Description:FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(see sections 10 & rule 13)
1. TITLE OF THE INVENTION
“NOVEL DEUTERIUM-SUBSTITUTED NEFAZODONE ANALOGUE AND PROCESS FOR SYNTHESISING THEREOF”
2. APPLICANT (S)
NAME NATIONALITY ADDRESS
CLEARSYNTH LABS LIMITED Indian
17th Floor, Lotus Nilkamal Business Park, New Link Road, Andheri [West], Mumbai - 400053, Maharashtra, India.
3. PREAMBLE TO THE DESCRIPTION

COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it is to be performed

FIELD OF INVENTION
The present invention relates to novel deuterium-substituted nefazodone analogue. More specifically, it pertains to novel deuterium-enriched analogues of nefazodone (compound of formula I), a phenylpiperazine anti-depressant, and process for synthesising thereof. The invention also relates to the use of these analogues in the treatment of depression, anxiety disorders, and other central nervous system (CNS) disorders.

BACKGROUND OF INVENTION
Many therapeutically active pharmaceutical agents, despite their potent efficacy profiles, suffer from unfavourable absorption, distribution, metabolism, and excretion (ADME) characteristics, which limit their clinical utility. A major contributor to the failure of drug candidates in clinical trials is rapid metabolism, which results in low plasma concentrations, poor pharmacokinetics, and formation of undesirable or toxic metabolites. This is especially true for drugs that are extensively metabolized by hepatic cytochrome P450 (CYP) enzymes.
Nefazodone is a phenylpiperazine antidepressant belonging to the class of serotonin antagonist and reuptake inhibitors (SARls), represented by following formula,

has demonstrated clinical effectiveness in treating major depressive disorder (MDD) and certain anxiety-related conditions.
However, despite its therapeutic potential, the clinical utility of nefazodone has been significantly curtailed due to its hepatotoxicity, leading to restrictions or market withdrawal in several countries.
Studies have shown that reactive metabolites, particularly those generated via CYP3A4-mediated oxidative metabolism of the triazolopyridinyl and phenylpiperazine moieties in nefazodone, play a significant role in the observed hepatotoxicity. The drug is rapidly metabolized into species such as hydroxy-nefazodone and triazoledione, which are suspected to be hepatotoxic or reactive. The short half-life and formation of toxic intermediates result in poor patient compliance, necessitating frequent dosing, increased risk of side effects, and overall limited benefit in long-term therapy.
Attempts to overcome these limitations using formulation changes or co­ administration with metabolic inhibitors (e.g., CYP3A4 inhibitors like ritonavir or CYP2D6 inhibitors like quinidine) have proven suboptimal. Such strategies often introduce additional safety concerns, increase pill burden, and risk unintended drug­drug interactions by interfering with the metabolism of other co-administered drugs.
In light of these shortcomings, deuterium modification has emerged as a promising and elegant strategy to modulate the metabolic profile of pharmaceutical compounds. Deuterium (2H) is a non-radioactive, stable isotope of hydrogen that forms stronger C-D bonds compared to C-H bonds. This kinetic isotope effect (KIE) can reduce the rate of metabolic cleavage at specific sites, potentially leading to enhanced metabolic stability, reduced formation of toxic metabolites, and improved safety and efficacy profiles.
Although the theoretical basis of deuterium substitution is well understood, the practical outcomes remain unpredictable and must be empirically validated. Several studies [(Fisher, M.B. et al., “The Complexities Inherent in Attempts to Decrease Drug Clearance by Blocking Sites of CYP-Mediated Metabolism,” Curr. Opin. Drug Discov. Devel., 9(1):101-109 (2006); Foster, A. B., “Deuterium Isotope Effects in Studies of Drug Metabolism,” Trends in Pharmacological Sciences, 5: 524-527 (1984)] shown that deuteration at specific metabolic “soft spots” can either slow metabolism or have negligible impact depending on the structural context.
Therefore, rational design and testing of deuterated analogues are essential to determine if such substitutions will positively influence a given drug's metabolic behaviour.
WO2023218251A1 discloses deuterium-enriched nefazodone analogues, especially Nefazodone-D4, and its preparation methods. WO’251 addresses the metabolic limitations of nefazodone by introducing deuterium to the main metabolic site. This deuterated analogue, nefazodone-D4, is designed to: (a) Slow CYP-mediated metabolism due to kinetic isotopic effects; (b) Reduce the formation of toxic metabolites, including m-Cholorophenylpiperazine (mCPP/MCP) and quinone-imine intermediates; (c) Improve pharmacokinetic stability and reduce first-pass metabolism; (d) Develop a safety profile with a special focus on reducing hepatotoxicity.
Despite the intended benefits, the following issues may still persist:
I. Residual toxic metabolites (Deuteration reduces the original hepatotoxic metabolites, but is not controlled; Metabolic shunting may generate new reactive species); II. Continued CYP3A4 involvement (Deuteration slows but does not eliminate CYP3A4 metabolism, maintaining the risk of drug–drug interactions); III. Uncertain long-term safety (Limited data is available on the long-term effects and in vivo safety of Nefazodone-D4); and IV. Potential for new metabolism (Altered metabolic pathways may lead to new metabolisms with unknown pharmacological or toxic effects).
The present invention described herein provides novel deuterium-enriched nefazodone analogues, Nefazodone-D10, wherein metabolically labile hydrogen atoms are selectively replaced with deuterium at positions most susceptible to CYP-mediated oxidation. These deuterated analogues are designed to reduce or prevent the formation of hepatotoxic metabolites, extend the drug's half-life, allow for lower or less frequent dosing, and improve overall patient compliance. Importantly, deuteration is achieved without significantly altering the molecular geometry or pharmacological activity of nefazodone.
Given the lessons learned from other drugs with similar metabolic vulnerabilities (e.g. ruxolitinib) which undergoes rapid oxidative metabolism and forms multiple active and inactive metabolites, nefazodone represents an ideal candidate for targeted deuterium substitution to overcome intrinsic metabolic liabilities (for example, reduced half-life, decreased bioavailability, formation of toxic metabolites).
Hence, the present invention provides a scientifically and clinically valuable advancement by offering deuterium-modified nefazodone analogues with improved absorption, distribution, metabolism and/or excretion (ADME) properties, which are expected to mitigate known hepatotoxic risks while preserving or enhancing the drug's anti-depressant efficacy.

