WO2020008382A1

WO2020008382A1 - Process for preparation of eribulin and intermediates thereof

Info

Publication number: WO2020008382A1
Application number: PCT/IB2019/055671
Authority: WO
Inventors: Philip Mark Jackson; Pieter David De Koning; Raja gopal PENUMANDLA; Prapulla kumar PALVAI; Debjit BASU; Sarvesh Kumar; Vishnu Vardhana Vema Reddy EDA; Srinivas ORUGANTI; Ravi Ram Chandra Sekhar Elati; Rajeev Rehani BUDHDEV
Original assignee: Dr. Reddy’S Laboratories Limited
Priority date: 2018-07-04
Filing date: 2019-07-03
Publication date: 2020-01-09

Abstract

The present application relate to a process for preparation of 4-methylene tetrahydrofuran compound of formula II, which is useful as an intermediate for the preparation of halichondrin B analogues such as eribulin and its pharmaceutically acceptable salts thereof. The present application also provide crystalline compound of formula III and crystalline compound of formula II.

Description

PROCESS FOR PREPARATION OF ERIBULIN AND INTERMEDIATES

THEREOF

INTRODUCTION

Aspects of the present application relate to a process for preparation of 4-methylene tetrahydrofuran compound of formula II, which is useful as an intermediate for the preparation of halichondrin B analogues such as eribulin.

The drug compound having the adopted name eribulin, is a synthetic analogue of halichondrin B, and is represented by structure of formula I.

I

Eribulin is a microtubule inhibitor indicated for the treatment of patients with metastatic breast cancer who have previously received at least two chemotherapeutic regimens for the treatment of metastatic disease. U.S. Patent No. 6,214,865 discloses eribulin and its pharmaceutically acceptable salts. Methylenetetrahydro-2H-pyran compound of formula II is used as key intermediate for the preparation of halichondrin B analogues such as eribulin and its pharmaceutically acceptable salt.

Process for the preparation of methylenetetrahydro-2H-pyran compound of formula II and its further conversion to halichondrin B analogues such as eribulin have been disclosed in U.S. Patent document No. 6,214,865 and PCT publication No.s WO 2005/118565A1. The present application provides an improved process for the preparation of methylenetetrahydro-2H-pyran compound of formula II, which is simple, economic and industrially viable, this compound in turn can be converted to eribulin. The present application also provide certain intermediates in crystalline form. Isolation of crystalline intermediates provide certain advantages like reduce the need of other purification steps such as preparative HPLC & column chromatography, increase the conversion rate and reduce the formation of carryforward by products or impurities in the subsequent steps which in turn lead to increase the overall yield in the synthesis.

SUMMARY

In the first embodiment, the present application provides process for preparation of methylenetetrahydro-2H-pyran compound of formula II,

which includes one or more of the following steps:

(a) converting compound of formula III to compound of formula IV,

(b) reacting compound of formula IV with compound of formula V to provide compound of formula Vlb,

wherein Pi is H or an alcohol protecting group; P₂ is H or an alcohol protecting group or - S0₂(R_I); wherein Ri is selected from straight or branched C₁-C₁₀ alkyl or optionally substituted C₅-Ci₂ aryl; X is halogen;

(c) cyclizing compound of formula VIb to provide compound of formula VI,

(d) deprotecting compound of formula VI to provide compound of formula VII,

(e) protecting compound of formula VII to provide compound of formula VIII; and

(f) converting compound of formula VIII to compound of formula II.

In the second embodiment, the present application provide an improved process for preparation of compound of formula IV comprising;

(a) converting compound of formula III to compound of formula IX,

(b) optionally isolating compound of formula IX,

(c) adjusting the pH of the reaction mass obtained from step (a) or (b) to below 7,

(d) converting compound of formula IX to compound of formula IV.

In the third embodiment, the present application provides a process for preparation of methylenetetrahydro-2H-pyran compound of formula Ila comprising:

(a) reacting compound of formula IVa with compound of formula Va to

provide compound of formula Via,

wherein Pi and P₃ is H or an alcohol protecting group; P₂ is H or an alcohol protecting group or -S0₂(R_I); wherein Ri is selected from straight or branched C1-C10 alkyl or optionally substituted C₅-Ci₂ aryl; X is halogen or Triflate (OTf);

(b) treating compound of formula Via with a reagent comprising 1,8- Diazabicyclo[5.4.0]undec-7-ene (DBU) to produce compound of formula Ila.

In the fourth embodiment, the present application provide crystalline compound of formula III characterized by its powder X-ray diffraction (PXRD) pattern having peaks at about 6.5 ± 0.2, 9.6 ± 0.2, 13.0 ± 0.2, 15.3 ± 0.2, 17.0 ± 0.2, 19.1 ± 0.2, 19.5 ± 0.2, 21.4 ± 0.2, 22.2 ± 0.2, 23.2 ± 0.2, 24.1 ± 0.2 and 26.1 ± 0.2 degrees 2theta.

In the fifth embodiment, the present application provide compound of formula III characterized by its PXRD pattern as illustrated by Figure 1.

In the sixth embodiment, the present application provide crystalline compound of formula II characterized by its powder X-ray diffraction (PXRD) pattern having peaks at about 5.2 ± 0.2, 10.2 ± 0.2, 13.6 ± 0.2, 14.6 ± 0.2, 15.5 ± 0.2, 16.3 ± 0.2, 17.0 ± 0.2, 18.0 ± 0.2, 18.6 ± 0.2 and 20.2 ± 0.2 degrees 2theta.

In the seventh embodiment, the present application provide compound of formula II characterized by its PXRD pattern as illustrated by Figure 2.

In the eighth embodiment, the present application provides substantially pure compound of formula II, compound of formula III and compound of formula IV having a purity of not less than 98.5% by HPLC obtained by a process of the present application.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an illustration of powder X-ray diffraction (“PXRD”) pattern of compound of formula III prepared according to example 1

FIG. 2 is an illustration of powder X-ray diffraction (“PXRD”) pattern of compound of formula II prepared according to example 8

DETAILED DESCRIPTION

which includes one or more of the following steps:

(a) converting compound of formula III to compound of formula IV,

(b) reacting compound of formula IV with compound of formula V to provide compound of formula VIb,

(c) cyclizing compound of formula VIb to provide compound of formula VI,

(d) deprotecting compound of formula VI to provide compound of formula VII,

(e) protecting compound of formula VII to provide compound of formula VIII; and

(f) converting compound of formula VIII to compound of formula II.

Converting compound of formula III to compound of formula IV as mentioned in step (a) may be carried out in two steps. The first step involves the dihydroxylation of compound of formula III to give compound of formula IX. The second step involves the conversion of vicinal diol compound of formula IX to compound of formula IV.

