Synthesis of Phosphoramidates

Abstract

A process for the preparation of a compound of formula (I) including all isomers, stereoisomers, enantiomers and diastereomers thereof (I), and salts thereof; the process comprising providing a mixture comprising a compound of formula (II) and a compound of formula (III) subjecting the mixture provided in a) to reaction conditions in the presence of one or more Lewis acids to the mixture provided in a), obtaining a mixture comprising the compound of formula (I).

##STR00001##

Claims

1. A process for the preparation of a compound of formula (I) including all isomers, stereoisomers, enantiomers and diastereomers thereof ##STR00214## and salts thereof, the process comprising a) providing a mixture comprising a compound of formula (II) ##STR00215## and a compound of formula (III) ##STR00216## b) subjecting the mixture provided in a) to reaction conditions in the presence of one or more Lewis acids to the mixture, obtaining a mixture comprising the compound of formula (I); wherein at each occurrence Ar is phenyl, naphthyl, quinolinyl, isoquinolinyl, quinazolinyl or quinoxalinyl, each optionally substituted with at least one of C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkoxy, C.sub.1-C.sub.6 cycloalkyl, aryl, halogen, COOH, CHO, C(O)(C.sub.1-C.sub.6 alkyl), C(O)(aryl), COO(C.sub.1-C.sub.6 alkyl), COONH.sub.2, COONH(C.sub.1-C.sub.6 alkyl) and CN; (Y—).sub.nR.sub.1 is a leaving group for nucleophilic substitution reaction, wherein n is 0 or 1 and wherein Y is O, N or S; R.sub.2 and R.sub.3 are independently H or C.sub.1-C.sub.6 alkyl optionally substituted with at least one of OH, C.sub.1-C.sub.6 alkoxy, aryl, heteroaryl, C.sub.1-C.sub.6 alkyl, C.sub.3-C.sub.6 cycloalkyl, F, Cl, Br, I, NO.sub.2, COOH, CHO, C(O)(C.sub.1-C.sub.6 alkyl), C(O)(aryl), COO(C.sub.1-C.sub.6 alkyl), COONH.sub.2, COONH (C.sub.1-C.sub.6 alkyl) and CN; R.sub.6 is C.sub.1-C.sub.6 alkyl or C.sub.3-C.sub.10 cycloalkyl optionally substituted with at least one of C.sub.1-C.sub.6 alkyl and aryl; Base is a purinyl residue or a pyrimidinyl residue linked to the furanose ring according to formula (III) through a carbon or nitrogen atom; R.sub.7 and R.sub.8 are independently H, OH, F, Cl, Br, I, azide, nitrile, NH.sub.2, NHR.sub.26, NR.sub.26R.sub.24, (CO)—NH.sub.2, (CO)—NHR.sub.26, (CO)—NR.sub.26R.sub.24, C.sub.1-C.sub.6 alkyl optionally substituted with C.sub.1-C.sub.6 alkyl, or C.sub.3-C.sub.10 cycloalkyl optionally substituted with C.sub.1-C.sub.6 alkyl, wherein R.sub.26 and R.sub.24 are independently C.sub.1-C.sub.6 alkyl; R.sub.9 is H, OH, C.sub.1-C.sub.6 alkoxy, OC(O)R.sub.25, or C.sub.1-C.sub.6 alkyl optionally substituted with C.sub.1-C.sub.6 alkyl or aryl, wherein R.sub.25 is C.sub.1-C.sub.6 alkyl or aryl.

2. The process of claim 1, wherein, when n is 1, R.sub.1 is alkyl, aryl, or heteroaryl, each optionally substituted with one or more electron-withdrawing groups, or R.sub.1 is a residue of formula (A) ##STR00217## a residue of formula (B) ##STR00218## a residue of formula (C) ##STR00219## or a residue of formula (D) ##STR00220## or wherein, when n is 0, R.sub.1 is a residue of formula (A1) ##STR00221## wherein at each occurrence X.sub.1 and X.sub.2 are independently O or S; R.sub.4 and R.sub.5 are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 alkoxy, or R.sub.4 and R.sub.5, together with the structure —C—N—C— according to formula (A), form an optionally substituted, 5-, 6-, or 7-membered saturated or partially unsaturated ring, wherein said ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.17 is an electron-withdrawing group; R.sub.18 and R.sub.18′ are independently F, Cl, Br, I, or C.sub.1-C.sub.6 alkoxy; each Q is independently C or N, wherein at least one Q is N; R.sub.19 and R.sub.19′ are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl optionally substituted with at least one of OH and NH.sub.2, or C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.19 and R.sub.19′ taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring, wherein the ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.20, R.sub.21, R.sub.22 and R.sub.23 are each independently H, aryl, or C.sub.1-C.sub.6 alkyl optionally substituted with at least one of C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.20 and R.sub.22, or R.sub.20 and R.sub.23, or R.sub.21 and R.sub.22, or R.sub.21 and R.sub.23 when taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring which is an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S.

3-8. (canceled)

9. The process of claim 1, wherein R.sub.1 is a residue of formula (IIb) ##STR00222## wherein X.sub.1 is O and X.sub.2 is O.

10-11. (canceled)

12. The process of claim 1, wherein the Lewis acid is selected from the group consisting of ZnBr.sub.2, ZnCl.sub.2, ZnI.sub.2, MgBr.sub.2, MgBr.sub.2.OEt.sub.2, CuCl.sub.2, Cu(acetylacetonate).sub.2, and Fe(II) fumarate.

13-19. (canceled)

20. The process of claim 1, wherein the compound of formula (II) is a compound of formula (II-A) ##STR00223##

21. (canceled)

22. The process of claim 1, wherein the compound of formula (I) is the compound of formula (I-A) ##STR00224##

23. The process of claim 1, wherein the one or more Lewis acids according to b) comprise a twice positively charged ion, or a three times positively charged ion.

24-31. (canceled)

32. The process of claim 1, further comprising providing the mixture according to a) by a process comprising (i) providing a mixture comprising a compound of formula (IV) ##STR00225## and a compound R.sub.1(—Y).sub.nH; (ii) subjecting the mixture provided in (i) to reaction conditions, obtaining a mixture comprising the compound of formula (II).