OBJECTS OF THE INVENTION
The principal object of the present invention is to provide novel deuterium-substituted nefazodone analogues with enhanced pharmacokinetic and safety profiles.
Another object of the present invention is to develop a process for synthesising said deuterium-substituted nefazodone analogues using accessible deuterated reagents.
Yet another object of the present invention is to reduce the formation of hepatotoxic metabolites of nefazodone by selectively blocking key metabolic positions with deuterium atoms.
Yet still another object of the present invention is to provide pharmaceutical compositions comprising the said analogues for treating major depressive disorder, anxiety, and related CNS conditions.
Yet another object of the present invention is to evaluate the in vitro and in vivo metabolic profiles and pharmacodynamics of the deuterated analogues versus other-deuterated Nefazodone as well as non-deuterated parent compound, nefazodone.  
SUMMARY OF THE INVENTION
One of the aspects of the present invention provides a compound of formula I represented by

or a pharmaceutically acceptable salt thereof,
wherein R1 to R10 are independently selected from hydrogen (H) and deuterium (D) and at least one of R5, R6, R7, R8, R9 or R10 is deuterium (D).
Another aspect of the present invention provides a process for synthesising compound of formula I, the process comprising:
a) contacting a compound of formula 1 with a compound of formula 2 in a solvent at a temperature in the range of 160oC to 200oC for a period in the range of 14 hrs to 18 hrs to obtain a compound of formula 3;
b) maintaining the isotopic purity by reacting compound of formula 3 with deuterium chloride (35% w/w in D2O) at a temperature in the range of 100oC to 130oC for a period in the range of 46 hrs to 50 hrs to obtain compound of formula 3 with isotopic purity (by QNMR) in the range of 98% to 99.99%;
c) treating a compound of formula 4 with a compound of formula 5 in presence of a base in a solvent at a temperature in the range of 0oC to 5oC for a period in the range of 1 hr to 2 hrs to obtain a compound 6;
d) reacting the compound of formula 6 obtained from step (c) with the compound of formula 3 obtained from step (b) in a base and solvent for 11 hrs to 13 hrs to obtain the compound of formula I;
wherein the compound of formula I is obtained with isotopic purity (by Mass) in the range of 98% to 99.99% and HPLC purity in the of 98% to 99.99%.

FIGURE OF THE INVENTION
Figure 1 depicts Verapamil Graphs for RLM (%PCR)
Figure 2 illustrates Verapamil Graphs for HLM (%PCR)
Figure 3 shows Verapamil Graphs for HLM (%PCR)
Figure 4 shows Verapamil Graphs for MLM (%PCR)
Figure 5 depicts Atenolol Graphs for RLM (%PCR)
Figure 6 shows Atenolol Graphs for HLM (%PCR)
Figure 7 depicts Atenolol Graphs for MLM (%PCR)
Figure 8 illustrates Nefazodone Graphs for RLM (%PCR)
Figure 9 depicts Nefazodone Graphs for MLM (%PCR)
Figure 10 shows Nefazodone Graphs for HLM (%PCR)
Figure 11 depicts Nefazodone-D10- Graphs for RLM (%PCR)
Figure 12 shows Nefazodone-D-10- Graphs for HLM (%PCR)
Figure 13 shows Nefazadone-D-10- Graphs for MLM (%PCR)
Figure 14 depicts Nefazadone-D4- Graphs for RLM (%PCR)
Figure 15 illustrates Nefazadone-D4- Graphs for MLM (%PCR)
Figure 16 depicts Comparative %PCR/API remaining between Nefazodone, Nefazodone-D4 and Nefazodone-D10
Figure 17 shows HPLC chromatogram of Nefadozone-D10
Figure 18 depicts 1H NMR of Nefazodone-D10
Figure 19 shows LCMS of Nefazodone-D10
 
DESCRIPTION OF THE INVENTION
For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are collected here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art.
The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.
It must also be noted that as used herein, the singular forms ‘a’, ‘an’ and ‘the’ include plural references unless the context clearly dictates otherwise. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, the preferred, systems are now described.
The terms ‘comprise’ and ‘comprising’ are used in the inclusive, open sense, meaning that additional elements may be included. Throughout this specification, unless the context requires otherwise the word ‘comprise’, and variations, such as ‘comprises’ and ‘comprising’, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.
The term ‘including’ is used to mean ‘including but not limited to’. The terms ‘Including’ and ‘including but not limited to’ are used interchangeably in the specification.
The term ‘at least one’ is used to mean one or more and thus includes individual components as well as mixtures/combinations. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described.
Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific functional and structural details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.
The term ‘compound’ or ‘compound of formula I’ used herein, is also intended to include any salts, solvates, or hydrates thereof. Thus, it is to be understood that when any compound is referred to herein by name and structure, salts, solvates, and hydrates thereof are included.
The terms ‘compound’ and ‘compound of formula I’ can be used interchangeably in the specification.
The term ‘pharmaceutically acceptable salt’ used herein means any non-toxic salt that, upon administration to a recipient, is capable of providing, either directly or indirectly, a compound of this invention.
The term ‘deuterium-substituted’ or ‘deuterium enriched’ used herein refers to at least one hydrogen atom is replaced with deuterium at a metabolically sensitive site. Specific sites include, but are not limited to, a methylene group adjacent to the triazole ring and/or a piperazine moiety. Such substitution improves metabolic stability and reduces the risk of hepatic side effects; and also having deuterium level that has been enriched to be greater than its natural abundance of 0.015%, should be considered unnatural and, as a result, novel over their nonenriched counterparts. The term ‘deuterium enriched’ and ‘deuterium-substituted’ can be used interchangeably throughout the specification.
‘D’ and ‘d’ both refer to deuterium. ‘D’ and ‘d’ can be used interchangeably in the specification.
The term ‘therapeutically effective amount’ used herein refers to an amount of a compound of the present invention that is effective when administered alone or in combination to treat the desired condition or disorder. The combination of compounds is preferably a synergistic combination.
The term ‘hydrate’ used herein means a compound which further includes a stoichiometric or non-stoichiometric amount of water bound by non- covalent intermolecular forces.
The term “solvates” used herein means a compound which further includes a stoichiometric or non-stoichiometric amount of solvent such as water, acetone, ethanol, methanol, dichloromethane, 2-propanol, or the like, bound by non- covalent intermolecular forces.
The term ‘solvent’ used herein refers to a substance that can dissolve another substance, or in which another substance is dissolved, forming a solution. The solvent used in the present invention can be polar or nonpolar solvent. The solvent includes such as but not limit to water, alcohols, ethers, ketones, acids, esters, acetonitrile (ACN) halogenated solvent(s) and/or deuterated form of water, alcohols, ethers, ketones, acids, esters, and/or deuterated halogenated solvent(s).
One of the embodiments of the present invention provides a compound of formula I represented by

or a pharmaceutically acceptable salt thereof,
wherein R1 to R10 are independently selected from hydrogen (H) and deuterium (D); and at least one of R5, R6, R7, R8, R9 or R10 is deuterium (D).
Another embodiment of the present invention provides a compound of formula I, wherein at least one of R5 to R10 is deuterium (D).
Another embodiment of the present invention provides a compound of formula I, wherein R1 to R10 are deuterium (D).
Another embodiment of the present invention provides a compound of formula I, wherein the compound of formula I is nefazodone-D10 having following formula II