Suitable reagents that may be used for the dihydroxylation of compound of formula III include osmium tetroxide ( O s 0_{4 )} - M c t h y 1 mo p ho line V-oxidc or, potassium permanganate, silver benzoate-iodine or any other suitable reagents that are known in the art. Suitable solvents that may be used for the dihydroxylation of compound of formula III include ketones, ethers, aliphatic and alicyclic hydrocarbons, halogenated hydrocarbons or mixtures thereof.

The reaction mixture obtained from first step may be optionally processed to remove any insoluble solids, and particles may be removed by methods such as decantation, centrifugation, gravity filtration, suction filtration, or any other techniques for the removal of solids. The product of first step may be isolated directly from the reaction mixture itself after the reaction is complete, or after conventional work up with techniques such as filtration, quenching with a suitable reagent, extraction, or the like. Optionally, the resulting product may be directly used for second step with or without isolation or it may be further purified.

Suitable reagents that may be used for the conversion of vicinal diol compound of formula IX to compound of formula IV includes periodic acid, sodium periodate or any other suitable reagent known in the art

The pH of the solution or suspension obtained by dissolving or suspending compound of formula IX in a solvent or water or mixture of solvent and water may be adjusted to 5.0 to 7.0, preferably 5.5 to 6.5 most preferably around 6.0.

Suitable solvents that may be used for the conversion of vicinal diol compound of formula IX to compound of formula IV include ketones, ethers, aliphatic and alicyclic hydrocarbons, halogenated hydrocarbons or mixtures thereof.

Step (b) involves reacting compound of formula IV with compound of formula V to provide compound of formula VIb;

Suitable reagents that may be used in the step (b) include, chromium chloride and optionally a ligand such as (S)-N-(2-(4-isopropyl-4,5-dihydrooxazol-2-yl)-6-methyl phenyl) methane sulfonamide and the like, nickel chloride and optionally a ligand such as 2,9- dimethyl- 1,10-phenanthro line and the like or any other suitable catalyst or ligands known in the art used in NHK reaction.

Suitable bases that may be used in the step (b) include, sodium hydride, potassium tert-butoxide, sodium methoxide, lithium hexamthyldisilazide, sodium amide and the like; other organic bases, such as for example, triethylamine, ethylenediamine, N- methylmorpholine, N-methylpyrrolidine, pyridine, 4-(N,N-dimethylamino)pyridine, morpholine, imidazole and the like or any other suitable base known in the art.

Suitable solvents that may be used in the step (b) include, ethers, aliphatic and alicyclic hydrocarbons, aromatic hydrocarbons, nitriles, polar aprotic solvents or mixtures thereof. The reaction mixture obtained from step (b) may be optionally processed to remove any insoluble solids, and particles may be removed by methods such as decantation, centrifugation, gravity filtration, suction filtration, or any other techniques for the removal of solids. The product of step (b) may be isolated directly from the reaction mixture itself after the reaction is complete in step (b), or after conventional work up with techniques such as filtration, quenching with a suitable reagent, extraction, or the like. Optionally, the resulting product may be directly used for step (c) with or without isolation or it may be further purified, if isolated, to improve the purity of the product.

Step (c) involves cyclizing compound of formula VIb to provide compound of formula VI,

Reported procedures involves the use of potassium bis(trimethylsilyl)amide (KHMDS) as non-nucleophilic bases for conversion of compound of formula VIb to compound of formula VI. The reported processes for preparation of compound of formula VI from formula VIb suffers from disadvantages like (i) addition of reagent and maintenance of reaction at lower temperature about -15 to -20 °C (ii) tedious workup procedures like quenching the reaction mass at lower temperature and reverse quenching the reaction mass into semi saturated ammonium chloride solution at lower temperature, (iii) removal of ligand used in the step before purification (b) required multiple isolations or purifications, (iv) use of large quantity of reagent leads to decomposition of starting material, (v) higher solvent volumes (about 150-200 volumes) and (vi) low yields and purity.

To overcome the above disadvantages the present application provides a simple, economic and commercial viable process for preparation of compound of formula VI. Further, majority of the ligand used in step (b) can be removed as a part of reaction work up and no separate purification or isolation method is required for the removal of the ligand.

Suitable reagents that may be used in step (c) include l,8-Diazabicyclo[5.4.0]undec- 7-ene (DBU) or l,5,7-Triazabicyclo(4.4.0)dec-5-ene (TBD), 7-Methyl-l,5,7- triazabicyclo(4.4.0)dec-5-ene (MTBD), l,5-Diazabicyclo[4.3.0]non-5-ene (DBN), 1, 1,3,3- Tetramethylguanidine (TMG), 2,2,6,6-Tetramethylpiperidine (TMP), Pempidine (PMP), Quinuclidine, Tributylamine, Triethylamine, l,4-Diazabicyclo[2.2.2]octan (TED), Collidine, 2,6-Lutidine (2,6-Dimethylpyridine) or any other suitable strong non-nucleophilic bases known in the art.

Suitable solvents that may be used in step (c) include, ethers, aliphatic and alicyclic hydrocarbons, aromatic hydrocarbons, nitriles, polar aprotic solvents or mixtures thereof. The reaction mixture obtained from step (c) may be optionally processed to remove any insoluble solids, and particles may be removed by methods such as decantation, centrifugation, gravity filtration, suction filtration, or any other techniques for the removal of solids. The product of step (c) may be isolated directly from the reaction mixture itself after the reaction is complete in step (c), or after conventional work up with techniques such as filtration, quenching with a suitable reagent, extraction, or the like. Optionally, the resulting product may be directly used for step (d) with or without isolation or it may be further purified, if isolated, to improve the purity of the product.

Step (d) involves deprotecting compound of formula VI to provide compound of formula VII.

Suitable reagents that may be used in step (d) include, hydrochloric acid, hydrobromic acid, hydro iodic acid, nitric acid, sulfuric acid, acetic acid, formic acid, phosphoric acid, methanesulfonic acid, p-toluenesulfonic acid, pyridinium p-toluenesulfonate (PPTS) and the like; ion exchange resins, such as: resins bound to metal ions, including lithium, sodium, potassium, and the like; and resins bound to acids, including phosphoric, sulfonic, methanesulfonic, p-toluenesulfonic, and the like or any other suitable reagents and mixtures thereof.

Suitable solvents that may be used in step (d) include water, alcohols, ketones, ethers, aliphatic and alicyclic hydrocarbons, halogenated hydrocarbons, aromatic hydrocarbons, nitriles, polar aprotic solvents, nitromethane or mixtures thereof.

The reaction mixture obtained from step (d) may be optionally processed to remove any insoluble solids, and particles may be removed by methods such as decantation, centrifugation, gravity filtration, suction filtration, or any other techniques for the removal of solids. The product of step (d) may be isolated directly from the reaction mixture itself after the reaction is complete in step (d), or after conventional work up with techniques such as filtration, quenching with a suitable reagent, extraction, or the like. Optionally, the resulting product may be directly used for step (e) with or without isolation or it may be further purified, if isolated, to improve the purity of the product.

Step (e) involves protecting compound of formula VII to provide compound of formula VIII.

