Synthesis and evaluation of 3-deoxy and 3-deoxy-3-fluoro derivatives of gluco- and manno-configured tetrahydropyridoimidazole glycosidase inhibitors

Carbohydrate Research 377 (2013) 35–43

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Synthesis and evaluation of 3-deoxy and 3-deoxy-3-fluoro derivatives of gluco- and manno-configured tetrahydropyridoimidazole glycosidase inhibitors Cécile Ouairy a, Thierry Cresteil a, Bernard Delpech a, David Crich a,b,⇑ a b

Centre de Recherche de Gif, Institut de Chimie des Substances Naturelles, CNRS, Avenue de la Terrasse, 91190 Gif-sur-Yvette, France Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, MI 48202, United States

a r t i c l e

i n f o

Article history: Received 1 March 2013 Received in revised form 11 May 2013 Accepted 13 May 2013 Available online 21 May 2013 Keywords: Glycosidases Glycosidic bond Transition-state mimics Tetrahydropyridoimidazole Tetrahydroimidazopyridines

a b s t r a c t Three tetrahydropyridoimidazole-type glycosidase inhibitors have been synthesized with the 3-deoxy ribo- and arabino-, and 3-deoxy-3-fluoro gluco-configurations and two of them screened for activity against a- and b-gluco- and mannosidase enzymes. Only one substance, the 3-deoxy-3-fluoro-derivative of the gluco-configured tetrahydropyridoimidazole was found to have any activity against a single enzyme, sweet almond b-glucosidase, and even then at a level 100-fold lower than that of the corresponding simple gluco-configured tetrahydropyridoimidazole thereby underlining the importance of the 3-hydroxy group in the key substrate–enzyme interactions. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction The glycoimidazoles, inspired by the natural N-acetyl-b-Dglucosaminidase inhibitor nagstatin 1,1 are some of the most potent inhibitors of glycosidase enzymes2,3 and are considered to be good mimics of the transition state for glycosidic bond hydrolysis by these enzymes4–7 for which they provide strong support for Vasella’s lateral protonation model.8,9 Work from the Davies group indicated the developing importance of the 3-OH–enzyme interaction in the course of the hydrolysis (i) of retaining b-mannopyranosides by the mannanase 26A from Pseudomonas cellulosa as the substrate proceeds along its 1S5?B2,5?OS2 pseudorotational conformational itinerary,10 and (ii) of retaining b-glucopyranosides by endoglucanase enzymes in the course of the 4C1?4H3?1S3 substrate pseudorotational itinerary for hydrolysis.11–13 The importance of this interaction inspired the synthesis and evaluation of the 3-deoxy- and 3-deoxy-3-fluoro analogs 2–5 of the gluco- and manno-configured tetrahydropyridoimidazoles 6 and 7 originally prepared by Tatsuta et al.14 Our interest in the synthesis of 2–5 was further heightened by the importance of the C3–O3 bond in the control of stereochemistry in the course of 4,6-O-benzylidene directed a-gluco- and b-mannopyranosylations noted in our laboratory,15,16 and by the distortions of the pyranose ring conforma-

⇑ Corresponding author. Tel.: +1 3135776203. E-mail address: [email protected] (D. Crich). 0008-6215/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carres.2013.05.011

tions observed crystallographically for 3-deoxy and 3-deoxy-3fluoroglucopyranoses.17,18 HO OH N HO

N

CO2H

NHAc 1

HO X

OH N N OH 2: X = H 4: X = F 6: X = OH

HO HO X

OH N N 3: X = H 5: X = F 7: X = OH

2. Results and discussion Adapting Vasella’s synthesis of 6 to our purposes,19–21 allyl 2,4,6-tri-O-benzyl-3-O-(2-naphthylmethyl)-a,b-D-glucopyranoside 822 was converted to the pyranose 9 by treatment with potassium tert-butoxide followed by iodine and water (Scheme 1).22 Swern oxidation23 afforded the lactone 10, which on exposure to methanolic ammonia gave the hydroxyl amide 11 (Scheme 1). Oxidation with the Dess–Martin periodinane24 afforded an approximately 1:1 mixture of the two cyclic hemiamidals 12, whose reduction with triethylsilane in the presence of boron trifluoride etherate provided the lactam 13. Heating of 13 with Lawesson’s reagent25,26 gave the corresponding thionolactam 14 which on treatment with glycinal dimethylacetal followed by exposure to p-toluenesulfonic acid

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C. Ouairy et al. / Carbohydrate Research 377 (2013) 35–43

OBn O

BnO NapO

BnO

DMSO, (COCl)2, OR

8: R = allyl

DMP

OBn NH

BnO NapO

O OHOBn

OBn NH BnO

Et3SiH, BF3,

99% 11

Lawesson's reagent

OBn NH

BnO NapO

BnO

49%

O

75%

13

BnO BnO NapO

i) H2NCH2CH(OMe)2, S

OBn OH CONH2 BnO

BnO NapO

10

12: 1:1

BnO NapO

NH3, MeOH, O

BnO

Et3N, 93%

i) tBuOK ii) I2, H2O, 91%

9: R = H

OBn O

BnO NapO

ii) TsOH.H2O, 88%

N

BnO + BnO NapO

N

OBn N N

BnO

14

15

16

3:2 DDQ

BnO BnO HO

N

BnO + BnO HO

N

OBn N N

BnO 18, 49%

17, 53%

Scheme 1. Synthesis of the selectively protected gluco- and manno-configured tetrahydropyridoimidazoles 17 and 18.

furnished the gluco and mannoimidazoles 15 and 16 in an approximately 3:2 ratio. Oxidative cleavage of the naphthylmethyl ether in 15 and 16 with DDQ27 then gave the corresponding 3-hydroxy gluco- and manno-configured tetrahydropyridoimidazoles 17 and 18 (Scheme 1). Compounds 17 and 18 were then processed to the corresponding 3-deoxy derivatives 21 and 22 in the standard manner by xanthate ester formation and subsequent treatment with tributyltin hydride and AIBN (Scheme 2).28 Individual treatment of 17 and 18 with sodium hexamethyldisilazide followed by N,N-ditriflyl-2-amino-5-chloropyridine (Comin’s reagent)29 gave the corresponding triflate esters 23 and 24, which on stirring with p-nitrobenzoic acid and cesium carbonate followed by methanolysis gave the corresponding allo- and altroimidazoles 25 and 26, respectively, albeit in low yields because of competing elimination of the triflate esters. Finally, treatment of the allo-isomer 25 with DAST30 gave the 3-deoxy-3-fluoro derivative 27 of gluco-configured tetrahydropyridoimidazole (Scheme 3). Unfortunately, all attempts to obtain the corresponding 3-deoxy-3-fluoro derivative 28 of manno-configured tetrahydropyridoimidazole by the same method resulted in failure. Finally, hydrogenolysis of compounds 21, 22, and 27 over palladium hydroxide on charcoal afforded the target glycoimidazoles 2–4, which were isolated in the form of their acetate salts (Scheme 4). The 3-deoxy derivative 3 of the manno-configured tetrahydropyridoimidazole and the 3-deoxy-3-fluoro derivative 4 of the

BnO BnO HO

N N OBn

17: gluco 18: manno

i) NaHMDS, CS2, ii) MeI

gluco-configured tetrahydropyridoimidazole were assayed for inhibitory activity of Saccharomyces cerevisiae a-glucosidase, almond b-glucosidase, Jack bean a-mannosidase, and Helix pomatia b-mannosidase. The 3-deoxy derivative of manno-configured tetrahydropyridoimidazole 3 was inactive against all four enzymes, whereas the 3-deoxy-3-fluoro derivative of gluco-configured tetrahydropyridoimidazole showed modest activity for the inhibition of almond b-glucosidase but not for that of the other three glycosidases (Table 1). The IC50 value for the inhibition of almond b-glucosidase by 4 was determined to be 13.5 ± 1.5 lM, while that for potent b-glucosidase inhibitor isofagomine2,3,31,32 29 measured in parallel was 0.22 ± 0.05 lM.

3. Conclusion Three 3-deoxy or 3-deoxy-3-fluoro derivatives of tetrahydropyridoimidazole glycosidase inhibitors have been synthesized and two of them screened for activity against a- and b-glucoand mannosidase enzymes. Only the 3-deoxy-3-fluoro derivative 4 of gluco-configured tetrahydropyridoimidazole showed any measureable activity and that only against sweet almond b-glucosidase. The IC50 for the inhibition of sweet almond b-glucosidase was approximately 100-fold less than that exhibited by the gluco-configured tetrahydropyridoimidazole 6 that retains the 3-hydroxy group, thereby underlining the importance of hydrogen bonding between the 3-hydroxy group and the enzyme noted by

BnO BnO O MeS

N N OBn

S 19: gluco, 85% 20: manno, 79%

Bu3SnH, AIBN, Δ

BnO BnO

N N OBn

21: ribo, 66% 22: arabino, 56%

Scheme 2. Deoxygenation of gluco and manno-configured tetrahydropyridoimidazoles 17 and 18.

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C. Ouairy et al. / Carbohydrate Research 377 (2013) 35–43

BnO BnO HO

i) NaHMDS,

N N OBn

ii) Comin's reagent

BnO BnO TfO

17: gluco 18: manno

BnO BnO

N OH

N

i) O2NC6H4CO2H, Cs2CO3 N OBn

ii) K2CO3, MeOH

23: gluco, 75% 24: manno, 78%

DAST N OBn

BnO BnO F

25: allo, 23% 26: altro, 22%

N N OBn

27: gluco, 46% 28: manno, Scheme 3. Introduction of fluorine at the 3-position.

BnO BnO

N N OBn

Pd(OH)2/C, H2, EtOAc, MeOH, H2O, AcOH

21: ribo 22: arabino BnO BnO F

HO HO

N NH OH AcO

2: ribo, 31% 3: arabino, 16%

N N

Pd(OH)2/C, H2, EtOAc, MeOH, H2O, AcOH

HO HO F

N

OBn 27

NH OH AcO

4, 85% Scheme 4. Hydrogenolytic deprotection affording glycoimidazoles 2, 3, and 4.