Another embodiment of the present invention provides a compound of formula I, wherein the compound of formula I is having Intrinsic Clearance Value 209.32 (µL/min/mg protein) and T 1/2 value 6.62 min in Mouse Liver Microsomes (MLM); and having Intrinsic clearance value 251.79 (µL/min/mg protein) and T 1/2 value 5.51 min in Human Liver Microsomes (HLM).
In another embodiment of the present invention there is provided a process for synthesising compound of formula I, the process comprising:
a) contacting a compound of formula 1 with a compound of formula 2 in a solvent at a temperature in the range of 160oC to 200oC for a period in the range of 14 hrs to 18 hrs to obtain a compound of formula 3;
b) maintaining the isotopic purity by reacting compound of formula 3 with deuterium chloride (35% w/w in D2O) at a temperature in the range of 100oC to 130oC for a period in the range of 46 hrs to 50 hrs to obtain compound of formula 3 with isotopic purity (by QNMR) in the range of 98% to 99.99%;
c) treating a compound of formula 4 with a compound of formula 5 in presence of a base in a solvent at a temperature in the range of 0oC to 5oC for a period in the range of 1 hr to 2 hrs to obtain a compound 6;
d) reacting the compound of formula 6 obtained from step (c) with the compound of formula 3 obtained from step (b) in a base and solvent for 11 hrs to 13 hrs to obtain the compound of formula I;
wherein the compound of formula I is obtained with isotopic purity (by Mass) in the range of 98% to 99.99% and HPLC purity in the of 98% to 99.99%.
Another embodiment of the present invention provides a compound of formula I,
wherein compound of formula 1, 2, 3, 4, 5 and 6 are represented by



In an embodiment, the compound of formula 1 is 3-Chloroaniline-d4; compound of formula 2 is Bis(2-chloroethyl) amine HCl; compound of formula 3 is 1-(3-chlorophenyl)piperazine-d4; compound of formula 4 is 3-ethyl-4-(2-phenoxyethyl)-1H-1,2,4- triazol-5(4H)-one; compound of formula 5 is Propane-d-1,3-diyl bis(4- methylbenzenesulfonate) & compound of formula 6 is 3-(3-ethyl-5-oxo-4-(2-phenoxyethyl)-4,5-dihydro-1H-1,2,4-triazol-1-yl)propyl-4-methyl benzenesulfonate-d6.
In another embodiment of the present invention there is provided a process for synthesizing compound of formula I, wherein base is selected from ammonia, diethyl amine, triethylamine, di-isopropylethylamine (DIPEA), pyridine, dimethylaminopyridine (DMAP), imidazole potassium carbonate, sodium carbonate, cesium carbonate, lithium carbonate, sodium bicarbonate, sodium hydroxide, lithium hydroxide, calcium hydroxide, potassium hydroxide, sodium alkoxide (for example sodium ethoxide, sodium-methoxide), magnesium hydroxide, n-butyllithium, sodium hydride (NaH), Bis(2-chloroethyl)amine hydrochloride and combinations thereof.
In an embodiment, base is sodium hydride (NaH).
In another embodiment of the present invention there is provided a process for synthesising compound of formula I, wherein solvent is selected from water, alcohol (such as methanol, ethanol, propyl alcohol, isopropanol, n-butanol, iso-butanol, the tert-butyl alcohol, n-amyl alcohol, isoamyl alcohol, ethylene glycol, propane diols, glycerine), N, N- dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), toluene, acetonitrile, dioxane, 1-methyl-2-pyrrolidinone, dichloromethane, chloroform, ethyl acetate, ether, glycol dimethyl ether, diethylene glycol dimethyl ether or glycol mono-ethyl ether, deuterated form of above-mentioned solvents and combinations thereof.
In an embodiment of the present invention there is provided a process for synthesizing such compounds using deuterated starting materials or using exchange reactions under controlled conditions.
In an embodiment of the present invention there is provided a pharmaceutical composition containing these analogs and pharmaceutically acceptable excipients are also disclosed, including their use in the treatment of depression and related disorders.
In an embodiment the present invention provides nefazodone-D10 or it’s pharmaceutically acceptable salts, esters, stereoisomers, tautomers, solvates, intermediates and pharmaceutical compositions thereof.
In an embodiment, the compound of formula I is Nefazodone-D10 or Nefazodone-d10. HCl.
Another embodiment of the present invention provides a pharmaceutical composition, the composition comprising:
a) therapeutically effective amount of compound of formula I; and
b) one or more pharmaceutically acceptable excipient.
The details of the present invention are provided in the examples given below to illustrate the invention only and therefore they should not be construed to limit the scope of invention.
EXAMPLES
A. SYNTHESIS OF NEFAZODONE-D10 (COMPOUND OF FORMULA (I/II)):
i. Synthesis of 1-(3-chlorophenyl) piperazine-d4 (compound of formula 3)
Reaction Scheme:

Raw Material:
S. No. Raw Material Qty. M. Wt. Moles Mole Ratio
1 3-Chloroaniline-d4 3g 131.6 0.022 1.0 eq.
2 Bis(2-chloroethyl) amine HCl 3.1g 142.0 0.022 1.0 eq.
3 Diglyme 7.5ml -- -- 2.5 Vol
4 DCl (35w/w% in D₂O) 7.5ml -- -- 2.5 Vol
Procedure:
To a clean and dried 50 mL IN RBF, 3-chloroaniline-d4 (3.0 g) and diglyme (7.5 mL) were charged. Bis(2-cloroethyl) amine. HCl (3.1 g) was added into the above reaction mixture. The reaction was maintained at 180°C for 16 hrs and monitored by TLC. After completion of the reaction, the reaction was cooled and added diethyl ether (10 mL) and filtered. The solid was washed with ethylacetate (2 x 50 mL) and dried under high vacuum to afford pure product as a brown solid. For isotopic purity enrichment, the product was added DCL (35 W/W% in D₂O) (7.5 mL) and the reaction was maintained at 120 °C for 48 h. After completion of the reaction the DCI was evaporated under reduced pressure to get the product as a brown solid. Wt.: 2.5 g; Yield: 54%; Appearance: Brown solid; Isotopic purity: 99.59% (QNMR).
ii. 3-(3-ethyl-5-oxo-4-(2-phenoxyethyl)- 4,5-dihydro-1H-1,2,4-triazol-1-yl) propyl-4-methylbenzenesulfonate-d6 (compound of formula 6)
Reaction scheme:

