PROCESS FOR PRODUCTION AND PURIFICATION OF CYCLIC PEPTIDES
Publication Date: 2005-Nov-03
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PROCESS FOR PRODUCTION AND PURIFICATION OF CYCLIC PEPTIDES ________________________________________________________________________
Somatostatin is known to possess a very broad therapeutic potential and can be
5 administered in a wide variety of clinical applications. The mean half-life in plasma of somatostatin is extremely short, therefore reducing the potential number of possible applications of this reagent. Research was carried out with the aim of developing analogs of somatostatin which exhibited greater stability and efficacy. One series of compounds which were evaluated as potentially useful somatostatin analogs were cyclic octapeptides. 10
Evaluation of the cyclic octapeptide, octreotide, demonstrated that the compound had excellent biological activity both in vitro and in vivo (Pless J., Metabolism 41, 5-6 (1992)). Octreotide has the following basic formula:
(SEQ. ID. NO. 1) wherein the sulfur atoms of the Cys residues at the positions 2 and 7 are 15 bounded by a disulfide bridge. The carboxylic group of the C-terminal amino acid, threonine (Thr), is reduced to the alcohol Thr-ol (threoninol) residue.
The presence of D-phenylalanine (D-Phe) at the N-terminal end and of an amino alcohol at the C-terminal end, along with the D-tryptophan (D-Trp) residue and the disulfide bridge, make the molecule very resistant to metabolic degradation. Octreotide 20 permits a 24 hour incubation in aggressive mediums, such as gastric juices or in intestinal mucosa.
Octreotide inhibits growth hormone for a lengthy period, inhibits the secretion of glucagon to a lesser degree, and inhibits insulin secretion only in a transient manner. Thus, octreotide is selective more than other somatostatin analogues in regulating the 25 levels of growth hormone in the body and therefore, presently is indicated in acromegaly to control and reduce the plasma levels of such hormone. Also, octreotide is useful in the treatment of cellular alterations of gastroenteropancreatic endocrine origin and of certain types of tumors.
The synthesis of octreotide and its derivatives has been described by two general
D-Phe Cys Phe D-Trp Lys Thr Cys Thr-ol
synthetic methods. The first method is a solution phase procedure, based on fragment condensation, as described by Bauer et al. European Patent Application No. 29,579 (1981) and U.S. Patent No. 4,395,403. The process generally comprises removing a protecting group from a protected hexapeptide residue; linking together two peptide units by an amide bond, wherein one comprises a hexapeptide residue; converting a functional 5 group at the N- or C-terminal end of the resulting polypeptide; and oxidizing the polypeptide. The process involves a time-consuming, multi-step synthesis, and presents additional problems during the separation of octreotide from the reaction mixtures because all the synthetic steps are carried out in solution phase.
The second method for the synthesis of octreotide synth...