This application claims the benefit of Indian Provisional Application No. 201621019405 filed on 6 ^th June 2016, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an improved process for the solution phase synthesis of an octapeptide, Lanreotide acetate and its key intermediates comprising coupling of suitably protected tetrapeptide fragments A and B, followed by deprotection, oxidation and acetic acid treatment to provide Lanreotide acetate (1) having desired purity.

BACKGROUND OF THE INVENTION

Lanreotide acetate (1), chemically known as [cyclo S-S]-3-(2-naphthyl)-D-alanyl-L- cysteinyl-L-tyrosyl-D-tryptophyl-L-lysyl-L-valyl-L-cysteinyl -L-threoninamide acetate salt (acetic acid ranges from 1.6 to 3.4) is a synthetic, cyclical octapeptide analog of the natural hormone, somatostatin. The amino acid sequence for the octapeptide is represented as follows,

Lanreotide acetate is indicated for long-term treatment of acromegaly and in the treatment of patients with locally advanced or metastatic gastroenteropancreatic neuroendocrine tumors.

Lanreotide acetate, developed by Ipsen with proprietary name Somatulin depot was first approved by USFDA on August 30, 2007 as an injection with strength of 60 mg/0.2 ml and 90 mg/0.3 ml.

Lanreotide acetate was first disclosed in US 4,853,371 wherein the synthetic process comprised treating benzhydryl amine -polystyrene resin (neutralized in the chloride ion form) with Boc-O-benzyl-threonine in presence of diisopropylcarbodiimide and the resulting amino acid resin is then coupled successively with Boc-S-methylbenzyl- Cys, Boc-Val, Boc-Ne-benzyloxycarbonyl-lysine, Boc-D-Trp, Boc-Tyr, Boc-S- methylbenzyl-Cys, and Boc-D-β-naphthylalanine. Further treatment of the resin with anisole, anhydrous hydrogen fluoride and precipitation in ether provided the crude peptide, which when treated with acetic acid, iodine in methanol, followed by HPLC purification and lyophilization provides the desired octapeptide, Lanreotide acetate. Later, EP 389180, WO 8904666 disclosed a similar synthetic process for Lanreotide. However, in these methods, the resultant octapeptide is iodinated using reagents such as Chloramine-T/ sodium iodide; Lactoperoxidase-glucose oxidase (LP-GO)/ sodium iodide; Iodine/ potassium iodide; Iodine monochloride etc. followed by purification using preparative HPLC.

WO 2013098802 discloses a solid phase peptide synthesis of Lanreotide comprising use of resin-bound Thr-amide wherein the resin, Fmoc-Thr(Resin)- NH2 « ^DIPEA Fmoc-Thr-NH2 was subjected to seven cycles of sequential deprotection and coupling steps to give Boc-D-2-Nal-Cys(Acm)-Tyr(Clt)-D-Trp- Lys(Mtt)-Val-Cys(Acm)-Thr(Resin)-NH ₂ which after the deprotection reaction followed by cleavage from the resin and simultaneous iodine oxidation yielded the desired compound.

CN 104497130 discloses a process wherein a combination of solid and liquid phase peptide synthesis methods was used to obtain Lanreotide.

The conventional synthesis of peptides is divided into two major types, solid phase and solution-phase peptide synthesis. Solid phase peptide synthesis methods comprise attachment of a C-terminal amino acid to resin, with a step by step building up of the peptide chain by utilizing pre-activated amino acids. These methods involve use of expensive resins and Fmoc/tert-butyl protected amino acids in three to four fold excess, necessitating complex purification procedures to separate the product from the impurities. These additional steps before isolation render these processes unsuitable for large scale industrial production of the product.

Solution phase synthetic methods for peptides, on the other hand, comprises independent synthesis of amino acids segments or blocks having the desired sequence, followed by condensation of these segments in solution. Such processes are comparatively economical and hence more suited for synthesis on industrial scale.

