Synthesis of 3-methyl-1, 2, 4-thiadiazole-5-carbohydrazide and methyl-d3 deuterated forms thereof

Abstract

The invention relates to a synthesis method of a compound (IV-2): # imgabs0. The method has the advantage that the purity of the generated isotope is very satisfactory. These compounds are key intermediates for the synthesis of pharmaceutical compounds, in particular non-azolintams and deuterated non-azolintams.

Description

Field of the Invention

[0001] The present invention relates to the field of chemical synthesis and provides a method for synthesizing compound (I) or a salt thereof:

[0002]

[0003] wherein R 1 represents methyl or methyl-d3, and thus corresponds to 3-methyl-1,2,4-thiadiazole-5-carbohydrazide or its methyl-d3 deuterated form. These compounds are key intermediates for synthesizing pharmaceutical compounds, especially fezolinetant and deuterated fezolinetant. Background of the Invention

[0005] Fezolinetan was developed as a selective antagonist of the NK-3 receptor and is a useful therapeutic compound, especially in the treatment and / or prevention of sex hormone-dependent diseases. Fezolinetant corresponds to (R)-(4-fluorophenyl)-(8-methyl-3-(3-methyl-1,2,4-thiadiazol-5-yl)-5,6-dihydro-[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl)methanone and is described in WO2014 / 154895.

[0006] Deuterated fezolinetan (R)-(4-fluorophenyl)-(8-methyl-3-(3-(methyl-d3)-1,2,4-thiadiazol-5-yl)-5,6-dihydro-[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl)methanone was also developed for the same purpose and is described in WO2019 / 012033.

[0007]

[0008] Methods for synthesizing fezolinetant and deuterated fezolinetan are described in WO2014 / 154895 and WO2019 / 012033. These methods involve 3-methyl-1,2,4-thiadiazole-5-carbohydrazide or its deuterated form as the key intermediate (I):

[0009]

[0010] wherein R 1 represents methyl or methyl-d3.

[0011] WO2013 / 050424 discloses a method for synthesizing the non-deuterated intermediate 3-methyl-1,2,4-thiadiazole-5-carbohydrazide (I-1), which is prepared from the corresponding methyl ester (II-1-a), and the methyl ester is prepared in one step from acetamide, chlorocarbonylsulfenyl chloride, and methyl cyanoformate:

[0012]

[0013] However, chlorocarbonylsulfenyl chloride and methyl cyanoformate are hazardous reagents, which cause raw material problems in large-scale production, and their use should be avoided for large-scale production. In addition, this synthetic route generates sulfur impurities, which have an adverse effect on the quality of the final pharmaceutical product. Moreover, even after optimization, the overall yield of intermediate (I-1) is still lower than 30%.

[0014] The method for obtaining the corresponding deuterated intermediate 3-(methyl-d3)-1,2,4-thiadiazole-5-carbohydrazide (I-2) is the same as that described in WO2019 / 012033, and it has the same disadvantages.

[0015] Therefore, there is a need for a safer, more robust, scalable, and more efficient method for synthesizing intermediate (I).

[0016] The present invention provides a method for synthesizing intermediate (I) from the corresponding ester (II), which ester itself is obtained by alkoxycarbonylation of the corresponding halogenated intermediate (III):

[0017]

[0018] or a salt thereof, wherein R 1 represents methyl or methyl-d3, R 2 represents an alkyl or aralkyl group, and X represents a halogen atom.

[0019] It has been reported that this type of alkoxycarbonylation reaction occurs on some more robust 5-membered heterocycles, such as thiophene, furan, thiazole, imidazole, oxazole, pyrazole, and indole. However, it has never been reported to occur on less robust heterocycles (i.e., containing more than 2 heteroatoms), which are more prone to ring opening, such as the thiadiazole ring in the present invention. In the case of forming an open intermediate of 1,2,4-thiadiazole, highly reactive intermediates (such as mercaptoamidine) and volatile by-products will be generated (especially when R 1 is methyl) (for a similar more robust oxazole, see: Verrier et al., Beilstein J. Org. Chem., 2011, 7, 1584 - 1601; Bellina et al., Current Org. Chem., 2008, 12(9), 774 - 790 and Strotman et al., Org. Lett., 2010, 12, 3578 - 3581).

[0020] The advantages of the method of the present invention are that it does not involve particularly dangerous chemistry of special reagents. The overall yield is very satisfactory (more than 67%), even after large-scale production, as demonstrated in the experimental section below.

[0021] The starting halogenated compound of formula (III) can be obtained from the amine compound of formula (IV) through the Sandmeyer reaction:

[0022]

[0023] The present invention also provides a new method for synthesizing the deuterated intermediate (IV). This method includes carrying out the Pinner reaction on deuterated acetonitrile (VII-2), first converting it into the Pinner salt (VI-2) (step a), then converting it into deuterated acetamidine (V-2) (step b), and then forming a thiadiazole ring (step c) to provide the compound (IV-2):

[0024]

[0025] The advantage of this method is that the resulting isotope purity is very satisfactory, as demonstrated by the following experimental section.

[0026] The present invention also provides an alternative new method for synthesizing the deuterated intermediate (IV). This method includes forming deuterated N-hydroxyacetamidine (IX-2) from deuterated acetonitrile (VII-2), then activating it by tosylation to form the intermediate (X-2), and then forming a thiadiazole ring to provide the compound (IV-2):

[0027]

[0028] This method also has the advantage of very satisfactory isotope purity. Summary of the Invention

[0030] Therefore, the present invention relates to a method for preparing a compound of formula (I) or a salt thereof:

[0031]

[0032] wherein R 1 represents methyl or methyl-d3;

[0033] The method comprises the following steps:

[0034] a) carrying out alkoxycarbonylation on the compound of formula (III):

[0035]

[0036] wherein X represents a halogen; R 1 represents methyl or methyl-d3;

[0037] to obtain the compound of formula (II):

[0038]

[0039] Wherein R 1 represents methyl or methyl-d3; R 2 represents an alkyl or aralkyl group;

[0040] and

[0041] b) forming the compound of formula (I) by reacting the compound of formula (II) with hydrazine monohydrate.

[0042] In one embodiment, in the process of the present invention, X represents bromine or iodine; preferably, X represents bromine. In one embodiment, in the process of the present invention, R 2 represents methyl or ethyl; preferably, R 2 represents ethyl.

[0043] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of carbon monoxide, a palladium catalyst, a base and an alcohol solvent, and optionally in the presence of an organophosphorus ligand.

[0044] In one embodiment, the palladium catalyst is Pd(OAc)2, the organophosphorus ligand is 4,5-bis(diphenylphosphino)-9,9-dimethyloxanthene (Xantphos), the base is sodium acetate, and the solvent is selected from ethanol, methanol, a mixture of methyl tert-butyl ether and ethanol or methanol. Preferably, step a) is carried out in ethanol as the solvent or in a mixture of ethanol and methyl tert-butyl ether. Preferably, step a) is carried out at a temperature of 50°C - 150°C; preferably at a temperature of 63°C - 67°C; more preferably at a temperature of about 65°C. In one embodiment, step a) is carried out in the presence of Fe(CO)5.

[0045] In another embodiment, the palladium catalyst is bis(triphenylphosphine)palladium(II) chloride (Pd(PPh3)2Cl2), the base is triethylamine, and the solvent is ethanol.

[0046] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out by lithium exchange, first contacting the compound of formula (III) with an organolithium reagent, and then adding a chloroformate or a cyanate. Preferably, the organolithium reagent is n-hexyl lithium, and the chloroformate is an alkyl chloroformate, preferably ethyl chloroformate.

[0047] In one embodiment, the method of the present invention includes a preliminary step of performing a Sandmeyer reaction on the compound of formula (IV) or its salt:

[0048]

[0049] Wherein R 1 represents methyl or methyl-d3;

[0050] Thereby, a compound of formula (III) is formed.

[0051] The Sandmeyer reaction can be carried out in an aqueous medium in the presence of sodium nitrite and hydrogen bromide. Alternatively, the Sandmeyer reaction can be carried out in the presence of tert-butyl nitrite and iodine or in the presence of potassium iodide and p-toluenesulfonic acid.

[0052] The present invention also relates to a process for preparing 3-(methyl-d3)-1,2,4-thiadiazol-5-amine (IV-2) or a salt thereof:

[0053]

[0054] which comprises the following steps:

[0055] a) Reacting d3-acetonitrile with ethanol in the presence of HCl to form a Pinner salt of formula (VI-2):

[0056]

[0057] b) Reacting the Pinner salt (VI-2) with ammonia to form d3-acetamidine (V-2) or a salt thereof:

[0058]

[0059] and

[0060] c1) Reacting d3-acetamidine (V-2) with bromine, a thiocyanate and sodium methoxide to obtain a compound of formula (IV-2); or

[0061] c2) Reacting d3-acetamidine (V-2) first with sodium hypochlorite (NaOCl) and then with a thiocyanate to obtain a compound of formula (IV-2).

[0062] Definitions

[0063] In the present invention, the following terms have the following meanings:

[0064] - "about", when appearing before a number, means within 10% of that numerical value, up or down.

[0065] - "alcohol solvent" means an alcohol that is capable of dissolving a solute (chemically different liquids, solids or gases) and forming a solution, i.e., an organic compound containing at least one hydroxyl functional group (-OH) attached to a carbon atom. Examples of alcohol solvents include methanol, ethanol and isopropanol.

[0066] - "Alkoxycarbonylation reaction" refers to a chemical reaction for forming a C-C bond, which is capable of introducing an alkoxycarbonyl moiety into a chain. "Alkoxycarbonyl moiety" refers to the group -C(=O)-O-alkyl, where alkyl is defined to include cases where the alkyl itself is substituted, such as being substituted by an aryl group (i.e., forming an aralkyl group), to form

[0067] -C(=O)-O-alkyl-aryl.

[0068] - "Alkyl" refers to a hydrocarbon group of the formula C n H 2n+1 where n is a number greater than or equal to 1. Generally, the alkyl groups of the present invention contain 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The alkyl group can be straight-chain or branched-chain and can be substituted as shown herein. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, butyl and its isomers (such as n-butyl, isobutyl and tert-butyl), pentyl and its isomers, hexyl and its isomers.

[0069] - "Aryl" refers to a polyunsaturated aromatic hydrocarbon group having a single ring (i.e., phenyl) or multiple fused aromatic rings (such as naphthalene), or multiple covalently linked rings, generally containing 5 to 12 atoms, preferably 6 to 10 atoms, where at least one ring is aromatic. The aromatic ring can optionally include one or two additional fused rings (cycloalkyl, heterocyclic or heteroaryl). Non-limiting examples of aryl groups include phenyl, biphenyl, biphenylene, naphthalen-1- or -2-yl. In one embodiment, the aryl group is phenyl. Optionally, the aryl group can be substituted by one or more groups, such as alkoxy groups.

[0070] In a specific embodiment, the aryl group is substituted by 1 to 3 alkoxy groups, preferably by 1 to 3 methoxy groups. - "Aralkyl" refers to the moiety of arylalkyl, where aryl and alkyl are as defined herein. Examples of aralkyl groups include benzyl, 4-methoxybenzyl (PMB), 2,4-dimethoxybenzyl (DMB) and 2,4,6-trimethoxybenzyl (TMB).

[0071] - "Carbonylation reaction" refers to a chemical reaction for forming a C-C bond, which is capable of introducing a carbonyl moiety into a chain,

[0072] such as -C(=O)-O-R 2 where R 2 is, for example, an alkyl or aralkyl group.

[0073] - "Chloroformate" refers to a reactant of the formula ROC(O)Cl, where R can represent, for example, an alkyl or aralkyl group, forming an alkyl chloroformate and an aralkyl chloroformate, respectively.