Suitable the source of the tert-Butyldimethylsilyl (TBS) used in step (d) include tert- Butyldimethylsilyl chloride, tert-Butyldimethylsilyl trifluoromethanesulfonate or any other TBS source known in the art. Suitable base that may be used in step (e) include triethylamine, tributylamine, N- methylmorpholine, N,N-diisopropylethylamine, N-methylpyrrolidine, pyridine, collidine 4- (N,N-dimethylamino)pyridine, morpholine, imidazole, 2-methylimidazole, 4- methylimidazole and the like or any other suitable base known in the art.

Suitable solvents that may be used in step (e) include ketones, esters, ethers, aliphatic and alicyclic hydrocarbons, halogenated hydrocarbons, aromatic hydrocarbons, nitriles, polar aprotic solvents, nitromethane or mixtures thereof.

The reaction mixture obtained from step (e) may be optionally processed to remove any insoluble solids, and particles may be removed by methods such as decantation, centrifugation, gravity filtration, suction filtration, or any other techniques for the removal of solids. The product of step (e) may be isolated directly from the reaction mixture itself after the reaction is complete in step (e), or after conventional work up with techniques such as filtration, quenching with a suitable reagent, extraction, or the like. Optionally, the resulting product may be directly used for step (f) with or without isolation or it may be further purified, if isolated, to improve the purity of the product.

Step (f) involves converting compound of formula VIII to compound of formula II.

Suitable reagents that may be used in step (f) include, hydrochloric acid, hydrobromic acid, hydro iodic acid, nitric acid, sulfuric acid, acetic acid, formic acid, phosphoric acid, methanesulfonic acid, p-toluenesulfonic acid, tetra-n-butylammonium fluoride (TBAF), pyridinium p-toluenesulfonate (PPTS), tris(dimethylamino)sulfonium difluorotrimethylsilicate, diisobutyl aluminum hydride (DIBAL-H), lithium aluminium hydride, boron trifluoride etherate, ammonia, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium t-butoxide, sodium t-butoxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and the like; ion exchange resins, such as: resins bound to metal ions, including lithium, sodium, potassium, and the like; and resins bound to acids, including phosphoric, sulfonic, methanesulfonic, p-toluenesulfonic, and the like or any other suitable reagents and mixtures thereof.

Suitable solvents that may be used in step (f) include water, alcohols, ketones, ethers, aliphatic and alicyclic hydrocarbons, halogenated hydrocarbons, aromatic hydrocarbons, nitriles, polar aprotic solvents, nitromethane or mixtures thereof.

The product obtained from step (f), which comprises compound of the formula II may be further purified using one or more purification methods including recrystallization, slurrying in a suitable solvent, acid-base treatment, column chromatography, treating with adsorbent materials including silica gel, aluminium oxide, synthetic resin, and the like or any other suitable methods known in the art.

In the second embodiment, the present application provides an improved process for preparation of compound of formula IV comprising;

(a) converting compound of formula III to compound of formula IX,

(b) optionally isolating compound of formula IX,

(d) converting compound of formula IX to compound of formula IV.

According to the reference example, M-14 impurity of formula X is observed more than 20% during the conversion of compound of formula III to formula IV.

The present application provides optimized conditions for controlling the formation of M- 14 impurity of formula X by adjusting the pH of the reaction mass obtained from step (a) to below 7.0, preferably 5.0 to 7.0, most preferably 5.5 to 6.5.

The compound of formula IV obtained in the present application free from one or more of impurities for example free from M-14 impurity of formula X.

(a) reacting compound of formula IVa with compound of formula Va to

provide compound of formula Via,

In the sixth embodiment, the present application provide crystalline compound of formula II characterized by its powder X-ray diffraction (PXRD) pattern having peaks at about 5.2 ± 0.2, 10.2 ± 0.2, 13.6 ± 0.2, 14.6 ± 0.2, 15.5 ± 0.2, 16.3 ± 0.2, 17.0 ± 0.2, 18.0 ± 0.2, 18.6 ± 0.2 and 20.2 ± 0.2 degrees 2theta. In the seventh embodiment, the present application provide compound of formula II characterized by its PXRD pattern as illustrated by Figure 2.

DEFINITIONS

The following definitions are used in connection with the present application unless the context indicates otherwise. In general, the number of carbon atoms present in a given group or compound is designated“C_x-C_y”, where x and y are the lower and upper limits, respectively. For example, a group designated as“Ci-C₆” contains from 1 to 6 carbon atoms. The carbon number as used in the definitions herein refers to carbon backbone and carbon branching, but does not include carbon atoms of the substituents, such as alkoxy substitutions or the like.

As used herein, "an alcohol protecting group" is a functional group that protects the alcohol group from participating in reactions that are occurring in other parts of the molecule. Suitable alcohol protecting groups that are used in step (a) include, acetyl, benzoyl, benzyl, b- methoxyethoxymethyl ether, methoxymethyl ether, dimethoxytrityl, p-methoxybenzyl ether, methylthio methyl ether, allyl ether, ί-butyl ether, pivaloyl, trityl, silyl ether (e.g., trimethyls ilyl (TMS), /-butyldimethylsilyl (TBDMS), /-. butyldiphenylsilyl (TBDPS), t- butyldimethylsilyloxymethyl (TOM) or triisopropylsilyl (TIPS) ether), tetrahydropyranyl (THP), methyl ether and ethoxyethyl ether (EE) or any suitable alcohol protecting group known in the art.

As used herein, the term“lower alkyl”,“alkyl” or“alk” includes both straight and branched chain hydrocarbons, containing 1 to 20 carbons, preferably 1 to 10 carbons, more preferably 1 to 8 carbons, in the normal chain, such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl, 4,4-dimethylpentyl, octyl, 2,2,4-trimethyl- pentyl, nonyl, decyl, undecyl, dodecyl, the various branched chain isomers thereof.

As used herein, the term“lower alkenyl” or“alkenyl” as used by itself or as part of another group refers to straight or branched chain radicals of 2 to 20 carbons, preferably 2 to 12 carbons, and more preferably 1 to 8 carbons in the normal chain, which include one to six double bonds in the normal chain, such as vinyl, 2-propenyl, 3-butenyl, 2-butenyl, 4- pentenyl, 3-pentenyl, 2-hexenyl, 3-hexenyl, 2-hep tenyl, 3-heptenyl, 4-heptenyl, 3-octenyl, 3- nonenyl, 4-decenyl, 3-undecenyl, 4-dodecenyl, 4,8,l2-tetradecatrienyl, and the like. As used herein, the term“halogen” or“halo” as used herein alone or as part of another group refers to chlorine, bromine, fluorine, and iodine.

As used herein, the term“aryl” as alone or as part of another group refers to monocyclic and bicyclic aromatic groups containing 6 to 10 carbons in the ring portion such as phenyl or naphthyl including 1 -naphthyl and 2-naphthyl and the like.