Raw Material:
S. No. Raw Material Qty. M. Wt. Moles Mole Ratio
1 3-ethyl-4-(2-phenoxyethyl)-1H-1,2,4- triazol-5(4H)-one 2g 233.27 0.008 1 eq.
2 Propane-d-1,3-diyl bis (4- methyl benzenesulfonate) 3.35g 390.50 0.008 1 eq.
3 NaH 0.192g 23.99 0.008 1 eq.
4 DMSO 20ml -- 10 vol
Procedure:
To a clean and dried 50 mL, 1Neck RBF, DMSO (20 mL) and 3-ethyl-4-(2-phenoxyethyl)-1H-1,2,4-triazol-5(4H)-one (2.0 g) was charged. To the above reaction mixture, sodium hydride (NaH) (0.192 g) was added portion wise at 0°C and stirred for 15 min. Propane-d6-1,3-diyl bis(4-methylbenzenesulfonate) (3.35 g) was added and maintained at RT for 1 hr. The progress of the reaction was monitored by TLC. After completion of the reaction, water (50 mL) was added to the reaction mixture and extracted with ethyl acetate (2 x 100 mL). The organic layer was washed with brine (50 mL) and dried over anhydrous sodium sulfate evaporated under reduced pressure to get crude compound. The crude was purified by column chromatography using silica-gel (100-200) and the compound was eluted in ethyl acetate. The pure fractions were combined and evaporated under vacuum to afford the product as a light brown gummy solid. Wt.: 680 mg; Yield: 17%; Appearance: Light brown gummy solid.
iii. Synthesis of Nefazodone-D10 (compound of formula I)
Reaction scheme:

Raw Material:
S. No. Raw Material Qty. M. Wt. Moles Mole Ratio
1 1-(3-chlorophenyl) piperazine-d4 250mg 200.70 1.245 1.0 eq.
2 3-(3-ethyl-5-oxo-4-(2-phenoxyethyl)- 4,5-dihydro-1H-1,2,4-triazol-1-yl) propyl-4-methylbenzenesulfonate-d6 674mg 451.57 1.494 1.2 eq.
3 Sodium Hydride (NaH) 90mg 23.99 3.735 3.0 eq.
4 DMSO 2.5ml -- -- 10 Vol
Procedure:
To a clean and dried 50 mL IN RBF, DMSO (2.5 mL) and 1-(3-chlorophenyl) piperazine-d4 (250 mg) were charged. To the above reaction mixture, NaH (90 mg) was added portion wise at 0°C and stirred for 15 min. To this, 3-(3-ethyl-5-oxo-4-(2-phenoxyethyl)-4,5-dihydro-1H-1,2,4-triazol-1-yl)propyl-4- methylbenzenesulfonate-d6 (674 mg) was added and maintained at RT for 12 h. The progress of the reaction was monitored by TLC. After completion of the reaction, water (25 mL) was added to the reaction mixture and extracted with ethyl acetate (2 x 50 mL). The organic layer was washed with brine (50 mL) and dried under sodium sulfate and evaporated under reduced pressure to get crude compound. The crude was purified by Prep-HPLC. The pure fraction was concentrated under reduced pressure, and lyophilized to afford the pure compound as an off-white gummy solid. Wt.: 104 mg; Yield: 14%; Appearance: Off white gummy solid; Isotopic purity: 99.71% (By Mass); HPLC purity: 99.1%.
B. CHARACTERISATION OF NEFAZODONE-d10 (COMPOUND OF FORMULA I/II)
The synthesised nefazodone-D10 is characterised by using HPLC, 1hNMR spectroscopy & Mass spectroscopy (LCMS) which were illustrated in figure 17, figure 18 & figure 19 respectively.
Purity by HPLC:

C. DETERMINATION OF THE METABOLIC STABILITY FOR A SERIES OF COMPOUNDS ALONG WITH THEIR DEUTERATED FORMS

1. STUDY OBJECTIVE
The objective of the study is to determine the metabolic stability for a series of compounds along with their deuterated forms.
2. SAFETY PRECATIONS
Safety measures were adopted to ensure adequate personal health and safety. Personal protective equipment including aprons, gloves, cap, face mask and goggle (if required) were used in addition to protective laboratory wares and followed the necessary safety precautions as per the MSDS/TIDS. In case of eye or skin contact, it was washed with soap and water with subsequent medical aid.
3. Chemicals and Reagents
Milli Q water; Di-potassium hydrogen phosphate; Potassium di-hydrogen phosphate; Acetonitrile; Dimethyl sulfoxide (DMSO); NADPH; Carbamazepine
4. EXPERIMENTAL PROCEDURE
4.1. Metabolic stability:
• 5µL of the working solution (100µM in phosphate buffer) of compound is added to 432.5µL of phosphate buffer and 12.5µL of Liver microsome.
• Experiment is conducted in duplicates (n=2).
• Mix and incubate for 10 minutes in water bath at 37 ºC.
• 50 µL of 20mM NADPH solution was added, vortexed and incubated in water bath at 37 ºC
• At each time point (0, 5, 10, 20, 30 and 45 min) 50 µL of aliquots are withdrawn and added with 200 µL of ice-cold acetonitrile containing internal standard.
• Samples are vortexed and centrifuged at 10000rpm for 10minutes.
• Supernatant was diluted with milli-Q water and analysed using LCMS/MS.
• Verapamil is used as positive control and Atenolol is used as negative control.
Calculation:

Where Kel is elimination constant; and Kel is slope.

