Preparation method of OTB-658 and intermediate thereof

Abstract

The invention belongs to the field of medicine preparation. The invention provides a brand new preparation method of OTB-658 and hydroxyl and amino intermediates thereof, and industrial production of the OTB-658 is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of pharmaceutical preparation, specifically relating to the preparation methods of OTB-658 and its hydroxyl intermediate (3R,3aS)-8-fluoro-3-(hydroxymethyl)-7-thiomorpholino-3a,4-dihydro-1H,3H-benzo[b]oxazol[3,4-d][1,4]oxazin-1-one and its amino intermediate (3S,3aS)-8-fluoro-3-(aminomethyl)-7-thiomorpholino-3a,4-dihydro-1H,3H-benzo[b]oxazol[3,4-d][1,4]oxazin-1-one. Background Technology

[0002] OTB-658 is a novel oxazolidinone antibacterial drug candidate intended for the treatment of infectious diseases, including tuberculosis. Its chemical name is N-(((3S,3aS)-8-fluoro-1-oxo-7-thiomorpholino-3a,4-dihydro-1H,3H-benzo[b]oxazol[3,4-d][1,4]oxazin-3-yl)methyl)acetamide, as shown in formula (II-b), and its structure is as follows:

[0003]

[0004] The article (Discovery of a Conformationally Constrained Oxazolidinone with Improved Safety and Efficacy Profiles for the Treatment of Multidrug-Resistant Tuberculosis. Journal of Medicinal Chemistry, 2020, 63(17): 9316-9339) and Chinese patent CN108727406A disclose the preparation of intermediates I and II-a and the preparation method of OTB-658 (see figure below).

[0005]

[0006]

[0007] In the synthesis of the compound shown in formula (I), the literature 1) uses a triphenylmethyl-protected or tert-butyldimethylsilyl-protected epoxy structure as a chiral substrate (obtained by Sharpless epoxidation) for subsequent reactions. The protecting group itself has a large molecular weight, and protection and deprotection operations are required, resulting in low atom economy and introducing many reaction steps; 2) In order to introduce the carbonyl group in compound I, the Cbz (benzyloxycarbonyl) fragment needs to be introduced in advance. In subsequent reactions, the part other than the carbonyl group leaves as a benzyl alcohol structure, resulting in low atom economy; 3) In the preparation of S13, the photo-extending reaction (Mitsunobu reaction) is used to remove a molar water to generate an ether, which requires the combined action of triphenylphosphine and azo reagents. The treatment of the triphenylphosphine oxy and azo hydrogenation products generated in the reaction needs to be considered; 4) Subsequently, in the presence of butyllithium reagent, cyclization is performed to form a benzoxazine oxazolidinone ring skeleton structure, which requires low-temperature reaction, is cumbersome, dangerous, and not conducive to industrial production.

[0008] In the synthesis of compound II-a, the article and patent use S8 as a raw material and employ the Gabriel amine synthesis method. The yield of the one-step reaction of replacing p-toluenesulfonate with potassium phthalimide is 88%, and the yield of the one-step reaction of methylamine hydrolysis is 89.2%. It is worth noting that methylamine solution is a chemical that is easily explosive.

[0009] In the synthesis of OTB-658(II-b), both the article and the patent use II-a as the raw material and acetic anhydride as the acetylation reagent, with a yield of 63.4%. Acetic anhydride is a controlled substance for manufacturing drugs. Summary of the Invention

[0010] The technical problem to be solved by this invention is to provide a novel synthetic method for OTB-658 and its intermediates I and II-a. This invention can shorten the reaction steps, increase the yield, and improve the low atom economy in the preparation of OTB-658 or its intermediates I and II-a. It also eliminates the use of easily explosive chemicals and controlled substances, and overall improves the yield of OTB-658, making it suitable for industrial production. This invention is based on the above findings. Invention Overview

[0012] This invention provides a method for preparing OTB-658(II-b) and its intermediates I and II-a, which is carried out via the following reaction route:

[0013]

[0014] Step A involves reacting compound S1 and compound S2 in an organic solvent under alkaline conditions to prepare compound S3.

[0015] Step B involves dissolving compound S3 in an organic solvent and reducing it to prepare compound S4.

[0016] Step C involves preparing compound S5 by heating compound S4 in an organic solvent to achieve a cyclization reaction.

[0017] Step D involves reacting compound S5 with a carbonylating agent in an organic solvent to prepare compound S6.

[0018] Step E involves reacting compound S6 with a reducing agent in an organic solvent to obtain compound (I).

[0019] Step F involves reacting compound S8 with either compound S10 or S11 in an organic solvent under alkaline conditions to prepare compound S9, wherein the structures of S10 and S11 are as follows:

[0020]

[0021] Where R1 is tert-butyl, benzyl, 4-methoxybenzyl, or 2,4-dimethoxybenzyl; R2 is tert-butyloxycarbonyl, benzyloxycarbonyl, 4-methoxybenzyloxycarbonyl, 2,4-dimethoxybenzylcarbonyl, or acetyl; and R is hydrogen or acetyl.

[0022] Step G involves reacting compound S9 in a solvent with an acidic reagent, a reducing reagent, or an oxidizing reagent to obtain compound II-a or II-b.

[0023] Chinese patent CN108727406A discloses a method for synthesizing S1, while the method for synthesizing S2 is prior art.