As used herein, the term“lower alkoxy”,“alkoxy”,“aryloxy” or“aralkoxy” as alone or as part of another group includes any of the above alkyl, aralkyl or aryl groups linked to an oxygen atom.

As used herein, the term“heteroaryl” as used herein alone or as part of another group refers to a 5- or 6- membered aromatic ring which includes 1, 2, 3 or 4 hetero atoms such as nitrogen, oxygen or sulfur, and such rings fused to an aryl, cycloalkyl, heteroaryl or cycloheteroalkyl ring (e.g. benzothiophenyl, indolyl), and includes possible N-oxides.

An“alcohol” is an organic compound containing a carbon bound to a hydroxyl group. “Ci-C₆ alcohols” include methanol, ethanol, 2-nitroethanol, 2-fluoroethanol, 2,2,2- trifluoroethanol, hexafluoroisopropyl alcohol, ethylene glycol, l-propanol, 2-propanol (isopropyl alcohol), 2-methoxyethanol, l-butanol, 2-butanol, i-butyl alcohol, t-butyl alcohol, 2-ethoxyethanol, diethylene glycol, 1-, 2-, or 3-pentanol, neo-pentyl alcohol, t-pentyl alcohol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, cyclohexanol, phenol, glycerol and the like.

An“aliphatic hydrocarbon” is a liquid hydrocarbon compound, which may be linear, branched, or cyclic and may be saturated or have as many as two double bonds. A hydrocarbon compound that contains a six-carbon group having three double bonds in a ring is called“aromatic.” Examples of “C₅-Cs aliphatic or aromatic hydrocarbons” include n- pentane, isopentane, neopentane, n-hexane, isohexane, 3-methylpentane, 2,3-dimethylbutane, neohexane, n-heptane, isoheptane, 3-methylhexane, neoheptane, 2,3-dimethylpentane, 2,4- dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 2,2,3-trimethylbutane, n-octane, isooctane, 3-methylheptane, neooctane, cyclohexane, methylcyclohexane, cycloheptane, petroleum ethers and the like.

An “aromatic hydrocarbon solvent” refers to a liquid, unsaturated, cyclic, hydrocarbon containing one or more rings which has delocalized conjugated p system. Examples of an aromatic hydrocarbon solvent include benzene toluene, ethylbenzene, m- xylene, o-xylene, p-xylene, indane, naphthalene, tetralin, trimethylbenzene, chlorobenzene, fluorobenzene, trifluorotoluene, anisole, C₆-Ci2 aromatic hydrocarbons and the like. An“ether” is an organic compound containing an oxygen atom -O- bonded to two other carbon atoms. “C2-C6 ethers” include diethyl ether, diisopropyl ether, methyl t-butyl ether, glyme, diglyme, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 4-dioxane, dibutyl ether, dimethylfuran, 2-methoxyethanol, 2-ethoxyethanol, anisole and the like.

A“halogenated hydrocarbon” is an organic compound containing a carbon bound to a halogen. Halogenated hydrocarbons include dichloro methane, l,2-dichloroethane, trichloroethylene, perchloroethylene, l,l,l-trichloroethane, l,l,2-trichloroethane, chloroform, carbon tetrachloride and the like.

A“nitrile” is an organic compound containing a cyano -(CºN) bonded to another carbon atom. “C2-C6 Nitriles” include acetonitrile, propionitrile, butanenitrile and the like.

A “polar aprotic solvents” include N, N-dimethylformamide, N, N- dimethylacetamide, dimethylsulfoxide, sulfolane, N-methylpyrrolidone and the like;

Certain specific aspects and embodiments of the present application will be explained in greater detail with reference to the following examples, which are provided only for purposes of illustration and should not be construed as limiting the scope of the application in any manner. Reasonable variations of the described procedures are intended to be within the scope of the present application. While particular aspects of the present application have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this application.

EXAMPLES

Example-1: Preparation of (S)-4-(((2R,3R,4S,5S)-5-allyl-3-methoxy-4-

((phenylsulfonyl)methyl)tetrahydrofuran-2-yl)methyl)-2,2-dimethyl-l,3-dioxolane.

A solution of (2R, 3R,4R,5S)-5-allyl-2-(((S)-2, 2-dimethyl- l,3-dioxo lan-4-yl)methyl)- 4-((phenylsulfonyl)methyl)tetrahydrofuran-3-ol (165 g) in THF (495 mL) was added to the reaction mass containing sodium tertiary butoxide (56 g) in THF (990 mL) at 1 °C under nitrogen atmosphere and the resultant reaction mixture was stirred for 30 minutes at 3 °C. Methyl iodide (33.6 mL) was added at 3 °C and stirred at 28 °C for 4 hours. Water (825 mL) was added to the reaction mass at 28 °C and stirred for 10 minutes. Reaction mass extracted with MTBE (2X825 mL), the combined organic layer washed with 10% Na₂S₂0₃ solution (825 mL), water (825 mL), brine solution (825 mL), dried over sodium sulfate and concentrated in vacuo. To the crude compound «-hexane (330 mL) was added and concentrated in vacuo. Mixture of 5% MTBE and n- hexane (495 mL) was added to the crude compound, heated to 45 °C and stirred at 45 °C for 1 hour. Cooled to 30 °C and stirred for 1 hour. Separated solid was filtered, washed with n-hexane and. The obtained wet compound was recrystallized from 5% MTBE and n-hexane and dried at 40 °C to afford title compound as a crystalline solid.

Purity by HPLC: 98.7%

Example-2:Preparation of 2-((2S,3S,4R,5R)-5-(((S)-2,2-dimethyl-l,3-dioxolan-4- yl)methyl)-4-methoxy-3-((phenylsulfonyl)methyl)tetrahydrofuran-2-yl)acet aldehyde.

A solution of the (S)-4-(((2R,3R,4S,5S)-5-allyl-3-methoxy-4-((phenylsulfonyl) methyl)tetrahydro furan-2-yl)methyl)-2, 2-dimethyl- l,3-dioxo lane (20.3 g) and N- methylmorpholine N-oxide (50% w/w in water; 15 mL) in MTBE (100 mL) and tBuOH (20 mL) was prepared. Potassium osmate dihydrate (90 mg) and water (12.5 mL) was added and the mixture was stirred at 2l°C for 18 hours. Saturated aqueous sodium thiosulfate solution (100 mL) was added and the mixture was stirred for 10 minutes. Layers were separated, aqueous phase was extracted with MTBE (50 mL). The combined MTBE extracts were washed with brine (30 mL). Water (200 mL) was added to the organic phase and the resulting mixture pH was adjusted to 6 by addition of acetic acid (2.5 mL) at below l5°C. Sodium periodate (11.2 g) was added and the mixture was stirred at l5-20°C for 15 minutes. Layers were separated and aqueous phase was extracted with MTBE (150 mL). The combined MTBE phase was washed with brine (50 mL), filtered through a pad of MgS0₄ and concentrated to give title compound.