[0074] - "Cyanoformate" refers to a reactant of the formula ROC(O)CN, wherein R may represent, for example, an alkyl or aralkyl group, forming alkyl cyanoformates and aralkyl cyanoformates, respectively.

[0075] - "Halogen" or "halogen group" refers to fluorine, chlorine, bromine or iodine. In the present invention, preferred halogen groups are bromine and iodine.

[0076] - "Methyl-d3" refers to the deuterated moiety -CD3.

[0077] - "Organolithium reagent" refers to a metal organic compound containing a carbon-lithium bond. Examples of organolithium reagents include n-hexyllithium and n-butyllithium.

[0078] - "organophosphorus ligands" refers to organic compounds containing phosphorus, preferably phosphine ligands,

[0079] That is, a compound of formula PR3, wherein R is an organic derivative. Examples of organophosphorus ligands include triphenylphosphine (PPh3), tri-tert-butylphosphine (PtBu3), 4,5-bis(diphenylphosphine)-9,9-dimethylxanthene (Xantphos), 2,2'-bis(diphenylphosphine)-1,1'-binaphthyl (BINAP), 1,3-bis(diphenylphosphine)propane (dppp) and di(1-adamantyl)-n-butylphosphine

[0080] - "Palladium catalyst" refers to a palladium complex capable of catalyzing a reaction. Examples of palladium catalysts include palladium acetate (Pd(OAc)2), palladium chloride (PdCl2), tris(dibenzylideneacetone)dipalladium, bis(dibenzylideneacetone)palladium, and bis(triphenylphosphine)palladium chloride (Pd(PPh3)2Cl2). Palladium catalysts include in situ activated precatalysts, such as Pd(PPh3)2Cl2, which are reduced to Pd(0) complexes or metallated to Pd(II) aryl complexes before participating in the catalytic cycle.

[0081] - "Pinner salt" refers to the product of the reaction of a nitrile with an alcohol, i.e., an imino ester salt (alkyl imino ester salt). - "Sandmeyer reaction" refers to the chemical reaction of synthesizing an aryl or heteroaryl halide from an aryl or heteroaryl diazonium salt via a free radical nucleophilic aromatic substitution reaction.

[0082] - "Thiocyanate" refers to the anion [SCN] - It can be used as a salt with counterions such as potassium or sodium.

[0083] - "Tosylation" refers to a reaction capable of introducing a p-toluenesulfonyl group (also known as tosyl group) on a hydroxyl moiety. In a preferred embodiment, tosylation is carried out using p-toluenesulfonyl chloride. Detailed implementation mode

[0084] Synthesis of compound (I)

[0085] The present invention relates to a method for preparing a compound of formula (I) or a salt thereof:

[0086]

[0087] wherein R 1 represents methyl or methyl-d3;

[0088] The method comprises the following steps:

[0089] a) Subjecting the compound of formula (III) to alkoxycarbonylation:

[0090]

[0091] wherein X represents halogen; R 1 represents methyl or methyl-d3;

[0092] to obtain a compound of formula (II):

[0093]

[0094] wherein R 1 represents methyl or methyl-d3; R 2 represents alkyl or aralkyl;

[0095] and

[0096] b) Forming the compound of formula (I) by reacting the compound of formula (II) with hydrazine monohydrate.

[0097] The final compounds or intermediates used in the method of the present invention may be in the form of salts, including acid addition salts and base salts. In one embodiment, the salt is a pharmaceutically acceptable salt. Suitable acid addition salts are, for example, acetate, adipate, aspartate, benzoate, benzenesulfonate, bicarbonate / carbonate, bisulfate / sulfate, borate, aminosulfonate, citrate, cyclohexylaminesulfonate, ethanedisulfonate, acetylsulfonate, formate, fumarate, gluconate, glucuronate, hexafluorophosphate, hippurate, hydrochloride / chloride, hydrobromide / bromide, hydroiodide / iodide, hydroxyethylsulfonate, lactate, malate, maleate, malonate, mesylate, naphthalenesulfonate, 2-naphthalenesulfonate, nicotinate, nitrate, orotate, oxalate, palmitate, pamoate, phosphate / hydrogenphosphate / dihydrogenphosphate, pyroglutamate, saccharate, stearate, succinate, tannate, tartrate, toluenesulfonate, trifluoroacetate, and cinofoate. Suitable base salts are, for example, salts of aluminum, arginine, benzathine, calcium, choline, diethylamine, diethanolamine, glycine, lysine, magnesium, meglumine, ethanolamine, potassium, sodium, tromethamine, 2-(diethylamino)ethanol, ethanolamine, morpholine, 4-(2-hydroxyethyl)morpholine, and zinc.

[0098] Step a) - Alkoxycarbonylation

[0099] In one embodiment, in the compound of formula (III), X represents bromine or iodine. In a preferred embodiment, in the compound of formula (III), X represents bromine. In another embodiment, in the compound of formula (III), X represents iodine.

[0100] In one embodiment, in the compound of formula (II), R 2 represents C1-C4 alkyl, preferably methyl or ethyl, and more preferably, R 2 represents ethyl. In another embodiment, in the compound of formula (II), R 2 represents aralkyl, preferably benzyl, 4-methoxybenzyl (PMB), 2,4-dimethoxybenzyl (DMB), or 2,4,6-trimethoxybenzyl (TMB).

[0101] CO / Pd alkoxycarbonylation reaction

[0102] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of carbon monoxide. In one embodiment, carbon monoxide is used at a pressure of 1-20 bar, preferably 3.5-8.5 bar, more preferably 4-5 bar.

[0103] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of a palladium catalyst. In one embodiment, the palladium catalyst is, for example, selected from palladium acetate (Pd(OAc) ), palladium chloride (PdCl ), tri(dibenzylideneacetone)dipalladium, bis(dibenzylideneacetone)palladium and bis(triphenylphosphine)palladium chloride (Pd(PPh ) 2Cl ). In a preferred embodiment, the palladium catalyst is palladium acetate. In a preferred embodiment, the palladium catalyst is bis(triphenylphosphine)palladium chloride.

[0104] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of an organophosphorus ligand. In one embodiment, the organophosphorus ligand is selected from: triphenylphosphine (PPh3), tri-tert-butylphosphine (PtBu3), 4,5-bis(diphenylphosphine)-9,9-dimethylxanthene (Xantphos), 2,2'-bis(diphenylphosphine)-1,1'-binaphthyl (BINAP), 1,3-bis(diphenylphosphine) propane (dppp) and di-(1-adamantyl) n-butylphosphine In a preferred embodiment, the organophosphorus ligand is 4,5-bis(diphenylphosphine)-9,9-dimethylxanthene (Xantphos). In another embodiment, the organophosphorus ligand is triphenylphosphine (PPh3).

[0105] Alternatively, the alkoxycarbonylation reaction of step a) is carried out in the absence of an organophosphorus ligand, based on a palladium catalyst. This is the case, for example, when bis(triphenylphosphine)palladium chloride (Pd(PPh3)2Cl2) is used as the palladium catalyst.

[0106] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of a base. In one embodiment, the base is selected from sodium acetate (NaOAc), N,N-diisopropylethylamine (DIPEA), lutidine, N-methylmorpholine (NMM), tributylamine, triethylamine (TEA) and mixtures thereof. In a preferred embodiment, the base is sodium acetate. In one embodiment, the base is used in dry form.

[0107] In one embodiment, step a) is carried out at a temperature suitable for obtaining the desired R 2 In one embodiment, step a) is carried out in an alcohol, preferably in methanol or ethanol. In one embodiment, step a) is carried out in a mixture of an alcohol solvent and methyl tert-butyl ether (MTBE), such as a mixture of MTBE and methanol or ethanol. In one embodiment, when R 2When it is ethyl, step a) is carried out in ethanol or in a mixture of ethanol and MTBE. The solvent can be dry or non-dry. In one embodiment, 2 - 30 volumes, preferably 5 - 10 volumes, more preferably about 10 volumes of the solvent are used.

[0108] In one embodiment, the concentration range of the compound of formula (III) used is 0.01M - 1M, preferably 0.1M - 0.5M, more preferably 0.2M - 0.4M.

[0109] In one embodiment, the molar equivalent number of the base (such as sodium acetate) relative to the compound (III) is 1 - 3, preferably 1.1 - 2, more preferably 1.1 - 1.5, more preferably about 1.3 equivalents.

[0110] In one embodiment, the molar equivalent number of the palladium catalyst (such as palladium acetate) relative to the compound (III) is 0.003 - 0.1, preferably 0.005 - 0.05, more preferably 0.005 - 0.01, more preferably about 0.005 equivalents.

[0111] In one embodiment, the molar equivalent number of the organic phosphorus ligand (such as Xantphos) relative to the compound (III) is 0.003 - 0.2, preferably 0.005 - 0.15, more preferably 0.005 - 0.05, more preferably about 0.005 equivalents.

[0112] In one embodiment, step a) is carried out at a temperature of 50°C - 150°C, preferably 63°C - 67°C, more preferably about 65°C. Alternatively, step a) can be carried out at a temperature of 90°C - 120°C, preferably 100°C - 110°C.

[0113] In one embodiment, step a) is carried out for a duration of at least 3 hours, preferably 10 hours - 48 hours, preferably 15 hours - 40 hours. In one embodiment, step a) is carried out for about 19 hours. In one embodiment, step a) is carried out for about 30 hours. In one embodiment, step a) is carried out for about 37 hours. The reaction duration matches the scale of the amounts involved in the reaction.

[0114] In one embodiment, after completion, the obtained product is extracted with dichloromethane, tert-butyl methyl ether or methylcyclohexane, preferably with methylcyclohexane.

[0115] In one embodiment, the obtained product (II) can be purified by distillation.

[0116] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of carbon monoxide, a palladium catalyst, an organophosphorus ligand, a base and an alcohol solvent. In one embodiment, the palladium catalyst is palladium acetate, the organophosphorus ligand is 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos), the base is sodium acetate, and the solvent is ethanol or a mixture of MTBE and ethanol. In another embodiment, the palladium catalyst is palladium acetate, the organophosphorus ligand is triphenylphosphine (PPh3), the base is triethylamine, and the solvent is ethanol or a mixture of MTBE and ethanol.

[0117] In another embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of carbon monoxide, a palladium catalyst, a base and an alcohol solvent. In one embodiment, the palladium catalyst is bis(triphenylphosphine)palladium(II) chloride (Pd(PPh3)2Cl2), the base is triethylamine, and the solvent is ethanol or a mixture of MTBE and ethanol.

[0118] Fe(CO)5 alkoxycarbonylation reaction

[0119] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in the presence of Fe(CO)5.

[0120] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out in an alcohol solvent in the presence of carbon monoxide, a palladium catalyst, an organophosphorus ligand, a base and Fe(CO)5. The above embodiments regarding the alkoxycarbonylation conditions and especially regarding these components are also applicable when using Fe(CO)5.

[0121] In one embodiment, the molar equivalent number of Fe(CO)5 is 0.01 - 0.5, preferably 0.05 - 0.2, more preferably about 0.01 equivalent, relative to compound (III).

[0122] Alkoxycarbonylation by lithium exchange

[0123] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out by lithium exchange.

[0124] In one embodiment, the alkoxycarbonylation reaction of step a) is carried out by first contacting the compound of formula (III) with an organolithium reagent and then adding a chloroformate or a cyanate to obtain the compound of formula (II).

[0125] In one embodiment, the organolithium reagent is selected from n-hexyl lithium and n-butyl lithium. Preferably, the organolithium reagent is n-hexyl lithium.

[0126] In one embodiment, the chloroformate is selected from: alkyl chloroformates and aralkyl chloroformates. Preferably, the alkyl chloroformates are selected from ethyl chloroformate, methyl chloroformate and n-butyl chloroformate. The aralkyl chloroformate is, for example, benzyl chloroformate. More preferably, the chloroformate is an alkyl chloroformate, such as ethyl chloroformate.