[0024] In some embodiments of the present invention,

[0025] The organic solvent in step A is selected from sulfoxide solvents, amide solvents, ketone solvents, nitrile solvents, ether solvents, aromatic solvents, alkane solvents, haloalkane solvents, or any mixture of the aforementioned solvents. Sulfoxide solvents are selected from dimethyl sulfoxide. Amide solvents are selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; ketone solvents are selected from acetone, dibutyl ketone, methyl isobutyl ketone, or cyclohexanone. Nitrile solvents are selected from acetonitrile, propionitrile, or butyronitrile; ether solvents are selected from tetrahydrofuran, methyl tert-butyl ether, cyclopentanehexyl ether, 1,4-dioxane, isopropyl ether, or ethylene glycol dimethyl ether; aromatic solvents are selected from toluene, xylene, chlorobenzene, or bromobenzene. Alkane solvents are selected from cyclohexane, n-hexane, or n-heptane. The haloalkane solvent is selected from chloroform, dichloromethane, carbon tetrachloride, 1,2-dichloroethane, preferably sulfoxide solvents and / or amide solvents, and more preferably N,N-dimethylformamide and / or dimethyl sulfoxide.

[0026] The alkali mentioned in step A is selected from alkali metal alkalis or organometal alkalis; the alkali metal alkali is selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, sodium hydride, cesium fluoride and / or potassium bicarbonate; the organometal alkali is selected from sodium methoxide, sodium ethoxide, aluminum isopropoxide, lithium tert-butoxide, sodium tert-butoxide and / or potassium tert-butoxide, preferably alkali metal alkalis, more preferably cesium carbonate, cesium fluoride and / or potassium carbonate.

[0027] In step A, the molar ratio of compound S1 to compound S2 is 1:1 to 3, preferably 1:1 to 2.5.

[0028] The molar ratio of compound S1 to the base is 1:0.1 to 10.

[0029] The reaction temperature in step A is preferably -10 to 100°C, more preferably 0 to 70°C, and even more preferably 0 to 50°C.

[0030] The reaction time for step A varies with the reaction temperature, but a time of approximately 1 hour to 100 hours is usually sufficient.

[0031] In some embodiments of the present invention,

[0032] The organic solvent in step B is selected from halogenated alkane solvents, alcohol solvents, sulfoxide solvents, amide solvents, ketone solvents, nitrile solvents, ether solvents, aromatic solvents, alkane solvents, ester solvents, or any mixture of the aforementioned solvents. Alcohol solvents are selected from methanol, ethanol, isopropanol, n-propanol, or tert-butanol. Sulfoxide solvents are selected from dimethyl sulfoxide. Amide solvents are selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. Ketone solvents are selected from acetone, dibutyl ketone, methyl isobutyl ketone, or cyclohexanone. Nitrile solvents are selected from acetonitrile, propionitrile, or butyronitrile. Ether solvents are selected from tetrahydrofuran, methyl tert-butyl ether, 1,4-dioxane, isopropyl ether, or ethylene glycol dimethyl ether. Aromatic solvents are selected from toluene, xylene, chlorobenzene, or bromobenzene. Alkane solvents are selected from cyclohexane, n-hexane, or n-heptane. The haloalkane solvent is selected from dichloromethane, chloroform, carbon tetrachloride, and 1,2-dichloroethane. The ester solvent is preferably ethyl acetate, isopropyl acetate, or butyl acetate. Chlorinated alkane solvents or mixtures of chlorinated alkane solvents with alcohol solvents, ester solvents, or ether solvents are preferred. Further preferred are chloroform, dichloromethane, carbon tetrachloride, 1,2-dichloroethane, or any mixture of the aforementioned solvents with methanol, ethanol, ethyl acetate, 1,4-dioxane, or tetrahydrofuran.

[0033] The hydrogenation system used in the reduction reaction in step B consists of a metal catalyst and a hydrogen donor. The metal catalyst is selected from dry palladium on carbon, wet palladium on carbon, rhodium on carbon, palladium hydroxide, or Raney nickel, and the hydrogen donor is selected from hydrogen or ammonium formate. The heavy metal catalyst is preferably dry palladium on carbon or wet palladium on carbon, and the hydrogen donor is preferably hydrogen. The reaction temperature is 0–60°C, preferably 0–40°C. The weight ratio of reactant S3 to catalyst is 100:1–30, preferably 100:5–20. A reaction time of 1 h–48 h is usually sufficient.

[0034] In some embodiments of the present invention,

[0035] The organic solvent in step C is selected from alcohol solvents, sulfoxide solvents, amide solvents, ketone solvents, nitrile solvents, ether solvents, aromatic solvents, alkane solvents, haloalkane solvents, ester solvents, or any mixture of the aforementioned solvents. Alcohol solvents are selected from methanol, ethanol, isopropanol, n-propanol, or tert-butanol. Sulfoxide solvents are selected from dimethyl sulfoxide. Amide solvents are selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. Ketone solvents are selected from acetone, dibutyl ketone, methyl isobutyl ketone, or cyclohexanone. Nitrile solvents are selected from acetonitrile, propionitrile, or butyronitrile. Ether solvents are selected from tetrahydrofuran, methyl tert-butyl ether, 1,4-dioxane, isopropyl ether, or ethylene glycol dimethyl ether. Aromatic solvents are selected from toluene, xylene, chlorobenzene, or bromobenzene. Alkane solvents are selected from cyclohexane, n-hexane, or n-heptane. The haloalkane solvent is selected from chloroform, dichloromethane, carbon tetrachloride, and 1,2-dichloroethane. The ester solvent is preferably ethyl acetate, isopropyl acetate, or butyl acetate. Alcohol solvents, ether solvents, sulfoxide solvents, amide solvents, nitrile solvents, and / or aromatic solvents are preferred, with alcohol solvents being even more preferred, and ethanol, isopropanol, and tert-butanol being even more preferred.

[0036] The heating temperature in step C is 40–150°C, preferably 60–120°C. A reaction time of 1–24 hours is sufficient.

