Method for preparation of peptides with psWang linker

Abstract

The invention discloses a method for the preparation of a peptide by liquid phase coupling of two fragments, an N-terminal fragment and a C-terminal fragment of the desired peptide, wherein the C-terminal fragment is protected on its C-terminal COOH by a psWang linker; the method is demonstrated with liraglutide wherein the C-terminal fragment carries the Palmitoyl-Glu-OtBu residue on the Lys.

Claims

1. A method for the preparation of a peptide (PEP) which comprises a coupling in liquid phase of two peptide fragments, an N-terminal fragment (FRAG1) of peptide (PEP) and a C-terminal fragment (FRAG2) of peptide (PEP); wherein the C-terminal COOH of the C-terminal fragment (FRAG2) is protected by a psWang residue; the psWang residue is a residue of formula (psWang); ##STR00018## wherein (*) denotes the covalent bond to the C atom of the CO residue of the C-terminal COOH of the C-terminal fragment (FRAG2); R1, R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of H, C.sub.1-4 alkyl, C.sub.1-4 alkoxy, CN, F, Cl and Br; R5 and R6 are identical or different and are, independent from each other, H or C.sub.1-4 alkyl; m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10; wherein the C-terminal fragment (FRAG2) is prepared by a solid phase peptide synthesis (SPPS); wherein the psWang linker or the psWang residue respectively is connected to a first resin used for the solid phase peptide synthesis (SPPS) by an ether bond (ETHBOND2); wherein the ether bond (ETHBOND2) is cleavable under weakly acidic conditions using trifluoroacetic acid (TFA), trifluoroethanol (TFE), or hexafluoroisopropanol (HFIP); and wherein the first resin is selected from the group consisting of a chlorotritykhloride ##STR00019## (CTC) resin, a Rink acid resin a SASRIN resin ##STR00020## a resin modified with 5-(4-hydroxymethyl-3,5-dimethoxyphenoxy)valeric acid (HAL), and a resin modified with 4-(4-hydroxymethyl-3-methoxyphenoxy)butyric acid (HMPB); wherein the Rink acid resin, the SASRIN resin, the resin modified with HAL, and the resin modified with HMPB are used in the chlorinated form.

2. The method according to claim 1, wherein R1, R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of H, C.sub.1-2 alkyl, C.sub.1-2 alkoxy and Cl; and R5 and R6 are identical or different and are independently from each other H or C.sub.1-2 alkyl.

3. The method according to claim 1, wherein m is 0, 1, 2, 3 or 4.

4. The method according to claim 1, wherein m is 0 and R1, R2, R3, R4, R5 and R6 are H.

5. The method according to claim 1, wherein the N-terminal NH.sub.2 of the N-terminal fragment (FRAG1) is protected by a protecting group (PROTGN) during the coupling of the N-terminal fragment (FRAG1) and the C-terminal fragment (FRAG2).

6. The method according to claim 1, wherein any amino acid residue of the N-terminal fragment (FRAG1) and the C-terminal fragment (FRAG2), that can be used in a side chain protected form, is used in a side chain protected form.

7. The method according to claim 1, wherein the N-terminal fragment (FRAG1) is prepared by solid phase peptide synthesis (SPPS) using a second resin.

8. The method according to claim 7, wherein the C-terminal amino acid of the N-terminal fragment (FRAG1) is connected to the second resin used for the solid phase peptide synthesis (SPPS) with an ester bond (ESTBOND1).

9. The method according to claim 8, wherein the ester bond (ESTBOND1) is cleaved under weakly acidic conditions using trifluoroacetic acid (TFA), trifluoroethanol (TFE), or hexafluoroisopropanol (HFIP).

10. The method according to claim 8, further comprising cleaving the ester bond (ESTBOND1) under weakly acidic conditions using trifluoroacetic acid (TFA), trifluoroethanol (TFE), or hexafluoroisopropanol (HFIP).

11. The method according to claim 10, wherein the ester bond (ESTBOND1) is cleaved under weakly acidic conditions using a mixture of from 0.01 to 25% trifluoroacetic acid (TFA) in a solvent which is inert against the trifluoroacetic acid (TFA).

12. The method according to claim 1, wherein the first resin is a chlorotritylchloride (CTC resin).

13. The method according to claim 1, wherein the N-terminal fragment (FRAG1) and the C-terminal fragment (FRAG2) are prepared by solid phase peptide synthesis (SPPS) using Fmoc/tBu strategy.

14. The method according to claim 1, wherein peptide (PEP) is liraglutide, and the (*) in formula (psWang) denotes the covalent bond to the C atom of the CO residue of Gly.sup.(31) of liraglutide.

15. The method according to claim 1, wherein the N-terminal fragment (FRAG1) is) Boc-H.sup.(1) AEGT.sup.(5) FTSDV.sup.(10) SSYLE.sup.(15) G.sup.(16)-OH (SEQ ID NO: 1); and the C-terminal fragment (FRAG2) is H-Q.sup.(17) AAK.sup.(20) (Palmitoyl-Glu-OtBu)EFIAW.sup.(25) LVRGR.sup.(30) G.sup.(31)-psWang (SEQ ID NO: 2).

16. The method according to claim 15, wherein the Palmitoyl-Glu-OtBu residue on the N.sup.6 of the Lys.sup.(20) of the C-terminal fragment (FRAG2) is a residue of formula (PALGLU), ##STR00021## with the (**) in formula (PALGLU) denoting the covalent bond between the COOH of the side chain of the Glu and the N.sup.6 of the Lys.sup.(20), and the Palmitoyl-Glu-OtBu residue is covalently bonded to the Lys.sup.(20) in a reaction (REACPALGLU), wherein the NH.sub.2 of the side chain of the Lys is reacted with a precursor of the residue of formula (PALGLU); reaction (REACPALGLU) is done before the C-terminal fragment (FRAG2) is cleaved from the first resin.

17. The method according to claim 16, wherein the precursor of the residue of formula (PALGLU) is a compound of formula (10); ##STR00022## with SuccO being a residue of formula (SuccO); ##STR00023## wherein the (***) denotes the covalent bond to the CO residue in the compound of formula (10).

18. The method according to claim 16, wherein the reaction (REACPALGLU) is done after the coupling of Ala.sup.(19) or after the coupling of Ala.sup.(18), and before removal of the protecting group of the alpha NH.sub.2 of Ala.sup.(19 or of Ala.sup.(18) respectively.

19. The method according to claim 1, further comprising cleaving the ether bond (ETHBOND2) under weakly acidic conditions using trifluoroacetic acid (TFA), trifluoroethanol (TFE), or hexafluoroisopropanol (HFIP).

