2,3-dihydrofuro[2,3-b]pyridine compounds

Abstract

The present invention provides a compound of Formula I: wherein R is H or F; or a pharmaceutically acceptable salt thereof, and the use of compounds of Formula I for treatment of neurodegenerative diseases, such as Alzheimer's disease. ##STR00001##

Claims

1. A compound of the formula: ##STR00031## wherein R is H or F, or a pharmaceutically acceptable salt thereof.

2. The compound according to claim 1 wherein R is H, or a pharmaceutically acceptable salt thereof.

3. The compound according to claim 1 wherein R is F, or a pharmaceutically acceptable salt thereof.

4. The compound according to claim 1 wherein the compound is (−)-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine, or a pharmaceutically acceptable salt thereof.

5. The compound according to claim 1 wherein the compound is (+)-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine, or a pharmaceutically acceptable salt thereof.

6. The compound according to claim 1 wherein the compound is (−)-5-fluoro-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine, or a pharmaceutically acceptable salt thereof.

7. The compound according to claim 6 which is: (−)-5-fluoro-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine.

8. The compound according to claim 1 wherein the compound is (+)-5-fluoro-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine, or a pharmaceutically acceptable salt thereof.

9. The compound according to claim 8 which is: (+)-5-fluoro-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine.

10. A method of treating Alzheimer's disease in a patient, comprising administering to a patient in need of such treatment an effective amount of a compound of claim 1, or a pharmaceutically acceptable salt thereof.

11. A method of preventing the progression of mild cognitive impairment to Alzheimer's disease in a patient, comprising administering to a patient in need of such treatment an effective amount of a compound of claim 1, or a pharmaceutically acceptable salt thereof.

12. A method of treating progressive supranuclear palsy in a patient, comprising administering to a patient in need of such treatment an effective amount of a compound of claim 1, or a pharmaceutically acceptable salt thereof.

13. A pharmaceutical composition, comprising a compound or a pharmaceutically acceptable salt thereof according to claim 1 with one or more pharmaceutically acceptable carriers, diluents, or excipients.

14. A process for preparing a pharmaceutical composition, comprising admixing a compound or a pharmaceutically acceptable salt thereof according to claim 1 with one or more pharmaceutically acceptable carriers, diluents, or excipients.

Description

PREPARATIONS AND EXAMPLES

(1) The following Preparations and Examples further illustrate the invention and represent typical synthesis of compounds of the invention. The reagents and starting materials are readily available or may be readily synthesized by one of ordinary skill in the art. It should be understood that the Preparations and Examples are set forth by way of illustration and not limitation, and that various modifications may be made by one of ordinary skill in the art.

(2) LC-ES/MS is performed on an AGILENT©HP1100 liquid chromatography system. Electrospray mass spectrometry measurements (acquired in positive and/or negative mode) are performed on a Mass Selective Detector quadrupole mass spectrometer interfaced to the HP1100 HPLC. LC-MS conditions (low pH): column: PHENOMENEX© GEMINI©NX C18 2.1×50 mm 3.0 μm; gradient: 5-100% B in 3 min, then 100% B for 0.75 min column temperature: 50° C.+/−10° C.; flow rate: 1.2 mL/min; Solvent A: deionized water with 0.1% HCOOH; Solvent B: ACN with 0.1% formic acid; wavelength 214 nm. Alternate LC-MS conditions (high pH): column: XTERRA©MS C18 columns 2.1×50 mm, 3.5 μm; gradient: 5% of solvent A for 0.25 min, gradient from 5% to 100% of solvent B in 3 min and 100% of solvent B for 0.5 min or 10% to 100% of solvent B in 3 min and at 100% of solvent B for 0.75 min; column temperature: 50° C.+/−10° C.; flow rate: 1.2 mL/min; Solvent A: 10 mM NH.sub.4HCO.sub.3 pH 9; Solvent B: ACN; wavelength: 214 nm.

(3) Preparative reversed phase chromatography is performed on an AGILENT® 1200 LC-ES/MS equipped with a Mass Selective Detector mass spectrometer and a LEAP® autosampler/fraction collector. High pH methods are run on a 75×30 mm PHENOMENEX© GEMINI©-NX, 5μ particle size column with a 10×20 mm guard. Flow rate of 85 mL/min. Eluent is 10 mM ammonium bicarbonate (pH 10) in acetonitrile unless noted otherwise.

(4) NMR spectra are performed on a Bruker AVIII HD 400 MHz NMR Spectrometer, obtained as CDCl.sub.3 or DMSO solutions reported in ppm, using residual solvent [CDCl.sub.3, 7.26 ppm; (CD.sub.3).sub.2SO, 2.05 ppm] as reference standard. When peak multiplicities are reported, the following abbreviations may be used: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), br-s (broad singlet), dd (doublet of doublets), dt (doublet of triplets). Coupling constants (J), when reported, are reported in hertz (Hz).

