title: Enzymatic semisynthesis of dicarba analogs of calcitonin.
abstract: The semisynthesis of eel[L-alpha-aminosuberic acid]calcitonin (elcatonin) was accomplished by alpha-chymotrypsin-catalyzed coupling of two peptide segments in a single reaction without the protection of any functional group. The eel calcitonin-(10-32)-peptide was prepared by a gene manipulation. The esters of cyclic desamino nonapeptide (segment 1-9) were synthesized by the conventional solution method including a thermolysin-mediated resolution of DL-alpha-aminosuberic acid via one-step tripeptide synthesis leading to the 7-9 sequence. The main aim of this work was to determine the conditions for protease-catalyzed segment condensation while avoiding a concurrent cleavage of other proteolytically labile peptide bonds in the hormone. The alpha-chymotrypsin condensation strategy under usual conditions led to a complicated mixture of split products with an insignificant amount of the required peptide. When the coupling reaction was carried out at 0 degrees C, the reaction resulted in a satisfactory yield of elcatonin with the complete conversion of the acyl donor (1-9 segment) accompanied by negligible concurrent peptide bond digestion. The same strategy was employed for the preparation of analogous dicarba salmon calcitonin using a synthetic elcatonin-(10-32)-peptide. Both calcitonin analogs exhibited hypocalcemic activity corresponding to the international standard of elcatonin. We demonstrate in this work a peptide synthesis based on the combination of genetic engineering, chemical synthesis and proteinase-catalyzed segment condensation. This approach enables effective incorporation of an unnatural amino acid into calcitonins without the side-chain protection.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Prague, Czech Republic. cerovsky@uochb.cas.cz
authors.forename: V
authors.initials: V
authors.lastname: Cerovský
authors.forename: E
authors.initials: E
authors.lastname: Wünsch
authors.forename: J
authors.initials: J
authors.lastname: Brass
mesh_terms: D000595:Amino Acid Sequence; D002116:Calcitonin / Q000031:analogs & derivatives / Q000138:chemical synthesis*; D002918:Chymotrypsin / Q000494:pharmacology*; D008969:Molecular Sequence Data
chemical_list: D002116:Calcitonin; D002918:Chymotrypsin