Purity by HPLC: 99.0% (M-14 impurity: Not detected)

Example-3: Preparation of 3-((2S,5S)-5-((3R,5R)-6-iodo-5-methyl-3-(((2,4,6-triiso propylphenyl)sulfonyl)oxy)hept-6-en-l-yl)-4-methylenetetrahydrofuran-2-yl) propyl pivalate

2,4,6-triisopropyl benzene sulphonylchloride (24.89 g) was added slowly to the reaction mass containing 3-((2S,5S)-5-((3R,5R)-3-hydroxy-6-iodo-5-methylhept-6-en-l-yl)- 4-methylenetetrahydrofuran-2-yl)propyl pivalate (26.21 g), dichloromethane (125 mL) and N,N-dimethylpyridin-4-amine (20.08 g) at 16 °C and the resultant reaction mixture was stirred at 26 °C for 6 hours. Water (125 mL) was added slowly to the reaction mass and stirred for 10 minutes. Layers were separated, organic phase was washed with saturated sodium bicarbonate solution (125 mL), saturated sodium chloride solution (125 mL) and concentrated in vacuo. The resultant crude compound was chased with acetonitrile (2x50 mL). Acetonitrile (125 mL) and heptane (125 mL) was added to the crude compound and stirred for 10 minutes. Water (62.5 mL) was added slowly and stirred for 10 minutes. Layers were separated, acetonitrile layer was extracted with heptane (50 mL) and the combined heptane layers were washed with saturated sodium chloride solution (125 mL). The resultant heptane layer was concentrated in vacuo to afford the title compound.

Example-4:Preparation of 3-((2S,5S)-5-((3R,5R,7R)-8-((2S,3S,4R,5R)-5-(((S)-2,2- dimethyl-l,3-dioxolan-4-yl)methyl)-4-methoxy-3-((phenylsulfonyl) methyl) tetra hydrofuran-2-yl)-7-hydroxy-5-methyl-6-methylene-3-(((2,4,6-triisopropylphenyl) sulfonyl)oxy)octyl)-4-methylenetetrahydrofuran-2-yl)propyl pivalate.

Chromium (II) chloride (0.924 g) was added to the reaction mixture containing (S)-N- (2-(4-isopropyl-4,5-dihydrooxazol-2-yl)-6-methylphenyl)methanesulfonamide (2.43 g) and anhydrous tetrahydrofuran (25 mL) at 28 °C in glove box. Triethylamine (0.768 g) was added dropwise to the reaction mass at 32-35 °C and stirred at 35-38 °C for 3 hours 30 minutes. Nickel (II) chloride (0.025 g) was added at 31 °C. Solution containing 2-((2S,3S,4R,5R)-5- (((S)-2, 2-dimethyl- l,3-dioxolan-4-yl)methyl)-4-methoxy-3-((phenyl

sulfonyl)methyl)tetrahydrofuran-2-yl)acetaldehyde (0.67 g), 3-((2S,5S)-5-((3R,5R)-6-iodo-5- methyl-3-(((2,4,6-triisopropylphenyl)sulfonyl)oxy)hept-6-en-l-yl)-4-ethylene

tetrahydrofuran-2-yl)propyl pivalate (1.573 g) and tetrahydrofuran (15 mL) was added slowly to the reaction mixture at 31 °C and stirred at 31 °C for 16 hours. Ethylenediamine (1.3 g) was slowly added to the reaction mass at -4 °C and stirred at 0-2 °C for 1 hour. Water (10 mL) was added slowly at 10 °C and n-heptane (20 mL) followed by MTBE (20 mL) was added slowly to the reaction mass at 16 °C and stirred for 20 minutes. The phases were separated, aqueous phase was extracted with MTBE (2X30 mL) and the combined organic phase was washed with solution of sodium bicarbonate (1.0 g) and sodium chloride (3 g) in water (12 mL). The organic extract was dried over anhydrous Na₂S0₄ and concentrated in vacuo. The resultant crude compound was chased with tetrahydrofuran (2x30 mL) and used for cyclization reaction (Next step).

Example-5: Preparation of 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-(((S)-2,2- dimethyl-l,3-dioxolan-4-yl)methyl)-4-methoxy-3-(phenylsulfonyl)methyl)

tetrahydrofuran-2-yl)methyl)-4-methyl-5-methylenetetrahydro-2H-pyran-2-yl) ethyl)-4- methylenetetrahydrofuran-2-yl)propyl pivalate KHMDS (0.5 M in toluene) (20.5 mL) was added in lots to the reaction mass containing 3-((2S,5S)-5-((3R,5R,7R)-8-((2S,3S,4R,5R)-5-(((S)-2,2-dimethyl-l,3-dioxolan-4- yl)methyl)-4-methoxy-3-((phenylsulfonyl)methyl)tetrahydrofuran-2-yl)-7-hydroxy-5-methyl- 6-methylene-3-(((2,4,6-triisopropylphenyl)sulfonyl)oxy)octyl)-4-methylenetetra hydro furan- 2-yl)propyl pivalate (1.675 g) and tetrahydrofuran (40 mL) at -20 °C and stirred at -20 °C for 1 hour. Reaction mass was cannulated to solution of ammonium chloride (5.0g) in water (50 mL) at -8 °C, MTBE (50 mL) was added and warmed to ambient temperature over 30 minutes. The phases were separated, aqueous phase was extracted with MTBE (2X30 mL) and the combined organic phase was washed with brine solution (30 mL). The organic extract was dried over anhydrous Na₂S0₄ and concentrated in vacuo. The obtained crude compound was subjected to Combiflash purification to afford title compound (0.52 g, 95.02% purity by HPLC).

Example-6:Preparation of 3-((2S,5S)-5-((3R,5R,7R)-8-((2S,3S,4R,5R)-5-(((S)-2,2- dimethyl-l,3-dioxolan-4-yl)methyl)-4-methoxy-3-((phenylsulfonyl) methyl) tetra hydrofuran-2-yl)-7-hydroxy-5-methyl-6-methylene-3-(((2,4,6-triisopropylphenyl) sulfonyl)oxy)octyl)-4-methylenetetrahydrofuran-2-yl)propyl pivalate.