Preparation 1

diethyl 2-(2,6-dichloro-3-pyridyl)propanedioate

(5) ##STR00008##

(6) Scheme 1, step A: A mixture of diethyl malonate (17.8 mL, 117 mmol), 2,6-dichloro-3-iodopyridine (21.8 g, 78.1 mmol), picolinic acid (1.2 g, 10.1 mmol), CuI (0.8 g, 4.3 mmol) and Cs.sub.2CO.sub.3 (74.8 g, 229.6 mmol) in 1,4-dioxane (200 mL), under nitrogen, is stirred at 80° C. for 6 h. The reaction mixture is cooled to RT and saturated aqueous NH.sub.4Cl (150 mL) is added. The resulting mixture is extracted twice with EtOAc, and the combined organic extracts are washed sequentially with saturated aqueous NH.sub.4Cl and saturated aqueous NaCl solution. The organic extracts are dried over MgSO.sub.4, filtered, and the filtrate is evaporated under reduced pressure to afford the title compound (29.4 g, 93% yield) as a brown oil, which is suitable for use without further purification. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 306/308 (M+H).

Preparation 2

2-(2,6-dichloro-3-pyridyl)acetic acid

(7) ##STR00009##

(8) Scheme 1, step B: A solution of diethyl 2-(2,6-dichloro-3-pyridyl)propanedioate (1.2 g, 2.5 mmol) in a 5 M aqueous solution of HCl (11 mL) is heated at reflux for 24 h. The reaction cooled to RT and the resulting white precipitate is collected by filtration to afford the title compound (362 mg, 64% yield) as a white powder. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 206/208 (M+H).

Preparation 3

2,6-dichloro-3-[(E)-2-ethoxyvinyl]pyridine

(9) ##STR00010##

(10) Scheme 1, step F: To a 1 necked round bottom flask, with stirrer, and air condenser, under nitrogen, is added 2,6-dichloro-3-iodo-pyridine (1.0 g, 3.8 mmol), 2-[(E)-2-ethoxyvinyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.9 g, 4.8 mmol), Cs.sub.2CO.sub.3 (3.75 g, 11.5 mmol), 1,4-dioxane (19.2 mL), and water (4.26 mL). This reaction mixture is purged 3 times alternating between vacuum and nitrogen, and [1,1′ bis(diphenylphosphino) ferrocene]dichloropalladium(II) (0.2 g) is added. The resulting mixture is stirred for 3 hr at 90° C., the reaction is poured onto saturated aqueous NH.sub.4Cl, and the aqueous mixture is extracted three times with EtOAc. The combined organic extracts are dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 0-100% EtOAc in cyclohexane, to afford the title compound (748 mg, 89% yield), after solvent evaporation of the desired chromatographic fractions. .sup.1H NMR (300 MHz, CDCl.sub.3): δ 1.37 (m, 3H), 3.97 (m, 2H), 5.97 (m, 1H), 6.99 (m, 1H), 7.16 (m, 1H), 7.60 (m, 1H).

Preparation 4

2,6-dichloro-3-vinyl-pyridine

(11) ##STR00011##

(12) Scheme 1, step D: To a round bottom flask is added 2,6-dichloro-3-iodo-pyridine (6.3 g, 22.9 mmol), potassium vinyltrifluoroborate (3.09 g, 23 mmol), bis(triphenlyphosphine)palladium(II) dichloride (327 mg, 0.46 mmol) and Na.sub.2CO.sub.3 (4.85 g, 45.7 mmol). The flask is evacuated and back-filled with nitrogen three times. EtOH (75.1 mL) is added and the flask is again evacuated and back-filled with nitrogen three times. The reaction mixture is heated at 90° C. overnight, diluted with EtOAc and water, the phases are separated, and the aqueous phase is extracted three times with EtOAc. The organic extracts are combined, dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 0-100% EtOAc in cyclohexane, to obtain the title compound (3.0 g, 69% yield), after solvent evaporation of the desired chromatographic fractions. .sup.1H NMR (300 MHz, CDCl.sub.3): δ 5.53 (m, 1H), 5.78 (m, 1H), 6.97 (m, 1H), 7.26 (m, 1H), 7.82 (m, 1H).

Preparation 5

2-(2,6-dichloro-3-pyridyl)ethanol

(13) ##STR00012##

(14) Scheme 1, step C: A solution of 2-(2,6-dichloro-3-pyridyl)acetic acid (8.1 g, 37 mmol) in THE (100 mL) is cooled in an ice-bath. A 1 M solution of BH.sub.3-THF complex in THF (55.5 mL, 55.5 mmol) is added slowly. The reaction mixture is stirred for 1 h, warmed to RT, and stirred for a further 20 h. MeOH (30 mL) is added cautiously, the resulting solution is stirred for 5 min, and concentrated under reduced pressure. The resulting residue is dissolved in MeOH and concentrated under reduced pressure again to afford the title compound as a thick brown oil (7.7 g, 98% yield), suitable for use without additional purification. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 192/194 (M+H).