[0037] In some embodiments of the present invention,

[0038] The organic solvent in step D is selected from sulfoxide solvents, amide solvents, ketone solvents, nitrile solvents, ether solvents, aromatic solvents, alkane solvents, haloalkanes solvents, ester solvents, or any mixture of the aforementioned solvents. Sulfoxide solvents are selected from dimethyl sulfoxide. Amide solvents are selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. Ketone solvents are selected from acetone, dibutyl ketone, methyl isobutyl ketone, or cyclohexanone. Nitrile solvents are selected from acetonitrile, propionitrile, or butyronitrile. Ether solvents are selected from tetrahydrofuran, methyl tert-butyl ether, 1,4-dioxane, isopropyl ether, or ethylene glycol dimethyl ether. Aromatic solvents are selected from toluene, xylene, chlorobenzene, or bromobenzene. Alkane solvents are selected from cyclohexane, n-hexane, or n-heptane. Haloalkanes are selected from chloroform, dichloromethane, carbon tetrachloride, or 1,2-dichloroethane. Ester solvents are preferably ethyl acetate, isopropyl acetate, or butyl acetate. Halogenated alkane solvents, ether solvents, and / or aromatic solvents are preferred, with halogenated alkane solvents and / or aromatic solvents being more preferred, and toluene and dichloromethane being even more preferred.

[0039] The carbonylating reagent in step D is selected from carbonyl diimidazole, dimethyl carbonate, diethyl carbonate, triphosgene, phosgene, methyl chloroformate, ethyl chloroformate, butyl chloroformate, isopropyl chloroformate, and benzyl chloroformate; preferably carbonyl diimidazole and triphosgene. A base may or may not be added during the reaction; the base is selected from triethylamine, diisopropylethylamine, DBU, pyridine, sodium carbonate, sodium acetate, or potassium carbonate, preferably triethylamine. The molar ratio of S5 to the carbonylating reagent is 1:0.3–2, preferably 1:0.3–1.5. The reaction temperature is 0–120°C.

[0040] In some embodiments of the present invention,

[0041] The organic solvent in step E is selected from ether solvents, aromatic solvents, alcohol solvents, or any mixture of the aforementioned solvents. Ether solvents are selected from tetrahydrofuran, methyl tert-butyl ether, 1,4-dioxane, cyclopentanehexyl ether, isopropyl ether, or ethylene glycol dimethyl ether. Aromatic solvents are selected from toluene, xylene, chlorobenzene, or bromobenzene. Alcohol solvents are selected from methanol, ethanol, isopropanol, n-propanol, or tert-butanol. Preferably, ether solvents and / or alcohol solvents are used, more preferably tetrahydrofuran, ethanol, methanol, or any mixture of the aforementioned solvents. The reducing agent is selected from borohydrides and aluminum-containing reducing agents. Borohydrides are selected from sodium borohydride, lithium borohydride, potassium borohydride, sodium triacetoxyborohydride, and sodium cyanoborohydride. Aluminum-containing reducing agents are selected from lithium aluminum hydride, red aluminum, and diisobutylaluminum hydride. The reducing agent is preferably a borohydride, more preferably sodium borohydride. The reaction temperature is -10 to 50°C, preferably 0 to 40°C.

[0042] In some embodiments of the present invention,

[0043] The organic solvent in step F is selected from sulfoxide solvents, amide solvents, ketone solvents, nitrile solvents, ether solvents, aromatic solvents, or any mixture of the aforementioned solvents. Sulfoxide solvents are selected from dimethyl sulfoxide. Amide solvents are selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. Ketone solvents are selected from acetone, dibutyl ketone, methyl isobutyl ketone, or cyclohexanone. Nitrile solvents are selected from acetonitrile, propionitrile, or butyronitrile. Ether solvents are selected from tetrahydrofuran, methyl tert-butyl ether, 1,4-dioxane, isopropyl ether, cyclopentanehexyl methyl ether, or ethylene glycol dimethyl ether. Aromatic solvents are selected from toluene, xylene, chlorobenzene, or bromobenzene. Preferably, amide solvents, nitrile solvents, and ether solvents are used. Further preferred materials include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, cyclopentanehexyl ether, or ethylene glycol dimethyl ether, and acetonitrile.

[0044] The alkali used in step F is selected from alkali metal alkalis or organometallic alkalis. Alkali metal alkalis are selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, sodium hydride, and / or potassium bicarbonate. Organometallic alkalis are selected from sodium methoxide, sodium ethoxide, aluminum isopropoxide, lithium tert-butoxide, sodium tert-butoxide, and / or potassium tert-butoxide. The molar ratio of S8 to S10 is 1:1 to 2, preferably 1:1 to 1.5. The molar ratio of S8 to alkali is 1:1 to 2, preferably 1:1 to 1.5, more preferably 1:1 to 1.3. The reaction temperature varies depending on the structure of S10 and S11, but a reaction within the range of 0 to 120°C is sufficient. The reaction time is sufficient within the range of 0.5 to 10 hours.

[0045] In some embodiments of the present invention,

[0046] The organic solvent in step G is selected from sulfoxide solvents, amide solvents, ketone solvents, nitrile solvents, ether solvents, aromatic solvents, alkane solvents, haloalkane solvents, alcohol solvents, water, or any mixture of the aforementioned solvents. Sulfoxide solvents are selected from dimethyl sulfoxide. Amide solvents are selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; ketone solvents are selected from acetone, dibutyl ketone, methyl isobutyl ketone, or cyclohexanone. Nitrile solvents are selected from acetonitrile, propionitrile, or butyronitrile; ether solvents are selected from tetrahydrofuran, methyl tert-butyl ether, 1,4-dioxane, cyclopentane-hexyl methyl ether, isopropyl ether, or ethylene glycol dimethyl ether; aromatic solvents are selected from toluene, xylene, chlorobenzene, or bromobenzene. Alkane solvents are selected from cyclohexane, n-hexane, or n-heptane. The halogenated alkane solvent is selected from dichloromethane, chloroform, carbon tetrachloride, and 1,2-dichloroethane; the alcohol solvent is selected from methanol, ethanol, isopropanol, and tert-butanol. Preferably, nitrile solvents, chloroalkane solvents, amide solvents, alcohol solvents, ether solvents, ester solvents, water, or any mixture of the aforementioned solvents are used. More preferably, acetonitrile, dichloromethane, chloroform, N,N-dimethylformamide, methanol, ethanol, isopropanol, tetrahydrofuran, cyclopentanehexyl ether, 1,4-dioxane, isopropyl ether, ethylene glycol dimethyl ether, ethyl acetate, water, or any mixture of the aforementioned solvents are used.