It is now evident that most of the synthetic methods disclosed in the aforementioned references involve use of expensive resins, costly reagents, elaborate deprotection and separation procedures at various intermediate stages of synthesis. Hence, there is a need for a convenient and economical process which involves utilization of peptide fragments that is developed in a facile manner using specific, selective, easily detachable, bulky protecting groups, as well as mild and selective reagents for coupling and deprotection to achieve the desired conversions. Use of bulky protecting groups gives solid intermediates which are easily isolated from the reaction mixtures and purified using simple techniques. Further, it was found that a combination of different fragment blocks comprising specific protecting groups and liquid phase synthesis leads to reduced formation of associated impurities as compared to prior art methods.

The present inventors have developed an economical and convenient process for solution phase synthesis of Lanreotide acetate (1) which provides the desired molecule in good yield overcoming the problems faced in the prior art. The use of 4+4 strategy comprising synthesis of two tetrapeptide fragments, clubbed with highly specific protection and deprotection methods and a facile condensation of the fragments facilitates in obtaining the desired molecule in fewer synthetic steps with lesser impurity formation, and consequently significant yield improvement as compared to prior art processes. OBJECT OF THE INVENTION

An objective of the present invention is to provide an industrially applicable, convenient process for solution phase synthesis of Lanreotide acetate (1), which avoids use of expensive resins, costly reagents in solid phase peptide synthesis and also lengthy reaction sequences and elaborate protection, deprotection, purification methods.

Another object of the invention relates to a 4+4 solution phase synthesis of Lanreotide acetate comprising mild reagents and facile, moderate reaction conditions for functional group protection and deprotection to provide the desired intermediates and subsequently, Lanreotide with desired purity.

SUMMARY OF THE INVENTION

An aspect of the invention relates to a 4+4 solution phase synthetic process for Lanreotide acetate (1) comprising coupling of two suitably protected tetrapeptide fragments, followed by deprotection, oxidation and acetic acid treatment to give Lanreotide acetate having desired purity. Yet another aspect of the invention relates to synthesis of Lanreotide acetate comprising reaction of tetrapeptide H-Lys(Boc)-Val-Cys(Acm)-Thr-NH ₂ (fragment A) with Boc-D-Nal-Cys(Acm)-Tyr-D-Trp-OH (fragment B) in presence of a suitable coupling agent, a base and in an organic solvent to give the octapeptide, which on subsequent deprotection, oxidation, followed by treatment with acetic acid gives Lanreotide acetate (1) having purity conforming to regulatory specifications.

The objectives of the present invention will become more apparent from the following detailed description. DETAILED DESCRIPTION OF THE INVENTION

While carrying out extensive experimentation aimed at designing a convenient, industrially applicable solution phase synthetic strategy for Lanreotide, the present inventors unexpectedly found that synthesis of two tetrapeptide fragments followed by a facile condensation reaction provided the desired octapeptide, Lanreotide in good yield. The inventors also serendipitously found that most of the intermediates in the said strategy were obtained as solids, due to which various laborious and cumbersome intermediate isolation and purification steps were avoided. This not only ensured notably higher yield for the desired compound but also led to a convenient and economical synthetic process for Lanreotide acetate which could easily be scaled up for commercial production. Further, during the synthesis of tetrapeptide fragment B, the allyl (-CH ₂ -CH=CH ₂ ) protection of the tryptophan carboxyl was easily deprotected by using Palladium (0) catalyst and avoiding use of bases like lithium hydroxide, thus significantly minimizing the problems of racemization which are very commonly observed in the polypeptide solution phase synthesis. The present strategy also comprises utilization of selective and specific, yet labile protecting groups at different stages, which are deprotected using mild acids, that do not adversely affect the chirality of the amino acids and intermediates in the synthetic sequence.

The synthetic process for obtaining Lanreotide acetate (1) is represented in three schemes viz. Scheme- 1 (tetrapeptide fragment A), Scheme-2 (tetrapeptide fragment B) and Scheme-3 (condensation of fragments A and B followed by deprotection and oxidation).