Alternate Procedure for Preparation 5

(15) Scheme 1, step G: To a 1 necked round bottom flask, with stirrer and air condenser, under nitrogen, is added 2,6-dichloro-3-[(E)-2-ethoxyvinyl]pyridine (748 mg, 3.4 mmol) to acetone (17.1 mL) and a 2M aqueous solution of HCl (8.6 mL) is added. The resulting mixture is heated at 60° C. with stirring for 3.5 h. The resulting mixture is cooled to RT, diluted with EtOAc, and quenched with saturated aqueous NaHCO.sub.3. The resulting aqueous mixture is extracted three times with EtOAc, the combined organic extracts are dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue is dissolved in MeOH (8.6 mL) and THE (4.9 mL), and NaBH.sub.4 (195 mg) is added portion-wise over 5 min. The reaction mixture is stirred at RT for 40 min, quenched with water, extracted three times with EtOAc, and the combined organic extracts are washed with saturated aqueous NaCl, dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 0-60% EtOAc in cyclohexane, to obtain the title compound (315 mg, 47% yield), after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 193 (M+H).

Alternate Procedure for Preparation 5

(16) Scheme 1, step E: To a flask was added 2,6-dichloro-3-vinyl-pyridine (3 g, 17.5 mmol) and THE (1.5 mL) at RT. The mixture was stirred in an ice-water bath and a 0.5M solution of 9-borabicyclo[3.3.1]nonane in THE (49.1 mL) is added dropwise over 2 min. The reaction mixture is stirred in a 45° C. heating block for 2 h. The reaction mixture is stirred in an ice-water bath, and 2N aqueous NaOH (26.3 mL) is added dropwise over 5 min, followed by a 35% aqueous solution of H.sub.2O.sub.2 (4.87 mL) over 2 min, and the resulting reaction mixture is stirred at RT for 2 h. The reaction mixture is diluted with water and extracted three times with EtOAc, the combined organic extracts are washed with saturated aqueous Na.sub.2S.sub.2O.sub.3-5H.sub.2O solution, dried over Na.sub.2SO.sub.4, and concentrated under reduced pressure. The resulting residue is purified by flash chromatography over silica gel, eluting with 0-50% EtOAc/cyclohexane, to obtain the title compound (1.8 g, 55% yield) after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 193 (M+H).

Preparation 6

6-chloro-2,3-dihydrofuro[2,3-b]pyridine

(17) ##STR00013##

(18) Scheme 2, step A: A solution of 2-(2,6-dichloro-3-pyridyl)ethanol (10.8 g, 56.3 mmol) and potassium tert-butoxide (9.5 g, 84.5 mmol) in 2-methyl-2-butanol (200 mL) is heated at 60° C. for 2 h. The reaction mixture is cooled to RT, concentrated to partial volume under reduced pressure, and the resulting mixture is diluted with CHCl.sub.3 and saturated aqueous NH.sub.4Cl. The resulting layers are separated, the aqueous phase is additionally extracted twice with CH.sub.3Cl, the combined organic extracts are dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure to obtain the title compound as brown oil (8.7 g, 84% yield), which solidified upon standing at RT, of sufficient purity for use without additional purification. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 156/158 (M+H).

Preparation 7

2,3-dihydrofuro[2,3-b]pyridine-6-carbonitrile

(19) ##STR00014##

(20) Scheme 2, step B: To a round bottom flask is added 6-chloro-2,3-dihydrofuro[2,3-b]pyridine (1.1 g, 7.2 mmol), 2-di-tert-butylphosphino-2′,4′,6′-triisopropylbiphenyl (126 mg, 0.3 mmol), allyl(2-di-tert-butylphosphino-2′,4′,6′-triisopropyl-1,1′-biphenyl)palladium(II) triflate (208 mg, 0.3 mmol), KOAc (353 mg, 3.6 mmol) and potassium ferrocyanide trihydrate (492 mg, 1.1 mmol). To the mixture is added water (2.2 mL) and 1,4-dioxane (7.2 mL) and nitrogen is bubbled through the mixture for 10 min at RT. The reaction mixture is stirred in a 100° C. heating block overnight. The reaction mixture is cooled to RT, diluted with EtOAc, quenched with water, the phases are separated, and the aqueous phase is additionally extracted three times with EtOAc. The combined organic extracts are washed with saturated aqueous NaCl, dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 0-40% EtOAc in cyclohexane, to obtain the title compound (600 mg, 57% yield), after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 147 (M+H).

Preparation 8

1-(2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanone

(21) ##STR00015##

(22) Scheme 2, step D: A mixture of 6-chloro-2,3-dihydrofuro[2,3-b]pyridine (8.6 g, 47.4 mmol), ethylene glycol monovinylether (13 mL, 145 mmol), [1,3-bis(diphenylphosphino)propane]palladium(II) dichloride (1.4 g, 2.4 mmol) and TEA (23 mL, 165 mmol) in ethylene glycol (100 mL) is heated to 160° C. for 1 h. The resulting mixture is cooled and concentrated under reduced pressure. An aqueous solution of 5 N HCl (50 mL) is added to the resulting residue, the mixture is stirred for 10 min, and extracted three times with DCM. The combined organic extracts are concentrated under reduced pressure and the resulting residue is slurried in EtOAc. The resulting mixture is filtered and the filtrate is washed three times with water. The organic phase is dried over MgSO.sub.4 and concentrated under reduced pressure to afford the title compound as brown oil, which slowly solidifies upon standing at RT (7.0 g, 82% yield), suitable for use without additional purification. ES/MS m/z: 164 (M+H).