[0127] In one embodiment, the cyanatoformate is selected from: alkyl cyanatoformates and aralkyl cyanatoformates. Preferably, the alkyl cyanatoformates are selected from ethyl cyanatoformate, methyl cyanatoformate and tert-butyl cyanatoformate. The aralkyl cyanatoformate is, for example, benzyl cyanatoformate. More preferably, the cyanatoformate is an alkyl cyanatoformate, such as ethyl cyanatoformate.

[0128] In one embodiment, the molar equivalent number of the organolithium reagent (preferably hexyllithium) relative to compound (III) is 1 - 2, preferably 1 - 1.5, more preferably about 1.1 equivalents.

[0129] In one embodiment, the molar equivalent number of the chloroformate (preferably ethyl chloroformate) relative to compound (III) is 1 - 10, preferably 4 - 8, more preferably about 6 equivalents.

[0130] In one embodiment, the lithium exchange is carried out under an inert atmosphere.

[0131] In one embodiment, the lithium exchange is carried out in a dry solvent, such as in methyltetrahydrofuran (MeTHF), tetrahydrofuran (THF), tert-butyl methyl ether (TBME), n-hexane and mixtures thereof, preferably in methyltetrahydrofuran.

[0132] In one embodiment, the lithium exchange is carried out at a temperature below 0 °C, preferably at about -65 °C.

[0133] In one embodiment, the obtained compound of formula (II) can be purified by distillation.

[0134] Step b) - Formation of acylhydrazine (Step b)

[0135] In step b), the compound of formula (I) is formed by reacting the compound of formula (II) with hydrazine, preferably hydrazine monohydrate.

[0136] In one embodiment, the molar equivalent number of hydrazine relative to the compound of formula (II) is 1 - 2, preferably 1.1 - 1.2, more preferably about 1.14 equivalents.

[0137] In one embodiment, step b) is carried out in a solvent selected from methanol, ethanol and isopropanol. In a preferred embodiment, the solvent is isopropanol. In another preferred embodiment, the solvent is ethanol.

[0138] In one embodiment, step b) is carried out at a temperature below 10 °C, preferably 0 °C - 5 °C.

[0139] In one embodiment, step b) is carried out for a duration of at least 30 minutes, preferably at least 1 hour, preferably 1 - 48 hours, more preferably 1 - 24 hours.

[0140] In one embodiment, after completion, the compound of formula (I) is recovered in solid form and can be washed with a solvent such as methanol or isopropanol.

[0141] Sandmeyer reaction (pre-step)

[0142] In one embodiment, the method of the present invention includes a preliminary step of carrying out a Sandmeyer reaction on the compound of formula (IV) to obtain the compound of formula (III). For example, when X is Br, the compound (III-1-a) can be obtained using the method reported by Goerdeler et al. in Chem. Ber., 1956, 89, 1534 - 1540 or US2007 / 0078155.

[0143] In one embodiment, a halide compound of formula (III) is obtained from the compound of formula (IV) by a Sandmeyer reaction:

[0144]

[0145] or a salt thereof, wherein R 1 represents methyl or methyl-d3.

[0146] In one embodiment, the Sandmeyer reaction is carried out by first forming a diazonium salt from an amine in the presence of nitrous acid formed in situ and then substituting it with a halide anion as a nucleophile.

[0147] In one embodiment, the bromination by the Sandmeyer reaction is carried out in the presence of sodium nitrite (NaNO2) and hydrogen bromide (HBr), preferably in an aqueous medium. In this case, in the compound of formula (III), X is bromine.

[0148] In one embodiment, the molar equivalent number of hydrogen bromide is 1 - 5, preferably 2 - 4, more preferably about 3 equivalents relative to the compound (IV).

[0149] In one embodiment, the molar equivalent number of sodium nitrite is 1.15 to 4, preferably 1.5 - 2, more preferably about 1.5 equivalents relative to the compound (IV).

[0150] In one embodiment, the Sandmeyer reaction is carried out at a temperature of from room temperature to 60 °C, preferably from 35 °C to 50 °C, more preferably from about 40 °C to about 45 °C.

[0151] In one embodiment, the Sandmeyer reaction is carried out for a duration of at least 30 minutes, preferably from 30 minutes to 22 hours, preferably from 30 minutes to 2 hours, more preferably about 1 hour.

[0152] In one embodiment, the Sandmeyer reaction is carried out in water in the presence of 1 molar equivalent of the amine compound of formula (IV), 3 molar equivalents of hydrogen bromide, and 1.5 molar equivalents of sodium nitrite. Preferably, the reaction is carried out at a temperature of about 40 °C. Preferably, the reaction is carried out in 5 volumes of water.

[0153] In one embodiment, after completion, the product is recovered by extraction with dichloromethane. Preferably, the organic phase is neutralized with an NaOH solution.

[0154] In another embodiment, bromination by the Sandmeyer reaction is carried out in the presence of tert-butyl nitrite (tBuONO) and CuBr2. In this case, in the compound of formula (III), X is bromine.

[0155] In one embodiment, the number of molar equivalents of CuBr2 is from 1 to 3, preferably from 1 to 1.1, more preferably about 1.03 equivalents, relative to compound (IV).

[0156] In one embodiment, the number of molar equivalents of tert-butyl nitrite is from 1 to 3, preferably from 1 to 2, more preferably about 1.5 equivalents, relative to compound (IV).

[0157] In one embodiment, the Sandmeyer reaction is carried out at a temperature of from 0 °C to 40 °C, preferably from 0 °C to room temperature.

[0158] In one embodiment, the Sandmeyer reaction is carried out for a duration of at least 30 minutes, preferably from 30 minutes to 10 hours, preferably from 30 minutes to 5 hours, more preferably from 2 hours to 3 hours.

[0159] In one embodiment, the Sandmeyer reaction is carried out in acetonitrile in the presence of 1 molar equivalent of the amine compound of formula (IV), 1.03 molar equivalents of CuBr2, and 1.5 molar equivalents of tert-butyl nitrite. Preferably, the reaction is first carried out at a temperature of about 0 - 5 °C and then at room temperature.

[0160] In one embodiment, after completion, the product is recovered by extraction with tert-butyl methyl ether.

[0161] In another embodiment, iodination by the Sandmeyer reaction is carried out in the presence of tert-butyl nitrite (tBuONO) and iodine. In this case, in the compound of formula (III), X is iodine. Preferably, the reaction is carried out in a solvent such as acetonitrile.

[0162] In one embodiment, the molar equivalent number of iodine is 1 - 3, preferably 1 - 2, more preferably about 1 equivalent, relative to the compound (IV).

[0163] In one embodiment, the molar equivalent number of tert-butyl nitrite is 1 - 5, preferably 3 - 5, more preferably about 4 equivalents, relative to the compound (IV).

[0164] In one embodiment, the Sandmeyer reaction is carried out in the temperature range from room temperature to reflux.

[0165] In one embodiment, the Sandmeyer reaction is carried out for a duration of at least 30 minutes, preferably 30 minutes - 5 hours, preferably 30 minutes - 2 hours, more preferably about 1 hour.

[0166] In one embodiment, the Sandmeyer reaction is carried out in the presence of 1 molar equivalent of the amine compound of formula (IV), 1 molar equivalent of iodine, and 4 molar equivalents of tert-butyl nitrite.

[0167] In one embodiment, after completion, the excess iodine is quenched, preferably by adding Na2SO3. Thereafter, the obtained compound can be extracted with methyl tert-butyl ether.

[0168] In another embodiment, iodination by the Sandmeyer reaction is carried out in the presence of sodium nitrite (NaNO2), potassium iodide (KI), and p-toluenesulfonic acid (TsOH). In this case, in the compound of formula (III), X is iodine.

[0169] In one embodiment, the molar equivalent number of potassium iodide is 1 - 4, preferably 2 - 3, more preferably about 2.6 equivalents, relative to the compound (IV).

[0170] In one embodiment, the molar equivalent number of sodium nitrite is 1 - 3, preferably 1.5 - 2.5, more preferably about 2 equivalents, relative to the compound (IV).

[0171] In one embodiment, the molar equivalent number of p-toluenesulfonic acid is 1 - 6, preferably 3 - 4, more preferably about 3.5 equivalents, relative to the compound (IV).

[0172] In one embodiment, the Sandmeyer reaction is preferably carried out at room temperature.

[0173] In one embodiment, the Sandmeyer reaction is carried out for a duration of at least 1 hour, preferably 1 hour to 24 hours, preferably about 12 hours.

[0174] In one embodiment, the Sandmeyer reaction is carried out in the presence of 1 molar equivalent of the amine compound of formula (IV), 2.6 molar equivalents of potassium iodide, about 2 molar equivalents of sodium nitrite, and 3.5 molar equivalents of p-toluenesulfonic acid.

[0175] Synthesis of deuterated compound (IV-2)

[0176] The non-deuterated intermediate (IV-1), i.e., the compound of formula (IV) where R 1 is methyl, also known as AMTD, is commercially available or can be obtained by methods known to those skilled in the art.

[0177] For the corresponding deuterated intermediate (IV-2), i.e., the compound of formula (IV) where R 1 is methyl-d3, it is not possible to predict what isotope purity can be achieved from the non-deuterated synthetic route. A method for synthesizing intermediate (IV-2) is provided herein, which can achieve a very high isotope purity, i.e., a total isotope purity greater than 90%, more preferably greater than 95%.

[0178] d3-acetamidine route

[0179] Accordingly, the present invention also relates to a method for preparing 3-(methyl-d3)-1,2,4-thiadiazol-5-amine (IV-2) or a salt thereof:

[0180]

[0181] which comprises the following steps:

[0182] a) Reacting d3-acetonitrile with ethanol in the presence of HCl to form the Pinner salt of formula (VI-2):

[0183]

[0184] b) Reacting the Pinner salt (VI-2) with ammonia to form d3-acetamidine (V-2) or a salt thereof:

[0185]

[0186] and

[0187] c1) Reacting d3-acetamidine (V-2) with bromine, thiocyanate, and sodium methoxide to obtain the compound of formula (IV-2); or

[0188] c2) React d3 - acetamidine (V - 2) first with sodium hypochlorite (NaOCl) and then with thiocyanate to obtain the compound of formula (IV - 2).

[0189] In this method, step a) forms a Pinner salt through the Pinner reaction. The "Pinner reaction" refers to the acid - catalyzed reaction of a nitrile (d3 - acetonitrile in this case) with an alcohol (ethanol in this case) to form an imino ether salt, also known as a Pinner salt. The Pinner salt itself is reactive and, for example, undergoes an additional nucleophilic addition with ammonia to form an amidine, as shown in step b).

[0190] The last step can be carried out via the "bromine route" (step c1) or via the "hypochlorite route" (step c2), both of which provide satisfactory results.

[0191] As described above, the final compound or the intermediate used in the method of the present invention can be in the form of salts, including acid - addition salts and base salts.

[0192] Step a) - Formation of Pinner salt

[0193] In step a), the Pinner salt of formula (VI - 2) is obtained by reacting d3 - acetonitrile with ethanol in the presence of HCl.

[0194] In one embodiment, in step a), the Pinner salt (VI - 2) is formed by bubbling HCl gas through a mixture containing ethanol (preferably anhydrous ethanol) and d3 - acetonitrile.

[0195] In one embodiment, the bubbling of HCl is carried out at a temperature below 15°C, preferably below 10°C.

[0196] In one embodiment, the HCl gas is bubbled through the mixture for a duration of at least 10 hours, preferably at least 8 hours, more preferably about 6 hours.