ABBREVIATIONS

Fmoc = Flourenylmethoxycarbonyl

Trt = Triphenyl methyl (Trityl)

Tbu = Tert-butyl

THF = Tetrahydrofuran

DMF = N, N- Dimethylformamide

DMSO = Dimethyl sulfoxide

DMAc = N, N- Dimethylacetamide

NMM = N-methylmorpholine

TEA = Triethylamine

DEA = Diethylamine

Bz = Benzyl

TFA = Trifluoroacetic acid

EDT = Ethanedithiol

TIS = Triisopropylsilane

HOBt = 1-Hydroxybenzotriazole

DCM = Dichloromethane

EDAC= 1 -Ethyl-3-(3-dimethylaminopropyl)carbodiimide HPLC= High performance liquid chromatography TLC = Thin layer chromatography

PTSA= p-toluene sulfonic acid

DTT =Dithiothreitol

MTBE =Methyl tertiary butyl ether

Scheme 2: Method for preparation of Fragment B

Scheme 3: Method for preparation of Lanreotide acetate (1) In an embodiment, L-Threonine amide (2) was coupled with Fmoc-Cys(Acm)-OH (3) in a suitable solvent in presence of a coupling agent and a base such as NMM to give Fmoc-Cys (Acm)-Thr-NH ₂ (4). The coupling reaction was carried out in the temperature range of 0 to 30°C and the solvent was selected from polar aprotic solvents like DMSO, DMF, DMAc etc. After completion, the reaction mass was quenched using mineral acid like hydrochloric acid to precipitate the intermediate (4), which was filtered and optionally treated with water and a hydrocarbon solvent prior to drying. The hydrocarbon solvent was selected from pentane, n-hexane, cyclohexane, heptane, toluene and mixtures thereof.

Compound (4) was treated with a suitable base like TEA in an organic solvent for deprotection of the Fmoc group to afford H-Cys(Acm)-Thr-NH ₂ (5). The solvent was selected from polar aprotic solvents like DMSO, DMF, and DMAc while the reaction was carried out in the temperature range of 0 to 30°C. After completion, the reaction mass was quenched using mineral acid followed by filtration, and extraction of the filtrate with a water immiscible organic solvent. Neutralization of the aqueous layer was followed by extraction with a water immiscible organic solvent which could be same or different from the previous one. Separation of the organic layer and concentration provided compound (5). The water immiscible organic solvent was selected from ethers such as MTBE, diethyl ether, diisopropyl ether, halogenated hydrocarbons such as dichlorome thane, ethylene dichloride and esters such as ethyl acetate, butyl acetate.

Alternatively, compound (2) was coupled with Boc-Cys(Acm)-OH (3A) in an organic solvent in presence of a coupling agent and a base like NMM to give Boc- Cys(Acm)-Thr-NH ₂ (4A). Boc deprotection of (4A) using suitable acids such as trifluoroacetic acid, hydrochloric acid or mixtures of acids in organic solvents like acetonitrile, ethyl acetate or dichloromethane gave H-Cys(Acm)-Thr-NH ₂ , compound (5). Coupling of (5) with Boc-Val-OH (6) in an organic solvent in presence of a coupling agent gave Boc-Val-Cys(Acm)-Thr-NH ₂ (7). The reaction was carried out in the temperature range of 0 to 30°C. After completion, the reaction mass was quenched using mineral acid to precipitate the intermediate, which was filtered and treated with water and a hydrocarbon solvent prior to drying. The hydrocarbon solvent was selected from pentane, n-hexane, cyclohexane, heptane, toluene and mixtures thereof.

Boc deprotection of (7) using suitable acids such as trifluoroacetic acid, hydrochloric acid either singular or in the form of acid mixtures like anhydrous HC1 in acetonitrile or ethyl acetate; or trifluoroacetic acid in an organic solvent such as dichlorome thane afforded H-Val-Cys (Acm)-Thr-NH ₂ (8). The reaction was carried out in temperature range of 0 to 30°C. After completion, concentration of the reaction mixture provided a residue containing compound (8) as its HC1 salt.