Table 1 IC50 measured and literature values33 for the inhibition of sweet almond b-glucosidase

a b

Compound

IC50 (lM)

4 6 7 29

13.5 ± 1.5a 0.14b 3.5b 0.22 ± 0.05a

This work. Reported in Ref. 33.

earlier workers11,34 and suggested to be a critical factor in the differentiation of glucose and mannose-based substrates.10 OH HO HO

NH

29: isofagomine

4. Experimental section 4.1. 2,4,6-Tri-O-benzyl-3-O-(2-naphthylmethyl)-a,b-Dglucopyranose (9) To a stirred solution of the allyl glucoside 822 (8.1 g, 12.9 mmol) in DMSO (25 mL) was added tBuOK (723 mg, 6.4 mmol) and the resulting mixture was stirred at 100 °C for 1 h. After cooling to room temperature, the reaction mixture was poured into water (220 mL) and extracted with MTBE (3  150 mL). The organic layer was washed with brine (300 mL), dried over MgSO4, and concentrated in vacuo to give the crude vinyl glycoside, which was taken up in a mixture of THF (50 mL) and H2O (10 mL), treated with iodine (6.5 g,

25.6 mmol) and stirred at room temperature for 12 h. Aqueous Na2SO3 (1 M, 160 mL) was then added and the mixture was stirred for 15 additional minutes before it was poured into a mixture of aqueous Na2SO3 and brine (1:1) (400 mL), extracted with EtOAc (3  200 mL), dried over MgSO4, and concentrated in vacuo to give the title glucopyranose (6.9 g, 91%) as a colorless oil which was directly used in the next step. [a]D: +4.7 (c 1.5, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.83–7.70 (m, 4H, Ar), 7.48– 7.09 (m, 18H, Ar), 5.22 (d, J = 3.6 Hz, 0.3H, H1a), 5.09 (d, J = 11.1 Hz, 0.3H, CH2), 5.07 (d, J = 11.1 Hz, 0.3H, CH2), 4.98 (d, J = 11.1 Hz, 0.7H, CH2), 4.84 (d, J = 11.1 Hz, 0.3H, CH2), 4.82 (d, J = 11.1 Hz, 0.3H, CH2), 4.77 (d, J = 11.1 Hz, 0.7H, CH2), 4.74 (d, J = 7.4 Hz, 0.7H, H1b), 4.70 (d, J = 11.1 Hz, 0.7H, CH2), 4.68 (d, J = 11.1 Hz, 0.3H, CH2), 4.59 (d, J = 12.0 Hz, 0.7H, CH2), 4.55 (m, 2.3H, CH2), 4.52 (d, J = 12.0 Hz, 0.7H, CH2), 4.48 (d, J = 12.0 Hz, 0.7H, CH2), 4.14–4.00 (m, 2H, H2, H5), 3.73–3.40 (m, 4H, H6, H4, H3). 13C NMR (CDCl3, 125 MHz): d 138.5 (Cq, Ar), 138.4 (Cq, Ar), 138.1 (Cq, Ar), 138.0 (Cq, Ar), 137.9 (Cq, Ar), 136.3 (Cq, Ar), 136.1 (Cq, Ar), 133.5 (Cq, Ar), 133.1 (Cq, Ar), 128.50 (CH, Ar), 128.48 (CH, Ar), 128.3 (CH, Ar), 128.19 (CH, Ar), 128.16 (CH, Ar), 128.10 (CH, Ar), 128.05 (CH, Ar), 128.0 (CH, Ar), 127.9 (CH, Ar), 127.84 (CH, Ar), 127.78 (CH, Ar), 126.6 (CH, Ar), 126.2 (CH, Ar), 126.12 (CH, Ar), 126.08 (CH, Ar), 125.9 (CH, Ar), 97.7 (C1b), 91.4 (C1a), 84.7 (C3b), 83.3 (C2b), 81.9 (C3a), 80.2 (C2a), 78.0 (C5b), 77.9 (C4a), 75.9 (CH2), 75.8 (CH2), 75.1 (CH2), 74,9 (CH2), 73.7 (CH2), 73.6 (CH2), 73.3 (CH2), 70.4 (C5a), 69.1 (C6b), 68.8 (C6a). FTIR: 3424, 1452, 1146, 1072, 1040, 852, 818, 745, 694 cm1. MS (ESI+): m/z 613.2 [M+Na]+. HRMS (ESI+): 613.2566 calcd for C38H38NaO6, found 613.2538. 4.2. 2,4,6-Tri-O-benzyl-3-O-(2-naphthylmethyl)-D-glucono-1,5lactone (10) To a stirred solution of DMSO (565 lL, 7.95 mmol) in CH2Cl2 (18 mL) at 78 °C, was added oxalyl chloride (575 lL, 6.59 mmol)

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C. Ouairy et al. / Carbohydrate Research 377 (2013) 35–43

dropwise. The reaction mixture was stirred at 78 °C for 30 min and the solution of glucopyranose 9 (1.56 g, 2.6 mmol) in CH2Cl2 (6 mL) was added slowly. The reaction mixture was stirred for 45 min at 78 °C. Triethylamine (1.85 mL, 13.27 mmol) was added dropwise and the reaction mixture was stirred for 30 min at 78 °C and then allowed to warm up to 0 °C before water was added to quench the reaction (80 mL). The reaction mixture was then diluted with CH2Cl2 (100 mL) and washed with water (80 mL) and brine (80 mL). The organic layer was dried over MgSO4 and concentrated in vacuo to give lactone 10 (1.45 g, 93%) as a yellow oil. [a]D: +63.7 (c 2.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.89–7.74 (m, 4H, Ar), 7.56–7.18 (m, 18H, Ar), 5.07 (d, J = 11.5 Hz, 1H, CH2), 4.95 (d, J = 11.5 Hz, 1H, CH2), 4.81 (d, J = 11.0 Hz, 1H, CH2), 4.77 (d, J = 11.0 Hz, 1H, CH2), 4.71 (d, J = 11.0 Hz, 1H, CH2), 4.62 (d, J = 11.6 Hz, 1H, CH2), 4.59 (d, J = 11.0 Hz, 1H, CH2), 4.55–4.50 (m, 2H, H5 + CH2), 4.22 (d, J = 6.8 Hz, 1H, H2), 4.07–4.00 (m, 2H, H3 + H4), 3.80 (dd, J = 11.1, 2.5 Hz, 1H, H6), 3.73 (dd, J = 11.1, 3.1 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 169.5 (C@O), 137.7 (Cq), 137.6 (Cq), 137.1 (Cq), 135.1 (Cq), 133.3 (Cq), 133.2 (Cq), 128.63 (CH, Ar), 128.59 (CH, Ar), 128.56 (CH, Ar), 128.4 (CH, Ar), 128.2 (CH, Ar), 128.1 (CH, Ar), 128.0 (CH, Ar), 127.8 (CH, Ar), 127.0 (CH, Ar), 126.3 (CH, Ar), 126.2 (CH, Ar), 126.1 (CH, Ar), 81.1 (C3), 78.3 (C5), 77.6 (C2), 76.2 (C4), 74.1(CH2), 74.0 (CH2), 73.9 (CH2), 73.7 (CH2), 68.4 (C6). FTIR: 1732, 1736, 1453, 1365, 1341, 1226, 1093, 1024, 827, 732, 695 cm1. MS (ESI+): m/z 611.3 [M+Na]+, 643.3 [M+Na+MeOH]+. HRMS (ESI+): calcd for C38H36NaO6 611.2410, found 611.2426. 4.3. 2,4,6-Tri-O-benzyl-3-O-(2-naphthylmethyl)-D-gluconamide (11) To a stirred solution of lactone 10 (1.52 g, 2.58 mmol) in MeOH (3 mL), was added a solution of ammonia in methanol (2 M, 3.20 mL, 6.40 mmol). The reaction mixture was stirred for 2 h before being evaporated. The amido alcohol was obtained as an orange foam (1.55 g, 99%) and directly used in the next step without further purification. [a]D: +10.8 (c 1.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.81–7.67 (m, 4H, Ar), 7.46–7.21 (m, 18H, Ar), 6.65 (s, 1H, NH2), 5.72 (br s, 1H, NH2), 4.85 (d, J = 11.1 Hz, 1H, CH2), 4.75 (d, J = 11.1 Hz, 1H, CH2), 4.74 (d, J = 11.1 Hz, 1H, CH2), 4.65 (d, J = 11.1 Hz, 1H, CH2), 4.60 (d, J = 11.1 Hz, 1H, CH2), 4.56 (d, J = 11.9 Hz, 1H, CH2), 4.53 (d, J = 11.9 Hz, 1H, CH2), 4.50 (d, J = 11.9 Hz, 1H, CH2), 4.29 (d, J = 3.0 Hz, 1H, H2), 4.15 (dd, J = 7.2, 3.6 Hz, 1H, H 3), 3.94 (m, 1H, H5), 3.89 (t, J = 7.2 Hz, 1H, H4), 3.68 (dd, J = 9.7, 3.0 Hz, 1H, H6), 3.62 (dd, J = 9.7, 5.5 Hz, 1H, H60 ), 2.89 (br s, 1H, OH). 13C NMR (CDCl3, 125 MHz): d 174.1 (C@O), 138.2 (Cq), 138.1 (Cq), 136.8 (Cq), 135.3 (Cq), 133.4 (Cq), 133.1 (Cq), 128.7 (CH, Ar), 128.44 (CH, Ar), 128.38 (CH, Ar), 128.3 (CH, Ar), 128.1 (CH, Ar), 128.0 (CH, Ar), 127.9 (CH, Ar), 127.8 (CH, Ar), 127.7 (CH, Ar), 127.1 (CH, Ar), 126.3 (CH, Ar), 126.1 (CH, Ar), 126.0 (CH, Ar), 80.8 (C3), 79.8 (C2), 77.6 (C4), 75.5 (CH2), 74.2 (CH2), 73.8 (CH2), 73.4 (CH2), 71.4 (C5), 71.1 (C6). FTIR: 3549, 3385, 3175, 1659, 1498, 1483, 1411, 1358, 1283, 1212, 1179, 857, 819, 732, 699 cm1. MS (ESI+): m/z 628.3 [M+Na]+. HRMS (ESI+): calcd for C38H39NNaO6 628.2675, found 628.2685 [M+Na]+. 4.4. (3R,4S,5S,6S)-3,5-Bis(benzyloxy)-6-((benzyloxy)methyl)-6hydroxy-4-(naphthalen-2-ylmethoxy)piperidin-2-one (6S-12) and (3R,4S,5S,6R)-3,5-bis(benzyloxy)-6-((benzyloxy)methyl)-6hydroxy-4-(naphthalen-2-ylmethoxy)piperidin-2-one (6R-12) To a stirred solution of the amido alcohol (898 mg, 1.48 mmol) in CH2Cl2 (2 mL) was added a solution of Dess–Martin periodinane in CH2Cl2 (5.20 mL, 0.43 M, 2.24 mmol) and water (25 lL, 1.39 mmol). The reaction mixture was stirred for 30 h at room temperature. It was then diluted with ether (80 mL) and treated with 80 mL of a mixture of 1 N aqueous Na2S2O3 and saturated