Units=µL/min/mg protein
5. ANALYSIS OF THE SAMPLES
• After transferring into vials, it was subjected to analysis in LCMS/MS.
• Mobile phase composition and column specifications are included in report
LCMS/MS conditions:
Mass Spec Triple Quadrapole Waters Xevo-TQS-Cronos with Mass Lynx v 4.2 software
HPLC Waters Acquity UPLC
Column Phenomenox Kinetix 5uM 50 *2.1 mmC18 LC Column
Mode ESI Positive mode
Method Gradient
Mobile Phase - A 0.1% Formic acid in Water (10%)
Mobile Phase - B 0.1% Acetonitrile in Water (90%)
Flow rate 0.350 mL/min
Run time 4 min
Injection volume 5 µL
Column oven Temp. 40˚ C
Auto sampler Temp. 10˚ C

MS tuning parameters:
Source parameters Values
Capillary voltage (kV) 2.45
Cone voltage (V) 28
Desolvation temp. (C) 500
Desolvation Gas flow (L/hr) 1000
Cone Gas flow (L/hr) 50
Collision energy MS (V) 4

6. Results:
6.1. Metabolic stability:
Verapamil Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2
(min) Clint
(Set 1 & Set 2
Rat Liver Microsome 0 min-1 224976 78525 2.8650 100.00 9.023 153.61
5 min-1 127378 72505 1.7568 61.32
10 min-1 82513 74099 1.1136 38.87
20 min-1 48145 75497 0.6377 22.26
30 min-1 32026 77132 0.4152 14.49
45 min-1 4486 65219 0.0688 2.40
0 min-2 222958 77537 2.8755 100.00 8.817 157.20
5 min-2 129218 72982 1.7705 61.57
10 min-2 83482 74105 1.1265 39.18
20 min-2 49041 76800 0.6386 22.21
30 min-2 32549 78954 0.4122 14.33
45 min-2 4485 70869 0.0633 2.20
45 min
(-NADPH)-1 276222.50 76827 3.5954 125.49 - -
45 min
(-NADPH)-2 279237.60 79211 3.5252 125.59 - -
Human Liver Microsome 0 min-1 285071 67095 4.2487 100.00 10.108 137.13
5 min-1 122575 65141 1.8817 44.29
10 min-1 67478 68231 0.9890 23.28
20 min-1 34729 68921 0.5039 11.86
30 min-1 17801 62617 0.2843 6.69
45 min-1 10980 65436 0.1678 3.95
0 min-2 282356 67283 4.1965 100.00 10.127 136.86
5 min-2 120769 65595 1.8411 43.87
10 min-2 70041 68266 1.0260 24.45
20 min-2 35313 68464 0.5158 12.29
30 min-2 20445 67935 0.3009 7.17
45 min-2 10314 63157 0.1633 3.89
45 min
(-NADPH)-1 263714 66733 3.9518 93.01 - -
45 min
(-NADPH)-2 257715 65440 3.9382 93.84 - -
Mouse Liver Microsome 0 min-1 173662 94020 1.8471 100.00 8.328 166.43
5 min-1 108018 95728 1.1284 61.09
10 min-1 49038 99495 0.4929 26.69
20 min-1 21607 106683 0.2025 10.96
30 min-1 11450 109065 0.1050 5.68
45 min-1 5142 117011 0.0439 2.38
0 min-2 173770 94100 1.8466 100.00 8.285 167.28
5 min-2 109706 95518 1.1485 62.20
10 min-2 49095 98622 0.4978 26.96
20 min-2 21811 107931 0.2021 10.94
30 min-2 11500 110544 0.1040 5.63
45 min-2 5091 116690 0.0436 2.36
45 min(-NADPH)-1 174405.30 93148 1.8724 101.37 -
45 min(-NADPH)-2 172939.60 94507 1.8299 99.10 -

Atenolol Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2
(min) Clint
(set 1 & set 2)

Rat Liver Microsome 0 min-1 8798 62143 0.1416 100.00 217.012 6.39
5 min-1 8096 61159 0.1324 93.50
10 min-1 7987 60593 0.1318 93.08
20 min-1 7817 60296 0.1296 91.53
30 min-1 7488 58589 0.1278 90.25
45 min-1 6964 58713 0.1186 83.76
0 min-2 8555 61466 0.1392 100.00 136.880 10.13
5 min-2 8733 61502 0.1420 102.01
10 min-2 7925 60542 0.1309 94.04
20 min-2 7604 58847 0.1292 92.82
30 min-2 7118 58206 0.1223 87.86
45 min-2 6512 58274 0.1117 80.24
45 min
(-NADPH)-1 8434 63176 0.1335 94.28 NA
45 min
(-NADPH)-2 7824 62474 0.1252 89.94
Human Liver Microsome 0 min-1 9391 68126 0.1379 100.00

-0.25
5 min-1 9901 68348 0.1449 105.08
10 min-1 10218 76632 0.1333 96.66
20 min-1 9168 68511 0.1338 97.03
30 min-1 10110 66966 0.1510 109.50
45 min-1 9162 67561 0.1356 98.33
0 min-2 10032 67884 0.1478 100.00 131.815 10.51
5 min-2 10907 68546 0.1591 107.65
10 min-2 12643 77866 0.1624 109.88
20 min-2 9527 68875 0.1383 93.57
30 min-2 8038 67150 0.1197 80.99
45 min-2 8813 67230 0.1311 88.70
45 min
(-NADPH)-1 9253 66054 0.1401 101.60 NA
45 min
(-NADPH)-2 9832 61939 0.1587 107.37

Atenolol Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2
(min) Clint
(Set 1 & Set 2)

Mouse Liver Microsome 0 min-1 16144 95019 0.1699 100.00 10783.31 -0.13
5 min-1 17183 94796 0.1813 106.71
10 min-1 16800 93233 0.1802 106.06
20 min-1 16795 92877 0.1808 106.42
30 min-1 16714 93048 0.1796 105.71
45 min-1 16121 92426 0.1744 102.65
0 min-2 17485 95137 0.1838 100.00 7859.012 0.18
5 min-2 16622 94567 0.1758 95.65
10 min-2 16586 93861 0.1767 96.14
20 min-2 16003 93340 0.1715 93.31
30 min-2 16809 93497 0.1798 97.82
45 min-2 16614 92726 0.1792 97.50
45 min
(-NADPH)-1 17736 96597 0.1836 108.06 - -
45 min
(-NADPH)-2 17385 96760 0.1797 97.77 - -

Nefazadone_HCl Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2
(min) Clint
(set 1 & set 2)
Rat Liver Microsome 0 min-1 43133 109040 0.3956 100.00 4.426 313.15
5 min-1 513 81140 0.0063 1.59
10 min-1 70 83446 0.0008 0.20
20 min-1 5 82429 0.0001 0.03
30 min-1 1 82013 0.0001 0.03
45 min-1 6 81244 0.0001 0.03
0 min-2 41863 104886 0.3991 100.00 4.484 309.09
5 min-2 624 81054 0.0077 1.93
10 min-2 37 83087 0.0005 0.13
20 min-2 28 81873 0.0003 0.08
30 min-2 7 81392 0.0001 0.03
45 min-2 11 81801 0.0001 0.03
45 min
(-NADPH)-1 43412 80171 0.5415 136.88 - -
45 min
(-NADPH)-2 46373 87474 0.5301 132.82 - -
Human Liver Microsome 0 min-1 36356 78497 0.4631 100.00 5.119 270.75
5 min-1 303 69005 0.0044 0.95
10 min-1 20 68367 0.0003 0.06
20 min-1 23 67941 0.0003 0.06
30 min-1 4 67616 0.0001 0.02
45 min-1 15 68133 0.0002 0.04
0 min-2 37413 79085 0.4731 100.00 5.671 244.40
5 min-2 333 67700 0.0049 1.04
10 min-2 69 71006 0.0010 0.21
20 min-2 42 68096 0.0006 0.13
30 min-2 32 67250 0.0005 0.11
45 min-2 19 70177 0.0003 0.06
45 min
(-NADPH)-1 31568 67322 0.4689 101.25 - -
45 min
(-NADPH)-2 31828 68445 0.4650 98.29 - -