20. The method according to claim 19, wherein the ether bond (ETHBOND2) is cleaved under weakly acidic conditions using a mixture of from 0.01 to 25% trifluoroacetic acid (TFA) in a solvent which is inert against the trifluoroacetic acid (TFA).

21. The method according to claim 19, wherein the method comprises two steps, a step STEP1 and a step STEP2; wherein step STEP1 comprises the coupling of the N-terminal fragment (FRAG1) and the C-terminal fragment (FRAG2) by liquid phase peptide synthesis; wherein step STEP1 provides a peptide (PEP-psWang); wherein step STEP2 comprises cleavage of psWang from the peptide (PEP-psWang) obtained in step STEP1.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Preferably, R1, R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of H, C.sub.1-2 alkyl, C.sub.1-2 alkoxy and Cl; and

(2) R5 and R6 are identical or different and are independently from each other H or C.sub.1-2 alkyl. More preferably, R1, R2, R3 and R4 are identical or different and independently from each other selected from the group consisting of H, methyl, methoxy and Cl; and

(3) R5 and R6 are identical or different and are independently from each other H or methyl. Even more preferably at least two of the substituents R1, R2, R3 and R4 are H.

(4) In particular, at least three of the substituents R1, R2, R3 and R4 are H. More particularly, R5 and R6 are H. Even more particularly, R1, R2, R3, R4, R5 and R6 are H.

(5) Preferably, in case that m is not 0 then at least one of the substituents R1, R2, R3 and R4 is C.sub.1-4 alkoxy, more preferably C.sub.1-2 alkoxy, even more preferably methoxy.

(6) In another preferred embodiment, in case that m is not 0 then R5 and R6 are not H.

(7) Preferably, m is 0, 1, 2, 3 or 4; more preferably, m is 0, 1 or 2; most preferably, m is 0.

(8) In particular, m is 0 and R1, R2, R3, R4, R5 and R6 are H, thereby the psWang residue is the p-hydroxymethylphenol residue, the residue of formula (psWang-1);

(9) ##STR00005##
wherein the (*) denotes the covalent bond to the C atom of the CO residue of C-terminal COOH of FRAG 2.
The psWang residue is derived from the unconnected psWang linker, which is compound of formula (psWangLINK);

(10) ##STR00006##
with m, R1, R2, R3, R4, R5 and R6 as defined herein, also with all their embodiments.

(11) Preferably, FRAG2 is prepared by SPPS. Preferably, FRAG2 is prepared by SPPS using Fmoc protocol, that is Fmoc protection of the alpha amino residues of the amino acid building blocks. More preferably, FRAG2 is prepared by SPPS wherein the C-terminal amino acid residue is covalently connected to the psWang residue, and the psWang residue is covalently connected to the resin used for the SPPS. Even more preferably, FRAG2 is prepared by SPPS wherein the alpha COOH of the C-terminal amino acid residue is covalently connected to the psWang residue, and the psWang residue is covalently connected to the resin used for the SPPS. Preferably, FRAG2 is prepared by SPPS on a resin used for the SPPS loaded with the psWang linker. Preferably, the psWang linker or the psWang residue respectively is connected to the resin used for the SPPS by an ether bond ETHBOND2; so the resin used for the SPPS of FRAG2 is a resin that allows to connect the psWang linker or the psWang residue respectively to the resin by ETHBOND2.

(12) Especially, FRAG2 is prepared by SPPS on a resin loaded with the psWang linker by firstly covalently bonding the psWang linker onto the resin by ETHBOND2, this is done by an etherification reaction ETHERREAC forming ETHBOND2. Thereafter preferably the C-terminal AA of FRAG2 is covalently bonded to the psWang linker that is on the resin, this is done by an esterification reaction, thereafter the other AA are coupled by SPPS onto the C-terminal AA and then onto the growing peptide chain respectively.

(13) Preferably, ETHBOND2 is cleavable under weakly acidic conditions, with the weakly acidic conditions as described herein; so the resin used for the SPPS of FRAG2 is a resin, that allows ETHBOND2 to be cleaved under weakly acidic conditions.

(14) Preferably, ETHERREAC is done in the presence of a base. Suitable bases are for example trialkylamines, like N,N-diisopropylethylamine (DIPEA) or triethylamine (TEA); N,N-dialkylanilines, like N,N-diethylaniline; 2,4,6-trialkylpyridines, like 2,4,6-trimethylpyridine; and N-alkylmorpholines, like N-methylmorpholine.

(15) Preferably, ETHERREAC is done in the presence of DIPEA as a base.

(16) Preferably, the molar amount of base is from 1 to 10 times of the molar loading capacity of the resin.

(17) Preferably, ETHERREAC can be done in any inert solvent which can dissolve the reactants. Preferred solvents for the coupling are water-miscible solvents like dimethyl sulfoxide (DMSO), dioxane, tetrahydrofurans such as tetrahydrofurane (THF) or methyltetrahydrofurane (Methyl-THF), 1-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), or any mixture thereof; and non water-miscible solvents like dichloromethane (DCM), ethyl acetate or any mixture thereof; and any suitable mixture between water-miscible and non water-miscible solvents, including mixtures with water.

(18) More preferably, ETHERREAC is done in a solvent selected from the group consisting of DMSO, dichloromethane, Me-THF, DMF, NMP, and mixtures thereof.

(19) Preferably, the ETHERREAC is done at atmospheric pressure. Preferably, the reaction temperature of the ETHERREAC is from −20 to 70° C.; more preferably from −5 and 40° C., even more preferably from 0 to 35° C.

(20) Preferably, the reaction time of the ETHERREAC is from 30 min to 12 h, more preferably from 30 min to 6 h, even more preferably from 30 min to 4 h.

(21) The covalent bonding during SPPS of the alpha COOH of the C-terminal AA of FRAG2 to the psWang, and the covalent bonding of the psWang residue to the resin, are shown in formula (FRAG2-psWang-RESIN).

(22) ##STR00007##
wherein
the (*) denotes the covalent bond to the C atom of the CO residue of the alpha COOH of the C-terminal AA of FRAG2;
the (****) denotes the covalent bond to the resin, preferably ETHBOND2;
with m, R1, R2, R3, R4, R5 and R6 as defined herein, also with all their embodiments.

(23) Preferably, the method comprises two steps, a step STEP1 and a step STEP2; STEP1 comprises the coupling of FRAG1 and FRAG2 by liquid phase peptide synthesis; STEP 1 provides a peptide PEP-psWang; STEP2 comprises cleavage of psWang from PEP-psWang obtained in STEP. Preferably, STEP2 provides PEP.