aqueous NaHCO3 (1:1). The aqueous layer was extracted with ether (2  30 mL). The organic layers were then combined, washed with water (80 mL) and brine (80 mL). The organic layers were combined, dried (MgSO4), and concentrated to give the hydroxylactams 6S-12 and 6R-12 (1:1) as a white foam and as a colorless oil, respectively. The crude mixture of isomers (883 mg) was engaged in the next step without further purification. Compound 6S-12: [a]D: +49.6 (c 2.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.83–7.70 (m, 4H, Ar), 7.48–7.17 (m, 18H, Ar), 6.24 (s, 1H, NH), 5.20 (d, J = 11.0 Hz, 1H, CH2), 5.04 (d, J = 11.4 Hz, 1H, CH2), 4.94 (d, J = 11.0 Hz, 1H, CH2), 4.92 (d, J = 11.0 Hz, 1H, CH2), 4.81 (d, J = 11.4 Hz, 1H, CH2), 4.57 (d, J = 11.0 Hz, 1H, CH2), 4.50 (d, J = 11.8 Hz, 1H, CH2), 4.44 (d, J = 11.8 Hz, 1H, CH2), 4,29 (dd, J = 9.2, 8.6 Hz, 1H, H3), 4.07 (d, J = 8.6 Hz, 1H, H2), 3.78 (d, J = 9.2 Hz, 1H, H4), 3.36 (d, J = 9.6 Hz, 1H, H6), 3.32 (s, 1H, OH), 3.28 (d, J = 9.6 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 171.3 (C@O), 137.9 (Cq), 137.0 (Cq), 135.7 (Cq), 135.3 (Cq), 133.4 (Cq), 133.1 (Cq), 128.7 (CH, Ar), 128.6 (CH, Ar), 128.5 (CH, Ar), 128. 33 (CH, Ar), 128.32 (CH, Ar), 128.2 (CH, Ar), 128.1 (CH, Ar), 128.0 (CH, Ar), 127.8 (CH, Ar), 126.8 (CH, Ar), 126.2 (CH, Ar), 126.14 (CH, Ar), 126.06 (CH, Ar), 82.0 (C5), 79.5 (C3 and C4), 77.5 (C2), 75.5 (CH2), 75.4 (CH2), 74.9 (CH2), 73.8 (CH2), 72.8 (C6). FTIR: 1676, 1452, 1346, 1064, 732, 694 cm1. MS (ESI+): m/z 626.3 [M+Na]+. HRMS (ESI+): calcd for C38H37NNaO6 626.2519, found 626.2533 [M+Na]+. 6R-12: [a]D : + 18.0 (c 1.8, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.74–7.59 (m, 4H, Ar), 7.39–6.96 (m, 18H, Ar), 6.31 (s, 1H, NH), 5.04 (d, J = 11.5 Hz, 1H, CH2), 4.79 (d, J = 11.5 Hz, 1H, CH2), 4.68 (d, J = 11.5 Hz, 1H, CH2), 4.64 (d, J = 11.5 Hz, 1H, CH2), 4.45 (s, 2H, CH2), 4.42 (d, J = 11.5 Hz, 1H, CH2), 4.29 (d, J = 11.5 Hz, 1H, CH2), 4.29 (d, J = 6.8 Hz, 1H, H2), 3.86 (dd, J = 6.8, 4.5 Hz, 1H, H3), 3.68 (d, J = 4.5 Hz, 1H, H4), 3.63 (s, 1H, OH), 3.54 (d, J = 9.0 Hz, 1H, H6), 3.43 (d, J = 9.0 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 170.5 (C@O), 138.0 (Cq), 137.2 (Cq), 136.9 (Cq), 135.1 (Cq), 133.2 (Cq), 133.1 (Cq), 128.6 (CH, Ar), 128.40 (CH, Ar), 128.38 (CH, Ar), 128.2 (CH, Ar), 128.00 (CH, Ar), 127.96 (CH, Ar), 127.8 (CH, Ar), 127.7 (CH, Ar), 127.1 (CH, Ar), 126.2 (CH, Ar), 126.1 (CH, Ar), 83.5 (C5), 79.8 (C4), 79.7 (C3), 78.4 (C2), 74.4 (CH2), 73.9 (CH2), 73.7 (CH2), 73.0 (CH2), 72.8 (C6). FTIR: 3413-3151, 1674, 1447, 1453, 1342,1209, 1070, 1028, 911, 855, 816, 733, 695 cm1. MS (ESI+): m/z 626.3 [M+Na]+. HRMS (ESI+): calcd for C38H37NNaO6 626.2519, found 626.2526 [M+Na]+. 4.5. 5-Amino-2,4,6-tri-O-benzyl-5-deoxy-3-O-(2naphthylmethyl)-D-glucono-1,5-lactam (13) To a stirred solution of hydroxylactams 12 (883 mg, 1.46 mmol) in CH2Cl2 (5 mL) at 10 °C, was added triethylsilane (795 lL, 4.98 mmol) dropwise. After 5 min, BF3OEt2 (220 lL (1.74 mmol) was added. The reaction mixture was stirred at 10 °C for 30 min and then allowed to warm up to 0 °C, before water was added to quench the reaction. The reaction mixture was then diluted with CH2Cl2 (20 mL) and washed with water (2  30 mL) and brine (30 mL). The organic layer was dried over MgSO4 and concentrated in vacuo to give lactam 13 (429 mg, 49%, 2 steps) as a white solid. Mp: 134.8–135.7 °C. [a]D: +51.9 (c 1.0, CHCl3). 1 H NMR (CDCl3, 500 MHz): d 7.70–7.40 (m, 7H, Ar), 7.28 –7.09 (m, 15H, Ar), 6.18 (s, 1H, NH), 5.42 (d, J = 11.3 Hz, 1H, CH2), 4.98 (d, J = 11.3 Hz, 1H, CH2), 4.93 (d, J = 11.3 Hz, 1H, CH2), 4.78 (d, J = 11.3 Hz, 1H, CH2), 4.77 (d, J = 11.3 Hz, 1H, CH2), 4.35 (d, J = 11.3 Hz, 1H, CH2), 4.12 (d, J = 11.3 Hz, 1H, CH2), 4.09 (d, J = 11.3 Hz, 1H, CH2), 4.05 (d, J = 7.9 Hz, 1H, H2), 3.90 (t, J = 7.9 Hz, 1H, H3), 3.46 (t, J = 8.7 Hz, 1H, H4), 3.32 (m, 1H, H5), 3.26 (dd, J = 10.0, 2.4 Hz, 1H, H6), 3.06 (dd, J = 10.0, 7.1 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 170.6 (C@O), 138.0 (Cq), 137.7 (Cq), 137.4 (Cq), 135.6 (Cq), 133.4 (Cq), 133.2 (Cq), 128.7 (CH, Ar),