Chromium (II) chloride (3.84 g) was added to the reaction mixture containing (S)-N- (2-(4-isopropyl-4,5-dihydrooxazol-2-yl)-6-methylphenyl)methanesulfonamide (9.21 g) and anhydrous tetrahydrofuran (100 mL) at 28 °C in glove box. Triethylamine (3.17 g) was added dropwise to the reaction mass at 40 °C and stirred at 40 °C for 4 hours. Nickel (II) chloride (0.103 g) was added at 40 °C. Solution containing 2-((2S,3S,4R,5R)-5-(((S)-2,2-dimethyl- l,3-dioxolan-4-yl)methyl)-4-methoxy-3-((phenyl sulfonyl)methyl)tetrahydrofuran-2- yl) acetaldehyde (3.32 g), 3-((2S,5S)-5-((3R,5R)-6-iodo-5-methyl-3-(((2,4,6- triisopropylphenyl)sulfonyl)oxy)hept-6-en-l-yl)-4-ethylene tetrahydrofuran-2-yl)propyl pivalate (5 g) and tetrahydrofuran (25 mL) was added slowly to the reaction mixture at 22 °C and stirred at 22 °C for 16 hours. Ethylenediamine (5.37 g) was slowly added to the reaction mass at 2 °C and stirred at 0-2 °C for 1 hour. Water (25 mL) was added slowly at 16 °C and n-heptane (25 mL) followed by MTBE (25 mL) was added slowly to the reaction mass at 19 °C and stirred for 20 minutes. The phases were separated, aqueous phase was extracted with MTBE (2X25 mL) and the combined organic phase was washed with saturated sodium bicarbonate solution (25 mL) and saturated sodium chloride solution (25 mL). The organic extract was dried over anhydrous Na₂S0₄ and concentrated in vacuo. The resultant crude compound was used for cyclization reaction (Next step). Example-7: Preparation of 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-(((S)-2,2- dimethyl-l,3-dioxolan-4-yl)methyl)-4-methoxy-3-(phenylsulfonyl)methyl)

tetrahydrofuran-2-yl)methyl)-4-methyl-5-methylenetetrahydro-2H-pyran-2-yl) ethyl)-4- methylenetetrahydrofuran-2-yl)propyl pivalate

l,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) (40 mL) was added to the crude compound obtained in example- 1 at 28 °C and the resultant reaction mass was stirred at 28 °C for 19 hours. MTBE (100 mL) and water (100 mL) was added at 27 °C and stirred at 27 °C for 20 minutes. The phases were separated, aqueous phase was extracted with MTBE (50 mL) and the combined organic phase was washed with water (50 mL), 14% ammonium chloride solution (75 mL), 25% sodium chloride solution (75 mL).The organic extract was dried over anhydrous Na₂S0₄ and concentrated in vacuo. The obtained crude compound was subjected to Combiflash purification to afford title compound (95.8% purity by HPLC).

Example-8: Preparation of 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-(((S)-2,2- dimethyl-l,3-dioxolan-4-yl)methyl)-4-methoxy-3-(phenylsulfonyl)methyl)

l,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) (1.33 mL) was added slowly to the solution of 3-((2S,5S)-5-((3R,5R,7R)-8-((2S,3S,4R,5R)-5-(((S)-2, 2-dimethyl- l,3-dioxolan-4- yl)methyl)-4-methoxy-3-((phenylsulfonyl) methyl) tetra hydrofuran-2-yl)-7-hydroxy-5- methyl-6-methylene-3-(((2,4,6-triisopropylphenyl) sulfonyl)oxy)octyl)-4- methylenetetrahydrofuran-2-yl)propyl pivalate (500 mg) and tetrahydrofuran (5 mL) at 28 °C and the resultant reaction mass was stirred at 26 °C for 36 hours. Ammonium chloride solution (15 mL) was added to the reaction mass at 2 °C. MTBE (15 mL) was added at 27 °C and stirred at 27 °C for 20 minutes. The phases were separated, aqueous phase was extracted with MTBE (2 x 7 mL) and the combined organic phase was washed with 25% sodium chloride solution (10 mL).The organic extract was dried over anhydrous Na₂S0₄ and concentrated in vacuo. The obtained crude compound was subjected to Combiflash purification to afford title compound.

Example-9: Preparation of 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-(((S)-2,2- dimethyl-l,3-dioxolan-4-yl)methyl)-4-methoxy-3-(phenylsulfonyl)methyl)

tetrahydrofuran-2-yl)methyl)-4-methyl-5-methylenetetrahydro-2H-pyran-2-yl) ethyl)-4- methylenetetrahydrofuran-2-yl)propyl pivalate l,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) (145 g) was added slowly to the solution of 3-((2S,5S)-5-((3R,5R,7R)-8-((2S,3S,4R,5R)-5-(((S)-2, 2-dimethyl- l,3-dioxolan-4- yl)methyl)-4-methoxy-3-((phenylsulfonyl) methyl) tetra hydrofuran-2-yl)-7-hydroxy-5- methyl-6-methylene-3-(((2,4,6-triisopropylphenyl) sulfonyl)oxy)octyl)-4- methylenetetrahydrofuran-2-yl)propyl pivalate (39.3 g) and tetrahydrofuran (150 mL) at 28 °C and the resultant reaction mass was stirred at 32 °C for 20 hours. MTBE (300 mL) followed by water (300 mL) was added at 27 °C and stirred at 27 °C for 30 minutes. The phases were separated, aqueous phase was extracted with MTBE (2 x 150 mL) and the combined organic phase was washed with water (2x 150 mL) 25% sodium chloride solution (150 mL).The organic extract was dried over anhydrous Na₂S0₄ and concentrated in vacuo. The obtained crude compound was subjected to Combiflash purification to afford title compound.

Example-10: Preparation of 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-((S)-2,3- dihydroxypropyl)-4-methoxy-3-((phenylsulfonyl)methyl)tetrahydrofuran-2-yl)methyl)- 4-methyl-5-methylenetetrahydro-2H-pyran-2-yl)ethyl)-4-methylene tetrahydrofuran-2- yl)propyl pivalate

1M aqueous hydrochloric acid solution (34.2 mL) was added to a solution of 3- ((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-(((S)-2, 2-dimethyl- l,3-dioxolan-4- yl)methyl)-4-methoxy-3-(phenylsulfonyl)methyl) tetrahydro furan-2-yl)methyl)-4-methyl-5- methylenetetrahydro-2H-pyran-2-yl)ethyl)-4-methylene tetrahydro furan-2-yl)propyl pivalate (9.5 g), methanol (95 mL), water (19 mL) at 25 °C and the resultant reaction mixture was stirred at 25 °C for 3 hours. 6% sodium bicarbonate solution (95 mL) was slowly added to the reaction mass at 4 °C and stirred for 15 minutes. DCM (190 mL) was added at 25 °C and stirred for 15 minutes. Layers were separated and aqueous phase extracted with DCM (2x95 mL). The combined organic phase washed with 20% sodium chloride solution (143 mL), dried over sodium sulfate and concentrated in vacuo to afford the title compound.