[0047] The acidic reagent in step G is selected from organic fatty acids, carboxylic acids, sulfonic acids, and inorganic acids. Organic fatty acids are selected from formic acid, acetic acid, trifluoroacetic acid, and propionic acid. Sulfonic acids are selected from methanesulfonic acid, p-toluenesulfonic acid, p-toluenesulfonate monohydrate, benzenesulfonic acid, or trifluoromethanesulfonic acid. Inorganic acids are selected from sulfuric acid, hydrochloric acid, and hydrobromic acid. The reducing agent consists of a catalyst and a hydrogen donor, wherein the metal catalyst is selected from dry palladium on carbon, wet palladium on carbon, rhodium on carbon, palladium hydroxide, or Raney nickel, and the hydrogen donor is selected from hydrogen gas or ammonium formate. The oxidizing agent used is selected from cerium nitrate ammonium.

[0048] In order to obtain the compounds of the present invention, it is sometimes necessary for those skilled in the art to select or modify the synthesis steps or reaction process, as well as the feed ratio and feed sequence, based on an existing implementation method.

[0049] Beneficial technical effects

[0050] The inventors have discovered that the preparation of compound I in the prior art suffers from problems such as the need for column chromatography purification of the product, protection and deprotection, low atom economy, waste products from the hydrogenation of phosphorus oxychloride and azo reagents resulting from the photoelectrophoresis reaction, the use of flammable n-butyllithium reagent, and the accompanying low-temperature reaction. The present invention uses S1 and a chiral substrate S2 derived from natural products (without the need for Sharpless epoxy construction) as raw materials to achieve column chromatography-free reaction at the gram scale, which is beneficial for industrial production.

[0051] Furthermore, the existing synthesis of II-a compounds uses the Gabriel amine synthesis method, in which the one-step reaction of potassium phthalimide replacing p-toluenesulfonate yields 88%, the one-step column chromatography reaction of methylamine hydrolysis yields 89.2%, and the two-step yield is 78.5%, and it requires the use of easily explosive methylamine alcohol solution. This invention employs a new synthetic route that eliminates the need for easily explosive methylamine alcohol solution and column chromatography, achieving a two-step yield of 75%–85%, making it more suitable for industrial production.

[0052] The existing technology for preparing II-b (i.e., OTB-658) requires a three-step reaction (using S8 as a starting material, followed by phthalimide potassium salt substitution, methylamine hydrolysis, and acetylation), with an overall yield of 50%. This invention requires only two steps (using S8 as a starting material, followed by substitution and deprotection), and does not require heating. The reaction conditions are mild, and the two-step yield is 79%–89%. Detailed Implementation

[0053] The present invention will be described in detail through the following embodiments, but this does not imply any adverse limitation on the invention. The present invention has been described in detail herein, and specific embodiments thereof have also been disclosed. It will be apparent to those skilled in the art that various changes and modifications can be made to the specific embodiments of the present invention without departing from the spirit and scope thereof.

[0054] For all the following examples, standard operating and purification methods known to those skilled in the art were used. Unless otherwise stated, all temperatures are expressed in °C (degrees Celsius). The structures of the compounds were determined by nuclear magnetic resonance (NMR) spectroscopy.

[0055] The structure of the compound was determined by nuclear magnetic resonance (NMR) hydrogen spectrum (1H NMR). 1 The NMR spectrum was determined by 1H NMR. The 1H NMR shift (δ) is given in parts per million (ppm). The coupling constant (J) is in Hertz (Hz). NMR spectra were determined using a Mercury-400 NMR spectrometer, with deuterated chloroform (CDCl3) or deuterated dimethyl sulfoxide (DMSO-d6) as solvent and tetramethylsilane (TMS) as internal standard. A Yanaco LY-300 electronic balance (Japan) was used. Column chromatography typically used 200–300 mesh or 300–400 mesh silica gel as the support. Anhydrous solvents were treated according to standard methods. All other reagents were commercially available analytical grade.

[0056] This invention uses the following abbreviations:

[0057] CDCl3 represents deuterated chloroform.

[0058] DMSO stands for dimethyl sulfoxide

[0059] DMF stands for N,N-dimethylformamide

[0060] CDI represents carbonyl diimidazole

[0061] RT represents room temperature

[0062] Ac represents acetyl group.