C. Ouairy et al. / Carbohydrate Research 377 (2013) 35–43

128.6 (CH, Ar), 128.5 (CH, Ar), 128.3 (CH, Ar), 128.20 (CH, Ar), 128.17 (CH, Ar), 128.12 (CH, Ar), 128.07 (CH, Ar), 128.0 (CH, Ar), 127.9 (CH, Ar), 127.8 (CH, Ar), 126.9 (CH, Ar), 126.23 (CH, Ar), 126.16 (CH, Ar), 126.1 (CH, Ar), 82.4 (C2), 79.0 (C3), 77.3 (C4), 74.9 (CH2), 74.79 (CH2), 74.78 (CH2), 73.5 (CH2), 70.2 (C6), 54.0 (C5). FTIR: 3192, 290, 2864, 1677, 1496, 1453, 1348, 1323, 1174, 1123, 1090, 1065, 1018, 858, 824, 750, 735, 700 cm1. MS (ESI+): m/z 610.3 [M+Na]+, 626.3 [M+K]+. HRMS (ESI+): calcd for C38H37NNaO5 610.2597, found 610.2569 [M+Na]+. 4.6. 5-Amino-2,4,6-tri-O-benzyl-5-deoxy-3-O-(2naphtylmethyl)-D-gluconothio-1,5-lactam (14) To a stirred solution of lactam 13 (344 mg, 0.59 mmol) in toluene (7 mL) was added Lawesson’s reagent (355 mg, 0.88 mmol). The reaction mixture was stirred at 27 °C for 24 h and then concentrated and purified by silica gel column chromatography (CH2Cl2) to afford thiolactam 14 (267 mg, 75%) as a yellow oil. [a]D: +80.0 (c 1.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 8.10 (s, 1H, NH), 7.84–7.69 (m, 4H, Ar), 7.50–7.90 (m, 18H, Ar), 5.04 (d, J = 11.4 Hz, 1H, CH2), 4.84 (d, J = 11.4 Hz, 1H, CH2), 4.76 (d, J = 11.4 Hz, 1H, CH2), 4.62 (d, J = 11.4 Hz, 1H, CH2), 4.59 (d, J = 11.4 Hz, 1H, CH2), 4.52 (d, J = 4.5 Hz, 1H, H2), 4.49 (d, J = 12.4 Hz, 1H, CH2), 4.46 (d, J = 13.2 Hz, 1H, CH2), 3.97 (t, J = 4.5 Hz, 1H, H3), 3.91 (td, J = 7.5, 4.5 Hz, 1H, H5), 3.66 (dd, J = 9.5, 4.5 Hz, 1H, H6), 3.61 (dd, J = 9.5, 4.5 Hz, 1H, H4), 3.41 (dd, J = 9.5, 7.5 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d = 200.6 (C@S), 137.6 (Cq), 137.5 (Cq), 137.2 (Cq), 134.9 (Cq), 133.3 (Cq), 133.2 (Cq), 128.7 (CH, Ar), 128.5 (CH, Ar), 128.45 (CH, Ar), 128.44 (CH, Ar), 128.3 (CH, Ar), 128.16 (CH, Ar), 128.15 (CH, Ar), 128.1 (CH, Ar), 128.0 (CH, Ar), 127.8 (CH, Ar), 126.3 (CH, Ar), 126.22 (CH, Ar), 126.19 (CH, Ar), 82.7 (C2), 81.4 (C3), 78.6 (C4), 73.6 (CH2), 73.0 (CH2), 72.80 (CH2), 72.78 (CH2), 68.5 (C6), 56.1 (C5). FTIR: 1508, 1453, 1362, 1306, 1070, 1027, 855, 816, 734, 695 cm1. MS (ESI+): m/z 604.3 [M+H]+, 626.3 [M+Na]+. HRMS (ESI+): calcd for C38H37NNaO4S 626.2341, found 626.2341 [M+Na]+. 4.7. (5R,6R,7S,8S)-7-(2-naphthylmethyl)-6,8-bis(benzyloxy)-5(benzyloxy)methyl-5,6,7,8-tetrahydroimidazo1,2-apyridine (15) and (5R,6R,7S,8R)-7-(2-naphthylmethyl)-6,8-bis(benzyloxy)-5(benzyloxy)methyl-5,6,7,8-tetrahydroimidazo1,2-apyridine (16) To thiolactam 14 (930 mg, 1.54 mmol) was added dimethylacetal aminoacetaldehyde (2.50 mL, 22.95 mmol) and the reaction mixture was stirred at room temperature overnight. Then ether (30 mL) and water (30 mL) were added and the layers were separated. The aqueous layer was extracted with ether (2  30 mL). The organic layers were then combined, washed with water (2  30 mL) and saturated aqueous NaCl (60 mL), dried (MgSO4), and concentrated to give the intermediate amidines (980 mg, 1.45 mmol), which were taken up in toluene (35 mL) and TsOHH2O (500 mg, 2.63 mmol) was added. The reaction mixture was stirred at 60 °C overnight, cooled and diluted with CH2Cl2 (80 mL) and saturated aqueous NaHCO3 (80 mL). The layers were separated and the aqueous layer was extracted with CH2Cl2 (80 mL). The organic layers were then combined, washed with brine (100 mL), dried (MgSO4), concentrated, and purified by silica gel column chromatography (heptane/AcOEt 50:50) to afford glucoimidazole 15 (515 mg) and mannoimidazole 16 (313 mg) both as a colorless oils (88%). Compound 15: [a]D: +52.3 (c 1.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.85–7.71 (m, 4H, Ar), 7.50–7.09 (m, 18H, Ar), 7.14 (s, 1H, H7), 7.07 (s, 1H, H8), 5,22 (d, J = 11.5 Hz, 1H, CH2), 5.00 (d, J = 11.5 Hz, 1H, CH2), 4.92 (d, J = 11.5 Hz, 1H, CH2), 4.88 (d, J = 11.2 Hz, 1H, CH2), 4.86 (d, J = 11.6 Hz, 1H, CH2), 4.80 (d, J = 5.8 Hz, 1H, H2), 4.53 (d, J = 11.2 Hz, 1H, CH2), 4.49 (d, J = 12.1 Hz, 1H, CH2), 4.46 (d, J = 12.1 Hz, 1H, CH2), 4.20 (m, 1H, H5), 4.16 (dd, J = 7.5, 5.8 Hz,

39

1H, H3), 3.90 (t, J = 7.5 Hz, H4), 3.88 (dd, J = 10.3, 2.9 Hz, 1H, H6), 3.79 (dd, J = 10.3, 5.0 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 144.2 (Cq), 138.4 (Cq), 137.8 (Cq), 137.5 (Cq), 135.5 (Cq), 133.4 (Cq), 133.2 (Cq), 129.5 (C7), 128.64 (CH, Ar), 128.56 (CH, Ar), 128.5 (CH, Ar), 128.3 (CH, Ar), 128.14 (CH, Ar), 128.11 (CH, Ar), 128.07 (CH, Ar), 128.0 (CH, Ar), 127.8 (CH, Ar), 127.7 (CH, Ar), 126.9 (CH, Ar), 126.2 (CH, Ar), 126.1 (CH, Ar), 117.4 (C8), 82.2 (C3), 76.2 (C4), 74.6 (C2), 74.4 (CH2), 74.3 (CH2), 73.4 (CH2), 72.9 (CH2), 68.5 (C6), 58.3 (C5). FTIR: 3028, 2919, 2862, 1495, 1453, 1361, 1279, 1089, 817, 734, 697 cm1. MS (ESI+): m/z [M+H]+ 611.3, [M+Na]+ 633.3. HRMS (ESI+): calcd for C40H39N2O4 611.2910, found 611.2910 [M+H]+. Compound 16: [a]D: 19.7 (c 1.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.83–7.72 (m, 4H, Ar), 7.48–7.07 (m, 18H, Ar), 7.18 (s, 1H, H8), 7.08 (s, 1H, H7), 5.06 (d, J = 11.3 Hz, 1H, CH2), 4.87 (d, J = 3.1 Hz, 1H, H2), 4.84 (d, J = 12.2 Hz, 1H, CH2), 4.78 (d, J = 12.2 Hz, 1H, CH2), 4.74 (d, J = 12.2 Hz, 1H, CH2), 4.71 (d, J = 12.2 Hz, 1H, CH2), 4.66 (d, J = 11.3 Hz, 1H, CH2), 4.49 (d, J = 12.7 Hz, 1H, CH2), 4.47 (d, J = 12.7 Hz, 1H, CH2), 4.35 (dd, J = 9.5, 7.3 Hz, 1H, H4), 4.17 (td, J = 7.3, 3.4 Hz, H5), 3.94 (dd, J = 9.5, 3.1 Hz, 1H, H3), 3.80 (dd, J = 10.1, 3.4 Hz, 1H, H6), 3.67 (dd, J = 10.1, 7.3 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 143.0 (Cq), 138.3 (Cq), 138.2 (Cq), 137.7 (Cq), 135.4 (Cq), 133.4 (Cq), 133.2 (Cq), 129.4 (C7), 128.62 (CH, Ar), 128.57 (CH, Ar), 128.42 (CH, Ar), 128.37 (CH, Ar), 128.30 (CH, Ar), 128.20 (CH, Ar), 128.03 (CH, Ar), 127.98 (CH, Ar), 127.8 (CH, Ar), 127.7 (CH, Ar), 126.8 (CH, Ar), 126.2 (CH, Ar), 126.1 (CH, Ar), 125.9 (CH, Ar), 119.5 (C8), 80.2 (C3), 75.0 (CH2), 74.4 (C4), 73.4 (CH2), 71.8 (CH2), 71.2 (CH2), 70.6 (CH2), 68.3 (C2), 60.0 (C5). FTIR: 3030, 2909, 2860, 1734, 1495, 1453, 1074, 817, 733, 697 cm1. MS (ESI+): m/z [M+H]+ 611.3, [M+Na]+ 633.3. HRMS (ESI+): calcd for C40H39N2O4 611.2910, found 611.2909 [M+H]+. 4.8. (5R,6R,7S,8S)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-7-ol (17) To a stirred solution of gluco-configured tetrahydropyridoimidazole 15 (736 mg, 1.21 mmol) in a mixture of CH2Cl2/H2O (12 mL, 9:1) was added DDQ (820 mg, 3.54 mmol). The reaction mixture was stirred at room temperature overnight before CH2Cl2 (30 mL) and saturated aqueous NaHCO3 (30 mL) were added and the layers were separated. The aqueous layer was extracted with CH2Cl2 (2  30 mL). The organic layers were then combined, washed with brine (50 mL), dried (MgSO4), and concentrated. The crude product was purified by silica gel column chromatography (pentane/AcOEt 20:80) to afford the title compound 17 (299 mg, 53%) as a colorless oil. [a]D: +63.8 (c 2.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.47–7.25 (m, 15H, Ph), 7.09 (s, 1H, H7), 7.00 (s, 1H, H8), 5.27 (d, J = 11.5 Hz, 1H, CH2), 4.92 (t, J = 11.5 Hz, 2H, 2  CH2), 4.60 (d, J = 11.5 Hz, 1H, CH2), 4.56 (d, J = 7.4 Hz, 1H, H2), 4.47 (d, J = 12.1 Hz, 1H, CH2), 4.44 (d, J = 12.1 Hz, 1H, CH2), 4.17 (t, J = 8.1 Hz, 1H, H3), 4.08 (m, 1H, H5), 3.86 (dd, J = 10.7, 2.6 Hz, 1H, H6), 3.80 (dd, J = 8.1, 7.4 Hz, 1H, H4), 3.74 (dd, J = 10.7, 4.6 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 144.3 (Cq, imidazole), 138.3 (Cq), 137.8 (Cq), 137.2 (Cq), 129.6 (C7), 128.6 (CH), 128.5 (CH), 128.3 (CH), 128.14 (CH), 128.10 (CH), 127.8 (CH), 117.0 (C8), 76.7 (C4), 75.6 (C2), 74.8 (C3), 74.6 (CH2), 73.3 (CH2), 73.2 (CH2), 68.3 (C6), 58.4 (C5). FTIR: 3028, 2868, 1495, 1453, 1086, 732, 695 cm1. MS (ESI+): m/z [M+H]+ 471.2, [M+Na]+ 493.2. HRMS (ESI+): calcd for C29H31N2O4 471.2284, found 471.2296 [M+H]+. 4.9. (5R,6R,7S,8R)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-7-ol (18) To a stirred solution of manno-configured tetrahydropyridoimidazole 16 (313 mg, 0.51 mmol) in a mixture of CH2Cl2/H2O (10 mL, 9:1) was added DDQ (349 mg, 1.51 mmol). The reaction mixture was stirred at room temperature overnight before CH2Cl2 (30 mL)