(24) Preferably, FRAG1 and FRAG2 independently from each other have up to 250, more preferably up to 200, even more preferably up to 150, especially up to 100, more especially up to 75, even more especially up to 50, in particular up to 30, more in particular up to 20, amino acid residues. Preferably, FRAG1 and FRAG2 independently from each other have at least 2, 3, 4 or 5 amino acid residues. Any of the possible minimum number of amino acid residues can be combined with any of the possible maximum number of amino acid residues of FRAG1 and FRAG2.

(25) Preferably, the N-terminal NH.sub.2 of FRAG1 is protected by a protecting group PROTGN during the coupling of FRAG 1 and FRAG2. PROTGN can be any protecting group suitable for protecting the N-terminal NH.sub.2 of FRAG 1. Commonly used PROTGN include protecting groups such as Boc, Fmoc, acetyl, Z or Trt. More preferably, PROTGN is Boc. Preferably, STEP 1 provides the peptide PROTGN-PEP-psWang.

(26) Preferably,

(27) FRAG1 is

(28) ##STR00008##
and
FRAG2 is

(29) ##STR00009##
p1 is an integer from 2 to 50 and denotes the total number of amino acid residues of FRAG1;
p2 is an integer from 2 to 50 and denotes the total number of amino acid residues of FRAG2;
n1 is an integer from 1 to p1 and denotes the amino acid residue in position n1 of FRAG1;
n2 is an integer from 1 to p2 and denotes the amino acid residue in position n2 of FRAG2;
AA.sup.(n1) and AA.sup.(n2) are the amino acid residues of FRAG1 and of FRAG2 on position n1 and on position n2 respectively, and are identical or different and independently from each other alpha amino acid residues.
Preferably,

(30) p1 is an integer from 2 to 30;

(31) p2 is an integer from 2 to 30;

(32) more preferably,

(33) p1 is an integer from 2 to 20;

(34) p2 is an integer from 2 to 20.

(35) Preferably, the amino acid residue of FRAG1 and FRAG2 are alpha amino acids residues which occur in natural peptides or in natural proteins. More preferably, the amino acid residue of FRAG1 and FRAG2 are selected from the group consisting of Ala, Arg, Asn, Asp, Cys, Glu, Gln, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr and Val. Preferably, any amino acid residue of FRAG1 and FRAG2, that can be used in a side chain protected form, is used in a side chain protected form.

(36) In case of side chain protected amino acid residue of FRAG1 and FRAG2, STEP1 provides side chain protected PEP-psWang.

(37) Preferably, amino acid residues of FRAG1 and FRAG2, that can be used in a side chain protected form and that are side chain protected in STEP 1, are selected from the group consisting of Arg, Asn, Asp, Cys, Glu, Gln, His, Lys, Ser, Thr, Trp and Tyr.

(38) The side chain protection of the side chains of the amino acid residues of FRAG1 and FRAG2 is preferably realized in form of side chain protection groups which are not cleavable under weakly acidic conditions, with the weakly acidic conditions as described herein.

(39) Preferably, side chain protection of Cys is Trt or Acm. Preferably, side chain protection of Asn and Gln is Trt. Preferably, side chain protection of His is Trt or Dnp. Preferably, side chain protection of Glu and Asp is OtBu. Preferably, side chain protection of Thr, Ser and Tyr is tBu. Preferably, side chain protection of Trp is Boc. Preferably, side chain protection of Arg is Pbf, Pmc, Mtr or MIS. Preferably, side chain protection of Lys is Alloc, Z or Boc.

(40) More preferably, side chain protection of Cys, Asn, His and Gln is Trt; side chain protection of Glu and Asp is OtBu; side chain protection of Thr, Ser and Tyr is tBu; side chain protection of Trp is Boc; side chain protection of Arg is Pbf; side chain protection of Lys is Alloc.

(41) Val and Ser, when they occur in the sequence of FRAG1 or of FRAG2 on adjacent positions as Val.sup.(n1) and Ser.sup.(n1+1) or as Val.sup.(n2) and Ser.sup.(n2+1) respectively, can also be used in the protected form of a pseudoproline Val-Ser[Psi.sup.(Me,Me)Pro]-OH.

(42) Also other possible pseudoprolines can be used, depending on the sequence of FRAG1 and FRAG2.

(43) Cleavage of any PROTGN and of psWang, and the cleavage of any side chain protecting group, also the cleavage of the tBu protecting group on the alpha COOH of the Glu of the Palmitoyl-Glu-OtBu residue, can be done separately or simultaneously. The cleavage is preferably done in STEP2. When the cleavage is done simultaneously, then the cleavage is usually called global deprotection.

(44) The conditions of such cleavage reactions are known to the skilled person and are dependent on the nature of protecting group. Many protecting groups require acidic conditions for cleavage, preferably strongly acidic conditions, with the strongly acidic conditions as defined herein, other protecting groups such as Z require cleavage by catalytic hydrogenation. Strongly acidic conditions means, in the context if this invention, using for cleavage a mixture of from 50 to 100%, preferably from 60 to 100%, more preferably from 70 to 100%, even more preferably from 80 to 100%, of TFA with a component COMPSTRONG, the % are vol-% and are being based on the total volume of the mixture of TFA and COMPSTRONG. Therefore, TFA can also be used neat. Preferably, COMPSTRONG is selected from the group consisting of SOLVSTRONG, phenol, water, TIS and a mixture thereof; SOLVSTRONG is solvent that is inert against TFA. Preferably, SOLVSTRONG is DCM. More preferably, COMPSTRONG is a mixture of phenol and TIS or a mixture of phenol, water and TIS.

(45) Preferably, the volume ratios of a mixture TFA:water:TIS are

(46) TFA: from 80 to 98;

(47) water: from 1 to 10;

(48) TIS: from 1 to 10;

(49) the individual volume ratios of the three components adding up to 100.

(50) Preferably, the volume ratios of a mixture TFA:phenol:water:TIS are

(51) TFA: from 70 to 97;

(52) phenol: from 1 to 10;

(53) water: from 1 to 10;

(54) TIS: from 1 to 10;

(55) the individual volume ratios of the four components adding up to 100.

(56) Preferably, the total amount of the mixture is from 5 to 20 ml per g of protected peptide.

(57) Preferably, the cleavage is done at atmospheric pressure.

(58) Preferably, the reaction temperature of the cleavage is from −20 to 70° C.; more preferably from −15 and 40° C., even more preferably from −15 to 35° C.

(59) Preferably, the reaction time of the cleavage is from 30 min to 12 h, more preferably from 30 min to 6 h, even more preferably from 30 min to 4 h.