Nefazadone_HCl Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2
(min) Clint
(set 1 & set 2)
Mouse Liver Microsome 0 min-1 49031 120176 0.4080 100.00 4.161 333.09
5 min-1 14 98388 0.0001 0.02
10 min-1 10 96027 0.0001 0.02
20 min-1 13 95331 0.0001 0.02
30 min-1 1 97001 0.0000 0.00
45 min-1 1 98121 0.0000 0.00
0 min-2 50523 123913 0.4077 100.00 6.638 208.81
5 min-2 40 95837 0.0004 0.10
10 min-2 4 94903 0.0000 0.01
20 min-2 32 94255 0.0003 0.07
30 min-2 26 97105 0.0003 0.07
45 min-2 6 98461 0.0001 0.02
45 min(-NADPH)-1 41629 89803 0.4636 113.63 - -
45 min(-NADPH)-2 41430 90245 0.4591 112.61 - -

Nefazadone_D10
HCl Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2 (min) Clint
(Set 1 & Set 2)
Rat
Liver Microsome 0 min-1 85880 84137 1.0207 100.00 8.858 156.46
5 min-1 2469 79160 0.0312 3.06
10 min-1 766 78390 0.0098 0.96
20 min-1 492 79622 0.0062 0.61
30 min-1 491 79682 0.0062 0.61
45 min-1 639 79585 0.0080 0.78
0 min-2 85994 84678 1.0155 100.00 8.087 171.38
5 min-2 2259 75698 0.0298 2.93
10 min-2 692 78571 0.0088 0.87
20 min-2 619 79414 0.0078 0.77
30 min-2 450 80034 0.0056 0.55
45 min-2 405 78135 0.0052 0.51
45 min
(-NADPH)-1 109473 81350 1.3457 131.84 - -
45 min
(-NADPH)-2 109574 80958 1.3535 133.28 - -
Human Liver Microsome 0 min-1 102953 76405 1.3475 100.00 3.491 397.07
5 min-1 1143 70203 0.0163 1.21
10 min-1 179 68998 0.0026 0.19
20 min-1 65 70032 0.0009 0.07
30 min-1 90 68695 0.0013 0.10
45 min-1 43 69862 0.0006 0.04
0 min-2 106310 77090 1.3790 100.00 3.256 425.62
5 min-2 1086 69176 0.0157 1.14
10 min-2 199 69121 0.0029 0.21
20 min-2 89 68658 0.0013 0.09
30 min-2 49 68719 0.0007 0.05
45 min-2 99 69077 0.0014 0.10
45 min
(-NADPH)-1 91123 67387 1.3522 100.35 - -
45 min
(-NADPH)-2 92183 67268 1.3704 99.38 - -

Nefazadone_D10
HCl Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2
(min) Clint
(Set 1 & Set 2)

Mouse Liver Microsome 0 min-1 105110 118308 0.8884 100.00 6.572 210.90
5 min-1 124 99162 0.0012 0.14
10 min-1 68 102088 0.0007 0.08
20 min-1 90 101881 0.0009 0.10
30 min-1 79 102026 0.0008 0.09
45 min-1 42 102829 0.0004 0.05
0 min-2 107494 120579 0.8915 100.00 6.672 207.73
5 min-2 83 100692 0.0008 0.09
10 min-2 91 102098 0.0009 0.10
20 min-2 51 102219 0.0005 0.06
30 min-2 85 101542 0.0008 0.09
45 min-2 44 102923 0.0004 0.04
45 min
(-NADPH)-1 93329 96812 0.9640 108.51 - -
45 min
(-NADPH)-2 94311 97099 0.9713 108.95 - -

6.2. Results from previous trial (VBPL-BAL-681-NG-U-2024) performed for evaluation of metabolic stability of Nefazadone-D4
Nefazadone-D4 Sample ID Analyte Area ISTD Area Area Ratio % PCR T1/2
(min) Clint
(set 1 & set 2)
Rat Liver Microsome 0 Min-1 22119 223953 0.099 100.0 5.426 255.42
5 Min-1 1308 218846 0.006 6.1
10 Min-1 323 220647 0.001 1.0
20 Min-1 180 217622 0.001 1.0
30 Min-1 112 217948 0.001 1.0
45 Min-1 66 219461 0.000 0.0
0 Min-2 22366 222355 0.101 100.0 5.407 256.31
5 Min-2 1312 220136 0.006 5.9
10Min-2 311 219779 0.001 1.0
20 Min-2 145 218951 0.001 1.0
30 Min-2 147 220214 0.001 1.0
45 Min-2 80 217545 0.000 0.0
45 Min
(-NADPH)-1 22108 221781 0.1 101.0 - -
45 Min
(-NADPH)-2 22491 224658 0.1 99.0 - -
Mouse Liver Microsome 0 min-1 21505 221366 0.097 100.0 5.556 249.47
5 min-1 1186 220291 0.005 5.2
10 min-1 299 218869 0.001 1.0
20 min-1 116 207147 0.001 1.0
30 min-1 123 214301 0.001 1.0
45 min-1 85 213923 0.000 0.0
0 min-2 21608 219563 0.098 100.0 5.436 254.96
5 min-2 1334 219160 0.006 6.1
10 min-2 297 217152 0.001 1.0
20 min-2 142 215881 0.001 1.0
30 min-2 116 206523 0.001 1.0
45 min-2 93 213058 0.000 0.0
45 min
(-NADPH)-1 21287 220179 0.097 100.0
45 min
(-NADPH)-2 21738 220609 0.099 101.0