Alternate Procedure for Preparation 8

(23) Scheme 2, step C: To a flask is added 2,3-dihydrofuro[2,3-b]pyridine-6-carbonitrile (349 mg, 2.4 mmol) in THE (4.7 mL). A 3 M solution of methylmagnesium bromide in Et.sub.2O (1.5 mL) is added at 0° C. and the resulting reaction mixture is stirred for 2 h. The mixture is quenched with saturated aqueous NH.sub.4Cl and stirred for 20 min. The mixture is extracted three times with EtOAc, and the combined organic extracts are washed with saturated aqueous NaCl, dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 0-40% EtOAc in cyclohexane, to obtain the title compound (339 mg, 87% yield), after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 164 (M+H).

Preparation 9

(−)-1-(2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanol

(24) ##STR00016##

(25) Scheme 2, step E: To a solution of 1-(2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanone (1.8 g, 11.2 mmol) in water (160 mL) and IPA (40 mL) is added KRED P3-C12 enzyme (0.9 g) and KRED recycle mix P (0.9 g). The reaction is stirred at 35° C. for 18 h and the resulting mixture is extracted three times with EtOAc. The combined organic extracts are washed sequentially with water and saturated aqueous NaCl, dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue is purified via flash chromatography over silica gel, eluting with a gradient of 50-100% Et.sub.2O:iso-hexane, to afford the title compound (1.35 g, 73% yield) after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 166 (M+H). [α].sub.D.sup.20=−58.2° (c=1, MeOH). As used hereinabove, the terms “(−)” or “(−) enantiomer” for Preparation 9 refers to the enantiomer of Preparation 9 which has an optical rotation which is counterclockwise (or “(−)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in methanol.

Preparation 10

(+)-6-[1-chloroethyl]-2,3-dihydrofuro[2,3-b]pyridine

(26) ##STR00017##

(27) Scheme 2, step F: A solution of (−)-1-(2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanol (1.35 g, 8.2 mmol) and TEA (2.8 mL, 20 mmol) in DCM (35 mL) is cooled in an ice-bath and methane sulfonylchloride (1.2 mL, 15 mmol) is added drop-wise. The reaction is warmed to RT, stirred for 7 days, and quenched with saturated aqueous NaHCO.sub.3 (20 mL). The mixture is poured through a phase separator cartridge, washing with DCM. After removing the solvent under reduced pressure, the resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of Et.sub.2O:iso-hexane, to afford the title compound (1.2 g, 76% yield) after solvent evaporation of the desired chromatographic fractions. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 184/186 (M+H). [α].sub.D.sup.20=+88.20 (c=1, DCM). As used hereinabove, the terms “(+)” or “(+) enantiomer” for Preparation 10 refers to the enantiomer of Preparation 10 which has an optical rotation which is clockwise (or “(+)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in DCM.

Preparation 11

2-chloro-4-(1,1-diethoxyethyl)-5-fluoro-pyrimidine

(28) ##STR00018##

(29) Scheme 3, step A: To a solution 1-(2-chloro-5-fluoro-pyrimidin-4-yl)ethanone (46.4 g, 266 mmol) in triethyl orthoformate (120 mL) is added trifluoromethanesulfonic acid (1 mL). The reaction is stirred for 72 h and concentrated in vacuo. The resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 5-15% Et.sub.2O/iso-hexane, to afford the title compound (53.9 g, 70% yield) after solvent evaporations of the desired chromatographic fractions. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 249/251 (M+H).

Preparation 12

1-(2-but-3-ynoxy-5-fluoro-pyrimidin-4-yl)ethanone

(30) ##STR00019##

(31) Scheme 3, step B: To an ice-bath cooled solution of 3-butyn-1-ol (17 mL, 218 mmol) in THE (400 mL) is added portion wise a suspension of 60% NaH in mineral oil (8.7 g, 218 mmol). The resulting mixture is stirred at RT for 1 hand 2-chloro-4-(1,1-diethoxyethyl)-5-fluoro-pyrimidine (53.9 g, 217 mmol) in THE (200 mL) is added dropwise. The dark-red mixture is stirred for 90 min and quenched with saturated aqueous NH.sub.4Cl. The aqueous mixture is extracted three times with EtOAc, the combined extracts are washed with saturated aqueous NaCl, dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure. The resulting residue in dissolved in THF (400 mL) and aqueous 2 N HCl (100 mL) is added. The resulting mixture is stirred for 3 h and concentrated under reduced pressure. The resulting precipitate is collected by filtration and triturated with cyclohexane to afford, after filtration, the title compound (39.6 g, 85% yield). ES/MS m/z: 209 (M+H).

Preparation 13

1-(5-fluoro-2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanone

(32) ##STR00020##

(33) Scheme 3, step C: A solution of 1-(2-but-3-ynoxy-5-fluoro-pyrimidin-4-yl)ethanone (3.25 g, 14.8 mmol) in sulfolane (20 mL) is heated to 235° C. for 30 min. The mixture is purified by flash chromatography over silica gel, eluting with a gradient of 40-80% MTBE:iso-hexane, to obtain a yellow oil after solvent evaporation of the desired chromatographic fractions. The resulting residue is further purified by flash chromatography over silica gel, eluting with a gradient of 30-50% MTBE:iso-hexane, to afford the title compound as a yellow solid (739 mg, 27% yield) after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 182 (M+H).