(60) Any SPPS can be done on any conventional resin. Preferably, the resin for the SPPS of FRAG2 is a resin that allows to connect the psWang linker covalently to the resin with an ETHBOND2; more preferably, with an ETHBOND2 that is cleavable under weakly acidic conditions, with the weakly acidic conditions as defined herein.

(61) Preferably, FRAG1 is prepared by SPPS.

(62) Preferably, FRAG1 is prepared by SPPS using Fmoc protocol, that is, Fmoc protection of the alpha amino residues of the amino acid building blocks.

(63) Preferably, the C-terminal amino acid of FRAG1 is connected to the resin used for the SPPS with an ester bond ESTBOND1; so the resin used for the SPPS of FRAG1 is a resin that allows to connect the C-terminal amino acid of FRAG1 to the resin with ESTBOND1.

(64) Preferably, ESTBOND1 is cleavable under weakly acidic conditions, with the weakly acidic conditions as defined herein.

(65) Preferably, the alpha COOH of the C-terminal AA of FRAG1 is covalently connected to the resin used for the SPPS.

(66) Resins used for SPPS, that allow to connect covalently to the resin the psWang linker with an ETHBOND2 or the C-terminal amino acid of FRAG1 with an ESTBOND1 respectively, that are cleavable under weakly acidic conditions, with the weakly acidic conditions as defined herein, are for example CTC resin, Rink acid resin, SASRIN resin, resin modified with HAL and resin modified with HMPB.

(67) Preferably, SPPS is done on a resin selected from the group consisting of CTC resin, Rink acid resin, SASRIN resin, resin modified with HAL and resin modified with HMPB; wherein the Rink acid resin, the SASRIN resin, the resin modified with HAL and the resin modified with HMPB are used in their chlorinated or brominated form. Chlorinated and brominated form means that the reactive OH of the resins or of the HAL or of the HMPB, respectively, onto which the psWang or the AA is coupled, is exchanged against a Cl or a Br. Preferably, SPPS is done on a CTC resin.

(68) More preferably, FRAG1 and FRAG2 are prepared by SPPS on a CTC resin.

(69) Even more preferably, FRAG2 is prepared by SPPS on a CTC resin that has been loaded with the psWang linker prior to the coupling of the C-terminal AA to the CTC resin.

(70) Preferably, the resins used in the SPPS show a loading capacity of from 0.5 to 2 mmol of reactive sites per g resin.

(71) Preferably, any SPPS is done by stepwise coupling of the individual amino acids.

(72) Preferably, FRAG1 and FRAG2 are prepared by SPPS using Fmoc/tBu strategy; with Fmoc as protecting group for the alpha NH.sub.2 of the amino acids used in the SPPS; more preferably except for the N-terminal amino acid of FRAG 1, where the alpha NH.sub.2 is protected with PROTGN.

(73) Weakly acidic conditions means, in the context if this invention, using for cleavage a mixture of from 0.01 to 25%, preferably from 0.01 to 15%, more preferably from 0.05 to 10%, even more preferably from 0.1 to 7.5%, TFA in a solvent SOLVWEAK, the % are vol-% and are being based on the total volume of the mixture of TFA and SOLVWEAK. SOLVWEAK is any solvent which is inert against TFA. Preferably SOLVWEAK is DCM, methyl THF or a mixture thereof. Preferably, the total amount of the mixture is from 5 to 20 ml per g of protected peptide. Preferably, the cleavage is done at atmospheric pressure.

(74) Preferably, the reaction temperature of the cleavage is from −20 to 70° C.; more preferably from −15 and 40° C., even more preferably from −15 to 35° C.

(75) Preferably, the reaction time of the cleavage is from 5 min to 12 h, more preferably from 5 min to 6 h, even more preferably from 10 min to 4 h.

(76) Cleavage under weakly acidic conditions can also be done using TFE or HFIP instead of TFA. Preferably, ESTBOND1 and ETHBOND2 are cleaved under weakly acidic conditions.

(77) In one embodiment, PEP is liraglutide, and the (*) in formula (psWang) denotes the covalent bond to the C atom of the CO residue of Gly.sup.(31) of liraglutide; also with all the embodiments described herein.

(78) Preferably,

(79) FRAG1 is Boc-H.sup.(1) AEGT.sup.(5) FTSDV.sup.(10) SSYLE.sup.(15) G.sup.(16)-OH (SEQ ID NO: 1); and

(80) FRAG2 is H-Q.sup.(17) AAK.sup.(20) (Palmitoyl-Glu-OtBu)EFIAW.sup.(25) LVRGR.sup.(30) G.sup.(31)-psWang (SEQ ID NO: 2).

(81) FRAG1 can also be depicted as Boc-[1-16]-OH or as compound of formula (I).
Boc-H-[2-15]-G-OH  (I)
FRAG2 can also be depicted as H-[17-31]-psWang or as compound of formula (II);

(82) ##STR00010##
with m, R1, R2, R3, R4, R5 and R6 as defined herein, also with all their embodiments. Liraglutide with psWang protection on the C-terminal COOH can also be depicted as compound of formula (III);

(83) ##STR00011##
with m, R1, R2, R3, R4, R5 and R6 as defined herein, also with all their embodiments.

(84) Preferably, Val.sup.(10) and Ser.sup.(11) are present in FRAG1 of liraglutide in form of a pseudoproline Val.sup.(10)-Ser.sup.(11) (psi.sup.Me,MePro).

(85) More preferably, FRAG1 has the sequence Boc-His.sup.(1) (Trt)-Ala-Glu(OtBu)-Gly-Thr.sup.(5) (tBu)-Phe-Thr(tBu)-Ser(tBu)-Asp(OtBu)-[Val.sup.(10)-Ser(psi.sup.Me,MePro)]-Ser(tBu)-Tyr(tBu)-Leu-Glu.sup.(15) (OtBu)-Gly.sup.(16)-OH(SEQ ID NO: 1), and is also called protected fragment 1.

(86) More preferably, FRAG2 has the sequence H-Gln.sup.(17) (Trt)-Ala-Ala-Lys.sup.(20) (Palmitoyl-Glu-OtBu)-Glu(OtBu)-Phe-Ile-Ala-Trp.sup.(25) (Boc)-Leu-Val-Arg(Pbf)-Gly-Arg.sup.(30) (Pbf)-Gly-psWang (SEQ ID NO: 2), and is also called protected fragment 2.

(87) In case of liraglutide, preferably, Val.sup.(10) and Ser.sup.(11) are used in the SPPS of FRAG1 in form of pseudoproline Fmoc-Val-Ser[Psi.sup.(Me,Me)Pro]-OH.