33-59. (canceled)

60. A composition of which at least 99.90 weight-% consists of the compound of formula (II) ##STR00226## wherein Ar is phenyl, naphthyl, quinolinyl, isoquinolinyl, quinazolinyl or quinoxalinyl, each optionally substituted with at least one of C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkoxy, C.sub.1-C.sub.6 cycloalkyl, aryl, halogen, COOH, CHO, C(O)(C.sub.1-C.sub.6 alkyl), C(O)(aryl), COO(C.sub.1-C.sub.6 alkyl), COONH.sub.2, COONH(C.sub.1-C.sub.6 alkyl) and CN; R.sub.2 and R.sub.3 are independently H or C.sub.1-C.sub.6 alkyl optionally substituted with at least one of OH, C.sub.1-C.sub.6 alkoxy, aryl, heteroaryl, C.sub.1-C.sub.6 alkyl, C.sub.3-C.sub.6 cycloalkyl, F, Cl, Br, I, COOH, CHO, C(O)(C.sub.1-C.sub.6 alkyl), C(O)(aryl), COO(C.sub.1-C.sub.6 alkyl), COONH.sub.2, COONH(C.sub.1-C.sub.6 alkyl) and CN; R.sub.6 is C.sub.1-C.sub.6 alkyl or C.sub.3-C.sub.10 cycloalkyl optionally substituted with at least one of C.sub.1-C.sub.6 alkyl and aryl; (Y—).sub.nR.sub.1 is a leaving group for nucleophilic substitution reaction, wherein n is 0 or 1 and wherein Y is O, N or S; wherein, when n is 1, R.sub.1 is a residue of formula (A) ##STR00227## a residue of formula (B) ##STR00228## a residue of formula (C) ##STR00229## or a residue of formula (D) ##STR00230## or wherein, when n is 0, R.sub.1 is a residue of formula (A1) ##STR00231## wherein at each occurrence X.sub.1 and X.sub.2 are independently O or S; R.sub.4 and R.sub.5 are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 alkoxy, or R.sub.4 and R.sub.5, together with the structure —C—N—C— according to formula (A), form an optionally substituted, 5-, 6-, or 7-membered saturated or partially unsaturated ring, wherein said ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.17 is an electron-withdrawing group; R.sub.18 and R.sub.18′ are independently F, Cl, Br, I, or C.sub.1-C.sub.6 alkoxy; each Q is independently C or N, wherein at least one Q is N; R.sub.19 and R.sub.19′ are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl optionally substituted with at least one of OH and NH.sub.2, or C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.19 and R.sub.19′ taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring, wherein the ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.20, R.sub.21, R.sub.22 and R.sub.23 are each independently H, aryl, or C.sub.1-C.sub.6 alkyl optionally substituted with at least one of C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.20 and R.sub.22, or R.sub.20 and R.sub.23, or R.sub.21 and R.sub.22, or R.sub.21 and R.sub.23 when taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring which is an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S; and wherein said composition has a content, based on the weight of the mixture, of less than 100 weight-ppm of an aryl-OH compound substituted with one or more electron-withdrawing groups.

61-65. (canceled)

66. The composition of claim 60, wherein R.sub.1 is a residue of formula (IIb) ##STR00232## wherein X.sub.1 is O and X.sub.2 is O.

67-75. (canceled)

76. A compound of formula (II) ##STR00233## wherein Ar is phenyl, naphthyl, quinolinyl, isoquinolinyl, quinazolinyl or quinoxalinyl, each optionally substituted with at least one of C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkoxy, C.sub.1-C.sub.6 cycloalkyl, aryl, halogen, COOH, CHO, C(O)(C.sub.1-C.sub.6 alkyl), C(O)(aryl), COO(C.sub.1-C.sub.6 alkyl), COONH.sub.2, COONH(C.sub.1-C.sub.6 alkyl) and CN; R.sub.2 and R.sub.3 are independently H or C.sub.1-C.sub.6 alkyl optionally substituted with at least one of OH, C.sub.1-C.sub.6 alkoxy, aryl, heteroaryl, C.sub.1-C.sub.6 alkyl, C.sub.3-C.sub.6 cycloalkyl, F, Cl, Br, I, COOH, CHO, C(O)(C.sub.1-C.sub.6 alkyl), C(O)(aryl), COO(C.sub.1-C.sub.6 alkyl), COONH.sub.2, COONH C.sub.1-C.sub.6 alkyl) and CN; R.sub.6 is C.sub.1-C.sub.6 alkyl or C.sub.3-C.sub.10 cycloalkyl optionally substituted with at least one of C.sub.1-C.sub.6 alkyl and aryl; (Y—).sub.nR.sub.1 is a leaving group for nucleophilic substitution reaction, wherein n is 0 or 1 and wherein Y is O, N or S; wherein, when n is 1, R.sub.1 is alkyl, aryl, or heteroaryl, each optionally substituted with one or more electron-withdrawing groups; or R.sub.1 is a residue of formula (A) ##STR00234## a residue of formula (B) ##STR00235## a residue of formula (C) ##STR00236## or a residue of formula (D) ##STR00237## or wherein, when n is 0, R.sub.1 is a residue of formula (A1) ##STR00238## wherein at each occurrence X.sub.1 and X.sub.2 are independently O or S; R.sub.4 and R.sub.5 are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 alkoxy, or R.sub.4 and R.sub.5, together with the structure —C—N—C— according to formula (A), form an optionally substituted, 5-, 6-, or 7-membered saturated or partially unsaturated ring, wherein said ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.17 is an electron-withdrawing group; R.sub.18 and R.sub.18′ are independently F, Cl, Br, I, or C.sub.1-C.sub.6 alkoxy; each Q is independently C or N, wherein at least one Q is N; R.sub.19 and R.sub.19′ are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl optionally substituted with at least one of OH and NH.sub.2, or C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.19 and R.sub.19′ taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring, wherein the ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.20, R.sub.21, R.sub.22 and R.sub.23 are each independently H, aryl, or C.sub.1-C.sub.6 alkyl optionally substituted with at least one of C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.20 and R.sub.22, or R.sub.20 and R.sub.23, or R.sub.21 and R.sub.22, or R.sub.21 and R.sub.23 when taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring which is an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S.