Preparation 14

1-(5-fluoro-2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanol

(34) ##STR00021##

(35) Scheme 3, step D: A solution of 1-(5-fluoro-2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanone (904 mg, 4.9 mmol) in THE (30 mL) and EtOH (5 mL) is cooled in an ice-bath. NaBH.sub.4 (194 mg, 5.1 mmol) is added and the mixture stirred for 1.5 h. The reaction is quenched by careful addition of saturated aqueous NH.sub.4Cl and concentrated under reduced pressure. Water and DCM are sequentially added to the resulting residue and the resulting biphasic mixture is filtered through a phase separator cartridge. The separated DCM filtrate is concentrated under reduced pressure to afford the title compound (845 mg, 94% yield). ES/MS m/z: 184 (M+H).

Preparation 15

6-(1-chloroethyl)-5-fluoro-2,3-dihydrofuro[2,3-b]pyridine

(36) ##STR00022##

(37) Scheme 3, step E: A solution of 1-(5-fluoro-2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanol (845 mg, 4.6 mmol) and DIPEA (1.8 mL, 10 mmol) in DCM (20 mL) is cooled in an ice bath and methane sulfonylchloride (0.8 mL, 10 mmol) is added drop-wise. The reaction is warmed to RT and stirred for 16 h. The mixture is diluted with DCM and quenched using saturated aqueous NaHCO.sub.3 (20 mL). The mixture is poured through a phase separator cartridge, washing with DCM. The DCM phase is collected, concentrated under reduced pressure, and the resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 50-100% Et.sub.2O:iso-hexane, to afford the title compound (858 mg, 83% yield) after solvent evaporation of the desired chromatographic fractions. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 202.0/204 (M+H).

Preparation 16

(−)-1-(5-fluoro-2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanol

(38) ##STR00023##

(39) Scheme 3, step D: Combine 1-(5-fluoro-2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanone (3.419 g, 18.9 mmol) and [N-[(1S,2S)-2-(amino-κN)-1,2-diphenylethyl]-4-methylbenzenesulfonamidato-N]chloro[(1,2,3,4,5,6-η)-1-methyl-4-(1-methylethyl)benzene]-ruthenium (1.0 g, 1.6 mmol) in HCOOH-TEA 5:2 complex (30 mL) and purge with nitrogen for 5 min with stirring. Heat the resulting mixture to 35° C. for 2 h under N.sub.2. Cool the reaction mixture and dilute with EtOAc and saturated aqueous NaHCO.sub.3. Extract the mixture three times with EtOAc. Dry the combined organic extracts over Na.sub.2SO.sub.4, filter, and remove the solvent from the filtrate under reduced pressure. Purify the crude product by flash chromatography over silica gel, using a mixture of 50% EtOAc in hexanes, to afford the title compound (3.0 g, 87% yield) after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 184 (M+H). [α].sub.D.sup.20=−16.80 (c=2, MeOH). As used hereinabove, the terms “(−)” or “(−) enantiomer” for Preparation 16 refers to the enantiomer of Preparation 16 which has an optical rotation which is counterclockwise (or “(−)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in methanol.

Preparation 17

(+)-6-[1-chloroethyl]-5-fluoro-2,3-dihydrofuro[2,3-b]pyridine

(40) ##STR00024##

(41) Scheme 3, step E: A solution of (−)-1-(5-fluoro-2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanol (3.0 g, 16.3 mmol) in DMF (75 mL) is treated dropwise with benzoyl chloride (2.9 mL, 25 mmol). The reaction mixture is stirred at RT for 16 h under nitrogen. The mixture is diluted with EtOAc and saturated aqueous NaHCO.sub.3. Extract the mixture three times with EtOAc, dry the combined organic extracts over Na.sub.2SO.sub.4, filter, and remove the solvent from the filtrate under reduced pressure. Purify the crude product by flash chromatography over silica gel, using a gradient of 5% to 100% EtOAc in hexanes, to afford the title compound (3.1 g, 95% yield) after solvent evaporation of the desired chromatographic fractions. ES/MS (.sup.35Cl/.sup.37Cl) m/z: 202.0/204 (M+H). [α].sub.D.sup.20=+68.2° (c=0.2, DCM). As used hereinabove, the terms “(−)” or “(−) enantiomer” for Preparation 17 refers to the enantiomer of Preparation 17 which has an optical rotation which is clockwise (or “(+)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in DCM.