(88) Preferably, the Palmitoyl-Glu-OtBu residue on the N.sup.6 of the Lys.sup.(20) of FRAG2 is the residue of formula (PALGLU),

(89) ##STR00012##

(90) with the (**) in formula (PALGLU) denoting the covalent bond between the COOH of the side chain of the Glu and the N.sup.6 of the Lys.sup.(20), and the Palmitoyl-Glu-OtBu residue is covalently bonded to the Lys.sup.(20) in a reaction REACPALGLU, wherein the NH.sub.2 of the side chain of the Lys is reacted with a precursor of the residue of formula (PALGLU); preferably, REACPALGLU is done before FRAG2 is cleaved from the resin.

(91) So REACPALGLU is done on-resin, that is REACPALGLU is done while FRAG2 or a precursor of FRAG2 is still covalently bonded to the resin. Preferably, the precursor of the residue of formula (PALGLU) is Pal-Glu(OSu)-OtBu, that is compound of formula (10);

(92) ##STR00013##
with SuccO being residue of formula (SuccO);

(93) ##STR00014##
wherein the (***) denotes the covalent bond to the CO residue in compound of formula (10).

(94) Preferably, REACPALGLU is done after the coupling of Ala.sup.(19) or after the coupling of Ala.sup.(18), and before removal of the protecting group of the alpha NH.sub.2 of Ala.sup.(19) or of Ala.sup.(18) respectively, preferably after the coupling of Ala.sup.(18).

(95) Preferably, any protecting group of the side chain of Lys.sup.(20) is cleaved before REACPALGLU.

(96) In case of liraglutide, preferably, Lys.sup.(20) is used in the SPPS of FRAG2 in form of Fmoc-Lys(Alloc)-OH; so the side chain protecting group of Lys.sup.(20), which is cleaved before REACPALGLU, is preferably Alloc. Preferably, cleavage of Alloc from the Lys.sup.(20) is done with a reaction CLEAVALLOC using Pd(PPh.sub.3).sub.4 and PhSiH. CLEAVALLOC can be done in the presence of an additive ADDALLOC, ADDALLOC is selected from the group consisting of morpholine, 1,3-dimethylbarbituric acid, pyrrolidine, triphenylphosphine, dimedone, and mixtures thereof. Preferably, the molar amount of ADDALLOC is from 2 to 7 times of the molar amount of the Alloc residue. Preferably, the molar amount of Pd(PPh.sub.3).sub.4 is from 0.01 to 10 times, more preferably from 0.02 to 5 times, even more preferably from 0.05 to 2 times, of the molar loading capacity of the resin.

(97) Preferably, the molar amount of PhSiH is from 1 to 30 times, more preferably from 2 to 20 times, even more preferably from 5 to 15 times, of the molar loading capacity of the resin.

(98) Preferably, CLEAVALLOC is done in a solvent selected from the group consisting of DMSO, dichloromethane, Me-THF, DMF, NMP, and mixtures thereof, more preferably the solvent is DCM. Preferably, CLEAVALLOC is done at atmospheric pressure. Preferably, the reaction temperature of CLEAVALLOC is from −20 to 70° C.; more preferably from −15 and 60° C., even more preferably from 5 to 35° C. Preferably, the reaction time of CLEAVALLOC is from 1 min to 2 h.

(99) Preferably, any coupling is for the ease of reading also called COUPL, such as a SPPS coupling reaction or such as the LPPS coupling reaction of FRAG1 and FRAG2, and can be carried out using reaction conditions known in the art of peptide synthesis.

(100) Preferably, coupling reagents, which can be used for COUPL and which are used in situ, are for example phoshonium or uronium coupling reagents, like benzotriazol-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP), benzotriazol-1-yloxy-tris(pyrrolidino)phosphonium hexafluorophosphate (PyBOP), O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU), O-(6-chlorobenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HCTU), O-(6-chlorobenzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TCTU), O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HATU), O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TATU), O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU), O-[cyano(ethoxycarbonyl)methylenamino]-1,1,3,3-tetramethyluronium tetrafluoroborate (TOTU) and (1-cyano-2-ethoxy-2-oxoethylidenaminooxy)dimethylamino-morpholino-carbenium hexafluorophosphate (COMU); or carbodiimide coupling reagents, like diisopropylcarbodiimide (DIC), dicyclohexylcarbodiimide (DCC) and water-soluble carbodiimides (WSCDI) like 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), optionally as salt like as hydrochloride salt.

(101) Other coupling techniques use pre-formed active esters, such as N-hydroxysuccinimide (HOSu) and p-nitrophenol (HONp) esters, pre-formed symmetrical anhydrides, non-symmetrical anhydrides such as N-carboxyanhydrides (NCAs) and acid halides, such as acyl fluorides or acyl chlorides.

(102) Preferred coupling reagents are carbodiimide coupling reagents and phoshonium coupling reagents, most preferred coupling reagents are selected from group consisting of PyBOP, DCC, DIC and EDC; more preferably, coupling reagent is PyBOP or DIC. EDC is preferably used as a salt, more preferably as EDC.HCl.

(103) Preferably, the molar amount of coupling reagent is from 1 to 10 times, more preferably from 1 to 5 times, of the molar loading capacity of the resin, or of the molar amount of the fragment to be coupled in LPPS respectively. More preferably, the molar amount of coupling reagent is from 1 to 10 times, more preferably from 1 to 5 times, of the molar amount of the substrate, such as the AA, to be coupled, or of the molar amount of the fragment to be coupled in LPPS respectively.

(104) COUPL can be done in the presence of a base, preferably a tertiary amine base, which both deprotonates the COOH residue of the carboxylic component and neutralizes any counterion of the NH.sub.2 residue of the amino component in COUPL, and thus facilitates the coupling reaction.

(105) Suitable bases are for example trialkylamines, like N,N-diisopropylethylamine (DIPEA) or triethylamine (TEA); N,N-dialkylanilines, like N,N-diethylaniline; 2,4,6-trialkylpyridines, like 2,4,6-trimethylpyridine; N,N-dialkylaminopyridines, like N,N-4-dimethylaminopyridine; and N-alkylmorpholines, like N-methylmorpholine. Preferably, COUPL is done in the presence of DIPEA as a base. Preferably, the molar amount of base is from 0.01 to 20 times, more preferably from 0.02 to 10 times, of the molar loading capacity of the resin, or of the molar amount of the fragment to be coupled in LPPS respectively. More preferably, the molar amount of base is from 0.01 to 20 times, more preferably from 0.02 to 10 times, of the molar amount of the substrate, such as the AA, to be coupled, or of the molar amount of the fragment to be coupled in LPPS respectively.

(106) COUPL can be done in the presence of an auxiliary nucleophile as additive due to their positive effect in suppressing undesired side reactions. Any known auxiliary nucleophile may be used.