[0063] Example

[0064] Example 1

[0065] Preparation of (2R,3R)-3-((4-fluoro-2-nitro-5-thiomorpholinophenoxy)methyl)ethylene oxide-2-carboxylic acid methyl ester

[0066]

[0067] Compound S1 (258 mg, 1 mmol), potassium carbonate (180 mg, 1.3 mmol), and cesium fluoride (30 mg, 0.2 mmol) were suspended in 3 mL of N,N-dimethylformamide and stirred. Compound S2 (234 mg, 1.2 mmol) was dissolved in 3 mL of N,N-dimethylformamide and added to the reaction mixture. The mixture was stirred at room temperature for 70 h. 120 mL of water was added, and the mixture was extracted three times with ethyl acetate. The combined organic phases were washed with brine, dried over anhydrous sodium sulfate, filtered, concentrated, and purified by silica gel column chromatography (petroleum ether / ethyl acetate = 3 / 10) to give 259 mg of compound S3 as a yellow solid, with a yield of 70%. 1 H NMR (400MHz, CDCl3) δ7.75(d,J=12.8Hz,1H),6.75(d,J=7.6Hz,1H),4.44(d,J=1.2Hz,1H),4 .43(d,J=3.2Hz,1H),3.82(s,3H),3.71-3.62(m,2H),3.66-3.58(m,4H),2.81-2.78(m,4H).

[0068] Examples 2 to 10

[0069] Compound S1 (258 mg, 1 mmol) was added as a feedstock, following the procedure in Example 1. The specific compounds S2, base, solvent, temperature, feed ratio, and yield of compound S3 are shown in the table below:

[0070]

[0071]

[0072] Example 11

[0073] Preparation of (2R,3R)-3-((4-fluoro-2-nitro-5-thiomorpholinophenoxy)methyl)ethylene oxide-2-carboxylic acid methyl ester

[0074]

[0075] Compound S1 (5 g), compound S2 (7.5 g), and K2CO3 (4 g) were dissolved in a 2 / 1 mixture of DMSO and DMF (50 mL) and stirred at room temperature for 50 h. 200 mL of water was added, and the mixture was extracted twice with ethyl acetate. The combined organic layers were washed once with 100 mL of water, then washed with brine, dried over anhydrous sodium sulfate, filtered, concentrated, and then stirred for 2 h with 50 mL of methanol. The mixture was filtered again, washed with 30 mL of methanol, and dried to give 4.9 g of a yellow solid, with a yield of 68%.

[0076] Example 12

[0077] Preparation of (2R,3R)-3-((2-amino-4-fluoro-5-thiomorpholinophenoxy)methyl)ethylene oxide-2-carboxylic acid methyl ester

[0078]

[0079] Compound S3 (100 mg, 0.27 mmol) was dissolved in dichloromethane (4 mL), and dry palladium on carbon (10% palladium supported on carbon, 20 mg) was added. The mixture was stirred for 12 h at room temperature and under a normal pressure hydrogen atmosphere. After filtration and washing with dichloromethane, the filtrate was concentrated to give 89 mg of compound S4, a pale yellow oil, with a yield of 97%. 1 H NMR (400MHz, DMSO-d6) δ6.61(d,J=8.0Hz,1H),6.43(d,J=13.6Hz,1H),4.74(s,2H),4.16(m,1H),4.05 (m,1H),3.81(d,J=4.4Hz,1H),3.70(s,3H),3.67-3.61(m,1H),3.12-3.04(m,4H),2.84-2.63(m,4H).

[0080] Example 13

[0081] Preparation of (2R,3R)-3-((2-amino-4-fluoro-5-thiomorpholinophenoxy)methyl)ethylene oxide-2-carboxylic acid methyl ester

[0082]

[0083] Compound S3 (4.9 g) was dissolved in dichloromethane (120 mL), and dry palladium on carbon (10% palladium supported on carbon, 0.98 g) was added. The mixture was stirred at room temperature under a hydrogen atmosphere for 16 h. The solution was filtered through diatomaceous earth, washed with dichloromethane, and the filtrate was concentrated to give 4.5 g of an oily substance. The crude product was used directly in the next step.

[0084] Example 14

[0085] Preparation of methyl (R)-2-((S)-6-fluoro-7-thiomorpholine-3,4-dihydro-2H-benzo[b][1,4]oxazine-3-yl)-2-hydroxyacetate

[0086]

[0087] Compound S4 (540 mg, 1.58 mmol) was dissolved in isopropanol (20 mL) and heated and stirred at 90 °C for 4 h. The reaction solution was concentrated and purified by silica gel column chromatography (petroleum ether / ethyl acetate = 2 / 5) to give 486 mg of compound S5, a pink oily substance, with a yield of 90%. 1 HNMR (400MHz, CDCl3) δ6.48 (dd, J=7.8, 2.2Hz, 1H), 6.41 (dd, J=12.4, 2.4Hz, 1H), 4.27-4.21 (m, 2H ),4.15-4.10(m,1H),3.83-3.80(m,3H),3.60-3.57(m,1H),3.32-2.99(m,4H),2.81-2.70(m,4H).

[0088] Example 15

[0089] Preparation of methyl (R)-2-((S)-6-fluoro-7-thiomorpholine-3,4-dihydro-2H-benzo[b][1,4]oxazine-3-yl)-2-hydroxyacetate

[0090]

[0091] Compound S4 (4.5 g) was dissolved in isopropanol (130 mL), protected with Ar, and heated at 90 °C for 14 h. The reaction solution was concentrated to obtain the crude product. The crude product was used directly in Example 18.

[0092] Example 16

[0093] Preparation of (3R,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazine-3-carboxylic acid methyl ester

[0094]

[0095] Compound S5 (206 mg, 0.6 mmol) was dissolved in anhydrous toluene (6 mL), and CDI (117 mg, 0.72 mmol) was added. The mixture was heated and stirred at 110 °C for 48 h under argon protection. The reaction solution was concentrated and purified by silica gel column chromatography (petroleum ether / ethyl acetate = 3 / 10) to give compound S6, 89 mg, a grayish-white solid, in 40% yield. 1 H NMR (400MHz, CDCl3) δ7.70 (d, J = 12.8Hz, 1H), 6.63 (d, J = 8Hz, 1H), 4.68 (d, J = 6.8Hz, 1H), 4.60 (dd, J = 10. 4,3.2Hz,1H),4.24-4.19(m,1H),3.91(s,3H),3.87-3.85(m,1H),3.34-3.24(m,4H),2.83-2.81(m,4H).

