https://www.google.com/patents/WO1999048885A1?cl=ensynthesis of (3S)-tetrahydro-3-furyl N-[(1S,2R)-3(4-amino-N-isobutylbenzenesulphonamido)-1-benzyl-2-hydroxypropyl]carbamate, hereinafter referred to as the compound of formula (I), and to novel intermediates thereto.The compound of formula (I) has the following structure

and was first described in PCT patent publication number WO94/05639 at Example 168. Currently there is considerable interest in the compound of formula (I) as a new chemotherapeutic compound in the treatment of human immunodeficiency virus (HIV) infection and the associated conditions such as acquired immune deficiency syndrome (AIDS) and AIDS dementia.

There exists at the present time a need to produce large quantities of the compound of formula (I) for clinical investigation into the efficacy and safety of the compound as a chemotherapeutic agent in the treatment of HIV infections.

An ideal route for the synthesis of the compound should produce the compound of formula (I) in high yields at a reasonable speed and at low cost with minimum waste materials and in a manner that is of minimum impact to the environment in terms of disposing of waste-materials and energy consumption.

We have found a new process for the synthesis of the compound of formula (I) with many advantages over previously known routes of synthesis. Such advantages include lower cost, less waste and more efficient use of materials. The new process enables advantageous preparation of the compound of formula (I) on a manufacturing scale.

The route of synthesis of the compound of formula (I) described in the specification of WO94/05639 is specifically described therein in examples 39A, 51A, 51B, 51C, 51D, 167 and 168. The overall yield from these examples is 33.2% of theory.

Generally the route described in WO94/05639 involves protecting the amino alcohol of formula (A) (Ex.39)

wherein P is a protecting group to form a compound of formula (B);

wherein P and P′ are each independently a protecting group;

deprotecting the compound of formula (B) to form a compound of formula (C) (Ex 51A);

wherein P′ is a protecting group;

forming a hydrochloride salt of compound (C) (Ex 51B) then reacting with N-imidazolyl-(S)-tetrahydrofuryl carbamate to form the compound of formula (D) (Ex 51C);

wherein P′ is a protecting group;

deprotecting the compound of formula (D) (Ex 51D) wherein P′ is a protecting group to form the compound of formula (D) wherein P′ is H (Ex 51E); and coupling the resultant secondary amine on the compound of formula (D) to a p-nitrophenylsulphonyl group to form a compound of formula (E) (Ex 167);

the resultant compound of formula (E) is then reduced to form the compound of formula (I) (Ex 168).

In summary, the process disclosed in WO94/05639 for producing the compound of formula (I) from the compound of formula (A) comprises 6 distinct stages:

1) protecting,

2) deprotecting,

3) reacting the resultant compound with an activated tetrahydrofuranol group,

4) deprotecting,

5) coupling with a p-nitrophenylsulfonyl group, and

6) reducing the resultant compound to form a compound of formula (I).

Applicants have now found a process by which the compound of formula (I) may be prepared on a manufacturing scale from the same starting intermediate, the compound of formula (A), in only 4 distinct stages instead of 6. In addition to the associated benefits of fewer stages, such as savings in time and cost, the improved process reduces the number of waste products formed. Furthermore, product may be obtained in a higher yield, of approximately 50% of theory

.

EXAMPLESExample 1

(1S,2R)-tert-butyl N-[1-benzyl-2-hydroxy-3-(isobutylamino)propyl]carbamate (127.77 g, 379.7 mmol) was heated in toluene (888 ml) to 80° C. and triethylamine (42.6 g, 417.8 mmol) added. The mixture was heated to 90° C. and a solution of p-nitrobenzene sulphonyl chloride (94.3 g, 425.4 mmol) in toluene (250 ml) was added over 30 minutes then stirred for a further 2 hours. The resultant solution of the nosylated intermediate {(1S,2R)-tert-butyl N-[1-benzyl-2-hydroxy-3-(N-isobutyl- 4-nitrobenzenesulphonamido)propyl]carbamate } was then cooled to 80° C. The solution was maintained at approximately 80° C., and concentrated hydrochloric acid (31.4 ml, 376.8 mmol) was added over 20 minutes. The mixture was heated to reflux (approx 86° C.) and maintained at this temperature for an hour then a further quantity of concentrated hydrochloric acid (26.4 ml, 316.8 mmol) was added. Solvent (water and toluene mixture) was removed from the reaction mixture by azeotropic distillation (total volume of solvent removed approx 600 ml), and the resultant suspension was cooled to 70-75° C. Denatured ethanol (600 ml) was added, and the solution was cooled to 20° C. The mixture was further cooled to approximately −10° C. and the precipitate formed was isolated by filtration, washed with denatured ethanol (50 ml) and dried at approximately 50° C., under vacuum, for approximately 12 hours, to give (2R,3S)-N-(3-amino-2-hydroxy-4-phenylbutyl)-N-isobutyl-4-nitrobenzene sulphonamide hydrochloride (160 g; 73% of theory yield corrected for assay). NMR: ¹H NMR (300Mhz, dmso-d₆): 8.37(2H, d, J=9 Hz), 8.16(NH₃ ⁺s), 8.06(2H, d, J=9 Hz), 7.31(5H, m), 5.65(1H, d, J=5 Hz), 3.95(1H, m), 3.39(2H, m), 2.95(5H, m), 1.90(1H, m), 0.77(6H, dd, J=21 Hz and 6 Hz).