1. Comparative Results, Summary & Conclusion
The acceptance criteria and the classification of compounds with their metabolic stabilities are as follows. For the assay results to be acceptable, the reference standards should qualify with the following limits:
 Clint value < 20 units = Low clearance
 Clint value 20-100 units = Intermediate clearance
 Clint value >100 units = High clearance
Results from the current (VBPL-BAL-894-NG-U-2024) in vitro metabolic stability experiments where test (Nefazodone and Nefazodone-D10) and reference (Verapamil & Atenolol) and the results from the previous (VBPL-BAL-681-NG-U-2024) metabolic stability experiments where Nefazodone-D4 when incubated with Rat liver microsomes (RLM), Mouse liver microsomes (MLM) and Human liver microsomes (HLM) showed that all Nefazodone compounds Nefazodone, Nefazadone-D4 and Nefazadone-D10 undergo high metabolism in RLM, HLM and MLM with Intrinsic clearance/Clint units and invitro half-life / T1/2 similar for high hepatic clearance class of compounds. Overall results are shown in the respective Tables/Figure below.
Verapamil and Atenolol were reference standards for high and low clearance compounds, respectively.
Table 1. Rat Liver Microsomes
Liver Microsomal Intrinsic Clearance data Summary
Clearance category
Compound Name Rat Liver Microsomes
Intrinsic clearance (µL/min/mg protein) T 1/2
(min)
Atenolol 8.26 176.94 Low
Verapamil 155.40 8.92 High
Nefazadone-Hcl 311.12 4.45 High
Nefazadone_D10_HCl 163.92 8.43 High
Nefazadone_D4_HCl 255.86 5.41 High
All results shown are mean of n=2 replicates
Table 2. Mouse Liver Microsomes
Liver Microsomal Intrinsic Clearance data Summary
Clearance category
Compound Name Mouse Liver Microsomes
Intrinsic clearance (µL/min/mg protein) T 1/2
(min)
Atenolol 0.02 No Calculated Low
Verapamil 166.86 8.30 High
Nefazodone- HCl 270.95 5.39 High
Nefazodone _D10_HCl 209.32 6.62 High
Nefazodone _D4_HCl 252.22 5.49 High
All results shown are mean of n=2 replicates
Note: Though Atenolol clearance was as per the trends with low clearance of Atenolol, the T1/2 for Atenolol had a negative slope based on its time versus Atenolol concentrations due to slightly higher (which is very much acceptable) observed concentrations over the nominal 100% PCR at 0 min, so the T1/2 was not calculated.
Table 3. Human Liver Microsomes
Liver Microsomal Intrinsic Clearance data Summary
Clearance category
Compound Name Human Liver Microsomes
Intrinsic clearance (µL/min/mg protein) T 1/2
(min)
Atenolol 5.13 No calculated Low
Verapamil 136.99 10.11 High
Nefazodone-HCl 257.58 5.39 High
Nefazodone_D10_HCl 251.79 5.51 High
All results shown are mean of n=2 replicates
Note: Though Atenolol clearance was as per the trends with low clearance of Atenolol, the T1/2 for Atenolol had a negative slope based on its time versus Atenolol concentrations due to slightly higher (which is very much acceptable) observed concentrations over the nominal 100% PCR at 0 min, so the T1/2 was not calculated.
CONCLUSION:
• Nefazodone, Nefazodone-D4 (D4 was tested only in RLM & MLM the results of which were extracted from the previous trial) and Nefazodone-D10 were found to be significantly metabolized in all tested species including Rat, Mouse and Human Liver microsomes.
• Though there is significant reduction in the Clint values for the deuterated Nefazodone-D10 over its non-deuterated counterpart Nefazodone when tested with RLM (311.2 for Nefazodone; 163.92 for Nefazodone-D10) and MLM (270.95 for Nefazodone; 209.32 for Nefazodone-D10), the ranges still fall in the High Clearance category indicating no major changes in the clearance class as a result of deuteration (D10) of Nefazodone.
• Generally, Nefazodone, Nefazodone-D4 and Nefazadone-D10 could be classified as High Clearance compounds based on their in vitro intrinsic clearance (Clint values) when tested with RLM, HLM and MLM albeit Nefazodone-D10 had notably lesser Clint values and T1/2 than its Nefazodone-D4 counterpart when tested in RLM and MLM (Table 1 and 2).
• The overall data summary from the metabolic stability experiments indicates that Nefazodone, Nefazodone-D4 and Nefazodone-D10 might form substrate for first pass metabolism in the liver (CYP450 mediated) resulting in high hepatic clearance based on their Clint trends.

We Claim:
1. A compound of formula I represented by

or a pharmaceutically acceptable salt thereof,
wherein R1 to R10 are independently selected from hydrogen (H) and deuterium (D).
2. The compound of formula I as claimed in claim 1, wherein at least one of R5, R6, R7, R8, R9 or R10 is deuterium (D).
3. The compound of formula I as claimed in claim 1, wherein R1 to R10 are deuterium (D).
4. The compound of formula I as claimed in claim 1, wherein the compound of formula I is nefazodone-D10 having following formula II

5. The compound of formula I as claimed in any of the claims 1 to 4, wherein the compound of formula I is having Intrinsic Clearance Value 209.32 (µL/min/mg protein) and T 1/2 value 6.62 min in Mouse Liver Microsomes (MLM); and having Intrinsic clearance value 251.79 (µL/min/mg protein) and T 1/2 value 5.51 min in Human Liver Microsomes (HLM).
6. A process for synthesising compound of formula I, the process comprising:
a) contacting a compound of formula 1 with a compound of formula 2 in a solvent at a temperature in the range of 160oC to 200oC for a period in the range of 14 hrs to 18 hrs to obtain a compound of formula 3;
b) maintaining the isotopic purity by reacting compound of formula 3 with deuterium chloride (35% w/w in D2O) at a temperature in the range of 100oC to 130oC for a period in the range of 46 hrs to 50 hrs to obtain compound of formula 3 with isotopic purity (by QNMR) in the range of 98% to 99.99%;
c) treating a compound of formula 4 with a compound of formula 5 in presence of a base in a solvent at a temperature in the range of 0oC to 5oC for a period in the range of 1 hr to 2 hrs to obtain a compound 6;
d) reacting the compound of formula 6 obtained from step (c) with the compound of formula 3 obtained from step (b) in a base and solvent for 11 hrs to 13 hrs to obtain the compound of formula I;
wherein the compound of formula I is obtained with isotopic purity (by Mass) in the range of 98% to 99.99% and HPLC purity in the of 98% to 99.99%.
7. The process as claimed in claim 6, wherein the compound of formula 1 is 3-Chloroaniline-d4; compound of formula 2 is Bis(2-chloroethyl) amine HCl; compound of formula 3 is 1-(3-chlorophenyl)piperazine-d4; compound of formula 4 is 3-ethyl-4-(2-phenoxyethyl)-1H-1,2,4- triazol-5(4H)-one; compound of formula 5 is Propane-d-1,3-diyl bis(4- methylbenzenesulfonate) & compound of formula 6 is 3-(3-ethyl-5-oxo-4-(2-phenoxyethyl)-4,5-dihydro-1H-1,2,4-triazol-1-yl)propyl-4-methyl benzenesulfonate-d6.
8. The process as claimed in claim 6, wherein the compound of formula I is Nefazodone-D10 or Nefazodone-d10. HCl.
9. The process as claimed in claim 6, wherein base is selected from ammonia, diethyl amine, triethylamine, di-isopropylethylamine (DIPEA), pyridine, dimethylaminopyridine (DMAP), imidazole potassium carbonate, sodium carbonate, cesium carbonate, lithium carbonate, sodium bicarbonate, sodium hydroxide, lithium hydroxide, calcium hydroxide, potassium hydroxide, sodium alkoxide (for example sodium ethoxide, sodium-methoxide), magnesium hydroxide, n-butyllithium, sodium hydride (NaH), Bis(2-chloroethyl)amine hydrochloride and combinations thereof.
10. The process as claimed in claim 6, wherein solvent is selected from water, alcohol (such as methanol, ethanol, propyl alcohol, isopropanol, n-butanol, iso-butanol, the tert-butyl alcohol, n-amyl alcohol, isoamyl alcohol, ethylene glycol, propane diols, glycerine), N, N- dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), toluene, acetonitrile, dioxane, 1-methyl-2-pyrrolidinone, dichloromethane, chloroform, ethyl acetate, ether, glycol dimethyl ether, diethylene glycol dimethyl ether or glycol mono-ethyl ether, deuterated form of above-mentioned solvents and combinations thereof.