77. The compound of formula (II) of claim 76, wherein (Y—).sub.nR.sub.1 is a leaving group for nucleophilic substitution reaction, wherein n is 0 or 1 and wherein Y is O, N or S; wherein, when n is 1, R.sub.1 is a residue of formula (A) ##STR00239## a residue of formula (B) ##STR00240## a residue of formula (C) ##STR00241## or a residue of formula (D) ##STR00242## or wherein, when n is 0, R.sub.1 is a residue of formula (A1) ##STR00243## wherein at each occurrence X.sub.1 and X.sub.2 are independently O or S; R.sub.4 and R.sub.5 are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 alkoxy, or R.sub.4 and R.sub.5, together with the structure —C—N—C— according to formula (A), form an optionally substituted, 5-, 6-, or 7-membered saturated or partially unsaturated ring, wherein said ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.17 is an electron-withdrawing group; R.sub.18 and R.sub.18′ are independently F, Cl, Br, I, or C.sub.1-C.sub.6 alkoxy; each Q is independently C or N, wherein at least one Q is N; R.sub.19 and R.sub.19′ are independently H, OH, NH.sub.2, C.sub.1-C.sub.6 alkyl optionally substituted with at least one of OH and NH.sub.2, or C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.19 and R.sub.19′ taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring, wherein the ring is optionally fused to a 5- or 6-membered, optionally substituted ring which is a C.sub.5-C.sub.6 cycloalkyl, an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S; R.sub.20, R.sub.21, R.sub.22 and R.sub.23 are each independently H, aryl, or C.sub.1-C.sub.6 alkyl optionally substituted with at least one of C.sub.1-C.sub.6 alkoxy optionally substituted with at least one of OH and NH.sub.2; or R.sub.20 and R.sub.22, or R.sub.20 and R.sub.23, or R.sub.21 and R.sub.22, or R.sub.21 and R.sub.23 when taken together form an optionally substituted 5-, 6-, or 7-membered saturated or partially unsaturated or aromatic ring which is an aryl, or a heterocycle comprising one or more heteroatoms independently being N, O or S.

78-92. (canceled)

93. The process of claim 1 wherein the one or more Lewis acids according to b) comprise a Zn ion, a Mg ion, a Cu ion, or an Fe ion, or a Mn ion.

Description

EXAMPLES

Reference Example 1: General Analytical Methods

[0732] Reactions were monitored by HPLC on a C-18 reverse phase column with a gradient of acetonitrile in 10 mM ammonium sulfamate aqueous buffer at pH 5.6. The diastereomeric ratio of N-hydroxysuccinimide phosphoramidate (II-a) was measured after methanolytic derivatization by GC using an HP-5 column and a temperature gradient. NMR spectra were recorded in CDCl.sub.3 on a 300 MHz spectrometer. .sup.1H and .sup.13C chemical shifts are given in ppm relative to TMS (0 ppm) with the solvent resonance as the internal standard (CDCl.sub.3, .sup.1H: 7.26 ppm, .sup.13C: 77.16 ppm).

Example 1: Synthesis of Intermediate Compounds of Formula (II)

1.1 General Procedure for the Synthesis of Isopropyl(Phenoxy)Phoshoryl)Aminopropanoates Intermediates of Formula (II)

[0733] ##STR00202##

[0734] To a solution of (2S)-isopropyl 2-((chloro(phenoxy)phosphoryl)amino)propanoate (IV) (prepared according to the reference J. Org. Chem 2011, 76, 8311) in MTBE or methylene chloride, 0.85 eq of a N, S or O nucleophile were added (e.g. N-hydroxysuccinimmide, oxazoli-dinone derivatives, hydroxyl pyridines or thiophenols). In addition, 1.1 eq of an amine base (e.g. triethylamine) were added and the reaction mixture was stirred until complete conversion was observed. The ammonium salt was removed (if precipitation occurred) by filtration. Aqueous work-up was carried out under slightly acidic conditions (e.g. aqueous ammonium chloride) promoting removal of left over salts of the amine base. Removal of the solvent led to the corresponding phosphoramidate as a diastereomeric mixture. Purification was possible via crystallization depending on the nature of the leaving group.

1.2 Synthesis of the Compound of Formula (II-a) with N-Hydroxysuccinimide as LG and Crystallization Thereof to Obtain Compound of Formula (II-a′).

##STR00203##

[0735] In a dry two-neck round bottom flask equipped with a dropping funnel was dissolved crude phosphoryl chloride (IV) prepared according J. Org. Chem 2011, 76, 8311 (20 g, 43.8 mmol, 1 equiv, 67% w/w purity by NMR) in dichloromethane (140 mL) and the solution was cooled to ca. 5° C. with an ice bath. N-hydroxysuccinimide (7.53 g, 65.4 mmol, 1 equiv) was added (only partial dissolution). To this suspension, triethylamine (10 mL, 71.9 mmol, 1.1 equiv) in dichloromethane (20 mL) was added dropwise with stirring, and the dropping funnel was rinsed with a further 5 mL of dichloromethane, whereby all of N-hydroxysuccinimide dissolved and a precipitation of triethylamine hydrochloride was observed. The ice bath was removed, the reaction mixture was allowed to warm up to room temperature and extracted with 90 mL of distilled water. The organic phase was washed with a further 40 mL of distilled water and the volatiles were removed under reduced pressure. The crude solid was dissolved in 160 mL MTBE (methyl tert-butyl ether), charged with 5 mL triethylamine and left to stir overnight, upon which a solid agglomerate was formed. The mixture was diluted with 75 mL of MTBE and warmed up to 50° C. until all of the solid dissolved. Upon cooling, crystals formed which were filtered and dried to give 10.53 g of (II-a′) (dr 68.5:31.5). This solid was suspended in 155 mL MTBE, warmed to 45° C. until complete dissolution and allowed to cool, whereby white needle crystals formed. The crystals were filtered and dried to give 3.09 g diastereopure (II-a′). The mother liquor was evaporated under reduced pressure, dissolved in 80 mL MTBE with heating and concentrated to 55 mL under reduced pressure. After 45 min of stirring, white crystals formed, which were filtered and dried to give 1.11 g diastereopure (II-a′), to give a total yield of 4.19 g of (II-a) (10.9 mmol, 25%). The diastereomeric purity of the product was determined by GC analysis after methanolytic derivatization in the following way: in a vial, 21.4 mg of the solid were dissolved in 1 mL of a 1.25M HCl solution in MeOH, the vial was capped, shaken and directly used for a GC injection.

1.3 One Pot Synthesis of Compound of Formula (II-a) and Crystallization Thereof to Obtain the Compound of Formula (II-a′) Starting from Phenyl Dichlorophosphate

##STR00204##

In a dry two-neck round bottom flask equipped with a mechanical stirrer and a dropping funnel was dissolved L-alanine isopropyl ester (20.0 g, 119 mmol, 1 equiv) in dichloromethane (125 mL) and the solution was cooled to −78° C. with a dry ice/acetone bath. To this solution, triethylamine (33 mL, 239 mmol, 2 equiv) was added via a dropping funnel with stirring, upon which a white precipitate was formed. Phenyl dichlorophosphate (sourced by Aldrich) (17.8 mL, 119 mmol, 1 equiv) in dichloromethane (125 mL) was then added dropwise over 1 h, and the reaction mixture was stirred for 30 min at −75° C. and for 2 h at 0° C. In a separate flask, N-hydroxysuccinimide (13.68 g, 119 mmol, 1 equiv) was suspended in dichloromethane (75 mL) and charged with triethylamine (16.5 mL, 119 mmol, 1 equiv) upon which a solution was obtained. This solution was added to the main reaction vessel dropwise over 40 min.