[0096] Example 17

[0097] Preparation of (3R,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazine-3-carboxylic acid methyl ester

[0098]

[0099] Compound S5 (203 mg, 0.59 mmol) was dissolved in anhydrous dichloromethane (6 mL), and triethylamine (417 μL, 2.96 mmol) and triphosgene (88 mg, 0.29 mmol) were added under ice bath conditions. The mixture was stirred at room temperature for 4 h. 20 mL of water was added, and the mixture was extracted three times with ethyl acetate. The combined organic layers were washed with brine, dried over anhydrous sodium sulfate, filtered, and the filtrate was concentrated and purified by silica gel column chromatography (petroleum ether / ethyl acetate = 3 / 10) to give compound S6, 137 mg of a grayish-white solid, in 63% yield.

[0100] Example 18

[0101] Preparation of (3R,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazine-3-carboxylic acid methyl ester

[0102]

[0103] Compound S5 (4.5 g) was dissolved in dichloromethane (50 mL), and triethylamine (9.3 mL) was added. The mixture was cooled in an ice-water bath, and then 1.96 g of triphosgene in dichloromethane (50 mL) was added dropwise to the reaction mixture. The mixture was kept at 0 °C for 10 min and stirred at room temperature for 1 h. 200 mL of water was added, and the mixture was extracted three times with dichloromethane. The combined organic layers were washed with brine, dried over anhydrous sodium sulfate, filtered, and the filtrate was concentrated. 22 mL of methanol was added, and the mixture was stirred to give 3.3 g of a grayish-white solid, with a yield of 68%.

[0104] Example 19

[0105] Preparation of (3R,3aS)-8-fluoro-3-(hydroxymethyl)-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazin-1-one

[0106]

[0107] Compound S6 (100 mg, 0.272 mmol) was dissolved in a mixed solution of anhydrous ethanol and tetrahydrofuran (9 mL, anhydrous ethanol / tetrahydrofuran = 2 / 1), and placed at 0–5 °C. Sodium borohydride (10 mg, 0.272 mmol) was added, and the mixture was stirred for 2 h under argon protection. The reaction was quenched with water, and the mixture was extracted twice with ethyl acetate. The combined organic layers were washed with brine, dried over anhydrous sodium sulfate, filtered, and the filtrate was concentrated to give 97 mg of crude white solid. This crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate = 4 / 5) to give compound S7, 82 mg of white solid, in 89% yield. 1 H NMR (400MHz, CDCl3) δ7.79 (d, J=12.8Hz, 1H), 6.70 (s, 1H), 4.50 (dd, J=10.8, 3.2Hz, 1H), 4.41-4.3 7(m,1H),4.20-4.15(m,1H),4.08-4.04(m,1H),3.91(t,J=10.4Hz,2H),3.34(s,4H),2.87(s,4H).

[0108] Example 20

[0109] Preparation of (3R,3aS)-8-fluoro-3-(hydroxymethyl)-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazin-1-one

[0110]

[0111] Compound S6 (3.3 g) was dissolved in a mixed solvent of anhydrous ethanol and tetrahydrofuran (75 mL, anhydrous ethanol / tetrahydrofuran = 2 / 1), and stirred at 0–5 °C for 5 min. 337 mg of sodium borohydride was added in portions, and after Ar protection, the mixture was reacted at 0–5 °C for 1.5 h. Water was added, and a white solid precipitated. This solid was filtered and dried to give 2.8 g of an off-white solid, yielding 93%.

[0112] Example 21

[0113] Preparation of tert-butyl carbamate (((3S,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazin-3-yl)methyl)carbamate

[0114]

[0115] Compounds S8 (3 g, 6.06 mmol), S10 (1.7 g, 7.9 mmol), and cesium carbonate (2.57 g, 7.9 mmol) were added to N,N-dimethylformamide (20 mL) and stirred at 80 °C for 1 hour. 20 mL of water was added, causing a solid to precipitate. This solid was filtered, and the aqueous filter cake was dried. 25 mL of methanol was added, and the mixture was stirred at room temperature, filtered, washed, and dried to give 2.8 g of an off-white solid, S9-a, in 85% yield. 1 H NMR(400MHz, CDCl3)δ7.74(d,J=13.2Hz,1H),6.64(brs,1H),4.51-4.40(m,2H),4.15(dd,J=6.4Hz,14 .8Hz,1H),4.00-3.92(m,2H),3.80(t,J=10.0Hz,1H),3.35-3.23(m,4H),2.83(brs,4H),1.53(s,18H).

[0116] Examples 22 to 23

[0117] Preparation of tert-butyl carbamate (((3S,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazin-3-yl)methyl)carbamate

[0118]

[0119] Compound S8 (1 mmol) was added as a feedstock, following the procedure in Example 21. The specific compounds S10, base, solvent, temperature, feed ratio, and yield of compound S9-a are shown in the table below:

[0120]

[0121] Example 24

[0122] Preparation of (3S,3aS)-3-(aminomethyl)-8-fluoro-7-thiomorpholino-3a,4-dihydro-1H,3H-benzo[b]oxazol[3,4-d][1,4]oxazin-1-one

[0123]

[0124] Compound S9-a (539 mg, 1 mmol) was dissolved in 3 mL of ethyl acetate, and a 4 N hydrochloric acid-ethyl acetate solution was added. The mixture was stirred for 0.5 h. After filtration, washing with water, and drying, 320 mg of a white solid of type II-a was obtained, with a yield of 94%. 1 H NMR(400MHz, CDCl3)δ:7.75(d,J=13.0Hz,1H),6.55(d,J=7.8Hz,1H),4.45(dd,J=3.0,10.4,Hz,1H),4.29-4.23(m,1H ),4.07-4.00(m,1H),3.86(t,J=10.2Hz,1H),3.32-3.20(m,4H),3.19-3.04(m,2H),2.83-2.76(m,4H),1.41(brs,2H).