Example-11: Preparation of 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-((S)-2,3- bis((tert-butyldimethylsilyl)oxy)propyl)-4-methoxy-3-((phenylsulfonyl)

methyl)tetrahydrofuran-2-yl)methyl)-4-methyl-5-methylenetetrahydro-2H-pyran -2-yl) ethyl) -4-methylenetetrahydrofuran-2-yl)propyl pivalate

A solution of tert-butyldimethylsilyl chloride (6.99 g) in DML (16.4 mL) was slowly added to the reaction mass containing 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-((S)- 2,3-dihydroxypropyl)-4-methoxy-3-((phenylsulfonyl)methyl) tetrahydrofuran-2-yl)methyl)-4- methyl-5-methylenetetrahydro-2H-pyran-2-yl)ethyl)-4-methylene tetrahydrofuran-2- yl)propyl pivalate (8.2 g), imidazole (4.74 g) and DMF (41 mL) at 2 °C and the resultant reaction mixture stirred at 26 °C for 6 hours. Water (164 mL) and MTBE (123 mL) were slowly added to the reaction mass and stirred for 10 minutes. Layers were separated and aqueous phase was extracted with MTBE (82 mL). The combined organic phase was washed with water (82 mL), 25% sodium chloride solution (123 mL), dried over sodium sulfate and concentrated in vacuo to afford title compound.

Example-12: Preparation of 3-((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-((S)-2,3- bis((tertbutyldimethylsilyl)oxy)propyl)-4-methoxy-3-((phenylsulfonyl)methyl) tetrahydrofuran-2-yl)methyl)-4-methyl-5-methylenetetrahydro-2H-pyran-2-yl)ethyl)-4- methylenetetrahydrofuran-2-yl)propan-l-ol (Compound of formula II)

A solution of DIBAL-H (86 mL; 1M in toluene) was slowly added to a solution of 3- ((2S,5S)-5-(2-((2S,4R,6R)-6-(((2S,3S,4R,5R)-5-((S)-2,3-bis((tert-butyldimethyl

silyl)oxy)propyl)-4-methoxy-3-((phenylsulfonyl)methyl) tetrahydrofuran-2-yl)methyl)-4- methyl-5-methylenetetrahydro-2H-pyran-2-yl) ethyl)-4-methylenetetrahydrofuran-2- yl)propyl pivalate (26.8 g) in toluene (134 mL) at -67 °C under nitrogen atmosphere and the resultant reaction mixture was stirred at -67 °C for 1 hour. Methanol (3.22 mL) was added at -67 °C and stirred for 30 minutes. 1M HC1 solution (268 mL) was slowly added at 8 °C and stirred for 15 minutes. MTBE (402 mL) was added and stirred for 30 minutes. Layers were separated and aqueous phase was extracted with MTBE (2X214 mL). The combined organic layer was washed with 6% sodium bicarbonate solution (402 mL), 25% sodium chloride solution (402 mL), dried over sodium sulphate and concentrated in vacuo. The resultant crude compound was purified using combiflash chromatography using ethyl acetate and hexane mixture. The pure fractions containing title product was concentrated in vacuo and co distilled with n-heptane (2x134 mL) in vacuo. To the resultant compound n-heptane (670 mL) and seed were added at 1 °C and stirred at the same temperature for 2-3 hours and subsequently stirred at -10 °C for 2-3 hours. Separated solid was filtered and pre-chilled n- heptane (134 mL) was added to the wet compound and stirred for 15 minutes at -10 °C and filtered. Pre-chilled n-heptane (134 mL) was added to the wet compound, stirred for 15 minutes at -10 °C and filtered. The obtained wet compound was dried at 28 °C under reduced pressure to afford the title crystalline compound.

Purity by HPLC: 99.4%; Single crystal X-Ray determination of compound of formula (II):

Single crystals were grown by dissolution of 30 mg of the title compound in 3 mL of n- heptane and stored at 4°C for several hours.

Data were measured using profile data from□ -scans of 0.5 per frame for 5.0 s using CuKn radiation (Rotating-anode X-ray tube, 40.0 kV, 30.0 mA).

Formula C9oH_l560_l8S₂Si4

Formula Weight 1702.62

Size/mm³ 0.26x0.12x0.04

Crystal System orthorhombic

Space Group P2i2i2i

Unit cell dimensions A= 11.28100(10) A a=90°

b=l2.93890(10) A b=90°

c= 67.2806(8) A g=90°

Volume 9820.53(16) A³

Z 4

Wavelength/A 1.54184

Example-13: Preparation of (S)-N-(2-(4-isopropyl-4,5-dihydrooxazol-2-yl)-6- methylphenyl)methanesulfonamide

Oxalyl chloride (52.5 g) was slowly added to the reaction mass containing 3-methyl- 2-nitro-benzoic acid (50 g) and toluene (250 mL) at 0-10 °C. N, N-Dimethyl formamide (2.0 g) was slowly added at 0-10 °C and the resultant reaction mass stirred at 30 °C for 2 hours. Reaction mass was concentrated under reduced pressure, toluene (100 mL) was added to the crude and concentrated under reduced pressure to afford 3-methyl-2-nitrobenzoyl chloride. A solution of 3-methyl-2-nitrobenzoyl chloride in toluene (200 mL) was slowly added to the reaction mass containing water (400 mL), potassium carbonate (38.14 g) and L-valinol (34.14 g) at 0-10 °C over a period of 60-90 minutes. The resultant reaction mass was stirred at 30 °C for 2 hours and the separated solid was filtered, washed with water (150 mL) and toluene (50 mL). The wet compound and ethyl acetate (150 mL) charged in to flask, heated to 65 °C and stirred at 65 °C for 30-45 minutes. Heptane (150 mL) was added at 30 °C and stirred at 30 °C for 4 hours. Separated solid was filtered, washed with mixture of heptane and ethyl acetate solution (100 mL; 1:1) and dried at 60 °C to afford (S)-N-(l-hydroxy-3-methylbutan-2-yl)-3- methyl-2-nitrobenzamide. (Yield: 95%, Chemical purity by HPLC: 99.1%, Chiral purity by HPLC: 99.97%) (S)-N-(l-hydroxy-3-methylbutan-2-yl)-3-methyl-2-nitrobenzamide (65 g), methanol (325 mL) and Raney Nickel (13 g) charged into autoclave vessel at ambient temperature. Hydrogen gas 60-65 psi filled in to the autoclave vessel at ambient temperature and stirred at same temperature for 10 hours. Evacuated the hydrogen gas, reaction mass filtered, washed with methanol (325 mL) and the resultant filtrate was concentrated under reduced pressure. Water (325 mL) was added at 7 °C and stirred at same temperature for 3 hours. Separated solid was filtered, washed with water (65 mL) and dried at 95-l00°C to afford (S)-2-amino- N-(l-hydroxy-3-methylbutan-2-yl)-3-methylbenzamide. (Yield: 93%, Chemical purity by HPLC: 99.6%, Chiral purity by HPLC: 99.8%)