Further coupling of compound (8) with Fmoc-Lys(Boc)-OH (9) in an organic solvent selected from DMF, DMSO etc., in presence of a coupling agent and a base such as NMM gave Fmoc-Lys(Boc)-Val-Cys(Acm)-Thr-NH ₂ (10). After completion, the reaction mass was quenched using mineral acid to precipitate the intermediate, which was filtered and treated with water and a hydrocarbon solvent prior to drying. The hydrocarbon solvent was selected from pentane, n-hexane, cyclohexane, heptane, toluene and mixtures thereof.

Compound (10) was further subjected to Fmoc deprotection using a suitable base like DEA, TEA in an organic solvent selected from DMF, DMSO etc., to afford H- Lys(Boc)-Val-Cys(Acm)-Thr-NH ₂ (Fragment A). The reaction was carried out in the temperature range of 20 to 50°C. After completion of the reaction, as monitored by TLC, the reaction mass was quenched with mineral acid such as hydrochloric acid and the resultant mass was filtered. Optional washing with water immiscible solvent selected from ethers like diethyl ether, diisopropyl ether, 1MTBE gave an aqueous layer. Neutralization and extraction of the aqueous layer with a halogenated hydrocarbon like DCM followed by concentration of the organic layer provided Fragment A.

In a further embodiment, D-Tryptophan (H-D-Trp-OH) was treated with allyl alcohol in presence of para toluene sulfonic acid in a hydrocarbon solvent such as toluene. The reaction was carried out between 80 to 100°C. After completion of the reaction as monitored by HPLC, the reaction mass was cooled, and quenched with base like aqueous bicarbonate. Extraction with an organic solvent selected from MTBE, ethyl acetate etc. and concentration of the organic layer provided the desired allyl ester of D-Tryptophan, H-D-Trp-OAll (11).

In yet another embodiment, Boc-Tyr-OH (12) was coupled with H-D-Trp-OAll (11) in presence of a coupling agent and a base such as NMM, and a suitable organic solvent selected from DMF, DMSO, DMAc etc., to give Boc-Tyr-D-Trp-OAll (13). After completion, the reaction mass was quenched using mineral acid like HC1 to precipitate the intermediate, which was washed with aqueous alkali solution, followed by water washing, filtration and drying to give (13).

Boc deprotection of (13) using acid mixtures such as anhydrous HC1 in acetonitrile or ethyl acetate, or trifluoroacetic acid in dichloromethane afforded H-Tyr-D-Trp-OAll (14). The reaction was carried out at ambient temperature using anhydrous HC1 in ethyl acetate and after completion, concentration of the reaction mixture provided a residue containing compound (14) as HC1 salt.

Coupling of (14) with Fmoc-Cys (Acm)-OH (3) using an organic solvent selected from DMF, DMSO, DMAc etc., in presence of a coupling agent and a base like NMM at 0 to 30°C gave Fmoc-Cys(Acm)-Tyr-D-Trp-OAll (15). After completion, the reaction mass was quenched with a mineral acid to precipitate the solid, which was filtered, optionally treated with alkali solution, water and dried to give (15). Fmoc deprotection of (15) in a halogenated hydrocarbon solvent like DCM using a suitable base such as TEA afforded H-Cys(Acm)-Tyr-D-Trp-OAll (16). The reaction was carried out at 0 to 30°C and after completion, quenching with water, followed by separation and concentration of the organic layer gave a residue. Treatment of the residue with hydrocarbon solvent selected from pentane, n-hexane, cyclohexane, heptane, toluene and mixtures thereof, followed by separation of solvent gave compound ( 16) as a solid.