[0197] In one embodiment, after the bubbling of HCl is completed, the reaction mixture is stirred at room temperature, preferably in the temperature range of 20°C - 25°C.

[0198] In one embodiment, after the bubbling of HCl is completed, the reaction mixture is stirred for a duration of at least 10 hours, preferably 10 hours - 24 hours, more preferably 15 hours - 20 hours, even more preferably about 16.5 hours.

[0199] In one embodiment, after completion, the reaction mixture is treated with tert - butyl methyl ether (TBME), preferably in the temperature range of 0°C - 5°C, so as to separate the Pinner salt (VI - 2) in solid form.

[0200] Step b) - Formation of deuterated acetamidine

[0201] In step b), deuterated acetamidine (V-2) is formed by reacting Pinner's salt (VI-2) with ammonia (NH3).

[0202] In one embodiment, the solvent used in step b) is an alcohol, such as ethanol or methanol, preferably ethanol, more preferably absolute ethanol.

[0203] In one embodiment, step b) is carried out at a temperature below 10 °C, preferably in the temperature range of 0 °C - 5 °C.

[0204] In one embodiment, ammonia (NH3) is used as a gas and is directly absorbed in the reaction mixture. Preferably, 3 - 5 molar equivalents, preferably 4.1 molar equivalents of ammonia are used relative to Pinner's salt (VI-2).

[0205] In one embodiment, the reaction of step b) is carried out for a duration of at least 1 hour, preferably 1 - 6 hours, preferably 2 - 4 hours, more preferably about 3 hours.

[0206] In one embodiment, after completion, the reaction mixture is evaporated and treated with methylcyclohexane to recover d3-acetamidine (V-2) in solid form.

[0207] Advantageously, the isotopic purity of the obtained d3-acetamidine (V-2) is at least 90%, preferably at least 95%.

[0208] Step c1) - Cyclization to form the thiadiazole ring via the "bromine route"

[0209] The last step of obtaining the compound of formula (IV-2) can be carried out by the "bromine route" (step c1).

[0210] In step c1), the compound of formula (IV-2) is obtained by reacting d3-acetamidine (V-2) with bromine, thiocyanate and sodium methoxide.

[0211] In one embodiment, the thiocyanate is preferably used in the form of potassium thiocyanate.

[0212] In one embodiment, sodium methoxide can be obtained by dissolving sodium in methanol.

[0213] In one embodiment, the molar equivalent number of thiocyanate relative to d3-acetamidine (V-2) is 1 to 2.6, preferably 1.1 equivalents.

[0214] In one embodiment, the molar equivalent number of sodium methoxide (NaOMe) relative to d3-acetamidine (V-2) is 2 - 5, preferably 3 - 3.5, more preferably about 3.1 equivalents.

[0215] In one embodiment, the molar equivalent number of bromine (Br2) relative to d3 - acetamidine (V - 2) is 1 - 3, preferably 1 - 2, more preferably about 1.5 equivalents.

[0216] In one embodiment, the solvent used in step c1) is an alcohol, preferably methanol. Preferably, the solvent is dry, preferably dry methanol.

[0217] In one embodiment, step c1) is carried out at a temperature below 10 °C, preferably in the temperature range of 0 °C - 5 °C.

[0218] In one embodiment, the reaction in step c1) is carried out for a duration of at least 1 hour, preferably 1 - 6 hours, preferably 1 - 3 hours, more preferably about 2 hours.

[0219] In one embodiment, extraction is carried out with ethyl acetate and the product is obtained in solid form.

[0220] Advantageously, the isotopic purity of the obtained thiadiazole product (IV - 2) is at least 90%.

[0221] Step c2) - Cyclization to form the thiadiazole ring via the "hypochlorite route"

[0222] Alternatively, the last step of obtaining the compound of formula (IV - 2) can be carried out via the "hypochlorite route" (step c2).

[0223] In step c2), by first reacting d3 - acetamidine (V - 2) with sodium hypochlorite (NaOCl), an intermediate (VIII - 2) or its salt is formed:

[0224]

[0225] Then, the formed intermediate (VIII - 2) is reacted with a thiocyanate to obtain the compound of formula (IV - 2).

[0226] In one embodiment, sodium hypochlorite (NaOCl) is used in the form of an aqueous solution and can be obtained by dissolving NaOCl pentahydrate in water.

[0227] In one embodiment, the molar equivalent number of sodium hypochlorite (NaOCl) relative to d3 - acetamidine (V - 2) is 1 - 5, preferably 1.5 - 2.

[0228] In one embodiment, the solvent used for the reaction with sodium hypochlorite is water, preferably deionized water.

[0229] In one embodiment, the reaction with sodium hypochlorite is carried out at a temperature below 10 °C, preferably in the temperature range of 0 °C - 5 °C.

[0230] In one embodiment, the reaction with sodium hypochlorite is carried out for a duration of at least 30 minutes, preferably 1 - 6 hours, more preferably 1 - 3 hours, and even more preferably about 2 hours.

[0231] In one embodiment, the resulting intermediate (VIII - 2) is extracted with ethyl acetate.

[0232] In one embodiment, the thiocyanate is preferably used in the form of sodium thiocyanate.

[0233] In one embodiment, the molar equivalent number of the thiocyanate relative to the intermediate (VIII - 2) is 1 - 2, preferably 1 - 1.5, and more preferably about 1.1 equivalents.

[0234] In one embodiment, the solvent used for the reaction of the intermediate (VIII - 2) with the thiocyanate is an alcohol, preferably methanol. Preferably, the solvent is dry, preferably dry methanol.

[0235] In one embodiment, the reaction of the intermediate (VIII - 2) with the thiocyanate is carried out at a temperature below 10°C, preferably in the temperature range of 0°C - 5°C.

[0236] In one embodiment, the reaction of the intermediate (VIII - 2) with the thiocyanate is carried out for a duration of at least 30 minutes, preferably 1 - 6 hours, more preferably 1 - 3 hours, and even more preferably about 1.5 hours.

[0237] In one embodiment, extraction is carried out with ethyl acetate and the product is obtained in solid form.

[0238] Advantageously, the isotopic purity of the obtained thiadiazole product (IV - 2) is at least 95%.

[0239] d3 - hydroxyacetamidine route

[0240] The present invention also relates to another method for preparing 3 - (methyl - d3) - 1,2,4 - thiadiazol - 5 - amine (IV - 2) or a salt thereof:

[0241]

[0242] It comprises the following steps:

[0243] a) Reacting d3 - acetonitrile with hydroxylamine (H2N - OH) to form d3 - hydroxyacetamidine (IX - 2) or a salt thereof:

[0244]

[0245] b) Tosylating d3 - hydroxyacetamidine (IX - 2) to form an intermediate (X - 2) or a salt thereof:

[0246]

[0247] and

[0248] c) Reacting the intermediate (X-2) with a thiocyanate to obtain a compound of formula (IV-2).

[0249] Step a) - Formation of deuterated hydroxyacetamidine

[0250] In step a), reacting d3-acetonitrile with hydroxylamine (H2N-OH) to obtain d3-hydroxyacetamidine (IX-2).

[0251] In one embodiment, hydroxylamine can be used in the form of hydroxylamine hydrochloride or an aqueous solution of hydroxylamine.

[0252] In one embodiment, the molar equivalent number of hydroxylamine relative to d3-acetonitrile is 1-4, preferably 2-2.5, more preferably about 2.2 equivalents.

[0253] In one embodiment, the solvent used in step a) is an alcohol, preferably ethanol.

[0254] In one embodiment, step a) is carried out at the reflux temperature.

[0255] In one embodiment, the reaction of step a) is carried out for a duration of at least 1 hour, preferably 1-24 hours, preferably about 18 hours.

[0256] Advantageously, the isotopic purity is retained during step a).

[0257] Step b) - Tosylation of deuterated hydroxyacetamidine

[0258] In step b), a tosylation reaction is carried out on d3-hydroxyacetamidine (IX-2) to obtain the corresponding tosylated intermediate (X-2). The tosylation can be carried out in the presence of p-toluenesulfonyl chloride and a base.

[0259] In one embodiment, the base is selected from: triethylamine (TEA), sodium acetate (NaOAc), N,N-diisopropylethylamine (DIPEA), N-methylmorpholine (NMM), and mixtures thereof. In a preferred embodiment, the base is triethylamine.

[0260] In one embodiment, the molar equivalent number of p-toluenesulfonyl chloride relative to d3-hydroxyacetamidine (IX-2) is 0.8-1.5, preferably 0.9-1.1, more preferably about 0.9 equivalents.

[0261] In one embodiment, the molar equivalent number of the base (e.g., triethylamine) relative to d3-hydroxyacetamidine (IX-2) is 1-2, preferably 1-1.5, more preferably about 1.3 equivalents.

[0262] In one embodiment, the solvent used in step b) is tetrahydrofuran, preferably anhydrous tetrahydrofuran.

[0263] In one embodiment, the addition of p-toluenesulfonyl chloride is carried out at a temperature below 10 °C, preferably in the temperature range of 0 °C - 5 °C. After the addition of p-toluenesulfonyl chloride is completed, the reaction is preferably carried out at room temperature.

[0264] In one embodiment, the reaction in step b) is carried out for a duration of at least 30 minutes, preferably 30 minutes - 3 hours, more preferably about 1 hour.

[0265] In one embodiment, the product is extracted with ethyl acetate.

[0266] Advantageously, the isotopic purity is retained during step b).

[0267] Step c) - Cyclization to form the thiadiazole ring

[0268] In step c), d3-tosyloxyacetamidine (X-2) is reacted with a thiocyanate to obtain the compound of formula (IV-2).

[0269] In one embodiment, the thiocyanate is preferably used in the form of potassium thiocyanate.

[0270] In one embodiment, step c) can optionally be carried out in the presence of a base. When a base is used, it can be selected from: N,N-diisopropylethylamine (DIPEA), sodium acetate (NaOAc), triethylamine (TEA), N-methylmorpholine (NMM), and mixtures thereof.

[0271] In one embodiment, the molar equivalent number of the thiocyanate relative to d3-tosyloxyacetamidine (X-2) is 1-5, preferably 2 to 4, more preferably about 3 equivalents.

[0272] In one embodiment, the molar equivalent number of the base (e.g., DIPEA) relative to d3-tosyloxyacetamidine (X-2) is 0-2, preferably 1-2, more preferably 1-1.5, still more preferably about 1.1 equivalents.

[0273] In one embodiment, the solvent used in step c) is selected from: alcohols (e.g., methanol), dimethylformamide (DMF), acetonitrile, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and mixtures thereof. In one embodiment, the solvent used in step c) is methanol.

[0274] In one embodiment, step c) is performed at a temperature in the range of 20°C to 50°C, preferably at a temperature of about 40°C.

[0275] In one embodiment, the reaction of step c) is carried out for a period of at least 1 hour, preferably 2-20 hours.

[0276] Advantageously, the thiadiazole product (IV-2) is obtained with an isotopic purity of at least 95%.

[0277] Example

[0278] The invention is further illustrated by the following examples. The reaction schemes described in the Examples section illustrate different possible processes by way of example.

[0279] Materials and methods

[0280] All reported temperatures are in degrees Celsius (°C); unless otherwise stated, all reactions were performed at room temperature (rt).

[0281] Analytical methods:

[0282] Analytical thin layer chromatography (TLC) was used to monitor the reaction, establish flash chromatography conditions, and verify the purity of intermediates or final products. The TLC plate used was Merck TLC aluminum sheet silica gel 60F 254 The TLC plate was displayed with KMnO4 developer at room temperature by irradiation with UV light (wavelength = 254 nm) or heating to 160° C. The KMnO4 TLC developer was prepared by dissolving 3 g potassium permanganate and 20 g sodium carbonate in 300 mL distilled water.