[0736] The reaction mixture was allowed to warm up to room temperature and stirred overnight. The crude reaction mixture was filtered washing with dichloromethane and extracted with a 1:1 mixture of sat. aq. NH.sub.4Cl and water (1×200 mL and 1×100 mL), followed by a 1:1 mixture of saturated aqueous NaCl and water (1×100 mL). The organic phase was separated and the volatiles were removed under reduced pressure. The crude oil was dissolved in 160 mL MTBE and seeded with pure (II-a′) and stirred, upon which a solid began to form slowly. The mixture was diluted with 100 mL of MTBE, warmed up until all of the solid dissolved and seeded with pure (II-a′) again, upon which needle-like crystalline solid began to form slowly. The mixture was diluted with 100 mL MTBE and left to stand overnight, then stirred at 0° C. in an ice bath. The solid was filtered and dried to give 3.25 g diastereopure (II-a) (8.4 mmol, 7%).

[0737] .sup.1H NMR (300 MHz, CDCl.sub.3): 7.41-7.29 (m, 4H), 7.25-7.17 (m, 1H), 5.03 (sept, J=6.2 Hz, 1H), 4.29-4.13 (m, 1H), 4.09 (dd, J=11.2 Hz, 9.8 Hz, 1H), 2.78 (s, 4H), 1.44 (d, J=7.0 Hz, 3H), 1.26 (apparent t, J=6.65 Hz, 6H).

[0738] .sup.13C NMR (75 MHz, CDCl.sub.3): 173.0 (d, J=7.6 Hz), 169.4, 150.4 (d, J=7.5 Hz), 129.9, 125.7, 120.2 (d, J=5.1 Hz), 69.5, 50.6 (d, J=2.3 Hz), 25.6, 21.8 (J=2.8 Hz), 20.8 (d, J=5.6 Hz).

1.4 Synthesis of the Compound of Formula (II-a′) with N-Hydroxysuccinimide as LG: Aqueous Workup

[0739] 20 g alaninisopropyl ester hydrochloride (119.3 mmol) was charged with 200 ml of dry THF and cooled to 0° C. To the mixture 21.4 ml phenylphosphorodichlorate (content: 95%, 131.2 mmol, 1.1 eq) was added and the mixture was stirred for 15 min at 0° C. To the mixture 34.8 ml triethyl amine (250-5 mmol, 2.1 eq) was added within 77 min while the reaction mixture was kept at temperature below 6° C. After complete addition the mixture was stirred for an additional hour at 0° C. until complete conversion was observed. To the mixture 17.8 g N-hydroxysuccinimide (155.09 mmol, 1.3 eq) as solid was added. Afterwards 24.8 ml triethyl amine (179.0 mmol, 1.5 eq) was slowly added to keep the mixture temperature below 5° C. The mixture was stirred for 2.5 h after complete addition until complete conversion was observed. To the mixture 1.2 L MTBE was added and afterwards the mixture was hydrolyzed with 1.2 L water. The organic phase was separated and washed with 200 ml brine. The organic phase was stripped with 4 times with 900 ml MTBE until no THF was detectable via GC in the organic phase. The total volume of the organic phase was adjusted to 920 ml by addition of MTBE. The mixture was heated to 42° C. and to the mixture 1.0 g N-hydroxysuccinimide (8.6 mmol, 7.5 mol %) and 5.0 ml trimethylamine (35.8 mmol, 0.3 eq) was added. The mixture was cooled to 27° C., when precipitation was observed. At that point, seeds of diastereomerically pure N-hydroxysuccinimide phosphoramidate (II-a′) were added. The mixture was stirred cooled to 0° C. over a period of 4 hours and afterwards stirred at 0° C. overnight. The precipitation was isolated via filtration and dried at <100 mbar at 20-25° C. leading to 24.5 g of N-hydroxysuccinimide phosphoramidate (II-a′) with a diastereomeric ratio of 88/12. The mixture was further purified by crystallization from MTBE leading to N-hydroxysuccinimide phosphoramidate (II-a′) with a diastereomeric ratio of >97/3.

1.5 Synthesis of the Compound of Formula (II-a′) with N-Hydroxysuccinimide as LG Water Free Workup

[0740] 20 g alaninisopropyl ester hydrochloride (119.3 mmol) was charged with 200 ml of dry THF and cooled to 0° C. To the mixture 17.1 ml phenylphosphorodichlorate (content: 95%, 107.4 mmol, 0.9 eq) was added and the mixture was stirred for 15 min at 0° C. To the mixture 34.8 ml triethyl amine (250-5 mmol, 2.1 eq) was added within 65 min while the reaction mixture was kept at temperature below 7° C. After complete addition the mixture was stirred for two additional hour at 0° C. until complete conversion was observed. To the mixture 17.8 g N-hydroxysuccinimide (155.09 mmol, 1.3 eq) as solid was added. Afterwards 24.8 ml triethyl amine (179.0 mmol, 1.5 eq) was slowly added to keep the mixture temperature below 7° C. The mixture was stirred for 2 h after complete addition until complete conversion was observed. To the mixture 200 ml MTBE was added an the mixture was stirred at 0° C. for 30 min. Afterwards the precipitation was removed (57.5 g, containing mainly triethylamine hydrochloride, N-hydroxysuccinimide salts with triethylamine and small amounts of the desired phosphoramidate). The volume of the filtrate was reduced to 59 g (still liquid with suitable viscosity for stirring) and 900 ml MTBE was added. After the addition of MTBE a precipitation occurred. The mixture 30 g silica gel was added and the mixture was stirred for 10 min. The precipitation was removed via filtration and the filter cake was washed with 100 ml MTBE to achieve a clear solution. The volume of the filtrate was reduced to 600 ml and heated to 30° C. At this temperature 5.0 ml triethyl amine was added and the mixture was cooled to 20° C. At this temperature seeds of the diastereomeric pure N-hydroxysuccinimide phosphoramidate (II-a′) were added. The mixture was cooled to 10° C. and stirred at that temperature for 3.5 h. Afterwards the mixture was cooled to 0° C. and stirred for 8 h at this temperature. The precipitation was isolated via filtration and the filter cake was washed with 30 ml of MTBE/HPT mixture (1/1). After drying at <100 mbar/40° C., 16.4 g of N-hydroxysuccinimide phosphoramidate (II-a′) with a diastereomeric ratio of 89/11 was isolated.