[0125] Example 25

[0126] Preparation of (3S,3aS)-3-(aminomethyl)-8-fluoro-7-thiomorpholino-3a,4-dihydro-1H,3H-benzo[b]oxazol[3,4-d][1,4]oxazin-1-one

[0127] Compound S9-a (1 g, 1.86 mmol) was added to 5 mL of methanol, followed by 6 N hydrochloric acid solution. The mixture was stirred for 20 min, and the reaction solution was added dropwise to an aqueous potassium carbonate solution. A solid precipitated out. The solid was filtered, washed with water, and dried to give 600 mg of a white solid of type II-a, with a yield of 95%.

[0128] Example 26

[0129] Preparation of (3S,3aS)-3-(aminomethyl)-8-fluoro-7-thiomorpholino-3a,4-dihydro-1H,3H-benzo[b]oxazol[3,4-d][1,4]oxazin-1-one

[0130] Compound S9-a (1 g, 1.86 mmol) was added to 1 mL of ethanol, followed by 9 mL of 4 N hydrochloric acid solution. The mixture was stirred overnight. The reaction solution was then added dropwise to an aqueous potassium carbonate solution, precipitating a solid. The solid was filtered, washed with water, and dried to give 630 mg of a white solid of type II-a, with a yield of 100%.

[0131] Examples 27 to 29

[0132] Preparation of tert-butyl acetyl(((3S,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazin-3-yl)methyl)carbamate

[0133]

[0134] Compound S11 (82 mg, 0.52 mmol) and cesium carbonate (171 mg, 0.52 mmol) were added to N,N-dimethylformamide (4 mL), stirred at room temperature, and then compound S8 (200 mg, 0.4 mmol) was added. The mixture was stirred at different temperatures for 2 hours each time. Post-treatment: 80 mL of water was added, and the mixture was extracted three times with ethyl acetate. The combined organic layers were washed with brine, dried over anhydrous sodium sulfate, filtered, and the filtrate was concentrated and purified by silica gel column chromatography (dichloromethane / methanol = 1 / 100–2 / 100) to obtain compound S9-b.

[0135] Example Temperature ℃ Yield % Example 27 60 91.1 Example 28 40 88.2 Example 29 RT 99

[0136] 1 H NMR (400MHz, CDCl3) δ7.69(d,J=12.8Hz,1H),6.56(d,J=8Hz,1H),4.46-4.41(m,2H),4.25-4.19(m,1H),4.07(dd,J=1 4.4, 4.4Hz, 1H), 3.90-3.85 (m, 1H), 3.79 (t, J = 10.2Hz, 1H), 3.30-3.23 (m, 4H), 2.80 (s, 4H), 2.52 (s, 3H), 1.57 (s, 9H).

[0137] Example 30

[0138] Preparation of tert-butyl acetyl(((3S,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazin-3-yl)methyl)carbamate

[0139]

[0140] Compound S11 (1.56 g, 9.9 mmol) and cesium carbonate (3.2 g, 9.9 mmol) were added to N,N-dimethylformamide (40 mL). After stirring at room temperature, compound S8 (3.75 g, 7.6 mmol) was added, and the mixture was stirred at room temperature for 4.5 hours. After cooling in an ice-water bath, 120 mL of water was added, and the precipitated solid was filtered. The solid was washed with 50 mL of water, and the filter cake was dried to obtain compound S9-b, a white solid weighing 3.5 g.

[0141] Example 31

[0142] Preparation of N-(((3S,3aS)-8-fluoro-1-oxo-7-thiomorpholine-3a,4-dihydro-1H,3H-benzo[b]oxazolo[3,4-d][1,4]oxazin-3-yl)methyl)acetamide

[0143]

[0144] Compound S9-b (567 mg, 1.18 mmol) was suspended in 6N hydrochloric acid solution (6 mL), and isopropanol (3 mL) was added and stirred for 5 h. The pH was adjusted by adding saturated sodium bicarbonate solution, filtered, and dried to give compound II-b, 402 mg of off-white solid, yield 90%. 1 HNMR (400MHz, CDCl3) δ7.70(d,J=12.8Hz,1H),6.55(d,J=8Hz,1H),6.13(s,1H),4.50(d,J=10Hz,1H),4.39( s,1H),3.91-3.89(m,1H),3.83(t,J=10.0Hz,1H),3.71(s,2H),3.27-3.24(m,4H),2.79(s,4H),2.05(s,3H).

[0145] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a compound of formula (I), Its features are, Includes the following steps: Step A involves reacting compound S1 and compound S2 in an organic solvent under alkaline conditions to prepare compound S3; Step B involves dissolving compound S3 in an organic solvent and reducing it to prepare compound S4. Step C involves preparing compound S5 by heating compound S4 in an organic solvent to achieve a cyclization reaction. Step D involves reacting compound S5 with a carbonylating agent in an organic solvent to prepare compound S6; Step E involves reacting compound S6 with a reducing agent in an organic solvent to obtain the compound shown in formula (I).

2. The preparation method according to claim 1, Its features are, The organic solvent in step A is selected from sulfoxide solvents, amide solvents, or a mixture of the aforementioned solvents; the base is selected from alkali metal bases; the temperature for the nucleophilic substitution reaction is 0–50 °C.