Alternatively, compound (14) was coupled with Boc-Cys(Acm)-OH (3 A) in an organic solvent in presence of a coupling agent and a base like NMM to give Boc- Cys(Acm)-Tyr-D-Trp-OAll (15 A). Boc deprotection of (15A) using suitable acids such as trifluoroacetic acid, hydrochloric acid or mixtures of acids in organic solvents like acetonitrile, ethyl acetate or dichloromethane gave compound (16). Coupling of (16) with Boc-D-Nal-OH (17) in presence of a coupling agent in a suitable organic solvent furnished Boc-D-Nal-Cys (Acm)-Tyr-D-Trp-OAll (18). The solvent was selected from polar aprotic solvents like acetonitrile, DMF, DMSO etc. and the reaction was carried out between 0 to 30°C. After completion, the reaction mass was filtered, quenched with a mineral acid to precipitate the solid intermediate, which was filtered, treated with alkali solution, followed by optional treatment with hydrocarbon solvent selected from pentane, n-hexane, cyclohexane, heptane, toluene and mixtures thereof, Further removal of solvent and drying gave compound (18).

In a further embodiment, allyl deprotection of (18) using the catalyst tetrakis(triphenylphosphine)palladium, morpholine and an organic solvent such as DMSO, DMF or DMAc at 0 to 30°C provided Boc-D-Nal-Cys (Acm)-Tyr-D-Trp- OH (Fragment B). After completion of reaction, filtration, followed by treatment of filtrate with a mineral acid gave a solid which, after filtration, was washed with a hydrocarbon solvent such as toluene, cyclohexane and dried to provide fragment B.

In yet another embodiment, coupling of Fragment A and Fragment B in presence of a coupling agent and a suitable organic solvent like DMF furnished the octapeptide Boc-D-Nal-Cys(Acm)-Tyr-D-Trp-Lys(Boc)-Val-Cys(Acm)-Thr-NH ₂ , which was in- situ subjected to Boc deprotection using acid mixtures such as anhydrous HC1 in acetonitrile or ethyl acetate, or trifluoroacetic acid in dichloromethane to give H-D- Nal-Cys(Acm)-Tyr-D-Trp-Lys-Val-Cys(Acm)-Thr-NH ₂ (19) as an oily residue. After completion of the reaction as monitored by HPLC, the oily product obtained from reaction mass was treated with a mineral acid and the precipitated solid was filtered. Treatment of the solid with a solvent selected from ethers such as MTBE, diethyl ether, diisopropyl ether and mixtures thereof provided compound (19). Compound (19) was dissolved in a halogenated hydrocarbon solvent like dichloromethane and was treated with TFA, in presence of anisole at 0 to 30°C to give (20). After completion, concentration of the reaction mixture gave a residue which was further treated with ether solvent like MTBE to give a solid after filtration. The solid was treated with aqueous acetic acid and iodine in presence of acetonitrile, followed by treatment with L- ascorbic acid to yield Lanreotide acetate (1).

The organic solvents were selected from the group comprising chlorinated hydrocarbons, aprotic solvents, ethers, esters and nitriles. Examples of these solvents are methylene chloride, chloroform, dichloroethane (EDC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), ethyl acetate, N- methyl-2-pyrrolidinone (NMP), acetonitrile, and combinations thereof. The coupling agent was selected from the group comprising substituted carbodiimides such as diisopropylcarbodiimide, dicyclohexylcarbodiimide, 1 -Ethyl - 3-(3-dimethylaminopropyl) carbodiimide (ED AC), BOP(Benzotriazol-l-yloxy- tris(dimethylamino)-phosphonium hexafluorophosphate), PyBOP (Benzotriazol-1- yloxy-tripyrrolidino-phosphonium-hexafluoro phosphate), PyBrOP