1.6 Crystallization of Diastereomeric Pure N-Hydroxysuccinimide Phosphoramidate (II-a′)

[0741] 16.4 g N-hydroxysuccinimide phosphoramidate (II-a′) (dr=9/1) are added to 246 ml MTBE and the mixture was heated to 40° C. The occurring suspension was cooled to 20° C. and stirred at that temperature for 2 h. Afterwards the mixture was cooled to 0° C. and stirred at this temperature for an additional hour. The precipitation was isolated via filtration. After drying (<100 mbar, 20-40° C.), 15.8 g N-hydroxysuccinimide phosphoramidate (II-a′) in diastereomeric pure form was isolated.

1.7 Synthesis of Compound of Formula (II-b) and Purification to Obtain the Diasteromerically Pure Compound (II-b′): (2S)-isopropyl 2-(((2-oxobenzo[d]oxazol-3(2H)-yl)(phenoxy)phosphoryl)amino)propanoate (Oxazolidone as Nuclephile)

##STR00205##

[0742] 20 g (65.4 mmol, 1 eq) of (2S)-isopropyl 2-((chloro(phenoxy)phosphoryl)amino)propanoate was dissolved in 500 ml methylene chloride. To the solution 7.5 g (55.5 mmol, 0.85 eq) 2-benzoxazolinone and 10 ml (72.1 mmol, 1.1 eq) triethyl amine were added. Complete conversion was observed after 3 h. The solvent was removed to dryness and the residue was suspended in 400 ml MTBE. The occurring solid was removed and the filtrate was washed with aqueous ammonium chloride and brine. The organic solvent was again removed to dryness and 22.9 g of an oil were isolated. The residue was treated with 40 mL ethyl acetate. After removal of 30 mL ethyl acetate via distillation a suspension was formed. The suspension was treated with 30 mL heptane and after 1 h stirring the solid was isolated via filtration. After drying 6.9 g were isolated as a diastereoisomerically pure product (II-b′) having configuration S at the “P” atom. From the mother liquor 13.9 g of the product were isolated after removal of the solvent as a mixture of diastereoisomers. Characterization of the product:

[0743] .sup.1H NMR (300 MHz, CDCl.sub.3): 7.76-7.32 (m, 1H), 7.29-7.26 (m, 5H), 7.18-7.11 (m, 5H), 5.02 (sept, J=7.0 Hz, 1H), 4.48-4.32 (m, 2H), 1.38 (d, J=7.6 Hz, 3H), 1.25-1.21 (m, 6H).

1.8 Synthesis of Phosphoramidates of Formula (II-c) from Phosphoric Acid Derivatives

##STR00206##

Step 1: Synthesis of (2S)-isopropyl 2-((hydroxy(phenoxy)phosphoryl)amino)propanoate of formula (IV′)

[0744] To a suspension of 2.0 g of alanine isopropylester hydrochloride in 30 ml THF, 2.29 g EDC.HCl (1 eq), 2.08 g phenylphosphoric acid (1.0 eq) and 2.6 mL N-methylmorpholine (2 eq) were added. The mixture was stirred for 3.5 h until complete conversion was observed. The reaction was hydrolyzed with 40 ml aqueous ammonium chloride and extracted with 50 mL methylene chloride. The aqueous phase was re-extracted with 30 mL methylene chloride and the solvent was removed from the combined organic phases. The product was crystallized from acetonitrile leading to 920 mg of the desired product (2S)-isopropyl 2-((hydroxy(phenoxy)phosphoryl)amino)propanoate. Characterization of the product:

[0745] .sup.1H NMR (300 MHz, CDCl.sub.3): 8.2 (b, 1H) 7.20-6.87 (m, 5H), 4.99-4.76 (m, 1H), 3.91-3.48 (m, 1H), 3.68 (b, 1H) 1.37-1.06 (m, 9H).

Step 2: Synthesis of Phosphoramidates of Formula (II-c)

[0746] 3.2 g (2S)-isopropyl 2-((hydroxy(phenoxy)phosphoryl)amino)propanoate (11.14 mmol) (prepared according to step 1) were dissolved in 60 mL acetonitrile. To the solution 2.42 g 2-chloro-4,6-dimethoxy-1,3,5-triazin (1.2 eq) and 2.4 mL N-methylmorpholine (2 eq) were added. After compete conversion, the solvent was removed to dryness and the residual was dissolved in 100 mL methylene chloride. The organic phase was washed with 100 mL water and brine and the organic solvent was removed to dryness. 4.7 g of an orange oil were isolated containing 61.5 area-% of the desired product (2S)-isopropyl 2-((((4,6-dimethoxy-1,3,5-triazin-2-yl)oxy)(phenoxy)phosphoryl)amino)propanoate. Characterization of the product:

[0747] .sup.1H NMR (300 MHz, CDCl.sub.3): 7.25-7.09 (m, 5H), 5.97 (m, 1H), 4.99 (m, 1H), 4.58 (m, 1H), 3.87 (s, 9H) 1.42 (d, J=7.9 Hz, 3H), 1.20-1.66 (m, 6H).

Example 2: Synthesis of Compound of Formula (I-S) Sofosbuvir with Lewis Acid (ZnBr.SUB.2.) by Reaction of Compound of Formula (III-S)

[0748] ##STR00207##

2.1 Synthesis of Compound (I-S): 0.195 Mmol Scale

[0749] The preparation of compound (III-S) was according to the glycosylation of the nucleobase disclosed in patent application WO2005/003147 and J. Med. Chem. 2005, 48, 5504. To a two-neck round bottom flask equipped with a reflux condenser and purged with nitrogen was added 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (50.8 mg, 0.195 mmol, 1 equiv), anhydrous THF (3 mL) and 4 Angstrom molecular sieves (powder, 1 heaped spatula tip), and the suspension was stirred for 5 min. N-hydroxysuccinimide phosphoramidate (II-a′) (150 mg, 0.390 mmol, 2 equiv, stored in a desiccator and checked periodically for hydrolysis) was added, followed by ZnBr.sub.2 (43.9 mg, 0.195 mmol, 1 equiv), and Et.sub.3N (27.2 microL, 0.195 mmol, 1 equiv). The mixture was heated at 40° C. for 2 hours. HPLC analysis with individual response factor correction indicated 11% of unreacted nucleoside (III-S), 82% (I-S) (97:3 dr) and 7% of 3′,5′-bis-phosphoramidate impurity (W-S) which represents the wrong region-isomers formed during the nucleophilic substitution reaction (dr not determined). “(dr)” is the diastereoisomer ratio when referring to two diastereoisomers that differ for the phosphorpus “P” chirality.