40

C. Ouairy et al. / Carbohydrate Research 377 (2013) 35–43

and saturated aqueous NaHCO3 (30 mL) were added and the layers were separated. The aqueous layer was extracted with CH2Cl2 (2  30 mL). The organic layers were then combined, washed with brine (50 mL), dried (MgSO4), and concentrated. The crude product was purified by silica gel column chromatography (pentane/AcOEt 20:80) then AcOEt 100%) to afford the title compound 18 (116 mg, 49%) as a colorless oil. [a]D: 5.98 (c 2.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.35–7.27 (m, 15H, Ph), 7.19 (s, 1H, H8), 7.11 (s, 1H, H7), 4.96 (d, J = 11.6 Hz, 1H, CH2), 4.92 (d, J = 11.3 Hz, 1H, CH2), 4.77 (d, J = 2.8 Hz, 1H, H2), 4.72 (d, J = 11.6 Hz, 1H, CH2), 4.61 (d, J = 11.3 Hz, 1H, CH2), 4.49 (2  d, J = 11.3 Hz, 2H, 2  CH2), 4.08 (m, 3H, H3, H4, H5), 3.86 (dd, J = 10.5, 2.0 Hz, 1H, H6), 3.71 (dd, J = 10.5, 5.8 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 142.5 (Cq, imidazole), 138.0 (Cq), 137.9 (Cq), 137.6 (Cq), 129.7 (C7), 128.64 (CH, Ar), 128.61 (CH, Ar), 128.3 (CH, Ar), 128.2 (CH, Ar), 128.1 (CH, Ar), 128.04 (CH, Ar), 127.95 (CH, Ar), 127.9 (CH, Ar), 119.0 (C8), 75.5 (C3), 74.8 (CH2), 73.4 (CH2), 72.5 (C4), 71.4 (CH2, C2), 70.4 (C6), 59.2 (C5). FTIR: 3029, 2862, 1495, 1453, 1207, 1073, 818, 732, 696 cm1. MS (ESI+): m/z [M]+ 470.9, [M+H]+ 471.2. HRMS (ESI+): calcd for C29H31N2O4 471.2284, found 471.2289 [M+H]+.

raphy on silica gel (heptane/AcOEt 70:30, then 50:50) provided the xanthate 20 as a white oil (126 mg, 79%). [a]D: 42.9 (c 2.0, CHCl3). 1 H NMR (CDCl3, 500 MHz): d 7.35–7.23 (m, 15H, Ph), 7.18 (d, J = 1.3 Hz, 1H, H8), 7.11 (d, J = 1.3 Hz, 1H, H7), 6.08 (dd, J = 9.8, 3.4 Hz, 1H, H3), 5.09 (d, J = 3.4 Hz, 1H, H2), 4.86 (d, J = 11.0 Hz, 1H, CH2), 4.74 (d, J = 11.9 Hz, 1H, CH2), 4.66 (d, J = 12.2 Hz, 1H, CH2), 4.60 (dd, J = 9.8, 7.5 Hz, 1H, H4), 4.55 (d, J = 11.0 Hz, 1H, CH2), 4.47 (s, 2H, CH2), 4.21 (td, J = 6.4, 3.0 Hz, 1H, H5), 3.80 (dd, J = 10.2, 3.1 Hz, 1H, H6), 3.69 (dd, J = 10.2, 6.4 Hz, 1H, H60 ), 2.59 (s, 3H, CH3). 13C NMR (CDCl3, 125 MHz): d 215.2 (C@S), 142.2 (Cq, imidazole), 138.1 (Cq), 137.52 (Cq), 137.50 (Cq), 130.0 (CH, C7), 128.7 (CH, Ph), 128.6 (CH, Ph), 128.4 (CH, Ph), 128.2 (CH, Ph), 128.1 (CH, Ph), 128.0 (CH, Ph), 127.9 (CH, Ph), 127.7 (CH, Ph), 119.2 (CH, C8), 82.3 (C3), 75.1 (CH2), 73.4 (CH2), 72.6 (C4), 71.2 (CH2), 70.2 (C6), 68.8 (C2), 59.7(C5), 19.5 (CH3). FTIR: 3029, 2917, 2868, 1724, 1494, 1453, 1204, 1062, 733, 696 cm1. MS (ESI+): m/z [M+H]+ 561.2, 583.2 [M+Na]+. HRMS (ESI+): calcd for C31H33N2O4S2 561.1882, 561.1887 found [M+H]+.

4.10. O-((5R,6R,7S,8S)-6,8-Bis(benzyloxy)-5((benzyloxy)methyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridin7-yl) S-methyl carbonodithioate (19)

AIBN (2.6 mg, 0.016 mmol) was added to a solution of the xanthate 19 (90.3 mg, 0.16 mmol) in toluene (4 mL) and the flask placed in an oil bath preheated to 110 °C. A solution of tributylstannane (130 lL, 0.48 mmol) was added dropwise and heating continued for 40 min. After cooling to rt the reaction mixture was partitioned between pentane/acetonitrile. The acetonitrile phase was separated, diluted with saturated aqueous NaHCO3 (50 mL), and extracted with diethyl ether (3  50 mL). The combined organic layers where washed with brine (50 mL), dried (MgSO4), and the solvent was evaporated. Purification of the residue by flash chromatography on silica gel (toluene then heptane/AcOEt 20:80) afforded the title compound 21 as a colorless oil (48 mg, 66%). [a]D: +50.9 (c 1.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.45–7.22 (m, 15H, Ph), 7.11 (d, J = 1.4 Hz 1H, H7), 7.03 (d, J = 1.4 Hz 1H, H8), 5.12 (d, J = 11.9 Hz, 1H, CH2), 4.87 (d, J = 11.9 Hz, 1H, CH2), 4.74 (d, J = 11.5 Hz, 1H, CH2), 4.66 (t, J = 5.9 Hz, 1H, H2), 4.46 (s, 2H, CH2), 4.45 (d, J = 11.0 Hz, 1H, CH2), 4.28 (q, J = 5.7 Hz, 1H, H4), 3.90 (m, 1H, H5), 3.77 (dd, J = 10.1, 4.0 Hz, 1H, H6), 3.69 (dd, J = 10.1, 4.9 Hz, 1H, H60 ), 2.46 (ddd, J = 13.6, 5.7, 3.3 Hz, 1H, H 3eq), 2.29 (ddd, J = 13.6, 8.0, 5.9 Hz, 1H, H 30 ax). 13C NMR (CDCl3, 125 MHz): d 144.7 (Cq, imidazole), 138.7 (Cq), 137.7 (Cq), 137.4 (Cq), 129.0 (CH, C7), 128.6 (CH, Ph), 128.5 (CH, Ph), 128.4 (CH, Ph), 128.1 (CH, Ph), 128.0 (CH, Ph), 127.9 (CH, Ph), 127.5 (CH, Ph), 117.8 (CH, C8), 73.4 (CH2), 71.8 (CH2), 71.6 (C5), 71.1 (CH2), 69.6 (C6), 68.2 (C2), 59.9 (C4), 31.6 (C3). FTIR: 3030, 2926, 2859, 1721, 1452, 1272, 1072, 734, 696 cm1. MS (ESI+): m/z [M+H]+ 471.2. HRMS (ESI+): calcd for C29H31N2O4 471.2284, 471.2285 found [M+H]+.

A 1.0 M solution of NaHMDS in THF (190 lL, 0.19 mmol) and carbon disulfide (225 lL, 3.72 mmol) was added to a solution of the alcohol 17 (87.5 mg, 0.19 mmol) in THF (500 lL) at 78 °C. After stirring for 30 min at 78 °C, the solution was warmed to 0 °C and iodomethane (25 lL, 0.40 mmol) was added. Stirring was continued for an additional 30 min at 0 °C before water (20 mL) was added and the mixture was extracted with ether (3  15 mL). The combined organic layers were dried with MgSO4 and the solvent was removed. Purification of the residue by flash chromatography on silica gel (heptane/AcOEt 20:80) provided the xanthate 19 as a white oil (90.3 mg, 85%). [a]D: +63.4 (c 2.0, CHCl3). 1 H NMR (CDCl3, 500 MHz): d 7.41–7.22 (m, 15H, Ph), 7.13 (s, 1H, H7), 7.04 (s, 1H, H8), 6.53 (t, J = 6.4 Hz, 1H, H3), 4.97 (d, J = 11.7 Hz, 1H, CH2), 4.86 (d, J = 11.7 Hz, 1H, CH2), 4.81 (d, J = 6.4 Hz, 1H, H2), 4.78 (d, J = 12.7 Hz, 1H, CH2), 4.49 (m, 3H, CH2), 4.34 (m, 1H, H5), 4.11 (t, J = 6.4 Hz, 1H, H4), 3.84 (dd, J = 10.5, 3.4 Hz, 1H, H6), 3.77 (dd, J = 10.5, 5.0 Hz, 1H, H60 ), 2.52 (s, 3H, CH3). 13C NMR (CDCl3, 125 MHz): d 214.8 (C@S), 142.8 (Cq, imidazole), 137.8 (Cq), 137.2 (Cq), 137.1 (Cq), 129.5 (CH, C7), 128.6 (CH, Ph), 128.5 (CH, Ph), 128.4 (CH, Ph), 128.3 (CH, Ph), 128.2 (CH, Ph), 128.1 (CH, Ph), 128.0 (CH, Ph), 127.7 (CH, Ph), 117.8 (CH, C8), 81.8 (C2), 74.6 (C4), 73.4 (CH2), 73.2 (CH2), 72.0 (CH2), 71.9 (C3), 68.0 (C6), 57.9 (C5), 19.4 (CH3). FTIR: 3028, 2864, 1732, 1453, 1199, 1061, 908, 732, 697 cm1. MS (ESI+): m/z [M+H]+ 561.2. HRMS (ESI+): calcd for C31H33N2O4S2 561.1882, 561.1890 found [M+H]+. 4.11. O-((5R,6R,7S,8R)-6,8-Bis(benzyloxy)-5((benzyloxy)methyl)-5,6,7,8-tetrahydroimidazo[1,2-a]pyridin7-yl) S-methyl carbonodithioate (20) A 1.0 M solution of NaHMDS in THF (280 lL, 0.28 mmol) and carbon disulfide (340 lL, 5.63 mmol) was added to a solution of the alcohol 18 (131 mg, 0.28 mmol) in THF (1 mL) at 78 °C. After stirring for 30 min at 78 °C, the solution was warmed to 0 °C and iodomethane (35 lL, 0.56 mmol) was added. Stirring was continued for an additional 30 min at 0 °C before water (20 mL) was added and the solution was extracted with ether (3  15 mL). The combined organic layers were dried with MgSO4 and the solvent was removed. Purification of the residue by flash chromatog-

