Human calcitonin. VI. Synthesis of calcitonin M

Abstract

AbstractA detailed account is given of the total synthesis of human calcitonin M, the hypocalcaemic hormone possessing the dotriacontapeptide sequence I. In the build up of I, the protected sequences 1–10 and 11–32 served as intermediates for the preparation of the protected precursor dotriacontapeptide 1–32 (II). While the synthesis of the fragment 1–10 has been reported previously [1], the present account includes a detailed description of the build up of the intermediate 11–32. Racemisation encountered in the synthesis of this fragment is discussed and conditions indicated in which it is minimized.From the final coupling step using dicyclohexylcarbodiimide‐N‐hydroxysuccinimide [3], the protected dotriacontapeptide II was obtained pure in a yield of 65% after counter‐current distribution.In the removal by acidolysis of the protecting groups from II even under optimal conditions two side reactions occur: alkylation of the 8‐methionine side chain and N to O acyl migration at the serine or threonine residues. By‐products from these reactions were removed by counter‐current distribution giving very pure I free of diastereoisomers and possessing the biological activity of highly purified natural calcitonin M. In the routine assay [4] after repeated testing its activity was evaluated at 100 ± 5 U/mg (calculated on content of free peptide).