2.2 Synthesis of Compound (I-S): 5.76 mmol Scale

[0750] To a two-neck round bottom flask equipped with a reflux condenser and purged with nitrogen was added 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (1.49 g, 5.76 mmol, 1 equiv), anhydrous THF (90 mL), ZnBr.sub.2 (1.31 g, 5.76 mmol, 1 equiv) and 4 Angstrom molecular sieves (9.0 g, powder), and the suspension was stirred for 10 min. N-hydroxysuccinimide phosphoramidate (II-a′) (4.44 g, 11.55 mmol, 2 equiv, stored in a dessicator and checked periodically for hydrolysis) was added in one portion, followed a dropwise addition of Et.sub.3N (0.8 mL, 5.76 mmol, 1 equiv). The mixture was heated at 40° C. for 23 hours, at which point HPLC analysis with individual response factor correction showed 8% of unreacted nucleoside (III-S), 88% of (I-S) (92:8 dr) and 4% of 3′,5′-bis-phosphoramidate impurity (dr not determined).

[0751] The crude reaction mixture was filtered, washed with THF (about 3 mL), and the solvent was removed under reduced pressure. The resulting amorphous solid was redissolved in 75 mL isopropyl acetate and extracted with a 1:1 mixture of saturated aqueous NaCl and water (1×40 mL), followed by of sat. aq. NaHCO.sub.3 (2×40 mL). The organic phase was separated and dried over Na.sub.2SO.sub.4, filtered, and the solvent was removed under reduced pressure to give a white amorphous solid (6.98 g). Of this crude solid, 996 mg were dissolved in toluene (2 mL) and charged with MTBE (2 mL). The mixture was seeded with pure (I-S) which resulted in immediate precipitation of a white crystalline solid. The mixture was stirred overnight under nitrogen, filtered washing with a 1:1 mixture of MTBE/dichloromethane (2×1 mL) and dried under vacuum at 50° C. overnight to give (I-S) as a white crystalline solid (350 mg, 0.66 mmol, 80% yield for the recrystallized portion).

[0752] HPLC analysis showed a total purity of 96.1%, with impurities composed of the other diastereoisomer of compound of formula (I) with R configuration at the “P” atom (I-R). (1.7%), N-hydroxysuccinimide (0.4%), hydrolysis product of the N-hydroxysuccinimide phosphoramidate (II-a′) (0.2%), N-hydroxysuccinimide phosphoramidate (II-a′) (0.5%) and an unknown impurity (1.1%). Characterization of the product:

[0753] .sup.1H NMR (300 MHz, CDCl.sub.3): 9.41 (br s, 1H), 7.47 (d, J=8.2 Hz, 1H), 7.38-7.28 (m, 2H), 7.25-7.13 (m, 3H), 6.17 (br d, J=18.7 Hz, 1H), 5.69 (d, J=8.1 Hz, 1H), 5.00 (sept, J=6.2 Hz, 1H), 4.60-4.36 (m, 2H), 4.24 (dd, J=11.9 Hz, 10.0 Hz, 1H), 4.15-4.03 (m, 2H), 4.03-3.83 (m, 2H), 1.38 (d, J=18.9 Hz, 3H), 1.33 (d, J=3.3 Hz, 3H), 1.22 (d, J=6.2 Hz, 6H).

2.3 Synthesis of Sofosbuvir (Compound (I-S))

[0754] 7.58 g N-hydroxysuccinimide phosphoramidate (II-a′) (85% content, dr 08.4/1.6, 16.8 mmol, 1.12 eq) was dissolved in 49 ml dry THF. To the mixture 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (14.95 mmol, 1 eq) and 3.37 g zinc bromide (14.95 mmol, 1 eq) was added and stirred for 10 min. Afterwards 4.14 ml triethyl amine (29.9 mmol, 2 eq) was added. The mixture was stirred overnight at room temperature leading to a conversion of 98% and dr for sofosbuvir of 97/3. The precipitation of the reaction mixture was removed via filtration and the filter cake was washed with 8.5 ml THF. The acidic work up of the filtrate was done via addition of 25 ml 1M aqueous HCl leading to a clear solution. The THF was removed from the mixture via evaporation (80 mbar, 45° C.). Afterwards 50 ml methylene chloride 10 ml brine was added to the mixture. The organic phase was separated and the volume was reduced to 33.7 g via evaporation at 35° C. The organic solution was cooled to 30° C. and seeds of sofosbuvir were added. Precipitation started at 30° C. The mixture was cooled to −10° C. within 5.5 h and stirred at −10° C. overnight. The precipitation was isolated via filtration and the filter cake was washed with −20° C. cooled methylene chloride. After drying (<100 mbar, 20° C.), 5.49 sofosbuvir (81% yield, dr=99.7/0.3) was isolated.

Example 3: General Procedure for Lewis Acids (0.192 mmol Scale)

[0755] ##STR00208##

[0756] To a two-neck round bottom flask equipped with a reflux condenser and purged with nitrogen was added 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (50 mg, 0.192 mmol, 1 equiv), 3 mL anhydrous THF and 4 Angstrom molecular sieves (powder, 1 heaped spatula tip), and the suspension was stirred for 5 min. N-hydroxysuccinimide phosphoramidate (II-a′) (148 mg, 0.384 mmol, 2 equiv unless specified otherwise) was added, followed by the Lewis acid (1 equiv), and Et.sub.3N (26.8 microL, 0.192 mmol, 1 equiv, unless otherwise specified).

[0757] The mixture was heated at 40° C. for 1 to 22 hours and analyzed by HPLC, taking into account the response factor of each reactant and product.

[0758] The above experiment was repeated by varying the reaction conditions (Lewis acid, base, temperature, reaction time) as reported in entries 1 to 15 of Table 1 below. Table 1 reports also the percentage based on the total mole conversion of compounds (I-S) and (W-S) and the diastereoisomer ratio of compound (I-S) relative to its diastereoisomer (I-R) (different chirality of the “P” atom).