4.12. (5R,6S,8R)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridine (21)

4.13. (5R,6S,8S)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridine (22) AIBN (4 mg, 0.024 mmol) was added to a solution of the xanthate 20 (110 mg, 0.20 mmol) in toluene (5 mL) and the flask placed in an oil bath preheated to 110 °C. A solution of tributylstannane (200 lL, 0.74 mmol) was added dropwise and heating continued for 40 min. After cooling to room temperature the reaction mixture was partitioned between pentane/acetonitrile, and the acetonitrile phase was separated and diluted with saturated aqueous NaHCO3 (50 mL), and extracted with diethyl ether (3  50 mL). The combined organic layers were washed with brine (50 mL), dried (MgSO4), and the solvent was evaporated. Purification of the residue by flash chromatography on silica gel (toluene then heptane/AcOEt 20:80) afforded the title compound 22 as a

C. Ouairy et al. / Carbohydrate Research 377 (2013) 35–43

colorless oil (65 mg, 56%). [a]D: 8.2 (c 2.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.39–7.27 (m, 15H, Ph), 7.22 (s, 1H, H8), 7.10 (s, 1H, H7), 4.86 (d, J = 11.5 Hz, 1H, CH2), 4.77 (t, J = 4.1 Hz, 1H, H2), 4.72 (d, J = 12.0 Hz, 1H, CH2), 4.67 (d, J = 11.5 Hz, 1H, CH2), 4.53 (s, 2H, CH2), 4.47 (d, J = 11.5 Hz, 1H, CH2), 4.22 (m, 1H, H4), 4.13 (m, 1H, H5), 3.91 (dd, J = 10.2, 3.0 Hz, 1H, H6), 3.71 (dd, J = 10.2, 3.0 Hz, 1H, H60 ), 2.60 (dt, J = 13.5, 4.1 Hz, 1H, H 3eq), 2.02 (ddd, J = 13.5, 10.2, 4.1 Hz, 1H, H30 ax). 13C NMR (CDCl3, 125 MHz): d 143.8 (Cq, imidazole), 138.7 (Cq), 137.8 (Cq), 137.7 (Cq), 129.1 (CH, C7), 128.6 (CH, Ph), 128.4 (CH, Ph), 128.08 (CH, Ph), 128.06 (CH, Ph), 128.0 (CH, Ph), 127.83 (CH, Ph), 127.78 (CH, Ph), 127.5 (CH, Ph), 118.7 (CH, C8), 73.4 (CH2), 71.6 (CH2), 70.94 (C2), 70.88 (CH2), 70.6 (C6), 68.0(C4), 60.1 (C5), 32.8 (C3). FTIR: 3030, 2930, 2864, 1723, 1453, 1271, 1073, 732, 695 cm1. MS (ESI+): m/z [M+H]+ 455.2. HRMS (ESI+): calcd for C29H31N2O3 455.2335, 455.2301 found [M+H]+. 4.14. (5R,6R,7S,8S)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-7-yl trifluoromethanesulfonate (23) To a stirred solution of 17 (149 mg, 0.32 mmol) in THF (1.1 mL), at 78 °C, was added Comins’ reagent (169 mg, 0.41 mmol) and 1 M NaHMDS in THF (380 lL, 0.38 mmol). The reaction mixture was stirred from 78 °C to 60 °C for 2 h and was then allowed to warm to room temperature before MTBE (30 mL) and water (30 mL) were added and the layers were separated. The aqueous layer was extracted with MTBE (2  30 mL). The organic layers were then combined, washed with brine (100 mL), dried (MgSO4), and concentrated. The crude product was purified by silica gel column chromatography (heptane/AcOEt 50:50) to afford the triflate 23 (144 mg, 75%) as a colorless oil. [a]D: +72.0 (c 1.0, CHCl3). 1H NMR (CDCl3, 300 MHz): d 7.39–7.11 (m, 15H, Ph), 7.06 (d, J = 1.3 Hz, 1H, H7), 6.87 (d, J = 1.3 Hz, 1H, H8), 5.21 (m, 2H, CH2, H3), 4.89 (d, J = 10.8 Hz, 1H, CH2), 4.81 (d, J = 6.6 Hz, 1H, H2), 4.77 (d, J = 11.0 Hz, 1H, CH2), 4.37 (m, 3H, CH2), 4.06 (m, 2H, H4, H5), 3.78 (m, 1H, H6), 3.72 (m, 1, H60 ). 13C NMR (CDCl3, 75 MHz): d 142.3 (Cq, imidazole), 136.9 (Cq), 136.7 (Cq), 136.4 (Cq), 130.0 (CH, C7), 128.8 (CH, Ph), 128.7 (CH, Ph), 128.6 (CH, Ph), 128.52 (CH, Ph), 128.46 (CH, Ph), 128.4 (CH, Ph), 128.2 (CH, Ph), 128.1 (CH, Ph), 128.0 (CH, Ph), 116.3 (CH, C8), 87.6 (C3), 76.0 (CH2), 74.6 (C4), 73.4 (CH2), 72.8 (CH2), 72.3 (CH2), 72.3 (C2), 66.4 (C6), 58.0 (C5). FTIR: 1497, 1455, 1412, 1244, 1206, 1139, 1085, 1029, 947, 881, 843, 734, 697 cm1. MS (ESI+): m/z [M+H]+ 603.2. HRMS (ESI+): calcd for C30H30F3N2O6S 603.1777, found [M+H]+ 603.1775. 4.15. (5R,6R,7S,8R)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-7-yl trifluoromethanesulfonate (24) To a stirred solution of 18 (175 mg, 0.37 mmol) in THF (1.2 mL), at 78 °C, was added Comins’ reagent (185 mg, 0.45 mmol) and 1 M NaHMDS in THF (450 lL, 0.45 mmol). The reaction mixture was stirred from 78 °C to 60 °C for 2 h and was then allowed to warm to room temperature before MTBE (30 mL) and water (30 mL) were added and the layers were separated. The aqueous layer was extracted with MTBE (2  30 mL). The organic layers were then combined, washed with brine (100 mL), dried (MgSO4), and concentrated. The crude product was purified by silica gel column chromatography (heptane/AcOEt 50:50) to afford the triflate 24 (168 mg, 76%) as a colorless oil. [a]D: 26.6 (c 1.1, CHCl3), 1 H NMR (CDCl3, 300 MHz): d 7.37–7.20 (m, 16H, Ph + H8), 7.13 (d, J = 1.3 Hz, 1H, H7), 5.15 (dd, J = 9.2, 3.1 Hz, 1H, H3), 4.99 (d, J = 3.1 Hz, 1H, H2), 4.91 (d, J = 11.0 Hz, 1H, CH2), 4.75 (d, J = 11.6 Hz, 1H, CH2), 4.64 (d, J = 11.6 Hz, 1H, CH2), 4.56 (dd, J = 9.2, 7.3 Hz, 1H, H4), 4.49 (d, J = 11.6 Hz, 1H, CH2), 4.40 (s, 2H, CH2),

41

4.17 (m, 1H, H5), 3.70 (dd, J = 9.5, 3.2 Hz, 1H, H6), 3.60 (dd, J = 9.5, 3.2 Hz, 1H, H60 ). 13C NMR (CDCl3, 75 MHz): d 140.8 (Cq, imidazole), 136.9 (Cq), 137.23 (Cq), 137.17 (Cq), 130.4 (CH, C7), 128.7 (CH, Ph), 128.69 (CH, Ph), 128.6 (CH, Ph), 128.54 (CH, Ph), 128.46 (CH, Ph), 128.3 (CH, Ph), 128.2 (CH, Ph), 128.0 (CH, Ph), 127.9 (CH, Ph), 119.4 (CH, C8), 86.6 (C3), 75.6 (CH2), 73.4 (CH2), 72.3 (C4), 71.0 (CH2), 69.7 (C2), 69.5 (C6), 59.9 (C5). FTIR: 1497, 1455, 1415, 1246, 1211, 1145, 1096, 787, 700 cm1. MS (ESI+): m/z [M+H]+ 603.2. HRMS (ESI+): calcd for C30H30F3N2O6S 603.1777, 603.1797 found [M+H]+. 4.16. (5R,6R,7R,8S)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-7-ol (25) The gluco-configured tetrahydropyridoimidazole 23 (144 mg) in DMF (1 mL) was added dropwise to a mixture of para-nitrobenzoic acid (100 mg, 0.60 mmol) and cesium carbonate (94 mg, 0.29 mmol) in 1.4 mL of DMF (1.4 mL) and stirred at room temperature overnight. MTBE (30 mL) and water (30 mL) were then added and the layers were separated. The aqueous layer was extracted with MTBE (3  30 mL). The organic layers were then combined, washed with brine (100 mL), dried (MgSO4), and concentrated. The concentrate was taken up in MeOH (8 mL), treated with potassium carbonate (50 mg, 0.36 mmol) and stirred at room temperature for 3 h. AcOEt (20 mL) and water (20 mL) were then added and the layers were separated. The aqueous layer was extracted with AcOEt (2  20 mL). The organic layers were then combined, washed with brine (60 mL), dried (MgSO4), and concentrated. The crude product was purified by silica gel column chromatography (heptane/AcOEt 20:80) to afford the title compound 25 (26 mg, 23%) as a colorless oil. [a]D: +87.7 (c 1.0, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.44–7.18 (m, 15H, Ph), 7.11 (d, J = 1.3 Hz 1H, H7), 6.99 (d, J = 1.3 Hz 1H, H8), 5.23 (d, J = 12.1 Hz, 1H, CH2), 4.94 (d, J = 12.1 Hz, 1H, CH2), 4.69 (d, J = 11.6 Hz, 1H, CH2), 4.56 (d, J = 4.1 Hz, 1H, H2), 4.55 (d, J = 11.6 Hz, 1H, CH2), 4.41 (m, 4H, H3, H5, CH2), 3.85 (dd, J = 7.1, 3.9 Hz, 1H, H4), 3.80 (dd, J = 10.4, 3.6 Hz, 1H, H6), 3.72 (dd, J = 10.4, 4.2 Hz, 1H, H60 ). 13C NMR (CDCl3, 125 MHz): d 143.6 (Cq, imidazole), 138.0 (Cq), 137.5 (Cq), 137.4 (Cq), 129.6 (CH, C7), 128.64 (CH, Ph), 128.61 (CH, Ph), 128.2 (CH, Ph), 128.11 (CH, Ph), 128.09 (CH, Ph), 128.0 (CH, Ph), 127.9 (CH, Ph), 117.5 (CH, C8), 75.1 (C4), 73.4 (CH2), 72.7 (CH2), 72.4 (CH2), 71.2 (C2), 68.7 (C6), 66.4 (C3), 55.7 (C5). FTIR: 2933-2897, 1710, 1496, 1454, 1362, 1282, 1207, 1072, 1027, 734, 696 cm1. MS (ESI+): m/z [M+H]+ 471.2. HRMS (ESI+): calcd for C29H31N2O4 471.2284, 471.2281 found [M+H]+. 4.17. (5R,6R,7R,8R)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)5,6,7,8-tetrahydroimidazo[1,2-a]pyridin-7-ol (26) The manno-configured tetrahydropyridioimidazole 24 (168 mg) in DMF (1 mL) was added dropwise to a mixture of para-nitrobenzoic acid (120 mg, 0.72 mmol) and cesium carbonate (110 mg, 0.34 mmol) in DMF and stirred at room temperature overnight. MTBE (30 mL) and water (30 mL) were then added and the layers were separated. The aqueous layer was extracted with MTBE (3  30 mL). The organic layers were then combined, washed with brine (100 mL), dried (MgSO4), and concentrated. To a stirred solution of the crude product in MeOH (250 lL) was added potassium carbonate (58 mg, 0.42 mmol). The reaction mixture was stirred at room temperature for 3 h before AcOEt (20 mL) and water (20 mL) were added and the layers were separated. The aqueous layer was extracted with AcOEt (2  20 mL). The organic layers were then combined, washed with brine (60 mL), dried (MgSO4), and concentrated. The crude product was purified by silica gel column chromatography (heptane/AcOEt 20:80) to afford the title compound 26 (29 mg, 22%) as a colorless oil. [a]D: 5.2 (c 0.6,