Dated this: 8th day of August 2025

Vijaykumar Shivpuje
IN/PA-1096
Agent for the Applicant

To
The Controller of Patents,
The Patent Office, Mumbai
 
ABSTRACT
“NOVEL DEUTERIUM-SUBSTITUTED NEFAZODONE ANALOGUE AND PROCESS FOR SYNTHESISING THEREOF”

The present invention provides a novel deuterium-substituted nefazodone analogue. More specifically, it pertains to novel deuterium-enriched analogues of nefazodone (compound of formula I), a phenylpiperazine anti-depressant, and process for synthesising thereof. The invention also relates to the use of these analogues in the treatment of depression, anxiety disorders, and other central nervous system (CNS) disorders. The compound of formula I is represented by

wherein R1 to R10 are independently selected from hydrogen (H) and deuterium (D) and at least one of R5, R6, R7, R8, R9 or R10 is deuterium (D).

, C , Claims:We Claim:
1. A compound of formula I represented by

or a pharmaceutically acceptable salt thereof,
wherein R1 to R10 are independently selected from hydrogen (H) and deuterium (D).
2. The compound of formula I as claimed in claim 1, wherein at least one of R5, R6, R7, R8, R9 or R10 is deuterium (D).
3. The compound of formula I as claimed in claim 1, wherein R1 to R10 are deuterium (D).
4. The compound of formula I as claimed in claim 1, wherein the compound of formula I is nefazodone-D10 having following formula II

5. The compound of formula I as claimed in any of the claims 1 to 4, wherein the compound of formula I is having Intrinsic Clearance Value 209.32 (µL/min/mg protein) and T 1/2 value 6.62 min in Mouse Liver Microsomes (MLM); and having Intrinsic clearance value 251.79 (µL/min/mg protein) and T 1/2 value 5.51 min in Human Liver Microsomes (HLM).
6. A process for synthesising compound of formula I, the process comprising:
a) contacting a compound of formula 1 with a compound of formula 2 in a solvent at a temperature in the range of 160oC to 200oC for a period in the range of 14 hrs to 18 hrs to obtain a compound of formula 3;
b) maintaining the isotopic purity by reacting compound of formula 3 with deuterium chloride (35% w/w in D2O) at a temperature in the range of 100oC to 130oC for a period in the range of 46 hrs to 50 hrs to obtain compound of formula 3 with isotopic purity (by QNMR) in the range of 98% to 99.99%;
c) treating a compound of formula 4 with a compound of formula 5 in presence of a base in a solvent at a temperature in the range of 0oC to 5oC for a period in the range of 1 hr to 2 hrs to obtain a compound 6;
d) reacting the compound of formula 6 obtained from step (c) with the compound of formula 3 obtained from step (b) in a base and solvent for 11 hrs to 13 hrs to obtain the compound of formula I;
wherein the compound of formula I is obtained with isotopic purity (by Mass) in the range of 98% to 99.99% and HPLC purity in the of 98% to 99.99%.
7. The process as claimed in claim 6, wherein the compound of formula 1 is 3-Chloroaniline-d4; compound of formula 2 is Bis(2-chloroethyl) amine HCl; compound of formula 3 is 1-(3-chlorophenyl)piperazine-d4; compound of formula 4 is 3-ethyl-4-(2-phenoxyethyl)-1H-1,2,4- triazol-5(4H)-one; compound of formula 5 is Propane-d-1,3-diyl bis(4- methylbenzenesulfonate) & compound of formula 6 is 3-(3-ethyl-5-oxo-4-(2-phenoxyethyl)-4,5-dihydro-1H-1,2,4-triazol-1-yl)propyl-4-methyl benzenesulfonate-d6.
8. The process as claimed in claim 6, wherein the compound of formula I is Nefazodone-D10 or Nefazodone-d10. HCl.
9. The process as claimed in claim 6, wherein base is selected from ammonia, diethyl amine, triethylamine, di-isopropylethylamine (DIPEA), pyridine, dimethylaminopyridine (DMAP), imidazole potassium carbonate, sodium carbonate, cesium carbonate, lithium carbonate, sodium bicarbonate, sodium hydroxide, lithium hydroxide, calcium hydroxide, potassium hydroxide, sodium alkoxide (for example sodium ethoxide, sodium-methoxide), magnesium hydroxide, n-butyllithium, sodium hydride (NaH), Bis(2-chloroethyl)amine hydrochloride and combinations thereof.
10. The process as claimed in claim 6, wherein solvent is selected from water, alcohol (such as methanol, ethanol, propyl alcohol, isopropanol, n-butanol, iso-butanol, the tert-butyl alcohol, n-amyl alcohol, isoamyl alcohol, ethylene glycol, propane diols, glycerine), N, N- dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), toluene, acetonitrile, dioxane, 1-methyl-2-pyrrolidinone, dichloromethane, chloroform, ethyl acetate, ether, glycol dimethyl ether, diethylene glycol dimethyl ether or glycol mono-ethyl ether, deuterated form of above-mentioned solvents and combinations thereof.