TABLE-US-00001 TABLE 1 Total mole Lewis acid, Base, (II-a′) Temp/ Time/ convers./ % % dr of Entry 1 eq 1 eq 1 eq ° C. h % (I-S) (W-S) (I-S)  1 Mn(acac).sub.3 Et.sub.3N 1 r.t.-40 17 8 8 0 62:38  2 CuCl.sub.2 Et.sub.3N 1 40 20.5 6 6 0 78:22  3 ZnI.sub.2 Et.sub.3N 1 40 20.5 12 12 0 80:20  4 Fe (II) fumarate Et.sub.3N 1 40-66 2.5 17 17 0 57:43  5 Cu(acac).sub.2 Et.sub.3N 1 40 1 12 12 0 54:46  6 MgBr.sub.2•OEt.sub.2 Et.sub.3N 1 40 22.5 9 7 2 97:3   7 Mn(acac).sub.3 none 1 40 10 64 54 10 79:21  8 Mn(acac).sub.3 Et.sub.3N 1 40 5.5 58 52 5 86:14  9 ZnCl.sub.2 Et.sub.3N 1 40 17 90 81 9 92:8  10 ZnCl.sub.2 Et.sub.3N 2 40 21 100 86 14 95:5  11 ZnBr.sub.2 Et.sub.3N 1 40 20 94 86 8 93:7  12 ZnBr.sub.2 Et.sub.3N 2 r.t. 18 92 86 6 98:2  13.sup.1) ZnBr.sub.2 Et.sub.3N 1 40 22 71 67 4 90:10 14 ZnBr.sub.2 DBU 1 40 22 91 84 7 93:7  15 ZnBr.sub.2 pyridine 1 40 18 41 40 1 72:28 16.sup.2) ZnBr.sub.2 Et.sub.3N 1.12 r.t over 98% 99.7:0.3  (2 eq) night .sup.1)Reaction performed in DMF .sup.2)Reaction according to example 2.3

[0759] As can be seen from the results reported in Table 1 with all tested Lewis acids according to the present invention, no prevalence of the wrong regioisomer (W-S) has been observed.

[0760] In some cases (entries 1 to 5), no formation of the wrong regioisomer has been detected.

[0761] Additionally, in all cases, a high percentage of the correct regioisomer (I-S) has been observed.

Comparative Example 1: Synthesis of Compound (I-S) with Grignard

[0762] ##STR00209##

[0763] To a dry two-neck round bottom flask equipped with a reflux condenser and purged with nitrogen was added 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (52.3 mg, 0.20 mmol, 1 equiv), 2 mL anhydrous THF and 4 Angstrom molecular sieves (powder, 1 heaped spatula tip), and the suspension was stirred for 5 min. Tert-butyl magnesium chloride (0.4 mL, 0.40 equiv, 2 equiv, 1 M in THF) was then added dropwise, upon which a thick white precipitate formed. The suspension was stirred for 10 min and N-hydroxysuccinimide phosphoramidate (II-a′) (154.5 mg, 0.40 mmol, 2 equiv, stored in a desiccator and periodically checked for hydrolysis) in anhydrous THF (1 mL) was added in one portion. The mixture was heated at 40° C. for 6 hours. HPLC analysis with individual response factor correction indicated 8% of unreacted nucleoside (III-S), 21% (I-S) (93:7 dr) and 71% of 3′,5′-bis-phosphoramidate impurity (W-S) (dr not determined). The results are given in Table 2 (entry 1). The above experiment was repeated with different reaction conditions (Grignard reagent, reaction time) as reported in entries 2 and 3 of Table 2. Table 2 reports also the percentage based on the total mole conversion of compounds (I-S) and (W-S) and the diastereoisomer ratio of compound (I-S) relative to its diastereoisomer (different chirality of the “P” atom)

TABLE-US-00002 TABLE 2 tert- BuMgCl (II-a′) Total mole % % dr of Entry 1 eq 1 eq Time/h convers./% (I-S) (W-S) (I-S) 1 2 2 6 92 21 71 93:7 2 2 1 1 27 19 8 98:2 3 1 1 19.5 39 24 16 97:3

[0764] In comparison with the process according to the invention, it can be seen in Table 2-entry 1 that the wrong regioisomer (W-S) is formed in higher percentage with respect to valuable compound (I-S). In general with Grignard reagents either a high conversion is observed that however leads to the prevalence of the wrong regioisomer (W-S) or a low conversion is observed. With the Lewis acid reaction according to the present invention, no prevalence of the wrong regioisomer (W-S) has been observed.

Comparative Examples 2: Synthesis of Compound 3 with Diethyl-Zinc

[0765] ##STR00210##

[0766] To a dry two-neck round bottom flask equipped with a reflux condenser and purged with nitrogen was added 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (51.4 mg, 0.198 mmol, 1 equiv), 2 mL anhydrous THF, and Et.sub.2Zn (198 microL, 0.198 mmol, 1 equiv, 1M in hexane) and the suspension was stirred for 10 min. N-hydroxysuccinimide phosphoramidate (II-a′) (76.1 mg, 0.198 mmol, 1 equiv) in anhydrous THF (1 mL) was then added in one portion. The mixture was heated at 40° C. for 19.5 hours. HPLC analysis with individual response factor correction indicated 39% of unreacted nucleoside (III-S), 48% (I-S) (92:8 dr) and 13% of 3′,5′-bis-phosphoramidate impurity (W-S) (dr not determined). The results are given in Table 3 (entry 1). The above experiment was repeated with different reaction times as reported in entries 2 to 4 of Table 3. Table 3 reports also the percentage based on the total conversion of compounds (I-S) and (W-S) and the diastereoisomer ratio of compound (I-S) relative to its diastereoisomer (different chirality of the “P” atom)

TABLE-US-00003 TABLE 3 Et.sub.2Zn Total mole % % dr of Entry 1 eq Time/h conversion/% (I-S) (W-S) (I-S) 1 0.5 5 47 36 11 88:12 2 1.25 2 63 38 25 77:23 3 3 4 15 10 5 41:59

[0767] In comparison with the process according to the invention, it can be appreciated that with the reaction according to the invention compound (I-S) is formed in higher percentage with respect to the wrong regioisomer (W-S).

Comparative Example 3: Synthesis of Compound (I-S) with Tert-BuZnBr and Further Bases

[0768] ##STR00211##

[0769] To a dry two-neck round bottom flask equipped with a reflux condenser and purged with nitrogen was added 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (51.6 mg, 0.198 mmol, 1 equiv), 2 mL anhydrous THF, and 4 Angstrom molecular sieves (powder, 1 heaped spatula tip), and the suspension was stirred for 5 min. tert-BuZnBr (790 microL, 0.397 mmol, 2 equiv, 0.5 M in THF) was added dropwise, whereby the reaction mixture remained homogeneous. N-hydroxysuccinimide phosphoramidate (II-a′) (76.1 mg, 0.198 mmol, 1 equiv) in anhydrous THF (1 mL) was then added in one portion. The mixture was heated at 40° C. for 2 hours (a precipitate was formed after 1 hour reaction time) and analyzed by HPLC, calculating for the response factor of each reactant and product. HPLC indicated 22% of unreacted nucleoside (III-S), 66% (I-S) (82:18 dr) and 12% of 3′,5′-bis-phosphoramidate impurity (W-S) (dr not determined). The results are given in Table 4 (entry 1). The above experiment was repeated with different reaction conditions (base and reaction time) as reported in entries 2 to 5 of Table 4. Table 4 reports also the percentage based on the total conversion of compounds (I-S) and (W-S) and the diastereoisomer ratio of compound (I-S) relative to its diastereoisomer (different chirality of the “P” atom)

TABLE-US-00004 TABLE 4 Total mole % % dr of Entry Base eq Time/h conversion/% (I-S) (W-S) (I-S) 1 t-BuOMg 2 2.5 55 34 21 90:10 2 Me.sub.3Al 1 3 24 12 13 95:5  3 Bu.sub.2Mg 1 3 50 24 24 95:5  4 n-BuLi 1 no reaction 5 MgH.sub.2 1 no reaction

[0770] In Table 4-entries 4 and 5 no reaction has been observed. Additionally in Table 4-entry 2 the wrong regioisomer (W-S) in former in higher percentage with respect to valuable compound (I-S) while in table Table 4-entry 4 the same % of (I-S) and (W-S) is obtained.