42

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CHCl3). 1H NMR (CDCl3, 300 MHz): d 7.36–7.19 (m, 15H, Ph), 7.19 (d, J = 1.1 Hz, 1H, H8), 7.09 (d, J = 1.1 Hz, 1H, H7), 4.87 (d, J = 12.2 Hz, 1H, CH2), 4.76 (d, J = 4.1 Hz, 1H, H2), 4.72 (d, J = 12.2 Hz, 1H, CH2), 4.69 (d, J = 12.2 Hz, 1H, CH2), 4.53 (d, J = 12.2 Hz, 1H, CH2), 4.50 (s, 2H, CH2 (OBn, C6)), 4.45 (m, 1H, H3), 4.26 (m, 1H, H5), 4.20 (dd, J = 8.6, 2.1 Hz, 1H, H4), 3.90 (dd, J = 10.4, 2.5 Hz, 1H, H6), 3.72 (dd, J = 10.4; 5.7 Hz, 1H, H60 ). 13C NMR (CDCl3, 75 MHz): d 142.5 (Cq, imidazole), 138.4 (Cq), 137.6 (Cq), 137.3 (Cq), 129.1 (CH, C7), 128.8 (CH, Ph), 128.6 (CH, Ph), 128.5 (CH, Ph), 128.37 (CH, Ph), 128.36 (CH, Ph), 128.03 (CH, Ph), 127.95 (CH, Ph), 127.9 (CH, Ph), 127.7 (CH, Ph), 118.6 (CH, C8), 73.7(C4), 73.4 (CH2), 72.3 (CH2), 71.9 (C2), 71.4 (CH2), 69.7 (C6), 67.8 (C3), 55.9 (C5). FTIR: 2925–2869, 1728, 1496, 1454, 1364, 1272, 1208, 1092, 913, 737, 698 cm1. MS (ESI+): m/z [M+H]+ 471.2. HRMS (ESI+): calcd for C29H31N2O4 471.2284, 471.2303 found [M+H]+. 4.18. (5R,6R,7S,8S)-6,8-Bis(benzyloxy)-5-((benzyloxy)methyl)-7fluoro-5,6,7,8-tetrahydroimidazo[1,2-a]pyridine (27) To a stirred solution of 25 (9.3 mg, 0.02 mmol) in CH2Cl2 (500 lL) at 0 °C was added dropwise DAST (8 lL, 0.058 mmol). The reaction mixture was stirred at 0 °C for 10 min and at room temperature overnight before CH2Cl2 (2 mL) and MeOH (2 mL) were added to the reaction mixture followed by stirring for 10 min. CH2Cl2 (10 mL) was added and the organic layer was washed with water (10 mL), saturated NaHCO3 (10 mL), brine (20 mL), dried (MgSO4), and concentrated. The crude product was purified by silica gel column chromatography (heptane/AcOEt 40:60) to afford the fluoro derivative 27 (4.3 mg, 46%) as a colorless oil. [a]D: +54.5 (c 0.9, CHCl3). 1H NMR (CDCl3, 500 MHz): d 7.48– 7.25 (m, 15H, Ph), 7.13 (s, 1H, H7), 7.01 (s, 1H, H8), 5.13 (d, J = 11.8 Hz, 1H, CH2), 7.01 (d, J = 11.8 Hz, 1H, CH2), 5.13 (d, J = 11.8 Hz, 1H, CH2), 5.05 (dt, J = 50.7, 8.3 Hz, 1H, H3), 4.97 (d, J = 11.8 Hz, 1H, CH2), 4.91 (d, J = 11.8 Hz, 1H, CH2), 4.81 (dd, J = 18.4, 8.3 Hz, 1H, H2), 4.54 (d, J = 11.8, 1H, CH2), 4.47 (d, J = 11.8, 1H, CH2), 4.44 (d, J = 11.8, 1H, CH2), 4.09 (m, 1H, H5), 4.00 (q, J = 8.4 Hz, 1H, H4), 3.87 (m, 1H, H6), 3.77 (dd, J = 10.0, 4.3 Hz, 1H, H60 ). 13C NMR (CDCl3, 75 MHz): d 143.1 (Cq, imidazole), 137.9 (Cq), 137.3 (Cq), 137.2 (Cq), 130.1 (CH, C7), 128.71 (CH, Ph), 128,69 (CH, Ph), 128,5 (CH, Ph), 128,34 (CH, Ph), 128,27 (CH, Ph), 128,1 (CH, Ph), 127,9 (CH, Ph), 117,2 (CH, C8), 96,1 (d, JC,F = 183,0 Hz, C3), 74,8 (d, JC,F = 21,0 Hz, C4), 74,5 (CH2), 73,5 (CH2), 73,3 (d, J = 24,6 Hz, C2), 72,9 (CH2), 67,3 (C6), 57,3 (d, JC,F = 7,6 Hz, C5). FTIR: 2926, 2858, 1724, 1455, 1276, 1071, 735, 697 cm1. MS (ESI+): m/z [M+H]+ 473.2. HRMS (ESI+): calcd for C29H30FN2O3 473.2240, 473.2263 found [M+H]+.

37.8 (C3), 24.2 (CH3, AcO). FTIR: 3702–2143, 1660, 1559, 1408, 1175, 1049, 879, 753, 659 cm1. MS (ESI+): m/z [M+H]+ 185.1. HRMS (ESI+): calcd for C8H13N2O3185.0926 found 185.0931 [M+H]+. 4.20. (5R,6S,8S)-5-(Hydroxymethyl)-5,6,7,8tetrahydroimidazo[1,2-a]pyridine-6,8-diol (3) A solution of 18 (65 mg, 0.14 mmol) in AcOEt/MeOH/H2O (3:1:1, 2 mL) was treated with AcOH (400 lL) and 65 mg Pd(OH)2/C (20%) was added. The suspension was hydrogenated at atmospheric pressure for 3 days and was then filtered through a pad of CeliteÒ. Evaporation of the filtrate followed by flash chromatography on silica gel AcOEt/MeOH/H2O (5:3:3) gave 3 (5.5 mg, 16%) as a colorless oil. [a]D: 1.9 (c 1.1, MeOH). 1H NMR (CD3OD, 500 MHz): d 7.27 (d, J = 1.4 Hz, 1H, H8), 7.01 (d, J = 1.4 Hz, 1H, H7), 4.91 (t, J = 5.4 Hz, 1H, H2), 4.36 (ddd, J = 7.4, 5.4, 4.5 Hz, 1H, H4), 4.06 (m, 1H, H6), 3.87 (m, 2H, H5, H60 ), 2.20 (m, 2H, H3eq, H30 ax), 1.92 (s, 3H, CH3, AcO). 13C NMR (CD3OD, 125 MHz): d 178.3 (Cq, C@O, AcO-), 147.6 (Cq, imidazole), 128.5 (CH, C8), 119.5 (CH, C7), 64.7 (C5), 64.5 (C4), 63.3 (C6), 62.2 (C2), 38.0 (C3), 23.3 (CH3, AcO). FTIR: 3675–2424, 1566, 1412, 1071, 930, 746 cm1. MS (ESI+): m/z [M+H]+ 185.1. HRMS (ESI+): calcd for C8H13N2O3 185.0926 found 185.0936. 4.21. (5R,6R,7S,8S)-7-Fluoro-5-(hydroxymethyl)-5,6,7,8tetrahydroimidazo[1,2-a]pyridine-6,8-diol (4) A solution of the 27 (12.6 mg, 0.027 mmol) in AcOEt/MeOH/H2O (3:1:1. 1 mL) was treated with AcOH (200 lL) and 12.6 mg of Pd(OH)2/C (20%) and hydrogenated at atmospheric pressure for 3 days. The suspension was filtered through a pad of CeliteÒ. Evaporation of the filtrate followed by flash chromatography on silica gel AcOEt/MeOH/H2O (5:3:3) gave the acetate salt of 4 as a colorless oil (6 mg, 85%). [a]D: 5.6 (c 0.5, MeOH). 1H NMR (CD3OD, 500 MHz): d 7.33 (s, 1H, H8), 7.07 (s, 1H, H7), 4.79 (dd, J = 16.6, 8.2 Hz, 1H, H2), 4.56 (td, J = 52.0, 8.2 Hz, 1H, H3), 4.21 (d, J = 11.5 Hz, 1H, H6), 4.13 (q, J = 9.4 Hz, H4), 3.99 (dd, J = 11.5, 3.8 Hz, 1H, H60 ), 3.94 (m, 1H, H5), 1.96 (s, 3H, CH3).13C NMR (CD3OD, 125 MHz): d 179.4 (Cq, C@O), 129.7 (C7), 125.2 (Cq, imidazole), 118.8 (CH, C8), 97.3 (d, J = 179.0 Hz, C3), 68.1 (d, J = 23.7 Hz, C2), 67.5 (d, J = 19.1 Hz, C4), 61.3 (C5, d, J = 7.7 Hz), 60.7 (C6), 22.7 (CH3). FTIR: 3702–2325, 1567, 1415, 1109, 1021, 752 cm1. MS (ESI+): m/z 185.1 [MOH]+, 203.1 [M+H]+, 225.1 [M+Na]+. HRMS (ESI+): calcd for C8H12FN2O3 203.0832, 203.0838 found [M+H]+. 4.22. Biological evaluation