Methane sulfonyl chloride (75 g) was slowly added to the reaction mass containing (S)-2-amino-N-(l-hydroxy-3-methylbutan-2-yl)-3-methylbenzamide (50 g), pyridine (150 mL) and DMAP (1.28 g) at 5 °C. The resultant reaction mass was stirred at 5 °C for 30 minutes followed by 4 hours at ambient temperature. Water (1000 mL) was slowly added to the reaction mass at 5 °C and stirred for 1-2 hours at ambient temperature. Separated solid was filtered and washed with water (150 mL). To the resultant wet compound water (350 mL) was added and stirred at ambient temperature for 1-2 hours. Separated solid was filtered and washed with water (150 mL). Toluene (400 mL) was added to the wet compound, stirred at ambient temperature for 20 minutes. Charcoal (5 g) was added, heated to 50 °C and stirred at 50 °C for 1 hour. Cooled to ambient temperature, filtered through Celite bed and washed with toluene (100 mL). The resultant filtrate concentrated up to 1 volume under reduced pressure, MTBE (125 mL) was added and heated 50 °C. After stirring 30 minutes at 50 °C then cooled to ambient temperature. Heptane (125 mL) was added at ambient temperature and stirred at same temperature for 3 hours. Separated solid was filtered, washed with mixture MTBE & heptane (50 mL; 1:1) and dried at 60 °C to afford title compound. (Chemical purity by HPLC: 99.8%, Chiral purity by HPLC: 99.95%)

(R)-N-(2-(4-isopropyl-4,5-dihydrooxazol-2-yl)-6-methylphenyl)methanesulfonamide was prepared by following the procedure given in the example- 13 using D-valinol

Reference Example: Preparation of 2-((2S,3S,4R,5R)-5-(((S)-2,2-dimethyl-l,3-dioxolan- 4-yl) methyl)-4-methoxy-3-((phenylsulfonyl)methyl)tetrahydrofuran-2-yl)acetaldehyde.

A solution of the (S)-4-(((2R,3R,4S,5S)-5-allyl-3-methoxy-4-((phenylsulfonyl) methyl)tetrahydro furan-2-yl)methyl)-2, 2-dimethyl- l,3-dioxo lane (17 g) in acetone (100 mL) was prepared in a 500 mL RBL. N-Methylmorpholine N-oxide monohydrate (8.4 g) was added, followed by water (17 mL) and acetone (70 mL) and the mixture was stirred at 2l°C while a solution of osmium tetroxide (4 wt% in water; 5 mL) was added. The resulting solution was stirred at 2l°C for 18 hours. The reaction mass was diluted with water (34 mL) and sodium periodate (9.5 g) was added. After 75 min, more sodium periodate (5.5 g), water (34 mL) and acetone (34 mL) was added and after 135 min an additional amount of sodium periodate (300 mg) and water (5 mL) was added. The reaction was diluted with dichloromethane (100 mL) and stirred for 10 min, then the solids were removed by filtration through a glass sinter funnel and washed with dichloromethane (3 x 100 mL). Layers were separated, aqueous phase was extracted with dichloromethane (100 mL) and then discarded. The combined organic phase was washed with 20% w/v aqueous sodium thiosulfate (50 mL) and saturated aqueous sodium chloride (50 mL), dried over MgS0₄ and concentrated to give the desired product as a thick brown oil (20.6 g). The resultant crude compound was purified using CombiFlash eluting with DCM/EtOAc

Purity by HPLC of the crude compound: 60%

Purity by HPLC after Combiflash purification: Mixture of compound of formula IV and M- 14 impurity (80:20); Title compound was separated from the mixture using preparative SFC.

Claims

1. A process for preparation of methylenetetrahydro-2H-pyran compound of formula II comprising one or more of the following steps:

(a) converting compound of formula III to compound of formula IV,

(b) reacting compound of formula IV with compound of formula V to provide

compound of formula VIb,

wherein Pi is H or an alcohol protecting group; P₂ is H or an alcohol protecting group or -S0₂(R_I); wherein Ri is selected from straight or branched Ci-Cio alkyl or optionally substituted C₅-Ci₂ aryl; X is halogen;

(c) cyclizing compound of formula VIb to provide compound of formula VI,

(d) deprotecting compound of formula VI to provide compound of formula VII,

(e) protecting compound of formula VII to provide compound of formula VIII; and

(f) converting compound of formula VIII to compound of formula II.

2. The process according to claim 1, wherein step (b) is carried out at a temperature of 30-40 DC.

3. The process according to claim 2, wherein step (b) is carried out at a temperature of 35-40 DC.

4. The process according to claim 1, wherein step (c) comprises cyclization of compound of formula VIb using base.

5. The process according to claim 4, wherein the base is l,8-Diazabicyclo[5.4.0]undec- 7-ene (DBU).

6. The process according to claim 4, wherein step (c) is carried out at a temperature of

25-35 DC

7. The process according to claim 6, wherein step (c) is carried out at a temperature of

30-35 DC

8. A process for preparation of compound of formula IV free from one or more impurities, said process comprising;

(a) converting compound of formula III to compound of formula IX,

(b) optionally isolating compound of formula IX,

(d) converting compound of formula IX to compound of formula IV.

9. The process according to claim 8, wherein the pH of the reaction mass obtained from step (a) or step (b) is adjusted to 5.5 to 6.5

10. The process according to claim 8, wherein the impurity is compound of formula X.

11. A process for preparation of methylenetetrahydro-2H-pyran compound of formula Ila comprising:

(a) reacting compound of formula IVa with compound of formula Va to provide compound of formula Via,

wherein Pi and P₃ is H or an alcohol protecting group; P₂ is H or an alcohol protecting group or -S0₂(Ri); wherein Ri is selected from straight or branched Ci-Cio alkyl or optionally substituted C₅-Ci₂ aryl; X is halogen or Triflate (OTf); (b) treating compound of formula Via with a reagent comprising 1,8- Diazabicyclo[5.4.0]undec-7-ene (DBU) to produce compound of formula Ila.

12. Crystalline compound of formula III.

13. Crystalline compound of formula III of claim 12, is characterized by powder X-ray diffraction (PXRD) pattern having peaks at about 6.5 ± 0.2, 9.6 ± 0.2, 13.0 ± 0.2,

15.3 ± 0.2, 17.0 ± 0.2, 19.1 ± 0.2, 19.5 ± 0.2, 21.4 ± 0.2, 22.2 ± 0.2, 23.2 ± 0.2, 24.1 ± 0.2 and 26.1 ± 0.2 degrees 2theta.

14. Crystalline compound of formula II characterized by powder X-ray diffraction (PXRD)

pattern having peaks at about 5.2 ± 0.2, 10.2 ± 0.2, 13.6 ± 0.2, 14.6 ± 0.2, 15.5 ± 0.2, 16.3 ± 0.2, 17.0 ± 0.2, 18.0 ± 0.2, 18.6 ± 0.2 and 20.2 ± 0.2 degrees 2theta.

15. Substantially pure compound of formula II, compound of formula III and compound of formula IV

wherein the purity of compound of formula II, compound of formula III and compound of formula IV is at least 98.5% by HPLC.

16. A process for preparation of eribulin or a pharmaceutically acceptable salt thereof from a compound of any one of claims 12-15.

17. A process for preparation of eribulin or a pharmaceutically acceptable salt thereof from the compound obtained from the process of any one of claims 1-11.