3. The preparation method according to claim 2, Its features are, The sulfoxide solvent is selected from dimethyl sulfoxide; the amide solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone; the alkali metal base is selected from sodium carbonate, potassium carbonate, cesium carbonate, sodium fluoride, potassium fluoride, cesium fluoride or any mixture thereof.

4. The preparation method according to claim 1, Its features are, The organic solvent in step B is selected from solvents containing chlorinated alkanes or mixed solvents containing chlorinated alkanes; the hydrogenation system used in the reduction reaction consists of a metal catalyst and a hydrogen donor; the reaction temperature is 0–40°C.

5. The preparation method according to claim 4, Its features are, The solvent for the chlorinated alkanes is selected from chloroform, dichloromethane, carbon tetrachloride, and 1,2-dichloroethane; the mixed solvent containing chlorinated alkanes is any mixture of the solvent of chlorinated alkanes and methanol, ethanol, acetic acid, ethyl acetate, 1,4-dioxane, and tetrahydrofuran; the metal catalyst is selected from dry palladium on carbon, wet palladium on carbon, rhodium on carbon, palladium hydroxide, or Raney nickel; the hydrogen donor is selected from hydrogen or ammonium formate.

6. The preparation method according to claim 1, Its features are, The organic solvent in step C is selected from alcohol solvents, 1,4-dioxane, toluene, or amide solvents; the alcohol solvent is selected from methanol, ethanol, isopropanol, or tert-butanol; the amide solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; the heating temperature is 60–120°C.

7. The preparation method according to claim 1, Its features are, The organic solvent in step D is selected from dichloromethane, toluene, tetrahydrofuran, tert-butyl dimethyl ether, N,N-dimethylformamide, acetone, or 1,4-dioxane; the carbonylating agent is selected from carbonyl diimidazole, dimethyl carbonate, diethyl carbonate, triphosgene, phosgene, methyl chloroformate, ethyl chloroformate, butyl chloroformate, isopropyl chloroformate, or benzyl chloroformate; a base may be added or not in the reaction, and the base is selected from triethylamine, diisopropylethylamine, DBU, pyridine, sodium carbonate, sodium acetate, or potassium carbonate; the reaction temperature is 0–120°C.

8. The preparation method according to claim 1, Its features are, The organic solvent in step E is selected from alcohol solvents and / or ether solvents; the reducing agent is selected from borohydrides; and the reaction temperature is -10 to 50°C.

9. The preparation method according to claim 8, Its features are, The alcohol solvent is selected from methanol, ethanol, isopropanol, and tert-butanol; the ether solvent is selected from tetrahydrofuran, methyl tert-butyl ether, cyclopentyl methyl ether, and 1,4-dioxane; and the borohydride is selected from sodium borohydride.

10. A method for preparing a compound of formula (II-a) or (II-b), Its features are, Includes the following steps: Step F involves reacting compound S8 with either compound S10 or S11 in an organic solvent under alkaline conditions to prepare compound S9, wherein the structures of S10 and S11 are as follows: Where R1 is tert-butyl, benzyl, 4-methoxybenzyl, or 2,4-dimethoxybenzyl; R2 is tert-butyloxycarbonyl, benzyloxycarbonyl, 4-methoxybenzyloxycarbonyl, 2,4-dimethoxybenzylcarbonyl, or acetyl; and R is hydrogen or acetyl. Step G involves reacting compound S9 in a solvent with an acidic reagent, a reducing reagent, or an oxidizing reagent to obtain compound II-a or II-b.

11. The preparation method according to claim 10, Its features are, The organic solvent in step F is selected from amide solvents, nitrile solvents, and ether solvents; the base is selected from alkali metal bases or organometal bases; and the reaction temperature is 0–120°C.

12. The preparation method according to claim 11, Its features are, The amide solvents are selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; the nitrile solvents are selected from acetonitrile, propionitrile, and butyronitrile; the ether solvents are selected from tetrahydrofuran, 1,4-dioxane, cyclopentane-hexane methyl ether, or ethylene glycol dimethyl ether; the alkali metal bases are selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, sodium hydride, and / or potassium bicarbonate; and the organometallic bases are selected from sodium methoxide, sodium ethoxide, aluminum isopropoxide, lithium tert-butoxide, sodium tert-butoxide, and / or potassium tert-butoxide.

13. The preparation method according to claim 10, The solvent in step G is selected from nitrile solvents, chloroalkane solvents, amide solvents, alcohol solvents, ether solvents, ester solvents and / or water; the acidic reagent is selected from organic fatty carboxylic acids, sulfonic acids, and inorganic acids; the reducing reagent is composed of a heavy metal catalyst and a hydrogen donor; and the oxidizing reagent is selected from cerium nitrate ammonium.

14. The preparation method according to claim 13, The nitrile solvent is selected from acetonitrile; the chloroalkane solvent is selected from dichloromethane and chloroform; the amide solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; the alcohol solvent is selected from methanol, ethanol, isopropanol, n-propanol, or tert-butanol; the ether solvent is selected from tetrahydrofuran, methyl tert-butyl ether, cyclopentanehexyl ether, 1,4-dioxane, isopropyl ether, or ethylene glycol dimethyl ether; the ester solvent is selected from ethyl acetate, isopropyl acetate, or butyl acetate; the organic fatty acid is selected from formic acid, acetic acid, trifluoroacetic acid, or propionic acid; the sulfonic acid is selected from methanesulfonic acid, p-toluenesulfonic acid, p-toluenesulfonate monohydrate, benzenesulfonic acid, or trifluoromethanesulfonic acid; the inorganic acid is selected from sulfuric acid, hydrochloric acid, or hydrobromic acid; the catalyst is selected from dry palladium on carbon, wet palladium on carbon, rhodium on carbon, palladium hydroxide, or Raney nickel; and the hydrogen donor is selected from hydrogen or ammonium formate.

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