(Bromotripyrrolidino phosphonium hexafluorophosphate), PyAOP (7-Aza- benzotriazol-l-yloxy-tripyrrolidinophosphonium hexafluorophosphate), DEPBT (3- (Diethoxyphosphoryloxy)-l,2,3-benzo[d]triazin-4(3H)-one), TBTU (2-(lH- Benzotriazol-l-yl)-N,N,N',N'-tetramethylaminium tetrafluoroborate), HBTU (2-(lH- Benzotriazol-l-yl)-N,N,N',N'-tetramethylaminium hexafluoroborate), HATU (2-(7- Aza-lH-benzotriazol-l-yl)-N,N,N',N' -tetramethylaminium hexafluorophosphate), COMU ( 1 -[ 1 -(Cyano-2-ethoxy-2-oxoethylideneaminooxy)-dimethylamino- morpholino] -uroniumhexafluorophosphate), HCTU (2-(6-Chloro- 1 H-benzotriazol- 1 - yl)-N,N,N',N'-tetramethylaminiumhexafluorophosphate) and TFFH (Tetramethylfluoroformamidinium hexafluorophosphate).

The base was selected from the group comprising diisopropylethylamine (DIEA), N- methylmorpholine (NMM), triethyl amine (TEA), diethyl amine (DEA), piperidine, 1- methyl-2-pyrrolidinone (NMP). The acid employed for deprotection was selected from the group comprising trifluoroacetic acid either neat or in dichloromethane (DCM), hydrogen chloride gas dissolved in ethyl acetate, acetonitrile or dioxane.

The following examples are meant to be illustrative of the present invention. These examples exemplify the invention and are not to be construed as limiting the scope of the invention. EXAMPLES

Example 1: Synthesis of of Fmoc-Cys (Acm)-Thr-NH ₂ (4)

Stirred solution of Fmoc-Cys(Acm)-OH (3, 200 g) in DMF (700 ml) was cooled to 0 to 10°C and HOBt (88.5 g) and L-Threonine amide (2, 57 g), were added to it, followed by addition of EDAC.HCl (138 g) and N-methylmorpholine (53 ml). Reaction mixture was stirred in the temperature range of 0 to 25 °C. After completion of the reaction, as monitored by TLC, the reaction mixture was quenched with dilute hydrochloric acid. The precipitated solid was filtered, optionally treated with water, cyclohexane and dried to give Fmoc-Cys (Acm)-Thr-NH ₂ (4).

Yield : 223 g (90%), Purity: 96% (HPLC)

Example 2: Preparation of Boc-Val-Cys (Acm)-Thr-NH ₂ (7)

Triethylamine (433 ml) was added to the solution of (4, 200 g) in DMF (500 ml) and the reaction mass was stirred between 25 to 45 °C. After completion of the reaction, as monitored by TLC, the reaction mass was quenched by gradually adding IN hydrochloric acid. The mass was filtered and extracted with ethyl acetate. Neutralization of the aqueous layer followed by extraction with ethyl acetate, and separation, concentration of the organic layer gave H-Cys (Acm)-Thr-NH ₂ (5).

The solution of compound (5) in DMF (400 ml) was gradually added to the mixture of Boc-Val-OH (6, 84.5 g) in DMF (200 ml), HOBt (72 g), EDAC.HCl (113 g) under stirring at 0-10 °C. The resulting reaction mass was stirred at 20-35 °C, till completion of reaction, as monitored by TLC. After completion, the mass was quenched using 0.5 N hydrochloric acid with continued stirring. Filtration of the precipitated solid, optional treatment with water, cyclohexane and drying gave Boc- Val-Cys (Acm)-Thr-NH ₂ (7).

Yield : 191 g, (80.7%), Purity :87% (HPLC). Example 3: Preparation of Fmoc-Lys (Boc)-Val-Cys (Acm)-Thr-NH ₂ (10)

Anhydrous HC1 in ethyl acetate (750 ml) was added in to Boc-Val-Cys (Acm)-Thr- NH ₂ (7, 150 g ) and the reaction mixture was stirred between 10-35 °C. After complete deprotection of the Boc group, as monitored by TLC, reaction mass was concentrated to give a crude residue of H-Val-Cys (Acm)-Thr-NH ₂ (8) as its hydrochloride salt.