[0771] In comparison with the process according to the invention it can be appreciated that in the reaction according to the invention compound (I-S) is formed in higher percentage with respect to the wrong regioisomer (W-S).

Comparative Example 4: Synthesis of Compound (I-S) in HCl

[0772] ##STR00212##

[0773] To a dry two-neck round bottom flask equipped with a reflux condenser and purged with nitrogen was added 2′-deoxy-2′-fluoro-2′C-methyluridine (III-S) (50.12 mg, 0.193 mmol, 1 equiv), 3 mL anhydrous THF, and 4 Angstrom molecular sieves (0.3 g, powder), and the suspension was stirred for 10 min. 4M HCl in dioxane (48 microL, 0.193 mmol, 1 equiv) was added, followed by N-hydroxysuccinimide phosphoramidate (II-a′) (74.0 mg, 0.193 mmol, 1 equiv). The mixture was heated at 40° C. for 1 hour, and analyzed by HPLC which indicated no conversion. Triethylamine (24.7 microL, 0.193 mmol, 1 equiv) was added and the reaction was further stirred overnight at 40° C. HPLC analysis with individual response factor correction indicated 94% of unreacted nucleoside (III-S) and 6% (I-S)(47:53 dr).

[0774] Using the same procedure but employing TFA as the Bronsted acid, similar results were obtained (13% conversion to (I-S), 57:43 dr after 19.5 h).

[0775] As can be seen, using an acid different from the present Lewis acid leads to a very low conversion with a dr ratio in favor of the wrong diastereoisomer (R configuration at the “P”).

Example 4: Synthesis of Sofosbuvir Starting from Compound (II-b)

4.1 Lewis Acid Mediated and 2-Benzo[d]Oxazole as LG

[0776] ##STR00213##

[0777] To a solution of 155.3 mg (0.48 mmol) of (2S)-isopropyl 2-(((2-oxobenzo[d]oxazol-3(2H)-yl)(phenoxy)phosphoryl)amino)propanoate in 2 ml THF 14 mg Mn(III)acetylacetonate (10 mol-%) were added. Afterwards 100 mg (0.38 mmol) deoxy-fluoro-methyl uridine were added and rinsed with 1 mL THF. To the reaction mixture 50 microL triethylamine were added and the mixture was heated to reflux for 44 h until no starting material was observed anymore. After cooling to room temperature the mixture was hydrolyzed with 7 mL aqueous ammonium chloride and extracted with 5 mL ethyl acetate. The organic phase contained a ½ mixture of two phosphor isomers of compound of formula (I) i.e. compound of formula (I-S) and diasteroisomer with the “P” having an R configuration (I-R).

Comparative Example 5: Synthesis of Sofosbuvir Starting from Compound (II-b′) and Grignard Mediated

[0778] To a solution of 150 mg deoxy-fluoro-methyl uridine (0.58 mmol) in 3 mL THF, 1.2 mL tert-butyl magnesium chloride solution in THF (1 M, 1.2 eq) were added. The occurring suspension was stirred for 30 min. Afterwards 261 mg (1.2 mmol, 2.1 eq)) of (2S)-isopropyl 2-(((2-oxobenzo[d]oxazol-3(2H)-yl)(phenoxy)phosphoryl)amino)propanoate dissolved in 2 mL THF were added. After complete conversion the reaction was hydrolyzed by the addition 10 mL aqueous ammonium chloride and extracted with 20 mL ethyl acetate. The organic phase was washed with 5% sodium carbonate solution and brine. After removal of the solvent 180 mg oil containing 45 area-% of one sofosbuvir diastereomer were isolated.

Comparative Example 6: Synthesis of Compound of Formula (I-S) Sofosbuvir Starting from Compound (II-b′) Diethylzink Mediated

[0779] To a solution of 51 mg deoxy-fluoro-methyl uridine (0.20 mmol) in 2 mL THF 200 microL diethylzinc solution in hexane (1 M, 1.02 eq) were added. The occurring suspension was stirred for 30 min. Afterwards 79.3 mg (0.20 mmol, 1.0 eq) of (2S)-isopropyl 2-(((2-oxobenzo[d]oxazol-3(2H)-yl)(phenoxy)phosphoryl)amino)propanoate dissolved in 2 mL THF were added. After complete conversion the reaction was hydrolyzed by the addition 10 mL aqueous ammonium chloride and extracted with 20 mL ethyl acetate. The organic phase was washed with water and the solvent was removed to dryness. 110 mg of a solid containing one sofosbuvir isomer were isolated (70 area-%).

Example 5: Synthesis of Compound of Formula (I-S) Sofosbuvir Lewis Acid Mediated and with Penta-Fluorophenol as LG

[0780] 5 g deoxyfluoromethlyuridine (19.3 mmol, 1 eq) was dissolved in 200 mL THF at room temperature. To the solution 9.6 g (S)-isopropyl 2-(((S)-(perfluorophenoxy)(phenoxy) phosphoryl)amino)propanoate (21.2 mmol, 1.1 eq) prepared according J. Org. Chem 2011, 76, 8311, 4.3 g zinc bromide (19.3 mmol, 1 eq) and 2.7 mL triethyl amine (19.3 mmol, 1 eq) were added. The mixture was stirred for 20.5 h until complete conversion was observed and formation of the double phosphorylated by product was below 4 area-%. The mixture was hydrolyzed with 200 mL 1 M aqueous HCl, and THF was removed via distillation. The aqueous phase was extracted with ethyl acetate and the organic phase was washed with sodium carbonate. The organic solvent was removed to dryness, obtaining 9.7 g of a white solid containing 68 area-% of sofosbuvir (64% yield).

CITED PRIOR ART

[0781] WO 2005/003147 [0782] WO 2008/121634 [0783] WO 2011/123668 [0784] WO 2010/135569 [0785] WO 2011/123645 [0786] WO 2011/123672 [0787] WO 2014/047117 [0788] J. Med. Chem. 2005, 48, 5504