[0283] Recorded on a Bruker Avance 500MHz 1 H and 13 C NMR spectrum. Chemical shifts are expressed in parts per million (ppm, delta units). Coupling constants are expressed in Hertz (Hz). The splitting pattern reflects the apparent multiplicity and is expressed as s (singlet), d (doublet), t (triplet), q (quartet), h (sextet), m (multiplet), or br (broad).

[0284] GC determination was carried out as follows: (Condition A) On a Varian 3900 with a flame ionization detector (FID) at 260 °C. The column used was RTX-1301, 30 m × 0.32 mm × 0.5 μm. The injector temperature was 200 °C, the split ratio was 50, the injection volume was 1 μL, and the following temperature program was adopted: The oven temperature was set at 60 °C for 4 minutes, linearly increased to 260 °C at a rate of 20 °C / minute, and held at 260 °C for 10 minutes; or (Condition B) On a Shimadzu GC-2010 with a flame ionization detector (FID) at 260 °C. The injector temperature was 200 °C, the split ratio was 50, the injection volume was 1 μL. The column used was Rxi-17Sil MS, 30 m × 0.32 mm × 0.25 μm, and the following temperature program was adopted: The oven temperature was set at 60 °C for 5 minutes, linearly increased to 300 °C at a rate of 20 °C / minute, and held at 300 °C for 8 minutes; or (Condition C) On a Varian 3900 with a flame ionization detector (FID) at 270 °C. The column used was DB-624, 60 m × 0.32 mm × 3 μm. The injector temperature was 200 °C, the split ratio was 50, the injection volume was 1 μL, and the following temperature program was adopted: The oven temperature was set at 80 °C for 4 minutes, linearly increased to 260 °C at a rate of 20 °C / minute, and held at 260 °C for 11 minutes.

[0285] GC-MS analysis was carried out on a Shimadzu GCMS-QP2010 with an electron ionization detector (EI) at 250 °C. The column used was Phenomenex XB-5MS, 30 m × 0.25 mm × 0.25 μm. The column flow rate was 1.50 mL / minute. The injector temperature was 250 °C, the split ratio was 50. The injection volume was 1 μL. The following temperature program was adopted: Held at 40 °C for 5 minutes initially, then heated to 250 °C at a rate of 20 °C / minute, and then held at 250 °C for 5 minutes.

[0286] The HPLC spectrum was obtained on a Thermo Science Ultimate 3000 HPLC device equipped with a UV monitor.

[0287] Condition A: The column used was Phenomenex-Kinetex EVO C18 50 × 4.6 mm × 2.6 μL. The eluent was a mixture of solution A (H2O solution of 10 mM HCO2NH4) and solution B (MeCN). A gradient was applied at a flow rate of 1.0 mL / minute: The initial condition of 1% solution B was maintained for 3 minutes, linearly increased to 90% solution B within 7 minutes, held at 90% for 2 minutes, returned to the initial condition within 1.0 minute and maintained for 5 minutes. -1 The flow rate was applied with a gradient: The initial condition of 1% solution B was maintained for 3 minutes, linearly increased to 90% solution B within 7 minutes, held at 90% for 2 minutes, returned to the initial condition within 1.0 minute and maintained for 5 minutes.

[0288] Condition B: The column used was Purospher Star RP18e 55 mm × 4.6 mm × 3.0 μm. The eluent was a mixture of Solution A (H2O solution of 20 mM HCO2NH4) and Solution B (MeCN). At a flow rate of 1.0 mL per minute -1 a gradient was applied: The initial condition of 2% Solution B was maintained for 1 minute, linearly increased to 90% Solution B in 8 minutes, maintained at 90% for 2 minutes, returned to the initial condition in 1.0 minute and maintained for 3 minutes.

[0289] The HPLC-MS spectra were obtained on a Shimadzu LCMS-2020 using a 210 nm UV monitor and electrospray ionization (ESI). In the selected ion monitoring mode, the isotopic purity was determined by comparing the peak areas of the respective isotopes.

[0290] Condition A: The column used was SeQuant ZIC-HILIC 150 × 4.6 mm × 5 μm. The eluent was a mixture of 25% Solution A (H2O solution of 20 mM NH4Ac) and 75% Solution B (MeCN), with a flow rate of 1 mL per minute -1 .

[0291] Condition B: The column used was YMC-Triart C18 100 × 3.0 mm × 3 μm. The eluent was a mixture of Solution A (H2O solution of 0.1% HCO2H) and Solution B (MeCN). At a flow rate of 0.5 mL per minute -1 a gradient was applied: The initial condition of 0% Solution B was maintained for 12 minutes, linearly increased to 90% Solution B in 5 minutes, maintained at 90% for 6 minutes, returned to the initial condition in 0.1 minute and maintained for 7 minutes.

[0292] Condition C: The column used was Phenomenex-Kinetex EVO C18 100 × 2.1 mm × 2.6 μm. The eluent was a mixture of Solution A (H2O solution of 0.1% HCO2H) and Solution B (MeCN). At a flow rate of 0.5 mL per minute -1 a gradient was applied: The initial condition of 2% Solution B was maintained for 1 minute, linearly increased to 90% Solution B in 9 minutes, maintained at 90% for 3 minutes, returned to the initial condition in 0.1 minute and maintained for 5 minutes.

[0293] Condition D: The column used was YMC-Triart C18 100 × 3.0 mm × 3 μm. The eluent was a mixture of Solution A (H2O solution of 0.1% HCO2H) and Solution B (MeCN). At a flow rate of 0.5 mL per minute -1Apply the gradient at a flow rate of: Maintain the initial condition of 90% solution B for 23 minutes, linearly decrease to 1% solution B within 0.1 minute and maintain for 7 minutes.

[0294] Alternatively, the HPLC-MS spectra are obtained on an Agilent LCMS with electrospray ionization (ESI). The Agilent device includes an autosampler 1100, a binary pump 1100, an ultraviolet multi-wavelength monitor 1100, and a 6100 single quadrupole mass spectrometer. Condition D: The column used is Sunfire 3.5 μm, C18, 3.0 × 50 mm. The eluent is a mixture of solution A (H2O solution with 0.1% TFA) and solution B (MeCN solution with 0.1% TFA). Apply the gradient (for analyzing the final compound and intermediates) at a flow rate of 1.3 mL / min: Maintain the initial condition of 5% solution B for 0.2 minute, linearly increase to 95% solution B within 6 minutes, maintain at 95% for 1.75 minutes, return to the initial condition within 0.25 minute and maintain for 2.0 minutes. -1 Apply the gradient (for analyzing the final compound and intermediates) at a flow rate of: Maintain the initial condition of 5% solution B for 0.2 minute, linearly increase to 95% solution B within 6 minutes, maintain at 95% for 1.75 minutes, return to the initial condition within 0.25 minute and maintain for 2.0 minutes.

[0295] The chloride ion content is obtained using a Mettler Toledo DL50 titrator or an equivalent titrator, a DM-141 or equivalent electrode, an analytical balance, and standard laboratory glassware. The chemical reagents used are: Titrant: 0.1 mol / L silver nitrate (Preparation of 0.1 mol / L silver nitrate: Weigh approximately 17 g of silver nitrate (AgNO3), place it in a 1000 mL volumetric flask, dissolve and dilute to the mark with deionized water). Determine the factor of the solution. Preparation of the sample: Weigh 30 - 500 mg of the solid sample on an analytical balance and place it in a container as a function of the halide content. Dilute to 60 mL with a solvent (deionized water, 2-propanol, etc.). Result evaluation:

[0296]

[0297] Where, Q1: Titrant at the equivalence point (mmol), M x : Molar mass (mg / mmol), m: Sample weight (mg), V: Sample volume (μL)

[0298] Halide Chloride <![CDATA[M x (mg / mmol)]]> 35.45

[0299] The determination based on the chloride ion content is calculated by chloride determination:

[0300]

[0301] Where, 97.56 g / mol is the molecular weight of compound (V-2), 53.45 g / mol is the molecular weight of NH4Cl, m 产物 is the mass of the separated HCl salt, w Cl- The weight percentage of chloride ions measured by titration.

[0302] Reactant

[0303] Unless otherwise specified, solvents, reagents, and starting materials are purchased and used as obtained from commercial suppliers.

[0304] The following abbreviations are used:

[0305] AMTD: 5 - amino - 3 - methyl - 1,2,4 - thiadiazole,

[0306] cca.: approximately,

[0307] DCM: dichloromethane,

[0308] eq: equivalent,

[0309] EtOAc: ethyl acetate,

[0310] EtOH: ethanol,

[0311] g: gram,

[0312] GC: gas chromatography,

[0313] Hex: n - hexane,

[0314] HPLC: high - performance liquid chromatography,

[0315] IPA: isopropanol,

[0316] L: liter,

[0317] LCMS: liquid chromatography - mass spectrometry,

[0318] MECN: acetonitrile,

[0319] MeOH: methanol,

[0320] mL: milliliter,

[0321] mol: mole,

[0322] mmol: millimole,

[0323] min: minute,

[0324] MS: mass spectrometry,

[0325] NMM: N - methylmorpholine

[0326] MW: molecular weight,

[0327] NMR: nuclear magnetic resonance,

[0328] rt: room temperature,

[0329] TBME: tert-butyl methyl ether,

[0330] TEA: triethylamine,

[0331] THF: tetrahydrofuran,

[0332] TLC: thin layer chromatography,

[0333] Ts: tosyl (i.e., p-toluenesulfonyl)

[0334] vol.: volume.

[0335] All compounds disclosed in this application were named using ChemDraw Ultra purchased from CambridgeSoft (Cambridge, Massachusetts, USA). Named.

[0336] Example 1A: Synthesis of deuterated d3-AMTD (IV-2) via the acetamidine route

[0337]

[0338] The d3-acetamidine (V-2) was obtained by the Pinner reaction through the Pinner salt (VI-2), and then cyclized through the "bromine route" (step c1) or the "hypochlorite route" (step c2) to form the thiadiazole ring of the compound (IV-2).

[0339] Step a: Formation of the Pinner salt (VI-2)

[0340] At 20 - 25 °C, in a 750 mL three-necked glass flask equipped with two inlets, a thermometer, and a magnetic stir bar, 74 mL of anhydrous diol and 51.2 g (1.161 mol, 1.0 eq) of d3-acetonitrile (VII-2) were charged, and then cooled to 0 - 5 °C (cooled by an ice-salt mixture). Keeping the temperature below 10 °C, HCl gas was bubbled through the mixture for 6 hours. The reaction mixture was heated to 20 - 25 °C and stirred for 16.5 hours (the mixture became a viscous white suspension that was difficult to stir). 500 mL of TBME was added to the mixture, and then the mixture became an easily stirred white suspension. Stirred at 0 - 5 °C for 1 hour, then filtered and washed with 2 × 50 mL of cold TBME. The filtered solid was dried under vacuum at 40 °C to obtain 104.3 g of a white solid Pinner salt (VI-2), which was used in the next step without further purification.

[0341] Step b: Formation of d3-acetamidine (V-2)

[0342] At 20 - 25 °C, 835 mL (658.8 g) of anhydrous ethanol was charged into a 2 L three-necked glass flask equipped with two inlets, a thermometer, and a magnetic stir bar. It was then cooled to 0 - 5 °C (cooled by an ice-salt mixture). At this temperature, 57.3 g (3.37 mol, 4.1 eq) of NH₃ gas was absorbed. Then, at 0 - 5 °C, 104.3 g (823.8 mmol, 1.0 eq) of Pinner salt (VI-2) was added and stirred for 3 hours. The reaction was monitored by HPLC. The reaction mixture was evaporated to dryness on a rotary evaporator at 30 °C. 200 mL of methylcyclohexane was added to the residue and stirred for 15 minutes at 0 - 5 °C (cooled by an ice bath). The white precipitate was filtered, washed with 25 mL of cold methylcyclohexane, and dried under vacuum at 45 °C. 77.1 g (790.3 mmol) of white solid d3-acetamidine hydrochloride (V-2) was obtained. Corrected yield: 89.3%. 1 ¹H-NMR (DMSO-d₆): δ 9.20 (br, 1H), 8.75 (br, 2H), 7.51 (br, 1H). HPLC-MS (Condition A) Isotopic purity: 95.8%. Chloride content: 38.46 w / w%. Determination based on chloride content: 93.1 w / w%.