N-methylmorpholine (41 ml) was added to the mixture of Fmoc-Lys(Boc)-OH (9, 129 g), in DMF (300 ml), HOBT (56 g), EDAC.HC1 (88 g) and the mixture was stirred at 0-10°C. The residue containing (8) as obtained above in DMF (200 ml) was further added to the resulting mass and the reaction mixture was stirred at 20-40°C till completion of reaction, as monitored by TLC. After completion, the reaction mixture was quenched with dilute hydrochloric acid. Filtration of the precipitated solid, optional treatment with water, cyclohexane and drying gave Fmoc-Lys (Boc)- Val-Cys (Acm)-Thr-NH ₂ (10).

Yield : 202 g (88 %), Purity : 84% (HPLC).

Example 4: Preparation of H-Lys (Boc)-Val-Cys (Acm)-Thr-NH ₂ (Fragment A)

Triethylamine (67 ml) was added to the mixture of (10, 50 g) in DMF (300 ml), and the mixture was stirred between 20 to 45°C. After completion of reaction, as monitored by TLC, the reaction mass was quenched by gradual addition of 1.0 N hydrochloric acid. The resulting mass was filtered, optionally washed with MTBE and the aqueous layer was neutralized using sodium bicarbonate. Extraction with DCM and concentration of the organic layer gave H-Lys(Boc)-Val-Cys(Acm)-Thr- NH ₂ (Fragment A) as an oily mass.

Example 5: Preparation of Boc-Tyr-D-Trp-OAll (13)

D-Tryptophan (150 g), and PTSA.FLO (280 g) were added to allyl alcohol (1500 ml) stirred at 25 to 35 °C, followed by addition of toluene (500ml). The resulting mixture was stirred at 80-95 C till completion of reaction, as monitored by TLC. After completion, the mass was cooled, and 5% aqueous sodium bicarbonate solution was added to it. Extraction with ethyl acetate followed by separation and concentration of the organic layer gave a residue containing H-D-Trp-OAll (11). Yield : 162 g, 90 %, Purity : 98% (HPLC)

Boc-Tyr-OH (12, 173 g) was added to the stirred mixture of H-D-Trp-OAll (11.150 g) and DMF (450 ml) at 25 to 35°C, followed by addition of HOBt (104 g). NMM (75 ml) and EDAC.HCl (142 g). The reaction mixture was stirred at 10 to 30°C, till completion, as monitored by TLC. After completion, the reaction mass was quenched with 0.5N HCl. The precipitated solid was filtered, treated with 5% aqueous sodium carbonate solution, filtered again and dried to give Boc-Tyr-D-Trp-OAll (13).

Yield : 280 g, 90%, Purity : 95% (HPLC) Example 6: Preparation of Fmoc-Cys (Acm)-Tyr-D-Trp-OAll (15)

Compound (13, 200 g) was added to the cooled mixture of anhydrous HCl in ethyl acetate (800 ml) under stirring and the reaction mass was stirred at 10 to 30°C till completion of the reaction, as monitored by TLC. After completion, the reaction mixture was concentrated and the obtained solid was dried to give H-Tyr-D-Trp-OAll (14) as its HCl salt.

Compound (14) was dissolved in DMF (600 ml) and Fmoc-Cys(Acm)-OH (3, 163 g), HOBT (73 g), NMM (44 ml)) were added to the mixture stirred at 25 to 30°C. EDAC.HCl (98 g) was then added to the reaction mixture and stirring was continued at 25 to 30°C till completion of the reaction, as monitored by TLC. After completion, the reaction mixture was added to the cooled solution of 0.5M hydrochloric acid and stirred at 0 to 5°C. The solid was filtered, treated with 5% aqueous sodium carbonate solution followed by water washing and drying to give Fmoc-Cys (Acm)-Tyr-D-Trp- OA11.