4.19. (5R,6S,8R)-5-(Hydroxymethyl)-5,6,7,8tetrahydroimidazo[1,2-a]pyridine-6,8-diol (2) A solution of 17 (25 mg, 0.055 mmol) in AcOEt/MeOH/H2O (3:1:1, 1 mL) was treated with AcOH (200 lL) and 25 mg of Pd(OH)2/C (20%) was added. The suspension was hydrogenated at atmospheric pressure, for 3 days and was then filtered through a pad of CeliteÒ. Evaporation of the filtrate followed by flash chromatography on silica gel AcOEt/MeOH/H2O (5:3:3) gave 2 (4.2 mg, 31%) as a colorless oil. [a]D: 25.2 (c 0.4, MeOH). 1H NMR (CD3OD, 500 MHz): d 7.28–7.27 (m, 1H, imidazole), 7.10–7.05 (m, 1H, imidazole), 4.79 (dd, J = 7.2, 5.7 Hz, 1H, H2), 4.18 (td, J = 8.7, 4.3 Hz, 1H, H5), 3.99 (dd, J = 12.0, 4.3 Hz, 1H, H6), 3.85 (dd, J = 12.0, 5.4 Hz, 1H, H60 ), 2.45 (ddd, J = 12.5, 5.7, 3.1 Hz, 1H, H3eq), 2.05 (td, J = 12.5, 7.2 Hz, 1H, H30 ax), 1.91 (s, 3H, CH3, AcO). 13C NMR (CD3OD, 125 MHz): d 180.5 (Cq, C@O, AcO), 148.3 (Cq, imidazole), 128.8 (CH, C7), 119.1 (CH, C8), 65.8 (C5), 64.8 (C4), 63.3 (C2), 62.6 (C6),

a- and b-glucosidase activities were assayed with 8 mM solutions of 4 methyl umbelliferyl a-D-glucopyranoside or 4methyl-umbelliferyl b-D-glucopyranoside (Carbosynth) and either Saccharomyces cerevisiae a-glucosidase or sweet almond b-glucosidase (Sigma) in 100 mM NaHPO4 buffer, pH 6.8 at 30 °C in a 384 well microplate format. Acarbose and isofagomine were used as reference inhibitors. Similarly, a- and b-mannosidase activities were assayed in 50 mM Na citrate pH 4.5 at 30 °C with 2.7 mM 4 methyl umbelliferyl a-D-mannopyranoside (Carbosynth) and Jack Bean a-mannosidase or 8 mM 4 methyl umbelliferyl b-D-mannopyranoside (Carbosynth) and Helix pomatia b-mannosidase (Sigma). Fluorescence was monitored (ex 364 nm, em 445 nm) over a 20 min period. For the initial screening, compounds were added at a concentration of 10 lM. For IC50 determinations, compounds were added at concentrations ranging 10 nM–50 lM in duplicate.

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Supplementary data Supplementary data (copies of the 1H and 13C NMR spectra of all new compounds) associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.carres.2013.05.011. References 1. Aoyama, T.; Naganawa, H.; Suda, H.; Uotani, K.; Aoyagi, T.; Takeuchi, T. J. Antibiot. 1992, 45, 1557–1558. 2. Bols, M.; López, O.; Ortega-Caballero, F. In Comprehensive Glycoscience; Kamerling, J., Ed.; Elsevier: Amsterdam, 2007; Vol. 1, pp 815–884. 3. Elbein, A. D.; Molyneux, R. J. In Comprehensive Natural Products II; Mander, L., Liu, H.-W., Eds.; Elsevier: Amsterdam, 2010; Vol. 6, pp 225–260. 4. Tailford, L. E.; Offen, W. A.; Smith, N. L.; Dumon, C.; Morland, C.; Gratien, J.; Heck, M.-P.; Stick, R. V.; Blériot, Y.; Vasella, A.; Gilbert, H. J.; Davies, G. J. Nat. Chem. Biol. 2008, 4, 306–312. 5. Gloster, T. M.; Davies, G. J. Org. Biomol. Chem. 2010, 305–320. 6. Davies, G. J.; Planas, A.; Rovira, C. Acc. Chem. Res. 2012, 45, 308–316. 7. Thompson, A. J.; Dabin, J.; Iglesias-Fernandez, J.; Ardevol, A.; Dinev, Z.; Williams, S. J.; Bande, O.; Siriwardena, A.; Moreland, C.; Hu, T.-C.; Smith, D. K.; Gilbert, H. J.; Rovira, C.; Davies, G. J. Angew. Chem., Int. Ed. 2012, 51, 10997– 11001. 8. Heightman, T. D.; Vasella, A. Angew. Chem., Int. Ed. 1999, 38, 750–770. 9. Varrot, A.; Schülein, M.; Pipelier, M.; Vasella, A.; Davies, G. J. J. Am. Chem. Soc. 1999, 121, 2621–2622. 10. Ducros, V. M.-A.; Zechel, D. L.; Murshudov, G. N.; Gilbert, H. J.; Szabo, L.; Stoll, D.; Withers, S. G.; Davies, G. J. Angew. Chem., Int. Ed. 2002, 41, 2824–2827. 11. Sulzenbacher, G.; Driguez, H.; Henrissat, B.; Schulein, M.; Davies, G. J. Biochemistry 1996, 35, 15280–15287. 12. Davies, G. J.; Mackenzie, L.; Varrot, A.; Dauter, M.; Brzozowski, A. M.; Schülein, M.; Withers, S. G. Biochemistry 1998, 34, 11707–11713.

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13. Tews, I.; Perrakis, A.; Oppenheim, A.; Dauter, Z.; Wilson, K. S.; Vorgias, C. E. Nat. Struct. Biol. 1996, 3, 638–648. 14. Tatsuta, K.; Miura, S.; Ohta, S.; Gunji, H. Tetrahedron Lett. 1995, 36, 1085– 1088. 15. Crich, D.; Vinogradova, O. J. Org. Chem. 2006, 71, 8473–8480. 16. Crich, D.; Li, L. J. Org. Chem. 2007, 72, 1681–1690. 17. Zhang, W. H.; Oliver, A. G.; Serianni, A. S. Acta Crystallogr. Sect. C 2011, 66, O557–O560. 18. Zhang, W.; Noll, B. C.; Serianni, A. S. Acta Crystallogr. 2007, C63, o578–o581. 19. Hoos, R.; Naughton, A. B.; Vasella, A. Helv. Chim. Acta 1993, 76, 1802–1807. 20. Granier, T.; Panday, N.; Vasella, A. Helv. Chim. Acta 1997, 80, 979–987. 21. Overkleeft, H. S.; van Wiltenburg, J.; Pandit, U. K. Tetrahedron Lett. 1994, 50, 4215–4224. 22. Wennekes, T.; van den Berg, R. J. B. H. N.; Donker, W.; van der Marel, G. A.; Strijland, A.; Aerts, J. M. F. G.; Overkleeft, H. S. J. Org. Chem. 2007, 72, 1088– 1097. 23. Mancuso, A. J.; Huang, S.-L.; Swern, D. J. Org. Chem. 1978, 43, 2480. 24. Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277–7287. 25. Thomsen, I.; Clausen, K.; Scheibye, S.; Lawesson, S.-O. Org. Synth. Colloid Vol. 1990, 7, 372–375. 26. Ozturk, T.; Ertas, E.; Mert, O. Chem. Rev. 2007, 107, 5210–5278. 27. Xia, J.; Abbas, S. A.; Locke, R. D.; Piskorz, C. F.; Alderfer, J. L.; Matta, K. L. Tetrahedron Lett. 2000, 41, 169–173. 28. Barton, D. H. R.; McCombie, S. W. J. Chem. Soc., Perkin Trans. 1 1975, 1574– 1585. 29. Comins, D. L.; Dehghani, A.; Foti, C. J.; Joseph, S. P. Org. Synth. 1997, 74, 77–81. 30. Dax, K.; Albert, M.; Ortner, J.; Paul, B. J. Carbohydr. Res. 2000, 327, 47–86. 31. Jesresen, T. M.; Bols, M.; Sierks, M. R.; Skrudstrup, T. Tetrahedron 1994, 50, 13449–13460. 32. Iminosugars: From Synthesis to Therapeutic Applications; Compain, P., Martin, O. R., Eds.; Wiley: Chichester, 2007. 33. Tatsuta, K.; Miura, S.; Ohta, S.; Gunji, H. J. Antibiot. 1995, 48, 286–288. 34. Li, T.; Guo, L.; Zhang, Y.-B.; Wang, J.; Zhang, Z.; Li, J.; Zhang, W.; Lin, J.; Zhao, W.; Wang, P. G. Bioorg. Med. Chem. 2011, 19, 2136–2144.