1,1′-carbonyidiimidazole (27.66 kg, 170.58 mol) was added to ethyl acetate (314.3 kg) with stirring to give 3-(S)-tetrahydrofuryl imidazole-1-carboxylate. (S)-3-hydroxytetrahydrofuran (157 kg, 178.19 mol) was added over 30 minutes, washed in with ethyl acetate (9.95 kg), then the mixture was stirred for a further hour. (2R,3S)-N-(3-amino-2-hydroxy-4-phenylbutyl)-N-isobutyl-4-nitrobenzene sulphonamide hydrochloride (65.08 kg, 142.10 mol) was added and the mixture heated to reflux for approximately 22 hours. The solution was cooled slightly, and denatured ethanol (98 l) was added. The solution was stirred at 60° C. for 10 minutes then cooled and the product allowed to crystallise. The mixture was cooled to <10° C. and stirred for 2 hours. The product was isolated by filtration, washed with denatured ethanol (33 l) and dried at approximately 50° C., under vacuum to give (3S)-tetrahydro-3-furyl N-[(1S,2R)-1-benzyl-2-hydroxy-3-(N-isobutyl-4-nitrobenzene sulphonamido)propyl]carbamate in a yield of 82% of theory.

NMR: ¹H NMR (500 Mhz, dmso-d₆): 8.38(2H, d, J=9Hz), 8.06(2H, d, J=9 Hz), 7.20(6H, m), 5.02(1H, d, J=5 Hz), 4.94(1H, m), 4.35(EtOH, broad s), 3.71(EtOH, q), 3.65(1H, m), 3.60(1H, m), 3.51(2H, broad m), 3.40(2H, m), 3.15(1H, dd, J=8 Hz and 14 Hz), 3.07(1H, dd, J=8 Hz and 15 Hz), 2.94(2H, m), 2.48(1H, m), 2.06(1H, m), 1.97(1H, m), 1.78(1H, m), 1.05(EtOH, t), 0.83(6H, dd, J=7 Hz and 16 Hz).

Product from the above stage (80.0 g, 149.4 mmol) was hydrogenated in isopropanol (880 ml) with 5% palladium on carbon (16 g, of a wet paste) and hydrogen pressure (approx 0.5 to 1.5 bar) at 25-50° C. for approximately 5 hours. The mixture was cooled and the catalyst removed by filtration. The solution was distilled to a volume of approximately 320 ml and water (80 ml) was added. This solution was divided into two for the crystallisation step.

To half of the above solution, decolourising charcoal (2 g) was added, the mixture stirred at approximately 32° C. for 4 hours, then filtered. The filtercake was washed with isopropanol (20 ml) then further water (40 ml) was added to the filtrate. The solution was seeded to induce crystallisation and stirred for 5 hours. Water (130 ml) was added slowly over 1 hour then the mixture was stirred for 4 hours. The resultant slurry was cooled to approximately 20° C. and the product was isolated by filtration and washed with a 1:4 mixture of isopropano/water (120 ml). The product was dried at approximately 50° C., under vacuum, for approximately 12 hours to give (3S)-tetrahydro-3-furyl N-[(1S,2R)-3-(4-amino-N-isobutylbenzenesulphonamido)-1-benzyl-2-hydroxypropyl] carbamate (30.3 g; 80% of theory yield).

NMR: ¹H NMR (300 Mhz, dmso-d₆): 7.39(2H, d, J=9 Hz), 7.18(6H, m), 6.60(2H, d, J=9 Hz), 6.00(2H, s), 4.99(1H, d, J=6 Hz), 4.93(1H, ddt), 3.64(5H, m), 3.34(1H, m), 3.28(1H, dd, J=14 Hz and 3 Hz), 3.01(1H, m, J=14 Hz and 3 Hz), 2.91(1H, m), 2.66(2H, m), 2.50(1H, m), 2.05(1H, m), 1.94(1H, m), 1.78(1H, m), 0.81(6H, dd, J=16 Hz and 7 Hz). m/z: 506.2(M+H⁺)

Example 11Synthesis of Amprenavir (1)To a solution of carbamate nitro derivative 15 (0.05 g, 0.09 mmol) in 2 mL of EtOAc was added SnCl₂.2H₂O (0.1 g, 0.5 mmol) at 70° C. The reaction mixture was heated for 1 h until starting material disappeared and the solution cooled to room temperature. It was then poured into saturated aq. NaHCO₃ solution and extracted with EtOAc. The organic extract was dried over anhyd. Na₂SO₄ and concentrated under reduced pressure. It was purified over chromatography using petroleum ether:EtOAc (3:2) to give amprenavir 1 (0.04 g, 90%).IR: (CHCl₃, cm⁻¹): υ_max 757, 1090, 1149, 1316, 1504, 1597, 1633, 1705, 2960, 3371; ¹H NMR (200 MHz, CDC₃): δ 0.86 (d, J=5.7 Hz, 3H), 0.90 (d, J=6.6 Hz, 3H), 1.78-2.21 (m, 3H), 235-3.11 (m, 6H), 3.58-4.11 (m, 7H), 4.25 (s, 2H), 5.01 (br s, 1H), 5.07 (br s, 1H), 6.65 (d, J=8.4 Hz, 2H), 7.20-7.28 (m, 5H), 7.51 (d, J=8.4 Hz, 2H); ¹³C NMR (50 MHz, CDC₃): δ 19.9, 20.2, 27.3, 32.8, 35.4, 35.7, 53.8, 55.0, 58.6, 66.8, 72.6, 73.2, 75.3, 114.0, 125.9, 126.5, 1280.4, 129.5, 137.7, 150.9, 155.9;

Anal. Calcd for C₂₅H₃₅N₃O₆S: C, 59.39; H, 6.98; N, 8.31; S, 6.34. Found: C, 59.36; H, 6.81; N, 8.25; S, 6.29%.

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