Preparation 18

tert-butyl 4-(acetamidocarbamoyl)piperidine-1-carboxylate

(42) ##STR00025##

(43) To a flask is added 1-tert-butoxycarbonylpiperidine-4-carboxylic acid (15.0 g, 65.8 mmol) in THF (150.8 mL). The solution is stirred in an ice-water bath and 1,1′-carbonyldiimidazole (15.2 g, 92.1 mmol) is added in one portion. The reaction mixture is stirred at RT for 2 h, and acethydrazide (6.5 g, 85.5 mmol) is added in one portion at 0° C. The reaction mixture is warmed to RT and stirred overnight, and diluted with saturated aqueous NaHCO.sub.3 solution (250 mL) and 2-methyltetrahydrofuran. The mixture is transferred to a separating funnel and the layers are separated. The aqueous layer is extracted with 2-methyltetrahydrofuran and the combined organic extracts are washed with saturated aqueous NaCl solution and dried over MgSO.sub.4. The aqueous layer is extracted twice with DCM and the combined organic extracts are washed with saturated aqueous NaCl solution and dried over MgSO.sub.4. The two organic solutions are combined and concentrated under reduced pressure to give a residue, which is combined with MTBE (300 mL). The mixture is stirred in a 50° C. heating block for 1 hr, stirred overnight at RT, filtered, and the filter cake is washed with MTBE. The filtered solid is dried under vacuum at 45° C. for 3 hr to obtain the title compound (14.5 g, 48.5 mmol, 73.7% yield) as a white solid. ES/MS m/z: 308 (M+Na).

Preparation 19

2-methyl-5-(4-piperidyl)-1,3,4-oxadiazole

(44) ##STR00026##

(45) To a flask is added triphenylphosphine (16.4 g, 61.9 mmol) and DCM (177 mL). The solution is stirred at RT and 12 (16.0 g, 61.9 mmol) is added portion-wise; TEA (10.9 mL, 77.4 mmol) is added and the reaction mixture is stirred at RT for 15 min. The mixture is stirred in an ice-water bath and tert-butyl 4-(acetamidocarbamoyl)piperidine-1-carboxylate (9.3 g, 31.0 mmol) is added. The reaction mixture is stirred in an ice-water bath for 2 h, saturated aqueous NaHCO.sub.3 solution is added, and the mixture is transferred to a separation funnel. The layers are separated and the aqueous layer is extracted with DCM. The combined organic extracts are dried over MgSO.sub.4, filtered, and the filtrate is concentrated under reduced pressure to give a residue, which is dissolved in DCM (186 mL). To the solution is added TFA (46.5 mL) and the reaction mixture is stirred at RT overnight. The mixture is concentrated under reduced pressure and the resulting residue is combined with DCM and water. The layers are separated and the aqueous layer is extracted twice with EtOAc. The aqueous layer is basified to pH 14 with 50% aqueous NaOH solution and extracted 6 times with DCM. The combined organic extracts are washed with saturated aqueous NaCl solution, dried over MgSO.sub.4, and concentrated under reduced pressure to give a solid, which is dried under vacuum at 40° C. for 2 h, to obtain the title compound (4.3 g, 25.9 mmol, 83% yield) as an off-white solid. ES/MS m/z: 168 (M+H).

Example 1

(−)-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine

(46) ##STR00027##

(47) Scheme 2, step G: A mixture of (+)-6-[1-chloroethyl]-2,3-dihydrofuro[2,3-b]pyridine (247 mg, 1.3 mmol), 4-(5-methyl-1,3,4-oxadiazol-2-yl)piperidine (476 mg, 2.7 mmol) and K.sub.2CO.sub.3 (195 mg, 1.4 mmol) in ACN (18 mL) is irradiated at 120° C. for 150 min in a microwave. The reaction mixture is diluted with EtOAc and quenched with saturated aqueous NH.sub.4Cl. The mixture is extracted with EtOAc and the organic phase is dried over MgSO.sub.4. The filtrate is evaporated under reduced pressure and the resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 0-10% MeOH:DCM, to obtain a yellow oil (333 mg) after solvent evaporation of the desired chromatographic fractions. This material is pooled with additional material produced by similar methodology from additional experimental runs (total 540 mg after chromatography over silica gel) and further purified by SFC chiral chromatography (Chiral AD-H column 250×30 mm, 5 μm; column temperature 35° C.; flow rate 120 g/min), eluting with 18% IPA/0.2% DMEA in CO.sub.2, to afford the title compound (383 mg) as an oil Analytical HPLC: t.sub.R=2.35 min, >99% ee (Amyl chiral column, 3.3×150 mm, flow rate 1.5 mL/min, 18% IPA/0.2% IPAm in 82% CO.sub.2, 35° C. column temperature, 287 nM). ES/MS m/z: 315.0 (M+H). [α].sub.D.sup.20=12.7 (c=0.24, MeOH). As used herein above, the terms “(−)” or “(−) enantiomer” for Example 1 refers to the enantiomer of Example 1 which has an optical rotation which is counterclockwise (or “(−)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in methanol.