Yield : 285 g, (88 %), Purity: 92% (HPLC) Example 7: Preparation of Boc-D-Nal-Cys (Acm)-Tyr-D-Trp-OAll (18)

Triethylamine (277 ml) was added to the mixture of (15, 200 g) in DCM (2000 ml) and the reaction mass was stirred at 20 to 30°C till completion of the reaction, as monitored by TLC. After completion, the reaction mass was quenched with water and the organic layer was separated. Concentration of the organic layer, followed by treatment of resultant solid with toluene: cyclohexane mixture gave H-Cys (Acm)- Tyr-D-Trp-OAll (16).

Boc-D-Nal-OH (17, 70 g) was added to the stirred mixture of compound 16 as obtained above in DMF (600 ml) at 20-30°C, followed by addition of HOBT (46 g). EDAC.HCl (72 g ) was then added to the reaction mixture and stirring was continued at 0 to 30°C till completion of the reaction, as monitored by TLC. After completion, the reaction mixture was filtered, added to the cooled solution of 0.5M hydrochloric acid and stirred at 0 to 5°C. The solid was filtered, treated with 5% aqueous sodium carbonate solution, optionally treated with toluene: cyclohexane (30:70) mixture and dried to give Boc-D-Nal-Cys ( Acm)-Tyr-D-Trp-OAll (18).

Yield: 164 g, (75%), Purity: 82% (HPLC)

Example 8: Preparation of Boc-D-Nal-Cys (Acm)-Tyr-D-Trp-OH (Fragment B)

Morpholine (45 g) and tetrakis (triphenylphosphine)palladium. (6.5g) were added to the mixture of (18, 100 g) in DMSO (400 ml). The reaction mixture was stirred at 15 to 30°C, till completion of the reaction, as monitored by TLC. After completion, the reaction mass was filtered and quenched with dilute hydrochloric acid. The obtained solid was filtered, and the wet cake was treated with water, followed by treatment with toluene: cyclohexane mixture. The solid so obtained was optionally treated with cyclohexane and dried to give Boc-D-Nal-Cys (Acm)-Tyr-D-Trp-OH (Fragment B). Yield: 76.0 g (80%), Purity: 88% (HPLC) Example 9: Preparation of Boc-D-Nal-Cys (Acm)-Tyr-D-Trp-Lys (Boc)-Val- Cys (Acm)-Thr-NH ₂ (19)

The mixture of Fragment A as obtained in example 4 in DMF (250 ml) was stirred at 0 -10°C and HOBt (l lg), EDAC.HC1 (17 g), were added to it with continued stirring. Fragment B (50 g) was added to the mixture and stirring was continued at 10-30°C till completion of the reaction, as monitored by TLC. After completion of the reaction, the mass was cooled to 0 to 5°C and quenched with DM water (50 vol) (The stirring was continued at 15-25°C and the precipitated solid was filtered The wet cake was washed with 5% dil. hydrochloric acid and then with 5% sodium bicarbonate solution to give the octapeptide, Boc-D-Nal-Cys (Acm)-Tyr-D-Trp-Lys (Boc)-Val- Cys (Acm)-Thr-NH ₂ (19).

Yield: 64.0 g (75%), Purity: 80% (HPLC)

Example 10: Preparation of Lanreotide acetate (1)

The mixture of (19, 55 g) in DCM (360 ml) was stirred and TFA (360 ml) was added to it. Reaction mass was stirred for 3 hrs at 25 to 30°C till completion of the reaction, as monitored by TLC. After completion, reaction mass was concentrated and the oily mass was precipitated using MTBE and filtered to give H-D-Nal-Cys (Acm)-Tyr-D- Trp-Lys-Val-Cys (Acm)-Thr-NH ₂ (20).

A mixture of acetic acid (60 ml), water (23.75 lit.) was added to the solution of compound 20 in 50% acetonitrile: water (2500 ml) which was stirred at 15-30°C, followed by addition of iodine (12.7 g) in methanol (290 ml). The stirring was continued till completion of the reaction, as monitored by HPLC. After completion, L-ascorbic acid (9.5 g) was added to the mixture. The resultant mass was filtered and purified using preparative HPLC to give Lanreotide acetate (1). Yield : 12 g ( 30 %), Purity : > 99 (HPLC)