[0343] Step c1: Synthesis of d3-AMTD (IV-2) via the bromine route

[0344] At 20 - 25 °C, 5.8 g (59.45 mmol, 1.0 eq) of d3-acetamidine hydrochloride (V-2) (isotopic purity: 96.5%, determination based on chloride content: 64.7 w / w%), 6.35 g (65.4 mmol, 1.1 eq) of KSCN, and 11 mL of dry MeOH were charged into a 250 mL four-necked glass flask equipped with two dropping funnels, a thermometer, and a magnetic stir bar (using Molecular sieve drying). The mixture (suspension) was cooled to below 10 °C with stirring. While maintaining the temperature at 0 - 5 °C, a solution of 42.6 mL (184.3 mmol, 3.1 eq) of 25 w / w% NaOMe in MeOH (54.03 g / mol) and 4.6 mL (14.26 g, 89.16 mol, 1.5 eq) of Br₂ (pure substance, MW: 159.81 g / mol, d: 3.119 g / mL) solution were added to the mixture simultaneously within 25 minutes. After addition, the mixture turned grayish-violet and then a white suspension formed. After addition, the mixture was stirred at 0 - 10 °C for 2 hours and monitored by TLC (eluent CH₂Cl₂:MeOH = 5:1). 20 mL of water was gradually added to the mixture while keeping the temperature below 25 °C. The mixture was stirred at ambient temperature for 15 minutes and then 40 mL of MeOH was distilled off under reduced pressure (80 - 120 mbar, 40 °C). The aqueous residue (about 40 mL) formed a suspension, which was filtered. The filter cake was washed with 3 × 40 mL of EtOAc to obtain 6.95 g of a white solid by-product. Each portion of the filtrate was used to extract the first aqueous filtrate. Extraction of the aqueous filtrate: 3 × 40 mL EtOAc (three washes of the filter cake), and then extraction with 3 × 40 mL of EtOAc. The combined organic phase was washed with 50 mL of saturated NaCl solution. The extract was concentrated in vacuo at 40 °C (100 - 120 mbar). The resulting slurry (30 mL) was heated and refluxed for 30 minutes and then cooled to 0 - 5 °C. After standing overnight at 0 - 5 °C, the suspension was filtered and washed with 2 × 5 mL of cold EtOAc. The resulting product (IV-2) was an off-white solid, 1.62 g. Corrected yield: 30%. Isotopic purity: 93.4% by HPLC-MS (Condition B), 1 93% by ¹H-NMR. Titrimetric determination: 85 w / w%. 1 ¹H-NMR (DMSO-d₆): δ 7.77 (br, 2H), 2.18 (s, 0.07H - related to the CD₂H signal).

[0345] Step c2: Synthesis of d³-AMTD (IV-2) via the hypochlorite route

[0346] At 20 - 25 °C, 15.15 g (132.5 mmol, 1.0 eq) of d3 - acetamidine hydrochloride (V - 2) (isotopic purity: 96.7%, determination based on chloride content: 85.7 w / w%) and 75 mL (5 volumes) of deionized water were charged into a 500 mL four - necked glass flask equipped with two dropping funnels, a thermometer and a magnetic stir bar. Then it was cooled to 0 - 5 °C. Maintaining the temperature at 0 - 5 °C, 26.95 g (164 mmol, 1.24 eq) of NaOCl pentahydrate dissolved in 160 mL (10.5 volumes) of water was added to the reaction mixture over 40 minutes. The reaction was monitored by TLC (CH2Cl2:MeOH = 5:1). After stirring for 1 hour, another portion of the reagent was added: maintaining the temperature at 0 - 5 °C, 13.48 g (82 mmol, 0.62 eq) of NaOCl pentahydrate dissolved in 80 mL (5.25 volumes) of water was added. The mixture was stirred at 0 - 5 °C for 1 hour. Then, 85 g of NaCl was added to the aqueous mixture, which was then extracted with 3 × 200 mL of EtOAc, dried over Na2SO4, filtered and evaporated in vacuo (40 °C, 10 mbar). Intermediate (VIII - 2): 10.0 red oil.

[0347] Then, 10.0 g of intermediate (VIII - 2) and 100 mL of dry MeOH (dried with molecular sieve) were charged into a 500 mL four - necked glass flask equipped with two dropping funnels, a thermometer and a magnetic stir bar, and then cooled to 0 - 5 °C. 11.75 g (145.5 mmol, 1.1 eq) of NASCN was carefully added to the solution over 20 minutes. The resulting suspension was stirred for 1.5 hours and then quenched with 60 mL of water. Then, the reaction mixture was filtered, and the MeOH was evaporated at 40 °C and 100 - 200 mbar in vacuo. The residue (80 mL) was filtered, and the precipitate was washed with 3 × 100 mL of EtOAc. The mother liquor from each wash was extracted, and then with 100 mL of EtOAc. The organic phases (4 × 100 mL) were combined and concentrated to 27 mL. The residue was refluxed for 15 minutes, then cooled to 0 - 5 °C, allowed to stand for 1 hour, and filtered. The filtered material was the product. Crude product: 26% (4.1 g) pale yellow solid. Corrected yield: 12% (1.93 g). HPLC (condition B): 47 w / w%. HPLC - MS (condition B) isotopic purity: 96.8%. 1 1H - NMR (DMSO - d6): δ 7.77 (br, 2H), 3.46 (br, 1H), 2.18 (s, 0.03H - related to CD2H signal).

[0348] Example 1B: Synthesis of deuterated d3-AMTD (IV-2) via the hydroxyacetamidine route

[0349]

[0350] d3-Hydroxyacetamidine (IX-2) was obtained from deuterated acetonitrile (VII-2). Subsequently, the corresponding tosyl intermediate (X-2) was cyclized in the presence of thiocyanate to form the thiadiazole ring of compound (IV-2).

[0351] Step a: Formation of d3-Hydroxyacetamidine (IX-2)

[0352] At 20 - 25 °C, in a 100 mL glass container equipped with a reflux condenser, thermometer, and magnetic stir bar, 5.5 mL (4.65 g, 105.4 mmol, 1.0 eq) of d3-acetonitrile (d: 0.844 g / mL), 33 mL of EtOH, and 25.1 mL (27.87 g, 422.3 mmol, 4.0 eq) of aqueous hydroxylamine solution (50 w / w%, MW: 33 g / mol, d: 1.11 g / mL) were charged. The mixture was heated to the reflux temperature and stirred at the reflux temperature for 5 hours. The solvent was evaporated from the reaction mixture under vacuum at 40 °C. The resulting product (IX-2) was a white solid. Yield: 84% (6.84 g). HPLC-MS (Condition C) Isotopic purity: 98.5%. 1 1H-NMR (DMSO-d6): δ 8.67 (br, 1H), 5.33 (br, 2H). 13 13C-NMR (DMSO-d6): δ 149.9, 16.3.

[0353] Step b: Tosylation of d3-Hydroxyacetamidine to form compound (X-2)

[0354] At 20 - 25 °C, in a 500 mL glass container equipped with a thermometer and a magnetic stir bar, charged with: 6.3 g (81.74 mmol, 1.0 eq) of d3-hydroxyacetamidine (IX-2) and 170 mL (151 g) of dry THF (dried over molecular sieves). Stirred for 30 minutes at ambient temperature, then added 14.8 mL (10.75 g, 106.3 mmol, 1.3 eq) of TEA at 20 - 25 °C. After stirring for 30 minutes, 45 mL of dry THF was added, but there was still some undissolved material remaining in the mixture. The mixture was cooled to 0 - 5 °C using an ice-salt bath, then 14.02 g (73.57 mmol, 0.9 eq) of p-toluenesulfonyl chloride was added portionwise to the mixture over 15 minutes. After addition, the cooling bath was removed, allowing the mixture to warm to 20 - 25 °C, and stirred at 20 - 25 °C for one hour. The mixture became a white suspension. TLC monitoring: CH2Cl2:MeOH = 95:5. After completion (p-toluenesulfonyl chloride completely consumed), the precipitate (9.9 g white solid) was filtered and washed with 2 x 40 mL of THF. The filtrate was evaporated to dryness under vacuum at 40 °C. 130 mL (118 g) of EtOAc was added to the residue, and the organic phase was washed with 1 x 65 mL of water and 1 x 65 mL of saturated NaCl solution. After the water wash, the organic layer was dried over Na2SO4, filtered, and washed with 2 x 20 mL of EtOAc. The solvent was evaporated under vacuum at 40 °C to give a colorless oil which solidified on standing. Yield: 84% (15.9 g, 68.88 mmol). HPLC-MS (Condition C) Isotopic purity was retained (98.5%).

[0355] Step c: Synthesis of d3-AMTD (IV-2)

[0356] At 20 - 25 °C, in a 100 mL glass container equipped with a thermometer and a magnetic stir bar, charge: 6.39 g (65.76 mmol, 3.0 eq) KSCN and 25 mL (19.8 g) of dry MeOH (dried over molecular sieves). While stirring, add 5.06 g (21.92 mmol, 1.0 eq) of d3-N-tosyloxyacetamidine (X-2) as a solid to the mixture. After stirring for 5 minutes at 20 - 25 °C, add 4.2 mL (3.12 g, 24.11 mmol, 1.1 eq) of DIPEA. The reaction mixture is stirred overnight at 20 - 25 °C and gradually turns into a white suspension. TLC monitoring: CH2Cl2:MeOH = 95:5, visualized with KMnO4. After 18 hours, the reaction is not complete, then it is heated to 40 °C and stirred for 2 hours. Thereafter, the precipitate (white solid) is filtered and washed with 2 x 20 mL of MeOH. 30 mL of water is added to the filtrate, and then MeOH is evaporated under vacuum (100 - 150 mbar) at 40 °C. The aqueous residue is extracted with 7 x 50 mL of EtOAc, the combined organic phases are dried over Na2SO4 and then evaporated. The crude product is 4.2 g of an orange oil. After treatment with 10 mL of CH2Cl2, 700 mg of a viscous precipitate is filtered and treated with 5 mL of iPrOAc, from which 173 mg of a pale yellow solid is isolated (crude yield: 7%). HPLC determination: 63 w / w% (condition B). HPLC-MS (condition B) isotopic purity: 73%. The mother liquors from the CH2Cl2 and iPrOAc treatments are combined and evaporated under vacuum at 40 °C to give 2.55 g of a viscous orange solid. HPLC determination: 10 w / w% (condition B). The corrected yield for the entire reaction: 14.5% (determined 0.109 g + 0.255 g).

[0357] Example 2: Synthesis of deuterated 3-(methyl-d3)-1,2,4-thiadiazole-5-carbohydrazide (I-2)

[0358]

[0359] In all steps, the isotopic purity is retained.