Alternate Procedure for Example 1

(48) Scheme 2, step H: To a stirred solution of 1-(2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanone (100 mg, 0.6 mmol) and 2-methyl-5-(4-piperidyl)-1,3,4-oxadiazole (200 mg, 1.2 mmol) in CHCl.sub.3 (5.2 mL) is added titanium(IV) isopropoxide (363 μL, 1.2 mmol) and the reaction mixture is stirred for 30 min. NaBH(OAc).sub.3 (390 mg, 1.8 mmol) is added and the reaction stirred at 40° C. overnight. The reaction mixture is diluted with EtOAc (5 mL) and saturated aqueous NaHCO.sub.3 (2 mL) for 20 min, the mixture is filtered through a bed of diatomaceous earth, and the filtrate is concentrated under reduced pressure. The resulting residue is purified by reverse phase chromatography over C18 silica gel (XBridge C18, 5 μm 19×100 mm; 214 nm and 300 nm; MS-ESI 100-800), eluting with a mixture of 10 mM aqueous NH.sub.4HCO.sub.3, pH: ˜9.0, in ACN (20% to 40% with a gradient time of 4 min), flow rate: 25 mL/min) with additional purification by SCF chiral chromatography (CHIRALPAK© AD-H column, 250×30 mm, 5 μm; column temperature 35° C.; flow rate 120 mL/min) eluting with 18% IPA/0.2% DMEA in CO.sub.2, to afford the title compound (27 mg, 55% yield), after solvent evaporation of the desired chromatographic fractions. t.sub.R=0.096 min, >99% ee (Amyl chiral column, 3.3×150 mm, flow rate 1.5 mL/min, 18% IPA/0.2% IPAm in 82% C02, 35° C. column temperature, 287 nM). ES/MS m/z: 315 (M+H).

Example 2

(−)-5-fluoro-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine

(49) ##STR00028##

(50) Scheme 3, step F: Heat a mixture of 6-(1-chloroethyl)-5-fluoro-2,3-dihydrofuro[2,3-b]pyridine (111 mg, 0.5 mmol), 4-(5-methyl-1,3,4-oxadiazol-2-yl)piperidine (107 mg, 0.6 mmol) and K.sub.2CO.sub.3 (85 mg, 0.6 mmol) in ACN (8 mL) at 80° C. for 27 h. Cool the reaction mixture, dilute with DCM, and quench with water. Pour the resulting biphasic mixture through a phase separator cartridge. Evaporate the DCM under reduced pressure, and purify the residue via flash chromatography over silica gel, eluting with a 50-100% gradient of EtOAc/iso-hexane, to obtain a white solid after solvent evaporation of the desired chromatographic fractions. Additionally purify by SFC chiral chromatography (CHIRALPAK© AZ-3 column 150×3 mm, 3 μm; column temp. 35° C.; flow rate 1.5 mL/min), eluting with 40% MeOH/0.2% IPA in CO.sub.2, to afford the title compound in >99% ee (44 mg, 39% yield) after solvent evaporation of the desired chromatographic fractions. Analytical HPLC: t.sub.R=3.7 min, >99% ee (Chiral AZ-3 column, 3.3×150 mm, flow rate 1.5 mL/min, 40% MeOH/0.2% IPAm in 60% CO.sub.2, 35° C. column temperature, 220 nM). ES/MS m/z: 333.0 (M+H). [α].sub.D.sup.20=−117.5° (c=0.2, DCM).

(51) Alternatively, a mixture (+)-6-(1-chloroethyl)-5-fluoro-2,3-dihydrofuro[2,3-b]pyridine (500 mg, 2.5 mmol), 4-(5-methyl-1,3,4-oxadiazol-2-yl)piperidine (829 mg, 5 mmol) and K.sub.2CO.sub.3 (1.0 g, 7.5 mmol) in ACN (25 mL) is heated to 65° C. for 72 h. The mixture is cooled, diluted with water, extracted the three times with EtOAc, and the combined organic extracts are dried over Na.sub.2SO.sub.4. Then extracts are filtered, and the filtrate is concentrated under reduces pressure. The resulting residue is purified by flash chromatography over silica gel, eluting with a gradient of 0.5% to 10% MeOH in DCM, to afford 586 mg of the title compound in 76.6% ee, after solvent evaporation of the desired chromatographic fractions. The title compound is further purified by SFC chiral chromatography (CHIRALPAK© AD-H, 21×250 mm, 3 μm; column temp. 40° C.; flow rate 80 mL/min), eluting with 15% MeOH/0.2% IPAm) in 85% CO.sub.2, to afford the title product in 96.5% ee (457 mg, 55% yield), after solvent evaporation of the desired chromatographic fractions. ES/MS m/z: 333.0 (M+H). Analytical HPLC t.sub.R=2.08 min, >96.5% ee (CHIRALPAK©AD-H, 4.6×150 mm, flow rate 5 mL/min; 15% MeOH/0.2% IPAm in CO.sub.2). [α].sub.D.sup.20=−109.9° (C=0.2, DCM). As used herein above, the terms “(−)” or “(−) enantiomer” for Example 2 refers to the enantiomer of Example 2 which has an optical rotation which is counterclockwise (or “(−)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in DCM.

Example 3

(+)-6-[(1R)-1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine

(52) ##STR00029##

(53) The title compound can be prepared from (−)-6-[1-chloroethyl]-2,3-dihydrofuro[2,3-b]pyridine and 4-(5-methyl-1,3,4-oxadiazol-2-yl)piperidine, or from 1-(2,3-dihydrofuro[2,3-b]pyridin-6-yl)ethanone and 2-methyl-5-(4-piperidyl)-1,3,4-oxadiazole utilizing chiral chromatography, in a manner analogous to the procedures set forth in Example 1. [α].sub.D.sup.20=+19.3° (c=0.20, MeOH)

(54) As used herein above, the terms “(+)” or “(+) enantiomer” for Example 3 refers to the enantiomer of Example 3 which has an optical rotation which is clockwise (or “(+)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in MeOH.

