Process for the synthesis of 37-mer peptide pramlintide

1. A process for the production of pramlintide, a disulfide-bridged peptide of formula (1):

wherein the Cys-Cys line indicates a cystine disulfide bridge;

comprising:

(a) coupling Fmoc-Tyr(X)-OH to an acid-labile Rink amide AM resin with a substitution value ranging from 0.15-0.60 mmol/g, in a single coupling reaction, to provide a sidechain-protected resin-bound tyrosine residue, Fmoc-Tyr(X)-Resin; then,

(b) removing the N-terminal Fmoc protecting group thereof using piperidine in 1-hydroxybenzotriazole (HOBt) in polar aprotic solvent to provide an N-terminal free amino group; then,

(c) assembling each respective Fmoc-protected aminoacid residue sequentially C-terminal to N-terminal under conditions suitable for peptide coupling, to provide sidechain-protected resin-bound peptide of the formula (2RBP):

Fmoc-Asn(Y)-Asn(Y)-Phe-Gly-Pro-Ile-Leu-Pro-Pro-Thr(X)-Asn(Y)-Val-Gly-Ser(X)-Asn(Y)-Thr(X)-Tyr(X)-Resin (SEQ ID NO:2);

wherein (X) and (Y) signify acid-labile sidechain protecting groups, wherein (X) can be removed under acidic conditions to yield a free OH group and (Y) can be removed under acidic conditions to yield a free NH or SH group; then,

(d) removing the N-terminal Fmoc group using piperidine in 1-hydroxybenzotriazole (HOBt) in polar aprotic solvent to provide an N-terminal free amino group; then,

(e) coupling Fmoc-Ser(X)-Ser(Ψ Me,Me Pro)-OH to the N-terminal free amino group, under conditions suitable for peptide coupling, wherein Ser(Ψ Me,Me Pro) signifies a pseudoproline serine-derived oxazolidine of formula

wherein each wavy line indicates a point of bonding in the peptide chain, to yield a sidechain-protected resin-bound peptide of Formula (3RBP):

Fmoc-Ser(X)-Ser(Ψ Me,Me Pro)-Asn(Y)-Asn(Y)-Phe-Gly-Pro-Ile-Leu-Pro-Pro-Thr(X)-Asn(Y)-Val-Gly-Ser(X)-Asn(Y)-Thr(X)-Tyr(X)-Resin (SEQ ID NO:3); then,

(f) further assembling each respective Fmoc-protected aminoacid residue sequentially C-terminal to N-terminal, under conditions suitable for stepwise N-terminal Fmoc removal and peptide coupling, to the sidechain-protected resin-bound peptide of formula (3RBP), to provide a sidechain-protected resin-bound peptide of formula (4RBP), wherein the Ser(Ψ Me,Me Pro is the sole pseudoproline serine-derived oxazolidine in the peptide of formula (4RBP):

Fmoc-Lys(Boc)-Cys(Y)-Asn(Y)-Thr(X)-Ala-Thr(X)-Cys(Y)-Ala-Thr(X)-Gln(Y)-Arg(Pbf)-Leu-Ala-Asn(Y)-Phe-Leu-Val-His(Y)-Ser(X)-Ser(Ψ Me,Me Pro)-Asn(Y)-Asn(Y)-Phe-Gly-Pro-Ile-Leu-Pro-Pro-Thr(X)-Asn(Y)-Val-Gly-Ser(X)-Asn(Y)-Thr(X)-Tyr(X)-Resin (SEQ ID NO:4);

with a purity of crude peptide of ≧30%; then,

(g) sidechain-deprotecting and cleaving a 37-mer cysteine-reduced peptide of Formula (4) from the resin by contacting with acid,

H-Lys-Cys-Asn-Thr-Ala-Thr-Cys-Ala-Thr-Gln-Arg-Leu-Ala-Asn-Phe-Leu-Val-His-Ser-Ser-Asn-Asn-Phe-Gly-Pro-Ile-Leu-Pro-Pro-Thr-Asn-Val-Gly-Ser-Asn-Thr-Tyr-NH 2 (formula (4); SEQ ID NO:5); then,

(h) oxidizing the peptide of formula (4) to the disulfide-bridged peptide of Formula (1) by air oxidation, or hydrogen peroxide or copper sulphate or iodine oxidation; and,

(i) purifying the peptide of formula (4), or the peptide of formula (1), or optionally both, by RP-HPLC, wherein the peptide of formula (1) has a purity of 98%, or of 99%, or of 99.9% by weight.

2. The process of claim 1 , wherein the acid-labile resin has a substitution value ranging from 0.25 to 0.35 mmole/gm.

3. The process of claim 1 , wherein the polar aprotic solvent used is dimethyl formamide(DMF).

4. The process of claim 1 , wherein the (X) group is selected from the group consisting of tBu, Trt, and chlorotrityl, and the (Y) group is selected from the group consisting of Trt, Tmob, Mtt, and Xan.

5. The process of claim 4 , wherein the (X) group is tBu.

6. The process of claim 4 , wherein the (Y) group is Trt.

7. The process of claim 1 , wherein Fmoc removal is carried out in a medium comprising 0.1M-0.5M-hydroxybenzotriazole (HOBt) in 20%-50% piperidine in DMF.