[0360] Step 1: Sandmeyer bromination to form (III-2-a)

[0361] At 20 - 25 °C, into a 25 mL glass container equipped with an outlet leading to a gas trap filled with 10 w / w% NaOH solution, a dropping funnel, a thermometer, and a magnetic stir bar, 2.7 mL (4.61 g of solution, containing 2.85 g of HBr, 35.2 mmol, 3.0 eq) of 62 w / w% HBr solution (d: 1.702 g / mL), 2.1 mL of water, and 1.39 g (11.76 mmol, 1 eq) of compound (IV - 2) (isotopic purity: 93.4%, titrimetric determination: 85%) were charged. The mixture was heated to 40 °C. Then, 1.22 g (17.64 mmol, 1.5 eq) of NaNO2 dissolved in 2 mL of water was added through the dropping funnel at a rate such that the temperature was maintained at 40 - 45 °C (within 5 minutes). During the addition, strong bubbling of brown gas could be observed in the absorber, and an oil phase separated at the bottom of the flask. After the addition, the mixture was stirred for 1 hour and monitored by TLC (Hex:EtOAc = 1:1) and HPLC. The reaction mixture was cooled to 20 - 25 °C. The two - phase system was extracted with 2 × 10 mL of dichloromethane. The combined organic phase (dark brown) was washed with 5 mL of 5 w / w% NaOH solution. The phases were separated. The organic phase was evaporated under vacuum (300 - 100 mbar) at 40 °C to obtain 1.51 g of a yellow oil (III - 2 - a). Yield: 78% (1.51 g). GC (condition A): 94.4%. GC - MS isotopic purity: 93.1%. The isotopic purity did not change.

[0362] Step 2: Ethoxycarbonylation to form (II - 2 - b)

[0363] At 20 - 25 °C, under an inert atmosphere, a 50 mL autoclave was charged with 1.2 g (6.60 mmol, 1.0 eq) of crude compound (III - 2 - a) (isotopic purity: 93.1%, GC: 94.9%), 12 mL (10 volumes) of anhydrous ethanol, and 706 mg (8.58 mmol, 1.3 eq) of NaOAc. Subsequently, nitrogen was bubbled through the mixture, and then 19 mg (0.033 mmol, 0.005 mol eq) of Xantphos and 7.5 mg (0.033 mmol, 0.005 mol eq) of Pd(OAc)₂ were added. The flask was sealed, purged with nitrogen four times, and then purged with CO four times, and then charged with CO to 4 bar. The mixture was heated to 65 °C with vigorous stirring. The reaction was maintained at 65 °C and the pressure was maintained at 4 bar until the reaction was complete (∼45 h). The reaction was monitored by GC. After removing CO and purging with nitrogen, the solvent was removed under vacuum at 40 °C, and then 15 mL of methylcyclohexane was added. The precipitate was filtered and washed with 5 mL of methylcyclohexane. The solvent was removed on a rotary evaporator at 40 °C (10 mbar) under vacuum. After this treatment, the product (II - 2 - b) was isolated as a green oil. It was used in the next step without further purification. Yield: 52% (706 mg). GC (Condition A): 81%. LCMS (Condition C) Isotopic purity: 93.4%. 1 ¹H - NMR (DMSO - d₆): δ 4.43 (q, J = 7.1 Hz, 2H), 1.34 (t, J = 7.1 Hz, 3H). 13 ¹³C - NMR (DMSO - d₆): 179.0, 175.9 (d), 158.4, 63.3, 18.2 (h), 14.3. The isotopic purity did not decrease.

[0364] Step 3: Hydrazinolysis to form (I - 2)

[0365] At 20 - 25 °C, in a 10 mL glass container equipped with a dropping funnel, a thermometer, and a magnetic stir bar, 4 mL of IPA and 177 μL (181 mg containing 100 mg, 3.11 mmol, 1.14 eq) of hydrazine hydrate (55 w / w% aqueous solution, d: 1.027 g / mL) were added. The reaction mixture was cooled to 0 °C. A solution of 595 mg (2.73 mmol, 1.0 eq) of compound (II - 2 - b) (isotopic purity: 93.4%, GC: 81%) in 2 mL of IPA was added to the mixture through the dropping funnel at a rate such that the temperature was maintained at 0 - 5 °C. After addition, the mixture was stirred at 0 - 5 °C for 1 hour and then overnight at room temperature. The reaction was monitored by HPLC. After completion, the suspension was cooled to 0 - 5 °C, then filtered, and the filter cake was washed with 2 × 1 mL of cold IPA and dried under vacuum at 35 °C. After this treatment, the product (I - 2) was isolated as a pale yellow solid. Yield: 72% (321 mg). HPLC - MS (Condition D): 96.4%. HPLC - MS (Condition C) isotopic purity: 93.4%. 1 1H - NMR (DMSO - d6): δ 10.50 (br, 1H), 4.79 (br, 2H). 13 13C - NMR (DMSO - d6): δ 183.4, 175.0 (d), 157.8 (d), 18.0 (h). The isotopic purity did not decrease.

[0366] Example 3: Synthesis of 3-methyl-1,2,4-thiadiazole-5-carbohydrazide (I-1)

[0367]

[0368] Step 1: Sandmeyer bromination to form (III - 1 - a)

[0369] Using 100 kg of 5 - amino - 3 - methyl - 1,2,4 - thiadiazole (AMTD), the Sandmeyer bromination reaction was successfully carried out with a yield of 82%.

[0370] 439.5 kg (295 L) of 48% HBr solution and 100.0 kg of AMTD were added to 54 kg (L) of water in a reactor. The solution was heated to a maximum of 40 °C and stirred until all starting materials were dissolved - checked by sampling. If the starting materials were not completely dissolved, stirring at 40 °C for 2 hours was sufficient. 89.7 kg of sodium nitrite was dissolved in 150 kg (L) of water in another apparatus, and then the solution was charged into a container. The sodium nitrite solution was charged into the reactor in batches, and this process took about 6 hours, maintaining the temperature at 40 - 45 °C. Samples were taken one hour after the addition was completed. Endpoint criterion: starting materials < 1.0%. If the starting materials > 1.0%, additional sodium nitrite solution (10 - 20%) needed to be added to the reaction mixture. If the reaction mixture reached the endpoint criterion, it was cooled to 20 - 25 °C, and 399.0 kg (300 L) of DCM was added. Stir for 10 minutes, and after standing for 10 minutes, the lower organic phase was charged into a container. The aqueous phase was extracted with 133.0 kg (100 L) of DCM in the reactor. 5% sodium hydroxide solution was added to adjust the pH of the combined organic phase to 10 - 11. If the pH exceeded 11, a large amount of water might form. The mixture was stirred for 20 minutes, and after standing for 30 minutes, the organic phase was separated into a drying apparatus and concentrated under vacuum (about -0.9 bar) at a maximum of 30 °C. Samples were taken, and the endpoint criterion for concentration was: maximum DCM content of 5.0%. After the distillation was completed, it was necessary to stir under vacuum for 4 - 6 hours to achieve a maximum DCM content of 5.0%. A DCM content of 2.0% was suitable for the next step. If the material met the endpoint criterion, it was filled into PE-lined barrels. 126.8 kg of compound (III-1-a) was obtained, yield: 81.6%, GC purity (condition C): 97.2%.

[0371] Step 2: Ethoxycarbonylation to form (II-1-b)

[0372] Using 87.5 kg of compound (III-1-a), the ethoxycarbonylation reaction was successfully carried out with a yield of 87%.

[0373] 87.5 kg of compound (III-1-a) was added to 44 kg of absolute ethanol in a PE-lined bucket and stirred until a clear solution was obtained. 383 kg (484 L) of absolute ethanol was charged into a dry, pressure-resistant apparatus. After inerting with N2, a catalyst solution prepared from 0.672 kg of palladium(II) acetate and 1.68 kg of Xantphos in 14.5 kg of glacial acetic acid was added. 52.5 kg of anhydrous sodium acetate was added to the mixture. The system was purged again with N2 and the reaction mixture was heated to 63 - 67 °C. CO was added to the apparatus to 4 - 4.5 bar and then the solution of (III-1-a) was added within 2 - 3 hours. After addition, 16 kg (20 L) of ethanol was used for rinsing. Samples were taken every 12 hours, end point criterion: maximum 1.0% of starting material (III-1-a). When the reaction reached the end point criterion, the pressure was released through a CATOX catalyst and the apparatus was purged 6 times with N2. The mixture was filtered through a production filter into a dry container - washed with 80 kg (100 L) of absolute ethanol. The filtrate was concentrated under reduced pressure at a maximum of 50 °C. The concentrate was diluted with 120 kg of methylcyclohexane and stirred for 30 - 40 minutes. The solution was filtered through a production filter and washed with 40 kg of methylcyclohexane. The solvent was removed under reduced pressure at a maximum of 50 °C and the product was separated by fractional vacuum distillation. 73.5 kg of compound (II-1-b) was obtained, yield: 87.0%, GC purity (condition A): 96.9%.

[0374] Step 3: Hydrazinolysis to form (I-1)

[0375] Using 50 kg of compound (II-1-b), the hydrazinolysis reaction was successfully carried out with a yield of 91%.

[0376] 50.0 kg of compound (II-1-b) was dissolved in 212.2 kg (270 L) of isopropanol. 26.7 kg of hydrazine hydrate (55% aqueous solution) was added to 340 kg (432 L) of isopropanol and the mixture was cooled to 0 °C. The solution of (II-1-b) was added to the cold hydrazine hydrate solution, which took 1 - 2 hours while maintaining the temperature at 0 - 5 °C. After addition, the mixture was stirred for another 1 hour at 0 - 5 °C. After stirring for 1 hour, the content of (II-1-b) was checked. If the content of (II-1-b) > 1.0%, the mixture was heated to 20 - 25 °C and samples were taken to monitor the reaction progress. The expected reaction time was 20 hours until the end point criterion was reached: (II-1-b) < 1.0%. If the reaction reached the end point criterion, the suspension was cooled to 0 - 5 °C and filtered. The filtered material was washed with 31.8 kg (40 L) of 0 - 5 °C isopropanol. 37.5 kg of compound (I-1) was obtained, yield: 91%, HPLC purity (condition A): 99.9%.

[0377] Example 4: Obtaining (III-1-a) by Sandmeyer bromination using tert-butyl nitrite

[0378]

[0379] Under N2, CuBr2 (14 g, 62.68 mmol, 1.03 eq), anhydrous MeCN (110 mL), and tert-butyl nitrite (11 mL, 92.59 mmol, 1.5 eq) were charged into a Schlenk flask, and then the resulting dark green mixture was cooled to 0 - 5 °C (ice bath). AMTD (7 g, 60.78 mmol, 1.0 eq) was added to the mixture over 1 minute. The resulting mixture was stirred at 0 - 5 °C for 30 minutes, then warmed to room temperature and stirred for 2 hours. The mixture was diluted with a 1:1 mixture of 25% aqueous ammonia (50 mL) and 10% Na2CO3 (50 mL), and TBME (100 mL) was added. The phases were separated, and the aqueous layer was extracted with TBME (2 × 50 mL). The combined organic phases were washed with brine (3 × 50 mL), dried over MgSO4, filtered, and concentrated to dryness under reduced pressure (1 mbar, 30 °C) to obtain compound (III-1-a) (7.16 g, 39.99 mmol, 66% yield, HPLC-MS purity > 98% (condition D)) as a yellow solid suspended in an orange oil. 1 1H-NMR (CDCl3): δ 2.69 (s, 3H).