(107) Examples of suitable auxiliary nucleophiles are ethyl (hydroxyimino)cyanoacetate, 1-hydroxybenzotriazole (HOBt), N-hydroxysuccinimide (HOSu), N-hydroxy-3,4-dihydro-4-oxo-1,2,3-benzotriazine (HOOBt) and 1-hydroxy-7-azabenzotriazole (HOAt). Preferably, HOBt or HOAt are used as auxiliary nucleophile. Preferably, the molar amount of auxiliary nucleophile is from 0.5 to 3 times of the molar amount of the amino residue that is to be coupled, or of the molar amount of the fragment to be coupled in LPPS respectively.

(108) Especially, COUPL is done using DIC/OxymaPure, DCC/HOBt, EDC/HOBt, PyBOP/HOBt or EDC/HOAt. Preferably, COUPL can be done in any inert solvent which can dissolve the reactants. Preferred solvents for COUPL are water-miscible solvents like dimethyl sulfoxide (DMSO), dioxane, tetrahydrofurans such as tetrahydrofurane (THF) or methyltetrahydrofurane (Methyl-THF), 1-methyl-2-pyrrolidone (NMP), N,N-Dimethylformamide (DMF), N,N-Dimethylacetamide (DMA), or any mixture thereof; and non water-miscible solvents like dichloromethane (DCM), ethyl acetate or any mixture thereof; and any suitable mixture between water-miscible and non water-miscible solvents, including mixtures with water. More preferably, COUPL is done in a solvent selected from the group consisting of DMSO, dichloromethane, Me-THF, DMF, NMP, and mixtures thereof.

(109) Preferably, the substrate in COUPL, for example any AA, that is reacted with the respective functional residue connected to the resin in SPPS, is preferably used in excess with regard to the molar loading capacity of the resin;

(110) more preferably, it is used in an molar amount of from 1 to 10 times, more preferably from 1 to 8 times, based on the molar loading capacity of the resin.

(111) The two fragments, that are to be coupled in LPPS, are usually used in stoichiometric amounts with respect to each other, but of course one fragment can also be used in excess over the other one.

(112) Preferably, COUPL is done at atmospheric pressure.

(113) Preferably, the reaction temperature of COUPL is from −20 to 70° C.; more preferably from −15 and 40° C., even more preferably from −15 to 35° C.

(114) Preferably, the reaction time of COUPL is from 30 min to 48 h, more preferably from 30 min to 24 h, even more preferably from 30 min to 12 h, especially from 30 min to 6 h.

(115) Preferably, the progress of COUPL is monitored by HPLC and thereby the necessary reaction time is determined.

(116) Preferably, the coupling of the first AA onto the resin in case of FRAG1 is an esterification reaction ESTERREACAA1. ESTERREACAA1 provides for ESTBOND1. The coupling of the first AA onto the psWang linker connected to a resin in case of FRAG2 is an esterification reaction ESTERREACAA2. Both ESTERREACAA1 and ESTERREACAA2 can be done with the reagents and the conditions as described for COUPL. ESTERREACAA1 can be done without using a coupling reagent.

(117) Preferably, the molar amount of Pal-Glu(OSu)-OtBu in REACPALGLU is from 1 to 15 times, more preferably from 1 to 10 times, even more preferably from 1 to 5 times, of the molar loading capacity of the resin. REACPALGLU can be done in the presence of a base, preferably a tertiary amine base. Suitable bases are for example trialkylamines, like N,N-diisopropylethylamine (DIPEA) or triethylamine (TEA); N,N-dialkylanilines, like N,N-diethylaniline; 2,4,6-trialkylpyridines, like 2,4,6-trimethylpyridine; and N-alkylmorpholines, like N-methylmorpholine. Preferably, REACPALGLU is done in the presence of DIPEA as a base. Preferably, the molar amount of base is from 1 to 10 times, more preferably from 3 to 8 times, of the molar loading capacity of the resin. Preferably, REACPALGLU is done in a solvent selected from the group consisting of DMSO, dichloromethane, Me-THF, DMF, NMP, and mixtures thereof, more preferably the solvent is DCM. Preferably, REACPALGLU is done at atmospheric pressure. Preferably, the reaction temperature of REACPALGLU is from −20 to 70° C.; more preferably from −15 and 60° C., even more preferably from 5 to 35° C. Preferably, the reaction time of REACPALGLU is from 1 to 48 h, more preferably from 5 h to 24 h, even more preferably from 10 h to 24 h.

(118) Fmoc cleavage is known to the skilled person, it is done with a base, preferably the base is a secondary amine, more preferably piperidine. The base is used in excess with regard to the molar loading capacity of the resin. Preferably, DMF is used as solvent in the Fmoc cleavage reaction. Preferably, the Fmoc cleavage is done at atmospheric pressure. Preferably, the reaction temperature of the Fmoc cleavage is from −20 to 70° C.; more preferably from −15 and 40° C., even more preferably from −15 to 35° C. Preferably, the reaction time of the Fmoc cleavage is from 1 min to 12 h, more preferably from 1 min to 6 h, even more preferably from 1 min to 1 h.

(119) PEP can be isolated, preferably after a global deprotection, according to standard methods known to the skilled such as precipitation, preferably with ether, centrifugation, filtration etc. PEP can be purified according to standard methods known to the skilled person, such as HPLC.

(120) A further subject of the invention is a peptide PEPTI, wherein the C-terminal COOH of PEPTI is protected by a psWang residue; with the psWang residue as defined herein, also with all its embodiments and definitions; wherein in the definition of the psWang residue the (*) denotes the covalent bond to the C atom of the CO residue of the C-terminal COOH of PEPTI.

(121) Preferably, PEPTI has up to 500, more preferably up to 400, even more preferably up to 300, especially up to 200, more especially up to 150, even more especially up to 100, in particular up to 60, more in particular up to 40, amino acid residues. Preferably, PEPTI has at least 4, 5, 6, 7, 8, 9 or 10 amino acid residues.

(122) Any of the possible minimum number of amino acid residues can be combined with any of the possible maximum number of amino acid residues of PEPTI.

(123) PEPTI can be any peptide bearing said C-terminal psWang residue, such as a final target peptide or a peptide fragment or a peptide intermediate. Preferably, PEPTI is similar to or identical with FRAG2, also with all the definitions and embodiments of FRAG2 as defined herein. Preferably, PEPTI is prepared in the same way as described herein for FRAG2, also with all the embodiments as described herein for the preparation of FRAG2; so all the steps and details of the preparation of FRAG2 apply also for PEPTI.

