)-2-(3,3-Dimethylbutyl)-5-(hydroxy-

2144
T. Li et al. / Bioorg. Med. Chem. 19 (2011) 2136–2144
6.1.13.9.
(5R,6R,7S,8S)-2-(4-Fluorophenethyl)-5-(hydroxy-
Acknowledgments
methyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine-6,7,8-triol
(9).
A white solid (46.4 mg, 72%). 1H NMR (400 MHz, CD3OD):
We are grateful to the National Basic Research Program of China
(973 Program: No. 2007CB914403) and Natural Science Founda-
tion of China (No. 20802037).
d 2.70–2.80 (m, 4H), 3.58 (t, J = 8.0 Hz, 1H), 3.67–3.83 (m, 3H), 4.04
(dd, J = 2.0 Hz, J = 11.6 Hz, 1H), 4.39 (d, J = 8.0 Hz, 1H), 6.84–7.10
(m, 5H); 13C NMR (100 MHz, CD3OD): d 31.06, 35.89, 61.35,
62.79, 69.24, 69.69, 76.65, 115.10, 115.76, 115.97, 131.05, 131.12,
138.99, 139.02, 142.10, 147.13; HRMS (ESI) calcd for
[C16H19FN2O4+H]+ 323.1402, found 323.1406.
Supplementary data
Supplementary data (1H NMR and 13C NMR spectra of new com-
pounds) associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.bmc.2011.02.043.
6.1.13.10. N-Phenyl-3-((5R,6R,7S,8S)-6,7,8-trihydroxy-5-(hydro-
xymethyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-2-yl)pro-
panamide (10).
A
white solid (44.6 mg, 65%). 1H NMR
(400 MHz, CD3OD): d 2.63–2.90 (m, 4H), 3.60 (t, J = 8.4 Hz, 1H),
3.73 (t, J = 8.4 Hz, 1H), 3.82–3.86 (m, 2H), 4.06 (dd, J = 2.0 Hz,
J = 11.6 Hz, 1H), 4.46 (d, J = 8.0 Hz, 1H), 6.96–7.43 (m, 6H); 13C
NMR (100 MHz, CD3OD): d 33.76, 36.80, 61.03, 63.57, 69.05,
69.12, 76.10, 116.41, 121.34, 125.27, 129.81, 139.11, 139.73,
147.25, 172.97; HRMS (ESI) calcd for [C17H21N3O5ÀH]À 346.1408,
found 346.1415.
References and notes
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6.1.13.11. 2,2-Dimethyl-N-phenyl-4-((5R,6R,7S,8S)-6,7,8-trihy-
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A white solid (51.4 mg, 66%).
1H NMR (400 MHz, CD3OD): d 1.38 (s, 6H), 2.16–2.20 (m, 2H),
2.59–2.63 (m, 2H), 3.58 (t, J = 8.8 Hz, 1H), 3.73 (t, J = 8.8 Hz, 1H),
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68.17, 68.61, 75.40, 117.29, 128.38, 129.55, 132.56, 136.68,
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