[0380] Example 5: Obtaining (III-1-b) by Sandmeyer iodination using tert-butyl nitrite

[0381]

[0382] In a 1000 mL three-necked glass flask equipped with an inlet, a dropping funnel, and a thermometer, 55.0 g (217.1 mmol, 1.0 eq) of iodine, 250 mL of dry CH3CN, and 102.7 mL (89.54 g, 868.4 mmol, 4.0 eq) of tBuONO were charged. The reaction mixture was stirred for 10 minutes. At room temperature, 25.0 g (217.1 mmol, 1.0 eq) of AMTD was added in portions as a solid. After a few minutes, the reaction mixture (brown) was rapidly heated to reflux, and strong gas evolution was observed. The reaction was cooled back to room temperature. According to TLC, this time (about 40 minutes) was sufficient to complete the reaction. 450 mL of a 20 w / w% aqueous Na2SO3 solution was added to quench the excess iodine. The mixture turned yellow, but turned brown again after standing. Further addition of an aqueous Na2SO3 (50 mL) solution made the mixture turn yellow, but it turned brown again. The phases were separated, and the aqueous phase was extracted with TBME (4 × 150 mL). The combined organic phases were washed with 200 mL of brine, dried over Na2SO4, filtered, and evaporated under vacuum at 30 °C. The product (III-1-b) was a brown solid with a crude yield of 72.2% (corrected yield: 65.7%) (35.4 g, HPLC purity (condition A): 92.3 area%, qNMR: 91 w / w%). The product was purified by recrystallization with refluxing 2-propanol (2 mL / crude g), and the yield was 63% (23.9 g, HPLC purity (condition A): 99.3 area%, qNMR: 99 w / w%). 1 1H-NMR (CDCl3): δ 2.73 (s, 3H). 13 13C-NMR (CDCl3): δ 175.9, 124.8, 18.9.

[0383] The iodinated intermediate (III-1-b) was successfully converted to compound (II-1-a) using the conditions of Example 3 - Step 2 (CO, Pd(OAc)2, Xantphos) or the conditions of Example 9 (CO, Pd(PPh3)2Cl2).

[0384] Example 6: Obtaining (III-1-b) by Sandmeyer iodination using sodium nitrite

[0385]

[0386] At 0 °C, an aqueous solution (0.5 mL) of sodium nitrite (70 mg, 1.01 mmol) and potassium iodide (215 mg, 1.3 mmol) was added to a solution of a mixture of AMTD (58 mg, 0.50 mmol) and p-toluenesulfonic acid monohydrate (305 mg, 1.74 mmol) in anhydrous MeCN (2 mL) over 5 minutes (the colorless solution turned yellow after the first drop, then black slurry, but turned into a black solution after the addition was complete). The reaction mixture was stirred overnight at room temperature. Subsequently, the reaction mixture was diluted with saturated NaHCO3 solution (15 mL) and extracted with EtOAc (3 × 10 mL). The combined organic layers were dried over MgSO4, filtered and concentrated to dryness under reduced pressure (1 - 2 mbar, 30 °C) to afford 149 mg of a dark oil. HPLC-MS (Condition D): 90 area %. 1 1H-NMR (CDCl3): δ 2.73 (s, 3H). 13 13C-NMR (CDCl3): δ 175.9, 124.8, 18.9.

[0387] Example 7: Ethoxycarbonylation via lithium exchange

[0388] The introduction of alkoxycarbonyl groups onto the thiadiazole can also be carried out by lithium exchange.

[0389]

[0390] In a three-necked glass container equipped with an inlet, a dropping funnel, and a thermometer, 10.0 g (55.87 mmol, 1 eq) of compound (III-1-a) was dissolved in 100 mL of dry MeTHF under argon. The resulting mixture was cooled to -65 °C. Then, a hexane solution (33%) of 15.6 g (22.0 mL, 55.87 mmol) of n-hexyllithium was added dropwise over 20 minutes while maintaining the temperature at -65 °C. After complete addition, a sample of the resulting brown reaction mixture was taken: reaction mixture + ethyl chloroformate + water + TBME. The TBME phase was analyzed by HPLC (Condition B). By control in the process, it was found that 5.5% of the starting material remained unreacted. Therefore, 2.2 mL (5.58 mmol) of a hexane solution of n-hexyllithium was added to the reaction mixture at -65 °C. After 20 minutes, it was detected that the starting bromide had been completely consumed. Therefore, the reaction mixture was transferred via a cooled cannula to a mixture of 32 mL (335.16 mmol, 6 eq) of ethyl chloroformate and 30 mL of dry MeTHF pre-cooled to -65 °C over 15 minutes. Then, the resulting dark orange reaction mixture was warmed to room temperature, and then 200 mL of deionized water was added. The phases were separated, and the organic phase was dried over Na2SO4 and concentrated to obtain 13.2 g of a brown crude product. Eight grams of the crude product was purified by vacuum distillation at 1 mbar, and four fractions were collected. After distillation, the collected fractions were combined to obtain 1.9 g of the product as a colorless oil (yield: 29%, HPLC purity (Condition B): 92%). 1 1H-NMR (CDCl3): δ 4.51 (q, J = 7.1 Hz, 2H), 2.77 (s, 3H), 1.44 (t, J = 7.1 Hz, 3H). 13 13C-NMR (CDCl3): δ 178.8, 175.2, 158.6, 63.4, 19.1, 14.3.

[0391] Example 8: Ethoxycarbonylation of Fe(CO)5

[0392] Alkoxycarbonylation was also successfully carried out in the presence of Fe(CO)5.

[0393]

[0394] At 20 - 25 °C, under an inert atmosphere, a 270 mL autoclave was charged with 5.0 g (28.0 mmol, 1.0 eq) of crude compound (III-1-a) (purity: 96 w / w%, containing 3% dichloromethane), 50.0 mL (10 volumes) of anhydrous ethanol (256 ppm water), and 3.0 g (36.55 mmol, 1.3 eq) of NaOAc (256 ppm water). Nitrogen was bubbled through the mixture for 5 minutes, after which 80.0 mg (0.14 mmol, 0.005 mol eq) of Xantphos, 31.5 mg (0.14 mmol, 0.005 mol eq) of Pd(OAc)2, and 376 μL (560 mg, 2.86 mmol, 0.1 eq) of Fe(CO)5 (d: 1.45 g / ml) were added. The flask was sealed, purged with nitrogen four times, and then purged with CO four times, after which CO was charged to 4 bar. The mixture was heated to 65 °C with strong stirring. The pressure reached 5 bar during heating. The reaction was maintained at 65 °C and the pressure was maintained at 4 bar until the reaction was complete (∼24 h). The reaction was monitored by GC (Condition A), and the sample was taken: 0.4 mL of the reaction mixture diluted with 3.6 mL of ethanol. GC conversion: 59% after 17.5 h and 84.5% after 24 h.

[0395] Example 9: Ethoxycarbonylation using Pd(PPh3)2Cl2 catalyst

[0396] Alkoxycarbonylation was also successfully carried out in the presence of the Pd(PPh3)2Cl2 catalyst.

[0397] Alkoxycarbonylation reaction on the brominated intermediate (III-1-a)

[0398]

[0399] At 20 - 25 °C, under an inert atmosphere, in an 800 mL autoclave equipped with a magnetic stir bar, 5.0 g (27.9 mmol, 1.0 eq) of distilled (III - 1 - a), 140 mL (28 vol) of anhydrous ethanol, and 5 mL (3.64 g, 35.9 mmol, 1.28 eq) of TEA were charged. The mixture was purged with nitrogen for 10 minutes, after which 1.0 g (1.42 mmol, 0.05 eq) of Pd(PPh3)2Cl2 was added. The flask was sealed, purged three times with nitrogen, and then three times with CO, after which CO was charged to 5 bar. The mixture was heated to 100 °C with vigorous stirring, and the pressure increased to 6.5 bar. It was stirred until complete reaction (∼31 h). The reaction was monitored by LCMS (Condition B) after 8 h, 14 h, and 31 h (sampling: 150 μL of the reaction mixture, filtered through diatomaceous earth, washed with ethanol (2 × 150 μL), and used directly). Thereafter, the reaction mixture was filtered through 5 g of diatomaceous earth and washed with 2 × 50 mL of ethanol. EtOH was evaporated from the filtrate under vacuum at 40 °C to obtain 12.09 g of a brown solid, which was suspended in 150 mL of TBME. The organic phase was then washed with 3 × 50 mL of water and then evaporated under vacuum at 40 °C to obtain a yellow mixture of an oil and a solid. Crude yield: 82.5% (3.96 g), LCMS (Condition B): 42 area%. 1 1H - NMR: Estimated to be 66 n / n% (excluding PPh3O).

[0400] Alkoxycarbonylation reaction on the iodinated intermediate (III - 1 - b)

[0401]

[0402] In an autoclave, a solution of compound (III - 1 - b) (1 g, 4.34 mmol), TEA (0.75 mL, 5.34 mmol), and palladium(II) dichloride bis(triphenylphosphine) (60 mg, 0.08 mmol) in anhydrous ethanol (20 mL) was charged. The container was then purged twice with carbon monoxide, pressurized to 10 bar, and heated to 110 °C. HPLC - MS monitoring (Condition D) showed complete conversion within 4 h. The mixture was filtered through diatomaceous earth, the solid was washed with EtOH (20 mL), and the filtrate was concentrated to dryness under reduced pressure (1 - 2 mbar, 40 °C) to obtain a yellow - orange solid. The latter was dissolved in dichloromethane (5 mL) and TBME (15 mL) was added until precipitation occurred. The off - white solid was filtered, washed with TBME (10 mL), and the filtrate was concentrated to dryness under high vacuum (2 mbar, 40 °C) to obtain 854 mg of an orange solid. Based on 1 1H - NMR, the purity was estimated to be 59 wt% (detecting PPh3O and TEA - HI salt), and the corrected yield was 67%.

[0403] Example 10: Ethoxycarbonylation using Pd(OAc)2 - PPh3 catalyst

[0404] In the presence of a Pd(OAc)2 - PPh3 catalyst, alkoxycarbonylation was also successfully carried out.

[0405]

[0406] At 20 - 25 °C, under an inert atmosphere, in a 250 mL autoclave equipped with mechanical stirring, 3.75 g (20.9 mmol, 1.0 eq) of distilled (III - 1 - a), 105 mL (28 volumes) of absolute ethanol, and 3.75 mL (2.73 g, 26.99 mmol, 1.29 eq) of TEA were charged. The mixture was purged with nitrogen for 10 minutes, after which 578 mg (1.05 mmol, 0.105 eq) of PPh3 and 235 mg (11.17 mmol, 0.05 eq) of Pd(OAc)2 were added. The flask was sealed, purged three times with nitrogen, and then three times with CO, after which CO was charged to 5 bar. The mixture was heated to 100 °C with strong stirring, and the pressure increased to 6.5 bar. It was stirred until complete reaction (∼17 h). The reaction was monitored by HPLC (Condition B) after 17 h (sampling: 150 μL of the reaction mixture, filtered through diatomaceous earth, washed with ethanol (2 × 150 μL), and used directly). Subsequently, the reaction mixture was filtered through 5 g of diatomaceous earth and washed with 2 × 50 mL of ethanol. EtOH was evaporated from the filtrate under vacuum at 40 °C to obtain 7.03 g of a brown solid, suspended in 150 mL of TBME. Subsequently, the organic phase was washed with 3 × 50 mL of water and then evaporated under vacuum at 40 °C to obtain a yellow mixture of an oil and a solid. Crude yield: 84.7% (3.05 g), LCMS (Condition B): 71 area%. 1 1H - NMR: Estimated to be 80 n / n% (excluding PPh3O).

Claims

1. A method for preparing 3-(methyl-d3)-1,2,4-thiadiazol-5-amine (IV-2) or a salt thereof: It comprises the following steps: a) Reacting d3-acetonitrile with ethanol in the presence of HCl to form the Pinner salt of formula (VI-2): b) Reacting the Pinner salt (VI-2) with ammonia to form d3-acetamidine (V-2) or a salt thereof: And c1) Reacting d3-acetamidine (V-2) with bromine, a thiocyanate and sodium methoxide to obtain the compound of formula (IV-2); or c2) Reacting d3-acetamidine (V-2) first with sodium hypochlorite (NaOCl), and then with a thiocyanate, to obtain the compound of formula (IV-2).

Images