(124) PEPTI can be used for the preparation of peptides in the same way as described herein for the use of FRAG2 in the preparation of PEP, also with all the embodiments as described herein for the method for the preparation of PEP.

(125) Therefore further subject of the invention is the use of PEPTI for the preparation of peptides in LPPS.

EXAMPLES

(126) AA

(127) The SPPS was done with the following AA, if not stated otherwise:

(128) Boc-His(Trt)-OH; Fmoc-Ala-OH; Fmoc-Glu(OtBu)-OH; Fmoc-Gly-OH; Fmoc-Thr(tBu)-OH; Fmoc-Phe-OH; Fmoc-Ser(tBu)-OH; Fmoc-Asp(OtBu)-OH; Fmoc-Tyr(tBu)-OH; Fmoc-Val-OH; Fmoc-Val-Ser[Psi.sup.(Me,Me)Pro]-OH for position (10) and (11); Fmoc-Leu-OH; Fmoc-Gln(Trt)-OH; Fmoc-Lys(Alloc)-OH; Fmoc-Ile-OH; Fmoc-Trp(Boc)-OH; Fmoc-Arg(Pbf)-OH

(129) Pal-Glu(OSu)-OtBu, that is compound of formula (10), was purchased from IRIS Biotech.

(130) Methods

(131) Ninhydrin Test, Also Called Kaiser Test

(132) The test is known to the skilled person, see Kaiser E. et al., Analytical Biochemistry 1970, 34, 595-598.

(133) Solution 1: Dissolve 5 g ninhydrin in 100 mL ethanol.

(134) Solution 2: Dissolve 40 g phenol in 10 mL ethanol.

(135) Solution 3: Add 2 mL of a 0.001 M aq. KCN solution to 98 mL pyridine.

(136) Procedure:

(137) 1. Wash resin with DCM (2 times).

(138) 2. Sample a few beads of resin in an Eppendorf tube.

(139) 3. Add one to two drops of each of the three solutions 1 to 3.

(140) 4. Mix well and heat to 120° C. for 3 to 5 min.

(141) 5. The presences of free resin-bound amines are indicated by blue resin beads.

(142) Coupling

(143) SPPS was done manually.

(144) Washing

(145) In the following examples washing with a solvent, such as DMF or DCM, was done by filtering the resin, suspending and stirring the resin in the solvent for a certain time and filtering again. For washes and Fmoc removal ca. 5 volumes of resin of the solvent was used; for couplings ca. 20 ml/g resin was used, if not stated otherwise. Stated in the examples are the number of repetitions of this washing cycle together with the time for stirring. Also in case of treating the resin with a reagent that is dissolved in a solvent this description of the number of repetitions of this treatment together with the time for stirring is used in the example, if not otherwise stated.
Yield
The yield was calculated on the basis of the synthesis scale with respect to resin loading capacity f and resin weight, if not otherwise stated.
Method for Determination of Purity
Peptide-resin (100 mg) is treated with ca. 2 ml of TFA:H.sub.2O:TIS in the volume ratio 94:3:3 and stirring for 1 h at RT. The suspension is filtered. The deprotected peptide is precipitated by addition of diisopropyl ether (20 ml) to the filtrate. The purity of crude deprotected fragment is checked by HPLC:
(A) Determination of Purity of Fragment 1: Column with C18 stationary phase Mobile phase A: 0.1% (v/v) TFA in water Mobile phase B: 0.1% (v/v) TFA in acetonitrile Gradient: 5% (v/v) B to 100% (v/v) B in 11 min Temperature: RT Flow rate: 1 ml/min Detection: 254 nm
(B) Determination of Purity of Fragment 2: Column with C18 stationary phase Mobile phase A: 0.1% (v/v) TFA in water Mobile phase B: 0.1% (v/v) TFA in acetonitrile Gradient: 5% (v/v) B to 100% (v/v) B in 13 min Temperature: 40° C. Flow rate: 1 ml/min Detection: 254 nm
(C) Determination of Purity of Crude Liraglutide: Column with C18 stationary phase Mobile phase A: 0.1% (v/v) TFA in water Mobile phase B: 0.1% (v/v) TFA in acetonitrile Gradient: 5% (v/v) B to 100% (v/v) B in 11 min Temperature: RT Flow rate: 1 ml/min Detection: 254 nm
Fmoc Determination, Also Used for Determination of Resin Loading:

(146) An analytical method based on the UV absorption of dibenzofulvene after cleavage of Fmoc on an aliquot of peptide-resin, the method is known to the skilled person. It can be done as follows:

(147) An aliquot of loaded resin (ca. 100 mg) is washed with DMF (3 times with 5 ml) and DCM (3 times with 5 ml). It is then dried under vacuum.

(148) 10 mg of dried resin is added to a 2 mL polypropylene tube, 0.8 mL of DMF is added and the resin is allowed to swell for 10 minutes. Then 0.2 mL of piperidine is added, then the mixture is shaken for 20 min. Then 10 microL of the supernatant is pipetted into a quartz cuvette and is diluted with 0.990 mL of DMF. The absorbance at lamda=301 nm is determined. The piperidine-dibenzofulvene adduct that is formed upon Fmoc deprotection has a molar extinction coefficient of epsilon=7800 L×mol.sup.−1×cm.sup.−1; thus, the loading value is determined using Beer-Lambert law.
Apparent pH

(149) The determination of the apparent pH is a way to measure the pH in an organic solvent (that is in a non aqueous solvent). The procedure is well known to the skilled person: One drop of the organic solvent or of the organic solvent solution is put on a wet pH paper stick, the resulting coloration gives the apparent pH.

Example 1: Synthesis of Liraglutide Using a Pseudo Wang Linker

(150) Synthesis of Liraglutide using a pseudo Wang linker was done according to Scheme 1:

(151) ##STR00015##

Example 1-1: SPPS of Protected Fragment 1 with Pseudoproline

(152) Protected fragment 1, that is protected Boc-His-(2-15)-Gly-OH, was synthesized by conventional Fmoc SPPS according to Scheme 2, wherein RESIN1 was a CTC resin, purchased from IRIS BioTech with loading capacity f=1.6 mmol/g, Val.sup.(10) and Ser.sup.(11) were coupled in form of a pseudo-Pro, Fmoc-Val-Ser(psi.sup.Me,Mepro)-OH, the His.sup.(1) was coupled as Boc-His.sup.(1) (Trt)-OH.