Example 4

(+)-5-fluoro-6-[1-[4-(5-methyl-1,3,4-oxadiazol-2-yl)-1-piperidyl]ethyl]-2,3-dihydrofuro[2,3-b]pyridine

(55) ##STR00030##

(56) The title compound can be prepared from 6-(1-chloroethyl)-5-fluoro-2,3-dihydrofuro[2,3-b]pyridine and 4-(5-methyl-1,3,4-oxadiazol-2-yl)piperidine utilizing chiral chromatography in a manner analogous to the procedure set forth in Example 2. t.sub.R=2.0 min under the same analytical HPLC conditions described in Example 2. [α].sub.D.sup.20=+107.3° (c=0.20, DCM)

(57) As used herein above, the terms “(+)” or “(+) enantiomer” for Example 4 refers to the enantiomer of Example 4 which has an optical rotation which is clockwise (or “(+)”) at 20° C. and 589 nm with the noted concentration “c” (g/100 mL) in DCM.

In Vitro Human OGA Enzyme Assay

(58) Generation of OGA Enzyme

(59) The nucleotide sequence encoding full-length human O-GlcNAc-β-N-acetylglucosaminidase (NM_012215) is inserted into pFastBacl (Invitrogen) vector with an N-terminal poly-histidine (HIS) tag. Baculovirus generation is carried out according to the Bac-to-Bac Baculovirus Expression system (Invitrogen) protocol. Sf9 cells are infected at 1.5×10.sup.6 cells/mL using 10 mL of P1 virus per Liter of culture and incubated at 28° C. for 48 hrs. Cells are spun down, rinsed with PBS and the pellets stored at −80° C. The above OGA protein (His-OGA) is purified as follows: 4 L of cells are lysed in 200 mL of buffer containing 50 mM Tris, pH 8.0, 300 mM NaCl, 10% glycerol, 10 mM imidazole, 1 mM dithiothreitol (DTT), 0.1% Triton™ X-100, 4 tablets of protease inhibitors (complete EDTA-Free, Roche) for 45 min at 4° C. This cell lysate is then spun for 40 min at 16500 rpm at 4° C., and supernatant incubated with 6 mL of Ni-NTA resin (nickel-nitrilotriacetic acid) for 2 hours at 4° C.

(60) Resin is then packed onto column and washed with 50 mM Tris, pH 8.0, 300 mM NaCl, 10% glycerol, 10 mM imidazole, 0.1% Triton™ X-100, 1 mM DTT, followed by 50 mM Tris, pH 8.0, 150 mM NaCl, 10 mM imidazole, 10% glycerol, 1 mM DTT. The proteins are eluted with 50 mM Tris, pH 8.0, 150 mM NaCl, 300 mM imidazole, 10% glycerol, 1 mM DTT. Pooled His-OGA containing fractions are concentrated to 6 ml and loaded onto Superdex75 (16/60). The protein is eluted with 50 mM Tris, pH 8.0, 150 mM NaCl, 10% glycerol, 2 mM DTT. Fractions containing His-OGA are pooled and protein concentration measured with BCA (Bradford Colorimetric Assay).

(61) OGA Enzyme Assay

(62) The OGA enzyme catalyses the removal of O-GlcNAc from nucleocytoplasmic proteins. To measure this activity Fluorescein di-N-acetyl-β-N-acetyl-D-glucosaminide (FD-GlcNAc, Kim, Eun Ju; Kang, Dae Ook; Love, Dona C.; Hanover, John A. Carbohydrate Research (2006), 341(8), 971-982) is used as a substrate at a final concentration of 6.7 μM (in a 384 well assay format). This fluorogenic substrate becomes fluorescent upon cleavage by OGA, so that the enzyme activity can be measured by the increase in fluorescence detected at 535 nm (excitation at 485 nm).

(63) The assay buffer is prepared to give a final concentration of 50 mM H.sub.2NaPO.sub.3—HNa.sub.2PO.sub.3, 0.01% bovine serum albumin and 0.01% Triton™ X-100 in water, at pH 7. Compounds to be tested are diluted in pure dimethyl sulfoxide (DMSO) using ten point concentration response curves. Maximal compound concentration in the reaction mixture is 30 or 1 μM. Compounds at the appropriate concentration are pre-incubated with OGA enzyme for 30 minutes before the reaction is started by the addition of substrate. The final enzyme concentration is 3.24 nM or 0.5 nM, for the 30 or 1 μM maximal compound concentration, respectively. Reactions are allowed to proceed for 60 minutes at room temperature. Then, without stopping the reaction, fluorescence is read. IC.sub.50 values are calculated by plotting the normalized data vs. log of the compound and fitting the data using a four parameter logistic equation.

(64) The compounds of Examples 1 to 4 were tested essentially as described above and exhibited the following IC.sub.50 values as set forth in Table 1:

(65) TABLE-US-00001 TABLE 1 Example IC.sub.50 (nM) 1 1.24 ± 0.66 (n = 7) 2 1.13 ± 1.02 (n = 6) 3 611.4 (n = 1) 4 2657 ± 606.7 (n = 2)

(66) These results demonstrate that the compounds of Examples 1 to 4 inhibit OGA enzyme activity in vitro.