(153) ##STR00016##

(154) The resin (2.01 g) was washed with DCM (3 times with 20 ml). Then the loading capacity of the resin was reduced to f=0.8 mmol/g by the addition of Fmoc-Gly-OH (0.5 eq; 0.478 g) and DIPEA (2 eq) in DCM (40 ml) and subsequent stirring for 2 h. Then the loading was checked by Fmoc determination and it was found to be f=0.71 mmol/g. Stepwise coupling of the other AAs was carried out at RT by adding the reagents AA:DIC:OxymaPure in the ratio 3 eq:3eq:3eq in 40 ml DMF and then stirring for 90 min. Removal of the Fmoc was done by treatment at RT with piperidine:DMF (2:8 v/v; 5 ml/g resin) for 1 time for 1 min and 1 time for 15 min. After each coupling, a ninhydrin test was done. In all cases except for Phe.sup.(6) and His.sup.(1), the ninhydrin test was negative. For Phe.sup.(6) and His.sup.(1), the coupling was repeated with stirring for 120 min instead of 90 min, and then the ninhydrin test was negative.

(155) Cleavage of the Peptide—Resin Bond

(156) After the introduction of the last amino acid, the resin was washed with DCM (5 ml/g; 5 time for 1 min), then washed with MeOH (5 ml/g; 5 time for 1 min) and dried. The protected fragment 1 was then cleaved from the resin using TFA/DCM (2/98 v/v; 40 ml; 3 times for 5 min). The TFA/DCM filtrates were collected and evaporated under vacuum. The residue was precipitated by addition of diisopropyl ether (40 ml), and isolated by filtration and drying under vacuum. Protected fragment 1 (2.93 g) was isolated with 81% yield and 92% purity. The purity was determined by HPLC.

Example 1-3: SPPS of Protected Fragment 2

(157) Protected fragment 2, that is protected H-Gln-(18-31)-psWang, was synthesized by conventional Fmoc SPPS according to scheme 3, wherein RESIN2 was the CTC resin purchased from IRIS Biotech.

(158) ##STR00017##

(159) 4-Hydroxymethylphenol (0.3 eq) and DIPEA (2 eq) in DMF (60 ml) were added to the 2-CTC-resin (3 g, f=1.6 mmol/g), and after stirring for 2 h, MeOH (10 ml) was added to cap the unreacted Cl. Then Fmoc-Gly-OH (3 eq taking into account a loading of 0.5 mmol/g) was added together with DIC (3 eq) and DMAP (0.3 eq) in DMF (60 ml) and stirred for 90 min. Then the resin was treated for 10 min with Ac.sub.2O: DIPEA 0.141 ml: 0.26 ml (1 eq) and the final loading as calculated by Fmoc determination was 0.45 mmol/g; the Fmoc determination also served for cleavage of Fmoc.

(160) Coupling of the remaining AA was done by treatment at RT with AA:DIC:OxymaPure (3 eq: 3 eq: 3 eq) for 90 min. Removal of the Fmoc after each coupling was done by treatment at RT with piperidine:DMF (2:8 v/v, 5 ml/g resin) for 1 time for 1 min and 1 time for 15 min. After each coupling, the ninhydrin test was carried out. In all cases except Phe.sup.(22), Ala.sup.18 and Gln.sup.(17) (Trt), the ninhydrin test was negative. For Phe.sup.(22), Ala.sup.(18), and Gln.sup.(17) (Trt), the coupling was repeated with stirring for 120 min instead of 90 min and then the ninhydrin test was negative.

(161) Incorporation of Pal-Glu(OSu)-OtBu

(162) After the coupling of Ala.sup.(18) and before the removal of its Fmoc protecting group, the Alloc protecting group of the side chain of Lys.sup.(20) was removed [by (i) washing the resin with DCM (5 times for 1 min each); (ii) treatment of the resin at RT with Pd(PPh.sub.3).sub.4:PhSiH in the ratio 0.1eq:10eq (2 times for 10 min each in DCM); (iii) washing with DCM (5 times for 1 min each)], thereafter the resin was treated at RT with Pal-Glu(OSu)-OtBu (3 eq) and DIPEA (6 eq) in DCM (20 ml/g resin) for 16 hours. The ninhydrin test confirmed that the reaction was finished and the coupling of the last amino acid Fmoc-Gln(Trt)-OH was done followed by the N-terminal Fmoc deprotection. In order to completely remove the traces of piperidine, the peptide resin is extensively washed with DMF (5 times 50 ml DMF for 1 min each), DCM (5 times 50 ml DMF for 1 min each), 0.01% TFA in DCM (5 times 50 ml DMF for 1 min each).

(163) Cleavage of Peptide-Resin Bond

(164) The peptide-resin bond is cleaved by means of 2% v/v TFA in DCM (3 times 50 ml for 5 min). The filtrates are collected and evaporated under vacuum. The residue is precipitated in water (100 ml), filtered and dried under vacuum at 30±5° C. Yield was ca 50%, purity was ca 85%. The purity was determined by HPLC.

Example 1-4: Coupling of Protected Fragments 1 and 2 to Provide Protected Liraglutide

(165) Protected fragment 2 (900.0 mg, 1.0 eq, prepared according to example 1-3) was dissolved in DMSO (25 mL), the resulting solution was added to a solution of protected fragment 1 (795.5 mg, 1.1 eq), prepared according to example 1-1, in DMSO (25 mL), then PyBOP (1.1 eq) was added and the apparent pH is adjusted to 7.5 to 8.5 by dropwise addition of DIPEA. After 2.5 h the reaction was quenched by precipitation into 5 wt % aqueous NaHCO.sub.3. The solid obtained after centrifugation was washed with 5 wt % aqueous citric acid. Yield: ca. 100% (ca. 1.6 g as it is).

Example 1-5: Global Deprotection of Protected Liraglutide

(166) The protected liraglutide (1.8 g, prepared according to example 1-4) was added to ca. 18 ml of a mixture of TFA:phenol:water:TIS (88:5:5:2 v/v) of 0° C. The mixture was stirred 2 h at 0° C. and then poured into ether (200 ml) of 0° C. The precipitate was isolated by centrifugation and was washed with ether (3 times with 20 ml) and was dried under vacuum at 20±5° C. Yield ca. 100% (1.3 g as it is). Purity: 71%.

Example 1-6: Purification of Liraglutide

(167) The following purification method is standard purification method which is not optimized for liraglutide and yield. Liraglutide, prepared according to example 1-5, was purified on XSelect® CSH C18 semi-preparative HPLC column (Waters). Mobile phase A: 0.1% (v/v) TFA in water. Mobile phase B: 0.1% TFA (v/v) in acetonitrile

(168) Gradient:

(169) TABLE-US-00001 t A B [min] [%] [%] 0 95 5 3 95 5 4 51 49 9 48.5 51.5 10 0 100 12 0 100 12.5 95 5
Liraglutide elutes at about minute 7 of the gradient. Purity: >99%. Purification yield: 10%.